Pennsylvanian Fusulinids From Southeastern Alaska
By RAYMOND C. DOUGLASS
GEOLOGICAL SURVEY PROFESSIONAL PAPER 706
A fauna of Middle Pennsylvanian age showing similarities with faunas from Japan and central British Columbia, Canada
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971﻿UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY William T. Pecora, Director
Library of Congress catalog—card No. 77—611482
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 70 cents (paper cover)﻿CONTENTS
Page
Abstract____________________________________________________ 1
Introduction________________________________________________ 1
Previous work__________________________________________ 1
Current study__________________________________________ 1
Significance of the fusulinid assemblages______________ 1
Correlation____________________________________________ 1
Localities_____________________________________________ 2
Disposition of material________________________________ 2
Acknowledgments________________________________________ 2
Page
Methods of study____________________________________________ 4
Presentation of data________________________________________ 4
Correlation of the local sections___________________________ 4
Systematic descriptions_____________________________________ 4
References cited____________________________________________ 19
Index________________________________,_________________ 21
ILLUSTRATIONS
[Plates follow index]
Plate
1.	Tetrataxis, endothyrids, and A ankinella sp., from Ladrones Islands.
2.	Staffella, Millerella, and Pseudostaffella rotunda Douglass, n. sp., from Peratovich Island.
3.	Fusulinella pinguis Douglass, n. sp., from Ladrones Islands.
4.	Bradyina sp., Ozawainella?, and Fusulinella alaskensis Douglass, n. sp., from Klawak Inlet.
5.	Fusulinella alaskensis Douglass, n. sp., from Klawak Inlet.
6.	Fusulinella alaskensis Douglass, n. sp., and Beedeina? sp., from Prince of Wales Island.
7.	Fusulina flexuosa Douglass, n. sp., from Klawak Inlet and Prince of Wales Island.
Figure
1.	Index maps______________________________________
2.	Spiral form for Pseudostaff ella rotunda n. sp___
3.	Summary graphs for Pseudostaff ella rotunda n. sp
4.	Spiral form for Fusulinella pinguis n. sp________
5.	Summary graphs for Fusulinella pinguis n. sp_____
6.	Spiral form for Fusulinella alaskensis n. sp_____
7.	Summary graphs for Fusulinella alaskensis n. sp_
8.	Spiral form for Fusulina flexuosa n. sp_________
9.	Summary graphs for Fusulina flexuosa n. sp_______
Page
3
6
7
9
10
13
14 16 18
TABLES
Tables 1-4. Summary numerical data:	Page
1. Pseudostaff ella rotunda n. sp________________________________________________________________________ 8
2.	Fusulinella pinguis n. sp_____________________________________________________________________________ 11
3.	Fusulinella alsakensis n. sp__________________________________________________________________________ 15
4.	Fusulina flexuosa n. sp_______________________________________________________________________________ 17
in﻿

﻿PENNSYLVANIAN FUSULINIDS FROM SOUTHEASTERN ALASKA
By Raymond C. Douglass
ABSTRACT
A fusulinid fauna from the Klawak Formation and Ladrones Limestone of Prince of Wales Island in southeastern Alaska includes eight genera of fusulinids and some smaller Foramini-fera. The fauna is similar to faunas of Middle Pennsylvanian age described from north-central British Columbia in Canada, and from parts of central Japan. Four of the taxa are new including Pseudostaffella rotunda n. sp., Fusulinella pinguis n. sp., Fusulinella alaskensis n. sp., and Fusulina flexuosa n. sp.
INTRODUCTION PREVIOUS WORK
The scarcity of evidence of marine rocks of Pennsylvanian age in Alaska was summarized by Dutro and Douglass (1961, p. B239). Rocks of Middle Pennsylvanian age were identified in Saginaw Bay at the north end of Kuiu Island. At that locality fusulinids w7ere recognized along with a varied megafauna. Muffler (1967, p. C19) assigned these rocks to the Saginaw Bay Formation of Carboniferous age.
CURRENT STUDY
In 1966 A. K. Armstrong collected a series of samples from measured sections of the Klawak Formation in the areas north of Craig and the Ladrones Limestone south of Craig, Prince of Wales Island. Samples were collected from every 10 feet or less through each section.
SIGNIFICANCE OF THE FUSULINID ASSEMBLAGES
The fusulinids represented in these samples include several genera characteristic of rocks of Middle Pennsylvanian age and include Nankinella, Staff ella, Pseudo-staffella, Fusulinella», and Fusulina. The species are relatively primitive forms and as such do not suggest latest Middle Pennsylvanian age. As no fusulinids have been identified in this general area below or above the samples studied, no definite limits can be determined for the age of the Klawak Formation and the Ladrones Limestone.
CORRELATION
The faunas described herein can be compared with faunas described from the Fort St. James area in central British Columbia, Canada, and with faunas described from as far away as Texas in the U.S.A. and from central Japan. The faunas described from central British Columbia by Thompson, Pitrat, and Sanderson (1953, p. 545) and by Thompson (1965, p. 224) include species assigned to each of the genera listed above and show similarity in stage of development. As I noted in the section on systematics, precise comparisons are difficult because of the paucity of data available for the Canadian material.
Comparison with the Texas faunas are even more difficult, but there is general similarity in the species of Nankinella, Staff ella, Pseudostaff ella, and Fusulinella. The counterpart of the Fusulina from Alaska and British Columbia has not been reported so far from the conterminous United States.
Faunas from three areas in Japan show similarities to the Alaskan fauna. The fauna described by Igo (1957, p. 167) from Fukuji in the Hida Massif of central Honshu contains species of NanJcinella, Staff ella, Pseudostaff ella, and Fusulinella resembling those from Alaska. The Shishidedai area on the northern edge of the Aki-yoshi Plateau in southern Honshu contains a fauna described by Toriyama (1953, p. 251,1958, p. 5) with forms similar to the Nankinella, Fusulinella, and Fusulina from Alaska. The faunas of the-Itadorigawa Group of western Shikoku described by Ishii (1958a, b; 1962) also show similarities to those from Alaska.
Comparisons were also attempted with material from other parts of the world where generally similar forms have been described or illustrated. Among these, some similarities were recognized in material from Spitsbergen (Forbes 1960, p. 212) and from Spain (van Ginkel 1965, p. 159).
l﻿2
PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
Wherever the fusulinid faunas of Middle Pennsylvanian age have been studied in detail, similarities at the generic level are obvious and the general character of the species is similar. Unfortunately, the data presented with most of the faunas previously described are inadequate for comparisons at the species level. Notable exceptions are the more fully documented studies by Ishii and van Ginkel.
LOCALITIES
The samples are from two areas in the vicinity of Craig, Prince of Wales Island (fig. 1 A, B). The southernmost samples arc from the Ladrones Islands, about 7 miles south-southeast of Craig (fig. 1C), and the northernmost samples are from the area north of Ivlawak and about 8 miles north-northeast of Craig (fig. ID).
Locality 29.—Ladrones Islands, field section 66x16 of A. K. Armstrong, Ladrones Limestone.
f23973. Sample taken 10 ft above the base of the exposed section above high tide. Light-gray calcarenite largely composed of fossil fragments in a sparry calcite matrix. Fragments of echinoderms, gastropods, and fusulinids are common. Tctrataxis sp., endothyrids, Nankinella sp., and Fusulinella pinguis n. sp.
f23974. Sample taken 20 ft above the base of the exposed section above high tide. The lithology and fauna of this sample is similar to that of f23973.
Locality 30.—Peratovieh Island, field section 66x4B of A. K. Armstrong, Klavvak Formation.
f23975. Sample taken from 101 ft above the base of the section measured on the small peninsula trending north-northwest in the center of the north half sec. 35, T. 72 S., R. 80 E., Craig (C-4) quadrangle map. Dark-gray coarse calcarenite largely composed of fossil fragments in a silty lime mud matrix. Fragments of echinoderms, brachiopods, bryozoans, gastropods, and fusulinids are common. Textularids, Millerella sp., Nun kind la sp., Staffella sp., and Pscudostaffella rotunda n. sp. f23976. Sample taken from 106 ft above the base of the section at the same locality. The lithology and fauna of this sample are similar to that of f23975.
Locality 3t.—Small unnamed island exposed at low tide between Peratovieh Island and the main part of Prince of Wales Island and about 1.5 miles north of Klawak. Filled section 66x4C of A. K. Armstrong, Klawak Formation.
f23977. Sample from 20 ft above the base of the section. Medium-gray coarse calcarenite composed largely of fragments of fossils in a silty lime mud and sparry climate matrix Textularids, Tctrataxis sp., Fusulinella alasken-sis n. sp., and Fusulina flexuosa n. sp. f23978. Sample from 35 ft above the base of the section. Dark-greenish-gray calcareous siltstone with abundant fossil fragments including echinoderms, bryozoans, coral, brachiopods, gastropods, and fusulinids. Textularids, Tctrataxis sp., Ozaicainclla? sp., Fusulinella sp., and Fusulina sp.
f23979. Sample from 45 ft above the base of the section. Medium-gray coarse calcarenite with a silty to sparry calcite matrix. Fragments of echinoderms, bryozoans,
brachipods, and Foraminifera. Textularids, Textrataxis sp., endothyrids including Bradyina sp., Fusulinella alaskensis n. sp., and Fusulina flexuosa n. sp. f23980. Sample from 65 ft above the base at the section. Mostly a dark-greenish-gray calcareous siltstone grading into some calcarenite with fragments of fossils in a sparry calcite matrix. Echinoderms, bryozoans, and Foraminifera. Textularids, Bradyina sp., Fusulinella alaskensis n. sp., and Fusulina flexuosa n. sp. f23981. Sample from 75 ft above the base of the section. Dark-gray coarse conglomeratic calcarenite with fragments of echinoderms, bryozoans, and fusulinids. Fusulinella alaskensis n. sp. and Fusulina flexuosa n. sp. f23982. Sample from 80 ft above the base of the section. Medium-gray coarse calcarenite with fragments of echinoderms, bryozoans, and Foraminifera in a sparry calcite matrix. Textularids, Tctrataxis sp., Bradyina sp., and Fusulinella alaskensis n. sp.
Locality 32.—Ledges exposed at low tide on west shore of Prince of Wales Island about 1.5 miles nortli-northeast of Klawak. Field section 66x4D of A. K. Armstrong. Klawak Formation. f23983. Sample from 20 ft above the base of the section. Light-gray medium-grained calcarenite with shell fragments in a sparry calcite matrix. Tctrataxis sp., Bradyina sp., and Fusulinella sp.
f23984. Sample from 40 ft above the base of the section. Light-gray fine- to medium-grained calcarenite with shell fragments in a sparry calcite matrix. Endothyrids including Bradyina sp. are present with a small Fusulinella sp. f23985. Sample from 55 ft above the base of the section. Medium-yellowish-gray fine calcarenite with shell fragments in a sparry calcite matrix. Endothyrids and a small Fusulinella sp.
f23986. Sample from 60 ft above the base of the section. Medium-gray coarse conglomeratic calcarenite with subrounded clasts up to an inch across of other limestone and volcanic rocks. The matrix is a calcarenite with abundant shell fragments and fusulinids. Textularids, Tctrataxis sp., Bradyina sp.. Fusulinella alaskansis n. sp., Fusulina flexuosa n. sp., and Bcedeina'i
DISPOSITION OF MATERIAL
The specimens used in this study are deposited in the collections of the U.S. National Museum (USNM), and specimen numbers are indicated on the plate explanations. The bulk material is filed in the U.S. Geological Survey collections at the U.S. National Museum under the sample numbers listed for each locality described in the preceding section of this report.
ACKNOWLEDGMENTS
I thank A. K. Armstrong for his careful collection of samples in measured sections from which those samples studied were selected. Richard Margerum did an outstanding job in the unusually difficult preparation of oriented thin sections of small fusulinids in a dark matrix. The computer programming and processing of numerical data were done by Nancy Cotner, Ralph Richer, and Paul Za'bel.﻿INTRODUCTION
3
Figure 1.—Index maps. A. Southeastern Alaska and adjacent Canada showing area of this report (patterned). B. Part of Prince of Wales Island showing the Ladrones Islands and the Klawak area. C. The Ladrones Islands area showing locality 29. D. The Klawak area showing localities 30, 31, and 32.﻿4
.PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
METHODS OF STUDY
Each sample was sliced and etched lightly with dilute hydrochloric acid and coated with thinned clear lacquer. Samples that contained fusulinids were prepared for further study by making oriented thin sections of the fusulinids. Measurements of radius, volution height, half length, wall thickness, and tunnel width were made at each half volution on axial sections. Measurements of radius, volution height, wall thickness, and septal spacing were made at each half volution on equatorial sections. The maximum outer diameter of the proloculus was measured for each specimen.
The data obtained from these measurements, made at half volutions, was converted to equivalent values at standard radii by linear interpolation of values using a computer to determine the values at each standard radius. Thus the wall thickness for each specimen could be interpolated for a radius of 0.5 mm (millimeter) for instance, even though the actual measurement was a 0.43 mm or 0.52 mm. The interpolated values of each attribute at each standard radius were summarized for each species in every sample.
The standard radii were selected so that the logarithms to base 10 of adjacent radii are 0.1 apart. This gives about two points in each volution. The radii used (in millimeters) are 0.10, 0.13, 0.16, 0.20, 0.25, 0.32, 0.40,0.50,0.63,0.79,1.00,1.26, and so on.
The statistical summaries provide values commonly needed for making comparisons between samples. How these values are derived is now common knowledge, and formulae used are given in Simpson, Roe, and Lewontin (1960). The computed values include the mean, variance, standard deviation, coefficient of variability, standard error of the mean, 95 percent confidence limits on the mean, and listing the observed maximum and minimum values for each attribute.
Graphs similar to those of Douglass (1970, p. G8-G9) showing the mean, confidence limits on the mean, and total Observed variation for each attribute plotted against the standard radii were prepared from these data. The form ratio (half length/radius vector) was also computed at each radius and plotted in a similar manner.
When more than one sample contained the same species, the data were combined for the samples and all statistical values recalculated and replotted. Two samples were assumed to contain the same species if specimens were of the same genus and all their measurable attributes when compared at standard radii were similar.
Comparisons with previously named or described species were more difficult. In some instances (Ishii 1958a,b,
1962; van Ginkel, 1965) enough data were provided to compare the specimens at standard radii. In most instances data were insufficient for meaningful comparison, and estimates had to be made, often from illustrations of poorly oriented sections.
PRESENTATION OF DATA
An attempt has been made to illustrate the material as well as possible at magnifications of X 10 with selected details at X 50; thus the many attributes that cannot be adequately measured can be compared. The data obtained by measurement of the specimens are too voluminous to be included in the report, but they are available on request from the author. The data summaries at standard radii are presented. Tables 1-4 give some of the data and the rest are presented graphically on figures 2-9.
CORRELATION OF THE LOCAL SECTIONS
The samples studied from the four measured sections can be assigned relative positions even though sample localities are not directly connected. Locality 29 is isolated from more closely associated localities 30-32. The fauna of locality 29 is older than that of localities
31	or 32 and is probably younger than that of locality 30, but the evidence on this point is not conclusive. The fauna of locality 29 is not found between localities 30 and 31, but it may be present in the rocks forming the floor of Klawak Inlet. There is good correlation between localities 31 and 32, in spite of some uncertainties. Field data suggest that the section at locality
32	is a continuation of that at locality 31. It is possible, however, that the two sections overlap. The specimens of Fusulinella alaskensis n. sp. in sample f23979 from locality 31 are most similar to those from sample f23986 of locality 32. On the other hand, the only sample that yields Beedema ? sp. is f23986, the top sample at locality 32. This may indicate a slightly younger age for this sample.
The local section is represented by locality 30 at the base followed in ascending order by locality 29, locality 31 and locality 32. Localities 31 and 32 may overlap in part.
SYSTEMATIC DESCRIPTIONS
Genus TETRATAXIS Ehrenberg, 1854 Tetrataxis sp.
Plate 1, figures 1-3
Specimens referred to this genus are present in most samples used in this study. The examples illustrated are representative.﻿SYSTEMATIC DESCRIPTIONS
5
Genus BRADYINA von Moller, 1879
Bradyina sp.
Plate 4, figure 1
Fragmental specimens referred to this genus were recognized in several collections at localities 31 and 32. The example illustrated is representative.
Endothyrid, undet.
Plate 1, figures 4, 5
The specimens illustrated from locality 29 are assigned to the family Endothyridae. They may be the inner volutions of a larger form, but no large en-dothyrids were recognized in these samples.
Genus OZAWAINELLA Thompson, 1935
Ozawainella? sp.
Plate 4, figures 2, 3
The specimens referred with question to this genus show considerable resemblance to Nankinella sp. described below, but the wall is not recrystallized. The significance of the preservation is not understood, but is considered to involve the original wall material. The specimens from locality 31 are similar to those illustrated as Ozawainella TmraJchovensis Manukalova (in Rauser-C'hernoussova and others, 1951, p. 135) but the resemblance may be due primarily to the oblique way in which both specimens were cut.
Genus MILLERELLA Thompson, 1942 Millerella sp. aff. M. marblensis Thompson, 1942
Plate 2, figures 2, 3.
aff. Millerella marblensis Thompson, 1942, p. 405-407, pi. 1, figs. 3-14.
Discussion.—The specimens illustrated are representative of the Millerella found in sample f23975 in association with Nankinella, Staffella, and Pseudostaffella. The size, shape, and degree to which coiling is evolute fit well into the range reported by Thompson (1942, p. 405; 1948, p. 76).
Genus STAEFELLA Ozawa, 1925 Staffella sp. aff. S. powwowensis Thompson 1948
Plata 2, figure 1
aff. Staffella powwowensis Thompson, 1948, p. 78-79, pi.
25 fig. 7-12.
Discussion.—The specimen illustrated is closely similar to the specimen illustrated as figs. 10-11 on plate 25 by Thompson (1947) and is also apparently similar to the holotype, illustrated mostly as a drawing. Not
enough is known about this genus for one to be able to distinguish species at the present time. The Alaskan specimen probably cannot be distinguished from the forms described from Powwow Canyon, Tex. The Texas form was found in association with Millerella, Nankinella, and Profusulinella. The Alaska form was found in sample f23975 with Millerella, Nankinella, and Pseudostaff ella.
Genus NANKINELLA Lee, 1933 Nankinella sp.
Plate 1, figures 6-22
Diagnosis.—Small, discoidal, planispiral, with broadly angular periphery throughout and umbilicate axial regions. Wall structure indistinct, apparently with three layers.
Description.—The spiral form is normal negative to negative with the diameter increasing rapidly through the early stages and less rapidly near maturity. The shape is discoidal throughout with a broadly angular periphery and an umbilicate axis. The chamber height is greatest equatorially and diminishes gradually toward the axis. The form ratio increases gradually from around 0.44 in the inner volutions to about 0.5 in the outer volutions. The proloculus varies in size. The few specimens cut through the proloculus show a range from about 60 to 100 microns, but smaller prolocular diameters are suggested in some of the sections.
The wall structure is indistinct and is probably recrystallized. In some specimens the wall appears to be composed of two dark layers with a lighter layer in between. In other sections it seems to have one dark layer with lighter layers above and below. The thickness is difficult to determine, as the wall is irregular and indistinct.
The septa are unfluted, closely spaced, and inclined anteriorly. The tunnel occupies most of the equatorial peripheral area of each volution. Parachomata are developed at each septum but they do not join to form true chomata.
Comparisons and remarks.—The small number of specimens available for this study precludes satisfactory description or comparison with other members of the genus. Unfortunately no species in this genus has been adequately described. The forms from Alaska resemble A. plummeri Thompson (1947, p. 155) from the Marble Falls Limestone of Texas and N. spp. of Thompson, Pitrat, and Sanderson (1953, p. 547) from central British Columbia. The Alaskan forms are more tightly coiled than the Texas or Columbia forms, but one cannot assess the significance of this without knowing the limits of variability in the described forms.
419-577 0-71-2﻿6
PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
Distribution.—Nankinella sp. is associated with Fusulinella pinguis n. sp. in samples f23973 and f23974. Other associated forms include Tetrataxis sp. (pi. 1, figs. 1, 2) and endothyrids (pi. 1, figs. 4, 5). Rare specimens of Nankinella sp. are noted in f23975 associated with Millerella sp., Staffella sp., and Pseudostajfella rotunda n. sp.
Genus PSEUDOSTAFFELLA Thompson, 1942 PseudostafEella rotunda n. sp.
Plate 2, figures 4-21
Diagnosis.—Shell small, globular with slightly um-bilicate poles, the first 1-2 whorls at right angles to later whorls, septa plane, chomata relatively small and asymmetrical.
Description.—Summaries of the numerical data are given in table 1. The spiral form is negative to normal
negative (fig. 2) with a tendency for an individual to increase in diameter rapidly at first and to grow less rapidly in the later stages. This is also expressed in figure 3 which shows the increase in volution height to be regularly arithmetic throughout most of the growth.
The length increases slowly relative to the radius (fig. 3). Note how closely similar the specimens are in this attribute. The form ratio increases in the early stages of growth and then gradually decreases (fig. 3). Individual specimens may develop a maximum form ratio of 1, but the mean form ratio is always less than 1.
Coiling starts in one plane but after 1 to 1 y2 volutions the axis rotates approximately 90° so that the third and subsequent volutions are at right angles to the juvenarium.
The proloculus ranges in outer diameter from 30 to 75 microns (fig. 3) with most specimens falling in the range of 50-60 microns.
Figure 2.—The spiral form of Pseudostaffella rotunda n. sp. shown by a plot of radius vector on a logarithmic scale against volution intervals on an arithmetic scale. Six specimens from samples f23975 and f23976 are represented.﻿HALF LENGTH,	VOLUTION HEIGHT,	WALL THICKNESS,
IN MILLIMETERS	IN MICRONS	IN MICRONS	SEPTAL SPACING, IN MICRONS
SYSTEMATIC DESCRIPTIONS
l
RADIUS VECTOR, IN MILLIMETERS
Figure 3.—Summary graphs for Pseudostaffella rotunda n. sp. The half length, volution height, wall thickness, septal spacing, form ratio, and tunnel width are plotted against radius vector. This shows the changes for each character during the ontogeny. The mean (*), confidence limits on the mean (o-o), and maximum and minimum (-|—|-) are
DIAMETER OF PROLOCULUS, IN MICRONS
shown at each standard radius. The numerical values for the means and confidence limits and the number of specimens on which they are based are given in table 1. The diameters of proloculi are plotted against the number of specimens.﻿8
PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
Table 1.—Summary numerical data for Pseudostaffella rotunda n. sp.
[The data are presented at standard radii. All numbers are expressed in exponential notation. The number of digits recorded does not imply degree of accuracy]
Character
Radius vector...........
Half length.............
Volution height.........
Wall thickness..........
Tunnel width............
Septal spacing..........
Half length/radius vector.
Radius vector...........
Half length.............
Volution height.........
Wall thickness..........
Tunnel width............
Septal spacing..........
Half length/radius vector.
Rad ius vector..........
Half length.............
Volu tion height........
Wall thickness..........
Tunnel width............
Septal spacing..........
Half le ngth/radius vector.
Radius vector...........
Ha If length............
Volution height.........
Wall thickness..........
Tunnel width............
Se ptal spacing_________
H alf length/radius vector.
Radius vector...........
Half length.............
Volution height_________
Wall thickness__________
Tunnel width............
Septal spacing__________
Half length/radius vector.
Radius vector___________
Half length................
Volution height_________
Wall thickness__________
Tunnel width____________
Septal spacing__________
Half length/radius vector.
Radius vector...........
Half length_____________
Volution height.........
Wall thickness..........
Septal spacing__________
Half length/radius vector.
Radius vector...........
Half length................
Volution height...........
Wall thickness..........
Septal spacing..........
Half length/radius vector.
Number of Mean specimens		Variance	Standard deviation	Coefficient of variability	Standard error of the mean
					
6	7.833E-02	3.767E-04	1.941E-02	2.478E+01	7.923E-03
35	3.934E-02	6.253E-05	7.907E—03	2.010E+01	1.337E—03
12	8.750E-03	2.386E-06	1.545E-03	1.765E+01	4.459E—04
11	4.400E+01	1.068E+02	1.033E+01	2.349E+01	3.116E+00
10	4. 0O0E+00	4.444E-01	6.667E—01	1.667E+01	2.108E-01
6	7.833E-01	3.767E-02	1.941E-01	2.478E+01	7.923E—02
					
8	1.175E-01	1.071E-04	1.035E—02	8.809E+00	3.660E-03
35	4.943E-02	6.161E-05	7.849E-03	1.588E+01	1.327E—03
26	9.192E-03	1.762E-06	1.326E-03	1.444 E+01	2.603E—04
15	5.680E+01	1.467 E+02	1.211E+01	2.133E+0X	3.128E+00
15	4.667 E+00	8.095 E—01	8.997E—01	1.928E+01	2.323E—01
8	9.038E-01	6.340E-03	7.962E-02	8.809E+00	2.815E-02
					
13	1.554E-01	3.603E-04	1.898E-02	1.222E+01	5.264E-03
35	5.757E-02	5.296E-05	7.277E-03	1.264E+01	1.230E-03
32	9.969E—03	1.386E-06	1.177E-03	1.181E+01	2.081E-04
16	7.200E+01	1.404E+02	1.185E+01	1.646E+01	2.962E+00
17	5.412E+00	1.007E+00	1.004E+00	1.855E+01	2.434E-01
13	9.712E-01	1.407E—02	1.186E-01	1.222E+01	3.290E-02
					
14	1.979E-01	4.643E-04	2.155E-02	1. 089E +01	5.759E-03
36	7.267E-02	7.183E-05	8.475E-03	1.166E+01	1.413E-03
35	1.169E-02	2.987E-06	1.728E-03	1.479E+01	2.921E-04
15	9. HOE+01	2.178E+02	1.476E+01	1.615E+01	3.811E+00
19	6.211E+00	6.199E-01	7.873E-01	1.268E+01	1.806E-01
14	9.893E-01	1.161E-02	1.077E—01	1.089E+01	2.879E-02
					
14	2. 429E-01	2. 989E-04	1.729E-02	7.119E+00	4. 621E-03
36	8. 656E-02	6. 443E-05	8. 027E-03	9. 273E+00	1.338E-03
35	1.320E-02	3.165E-05	1.779E-03	1. 348E+01	3. 007E—04
11	1. 277E+02	5.972E+02	2. 444E+01	1. 913E+01	7. 368E+00
20	7. 500 E+00	1.316E+00	1.147E+00	1. 529E+01	2. 565E—01
14	9. 714E-01	4. 782E-03	6.916E-02	7.119E+00	1. 848E—02
					
13	2.969E-01	5. 731E-04	2. 394E-02	3. 062E+00	6. 639E-03
33	1.082E-01	6. 600E-05	8.124E-03	7. 506E+00	1.414E-03
32	1.519E-02	5. 319E-06	2. 305E-03	1. 513E+01	4. 077E-04
5	1. 564E+02	3.173E+03	5. 633E+01	3. 602E+01	2. 519E+01
18	9. 222E+00	2. 065E+00	1. 437E+00	1.558E+01	3.387E-01
13	9. 279E-01	5.596E-03	7.481E-02	8.062E+00	2. 075E-02
22	4.000E-01 ..				
8	3.725E-01	5.929E-04	2. 435E-02	6. 537E+00	8. 609E-03
22	1.306E-01	1. 099E-04	1.048E-02	8. 023E+00	2. 235E-03
22	1.759E-02	5.968E-06	2. 443 E-03	1. 389E+01	5. 208E-04
12	1.108E+01	7. 720E+00	2. 778E+00	2. 507E+01	8. 021E-01
8	9.312E-01	3. 705E-03	6. 087E-02	6. 537E+00	2.152E-02
9	5. 000E-01 ..				
3	4. 533 E-01	2.333E-04	1.528E-02	3. 370E+00	8.819E-03
9	1.512E-01	2. 327E-04	1.525E-02	1. 009E+01	5. 085E-03
8	1.837E-02	1. 055E-05	3. 249E-03	1. 768E+01	1.149E-03
4	1.475E+01	7. 583E+00	2. 754E+00	1. 867E+01	1.377E+00
3	9. 067E-01	9.333E-04	3.055E-02	3. 370E+00	1.764E-02
The character of the wall is not altogether clear. In some parts of the shell it is composed of tectum and diaphanotheca alone, but in other parts tectoria are developed. The wall thickness (fig. 3) increases gradually from about 9 microns to just over 20 microns. These measurements taken on equatorial sections are of tectum and diaphanotheca. The tectoria are generally restricted to the vicinity of the septa.
The septa are plane. The septal spacing increases arithmetically to about 150 microns in large specimens (fig. 3). The spacing is not regular, however, and the last few chambers are commonly widely spaced. The septa thicken toward their bases in the vicinity of the tunnel.
The tunnel is well defined and generally less than half the volution height. The width is variable (fig. 3) and
tends to increase rapidly. It is bounded by relatively small asymmetrical chomata that may appear large in some sections where they coincide with the septal plane.
Comparisons and remarks.—These specimens belong to a group of medium-sized Pseudostaffellas intermediate in character between Pseudostaffella antiqua (Dutkevich) and P. sphaeroidea (Muller). They differ from P. antiqua in being larger and possibly in regularity of coiling. Unfortunately, orientation of sections is a problem with these forms; hence, it is difficult to make comparisons based on the published data. Closely similar forms include the following: P. cf. P. antiqua (Dutkevich) of Forbes 1960 from the lower part of the Passage Beds in Spitsbergen; the specimens described by Forbes have smaller proloculi, do not attain the size of the Alaska specimens, and have smaller chomata.﻿SYSTEMATIC DESCRIPTIONS
9
P. Jcanumai Igo, 1957 from the lowest part of the Ichi-notani Formation in central Japan; the specimens described are a little smaller and have a larger form ratio than those from Alaska. P. sandersoni Thompson, 1965 from the Fort St. James area in British Columbia, Canada; the specimens described by Thompson are smaller, less regularly coiled, and less round than the specimens from Alaska.
Material studied.—The description and illustrations are based on samples f23975 and f23976 in which Pseu-dostaffella is common and is associated with rare Millerella,. NanMnella, Staffella sp., and possible Gli-macammina sp. Thirty-six oriented sections were measured, and many other specimens in 60 thin sections wTere used to describe this species. No larger fusulinids were found in the section sampled on Peratovich Island.
Designation of types.—The specimen illustrated on plate 2 as figures 4a and 4b is designated the holotype. The other specimens studied are paratypes.
Genus FUSULINELLA Moller, 1877 Fusulinella pinguis n. sp.
Plate 3, figures 1-28
Diagnosis.—Shell small, attaining lengths around 2.5 mm and widths around 1.5 mm in about five volutions. The shape is inflated fusiform with convex to concave lateral slopes and bluntly pointed poles. The coiling is relatively loose and the septa nearly straight with some secondary deposits extending poleward from the chomata.
Description.—Summaries of the numerical data are given in table 2. The spiral form is normal to normal negative, with a tendency to be positive in the early stages so that the whole curve is weekly sigmoidal (fig. 4). The diameter increase is shown in the plots for height of volution (fig. 5) and it is apparent that the height increases rapidly in the inner volutions and then increases less rapidly in the outer volutions.
Figure d.—The spiral form of Fusulinella pinguis n. sp. shown by a plot of radius vector on a logarithmic scale against volution intervals on an arithmetic scale. Nine specimens from samples f23973 and f23974 are represented.﻿10
PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
o
cr
o
o
<
CL
(f)
£
CL
300
200
100
co
23 c* !§ il
<
£
0
30
20
10
0
300
	
	+ + O *
■ + + + o		1	 + * O +
+ o * ° +:?° ° + - + og° + + ^++ + +	- o
	
+ + + +++* 8 ^ - 8 + + g8++ +	t ° * D * * - * ; * -
O
cr
o
X
CD
X
z
o
o
>
	+ 1
+ + + 8 8		>xo + i		i	
+++ 8 _ + 8S + +A + #+	
z!
< ■
X •
RADIUS VECTOR, IN MILLIMETERS
Figure 5.—Summary graphs for Fusiilinella pinguis n. sp. The half length, volution height, wall thickness, septal spacing, form ratio, and tunnel width are each plotted against the radius vector. This shows the changes for each character during the ontogeny. The mean(*), confidence limits on the
300
co
z
o
cr
o
X I— □
cr
O
o
LU
>
O 2 (x Q
^ s
^ x cr i-
o o
<
x
- + ; + 0 ( 			
O + o * ° + + o + *	-
+ r + o o + o + o° §°+ +++	
	
	f + + + +	
+ + ^ - 5°++ + + + ' ++	+ 1 ? * + + o
0.50
RADIUS VECTOR, IN MILLIMETERS
mean (o-o), and maximum and minimum (H—|-) are shown at each standard radius. The numerical values for the means and confidence limits and the number of specimens on which each is based are given in table 2. The diameters of proloculi are plotted against the number of specimens.﻿SYSTEMATIC DESCRIPTIONS
11
Table 2.—Summary numerical data for Fusulinella pinguis n. sp.
[The data are presented at standard radii. All numbers are expressed in exponential notation. The number of digits recorded does not imply degree of accuracy.]
Number	Standard Coefficient Standard
Character	of	Mean	Variance deviation	of	error of
specimens	variability the mean
Radius vector___________________________________________________________ 56	1.000E-01 _____________ ..	........
Halflength---------------------------------------------------------------------  34	1.215E-01	5.584E-04	2.363E-02	1. 945E+61	4 053E-03
Volution height---------------------------------------------------------------     56	3.757E-02	4.112E-05	6.413E-03	1.707E+01	8 569E-04
Wall thickness----------------------------------------------------------------    22	8.091E-03	2.944E-06	1. 716E-03	2.121E +01	3 658E-04
Tunnelwidth------------------------------------------------------------------      31	3.729E+01	7.048E+01	8.395E+00	2.251E+01	l'508E+00
Septal spacing---------------------------------------------------------------       21	3.667E+00	9.333E-01	9.661E-01	2.635E+01	2 108E-01
Half length/radius vector-----------------------------------------------------     34	1.215E+00	5.584E-02	2.363E-01	1.945E+01	A053E-02
Radiusvector____________________________________________________________ 63	1.300E—01..............
Halflength---------------------------------------------------------------------   39	1.667E-01	1.186E-03	3.444E-02	2.066E+6i......(TsUE-OS
Volution height---------------------------------------------------------------     63	4.784E-02	6.336E-05	7.960E-03	1.664E+01	1 003E-03
Wall thickness----------------------------------------------------------------    36	9.306E-03	2.447E-06	1.564E-03	1.681E+01	2 607E-04
Tunnelwidth..----------------------------------------------------------------      37	4.951E+01	2.330E+02	1.527E+01	3.083E+01	2 510E+00
Septal spacing-----------------------------------------------------------------   24	4.292E+00	1.433E+00	1.197E+00	2.789E+01	2 444E-01
Half length/radius vector----------------------------------------------------      39	1.282E+00	7.018E-02	2.649E-01	2.066E+01	4.242E-02
Radiusvector------------------------------------------------------------ 64	1.600E-01 ____________ ______________________
Halflength---------------------------------------------------------------------   39	2.297E-01	1.282E-03	3.580E-02	1.558E+oi	" 5 732E-03
Volution height----------------------------------------------------------------   64	5.758E-02	6.025E-05	7.762E-03	1.348E+01	9 702E-04
Wall thickness_________________________________________________________________   52	1.029E-02	2.327E-06	1.525E-03	1.483E+01	2 115E-04
Tunnelwidth--------------------------------------------------------------------   37	6.297E+01	2.884E+02	1.698E+01	2.697E+01	2 792E+00
Septal spacing---------------------------------------------------------------       25	5.040E+00	9.567E-01	9.781E-01	1.941E+01	1.956E-01
Half length/radius vector------------------------------------------------------   39	1.436E+00	5.006E-02	2.237E-01	1.558E+01	3.583E-02
Radiusvector____________________________________________________________ 64	2.000E-01.................. .................
Half length--------------------------------------------------------------------   39	3.105E-01	2.252E-03	4.746E-02	1.528E+oi	7 6obE-63
Volution height______________________________________________________________       64	7.023E-02	1.099E-04	1.048E-02	1.493E+01	1 311E-03
Wall thickness-----------------------------------------------------------------   60	1.140E-02	3.566E-06	1.888E-03	1.657E+01	2.438 -04
Tunnelwidth--------------------------------------------------------------------   37	8.235E+01	3.287E+02	1.813E+01	2.201E+01	2.980E+00
Septal spacing-----------------------------------------------------------------   25	6.000E+00	2.083E+00	1.443E+00	2.406E+01	2.887E-01
Half length/radius vector-----------------------------------------------------    39	1.553E+00	5.631E-02	2.373E-01	1.528E+01	3.800E-02
Radiusvector____________________________________________________________ 64	2.500E-01 ..............
Halflength--------------------------------------------------------------------     39	3.990E-01	2.662E-03	5.i60E-02	"l.293E+bi	8.262E-03
Volution height---------------------------------------------------------------     64	8.777E-02	1.348E-04	1.161E-02	1.323E+01	1 452E-03
Wall thickness....----------------------------------------------------------        64	1.269E-02	7.004E-06	2.654E-03	2.092E+01	3 317E-04
Tunnelwidth__________________________________________________________________      35	1.069E+02	6.448E+02	2.539E+01	2.374E+Q1	4 292E+00
Septal spacing....----------------------------------------------------------        25	7.440E+00	2.757E+00	1.660E+00	2.232E+01	3.321E-01
Half length/radius vector------------------------------------------------------   39	1.596E+00	4.259E-02	2.064E-01	1.293E+01	3.305E-02
Radiusvector____________________________________________________________ 64	3.200E— 01____________ ____________________________
Halflength---------------------------------------------------------------------   39	5.218E-01	4.157E-03	6.448E-02	1.236E+01	1.032E-02
Volution height---------------------------------------------------------------     64	1.045E-01	2.389E-04	1.546E-02	1.479E+01	1.932E-03
Wall thickness---------------------------------------------------------------       64	1.473E-02	7.881E-06	2.807E-03	1.905E+01	3.509E-04
Tunnelwidth-----------------------------------------------------------------        30	1.455E+02	9.896E+02	3.146E+01	2.162E+01	5.743E+00
Septal spacing---------------------------------------------------------------       25	8.560E+00	3.767E+00	1.938E+00	2.264E+01	3.876E-01
Half length/radius vector-----------------------------------------------------     39	1.631E+00	4.060E—02	2.015E—01	1. 236E+01	3.226E—02
Radiusvector............................................................ 58	4.000E-01 ........................................
Halflength____________________________________________________________________     36	6.522E-01	5.841E-03	7.642E-02	1.172E+01	1.274E-02
Volution height----------------------------------------------------------------   58	1.267E-01	2.676E-04	1.636E-02	1.291E+01	2.148E-03
Wall thickness....____________________________________________________________    58	1.698E-02	1.167E-05	3.416E-03	2.011E+01	4.485E-04
Tunnelwidth-------------------------------------------------------------------     23	2.011E+02	1.555E+03	3.943E+01	1.961E+01	8.222E+00
Septal spacing_______________________________________________________________      22	1.009E+01	5.610E+00	2.369E+00	2.347E+01	5.050E-01
Half length/radius vector_____________________________________________________     36	1.631E+00	3.650E-02	1.911E-01	1.172E+01	3.184E-02
Radiusvector____________________________________________________________ 51	5. OOOE—01 ........... ...	.............
Halflength-------------------------------------------------------------------      31	7.761E-01	4.651E-03	6.820E-02	8. 787E+00	i.225E-02
Volution height______________________________________________________________       51	1.534E-01	3.034E-04	1.742E-02	1.136E+01	2.439F-03
Wall thickness________________________________________________________________     49	1.973E-02	1.499E-05	3.872E-03	1.962E+01	5.533E-04
Tunnelwidth____________________________________________________________________   14	2.412E+02	2.072E+03	4.551E+01	1.887E+01	1.216E+01
Septal spacing_______________________________________________________________      19	1.284E+01	5.251E+00	2.292E+00	1.784E+01	5.257E-01
Half length/radius vector....................................................      31	1.552E+00	1.860E-02	1.364E—01	8. 787E+00	2.450E—02
Radius vector___________________________________________________________ 29	6. 300E -01 ......................................
Half length__________________________________________________________________      17	9.629E-01	8.960E-03	9.465E-02	9.830E+00	2.296E-02
Volution height________________________________________________________________   28	1.856E-01	4.089E-04	2.022E-02	1.089E+01	3.822E-03
Wall thickness_______________________________________________________________      26	2.058E-02	2.097E-05	4.580E-03	2.226E+01	8.982E-04
Septal spacing.............................................................          12	1.808E+01	1.154E+01	3.397E+00	1.878E+01	9.806E-01
Half length/radius vector....................................................       17	1.528E+00	2.257E-02	1.502E-01	9.830E+00	3.644E-02
Radius vector........................................................... 6	7. 900E—01 ...........................................
Halflength...................................................................       3	1.063E+00	8.533E-03	9.238E-02	8.687E+00	5.33311-02
Volution height...............................................................      6	2.197E-01	4.103E-04	2.026E-02	9.221E+00	8.269E-03
Wall thickness...............................................................        6	2.117E-02	9.367E-06	3.061E-03	1.446E+01	1.249E-03
Septal spacing...............................................................        3	2.067E+01	3.433E+01	5.859E+00	2.835E+01	3.383E+00
Half length/radius vector.....................................................     3	1.346E+00	1.367E-02	1.169E-01	8.687E+00	6.751E-02
The length increases logarithmically in relation to the diameter in the smaller part of the test; it increases more slowly in the larger parts (fig. 5). The plot of the form ratio at various radii (fig. 5) shows the rapid increase and then gradual decrease during growth.
The proloculus ranges in outer diameter from about 30 to 180 microns with most specimens fairly evenly distributed in the 60-120 micron range and only 14 speci-
mens falling outside that range (fig. 5). A few micro-spheric forms were found.
The wall thickness in the small parts of the shell increases regularly and arithmetically in relation to the radius; it increases less rapidly after specimens attain a radius of about half a millimeter (fig. 5). The maximum thickness recorded was 30 microns. The measurements were all made in the equatorial area and﻿12
PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
did not include secondary deposits of the kind shown in fig. 17 b, pi. 3. The wall appears to thin toward the poles, but no measurements were made. The wall has a tectum, a well-defined diaphanotheca, and generally a well-defined thin inner tectorium. Development of an outer tectorium or other secondary deposits is discontinuous and commonly confined to areas at the base of the septa.
The septa are plane or only slightly fluted toward the poles. They are spaced rather regularly, and the spacing tends to increase arithmetically with increasing radius (fig. 5). The septa tend to thicken in the vicinity of the tunnel.
The tunnel is well defined and generally about half the height of the volution. It increases rapidly in width with increasing radius (fig. 5) and is bounded by asymmetrical chomata that may overhang the tunnel. The distinction between chomata, as such, and thickening of the septa in the tunnel area is not clear. Where the plane septa are intercepted by the section (pi. 3, figs. 6b, 27) there is a suggestion of axial filling, but this is not true axial filling.
Comparisons and remarks.—Fusulinella pinguis n. sp. is similar in many respects to the general group of F. bocki Moller, 1878. The size and shape, the generally straight septa, the narrow tunnel with well-developed chomata, and the wall structure all lend similarity to the general group that includes at least the following named forms: F. bocki Moller 1878, p. 104; F. bocki timanica Hauser 1951, p. 224 (in Rauser-Cherroussova and others, 1951); F. jamesensis Thompson, Pitrat, and Sanderson 1953, p. 548; F. simplicata Toriyama 1958, p. 36; F. simplicata simplicata Toriyama of Ishii 1962, p. 15; F. pygmaea Ishii 1962, p. 19; F. bocki bocki Moller of Ishii 1962, p. 22; F. bocki rotunda Ishii 1962, p. 24; F. bocki biconiformis Ishii 1962, p. 25; F. pandae Ginkel 1965, p. 149; F. maldrigensis Ginkel 1965, p. 150; F. ex gr bocki Moller of Ginkel 1965, p. 159; and F. alaskensis n. sp. described below.
Numerical data for a detailed comparison are available for some of the forms within this group. Using these data, the author made interpolations to facilitate comparisons at standard radii. The wall thickness of F. pinguis is consistently thinner than that of any of the above forms with no overlap in the outer volutions of most specimens. The most similar form in this respect is F. pygmaea Ishii in which, although the wall is consistently thicker, there is some overlap in the total range of thickness.
The form ratio (half length/radius vector) in F. pinguis is smaller than for most of this group. The specimens described by Ishii 1962 as F. bocki bocki, F. b. rotunda, and F. b. biconiformis have a smaller mean form ratio than F. pinguis with some overlap in the
total range. The greatest similarity in all characters studied is to F. bocki bocki of Ishii, but the greater wall thickness in that form distinguishes it without difficulty. Comparisons with F. alaskensis n. sp. are given under that species.
Material studied.—F. pinguis n. sp. is common in samples f23973 and f23974 at locality 29 where it is associated with Tetrataxis sp., endothyrids, and Nankinella sp. Sixty-four oriented sections were measured, and many other specimens in 91 thin sections were used to describe this species.
Designation of types.—The specimen illustrated on plate 3 as figures la-b designated the holotype. The other specimens studied are paratypes.
Fusulinella alaskensis n. sp.
Plate 4, figures 4-30; Plate 5, figures 1-8; Plate 6, figures 1-15
Diagnosis.—Shell small, attaining lengths around 4 mm and widths around 2 mm in about 6 volutions. The shape is fusiform with irregular to concave lateral slopes and bluntly pointed poles. The coiling is relatively loose and the chambers relatively open with little secondary filling and small chomata.
Description.—Summaries of the numerical data are given in table 3. The spiral form is normal to normal negative increasing regularly through the early volutions and increasing only slightly less in the outer volutions (fig. 6.). The pattern for the increase in height of volution for combined samples of this species is shown in figure 7 where it is seen that the increase is quite regular throughout most of the growth.
The length increases logarithmically in relation to the diameter. Figure 7 shows a straight-line plot of log half lengths against radius vector. Note that the spread is narrow throughout, indicating a close homogeneity in specimens from the seven samples.
The form ratio increases rapidly in the early stages of growth and then remains almost constant (fig. 7). The shape is fusiform throughout, with a tendency to develop concave lateral slopes even in some of the early volutions.
The proloculus ranges in outer diameter from about 50 to 130 microns in the megalospheric specimens. More than a third of the specimens are in the 75 to 90 micron range (fig. 7), and the rest fall about equally to each side of this central cluster. Several microspheric juve-naria were found with proloculi about 25 microns in diameter. Some specimens with larger proloculi seem intermediate in form with the initial chambers at an angle to the adult chambers (pi. 5, fig. 3, 8).
The wall thickness increases regularly as shown in figure 7. The maximum thickness recorded was 32 microns. All measurements were taken from the equatorial﻿SYSTEMATIC DESCRIPTIONS
13
VOLUTION INTERVALS
Figure 6.—The ispiral form of Fusulinella alaskensis n. sip. shown by a plot of radius vector on a logarithmic scale against volution intervals on an arithmetic scale. Ten specimens from samples f23977, f23979, and f23986 are represented.
area and, although the wall appears to thin gradually toward the poles no measurements were taken in that area. The wall has a tectum and well-defined diaphano-t.heca (pi. 5) and thin, irregular tectoria, mostly in the vicinity of the septa.
The septa tend to be plane or slightly fluted and are spaced rather regularly throughout most of the shell. The septal spacing increases arithmetically with increasing radius (fig. 7). The septa are thickened to wedges or bulbs by secondary deposits in the vicinity of the tunnel and chomata.
The tunnel is well defined by the chomata. It is generally low, extending less than half the height of the chambers. It tends to be straight or only slightly irregular and increases rapidly in width (fig. 7.). The bounding chomata are small and tend to be symmetrical. Where the plane of the septa coincides or nearly coincides with the plane at the section, the chomata appear to be more massive and asymmetrical because of the extension of secondary deposits along the septa (pi. 5. figs. 1,2,6).
Comparisons and remarks.—Fusulinella alaskensis n. sp. somewhat resembles the forms listed in the discussion of F. pinguis n. sp., but increases more rapidly in length than most of those forms and, therefore has a larger form ratio. One exception is F. simplicata Toriyama 1958, p. 36. The specimens measured by Tori-yama have a large, though variable, form ratio, and the four specimens have a consistently higher mean than F. alaskensis. This is in contrast with the several subspecies of F. simplicata described by Ishii (1962) from Shikoku.
Other species with which F. alaskensis may be compared are: F. iyoensis Ishii 1962, p. 14, which has the same general shape but a thicker wall and smaller form ratio; F. thompsoni Skinner and Wilde 1954, p. 797, which has less concave lateral slopes, more strongly fluted septa, and a much thicker wall; and F. peruana Dunbar and Newell 1946, p. 486, which is similar to F. thompsoni but has a slightly larger form ratio and an even thicker wall at maturity. Comparison between F. pinguis n. sp. and F. alaskensis n. sp. shows that the
419-577 0-71-3﻿14
PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
o--------------------------------------------
O	0.50	1.00
RADIUS VECTOR, IN MILLIMETERS
DIAMETER OF PROLOCULUS, IN MICRONS
Figure 7.—Summary graphs for Fusulinella alaskensis n. sp. The half length, volution height, wall thickness, septal spacing form ratio, and tunnel width are each plotted against the radius vector. This shows the changes for each character during the ontogeny. The mean(*), confidence limits on the
mean (0-0), and maximum and minimum (-|—|-) are shown at each standard radius. The numerical values for the means and confidence limits and the number of specimens on which each is based are given in table 3. The diameters of proloculi are plotted against the number of specimens.﻿SYSTEMATIC DESCRIPTIONS
15
Table 3.—Summary numerical data for Fusulinella alaskensis n. sp.
[The data are presented at standard radii. All numbers are expressed in exponential notation. The number of digits recorded does not imply degree of accuracy]
	Character	Number of specimens	Mean	Variance	Standard deviation	Coefficient of variability	Standard error of the mean
Radius vector						 77	1.000E-01 ..				
Half length
Volution height..........
Wall thickness...........
Tunnel width.............
Septal spacing___________
Half length/radius vector..
Radius vector............
Half length______________
Volution height__________
Wall thickness...........
Tunnel width.............
Septal spacing...........
Half length/radius vector..
Radius vector............
Half length..............
Volution height..........
Wall thickness...........
Tunnel width.............
Septal spacing-----------
Half length/radius vector..
Radius vector____________
Half length..............
Volution height..........
Wall thickness...........
Tunnel width.............
Septal spacing...........
Half length/radius vector.
Radius vector............
Half length...............
Volution height...........
Wall thickness............
Tunnel width.............
Septal spacing...........
Half length/radius vector..
Radius vector.............
Half length...............
Volution height___________
Wall thickness............
Tunnel width..............
Septal spacing............
Half length/radius vector...
Radius vector.............
Half length...............
Volution height...........
Wall thickness............
Tunnel width..............
Septal spacing............
Half length/radius vector...
Radius vector.............
Half length...............
Volution height...........
Wall thickness____________
Tunnel width..............
Septal spacing............
Half length/radius vector...
Radius vector.............
Half length_______________
Volution height...........
Wall thickness____________
Tunnel width______________
Septal spacing____________
Half length/radius vector...
Radius vector___________
Half length...............
Volution height___________
Wall thickness............
Tunnel width..............
Septal spacing............
Half length/radius vector...
Radius vector.............
Half length...............
Volution height___________
Wall thickness____________
Half length/radius vector...
60
77 6
60
17 60
78 60 78 28 60
18 60
78
60
78
48
60
18
60
78
60
78
68
59 18
60
77
60
77
77
58 17 60
77
60
77
76
57
17 60
73
57
73
73
53
15
57
70
56
70
70
40
14
56
59 46 59
57
18 12 46
37
28
37
37
6
9
28
7
6
7
7
6
1.408E-01 3. 800E-02
8.	400E-03
3.	255 E+01
4.	212E+01 1.408E+00
1.300E-01 1. 992E—01 4. 681E-02
9.	286E-03 4. 075E+01
4.	817E+01
1.	532 E+00
1.600E-01
2.	653E-01
5.	709E-02 1.015E-02 5.413E+01
5.	683E+01
1.	658E+00
2.	0O0E-01 3.460E-01 7. 036E-02 1.078E-02
7.	017E+01
6.	706E+01 1. 730E+00
2.500E-01 4.400E-01
8.	630E -02 1.206E-02
9.	690E+01 8. 382E+01 1. 760E+00
3.	200E-01 5.657E-01 1.054E-01 1.376E-02 1.333E+02 1.017 E+02 1.768E+00
4.000E-01 7.195 E-01 1.306E-01 1. 621E-02 1. 867E+02 1. 273E+02 1. 799E+00
5.000E—01 8.905E-01 1.630E-01 1. 841E—02 2.376E+02 1.556E+02
1.	781E+00
6.300E-01 1.143E+00 2.029E—01 2.116E-02
2.	964 E+02
1.	860E+02 1.815E+00
7.	900E-01 1.402E+00
2.	499E-01 2. 486E-02 3.527E+02 2. 488E+02 1. 775E+00
1. 000E+00
1.	742E+00
2.	973E-01 2. 786E-02 1. 742E+00
5. 366E-04 2.926E-05 8.000E-07 4. 693E+01 9. 224 E+01 5.366E-02	2. 316E-02 5.410E-03 8. 944E-04 6. 851E+00 9.604E+00 2.316E-01	1. 645E+01 1.424E+01 1.	065E+01 2.105 E+01 2.	280E+01 1. 645 E+01	2. 990E -03 6.165E-04 4. 000E-04 8. 844E-01 2. 329E+00 2. 990E—02
7.129E-04 3.	330E-05 1.545E-06 8. 636E+01 1. 364E+02 4.	218E-02	2.670E-02 6. 771E-03 1.243E-03 9. 293E+00 1.168E+01 2.054E-01	1. 341E+01 1. 233 E+01 1.339E+01 2.280E+01 2.425 E+01 1.341E+01	3.447E—03 6. 534E-04 2. 349E-04 1.200E+00 2. 753E+00 2. 651E-02
1.225E-03 4.245E-05 8. 506E-07 1.153E+02 1. 776E+02 4. 786E-02	3.500E-02 6. 515E-03 9.223E-04 1. 074E+01 1. 333E+01 2.188E-01	1.319E+01 1.141E+01 9.090E+00 1.	984 E+01 2.	345E+01 1. 319E+01	4.519 E —03 7. 377E-04 1.331E-04 1. 386E+00 3.141E+00 2.824E-02
1.007E-03 6. 361E-05 1.607E-06 2. 302 E+02 1.159E+02 2. 519E-02	3.174E-02 7. 976E-03 1.268E-03 1. 517E+01 1. 077E+01 1.587E-01	9.174E+00 1.134 E+01 1.176E+01 2.162 E+01 1. 606 E+01 9.174E+00	4.098E-03 9.031E-04 1.537E-04 1. 975E+00 2.538E+00 2.049E -02
1.932E-03 8. 361E -05 2.588E-06 5. 017E+02 3.418E+02 3.092E-02	4.396E-02 9.144 E-03 1.609E-03 2. 240E+01 1. 849E+01 1. 758E-01	9. 990E+00 1. 060E+01 1.	333E+01 2.	312E+01 2. 205 E+01 9. 990E+00	5. 675 E-03 1.	042E-04 1.833E-04 2.	941E+00 4. 484 E+00 2.270E-02
3. 296E-03 1.838E-04 5. 276E-06 8.891E+02 2.	442E+02 3.	219E-02	5. 741E-02 1.356E-02 2. 297E-03 2. 982E+01 1.563E+01 1. 794E-01	1. 015E+01 1. 286E+01 1.	669E+01 2.	237E+01 1. 537E+01 1.015E+01	7. 412E-03 1.545E-03 2.635E-04 3. 949E+00 3. 790E+00 2.316E-02
5. 259E-03 1.695E-04 6.054E-06 1. 758E+03 1. 987E+02 3. 287E-02	7. 252E-02 1.302E-02 2. 461E-03 4.193E+01 1. 409E+01 1.813E-01	1.008E+01 9. 970E+00 1.518E+01 2. 245 E+01 1.107E+01 1.008E+01	9.605E-03 1.524E-03 2.880E-04 5. 759E+00 3. 639E+00 2. 401E-02
8.154E-03 2.522E-04 9. 956E-06 1. 627E+03 4. 827E+02 3.262E-02	9.030E-02 1.588E-02 3.155E-03 4. 034E+01 2.197E+01 1.806E-01	1. 014E+01 9. 743E+00 1. 714E+01 1. 697E+01 1. 412E+01 1. 014E+01	1.207E—02 1.898E-03 3. 771E-04 6. 378E+00 5. 872E+00 2.413E-02
1.492E-02 4.500E-04 1.521E-05 3. 692E+03 6. 862E+02 3.758E-02	1. 221E-01 2.121E-02 3.900E-03 6.077E+01 2.620E+01 1.939E-01	1.068E+01 1.045E+01 1. 843E+01 2.050E+01 1. 408E+01 1.068E+01	1.	801E -02 2.	762E-03 5.165E-04 1.	432E+01 7.562E+00 2.	858E-02
1.751E-02 3.181E-04 1.084E-05 2. 803E+03 1.	937E+02 2.	806E—02	1.323E-01 1.784E-02 3. 293E-03 5. 295E+01 1.392E+01 1.675E-01	9. 438E+00 7.136E+00 1.324E+01 1.501E+01 5. 594E+00 9.438E+00	2.501E—02 2.932E-03 5. 413E-04 2.162E+01 4.639E+00 3.166E-02
5. 657E-03 4.	786E-04 1.048E-05 5.	657E-03	7.521E-02 2.188E-02 3. 237E-03 7.521E-02	4. 318E+00 7.359E+00 1.162E+01 4. 318E+00	3. 070E -02 8. 268E-03 1.223E-03 3.070E-02﻿16
PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
form ratio of F. alaskensis is consistently larger, the septal spacing is consistently wider, the tunnel is consistently narrower, and there is considerable overlap in wall thickness. Except for wall thickness, many of the F. bocki group are in intermediate positions between these two species. The wall in most of the other forms is thicker.
Material studied.—F. alaskensis n. sp. is common at localities 31 and 32 where it occurs in a number of samples (see locality descriptions) but is most common in samples f23977 and f23979 at locality 31 and sample f23986 at locality 32. Seventy-eight oriented sections were measured and many others studied in 171 thin sections.
F. alaskensis n. sp. occurs in association with tex-tularids, Tetrataxis sp., endothyrids including Brady-ina sp., Ozawinetta'l, and Fusulina flexuosa n. sp. In addition, in sample f23986 it is associated with
Beedeina'i
Designation of types.—The specimen illustrated on plate 4 as figure 6 and plate 5 as figure 1 is designated
the holotype. The other specimens studied are para-types.
Genus FUSULINA Fischer de Waldheim 1829 Fusulina flexuosa n. sp.
Plate 7, figures 1-20
Diagnosis.—Shell small, attaining lengths up to 9 mm and widths of 1.5 mm in 6 volutions. The shape is irregular subcylindrical, commonly with an irregular axis. The inner volutions are rather fusiform with relatively pointed poles. The coiling is relatively tight with numerous septa in each volution. Chomata are weakly developed. The spirotheca is thin and composed of tectum and diaphanotheca and locally developed tectoria.
Description.—Summaries of the numerical data are given in table 4. The spiral form is normal negative increasing regularly through all but the last volutions in which the rate of increase diminishes as shown in figure 8. The volution height increases with increasing radius as shown for the combined samples in figure 9.
Figure 8.—The spiral form of Fusulina flexuosa n. sp. shown by a plot of radius vector on a logarithmic scale against volution intervals on an arithmetic scale. Six specimens from samples f23979, f23981, and f23986 are represented.﻿SYSTEMATIC DESCRIPTIONS
17
Table 4.—Summary numerical data for Fusulina flexuosa n. sp.
[The data are presented at standard radii. All numbers are expressed in exponential notation. The number of digits recorded does not imply degree of accuracy recorded]
	Number			Standard	Coefficient	Standard
Character	of specimens	Mean	Variance	deviation	of variability	error of the mean
Radius vector........................................................... 3	1.000E—01 __________________________________________________________
Half length.._______________________________________________________________      2	1.700E-01	2.000E-04	1.414E-02	8.319E+00	1.000E-02
Volution height_______________________________________________________________    3	3.867E-02	5.333E-06	2.309E-03	5.973E+00	1.333E-03
Tunnel width..______________________________________________________________      3	4.333E+01	3.333E+01	5.774E+00	1.332E+01	3.333E+00
Half length/radius vector_______________________________________________________  2	1.700E+00	2.000E-02	1.414E-01	8.319E+00	1.000E-01
Radius vector........................................................... 9	1.300E—01 ..........................................................
Half length_____________________________________________________________________  8	2.212E-01	5.355E-03	7.318E-02	3.308E+01	2.587E-02
Volution height_______________________________________________________________    8	5.050E-02	4.857E-05	6.969E-03	1.380E+01	2.464E-03
Wall thickness................................................................    7	9.143E-03	5.476E-06	2.340E-03	2.560E+01	8.845E-04
Tunnel width___________________________________________________________________   6	7.417E+01	7.146E+02	2.673E+01	3.604E+01	1.091E+01
Half length/radius vector____________________________________________________     8	1.702E+00	3.169E-01	5.629E-01	3.308E+01	1.990E-01
Radius vector___________________________________________________________ 13	1. 600E —01 ________________________________________________________
Half length..._________________________________________________________________  12	3.292E-01	2.481E-03	4.981E-02	1.513E+01	1.438E-02
Volution height__________________________________________________________        13	6.331E-02	1.377E-04	1.174E-02	1.854E+01	3.255E-03
Wall thickness_____________________________________________________________      12	1.158E-02	2.083E-06	1.443E-03	1.246E+01	4.167E-04
Tunnel width________________________________________________________________      9	9.800E+01	6.358E+02	2.521E+01	2.573E+01	8.405E+00
Half length/radius vector_____________________________________________________   12	2.057E+00	9.692E-02	3.113E-01	1.513E+01	8.987E-02
Radius vector........................................................... 17	2.000E—01 __________________________________________________________
Half length_________________________________________________________________     16	4.781E-01	6.403E-03	8.002E-02	1.674E+01	2.000E-02
Volution height____________________________________________________________      17	7.147E-02	4.314E-05	6.568E-03	9.190E+00	1.593E-03
Wall thickness.______________________________________________________________    16	1.300E-02	5.733E-06	2.394E -03	1.842E+01	5.986E-04
Tunnel width...________________________________________________________________  14	1.367E+02	2.259E+03	4.753E+01	3.477E+01	1.270E+01
Half length/radius vector_______________________________________________________ 16	2.391E+00	1.601E-01	4.001E-01	1.674E+01	1.000E-01
Radiusvector............................................................ 18	2.500E—01 __________________________________________________________
Half length___________________________________________________________________   17	6.747E-01	9.389E-03	9.690E-02	1.436E+01	2.350E-02
Volution height________________________________________________________________  18	8.956E-02	1.147E-04	1.071E-02	1.196E+01	2.525E-03
Wall thickness__________________________________________________________________ 18	1.439E-02	4.840E-06	2.200E-03	1.529E+01	5.185E-04
Tunnel width____________________________________________________________________ 14	1.624E+02	2.412E+03	4.912E+01	3.024E+01	1.313E+01
Half length/radius vector____________________________________________________    17	2.699E+00	1.502E-01	3.876E-01	1.436E+01	9.400E-02
Radiusvector............................................................ 18	3.200E—01...........................................................
Half length_________________________________________________________________     17	9.159E-01	2.441E-02	1.562E-01	1.706E+01	3.790E-02
Volution height___________________________________________________________       18	1.065E-01	1.413E-04	1.189E-02	1.116E+01	2.802E-03
Wall thickness-............................................................      18	1.678E-02	1.089E-05	3.300E-03	1.967E+01	7.778E-04
Tunnel width.________________________________________________________________    12	2.229E+02	4.601E+03	6.783E+01	3.043E+01	1.958E+01
Half length/radius vector______	  17	2.862E+00	2.384E-01	4.883E-01	1.706E+01	1.184E-01
Radiusvector____________________________________________________________ 17	4.000E—01...........................................................
Half length_________________________________________________________________     16	1.217E+00	4.015E-02	2.004E-01	1.646E+01	5.010E-02
Volution height_________________________________________________________________ 17	1.231E-01	2.072E-04	1.440E-02	1.169E+01	3.491E-03
Wall thickness__________________________________________________________________ 16	1.900E-02	9.333E-06	3.055E-03	1.608E+01	7.638E-04
Tunnel width_____________________________________________________________________ 8	3.160E+02	7.585E+03	8.709E+01	2.756E+01	3.079E+01
Half length/radius vector_______________________________________________________ 16	3.044E+00	2.510E-01	5.010E-01	1.646E+01	1.252E-01
Radiusvector............................................................ 15	5.000E— 01 _________________________________________________________
Half length_____________________________________________________________________ 15	1.619E+00	8.017E-02	2.831E-01	1.749E+01	7.311E-02
Volution height_________________________________________________________________ 15	1.477E-01	1.151E-04.	1.073E-02	7.261E+00	2.770E-03
Wall thickness__________________________________________________________________ 15	2.073E-02	1.278E-05	3.575E-03	1.724E+01	9.231E-04
Tunnel width_____________________________________________________________________ 5	5.064E+02	2.986E+04	1.728E+02	3.412E+01	7.728E+01
Half length/radius vector_______________________________________________________ 15	3.237E+00	3.207E-01	5.663E-01	1.749E+01	1.462E-01
Radius vector. ......................................................... 9	6.300E—01 . ________________________________________________________
Half length____________________________________________________________________   9	2.169E+00	1.816E-01	4.261E-01	1.965E+01	1.420E-01
Volution height__________________________________________________________         9	1.867E-01	6.985E-04	2.643E-02	1.416E+01	8.810E-03
Wall thickness—___________________________________________________________        9	2.222E-02	2.494E-05	4.994E-03	2.247E+01	1.665E-03
Half length/radius vector._______________________________________________________ 9	3.443E+00	4.575E-01	6.764E-01	1.965E+01	2.255E-01
Radiusvector............................................................ 5	7. 900E—01 .........................................................
Half-length___________________________________________________________________    5	2.964E+00	2.720E-01	5.216E-01	1.760E+01	2.333E-01
Volution height....___________________________________________________________    5	2. HOE-01	1.085E-04	1.042E-02	4.867E+00	4.658E—03
Wall thickness________________________________________________________________    4	2.325E-02	2.092E-05	4.573E-03	1.967E+01	2.287E-03
Half length/radius vector...................................................      5	3.752E+00	4.359E-01	6.602E-01	1.760E+01	2.953E-01
The shell length increases in relation to the width at a rate more rapid than simple logarithmic growth (fig. 9). This feature is reflected in the plot of form ratio against radius (fig. 9); the form ratio increases rapidly in the earlier stages of growth and increases less rapidly to maturity. The axis of coiling varies from nearly straight to highly irregular, commonly curved in more than one plane.
The proloculus ranges from 120 to 340 microns in diameter (fig. 9), although most specimens fall in the 150 to 280 micron range. The larger proloculi are of irregular shape. No microspheric specimens were recognized.
The wall thickness increases regularly through the smaller parts of the test and then less rapidly in the last stages of growth (fig. 9). The wall is composed of a thin tectum and a diaphanotheca. Inner and outer tectoria are developed intermittently but are never prominent.
The septa are irregular but tend to be tightly fluted across the entire length of the test They are less fluted in the inner volutions, especially in the forms with smaller proloculi (pi. 7, figs. 2a, b). The septa appear closely spaced, but not enough spacing data are available for a meaningful statement.
The tunnel is poorly defined, wanders in the equatori-﻿18
PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
X
o
<
X
	
	+ . ° 4 *
+ 5 + 8	*
	
0	0.50	1.00
RADIUS VECTOR, IN MILLIMETERS
(/)
o
cr
o
x
i~
9
£
-	
	
+	
o + *	
o + O *	-
o o + o jjc + * o o * 0 +	
**	 *° + o + + o	
o -----------------------------------------
0	0.50	l.oo
RADIUS VECTOR, IN MILLIMETERS
NUMBEROF
SPECIMENS
	
-	1	1	lJ		1 i 1j 1	, i-LLi	i	:
0 _______I__I___u____11 J___U I_____1 II 1 I------1_____
0	100	140	180	220	260	300	340	360
DIAMETER OF PROLOCULUS, IN MICRONS
Figure 9.—Summary graphs for Fusulma flexuosa n. sp. The half length, volution height, wall thickness, form ratio, and tunn width are each plotted against the radius vector. This shows the changes for each character during the ontogeny. Tl mean(*), confidence limits on the mean(o-o), and maximum and minimum (-|—f-) are shown at each standard radius. Tl numerical values for the means and confidence limits and the number of specimens on which each is based are given table 4. The diameters of proloculi are plotted against the number of specimens.﻿SYSTEMATIC DESCRIPTIONS
19
al plane, and is bordered by low, discontinuous chomata or parachomata. The tunnel height varies from less than half to possibly the entire height of the chamber. The tunnel width increases rapidly (fig. 9), but measurements in the outer volutions are probably not reliable because of indeterminate tunnel margins.
Axial filling is present, especially in the inner volutions, but it is irregular and does not appear in all specimens.
Comparison and remarks.—Fusulina flexuosa n. sp. is related to a general group that includes the type species, F. cylindrica Fischer de Waldheim 1829, F. ? occasa Thompson 1965, and Akiyoshiella toriyamai Thompson, Pitrat, and Sanderson 1953. A meaningful comparison with these forms is difficult because little data are available for them. The range of variability of Fusulina flexuosa n. sp. is sufficient to overlap that of the three forms above, but without additional data on the latter their variability cannot be determined. It is possible that each named form, when properly studied, will show more limited ranges within the general areas of overlap ; therefore they are not being combined at this time.
Material studied.—F. flexuosa n. sp. was recognized in samples f23977 and f23981 of locality 31 and in sample f23986 at locality 32. Eighteen oriented thin sections were measured and many others studied in about 50 thin sections. F. flexuosa n. sp. occurs with Tetrataxis sp., endothyrids, Ozawainella?, Fusulinella alaskensis, and (in sample f23986) Beedeina’1.
Designation of types.—The specimen illustrated on plate 7 as figures la-b is designated the holotype. The other specimens studied are paratypes.
Genus BEEDEINA Galloway 1933 Beedeina? sp.
Plate 6, figures 16,17a-b
The genus Beedeina as discussed by Ishii (1957, p. 655) and others seems to be represented in the Alaskan collections by a relatively small, tightly coiled form resembling Fusulina ylychensis Eauser 1951 (in Kauser-Chernoussova and others, 1951, p. 296). Only two oriented sections were obtained. These show the tight coiling, closely spaced and tightly fluted septa, moderately thick wall composed of tectum, diaphanotheca, and tectoria, a relatively narrow tunnel well defined by asymmetrical chomata, and no other obvious epithecal deposits. These specimens cannot be assigned to Fusulinella alaskenis n. sp. or to Fusulina flexuosa n. sp., the other larger fusulinids found in this sample. They are not typical of Beedeina either, but seem to be within the morphologic range of that genus.
REFERENCES CITED
Douglass, R. C., 1970, Morphologic studies of fusulinids from the Lower Permian of West Pakistan: U.S. Geol. Survey Prof. Paper 643-G, 13 p., 7 pis., 6 text figs.
Dunbar, C. O., and Newell, N. D., 1946, Marine Early Permian of the Central Andes and its fusuline faunas: Am. Jour. Sci., v. 244, no. 6, p. 377-402; no. 7, p. 457-491, pis. 1-12.
DutkeviOh, G, A., 1934, Some new species of Fusulinidae from the Upper and Middle Carboniferous of Verkhne-Chus-sovskye Gorodki of the Chussovaya River (western slope of the middle Urals) :	[U.S.S.R.] Neftyanoi Geologo-
Rezvedochnyi Inst. Trudy, ser. A, v. 36, p. 1-98, pis. 1-6. [In Russian, English summary.]
Dutro, J. T., Jr., and Douglass, R. C., 1961, Pennsylvanian rocks in southeastern Alaska, in Geological Survey research 1961: U.S. Geol. Survey Prof. Paper 424-B, p. B239-B241, 1 text fig.
Ehrenberg, C. G., 1854, Mikrogeologie: Leipzig, L. Voss, 374 p., 40 pis.
Fischer de Waldheim, G., 1829, Sur les Cephalopodes fossiles de Moscou et de ses environs, en montrant des objects en nature: Moscuo Imp. Soc. Nat. Bull., v. 1, p. 300-331.
Forbes, C. L., 1960, Carboniferous and Permian Fusulinidae from Spitsbergen: Palaeontology, v. 2, pt. 2, p. 210-225, pis. 30-33,1 fig., 1 table.
Galloway, J. J., 1933, A manual of Foraminifera (James Furman Kemp memorial series Pub. no. 1) : Bloomington, Ind., The Principia Press Inc., 483 p., 42 pis.
Ginkel, A. C. van, 1965, Carboniferous fusulinids from the Cantabrian Mountains (Spain) : Leidse Geol. Meded., v. 34, p. 1-225, pis. 1-53, 13 figs, maps, correlation charts.
Igo, Hisayoshi, 1957, Fusulinids of Fukuji, southeastern part of the Hida Massif, Central Japan: Tokyo Kyoiku Daigaku Sci. Repts., sec. C, no. 47, p. 153-246, pis. 1-15, 2 text figs.
Ishii, Ken-iclii, 1957, On the so-called Fusulina: Japan Acad. Proc. v. 33, no. 10, p. 652-656,2 text-figs.
------1958a, Fusulinids from the middle Upper Carboniferous
Itadorigawa group in western Shikoku, Japan; part I Genus Fusulina: Osaka City Univ., Inst. Polytech. Jour., ser. G, Geoscience, v. 4, p. 1-28, pis. 1-5, tables 1-3.
------1958b, On the phylogeny, morphology and distribution of
Fusulina, Beedeina and allied fusulind genera: Osaka City Univ., Inst. Polytech. Jour., ser. G, Geoscience, v. 4, p. 29-70, pis. 1-4, text figs. 1-5
------■ 1962, Fusulinids from the middle Upper Carboniferous
Itadorigawa Group in western Shikoku, Japan Part II. Genus Fusulinella and other fusulinids: Osaka City Univ. Jour. Geosciences, v. 6, art. 1, p. 1—43, pis. 6-12.
Lee, J. S., 1933, Taxonomic criteria of Fusulinidae with notes on seven new Permian genera : Natl. Research Inst, of Geology (Acad. Sinica), Mem., v. 14, p. 1-32, pis. 1-5, 8 text figs.
Mol'ler, V. von, 1878, Die Spiral-Gewundene Forminiferen des Russischen KOhlen Kalks: St. Petersbourg Akad. Imp. Sci. Mem., ser. 7, v. 25, no. 7, p. 1-147, pis. 1-15.
-------- 1879, Die Foraminiferen des russischen Kohlen Kalks:
St. Petersbourg Akad. Imp. Sci. Mem., ser 7, v. 27, p. 1-131, pis. 1-7. text figs 1-30.
Muffler, L. J. P., 1967, Stratigraphy of the Keku Islets and neighboring parts of Kuiu and Kupreanof Islands, southeastern Alaska : U.S. Geol. Survey Bull. 1241-C, p. 1-52, pi. 1, figs. 1-15.﻿20
PENNSYLVANIAN FUSULINIDS, SOUTHEASTERN ALASKA
Ozawa, Yoshiaki, 1925, On the classification of Fusulinidae: Tokyo Imp. Univ. Jour. Coll. Sci., v. 45, art. 4, p. 1-26, pis. 1-4, 3 text figs.
Rauser-Ohernoussova D. M., and others, 1951, Middle Carboniferous fusulinids of the Russian Platform and adjoining regions: Moscow, Akad. Nauk SSSR, Inst. Geol. Nauk, 380 p., 58 pis., 30 text figs, (in Russian).
Simpson, G. G., Roe, Anne, and Lewontin, R. C., in 1960, Quantitative zoology, revised ed.: New York, Harcourt, Brace and Company, 440 p., 64 figs.
Skinner, J. W. and Wilde, G. L., 1954, New early Pennsylvanian fusulinids from Texas: Jour. Paleontology, v. 28, no. 6, p. 796-803, pis. 95-96.
Thompson, M. L., 1935, The fusulinid genus Staffclla in America : Jour. Paleontology, v. 9, no. 2, 111-120, pi. 13.
------1942, New genera of Pennsylvanian fusulinids : Am. Jour.
Sci., v. 240, p. 403-420, pis. 1-3.
------ 1947. Stratigraphy and fusulinids of pre-Desmoinesian
Pennsylvanian rocks, Llano Uplift, Texas: Jour. Paleontology, v. 21, no. 2, p. 147-164, pis. 31-33, 2 text figs.
------1948, Protozoa; Studies of American fusulinids: Kansas
Univ. Paleont. Contr., art. 1, p. 1-184, pis. 1-38, 7 text figs.
------1965, Pennsylvanian and Early Permian fusulinids from
Fort St. James area, British Columbia, Canada: Jour. Paleontology, v. 39, no. 2, p. 224-234, pis. 33-35, 1 text fig.
Thompson, M. L., Pitrat, C. W., and Sanderson, G. A., 1953, Primitive Cache Creek fusulinids from central British Columbia: Jour. Paleontology, v. 27, no. 4, p. 545-552, pis. o7—08.
Toriyama, Ryuzo, 1953, New peculiar fusulinid genus from the Akiyoshi limestone of southwestern Japan: Jour. Paleontology, v. 27, p. 251-256, pis. 35, 36, tables 1,2.
--------1958, Geology of Akiyoshi; part 3, Fusulinids of Akiyoshi : Kyushu Univ., Fac. Sci. Mem., ser. D, v. 7, 264 p., 48 pis.﻿INDEX
[Italic page numbers indicate major references and descriptions]
A
Page
Akiyoshiella toriyamai__________________________ 19
alaskensis, Fusulinella___1, 2, 4, 12, 19; pis. 4, 5, 6
antiqua, Pseudostaffella------------------------- 8
Armstrong, A. K._______________________________ 1,2
B
Beedeina_______________________________2, 4, 16, 19
sp____________________________________19; pi. 6
biconi for mis, Fusulinella bocki______________ 12
jbocki, Fusulinella------------------------- 12,16
Fusulinella bocki__________________________ 12
bocki bocki, Fusulinella_______________________ 12
biconiformis, Fusulinella _________________ 12
rotunda, Fusulinella_______________________ 12
timanica, Fusulinella---------------------- 12
Brady ina_______________________________________ 5
sp_______________________________2, 5, 16; pi. 4
British Columbia___________________________ 1, 5
Fusulinella—Continued
maldrigensis______
pandae____________
peruana___________
pinguis___________
pygmaea___________
simplicata________
simplicata____
thompsoni_________
sp----------------
Page
12
12
13
1, 2, 6, 9, 12; pi. 3
12
12,13
12
13
2
I
Ichinotani Formation___________________________ 9
Itadorigawa Group______________________________ 1
iyoensis, Fusulinella_________________________ 13
J
jamesensis, Fusulinella.
12
P
pandae, Fusulinella________
Passage Beds_______________
Pennsylvanian age, Middle.
Peratovich Island__________
peruana, Fusulinella_______
pinguis, Fusuline lla______
plummeri, Nankinella_______
Powwow Canyon, Texas_______
Prince of Wales Island_____
Pro fusulinella____________
Pseudostaff ella___________
antiqua_______________
kanumai_______________
rotunda_______________
sandersoni____________
sphaeroidea___________
pygmaea, Fusulinella_______
Page
___________ 12
___________ 8
___________ 1,2
______________ 2,9
_______________ 13
1, 2, 6, 9, 12; pi. 3
________________ 5
................ 5
............ 1,2
________________ 5
...........1, 5, 6
____________ 8
________________ 9
______1, 2, 6; pi. 2
...............  9
____________ 8
____________ 12
K
R
C
Carboniferous age___________________________ 1
Climacammina sp_____________________________ 9
Craig_____________________________________ 1,2
cylindrica, Fusulina_______________________ 19
E
Endothyrid______________________________5; pi. 1
Endothyridae________________________________ 5
F
flexuosa, Fusulina____
Fort St. James_______
Fukuji area, Japan. _
Fusulina_____________
cylindrica_______
flexuosa_________
occasa___________
ylychensis_______
sp---------------
Fusulinella__________
alaskensis_______
bocki____________
biconiformis
bocki_______
rotunda_____
timanica____
iyoensis_________
jamesensis_______
_____________1, 2, 16; pi. 7
................... 1
___________________ 1
___________________ 1,16
______________________ 19
_____________1, 2, 16; pi. 7
_____________________  19
______________________ 19
................... 2
....................  1,9
1, 2, 4, 12, 19; pis. 4, 5, 6
...................12,16
___________________ 12
___________________ 12
................... 12
___________________ 12
______________________ 13
................... 12
kanumai, Pseudostaff ella_____________________ 9
Klawak________________________________________ 2
Klawak Formation_________________________ 1, 2
Klawak Inlet__________________________________ 4
Kuiu Island___________________________________ 1
kurakhovensis, Ozawainella____________________ 6
L
Ladrones Islands______________________________ 2
Ladrones Limestone__________________________ 1,2
M
maldrigensis, Fusulinella____________________ 12
Marble Falls Limestone________________________ 5
marblensis, Millerella___________________5; pi. 2
Millerella__________________________________ 5,9
marblensis__________________________5; pi. 2
sp______________________________2, 5, 6; pi. 2
rotunda, Fusulinella bocki__________________ 12
Pseudostaff ella_________________1, 2, 6; pi. 2
S
Saginaw Bay____________________________________ 1
Saginaw Bay Formation__________________________ 1
sandersoni, Pseudostaff ella___________________ 9
Shikoku, Japan_________________________________ 1
Shishidedai area, Japan________________________ 1
simplicata, Fusulinella____________________12,13
simplicata, Fusulinella__________________ 12
Spain__________________________________________ 1
sphaeroidea, Pseudostaff ella__________________ 8
Spitsbergen__________________________________ 1,8
Staff ella___________________________________ 1,5
powwowensis___________________________5; pi. 2
sp______________________________2, 5, 6, 9; pi. 2
N
T
Nankinella____
plummeri. sp-------
....... 1, 5, 9
_______	5
2, 5, 12; pi. 1
O
Tetrataxis________________________________________ U
Tetrataxis sp___________________2, 4, 6, 12, 16; pi. 1
thompsoni, Fusulinella___________________________ 13
timanica, Fusulinella bocki______________________ 12
toriyamai, Akiyoshiella__________________________ 19
occasa, Fusulina_______________________________ 19
Ozawainella_______________________________ 5,16
kurakhovensis______________________________ 6
sp___________________________________2, 5; pi. 4
Y
ylychensis, Fusulina_________________________ 19
21
U. S. GOVERNMENT PRINTING OFFICE : 1971 O - 419-577﻿

﻿PLATES 1-7
[Contact photographs of the plates in this report are available, at cost, from U.S. Geological Survey Library, Federal Center, Denver, Colorado 802215]﻿PLATE 1
Figures 1-3. Telrataxis sp. (p. 4) from locality 29 Ladrones Islands.
la-b. Axial section X	10	and	X	50,	specimen f23973-28, USNM	167022.
2a-b. Axial section X	10	and	X	50,	specimen f23973-31, USNM	167023.
3.	Axial section X 50, specimen f23974-l, USNM 167024.
4,	5. Endothyrid undet. (p. 5) from locality 29 Ladrones Islands.
4.	Axial section X 50, specimen f23974~12, USNM 167025.
5.	Axial section X 50, specimen f23974-3, USNM 167026.
6-22. Nankinella sp. (p. 5) from locality 29 Ladrones Islands.
6a-b. Axial section X	10	and	X	50,	specimen f23973-16, USNM	167027.
7a-b. Axial section X	10	and	X	50,	specimen f23973-3, USNM 167028.
8a-b. Equatorial section X 10 and X 50, specimen f23974-20, USNM 167029. 9a-b. Equatorial section X 10 and X 50, specimen f23974-4, USNM 167030.
10.	Axial section X 50, specimen f23974-17, USNM 167031.
11.	Axial section X 50, specimen f23973-2, USNM 167032.
12.	Axial section X 50, specimen f23973-39, USNM 167033.
13.	Axial section X 50, specimen f23973-35, USNM 167034.
14.	Equatorial section X 50, specimen f23973-33, USNM 167035.
15.	Subaxial section X 50, specimen f23973-28, USNM 167036.
16.	Axial section X 50, specimen f23973-33, USNM 167037.
17.	Deep tangential section X 50, specimen f23974-3, USNM 167038.
18.	Subaxial section X 50, specimen f23974-9, USNM 167039.
19.	Subaxial section X 50, specimen f23974-5, USNM 167040.
20.	Axial section with twisted axis X 50, specimen f23973-35, USNM 167041.
21.	Tangential section X 50, specimen f23974-8, USNM 167042.
22.	Tangential section X 50, specimen f23973-17, USNM 167043.﻿TETRATAXIS, ENDOTHYRIDS, AND NANKINELLA SP. FROM LADRONES ISLANDS﻿PLATE 2
Figure 1. Staffella sp. aff. S. powwowensis Thompson 1948 (p. 5) from locality 30 on Peratovich Island. Axial section X 50 specimen f23975-13, USNM 167044.
2-3. Millerella sp. aff M. marblensis Thompson 1942, (p. 5) from locality 30 on Peratovich Island.
2.	Axial section X 50, specimen f23975-4, USNM 167045.
3.	Axial section X 50, specimen f23975-8, USNM 167046.
4-21. Pseudostajfella rotunda Dougiass, n. sp. (p. 6) from locality 30 on Peratovich Island.
4a-b. Axial section of the holotype X 10 and X 50, specimen f23975-12, USNM 167047.
5a-b. Oblique deep tangential section X 10 and X 50 showing the relationship between the chomata and the septa specimen f23976-l, USNM 167048
6a-b. Axial section X 10 and X 50, specimen f23975-8, USNM 167049.
7. Equatorial section X 10, specimen f23975-6, USNM 167050.
8a-b. Equatorial section X 10 and X 50, specimen f23975-5, USNM 167051.
9a-b. Equatorial section X 10 and X 50, specimen f23975-4, USNM 167052. lOa-b. Oblique equatorial section X 10 and X 50, specimen f23975-3, USNM 167053. lla-b. Equatorial section X 10 and X 50, specimen f23976-2, USNM 167054.
12. Tangential section X 50, specimen f23975-ll, USNM 167055.
13. Equatorial section X 50, specimen f23975-10, USNM 167056.
14.	Equatorial section X 50, specimen f23976-9, USNM 167057.
15.	Axial section X 50, specimen f23976-4, USNM 167058.
16.	Axial section X 50, specimen f23975-ll, USNM 167059.
17.	Axial section X 50, specimen f23976-5, USNM 167060.
18.	Equatorial	section	X	50, specimen	f23976-6,	USNM	167061.
19.	Equatorial	section	X	50, specimen	f23975-7,	USNM	167062,
20.	Equatorial	section	X	50, specimen	f23975-9,	USNM	167063.
21.	Equatorial	section	X	50, specimen	f23976-7,	USNM	167064.﻿STAFFELLA, MILLERELLA, AND PSEUDOSTAFFELLA ROTUNDA DOUGLASS N SP
FROM PERATROVICH ISLAND﻿PLATE 3
Figures 1-28. Fusulinella pinguis Douglass, n. sp. (p. 9) from locality 29, Ladrones Islands.
la-b. Axial section of the holotype X 10 and X 50, specimen f23973-3, USNM 167065.
2.	Axial section X 10, specimen f23973-5, USNM 167066.
3.	Axial section X 10, specimen f23973-12, USNM 167067.
4.	Axial section X 10, specimen f23973-14, USNM 167068.
5.	Axial section X 10, specimen f23973-22, USNM 167069.
6a-b. Axial section X 10 and X 50, specimen f23973-24, USNM 167070. A microspheric specimen.
7.	Axial section X 10, specimen f23974-5, USNM 167071.
8.	Axial section X 10, specimen f23974-12, USNM 167072.
9.	Axial section X 10, specimen f23974-15, USNM 167073.
10.	Axial section X 10, specimen f23974-l, USNM 167074.
11.	Axial section X 10, specimen f23974-3, USNM 167075.
12.	Axial section X 10, specimen f23974-6, USNM 167076.
13.	Equatoiial section X 10, specimen f23973-25, USNM 167077.
14.	Equatorial section X 10, specimen f23973-27, USNM 167078.
15a-b. Equatorial section X 10 and X 50, specimen f23973-32, USNM 167079.
16. Equatorial section X 10, specimen f23973-37, USNM 167080.
17a-b. Equatorial section X 10 and X 50, specimen f23973-39, USNM 167081.
18.	Tangential section	X	10,	specimen f23973-27,	USNM 167082.
19.	Tangenital section	X	10,	specimen f23974-22,	USNM 167083.
20.	Equatorial section	X	10,	specimen f23974-17,	USNM 167084.
21.	Equatorial section	X	10,	specimen f23974-22,	USNM 167085.
22a-b. Equatorial section X 10 and X 50, specimen f23974-21, USNM 167086.
23.	Equatorial section	X	10,	specimen f23974-16,	USNM 167087.
24.	Equatorial section	X	10,	specimen f23973-38,	USNM 167088.
25.	Rock slice X 10 showing axial, tangential and subequatorial section of Fusulinella and a subaxial section
of Nankinella, slide f23974-9.
26.	Rock slice X 10 showing random slices of Fusulinella, Nankinella, and a textularid, slide f23974-25, USNM
167089.
27.	Axial section X 50, specimen f23974-8, USNM 167090.
28.	Axial section X 50 from slice shown in fig. 25, specimen f23974-9, USNM 167091.﻿GEOLOGICAL SURVEY
PROFESSIONAL PAPER 706 PLATE 3
FUSULINELLA PINGUIS DOUGLASS, N. SP., FROM LADRONES ISLANDS﻿PLATE 4
Figure 1. Bradyina sp. (p. 5) from locality 31, Klavvak inlet. Axial section X 10, specimen f23979-3, USNM 167092. 2-3. Ozawainella? sp. (p. 5) from locality 31, Llawak Inlet.
2.	Tangential section X 50, specimen f23977-2, USNM 167093.
3.	Oblique axial section X 50, specimen f23978-2, USNM 167094.
4-30. Fusulinella alaskensis Douglass, n. sp. (p. 12) from locality 31, Klawak Inlet.
4.	Axial section X 10, specimen f23982-2, USNM 167095.
5a-b. Equatorial section X 10 and X 50, specimen f23982-4, USNM 167096.
6.	Axial section of the holotype X 10, specimen f23982-l, USNM 167097.
7.	Subaxial section X 10, specimen f23981-3, USNM 167098.
8.	Equatorial section X 10, specimen f23980-5, USNM 167099.
9.	Axial section X 10, specimen f23981-l USNM 167100.
10. Axial section X 10, specimen f23980-2, USNM 167101.
11. Axial section X 10, specimen f23980-l, USNM 167102.
12.	Axial section X 10, specimen f23979-5, USNM-167103.
13.	Axial section X 10, specimen f23979-3 USNM 167104.
14.	Axial section X 10, specimen f23979-2 USNM 167105.
15.	Equatorial section X 10, specimen f23979-19, USNM 167106.
16.	Equatorial section X 10, specimen f23979-16, USNM 167107.
17.	Tangential section X 10, specimen f23979-19, USNM 167108.
18.	Equatorial section X 10, specimen f23979-14, USNM 167109.
19.	Equatorial section X 10, specimen f23979-20, USNM 167110.
20.	Axial section X 10, specimen f23979-l, USNM 167111.
21.	Axial section X 10, specimen f23979-8, USNM 167112.
22.	Equatorial section X 10, f23977-12, USNM 167113.
23.	Equatorial section X 10, specimen f23977-13, USNM 167114.
24a-b. Equatorial section X 10 and X 50, specimen f23977-14, USNM 167115.
25a-b. Equatorial section X 10 and X 50, specimen f23977-15, USNM 167116.
26.	Axial section X 10, specimen f23977-ll, USNM 167117.
27.	Axial section X, 10, specimen f23977-5, USNM 167118.
28.	Axial section X 10, specimen f23977-8, USNM 167119.
29.	Axial section X 10, specimen f23977-10, USNM 167120.
30.	Juvenarium of microspheric specimen X 50, f23977-6, USNM 167121.﻿GEOLOGICAL SURVEY
00	24b	PRh
“ SP"	N.
PROFESSIONAL PAPER 706 PLATE 4
24a
25a﻿PLATE 5
Figures 1-8. Fusulinella alaskensis Douglass, n. sp. (p. 12) from locality 31, Klawak Inlet. All X 50.
1.	Axial section of the holotype shown on pi. 4, fig. 6, showing the difference in appearance of the chomata at
the septa and between septa. USNM 167097.
2.	Subaxial section of the specimen shown on pi. 4 as fig. 7. The septa are in the plane of the section at the right
side of the tunnel. Contrast this with the open look of fig. 5. USNM 167098.
3.	Axial section of the specimen shown on pi. 4, fig. 11. The juvenariaum is at an angle to the adult and the
proloculus is small, but the specimen is not a typical microspheric form. USNM 167102.
4.	Axial section of a small specimen showing regular growth. Specimen f23979-ll, USNM 167122.
5.	Axial section of the specimen shown on pi. 4, fig. 13, showing the openness in most volutions where the septa
are not intercepted. Note the chomata are formed in several layers of different densities. USNM 167104.
6.	Subaxial section of a specimen that appears to have massive chomata because of the intersection of the septa
in the plane of section. Specimen f23979-24, USNM 167123.
7.	Axial section of the specimen shown on pi. 4, fig. 27, showing regular development from a relatively small
proloculus, USNM 167118.
8.	Axial section of the specimen shown on pi. 4, fig. 26 showing an endothyrid juvenarium with one volution at
a large angle to the axis of the adult, USNM 167117.﻿GEOLOGICAL SURVEY
PROFESSIONAL PAPER 706 PLATE 5
FUSULINELLA ALASKENSIS DOUGLASS, N. SP., FROM KLAWAK INLET﻿PLATE 6
Figures 1-15. Fusilinella alaskensis Douglass n. sp. (p. 12) from locality 32, sample f23986, Prince of Wales Island.
1. Axial section X 10, specimen 1, USNM 167124.
2a-b. Axial section X 10 and X 50, specimen 9, USNM 167125. Plane of septa nearly coincide with section in upper part giving the impression of more massive chomata.
3. Axial section X 10, specimen 10, USNM 167126.
4a-b. Axial section X 10 and X 50, specimen 16, USNM 167127.
5a-b. Equatorial section X 10 and X 50, specimen 42, USNM 167128.
6. Axial section X 10, specimen 20, USNM 167129.
7a-b. Axial section X 10 and X 50, specimen 2, USNM 167130 cut in a plane where many of the septa nearly coincide with the section and the impression of massive chomata is developed.
8.	Axial	section	X	10, specimen	13,	USNM	167131.
9.	Axial	section	X	10, specimen	19,	USNM	167132.
10.	Axial section X 10, specimen 6, USNM 167133.
11.	Tangential section X 10, specimen 29, USNM 167134.
12.	Axial	section	X	10, specimen	23,	USNM	167135.
13.	Axial	section	X	10, specimen	12,	USNM	167136.
14.	Tangenital section X 10, from same thin section as specimen 2, figures 7a-b.
15.	Axial section X 50, specimen 3, USNM 167137.
16-17. Beedeinaf sp. (p. 19) from locality 32, sample f23986, Prince of Wales Island.
16.	Equatorial section X 10, specimen 44, USNM 167138.
17a-b. Axial section X 10 and X 50, specimen 48, USNM 167139.﻿GEOLOGICAL SURVEY	PROFESSIONAL PAPER 706 PLATE 6
7b	17b
FUSULINELLA ALASKENSIS DOUGLASS, N.SP.,AND BEEDEINA1 SP. FROM PRINCE OF WALES ISLAND﻿PLATE 7
Figures 1-20. Fusulina flexuosa Douglass, n. sp. (p. 16) from localities 31 and 32., Klawak Inlet and Prince of Wales Island.
la-b. Axial section X 10 and X 50 of the holotype, one of the most regular specimens cut in a plane that misses most septa. Specimen f23977-17, USNM 167140.
2a-b. Axial section X 10 and X 50 of a specimen with small proloculus showing tightly coiled inner volutions. Specimen f23979-22, USNM 167141.
3a-b. Deep tangential section of a specimen with small proloculus showing discontinuous chomata even in the early volutions. Specimen f23986-36, USNM 167142.
4.	Axial section X 10, partly silicified specimen f23979-21, USNM 167143.
5.	Axial section X 10, specimen f23977-18, USNM 167144.
6.	Deep tangential X 10, specimen f23979-23, USNM 167145.
7.	Axial section X 10, specimen f23986-33, USNM 167146.
8.	Axial section	X	10, specimen f23981-8, USNM 167147.
9a-b.	Axial section	X	10 and X 50, specimen f23981-6, USNM	167148.
lOa-b.	Axial section	X	10 and X 50, specimen f23986-28, USNM 167149.
lla-b.	Axial section	X	10 and X 50, specimen f23981-9, USNM	167150.
12.	Axial section	X	10, specimen f23981-7, USNM 167151.
13.	Axial section X 10 of a specimen with a large proloculus. Specimen f23986-31, USNM 167152.
14.	Axial section	X	10,	specimen f23986-29,	USNM	167153.
15.	Axial section	X	10,	specimen f23986-27,	USNM	167154.
16.	Axial section	X	10,	specimen f23986-30,	USNM	167155.
17.	Axial section	X	10,	specimen f23986-34,	USNM	167156.
18.	Subaxial section X 10, specimen f23986-35, USNM 167157.
19. Equatorial section X 10, specimen f23986-40, USNM 167158.
20. Tangential section X 10, specimen f23986-38, USNM 167159﻿GEOLOGICAL SURVEY
PROFESSIONAL PAPER 706 PLATE 7
ittiauw
FUSULINA FLEXUOSA DOUGLASS, N. SP., FROM KLAWAK INLET AND PRINCE OF WALES ISLAND﻿

﻿

﻿


﻿﻿
﻿i£nw^
Interpretation of an Aeromagnetic
■'qg
l Survey of the Amchitka Island
by
Area, Alaska

GEOLOGICAL SURVEY PROFESSIONAL PAPER 707
Prepared on behalf of the U.S. Atomic Energy Commission
DOCUMENTS department NOV 6 1972
^s.s. nr﻿\﻿Interpretation of an Aeromagnetic Survey of the Amchitka Island Area, Alaska
By G. D. BATH, W. J. CARR, L. M. GARD, Jr. and W. D. QUINLIVAN
GEOLOGICAL SURVEY PROFESSIONAL PAPER 707
Prepared on behalf of the U.S. Atomic Energy Commission
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972﻿UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY V. E. McKelvey, Director
Library of Congress catalog-card No. 70-189816
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 Stock Number 2401-2087﻿CONTENTS
Page
Abstract.................................................. 1
Introduction.............................................. 1
Previous magnetic surveys................................. 2
Aeromagnetic survey....................................... 3
Reduction of data.................................... 3
Ground magnetic surveys................................... 3
Magnetic properties of rock samples....................... 4
Measuring magnetic susceptibility.................... 4
Measuring remanent magnetization..................... 4
Geologic setting.......................................... 5
Volcanic breccia........................................   6
Magnetic properties.................................. 6
Aeromagnetic anomalies............................... 8
Ground survey anomalies.............................. 8
Volcanic sandstone, siltstone, and tuif breccia........... 9
Dikes and small sills.................................... 10
Intrusive rocks.......................................... 11
Magnetic properties................................. 11
Aeromagnetic anomalies.............................. 12
Lava flows and thick sills............................... 12
Magnetic properties................................. 14
Page
Lava flows and thick sills — Continued
Aeromagnetic anomalies........................... 16
Ground survey anomalies.......................... 16
Analysis of magnetic anomalies........................ 17
Depth estimates.................................. 17
Dipole and sheetlike models.....................  19
Interpretation of anomalies.........................   19
East Cape anomaly................................ 20
White House Cove and shelf-break anomalies....... 20
Pillow Point and Rifle Range Point anomalies..... 22
St. Makarius Point anomaly....................... 22
Mex Island anomaly..............................  23
Bird Rock, Windy Island, Chitka Point-Constantine
Point anomalies................................ 23
Site B anomaly................................... 23
—780 anomaly..................................... 23
Site F anomaly................................... 23
Relation of submarine structure south of Amchitka
to aeromagnetic anomalies...................... 24
References cited...................................... 24
ILLUSTRATIONS
Page
Plate 1. Aeromagnetic map of Amchitka and Rat Islands and surrounding area, Alaska............................... In pocket
2.	Residual magnetic anomaly and generalized geologic map of Amchitka Island, Alaska.................... In pocket
3.	Plots of magnetic anomaly and standard error from ground survey data at stations 0.1 mile apart
on Amchitka Island, Alaska....................................................................... In pocket
Figure 1. Index map of Amchitka Island and the Aleutian arc............................................................. 2
2-4. Histograms of Koenigsberger ratio, density, remanent intensity, and magnetic susceptibility:
2.	Volcanic breccia..................................................................................... 7
3.	Volcanic breccia fragments........................................................................... 8
4.	Volcanic sandstone, siltstone, and tuff breccia from drill hole EH-5................................. 9
5.	Equal-area projections of remanent directions of magnetization for volcanic sandstone and siltstone and
tuff breccia from drill hole EH-5....................................................................... 10
6.	Histograms of Koenigsberger ratio, density, remanent intensity, and magnetic susceptibility
for intrusive rock...................................................................................... 12
7.	Equal-area projections of remanent and total directions of magnetization for intrusive rock collected
from surface exposures of the White House Cove instrusive............................................... 13
8.	Equal-area projections of remanent and total directions of magnetization for intrusive rock
collected from surface exposures of the East Cape pluton................................................ 13
9.	Histograms of Koenigsberger ratio, density, remanent intensity, and magnetic susceptibility for surface
specimens of andesitic and basaltic flows, sills, and dikes............................................. 14
10.	Histograms of Koenigsberger ratio, density, remanent intensity, and magnetic susceptibility for drill-core
specimens of andesitic and basaltic flows, sills, and dikes............................................. 15
11.	Equal-area projections of remanent and total directions of magnetization for andesitic lava collected
from surface exposures of the Chitka Point Formation.................................................... 16
12.	Equal-area projections of remanent and total directions of magnetization for basaltic lava collected from
surface exposures of the Banjo Point Formation.......................................................... 17
ill﻿CONTENTS
IV
Figures 13-15. Diagrams:	Pagc
13.	Observed data from magnetometer record and from low-sensitivity plot superimposed on profile
A-A' along flight line 111....................................................................... 18
14. Theoretical magnetic anomalies computed for five directions of traverse over a dipole source.......... 20
15. Theoretical magnetic anomalies computed for seven traverses striking over sheetlike models............ 21
TABLES
Page
Table 1. Average of densities and magnetic properties for eight specimens collected from the East Cape pluton and
16 specimens collected from the White House Cove intrusive................................................ 11
2. Average remanent directions and intensities for three specimens collected from the East Cape pluton,
measured at natural state and after partial alternating field demagnetization to 100 and 200 oersteds..... 12﻿INTERPRETATION OF AN AEROMAGNETIC SURVEY OF THE AMCHITKA ISLAND AREA, ALASKA
By G. D. Bath, W. J. Carr, L. M. Gard, Jr., and W. D. Quinlivan
ABSTRACT
An aeromagnetic survey of about 1,800 square miles of Amchitka Island and the adjacent insular shelf has provided information on Tertiary volcanic, intrusive, and sedimentary rocks. This includes identification of rocks that cause anomalies and the lateral extents, structures, and approximate depths of those rocks. Near proposed drill sites, anomalies were examined for features that might be related to faulting. The survey was facilitated by data on the magnetic properties of 347 rock specimens collected from surface exposures and 216 from drill cores and by plots of 25 miles of ground magnetic traverse. The data on magnetic properties furnished bases on which anomalies were related to geologic features; ground surveys classified near-surface rocks as either lava or breccia.
The total magnetization of volcanic breccia, tuff breccia, volcanic sandstone, and siltstone averages about 7.0 Xl0~4 gauss, an effective direction generally being along the earth’s magnetic field. This value is designated as the “ambient magnetization level” for the area. The prominent anomalies come directly from lava flows and thick sills that have total magnetizations which differ from the ambient level for the island. Anomalies also come indirectly from large bodies of intrusive rock that have altered and destroyed the magnetite content of overlying flow rocks. The average for 219 surface and 81 core specimens of lava is 14.2X10-4 gauss induced intensity and 12.8 xlO-4 gauss remanent intensity. Lavas of the Chitka Point Formation have normal remanent polarities and produce positive anomalies. The basalt lavas of the Banjo Point Formation, as well as the pillow lavas and breccias of Kirilof Point in the upper part of the Amchitka Formation, have both normal and intermediate polarities and produce positive and negative anomalies. Individual breccia samples from the Banjo Point Formation and the lower part of the Amchitka Formation have significant values of remanent intensity, but directions vary so greatly from sample to sample that a thick section of breccia does not give a magnetic anomaly. Although dikes and small sills have total magnetizations well above the ambient level, their thicknesses are too small to give a significant effect at the datum plane 1,600 feet above sea level. The normal polarity of the White House Cove intrusive and the reversed polarity of the East Cape intrusive confirm that these intrusives are separate features, emplaced at different geologic times.
Computation of the effects of sheetlike models shows that the steeper gradients of theoretical anomalies are positioned near the ends of flows or sills that have been terminated by faulting. Drill sites were selected in areas away from gradients considered to be fault related.
Nearly all prominent anomalies over land and many over water can be reasonably interpreted and can be correlated with known geologic features. Anomalies and geologic data suggest that the magma of the Chitka Point Formation originated in a large volcanic center on western Amchitka Island and eastern Rat Island. Faults that are well delineated by aeromagnetic contours on Amchitka do not appear to extend very far seaward, and marked submarine trenches that have the same general trend are not well defined magnetically.
INTRODUCTION
An aeromagnetic survey of Amchitka and Rat Islands and the adjacent insular shelf was made during December 1966 and January 1967 to gain information on the structure and subsurface distribution of Tertiary extrusive and intrusive rocks. An area of about 1,800 square miles was covered by the aeromagnetic survey. The resulting data were supplemented by laboratory data on the magnetic properties of 347 rock specimens collected from surface exposures and of 216 from drill cores and by plots of 25 miles of ground magnetic traverse.
The main purpose of the study was to investigate anomalies near proposed drill sites (fig. 1; see also pi. 2), particularly emphasizing the recognition of features that might be related to faulting and the detection of large intrusive bodies at depth. Major faults may control the initial deposition or emplacement of magnetized rock or may displace rock boundaries and their associated magnetic anomalies. Anomalies in random pattern seldom indicate structure, but those that have dominant or drawn-out trends or abrupt terminations suggest a relation to faulting.
1﻿2
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
To identify near-surface rock sources, positions of anomalies were compared with geologic units as mapped by Carr and Quinlivan (1969). The magnetic properties of surface and drill-core rock sam-
ples were investigated to determine whether the geologic units possessed magnetic properties that could cause anomalies.
160°
Figure 1. — Index map of Amchitka Island and the Aleutian arc.
PREVIOUS MAGNETIC SURVEYS
One of the most exciting investigations in recent years surrounded the discovery by Mason (1958) that the floor of the Pacific Ocean produces remarkably regular magnetic anomalies, or magnetic linea-tions, which form parallel patterns, often extending for distances of several hundred miles. Since then, studies by numerous investigators have resulted in the discovery of similar anomalies in the Atlantic and Indian Oceans and in the development of comprehensive new theories that make use of the concepts of paleomagnetism (Cox and others, 1964), sea-floor spreading (Vine, 1966), and continental drift (LePichon, 1968) to explain the geologic history of oceanic areas.
Hayes and Heirtzler (1968) discussed the relation of magnetic lineations south of Amchitka, beyond the Aleutian trench, to the Aleutian Islands arc and trench. Abrupt changes in continuity of the anomalies south of the trench suggest large north-south displacements or faults in the sea floor that offset anomaly patterns as much as 150 miles. The limited
data now available from shipborne surveys do not indicate that any displacements trend toward Amchitka Island. Grim and Erickson (1968) inferred a small north-south offset in the magnetic pattern near long 177° W., 175 miles east of Amchitka, which they called the Adak fracture zone. Hayes and Heirtzler inferred a large north-south fracture zone at long 176° E., 100 miles west of Amchitka.
No anomaly lineations have been reported over the oceans north of the Aleutian trench, and neither the magnetic anomalies nor the magnetic properties at Amchitka resemble those from ocean areas. In a study of 94 submarine lava samples, Ade-Hall (1964) found that 67.5 percent of the samples had magnetic susceptibilities less than 10X10-4 gauss per oersted and that 61 had Koenigsberger ratios greater than 10. On Amchitka, less than 10 percent of the andesitic and basaltic lavas (see histograms, figs. 9, 10) had susceptibilities less than 10X10-4 gauss per oersted or Koenigsberger ratios greater than 10. Although basaltic lavas do show high Koenigsberger ratios, their susceptibilities are also high, averaging about 40X10-4 gauss per oersted.﻿GROUND MAGNETIC SURVEYS
3
Keller, Meuschke, and Alldredge (1954) published aeromagnetic survey data for northern Adak Island, part of Umnak Island, and Great Sitkin Island. Magnetic properties are unknown for the volcanic formations on these islands, and the anomalies cannot be discussed in terms of geologic features. The fairly large number of positive anomalies suggests the presence of normally magnetized lava, such as the Chitka Point lavas on Amchitka. Richards, Vac-quier, and Van Voorhis (1967) computed the direction and intensity of magnetism for the Quaternary volcanic rocks that form the topographic relief of Great Sitkin volcano on Great Sitkin Island, and of Mount Adagdak, Mount Moffett, and a parasitic cone on the northeastern side of Mount Moffett on Adak Island. Directions of magnetization for the four volcanoes are quite different, a fact indicating that the anomaly-producing rocks are products of separate eruptive episodes.
AEROMAGNETIC SURVEY
As shown on the aeromagnetic map (pi. 1), more than 65 flight lines were flown: 12 long lines and a few short lines were flown northwest and southeast at about a mile spacing along the axis of the island, and 51 long lines were flown northeast and southwest at about a 1-mile spacing; two tielines were flown in the northwest direction, one over the north insular slope and one over the south insular slope. A barometric elevation of about 1,600 feet was maintained throughout the survey by means of a continuously recording radio altimeter. The magnetic measurements were made by a continuously recording Gulf fluxgate magnetometer, installed in a DC-3 aircraft equipped with loran and Doppler navigational systems. Aero Service Corp. performed the aerial survey and compiled the data shown on plate 1.
REDUCTION OF DATA
The observed data consist of both residual and regional magnetic anomalies. The residual anomalies are of particular interest because they come from geologic features that are near surface or buried only a mile or two. The regional anomaly is not important in this study because it comes from the northward increase in the geomagnetic field and from rock sources too deep to investigate by drilling. A least-squares method (Richards and others, 1967) was used to eliminate the regional anomaly or, that not being possible, to reduce its contribution to a minimum in the small area of the survey.
On the assumption that a planar surface would best fit the data and represent the regional anomaly to be discarded, the observed data of plate 1 were plotted on a rectangular grid representing a length of 50 miles in the x direction (S. 55° E. along the island axis) and a width of 30 miles in the y direction. Based on 1,500 data samples taken at 1-mile grid intervals, the least-squares adjustment, arrived at by means of an electronic computer, provided the following equation for the regional anomaly:
T (%yy) =CiX-\-C2y-\-C3.
T(x,y) is the regional anomaly, in gammas, computed for coordinates x, y, Ci equals 1.70 gammas per mile, C2 equals —9.64 gammas per mile, and C3 equals 4,304.6 gammas at lat 51°54.6' N. and long 178°56.0' E.
The residual anomaly, which is the near-surface magnetic expression of a geologic feature, was graphically determined by subtracting data on the regional anomaly from the observed data. The 50-gamma contours of plate 2 show detailed residual anomalies for most of the area of the survey at a scale of 1:100,000.
GROUND MAGNETIC SURVEYS
Ground magnetic surveys, taken along roads, were conducted to determine if there are significant differences in anomaly patterns over volcanic breccia and over basaltic lava flows. The ground surveys also served to provide the detail needed to better delineate the aeromagnetic anomalies. Plate 3 shows the residual magnetic anomaly and standard error data obtained from stations 0.1 mile apart along Infantry Road from mile 0 on Kirilof Point to mile 23 northwest of drill hole UAe-3, along Clevenger Road, and along the access road to drill hole UAe-1. At each station, five readings were taken 5 feet apart, and the values were averaged to give the magnetic anomaly at that station. Anomaly-producing rocks are close to the surface beneath the tundra, and the proximity of strongly magnetized rock introduces extreme local anomalies. A measure of these effects is shown by computing the standard error of the five readings and plotting the error as a bar, as done in the lower diagram, “Standard Error, In Gammas,” plate 3.
The Sharpe MF-1 fluxgate magnetometer used in the survey provided values of the vertical component of the earth’s magnetic field. Owing to the effects of temperature changes and other factors, readings could only be repeated to within ±20 gammas. Four base stations were established, and one base was reoccupied about every 3 hours to correct for large changes in the earth’s diurnal field.﻿4	INTERPRETATION OF AN AEROMAGNETIC
MAGNETIC PROPERTIES OF ROCK SAMPLES
A magnetic survey detects those geologic features that have magnetic properties unusual enough to cause a disturbance, or an anomaly, in the earth’s magnetic field. The anomaly arises when a feature has a total magnetization that is significantly different from the total magnetization of the surrounding rocks.
The average total magnetization of a uniformly magnetized rock mass, denoted as the vector Jt, is defined as the vector sum of the induced magnetization, Jh and remanent magnetization, Jr, of the mass: Jt=h+Jr.	(1)
The direction of induced magnetization is assumed along the earth’s field, and the intensity of induced magnetization is a function of the magnetic susceptibility, k, and the strength, H„, of the earth’s field: Ji=kHa.	(2)
The direction and intensity of the earth’s magnetic field are known for Amchitka (explanation, pi. 1) ; therefore, it is magnetic susceptibility, direction, and intensity of remanent magnetization that must be measured to evaluate total magnetization. For this study, the dry bulk density of each sample was measured to provide an independent parameter that could help in determining whether or not the selected rock samples were representative.
Histograms give magnetic properties and densities for 563 rock specimens collected from surface outcrops and drill cores (figs. 2-4, 6, 9, 10). Numbers and types of rock specimens used were: 85 surface and 74 drill-core specimens of volcanic breccia; 61 drill-core specimens of volcanic sandstone, siltstone, and tuff breccia; 43 surface specimens of intrusive rock; and 219 surface and 81 drill-core specimens of andesitic and basaltic flows, sills, and dikes. Koenigs-berger ratios (the ratios of remanent to induced intensities of rock samples Jr/Ji), are also included as a histogram. Site locations for the surface samples are shown on plate 2.
In reporting units of magnetic intensity, the authors followed Collinson, Creer, and Runcorn (1967) in their attempt to specify electromagnetic units more precisely. Magnetic susceptibility is expressed in gauss per oersted, and induced, remanent, and total intensities are expressed in gauss.
The extreme scatter found in magnetic property data indicates that the usual procedure of using an arithmetic mean places too much emphasis on large values and yields an average value that is greater than the true total magnetization of a geologic feature. Statistical studies by Irving, Molyneux, and Runcorn (1966) suggest that histograms of mag-
SURVEY, AMCHITKA ISLAND AREA, ALASKA
netic properties may conform more closely to a normal distribution when the abscissas are plotted as logarithms. Our studies, though incomplete, tend to confirm their conclusions, and the histograms included in this report were therefore plotted with logarithmic abscissas.
The reader will note the use of the words “sample,” “specimen,” and “sampling site.” Rock samples were collected from points separated by at least 50 feet. Specimens were taken closer together vertically, coming from the same core run of 10-foot length, or from two or three pieces drilled from the same surface sample. Sampling sites were as much as 1 mile apart.
MEASURING MAGNETIC SUSCEPTIBILITY
Reversible magnetic susceptibilities were determined by inserting samples into one of a pair of matched Helmholtz coils connected to an induction comparison bridge. For large roughhewn samples, coils whose inside diameter is 8^4 inches were used; and for small, 1-inch diameter by 1-inch length drilled plugs, coils whose inside diameter is 21/2 inches were used. Meter deflections were calibrated against a commercially available alternating-current bridge by using a set of standard samples.
MEASURING REMANENT MAGNETIZATION
The intensity, azimuth, and inclination of remanent magnetization were determined for both large roughhewn and small drilled plugs by means of a commercially available fluxgate-type clip-on milli-ammeter, modified to function as a magnetometer. Jahren and Bath (1967) described the procedure that the present authors used.
Surface samples were oriented before they were removed from the outcrop by marking a north arrow on the sample top and a horizontal line on two or more sides. An arrow pointing upward was marked on all pieces of drill core immediately after the core was taken from the core barrel. Although the geographic azimuth is unknown, the intensity and inclination of remanent magnetization were obtained for cores from vertical holes. Most of the samples collected during the geological reconnaissance were not oriented; however, the remanent intensity was determined for many of them.
At the Nevada Test Site (Bath, 1967), lightning introduces a relatively strong component of remanent magnetism that is confined to near-surface rocks. Tabulation of data from these samples will not give a true value of average magnetism for a geologic feature under study. In Nevada, data were used from underground samples that were free from these effects and from surface samples in which remanent﻿GEOLOGIC SETTING
5
direction remained constant during partial alternating-field demagnetization in the laboratory. Although lightning has rarely been observed on Amchitka, the possibility of contamination effects cannot be ignored, because parts of the island have been above sea level for perhaps 1 million years (Powers and others, 1960). The present authors partially demagnetized 24 surface and seven drill-core samples of andesitic and basaltic lava in alternating-current fields of 100 and 200 oersteds and found no significant directional changes in the moderately to strongly magnetized rocks that produce the aeromagnetic anomalies. Some of the weakly magnetized rocks did show changes in their remanent directions. This change is explained as being the result of a component of viscous magnetization or the remanent effect acquired when a rock remains in the earth’s magnetic field over a long period of time. In this study, it has been assumed that lightning has not introduced a significant error in the magnetization values.
GEOLOGIC SETTING
The stratigraphy and structure of Amchitka are now fairly well known as the result of recent studies by Carr and Quinlivan (1969) and earlier work by Powers, Coats, and Nelson (1960). As shown on the generalized geologic map (pi. 2), the rocks are divided into (1) the Amchitka Formation, which comprises a lower unit of older breccias and an upper unit of the pillow lavas and breccias of Kirilof Point, (2) the Banjo Point Formation, and (3) the Chitka Point Formation.
The lower Tertiary Amchitka Formation is the oldest formation exposed on the island. Rocks in the northwestern part of Amchitka formerly mapped as Amchitka Formation are now included in the Chitka Point Formation (Carr and others, 1970), and rocks on eastern Amchitka are included either in the older breccias or in the pillow lavas and breccias of Kirilof Point.
The outcrops of older breccias of the Amchitka Formation are restricted to the eastern part of Amchitka, mainly between Constantine Harbor and the quartz diorite intrusive rocks of East Cape. Inliers of hornfels occur within the intrusive masses. The unit consists of fine- to coarse-grained sedimentary breccias and lavas with poorly developed pillows interbedded with small amounts of sandstone, silt-stone, and claystone which contain volcanic debris. Most of the rocks are propylitically altered. The degree of alteration increases erratically eastward toward the intrusive complex, and strongly metamorphosed older breccias occur adjacent to the intrusive masses. The upper contact of the older
456-237	0-72-2
breccias is placed at the base of a locally glassy lava sequence and at the top of a thin interval of sedimentary rocks. Numerous dikes, many of hornblende andesite, cut the breccias on the eastern part of Amchitka. More than 3,000 feet of the older breccias is exposed, but because of the thickness of numerous dikes and sills that intrude the section and the possibility of fault repetition, this value indicates a maximum thickness.
The pillow lavas and breccias of Kirilof Point consist of glassy monolithologic breccias and subordinate pillow lava flows and a lesser amount of bedded volcanic sedimentary rocks. All these were probably deposited in a submarine environment. Composition-ally, the rocks of Kirilof Point are less mafic than others known on Amchitka; Powers, Coats, and Nelson (1960) published an analysis of hydrated glassy breccia from Kirilof Point which indicates that the rock is a latite. The Kirilof Point rocks are about 3,500 feet thick in the vicinity of Pillow Point.
The Banjo Point Formation overlies the Amchitka Formation, showing only a slight unconformity, and is composed mainly of basaltic breccias, a few pillow lavas, and volcaniclastic sedimentary rocks, all of submarine deposition. Hornblende andesite and basalt sills are present locally. Because of a major erosional unconformity at the top, no complete section of the Banjo Point is exposed. The formation is probably between 2,000 and 5,000 feet thick and is late Eocene or Oligocene in age (Carr and others, 1970).
The Chitka Point Formation overlies the Banjo Point Formation with marked unconformity and is restricted (Carr and others, 1970) to subaerial hornblende andesite and pyroxene andesite lava flows, breccias, tuffs, and conglomerate in the northwestern part of Amchitka (pi. 2). Included in the Chitka Point Formation by the present authors are all rocks previously mapped by Powers, Coats, and Nelson (1960) as Amchitka Formation on the northwestern part of the island and some rocks in small areas along the Bering Sea coast (between about lat 51°30' N. and Cyril Cove), previously mapped as Banjo Point Formation. The Chitka Point ranges in thickness from 0 near the middle of Amchitka to at least 2,000 feet in the vicinity of Top Side in northwestern Amchitka. On the basis of a potassium-argon date and other evidence, the Chitka Point Formation is determined to be Miocene (Carr and others,1970).
Dioritic intrusive rocks cut the Chitka Point Formation on the westerii part of Amchitka and the older breccias of the Amchitka Formation on the eastern part of the island. Intense hydrothermal al-﻿6
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
teration of the Chitka Point Formation in the Chitka Cove area may be related to the diorite that crops out at White House Cove (pi. 2). Much of the Chitka Point Formation and the older breccias of the Am-chitka Formation are affected by weak to strong propylitic alteration, producing epidote, quartz, cal-cite, chlorite, and pyrite. In addition to causing locally intense alteration, the intrusives gently tilt the invaded rocks at White House Cove and on the eastern part of Amchitka east of St. Makarius Point.
Although faults are not as abundant as aerial photograph lineaments suggest, there are perhaps a dozen major fault zones, a few of which may have a width of several thousand feet and within which the rocks may be highly fractured. Most of the major faults trend about N. 70° E. and dip northwest at 75°-90°. Although some of the movement appears to be lateral, some faults have stratigraphic displacement of as much as 4,000 ft. The middle third of the island is a series of fault blocks that repeat the southeastward-dipping section. Most of the major faulting predates the Chitka Point Formation.
Within the area of the aeromagnetic survey are three important submarine fault systems. One lies 5-10 km (kilometers) (3-6 miles) north of Amchitka and Rat Islands along a prominent escarpment. In addition to outlining the escarpment, faults of this system border the basins and ridges between Amchitka and Semisopochnoi Islands. Most of these structural features appear to be younger than the Chitka Point Formation. Southeast of Amchitka about 40 km (25 miles), on the slopes descending into Amchitka Canyon and Ward Basin, are east-northeast-trending faults that parallel those on Amchitka and probably have the same general sense of displacement. About 25 km (15 miles) south of Amchitka on the insular slope are several sharply incised asymmetric submarine canyons. These mark northeast-trending faults, downthrown on the northwest. These faults cannot be connected with certainty to any exposed on Amchitka.
VOLCANIC BRECCIA
Breccias are an important part of the entire stratigraphic section on Amchitka; most of the samples were collected from the Banjo Point Formation. L. M. Gard and W. E. Hale (unpub. data, 1964) showed that the Banjo Point consists of a thick series of submarine basaltic breccias, lapilli tuffs, and conglomerates, and a small number of intercalated beds of volcanic sandstone, siltstone, shale, and tuff.
MAGNETIC PROPERTIES
The volcanic breccia consists mostly of coarse fragments of volcanic material that was rapidly deposited at low temperature by submarine landslides. During deposition, the earth’s magnetic field alines the smaller magnetized fragments so that they settle to the ocean bottom in a consistent direction of remanent magnetization. If this alinement is maintained throughout consolidation and cementation, a deposit consisting mainly of small fragments will acquire a bulk magnetization that is directed along the earth’s magnetic field. The earth’s field could not, however, affect larger pieces of magnetized material, especially those deposited rapidly. These larger pieces, therefore, would give the breccia a random remanent magnetization.
Experiments with breccia core runs of the Banjo Point from exploratory drill hole UAe-1 verify that the remanent directions are basically random. Measurements on 15 core pieces from core run 1 (Gard and others, 1969), oriented with arrows pointing upward, gave seven upward or negative inclinations, six downward or positive inclinations, and two nearly horizontal inclinations. Inclinations for the 14 pieces of breccia from core run 2 were: seven negative, five positive, and two horizontal. Other breccia core pieces gave similar results.
The present authors concluded that this wide scatter effect of disoriented breccia fragments on remanent magnetization will cancel most of the remanent contribution to the total magnetization of a large breccia deposit. Equation 1 then reduces to Jt * Ji■
The histograms of figure 2 present data from 97 breccia specimens, all the breccia measured to date. Logarithmic averages are 14.8XlO-4 gauss per oersted for magnetic susceptibility, 5.1 XlO-4 gauss for remanent intensity, and 0.72 for Koenigsberger ratio. The average density is 2.36 g/cc (grams per cubic centimeter). Equations 2 and 3 (p. 4, 11) determine that the total magnetization becomes 7.1 XlO-4 gauss in the direction of the earth’s magnetic field. Because breccia is the predominant lithology of Amchitka, the authors have designated this total magnetism of breccia as the ambient level for the island. A large geologic structure having a magnetization that differs in intensity or direction from the ambient level should, therefore, produce a residual magnetic anomaly.
The 41 core samples from the Long Shot drill hole EH-5, collected at depths from 76 to 1,999 feet, are considered to be representative of breccia of the Banjo Point Formation. Data from these samples﻿MAGNETIC PROPERTIES OF VOLCANIC BRECCIA
7
have the following averages: Dry bulk density, 2.36 g/cc; magnetic susceptibility, 19.8X10-4 gauss per oersted; remanent intensity, 16.0X10-4 gauss; and total intensity, 9.5xl0~4 gauss in the direction of
LOG 10 KOENIGSBERGER RATIO
the earth’s magnetic field. The relatively high rem-anence of these pieces of core is apparently caused by a few large breccia fragments and is not the remanence of the rock as a whole.
LOG REMANENT INTENSITY (GAUSS)
DRY BULK DENSITY (GRAMS PER CUBIC CENTIMETER)
Figure 2. — Histograms of Koenigsberger ratio, de for 97 specimens of volcanic brec
Histograms (fig. 3) list properties for 62 lithic fragments removed from two surface samples of the breccia of the Banjo Point Formation. Most of the pieces are from lava flows that were probably originally emplaced away from the present island area.
Core sections of the breccia of Kirilof Point and the underlying older breccias from UAe-1 have rather different average total magnetizations. Thirteen samples of breccia of Kirilof Point from depths
LOG10 MAGNETIC SUSCEPTIBILITY (GAUSS PER OERSTED)
ity, remanent intensity, and magnetic susceptibility a. Arrow indicates average value.
of 2,415-4,925 feet gave averages of 2.32 g/cc for density, 4.9 xlO-4 gauss per oersted for magnetic susceptibility, 5.1 XlO-4 gauss for remanent intensity, and 2.4X10-4 gauss for total intensity. Thirteen samples of older breccia from depths of 5,756-6,997 feet gave averages of 2.45 g/cc for density, 33.9XlO-4 gauss per oersted for magnetic susceptibility, 5.9X 10~4 gauss for remanent intensity, and 16.2X10-4 gauss for total intensity.﻿8
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
LOG 10 REMANENT INTENSITY (GAUSS)
c/>
z
Hi
5
o
uj
0-
co
o
£E
UJ
m
z
DRY BULK DENSITY (GRAMS PER CUBIC CENTIMETER)
LOG jo MAGNETIC SUSCEPTIBILITY (GAUSS PER OERSTED)
Figure 3.-—-Histograms of Koenigsberger ratio, density, remanent intensity, and magnetic susceptibility for 62 specimens of volcanic breccia fragments. Arrow indicates average value.
AEROMAGNETIC ANOMALIES
Aeromagnetic traverses over the large area of Banjo Point breccias and the older breccias (pi. 2) show an anomaly level that is generally above the regional value but is interrupted by several prominent and many local negative and positive anomalies. In the area of the Banjo Point Formation, the marked negative anomalies have been named “Mex Island,” “—780,” and “Rifle Range Point” anomalies. The most marked positive effect is named the “Site B” anomaly. As will be pointed out in a following section, the marked positive and negative anomalies come from lava flows or sills and do not represent the magnetic effect of breccia. The magnetic field becomes fairly uniform after lava-related anomalies are removed.
GROUND SURVEY ANOMALIES
A striking difference in average anomaly amplitude and standard error is present over breccia and lava flows. The magnetic expressions of the breccia are relatively uniform and have lower values than
the lavas, except that the contrast is not great between the Chitka Point lava flows and the Banjo Point breccias. In the Infantry Road traverse (pi. 3), the 8V2 miles over the Banjo Point Formation (from mile 8 to mile 16.5) and the 61/2 miles over the Chitka Point Formation (from mile 16.5 to mile 23) averaged less than 1,000 gammas for anomaly amplitude and less than 50 gammas for standard error. Low values of standard error come from near-surface breccia; high values^from small near-surface features such as flows, dikes, or sills.
From mile 0 to mile 5, the pillow lavas and breccias of Kirilof Point as mapped by Carr and Quinlivan (1969) show extreme magnetic effects. Anomaly amplitudes reach values of 5,000 gammas and show standard errors of 600 gammas over nearsurface and strongly magnetized lava flows. From the data of plate 3 the following near-surface source rocks may be identified: lava from mile 0 to mile 0.7, breccia from 0.8 to 1.1, mostly lava from 1.2 to 2.1, mostly breccia from 2.2 to 3.0, and mostly lava from 3.1 to 4.﻿VOLCANIC SANDSTONE, SILTSTONE, AND TUFF BRECCIA
9
The short traverse along the access road to drill hole UAe-1 presents an excellent example of the characteristic low values of standard error that are found over near-surface breccia. The traverse also locates the Mex Island anomaly more accurately than the aeromagnetic survey does. The ground data of plate 3 place the anomaly minimum at 0.3 mile from UAe-1, not at 0.6 mile as indicated by the aeromagnetic data (pi. 2).
VOLCANIC SANDSTONE, SILTSTONE, AND TUFF BRECCIA
Although Carr and Quinlivan (1969) reported interbedded sedimentary rocks in the Chitka Point and Banjo Point Formations and in the older breccias of the Amchitka Formation, the beds are too thin
to be mapped at the 1:100,000 scale, and the outcrop areas are too small to be correlated with individual aeromagnetic anomalies. Sedimentary rocks may be more extensive in some areas offshore as suggested by the abrupt change of the character of the magnetic field (pi. 1) in the area of the broad positive anomaly about 10 miles north of Chitka Point. A thick deposit of rocks having consonant total magnetizations is required to explain the uniform nature of the field.
The histograms of figure 4 present data from 30 core specimens of volcanic sandstone and siltstone and 31 specimens of tuff breccia, collected at depths ranging from 543 to 2,225 feet in drill hole EH-5. Logarithmic averages are ll.OxlO-4 gauss per oersted for magnetic susceptibility, 1.4X10-4 gauss for remanent intensity, and 0.26 for Koenigsberger ratio.
C/)
z
LlI
O
LlI
Q_
C/3
Li_
o
tr
LlI
m
D
Z
2.0	2.5	3.0
DRY BULK DENSITY (GRAMS PER CUBIC CENTIMETER)
LOGio MAGNETIC SUSCEPTIBILITY (GAUSS PER OERSTED)
Figure 4. — Histograms of Koenigsberger ratio, density, remanent intensity, and magnetic susceptibility for 61 specimens of volcanic sandstone, siltstone, and tuff breccia from drill hole EH-5. Arrow indicates average value.﻿10
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
The average density is 2.16 g/cc. Except for remanent direction, average values are similar for the volcanic sandstone and siltstone and the tuff breccia.
The authors assumed no structural tilting and obtained true values of remanent inclinations by measurement of drill cores that were referenced to a vertical drill hole. Remanent azimuths are unknown, but a measurement of variation was obtained by referencing azimuth to a line marked along seven continuous lengths of drill core before these lengths were cut into several specimens. Figure 5 gives inclinations and variations in azimuth for drill-core samples collected from EH-5. The low average inclination of 27° for 16 specimens of volcanic sandstone and siltstone is difficult to explain. One possible explanation is the tendency of platy magnetic particles to settle horizontally and thus be only partially
N
alined by the earth’s magnetic field. Most of these samples are from graded beds or fine-grained, rapidly deposited sediments. For 17 specimens of tuff breccia, the average inclination is 67°, or close to the 62° value for the geomagnetic field, a condition which suggests the effect of a viscous magnetization acquired after emplacement.
The total magnetization of volcanic sandstone, siltstone, and tuff breccia is controlled by magnetic susceptibility, or induced magnetism. The low Koe-nigsberger ratio of 0.26 shows that the contribution of remanent magnetism is relatively unimportant. The authors therefore assign these fine-grained sedimentary rocks an average total magnetization of 6.5X10-4 gauss in the direction of the geomagnetic field.
N
Figure 5. — Equal-area projections of remanent directions of magnetization for specimens cut from continuous lengths of core from drill hole EH-5: A, 16 specimens of volcanic sandstone and siltstone; B, 17 specimens of tuff breccia. Differences in azimuth are referenced to an arbitrary line marked along the core before it was cut. The average of all azimuths is assumed northward, but inclinations are referenced to a vertical drill hole and are, therefore, true values. •, lower hemisphere; O, upper hemisphere; x, present geomagnetic field.
DIKES AND SMALL SILLS The presence of dikes and sills beneath prominent aeromagnetic anomalies suggests that the magnetic contribution of several of these small features is sufficient to explain some of the anomalies. For example, the —780 and St. Makarius Point anomalies shown on plate 2 are over complexes of basaltic dikes and small sills intruded into the Banjo Point Forma-
tion. Most of the dikes and sills exposed in these areas have thicknesses that are less than 50 feet. From the geologic detail shown by Carr and Quin-livan (1969), it seems clear that these features should be considered as possible source rocks. The St. Makarius Point and —780 anomalies are discussed in more detail under the section on “Interpretation of Anomalies.”﻿INTRUSIVE ROCKS
11
Data are available for 30 surface samples collected from dikes and small sills (pi. 2). Logarithmic averages are 25.7X10“' gauss per oersted for magnetic susceptibility, 5.5xl0“4 gauss for remanent intensity, and 0.45 for Koenigsberger ratio. A maximum value of 17.8x10“' gauss for total magnetization is computed from these data. Subtracting the ambient level value (7.0x10“') from 17.8xl0“4 gauss, the effective total magnetization for the 30 samples collected from dikes and small sills becomes 10.8X10-4 gauss. A single dike or small sill that has this value of effective total magnetization will produce an aero-magnetic anomaly of little importance at the datum plane 1,600 feet above sea level. Assuming a thickness, e, of 50 feet and a depth, t, of 1,200 feet, computations using the equation 2J, e 105
A71max= -----1----- gammas	(3)
give a maximum anomaly, ATmnx, of only 9 gammas for a total magnetization, Jt, of 10.8X10-4 gauss. Computation for a sill 50 feet thick at a depth of 1,200 feet,
2.4J( e 105
ATm„x= -----t---- gammas,
(4)
gives a maximum anomaly of only 11 gammas (fig. 15). Because the effect of a single dike is small, the authors have concluded that a complex of many dikes is required to explain a prominent aeromagnetic anomaly.
INTRUSIVE ROCKS
Samples of intrusive rock were collected from the complex of diorites and andesites exposed on the eastern part of the island, from exposures on White House Cove, Chapel Cove, and Ivakin Point, and from intrusive features that are too small to be shown on plate 2.
MAGNETIC PROPERTIES
The histograms of figure 6 present data from 43 specimens of intrusive rock. Logarithmic averages are 12.5xl0“4 gauss per oersted for magnetic susceptibility, 5.1X10”4 gauss for remanent intensity, and 0.85 for Koenigsberger ratio. The average density is 2.55 g/cc. The broad spectrum of values shown in the remanent intensity histogram indicates the presence of more than one pluton. A closer inspection of the data reveals that the lower values come from the complex exposed on the eastern part of the island, including Ivakin Point. Table 1 shows an average remanent intensity of 1.3xl0“4 gauss for eight specimens from the East Cape pluton and
19.7X10-4 gauss for 16 specimens from the White House Cove intrusive.
Table 1. — Average of densities and magnetic properties for eight specimens collected from the East Cape pluton and 16 specimens collected from the White House Cove intrusive
East Cape White House
		pluton	Cove intrusive
Density			g/cc..	2.58	2.50
Magnetic susceptibility...	..X10-4 gauss per oersted..	11.9	20.8
		5.7	10.0
Induced direction:		7	7
		62	62
		1.3	19.7
Remanent direction:		181	5
		75	69
		6.6	29.6
Total direction :		8	6
		69	66
Difference in directions of remanent magnetism supports the concept of two separate episodes of intrusion. Experts in paleomagnetic investigations of remanent directions now generally agree that, during cooling and crystallization, the magnetic minerals in igneous rocks become magnetized in the direction of the earth’s magnetic field. In the geologic past, the earth’s magnetic field has changed direction and has undergone numerous complete reversals of polarity (Cox and others, 1964). Directions for 16 specimens collected from the White House Cove intrusive (fig. 7) have a normal polarity that averages 5° in declination and 69° in inclination, a direction that approximates the 7° declination and 62° inclination of the present geomagnetic field on Amchitka. Partial demagnetization of three of the specimens in alternating fields of 100 and 200 oersteds did not result in a significant change in direction, and the natural-state magnetism appears to be stable and related to the direction of an ancient geomagnetic field.
In marked contrast, the remanent data of figure 8 from eight specimens of the East Cape pluton show an intermediate polarity, having an average declination of 181° and an inclination of 75°. The natural-state magnetism contains an unstable component of viscous remanent magnetization which was removed by partial demagnetization. At 100 oersteds (table 2), inclination changed from plus to minus. The average direction for three specimens at 200 oersteds gives a reversed polarity, or a declination of 188° and an inclination of —49°.
Table 1 gives the total magnetization values that are used in the interpretive studies of the two plu-tons. The reader may be surprised to find that even though the direction of fossil remanent magnetization for the East Cape pluton is reversed, the aver-﻿12
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
age direction of total magnetization, shown in figure 8, is normal and approximates the earth’s present magnetic field. This is the result of the low 0.23 value of Koenigsberger ratio. The remanent effect becomes trivial when it is added vectorially to the induced effect.
importance are the thick andesite lava flows of the Chitka Point Formation, the andesitic and basaltic lavas within the Banjo Point Formation, and the latitic pillow lavas of Kirilof Point in the Amchitka Formation.
AEROMAGNETIC ANOMALIES
The positions of several aeromagnetic anomalies that have values well below the regional level correlate with the positions of large exposures of intrusive rock. The East Cape negative anomaly is over a complex of diorites on the eastern end of the island (pi. 2). The White House Cove negative anomalies are over exposures of intrusive rock at White House and Chapel Coves. A less pronounced low occurs near the intrusive complex at Ivakin Point.
LAVA FLOWS AND THICK SILLS
Lava flows and thick sills produce most of the pronounced aeromagnetic anomalies. Of particular
Table 2. — Average remanent directions and intensities for three specimens collected from the East Cape pluton, measured at natural state and after partial alternating field demagnetization to 100 and 200 oersteds
[Collected at sample site 13, pi. 2]
		Natural state	Demagnetization level 100 200 oersted oersted	
Specimen B25A1-67:		189	199 -49 3.0 187	203 —58 2.9 184 —45
		44		
		3.3		
Specimen B25A2-67:		169		
		66	—45	
		1.5	.7	.7 178
Specimen B25C1-67:		128	170	
		72	—40	—45
		1.7	.4	.3
				
LOG10 KOENIGSBERGER RATIO	LOGio REMANENT INTENSITY (GAUSS)
DRY BULK DENSITY	LOG i0 MAGNETIC SUSCEPTIBILITY
(GRAMS PER CUBIC CENTIMETER)	(GAUSS PER OERSTED)
Figure 6. — Histograms of Koenigsberger ratio, density, remanent intensity, and magnetic susceptibility for 43 specimens of intrusive rock. Arrow indicates average value.﻿LAVA FLOWS AND THICK SILLS
13
N	N
Figure 7. — Equal-area projections of remanent (A) and total (B) directions of magnetization for 16 specimens of intrusive rock collected from surface exposures of the White House Cove intrusive. •, lower hemisphere; X, present geomagnetic field; +, average direction.
N	N
FIGURE 8. — Equal-area projections of remanent (A) and total (B) directions of magnetization for 8 specimens of intrusive rock collected from surface exposures of the East Cape pluton. •, lower hemisphere; X, present geomagnetic field; +, average direction.
456-237 0 - 72 -3﻿14
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
MAGNETIC PROPERTIES
The histograms of figures 9 and 10 present data from 219 surface and 81 drill-core specimens of lava flows, sills, and dikes. The surface samples (fig. 9) were collected from all areas of the island except the areas of undivided intrusive rocks (pi. 2). Their logarithmic averages are 22.9X10-4 gauss per oersted for magnetic susceptibility, 9.8 XlO-4 gauss for remanent intensity, and 0.89 for Koenigsberger ratio. The average density is 2.6 g/cc. The subsurface data (fig. 10) were taken from the following: 30 specimens from drill hole EH-5, 12 from UAe-1, 24 from UAe-2, 10 from UAe-3, and five from UAe-7c. Their
logarithmic averages are 36.3X10-4 gauss per oersted for magnetic susceptibility, 15.9Xl0~4 gauss for remanent intensity, and 0.91 for Koenigsberger ratio. The average density is 2.49 g/cc.
Although remanent directions at Amchitka appear generally constant throughout individual flows or sills, average directions may change from formation to formation, and even within some formations. For example, all pieces of the pillow lavas of Kirilof Point from core runs 4, 5, 6, 16, and 18 of UAe-1 (Gard and others, 1969) have negative inclinations that average about —60°. The change from formation to formation is demonstrated by the data from
DRY BULK DENSITY	LOG 10 MAGNETIC SUSCEPTIBILITY
(GRAMS PER CUBIC CENTIMETER)	(GAUSS PER OERSTED)
Figure 9. — Histograms of Koenigsberger ratio, density, remanent intensity, and magnetic susceptibility for 219 surface specimens of andesitic and basaltic flows, sills, and dikes. Arrow indicates average value.﻿MAGNETIC PROPERTIES OF LAVA FLOWS AND THICK SILLS
15
drill hole UAe-2, located about 5 miles southeast of UAe-1. Four core samples of lava collected from the Banjo Point Formation at depths of 2,578-3,103 feet have positive rather than negative inclinations that average 68°. However, not all units in the Banjo Point have the same magnetic characteristics, as illustrated by the negative inclinations of lava samples at depths of 2,227-2,244 feet in drill hole EH-5.
Small changes in remanent inclination can be interpreted in a similar manner. Inclinations of andesite core from EH-5 have the following aver-
ages and 95-percent confidence intervals: 76°±6° for seven samples from 2,340.8- to 2,342.2-foot depth; 55° ±11° for eight samples from 2,466- to 2,468.3-foot depth; and 41° ±4° for five samples from 2,479.7-to 2,480.9-foot depth. The 76° average differs significantly from the 55° and 41° averages, and the authors thus assume that the andesite at the more shallow depth was emplaced at a different time.
The remanent data plotted in figure 11 indicate that the thick lava flows of the Chitka Point Formation have normal polarities. The 58 surface speci-
LOG10 KOENIGSBERGER RATIO	LOGi0 REMANENT INTENSITY (GAUSS)
DRY BULK DENSITY (GRAMS PER CUBIC CENTIMETER)
LOGio MAGNETIC SUSCEPTIBILITY (GAUSS PER OERSTED)
Figure 10. — Histograms of Koenigsberger ratio, density, remanent intensity, and magnetic susceptibility for 81 drill-core specimens of andesitic and basaltic flows, sills, and dikes. Arrow indicates average value.﻿16
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
mens collected from 26 samples at 11 sampling sites average 26.4X10-4 gauss per oersted for magnetic susceptibility and 15.1X10-4 gauss for remanent intensity. Average total magnetization, having a direction that approximates the present geomagnetic field, is 27.4X10-4 gauss.
A few strongly magnetized surface samples that the authors have collected to date show intermediate remanent polarities. For example, the 10 surface
N
specimens of basalt collected from five samples at four sampling sites in the Banjo Point Formation average 29.1X10-4 gauss per oersted for magnetic susceptibility and 114.6xl0~4 gauss for remanent intensity. The intermediate directional data for these samples are shown in figure 12. The average total magnetization for these samples is 111.5X10-4 gauss, having a declination of 316° and an inclination of -26°.
N
Figure 11. — Equal-area projections of remanent (A) and total (B) directions of magnetization for 58 specimens of andesitic lava collected from surface exposures of the Chitka Point Formation. •, lower hemisphere; X, present geomagnetic field; +, average direction.
AEROMAGNETIC ANOMALIES
The positions of several aeromagnetic anomalies having values well above the regional anomaly correlate with the positions of known exposures of relatively young andesite lava flows of the Chitka Point Formation. Bird Rock, Windy Island, and Site F positive anomalies are over these flows on the northwestern part of the island (pi. 2). The Infantry Road anomaly is over exposures that are mainly breccia, but flows probably lie beneath the breccia. The edge of the large positive feature named the Chitka Point-Constantine Point anomaly is also over the flows. It has been previously pointed out (p. 8) that the positive Site B anomaly and the negative Mex Island, —780, Rifle Range Point, and Pillow Point anomalies are at least partly related to older lavas that are buried within or beneath the Banjo Point Formation.
GROUND SURVEY ANOMALIES
The data obtained from the traverses and plotted on plate 3 show the characteristic irregular pattern of magnetic anomalies over lava. Weiss (1949) was perhaps the first investigator to point out the extreme variations in the ground anomalies beneath the aeromagnetic anomalies caused by near-surface and reversely magnetized rocks.
Data obtained from the short traverse along Clevenger Road illustrate the effects of strongly magnetized rock buried beneath nonmagnetic rock. The irregular and negative residual anomalies indicate rocks having strong remanent intensities and reverse polarities that are assumed to be the pillow lavas of Kirilof Point. The low values of standard error indicate near-surface rocks that are considered nonmagnetic, such as breccia or alluvium.﻿ANALYSIS OF MAGNETIC ANOMALIES
17
N	N
Figure 12. — Equal-area projections of remanent (A) and total (B) directions of magnetization for 10 specimens of basaltic lava collected from surface exposures of the Banjo Point Formation. • , lower hemisphere; O, upper hemisphere; X, present geomagnetic field; +, average direction.
ANALYSIS OF MAGNETIC ANOMALIES
A detailed investigation of the complex anomaly patterns given in the Amchitka aeromagnetic survey is possible in areas where individual anomalies stand out so clearly that they can be separated from neighboring magnetic effects. The understanding of geologic structure and magnetic properties of the rocks on the island enables one to identify many of the anomaly-producing features, compute estimates of depths to their tops, and make inference about their lateral extents and thicknesses.
The identification of anomaly-producing features becomes more difficult over the insular shelf where little is known about marine geology. However, considerations of magnetic properties and magnetic anomalies over the island units permit a qualitative analysis of many of the anomalies shown on plate 2. The most likely causes of complex anomaly patterns are the strongly magnetized lava flows and thick sills within the Amchitka and Banjo Point Formations; the positive anomalies being related to rocks which have positive inclinations of remanent direction, and the negative anomalies to rocks which have negative inclinations of remanent direction. Most of the broad positive anomalies with the more moderate anomaly patterns are undoubtedly produced by normally magnetized lava flows of the Chitka Point Formation.
Areas of relatively uniform anomaly could overlie large volumes of either intrusive rock, sedimentary rock, or volcanic breccia.
DEPTH ESTIMATES
Several investigators working in petroleum-rich areas pointed out the advantage of using aeromagnetic data to obtain preliminary estimates of the thickness of the sedimentary section throughout extensive areas (Steenland, 1965; Henderson and Zietz, 1958). Their premise is that sedimentary rocks are nonmagnetic and any magnetic anomalies must originate from the underlying igneous rocks. Calculation of depth to the magnetic rock therefore yields a thickness estimate for the sedimentary rocks.
On Amchitka, the igneous rocks are at or very near the surface. Some rocks, such as volcanic breccia, are relatively nonmagnetic and do not significantly distort aeromagnetic anomalies arising from deeper, strongly magnetized rocks. These magnetic anomalies were analyzed to determine thicknesses of breccia, some lava flows, and other rocks having low magnetizations. Computed depths were compared with the actual depths of known geologic features that had been obtained by drilling.
In general, shallow sources give sharp anomalies having short wavelengths, and deep sources give﻿18
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
broad anomalies having long wavelengths. Numerous simple rules have been introduced to determine depth or some other dimension of the anomaly source (Vac-quier and others, 1951; Grant and West, 1965). Most rules are made in accordance with some property of an anomaly calculated for models of varying depth, length, width, thickness, magnetization, or geomagnetic latitude. Often the property consists of the horizontal distance between two critical points of the anomaly. For most Amchitka anomalies, computations were made for horizontal sheet and dipole
models: first, the extent of maximum slope (Vac-quier and others, 1951) ; second, the interval between the one-half maximum slope intersections with the anomaly curve (Peters, 1949) ; and third, the interval between inflection points (Bean, 1966). Comparison of these computed anomaly properties with similar properties of an actual anomaly will yield the depth estimate.
Figure 13 was prepared to illustrate observed data from magnetometer records, anomalies produced by near-surface rocks, and an anomaly produced by
>
Infantry Road
A	A'
Figure 13. — Observed data from magnetometer record and from low-sensitivity plot superimposed on profile A-A’ along
flight line 111, as shown on plate 2.﻿INTERPRETATION OF ANOMALIES
19
rocks below sea level. The data were recorded at a scale of about 1:30,000, and the distance from airplane to ground and water surface was obtained by radio altimeter. Anomaly analysis indicates that the rocks causing the shelf-break anomaly are along the shelf break and 1,100 feet below sea level, those causing Bird Rock anomaly are at the ground surface, those causing the two dipole anomalies on the north side of Infantry Road anomaly are at the ground surface, and those causing the Infantry Road anomaly and the dipole anomaly on its south side are buried 500 feet beneath the ground surface.
DIPOLE AND SHEETLIKE MODELS
In spite of the complexity of the earth’s magnetic field at a barometric elevation of 1,600 feet (pi. 1), certain individual anomalies do stand out (pi. 2), and they appear to represent the effect of single magnetized bodies. For these anomalies, a quantitative method of interpretation may give information on the length, width, and thickness of the magnetic feature. The method consists of finding the model, or models, that are both geologically reasonable and capable of causing an effect equivalent to the anomaly.
A sharp anomaly having an interval of only about one depth unit (or less) between maximum and minimum values was considered as a model of point dipole effect. One depth unit is equal to the distance from airplane to anomaly-producing rocks. Such a model represents a fairly small geologic feature that has roughly the same dimensions in all directions. Experimental examples of dipoles are the three small anomalies shown superimposed on the Infantry Road anomaly of figure 13, and theoretical examples are data on the five traverses shown in figure 14. The dipole anomaly portrays the limiting case that gives no information on the dimensions of the source. A strongly magnetized body that measures only a few feet on a side will produce the same anomaly configuration as a body with dimensions up to about half a depth unit. Larger dimensions will distort the anomaly and thus show a shape effect.
To investigate the dipole effect, anomalies for five directions of traverse over a dipole source were com-
A Tt3
puted from —— (eq 8 of Hall, 1959, p. 1947), as
shown in figure 14. The depth from datum line to source is designated t, and traverse distance, x, is expressed in depth units. The direction of total magnetization is parallel to the earth’s magnetic field at Amchitka, fi is the dipole moment, and AT is the anomalous total magnetic field measured by the airborne magnetometer.
Lava flows frequently occur as well-defined magnetic bodies that have dimensions nearly approaching those of a horizontal sheetlike model. The sheet model has practical importance also because its anomaly does not change in shape for the sake of increases in thickness up to about one depth unit. The anomaly pattern does change for increases in length (fig. 15A) and for increases in width (fig. 155). Also, when the average total magnetization of the body is known, calculations based on the anomaly amplitude will give an estimate of thickness.
By using a thickness of one-third depth unit and then converting to the sheet notation, the anomalies of figure 15A were computed from equations 4.3a and 4.3b of Werner (1953, p. 17), and the anomalies of figure 155, from the prismatic models of Vacquier, Steenland, Henderson, and Zietz (1951). The direction of total magnetization, Jt, is parallel to the earth’s magnetic field at Amchitka, and the thickness of the sheet model, e, is expressed in depth units, e', £
where £'=j- The m0(iel length, l, width, w, and the
traverse distance, x, are also expressed in units of depth, t.
INTERPRETATION OF ANOMALIES
The following discussion deals with some of the magnetic anomalies that can be explained by known geologic facts. Also discussed are some anomalies and anomaly patterns that are subject to more conjectural interpretations.
The lava flows and thick sills produce most of the anomalies in the aeromagnetic survey. The theoretical magnetic anomalies plotted in figure 15 show steeper gradients near the boundaries of models, which represent simplified configurations for flows or sills having horizontal attitudes. Most drill holes are located away from the strong anomalies that have dominant trends or are terminated abruptly. Termination may also be caused by erosion or other geologic processes, and the present authors have relied heavily on geologic evidence before designating a feature as fault related.
Remanent magnetization exerts the most marked influence on the total magnetization of flows and sills, and remanent direction thereby becomes a dominant factor in determining anomaly configurations. The Koenigsberger ratio averages 0.9 for all the measured andesite and basalt specimens, and the ratio increases for many anomaly-producing formations. For example, the 58 specimens from the Chitka Point lavas (fig. 11) have a ratio of 1.2, and 10 specimens of basalt (fig. 12) have a ratio of 14.0.﻿20
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
EAST CAPE ANOMALY
At East Cape, Pillow Point, and Ivakin Point, the diorite complex intrudes both the older breccia and the breccias and pillow lavas of Kirilof Point. Contact metamorphism has locally changed some of the wallrock to hornfels. Explanation of the broad negative anomaly in the area of East Cape is based on the very low remanent intensity of the diorite and the somewhat higher values of the intruded breccia. Eight specimens of diorite (table 1) have a low average total intensity of 6.6X10-4 gauss along the direction of the geomagnetic field, which is a value just under the ambient level for the island. Thirteen samples of breccia, dikes, and sills from the area mapped as older breccia and hornfels (pi. 2) have somewhat higher average values—4.4 xlO-4 gauss for remanent intensity, and 10.0X10-4 gauss for induced intensity — but the contrast is probably insufficient to explain the anomaly. We therefore conclude that lava flows in the older breccia are strongly enough magnetized to cause the contrast. Examples are samples Q57-66
and Q12-67 (sample sites 12 and 11, pi. 2) which have high average remanent and induced intensities of 156X10-4 and 24.5X10-4 gauss. Drill hole UAe-2 at site B penetrated several thick bodies of mafic magnetic rock in this general part of the section. For example, a hornblende andesite sample, collected at a depth of 6,002 feet, has remanent and induced magnetizations of 14.0X10-4 and 20.9xl0~4 gauss.
WHITE HOUSE COVE AND SHELF-BREAK ANOMALIES
Another prominent negative anomaly related to intrusive rock is at White House Cove directly over outcrops of diorite porphyry that intrude the Banjo Point Formation and probably the Chitka Point Formation. The anomaly curves across the island to the Bering Sea side of Amchitka where there is a small outcrop of diorite (Carr and Quinlivan, 1969).
To explain the negative anomalies, two possibilities that require relatively low values of magnetization were considered. The first assumes that the White House Cove intrusive has a total magnetization lower than that of the adjacent rocks. The limited sample
Figure 14. — Theoretical magnetic anomalies, AT computed for five directions of traverse over a dipole source magnetized along the geomagnetic field having an inclination of 60°. Strike of traverse lines: A, magnetic north; B, 22.5° east or west of magnetic north; C, 45° east or west of magnetic north; D, 67.5° east or west of magnetic north; E, magnetic east, t, depth from datum line to source; m, dipole moment, x, traverse distance, is expressed in units of depth, t.﻿INTERPRETATION OF ANOMALIES
21
Figure 15. — Theoretical magnetic anomalies, AT, computed for the following: A, traverses striking magnetic north over the centers of four rectangular sheetlike models; B, traverses striking magnetic east over the centers of three square sheetlike models. All models magnetized along the geomagnetic field having an inclination of 60°. Model length, l, width, w, thickness, c, and traverse distance, x, are expressed in units of depth, t. e'—e/t; J,, intensity of total magnetization.﻿22	INTERPRETATION OF AN AEROMAGNETIC
data now available do not support this concept. According to table 1, the diorite has a total intensity which is well above the ambient level for the island and which is about equal to the total intensity of the Chitka Point lavas. This comparatively high value of magnetism would result in a positive rather than a negative anomaly relative to the Banjo Point and practically no anomaly relative to the Chitka Point.
The second possible explanation of the anomaly seems to be more reasonable. It requires a local decrease of magnetism in the near-surface volcanic rocks that overlie the pluton, and it requires a lac-colithic structure that would give the pluton a thickness about equal to the total thickness of the Chitka Point lavas. A thicker intrusive could change the anomaly from negative to positive. The anomaly also extends over intensely altered lava flows of the Chitka Point Formation (pi. 2). This hydrothermally altered rock is represented by samples B4-67, B5-67, and Q30-67 (sample sites 4, 6, and 5, pi. 2), which have an extremely low total average magnetization of 0.5Xl0~4 gauss, a condition indicating the almost complete destruction of magnetite. Lava and breccia samples collected beneath the anomaly but outside the intensely altered zone such as samples B19-67, C75-67, and C76-67 (sample sites 3, 2, and 1, pi. 2) have an average total magnetization of 5xl0-4 gauss, which is also well below the regional level. Much of this area shows evidence of weak to strong propylitic alteration, the chief minerals of which are pyrite, chlorite, and quartz.
Plate 1 shows that the White House Cove anomaly is only part of a much bigger negative anomaly that extends from the Bering Sea coast of Amchitka northwestward more than 25 miles, culminating in a very pronounced negative anomaly over the eastern part of Rat Island. The part north of the northwestern tip of Amchitka is designated as the shelf-break anomaly on plate 2. Its termination may be related to faulting along the shelf break, the escarpment that parallels Rat Island and Amchitka Island on the north. On Rat Island, the anomaly is over diorite porphyry that appears to be identical with the diorite on Amchitka. Alteration is also locally intense on this part of Rat Island. The total pattern of the anomaly thus subtends an elongated partial oval inside of which are lavas and probably source vents for the Chitka Point andesite lava flows. Gravity data (Miller and others, 1969) show that the western end of Amchitka is a gravity low. In addition, the fact that remanent directions shown in figures 10 and 11 are very similar for the White House Cove intrusive and the surrounding Chitka Point lava flows indicates that these rocks may be nearly con-
SURVEY, AMCHITKA ISLAND AREA, ALASKA
temporaneous. The two rocks — intrusive and lava — are also similar petrographically. All these data, though sketchy, suggest that the western end of Amchitka and the eastern end of Rat Island may constitute a large volcanic center related to the Chitka Point Formation and that the diorite porphyry may be a series of large ring dikes related to the volcanic center.
PILLOW POINT AND RIFLE RANGE POINT ANOMALIES
Analysis of the negative anomalies that trend southeastward from Pillow Point (pi. 2) indicates source rocks that are (1) near surface, (2) magnetized in a negative or upward direction, and (3) elongated in the direction of strike. The anomaly is less than 2,000 feet wide but extends southeast from the island 6 miles. At the shoreline of Amchitka the anomaly correlates with pillow lavas of Kirilof Point as mapped by Carr and Quinlivan (1969). The anomaly is also over intrusive rocks at Pillow Point. Although intrusive rock samples C83-66 and Q79-66 (sample sites 10 and 9, pi. 2) were not oriented to determine remanent direction, other data show that they do not have the required total magnetization and have a negative or upward direction. Their average induced intensity (20.1 XlO-4 gauss) is greater than the remanent intensity (17.8X10-4 gauss), and this will result in a total magnetization having a downward direction. The pillow lavas of Kirilof Point, however, are known to have upward total direction, and these rocks crop out beneath the anomaly and have a strike that is nearly the same as the anomaly.
Part of the Rifle Range Point anomaly (pi. 2) correlates fairly well with those pillow lavas of the Kirilof Point that are presumed responsible for the Pillow Point anomaly. However, the anomaly diverges from outcrops of the pillow lavas and appears to follow the southeast side of the Rifle Range fault out into the Pacific. The rocks that cause this part of the anomaly have not been identified, but a possible explanation is given in the following discussion of the St. Makarius Point anomaly.
ST. MAKARIUS POINT ANOMALY
The downward inclination of the total magnetization of the five samples collected from dikes and sills beneath the St. Makarius Point negative anomaly (pi. 2) shows that these are not source rocks. Depth estimates support this interpretation. The depth estimated from the negative anomaly on profile T-16 (pi. 1) is at least 500 feet below the surface. The anomaly is near the axis of a gentle northeast-trending syncline. This fold may be a result of uplift due﻿INTERPRETATION OF ANOMALIES
23
to intrusion of the diorite to the east. It seems reasonable to assume that the St. Makarius Point anomaly is caused by reversely magnetized but locally thicker pillow lavas near the top of the Kirilof Point rocks. These would lie between 1,000 and 1,500 feet below the surface at the location of the anomaly. The apparent thickening of this reversely magnetized lava in a structural depression further suggests that this depression was present in late Kirilof Point time. This means that structural movements may have begun in Kirilof Point time. Support for this concept is also found in the previously mentioned Rifle Range Point anomaly in which the buried source rocks of the strongest negative anomalies are removed from the trend of the present strike of these lavas. Here, too, the only rocks known to be capable of causing the anomaly are pillow lavas of Kirilof Point. These may be thicker and structurally localized in the Rifle Range Point area, just as they are thought to be in the St. Makarius Point area. Furthermore, the largest and most intense negative anomalies on or near Amchitka lie offshore (pi. 1), south and west of the Rifle Range Point anomaly where one string of negative anomalies projects seaward. This culminates in a large negative anomaly about 4 miles southwest of Rifle Range Point.
MEX ISLAND ANOMALY
This negative anomaly appears to be another that is attributable to the pillow lavas of Kirilof Point. Like the anomalies at Rifle Range and St. Makarius Points, it occupies a position on the upthrown side of a major fault. Although the Kirilof Point does not crop out in this area, pillow lavas of the Kirilof Point were found in drill hole UAe-1 at a depth of about 1,400 feet. The depth estimated from the anomalies on profiles T-130 and T-8 (pi. 1) is 1,300 feet to the top of the source rocks. A considerable part of the section penetrated between 1,400 and 6,100 feet in UAe-1 is reversely magnetized, although at most depths the remanence is weak. Like the Rifle Range Point anomaly, the Mex Island anomaly extends seaward several miles to a large pronounced low over the ocean floor (pi. 2).
BIRD ROCK, WINDY ISLAND. CHITKA POINT-CONSTANTINE POINT ANOMALIES
The Chitka Point andesite lava flows are normally magnetized, and, where relatively thick or high in total intensity, they produce positive anomalies. Examples are the Bird Rock, Windy Island, and Chitka Point-Constantine Point anomalies (pi. 2). Almost all oriented samples collected beneath these anomalies have positive remanent inclinations. The one
notable exception which has a high negative inclination value, sample B7-67 (sample site 7, pi. 2), was collected from a feature that is probably too small to give an aeromagnetic anomaly.
The Windy Island anomaly corresponds to a pile of fairly young subaerial andesite lava flows that make up the highest part of Amchitka. These flows dip seaward from the high points of the island, and the aeromagnetic data suggest that they extend well out into the ocean, particularly south of Windy Island. As previously described, the White House Cove anomaly, a result of alteration associated with intrusion, appears to cut across the anomaly produced by the less altered lavas of the Chitka Point Formation.
The Chitka Point-Constantine Point anomaly is mostly over water, but at the northwestern end it is over lava flows of the Chitka Point Formation. It seems reasonable to assume that these lavas, which appear to dip seaward, thicken or are less altered northeast of Amchitka in the area of the anomaly. It is also possible that the southeastern part of the anomaly is due to basaltic rocks in the Banjo Point Formation.
The Infantry Road anomaly, also over the Chitka Point Formation, is mostly over altered andesitic breccias that are not highly magnetic. The anomaly may result from andesite lava flows buried beneath the breccias. Andesite is reported at a depth of about 80 feet in a drill hole in the eastern part of this area.
SITE B ANOMALY
This anomaly, just north and on the downthrown side of the Rifle Range fault, is one of several positive anomalies over faultblock wedges of the Banjo Point Formation. Another unnamed anomaly lies in a similar position north of the major fault between St. Makarius Bay and Constantine Harbor.
—780 ANOMALY
This negative anomaly appears to be produced by a reversely magnetized near-surface lava flow or sill in the Banjo Point Formation. The body is represented by sample C24-67 (sample site 8, pi. 2). It has a magnetic susceptibility of 35.5XlO-4 gauss per oersted, a remanent intensity of 37.5X10-4 gauss, a remanent declination of 210°, and a remanent inclination of —57°.
SITE F ANOMALY
The anomalies discussed so far stand out clearly from those in neighboring areas, and they are reflected by data taken on several aeromagnetic traverses. The Site F anomaly is one of the numerous small anomalies that relate to only one or two traverses. The anomaly has an amplitude of 150 gam-﻿24
INTERPRETATION OF AN AEROMAGNETIC SURVEY, AMCHITKA ISLAND AREA, ALASKA
mas in the aeromagnetic survey (pi. 2) and 500 gammas in the ground magnetic survey (pi. 3).
A depth estimate from profile T-123 (pi. 1) places the anomaly-producing rocks at about 100 feet below the ground surface. Drill hole UAe-3, which started in breccia, penetrated Chitka Point andesite at a depth of 180 feet (Lee, 1969). Four drill-core specimens of the lava average 36.0X10-4 gauss per oersted for magnetic susceptibility, 3.9xl0“4 gauss for remanent intensity, and 68° for remanent inclination. If we assume a northward declination, the average total magnetization becomes 21.2X10-4 gauss for intensity, 6° for declination, and 64° for inclination.
RELATION OF SUBMARINE STRUCTURE SOUTH OF AMCHITKA TO AEROMAGNETIC ANOMALIES
A comparison of plate 1 with the generalized geologic map (pi. 2) showing possible submarine faults beneath the Pacific Ocean indicates that landward projections of the pronounced submarine canyons, on which the existence of these faults is inferred, do not show a consistent relationship with aeromagnetic contours. Many of the hypothetical faults cross the aeromagnetic contours at fairly large angles. There is a suggestion of local parallelism between aeromagnetic contours and inferred submarine faults above the submarine terrace at about 325 feet below sea level. But most faults on Am-chitka, such as the pronounced Rifle Range fault (pi. 2), apparently either die out seaward or are overlapped by anomaly-producing rocks. Carr and Quinlivan (1969) inferred from submarine contours a northeast-trending fault through South Bight which would have to cross the Pillow Point anomaly and not produce any marked effect on the aeromagnetic pattern. South of Amchitka, the erratic distribution of anomalies with respect to submarine topography (pi. 2) might be explained by an intersecting fault system, by interruption of faults by intrusive masses, or by a combination of both.
REFERENCES CITED
Ade-Hall, J. M., 1964, The magnetic properties of some submarine oceanic lavas: Geophys. Jour., v. 9, no. 1, p. 85-92. Bath, G. D., 1967, Aeromagnetic anomalies related to remanent magnetism in volcanic rocks, Nevada Test Site: U.S. Geol. Survey open-file report, 20 p.
Bean, R. J., 1966, A rapid graphical solution for the aeromagnetic anomaly of the two-dimensional tabular body: Geophysics, v. 31, no. 5, p. 963-970.
Carr, W. J., and Quinlivan, W. D., 1969, Progress report on the geology of Amchitka Island, Alaska: U.S. Geol. Survey Rept. USGS-474-44, 15 p.; available only from U.S. Dept. Commerce Natl. Tech. Inf. Service, Springfield, Va. 22151.
Carr, W. J., Quinlivan, W. D., and Gard, L. M., Jr., 1970, Age and stratigraphic relations of Amchitka, Banjo Point, and Chitka Point Formations, Amchitka Island, Aleutian Islands, Alaska, in Cohee, G. V., Bates, R. E., and Wright, Wilna, Changes in stratigraphic nomenclature, U.S. Geological Survey, 1969: U.S. Geol. Survey Bull. 1324-A, p. A16-A22.
Collinson, D. W., Creer, K. M., and Runcorn, S. K., eds., 1967, Methods in paleomagnetism; Proceedings, Part 3 of Developments in solid earth geophysics: New York, Elsevier Publishing Co., 609 p.
Cox, Allan, Doell, R. R., and Dalrymple, G. B., 1964, Reversals of the earth’s magnetic field: Science, v. 144, no. 3626, p. 1537-1543.
Gard, L. M., Lee, W. H., and Way, R. J., 1969, Preliminary lithologic log of drill hole UAe-1 from 0 to 5,028 feet, Amchitka Island, Alaska: U.S. Geol. Survey Rept. USGS-474-46, 2 p.; available only from U.S. Dept. Commerce Natl. Tech. Inf. Service, Springfield, Va. 22151.
Grant, F. S., and West, G. F., 1965, Interpretation theory in applied geophysics: New York, McGraw-Hill Book Co., 583 p.
Grim, P. J., and Erickson, B. H., 1968, Marine magnetic anomalies and fracture zones south of the Aleutian Trench, in Abstracts for 1967: Geol. Soc. America Spec. Paper 115, p. 84.
Hall, D. H., 1959, Direction of polarization determined from magnetic anomalies: Jour. Geophys. Research, v. 64, no. 11, p. 1945-1959.
Hayes, D. E., and Heirtzler, J. R., 1968, Magnetic anomalies and their relation to the Aleutian Island arc: Jour. Geophys. Research, v. 73, no. 14, p. 4637-4646.
Henderson, J. R., Jr., and Zietz, Isidore, 1958, Interpretation of an aeromagnetic survey of Indiana: U.S. Geol. Survey Prof. Paper 316-B, p. 19-37.
Irving, E., Molyneux, L., and Runcorn, S. K., 1966, The analysis of remanent intensities and susceptibilities of rocks: Geophys. Jour., v. 10, no. 5, p. 451-464.
Jahren, C. E., and Bath, G. D., 1967, Rapid estimation of induced and remanent magnetization of rock samples, Nevada Test Site: U.S. Geol. Survey open-file report, 29 p.
Keller, Fred, Jr., Meuschke, J. L., and Alldredge, L. R., 1954, Aeromagnetic surveys in the Aleutian, Marshall, and Bermuda Islands: Am. Geophys. Union Trans., v. 35, no. 4, p. 558-572.
Lee, W. H., 1969, Preliminary lithologic log of drill hole UAe-3 from 0 to 4,816 feet, Amchitka Island, Alaska: U.S. Geol. Survey Rept. USGS-474-50, 3 p.; available only from U.S. Dept. Commerce Natl. Tech. Inf. Service, Springfield, Va. 22151.
LePichon, Xavier, 1968, Sea-floor spreading and continental drift: Jour. Geophys. Research, v. 73, no. 12, p. 3661-3697.
Mason, R. G., 1958, A magnetic survey off the west coast of the United States between latitudes 32° and 36° N, longitudes 121° and 128° W: Geophys. Jour., v. 1, no. 4, p. 320-329.
Miller, C. H., Kibler, J. D., and Tuttle, T. J., 1969, Reconnaissance gravity survey of the Rat Islands, with emphasis on Amchitka Island, Alaska: U.S. Geol. Survey Rept. USGS-474-49, 10 p.; available only from U.S. Dept. Commerce Natl. Tech. Inf. Service, Springfield, Va. 22151.
Peters, L. J., 1949, The direct approach to magnetic interpretation and its practical application: Geophysics, v. 14, no. 3, p. 290-320.﻿REFERENCES CITED
25
Powers, H. A., Coats, R. R., and Nelson, W. H., 1960, Geology and submarine physiography of Amchitka Island, Alaska: U.S. Geol. Survey Bull. 1028-P, p. 521-554.
Richards, M. L., Vacquier, Victor, and Van Voorhis, G. D., 1967, Calculation of the magnetization of uplifts from combining topographic and magnetic surveys: Geophysics, v. 32, no. 4, p. 678-707.
Steenland, N. C., 1965, Oil fields and aeromagnetic anomalies: Geophysics, v. 30, no. 5, p. 706-739.
Vacquier, Victor, Steenland, N. C., Henderson, R. G., and Zietz, Isidore, 1951, Interpretation of aeromagnetic maps: Geol. Soc. America Mem. 47, 151 p.
Vine, F. J., 1966, Spreading of the ocean floor — New evidence: Science, v. 154, no. 3755, p. 1405-1415.
Weiss, Oscar, 1949, Aerial magnetic survey of the Vredefort dome in the Union of South Africa: Mining Eng., v. 1, no. 12, p. 433-438.
Werner, S., 1953, Interpretation of magnetic anomalies at sheet-like bodies: Sveriges Geol. Undersokning Arsb. 43, no. 6, ser. C, no. 508, 130 p.
U. S. GOVERNMENT PRINTING OFFICE : 1972 O - 456-237﻿UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
178° 10'
52°00'
5 760 000 N I--
590 000 E 20'
PREPARED ON BEHALF OF THE
U.S. ATOMIC ENERGY COMMISSION
PROFESSIONAL PAPER 707 PLATE 1
179°50'
- 52°00'
51o10'
51°10'
- — 5 670 000 N
178-10'
179°50'
456 237 O - 72 (In pocket)﻿UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
PREPARE) ON BEHALF OF THE
U.S. ATOMIC ENERGY COMMISSION
PROFESSIONAL PAPER 707 PLATE 3
Chitka
750
w 500 <
<
v 250
£r o cc cr
11" .........|m11-t*11h| ..............11 ii 1111 rij-f
Ml HI HI | I
+H-
i i*ii mu m

i in n |i 111
>i-hu|hHI
mm

HI
1.75
1.05
I
O
U)
ce
i 11 m H-
r 750
500 <J) < 5 5 <
250 u
ce
o
CE
CE
UJ
% -250 D Z <
c/> -500 -
-750 J
-250
NOTE
At each station, the data from five observations spaced 5 feet apart are averaged to give the magnetic anomaly and computed to give the standard error.
5 MILES
<
-500 5)
L -750
PLOTS OF MAGNETIC ANOMALY AND STANDARD ERROR FROM GROUND SURVEY DATA
AT STATIONS 0.1 MILE APART ON AMCHITKA ISLAND, ALASKA
456 237 O - 72 (In pocket)﻿7 iY
Ground-Water Hydraulics
GEOLOGICAL
SURVEY
PROFESSIONAL PAPER 708﻿﻿Ground-Water Hydraulics
By S. W. LOHMAN
GEOLOGICAL SURVEY PROFESSIONAL PAPER 708
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972﻿UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY W. A. Radlinski, Acting Director
Library of Congress catalog-card No. 74-180716
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 Stock Number 2401-1194﻿CONTENTS
►
»
i
Symbols and dimensions------------------------------------
Introduction...............................—..............
Divisions of subsurface water in unconfined aquifers—.....
Saturated zone---------------------------------------
Water table--------------------------------------
Capillary fringe__________.______________________
Unsaturated zone_____________________________________
Capillarity_______________________________________________
Hydrologic properties of water-bearing materials----------
Porosity_____________________________________________
Primary__________________________________________
Secondary----------------------------------------
Conditions controlling porosity of granular materials— Arrangement of grains (assumed spherical and of
equal size)____________________________________
Shape of grains__________________________________
Degree of assortment_____________________________
Void ratio___________________________________________
Permeability_________________________________________
Intrinsic permeability_______________________________
Hydraulic conductivity--------------------------------
Transmissivity_______________________________________
Water yielding and retaining capacity of unconfined aquifers..
Specific yield_______________________________________
Specific retention___________________________________
Moisture equivalent__________________________________
Artesian wells—confined aquifers__________________________
Flowing wells—unconfined aquifers_________________________
Confined aquifers_________________________________________
Potentiometric surface_______________________________
Storage properties___________________________________
Storage coefficient______________________________
Components__________________________________
Land subsidence__________________________________
Elastic confined aquifers___________________
Nonelastic confined aquifers and oil-bearing
strata____________________________________
Movement of ground water—steady-state flow________________
Darcy’s law__________________________________________
Velocity_____________________________________________
Aquifer tests by well methods—point sink or point source__
Steady radial flow without vertical movement_________
Example__________________________________________
Partial differential equations for radial flow_______
Nonsteady radial flow without vertical movement______
Constant discharge_______________________________
Example_____________________________________
Straight-line solutions_____________________
Transmissivity__________________________
Storage coefficient_____________________
Example____________________________
Precautions_____________________________
Page
VI
1
1
1
1
2
2
2
3
3
4 4 4
4
4
4
4
4
5
6 6 6 6 6 6 7
7
8 8 8 8 9 9 9
9
10
10
10
11
11
12
13
15
15
19
19
19
21
22
22
Aquifer tests by well methods—Continued
Nonsteady radial flow without vertical movement— Continued
Constant drawdown. ______________________________
Straight-line solutions______________________
Example__________________________________
Instantaneous discharge or recharge______________
“Slug” method________________________________
Example__________________________________
Bailer method________________________________
Leaky confined aquifers with vertical movement-------
Constant discharge..._____________________________
Steady flow__________________________________
Nonsteady flow_______________________________
Hantush-Jaeob method_____________________
Example______________________________
Hantush modified method__________________
Example______________________________
Constant drawdown________________________________
Unconfined aquifers with vertical movement___________
Example for anisotropic aquifer__________________
Example for delayed yield from storage___________
Aquifer tests by channel methods—line sink or line source
(nonsteady flow, no recharge)..........................
Constant discharge___________________________________
Constant drawdown____________________________________
Aquifer tests by areal methods____________________________
Numerical analysis___________________________________—
Example__________________________________________
Flow-net analysis____________________________________
Example__________________________________________
Closed-contour method_________________________________
Unconfined wedge-shaped aquifer bounded by two
streams____________________________________________
Methods of estimating transmissivity______________________
Specific capacity of wells___________________________
Logs of wells and test holes_________________________
Methods of estimating storage coefficient_________________
Methods of estimating specific yield______________________
Drawdown interference from discharging wells______________
Relation of storage coefficient to spread of cone of depression.
Aquifer boundaries and theory of images___________________
“Impermeable” barrier________________________________
Line source at constant head—perennial stream________
Application of image theory__________________________
“Safe yield”______________________________________________
The source of water derived from wells____________________
Examples of aquifers and their development___________
Valley of large perennial stream in humid region_
Valley of ephemeral stream in semiarid region____
Closed desert basin------------------------------
Southern High Plains of Texas and New Mexico_____
Grand Junction artesian basin, Colorado__________
References cited__________________________________________
Page
23
23
25
27
27
29
29
30 30 30 30
30
31
32 32 34 34 36 38
40
40
41 43
43
44
45
45
46
49
52
52
53 53 53
55
56
57
57
58
59 61 62 64 64
64
65
65
66 67
III﻿IV
CONTENTS
ILLUSTRATIONS
[Plates are in pocket]
Plate 1. Logarithmic plot of a versus G(a).
2.	Type curves for H/H0 versus Tt/rc2 for five values of a.
3.	Two families of type curves for nonsteady radial flow in an infinite leaky artesian aquifer.
4.	Family of type curves for l/u versus H(u, /3), for various values of /3.
5.	Logarithmic plot of a versus G(a, rw/B).
6.	Curves showing nondimensional response to pumping a fully penetrating well in an unconfined aquifer.
7.	Curves showing nondimensional response to pumping a well penetrating the bottom three-tenths of the thickness of an unconfined
aquifer.
8.	Delayed-yield type curves.
9.	Logarithmic plot of 2 IF (it) versus 1 /uv.
Page
Figure 1. Diagram showing divisions of subsurface water in unconfined aquifers_____________________________________________________ 2
2-5. Sketches showing—
2.	Water in the unsaturated zone_________________________________________________________________________________ 2
3.	Capillary rise of water in a tube______________________-______________________________________________________ 3
4. Rise of water in capillary tubes of different diameters________________________________________________________ 3
5. Sections of four contiguous spheres of equal size______________________________________________________________ 4
6.	Graph showing relation between moisture equivalent and specific retention____________________________________________ 7
7.	Diagrammatic section showing approximate flow pattern in uniformly permeable material which receives recharge in
interstream areas and from which water discharges into streams____________________________________________________ 7
8.	Diagrammatic sections of discharging wells in a confined aquifer and an unconfined aquifer____________________________ 8
9.	Sketch showing hypothetical example of steady flow___________________________________________________________________ 10
10.	Half the cross section of the cone of depression around a discharging well in an unconfined aquifer__________________ 11
11.	Semilogarithmic plot of corrected drawdowns versus radial distance for aquifer test near Wichita, Kans_______________ 13
12.	Sketch of cylindrical sections of a confined aquifer_________________________________________________________________ 14
13.	Sketch to illustrate partial differential equation for steady radial flow____________________________________________ 14
14.	Logarithmic graph of W(u) versus u_________________________________________________________________________________   17
15.	Sketch showing relation of W(u) and u to s and r2/t, and displacements of graph scales by amounts of constants shown_	18
16.	Logarithmic plot of s versus r2/t from table 6_______________________________________________________________________ 20
17-19. Semilogarithmic plot of—
17.	sw/Q versus t/rw2__________________________________________*_________________________________________________ 25
18.	Recovery (sw) versus t_______________________________________________________________________________________ 26
19.	Data from “slug” test on well at Dawsonville, Ga_____________________________________________________________ 28
20.	Logarithmic plot of s versus t for observation well 23S/25E-17Q2 at Pixley, Calif____________________________________ 33
21.	Sketch showing relation of z to 6 of pumped and observation wells on plates 6 and 7__________________________________ 35
22-25. Logarithmic plot of—
22.	s versus t for observation	well B2-66-7dda2, near lone, Colo_________________________________________________ 37
23.	s versus t for observation	well 139, near Fairborn, Ohio_____________________________________________________ 39
24.	D(u)q versus u2 for channel method—constant discharge________________________________________________________ 41
25.	D(u)h versus u2 for channel method—constant drawdown________________________________________________________  42
26.	Sketch showing array of nodes used in finite-difference analysis_____________________________________________________ 44
27.	Plot of 2h versus Aho/At for winter of 1965-66, when W = 0___________________________________________________________ 46
28.	Plot of 2h versus Aho/At for spring of 1966__________________________________________________________________________ 47
29.	Sketch showing idealized square of flow net__________________________________________________________________________ 47
30.	Map of Baltimore industrial area, Maryland, showing potentiometric surface in 1945 and generalized flow lines in the
Patuxent Formation________________________________________________________________________________________________ 48
31.	Sketch map of a surface drainage pattern, showing location of observation wells that penetrate an unconfined aquifer_	49
32.	Example hydrograph from well A	of figure 31, showing observed and projected water-level	altitudes_________________ 50
33.	Graph of s/so versus t taken from	hydrograph of well A (see fig. 32), showing	computation	of	T/S_________________ 50
34.	Graph of s/so versus Tt/r2S for 00 = 75°; 0/0o =0.20_________________________________________________________________ 51
35.	Family of semilogarithmic curves showing the drawdown produced at various distances from a well discharging at stated
rates for 365 days from a confined aquifer for which T = 20 ft2day_1 and <S = 5 X10-6_____________________________ 54
36.	Family of semilogarithmic curves showing the drawdown produced after various times at a distance of 1,000 ft from a
well discharging at stated rates from a confined aquifer for which T = 20 ft2day_1 and S = 5 X10-6________________ 55
37.	Idealized section views of a discharging well in an aquifer bounded by an “impermeable” barrier and of the equivalent
hydraulic system in an infinite aquifer___________________________________________________________________________ 56
38.	Generalized flow net in the vicinity of discharging real and image wells near an “impermeable” boundary______________ 57
39.	Effect of “impermeable” barrier on semilogarithmic plot of s versus t/r2_____________________________________________ 58
40.	Idealized section views of a discharging well in an aquifer bounded by a perennial stream and of the equivalent hydraulic
system in an infinite aquifer_____________________________________________________________________________________ 59﻿CONTENTS	V
Page
41. Generalized flow net in the vicinity of a discharging well dependent upon induced infiltration from a nearby stream_ 60
42. Effect of recharging stream on semilogarithmic plot of s versus f/rl________________________________________________ 61
43-47. Diagrammatic sections showing development of ground water from—
43.	Valley of large perennial stream in humid region____________________________________________________________ 64
44.	Valley of ephemeral stream in semiarid region_______________________________________________________________ 64
45.	Bolson deposits in closed desert basin_________________________________________________________________ 65
46.	Southern High Plains of Texas and New Mexico___________________________________________________________ 66
47.	Grand Junction artesian basin, Colorado________________________________________________________________ 66
TABLES
Page
Table 1. Capillary rise in samples having virtually the same porosity, 41 percent, after 72 days_____________________________ 3
2.	Relation of units of hydraulic conductivity, permeability, and transmissivity________________________________ 5
3.	Land subsidence in California oil and water fields______________________________________________________________ 10
4.	Data for pumping test near Wichita, Kans________________________________________________________________________ 12
5.	Values of W(u) for values of u between 10~16 and 9.9____________________________________________________________ 16
6.	Drawdown of water level in observation wells N-l, N-2, and N-3 at distance r from well being pumped at constant rate
of 96,000 ft3 day-1_____________________________________________________________- ........................ 19
7.	Values of G(a) for values of a between 10-4 and 1016...______________________________________________________ 24
8.	Field data for flow test on Artesia Heights well near Grand Junction, Colo.,	September	22,	1948_________________ 24
9.	Field data for recovery test on Artesia Heights well near Grand Junction,	Colo., September	22,	1948_____________ 26
10.	Recovery of water level in well near Dawsonville, Ga., after instantaneous withdrawal of	weighted float________ 29
11.	Postulated water-level drawdowns in three observation wells during a hypothetical test of an infinite leaky confined aquifer- 31 12-14. Drawdown of water levels in—
12.	Observation well 23S/25E-17Q2, 1,400 ft from a well pumping at constant rate of 750 gpm, at Pixley, Calif.,
March 13, 1963___________________________________________________________-............................ 32
13.	Observation well B2-66-7dda2, 63.0 ft from a well pumping at average rate of 1,170 gpm, near lone, Colo.,
August 15-18, 1967____________________________________________________________________________________ 38
14.	Observation well 139, 73 ft from a well pumping at constant rate of 1,080 gpm, near Fairborn, Ohio, October
19-21, 1954___________________________________________________________________________________________ 38
15.	Values of Z)(w)„ u, and u2 for channel method—constant discharge_______________________________________________ 41
16.	Values of D(u)h, u, and w2 for channel method—constant drawdown________________________________________________ 43
17.	Average values of hydraulic conductivity of alluvial materials in the Arkansas River valley, Colorado_______ 53
18.	Computations of drawdowns produced at various distances from a well discharging at stated rates for 365 days from a
confined aquifer for which T = 20 ft2 day-1 and S = 5 X10-6_______________________________________________ 54
19.	Computations of drawdowns produced after various times at a distance of 1,000 ft from a well discharging at stated rates
from a confined aquifer for which T = 20 ft2 day-1 and S = 5 X10-6________________________________________ 55﻿SYMBOLS AND DIMENSIONS
[Number in parentheses refers to the equation, page, or illustration where the symbol first appears or where additional clarification may be obtained. Symbols are also defined in the text. There is some duplication of symbols because of the desire to preserve the notation used in the original papers]
Symbol	Dimensions	Description
A	L1	Area (8); area of influence (145).
B		1 /VT/(K'/b') (95).
B	L~l	VT/aS, (107).
B	ZJT-i	Constant (140).
BE		Barometric efficiency of artesian well (22).
C	—	Constant (7).
C, C	Ll	Constant of proportionality (144).
D	LT 1	Discharge rate per unit area (151).
D{u)q		D (drain) function of u for constant discharge (112).
D(u)h		D (drain) function of u for constant drawdown (118).
E.	ML 1T~i	Bulk modulus of elasticity of solid
	ML~lT~i	skeleton of aquifer (20).
Ew		Bulk modulus of elasticity of water (20).
F(e„, e/6o,		F function of do, 9/8o, r/a, Tt/r2S
r/a, Tt/r'S) GW
GW rJB)
H
H o
H(u, jS)
J
Jo, Jo(x)
Ji(x)
K
K
K
K', K"
Kr
K.
Ka
Xi
In, Lo
L(u,v)
M
Nr
t after “slug”
instant of of “slug”
ML2T~ 2
LT-i
LT-i
LT~i
LT~'
LT~l
(P- 49).
G function of a (68).
G function of a, rw/B (96).
Head inside well at time injection or removal of (75).
Head inside well at injection or removal (75).
H function of u, f) (91).
Joule (9).
Bessel function of zero order, first kind (68), (100).
Bessel function of first order, first kind (75).
Hydraulic conductivity (13), (92).
Average hydraulic conductivity (p.
11).
Constant r</r„ (150).
Vertical hydraulic conductivity of confining beds (86), (92).
Radial hydraulic conductivity (102).
Vertical hydraulic conductivity (102).
Modified Bessel function of second kind, zero order (96).
Modified Bessel function of second kind, first order (96).
Lengths of two concentric closed contours (137).
L (leakance) function of u, v (87).
Moisture equivalent (18).
Ratio: specific retention/moisture equivalent (18).
Symbol	Dimensions
Q	L3 T~l
Qo	L*T~l
Qt	IJT~l
P	ML~lT~2
R	LT-1
S	
S'	
S’, S"	
Se	
s,	
Sr	
Ss, S/, S."	L~l
So	
T	MT~2
T	IAT-1
TE	
V	U
V(+,t)	
W	LT~l
W (w)	
Fo(x)	
Yi(x)	
a	L
b	L
V	L
cm	L
cgs	LMT
d	L
d	
e	
ft	L
9	LT
gal	L3
g	M
gpd	L3T~l
gpm	L3T~l
h	L
ho	L
hi to hi	
hc	L
in.	L
k	L2
kg	M
Description
Flow rate (8); constant discharge rate (19); total flow (132). Constant discharge rate of drain per unit length of drain (112). Discharge of aquifer to drain per unit length of drain (120). Pressure (fig. 3).
Recharge rate per unit area (151). Storage coefficient (19).
Corrected value of storage coefficient (64).
Storage coefficients of aquifer and semipervious confining layers (92). Early time storage coefficient (107). Later time specific yield (107). Specific retention (17).
Specific storage of aquifer and confining beds, respectively (92). Specific yield (16).
Surface tension of fluid (1). Transmissivity (26), (19).
Tidal efficiency of artesian well (22). Total volume (4).
V function of and r (103).
Rate of accretion (126).
W (well) function of u (46).
Bessel function of zero order, second kind (68).
Bessel function of first order, second kind (77).
Finite length (128).
Thickness of aquifer (p. 6). Thickness of confining bed (86). Centimeter (p. 3), (11). Centimeter-gram-second (11).
Mean grain diameter (7).
Derivative (8).
Base of Naperian logarithms, 2.71828
(p. 19).
Foot (13).
Standard acceleration due to gravity
(8).
U.S. gallon (36).
Gram.
Gallons per day (p. 6).
Gallons per minute (p. 8).
Head (8), (116), (130).
Head at node (well) 0 (128), (129). Head at nodes (wells) 1 to 4 (fig. 26), (128).
Height of capillary rise (1).
Inch (p. 9).
Intrinsic permeability (7), (8). Kilogram (9).
VI﻿SYMBOLS AND DIMENSIONS
VII
Symbol	Dimensions	Description
i	L	Length of flow (8).
lb	MLT-*	Pound (p. 9).
m	L	Meter (9).
mm	L	Millimeter (p. 3).
min	T	Minute (36).
n		Se+S,/Se (108).
rid		Number of potential drops (133).
n,		Number of flow channels (132).
V	ML~lT-*	Pressure (11).
9	LT~l	Rate of flow per unit area (specific
		discharge) (8), (151).
r	L	Radius or radial distance (1), (19).
rc	L	Radius of casing in interval over
		which water level fluctuates (76).
r\	L	Radial distance from observation
		well to image well (148).
rP	L	Radial distance from observation
		well to pumped well (148).
r,	L	Radius of well screen or open hole
		(76).
rw	L	Radius of discharging well (67),
		(139).
s	L	Drawdown (19), (114).
s'	L	Residual drawdown (81).
Si	L	Drawdown in image well (146).
So	L	Abrupt change in drain level at
		t = 0 (118); abrupt change in
		water level (fig. 32).
So	L	Algebraic sum of s„ and s; (146).
sp	L	Drawdown in pumped well (146).
s„	L	Drawdown in discharging well (67),
		(139).
sec	T	Second (9).
t	T	Time since discharge began or
		stopped (19).
u		Variable of integration (19); r2S/4Tt
		(45), (85), (91); xy/S/^Tt (113).
Ui		(n/rp)hip (149).
Up		Ui/(n/rpy (149).
V	L3T~l	Volume of water per unit time (37).
V		r/tVK'/b'T (85), (86).
V	LT	Average velocity (28).
v.	L3	Volume of water drained by gravity
		(16).
Vi	L3	Volume of interstices (4).
Symbol	Dimensions	Description
Vm	L3	Volume of mineral particles (4).
Vr	L3	Volume of water retained against
		gravity (17).
vw	L3	Volume of water (4).
W	L	Length (130).
X		Variable of integration (68), (108).
X	L	Distance from drain to point of
		observation (112).
X	L	Coordinate in x direction (126).
y	L	Coordinate in y direction (126).
V		Variable of integration (85), (91).
Z	L	Elevation head (99).
Z	L	Coordinate in z direction (fig. 21).
00		Infinity (19).
s		Summation (128).
CL		Angle (1); Tt/SrJ (67), (94);
		r'S/r* (76); (r/B)*/r'S, (107).
a	M~3LT3	1 /E. (21).
p	M~lLT2	1 /Ew (21).
0		Tt/r3 (77);
y	ML~*T-»	Specific weight per unit area (20).
A		Finite difference, change in (24).
d		Partial derivative (37).
		x2
		x*-\-l
V	ML~lT~l	Dynamic viscosity (10).
e		Porosity (4); angle (138).
00		Angle (138).
M		Micro (10-6) (p. 5).
X		Variable of integration (100).
V	UT~l	Kinematic viscosity (8), (10).
		3.1416.
p	ML~3	Density of fluid (1).
Pd	ML~3	Density of dry sample (bulk den-
		sity) (5).
Pm	ML~3	Mean density of mineral particles
		(grain density) (5).
Pw	ML~3	Density of water (18).
T		Kt/Sb (100), (101); variable of
		integration (107).
<P	L3T“»	Potential (8).
*		r/b (100), (101).﻿r﻿GROUND-WATER HYDRAULICS
By S. W. Lohman
INTRODUCTION
The science of ground-water hydrology is concerned with evaluating the occurrence, availability, and quality of ground water. Although many ground-water investigations are qualitative in nature, quantitative studies are necessarily an integral part of the complete evaluation of occurrence and availability. The worth of an aquifer as a source of water depends largely upon two inherent characteristics—its ability to store and to transmit water.
Thorough knowledge of the geologic framework is essential to understand the operation of the natural plumbing system within it. Ground-water hydraulics is concerned with the natural or induced movement of water through permeable rock formations. The principal method of analysis in ground-water hydraulics is the application, generally by field tests of discharging wells, of equations derived for particular boundary conditions. Prior to 1935, such equations were known only for the relatively simple steady flow condition, which incidentally generally does not occur in nature. The development by Theis (1935) of an equation for the nonsteady flow of ground water was a milestone in ground-water hydraulics. Since 1935 the number of equations and methods has grown rapidly and steadily. These are described in a wide assortment of publications, some of which are not conveniently available to many engaged in ground-water studies. The essence of many of these will be presented and briefly discussed, but frequent recourse should be made to the more exhaustive treatments given in the references cited.
The material presented herein was adapted from the lecture notes which I prepared for a series of five lectures on ground-water hydraulics presented in May 1967 to the students of the 1967 Ground Water School of the Australian Water Resources Council at Adelaide, South Australia. Problems given in the lecture notes have been changed to examples in this report, and the solutions of these examples are complete with tabulated data and data plots. Nine plates and three figures of type curves are reproduced at scales to fit readily available logarithmic or semilogarithmic translucent graph paper, and most of the data plots also are reproduced at scales to fit the proper type curves.
Thus, all the type curves may be used in the solution of actual field problems.
I am indebted to the following colleagues of the Geological Survey for their critical reviews of the lecture notes, or the present version, or both: R. R. Bennett, R. H. Brown, H. H. Cooper, Jr., W. J. Drescher, J. M. Dumeyer, P. A. Emery, J. G. Ferris, C. L. McGuinness, E. A. Moulder, E. A. Sammel, R. W. Stallman, C. V. Theis, and E. P. Weeks.
Before getting into ground-water hydraulics, let us review briefly the divisions of subsurface water and some of the fundamental properties of aquifers.
DIVISIONS OF SUBSURFACE WATER IN UNCONFINED AQUIFERS
Unconfined aquifers composed of granular materials, such as mixtures of clay, silt, sand, and gravel, may contain all or part of the divisions of subsurface water shown in figure 1. All divisions generally are present in areas of relatively deep water table after rather prolonged dry spells. In other areas, the divisions may be present only in part, in order from bottom to top. Thus, beneath lakes, streams, and some swamps, surface water is underlain directly by unconfined ground water and the capillary fringe is absent. In some swamps the saturated part of the capillary fringe reaches the surface, but the unsaturated zone is absent.
SATURATED ZONE WATER TABLE
The unconfined ground water below the water table (fig. 1) is under pressure greater than atmospheric.
When a well is sunk a few feet into an unconfined aquifer, the water level remains, for a time, at the same altitude at which it was first reached in drilling (fig. 1), but of course this level may fluctuate later in response to many factors. This level is one point on the water table, which may be defined as that imaginary surface within an unconfined aquifer at which the pressure is atmospheric. (See Hubbert, 1940, p. 897, 898; Lohman, 1965, p. 92.) The water level in wells sunk to greater depths in unconfined aquifers may stand at, above, or below the
1﻿2
GROUND-WATER HYDRAULICS
Pressure	Zone	Divisions	Well
Gas phase, equals atmospheric Liquid phase, less than atmospheric	Unsaturated zone	
		
Less than		
atmospheric		
	Saturated	
Atmospheric	zone1	w a ter ta Die
Greater than		Unconfined
atmospheric		ground water
'As redefined by Hubbert (1940, p. 897, 898). See also Lohman (1965, p. 92).
Figure 1.—Divisions of subsurface water in unconfined aquifers.
water table, depending upon whether the well is in the discharge or recharge area of the aquifer. (See “Flowing Wells—Unconfined Aquifers” and fig. 7.)
Unconfined aquifers containing bodies of perched ground water above the regional water table may have repetitions of all or part of the divisions shown in figure 1.
CAPILLARITY
The rise of water or other fluids in tubes or in the interstices in rocks or soil may be considered to be caused by (1) the molecular attraction (adhesion) between the solid material and the fluid, and (2) the surface tension of the fluid, an expression of the attraction (cohesion) between the molecules of the fluid.
The molecular attraction between the solid material and the fluid depends in part upon the composition of the fluid and upon the composition and cleanliness of the material, and, as will be shown below, the height of capillary rise is governed by the size of the tube or opening. Water will wet and adhere to a clean floor, whereas it will remain in drops without wetting a floor covered with dust.
The surface of water resists considerable tension without losing its continuity. Thus, a carefully placed greased needle floats on water, as do certain insects having greasy pads on their feet.
In figure 3, the water has risen a height hc in a tube of radius r immersed in a vessel of water. The relations shown in figure 3 may be expressed
CAPILLARY FRINGE
The capillary fringe ranges in thickness from a small fraction of an inch in coarse gravel to more than 5 ft in silt. Its lower part is completely saturated, like the material below the water table, but it contains water under less than atmospheric pressure, and hence the water in it normally does not enter a well. The capillary fringe rises and declines with fluctuations of the water table, and may change in thickness as it moves through materials of different grain sizes. Some capillary water may be drawn into wells by way of the saturated zone if the body of capillary water declines into coarser material and moves below the water table within the cone of depression of a discharging well. The saturated part of the capillary fringe was termed the “zone of complete capillary saturation” by Terzaghi (1942) and the “capillary stage” by Versluys (1917).
UNSATURATED ZONE
The unsaturated zone contains water in the gas phase under atmospheric pressure, water temporarily or permanently under less than atmospheric pressure, and air or other gases. The fine-grained materials may be temporarily or permanently saturated with water under less than atmospheric pressure, but the coarse-grained materials are unsaturated and generally contain liquid water only in rings surrounding the contacts between grains, as shown in figure 2. The soil may be temporarily saturated with soil water during or after periods of precipitation or flooding. The unsaturated zone may be absent beneath swamps, streams, or lakes. For a more sophisticated account of the unsaturated zone, see Stallman (1964).
Tr2pghc = 2irrT cosa	\_MLT~2],	(1)
where
r — radius of capillary tube, p=density of fluid, g = acceleration due to gravity, hc = height of capillary rise,
T = surface tension of fluid, and a = angle between meniscus and tube.
Note that, according to equation 1, weight equals lift by surface tension. Solving equation 1 for hc,
2 T
hc-—cosa [L].	(2)
rpg
For pure water in clean glass, a = 0, and cos a — 1. At 20°C, T = 72.8 dyne cm-1, p may be taken as 1 g cm-3, and﻿HYDROLOGIC PROPERTIES OF WATER-BEARING MATERIALS
3
Figure 3.—Capillary rise of water in a tube (diameter greatly exaggerated).
g = 980.665 cm sec-2, whence ,	0.15
hc= —	L-^3-	(3)
r
Surface tension is sometimes given in grams per centimeter and for pure water in contact with air, at 20°C, its value is
Table 1.—Capillary rise in samples having virtually the same porosity, 41 percent, after 72 days
[From A. Atterberg, cited in Terzaghi (1942)]
Material	Grain size (mm)	Capillary rise (cm)
Fine gravel 	 			 5-2	2.5
Very coarse sand 				 2-1	6.5
Coarse sand.. 	 			 1-0.5	13.5
Medium sand				 0.5-0.2	24 6
Fine sand			 .2-0.1	42.8
Silt			 .1-0.05	105.5
Silt			 .05-0.02	>200
1 Still rising after 72 days.
Figure 4.—Rise of water in capillary tubes of different diameters (diameters greatly exaggerated).
0.074 g cm-1. In order to express it in grams per centimeter, we must divide 72.8 by g, the standard acceleration of gravity; thus 72.8 dyne cm-1/980.665 cm sec-2 = 0.074 g cm-1.
From equation 3 it is seen that the height of capillary rise in tubes is inversely proportional to the radius of the tube. The rise of water in interstices of various sizes in the capillary fringe (fig. 1) may be likened to the rise of water in a bundle of capillary tubes of various diameters, as shown in figure 4. In table 1, note that the capillary rise is nearly inversely proportional to the grain size.
HYDROLOGIC PROPERTIES OF WATER-BEARING MATERIALS
POROSITY
The porosity of a rock or soil is simply its property of containing interstices. It can be expressed quantitatively as the ratio of the volume of the interstices to the total volume, and may be expressed as a decimal fraction or as a percentage. Thus
Vi Vw F vm vm _ .	.	_.	..
9= — = — = —— =1- — [dimensionless] (4)
where
6 = porosity, as a decimal fraction,
Vi=volume of interstices,
V = total volume,
vw = volume of water (in a saturated sample), and Vm,= volume of mineral particles.﻿4
GROUND-WATER HYDRAULICS
Porosity may be expressed also as
8 = ——— = 1 — — [dimensionless] (5) Pm	Pm
where
pm = mean density of mineral particles (grain density) and
pa = density of dry sample (bulk density).
Multiplying the right-hand sides of equations 4 and 5 by 100 gives the porosity as a percentage.
PRIMARY
Primary porosity comprises the original interstices created when a rock or soil was formed in its present state. In soil and sedimentary rocks the primary interstices are the spaces between grains or pebbles. In intrusive igneous rocks the few primary interstices result from cooling and crystallization. Extrusive igneous rocks may have large openings and high porosity resulting from the expansion of gas, but the openings may or may not be connected. Metamorphism of igneous or sedimentary rocks generally reduces the primary porosity and may virtually obliterate it.
SECONDARY
Fractures such as joints, faults, and openings along planes of bedding or schistosity in consolidated rocks having low primary porosity and permeability may afford appreciable secondary porosity. In some rocks such secondary porosity affords the only means for the storage and movement of ground water. Solution of carbonate rocks such as limestone or dolomite by water containing dissolved carbon dioxide takes place mainly along joints and bedding planes and may greatly increase the secondary porosity. Similarly, solution of gypsum or anhydrite by water alone may greatly increase the secondary porosity.
CONDITIONS CONTROLLING POROSITY OF GRANULAR MATERIALS
ARRANGEMENT OF GRAINS (ASSUMED SPHERICAL AND OF EQUAL SIZE)
If a hypothetical granular material were composed of spherical particles of equal size, the porosity would be independent of particle size (whether the particles were the size of silt or the size of the earth) but would vary with the packing arrangement of the particles. As shown by Slichter (1899, p. 305-328), the lowest porosity of 25.95 (about 26) percent would result from the most compact rhombohedral arrangement (fig. 5A) and the highest porosity of 47.64 (about 48) percent would result from the least compact cubical arrangement (fig. 5C). The porosity
Figure 5.—Sections of four contiguous spheres of equal size. A, most compact arrangement, lowest porosity; B, less compact arrangement, higher porosity; C, least compact arrangement, highest porosity. Sketches from Slichter (1899, pi. 1).
of the other arrangements, such as that shown in figure 5B, would be between these limits.
SHAPE OF GRAINS
Angularity of particles causes wide variations in porosity and may increase or decrease it, according to whether the particles tend to bridge openings or pack together like pieces of a mosaic.
DEGREE OF ASSORTMENT
The greater the range in particle size the lower the porosity, as the small particles occupy the voids between the larger ones.
VOID RATIO
The void ratio of a rock or soil is the ratio of the volume of its interstices to the volume of its mineral particles. It may be expressed:
Void ratio = — = — = ----- [dimensionless], (6)
vm vm	1 — 6
where the symbols are as defined for equation 4.
PERMEABILITY
The permeability of a rock or soil is a measure of its ability to transmit fluid, such as water, under a hydropotential gradient. Many earlier workers found that the permeability is approximately proportional to the square of the mean grain diameter,
fc^Cd2 [L2],	(7)
where
k = intrinsic permeability,
C — a dimensionless constant depending upon porosity, range and distribution of particle size, shape of grains, and other factors, and d = the mean grain diameter of some workers and the effective grain diameter of others.﻿HYDROLOGIC PROPERTIES OF WATER-BEARING MATERIALS
5
INTRINSIC PERMEABILITY
Inasmuch as permeability is a property of the medium alone and is independent of the nature or properties of the fluid, the U.S. Geological Survey is adopting the term “intrinsic permeability,” which is not to be confused with hydraulic conductivity as the latter includes the properties of natural ground water. Intrinsic permeability may be expressed
where
k = —
g(dh/dl)
q*
(dip/dl)

(8)
k = intrinsic permeability, q = rate of flow per unit area = Q/A, v = kinematic viscosity, g = acceleration of gravity,
dh/dl = gradient, or unit change in head per unit length of flow, and
dip/dl — potential gradient, or unit change in potential per unit length of flow.
From equation 8 it may be stated that a porous medium has an intrinsic permeability of one unit of length squared if it will transmit in unit time a unit volume of fluid of unit kinematic viscosity through a cross section of unit area measured at right angles to the flow direction under a unit potential gradient.
If q is measured in meters per second, v in square meters per second, <p in Joules per kilogram, and l in meters, the unit for k is in square meters. Thus, equation 8 may be written
(m3) (m2 sec-1)
(m2) (sec) ( —J kg-1 m-1)
(m3) (m2 sec-1)
(m2) (sec) (— kg m sec-2 m kg-1 m-1)
= nr

(9)
The Geological Survey will express k in square micrometers, (pm)2 = 10-12 m2= 10-8 cm2, which is 10-12 times the value in equation 9.
The kinematic viscosity (*) is related to the dynamic viscosity (17) thus
Table 2.—Relation of units of hydraulic conductivity, permeability, and transmissivity
[Equivalent values shown in same horizontal lines, [ indicates abandoned term]
A. Hydraulic conductivity
Hydraulic conductivity (K)		fField coefficient of permeability (P/)
Feet per day (ft day-*)	Meters per day (m day-1)	"[Gallons per day per square foot [(gal day-1 ft-2)
One	0.305	7.48
3.28	One	24.5
.134	.041	One
B. Transmissivity {T)		
Square feet per day (ft2 day-1)	Square meters per day (m2 day-1)	[Gallons per day per foot t(gal day-1 ft-1)
One	0.0929	7.48
10.76	One	80.5
.134	.0124	One
C. Permeability		
Intrinsic permeability	Darcy =	[Coefficient of permeability
k qv		9 (at 60°F.)
d^/dl	dp/dl-\-pgdz/dl	P °T m dh/dl
[(/xm)2 = 10-8 cm2]	[0.987 XlO-s cm2]	[[gal day-1 ft-2 at 60°F.]
One	1.01	18.4
0.987	One	18.2
.054	.055	One
though, as pointed out by Hubbert (1940, p. 921) “* * * this equation is physically erroneous as an expression of Darcy’s law, owing to the use of pressure as a potential function * * at least one of the expressions has been widely used, so they will be taken up briefly.
In 1930, Nutting (1930, p. 1348) defined a “rational cgs measure of permeability” then in use in his U.S. Geological Survey laboratory, and intended for general use by the petroleum industry, as “the flow in cubic centimeters per second through each square centimeter, of a fluid of 0.01 [poise] viscosity under a pressure of 1 megadyne per centimeter * * *.” Nutting doubtless meant a pressure gradient of 1 megabarye per centimeter, or 1 megadyne per square centimeter per centimeter. Thus corrected, Nutting’s definition may be expressed, in centimeter-gram-second units,
dp/dl
i! = vP	[ML-1T-1],	(10)
where p = density.
Other expressions for intrinsic permeability referred to in the literature (table 2) involve pressure gradients rather than head or potential gradients and were intended mainly for laboratory use where gas (generally nitrogen) perme-ameters rather than water permeameters are used. Al-
(cm3) (10-2 dyne-sec cm-3)
(cm2) (sec) (—106 dyne cm-2 cm-1)
= 10-8 cm2= (pm)2	[A2].	(11)
Four years later Wyckoff, Botset, Muskat, and Reed (1934, p. 166) seemingly ignored the Nutting definition of permeability in consistent units and proposed the darcy in inconsistent units, wherein the atmosphere was used in﻿6
GROUND-WATER HYDRAULICS
place of the megabarye. Thus
the aquifer. In the units of equations 13 and 14, T becomes
(cm3) (10-2 dyne-sec cm-2)
arCy (cm2) (sec) (—1.0132X106 dyne cm-2 cm-1)
= 0.987 X10-8 cm2 = 0.987 (Mm)2	[L2].	(12)
To make matters still worse, in 1935 the American Petroleum Institute (1942, p. 4) redefined the darcy for adoption by the petroleum industry by changing the volume in equation 12 from cubic centimeters to milliliters. Inasmuch as 1 milliliter is 27 parts per million greater than 1 cubic centimeter, at ordinary temperatures, the darcy, as redefined, embodies the doubly inconsistent units milliliter, centimeter, and atmosphere.
HYDRAULIC CONDUCTIVITY
The Water Resources Division, U.S. Geological Survey, is adopting hydraulic conductivity (K) in consistent units to replace (P) the “coefficient of permeability” in the inconsistent units gpd ft-2 (gallons a day per square foot). K may be defined thus: A medium has a hydraulic conductivity of unit length per unit time if it will transmit in unit time a unit volume of ground water at the prevailing viscosity through a cross section of unit area, measured at right angles to the direction of flow, under a hydraulic gradient of unit change in head through unit length of flow. The suggested units are:
T = ft2 day"1, or m2 day"1 [L2!1"1].	(15)
The relation of the new and old units is given in table 2.
WATER YIELDING AND RETAINING CAPACITY OF UNCONFINED AQUIFERS
SPECIFIC YIELD1
In general terms, the specific yield is the water yielded from water-bearing material by gravity drainage, as occurs when the water table declines. More exactly, the specific yield of a rock or soil has been defined (Meinzer, 1923, p. 28) as the ratio of (1) the volume of water which, after being saturated, it will yield by gravity to (2) its own volume. This may be expressed
Sy= ^ [dimensionless],	(16)
where
Sy = specific yield, as a decimal fraction, v„ = volume of water drained by gravity, and V = total volume.
Note that the duration of the drainage has not been specified; I suggest that it should be stated when known. Multiplying the right-hand side of equation 16 by 100 gives the result in percent.
SPECIFIC RETENTION
ft3
ft2 day ( — ft ft-1)
= ft day-
or
K =
m*
m2day(-mm-1)
= m day-
[LT-1],	(13)
[LT-1],	(14)
where the symbols are as defined for equation 12. The minus signs in equations 13 and 14 result from the fact that the water moves in the direction of decreasing head. The relation of the new and old units is given in table 2.
TRANSMISSIVITY
The transmissivity (T) is the rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of the aquifer under a unit hydraulic gradient. It replaces the term “coefficient of transmissibility” because it is considered by convention a property of the aquifer, which is transmissive, whereas the contained liquid is transmissible. Hence, though spoken of as a property of the aquifer, it is a property of the confined liquid also. It is equal to Kb, where b is the thickness of
The specific retention of a rock or soil with respect to water has been defined (Meinzer, 1923, p. 28, 29) as the ratio of (1) the volume of water which, after being saturated, it will retain against the pull of gravity to (2) its own volume. It may be expressed
V
Sr= =8—Sy [dimensionless], (17)
where
Sr = specific retention, as a decimal fraction, and vr = volume of water retained against gravity, mostly by molecular attraction.
From equation 17, it may be noted also that Sy = 8 — Sr.
MOISTURE EQUIVALENT
As used in the Hydrologic Laboratory of the U.S. Geological Survey, the moisture equivalent of waterbearing materials is the ratio of (1) the weight of water which the material, after saturation, will retain against
1 See also “Storage Coefficient.”﻿FLOWING WELLS—UNCONFINED AQUIFERS
7
SPECIFIC RETENTION
RATIO______________________
MOISTURE EQUIVALENT
Figure 6.—Relation between moisture equivalent and specific retention from Piper (1933, p. 485). Modified by A. I. Johnson.
a centrifugal force 1,000 times the force of gravity, for 2 hours at 20°C., and under 100 percent humidity, to (2) the weight of the material when dry. Note that this ratio is by weight, whereas specific retention is a ratio by volume. The relation between the two concepts may be expressed
Sr = MNr—	[dimensionless],	(18)
Pw
where
Sr = specific retention, in percent by volume,
M = moisture equivalent, in percent by weight,
Nr = ratio: specific retention/moisture equivalent,
Pd — dry density of sample, and pw = density of water.
Piper (1933) found that the relations shown in figure 6 prevail between specific retention and moisture equivalent. Note that the ratio is essentially 1 for moisture equivalents between 34 and 12 percent but ranges from 1 to 2.5 for values between 12 and 2 percent.
ARTESIAN WELLS-CONFINED AQUIFERS
Confined aquifers, as the name suggests, contain ground water that is confined under pressure between relatively impermeable or significantly less permeable material and that will rise above the top of the aquifer. If the water rises above the land surface it will flow naturally. A well drilled into such a confined aquifer is an artesian well, and if the water rises above the land surface, it may be termed a “flowing artesian well.” As will be shown in the next section, however, flowing wells also may be constructed in unconfined aquifers.
FLOWING WELLS-UNCONFINED AQUIFERS
Consider a hilly area underlain by uniformly permeable material that receives recharge from precipitation in interstream areas and from which water discharges into streams. The approximate flow pattern is illustrated by the solid lines with arrows in an idealized cross section (fig. 7);
Figure 7.—Approximate flow pattern in uniformly permeable material which receives recharge in interstream areas and from which water discharges into streams. From Hubbert (1940, p. 930, fig. 45).
the dashed lines at right angles to the flow lines are lines of equipotential. There is an infinity of flow and equipotential lines, only a few of which are shown. Cased wells at or near the streams reach water under greater head as the depth increases and, as may be inferred from the horizontal dashed lines, wells open at moderate depth will flow at the surface. Note also in figure 7 that cased wells on the hill reach water at progressively lower heads as the depth increases.﻿8
GROUND-WATER HYDRAULICS
CONFINED AQUIFERS
POTEN TIOMETRIC SURFACE
The potentiometric surface is an imaginary surface connecting points to which water would rise in tightly cased wells from a given point in an aquifer. It may be above or below the land surface. The water table (p. 1) is a particular potentiometric surface. Potentiometric is preferable to the term “piezometric,” which was used by many in the past.
Confined and unconfined aquifers are compared in figure 8. The well tapping the confined aquifer in figure 8
Figure 8.—Discharging wells in a confined aquifer (right) and an unconfined aquifer (left). Although the water levels in wells A and B have declined because of pumping from the nearby well, wells A and B remain usable; however, shallower well C has been “dried up” by the pumping. The water levels in wells E and F have declined because of flow from the nearby well, but in well D, which taps a shallower aquifer, the water level is not affected by flow from the deeper aquifer.
is a flowing well; if the potentiometric surface were at or below the ground surface, however, this well would have to be pumped.
STORAGE PROPERTIES
Prior to 1925, confined, or artesian, aquifers were considered mainly as conduits for delivering water from recharge areas to distant wells or springs. They were not thought of as having storage properties except, of course, for volume times porosity. Confining beds generally were thought to be wholly or relatively impermeable, whereas they are now known to range from nearly impermeable to moderately permeable.
In 1925 Meinzer and Hard (1925, p. 92), from studies of flowing artesian wells tapping the Dakota Sandstone in the Ellendale area, South Dakota, postulated that, although in
the preceding 38 years the average rate of discharge of a selected group of wells was 3,000 gpm, only about 500 gpm could have been transmitted from the recharge area and that the remaining 2,500 gpm was released from storage by elastic compression of the aquifer as the pressure supporting the load gradually declined. This led to Meinzer’s classic theory of the compressibility and elasticity of artesian aquifers (Meinzer, 1928). It is now known also that part of the water released from storage comes from expansion of the water. (See also, Swenson, 1968.) It is also known that much of the water released by lowering of head in some aquifers comes from inelastic compression of silty or clayey lenses or beds within or adjacent to the aquifers. (See “Nonelastic Confined Aquifers and Oil-Bearing Strata.”)
STORAGE COEFFICIENT
The storage property of confined aquifers was given quantitative significance for the first time by Theis (1935), who introduced the storage coefficient (&) in his classic equation:
where
s = drawdown,
Q = constant discharge rate from well,
T = transmissivity,
r = distance from discharging well to point of observation of s,
S = storage coefficient,
< = time since discharge began, and u = variable of integration.
The current version of Theis’ definition (1938) of the storage coefficient is: The volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head. Note from the definition that the storage coefficient is dimensionless.
The storage coefficient of unconfined aquifers is virtually equal to the specific yield, as most of the water is released from storage by gravity drainage and only a very small part comes from compression of the aquifer and expansion of the water.
The storage coefficient of most confined aquifers ranges from about 10-6 to 10-3 and is about 10-6 per foot of thickness. In contrast, the specific yield of most unconfined aquifers ranges from about 0.1 to about 0.3 and averages about 0.2. Inasmuch as the storage coefficient of confined aquifers generally is so small, the question might be raised as to how much water can be released from storage. To illustrate that large quantities of water can be so released, assume that, in a confined aquifer having a storage coefficient of 2 X10-4, the head declines 400 ft throughout 1﻿CONFINED AQUIFERS
9
square mile; then (2X10-4) (4X102 ft)(2.8Xl07 ft2) = 2.24Xl06ft3—a large volume of water. In the Denver artesian basin, Colorado, the head has declined much more than this in an area of perhaps 100 square miles.
COMPONENTS
Jacob (1940, p. 576) showed that for an elastic confined aquifer, neglecting any release of water from the confining beds,
S = dyb (-A + —) [dimensionless], (20)
where
0 = porosity, as a decimal fraction;
y = specific weight per unit area, 62.4 lb ft-3/144 in2 ft-2 = 0.434 lb in-2 ft-1;
6 = thickness, in feet;
Ew = bulk modulus of elasticity of water, 3 X105 lb in-2, at ordinary temperatures; and
C = a dimensionless ratio, which may be considered unity in an uncemented granular material. In a solid aquifer, as a limestone having tubular solution channels, C is apparently equal to the porosity. The value for a sandstone doubtless ranges between these limits, depending upon the degree of cementation.
2?, = bulk modulus of elasticity of the solid skeleton of the aquifer, as confined in situ, in pounds per square inch.
An alternate expression of equation 20 for elastic confined aquifers in which C may be considered unity is
a\
/3+ -1 [dimensionless], (21)
where
(3 = l/Ew = 3.3 X 10~6 in2 lb-1, and
a = l/E„ in square inches per pound.
Let us consider the part of the storage coefficient that results only from the expansion of water in a confined aquifer having 0 = 0.2 and b = 100 ft. From equation 21, S = Oybp= (0.2) (0.434 lb in~2 ft"1)(100 ft)(3.3X10~6 in2 lb-1) = 2.9 X10-5. Although this value obviously is too small inasmuch as it does not include the compression of the aquifer, it is of value for comparison with the storage coefficient determined by testing an aquifer of this porosity and thickness. If the determined value is comparable to or less than this computed value for water alone, obviously the determined value is in error.
If S and other terms are known, a, the reciprocal of the modulus of elasticity of the aquifer, can be determined
from equation 21. Jacob (1940, p. 583) showed also that S = 8yb@	= Oybfi	[dimensionless],
(22)
where
BE = barometric efficiency of artesian well, and TE = tidal efficiency of artesian well near seacoast.
Other terms are defined for equations 20 and 21.
LAND SUBSIDENCE
ELASTIC CONFINED AQUIFERS
I (Lohman, 1961) showed that for elastic confined aquifers for which C may be assumed to equal 1, equations 20 and 21 may be rewritten
A = - -06/3	[L2M_1T2]	(23)
E, y
and that Hooke’s Law (strain is proportional to stress, within the elastic limit) may be expressed
Ab= A ap [L],	(24)
&8
where
Ab = change in b, in feet, and
Ap = change (generally decline) in artesian pressure, in pounds per square inch.
Combining equations 23 and 24,
A6 = Ap	— dbp'j	[L].	(25)
Equation 25 gives the amount of land subsidence, A6, for an elastic confined aquifer of known S, d, and /3, for a given decline in artesian pressure, Ap. For example, assume <S = 2X10-4, 0 = 0.3, 6 =100 ft, Ap = 100 lb in-2, and note that it is convenient to use 1/y, which equals 2.31 ft lb-1 in2. Then, from equation 25,
Ab = 102 lb in-2(2 X 10~4 X 2.31 ft lb"1 in2
-0.3 X102 ftX3.3X 10-6 in2 lb-1)
= 0.04 ft (rounded).
Similarly, for 6=1,000 ft, Ap= 1,000 lb in-2, S = lO-3, 0 = 0.3, A6= 1.3 ft.
NONELASTIC CONFINED AQUIFERS AND OIL-BEARING STRATA
Clay or silty clay beds or lenses in confined aquifers or oilbearing strata, and in associated confining beds, are much﻿10
GROUND-WATER HYDRAULICS
Table 3.—Land subsidence in California oil and water fields
Well field	Subsidence (ft)	Through year
Wilmington oil field (see Gilluly and Grant, 1949)		129	1966
Water fields: Santa Clara Valley (San Jose)	13	1967
San Joaquin Valley: Los Banos-Kettleman Hills area_ 		26	1966
Tulare-Wasco area.-	12	1962
Arvin-Maricopa area. _	8	1965
1 Stabilized at this amount by repressuring. This figure includes some recovery due to repressuring.
more porous than associated sands or gravels; hence, they contain more fluid per unit volume at a given fluid pressure. When the pressure is gradually reduced, as by discharge of fluids from wells, such beds slowly release fluids and undergo nonelastic (plastic), generally irreversible, compaction. (See Athy, 1930; Hedberg, 1936; and Poland and Evenson, 1966.) Compaction of this type is much greater than purely elastic compression, and it has caused appreciable subsidence of the land surface in both oil and water fields in California, Texas, and elsewhere. Latest available data for several California oil and water fields (J. F. Poland, U.S. Geol. Survey, written commun., Oct. 27, 1967) are given in table 3.
MOVEMENT OF GROUND WATER-STEADY-STATE FLOW
In steady-state flow, hereinafter referred to simply as steady flow, as of ground water through permeable material, there is no change in head with time. Mathematically, this statement is symbolized by dh/dt = 0, which says that the change in head, dh, with respect to the change in time, dt, equals zero. Steady flow generally does not occur in nature, but it is a very useful concept in that steady flow can be closely approached in nature and in aquifer tests, and this condition may be symbolized by dh/dt-* 0.
Figure 9 shows a hypothetical example of true steady radial flow. Here steady radial flow will be reached and maintained when all the recoverable ground water in the cone of depression has been drained by gravity into the well discharging at constant rate Q.
DARCY’S LAW
Although Hagen (1839) and Poiseuille (1846) found that the rate of flow through capillary tubes is proportional to the hydraulic gradient, Darcy (1856) seemingly was the first to experiment with the flow of water through sand, and he found that the rate of laminar (viscous) flow of water through sand also is proportional to the hydraulic gradient. This is known as Darcy’s law and it is generally
Figure 9.—Hypothetical example of steady flow (well discharging at constant rate Q from a cylindrical island in a lake of constant level).
expressed, by rewriting equation 13,
Q Kdh = A=~ ~df
(26)
It will be noted that K, the constant of proportionality in Darcy’s law, is the hydraulic conductivity.
To illustrate the use of equation 26 (Darcy’s law), assume that we wish to compute the total rate of ground-water movement in a valley where A, the cross-sectional area, is 100 ft deep times 1 mile wide, where K = 500 ft day-1, and dh/dl = 5 ft per mile. Then
Q= ~ (100 ft) (5,280 ft) (500 ft day-1)
= 250,000 ft3 day-1.
(27)
VELOCITY
Because the hydraulic conductivity, K, has the dimensions of velocity, LT-1, some might mistake this for the particle velocity of the water, whereas, as may be seen from equations 13 and 14, K is actually a measure of the volume rate of flow through unit cross-sectional area. For the average particle velocity, v, we must also know the porosity of the material. Thus
Q = 'vAd=-KA
where
v = average velocity, in feet per day, and 6 = porosity, as a decimal fraction.
Other terms are defined for equation 13. Rewriting the above equation,
Kdh/dl
[LT-1].
(28)
For example, using the values of K and dh/dl given in﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
11
equation 27, and assuming d = 0.2,
(500 ft day-1) (-5 ft/5,280 ft)
v=------------------------------
0.2
= 2.4 ft day-1 (rounded).	(29)
It should be stressed that the solution of equation 29 is the average velocity and does not necessarily equal the actual velocity between any two points in the aquifer, which may range from less than to more than this value, depending upon the flow path followed. Thus, equation 28 should not be used for predicting the velocity and distance of movement of, say, a contaminant introduced into the ground.
AQUIFER TESTS BY WELL METHODS-POINT SINK OR POINT SOURCE
STEADY RADIAL FLOW WITHOUT VERTICAL MOVEMENT
The first mathematical analysis of steady flow, using a discharging well, was made by Dupuit (1848), who made the important assumption that within the cone of depression of a discharging well the head is constant throughout any vertical line through the water body and therefore is represented by the elevation of the water table. Actually, this is true only in confined aquifers having uniform hydraulic conductivity and having a fully penetrating discharging well, or in confined aquifers remote from the discharging well. Nevertheless, methods based upon this assumption can be applied satisfactorily when certain precautions are taken.
Much of the mathematical analysis of Dupuit was repeated by Adolph Thiem (1887), but it remained for his son Gunther Thiem (1906) to develop a readily usable solution, by determining that the Dupuit-Thiem methods could be applied to any two intermediate points on the cone of depression of a discharging well to determine the hydraulic conductivity of the aquifer. As will be shown later, it is now known that many more points may be used.
In order to derive the Thiem equation and show its relation to Darcy’s law, let figure 10 represent half the cross section of the cone of depression in an unconfined aquifer around well A that has been pumped at constant rate Q long enough that steady flow is being closely approached, and the quantity of water still draining from storage is negligible compared with the quantity of water moving toward well A. Although figure 10 depicts an unconfined aquifer, the method is applicable also to confined aquifers. If the material is reasonably homogenous, and if the base of the aquifer and the undisturbed water table are assumed to be parallel and horizontal; then, by the law of continuity, and provided that changes in storage are negligible compared to Q, virtually equal quantities of
Q
|	Q.
Figure 10.—Half the cross section of the cone of depression around a discharging well (A) in an unconfined aquifer.
water are discharged from well A (Q) and flow radially toward well A through any two concentric cylinders within the cone of depression, as at observation well B (Qi) at radius n or at observation well C (Q2) at radius r2. Thus Q~Qi~Q2. Under these assumed conditions Darcy’s law may be expressed as a first-order ordinary differential equation in cylindrical coordinates
Q=-K2irrh ~	(30)
Separating variables,
dr
r
2 tK
Q
hdh.
Integrating between rx and r2, hi and A2,
Converting to common logarithms and solving for K,
2.30Q logio r2/rt
■7r(/l22 —/li2)
[LT-1].
(31)
In confined aquifers (where there is no unwatering) or in thick unconfined aquifers (where s is negligible compared to b), hi-\-hi may be assumed equal to 2b. Then, as A22—Ai2= (Zi2+Ai) (A2 — Ai), h,2 — hi = si — S2, and T = Kb,﻿12
GROUND-WATER HYDRAULICS
equation 31 may be rewritten
2.30Q logio r2/ri
T=-
27r(Sl —S2)
[Lsr-1].
(32)
Equations 31 and 32 are forms of the Thiem equation, and later it will be shown how equation 32 can be derived also as a special solution of the nonsteady flow equation.
In thin unconfined aquifers, in which s is an appreciable proportion of b, Jacob (1963a) showed how to correct the drawdowns (si and s2) to the values that would have been observed had there been no diminution in saturated thickness (as in a confined aquifer of thickness 6). Note from figure 10 that &2 = & —s2, and hl = b — s1. Substituting these values in equation 31 and, for convenience, multiplying both sides of the equation by 2b,
K=-
2.30Q logio r2/r 1
2 ivb
(62 —26s2+s22) — (62 — 26s!+si2) 2b
and
_______2.30Q logio r2/n_____
2ir[(si —Si2/26) — (s2 —s22/26)]
[L2T-1].	(33)
In equations 32 and 33 note that a straight line should result when values of logio r are plotted at logarithmic scale against corresponding values of s or s—s2/2b at arithmetic scale. Thus, when using semilogarithmic paper, equations 32 and 33 may be written, respectively,
T= —
and
T =
2.30Q
2ttAs/Alogio r
2.30Q
[L2T_1]
(34)
27r A (s — s2/2 b) / Alogio r
[L'r-1].	(35)
As or A(s —s2/26) is taken over one logio cycle of r, for which Alogio r is 1. Equation 34 is used for tests in confined aquifers.
To my knowledge the first pumping test by the Thiem method made by a member of the U.S. Geological Survey was in 1929 by R. M. Leggette (1936, p. 117-119) at Meadville, Pa., and this may well have been the first one made in the United States. The method was thoroughly investigated and validated in 1931 by Wenzel (1936), who ran two elaborate Thiem tests near Grand Island, Nebr., and by Theis (1932, p. 137-140), who made a test by this method at Portales, N. Mex., in 1931 and two more tests in the same area in 1932 (Theis, 1934, p. 91-95). The fourth locality tested by this method was near Elizabeth City, N.C., by me (Lohman, 1936, p. 42-44) in the spring of 1933. Three additional Thiem tests were made in
Nebraska in the fall of 1933 by Wenzel (1942), and I made an 18-day test, the longest known to me, by this method near Wichita, Ivans., in 1937. (See Wenzel, 1942, p. 142-146; Williams and Lohman, 1949, p. 104-108; Jacob, 1963a, p. 249-254.)
Example
Use of the Thiem method as modified by Jacob for thin unconfined aquifers may be demonstrated from data (table 4) obtained in the 18-day pumping test mentioned above (given in Wenzel, 1942, p. 142; Williams and Lohman, 1949, p. 104-108; and Jacob, 1963a, p. 249-254). The discharge, Q, was held virtually constant at 1,000±7 gpm for nearly 19 days, when lightening tripped the circuit breaker and stopped the test. The well tapped unconfined alluvial sand and gravel, and the initial saturated thickness, b, was 26.8 ft. Table 4 gives the data for six observation wells out of a total of 22 at the end of 18 days; three of the wells were on a line extending north from the pumped well, and three were on a line to the south. Wells N-3 and S-3 were planned to be 200 ft from the pumped well, but a property line made it necessary to reduce the distance to 190 ft. Inasmuch as the drawdown correction (s2/2b) ranges from about 0.2 to 0.65 ft, it is necessary to use the corrected drawdowns given in the last column. In figure 11, the corrected drawdowns in the six observation wells are plotted on the linear scale against the radial distance on the logarithmic scale, then a straight line is drawn through the three graphic average points (x). Graphic rather than arithmetic averages should be used, because if one of the six drawdown values is spurious for some geologic or other reason, this point may be ignored in drawing the straight line. Note that, although two points determine a straight line, it is much more contorting to have three or more points that fall on or close to a straight line.
Using the slope of the straight line and other data given, T is computed from equation 35:
(2.30) (1,000 gal min-1) (1,440 min day-1)
= _ (2x) (7.48 gal ft-3)[- (4.05 ft-0.65 ft)]
= 20,700 ft2 day-1.	(36)
Table 4.—Data for -pumping test near Wichita, Kans.
		r	r*	8	82/2b	8 —8*/2b
Line	Well	(ft»	(ft*>	(ft)	(ft)	(ft)
North -.	__ 1	49.2	2,420	5.91	0.65	5.26
	2	100.7	10,140	4.58	.39	4.19
	3	189.4	35,900	3.42	.22	3.20
South		__ 1	49.0	2,400	5.48	. 56	4.92
	2	100.4	10,080	4.31	.35	3.96
	3	190.0	36,100	3.19	.19	3.00﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
13
RADIAL DISTANCE (r), IN FEET
Figure 11.—Semilogarithmic plot of corrected drawdowns versus radial distance for aquifer test near Wichita, Kans.
Later (see “Storage Coefficient”), it will be shown how figure 11 may be used to determine the storage coefficient. Column 4 (r2) is included in table 4 so that the data may be used also in the Theis equation, which gives the same value for T as equation 36, thus indicating that steady flow had been closely approached as far away as 190 ft after 18 days of pumping.
A good arrangement of observation wells for aquifer tests by the Thiem method, particularly for thin unconfined aquifers, was suggested to me by the late C. E. Jacob (written commun., Jan. 28, 1946) and was used successfully in 39 tests in the San Luis Valley, Colo. (Powell, 1958, table 6, p. 130-133). Three pairs of observation wells are put down along a straight line on one side of the pumped well extending in any convenient direction from the pumped well and spaced at distances of 16, 26, and 46 from the well (where 6 is the initial saturated thickness of the unconfined aquifer). One observation well of each pair is cased to the bottom of the aquifer; the other extends just
below the cone of depression created by the pumped well. The drawdowns or corrected drawdowns in the six observation wells are plotted on semilogarithmic paper, and graphic averages are used to determine the position and slope of the straight line, as shown in figure 11. This arrangement is an effective means of correcting for partial penetration (see p. 35) of the aquifer by the pumped well and for local inhomogeneities along this line in the aquifer. (See also Jacob, 1936.)
PARTIAL DIFFERENTIAL EQUATIONS FOR RADIAL FLOW
Figure 12 represents two cylindrical sections of a confined aquifer of thickness 6 and radii r and r+dr, respectively, from which a central well is discharging at constant rate Q. Let the gradient across the annular cylindrical section of infinitesimal thickness dr, between points h2 and hi on the potentiometric surface, be dh/dr. Then, according﻿14
GROUND-WATER HYDRAULICS
to R. W. Stallman (written commun., Feb. 1967),
^ = ~ y dr = 2rrS f dr	[UT~‘],	(37)
dt	dr	at
in which
—— = change in volume of water between h2 and hi, with time,
dQ
dr
= change in rate of flow between hi and hi, with distance,
dh
dt
= change in head between hi and hi, with time, and
S=storage coefficient.
The expression of Darcy’s law in equation 26 may be altered to the form
Q— —2irTr —	[DT-1],	(38)
dr
in which T = Kb, b replaces h, and dh/dr, the partial derivative, replaces dh/dr. Differentiating equation 38 with respect to dr,
Figure 12.—Cylindrical sections of a confined aquifer.
For the benefit of those who have difficulty in visualizing the meaning of the differential terms in equation 41, let us multiply both sides of this equation by r to reduce it to the dimensionless form
dh d2h
— H-----; r = 0
dr	dr2
(42)
/dr dh	d2h
\dr dr	dr2
)
In figure 13, the curve represents a part of the cross section
[IT-1].	(39)
Combining equations 37 and 39, we obtain
_	/dh	d2h\ _ dh
2ttT (---\-r —- ) - 2irrS — .
\dr dr2/
dt
Dividing both sides of this equation by 2wTr, we obtain
ldh ,d2h_Sdh r dr + dr2~ T dt L
(40)
which is the partial differential equation for nonsteady radial flow. For steady radial flow, dh/dt = 0, and equation 40 becomes
1 dh	d*h
r dr	dr2
[L-1].
(41)
Note that when dh/dt = 0, the entire right-hand member of equation 40 is zero; this indicates that there are no changes in storage in the aquifer. Equation 41 may be expressed also in ordinary differentials.
/'
Figure 13.—Sketch to illustrate partial differential equation for steady radial flow.﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
15
of a cone of depression in which steady radial flow has been reached. Let
(~) •»<! (~)
\drj1	\dr/2
be the slopes of the curve at each end of radial distance Ar; then note that the difference in the two slopes, represented by dashed tangent lines, is graphically equal to the change in slope over distance Ar, represented by the arc labeled
d2h
—r Ar.
dr2
Stated mathematically,
/dh\ _ /dh\ _ \dr)l \dr/2
d*h dr2
Ar,
or
/dh\ _ /dh\ \dr/2 Vdr/i
d2h
-|----- Ar = 0.
dr2
(43)
Equation 43 is equivalent in form to equation 42 when applied over distance r.
I have not found a practicable way to portray graphically the meaning of equation 40, but it may help to note that the
S
dh
dt
assumptions of homogeneity, isotropy, and complete well penetration which characterize the steady state equations that have been given so far. The assumption of a constant coefficient of storage, which is used in all the transient flow equations that have been developed (there are a few exceptions where modifications of the assumption are explicitly stated), is of doubtful validity, especially when applied to unconfined water bodies. The justification for this assumption is entirely empirical; it has been applied with some success for some decades, and deviations from it involve generally complex numerical computations. The student should be wary of many solutions for Darcian flow that do not explicitly state the tacit assumptions made.
Equation 19 cannot be integrated directly, but its value is given by the infinite series in the following equation:
or	u2 u3	1
S_ ^[-0-577216—log.— +— — ■-J
m, (44)
where
r2S
u =	[[dimensionless],
(45)
in the right-hand member represents the change in storage per unit area of the aquifer, as the head changes with time.
NONSTEADY RADIAL FLOW WITHOUT VERTICAL MOVEMENT
CONSTANT DISCHARGE
In 1935 C. V. Theis introduced equation 19 with the assistance of C. I. Lubin, who developed the equation for a continuous point source for the heat conduction problem. Equation 19 is a solution of equation 40 for constant discharge that involves the following assumptions, stated by Theis (1935): (1) the aquifer is homogeneous and isotropic, (2) the water body has infinite areal extent (practically its boundaries are beyond the effects of the well in the time considered), (3) the discharging well penetrates the entire thickness of the aquifer, (4) the well has an infinitesimal diameter (of no practical significance for periods of pumping longer than a few minutes) and (5) the water removed from storage is discharged instantaneously with decline in head. Thus, the assumption of a constant coefficient of storage has been added to the
which is the lower limit of integration in equation 19; the value of the series is commonly expressed as W (u)—the well function of u. Values of W (u) for values of u from 10-15 to 9.9 are tabulated in Wenzel (1942, p. 89), in Ferris, Knowles, Brown, and Stallman (1962, p. 96, 97), and are given in table 5. For given values of u and W (u), T may be determined from
Q
T = -r-W(u) 4irs
[L’T-1],
(46)
and S may be determined by rewriting equation 45,
[[dimensionless]. (47)
„ 4 Ttu	4Tu
S= —— or
r2/t
C. V. Theis (Wenzel, 1942, p. 88, 89) devised a simple graphical method of superposition that makes it possible to obtain solutions of equations 46 and 47. Selected values of W (u) versus u from table 5 were plotted on logarithmic graph paper to form the type curve shown in figure 14. Equations 46 and 47 may be rearranged to obtain
or
log™ s
[irfj
= [loSi°^] +l°gio W(u)
W(u)
[L],	(48)﻿16
GROUND-WATER HYDRAULICS
Table 5.—Values of W(u) for values of u between 10~u and 9.9
[From Ferris, Knowles, Brown, and Stallman (1962, p. 96)]
\“ N \	A'XIO-1*	ivxio-H	iVXlO-11	NX 10-i*	iVXKH1	NX 10-«	2VXKH	iVX10-‘	NX 10-7	2VX10-*	JVX10-!	NX 1(H	ivxio-*	NX 10-»	NX 10-‘	N
1.0	33. 9616	31.6590	29.3564	27.0538	24. 7512	22. 4486	20.1460	17. 8435	15. 5409	13. 2383	10. 9357	8.6332	6.3315	4.0379	1.8229	0. 2194
1.1	33. 8662	31. 5637	29. 2611	26. 9585	24. 6559	22.3533	20. 0507	17. 7482	15. 4456	13.1430	10. 8404	8. 5379	6. 2363	3. 9436	1. 7371	.1860
1.2	33. 7792	31. 4767	29.1741	26. 8715	24. >5689	22.2663	19. 9637	17. 6611	15. 3586	13. 0560	10. 7534	8. 4509	6.1494	3. 8576	1. 6595	.1584
1.3	33.6992	31.3966	29.0940	26. 7914	24.4889	22.1863	19. 8837	17. 5811	15. 2785	12.9759	10. 6734	8.3709	6.0695	3. 7785	1.5889	.1355
1.4	33. 6251	31.3225	29.0199	26. 7173	24. 4147	22.1122	19.8096	17. 5070	15. 2044	12.9018	10. 5993	8.2968	5. 9955	3.7054	1.5241	. 1162
1.5	33. 5561	31. 2535	28. 9509	26. 6483	24. 3458	22.0432	19. 7406	17. 4380	15.1354	12. 8328	10.5303	8. 2278	5. 9266	3.6374	1.4645	.1000
1.6	33. 4916	31.1890	28. 8864	26. 5838	24. 2812	21. 9786	19. 6760	17.3735	15.0709	12. 7683	10. 4657	8.1634	5. 8621	3. 5739	1.4092	.08631
1.7	33. 4309	31.1283	28. 8258	26. 5232	24.2206	21. 9180	19.6154	17.3128	15.0103	12. 7077	10. 4051	8.1027	5.8016	3. 5143	1. 3578	.07465
1.8	33.3738	31.0712	28. 7686	26. 4660	24.1634	21. 8608	19. 5583	17. 2557	14.9531	12. 6505	10. 3479	8.0455	5. 7446	3.4581	1.3089	.06471
1.9	33.3197	31.0171	28. 7145	26. 4119	24.1094	21.8068	19. 5042	17. 2016	14.8990	12. 5964	10. 2939	7.9915	5.6906	3.4050	1.2649	.05620
2.0	33.2684	30. 9658	28.6632	26. 3607	24. 0581	21. 7555	19.4529	17.1503	14.8477	12. 5451	10. 2426	7. 9402	5.6394	3.3547	1.2227	.04890
2.1	33. 2196	30. 9170	28.6145	26.3119	24. 0093	21. 7067	19.4041	17.1015	14. 7989	12. 4964	10.1938	7. 8914	5. 5907	3.3069	1.1829	.04261
2.2	33.1731	30. 8705	28. 5679	26. 2653	23. 9628	21. 6602	19.3576	17.0550	14. 7524	12. 4498	10.1473	7. 8449	5. 5443	3. 2614	1.1454	. 03719
2.3	33.1286	30. 8261	28. 5235	26. 2209	23.9183	21. 6157	19. 3131	17.0106	14.7080	12. 4054	10.1028	7.8004	5. 4999	3. 2179	1.1099	.03250
2.4	33.0861	30. 7835	28.4809	26.1783	23.8758	21. 5732	19. 2706	16. 9680	14. 6654	12. 3628	10.0603	7. 7579	5. 4575	3.1763	1.0762	.02844
2.5	33. 0453	30. 7427	28.4401	26.1375	23.8349	21. 5323	19. 2298	16. 9272	14.6246	12. 3220	10.0194	7. 7172	5.4167	3.1365	1. 0443	.02491
2.6	33.0060	30. 7035	28. 4009	26.0983	23. 7957	21.4931	19.1905	16. 8880	14. 5854	12. 2828	9. 9802	7.6779	5.3776	3. 0983	1.0139	.02185
2.7	32. 9683	30. 6657	28.3631	26.0606	23. 7580	21.4554	19.1528	16 8502	14. 5476	12. 2450	9. 9425	7.6401	5. 3400	3.0615	.9849	.01918
2.8	32. 9319	30. 6294	28. 3268	26.0242	23. 7216	21.4190	19.1164	16. 8138	14. 5113	12. 2087	9.9061	7.6038	5.3037	3.0261	.9573	.01686
2.9	32. 8968	30. 5943	28 2917	25.9891	23.6865	21.3839	19.0813	16. 7788	14.4762	12.1736	9.8710	7.5687	5. 2687	2.9920	.9309	. 01482
3.0	32. 8629	30. 5604	28. 2578	25.9552	23. 6526	21.3500	19.0474	16. 7449	14.4423	12.1397	9.8371	7. 5348	5. 2349	2.9591	.9057	.01305
3.1	32.8302	30. 5276	28. 2250	25. 9224	23. 6198	21.3172	19.0146	16. 7121	14.4095	12.1069	9. 8043	7. 5020	5. 2022	2. 9273	.8815	.01149
3.2	32. 7984	30.4958	28.1932	25. 8907	23. 5880	21. 2855	18.9829	16.6803	14.3777	12.0751	9. 7726	7.4703	5.1706	2. 8965	.8583	.01013
3.3	32. 7676	30. 4651	28.1625	25.8599	23. 5573	21. 2547	18. 9521	16. 6495	14.3470	12.0444	9. 7418	7. 4395	5.1399	2. 8668	.8361	.008939
3.4	32. 7378	30. 4352	28.1326	25.8300	23.5274	21. 2249	18. 9223	16. 6197	14.3171	12.0145	9. 7120	7.4097	5.1102	2. 8379	.8147	. 007891
3.5	32. 7088	30. 4062	28.1036	25. 8010	23.4985	21.1959	18. 8933	16. 5907	14. 2881	11. 9855	9. 6830	7.3807	5.0813	2. 8099	.7942	.00697C
3.6	32. 6806	30. 3780	28.0755	25. 7729	23. 4703	21.1677	18.8651	16. 5625	14. 2599	11. 9574	9. 6548	7. 3526	5.0532	2. 7827	.7745	.006160
3.7	32. 6532	30.3506	28. 0481	25. 7455	23. 4429	21.1403	18. 8377	16. 5351	14. 2325	11. 9300	9. 6274	7.3252	5. 0259	2. 7563	.7554	.005448
3.8	32. 6266	30. 3240	28.0214	25. 7188	23. 4162	21.1136	18. 8110	16. 5085	14. 2059	11.9033	9. 6007	7. 2985	4. 9993	2. 7306	. 7371	.004820
3.9	32. 6006	30. 2980	27.9954	25. 6928	23.3902	21.0877	18. 7851	16.4825	14.1799	11.8773	9. 5748	7. 2725	4. 9735	2.7056	.7194	.004267
4.0	32. 5753	30.2727	27.9701	25. 6675	23.3649	21.0623	18. 7598	16. 4572	14.1546	11.8520	9. 5495	7. 2472	4.9482	2.6813	.7024	.003779
4.1	32. 5506	30. 2480	27. 9454	25. 6428	23. 3402	21.0376	18. 7351	16. 4325	14.1299	11.8273	9. 5248	7. 2225	4. 9236	2. 6576	.6859	.003349
4.2	32. 5265	30. 2239	27. 9213	25. 6187	23.3161	21.0136	18. 7110	16. 4084	14.1058	11.8032	9. 5007	7.1985	4. 8997	2. 6344	.6700	.002969
4.3	32. 5029	30. 2004	27. 8978	25. 5952	23. 2926	20. 9900	18.6874	16.3884	14.0823	11. 7797	9.4771	7.1749	4. 8762	2. 6119	.6546	.002633
4.4	32. 4800	30.1774	27.8748	25. 5722	23. 2696	20. 9670	18. 6644	16. 3619	14.0593	11. 7567	9. 4541	7.1520	4. 8533	2. 5899	.6397	. 002336
4.5	32. 4575	30.1549	27. 8523	25. 5497	23. 2471	20.9446	18. 6420	16. 3394	14.0368	11. 7342	9. 4317	7.1295	4.8310	2. 5684	.6253	.002073
4.6	32. 4355	30.1329	27. 8303	25. 5277	23. 2252	20.9226	18.6200	16. 3174	14.0148	11. 7122	9.4097	7.1075	4. 8091	2. 5474	.6114	. 001841
4.7	32. 4140	30.1114	27. 8088	25. 5062	23.2037	20.9011	18. 5985	16. 2959	13. 9933	11.6907	9.3882	7.0860	4.7877	2. 5268	.5979	.001635
4.8	32. 3929	30.0904	27. 7878	25. 4852	23.1826	20. 8800	18. 5774	16. 2748	13. 9723	11. 6697	9. 3671	7.0650	4. 7667	2.5068	.5848	.001453
4.9	32. 3723	30.0697	27. 7672	25. 4646	23.1620	20. 8594	18. 5568	16. 2542	13.9516	11. 6491	9. 3465	7.0444	4. 7462	2.4871	.5721	.001291
5.0	32.3521	30.0495	27. 7470	25. 4444	23.1418	20.8392	18. 5366	16.2340	13.9314	11.6289	9.3263	7.0242	4. 7261	2.4679	.5598	.001148
5.1	32. 3323	30. 0297	27. 7271	25. 4246	23.1220	20. 8194	18. 5168	16. 2142	13.9116	11.6091	9. 3065	7.0044	4.7064	2. 4491	.5478	. 001021
5.2	32. 3129	30.0103	27. 7077	25. 4051	23.1026	20.8000	18.4974	16.1948	13. 8922	11. 5896	9. 2871	6. 9850	4. 6871	2. 4306	.5362	.0009086
5.3	32. 2939	29. 9913	27. 6887	25.3861	23.0835	20. 7809	18. 4783	16.1758	13.8732	11.5706	9.2681	6. 9659	4.6681	2.4126	.5250	.0008086
5.4	32. 2752	29. 9726	27. 6700	25. 3674	23. 0648	20. 7622	18.4596	16.1571	13. 8545	11. 5519	9. 2494	6. 9473	4.6495	2.3948	.5140	.0007198
5.5	32. 2568	29. 9542	27.6516	25. 3491	23.0465	20. 7439	18.4413	16.1387	13.8361	11.5336	9.2310	6. 9289	4.6313	2.3775	.5034	.0006409
5.6	32. 2388	29. 9362	27. 6336	25.3310	23. 0285	20. 7259	18. 4233	16.1207	13.8181	11.5155	9. 2130	6.9109	4. 6134	2. 3604	.4930	.0005708
5.7	32. 2211	29. 9185	27. 6159	25. 3133	23.0108	20. 7082	18.4056	16.1030	13. 8004	11.4978	9.1953	6. 8932	4. 5958	2.3437	.4830	.0005085
5.8	32. 2037	29.9011	27. 5985	25. 2959	22. 9934	20. 6908	18.3882	16. 0856	13. 7830	11.4804	9.1779	6. 8758	4. 5785	2.3273	.4732	.0004532
5.9	32.1866	29.8840	27. 5814	25. 2789	22. 9763	20.6737	18.3711	16. 0685	13. 7659	11.4633	9.1608	6.8588	4. 5615	2.3111	.4637	.0004039
6.0	32.1698	29. 8672	27. 5646	25. 2620	22.9595	20. 6569	18.3543	16.0517	13. 7491	11. 4465	9.1440	6. 8420	4. 5448	2.2953	.4544	.0003601
6.1	32.1533	29. 8507	27. 5481	25. 2455	22. 9429	20. 6403	18.3378	16.0352	13. 7326	11.4300	9.1275	6. 8254	4. 5283	2.2797	.4454	.0003211
6.2	32.1370	29. 8344	27. 5318	25.2293	22. 9267	20. 6241	18.3215	16.0189	13. 7163	11.4138	9.1112	6. 8092	4. 5122	2. 2645	.4366	.0002864
6.3	32.1210	29. 8184	27. 5158	25. 2133	22. 9107	20. 6081	18. 3055	16. 0029	13. 7003	11.3978	9.0952	6. 7932	4. 4963	2. 2494	.4280	.0002555
6.4	32.1053	29.8027	27. 5001	25.1975	22. 8949	20. 5923	18. 2898	15. 9872	13. 6846	11. 3820	9.0795	6. 7775	4. 4806	2.2346	.4197	.0002279
6.5	32. 0898	29. 7872	27. 4846	25.1820	22. 8794	20. 5768	18. 2742	15. 9717	13. 6691	11.3665	9.0640	6. 7620	4. 4652	2. 2201	.4115	.0002034
6.6	32. 0745	29. 7719	27. 4693	25.1667	22. 8641	20. 5616	18. 2590	15. 9564	13. 6538	11. 3512	9. 0487	6. 7467	4. 4501	2.2058	.4036	.0001816
6.7	32. 0595	29. 7569	27. 4543	25.1517	22. 8491	20. 5465	18. 2439	15. 9414	13. 6388	11.3362	9.0337	6. 7317	4. 4351	2.1917	. 3959	.0001621
6.8	32. 0446	29. 7421	27. 4395	25.1369	22. 8343	20. 5317	18.2291	15. 9265	13. 6240	11.3214	9. 0189	6. 7169	4. 4204	2.1779	.3883	.0001448
6.9	32. 0300	29. 7275	27. 4249	25.1223	22.8197	20. 5171	18. 2145	15. 9119	13.6094	11.3608	9.0043	6. 7023	4.4059	2.1643	.3810	.0001293
7.0	32.0156	29. 7131	27. 4105	25.1079	22. 8053	20. 5027	18. 2001	15. 8976	13. 5950	11. 2924	8. 9899	6. 6879	4.3916	2.1508	.3738	.0001155
7.1	32. 0015	29. 6989	27. 3963	25. 0937	22. 7911	20. 4885	18.1860	15. 8834	13. 5808	11. 2782	8.9757	6.6737	4. 3775	2.1376	.3668	.0001032
7.2	31. 9875	29. 6849	27.3823	25.0797	22. 7771	20. 4746	18.1720	15. 8694	13. 5668	11.2642	8. 9617	6. 6598	4. 3636	2.1246	.3599	.00009219
7.3	31.9737	29. 6711	27. 3685	25. 0659	22. 7633	20. 4608	18.1582	15. 8556	13. 5530	11. 2504	8. 9479	6. 6460	4. 3500	2.1118	.3532	.00008239
7.4	31. 9601	29. 6575	27.3549	25.0523	22. 7497	20.4472	18.1446	15. 8420	13. 5394	11. 2368	8. 9343	6. 6324	4.3364	2.0991	.3467	.00007364
7.5	31. 9467	29. 6441	27.3415	25.0389	22. 7363	20. 4337	18.1311	15. 8286	13. 5260	11.2234	8. 9209	6. 6190	4.3231	2.0867	.3403	.00006583
7.6	31. 9334	29. 6308	27.3282	25. 0257	22. 7231	20. 4205	18.1179	15. 8153	13. 5127	11. 2102	8. 9076	6. 6057	4.3100	2.0744	.3341	.00005886
7.7	31. 9203	29. 6178	27.3152	25.0126	22. 7100	20.4074	18.1048	15. 8022	13.4997	11.1971	8.8946	6. 5927	4. 2970	2.0623	.3280	.00005263
7.8	31.9074	29. 6048	27.3023	24. 9997	22. 6971	20. 3945	18. 0919	15. 7893	13.4868	11.1842	8. 8817	6. 5798	4.2842	2.0503	.3221	. 00004707
7.9	31. 8947	29. 5921	27. 2895	24. 9869	22.6844	20.3818	18.0792	15. 7766	13.4740	11.1714	8. 8689	6. 5671	4. 2716	2.0386	.3163	.00004210
8.0	31. 8821	29. 5795	27.2769	24.9744	22. 6718	20. 3692	18.0666	15. 7640	13.4614	11.1589	8.8563	6. 5545	4. 2591	2.0269	.3106	.00003767
8.1	31. 8697	29. 5671	27. 2645	24. 9619	22. 6594	20. 3568	18.0542	15. 7516	13. 4490	11.1464	8. 8439	6. 5421	4.2468	2.0155	.3050	.00003370
8.2	31. 8574	29. 5548	27. 2523	24. 9497	22. 6471	20. 3445	18.0419	15. 7393	13. 4367	11.1342	8.8317	6. 5298	4. 2346	2.0042	.2996	
8.3	31. 8453	29. 5427	27. 2401	24. 9375	22. 6350	20. 3324	18. 0298	15. 7272	13. 4246	11.1220	8. 8195	6. 5177	4.2226	1.9930	.2943	
8.4	31.8333	29. 5307	27. 2282	24. 92.56	22. 6230	20. 3204	18.0178	15. 7152	13. 4126	11.1101	8. 8076	6. 5057	4. 2107	1.9820	.2891	
8.5	31.8215	29. 5189	27. 2163	24. 9137	22. 6112	20. 3086	18. 0060	15. 7034	13. 4008	11.0982	8. 7957	6. 4939	4.1990	1.9711	. 2840	
8.6	31. 8098	29. 5072	27. 2046	24. 9020	22. 5995	20. 2969	17. 9943	15. 6917	13. 3891	11.0865	8. 7840	6. 4822	4.1874	1.9604	.2790	
8.7	31.7982	29.4957	27.1931	24. 8905	22. 5879	20. 2853	17. 9827	15.6801	13.3776	11.0750	8. 7725	6.4707	4.1759	1.9498	. 2742	
8.8	31. 7868	29. 4842	27.1816	24. 8790	22. 5765	20. 2739	17.9713	15. 6687	13.3661	11.0635	8. 7610	6. 4592	4.1646	1. 9393	.2694	
8.9	31. 7755	29.4729	27.1703	24. 8678	22. 5652	20. 2626	17.9600	15. 6574	13.3548	11.0523	8. 7497	6.4480	4.1534	1.9290	.2647	.00001390
9.0	31.7643	29. 4618	27.1592	24. 8566	22.5540	20. 2514	17. 9488	15. 6462	13.3437	11.0411	8. 7386	6.4368	4.1423	1. 9187	.2602	
9.1	31. 7533	29. 4507	27.1481	24. 8455	22. 5429	20. 2404	17. 9378	15. 6352	13.3326	11.0300	8. 7275	6.4258	4.1313	1.9087	.2557	
9.2	31. 7424	29. 4398	27.1372	24.8346	22.5320	20.2294	17. 9268	15. 6243	13. 3217	11.0191	8. 7166	6.4148	4.1205	1. 8987	. 2513	
9.3	31. 7315	29. 4290	27.1264	24. 8238	22. 5212	20. 2186	17. 9160	15. 6135	13.3109	11.0083	8. 7058	6.4040	4.1098	1.8888	. 2470	
9.4	31. 7208	29.4183	27.1157	24. 8131	22. 5105	20. 2079	17. 9053	15. 6028	13.3002	10.9976	8. 6951	6. 3934	4.0992	1. 8791	. 2429	
9.5	31. 7103	29. 4077	27.1051	24. 8025	22.4999	20.1973	17. 8948	15. 5922	13. 2896	10. 9870	8. 6845	6.3828	4.0887	1.8695	.2387	
9.6	31. 6998	29.3972	27. 0946	24. 7920	22.4895	20.1869	17.8843	15. 5817	13. 2791	10. 9765	8.6740	6.3723	4.0784	1.8599	.2347	
9.7	31.6894	29. 3868	27.0843	24. 7817	22. 4791	20.1765	17. 8739	15.5713	13. 2688	10. 9662	8.6637	6.3620	4.0681	1.8505	.2308	
9.8	31. 6792	29. 3766	27,0740	24. 7714	22. 4688	20.1663	17. 8637	15. 5611	13. 2585	10. 9559	8. 6534	6.3517	4.0579	1.8412	. 2269	
9.9	31.6690	29. *3664	27.0639	24. 7613	22.4587	20.1561	17.8535	15. 5509	13. 2483	10. 9458	8.6433	6.3416	4.0479	1.8320	.2231	.000004637﻿w
T

u, CURVE A
IQ"2
10"1
10
10-
10-2
Figure 14.—Logarithmic graph of W(u) versus u.
AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE﻿18
GROUND-WATER HYDRAULICS
logio r*/t
Figure 15.—Relation of W(u) and w to s and r2/t, and displacements of graph scales by amounts of constants shown.
and
t
u
or
logioy =
logi
471]
’ S J
+log10M [L2?1-1].	(49)
If the discharge, Q, is held constant, the bracketed parts of equations 48 and 49 are constant for a given pumping test, and W (u) is related to u in the manner that s is related to r2/t, as shown graphically in figure 15. Therefore, if values of s are plotted against r2/t (or l/t if only one observation well is used) on logarithmic tracing paper to the same scale as the type curve, the data curve will be similar to the type curve except that the two curves will be displaced both vertically and horizontally by the amounts
of the bracketed constants in equations 48 and 49. The data curve is superimposed on the type curve, and a fit, or near fit, is obtained, keeping the coordinate axes of the two curves parallel. An arbitrary match point is selected anywhere on the overlapping parts of the two sheets, the four values of which (two for each sheet) are then used in solving equations 46 and 47. It is convenient to choose a point whose coordinates on the type curve are both unity— that is, where W (u) = 1.0 and w= 1.0. In some plots it may be desirable to use a power of 10 for one coordinate. (See fig. 16.)
A convenient alternative method is to plot W (u) versus 1 /u as the type curve; then for the data curve, s may be plotted against t/r2 (or t, if only one observation well is used). This procedure is illustrated on plate 9, which also may be used for solutions of the Theis equation by superposing plots of t/r2 or t versus s on the heavy parent type curve.﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
19
Table 6.—Drawdown of water level in observation wells N-l, N-S, and N-S at distance r from well being pumped at constant rate of 96,000 ft3 day~l [Logarithmic plot of data, except values preceded by an asterisk, shown in figure 16. Data from J. G. Ferris]						
Time since pumping s (min)	<f	N-l =200 ft)	N-2 (r =400 ft)		(r	N-3 = 800 ft)
	Observed tarted, tm drawdown, s (ft)	r>/t (ft* day-1)	Observed drawdown, s (ft)	r*/t (ft* day-1)	Observed drawdown, s (ft)	r'/t (ft* aay-1)
1.0			 0.66	5.76X107	0.16	2.3 X108	0.0046	9.23 X10s
1.5			 .87	3.84X10’	.27	1.53X108	.02	6.15X10*
2.0			 .99	2.88X107	.38	1.15X10s	.04	4.6 X108
2.5			 1.11	2.30X10’	.46	9.2 X107	.07	3.7 X108
3.0			 1.21	1.92X10’	.53	7.65X107	.09	3.1 X108
4			 1.36	1.44X10’	.67	*5.75X10’	.16	2.3 X108
5			 1.49	1.15X10’	.77	4.6 X107	.22	1.85X108
6			 1.59	9.6 X106	.87	*3.82X10’	.27	1.54X108
8			 1.75	7.2 X106	.99	*2.87X10’	.37	1.15X108
10			 1.86	5.76X10®	1.12	*2.3 X10’	.46	*9.23X10’
12			 1.97	4.80X10®	1.21	1.92X10’	.53	*7.7 X10’
14			 2.08	4.1 X10®	1.26	1.75X10’	.59	6.6 X10’
18			 2.20	3.2 X106	1.43	1.28X10’	.72	5.1 X10’
24			 2.36	2.4 X106	1.58	*9.6 X106	.87	*3.84X10’
30			 2.49	1.92X10®	1.70	7.65X10®	.95	3.1 X10’
40			 2.65	1.44X10®	1.88	*5.75X10®	1.12	*2.3 X10’
50			 2.78	1.15X106	2.00	4.6 X10®	1.23	*1.85X10’
60			 2.88	9.6 X105	2.11	3.82X106	1.32	1.54X10’
80			 3.04	7.2 X10®	2.24	2.87X106	1.49	*1.15X10’
100			 3.16	5.76X105	2.38	2.3 X10®	1.62	*9.23 X106
120			 3.28	4.8 X105	2.49	*1.92x10®	1.70	*7.7 X106
150			 3.42	3.84X105	2.62	1.53X10®	1.83	6.15X10®
180			 3.51	3.2 X10®	2.72	1.28X106	1.94	5.1 X10®
210			 3.61	2.74X105	2.81	1.1 X106	2.03	4.4 X10®
240			 3.67	2.5 X10®	2.88	*9.6 X106	2.11	*3.84X10®
Example
Use of equations 46 and 47 for determining T and S by the curve-matching procedure may be demonstrated from the data given in table 6, which gives the drawdowns in water levels in a theoretical confined aquifer at distances of 200, 400, and 800 ft from a well being pumped at the constant rate of 96,000 ft3 day-1. Most of these data are plotted in figure 16 except for values preceded by an asterisk, which would plot too close to adjacent points, and except for values of r2/t of 108 or larger, which would have required 2X4 cycle paper. Superposition of figure 16 on curve B of figure 14 gave the match point shown, whose values are IT(w) = 1.0, w=10-1, s = 0.56 ft, and r2/t = 2.75 X107 ft2 day-1. Using equation 46,
tween brackets in equation 44 may be neglected. Under these conditions, equation 44 may be closely approximated by
S=4^[~a577216_l0geS CL]' (50)
This may be rewritten and simplified;
Q r	4Ttl
r-^og.a^+.og.-J
2.30Q
4irS
logu
2.25 Tt ’ r2S
[L2T-1].
(51)
_ (96,000 ft3 day-1) (1.0)
(4t) (0.56 ft)
= 13,700 ft2 day-1 = 14,000 ft2 day-1 (rounded).
Using equation 47,
(4) (13,700 ft2 day-1) (10-1) 2.75 X107 ft2 day-1
= 2 X10-4.
STRAIGHT-LINE SOLUTIONS
TRANSMISSIVITY
Cooper and Jacob (1946) showed that for values of u = r2S/4:Tt<about 0.01, all but the first two terms be-
Note that in equation 51 Q, T, and S are constants, and that either t or 1/r2 may be considered a constant. Thus equation 51 may be written

2.30Q [\	2.25T
llog" ~ir
[L2T-1].
By differential calculus, remembering that the derivative of a constant is zero, we may obtain from the above equation
2.30Q
4irds/dlogio t/r2
[L2T-1].
(52)﻿to
o
r*/t, IN SQUARE FEET PER DAY
Figure 16.—Logarithmic plot of s versus r2/t from table 6.
GROUND-WATER HYDRAULICS﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
21
Similarly, considering also r as a constant, 2.30Q
4irds/dlogio t
Considering t as a constant,
2.30Q	2.30Q
[L2T_1].
(53)
T =
47rds/dlogio 1/r2
27rds/dlogio r
[L2T-1]. (54)
As the relation of s to the log terms is linear on semi-logarithmic plots, we may change from infinitesimals (derivatives) to finite values, whence equations 52 though 54 become, respectively,
T =
T =
2.30 Q
4it As/ Alogio t/r2 2.30 Q
Aw As/ Alogio t
[L2^1],
[L2T-1],
(55)
(56)
and
equations 55 and 58, whence a minus sign preceded the right-hand sides of their equations and the slope of the straight line was reversed.
STORAGE COEFFICIENT
In plotting data for the straight-line solutions of equations 52 through 54, it is convenient to consider the top of the arithmetic scale as the line of zero drawdown, as shown on figure 11. The drawdown then increases downward, as in the well. Cooper and Jacob (1946) showed that by extending the straight line until it intersects the line of zero drawdown, and noting the value of t, t/r2, r2/t, or r at the point of intersection, the storage coefficient can be determined as follows. At zero drawdown, from equation 50,
s =
Q_
AwT
ATt
1*S
-0.577216
]-°-
!°ge^ = 0.577216 = loge 1.781,
rS
2.30Q
2irAs/Alogio r
[L2T-1].
(57)
4 Tt
MS
1.781,
Note that equation 57, obtained by simplification and differentiation of equation 51 for nonsteady flow, is identical to equation 34—the steady flow, or Thiem, equation for confined aquifers or for relatively thick unconfined aquifers. In testing relatively thin unconfined aquifers, equation 35, which contains Jacob’s drawdown correction, should be used rather than equations 34 or 57, for reasons given earlier.
Equations 55 through 57 are readily solved using semi-logarithmic paper, by plotting values of s on the linear scale against corresponding values of the log terms on the logarithmic scale and determining the value of As for one log cycle. Figure 11 illustrates the method.
For preparing a composite graph for several observation wells and several wells being pumped at constant but different rates, Qh Q2, Qs, and so on, the following equation may be used:
________2J30_________
Aw A (s/Q) / Alogio t/r2
[L2?1-1].	(58)
In using equation 58 for, say, three pumping wells within an area of overlapping cones of depression, values of si/Qi, t\/ri1; S2/Q2, h/r22; and s3/Q3, t3/r32 are plotted on the same semilogarithmic graph, and, if u is less than or equal to 0.01 for all values, all points should fall on or near a straight line and may be used in determining a single set of values of T and S for the entire well field.
Cooper and Jacob (1946) used r2/t rather than t/r2 in
and
5=2257 (?).
(at point of zero drawdown). (59)
Equation 59 gives the desired result satisfactorily if the straight line has sufficient slope so that its zero arithmetic coordinate can be found within the confines of the plot, as in figure 11. However, if the slope is nearly flat, so that the zero arithmetic coordinate occurs outside the confines of the plot, error may result from graphical extrapolation onto an adjoining sheet of graph paper. In order to avoid such errors, I described the following method (Lohman, 1963) for determining S within the data region of straight-line plots without the need for mechanical extrapolation. Equation 51 may be rewritten
2.25Tt/r2
logio_1[4irTs/2.30Q]
(60)
Combining equations 55 and 60 for the value of As for one logio cycle of t/r2 (unity), we obtain
2.25 Tt/r2 logio-1 [s/As] ‘
(61)
Note that in equation 61 the values of T, s, and As are the same as those used in equations 55 and 56 for determining T. For equations 57 and 58, the comparable equations for﻿22
GROUND-WATER HYDRAULICS
S are, respectively,
s_ 2.25Tt/r2 logio_1[-2s/A.s]
for plots of s versus r and
_________2.25 Tt/r2
logio_1[(s/Q)/A(s/Q)]
fortunately true that they have been improperly applied by many workers. It was stated in their derivation that (62) they can be used only when u is less than or equal to about 0.01, but the importance of this seemingly has been forgotten all too often. Let us consider the several parameters involved in this criterion by reexamining equation 45:
(63)
u =
AS
47V
for plots of s/Q versus </A
Example
Note in figure 11 that the extrapolated straight line reaches the line of zero drawdown at r= 1,560 ft. Using equation 59 and the results of the Thiem test accompanying figure 11,
(2,25) (20,700 ft2 day-1) (18 days)	d)
(1,560 ft)2
Similarly, using equation 62,
(2.25) (20,700 ft2 day-1) (18 days)/(100 ft)2 log10-1[-2(-4.05/3.40)]
83.9
log10-1[2.38235]
83.9
241.19
= 0.35 (rounded).
Note that in the final bracketed denominator .38235 is the mantissa, which determines the digits 24119, and that the 2. is the characteristic, which determines the three digits to the left of the decimal point, giving the final antilog as 241.19.
Jacob (1963a, p. 247) showed that in thin unconfined aquifers, such as the one tested near Wichita, Kans., a drawdown correction must be applied in solving for both T and S. The correction to be applied to S (after the drawdowns have been corrected) is
<64)
where
S' is the corrected value; b, for the Wichita test, was 26.8 ft; and s, for the Wichita test at the geometric mean distance of 100 ft, was 4.5 ft.
Hence,
S' =
0.35 = 0.29 = 0.3 (rounded).
PRECAUTIONS
Although the straight-line solutions described above give very satisfactory results when properly used, it is un-
and letting u be less than or equal to about 0.01.
First note that because S appears in the numerator (other things being equal including time, t), the value of u is considerably greater for an unconfined aquifer of specific yield from 0.1 to 0.3 than for a confined aquifer whose storage coefficient may range from only say 10~5 to 10-3. To compensate for this, t must be greater by several orders of magnitude in testing an unconfined aquifer than in testing a confined aquifer. Equally important is the fact that pumping time in an unconfined aquifer must be long enough to allow reasonably complete drainage of material within that part of the cone of depression being observed. On the contrary, release of water from a reasonably elastic confined aquifer not unwatered during testing is virtually instantaneous.
Note that r appears as r2 in the numerator. Thus, other things being equal, the greater the distance r, the longer t must be to allow u to reduce to the required maximum value.
In the denominator, 4 and T are constants, but again, other things being equal, the smaller the value of T, the more time is required for u to reduce to 0.01 or less.
For a given array of wells in a particular aquifer, assuming that sufficient pumping time is allowed to adequately drain the cone of depression in an unconfined aquifer, all parameters except t are constants; therefore pumping time generally is the only control for reducing u to or below its maximum permissible value, and this is the parameter generally neglected by many.
In a drawdown-time test (s versus logio t or logio t/r2), data points for any particular distance r will begin to fall on a straight line only after the time, t, is sufficiently long to satisfy the above criteria. In a drawdown-distance test (s versus logior, Thiem test), the well must be pumped long enough that the data for the most distant observation will satisfy the requirements; then only the drawdowns at or after this value of t may be analyzed on a semilogarithmic plot for one particular value of t.
Equation 56 may be used for a time-drawdown or time-recovery test on a pumped well in a confined aquifer or in an unconfined aquifer that drains rapidly and reasonably completely during the test. When properly used, equation 56 gives the same results as the more complicated recovery equation of Theis (1935). In an unconfined aquifer that drains very slowly or incompletely or both, however, the﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
23
results obtained by use of equation 56 may be badly in error. In the absence of any observation wells, it is realized that drawdown or recovery of a pumped well may be the only means available for obtaining at least an estimate of T. Similarly, considerable judgment should be exercised in using equations 55 and 58 for tests in unconfined aquifers.
Let us now apply the above criteria to the Thiem test near Wichita, Kans. (table 4, fig. 11), for the most distant observation well at r = 190 ft:
(190 ft)2 (0.29)
(4) (20,700 ft2 day-1) (18 day)
= 0.007.
Thus, even at the most distant observation well, u was less than 0.01, and the data at 18 days are valid in this respect.
If S and T can be estimated in advance, as from the results of other tests in the same aquifer, then, for arrays having the farthest observation well(s) at distance r, the minimum permissible pumping time, t, may be estimated from
_ rhS 4Tu
[T],
(65)
Assume that £ = 0.2, T=20,000 ft2 day-1, r = 200 ft (farthest observation well), and w = 0.01. Then
t =
(200 ft)2 (0.2)
(4) (20,000 ft2 day-1) (0.01)
= 10 days.
Thus, under the assumed conditions, all observations made 10 days or more after the beginning of pumping may be used in straight-line plots.
CONSTANT DRAWDOWN
Jacob and Lohman (1952) derived equations for determining T and S from tests in which the drawdown is constant and the discharge varies with time. These conditions are met when a naturally flowing well in a confined aquifer is shut in long enough for the head to recover, then the well is opened and allowed to flow for a period of 2 to 4 hours, during which period timed measurements are made of the declining rate of flow. The equation, based upon the assumptions that the aquifer is homogeneous, isotropic, and extensive laterally and that T and S are constant at all times and places, was developed from analogous thermal conditions in an equivalent thermal system. The equation, which is another solution of equation 40, is
T =
Q
2irG(a)sm
C VT-'l
(66)
where
and
sw = constant drawdown in discharging well, rw = radius of discharging well, and G(a) =the G function of a, given by
where Jo(x) and Y0(x) are Bessel functions of zero order of the first and second kinds, respectively.
Equation 68 is not tractable by integration, but the integral was replaced by a summation and solved by numerical methods. The resulting values of G(a) for corresponding values of a are given in table 7.
Plate 1 is a logarithmic plot of the type curve from data given in table 7. On translucent logarithmic paper, to the same scale, values of Q/sw are plotted against values of t/rw2, or values of Q may be plotted against values of t. Then, by placing the experimental curve over the type curve, the solutions are obtained in the same manner as described for the Theis equation (eqs. 46-49). T is obtained from equation 66, and S is determined by rewriting equation 67,
S=
Tt
arw
(69)
This curve-matching method, though laborious, was very useful before the straight-line solutions described below were derived. It is recommended that the much simpler straight-line solutions be used, for in such a test on a single well in a confined aquifer, u reaches a value of <0.01 very quickly because of the small values of r and S. (See p. 27.)
STRAIGHT-LINE SOLUTIONS
Jacob and Lohman (1952) showed that for all but extremely small values of t, the function G(a) can be approximated very closely by 2/W(u). It was shown in equation 51 that for sufficiently small values of u, W(u) can be closely approximated by 2.30 logi0 2.25Tt/r2S. Making these substitutions in equation 66, and adding the subscript w to r2, we obtain
T =
2.30 Q
4 irsw
logio
2.2577
rw2S
IL'T-'l
(70)
which is identical to equation 51 except for the subscripts. Differentiating equation 70 and changing from infinitesimals to finite values, as was done for equations 52 through 57, gives
a =
Tt
SrJ
[dimensionless]
(67)
_________2130_________
4irA (sw/Q) / Alogio t/rj
[L2T~l~]
(71)﻿24
GROUND-WATER HYDRAULICS
Table 7.—Values of G(a) for values of a between 10~' and 1016
[Modified from Jacob and Lohman (1952, p. 561)]
10-* 10“' 10-2 10-' 1 10 10' 10' 10*
1........_...........__ 56.9
2	____________________ 40.4
3	_____________________33.1
4	_____________________28.7
5	_____________________25.7
6	____________________ 23.5
7	_____________________21.8
8	____________________ 20.4
9	____________________ 19.3
10	___________________ 18.3
18.34	6.13	2.249
13.11	4.47	1.716
10.79	3.74	1.477
9.41	3.30	1.333
8.47	3.00	1.234
7.77	2.78	1.160
7.23	2.60	1.103
6.79	2.46	1.057
6.43	2.35	1.018
6.13	2.25	.985
0.985	0.534	0.346
.803	.461	.311
.719	.427	.294
.667	.405	.283
.630	.389	.274
.602	.377	.268
.580	.367	.263
.562	.359	.258
.547	352	.254
.534	.346	.251
0.251	0.1964	0.1608
.232	.1841	. 1524
.222	.1777	.1479
.215	.1733	.1449
.210	.1701	.1426
.206	. 1675	.1408
.203	.1654	.1393
.200	.1636	.1380
.198	.1621	.1369
.196	.1608	.1360
10* 10' 10» 10» 10" 10" 10" 10" 10" 10"
1........................ 0.1360	0.1177
2	_______________________ .1299	.1131
3	_______________________  .1266	.1106
4	________________—	.1244	.1089
5	_____________________  .1227	.1076
6	.......................  .1213	.1066
7	____________________ . 1202	.1057
8	_______________________ .1192	.1049
9	______________________   .1184	.1043
10	_______________________ .1177	.1037
0.1037	0.0927	0.0838	0.0764
.1002	.0899	.0814	.0744
.0982	.0883	.0801	.0733
.0968	.0872	.0792	.0726
.0958	.0864	.0785	.0720
.0950	. 0857	.0779	.0716
.0943	.0851	.0774	.0712
.0937	.0846 -	.0770	.0709
.0932	.0842	.0767	.0706
.0927	.0838	.0764	.0704
0.0704	0.0651	0.0605	0.057
or
T =
________2,30
4tsto (Al/Q)/ Alog101
[L2r-‘].
(72)
By extrapolating the straight line to sw/Q = 0, S may be determined from
S = 2.25t(—)	(73)
v« /0
or, in the same manner as shown for equations 61 through
63, S may be determined within the data region of the straight-line plot from
2.25Tt/rJ
(74)
Note that S may be determined when T is determined from equation 71, where rw (radius of flowing well) is known, but S may not be determined when rw is not known
		Table 8.—Field data for flow test [Valve opened at 10:29 a.m. sw		on Artesia Heights well near Grand Junction, Colo., September 22, 19 =92.33 ft; rw =0.276 ft. Data from Lohman (1965, tables 6 and 7, well 28))			
	Time of observation		Rate of flow Flow interval (gpm) (min)		Total flow during interval (gal)	Time since flow started (min)	8w Q (ft gal-1 min)
10:30.				i	7.28	i	12.7
10:31.				i	6.94	2	13.3
10:32.				i	6.88	3	13.4
10:33.				i	6.28	4	14.7
10:34.				i	6.22	5	14.8
10:35.				i	6.22	6	15.1
10:37.				2	11.90	8	15.5
10:40				3	17.55	11	15.8
10:45.				5	28.30	16	16.3
10:50.				5	27.50	21	16.8
10:55.				5	26.70	26	17.3
11:00				5	26.70	31	17.3
n:i0i_				10.5	54.81	41.5	17.7
Ji:zo.				9.5	48.83	51	18.0
11:30.				10	51.10	61	18.1
11*45_	(noon)			15	75.75	76	18.3
12:00 12:12.				 5.00	15 12	75.00 59.04	91 103	18.5 18.8
12:22				11	53.68	113	18.9
	Total'				 114	596.98		
r®'
(min ft"’)
13.1
26.3
39.4
52.6
65.7
78.8 105 145 210 276 342 407 345 670 802 999
1,196 1,354 1,485﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE	25
Figure 17.—Semilogarithmic plot of sw/Q versus </r„2.
as in equation 72. If the value of rw is in doubt, owing to well construction, well development, or caving, do not try to determine S by these methods.
Example
Table 8 gives the field data from a flow test on the Artesia Heights well near Grand Junction, Colo. (Lohman, 1965, tables 6 and 7, well 28), which I made with the help of Mahmood Hussain on September 22, 1948. After the well was shut in for a period of several days, the static head just prior to the test was 94.55 ft above the measuring point (92.33 ft above discharge point). Static and recovering heads were measured by an inkwell mercury gage which I designed and built and which reads directly in feet and tenths of feet of water. Hundredths of feet are readily interpolated. Discharge was measured by timing with a stopwatch the filling of a 4-gal container. Data in the last two columns of table 8 are plotted in figure 17. From the values of sw/Q, A(sw/Q), and t/rj obtained from this
plot, we obtain, using equation 71,
(2.30) (1.44X103 min day-1)
(47r) [(18.4—15.38) ft gal-1 min](7.48 gal ft-3)
= 11.7 ft2 day-1,
which rounds to 12 ft* day-1. Note that it is not convenient to determine S using equation 73, because considerable extrapolation off the sheet would be required to reach the line where sw/Q = 0. However, S is readily determined from equation 74:
(2.25) (11.7 ft2 day-1) (103 min ft-2) logio-1[18.4/3.02](l,440 min day"1)
= (2.25) (1.17X101) (103)
(1.23X106) (1.44X103)
Note that in table 8 and in figure 17 Q and t are in﻿26
GROUND-WATER HYDRAULICS
1 10 102 103
t, IN MINUTES
Figure 18.—Semilogarithmic plot of recovery (s„) versus t.
gallons per minute and in minutes, respectively, whereas they are in cubic feet per day and in days in equations 71 and 74; hence, conversion factors were used in the solutions. The bracketed part of the denominator in equation 74 is a dimensionless ratio, so the units do not have to be converted. The slight deviations from the straight line of all data points except that for 10:32 a.m. are believed to have resulted from fluctuations in barometric pressure during the test. These were largely self-compensating and seem not to have materially affected the slope of the straight line; however, it is possible to correct the head and discharge with data from a barograph. The value at 10:32 a.m. may have resulted, at least in part, from an error in measuring or recording the discharge.
Columns 3 and 4 in table 8 are included to obtain a weighted average discharge during the 113-min flow period for use in applying the recovery method. The 2-in. gate valve on the well was closed at 12:23 p.m., and the slowly recovering head was measured as shown in table 9 and figure 18. The recovery method (eq. 56) is strictly
Table 9.—Field data for recovery test on Artesia Heights well near Grand Junction, Colo., September 22, 1948
[Valve closed at 12:23 p.m. Weighted average discharge, 5.23 gpm. Data from Lohman (1965, tables 6 and 7, well 28)]
Time since flow Head (ft above Time of observation	stopped, t (min) land surface)
12:25				2	66.80
12:26		3	69.10
12:27		4	71.30
12:28		5	72.95
12:29		6	74.26
12:30		7	75.37
12:31			 8	76.33
12:32			 9	77.16
12:33			 10	77.89
12:34		11	78.57
12:35		12	79.19
12:37		14	80.26
12:39		16	81.17
12:40		17	81.55
12:42		19	82.29
12:45		21	83.27
12:50		26	84.64
12:55			 31	85.76
1:01				37	86.82
1:05		41	87.41﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
27
applicable only to tests of constant discharge and variable drawdown or recovery, whereas the flow test involves constant drawdown and gradually declining discharge. Nevertheless, recovery tests generally give values of T in close agreement with the flow tests and may be useful as corroborative checks. The results by the two methods generally do not agree precisely. For one thing, the weighted average discharge obtained by the method given in table 8, although close enough for the purpose, is not as accurate as would be obtained by use of an accurate water meter, which would integrate the entire discharge during the flow period.
Using the data from table 9 and figure 16 in equation 56,
(2.30) (5.23 gal min-1) (1,440 min day-1)
= (4tt) [(85.75-69.25) ft] (7.48 gal ft-3)
assumptions, Cooper, Bredehoeft, and Papadopulos (1967, p. 264, 265) derived the following equation, which is another solution of equation 40, for the response of a finite-diameter well to such an instantaneous “slug” of water:
H = 8H0-- f exp (^) ~	[L],	(75)
it J0 \ a / uAu
where
H = head inside the well at time t after injection or removal of the “slug,” above or below initial head [L],
7/0 = head inside the well above or below initial head at instant of injection or removal of “slug” [L],
and
= 11.2 ft2 day-1,
which rounds to 11 ft2 day-1. This value is very close to the value of 12 ft2 day-1 obtained from the flow test. (Values before rounding were even closer: 11.7and 11.2 ft2 day-1.)
Let us test the data using equation 65 to determine if even the earliest observations meet the requirement that u is less than or equal to about 0.01:
_ (0.076 ft2) (1.5X10-5) (1,440 min day-1)
(4) (12 ft2 day-1) (0.01)
= 3.4X10-3 min.
Thus, largely because of the low values of r2 and S, all observations made 0.003 min or more after discharge or recovery began satisfy this requirement. The earliest observation was 1 min after discharge began (table 8).
INSTANTANEOUS DISCHARGE OR RECHARGE
“SLUG” METHOD
In areas lacking either flowing wells or wells equipped with pumps, it may be desirable to obtain at least an estimate of the transmissivity of the aquifer by use of the so-called “slug” method. In this method a known volume or “slug” of water is suddenly injected into or removed from a well and the decline or recovery of water level is measured at repeated closely spaced intervals during the ensuing minute or two. The method is strictly applicable only to fully penetrating or fully screened wells in confined aquifers of rather low transmissivity—say less than about 7,000 ft2 day-1. For partially penetrating wells, the value of transmissivity obtained generally would apply only to that part of the aquifer in which the well is screened or open. Application of the method to wells in unconfined aquifers would require considerable judgment, and the results should be regarded with skepticism.
Under the above conditions, and with the usual
[dimensionless],
(76)
where
r„ = radius of well screen or open hole [L], and rc = radius of casing in interval over which water level fluctuates [L],
In equation 75
Tt
|8= — [dimensionless]	(77)
r?
Au = [vJ0(u) — 2aJi(u)'¥+[uYo(u) —2oFi(y)2], where
Jo = Bessel function of first kind, zero order,
Ji = Bessel function of first kind, first order,
F0 = Bessel function of second kind, zero order, Fi = Bessel function of second kind, first order,
and
u = variable of integration.
Values of H/H0 versus Tt/r? for five different values of a obtained by numerical solution of equation 75 given by Cooper, Bredehoeft, and Papadopulos (1967, table 1) are plotted as a family of semilogarithmic curves on plate 2, which is similar to their figure 3. V, the measured volume of water injected or removed from the well, obviously is equal to Hoirr,2, so the value of H0 (at the instant of injection or removal) is obtained from
Ho= —2	[L],	(78)
7rrc2
From measured values of H at repeated intervals, values﻿28
GROUND-WATER HYDRAULICS
tt!
	p?—»———•—i	t 	1——i	r—i—i—r-		
O		
	O	
	o 	O		
	( o o	
		c o o I °
	o <u </> r—* ll	9 0 T\ cl * o o o
t, IN SECONDS
Figure 19.—Semilogarithmic plot of data from “slug” test on well at Dawsonville, Ga. From Cooper, Bredehoeft, and Papadopulos (1967, table 3).
of H/H0 are computed and are plotted on the linear scale of semilogarithmic paper of the same scale as plate 2 against the time of measurement, t, in seconds, on the logarithmic scale. Note that H/H0 is a dimensionless ratio, hence any convenient units of measurement may be used without
affecting the final results in any way. The data curve is then superposed on plate 2 by the usual curve matching procedure, and a match line is selected for the value of t at Tt/rc2= 1.0 (match point values of H/H0 are not needed). The transmissivity is then determined from the following﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
29
form of equation 77:
1 Or 2
T=	[L2T-1].	(79)
By rewriting equation 76, the storage coefficient may be determined from
y 2
S=-^~a [dimensionless],	(80)
nr 2
1 s
but, as pointed out by Cooper, Bredehoeft, and Papa-dopulos (1967, p. 267): “However, because the matching of the data plot to the type curves depends upon the shapes of the type curves, which differ only slightly when a differs by an order of magnitude, a determination of S by this method has questionable reliability.” They go on to say:
The determination of T is not so sensitive to the choice of the curves to be matched. Whereas the determined value of S will change by an order of magnitude when the data plot is moved from one type curve to another, that of T will change much less. From a knowledge of the geologic conditions and other considerations one can ordinarily estimate S within an order of magnitude [see “Methods of Estimating Storage Coefficient” and “Methods of Estimating Specific Yield”] and thereby eliminate some of the doubt as to what value of a is to be used for matching the data plot.
In 1954 J. G. Ferris and D. B. Knowles (see Ferris and others, 1962, p. 104, 105) described a “slug” test based upon an instantaneous line source rather than a well of finite diameter. Their equation is identical to equation 81, except for algebraic sign. As shown by Cooper, Bredehoeft, and Papadopulos (1967, p. 265), however, the method of Ferris and Knowles is strictly applicable only for relatively large values of Tt/rc2, and hence of t, and should not be used for the values of t generally measured during a “slug” test.
Example
Cooper, Bredehoeft, and Papadopulos (1967, p. 265-268) illustrated the “slug” method using data obtained from a “slug” test on a well near Dawsonville, Ga., and described the well and procedure as follows. The well is cased to 24 m with 15.2-cm (6-in.) casing and drilled as a 15.2-cm open hole to a depth of 122 m. A nearly instantaneous decline in water level was obtained by the sudden withdrawal of a long weighted float whose total weight was 10.16 kg. From Archimedes’ principle, they determined that the float had displaced a volume of 0.01016 m3 of water when floating in the well; hence, F = 0.01016 m3. From equation 78, H0 was found to be 0.560 m. Their recovery data, obtained from an electrically operated recorder actuated by a pressure transducer in the well, are given in table 10 and are shown in figure 19.
By superposition of figure 19 on plate 2, the data are found to fit the type curve for a —10-3. The value of t for the match line where Tt/r?—1.0 is 11 sec. Therefore, from
Table 10.—Recovery of water level in well near Dawsonville, Ga., after instantaneous withdrawal of weighted float [#o =0.560 m. From Cooper, Bredehoeft, and Papadopulos (1967, table 3)]
Head above
t	datum	H
(sec)	(m)	(m)	H/Ho
-1			 0.896	,	
0			 .336	0.560	1.000
3			 .439	.457	.816
6			 .504	.392	.700
9			 .551	.345	.616
12			 .588	.308	. 550
15			 .616	.280	.500
18			 .644	.252	.450
21			 .672	.224	.400
24			 .691	.205	.366
27			 .709	.187	.334
30			 .728	.168	.300
33			 .747	.149	.266
36			 .756	.140	.250
39			 .765	.131	.234
42			 .784	.112	.200
45			 .788	.108	.193
48			 .803	.093	.166
51			 .807	.089	.159
54			 .814	.082	.146
57			 .821	.075	.134
60			 .825	.071	.127
63			 .831	.065	.116
equation 79,
T =
(1.0) (7.6 cm)2 11 sec
= 5.3 cm2 sec-1
or
(1.0) (7.6 cm)2(8.64Xl04 sec day-1)
(11 sec) (0.929 X103 cm2 ft-5)
= 490 ft2 day-1.
BAILER METHOD
Skibitzke (1958) proposed a method for determining the transmissivity from the recovery of water level in a well that has been bailed. At any given point on the recovery curve the following equation applies:
T= 47rs,<[e^Js/4Ti]	(81)
where
s' — residual drawdown [L],
V = volume of water removed in one bailing cycle [I/3], t = length of time since bailing stopped [71], and rw — effective radius of the well [L],
As rw is small, the term in brackets in equation 81 approaches e°, or unity, as t increases; therefore, for large values of t, equation 81 may be rewritten:
r- <82>
If the residual drawdown is observed at some time after the﻿30
GROUND-WATER HYDRAULICS
completion of n bailing cycles, the following equation applies:
_irzi+z?+^+...+i=l
4tts' L<1 k u	f„ J
[L2T-1].	(83)
If approximately the same volume of water is bailed during each cycle, equation 83 becomes
t= r-Jr + r + r+'-'+fl	(84)
47rs Lh k k	tn J
Equation 84 is applied to single values of V and s' and the summation of the reciprocal of the elapsed time between the time each bailer was removed from the well and the time of observation of s'. If T is to be expressed in square feet per day, then obviously V should be expressed in cubic feet, s' in feet, and t in days, or suitable conversions of units should be made.
The bailer method should give satisfactory estimates of T for wells in confined aquifers having sufficiently shallow water levels to permit short time intervals between bailing cycles. In wells in unconfined aquifers, or in wells having relatively deep water levels, the method should be used with considerable judgment or not at all. (See also “Precautions.”)
Unfortunately, I have no data available with which to illustrate the bailer method.
LEAKY CONFINED AQUIFERS WITH VERTICAL MOVEMENT
The flow equations for confined aquifers under conditions of both constant discharge and constant drawdown discussed in earlier sections of this report all are based upon the assumptions that the confining beds are impermeable (or have very low permeability), that they release no water from storage, and that vertical flow components are negligible. It is well known that no rocks are wholly impermeable and that some confining beds have finite permeability. We will now take up the equations for both steady and nonsteady radial flow from infinite aquifers whose confining beds leak water either from or to the aquifer.
The change may be either a decrease in the rate of leakage out of the aquifer or an increase in the rate of leakage into the aquifer, but either way the change results in a net increase in the supply of water to the aquifer and, therefore, constitutes capture of water.
Jacob (1946) derived an equation of steady flow near a well discharging at a constant rate from such an infinite leaky confined aquifer and described a graphical method for determining the transmissivity of the aquifer and the “leakance” of the confining bed. The leakance is the ratio K'/b', in which K' and b' are the vertical hydraulic conductivity and the thickness, respectively, of the confining beds. Hantush and Jacob (1954) derived equations for steady flow in variously bounded leaky confined aquifers. Later, equations for the more generally encountered non-steady flow in such aquifers were developed, and these will now be taken up.
NONSTEADY FLOW
HANTUSH-JACOB METHOD
Hantush and Jacob (1955) derived the following equation for nonsteady radial flow in an infinite leaky confined aquifer:
^-=2Ko(2v)- r - exp	— \ dy
Q/4ttT	J,2luy \ y }
[dimensionless form], (85)
where
K0 = the modified Bessel function of the second kind
and
of zero order,
T IKf
v=2\bT [dimensionless],
(86)
where
K' = the vertical hydraulic conductivity of the confining bed [LT-1],
b' = the thickness of the confining bed [L], and T = the transmissivity of the aquifer [L2T_1],
CONSTANT DISCHARGE
STEADY FLOW
Consider an aquifer overlain by a confining bed of low but finite permeability, which in turn is overlain by an unconfined aquifer. When discharge occurs from a well in a confined aquifer, the potentiometric surface is lowered throughout a large circular area (Cooper, 1963, p. 48). This lowering changes the relative head between the confined and unconfined aquifers and results in turn in a change in the rate of leakage through the confining bed.
u = r2S/4iTt [dimensionless], and y = the variable of integration.
The authors gave two series expressions for the formal solutions of equation 85—one for large values of t and one for small values—and gave a few examples in both tabular and graphic form. In January 1956, Hilton H. Cooper, Jr., computed many values and prepared two families of type curves which were later published (Cooper, 1963, pi. 4). Meanwhile, unknown to Cooper, Hantush (1955) also had computed many values. (See also Hantush, 1956.)﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
31
Table 11.—Postulated, water-level drawdotvns in three observation wells during a hypothetical test of an infinite leaky confined aquifer
[Pumped well began discharging 1,000 gal min-1 at 1=0 min.] From Cooper (1963, p. 54)
Well 1	Well 2	Well 3
(r =100 ft)	(r =500 ft)	(r = 1,000 ft)
Time since pumping began, t
t_
r*
Min	Day	(day ft-1)	(ft)	(day ft-1)	(ft)	(day ft-*)	(ft)
0.2		... 0.000139	1.39X10-*	1.76	5.56X10-10	0.01	1.39 X lO-10	0.00
.5			.000347	3.47X10-8	2.75	1.39X10-8	.14	3.47 X 10_1°	.00
1		.000694	6.94X10-8	3.59	2.78X10-8	.45	6.94X10-10	.02
2		.00139	1.39X10-7	4.26	5.56X10-9	.93	1.39X10-"	.14
5		.00347	3.47X10-7	5.28	1.39X10-8	1.76	3.47X10-"	.55
10		.00694	6.94X10-7	5.90	2.78X10-8	2.34	6.94X10-"	.99
20		.0139	1.39X10-6	6.47	5.56X10-8	2.85	1.39X10"8	1.46
50		.0347	3.47X10“"	6.92	1.39 X10-7	3.31	3.47X10-*	1.95
100		.0694	6.94X10-8	7.11	2.78X10-’	3.50	6.94X10"8	2.10
200		.139	1.39X10-5	7.20	5.56X10-’	3.51	1.39X10"’	2.11
500		.347	3.47X10-8	7.21	1.39X10-"	3.52	3.47X10-’	2.11
1,000		.694	6.94X10-8	7.21	2.78X10-"	3.52	6.94X10"7	2.11
As described by Cooper (1963), if the right-hand side of equation 85 is represented by L(u, v), the L, or Ieakance, function of u and v, equation 85 may be written
S=£tL{U’v) CL]’	(87)
S is determined by
t / T^
<S = 4T ——	[dimensionless]	(88)
1/M
When K' and, hence, v approach zero, it can be shown that L(u,v) approaches W{u), and equation 87 becomes equation 46, the Theis equation. An enlargement of two families of type curves of L(u, v) versus 1/w prepared by Cooper (1963, pi. 4) is shown on plate 3A. In one family of curves, v is the parameter; in the other, v2/u is the parameter. The solid-line type curves (v) correspond to a plot of s (vertical) versus t at some constant r, plotted as t/r2 (horizontal). The dashed-line curves (v2/u) correspond to a plot of s versus t/r2 at some constant t.
Example
Table 11 from Cooper (1963, p. 54) gives postulated drawdowns in observation wells at distances of 100, 500, and 1,000 ft from a well discharging at the constant rate of 1,000 gpm for 1,000 min from a leaky confined aquifer. Values of s versus t/r2 for the three wells are shown on plate 3B superposed on the type curves. Note that a match point was chosen where a(u, v) = 1.0, l/u= 1.0, s= 1.15 ft, and t/r2 = 1.87 X10-9 day ft-2. Substituting appropriate values in equations 87 (solved for T) and 88 gives,
respectively,
(1,000 gal min-1) (1,440 min day-1) (1.0) =	(4:r)(1.15 ft) (7.48 gal ft-3)
= 13,300 ft2 day-1 (rounded)
and
S= (4) (13,300 ft2 day-1)
(1.87 X 10~9 day ft-2)
1.0
=10-4(rounded).
The plotted values for observation well 1 fall slightly below the solid-line curve for v = 0.02, or at about 0.025. Substituting r=100ft, v- 0.025, and T = 13,300 ft2 day-1 in the first part of equation 89 gives
K'	10 02512
-- = (4) (13,300 ft2 day-1) )'*. =0.0033 day-1.
b'	(100 ft)2
Assume b' —100 ft, then K' = 0.33 ft day-1.
As the data in table 11 represent idealized conditions, the same values for K'/b' wrould be obtained using the data for observation wells 2 and 3. Also, the same values of K'/b' would be obtained using the dashed-line curves by plotting the values of s for each observation well for some constant t, say 100 min (0.0694 day), and substituting the value of v2/u, s, and t in the second part of equation 89.
Cooper (1963, p. 55) gives the following pertinent conclusions in regard to this method:
Because the adjustment of the hydraulic gradient through a confining bed generally lags considerably behind the decline in head, the water yielded by an artesian aquifer is derived largely, if not entirely, from storage in the confining bed. For this reason, most time-drawdown plots deviate from the Theis curve to a greater degree than if leakage alone were involved. The method for determining Ieakance is presented with reservation because, if applied under the mistaken assumption that the deviations are due to leakage, it yields erroneously large values. However, whenever the results of an aquifer test indicate that leakage occurs, the deter-﻿32
GROUND-WATER HYDRAULICS
mination of T and S by use of the family of type curves described in this paper has advantages over that by use of the Theis type curve alone.
HANTUSH MODIFIED METHOD
Hantush (1960) presented an important modification of the theory of leaky confined aquifers in which the storage of water in the semipervious confining bed or beds is taken into account. His main equations are:
T=^-H{u,p)	[L’T-1],	(90)
47rs
where
H(u, p) — f
— erfc
y
P/Vu, \ Vy(y-u)J y
[dimensionless],
u —
rW
4Tt
[dimensionless],
(91)
as in the Theis equation, and
s. +	wime™iMle8si <92>
where
Calif., in 1961 from tabulated values by Hantush (1961). Time-drawdown or time-recovery data from tests in aquifers whose confining bed or beds are suspected of releasing water from storage are plotted (as s versus t) on 3 X 5-cycle logarithmic paper having the same scale as plate 4 (such as K & E 359-125G or 46-7522), and this is superposed on plate 4 until a fit is obtained on one of the type curves by the usual curve-matching procedure. From values of the four parameters at a convenient match point, T and S may be determined from equations 90 and 47, respectively.
Thorough knowledge of the geology, including the character of the confining beds, should indicate in advance which of the two leaky-aquifer type curves to use, or whether to use the Theis type curve for nonleaky aquifers.
Example
Table 12 gives the time-drawdown measurements in an observation well at Pixley, Calif., 1,400 ft from a well pumping 750 gpm, supplied by Francis S. Riley (U.S. Geological Survey, Sacramento, Calif., written commun., March 5, 1968). The pumped well, which is 600 ft deep, obtains water from gravel, sand, sandy clay, and clay of the Tulare Formation in an area where considerable land subsidence has resulted from prolonged pumping from confined aquifers containing appreciable amounts of clay.
K = hydraulic conductivity of main aquifer,
K\ K" = hydraulic conductivities of semipervious confining layers,
S = bS,	Storage coefficients of the main aquifer
S' = b’S/	and of the semipervious confining
aS" = 6"&/'J layers, respectively, and S„ S,', (S'," = specific storage (storage coefficient per vertical unit of thickness) of the main aquifer and confining layers (6, b', and b"), respectively.
The versatility of equations 90 through 92 lies in the fact that they are the general solutions for the drawdown distribution in all confined aquifers, whether they are leaky or nonleaky. Thus, if K' and K" approach zero or are made equal to zero, P approaches or equals zero, and equation 90 becomes equation 46, the Theis equation for nonleaky confined aquifers. Hantush (1960, p. 3716-3718) gives general solutions for three different configurations of aquifers and sets of confining beds. If K", S', and S" approach zero or are made equal to zero, two of these solutions become equal to equation 85 of Hantush and Jacob (1955)—the equation for leaky confined aquifers for which release of stored water from the confining beds is considered negligible.
Plate 4 is a logarithmic plot of \/u versus H (u, p) for various indicated values of p, copied from a plot made by E. J. McClelland, U.S. Geological Survey, Sacramento,
Table 12.—Drawdown of water level in observation well 23S/25E-17Q2, 1,400 ft from a well pumping at constant rate of 750 gpm, at Pixley, Calif., March 13, 1963
[Drawdown corrected for pretest trend. Data from Francis S. Riley (written commun., March 5, 1968)]
Time since pumping began,/ (min)	Drawdown, « (ft)		Time since pumping began,t (min)	Drawdown, 8 (ft)
6.37		0.01		90		0.75
8.58		.02		100		.82
10.23		.03		137		1.04
11.90		.04		150		1.12
12.95		.05		160		1.17
14.42		.06		173		1.24
15.10		.07		184		1.27
16.88		.08		200 		1.35
17.92		.10		210		1.40
21.35		.12		278		1.68
21.70		.13		300		1.76
22.70		.14		315		1.83
23.58		.15		335		1.87
24.65		.17		365		1.99
29		.21		390		2.10
30		.22		410		2.13
32		.24		430 		2.20
34		.26		450		2.23
36		.28		470		2.29
38		.30		490		2.32
41		.33		510		2.39
44		.36		560 		2.48
47		.38		740		2.92
50		.42		810		3.05
54		.46		890		3.19
60		.52	1	,255		3.66
65		.56	1	,400		3.81
70		.60	1	,440		3.86
80		.65	1	,485		3.90﻿!, IN FEET
1 10	1 02	103 1 0*
t, IN MINUTES
Figure 20.—Logarithmic plot of s versus t for observation well 23S/25E-17Q2 at Pixley, Calif.
co
CO
AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE﻿34
GROUND-WATER HYDRAULICS
(See table 3, “Tulare-Wasco area.”) The aquifer is confined by the Corcoran Clay Member, about 6 ft thick, above which is an unconfined aquifer about 200 ft thick. A logarithmic plot of s versus t from table 12 is shown in figure 20, which shows also the match-point values of the four parameters obtained by superposition on plate 4. From these data, T and S are computed from equations 90 and 47, as follows:
7= H(u, 0)
47TS
(750 gal min-1) (1,440 min day-1) (1.0)
=	(4x) (5.3 ft) (7.48 gal ft-3)
= 2,170 ft2 day-1, rounded to 2,200 ft2 day-1, and
\Ttu (4) (2,170 ft2 day-1) (12.6 min) r2 (1,400 ft)2(l,440 min day-1) (1/1.0)
= 3.9X10-5, rounded to 4X10-5.
Preliminary attempts to fit both early and late data from table 12, and similar drawdown and recovery data from two other observation wells at r = 650 and 1,220 ft, to the Theis curve gave apparent values of T from 5 to 20 times the more realistic value computed above, and apparent values of S from 17 to 25 times the value computed above.
where
Ki = Modified Bessel function of second kind, first order,
Ko — Modified Bessel function of second kind, zero order,
Jo = Bessel function of first kind, zero order,
F0 = Bessel function of second kind, zero order, and u = variable of integration.
The integral in equation 96 cannot be integrated directly but was evaluated numerically, and values of the parameters are given by Han tush (1959, table 1) from which plate 5 was drawn after Walton (1962, pi. 4). When 2? =<®, rw/B and K'b' (equal to T/B2) = 0, so that the parent-type curve on plate 5 is the same as on plate 1—the nonleaky-type curve of Jacob and Lohman (1952, fig. 5) — except, of course, that the values of the parameters differ.
On translucent logarithmic paper of the same scale as plate 5 (such as Codex 4123) values of Q are plotted on the vertical scale against values of t on the horizontal scale, and the data curve is superposed on plate 5. From the match point obtained by the usual curve matching procedure, preferably at G(a, rw/B) and a = 1.0, values of the four parameters G(a, rw /B), a, Q, and t are obtained. T is then determined using equation 93, and S is determined by rewriting equation 94:
Tt
S= ——	[dimensionless].	(97)
rw2a
CONSTANT DRAWDOWN
Hantush (1959) derived an equation for determining T and S for a well of constant drawdown that is discharging by natural flow from an infinite leaky confined aquifer, and he also gave solutions for a circular leaky confined aquifer with zero drawdown on the outer boundary and for a closed circular aquifer. The equations for the infinite leaky confined aquifer follow:
	T — ® YL2T~l~\ 2tswG(a, rw/B)	(93)
where	Tt a = ——- [dimensionless], Srw2	(94)
and	rJB-rWTKK'/V) [A2],	(95)
«(«■!)	(rw\ Ki(rw/B) , r [ A-VI -Uw./B>4ven “U)J	
Unfortunately, I have no field data with which to illustrate this method.
UNCONFINED AQUIFERS WITH VERTICAL MOVEMENT
Boulton (1954a) derived an integral equation for the drawdown of the water table near a discharging well before the flow approaches steady state, which is founded partly on a consideration of vertical flow components, such as those that prevail near the well during the early stages of a pumping test in an unconfined aquifer. (See Stallman, 1961a.) In our notation, his partial differential equation describing the head (h) at the water table is
MKSM0-S] <->
As equation 98 is nonlinear and cannot readily be solved, he assumes that the head gradients are small enough that their squares may be neglected, whence
u exp (— au2) du Jo2M + Y02(u)'u2+(rJB)2
[dimensionless],
dh K dh dt + S dz
[LT-1],
(99)
(96) where h = pressure head (p/gp) plus elevation head (z).﻿AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE
35
Boulton’s solution for an isotropic unconfined aquifer, in which the vertical and horizontal permeability are equal, is
s= —f	[1— exp(rX tan/iX) ]d\
2tt/vO •'q X
where
and
'
[dimensionless],
>
[dimensionless],
M,
(100)
(101)
Jo = Bessel function of the first kind of zero order, and X = variable of integration.
For anisotropic aquifers, in which the vertical hydraulic conductivity, Kz, differs from the horizontal (radial) hydraulic conductivity, Kr, equation 101 becomes
(102)
Equation 100 may be written:
T~ 2ns V(^’ t)	(103)
where V (yp, r) = the V function of yp and t. When r is sufficiently large, equation 103 reduces to the Theis equation (eq. 46). When r is small, the Boulton equation 103 and the Theis equation (46) are related thus:
V _ rW
4r ~ 4Tt
[dimensionless].
(104)
Boulton (1954a) gave a short table of values for V (yp, r) which was extended considerably by Stallman (1961b) with the aid of a digital computer. Stallman (1961a) also plotted values of 2V(\p, t),otW(u), versus 1/w for various values of yp) values of 2V(yp, r) versus yp, for various values of r; and s versus t/r2, for values of yp and r, for pumping-test data for unconfined aquifers in Kansas and Nebraska.
From finite-difference expressions of partial differential equations similar to Boulton’s, Stallman (1963a, 1965) designed electric-analog models simulating the assumed hydraulic model of an anisotropic aquifer, which he used to compute various values of the parameters for different penetrations of both pumping and observation wells. The principal results are given in his figures 10 and 12 (Stall-man, 1965), which are here reproduced at larger scale on plates 6 and 7. These are nondimensional logarithmic plots
of sT/Q versus Tt/r2S, for observation wells at different values of yp and for a pumping well for which yp = 0.002. Plate 6 is for a fully penetrating pumping well, for five different penetrations of observation wells; plate 7 is for a pumping well open only for the bottom 0.36 and for the same five penetrations of observation wells.
For tests of aquifers whose values of Kz and Kr are suspected to differ appreciably, observed values of s versus t, t/r2, or 1/r2 (for constant t) are plotted on translucent logarithmic graph paper of the same scale as plates 6 and 7 (such as K & E 359-125b or 46-7522, 3X5 cycle) and are fitted to the appropriate curve of plate 6 or 7 by the usual curve-matching procedure. From the four values of parameters at the match point, assuming that the match point is chosen so that both sT/Q and Tt/r2S are equal to 1.0, T obviously is obtained from
T = 1.0 —	[L2T~l~]	(105)
s
and S is obtained from Tt
S= ------ [dimensionless].	(106)
l.Or2
Of course the values of any other match points, such as 10 or 10"1, may be used in these equations, but the ones assumed are most convenient. Note that, in plotting his type curves, Stallman omitted the 4r and 4 from the parameters sT/Q and Tt/r2S, respectively, thus omitting these pure numbers also in the computations using equations 105 and 106.
The relation of z to 6 in both the pumped and observation wells for curves on plates 6 and 7 is shown in figure 21. A well for which z — 0 would fully penetrate the aquifer but would be open only at the bottom. Dagan (1967) gave
Figure 21.—Relation of z to 6 of pumped and observation wells on plates 6 and 7.﻿36
GROUND-WATER HYDRAULICS
a digital computer solution for producing curves like those on plates 6 and 7 for any degree of penetration.
Boulton (1954b, 1963, 1964) also derived an equation to take account of the delayed yield from storage, which occurs in unconfined aquifers during the early part of the pumping. Boulton’s (1963) differential equation is, in slightly modified notation,
e-“(‘-T)dr
ILT-1],
(107)
where
where
and
Se = early time apparent specific yield, Si = later time specific yield, and t = variable of integration.
When n = oo, where
n =
S.+ Si S'
Boulton’s solution of equation 107, for the drawdown at distance r from a pumped well that completely penetrates the aquifer, is
[L],	(108)
where
Jo = Bessel function of the first kind of zero order, x = variable of integration,
and
^•2
« = ^-^exp{-arj«(x2+l)}.
For sufficiently small values of t, equation 108 becomes equal to equation 85, the leaky confined aquifer equation of Hantush and Jacob (1955).
Boulton (1963, p. 480, 481) gives tables of solutions of equation 108 for his W function (AwTs/Q) for various values of, in our notation, \/ue = ATt/r2Se, for his type A curves, for various values of \/ui = ATt/r2Si, for his type B curves, and for various values of r/B. Families of Boulton delayed-yield type curves based upon these tabulated
values are shown on plate 8, which is similar to Boulton’s (1963) figure 1. His type A curves (1/w,) are shown to the left of the break in the curves; his type B curves (1 /u{) are shown to the right of the break. Note that the type A curves are essentially the same as those shown on plate 3A for leaky confined aquifers. Note also that the Theis type curve is asymptotic to the left of the type A family of curves and to the right of the type B family.
Logarithmic time-drawdown plots for tests of unconfined aquifers in which delayed yield from storage is suspected may be superposed on plate 8, and a match point may be obtained for a suitable value of r/B. From the four parameters s, t, AwTs/Q, and ATt/r2Se or 4Tt/r2Si thus obtained, the desired values of T and Se or Si may be obtained as follows, assuming that the dimensionless parameters chosen on plate 8 are both equal to 1.0:
T= 11215	[L2T-1].
4tts
(109)
For early values of t,
= ATt
e r2(1.0)
for later values of t,
ATt
[top scale, dimensionless]; (HO)
Si =
r2(1.0)
[bottom scale, dimensionless]. (Ill)
Example for Anisotropic Aquifer
Table 13 gives the time-drawdown data for an observation well of z = 0.56 which was 63.0 ft from a fully penetrating, fully screened well (2 = 6) pumped at an average rate of 1,170 gpm, near lone, Colo. The wells are in unconfined alluvium having a prepumping saturated thickness (6) of 39.4 ft. The pumped well is 56.5 ft deep and the observation well is 25.8 ft (0.526) deep. Figure 22 is a logarithmic plot of the data given in table 13, and also it shows the values of the four parameters at the match point obtained by superposing figure 22 on plate 6D.
From equation 105,
(1.0) (1,170 gal min-1) (1,440 min day-1)
=	(10.3 ft) (7.48 gal ft-3)
= 2.2X104 ft2 day-1. From equation 106,
S =
(2.2 X104 ft2 day-1) (52 min) (1.0) (63 ft)2(l,440 min day-1)
Using equation 102,
= 0.2 (rounded).﻿i, IN FEET
		1	1	1	1	1—1—1—I—	i i i i i i i i	1 1 1 1 1 1 1 1
-	•		' —
-	MATCH POINT		.
-	Tt/r2S=\.0		-
-	s77 Q=1.0		-
-	s= 10.3 ft		
	t=52 min		
			o°o
-			r, CBCGfflP
			
-		0 o o O	
-		O O O O O O O O O O c	-
		o	
	Ao		
	o °		
	o		
-	o ° 1		.
-	o °		-
-	0 o o o		-
-			.
o o o o o			-
o			
o o			
)			-
			
t, IN MINUTES
Figure 22.—Logarithmic plot of s versus t for observation well B2-66-7dda2, near lone, Colo.
oo
AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE﻿38
GROUND-WATER HYDRAULICS
Table 13.—Drawdown of water level in observation well B2-66-7dda2, 63.0 ft from, a well pumping at average rate of 1,170 gpm, near lone, Colo., August, 15-18 1967
[Data from D. R. Albin, written commun., January 1968J
Time since pumping began,t (min)	Corrected drawdown, a (ft)	Time since pumping began, t (min)	Corrected drawdown, a (ft)
i		0.28	520		2.66
2		.38	580		2.74
3		.38	700		2.91
4		.44	820		3.02
5		.48	940		3.17
6		.50	1,060		3.22
7		.52	1,300		3.41
8		.53	1,360		3.44
9		.56	1,420		3.48
10		.56	1,480		3.48
12		.61	1,540		3.51
14		.65	1,600		3.56
16		.67	1,660		3.57
18		.70	1,720		3.59
20		.72	1,810		3.64
24		.79	1,900		3.67
28		.82	1,960		3.70
36		.92	2,020		3.73
40		.96	2,380		3.84
50		1.00	2,740		3.94
60		1.15	2,800		3.96
70		1.24	2,860		3.97
80		1.30	2,920		3.98
90		1.38	2,980		3.99
100		1.42	3,040		4.00
120		1.55	3,100		4.01
140		1.67	3,160		4.02
160		1.74	3,220		4.04
180		1.84	3,280		4.03
200		1.93	3,340		4.05
240		2.05	3,400		4.05
280		2.17	3,460		4.07
320		2.27	3,820		4.14
360		2.36	4,180		4.20
400		2.48	4,240		4.21
460		2.55	1 4,270		4.20
Table 14.—Drawdown of water level in observation well 139, 73 ft from a well pumping at constant rate of 1,080 gpm, near Fairborn, Ohio, October 19-21, 1954
[Data from S. E. Norris (written commun., Apr. 29, 1968)]
Time since pumping began,t (min)	Corrected drawdown, a (ft)	Time since pumping began,t (min)	Corrected drawdown, a (ft)
0.165		0.12	10		1.02
.25		.195	12		1.03
.34		.255	15		1.04
.42		.33	18		1.05
.50		.39	20		1.06
.58		.43	25		1.08
.66		.49	30		1.13
.75		.53	35		1.15
.83		.57	40		1.17
.92		.61	50		1.19
1.00		.64	60		1.22
1.08		.67	70		1.25
1.16		.70	80		1.28
1.24		.72	90		1.29
1.33		.74	100		1.31
1.42		.76	120		1.36
1.50		.78	150		1.45
1.68		.82	.200		1.52
1.85		.84	250		1.59
2.00		.86	300		1.65
2.15		.87	350		1.70
2.35		.90	400		1.75
2.50		.91	500		1.85
2.65		.92	600		1.95
2.80		.93	700		2.01
3.0		.94	800		2.09
3.5		.95	900		3.15
4.0		.97	1,000		2.20
4.5		.975	1,200		2.27
5.0		.98	1,500		2.35
6.0		.99	2,000		2.49
7.0		1.00	2,500		2.59
8.0		1.01	3,000		2.66
9.0		1.015		
by interpolation,
r (0.9) (39.4 ft) T Kr L (63.0 ft) J ' :
Kz = 0.3Kr ft day-1,
and
2.2 X Wft2 day-1 39.4 ft
= 560 ft day-1;
therefore,
Kz = (0.3) (560 ft day-1) = 168 ft day-1.
For additional examples of this method and evaluations of results, see Norris and Fidler (1966).
supplied by S. E. Norris (U.S. Geological Survey, Columbus, Ohio, written commun., Apr. 29, 1968). The pumped well, which is 85 ft deep and is reportedly screened to full depth, obtains water from glacial sand and gravel. The observation well is 95 ft deep, but it penetrates only 75 ft of water-bearing material, the rest being 20 feet of clay in four beds. This is the same test as that for observation well 1 analyzed by Boulton (1963, fig. 2, p. 475-476) and by Walton (1960). The water-level measurements from 0 to 2.80 min were made using a technique described by Walton (1963). A logarithmic plot of s versus t from table 14 is shown in figure 23, which also shows the match-point values of the four parameters obtained by superposition on plates 6C and 8.
Using the parameters of the lower match point in figure 23 for Boulton’s type B curves on plate 8, T is obtained from equation 109:
Example for Delayed Yield from Storage
Table 14 gives the time-drawdown measurements in an observation well 73 ft from a well pumping at constant rate of 1,080 gpm near Fairborn (near Dayton), Ohio,
(1.0) (1.08X103 gal min-1) (1.44X103 min day-1) (1.257 X101) (4.22 X10-1 ft) (0.748 X101 gal ft-3)
= 4 X104 ft2 day-1 (rounded).﻿IN FEET
-		• MATCH POINT PLATE 6C sT/Q=\.0 Tt/r2S=\.0 t=26.5 min 8=6 ft ^=0.154 Q o o O O o O oo« L n n 0 O 0		: T”"’"" ""1 . ■ ■ ill	“I	1	1	1	1	1	1	1	 o o o o o
	Ocpoo O ° ° u O-O-O-			
	~oOO°			
-	o o o % c			-
o				
o				"
o	•			
0	MATCH POINT			
o	PLATE 8			
	47rTs/Q = 1.0			'
o	4 Tt/r2Si=\.0			
	t==4.4 min			
o	s = 0.422 ft			-
	r/B—OA			
o 	1	1	1	1	1	1	1	1			1	1	1	1	1	1	1	1				
t, IN MINUTES
Figure 23.—Logarithmic plot of s versus t for observation well 139, near Fairborn, Ohio. From Walton (1960, fig. 4).
co
CO
AQUIFER TESTS BY WELL METHODS—POINT SINK OR POINT SOURCE﻿40
GROUND-WATER HYDRAULICS
Similarly, using equation 111,
=	(4) (4X104 ft2 day-1) (4,4 min)
1	(5.33 X103 ft2) (1.44 X103 min day-1)
Matching the early data to Boulton’s type A curves gave the same value for T, but a value of Se of 3X10-3. This value of Se seems to be about one order of magnitude too large for a confined aquifer less than 100 ft thick; on the other hand, the value of Se seems too small for the unconfined aquifer and suggests that it is only an apparent-value observed before gravity drainage was completed.
Using the upper match point in figure 23 for Stallman’s type curve in plate 6(7, T is obtained from equation 105:
(1.0) (1.08X103 gal min-1) (1.44X103 min day-1)
=	(6 ft) (0.748X101 gal ft-3)
= 3.5 X104 ft2 day-1,
which is of the same order of magnitude as that obtained from Boulton’s curves (pi. 8).
Similarly, from equation 106,
AQUIFER TESTS BY CHANNEL METHODS-LINE SINK OR LINE SOURCE (NONSTEADY FLOW, NO RECHARGE)
CONSTANT DISCHARGE
In 1938 C. V. Theis (Wenzel and Sand, 1942, p. 45) developed an equation for determining the decline in head at any distance from a drain discharging water at a constant rate from a confined aquifer. The equation is based upon the following assumptions: The aquifer is homogeneous, isotropic, and of semi-infinite areal extent (bounded on one side only by the drain); the discharging drain completely penetrates the aquifer; the aquifer is bounded above and below by impermeable strata; the flow is laminar and unidimensional; the release of water from storage is instantaneous and in proportion to the decline in head; and the drain discharges at a constant rate. Theis derived his equation by analogy with heat flow in an analogous thermal system; later Ferris (1950) derived a similar equation from hydrologic concepts. In slightly modified form, Ferris’ equation (Ferris and others, 1962, p. 123) may be written:
S =
(3.5 X104 ft2 day-1) (26.5 min)
----------——----------■—-———- =0.1 (rounded)
(5.33 X103 ft2) (1.44X103 mm day-1)
T =
Qt>x I" e-“2 2s L U\^ir
-1 +
L
x/iy/Tt/S
which is virtually identical to the 0.09 value. As the observation well is reported to be fully screened through the aquifer, figure 23 should have matched one of the type curves on plate 6A. The fact that it exactly matches the curve for ^ = 0.154 on plate 6C for 2 = 0.756 suggests that the intercalated clay beds may have changed the shape of the response curves, but this is only speculation.
From equation 102,
73
78 'A,
= 0.154,
where
or
and
[dimensionless]
[dimensionless],
[L2T-1],
(112)
(113)
K_z
Kr
"(0.154) (78) T 73
0.027,
S =
ATtu2
[dimensionless],
(114)
3.5 X104 ft2 day-1 .78X102 ft
= 4.5 X102 ft day-1,
and
Kz = 2.7 X10-2X4.5 X102 ft day-1 = 12 ft day-1.
The low vertical hyraulic conductivity compared to the radial value indicates that the aquifer is anisotropic and suggests a valid reason for the delayed drainage from storage, even after some 50 hours of pumping. This also suggests the desirability of trying both plates 6 or 7 and 8 for matching data curves similar to figure 23, knowledge of the local geology may help decide on which results to choose if they differ significantly.
s = drawdown at any point in the vicinity of the drain, Qt = Constant discharge rate (base flow) of the drain, per unit length of drain,
x = distance from drain to point of observation, and t = time since drain began discharging.
The part of equation 112 in brackets may be written D(u)q, the drain function of u; the subscript q identifies the constant discharge of the drain. Equation 112, therefore, may be written:
T~ TT- D(u) q [L2T-1].	(115)
2s
Values of D(u)q for corresponding values of u and u2 are﻿AQUIFER TESTS BY CHANNEL METHODS—LINE SINK OR LINE SOURCE
41
Figure 24.—Logarithmic plot of D{u)q versus u* for channel method—constant discharge.
given in table 15, and a logarithmic plot of D (u) q versus u2 is shown in figure 24.
Observed values of s versus x2/t are plotted on translucent logarithmic graph paper of the same scale as figure 24 (such as K&E 358-112) and are fitted to figure 24 by the usual curve-matching procedure. From the four values of parameters at the match point, assuming that the
Table 15.—Values of D(u)„, u, and u2 for channel method—constant
discharge
[From Ferris, Knowles, Brown, and Stallman (1962, table 5)]
u		D(u)q || V			£>(«)«
0.0510	0.0026	10.091	0.2646	0.070	1.280
.0600	.0036	8.437	.3000	.090	1.047
.0700	.0049	7.099	.3317	.110	.8847
.0800	.0064	6.097	.3605	.130	.7641
.0900	.0081	5.319	.4000	.160	.6303
.1000	.010	4.698	.4359	.190	.5327
.1140	.013	4.013	.4796	.230	.4370
.1265	.016	3.531	.5291	.280	.3516
. 1414	.020	3.069	.5745	.330	.2895
.1581	.025	2.657	.6164	.380	.2426
.1732	.030	2.355	.6633	.440	.1996
.1871	.035	2.120	.7071	.500	.1666
.2000	.040	1.933	.7616	.580	.1333
.2236	.050	1.648	.8124	.660	.1084
.2449	.060	1.440	.8718	.760	.08503
			.9487	.900	.06207
			1.0000	1.000	.05026
match point is chosen so that both D(u)q and u2 are equal to 1.0, T is obtained from
T= ^L0)	[L2?1-1]	(116)
2s
and S is obtained from 47V1.0)
S= ——— [dimensionless].	(117)
Unfortunately reliable field data to illustrate the method were not available.
CONSTANT DRAWDOWN
Stallman (in Ferris and others, 1962, p. 126-131) found a solution for a similar drain, in which the head abruptly changes by a constant amount and the discharge declines slowly, by borrowing the solution to an analogous heat-flow problem (Ingersol and others, 1954, p. 88). The basic assumptions are the same as those for equation 112 just described. Stallman’s equation is
[2 rx/ty/Tt/S	"I
1— J e~“2dwj =s0D(u)h [L],
(118)﻿IX.u\
rf>-
bO
Figure 25.—Logarithmic plot of D{u)k versus v? for channel method—constant drawdown.
GROUND-WATER HYDRAULICS﻿AQUIFER TESTS BY AREAL METHODS
43
Table 16.—Values of D(u)h, u, and u2 for channel method—constant
drawdown
[From Ferris, Knowles, Brown, and Stallman (1962, table 6)]
u	U*	DMh |	U		D(u)k
0.03162	0.0010	0.9643	0.6325	0.40	0.3711
.04000	.0016	.9549	.7746	.60	.2733
.05000	.0025	.9436	.8944	.80	. 2059
.06325	.0040	.9287	1.000	1.00	.1573
.07746	.0060	.9128	1.140	1.30	.1069
.08944	.0080	.8994	1.265	1.60	.0736
.1000	.010	.8875	1.378	1.90	.0513
.1265	.016	.8580	1.483	2.20	. 0359
.1581	.025	.8231	1.581	2.50	.0254
.2000	.040	.7730	1.643	2.70	.0202
.2449	.060	.7291	1.732	3.00	.0143
.2828	.080	.6892	1.789	3.20	.0114
.3162	.10	. 6548			
.4000	.16	.5716			
.5000	.25	.4795			
where
So = the abrupt change in drain level at t = 0.
D(u)h represents the bracketed part of equation 118 and is the drain function of u for constant drawdown, and where
u2= — [dimensionless],	(119)
the bracketed part of equation 118 is the complementary error function, cerf, solutions of which are available.
The discharge of the aquifer from both sides of the drain per unit length of drain, Qb, resulting from the change in drain stage, s0, is
Q„ = ^ VST [Z/2T-1].	(120)
Solving equation 120 for ST, we obtain
ST= ^	[L2T-1].	(121)
4s02
Dividing equation 121 by equation 119 to eliminate S, and replacing s0 by s/D(u)k,
T=	a/tt [L2?1-1].	(122)
Solving equation 119 for S,
S= ——	[dimensionless].	(123)
x2/t
Values of D(u)h for corresponding values of u and m2 are
given in table 16, and a logarithmic plot of D(u)h versus w2 is shown in figure 25.
Observed values of s versus x2/t are plotted on translucent logarithmic graph paper of the same scale as figure 25 (such as K&E 358-112) and are fitted to figure 25 by the usual curve-matching procedure. From the four values of the parameters at the match point, assuming that the match point is chosen so that both D(u)h and v? are equal to 1.0, whence u is also equal to 1.0, T is obtained by rewriting equation 122,
^ <12*>
and S is obtained from equation 123 using the value of T determined from equation 124,
47V1.0)
S= ----——	[dimensionless], (125)
x2/t
Unfortunately, field data to illustrate the method were not available to me, but the method was successfully used by Bedinger and Reed (1964). (See also Pinder and others, 1969.)
Jacob (1943) developed methods for an unconfined aquifer subject to a constant rate of recharge {W) and bounded by two parallel and assumedly fully penetrating streams. The base flow of streams or the average rate of ground-water recharge may be estimated from the shape of the water table, as determined from water-level measurements in wells, in such a bounded aquifer. Rorabaugh (1960) gave methods, equations, and charts for estimating the aquifer constant T/S (hydraulic diffusivity) from natural fluctuations of water levels in observation wells in finite aquifers having parallel boundaries. Examples of such aquifers are: a long island or peninsula, an aquifer bounded by parallel streams, and an aquifer bounded by a stream and a valley wall. For similar bounded aquifers, Rorabaugh (1964) also developed methods for estimating ground-water outflow into streams and for forecasting streamflow recession curves. The component of outflow related to bank storage is computed from river fluctuations; the component related to recharge from precipitation and irrigation is computed from water levels in a well. Rorabaugh’s methods have widespread application in areas having the required boundary conditions.
AQUIFER TESTS BY AREAL METHODS NUMERICAL ANALYSIS
The equations given above for the radial flow of ground water were derived from ordinary or partial differential equations by means of the calculus, for various assumed﻿44
GROUND-WATER HYDRAULICS
boundary conditions. Stallman (1956, 1962) showed that, after the manner of Southwell (1940, 1946), the partial differential equation for two-dimensional nonsteady flow in an unconfined homogeneous and isotropic aquifer subject to a steady rate of accretion, W, can be closely approximated by a finite-difference equation in which, for example, dh/dt is replaced by Ah/At. He has since (written commun., 1965) developed a simplified application for use during winter periods when there is little or no transpiration from plants and no recharge from precipitation and, hence, when W = 0. He (later he and C. T. Jenkins) developed comparable equations for nonhomogeneous isotropic aquifers (R. W. Stallman and C. T. Jenkins, written commun., January 1969).
For homogeneous isotropic aquifers, the equations with and without W are
by two systems of equally spaced parallel lines at right angles to each other. One system is oriented in the x direction and the other, in the y direction; the spacing of lines equals the distance a. A set of five gridline intersections, or nodes (observation wells), as shown in figure 26, is called an array.
The first two differentials in equations 126 and 127 can be expressed in terms of the head values at the nodes (wells) in the array, thus
d* 2h	h\ -f- hz — 2ho
— «-------------- [I/-1]
dx2	a2
and
d2h	h2+hi—2h0	r -.
—-	---------- ru-n
d2h d2h S dh W dx2 + dy2 ~ Tdt ~ T
and
d2h dVi _ S dh dx2 + dy2~ T dt
where h is the head at any point whose coordinates are x and y. Let the infinitesimal lengths dx and dy be expanded so that each is equivalent to a finite length, a, and similarly, let dt be considered equivalent to At. A plan representation of the region of flow to be studied may then be subdivided
(126)
(127)
X
Figure 26.—Array of nodes used in finite-difference analysis.
where the subscripts refer to the numbered nodes in figure 26. Substituting these closely equivalent expressions in equations 126 and 127, and letting dh/dt be considered equivalent to Ah0/ At, we obtain
h+ht+h+h-Mo^j: htt ~	~	[i]
T At T
(128)
and
hi-\-h2-\-h2-\-hi—4ho = X htt — —	\_L~\	(129)
T At
where Ah0 is the change in head at node (well) 0 during the time interval At.
Example
R. W. Stallman tried this method on several such arrays in the Arkansas River valley, Colorado, during the winter of 1965-66 and the summer of 1966. Wells 1-4 were spaced 1,000 ft apart so that o = 1,000 ft V2/2 = 707 ft, and a2 — 5 X106 ft2. From estimated values of T and S, a normally is determined from the convenient empirical relation a2S/T = about 10 days, but in the Arkansas River valley, nearby boundaries made it necessary to use a2S/T = about
4	days. The elevations of the measuring points at each of the five wells were determined by precise leveling above a convenient arbitrary datum, and the water levels in feet above datum were obtained from automatic water-level
sensors.
The winter data from a test near Lamar, Colo., are
shown in figure 27. The slope of the straight line in figure 27
is A X! h/ (Aho/At) =4.25 days, whence a2S/T = 4.25 days.
5	was obtained from neutron-moisture-probe tests (see
Meyer, 1962), made during periods of both high and low water table, and was determined to be about 0.18. Then,﻿AQUIFER TESTS BY AREAL METHODS
45
the contour interval of the equipotential lines. The contour interval indicates that the total drop in head in the system is evenly divided between adjacent pairs of equipotential lines; similarly the flow lines are selected so that the total flow is equally divided between adjacent pairs of flow lines. The movement of each particle of water between adjacent equipotential lines will be along flow paths involving the least work, hence it follows that, in isotropic aquifers, such flow paths will be normal to the equipotential lines, and the paths are drawn orthogonal to the latter.
The net is constructed so that the two sets of lines form a system of “squares.” Note on the map that some of the lines are curvilinear, but that the “squares” are constructed so that the sum of the lengths of each line in one system is closely equal to the sum of the lengths in the other system. Figure 29 represents one idealized “square” of figure 30, whose dimensions are Aw and Al. By rewriting Darcy’s law (eq. 26) as a finite-difference equation for the flow, AQ, through this elemental “square” of thickness b, we obtain
Ah	Ah
AQ= — KbAw — = — TAw —-	[L3T-1]. (130)
Al	At
FLOW-NET ANALYSIS	But Aw= Al, by construction, so
The following discussion of flow-net analysis has been adapted in part from Bennett (1962) and from Bennett and Meyer (1952, p. 54-58), to whose reports you are referred for further details.
In analyzing problems of steady ground-water flow, a graphical representation of the flow pattern may be of considerable assistance and may provide solutions to problems not readily amenable to mathematical solution.
The first significant development in graphical analysis of flow patterns was made by Forchheimer (1930), but additional information was given by Casagrande (1937, p. 136, 137) and Taylor (1948).
A flow net, which is a graphical illustration of a flow pattern, is composed of two families of lines or curves.
(See fig. 30.) One family of curves, called equipotential lines (solid lines on map), represents contours of equal head in the aquifer on the potentiometric surface or on the water table. Intersecting the equipotential lines at right angles (in isotropic aquifers) is another family of curves (dashed lines on map) representing the streamlines, or flow lines, where each curve indicates the path followed by a particle (molecule) of water as it moves through the aquifer in the direction of decreasing head.
Although the real flow pattern contains an infinity of possible flow and equipotential lines, it may be represented conveniently by constructing a net that uses only a few such lines, the spacing being conveniently determined by
AQ=-TAh [L3T-1].
(131)
If 71/= number of flow channels, nd = number of potential drops, and Q = total flow, then
Q = nfAQ, or AQ =
Q
71/
and
h = ndAh, or Ah =
nd
[L3T-1],	(132)
m.
(133)
Substituting equations 132 and 133 in equation 131, we obtain
Q= — T7— h
nd
[L3?1-1],
(134)
or
T= —
Q
(nf/nd)h
[L2T-1].
(135)
Example
According to Bennett and Meyer (1952, p. 55), the average discharge from the Patuxent Formation in the Sparrows Point district in 1945 was 1 million ft3 day-1. The map (fig. 30) shows 15 flow channels surrounding the
using equation 129,
a?S
A D h/(Ah0/At)
(5X105 ft2) (0.18) 4.25 days
^2 X104 ft2 day-1 (rounded).
The straight line in figure 27 has been transferred to the plot of spring and summer data shown in figure 28. In figure 28, points to the right of the straight line indicating W=0 show recharge to the water table; those to the left show discharge from the water table by evapotranspiration. The average value of above the line is about 0.1 ft. Using T^2 X104 ft2 day-1 and a2 = 5X105ft2, from equation 128,
0.1 ftss-
(5X105 ft2) (IF) 2X104 ft2 day-1
and
Trr (2 X104 ft2 day-1) (0.1 ft)
W -------------------------
5X105 ft2
i—4X10-3ft day-1 (rounded).﻿46
GROUND-WATER HYDRAULICS
10zAfco/At, IN FEET PER DAY
Figure 27.—Plot of 2h versus A/io/A< for winter of 1965-66, when W = 0.
district, hence n/=15. The number of equipotential drops between the 30- and 60-ft contours is three, so nd = 3. The total potential drop between the 30- and 60-ft contours is 30 ft, so A = 30 ft. Then, from equation 135,
10®	Hav—^
T =------v	v =6,670 ft2 day-1 = 6,700 ft2 day"1.
(15/3) (-30 ft)
Note that the value of T thus determined is for a much
larger sample of the aquifer than that determined by a pumping test on a single well. This method has been largely neglected and is deserving of more widespread application.
CLOSED-CONTOUR METHOD
A water-level contour map containing closed contours around a well or group of wells of known discharge rate may be used to determine or estimate the transmissivity﻿AQUIFER TESTS BY AREAL METHODS
47
Figure 28.—Plot of 2h versus Aha/At for spring of 1966.
of an aquifer under steady flow conditions. Equation 26 may be rewritten:
Q= -
KAAh A r
TLAh A r
[L3r-1],	(136)
which, for any two concentric closed contours of length Li and Ln, may be written
r=-
2 Q
([<\+ L2) Ah/ At
[L2r-1],	(137)
where Ah is the contour interval and Ar is the average distance between the two closed contours. An example will illustrate the method.
. Assume that two irregularly shaped closed contours		
1 1 1 1 1 1 1 1 1 1 1 1	1 1 1 1 1 1 A l 1 1 1	have measured lengths (as by wheel-type map measure) of 27,600 and 44,000 ft, respectively, that the contour interval is 10 ft, that the average distance between the two contours is (1,800+2,200+2,100+1,700)/4=l,950 ft, and that the rate of withdrawal from a well field within the lowest closed contour is 1 million gal day-1. Using equation 137,
Aw	1 1 1 1	(2) (106 gal day-1) (7.16 X104 ft) [ — (10 ft)/(1.95 X103 ft) 3(7.48 gal ft-8)
1 1 1 1	1 1 1 1	= 730 ft2 day-1 (rounded).
1 1 Figure 29.—Idealized square of flow net.		The regularity or irregularity of the shape and spacing of the contours, the density and accuracy of the water-﻿00
Figure 30.—Map of Baltimore industrial area, Maryland, showing potentiometric surface in 1945 and generalized flow lines in the Patuxent
Formation. From Bennett and Meyer (1952, pi. 7).
GROUND-WATER HYDRAULICS﻿AQUIFER TESTS BY AREAL METHODS
49
level data, and the accuracy to which Q is known control the accuracy of T and should be carefully considered to guide the rounding of the final result. In the above hypothetical example, greater irregularity in the contours would necessitate rounding the result to 700 ft2 day-1. In the example, four measurements of Ar were averaged, but the number required would range from one, for concentric circles, to perhaps eight or 10 for more complicated patterns. Use of my method may save the trouble of drawing a flow net.
UNCONFINED WEDGE-SHAPED AQUIFER BOUNDED BY TWO STREAMS
Stallman and Papadopulos (1966) presented a method for determining T/S (hydraulic diffusivity) from water-level recession in an observation well caused by dissipation of recharge from an unconfined wedge-shaped aquifer between two perennial streams. The hydraulic system here is analogous to a nonsteady heat-flow problem solved by Jaeger (1942) by means of a complex integral equation, which may be evaluated only by very laborious numerical methods (Papadopulos, 1963). The close fit between observed and theoretical water-level recession curves computed from Jaeger’s equation for three observation wells in Wisconsin (Weeks, 1964) led to the computation of many evaluations by a digital computer. The following four illustrations from Stallman and Papadopulos (1966) show the method.
A simplified form of Jaeger’s equation is s	( 0 t Tt \
— =F ( 90, — , - , — ) [dimensionless], (138) s0	\ d0 a r2S/
where F is simply a function of the four parameters in parentheses: 90, 9, r, and a are as shown in figure 31; s and so are as shown in figure 32; the components of Tt/r2S are as defined previously; and the solution for T/S is given in figure 33.
Note in the example in figure 31 that observation well A is near the confluence of two of several streams that drain an unconfined aquifer. The two tributaries form a wedge having an angle 90, of approximately 75°, and the angle 9, between the well and one side of the wedge, is 15°. Radius r, to the well, is about 5 miles. Radius a, the distance from the apex to the circumference along which water levels are presumed to be constant, was chosen to be 20 miles, so that r/a = 0.25. Note in figure 34 (and on many of the plates in the report by Stallman and Papadopulos) that as r/a approaches zero (larger and larger values of a), the response curves form an envelope on the lower right, and that values larger than 20 miles would not affect the final result in the example given.
In the hypothetical hydrograph in figure 32, the water level was declining until about mid-May, when the aquifer received recharge during the spring thaw; this raised the water level by late May by the amount s0 at t = 0. For times after t = 0, values of s were determined by subtracting altitudes of the projected water-level trend, had no recharge occurred, from the smoothed curve of actual water levels. Values of s/s0 (linear scale) and t (log scale) were
Figure 31.—Surface drainage pattern, showing location of observation wells that penetrate an unconfined aquifer.
then plotted on semilogarithmic tracing paper (such as Codex 31,227) to the same scale as figure 34, and the data curve was then matched to the type curves by a procedure slightly different from those described earlier. The s/s0 axes are kept coincident, and the data curve is moved from side to side until the data curve fits the theoretical response curve for r/a = 0.25. Any convenient match of Tt/r‘2S in figure 34 and t on the data curve is then selected; the one﻿50
GROUND-WATER HYDRAULICS
Figure 32.—Example hydrograph from well A of figure 31, showing observed and projected water-level altitudes.
chosen in the example in figure 33 was for Tt/r2S =1.0 and t = 360 days. From the value Tt/r2S = 1.0, T/S= 1.0Xr2/< = 1.0 X 6.98 X 10s ft2/360 days = 1.94 X106 ft2 day-1. If S is known or estimated to be, say 0.2, then T = 0.2 X 1.94 X106 ft2 day-1 = about 4X105 ft2 day-1. Note that in figure 34,
0
0.2
0.4
a
Sq
0.6
0.8
1.0
Figure 33.—s/s0 versus t taken from hydrograph of well A (see fig- 32), showing computation of T/S.
"1 I I TTTTT| I I I I I I I I ] I I l I I I I I
/ ''Observed
a ^Theoretical response
/	Match line at
/	-^ = 1.00
/	<=360 days
j	Computation:
/ Z= 1 00 x 6.98xl0_B=194xl061 / S	360
-J—ii ....I i i i i i i m
i i___i i 1111
10 100 t. IN DAYS
1000
which is a nondimensional plot, Stallman and Papadopulos omitted the pure number 4 from the numerator of Tt/r2S, thus eliminating the necessity of using it in computations.
In the hypothetical data plotted in figures 32 and 33, values of s/s0 were plotted for t from 5 to 200 days, but the authors warn that in actual practice it would be difficult to reliably project the water-level trend much beyond July and that, in general, values of s/s0 for only about 50 days after cessation of recharge should be considered useful.
Note in figure 31 that observation well B is considered to be within a circular area of 8(> = 360° and a radius of 16 miles surrounded by streams but that only the stream at 8 = 108° was considered. R. W. Stallman (U.S. Geological Survey, oral commun., 1968) indicated that this rather extreme example might be improved by reducing radius a to about 12 miles, so that it just intersects the streams to the northwest, west, and south.
Figure 34 is but one of 120 sheets containing in all some 1,500 response curves for various values of 60, 9/do, and r/a. This method should have widespread application in many places where unconfined aquifers are traversed by perennial streams, and where at least a few wells are available for observation of water levels preceding and following periods of recharge. In some studies this method might provide the only values of T/S and estimates of T; in others, it could conveniently supplement values obtained by other﻿AQUIFER TESTS BY AREAL METHODS
51
°s/s
Figure 34.—s/s0 versus Tf/rtS for 0o = 75°; 0/0o = O.2O.﻿52
GROUND-WATER HYDRAULICS
methods. In areas where T is known, this method also could be used to estimate S.
METHODS OF ESTIMATING TRANSMISSIVITY
In some ground-water investigations, such as those of a reconnaissance type, it may be necessary to estimate the transmissivity of an aquifer from the specific capacity (yield per unit of drawdown) of wells, as the determination of T by use of some of the equations discussed above may not be feasible. On the other hand, some of our modern quantitative studies, such as those for which electric-analog models or mathematical models are constructed, require a sufficiently large number of values of T that transmissivity-contour maps (T maps) may be constructed. In unconfined aquifers, such T maps generally require also the construction of water-level contour maps and bedrock-contour maps, from which may be obtained maps showing lines of equal saturated thickness, b, for we have seen that T — Kb. For example, a quantitative investigation of a 150-mile reach of the Arkansas River valley, in eastern Colorado, required a T map based upon about 750 values, or about 1% values per square mile. About 25 of these values were obtained from pumping tests, selected as reliable tests from a greater number of tests conducted. About 200 values of T were estimated from the specific capacity of wells, by one of the methods to be described. About 525 values were estimated by geologists from studies of logs of wells and test holes, by methods to be described. Thus, only about 3 percent of the values were actually determined from pumping tests.
SPECIFIC CAPACITY OF WELLS
Several methods for estimating transmissivity from specific capacity have been published, some of which are cited below. If we solve equation 51 for Q/sw (specific capacity), using sw as the drawdown in the discharging well, and rw as the radius of the well, and assuming that the well is 100 percent efficient, we obtain
Q	4ttT
sw ~ 2.301og10 2.25Tt/rJS
[L2T-1],	(139)
which shows the manner in which Q/sw is approximately related to the other constants (T, S) and variables (rw, t). As rw is constant for a particular well being pumped, we see that Q/sw is nearly proportional to T at a given value of t, but gradually diminishes as t increases, by the amount 1 /logio t. Thus, for a given well, considered 100-percent efficient, and assuming that water is discharged instantaneously from storage with decline in head, we may symbolize the foregoing statements by the following
equation:
Q B
__ _________
Syj lO^JO t
[L’T-1],
(140)
where B = a constant for the well, including other terms as in equation 139.
No wells are 100-percent efficient, but, according to construction, age, and so forth, some wells are more efficient than others. Jacob (1947, p. 1048) has approximated the head loss resulting from the relatively high velocity of water entering a well or well screen as being proportional to some power of the velocity approaching the square of the velocity, which in turn is nearly proportional to Q2; thus head loss is nearly equal to CQ2, where C = a constant of proportionality. Adding this to equation 140,
Q B
___ ________________
't''w	logio t
+CQ2
[L2T~l~\.
(141)
Thus we see that Q/sw diminishes not only with time but with pumping rate Q. In unconfined aquifers it may be necessary to adjust factor B further to account for delayed yield from storage.
In an uncased well in, say, sandstone, rw may be assumed equal to the radius of the well, but in screened wells in unconsolidated material, in which the finer particles have been removed near the screen by well development, or in gravel-packed wells, the effective rw generally is larger than the screen diameter. Jacob (1947) described a method for determining the effective rw and the well loss (CQ2) from a multiple-step drawdown test.
Most other investigators have neglected well loss in their equations, which are then equations for wells of assumed 100 percent efficiency, such as equation 140, but some have arbitrarily adjusted for this loss by selection of an arbitrary constant for wells of similar construction in a particular area or aquifer, which generally gives satisfactory results when used with caution.
Theis (1963a) gave equations and a chart, based upon the Theis equation, for estimating T from specific capacity for constant »S and variable t, with allowance for variable well diameter but not well efficiency. Brown (1963) showed how Theis’ results may be adapted to artesian aquifers. Meyer (1963) gave a chart for estimating T from the specific capacity at the end of 1 day of pumping, for different values of S and for well diameters of 0.5, 1.0, and 2.0 ft. Bedinger and Emmett (1963) gave equations and a chart for estimating T from specific capacity, based upon a combination of the Thiem and Theis equations and upon average values of T and S for a specific area, for well diameters of 0.5, 1.0, and 2.0 ft. Hurr (1966) gave equations and charts based upon the Theis and Boulton﻿METHODS OF ESTIMATING SPECIFIC YIELD
53
(1954a) equations, which.allow for delayed yield from storage, for determining T from specific capacity at different values of t for a well 1.0 ft in diameter. None of the methods just cited includes corrections for well efficiency, but this can be added in an approximate manner.
LOGS OF WELLS AND TEST HOLES
As noted above, about 525 values of T out of 750 total values in the Arkansas River valley of eastern Colorado were estimated by geologists from studies of logs of wells and test holes and from drill cuttings from test holes. Wherever possible, pumping tests were made on wells for which or near which logs were available; otherwise, test holes were drilled near the well tested. From several or many such pumping tests accompanied by logs, the values of T were carefully compared with the water-bearing bed or beds, and, as T = Kb, the total T was distributed by cut and try among the several beds, according to the following equation:
T = 2Z Kmbm = K\bi~\-Kzhz~\- • • • -\-Knbn
i
(142)
From this, table 17 was prepared, comparing average values of K for different alluvial materials in the valley. Equation 142 may be solved also by multiple regression using a digital computer or graphical method (Jenkins, 1963).
R. T. Hurr, who prepared table 17, then carefully examined the logs of other wells and test holes for which no pumping tests were available. He assigned values of K to each bed of known thickness on the basis of the descriptive words used by the person who prepared the log. The values of K that were assigned may have been (1) equal
Table 17.—Average values of hydraulic conductivity of alluvial materials in the Arkansas River valley, Colorado [Courtesy of R. T. Hurr]
Hydraulic
conductivity1
Material	(ft day _1)
Gravel:
Coarse----------------------------------- 1,000
Medium________________________________________  950
Fine------------------------------------------  900
Sand:
Gravel to very coarse__________________________ 800
Very coarse____________________________________ 700
Very coarse to	coarse__________________________ 500
Coarse_________________________________________ 250
Coarse to medium_______________________________ 100
Medium________________________________________   50
Medium to fine__________________________________ 30
Fine_________________________________________    15
Fine to very fine_______________________________  5
Very fine_______________________________________  3
Clay...............-.......-__________________ 1
1 Values were converted from gallons per day per square foot and were rounded.
to, (2) more than, or (3) less than values given in the table (depending upon cleanliness, sorting, and so forth), and thus they necessarily involved subjective judgment. As experience was gained, however, the geologist who prepared the table generally could estimate K and T with fair to good accuracy. The T values from all sources also were compared carefully with the saturated-thickness map. This method for estimating T has been used successfully in the Arkansas River valley in Colorado, in the Arkansas Valley in Arkansas and Oklahoma (Bedinger and Emmett, 1963), in Nebraska, in California, and elsewhere.
Laboratory determinations for K of cores of consolidated rocks, such as partly to well cemented sandstone, may be used in place of estimates. Reconstitution of disturbed samples of unconsolidated material is not possible, however, so laboratory determinations for K generally do not give reliable values. However, they may be very useful in indicating relative values, as was done in Arkansas and Oklahoma.
The above methods may also be used by the geologist for estimating the hydraulic properties of exposed sections of rocks containing water-bearing beds.
METHODS OF ESTIMATING STORAGE COEFFICIENT
In examining logs of wells or test holes in confined aquifers, or in measuring sections of exposed rocks that dip down beneath confining beds to become confined aquifers, the storage coefficient may be estimated from the following rule-of-thumb relationship:
s
b	b
(ft)	S	(ft-1)
l.__________________________________________     I0-*1
10______________________________________________ 10-‘l	10-6
100___________________________________________ 10—‘f
1,000___________________________________________ 10-3J
One may either multiply the thickness in feet times 1(R6 ft-1 or interpolate between values in the first two columns; thus, for 6 = 300 ft, )Sft:3X10-4, and so on. Values thus estimated are not absolutely correct, as no allowances have been made for porosity or for compressibility of the aquifer, but they are fairly reliable for most purposes. Such estimates may be improved upon by comparison with values obtained from reliable pumping or flow tests, then extrapolated to other parts of an aquifer with adjustments for thickness if needed.
METHODS OF ESTIMATING SPECIFIC YIELD
Earlier it was stated that the specific yield generally ranges between 0.1 and 0.3 (10-30 percent) and that long﻿54
GROUND-WATER HYDRAULICS
periods of pumping may be required to drain waterbearing material. Thus, in the absence of any determination, as in a rapid reconnaissance, we would not be very far off in assuming that, for supposedly long periods of draining, the specific yield of an unconfined aquifer is about 0.2—the average value between the general limits indicated.
Better estimates of specific yield—which might be slightly more or less than the average—could be obtained
from (1) careful study of the grain sizes and degree ot sorting, if logs of wells or test holes are available, (2) data from a few reliable pumping tests, (3) values obtained from the use of neutron-moisture probes (Meyer, 1962), and (4) laboratory determinations of the specific yield of disturbed samples (values of laboratory determinations are likely to be larger than those obtained in the field). Data from the sources listed could also be extrapolated to similar types of material elsewhere in the aquifer.
Table 18.—Computations of drawdowns produced at various distances from a well discharging at slated rales for 365 days from a confined aquifer
for which T = 20 ft2 day~l and S = 5X10“*
_s_
4Tt	r	r,
(ft'*)	(ft)	(ft*)
u
1
4tcT
TF(m) (ft-* day)
8 (ft) for Q (ft* day-1)
10*	2X10*	3X10*	4X10*	5X10*	6X10*	7X10*
1.71X10-9 1	1	1.71X10-*	19.61 3.98X10-*	78.1	156	234	312	391	469	547
10	102	1.71X 10“7	15.01	59.7	119	179	239	299	358	418
102	104	1.71X10-*	10.40	41.4	82.8	124	166	207	248	290
102	106	1.71 X10-*	5.80	23.1	46.2	69.3	92.4	116	139	162
2X103	4X106	6.84X10-*	4.41	17.6	35.1	52.2	70.2	87.8	105	123
4X102	1.6 X107	2.74X10-2	3.23	12.9	25.7	38.6	51.4	64.3	77.2	90.0
6X103	3.6 X107	6.16X10-*	2.27	9.0	18.0	27.0	36.0	45.0	54.0	63.0
8X103	6.4 X107	1.09X10-*	1.74	6.9	13.8	20.7	27.6	34.5	41.4	48.3
104	10s	1.71X10-*	1.35	5.4	10.8	16.2	21.6	21.0	32.4	37.8
1.5X104	2.25X10*	3.85X10-*	.73	2.9	5.8	8.7	11.6	14.5	17.4	20.3
2X104	4X10*	6.84X10-*	.39	1.6	3.2	4.8	6.4	8.0	9.6	11.2
3X104	9X10*	1.54	.10	.15	.30	.45	.60	.75	.90	1.05
4X104	1.6 X10*	2.74	.02	.08	.16	.24	.32	.40	.48	.56
Figure 35.—Family of semilogarithmic curves showing the drawdown produced at various distances from a well discharging at stated rates for 365 days from a confined aquifer for which T — 20 ft2 day-1 and <S = 5X 10~*.﻿DRAWDOWN INTERFERENCE FROM DISCHARGING WELLS
55
DRAWDOWN INTERFERENCE FROM DISCHARGING WELLS
If T and S are known, as from discharging well tests, the effect of one discharging well upon a nondischarging well, or other point, in an infinite, or at least extensive, homogeneous and isotropic aquifer is readily obtained by use of equation 47 solved for u, equation 46, and table 4, for any
distance (r) for known or assumed values of t and constant Q, or for any time t for known or assumed values of r and Q. Tables 18 and 19 show the methods of computation of the drawdowns and figures 35 and 36 illustrate the results. These examples are modified from Lohman (1965, fig. 43). (See also Theis, 1963c).
Note on tables 18 and 19 that the computations are greatly facilitated by proper arrangement of headings.
Table 19.—Computations of drawdowns produced after various times at a distance of 1,000ft from a well discharging at staled rates from a confined
aquifer for which T = 20 ft* day“* and S =6X10~6
r*S
8 (ft) for Q (ft* day *)
(day)	(day)	(day-1)	U	W(u)	(ft-2 day)	10*	2X10*	3X10*	4X10'	5X10*	6X10*	7X10*
6.25X10“*	0.2	5.0	3.13	10-2	3.98X10-3	0.0398	0.0796	0.119	0.159	0.199	0.239	0.279
	.3	3.3	2.06	5X10-2		.199	.398	.597	.796	.995	1.19	1.39
	.4	2.5	1.56	9X10-2		.358	.716	1.07	1.43	1.79	2.15	2.51
	.6	1.66	1.04	2.1X10-*		.836	1.67	2.51	3.34	4.18	5.02	5.85
	.8	1.25	7.8 X10“*	3.2X10-*		1.27	2.54	3.87	5.08	6.35	7.62	8.89
	1	1.0	6.25X10-*	4.3X10“*		1.71	3.42	5.13	6.84	8.55	10.26	11.97
	2	.5	3.13X10-*	8.7X10“*		3.46	6.92	10.38	13.84	17.30	20.76	24.22
	4	.25	1.56X10-*	1.43		5.69	11.4	17.1	22.8	28.5	34.1	39.8
	6	.166	1.04X10-*	1.79		7.12	14.2	21.4	28.5	35.6	42.7	49.8
	8	.125	7.81X10-2	2.05		8.16	16.3	24.5	32.6	40.8	49.0	57.1
	10	io-‘	6.25X10-2	2.26		9.00	18.0	27.0	36.0	45.0	54.0	63.0
	10*	io-2	6.25X10-3	4.50		17.91	35.8	53.7	71.6	89.6	108	125
	103	10-3	6.25X10-4	6.80		27.06	54.1	81.2	108	135	162	189
	104	10-4	6.25X10-5	9.10		36.22	72.4	109	145	181	217	254
Figure 36.—Family of semilogarithmic curves showing the drawdown produced after various times at a distance of 1,000 ft from a well discharging at stated rates from a confined aquifer for which T = 20 ft2 day-1 and S = 5X10-6.﻿56
GROUND-WATER HYDRAULICS
Thus, single values of S/4Tt or r2S/4T multiplied by various values of r2 or l/t, respectively, give values of u from which values of W(u) are obtained from table 5. Then, a single value of l/4xT multiplied by various values of W (u) and by Q = 103 ft3 day-1 gives the drawdowns for this discharge rate. Then the drawdowns for other values of Q are obtained by simple multiplication by 2 through 7. Note that only a few values establish the straight-line parts of the curves but that more are required for the curvilinear parts.
The examples just given are for constant discharge and variable drawdown, but other equations for different boundary conditions could be similarly used to determine drawdown interference. Thus, for example, equations 66 and 67 and table 7 could be used for discharging wells of constant drawdown and variable discharge. In these examples, discharging wells constitute hydraulic boundaries of the point-sink type; recharging wells constitute boundaries of the point-source type. Other types of boundaries are discussed in later sections.
Figures 35 and 36 show only the drawdown caused by one discharging well at a nondischarging well or point within the cone of depression. Where many discharging wells are mutually interfering with each other and with other points, such as nondischarging wells, the problem becomes much more complex and is best handled by an electric analog-model computer or by a digital computer. The drawdown interference from certain groupings of discharging wells is treated by Hantush (1964, p. 374-382).
RELATION OF STORAGE COEFFICIENT TO SPREAD OF CONE OF DEPRESSION
It has been shown (Lohman, 1965, p. 109, 110) that if equation 51 is solved for r2, there results
2.25 Tt
S Iogio_1[47r7,s/2.30Q]
CL2].
(143)
For a given set of conditions, all terms except r2 and S may be considered constant; then, using C as a constant of proportionality,
C
S
[L2].
(144)
For convenience, multiply both sides of equation 144 by x, then
As an example, equation 145 may be used to compare the area of influence, Ah in a confined aquifer having a storage coefficient of, say 5X10-5, with the area of influence, A2, in an unconfined aquifer having a specific yield of, say 0.20. Assuming that T, Q, and s are the same for both aquifers, and that t also is the same and is long enough so that «<0.01 and that the material in the cone of depression in the unconfined aquifer has had time to be drained, then
A i
A2
075X10-*
cyo.20
= 4X103.
Thus, under the assumed conditions, the area of influence in the confined aquifer is 4,000 times larger than that in the unconfined aquifer, or the ratio of the radius extending to the circumference of negligible drawdown in the confined aquifer to that in the unconfined aquifer, r\/r2, is y/4X103 = 63.2. Thus, changes in water level in a confined aquifer spread outward very rapidly from a discharging well, whereas in an unconfined aquifer changes in water level spread very slowly as gravity drainage takes place.
NOTE: Aquifer thickness 6 should be very large compared to resultant drawdown near real well
Drawdown component of
Discharging real
rawdown component of real well
Discharging well
. ‘.Aquifer
B. HYDRAULIC COUNTERPART OF REAL SYSTEM
xr2 = A = j [L2],	(145)
where A = area of influence.
Figure 37.—Idealized section views of a discharging well in an aquifer bounded by an “impermeable” barrier and of the equivalent hydraulic system in an infinite aquifer. From Ferris, Knowles, Brown, and Stallman (1962, fig. 37).﻿AQUIFER BOUNDARIES AND THEORY OF IMAGES
57
AQUIFER BOUNDARIES AND THEORY OF IMAGES
Thus far, the flow equations have all been assumed to be applicable only in aquifers of infinite or semi-infinite areal extent. Many wells are far enough from aquifer boundaries so that this assumption is satisfied reasonably well, but some wells are near boundaries, such as the relatively impermeable bedrock wall of an alluvium-filled valley, a dike, a fault, or a nearby stream or lake. Such boundaries, if close enough to a discharging well, may invalidate the results obtained by use of the flow equations unless suitable adjustments are made.
The method of images used for the solution of boundary problems in the theory of heat conduction in solids has been adapted to the solution of boundary problems in ground-water flow. In this method imagery wells or streams, referred to as images, are placed at proper locations so as to mathematically duplicate the hydraulic effect on ground-water flow caused by the real geologic or hydrologic boundary. Following heat-flow terminology, a discharging image well is regarded as a point sink, a
recharging image well as a point source. A discharging image stream or drain is regarded as a line sink, a recharging image stream as a line source. By use of various combinations of such sinks and sources, corrections for almost every conceivable type and shape of linear boundary have been made so as to permit solution of the appropriate ground-water flow equation.
We will take up a few single boundary problems involving single images. Problems involving two or more boundaries at least two of which are parallel have images extending to plus and minus infinity, somewhat like reflections from two facing parallel mirrors. For examples of single and multiple boundary problems, see Ferris, Knowles, Brown, and Stallman (1962, p. 144-166), and Brown (1953).
“IMPERMEABLE” BARRIER
Figure 37A (Ferris and others, 1962, fig. 37) shows a discharging well in an aquifer bounded on the right by a barrier of relatively impermeable material. Here it is assumed that no ground water can flow across the barrier.
Figure 38.—Generalized flow net in the vicinity of discharging real and image wells near an “impermeable” boundary.
From Ferris, Knowles, Brown, and Stallman (1962, fig. 38).﻿58
GROUND-WATER HYDRAULICS
10"s	10-4	io~3	10“2
t/r2, IN DAY PER SQUARE FOOT
Figure 39.—Effect of “impermeable” barrier on semilogarithmic plot of s versus t/r2.
The image system in the hydraulic counterpart of figure 37 A, which permits a solution of the real problem by use of the flow equations, is shown in figure 37B. Here in an assumed infinite aquifer an image well having a discharge equal to that of the real well is placed the same distance (a) from the now imaginary barrier. The dashed theoretical cones of depression of the real and image wells intersect to form a ground-water divide at the hydraulic barrier, across which no flow can take place, thus satisfying the hydraulic conditions along the barrier. The resultant real cone of depression (heavy line) is the algebraic sum of the theoretical cones of depression (dashed lines) of the real and image wells. Figure 38 depicts the flow net of the two-well system. If the image well and image flow net are removed, the flow net on the left represents the effect of the “impermeable” boundary upon the discharging well.
If the drawdown (s) in an observation well near the real
well shown in figures 37 and 38 were plotted against t or t/r1 on semilogarithmic paper, the curve would deviate downward from the theoretical straight-line plot as shown in figure 39. This shows that the effect of the barrier began to be felt at t/r2 = about 1.8 X10-4 day ft-2 and that the full effect was apparent at t/r2 = about 7.4 X10-4 day ft-2. After the full effect was apparent, the slope of the lower straight line was two times the slope of the theoretical straight line, indicating an apparent transmissivity that was half that of the true value.
LINE SOURCE AT CONSTANT HEAD-PERENNIAL STREAM
If a well in an unconfined aquifer near a large perennial stream hydraulically connected to the aquifer is pumped, obviously the cone of depression cannot extend beyond﻿AQUIFER BOUNDARIES AND THEORY OF IMAGES
59
Discharging well\|		Perennial / stream / Land surface	
• \. •.		: • • .'x		.**•**, * . * • *••'*.*•••• ••
			' ^Nonpumping water level ^
; Aquifer •'•.vs	mmi		Aquifer : . . t •
	rEHKrll-ConfiningZI-I		
—	& 2=|		
A. REAL SYSTEM
B. HYDRAULIC COUNTERPART OF REAL SYSTEM
Figure 40.—Idealized section views of a discharging well in an aquifer bounded by a perennial stream and of the equivalent hydraulic system in an infinite aquifer. From Ferris, Knowles, Brown, and Stallman (1962, fig. 35).
the stream as the water level in such a stream remains relatively constant, assuming that the well discharge is small relative to the stream discharge. Such a situation is shown in figure 40A, in which the nearly straight, partly penetrating perennial stream is shown to be straight and fully penetrating and, hence, is equivalent to a line source at constant head.
The hydraulic counterpart in an assumed infinite aquifer is shown in figure 405, where a recharging image well, or point source, has been placed on a line connecting the real and image wells at right angles to the stream, at the same distance, a, from the stream. The recharge and discharge rates, Q, are assumed equal. The resulting cone of depression (heavy solid line), which is the algebraic sum of the dashed cones of depression of the real and image wells, intersects the level of the stream, as it should. The flow net for these conditions is shown in figure 41. Note that if the image well and its flow net are removed, the flow net on the left is that of the real well obtaining water by induced infiltration from the stream.
If the drawdown (s) in an observation well near the real well shown in figures 40 and 41 were plotted against t or
t/r2 on semilogarithmic paper, the curve would deviate upward from the theoretical straight-line plot as shown in figure 42. This shows that the effect of the stream began to be felt at f/r2 = about 2.8 X 10~4 day ft-2 and that the full effect was apparent at i/r2 = about 3.5 X10-3 day ft-2. After the full effect was apparent, the slope of the upper straight line became horizontal, indicating an apparent infinite transmissivity.
One of the first applications of the image-well theory to ground-water flow was made by Theis (1941), who developed an equation and presented a graph for computing the percentage of the water pumped from a well near a stream that is diverted from the stream at a known distance from the well. (See also Glover and Balmer, 1954; Jenkins, 1968a, 1968b; Theis, 1963b; and Theis and Conover, 1963.)
APPLICATION OF IMAGE THEORY
It was evident in figure 39 that, for a discharging well in an aquifer bounded by a relatively impermeable barrier, a drawdown-time plot for an observation well near the pumped well was steepened (greater drawdown) at the value of t after the cone of depression reached the barrier, and that in figure 42, the converse was true. However, figures 39 and 42 are hypothetical straight-line curves; hence, they would hold true only when «<0.01. For larger values of u, as for small values of t, large values of r, or for most unconfined aquifers, it is necessary to plot drawdown-time curves on logarithmic paper for comparison with the Theis curve (fig. 14), for which occur similar but curvilinear deviations from the theoretical curves. Computation of T and S by the usual curve-matching procedure would then be valid only for the early data before the boundary effects changed the slope of the curve. This would offer no problem for most confined aquifers, but in an unconfined aquifer sufficient time might not have elapsed to allow for reasonably complete drainage from storage.
Ferris, Knowles, Brown, and Stallman (1962, p. 161— 164) described a method of plotting s versus t or r2/t for matching with the Theis curve (fig. 14) that permits solving for T and S and also for the distance from the discharging well to the image well, which of course is at twice the distance to the actual boundary. If the boundary is concealed, as a hidden fault, three or more observation wells are required to locate the boundary. (See Ferris and others, 1962, p. 164-166; Moulder, 1963.)
A similar but much simpler method for the solution of single-boundary problems involving either a source or a sink was devised by Stallman (1963b). From figures 37 and 40, it is evident that if s0 is the drawdown in an observation well, and sp and s, are the components of that drawdown caused, respectively, by the pumped (real) well and by the discharging or recharging image well, then s„ is the alge-﻿60
GROUND-WATER HYDRAULICS
Figure 41.—Generalized flow net in the vicinity of a discharging well dependent upon induced infiltration from a nearby stream.
From Ferris, Knowles, Brown, and Stallman (1962, fig. 36).
braic sum of sp and st, or
S0 — SpdzS, [T/].
(146)
For this condition, equations 46 and 47 may be rewritten, respectively,
So= £t CWr(«)p±Wr(«)<]= E W{U) [L],
and
and
rp*S Up~ ATt
Ui-
rfS
ATt ’
(147)
(148)
in which rp is the distance from the pumped well to the
observation well, and rt is the distance from the observation well to the image well. In equations 148, up and Ui are seen to be related thus:
or
where
(149)
(150)
Note: The K in equations 149 and 150 of Stallman is simply a constant of proportionality and is not to be confused with the K used previously to symbolize hydraulic conductivity.
Stallman plotted a family of logarithmic type curves of E W (u) versus l/up for many values of his K = r;/rp, as shown on plate 9. For an aquifer in which a single boundary﻿“SAFE YIELD”
61
Figure 42.—Effect of recharging stream on semilogarithmic plot of s versus f/r2.
may be suspected, the drawdown (s0) versus time (<) in an observation well near the pumped well is plotted on logarithmic paper of the same scale as plate 9 (drawdown increasing upward at left, time increasing to right). The plot of observed data is superposed on the family of type curves, as in matching the Theis type curve, and a match point is found for values of J2 W (u) and l/up corresponding to values of s„ and t, respectively. Equation 147 can then be solved for T, after which equation 148 can be solved for S by rewriting equations 147 and 148 for solutions of T and S, respectively. From the value of K for the particular modified curve followed by the observed data, the value of rt can be computed from equation 150.
If a suspected boundary is absent, and, therefore, the aquifer is extensive, the observed data should fit the heavy parent type curve, which is the Theis type curve. If a boundary exists, the observed data will follow the parent curve until the boundary is first “felt,” then it will deviate from the parent curve along one of the modified curves.
Deviations below the parent curve are caused by recharging images; those above, by discharging images.
“SAFE YIELD”
The term “safe yield” has about as many definitions as the number of people who have defined it. There are questions as to the validity of the term, but if it is valid there remains the question as to who should determine it— ground-water hydrologists or ground-water managers? Let us review briefly the history, meaning, and limitations of the term.
The term “safe yield” seemingly was first defined by Meinzer (1920, p. 330) as “* * * the rate at which the ground water can be withdrawn year after year, for generations to come, without depleting the supply.” Later Meinzer (1932, p. 99) modified his definition to “The ‘safe yield’ of an underground reservoir [is the] practicable rate of withdrawing water from it perennially﻿62
GROUND-WATER HYDRAULICS
for human use * * *.” Although there was nothing wrong with Meinzer’s early definitions, they seemingly did not wholly satisfy all ground-water hydrologists, for beginning about 20 years later many began redefining the concept in more and more precise terms to suit themselves or to suit the particular ground-water conditions with which they were concerned. For a r<5sum6 of many of these definitions, see Kazmann (1951, 1956), Hantush (1955, p. 71), and Todd (1959, p. 200-218).
As stated by Kazmann (1956, p. 1103-2), “The thought became current that the ‘safe yield’ of an aquifer was surely determinable in advance of ground-water development—or even after development had begun.” I might add that the thought also became current that one could put a number on the safe yield of a ground-water reservoir regardless of its method of development. However, as stated by Thomas (1951, p. 262):
In a ground-water reservoir where the water is unconfined in certain areas (recharge areas) and under artesian pressure in other places, the safe yield will be a certain quantity if it is specified that all withdrawals must be by flow from artesian wells, a larger quantity if it is permissible to pump water from depths as great as 50 feet, and still more if allowable pumping lifts are as much as 500 feet. But the safe yield will vary also depending upon the locations of wells and the type of wells constructed. Assuming that the well construction and spacing of individual wells are suitable for maximum recovery of water, the safe yield will be a certain quantity if all wells are 40 miles from the recharge area, considerably greater if they are about 10 miles away, and still more if they are adjacent to or within the recharge area.
The multiplicity and looseness of definitions led Kazmann to title his 1956 paper “ ‘Safe Yield’ in Ground-Water Development, Reality or Illusion?,” and led Thomas (1951, p. 261) to say: “ ‘Safe yield.’ This term, originated by hydrologists, may well prove awkward for them because of the variety of interpretations possible. ‘Safe yield’ is an Alice-in-Wonderland term which means whatever its user chooses.”
I have a definition which I taught at U.S. Geological Survey Ground Water Short Courses beginning in 1952, namely, “The amount of ground water one can withdraw without getting into trouble.” “Withdraw” may mean from flowing or pumped wells, and it may mean continuously, as for many industrial or municipal supplies, or seasonally, as for irrigation. “Trouble” may mean anything under the sun; such as (1) running out of water,
(2)	drawing in salt water, or other undesirable water,
(3)	getting shot, or shot at, by an irate nearby wellowner or landowner, (4) getting sued by a less irate neighbor, or (5) getting sued for depleting the flow of a nearby stream for which the water rights have been appropriated. My definition may sound facetious to some, but remembering that I would not attempt to put a number on it before development or in the early stages of development, espe-
cially if I did not know where and how the withdrawal would be made, it actually makes more sense than many definitions, does not differ significantly from Meinzer’s original definitions, and is very close to the later definition of Todd (1959, p. 200): “The safe yield of a ground water basin is the amount of water which can be withdrawn from it annually without producing an undesired result.”
To determine whether or not a desired quantity and quality of water can be withdrawn from a given ground-water reservoir generally requires an adequate knowledge of the geologic framework and its plumbing system plus the application of philosophy, common sense, and knowledge of the proposed type of development that owners or managers have in mind. As problems become more and more complex, however, such as those involving large investments in land and wells, withdrawal of water from both streams and wells that tap a common source, or conflicts in water rights, then the solution may require highly detailed study. The modern approach is for the hydrologist to acquire sufficient detail concerning the combined ground- and surface-water system so aquifer response can be predicted by electric-analog or mathematical models. Then management, such as state or local water-conservation agencies, within the framework of prevailing laws or regulations, may test the response of the system to various assumed stresses and thereby select the most desirable or equitable distribution of available water. Thus the role of the hydrologist is to gather and present the facts; the water manager determines who shall have how much water and from what source. In so doing, the manager generally requires and obtains considerable continuing assistance from the hydrologist. (See Wood and Gabrysch, 1965; Walton and Prickett, 1963; Moore and Wood, 1967.)
In the sections that follow, some additional references will be made to safe yield in discussing examples of different types of ground-water reservoirs.
THE SOURCE OF WATER DERIVED FROM WELLS
Under the above title Theis (1940) stated concisely the hydrologic principles upon which depend much of our present quantitative approach to ground-water problems. The statements that follow are summarized from these principles.
The essential factors that determine the response of aquifers to development by wells are:
1.	Distance to, and character of, the recharge.
2.	Distance to the locality of natural discharge.
3.	Character of the cone of depression in the aquifer,
which depends upon the values of T (which contains K and b) and S.﻿THE SOURCE OF WATER DERIVED FROM WELLS
63
Prior to development by wells, aquifers are in a state of dynamic equilibrium, in that over long periods of time recharge and discharge virtually balance. Discharge from wells upsets this balance by producing a loss from storage, and a new state of dynamic equilibrium cannot be reached until there is no further loss from storage. This can only be accomplished by:
1.	Increase in recharge (natural or artificial).
2.	Decrease in natural discharge.
3.	A combination of 1 and 2.
The above statements were put into equation form with terms having the dimensions L3T~l by Hilton H. Cooper, Jr., U.S. Geological Survey (written commun., April 1967). I have added the Ah/ At and have assigned to the terms the dimensions LT~l as follows:
Ah
R+AR = D+AD+q+S— [L71-1],	(151)
At
where
R - recharge rate per unit area,
AR = change in recharge rate per unit area,
D = natural discharge rate per unit area,
AD = change in discharge rate per unit area, q = rate of withdrawal from wells per unit area, and
_ Ah	. ,
S — = rate of change in storage per unit area.
At
Assuming that additions to the aquifer (left-hand terms in eq. 151) are positive, that withdrawals from the aquifer (right-hand terms in eq. 151) are negative, and that over the years R~D, then solving equation 151 for q, we obtain
q&AR-(-AD)-(-S^j	[LT"1].	(152)
If dynamic equilibrium can be reestablished, there will
Ah
be no further withdrawals from storage, so that S —
At
and equation 152 becomes
qttAR-(-AD) [LT~l~\.	(153)
We will see in the last section that equation 153 is applicable only to certain types of aquifer systems. For aquifers in which a new dynamic equilibrium is not attainable, continued withdrawal from storage may be greater than changes in recharge or discharge rates, and storage may be the principal or sole source of water. Under such conditions equation 152, or a part of it, is applicable. If we wish to know the total volumes of water involved, each term in equations 152 or 153 must be multiplied by the area (A) over which the changes occur.
Before taking up examples of different types of aquifers, let us review the following summary statements by Theis (1940, p. 280), which are important enough to quote completely:
1.	All water discharged by wells is balanced by a loss of water
somewhere.
2.	This loss is always to some extent and in many cases largely
from storage in the aquifer. Some ground water is always mined. The reservoir from which the water is taken is in effect bounded by time and by the structure of the aquifer as well as by material boundaries. The amount of water removed from any area is proportional to the drawdown, which in turn is proportional to the rate of pumping. Therefore, too great concentration of pumping in any area is to be discouraged and a uniform areal distribution of development over the area where the water is shallow should be encouraged, so far as is consistent with soil and marketing or other economic conditions.
3.	After sufficient time has elapsed for the cone to reach the area
of recharge, further discharge by wells will be made up at least in part by an increase in the recharge if previously there has been rejected recharge. If the recharge was previously rejected through transpiration from nonbenefieial vegetation, no economic loss is suffered. If the recharge was rejected through springs or refusal of the aquifer to absorb surface waters, rights to these surface waters may be injured.
4.	Again, after sufficient time has elapsed for the cone to reach the
areas of natural discharge, further discharge by wells will be made up in part by a diminution in the natural discharge. If this natural discharge fed surface streams, prior rights to the surface water may be injured.
5.	In most artesian aquifers—excluding very extensive ones, such
as the Dakota sandstone—little of the water is taken from storage. In these aquifers, because the cones of depression spread with great rapidity, each well in a short time has its maximum effect on the whole aquifer and obtains most of its water by increase of recharge or decrease of natural discharge. Such an artesian basin can be treated as a unit, as is done in the New Mexico ground-water law, and the laws of some other Western States that follow this law. In large nonartesian aquifers, where pumping is done at great distances from the localities of intake or outlet, however, the effects of each well are for a considerable time confined to a rather small radius and the water is taken from storage in the vicinity of the well. Hence these large ground-water bodies cannot be considered a unit in utilizing the ground water. Proper conservation measures will consider such large aquifers to be made up of smaller units, and will attempt to limit the development in each unit. Such procedure would also be advisable, although not as necessary, in an artesian aquifer.
6.	The ideal development of any aquifer from the standpoint of the
maximum utilization of the supply would follow these points:
(a)	The pumps should be placed as close as economically pos-
sible to areas of rejected recharge or natural discharge where ground water is being lost by evaporation or transpiration by nonproductive vegetation, or where the surface water fed by, or rejected by, the ground water cannot be used. By so doing this lost water would be utilized by the pumps with a minimum lowering of the water level in the aquifer.
(b)	In areas remote from zones of natural discharge or re-
jected recharge, the pumps should be spaced as uniformly as possible throughout the available area. By so﻿64
GROUND-WATER HYDRAULICS
doing the lowering of the water level in any one place would be held to a minimum and hence the life of the development would be extended.
(c) The amount of pumping in any one locality would be limited. For nonartesian aquifers with a comparatively small areal extent and for most artesian aquifers, there is a perennial safe yield equivalent to the amount of rejected recharge and natural discharge it is feasible to utilize. If this amount is not exceeded, the water levels will finally reach an equilibrium stage. If it is exceeded, water levels will continue to decline.
In localities developing water from nonartesian aquifers and remote from areas of rejected recharge or natural discharge, the condition of equilibrium connoted by the concept of perennial safe yield may never be reached in the predictable future and the water used may all be taken from storage. If pumping in such a locality is at a rate that will result in the course of 10 years in a lowering of water level to a depth from which it is not feasible to pump, pumping at half this rate would not cause the same lowering in 100 years. Provided there is no interference by pumping from other wells, in the long run much more water could be taken from the aquifer at less expense.
Thorough knowledge of these hydrologic principles plus the gathering and proper interpretation of the pertinent field data should permit the solution of virtually any quantitative ground-water problem, although in some areas the solution may be very difficult.
EXAMPLES OF AQUIFERS AND THEIR DEVELOPMENT
Let us see how the above principles and equations 152 and 153 apply to several types of aquifers. In the real situations the water would be withdrawn from many wells, but for simplicity only one or two wells are shown in the examples.
VALLEY OF LARGE PERENNIAL STREAM IN HUMID REGION
Setting.—Thick, permeable alluvium filling old valley cut into shale; permeable channel beneath large perennial stream; shallow water table; many phreatophytes; moderately heavy precipitation (fig. 43).
Figure 43.—Development of ground water from valley of large perennial stream in humid region.
Sources of water.— (1) Withdrawal from storage which creates cone of depression. (2) Salvaged rejected recharge: Lowering of water table provides more room for recharge from precipitation and, hence, reduces or prevents surface runoff to stream. (3) Salvaged natural discharge by (a) lowering water table beneath phreatophytes and (b) decreasing gradient toward stream thus decreasing discharge of ground water into stream. Sources (2) and (3) may suffice for small to moderately large ground-water developments. (4) Recharge directly from stream: Large withdrawal will cause cone of depression to spread until it reaches the stream, then gradient will be reversed and stream water will move toward wells.
Operation of system.—In applying equation 152 to such a development, we assume that RttD and that equilibrium
Ah
has been reestablished so that S — ~0; then
At
qttAR-(-AD) [LT-1],
equation 153, in which AR may suffice for moderately large developments, but AD, capture of stream water, becomes the principal source for large developments.
Limitations.—The amount of possible withdrawal is virtually limited to the streamflow. Lowering of the water table may impair or destroy useful phreatophytes or interfere with other ground-water developments, and the reduction in streamflow may interfere with the established rights of others.
VALLEY OF EPHEMERAL STREAM IN SEMIARID REGION
Setting.—Moderately thick, permeable alluvium filling old valley cut into shale; permeable channel beneath ephemeral stream; water table beneath stream channel and below reach of all vegetation except a few cottonwood trees along banks of stream; precipitation, about 15 in. a year; stream dry most of year but floods after heavy rains or cloudbursts in high headwater region (fig. 44).
Figure 44.—Development of ground water from valley of ephemeral stream in semiarid region.﻿THE SOURCE OF WATER DERIVED FROM WELLS
65
Sources of water.—(1) Withdrawal from storage which creates cone of depression. (2) Salvaged rejected recharge from precipitation—none; there is more than enough room for the meager recharge from low precipitation. (3) Salvaged natural discharge—very small; the only phreat-ophytes are a few cottonwoods along banks of stream. (4) Recharge directly from stream: May be very large from floods, provided water table is kept sufficiently lowered by pumping to provide room for all or most of the floodwater, which percolates rapidly downward through the permeable channel. Thus, the system functions effectively as an evaporation-free flood-control reservoir.
Operation of system.—In applying equation 152 to such a development, we assume that AD^O and that equilibrium cannot be reestablished; then
[LT-1],
in which AR, capture of floodwater with attendant in-
crease in ground-water storage

becomes the
principal source of water. Bewteen floods, when AR = 0,
loss from storage
(-£)‘
is the sole source. This proce-
dure has been successful in some ephemeral stream valleys of eastern Colorado, where water is pumped seasonally for irrigation.
Limitations.— (1) The relation of flood frequency to water needs. (2) The water table must be kept low enough (by pumping) to provide adequate storage space for floodwaters, yet it must be high enough for successful or economical well operation.
CLOSED DESERT BASIN
Setting.—Large desert basin receiving 3-5 in. of precipitation annually, surrounded by high mountains that receive 20-30 in. of precipitation (fig. 45). Aquifer comprises thick bolson deposits built up by coalescing alluvial fans, coarse and permeable near mountains, fine grained and much less permeable at and near playa. Water table at or near surface at playa, deep near mountains. Streams, all ephemeral. Phreatophytes, only near playa in middle of basin.
Sources of water.— (1) Withdrawal from storage creates cone of depression. (2) Salvaged rejected recharge from precipitation—little or none; virtually all the precipitation that falls in the valley evaporates or is transpired in and near playa. Recharge comes mainly at irregular intervals from small ephemeral streams that head in surrounding mountains; incompletely saturated fan areas absorb much of streamflow, but some flood flows reach playa, where
Figure 45.—Development of ground water from bolson deposits in closed desert basin.
water evaporates rapidly. (3) Salvaged natural discharge by (a) development near playa (well A), may be large, by lowering water table below reach of evaporation and transpiration by phreatophytes and (b) development along border of basin (well B), where some discharge toward playa may be salvaged by reducing the gradient.
Water near playa (well A) generally is too highly mineralized for most uses, and materials have low permeability. Development of water of better quality in bordering areas (well B) may be limited in quantity and by pumping lift; however, withdrawals from bordering areas can be greatly increased by the construction of retention dams in canyons of bordering mountains so that flood-waters that normally reach and temporarily flood playa may be stored and released slowly for recharge into the heads of alluvial fans, as has been done in California and perhaps elsewhere.
Operation of system.—Assuming that AD is small but finite and that AR by release from retention dams is fairly constant, then equilibrium can be reestablished
and equation 152 becomes equation 153,
qttAR — ( — AD) [LT-1],
in which AR is the principal source.
Without the retention dams, AR will not be constant and, for large withdrawals, equilibrium cannot be reestablished, so equation 152, for well B, becomes
ff«Aft-(-AD)-	[DT-1].
SOUTHERN HIGH PLAINS OF TEXAS AND NEW MEXICO
Setting.—Remnant of High Plains sloping gently from west to east, cut off from external sources of water by﻿500 ft
66
GROUND-WATER HYDRAULICS
Figure 46.—Development of ground water from southern High Plains of Texas and New Mexico.
escarpments upstream and downstream (fig. 46). Water is in Tertiary deposits (Ogallala Formation), which have a maximum thickness of about 600 ft and an average thickness of about 300 ft. The material is moderately permeable and rests on relatively impermeable rocks. The recharge, which is derived solely from scanty precipitation, is estimated to range from 3^o t° XA. in- per year, or of the order of 3X109 ft3 year-1. The natural discharge, of the same estimated order, is from seeps and springs along the eastern escarpment. The storage of ground water prior to development was very large, of the order of 2X1013 ft3. The withdrawal by pumping has increased from about 4X109 ft3 year-1 in 1934 to more than 2X1011 ft3 year-1 and is used mainly for irrigation.
Sources of water.— (1) Withdrawal from storage creates cone of depression.. (2) Salvaged rejected recharge—virtually none; water table lies 50 ft or more beneath surface in most of the area, so that there is more than ample space for all possible natural recharge. (3) Salvaged natural discharge—virtually none; gradient toward eastern escarpment has been virtually unchanged, but even if all discharge could be salvaged, it would only amount to 1 or 2 percent of the withdrawal rate.
Operation of system.—Assuming that A 72^0 and AD~0, equation 152 becomes
which means that virtually all water is being mined from storage and that equilibrium is not being reestablished. Because ground water is a mineral that is being mined without hope of natural replacement, the Federal courts have affirmed the right of eligible ground-water users (those who have, in effect, paid for the wTater in the form of land prices higher than that of land lacking a good supply) to claim a depletion allowance for Federal income-tax purposes.
Possible remedial measures.—(1) In the Texas section of the region, a water conservation district, to which most
affected counties belong, has sought to retard depletion by encouraging water-saving practices and by requiring proper spacing of wells. In the New Mexico section, the State law based on prior appropriation is applied by allowing, in a particular area, appropriations until the remaining supply is judged sufficient for an additional period (such as 30 or 40 years) to enable recovery of investments in land and wells and the creation of wealth through extraction of this “minable” resource; the area is then declared fully appropriated and additional appropriations are not permitted. (2) Artificial recharge from ephemeral ponds through recharge wells has been tried but so far has not been successful over long periods. Had it been successful, it would have been sufficient only to retard depletion. (3) The importation of water by lifting it several hundred feet from the Canadian River was considered, but was judged too costly. The feasibility of importing water from the distant Mississippi or Missouri River is now (1971) being considered to alleviate water shortages in this and other parts of the High Plains.
GRAND JUNCTION ARTESIAN BASIN, COLORADO
There are three artesian aquifers in the Grand Junction artesian basin (Lohman, 1965), but for simplicity only one, the Jurassic Entrada Sandstone, is taken up here (fig. 47). Conditions here are typical of artesian aquifers of low permeability.
Setting.—Aquifer is fine-grained sandstone partly cemented with calcium carbonate, about 150 ft thick. T = 20 ft2 day-1, <S = 5X10-6. Precipitation is about Ifi inches per year. Recharge occurs only where outcrops are in contact with the alluvium of small ephemeral streams. The alluvium remains partly saturated for short periods after streamflow. Natural discharge is very small and is limited to upward leakage through 500 to 1,000 ft of
Figure 47.—Development of ground water from the Grand Junction artesian basin, Colorado.﻿REFERENCES CITED
67
relatively impermeable siltstone and mudstone. The artesian head before development was dependent in part upon the local topography but was as much as 160 ft above land surface.
Sources of water.— (1) Withdrawal from artesian storage (no unwatering) creates large, overlapping cones of depression. (2) Salvaged rejected recharge—virtually none; movement of water from already saturated recharge areas is greatly restricted by very low transmitting capacity of aquifer. (3) Salvaged natural discharge—very small; limited to upward leakage through confining beds of very low permeability.
Operation of system.—Assuming that AA~0 and AD~0, as in the High Plains, equation 152 becomes
«*-(-«£)
which means that virtually all water is being “mined” from artesian storage and that equilibrium cannot be reestablished.
However, there is a significant difference between the mining of water in the High Plains and in the Grand Junction artesian basin. The Ogallala Formation has a specific yield of perhaps 0.15, so for each foot of decline in water level, each cubic foot of drained water-bearing material yields about 0.15 ft3 of water. For each foot of decline in head, 1 square foot of the Entrada Sandstone yields only about 5 X10-5 ft3 of water. Thus it is perhaps fair to say that, in the High Plains, it is mainly the water that has been mined; in the Grand Junction artesian basin, it is mainly the artesian head that has been mined, for the aquifer is still saturated.
Possible remedial measures.—Most of the water withdrawn from the Entrada Sandstone to date has been used for domestic purposes, either by piping to nearby homes or by hauling to the cisterns of other rural residents. Now most rural residents have been supplied by water piped from distant surface sources. If the draft on the wells is thereby reduced sufficiently, the decline in artesian head should be arrested somewhat and eventually the head may slowly recover (Lohman, 1965, p. 122).
REFERENCES CITED
American Petroleum Institute, 1942, Standard procedure for determining permeability of porous media [2d ed.]: Am. Petroleum Inst. Code 27, 21 p.
Athy, L. F., 1930, Density, porosity, and compaction of sedimentary rocks: Am. Assoc. Petroleum Geologists Bull., v. 14, no. 1, p. 1-24.
Bedinger, M. S., and Emmett, L. F., 1963, Mapping transmissibility of alluvium in the lower Arkansas River valley, Arkansas, in Short papers in geology and hydrology: U.S. Geol. Survey Prof. Paper 475-C, p. C188-C190.
Bedinger, M. S., and Reed, J. E., 1964, Computing stream-induced ground-water fluctuation, in Geological survey research 1964: U.S. Geol. Survey Prof. Paper 501-B, p. B177-B180.
Bennett, R. R., 1962, Flow net analysis, in Ferris, J. G., Knowles, D. B., Brown, R. H., and Stallman, R. W., Theory of aquifer tests: U.S. Geol. Survey Water-Supply Paper 1536-E, p. 139-144.
Bennett, R. R., and Meyer, R. R., 1952, Geology and ground-water resources of the Baltimore area [Maryland]: Maryland Dept. Geology, Mines and Water Resources Bull. 4, 573 p.
Boulton, N. S., 1954a, Unsteady radial flow to a pumped well allowing for delayed yield from storage: Internat. Assoc. Sci. Hydrology Pub. 37, p. 472-477.
------- 1954b, The drawdown of the water table under nonsteady
conditions near a pumped well in an unconfined formation: Inst. Civil Engineers Proc. [London], pt. 3, p. 564-579.
------- 1963, Analysis of data from non-equilibrium pumping tests
allowing for delayed yield from storage: Inst. Civil Engineers Proc. [London], v. 26, p. 469-482.
------- 1964, Discussion of “Analysis of data from non-equilibrium
pumping tests allowing for delayed yield from storage” by N. S. Boulton: Inst. Civil Engineers Proc. [London], v. 28, p. 603-610. [Discussions by R. W. Stallman, W. C. Walton, and J. Ineson and reply by author.]
Brown, R. H., 1953, Selected procedures for analyzing aquifer test data: Am. Water Works Assoc. Jour., v. 45, no. 8, p. 844-866.
------- 1963, Estimating the transmissibility of an artesian aquifer
from the specific capacity of a well, in Bentall, Ray, compiler, Methods of determining permeability, transmissibility, and drawdown: U.S. Geol. Survey Water-Supply Paper 1536-1, p. 336-338.
Casagrande, Arthur, 1937, Seepage through dams: Harvard Graduate School Eng. Pub. 209.
Cooper, H. H., Jr., 1963, Type curves for nonsteady radial flow in an infinite leaky artesian aquifer, in Bentall, Ray, compiler, Shortcuts and special problems in aquifer tests: U.S. Geol. Survey Water-Supply Paper 1545-C, p. C48-C55.
Cooper, H. H., Jr., and Jacob, C. E., 1946, A generalized graphical method for evaluating formation constants and summarizing well-field history: Am. Geophys. Union Trans., v. 27, no. 4, p. 526-534.
Cooper, H. H., Jr., Bredehoeft, J. D., and Papadopulos, I. S., 1967, Response of a finite-diameter well to an instantaneous charge of water: Water Resources Research, v. 3, no. 1, p. 263-269.
Dagan, G., 1967, A method of determining the permeability and effective porosity of unconfined anisotropic aquifers: Haifa, Israel, Hydraulics Lab. P. N. 1/1967, 49 p.
Darcy, Henry, 1856, Les fontaines publiques de la ville de Dijon: Paris, Victor Dalmont, 647 p.
Dupuit, J., 1848, Etudes theoriques et practiques sur le mouvement des eaux courantes: Paris, Carilian-Goeury et V. Dalmont, 275 p.
Ferris, J. G., 1950, Quantitative method for determining ground-water characteristics for drainage design: Agr. Eng., v. 31, no. 6, p. 285-291.
Ferris, J. G., Knowles, D. B., Brown, R. H., and Stallman, R. W., 1962, Theory of aquifer tests: U.S. Geol. Survey Water-Supply Paper 1536-E, p. 69-174.
Forchheimer, Philipp, 1930, Hydraulik [3d ed.]: Leipzig and Berlin, Teubner.
Gilluly, James, and Grant, U. S., 1949, Subsidence in the Long Beach Harbor area, California: Geol. Soc. America Bull., v. 60, p. 461-529.﻿68
GROUND-WATER HYDRAULICS
Glover, R. E., and Balmer, C. G., 1954, River depletion resulting from pumping a well near a river: Am. Geophys. Union Trans., v. 35, p. 468-470.
Hagen, G. H. L., 1839, Ueber die Bewegung des Wassers in engen cylindrischen Rohren: Annalen Physik u. Chemie [Leipzig], v. 36, p. 423-442.
Hantush, M. S., 1955, Preliminary quantitative study of the Roswell ground-water reservoir, New Mexico: New Mexico Inst. Mining and Technology, 113 p.
------- 1956, Analysis of data from pumping tests in leaky aquifers:
Am. Geophys. Union Trans., v. 37, no. 6, p. 702-714.
------- 1959, Nonsteady flow to flowing wells in leaky aquifer: Jour.
Geophys. Research, v. 64, no. 8, p. 1043-1052.
------- 1960, Modification of the theory of leaky aquifers: Jour.
Geophys. Research, v. 65, no. 11, p. 3713-3725.
------- 1961, Tables of the function H(u, p) = f —
y
(p-\/u	\
—.	I dy: New Mexico Inst. Mining and Tech-
Vy(y-u)/
nology, Prof. Paper 103, 14 p.
------- 1964, Hydraulics of wells, in Chow, Yen Te, ed., Advances in
hydroscience, volume 1: New York, Academic Press Inc., p. 281-442.
Hantush, M. S., and Jacob, C. E., 1954, Plane potential flow of ground water with linear leakage: Am. Geophys. Union Trans., v. 35, no. 6, p. 917-936.	-
------- 1955, Nonsteady radial flow in an infinite leaky aquifer:
Am. Geophys. Union Trans., v. 36, no. 1, p. 95-100.
Hedberg, H. D., 1936, Gravitational compaction of clays and shales: Am. Jour. Sci., v. 31, p. 241-287.
Hubbert, M. K., 1940, The theory of ground-water motion: Jour.
Geology, v. 48, no. 8, pt. 1, p. 785-944.
Hurr, R. T., 1966, A new approach for estimating transmissibility from specific capacity: Water Resources Research, v. 2, no. 4, p. 657-664.
Ingersol, R. I., Zobel, O. J., and Ingersol, A. C., 1954, Heat conduction, with engineering, geological, and other applications: Madison, Wisconsin Univ. Press, 325 p.
Jacob, C. E., 1940, On the flow of water in an elastic artesian aquifer: Am. Geophys. Union Trans., pt. 2, p. 574-586.
------- 1943, Correlation of ground-water levels and precipitation
in Long Island, New York: Am. Geophys. Union Trans., v. 24, pt. 2, p. 564-573.
------- 1946, Radial flow in a leaky artesian aquifer: Am. Geophys.
Union Trans., v. 27, no. 2, p. 198-205.
------- 1947, Drawdown test to determine effective radius of artesian well: Am. Soc. Civil Engineers Trans., v. 112, p. 1047-1070.
------- 1963a, Determining the permeability of water-table aquifers, in Bentall, Ray, compiler, Methods of determining permeability, transmissibility, and drawdown: U.S. Geol. Survey Water-Supply Paper 1536-1, p. 245-271.
------- 1963b, Correction of drawdowns caused by a pumped well
tapping less than the full thickness of an aquifer, in Bentall, Ray, compiler, Methods of determining permeability, transmissibility, and drawdown: U.S. Geol. Survey Water-Supply Paper 1536-1, p. 272-292.
Jacob, C. E., and Lohman, S. W., 1952, Nonsteady flow to a well of constant drawdown in an extensive aquifer: Am. Geophys. Union Trans., v. 33, p. 559-569.
Jaeger, J. C., 1942, Heat conduction in a wedge, or an infinite cylinder whose cross section is a circle or sector of a circle: Philos. Mag., ser. 7, v. 33, no. 222, p. 527-536.
Jenkins, C. T., 1963, Graphical multiple-regression analysis of aquifer tests, in Short papers in geology and hydrology: U.S. Geol. Survey Prof. Paper 475-C, p. C198-C201.
------ 1968a, Techniques for computing rate and volume of stream
depletion of wells: Ground Water, v. 6, no. 2, p. 37-46.
------ 1968b, Electric-analog and digital-computer model analyses
of stream depletion by wells: Ground Water, v. 6, no. 6, p. 27-34.
Kazmann, R. G., 1951, The role of aquifers in water supply: Am. Geophys. Union Trans., v. 32, no. 2, p. 227-230.
------ 1956, “Safe yield” in ground-water development, reality or
illusion?: Am. Soc. Civil Engineers Proc., Irrig. Drainage Div. Jour., v. 82, no. IR3, p. 1103-1-1103-12.
Leggette, R. M., 1936, Ground water in northwestern Pennsylvania: Penna. Geol. Survey Bull. W-3, 215 p.
Lohman, S. W., 1936, Geology and ground-water resources of the Elizabeth City area, North Carolina: U.S. Geol. Survey Water-Supply Paper 773-A, 57 p.
------ 1961, Compression of elastic artesian aquifers, in Short
papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-B, p. B47-B49.
------ 1963, Method for determination of the coefficient of storage
from straight-line plots without extrapolation, in Bentall, Ray, compiler, Shortcuts and special problems in aquifer tests: U.S. Geol. Survey Water-Supply Paper 1545-C, p. C33-C37.
------ 1965, Geology and artesian water supply of the Grand
Junction area, Colorado: U.S. Geol. Survey Prof. Paper 451, 149 p.
Meinzer, O. E., 1920, Quantitative methods of estimating ground-water supplies: Geol. Soc. America Bull., v. 31, p. 329-338.
------ 1923, Outline of ground-water hydrology, with definitions:
U.S. Geol. Survey Water-Supply Paper 494, 71 p.
------ 1928, Compressibility and elasticity of artesian aquifers:
Econ. Geology, v. 23, p. 263-291.
------ 1932, Outline of methods for estimating ground-water supplies: U.S. Geol. Survey Water-Supply 638-C, 45 p.
Meinzer, O. E., and Hard, H. H., 1925, The artesian water supply of the Dakota Sandstone in North Dakota, with special reference to the Edgeley quadrangle, in Contributions to the hydrology of the United States, 1923-24: U.S. Geol. Survey Water-Supply Paper 520, p. 73-95.
Meyer, R. R., 1963, A chart relating well diameter, specific capacity, and the coefficient of transmissibility and storage, in Bentall, Ray, compiler, Methods of determining permeability, transmissibility, and drawdown: U.S. Geol. Survey Water-Supply Paper 1536-1, p. 338-340.
Meyer, W. R., 1962, Use of a neutron-moisture probe to determine the storage coefficient of an unconfined aquifer, in Short papers in geology, hydrology, and topography: U.S. Geol. Survey Prof. Paper 450-E, p. El 74-El 76.
Moore, J. E., and Wood, L. A., 1967, Data requirements and preliminary results of an analog-model evaluation—Arkansas River valley in eastern Colorado: Ground Water, v. 5, no. 1, p. 20-23.
Moulder, E. A., 1963, Locus circles as an aid in the location of a hydrogeologic boundary, in Bentall, Ray, compiler, Shortcuts and special problems in aquifer tests: U.S. Geol. Survey Water-Supply Paper 1545-C, p. C110-C115.
Norris, S. E., and Fidler, R. E., 1966, Use of type curves developed from electric analog studies of unconfined flow to determine the vertical permeability of an aquifer at Piketown, Ohio: Ground Water, v. 4, no. 3, p. 43—48.
Nutting, P. G., 1930, Physical analysis of oil sands: Am. Assoc. Petroleum Geologists Bull., v. 14, p. 1337-1349.
Papadopulos, I. S., 1963, Preparation of type curves for calculating T/S of a wedge-shaped aquifer, in Short papers in geology and hydrology: U.S. Geol. Survey Prof. Paper 475-B, p. B196-B198.﻿REFERENCES CITED
69
Pinder, G. F., Bredehoeft, J. D., and Cooper, H. H., Jr., 1969, Determination of aquifer diffusivity from aquifer response to fluctuations in river stage: Water Resources Research, v. 5, no. 4, p. 850-855.
Piper, A. M., 1933, Notes on the relation between the moisture-equivalent and the specific retention of water-bearing materials: Am. Geophys. Union Trans., 14th Ann. Mtg., p. 481-487.
Poiseuille, J. L. M., 1846, Experimental investigations on the flow of liquids in tubes of very small diameter: Acad. Royal Sci. et Inst. France, Math. Phys. Sci. Mem., v. 9, p. 433-543.
Poland, J. F., and Evenson, R. E., 1966, Hydrogeology and land subsidence, great Central Valley, California: California Div. Mines Bull. 190, p. 239-247.
Powell, W. J., 1958, Ground-water resources of the San Luis Valley, Colorado: U.S. Geol. Survey Water-Supply Paper 1379, 284 p.
Rorabaugh, M. I., 1960, Use of water levels in estimating aquifer constants in a finite aquifer: Internat. Assoc. Sci. Hydrology Pub. 52, p. 314-323.
------ 1964, Estimating changes in bank storage and ground-water
contribution to streamflow: Internat. Assoc. Sci. Hydrology Pub. 63, p. 432-441.
Skibitzke, H. E., 1958, An equation for potential distribution about a well being bailed: U.S. Geol. Survey open-file rept.
Slichter, C. S., 1899, Theoretical investigations of the motion of ground waters: U.S. Geol. Survey 19th Ann. Rept., pt. II-C, p. 295-384.
Southwell, R. V., 1940, Relaxation methods in engineering science: London, Oxford Univ. Press.
------ 1946, Relaxation methods in theoretical physics: London,
Oxford Univ. Press.
Stallman, R. W., 1956, Numerical analysis of regional water levels to define aquifer hydrology: Am. Geophys. Union Trans., v. 37, no. 4, p. 451-460.
------ 1961a, Boulton’s integral for pumping-test analysis, in
Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-C, p. C24-C29.
------ 1961b, The significance of vertical flow components in the
vicinity of pumping wells in unconfined aquifers, in Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-B, p. B41-B43.
------ 1962, Numerical analysis, in Ferris, J. G., Knowles, D. B.,
Brown, R. H., and Stallman, R. W., Theory of aquifer tests: U.S. Geol. Survey Water-Supply Paper 1536-E, p. 135-139.
------ 1963a, Electric analog of three-dimensional flow to wells
and its application to unconfined aquifers: U.S. Geol. Survey Water-Supply Paper 1536-H, 38 p.
------ 1963b, Type curves for the solution of single boundary problems, in Bentall, Ray, compiler, Shortcuts and special problems in aquifer tests: U.S. Geol. Survey Water-Supply Paper 1545-C, p. C45-C47.
■— --- 1964, Multiphase fluids in porous media—A review of
theories pertinent to hydrologic studies: U.S. Geol. Survey Prof. Paper 411-E, 51 p.
——-— 1965, Effects of water-table conditions on water-level changes near pumping wells: Water Resources Research, v. 1, no. 2, p. 295-312.
Stallman, R. W., and Papadopulos, I. S., 1966, Measurement of hydraulic diffusivity of wedge-shaped aquifers drained by streams: U.S. Geol. Survey Prof. Paper 514, 50 p., 120 pis.
Swenson, F. A., 1968, New theory of recharge to the artesian basin of the Dakotas: Geol. Soc. America Bull., v. 79, p. 163-182.
Taylor, D. W., 1948, Fundamentals of soil mechanics: New York, John Wiley and Sons, p. 156-198.
Terzaghi, Karl, 1942, Soil moisture and capillary phenomena in
soils, Chapter 10-A in Meinzer, O. E., ed., Hydrology: New York, McGraw Hill Book Co., p. 331-363.
Theis, C. V., 1932, Ground water in Curry and Roosevelt Counties, N. Mex.: New Mexico State Engineer 10th Bienn. Rept., 1930-32, p. 99-160.
------- 1934, Progress report on ground-water supply of Portales
Valley, N. Mex.: New Mexico State Engineer 11th Bienn. Rept., 1932-34, p. 89-108.
------- 1935, The relation between the lowering of the piezometric
surface and the rate and duration of discharge of a well using ground-water storage: Am. Geophys. Union Trans., v. 16, p. 519-524.
------- 1938, The significance and nature of the cone of depression
in ground-water bodies: Econ. Geology, v. 33, no. 8, p. 889-902.
------- 1940, The source of water derived from wells: Civil Eng.,
v. 10, no. 5, p. 277-280.
------- 1941, The effect of a well on the flow of a nearby stream:
Am. Geophys. Union Trans., v. 22, p. 734-738.
------- 1963a, Estimating the transmissibility of a water-table
aquifer from the specific capacity of a well, in Bentall, Ray, compiler, Methods of determining permeability, transmissibility, and drawdown: U.S. Geol. Survey Water-Supply Paper 1536-1, p. 332-336.
------- 1963b, Drawdowns caused by a well discharging under
equilibrium conditions from an aquifer bounded by a finite straight-line source, in Bentall, Ray, compiler, Shortcuts and special problems in aquifer tests: U.S. Geol. Survey Water-Supply Paper 1545-C, p. 101-105.
------- 1963c, Chart for the computation of drawdown in the
vicinity of a discharging well, in Bentall, Ray, compiler, Shortcuts and special problems in aquifer tests: U.S. Geol. Survey Water-Supply Paper 1545-C, p. 10-15.
Theis, C. V., and Conover, C. S., 1963, Chart for determination of the percentage of pumped water being diverted from a stream or drain, in Bentall, Ray, compiler, Shortcuts and special problems in aquifer tests: U.S. Geol. Survey Water-Supply Paper 1545-C, p. 106-109.
Thiem, Adolph, 1887, Verfahren fur Messung naturlicher Grund-wassergeschwindigkeiten: Polytech. Notizbl., v. 42.
Thiem, Gunther, 1906, Hydrologische methoden: Leipzig, J. M. Gebhart, 56 p.
Thomas, H. E., 1951, The conservation of ground water: New York, Toronto, London, McGraw Hill Book Co., Inc., 327 p.
Todd, D. K., 1959, Ground-water hydrology: New York, John Wiley and Sons, Inc., 336 p.
Versluys, J., 1917, Die Kappilaritat der Boden: Inst. Mitt. Bodenk., v. 7, p. 117-140.
Walton, W. C., 1960, Application and limitations of methods used to analyze pumping test data: Water Well Jour., pt. 1, v. 14, no. 2, p. 22, 23, 49, 53, 56; pt. 2, v. 14, no. 3, p. 20, 46, 48, 50, 52.
------- 1962, Selected analytical methods for well and aquifer
evaluation: Illinois State Water Survey Bull. 49, 81 p.
------- 1963, Microtime measurements of ground-water level
fluctuations: Ground Water, v. 1, no. 2, p. 18, 19.
Walton, W. C., and Prickett, T. A., 1963, Hydrologic electric analog computer: Am. Soc. Civil Engineers Proc., Hydraulics Div. Jour., v. 89, no. HY6, p. 67-91.
Weeks, E. P., 1964, Use of water-level recession curves to determine the hydraulic properties of glacial outwash in Portage County, Wisconsin, in Geological Survey research 1964: U.S. Geol. Survey Prof. Paper 501-B, p. B181-B184.
Wenzel, L. K., 1936, The Thiem method of determining permeability of water-bearing materials and its application to the determination of specific yield, results of investigations in the Platte﻿70
GROUND-WATER HYDRAULICS
River valley, Nebraska: U.S. Geol. Survey Water-Supply Paper 679-A, 58 p.
------ 1942, Methods for determining permeability of water-bearing
materials, with special reference to discharging well methods: U.S. Geol. Survey Water-Supply Paper 887, 192 p.
Wenzel, L. K., and Sand, H. H., 1942, Water supply of the Dakota sandstone in the Ellendale-Jamestown area, North Dakota, with references to changes between 1923 and 1938: U.S. Geol. Survey Water-Supply Paper 889-A, 82 p.
Williams, C. C., and Lohman, S. W., 1949, Geology and ground-
water resources of a part of south-central Kansas, with special reference to the Wichita municipal water supply: Kansas Geol. Survey Bull. 79, 455 p.
Wood, L. A., and Gabrysch, R. K., 1965, Analog model study of ground water in the Houston district, Texas, with a section on design, construction, and use of electric analog models by E. P. Patten, Jr.: Texas Water Comm. Bull. 6508, 103 p.
Wyckoff, R. D., Botset, H. G., Muskat, Morris, and Reed, D. W., 1934, Measurement of permeability of porous media: Am. Assoc. Petroleum Geologists Bull., v. 18, no. 2, p. 161-190.
* U.S. GOVERNMENT PRINTING OFFICE: 1971 0-438-177﻿G(a)
UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
PROFESSIONAL PAPER 708 PLATE 1
107	108	109	1010	10"
ion	!0i2	1013	10'4	10'5
a
LOGARITHMIC PLOT OF a VERSUS G («)
After Jacob and Lohman (1952, fig. 5)﻿H/Hc
UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
PROFESSIONAL PAPER 708 PLATE 2
TYPE CURVES FOR H/HQ VERSUS Tt/rc2 FOR FIVE VALUES OF a
After Cooper, Bredehoeft, and Popadopulos (1967, table 1)﻿DRAWDOWN (s), IN FEET
UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
PROFESSIONAL PAPER 708 PLATE 3
l/w
B.DATA PLOTS SUPERPOSED ON TYPE CURVES
TWO FAMILIES OF TYPE CURVES FOR NONSTEADY RADIAL FLOW IN AN INFINITE LEAKY ARTESIAN AQUIFER
After Cooper,(1963, pi. 4)﻿H(u,/3)
After E. J. McClelland (unpub. data, 1961)﻿(ay mr»)0
UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
PROFESSIONAL PAPER 708 PLATE 5
LOGARITHMIC PLOT OF a VERSUS G(<x,rw/B)
After Walton (1962, pi. 4)﻿sT/Q
UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
PROFESSIONAL PAPER 708 PLATE 6
C
D
Tt/r2S
E
CURVES SHOWING NONDIMENSIONAL RESPONSE TO PUMPING A FULLY PENETRATING WELL IN AN UNCONFINED AQUIFER
The observation well in A is at z=1.06 (at the water table); B, at z = 0.9b; C, at z = 0.756;
D, at z = 0.56; E, at z = 0 (at the base of the aquifer). For the relation of z to 6, see fig.
21. After Stallman (1965, fig. 10)﻿sT/Q
UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
PROFESSIONAL PAPER 708 PLATE 7
A	B
CURVES SHOWING NONDIMENSIONAL RESPONSE TO PUMPING A WELL PENETRATING THE BOTTOM THREE-TENTHS OF THE THICKNESS OF AN UNCONFINED AQUIFER
The observation well in A is at z = 1.06 (at the water table); B, at z = 0.96; C, at z = 0.756;
D, at z=0.56; E, at z=0 (at the base of the aquifer). For the relation of z to 6, see fig.
21. After Stallman (1965, fig. 12)﻿4*Ts/Q
9
UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
PROFESSIONAL PAPER 708 PLATE 8
DELAYED-YIELD TYPE CURVES
After Boulton(1963, fig. 1)
►﻿(n)MZ
w 9
UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY
PROFESSIONAL PAPER 708 PLATE 9
LOGARITHMIC PLOT OF XW(u) VERSUS l/uP
After Stallman (1963b, PI. 3)
V﻿K«rm
enENCEs
UBRAR''
7 DAY
\J^ Geochemical Reconnaissance
U
' In the Wiseman and Chandalar Districts and Adjacent Region, Southern Brooks Range, Alaska
GEOLOGICAL SURVEY PROFESSIONAL PAPER 709
U.S.S.D.﻿﻿Geochemical Reconnaissance In the Wiseman and Chandalar Districts and Adjacent Region, Southern Brooks Range, Alaska
By W. P. BROSGE and H. N. REISER
GEOLOGICAL SURVEY PROFESSIONAL PAPER 709
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972﻿UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY V. E. McKelvey, Director
Library of Congress catalog-card No. 72-189156
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 40 cents (paper cover)﻿CONTENTS
Page
Abstract _________________________________________________________________________ 1
Introduction _____________________________________________________________________ 1
Geologic Setting _________________________________________________________________ 1
Mining history ___________________________________________________________________ 3
Placer-gold sources___________________________________________________________ 3
Geochemical sampling______________________________________________________________ 3
Discussion of anomalous areas_____________________________________________________ 8
Wiseman district______________________________________________________________ 8
Chandalar mining area________________________________________________________ 13
Other metal occurrences in the Chandalar area-------------------------------- 16
Other anomalous areas _______________________________________________________ 19
Summary _________________________________________________________________________ 20
References cited_________________________________________________________________ 20
ILLUSTRATIONS
Page
Figure 1. Index map of Alaska showing location of Wiseman and Chandalar quadrangles and of areas of figures 2,
4,	and 9 __________________________________________________________________________________________ 2
2. Map showing stream-sediment sample localities and generalized geologic map___________________________ 4
3. Map showing gold in stream-sediment, rock, and soil samples from Wiseman-Chandalar region____________ 6
4-8. Map of the Nolan-Hammond River area showing—
4.	Sample localities and unconsolidated deposits __________________________________________________ 9
5.	Gold in stream-sediment, rock, and soil samples _______________________________________________ 10
6.	Arsenic and antimony in stream-sediment, rock, and soil samples _______________________________ 11
7.	Anomalous concentrations of antimony in stream-sediment samples in and near the Nolan-Ham-
mond River area_____________________________________________________________________*___ 12
8.	Silver and zinc in stream-sediment, rock, and soil samples ____________________________________ 13
9-12. Map of the Chandalar area showing —
9.	Sample localities and geologic map ____________________________________________________________ 14
10.	Gold, silver, molybdenum, arsenic, antimony, lead, and zinc in rock, soil, and stream-sediment
samples near gold deposits ________________________________________________________________ 15
11.	Gold and silver in stream-sediment, rock, and soil samples_____________________________________ 16
12.	Zinc, lead, arsenic, antimony, copper, and molybdenum in stream-sediment, rock, and soil samples. 17
13.	Map showing silver and lead in stream-sediment samples and silver in rock and soil samples from the
Wiseman-Chandalar region __________________________________________________________________________ 18
hi﻿﻿GEOCHEMICAL RECONNAISSANCE IN THE WISEMAN AND CHANDALAR DISTRICTS AND ADJACENT REGION, SOUTHERN BROOKS RANGE, ALASKA
By W. P. Brosge and H. N. Reiser
ABSTRACT
Reconnaissance geochemical sampling in the Wiseman-Chandalar region shows that gold and silver anomalies are usually accompanied by base-metal anomalies and occur in three areas—the Wiseman mining district, the Chandalar mining district, and an unexplored zone in carbonate rocks north of the mining districts. The preservation of gold placers in mountain valleys least affected by glaciation suggests a local bedrock source of gold. Near Wiseman, detailed sampling in the apparent source area of the richest gold placers shows that gold occurs in small veins of quartz and quartz-stibnite. The highest gold content found in the stibnite veins is 9.2 ppm, and in the quartz veins 5.8 ppm. In the Chandalar district, gold and base metals are concentrated in an area of northwest-trending shear zones. The known gold lodes are in these shear zones; gold also occurs along extensions of one and possibly two of the shear zones a mile or more west of the lode mines. In both the Chandalar and the Wiseman areas, arsenic is a good pathfinder for gold, and zinc is associated with the highest concentrations of gold and silver.
INTRODUCTION
Placer deposits near Wiseman and Chandalar have yielded nearly 300,000 ounces of gold. The Chandalar area (fig. 1) includes the only active lode-gold mining district in the Brooks Range. Although gold has been known from this region since before 1900, the geology is known mostly from reconnaissance studies, and the lode sources of many placer deposits, as well as the extent of the lode deposits, are still uncertain. As part of the investigation for heavy metals by the U.S. Geological Survey, samples were collected in 1967 to determine whether there is a lode-gold source near the placer deposits at Wiseman and whether the lode gold at Chandalar extends beyond the known deposits. Samples were also collected in the larger region around the two mining districts to help complete reconnaissance traverses across the southern Brooks Range in the Chandalar and eastern Wiseman quadrangles (fig. 2) begun during the geologic mapping in 1958-60 (Brosge and Reiser, 1960 and 1964). This regional sampling indicates that the principal
gold mineralization is in the quartz-mica schist and phyllite of the two known mining areas and that silver mineralization may occur in carbonate rocks farther north.
The geology, gold deposits, and mining history of the region were described by Schrader (1900), Maddren (1913), Mertie (1925), Reed (1938), White (1952), and Marshall (1933). Cobb’s (1962 and 1964) maps show locations of and give references for the individual lode and placer deposits. Chipp (1970) mapped and sampled the area around the Chandalar lode mines in detail and refined the stratigraphy shown by the regional mapping.
Access to the mining areas is mostly by air. Dirt roads connect Nolan and the Hammond River mines with a landing strip for multiengine airplanes at Wiseman. A tractor road connects the Chandalar mines with a strip at Chandalar Lake, and the ice on Chandalar and Squaw Lakes furnishes a seasonal landing area. Strips for light planes give direct access to the Chandalar placer mines and to several of the mines along the Middle Fork of the Koyukuk. The access road for an oil pipeline planned along the Middle Fork and Dietrich Rivers would bring heavy equipment into the area from Fairbanks.
During our work the miners helped us in many ways. For furnishing housing and transportation, we are especially grateful to Frank Birch and Wayne Adney of Chandalar, Andrew Miscovich of Porcupine Creek, and Smith Wanamaker and Harry Leonard of Wiseman.
GEOLOGIC SETTING
The southern flank of the Brooks Range, including the Chandalar and Wiseman districts, is underlain mainly by schist of Paleozoic age intruded by Mesozoic granitic rocks (figs. 1, 2). Paleozoic sedimentary rocks that lie immediately to the north of the granite and schist are mainly limestone and calcareous shale. A broad lowland south of the schist and granite is underlain by Paleozoic and Mesozoic
l﻿2
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
170°	166°	162°	158°	154°	150°	146°	142°	138°
Figure 1.—Index map of Alaska showing location of Wiseman and Chandalar quadrangles. Areas of figures 2, 4, and 9 are shown in relation to the areas of schist and granite and to the gold placers (black dots).
phyllite and clastic rocks. Mafic intrusive and extrusive rocks occur in the phyllite and clastic rocks of this lowland and also in the schist and Paleozoic sedimentary rocks in the Brooks Range to the north.
Glaciers of at least three advances have trenched and filled the main through-going valleys of the southern Brooks Range and have left the lowland south of the range largely covered by drift and outwash. Erratic boulders indicate that ice of an
early advance overrode the lower mountains, whereas cirque glaciers occurred in the high mountains near the Brooks Range divide and in the southern part of the metamorphic belt. High alluvial terraces that probably are related to the two younger glacial advances extend up some of the major rivers and their tributaries.
The relation of the various glacial advances to the gold placers is uncertain, but some of the placer﻿GEOLOGIC SETTING
3
deposits are older than at least the latest advance. Mertie (1925) described placers stratigraphically above and below the glacial deposits near Chan-dalar Lake, and deep placers near Nolan are buried by alluvium that is graded to the level of glacial fill in Wiseman Creek valley.
MINING HISTORY
Since 1899, when gold was discovered on the Middle Fork of the Koyukuk River, most of the Koyu-kuk’s tributaries for a distance of about 35 miles from Gold Creek to Tramway Bar have produced placer gold. The greatest production was before 1917; at present only a few one- or two-man open-cut mines are in operation. The richest producers have been in the small area north of Wiseman shown in figure 2; there approximately 200,000-250,000 ounces has been produced from Nolan Creek, the Hammond River, and their tributaries. Placer gold in these streams and the stibnite prospects in the small area between them suggest that lode-gold deposits also might be present.
Placer-gold deposits in the Chandalar area are clustered around the known lode-gold deposits (fig. 9). More than 29,000 ounces of placer gold has been produced since the discovery of gold deposits on Big Creek in 1906 (U.S. Bureau of Mines, written commun., 1968). Exploration of the gold-bearing quartz veins also began about this time. The known gold-bearing veins are in a narrow zone that extends about 3 miles northeastward across the strike of the country rock. Most exploration has been on the Mikado and Little Squaw lodes; the Mikado mine is now in production (Alaska Div. Mines Bull., 1969).
PLACER-GOLD SOURCES
Most of the placer gold produced in the southern Brooks Range has been mined from deposits found in a belt of low rounded mountains and hills that trends westward along the northern limit of the schistose rocks from Big Lake through Wiseman to Wild Lake (figs. 1, 2). The parallelism of this placer belt with the regional strike suggests that the gold has a local source—in fact gold is found in the veins near Wiseman. The preservation of the older and deeper gold-bearing alluvial sediments within this belt of low hills may have resulted from the absence of local glaciers; the most recent glaciation there seems to have been restricted to the main valleys.
Other shallow gold placers extend far upstream on creeks that rise in the higher mountains well within the area of schistose rocks, particularly on
the cirque-free southern slopes. The gold in each of these probably comes from a local source in the schist, and a local source is evident at Chandalar, where the placers surround known gold lodes.
Placer gold that occurs in the lowland south of the mountains may in part have been reworked from glacial drift of the Middle Fork of the Koyukuk (Reed, 1938). Glacial erratic boulders occur in the gold-bearing gravel deposits of a former high-level channel of the Middle Fork at Tramway Bar. Erratics also occur in placer deposits on the low pass between the Middle and South Forks (Reed, 1938), and the placers along the South Fork of the Koyukuk (just south of fig. 2) are directly below the mouths of former glacial spillways from the Middle Fork.
GEOCHEMICAL SAMPLING
Most of the 309 stream-sediment samples are of predominantly silt-size material. About half of these are from the two small areas of detailed sampling near Wiseman and Chandalar, and the other half from the regional reconnaissance. The regional samples were collected along a traverse across the sedimentary, volcanic, and metamorphic rocks in the upper Koyukuk area, and a traverse across the granitic rocks along the North Fork of the Chandalar. A few scattered samples were collected mainly from areas of metamorphic rocks. In addition, panned concentrates of stream gravel were collected along the North Fork of the Koyukuk.
Most of the 207 samples of rocks and residual soils are grab samples collected on traverses across the known or suspected mineralized areas of Wiseman and Chandalar. Those samples collected outside the mining districts are from quartz veins and mineralized rock collected during regional mapping.
The analyses and frequency-distribution statistics for all stream-sediment samples and the analyses of the rock and soil samples from the Wiseman and Chandalar districts have been placed on open file by the U.S. Geological Survey (Brosge and Reiser, 1970a, b). The analyses by atomic absorption and colorimetric methods were done by H. H. Mehnert, J. B. McHugh, W. W. Janes, W. L. Campbell, J. Frisken, E. E. Martinez, R. L. Miller, K. R. Murphy, S. Rickard, T. A. Roemer, Z. Stephenson and R. Vaughn. The spectrographic analyses were made by M. DeValliere, A. Farley, Jr., E. E. Martinez, and Chris Heropoulos.
The locations of samples with detectable gold and of those with high or anomalous concentrations of j silver or some base metals are shown by maps﻿4
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
Base from U.S. Geological Survey Wiseman and Chandalar 1:250,000, 1956
Figure 2?—Stream-sediment sample﻿SAMPLING
5
147"00'
Geology by W. P. Brosge, H. H. Reiser, C. L. Whittington, W. L. Nystrom, 1958 W. P. Brosge, H. N. Reiser, J. 0. Berkland, D. F. Kellum, 1959 W. P. Brosge, H. N. Reiser, J. 0. Berkland, N. K. Hagen, 1960 W. P. Brosge, H. N. Reiser, B. L. Hoffman, D. Biberdorf, 1967
EXPLANATION
ROCK TYPES
ud
Unconsolidated deposits
Granitic rocks
Mafic volcanic rocks
Greenstone and green schist
ish
Noncalcareous sedimentary rocks and phyllite
sch
Quartz-mica schist
Albite-chlorite-mica schist
Limestone, marble, calcareous schist, phyllite, and tactite
Contact
Approximate; includes some faults
Stream-sediment sample locality
localities and generalized geologic map,﻿6
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
0	5	10	15	20	MILES
■	I I I » I----------1-----------1-----------1
Base from U.S. Geological Survey Wiseman and Chandalar 1:250,000, 1956
Figure 3.—Gold in stream-sediment, rock, and soil samples from Wiseman-Chandalar﻿SAMPLING
7
North
Little Squaw 'Creek
Sqimw-
Lake
Chandalar Lake /
Chandalar
Tobin
Thazzik
Mountair
EXPLANATION
Concentration of gold, in parts per million, in samples
o
Stream sediments
<3
0.02-0.039
9
0.04-0.049
9
0.05-0.059
•
0.08-0.2
None found 0.06-0.079
o
Rocks
<*
0.02-.039
<>
0.04-.079
♦
0.08-0.26
♦
0.8-18.0
Value shown for concentrations greater than 1.0. None found unthin range 0.27-0.79
□
Soil
a
0.04-0.079
a
0.08-0.26
Panned concentrates of gravel
Concentration shown in parts per million
For gold in rocks and soil near Wiseman and Chandalar see figs. 5 and 11 Samples with gold in concentrations too small to be detected (Au <0.02 ppm) not shown
Gold placer
(From Reed, 1938)
X
Gold-placer mine active since 1955
region. For details near Wiseman and Chandalar, see figures 5 and 11.﻿8
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
(figs. 3, 5-8, 10-13). The cutoff values for the concentrations described as anomalous or high are interpretive, but are at approximately the 97V£ and 95th percentile levels of the continuous part of the frequency distribution for each metal.
Although analyses of stream-sediment samples have detected some gold, even in localities outside the known placer areas, samples of the type collected seem generally inadequate to detect placer gold. Of the 48 samples taken from streams at or just below known placers, gold was detected in only 14.
In the discussion of silver, the data for the 79 stream-sediment samples collected before 1967 are omitted because the analytical values of these samples seem about four times too high when compared with those of the later samples.
DISCUSSION OF ANOMALOUS AREAS
Gold in detectable amounts seems to be fairly widespread in the Wiseman-Chandalar region, for it is found in many of the quartz vein samples and in most of the panned samples taken along the North Fork of the Koyukuk (fig. 3). It occurs not only in and near the schist and granitic rocks, but also in the area of sedimentary rocks to the north. Gold concentrations greater than 0.1 ppm (parts per million) in rock samples are present, however, only in or close to the metamorphic belt, and gold in panned samples increases abruptly where the North Fork enters the placer belt along the north margin of the metamorphic rocks.
The most prominent anomalous areas indicated by steam-sediment samples are the Chandalar and the Nolan-Hammond River areas. These areas contain a disproportionate share of the samples with detectable gold and of samples with high to anomalous concentrations of one or more base metals— lead, arsenic, and molybdenum at Chandalar; antimony, in the Nolan-Hammond River area (figs. 3, 7, 12). The association of gold and base-metal anomalies in stream sediments from these areas reflects the mineral association in the vein and rock samples. If the two mining districts are typical, then significant gold mineralization in this region is marked by associated base-metal anomalies.
WISEMAN DISTRICT
The bedrock in the Nolan-Hammond River area consists mainly of black phyllite and gray schistose quartz siltstone with some calcareous beds. Disseminated pyrite is common in both the phyllite and
the quartzose rocks. Quartz occurs in crenulated stringers and knots and locally, with stibnite, in veins and fracture fillings that postdate metamorphism and folding. A buried pluton south of Wiseman is suggested by heavily tourmalinized vein quartz on the west flank of Emma Dome and by silicated limestone at the base of the east flank of Emma Dome.
Placer deposits are of three ages: present stream deposits, old buried channel fillings, and probably still older high bench deposits. Glacial debris and erratics indicate that an early stage of glacial ice covered part of the Nolan Creek-Hammond River divide and could have been the source of the reworked erratic boulders in the high bench placer gravels on the Nolan Creek and lower Hammond River drainages. The buried bedrock valley of Nolan Creek is a V-shaped gulch (Maddren, 1913), and the lower Hammond valley is in part a buried canyon ; both were probably incised after the retreat of ice of this early stage and partly refilled with gold-bearing gravel before the next recognizable glacial advance. The gravel fill in Nolan Creek consists mainly of chips of locally derived black phyllite.
Drift of unknown thickness covers the main valley floors of Wiseman Creek, the Middle Fork Koyukuk River, and the upper Hammond River; Pleistocene muck and gravel buries the placers in the old bedrock channel of Nolan Creek to depths about 210 feet near the mouth to about 20 feet near the head. Ice of the later advance seems to have scoured the main valleys, but not the gold-bearing tributaries. Reed (1938) reported that the buried bedrock channels of the Hammond River and Gold Creek (fig. 3) extended out about three-fourths of a mile into the Middle Fork Koyukuk valley at depths of 115 and 100 feet, but steep dropoffs of bedrock beyond this point suggest that these tributary channels have been cut off by glacial scouring of the Middle Fork Koyukuk.
Traces of gold are common in stibnite and quartz veins in the Nolan-Hammond River area; these veins are therefore thought to be part of a system whose erosion yielded the placer deposits. (See figs. 4, 5).
Small amounts of gold (0.02-0.05 ppm) were detected in most of the area examined. The highest concentrations were found in a small stibnite prospect at the head of Fay Creek, where one sample contained 9.2 ppm gold, and in a thin quartz vein at the head of Thompson Pup, where 5.8 ppm and 0.97 ppm gold were measured by duplicate analyses of one sample. The next highest concentrations﻿DISCUSSION OF ANOMALOUS AREAS
9
found are only 0.06-0.08 ppm gold—concentrations no greater than are found in some of the samples outside the mining districts (fig. 3).
Gold in the veins is closely associated with anti-
mony and arsenic (fig. 6). All samples of quartz-stibnite veins from lower Smith Creek, Midnight Dome, and the head of Fay Creek contain detectable gold, and with one exception, all gold concentrations
150’ 15'
150°00'
I y \ ''•nsx				v r	
			/p-Qa/ 		1	•• y.Qa
/ 1 / \ ^				J	
/ / rr*	/ Qt (			•ft	Alluvium
2n Vermont u Dome
Qg
EXPLANATION
UNCONSOLIDATED
DEPOSITS
	1 Thomson	□ 3
	/ h,'\	□ 2
		Q8
\ c/yys4		°i
	—11 \	^-o6
'WfP'		
/Jo		Smith
ffl &S/'''QtP	D1 n3	Creek
	LI	Dome
Ci2		
// \ X.7NV	Qt	
$^VQtP^ a—13	Crej\y	
Midnight
Dome
Qg
Glacial and glacioflu-vial deposits
----P
Qt
____
Qtp
High-terrace deposits containing glacial boulders
Qtp. deposits non' mostly re-nionetl by placer minimi )
Contact
MINES AND PROSPECTS
Stream where placer gold has been mined in present channel or old, deeply buried channel (From Reed, 1938)
Stibnite prospect
GEOCHEMICAL
SAMPLES
Stream-sediment sample locality
2 5 □ CD
Rock-and soil-sample locality or traverse, showing number of samples collected
Figure 4.—Sample localities and unconsolidated deposits in Nolan-Hammond River area.﻿10
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
150° 15'
150°00'
EXPLANATION
Concentration of gold, in parts per million
O
Stream-sediment sample
0
0.02-0.039
0
0.04-0.049
9
0.05-0.059 (none >0.059)
Rock sample
V, indicates vein sample. Others are country rock
O
0.02-0.039
o
0.04-0.079
♦
0.08-0.29
^9.2
0.3-9.2
Values for single and duplicate analyses shown
□
Soil sample
a
0.02-0.039
Cl
0.04-0.079 (none >0.079)
Figure 5.—Gold in stream-sediment, rock, and soil samples from Nolan-Hammond River area.﻿DISCUSSION OF ANOMALOUS AREAS
11
EXPLANATION
Concentration of arsenic and antimony, in parts per million
O
Stream-sediment sample
©
As 100 (none >100, none 80-99)
©
Sb 10
©
Sb 15-3000. Value shown where >99
ov
Rock sample
V, indicates vein sample. Others are country rock
o
As 120-199
❖
As 200-5000. Value shown where >999
o
Sb 40-99
Sb 100->10,000. Value shown where >999
□
Soil sample
□
As 120-199
H
As 200-800
H
Sb 40-99
B
Sb 100-3000. Value shown where >999
Figure 6.-—Arsenic and antimony in stream-sediment, rock, and soil samples from Nolan-Hammond River area. Some
concentration symbols are combined in the figure.﻿12
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
greater than 0.05 ppm are in rocks that contain anomalous antimony and arsenic. The exception is the richer of the two veins at the head of Thompson Pup, and this vein is close to the only antimony anomaly detected north of the stibnite prospects.
Antimony anomalies are present in stream sediments on the west flank of Smith Creek Dome but absent on the east flank. Anomalous concentrations of antimony also occur farther west in sediments from Acme Creek, Washington Creek, and unnamed creeks near Pasco Pass, as well as to the south in Jap Creek and Minnie Creek (figs. 6, 7). In these creeks, gold was detected analytically only in sediments of Jap Creek, but it is reported to occur in Washington Creek and Minnie Creek, and some of the gold in the buried channel of Nolan Creek may have come down Acme Creek (Reed, 1988). Stibnite pebbles were also reported from the placers on Gold Creek about 5 miles east of the Nolan-Hammond River area (Schrader, 1904). The gen-
eral association of gold and antimony suggests that the source of the antimony anomalies in stream sediments should be investigated.
Zinc is associated with gold in the area between the heads of Fay Creek and Thompson Pup where most of the high vein and bedrock concentrations of gold were found (fig. 8), and may therefore be a useful pathfinder element. The zinc content does not always correlate directly with the gold; the zinc is more concentrated in soil than in rock and occurs in the bedrock as well as in the veins. A small amount of silver (2.9 ppm) occurred with gold in a milky quartz vein at the head of Thompson Pup. Generally, though, the low content of silver in rock, soil, and stream-sediment samples suggests that silver is not a useful pathfinder element for gold in this area.
Maddren (1913) suggested that gold occurs in the pyritic country rock. Although some pyritic bedrock samples contain relatively high (0.4-0.65
150° 15'	150°00'
EXPLANATION
Concentration of antimony, in parts per million
Stream-sediment sample ©
100-300
700-3000 (Sb=500 not found)
Figure 7. Anomalous concentrations of antimony in stream-sediment samples in and near the Nolan-Hammond River
area, the highest in the Wiseman-Chandalar region.﻿DISCUSSION OF ANOMALOUS AREAS
13
Figure 8.—Silver and zinc in stream-sediment, rock, and soil samples from Nolan-Hammond River area.
ppm) concentrations of silver, the only gold detected in bedrock was from samples near gold-bearing veins or from surfaces likely to have been contaminated by placer gold.
CHANDALAR MINING AREA
The bedrock of the Chandalar mining area is mainly gray quartz-muscovite schist with sills of mafic greenschist and some calcareous and quartzose
beds (fig. 9). Black finely crystalline schist and phyllite containing greenstone sills underlies this schist along upper Big Creek and Tobin Creek. Chipp (1970) showed the contact with the black schist as a thrust fault.
The major structural feature of the Chandalar area is a broad northeast-plunging antiform. The dominant structural trend in the area east and south of the mining area is northeast; however, near﻿14
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
148°30'	148°15'	148°00'
EXPLANATION
ROCK TYPES
ud
Unconsolidated deposits
Greenstone and greenschist
Gray quartz-mica schist
bs
Black schist and phyllite
Distinguished locally
Calcareous schist and hornfels
Contact
Fault
Inferred thrust fault
Sawteeth on upper plate
Inferred shear zone
-------j-—*•
Anticline, showing direction of plunge
|	a40
Measured strike and dip of foliation, and strike and dip from distant view
MINES AND PROSPECTS
Stream with mined gold placer
X
Gold deposit or prospect GEOCHEMICAL SAMPLES O Stream-sediment sample □ Soil-sample locality A Rock-sample locality a Rock-and soil-sample traverse, showing number of samples collected
Figure 9.—Sample localities and geologic map, Chandalar area. (Enlarged from regional geologic map. For detailed map
of northern part see Chipp (1970).)
the known gold deposits, the linear elements trend northwest. A northeast-striking high-angle fault parallel to upper Big Creek and a northwTest-striking fault in Tobin Pass bound this area of dominant northwest trends. The most conspicuous northwesttrending element is a shear zone that has been exposed in the Mikado mine. On the ridge crest east of the mine, this shear zone is marked by discordant dips. In the tunnel and trenches at the mine, the zone is about 50 feet wide and dips steeply, generally to the northwest (Frank Birch, written commun., 1968). Schist within this zone is obliquely sheared
and contains subparallel sheared and brecciated gold-bearing quartz veins and lenses. The larger veins are near the two walls of the shear zone.
Glacial drift makes up most of the unconsolidated deposits in the main valleys and extends up Squaw and Little Squaw Creeks to the gold placers (Mertie, 1925, p. 254). However, the alluvial deposits in upper Tobin and Big Creeks seem to be entirely of local rocks.
Samples of mineralized rock from the worked deposits show an association of metals that may be a guide to other lode deposits in the area. Arsenopy-﻿DISCUSSION OF ANOMALOUS AREAS
15
rite, sphalerite, and minor galena and stibnite are present in ore from the Mikado mine (Maddren, 1913), and high concentrations of silver, arsenic, lead, antimony, and zinc were measured in the samples (fig. 10). The copper content of mineralized rock is generally low.
Soil samples show a similar association of metals.
Samples near the Little Squaw and Mikado deposits generally contain above average amounts of lead, molybdenum, and either antimony or arsenic, and high zinc content is associated with high gold and silver content at the Mikado mine and Star prospect. The copper content of soils near the prospects is generally low. The highest concentration of gold
D. LEAD AND ZINC
0	Vi	1 MILE
1	___I___I---------1
EXPLANATION
Inferred shear zone
X
Gold deposit or prospect
O
Stream-sediment sample
Rock sample
V, indicates vein sample
n e>
B ❖
Q O
a ❖
©
□
Soil sample
Concentration, in parts per million
A	Gold	
a	0.02-0.039	
n <>	0.04-0.079	
a ♦	0.08-0.29	
■ ♦	0.3-392	
	(Value shown)	
a	0.05-0.059	
B.	C.	D.
Ag	As	Pb
0.4-0.99	120-199	70
Ag	As	Pb
1.0-7.2	200-20,000	100-700
(Va 1	u e shown)	
Mo	Sb	Zn
5	40-99	100-159
Mo	Sb	Zn
7	100-1500	160-2500
	(Value	shown)
	As	Pb
	80-99	30
(Value shown)
Figure 10.—Gold, silver, molybdenum, arsenic, antimony, lead, and zinc in rock, soil, and stream-sediment samples near gold deposits in the Chandalar area. For location see figures 11 and 12. Some concentration symbols are combined in the figure.﻿16
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
in the soil was found about 100 yards west of the Mikado portal, and most of the samples with high concentrations of silver and arsenic were also west of the portal. Conversely, the highest concentrations of antimony and molybdenum are east of the portal. The Mikado shear zone is also mineralized a mile west of the portal; there gold occurs in quartz veins and in soil on the topographic trace of the shear zone, and the soil contains anomalous amounts of arsenic and above average amounts of silver, lead, and zinc.
Sediments in streams that drain the lode pros-
pects contain gold and above average amounts of zinc, lead, or silver. Most of the high concentrations of arsenic and copper in stream sediments are at localities near the lodes (figs. 11, 12). Chipp (1970) also found that concentrations of copper, and possibly silver, are significantly higher in these streams near the lodes.
OTHER METAL OCCURRENCES IN THE CHANDALAR AREA
Base-metal mineralization seems to be largely within the area of northwest-trending shear zones. Base-metal anomalies in stream sediment samples
EXPLANATION
Fault
Includes thrust faults
Inferred shear zone
Anticline, showing direction of plunge
Concentration of gold and silver, in parts per million
O
Stream-sediment sample
O
Au 0.02-0.039
3
Au 0.04-0.049 Au 0.05-0.059
Au 0.08-0.2. (value shown)
O
Ag 0.5-0.59
Au <0.02 and Ag <0.5 not shown
ov
Rock sample
V indicates vein sample
O
Au 0.02-0.039 <>
Au 0.04-0.079 ♦
Au 0.3-1.7
Oa*-5
Ag 0.5-0.59 (value shown) □
Soil sample QAg .53
Ag 0.5-1.4 (value shown)
See fig. 10 for Au and Ag in rock and soil samples in Mikado and Little Squaw areas
148°30'	148°15'	148°00'
FIGURE 11.__Gold and silver in stream-sediment, rock, and soil samples from the Chandalar area.﻿DISCUSSION OF ANOMALOUS AREAS
17
EXPLANATION
Fault
Includes thrust faults
Inferred shear zone —
Anticline, showing direction of plunge
Stream-sediment samples with high or ana-malous concentrations of Zn, Pb, As, Sb.Cu or Mo
Pb 30
©
1 metal
Pb 30 3 As 80 2 metals
Zn 150 Mo 15 Zn 150 As 200 ®As 120	• Pb 30 Cu 70
3 metals	4 metals
Showing metals and concentration, in parts per million
X
Gold deposit or prospect
Rock and soil samples with high or anomalous concentrations of As, Pb, Cu, and Mo. For As, Pb, and Mo in Mikado and Little Squaw areas, and for all samples with high concentrations of antimony and zinc, see fig. 10
ov
Rock sample
V, indicates vein sample
□
Soil
/%Cu 50 r«Cu 50	/kAs 160
^	^ Mo 7
1 metal	2 metals
Showing metals and concentration, in parts per million
Figure 12.—Zinc, lead, arsenic, antimony, copper and molybdenum in stream-sediment, rock, and soil samples from the
Chandalar area.
are concentrated within this area, and, with one exception, the samples of rock and soil from outside this area have low base-metal contents. Gold, however, occurs in many stream sediments east of the area and on the north side of Lake Creek-Grave Creek valley. Some of this gold may have been dispersed by glacia'tion, but most of the gold detected probably is locally derived, for it occurs mostly in headwaters and small tributaries above the level of glacial deposits.
The greatest concentration of anomalies in stream sediments outside the drainage from known lodes
is on McNett Fork and the unnamed stream to the northwest, where gold occurs with silver or lead and with above average copper and zinc. Chipp’s (1970) samples did not show base-metal anomalies in these two streams, but did show them in the next stream northwest. An inferred northwest-trending shear zone close to the sample localities, mapped only from aerial photographs, merits examination.
Gold is also present outside the mining area in sediments from streams that cross inferred north-east-trending shear zones near McLellan Creek, Day Creek, and Rock Creek and south of the inferred﻿18
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
northwest-trending fault along Big Creek. High contents of molybdenum, lead, arsenic, and zinc are present locally in sediment samples near Day Creek
and south of the inferred Big Creek fault. The high gold content (5.2 ppm) of a sediment sample from a small tributary south of Big Creek was not con-
Figure 13.—Silver and lead in stream-sediment samples and﻿DISCUSSION OF ANOMALOUS AREAS
19
firmed by a duplicate analysis and probably reflects the effect of a single gold particle.
The concentrations of lead and molybdenum are high in stream sediments of Big Joe Creek and its tributaries, and gold occurs in quartz veins at the
prospect near the headwaters of Big Joe Creek and on the mountain southwest of Big Joe Creek.
OTHER ANOMALOUS AREAS
A third association of anomalies is found in the carbonate terrane at the north margin of granitic
North
Little Squaw , Creek
Sqitaur
Lake
Chandalar
Lake/
Thazzik^
Mountain
EXPLANATION
Concentration of silver, in parts per million, in samples
O
Stream sediments
(1967 samples only)
e
0.5-0.59
©
0.6-1.15
<0.5 not shown
o
Rocks
o
1.0-	3.0
♦
6.0-19.0. None found in range 3.1-5.9 <1.0 not shown
□
Soil
a
1.0-	3.0
<1.0 not shown
Concentration of lead, in parts per million, in stream-sediment samples
O
50-1000
Value shown for concentrations greater than 100
silver in rock and soil samples from Wiseman-Chandalar region.﻿20
GEOCHEMICAL RECONNAISSANCE, SOUTHERN BROOKS RANGE, ALASKA
rocks on the North Fork of the Chandalar. Here, gold in stream-sediment and rock samples is associated with anomalous concentrations of lead, zinc, and copper and relatively high concentrations of silver. Relatively high concentrations of silver also occur in rocks and stream sediments in a poorly defined zone that follows the trend of the carbonate rocks southwestward from the North Fork of the Chandalar to the North Fork of the Koyukuk (fig. 13). Although the maximum silver concentrations in the stream-sediment samples are only four or five times higher than the median value, higher concentrations are known at three localities in this zone. Schrader (1900) collected a vein sample that assayed 6 ppm silver and 18 ppm gold from a locality on the North Fork of the Chandalar whose approximate position is shown by a question mark on figure 13. A sample of galena submitted from a prospect in the nearby limestone (not shown on fig. 13) assays 360 ppm silver and 6.5 ppm gold. Farther west, silver and copper nuggets were found in the gold placer on Mule Creek according to Mad-dren (1913).1
The relatively high silver concentrations are principally in the area where the carbonate and calcareous rocks have been intruded by granitic and mafic rocks and are in part metamorphosed. Schrader ascribed his sample to the mafic rock unit, but the closeness of his locality to a granite sill makes an association with the mafic rocks uncertain.
Gold was detected in some samples outside the three main anomalous areas. A high concentration of gold occurs with silver in samples from one thin arsenic-rich vein in the system of east-trending quartz veins north of Thazzik Mountain. Gold was detected in sediment samples from many of the streams south of Wiseman that contain placer gold and from one stream that flows almost entirely in the glacial drift south of the mountains, but none of these samples contain high concentrations of other metals. Although many of the placers south of Wiseman probably have local sources, gold and silver in a quartz vein southwest of Emma Dome is the only direct evidence of mineralization in that area. A large gossan on Redstar Mountain in the northwestern part of the region contains high concentrations of arsenic, antimony, and molybdenum but no detectable gold.
SUMMARY
Gold-bearing quartz and quartz-stibnite veins are common in the Nolan-Hammond River area adjacent
to the placer deposits and are probably part of the vein system that was the source of the placers. Although gold is generally present in trace amounts only, concentrations of as much as 9.2 ppm in stibnite and 5.8 ppm in quartz are present. Gold was not detected in the pyritic bedrock except near veins or where the bedrock may have been contaminated by placer gold. Antimony anomalies in stream sediments on and west of Acme Creek suggest the presence of veins west of the Nolan Creek placer deposits.
Near Chandalar most mineralization coincides with an area of northwest-trending shear zones that contains the known gold lodes. Within this area gold and arsenic were detected about 1 mile northwest of the Mikado mine along the strike of the Mikado shear zone. Gold and base-metal anomalies in stream-sediment samples 2-4 miles northwest of the Little Squaw mine indicate that an inferred shear zone near these anomalies may also be mineralized. Both shear zones merit further investigation. Gold was also detected in several streams outside the lodebearing area. In most of these streams, gold is not accompanied by other metal anomalies.
North of the Wiseman-Chandalar mining area, reconnaissance sampling shows relatively high concentrations of silver accompanied by gold and lead in a zone that is poorly defined but follows the regional strike of the carbonate rocks along the north edge of the schist and granitic rocks. One lead-silver prospect is known, but much more sampling is required to determine the significance of this zone.
REFERENCES CITED
Alaska Division of Mines and Geology, 1969, Mining activities: Alaska Div. Mines Bull., v. 17, no. 10, p. 2.
Brosge, W. P., and Reiser, H. N., 1960, Progress map of the geology of the Wiseman quadrangle, Alaska: U.S. Geol. Survey open-file map, scale 1:250,000.
------1964, Geologic map and sections of the Chandalar
quadrangle, Alaska: U.S. Geol. Survey Misc. Geol. Inv. Map 1-375, scale 1:250,000.
------1970a, Chemical analyses of stream-sediment samples
from the Chandalar and eastern Wiseman quadrangles, Alaska: U.S. Geol. Survey open-file report, 56 p., tables, map.
------ 1970b, Chemical analyses of rock and soil samples
from the Chandalar and eastern Wiseman quadrangles, Alaska: U.S. Geol. Survey open-file report, 8 p., 3 maps. Chipp, E. R., 1970, Geology and geochemistry of the Chandalar area, Brooks Range, Alaska: Alaska Div. Mines and Geology, Geologic Rept. no. 42, 39 p.
Cobb, E. H., 1962, Lode gold and silver occurrences in Alaska: U.S. Geol. Survey Mineral Inv. Map MR-32, scale 1:2,500,000.
1 Since this report was submitted, about 240 claims in seven prroups have been staked north and northeast of Mule Creek, near two of the silver localities shown in figure 13.﻿REFERENCES CITED
21
------1964, Placer gold occurrences in Alaska: U.S. Geol.'
Survey Mineral Inv. Map MR-38, scale 1:2,500,000.
Maddren, A. G., 1913, The Koyukuk-Chandalar region, Alaska: U.S. Geol. Survey Bull. 532, 119 p.
Marshall, Robert, 1933, Arctic Village: New York Literary Guild, 397 p.
Mertie, J. B., Jr., 1925, Geology and gold placers of the Chandalar district, Alaska: U.S. Geol. Survey Bull. 773-E, p. E215-E263.
Reed, I. M., 1938, Upper Koyukuk region, Alaska: Alaska Dept. Mines [rept. unpub.], 169 p.
Schrader, P. S., 1900, Preliminary report on a reconnaissance along the Chandalar and Koyukuk Rivers, Alaska, in 1899: U.S. Geol. Survey 21st Ann. Rept., p. 443-486.
------ 1904, A reconnaissance in northern Alaska: U.S.
Geol. Survey Prof. Paper 20, 139 p.
White, M. G., 1952, Radioactivity of selected rocks and placer concentrates from northeastern Alaska: U.S. Geol. Survey Circ. 195, 12 p.
U. S. GOVERNMENT PRINTING OFFICE : 1972 o - 455-676﻿
﻿

﻿﻿Jasperoid in the United States— Its Characteristics, Origin, and Economic Significance
GEOLOGICAL SURVEY PROFESSIONAL PAPER 710
pOCUMENTFoffARTMENfj FEB U 1973﻿﻿Jasperoid in the United States— Its Characteristics, Origin, and Economic Significance
By T. G. LOVERING
GEOLOGICAL SURVEY PROFESSIONAL
Jasperoid consists dominantly oj quartz replacing older host rocks, commonly limestone or dolomite.
It is a useful ore guide in many mining districts
PAPER 710
UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1972﻿UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary
GEOLOGICAL SURVEY V. E. McKelvey, Director
Library of Congress catalog-card No. 77-187908
For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $1.75 (paper cover)
Stock Number 2401-1218﻿CONTENTS
Page
Abstract ................................................. 1
Introduction ............................................. 2
Purpose and scope of the investigation............... 2
Definition of jasperoid ............................. 2
Acknowledgments ..................................... 3
Distribution of jasperoid ..............................   3
Geographic distribution ............................. 3
Geologic distribution ............................... 6
Host rock ....................................... 6
Structural control .............................. 6
Geologic age .................................... 6
Physical properties of jasperoid ......................... 7
Megascopic features ................................. 7
Color ........................................... 7
Texture ......................................... 7
Associated minerals ............................. 9
Microscopic features ................................ 9
Grain size ...................................... 9
Fabric texture ................................. 11
Accessory minerals ............................. 15
Other physical properties .......................... 29
Density and porosity ........................... 29
Differential thermal analysis .................. 30
Composition of jasperoid ................................ 30
Major constituents ................................. 30
Minor constituents ................................. 34
Genesis of jasperoid .................................... 35
Source of silica ................................... 35
Solution and transportation of silica .............. 36
Solubility of various forms of silica in pure
water at low temperature and pressure.......	37
Solubility of various forms of silica in pure water at higher temperature and pressure ....	37
Solubility of various forms of silica in aqueous solutions at low temperature and
pressure ..................................... 39
Solubility of various forms of silica in aqueous solutions at higher temperature
and pressure ................................. 40
Summary ......................................   41
Composition of natural silica-bearing solutions .... 41
Deposition of silica ............................... 43
Deposition at low temperature .................. 43
Deposition at high temperature.................. 44
Genesis of various forms of silica in
jasperoid .................................... 45
Replacement of host rock by silica ................. 46
Physical factors ............................... 46
Chemical factors ............................... 48
Theory of replacement process .................. 49
Jasperoid as a guide to ore ............................. 50
Definition of favorable and unfavorable jasperoid.... 50
Methods of data analysis ........................... 51
Comparison of megascopic characteristics ........... 53
Comparison of microscopic characteristics .......... 54
Comparison of other physical properties ............ 54
Comparison of chemical composition ................. 55
Jasperoid as a guide to ore—Continued
Summary of criteria for evaluation of jasperoid
samples ........................................
Characteristics of jasperoid in major mining districts
of the United States ................................
Tri-State district, Oklahoma, Kansas, and
Missouri .......................................
Clifton-Morenci district, Arizona .................
Bisbee (Warren) district, Arizona .................
Ely (Robinson) district, Nevada ...................
Leadville district, Colorado ......................
Tintic and East Tintic districts, Utah ............
Gilman (Red Cliff) district, Colorado .............
Aspen district, Colorado ..........................
Eureka district, Nevada ...........................
Summary of jasperoid in the major districts........
Characteristics of jasperiod in other than the major
mining districts of the United States ...............
Alabama ...........................................
Alaska ............................................
Southern Seward Peninsula area ...............
Salmon River district ........................
Arizona ...........................................
Banner district ..............................
Cameron area .................................
Courtland-Gleeson district ...................
Jerome district ..............................
Pima district ................................
Other occurrences ............................
Arkansas ..........................................
Northern Arkansas zinc-lead district .........
California ........................................
Darwin district ..............................
Bidwell Bar district .........................
Ivanpah district .............................
East Shasta district .........................
Other occurrences ............................
Colorado ..........................................
Horseshoe-Sacramento district ................
Kokomo district ................................
La Plata district ..............................
Pando area ...................................
Rico district ................................
Uncompahgre district .........................
Other occurrences ............................
Georgia ...........................................
Cartersville district ........................
Other occurrences ............................
Idaho .............................................
Illinois, Iowa, Kentucky, and Wisconsin ...........
Upper Mississippi Valley district ............
Kentucky-Illinois district....................
Central Kentucky district.....................
Michigan ..........................................
Missouri ..........................................
Southeastern Missouri district ...............
Page
56
57
58 61 63 67 71 73 78 81 84 88
88
89
89
90 90
90
91
91
92
93 93
93
94 94 94 96 96 96
96
97 97 97 99 99 99
100
101
102
102
102
103
104 104 104 106 106 106 107 107
in﻿IV
CONTENTS
Page
Characteristics of jasperoid in other than the major mining districts of the United States—Continued
Montana ............................................... 107
Phillipsburg district ............................ 108
Nevada ................................................ 108
Atlanta district ................................. 108
Bald Mountain district............................ 110
Boyer district ................................... 110
Candelaria district .............................. 110
Cedar Mountain district .......................... Ill
Cherry Creek district ............................ Ill
Contact district ................................. Ill
Cortez and Mill Canyon districts ................. Ill
Delmar district .................................. 112
Dolly Varden district ............................ 112
Dyer district .................................... 113
Ferguson district ................................ 113
Getchell mine area (Potosi district) ............. 114
Gilbert district ................................. 114
Goodsprings district ............................. 114
Groom district .................................   115
Kern district ...................................  115
Lewis district ................................... 115
Manhattan district ............................... 116
Mineral Hill district ............................ 116
Patterson district ............................... 116
Santa Fe district................................. 116
Silverhorn district............................... 117
Silver Peak district ............................. 117
Taylor district ................................   117
Tecoma district .................................. 119
Ward district and West Ward area ................. 119
White Pine (Hamilton) district ................... 121
Willow Creek district ............................ 122
Wyndypah district ................................ 122
Other occurrences ................................ 122
New Mexico ............................................ 123
Bishop Cap district .............................. 124
Carpenter district ............................... 125
Cooks Peak district............................... 125
Cuchillo Negro district .......................... 125
Hadley (Graphic) district ........................ 125
Hermosa (Sierra Caballos) district ............... 126
Hillsboro district ............................... 126
Kingston district ................................ 126
Lake Valley district ............................. 126
Magdalena district ............................... 127
Organ district ................................... 127
Santa Rita district .............................. 128
Steeple Rock district............................. 128
Tierra Blanca district ........................... 128
Tres Hermanas district ........................... 129
Page
Characteristics of jasperoid in other than the major mining districts of the United States—Continued
Victorio district ............................. 129
Other occurrences ............................. 129
North Carolina and South Carolina................... 130
Pennsylvania and New Jersey ........................ 130
Friedensville district ........................ 131
Other occurrences ............................. 131
South Dakota ....................................... 131
West Lead district ..........................   132
Ragged Top Mountain district .................. 133
Carbonate district ..........................   134
Tennessee .......................................... 134
Bumpass Cove district ......................... 134
Eastern Tennessee zinc district................ 134
Central Tennessee district	................ 135
Other occurrences ............................. 135
Texas .............................................. 135
Shafter district .............................. 135
Eagle Mountains district ...................... 136
Other occurrences ............................. 136
Utah .............................................   137
Bingham district .........................——	137
Bull Valley (Goldstrike) district ............. 139
Clifton district .............................. 139
Drum Mountains (Detroit)	district ........... 139
Dugway district ............................... 140
Gold Hill district ............................ 140
Lucin district ................................ 142
Mercur and Ophir districts .................... 142
Mount Nebo district ........................... 143
North Tintic district ....................-... 144
Rush Valley (Stockton) district ............... 144
San Francisco district and	vicinity ........... 144
San Rafael Swell area.....................-... 145
Silver Islet district.......................... 146
Tutsagubet district .........................   146
Other occurrences ...........................-	146
Virginia and West Virginia ......................... 147
Austinville district .......................... 147
Howell mine area ..................-.......... 147
Timberville district........................... 147
Other occurrences ............................. 147
Washington .......................................—	148
Metaline district ............................. 148
Other occurrences ............................. 149
Wyoming ............................................ 149
Miller Hill area .............................. 149
References cited ....................................... 149
Index .................................................. 157
ILLUSTRATIONS
Figure 1.
2.
3.
Page
Map showing jasperoid-bearing localities and provinces of the conterminous United
States ........................................................................... 4-5
Photographs: A, Typical outcrop of jasperoid; B, Hand specimen of jasperoid showing preservation of primary bedding texture .......................................... 8
Diagram showing mean size and size range of jasperoid grains in 200 samples .......... 10﻿CONTENTS
V
Page
Figuke 4. Diagram showing frequency distributions of mean size and size range of jasperoid
grains ............................................................................... 11
5-13. Photomicrographs of jasperoid showing—
5.	Typical jigsaw-puzzle texture ................................................... 11
6.	Typical xenomorphic texture ..................................................... 11
7.	Granular texture ................................................................ 12
8.	Feathery and fibrous textures ................................................... 13
9.	Reticulated texture ............................................................. 13
10.	Stages in the replacement of limestone by jasperoid ............................. 14
11.	Typical calcite dust-sized particles ............................................ 14
12.	Incipient jasperoid in dolomite ................................................. 15
13.	Selective replacement of calcite containing dolomite ............................ 15
14.	Photograph (A) and photomicrograph (B) of jasperoid contact with limestone ......... 16
15-31. Photomicrographs of jasperoid showing—
15.	Ghost colloform banding ......................................................... 17
16.	Zoned allophane inclusions ...................................................... 17
17.	Chert and fine-grained jasperoid cemented by coarser grained jasperoid .......... 17
18.	Veinlet of fine-grained quartz cutting coarse-grained jasperoid	matrix .......... 18
19.	Brecciated chert cut and cemented by coarser quartz ............................. 18
20.	Barite veinlet cutting jasperoid ................................................ 20
21.	Chalcedony ...................................................................... 20
22.	Goethite lining vugs filled with coarse supergene quartz, in limonite gossan ....	22
23.	Hematite pseudomorphous after pyrite in oxidized jasperoid .....................  22
24.	Jarosite inclusion in late coarse quartz, filing fractures and cavities in jas-
period ....................................................................   23
25.	Limonite particles disseminated through aphantic jasperoid ................ 23
26.	Lussatite lining vug in goethite ................................................ 24
27.	Fine-grained supergene jasperoid impregnated with manganese oxide ............... 24
28.	Opal groundmass cut by hematite veinlets and younger chalcedony veinlet ......... 25
29.	Alternating colloform bands of pyrite and chalcedonic jasperoid	................. 26
30.	Small pyrite grains disseminated in Arkansas Novaculite ......................... 26
31.	Quartz grain inclusions in jasperoid, showing accretionary overgrowths in
optical continuity ........................................................   27
32.	Histograms showing distributions of density and porosity in 124 jasperoid samples .. 29
33.	Histograms showing distributions of elements detected in the majority of jasperiod
and chert samples .................................................................... 32
34.	Diagrams showing solubility of quartz in H20: A, At 300 atm pressure; B, at 400°C ....	38
35.	Graph showing comparison of scores for megascopic plus microscopic criteria with
scores for chemical criteria on all samples .................................... 58
36-50. Maps showing jasperoid-bearing areas in—
36.	Southwest Missouri, Oklahoma, Kansas, and Arkansas .............................. 59
37.	Alaska .......................................................................... 89
38.	Arizona ......................................................................... 90
39.	California ...................................................................... 95
40.	Colorado ........................................................................ 98
41.	Georgia, North Carolina, South Carolina, Tennessee, and southwest Virginia ..	103
42.	Idaho and Montana .............................................................. 104
43.	Illinois, Iowa, Kentucky, Wisconsin, and southeastern Missouri ................. 105
44.	Nevada ......................................................................... 109
45.	New Mexico ..................................................................... 124
46.	Pennsylvania, New Jersey, northern Virginia, and West Virginia ................. 130
47.	South Dakota and Wyoming ....................................................... 131
48.	Texas ................................................-.................... 136
49.	Utah ........................................................................... 137
50.	Washington ..................................................................... 148﻿VI
CONTENTS
TABLES
Page
Table 1.	Colors of fresh and weathered surfaces of oxidized hypogene	jasperoid	samples ......... 7
2.	Accessory minerals found in jasperoids, showing age relative	to silicification	of host
rock and approximate abundance .......................................................... 19
3.	Jasperoid-associated minerals reported in the literature, other than those discussed in
the text ...............................-............................................ 28
4.	Analyses of jasperoid and other similar rocks ............................................. 31
5.	The observed range and average concentrations of the 13 commonly reported oxides
plus sulfur for 10 representative jasperoid samples compared with those of certain other rock types ......................................................................   31
6.	Distribution of minor elements in jasperoid ............................................... 35
7.	Median concentrations of elements detected in jasperoid samples ........................... 36
8.	Composition of some natural silica-bearing waters ......................................... 42
9.	Distribution of megascopic characteristics in 95 favorable and 53 unfavorable oxi-
dized jasperoid samples ................................................................. 53
10.	Distribution of microscopic characteristics in 95 favorable and 53 unfavorable jas-
peroid samples .......................................................................... 54
11.	Distribution of density and porosity in 72 favorable and 41 unfavorable jasperoid
samples ................................................................................. 54
12.	Maximum difference in cumulative proportions of characteristic and common ele-
ments between favorable and unfavorable samples, and significance of this difference ................................................................................. 55
13.	Distribution of minor elements in 95 favorable and 53 unfavorable jasperoid sam-
ples .................................................................................... 55
14.	Evaluation of criteria for distinguishing between favorable and unfavorable jasperoid
samples ................................-............................................ 56
15.	Summary of percentages of misclassified samples scored according to various com-
binations of classifications ............................................................ 57
16.	Age relations of minerals in Ely district jasperoid to the jasperoid quartz................ 69
17.	Minor-element distribution in 26 samples of jasperoid from the Ely district, Nevada.. 70
18.	Relative abundance of 15 most abundant elements in 26 samples of jasperoid from the
Ely district, Nevada .................................................................... 70
19.	Minor-element distribution in 25 samples of jasperoid from the Tintic and East Tintic
districts, Utah ......................................................................... 77
20.	Relative abundance of 13 most abundant elements in 25 samples of jasperoid from the
Tintic and East Tintic districts, Utah .................................................. 77
21.	Characteristics of jasperoid in major districts of the United States ................... 86-87﻿JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
By T. G. Lovering
ABSTRACT
Jasperoid is a rock composed dominantly of silica, most commonly quartz, that has formed largely by epigenetic replacement. It is a common product of hydrothermal alteration of carbonate rocks in many mineralized areas.
Although jasperoid in the United States is most abundant in limestone and dolomite, it also occurs in shale, mudstone, extrusive igneous rocks, and metamorphic rocks. Most bodies of jasperoid are localized along faults, fracture zones, and shear zones, and they spread laterally from such conduits through beds of favorable lithology or permeability, or beneath impermeable caprocks. In many mining districts of the Western United States, the jasperoid bodies seem to be both spatially and genetically related to siliceous igneous intru-sives.
Individual bodies of jasperoid range in size from pods a few feet in diameter to masses more than a quarter of a mile in their greatest dimension. Many form crosscutting veins or reefs; others form concordant mantos or sheets. Some are lenticular, and some are extremely irregular in shape with many projecting apophyses.
Large masses of jasperoid characteristically form prominent rugged outcrops that shed a talus of angular broken blocks. They tend to be strongly brecciated and recemented by younger quartz. The rock is fine grained to aphanitic in texture; the coarser varieties resemble fine-grained quartzite, and the finer varieties resemble chert. Vugs are commonly abundant and conspicuous. Jasperoid in most outcrops is oxidized and is stained by iron oxides in various shades of brown, yellow, and red. Unoxidized jasperoid is predominantly gray or black. Some jasperoid retains both the color and texture of the host rock, and is distinguishable only by its greater hardness. Some masses of jasperoid have sharp contacts with unreplaced host rocks; others grade into the host through a transition zone of tiny irregular quartz veinlets and disseminated quartz grains.
Quartz in jasperoid displays a variety of microtextures. The two most common are irregularly interlocking grain boundaries, comparable to xenomorphic texture in igneous rocks, and extremely irregular sinuous boundaries with individual grains interlocking like the pieces of a jigsaw puzzle. A less common texture, which seems to be confined to jasperoid and which may be used to distinguish it from other forms of quartz, consists of randomly oriented euhedral to subhedral quartz laths that form a reticulated net, with the interstices filled by interlocking anhedral grains.
Although jasperoid is composed predominantly of quartz, only a few varieties are composed entirely of quartz. The most common of nearly 100 observed accessory minerals are allophane, barite, calcite, chalcedony, dolomite, goethite, hematite, hydromica, jarosite, kaolinite, limonite, opal, pyrite,
sericite, tourmaline, and zircon. Some accessory minerals are unreplaced inclusions in, or remnants of, host rock. A few are nearly contemporaneous with the matrix quartz, but most are younger than the matrix quartz and form crosscutting veinlets, vug fillings, or oxidation pseudomorphs of older minerals.
Chemical analyses of selected samples indicate that typical jasperoid consists of about 80-99 percent silica; the remainder is mostly iron, aluminum, calcium, magnesium, and water, in varying proportions. Forty-three elements were detected, by spectrographic analyses, in one or more of 200 samples; of these elements, only silicon, aluminum, iron, magnesium, calcium, titanium, manganese, barium, chromium, copper, nickel, strontium, and vanadium were detected in most of the samples.
The prerequisites to the formation of jasperoid are (1) an adequate source of silica, (2) solutions that can transport silica to the site of deposition, (3) an environment at this site that inhibits the solubility of silica and promotes solution of host rock, and (4) reaction rates that cause the host rock to dissolve at least as fast as silica precipitates.
Possible sources of silica are (1) a cooling magma at depth contributing juvenile siliceous emanations, (2) silica-bearing rocks above or below the host rock, and (3) silica disseminated through the host rock itself.
The capacity of an aqueous fluid to transport silica depends largely on the form of silica available, and on the temperature, pressure, and chemical composition of the system. Although hydrothermal fluids are generally capable of transporting silica in higher concentrations than is cool water, ground water can also transport large quantities of silica under the proper conditions during a longer period of time.
Ionic solubility of silica varies directly with the fluid density of the solvent. At low temperature, saturation with respect to ionic silica is low in strongly acid solutions, increases slightly in weakly acid solutions, declines to a minimum in neutral solutions, rises in slightly alkaline solutions, and rises rapidly in strongly alkaline solutions. Dispersed silica sols tend to be stable at low pH; consequently, acid solutions are capable of transporting large quantities of silica.
The silica content of natural waters ranges from a low of about 6 parts per million in sea water to a high of several hundred parts per million in thermal springs of volcanic origin. The concentration of silica in natural water seems to be largely independent of the total dissolved solids in the water.
Precipitation of silica can result from (1) decrease in fluid density, (2) evaporation of the solvent, (3) neutralization of acid or alkaline waters, (4) contact with a solid form of silica, (5) changes in the concentration of certain dissolved salts, (6) the mingling of dispersed sols with opposite elec-
1﻿2
JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
trical charges, or (7) a combination of these factors. Iron and aluminum promote precipitation of silica from acid solutions, and barium and fluorine promote its precipitation from alkaline solutions. Sodium chloride causes silica to precipitate from supersaturated solutions and to dissolve in undersaturated solutions. Increases in temperature and pressure accelerate the conversion of silica gel to quartz.
Although some jasperoid bodies probably result from solution of host rock at an early stage and from precipitation of silica in the resulting voids at a later stage, the common preservation of original host rock textures in replacing jasperoid furnishes evidence that simultaneous solution of host rock and precipitation of silica by the same solution must also be an important process in the formation of such bodies.
If a hot aqueous silica-bearing fluid containing dissolved COa and NaCl rose under pressure along an insulated conduit into a layer of carbonate rocks that was highly permeable, the resulting rapid change in physical and chemical environment would be conducive to this type of volume-for-volume replacement. Both carbonic acid and sodium chloride increase the solubility of carbonate rocks. The rising pH of the solution resulting from reaction with these rocks, and the drop in both temperature and pressure as the solution spread from the feeding conduit through the permeable zone, would tend to supersaturate the solution with silica. The presence of sodium chloride would, however, inhibit such supersaturation and cause the excess silica to precipitate as the carbonate rock dissolved. If the silica precipitated as a gel rather than as crystalline quartz, the rate of replacement would decline as the reaction became dependent on diffusion of solution through the thickening gel layer. However, the higher temperature of solutions on the inlet side of the system would promote rapid conversion of silica gel to quartz. The loss in volume resulting from such a conversion would open new channels for solutions to move toward the reaction interface with the host rock. If silica precipitated directly as quartz disseminated through the host, solutions could continue to flow along intergrain boundaries and tiny fractures in the host rock and the growing nuclei of quartz within it.
The appearance, texture, mineralogy, and composition of ore-related jasperoid samples from many different localities were studied and compared statistically with the same attributes of non-ore-related samples. Characteristics found to be significantly more common in ore-related samples include phaneritic texture, abundant vugs, brown color, highly variable grain size, reticulated microtexture, the presence of goethite, jarosite, pyrite, and >0.00015 percent Ag, >0.0015 percent Pb, >0.015 percent Zn, >0.003 percent Cu, >0.0007 percent Mo, >0.15 percent As, >0.0007 percent Ga, >0.0007 percent In, >0.0015 percent Sn, >1.5 percent Fe. Characteristics found to be significantly more common in samples not associated with ore are red color, jigsaw-puzzle microtexture, and the presence of yellow limonite, montmorillonite, hydromica, sericite, and >0.01 percent Mg.
Numerical scores were awarded to each characteristic according to its statistical level of significance, and the scores were summed for each sample in both groups. More than 90 percent of the ore-related samples yielded scores of 5:5, and more than 90 percent of the non-ore-related samples yielded scores of ^5.
Each of the nine major jasperoid-bearing mining districts in the United States has yielded ore worth at least $100 million. These districts, in order of decreasing production, are
Tri-State, Clifton-Morenci, Bisbee (Warren), Ely (Robinson), Leadville, Tintic, Gilman, Aspen, and Eureka. The distribution and characteristics of jasperoid in each of these districts are discussed in some detail. Information on jasperoid in 99 other mining districts and mineralized areas in the United States is summarized more briefly, and 97 other occurrences of jasperoid or silicified rock that may be jasperoid are named and located.
INTRODUCTION
PURPOSE AND SCOPE OF THE INVESTIGATION
The common association of bodies of silicified rocks (jasperoid) with replacement ore deposits in mining districts of the Western United States prompted this investigation. The major objectives are twofold: first, to establish criteria for distinguishing jasperoids that are closely associated with replacement ore bodies (favorable jasperoids) from similar siliceous bodies that are unrelated to ore (unfavorable jasperoids and cherts); second, to obtain information on the physical and chemical nature of jasperoid as a rock type and on the environment in which it forms.
Much of the information has been derived from geologic literature, and most of the rest, from examination and analysis of jasperoid samples contributed by my colleagues.
DEFINITION OF “JASPEROID”
Although the term “jasperoid” has been established in the literature since the late 19th century, some confusion still exists as to its exact meaning. This confusion is due in part to the many names that have been applied to jasperoids. These include blout, flint, quartz, jasper, hornstone, chert, secondary chert, hydrothermal chert, limestone quartzite, ozarkite, cherokite, silicified limestone, and silicified dolomite.
The term “jasperoid” was first introduced by Spurr (1898, p. 219-220), who wrote:
Jasperoid may then be defined as a rock consisting essentially of cryptocrystalline, chalcedonic, or phenocrystalline silica, which has formed by the replacement of some other material, ordinarily calcite or dolomite. This jasperoid may be white or various shades of red, gray, brown, or black, the colors resulting from different forms of iron in varying proportions.
Lindgren (1901, p. 678), in his report on meta-somatic processes in fissure veins, wrote as follows:
Many tiny quartz grains first appear scattered through the rock, chiefly along areas of slight shearing or fracture. Here and there appear long slender quartz crystals entirely surrounded by fresh limestone. As silicification proceeds, the slender crystals multiply, forming a characteristic network, sometimes enclosing small areas of calcite which are sprinkled with small, irregular quartz-grains of varying size, in which﻿INTRODUCTION
3
the retiform structure is still apparent, and which rock resembles a chert or a fine-grained and altered quartzite, and is generally somewhat porous, drusy, and also often colored red or yellow. In structure, appearance, and origin, this cherty rock is identical with the jaspers of Lake Superior. Mr. Spurr proposes “jasperoid” as a term for this rock, consisting essentially of cryptocrystalline, chalcedonic or phanero-crystalline silica formed by the replacement of other rocks, chiefly limestone.
Lindgren did not stipulate an origin due to the agency of circulating water, as did Spurr. Further confusion regarding the definition of the term “jasperoid” is caused by the fact that both Lindgren and Spurr regarded the jasper of the Lake Superior region as being a jasperoid. Van Hise and Leith (1911, p. 124, 556), in their famous monograph on the geology of this region, did not commit themselves to a replacement origin for the jasper, and regarded the interbedded iron ore as syngenetic. In an investigation of the Ironwood Iron-Formation, Huber (1959, p. 111-113) stated that the jasper is primary.
The characteristic features of jasperoid described by Lindgren are evident in much of the jasperoid from the type locality at Aspen, Colo., but some of them are not apparent in many rocks called jasper-oids by later investigators in other areas. Smith and Siebenthal (1907, p. 14) applied the term to the dense black siliceous rock in the Joplin district, Missouri-Kansas, which is commonly associated with the galena and sphalerite ore bodies. Soon afterward, Irving (1911, p. 630-631) described gold-bearing jasperoid bodies in the Black Hills of South Dakota whose contacts with the enclosing dolomite are knife-edge sharp. Duke (1959) defined jasperoid as “any rock which is composed mostly of secondary silica.”
There seems to be general agreement on two points: (1) jasperoids are composed predominantly of silica, which in most places is in the form of aphanitic to fine-grained quartz, and (2) jasperoids form by replacement of the enclosing rock. For this study, I return to Spurr’s definition (1898) by restricting the usage of the term “jasperoid” to mean “an epigenetic siliceous replacement of a previously lithified host rock.” Jasperoid, thus defined, excludes syngenetic or diagenetic forms of silica, such as primary chert and novaculite.
ACKNOWLEDGMENTS
I am deeply indebted to H. T. Morris, A. V. Heyl, and T. S. Lovering, who not only contributed a vast amount of valuable information on jasperoid and constructive criticism of this manuscript, but also provided many of the specimens in my collection.
Thanks are also given to Frank Howd and Arthur Rose of the Bear Creek Mining Co., and to D. A. Brobst, the late A. H. Koschmann, J. H. McCarthy, Jr., Arthur Pierce, J. J. Norton, J. C. Ratte, D. R. Shawe, A. F. Shride, Ogden Tweto, E. J. Young, and many other geologists of the U.S. Geological Survey who furnished jasperoid samples from many mining districts. Richard Taylor took many excellent photomicrographs illustrating jasperoid textures. Mrs. Elizabeth Tourtelot carefully searched the literature on mining districts and compiled much of the information that is included in the district summaries. J. C. Hamilton made most of the spectro-graphic analyses of my j asperoid samples.
DISTRIBUTION OF JASPEROID GEOGRAPHIC DISTRIBUTION
Jasperoid bodies have been recognized and reported from more than 200 mining districts and mineralized areas in the United States (fig. 1), and they undoubtedly occur in many more areas. Bodies of jasperoid that are apparently unrelated to commercial ore deposits are also common throughout large areas of the Western United States, but because most of them are small, widely scattered, and of no known economic importance, they rarely are shown on small-scale regional geologic maps. Thus, the localities shown on figure 1 probably represent less than half the actual jasperoid localities in the United States.
Many of the known localities are concentrated in certain areas, or jasperoid provinces; others are widely scattered. Jasperoid provinces may be of significance in broad-scale economic exploration programs because they represent regions within which jasperoid seems to be associated with ore. These provinces, shown in figure 1, are: (1) a large area in eastern Nevada and western Utah, (2) an area west and southwest of Tonopah, Nev., extending southward into California, (3) an area in central Colorado surrounding Leadville, (4) a long narrow area in southwestern New Mexico extending from Magdalena southward to the Mexican border, (5) the Tri-State “district” (in reality a very large region of many “districts,” as the term is used in the West) surrounding the common corner of Kansas, Oklahoma, and Missouri, and (6) the lead-zinc “district” of northern Arkansas. In each of these provinces are many districts in which jasperoid bodies are associated, both genetically, and spatially, with sulfide ore deposits. It is also noteworthy that major mining districts lie near the center of many of these provinces, for example, Ely, Nev., Leadville, Colo., and the “Picher Field,” Okla.﻿4	JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
128”	126”	124”	122”	120”	118”	116”	114”	112”	110°	108°	106”	104”	102”	100”	98°	96”
114”	112°	110”	108°	106”	104”	102”	100°
Figure 1.—Jasperoid-bearing localities and﻿5
DISTRIBUTION OF JASPEROID
96°	94°	92°	90°	88°	86°	84°	82°	80°	78°	76°	74°	72°	70°	68°	66°	64°﻿6	JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
In the Eastern United States the scarcity of jasperoid-bearing mining districts may reflect a scarcity of such districts with readily silicified host rocks and may also reflect a lack of published information on jasperoid in certain districts where jasperoid does exist.
Many jasperoid-bearing mining districts in other countries have been reported in the literature. A few of these are listed below.
Central and South America, Antilles
Sierra Mojada district, Coahuila, Mex.
Santa Barbara district, Chihuahua, Mex.
Santa Eulalia district, Chihuahua, Mex.
Colquijirca mine near Cerro de Pasco, Peru Eastern Cuba Western Haiti Europe
Vosges Mountains, France Rosia district, Tuscany, Italy
Kostajnika district, Southern Croatia, Yugoslavia Africa
Anti-Atlas Mountains, Morocco Tsumeb district, South-West Africa Postmasburg district, Cape Province Pilgrims Rest district, North-East Transvaal Australia
Tasmania
Asia
Tienpaoshan district, Sinkiang Province, China South Fergana district, Uzbek, USSR Kara Tau Mountains, Kazak, USSR
GEOLOGIC DISTRIBUTION
HOST ROCK
Rocks vary greatly in their susceptibility to replacement by silica. The most susceptible rocks are limestone and dolomite; shale and siltstone are also replaceable, although considerably less so than the calcareous rocks. Siliceous hypabyssal and extrusive igneous rocks and pyroclastics have a susceptibility to replacement by silica comparable to that of shale. Plutonic igneous rocks and metamorphic rocks, except for marble and metavolcanic rocks, appear to be most resistant to siliceous replacement. Sandstones and conglomerates that are impregnated with silica and brecciated rocks that are recemented by silica are, by definition, not jasperoids.
Most of the jasperoid bodies reported in the geologic literature have formed by the replacement of limestone or dolomite. Commonly, other rock types that have been jasperoidized are closely associated with similarly altered calcareous rocks.
Jasperoids occur in host rocks of all ages, from Precambrian to Tertiary; however, the greatest concentration of jasperoid bodies in the Western United States is in rocks of Devonian, Mississippian, and Pennsylvanian ages. Probably, this concentration
merely reflects the fact that calcareous rocks of these ages cover a considerably larger area of the Western United States than do calcareous rocks of any other age.
STRUCTURAL CONTROL
Most jasperoid bodies are localized along zones of structural disturbance, such as breccia zones, shear zones, and faults, and this structural control is the best criterion for distinguishing jasperoid from chert or novaculite. Channelways created by these zones of structural weakness provide the plumbing system through which the silica-bearing solutions gain access to the host rocks. In other localities a relatively impermeable caprock has caused widespread lateral migration of silicifying solutions at the contact, resulting in a jasperoid blanket conformable with the host rock. Such bodies may closely resemble bedded chert on the outcrop, but they can be identified as jasperoids by such features as local silicification of the caprock, transgression of the bedding, or by the presence of feeding channels. Layers of jasperoid may also form by selective replacement of certain favorable beds in a carbonate series. The jasperoid in this type of deposit closely resembles bedded chert, but it can be distinguished from chert by the following criteria: (1) jasperoid beds are localized in a relatively small area, in contrast to the broad regional distribution of bedded cherts, and (2) such jasperoid layers commonly grade laterally into larger masses with evident structural control. Jasperoid blankets may also form in the permeable zone along a buried erosion surface, and jasperoid may replace limestone adjacent to old drainage channels and sinkholes beneath such a surface.
Jasperoid deposits are most prevalent in the vicinity of intrusive bodies of igneous rocks, to which they are genetically related. The presence of an intrusive mass, however, is not a prerequisite for the occurrence of jasperoid. Large masses of jasperoid are found far removed from any known intrusive stocks—for example, in the Tri-State district of Kansas, Oklahoma, and Missouri.
GEOLOGIC AGE
The laboratory methods of geochronology that have been applied to plutonic and hypabyssal igneous rocks cannot be applied to jasperoids, and their age is therefore difficult to determine. Most of the jasperoid bodies whose distribution is shown in figure 1 are presumed to be of “Laramide” age (late Mesozoic or early Cenozoic). Jasperiod masses of known Precambrian age have been reported from﻿PHYSICAL PROPERTIES OF JASPEROID
7
the Jerome district and the Fort Apache iron district of north-central Arizona, and from Tasmania, Australia'; rounded detrital pebbles of jasperoid, presumably of Permian age, have been found in the Triassic Shinarump Member of the Chinle Formation and in the Jurassic Morrison Formation in the northern Colorado Plateau; and jasperoid replaces Tertiary marine limestones and associated volcanic rocks in Cuba and Haiti (Goddard and others, 1947, p. 34-37; Park, 1942, p. 81-82, 92-93). There is a suggestion that jasperoid bodies may be forming today beneath some of the hot springs in the Yellowstone Basin. The waters of some of these springs are rich in calcium bicarbonate and deficient in silica; these chemical characteristics strongly indicate contact with carbonate rocks at depth, and it seems a reasonable hypothesis that they lost silica to these rocks as they leached calcium carbonate (D. E. White, written commun., 1957).
PHYSICAL PROPERTIES OF JASPEROID MEGASCOPIC FEATURES
Jasperoid varies widely in physical appearance; commonly, a single body contains several distinguishable varieties of jasperoid with distinctive colors, textures, and assemblages of associated minerals.
COLOR
Many jasperoids range in color from white through various shades of gray to coal black; this is particularly true of unoxidized varieties. An iron content of 0.1-1 percent generally is sufficient to impart various shades of brown, yellow, orange, and, less commonly, red and pink to most oxidized jasperoid outcrops. Less colorful outcrops are common in areas where the iron content of the jasperoid is unusually low, or where the jasperoid is so dense that little or no oxidation of the iron present has taken place. In some jasperoid the pigmentation is primary and colors the rock below the zone of surface oxidation.
The relative frequency of various color occurrences in my suite of oxidized jasperoid samples, from more than 50 localities, is shown in table 1. Most of the samples are mottled, veined, streaked, or banded with more than one color, which accounts for the total of the various colors being higher than the total number of samples. The prevailing colors of fresh exposures of oxidized jasperoid are shades of gray, followed by light to medium brown and orange. The prevailing colors of weathered jasperoid are medium brown, light brown, and orange, followed by dark brown, reddish brown, and dark gray.
Table 1.—Colors of fresh and weathered surfaces of oxidized hypogene jasperoid samples from more than 50 localities in the United States
[The 12 most common colors are listed, in order of decreasing frequency of occurrence]
Fresh surface (267 samples)		Weathered surface (205 samples)	
	Number		Number
Color	of samples	Color	of samples
1....Medium gray 		109	1....Medium brown ....	68
2....Medium brown ....	56	2....Light brown 		47
3--Dark gray-black..	54	3....Orange 		40
4....Light brown 		54	4....Medium gray		25
5....Orange 		52	5....Dark brown 		23
6....White to light		6....Reddish brown ....	22
gray 		35	7....Dark gray-black ..	20
7....Reddish brown ..	27	8 ...Dark red 		16
8....Yellow 		24	9—.White to light	
9....Medium red 		23	gray 				14
10....Pink 		22	10....Yellow 		11
11....Dark red 		20	11....Medium red 		10
12....Olive gray 		20	12....Olive gray 		10
Red and pink jasperoids are relatively uncommon, as may be seen in table 1.
My collection contains only 35 samples of unoxidized jasperoid, from 15 localities. Dark gray is the predominant color of this suite, followed by medium gray and white. Individual specimens also show various shades of olive gray, brown, yellowish gray, and grayish orange.
I also have 11 samples of supergene jasperoid that are gradational into siliceous gossans. These samples are a variety of dark colors, including dark gray, dark brown, dark yellowish orange, dark reddish brown, and dark red.
TEXTURE
Jasperoid bodies are resistant to weathering and commonly exhibit prominent rough outcrops (fig. 2A). Where their distribution is controlled by faults, these outcrops tend to stand up as uneven walls or “reefs.” Jasperoid is both hard and brittle and therefore is commonly highly fractured and brecciated in zones of structural instability. This shattering causes both characteristic rough outcrops and aprons of angular sharp-edged talus blocks below such outcrops. Gilluly (1932, p. 98) described jasperoid bodies, in the Mercur and Ophir districts of Utah, as being cut by many randomly curved and slickensided fracture surfaces that terminate abruptly at the contact with the country rock, suggesting differential movement of blocks within the body after its solidification.
Another distinctive feature of jasperoid exposures in many districts is the abundance of vugs. These range in size from microscopic openings to﻿8 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Figure 2.-A, Typical outcrop of jasperoid, Lake Valley district, New Mexico (photograph by E. J. Young). B, Hand specimen of jasperoid showing preservation of primary bedding texture.﻿PHYSICAL PROPERTIES OF JASPEROID
9
cavities several inches in diameter. The larger vugs characteristically are lined with crystals of quartz or calcite. Vugs in jasperoid commonly show a random orientation and distribution, but many are restricted to well-defined zones. Locally, they have a strong preferred orientation, forming lenticular voids parallel to the walls of the jasperoid mass in which they occur.
Many jasperoid bodies have sharp, well-defined contacts with their host rocks. Some have transitional contacts, grading outward through a zone of unreplaced fragments of host rock in jasperoid into a zone of shattered host rock cut by anastomosing veinlets of jasperoid, and finally into a zone of quartz grains or slender, doubly terminated quartz crystals randomly disseminated through the host. Others are bordered by a zone of soft friable carbonate rock, which breaks down on weathering so that the contact is not exposed at the surface.
In some places jasperoid differs strikingly in appearance and texture from its host. Elsewhere, the color, texture, and primary bedding of the host rock are faithfully preserved in the replacing jasperoid (fig. 2B). Extensive bodies composed exclusively of a single homogeneous type and generation of jasperoid are rare. Most jasperoid masses consist of several distinct varieties of jasperoid, in which the oldest generation has been fractured or brecciated and then recemented by a second generation. This second generation, in turn, has been cut by a third generation, and so on, so that it is not uncommon to find five or more distinct ages and types of jasperoid in large exposures. In most such bodies, only the oldest generation is a true jasperoid, strictly speaking, formed by replacement of the host. The younger generations have merely filled fractures, without replacement. It is customary, however, to refer to the entire mass as jasperoid.
The typical texture of jasperoid is aphanitic, almost glassy, but fine-grained phaneritic jasperoid with a “sugary” texture is common in some areas. Locally, jasperoid with an average grain size of as much as 1 millimeter is found. In mining districts where relatively coarse grained jasperoid forms the host rock for disseminated sulfide minerals, or where jasperoid is disseminated in a carbonate host rock, leaching in the zone of oxidation has produced light friable porous masses of “honeycomb quartz.” Such masses from the Lowell mine at Bisbee, Ariz., were described by Ransome (1904, p. 131) and from the Bingham district, Utah, by Boutwell (1905, p. 68, 118,202).
ASSOCIATED MINERALS
Jasperoid that constitutes the host rock for ore bodies commonly contains a wide variety of visible accessory ore minerals. Considerably fewer minerals, recognizable in hand specimen, are common in oxidized jasperoid not closely associated with ore. They are chalcedony, calcite, dolomite, hematite, limonite, “manganese oxides,” and, more rarely, pyrite, fluorite, barite, siderite, opal, chlorite, and apatite. These minerals occur either disseminated through the jasperoid matrix or concentrated in veinlets and on the walls of vugs.
Primary jasperoid, produced by hydrothermal alteration, commonly exhibits oxides of iron and manganese as surface stains and fracture coatings, and, locally in the zone of oxidation, it contains scattered iron oxide pseudomorphs after original sulfides. Secondary or supergene jasperoid, produced by siliceous alteration from ground water during weathering and oxidation of an ore body, commonly contains oxides of iron and manganese intimately mixed with, and disseminated through, the siliceous matrix; it rarely exhibits sulfide pseudomorphs.
MICROSCOPIC FEATURES
Thin sections of jasperoid, examined with a petrographic microscope, exhibit considerable variation in grain size, a wide range of textures, and a much more extensive suite of accessory minerals than is visible to the naked eye. A jasperoid sample that in hand specimen appears to be simple, dense, and relatively homogeneous may reveal, when examined under the microscope, a complex history, starting with replacement, followed by successive brecciation and recementation, and ending with weathering and oxidation.
GRAIN SIZE
The mean grain size and size range of grains in recognizable distinct varieties of jasperoid in 200 thin sections were recorded and plotted on a scatter diagram (fig. 3). Size range was recorded as the ratio of the mean diameter of the largest grains to that of the smallest. The high concentration of points in the lower left corner of this diagram shows that jasperoid is commonly very fine grained, having a mean grain size of <0.05 mm, and is relatively homogeneous, with a ratio of largest grain to smallest grain of <10:1. It is the abundance of this type of jasperoid that makes it so difficult to distinguish between jasperoid and chert in hand specimens. The nature of the mean size and size-range distributions of these samples is further shown by the histograms in figure 4. The class intervals chosen﻿MEAN SIZE, IN MILLIMETERS
10 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Figure 3.—Mean size and size range of jasperoid grains in 200 samples. □, unfavorable; •, favorable; X, not known.﻿PHYSICAL PROPERTIES OF JASPEROID
11
o
H
LlI
0
<
o cr
SIZE
RANGE (MEAN DIAMETER OF LARGEST GRAINS/MEAN DIAMETER OF SMALLEST GRAINS)
MEAN GRAIN SIZE, IN MILLIMETERS
Figure 4.—Frequency distribution of mean size and size range of jasperoid grains.
for these histograms are approximately equal on a logarithmic scale, except for the two open-end classes. The resulting distributions after the logarithmic transformation still show a pronounced positive skewness, thus emphasizing that most jasperoid is extremely fine grained and relatively homogeneous.
FABRIC TEXTURE
The shapes of jasperoid grains and their mutual boundaries produce several different characteristic textural patterns.
One of the most common microtextures in jasperoid consists of highly irregular grains that are tightly interlocked—in somewhat the same way as are the pieces of a jigsaw puzzle (fig. 5). This texture is typical of extremely fine grained and relatively homogeneous varieties of jasperoid, and probably represents the crystallization of an original silica gel into quartz. Relatively coarse grained jasperoid may also exhibit “jigsaw-puzzle” texture. Such coarse jigsaw-puzzle jasperoid is commonly as-
Figuke 5.—Typical jigsaw-puzzle texture in aphanitic jasperoid. Crossed polars. X 100.
sociated with masses of fibrous chalcedony, filling voids in an older generation of jasperoid.
Jasperoid grains that are somewhat irregular at their boundaries but lack the deep sinuous indentations and amoeboid forms that characterize the jig-
Figure 6.—Typical xenomorphic texture in coarse-grained heterogeneous jasperoid. Crossed polars. X 40.﻿12 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
saw-puzzle texture produce a textural pattern very similar to the xenomorphic texture commonly observed in nonporphyritic igneous rocks. This texture is characteristic of many jasperoids that have a heterogeneous grain-size distribution in which smaller grains form inclusions in, or fill interstices between, larger grains (fig. 6), and it may also occur in jasperoids that have relatively homogeneous grain-size distribution. Textural gradations from jigsaw puzzle to xenomorphic are common within a single jasperoid type, and these two textural varieties characterize most jasperoids.
The granular texture that is typical of finegrained detrital sedimentary rocks is also found in a few jasperoids of replacement origin. The grains are all about the same size, are nearly equant, and have smooth, simple boundaries (fig. 7A). Rarely, when the individual granules are examined under the microscope with crossed nicols, they do not extinguish as a unit but show a peculiar hourglass type of extinction in which different quadrants of a granule extinguish in different positions (fig. 7B). Granular texture is relatively rare in jasperoid, although it is characteristic of silicified siltstone, which may be indistinguishable from jasperoid in hand specimens.
Masses or veinlets of jasperoid quartz that have formed from original chalcedony may exhibit a peculiar “feathery” texture (fig. 8A) or a “crossfiber” texture, suggestive of chrysotile veinlets in serpentine of the type shown in figures 8B and C. These textures in quartz are rare, however, because chalcedony seems to be a stable mineral in most jasperoids.
Another type of texture that is common in the coarser grained varieties of jasperoid consists of abundant elongated grains with a length-to-width ratio of 3:1 or greater. Such grains are elongated parallel to the c axis, and some show crystal faces. They are randomly distributed in a matrix of smaller, nearly equant, anhedral grains, and commonly give the appearance of a crude mesh or network. This reticulated texture (fig. 9) is useful in distinguishing jasperoid from other siliceous bodies, such as chert and novaculite, because it seems to be peculiar to jasperoid. Unfortunately, only a relatively small proportion of jasperoids has this texture; therefore, its absence in a sample cannot be considered as evidence that the rock is not a jasperoid. The origin of reticulated texture in jasperoid has been discussed by Lindgren (1901, p. 678; quoted on p. 2 of present report). His statements therein appear to be valid, except for the implication that all jasperoids form in a manner that pro-
Figure 7.—Granular texture. A, Granular texture in Pre-cambrian jasperoid. Crossed polars. X 68. B, Granular jasperoid with hourglass extinction. Crossed polars. X 68.
duces this texture; actually, only a small proportion of them seem to do so. The presence of reticulated texture in jasperoid is evidence of the original deposition of silica as crystalline quartz rather than as a colloidal gel and is most common in bodies whose contacts with the host rock are gradational.
The first phase in the formation of this type of﻿PHYSICAL PROPERTIES OF JASPEROID
13
Figure 9.—Reticulated texture in jasperoid. Crossed polars.
X 68.
jasperoid is commonly a recrystallization or mar-morization of limestone that results in the formation of numerous coarse grains of calcite. Accompanying, or closely following, this recrystallization is the formation of small grains and slender euhedral crystals of quartz randomly scattered through the calcite (fig. 10A). As silicification proceeds, there is a selective replacement, outward from tiny fractures (fig. 105), of the smaller calcite grains by fine-grained aggregates of anhedral quartz. Finally, only irregular remnants of the coarse calcite grains remain as inclusions in the jasperoid matrix (fig. 10C). The jasperoid quartz formed by this process is commonly clouded by tiny dust-sized particles of calcite, a few microns in diameter (fig. 11). These particles are characteristically round or oval in section, and, rather than being tiny unreplaced remnants of the original host rock, they appear to have exsolved as the quartz crystallized. Such carbonate particles are also found in jasperoid that has jigsaw-puzzle and xenomor-phic textures. Wherever the particles occur, they provide evidence of the origin of the enclosing quartz by replacement of a carbonate host rock.
Figure 8.—Feathery and fibrous textures. A, Feathery texture in jasperoid quartz recrystallized from chalcedony. Crossed polars. X 100. B, “Crossfiber” texture in quartz veinlet (Q). Crossed polars. X 68. C, Detail of quartz vein-let shown in B. Crossed polars. X 170.﻿14 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Figure 11.—Typical calcite dust-sized particles in jasperoid. Crossed polars. X 250.
The replacement process just outlined is common in limestone, but for some reason the growth of euhedral quartz crystals seems to be inhibited by a dolomitic host rock, although the recrystallization of the host rock and the selective replacement of smaller grains by aggregates of anhedral quartz (fig. 12) proceed in a manner similar to that outlined for limestone. Dolomite is more resistant to replacement by silica than is limestone, and unreplaced original dolomite crystals may be preserved in a completely jasperoidized limestone (fig. 13). Where aphanitic jasperoid, of the type shown in figure 5, comes in contact with a carbonate host rock, that contact is normally sharp and well defined (fig. 14), in contrast to the gradational contacts just discussed. Sharp contacts of this type probably are indicative of rapid precipitation of silica, as a gel, from solutions that were highly supersaturated with silica.
Evidence of the colloidal origin of some jasperoid may be preserved in delicate repeated colloform
Figure 10.—Stages in the replacement of limestone by jasperoid. A, First stage, disseminated quartz grains and crystals (Q) in a matrix of coarse recrystallized calcite. Crossed polars. X 30. B, Second stage, selective replacement of smaller calcite grains by fine-grained anhedral quartz aggregates (Q). Crossed polars. X 40. C, Third stage, remnants of coarse calcite (C) in a jasperoid matrix. Crossed polars. X 100.﻿PHYSICAL PROPERTIES OF JASPEROID
15
Figure 12.—Incipient jasperoid in dolomite (note similarity to fig. 105). Crossed polars. X 100.
bands, which bear no relation to existing grain boundaries or textural variations and which disappear under crossed nicols (fig. 15). This type of texture has its counterpart in zonally arranged inclusions of allophane or carbonate particles that preserve the euhedral outlines of original seed crystals of quartz in a mass composed of an aggregate of coarse anhedral grains (fig. 16). These zoned inclusions around euhedral cores provide good evidence that the early jasperoid was deposited directly as quartz rather than as a gel. They are most common in late quartz that fills veinlets or voids in an older generation of matrix jasperoid, but they may also occur within a matrix of coarse jasperoid.
Where more than one generation of quartz is present in a jasperoid, as is generally true, the younger generations are commonly coarser grained and more heterogeneous than the oldest generation (fig. 17) ; but in some jasperoids the younger quartz is finer grained than the matrix (fig. 18). Some chert layers in limestone are locally brecciated and recemented by younger quartz (fig. 19).
ACCESSORY MINERALS
The accessory minerals associated with jasperoid quartz may be divided into three groups on the basis of their age relative to the main period of silicifica-tion. These groups are (1) early—older minerals, remnants of unreplaced host rock or accessory min-
0.2 mm
Figure 13.—Selective replacement of calcite containing dolomite, by jasperoid. A, Dolomite rhomb in coarse calcite remnant in jasperoid matrix. Crossed polars. X 100. B, Disseminated dolomite rhombs in jasperoid matrix, which has replaced calcite (same section as that shown in A). Crossed polars. X 100.
erals from the host rock preserved in the jasperoid;
(2)	contemporary—minerals formed penecontempo-raneously with silicification of the host rock; and
(3)	late—the large group of minerals that were﻿16 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Figure 14.—Jasperoid contact with limestone. A, Abrupt contact between jasperoid (J) and limestone (L), showing later brecciation and cementation by coarse calcite (C). Specimen from the Egan Range, Nev. Natural size. B, Jasperoid (J) contact with limestone (L). Same specimen as that shown in figure A. Crossed polars. X 40.﻿PHYSICAL PROPERTIES OF JASPEROID
17
Figure 15.—Ghost colloform banding. A, Plane polarized light. X 68. B, Crossed polars. X 68.
emplaced after the initial silicification; this group includes both minerals deposited from late hypogene hydrothermal solutions and strictly supergene minerals formed as a result of weathering and oxidation. The distinction between the two categories of minerals included in the third group may be clear where both outcrop samples and samples taken from
Figure 16.—Zoned allophane inclusions outlining original quartz crystal nuclei (N) and growth stages (G), in coarse xenomorphic jasperoid. Crossed polars. X 170.
Figure 17.—Chert (ch) and fine-grained jasperoid (F) cemented by coarser grained jasperoid (C), with late coarse quartz (Q). Crossed polars. X 40.﻿18 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
0.5 mm
Figure 18.—Veinlet of fine-grained quartz cutting coarsegrained jasperoid matrix. Crossed polars. X 68.
studied are outcrop samples; hence, I made no attempt to differentiate between these two categories. Table 2 gives the paragenesis, in terms of these three groups, of accessory minerals that I identified in thin sections of 250 jasperoid samples collected from about 40 different mining districts and unmineralized localities.
ALLOPHANE
Allophane is a common, though minor, constituent of jasperoid quartz. It forms tiny inclusions, a few microns in diameter, embedded in the quartz grains. Where more than one generation of quartz is present, the allophane is most highly concentrated in the oldest generation. Allophane particles may be zoned either in hexagonal patterns around original qu&rtz crystal cores (fig. 16) or in wavy colloform patterns (fig. 15A). These zonal patterns, where present, are useful indicators of the form in which the silica was originally deposited; colloform patterns suggest crystallization of jasperoid from a colloidal silica gel, whereas hexagonal patterns indicate deposition of silica directly in the form of quartz crystals.
Figure 19.—Brecciated chert (ch) cut and cemented by coarser quartz (Q). Crossed polars. X 40.
below the zone of oxidation are available from the same jasperoid body; however, this distinction becomes much more difficult to make where only the outcrop can be sampled. Most of the samples I
ANKERITE
Ankerite is very sparse in jasperoid, but where it occurs, it is in the form of relict inclusions. It is indicative of a hydrothermal carbonate phase of host-rock alteration preceding silicification.
BARITE
Barite is relatively common in jasperoids, particularly those associated with ore deposits; however, in regions characterized by abundant barite, such as north-central Nevada, it is found in jasperoid bodies far removed from sulfide deposits. It may form granular aggregates or euhedral crystals older than the quartz, it may be disseminated through the matrix in small grains deposited penecontempo-raneously with the silica, or it may be present in younger masses and veinlets (fig. 20) and as crystals that line vugs.
BEIDELLITE (?)
Small aggregates and disseminated particles of a mineral belonging to the montmorillonite group, tentatively identified as beidellite, were observed in a few jasperoid samples. This mineral is approximately contemporaneous with the matrix quartz in which it occurs; but positive identification could not be made with the petrographic microscope, and the mineral is not sufficiently abundant to furnish a sample for X-ray identification.﻿PHYSICAL PROPERTIES OF JASPEROID
19
Table 2.—Accessory minerals found in jasperoids during the present study, together with their composition, relative age,
and relative abundance
[The minerals were identified, by T. G. Lovering, in thin sections of 250 jasperoid samples collected from about 40 mining districts and unmineralized localities]
Mineral
Composition
Age and relative abundance 1 Early Contemporary Late
Allophane .................... A1203, Si02, toH20 ...........
Ankerite ..................... CaO • (Mg,Fe) O • 2C02 ......
Barite ....................... BaO • S03 ...................
Beidellite? .................. Al203±SiOa • 3±H20 ..........
Biotite ...................... K20 • 4(Mg,Fe) 0 • 2(Al,Fe)20;
Brochantite .................. HCuO • S03 • 3H20 .................
Calcite ...................... CaO • C02 ..........................
Carbon ....................... C ..................................
Cerussite .................... PbO • C02 .........................
Chalcedony ................... Si02 ..............................
Chalcopyrite ................. CuFeSa ............................
Chlorapatite ................. 9CaO • 3P205 • CaCl2 ..............
Chlorite ..................... H<Mg3Si2O.-H<Mg2Al2Si09 ...........
Dickite ...................... A1203 • 2Si02 • 2H20 ..............
Dolomite ..................... CaO • MgO • 2C02 ..................
Epidote ...................... Ca2(Al,Mn,Fe)3Si3Oi2(OH) ..........
Fluorite ..................... CaF2 ..............................
Galena ....................... PbS ...............................
Glauconite ................... Si02,Al203,Fe203,Fe0,Mg0,K20,H20 ..
Goethite ..................... Fe203 • H20 + »H20 ................
Halloysite ................... A1203 • 2Si02 ■ 2H20 ..............
Hematite ..................... Fe203 ..............................
Hydromica .................... (Al,Fe),(Al,Si)< • K<-5(OH)2• wH20
Jarosite ..................... K20 • 3Fe203 • 4S03 • 6H20 .........
Kaolinite .................... A1203 • 2Si02 • 2H20 ...............
Limonite ..................... Fe203 • reH.O ......................
Lussatite .................... Si03'wH20(?)	...................
Magnetite .................... Fe203 • FeO ........................
Malachite .................... 2CuO • C02 ■ H20 ..................
“Manganese oxide” ............ Mn0,Mn203,±nH20 ....................
Microcline ................... K20 • A1203 • 6Si02 ...............
Montmorillonite .............. MgO • A1203 ■ 4Si02 • wH20 ........
Muscovite .................... K20 • 3A120
Nontronite ................... (Ca,Mg)0
Opal ......................... Si02 rtH20
Orthoclase ................... K20 • A120:
6Si02 • H20
3 ■ 6Si02 • 2H20 .....
• 2Fe203 • 8Si02 • 7 ± H20
Si02
• 3A1203 C02 . C02 .
6Si02 • 2H20
Plagioclase ................... Na20 ■ A1203 • 6SiOa-CaO • A1203 • 2Si02
Pyrite ........................ FeS2 .................................
Quartz ........................ Si02 .................................
Sericite ...................... K20 •
Siderite ........................ FeO	•
Smithsonite ..................... ZnO	•
Sphalerite .................... ZnS .......................
Sphene ........................ CaO • Ti02 • Si02 .........
Stibiconite ................... Sb2Ot • mH20 ? ............
Tourmaline .................... Na20 • 8FeO • 8A1203 • 4B203
Tremolite ..................... 2CaO • 5MgO • 8Si03 • H20 .
Wulfenite ..................... PbO • Mo03 ................
Zircon ......................... Zr02	•	Si02 ..............
16Si02 ■ 5H20
x
x
X
x
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X?
X
1X, major accessory; x, minor accessory.
BIOTITE
Biotite is very sparse in jasperoid, and where it occurs, it seems to be a relict mineral older than the enclosing quartz.
BROCHANTITE
Brochantite is present in minor amounts, as a late mineral, in veinlets cutting jasperoid in the oxidized zone of some copper districts. In one sample from the Bisbee district, Arizona, brochantite lines the walls of a veinlet that is filled with still younger supergene quartz.
CALCITE
Calcite is the major constituent of the most common host rock for jasperoid and is present in nearly all jasperoid bodies. Very fine grained limestones are in many places recrystallized into coarsely crystalline calcite adjacent to jasperoid bodies, and relict grains and breccia fragments of unreplaced calcite and limestone are common in these bodies. Where replacement of the host rock is more nearly complete, tiny particles of calcite are locally preserved in the quartz (fig. 11). These particles may﻿20 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Figure 20.—Barite veinlet (B) cutting jasperoid. Crossed polars. X 100.
be concentrated in patterns, similar to those for allophane, that indicate the form in which the silica was deposited, or they may be randomly distributed. Late calcite fills veinlets that cut the matrix or forms layers that coat vugs. Much of this late calcite may be of supergene origin, deposited in cavities by circulating ground water, but some was probably deposited by late hydrothermal solutions.
CARBON
Amorphous, opaque, very dark brown or black organic material occurs in some jasperoids. It may be present as irregular masses or as streaks or particles disseminated in the matrix quartz, or it may be concentrated along grain boundaries. In some places it is concentrated in a zone adjacent to the host rock in which abundant relict grains of unreplaced calcite or dolomite remain. Most of this organic material in jasperoid represents an inert impurity inherited from the host. The carbon particles disseminated in some jasperoids however, may have been introduced and deposited by the silicify-ing solutions.
CERUSSITE
Cerussite, a constituent of lead ore-bearing jasperoid, occurs in the zone of oxidation. It is an alteration product of galena, and commonly forms
either pseudomorphs of galena crystals or alteration rims around relict grains of galena.
CHALCEDONY
Chalcedony is abundant in jasperoid. It forms spherulites and irregular masses that are penecon-
0.2 mm
Figure 21.—Chalcedony. A, Chalcedony (C) transitional into late quartz (Q), lining a vug. Crossed polars. X 40. B, Veinlet of fibrous chalcedony cutting aphanitic jasperoid. Crossed polars. X 130.﻿PHYSICAL PROPERTIES OF JASPEROID
21
temporaneous with the jasperoid quartz matrix (fig. 21 A,B), but more commonly it fills veinlets and lines cavities (fig. 21 A,B) in the jasperoid. Rarely, breccia fragments of chalcedony are enclosed in the matrix. Sparse and peculiar feathery or fibrous forms of jasperoid quartz appear to have formed from the dehydration of original chalcedony (fig. 8 A). Chalcedony is more abundant in fine-grained jasperoid than in the coarser varieties.
CHALCOPYRITE
Chalcopyrite, like galena, occurs locally in unoxidized samples of productive jasperoid. It is characteristically slightly younger than the first generation of matrix silica.
CHLORAPATITE
Rounded grains of chlorapatite, older than the matrix jasperoid, are present in some samples from the Ely district, Nevada. An unusual sample from the Shirley Basin, Wyo., contains, as a major constituent, an aphanitic uraniferous chlorapatite that is associated with veinlets of younger chalcedony. This mineral is rarely present in jasperoids.
CHLORITE
Chlorite is a sparse relict mineral in jasperoid. It also occurs locally as a late hydrothermal mineral in the jasperoids of some major districts. T. S. Lovering (1949, p. 39) reported abundant younger chlorite in some jasperoid from the Tintic district, Utah, where it formed close to the mineralizing conduits.
DICKITE
Dickite was sufficiently abundant for identification in only one thin section, and there it appeared to be older than the matrix quartz. It is highly probable, however, that minor amounts of dickite are intimately associated with kaolinite in other specimens, but the mineral was not recognized because of the similarity of its optical properties to those of kaolinite.
DOLOMITE
Dolomite, like calcite, is a very abundant constituent of jasperoid. It generally appears as unreplaced remnant grains and aggregates in jasperoid masses that replace a dolomitic host rock. Another common mode of occurrence is as tiny euhedral rhombs disseminated through the matrix. These rhombs may have been deposited at the same time as the silica, or they may be relicts from the selective
replacement of limestone in which they were originally embedded (fig. 13). Veinlets of late dolomite that cut jasperoid are extremely sparse. Late carbonate, in jasperoid that replaces dolomite, is generally calcite rather than dolomite.
EPIDOTE
Although epidote is a common constituent of the higher temperature lime silicate rocks, it is extremely sparse in jasperoid. It was identified in only one thin section, where it is present as small corroded grains in a brecciated zone that was later silicified.
FLUORITE
Fluorite is relatively sparse in jasperoid, but where it does occur, it is generally a late hypogene mineral in the form of veinlets that cut the matrix, or as masses that enclose grains and aggregates of early jasperoid quartz. Locally, it lines vugs and cavities in the matrix.
GALENA
Below the zone of oxidation, bodies of jasperoid that are host rocks for sulfide ore commonly contain disseminated grains and crystals of galena associated with pyrite. In most of these occurrences, the sulfides are clearly introduced after the silicifi-cation of the host rock. Locally, deposition of silica and sulfides may have been contemporaneous. Galena is rarely formed before the enclosing quartz.
GLAUCONITE
Glauconite was identified in only one sample, and there it is present as tiny rounded grains in a fragment of silicified sandstone incorporated in a matrix of coarse quartz.
GOETHITE
Goethite is common in oxidized jasperoids, where it forms late veinlets and irregular masses. It also rims vugs, or it may be disseminated as tiny grains through the matrix quartz. Crystalline orange goethite is commonly associated with amorphous isotropic brown or yellow limonite with hematite, and less commonly, with jarosite. It is generally a very late mineral, younger than both the matrix quartz and the limonite; however, in the relatively few samples in which it is disseminated through the quartz matrix it appears to be contemporaneous in origin with the silica and is indicative of supergene jasperoid. Sharp euhedral pseudomorphs of goethite after pyrite are common in jasperoid outcrops in﻿22 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Figure 22.—Goethite (G) lining vugs filled with coarse supergene quartz (Q), in limonite gossan (black). Crossed polars. X 68.
mineralized areas, but similar pseudomorphs of limonite or jarosite are sparse. In some samples, vugs, cavities, and veinlets are rimmed with orange goethite and are filled with younger coarse xeno-morphic quartz (fig. 22). The fact that the introduction of this quartz did not result in the conversion of goethite to hematite indicates that such quartz may form at low temperatures. Indeed, in many places there is strong evidence that it was deposited by downward-percolating surface waters during weathering and oxidation of the outcrop.
HALLOYSITE
Halloysite is a sparse late mineral that accompanies kaolinite. It lines vugs and fills fractures.
HEMATITE
Like goethite, hematite is abundant in the oxidized parts of some jasperoid bodies, to whose outcrops it imparts a characteristic deep-red color, it is generally a late mineral that fills fractures and permeates the rock along quartz-grain boundaries, and it commonly forms good pseudomorphs after original pyrite crystals (fig. 23). Unlike goethite, however, hematite occurs in many samples as an early hypo-gene mineral, either coprecipitated with original silica and disseminated through the resulting jasperoid, or as irregular masses cut by later jasperoid
Figure 23. Hematite (H) pseudomorphous after pyrite in oxidized jasperoid. Crossed polars. X 68.
quartz. In most samples that contain both hematite and goethite the hematite is older, but in some samples the two minerals seem to be nearly contemporaneous. Hematite that is definitely younger than associated goethite is very rare. According to Tunell and Posnjak (1931), goethite is unstable above 130°C. There is ample evidence, however, that either hematite or goethite can form at low temperatures. Iron oxide, like silica, apparently may be precipitated at relatively low temperatures—either as a colloidal hydrosol or directly in anhydrous form. Once it is precipitated as hematite it is stable, but the hydrosol may crystallize into goethite, maintain its amorphous form, and partly desiccate to form limonite, or, depending on its environment after deposition, it may even undergo complete dessication to form hematite.
HYDROMICA
Hydromica is a common constitutent of early hypogene jasperoid quartz, through which it may be disseminated. Sericite normally accompanies the hydromica, and has the same habit of occurrence. Most of the hydromica in jasperoid apparently precipitated concurrently with the early silica, but locally it occurs in older clay pockets and lenses. It is much less abundant in younger generations of jasperoid quartz, and has not been observed as a late, postsilica mineral.﻿PHYSICAL PROPERTIES OF JASPEROID
23
CjM			
A	I/O		c. *
Figure 24.—Jarosite inclusion (J) in late coarse quartz (Q),
filling fractures and cavities in jasperoid. Crossed polars.
X 100.
JAROSITE
The oxidation of pyrite in, or adjacent to, jasperoid bodies in arid regions commonly causes the precipitation of jarosite from the acid potassiumbearing sulfate waters. Jarosite—in veinlets and as vug coatings, disseminated granules, and irregular masses—accompanies goethite, hematite, and limo-nite in weathered jasperoid (fig. 24). Massive jarosite only rarely forms the matrix for breccia fragments of jasperoid. In many places jarosite is clearly derived from the alteration of pyrite, but it has not been observed as a direct pseudomorph of pyrite crystals. Jarosite is a late supergene mineral, generally even later than associated goethite.
KAOLINITE
Kaolinite is a major constitutent of relict clay pockets and lenses that are incorporated in silicified breccias or are inherited from impure argillaceous carbonate rocks. It may also be associated, in minor amounts, with hydromica and sericite introduced contemporaneously with the silica. It is locally a late mineral, occurring with halloysite, coating vugs, and filling fractures in the matrix quartz. It is not abundant in most jasperoids.
LIMONITE
The amorphous isotropic forms of hydrous iron oxide that are abundant as stains and fracture coat-
Figure 25.—Limonite particles disseminated through apha-nitic jasperoid. Crossed polars. X 170.
ings on outcrops, and in the oxidized zone beneath, have been lumped together under the heading of “limonite.” These limonites are normally some shade of brown, ranging from a dark chocolate brown to light tan, but some are yellow or orange. In some supergene jasperoids, limonite particles are evenly disseminated through the groundmass and contemporaneous with it (fig. 25). Rarely, limonite inclusions are present in younger jasperoid quartz. In most samples, however, it is definitely later than the quartz, and it coats fractures and lines vugs. Limonite normally is associated with late hematite, goethite, and jarosite, but in many jasperoid samples it is the only iron mineral present. The reason for the wide variation in the color of limonite is not known, although the dark-brown varieties seem to be most commonly derived from the oxidation of sulfides, particularly copper-iron sulfides.
LUSSATITE
Lussatite, a very sparse form of silica, has the refractive indices of opal and the birefringence of quartz (fig. 26). It is fibrous, has positive elongation and parallel extinction, and gives a disorder cristo-balite pattern on X-ray. Rogers and Kerr (1942, p. 190) regarded it as probably a mixture of fibrous chalcedony and opal. In Dana’s “A textbook of Mineralogy, 4th ed.” (Ford, 1932, p. 473), lussatite is mentioned as having a structure like chalcedony,﻿24 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
but the opposite sign, and the specific gravity and refractive index of opal. According to Frondel (1962, p. 280-281), lussatite is a fibrous form of low-temperature cristobalite with a composition similar to that of opal but containing less water. In the present study, lussatite was observed in two samples—a jasperoid breccia from the Ely Lime-
Figure 26.—Lussatite (L) lining vug in goethite, showing fibrous character. A, Crossed polars. X 170. B, Same field, with stage rotated. Plane polarized light. X 170.
stone in the Ely district, Nevada, and a silicified siltstone sample from the Deadwood Formation in the southwestern part of the Lead district, South Dakota. In the first sample, fragments of jasperoid are cemented by vuggy limonite and goethite, in a vein about 3 inches wide, between walls of opal; open vugs in the limonite are rimmed with orange goethite, and the goethite is encrusted with a thin film of lussatite. In the sample from the Deadwood Formation a succession of narrow bands, suggestive of Liesegang bands, consists of goethite and chalcedony. The goethite in these bands is full of microvugs that are lined with lussatite. In both, the occurrence of lussatite as a very late incrustation on goethite suggests that it was deposited at low temperature, probably from downward-moving1 surface waters.
MAGNETITE
Magnetite is a very sparse constitutent of hypo-gene jasperoids. It occurs as small rounded grains and short irregular veinlets in a fine-grained siliceous dolomite, which is locally replaced by jasperoid quartz, in the Pahasapa Limestone in the northern Black Hills of South Dakota. This magnetite is older than the jasperoid.
MALACHITE
Malachite is associated with jarosite, goethite, and brown limonite as an oxidation product from
Figure 27.—Fine-grained supergene jasperoid impregnated with manganese oxide (black areas). Crossed polars. X 40.﻿PHYSICAL PROPERTIES OF JASPEROID
25
the weathering of copper sulfide-bearing jasperoid. In most places it fills fractures and coats fractures, and it appears to be younger than the associated supergene iron minerals. Locally, it forms crystals embedded in remnant masses of recrystallized limestone or dolomite, in a matrix of jasperoid quartz.
“manganese oxides”
Aphanitic, black, opaque, supergene manganese oxides are abundant in a few oxidized jasperoids in mineralized areas. These normally are too finely divided to permit optical identification of the mineral species present. They characteristically impregnate the matrix quartz of supergene jasperoid (fig. 27), and are associated with limonite and goethite. They range in size from thin films to large irregular masses containing scattered quartz grains. In some places these masses are fractured and veined with younger quartz.
MICROCLINE
Most microcline found in jasperoids occurs as relict grains or crystals, inherited from the host rock, or as small angular breccia fragments. A few jasperoids, in the outer part of a contact-metamorphic zone surrounding an intrusive, however, contain younger microcline in veinlets that cut the jasperoid. Where this happens, the jasperoid matrix normally is impregnated with sericite.
MONTMORILLONITE
Montmorillonite is not a common constituent of jasperoid. It is occasionally observed in the form of tiny disseminated particles that cloud the matrix quartz, or more rarely, as a filling in late veinlets that cut the matrix.
MUSCOVITE
Rarely, coarse flakes of muscovite are incorporated in jasperoid breccias, or they are inherited from micaceous rocks that have been replaced by jasperoid.
NONTRONITE
Nontronite that occurs in jasperoids is, like hal-loysite, predominantly of supergene origin. Thin veinlets of nontronite cut jasperoid quartz in the zone of oxidation. The mineral also lines vugs and open cavities. In some samples it is associated with late calcite and goethite.
OPAL
Opal is a sparse, late, minor constitutent of jasperoid. It fills veinlets and coats cavities in association with chalcedony and goethite, and is commonly
Figure 28.—Opal groundmass (0), cut by hematite veinlets (H) and younger chalcedony veinlet (C). Plane polarized light. X 40.
of supergene origin. In one sample of supergene jasperoid, opal takes the place of quartz as the major silica mineral in the matrix. Here, the opaline groundmass contains disseminated red hematite and is cut by veinlets of hematite and of chalcedony (fig. 28). This opal replaced dolomite at the base of a volcanic flow.
ORTHOCLASE
Orthoclase, like microcline, locally occurs as breccia fragments, or as unreplaced inclusions, in a silicified matrix. It is very sparse, and has not been found as a contemporaneous or younger constitutent of jasperoid.
PLAGIOCLASE
The remarks made about orthoclase apply equally to plagioclase. Where remnant inclusions of plagio-clase do occur, they normally show sericitic alteration.
PYRITE
Pyrite is a common but not abundant constitutent of unoxidized jasperoids. Most pyritic jasperoids are spatially and genetically related to sulfide ore bodies in mining districts. However, pyrite also occurs as an early mineral in a considerable number of jasperoids that apparently are unrelated to any other sulfide mineralization, and therefore its presence﻿26 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
cannot be regarded as a reliable guide to ore. Pyrite is predominantly contemporaneous with, or slightly younger than, the oldest generation of matrix quartz. In a few samples, pyrite occurs as an aphanitic colloidal precipitate, contemporaneous
Figure 29.—Alternating colloform bands of pyrite and chal-cedonic jasperoid. A, Colloform banding. Dark bands are largely pyrite. Reflected light. X 40. B, Enlargement showing abundance of chalcedony (C) in some silica bands, and quartz (Q) in others. Black bands are largely pyrite. Crossed polars. X 100.
Figure 30.—Small pyrite grains (P) disseminated in Arkansas Novaculite. Crossed polars. X 170.
with the silica matrix (fig. 29). Pyrite in jasperoid generally crystallizes in cubic form, and in oxidized samples its former presence is shown by masses of cubic hematite or goethite or by square pits. In aphanitic, “cherty”-looking, barren jasperoid, pyrite may occur as tiny well-formed cubes, a few hundredths of a millimeter in diameter, evenly disseminated through the matrix and apparently contemporaneous with it. A similar occurrence of pyrite has been observed in fresh drill-hole samples of Arkansas Novaculite, in which both pyrite and quartz appear to have formed from a syngenetic marine chemical precipitate (fig. 30). Neither pyrite nor its pseudomorphs have been observed in supergene jasperoid.
quartz
The major constituent of nearly all jasperoids is quartz. It occurs both as a replacement and as an accessory mineral. Older quartz grains, inherited after the replacement of a sandy dolomite or limestone, are commonly found in jasperoids. Many of these grains show zonal overgrowths of jasperoid silica in optical continuity with the grain (fig. 31). Quartz of nonreplacement origin commonly fills veinlets that cut the matrix, or it forms well-formed crystals that line vugs and cavities. Some of these crystals are long, slender, and prismatic, but most are short and stubby or show only the pyramidal﻿PHYSICAL PROPERTIES OF JASPEROID
27
Figure 31.—Quartz grain inclusions (Q) in jasperoid, showing accretionary overgrowths of jasperoid silica in optical continuity. Crossed polars. X 68.
terminations. The theory that quartz may be precipitated directly from cold water as relatively coarse grained aggregates, or as crystals, is substantiated by its presence in these forms in veinlets in, and crusts on, supergene minerals such as goethite (fig. 22) and brochantite.
SERICITE
Sericite is a common constituent of the earliest generation of hypogene jasperoid quartz. It is characteristically present in the form of tiny shreds and flakes which are randomly disseminated through the groundmass and which seem to have been introduced with the replacing silica. Sericite may also be present in pockets of older clay, or as an alteration product in relict feldspar. It is notably less abundant in younger generations of quartz that cuts the matrix. It is commonly associated with hydromica and, locally, with kaolinite. The prevalence of sericite in association with hypogene jasperoid suggests that potassium is a major constituent of the silicabearing solutions that are responsible for the replacement by which this jasperoid formed.
SIDERITE
Siderite, like ankerite, is very sparse in jasperoid. It locally occurs in the form of relict grains and masses in the matrix, indicating an iron carbonate phase of rock alteration that preceded silicification. Rarely, it fills veinlets younger than the jasperoid quartz.
SMITHSONITE
Grains of sphalerite in ore-bearing jasperoid are locally replaced by smithsonite in the zone of oxidation, but, more commonly, the sphalerite either remains in its original form or is leached away entirely or is replaced in part by hemimorphite and jasperoid.
SPHALERITE
In many mining districts hypogene jasperoid forms a siliceous gangue for sphalerite ore. Normally, sphalerite is slightly younger than the quartz, but it may also be of about the same age. It is most commonly associated with pyrite and galena.
SPHENE
Small rounded detrital grains of sphene, originally present in the host rock, at places occur as relict inclusions in the replacing jasperoid.
stibiconite (?)
An aphanitic yellowish-brown antimony mineral that has a high index of refraction is a major con-stitutent of a jasperoid sample from the Taylor district, Nevada. It forms irregular massive inclusions in a jasperoid breccia that shows several periods of silicification. The mineral appears to be approximately contemporaneous with the youngest generation of quartz, and is probably a supergene alteration product of stibnite, which is relatively common in this district, although none was observed in the sample. This mineral has been tentatively identified as the hydrous antimony oxide stibiconite, which was reported from the Mercur district, Utah, by Gilluly (1932, p. 116), and from Kostajnika, Yugoslavia, by Beck (1905, p. 581) under the name “antimony ochre.”
TOURMALINE
Tourmaline, like sphene, in most places occurs in the form of rounded detrital grains inherited from the host rock. In a few places, however, tourmaline appears as tiny slender euhedral crystals that seem to have formed at about the same time as the quartz matrix in which they are embedded.
TREMOLITE
Tremolite, in association with diopside and coarsegrained calcite, is locally found in the outer fringe of contact metamorphic zones surrounding intrusive rocks, in veinlets that cut dense aphanitic siliceous rocks. Some of these siliceous rocks may be jasperoid, but most of them probably are chert.﻿28 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE Table 3.—Jasperoid-associated minerals reported in the literature other than those discussed in the text
Mineral
Composition
Locality
District	State or country
Reference
			Utah 	
		Organ 		New Mexico 	
		Tri-State 		Oklahoma, Kansas,
			Missouri.
			
		Horseshoe-Sacramento..	Colorado 	
		Mercur-Ophir 		Utah 	
		Mineral Hill 		Nevada 	
		Phillipsburg 		Montana 	
Arsenopyrite 		. FeAsS 		.. Gold Hill 		Utah 	
		Manhattan 		Nevada 	
Aurichalcite 		. 7(Zn,Cu)0.3C02*4H20 		.. Mercur-Ophir 		Utah 	
	. 3CuO2C02*H20 			
		Mineral Hill 		Nevada 	
		Phillipsburg 		Montana 	
		Pilgrims Rest 		South Africa 	
		Tutsagubet 		Utah 	
	Bi203*3H20( ?) 			
	. AgCl 			
		Lake Valley 		
		Mercur-Ophir 		Utah 	
		Mineral Hill 		Nevada 	
		Phillipsburg 		Montana 	
Chalcocite 		. CU2S 		Ely 		Nevada 	
		Phillipsburg 		Montana 	
Chrysocolla 		. Cu0*Si02*nH20 ( ?) 		» Lucin 		Utah 	
		Mercur-Ophir 		
		Phillipsburg 		Montana 	
			Utah 	
			
Freibergite 		. 5(Cu,Ag)2S*2(Cu,Fe)S*2Sb2S3	-- Phillipsburg 		Montana 	
Gold 		. Au 		- Bull Valley 		Utah 	
		Kingston 		New Mexico 	
		Pilgrims Rest 		South Africa 	
		Terry 		South Dakota 	
Gypsux** 		. Ca0*S03*2H20 		- Mercur-Ophir 		Utah 	
			
			
Manganocalcite 		, (Ca,Mn)0*C02 		- Kingston 		New Mexico 	
		Ouray 		Colorado 		
Manganosiderite 		. (Fe,Mn)0#C02 		- Leadville 			 do 	
			
		Tri-State 		Oklahoma, Kansas,
			Missouri.
Melaconite 		CuO 		- Mercur-Ophir 		Utah 	
Orpiment 		. AS2S3 		- Manhattan 		Nevada 	
		Mercur-Ophir 		Utah 		
			
Plumbojarosite 		. Pb0*3Fe203*4S03*6H20 		• Mercur-Ophir 		Utah 	
		Tutsagubet 		
Pyrargerite 		3Ag2S*Sb2S3 		- Ouray 		Colorado 	
	9Pb0.3P205*PbCl2 			
Pyrrhotite 		Fei-aS 		.. Ely 		Nevada 	
Realgar 		AsS 		. Manhattan 		
		Mercur-Ophir 		Utah 	
			
		Kingston 		New Mexico 	
		Ouray 		Colorado 	
		Phillipsburg 		Montana 	
Rhodonite 		(Mn,Mg,Fe,Ca) MnSi20a 		. Diadem Lode 		California 	
Scorodite 		Fe203*As205*4H20 		. Mercur-Ophir 		Utah 	
Senarmantite 		Sb20s 		. Kostajnika 		Yugoslavia	
		Rosia 		Italy 	
			
		Georgetown 		New Mexico 	
		Lake Valley 		
			
		Kostajnika 		Yugoslavia	
		Manhattan 		Nevada 	
		Mercur-Ophir 		Utah 	
		Rosia 		Italy 	
Stromeyerite 		(Ag.CuHS 		. Colquijirca 		Peru 	
		Cortez 		Nevada 	
	s			
		Mercur-Ophir 		Utah 	
		Rosia 		Italy 	
Sylvite 		KC1 		. Ely 		Nevada 	
Tennantite 		5Cu2S*2(Cu,Fe) S*2As2S." 		Cartersville 		Georgia 	
		Colquijirca 		Peru 	
		Horseshoe-Sacramento..	Colorado 	
Tetrahedrite 		5Cu2S*2 (Cu,Fe) S*2Sb2S3 		. Bingham 		Utah 	
		Cortez 		Nevada 	
		Gold Hill 		Utah 	
		Mineral Hill 		Nevada 	
		Ouray 		Colorado 	
		Stockton 		Utah 	
Wittichenite 		3Cu2S*Bi2S3 		. Colquijirca 		Peru 	
Gilluly (1932, p. 116).
Dunham (1935, p. 126-129).
Weidman (1932, p. 68).
Anderson, E. C. (1957,,p. 67).
Butler and Singewald (1940, p. 809).
Gilluly (1932, p. 116).
Emmons, W. H. (1910, p. 97).
Emmons and Calkins (1913, p. 213-219).
Nolan (1935, p. 102-103).
Ferguson (1921, p. 15).
Gilluly (1932, p. 116).
Do.
Emmons, W. H. (1910, p. 97).
Emmons and Calkins (1913, p. 213-219).
Beck (1905, p. 576-577).
Butler, Loughlin, Heikes, and others (1920, p. 595). Beck (1905, p. 576-577).
Anderson, E. C. (1957, p. 67).
Harley (1934, p. 176-178).
Gilluly (1932, p. 116).
Emmons, W. H. (1910, p. 97).
Emmons and Calkins (1913, p. 213-219).
Spencer (1917, p. 99).
Emmons and Calkins (1913, p. 213-219).
Butler, Loughlin, Heikes, and others (1920, p. 493). Gilluly (1932, p. 116).
Emmons and Calkins (1913, p. 213-219).
Butler, Loughlin, Heikes, and others (1920, p. 493). McKinstry (1936, p. 622).
Emmons and Calkins (1913, p. 213-219).
Butler, Loughlin, Heikes, and others (1920, p. 598). Harley (1934, p. 98).
Beck (1905, p. 576-577).
Irving (1911, p. 631).
Gilluly (1932, p. 116).
McKinstry (1936, p. 622).
Du Toit (1933, p. 113).
Harley (1934, p. 98).
Burbank (1940, p. 207).
Emmons, Irving, and Loughlin (1927, p. 218). Lindgren (1935, p. 334).
Weidman (1932, p. 68).
Gilluly (1932, p. 116).
Ferguson (1921, p. 15).
Gilluly (1932, p. 116).
Burbank (1940, p. 207).
Gilluly (1932, p. 116).
Butler, Loughlin, Heikes, and others (1920, p. 598). Burbank (1940, p. 207).
Emmons, W. H. (1910, p. 97).
Spencer (1917, p. 116).
Ferguson (1921, p. 15).
Gilluly (1932, p. 99).
Boutwell (1905, p. 160).
Harley (1934, p. 98).
Burbank (1940, p. 207).
Emmons and Calkins (1913, p. 213-219).
Turner (1899, p. 389).
Gilluly (1932, p. 116).
Beck (1905, p. 578-580).
Do.
Lindgren (1935, p. 334).
Anderson, E. C. (1957, p. 67).
Harley (1934, p. 176-178).
Emmons, W. H. (1910, p. 103-104).
Beck (1905, p. 578-581).
Ferguson (1921, p. 15).
Gilluly (1932, p. 99).
Beck (1905, p. 581).
Lindgren (1935, p. 334).
Emmons, W. H. (1910, p. 103-104).
Beck (1905, p. 578-581).
Gilluly (1932, p. 116).
Beck (1905. p. 581).
Spencer (1917, p. 63).
Kesler (1950, p. 48).
Lindgren (1935, p. 334).
Butler and Singewald (1940, p. 809).
Boutwell (1905, p. 160).
Emmons, W. H. (1910, p. 103-104).
Nolan (1935, p. 153).
Emmons, W. H. (1910, p. 97).
Burbank (1940, p. 207).
Butler, Loughlin, Heikes, and others (1920, p. 372). Lindgren (1935, p. 334).﻿PHYSICAL PROPERTIES OF JASPEROID
29
WULFENITE
Wulfenite has been observed in jasperoid from only one locality, the Seventy Nine mine in the Banner district, Arizona. Here, it forms crystals, associated with goethite, that line vugs in a jasperoid body that crops out near the entrance to the mine.
ZIRCON
Small rounded grains of zircon, associated with tourmaline, sphene, and other detrital minerals, are commonly preserved in jasperoid that has resulted from the silicification of siltstone and impure carbonate rocks.
OTHER MINERALS
Other minerals which are locally associated with jasperoid and which have been reported in the literature are listed in table 3. It is noteworthy that most of these minerals are those characteristic of shallow epithermal deposits. They consist largely of salts of Ag, As, Bi, Cu, Mn, Pb, and Sb.
OTHER PHYSICAL PROPERTIES
Studies were made of the density, porosity, and response to differential thermal analysis of some representative jasperoid samples in order to (1) estimate the nature of the. distribution of these properties in jasperoid and (2) ascertain whether variations in any of them could be useful in distinguishing barren jasperoid bodies from those related to ore. The results of this second phase of the investigation will be discussed in a subsequent chapter of this report.
DENSITY AND POROSITY
Bulk and powder density determinations were made on 124 jasperoid samples representing 19 districts. The porosity of the sample (in percent) was calculated from the equation,
[/ Bulk density \ 1
1 - ( Powder density") J X 100'
The observed range of powder densities is 2.50-3.61; that of porosities is from <1 to 17 percent. The frequency distributions for both density and porosity are distinctly skewed with modes in the low values (fig. 32). The sample frequency distribution for density approximates a log normal distribution, truncated in the low values. The distribution of sample porosity data is highly irregular.
The relatively large number of jasperoid samples with powder densities in the range 2.5-2.6 is surprising, because the major identifiable minerals in jasperoid (quartz, chalcedony, calcite, dolomite,
POWDER DENSITY
POROSITY, IN PERCENT
Figure 32.—Histograms showing distributions of density and porosity in 124 jasperoid samples.
limonite, kaolinite, sericite) all have specific gravities >2.6.
Many of the extremely fine grained cherty varieties of jasperoids may contain appreciable quantities of air or water trapped in submicroscopic pores, along fractures and grain boundaries, and in fluid inclusions, or the anomalously low birefringence of some of these varieties may reflect, in part, the presence of cristobalite or opal granules too small for identification but sufficiently abundant to lower the density of the rock. However, differential thermal analysis of some of these low-density samples﻿30 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
did not confirm the presence of abundant pore water, opal, or cristobalite.
The experimental error factor in these density determinations was appreciable, and may have been sufficient to account for the low-density values. The likelihood that these low values are due entirely to experimental error is considerably reduced, however, by the fact that some of them are based on independent determinations on replicate splits of the same sample made in different laboratories. The porosity values calculated from the ratios of two separate density determinations, both of which were subject to considerable analytical error, must be regarded as rough approximations. It is doubtful, however, that refinements in the determination of sample porosity would alter the general observation that dense jasperoid of low porosity is considerably more abundant than jasperoid of high porosity.
DIFFERENTIAL THERMAL ANALYSIS
Differential thermal analyses (hereafter referred to as DTA) were made on 12 selected jasperoid samples and on two chert samples in order to (1) test the theory that chert and aphanitic cherty jasperoid may contain appreciable quantities of opaline silica,
(2)	determine whether the DTA curves for syn-gepetic chert differed from those for jasperoid, and
(3)	ascertain whether the presence of finely divided sulfides, or their alteration products, in jasperoid would produce diagnostic peaks on the curves. All samples were run on a portable DTA apparatus, after calibration of the cells with a standard mont-morillonite sample.
Most of the jasperoid samples and one chert sample gave endothermic peaks at various temperatures between 100° and 800°C, but no consistent pattern was apparent. One jasperoid sample known to contain opal as a major constitutent showed, as expected a strong endothermic peak at about 100°C. A pyritic sample showed an endothermic peak at about 650 °C, and a sample containing much sphalerite showed a similar peak at about 750°C. Some samples that consist predominantly of aphanitic silica proved to be inert, but other samples of similar composition gave a pronounced isolated endothermic peak in the range of 500°-550°C. This range is too broad, and the peak too strong, to mark the inversion of a quartz to /3 quartz. The presence of this peak is difficult to interpret in terms of the known mineralogy of the samples. It comes at too high a temperature to mark the dehydration of clay minerals or hydrous iron oxides, and at too low a temperature to be caused by the breakdown of cal-cite or dolomite. Alunite could give such a peak, but
no alunite is visible in thin sections of these rocks.
Neither the “cherty” jasperoid samples nor the two samples of true chert showed any marked endothermic inflections in the range 80°~300°C. This casts considerable doubt on the theory that opal or well-crystallized cristobalite is present in any appreciable amount. The DTA curves of cristobalite, reported by Eitel (1957, p. 148), all show strong single endothermic peaks between 230° and 260°C.
This small sampling indicates that many jasper-oids and some cherts do give pronounced inflections on DTA graphs, but that these two rock types cannot be distinguished from each other by this method.
COMPOSITION OF JASPEROID
The connotation of a rock composed principally of fine-grained or dense replacement silica has been either stated or implied in the various definitions of jasperoid since the term was first introduced by Spurr in 1898. However, jasperoid grades into partly silicified mudstone, dolomite, and limestone with increasing alumina and carbonate content and decreasing silica content; into siliceous iron and manganese ore with increase in the oxides of these metals; and into siliceous sulfide ore with increasing sulfide content. The boundaries are vague and ill defined. They commonly have been established arbitrarily at the discretion of individual investigators in individual districts. Jasperoid that is minable for one or more metals is designated by the mining industry as siliceous ore. I consider that a rock matrix must consist of at least 50 percent replacement silica to be called a jasperoid.
MAJOR CONSTITUENTS
The few available complete analyses of jasperoids show considerable range in the concentration of major constituents, and do not differ notably from analyses of other similar rocks of different origin, with the exception of iron-formation jaspilites (tables 4, 5).
Any attempt to draw general conclusions as to characteristic differences in composition between jasperoids and the other silica rock types, with the possible exception of jaspilite, from the limited amount of data given in tables 4 and 5 is unwarranted. Some apparent differences in the sample data suggest the possibility of corresponding tendencies in the rock types, but, until considerably more analytical data become available for comparison, these differences must be regarded as suggestive only. Jaspilite samples contain about half as much silica and several times as much ferric oxide as the jasperoid samples, and somewhat less water. These﻿COMPOSITION OF JASPEROID
31
Table 4.—Analyses of jasperoid and other similar rocks
[I.L., ignition loss; .. no analyses]
Jasperoid
Chert, flint, and novaculite
Siliceous
Silcrete	sinter
	1	2	3	4	5	6	7	8	9	10		11	12	13	14	15	16	17	18	19	20
SiOa		.... 96.79	95.75	93.28	81.70	96.27	79.11	95.26	95.77	97.33	97.07	97.32		98.17	95.50	98.19	99.47	95.10	97.05	94.92	72.25	92.67
AI2O3			52	1.12	1.01	3.24	.26	3.82	.57			1.05		.52)	.83	^ .10	.00	.17	2.03	.95	2.32	10.96)	.80
Fe203		... 1.02	.36	1.29	5.41	.26	.44	.00	1.84	1.89	.53		.30/		) 1.95	.02	.12	.53	.14	.31	.76[	
FeO			17	.19	.37	.28	.19	.69	.69					.02		.15						.31	
MgO			16	.01	.04	.16	.19	1.19	.05	.24	.09	Trace		.02	.01	Trace	.21	.05	.20	.0		.10	.05
CaO			14	.00	.14	.44	1.16	.62	.25	.54	.11	.51		.52	.05		.30	.09	.16	.0		.74	.14
	.01	.00	.03	.12	.05	.31				.99	i 1	.02		Trace	.08	.15				3.55	.75
K2O			09	.09	.07	1.10	.11	.54							.03			.03	.07				1.66	.18
H2O +			35	.75	.31	2.16	.42	2.68		)	1.17	J .77			.491	.78	1.43	1.11'	.12	.46	.47	1.38)	9.02)	5.45
H2O-			05	.05	.06	.29	.03	.81		i					.161	I.L.	I.L.	.33	I.L.	I.L	I.L	I.Lf	I.L|	I.L.
Ti02		... .04	.03	.03	.20		.81				.04		.02					1.58	1.43	1.14		
P2O5			01	.06	.08	.05		.42						.02			.03						
MnO			03	.03	.03							Trace		.02 .38									
cos			09	.16	.05		.96										.24						
s		... .00	.08	1.05	12.97	.05	2 3.01						.00			.00					i.45	
BaO			00	.00	.00	.43	.06							.00									
Subtotal	 Other		.... 99.47	98.68 a—.04	97.84 3-.53	98.55 4 1.42	100.01 2.11	94.45 5 5.19	96.82	99.56	100.19	100.19 °.04	99.84		99.84	99.13	100.54	100.24	100.06	100.04	100.07	99.80 7.36	100.04
Total.......... 99.47	98.64	97.31	99.97 100.12 99.64 96.82 99.56 100.19 100.23 99.84 99.84	99.13 100.54 100.24 100.06 100.04 100.07 100.16 100.04
1 As SOa. 2 Au+Ag+Te. 8 Oxygen correction. 4 Sb20s+As205. 5 Cu+Fe as sulfides. 6 Cu+Zn+Ni+Co. 7 NaCl.
No.	Description
1	... Oxidized jasperoid .............
2	..........do .......................
3	... Unoxidized jasperoid ...........
4	... Oxidized jasperoid .............
5	... Unoxidized jasperoid ...........
6 ... Composite jasperoid sample ....
7	... Jasperoid ......................
8	..........do .......................
9	..........do .......................
10	..........do .......................
11	... Chert ..........................
12	..........do .......................
13	... Irish chert ....................
14	... English flint ..................
15	... Arkansas novaculite ............
16 ... Silcrete .......................
17	..........do .......................
18	..........do .......................
19	... Siliceous sinter ...............
20	..........do .......................
Locality
Minturn quadrangle, Colorado ............
Tintic district, Utah ...................
Tri-State district, Oklahoma.............
Mercur district, Utah ...................
Black Hills, S. Dak .....................
Ely district, Nevada ....................
Joplin, Mo ..............................
Joplin district, Missouri................
Galena, Kans.............................
Bull Frog mine, Chitwood, Mo ............
Custer County, S. Dak ...................
Belleville, Mo ..........................
Ireland .................................
England .................................
Arkansas ................................
Albertina, Cape Province, South Africa..
.... do .................................
.... do .................................
Yellowstone Park, Wyo ...................
Steamboat Springs, Nev...................
Source of data
Present study (E. L. Munson, analyst). Do.
Do.
Gilluly (1932, p. 114).
Irving (1911, p. 647).
Spencer (1917, p. 117).
Bain (1901, p. 121).
Cox, Dean, and Gottschalk (1916, p. 16) Do.
Do.
Present study (E. L. Munson, analyst). Clarke (1924, p. 551).
Do.
Weymouth and Williamson (1951, p. 580) Clarke (1924, p. 551).
Frankel (1952, p. 179).
Do.
Do.
Clarke (1924, p. 207).
Do.
Table 5.—The observed range and average concentrations, in percent, of the 13 commonly reported oxides plus sulfur for 10 representative jasperoid samples compared with those of certain other rock types
[Leaders (..) indicate no information]
Jasperoid	Chert	Silcrete	Siliceous sinter	Jaspilite
		Range	Average	Range .*		Average	Range		Average	Range		Average	Range	Average
SiOa 				 80 -97	92.8	95.5	-99.5	97.7	95	-97	95.7	72 ■	-93	82.5	34.3 -61.4	47.3
			3-4	1.4	0	- .5	.2	1	- 2.3	1.8	.8 ■	-12	6.2	0 - 4.6	1.2
FeaOa 			0-5	1.3	0	- 2	.6	.1	- .5	.3				30.6 -53.1	45.2
FeO 				15- .7	.4	0	- .15	.08							.4 - 5.7	2
MgO 				 0-1	.2	0	- .2	.06	0	- .2	.1	.05	- .1	.07	0 - 2.7	.5
CaO 				 0 - 1	.4	.05	;- .5	.25	0	- .16	.08	.15	- .75	.4	0 - 4.2	1.3
Na20 				 0 - .3	.1	0	- .15	.06				.8	- 3.5	2.1	0 - 1.7	.6
K20 				1-1	.3	0	- .07	.04				.2 ■	-1.7	.9		
H»0 (total	) 			4 - 3.2	1.2	.1	- 1.5	.8	.45	- 1.4	.6	5.5	- 9	7.2	0 1 CO	.7
TiOa . .		.03- .8	.2				1.1	- 1.6	1.4				0 - .3	.1
P2Os 			.01- .4	.1										.05- .6	.3
CO2 				 0-1	.3	0	- .4	.3							.06- 2.9	1.3
S 				 0 - 3	1.2	0		0							0 - .2	.09
BaO 				 0 - .4	.1	0		0								﻿PERCENT OF TOTAL SAMPLES	PERCENT OF TOTAL SAMPLES
32 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Figure 33.—Distributions of elements detected by semiquantitative spectrographic analysis in most of the jasperoid (black) and chert (stippled) samples. M, median, x arithmetic mean. Distribution in parts per million, n, number of samples analyzed.﻿PERCENT OF TOTAL SAMPLES
co
o
-P»
o
<0.0007
0.0007
0.0015
0.003
0.007
0.015
0.03
<0.0015
0.0015
0.003
0.007
0.015
0.03
ffllfl

-xi
II
ro
o
0.07
STRONTIUM	-i	VANADIUM
PERCENT OF TOTAL SAMPLES
0.015		_J	1	1	1			i	i		
0.03						
0.07						
0.15					—	
0.3				—£		
0.7			s II		m i	
1.5				ro	■utm-xi	
3.	_				gr	
7.						
>7.						
O
>
o
c
1 ■*1	1 1 !
		-s
r		
	1WI S
	*i 11 \ to	
■	
>
z
o
>
z
m
(/)
00
00
COMPOSITION OF JASPEROID﻿34 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
differences reflect the fact that jaspilite consists of alternating layers of hematite and jasper.
The silica content of the jasperoid samples is slightly lower than that of the cherts and silcretes; Fe203 and A1203 are higher in the jasperoids than in the cherts, but lower than in the siliceous sinters. Differences in MgO and CaO contents between the rock types are minor; K20 is higher than Na20 in jasperoid samples, but the reverse is true in chert and siliceous sinter samples. Data for combined water versus free water are available only for the jasperoids, so no direct comparison can be made of these components; ignition loss in the chert and silcrete samples is comparable to the sum of H20+ and H20_ in the jasperoid samples, but it is considerably higher in the siliceous sinter samples. Ti02 is nearly an order of magnitude higher in samples of silcrete than in those of jasperoid, but the silcretes all came from the same area, and therefore, they may not be truly representative of this type of rock. It would be interesting to ascertain whether other representatives of ground-water-precipitated silica, such as the duricrusts in Australia and the silica-cemented gravels elsewhere, show the same tendency toward high titanium content.
MINOR CONSTITUENTS
Semiquantitative spectrographic analyses for 64 elements were made on about 200 samples of jasperoid and 20 samples of chert and novaculite by J. C. Hamilton of the U.S. Geological Survey, using a method described by Myers, Havens, and Dunton (1961). Only 43 elements were detected in one or more of the samples, and only 13 are present in detectable concentrations in most of the samples. These 13 are Si, Al, Fe, Mg, Ca, Ti, Mn, Ba, Cr, Cu, Ni, Sr, and V; Si, of course, is a major constituent of all the samples. Frequency distributions of the other 12 elements in the jasperoid and chart samples are shown in figure 33.
STATISTICAL SUMMARY
The class intervals of the histograms are those in which the analyses were reported. Some replicate samples were submitted to check the precision of the analyses. About 60 percent of the reported concentrations of the elements in these check samples duplicated the original determinations; about 90 percent came within one reporting interval of the original value.
All the jasperoid sample distributions are positively skewed, with an arithmetic mean higher than the median, and all but Ba, Ca, and Sr are unimodal.
Ba and Ca display a single intermodal class which is only slightly lower than the adjacent modal classes; thus, the bimodality of the sample distributions may reflect a slight analytical or sampling bias in samples from populations with platykurtic distributions. Cumulative frequency-distribution plots on logarithmic probability paper reveal four different types of sample distributions of these 12 elements in jasperoid. Al, Fe, Mg, and Ni display straight-line plots closely approximating single log normal distributions; Ca, Mn, Ba, Cu, and V all display plots in which the low values fall close to one straight line and the high values close to another straight line with lower slope, with a pronounced breakpoint where the two lines intersect. This suggests that for these five elements the samples represent a mixture of two populations—one of low values with relatively small dispersion and one of high values with greater dispersion, both populations being approximately log normal. Cr and Ti also display plots characterized by two straight lines with a breakpoint, but the high values have a greater slope than the low, suggesting a smaller dispersion in the high values. Sr displays a very irregular cumulative frequency-distribution curve with three breaks in slope. The medians of the cumulative distributions for all the elements in which these distributions show a break in slope fall below or nearly on this break; thus, the sample median values are probably the best representative measures of central tendency for the concentration of these elements in jasperoid. The arithmetic-mean concentrations of many of these elements are strongly influenced by the presence of a few samples in which the elements are present in abnormally high concentration, and it is doubtful that the proportion of such samples in the suite of 200 samples analyzed is adequately representative of the proportion of jasperoids containing this high a concentration of these elements. Thus, for the elements Ca, Mg, Ba, and Cu in which the arithmetic mean is an order of magnitude or more higher than the median, the mean does not furnish a good representative value for the normal concentration of these elements in jasperoid.
The number of chert samples for which comparable analyses are available is so small (12 for Al and Ca; 20 for the other elements) that any general conclusions drawn from a comparison of these sample frequency distributions with the corresponding ones for jasperoid are of dubious validity. In all but three of the elements the mean and median values for chert either are bracketed by those for jasperoid or correspond closely to them. These three exceptions are Fe, Cu, and Sr; for Fe and Cu, both the﻿COMPOSITION OF JASPEROID
35
mean and median values for chert are below the median for jasperoid. The sample data suggest, therefore, that iron and copper concentrations are characteristically higher in jasperoid than in chert, but a considerably larger number of representative chert sample analyses would be needed to establish this hypothesis. The median value for strontium in chert is slightly lower than in jasperoid, and the arithmetic mean in chert is slightly higher than the jasperoid median; however, in view of the highly irregular frequency distributions of this element in the samples of both rock types and the small number of samples involved, it is doubtful that any general significance can be ascribed to this fact.
Frequency distributions and estimated median values for the remaining 30 elements detected in one or more of the jasperoid samples are given in table 6. The median values of all 42 elements in the 200 jasperoid samples are given in table 7. The average abundance of these elements in igneous rocks is also shown for comparison (Rankama and Sahama, 1950, p. 39-40). Most of the elements seem to be deficient in jasperoid as compared with igneous rocks. Only Ag, As, Bi, In, and Sb are significantly enriched in jasperoid, and all five of these are chalcophile elements. This apparent tendency toward enrichment of chalcophile elements in jasperoid is reasonable, because most jasperoid is a
product of hydrothermal alteration and chalcophile elements are likely to have been most concentrated in such solutions.
Concentrations of chalcophile elements in jasperoid may provide diagnostic criteria for distinguishing jasperoids from syngenetic and diagenetic chert. As shown in table 6, however, there is a wide variation in content of the chalcophile elements in jasperoid. Thus, their presence in abnormally high concentration may indeed be indicative of jasperoid rather than chert, but low concentrations are not indicative of chert.
GENESIS OF JASPEROID
The existence of a body of silicified rock (jasperoid) implies the existence of the following: (1) An adequate source of silica; (2) fluids capable of dissolving and transporting the silica to the site of deposition; (3) conditions at the site of deposition that caused silica to replace the host rock, and (4) reaction rates at this site such that host rock dissolved at the same rate or a little faster than silica precipitated. Any theory that seeks to explain the genesis of jasperoid must, therefore, account for each of these conditions.
SOURCE OF SILICA
The silica emplaced in jasperoid bodies may have
Table 6.—Distribution of minor elements in 200 selected jasperoid samples
[J. C. Hamilton, analyst. Numbers in parentheses ( ) indicate number of samples in which element is present in trace amounts. Leaders in figure columns ( ) indicate no data (no samples in group). Query (?) indicates estimate for elements detected in 5 percent or less of the samples]
Number of	Abundance
samples in Estimated in igneous
Element	Number of samples in which element detected in parts per million shown	which ele- median 1 rocks2
in first entry in figure columns	ment not
detected (ppm)	(ppm)
>0.07	0.7	0.3	0.15	0.07	0.03	0.015	0.007	0.003	0.0015	0.0007	0.0003	0.00015			
Na 	 3		2	5	17	(12)								161	0.003	2.8
K 	 3	7												190	.02?	2.7
P 	 2	4												194	.005?	.12
Ag 			1		4	5	10	6	22	14	11	13	12	102	.0001	.00001
As 	 13		9	6	2									170	.001	.0005
B 			1					3	28	6				162	.0005	.0003
Be 										3	5	13	25	154	.00002	.0006
Bi ..	2		1		5	5	4	10	13	(3)			157	.00005	.00002
Cd ...					3	1	3						193	.00001?	.00001
Ce ...					5	(1)							194	<.00001	.005
Co 							1	1	1	4	(11)			182	.00005?	.002
Ga 								1	1	3	12	(16)		168	.00003	.0015
Ge 								2	2	2				194	.000001 ?	.0007
					1		3	3	(17)				176	.0001	.00001
							5	(10)					185	.0001?	.002
Li 						1								199	<•00001?	.0065
Mo 		1		1				7	17	28	21			125	.0002	.0005±
Nb ....									(6)				194	<.000001 ?	.002
Nd ...						1							199	<.000001?	.002
Pb 	 10	4	7	7	11	12	14	22	19	(14)				80	.002	.0016
Sb 	 1	1	1	4	4	10	10							169	.0006	.0001
Sc 										3	6			191	.00005?	.0005
Sn 				2		1	2	5	5	(IB)				170	.00005	.004
Ti .						1							199	<.000001 ?	.0001
U 				1										199	<.00001?	.0004
W 							2	1						197	.000001?	.002
Y 							1		12	37	(3)			147	.0004	.003
Yb 										1		10	39	150	.00004	.0003
Zn 	 4	4	7	11	23	21	2	(23)						105	.002	.013
Zr 					1	8	10	27	39	48				67	.001	.02
1 Median estimated by extrapolation of truncated cumulative frequency distribution.
2 Data from Rankama and Sahama (1950, p. 39-40).﻿36 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Table 7.—Median concentrations of elements detected in the 200 jasperoid samples studied during the present investigation compared with average concentrations in igneous rocks as given by Rankama and Sahama (1950, p. 39-AO)
Element concentrations (in percent) in—
Element1	200 jasperoid	Igneous rocks
samples	(average)
(median)2 (from Rankama and (present study) Sahama, 1950, p. 39-40)
Fe 			 0.7	5
A1 			25	8.1
Ca 			18	3.6
Mg 			03	2.1
K 			 (.02)?	2.7
Ti 			016	.4
Mn 			011	.1
Ba 			008	.025
P 			 (.005)?	.12
Cu 			003	.007
Na 			 (.003)	2.8
Pb 			 (.002)	.0016
Zn 			 (.002)	.013
As 			 (.001)	.0005
Sr 			001	.03
V 			001	.015
Zr 			 (.001)	.02
Cr 			0008	.02
Ni 			0006	.008
Sb 			 (.0006)	.0001
B 			 (.0005)	.0003
Y 			 (.0004)	.003
Mo 			 (.0002)	.0005 ±
Ag 			 (.0001)	.00001
In 			 (.0001)	.00001
La 			 (.0001)?	.002
Bi 			 (.00005)	.00002
Co 			 (.00005)	.002
Sc 			 (.00005)?	.0005
Sn				 (.00005)	.004
Yb 			 (.00004)	.0003
Ga 			 (.00003)	.0015
Be 			 (.00002)	.0006
Cd 			 (.00001)?	.00001
Ce 			 (C.OOOOl)?	.005
Li 			 (<.00001)	.0065
Ge 			 (<.00001)	.0007
Nb 			 (<.00001)	.002
Nd 			 (<.00001)	.002
Tl 			 (<.00001)	.0001
U 			 (<.00001)	.0004
W 			 (<.00001)	.002
1	Elements are given in order of decreasing abundance in jasperoid.
2	Medians that are estimated by extrapolation from censored distributions are in parentheses; those for rarely detected elements, reported in 5 percent or less of the samples, are in parentheses followed by a question mark.
been derived from one or more of four major sources: (1) the silica-rich residual fluids emanating from a cooling magma; (2) silica released by reaction of a hypogene mineralizing solution with wall-rock minerals en route to the site of silicification; (3) silica in the form of chert, siliceous organisms such as diatoms and sponge spicules, or siliceous shale beds and argillaceous and siliceous fractions already present in the host rock, and (4) silica released by weathering of overlying or adjacent rocks. Silica, in minor amounts, may also be released during the alteration of silicate minerals, such as the conversion of montmorillonite to kaolinite by dia-
genetic or hydrothermal alteration or by weathering. Only the four principal sources just listed, however, seem adequate to supply the hundreds of thousands of cubic feet of silica commonly contained in the larger jasperoid bodies.
There is some question as to whether masses of siliceous rock composed of silica derived from ground water and furnished by sources 3 and 4 should be included under jasperoid, or whether the term “jasperoid” should be restricted to bodies composed of silica derived only from hydrothermal solutions. Examples of bodies that originated from silica in ground water include (1) silicified erosion surfaces in the Apache Group in north-central Arizona (Leith 1925, p. 515-516; A. F. Shride, oral com-mun., 1961), (2) the silcretes of South Africa (Frankel, 1952, p. 181-182), the duricrusts of Australia (Woolnough, 1928, p. 32), and certain silicified rocks from Tanganyika (Bassett, 1954), (3) some epigenetic “chert” bodies and the “case-hardened” limestone which are common in many arid and semiarid regions, and (4) highly silicified gossans replacing sulfides and host rock at and near the surface. Undoubtedly, a great many siliceous replacement bodies that have been designated as chert or hydrothermal jasperoid really belong in the category of bodies that originated from silica in ground water; however, there is at present no inclusive genetic term by which to designate the category. Furthermore, many “hydrothermal jasperoids” may have formed from juvenile solutions mixed with heated ground waters. Because of the practical difficulty in distinguishing between siliceous replacements derived from hot water and those derived 'from cold water, it seems best, for the present, to retain the term “jasperoid” as originally used by Spurr (1898, p. 219-220) to include all epigenetic siliceous replacement bodies, of whatever origin.
The primary source or sources of silica for most jasperoids cannot be conclusively established. In many mining districts there is strong field evidence that silicifying solutions rose from depth along faults and fractures, but whether this silica emanated directly from a cooling magma or was leached from siliceous rocks by upward-moving solutions is indeterminate. In a few places, such as the Gilman district of central Colorado and the Upper Mississippi Valley district, there is evidence that silica has been leached in quantity from rocks beneath the host rocks for the jasperoid.
SOLUTION AND TRANSPORTATION OF SILICA
The solvent properties of aqueous fluids for silica depend on the form in which silica is available, the﻿GENESIS OF JASPEROID
37
temperature and pressure of the system, and the nature and concentration of other chemical components in the solution. Once silica is taken into the fluid and begins to move, it tends toward a dynamic equilibrium between ionic (monomeric) silica, and polymeric silica in true solution, and colloidally dispersed silica in the form of a peptized sol if the solution is supersaturated with respect to ionic and polymeric silica. Changes in any of the factors that influence release of silica to the solution also influence this equilibrum. Under controlled laboratory conditions, where all factors are held constant, days or even months may be required to establish such an equilibrium; thus, it probably is very rarely attained in moving hydrothermal solutions.
Considerable experimental data have accumulated on the solubility of silica under various conditions. These data may be divided roughly into four main categories: (1) solubility of various forms of silica in pure water at low temperature and pressure; (2) solubility of silica in pure water at higher temperature and pressure; (3) solubility of silica in various aqueous solutions at low temperature and pressure; and (4) solubility of silica in various aqueous solutions at higher temperature and pressure. Each of these categories may be further divided into (1) thermodynamic investigations of equilibrium solubility and (2) investigations of rates of solution and of equilibration.
SOLUBILITY OF VARIOUS FORMS OF SILICA IN PURE WATER AT LOW TEMPERATURE AND PRESSURE
Data on the solubility of quartz, powdered silica gel, and opal in water at 25°C and 1 atm (atmosphere) are given by Siever (1962, p. 129-133). He found that quartz particles on the order of 5 microns in diameter showed no measurable solubility in 3 years, but by extrapolating quartz solubility at higher temperatures downward, he calculated an equilibrium solubility of quartz at 25°C of about 10 ppm. Solubility of opal under these conditions is reported as about 120 ppm; that of powdered silica gel, about 140 ppm. On the other hand, quarts grains sized to —100, +200 mesh put under pressure of a steel rod in water at 25 °C and 1 atm gave a solubility close to that of amorphous silica. Quartz grains kept in motion in a rotating polyethylene vessel at 1 atm and room temperature gave values that increased gradually to a maximum of 80 ppm at 386 days, then dropped abruptly to 6 ppm due to precipitation of quartz (Morey and others, 1962, p. 1036-1037). Krauskopf (1956, p. 5) gave the solubility of quartz in pure water at low temperature and pressure as 6 ppm; Iler (1955, p. 9) stated that
solubility of quartz increases with diminishing particle size below 100 microns from about 7 ppm at 100 microns diameter to about 930 ppm at 3 microns diameter.
Experimental data on the equilibrium concentration of dissolved (monomeric) silica in pure water at 25°C and 1 atm in solutions supersaturated with total silica are not in complete agreement, possibly because silica can also form polymeric ion complexes. Iler (1955, p. 11-12) reported 100 ppm; Siever (1962, p. 129-130), 120-140 ppm; Alexander, Heston, and Iler (1954), 120 ppm; and Cor-rens (1951, p. 51), about 250 ppm. In an experiment that I conducted (Lovering and Patten, 1962, p. 790), the monomeric silica content of a solution that contained 1,000 ppm total silica in pure water at room temperature and pressure dropped from an initial value of 270 ppm to 90 ppm within a week. The silica in solution remained at 90 ppm for 2 months, but when the experiment was discontinued at the end of 5 months, it had risen to 100 ppm.
SOLUBILITY OF VARIOUS FORMS OF SILICA IN PURE WATER AT HIGHER TEMPERATURE AND PRESSURE
Many problems are associated with the study of silica solubility in aqueous fluid at higher temperature and pressure.
1.	Solubility varies as a function of the form of
silica available; in general, it is lower for quartz at any given temperature and pressure than for the various forms of amorphous silica.
2.	Equilibrium solubility at moderate temperature
and pressure is established very slowly; Gruner (1930, p. 702) obtained a solubility for quartz at 200°C and 15 atm of 30 ppm after 24 hours, whereas Kennedy (1950, p. 636) reported its solubility under these conditions as 240 ppm after 230 hours.
3.	Solubility does not vary directly with pressure at
constant temperature nor with temperature at constant pressure; instead, it is a function of solution density at high temperature and pressure.
4.	The reported “solubility” of amorphous forms of
silica, such as silica glass, commonly is not a true equilibrium solubility; a change in conditions of the system that results in solution of silica may not, if reversed, cause precipitation of silica because of the tendency of solutions to remain supersaturated (Morey and Hessel-gesser, 1951, p. 830).
5.	Early investigators reported solubility of amor-
phous forms of silica equal to the total silica content of the aqueous phase, whereas more﻿38 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
TEMPERATURE, IN DEGREES CENTIGRADE
recent investigators report only the ionic solubility, recognizing that much of the silica is present in the form of dispersed submicro-scopic colloidal particles in a sol, a colloidal solution.
The solubility of quartz in H20 has been investigated over a wider range of temperature and pressure than that of any other form of silica, and the data obtained by various investigators are more nearly in agreement. A large part of the solubility field of quartz was systematically studied by Kennedy (1950), and his work has since been supplemented by that of Morey and Hesselgesser (1951), Ellis and Fyfe (1957), Morey, Fournier, and Rowe (1962), and Siever (1962). Kennedy covered the region around the critical point of water, from 200° to 500°C at 200-1,000 atm pressure; Ellis and Fyfe obtained some solubility data for temperatures of 500° and 600°C at 1,000-3,000 atm pressure. Morey and Hesselgesser partly duplicated the field covered by Kennedy, obtaining nearly the same values, but they also obtained some critical information on solubility at high temperature and relatively low pressure. Morey, Fournier, and Rowe investigated quartz solubility in H20 at 1,000 atm pressure in the temperature range of 45°-300°C; Siever investigated quartz solubility in the range of 100°-200°C at low pressure (the vapor pressure of the system). Data from these various sources have been combined in figures 34A and 34B showing the iso-baric solubility of quartz as a function of temperature at 300 atm pressure and the isothermal solubility of quartz at 400°C as a function of pressure.
The marked inflection point on the isobaric solubility curve (fig. 34A) in the vicinity of the critical point, with decreasing solubility at higher temperatures, is a characteristic feature of these curves up to a pressure of about 700 atm; at pressures higher than this, solubility increases directly with temperature. If solubility is plotted at a constant specific volume of H20 rather than at constant pressure, it increases steadily with temperature in the two-phase fields (quartz plus liquid and quartz plus gas), with no inflection at the boundary between these fields (Kennedy, 1950, p. 639, 642). The attenuated S-shaped isothermal solubility curve (fig. 341?) shows the marked effect of moderate pressure changes on quartz solubility at relatively high temperature in the range of 100-500 atm; a threefold increase in pressure (100-300 atm) results in a hundredfold increase in solubility of quartz at
Figure 34.—Solubility of quartz in H-O. A, At 300 atm pressure. B, At 400°C.﻿GENESIS OF JASPEROID
39
400°C. Thus, even a moderate throttling of a hydro-thermal conduit could result in undersaturation below the constriction with solution of quartz and in a high degree of supersaturation with Si02 in the hydrothermal fluid above the constriction.
Published data on Solubility of other forms of silica in aqueous fluid at various temperatures and pressures are difficult to compare, because many of them represent unique metastable equilibrium conditions. Some investigators report total silica, and others report ionic silica. In much of the early work it is questionable whether the stated conditions of the experiment were maintained long enough for equilibrium to be established. Kennedy’s paper (1944), in which he summarized earlier work by Lenher and Merrill (1917) and Gruner (1930), is one of the most systematic studies of this difficult experimental field. His data suggest that the solubilities of various noncrystalline forms of Si02 conform to much the same solubility curves as quartz at intermediate conditions of temperature and pressure, but are commonly somewhat higher than those of quartz under the same conditions. Siever (1962, p. 133) stated that the solubility versus temperature curves for quartz and amorphous silica converge toward higher temperature.
The rate of solution of quartz is extremely slow in water at low to moderate temperature and pressure. Kennedy reported that 230 hours was required to achieve saturation at 200°C and 15 atm pressure. Carr and Fyfe (1958, p. 913-914) determined that quartz dissolves at the rate of 1 mg per hr (milligrams per hour) at 270°C and 1,000 atm, which increases to 18 mg per hr at 500°C under the same pressure; at 400°C, an increase in pressure from 345 to 1,725 atm increased the solution rate from 2 to 12 mg per hr.
SOLUBILITY OF VARIOUS FORMS OF SILICA IN AQUEOUS
SOLUTIONS AT LOW TEMPERATURE AND PRESSURE ACID SOLUTIONS
The amount of monomeric silica in equilibrium with colloidal silica in slightly acid solutions does not differ appreciably from that in pure water, but it declines in strongly acid solutions. Iler (1955, p. 11-12) reported 140 ppm Si02 at a pH of 1, rising to a maximum of 150 ppm at about a pH of 3 and then declining to 110 ppm at a pH of 5.7. Elmer and Nordberg (1958, p. 518-519) found 160 ppm Si02 in solution in O.OOliV HN03 as opposed to 115 ppm in 0.8N HN03. Lenher and Merrill (1917, p. 2636) reported that Si02 content of sulfuric acid solutions containing less than 5 percent H2SO4 is virtually the same as that in pure water; also, that concentrated
HC1 will dissolve only 8 ppm of Si02, but that 3 percent HC1 solution will dissolve 140 ppm. Lovering and Patten (1962, p. 789) obtained 320 ppm of monomeric silica in H2S04 solution at a pH of 2.3, and 220 ppm at a pH of 3.6 after 1 month. In dilute carbonic acid solution with a pH of 5.2 they found 110 ppm of ionic silica in equilibrium with colloidal silica, virtually the same as that in pure water. Siever (1962, p. 132) reported that humic acid solutions repress the solubility of silica gel to about 15 ppm of monomeric silica.
Moore and Maynard (1929, p. 277) recognized that much of the silica transported by natural acid water is in the form of a dispersed hydrosol. The decline in true solubility of silica in highly acid solutions is counteracted by the stabilizing effect of such solutions on dispersed silica sols. This stabilizing effect will prevent the precipitation of silica from highly supersaturated solutions, even in the presence of strong electrolytes; a solution containing 2,000 ppm of total silica in the form of sodium silicate remained perfectly clear for a month at a pH of 2.3, although the monomeric silica content of the solution after that time was only 320 ppm (Lovering and Patten, 1962, p. 789). On the other hand, solutions highly supersaturated with silica become unstable in weakly acid solutions and tend to precipitate excess silica. This precipitation is accelerated by the presence of strong electrolytes, but it will occur even in their absence. Frondel (1938, p. 10) noted that the addition of HC1 to a colloidal silica sol reverses the negative charge on the sol. The reversal of charge probably accounts for the buffering effect of strong acids against precipitation by electrolytes.
The solubility of silica derived from common silicate rocks and minerals in acid solutions has not been systematically investigated.
Gruner (1922, p. 435) reported that the solubility of silica from silicate minerals in acid solutions is inversely proportional to the silica content of the silicate. According to T. S. Lovering (1950, p. 237, 240), the attack of acid solutions on silicates results in solution of their bases, causing decomposition, although actual solution of silica is minor. He listed the common rock silicates in order of decreasing susceptibility to attack by acid solutions as follows: Zeolites, feldspathoids, calcic plagioclase, augite, hornblende, biotite, oligoclase, orthoclase, albite, muscovite, and quartz.
ALKALINE SOLUTIONS
The ionic solubility of silica, in equilibrium with colloidally dispersed silica, rises slowly in alkaline﻿40 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
solutions from a minimum of about 100 ppm at a pH of 7 to about 200 ppm at a pH of 9.8, and then rapidly to about 500 ppm at a pH of 10.3, 1,100 ppm at a pH of 10.6, and 5,000 ppm at a pH of 11 (Iler, 1955, p. 11-12; Alexander and others, 1954). This rapid increase in solubility at a high pH is due to an increase in the concentration of polymeric silica— Si (OH) 4+ (OH)-->(HO)sSiO- + H20. Near the neutral point, supersaturated silica solutions become unstable in the presence of electrolytes, and excess silica readily precipitates. Above a pH of about 8, however, highly supersaturated solutions may remain stable for a considerable length of time, even in the presence of a moderate concentration of electrolytes. A solution containing 2,000 ppm total silica, 120 ppm ionic silica, and 1,650 ppm sodium remained clear for a month at a pH of 9 (Lovering and Patten, 1962, p. 789). Iler (1955, p. 48) reported that the stability of colloidal silica sols in the pH range 7-10 depends on the Si02 :Na20 ratio; an increase in this ratio increases the sizes of particles in the sol, which favors nucleation and precipitation. He (p. 14) also stated that the presence of sodium chloride and alkaline carbonates accelerates the solution of colloidal silica in alkaline solutions.
The solubility of quartz, opal, chalcedony, actino-lite, and glauconite in NaOH, Na2C03, CaH2(C03)2, and MgH2(C03)2 solutions was investigated by T. S. Lovering (1923, p. 528-531). He found that opal and chalcedony are strongly attacked by dilute NaOH solutions and that Na2C03 is an even stronger solvent for opal; MgH2(C03)2 is a moderately effective solvent with nearly uniform effect on all the silicates including quartz; the effect of CaH2 (C03) 2 is similar to, but much weaker than, that of magnesium bicarbonate. Later, Lovering (1950, p. 240) reported that mildly alkaline solutions are relatively ineffectual in causing decomposition of rock silicate minerals, although the cation present in highest concentration in such solution tends to be exchanged for any different soluble cation in the mineral; however, Si02 may be leached if the solution is undersaturated with silica. Van Lier, De Bruyn, and Overbeek (1960) established that dilute NaCl greatly accelerates the equilibration of Si02 in solution, resulting in precipitation of silica from supersaturated solutions and accelerated solution of quartz in contact with undersaturated solutions. Sodium chloride does not appreciably affect the solubility of silica unless present in concentrations greater than 0.1V. Such concentrated brines increase the solubility of silica (Van Lier and others, 1960, p. 1675, 1681-1682).
SOLUBILITY OF VARIOUS FORMS OF SILICA IN AQUEOUS SOLUTIONS AT HIGHER TEMPERATURE AND PRESSURE ACID SOLUTIONS
Systematic studies of the monomeric silica content of acid solutions supersaturated with colloidal silica thus far have been limited to 1 atm pressure and temperatures below 100°C. Within this restricted range, silica in solution increases with temperature for any given composition of solution. For any given acid, solubility declines with increasing acid concentration above 0.1 N at higher temperatures. Approximate equilibrium solubilities in parts per million at 90 °C for common acids of comparable concentrations are as follows:
Solvent		HC11	HNOs2	H2S041
Concentration	0.1 N 			420	415	425
5	percent 			320	350	410
20	per cent 			 60	140	190
1	Lenher and Merrill (1917, p. 2636).
2	Elmer and Nordberg (1958, p. 518).
The solubility of silica in pure water at 90 °C is about 430 ppm (Okamoto and others, 1957, p. 124).
Equilibrium solubility is attained more rapidly, at constant temperature, in strongly acid solutions than in weakly acid solutions. Elmer and Nordberg (1958, p. 518-519) found that at 90°C, 96 hours is required to reach equilibrium in 0.1W • HN03, but only about 48 hours in 0.8V • HN03.
A few studies have been made of the leaching of silica from rock silicates in acid solutions at elevated temperature and pressure. Lenher and Merrill (1917, p. 2636) reported that about 320 ppm of silica was leached from weathered chert and 200 ppm from fresh chert in a 4.6 percent HC1 solution held at 90°C for 2 days. Blanck, Passarge, Rieser, and Heide (1925, p. 75) leached about 4.6 percent of the Si02 out of fresh Egyptian granite in boiling concentrated hydrochloric acid in 1 hour. White, Brannock, and Murata (1956, p. 52) proposed that hot waters highly charged with C02 will attack silicate minerals and will dissolve silica in the monomeric form. Ingerson (1947, p. 560) stated, however, that the presence of C02 in aqueous fluid at high temperature and pressure decreases the solubility of Si02, and his statement has been confirmed in the laboratory by Robert Fournier (written commun., 1962). These statements are not necessarily incompatible, because equilibrium solubility is achieved more rapidly in highly acid solutions than in dilute solutions, even though the saturation concentration is lower. The solubility of silica in boiling concentrated HC1 is less than 100 ppm, yet such a solution leached more than 4 percent of the silica out of fresh granite in only 1 hour.﻿GENESIS OF JASPEROID
41
ALKALINE SOLUTIONS
Equilibrium solubility of monomeric silica in supersaturated alkaline solutions, of a pH of at least 10 and a temperature of 200°C, has been studied by Okamoto, Okura, and Goto (1957). They found that solubility increases in linear fashion independent of pH up to 100°C in the range of pH 7-pH 9 (from about 100 ppm at 0° to about 500 ppm at 100°C). From 100° to 200°C solubility increases with increasing alkalinity as well as increasing temperature in this range; at 200°C, solubility increases from about 920 ppm at pH 7, 980 ppm at pH 8, to 1,150 ppm at pH 9. At a pH of 10, the solubility is considerably higher at all temperatures from 0° to 200°C than it is at a pH of 9, but the solubility versus temperature curve is nearly parallel to that for a pH of 9 (about 800 ppm at 100°C, about 1,400 ppm at 200°C). The pressure was not specified by Okamoto, Okura, and Goto, but presumably it was equal to the vapor pressure of the system. T. S. Lovering (1950, p. 234) reported that the solubility of colloidal silica in Na2C03 solution at 100°C increases from about 3,500 ppm in 0.25A solution to about 8,000 ppm in IN solution. Its solubility in O.liV NaOH at this temperature is about 12,500 ppm. Gruner (1930, p. 702) ran some experiments on the solubility of quartz and gabbro in sodium bicarbonate solutions maintained at 300 °C in sealed metal bombs for 24 hours. He obtained 742 ppm of SiOo from the quartz and 64 ppm from the gabbro, which is less for both quartz and gabbro than the solubility in pure H20 under the same conditions. Carr and Fyfe (1958, p. 916) maintain, however, that alkalies in aqueous solutions at high temperature and pressure accelerate the solution of silica; and Iler (1955, p. 161) stated that in alkaline solutions under these conditions a high concentration of Na+ in the system causes the precipitation of excess colloidal silica. Thus, the main effect of alkalinity on silica solubility with increasing temperature and pressure probably is to maintain equilibrium solubility. Solutions undersaturated with Si02 should rapidly dissolve silica until they become saturated, and solutions that were supersaturated should precipitate the excess silica.
SUMMARY
The solubility of amorphous silica at low temperatures and pressures is highly dependent on pH; the solubility is greatest in strongly alkaline solutions and moderately high in weakly acid to neutral solutions. Solutions supersaturated with silica are metastable in highly acid and moderately acid solutions; unstable in weakly acid, neutral, and weakly
alkaline solutions; and metastable in moderately alkaline solutions. Increasing pressure at low temperature increases solubility at any pH, but no data are available on the effect of pressure versus pH on stability of supersaturated solutions at low temperature. With increasing temperature at low pressure, solubility increases to the boiling point, then drops sharply in the vapor phase. Just below boiling, the solubility rises gradually from about 350 ppm at a pH of 0.1 to about 500 ppm at a pH of 9.2; then it increases rapidly in more highly alkaline solutions. At high temperature and pressure, solubility is highest in nearly neutral solutions; it drops off in both alkaline and acid solutions. Under these conditions, supersaturated solutions are unstable in alkaline systems, but no data are available on their stability in acid and neutral systems. Solubility is very low at low pressure in neutral solutions at supercritical temperatures, and it does not surpass room-temperature solubility until the pressure reaches about 300 atm. At still higher pressures, solubility increases rapidly with pressure. Solubility of silica in high pressure-temperature neutral aqueous systems varies directly with fluid density, or inversely with specific volume of the fluid phase.
COMPOSITION OF NATURAL SILICA-BEARING SOLUTIONS
Silica content of natural water is lowest in the oceans, < 10 ppm; in river water, it ranges from a trace to about 60 ppm and averages about 10 ppm; and in nonvolcanic lake water it ranges from a trace to about 150 ppm, although, like river water, it averages about 10 ppm. Hot springs of nonvolcanic origin can carry as much as 250 ppm silica; however, the most siliceous of the naturally occurring waters are found in hot springs, pools, and geysers emanating from regions of recent volcanism. Most of these contain more than 300 ppm silica, and a few contain nearly 1,000 ppm. White, Brannock, and Murata (1956, p. 29-30) reported that total silica content of supersaturated hot spring water from Yellowstone Park and Iceland ranged from 500 to 700 ppm. They found that at 100°C about 400 ppm of this is dissolved (monomeric) silica, and that the remainder is in dispersed colloidal form. They (p. 51) also found that the silica content of calcium bicarbonate hot springs that deposit travertine is very low (about 50 ppm) ; this fact, they suggest, may be due to the exchange of silica for calcium carbonate at depth. Thus, such springs at the surface may indicate formation of jasperoid replacement bodies below.
Clarke (1924) reported many analyses of various types of natural water. Table 8 gives a few of the﻿42 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Table 8.—Composition, in parts per million, of some samples of natural silica-bearing waters
Cold waters	Hot waters
Nonvolcanic
Rivers	Lakes	hot springs	Volcanic hot springs and geysers
	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	19a
COs		... 89	58	145	124	25	112	180	1,529	30	2,963				3	122	115			145	312
S04		... 67	24	53	164	8	190	9	85	18	43,579	5,781	4,572	5,330	34	18	102	75	136	131	129
Cl		... 7	7	30	304	9	9	3	115	11	356	2		34,549	670	439	153	550	1,030	998	949
Ca		... 48	29	69	82	9	44	42	249	3	4,759	577	22	132	7	2		8	71	7	12
Mg		... 11	5	14	26	<1	48	25	215	<1	8,220	76	313	612	1	<1	<1	2	5	<1	<1
Na		.. 24	161	57	(261	16	37	62	589	56	1,865	102	32	12,455	394	367	223	700	665	865	707
K		^ 7	21		1 24	5	5			5	218	19	5	1,819	81	27	21	21	10	108	75
Al20a+Fe203		.. <i	5	3		4	2	<1	33		12 1 137	1,158 2 157	161	3,950 3 438				—	—	<1 4 253	<1 4 192 317
SiC>2		 Total dissolved	... 48	66	48	48	42	107	57	150	95	262	131	362	738	580	383	510	700	820	325	
solids		... 302	212	422	1,023	118	554	379	2,966	218	62,371	8,150	5,467	60,023	1,830	1,388	1,131	2,064	2,735	2,850	2,508
iNH4. 2 H3ASO4. 3P04. 4 B2O3.
Source of samples:
1.	Platte River at Fremont, Nebr.
2.	Laramie River 20 miles north of
Laramie, Wyo.
3.	Republican River at Junction, Kans.
4.	Gila River at head of Florence Canal, Ariz.
5.	Yellowstone Lake, Wyo.
6.	Bigstone Lake, Minn.
7.	Silver Lake, Oreg.
8.	Moses Lake, Wash.
9.	Pyrenees Mountains, France
10.	Bitter Spring, Laa, Austria
11.	Roncegno, Southern Tyrol, Italy
12.	Acid Spring, California Geysers, Sonoma
County, Calif.
13.	Green Lake, Taal Volcano, Luzon, Philippine
Islands
14.	Coral Spring Norris Basin, Yellowstone
Park, Wyo.
15.	Old Faithful Geyser, Yellowstone Park,
Wyo.
16.	Great Geyser, Iceland
17.	Te Tarata, Rotorua, New Zealand
18.	Otukapurang, Rotorua, New Zealand 19-19a. Steamboat Springs, Nev.
Source of Data:
Samples 1-19, Clarke (1924, p. 80-87, 164, 189-190, 196-197, 200-201); 19a, Brannock (1948).
most siliceous representatives of these waters and the content of their major components, converted from percent of total salinity to parts per million to facilitate comparison. Sample 19a, a thermal spring water, is from the same area as sample 19, whose analysis was quoted by Clarke. The general agreement between the two analyses is remarkably good, considering that they were made more than 50 years apart and by different methods, and that they probably do not represent the same spring.
The data given in table 8 seem to indicate that silica content of natural water is largely independent of the nature of the principal anion complex and also of the relative abundance of the alkalies (Na and K) versus the alkaline earths (Ca and Mg). The volcanic hot springs and geysers form a possible exception to the rule, inasmuch as all but one of them contain Na+1 and Cl-1 as the most abundant constituents other than silica. However, sample 12, from the California geysers, is a high sulfate water with no chlorine and a Ca + Mg to Na + K ratio of almost 10:1. Another generalization suggested by the data in table 8 is that, for any given type of water, the silica content is largely independent of the total dissolved solids. The Platte River sample (1) has 48 ppm Si02 out of a total of 302, as compared with one from the Gila River (4), which has 48 ppm Si02 out of a total of 1,023. One volcanic thermal water (17) has 700 ppm Si02 out of 2,064, another (13) has 738 ppm Si02 out of 60,023. Iron and alumina are negligible in, or absent from, most of these waters, but in two of the thermal water
samples (11, 13) Fe203 + A1203 exceeds 1 gram per liter, which is considerably more than the silica content of any of the samples. The presence of appreciable quantities of ammonia, phosphate, arsenic, and boron as accessory constituents in some thermal waters is also noteworthy. Each of these constituents is normally not detectable, yet each may, under unusual circumstances, be transported along with silica in considerable quantities by hot aqueous solutions.
The total composition of a natural water seems to have relatively little effect on its ability to transport silica. A relatively pure water in which silica is a major constituent may carry about the same amount of silica as a highly saline one in which silica is a minor constituent. Clarke (1924, p. 96-97) mentioned the high proportion of silica to dissolved salts (46-56 percent) carried by some South American rivers, yet the total amount of silica in these waters is less than 40 ppm.
The aqueous fluid in primary fluid inclusions in quartz is another type of natural solution; its composition may be close to that of the solution from which the quartz was deposited. Fluid from a quartz crystal in a vein cutting rhyolite contained 0.047 percent Na, 0.011 percent K, 0.006 percent Ca, 0.063 percent Cl, and 0.063 percent S04 (Roeder and others, 1963, p. 368). Fluid inclusions in quartz from the Cave-in-Rock fluorite district of Illinois, which was deposited just before the ore sulfides, may bear an even closer resemblance to those from which ore-related jasperoids are deposited. This﻿GENESIS OF JASPEROID
43
fluid contained 1.73 percent Na, 0.43 percent K, 0.84 percent Ca, 0.28 percent Mg, 4.7 percent Cl and 1.29 percent S04 (Hall and Friedman, 1963, p. 898).
Laz’ko (1965, p. 384-386) summarized some information on the composition of fluid inclusions from quartz veins in Russia. He found that Na> K>Ca in these inclusions and further stated (p. 384) that “The calculated dissolved Si, as Si03-2 (assuming its quantitative preponderance in the solution) indicates its total concentrations as high as 6-12 percent.”
Laz’ko also reported that C02 is present in appreciable amounts in some inclusions, and he concluded that the mineralizing solutions, from which quartz is deposited, are primarily aqueous alkali chlorides.
DEPOSITION OF SILICA
The ability of natural waters and hot aqueous fluids to transport vast quantities of silica, in both monomeric and colloidal form, has been well established. We now consider the factors that induce precipitation of silica, the form in which silica is precipitated, and the causes of the conversion of a precipitated silica gel into the more stable forms of silica found in nature.
DEPOSITION AT LOW TEMPERATURE
Cold-water solutions that are supersaturated with respect to colloidal silica may, for a variety of reasons, precipitate some or most of this excess as hydrated amorphous silica; however, solutions that are just saturated or unsaturated with respect to colloidal silica, though highly supersaturated with silica relative to quartz, tend to maintain their metastable equilibrium and do not precipitate quartz under normal conditions. Geologic field evidence, on the other hand, strongly supports the conclusion that quartz can be precipitated directly from solution at relatively low temperatures. The evidence is in quartz crystals in geodes in unmetamorphosed limestone and shale, quartz-cemented surface gravels, and coarse quartz veining and lining cavities in limonite gossans. Murray and Grovenor (1953) reported that X-ray spectrometer and powder-photograph analyses of oceanic muds and the fine fractions of the insoluble residues of limestone and shale reveal abundant quartz particles less than a micron in diameter. They suggested that these particles may have been precipitated directly from solution.
The works of Siever (1962) and Morey, Fournier, and Rowe (1962) show that quartz subjected to abrasion or differential pressure in cold water will
eventually supersaturate the solution as much as tenfold relative to its theoretical solubility, and that after a long time quartz will spontaneously precipitate from such a solution to reestablish equilibrium. The same process might occur more rapidly in dilute sodium chloride solutions, according to the evidence presented by Van Lier, De Bruyn, and Overbeek (1960).
According to Boydell (1927, p. 51), the precipitation of colloidal silica from supersaturated solutions can result from (1) mixing with solutions that contain a high concentration of electrolytes; (2) the mixing and reaction with a dispersed sol of opposite charge, such as a metal hydroxide sol; (3) the chemical removal of a protecting (peptizing) agent, such as fluorine in acid solutions; and (4) decrease in pressure or temperature of the system.
Evaporation.—One other way in which silicabearing solutions may be induced to precipitate silica is by evaporation of such solutions under arid conditions. Clarke (1924, p. 366) stated that evaporation of acid siliceous waters forms opal. Rankama and Sahama (1950, p. 553-554) reported that the silica in alkaline solutions concentrated by evaporation precipitates as an amorphous silica gel. The siliceous duracrust of the Australian desert is thought by Woolnough (1928, p. 32) to have formed by the evaporation of siliceous ground water drawn to the surface by capillary action during dry cycles.
Neutralization.—Another factor that might contribute to the precipitation of dispersed colloidal silica is a change in pH; peptized sols that are stable under either strongly acid or strongly alkaline conditions become unstable as they are neutralized. Iler (1955, p. 45) wrote that gelation or precipitation of colloidal silica takes place most readily in the pH range 5-6. Lovering and Patten (1962, p. 789) found that supersaturated sodium silicate solutions that contain 1,000 ppm Si02 become unstable and precipitate colloidal silica in the pH range 4-8. These solutions remained clear and free of precipitate for a period of 2 months both in acid solutions with a pH lower than 4 and in alkaline solutions with a pH higher than 8. Solutions with the same silica content, from which sodium had been removed, remained clear at a pH of 7 for 3 months. Thus, the neutralization of a strongly acid or alkaline solution highly supersaturated with silica may not cause silica to precipitate unless some other agent that favors precipitation is also present.
Contact with solid phase.—Contact with a solid silica phase may also induce precipitation of colloidal silica. Nutting (1943, p. 220) observed that particles of solid silica will cause the precipitation﻿44 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
of excess colloidal silica from supersaturated solutions in a few days and that “certain clays” will do the same thing in a few hours. The efficacy of opaline sinter, quartz, and chalcedony in causing the precipitation of amorphous silica from siliceous hot spring waters was noted by White, Brannock, and Murata (1956, p. 49). The effectiveness of various forms of solid silica in causing such precipitation must depend in part on the nature of the surface area that is in contact with the solutions, inasmuch as it is possible to keep supersaturated silica solutions in silica glass bottles for years without any precipitation.
Soluble salts.—Many investigators have commented on the precipitation of colloidal silica caused by the introduction of various soluble compounds, both electrolytes and nonelectrolytes, into supersaturated silica solutions or dispersed silica sols. Iler (1955, p. 14, 41-45, 93) reported that the addition of soluble salts causes gelation or flocculation of supersaturated silica solutions; sodium salts increase the viscosity of dispersed sols and, if present in high concentration, cause silica to precipitate. Boydell (1924, p. 89) stated that the addition of an electrolyte also increases the rate of diffusion of dispersed sol particles, and Gruner (1922, p. 445) believed that colloidal silica in acid solutions is precipitated on contact with alkaline chloride or alkaline carbonate solutions. Boydell (1924, p. 7) and Cox, Dean, and Gottschalk (1916, p. 6) agreed that calcium bicarbonate is one of the most effective natural electrolytes in causing precipitation of colloidal silica. Lovering and Patten (1962, p. 791-795) showed that relatively dilute carbonic acid solutions will precipitate colloidal silica from highly supersaturated solutions, even in the absence of cation electrolytes. Bassett (1954) mentioned the precipitation of silica from ground water in African freshwater lake marls as disseminated grains of amorphous silica, deposited with calcite and dolomite.
According to Iler (1955, p. 14), aluminum in solution inhibits the solubility of silica, and some experiments conducted by Okamoto, Okura, and Goto (1957, p. 129) indicate that soluble aluminum added to dispersed silica sols in concentrations as low as 10 ppm will precipitate as much as 90 percent of the excess colloidal silica from acid solutions with a pH of 4-5, provided the ratio of colloidal silica to A1+3 in solution is not greater than 50:1. At a pH lower than 4 or higher than 5, soluble aluminum has little effect on these sols. Okamoto, Okura, and Goto (1957) also found that aluminum in solution, if present in excess of 200 ppm, will precipitate dissolved (monomeric) silica from solution most effec-
tively in the pH range 8-10. Harder (1965) has also shown experimentally that aluminum will precipitate silica from natural waters, and that the excess silica in the precipitated colloid will crystallize as quartz. The silcretes of South Africa are thought to have formed by replacement of selected clay layers by ground-water silica derived from adjacent shale or tillite (Frankel, 1952, p. 180-182) ; such an origin would substantiate the effectiveness of A1+3 as a silica precipitant. Okamoto, Okura, and Goto (p. 131) also stated that the action of Fe+3 ion is similar to that of A1+3. Harder (1919, p. 73) wrote that ferrous sulfate solutions will react with alkaline silicate solutions in a reducing environment to precipitate ferrous silicate and colloidal silica, but that such solutions will also precipitate ferric hydroxide in an oxidizing environment.
Mixing of sols.—Neither ferric iron nor aluminum can exist in ionic form in high concentration except in moderately acid waters, because both tend to hydrolyze in near-neutral and alkaline solutions— Fe+3 at a pH of 3 and A1+3 at a pH of 5, according to Rankama and Sahama (1950, p. 228). Dispersed hydrosols of these metals in neutral or alkaline solutions may, however, on mixing with dispersed silica hydrosols, react to precipitate both silica and the metal hydroxide in colloidal form. The mutual precipitation of silica and metal hydroxide on mixing of dispersed hydrosols is caused by neutralization of the charges on the sols, silica being negative and metal hydroxide positive; such mutual precipitation begins at a slightly lower pH than that at which the metal hydroxide would precipitate alone. The completeness of flocculation and precipitation, as well as the relative proportions of the two colloids in the precipitate, depends upon the concentrations of the two sols that are mixed, and the pH, Eh, and temperature at which mixing takes place. When alkaline silicate is present in excess, it tends to form a protective layer of colloidal silica on the metal hydroxide particles, inhibiting precipitation (Rankama and Sahama, 1950, p. 235; Iler, 1955, p. 182-183). Moore and Maynard (1929, p. 284) found that mixing of ferric hydroxide and silica hydrosols precipitates most of the iron but only a little silica unless the Si:Fe ratio is greater than 3:1.
DEPOSITION AT HIGH TEMPERATURE
Because the solubility of silica at low pressure increases only slightly with temperature as high as the boiling point of water, the chief effect of increasing temperature in this range on supersaturated silica solutions is that it allows the various factors summarized in the preceding section to act more﻿GENESIS OF JASPEROID
45
rapidly in causing precipitation of the excess silica. Her (1955, p. 161) reported that precipitation of silica from supersaturated hot alkaline solutions is promoted by the presence of Na+1, Ba+2, and F_1 ions in the solution. Thus, it is probably no accident that barite and fluorite are relatively common accessory minerals in'jasperoids.
Colloidal silica can be converted readily to quartz, particularly in alkaline solutions, at supercritical temperatures and moderate to high confining pressures. Siever (1962, p/ 133) reported that above 200 °C quartz precipitates readily as amorphous silica dissolves, and Boydell (1924, p. 15-16) reported that quartz crystals have been obtained by heating silica sol or gel in closed tubes at a temperature of 250°C. In alkaline solutions near the critical point, fused silica rods dissolve and quartz crystals precipitate. The maximum growth rate of these crystals was obtained in 0.3N NaHC03 solution, in a period of 6 hours. Then the growth declined, and after 20 hours it ceased owing to the growth of a layer of porous quartz needles on the nutrient glass rods (Walker, 1953, p. 250-251).
The mechanism of the conversion of silica gel to quartz at high temperature and pressure was investigated by Ellis and Fyfe (1957, p. 270) and by Carr and Fyfe (1958, p. 909). They found that this transformation proceeds through two intermediate metastable phases; thus, silica gel -» crystobalite -> silica K (keatite) -» quartz. Quartz will not form in the presence of crystobalite, but once keatite is formed it inverts rapidly to quartz. The reaction rate increases with both temperature and pressure, but it is more sensitive to pressure than to temperature; the presence of alkaline solutions also speeds the reaction. These conclusions corroborate the findings of Wyart (1943, p. 483), who converted silica glass to crystobalite at 374°C and 220 atm in pure HoO, but in similar experiments with 0.05M KOH solutions he obtained quartz instead. On short runs with aqueous fluid, Wyart got a mixture of silica gel and crystobalite, but in none of his experiments did he obtain crystobalite-quartz mixtures. The conversion of colloidal silica to jasperoid in nature would thus be facilitated by alkaline solutions in an environment of increasing temperature and pressure.
The temperature at which the fine-grained quartz of jasperoid has formed may be susceptible to geothermometric measurement, because quartz that is known to have formed at low temperatures is richer in O18 than quartz that formed at high temperatures (Keith and others, 1952). Fluid inclusions might also provide information on the formation tempera-
ture of jasperoid quartz, were it possible to find any in such a rock that has an average grain diameter of less than a tenth of a millimeter.
GENESIS OF VARIOUS FORMS OF SILICA IN JASPEROID
Relatively little is known of the natural conditions under which the various common types of silica found in jasperoid are formed. Silica deposited in colloidal form is metastable and commonly converts in time to some other form, normally quartz or chalcedony, yet the presence of opaline silica in some jasperoid shows that, under some conditions, it can remain amorphous for a long time.
Quartz.—The natural conditions under which quartz precipitates directly from solution at low temperature are still largely unknown, although at high temperature the deposition of silica in this stable anhydrous form proceeds readily. Quartz is probably deposited from solutions undersaturated with silica relative to colloidal silica but supersaturated with silica relative to quartz itself at the temperature of deposition (White and others, 1956, p. 55; Morey and others, 1962, p. 1036-1037). Its deposition at low temperature must require a long span of time under stable conditions. According to Adams (1920, p. 640), variety of form and heterogeneity of grain size are characteristic of quartz that originated at shallow depth. The conversion of various forms of amorphous silica, including silica gel, into quartz has been accomplished in the laboratory by simply raising the temperature in a closed system to about 250 °C. Presumably, the same thing happens in nature at a lower temperature over a longer period of time. Folk and Weaver (1950) found that ordinary chert consists of a mixture of quartz and chalcedony, with no opal or other noncrystalline forms of silica, yet the extremely fine texture and prevalence of colloform banding in chert and in many jasperoids are evidence that these rocks were originally colloidal silica. Indeed, such textures in jasperoid give indirect evidence of its deposition at relatively low temperature, because at high temperature silica tends to deposit directly as quartz. Boydell (1924, p. 57-58) expressed the opinion that crystalline aggregates may be produced from a gel either by strain (which implies pressure) or by increasing temperature. White, Bran-nock, and Murata (1956, p. 55) found evidence at Steamboat Springs, Nev., of the replacement of opaline sinter by quartz and chalcedony at relatively shallow depth (50+ ft) ; they also found complete gradations from fine-grained mosaic-textured quartz to chalcedony, a feature that has also been observed in jasperoid samples.﻿46 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Chalcedony.—Folk and Weaver (1950) have shown that chalcedony is a fibrous, spongy variety of quartz that contains abundant submicroscopic bubbles filled with trapped water. These bubbles impart to chalcedony its distinctive optical properties. The nature of chalcedony also explains its gradation into ordinary' quartz. Adams (1920, p. 626) reported that chalcedony forms only in nearsurface deposits, whereas White, Brannock, and Murata (1956, p. 54) found that at Steamboat Springs, Nev., chalcedony formed only at depth as a replacement of opaline sinter or as bands lining the walls of cavities in this sinter. These bands are thicker on the bottom than on the sides of such cavities, and the bottom layers are horizontal. Such textures suggest precipitation of silica under the influence of gravity, even though the available evidence does not indicate whether chalcedony deposited directly or whether colloidal silica precipitated and was later converted to chalcedony. The difference in the opinions expressed by Adams (1920) and by White, Brannock, and Murata (1956) as to the environment in which chalcedony forms is more apparent than real, because Adams was discussing forms of silica characteristic of deep-seated high-temperature vein deposits as contrasted with those found in veins formed at shallower depths, whereas White, Brannock, and Murata were dealing with forms of silica deposited from hot springs at, or about 200 feet below, the surface. Chalcedony apparently forms in a rather restricted environment, characterized by low to intermediate conditions of temperature and pressure.
White and Corwin (1959) reported the successful synthesis of chalcedony by replacement of silica glass in alkaline solutions at 400 °C and 340 atm pressure. They believed that natural chalcedony forms not by precipitation from solution but by replacement of amorphous silica in an alkaline environment.
Opal.—According to Clarke (1924, p. 366), opal is formed by the evaporation of acid siliceous water, and White, Brannock, and Murata (1956, p. 53-54) expressed the opinion that opal generally forms by direct precipitation of monomeric silica, or small polymeric molecules of silica, from the rapid evaporation of near-boiling water. They also reported that opal may form as an end product of the nearsurface leaching of silicate minerals by hot acid solutions. Opal apparently is stable in the presence of H20 only at low pressure and at a temperature not much above the boiling point. A sample of opal in a drill core taken from a depth of 220 feet, temperature 140°C, in the Norris Basin of Yellowstone
National Park, showed incipient conversion to chalcedony.
REPLACEMENT OF HOST ROCK BY SILICA
The term “jasperoid” implies replacement of host rock by silica, and in many localities jasperoid bodies faithfully preserve the original textural features, the delicate fossils, and even the color of the rocks they replace (fig. 2B). This type of replacement requires (1) that solution of host rock and precipitation of silica must have taken place simultaneously in a thin layer at the contact; (2) that the silica, in whatever form deposited, must have been sufficiently competent to withstand the existing pressure without deformation and yet be sufficiently permeable to allow diffusion of solutions through it, carrying silica toward the replacement interface and host rock in solution away from it; (3) that the composition of these solutions must have been such that the host rock was soluble and that silica at the contact was less soluble; and finally (4), that these conditions must have persisted long enough to allow replacement of many thousands of cubic feet of rock. Considering the stringency of these requirements, it is not surprising that the mechanism of volume-for-volume siliceous replacement is a riddle that has baffled geologists for years, and that no one has .yet succeeded in duplicating this phenomenon in the laboratory.
Another common type of siliceous replacement that results in courser grained jasperoid, commonly with reticulated texture, destroys the primary textural features and fossils of the host rock. Formation of this type of jasperoid does not require strictly simultaneous removal of host rock and deposition of silica. Neither does it require diffusion of solutions through an advancing silica layer; the silica can be deposited directly as quartz disseminated in the host rock.
PHYSICAL FACTORS
Although the silicification of host rocks by silicabearing water was known to many early investigators, it was not until after 1900 that the physicochemical environment or the manner in which this process takes place was discussed. Church (1862, p. 109) described an experiment that resulted in the substitution of CaC03 for Si02 in solution at room temperature, and Spurr (1898, p. 217-220) recognized the epigenetic replacement origin of jasperoid at Aspen, Colo., and described the macroscopic and microscopic features of this rock.
Lindgren (1901), one of the first geologists to speculate seriously on the mechanism of siliceous re-﻿GENESIS OF JASPEROID
47
placement, stated (p. 602) that “waters containing carbon dioxide and silica deposit the latter, while simultaneously dissolving a corresponding proportion of calcite.” Lindgren (1925, p. 258) later recognized that such replacement can produce either crystalline quartz disseminated through the host or amorphous silica that replaces the limestone completely and advances as a wave through the host rock. Irving (1904, p. 173; 1911, p. 630-631) described the replacement of carbonate rocks by jas-peroid in the Black Hills, preserving original textures and colors and having sharp contacts with the unreplaced host rock. Later, Lindgren (1933, p. 91) wrote the famous equal-volume law of replacement:
Replacement is the process of practically simultaneous capillary solution and deposition by which a new mineral of partly or wholly differing chemical composition may grow in the body of an old mineral or mineral aggregate * * *. The most fundamental changes in rocks take place with practical constancy of volume.
Lindgren (1933, p. 173, 176-177) also discussed the mechanism by which the reacting solution reaches the replacement interface. Penetrating solutions under heavy pressure permeate the rocks; such rocks then act as semipermeable membranes through which electrolytes and gases diffuse rapidly but colloids and slightly ionized compounds diffuse very slowly. Diffusion takes place in response to concentration gradients, but it is a slow process, does not act over long distances, and ceases after a certain time. Thus, in the formation of large replacement deposits the mechanism of diffusion must be supplemented by solution movement along openings.
The maximum distance from such channels at which replacement by diffusion can be effective is not known. Irving (1911, p. 538) stated that, in exceptional cases, replacement may extend outward as much as 100 feet from feeding channels; however, he was probably referring to large trunk channels rather than small fractures that could act as subsidiary feeding channels. According to Holser (1947, p. 395), transport of material in solution occurs mainly by bodily flow in any openings of larger-than-capillary size, but in capillary and subcapillary openings such transport is largely by diffusion. Such diffusion transport at the replacement interface is a necessary prerequisite to completing fine-grained replacement. These conclusions of Lindgren and Holser that large-scale complete replacement is dependent on transport by moving solutions supplemented by local diffusion over short distances were corroborated by Garrels and Dreyer (1952, p. 374-375). They calculated that a minimum of 3,000 years
would be required for the replacement of the most permeable limestone beds in the Tri-State district by a layer of galena 1 cm thick deposited by dilute lead-bearing solutions in which the lead moved only by simple diffusion in response to concentration gradients. Thus, the ideal conditions for replacement occur in shatter zones characterized by numerous small closely spaced fractures.
The replacement product, as well as the host rock, must be permeable to the solutions; otherwise, replacement would cease as soon as a thin layer of this product had formed, for it would seal off and protect the host rock from further attack. Garrels and Dreyer (1952, p. 352) concluded that such a situation would occur if the volume of the guest mineral precipitated were greater than the volume of host mineral dissolved, and that the total amount of rock replaced depends only on this volume ratio of guest to host, not on solution concentration or rate of reaction. Solutions moving in response to a high pressure gradient might force their way through a somewhat thicker layer of reaction product, however, before the host rock became completely sealed by precipitation. Such a conclusion is logical regarding the advancing-wave type of massive replacement, but it would not necessarily apply with equal force to the disseminated type, in which replacement proceeds outward from a number of isolated nuclei scattered through the host. Even in this type, however, replacement by a larger volume guest mineral should eventually stop when the individual replacement fronts near the main supply channel coalesce. Ames (1961d, p. 1443-1444) also recognized the importance of the host-guest volume ratio in a continuing replacement process, though he pointed out that
Volume relationships are a result of a given replacement reaction, but do not initially cause or prevent the reaction * * *. Starting with equivalent experimental conditions such as surface area, the initial significant correlation is between ion fraction reacted and activity product ratios. As the reactions proceed, the significant correlation tends to be between ion fraction reacted and molar volume change.
He concluded that replacement reactions resulting in a negative theoretical volume change may show little actual volume change due to changes in bulk density, whereas reactions involving a positive theoretical volume change decrease the permeability of the host, forcing replacement to become diffusion dependent and hence very slow, but the larger volume replacing mineral tends to occupy the same actual volume as the mineral replaced.
If the volume ratio theory of replacement is strictly valid, then it would seem to follow that﻿48 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
large-scale volume-for-volume replacement with preservation of original texture could proceed only if the guest mineral has a density equal to, or greater than, that of the host. This would preclude the replacement of limestone by any form of silica lighter than quartz, and it would preclude the replacement of dolomite by any form of silica at all! Such a conclusion is at variance with the field evidence in many districts that dolomite as well as limestone has been silicified, and furthermore, that the silica was originally deposited in the form of silica gel, which would have a specific volume nearly twice that of the carbonate it replaces (Nolan, 1935, p. 94; Gilluly, 1932, p. 100; Cox and others, 1916, p. 11; Lindgren, 1925, p. 258; and many others). The replacement of large volumes of carbonate rock by silica probably proceeds both by diffusion of the reaction products through the gel layer and by movement of silica-bearing solutions along fractures.
Chemical reactions involving the movement of ions through a silica gel from an aqueous solution have been carried out successfully in the laboratory for more than half a century (Hatschek and Simon, 1912, p. 452) ; hence, there is experimental support for the theory that replacement can be accomplished in this manner. Furthermore, as pointed out by Garrels and Dreyer (1952, p. 347-348), the rate of diffusion increases with temperature.
CHEMICAL FACTORS
Ames (1961b, p. 528; 1961c, p. 737; 1961a, p. 1022, 1024) conducted many experiments on the replacement of limestone by minerals containing a common ion (either Ca+2 or C03-2). In all of these he concluded that the dominant prerequisite t6 replacement was that the guest mineral is less soluble in the system than the host. In complex systems in which several possible alteration products are less soluble than the host, only the least soluble of these will form.
If, as stated by Ames, replacement can take place only in a system in which the guest compound is less soluble than the host, then siliceous replacement of limestone requires greater solubility of CaC03 than of Si02 in the solution at the replacement interface. The same requirement also applies to the siliceous replacement of other rock types, but consideration of the chemical processes involved is much simplified by limiting discussion to the replacement of calcite by silica.
CaC03 is less soluble than Si02 in pure H20 at all temperatures above the freezing point, and the discrepancy between the relative solubilities of these compounds becomes greater as the temperature in-
creases. Although the solubility of calcite does increase slightly with increasing pressure (a threefold increase in solubility for an increase in pressure from 1 to 1,000 atm, according to Garrels and Dreyer, 1952, p. 339-341), that of silica increases much more rapidly with pressure at constant temperature (fig. 345). Thus, the replacement of limestone by silica derived from an aqueous fluid containing no other components should be impossible. The same thing is true of hot alkaline solutions, in which calcium carbonate is even less soluble than it is in pure water. However, as the pH of a solution decreases below the neutral point, the solubility of calcite rises rapidly; 100 times for each pH unit, according to Garrels and Dreyer (1952, p. 339-341). The ionic solubility of silica is relatively low in acid solutions, but such solutions are capable of carrying many times their saturation concentration of silica in the form of a dispersed sol.
Another factor that increases the solubility of calcite is increasing salinity of the solution (Siever, 1962, p. 145). Miller (1952, p. 173-175) ran a series of experiments on the solubility of calcite in water and in 0.5M NaCl solutions at various temperatures as high as 100 °C and under various partial pressures of C02 from 1 to 100 atm. He found that CaC03 solubility increased steadily with increasing C02 pressure at constant temperature and decreased steadily with increasing temperature at constant C02 pressure; furthermore its solubility in the NaCl solution was 50-100 percent greater than in water at any given temperature and C02 pressure within the range of his experiment. The effect of salinity on silica solutions is to greatly accelerate the equilibration of these solutions without appreciably affecting the silica solubility (Van Lier and others, 1960, p. 1675). Thus, a warm siliceous brine should be saturated, or nearly saturated, with ionic silica under the prevailing conditions of pressure, temperature, and pH, and any change in these conditions that would decrease its solubility should cause the excess silica to precipitate, rather than to supersaturate, the solution.
The importance of C02 in promoting the simultaneous solution of calcite and deposition of silica has long been recognized. The increase in carbonate solubility with increasing C02 content of the solution is due to the increasing acidity caused by the formation of carbonic acid. Garrels and Dreyer (1952, p. 341) found that the solubility of calcite actually decreases with increasing C02 content of the solution if the pH is held constant. The pH of solutions saturated with volatile acid-forming gases such as C02 or H2S is strongly pressure dependent. C02 under﻿GENESIS OF JASPEROID
49
pressure corresponding to the hydrostatic pressure at a depth of 2,000 feet would cause the pH of water to drop to a value of 3.2 (Garrels and Dreyer, 1952, p. 371-372).
Solubility versus temperature curves for calcite and silica trend strongly in opposite directions, and at any given temperature the pH of the system, in the acid range, has a great effect on carbonate solubility but has relatively slight effect on silica solubility. Thus, at 1 atm C02 pressure, calcite is more soluble in H20 than is silica up to a temperature of about 65°C; in 0.5M NaCl solution up to a temperature of about 90°C; at 100 atm C02 pressure the extrapolated solubility curves would cross at about 125°C for pure H20 and at 150°C for 0.5M NaCl solution. These data, taken in conjunction with Ames’ observation that replacement cannot occur unless the replacing substance is less soluble in the system than the material it replaces, suggest that the silicification of limestone must be a relatively low-temperature phenomenon. Such a conclusion is further substantiated by the field evidence, in many districts, that silica was originally deposited as a gel. As stated previously, silica will precipitate in the anhydrous form at temperatures above 200°C.
If a carbonated, silica-saturated brine attacked and dissolved calcium carbonate, this would tend to neutralize the solution at the reaction interface and thus promote the precipitation of silica, because the ionic solubility of silica is lower in a neutral solution than in an acid solution, and the presence of NaCl would prevent the excess silica from supersaturating.
THEORY OF REPLACEMENT PROCESS
We can now speculate on a hypothetical mechanism by which silica may replace limestone, which is consistent with the various observations previously discussed. Let us assume that hot emanations saturated, or nearly saturated, with silica, and also containing appreciable quantities of dissolved C02, H2S, and possibly HC1 are rising along a deep conduit, such as a major fault, into a thick sedimentary series containing abundant limestone beds, and that this conduit penetrates the zone of ground water but does not, initially, extend directly to the earth’s surface. At great depth, where the rocks are tight, solution movement will largely be confined to the main conduit, the wallrocks will be hot, and changes in temperature and pressure within the solution will be slight. Such a solution will, in all probability, be out of chemical equilibrium with the wallrock of the conduit, and we can expect initial alteration of these rocks adjacent to the channel, such as silication of
carbonate rocks and argillic alteration of other rock types. This will result in the formation of an alteration envelope around the conduit insulating the rock beyond it from further attack by the upward-moving solutions.
As the system approaches to within a few thousand feet of the earth’s surface, the juvenile solutions will begin to mingle with connate brines and ground water, and numerous subsidiary fractures, minor faults, and other secondary channels will begin to tap the main line of the plumbing system. This will cause a relatively rapid drop in both temperature and pressure of the system as well as a change in its chemical composition, so that in place of a superheated aqueous fluid moving along a major channel, hot, acid, silica-bearing water with added alkaline chlorides is seeping upward through a broad fracture zone. Such a change will result in supersaturating the system with silica; however, so long as the pH remains low, this silica will not necessarily precipitate but will be carried as a dispersed colloidal sol. As soon as the solution enters a brecciated bed of limestone, the limestone will begin to dissolve, and this reaction will tend to neutralize the solution. The presence of dissolved alkaline chlorides will increase the solubility of the limestone, and at the same time cause the colloidal silica to become unstable as the pH of the solution rises. Thus, silica will precipitate as limestone dissolves. As the acid solutions penetrate and permeate the limestone, the initial solution of this rock must proceed slightly faster than the precipitation of silica from the more nearly neutral solutions resulting from the reaction. This may be the explanation for the commonly observed selvage of sanded limestone or dolomite intervening between jasperoid bodies and fresh host rock.
If the precipitated silica is in the form of colloidal particles or a gel, it coats the walls and fills the fractures; the rising pH of the solution tends to reduce the host-rock solubility on the outlet side of the fractured limestone. Both processes tend to inhibit further replacement. However, solutions can still diffuse through the aqueous gel, and this diffusion can be speeded by the development of a gas phase as C02 and H2S come out of solution in response to decreasing pressure. Furthermore, the decline in carbonate solubility resulting from a rising solution pH is offset, at least in part, by an increase in carbonate solubility, as calcium bicarbonate, caused by the temperature drop resulting from exsolution of the acid gases.
As the gel layer thickens close to the point of entry of solutions into the limestone, the hot rising﻿50 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
solutions increase the temperature of this gel and thus tend to promote its conversion to quartz. Such a conversion results in a considerable decrease in volume of the silica, accompanied by a corresponding increase in porosity and permeability, thus allowing continued movement through it of silica-bearing solutions toward the replacement interface, in response to both pressure and concentration gradients.
If silica precipitates directly in the anhydrous form as either quartz or cristobalite, rather than as a hydrous gel, the result will be either a layer of fine-grained crystals along the openings resulting from solution of calcite or a number of isolated quartz or cristobalite nuclei disseminated through the host, growing slowly by accretion. In either case, reacting solutions can continue to move through the replacement product along intergrain boundaries toward the replacement front.
Replacement eventually ceases as a result of one or more of the following conditions:
1.	The pH of the solution at the replacement inter-
face rises to the point where limestone is less soluble than silica under the prevailing temperature and pressure.
2.	The whole rock body becomes too hot for the re-
action to continue.
3.	The silica layer becomes too thick or too im-
permeable to permit further diffusion of the reacting substances through it.
4.	The supply of silica becomes depleted.
5.	The main conduit breaks through to the surface
along a different route.
If silica is initially deposited as a gel, this gel will rupture as it shrinks and inverts to quartz. Solutions circulating through the fractures thus formed will cause local solution and reprecipitation of silica, thus forming the veinlets and vug linings of late coarse quartz that are common in jasperoid bodies.
Low-temperature replacement of limestone by silica-bearing ground water and connate brines below the water table must largely be a pressure-dependent process. Such waters at depth are probably alkaline chloride solutions containing sufficient carbonic acid in solution to prevent the precipitation of excess silica. Movement of such solutions under pressure gradients into fracture zones in limestone decreases their ability to retain silica, both by decreasing silica solubility because of decreasing pressure and by neutralization caused by reaction of carbonic acid with limestone. Thus, silica precipitates as limestone is dissolved.
The replacement theory just outlined still does not account for replacement of rocks other than carbonate rocks by jasperoid. Neither does it en-
tirely account for the replacement of limestone by supergene jasperoid during the oxidation and weathering of silica-bearing sulfide ore bodies nor the formation of younger jasperoid matrix, cementing fragments of older jasperoid. The chemical nature of the solutions involved in these processes is so complex that more research is required before they can be fully explained.
JASPEROID AS A GUIDE TO ORE
In many mining districts, bodies of jasperoid are both genetically and spatially related to replacement ore deposits. In other districts, jasperoid shows no such relationships, and is not useful as a guide to ore. Not uncommonly, both types of jasperoids are found in the same district, and methods of distinguishing between them are important for effective exploration.
DEFINITION OF FAVORABLE AND UNFAVORABLE JASPEROID
In this study, jasperoids are divided into two categories: (1) jasperoid related to, and associated with, ore (favorable jasperoid) ; (2) jasperoid unrelated to ore (unfavorable jasperoid). As in most rock classification systems, some borderline rock types are difficult to classify. The jasperoid may have been deposited from mineralizing solutions that later brought in ore metals, but, if the jasperoid bodies formed as an outer alteration zone at a considerable distance from the later ore deposits, a genetic relationship would be difficult to establish. Such jasperoids, even though genetically related to ore, could not be classed as favorable, inasmuch as they are not helpful in locating ore. This kind of jasperoid occurs in the Gilman mining district of central Colorado. Here, the major sulfide-replacement ore bodies show little or no silicification of carbonate host rock adjacent to the ore. Yet these rocks have been converted to dense aphanitic jasperoid, commonly preserving original textures, that extends along major fractures from half a mile to several miles updip from the ore bodies on the outlet side of the hydrothermal plumbing system. Conversely, silicification may be younger than the ore stage of mineralization and genetically unrelated to it. Where such late silicifying solutions pass through ore bodies they may become contaminated by the ore metals, and the resulting jasperoid bodies may be favorable for effective exploration. Possible examples of this type of jasperoid are present in the Clifton-Morenci district of Arizona.
The criteria for distinguishing favorable jasperoid from unfavorable jasperoid were developed from﻿JASPEROID AS A GUIDE TO ORE
51
the comparison of samples taken from, or adjacent to, mine workings with samples taken more than a quarter of a mile from any mine workings. For this study, the first group was designated as favorable, the second, as unfavorable. Such a classification, based entirely on the presence or absence of spatial association with developed ore deposits, inevitably results in the misclassification of some samples in both categories. A further assumption, implicit in any attempt to reach general conclusions on the basis of sample investigation, is that the samples chosen for study are reasonably representative of the bodies from which they were taken. The samples included in this study were not selected according to a statistically randomized sampling plan; instead, an effort was made to obtain “typical” samples at each locality. Some samples of unfavorable jasperoid bodies that happened to be near, or penetrated by, mines are classified as favorable; some samples of favorable jasperoid related to undeveloped ore bodies are classified as unfavorable. The assumption was made that the number of such erroneously classified samples would be so small in proportion to the total that they would not obscure any significant differences that could be used as criteria for distinguishing between the two groups. After diagnostic criteria evolved from the initial study they were applied to each sample in both original groups to locate and reclassify samples that had been mis-classified on the basis of field association alone; they were also applied to samples not included in the original study groups because their field relations to ore either were unknown or were not diagnostic.
METHODS OF DATA ANALYSIS
The characteristics of jasperoid specimens chosen for study were initially divided into two groups: (1) discontinuously distributed properties—those that may be either present or absent, such as a specific color, texture, or accessory mineral; and (2) continuously distributed properties—those that may be measured on a continuous scale, such as porosity, density, or concentration of a specific element. These two groups of properties require different statistical tests to appraise the significance of differences between the two categories of jasperoid samples.
For discontinuously distributed properties, the number of samples in each category that exhibits a specified property is recorded; also recorded is the number of samples that do not exhibit the property. This generates a 2X2 contingency table of the form
Favorable Unfavorable
Positive (+)	A	B
Negative ( —)	C	D
with entries in each of the cells, A, B, C, and D. The data in these cells are then substituted in the formula for chi square given by Siegel (1956, p. 107-109).
N (\AD-BC\Y)
x' = (A+B) (C+D) (A+C) (B+D) where N=A+B + C+D.
The value of chi square thus obtained is then checked against a table of critical values of chi square with 1 degree of freedom, such as table C in Siegel (1956, p. 249). Values of chi square less than the tabulated value for a probability of 0.10 (x2=2.71) are considered to indicate no significant difference in the frequency of occurrence of the property between the favorable and unfavorable sample groups.
As an example of the calculations, let us consider the distribution of vuggy texture between the favorable and unfavorable sample groups. Of 95 favorable samples, 55 were vuggy, and of 53 unfavorable samples, 18 were vuggy. This gives the following 2X2 contingency table distribution:
Favorable Unfavorable
Positive (+)	A. 55	BiS
Negative ( —)	C«	D35	N = 148
9_ 148(| (55X35) - (40X18) |-74)2 x2~ (55 + 18) (40+35) (55+40) (18+35)
_ 148 (1925-720-74)2 73X75X95X53
189,315,828
=	—C Q7
27,566,625
Reference to a table of critical values for x2 with 1 degree of freedom shows that the probability level associated with this value of x2 is slightly less than 0.01 (x20.01 = 6.64). This means that there is only about one chance in a hundred of obtaining such a great discrepancy between the favorable and unfavorable sample distributions if, in fact, the property of vugginess were equally common in both types of jasperoid. Thus, we may conclude that favorable jasperoids are more likely to be vuggy than unfavorable ones; consequently, vugginess becomes one of our significant criteria for favorable jasperoid.
For continuously distributed properties, the Kolmogorov-Smirnov two-sample test (Siegel, 1956, p. 127) may be used. This tests the null hypothesis that there is no significant difference between the parent populations (favorable and unfavorable jasperoids) with respect to the measured property under consideration. The test compares the cumula-﻿52 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
tive frequency distributions of the property in the two groups. If the greatest discrepancy between these distributions is sufficiently large to be significant at the chosen probability level, the null hypothesis of no significant difference is rejected. As with the chi-square test, we may use a probability level of 0.10; that is, if a maximum discrepancy between the cumulative distributions as great as, or greater than, the one observed may be expected to occur by chance as frequently as one time out of 10, in samples drawn from the same population, then we will assume that there is no significant difference.
Class midpoint	Favorable	Unfavorable Difference
Percent Fe	F	P= F IF	SPf	F	II	2Pu	SPj—SPu
>10 		... 8	0.084	0.084	i	0.019	0.019	0.065
7 		... 16	.168	.252	0	.000	.019	.233
3 		... 14	.147	.399	3	.057	.076	.323
1.5 		... 13	.137	.536	14	.264	.340	.196
.7 		... 17	.179	.715	13	'.245	.585	.130
.3 		... 12	.126	.841	13	.245	.830	.011
.15 		... 11	.116	.957	7	.132	.962	.005
.07 		... 4	.043	1.000	2	.038	1.000	
Total		... 95			53			
D = 0.323 at 3 percent Fe.
D.=K	0.1TK
The data for both sets of samples are tabulated in frequency distributions, using the same class intervals. It is convenient to use the same intervals in which the data are reported for grouped data such as semiquantitative spectrographic analyses (Myers and others, 1961). Ungrouped raw data such as density measurements, may be grouped in any convenient classes that will adequately define the frequency distributions.
The number of samples in each class is first tabulated for both groups, with the class representing the highest magnitude of the variable at the top of the table, and the class representing the lowest magnitude at the bottom. The number of samples in each class (frequency) is then converted to a proportion of the total samples in the group in a second parallel column (P), and the cumulative proportion is recorded in a third column (£P). The difference between the cumulative proportion values for the two groups is then recorded, class by class, in another column headed “Difference,” and the maximum difference in this column, together with the class to which it belongs, is recorded at the bottom of the table as D. The value of D thus obtained may then be tested for significance (Siegel, 1956, p. 127-135, 279). The formula used is
Da = K
n!+n2
n1Xn2
where if is a constant dependent on the level of significance desired, and ni and n2 are the total numbers of samples in each of the two categories.
As an example, let us test the significance of iron concentration in the two categories of jasperoid. The data and calculations are as follows:
K 0.10 = 1.22	D 0.10 = 0.027
K .05 = 1.36	D .05= .231
K .01 = 1.63	D .01= .277
The numbers in the “Class midpoint” column are the figures reported in grouped (three-step) spectrographic analysis (Myers and others, 1960) and represent the midpoints of three class intervals for each order of magnitude. The intervals are approximately equal on a logarithmic scale.
The D value of 0.323 at the iron concentration of 3 percent is significant at the 0.01 probability level, which can be interpreted as indicating that iron concentrations of 3 percent or more occur With significantly greater frequency in favorable jasperoids than in unfavorable jasperoids.
Although each of the properties vugginess and high iron content (given as examples in the preceding discussion) shows a statistically significant association with jasperoids of the favorable type, neither one by itself furnishes a diagnostic criterion for distinguishing between the two types. Of the favorable samples, 58 percent were vuggy and 42 percent were not, whereas of the unfavorable samples, 34 percent were also vuggy. Iron content was significantly high in about 40 percent of the favorable samples and also in about 8 percent of the unfavorable samples.
The application of these statistical tests to all the observed properties in both categories of samples revealed a number of properties significantly associated in varying degree with either favorable or unfavorable types of jasperoid. Each of these properties was then listed as a criterion and given a rank depending on its level of significance; 1 for the 0.1-0.01 level, 2 for the 0.01-0.001 level and 3 for the > 0.001 level; plus ( + ) if associated with favorable samples and minus ( —) if associated with unfavorable samples. Many of the chemical elements show significant differences at relatively low con-﻿JASPEROID AS A GUIDE TO ORE
53
centrations; for these elements an additional scoring point was added arbitrarily for each order of magnitude of concentration above the one at which the significant value occurred. Thus, lead showed a D value that is significant at the 0.001 level, corresponding to a concentration of 0.0015 percent lead; so a sample containing 0.015 percent lead would have a score of +4 for this property instead of +3.
All the criteria were applied to each of the samples in the collection, and final classification of the sample was made on the basis of its total score. This last operation, although empirical rather than statistical, resulted in the separation of a large majority of the samples in the collection into those with distinctly favorable characteristics and those with distinctly unfavorable characteristics. It changed the classification for some samples in the original study groups, and it suggested a classification for many samples not included in these groups
because their field relations to ore either were unknown or were not diagnostic.
COMPARISON OF MEGASCOPIC CHARACTERISTICS
The megascopic characteristics that were recorded for comparison between the favorable and unfavorable groups of jasperoid samples were color, based on the National Research Council “Rock-Color Chart” (Goddard and others, 1948), and macrotexture, including phaneritic, brecciated, and vuggy. Table 9 shows the frequency of occurrence and nonoccurrence of these characteristics in both sample groups, the computed value of x2> and the level of significance associated with this value.
From table 9, it seems that light- to moderate-red colors are more characteristic of unfavorable jasperoid, and a dark-brown color, of favorable jasperoid. The latter association was also noted by Locke (1926) and by Blanchard and Boswell (1928)
Table 9.—Distribution of megascopic characteristics in favorable and unfavorable oxidized jasperoid samples
[Rock-color designations are from Goddard and others (1948)]
Characteristic	Favorable 1	Unfavorable1	X2
	+	+	Computed value Significance level 2
			
Color			
Pink and light red (5R —)			 0	94	10	97	7.35	0.001-0.01
Medium red and grayish red (5R|A)			 1	93	17	90	11.70	<.001
Dark red (5R 2 * )			 6	88	5	102	.05	N.S.
Orange pink (lORl^f)			 2	92	5	102	.35	N.S.
Reddish brown (10R|-|)			 4	90	8	99	.43	N.S.
Dark reddish brown (10R|A)			 10	84	5	102	1.78	N.S.
Grayish pink (5YR ®-8)			 5	89	5	102	.01	N.S.
Light brown and medium brown (5Y-R-1A)			 24	70	5	102	15.96	<.001
Dark brown (5T'R-|:|)			 7	87	2	105	2.42	.05-.1
Light brownish gray (5YR-yt)			 6	88	5	102	.05	N.S.
Grayish orange (lOUR-Lf)			 14	90	12	95	.09	N.S.
Yellowish brown (10FR|A).—			 19	75	16	91	.63	N.S.
Dark yellowish brown (10YE2"4)			 4	90	3	104	.03	N.S.
Olive gray (5F-?y)			 10	84	17	90	.77	N.S.
White and light gray (AT7-9)			 30	64	34	73	.02	N.S.
Medium gray (A14-6)			 25	69	32	75	.23	N.S.
Dark gray and black (NS-1)			 11	83	15	92	.08	N.S.
Macrotexture
Phaneritic 			 66	29	22	31	9.91	0.001-0.01
Brecciated 			 33	62	23	30	.74	N.S.
Vuggy 			 55	40	18	35	6.87	.001- .01
1	Plus ( + ) indicates frequency of occurrence; minus ( —) indicates frequency of nonoccurrence.
2	N.S. indicates not significant.﻿54 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
in connection with leached outcrops overlying sulfide ore bodies. Coarse grain and vuggy texture also seem to be considerably more common in productive jasperoid than in barren jasperoid. Brecciated texture is common in all jasperoids, but it is not significantly more abundant in either type.
COMPARISON OF MICROSCOPIC CHARACTERlS i ic.s
The microscopic characteristics chosen for comparison between favorable and unfavorable categories of jasperoid samples were microtexture and the presence of various accessory minerals (table 10). The sulfide ore minerals, such as galena, sphalerite, and chalcopyrite, and their oxidation products have been excluded from the lists in table 10 because these minerals are present only in favorable jasperoid, and no statistical test of their significance is needed.
A heterogeneous texture, characterized by a wide range in grain size of quartz, and a reticulated tex-
Table 10.—Distribution of microscopic characteristics in 95 favorable and 53 unfavorable jasperoid samples
Characteristic	Favorable 1		Unfavorable 1			x 2
	+	-	+	-	Computed value	Significance level 2
Microtexture3						
Size range of quartz						
grains >10X4 			 57	38	17	36	9.52	0.001-0.01
Xenomorphic 			 63	32	35	18	.02	N.S.
Jigsaw puzzle 			 48	47	40	13	7.78	.001- .01
Granular 			 15	80	5	48	.69	N.S.
Reticulated 			 31	64	5	48	8.73	.001- .01
Accessory minerals that are generally older than, or contemporaneous with, jasperoid silica
Barite 		... 15	80	3	50	2.39	N.S.
Calcite 		... 12	83	8	45	.03	N.S.
Carbonate dust 			... 26	69	16	37	.03	N.S.
Chalcedony 			... 9	86	7	46	.18	N.S.
Chlorite or biotite 		... 3	92	2	51	.08	N.S.
Clay (kaolinite group) ..	... 33	62	12	41	1.82	N.S.
Clay (montmorillonite group) 		... 0	95	3	50	3.01	0.05 -0.10
Dolomite 		... 5	90	1	52	.32	N.S.
Hematite 			... 11	84	8	45	.13	N.S.
Pyrite 		... 29	66	6	47	5.93	.02 - .05
Sericite or hydromica 		... 25	70	22	31	2.96	.05 - .10
Tourmaline 		... 4	91	0	53	.97	N.S.
Zircon 		... 2	93	0	53	.10	N.S.
Accessory minerals that are generally younger than jasperoid silica
Calcite 		.. 15	80	17	36	4.41	0.02 -0.05
Chalcedony 		... 7	88	3	50	<■01	N.S.
Clay (kaolinite group) ..	... 4	91	0	53	.97	N.S.
Clay (montmorillonite						N.S.
group) 		.. 1	94	1	52	.10	
Fluorite 		... 5	90	0	53	1.50	N.S.
Goethite 		... 45	50	12	41	7.77	.001- .01
Hematite		... 20	75	14	39	.29	N.S.
Jarosite 		.. 23	72	3	50	6.85	.001- .01
Brown limonite 		.. 22	73	12	41	.02	N.S.
Yellow-orange limonite ..	.. 1	94	5	48	4.18	.02 - .05
Opal		... 3	92	0	53	.49	N.S.
1	Plus ( + ) indicates frequency of occurrence; minus ( —) indicates frequency of nonoccurrence.
2	N.S. indicates not significant.
8 See pages 11-15 for definitions of textural designations.
4 The ratio of the diameter of the largest common quartz grains in the groundmass to the diameter of the smallest common quartz grains is >10.
ture seem to be significantly associated with favorable jasperoid, whereas jigsaw-puzzle texture shows a significantly greater association with unfavorable jasperoid. Pyrite is the only older mineral given that is more characteristic of favorable than of unfavorable jasperoid, but older sericite and montmoril-lonite clay are more common in the unfavorable variety. Among the younger minerals, goethite and jarosite are suggestive of favorable jasperoid; cal-cite and yellow-orange limonite are suggestive of unfavorable jasperoid in the oxidized zone.
COMPARISON OF OTHER PHYSICAL PROPERTIES
The only physical properties other than color and texture determined for representative groups of favorable and unfavorable jasperoid samples were density and porosity; the porosity was computed from the ratio of bulk density to powder density. These properties were tested on the theory that favorable jasperoid samples might tend toward greater density because of incorporated ore element compounds, or that higher porosity might increase permeability of jasperoid for mineralizing solutions. The results of the Kolmogorov-Smirnov two-sample test on 72 favorable samples and 41 unfavorable samples are given in table 11.
The marked similarity in distributions of both powder density and porosity in the two groups of jasperoid samples suggests that these properties are of no use as criteria for distinguishing favorable jasperoid from unfavorable jasperoid. Furthermore,
Table 11.—Distribution of density and porosity in 72 favorable and U1 unfavorable jasperoid samples
[Density determinations by R. F. Gantnier]
	Cumulative Frequency Proportion proportion				Differ- ence
	Favor- able	• Unfavor- Favorable able	Unfavor- Favorable able	Unfavor- able	
		Density distribution (percent)			
[D = 0.080 at 2.65-<2.70; Ds (0.10) =0.237;			; D<Ds(0.10), is not significant1]		
Density;					
<2.60	17	9 0.236	0.219 0.236	0.219	0.017
2.60-<2.65	19	14 .263	.342 .499	.561	.062
2.65-<2.70	4	3 .055	.073 .554	.634	.080
2.70-<2.75	11	4 .153	.098 .707	.732	.025
2.75-<2.80	5	4 .070	.098 .777	.830	.053
2.80-<2.85	2	1 .028	.024 .805	.854	.049
>2.85	14	6 .195	.146 1.000	1.000	
		Porosity distribution (percent)			
[D = 0.127 at 3—<5 percent; Ds (0.10) =0.237;					
	D<Ds(0.10), is not		significant1]		
Porosity;					
<i	9	7 0.125	0.171 0.125	0.171	0.046
l-<3	22	10 .306	.244 .431	.415	.016
3-< 5	15	4 .208	.097 .639	.512	.127
5-<7	9	7 .125	.171 .764	.683	.081
7-<9	6	8 .083	.195 .847	.878	.031
9-< 11	4	2 .056	.049 .903	.927	.024
>11	7	3 .097	.073 1.000	1.000	
1 D=greatest difference in cumulative proportions; Ds(0.10)= difference required for statistical significance at 10 percent level.﻿JASPEROID AS A GUIDE TO ORE
55
a series of check determinations on replicate subsamples from the same original specimen showed variations of as much as 0.2 in both powder-density and bulk-density determinations. This heterogeneity of density distributions within a sample, coupled with the narrow range of density values for both groups of samples, suggests that density and porosity measurements on jasperoid serve no useful purpose beyond indicating the general range of these properties in this type of rock.
A few selected samples of favorable and unfavorable jasperoid were subjected to differential thermal analysis. The resulting curves showed no distinctive patterns that would be useful for distinguishing between the two types except for one highly favorable unoxidized sample that contained much visible pyrite and sphalerite.
Although none of the three physical properties investigated proved useful in distinguishing between the two types of jasperoid, it is possible that other such properties, which were not determined, might do so.
COMPARISON OF CHEMICAL COMPOSITION
Semiquantitative spectrographic analyses for 69 elements were made on 95 favorable jasperoid samples and 53 unfavorable jasperoid samples (most of them from the oxide zone). Only 42 of these elements (other than silicon) were present in detectable concentrations in any of the samples analyzed, and only 28 were present in detectable concentrations in more than 10 percent of the samples analyzed. The sensitivity of the analytical method varies considerably for different elements.
These elements may be classified, according to the proportion of samples in which they occur in detectable concentrations, as follows:
Percent of samples
Elements	Classification in which elements
of elements	occur in detectable
concentrations
Al, Fe, Mg, Ca, Mn, Ti,		•*
Ba, Cr, Cu		Characteristic ....	>90
Ni, Pb, Sr, V, Zr		Common 		50-90
Na, Ag, As, B, Be, Bi, Ga, In, Mo, Sb, Sn, Y,		
Yb, Zn		Minor 		10-50
K, P, Cd, Ce, Co, Ge, La,		
Nb, Sc		Sparse 		2-10
Li, Nd, Ta, U, W		Very sparse 		<2
Significant differences in the distributions of characteristic and common elements between favorable and unfavorable jasperoid samples were also tested statistically by the Kolmogorov-Smirnov two-sample test, as summarized in table 12. Among the elements
Table 12.—Maximum difference in cumulative proportions of characteristic and common elements between favorable and unfavorable samples, and significance of this difference
[Data from semiquantitative spectrographic analyses by J. C. Hamilton]
2P at concentra-
Element	Concentration C at which D occurs (percent)	tion C		Difference D |SPf-SPu	Significance level1 i
		Favor- able	Unfavor- able		
Al 		.... 0.3	0.725	0.515	0.210	N.S.
Fe 		.... 1.5	.605	.905	.300	0.01-.0001
Mg 			015	.375	.130	.245	.05-.02
Ca 			15	.560	.450	.110	N.S.
Mn 			007	.370	.275	.095	N.S.
Ti 			015	.450	.540	.090	N.S.
Ba 			007	.535	.440	.095	N.S.
Cr 			0007	.395	.535	.140	N.S.
Cu 			003	.355	.830	.475	.001
Ni 			0003	.420	.350	.070	N.S.
Pb 			0015	.210	.760	.550	.001
Sr 			0015	.505	.595	.090	N.S.
V 			0007	.460	.280	.180	N.S.
Zr 			0015	.235	.350	.115	N.S.
1 N.S. indicates not significant.
of this group, concentrations of >0.003 percent copper, >0.0015 percent lead, and >1.5 percent iron are characteristic of favorable jasperoid. Magnesium in concentrations >0.015 percent shows a barely significant association with unfavorable jasperoid.
The minor elements, which were detected in less than half the samples analyzed, require a somewhat less conservative statistical test to evaluate significant differences between the two groups of samples, because the Kolmogorov-Smirnov test requires a difference of 0.23 between the cumulative proportions for the two groups in order to attain the threshold significance level of 0.10. Thus, an element that was detected in 20 percent of the favorable samples and in none of the unfavorable samples
Table 13.—Distribution of minor elements in 95 favorable and 53 unfavorable jasperoid samples [Data from semiquantitative spectrographic analyses by J. C. Hamilton]
Favorable1 Unfavorable1	x2
Detection ----------------------------------------------——
Element	limit	Computed Significance
(percent) +	—	+	—	value	level2
Na ......... 0.03	17 78	9 44	0.007 N.S.
Ag ............00015	65	30	6	47	42.183	0.001
As ............15	21	74	1	52	9.450	.01
B .............003	15	80	10	43	.063	N.S.
Be ............00015	19	76	15	38	.897	N.S.
Bi ............0007	32	63	0	53	20.833	.001
Ga ............00007	21	74	4	49	4.151	.05
In ............0007	20	75	0	53	11.163	.001
Mo ............0007	49	46	7	46	19.696	.001
Sb ............015	18	77	5	48	1.677	N.S.
Sn ............0015	23	72	0	53	13.404	.001
Y .............0007	21	74	13	40	.017	N.S.
Yb ............00007	25	70	15	38	.005	N.S.
Zn ............015	62	33	10	43	27.485	.001
1	Pius ( + ) indicates frequency of occurrence; minus ( —) indicates frequency of nonoccurrence.
2	N.S. indicates not significant.﻿56 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
would fail of significance by this test, although, logically, such an element would certainly be considered as characteristic of favorable jasperoid.
Differences between minor-element distributions for the two groups can be tested for significance by returning to the chi-square test which was used for the evaluation of color, texture, and accessory minerals. For this test the two sample groups are dichotomized into those samples in which the element was detected and those in which it was not, as shown in table 13. The minor elements whose presence in detectable concentrations shows significant differences in frequency between the two groups are: Ag, As, Bi, Ga, In, Mo, Sn, and Zn. All these elements are more commonly detected in favorable jasperoid than in unfavorable jasperoid.
No statistical test can evaluate the significance of the sparse and very sparse elements in jasperoid. Some of these (Cd, Co, Ge) appear only in analyses of samples showing high concentrations of zinc, lead, silver, or copper, such that the sample would clearly fall in the favorable category on the basis
of its content of these more common metals. Others (W, U) suggest areas of abnormally high concentration of these metals, which could be of economic interest. The detection of a sparse element in a jasperoid sample is highly significant if deposits containing that element are of commercial interest.
SUMMARY OF CRITERIA FOR EVALUATION OF JASPEROID SAMPLES
The criteria for distinguishing favorable jasperoid from unfavorable jasperoid, together with the scoring points for each criterion, are summarized in table 14, in which the criteria are divided into three categories—megascopic characteristics, microscopic characteristics, and chemical composition. The theoretical range for megascopic characteristics is from +8 to —5; for microscopic and megascopic characteristics it is from +17 to —11; and for chemical composition it is from +52 to —3. Thus, the highest possible combined score is +77, and the lowest is —19. The observed range in the two groups of samples was from +5 to —3 for megascopic
Table 14.—Evaluation of criteria for distinguishing
between favorable and unfavorable jasperoid samples
[Rock-color designations are from Goddard and others (1948). >, greater than or equal to]
	Megascopic characteristics					Microscopic characteristics				
	Criterion	Significance level		Score	Criterion			Significance level		Score
	Color				Texture					
Pink and light red (5R^s)			... Unfavorable..	0.01	-2	Size range of quartz grains >10X..			Favorable		0.01	+ 2
Medium red and grayish red			do		.01	-3	Reticulated 					do		.01	+ 2
					Jigsaw puzzle 				Unfavorable..	.01	-2
Light brown and medium brown		Favorable		.001	+ 3	Older minerals					
(5 YRg).					Clay, montmorillonite group 				Unfavorable..	.10	-1
Dark brown	(5YR^) 			do		.1	+ 1	Pyrite 				Favorable		.05	+ 1
	Texture				Sericite or hydromica 				Unfavorable..	.10	-1
Phaneritic ..		... Favorable		.01	+ 2	Younaer minerals					
Vuggy 					do		.01	+ 2	Calcite 				Unfavorable..	.05	-1
					Goethite 				Favorable		.01	+ 2
					Jarosite 					do		.01	+ 2
					Yellow-orange limonite ...			Unfavorable..	.05	-1
Chemical composition										
						Higher concentration scores				
	Significant									
Element	concentration	Significance				Score	Concentration	Score Concentration		Score
	(percent)				(percent)		(percent)	(percent)		
Fe 			 >1.5	Favorable		0.01		+ 2					
Mg 			 > .015	Unfavorable....	.05		-1 >0.15	-2	>1.5	-3		
Cu 			 > .003	Favorable		.001		+ 3 > .03	+ 4	> .3	+ 5 >3		+ 6
Pb 			 > .0015		do		.001		+ 3 > .015	+ 4	> .15	+ 5 >1.5		+ 6
Ag 			 > .00015		do		.001		+ 3 > .0015	+ 4	> .015	+5 >	.15	+ 6
As 			 > .15		do		.01		+ 2 >1.5	+ 3				
Bi 			 > .0007		do		.001		+ 3 > .007	+ 4	> .07	+ 5		
Ga 			 > .00007		do		.05		+ 1 > .0007	+ 2	> .007	+ 3		
In 			 > .0007		do		.001		+ 3 > .007	+ 4	> .07	+ 5		
Mo 			 > .0005		do		.001		+ 3 > .007	+ 4	> .07	+ 5 >	.7	+ 6
Sn 			 > .0015		do		.001		+ 3 > .015	+ 4	> .15	+ 5		
Zn 			 > .015		do		.001		+ 3 > .15	+ 4	>1.5	+ 5		﻿JASPEROID AS A GUIDE TO ORE
57
characteristics, from +13 to —7 for microscopic and megascopic characteristics, and from +36 to —2 for chemical characteristics; the combined scores ranged from a high +44 to a low of —8.
By comparing, the frequency distributions associated with total scores for samples in the two groups, it is possible to decide the total score at which to draw the line between favorable and unfavorable samples in the various categories so as to minimize the number of samples that are mis-classified. The sample frequency distributions for megascopic characteristics are as follows:
Cumulative
Frequency	Proportion	proportion
Score	Favor- able	Unfavor- able	Favor- able	Unfavor- able	Favor- able	Unfavor- able	Difference
<o	i	2	0.011	0.038	0.011	0.038	0.027
0	13	27	.137	.510	.148	.548	.400
+ 1	4	2	.042	.038	.190	.586	.396
+ 2	40	19	.421	.357	.611	.943	.332
+ 3	12	1	.126	.019	.737	.962	.225
+ 4	18	2	.189	.038	.926	1.000	.074
+ 5	7	0	.074		1.000		
Evidently the lower the score at which the line is drawn between presumably favorable and presumably unfavorable samples the larger will be the proportion of actually unfavorable samples that will be misclassified as favorable. In a field reconnaissance investigation of jasperoid bodies, however, one would normally be more concerned about overlooking favorable bodies than about needlessly sampling unfavorable ones, and so the line might reasonably be drawn between a score of 0 and a score of +1, the point of maximum difference between the two distributions. If the samples included in this study had been classified on this basis, according to megascopic criteria alone, only about one favorable sample out of seven would have been misclassified as unfavorable, but nearly half (45 percent) of the unfavorable samples would have been thrown into the potentially favorable category. If all samples are classified on the basis of the combined megascopic and microscopic criteria, the maximum difference between the two sample distributions comes at a score of +2; if this is taken as the cutoff between unfavorable and favorable, about one sample out of five will be misclassified either way. By lowering the cutoff to +1, the number of favorable samples misclassified as unfavorable will be cut to about one in 10, and the number of unfavorable samples called favorable will increase to about one in three. The changes in the proportions of misclassified samples using various combinations of classification at the
Table 15.—Summary of percentages of misclassified samples scored according to various combinations of classifications
Classification	Cutoff score	Favorable misclassified (percent)	Unfavorable misclassified (percent)
Megascopic alone		.. >0	14.8	45.2
Megascopic plus microscopic ..	.. >+i	10.6	37.7
Chemical alone 		.. > + 5	10.5	13.2
Chemical plus megascopic 		.. > + 5	7.3	13.2
Complete classification		.. > + 5	5.3	7.6
appropriate cutoff scores are summarized in table 15.
Table 15 illustrates how the discrimination between favorable and unfavorable jasperoid samples improves as the number of criteria increases. It also shows that a classification based on chemical criteria alone is considerably better than one based on a combination of megascopic and microscopic criteria; and one based on a combination of megascopic and chemical criteria is very nearly as good as one based on a combination of all three categories. Figure 35 illustrates the relationship between scores for megascopic plus microscopic criteria and scores for chemical criteria on 148 samples. This classification system may be further refined by grouping samples on the basis of their combined scores as follows: 0 and <0=unfavorable, +1 to <+5=probably unfavorable, + 5 to <+ 10=probably favorable, +10 to <+15=favorable, and > + 15=highly favorable.
The practical evaluation of jasperoid bodies as ore guides in an exploration program could be done in three stages: (1) field sampling of jasperoid outcrops that revealed at least one favorable megascopic criterion, (2) analysis of these samples for the 12 elements given in table 14, and (3) scoring of these samples on their combined megascopic and chemical criteria. In drill core and mines, a distinction between oxidized and unoxidized jasperoids should first be made and then the evaluation continued as above.
If thin sections of jasperoid samples can be procured more quickly and cheaply than chemical analyses, microscopic criteria can also be used with some gain in discrimination; however, in most cases this gain would be offset by the cost of procuring and studying the samples.
CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
This chapter contains brief resumes of the available information on the characteristics of jasperoid in each of the major mining districts where it is prevalent. Much of the information has been ab-﻿58 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
CHEMICAL CRITERIA SCORES
Figure 35.—Comparison of scores for megascopic plus microscopic criteria with scores for chemical criteria on all samples.
Field classification: X, unfavorable; •, favorable.
stracted from the literature; it is supplemented by-data on jasperoid samples studied by the author.
Ideally, a district resume includes information on the distribution, genesis, relationship to ore bodies, physical appearance, microtexture, mineralogy, and composition of jasperoid within the district. Unfortunately, such complete information is not available on all the major districts, but whatever information is available is given in the aforementioned order for each district.
Major districts are here defined as those whose total production is in excess of $100 million. The nine such districts that are characterized by the presence of conspicuous jasperoid bodies are discussed in order of total production as follows:
Loc. no.	District	State(s)	Production in
(fig. i)			excess of—
1			Oklahoma, Kansas, Missouri.... Arizona 		$2,000,000,000 $1,400,000,000
2		.Clifton-Morenci 			
3				$1,200,000,000 $800,000,000
4		.Ely (Robinson) 		Nevada 		
5		.Leadville 		Colorado 		$500,000,000
6			Utah 		$400,000,000 $150,000,000
7		.Gilman (Red Cliff)..	Colorado 		
8		.Aspen 			 do 		$100,000,000
9		.Eureka 		Nevada 		$100,000,000
Bodies of jasperoid are present in some other
major districts, such as the Bingham district, Utah, the Santa Rita district, New Mexico, and the Upper Mississippi Valley district of Wisconsin and Iowa, but they either are not a major feature of the alteration or have not been described in the literature; consequently, these districts are not included in this list. The number in parentheses below district names that head the following discussions indicates the district number on the index map (fig. 1) and on the maps for the individual States or areas (figs. 36-50).
TRI-STATE DISTRICT, OKLAHOMA, KANSAS,
AND MISSOURI
(1, fig. 1; 2, fig. 36)
The Tri-State district covers a large region surrounding the common corner of Oklahoma, Kansas, and Missouri (fig. 36). In the first half of the 20th century it was the largest producer of lead and zinc ore in the United States. Most of the ore has been produced from two subdistricts or fields, Miami-Picher in Oklahoma and Joplin in Missouri, but the mineralized region also extends well into southeastern Kansas and into many smaller areas of western Missouri. Marine sedimentary rocks ranging in age from Ordovician to Pennsylvanian have a gentle northwesterly regional dip, which is modified﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
59
Figure 36.—Map showing the location of large jas-peroid-bearing mining districts in Missouri, Oklahoma, Kansas, and Arkansas. 1, Northern Arkansas.
2, Tri-State; A, Miami-Picher field; B, Joplin field.
by numerous warps and open folds. A few persistent northeast-trending faults occur in some parts of the district. Lead and zinc sulfide deposits are largely confined to the Boone Formation, a marine limestone of Mississippian age that contains many chert beds. Replacement ore bodies occur in long narrow “runs” along breccia zones in the chert beds, where sulfide ore forms a matrix cementing breccia fragments of chert, and in wide thin irregular mantos, locally termed “sheet ground,” that replace limestone between two chert beds (Smith and Sieben-thal, 1907).
DISTRIBUTION
The Tri-State region is characterized by many different types and ages of siliceous bodies in the Mississippian limestone. The oldest of these bodies is nodular chert, which is widely distributed in certain beds and is thought by most investigators to be of syngenetic or diagenetic origin. The youngest replacement silica is dark gray to black and cryptocrystalline; it commonly occupies an intermediate position between sulfide ore and dolomitized limestone. This variety is generally conceded to be jas-peroid that is genetically related to sulfide mineralization.
Two more distinctive forms of replacement silica, widely distributed in the area, are intermediate in age between the early chert and the late jasperoid. One of these types is light gray, white, or buff, has a
porous appearance, and commonly contains inclusions of older chert. It has been called younger chert by Fowler, Lyden, Gregory, and Agar (1935, p. 108) and forms irregular replacement bodies in the Boone Formation which are most abundant around the fringes of ore bodies (A. V. Heyl, written commun., 1967). The second type is yellow to brown, massive, and cryptocrystalline. It is typically represented by the Grand Falls Chert Member of the Boone. This variety forms distinctive stratigraphic marker zones near faults and ore bodies; however, in many unmineralized and unfaulted areas these same stratigraphic units consist only of limestone with chert nodules. Siebenthal (1915, p. 27) regarded the Grand Falls Chert Member as a jasperoid replacement of cherty limestone, but many other geologists who are familiar with the district consider it to be a true massive chert bed. Both the younger chert and the Grand Falls Chert Member may be early unfavorable varieties of jasperoid, as the terms are used here. However, their age, genesis, and relationship to mineralization, if any, are in dispute.
The late black jasperoid in the Tri-State district shows a general distribution that is closely related to that of the sulfide ore bodies, of which it is the principal gangue. It cements older chert breccia in the “runs,” and replaces limestone or dolomite between chert beds in the underlying “sheet ground.” Lyden (1950, p. 1256-1257) stated that the jasperoid shows a zonal distribution with respect to the “sheet ground” deposits in the Picher field, where it surrounds a core of barren hydrothermal dolomite and grades outward through unmineralized jasperoid into unreplaced limestone.
GENESIS
Most investigators agree that the late black Tri-State jasperoid was formed by metasomatic replacement of the carbonate host rock, that it was deposited penecontemporaneously with sphalerite, galena, and dolomite, and also, that most of the silica was transported in dispersed colloidal form; however, there is a considerable difference of opinion as to the origin and composition of the transporting solutions, the temperature and depth at which deposition of silica took place, and the form in which it was deposited. Smith and Siebenthal (1907, p. 14) concluded that meteoric waters highly charged with silica and with ore metals in the form of soluble sulfates moved downward along the flanks of the Ozark uplift and deposited both silica and ore in permeable zones in the limestones,﻿60 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
whose high organic content reduced the metal sulfates to sulfides, causing them to precipitate. Sieben-thal (1915, p. 42, 179, 183) presented the theory that ore and jasperoid were both deposited from ascending alkaline saline waters and that the silica was deposited in colloidal form. Laney (1917, p. 108) also concluded that most of the silica was deposited as a colloid, but he did not speculate on the nature of the transporting solutions.
Weidman (1932, p. 82-84) and Tarr (1933, p. 475-478) believed that jasperoid silica was derived from ascending hydrothermal solutions of magmatic origin and that it was deposited in the temperature range of 100°-300°C. Tarr ascribed the origin of jasperoid to precipitation of silica directly as quartz from highly supersaturated solutions in preexisting solution channels and caverns in the limestone beneath the overlying impermeable Pennsylvania shale. He believed that precipitation was due largely to the escape of volatiles (C02 and H3S) from the transporting solutions, resulting from the sudden release of pressure when these solutions penetrated the open solution channels. He conceded that replacement of limestone by silica occurred, but in his opinion this replacement was subordinate to cavity filling by precipitation. Bastin (1939, p. 108-110, 136, 142) concluded that the late black jasperoid was deposited as quartz rather than colloidal silica just before deposition of the sulfide minerals and that the sulfides were deposited from hydrothermal solutions of magmatic origin at temperatures of about 130°C. McKnight (in Behre and others, 1950, p. 58) stated “The ores are believed to have been deposited by hydrothermal solutions of magmatic origin.”
RELATIONSHIP TO ORE
The jasperoid bodies are closely related to sulfide ore both spatially and genetically, forming the common host rock for these sulfides, with which they are penecontemporaneous. However, the Tri-State district is also characterized by the presence of widely distributed “chert” bodies. Fowler, Lyden, Gregory, and Agar (1935, p. 108) recognized two different ages of “chert,” both younger than the Boone but older than the overlying Upper Mississip-pian (Chester) rocks. The older chert appears to be a true diagenetic bedded nodular chert, but the younger “chert” was formed by structurally controlled replacement of limestone (A. V. Heyl, written commun., 1967). The older chert is more limited in distribution and occurs as breccia fragments in the younger “chert,” which is abundant in the Boone Formation throughout a vast region of northern
Arkansas, southwestern Missouri, and eastern Kansas and Oklahoma. If these conclusions concerning the age and origin of the younger “chert” are correct, then I would consider it to be early unfavorable jasperoid. However, both the age and mode of origin of this chert have been disputed (Fowler and others, 1935, p. 151-163) ; there is general agreement only that it is older than the jasperoid and unrelated to the ore deposits.
APPEARANCE OF JASPEROID AND CHERT
The jasperoid is typically dark gray, dark brown, or black, dense, and finely saccharoidal textured. Locally, it exhibits rhythmic parallel banding in various shades of gray. It weathers to a light gray on the outcrop. In the transition zone between jasperoid and unreplaced carbonate host rock, where the carbonate matrix has been leached, the rest of the jasperoid silica is porous and spongy and crumbles readily into quartz sand.
The older chert is dark brown, light gray or white, and aphanitic with local concentric banding. It commonly contains abundant spherulitic inclusions of chalcedony that impart an oolitic appearance to the rock.
The younger “chert” (Fowler and others, 1934) is similar in appearance to the older, though it is generally lighter in color and contains less chalcedony. It fills fractures in the older chert and replaces the limestone, commonly preserving the original bedding structure, and in many places it contains abundant partly silicified fossils. It grades outward into limestone through a zone of soft chalky white material, locally called cotton rock (Fowler and others, 1934).
MICROTEXTURE AND MINERALOGY OF JASPEROID AND CHERT
The jasperoid matrix quartz consists of irregularly interlocking grains (jigsaw-puzzle texture) which range in diameter from about 0.03 mm to <0.001 mm and which locally contain abundant larger quartz laths elongated parallel to the c axis. These grains are randomly oriented, have a length-to-width ratio of about 3:1, and some show pyramidal terminations; locally, they impart a reticulated texture to the rock. Smith and Siebenthal (1907, p. 14) noted that incipient jasperoidization of the host rock is marked by the presence of scattered quartz crystals in the carbonate matrix. The Tri-State jas-peroids locally contain, in addition to quartz, penecontemporaneous inclusions of dolomite, sphalerite, and pyrite, and remnants of unreplaced calcite, as well as interstitial films of carbonaceous material﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
61
and clay. The sulfide inclusions are largely anhedral, but most of the dolomite is in well-developed rhombs, some of which contain poikilitic quartz-grain inclusions.
The older chert exhibits abundant small oval masses of light-brown fibrous chalcedony, and sponge spicules in a matrix of aphanitic irregularly interlocking quartz grains less than 0.02 mm in diameter. It locally contains inclusions of pyrite, marcasite, and tourmaline (Fowler and others, 1934, p. 35, 45). According to Laney (1917, p. 101), many of the quartz grains in the older chert show undula-tory extinction that was probably induced by internal stress during crystallization from a colloidal gel.
The younger “chert” (Fowler and others, 1934) is similar in texture to the older, but chalcedony and sponge spicules are less abundant, and the chalcedony lacks the oval form which characterizes its appearance in the older chert. Furthermore, the younger “chert” contains numerous partly silicified calcareous fossils that are absent in the older chert.
COMPOSITION OF JASPEROID AND CHERT
Numerous standard rock analyses of both chert and jasperoid samples from the Tri-State district have been published (Cox and others, 1916, p. 14; Laney, 1917, p. 102; Fowler and others, 1934, p. 35-36), and a few of these are reproduced in table 7 of this report. Laney (1917, p. 103) noted that the average jasperoid sample contains a little less silica and a little more iron and aluminum than the average chert sample; also, that the jasperoid samples showed greater ignition losses and contained appreciable amounts of carbonaceous matter, which is absent in the chert samples. F. E. Gregory (in Fowler and others, 1934, p. 36) stated that samples of older chert show more A1203, less CaC03, and less loss on ignition than do samples of younger “chert”; also, he noted that samples of younger “chert” are considerably more variable in composition than samples of older chert.	.
A semiquantitative spectrographic analysis of a specimen of ore-bearing jasperoid from the Miami shear trough in the Picher Field of Ottawa County in northeastern Oklahoma showed surprisingly low concentrations of indicator elements for a favorable jasperoid; only copper and zinc were detected in significant amounts.
CONCLUDING REMARKS
In spite of all the work that has been done in the Tri-State district, the genesis and significance of the younger “chert” remain in dispute. The chert
may be of late diagenetic origin, it may represent barren silicification along old structures in pre-Pennsylvanian time, or it may represent a very early barren stage of alteration related to the jasperoid and sulfide mineralization, and thus be early unfavorable jasperoid.
The undisputed jasperoids in the Tri-State district are unusual in their relative uniformity and simplicity. They exhibit only one major generation, contemporaneous with, or just preceding, the early stage of sulfide deposition, in contrast to the jasperoid bodies of other major districts, such as Tintic and Ely, which are marked by great diversity in color, texture, mineralogy, composition, and age of formation. Tri-State jasperoids also differ from most other favorable jasperoids in their fine-grained texture, scarcity of vugs, and in their lack of high concentrations of most of the “indicator” elements.
The fact that incipient jasperoidization is represented by disseminated quartz crystals in the carbonate host rock suggests that the first phase of jasperoid formation was marked by the deposition of silica from solution directly in the form of quartz, although the deposition of colloidal silica as a hydrogel from solutions more highly charged with silica must have followed shortly thereafter.
CLIFTON-MORENCI DISTRICT, ARIZONA
(2, fig. 1;5, fig. 38)
The Clifton-Morenci district of southeastern Arizona (Lindgren, 1905) is in an area in which Pre-cambrian schist and granite are overlain by about 800 feet of lower and middle Paleozoic limestone and shale with quartzite at the base. A few hundred feet of Cretaceous shale and sandstone rests unconform-ably on the Paleozoic sedimentary rocks. Porphyritic igneous rocks ranging in composition from granite to diorite were intruded along northeast-trending fissures during the Laramide orogeny to form a stock with associated dikes, sills, and laccoliths. Strong younger faults of northeasterly trend broke the intrusives and enclosing sedimentary rocks and served as conduits for hydrothermal solutions that deposited sulfide minerals. After a period of erosion that denuded the intrusive bodies and exposed the sulfide deposits to oxidation, the area was covered by a thick series of volcanic flows, breccias, and tuffs ranging in composition from rhyolite to basalt.
The sedimentary rocks were pyrometasomatically altered by the Laramide igneous intrusions, and both intrusives and sediments were later hydrothermally altered along the northeast-trending faults and fractures. In the area of most intense mineralization this hydrothermal alteration took the form of propylitiza-﻿62 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
tion and sericitization of the host rock, but jasperoid replaced carbonate rock farther out in peripheral zones.
DISTRIBUTION
The jasperoid bodies of the Clifton-Morenci district are not mentioned in either of the two reports that discuss the wallrock alteration of the district in detail (Lindgren, 1905; Reber, 1916). This discussion probably was omitted because the ore deposits are largely within the igneous rocks and contact metamorphosed sediments, where the later hydrothermal alteration resulted in propylitization and sericitization rather than silicification of the host rock. Jasperoid does, however, form replacement bodies in the Cambrian and Ordovician Longfellow Limestone south and southeast of the main mineralized area. Lindgren (1905, p. 62-63) recognized the replacement origin of these bodies, for in his description of the Longfellow Limestone he mentioned the presence of a bed of buff to brownish-gray cherty limestone, 110-200 feet thick, near the top of the formation. His petrographic description of this rock contains the following statement.
The chert occurs in irregular bands of nodules, which under the microscope appear as an aggregate of greatly varying grain. Some of it consists of irregular quartz grains, while other parts contain much cryptocrystalline and fibrous chalcedonic material. Ragged calcite grains lie embedded in this mass, giving distinct evidence of the metasomatic origin of the chert by replacement of calcite by siliceous waters.
Perhaps Lindgren did not consider this as true jasperoid because most of the rock he described does not exhibit the reticulated texture characteristic of the rock in the Aspen district of Colorado, for which Spurr (1898) had coined the name “jasperoid.” The broader definition of the term “jasperoid” as used today was not commonly accepted until long after the report of Lindgren (1905).
The six jasperoid samples from this district that were examined during the present study all came from brecciated zones along faults in the Longfellow Limestone in the town of Morenci south and southeast of the open pit.
GENESIS
Petrographic study of the jasperoid samples suggests that the host limestone was recrystallized and permeated by iron-bearing solutions in a reducing environment, before the introduction of silica. Some of the iron combined with carbonate to form siderite, and some was precipitated as disseminated pyrite. The earliest silica-bearing solutions were apparently rather dilute, and locally permeated the recrystallized host rock and precipitated silica in the form of
disseminated quartz crystals. This stage was closely followed by a wave of solutions which were supersaturated with both silica and iron and which also contained potassium. These constituents replaced the host rock, probably as colloidal gels, in an oxidizing environment. Desiccation of the gels was accompanied by minor movement along fractures and by introduction of later silica, which formed dense cherty jasperoid in some places and coarse vein quartz in others. The youngest silica-bearing solutions formed chalcedony as coatings on open cavities.
The available evidence suggests that much of the jasperoid in the Clifton-Morenci district was formed by replacement of favorable beds in the Longfellow Limestone close to fractures that served as conduits for the silicifying solutions, at relatively low temperature and sufficiently close to the surface to be within the zone of oxidation; also, that most of it formed subsequent to the main period of sulfide mineralization in the district. Only a more detailed study of these rocks can resolve the question as to whether silicification was induced by spent hydrothermal solution mingling with ground water or by much younger ground water that had leached its constituents from the siliceous and ferruginous rocks closer to the main center of mineralization.
APPEARANCE
The jasperoid is predominantly shades of red, yellow, and brown; it is commonly brecciated, with large angular breccia fragments of older jasperoid in a matrix of younger jasperoid heavily stained by oxides of iron and manganese. Locally, the rock contains numerous open vugs lined with quartz crystals, and in some places it is cut by veinlets of coarse calcite or vein quartz. The texture, however, is predominantly aphanitic.
MICROTEXTURE AND MINERALOGY
Four different textural varieties of quartz, in addition to the late chalcedony, can be distinguished. From oldest to youngest these are as follows:
1.	Dense, relatively homogeneous quartz that has
an average grain size of <0.005 mm, jigsaw-puzzle texture, and anomalously low birefringence. Locally, it contains quartz pseudomorphs after original dolomite rhomb inclusions. This quartz forms small scattered breccia fragments and is probably diagenetic or syngenetic chert.
2.	Dense to locally vuggy, heterogeneous quartz
whose grain size ranges from 0.01 to 0.3 mm and averages about 0.03 mm. This quartz ranges in texture from xenomorphic to reticulated, and it commonly contains clouds of car-﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
63
bonate particles which indicate its origin by-replacement of the carbonate host rock. This variety forms the matrix in some localities and occurs as breccia fragments in others.
3.	A generation of fine-grained heterogeneous jig-
saw-puzzle-textured quartz whose grain size ranges from 0.003 to 0.05 mm and averages about 0.005 mm. It is characteristically dense, but vugs occur locally. This variety forms the matrix in which breccia fragments of older jasperoid and chert are locally incorporated.
4.	A relatively homogeneous and coarse-grained
quartz that has a mean grain diameter of about 0.08 mm, a range of 0.04-0.3 mm, and a xeno-morphic texture; it is notably clean and free of inclusions. This youngest quartz fills veinlets and lines vugs in the older jasperoid.
Veinlets and vug fillings of late fibrous chalcedony are locally abundant. In one sample a vug lined with late quartz was filled with chalcedony, which thus seems to be the latest form of silica deposited and is probably of supergene origin.
Other minerals that are associated with all the varieties of jasperoid quartz, in the samples examined, are dolomite, siderite, calcite, sericite, pyrite, hematite, goethite, limonite, and manganese oxides. Dolomite was present as disseminated rhombs in the chert (variety 1), but in the sample studied the rhombs have been replaced by quartz. Siderite and calcite form ragged unreplaced remnant inclusions in the jasperoid quartz (varieties 2 and 3), and a younger generation of coarse calcite also fills fractures that cut the jasperoid. Clouds of carbonate particles in some of the first-generation jasperoid (variety 2) probably are calcite, but these particles are too small for positive identification. Sericite appears to be contemporaneous with the first generation of jasperoid silica (variety 2); it forms small flakes locally disseminated through the groundmass. Original pyrite has been converted to limonite or hematite pseudomorphs in the early jasperoid (variety 2). From its petrographic relations, the pyrite must be either older than, or contemporaneous with, the enclosing silica; the quartz surrounding the pyrite pseudomorphs is heavily impregnated with contemporaneous iron oxides (hematite, goethite, and brown limonite), and for this reason it seems probable that pyrite was introduced before the silic-ification of the enclosing limestone. The oxides of iron and manganese form abundant penecontempo-raneous inclusions in both older and younger jasperoid (varieties 2 and 3). These oxides also constitute the matrix cement for jasperoid breccia fragments or fill veinlets that cut the jasperoid in some places;
elsewhere, masses of iron and manganese oxides are cut by veinlets of late quartz (variety 4) or calcite. In general, hematite seems to be older than brown limonite, which is older than goethite and manganese oxide; but local departures from this sequence are common.
COMPOSITION
Information available on the chemical composition of the jasperoid of the Clifton-Morenci district is limited to the results of semiquantitative spectro-graphic analysis of the six samples in my collection. All these samples contain abnormally large concentrations of lead and zinc; most are rich in iron, beryllium, gallium, molybdenum, and silver; about half are rich in magnesium, manganese, copper, indium, vanadium, and nickel; and one or two samples contain abundant barium, bismuth, cobalt, and germanium. The abundance of ore metals and indicator elements in these jasperoids that are not closely associated with ore bodies is unusual. It seems reasonable that the silica-bearing solutions passed through previously formed sulfide ore bodies, leaching some of these elements from the ore. When the silica later precipitated as a colloidal gel, many of these elements probably were adsorbed on the surface of the gel particles and thus became fixed in the rock when the gel desiccated and crystallized.
CONCLUDING REMARKS
The jasperoid bodies in the Clifton-Morenci district and the surrounding area have not been studied in detail. The results of this preliminary investigation, together with the information available in the stratigraphic section of Lindgren’s report (1905, p. 62-63) on the district, suggest that these bodies are concentrated in the upper part of the Longfellow Limestone, that they are younger than the ore deposits, and that they were efficient accumulators of ore metals leached from these deposits by solutions moving through them along faults and fracture zones. Thus, the study of jasperoids in the Longfellow Limestone in the area surrounding this district might furnish clues to the occurrence of undetected blind ore bodies in the vicinity.
BISBEE (WARREN) DISTRICT, ARIZONA
(3, fig. 1;3, fig. 38)
The Bisbee district is in the south-central Mule Mountains near the southeast corner of Arizona. Here, Precambrian schist and granite are overlain by about 5,200 feet of rocks which range in age from Cambrian to Pennsylvanian and which consist largely of limestone above a basal quartzite. These rocks﻿64 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
are truncated by an erosional unconformity and are overlain by about 5,000 feet of Cretaceous sedimentary rocks which consist largely of conglomerate, sandstone, and shale and which contain a thick limestone bed near the top. The Paleozoic rocks were complexly faulted and intruded by siliceous porphy-ritic rocks, which resulted in the formation of numerous dikes, sills, and, at Sacramento Hill, a small granite porphyry stock. This stock, which lies on the east-trending Dividend fault, intrudes Precambrian schist on the north and Paleozoic limestone on the south. It is a focal point for much of the faulting, alteration, and mineralization in the district. Tectonic movement, subsequent to the igneous intrusions and major period of mineralization, produced thrust faults and related high-angle faults that cut the Cretaceous rocks. Copper ore is disseminated in the altered porphyry of the Sacramento stock, and sulfide replacement ore bodies are localized along faults in the limestone south of the Dividend fault.
DISTRIBUTION
Jasperoid breccia forms a nearly continuous belt in the limestone adjacent to the Sacramento stock eastward from the vicinity of the Gardner shaft. This belt, which is irregular both vertically and horizontally, grades outward into recrystallized limestone 200-1,000 feet from the porphyry contact (Ransome, 1904, p. 83-131, pis. I, III; Bonillas and others, 1917, p. 319). Irregular pods and lenses of jasperoid breccia are also widely distributed throughout the district, especially along faults and fractures, where these cut favorable beds in the Paleozoic limestone. Some major centers of jasperoidization mentioned in the literature are (1) the area of the lower workings of the Lowell mine (Ransome, 1904, p. 131; Bonillas and others, 1917, p. 319); (2) the vicinity of the Czar fault where it crosses Hendricks Gulch; (3) in Uncle Sam Gulch above the mine and adjacent to a granite porphyry contact (Ransome, 1904, p. 83; and (4) just above the contact between the Martin and Escabrosa Limestones in Abrigo Canyon (Ransome, 1904, p. 97, pis. I, III). One type of jasperoid is commonly found in the vicinity of sulfide replacement deposits, and tends to occur at various distances above them along the plane of the controlling fault or fracture, particularly in cherty zones in the limestone (Trischka, 1938, p. 36). Bonillas, Tenney, and Feuchere (1917, p. 320) stated that jasperoid bodies related to porphyry intrusions are more abundant in the Abrigo and Martin Limestones than in the Escabrosa Limestone. However, Trischka wrote that the fault- and fracture-controlled jasperoid breccias are most abundant in the Escabrosa.
Bodies of jasperoid breccia are found in all the Paleozoic formations in the district.
A distinctly younger type of jasperoid, which Trischka (1928, p. 1048-1050) described and termed “boxworks silica,” is concentrated along post-Cretaceous faults and fractures. It is most abundant in the coarse Cretaceous conglomerates resting on the pre-Cretaceous erosion surface, although it also occurs a short distance below this surface in the Paleozoic limestone and a short distance above it in the Cretaceous shale and sandstone.
GENESIS
Both types of jasperoid in the district are considered by Trischka (1928, p. 1045-1049) to be of hypo-gene hydrothermal origin. According to Bonillas, Tenney, and Feuchere (1917, p. 319-320), the source of the hydrothermal solutions that silicified and otherwise altered the porphyry stock and the Paleozoic limestone along its southern margin was within or beneath the stock and genetically related to it. The various authors who have studied the district generally agree that a close genetic connection exists between this hydrothermal alteration and the primary ore mineralization which closely followed it, both within and adjacent to the stock, and outward from it along faults and fractures related to the intrusion. The general sequence of events appears to have been (1) faulting before igneous intrusion; (2) forceful intrusion of the stock and related dikes and sills, accompanied by further faulting and minor contact metasomatic silication of limestone adjacent to the stock; (3) crystallization and solidification of intrusive rocks; (4) further fracturing of intrusives and host rocks; and (5) hydrothermal alteration by fluids moving through these fractures, beginning with sericitic and chloritic alteration, progressing through hematitic alteration and silicificatron, and culminating with sulfide deposition.
The early “silica breccia” type of jasperoid resulting from this process was thought by Trischka (1928, p. 1047-1048) to have formed in the following manner. Brittle limestone beds were dragged apart, fractured, brecciated, and ground during faulting, producing a highly permeable breccia of angular limestone fragments in a matrix of powdered limestone. This powdery matrix was first recrystallized to coarse calcite and impregnated with red hematite by the mineralizing solutions. Both the matrix and the breccia fragment inclusions were then completely replaced by silicia, forming a dark-red aphanitic iron-silica matrix cementing creamy-white silicified limestone breccia fragments and, locally, gray breccia fragments of unreplaced primary chert. The com-﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
65
pleteness of the replacement, the angularity of the breccia fragments, the preservation of original textures and fossils in these fragments, and the general absence of vugs in the matrix led Trischka (1928, p. 1049) to conclude that silicification was a slow volume-for-volume replacement process without prior solution of calcium carbonate.
The late “boxworks silica” type of jasperoid originated also from hydrothermal silica-bearing solutions, according to Trischka (1928, p. 1048-1050). He expressed the opinion that it was formed by rapidly moving hydrothermal solutions, ascending along open fractures; these solutions partly dissolved and partly replaced the calcareous matrix and rock fragments they encountered. Later weathering and leaching away of the unsilicified remnants contributed to the rough vuggy texture that is characteristic of this rock. The ultimate source of these late siliceous emanations was not discussed, beyond the statement that they are later than, and unrelated to, the mineralizing solutions that produced the primary ore deposits.
RELATIONSHIP TO ORE
The early “silica breccia” type of jasperoid of Trischka (1928, p. 1047-1048) is thought by him to be related both genetically and spatially to sulfide replacement deposits in the Paleozoic limestones, and thus is of the favorable type. In contrast, the late “boxworks silica” type appears to be unrelated to ore, and is consequently unfavorable. Bodies of favorable jasperoid generally lie above the sulfide replacement deposits. In some places the sulfides are within the jasperoid, or immediately adjacent to it, and locally they penetrate it along small veinlets (Hogue and Wilson, 1950, p. 26; Mitchell, 1921, p. 248). Elsewhere, the ore bodies are at some distance from the jasperoid down the feeding fissure. The jasperoid then serves only as an indicator of sulfide deposits in the general vicinity, rather than in immediate proximity (Trischka, 1928, p. 1048).
In many places within the zone of oxidation the primary sulfides of iron, copper, and zinc have been leached from jasperoid, leaving porous soft and yielding masses of silica, or, where the leached jasperoid has been crushed under the weight of the overlying rocks, pockets of coarse sand containing cerussite. One such mass of leached jasperoid in the Lowell mine was described by Ransome (1904, p. 131). Layers of chalcocite and crystals of cerussite locally partly fill voids in the oxidized jasperoid (Mitchell, 1921, p. 248). Trischka (1938, p. 37) described a locality in Hendricks Gulch in which gold was suffi-
ciently concentrated in a pocket of jasperoid sand to produce a minable ore body.
APPEARANCE
Bodies of jasperoid in the district form rough and irregular outcrops. Ransome (1904, p. 83) described them as “a rusty, cavernous siliceous rock, looking superficially not unlike a weathered amygda-loidal lava.” According to Trischka (1928, p. 1045; 1938, p. 34), these outcrops form continuous veinlike bodies as much as 40 feet wide and 30 feet high in some places; elsewhere, they are smaller irregular pods strung out discontinuously along faults and fractures. The silica breccia type of jasperoid is generally a dark-red aphanitic rock containing conspicuous angular inclusions of white or cream-colored silicified limestone and, locally, of gray chert. In many places this rock has been repeatedly fractured and recemented with later silica, forming a network of quartz veinlets.
The late jasperoid (boxworks silica) was described by Trischka (1928, p. 1045, 1049) as a pale-yellow or pink rock with abundant open cavities, which are commonly coated with small quartz crystals. This siliceous matrix cements rounded, corroded, and partly replaced pebbles and breccia fragments of limestone and other rocks. It forms smaller bodies than the older jasperoid, but they are distributed over a larger area.
Four jasperoid samples from the Bisbee district are included in my collection. Three of these samples are of the older jasperoid, and one is of the younger jasperoid.
Two of the older jasperoid specimens are definitely favorable, having been collected from surface exposures above known ore bodies. One of these specimens is derived from Martin Limestone of Devonian age near the Dividend fault a short distance east of its junction with the Czar fault; the other is derived from Naco Limestone of Pennsylvanian age in a breccia zone along the Junction fault. Both samples are similar in appearance, consisting of shattered and brecciated dense white and gray silicified limestone cemented by veinlets and interstitial masses of dark-red hematite and silica, with local small patches of green malachite.
The third sample of older jasperoid is from a replacement of Mississippian Escabrosa Limestone along a roadcut about a mile east of Don Luis. This body is not related to any known ore deposits. The sample differs from the other two in that it is massive, pinkish gray, is cut by veinlets of coarse-grained calcite, and contains little hematite. It resembles the﻿66 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
two favorable jasperoid samples in its aphanitic texture.
The sample of late unfavorable jasperoid came from Cambrian Abrigo Limestone along the Black Gap fault a short distance south of the contact between the Paleozoic rocks and the unconformably overlying Cretaceous rocks. It consists of partly rounded breccia fragments 1-3 inches in diameter of pale-brown slightly vuggy fine-grained silicified limestone in a matrix of fine-grained white quartz containing irregular open vugs as much as a quarter of an inch in diameter.
MICROTEXTURE AND MINERALOGY
The groundmass in all three samples of older jasperoid consists of dense, relatively homogeneous aphanitic quartz that has a jigsaw-puzzle texture and an average grain size of about 0.01 mm.
The two samples of favorable jasperoid have a groundmass locally impregnated with red hematite dust particles. This matrix is cut by veinlets and irregular masses of late homogeneous xenomorphic quartz that has an average grain diameter of 0.05 mm. Locally, masses of this late quartz, which line the walls of original cavities between breccia fragments of the fine-grained matrix jasperoid, have cores of flamboyant fibrous chalcedony. In one sample the walls of fractures that cut the matrix are locally coated with small fibrous masses of brochantite, which are enveloped by late xenomorphic quartz that fills the fracture. These quartz stringers are cut by later fractures partly filled with porous red hematite, and these, in turn, are cut by thin veinlets of malachite. Thus, a rather complex history of supergene mineralization is revealed.
The aphanitic groundmass in the third sample of older jasperoid contains irregular remnant grains of calcite and also a few grains of specular hematite that appear to be either contemporaneous with, or slightly younger than, the quartz. The matrix is cut by veinlets of coarse calcite as much as a centimeter wide and by narrower younger veinlets in which calcite is mixed with opaque brown limonite. This sample does not contain any of the late xenomorphic quartz that is prevalent in the other two, older, jasperoid samples.
The sample of late unfavorable jasperoid from the Black Gap fault, east of Bisbee, differs strikingly in its microtexture and mineralogy from the samples of older jasperoid. The breccia fragments are composed of heterogeneous xenomorphic quartz grains whose diameter ranges from 0.005 to 0.1 mm and averages about 0.02 mm. Inclusions of carbonate particles are common, and sparsely scattered through
the groundmass are sericite flakes and larger masses of coarse-grained relict carbonate with high relief (probably ankerite or siderite). Small vugs are abundant, and some of these are lined with xenomorphic quartz having a mean grain diameter of about 0.1 mm. The matrix quartz that cements the breccia fragments has a heterogeneous granular to xenomorphic texture and a grain diameter that ranges from 0.015 to 0.1 mm and averages about 0.03 mm. It contains sparse allophane particles, but no carbonate. Vugs in the matrix are larger than those in the breccia fragments, and are lined with heterogeneous jigsaw-puzzle-textured quartz, which has a grain diameter that ranges from 0.005 to 0.05 mm and averages 0.02 mm, and which contains carbonate particles.
The appearance of this sample under the microscope clearly reveals its true identity, in contrast to the older jasperoid samples which closely resemble brecciated chert.
COMPOSITION
Semiquantitative spectrographic analyses were made on splits from each of the four samples previously described. All four samples show abnormally high concentrations of nickel and lead. The two favorable samples contain abundant iron, copper, vanadium, and yttrium, and one of these two is also rich in silver, bismuth, and ytterbium; the other contains unusual quantities of lanthanum. Strontium is concentrated in one favorable sample and in the unfavorable sample of older jasperoid; the latter sample is the only one of the four to show an abnormal amount of manganese. Beryllium and molybdenum both show slightly larger-than-normal concentrations in one of the favorable samples and in the sample of late unfavorable jasperoid. Zirconium is the only element present in abnormal amounts in this sample of younger jasperoid but not in any of the older jasperoid samples.
The evidence furnished by these four samples is insufficient to warrant any conclusions as to diagnostic indicator elements associated with favorable jasperoids in this district. However, it does suggest the possibility that one or more elements of the group that includes copper, silver, bismuth, lanthanum, vanadium, yttrium, and ytterbium, which were abnormally concentrated only in the favorable samples, might be useful for this purpose. Zirconium might be a useful element to distinguish the late unfavorable jasperoid.﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
67
CONCLUDING REMARKS
The jasperoids of the Bisbee district are unusual in that the color and texture that are generally indicative of unfavorable jasperoid are here associated with the favorable type, whereas the color and texture that would normally lead one to suspect favorable jasperoid are characteristic of the late unfavorable type. Nevertheless, the two types are generally distinguishable by color, texture, and mode of occurrence, and the use of j asperoids as a tool in the search for new ore bodies seems to have considerable promise in this area.
ELY (ROBINSON) DISTRICT, NEVADA
(4, fig. 1; 19, fig. 44)
Near the town of Ely, in the Egan Range of eastern Nevada, Paleozoic sedimentary rocks, consisting largely of limestone and shale, have been arched into a broad east-trending anticline, transverse to the trend of the range (Spencer, 1917). The western part of the axial area of this anticline is cut by low-angle thrust faults; near the center it is broken into alternating horsts and grabens by north-trending normal faults, and farther east, by minor faults along its flanks and across its axis. Major faulting was followed by the intrusion of a series of dikes, stocks, and sills of Tertiary monzonite porphyry along the trend of the anticlinal axis. These intrusive rocks together with the enclosing host rocks, were complexly shattered by renewed fault movement, hy-drothermally altered, and mineralized with the disseminated porphyry-type copper deposits for which the district is famous; at the same time, replacement, vein, and breccia-type deposits of copper, lead, zinc, silver, and gold were formed in the Mississippian, Pennsylvanian, and Permian shales and limestones in the vicinity of the intrusives. After a long erosion interval, rhyolite was both intruded and extruded in the area, the extrusive flows partly covering the mineralized monzonite porphyries.
DISTRIBUTION
Irregular bodies of jasperoid are abundant in the western and central parts of the district (Spencer, 1917, pis. 6, 10). They range in size from small bodies covering a few hundred square feet to huge masses that can be traced for several thousand feet along the outcrop and are as much as 1,500 feet wide in places. Many of them either are at the contact of the monzonite porphyry with the enclosing limestone and shale or they cap ridges within the porphyry, but some form replacements in limestone at a considerable distance from the contact; the latter tend
to form elongated veinlike bodies or “reefs” along fault and fracture zones. Lawson (1906, p. 325) concluded that the jasperoid originally formed a discontinuous and irregular envelope along the sides and over the top of the monzonite porphyry stocks, separating them from the adjacent sediments. He also noted (p. 329) that many jasperoid bodies terminate abruptly “at no great depth.”
GENESIS
The close spatial association between the monzonite porphyry intrusives and many of the larger jasperoid bodies in the district, noted by Lawson (1906) and also by Spencer (1917, p. 51), may indicate that much of the jasperoid in the Ely district is genetically related to these intrusives rather than to the subsequent hydrothermal alteration and mineralization. However, many of these large bodies locally contain chalcopyrite and pyrite; hence, they may also be favorable jasperoid of hydrothermal origin (A. V. Heyl, written commun., 1967), or they may also be older jasperoid that was locally mineralized by the ore-stage fluids. This silicification along the intrusive contacts must have occurred after the crystallization of the intrusives, because the porphyry as well as the host rock has locally been converted to jasperoid, and in some places jasperoid overlies remnants of contact metasomatic garnet rock.
Some of the jasperoid bodies are localized by faults and fracture zones rather than by proximity to intrusive contacts, and some contain disseminated sulfides of their oxidation products; this fact suggests that a considerable amount of late jasperoid silica was also introduced by hydrothermal solutions preceding or accompanying ore mineralization. Such a theory is further supported by the presence of two or more distinct generations of quartz in many samples from the district.
On the basis of studies of fluid inclusions in jasperoid quartz, Spencer (1917, p. 63) concluded that the Ely jasperoids formed at minimum temperatures between 160° and 270 °C, and that the replacement of limestone by silica was accomplished by cooling solutions, since the replacement reaction is exothermic, evolving 2,600 calories for each gram of calcite replaced. He (p. 64-69) also expressed the opinion that the early siliceous emanations, containing H2S, HC03, KOH, F, Fe, and Cu, were slightly acid, that they became alkaline through reaction with the host rock as silica and sulfides were deposited, and that they finally were neutralized as they cooled.
RELATIONSHIP TO ORE
The early jasperoid, related to the monzonite por-﻿68 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
phyry intrusives, is generally unfavorable, according to Lawson (1906, p. 329) and Spencer (1917), although locally it has been mineralized by later hydrothermal solutions. Lawson (p. 329) reported that numerous outcrops of “blout” (jasperoid) in the district have been explored, and that most of them do not contain ore, except for small pockets and coatings of secondary copper minerals and remnants of disseminated pyrite. Spencer (p. 74), on the other hand, distinguished between a porous brecciated rub-bly type of jasperoid that was associated with sulfide mineralization and a dense massive resistant type of jasperoid that was unrelated to ore. Most of the unoxidized ore-related jasperoids contain disseminated pyrite and chalcopyrite, although chalcocite-bearing jasperoid is found in the Veteran and Boston-Ely mines. Some small fracture-controlled jasperoid bodies in unmetamorphosed limestone lie above pockets of chalcocite ore. Most of the favorable jasperoids are associated with copper ore bodies in the western and central parts of the district; however, outlying jasperoid bodies also occur in the vicinity of silver-lead-zinc-, and gold-bearing galena-sphalerite replacement deposits in limestone (Spencer, 1917, p. 51, 99, 122-123, 128).
My jasperoid samples from the Ely district display a great variety of colors and textures and also a wide range in scores for favorability. However, those at the low end of the favorability scale with scores of <5 and those at the high end with scores of >18 are distinctive. The unfavorable samples, which probably represent Spencer’s dense massive resistant type, are light gray or yellowish gray and have an aphanitic texture. The highly favorable samples, which probably represent his porous brecciated rub-bly type, are heavily impregnated with moderate-brown to dark-brown iron oxides on the outcrop, and they are porous, vuggy, and coarse grained.
APPEARANCE
Lawson (1906, p. 327-329) recognized four varieties of “blout” (jasperoid) in the Ely district, which he classified as compact and massive, cavernous weathering, brecciated, and cellular, and which he described as follows. The compact and massive variety, the most abundant, is glassy, white or pale yellow, and it locally resembles a massive quartzite. It commonly has a bedded appearance, and adjacent layers are different in both color and texture. This layering is inherited from the bedding of the host limestone. In most places the outcrops are heavily stained with iron oxide. This rock weathers into rounded knobs or breaks down into talus of irregular angular blocks. The cavernous-weathering variety
weathers into very irregular forms “with rugged chambers and straggling channels,” in the bottoms of which unaltered remnants of limestone occur locally. The brecciated variety consists of angular fragments ranging from minute particles to blocks 4 inches in diameter, cemented in a matrix of quartz or, less commonly, of calcite. The breccia fragments are predominantly light colored, whereas the matrix characteristically consists of red or dark-yellow jasper. The cellular variety is light colored and porous, and it weathers to a rubble of small fragments. It represents silicified porphyry rather than silicified limestone, and it locally preserves textures of the porphyry and grades into unsilicified porphyry.
Spencer (1917, p. 74) emphasized two major types of jasperoid in the district, a massive barren variety and a porous friable sulfide-bearing variety. The barren type weathers to form prominent outcrops, in contrast to the sulfide-bearing type which breaks down into a rubble of small angular fragments stained rusty brown from oxidation of the pyrite.
My collection from the Ely district consists of 26 samples of jasperoid, all of which were derived from limestone. Twenty-one of these samples are in the vicinity of ore deposits and were classified as favorable ; five are not associated with any known ore deposits and were classified as unfavorable. Two of the unfavorable samples were collected at the site of the old town of Ruth, one came from Verzan Canyon half a mile north of the east end of the Ruth ore body, and the remaining two from the east-trending ridge northeast of Weary Flat about a mile north of the Liberty Pit. All five are aphanitic to fine grained and fractured; one has been brecciated and recemented with younger silica. Their color on weathered surfaces ranges from pale yellow to grayish brown and on fresh surfaces, from light yellowish gray through light gray to medium gray.
Four of the favorable samples came from the area of the Veteran and Boston-Ely mines at the west end of the district, and two from small mines I-IV2 miles northeast of Lane at the east end; the remainder were collected at various localities in the central part of the district (south of the Liberty Pit, in the vicinity of the Ruth ore body, and in the vicinity of the Jupiter mine). This group shows a much wider range in both color and texture than does the barren sample group. The weathered surfaces are predominantly brown, in various shades ranging from light yellowish brown through moderate brown and dark brown to very dark brownish gray, almost black; one sample is brick red, and two or three are predominantly light gray. On fresh fractures a few of the brown-weathering samples are light to mod-﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
69
erate gray or variegated brown and gray, but most of them show the brown color on fresh exposures as well as on weathered surfaces. Most of these samples are aphanitic to fine grained, but otherwise they are not consistent in texture; some are dense and massive, some are, brecciated, some are vuggy; some weather to relatively smooth surfaces and some to very rough uneven surfaces. The 10 samples from this suite that scored +19 or higher on the basis of concentration of indicator elements are more similar in appearance; all are vuggy, rough weathering, and heavily stained with moderate- to dark-brown limonite.
MICROTEXTURE AND MINERALOGY
Spencer (1917, p. 51, 100-101) reported that the typical jasperoid of the Ely district consists of finegrained quartz aggregates that locally contain abundant tiny vacuoles, some of which are partly filled with fluid. A few of these fluid inclusions also contain very minute crystals of halite or sylvite. Chalcedony is locally abundant; it is younger than the first generation of matrix quartz, but older than some of the late quartz. Other common accessory minerals in the jasperoid are fluorite, apatite, calcite, mica, and, locally, pyrite and chalcopyrite. Spencer (1917, p. 117) also reported that a variety of ore-bearing jasperoid from the Veteran mine also contains rutile, magnetite, pyrrhotite, and chalcocite.
Most of my jasperoid samples from the Ely district range in grain size from 0.01 to 0.1 mm, although a few are as much as 1 mm in diameter. Fluid inclusions are present in some of the coarsegrained samples. All the common jasperoid fabric textures discussed on pages 11-15 of this report are represented in the suite of Ely samples. Xeno-morphic and jigsaw-puzzle textures are most abundant, but granular, reticulated, and fibrous textures are also present. Most of the samples exhibit at least two distinct generations of jasperoid quartz, and some show as many as four generations. In general, the older generation is granular to xenomorphic in texture and somewhat coarser grained than the younger generation, which commonly exhibits a jigsaw-puzzle texture. These observations tend to support the theory of early high-temperature, diffuse, siliceous emanations, from which silica probably deposited directly in the form of quartz, followed by late denser and cooler hydrothermal silica-bearing solutions from which silica deposited as a colloidal gel, giving rise to an aphanitic jigsaw-puzzle texture in the resulting jasperoid. Local exceptions, in which the latter type is followed by coarser xenomorphic or reticulated jasperoid, may indicate that late-stage
hydrothermal solutions with lower silica concentration were in contact with previously silicified and therefore nonreactive rocks, again resulting in relatively slow deposition of Si02 as quartz. These exceptions are economically important because a late stage of coarse vuggy xenomorphic to locally reticulated quartz is characteristic of the most highly favorable type of samples in the Ely suite.
In thin sections cut from 25 jasperoid samples from the Ely district, 21 minerals, in addition to quartz, were identified. In order of decreasing abundance these are (1) chalcedony, hematite, and limonite (10 samples) ; (2) allophane dust and goethite (eight samples); (3) jarosite and calcite (six samples) ; (4) carbonate dust (five samples); (5) seri-cite, kaolinite, apatite, fluorite, and pyrite (three samples);	(6) hydromica, halloysite, opal, and
sphene (two samples) ; and (7) lussatite, zircon, sid-erite, and cerussite (one sample). The age relations of these 21 minerals to the jasperoid quartz are broadly indicated in table 16.
The samples were divided, on the basis of their indicator-element content, into three groups as follows: Highly favorable (score ^ + 19), intermediate (score < + 19 but >+5), and unfavorable (score <+5). This classification resulted in 10 samples in the first group, 10 in the second, and five in the third. The seven most abundant minerals (those recognized in more than five samples) were then classi-
Table 16.—Age relations of minerals in Ely district jasperoid to the jasperoid quartz
Mineral	Older1 Contemporaneous2 Younger3
Apatite ..................... +
Zircon ...................... +
Siderite .................... +
Sericite .................... +
Pyrite ...................... +
Hydromica ................... +
Sphene ...................... +
Calcite (carbonate dust) ....	+
Allophane .....................
Hematite .................... +
Limonite ......................
Goethite ......................
Chalecdony ....................
Kaolinite .....................
Halloysite ....................
Fluorite ......................
Jarosite ......................
Cerussite .....................
Opal ..........................
Lussatite .....................
1	Older than the first generation of jasperoid quartz.
2	Formed simultaneously with a major generation of quartz or between two major generations.
3	Formed after the youngest major generation of jasperoid quartz, but not necessarily after the youngest quartz veinlets and vug linings.﻿70 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
fied as to the proportion of the total samples in each group in which they occur, as follows.
Frequency (as percent of total group)
Mineral	Highly
favorable Favorable Unfavorable
Jarosite ........................ 50	10	0
Goethite ........................ 30	50	0
Limonite ........................ 60	30	20
Hematite ........................ 40	50	20
Chalcedony ...................... 30	50	40
Allophane ....................... 20	50	20
Calcite ......................... 30	20	20
This limited amount of data suggests that among the more abundant minerals only jarosite, goethite, and possibly limonite are significantly more common in the favorable variety of Ely district jasperoid than in the unfavorable variety.
COMPOSITION
Spencer (1917, p. 117) reported a quantitative chemical analysis of a composite sample of ore-bearing jasperoid from the Veteran mine. This jasperoid contained rutile, magnetite, pyrrhotite, and chalcocite, which are not present in most jasperoids of the district, and therefore does not represent ordinary Ely district jasperoid. The analysis is as follows :
Element	Percent	Element	Percent
SiO,		79.11	h2o- 		.... 0.81
A1203 			 3.82	h2o+ 			 2.68
FeoOa 		.44	Ti02 			81
FeO 			69	P20„ 			42
MgO 			 1.19	S 			 ^.Ol
CaO 			62	Cu 			 *2.55
Na20 			31	Fe 			 12.64
K20 			54	Total 			 99.64
1 In sulfide inclusions.
Semiquantitative spectrographic analyses were made of splits from the 25 samples studied in the present investigation, and in one or more of these samples 33 elements other than Si were detected, as shown in table 17.
The actual relative abundance of these elements is difficult to evaluate, because many of them have highly irregular frequency distributions and because the limit of sensitivity of the analytical method varies widely from element to element. This evaluation difficulty is illustrated by table 18, in which the 15 most abundant elements are listed in order of decreasing concentration according to arithmetic mean, median, and maximum reported concentration. In
Table 17.—Minor-element distribution in 26 samples of jasperoid from the Ely district, Nevada
[J. C. Hamilton, analyst. Leaders (...) indicate no information]
Element	Limit of detection (percent)	Number of samples in which detected	Minor-element distribution (in percent)			
			Range	Mean	Median	Mode
Ag 		... 0.0001	12	<0.0001- .07	0.0048	<0.0001	<0.0001
A1 		... .001	26	.15 - .*7	.27	.14	.15
As 		.. .1	3	<.l -1.5			
B 		.002		<.002 .003			
Ba 		... .0002	26	'.0007- .07	.0087	.003	.003
Be 		... .0001	3	<.0001- .00015			
Bi 		... .001	11	<.001 - .7	.036	<.001	<.001
Ca 		.. .005	26	.07 ->10.0	1.2	.12	.15
Cr 		... .0001	26	.0003- .007	.0023	.0014	.003
Cu 		.. .0001	26	.0007- .15	.027	.007	.03
Fe 		.. .0008	26	.07 ->10.	3.9	1.0	3.
Ga 		.. .0002	6	<.0002- .003			
Ge 		.. .001	1	<.001 - .007			
In 		.. .001	5	<.001 - .0015			
La 		.. .002	2	<.002 - .003			
Mg 		.. .0005	26	.007 - .3	.061	.021	.03
Na 		.. .05	1	<.05 - .07			
Mn 		.. .0002	26	.0015- .7	.044	.0095	.015
Mo 		.. .0005	17	<.0005- .007	.0015	.0007	<.0005
Nb 		.. .001	1	<.001 - .0015			
Ni 		.. .0003	8	<.0003- .0015	.00023		
P 		.. .2	1	<.2 - .7			
Pb 		.. .001	17	<.001 -7.	.39	.003	<.001
Sb 		.. .01	1	<.01 - .015			
Sn 		.. .001	15	<.001 - .15	.0081	<.001	<.001
Sr 		.. .0002	24	<.0002- .03	.003	.0008	.0007
Ti 		.. .0002	26	.007 - .3	.052	.023	.07
V 		.. .001	14	<.001 - .015	.0027	.001	<.001
w 		.. .01	2	<.01 - .015			
Y 		.. .001	6	<.001 - .0015			
Yb 		.. .0001	8	<.0001- .00015	.00003		
Zn 		.. .01	16	<.01 - .3	.051	.015	<.01
Zr 		.. .001	22	<.001 - .07	.0084	.003	.007
spite of the uncertainties regarding the true abundance of the various elements, which are inherent in the nature of the samples, of the analytical data, and of the analytical method, it is apparent that bismuth, tin, and zinc are abnormally concentrated in this group of samples. However, a much larger number of samples would be required to ascertain whether these elements are characteristically high in jasperoid bodies of the district as a whole.
Comparison of the median concentrations of the various elements in the group of 10 highly favorable samples and the group of five unfavorable samples
Table 18.—Relative abundance, in percent, of 15 most abundant elements in 26 samples of jasperoid from the Ely district, Nevada
Arithmetic mean	Median	Maximum reported
concentration	concentration	concentration
Fe 			 3.9	Fe 			 1	Fe 			>10
Ca 			 1.2	Ca 			15	Ca 			>10
Pb 			39	A1 			14	Pb 			 7
AI 			27	Ti 			023	As 			 1.5
Mg 			061	Mg 			021	A1 			7
Ti 			052	Zn 			015	Bi 			7
Zn 			051	Mn 			0095	Mn 			7
Mn 			044	Cu 			007	P 			7
Bi 			036	Pb 			003	Mg			3
Cu 			027	Ba 			003	Ti 			3
Ba 			0087	Zr 			003	Zn 			3
Zr 			0084	Cr 			0014	Cu 			15
Sn 			0081	V 			001	Sn 			15
Ag 			0048	Sr 			0008	Ag 			07
Sr 			0030	Mo 			0007	Ba 			07﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
71
showed that among the common elements only iron exhibits a difference of an order of magnitude or more between the two median values (4 percent in the favorable group, 0.13 percent in the unfavorable group); similar differences were also noted in the ore metals, silver, bismuth, copper, lead, tin, and zinc, but these can be ascribed largely to the criteria used to establish the two groups.
CONCLUDING REMARKS
The available data suggest two major generations of jasperoid in the Ely district: (1) an early unfavorable generation, genetically related to the monzo-nitic intrusive rocks, that is dense and massive and has a fine-grained granular to xenomorphic texture; and (2) a late, locally favorable generation genetically related to hydrothermal solutions younger than the intrusives. This late jasperoid again may be subdivided into two types: an aphanitic variety that has a jigsaw-puzzle texture, which is generally unfavorable, and a coarser grained vuggy xenomorphic to reticulated variety associated with abundant iron oxide, which is commonly favorable. A more detailed study of the district would be needed to establish the distribution patterns, structural controls, and age relations of the various types of jasperoid.
LEADVILLE DISTRICT, COLORADO
(5, fig. 1; 9, fig. 40)
The Leadville district of central Colorado is on the western slope of the Mosquito Range near the head of the Arkansas River (Emmons and others, 1927). It has produced large quantities of silver, lead, and zinc and some gold, manganese, and copper.
Here, Precambrian granite, schist, and gneiss are covered by about 150 feet of Cambrian quartzite and shale, which, in turn is overlain by about 350 feet of Ordovician, Devonian, and Mississippian rocks that consist dominantly of limestone and dolomite. The Mississippian and Devonian rocks are overlain by about 2,500 feet of Pennsylvanian continental and marginal marine sedimentary rocks, which are largely shale, siltstone, and arkose with a few interbed-ded limestones.
During Cretaceous time the sedimentary rocks were intruded by dikes and sills of monzonite and granodiorite. After these intrusions were emplaced, strong compressive forces folded the rocks and produced large northwest-trending thrust faults. This was followed by the intrusion of a small quartz-monzonite stock at Breece Hill, together with related dikes. Subsequent to the emplacement of this stock the area was again broken by numerous normal and
reverse faults. These faults served as conduits for hydrothermal solutions which emanated from within or beneath the stock and which altered and mineralized the rocks adjacent to the faults. Still later, northeast-trending normal faults broke and offset many of the ore bodies, and plugs and dikes of rhyolite were locally intruded, probably in Pliocene time. This complex orogenic history has complicated the regional distribution pattern of ore deposits and related types of alteration, including jasperoid.
DISTRIBUTION
The Leadville district is close to the center of a jasperoid province (fig. 1) that extends outward from the district for many miles to the northeast, east, and southeast. Thus, it is difficult to establish boundaries between jasperoid bodies of the Leadville district (9, fig. 40) and those of the Kokomo district (7, fig. 40) and Pando area (14, fig. 40) to the north, and the Horseshoe-Sacramento district (6, fig. 40) to the southeast. Within this region replacement bodies of jasperoid are most abundant in the upper part of the Mississippian Leadville Limestone, particularly in areas where this formation is capped by porphyry sills and has been cut by faults and fractures that provided access for mineralizing solutions. Jasperoid bodies are also found locally in the Devonian Dyer Dolomite Member of the Chaffee Formation and in the Ordovician Manitou Limestone beneath the Leadville Limestone; they are also found in some limestone beds in the lower part of the Pennsylvanian Minturn Formation above the Leadville Limestone. Igneous intrusive rocks close to centers of intense alteration are also strongly silicified locally.
Emmons, Irving, and Loughlin (1927, p. 172, pi. 13) referred to many jasperoid replacement bodies in the Leadville Limestone on Fryer Hill and in the Downtown area. Additional areas that contain abundant jasperoid (Loughlin and Behre, 1934, p. 226, 229, 234, 240) are Iron Hill, the southeastern part of Carbonate Hill, the head of Evans Gulch, and a small area west of the Mike fault opposite Empire Hill. Many of the most extensive jasperoid bodies are also associated with the Tucson Maid fault west of Breece Hill in the central part of the district.
The six Leadville district samples in my collection are all dump samples from the northwestern and western parts of the district. Two are from Canterbury Hill, one about 1 mile and the other 1(4 miles northeast of the center of Leadville. The remaining four samples are from mines on Fryer Hill and Stray Horse Ridge, (4-1 mile east of Leadville.﻿72 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
GENESIS
Much of the jasperoid in the district apparently was formed by hydrothermal silica-bearing solutions emanating from within or beneath the Breece Hill stock. Emmons, Irving, and Loughlin (1927, p. 218) concluded that the main period of jasperoidization in the district occurred during and after the ore stage of mineralization. Quartz was deposited in veins before the deposition of the sulfides, which partly replaced the vein quartz, displacing the silica outward to form jasperoid. However, Loughlin and Behre (1934, p. 226) pointed out that many of the jasperoid bodies are impregnated with sulfides and are cut by sulfide veins, and therefore, that some of the jasperoid must have formed before the ore-sulfide stage of mineralization.
Loughlin and Behre (1934, p. 221) classified the deposits of the district, on the basis of mineral assemblages representing successively lower temperatures of formation, into pyrometasomatic, hypo-thermal, high mesothermal, intermediate mesother-mal, low mesothermal, and epithermal or telethermal. They regarded (p. 225) the jasperoids as most characteristic of the intermediate mesothermal deposits, which were formed outward from, and at lower temperatures than, the manganosiderite deposits that characterize the high mesothermal class; but they also mentioned the association of jasperoid with some deposits of the low mesothermal and epithermal classes.
Emmons, Irving, and Loughlin (1927, p. 218) mentioned the fact that much of the Leadville jasperoid is heavily impregnated with “products of oxidation.” Indeed, most of the Leadville jasperoid samples in my collection are of this type, in which the jasperoid silica is intimately mixed with limonite and manganese oxides, suggesting a possible supergene origin.
RELATIONSHIP TO ORE
The favorable jasperoids of the district tend to form a floor beneath, or a casing around, massive sulfide deposits. Jasperoid impregnated with sulfide ore is relatively sparse. Many extensive jasperoid bodies, particularly those in the northwestern part of the district, are unfavorable (Loughlin and Behre, 1934, p. 228). At the Continental Chief mine, near the head of Evans Gulch, favorable jasperoid, which retains the color and texture of the carbonate host rock, forms a casing adjacent to the mineralized fissures, but prominent ledges of unfavorable jasperoid also crop out in the same vicinity (Loughlin and Behre, 1934, p. 234). Favorable jasperoid is most commonly associated with lead-silver ore and is less abundant around the zinc and copper ore bodies (Ogden Tweto,
oral commun., 1965). Many of the dense dark-colored jasperoids impregnated with iron and manganese oxides have the composition of favorable jasperoid; however, their spatial relations to ore bodies are not yet known.
APPEARANCE
All the jasperoid samples from the Leadville district, in my collection, are dark gray to black, apha-nitic on the outer surface, with local brown patches. Most of the samples are homogeneous in texture, but one sample, from the dump of the Annie 5 mine on Fryer Hill about half a mile east of Leadville, has a shell or rind of dense black manganiferous jasperoid coating a core of porous vuggy friable light-gray and light-brown saccharoidal jasperoid. The contact between shell and core of this sample is knife-edge sharp, suggesting leaching and thorough oxidation of the core before formation of the rind. The only sample of clearly hypogene jasperoid in the collection came from the dump of the Forepaugh mine, also on Fryer Hill. This sample is dark to medium gray and aphanitic, and it contains abundant fine-grained disseminated pyrite and a few tiny vugs that appear to have been formed by local leaching of the original pyrite.
MICROTEXTURE AND MINERALOGY
The hypogene jasperoid in the sample from the dump of the Forepaugh mine is fine to medium grained (0.005-0.1 mm) and heterogeneous, and has a jigsaw-puzzle texture. The extremely fine grained quartz is locally segregated in bands, and thin vein-lets of coarser xenomorphic quartz cut the matrix. Abundant inclusions of pyrite and younger sphalerite are present. Some, if not all, of the quartz is older than the sulfides as shown by the presence of quartz-grain inclusions in some of the pyrite. The same heterogeneous jigsaw-puzzle texture is also characteristic of the quartz in the core of the sample from the dump of the Annie 5 mine and of rounded inclusions of older jasperoid in a matrix of younger iron and manganese oxides found in a sample from a dump on the North Fork of Little Evans Gulch.
Jasperoid of possible supergene origin forms the outer rim of the specimen from the dump of the Annie 5 mine and constitutes nearly all the remaining specimens, exclusive of the one from the Forepaugh mine dump previously described. This rock is characterized by small scattered inclusions of quartz and dolomite, in a matrix of earthy, vuggy, and porous iron and manganese oxides, which are locally crystallized into pyrolusite, goethite, and hematite. In some places the pores are filled with﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
73
late quartz; in others, bands of xenomorphic mediumgrained quartz alternate with bands of manganese oxide; and in nearly all samples veinlets of mediumgrained homogeneous xenomorphic quartz cut the matrix oxides. Thus, if these oxides are supergene, the late silica associated with them must also be supergene. However, this rock may not be a true replacement jasperoid but rather a variety of case-hardened gossan. Because the samples were not taken in place, the field relationships of this rock to its host could not be ascertained; however, the abundant quartz and dolomite grains suggest that these minerals may have been original inclusions in limestone, of which the calcite has been replaced by supergene iron and manganese oxides and silica.
COMPOSITION
Semiquantitative spectrographic analyses available on four of the supergene (?) samples and the single definitely hypogene sample showed that all five have a composition characteristic of favorable jasperoid. Of the five, the hypogene sample has the smallest suite of minor elements present in abnormally high concentrations. After the associated sulfide minerals had been largely removed from this sample by heavy liquid separation, the remaining jasperoid quartz showed only Ag, Ba, Mo, Pb, and Zn present in concentrations more than one order of magnitude higher than the median concentration for all jasperoid samples in the collection. The quartz of the remaining four samples was not separated before analysis, and the resulting data show that in them silica is subordinate to iron and manganese. The high concentrations of a number of minor elements in these samples, therefore, probably represents association with iron and manganese oxide rather than with quartz. These samples are consistently rich in Fe, Mn, Ag, Ba, Pb, Ni, and Zn; three of the four are also high in Cu and Sr; and two are high in In and Mo. High In is associated with high Cu, but high Mo is not.
CONCLUDING REMARKS
Although both favorable and unfavorable jasperoid samples have been reported from this district, only favorable samples are represented in my collection. Thus, no direct comparison between favorable and unfavorable jasperoid in the Leadville district is possible here. According to Ogden Tweto (oral commun., 1965), there is a marked similarity in appearance between the two types, such that they are not readily distinguishable in the field. The known presence of both varieties in the area, however, and the abnormally high concentrations of the indicator elements Ag, Pb, and Zn in all the available favorable
samples suggest that a detailed study of the Leadville jasperoids, coupled with adequate sampling and analysis for these elements, might be a fruitful adjunct of any comprehensive exploration program in the district.
TINTIC AND EAST TINTIC DISTRICTS, UTAH
(6, fig. 1; 21, fig. 49)
The Tintic and East Tintic mining districts in Utah are about 70 miles south of Great Salt Lake in a mineralized belt that crosses the East Tintic Mountains, whose crest forms part of the boundary between Juab County on the west and Utah County on the east (Lindgren and Loughlin, 1919).
A thick sequence of Paleozoic limestone, dolomite, and shale with a Cambrian quartzite at the base in this area is largely covered by Tertiary extrusive quartz latite, latite, and associated pyroclastics, all of which were later intruded by monzonite stocks and dikes. Before the extrusion of the Tertiary volcanic rocks, the sedimentary strata were folded into a series of north-trending asymmetrical anticlines and synclines, and were cut by high-angle transcurrent faults that were accompanied by overthrust faulting, particularly in the eastern part of the area. The major high-angle faults have predominating northeasterly and northwesterly trends; their major displacement predates the volcanics, although there has been some renewed postvolcanic movement on some of them. The intrusion of monzonite and quartz monzonite was accompanied and followed by hydro-thermal alteration of both the volcanics and the underlying sedimentary rocks, culminating in ore deposition. The primary ore bodies consist of sulfidebearing veins and replacement deposits in the sedimentary rocks..-Most of the production of the districts has come from the lead-zinc-silver replacement deposits in limestone and dolomite; but copper and gold, which commonly occur in fissure vein deposits and pipes cutting Cambrian quartzite, are also economically important locally.
DISTRIBUTION
The distribution of jasperoid bodies in the East Tintic district is shown by Lovering (1949, pi. 4) and by Lovering and others (1960), and in the main Tintic district, by Morris (1964a, pi. 1; 1964b, pi. 1).
Bodies of silicified rock occur in all of the Paleozoic sedimentary formations in the two districts and in the Tertiary volcanic rocks as well. In the East Tintic district, however, jasperoid bodies are most abundant in the carbonate rocks that have been altered to hydrothermal dolomite along faults (Lovering, 1949, p. 29). This structural control is very pronounced; the jasperoid bodies form envelopes around﻿74 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
the faults and fissures that served as conduits for the hydrothermal solutions. The jasperoids of the Tintic and East Tintic districts show no direct relationship to the monzonitic intrusive rocks; they are found in areas where these intrusives are lacking, although they are somewhat more abundant in areas marked by centers of intrusion.
GENESIS
The formation of jasperoid largely represents a late stage in a long and complex history of hydro-thermal alteration in the districts, which culminated with the emplacement of sulfide ore bodies. Lovering (1949, p. 16-17) recognized five distinct stages of alteration, each with its own characteristic mineral assemblage; these, in chronological order, he called the early barren stage, the middle barren stage, the late barren stage, the early productive stage, and the productive stage. Silicification resulting in the formation of favorable jasperoid was largely confined to the late barren stage (Lovering, 1949, p. 28). Locally, argillic alteration of the middle barren stage was accompanied by minor silicification (Lovering, 1949, p. 38).
Lindgren and Loughlin (1919, p. 156-157) concluded that the favorable variety of jasperoid formed as a result of the replacement of carbonate rock by colloidal silica. The characteristically abrupt contacts between jasperoid and host rock led them to express the opinion that the silicifying solutions moved outward in a wave from the feeding channels, converting all the rock behind the advancing wave front into silica gel. As this gel later desiccated and crystallized into jasperoid quartz and chalcedony it also shrank, causing the formation of vugs and fractures. These openings were later filled or coated with younger jasperoid, quartz crystals, barite, and sulfides. Local banding in the jasperoid is ascribed to penetration of the original gel by electrolyte-bearing solutions, resulting in Liesegang diffusion banding.
Lovering (1949, p. 56-58) expressed the opinion that the jasperoidizing solutions were highly charged with silica, iron, barium, carbonic acid, and sulfate; they were hot neutral or slightly alkaline solutions, partly of magmatic origin, rising along major fractures through the quartzite, from which they may have leached silica and iron. As these solutions rose into the carbonate rocks, they cooled, and the carbonates became more soluble and silica less soluble. The calcium and magnesium that were replaced during the silicification moved upward into the overlying volcanic rocks, resulting in calcitic and chloritic alteration of these rocks.
An unfavorable type of jasperoid occurs in carbo-
nate rocks just below the base of the Tertiary rhyolite flows. This type is controlled by proximity to the unconformity rather than by faults and fractures. It appears to have formed as a result of the leaching of silica from these flows by water seeping downward through them, and subsequent precipitation of the silica when this water was neutralized by reaction with the underlying carbonate rock. Much of this jasperoid probably formed during the period when the flows were still cooling, as a result of alteration by hot-spring and fumerole emanations; some of it may be due to leaching of silica by acid waters generated by the oxidation of pyrite disseminated through the flows, and thus may be of comparatively recent origin (T. S. Lovering, oral commun., 1964). This type of jasperoid is, in either case, unrelated to the hydrothermal alteration that culminated in sulfide mineralization.
Bodies of possibly supergene jasperoid have been found in and near large oxidized ore bodies in some of the mines on the north slopes of Eureka Peak and Godiva Mountain near the town of Eureka (A. V. Heyl, written commun., 1967). These jasperoid bodies presumably formed by reaction of silicabearing ground waters with carbonate host rock during the oxidation of sulfide ore bodies.
RELATIONSHIP TO ORE
Howd (1957, p. 125-132) presented an excellent historical summary of the views of various investigators concerning the relationship between jasperoid and sulfide ore in the Tintic and East Tintic mining districts. The close association between jasperoid and many of the sulfide replacement deposits in carbonate rocks was recognized by the miners early in the development of the districts. This association was reported by Lindgren and Loughlin (1919, p. 155), who concluded that the jasperoid, although older than the ore, was closely related to it and that it formed envelopes around the ore bodies. Lovering (1949, p. 28) recognized that jasperoid forms a broad envelope around the major circulation channels that were open during the late preore stage of alteration, of which it is the most characteristic product. Many of these same channels later served as conduits for ore solutions, giving rise to the association noted by Lindgren and Loughlin (1919, p. 155-157). However, some channels were completely sealed off by the early silica so that no sulfides could form in them; in other places, ore solutions followed new channels and thus resulted in ore bodies not intimately associated with jasperoid. Thus, late barren-stage jasperoid in the carbonate rocks of the district is not, by itself, a wholly reliable indicator of prox-﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
75
imity to ore, nor does its absence preclude the possibility of ore in an area. Furthermore, not all the jasperoid bodies in the districts were formed during the late barren stage of alteration.
Favorable jasperoid, of possibly supergene origin, locally forms bodies on the lower carbonate wallrock side of oxidized zinc ore pipes and mantos (A. V. Heyl, written commun., 1967). The jasperoid that is localized at the contact between the volcanic and sedimentary rocks appears to be completely unrelated to ore, and this unfavorable type is widely distributed, particularly in the area north of Eureka (H. T. Morris, written commun., 1957). The known presence of both favorable and unfavorable jasperoids in the Tintic and East Tintic districts prompted personnel of the Bear Creek Mining Co. to make a detailed study and comparison of suites of samples of the two types in an effort to establish criteria for the recognition of the favorable type. The results of this study are summarized by Howd (1957), Duke (1959), and Bush, Cook, Lovering, and Morris (1960b, p. 1516-1517).
APPEARANCE
The jasperoid bodies in the Tintic and East Tintic districts are characterized by sharp contacts between completely siliciffed rock and completely unsilicified host rock. Many bodies form elongated narrow “reefs” along fractures, but some are highly irregular in shape. They tend to be smaller, but more widely distributed, than those at Ely. The largest attain a maximum dimension in excess of 1,000 feet, but most have an outcrop area of only a few hundred to a few thousand square feet.
Lindgren and Loughlin (1919, p. 154) described the typical Tintic jasperoid as a fine-grained, dark-gray to bluish-gray rock, locally resembling a finegrained quartzite. According to H. T. Morris (written commun., 1957), some of the favorable hypogene jasperoids are locally coarse grained, many show textural as well as color banding with textures and structures suggestive of colloidal deposition, all are distinctly vuggy, and some show several periods of brecciation and recementation by later silica. One variety has a saccharoidal texture, and most of the favorable jasperoids contain megascopically visible platy crystals of barite. Although the favorable jasperoids range widely in color, most of them are lighter hued and more translucent on thin edges than the unfavorable jasperoids.
The unfavorable jasperoids, as a group, are dense and have a flinty appearance. They are predominantly black to brown or gray and are characterized by uniform texture and scarcity of vugs.
According to A. V. Heyl (written commun., 1967), the possibly supergene favorable jasperoid forms vuggy banded colloform casings adjacent to oxidized sulfide ore bodies. It contains abundant limonite and hemimorphite and sparse chrysocolla and malachite. This jasperoid is distinguishable from oxidized hypogene jasperoid by its lack of relict sulfides or of pits and pseudomorphs revealing their former presence.
My collection from the Tintic and East Tintic districts consists of 25 samples from 14 localities of which eight samples from four localities represent oxidized unfavorable jasperoid bodies, and the rest represent hypogene favorable jasperoid bodies. Six of the sample localities are in the vicinity of Eureka, four are in the southern part of the district on Mammoth Peak, one is near the center of the East Tintic district, one is on Pinyon Peak, one in Fremont Canyon, and one on Old Baldy Peak.
In this suite, all favorable jasperoid samples that are unoxidized and most that are oxidized are various shades of gray; several oxidized samples are white or moderate brown to dark brown, and a few show green copper stains or yellow iron sulfate stains. Many of the samples are mottled, banded, or streaked. Nearly all the favorable samples are brec-ciated and conspicuously vuggy, and some are porous and friable as well. Although a saccharoidal texture is evident in one or two of these samples, most are aphanitic; a few contain abundant randomly oriented blades of barite.
The few samples of unfavorable jasperoid in my collection are dark red, dark gray, bright yellow, or lavender gray, commonly variegated. All are dense, and one has a glassy texture and conchoidal fracture.
MICROTEXTURE AND MINERALOGY
Lindgren and Loughlin (1919, p. 155-156) described “typical” Tintic jasperoid as composed of quartz grains less than 0.25 mm in diameter with wavy extinction and commonly abrupt variations in grain size. They mentioned a local variety from the Gemeni mine which is strongly microbanded with alternating dark bands of cryptocrystalline quartz and light bands of spherulitic light-brown chalcedony, with minute grains of sulfides disseminated through both types of bands (fig. 30).
Lovering (1966) reported the presence of asymmetrically zoned quartz in much of the late barren stage jasperoid and made a petrofabric study of the preferred orientation of the asymmetry of the zonal overgrowths. Plots of the direction of displacement of the c axis showed consistent relations that were interpreted as indicating the dominant direction of﻿76 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
movement of the jasperoidizing solutions. These directions seem to coincide with the rake of the associated but later ore. The jasperoid quartz contains abundant minute low-index inclusions, which may be allophane; some of it also contains nearly isotropic particles, with an index of about 1.65, which may be barite. Chalcedony is most abundant in jasperoids replacing dolomite and shale away from the main channels of mineralization; opal is sparsely distributed and is supergene; barite is present in several generations, some older than jasperoid quartz and some younger; chlorite is younger than jasperoid quartz, in which it is locally abundant near mineralizing conduits; in the zone of oxidation, chlorite is largely altered to kaolinite; and disseminated pyrito-hedral pyrite is abundant in the jasperoid and is of about the same age as the chlorite.
The most comprehensive study yet made of the microtexture and mineralogy of Tintic jasperoids was done under the auspices of the Bear Creek Mining Co. The results of this work are summarized in reports by Howd (1957), Duke and Howd (1959), and Bush, Cook, Lovering, and Morris (1960a, b), and are discussed in detail by Duke (1959). A suite of “barren” jasperoid samples from an area north of Eureka was compared petrographically with a suite of “productive” jasperoid samples from various mines in the Tintic and East Tintic districts.
Seven textures were distinguished by Duke (1959) as follows: (1) Anhedral quartz mosaic—consisting of relatively homogeneous aggregates of anhedral quartz grains ranging from 0.1 to 0.2 mm in diameter; (2) colloform texture; (3) cryptocrystalline texture—aggregates in which all quartz grains have diameters less than 0.02 mm; (4) microbrecciated texture-angular fragments of jasperoid in a matrix of coarser quartz; (5) variable grain size—heterogeneous mixture of minute particles and coarse grains; (6) veinlets; and (7) vuggy texture. The minerals identified are barite, calcite, chalcedony, clay, dolomite, galena, hematite, jarosite, limonite, magnetite, manganese oxides, pyrite, quartz, sericite, and sphalerite. Duke (1959) compared the frequency of occurrence of these textures and minerals in the two groups of samples and concluded that cryptocrystalline and anhedral quartz mosaic textures in the same sample, variable grain size, microbreccia-tion, and vugginess were significantly more common in the “productive” group, as were the minerals barite, galena, hematite, and sphalerite. He considered chalcedony, clay, and jarosite to be more abundant in the “barren” samples.
In a petrographic study of 17 favorable jasperoid samples and eigh unfavorable jasperoid samples, I
distinguished 10 different textures and 21 accessory minerals in the combined suite of 25 samples. These textures I designated as (1) multiple generations (approximately equivalent to microbrecciated texture of Duke, 1959), (2) homogeneous coarse-grained (approximately equivalent to Duke’s anhedral quartz mosaic), (3) homogeneous fine-grained (cryptocrystalline of Duke), (4) heterogeneous (variable grain size of Duke), (5) colloform banding, (6) vuggy, (7) reticulated, (8) xenomorphic, (9) granular, and (10) jigsaw puzzle. The last four of my textural classifications, referring to the shape of the quartz grains, have no counterpart in Duke’s classification. The accessory minerals recognized, in order of decreasing abundance, are (1) hematite; (2) goethite; (3) allophane; (4) sericite; (5) limonite; (6) jarosite and barite; (7) pyrite; (8) chalcedony; (9) galena and sphalerite; (10) dolomite, siderite, malachite and wurtzite; (11) kaolinite, biotite, opal, smithsonite, and cerussite.
The frequency of occurrence of these textures and minerals was tabulated in each of the two groups. Although statistical tests of significance are difficult to apply to such small sample groups, a qualitative impression of the significance of certain textures and minerals, suggestive of favorable or unfavorable jasperoids, can be gained from the following tabular summaries, which show the differences in frequency
Common textures and minerals (observed in 20 percent or more of all samples) suggestive of favorable and unfavorable jasperoid in the Tintic and East Tintic districts
Percent
Difference
Favorable jasperoid
Texture
Heterogeneous ................
Homogeneous, coarse grained
Vuggy .......................
Xenomorphic ..................
Multiple generations ........
Reticulated .................
Mineral
Jarosite ....................
Barite ......................
Allophane ...................
Pyrite ......................
Goethite ....................
(Ff-Fu) 52 41 35 30 28 24
41
41
40
35
28
Unfavorable jasperoid
Texture
Homogeneous, fine grained
Jigsaw puzzle ............
Granular .................
Mineral
Sericite .................
Hematite .................
Limonite .................
Chalcedony ...............
(Fv-Frt)
70
47
26
58
40
38
35﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
77
of occurrence, expressed as percent of the group, between favorable and unfavorable jasperoid for the common textures and minerals.
The agreement between Duke’s criteria (1959) and mine is much closer for jasperoid-quartz microtextures than for associated minerals. This is reasonable because oxidation would have relatively little effect on jasperoid micro texture, but it would have a profound effect on the associated mineral assemblage. All of my unfavorable samples and most of my favorable samples were oxidized. Although the relative proportions of oxidized and unoxidized samples in the two groups studied by Duke were not specifically stated, it is improbable that the proportions of oxidized and unoxidized samples in his “productive” group were the same as in his “barren” group, or the same as in my favorable and unfavorable groups.
COMPOSITION
An outcrop sample of favorable jasperoid from near the Eureka Hill mine submitted by the author was analyzed by E. L. Munson. An analysis of “productive” jasperoid from the Tintic Standard mine was published by Lovering (1949, p. 54). Analyses of the two samples, in percent, are as follows:
Mine
Eureka Hill Tintic Standard
SiOa ............................ 95.75	90.12
A1203 ............................ 1.12	4.38
FeaOs ............................. .36	.20
FeO .................................19	.36
MgO................................ .01	.55
CaO .................................00	.02
Na20 ................................01	0
K20 .................................09	.87
H20 + ...............................75	2
H20- ................................05	.45
TiOa ................................03	.31
P205 ................................06	.02
MnO .................................03	Trace
C02 .................................16	.08
S ...................................08
BaO .................................00
Total.......................... 98.68	99.36
The agreement between these two analyses is surprisingly close, considering that they represent jasperoid replacement of different formations from different localities and that one sample is oxidized, the other, unoxidized. However, the variation in composition of favorable jasperoids in the district probably is considerably greater than is reflected by this pair of analyses. No quantitative chemical analyses of unfavorable jasperoid from the Tintic or East Tintic districts are available.
Semiquantitative spectrographic analyses were made of splits from the 17 favorable samples and eight unfavorable samples in my collection. Thirty- |
Table 19.—Minor-element distribution in 25 samples of jasperoid from the Tintic and East Tintic districts, Utah
[J. C. Hamilton, analyst. Leaders (.) indicate no information. Amounts
in parentheses are extrapolated values]
Limit of Number of
Element	detection (percent)	samples in which detected	Minor-element distribution (percent)			
			Range	Mean	Median	Mode
A1 		... 0.001	25	0.07 -3	0.33	0.12	0.15
Fe 		... .0008	25	.15 ->10	2.6	.43	.7
Mg 		... .0005	25	.007 - .3	.039	.014	.015
Ca 		... .005	25	.015 - .7	.098	.041	.07
Na 		... .05	4	<.03 - .07			<•03
K 		... .7	1	<.7 - .7			<•7
Ti 		... .0002	23	<.0015 - .15	.024	.009	.007
Mn 		... .0002	25	.003 -1.5	.077	.0075	.007
Ag 		... .0001	18	<.00015- .3	.022	.001	<.00015
As 		... .15	9	<.15 -3			<■15
B 		... .002	1	<.0015 - .003			<.0015
Ba 		... .001	25	.0015 ->10	2.45	.013	.003
Be 		... .0001	14	<.00015- .0015	.0002	(.0001)	<.00015
Bi 		... .001	9	<.0015 - .7			<.0015
Cd 		... .005	4	<•007 - .03			<.007
Co 		... .0005	3	<.0007 - .0007			<.0007
Cr 		... .0001	25	.00015- .003	.0006	.0002	.00015
Cu 		... .0001	25	.0007 -1.5	.135	.005	.003
Ga 		... .0002	5	<.00015- .007			<.00015
In 		... .002	6	<.003 - .007			<.003
La 		... .002	2	<.003 - .003			<.003
Mo 		... .0005	8	<.0007 - .003			<.0007
Ni 		... .0005	10	<.0007 - .007			<.0007
Pb 		... .005	19	<•007 -7	.491	.04	<.007
Sb 		... .01	8	<.015 - .7			<.015
Sc 		... .0005	1	<.0007 - .0007			<.0007
Sn 		... .002	4	<.0015 - .15			<.0015
Sr 		... .0002	19	<.0007 - .7	.073	.002	<.0007
V 		... .002	12	<.0015 - .007			<.0015
Y 		... .002	4	<.0015 - .015			<.0015
Yb 		... .0002	5	<.00015- .0015			<.00015
Zn 		... .005	16	< .007 -3	.182	(.005)	<.007
Zr 		... .002	12	<.0015 - .007			<.0015
three elements other than silicon were detected in one or more of these samples. These analytical data are summarized in table 19, in the same way as the spectrographic data on the samples of jasperoid from the Ely district were summarized in table 17.
The relative abundance of the 13 elements that were detected in more than half of the samples, as expressed by the mean, median, and maximum concentrations, is given in table 20. These data suggest that barium, lead, and silver are highly concentrated in this group of samples.
Semiquantitative spectrographic analyses of suites
Table 20.—Relative abundance, in percent, of 13 most abundant elements in 25 samples of jasperoid from the Tintic and East Tintic districts, Utah
Arithmetic mean	Median	Maximum reported
concentration	concentration	concentration
Fe 			 2.6	Fe 			 0.43	Fe 			>10
Ba 			 2.45	A1 			12	Ba 			>10
Pb 			49	Ca 			041	Pb 			 7
A1 			33	Pb 			04	A1 			 3
Zn 			18	Mg 			014	As 			 3
Cu 			14	Ba 			013	Zn 			 3
Ca 			10	Ti 			009	Mn 			 1.5
Mn 			077	Mn 			007	Cu 			 1.5
Sr 			073	Cu 			005	Ca 			7
Mg 			039	Zn 			005	K 			7
Ti 			024	Sr 			002	Bi 			7
Ag 			022	Ag 			001	Sb 			7
Cr 			0006	Cr 			00*>2	Sr 			7
• 1﻿78 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
of “barren” and “productive” jasperoids were made by the Bear Creek Mining Co. to ascertain which elements were characteristically concentrated in either type. The results of this investigation were summarized by Duke and Howd (1959) and Bush, Cook, Lovering, and Morris (1960b). Duke and Howd stated that Sb, Bi, Cd, Cu, Pb, Ag, Na, Th, and Zn are more abundant in “productive” jasperoids, whereas Ca and Mg are more abundant in “barren” jas-
peroids. Bush, Cook, Lovering, and Morris (1960b) listed Sb, Bi, Cu, Pb, Zn, Ag, Na, and Th as elements characteristically concentrated in “productive” jas-peroid, and Ca and Mn, in “barren” jasperoids. They supported this conclusion with a table giving the average concentration of each of these elements in each sample group in parts per million. These averages, converted into percent for comparison with my data, are as follows:
	Ag	Bi	Ca	Cu	Mn	Na	Pb	Sb	Th	Zn
Productive 	 Barren 			0.0046 	00016	0.0093 .0040	0.41 .68	0.073 .027	0.039 .13	0.21 .14	0.42 .02	0.0055 .0045	0.0020 a)	0.23 .13
1 Not detected.
The median values of the distributions of the commonly detected elements in my suites of favorable and unfavorable jasperoid samples were compared. Medians were used in preference to means, because most of the distributions are erratic and cover a large concentration range and therefore the mean values are strongly influenced by one or two high
values. The elements that showed an appreciable difference in median concentrations between the two groups are given in the following table, in which median values are given only for those elements that showed a greater-than-twofold difference between the two groups; smaller differences were considered unlikely to be significant.
Median values, in percent, of selected elements in 12 favorable and eight unfavorable jasperoid samples from the Tintic and
East Tintic districts, Utah
[Values in parentheses are extrapolated]
	Ag	As	Ba	Be	Bi	Cu	Pb	Sr	Ti	Zn
Favorable 	 Unfavorable 			 0.003 	 ( .00005)	(0.07 ) (0.001)	0.03 .007	(0.00003) .0001	(0.0008) ( .0001)	0.025 .001	0.07 ( .001)	0.0013 .0005	0.007 .03	0.02 ( .001)
Some of the elements listed by Duke and Howd and by Bush and Cook were detected in few or none of my samples, and some elements in my list were not mentioned by these authors. Such differences are to be expected where different sample groups are analyzed independently with different analytical equipment.
In summary, it seems that Ba, Na, Th, and possibly Sr, in addition to the ore metals, tend to concentrate in the favorable jasperoids of the late barren alteration stage. Be, Mn, and Ti seem to be higher in the unfavorable jasperoid related to the unconformity at the base of the volcanic rocks.
CONCLUDING REMARKS
At Tintic, apparently two distinct major types of hypogene jasperoid are present. One is genetically related to the hydrothermal alteration that culminated in ore mineralization, and is commonly, though not universally, associated with ore bodies. The other type is not related to this alteration and is consequently unfavorable. The available evidence suggests that this is also true of the Ely district, Nevada. A more detailed study of the late barren-stage jasper-
oids of the Tintic district is needed to establish the relative favorability of various jasperoid types within this group, as well as the geographic patterns of distribution of the various minor elements in it.
GILMAN (RED CLIFF) DISTRICT, COLORADO
(7, fig. 1; 5, fig. 40)
The Gilman (Red Cliff) district is in central Colorado on the east side of the Eagle River in Eagle County, about 25 miles north of Leadville (Crawford and Gibson, 1925). It is on the gently dipping southwestern limb of a northwest-plunging asymmetrical syncline formed in Paleozoic sedimentary rocks that lie between the Precambrian rocks exposed in the Sawatch Range just west of the district and the Precambrian rocks of the Gore Range about 7 miles to the northeast. The Precambrian granitic rocks, schists, and gneisses of the district are overlain by about 250 feet of quartzite, shale, and minor dolomite ranging in age from Cambrian to Ordovician. These rocks, in turn, are overlain by an approximately equal thickness of predominantly carbonate rocks consisting of the Devonian Dyer Dolomite Member of the Chaffee Formation and the dolomi-tized Mississippian Leadville Limestone. The Lead-﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
79
ville Limestone in this area is capped by a thin, persistent, - and highly altered sill of quartz latite porphyry, which separates it from the nearly 5,000 feet of Pennsylvanian shale, siltstone, arkose, and minor limestone that constitutes the rest of the Paleozoic section.
The ore deposits of the Gilman (Red Cliff) district consist of gold-silver veins in the Precambrian rocks and the Cambrian quartzite, auriferous mangano-siderite mantos in the quartzite, large pyritic copper-silver chimney deposits in the carbonate rocks that underlie the upper part of the Leadville Limestone, and extensive lead-zinc manto deposits extending up-dip from the chimney deposits in the upper part of the Leadville Limestone. Most of the district’s production has come from the deposits in the carbonate rocks. Faults in the main district tend to be small and traceable only for short distances. Sulfide distribution in the Leadville Limestone appears to have been largely controlled by open channels, many of which follow older joints and fractures. Some of these channels are of pre-Pennsylvanian age; others were formed or enlarged by early hydrothermal solutions related to mineralization.
DISTRIBUTION
There is no close spatial association between jas-peroid and the major sulfide ore bodies in the Gilman (Red Cliff) district. Crawford and Gibson (1925, p. 57, 59) reported jasperoid outcrops in the Leadville Limestone near the junction of Turkey Creek and the Eagle River at the south end of the district, and in a large body about three-quarters of a mile north of Gilman, beyond the north end of the district. They also mentioned the occurrence of small blocks of jasperoid on the dumps of some of the old mines on Battle Mountain south of Gilman, although jasperoid does not crop out at the surface in this area. Large masses of jasperoid replace the Dyer Dolomite Member northwest of the district on the flanks of the Sawatch Range north of Cross Creek, and the overlying Leadville Limestone is locally jasperoid-ized, according to Lovering and Tweto (1944, p. 77). Very little jasperoid is present in the Pennsylvanian rocks east of Gilman, although there is local minor silicification on some of the faults. Similar bodies of jasperoid are also abundant in the Leadville Limestone and Dyer Dolomite Member of the Chaffee Formation south of Red Cliff all the way to the East Fork of the Eagle River near the south boundary of Camp Hale, but this jasperoid is too far away to be considered in the Gilman (Red Cliff) district and is discussed separately under the heading “Pando Area” on page 99 of this report.
GENESIS
The jasperoid bodies in the vicinity of Gilman are considered by Crawford and Gibson (1925, p. 56-57, 59) to be the result of replacement of dolomite by silica gel, the silicifying solutions moving outward in a wave from major circulation channels along faults and fractures. They advocate the same origin for this rock as that suggested by Lindgren and Loughlin (1919, p. 156-157) for the Tintic jasperoids of the late barren stage. The source of the silicabearing solutions is tentatively postulated as a cupola on a buried monzonitic stock or batholith. Crawford and Gibson (1925, p. 65) further stated: “It is evident that both jasperoid and dolomite were deposited after—though in part perhaps contemporaneously with—the ore minerals, and it is probable that solutions that brought in both metallic and non-metallic minerals had a common source.” Lovering and Tweto (1944), on the other hand, found strong evidence that hydrothermal dolomitization preceded sulfide mineralization in the Gilman (Red Cliff) district. They found “zebra rock” texture preserved in jasperoid replacing the Dyer Dolomite Member and concluded that jasperoidization took place after this phase of dolomitic alteration; however, they made no statement as to the relative ages of jasperoidization and sulfide mineralization. Some of the silica that formed the jasperoid may have been leached from the Cambrian quartzite by hydrothermal solutions, but this source alone is regarded as insufficient to account for the large volume of silica now present as jasperoid in the area northwest of Gilman (Lovering and Tweto, 1944, p. 77-78).
The jasperoids of the Gilman (Red Cliff) district seem to be relatively simple and homogeneous in composition. This fact suggests that there was only one major period of jasperoid formation, and that the silica-depositing solutions were different in composition from those that deposited the sulfide ore.
RELATIONSHIP TO ORE
Crawford and Gibson (1925) and Lovering and Tweto (1944) generally agree that jasperoids in the vicinity of Gilman are a product of the hydrothermal alteration that, at some stage, produced the sulfide mineralization. Crawford and Gibson (1925) regarded jasperoid as a favorable guide to ore in the vicinity. They pointed out that ore occurs near jasperoid in the Leadville Limestone in several small mines in the southern part of this district, on Battle Mountain, and around Red Cliff, and suggested that “good prospecting ground” should lie east or northeast of jasperoid bodies that occur along faults. Lovering and Tweto (1944) regarded jasperoid as a﻿80 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
fringe effect of the mineralization at Gilman because silicification is generally absent in the altered host rocks adjacent to the major ore bodies. These rocks have been converted to jasperoid along faults and fractures updip from the ore deposits to the west and northwest at distances ranging from a quarter of a mile to several miles from the major ore bodies. The information now available indicates that most of the Gilman jasperoid bodies should be classed as unfavorable because they show no close spatial association with ore bodies.
APPEARANCE
Crawford and Gibson (1925, p. 56-57) described the jasperoid of the Gilman area as being dark gray to medium gray and locally yellowish gray or brownish gray, varying in texture from flinty to “gritty,” and having uneven fracture locally resembling a finegrained quartzite. Both varieties are characterized by abundant cavities and open fractures, and the dense variety commonly exhibits alternating light and dark streaks or bands. Some of the cavities in the jasperoid are lined with small quartz crystals. Jasperoid breccias, containing angular masses of material that is coarser grained and lighter colored than the matrix, are locally abundant along faults. These breccias probably resulted from the silicification of previously brecciated carbonate rock, rather than from brecciation and recementation of massive jasperoid.
The large masses of jasperoid northwest of Gilman consist largely of yellowish-brown, brown, and locally grayish, aphanitic to microcrystalline silicified Dyer Dolomite Member, which is commonly brecciated and vuggy with quartz crystals lining the vugs. Textures inherited from the dolomite are locally preserved in this jasperoid, including brecciation and “zebra texture,” which indicates that jas-peroidization of these rocks was younger than the early hydrothermal dolomitization.
My collection includes seven jasperoid samples from the vicinity of the Gilman (Red Cliff) district. Five of these are of jasperoid in the Dyer Dolomite Member 1-3 miles northwest of Gilman, one is from near the base of the Leadville Limestone in the same area, and one is a float sample from the Minturn Formation on Battle Mountain that presumably is residual from a locally silicified zone along a fault where it cut a limestone bed.
The samples from the Dyer Dolomite Member are predominantly light brown on weathered surfaces and light yellowish brown on fresh surfaces; one is medium gray, and one is moderate red with yellowish-brown patches. All are fine grained to aphanitic.
The sample from the Leadville is light gray and aphanitic. The float sample from the Minturn Formation is light gray and fine grained, and it contains abundant small irregular vugs lined with tiny crystals of quartz and calcite.
MICROTEXTURE AND MINERALOGY
Typical jasperoid, according to Crawford and Gibson (1925, p. 56-57), consists of anhedral aggregates segregated in some places into coarser and finer grained bands or masses, with locally abundant tiny inclusions of carbonaceous matter or limonite; these impurities tend to concentrate in the finer grained material, whereas rounded detrital quartz grains are more abundant in the coarser material. Sparsely scattered shreds of sericite are present in both types. Carbonate inclusions are sparse, except locally near the contact with the host rock; in one thin section transverse to such a contact, these authors reported that aphanitic streaky jasperoid ends abruptly in a wavy line against unsilicified dolomite.
Lovering and Tweto (1944, p. 78) described the jasperoids in the Dyer Dolomite Member of the Chaffee as a mixture of cryptocrystalline quartz, brown limonite, and carbonaceous dust, with local vague wavy bands of high limonite content. Vugs locally contain carbonate minerals, sericite, chlorite, and barite.
Three of my samples of jasperoid from the Dyer have a xenomorphic to jigsaw-puzzle texture in the matrix, which is relatively homogeneous, and an average grain size of 0.02 mm. Rounded detrital quartz grains, some of which show irregular overgrowths, are sparsely scattered through this matrix; one sample shows a veinlet of late coarse xenomorphic quartz. Goethite and limonite are abundant in all samples, both as dusty inclusions in the matrix and as coatings on fractures cutting the matrix. The matrix of some samples contains, in addition to limonite, dust particles of allophane and carbonate.
One sample from altered Dyer along an easttrending fault zone is strikingly different from the others. It consists of relatively coarse ferroan dolomite (0.1-2 mm) about half replaced by disseminated coarse quartz (0.05-1 mm). The ferroan dolomite shows deformation of cleavage traces and microbrec-ciation along grain boundaries. Fine-grained orange goethite fills fractures in it. The goethite is also disseminated through the quartz, suggesting hydro-thermal recrystallization of dolomite, followed by fracturing and oxidation along the fractures, followed by silicification.
A similar history is revealed by a sample of incipient jasperoid from the base of the dolomitized﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
81
Leadville Limestone. In this sample, fine-grained brown ferroan dolomite, containing abundant inclusions of orange goethite, has been brecciated and cemented by veinlets lined with coarse quartz and filled with coarse crystalline calcite. The dolomite fragments have been silicified in a zone about 1 mm wide bordering these veinlets, and the grain size of the replacing quartz changes progressively from about 0.15 mm adjacent to the vein down to about 0.02 mm adjacent to the unreplaced dolomite core, where it contains abundant inclusions of orange goethite.
The sample of completely jasperoidized Leadville Limestone consists of clean aphanitic homogeneous quartz that has a jigsaw-puzzle texture and an average grain size of about 0.01 mm; this matrix is cut by sparse thin veinlets of calcite.
The sample of jasperoid float from the Minturn Formation has a matrix of fine-grained quartz that has a jigsaw-puzzle texture and a size range of 0.01-0.04 mm. Within this matrix are wavy concentric bands and small rounded masses as “ghost” textures that are visible with reflected light but invisible under crossed polars, suggesting original deposition of silica as a gel. The matrix is cut by many irregular masses of coarser xenomorphic quartz, which is most abundant around vugs and along fractures. Local concentrations of tiny equant red hematite grains, about 0.05 mm in diameter, and sparse flakes of sericite are present in the younger xenomorphic quartz but not in the matrix, which suggests that these two minerals may have formed from the same solutions that brought in the second-stage quartz.
COMPOSITION
A quantitative standard rock analysis of a typical sample of jasperoidized Dyer Dolomite Member of the Chaffee Formation (field No. 183A-T-41) by E. L. Munson gave the following results:
Element	Percent	Element	Percent
Si02 			 96.79	H20- 			 0.05
AI2O3 				52	TiO; 			04
F62O3 				 1.02	P:0., 			01
FeO 			17	MnO 			03
MgO 			16	C02 			09
CaO 			14	S 			00
Na20 			01	BaO 			00
k'2() 			09		
H20+ 			35	Total			99.47
This sample contains somewhat more ferric iron than normal, as was anticipated because of abundant limonite in the specimen; otherwise, there appears to be nothing unusual in its composition.
Semiquantitative spectrographic analyses were
run by J. C. Hamilton on five of the previously described samples, including the one with the foregoing standard rock analysis. Only 16 elements other than silicon were detected in this group, and only 11 of these were detected in three or more of the five samples. These elements and their observed range in concentration follow:
Element	Range (percent)	Element	Range (percent)
A1 		... 0.015 -0.15	Cr		.. 0.0007 -0.0015
Fe 		... .7 - .3	Cu 		.. .0015 - .007
Mg 		... .015 - .15	Mo 		.. <.0007 - .0015
Ca 		... .07 - .3	Ni 		.. .0007 - .003
Ti 		... .0015- .015	Pb 		.. <.007 - .007
Mn 			007 - .07	V 		.. <.0015 - .003
Ba 		... .0015- .03	Yb 		.. C.00015-.00015
Co 		... <.0007- .0007	Zn 		.. <.007 - .007
The concentration ranges exhibited by these few elements are no greater than could be expected from five replicate samples taken from a single outcrop; yet one of these samples is from the Minturn Formation, one from the Leadville Limestone, and three from the Dyer Member, all taken at widely separated localities. Thus, it seems that the jasperoid bodies peripheral to the ore deposits of the Gilman district are unusually uniform in composition and, except for iron, unusually low in minor elements.
CONCLUDING REMARKS
The age relations of the Gilman jasperoids to the sulfide ore bodies cannot be established from the information now available. They seem to have formed at various, but commonly considerable, distances above or updip from these ore bodies, and therefore, if they are genetically related to the mineralization they formed on the outlet side from solutions that were poor in the ore elements. Apparently, they formed in an oxidizing environment, probably under conditions of low temperature and pressure and probably from a common but unknown source. These jasperoids seem to be of little value as direct guides to ore.
ASPEN DISTRICT, COLORADO
(8, fig. 1; 1, fig. 40)
The Aspen district is in Pitkin County, Colo., on the west side of the Sawatch Range on the Roaring Fork River, about 75 miles west of Leadville (Spurr, 1898). The ore deposits of the district are confined to a relatively narrow, north- to northeast-trending belt of pre-Pennsylvanian Paleozoic sedimentary rocks between Precambrian schists and gneisses on the east and Pennsylvanian and Cretaceous sedimentary rocks on the west. A few miles south of Aspen this belt bifurcates around a narrow north-﻿82 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
plunging syncline, the trough of which is filled with predominantly clastic Pennsylvanian sedimentary rocks. The western fork of the belt is bounded by the large Castle Creek normal fault and terminates northward at the edge of the town of Aspen. The eastern fork swings to a northeasterly trend where it crosses the river just east of Aspen and continues in that direction for many miles, beyond the limits of the district. This belt has a stratigraphic thickness of about 900 feet. The lower part of it is composed largely of quartzites and shales of Cambrian and Ordovician age; the middle and upper parts consist dominantly of carbonate rocks of Ordovician, Devonian, and Mississippian age. In addition to the Castle Creek fault, which bounds the district on the west and extends far beyond it to the south and to the northwest, the district is cut by numerous small faults that form two general groups, one of which trends northerly, the other westerly or northwesterly. The major ore deposits of the district consist of silver and lead vein and replacement deposits in the Mississippian Leadville Limestone, which were localized by the intersections of cross faults with bedding-plane faults or with favorable beds (Spurr, 1898; Vanderwilt, 1935). These known deposits were largely mined out by the end of World War I and there has been little mining activity in the district since that time.
DISTRIBUTION
The available geologic maps of the Aspen district do not show the distribution of the jasperoid bodies. According to Spurr (1898, p. 217, 220), these bodies formed along faults, fractures, and bedding planes in the limestone and dolomite, as did the ore bodies; however, jasperoid is more abundant and widely distributed than is the ore.
I have 12 jasperoid samples from nine localities in the Aspen district. These are all from the northtrending ridge formed by Aspen Mountain and Richmond Hill; the northernmost locality is on Pioneer Gulch about half a mile south of Aspen, and the southernmost locality is near the head of McFarlane Creek about 6 miles south of Aspen.
GENESIS
Spurr (1898, p. 217-218, 220, 229) concluded that the jasperoid at Aspen was introduced by hydro-thermal solutions related to, but older than, those that deposited the primary sulfide ores of the district. These solutions probably were rich in iron, magnesium, and carbonate in addition to silica, because dolomite, siderite, and some pyrite are pene-contemporaneous in origin with the jasperoid.
Petrographic study of my suite of oxidized jasperoid samples suggests that much of the coarsegrained reticulated type of jasperoid quartz is contemporaneous with, or younger than, the associated limonite, and may therefore be of supergene origin.
RELATIONSHIP TO ORE
The jasperoid bodies apparently Were localized by the same structures and rock units that influenced the deposition of the sulfide ore bodies. Spurr (1898, p. 220) stated that silicification always accompanies the ore deposition and that jasperoid quartz is an important gangue of the ore, although jasperoid is more widespread and is also found in areas where there has been no ore mineralization. However, Vanderwilt (1935, p. 238) noted that the massive jasperoid bodies of the district commonly are not found in close proximity to the ore bodies, but that disseminated quartz crystals in the carbonate host rocks, which appear to represent incipient jasper oid-ization, are common on old stope walls and in mineralized fractures and breccia zones.
The favorable jasperoid that forms a gangue for the ore may have been completely removed from the old stopes, and, as a result, only incipient jasperoid now remains in the stope walls. Samples of jasperoid taken from old mine dumps contain abundant ore minerals.
APPEARANCE
Some of the jasperoid bodies in the Aspen district have sharply defined contacts with the host rock; others grade outward through a zone marked by disseminated quartz grains or euhedral quartz crystals in a carbonate matrix, or by narrow anastomosing quartz veinlets that become visible only on weathered surfaces. The massive jasperoid is commonly red or yellow, and conspicuously vuggy. Its texture ranges from aphanitic, resembling chert, to fine grained, resembling quartzite. The vugs in this rock are commonly lined with chalcedony or small quartz crystals. Local leaching of the coarser grained variety has produced a porous, spongy mat of quartz (Spurr, 1898, p. 217-219; Vanderwilt, 1935, p. 238).
All my jasperoid samples that were taken from outcrops are shades of brown, yellow, and orange. They range from light brown, yellowish brown, and yellowish orange through moderate brown to dark brown. Two specimens taken from mine dumps are gray, indicating that the outcrop colors probably are the result of near-surface weathering and oxidation.
MICROTEXTURE AND MINERALOGY
Spurr (1898) described and illustrated the gradual﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
83
transition from carbonate rock containing scattered quartz crystals and disseminated grains, through jasperoid containing abundant interlocking quartz crystals and unreplaced remnant inclusions, to jasperoid in which the inclusions have disappeared and the interstices of the quartz crystal net have been completely filled with anhedral quartz, producing a reticulated texture.
This texture is well illustrated in many of the samples. Some of them show gradations from coarse reticulated jasperoid to masses of coarse-grained relict carbonate, or carbonate replaced by limonite, containing abundant doubly terminated quartz crystals as much as 3 mm in length. Most of the samples contain abundant limonite or goethite associated with medium- to coarse-grained xenomorphic or reticulated quartz. The larger quartz grains in many of these samples exhibit poikilitic inclusions of limonite, limonite particles in their cores, or thin septa of limonite outlining growth stages in individual quartz crystals. Thus, a considerable overlap probably existed in the formation of limonite and quartz, both of which replaced limestone, and must have done so under oxidizing conditions at relatively low temperature.
An older, and less abundant, generation of jasperoid is present in one of the unoxidized mine dump samples and as breccia fragments in some of the outcrop samples. It consists of aphanitic quartz with xenomorphic to jigsaw-puzzle texture and sericite inclusions. This quartz is older than the ore sulfides, and in one sample it preserves the original texture of the lithographic limestone it has replaced.
Accessory minerals observed in this suite of samples include hypogene pyrite, sphalerite, galena, barite, and sericite; probably supergene hematite, limonite, and manganese oxides; and supergene goethite, calcite, jarosite, cerussite, smithsonite lus-satite, and an unknown apparently isotropic dark-brown mineral that forms very minute hairlike overgrowths on grains of hematite and limonite in a quartz matrix.
Spurr (1898, p. 218-220) referred to dolomite both as relict inclusions and zoned rhombohedral crystals; siderite and pyrite as contemporaneous inclusions in the jasperoid; and also to barite, hematite, and limonite as minerals that commonly accompany it.
COMPOSITION
My 12 samples of jasperoid from the Aspen district were analyzed spectrographically. All 12 are anomalously rich in lead and zinc, and most of them contain anomalous concentrations of copper and barium. About half of the samples contain high
values for Fe, Mn, Ag, Be, Co, and Mo, and one or two contain the rarely detected elements As, Cd, Ce, Ga, Ge, La, Nd, and Sb. Samples collected near the center of the sampled area, between Bell Mountain on the north and the head of Queens Gulch on the south, all show the presence of Mo, which does not occur in detectable concentrations in any of the other samples from the district.
A suite of three samples was taken from an elongated jasperoid outcrop along a small fracture about half a mile southwest of the nearest mines in Tour-tellotte Park. One of these samples is oolitic Lead-ville Limestone host rock adjacent to the body, one is ferruginous jasperoid near the edge of the body, and one is highly ferruginous vuggy jasperoid from near the center of the body. The limestone sample shows a few small quartz grains and crystals, representing incipient jasperoidization, but otherwise appears fresh. It contains anomalous concentrations of Ba and slightly anomalous concentrations of Pb. The jasperoid sample from near the edge of the body is also high in Ba and contains considerably more Pb than the limestone; in addition, it contains anomalous Be, Co, Cu, Ga, Mo, and Zn. The sample from near the center of the body contains more of all these elements than the one from near the edge, and also contains anomalous Ag, As, B, Ge, V, Y, and Yb. This apparently systematic increase in both number and concentration of detectable minor elements toward the center of the body may be fortuitous because only one such suite of samples is available for study. The strong contrast between anomalous minor elements detected in the host rock and those in the jasperoid does indicate that all of them, except possibly Ba, were introduced and not inherited from the host rock.
The 12 jasperoid samples yield indicator-element scores in the range +5-+19. Seven samples, including the three samples from mine dumps, scored +15 or higher; three samples had scores in the range + 10-+15 and the other two scored +5 and +6. Thus, all but the last two fall in the definitely favorable category, and these two are in the possibly favorable category.
CONCLUDING REMARKS
The presence of anomalously large amounts of lead and zinc in all jasperoid samples from the Aspen district and of copper and silver in most of them, together with the fact that all such samples taken from mine dumps yield high favorability scores, suggests that this area should be excellent for exploration based on field geochemical analysis of jasperoid samples. The apparent contradiction between﻿84 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Spurr’s conclusion (1898) that jasperoid is older than sulfide mineralization, and the petrographic evidence that much of it is younger than limonitic alteration of the host rock, can be resolved only by a detailed study with emphasis on jasperoid bodies below the zone of oxidation. Certainly a presulfide generation of jasperoid is present, but examination of surface samples of the coarse-grained reticulated jasperoid described by Spurr suggests that it is not only younger than the sulfides but also younger than the oxidation of the sulfides.
EUREKA DISTRICT, NEVADA
(9, fig. 1; 20, fig. 44)
The Eureka district lies south and west of the old town of Eureka in eastern Eureka County, Nev., about 60 miles west-northwest of Ely; Nolan (1962) has discussed it in detail. Eureka has been one of the principal silver-lead districts of the Western United States. Paleozoic and Cretaceous sedimentary rocks in this district have been broken by a complicated network of faults, which locally served as channelways for mineralizing solutions that formed both fissure vein deposits and replacement deposits in carbonate rocks. Jasperoid in this district is not confined to any one stratigraphic unit, for it occurs in carbonate rocks of Cambrian, Ordovician, Permian, and Cretaceous age.
DISTRIBUTION
In the heavily mineralized Adams Hill area in the northern part of the district, the Cambrian Hamburg Dolomite has been extensively replaced by jasperoid adjacent to the overlying Cambrian Dunderberg Shale, although relatively little silica is associated with sulfide replacements in the younger Cambrian Windfall Formation and Cambrian and Ordovician Pogonip Group in the same area (Nolan, 1962, p. 63). This silicification of the Hamburg Dolomite is attributed to the blanketing effect of the shale.
A. V. Heyl (written commun., 1967) described “the Burnouts,” the original discovery area of the Eureka district, on the upper south slope of Adams Hill, as follows:
At the surface, the area of “the Burnouts,” the original discovery area of the district, consists of huge outcropping red and brown masses of oxidized jasperoid replacing limestone. Deep pits, small opencuts, many shafts, and several adits have mined the parts of the jasperoid masses containing rich yellow-brown veins and replacement masses of silverbearing plumbojarosite, anglesite and cerussite that made up the original rich bonanza-bodies of silver lead ore. The jasperoid is dense and aphanitic, but slightly sugary with some jigsaw-puzzle texture. The jasperoid is veined with limonite; cavities in the jasperoid contain white radiating masses of hemimorphite and small yellow areas of plumbo-
jarosite. The large outcrops of jasperoid that still remain total many thousands of tons.
Nolan (1962, p. 72) mentioned prominent masses of jasperoid in the Cambrian Eldorado Dolomite near the Burning Moscow mine south of Prospect Peak. In lower New York Canyon, dolomite beds in the Ordovician Hanson Creek Formation have locally been brecciated and replaced by jasperoid close to the contact with the underlying Ordovician Eureka Quartzite, along steep northwest-trending faults (Nolan, 1962, p. 71). The Permian Carbon Ridge Formation, which consists of thin-bedded impure limestones with local chert pebble zones, contains no economically important ore bodies; but locally, particularly near its fault contact with Eureka Quartzite on Hoosac Mountain, it is replaced by jasperoid. In this same general area, fresh-water limestone of the Cretaceous Newark Canyon Formation is also locally silicified (Nolan, 1962, p. 12, 71).
Many other small jasperoid bodies are shown on the geologic map of the Eureka district accompanying Nolan’s report.
GENESIS AND RELATIONSHIP TO ORE
Although little specific published information is available on the genesis and economic significance of jasperoid in the Eureka district, the localization of massive jasperoid bodies in the upper part of the Hamburg Dolomite, beneath the relatively impermeable Dunderberg Shale on Adams Hill (Nolan, 1962, p. 63), suggests a hydrothermal origin for some of this rock. On the other hand, Nolan’s observation (1962, p. 43) that oxidized ore minerals in this area locally contain considerable quantities of fine-grained quartz intermixed with them indicates that supergene jasperoid is also present.
Samples of jasperoid from the Eureka district in my collection provide evidence that both favorable and unfavorable varieties are present and can be distinguished by the criteria discussed on page 56 of the present report.
APPEARANCE, MICROTEXTURE, AND MINERALOGY
I have nine samples from the Eureka district; however, only three of these are wholly or predominantly jasperoid, four represent incipient jasperoid-ization of altered limestone or dolomite, and the remaining two are silicified limy siltstones. Four of the samples are from the heavily mineralized Adams Hill area west of Eureka; the other five represent widely separated outcrops along New York Canyon and Windfall Canyon south of Eureka (Nolan, 1962, pi. 1). The host rock for four of the samples is the Cambrian Hamburg Dolomite; two samples are from﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
85
the Ordovician Hanson Creek Formation, and one sample each was taken from the Cambrian Windfall, the Permian Carbon Ridge, and the Cretaceous Newark Canyon Formations.
All four samples from the Hamburg Dolomite are from within 200 feet of mine workings; three are from the Adams Hill area, and one is from an outcrop near the Catlin shaft at the head of New York Canyon. Samples 1 and 2, from the vicinity of the Helen shaft on Adams Hill, are aphanitic medium-gray jasperoids that have a heterogeneous xeno-morphic to jigsaw-puzzle texture and a grain diameter that averages 0.03 mm and ranges from 0.01 to 0.15 mm. Relict carbonate grains are locally abundant; the quartz contains abundant carbonate particles and is cut by late calcite veinlets. Both samples contain abnormally high concentrations of Ag, Pb, Zn, and Sr, and both yield scores that place them in the favorable category. Samples 3 and 4, one from near the Helen shaft and the other from near the Catlin shaft, consist largely of brecciated and recrystallized Hamburg Dolomite showing incipient jasperoidization. Both samples are aphanitic and weather brown with a rough surface. Sample 3 is medium gray with dark-gray inclusions; sample 4 is dark yellowish brown. Sample 3 is a finely comminuted microbreccia that contains tiny fragments of chert and vein quartz as well as dolomite. It also contains abundant irregular masses of an aphanitic opaque mineral, creamy white by reflected light, which was unidentifiable in thin section but which is probably a supergene lead-arsenic compound. Sample 4 contains only dolomite fragments and supergene orange goethite in addition to introduced silica. Two generations of introduced silica are distinguishable in both samples; the older of these is jasperoid similar in texture to that of the two jas-peroid samples first described, but slightly coarser in average grain size. The quartz is disseminated as grains and small isolated aggregates in the dolomite. These aggregates become more numerous and coalesce through a narrow transition zone into a jasperoid matrix heavily contaminated with carbonate particles and containing numerous inclusions of the larger dolomite grains. Both dolomite and jasperoid are cut by veinlets of aphanitic quartz that has a jigsaw-puzzle texture and an average grain diameter of about 0.01 mm. Both samples 3 and 4 are rich in Ag, Ba, Cu, Pb, and Zn, and sample 3 also contains abundant As and Sb. They scored +21 and +12, respectively, on their indicator element content.
One sample of partly silicified dolomitic limestone of the Cambrian Windfall Formation was taken from an isolated outcrop surrounded by valley fill a quar-
ter of a mile southwest of the Silver Lick group of mines on Adams Hill, the nearest mine workings. This sample is dense, fine grained, and pale yellowish gray, weathering yellowish brown, and has a rough pitted surface. In thin section the texture of the jasperoid and the manner in which it replaces the limestone are similar to those in the two dolomite samples described in the preceding paragraph; however, no late quartz veinlets or accessory minerals are visible. In addition to the Mg, Ca, and Ce of the host rock, this sample is slightly high in Na, Ag, Cu, Pb, Sr, and V. It yields a score of + 6 on the basis of its indicator-element content.
Two samples of jasperoidized dolomite of the Ordovician Hanson Creek Formation were collected from outcrops in New York Canyon. One of these outcrops is near the mouth of the canyon about a mile from the nearest mines; the other is about halfway up the canyon and 200 yards south of the 76 mine shaft. The first consists largely of brecciated yellowish-gray and light-olive-gray dolomite cut and cemented by medium-gray jasperoid; the second is a dense dark-gray fine-grained jasperoid with inclusions of dolomite fragments. Incipient jasperoid in the first sample differs from that in the Cambrian rocks previously described in that it is both coarser grained and more homogeneous, having an average grain diameter of about 0.2 mm; this probably reflects the more coarsely crystalline nature of the host rock. The second sample consists of heterogenous xenomorphic quartz that has a grain diameter that averages 0.1 mm and ranges from 0.02 to 0.5 mm; it contains inclusions of coarse-grained dolomite. In both samples the quartz contains abundant carbonate dust, and the dolomite fragments are clouded with opaque dark-brown or black dust particles, which are largely concentrated near the rims of the grains. Both samples are slightly high in Na, Ag, Ba, Pb, and Sr in addition to Ca and Mg; the second sample (from near the 76 mine) is also higher than normal in Mn and Zn. Indicator-element scores are +3 for the first sample, and + 7 for the second.
A sample of silicified limy siltstone of the Permian Carbon Ridge Formation was taken from Windfall Canyon near the junction of the Windfall Canyon road and the cutoff road to New York Canyon. This outcrop is in a brecciated zone along a strong fault that brings the Mississippian Chainman Shale in contact with the Carbon Ridge Formation; it is about a mile from the nearest mines. The rock is fine grained with local sparse vugs, dusky yellowish brown to dark gray, and weathers moderate yellowish brown. It has a matrix of aphanitic jasperoid quartz that has a jigsaw-puzzle texture and grain﻿86 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Table 21.—Characteristics of jasperoid
District	Major generations
or types
Field relations of jasperoid
(characteristics of jasperoid bodies of the district as a whole)
Appearance of jasperoid
(characteristics of particular jasperoid bodies considered to be typical)
Host rocks
Structural control Relationship to intrusives Relationship to ore Nature of contact
Tri State, Oklahoma-Kansas-Missouri.
Clifton-Morenci,
Ariz.
1 generation
Probably 2 generations but not distinguished.
Mississippian
limestone.
Cambrian and Ordovician limestone.
Related to fractures and bedding planes.
No known intrusives..
Related to faults and May be genetically rebreccia zones.	lated to felsic Lara-
mide intrusives, but spatially remote from intrusive centers.
Late preore, commonly adjacent to sulfide ore bodies.
Probably postore; spatially remote from major deposits; relationship not studied in detail.
Commonly gradational into host rock on one side and ore on the other.
Commonly abrupt....
Bisbee, Ariz ______ Early
Late
Ely, Nev ........ Early
Paleozoic limestone.
Cretaceous basal conglomerate.
Paleozoic limestone and shale; Tertiary mon-zonite.
Localized by strong faults and proximity to intrusive contacts.
Genetically and in part spatially related to siliceous porphyritic intrusives.
Localized by uncon- None known formity at base of Cretaceous and by faults and fractures cutting it.
Localized by proximity to monzonite porphyry intrusives.
Late preore, genetical- ______do
ly and commonly spatially related to ore.
None
Commonly irregular, locally gradational.
Genetically and spatially related to intrusives.
do ............. Commonly abrupt, lo-
cally gradational with intrusives.
Late
. do .
Leadville, Colo .... Not distinguished ..
Tintic, Utah
Early ( ?)
Late
Localized by faults None known and fractures.
Ordovician, Devonian, and Mississippian limestone and dolomite.
Paleozoic sedimentary rocks, largely dolomite.
. do.
Localized by faults and fracture zones.
Related to unconformity at base of Tertiary extrusive rocks.
Genetically related to quartz monzonite stock, but spatially remote.
Genetically and locally spatially related to ore.
Largely contemporaneous to postore; some is spatially associated, some is not.
Commonly abrupt .
No information .
None apparent ...... None apparent ........ Commonly abrupt .
Related to faults and Genetically related to Preore, genetically and .............do
fractures.	monzonitic intrusive, commonly spatially
but spatially remote. related to ore.
Gilman, Colo .... 1 generation
Devonian and Mississippian dolomite.
Related to faults . None apparent .
Possible genetic rela- .......do
tionship; no close spatial relationship.
Aspen, Colo
Probably 2 generations, but not distinguished.
Mississippian carbonate rocks.
Related to faults and ...... do
fractures.
Preore, genetically related and locally spatially related to
Transitional in some places, abrupt in others.
Eureka, Nev ...... Not subdivided
Cambrian, Ordo- ..... do
vician, Permian, and Cretaceous carbonate rocks.
do
Genetically related to .....do
mineralization; locally spatially related to ore.﻿CHARACTERISTICS OF JASPEROID IN MAJOR MINING DISTRICTS OF THE UNITED STATES
87
in major districts of the United States
Appearance of jasperoid—Continued	Microtexture and composition of particular jasperoid samples
(characteristics of particular jasperoid bodies considered to be typical)—Continued
Other information
Grain type and	Elements
Color	Macrotexture Other information Fabric texture	size	Mineralogy	concentrated
Dark gray to Dense, fine grained, Weathers light gray; Largely jigsaw-puz-black.	locally banded.	porous and friable zle texture; local-
in transition zone	ly reticulated,
to host rock.
Red, yellow, Largely aphanitic; None...................... Older host predomi-
brown.	locally brecciated	nantly jigsaw-
and cemented by	puzzle texture;
younger quartz.	younger is xeno-
morphic, locally reticulated.
Locally associated with older chert, which may be of replacement origin.
Many textural types distinguishable in thin section suggesting more than 1 major generation.
mm.
Generally homogeneous; 0.001-0.03 mm.
Older, homogeneous, <0.005 mm; younger, heterogeneous, <0.005-0.3
Carbon, clay, dolomite, pyrite, sphalerite.
Dolomite, siderite, calcite, sericite, pyrite, hematite, goethite, limo-nite, Mn oxides.
Fe, Al. C, Ni, Pb, Zn.
Pb, Zn, Fe, Be, Ga, Mo, Ag.
Dark red, gray.. Aphanitic, locally	Locally weathers to	J igsaw-puzzle to lo-	Homogeneous;
vuggy.	porous friable	cally xenomorphic	about 0.005
	masses or to	texture.	mm.
	quartz sand.		
Hematite, chalced- Fe, Cu, Ni, Pb, ony, calcite,	V, Y, Yb,
brochantite, mal- Ag, Bi. achite, limonite.
J asperoid is post-Pennsylvanian and pre-Late Cretaceous in age.
Pale yellow, Vuggy, fine	None,
pink.	grained; abun-
dant inclusions of host rock.
Xenomorphic to granular texture.
Heterogeneous; 0.005-0.1 mm.
Siderite, calcite dust, sericite.
Ni, Pb, Mo, Be, Zr.
Jasperoid is probably Tertiary in age.
White, pale yellow.
Dense, massive, Forms prominent fine grained; lo- outcrops, cally brecciated.
Xenomorphic to jig- Relatively homosaw-puzzle tex-	geneous;
ture, locally granu- 0.01-0.1 mm. lar.
Chalcedony, hema- No informa-tite, limonite, al- tion. lophane, goethite, jarosite, calcite, sericite, kaoli-nite, apatite, fluorite, pyrite.
None.
Dark red, dark yellow, shades of brown.
Vuggy, locally porous, commonly brecciated.
Weathers to a rubble of small fragments.
Jigsaw-puzzle texture, locally xenomorphic or reticulated.
Heterogeneous; 0.005-1 mm.
.do.
Bi, Sn, Zn, Fe, None. Ag, Cu, Pb.
Gray to black; Largely aphanitic.. None, locally brown.
Jigsaw-puzzle to lo- Heterogeneous; cally xenomorphic 0.005-0.1 mm. texture.
Mn oxides, goethite, Ag, Ba, Mo, Pb, limonite, hema- Zn, Fe, Mn. tite, pyrite.
Some jasperoid may be of supergene origin.
Black, dark Aphanitic gray, brownish red, yellow.
Commonly opaque on thin edges.
Jigsaw-puzzle to granular texture.
Homogeneous; <0.01 mm.
Sericite, hematite, limonite, chalcedony.
Be, Mn, Ti, Ca, Particularly abundant Mg.	in north part of
Tintic district.
Shades of gray Vuggy, commonly Variable grain size, and brown. banded and brec- commonly translated; aphanitic	lucent on thin
to fine grained.	edges.
Xenomorphic to reticulated texture, more than 1 generation, vuggy.
Heterogeneous, commonly coarse grained; >0.1 mm.
Barite, jarosite, goethite, allo-phane, pyrite.
Ba, Pb.Ag, Sb, None. Bi, Cu, Zn,
As, Na, Th,
Sr.
... do ....... Commonly vuggy	Locally preserves	Xenomorphic to
and brecciated;	primary and older	jigsaw-puzzle
aphanitic to fine	alteration (zebra)	texture,
grained.	textures.
Shades of yel-	Aphanitic to me-	Leached; coarser	Reticulated to jig-
low, brown,	dium grained,	grained varieties	saw-puzzle tex-
and gray.	vuggy.	are commonly po-	ture.
rous and spongy.
do
Largely aphanitic..
Incipient jasperoid locally developed in dolomite.
Xenomorphic to jigsaw-puzzle texture.
Commonly homogeneous;
<0.05 mm.
Reticulated type, coarse and heterogeneous, >0.1 mm; jigsaw-puzzle type, homogeneous, <0.05 mm.
Some varieties homogeneous, <0.05 mm; others heterogeneous, 0.02-0.5 mm.
Limonite, goethite, carbonaceous matter, sericite, barite.
Dolomite, siderite, pyrite, barite, hematite, limonite, Mn oxides.
Calcite, dolomite, limonite, goethite, chalcedony, sericite, zircon, tourmaline.
None in un- None, usual abundance.
Fe, Mg.Mn.Ag, Ba, Co, Cu, Pb, Sr, Zn.
Ore bodies commonly associated with incipient jasperoid and locally with coarse reticulated jasperoid.
Ca, Mg, Na.Ag, None. Ba, Cu, Pb,
Sr, Zn.﻿88 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
diameter less than 0.01 mm; it contains sparse detri-tal zircon and tourmaline and abundant detrital quartz grains with overgrowths in optical continuity with the grains. The matrix is cut by veinlets of late orange goethite and chalcedony, and chalcedony also lines vugs. Analysis shows this sample to be slightly high in Al, Fe, Mg, Ag, B, Ba, Cu, Ni, Pb, Sr, Y, Yb, and Zn, and abnormally high in Sb and Zr. Its indicator-element score is +11.
A sample of similar material from the Cretaceous Newark Canyon Formation near the head of Windfall Canyon, about a mile from the nearest mines, consists of dense fine-grained pale-yellowish-brown silicified limy siltstone or silty limestone that weathers moderate brown. The matrix is homogeneous aphanitic quartz that has a jigsaw-puzzle texture as in the specimen described in the preceding paragraph. It also contains disseminated flakes of seri-cite and masses of chalcedony, as well as numerous detrital grains of zircon and tourmaline and abundant detrital quartz. However, there are no overgrowths on the quartz grains, and the sample also lacks disseminated limonite particles and late orange goethite. Analysis shows it to be slightly high in Ca, Mg, Na, B, Ba, Ni, V, Y, Yb, and Zr; it yields an indicator-element score of —2.
CONCLUDING REMARKS
With one exception the indicator-element scores of specimens from the Eureka district reflect their location relative to known ore deposits. The four samples taken close to mine workings yielded scores in the favorable range; two samples taken within a quarter of a mile of mines, but more than 100 yards from them, yielded scores in the probably favorable range; two of the three samples taken about a mile from the nearest mines scored in the unfavorable or probably unfavorable category. The third such sample (from the Carbon Ridge Formation) yielded a score in the probably favorable category. This sample, from a breccia zone along a strong fault, may reflect updip leakage from a buried center of mineralization.
SUMMARY OF JASPEROID IN THE MAJOR DISTRICTS
The main characteristics of jasperoids in each of the major districts are summarized in table 21. It should be noted that the characteristics given under “Field relations of jasperoid” in the left part of the table apply to jasperoid bodies of the district as a whole; those given under “Appearance of jasperoid” are more restrictive, in general applying to particular jasperoid bodies that were examined and considered to be “typical”; and those given under “Micro-
texture and composition of particular jasperoid samples” are still more restrictive, applying only to those samples that were collected, studied, and ana* lyzed. As a result, the confidence that can be placed in the stated characteristics, as representative of the jasperoid bodies of the district, decreases toward the right in the table. Thus, interdistrict comparisons based on field relations are more reliable than those based on appearance, and these, in turn, are more reliable than comparisons based on microtexture and composition.
Certain generalizations are apparent from the field relations. In all the major districts Paleozoic carbonate rocks are the hosts for at least one major generation of jasperoid. In the districts characterized by a close spatial and genetic relationship between intrusive bodies and jasperoid, the intrusives are felsic, generally monzonitic in composition, and there is also a younger jasperoid localized by faults and fractures. In most of the districts in which a major generation of jasperoid is associated with ore, this jasperoid formed during a late stage of preore alteration.
Jasperoid samples that have coarse or highly variable texture, abundant vugs, or a porous friable texture commonly are related to ore; those characterized by an aphanitic texture are commonly unfavorable. Sulfides, or the oxidation products of sulfides, and unusually high concentrations of the ore metals as trace elements are characteristic of favorable jasperoid samples.
CHARACTERISTICS OF JASPEROID IN OTHER THAN THE MAJOR MINING DISTRICTS IN THE UNITED STATES
Jasperoid has been reported from nearly 200 mining districts or mineralized areas in the United States in addition to the nine major districts discussed in the preceding chapter (fig. 1). Some of these are large districts in which jasperoid is not sufficiently abundant to warrant inclusion in the preceding chapter; others are large districts in which the abundance of jasperoid is not clear and needs further study; most are smaller districts characterized by abundant jasperoid; a few are mineralized areas that have as yet produced no ore.
Information on these jasperoid localities has been derived in part from the literature and in part from examination and analyses of samples. This information ranges from detailed description with numerous analyses to only a brief mention of occurrence.
Summary discussions in this chapter are arranged alphabetically by State. The discussion of each lo-﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES
cality includes a brief summary of available information on (1) the distribution and field relations of jasperoid bodies, (2) genesis and relationship of jasperoid to ore, (3) appearance and petrography of jasperoid, and (4) minor-element content of jasperoid samples.
ALABAMA
No descriptions of jasperoid in specific districts in Alabama have been found. However, in a resume of cobalt-bearing manganese deposits of Alabama, Georgia, and Tennessee, Pierce (1944, p. 265) observed that “Cobalt-bearing manganese oxide is commonly associated with some variety of siliceous rock, such as sandstone, quartzite, or chert, or with a finegrained crystalline quartz which Kesler has identified as jasperoid.”
In an old report on the upper gold belt of northern Alabama, Brewer (1896, p. 12) mentioned deposits
similar to those of Cartersville, Ga., in which ore is associated with “whitish flinty quartz, highly sul-pheretted.” Thus, it seems that Alabama is not devoid of jasperoid occurrences, though their prevalence, nature, and economic significance cannot be evaluated from the information available.
ALASKA
Siliceous replacements associated with sulfide ore bodies have been reported from two areas in Alaska (fig. 37). One of these is the southern Seward Peninsula area where copper, lead, and zinc deposits are commonly associated with jasperoid in Paleozoic limestone. The other is the Salmon River district, near the head of the Portland Canal in the southeastern part of the Alaskan panhandle. Here, Jurassic greenstones have been locally silicified near deposits of copper sulfide.
4*C*IC
Figure 37.—Map showing the location of jasperoid-bearing areas in Alaska.﻿90 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
SOUTHERN SEWARD PENINSULA AREA
Cathcart (1922, p. 179, 181) mentioned bleached and silicified limestone with copper deposits at Casedepaga, on Penny River in the Solomon district, on Mount Dixon, on Slate Creek, on Manila Creek, and on Iron Creek at Copper Mountain. Cathcart said of these jasperoids: “The quartz bodies in which the copper minerals occur seem to conform with the bedding of the limestone. The quartz contains many shrinkage cavities and retains the original bedding planes of the replaced rock. The most noticeable feature of the rock is its banded structure.” The jasperoids of the Iron Creek district he (p. 212-213) described as being adjacent to bleached limestone and consisting of shattered and strained quartz cut by veinlets of sericite and chlorite. Chalcopyrite is locally present in these bodies in layers roughly parallel to the original bedding.
SALMON RIVER DISTRICT
Bodies of greenstone, which resulted from the
metamorphism of tuff and lava, have been intensely silicified in mineralized areas. This rock is bleached and locally resembles quartzite, both in macrotexture and composition. Sulfide minerals were introduced at about the same time as the silica. In some places the quartz replacement bodies contain abundant cal-cite or sericite, and at one locality (Summit claim) masses of nearly pure pyrrhotite are enclosed in silicified greenstone (Westgate, 1922, p. 123, 133, 137-138).
ARIZONA
Although no jasperoid provinces have been defined in Arizona that are comparable to those in the adjoining States of California, Nevada, Utah, Colorado, and New Mexico, jasperoid is present in at least 17 mineralized areas in the State, and some information is available on seven of these (fig. 38). Besides the major districts of Clifton-Morenci (5, fig. 38) and Bisbee (3), previously discussed, these are the Banner district (2), the Cameron area (4), the Court-
112*
110"
EXPLANATION
•
Major district
x
Minor district or area •
Reported occurrence
DISTRICTS, AREAS, AND OCCURRENCES
1.	Aravaipa
2.	Banner
3.	Bisbee
4.	Cameron
5.	Clifton-Morenci
6.	Courtland-Gleeson
7.	Fort Apache
8.	Globe-Miami
9.	Helvtia
10.	Jerome
11.	Mazatzal Mountains
12.	Mule Mountains
13.	Patagonia
14.	Pima
15.	Swisshelm
16.	Tombstone
17.	Winchester Mountains
Figure 38.—Map showing the location of jasperoid-bearing areas in Arizona.﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES
91
land-Gleeson district (6), the Jerome district (10), and the Pima district (14). Except for Cameron and Jerome, all of these are in the southeast quarter of the State. This geographic distribution may be largely attributable to the tendency of such siliceous replacements to occur in Paleozoic limestones and dolomites. Mineral deposits in these rocks are largely restricted to the southeastern part of the State. However, jasperoid bodies have also been reported in Triassic siltstone near Cameron (Abdel-Gawad and Kerr, 1963; Barrington and Kerr, 1963) and in Precambrian metamorphosed tuffaceous rocks near Jerome (Anderson and Creasey, 1958, p. 43-44, 109-111).
BANNER DISTRICT (2, fig. 38)
The Banner district is in southern Gila County a few miles north of Hayden (Kiersch, 1951). At the Seventy Nine mine copper-lead-zinc-sulfide replacement deposits in faulted and fractured Pennsylvanian Naco Limestone are associated with massive jasperoid bodies. One of these forms a circular outcropping mass 15 feet high directly overlying a pyritic ore body; similar jasperoid bodies appear to be localized by the Keystone fault near the mine. Many of these form lenses parallel to the bedding of the Naco Limestone. Lenses and irregular masses of jasperoid have been penetrated by mine workings as deep as the seventh level.
According to Kiersch (1951, p. 78-79), the sulfide ore bodies are cut and replaced by stringers, veins, and masses of quartz, which is the youngest hypo-gene mineral. Although Kiersch did not directly stipulate the age of the jasperoid bodies relative to the sulfide ore, the preceding statement implies that he regarded them as a product of the late-stage hydrothermal silica-bearing solutions. Regardless of their genesis, many of them are closely associated spatially with ore bodies.
The three samples from the Seventy Nine mine in my collection show considerable variation in color, texture, and mineralogy. Two are outcrop samples, and these are aphanitic and dark red to reddish brown. Their texture is heterogeneous and largely xenomorphic, locally almost granular or reticulated. The quartz is cut by veinlets of red hematite. One outcrop sample contains numerous microvugs surrounded by clean xenomorphic quartz showing zonal overgrowths. The other outcrop sample shows no vugs; but the quartz contains numerous inclusions of chlorite, sericite, rutile, hematite pseudomorphs after pyrite, and a high-index carbonate which is probably cerussite. The third sample, from the mine
dump, is coarse grained, vuggy, and white stained with various shades of brown. Its texture is heterogeneous and strongly reticulated. The larger quartz laths contain numerous two-phase fluid inclusions, as well as flakes of sericite and tiny needles of rutile. Vugs and late fractures contain cerussite and wul-fenite in addition to the ubiquitous limonite and goethite.
All three samples scored high in the favorable category on their minor-element content. All were high in lead; two were high in Ag, Cu, Ga, In, and Zn; and one was high in Bi, Mo, and V.
CAMERON AREA (4, fig. 38)
The town of Cameron seems to be near the center of a considerable area of scattered jasperoid bodies in the Triassic sedimentary rocks, and locally in the underlying Permian Kaibab Limestone (Barrington and Kerr, 1963, p. 1252-1253). A silicified zone 5-10 feet thick is present at the top of the Shinarump Member of the Chinle Formation in two areas in Coconino County—one on the west side of the Little Colorado River a few miles southeast of Cameron, and the other near Shadow Mountain, 11 miles north of Cameron (Abdel-Gawad and Kerr, 1963, p. 25-26). Near the junction of the Colorado and Little Colorado Rivers about 15 miles west of Cameron, a group of silicified breccia pipes, containing fragments of Shinarump and Kaibab Limestone, crops out in the shale and siltstone of the Moenkopi Formation (Barrington and Kerr, 1963, p. 1238). Both the silicified zone in the Shinarump and the silicified pipes in the Moenkopi are ascribed to alteration by siliceous hydrothermal solutions.
The jasperoid in the area southeast of Cameron forms anastomosing veins and lenses, locally as much as 7 feet thick, in sandstone and siltstone at the top of the Shinarump Member just below a thin gray shale of the Chinle. It is variegated and mottled in various shades of red, purple, and yellow and is commonly surrounded by a bleached kaolinized zone in the host rock. The surface is covered by an angular rubble of jasperoid surrounding the outcrops. Jasperoid here consists largely of dense aphanitic quartz and red chalcedony (Abdel-Gawad and Kerr, 1963, p. 25-26).
The silicified pipes west of Cameron present a very different appearance. They are nearly vertical pipes filled with a rubble of silica-cemented fragments of quartzite, limestone, siltstone, sandstone, and clay derived from the underlying Kaibab Limestone and Shinarump. The Moenkopi sandstone and siltstone surrounding these pipes have been bleached in ir-﻿92 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
regular halos, which represent a combination of kaolinitic and sericitic alteration. These pipes form prominent conical, irregular, black-weathering outcrops. Some breccia fragments in the cores are silici-fied, others are not. The cryptocrystalline silica cement is vuggy and porous and has cavities lined with crystals of anhydrite. Locally, silicified breccia fragments are embedded in a matrix of yellow kao-linite clay. Silica is confined to the vents and does not replace the wallrock. All the pipes are anomalously radioactive. The siliceous matrix is stained with limonite in addition to manganese oxide, and it locally contains malachite and azurite. Disseminated pyrite is present at depth in the altered wallrock surrounding some of the pipes (Barrington and Kerr, 1963, p. 1242-1246).
The silicification that produced both the zone and the pipes probably occurred at temperatures of about 200 °C and at moderate pressure. Silicification probably was accompanied, in the early stages, by kao-linization of the wallrock and, in the later stages, by the local introduction of oxides of uranium and manganese and sulfides of copper and iron, with excess sulfur resulting locally in the conversion of calcite to anhydrite (Abdel-Gawad and Kerr, 1963, p. 34, 44; Barrington and Kerr, 1963, p. 1246-1247). The ultimate source of the hydrothermal fluids is not known in this area. The jasperoid layers and lenses in the area southeast of Cameron are beneath, and near, small uranium deposits in sandstone beds of the Chinle Formation. No ore bodies have been developed in the area of the silica pipes, but the fact that the pipes show anomalous radioactivity and locally contain copper minerals as well as disseminated pyrite suggests that uranium and base-metal sulfide replacement ore bodies, if they are present in this area, probably are associated both spatially and genetically with jasperoid.
Jasperoid bodies in the Shinarump Member near Shadow Mountain are not described separately.
COURTLAND-GLEESON DISTRICT (6, fig. 38)
The Courtland-Gleeson district occupies an area of about 8 square miles near the southeast margin of the Dragoon Mountains 15 miles east of Tombstone and 20 miles north of Bisbee in Cochise County. Ore deposits consist of pyritic copper and lead-zinc-silver replacement deposits in Carboniferous carbonate rocks. They are localized by west-dipping thrust faults and younger north- and east-trending normal faults and fractures (Wilson, 1951, p. 12, 14).
The jasperoid bodies of this district are not discussed in the literature, although Wilson (1951, p.
14-15) mentioned a prominent limonitic silicified breccia zone along a north-trending mineralized fault on the west slope of Gleeson Ridge.
Three samples from this district are included in my collection. One sample, from an outcrop near the Shannon shaft, near Gleeson, is of the favorable oxidized type; the other two are of unfavorable oxidized jasperoid—one from a pit south of the Marine shaft near Courtland, the other from a breccia zone outcrop about a mile south of Browns Peak. The favorable sample, from a silicified breccia zone along a fault, consists of angular pale-orange and medium-gray breccia fragments of aphanitic jasperoid in a slightly vuggy moderate-brown siliceous matrix. The fragments have a homogeneous aphanitic jigsaw-puzzle texture. The matrix, which is similar in texture, contains abundant brown limonite and is cut by veinlets of orange goethite and younger coarse xenomorphic quartz; it also contains sparse open vugs as much as 1 mm in diameter.
The unfavorable sample from the prospect pit near Courtland is fine grained, light gray, and dense and is cut by thin veinlets of calcite. It has a heterogeneous granular to jigsaw-puzzle texture and a grain size of 0.005-0.15 mm. The larger grains have sutured boundaries and poikilitic inclusions of smaller grains. Accessory inclusions consist of fibrous chalcedony, calcite, and abundant large masses of tremolite. It also exhibits sparse elongated open vugs.
The second unfavorable sample, from south of Browns Peak, is fine to medium grained, grayish orange pink, and contains scattered vuggy areas and square pits. The matrix consists of homogeneous aphanitic jigsaw-puzzle-textured quartz, which has been fractured and recemented by late coarse xenomorphic quartz. The late quartz contains abundant allophane dust, much of which shows zonal overgrowth patterns on original euhedral crystals, and scattered embedded hematite pseudomorphs after original pyrite, which suggests that this jasperoid body may be of the fringe-zone favorable type rather than the truly unfavorable type.
The favorable sample from the Gleeson district is higher than normal in Fe, Ag, Bi, Cu, Ga, Mo, Pb, Sn, and Zn. The unfavorable sample from the pit near Courtland is abnormally rich only in Ba, and the unfavorable sample from south of Browns Peak is slightly high in B and Pb.
Differences in appearance, texture, mineralogy, and minor-element content among the three available samples show that several distinct types of jasperoid exist in this district, but their relationships to the ore bodies and to each other have not yet been determined.﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES
93
JEROME DISTRICT (10, fig. 38)
Several occurrences of jasper and silicified bodies in Precambrian metavolcanic and metasedimentary rocks in the Jerome district, Yavapai County, were described by Anderson and Creasey (1958).
In the vicinity of the United Verde ore body, tuffaceous rocks of the Grapevine Gulch Formation were locally replaced by fine-grained quartz adjacent to an intrusive gabbro^ contact, before the further replacement of this rock and the underlying quartz porphyry by massive pyrite. The jasperoid bodies thus formed are lenticular to irregular in form; they are most abundant in the tuffaceous sediments although some isolated masses are completely enclosed within the pyrite, and small jasperoid nodules are present in the quartz porphyry on the footwall side of the pyritic pipe. The largest jasperoid bodies, as much as 500 feet long and 150 feet wide, are localized by structural terraces in the hanging-wall gabbro (Anderson and Creasey, 1958, p. 109-111). Both the silicification and the sulfide mineralization in this deposit are clearly Precambrian. These are the only bodies of favorable jasperoid of unquestionable Precambrian age known to the author, though it is probable that hard massive quartz containing small chalcocite bodies in the upper levels of the United Verde extension ore body (Anderson and Creasey, 1958, p. 143) and pods of jasperoid in andesitic tuffs of the Alder Group between the United Verde and Copper Chief mines (Anderson and Creasey, 1958, p. 43-44) are also Precambrian. Other such bodies, remote from mineralized areas, in the Deception Rhyolite along shear zones and along the contact with the Grapevine Gulch Formation were reported by Anderson and Creasey (1958, p. 44), who believed them to be of Precambrian age but younger than the regional deformation.
The jasperoid of the United Verde deposit is fine grained, almost flinty, and red, black, or white with gradational color variations (Anderson and Creasey, 1958, p. 111).
Jasper magnetite beds are also locally intercalated with dacite flows in the Grapevine Gulch Formation, but these beds probably represent metamorphosed chemical precipitates, rather than epigenetic siliceous replacements (Anderson and Creasey, 1958, p. 19).
PIMA DISTRICT (14, fig. 38)
At the San Xavier mine in the northern part of the Pima district, Pima County, about 20 miles south of Tucson, a few small masses of favorable jasperoid are associated with base-metal sulfide replacement
deposits in Permian limestone. Wilson (1950, p. 46-47) summarized the geology and ore deposits of this mine, but he did not mention jasperoid.
Two samples of favorable jasperoid from the San Xavier mine area are included in my collection. One is a dump sample; the other is from a small outcrop, which caps an ore body, in limestone near the service shaft. The distribution of the ore bodies, and apparently of the jasperoid, is largely controlled by the intersection of a strong northeast-trending fault zone with favorable limestone beds.
Both samples are porous, vuggy, and heavily stained with iron oxide. The quartz is coarse grained and heterogeneous, and it has a xenomorphic to locally reticulated texture. In both samples the quartz is clouded with carbonate particles, and in one of them, small fluid inclusions are present in some of the coarser grains. In one sample, abundant relict grains and masses of siderite form inclusions in the quartz; in the other sample, porous masses of brown limonite and orange goethite cement fragments of jasperoid quartz, and late fibrous chalcedony partly fills the voids.
Both samples are rich in Ag, Bi, Cu, Mo, Pb, and Zn. One sample also shows high V, and the other one, high Ni.
OTHER OCCURRENCES
In the Winchester silver district (17, fig. 38) in the northeast corner of the Dragoon quadrangle, Cochise County, limestone of Paleozoic age has locally been replaced by jasperoid bodies, some of which are as much as 100 feet wide and 1,000 feet long. These jasperoid bodies are host rocks for silver ore deposits, although the distribution of silver is erratic and only small parts of the bodies are min-able (Cooper and Silver, 1964, p. 161).
In the Helvetia district (9, fig. 38), in the Santa Rita Mountains, the footwall of a copper ore body in the Copper World mine consists of highly silicified gray limestone, although the ore itself is not very siliceous (Schrader, 1915, p. 103). In the Patagonia district (13, fig. 38), at the Mowry mine, a silicified breccia zone as much as 250 feet wide occurs along a fault in limestone, according to Schrader (1915, p. 302), who wrote, in his general description of alteration in the district, that
The quartz in limestone occurs mostly in irregular masses locally developed in association with the garnet along the contact zone and in the impure cherty zones or metamorphic bands in the sedimentary rocks. Here and there it replaces chert and the earlier metamorphic minerals, such as calcite and actinolite, whose crystalline forms are preserved in masses of relatively pure pseudomorphic silica.
Jasperoid bodies have been reported in the Penn-﻿94 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
sylvanian Naco Limestone in the Swisshelm district (15, fig. 38), Cochise County, about 30 miles north of Douglas (J. R. Cooper, oral commun., 1962), and in the Cretaceous Bisbee Group of the Mule Mountains (12, fig. 38), Cochise County, north of the Bisbee district (P. T. Hayes, oral commun., 1964). The “novaculite” in the Naco Limestone at Tombstone (16, fig. 38), Cochise County, which is asso-cited with replacement ore deposits (Butler and Wilson, 1938, p. 108), also may be at least partly jasperoid.
At the Grand Reef mine in the Aravaipa district (1, fig. 38), Graham County, Ross (1925, p. 62) described lode deposits of lead and zinc sulfides in a silicified breccia of country rock, and also “irregular masses of white and pink glassy quartz.”
In the Fort Apache iron district (7, fig. 38) in Navajo County, near Young, silicified chert breccias occur in the Precambrian Mescal Limestone. Silicifi-cation was controlled partly by proximity to an old erosion surface and partly by the intersection of joints and fractures with favorable beds. The alteration took place in Precambrian time and seems to have been characterized by repeated cycles of brec-ciation and silicification (A. F. Shride, oral commun., 1962). In some places these silicified zones are peripheral to, and grade into, bedded iron ore deposits. Silica of both the breccia fragments and the matrix tends to be aphanitic, and it has a jigsaw-puzzle texture. The rocks are variegated in color, commonly banded in shades of gray, red, pink, yellow, and brown, and locally display small vugs and open cavities. It is doubtful that these silicified breccias represent true jasperoids in the sense of bodies formed by heated upward-moving silica-bearing solutions; more probably their origin, like that of the silcretes of South Africa and the duricrusts of Australia, was due to cementation by silica-bearing ground and surface water at or near an erosion surface.
In the Mazatzal Mountains (11, fig. 38), Maricopa County, near some mercury deposits on Alder and Sycamore Creeks, conspicuous bands of red jasper in a pale-yellow Precambrian dolomitic limestone that is interbedded with schist and slate were reported by Lausen and Gardner (1927, p. 63, 65).
In the Globe-Miami district (8, fig. 38), Gila County, quartz monzonite and granite porphyry are completely replaced by quartz and pyrite along some major faults and breccia zones of the Copper Cities deposit, according to Peterson (1962, p. 92)
ARKANSAS
Jasperoid is associated with many of the small
zinc and lead deposits scattered through the Ordovician and Mississippian carbonate rocks of northern Arkansas, in Washington, Boone, and Marion Counties on the west, and in Lawrence and Sharp Counties about 100 miles to the east. The deposits in the main northern Arkansas zinc district are most concentrated in Boone and Marion Counties in the north-central part of the region. The deposits, although numerous, are small, and the total value of all the zinc and lead produced from the entire region is less than $10 million.
NORTHERN ARKANSAS ZINC-LEAD DISTRICT (fig. 36)
In this district, as in the Tri-State district to the northwest, many of the dolomite and limestone beds contain large masses of preore jasperoid that resembles chert, which locally replaces the enclosing rocks, although McKnight (1935, p. 19-23) stated that it is probably only slightly younger than these host rocks. The deposits are very similar to, but smaller than, those in the Tri-State district.
Gray or brown jasperoid is closely associated both spatially and genetically with many of the sulfide replacement ore bodies. It selectively replaces limestone rather than dolomite in mineralized areas where the two rock types are present. 'McKnight (1935, p. 119-120, 138-150) believed that the gray jasperoid was deposited from hydrothermal solutions that resulted from the mingling of far-traveling magmatic emanations with ground water. He regarded it as the first stage of mineralization, immediately preceding the stage of sulfide deposition, and believed that the silica of which it is composed precipitated directly in the form of quartz, rather than crystallizing from a silica gel.
Incipient jasperoidization is commonly marked by the presence of disseminated quartz prisms in the carbonate host, and the massive jasperoid characteristically contains numerous relict grains of carbonate. Unreplaced dolomite rhombs occur in some samples of completely jasperoidized limestone. The jasperoid is typically a fine-grained dense dark-gray to black rock that has a heterogeneous reticulated texture (McKnight, 1935, p. 111-112, pis. 10, 11).
CALIFORNIA
Four mining areas in California that are characterized by large bodies of jasperoid are discussed in the literature: the Darwin district (3, fig. 39), the Diadem lode in the Bidwell Bar district (1), the Mescal mine in the Ivanpah district (6), and the East Shasta district (4). The first is a base-metal sulfide and scheelite district in the northwestern Mojave﻿95
CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES
124•
120'
DISTRICTS, AREAS, AND OCCURRENCES
1. Bid well Bar	12. Nopah
2. Black Hawk	13. Reward
3. Darwin	14. Russ
4. East Shasta	15. Slate Range
5. Grapevine	16. Soda Lake
6. Ivanpah	17. South Park
7. Kingston Range	18. Swansea
8. Lee	19. Tecopa
9. Lemoigne	20. Tungsten Hills
10. Lone Pine	21. Ubehebe
11, Mayacmas and Sulphur	
Bank	
Minor district or area Reported occurrence
Jasperoid province
Figure 39.—Map showing the location of jasperoid-bearing areas in California.﻿96 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Desert near Owens Lake; the second is a gold district near the north end of the Mother Lode gold belt; the third is an antimony-silver mine in the eastern Mojave Desert near the Nevada State line; and the fourth is a copper-zinc district in Shasta County. Jasperoid is known to be present in many other areas in California (fig. 39), but the literature on mining districts in the State contains little information about it.
DARWIN DISTRICT (3, fig. 39)
The Darwin district is in hills that lie between the south end of the Inyo Mountains and the north end of the Argus Range, about 20 miles east of the south end of Owens Lake in Inyo County (Hall and Mac-Kevett, 1962). The Panamint Springs, Zinc Hill, and Modoc mining districts a few miles west of Darwin in the Argus Range also contain abundant jasperoid (A. V. Heyl, written commun., 1967).
A series of upper Paleozoic carbonate rocks in the area has been metasomatically altered to calc-silicate rocks in broad zones surrounding Mesozoic felsic intrusive stocks and batholiths. Most of the ore bodies are in fissure veins and bedded replacements within this zone of contact metamorphism.
Knopf (1915, p. 16-18) noted the occurrence of “iron-bearing jasper” gangue at the Lane, Columbia, and Wonder mines in this district. Hall and Mac-Kevett (1958, p. 17-18; 1962, p. 63, 68, 76) listed “jasper” as an important gangue for some of the ore bodies formed in major fault zones and stated that it is particularly abundant at the Santa Rosa mine. “Jasper” in this district apparently is confined to the fault zones and does not appreciably replace the host rock. However, this rock replaces breccia within the fault zones and thus is true jasperoid (A. V. Heyl, written commun., 1967).
B1DWELL BAR DISTRICT (1, fig- 39)
Turner (1899, p. 389-390) described a replacement of Carboniferous limestone and dolomite on the Diadem lode in the Bidwell Bar district, Plumas County, Calif., near the north end of the Mother Lode gold belt. This body is localized by a strong fault zone, and attains a maximum width of 60 feet. Silicified foramanifera are present in this rock, which consists largely of iron- and manganese-stained quartz and chalcedony and, locally, of finegrained silicified shale beds. The jasperoid contains selenides of Au, Ag, Pb, and Cu in addition to free gold. Ore mineralization is regarded as penecon-temporaneous with silicification.
IVAN PAH DISTRICT (6, fig. 39)
The Mescal mine is in the Ivanpah district, on the northeast slope of the Mescal Range about a mile south of U.S. Highway 91 in eastern San Bernardino County, close to the Nevada State line. Hewett (1956, p. 132) has summarized the geology and ore deposit at this mine.
The host rock is lower Paleozoic Goodsprings Dolomite, which at this locality is a thin-bedded dark-gray dolomite intruded by a rhyolite sill. The ore zone is along a minor thrust fault in the dolomite, nearly parallel to the bedding. Stibnite, pyrite, and other sulfides are disseminated through a jasperoid body replacing the dolomite along this fault. According to Hewett, “these sulfides fill the pores of the spongelike mass of quartz that replaced the dolomite.” A. V. Heyl (written commun., 1967) reported that jasperoid is abundant at many other silver and base-metal mines in this district.
EAST SHASTA DISTRICT (4, fig. 39)
The East Shasta district is on Shasta Lake in central Shasta County, about 20 miles northeast of Redding. Massive base-metal sulfide deposits form lenses along shear zones and faults in Triassic rhyolite. The geology of the district is complex, and rocks ranging in age from Devonian to late Tertiary or early Quaternary are exposed within it. These are predominantly extrusive rocks and pyroclastics of many different ages, with subordinate interbedded shales and mudstones and a few limestone beds; a small stock of felsic plutonic rocks was emplaced in Late Jurassic or Early Cretaceous time.
Albers and Robertson (1961, p. 51, 52, 73, 97) mentioned silicification of rocks of many kinds, including Mississippian and Permian limestone, in the district; however, the rhyolitic host rock for the ore deposits is the most conspicuously silicified rock unit, and it is this silicification of the rhyolite that they discussed, as summarized in the following paragraph.
In its more intensely silicified phases both the groundmass and the feldspar phenocrysts of this rock have been replaced by anhedral microcrystalline quartz, and only the relict quartz phenocrysts remain. Silica, liberated during the replacement of rhyolite by sulfates and sulfides, probably moved outward to replace feldspar in the rhyolite at the Rising Star mine, where sulfide lenses are largely enclosed by intensely silicified rhyolite. A dense reddish-brown flintlike jasperoid containing disseminated sulfides in the Bully Hill mine appears to be a siliceous﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 97
replacement of metadiabase, and Albers and Robertson (1961, p. 97) stated that “its presence near prominent ore shoots seems to be an important indicator of mineralization within the metadiabase.”
Jasperoids of the favorable type are thus abundant in parts of the East Shasta district, though they are somewhat unusual in that they replace igneous rocks rather than sedimentary carbonate rocks.
OTHER OCCURRENCES
oerpentine in the vicinity of mercury deposits in the Mayacmas and Sulphur Bank districts (11, fig. 39), Sonoma County, was reported by Ross (1940, p. 333, 340) to have been hydrothermally altered to a fine-grained rock composed of quartz, chalcedony, opal, and carbonates. In the Tungsten Hills (20, fig. 39), Inyo County, 10 miles west of Bishop at the east base of the Sierra Nevada, roof pendants of metamorphosed sedimentary rocks are enclosed in granite and form the host rocks for scheelite deposits. Lemmon (1941, p. 502) wrote that “The calcareous rocks, limestone, shaly limestone, and calcareous shale show the most varied alteration. Some beds are silicified and on casual inspection resemble quartzite.”
A. V. Heyl (written commun., 1967) reported that jasperoid is common or abundant in the following lead and zinc mining districts in Inyo, San Bernardino, and Kern Counties in eastern California: Tecopa (19, fig. 39), Black Hawk (2), Lemoigne (9), Grapevine (5), Kingston Range (7), Nopah (12), Reward (13), Slate Range (15), Russ (14), Ubehebe (21), and Panamint Springs (hypogene jasperoid) ; Zinc Hill, Modoc, and Swansea (18) (both hypogene and supergene jasperoid) ; Lee (8), Clark Mountain, Soda Lake (16), Lone Pine (10), and South Park (17) (supergene jasperoid). The host rock of the jasperoid in most of these districts is limestone or dolomite; however, jasperoid replaces andesite and tuff in the Grapevine district.
COLORADO
Most of the small jasperoid-bearing mining districts of Colorado are within the central Colorado jasperoid province (fig. 1), which covers parts of Eagle, Summit, Lake, Park, Pitkin, Chaffee, Saguache, and Gunnison Counties, and includes the major districts of Leadville (9, fig. 40), Gilman (5), and Aspen (1), previously described. These smaller districts within the province include the Horseshoe-Sacramento district (6) in the Mosquito Range southeast of Leadville, the Kokomo district (7) in the Gore Range a few miles north of Climax, the Pando area (14) in the upper Eagle River Valley
between Tennessee Pass and Red Cliff, the Sedalia district (18) near Salida, the Monarch-Tomichi (12), Quartz Creek (15), Tincup (22), and Sugar Loaf and St. Kevin (21) districts in the Sawatch Range, the Lenado (10) and Snowmass Mountain
(19)	districts near Aspen, the Spring Creek district
(20)	north of Gunnison, and the Bonanza district (2) in the northeastern Saguache County. Isolated occurrences of jasperoid have also been reported from the Uncompahgre (23) and Red Mountain (16) districts near Ouray in the northern San Juan Mountains, in the Rico (17) and La Plata (8) districts in the southwestern San Juan Mountains, the Massadona-Youghall district (11) in Moffat County, and the Carbonate district (4) in eastern Garfield County outside the jasperoid province (fig. 40). The host rocks for nearly all these jasperoids are limestone and dolomites ranging in age from Devonian to Pennsylvania.
HORSESHOE-SACRAMENTO DISTRICT (6, fig. 40)
The Horseshoe-Sacramento district is south of Alma and southeast of Leadville on the east slope of the Mosquito Range in Park County. The nature and genesis of its jasperoid bodies were discussed in detail by Butler and Singewald (1940), from which the following information is abstracted.
The ore deposits consist of lead-zinc-silver sulfide vein and replacement deposits in Devonian Dyer Dolomite Member of the Chaffee Formation and the overlying Mississippian Leadville Limestone on the steep west limb of a northwest-trending anticline, which is cut off by the major north-northwest-trending London fault on the west. This fault brings barren Pennsylvanian shale, arkose, and siltstone in contact with the ore-bearing carbonate rocks.
Silicification of the carbonate rocks was preceded by the formation of vein quartz that fills faults and small fractures. Several distinct types and ages of jasperoid were distinguished in the area, and they exhibit both abrupt and transitional contacts with their host rocks (Butler and Singewald, 1940, p. 820-828). The jasperoid forms lenticular bodies parallel to the bedding and silicified breccia zones along major faults, which locally act as “feeder dikes” to the lenticular bodies. Butler and Singewald recognized four types of jasperoid, which they designated as coarse euhedral, coarse granular, fine granular, and nodular. These types grade transitionally into each other and exhibit a crude regional zonation outward from a core of coarse euhedral jasperoid to a peripheral zone of nodular jasperoid. They (p. 828-831, 835-836) believed that this tex-﻿98 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Figure 40.—Map showing the location of jasperoid-bearing areas in Colorado.
EXPLANATION
•
Major district x
Minor district or area •
Reported occurrence
□
Jasperoid province
DISTRICTS, AREAS, AND OCCURRENCES
1.	Aspen
2.	Bonanza
3.	Breckenridge
4.	Carbonate
5.	Gilman (Red Cliff)
6.	Horseshoe-Sacramento
7.	Kokomo
8.	La Plata
9.	Leadville
10.	Lenado
11.	Massadona-Youghall
12.	Monarch-Tomichi
13.	Mosquito Range
14.	Pando
15.	Quartz Creek
16.	Red Mountain
17.	Rico
18.	Sedalia
19.	Snowmass Mountain
20.	Spring Creek
21.	Sugar Loaf and St. Kevin
22.	Tincup
23.	Uncompahgre
tural gradation reflected a change from relatively dilute and relatively low temperature silica-bearing solutions precipitating quartz to form coarse euhedral jasperoid, through successively hotter and more concentrated silica solutions to a hot, highly supersaturated solution, which precipitated silica gel that later crystallized to form the aphanitic nodular type of jasperoid.
The coarse euhedral jasperoids are restricted to a small area at the southeast end of the larger jasperoid-bearing area. This rock resembles finegrained quartzite and is transitional into the recrystallized dolomite host rock through a zone characterized by skeletal quartz crystals or disseminated quartz prisms in the dolomite gangue. In thin section it shows a coarse reticulated texture with carbonate particles in the laths, which are cemented by, and locally overgrown with, clear quartz. Late clear coarse quartz also forms veinlets and drusy coatings of cavities and vugs. Relict inclusions of dolomite and grains of barite partly replaced by jasperoid are common. Flakes of sericite are locally abundant, and late ferruginous carbonate replaces some of the jasperoid. This type of jasperoid is closely associated with, and grades into, baritic sulfide ore consisting largely of galena, sphalerite, and
pyrite in a gangue of barite, dolomite, and jasperoid (Butler and Singewald, 1940, p. 808, 821-823).
Euhedral jasperoid grades into coarse granular jasperoid consisting of sparse, poorly terminated quartz laths embedded in a groundmass of relatively coarse anhedral quartz grains. This type also contains relict inclusions of carbonate host, but it lacks the carbonate particles that characterize the euhedral variety. The coarse granular jasperoid grades outward into fine granular jasperoid with the disappearance of quartz laths and gradual diminution in grain size. This type could have formed either by the crystallization of colloidal silica or by the rapid precipitation of quartz from solution at abundant centers of nucleation. Both barite and the early quartz laths show strain, brecciation, and corrosion by the granular matrix quartz (Butler and Singewald, 1940, p. 826-827, 831).
The fine granular jasperoid is transitional outward into nodular jasperoid that consists of nodules of fine-grained jasperoid quartz in a matrix of aphanitic cherty-looking quartz whose average grain size is a few thousandths of a millimeter. The nodules lack spherulitic or chalcedonic banding, but they commonly contain carbonate particles that are segregated in the cores of some nodules and concentrated in the rims of others. Both nodules and matrix﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 99
are cut by veinlets of late coarse clear quartz. This nodular jasperoid, which is most abundant on the outer fringes of the jasperoid area, characteristically exhibits sharp contacts with the host rock and is thought to represent the recrystallization of a silica gel deposited by-hot solutions highly supersaturated with silica (Butler and Singewald, 1940, p. 824-825). Ore bodies associated with this type of jasperoid apparently consist of pyrite, sphalerite, and galena and subordinate tennantite, argentite, and ehalcopy-rite, although this relationship is merely inferred and not directly stated by Butler and Singewald. They did state that this assemblage of ore minerals is characteristic of the nonbaritic ores and that barite is abundant in the euhedral jasperoid and not in the nodular jasperoid.
KOKOMO DISTRICT (7, fig. 40)
The Kokomo district is a few miles north of Climax, near the south end of the Gore Range in Summit County. The White Quail Limestone Member, one of several limestones in a thick section of siltstone, shale, and arkose in the Pennsylvanian Minturn Formation, is the host rock for lead-zinc sulfide replacement deposits along northeast-trending faults and fractures. Masses of jasperoid are closely associated with some of these ore bodies, and, in places, jasperoid quartz forms the matrix for siliceous ore.
The ore zone was argillized before it was silicified, and silicification preceded deposition of the sulfides. Limestone beds above and below the ore zone show no visible alteration, suggesting that the mineralizing solutions moved updip from their feeding channels for some distance in the ore zone before reacting to form the ore bodies and their associated alteration (A. H. Koschmann, oral commun., 1959).
Kokomo jasperoid, where unoxidized, is typically medium to dark gray, coarse grained, vuggy, and heavily impregnated with pyrite, which ranges from tiny disseminated grains to masses an inch or more in diameter, and locally forms a network of veinlets cutting the quartz. Much of the pyrite is euhedral, with striated cube faces predominating, although these are locally modified by octahedral and pyrito-hedral faces. Breccia fragments of light-gray soft friable argillized wallrock are commonly incorporated in the jasperoid. Masses of coarse-grained cal-cite cement the jasperoid fragments in places, and most vugs in the jasperoid are encrusted with prismatic quartz crystals associated with pyrite and younger dark sphalerite.
In thin section the jasperoid quartz is coarse
grained, and it has a heterogeneous texture that grades from reticulated to xenomorphic. Many quartz grains contain carbonate particles, and some of the larger quartz grains have zone inclusions of allophane. Flakes of sericite, penecontemporaneous with the matrix quartz, are abundant. Pyrite, galena, and sphalerite inclusions are all younger than jasperoid quartz and seem to have formed in approximately the order in which they are listed. Veinlets of calcite and of quartz cut both the sulfides and the jasperoid.
Spectrographic analyses of two jasperoid samples from Kokomo show abnormally high concentrations of Fe, Mn, Ag, Bi, Ge, Pb, and Zn, and thus confirm that it is a favorable jasperoid.
LA PLATA DISTRICT (8, fig. 40)
The La Plata district is in western La Plata County, about 20 miles northwest of Durango. Complex gold and silver ore has been mined, largely from vein deposits in sedimentary rocks that range in age from Pennsylvanian to Cretaceous, in an area cut by many dikes and sills of Tertiary felsic igneous rocks. The sedimentary rocks, which consist largely of silt-stone, shale, and sandstone, are commonly silicified adjacent to the veins in zones as much as 3 feet thick. This silicification ranges in intensity from cementation to nearly complete replacement (Eckel, 1949, P- 77).
The Jurassic Pony Express Limestone Member of the Wanakah Formation has been largely replaced by sugary quartz and pyrite on Jackson Ridge, particularly on the slope south of Rush Basin (Eckel, 1949, p. 111). Hydrothermal alteration and subsequent mineralization in the district closely followed intrusion of the Tertiary igneous rocks and are probably genetically related to the intrusives.
PANDO AREA (14, fig. 40)
The Pando area of central Colorado is west of Kokomo, north of Tennessee Pass, and south of Red Cliff. It comprises about 50 square miles bounded approximately by the valleys of the Eagle River and Homestake Creek on the west, the east fork of the Eagle River on the south, the crest of the Gore Range on the east, and the divide south of Turkey Creek on the north. It is in Eagle County and includes the Camp Hale Military Reservation. A few small mines and prospects in pre-Pennsylvanian rocks in the western part of the area produced some oxidized lead, silver, and gold ore before 1900; but these﻿100 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
mines and prospects are now idle, and there is no mining activity in the area at present.
The Devonian Dyer Dolomite Member of the Chaffee Formation and the hydrothermally dolomi-tized Mississippian Leadville Limestone overlying it have been extensively replaced by jasperoid at many places along the valley of the Eagle River from its confluence with the East Fork of the Eagle River northward to the north boundary of the Pando area. Scattered bodies of jasperoid are also found in carbonate beds in the thick pile of dominantly clastic sedimentary rocks of the Pennsylvanian Minturn Formation overlying the Leadville Limestone to the northeast.
The jasperoid bodies of this area, together with those of the adjoining Gilman district (5, fig. 40), were first described by Crawford and Gibson (1925, p. 56-59), and their observations have been summarized in my section on the Gilman district (p. 78). Tweto (1953), in a more recent study of these rocks, pointed out the association of jasperoid with previously hydrothermally dolomitized and brecci-ated rock, particularly in the permeable Gilman Sandstone Member of the Leadville Limestone and the adjacent dolomite beds of the Dyer below and the Leadville above. This zone and local channels in the old karst erosion surface at the top of the Leadville served as major conduits for the silicifying solutions.
Carbonate beds in the Pennsylvanian Minturn Formation are also strongly jasperoidized along faults near the heads of Cataract and Pearl Creeks and on North Sheep Mountain.
Silicification that resulted in the formation of jasperoid seems to represent a late barren stage in a long period of hydrothermal alteration that began with pervasive conversion of the Leadville Limestone into fine-grained dolomite, with subsequent recrystallization of the dolomite into “zebra rock,” sanding of the dolomite along channels, and breccia-tion preceding silicification. Local fracturing and brecciation continued during silicification, which was followed by weak local sulfide mineralization. Tweto regarded this sequence as probable manifestations of fringe zone mineralization leaking updip from a major center of mineralization that lies buried beneath the thick section of Pennsylvanian rocks, to the northeast of Camp Hale. The scattered areas of alteration in the Pennsylvanian carbonate rocks may also represent leakage upward, along strong faults, from this same source.
Many varieties of jasperoid are present in the area, and some of the larger bodies exhibit several distinctive types and generations. Most of these varieties seem to be unfavorable; but small grains of
pyrite, cerussite, and cerargyrite occur locally, and barite is common (Tweto, 1953).
My samples from the Pando area exhibit wide variations in appearance. Some are mottled, some show thin alternating color bands like varves, some are silicified breccias that contain angular fragments of chert and older jasperoid, and some are mega-scopically homogeneous. The samples are white mixed with various shades of gray, brown, brick red, yellow, or orange. Most samples have aphanitic textures, but some are vuggy and have a saccharoidal texture like fine-grained quartzite.
Many of the Pando samples have a homogeneous aphanitic jigsaw-puzzle texture, which in some samples characterizes an older generation that is cut by veinlets and masses of coarser xenomorphic quartz. Wavy colloform banding is characteristic of some samples. Heterogeneous textures with abrupt variations in grain size characterize a few samples, and one of these has a strongly reticulated texture suggestive of favorable jasperoid. Common accessory minerals include hematite, pyrite, barite, chalcedony, and late orange goethite; flakes of sericite are scattered through the matrix in a few samples, and much of the aphanitic jasperoid quartz is clouded with abundant dust-sized inclusions of allophane, carbonaceous particles, or carbonate.
Spectroscopic analyses were obtained on three samples from the Pando area. One of these samples is from Dyer Dolomite Member near a small adit in the Eagle River Canyon near the north boundary of the area; the second is from an unmineralized body in the lower dolomitized part of the Leadville Limestone in the Eagle River Canyon a little farther south; and the third is from a body replacing a dolomite bed in the Pennsylvanian Minturn Formation on a ridge south of Pearl Creek in the east-central part of the area. The first of these is high in Ba, Be, Na, Sr, and Ti; the second is high in Ba, Be, Sr, Yb, and Zr; and the third shows no abnormally high concentrations of minor elements but is deficient in Fe, Ti, and Cr. Although none of these samples contain high concentrations of the indicator elements for productive jasperoid, it is highly probable that some of the jasperoid bodies in the lower Paleozoic carbonate rocks along the Eagle River valley do contain them, and a detailed study of these bodies might outline favorable areas for exploration.
RICO DISTRICT (17, fig. 40)
The Rico mining district is in eastern Dolores County, in the western part of the San Juan Moun-﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 101
tains, about 35 miles north-northwest of Durango and 30 miles southwest of Ouray. It lies about 20 miles northward from the La Plata district (8, fig. 40) in the same part of the San Juan Mountains.
According to Cross and Ransome (1905, p. 14-15, 20), the major ore deposits of the district are blanket replacements of limestone and shale of the Pennsylvanian Hermosa Formation by silver-bearing galena associated with sphalerite and abundant pyrite. The sedimentary rocks in the district were intruded by sills of monzonite porphyry in late Tertiary time at the beginning of a domal uplift that culminated with profound faulting. Bedding-plane faults and north-east-trending normal faults, formed at this time, served as conduits for later mineralizing solutions that silicified the wallrocks and deposited the ores. Black shale, limestone, and monzonite porphyry sill rocks have locally been replaced by jasperoid.
Ransome (in Cross and Ransome, 1905, p. 14-15) stated:
In the form of jasperoid (a cryptocrystalline aggregate commonly associated with replacement deposits) quartz occurs in the Blackhawk mine and in the blanket of the Sambo mine. In the former mine, also, are found spongy, cavernous masses of rusty quartz, apparently due to the removal of limestone, by solution, from a network of quartz stringers. Quartz is abundant in some of the blanket breccias as a replacement of breccia material.
In a further description of the Blackhawk mine, Ransome (p. 19) stated that massive sulfide ore bodies have selectively replaced a limestone bed and that the limestone next to the ore is commonly changed to jasperoid.
UNCOMPAHGRE DISTRICT (23, fig. 40)
The Uncompahgre mining district is in the northern San Juan Mountains near Ouray, the county seat of Ouray County. This district, like the Leadville district (9, fig. 40), is characterized by fissure vein deposits of copper, lead, zinc, gold, and silver. The deposits show a zonal arrangement around a center of mineralization that developed at the intersection of major northeasterly and northwesterly structural trends. High-temperature pyritic gold ore was deposited in the core area, which is surrounded by an intermediate zone of base-metal sulfides; this, in turn, is surrounded by a silver belt that forms the outer zone of commercial mineralization. Jasperoid bodies are largely confined to this outer zone (Burbank, 1940).
Jasperoid formed during a preore stage of hydro-thermal alteration that was preceded or accompanied by leaching of carbonate rocks, which opened up
solution channels. This stage was followed by the formation of ankerite, sericite, pyrite, and barite immediately preceding the ore stage of mineralization. During the ore stage, pyrite, sphalerite, chal-copyrite, galena, tetrahedrite, pearceite, pyrargyrite, rhodochrosite, and manganocalcite were deposited. This was followed by the emplacement of late calcite, quartz, and barite (Burbank, 1940, p. 207).
At the Mineral Farm mine, about a mile south of Ouray, silicification and subsequent mineralization were localized by an unconformity between the Leadville Limestone and the overlying shales and silt-stones of the Mississippian and Pennsylvanian Molas Formation. Small fractures in the top of the Leadville were opened up by hydrothermal leaching, and the overlying red shale of the Molas was silicified. The larger ore bodies formed in these open channels in the Leadville beneath the competent and impermeable caprock of silicified shale. The mineralized upper part of the Leadville is coarsely clastic and contains interbedded porous sandstone layers, indications that it was highly permeable during mineralization (Burbank, 1940, p. 209-210). I have three samples of partly oxidized jasperoid from the Mineral Farm mine, taken from the walls of a sulfide deposit that formed in one of these channels at the top of the Leadville Limestone. They range in color from light gray through light olive gray and from grayish orange to pale yellowish brown, have a distinctly saccharoidal texture, small sparse vugs, and visible disseminated grains of pyrite and galena. One sample contains angular breccia fragments of white, light-gray, and dark-gray aphanitic silica and coarse-grained white vein quartz with disseminated pyrite. This latter inclusion suggests that some pyrite must be older than the matrix jasperoid.
Thin sections reveal that the sample with the most abundant sulfides has a coarse heterogeneous reticulated texture, characteristic of favorable jasperoid; pyrite and galena in this sample show incipient alteration to limonite and cerussite, respectively, and the matrix quartz contains local concentrations of allophane and carbonate particles. The other two samples consist largely of rounded detrital-looking quartz grains cemented by aphanitic quartz that has a jigsaw-puzzle texture. These probably represent a silicified sandstone bed in the limestone.
The favorable jasperoid sample is rich in Ag, Cd, Co, Cu, Mo, Ni, Pb, Te, Zn, and Zr. The two samples of silicified sandstone contain abnormally high concentrations of Ti, Ag, Cu, Nb, Pb, Te, Zn, and Zr, but they do not yield as high a score on indicator elements as the favorable jasperoid sample.﻿102 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
OTHER OCCURRENCES
White sulfide-bearing jasperoid in the Pennsylvanian Hermosa Formation at the Black Queen mine, on the south slope of Sheep Mountain in northern Gunnison County, was reported by Vanderwilt (1937, p. 106, 116). He also mentioned a bed of barren white jasperoid in Pennsylvanian sedimentary rocks near the head of Yule Creek in the same area. Intensely silicified Cretaceous shale in the Wellington mine at Breckenridge (3, fig. 40), Summit County, was described by Lovering (1934, p. 56), who stated that “Much of the limy shale has been strongly silicified near the veins and is converted into black jasperoid, locally called jasper.” In the Sugar Loaf and St. Kevin districts (21, fig. 40), Eagle County, in the northern part of the Sawatch Range, the widespread occurrence of “chert” dikes, zones, and veins cutting Precambrian igneous and meta-morphic rocks was reported by Singewald (1955, p. 260). The larger “chert” zones are as much as 350 feet wide, and Singewald ascribed their origin to replacement of the country rock along strong faults.
Burbank (1932, p. 72) described the replacement of Tertiary volcanic rocks by silica adjacent to faults in the Bonanza district (2, fig. 40), Saguache County, and (1941, p. 203) similar silicification forming “casings” around ore channels in quartz latite of the Red Mountain district (16, fig. 40), San Juan County.
Replacement of limestone by silica, adjacent to sulfide replacement deposits in limestone, in the Quartz Creek (15, fig. 40), Tincup (22), and Monarch-Tomichi (12) districts, Gunnison and Chaffee Counties, was noted by Dings and Robinson (1957, p. 60, 63-64, 69). Behre (1953, p. 99, 100) mentioned jasperoid in densely packed anhedi'al grains replacing the groundmass of porphyry near some ore bodies and also replacing carbonate rocks, particularly the Leadville Limestone, on the west slope, of the Mosquito Range (13, fig. 40), Lake County, east and southeast of the Leadville district.
Jasperoid is also mentioned by Heyl (1964, p. C25) as a gangue mineral in oxidized zinc veins of the Massadona-Youghall deposit (11, fig. 40) in central Moffat County near the Yampa River. Brecciated upper Paleozoic limestone is both replaced and cemented by large masses of jasperoid that form the principal gangue of an oxidized zinc-lead replacement ore body at the Doctor mine in the Spring Creek district (20, fig. 40) north of Gunnison in Gunnison County (Heyl, 1964, p. C25, C28, C29). Heyl (written commun., 1967) also reported the presence of abundant jasperoid associated with oxidized zinc and lead deposits in the Lenado district
(10, fig. 40), Pitkin County, north of Aspen, the Sedalia district (18, fig. 40), Chaffee County, on the Arkansas River north of Salida, and the Carbonate district (4, fig. 40) on the White River Plateau in eastern Garfield County.
GEORGIA
CARTERSVILLE DISTRICT
(1, fig- 41)
An economically important mining district in Georgia that contains large bodies of jasperoid is the Cartersville iron and manganese district about 40 miles northwest of Atlanta in Bartow County in the southern Appalachian Mountains. The Cartersville district is largely underlain by folded and slightly metamorphosed shale, limestone, and dolomite of Cambrian age. The rocks were apparently folded in Carboniferous time; folding was closely followed by high-angle faulting and fracturing. These faults and fractures later served as conduits for hydrothermal solutions that formed fissure vein and replacement deposits of jasperoid, hematite, barite, siderite, pyrite, and base-metal sulfides. Deep weathering accompanied by supergene alteration and enrichment, during the Tertiary Period, produced commercial deposits of manganese oxide and brown iron ore (Kesler, 1950, p. 1-2).
Jasperoid bodies are not restricted to any one stratigraphic zone, although they are confined to carbonate rocks or to residual clay underlain by carbonate rocks in the vicinity of faults and fractures. They decrease in size and abundance from east to west across the district. Residual clays derived from weathering of carbonate rock contain irregularly distributed bodies of jasperoid ranging from small nodules to masses 20 feet in diameter.
Jasperoidization is related to deposition of primary ore and gangue minerals. Local preservation of original carbonate bedding textures and fossils in jasperoid gives clear indication of its replacement origin. Angular inclusions of barite and sulfidebearing vein quartz in jasperoid matrix show that some silicification took place subsequent to sulfide mineralization. However, similar inclusions of dense fine-grained jasperoid in a matrix of coarse-grained jasperoid also show that there was more than one period of silicification. Primary ore and gangue minerals consisting of sulfides, barite, vein quartz, and carbonate were introduced by hydrothermal solutions moving upward along faults and fractures. The deposition of these minerals preceded renewed faulting and brecciation, which was followed by silicification in the form of jasperoid of both vein﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 103
1.	Cartersville
2.	Gold Hill
3.	Howie and Whitney
4.	Brewer
EXPLANATION
Area of large mining district
x
Minor district or area •
Reported occurrence
LIST	OF DISTRICTS, AREAS, AND OCCURRENCES
5.	Haile	8.	Eastern Tennessee
6.	Bumpass Cove	9.	Sweetwater
7.	Central Tennessee	10.	Austinville
Figure 41.—Map showing location of jasperoid-bearing areas in Georgia, North Carolina, South Carolina, Tennessee,
and southwest Virginia.
carbonate and wallrock carbonate (Kesler, 1950, p. 49-50).
Some jasperoids of the Cartersville district are thinly bedded and aphanitic, but most are massive and have a saccharoidal texture. The fresh rock is light to dark gray; but in the zone of alteration, and particularly in the residual clay, it is commonly heavily stained and colored by oxides of iron and manganese. Much of this weathered jasperoid consists of porous friable masses of ocherous quartz, coated with minute euhedral supergene quartz crystals; unweathered jasperoid does not contain these crystals. Coarse-grained massive jasperoid commonly contains angular breccia fragments of aphanitic jasperoid, and locally it also contains disseminated grains of pyrite, chalcopyrite, and tennantite. Coarser textured jasperoid replaced coarse vein carbonate; aphanitic jasperoid replaced carbonate host rock. Near the close of jasperoid deposition a late generation of crystalline barite, pyrite, and
hematite was locally deposited as crystals lining vugs in the jasperoid.
In thin section, jasperoid typically consists of minute anhedral interlocking grains of quartz, though locally the coarser textured variety faithfully preserves the form and even the cleavage of the coarse vein carbonate it replaced (Kesler, 1950, p. 48, pi. 13L>).
OTHER OCCURRENCES
Pardee and Park (1948, p. 131-140) described some lode gold deposits in Precambrian schists and associated felsic intrusive rocks in Lumpkin County in northern Georgia, in which the gold occurs in irregular veins and lenticular masses in silicified wall-rock. Both the schists and associated intrusives are locally replaced by, as well as impregnated with, silica; however, most of the quartz lodes appear to be fracture fillings rather than replacement bodies.﻿104 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
EXPLANATION
X
Minor district or area
Reported occurrence
Figure 42.—Map showing location of jasperoid-bearing areas in Idaho and Montana. 1, Bay-horse; 2, Challis; 3, Lemhi; 4, Skull Canyon;
5, Phillipsburg.
IDAHO
A search of the literature has failed to reveal any description of replacement bodies of jasperoid in the mining districts of Idaho, although the existence of such bodies in Paleozoic carbonate rocks of Custer County may be inferred from references in various reports. Umpleby (1917, p. 80) stated that the copper veins in Skull Canyon (4, fig. 42) near Mackay, are composed of heavily iron stained jaspery material enclosing irregular lenses and slabs of limestone and large bunches of hematite. Ross (1937, p. 101) wrote of the lead-silver replacement deposits in Custer County in the Bayhorse Dolomite near the town of Bayhorse (1, fig. 42): “Commonly the rock in and near the ore is more or less completely silici-fied, silicification being evidently one of the earliest and volumetrically one of the greatest effects of the mineralizing solutions.” In a report on fluorspar deposits in this same formation in Custer County near Challis (2, fig. 42), Anderson (1954, p. 11)
mentioned, but did not describe, silicified ledges of dolomite.
It seems logical that jasperoid should also occur with the lead and zinc replacement deposits in Paleozoic carbonate rocks in Lemhi County; however, the only “jasperoid” mentioned in association with ore deposits in Lemhi County (3, fig. 42) is in Precambrian quartzite of the Belt Supergroup. Sharp and Cavender (1962, p. 21, 22, 25, 40) discussed copper-gold-thorium vein and replacement deposits in micaceous quartzite associated with “dense brown jasperoid” formed by the silicification of hydrous iron oxide gangue.
ILLINOIS, IOWA, KENTUCKY, AND WISCONSIN
Three districts in which base-metal sulfide ore deposits are locally associated with jasperoid have been reported in the region that comprises Illinois, Iowa, Kentucky, and Wisconsin. (1) The upper Mississippi Valley zinc-lead district (3, fig. 43) in southwestern Wisconsin and northwestern Iowa, where zones of thin veins, breccias, and replacement deposits of sphalerite, galena, pyrite, and barite are found in carbonate rocks of Ordovician age. (2) The Kentucky-Illinois district (2, fig. 43), in northwestern Kentucky and adjacent parts of southeastern Illinois, in which many fissure veins and a few replacement deposits of fluorite are associated with sphalerite, barite, galena, and jasperoid in Mississip-pian carbonate rocks. (3) The central Kentucky mineral district (1, fig. 43), where barite, fluorite, and base-metal sulfide veins cut Ordovician limestone, and where breccia fragments of limestone in some of these veins are locally replaced by jasperoid.
UPPER MISSISSIPPI VALLEY DISTRICT (3, fig. 43)
Siliceous replacement of carbonate rocks in this district is confined to the sulfide ore bodies and the wallrock adjacent to them. Jasperoid is most abundant in dolomite of the Lower Ordovician Prairie du Chien Group. The overlying Ordovician St. Peter Sandstone has been locally silicified along major faults and fracture zones; the carbonate rocks of the Ordovician Platteville and Decorah Formations and the Galena Dolomite, above the St. Peter Sandstone, have been replaced by jasperoid to a much smaller degree than those of the Prairie du Chien Group, generally within, and adjacent to, the larger sphalerite ore bodies. Jasperoid is most prevalent along faults, shears, and shatter zones, extending outward from these channels along selected beds for short distances. In the Galena Dolomite, dark-gray pyritic jasperoid locally forms overgrowths on older﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 105
Figure 43.—Map showing location of large jasperoid-bearing mining districts in Illinois, Iowa, Kentucky, Wisconsin, and southeastern Missouri. 1, Central Kentucky; 2, Kentucky-Illinois; 3, Upper Mississippi Valley; 4, Southeastern Missouri.
sedimentary chert nodules in intensely mineralized areas. Silicified zones in the Platteville and Decorah Formations are notably more abundant in the southern part of the district than in the northern part. Where the larger reverse faults flatten along bedding planes, the wallrock is commonly replaced by jas-peroid in ore bodies. In such areas, as in the Tri-State district, all the lithologic units that are cut by the faults are replaced by gray or brown jasperoid
or by white “cotton rock,” but, unlike the Tri-State district, jasperoid is very abundant in only a few deposits.
Jasperoid is massive, dense, locally banded, brown or gray, and, because it commonly preserves both the color and texture of the host rock so faithfully, it can be distinguished from unaltered rock' only by its superior hardness. At one locality (the Hoskins mine), jasperoid preserves the original appearance﻿106 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
not only of the carbonate rocks but of interbedded carbonaceous shale as well. Thin sections of jasperoid show a grain-for-grain equal volume replacement of the host rock (Heyl, and others, 1959, p. 101-105).
KENTUCKY-ILLINOIS DISTRICT (2, fig. 43)
Jasperoid in western Kentucky was first reported by Smith (1905, p. 128, 139-140). He noted its replacement of limestone adjacent to fissure veins and of breccia fragments within the veins and concluded (p. 139): “This silicification of limestone by quartz is believed to be related to the process of fissure filling, and not to be a common characteristic of the limestones of the district.”
According to Fohs (1910, p. 382, 384), fluorite, barite, zinc, and lead veins and a few replacement deposits in Mississippian limestone are irregularly distributed through an area about 80 miles long, east and west, by about 50 miles wide, north and south. Most of the production from this district has come from mines in Caldwell, Crittenden, and Livingston Counties in Kentucky and in Hardin, Pope, and Saline Counties in Illinois. Jasperoid and fluorspar are associated both genetically and spatially with many of these deposits. The jasperoid and fluorspar probably were deposited penecontemporaneously, at least in part. In some localities, laminated limestone is replaced by alternating bands of jasperoid (or quartz) and fluorspar.
Hardin (1955, p. 24) estimated that 5-20 percent of the limestone within 10 feet of many of the veins had been replaced by cryptocrystalline quartz. He believed that this silicification largely preceded the deposition of fluorite.
The paragenesis of ore and gangue minerals from this district and the composition of their primary fluid inclusions have been studied by Hall and Friedman (1963). They believed that several recognizable generations of fluorite preceded the deposition of vein quartz and sulfides, which was followed by deposition of late fluorite, calcite, barite, and with-erite. They concluded (p. 902) that the fluids trapped in the early fluorite are mainly connate brines, that a water of different and possibly magmatic origin was introduced during the quartz-sulfide stage, and that the composition of the fluid returned to that of a normal brine during formation of the late gangue minerals.
Silicified breccia pipes and dikelike bodies are present near the center of Hicks dome, a broad structural dome in western Hardin County, 111. The host rock of these breccia bodies is cherty Devonian limestone, and in drill-core samples below the zone of
oxidation, the bodies consist largely of angular breccia fragments of chert and partly silicified host rock in a matrix of fine-grained iron-stained microcrystalline quartz, with accessory fluorite and apatite and minor sulfides. Locally, this breccia is slightly radioactive, although no uraniunuminerals have been recognized in it. The breccias are considered to be explosion breccias formed by the explosive venting of steam and hot gases possibly related to deeply buried igneous intrusive rocks (Brown and others, 1954; Bradbury and others, 1955, p. 1-8).
CENTRAL KENTUCKY DISTRICT
(1, %• 43)
This district covers an area of about 3,600 square miles extending from Owen and Henry Counties on the north to Lincoln County on the south and from Bourbon and Clark Counties on the east to Anderson and Mercer Counties on the west. This large area roughly follows the trend of the Cincinnati arch and is best developed near the Lexington dome.
Ore deposits within the district consist largely of fracture fillings in veins or of breccia-zone replacements along numerous faults and fractures. These deposits show a zonal arrangement outward from a central zone characterized by fluorite, calcite, and black sphalerite through a transition zone of fluorite, barite, calcite, and both light and dark sphalerite, to a broad peripheral zone of barite, galena, and light-colored sphalerite with little fluorite (Jolly and Heyl, 1964, p. 597, 605, 615). The host rocks for these deposits are of Ordovician age and consist largely of limestone.
Jasperoid is not abundant in the Central Kentucky district, but it does occur in a few of the breccia zones in the veins. Jolly and Heyl (1964) stated that gray jasperoid replaces breccia fragments of limestone and older ore and gangue minerals, and that this jasperoid is probably younger than most of the fluorite, barite, and sulfide minerals. They ascribed the origin of these deposits to hydrothermal solutions, mainly heated connate brines and a lesser magmatic solution fraction, ascending along faults from a deep-seated magmatic source centered beneath the Lexington dome.
MICHIGAN
The word “jasperoid” was originally coined by Spurr (1898) because of the resemblance of this rock to the Precambrian jasper of the iron formations in Michigan and Minnesota. Although the jasper beds of the iron formation are now considered by Huber (1959, p. 111-113) to be of syngenetic origin, some Precambrian dolomites in the Michigan iron ranges﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 107
have been extensively silicified in places, subsequent to their lithification. Leith (1925, p. 515-516) described silicified chert breccias in the upper part of the Randville Dolomite on the Menominee Range and in the upper part of the Kona Dolomite in the Marquette district of Marquette County in the Upper Peninsula (fig. 1). These siliceous replacements he ascribed to the action of silica-bearing ground water on residual chert rubble accumulating on an old erosion surface. However, Gair, Thaden, and Jones (1961, p. C79-C80), after a detailed study of silicifi-cation in the Kona Dolomite, concluded that the silicification was more probably caused by silicabearing solutions migrating laterally or upward along faults and fractures.
MISSOURI
Jasperoid is abundantly associated with bedded sulfide replacement deposits in the vicinity of Joplin, in southwestern Missouri. These deposits are within the big Tri-State district or province (2, fig. 36), which has been discussed previously in the present report. Copper, lead, and zinc sulfide deposits are also concentrated in southeastern Missouri, in St. Francois and Washington Counties; most of these are vein deposits in carbonate rocks of Cambrian and Ordovician age.
SOUTHEASTERN MISSOURI DISTRICT
(4, fig. 43)
The genesis of much of the silica in the carbonate host rocks for the sulfide deposits in this area is controversial. Buckley (1909, p. 51-52, 59-60) mentioned the association of lead deposits with pipelike, sheetlike, and lenticular chert bodies in dolomite beds of the Potosi, Bonneterre, and Gasconade Dolomites. These “chert” bodies in the Potosi he described as irregular crosscutting bodies of honeycombed chert with drusy quartz nodules. In describing the deposits of the Gasconade Dolomite, he (p. 60) wrote: “The horizons at which occur lens-like masses or pockets of chert have associated with them galena, blende, and barite.” Buckley (p. 225-226) concluded that both silicification and later sulfide deposition in the Potosi resulted from ground-water circulation in Pennsylvanian or pre-Pennsylvanian time. However, he (p. 225-233) attributed similar deposits in the Bonneterre Dolomite to metasomatic replacement of dolomite (by downward percolating solutions) in post-Pennsylvanian time.
Spurr (1926, p. 974) stated that these deposits in general are characterized by the lack of major gangue minerals or wallrock alteration, and he attributed their origin to the injection of a fluid sulfide
ore magma. However, he (p. 975) also stated that “silicification of wall rocks took place during the deposition of the original sulphides.”
Ohle and Brown (1954, p. 219-221), in a paper on the lead deposits of the main Southeast Missouri district, ascribed the origin of the ore to aqueous fluids that rose from a deep source and migrated laterally along favorable structures. However, they did not mention silicification in their discussion of wallrock alteration. Brown (1958, p. 6-7) proposed that hot mineralizing fluids rose from an igneous basement along favorable structures and spread laterally; then, as these fluids cooled and mingled with ground water, they changed to downward-moving mineralizing solutions that deposited the ore. Heyl, Delevaux, Zartman, and Brock (1966, p. 952) mentioned a marked similarity in isotopic composition of lead derived from two galena samples in this area, one from an alkalic peridotite dike and the other from a bedded replacement ore body in dolomite.
The Cornwall copper mines, in Madison County near the east edge of this district, have been described by Rust (1935). They are mostly copper-iron-zinc sulfide deposits in pockets and lenses along favorable stratigraphic zones in massive Ordovician dolomites. Solution of the dolomite preceded ore deposition. The remaining pillars between these solution cavities locally collapsed forming “crush breccias” ; the dolomite in these breccias was then replaced by silica to form a dense aphanitic rock containing abundant angular breccia fragments of primary chert. The sulfides were then deposited in the remaining open cavities as colloids by far-traveling hydrothermal solutions contaminated with ground water.
Although there is considerable argument as to the origin of the base-metal sulfide and barite deposits of southeastern Missouri, there seems to be general agreement that bodies of silica replacing carbonate rocks are associated, both spatially and genetically, with many of them.
MONTANA
I know of only one mining district in Montana that is characterized by the development of jasperoid; this is on the west flank of the Flint Creek Range near Philipsburg in Granite County, about 50 miles northwest of Butte. The Philipsburg (or Flint Creek) mining district and several smaller districts are in this area. There probably are other jasperoid-bearing areas in the State, but they are not described in the literature. Much of the following data on the﻿108 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Philipsburg district is from W. C. Prinz (written commun,, 1967; 1967, p. 2-10).
PHILIPSBURG DISTRICT (5, fig. 42)
The Philipsburg district has yielded $70 million in base and precious metals from steeply dipping quartz veins in Tertiary granodiorite and intruded Pre-cambrian rocks and Paleozoic limestone, shale, and quartzite and from quartz-rich bedding veins in Paleozoic limestone. In addition, the district has produced substantial amounts of manganese oxide ore that was derived from the weathering of primary manganese carbonate replacement deposits in Paleozoic limestone and marble.
Two types of favorable jasperoid are recognized in the district, but nowhere is jasperoid abundant. One type is associated with primary manganese and vein deposits and is most abundant in the manganese deposits, where it consists of light- to medium-gray or greenish-gray silicified limestone that is commonly brecciated and cemented by rhodochrosite and manganoan dolomite. In a few places jasperoid also occurs along the borders of steeply dipping quartz veins where they cut carbonate rocks. Some of this jasperoid is brown, probably owing to admixed very fine grained sphalerite.
The second type of jasperoid in the Philipsburg district is associated with the oxidized manganese deposits. Medium- to dark-gray silicified limestone occurs locally along the borders of these deposits and in remnants, veinlets, or cavity fillings within the deposits. That some jasperoid fills cavities in manganese oxides shows that it is, at least in' part, supergene in origin.
Emmons and Calkins (1913, p. 68-69) also referred to the prevalence of abundant irregular masses of “chert” in the upper part of the Madison Limestone along Flint Creek 6 miles south of Philipsburg and to one large mass of this “chert” nearly 100 feet thick along a fault that forms the contact between Madison Limestone and Precambrian rocks, near the mouth of Boulder Creek 8 miles north of Philipsburg. The mass along Boulder Creek, they said, is probably the result of silicification along the fault zone. The irregular masses of “chert” in the upper part of the Madison they described as consisting chiefly of fine-grained cryptocrystalline quartz in allotriomorphic grains, mixed with some carbonate. From these descriptions it seems probable that much of the “chert” in the Madison is really unfavorable jasperoid.
NEVADA
Information is available on jasperoid bodies in at least 33 mining districts in Nevada besides the Ely (Robinson) (19, fig. 44) and Eureka (20) districts, which are previously described in this report. Silicified rocks that are probably jasperoid also have been noted, but not described, in another 20 districts (fig. 44). These districts are scattered throughout most of the State east of long 118° W. and north of lat 37°30' N., but they seem to be most concentrated in two provinces. One province comprises most of Eureka and White Pine Counties as well as parts of Elko, Lander, and Lincoln Counties in eastern and north-central Nevada, and it extends eastward into Utah. A second province comprises Esmeralda County and the eastern part of Mineral County in southwestern Nevada, and it extends southward into California.
In most of these districts, jasperoid is associated with either silver-bearing or non-silver-bearing base-metal replacement deposits in Paleozoic carbonate rocks and in felsic volcanic rocks. The jasperoid in these districts generally is localized by faults or fracture zones that also served as conduits for the ore-stage mineralizing solutions, and in many districts it also seems to be related to intrusive siliceous dikes and stocks. The Atlanta (2, fig. 44), Delmar (14), and Getchell (23) districts are mainly gold producers; Boyer (5) is a nickel-cobalt district; in the Cortez district (12) antimony, silver, and gold are abundant; the Manhattan district (34) produced gold, arsenic, and antimony; and the Taylor district (47) produced antimony, lead, and silver.
ATLANTA DISTRICT (2, fig. 44)
The Atlanta mining district lies close to the Utah border in northeastern Lincoln County about 40 miles northeast of Pioche. Silicified pipes, faults, and fracture zones in Ordovician limestone and dolomite were mined for gold and silver in the early part of the 20th century, and small silicified pods containing uranium were developed during the 1950’s (Hill, 1916; Sharp and Myerson, 1956).
Hill (1916, p. 116-117) mentioned prominent bodies of jasperoid along a north-trending fault zone in the vicinity of the Atlanta mine, and argentiferous red jasper bodies in quartzite at the Bradshaw mine about a mile south of Atlanta. According to Sharp and Myerson (1956, p. 10), breccia pipes and fault zones in dolomite overlying the quartzite are extensively silicified into drusy quartz and jasperoid in the area of mineralization, and some of the silicified pipes contain gold, silver, and uranium minerals﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 109
LIST OF DISTRICTS, AREAS, AND OCCURRENCES
EXPLANATION
•
Major district x
Minor district or area •
Reported occurrence
Jasperoid province
1. Antelope	15. Diamond	29. Kingston	43. Silverhom
2. Atlanta	16. Dolly Varden	30. Klondike	44. Silver Peak
3. Bald Mountain	17. Duck Creek	31. Lewis	45. Spruce Mountain
4. Belmont	18. Dyer	32. Lida	46. Success
5. Boyer	19. Ely (Robinson)	33. Lone Mountain	47. Taylor
6. Candelaria	20. Eureka	34. Manhattan	48. Tecoma
7. Cedar Mountain	21. Ferguson	35. Mill Canyon	49. Ward
8. Chief (Caliente)	22. Fireball	36. Mineral Hill	50. West Ward
9. Cherry Creek	23. Getchell (Potosi)	37. Mount Hope	51. White Pine (Hamilton)
10. Columbia	24. Gilbert	38. Mud Springs	52. Willow Creek
11. Contact	25. Gold Banks	39. Nevada	53. Wyndypah
12. Cortez	26. Goodsprings	40. Patterson	54. Yerington
13. Delano	27. Groom	41. Santa Fe	
14. Delmar	28. Kern	42. Sheba-De Soto	
Figure 44.—Map showing location of jasperoid-bearing areas in Nevada.﻿110 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
disseminated in the jasperoid. At the Atlanta mine, breccia fragments of limestone, quartzite, rhyolite, and jasper are cemented by quartz containing gold and silver minerals, manganese oxides, limonite, and barite'. Northeast-trending reefs of red jasperoid east of the Atlanta mine contain some low-grade gold ore (Hill, 1916, p. 117).
BALD MOUNTAIN DISTRICT (3, fig. 44)
The Bald Mountain district is in the northwest corner of White Pine County, near the south end of the Ruby Range and about 60 miles northwest of Ely. Ordovician limestone is here intruded by a quartz monzonite stock. Sulfide deposits form replacement ore bodies in the limestone and vein ore bodies in the stock and its aureole of lime-silicate rock. Some of the ore bodies in the limestone consist of pockets of copper carbonate in jasperoid (Hill, 1916, p. 159-160).
Four jasperoid samples from this district are included in my collection; one of these is from a shaft dump, the other three are from outcrops a few hundred feet, a quarter of a mile, and half a mile from the nearest mine workings. The dump sample consists of medium-gray aphanitic jasperoid which is cut by veinlets of brown limonite and which contains sparse small vugs filled with white clay. The other three samples are jasperoid breccias in which both breccia fragments and matrix are dense and aphanitic. The fragments are shades of gray, and the matrix is yellowish brown, moderate brown, or reddish brown, locally banded and streaked.
In thin section the sample from the mine dump consists of heterogeneous xenomorphic quartz that has an average grain diameter of about 0.03 mm. It contains locally abundant carbonate particles and sparse scattered grains of pyrite and zircon. Two of the outcrop samples, taken from breccia zones, contain fragments of jasperoid similar to those in the dump sample, as well as aphanitic cherty fragments, and masses of feathery-textured jasperoid (apparently derived from chalcedony). The matrix has texture and grain size similar to those of the older jasperoid fragments. It is heavily loaded with dustsized particles of brown limonite and carbonate, and also contains abundant inclusions of a pale-yellowish mineral with low anomalous birefringence, which is probably one of the chlorite group. The matrix is cut locally by jarosite veinlets. The remaining outcrop sample consists of dense cherty-looking quartz containing abundant tiny particles of brown limonite, goethite, and sericite. This matrix has been shattered, and the fractures have been filled with a mixture
of limonite, goethite, cryptocrystalline apatite, and kaolinitic clay in various proportions.
All four samples are slightly richer than average in copper, nickel, and zirconium. One of the outcrop samples from a breccia zone contains detectable amounts of the rare-earth elements cerium, lanthanum, yytrium, and ytterbium as well as arsenic, molybdenum, and vanadium. The sample last described above, which is the farthest from mine workings, contains abundant phosphorus and strontium as well as detectable amounts of gallium, scandium, vanadium, yttrium, and ytterbium. None of the samples scored higher than +10 on their indicator elements, and the dump sample scored only +5.
BOYER DISTRICT (5, fig. 44)
The Boyer district is in northeastern Churchill County, about 30 miles southeast of Lovelock. Nickel and cobalt ore occurs here in small veinlets cutting quartzite and silicified limestone near an intrusive body of diorite (Ferguson, 1939, p. 8, 12). Within the partly silicified limestone are conspicuous bodies of dense white silica that may be either bleached chert or jasperoid. Silicification of the limestone in and around the Nickel mine in Cottonwood Canyon was specifically mentioned by Ferguson (p. 17, 20), but, unfortunately, no description or analysis of this jasperoid was included in his report.
CANDELARIA DISTRICT (6, fig. 44)
Candelaria is about 50 miles west of Tonopah in southeastern Mineral County. Deposits of gold, silver, lead, and zinc are present here in veins cutting highly altered Ordovician, Permian, and Triassic rocks, which originally consisted predominantly of shale and a few thin beds of carbonate rocks and sandstone. Within the mineralized area the shale has been intensely silicified, sericitized, argillized, carbonatized (Page, 1959, p. 21, 44-46), and stained gray and black by manganese. The most extensive alteration in the area is carbonatization, which has converted large volumes of argillite and associated fine-grained metadolorite intrusive rock to a dense fine-grained grayish-white hydrothermal dolomite. Bodies of jasperoid resembling fine-grained quartzite nearly everywhere form prominent outcrops associated with the hydrothermal dolomite. These jasperoid bodies are particularly conspicuous near the Lucky Hill mine.﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 111
CEDAR MOUNTAIN DISTRICT (7, %. 44)
Cedar Mountain is in eastern Mineral County about 20 miles northeast of Mina. Triassic limestones and interbedded quartz keratophyres have been intruded by granodiorite, which is cut by dikes of aplite, lamprophyre, alaskite porphyry, and dio-rite porphyry. Replacement deposits of argentiferous galena and sphalerite are encased in a dark-gray fine-grained jasperoid replacing limestone adjacent to dikes and fractures. These latter have been cut and offset in places by postmineral faults (Knopf, 1922, p. 370-373).
CHERRY CREEK DISTRICT (9, fig. 44)
Cherry Creek is in northern White Pine County, about 30 miles east of the Bald Mountain district (3) and 40 miles north of Ely, at the south end of the Cherry Creek Range. The ore deposits of the district consist largely of fissure veins of lead, zinc, and silver in lower Paleozoic quartzite and shale and in small bodies of quartz monzonite that locally intrude these rocks. Contact-metamorphic bodies of scheelite were mined in the 1950’s. A few manto-type replacement deposits of base and precious metals have also been developed in the northern part of the district in a massive lower Paleozoic limestone over-lying the shale, and it is with these deposits that jasperoid is associated. The geology and ore deposits of the Cherry Creek district have been summarized by Hill (1916, p. 161-172) ; however, most of the ore deposits in limestone have been developed since that report was written. The only mine of this type described by Hill is the Biscuit mine, of which he (p. 166) stated that lenslike bodies of white quartz occur in limestone, and these lenses locally contain disseminated particles of a soft black metallic silver mineral.
I have five jasperoid samples from the Cherry Creek district, taken from localities in the limestone north and west of the mines described by Hill (1916). Three are from outcrops adjacent to mine workings, one is from the dump of a prospect pit, and one is from a breccia zone along a gently dipping fault near a small quartz monzonite dike, about half a mile from the nearest mine workings. All five jasperoid bodies sampled appear to have been localized by breccia zones along faults in the limestone.
Three distinct ages and types of quartz are distinguishable in jasperoids from this district. The oldest of these is dark gray and dense, and has a homogeneous xenomorphic texture, an average grain
size of about 0.02 mm, and abundant tiny inclusions of sericite and hematite. This type is cut by, and locally forms inclusions in, a light- to medium-gray compact coarse-grained jasperoid that has a heterogeneous, strongly reticulated texture and a grain diameter that averages about 0.1 mm and ranges from 0.01 to 1 mm; it contains abundant carbonate particles locally concentrated in the cores of the larger grains. This type commonly contains relict inclusions of coarse crystalline calcite. The youngest generation of quartz has a coarse xenomorphic texture, an average grain diameter of about 0.2 mm, and sparse local concentrations of allophane dust. It fills veinlets cutting the older jasperoid and commonly lines sparse small vugs.
The two types of jasperoid were not analyzed separately, and therefore, no comparison of their chemical composition is possible. Analyses of the five whole-rock samples show that most are anomalously high in Ag, Pb, and Zn, as well as Ca, Mg, and Sr. The high concentration of Ca, Mg, and Sr reflects the abundance of calcite in the samples. Silver (lead, and zinc) may be useful indicator elements in jasperoids of the Cherry Creek district; all four samples taken in the vicinity of mine workings are anomalously high in silver, which was not detected in the sample taken half a mile from the nearest mine.
CONTACT DISTRICT (11, fig. 44)
The Contact district is in northeastern Elko County about 15 miles south of the Idaho State line and 40 miles west of the Utah State line. The ore deposits consist of copper oxides and carbonates in replacement deposits and veins cutting Paleozoic limestone close to the contact with a small granodiorite stock. Limestone adjacent to the intrusive contact is metasomatized to a lime-silicate skarn, but beyond this contact zone, jasperoid is abundant. Schrader (1912, p. 118, 121, 130, 137) spoke of conspicuous bodies of silicified limestone in the Blue Bird, Brooklyn, Queen of the Hills, Ivy Wilson, and War Eagle mines. Some of this jasperoid he described as light colored and fine grained, resembling quartzite, and some as blue and chloritic. Both silicification and ore mineralization in the district seem to be genetically related to the intrusion of the stock.
CORTEZ AND MILL CANYON DISTRICTS (12 and 35, fig. 44)
The old mining districts of Cortez (12) and Mill Canyon (35) straddle the county line between Eureka and Lander Counties, a few miles north of the﻿112 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
40th parallel and about 40 miles south-southeast of Battle Mountain. The Cortez district is just south of Mount Tenabo, a prominent peak at the south end of the Cortez Range; the Mill Canyon district is on the northern flanks of Mount Tenabo.
The geology and ore deposits of these two districts have been surilmarized by Emmons (1910, p. 100-108), and the general geology of the area is discussed in more detail by Gilluly and Masursky (1965). Emmons reported that the ore bodies of the Cortez district consist of irregular bedded replacement deposits in Paleozoic limestone. These deposits are localized by northeast-trending fractures, and consist of galena, sphalerite, stibnite, stromeyerite, tetra-hedrite, and other arsenic antimony sulfosalts, associated with pyrite and calcite, in a siliceous (jasperoid) matrix. A number of small silver deposits in jasperoid were mentioned “on the trail between Cortez and Mill Canyon.” In the Mill Canyon district argentiferous base-metal sulfide deposits in a siliceous gangue are localized by the intersection of fractures with favorable beds in limestone close to its contact with an intrusive granodiorite stock.
A few miles west of the Mill Canyon district, the Roberts Mountain thrust fault brings Ordovician siliceous shale and chert in the upper plate over Silurian shale and Devonian limestone in the lower plate. Both upper and lower plates are broken by high-angle normal faults and are intruded by small dikes and lenticular masses of Tertiary felsic plu-tonic rocks. Geochemical mapping of altered rocks close to these faults and intrusive masses in both upper and lower plate rocks has defined pronounced copper, lead-zinc-silver, arsenic, bismuth, and manganese anomalies in the siliceous rocks of the upper plate close to the trace of the thrust fault and gold, arsenic, antimony, and tungsten anomalies in the carbonate rocks of the lower plate adjacent to a strong northeast-trending normal fault (Erickson and others, 1961, 1964b).
Thirteen samples of jasperoid are included in the suite from the lower plate rocks collected and analyzed by Erickson and his colleagues (1964a). Most of these samples contain anomalously high concentrations of As, Ba, Sb, and Zr, and many of them are also high in B, Be, V, and W. Only five of the 13 samples score as possibly or probably favorable on the basis of their indicator-element concentrations. Only two of these samples were described as conspicuously vuggy, and these two yielded the highest scores, +12 and +9, respectively. Four of the five jasperoid samples scoring +5 or higher came from close to the strong northeast-trending fault in the area with the strongest geochemical anomaly
(Erickson and others, 1964b, p. B93). Although no gold assays are reported on these samples, the recent discovery of a large low-grade gold ore body in the area suggests that gold is also present.
DELMAR DISTRICT (14, fig. 44)'
The Delmar district is in south-central Lincoln County about 40 miles southwest of Pioche. Most of the production from the district has been of gold ore from veins and breccia zones in the Lower Cambrian Prospect Mountain Quartzite; however, evidence of mineralization is also found in Middle Cambrian shale and limestone above this quartzite (Callaghan, 1937, p. 33, 40, 45-49).
The quartzite breccia fragments are commonly cemented and partly replaced by fine-grained vuggy ore-bearing silica, and some limestone beds in the thick shale units have been completely replaced by jasperoid in places. The thick Middle and Upper Cambrian Highland Peak Formation has locally been converted to aphanitic dark-gray jasperoid along faults and breccia zones in the southern part of the district, particularly near the wash northeast of Big Lime Mountain (Callaghan, 1937, p. 45). A small body of rhyolite on the Jumbo claim has been completely replaced by silica with preservation of the original quartz phenocrysts.
DOLLY VARDEN DISTRICT (16, fig. 44)
The Dolly Varden district is in southeastern Elko County in a small group of mountains at the south end of Goshute Valley about 35 miles southwest of Wendover. The general geology and ore deposits of the area were summarized by Hill (1916, p. 76-88).
A small quartz monzonite stock in the northern part of the district is in intrusive contact with Carboniferous shale and limestone near the center of the district. These sedimentary rocks form the bedrock in the rest of the district, south and east of Dolly Varden Pass. Close to the edge of the intrusive these rocks have locally been contact metasomatized to skarn, hornfels, and white marble. In the southeastern part of the district, around Castle Peak, the unmetamorphosed sedimentary rocks consist of a thick section of medium-bedded limestone overlain by calcareous and cherty shale and argillite. Oxidized copper ore bodies are associated with lime-silicate rocks near the intrusive, and bedded replacement lead deposits occur in limestone in the southeastern part of the district.
Hill (1916) mentioned a prominent iron-stained siliceous outcrop containing copper carbonate on the﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 113
Hidden Treasure claim in limestone south of Watson Spring. He also mentioned a jasperoid body on the Victoria claim in Watson Canyon west of Watson Spring, of which he (p. 86) wrote: “The croppings, iron-stained cellular quartz and jasper, with some copper carbonates, stand about 10 feet above the surrounding country and cover an area about 100 feet long north and south by 75 feet wide.” The ore on this property consists of secondary copper minerals in iron-stained silicified limestone containing abundant tremolite.
Three samples of jasperoid from the Dolly Varden district are included in my collection. One of these samples is from an outcrop close to the Victoria mine shaft, probably the same one described by Hill (1916) ; the other two are from outcrops adjacent to old mine workings in the lead-bearing southeastern part of the district on both sides of Spring Canyon north of Castle Peak.
The sample from the outcrop near the Victoria mine shaft looks barren in the hand specimen. It is aphanitic and dark red to reddish brown on fresh surfaces and weathers almost black. It consists of heterogeneous matrix quartz that has xenomorphic to jigsaw-puzzle texture and a grain diameter that ranges from 0.01 to 0.15 mm and averages 0.03 mm, and it contains abundant disseminated grains and interstitial masses of red hematite. The brown areas consist of irregular ragged quartz particles disseminated through a mixture of hematite and orange goethite. Spectrographic analysis of this sample, however, belies its unpromising appearance. It contains abundant copper (0.15 percent) and is also anomalously high in Fe, Bi, In, Mo, Ni, and V. The concentrations of indicator elements in the sample yield a score of +15, which places it in the highly favorable category.
One of the two remaining samples, from the dump of a prospect pit, appears to be a silicified siltstone; the other is from a jasperoid outcrop in limestone close to the collars of two adjacent inclined shafts. These samples are similar in appearance but are strikingly different from the sample previously described. They are light gray, yellowish gray, brownish gray, and aphanitic, and they contain local porous areas honeycombed with microvugs. Both are fractured though not brecciated, and the fractures are coated with brown limonite and, locally, with green copper stains.
The dump sample has a matrix of rounded quartz grains and sparse accessory tourmaline, zircon, sphene, and hematite. This matrix is cut by veinlets rimmed with fibrous chalcedony and commonly filled with coarse jigsaw-puzzle-textured quartz. Thin
veinlets of orange goethite cut the chalcedony quartz veinlets, and goethite is also disseminated through the matrix in scattered equant grains that look to be pseudomorphous after pyrite.
The outcrop sample has a granular to xenomorphic heterogeneous matrix whose grain diameter ranges from <0.01 to 0.1 mm and averages 0.03 mm. Small barite crystals and an unidentified aphanitic yellow mineral with low birefringence and indices of refraction greater than quartz but less than those for barite form abundant inclusions in the matrix, which also contains sparse hematite and goethite pseudomorphs after original pyrite. Small irregular open vugs are moderately abundant in the finer grained matrix quartz.
The dump sample of silicified siltstone is high in B and moderately high in Fe, Na, Be, Cr, Mo, Pb, Sc, Sr, V, and Zr. The outcrop sample of jasperoid is high in Ag and moderately high in B, Bi, Pb, and Sr. Both samples yielded a score of +9 for their indicator elements.
The indicator elements present in these favorable jasperoid samples faithfully reflect the nature of the ores with which they are associated. The sample from the copper mine in the central part of the district is high in copper and its associated minor elements indium, molybdenum, and nickel but low in lead and silver; whereas the samples from the southeastern part of the district are high in lead and silver but low in copper, indium, molybdenum, and nickel. All samples are moderately high in bismuth.
DYER DISTRICT (18, fig. 44)
The Dyer district is in western Esmeralda County close to the California State line and about 45 miles west of Goldfield. Little information has been published about the geology and ore deposits of this small district, which has long been abandoned. Spurr (1906b, p. 84-85) mentioned the occurrence here of replacement deposits of siliceous black argentiferous copper sulfide ore along bedding-plane faults in lower Paleozoic limestone; he also referred to small irregular pods of jasperoid scattered abundantly through this limestone.
FERGUSON DISTRICT (21, fig. 44)
A group of small abandoned mines and prospects, just west of U.S. 50 Alternate Highway at Ferguson Springs, Elko County, Nev., about 25 miles south of Wendover, and 7 miles west of the Utah State line, constitutes the Ferguson district. In a brief summary of this district, Hill (1916, p. 97-98) stated that﻿114 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
mineralization is concentrated in Paleozoic limestone along an east-trending fracture zone. The ore consists of irregular replacement deposits of barite and limonite, locally stained with copper carbonate. He mentioned the occurrence of large bodies of dark chert in the limestone but said nothing about silicifi-cation related to the mineralization.
Three samples collected from this district consist of aphanitic gray slightly vuggy jasperoid or jas-peroid breccia fragments in a yellowish-brown siliceous matrix with similar texture; the rock weathers yellowish brown or dark brown. Both the older j asperoid quartz and the younger matrix quartz have a slightly heterogeneous xenomorphic texture and an average grain diameter of about 0.02 mm. The older jasperoid contains sparse detrital grains of tourmaline and sphene and local concentrations of carbonate particles. The matrix quartz is heavily clouded with yellow limonite dust, and it contains abundant shreds of sericite. Vugs in both older jasperoid and matrix are largely open, though a few are lined with calcite, which also fills late fractures cutting the matrix. These samples are all slightly high in Ba, Sr, and Zr, and one sample, taken at a prospect pit, also is slightly high in B, Ga, Ni, and V. All three samples yielded indicator-element scores of —1.
GETCHELL MINE AREA (POTOSI DISTRICT)
(23, fig. 44)
The Getchell mine is at the northeast end of the Potosi district on the northeast flank of the Osgood Mountains, in Humboldt County, about 30 miles northeast of Winnemucca. In this area Cambrian shale and argillite with some interbedded limestone have been intruded by a granodiorite stock of Cretaceous age. A strong steeply eastward-dipping fault zone strikes northerly along the east base of the range in the sedimentary rocks. Gold deposits of the Getchell mine are largely concentrated along sheeted zones in black shale within this fault zone. Much arsenic and some mercury are associated with the gold ore (Erickson, Marranzino, Oda, and Janes, 1964, p. A2-A4). Tungsten has been mined in the mountains west of the fault, in tactite zones adjacent to the granodiorite stock (Hobbs and Clabaugh, 1946).
Jasperoid bodies are exposed in Paleozoic rocks on the east side of the fault. One such occurrence is in limestone of Permian and Pennsylvanian age about a quarter of a mile east of the northern workings of the Getchell mine, and another is in interbedded argillite and limestone of Ordovician age about 2 miles south of the southern workings of the mine.
The jasperoid replaces the country rock along
small shears and fractures. It is commonly brecciated and heavily stained on the outcrop in various shades of yellow, brown, and red. Analyses of four samples of jasperoid from the northern area and 11 from the southern area (by Erickson and others, 1964, tables 2, 4, 5) show that most of the jasperoid samples from the northern area are anomalously high in As, Ba, Pb, and Zn, and that most of the samples from the southern area are anomalously high in As, B, Ba, Sr, and W. All samples from the northern area yield favorable scores. Four from the southern area would be classified as favorable, four as possibly favorable, and three as barren.
GILBERT DISTRICT (24, fig. 44)
The Gilbert district is in northern Esmeralda County, about 20 miles northwest of Tonopah, at the east end of the Monte Cristo Mountains. Tertiary volcanic rocks cover most of the district, but older rocks are exposed in the vicinity of the Carrie mine in the northwestern part of the district. These older rocks consist of massive crystalline limestone, of probable Ordovician age, interbedded with a little dark shale and tuff and intruded by dikes of quartz monzonite. The limestone has been silicified near the dikes to form prominent jasperoid “ledges” cut by abundant quartz veins (Ferguson, 1928, p. 130, 138).
At the Carrie mine silver-bearing base-metal sulfide deposits formed in these quartz veins. Ferguson (1928) noted that the jasperoid contains sericite and epidote, and that the ratio of epidote to quartz increases with distance from the dikes. In his description of the Carrie mine, Ferguson (p. 139) stated:
The silicified wall rock is texturally the equivalent of the jasperoid ledges which occur in the district. The vein locally includes a considerable proportion of this jasperoid in relations that suggest a gradation between the replaced limestone cut by later veinlets of crystalline quartz and the massive quartz veins themselves.
The jasperoid and its associated quartz veins are older than the Tertiary volcanic rocks.
GOODSPRINGS DISTRICT (26, fig. 44)
Jasperoid has been reported in the Goodsprings district by Albritton, Richards, Brokaw, and Reine-mund (1954, p. 25-26), and was described under other names by Hewett (1931). This district is in southwestern Clark County, close to the California line and about 35 miles southwest of Las Vegas. Mississippian limestone in the district has been cut by numerous faults and fractures that controlled the mineralizing solutions that formed base-metal﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 115
sulfide deposits as both replacements and veins. Jas-peroid is not abundant in this district. Hill (1914) did not mention it, and, in fact, he (p. 246) stated that most of the limestone replacement deposits in the district are characterized by absence of gangue minerals. Hewett (1931, p. 57) noted that, although silicification is not a conspicuous feature of the district, “ferruginous chert” is abundant in some mines, and that Yellow Pine, Double Up, Boss, and John mines contain appreciable silica related to ore deposition. Although Hewett did not refer to either of these rocks as jasperoid, his description clearly indicates that the ferruginous chert corresponds to supergene jasperoid and that the silica related to ore deposition corresponds to hypogene favorable jasperoid.
Hewett (1931, p. 83) described a dense, opaque, yellowish-brown to dark-brown ferruginous chert, associated with limonite and jarosite, which is locally abundant at and near the surface and grades downward into cream-colored chert containing scattered quartz grains. This variety forms veinlike masses replacing shale or dolomite, and is absent at depths of 100-250 feet below the surface. The origin of this “chert” is ascribed to the action of circulating surface water.
Hewett also referred to masses of cavernous gray quartz, exposed in some copper and silver mines, that is composed of interlocking grains that are 0.05-0.2 mm in diameter and that contain minute inclusions of octahedrite and rutile, and of cavities filled with a white powder consisting of tiny doubly terminated quartz crystals. He described hypogene silicification of dolomitic wallrock at the Double Up and Pilgrim mines resulting in veinlets and poorly defined areas of quartz that in part replace and in part fill cavities in the dolomite. A broad fracture zone at the Double Up mine contains lenses of dark fine-grained quartz as much as 35 feet long, 20 feet wide, and 5 feet thick bordered by a porous limonitic zone. A similar mass forms a lenticular pipe which is the main ore body at the Boss mine. This pipe consists of dark coherent cellular masses composed of interlocking quartz grains that are 0.03-0.1 mm in diameter, interspersed with white crystalline quartz powder, surrounded by an envelope of limonite that grades outward into dolomite impregnated with copper carbonates. Assays of the dark cellular quartz in the core of this pipe yielded as much as 12 oz Au, 11 oz Ag, 7 oz Pt, and 4.5 oz Pd per ton (Hewett, 1931, p. 82, 109, 115-116).
Albritton and his colleagues (1954, p. 25-26) reported jasperoid near the Yellow Pine and Prairie Flower mines. These two mines are on the east slope of Shenandoah Peak in the Spring Mountains near
the center of the district. In this area the limestone has been intruded by irregular dikes and sills of quartz monzonite porphyry and extensively altered by hydrothermal solutions. The limestone is dolomi-tized and silicified. Silicified zones are generally parallel to the bedding and range from a fraction of a foot to 25 feet in thickness. Within these zones the jasperoid in part preserves the original color and texture of the limestone, and in part consists of irregular gray, black, and brown cherty lentils and pods. Veins of brown “chert” follow many fractures and faults (Albritton and others, 1954, p. 25-26).
GROOM DISTRICT (27, fig. 44)
The Groom district is in southwestern Lincoln County, about 75 miles west-southwest of Caliente and 35 miles west of Alamo. The district is in a downfaulted block of Cambrian shale and limestone; the internal structure of this block is complex. Replacement deposits, which consist largely on argentiferous galena, occur both along fractures and as mantos in the limestone (Humphrey, 1945, p. 9, 17, 32). This limestone is commonly silicified along faults and fractures in the vicinity of the ore bodies.
KERN DISTRICT (28, fig. 44)
Hill (1916, p. 207) mentioned the occurrence of jasperoid in Water Canyon about 12 miles southeast of Tippett, near the south end of the Kern Mountains in northeastern White Pine County. Dark-blue Paleozoic limestone has been replaced by lenticular masses of quart?, parallel to the bedding near the contact of the limestone with an intrusive granitic stock. The jasperoid quartz locally contains hematite, and some of it is coated with yellow cerussite along fractures.
LEWIS DISTRICT (31, fig. 44)
The Lewis district is near the north end of the Shoshone Range in northeastern Lander County, about 12 miles southeast of Battle Mountain. Paleozoic quartzite and limestone in this area have been intruded by granodiorite porphyry of Laramide age. The ore deposits consist of pyritic gold-quartz veins in the intrusive rocks and quartzite and of base-metal sulfide replacement bodies in the limestone. One of these replacement deposits, at the Starr Grove mine, contains disseminated sulfides in a siliceous baritic gangue. Emmons (1910, p. 126) stated that the main ore body is a large tabular-bedded replacement body in dark-gray limestone overlain by massive quartzite.﻿116 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
This body consists of barite and quartz with disseminated pyrite, galena, and sphalerite. The barite is older than both quartz and sulfides, as shown by the fact that breccia fragments of barite occur in a matrix of quartz with disseminated sulfides. From Emmons’ brief description, it cannot be ascertained whether the quartz gangue in this deposit is a true replacement jasperoid or whether it consists only of vein quartz filling fractures and cavities in an older barite body.
MANHATTAN DISTRICT (34, fig. 44)
The Manhattan district is in the southern part of the Toquima Range in northwestern Nye County, about 35 miles north of Tonopah. Fissure veins and replacement deposits in Cambrian limestone have been mined for gold, arsenic, and antimony. The following description is taken from Ferguson’s report (1921) on the geology and ore deposits of this district.
The ore-bearing limestone beds are concentrated near the bottom and near the top of a thick section composed mostly of micaceous schist with some in-terbedded lenticular sandstones and quartzites. These Cambrian rocks are overlain by about 400 feet of Ordovician schists, and these schists, in turn, by a similar thickness of dark-gray thin-bedded barren limestone containing abundant black to dark-gray jasperoid. The main ore bed, known locally as the “White Caps limestone,” is cut by a number of closely spaced preore normal faults, some of which show postore movement. These faults were the conduits for mineralizing solutions that formed replacement ore bodies in the limestone.
The earliest gangue mineral is coarse white cal-cite, which was followed by dark-gray fine-grained jasperoid that replaced both the early calcite and the limestone host rock in the immediate vicinity of the ore bodies. Muscovite and fine-grained auriferous pyrite and arsenopyrite formed penecontemporane-ously with this jasperoid and are disseminated through it. Younger stibnite and realgar replace coarse calcite and, to a lesser extent, the jasperoid.
Numerous lenticular vugs, elongated parallel to the bedding of the host rock, are present in the jasperoid, and many of these are encrusted with one or more of the following minerals: quartz, calcite, dolomite, fluorite, stibnite, pyrite, orpiment, and realgar. The dark-gray to black color, characteristic of the jasperoid in this district, is caused by abundant carbonaceous particles disseminated through it. In some places, jasperoid has been brecciated by postore movement on the faults. The deposits of this
district were considered by Ferguson (1921, p. 34) to be of probable Tertiary age and to have formed at shallow depth.
MINERAL HILL DISTRICT (36, fig. 44)
The Mineral Hill district is on the west side of the Pinyon Range in east-central Eureka County, about 50 miles south-southwest of Elko. According to Emmons (1910, p. 95-99), argentiferous base-metal sulfides form replacement deposits in gray crystalline Paleozoic limestone along a north-trending silicified fracture zone. These deposits are all shallow, and were chiefly mined for silver. The ore bodies are irregular, highly silicified bodies that are localized by fractures transgressing the bedding of the host rock. In some places, quartz and sulfides have replaced the host rock; in others, they merely cement breccia fragments in a fracture zone. Iron-stained jasperoid forms prominent outcrops over many of the ore bodies. Near the surface the sulfides have oxidized to cerargyrite, malachite, azurite, pyro-morphite, cerussite, limonite, and manganese oxides. Primary ore and gangue minerals of the deposits are sparse sulfides (pyrite, galena, sphalerite, tetra-hedrite, and argentite) and quartz, barite, and calcite.
PATTERSON DISTRICT (40, fig. 44)
The Patterson district is in northwestern Lincoln County, about 45 miles north-northwest of Pioche, and 50 miles south of Ely, near the south end of the Schell Creek Range. According to Schrader (1931a, p. 7, 11, 15), the country rock in the district is Cambrian shale, quartzite, and limestone. Ore deposits consist of siliceous copper-lead-silver minerals in quartz-carbonate replacement veins in limestone that is commonly silicified to a jasperoid. In his description of ore deposits on the Streater claims, Schrader (p. 15) wrote that
The ores occur mostly as replacement deposits in silicified limestone in a gangue of quartz, barite, and altered rock. The chief ore mineral is argentiferous galena * * *. Some of the ore consists chiefly of silicified limestone, stained by yellowish-brown iron oxide and by lead and copper carbonates. It is crudely ribbed or banded with stringers of replacement quartz as much as two-tenths of an inch wide * * *.
I
SANTA FE DISTRICT (41, fig. 44)
The Santa Fe district is in eastern Mineral County, near Luning, in the Pilot Mountains. White and gray crystalline limestone of probable Triassic age has been intruded by quartz monzonite and quartz diorite﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OP THE UNITED STATES 117
and metasomatized to garnet rock adjacent to the intrusive contacts (Hill, 1915, p. 159-160).
In addition to the typical contact skarns, which are host rocks for copper and lead sulfide ores, partly metasomatized limestone has been locally silicified to form jasperoid bodies with calc-silicate inclusions. Hill (1915, p. 168-170) described the Giroux Ledge as a dark-gray, brown-weathering jasperoid containing angular breccia fragments of white cellular quartz; at the Mayflower property the top of a hill is altered to greenish-white jasperoid containing garnet and epidote; and at the Wall Street mine supergene copper minerals form thin films and irregular masses in reddish-brown jasperoidal limestone.
SILVERHORN DISTRICT (43, fig. 44)
The Silverhorn district, in northern Lincoln County, is about 20 miles northwest of Pioche and 4 miles north of Bristol Pass. Westgate and Knopf (1932, p. 51) described huge outcrops of jasperoid, as much as several hundred yards long and several hundred feet wide, in the Mississippian Bristol Pass Limestone in this district. It is apparent that this jasperoid is structurally controlled and that it locally formed the host rock for oxidized silver deposits. An adit in the district cuts an 80-foot-thick jasperoid body 200 feet below the outcrop. This body replaces limestone along its fault contact with shale and, according to Westgate and Knopf (1932, p. 51), “is the normal fine-grained siliceous rock that is formed as a result of the replacement of limestone by minutely crystalline quartz.”
SILVER PEAK DISTRICT (44, fig. 44)
The Silver Peak district is about 25 miles west of Goldfield in central Esmeralda County. Most of the production from this district has come from mines on Mineral Ridge, 4 miles northwest of the town of Silver Peak. The ore bodies are bedded replacements in Cambrian and Ordovician limestone and dolomite associated with intrusive dikes and sills of alaskite. The ore consists of a black copper-silver sulfide locally disseminated through white jasperoid, according to Spurr (1906b, p. 73-74). He described the jasperoid as a mesh of interlocking quartz crystals with the interstices filled by finer grained an-hedral quartz (reticulated texture) ; the jasperoid is coarser grained in the vicinity of the sulfides than elsewhere. It is approximately contemporaneous with the sulfides, and it has gradational contacts with the enclosing carbonate rock.
I have one sample from this area, taken from the north end of Mineral Ridge, about 6 miles north of the town of Silver Peak and more than 1 mile from the mines. This sample is light gray and aphanitic with local porous areas, it has dark-yellowish-orange fracture coatings, and it weathers grayish brown. In thin section it does not exhibit the reticulated texture described by Spurr, but it has a heterogeneous xenomorphic texture and an average grain size of 0.04 mm. It contains abundant disseminated grains of microcline approximately contemporaneous with the quartz. It also contains numerous red hematite inclusions pseudomorphic after pyrite, shreds of sericite, and irregular masses of opaque dark-brown limonite. The matrix is cut by veinlets of coarse calcite.
Spectrographic analysis shows this sample to be slightly high in Fe, Na, K, Ti, Ba, Co, Cr, Ga, Sc, Sr, V, Y, Yb, Zn, and Zr. It yields a score of +4 on the indicator elements. The absence of reticulated texture and of high Cu and Ag suggests that this sample probably does not represent the ore-bearing jasperoid described by Spurr.
TAYLOR DISTRICT (47, fig. 44)
The Taylor district is near the south end of the Schell Creek Range in White Pine County, about 15 miles southeast of Ely. The geology and ore deposits of this district have been briefly described by Hill (1916, p. 200-201) and, more recently, by Drewes (1962, 1967).
According to Hill, the ore deposits at the Argus mine are in a massive brownish-gray bed of limestone, 70 feet thick, which is cut by north-trending block faults. The limestone is brecciated near the faults, and it has been selectively silicified in two bands, one about 15 feet above the base and the other about 15 feet below the top of the bed. These silicified bands contain most of the ore. They are heavily stained with carbonates of lead and copper and contain a disseminated dark-gray metallic sulfo-salt with Fe, Cu, and minor As, Ag, and Pb. Both mineralization and silicification extend outward irregularly into the limestone from these high-grade bands. The silicified rock is cut by veinlets of late calcite.
According to Drewes (1962), most of the ore in the district is concentrated in two stratigraphic units, the upper member of the Devonian Guilmette Formation and the upper part of the Mississippian Joana Limestone. Both of these units are thin-bedded limestones that are overlain by black shale. Most of the production from the district has come from mines﻿118 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
in the Guilmette Formation, which was the unit described by Hill. Mineralization is largely restricted to silicified zones in limestone, and these zones, in turn, are controlled structurally by proximity to faults and stratigraphically by thick shale cappings over the limestone host rock. Many thick short rhyolitic dikes are present in the district, and these dikes may be related to mineralization (Drewes, 1962).
Although the ore in the district has been mined mostly for its silver content, it also contains gold, copper, lead, zinc, and antimony in various places. A number of grab samples of jasperoid taken by Drewes from abandoned mine workings in the central part of the district were analyzed spectro-graphically. Seven of these samples were abnormally high in Ag, Cu, Pb, and Zn and slightly high in B. Most of the samples were also high in Ba, Cd, Sb, and Zr. Their indicator-element scores range from + 18 to +26, placing them high in the favorable category (Harald Drewes, written commun., 1965).
Seven samples from the Taylor district and its vicinity are included in my collection. Three of these samples were collected about 2 miles north of Taylor close to the road leading to Taylor Springs; the stratigraphic unit represented by these samples is probably Guilmette Formation. One sample of jasperoid from the Joana Limestone was collected from the dump of an adit along a strong fault on the North Star claim half a mile north of the main workings of the district. The remaining three samples are of jasperoid from the upper member of the Guilmette Formation near the center of the district and close to the old Monitor and Argus mines. These three samples are from a large brecciated zone not far from major faults; all the other samples are from silicified fault zones. The first three samples, from the ridgecrest above the Silver Queen shaft and the small saddle just west of it, close to the road, are all more than a mile from mine workings and hence, presumably are unfavorable; however, they vary considerably in both appearance and other characteristics.
One of these samples consists oi light-gray breccia fragments in a dark-gray slightly vuggy matrix. In thin section two types of breccia fragments can be distinguished: aphanitic pale-brown cherty-look-ing fragments and fine-grained heterogeneous reticulated jasperoid fragments that have an average grain diameter of about 0.03 mm. These fragments are embedded in quartz that has a xenomorphic to reticulated texture and a grain diameter that averages 0.02 mm and ranges from <0.01 to 0.1 mm. Calcite is present as ragged relict grains in jasperoid breccia fragments, as carbonate particles in both breccia
fragments and matrix, and as filling in late veinlets cutting the matrix. The sample showed anomalously high values for Na, As, B, Mo, Pb, Sb, Sr, Zn, and Zr, and it yielded an indicator-element score of +9 (probably favorable). Thus, this sample may indicate leakage along the fault from ore deposits at depth.
A second sample of this group appears to represent the same jasperoid that formed the breccia fragments in the first one. It has a similar appearance and microtexture, but it contains tiny red hematite grains and interstitial yellow limonite in addition to the carbonate particles. B, Ba, Pb, Sr, and Zn are slightly high, and the indicator-element score is +5.
The third sample of this group is dense, dark-red, streaked with light brown, xenomorphic jasperoid quartz whose grain diameter averages 0.03 mm and ranges from 0.01 to 0.2 mm. The quartz contains abundant carbonate particles, and it is cut by a mesh of red hematite veinlets, many of which are filled with a microbreccia of jasperoid particles. The trace-element suite associated with it consists of Fe, B, Ba, Ni, Sb, Sr, V, Y, Yb, and Zr. Its indicator-element score is —1; this jasperoid, therefore, is classified as unfavorable.
The single sample of jasperoid from the Joana Limestone, from the adit dump on the North Star claim, is unusual in that it contains antimony as a major constituent. It is light olive gray and dark yellowish brown, fine grained, and compact, and it is cut by veinlets of relatively coarse white quartz. The matrix jasperoid is xenomorphic, and its grain diameter averages 0.02 mm and ranges from 0.01 to 0.1 mm. The late white quartz is also xenomorphic, and its grain diameter averages 0.1 mm and ranges from 0.03 to 0.5 mm; it contains sparse irregular open vugs. The antimony mineral, which forms abundant irregular inclusions in the matrix, is aphanitic and yellowish brown, and it has a high index of refraction. It probably is a supergene alteration product of stibnite and may be the basic antimony sulfate klebelsbergite. In addition to Sb, this sample is highly enriched in Ag and slightly enriched in As, B, Ba, Pb, Ni, Sr, Y, Yb, and Zn. It yields a score of +14.
The three samples of jasperoid from the central part of the district are light gray to yellowish brown, fine grained, and locally vuggy with abundant limonite stains and fracture coatings. They exhibit a reticulated to xenomorphic texture, and their grain diameter averages about 0.05 mm and ranges from 0.01 to 0.1 mm. The samples are locally cut by vein-lets of slightly coarser xenomorphic quartz. The matrix contains abundant carbonate particles; limo-﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 119
nite, jarosite, and hematite are locally abundant as supergene inclusions and fracture fillings. Minor-element content varies considerably among the three samples, but there is general enrichment in Ag, B, Cu, Pb, Sb, Sr, Yb, Zn, and Zr. Presumably, these samples are similar to those collected by Drewes from the same locality, though they do not yield as high scores; the maximum score obtained from my group is +13.
Ore deposits of this district appear to be closely associated both spatially and genetically with jas-peroid bodies, and jasperoid in the immediate vicinity of such deposits commonly exhibits favorable characteristics; thus, these jasperoids should provide a useful tool for any future exploration in the area.
TECOMA DISTRICT (48, fig. 44)
The Tecoma district is in northeastern Elko County, about 4 miles west of the Utah State line and 35 miles south of the Idaho State line in the southwestern part of the Goose Creek Range. The ore deposits in the district are largely oxidized lead and zinc sulfide vein deposits in complexly faulted Paleozoic sedimentary rocks, consisting predominantly of limestone and dolomite.
Near the Jackson mine coarse-grained quartzite is in fault contact with Devonian blue-gray limestone and dolomite. These carbonate rocks are cut by several north-trending faults that locally have served as conduits for silicifying solutions producing large jasperoid bodies. One such body, about 500 feet long and 40 feet wide, is the host rock for the ore bodies in the mine. These bodies consist of silverbearing cerussite, a little smithsonite, and a few residual pods of galena in a gangue of oxidized rusty jasperoid; limonite, calcite, clay, and barite occupy fracture zones in the jasperoid. A larger, but apparently unmineralized jasperoid body, crops out 1,000 feet northeast of the mine; it is about 200 feet wide and extends northward for several thousand feet. Contacts between jasperoid and host rock are commonly brecciated (Granger and others, 1957, p. 149-150).
WARD DISTRICT AND WEST WARD AREA (49 and 50, fig. 44)
The Ward district (49) is in White Pine County about 10 miles south of Ely, on the east side of the Egan Range. A second mineralized area, centered about 214 miles west of the Ward district on the opposite side of the Egan Range, is characterized by magnetic and geochemical anomalies and by locally
abundant jasperoid (Brokaw and others, 1962). This area I refer to as the West Ward area (50).
The geology and ore deposits of the Ward district have been summarized by Hill (1916, p. 180-186). Paleozoic limestone beds, which make up a thick section and which have gentle easterly dips throughout most of the district, are locally intruded by north-trending quartz monzonite dikes. Both dikes and limestones are cut by younger faults and have been hydrothermally altered by mineralizing solutions. The ore deposits are closely associated with the dikes, and they generally occur close to the contacts as bedded replacements in the limestone and as veins in both the limestone and the dikes. Within the zone of oxidation the ore consists largely of argentiferous cerussite, hemimorphite, smithsonite, and copper oxidation products in a siliceous limonite gangue. Primary sulfides below the zone of the oxidation are galena, sphalerite, pyrite, and a little chalcopyrite. Limestone is locally silicified near the dikes, and in some places the ore bodies are in this silicified zone. The Defiance ore body, 500 feet below its outcrop, is a silicified zone 300 feet wide impregnated with pyrite and galena adjacent to a strong northeast-trending fault (Hill, 1916, p. 183-184). Silicified limestone adjacent to porphyry dikes is also present in the lower Paymaster tunnel and the Welcome Stranger Tunnel (Hill, 1916, p. 185-186).
I have three jasperoid samples from the Ward district. The host rock for all three samples is Mississip-pian, Pennsylvanian, and Permian Ely Limestone. One sample is from a silicified zone along a north-east-trending fault about a mile south of the district. Another sample is from a zone adjacent to a quartz monzonite dike a few hundred feet south of the strong east-west fault that marks the south boundary of the district and about a quarter of a mile southwest of the 280 Tunnel. The third sample is siliceous gossan from the outcrop of a vein in a fault zone adjacent to a large quartz monzonite dike; it was taken within a few feet of mine workings about half a mile west of the 280 Tunnel.
The first sample is grayish red and aphanitic, and it contains sparse irregular vugs, of which some are open and some are filled with coarse white calcite. Its microtexture is xenomorphic, and its grain diameter averages 0.02 mm and ranges from 0.01 to 0.1 mm. The larger grains have carbonate particles, and some show zonal overgrowths. Red hematite is abundant both as disseminated particles and as irregular inclusions. The sample is slightly high in Ag and Sr and yields a score of +2.
The second sample is dark gray and dense and is cut by sparse veinlets of white calcite. The matrix﻿120 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
has a homogeneous granular texture, and an average grain diameter of 0.06 mm. It contains partly assimilated breccia fragments of feathery chalcedony mixed with jigsaw-puzzle textured quartz having an average grain diameter of 0.05 mm, and also of similar, but more heterogeneous, quartz without the chalcedony. Ragged relict grains of calcite are abundant in both matrix and inclusions. Small flecks of brown limonite are scattered through the matrix, and some of these surround tiny grains of pyrite. In addition to abundant Ca and Mg, the sample is slightly high in Al, Cr, Ni, Pb, Sr, Y, Yb, and Zr.
The third sample is moderate brown, brownish-black weathering, aphanitic, and porous. The matrix is vuggy orange goethite cementing isolated grains and small breccia fragments of coarse reticulated jasperoid quartz that has a grain diameter that averages 0.1 mm and ranges from 0.03 to 0.8 mm. Carbonate particles are moderately abundant in the quartz. This sample is unusually rich in minor elements; Fe, Ag, As, and Pb are enriched by more than two orders of magnitude above the norm, and Ca, Mg, Ti, Bi, Cr, Cu, In, Mo, Ni, Sn, Sr, V, Zn, and Zr are enriched by more than one order of magnitude. The indicator-element score is +31 (very favorable).
The geology of the West Ward area and the results of a geochemical exploration program in the area were summarized by Brokaw, Gott, Mabey, McCarthy, and Oda (1962, p. 7). On the geologic map accompanying their report, jasperoid in the Missis-sippian Joana Limestone is shown in a stippled pattern. The West Ward area is underlain by a thick section of middle Paleozoic marine sedimentary rocks consisting largely of limestone, dolomite, ancl shale. This section is broken by both low-angle thrust faults and high-angle normal faults.
Spectrographic analyses of 27 jasperoid samples from the Joana (Mississippian) and Arcturus (Permian) Limestones in the West Ward area, given to me by J. H. McCarthy, show that the modal concentrations of Ti, Ag, Ba, Cr, Ni, and V are appreciably higher than in my reference groups of 200 samples from various localities. Geochemical anomaly maps for various elements, based on analyses of both jasperoid and limonite samples, are illustrated by Brokaw, Gott, Mabey, McCarthy, and Oda (1962, p. 5-6).
Five additional samples of jasperoid from the Joana Limestone in the West Ward area are in my collection. These samples have been analyzed both petrographically and spectrographically. Three samples are from the vicinity of a small prospect about a quarter of a mile north of the abandoned Old
Quake mine. The exact sample localities for the other two samples are not known, but they represent bodies not associated with any known ore.
One sample, from the group of three, consists of angular and irregular crudely stratified inclusions of aphanitic dark-reddish-brown and dark-brown jasperoid in a matrix of coarse white quartz. Three distinct generations of quartz are in the sample. The oldest generation consists of homogeneous xenomor-phic quartz having an average grain diameter of 0.015 mm, sparse carbonate dust, and abundant interstitial yellow limonite. This generation forms inclusions in a cleaner and coarser heterogeneous xenomorphic matrix that has a grain diameter that averages 0.03 mm and ranges from 0.01 to 0.12 mm. The matrix is cut by the coarse vein quartz whose grains are as much as 3 mm in diameter. In spite of its complex nature, this sample has a very ordinary composition, exhibiting a minor anomaly only for Ba, and yielding an index element score of — 1 (unfavorable).
The second sample from this group of three samples is dark gray and dense; it is cut by vuggy white quartz veinlets, and it weathers olive gray to pale yellowish brown. The matrix has a jigsaw-puzzle texture and a grain diameter that averages 0.01 mm and ranges from <0.01 to 0.06 mm. It contains sparse carbonate and hematite particles and is cut by veinlets of xenomorphic quartz that has a grain diameter that averages 0.07 mm and ranges from 0.01 to 0.2 mm. Most vugs in this late quartz are open, but a few are partly filled with jarosite. The sample contains anomalous concentrations of Ag and Ba and slightly anomalous concentrations of Cr, Cu, Sb, Sr, V, Y, Yb, and Zr, yielding an indicator-element score of +6 (probably favorable).
The last sample in this group is similar in appearance to the second, but it lacks the late quartz vein-lets and weathers dark gray. It consists of homogeneous quartz particles that have an average grain diameter of 0.02 mm in a matrix of dark-brownish-gray to black amorphous opaque material, presumably organic, that contains abundant shreds of sericite and grains of goethite as well as sparse irregular masses of nontronite. The matrix is cut by sparse lenticular masses of younger quartz that has a jigsaw-puzzle texture and a grain diameter that averages 0.02 mm and ranges from <0.01 to 0.15 mm. Some of the larger grains of this younger quartz contain sparse carbonate particles and small fluid inclusions. This sample contains highly anomalous concentrations of Ag, Ba, Cr, Ni, Sr, and Zr, as well as slightly anomalous concentrations of Na, K, Ti, B,﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OP THE UNITED STATES 121
Cu, La, Pb, Sb, V, Y, Yb, and Zn; it gives an indicator-element score of + 15 (favorable).
One of the two remaining samples in my collection is dark gray, dense, brecciated, and cemented by coarse white calcite. It has a homogeneous jigsaw-puzzle texture and an average grain diameter of <0.01 mm; it contains carbonate particles and is cut by veinlets of coarser xenomorphic quartz as well as coarse calcite; and it grades transitionally through a zone about 2 mm wide into lithographic limestone that contains scattered grains and irregular masses of coarse-grained epigenetic calcite. Tiny subhedral grains of hematite, which appear to be pseudomor-phous after pyrite, are sparsely disseminated in both jasperoid and limestone. This jasperoid sample is slightly high in Na, Ag, Ce, Cu, and Ga, and it yields a score of +4. Comparison of spectrographic analyses of the jasperoid and the adjacent Joana Limestone host rock shows the j asperoid to be significantly enriched in Si, Fe, Ag, Cr, Cu, Ga, and Ni relative to the limestone.
The other remaining sample is a breccia composed of angular fragments of dark-gray aphanitic jasperoid in a matrix of fine-grained, locally vuggy, dark-yellowish-orange to moderate-brown jasperoid. In thin section several different types of breccia fragments can be distinguished. One type consists of clean coarse homogeneous xenomorphic quartz that has an average grain diameter of 0.4 mm. Another type has a xenomorphic to jigsaw-puzzle texture and average grain diameter of 0.2 mm; it is locally vuggy and it contains abundant carbonate particles. A third type has a jigsaw-puzzle texture gradational to fibrous chalcedony and an average grain diameter of 0.03 mm; it contains sparse carbonate particles. The last type of inclusion is similar to the matrix jasperoid in the specimen discussed in the preceding paragraph. The cementing matrix for all these fragments is a vuggy limonitic microbreccia of smaller jasperoid particles. This sample is very high in As, Sb, and Ti and slightly high in Al, Fe, Na, Ba, Cr, Cu, Ga, Mo, Ni, and Y, and it yields a score of +8 (probably favorable).
WHITE PINE (HAMILTON) DISTRICT (51, fig. 44)
The White Pine district is in western White Pine County, about 30 miles west of Ely in the White Pine Mountains. The sedimentary section in the main mineralized area consists predominantly of Devonian and Mississippian limestone and shale, broken by strong north-trending faults and smaller subsidiary faults and fractures. About 5 miles west of this area the Paleozoic sedimentary rocks have been intruded
and locally metasomatized by a small stock of quartz monzonite. The stock rock is strongly brecciated and silicified, but neither the stock nor the altered sediments surrounding it have thus far yielded any economically important ore deposits.
Bonanza silver deposits of cerargyrite and silver-manganese-bearing calcite were mined in the early days on Treasure Hill. In recent years most of the ore in the district has come from argentiferous base-metal sulfide replacement deposits, oxidized near the surface, in the Devonian Nevada Limestone west-southwest of Treasure Hill. This host rock is over-lain, as in the Taylor district (47), successively by the Pilot Shale of Devonian and Mississippian age and by the Joana Limestone and the Chainman Shale, both of Mississippian age. Jasperoid bodies are largely confined to the upper part of the Joana Limestone near its contact with the Chainman Shale and close to faults and fracture zones. The Joana Limestone, however, is largely barren of ore (Humphrey, 1960, p. 32, 46-47, 88). Jasperoid in the Joana Limestone typically is brecciated, dark reddish brown, and fine grained, and it resembles quartzite. Jasperoid bodies similar in appearance to those in the Joana Limestone, except that they are not conspicuously brecciated, are present locally in limestone beds above the Chainman Shale (Humphrey, 1960, p. 35). I have 13 jasperoid samples from within or near the White Pine district. Most of them were taken from the Treasure Hill area of the main silver district; but two samples of supposedly barren jasperoid in the Joana Limestone were collected 11/2 and 5 miles southwest of this area, and three more, from the same stratigraphic zone, were collected 5 miles north and about 10 miles northeast of it. Five of the eight samples from within the Treasure Hill area of the district are of jasperoid from the Joana Limestone; the other three are of silicified Pilot Shale in breccia zones along the contact with Nevada Limestone.
All five of these jasperoid samples from the Joana Limestone show two distinct generations of silica. The older is predominantly light gray to moderate gray and aphanitic. It has j igsaw-puzzle texture and contains abundant inclusions of chalcedony; locally, it contains microvugs, some of which have been filled with coarse xenomorphic quartz, and in places it is clouded with dusty particles of limonite or carbonate. The younger silica forms a matrix surrounding inclusions of the older silica. It is various shades of yellow, orange, brown, and red, and it has a heterogeneous jigsaw-puzzle texture and an average grain size markedly coarser than that of the older silica; it also contains larger and more abundant vugs. It﻿122 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
commonly contains abundant particles of hematite, limonite, jarosite, or carbonate as well as larger masses of jarosite and barite. These minerals, together with coarse xenomorphic quartz, also fill fractures and vugs. All five of these samples are anomalously high in Fe and Ba, and some are also high in Na, Cr, Ni, Pb, Sr, V, and Zn. Their indicator-element scores range from +1 to +19 and average about +9.
The three remaining samples from the mineralized area are of silicified Pilot Shale in breccia zones close to the Nevada Limestone contact. These, too, contain gray and brown angular chert inclusions in a slightly coarser, gray, red, yellow, or brown locally vuggy matrix, which, in two of the samples, is itself brec-ciated and cemented by coarse white vein quartz. The matrix is heavily clouded with dust-sized particles of carbon, limonite, and hematite, and it contains abundant shreds of sericite. These breccia-zone samples, which contain several different kinds of fragments and which are from mineralized zones, display more elements in anomalously high concentration than do the samples of jasperoid from the Joana Limestone. Ba, Pb, and Sr are high in all three samples; Al, Mg, Na, P, Ag, B, Cu, La, Ni, Y, Yb, Zn, and Zr are high in two of them. Their indicator-element scores are +6, +12, and +16.
Five samples of barren jasperoid from the Joana Limestone represent four localities, two of which are several miles south and southwest of the district, and two of which are several miles north and northeast of the district. These five samples are pastel shades of red, yellow, brown, pink, and orange. Some of them contain chert fragments; the matrix jasperoid has a fine-grained jigsaw-puzzle texture and a grain diameter that averages about 0.01 mm and ranges from <0.005 to about 0.03 mm. The microtexture of jasperoid samples from this stratigraphic zone is remarkably consistent in all 10 samples collected at intervals over a distance of about 30 miles. These unfavorable samples also contain hematite, limonite, and, locally, jarosite inclusions both as small discrete grains and as dust-sized particles. They differ most notably from the samples in the mineralized area in that they contain fewer minor elements in higher than normal concentration. Most of them are high in Ba and Sr; those from the southwest are high in B and Ni, and those from the northeast are high in Na. The indicator-element scores of these samples range from —1 to —3.
WILLOW CREEK DISTRICT (52, fig. 44)
The Willow Creek district in Nye County is about
12 miles north of lat 38° N. and 15 miles east of long 116° W. on the northwest side of the Quinn Canyon Mountains and near the south end of Railroad Valley. Oxidized argentiferous base-metal deposits are found here in veins cutting shaly siliceous Ordovician limestone near a small intrusive stock of quartz monzonite.
At the Queen of the Hills mine, 3 miles southeast of Mormon Well, limonitic jasperoid replaces a massive limestone bed just above its contact with a shaly limestone. This jasperoid contains copper carbonates and a little silver (Hill, 1916, p. 144-145, 150).
WYNDYPAH DISTRICT (53, fig. 44)
The Wyndypah district is in south-central Esmeralda County on the northeast flank of the south end of the Silver Peak Range, about 15 miles southwest of Silver Peak. Argentiferous copper deposits occur here in veins close to the contact of a small intrusive granitic stock with lower Paleozoic calcareous sedimentary rocks.
At the Chloride mine a vein containing breccia fragments of brown jasperoid and partly silicified limestone in a quartz gangue follows the contact between an alaskite porphyry dike and altered limestone a few hundred feet from the granite contact. This vein contains some disseminated black silver-copper sulfide ore. A similar vein, in altered limestone near the granite contact about a mile south of the Chloride mine, has also been explored (Spurr, 1906b, p. 90-91).
OTHER OCCURRENCES
Silicified limestone containing barite is the host rock for small oxidized zinc and argentiferous lead replacement ore bodies along bedding planes adjacent to basalt dikes in the Antelope district (1, fig. 44) southwest of Eureka, Nev. Nearly all the ore is oxidized and consists of cerussite, smithsonite, hemimorphite, manganese oxides, and jasperoid. In the Diamond district (15), also, the prevailing formation is silicified limestone cut by veins containing argentiferous galena, cerussite, and stibnite in a quartz and calcite gangue (Vanderburg, 1938, p. 17, 28-29). Both of these districts are in Eureka County.
In the Belmont district (4, fig. 44), a few miles east of Manhattan, in Nye County, cerargyrite pods are found in quartz veins and lenses in metasoma-tized slate and limestone close to an intrusive granite stock. Slate is altered to mica schist, and limestone to jasperoid near this contact (Krai, 1951, p. 20). Emmons (1910, p. 73) mentioned “decomposed silici-﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 123
tied limestone” gangue enclosing base-metal sulfides in the Jack Pot mine, Columbia district (10), in Elko County.
Ore bodies of the Delano district (13, fig. 44), also in northern Elko County, occur in two parallel beds in Paleozoic carbonate rocks adjacent to a quartzitic sandstone. These ore beds consist of cerus-site, residual galena, anglesite, and copper carbonates in a brecciated gangue of amorphous silica. The beds are separated by a partly silicified dolomite bed 6-8 feet thick (Granger and others, 1957, p. 45-46).
The small, isolated Fireball district (22, fig. 44) in northwestern Churchill County contains gold- and silver-bearing quartz veins in silicified limestone that is cut by rhyolite and andesite dikes (Vanderburg, 1940, p. 30). Gold- and silver-bearing quartz veins are also reported along shear zones that cut highly silicified Tertiary rhyolite in the Gold Banks district (25), Pershing County. Dreyer (1940, p. 15) described this rock as having a conchoidal fracture and closely resembling chert, and wrote: “The feldspar is in part replaced by a chalcedonic silica which in some places is in contrast with the more coarsely silicified groundmass, and thereby preserves the feldspar outlines.”
At the Victorine mine, Kingston district (29, fig. 44), Lander County, pockets of base-metal sulfide in a quartz gangue are irregularly scattered through a 25-foot-thick bed of silicified Paleozoic limestone, interbedded with black shale and slate (Hill, 1915,
p. 128).
Spurr (1906a, p. 376) reported silver-bearing quartz and jasperoid veins cutting Cambrian and Silurian limestone in the southern Klondike district (30, fig. 44), about 10 miles south of Tonopah in Esmeralda County. These limestones are intruded by granitic rocks and are surrounded by Tertiary rhyolitic extrusive rocks.
The Nevada district (39, fig. 44), in White Pine County, about 10 miles southeast of Ely, contains pods and pipes of manganese oxides in Devonian limestone. The host rocks for these ore bodies are “irregular jaspery quartz lodes that replace the limestone along fractures, joints, and bedding planes” (Lincoln, 1923, p. 252).
Cameron (1939, p. 582, 593, 621), in discussing the geology and ore deposits of the northeastern Humboldt Range, Pershing County, stated that chert bands and nodules are locally conspicuous in limestone of the Triassic Star Peak Group, and that several limestone specimens “show partial replacement by quartz of the jasperoid variety.” However, he also noted that silicification of calcareous wall-
rocks adjacent to ore deposits had been observed in only a few places, principally at the Sheba-De Soto mine (42, fig. 44), where bands of aphanitic cherty silica in the lower limestone beds are tentatively ascribed to hydrothermal silicification. This mine produced silver from argentiferous sulfides and sulfosalts in veins and stockworks that cut the limestone.
The Yerington district (54, fig. 44), in central Lyon County, contains economically important con-tact-metasomatic copper deposits in calc-silicate rocks resulting from the intense metamorphism of Triassic limestone by intrusions of granodiorite and quartz monzonite (Knopf, 1918, p. 7). Although contact metamorphism within the mineralized area was evidently too intense for the development of jasperoid, I have two samples of dense light-gray jasperoid taken from unmetasomatized limestone at localities about 3 miles south of the district. Both of these are unfavorable.
In the Lone Mountain district (33, fig. 44), at the Alpine mine about 15 miles west of Tonopah v in Esmeralda County, replacement ore bodies of galena and cerussite surrounded by jasperoid zones in white dolomitic limestone near an intrusive granitic stock were described by Spurr (1906b, p. 81). He (p. 12) also referred to bedded replacement “veins” of gold and silver in a siliceous gangue in Paleozoic limestone and dolomite in this district.
In the Chief (Caliente) district (8, fig. 44), near Caliente in Lincoln County, the presence of jasperoid associated with oxidized gold-silver-lead ore in veins cutting limestone was mentioned by Callaghan (1936, p. 16, 17, 28). A. V. Heyl (written commun., 1967) also reported abundant jasperoid in this district.
The Spruce Mountain district (45, fig. 44), at the south end of the Goshute Range in southeastern Elko County, contains prominent masses of jasperoid near the Spruce Standard mine (Schrader, 1931b, p. 9, 24). These jasperoid “blowouts” consist of masses of iron-stained quartz breccia as much as 500 feet in diameter.
A. V. Heyl (written commun., 1967) further reported that jasperoid is also common to abundant in the lead and zinc deposits of the Duck Creek (17, fig. 44) and Success (46) districts in White Pine County, the Mount Hope district (37) in Eureka County, the Mud Springs district (38) in southern Elko County, and the Lida district (32) in southern Esmeralda County.
NEW MEXICO
Information is available on jasperoids from 16 mining districts in New Mexico (fig. 45), and jas-﻿124 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
EXPLANATION
x
Minor district or area •
Reported occurrence
Jasperoid province
DISTRICTS, AREAS, AND OCCURRENCES
1.	Bishop Cap
2.	Carpenter
3.	Cooks Peak
4.	Cuchillo Negro
5.	Georgetown
6.	Goodfortune Creek
7.	Hadley (Graphic)
8.	Hansonburg
9.	Hermosa (Sierra
Caballos)
10.	Hillsboro
11.	Hot Springs
12.	Kingston
13.	Lake Valley
14.	Magdalena
15.	Mockingbird Gap
16.	Organ
17.	Santa Rita
18.	Steeple Rock
19.	Tierra Blanca
20.	Tres Hermanas
21.	Velarde
22.	Victorio
23.	Victorio prospect
24.	Water Canyon
Figure 45.—Map showing location of jasperoid-bearing districts and prospects in New Mexico.
peroid is known to be present in eight other districts. All these localities are in the southwestern part of the State—in Dona Ana, Grant, Luna, Sierra, and Socorro Counties; most of them are concentrated in an irregular belt or province extending south-south-west from the Magdalena district in Socorro County at least as far as the Mexican border.
Most of these jasperoid-bearing districts contain oxidized, locally argentiferous base-metal sulfide vein and replacement deposits in silicified Paleozoic limestone and dolomite. In the Hadley (7, fig. 45) and Steeple Rock (18) districts, base-metal sulfide vein deposits are in silicified Tertiary volcanic rocks. Replacement deposits in jasperoidized Paleozoic limestone in the Bishop Cap (1) district and at the Hot Springs (11), Velarde (21), and Victorio (22) prospects consist of fluorspar rather than base metals. The Lake Valley (13) and the Georgetown (5) districts have produced high-grade oxidized silver ore associated with manganese oxides.
BISHOP CAP DISTRICT (1,	45)
The Bishop Cap district is 11 miles southeast of Las Cruces at the south end of the Organ Mountains in Dona Ana County.
Limestones and interbedded shales of the Pennsylvanian Magdalena Formation are cut by three distinct sets of faults in the mineralized area. The oldest faults strike north and contain the principal fluorspar deposits; a younger set of barren faults strikes northeast. The third, and youngest set, strikes nearly east and occupies an intensely silicified zone. Within this zone, fluorite and jasperoid quartz are largely concentrated along the footwall; in contrast, calcite and barite are abundant along the hanging wall. The jasperoid quartz is white, largely massive, and aphanitic, and it contains local vugs and fractures coated by drusy quartz deposited by descending surface water. The mineralization is of probable Tertiary age and genetically related to intrusion of﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 125
the Organ Mountains batholith (Rothrock and others, 1946, p. 62).
CARPENTER DISTRICT (2, fig. 45)
The Carpenter district is in Grant County, about 6 miles southwest of Kingston on the west slope of the Black Range.
Base-metal sulfide deposits are concentrated along shear zones in the Ordovician Montoya Dolomite. Locally, this limestone has been replaced by jasperoid containing small bunches and veinlets of sulfide ore. At the Grand Central mine such a shear zone about 25 feet wide strikes northerly, dips steeply to the east, and has ore-bearing jasperoid on the footwall side (Harley, 1934, p. 110-111).
COOKS PEAK DISTRICT (3, fig. 45)
The Cooks Peak mining district is about 2 miles north of Cooks Peak, a conspicuous landmark about 18 miles north-northeast of Deming, in Luna County. Silver and base metals were produced from oxidized replacement and fissure vein ore bodies in the Silurian Fusselman Dolomite close to its contact with the overlying Devonian Percha Shale.
Both the upper part of the Fusselman Dolomite and the lower part of the Percha Sale are intensively silicified in the mineralized area. According to Jicha (1954, p. 62), this jasperoid layer has been brec-ciated and recemented at different times by successive generations of silica as shown by the presence of several different colors and types of jasperoid. Some of these types contain conspicuous vugs lined with small quartz crystals. Silicification extended over a considerable period of time. Some jasperoid is postore, but some may also be preore. Most of the ore bodies are encased in jasperoid, and the intensity of silicification tends to diminish away from them.
Three jasperoid samples from the Fusselman Dolomite in this district are included in my collection. Two samples were collected near the east end of the east-trending mineralized Othello fault, and the third, from the same area about 500 feet north of the fault; all three samples were taken about a quarter of a mile from the nearest mine workings.
Both samples from the fault zone are gray on fresh surface, shades of brown on the weathered surface, fine grained, and vuggy, and they have a reticulated microtexture. One has hematite pseudo-morphs after pyrite and breccia fragments of dense aphanitic cherty jasperoid. These two samples have slightly anomalous concentrations of Ba, Be, Ga, Pb,
and Zn, yielding indicator-element scores of + 6 and
+ 2.
The single sample from the locality north of the fault zone is similar in color but has an aphanitic jigsaw-puzzle texture and fewer vugs, and it contains detrital-looking quartz grains. This sample is slightly high in Na, Ti, Ba, Be, Ga, and Ni, yielding a score of —2.
CUCHILLO NEGRO DISTRICT (4, fig. 45)
The Cuchillo Negro district is in northwestern Sierra County in the Cuchillo Mountains, about 5 miles east of the small town of Fairview. In this area Pennsylvanian limestones of the Magdalena Group have been intruded by a large sill of Tertiary quartz monzonite porphyry, which intrusion has caused local contact metasomatism of the limestone. Small oxidized base-metal sulfide replacement deposits are in the limestone close to the intrusive contact. Limestone on the Black Knife property has been converted to jasperoid along the intrusive contact and along small fractures extending upward from this contact, above the ore bodies. A 10-foot-wide north-northwest-trending silicified shear zone cuts the limestone a few hundred feet east of the Black Knife claims. This silicified zone with jasperoid contains fluorite and calcite, and it is slightly mineralized at its contact with the porphyry a quarter of a mile to the south (Harley, 1934, p. 113-122).
HADLEY (GRAPHIC) DISTRICT (7, fig. 45)
The Hadley (Graphic) district is in northern Luna County, about 16 miles north of Deming and 5 miles east of Cooks Peak. Lead and zinc ores have been mined here from fissure veins cutting Tertiary andesite. According to Jicha (1954, p. 67-68), silicification of the country rock is conspicuous along veins and faults near the mines, but the richest ore occurs in the less intensely silicified areas. Extensive silicification preceded ore mineralization, and more localized silicification accompanied or followed it.
Two jasperoid samples taken from an outcrop near the southwestern end of this district are included in my collection. This body of jasperoid is massive and grayish brown, and is partly surrounded by a zone of bleached kaolinized andesite.
Both samples are dense and massive. One is grayish orange to pinkish gray and consists of homogeneous medium-grained quartz that has a jigsaw-puzzle texture and contains local concentrations of fibrous chalcedony. The other is white to pale orange with local dusky-brown spots of limonite; it has an﻿126 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
aphanitic cherty texture and contains disseminated clay as well as limonite. Both samples are slightly high in Mg, Ti, Ba, and Pb; one also contains a little Ag, and the other shows anomalous concentrations of Ga, Mo, and Sr. One sample yields an indicator-element score of +9, the other, +2.
HERMOSA (SIERRA CABALLOS) DISTRICT (9, fig. 45)
The Hermosa silver-lead district is on the east slope of the Black Range in Sierra County; it extends from Monument Creek southward to Seco Creek, about 25 miles west of Truth or Consequences.
Pennsylvanian limestone has been extensively silic-ified near the north-trending Pelican fault north of Palomas Creek. The Pelican shaft, on the west side of this fault, passed through jasperoid cut by galena-bearing quartz veinlets above a black shale bed; below the shale it entered unsilicified limestone cut by veinlets of high-grade lead-silver ore (Harley, 1934, p. 96).
HILLSBORO DISTRICT (10, fig. 45)
The Hillsboro district is in southwestern Sierra County along Percha Creek in the western foothills of the Black Range. Most of the mineral production from this district has come from gold, silver, and base-metal-bearing quartz veins cutting Tertiary andesitic rocks.
A belt of jasperoidized Silurian Fusselman Dolomite forms a prominent escarpment on the east side of a strong north-trending fault about a mile east of Hillsboro on the north side of Percha Creek. This rock is red to brown and strongly brecciated and is cut by numerous veinlets of white quartz. The j dsper-oid is locally vuggy and weathers to a rubble of large iron-stained boulders. The base of the Devonian Percha Shale above the Fusselman Dolomite has also been altered locally to a dense red jasperoid. No mines have been developed in this large jasperoid body, and Harley (1934, p. 125^126, 130) regarded it as barren.
I have six samples of the Fusselman jasperoid from the top of the escarpment about midway between the north end of the ridge and Percha Creek. These samples range in color from light gray through yellowish brown, yellowish orange, and grayish red to moderate red. Most of them are brecciated, vuggy, and aphanitic.
The samples consist of an older generation of cherty jasperoid that has a jigsaw-puzzle texture and a younger generation of medium- to coarse-grained heterogeneous xenomorphic quartz that fills vugs
and fractures in the older jasperoid and locally forms the matrix in which angular breccia fragments of older jasperoid are embedded.
The older jasperoid contains abundant red hematite as both disseminated particles and red stain; it also contains carbonate particles locally. The younger quartz is associated with penecontemporaneous yellow to brown limonite and fibrous chalcedony.
Most of the five samples that were analyzed are anomalously high in Fe, Ba, Be, Pb, and Zn, and one sample is also high in Mn, Cu, and Ga. The suite of samples yields indicator-element scores of +3, +3, +8, +9, and +10. The presence of jasperoid with probably favorable characteristics in this body suggests that ore may exist downdip in the Fusselman Dolomite.
KINGSTON DISTRICT (12, fig. 45)
The Kingston base-metal district in Sierra County extends from the crest of the Black Range eastward between the North and South Forks of Percha Creek about 11/2 miles beyond the town of Kingston.
Fusselman Dolomite has been silicified in an irregular zone at its contact with Percha Shale adjacent to a small stock of quartz monzonite porphyry. In this zone the replacement jasperoid is a fine-grained white to pink breccia partly cemented by white crystalline quartz. Elsewhere in the district, Percha Shale has been converted to dense red jasperoid, which contains disseminated pyrite, adjacent to its contact with unaltered Fusselman Dolomite.
Silicifying solutions, considered by Harley (1934, p. 98-102) to be genetically related to the quartz monzonite intrusive, rose along fractures and shear zones in the dolomite and spread out along the contact with the overlying shale, locally converting the adjacent rock to jasperoid; this jasperoid apparently formed an impermeable seal that trapped later ore solutions rising along the same conduits. Locally, the jasperoid is slightly auriferous; the younger sulfide ore bodies are vein and replacement deposits of galena, sphalerite, chalcopyrite, and pyrite in a gangue of quartz, rhodochrosite, and manganiferous calcite.
LAKE VALLEY DISTRICT (13, fig. 45)
The Lake Valley district is in southwestern Sierra County, about 15 miles south of Hillsboro and 18 miles west of the Rio Grande.
Manto deposits of silver and manganese ores were formed here in Mississippian Lake Valley Limestone that is now exposed in a fault block of Paleozoic sedi-﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 127
mentary rocks, largely surrounded by Tertiary volcanic rocks.
A thin persistent layer of “chert” or jasperoid at the contact between the Alamogordo Member (blue limestone) and the Nunn Member (crinoidal limestone) of the Lake Valley Limestone forms the foot-wall of many silver and manganese ore mantos in the central part of the district. Near the major fault that bounds the district on the southwest, this layer has been brecciated and recemented with younger ferruginous, manganiferous, and argentiferous jasperoid that displays a variety of colors (Harley, 1934, p. 176-177).
Silurian Fusselman Dolomite has also been extensively replaced by jasperoid beneath the Percha Shale west of the mined area in the district. Younger quartz has recemented breccia blocks of silicified limestone in large irregular masses with rough craggy outcrops that weather to a rubble of talus blocks (fig. 2A). The older jasperoid in the breccia fragments is milky and granular, and, in some places, it resembles quartzite; elsewhere, it is stained red with abundant hematite. The younger cementing quartz is slightly coarser and has abundant vugs lined with quartz crystals (Harley, 1934, p. 173). No known ore deposits are associated with the jasperoid bodies in the Fusselman Dolomite, although the texture, mineralogy, and chemical composition of some of them furnish criteria that place them in the favorable category (Young and Lovering, 1966).
Many jasperoid samples collected from this district have been described in detail (Young and Lovering, 1966); therefore, these descriptions will not be repeated here.
According to Harley (1934, p. 177), early mineralizing solutions, preceding the primary ore stage in the district, were rich in silica, but those that emplaced the primary ore minerals were rich in calcium carbonate and relatively poor in silica. This conclusion, together with the occurrence of favorable jasperoid in the Fusselman Dolomite close to the south boundary fault and the known occurrence of sulfide ore bodies in this stratigraphic zone at Kingston and Cooks Peak, led Young and Lovering (1966, p. D24-D26) to the opinion that similar ore bodies may exist in the Lake Valley district at the top of the Fusselman Dolomite close to the south boundary fault.
MAGDALENA DISTRICT (14, fig. 45)
The Magdalena district in Socorro County, about 20 miles west of Socorro, at the north end of the Black Range, has been one of the major lead, zinc, and copper producers in the State. Most of the ore
deposits are concentrated in a zone of contaet-metasomatized upper Paleozoic sedimentary rocks surrounding quartz monzonite stocks and smaller intrusive bodies of Laramide age.
The same siliceous emanations that formed lime-silicate rock adjacent to the intrusives also rose along fractures in the Mississippian Kelly Limestone and spread out beneath overlying shale at the base of the Pennsylvanian Sandia Formation, forming jasperoid in the southern part of the district, farther from their source (Loughlin and Koschmann, 1942, p. 53).
The jasperoid is light gray and various shades of brown, and it contains abundant drusy vugs that are lined with quartz crystals and are elongated parallel to the bedding of the limestone host rock. In some places, the jasperoid has been brecciated and recemented by white vein quartz containing vugs that are locally lined with crystals of quartz, barite, and sulfides. Boundaries between jasperoid and host rock appear to be sharp, but petrographic study of thin sections cut across the contact reveals the presence of euhedral quartz crystals disseminated in the limestone. The primary jasperoid is preore, but the white vein quartz that cuts and cements it belongs to the ore stage of mineralization. The relationships of jasperoid to contact-metasomatic skarn and ore deposits at Magdalena are suggestive of those at Yer-ington, Nev.
ORGAN DISTRICT (16, fig. 45)
The Organ district is in Dona Ana County, 15 miles northeast of Las Cruces at the west base of San Augustine Pass between the Organ Mountains and the San Andres Mountains. In this district, base-metal sulfides were deposited in veins and as replacements in limestones of the Magdalena Group along a strong north-trending fault and fracture zone.
Bodies of white fine-grained locally vuggy jasperoid crop out within this zone in the vicinity of the ore bodies. The jasperoid commonly preserves the primary textures of limestone and dolomite breccia fragments it has replaced. Sparse vugs within it are locally lined with crystals of quartz, aragonite, and dolomite. An unusual feature of these jasperoid bodies is that they are present only near the surface and die out abruptly at depths of less than 200 feet into a rubble of breccia fragments of unaltered carbonate rock (Dunham, 1935, p. 126-129, 160).
A sample of this jasperoid from a brecciated outcrop near the center of the district is light yellowish gray, fine grained, and vuggy. In thin section it has a heterogeneous xenomorphie to locally reticulated texture with small vugs. It contains sparse dissemi-﻿128 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
nated grains of apatite and of hematite pseudo-morphs after pyrite, also disseminated dust-sized particles and local aggregates of a yellowish-orange clay mineral, probably nontronite. Spectrographic analysis shows slightly high concentrations of Mn, Ba, and Cu, yielding an indicator-element score of +3.
SANTA RITA DISTRICT (17, fig. 45)
The Santa Rita mining district in Grant County is the foremost producer of copper, lead, and zinc in the State. Because of its commercial importance, this district would have been discussed under the major mining districts but for the fact that jasperoid bodies are not abundant.
Of three samples taken from small masses of jasperoid in and near the district, two are from exposures in the town of Santa Rita, one about a quarter of a mile northeast and the other about the same distance north-northeast of the old north pit of the Chino copper mine; the third is from an outcrop close to the Georgetown Road, about 2 miles northeast of Santa Rita in an unmineralized area. All three samples are of silicified limestones in the Magdalena Group.
Both samples from Santa Rita are brecciated and vuggy, and they weather brown on the outcrop. Their breccia fragments are aphanitic and light brown. The matrix of one sample consists largely of hematite and orange goethite, which contains numerous veinlets and drusy vugs of coarse vein quartz; the matrix of the other sample is fine-grained medium-gray quartz with lenticular vugs, parallel to the bedding, that are coated and locally filled with brown limonite. The breccia fragments have a homogeneous aphanitic jigsaw-puzzle texture and are heavily impregnated with yellowish-brown limonite particles. Matrix quartz in the second specimen is medium grained and heterogeneous; it has a xenomorphic to locally reticulated texture and contains inclusions of jaro-site, goethite, specular hematite, and a little sericite.
The sample of aphanitic jasperoid from the unmineralized area 2 miles northeast of Santa Rita is aphanitic and pale red to moderate red. It has a finegrained heterogeneous xenomorphic to jigsaw-puzzle texture. Some of the numerous original microvugs have been filled with somewhat coarser xenomorphic quartz. This matrix contains a few granules of chalcedony and breccia fragments of silicified grayish-brown coquina in which the original shell textures are well preserved.
Although both samples from Santa Rita are high in Fe, Hg, Ni, Y, and Zn, they show a marked differ-
ence in the accompanying suites of other minor elements. The sample with the iron oxide matrix is slightly high in Be, Co, Ga, In, Mo, Sn, and V. The sample with the quartz matrix is slightly high in Ag, Bi, Cu, Pb, and Te. This difference in minor-element content may be caused, in part, by the difference in iron oxide content; colloidal iron oxide may selectively retain a different suite of minor elements than does colloidal silica. The third sample, from northeast of Santa Rita, shows traces of Ag and Hg, but otherwise it contains no unusual concentrations of minor elements. The indicator-element scores of these three samples are +15, +16, and +2.
Although bodies of jasperoid are not numerous in the Santa Rita area, those that are present seem to conform to the criteria for the recognition of favorable and unfavorable jasperoids.
STEEPLE ROCK DISTRICT (18, fig. 45)
The Steeple Rock district is in the northwest corner of Grant County about 50 miles northwest of Silver City. Base-metal sulfide ore deposits in the district are localized by a strong fault in Tertiary andesitic rocks.
The country rock has been strongly brecciated, and locally replaced by silica adjacent to the fault, in the vicinity of the ore bodies. These ore bodies consist of fissure-vein and replacement deposits of sphalerite, galena, and chalcopyrite in a gangue of vein quartz or jasperoidized andesite. The ore occurs both as coarse-grained masses relatively free of gangue and as fine-grained disseminations in vein quartz and jasperoid (Russell, 1947, p. 5, 6).
TIERRA BLANCA DISTRICT (19, fig. 45)
The Tierra Blanca district is in Sierra County on the east slope of the Black Range near the head of Tierra Blanca Creek, about 6 miles south of Kingston. Lower Paleozoic sedimentary rocks in the area have been intruded by a small stock and numerous dikes of Tertiary quartz monzonite. Silver-lead replacement deposits occur in the Lake Valley Limestone along north-trending faults. The Fusselman Dolomite, at its contact with the overlying Percha Shale, has been extensively replaced by a finegrained pink and white jasperoid. This jasperoid is commonly brecciated, and the breccia fragments are cemented by coarser grained vuggy quartz. The jasperoid contains a little gold and is similar to the jasperoid in the Fusselman Limestone at Kingston (12) (Harley, 1934, p. 108-110).﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 129
TRES HERMANAS DISTRICT (20, fig. 45)
The Tres Hermanas district is in southern Luna County, about 30 miles south-southwest of Deming and 5 miles north of the Mexican border. It has produced small quantities of base-metal sulfide and oxidized ores from replacement deposits in contact-metasomatized Paleozoic sedimentary rocks close to a quartz monzonite stock. A large xenolith of Missis-sippian Escabrosa Limestone in the northern part of the district has locally been replaced by nodules and larger irregular masses of massive fine-grained gray to white jasperoid. Silicified fault zones in the limestone have been prospected without result. This jasperoid is thought to be genetically related to the quartz monzonite intrusion, but it appears to be older than, and unrelated to, the ore mineralization (Griswold, 1961, p. 50-53).
In spite of Griswold’s conclusion that jasperoid is not related to ore in the district, some jasperoid bodies are, at least spatially, related to sulfide ore. A sample of jasperoidized Escabrosa Limestone from the Mahoney mine in the northern part of the district contains fine-grained galena and is taken from a body adjacent to ore. This jasperoid is dense, fine grained, and light gray. It has a homogeneous granular texture and an average grain diameter of 0.05 mm. The rock is cut by veinlets of coarse white calcite, but the quartz matrix is unusually clean and free of inclusions. In spite of its unpromising appearance, the rock is high in several indicator elements. It is rich in Ag, Ce, Cu, Pb, and Zn, and yields a score of +23, and thus it is markedly favorable.
VICTORIO DISTRICT (22, fig. 45)
The Victorio district is in the southeast corner of the panhandle of Grant County. It is about 60 miles south of Silver City and 25 miles west of Tres Hermanas.
Griswold (1961, p. 79) reported several large irregular masses of jasperoid in Fusselman Dolomite on Mine Hill, near the center of this base-metal sulfide district. These masses he regarded as having formed contemporaneously with barren quartz veins that commonly fill preore fault zones. He stated that most of the jasperoid bodies are barren, but that a little galena, chalcocite, and tetrahedrite are present in one of them.
A sample of jasperoid from the Victorio district, taken from a large boulder near the portal of the Chance mine adit, presumably represents this body of ore-bearing jasperoid referred to by Griswold. It consists of coarse-grained vuggy light-yellowish-gray
jasperoid resembling quartzite in texture and color; it contains coarse inclusions of galena as much as an inch in diameter. The vugs are lined with clear quartz crystals.
In thin section the sample appears to be a breccia of coarse-grained, relatively homogeneous jasperoid fragments that have a reticulated texture and a grain diameter that averages 0.1 mm, in a matrix of even coarser grained heterogeneous xenomorphic to reticulated quartz that ranges in grain diameter from 0.2 to 3 mm. The older jasperoid contains rutile needles and some fluid inclusions in negative quartz crystals. Both generations contain local inclusions of diopside and small pyritohedral pseudomorphs of hematite after pyrite, as well as abundant dust-sized particles of allophane and an unidentified yellowish-gray opaque mineral with high relief.
The sample is unusually high in Ag, Ba, Cu, Pb, Sb, Sn, and Zn and yields an indicator-element score of +22 and thus is very favorable.
OTHER OCCURRENCES
At the old Georgetown district (5, fig. 45) in Grant County, about 5 miles northeast of Santa Rita, high-grade silver ore was mined from replacement deposits in silicified Fusselman Dolomite beneath the Percha Shale. Silicification of the limestone and deposition of the primary ore probably were caused by solutions genetically related to the intrusion of Tertiary latite porphyry dikes in the area (Paige, 1916, p. 14).
In the Hansonburg district (8, fig. 45), along the west front of the Sierra Oscura in eastern Socorro County, Lasky (1932, p. 67-69) reported jasperoid that locally replaced limestone of the Magdalena Group. This jasperoid is locally cut by veins containing galena and chalcopyrite. Lasky (p. 79, 81) also mentioned silicified breccia zones along faults in Paleozoic limestone in the Goodfortune Creek (6) and Mockingbird Gap (15) districts near the north end of the San Andres Mountains.
In the Water Canyon district (24, fig. 45), which adjoins the Magdalena district on the southeast, base-metal sulfide vein and bedded replacement deposits- have formed at the intersections of faults and fractures in the Lake Valley Limestone, which has been locally silicified (Lasky, 1932, p. 48-53), but it is not clear whether this is jasperoid or a coarser form of quartz.
Sheridan (1947, p. 4-5) reported a small fluorspar deposit with minor galena along fault zones in partly jasperoidized Paleozoic limestone in Sierra County just across the Rio Grande from Hot Springs (11, fig. 45), now known as Truth or Consequences.﻿130 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
At the Velarde prospect (21, fig. 45), 6 miles northeast of Garfield in the southern Caballos Mountains, southeastern Sierra County, fluorite fills cavities in a bed of jasperoidized limestone in the Magdalena Group (Rothrock and others, 1946, p. 156). The Victorio prospect (23) in the Sierra Cuchillo Range,' 2 miles east of Chise in northwestern Sierra County, explores a fluorite-quartz vein cutting jasperoidized Paleozoic limestone (Rothrock and others, 1946, p. 169).
NORTH CAROLINA AND SOUTH CAROLINA
The only reference I have found in the literature to rock that could be considered jasperoid in these States is contained in Pardee and Park’s discussion (1948, p. 35, 42-44, 50) of rock alteration at the Howie (3, fig. 41), Whitney (3), and Gold Hill (2) mines in North Carolina, and the Haile (5) and Brewer (4) mines in South Carolina, and Sundelius and Bell’s report (1964, p. 212-214) on the Heglar prospect in the Gold Hill district (2), North Carolina.
The gold-mining region in which these mines are located is in the Piedmont belt east of the Blue Ridge Mountains just east of the Catawba River where it crosses the border between North Carolina and South Carolina, from about 20 to about 50 miles south of Charlotte, N.C. These deposits are in metamorphosed Paleozoic volcanic rocks.
Pyritic gold ore is disseminated through intensely silicified zones. The ore bodies grade transitionally outward into barren quartz. The quartz is dense, fine grained, and light gray to dark bluish gray, commonly preserving primary textures of the metamorphosed volcanic rocks it replaces. Silicification preceded mineralization but followed regional metamorphism. It probably occurred in late Paleozoic or Triassic time.
The Heglar prospect in the Gold Hill district (2, fig. 41) of North Carolina, is in a belt of lower Paleozoic amphibolite, which is intruded by granitic rocks. The prospect is in a deeply weathered contact-metamorphic zone consisting largely of pyrite and garnet in a siliceous gangue, and of subordinate epidote, allanite, apatite, chalcopyrite, magnetite, and barite. Allanite, or its alteration products, is largely responsible for both the rare-earth elements and the radioactivity. Silica, in the form of opal, chalcedony, and aphanitic quartz, was introduced late in the paragenetic sequence, and has replaced garnet, sulfides, allanite, and other gangue minerals (Sundelius and Bell, 1964, p. 214-215).
PENNSYLVANIA AND NEW JERSEY
Jasperoid is associated with zinc deposits in lower
EXPLANATION
Area of large mining district X
Minor district or area •
Reported occurrence
Figure 46.—Map showing location of jasperoid-bearing areas in parts of Pennsylvania, New Jersey, northern Virginia, and West Virginia. 1, Bamford; 2, Califon (German Valley) ; 3, Friedensville; 4, New Galena; 5, Howell; 6, Rappa-hanock; 7, Timberville.
Paleozoic carbonate rocks in southeastern Pennsylvania. Miller (1924, p. 62; 1941, p. 337, 340) mentioned silicified Ordovician Beekmantown Limestone associated with zinc ore in the Friedensville district (3, fig. 46) near Bethlehem in eastern Lehigh County. He noted a similar occurrence in the same approximate stratigraphic zone in the Bamford district (1) near Lancaster, and in the Califon (German Valley) district (2) in northwestern New Jersey. Argentiferous base-metal sulfide ores are associated with jasperoid replacing Triassic shale at New Galena (4) in Bucks County. Miller (1941, p. 260) also referred to “jasperoid quartzite” associated with iron ores in Lehigh County; however, these rocks are metaquartzites formed by silica cementation of Cambrian sandstone, and hence are not jasperoids in the sense used here. However, A. V. Heyl (written commun., 1967) reported the presence of large bodies of true jasperoid at the contact of this quartzite or sandstone with the overlying Cambrian limestone at﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 131
Allentown, Topton, Macungi, and Zionsville, all in the vicinity of Friedensville.
FRIEDENSVILLE DISTRICT (3, fig. 46)
Sphalerite in the Friedensville district forms both vein and replacement ore bodies in the Ordovician Beekmantown Limestone associated with pyrite and vein quartz. No galena is found in these deposits, and the sphalerite is so low in iron that it is light bluish gray, resembling dolomitic limestone. Miller (1941, p. 340) stated:
Quartz is especially abundant and occurs as a compact quartzite produced by metasomatic replacement of limestone, as thin veins cutting the limestones in all directions, and as small crystals lining cavities in the somewhat porous altered limestones.
The jasperoid at Friedensville is older than the sulfides, but it appears to be closely related to them both spatially and genetically. I have two samples of this rock, which is slightly darker gray than the dolomitized aphanitic limestone it replaces, but which resembles it closely in texture. Indeed, this jasperoid is so dense and so fine grained that, except for its field relations, it could easily be mistaken for common chert. The contact between jasperoid and host dolomite is megascopically sharp; however, a thin section shows abundant tiny relict grains and rhombs of dolomite in the jasperoid and incipient silicifica-tion of dolomite along grain boundaries close to the contact. Both dolomite and jasperoid are cut by vein-lets of coarse calcite that contains vugs lined with sphalerite and pyrite and filled with late vein quartz. This rock is remarkably deficient in associated minor elements for an ore-bearing jasperoid. It contains, in addition to Ca, Mg, Fe, and Zn (which are present in visible inclusions of dolomite, pyrite, and sphalerite), slightly abnormal concentrations of Na, Ce, Ga, and Mo.
Jasperoid is also present in large bodies in Cambrian limestone and quartzite at Allentown, Topton, Macungi, and Zionsville, all within a few miles of Friedensville and included in the Friedensville district as shown in figure 46. This jasperoid is red or brown from abundant iron oxide, and it differs strikingly in appearance from the dark-gray jasperoid that is characteristic of the main Friedensville district (A. V. Heyl, written commun., 1967).
OTHER OCCURRENCES
Jasperoid at Bamford (1, fig. 46), in Lancaster County, is light gray and is closely associated with galena and sphalerite. At New Galena (4), in Bucks County, dark-gray jasperoid replaces black Triassic
shale in a mineralized fault zone. It is associated with galena, sphalerite, and white vein quartz (A. V. Heyl, written commun., 1967).
At Califon (German Valley), in Warren County, N.J., jasperoid replaces Beekmantown Dolomite, and is closely associated with oxidized lead and zinc ore and iron deposits.
SOUTH DAKOTA
In South Dakota, jasperoid-bearing mining districts are concentrated in a roughly triangular area, about 5 miles on a side, in Lawrence County in the northwestern Black Hills. The apices of this triangle are formed by the West Lead district (3, fig. 47) about 3 miles west of Lead, on the southeast, the Ragged Top Mountain district (2) just east of Spearfish Creek on the southwest, and the Carbonate district (1) north of Squaw Creek near its junction with Spearfish Creek on the north.
The West Lead district contains gold-bearing jasperoid that replaces thin dolomite beds in the Cambrian and Ordovician Deadwood Formation. In the Ragged Top Mountain district, jasperoid bodies in Carboniferous limestone have been mined for gold and silver. In the Carbonate district, jasperoid
108”	106”	104°
1. SHERIDAN \	 \ BIG A HORN ( i	j i ! CROOK j CAMPBELL j	BUTTE i 2x\ J xx 6 i_t LAWRENCE j
1 I JOHNSON	i	i	
W A S H A K 1 E j ! ; i	j WESTON J" i	H PENNINGTON O	 <£ CUSTER Q
| j z ! o • 2 | NATRONA : i | j i. - .	ci i i! i o r CONVERSE i s-l ! * j NIOBRARA | i I i	X \- ALL RIVER tn ... £ 1 cn ! DO l, . . -
i 1 i	* ' *	1 j • PLATTE ! 1 |GOSHEN	lli j z j i ‘i
h er j Ul Ul )		
		
§ < !		SCOTTS BLUFF 1
w $ J		
I CARBON |	ALBANY [	
i	r i		banner |
! x4 ■ ■ j	1		j
	j LARAMIE	
i |	i	KIMBALL '
A	J. .	# CHEYENNE	j	
0	50	100 MILES
Figure 47.-—Map showing location of minor jasperoid-bearing districts or areas in South Dakota and Wyoming. 1, Carbonate; 2, Ragged Top Mountain; 3, West Lead; 4, Miller Hill.﻿132 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
in the same limestone forms the gangue of argentiferous galena ore bodies.
WEST LEAD DISTRICT (3, fig. 47)
According to Irving (1904, p. 112), auriferous jasperoid replacement deposits in the Deadwood Formation have been developed at West Lead and Bald Mountain, and also in the neighboring mining camps of Yellow Creek, Garden, and Squaw Creek a few miles northwest of Lead. The nature of the occurrence of ore and jasperoid is similar in all these places, and these deposits have been described as a group by Irving under the heading “Refractory Siliceous Ores.” The deposits are in blankets very similar to those in the Mississippi Valley.
These jasperoid bodies are flat-banded masses of channellike form, following fracture zones in thin beds of impure dolomite that alternate with beds of shale and siltstone. The banding in the jasperoid preserves original bedding texture in the host dolomite (fig. 2). Where this rock is fresh, it is dense, gray, hard, and brittle, and contains pyrite, fluorite, and other minor accessory minerals. At and near the outcrop, however, it has been oxidized to various shades of red and brown and has local porous layers that contain abundant small vugs. Individual bodies commonly terminate abruptly against impervious shale beds. They exhibit a complete gradation from narrow stringers closely confined to the feeding fractures to broad mantolike conformable masses whose widths are many times their thicknesses (Irving, 1904, p. 124).
In thin section the unoxidized ore consists of irregularly bounded quartz and chalcedony with finely divided disseminated pyrite. The proportions, of chalcedony to quartz vary, but quartz is commonly more abundant. Detrital quartz grains and residual masses of glauconite, as well as fluorite, calcite, barite, and sufide minerals, are locally abundant (Irving, 1904, p. 137).
I have suites of jasperoid samples from the Dead-wood Formation at two localities. One is the dump of the Clinton portal of the Bald Mountain mine about a mile northwest of the summit of Bald Mountain ; the other is the dump of the Annie Creek mine near the head of Annie Creek about 2 miles west of Bald Mountain.
Six of the seven samples from the Bald Mountain mine show conspicuous banding or layering parallel to the original bedding; the seventh sample is a silica-cemented breccia of various types of rock. The rock is extremely variable in color, showing variegated bands of black, dusky red, and various shades of
brown; many of the thinner bands are porous and friable, and as a result, the rock tends to break along these zones of weakness into flat slabs. Some layers are poorly sorted ferruginous siltstone, and these alternate with layers of impure silty dolomite. Both siltstone and dolomite have been replaced by silica, but replacement is more extensive and complete in the dolomite.
In thin section the j asperoid samples show detrital grains of quartz, microcline, dolomite, tourmaline, chert, muscovite, glauconite, clay, and zircon. The replacing silica contains penecontemporaneous pyrite, sericite, and fluorite; the samples are heavily stained and are cut by anastomosing veinlets of supergene hematite, limonite, goethite, and jarosite. Matrix quartz in different layers ranges in texture from aphanitic homogeneous with jigsaw-puzzle texture to medium-grained moderately heterogeneous with xenomorphic texture. Many of the apparently detrital quartz grains contain hematite pseudo-morphs after pyrite; some exhibit peculiar braided microveinlets of goethite, with a strong preferred orientation, which terminate at the grain boundaries.
The suite of samples from the Annie Creek mine area is similar in appearance to the one from the Bald Mountain mine. These rocks are also variegated in color and are banded or laminated with local thin porous vuggy layers. Most of the samples under the microscope are revealed as silicified impure siltstones with a supergene liesegang banding caused by alternating bands of fibrous chalcedony and iron oxides (limonite, goethite, and hematite). The iron oxide-rich bands commonly are conspicuously vuggy, and many of the original vugs have been filled or lined with opal. In one sample, vugs in limonite are lined with lussatite rather than ordinary opal.
One sample consists of breccia fragments of dense medium-gray jasperoid cemented by fine-grained medium- to light-gray silica, which is locally porous and vuggy. The jasperoid has a heterogeneous jigsaw-puzzle texture and a grain diameter that averages 0.01 mm and ranges from 0.005 to 0.05 mm; it contains numerous microvugs. Sparse rounded detrital grains of tourmaline form inclusions, and fine-grained pyrite and barite are heavily disseminated through the matrix; some of the vugs have been filled with opal. The silica cement consists of xenomorphic quartz that has an average grain diameter of 0.04 mm.
The samples from both the Bald Mountain and Annie Creek mines contain an unusually large number of minor elements present in greater-than-normal abundance. Many of these elements can be attributed to the abundant and varied detrital min-﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 133
eral inclusions in these rocks, but some appear to have been introduced by the hydrothermal silicifying solutions. The following elements are abnormally high in most of the samples from both localities: Al, Fe, Na, K, Ag, As, Ba, Be, Ga, Ni, Pb, Sr, V, Y, and Yb. One or more samples also contain higher-than-normal concentrations of Mn, Co, Cu, In, Nb, Nd, Sc, Tl, Zn, and Zr.
Indicator-element scores on eight samples analyzed ranged from +28 to +4. Three of these samples yielded scores of > + 15, three yielded scores between + 10 and +15, and two yielded scores of +4.
RAGGED TOP MOUNTAIN DISTRICT (2, fig. 47)
At Ragged Top Mountain a laccolith of phonolite has been intruded at the base of massive Carboniferous limestone. Locally, this limestone has been replaced by jasperoid, which contains gold and silver telluride ore along fracture zones north, south, and west of the intrusion.
On the Dacy claims just north of the mountain, locally brecciated limestone in a northeast-trending fracture zone has been replaced by fine-grained dense gold-bearing jasperoid that preserves both the texture and the color of the host rock, yet has a sharp contact with this rock. In the zone of oxidation near the surface the jasperoid consists of irregular boulders and masses of iron-stained silicified limestone breccia fragments cemented by coarser quartz which contains many sharp angular cavities lined with quartz crystals (Irving, 1911, p. 646; 1904, p. 172-176).
At the Ulster mine on the south side of Ragged Top Mountain, according to Irving (1904, p. 176),
The ore occurs as irregular masses of silicified limestone with which are associated quantities of brilliant purple fluorite. These masses are generally in the limestone at the contact of that rock with irregular bodies of porphyry * * *. The portion containing fluorite is usually lower in gold than other parts of the rock, and the highest values are contained in the dark-colored silicified limestone.
* * * * * *
The general character of the ores is such that they may readily be seen to be replacements of limestone by silica and fluorite with small quantities of gold, silver, and tellurium.
Five samples of jasperoid taken from blocks that were excavated from opencuts of a mine between Johnson Gulch and Calamity Gulch about a mile west of the summit of Ragged Top Mountain consist largely of angular dense jasperoid breccia fragments. They are light gray, medium gray, pinkish gray, and grayish orange, and have an aphanitic, locally vuggy, quartz matrix that is heavily impregnated with iron oxides, which impart to it various shades of brown and red.
The breccia fragments are homogeneous to slightly heterogeneous quartz that has a jigsaw-puzzle texture and a grain diameter that averages about 0.01 mm and ranges from 0.005 to 0.05 mm. The fragments contain sparse microvugs, allophane particles, local concentrations of tiny black opaque particles, and tiny hematite cubes pseudomorphous after pyrite. Some of them contain aggregates of coarser (0.01-0.15 mm) xenomorphic to subhedral quartz grains with abundant carbonate particles in their cores.
The matrix quartz is vuggy and has a heterogeneous xenomorphic texture that is coarser than that of the breccia fragments; its grain diameter averages about 0.05 mm and ranges from <0.01 to 0.3 mm. It contains abundant goethite, brown and orange limonite, hematite, and irregular masses of fluorite.
Irving (1904, p. 174-175) mentioned the occurrence of a pinkish-brown pigment uniformly distributed as a thin coating on quartz grains of jasperoid ore from the Dacy claims. This material was thought to be an oxidation product of sylvanite.
Standard oxide analyses of two samples of this ore (Irving, 1904, p. 174) are given, in percent, in the following table. It is noteworthy, though possibly fortuitous, that the sample that showed the higher silica content also showed more Ag and Au. (In the table, “N.d.” indicates not detected.)
Sample	Sample
	1	2		1	2
SiC>2 			 90.990	96.27	H20- 105° I H20+ 105° j	0.110	0.03
AI2O3 			 2.970	.26			.42
		.26	C02 			.96
FeO 			 3.024	.19	Volatile 			802	
MgO -		.19	S 			 N.d.	.05
CaO 			 1.138	1.16	Au 			053	.06
BaO 			 N.d.	.06	Ag 			003	.02
		 N.d.	.05 .11 ng trace	Te 			091	.03
K20 	 Li20 			 N.d. 	 N.d. Stro		Total			99.181	100.12
Most of the five samples from the mine west of Ragged Top Mountain are high in Fe, Ba, Be, Mo, Ni, Pb, and V, as shown by spectrographic analyses. The richest sample also contains abnormally high concentrations of As, In, Sb, and Zn. Indicator-element scores on the five samples are +20, +12, + 7, +3, and +3. Although fewer minor elements are included in this list than in the one for samples from the West Lead district, all these samples contain detectable amounts of molybdenum (0.15 percent in one sample), whereas this element was not detected in most of the samples from the West Lead district.﻿134 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
CARBONATE DISTRICT (1, fig. 47)
In the Carbonate district, on the north side of Squaw Creek, Carboniferous limestone is intruded by sills, dikes, and irregular masses of porphyry. Locally, replacement deposits of argentiferous galena, oxidized near the surface to cerussite, are present in silicified limestone adjacent to these in-trusives. At the Iron Hill mine, the largest in the district, an ore body of this type was developed to a depth of 300 feet on the east side of a thick dike of fine-grained white porphyry. In the Seabury mine a fracture filled with pinkish-red auriferous gouge is encased in ferruginous j asperoid that replaces the limestone for as much as 3 feet from the fracture. This j asperoid locally contains galena, cerussite, and cerargyrite in amounts sufficient to be profitably worked (Irving, 1904, p. 177-178).
TENNESSEE
In Tennessee, bodies of j asperoid are known in the mining districts of Bumpass Cove (6, fig. 41), Eastern Tennessee (8), Central Tennessee (7), and Sweetwater (9). In the Bumpass Cove area large masses of j asperoid are associated with iron and manganese deposits in a residual clay overlying Lower Cambrian Shady Dolomite and with the oxidized base-metal sufide deposits in this dolomite.
The Eastern Tennessee district is characterized by extensive zinc sulfide replacement deposits in dolomi-tized limestone of the Ordovician Kingsport Formation ; in some places the host rock has been replaced by jasperoid adjacent to these ore bodies. The Central Tennessee district covers a large area south and east of Nashville in which small fissure vein deposits of sphalerite, galena, barite, and fluorite cut Ordovician limestone and dolomite; breccia fragments of carbonate host rock in some of these veins have been replaced by buff to gray jasperoid, but silicifi-cation of the host rock outward from the veins is not abundant. It is more abundant in the Hoover and Knight zinc veins than in some of the others.
BUMPASS COVE DISTRICT (6, fig. 41)
Bumpass Cove is near the east end of Tennessee in Washington and Unicoi Counties a few miles north of the North Carolina State line. Masses of ferruginous, manganiferous, and zinciferous jasper-oids are locally abundant in this area in residual clay overlying the Shady Dolomite, although, commonly, the fresh dolomite beneath the clay contains little jasperoid. Similar jasperoids are also present south of Mountain City at the northeast tip of Ten-
nessee. Here, the jasperoid is locally jointed and brecciated and is most abundant where the underlying dolomite has been cut by faults. In the Bumpass Cove district, however, most of the jasperoid is apparently unrelated to faults, although it is concentrated in areas where the dolomite shows considerable deformation (King and others, 1944, p. 22-23).
This j asperoid forms irregular, but approximately, equidimensional bodies ranging in size from small nodules to masses 20 feet in diameter. Generally, it is yellowish brown, but, locally, it is white, gray, black, red, or dark brown. In some places it forms open boxworks lined with light-colored drusy sac-charoidal quartz or mammillary cryptocrystalline silica. Silicified oolites and molds of dolomite rhombs in this jasperoid provide evidence that it formed by replacement of dolomite. The jasperoid is commonly associated with deposits of iron, manganese, and zinc oxides, which have replaced the matrix clay and, in some places, the jasperoid (Rodgers, 1948, p. 15-16).
Silica in the dolomite beneath the clay is largely limited to light-colored friable quartz, which coats fractures and open cavities but which does not replace the dolomite. It is similar in appearance and mode of occurrence to the late quartz found in voids in the jasperoid.
The clay in which the jasperoid is found is largely confined to high dissected terraces and is overlain in most places with old terrace gravels. Jasperoid is thought to have formed by silicification of dolomite contemporaneous with its weathering during an ancient, more humid climatic cycle (King and others, 1944, p. 24; Rodgers, 1948, p. 17).
EASTERN TENNESSEE ZINC DISTRICT (8, fig. 41)
Large replacement deposits of sphalerite in the Ordovician Kingsport Formation in the Eastern Tennessee district, north and northeast of Knoxville, are associated with extensive preore dolomitization of limestone beds and brecciation of the dolomite. Locally, replacement of the carbonate host rock by early gray and black jasperoid has occurred adjacent to the ore bodies. This jasperoid, which generally extends only a few feet from the ore bodies, contains disseminated sphalerite, with which it is considered to be penecontemporaneous (Hoagland and others, 1965, p. 708).
Two samples of this jasperoid are aphanitic in hand specimen and have a greasy luster and irregular color bands of light gray, olive gray, greenish gray, and moderate brown; locally, they contain small irregular masses of white calcite.
In thin section the matrix is seen to consist largely﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 135
of homogeneous aphanitic jigsaw-puzzle-textured quartz, which contains scattered relict grains and small masses of dolomite. Chalcedony is abundant, both as small spherical or ellipsoidal masses with concentric colloform bands and as coarser grained feathery masses filling former vugs. Some former vugs have been filled with medium-grained xeno-morphic quartz-. A rounded mass of white coarsely crystalline calcite surrounded by matrix jasperoid in one of the samples is probably an inclusion, but it could also be a late vug filling. This calcite mass contains abundant disseminated euhedral quartz crystals which, in turn, contain dust-sized carbonate particles. Thin veinlets of late calcite and pale-yellow opal cut the matrix in places. The contact between the dense jasperoid and equally dense dolomitic host rock is sharp in some places, though generally it is marked by a transition zone about 0.1 mm wide that consists of slightly coarser recrystallized dolomite with intergranular veinlets and scattered disseminated masses of jasperoid quartz.
Spectrographic analyses of these samples show that they contain only Na, Ba, and Sr in greater-than-average abundance. The absence of indicator elements from this list is unusual in view of the close association of the jasperoid with sphalerite ore, both spatially and genetically. The cherty appearance of this jasperoid and the abundance of colloform textures and chalcedony suggest that it was originally deposited as a silica gel.
CENTRAL TENNESSEE DISTRICT (7, fig. 41)
The Central Tennessee district is within the Nashville Dome south of Nashville. Middle Ordovician limestone and dolomite exposed in this broad upwarp have been cut by many faults and small fractures. These locally are filled by base-metal sulfide, barite, and fluorite veins. Breccia fragments of host rock in these fissures locally have been completely silicified, and in a few places the vein walls also have been converted to jasperoid for a distance of 1-2 feet outward from the vein (A. V. Heyl, written com-mun., 1965).
Two jasperoid samples from the Hoover mine, south of Milton in the Central Tennessee district, are replacements of limestone breccia fragments— one from the vein and the other from the vein wall. Both samples are dense, fine grained, and dark gray, and the one from the vein also contains abundant disseminated dark-yellowish-orange sphalerite. The matrix quartz is fine grained and somewhat heterogeneous ; it has a reticulated to xenomorphic texture, a mean grain diameter of about 0.02 mm, and a size
range of 0.005-0.15 mm. Relict carbonate grains and dust-sized carbonate particles are abundant in the quartz. Narrow veinlets of white calcite cut the matrix. Sphalerite grains locally surround matrix quartz grains. The sample from the vein wall shows a well-marked transition zone about 1 cm wide between jasperoid and limestone host rock. This zone is marked by a gradual change from fine-grained quartz with sparse interstitial calcite to fine-grained calcite with sparse interstitial quartz. These specimens and those of typical black jasperoid from the Blue Goose mine in the Joplin area of the Tri-State district are strikingly similar in appearance.
The sphalerite-bearing jasperoid sample from the breccia fragment in the vein is abnormally high in Cu, Ga, Pb, and Zn, and yields an indicator-element score of +15. The sample from the vein wall shows high Nb, Sr, and Zn and yields an indicator-element score of +3.
OTHER OCCURRENCES
Jasperoid, which contains barite and fluorite but which otherwise is similar to that of the East Tennessee district, is present in the Sweetwater district (9, fig. 41) in northwestern Polk County, about 50 miles southwest of Knoxville (A. V. Heyl, written commun., 1967).
TEXAS
Jasperoid has been reported from two mining districts in western Texas, close to the Rio Grande. One is the Shatter silver-lead-zinc district (3, fig. 48) in south-central Presidio County, about 200 miles southeast of El Paso, where structurally controlled sulfide replacement deposits occur in Permian limestone. The other district, the Eagle Mountains (1), is a fluorspar district near Eagle Peak in southern Hudspeth County, about 100 miles southeast of El Paso, where the ore deposits are replacement bodies in Cretaceous limestone and vein fillings in Tertiary rhyolite.
SHAFTER DISTRICT (3, fig. 48)
A massive section of Permian limestone 1,000 feet thick contains most of the ore in the Shatter district. This limestone is overlain unconformably by about 1,500 feet of Lower Cretaceous rocks that also consist largely of limestone. The ore is principally in the form of mantos, controlled by high-angle normal faults and, to a lesser extent, by low-angle thrust faults and related shear zones in the Permian limestone. There has also been some mineralization of the overlying Cretaceous rocks, but it has not re-﻿136 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
104°	102°
i |	\ . i i | V,, WINKLER j ! ‘ V'l LOVING j | | M,D '-v, 1 j cc,°" i	i _ i
j	<c-\	r~ - * T ' ‘	i
! CULBERSON / i	‘i—, i c"*Nsi » E e v e ^ ^	j
T E / li x-x x % i x-v-'. 1	X A S / \ !	. -L. .
	V / ‘-'v. 's / S'n /	\
\L"'' JEFF D	'x/	
\ '			__	/x 	r	)
		i
\ 	(	j \ 		1 x I TERRE \j *2	L.	 L L j i
* P R E S 1 D	i o i \	i
\ X3	! BREWSTER _	
	/	
\	j	
		
	X*	L		
EXPLANATION
x
Minor district or area •
Reported occurrence
Figure 48.—Map showing location of jasperoid-bearing areas in Texas. 1, Eagle Mountains; 2, Sanderson;
3, Shatter.
suited in minable ore deposits. Hydrothermal alteration and mineralization in the district apparently occurred in the following sequence: (1) Dolomitiza-tion of limestone, (2) siliceous replacement of limestone and dolomite, (3) deposition of calcite and ore sulfides, and (4) supergene alteration of sulfide ore (Ross, 1943, p. 45). Hypogene ore and gangue minerals include dolomite, calcite, quartz, pyrite, sphalerite, galena, and argentite and minor chalcopy-rite and tetrahedrite. Extensive supergene alteration of the ore bodies has largely converted the primary sulfide minerals into a variety of minerals, including iron and manganese oxides, plumbojarosite, cerargy-rite, native silver, cerussite, anglesite, descloizite, covellite, and chrysoeolla.
The ore bodies contain abundant fine-grained jasperoid, and the limestone host rock adjacent to the ore bodies has locally been replaced by silica, partly as disseminated quartz grains in the host rock and partly as massive jasperoid in irregular masses and layers along bedding planes. Ross (1943, p. 104) stated that “In much of the better ore, silicification appears to have been nearly complete.” Although quartz veins are not found in the ore zone, much of the ore has been brecciated and recemented by silica, after the original jasperoidization of the limestone.
Andesite and basalt dikes in the area are partly silicified, and beds of the Lower Cretaceous Presidio Formation have been locally silicified along fractures (Ross, 1943, p. 104-105).
EAGLE MOUNTAINS DISTRICT (1, fig. 48)
The Eagle Mountains district consists of several small fluorspar deposits that are concentrated in the vicinity of a Tertiary syenite stock at Eagle Peak, in southern Hudspeth County. These deposits consist of replacement mantos in Lower Cretaceous limestone and also of fillings and breccia cement in veins and faults cutting the limestone and the overlying Tertiary rhyolite (Gillerman, 1953, p. 1, 91).
Quartz occurs in the limestone manto deposits both as detrital sand grains and as recrystallized quartz intimately associated with fluorite. Locally, the host limestone adjacent to such replacement deposits has also been extensively silicified. In Spar Valley and in deposits at Rocky Ridge, fluorspar veins in limestone are encased in conspicuous masses of fine-grained dense brown or bluish-gray jasperoid. Gillerman (1953, p. 85) wrote of the deposits at Rocky Ridge:
The effects of recrystallization and silicification are present throughout the limestone sequence, and it is generally difficult to determine the original nature of the rock. Complete silicification of the limestone resulted in a brown or blue-gray hard quartzitic-appearing rock that breaks with a conchoidal fracture and a smooth surface. Gradations from pure unaltered limestone to these quartzitic-appearing rocks can be observed in the same boulder or outcrop. The recrystallization and silicification of the limestone is due primarily to mineralizing solutions travelling along many faults and other fractures in the area.
OTHER OCCURRENCES
Near Sanderson (2, fig. 48) in Terrell County, high terrace gravels presumed to be of Pleistocene age contain abundant rounded pebbles which consist of light-gray aphanitic silica shells surrounding irregular cores of altered Cretaceous limestone (V. L. Freeman, oral commun., 1965). Examination of a thin section cut through one of these pebbles shows that the outer part of the limestone core is weathered and porous with numerous large irregular vugs in the contact zone. The shell consists of vuggy heterogeneous medium-grained quartz that has a jigsaw-puzzle texture, masses of flamboyant chalcedony, and abundant carbonate particles in the quartz. This suggests that the limestone core fragment was partly weathered before the silica shell was formed, that silica was precipitated as a colloidal gel, and that it partly replaced limestone in the contact zone.﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 137
UTAH
Jasperoids in the major districts (21, fig. 49) of Utah, the Tintic and East Tintic, have been discussed previously in this report. Fifteen other districts in the State also contain abundant jasperoid, and nine additional localities are known in which siliceous replacement bodies have been noted (fig. 49).
Most of the jasperoid-bearing districts of Utah are scattered through the Great Basin province, which occupies approximately the western third of the State; however, jasperoid is also present in the San Rafael Swell, west of Moab, in eastern Utah. Most Utah mining districts that are distinguished by jasperoid bodies are argentiferous base-metal sulfide producers in which both jasperoid and ore formed as structurally controlled replacements in Paleozoic carbonate rocks. The Bull Valley district (3, fig. 49) produced gold from veins that cut Pennsylvanian limestone. In the uranium mines of the San Rafael Swell area (18) and the silver mines at Silver Reef (20), silica has replaced Triassic siltstone or shale below the ore zone.
BINGHAM DISTRICT (2, fig. 49)
In the Bingham mining district in Salt Lake County, north-central Utah, a thick Pennsylvanian quartzite, containing interbedded limestone, has been folded into an open syncline that plunges northwest; it is intruded by quartz monzonite porphyry stocks and several dikes and sills. Both the sedimentary and the intrusive rocks are cut by numerous northwest- and northeast-trending faults. One of the quartz monzonite porphyry stocks contains a large low-grade disseminated “porphyry copper ore body”; numerous smaller, higher grade copper, lead, and silver deposits replace the limestone beds south and west of the stock. The ores show a zonal distribution in which copper predominates in and close to the stock, and lead and silver predominate farther out. Mineralization was preceded and accompanied by marmarization and jasperoidization of the carbonate beds (Boutwell, 1905; Cook, 1961).
Although Bingham is the largest mining district in Utah, the abundance and significance of jasperoid
114°	112°
EXPLANATION
Area of large mining district
•
Major district
x
Minor district or area •
Reported occurrence
Jasperoid province
DISTRICTS, AREAS, AND OCCURRENCES
1.	Argentia
2.	Bingham
3.	Bull Valley (Goldstrike)
4.	Castle Creek
5.	Clifton
6.	Drum Mountains
(Detroit)
7.	Dugway
8.	Fish Springs
9.	Gold Hill
10.	Lakeside
11.	Lucin
12.	Mercur and Ophir
13.	Mount Nebo
14.	North Tintic
15.	Park City
16.	Rush Valley (Stockton)
17.	San Francisco and
vicinity
18.	San Rafael Swell
19.	Silver Islet
20.	Silver Reef
21.	Tintic and East Tintic
22.	Tutsagubet
23.	Vernon
24.	West Tintic
Figure 49.—Map showing location of jasperoid-bearing areas in Utah.﻿138 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
in it are uncertain. Boutwell (1905, p. 67-68, 118, 133, 189-192, 202) discussed at length the jasperoid at Bingham; however, Hunt (1924, p. 879) stated that much of the presumed “jasperoid” is only altered quartzite and that suites of samples from highly mineralized limestone show very little silicifi-cation. According to Winchell (1924, p. 898), much silica was deposited with the replacement ore bodies in the limestone, but very little silica was deposited elsewhere. A more recent comprehensive report (Cook, 1961) on the Bingham district and surrounding area does not mention jasperoid.
Jasperoid is present in many limestone beds in the mineralized area but is most abundant in limestone of the Oquirrh Group. Large, siliceous bodies are present on the east flank of Clipper Peak, others are scattered irregularly through a belt about a mile wide between the stock and the ridge running easterly from West Mountain to the head of Bear Gulch, and a large mass caps the northeast-trending ridge at the head of Yosemite Gulch, east of the Bingham stock.
Mineralization was accompanied, or immediately preceded, by jasperoidization that was localized along fractures. This silicification started with small isolated masses of fine-grained quartz, followed by coarse crystalline quartz with contemporaneous pyrite and chalcopyrite; it resulted in selective replacement of favorable carbonate beds outward from northeast-trending fractures (Boutwell, 1905, p. 189-192, 199).
The jasperoids are closely related both spatially and genetically to some of the sulfide replacement deposits in limestone, and pockets of barren'altered material within the ore bodies commonly consist largely of jasperoid quartz.
According to Boutwell (1905, p. 38, 118, 133, 202), the jasperoids of the Bingham district vary widely in physical appearance. Some bodies retain the texture and color of the original host rock, which they resemble so closely as to be indistinguishable, except for their superior hardness; others are dense, white, and coarse grained with a saccharoidal texture. Locally, beds of white marble alternate with beds of dense cherty jasperoid that are white, black, bluish gray, and various shades of yellow, brown, and red. Limestone in mineralized areas is commonly replaced by porous spongy masses of quartz.
Incipient jasperoidization of the carbonate rocks is marked, in some areas, by thin, anastomosing veinlets of quartz and chalcedony following joint planes and fractures. In other places it takes the form of tiny disseminated quartz particles in re-
crystallized limestone. In the Commercial mine thin veinlets of green and brown opal cut brown recrystallized limestone (Boutwell, 1905, p. 68).
I have only four jasperoid samples from the Bingham district. One is from a small outlying jasperoid body on the divide about 11/2 miles east of West Mountain. The other three are from a larger jasperoid body near the quartz monzonite contact a few hundred feet north of a saddle on the divide, which is about two-tenths of a mile east of Copper-field.
The sample from the ridge east of West Mountain has a dense, heterogeneous, largely xenomorphic groundmass with a few scattered elongated laths. The grain size of the quartz particles ranges from 0.01 to 0.3 mm, and the large grains are locally segregated in irregular masses. Many of the larger grains show zoning of allophane inclusions around cores. The matrix contains abundant disseminated grains of red hematite, a few of which have small residual pyrite cores. The jasperoid is cut by vein-lets and irregular masses of earthy yellow to orange limonite and also by narrow veinlets of jasperoid microbreccia particles in a clay matrix (probably kaolinite and halloysite).
The three samples from the ridge above Copper-field consist of angular breccia fragments of jasperoid in a matrix of orange-brown limonite and, locally, of jarosite. The larger fragments contain abundant irregular open vugs. In texture the matrix quartz ranges from medium-grained homogeneous xenomorphic to heterogeneous xenomorphic. The diameter of the quartz particles ranges from 0.02 to 0.4 mm; local masses and bands of finer grained quartz average 0.01 mm. The quartz contains interstitial brown limonite with local concentrations of carbonate dust particles and scattered flakes of sericite.
The four whole-rock samples previously discussed were ground and submitted to semiquantitative spectrographic analysis. The three samples from the vicinity of Copperfield contained an appreciable quantity of matrix limonite in addition to jasperoid quartz, and the abnormally high concentrations of some of the elements detected in these samples may reflect this contamination.
All four samples showed greater-than-average concentrations of lead and zirconium. Zinc was detected in the single outlying sample but not in any of the three close to the stock. Copper is an order of magnitude higher in these three samples than in the outlying sample. Silver is distributed erratically; in the outlying sample it shows 3 ppm, and in other﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 139
samples it shows 3 ppm, 30 ppm, and below the limit of detection. None of the remaining elements detected in the single sample from the ridge east of West Mountain are present in greater-than-average abundance. The group of samples from near Copper-field on the edge of the Bingham pit contains abnormally high concentrations of Fe, Na, As, Ba, Bi, Mo, Ni, and Sn in addition to the elements previously discussed.
The scores of these four samples suggest that the single sample from the ridge east of West Mountain is in the probably favorable category, probably near the fringe of the zone of sulfide mineralization; the other three samples from the edge of the pit, above Copperfield, all fall in the favorable category.
BULL VALLEY (GOLDSTRIKE) DISTRICT (3, fig. 49)
The Bull Valley mining district is in western Washington County near the north end of the Beaver Dam Mountains, about 50 miles west-southwest of Cedar City and about 10 miles from the Nevada State line. In this area Pennsylvanian limestone has been highly silicified locally along fractures, forming conspicuous outcrops of jasperoid that is stained yellow and brown by iron oxides. This rock contains free gold disseminated in the gangue of quartz, cal-cite, jarosite, and limonite (Butler and others, 1920, p. 598).
CLIFTON DISTRICT (5, fig. 49)
The Clifton district is in western Tooele County at the north end of the Deep Creek Range, a few miles north of Gold Hill and about 12 miles east of the Nevada State line. Here, a thick Mississippian limestone has been intruded by a small stock of Tertiary quartz monzonite. Sulfide ore bodies formed in fissure veins that cut the stock; they are also in the zone of contact metasomatic alteration surrounding it. Beyond this zone of high-temperature alteration the limestone has been replaced by large bodies of cherty fine-grained jasperoid associated with some limonite. These bodies form conspicuous outcrops near the Gold Hill-Clifton road about 11/2 miles south of Clifton. A small amount of prospecting on these “reefs” has failed to locate any ore bodies (Butler and others, 1920, p. 479).
DRUM MOUNTAINS (DETROIT) DISTRICT (6, fig. 49)
The Drum Mountains, or Detroit, district straddles the line between Juab and Millard Counties about 30 miles northwest of Delta. The small desert
range in which the district lies is situated between the Sevier Desert on the east and Whirlwind Valley on the west. This range is a westward-tilted block, composed of a thick series of Precambrian and Cambrian quartzite overlain by Cambrian limestone and dolomite. In the mineralized area these rocks are cut by numerous east- to northeast-trending faults that have displacements ranging from a few feet to a few thousand feet.
The district was originally worked for gold and copper, mostly during 1895-1918, but more recently it has produced manganese ores. The ore bodies are localized by the intersection of fractures with favorable carbonate beds. Although the manganese and gold-copper ores are related genetically, they are separate and distinct in occurrence and composition. Manganese ore bodies contain only traces of gold and copper, and gold-copper ore bodies contain little manganese (Crittenden and others, 1961, p. 507).
Many of the stronger faults served as conduits for silica-bearing hydrothermal solutions that silicified adjacent limestone and dolomite locally and formed conspicuous yellowish-brown jasperoid reefs. These reefs contain disseminated pyrite or limonite after pyrite, chalcopyrite and its oxidation products, and small amounts of other sulfides in and near gold-copper ore bodies (Butler and others, 1920, p. 464). Crittenden, Straczek, and Roberts (1961, p. 515) believed that jasperoid may be closely related genetically to manganese, as well as to copper and gold, and recommended the exploration of jasperoid bodies where they intersect the basal carbonate beds near the Martha mine.
Ten samples of jasperoid from the Drum Mountains district were collected by Lovering (in Lovering and others, 1963, p. Bl) in the course of an investigation of hydrothermal dolomite in the area. All these samples were taken from bodies along faults and strong fractures; three are from mine prospects, and seven are from bodies that have not been prospected.
The jasperoid samples appear to represent two distinct types of rock. Most of the samples, including the three from prospected bodies, are crystalline, vuggy, and heavily iron stained in various shades of yellow, brown, and red. They have a relatively coarse-grained heterogeneous and distinctly reticulated texture and distinct zonal overgrowths on some of the larger quartz crystals. The quartz crystals are locally disseminated through coarsegrained patches of calcite. The jasperoid samples also contain abundant hematite, goethite, and brown limonite; sparse patches of malachite are visible in﻿140 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
one sample from a mine adit, and chalcedony locally lines vugs in the quartz.
The other type of jasperoid is represented by three samples from faults and fracture zones near the abandoned townsite of Joy, northwest of the main mining district. These samples consist of light-gray, yellowish-gray, and brownish-gray cherty-looking quartz which locally is stained brown by iron oxides and which in some places contains large irregular open vugs. The quartz is fine grained and homogeneous and has a xenomorphic to jigsaw-puzzle texture. Yellow limonite and fine-grained cal-cite are abundant, and chalcedony locally lines vugs.
Most jasperoid samples of both types contain anomalously high concentrations of Ag, Au, Bi, Cu, Pb, and Sb. The coarser grained jasperoid with reticulated texture generally shows more minor elements with abnormally high concentrations than does the aphanitic variety. In addition to the elements listed above, most samples in this group also show abundant Ba, Ni, and Zn; one or two of them are also high in As, Co, Ga, Sn, and V. All but two of the samples contain >0.02 ppm of Au, and one sample contains 26 ppm Au.
Indicator-element scores for the group range from +2 to +22. The sample that yielded the highest score contains >1 percent Cu, 0.05 percent Ag, 0.05 percent Zn, and 1.7 ppm Au.
The association of Ag, Bi, Cu, and Pb in this group of samples is noteworthy because it also characterizes jasperoids of the Bingham (2, fig. 49) and Ely (19, fig. 44) districts. This similarity and the high gold content of the jasperoid suggest that the Drum Mountains district may contain considerably more ore than has thus far been mined.
DUGWAY DISTRICT (7, fig- 49)
The Dugway district is in south-central Tooele County, near the north end of the Granite Range, about 55 miles southwest of Tooele. Faults and fractures cutting Mississippian limestone in this district have localized replacement ore bodies of argentiferous galena and sphalerite, all partly oxidized. In the northern part of the district, in the vicinity of the Four Metals mine, the limestone has been highly fractured and replaced with jasperoid near the oxidized ore bodies (Butler and others, 1920, p. 463).
GOLD HILL DISTRICT (9, fig. 49)
The Gold Hill district is in southwestern Tooele County in Tps. 7 and 8 S., R. 18 W., at Gold Hill,
a few miles south of the Clifton district and about 15 miles east of the Nevada State line. Paleozoic shales and carbonate rocks in this area have been broken by both low-angle thrust faults and high-angle faults and intruded by a Tertiary quartz monzonite stock and several smaller igneous bodies. Mining activity in the district centered at Gold Hill, a small northwest-trending ridge, about V/% miles west of Gold Hill townsite, and at the U.S. mine about half a mile south of the townsite. Large replacement ore bodies of arsenopyrite and base-metal sulfides associated with jasperoid were developed here in Carboniferous and Permian limestone. Many other jasperoid bodies are present in various parts of the district in the Mississippian Ochre Mountain Limestone and in carbonate beds of the Mississippian to Permian Oquirrh Formation. These jasperoids are thoroughly discussed by Nolan (1935) and are also shown on the geologic map of the district that accompanies his report.
Nolan (1935, p. 93) stated that jasperoid bodies tend to be concentrated close to the quartz monzonite contact or along faults in the Ochre Mountain Limestone and the Oquirrh Formation that predate the quartz monzonite, and that large jasperoid bodies are exposed on Gold Hill, near the mouth of Barney Reevey Gulch, and at the U.S. mine south of Gold Hill townsite. The district map that accompanies Nolan’s report also shows a mass of jasperoid that is more than 1 mile long and as much as 1,000 feet wide in places along an east-trending fault about li/2 miles south of the summit of Ochre Mountain, outside the main mining area in the district.
Nolan (1935, p. 152-153) described these outcrops as consisting of jagged reddish-brownweathering jasperoid that has been brecciated and recemented by several generations of quartz exhibiting different textures and colors. This jasperoid is commonly vuggy, with breccia fragments of unreplaced limestone and, locally, visible plates of barite, oxidized copper minerals, and masses of green chalcedony. The jasperoid outcrop on Gold Hill is more than 100 feet wide and has been cut by mine workings at a depth of 700 feet, where it has a sharp contact with unreplaced limestone.
The older jasperoid quartz matrix is fine grained, crystalline, and free of fluid inclusions; it shows features that may be desication cracks which partly controlled the location of younger veinlets of coarser quartz. These veinlets commonly exhibit vague outlines of crystals which are normal to the walls and which are now recrystallized to aggregates of an-hedral quartz grains; contacts of veinlets with ma-﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 141
trix quartz are gradational. Where associated with ore the jasperoid commonly contains pyrite, arseno-pyrite, galena, sphalerite, and tetrahedrite or their oxidation products. Elsewhere, barite, chlorite, chalcedony, opal, calcite, and sericite are common accessory mineralsi Contacts between sulfide ore bodies and jasperoid tend to be gradational in contrast to the characteristically abrupt contacts between jasperoid and host rock.
Nolan (1935, p. 94)' expressed the opinion that the silica that formed the original jasperoid was deposited as a gel and that the younger quartz veinlets in it may have formed by the expulsion of silicabearing fluid into shrinkage cracks during the crystallization of this gel.
The jasperoid of the Gold Hill district is younger than the contact metasomatism and recrystallization of carbonate rocks that accompanied intrusion of the quartz monzonite. In the major arsenic replacement ore bodies of the U.S. mine, quartz is continuous and contemporaneous with jasperoid replacing the limestone host rock. At the Gold Hill mine, jasperoid is closely related to tetrahedrite-bearing quartz veins in the limestone, and limestone adjacent to ore bodies is locally replaced by fine-grained pale-gray jasperoid. Within these ore bodies, in some places arsenopyrite ore has been brecciated and recemented by fine-grained quartz resembling jasperoid; however, it seems that sphalerite is nearly contemporaneous with the silica, and that galena, jamesonite, and stibnite are somewhat younger.
Of nine samples from the vicinity of Gold Hill, two are from outcrops about 5 miles northwest of the townsite, one is from the townsite, and six are from exposures on the south side of Ochre Mountain, 5-6 miles southwest of the townsite. Unfortunately, I have no samples of the jasperoid described by Nolan as being associated with the ore bodies on Gold Hill or at the U.S. mine.
The two samples from the area northwest of Gold Hill may represent the bodies of barren jasperoid mentioned by Butler, Loughlin, Heikes, and others (1920, p. 479) in their description of the Clifton district (5, fig. 49). These two samples were taken from conspicuous outcrops close to the road about midway between the two districts. Both samples represent brecciated and silicified fault zones in Paleozoic limestone. Both consist of gray breccia fragments enclosed in a dense grayish-orange to moderate-brown matrix. Breccia fragments consist of dense dark-gray material that looks like chert and of medium-gray heterogeneous quartz that has a xenomorphic to jigsaw-puzzle texture and an aver-
age grain diameter of about 0.02 mm, cemented in a matrix whose appearance is so similar to that of the fragments that, commonly, the boundaries between fragments and matrix are clearly visible only by reflected light. The matrix contains irregular masses of yellow to brown limonite, and locally shows disseminated grains of hematite that may be pseudo-morphs of original pyrite. Small vugs in the matrix, and fractures cutting it, are commonly lined with coarse xenomorphic quartz, some of which show crystal faces and zonal overgrowths; these fractures and vugs are locally filled with coarse late calcite. Both samples are slightly higher than normal in Ba, Ni, and Pb, but not sufficiently so to place them in the favorable category.
The single sample from Gold Hill townsite was taken from a prominent knob adjacent to an old millsite about 100 yards west of some abandoned buildings. It is not a true jasperoid, but rather a fault breccia composed of comminuted chert and limestone fragments, cemented by indurated calcite microbreccia that shows incipient replacement by quartz that has a coarse jigsaw-puzzle texture and wavy extinction. Opaque orange limonite forms irregular veinlets cutting the carbonate. The sample shows slightly anomalous concentrations of Na, Ba, Cr, Pb, Sr, V, and Zr, but it yields an indicator-element score of only +2.
The six samples from outcrops on the south side of Ochre Mountain, well beyond the limits of the main productive area, are mostly breccias that consist of chert or jasperoid fragments in a matrix of younger jasperoid. The matrix is commonly light olive gray to pale yellowish brown on fresh exposures, grayish orange to yellowish orange on weathered surfaces; breccia fragments are commonly dark yellowish brown to dark gray, darker than the matrix. The breccia fragments are uniformly aphanitic and dense; the matrix is also aphanitic but is locally porous and vuggy. In thin section, both matrix and inclusions have a relatively homogeneous jigsaw-puzzle to locally xenomorphic texture and an average grain size of 0.01 mm; both commonly contain relict dolomite rhombs and carbonate particles. The inclusions are dense, and some are full of opaque carbon particles; whereas the matrix is free of carbon and locally contains abundant open microvugs. Veinlets of calcite, brown limonite, and coarser grained xenomorphic quartz cut the matrix. Two samples taken about 100 yards from a small abandoned shaft contained disseminated pyrite that is largely altered to hematite, and one of these samples also exhibits late veinlets filled with goethite and jarosite. All six samples are higher than average﻿142 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
in Ba, and most of them are also high in Ni and Sr. The two samples that contain disseminated pyrite also show traces of Pb. One of them contains a little Ag and Zn, and the other, detectable As and Bi; their indicator-element scores are +8 and +4, respectively. The other four samples yielded scores ranging from —2 to +3.
LUCIN DISTRICT (11, fig. 49)
The Lucin district is in Box Elder County in T. 6 N., R. 19 W., about 10 miles southwest of Lucin. The district overlaps the Utah-Nevada State line, but most of it is in Utah. Ore deposits consist of copper and lead-zinc-silver fissure replacement ore bodies in Pennsylvanian limestone, which has been intruded by a small stock of Tertiary quartz monzo-nite with local contact metasomatic alteration. The Copper Mountain mine developed copper replacement ore in jasperoid in, and adjacent to, a strong north-trending fault. At the south end of the deposit, massive copper-bearing limonite grades into barren iron-stained jasperoid along this fault (Butler and others, 1920, p. 493).
A jasperoid sample from this district taken from near the head of a gulch about 3 miles north of Bald Eagle Mountain and 1 mile east of the Nevada line, about half a mile from the nearest mine workings, consists of sparse dense dark-gray breccia fragments cemented by a porous fine-grained dark-yellowish-orange matrix. A thin section shows heterogeneous matrix quartz that has a xenomorphic texture and a size range of 0.01 to 0.06 mm; it contains numerous small rounded inclusions of older quartz, minor sericite, carbonate particles, and allophane. Orange-brown limonite is abundant in short veinlets, irregular masses, and as a coating on quartz grains. The sample is slightly high in Ba, Be, Cu, Li, Mo, and Sr, yielding an indicator-element score of +5.
MERCUR AND OPHIR DISTRICTS (12, fig. 49)
These two districts are about 4 miles apart in eastern Tooele County on the western flank of the Oquirrh Mountains, 15-20 miles south-southeast of Tooele. In both districts the ore deposits are largely localized by intersections of faults and fractures with favorable carbonate beds of Mississippian age. Mercur, the southern district, was a famous gold camp early in the 20th century, and it also produced some silver. The Ophir district produced silver, lead, zinc, and copper, but relatively little gold.
According to Gilluly (1932, p. 97), jasperoid is abundant between Mercur and Lion Hill, near West
Mercur, near the mouth of Silverado Canyon, in Dry Canyon, and in the hills between Dry Canyon and Ophir. Although most jasperoid bodies in the two districts are in Mississippian rocks of either the Great Blue Limestone or the Humbug Formation, their distribution is erratic and discontinuous. Structural control of the distribution of jasperoid bodies is shown by their tendency to transgress bedding and by their local association with fracture zones. The outcrops typically are conspicuous, jagged, rusty brown, and thoroughly brecciated, and they contain angular blocks of unreplaced limestone. Contacts between jasperoid and host rock are sharp with no visible transition zone. Coarse-grained white vein quartz commonly cements jasperoid breccia and lines vugs in the jasperoid. Many of these vugs are filled with white calcite. Fresh jas-period is light gray to black and aphanitic to fine grained.
Two common varieties of jasperoid are readily distinguished under the microscope. One consists of cryptocrystalline anhedral interlocking quartz grains <0.03 mm in diameter and accessory chalcedony, tourmaline, sericite, calcite, epidote, apatite, and zircon. The other variety consists of interlocking euhedral to subhedral quartz crystals averaging about 0.2 mm in diameter (reticulated4 texture) and carbon and carbonate dust particles in addition to the accessory minerals that characterize the first variety. The aphanitic variety commonly contains streaks and lenses of coarser quartz with wavy extinction, which is associated with barite and, locally, with stibnite. Younger flamboyant vein quartz with barite cuts both varieties of jasperoid and, locally, this vein quartz is cut, in turn, by still younger brown-stained veinlets of cryptocrystalline quartz and accessory tourmaline, apatite, calcite, and zircon.
Gilluly (1932, p. 100) concluded that the first stage in the formation of jasperoid at Mercur was the replacement of carbonate rock by colloidal silica gel. Rapid crystallization of this gel led to the formation of aphanitic cherty jasperoid, whereas more gradual crystallization produced the coarser grained (reticulated) variety. Crystallization of the gel was accompanied by shrinkage. Coarser grained vein quartz associated with barite and, locally, stibnite and chalcopyrite then filled the shrinkage cracks. Brecciation and fracturing of this mass was followed by introduction of the late-stage cryptocrystalline brown quartz; local replacement was marked by blended contacts. The association of tourmaline with early jasperoid was cited by Gilluly (p. 101) as evidence favoring a relatively high temperature of﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 143
replacement of limestone by silica. He pointed out that barite and stibnite are not present in the oldest jasperoid, and that calcite is abundant only in the youngest.
The genetic and spatial relationships between the various types of jasperoid and the primary ore deposits were not stressed by Gilluly (1932, p. 135), although he noted that in certain parts of the districts (near Mercur and in the hills between Ophir and Dry Canyon) ore deposits are commonly localized within or beneath jasperoid bodies. His detailed description of the various types and ages of jasperoid and the minerals commonly associated with each suggests that the original replacement of limestone by silica gel preceded ore-stage mineralization, but that the later silica, which cements jasperoid breccia and forms quartz veinlets cutting jasperoid, was approximately contemporaneous with it.
Sixteen samples of jasperoid from the Mercur-Ophir area are in my collection; eight are from the main mineralized area close to the old town of Mercur, three are from outcrops in the relatively unmineralized area between the two districts, and five are from the Ophir district.
The samples from Mercur were taken in the vicinity of the Franklin Lease mine west of the townsite and the Sacramento mine south of the townsite. They contain examples of the two types of older gray jasperoid and of the younger brown jasperoid described by Gilluly (1932). The aphanitic variety with jigsaw-puzzle texture is largely free of inclusions, but it contains sparse carbonate and allophane dust particles. The coarser grained reticulated variety contains pyrite, or its oxidation products, and barite in addition to sericite, and carbonate particles. The brown jasperoid contains all these minerals plus abundant limonite particles and, locally, tourmaline.
The three specimens from outside the main mining districts were collected from near the top of Rover Hill, near the mouth of Silverado Canyon, and about half a mile up Silverado Canyon. The sample from Rover Hill is of the coarser grained reticulated older jasperoid and contains sericite, carbonate particles, and sparsely disseminated pseudomorphs of jarosite after pyrite. Both samples from Silverado Canyon are of the aphanitic older jasperoid and contain only sparsely disseminated sericite, allophane, and carbonate particles.
Of the five samples from the Ophir district, two are from the vicinity of the Chloride Point mine about a mile south-southeast of Ophir, two are from the outskirts of the townsite of Ophir, and one is from an outcrop near the Lakes of Killarney mine
about 2 miles west of Ophir. Four of these samples show the coarse-grained reticulated jasperoid, but the fifth one, which was collected close to a porphyry contact, has a coarse-grained heterogeneous xeno-morphic texture. The sample from near the Lakes of Killarney mine is from a fault zone and is the only one in the suite that shows well-defined examples of both the older jasperoid types described by Gilluly (1932). In this specimen, breccia fragments of aphanitic jasperoid are cemented by a matrix of coarser reticulated jasperoid that is cut by veinlets of still coarser xenomorphic quartz; the whole mass was then rebrecciated and cemented by coarse calcite. Accessory minerals in these jasper-oids are the same as in their counterparts from the Mercur district: carbonate particles, sericite, pyrite, or its oxidation products, and, locally, barite.
There appears to be some difference between the suites of minor elements present in abnormally high concentrations in the jasperoid samples from the two districts. Nearly all the Mercur samples are high in Ba and Hg, and most of them are high in Ag, Sr, and Te. Nearly all the Ophir samples are high in Sr, Ag, Cu, Pb, and Zn, and most of them are high in Ba, Hg, Ni, Sb, Te, and Zr. Two of the Mercur samples contain detectable amounts of As and Mo, elements not found in any of the Ophir samples. Two samples from Ophir, however, contain Bi, Nb, and Sc, elements not found in the Mercur samples.
Only three of the eight samples from the Mercur district yield indicator-element scores greater than + 5, and the highest was +11. Four of the five samples from the Ophir district yield scores greater than + 10. The highest score for this group was +18, and the lowest, +1. All three of the samples taken between the two districts gave scores of —1.
MOUNT NEBO DISTRICT (13, fig. 49)
The Mount Nebo district is in the northeast corner of Juab County in the Wasatch Range, about 10 miles northeast of Nephi. Sulfide ore deposits in the district form replacement bodies along faults and fractures in Paleozoic carbonate rocks.
At the Santaquin Chief mine a pipelike ore body of galena in a gangue of quartz and calcite has been developed at the intersection of north- and easttrending fractures in jasperoidized Mississippian limestone. This jasperoid contains sericite, chlorite, titanite, fluorite, limonite after pyrite, and galena as both disseminated grains and narrow streaks and lenses. Vugs in the jasperoid are lined with crystalline quartz and calcite (Butler and others, 1920, p. 332).﻿144 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
NORTH TINTIC DISTRICT (14, fig. 49)
The North Tintic district is on the line between Utah and Tooele Counties, about 5 miles north of Eureka in the northern East Tintic Mountains. It lies just north of the Tintic and East Tintic districts (21, fig. 49), which were previously discussed in the present report. Oxidized lead and zinc deposits, lean in silver, were mined in the district. Paleozoic sedimentary rocks in the area, consisting largely of limestones and dolomites, have been folded into a north-trending asymmetrical anticline and syncline; these folds are cut by several north-trending, westdipping thrust faults that were, in turn, cut by north- and northeast-trending high-angle faults before early Tertiary volcanism that blanketed the area with flows and pyroclastics (Proctor, 1964, p. 1565-1567).
Dikelike and bedded replacement bodies of jas-peroid are abundant in and near Chiulos Canyon, largely in the Deseret and Humbug Formations, but, locally, in the Great Blue Limestone above the Humbug. These dark-brown to reddish-brown bodies are as much as 100 feet thick and several hundred feet long and form conspicuous outcrops. North and northeast of this area of intense jasperoidization is a zone in which smaller bodies of fine-grained gray jasperoid occur as replacement masses in brecciated fault zones. Intensity of jasperoidization is greatest in the southwestern part of the area closest to the Tintic and East Tintic mining districts.
The jasperoid consists of fine-grained quartz that has an average grain diameter of <0.1 mm. Vugs are abundant locally, and they are commonly lined with euhedral quartz crystals. Brecciation of jasperoid and recementation by later quartz are conspicuous in some places. Red iron oxide commonly accompanies this late quartz, a few hematite pseudo-morphs after pyrite have been noted in thin sections, and late calcite also fills some fractures in jasperoid (Proctor, 1964, p. 1575).
In this area, as in the Tintic and East Tintic districts (21, fig. 49) to the south, hydrothermal dolomitization preceded jasperoidization which, in turn, preceded sulfide mineralization.
RUSH VALLEY (STOCKTON) DISTRICT (16, fig. 49)
The Rush Valley district is in eastern Tooele County, about 8 miles south of Tooele and 10 miles northwest of the Ophir district.
In this district replacement base-metal sulfide deposits have been formed close to the axis of a northward-plunging anticline in favorable beds of Car-
boniferous limestone and quartzite, where fractures and small faults, parallel to the anticline, cut these rocks. Highly altered felsic dikes fill some of these fissures. Jasperoid replacing limestone adjacent to the fractures is locally abundant, as it is in the Ophir district.
At the Muscatine mine, near the SW cor. T. 4 S., R. 4 W., abundant jasperoid and hornfels are associated with pyrite, sphalerite, and galena replacement bodies in limestone (Gilluly, 1932, p. 163).
SAN FRANCISCO DISTRICT AND VICINITY (17, fig. 49)
The San Francisco mining district is at the south end of the San Francisco Mountains in Beaver County, about 15 miles west-northwest of Milford. A much larger area, which extends from the Escalante Valley on the east to the Wah Wah Mountains on the west and from the Iron County line on the south to the Millard County line on the north, contains many widely scattered small silver, lead, zinc, and copper mines and areas of hydrothermally silici-fied rocks. This larger area is considered here, for convenience, with the San Francisco district.
At the Horn Silver mine, in the main San Francisco district, volcanic rocks on the hanging-wall side of a strong mineralized fault zone have been extensively leached of all their principal constituents, except iron and silica, yielding a rock composed chiefly of fine-grained quartz with disseminated pyrite and some barite. Limestone on the footwall side of this zone is much less altered, although it has been generally recrystallized and locally silicified along fissures (Butler, 1913, p. 168).
At the Harrington-Hickory mine in the Star district on the east side of the Star Range, 5 miles from Milford, Triassic limestone, interbedded with siliceous shale and quartzite, has been replaced by argentiferous galena and sphalerite ore bodies along small fractures, and has been converted to jasperoid for as much as 30 feet outward from the fractures, although the associated shale and quartzite are only slightly altered. The jasperiod quartz contains accessory galena, pyrite, orthoclase, apatite, titanite, garnet, and magnetite (Butler, 1913, p. 195).
Of 10 samples from the San Francisco district and surrounding area in my collection, three are from the south end of the main district along State Highway 21, close to Squaw Spring; three are from a prominent jasperoid ridge surrounded by altered Tertiary volcanic rocks about 10 miles south of Squaw Spring; and the remaining four were collected in T. 30 S., R. 14 W., at intervals along a dirt road running from Milford around the south end of﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 145
the Wah Wah Mountains far south of the old Wah Wah lead-zinc district. Two of this last group are jasperoid samples, and the other two are dolomite showing incipient silicification.
The samples from near Squaw Spring weather yellowish brown to reddish brown; one of these is light brownish gray on fresh surfaces, and the other two are pale red. They were collected from an easttrending breccia zone in Cambrian limestone, about a mile from the nearest large mines. The rocks are microbreccias of small angular jasperoid and limestone fragments cemented by aphanitic quartz that has a jigsaw-puzzle texture. Some of the jasperoid fragments are coarser grained and have a heterogeneous, locally xenomorphic texture, and contain abundant carbonate dust particles. The matrix is cut by veinlets of xenomorphic quartz that has an average grain diameter of about 0.1 mm. Hematite is locally abundant in irregular masses and anasta-mosing veinlets that cut the matrix, but it shows no evidence of derivation from original pyrite. Sparse irregular inclusions of barite as much as 1 mm in diameter were observed in one sample. All three samples are slightly high in Pb and Sr, one is slightly enriched in Ba, and another in Hg. The indicator-element scores for the three are +2, —2, and —3, respectively.
The three samples from the locality 10 miles south of Squaw Spring were collected from the north end, center, and south end of a strongly jasperoidized limestone ridge about a quarter of a mile long, surrounded by argillized and pyritized Tertiary volcanic rocks. The nearest known ore deposits are in the Star Range 5 miles to the northeast. All three samples are aphanitic, dark gray on fresh exposures and yellowish brown on weathered surfaces; the sample from the north end of the ridge contains aphanitic olive-gray breccia fragments, and the one from the south end is cut by small veinlets of yellowish-gray fine-grained quartz with sparse tiny vugs. Petrographic study reveals three generations of silica. The oldest of these is aphanitic with jigsaw-puzzle texture, is pale brown by transmitted light, and contains rounded detrital quartz grain inclusions. The intermediate generation has a heterogeneous xenomorphic to reticulated texture and an average quartz grain diameter of 0.02 mm; carbonate particles are abundant in the grains, and opaque amorphous brownish-black carbonaceous material is concentrated along the grain boundaries. In one specimen the quartz of this generation contains disseminated jarosite and hydromica. The youngest generation of quartz fills veinlets. It is coarser grained, has a xenomorphic texture, and is free of
inclusions. All three samples contain traces of Ag, Y, and Yb and slightly anomalous Zr. Two of the three also show higher-than-normal Ba, La, Ni, and Sr. The indicator-element scores are all low ( — 1, — 1, and +2).
The four samples from near the south end of the Wah Wah Mountains represent bodies located many miles from the nearest known mineral deposits. These bodies are localized by fracture zones in Paleozoic limestone and dolomite, and many of them exhibit a well-marked transition zone characterized by an interlacing network of quartz veinlets in the host rock. Two samples are from these transition zones, and the other two are from the main jasperoid bodies. Both of the jasperoid samples have a moderate-gray medium-grained locally vuggy matrix, cut by coarser grained quartz veinlets. The matrix consists of heterogeneous xenomorphic to locally reticulated quartz that has an average grain diameter of about 0.05 mm; it contains abundant carbonate particles, small ragged masses of relict calcite, and numerous open vugs. The veinlets have a xenomorphic texture and an average grain diameter of about 0.2 mm, and they are free of inclusions. Although the texture of these samples is promising, the scarcity of accessory minerals in them is reflected in the chemical analyses, which show only Ba, Sr, and Zr in slightly abnormal concentrations. Both samples yield scores of —1.
The samples from the transition zones are carbonate breccias consisting of angular fragments of coarse-grained recrystallized dolomite in a matrix of intimately mixed fine-grained carbonate and quartz in various proportions. The quartz in this matrix has "a heterogeneous texture and contains abundant carbonate particles. Numerous veinlets of clear homogeneous xenomorphic quartz cut the matrix ; although these contain local inclusions of coarse-grained calcite, the vein quartz is free of carbonate particles. The rock was thoroughly brec-ciated before silica was introduced; however, it is not clear from examination of these samples whether the brecciated host rock was first cut by the coarser quartz veinlets and then replaced by the finer grained matrix jasperoid, or whether replacement was followed by vein filling.
SAN RAFAEL SWELL AREA (18, fig. 49)
The San Rafael Swell is a broad anticlinal flexure in southwestern Emery County between the San Rafael River on the north and the Muddy River on the south. Uranium deposits in continental mudstones, sandstones, and conglomerates of Triassic﻿146 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
age have been mined in this area since early in the 20th century, but mining was most active in the late 1940’s and early 1950’s. Most of these deposits are in the lower part of the Chinle Formation near the erosional unconformity that separates it from the underlying Moenkopi Formation.
At several localities in this area, basal siltstones, mudstones, and shales of the Chinle Formation have been silicified, dolomitized, and argillized beneath, and adjacent to, uranium deposits. The following information has been abstracted from a report by Abdel-Gawad and Kerr (1963, p. 27-33).
At the Magor mine, 11 miles southwest of Temple Mountain, a silicified green clay about 2 feet thick underlies uranium-bearing sandstone. Reddish-tan and light-tan silica layers and lenses with abundant chalcedony are prevalent in this clay. Coalified logs in the ore zone have been partly replaced by dark-brown to black silica, a jasperoid that is cut by veinlets of white quartz and calcite. Ore minerals consist of galena, sphalerite, pyrite, uraninite, chal-copyrite, bornite, covellite, and their oxidation products. Silicification disappears within a few hundred feet of the ore. At the Green Dragon 3 mine, uranium ore occurs at the base of a sandstone channel scoured into the siltstone, in a silicified zone surrounded by a halo of argillic alteration.
At the Dirty Devil 6 mine a layer of altered greenish-gray siltstone contains abundant layers, lenses, and veins of reddish-tan cherty jasperoid. Rounded quartz pebbles are sparsely distributed through this bed, and in its silicified parts, chalcedony locally cements these pebbles as well as sand and clay. Pyrite-, marcasite-, sphalerite-, and cof-finite-bearing asphaltite are disseminated through the silicified zones in close association with the younger chalcedony veinlets that cut the jasperoid. Cavities in this silica are rimmed with chalcedony and filled with cockscomb quartz.
At the Lucky Strike mine, two types of jasperoid are distinguishable in siltstone. One forms thinly banded brick-red layers and lenses a few inches thick. The other is more crudely banded, brownish to bluish gray, and contains urano-organic material filling fractures and cavities. The silicified zone is surrounded by a bleached argillized halo.
At the Conrad mine, layers of jasperoid are associated with dolomite in green clay in the basal siltstone of the Chinle Formation. Radioactive asphaltite fills fractures and cavities in these silicified layers.
These jasperoid zones consist largely of chalcedony and microcrystalline quartz with local late coarse quartz filling cavities. Much of the original
silica probably precipitated in colloidal form from hydrothermal solutions supersaturated with silica. This process probably was accompanied by a drop in temperature and an increase in pH from slightly acid to slightly alkaline. Temperature of silica deposition probably was slightly above 100°C. Silicification was accompanied by argillic alteration and closely followed by deposition of carbonates and sulfides; this deposition, in turn, was followed by urano-organic mineralization (Abdel-Gawad and Kerr, 1963, p. 34, 44).
SILVER ISLET DISTRICT (19, fig. 49)
The Silver Islet district is in northwestern Tooele County, just south of the Box Elder County line, and about 15 miles northeast of Wendover, near the north end of the Desert Range.
In this area Ordovician limestone has been cut by north-northeast-trending faults and fractures and by northwest-trending dikes of diorite porphyry. The limestone adjacent to one such dike on the west side of the range has been recrystallized near its junction with a north-trending vein. Outward from the recrystallized zone for a distance of 10-12 feet the limestone is replaced by red jasperoid containing abundant hematite, calcite, and muscovite. The vein contains argentiferous lead and copper carbonates and limonite in a quartz gangue (Butler and others, 1920, p. 488).
TUTSAGUBET DISTRICT (22, fig. 49)
The Tutsagubet district is in southwestern Washington County in the Beaver Dam Mountains, about 15 miles west of St. George. At the Dixie mine in this district, an irregular, chimney-shaped replacement deposit of oxidized ore cuts Pennsylvanian limestone. This limestone has locally been replaced by brown and yellow jasperoid adjacent to the pipe, which contains carbonates and sulfates of iron, lead, and copper associated with limonite.
OTHER OCCURRENCES
Abdel-Gawad and Kerr (1963, p. 33) mentioned silicification of the lower part of the Chinle Formation 11 miles northeast of Moab, Grand County, near the junction of Castle Creek and the Colorado River (4, fig. 49). No ore deposits are known in the immediate vicinity of this occurrence.
At Silver Reef (20, fig. 49) about 34 miles southwest of Cedar City, in Washington County, red “jasper” replaces a green shale in the Chinle Formation a few feet beneath the silver-, copper-, vana-﻿CHARACTERISTICS OF JASPEROID IN OTHER THAN MAJOR MINING DISTRICTS OF THE UNITED STATES 147
dium-, and uranium-bearing “Silver Reef sandstone,” a local economic term. The “jasper” replaces shale, as an aggregate of very fine grained red quartz, over a large area (Proctor, 1953, p. 120). From Proctor’s description, this material apparently is very much like the red cherty jasperoid in the Chinle Formation in the San Rafael Swell, as described by Abdel-Gawad and Kerr.
I have a specimen of jasperoid from Paleozoic limestone just east,of Vernon (23, fig. 49) in southeastern Tooele County. This locality is only about 12 miles northwest of the Tintic district (21), but there are no known ore deposits in the vicinity. The sample is grayish red, has a heterogeneous xeno-morphic to reticulated texture, and contains abundant carbonate particles and hematite; some of the hematite is pseudomorphous after pyrite. In spite of its favorable texture and mineralogy, the sample is slightly high only in Ga, Sr, and Zr, and has a trace of Zn.
Butler, Loughlin, Heikes, and others (1920, p. 441) mentioned the occurrence of a bed or vein of jasperoid in Paleozoic limestone at the “88” mine in the West Tintic district (24, fig. 49), about 15 miles southwest of the Tintic district, in Juab County. However, H. T. Morris (oral commun., 1965) reported very little jasperoid from this district.
Abundant masses of hypogene jasperoid are associated with lead-zinc replacement deposits in the Argentia district (1, fig. 49) in Morgan County, the Fish Springs district (8) in western Juab County, and the Lakeside district (10) in northeastern Tooele County (Heyl, 1963, p. B44, B57, B79). Hypogene jasperoid is also present in small amounts, in a few of the lead-zinc ore bodies of the important Park City district (15) in southwestern Summit County (C. S. Bromfield, written commun., 1967).
VIRGINIA AND WEST VIRGINIA
Jasperoid bodies have been recognized in three areas in these two States: the Austinville district (10, fig. 41) in Wythe County in southwestern Virginia, the Timberville district (7, fig. 46) in Rockingham County in western Virginia, and the Howell property (5, fig. 46) in Jefferson County at the eastern tip of West Virginia. In all three places gray and grayish-black jasperoid is associated with sphalerite and galena breccia and replacement deposits in lower Paleozoic limestone or dolomite. In addition to these areas, the north end of the piedmont gold belt (6, fig. 46) in Fauquier County, Va., on both sides of the Rappahannock River, contains disseminated gold deposits in massive quartz along
shear zones in schist; field evidence indicates partial replacement of the host rock by silica before mineralization.
AUSTINVILLE DISTRICT (10, fig. 41)
At Austinville, in southern Wythe County, Va., large replacement deposits of sphalerite have been localized by breccia zones in the Lower Cambrian Shady Dolomite. In the main mine cherty quartz of two types has been noted: One is dense “black chert” that appears to be older than both recrystallization of dolomite and sulfide mineralization. The other variety is also dense, but it is nearly white and is much younger than the first type; it may be younger than the sulfide mineralization (Currier, 1935, p. 79). Although the silica at Austinville strongly resembles chert in appearance, the bodies are structurally controlled, giving evidence of their epigenetic replacement origin (A. V. Heyl, written commun., 1964).
HOWELL MINE AREA (5, fig. 46)
A small zinc deposit in Jefferson County, W. Va., known as the Howell mine, has been developed along a breccia zone in the Cambrian Tomstown Formation. In this zone a core of coarse white dolomite is surrounded by sphalerite ore which, in turn, is enveloped by a marginal zone of jasperoid (Ludlum, 1955, p. 860; A. V. Heyl, written commun., 1964).
TIMBERVILLE DISTRICT (7, fig. 46)
Small replacement deposits of sphalerite are present in the Ordovician Beekmantown Dolomite in an area about 50 miles long and 25 miles wide in western Virginia, centered near the town of Timberville, in Rockingham County. These deposits probably were formed from low-temperature hydrothermal solutions, according to Herbert and Young (1956, p. 1-3). Although they did not mention silica associated with these deposits, dense black cherty-looking jasperoid that cemented dolomite breccia at an early stage during the general period of sulfide deposition is common at the Tri-State Zinc Co.’s Bowers-Campbell mine (A. V. Heyl, written commun., 1964).
OTHER OCCURRENCES
On both sides of the Rappahannock River (6, fig. 46) in Fauquier County in northeastern Virginia, a belt of Precambrian schist has been cut by shear zones that locally are strongly silicified. This silicifi-cation has resulted in large coarse-grained quartz﻿148 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
bodies which replace the schist but locally preserve its texture, and which contain disseminated gold deposits at the Vauclause, Mellville, and Franklin mines (Pardee and Park, 1948, p. 35, 47).
WASHINGTON
Abundant masses of jasperoid are closely associated with replacement deposits of sphalerite and galena in the Cambrian Metaline Limestone in the Metaline district (2, fig. 50), Pend Oreille County, near the northeast corner of Washington. A similar, but much smaller, deposit, known as the Anderson prospect (1, fig. 50), is also in Metaline Limestone in northeastern Stevens County, a few miles west of the Metaline district.
METALINE DISTRICT (2, fig. 50)
The close association between jasperoid and lead-zinc replacement ore bodies in breccia zones in the upper part of the thick Metaline Limestone in the Metaline district has been described and discussed by Park (1938), Park and Cannon (1943), $nd Dings and Whitebread (1965).
Park (1938, p. 723) described typical Metaline jasperoid as a dense dark-gray to black rock that
122° 120° 118°
EXPLANATION
x
Minor district or area
Reported occurrence
Figure 50.—Map showing location of jasperoid-bearing areas in Washington. 1, Anderson; 2, Metaline.
commonly preserves the texture of the carbonate host rock it replaces and shows gradational contacts with it, merging outward through a zone of anastomosing quartz veinlets and disseminated quartz crystals into unreplaced dolomite or limestone. Small vugs in this jasperoid are commonly lined with quartz crystals.
Park and Cannon (1943, p. 44-46) reported that, although jasperoid is widespread throughout the district, it is particularly abundant at the Lead Hill and Pend Oreille mines, where it commonly forms the gangue of the sulfide ore. Both jasperoid and ore appear to have formed from the same, presumably hydrothermal, solutions, but the ore for the most part is younger than the jasperoid. Nodules and small masses of light-gray chert are locally abundant in the upper part of the Metaline Limestone.
Dings and Whitebread (1965, p. 18) reported that this chert is composed of fine- to medium-grained, locally recrystallized quartz. Some chert nodules are surrounded by a rim of coarse-grained calcite. The chert is most abundant in the upper 200 feet of the Metaline Limestone on Lead Hill and Lead King Hill. In some places near ore bodies this chert grades transitionally into dark-gray jasperoid.
The jasperoid is most abundant in breccia zones 30-200 feet beneath the contact of the Metaline Limestone with the overlying Ordovician Ledbetter Slate. The jasperoid commonly occurs as irregular bodies as much as 200 feet across, replacing limestone and dolomite breccia fragments and the more coarsely crystalline dolomite that forms the matrix for these fragments. Most of the sphalerite and galena occurs either within the jasperoid or adjacent to it; however, some jasperoid bodies are barren of sulfides, and some sulfide deposits are not associated with jasperoid. The coarsely crystalline white dolomite that forms the original matrix in the breccia zones is presumed to be largely of hydrothermal origin, and this dolomite is the preferred host material for the jasperoid and sulfides. Dolomitization, silicification, and mineralization are thought to have resulted from hydrothermal fluids that originated in the deep-seated magma chamber of a large body of plutonic rock related to the Jurassic Kaniksu batho-lith (Dings and Whitebread, 1965, p. 54, 62-64, 68).
A sample of dark-gray sphalerite-bearing jasperoid from the Metaline district in my collection is relatively coarse grained and has a very heterogeneous xenomorphic to locally reticulated texture. The quartz grains range in diameter from about 0.02 to about 1.5 mm, and the smaller grains commonly form inclusions in the larger ones. Ragged remnants of coarse crystalline dolomite are scattered through﻿REFERENCES CITED
149
the quartz, and carbonate dust particles are abundant in the larger quartz grains. Irregular masses of light-gray sphalerite cut the jasperoid quartz and locally contain quartz grain inclusions. Spectro-graphic analysis of the sample showed slightly high Cd, Ga, Ge, Mo, and Sr, as well as very high Zn. The indicator-element score is +11.
OTHER OCCURRENCES
The Anderson prospect (1, fig. 50) in northeastern Stevens County, a few miles west of the Metaline district, consists of galena, sphalerite, and minor pyrite disseminated through jasperoid gangue in the Metaline Limestone. The ore-bearing bed is about 100 feet thick; the silicified ore zone is about 50 feet wide and follows the general course of a lamprophyre dike (Lorain and Gammell, 1947, p. 4).
WYOMING
A jasperoid occurrence in Wyoming is reported from the Miller Hill area (4, fig. 47), about 25 miles south of Rawlins in Carbon County (Vine and Prichard, 1959). At this locality small amounts of uranium are concentrated in silicified fresh-water limestone in Tertiary rocks that have been tentatively correlated with the North Park Formation.
MILLER HILL AREA (4, fig. 47)
The North Park(?) Formation in this area is about 800 feet thick and consists largely of porous tuffaceous sandstone with some interbedded freshwater limestone. These limestone beds are 3-10 feet thick, and have locally been brecciated and replaced by chalcedonic jasperoid, which locally contains concentrations of uranium ore. Silica and uranium are thought to have been leached by ground water from the porous tuffaceous sandstone and precipitated from the ground water by reaction with the limestone (Vine and Prichard, 1959, p. 210, 215-217, 225).
REFERENCES CITED
Abdel-Gawad, A. M., and Kerr, P. F., 1963, Alteration of Chinle siltstone and uranium emplacement, Arizona and Utah: Geol. Soc. America Bull., v. 74, no. 1, p. 23—46. Adams, S. F., 1920, A microscopic study of vein quartz: Econ.
Geology, v. 15, no. 8, p. 623-664.
Albers, J. P., and Robertson, J. F., 1961, Geology and ore deposits of east Shasta copper-zinc district, Shasta County, California: U.S. Geol. Survey Prof. Paper 338, 107 p. [1962],
Albritton, C. C., Jr., Richards, Arthur, Brokaw, A. L., and Reinemund, J. A., 1954, Geologic controls of lead and zinc deposits in Goodsprings (Yellow Pine) district, Nevada: U.S. Geol. Survey Bull. 1010, 111 p. [1955].
Alexander, G. B., Heston, W. M., and Iler, R. K., 1954, The solubility of amorphous silica in water: Jour. Phys. Chemistry, v. 58, no. 6, p. 453-455.
Ames, L. L., Jr., 1961a, Cation metasomatic replacement reactions: Econ. Geology, v. 56, no. 6, p. 1017-1024.
-------1961b, Anion metasomatic replacement reactions: Econ.
Geology, v. 56, no. 3, p. 521-532.
-------1961c, The metasomatic replacement of limestones by
alkaline, fluoride-bearing solutions: Econ. Geology, v. 56, no. 4, p. 730-739.
-------1961d, Volume relationships during replacement reactions : Econ. Geology, v. 56, no. 8, p. 1438-1445.
Anderson, A. L., 1954, A preliminary report on the fluorspar mineralization near Challis, Custer County, Idaho: Idaho Bur. Mines and Geology Pamph. 101, 13 p.
Anderson, C. A., and Creasey, S. C., 1958, Geology and ore deposits of the Jerome area, Yavapai County, Arizona: U.S. Geol. Survey Prof. Paper 308, 185 p.
Anderson, E. C., 1957, The metal resources of New Mexico and their economic features through 1954: New Mexico Bur. Mines and Mineral Resources Bull. 39, 183 p.
Bain, H. F., 1901, Preliminary report on the lead and zinc deposits of the Ozark region: U.S. Geol. Survey 22d Ann. Rept., pt. 2, p. 23-228.
Barrington, Jonathan, and Kerr, P. F., 1963, Collapse features and silica plugs near Cameron, Arizona: Geol. Soc. America Bull., v. 74, no. 10, p. 1237-1258.
Bassett, H., 1954, Silicification of rocks by surface waters: Am. Jour. Sci., v. 252, no. 12, p. 733-735.
Bastin, E. S., ed., 1939, Contributions to a knowledge of the lead and zinc deposits of the Mississippi Valley region: Geol. Soc. America Spec. Paper 24, 156 p.
Beck, Richard, 1905, The nature of ore deposits [translation and revision by W. H. Weed] : New York, McGraw-Hill Book Co., 2 v., 685 p.
Behre, C. H., Jr., 1953, Geology and ore deposits of the west slope of the Mosquito Range [Colorado]: U.S. Geol. Survey Prof. Paper 235, 176 p.
Behre, C. H., Jr., Heyl, A. V., and McKnight, E. T., 1950, Zinc and lead deposits of the Mississippi Valley, in Dunham, K. C., ed., Symposium on the geology, paragenesis, and reserves of the ores of lead and zinc: Internat. Geol. Cong., 18th, Great Britain, 1948, Rept., pt. 7, p. 51-69.
Blanchard, Roland, and Boswell, P. F., 1928, Status of leached outcrops investigation: Eng. and Mining Jour., v. 125, no. 7, p. 280-285; no. 9, p. 373-377.
Blanck, E., Passarge, S., Rieser, A., and Heide, F., 1925, Die chemischen verwitterung in der Agyptischen Wuste [The chemical weathering in the Egyptian desert] : Hamburg Univ. Abh. Gebiet Auslandskunde 17, 110 p.
Bonillas, Y. S., Tenney, J. B., and Feuchere, Leon, 1917, Geology of the Warren mining district [Ariz.] : Am. Inst. Mining Engineers Trans., v. 55, p. 284-355.
Boutwell, J. M., 1905, Economic geology of the Bingham mining district, Utah: U.S. Geol. Survey Prof. Paper 38, 413 p.
Boydell, H. C., 1924, The role of colloidal solutions in the formation of mineral deposits: Inst. Mining and Metallurgy Bull. 243, 108 p.
-------1927, Operative causes in ore deposition: Inst. Mining
and Metallurgy Bull. 277, 85 p.
Bradbury, J. C., Ostrom, M. E., and McVicker, L. D., 1955, Preliminary report on uranium in Hardin County, Illinois: Illinois Geol. Survey Circ. 200, 21 p.
Brannock, W. W., 1948, Preliminary geochemical results at﻿150 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Steamboat Springs, Nevada: Am. Geophys. Union Trans.,* v. 29, no. 2, p. 211-226.
Brewer, W. M., 1896, A preliminary report on the upper gold belt of Alabama in the counties of Cleburne, Randolph, Clay, Talladega, Elmore, Coosa, and Tallapoosa: Alabama Geol. Survey Bull. 5, p. 1-105.
Brokaw, A. L., Gott, G. B., Mabey, D. R., McCarthy, Howard, and Oda, Uteana, 1962, Mineralization associated with a magnetic anomaly in part of the Ely quadrangle, Nevada: U.S. Geol. Survey Circ. 475, 7 p.
Brown, J. S., 1958, Southeast Missouri Lead Belt, in Geol. Soc. America Guidebook Field Trip No. 1, St. Louis Mtg., 1958: p. 1-7.
Brown, J. S., Emery, J. A., and Meyer, P. A., Jr.* 1954, Explosion pipe in test well on Hicks Dome, Hardin County, Illinois: Econ. Geology, v. 49, no. 8, p. 891-902.
Buckley, E. R., 1909, Geology of the disseminated lead deposits of St. Francois and Washington Counties, Missouri: Missouri Bur. Geology and Mines, Rept. Ser. 2, v. 9, pt. 1, 259 p.
Burbank, W. S., 1932, Geology and ore deposits of the Bonanza mining district, Colorado: U.S. Geol. Survey Prof. Paper 169, 166 p.
-------1940, Structural control of ore deposition in the Un-
compahgre district, Ouray County, Colorado: U.S. Geol. Survey Bull. 906-E, p. 189-265 [1941],
-------1941, Structural control of ore deposition in the Red
Mountain, Sneffels, and Telluride districts of the San Juan Mountains, Colorado: Colorado Sci. Soc. Proc., v. 14, no. 5, p. 141-261.
Bush, J. B., Cook, D. R., Lovering, T. S., and Morris, H. T., 1960a, The Chief Oxide-Burgin area discoveries, East Tintic district, Utah, A case history—Part 1, U.S. Geological Survey studies and exploration, by T. S. Lovering, D. R. Cook, and H. T. Morris: Econ. Geology, v. 55, no. 6, p. 1116-1147.
-------1960b, The Chief Oxide-Burgin area discoveries, East
Tintic district, Utah, A case history—Part 2, Bear Creek Mining Company studies and exploration, by J. B. Bush and D. R. Cook: Econ. Geology, v. 55, no. 7, p. 1507-1548.
Butler, B. S., 1913, Geology and ore deposits of the San Francisco and adjacent districts, Utah: U.S. Geol. Survey Prof. Paper 80, 212 p.
Butler, B. S., Loughlin, G. F., Heikes, V. C., and others, 1920, The ore deposits of Utah: U.S. Geol. Survey Prof. Paper 111, 672 p.
Butler, B. S., and Wilson, E. D., 1938, Structural control of the ore deposits at Tombstone, Arizona, in Some Arizona ore deposits, Part 2, Mining districts: Arizona Bur. Mines Bull. 145, Geol. Ser. 12 (Arizona Univ. Bull., v. 9, no. 4), p. 104-110.
Butler, R. D., and Singewald, Q. D., 1940, Zonal mineralization and silicification in the Horseshoe and Sacramento districts, Colorado: Econ. Geology, v. 35, no. 7, p. 793-838.
Callaghan, Eugene, 1936, Geology of the Chief district, Lincoln County, Nevada: Nevada Univ. Bull., v. 30, no. 2, 32 p.
-------1937, Geology of the Delamar district, Lincoln County,
Nevada: Nevada Univ. Bull., v. 31, no. 5, 72 p.
Cameron, E. N., 1939, Geology and mineralization of the northeastern Humboldt Range, Nevada: Geol. Soc. America Bull., v. 50, no. 4, p. 563-633.
Carr, R. M., and Fyfe, W. S., 1958, Some observations on the crystallization of amorphous silica: Am. Mineralogist, v. 43, nos. 9-10, p. 908-916.
Cathcart, S. H., 1922, Metalliferous lodes in southern Seward Peninsula, Alaska: U.S. Geol. Survey Bull. 722-F, p. 163-266.
Church, A. H., 1862, Observations on silica: Chem. Soc. Jour., v. 15, p. 107-110.
Clarke, F. W., 1924, The data of geochemistry [5th ed.]: U.S. Geol. Survey Bull. 770, 841 p. (repr.).
Cook, D. R., ed., 1961, Geology of the Bingham mining district and northern Oquirrh Mountains: Utah Geol. Soc. Guidebook to the geology of Utah, no. 16, 145 p.
Cooper, J. R., and Silver, L. T., 1964, Geology and ore deposits of the Dragoon quadrangle, Cochise County, Arizona: U.S. Geol. Survey Prof. Paper 416, 196 p.
Correns, C. W., 1951, Zur Geochemie der Diagenese; I, Das Verhalten von CaC03 und Si02: Geochim. et Cosmochim. Acta, v. 1, no. 1, p. 49-54.
Cox, G. H., Dean, R. S., and Gottschalk, V. H., 1916, Studies on the origin of Missouri cherts and zinc ores: Missouri Univ. School Mines Bull., Tech. Ser. 3, no. 2, 34 p.
Crawford, R. D., and Gibson, Russell, 1925, Geology and ore deposits of the Red ClifT district, Colorado: Colorado Geol. Survey Bull. 30, 89 p.
Crittenden, M. D., Jr., Straczek, J. A., and Roberts, R. J., 1961, Manganese deposits in the Drum Mountains, Juab and Millard Counties, Utah: U.S. Geol. Survey Bull. 1082-H, p. 493-544.
Cross, Whitman, and Ransome, F. L., 1905, Description of the Rico quadrangle [Colorado]: U.S. Geol. Survey Geol. Atlas, Folio 130, 20 p.
Currier, L. W., 1935, Zinc and lead region of southwestern Virginia: Virginia Geol. Survey Bull. 43, 122 p.
Dings, M. G., and Robinson, C. S., 1957, Geology and ore deposits of the Garfield quadrangle, Colorado: U.S. Geol. Survey Prof. Paper 289, 110 p.
Dings, M. G., and Whitebread, D. H., 1965, Geology and ore deposits of the Metaline zinc-lead district, Pend Oreille County, Washington: U.S. Geol. Survey Prof. Paper 489, 109 p.
Drewes, Harald, 1962, Stratigraphic and structural controls of mineralization in the Taylor mining district near Ely, Nevada, in Short papers in geology, hydrology, and topography: U.S. Geol. Survey Prof. Paper 450-B, p. B1-B3.
-------1967, Geology of the Connors Pass quadrangle, Schell
Creek Range, east-central Nevada: U.S. Geol. Survey Prof. Paper 557, 93 p.
Dreyer, R. M., 1940, Goldbanks mining district, Pershing County, Nevada: Nevada Univ. Bull., v. 34, no. 1, 38 p.
Duke, D. A., 1959, Jasperoid and ore deposits in the East Tintic mining district: Utah Univ. unpub. M.S. thesis.
Duke, D. A., and Howd, F. H., 1959, Jasperoid and ore deposits in the Tintic and East Tintic mining districts, Utah [abs.]: Geol. Soc. America Bull., v. 70, no. 12, pt. 2, p. 1593.
Dunham, K. C., 1935, The geology of the Organ Mountains, with an account of the geology and mineral resources of Dona Ana County, New Mexico: New Mexico School Mines Bull. 11, 272 p.
Du Toit, A. L., 1933, The manganese deposits of Postmasburg, South Africa: Econ. Geology, v. 28, no. 2, p. 95-122.
Eckel, E. B., 1949, Geology and ore deposits of the La Plata district, Colorado: U.S. Geol. Survey Prof. Paper 219, 179 p.
Eitel, Wilhelm, 1957, Structural anomalies in tridymite and cristobalite: Am. Ceramic Soc. Bull., v. 36, no. 4, p. 142-148.﻿REFERENCES CITED
151
Ellis, A. J., and Fyfe, W. S., 1957, Hydrothermal chemistry: Rev. Pure and Appl. Chemistry, v. 7, p. 261-316.
Elmer, T. H., and Nordberg, M. E., 1958, Solubility of silica in nitric acid solutions: Am. Ceramic Soc. Jour., v. 41, no. 12, p. 517-520.
Emmons, S. F., Irving, J. D., and Loughlin, G. F., 1927, Geology and ore deposits of the Leadville mining district, Colorado: U.S. Geol. Survey Prof. Paper 148, 368 p.
Emmons, W. H., 1910, A reconnaissance of some mining camps in Elko, Lander, and Eureka Counties, Nevada: U.S. Geol. Survey Bull. 408, 130 p.
Emmons, W. H., and Calkins, F. C., 1913, Geology and ore deposits of the Philipsburg quadrangle, Montana: U.S. Geol. Survey Prof. Paper 78, 271 p.
Erickson, R. L., Marranzino, A. P., Oda, Uteana, and Janes, W. W., 1964, Geochemical exploration near the Getchell mine, Humboldt County, Nevada: U.S. Geol. Survey Bull. 1198-A, 26 p.
Erickson, R. L., Masursky, Harold, Marranzino, A. P., and Oda, Uteana, 1961, Geochemical anomalies in the upper plate of the Roberts Thrust near Cortez, Nevada, in Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-D, p. D316-D320.
Erickson, R. L., Masursky, Harold, Marranzino, A. P., Oda, Uteana, and Janes, W. W., 1964a, Semiquantitative spectrographic and chemical analyses of rocks from the lower plate of the Roberts Thrust, north-central part of the Cortez quadrangle, Nevada: U.S. Geol. Survey open-file report, 2 sheets.
------1964b, Geochemical anomalies in the lower plate of the
Roberts Thrust near Cortez, Nevada, in Geological Survey research 1964: U.S. Geol. Survey Prof. Paper 501-B, p. B92-B94.
Ferguson, H. G., 1921, The limestone ores of Manhattan, Nevada: Econ. Geology, v. 16, no. 1, p. 1-36.
------1928, The Gilbert district, Nevada: U.S. Geol. Survey
Bull. 795-F, p. 125-145.
------1939, Nickel deposits in Cottonwood Canyon,
Churchill County, Nevada: Nevada Univ. Bull., v. 33, no. 5, Geology and Mining Ser. 32, 21 p.
Fohs, F. J., 1910, The fluorspar, lead, and zinc deposits of western Kentucky: Econ. Geology, v. 5, no. 4, p. 377-386.
Folk, R. L., and Weaver, C. E., 1950, Surface features of chert as studied by the electron microscope [abs.]: Geol. Soc. America Bull., v. 61, no. 12, pt. 2, p. 1461-1462.
Ford, W. E., 1932, A textbook of mineralogy, with an extended treatise on crystallography and physical mineralogy, by E. S. Dana; 4th ed. revised and enlarged by W. E. Ford: New York, John Wiley & Sons, 851 p.
Fowler, G. M., Lyden, J. P., Gregory, F. E., and Agar, W. M., 1934, Chertification in the Tri-State (Oklahoma-Kansas-Missouri) mining district: Am. Inst. Mining Metall. Engineers Tech. Pub. 532, 50 p.
------1935, Chertification in the Tri-State (Oklahoma-
Kansas-Missouri) mining district [with discussion] : Am. Inst. Mining Metall. Engineers Trans., v. 115, Mining Geology, p. 106-163.
Frankel, J. J., 1952, Silcrete near Albertinia, Cape Province: South African Jour. Sci., v. 49, no. 5, p. 173-182.
Frondel, Clifford, 1938, Stability of colloidal gold under hydrothermal conditions: Econ. Geology, v. 33, no. 1, p. 1-20.
------1962, The system of mineralogy of James Dwight Dana
and Edward Salisbury Dana, Yale University, 1837-1892;
v. 3, Silica minerals [7th ed.] : New York, John Wiley & Sons, 334 p.
Gair, J. E., Thaden, R. E., and Jones, B. F., 1961, Silicification of the Kono dolomite in the eastern part of the Marquette iron range, Michigan, in Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-C, p. C78-C80.
Garrels, R. M., and Dreyer, R. M., 1952, Mechanism of limestone replacement at low temperatures and pressures: Geol. Soc. America Bull., v. 63, no. 4, p. 325-379.
Gillerman, Elliot, 1953, Fluorspar deposits of the Eagle Mountains, Trans-Pecos, Texas: U.S. Geol. Survey Bull. 987, 98 p.
Gilluly, James, 1932, Geology and ore deposits of the Stockton and Fairfield quadrangles, Utah: U.S. Geol. Survey Prof. Paper 173, 171 p.
Gilluly, James, and Masursky, Harold, 1965, Geology of the Cortez quadrangle, Nevada: U.S. Geol. Survey Bull. 1175, 117 p.
Goddard, E. N., Gardner, L. S., and Burbank, W. S., 1947, Manganese deposits of the Republic of Haiti: U.S. Geol. Survey Bull. 953-B, p. 27-52.
Goddard, E. N., chm., and others, 1948, Rock-color chart: Natl. Research Council (repub. by Geol. Soc. America, 1951)
6 p.
Granger, A. E., Bell, M. M., Simmons, G. C., and Lee, F. J., 1957, Geology and mineral resources of Elko County, Nevada: Nevada Bur. Mines Bull. 54, 190 p.
Griswold, G. B., 1961, Mineral deposits of Luna County, New Mexico: New Mexico Bur. Mines and Mineral Resources Bull. 72, 157 p.
Gruner, J. W., 1922, Organic matter and the origin of the Biwabik iron-bearing formation of the Mesabi range: Econ. Geology, v. 17, no. 6, p. 407-460.
------1930, Hydrothermal oxidation and leaching experiments; their bearing on the origin of Lake Superior hematite-limonite ores: Econ. Geology, v. 25, no. 7, p. 697-719; no. 8, p. 837-867.
Hall, W. E., and Friedman, Irving, 1963, Composition of fluid inclusions, Cave-in-Rock fluorite district, Illinois, and Upper Mississippi Valley zinc-lead district: Econ. Geology, v. 58, no. 6, p. 886-911.
Hall, W. E., and MacKevett, E. M., Jr., 1958, Economic geology of the Darwin quadrangle, Inyo County, California: California Div. Mines Spec. Rept. 51, 73 p.
------1962, Geology and ore deposits of the Darwin quadrangle, Inyo County, California: U.S. Geol. Survey Prof. Paper 368, 87 p. [1963].
Harder, E. C., 1919, Iron-depositing bacteria and their geologic relations: U.S. Geol. Survey Prof. Paper 113, 89 p.
Harder, Hermann, 1965, Experimente zur “Ausfallung” der Kieselsaure: Geochim. et Cosmochim. Acta, v. 29, no. 5, p. 429-442.
Hardin, G. C., Jr., 1955, Babb fault system, Crittenden and Livingston Counties: U.S. Geol. Survey Bull. 1012-B, p. 7-37.
Harley, G. T., 1934, The geology and ore deposits of Sierra County, New Mexico: New Mexico School Mines Bull.
10, 220 p.
Hatschek, E., and Simon, A. L., 1912, Gels in relation to ore deposition: Inst. Mining and Metallurgy Trans., v. 21, p. 451-480.
Herbert, Paul, Jr., and Young, R. S., 1956, Sulfide mineralization in the Shenandoah Valley of Virginia: Virginia Div. Geology Bull. 70, 58 p.﻿152 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
Hewett, D. F., 1931, Geology and ore deposits of the Good-springs quadrangle, Nevada: U.S. Geol. Survey Prof. Paper 162, 172 p.
-------1956, Geology and mineral resources of the Ivanpah
quadrangle, California and Nevada: U.S. Geol. Survey Prof. Paper 275, 172 p.
Heyl, A. V., 1963, Oxidized zinc deposits of the United States— Part 2, Utah: U.S. Geol. Survey Bull. 1135-B, 104 p.
-------1964, Oxidized zinc deposits of the United States—
Part 3, Colorado: U.S. Geol. Survey Bull. 1135-C, 98 p.
Heyl, A. V., Agnew, A. F., Lyons, E. J., and Behre, C. H., Jr., 1959, The geology of the Upper Mississippi Valley zinc-lead district: U.S. Geol. Survey Prof. Paper 309, 310 p. [I960].
Heyl, A. V., Delevanux, M. H., Zartman, R. E., and Brock, M. R., 1966, Isotopic studies of galenas from the Upper Mississippi Valley, the Illinois-Kentucky, and some Appalachian Valley mineral districts: Econ. Geology, v. 61, no. 5, p. 933-961.
Hill, J. M., 1914, The Yellow Pine mining district, Clark County, Nevada: U.S. Geol. Survey Bull. 540, p. 223-274.
-------1915, Some mining districts in northeastern California
and northwestern Nevada: U.S. Geol. Survey Bull. 594,
200 p.
-------1916, Notes on some mining districts in eastern Nevada:
U.S. Geol. Survey Bull. 648, 214 p.
Hoagland, A. D., Hill, W. T., and Fulweiler, R. E., 1965, Genesis of the Ordovician zinc deposits in east Tennessee: Econ. Geology, v. 60, no. 4, p. 693-714.
Hobbs, S. W., and Clabaugh, S. E., 1946, Tungsten deposits of the Osgood Range, Humboldt County, Nevada: Nevada Univ. Bull., v. 40, no. 5, Geology and Mining Ser. 44, 32 p.
Hogue, W. G., and Wilson, E. D., 1950, Bisbee or Warren district, chap. 2 in Part 1 of Arizona zinc and lead deposits: Arizona Bur. Mines Bull. 156, Geol. Ser. 18, p. 17-29.
Holser, W. T., 1947, Metasomatic processes: Econ. Geology, v. 42, no. 4, p. 384-395.
Howd, F. H., 1957, Hydrothermal alteration in the East Tintic mining district, in Utah Geol. Soc. Guidebook to the geology of Utah, no. 12, Geology of the East Tintic Mountains and ore deposits of the Tintic mining districts: Utah Geol. and Mineralog. Survey, p. 124-134.
Huber , N. K., 1959, Some aspects of the origin of the Ironwood iron-formation of Michigan and Wisconsin: Econ. Geology, v. 54, no. 1, p. 82-118.
Humphrey, F. L., 1945, Geology of the Groom district, Lincoln County, Nevada: Nevada Univ. Bull., v. 39, no. 5, Geology and Mining Ser. 42, 53 p.
-------1960, Geology of the White Pine mining district, White
Pine County, Nevada: Nevada Bur. Mines Bull. 57, 119 p.
Hunt, R. N., 1924, The ores in the limestones at Bingham, Utah: Am. Inst. Mining Metall. Engineers Trans., v. 70, p. 856-883.
Iler, R. K., 1955, The colloid chemistry of silica and silicates: Cornell Univ. Press, 324 p.
Ingerson, Earl, 1947, X—Transportation and deposition of silica in Johnston, W. D., Jr., chm., Report of the Committee on Research on Ore Deposits of the Society of Economic Geologists: Econ. Geology, v. 42, no. 6, p. 560-562.
Irving, J. D., 1904, Economic resources of the northern Black Hills: U.S. Geol. Survey Prof. Paper 26, 222 p.
-------1911, Replacement ore bodies; and the criteria for their
recognition: Econ. Geology, v. 6, no. 6, p. 527-561; no. 7, p. 619-669.
Jicha, H. L., Jr., 1954, Geology and mineral deposits of Lake Valley quadrangle, Grant, Luna, and Sierra Counties, New Mexico: New Mexico Bur. Mines and Mineral Resources Bull. 37, 93 p.
Jolly, J. L., and Heyl, A. V., 1964, Mineral paragenesis and zoning in the central Kentucky mineral district: Econ. Geology, v. 59, no. 4, p. 596-624.
Keith, M. L., Tuve, M. A., Davis, G. L., and Doak, J. B., 1952, Ratio of oxygen isotopes in quartz of contrasted origin [abs.] : Geol. Soc. America Bull., v. 63, no. 12, pt. 2, p. 1270.
Kennedy, G. C., 1944, The hydrothermal solubility of silica: Econ. Geology, v. 39, no. 1, p. 25-36.
-------1950, A portion of the system silica-water: Econ. Geology, v. 45, no. 7, p. 629-653.
Kesler, T. L., 1950, Geology and mineral deposits of the Cartersville district, Georgia: U.S. Geol. Survey Prof. Paper 224, 97 p.
Kiersch, G. A., 1949, Structural control and mineralization at the Seventy Nine mine, Gila County, Arizona: Econ. Geology, v. 44, no. 1, p. 24-39.
-------1951, Seventy Nine mine area, in Part 2 of Arizona
zinc and lead deposits: Arizona Bur. Mines Bull. 158, p. 67-81.
King, P. B., Ferguson, H. W., Craig, L. C., and Rodgers, John, 1944, Geology and manganese deposits of northeastern Tennessee: Tennessee Div. Geology Bull. 52, 283 p.
Knopf, Adolph, 1915, The Darwin silver-lead mining district, California: U.S. Geol. Survey Bull. 580-A, p. 1-18.
-------1918, Geology and ore deposits of the Yerington district, Nevada: U.S. Geol. Survey Prof. Paper 114, 68 p.
-------1922, Ore deposits of Cedar Mountain, Mineral County,
Nevada: U.S. Geol. Survey Bull. 725-H, p. 361-382.
Krai, V. E., 1951, Mineral resources of Nye County, Nevada: Nevada Univ. Bull., v. 45, no. 3, Geology and Mining Ser. 50, 223 p.
Krauskopf, K. B., 1956, Dissolution and precipitation of silica at low temperatures: Geochim. et Cosmochim. Acta, v. 10, nos. 1-2, p. 1-26.
Laney, F. B., 1917, The chert or flint of the Joplin district, p. 99-108 in Higgins, Edwin, and others, Siliceous dust in relation to pulmonary disease among miners in the Joplin district, Missouri: U.S. Bur. Mines Bull. 132, 116 p.
Lasky, S. G., 1932, The ore deposits of Socorro County, New Mexico: New Mexico School Mines Bull. 8, 139 p.
Lausen, Carl, and Gardner, E. D., 1927, Quicksilver (mercury) resources of Arizona: Arizona Bur. Mines Bull. 122, 112 P-
Lawson, A. C., 1906, The copper deposits of the Robinson mining district, Nevada: California Univ. Dept. Geology Bull. 4, p. 287-357.
Laz’ko, Y. M., 1965, Some characteristics of quartz-forming solutions, p. 382-394 in Yermakov, N. P., and others, Research on the nature of mineral-forming solutions, with special reference to data from fluid inclusions: Elmsford, N.Y., Pergamon Press, 743 p.
Leith, C. K., 1925, Silicification of erosion surfaces: Econ. Geology, v. 20, no. 6, p. 513-523.
Lemmon, D. M., 1941, Tungsten deposits in the Tungsten Hills, Inyo County, California: U.S. Geol. Survey Bull. 922-Q, p. 497-514.﻿REFERENCES CITED
153
Lenher, Victor, and Merrill, H. B., 1917, Solubility of silica: Am. Chem. Soc. Jour., v. 39, p. 2630-2638.
Lincoln, F. C., 1923, Mining districts and mineral resources of Nevada: Reno, Nevada Newsletter Publishing Co., 295 p.
Lindgren, Waldemar, 1901, Metasomatic processes in fissure veins: Am. Inst. Mining Engineers Trans., v. 30, p. 578-692. •
-------1905, The copper deposits of the Clifton-Morenci district, Arizona: U.S. Geol. Survey Prof. Paper 43, 375 p.
-------1925, Metasomatism: Geol. Soc. America Bull., v. 36,
no. 1, p. 247-261.
-------1933, Mineral deposits [4th ed.] : New York, McGraw-
Hill Book Co., 930 p.
-------1935, The silver mine of Colquijirca, Peru: Econ. Geology) v. 30, no. 4, p. 331-346.
Lindgren, Waldemar, and Loughlin, G. F., 1919, Geology and ore deposits of the Tintic mining district, Utah: U.S. Geol. Survey Prof. Paper 107, 282 p.
Locke, Augustus, 1926, Leached outcrops as guides to copper ore: Baltimore, Williams and Wilkins Co., 175 p.
Lorain, S. H., and Gammell, R. M., 1947, Anderson zinc-lead prospect, Stevens County, Washington: U.S. Bur. Mines Rept. Inv. 4043, 5 p.
Loughlin, G. F., and Behre, C. H., Jr., 1934, Zoning of ore deposits, Leadville district, Colorado: Econ. Geology, v. 29, no. 3, p. 215-254.
Loughlin, G. F., and Koschmann, A. H., 1942, Geology and ore deposits of the Magdalena mining district, New Mexico: U.S. Geol. Survey Prof. Paper 200, 168 p. [1943].
Lovering, T. G., and Patten, L. E., 1962, The effect of C02 at low temperature and pressure on solutions supersaturated with silica in the presence of limestone and dolomite: Geochim. et Cosmochim. Acta, v. 26 (July), p. 787-796.
Lovering, T. S., 1923, The leaching of iron protores; solution and precipitation of silica in cold water: Econ. Geology, v. 18, no. 6, p. 523-540.
-------1934, Geology and ore deposits of the Breckenridge
mining district, Colorado: U.S. Geol. Survey Prof. Paper 176, 64 p.
-------1949, Rock alteration as a guide to ore—East Tintic
district, Utah: Econ. Geology Mon. 1, 65 p.
-------1950, The geochemistry of argillic and related types of
rock alteration, in Van Tuyl, F. M., and Kuhn, T. H., eds., Applied geology, a symposium: Colorado School Mines Quart., v. 45, no. IB, p. 231-260.
-------1966, Direction of movement of jasperoidizing solution:
U.S. Geol. Survey Bull. 1222-F, 25 p.
Lovering, T. S., McCarthy, J. H., and Friedman, Irving, 1963, Significance of 018/016 and C13/C12 ratios in hydrotherm-ally dolomitized limestones and manganese carbonate replacement ores of the Drum Mountains, Juab County, Utah, in Short papers in geology and hydrology: U.S. Geol. Survey Prof. Paper 475-B, p. B1-B9.
Lovering, T. S., and others, 1960, Geologic and alteration maps of the East Tintic district, Utah: U.S. Geol. Survey Mineral Inv. Field Studies Map MF-230.
Lovering, T. S., and Tweto, Ogden, 1944, Preliminary report on the geology and ore deposits of the Minturn quadrangle, Colorado: U.S. Geol. Survey open-file report, 115 p.
Ludlum, J. C., 1955, Regional setting and mineralogic features of the Howell zinc prospect, Jefferson County, West Vir-
ginia: West Virginia Geol. Survey Rept. Inv. 11, p. 855-861 (repr.).
Lyden, J. P., 1950, Aspects of structure and mineralization used as guides in the development of the Picher field [Okla.-Kans.] : Mining Eng., v. 187, no. 12, p. 1251-1259.
McKinstry, H. E., 1936, Geology of the silver deposit at Colquijirca, Peru: Econ. Geology, v. 31, no. 6, p. 618-635.
McKnight, E. T., 1935, Zinc and lead deposits of northern Arkansas: U.S. Geol. Survey Bull. 853, 311 p.
Miller, B. L., 1924, Lead and zinc ores of Pennsylvania: Pennsylvania Geol. Survey 4th Ser. Bull. M5, 91 p.
------1941, Lehigh County, Pennsylvania: Pennsylvania Geol.
Survey 4th Ser. Bull. C39, 492 p.
Miller, J. P., 1952, A portion of the system calcium carbonate-carbon dioxide-water, with geological implications: Am. Jour. Sci., v. 250, no. 3, p. 161-203.
Mitchell, G. J., 1921, Replacement copper deposits in the Warren district [Bisbee, Ariz.]: Eng. and Mining Jour., v. 112, no. 7, p. 246-250.
Moore, E. S., and Maynard, J. E., 1929, Solution, transportation, and precipitation of iron and silica: Econ. Geology, v. 24, no. 3, p. 272-303; no. 4, p. 365-402; no. 5, p. 506-527.
Morey, G. W., Fournier, R. O., and Rowe, J. J., 1962, The solubility of quartz in water in the temperature interval from 25° to 300°C: Geochim. et Cosmochim. Acta, v. 26 (Oct.), p. 1029-1043.
Morey, G. W., and Hesselgesser, J. M., 1951, The solubility of some minerals in superheated steam at high pressures: Econ. Geology, v. 46, no. 8, p. 821-835.
Morris, H. T., 1964a, Geology of the Eureka quadrangle, Utah and Juab Counties, Utah: U.S. Geol. Survey Bull. 1142-K, 29 p.
------1964b, Geology of the Tintic Junction quadrangle,
Tooele, Juab, and Utah Counties, Utah: U.S. Geol. Survey Bull. 1142-L, 23 p.
Murray, H. H., and Gravenor, C. P., 1953, Colloidal-size silica in sediments: Science, v. 118, no. 3053, p. 25-28.
Myers, A. T., Havens, R. G., and Dunton, P. J., 1961, A spec-trochemical-method for the semiquantitative analysis of rocks, minerals, and ores: U.S. Geol. Survey Bull. 1084-1, p. 207-229.
Nolan, T. B., 1935, The Gold Hill mining district, Utah: U.S. Geol. Survey Prof. Paper 177, 172 p.
------1962, The Eureka mining district, Nevada: U.S. Geol.
Survey Prof. Paper 406, 78 p.
Nutting, P. G., 1943, The action of some aqueous solutions on clays of the montmorillonite group: U.S. Geol. Survey Prof. Paper 197-F, p. 219-235.
Ohle, E. L., Jr., and Brown, J. S., eds. 1954, Geologic problems in the Southeast Missouri lead district: Geol. Soc. America Bull., v. 65, no. 3, p. 201-221.
Okamoto, Go, Okura, Takeshi, and Goto, Katsumi, 1957, Properties of silica in water: Geochim. et Cosmochim. Acta, v. 12, nos. 1-2, p. 123-132.
Page, B. M., 1959, Geology of the Candelaria mining district, Mineral County, Nevada: Nevada Bur. Mines Bull. 56, 67 p.
Paige, Sidney, 1916, Description of the Silver City quadrangle [New Mexico]: U.S. Geol. Survey Geol. Atlas, Folio 199, 19 p.
Pardee, J. T., and Park, C. F., Jr., 1948, Gold deposits of the southern Piedmont: U.S. Geol. Survey Prof. Paper 213, 156 p.
Park, C. F., Jr., 1938, Dolomite and jasperoid in the Metaline﻿154 JASPEROID IN THE UNITED STATES—ITS CHARACTERISTICS, ORIGIN, AND ECONOMIC SIGNIFICANCE
district, northeastern Washington: Econ. Geology, v. 33, no. 7, p. 709-729.
-------1942, Manganese deposits of Cuba: U.S. Geol. Survey
Bull. 935-B, p. 75-97.
Park, C. F., Jr., and Cannon, R. S., Jr., 1943, Geology and ore deposits of the Metaline quadrangle, Washington: U.S. Geol. Survey Prof. Paper 202, 81 p.
Peterson, N. P., 1962, Geology and ore deposits of the Globe-Miami district, Arizona: U.S. Geol. Survey Prof. Paper 342, 151 p.
Pierce, W. G., 1944, Cobalt-hearing manganese deposits of Alabama, Georgia, and Tennessee: U.S. Geol. Survey Bull. 940-J, p. 265-285.
Prinz, W. C., 1967, Geology and ore deposits of the Philips-burg district, Granite County, Montana: U.S. Geol. Survey Bull. 1237, 66 p.
Proctor, P. D., 1953, Geology of the Silver Reef (Harrisburg) mining district, Washington County, Utah: Utah Geol. and Mineralog. Survey Bull. 44, 169 p.
-------1964, Fringe zone alteration in carbonate rocks, north
Tintic district, Utah: Econ. Geology, v. 59, no. 8, p. 1564-1587.
Rankama, K. K., and Sahama, T. G., 1950, Geochemistry: Chicago Univ. Press, 912 p.
Ransome, F. L., 1904, The geology and ore deposits of the Bisbee quadrangle, Arizona: U.S. Geol. Survey Prof. Paper 21, 168 p.
Reber, L. E., Jr., 1916, The mineralization at Clifton-Morenci [Arizona] : Econ. Geology, v. 11, p. 528-573.
Rodgers, John, 1948, Geology and mineral deposits of Bumpass Cove, Unicoi and Washington Counties, Tennessee: Tennessee Div. Geology Bull. 54, 82 p.
Roedder, Edwin, Ingram, Blanche, and Hall, W. E., 1963, Studies of fluid inclusions—[Pt.] 3, Extraction and quantitative analysis of inclusions in the milligram range: Econ. Geology, v. 58, no. 3, p. 353-374.
Rogers, A. F., and Kerr, P. F., 1942, Optical mineralogy, published formerly under the title, Thin-section mineralogy [2d ed.] : New York, McGraw-Hill Book Co., 390 p.
Ross, C. P., 1925, Geology and ore deposits of the Aravaipa and Stanley mining districts, Graham County, Arizona: U.S. Geol. Survey Bull. 763, 120 p.
-------1937, Geology and ore deposits of the Bayhorse region,
Custer County, Idaho: U.S. Geol. Survey Bull. 877, 161 p. [1938].
------—1940, Quicksilver deposits of the Mayacmas and Sulphur Bank districts, California, a preliminary report: U.S. Geol. Survey Bull. 922-L, p. 327-353 [1941],
-------1943, Geology and ore deposits of the Shafter mining
district, Presidio County, Texas: U.S. Geol. Survey Bull. 928-B, p. 45-125.
Rothrock, H. E., Johnson, C. H., and Hahn, A. D., 1946, Fluorspar resources of New Mexico: New Mexico Bur. Mines and Mineral Resources Bull. 21, 239 p.
Russell, P. L., 1947, Steeple Rock zinc-lead district, Grant County, New Mexico: U.S. Bur. Mines Rept. Inv. 4073,
12 p.
Rust, G. W., 1935, Colloidal primary copper ores at Cornwall mines, southeastern Missouri: Jour. Geology, v. 43, no. 4, p. 398-426.
Schrader, F. C., 1912, A reconnaissance of the Jarbidge, Contact, and Elk Mountain mining districts, Elko County, Nevada: U.S. Geol. Survey Bull. 497, 162 p.
-------1915, Mineral deposits of the Santa Rita and Patagonia
Mountains, Arizona: U.S. Geol. Survey Bull. 582, 373 p.
-------1931a, Notes on ore deposits at Cave Valley, Patterson
district, Lincoln County, Nevada: Nevada Univ. Bull., v. 25, no. 3, 16 p.
-------1931b, Spruce Mountain district, Elko County, and
Cherry Creek, Egan Canyon district, White Pine County: Nevada Univ. Bull., v. 25, no. 7, 39 p.
Sharp, B. J., and Myerson, B. L., 1956, Preliminary report on a uranium occurrence in the Atlanta area, Lincoln County, Nevada: U.S. Atomic Energy Comm. Rept. RME-2048 (revised), 18 p.
Sharp, W. N., and Cavender, W. S., 1962, Geology and thoriumhearing deposits of the Lemhi Pass area, Lemhi County, Idaho, and Beaverhead County, Montana: U.S. Geol. Survey Bull. 1126, 76 p. [1963],
Sheridan, M. J., 1947, United States Fluorspar Co. property, Sierra County, New Mexico: U.S. Bur. Mines Rept. Inv. 4017, 15 p.
Siebenthal, C. E., 1915, Origin of the zinc and lead deposits of the Joplin region, Missouri, Kansas, and Oklahoma: U.S. Geol. Survey Bull. 606, 283 p.
Siegel, Sidney, 1956, Nonparametric statistics; for the behavioral sciences: New York, McGraw-Hill Book Co., 312 p.
Siever, Raymond, 1962, Silica solubility, 0°-200°C, and the diagenesis of siliceous sediments: Jour. Geology, v. 70, no. 2, p. 127-150.
Singewald, Q. D., 1955, Sugar Loaf and St. Kevin mining districts, Lake County, Colorado: U.S. Geol. Survey Bull. 1027-E, p. 251-297 [1956].
Smith, W. S. T., 1905, Ore deposits and mines, Part 2 of The lead, zinc, and fluorspar deposits of western Kentucky: U.S. Geol. Survey Prof. Paper 36, p. 107-218.
Smith, W. S. T., and Siebenthal, C. E., 1907, Description of the Joplin district [Missouri-Kansas]: U.S. Geol. Survey Geol. Atlas, Folio 148, 20 p.; (repr., 1914).
Spencer, A. C., 1917, The geology and ore deposits of Ely, Nevada: U.S. Geol. Survey Prof. Paper 96, 189 p.
Spurr, J. E., 1898, Geology of the Aspen mining district, Colorado, with atlas: U.S. Geol. Survey Mon. 31, 260 p., and atlas of 30 sheets folio.
-------1906a, The southern Klondike district, Esmeralda
County, Nevada; a study in metalliferous quartz veins of magmatic origin: Econ. Geology, v. 1, no. 4, p. 369-382.
-------1906b, Ore deposits of the Silver Peak quadrangle,
Nevada: U.S. Geol. Survey Prof. Paper 55, 174 p.
-------1926, The southeast Missouri ore magmatic district:
Eng. and Mining Jour., v. 122, no. 25, p. 968-975.
Sundelius, H. W., and Bell, Henry, 3d, 1964, An unusual radioactive, rare earth-bearing sulfide deposit in Cabarrus County, North Carolina: Southeastern Geology, v. 5, no. 4, p. 207-221.
Tarr, W. A., 1933, The Miami-Picher zinc-lead district: Econ. Geology, v. 28, no. 5, p. 463-479.
Trischka, Carl, 1928, The silica outcrops of the Warren mining district, Arizona: Eng. and Mining Jour., v. 125, no. 26, p. 1045-1050.
-------1938, Some Arizona ore deposits; Part 2, Mining districts, Bisbee district: Arizona Bur. Mines Bull. 145, Geol. Ser. 12 (Univ. Bull., v. 9, no. 4), p. 32-41.
Tunell, George, and Posnjak, Eugen, 1931, The stability relations of goethite and hematite [discussion]: Econ. Geology, v. 26, no. 3, p. 337-343; no. 8, p. 894-898.﻿REFERENCES CITED
155
Turner, H. W., 1899, Replacement ore deposits in the Sierra Nevada: Jour. Geology, v. 7, no. 4, p. 389-400.
Tweto, Ogden, 1953, Geologic map of the Pando area, Eagle and Summit Counties, Colorado: U.S. Geol. Survey Mineral Inv. Field Studies Map MF-12 [1954].
Umpleby, J. B., 1917, Geology and ore deposits of the Mackay region, Idaho: U.S. Geol. Survey Prof. Paper 97, 129 p.
Vanderburg, W. O., 1938, Reconnaissance of mining districts in Eureka County, Nevada: U.S. Bur. Mines Inf. Circ. 7022, 66 p.
------1940, Reconnaissance of mining districts in Churchill
County, Nevada: U.S. Bur. Mines Inf. Circ. 7093, 57 p.
Vanderwilt, J. W., 1935, Revision of structure and stratigraphy of the Aspen district, Colorado, and its bearing on the ore deposits: Econ. Geology, v. 30, no. 3, p. 223-241.
------1937, Geology and mineral deposits of the Snowmass
Mountain area, Gunnison County, Colorado: U.S. Geol. Survey Bull. 884, 184 p. [1938].
Van Hise, C. R., and Leith, C. K., 1911, The geology of the Lake Superior region: U.S. Geol. Survey Mon. 52, 641 p.
Van Lier, J. A., De Bruyn, P. L., and Overbeek, J. Th. G., 1960, The solubility of quartz: Jour. Phys. Chemistry, v. 64, no. 11, p. 1675-1682.
Vine, J. D., and Prichard, G. E., 1959, Geology and uranium occurrences in the Miller Hill area, Carbon County, Wyoming: U.S. Geol. Survey Bull. 1074-F, p. 201-239 [I960].
Walker, A. C., 1953, Hydrothermal synthesis of quartz crystals: Am. Ceramic Soc. Jour., v. 36, no. 8, p. 250-256.
Weidman, Samuel, 1932, The Miami-Picher zinc-lead district, Oklahoma: Oklahoma Geol. Survey Bull. 56, 177 p.
Westgate, L. G., 1922, Ore deposits of the Salmon River dis-
trict, Portland Canal region: U.S. Geol. Survey Bull. 722-C, p. 117-140.
Westgate, L. G., and Knopf, Adolph, 1932, Geology and ore deposits of the Pioche district, Nevada: U.S. Geol. Survey Prof. Paper 171, 79 p.
Weymouth, J. H., and Williamson, W. O., 1951, Some physical properties of raw and calcined flint: Mineralog. Mag., v. 29, p. 573-593.
White, D. E., Brannock, W. W., and Murata, K. J., 1956, Silica in hot spring waters: Geochim. et Cosmochim. Acta, v. 10, nos. 1-2, p. 27-59.
White, J. F., and Corwin, J. F., 1959, Synthetic chalcedony [abs]: Geol. Soc. America Bull., v. 70, no. 12, pt. 2, p. 1696-1697.
Wilson, E. D., 1950, General features, chap. 1 in Part 1 of Arizona zinc and lead deposits: Arizona Bur. Mines Bull. 156, Geol. Ser. 18, p. 46-47.
------1951, Dragoon Mountains, chap. 2 in Part 2 of Arizona
zinc and lead deposits: Arizona Bur. Mines Bull. 158, Geol. Ser. 19, p. 10-29.
Winchell, A. N., 1924, Petrographic studies of limestone alterations at Bingham [Utah] (with discussion) : Am. Inst. Mining and Metall. Engineers Trans., v. 70, p. 884-903.
Woolnough, W. G., 1928 Chemical criteria of peneplanation— The duricrust of Australia—Presidential address: Royal Soc. New South Wales Jour, and Proc., v. 61, p. 1-33.
Wyart, Jean, 1943, Sur la crystallisation de la silice en presence de 1-eau sous pression: Soc. Frangaise Mineralogie Bull., v. 66, no. 1-6, p. 479-489.
Young, E. J., and Lovering, T. G., 1966, Jasperoids of the Lake Valley mining district, New Mexico: U.S. Geol. Survey Bull. 1222-D, 27 p.﻿﻿INDEX
[Italic page numbers indicate major references]
Page
A
Abrigo Canyon, Ariz------------------------ 64
Abrigo Limestone------------------------ 64, 66
Accessory minerals, classification by age__ 15 Accessory minerals, use in categorizing
jasperoid ------------------------------ 54
Acid, solubility of silica in-------------- 39
Acid solutions, solubility of silica in-	40
Acknowledgments ---------------------------- 3
Adams Hill area, Eureka district,
Nevada ------------------------------84, 85
Alabama, jasperoid bodies _________________ 89
Alamo, Nevada ---------------------------- 115
Alamogordo Member of the Lake Valley
Limestone ----------------------------- 127
Alaska, jasperoid bodies ------------------ 89
Albers, J. P., and Robertson, J. F.,
quoted --------------------------------- 97
Alder Creek, Ariz-------------------------- 94
Alder Group ------------------------------- 93
Alkaline solutions, solubility of silica in— 39,
41
Allentown, Pa----------------------------- 131
AHophane _________________________________  18
Alma, Colo--------------------------------- 97
Alpine mine, Nevada----------------------- 123
Alteration. See Hydrothermal alteration.
Ames, L. L., Jr., quoted ------------------ 47
Analyses, jasperoid samples ......- 55, 66, 70,
73, 77, 81, 83, 91, 93, 96, 99, 100, 101, 110, 111, 112, 113, 114, 117, 118, 120, 122, 125, 126, 128, 129, 131, 133, 135, 138, 141, 142,
143, 144, 147, 149
Analysis, thermal differential ---------30,	55
Anderson County, Ky------------------------ 106
Anderson prospect, Washington---------148, 149
Ankerite ------------------------------------ 18
Annie Creek mine, South Dakota------------- 132
Annie 5 mine, Colorado----------------------- 72
Antelope district, Nevada------------------ 122
Antimony deposits, California —*---------	96
Nevada _______________________z__108, 116
Apache Group _______________________________ 36
Appalachian Mountains, Ga------------------ 102
Aravaipa district, Arizona ----------------- 94-
Arcturus Limestone ------------------------ 120
Argentia district, Utah -------------------- 147
Argus mine, Nevada --------------------117,	118
Argus Range, Calif-------------------------- 96
Arizona, jasperoid bodies ---------------90,	93
Arkansas, jasperoid bodies ------------------ 94
Arkansas Novaculite ------------------------ 26
Arkansas River, Colo--------------------71,	102
Arkansas zinc district ...............—-	94
Arsenic deposits, Nevada --------------108,	116
Aspen, Colo--------------------------------3,	46
Aspen district, Colorado ----------------81,	97
Aspen Mountain, Colo------------------------ 82
Atlanta district, Nevada ------------------ 108
Atlanta mine, Nevada ------------------ 108,	110
Austinville district, Virginia ------------ 147
Australia, duricrusts ---------------------- 36
Page
B
Bald Eagle Mountain, Utah ----------------- 142
Bald Mountain, S. Dak--------------------- 132
Bald Mountain district, Nevada--------110, 111
Bald Mountain mine, South Dakota-------	132
Bamford, Pa________________________________ 131
Bamford district, Pennsylvania ------------ 130
Banner district, Arizona -------------29, 90, 91
Barite ____________________________________ 18
Barney Reevey Gulch, Utah ----------------- 140
Bartow County, Ga-------------------------- 102
Base-metal deposits, Central Kentucky
district ________________________________ 104
Georgia ______________________________ 102
Iowa _________________________________ 104
Kentucky-Ulinois district ____________ 104
Mississippi Valley district ---------- 104
Montana ______________________________ 108
Utah ........................... 137,	140
Wisconsin ____________________________ 104
Battle Mountain, Colo_________________79, 80
Battle Mountain, Nev----------------- 112,	115
Bayhorse, Idaho ___________________________ 104
Bayhorse Dolomite _________________________ 104
Bear Creek Mining Co------------- 75, 76, 78
Bear Gulch, Utah __________________________ 138
Beaver County, Utah ----------------------- 144
Beaver Dam Mountains,	Utah---------139,	146
Beekmantown Limestone -----------130, 131, 147
Beidellite -------------------------------- 18
Bell Mountain, Colo------------------------ 83
Belmont district, Nevada ------------------ 122
Belt Supergroup --------------------------- 104
Bethlehem, Pa------------------------------ 130
Bibliography ------------------------------ 149
Bidwell Bar district, California -----94, 96
Big Lime Mountain, Nevada------------------ 112
Bingham district, Utah __________9, 58, 137
Biot ite ---------------------------------- 19
Bisbee, Ariz--------------------------9, 66, 92
Bisbee Group ------------------------------ 94
Bisbee (Warren) district, Arizona ----------19,
63, 90, 94
Biscuit mine, Nevada----------------------- 111
Bishop, Calif------------------------------ 97
Bishop Cap district, New Mexico-------	124
Black Gap fault, Arizona ------------------ 66
Black Hawk district, California ----------- 97
Black Hills, S. Dak_............. 3, 24, 47, 131
Black Knife property, New Mexico_______	125
Black Queen mine, Colorado ---------------- 102
Black Range, N. Mex________ 125, 126, 127, 128
Blackhawk mine, Colorado ------------------ 101
Blue Bird mine, Nevada -------------------- 111
Blue Goose mine---------------------------- 135
Blue Ridge Mountains----------------------- 130
Bonanza district, Colorado ------------97,	102
Bonneterre Dolomite ______________________ 107
Boone County, Ark-------------------------- 94
Boone Formation ---------------------- 59, 60
Boss mine, Nevada------------------------- 115
Boston-Ely mine, Arizona ------------------ 68
Boulder Creek, Mont------------------------ 108
Bourbon County, Ky------------------------- 106
Bowers-Campbell mine, Virginia ------------ 147
Page
Box Elder County, Utah ---------------142,	146
Boyer district, Nevada	___________ 108,	110
Bradshaw mine, Nevada ____________________ 108
Breckenridge, Colo________________________ 102
Breece	Hill, Colo________________________ 71
Brewer, W. M., quoted --------------------- 89
Brewer	mine, South	Carolina ___________ 130
Bristol	Pass, Nev------------------------ 117
Bristol	Pass Limestone ------------------ 117
Brochantite _______________________________ 19
Brooklyn mine, Nevada ____________________ 111
Browns Peak, Ariz-------------------------- 92
Buckley, E. R., quoted ------------------- 107
Bucks County, Pa--------------------- 130,	131
Bull Valley (Goldstrike) district,
Utah ----------------------------- 137,	139
Bully Hill mine, California _______________ 96
Bumpass Cove district, Tennessee________	134
Burning Moscow mine, Nevada --------------- 84
C
Caballos Mountains, N. Mex---------------- 130
Calamity Gulch, S. Dak-------------------- 133
Calcite ___________________________________ 19
Caldwell County, Ky----------------------- 106
Caliente, Nev------------------------ 115,	123
Caliente district, Nevada ________________ 123
Califon (German Valley) district,
New Jersey ----------------------- 130,	131
California, jasperoid bodies ______________ 94
Cameron, Ariz______________________________ 91
Cameron area, Arizona -----------------90,	91
Camp Hale, Colo________________________79,	100
Candelaria district, Nevada ______________ 110
Canterbury Hill, Colo______________________ 71
Carbon ____________________________________ 20
Carbon County, Wyo________________________ 149
Carbon Ridge Formation ____________ 84, 85, 88
Carbonate district, Colorado __________97,	102
South Dakota ------------------- 131,	134
Carbonate Hill, Colo----------------------- 71
Carbonate rocks, replacement	of ____48,	49
See also Host rocks.
Carpenter district, New Mexico ___________ 125
Carrie mine, Nevada ______________________ 114
Cartersville district, Georgia ___________ 102
Casedepaga, Alaska ------------------------ 90
Castle Creek, Utah ----------------------- 146
Castle Creek fault, Colorado -------------- 82
Castle Peak, Nev__________________________ 112
Cataract Creek, Colo---------------------- 100
Catawba River ---------------------------- 130
Cathcart, S. H., quoted ------------------- 90
Caclin shaft, Nevada ---------------------- 85
Cave-in-Rock fluorite district, Illinois —	42
Cedar City, Utah -------------------- 139,	146
Cedar Mountain district, Nevada ---------- 111
Central Kentucky district ---------------- 106
Central Tennessee district, Tennessee_____134,
135
Cerussite _________________________________ 20
Chaffee County, Colo-------------------97,	102
Chaffee Formation —	71, 78, 79, 81, 97,	100
Chainman Shale _______________________ 85,	121
Chalcedony ____________________________20,	46
157﻿158
INDEX
Page
Chalcopyrite. --------------------------- 21
Challis, Idaho ..........................- 104
Chance mine, New Mexico ----------------- 129
Charlotte, N.C.............................  130
Chemical analyses. See Analyses.
Chemical composition. See Composition of jasperoid.
Cherry Creek district, Nevada--------------- 111
Cherry Creek Range, Nev--------------------- 111
Chert, Philipsburg district, Montana —	107
Tri-State district ------------ 59, 60, 61
Chi-square test ----------------------------- 56
Chief (Caliente) district, Nevada ---------- 123
Chinle Formation ------------ 7, 91, 92, 146, 147
Chino copper mine, New Mexico -------------- 128
Chise, N. Mex..............................  130
Chiulos Canyon, Utah ----------------------- 144
Chlorapatite ________________________________ 21
Chloride mine,	Nev----------------------- 122
Chloride Point	mine, Utah --------------- 143
Chlorite ____________________________________ 21
Chochise County, Ariz_----------------------- 93
Churchill County,	Nev--------------- 110,	123
Cincinnati arch ---------------------------- 106
Clark County,	Ky------------------------ 106
Clark County,	Nev___...................  114
Clark Mountain district, California------	97
Clifton district,	Utah --------------- 189,	140
Clifton-Morenci district,	Arizona 50, 61,	90
Climax,	Colo---------------------------97,	99
Clipper Peak, Utah ------------------------- 138
Cobalt deposits, Alabama -------------------- 89
Nevada _________________________ 108,	110
Cochise	County,	Ariz-------------------92,	94
Coconino County, Ariz------------------------ 91
Colorado, jasperoid bodies ------------------ 97
Colorado Plateau ------------------------—	7
Colorado River	--------------------91,	146
Colors, characteristic, jasperoid ------------ 7
use of in categorizing jasperoid
samples ----------------------------- 53
Columbia district, Nevada ------------------ 123
Columbia mine, California ------------------- 96
Commercial mine, Utah ---------------------- 138
Composition, silica-bearing solutions __	1*1
Composition of jasperoid, Aspen district,
Colorado --------------------------------- 83
Bisbee (Warren) district, Arizona _	66
chemical ------------------------------ 80
Clifton-Morenci district, Arizona —	63
comparison of _________________________ 55
Ely district, Arizona _________________ 70
Gilman district, Colorado ------------- 81
Leadville district, Colorado ---------- 73
statistical summary ___________________ 34
Tintic and East Tintic districts,
Utah ________________________________ 77
Tri-State district -------------------- 61
Conrad mine, Utah __________________________ 146
Constituents of jasperoid, major ------------ 30
minor _________________________________ 34
Contact district, Nevada-------------------- 111
Continental Chief mine, Colorado ------------ 72
Cooks Peak, N. M____________________________ 125
Cooks Peak district, New Mexico __ 125, 127
Copper Chief mine, Arizona ------------------ 93
Copper Cities deposit, Ariz------------------ 94
Copper	deposits,	Alaska --------------89,	90
Arizona ------------------------------- 93
California ---------------------------- 96
Colorado ----------------------------- 101
Idaho ________________________________ 104
Missouri _____________________________ 107
Nevada ___________112, 113, 115, 117, 123
New Mexico ________________________ 127, 128
Utah __________________________ 137, 142, 144
Copper Mountain, Alaska _____________________ 90
Copper Mountain Mine, Utah _________________ 142
Copper World mine, Arizona __________________ 93
Page
Copperfield, Utah ______________________ 138,	139
Cornwall copper mines, Missouri -------------- 107
Cortez district, Nevada _________________108,	111
Cortez Range, Nev__________________________ 112
Cottonwood Canyon, Nev------------------------ 110
Courtland, Ariz---------------------------- 92
Courtland-Gleeson district, Arizona--------90, 92
Crittenden County, Ky---------------------- 106
Crystobalite __________________________________ 45
Cuba, jasperoid occurrences	_______________ 7
Cuchillo Mountains, N. Mex----------------- 125
Cuchillo Negro district, New	Mexico —	125
Custer County, Idaho _________________________ 104
Czar fault, Arizona -----------------------64, 65
D
Dacy claims, South Dakota -------------------- 133
Darwin district, California ---------------94, 96
Data analysis, methods of---------------------- 51
Deadwood Formation ----------------24, 131, 132
Deception Rhyolite ------------------------ 93
Decorah Formation ---------------------- 104,	105
Deep Creek Range, Utah ----------------------- 139
Defiance ore body, Nevada -------------------- 119
Definition, favorable jasperoid _______________ 50
unfavorable jasperoid ___________________ 50
Definition of jasperoid ------------------------ 2
Delano district, Nevada ---------------------- 123
Delmar district, Nevada ________________ 108,	112
Delores County, Colo-------------------------- 100
Delta, Utah ............................... 139
Deming, N. Mex------------------------------- 125,	129
Density, use of in categorizing
jasperiod samples -------------------------- 56
Density of jasperoid--------------------------- 29
Deposition of silica ------------------------- 1*8
Description of jasperoid, Aspen district,
Colorado -------------------------------- 82
Atlanta district, Nevada --------------- 108
Austinville district, Virginia --------- 147
Bald Mountain district, Nevada —	110
Banner district, Arizona ---------------- 91
Bidwell Bar district, California______	96
Bingham district, Utah ----------------- 137
Bisbee (Warren) district, Arizona _	65
Bishop Cap district, New Mexico________	124
Bull Valley (Goldstrike) district,
Utah ___________________________________ 139
Bumpass Cove district, Tennessee __	134
Cameron area, Arizona ___________________ 91
Candelaria district, Nevada ____________ 110
Carbonate district, South Dakota —	134
Cartersville district, Georgia --------- 102
Cedar Mountain district, Nevada —	111
Central Kentucky district ______________ 106
Central Tennessee district______________ 135
Cherry Creek district, Nevada________	111
Clifton district, Utah ----------------- 139
Clifton-Morenci district, Arizona —	62
Contact district, Nevada _______________ 111
Cooks Peak district, New Mexico________	125
Courtland-Gleeson district, Arizona.	92
Cuchillo Negro district.
New Mexico _____________________________ 125
Darwin district, California _____________ 96
Delmar District, Nevada ---------------- 112
Dolly Varden district, Nevada ---------- 113
Drum Mountains (Detroit) district,
Utah ..................................  139
Eagle Mountains district, Texas------	136
East Shasta district, California-----	96
Eastern Tennessee zinc district------	134
Eureka district, Nevada ----------------- 84
Ferguson district, Nevada -------------- 114
Fort Apache iron district, Arizona.	94
Friedensville district, Pennsylvania..	131
Getchell mine area, Nevada ------------- 114
Gilman district, Colorado --------------- 80
Page
Description of jasperoid—Continued
Gold Hill district, Utah -------------- 140
Goodsprings district, Nevada ---------- 115
Hadley (Graphic) district,
New Mexico ---------------------------- 125
Hillsboro district, New Mexico---------	126
Horseshoe-Sacramento district,
Colorado ------------------------------ 97
Ivanpah district, California ---------- 96
Jerome district, Arizona--------------- 93
Kentucky-Illinois district ------------ 106
Kern district, Nevada ----------------- 115
Kingston district, New Mexico__________	126
Kokomo district, Colorado ------------- 99
La Plata district, Colorado ----------- 99
Lake Valley district, New Mexico __	127
Leadville district, Colorado ---------- 72
Lucin district, Utah ------------------ 142
Magdalena district, New Mexico __	127
Manhattan district, Nevada ------------ 116
Mercur district, Utah —-.-------------- 142
Metaline district, Washington _________ 148
Mount Nebo district, Utah ------------- 143
North Carolina ------------------------ 130
North Tintic district, Utah ----------- 144
northern Arkansas zinc-lead
district _________________________________ 94
Organ district, New Mexico--------------- 127
Pando area, Colorado -------------------- 100
Philipsburg district, Montana ___________ 108
Pima district, Arizona ------------------- 93
Ragged Top Mountain district,
South Dakota ---------------------------- 133
Rico district, Colorado _________________ 101
San Francisco district, Utah ------------ 144
San Rafael Swell area, Utah ------------- 146
Sanderson, Tex--------------------------- 136
Santa Fe district, Nevada --------------- 117
Santa Rita district, New Mexico________	128
Silver Islet district, Utah ------------- 146
Silver Peak district, Nevada------------- 117
Silverhorn district, Nevada _____________ 117
South Carolina -------------------------- 130
Southeastern Missouri district---------	107
Taylor district, Nevada ----------------- 118
Tierra Blanca district,
New Mexico ______________________________ 128
Tintic and East Tintic district,
Utah _____________________________________ 75
Tres Hermanas District,
New Mexico ------------------------------ 129
Tri-State district _______________________ 60
Tutsagubet district, Utah --------------- 146
Uncompahgre district, Colorado __________ 101
Upper Mississippi Valley district —	104
Victorio district, New Mexico ----------- 129
Ward district, Nevada ___________________ 119
West Lead district, South Dakota —	132
West Ward district, Nevada--------------- 120
White Pine (Hamilton) district,
Nevada __________________________________ 121
Deseret Formation ---------------------------- 144
Desert Range, Utah --------------------------- 146
Diadem lode, California --------------------94, 96
Diamond district, Nevada --------------------- 122
Dickite _______________________________________ 21
Differential thermal analysis---------------80, 55
Dirty Devil 6 mine, Utah _____________________ 146
Distribution of jasperoid, Aspen district,
Colorado _________________________________ 82
Bisbee district, Arizona ----------------- 64
Clifton-Morenci district, Arizona —	61
Ely district, Nevada --------------------- 67
Eureka district, Nevada ------------------ 84
Gilman district, Colorado ________________ 79
Leadville district, Colorado ------------- 71
Tintic and East Tintic districts,
Utah _____________________________________ 73
Tri-State district _______________________ 59﻿INDEX
159
Page
Dividend fault, Arizona --------------- 64, 65
Dixie mine, Utah ----------------------------- 146
Doctor mine, Colorado ------------------------ 102
Dolly Varden district, Nevada ---------------- 112
Dolly Varden Pass, Nev------------------------ 112
Dolomite -------------------------------------- 21
Don Luis, Ariz--------------------------------- 65
Dona Ana County, N. Mex----------------124, 127
Double Up mine, Nevada--------------- 115
Douglas, Ariz------------------------- 94
Downtown area, Colorado--------------- 71
Dragoon Mountains, Ariz--------------- 92
Dreyer, R. M., quoted ------------------------ 123
Drum Mountains (Detroit) district,
Utah ____________________________________ 139
Dry Canyon, Utah ----------------------------- 142
Duck Creek district, Nevada ------------------ 123
Dugway district, Utah ------------------------- HO
Dunderberg Shale ------------------------------ 84
Durango, Colo--------------------------99,	101
Duricrusts, Australia ------------------------- 36
Dyer district, Nevada------------------------- 113
Dyer Dolomite Member, Chaffee Formation __________71, 78, 79, 80, 81, 97, 100
E
Eagle County, Colorado---------- 78, 97, 99, 102
Eagle Mountains district,	Texas ------135,	136
Eagle Peak, Tex---------------------- 136
Eagle River ____________________ 78, 79, 99, 100
Eagle River Canyon, Colo---------------------- 100
Eagle River Valley, Colo----------------------- 97
East Shasta district, California ------94, 96
East Tintic district, Utah ----- 73, 137, 144
East Tintic Mountains,	Utah ---------73,	144
Eastern Tennessee district, Tennessee	—	184
Egan Range, Nev_______________________ 67,	119
“88” mine, Utah ------------------------------ 147
Eldorado Dolomite ----------------------------- 84
Elko, Nev------------------------------------- 116
Elko County, Nev_ 108, 111, 112,	113,	119,	123
Ely, Nev____ 3, 75, 84, 111, 116,	117,	119,	123
Ely Limestone ------------------------ 24,	119
Ely (Robinson) district, Nevada	--------21,
24, 67, 77,	78,	108,	140
Emery County, Utah --------------------------- 145
Empire Hill, Colo_____________________ 71
Epidote --------------------------------------- 21
Escabrosa Limestone ------------ 64, 65, 129
Escalante Valley, Utah ----------------------- 144
Esmeralda County, Nev-----------108, 113, 114,
117, 122, 123
Eureka, Nev................74, 75, 84, 122, 144
Eureka County, Nev------ 84, 108, 111, 116, 125
Eureka district, Nevada ---------------84, 108
Eureka Hill mine, Utah----------,------ 77
Eureka Peak, Utah ----------------------------- 74
Eureka Quartzite ------------------------------ 84
Evans Gulch, Colo----------------------71, 72
Evaporation, effects on deposition of silica -------------------------------- 43
F
Fairview,	N. Mex---------------------------- 125
Fauquier County, Va--------------------------- 147
Favorable	jasperoid, definition of ---------- 50
Ferguson,	H. G., quoted -------------------- 114
Ferguson district, Nevada -------------------- 113
Ferguson	Springs, Nev---------------------- 113
Fireball district, Nevada -------------------- 123
Fish Springs district, Utah ------------------ 147
Flint Creek Range, Mont----------------------- 107
Fluorite -------------------------------------- 21
Fluorspar	deposits, Idaho ------------------ 104
Texas ---------------------------- 135, 136
Forepaugh mine, Colorado ---------------------- 72
Fort Apache district, Arizona ---------7, 94
Page
Fossils ____________________ 36, 46, 65. 96, 102
Four Metals mine, Utah ---------------------- 140
Franklin Lease mine, Utah ___________________ 143
Franklin mine, Virginia --------------------- 148
Friedensville, Pa---------------------------- 131
Friedensville district, Pennsylvania —130, 131 Fryer Hill, Colo__________________________71, 72
Fusselman Dolomite___ 125, 126, 127, 128, 129
G
Galena ---------------------------------------- 21
Galena Dolomite ------------------------------ 104
Garden mine, South Dakota -------------------- 132
Gardner shaft, Arizona ------------------------ 64
Garfield, N. Mex------------------------------ 130
Garfield County, Colo----------------------97, 102
Gasconade Dolomite ___________________________ 107
Gemeni mine, Utah ----------------------------- 75
Genesis of jasperoid, Alabama ----------------- 89
Aspen district, Colorado ----------------- 82
Austinville district, Virginia ---------- 147
Banner district, Arizona ----------------- 91
Bisbee district, Arizona ----------------- 64
Bishop Cap district, New Mexico __	124
Bumpas Cove district, Tennessee —	134
Cameron area, Arizona -------------------- 91
Cartersville district, Georgia ---------- 102
Central Kentucky district --------------- 106
Clifton-Morenci district, Arizona __	62
Cooks Peak district, New Mexico ___	125
Courtland-Gleeson district, Arizona -	92
Darwin district, California -------------- 96
Eagle Mountains district, Texas —	136
East Shasta district, California------	96
Eastern Tennessee zinc district-------	135
Ely district, Nevada --------------------- 67
Eureka district, Nevada ------------------ 84
Fort Apache iron district, Arizona. 94
Gilbert district, Nevada ---------------- 114
Gilman district, Colorado----------------- 79
Gold Hill district, Utah ---------------- 141
Horseshoe-Sacramento district,
Colorado --------------------------------- 97
Ivanpah district, California ---------.	96
Jerome district, Arizona ----------------- 93
Kentucky-Illinois district -------------- 106
Kingston district, New Mexico---------	126
Kokomo district, Colorado ---------------- 99
La Plata district, Colorado -------------- 99
Lake Valley district, New Mexico __	127
Leadville district, Colorado ------------- 72
Magdalena district, New Mexico —	127
Mercur district, Utah ------------------- 142
Metaline district, Washington ----------- 148
Michigan ________________________________ 107
Miller Hill area, Wyoming---------------- 149
North Carolina -------------------------- 130
North Tintic district, Utah ------------- 144
Pando area, Colorado -------------------- 100
Rico district, Colorado ----------------- 101
San Rafael Swell area, Utah ------------- 146
Sanderson, Tex--------------------------- 136
Shafter district, Texas ----------------- 135
South Carolina -------------------------- 130
Southeastern Missouri district--------	107
Timberville district, Virginia ---------- 147
Tintic and East Tintic districts,
Utah _____________________________________ 74
Tri-State district ----------------------- 59
Uncompahgre district, Colorado >_	101
Geology, Anderson prospect,
Washington ------------------------------ 149
Aspen district, Colorado _________________ 81
Atlanta district, Nevada ---------------- 108
Austinville district, Virginia ---------- 147
Bald Mountain district, Nevada--------	110
Banner district, Arizona ----------------- 91
Bidwell Bar district, California______	96
Page
Geology—Continued
Bingham district, Utah ------------------- 137
Bisbee (Warren) district, Arizona .	63
Bishop Cap district, New Mexico	—	124
Boyer district, Nevada ------------------- 110
Bull Valley (Goldstrike) district,
Utah .....................................  139
Bumpass Cove district, Tennessee	—	134
Cameron area, Arizona -------------------- 91
Candelaria district, Nevada -------------- 110
Cartersville district, Georgia ----------- 102
Cedar Mountain district, Nevada	__	111
Central Kentucky district --------------- 106
Central Tennessee district -------------- 135
Cherry Creek district, Nevada---------	111
Clifton district, Utah ------------------ 139
Clifton-Morenci district, Arizona	—	61
Contact district, Nevada ----------------- 111
Cooks Peak district, New Mexico_________	125
Cortez district, Nevada ----------------- 112
Courtland-Gleeson district,
Arizona __________________________________ 92
Cuchillo Negro district,
New Mexico _______________________________ 125
Darwin district, California--------------- 96
Delmar district, Nevada _________________ 112
Dolly Varden district, Nevada---------	112
Drum Mountains (Detroit) district,
Utah _____________________________________ 139
Dugway district, Utah ___________________ 140
Eagle Mountains district, Texas __	136
East Shasta district, California_______	96
East Tintic district, Utah _______________ 73
Eastern Tennessee zinc district________	134
Ely district, Nevada _____________________ 67
Eureka district, Nevada ------------------ 84
Fort Apache district, Arizona ____________ 94
Getchell mine area, Nevada ______________ 114
Gilbert district, Nevada _________________ 114
Gilman district, Colorado ---------------- 78
Gold Hill district, Utah _________________ 149
Goodsprings district, Nevada _____________ 114
Groom district, Nevada_____________-___ 115
Hadley (Graphic) district,
New Mexico _______________________________ 125
Hermosa (Sierra Caballos) district,
New Mexico ------------------------------- 126
Hillsboro district, New Mexico________	126
Horseshoe-Sacramento district,
Colorado _________________________________ 97
Howell mine, West Virginia _______________ 147
Ivanpah district, California ------------- 96
Jerome district, Ariz--------------------- 93
Kentucky-Illinois district --------------   106
Kokomo district, Colorado ________________ 99
La Plata district, Colorado ______________ 99
Lake Valley district, New Mexico __	127
Lewis	district,	Nevada _______________ 115
Lucin	district,	Utah _________________ 142
Magdalena district, New Mexico_________	127
Manhattan district, Nevada _______________ 116
Mercur district, Utah ____________________ 142
Metaline district, Washington ____________ 148
Mill Canyon district, Nevada _____________ 112
Miller Hill area, Wyoming ________________ 149
Mineral Hill district, Nevada------------- 116
Mount Nebo district, Utah ---------------- 143
North Tintic district, Utah -------------- 144
Northern Arkansas zinc-lead
district _________________________________ 94
Organ	district,	New Mexico ___________ 127
Pando	area, Colorado ---------------- 100
Patterson district, Nevada---------------- 116
Ragged Top Mountain district,
South Dakota ----------------------------- 133
Rico district, Colorado __________________ 101
Rush Valley (Stockton) district,
Utah _____________________________________ 144
San Francisco district, Utah----------	144﻿160
INDEX
Page
Geology—Continued
San Rafael area, Utah ------------------ 146
Santa Fe district, Nevada--------------- 116
Shafter district, Texas ---------------- 135
Silver Islet district, Utah------------- 146
Silver Peak district, Nevada ___________ 117
Silverhorn district, Nevada ------------ 117
Southeastern Missouri district --------- 107
Steeple Rock district, New Mexico _	128
Taylor district, Nevada ________________ 117
Tecoma district, Nevada ---------------- 119
Tintic district, Utah ------------------- 73
Tres Hermanas district,
New Mexico _____________________________ 129
Tri-State district ______________________ 58
Tutsagubet district, Utah -------------- 146
Uncompahgre district, Colorado_______	101
Upper Mississippi Valley district —	104
Ward district, Nevada __________________ 119
West Lead district, South Dakota	132
West Ward area, Nevada ----------------- 120
White Pines (Hamilton) district,
Nevada --------------------------------- 121
Willow Creek district, Nevada __________ 122
Wyndypah district, Nevada -------------- 122
Georgetown district, New Mexico — 124, 129
Georgia, jasperoid bodies ------------------- 102
Getchell district, Nevada ------------------- 108
Getchell mine area (Potosi district),
Nevada ------------------------------------ 114
Geysers, silica content ---------------------- 41
Gila County, Ariz----------------------91, 94
Gila River, silica content ___________________ 42
Gilbert district, Nevada -------------------- Ilk
Gillerman, Elliot, quoted ___________________ 136
Gilman (Red Cliff) district,
Colorado __________________ 36, 50, 78, 97, 100
Gilman Sandstone Member, Leadville
Limestone --------------------------------- 100
Giroux Ledge, Nev---------------------------- 117
Glauconite ----------------------------------- 21
Gleeson, Ariz--------------------------------- 92
Gleeson Ridge, Ariz........................... 92
Globe-Miami district, Arizona ---------------- 94
Godiva Mountain, Utah ________________________ 74
Goethite _____________________________________ 21
Gold Banks district, Nevada__________________ 123
Gold deposits, Alabama _______________________ 89
Arizona _________________________________ 65
California ------------------------------ 96
Colorado ----------------------- 79, 99, 101
Georgia --------------------------------- 89
Montana -------------------------------- 108
Nevada _ 108, 110, 112, 114, 115, 116, 123
New Mexico ----------------------------- 126
North Carolina _________________________ 130
South Carolina ------------------------- 130
South Dakota	---------------- 131,	133
Utah .............................—	142
Virginia _______________________________ 148
Gold Hill, Utah _______________________ 139,	140
Gold Hill district, North Carolina------	130
Gold Hill mine, North Carolina -------------- 130
Goldfield, Nev____...................... 113,	117
Goldstrike district,	Utah _____________ 137,	139
Goodfortune Creek district,
New Mexico -------------------------------- 129
Goodsprings district, Nevada ________________ 114
Goodsprings Dolomite _________________________ 96
Goose Creek Range, Nev----------------------- 119
Gore Range, Colo--------------------- 78, 97, 99
Goshute Valley, Nev-------------------- 112,	123
Gossans, silicified __________________________ 36
Graham County, Ariz--------------------------- 94
Grain size, jasperoid _________________________ 9
Grand Central mine, New Mexico ______________ 125
Grand County, Utah -------------------------- 146
Grand Falls Chert Member, Boone Formation ----------------------------------- 59
Page
Grand Reef mine, Arizona_____________________ 94
Granite County, Mont------------------------ 107
Granite Range, Utah ________________________ 140
Grand County, N. Mex________ 124, 125, 128, 129
Grapevine district, California ______________ 97
Grapevine Gulch Formation	______________ 93
Graphic district, New Mexico. See Hadley (Graphic) district, New Mexico.
Great Basin province _______________________ 137
Great Blue Limestone _________________ 142,	144
Great Salt Lake, Utah ----------------------- 73
Green Dragon 3 mine, Utah ------------------ 146
Groom district, Nevada _____________________ 115
Ground water, formation of
jasperoid ----------------------------36,	149
silica-bearing ________________ 74, 94, 107
Guilmette Formation __________________ 117,	118
Gunnison, Colo------------------------------- 97
Gunnison County, Colo-------------------97,	102
H
Hadley (Graphic) district,
New Mexico ______________________ 124,	125
Haile mine, South Carolina -------------- 130
Haiti, jasperoid occurrences ______________ 7
Halloysite —-----------------------------  22
Hamburg Dolomite ---------------------84,	85
Hamilton district, Nevada. See White Pine (Hamilton) district, Nevada.
Hanson Creek Formation _______________84,	85
Hansonburg district, New Mexico________	129
Hardin County, 111_______________________ 106
Harrington-Hickory mine, Utah ----------- 144
Hayden, Ariz______________________________ 91
Heglar prospect, North Carolina__________ 130
Helen shaft, Nevada ______________________ 85
Helvetia district, Arizona _______________ 93
Hematite _________________________________ 22
Hendricks Gulch, Ariz________________ 64,	65
Henry County, Ky_________________________ 106
Hermosa Formation __________________ 101,	102
Hermosa (Sierra Caballos) district,
New Mexico ___________________________ 126
Hewett, D. F., quoted ____________________ 96
Heyl, A. V., quoted ______________________ 84
Hidden Treasure claim, Nevada ___________ 113
Highland Peak Formation _________________ 112
Hillsboro, N. Mex________________________ 126
Hillsboro district, New Mexico___________ 126
Homestake Creek, Colo--------------------- 99
Hoosac Mountain, Nev---------------------- 84
Hoover mine, Tennessee _____________ 134,	135
Horn Silver mine, Utah __________________ 144
Horseshoe-Sacramento district,
Colorado ------------------------- 71,	97
Hoskins mine, Wisconsin _________________ 105
Host rocks, jasperoid --------------------- 6
replacement, by silica ______________ 46
theory __________________________ 49
Hot Springs, N. Mex______________________ 129
Hot springs, silica content ______________ 41
Hot Springs prospect, New Mexico_______	124
Howell mine, West Virginia ______________ 147
Howie mine, North Carolina ______________ 130
Hudspeth County, Tex--------------------- 136
Humboldt County, Nev_____________________ 114
Humboldt Range, Nev______________________ 123
Humbug Formation ___________________ 142,	144
Hydromica ________________________________ 22
Hydrothermal alteration ______ 61, 64, 67, 74,
79, 84, 91, 99, 100, 101, 102, 106, 136, 144, 146, 147, 148
Hydrothermal solutions __ 60, 64, 67, 79, 92, 94 Hypogene jasperoid ----------------------- 97
I
Iceland ---------------------------------- 41
Page
Idaho, jasperoid bodies ___________________ 104
Illinois, jasperoid bodies ________________ 104
Inyo County, Calif-------------------------- 97
Inyo Mountains, Calif----------------------- 96
Iowa, jasperoid bodies -------------------- 104
Iron	County, Utah _______________________ 144
Iron	Creek, Alaska ----------------------- 90
Iron	Creek district, Alaska_______________ 90
Iron	Hill, Colo--------------------------- 71
Iron	Hill mine, South Dakota ____________ 134
Iron	ore deposits, Arizona _______________ 94
Colorado _____________________________ 102
Georgia ______________________________ 102
Pennsylvania ------------------------- 130
Tennessee ---------------------------- 134
Ironwood Iron-Formation _____________________ 3
Irving, J. D., quoted _____________________ 133
Ivanpah district, California ____________94,	96
Ivy Wilson mine, Nevada ___________________ 111
J
Jack Pot mine, Nevada _____________________ 123
Jackson mine, Nevada ______________________ 119
Jackson Ridge, Colo------------------------- 99
J arosite __________________________________ 23
Jasper, Lake Superior region ---------------- 3
Jasperoid, age dating of ____________________ 6
as guide to ore _______________________ 50
characteristics, megascopic ---------7,	53
microscopic _____________________9,	54
colors --------------------------------- 7
composition --------------------------- SO
constituents, major ------------------- SO
minor ---------------------------   34
criteria for use as ore indicator____	56
definition ----------------------------- 2
density _______________________________ 29
distribution, geographic --------------- 3
geologic --------------------------- 6
favorable _____________________________ 50
genesis of ____________________________ 35
See also Genesis of jasperoid.
geologic age --------------------------- 6
host rock types _____________________6,	46
hypogene ------------------------------ 97
in major mining districts __________57,	88
in minor mining districts _____________ 88
minerals associated with _______________ 9
porosity ------------------------------ 29
texture ________________________________ 7
unfavorable ___________________________ 50
use as ore indicator ----------------50-56
Jasperoid-bearing mining districts,
foreign ----------------------------------- 6
Jasperoid bodies, structural control —	6
Jasperoid provinces ----------------------3, 4
Jefferson County, W. Va-------------------- 147
Jerome district, Arizona -------------7, 91, 93
Joana Limestone _____________117, 118, 120, 121
John mine, Nevada _________________________ 115
Johnson Gulch, S. Dak---------------------- 133
Joplin, Mo_________________________________ 135
Joplin district, Missouri-Kansas ____________ 3
Joplin field, Missouri _____________________ 58
Juab County, Utah ----------- 73, 139, 143, 147
Jumbo claim, Nevada ----------------------- 112
Junction fault, Arizona ____________________ 65
Jupiter mine, Arizona ______________________ 68
K
Kaibab Limestone ___________________________ 91
Kaolinite ---------------------------------- 23
Kelly Limestone ___________________________ 127
Kentucky, jasperoid bodies ________________ 106
minor jasperoid bodies---------------- 104
Kentucky-Illinois district ___________ 104, 106
Kentucky mineral district__________________ 104﻿INDEX
161
Page
Kern County, Calif--------------------------- 97
Kern district, Nevada ---------------------- 115
Kern Mountains, Nev------------------------- 115
Keystone fault, Arizona --------------------- 91
Kingsport Formation ------------------------ 134
Kingston, N, Mex______________ 125, 126, 127, 128
Kingston district, Nevada ------------------ 123
New Mexico----------------------------- 126
Kingston Range mining district,
California -------------------------------- 97
Klondike district, Nevada ------------------ 123
Knight zinc veins, Tennessee---------------- 134
Knoxville, Tenn----------------------------- 135
Kokomo district, Colorado ------------71, 97, 99
Kolmogorov-Smirnov two-sample test ----------51,
54, 55
Kona Dolomite ------------------------------ 107
Kostajnika, Yugoslavia ---------------------- 27
L
La Plata district, Colorado — 97, 99, 101
Lake County, Colo------------------------- 97, 102
Lake Superior region ------------------------- 3
Lake Valley district, New Mex------8, 124, 126
Lake Valley Limestone--------- 126, 127, 128, 129
Lake water, silica	content -------------- 41
Lakes of Killarney	mine,	Utah ---------- 143
Lakeside district, Utah ____________________ 147
Lancaster, Pa------------------------------- 130
Lancaster County,	Pa-------------------- 131
Lander County, Nev------------108, 111, 115, 123
Lane mine, California ----------------------- 96
Laramide orogeny ____________________________ 61
Las Cruces, N. Mex-------------------- 124, 127
Lawrence County,	Ark-------------------- 94
S. Dak__............................... 131
Lead, S. Dak_............................... 131
Lead deposits, Alaska _______________________ 89
Arizona -------------------------------- 94
Arkansas ------------------------------- 94
Colorado ________________ 82, 99, 101, 102
Idaho ________________________________  104
Missouri ------------------------------ 107
Nevada_____84, 110, 112, 116, 117, 119, 123
New Mexico __________________ 125, 127, 128
South Dakota -------------------------- 132
Utah ........................ 142, 144, 147
Washington ____________________________ 148
Lead district, South Dakota------------------ 24
Lead Hill, Wash_____________________________ 148
Lead Hill mine, Washington ----------------- 148
Lead King Hill, Wash________________________ 148
Leadville, Colo___________________3, 71, 78, 81
Leadville district, Colorado _____71, 97, 102
Leadville Limestone __ 71, 78, 79, 80, 81, 82, 83, 97, 100, 101, 102
Ledbetter Slate ---------------------------- 148
Lee district, California ____________________ 97
Lehigh County, Pa___________________________ 130
Lemhi County, Idaho ------------------------ 104
Lemmon, D. M., quoted _______________________ 97
Lemoigne district, California _______________ 97
Lenado district, Colorado ____________97, 102
Lewis district, Nevada _____________________ 115
Lexington dome ----------------------------- 106
Liberty Pit, Ariz---------------------------- 68
Lida district, Nevada_______________________ 123
Limonite ____________________________________ 23
Lincoln, F. C., quoted --------------------- 123
Lincoln County, Ky-------------------------- 106
Nev_____________108, 112, 115, 116, 117, 123
Lindgren, Waldemar, quoted _______________2, 47
Lion Hill, Utah ___________________________  142
Little Colorado River, Ariz__________________ 91
Little Evans Gulch, Colo--------------------- 72
Livingston County, Ky----------------------- 106
London fault, Colorado ---------------------- 97
Lone Mountain district, Nevada _____________ 123
Page
Lone Pine district, California ----------- 97
Longfellow Limestone _________________62,	63
Lovelock, Nev____________________________ 110
Lowell mine, Arizona ______________9, 64, 65
Lucin, Utah _____________________________ 142
Lucin district,	Utah ------------------- 142
Lucky Hill mine, Nevada------------------ 110
Lucky Strike mine, Utah ----------------- 146
Lumpkin County, Ga----------------------- 103
Luna County, N. Mex------------- 124, 125, 129
Luning, Nev______________________________ 116
Lussatite -------------------------------- 23
Lyon County,	Nev---------------------- 123
M
Mackay, Idaho ___________________________ 104
Macrotexture, use of in categorizing
jasperoid samples --------------------- 53
Macungi, Pa______________________________ 131
Madison County, Mo----------------------- 107
Madison Limestone ----------------------- 108
Magdalena, New Mex------------------------- 3
Magdalena district, New Mexico ----------124,
127, 129
Magdalena Formation --------------------- 124
Magdalena Group —. 125, 127, 128, 129, 130
Magma, source of silica solutions -------- 36
Magnetite ________________________________ 24
Magor mine, Utah ------------------------ 146
Mahoney mine, New Mexico ________________ 129
Malachite ________________________________ 24
Mammoth Peak, Utah________________________ 75
Manganese deposits, Alabama -------------- 89
Georgia ____________________________ 102
Montana ____________________________ 108
New Mexico ------------------------- 126
Tennessee __________________________ 134
Utah _______________________________ 139
“Manganese oxides” ----------------------- 25
Manhattan, Nev -------------------------- 122
Manhattan district, Nevada	.------108,	116
Manila Creek, Alaska---------------------- 90
Manitou Limestone ________________________ 71
Manto deposits, Colorado ----------------- 79
New Mexico _____________________126,	127
Texas _________________________ 135,	136
Maricopa County, Ariz--------------------- 94
Marion County, Ark------------------------ 94
Marquette County, Mich------------------- 107
Marquette district, Michigan ------------ 107
Martha mine, Utah _______________________ 139
Martin Limestone -------------------- 64,	65
Massadona-Youghall district,
Colorado __________________________97,	102
Mayacmas district, California ____________ 97
Mayflower property, Nevada ______________ 117
Mazatzal Mountains, Ariz------------------ 94
Megascopic characteristics, use of _______ 53
Mellville mine, Virginia ________________ 148
Menominee Range, Mich-------------------- 107
Mercer County, Ky------------------------ 106
Mercur, Utah ---------------------------- 142
Mercur district, Utah -------------7, 27, 142
Mercury deposits, Arizona ---------------- 94
Mescal Limestone ------------------------- 94
Mescal mine, California --------------94,	96
Mescal Range, Calif--------------------	96
Metaline district, Washington _______148,	149
Metaline Limestone ----------------- 148,	149
Metasomatical alteration -------------96,	107
See also Replacement.
Miami-Picher field, Oklahoma _____________ 58
Michigan, jasperoid bodies -------------- 106
Microline ________________________________ 25
Microscopic characteristics, in
categorizing jasperoid ---------------- 54
Microscopic features, accessory minerals _____________________________ 15
Page
Microscopic features—Continued
fabric texture ------------------------- 11
grain size ______________________________ 9
jasperoid ------------------------------- 9
Microtexture, use of in categorizing
jasperoid samples ________________________ 54
Microtexture of jasperoid, Aspen
district, Colorado _______________________ 82
Bisbee (Warren) district, Arizona _	66
Clifton-Morenci district, Arizona_____	62
Ely district, Arizona __________________ 69
Eureka district, Nevada ---------------- 84
Gilman district, Colorado -------------- 80
Leadville district, Colorado------------ 72
Tintic and East Tintic districts,
Utah __________________________________  75
Tri-State district --------------------- 60
Mike fault, Colorado ________________________ 71
Milford, Utah ______________________________ 144
Mill Canyon district, Nevada _______________ 111
Millard County, Utah ________________ 139, 144
Miller, B. L., quoted ---------------------- 131
Miller Hill area, Wyoming ------------------ 149
Milton, Tenn-------------------------------- 135
Mina, Nev___________________________________ 111
Mine Hill, N. Mex___________________________ 129
Mineral County, Nev----------108, 110, 111, 116
Mineral Farm mine, Colorado ________________ 101
Mineral Hill district, Nevada ______________ 116
Mineral Ridge, Nev__________________________ 117
Mineralization, hypogene, source of silica
solutions ________________________________ 36
Mineralizing solutions ______________________ 84
Mineralogy of jasperoid, Aspen
district, Colorado _______________________ 82
Banner district, Arizona________________ 91
Bisbee (Warren) district, Arizona _	66
Clifton-Morenci district, Arizona —	62
Courtland-Gleeson district,
Arizona ________________________________ 92
Ely district, Arizona __________________ 69
Eureka district, Nevada ________________ 84
Gilman district, Colorado ______________ 80
Leadville district, Colorado ----------- 72
Northern Arkansas district _____________ 94
Tintic and East Tintic districts,
Utah ___________________________________ 75
Tri-State district _____________________ 60
Mining districts, major, jasperoid in —	57
minor, jasperoid in ____________________ 88
Minor-element contents. See Analyses, jasperoid samples.
Minturn Formation ___________ 71, 80, 81, 99, 100
Mississippi Valley ------------------------- 132
Mississippi Valley district --------- 36, 58, 104
Missouri, jasperoid bodies ----------------- 107
Moab, Utah ____________________________ 137,	146
Mockingbird Gap district, New Mexico.. 129
Modoc mining district, California--------96, 97
Moenkope Formation ----------------------91,	146
Moffat County, Calif---------------------97,	102
Mojave Desert, Calif------------------------- 94
Molas Formation ---------------------------- 101
Monarch-Tomichi district, Colorado __ 97, 102
Monitor mine _____________________________   118
Montana, jasperoid bodies ------------------ 107
Monte Cristo Mountains, Nev----------------- 114
Montmorillonite ----------------------------- 25
Montoya Dolomite --------------------------- 125
Monument Creek, N. Mex---------------------- 126
Morgan County, Utah ------------------------ 147
Mormon Well, Nev---------------------------- 122
Morrison Formation ___________________________ 7
Mosquito Range, Colo-----------------71, 97, 102
Mother Lode gold district, California______	96
Mount Dixon, Alaska ------------------------- 90
Mount Hope district, Nevada ---------------- 123
Mount Nebo district, Utah __________________ 143
Mount Tenabo, Nev--------------------------- 112﻿162
INDEX
Page
Mountain City, Tenn_________________________ 134
Mowry mine, Arizona__________________________ 93
Mud Springs district, Nevada _______________ 123
Muddy River, Utah -------------------------- 145
Mule Mountains, Ariz--------------------- 63, 94
Muscatine mine, Utah ----------------------- 144
Muscovite ----------------------------------- 25
N
Naco Limestone ______________________65, 91, 94
Nashville, Tenn----------------------------- 134
Nashville Dome ----------------------------- 135
Navajo County, Ariz-------------------------- 94
Nephi, Utah -------------------------------- 143
Neutralization of solutions, as cause of
silica deposition ------------------------ 43
Nevada, jasperoid bodies ___________________ 108
Nevada district, Nevada -------------------- 123
Nevada Limestone --------------------- 121,	122
New Galena, Pa------------------------ 130,	131
New Jersey, jasperoid bodies________________ 180
New Mexico, jasperoid bodies --------------- 128
New York Canyon, Nev---------------------84, 85
Newark Canyon Formation _____________ 84, 85, 88
Nickel deposits, Nevada _________________ 108, 110
Nickel mine, Nevada _________________-—	110
Nontronite ---------------------------------- 25
Nopah lead and zinc mining district,
California ------------------------------- 97
Norris Basin, Yellowstone National
Park ------------------------------------- 46
North Carolina, jasperoid bodies------------ 130
North Fork, Little Evans Gulch -------------- 72
North Park ( ?) Formation __________________ 149
North Sheep Mountain, Colo------------------ 100
North Star claim, Nevada ___________________ 118
North Tintic district, Utah ----------------- HU
Northern Arkansas zinc-lead district______ 9U
Nunn Member, Lake Valley Limestone _	127
Nye County, Nev----------------------- 116,	122
O
Ochre Mountain, Utah _________________ 140,	141
Ochre Mountains Limestone------------------- 140
Old Baldy Peak, Utah ------------------------ 75
Old Quake mine, Nevada --------------------- 120
Opal ________________________ 25, 37, 43, 45, 46
Ophir district, Utah ----------------7, 1U2, 144
Oquirrh Formation -------------------------- 140
Oquirrh Group ______________________________ 138
Oquirrh Mountains, Utah--------------------- 142
Ore, jasperoid as a guide to----------------- 50
relationship to jasperoid, Alabama __	89
Anderson prospect,
Washington ---------------------- 149
Aspen district, Colorado ___________ 82
Atlanta district, Nevada ---------- 108
Austinville district, Virginia____	147
Bidwell Bar district,
California ------------------------- 96
Bingham district, Texas ___________ 138
Bisbee (Warren) district,
Arizona ____________________________ 65
Bishop Cap district,
New Mexico ------------------------ 124
Carbonate district, South
Dakota ---------------------------- 134
Cartersville district, Georgia —_	102
Central Kentucky district --------- 106
Central Tennessee district------	135
Clifton district, Utah ------------ 139
Contact district, Nevada ---------- 111
Cooks Peak district, New
Mexico ---------------------------- 125
Cortez district, Nevada ----------- 112
Cuchillo Negro district,
New Mexico ------------------------ 125
Page
Ore—Continued
relationship to jasperoid—Continued
Darwin district, California_______	96
Drum Mountains (Detroit)
district, Utah ---------------------- 140
Dugway district, Utah --------------- 140
Eagle Mountains district,
Texas ------------------------------- 136
East Shasta district, California. 96 Eastern Tennessee zinc
district ____________________________ 134
Ely district, Nevada ------------------ 67
Eureka district, Nevada --------------- 84
Friedensville district,
Pennsylvania ------------------------ 131
Getchell mine area, Nevada________	114
Gilbert district, Nevada ____________ 114
Gilman district, Colorado_________	79
Gold Hill district, Utah ------------ 140
Goodsprings district, Nevada	115
Groom district, Nevada ______________ 115
Hadley (Graphic) district,
New Mexico -------------------------- 125
Hillsboro district, New Mexico_____	126
Horseshoe-Sacramento district,
Colorado _____________________________ 98
Ivanpah district, California______	96
Jerome district, Arizona ------------- 93
Kentucky-Illinois district __________ 106
Kern district, Nevada --------------- 115
Kingston district, New Mexico..	126
Kokomo district, Colorado---------	99
La Plata district, Colorado_______	99
Lake Valley district, New
Mexico ___________________'_____ 127
Leadville district, Colorado______	72
Lewis district, Nevada ______________ 115
Lucin district, Utah ---------------- 142
Magdalena district,
New Mexico -------------------------- 127
Manhattan district, Nevada________	116
Mercur district, Utah --------------- 143
Metaline district, Washington	._	148
Mill Canyon district, Nevada	—	112
Miller Hill area, Wyoming---------	149
Mount Nebo district, Utah_________	144
North Carolina ______________________ 130
North Tintic district, Utah_______	144
Northern
Arkansas zinc-lead district_______	94
Organ district, New Mexico	__	127
Pando area, Colorado ________________ 100
Patterson district, Nevada __________ 116
Rico district, Colorado _____________ 101
Rush Valley (Stockton)
district, Utah ---------------------- 144
San Francisco district, Utah	__	144
San Rafael Swell area, Utah	._	146
Santa Fe district, Nevada_________	117
Shafter district, Texas _____________ 136
Silver Islet district, Utah _________ 146
Silver Peak district, Nevada	._	117
Silverhorn district, Nevada_______	117
South Carolina ---------------------- 130
Southeastern Missouri district	—	107
Steeple Rock district,
New Mexico -------------------------- 128
Taylor district, Nevada _____________ 118
Tecoma district, Nevada _____________ 119
Tennessee --------------------------- 134
Tintic and East Tintic districts,
Utah ................................  74
Tres Hermanas district,
New Mexico -------------------------- 129
Tri-State district--------------- 60
Uncompahgre district, Colorado.	101
Utah ________________________________ 137
Victorio district, New Mexico	_	129
West Lead district,
Page
Ore—Continued
relationship to jasperoid—Continued
South Dakota____________________ 132
Organ district, New Mexico ______________ 127
Organ Mountains, N. Mex_________ 124, 125, 127
Origin of jasperoid. See Genesis of jasperoid.
Orthoclase ------------------------------- 25
Osgood Mountains, Nev____________________ 114
Othello fault, New Mexico _______________ 125
Ouray, Colo---------------------------97, 101
Owen County, Ky__________________________ 106
Owens Lake, Calif_________________________ 96
Oxidized deposits, Colorado _____________ 102
Montana ---------------------------- 108
New Mexico ________________ 124, 125, 129
Tennessee __________________________ 134
Utah ------------------------------- 144
P
Pahasapa Limestone-------------------------- 24
Palomas Creek, N. Mex______________________ 126
Panamint Springs district, California _ 96, 97
Pando area, Colorado ____________ 71, 79, 97, 99
Park City district,	Utah ________________ 147
Park County, Colo___________________________ 97
Patagonia district, Arizona_________________ 93
Patterson district,	Nevada ______________ 116
Paymaster Tunnel,	Nev__________________ 119
Pearl Creek, Colo__________________________ 100
Pelican fault, New Mexico _________________ 126
Pelican shaft, New Mexico__________________ 126
Pend Oreille County, Wash__________________ 148
Pend Oreille mine, Washington _____________ 148
Pennsylvania, jasperoid bodies ____________ 180
Penny River, Alaska ________________________ 90
Percha Creek, N. Mex_______________________ 126
Percha Shale _________ 125, 126, 127, 128, 129
Pershing County, Nev_______________________ 123
Petrography. See Geology.
Petrology. See Description of jasperoid.
Philipsburg district, Montana --------107,	108
Physical properties, jasperoid ______________ 7
“Picher Field,” Okla_________________________ 3
Pierce, W. G., quoted----------------------- 89
Pilgrim mine, Nevada_______________________ 115
Pilot Mountains, Nev_______________________ 116
Pilot Shale.........................  121,	122
Pima district, Arizona _________________91, 93
Pinyon Peak, Utah -------------------------- 75
Pinyon Range, Nev ------------------------- 116
Pioche, Nev ......................108, 116, 117
Pioneer Gulch, Colo ________________________ 82
Pitkin County, Colo ----------------81, 97, 102
Plagioclase ________________________________ 25
Platte River, silica content________________ 42
Platteville Formation ________________104,	105
Plumas County, Calif------------------------ 96
Pogonip Group ______________________________ 84
Polk County, Tenn _________________________ 135
Pony Express Limestone Member,
Wanakah Formation _______________________ 99
Pope County, 111 -------------------------- 106
Porosity _______________________________29, 54
Portland Canal, Alaska --------------------- 89
Potosi District, Nevada. See Getchell mine area, Nevada.
Potosi Dolomite --------------------------- 107
Prairie du Chien Group--------------------- 104
Prairie Flower mine, Nevada---------------- 115
Precipitation of silica, See Deposition of silica.
Presidio County, Tex----------------------- 135
Presidio Formation ------------------------ 136
Pressure, effects on solubility of silica— 37, 40
Prospect Mountain Quartzite---------------- 112
Prospect Peak, Nev-------------------------- 84
Pyrite _____________________________________ 25﻿INDEX
163
Page
Q
Quartz, accessory mineral	 --------------- 26
conversion of silica gel --------------- 45
in jasperoid -------------------------   45
solubility _____________________________ 37
Quartz Creek district, Colorado---------97, 102
Queen of the Hills mine, Nevada---------111, 122
Queens Gulch, Colo -------------------------- 83
Quinn Canyon Mountains,	Nev------------ 122
R
Ragged Top Mountain District,
South Dakota --------------------- 131,	133
Railroad Valley, Nev --------------------- 122
Randville Dolomite ----------------------- 107
Ransome, F. L., quoted ------------------- 101
Rappahannock River, Va ------------------- 147
Rawlins, Wyo ----------------------------- 149
Red Cliff, Colo ___________________ 79, 97, 99
Red Mountain district, Colorado------- 97, 102
Redding, Calif ---------------------------- 96
Replacement, chemical factors ------------- 48
host rocks ---------------------- 4 6
physical factors --------------------- 46
theory -------------------*------ 49
Reward district, California --------------- 97
Richmond Hill, Colo ----------------------- 82
Rico district, Colorado -------------- 97,100
Rio Grande -------------------- 126, 129, 135
River water, silica content --------------- 41
Roaring Fork River ------------------------ 81
Roberts Mountain thrust fault, Nevada. 112,
Rock-Color Chart, use of------------------- 53
Rockingham County, Va -------------------- 147
Rocky Ridge, Tex ------------------------- 136
Ross, C. P., quoted ------------------ 104, 136
Rover Hill, Utah -----------------------   143
Ruby Range, Nev -------------------------- 110
Rush Basin, Colo -------------------------- 99
Rush Valley (Stockton) district, Utah— 144
Russ district, California------------------ 97
Ruth, Ariz -------------------------------- 68
S
Sacramento mine, Utah -------------------- 143
Sacramento stock, Arizona ----------------- 64
Saguache County,	Colo ------------- 97,	102
St. Francois County, Mo. ----------------- 107
St. George, Utah ------------------------- 146
St. Kevin district,	Colorado-----------97,	102
St. Peter Sandstone ---------------------- 104
Salida, Colo ------------------------- 97,	102
Saline County, 111 ----------------------- 106
Salmon River district, Alaska --------89, 90
Salt Lake County, Utah ------------------- 137
Sambo mine, Colorado --------------------- 101
San Andres Mountains, N. Mex.---------127, 129
San Augustine Pass, N. Mex --------------  127
San Bernardino County, Calif ---------96, 97
San Francisco district, Utah ------------- 144
San Francisco Mountains, Utah ------------ 144
San Juan County, Colo -------------------- 102
San Juan Mountains, Colo ------------- 97, 100
San Rafael River, Utah ------------------- 145
San Rafael Swell area, Utah--------137, 145, 147
San Xavier mine, Arizona ------------------ 93
Sanderson, Tex --------------------------- 136
Sandia Formation ------------------------- 127
Santa Fe district, Nevada ---------------- 116
Santa Rita, N. Mex ------------------- 128, 129
Santa Rita district, New Mexico-------58, 128
Santa Rita Mountains, Ariz----------------- 93
Santaquin Chief mine, Utah --------------- 143
Sawatch Range, Colo-------- 78, 79, 81, 97, 102
Scheelite deposits, California -........... 94
Nevada ------------------------------ 111
Page
Schell Creek Range, Nev -------------- 116,	117
Schrader, F. C., quoted _______________ 93,	116
Seabury mine, South	Dakota ----------------- 134
Seco Creek, N. Mex--------------------------- 126
Sedadlia district, Colorado ___________ 97,	102
Sericite --------------------------------------27
Seventy Nine mine, Arizona ____________29, 91
Sevier Desert, Utah ------------------------- 139
Seward Peninsula area, Alaska ---------89, 90
Shadow Mountain, Ariz ________________________ 91
Shady Dolomite ------------------------- 134,	147
Shafter district, Texas______________________ 135
Shannon shaft, Arizona _______________________ 92
Sharp County, Ark ---------------------------- 94
Shasta County, Calif ------------------------- 96
Shasta Lake, Calif --------------------------- 96
Sheba-de Soto mine, Nevada ------------------ 123
Sheep Mountain, Colo ________________________ 102
Shenandoah Peak, Nev ------------------------ 115
Shinarump Member of the Chinle
Formation _________________________________ 7,	91
Shirley Basin, Wyo ___________________________ 21
Shoshone Range, Nev _________________________ 115
Siderite _____________________________________ 27
Sierra Caballos district, New Mexico.
See Hermosa (Sierra Caballos) district, New Mexico.
Sierra Cuchillo Range, N. Mex --------------- 130
Sierra County, N.M..124, 125, 126, 128, 129, 130
Sierra Nevada, Calif ------------------------- 97
Sierra Oscura, N. Mex ----------------------- 129
Silcretes, South Africa ---------------------- 36
Silica, deposition of ------------------------ US
replacement theory ______________________ 46
solubility ______________________________ 37
sources of ______________________________ 35
transportation -------------------------- 36
types in jasperoid ______________________ 45
Silica-bearing solutions_____41, 62, 65, 79, 91,
94, 98, 107
Silica gel, conversion to quartz _____________ 45
deposition ------------------------------ 81
Siliceous replacement, Alaska ________________ 89
Silicified rocks, Tanganyika ----------------- 36
Silver City, N. Mex____________________ 128, 129
Silver deposits, Arizona _______________92,	93
California ______________________________ 96
Colorado ___________________ 79, 82, 99, 101
Idaho .................................  104
Montana -------------------------------- 108
Nevada — 84, 108, 110, 112, 114, 115, 116, 117, 121, 123
New Mexico______________ 124, 125, 126, 129
South Dakota --------------------- 131, 133
Utah ....................... 137, 142, 144
Silver Islet district, Utah ----------------- 146
Silver Lick mines, Nevada ____________________ 85
Silver Peak, Nev ______________________ 117, 122
Silver Peak district, Nevada ---------------- 117
Silver Peak Range, Nev----------------------- 122
Silver Queen shaft, Nevada __________________ 118
Silver Reef, Utah --------------------- 137, 146
“Silver Reef sandstone” --------------------- 147
Silverado Canyon, Utah _________________ 142,	43
Silverhorn district, Nevada ----------------- 117
Skull Canyon, Idaho _________________________ 104
Slate Creek, Alaska __________________________ 90
Slate Range district, California ------------- 97
Smith, W. S. T., quoted______________________ 106
Smithsonite __________________________________ 27
Snowmass Mountain, Colorado ------------------ 97
Socorro County, N. Mex----------- 124, 127, 129
Soda Lake lead and zinc mining
district, California ______________________ 97
Solomon district, Seward Peninsula,
Alaska ------------------------------------ 90
Sols, mixing of, effects on deposition—	44
Soluble salts, as a cause of deposition of silica __________________________________ 44
Page
Solution of silica _________________________ 36
Solutions, hydrothermal.. 60, 64, 67, 79, 92, 94
Sonoma County, Calif ----------------------- 97
South Africa, silcretes -------------------- 36
South Carolina, jasperoid bodies __________ 130
South Dakota, jasperoid bodies ------------ 131
South Park district, California ____________ 97
Southeastern Missouri district ------------ 107
Spar Valley, Tex __________________________ 136
Spearfish Creek, S. Dak ___________________ 131
Spectrographic analyses. See Analyses, jasperoid samples.
Sphalerite _________________________________ 27
Sphene _____________________________________ 27
Spring Canyon, Nev ________________________ 113
Spring Creek district, Colorado________97, 102
Spring Mountains, Nev _____________________ 115
Spruce Mountain district, Nevada __________ 123
Spruce Standard mine, Nevada_______________ 123
Spurr, J. E., quoted ------------------2, 107
Squaw Creek, S. Dak ___________________ 131, 134
Squaw Creek mine, South Dakota ____________ 132
Squaw Spring, Utah ------------------------ 144
Standard rock analyses _____________________ 81
Star district, Utah ----------------------- 144
Star Peak Group ___________________________ 123
Star Range, Utah __________________________ 144
Starr Grove mine, Nevada __________________ 115
Statistics, use of, for evaluation of
japeroid samples ________________________ 51
Steamboat Springs, Nev ________________45, 46
Steeple Rock district, New Mexico — 124, 128
Stevens County, Wash ______________________ 149
Stibiconite ________________________________ 27
Stray Horse Ridge, Colo ____________________ 71
Streater claims, Nevada ___________________ 116
Success district, Nevada __________________ 123
Sugar Loaf district, Colorado _________ 97, 102
Sulfide deposits, Alaska ------------------- 89
Arizona ---------------------- 65, 91, 93, 94
California ____________________________ 96
Colorado _________________ 79, 99, 101, 102
Kentucky _____________________________ 106
Missouri _____________________________ 107
Nevada — 84, 110, 111, 112, 113, 115, 116, 117, 119, 121
New Mexico_____________ 124, 125, 126, 129
Pennsylvania _________________________ 130
Tennessee ------------------------ 134, 135
Texas ________________________________ 135
Tri-State district -------------------- 60
Utah __________________ 74, 137, 141, 143
Washington --------------------------- 148
Sulphur Bank district, California ---------- 97
Summit claim, Salmon River district,
Alaska ---------------------------------- 90
Summit County, Colo ----------- 97, 99, 102, 147
Supergene jasperoid _______________ 84, 97, 115
Surface water, silica-bearing -------------- 94
Swansea district, California _______________ 97
Sweetwater district, Tennessee -------- 134, 135
Swisshelm district, Arizona ---------------- 94
Sycamore Creek, Ariz------------------------ 94
T
Tanganyika, silicified rocks _______________ 36
Taylor, Nev-------------------------------- 118
Taylor district, Nev--------------- 27, 108, 117
Taylor Springs, Nev------------------------ 118
Tecoma district, Nevada ------------------- 119
Tecopa district, California ---------------- 97
Telluride ore, South Dakota _______________ 133
Temperature, effects on solubility of
silica ----------------------------- 37, 40, 43
Temple Mountain, Utah --------------------- 146
Tennessee, jasperoid bodies---------------- 134
Tennessee Pass, Colo-------------------97, 99
Terrell County, Tex------------------------ 136﻿164
INDEX
Page
Texas, jasperoid bodies ------------------- 135
Texture, categorizing jasperoid ------------ 53
fabric __________________________________ H
in jasperoid ---------------------------- 7
Texture of jasperoid. See Microtexture of jasperoid.
“The Burnouts,” Nevada --------------------- 84
Thermal analysis, differential --------SO, 55
Thermal springs, silica content ------------ 41
Tierra Blanca Creek, N. Mex---------------- 128
Tierra Blanca district, New Mexico —	128
Timberville, Va---------------------------- 147
Timberville district, Virginia ------------ 147
Tincup district, Colorado -------------97, 102
Tintic district, Utah __ 21, 61, 73, 137, 144,
147
Tippett, Nev------------------------------- 115
Tombstone, Ariz------------------------92, 94
Tomstown Formation ________________________ 147
Tonopah, Nev_______________3, 110, 114, 116, 123
Tooele, Utah ______________________________ 144
Tooele County, Utah ------------ 139, 140, 142,
144, 146, 147
Top ton, Pa-------------------------------- 131
Toquima Range, Nev------------------------- 116
Tourmaline _________________________________ 27
Tourtellotte Park, Colo--------------------- 83
Transportation of silica solutions --------- 36
Treasure Hill, Nev------------------------- 121
Tremolite ---------------------------------- 27
Tres Hermanas, N. Mex---------------------- 129
Tres Hermanas district, New Mexico —	129
Tri-State district ________ 3, 6, 47, 58, 94, 105,
107, 135
Truth or Consequences, N. Mex----------126, 129
Tucson Maid fault, Colorado ---------------- 71
Tungsten deposits, Nevada ----------------- 114
Tungsten Hills, Calif----------------------- 97
Turkey Creek, Colo.....................79, 99
Tutsagubet district, Utah ................. 146
280 Tunnel, Nev............................ 119
U
Ubehebe district, California --------------- 97
Ulster mine, South Dakota ----------------- 133
Uncle Sam Gulch, Ariz----------------------- 64
Uncompahgre district, Colorado --------97, 101
Unfavorable jasperoid, definition----------- 50
Unicoi County, Tenn------------------------ 134
U.S. mine, Utah ....................... 140, 141
United Verde mine, Arizona ----------------- 93
Upper Mississippi Valley district — 36, 58, 104 Upper Peninsula, Mich---------------------- 107
Page
V
Uranium deposits, Arizona ----------------- 92
Nevada _______________________________ 108
Utah _________________________________ 145
Wyoming ______________________________ 149
Utah, jasperoid bodies ______________137, 146
Utah County, Utah ____________________73, 144
Vauclause Mine, Virginia ----------------- 147
Velarde prospect, New Mexico---------124, 130
Vernon, Utah _____________________________ 147
Verzan Canyon, Ariz------------------------ 68
Veteran mine, Arizona __________________68,	69
Victoria mine, Nevada ____________________ 113
Victorine mine, Nevada ------------------- 123
Victorio district, New Mexico------------- 129
Victorio prospect, New Mexico _______124, 130
Virginia, jasperoid bodies _______________ 147
Volcanism, relation to silica-bearing
water ----------------------------------- 41
Vugs, abundance ---------------------------- 7
W
Wah Wah district, Utah ------------------- 144
Wah Wah Mountains, Utah ------------------ 144
Wall Street mine, Nevada ----------------- 117
Wanakah Formation ------------------------- 99
War Eagle mine, Nevada ------------------- 111
Ward district, Nevada -------------------- 119
Warren County, N.J------------------------ 131
Wasatch Range, Utah ---------------------- 143
Washington, jasperoid bodies ------------- 148
Washington County, Ark--------------------- 94
Mo ___________________________________ 107
Tenn _________________________________ 134
Utah ___________________________  139,	146
Water, hot springs, silica content------	41
silica-bearing ------------------------ 94
solubility of silica in -------------37-39
See also Ground water.
Water Canyon, Nev------------------------- 115
Water Canyon district, New	Mexico —	129
Watson Canyon, Nev------------------------ 113
Watson Spring, Nev------------------------ 113
Weary Flat, Ariz--------------------------- 68
Weathering, source of silica	solutions —	36
Welcome Stranger Tunnel,	Nev------ 119
Wellington mine, Colorado	---------- 102
Wendover, Nev------------------------ 113,	146
West Lead, S. Dak------------------------- 132
West Lead district, South Dakota __ 131, 132
West Mercur, Utah ------------------------ 142
West Mountain,	Utah -------------- 138,	139
West Tintic district, Utah --------------- 147
Page
West Virginia, jasperoid bodies ---------- 147
West Ward district, Nevada --------------- 119
Whirlwind Valley, Utah-------------------- 139
“White Caps limestone” ------------------- 116
White Pine, Nev--------------------------- 115
White Pine County, Nev__ 108, 110, 111, 117,
119, 121, 123
White Pine (Hamilton) district,
Nevada ---------------------------------- 121
White Pine Mountains, Nev----------------- 121
White Quail Limestone Member, Minturn
Formation ------------------------------- 99
White River Plateau, Colo----------------- 102
Whitney mine, North Carolina-------------- 130
Willow Creek district, Nevada------------- 122
Winchester district, Arizona ______________ 93
Windfall Canyon, Nev-------------------84, 88
Windfall Formation ________________________ 84
Winnemucca, Nev--------------------------- 114
Wisconsin, jasperoid bodies--------------- 104
Wonder mine, California ------------------- 96
Wulfenite --------------------------------- 29
Wyndypah district, Nevada ---------------- 122
Wyoming, jasperoid bodies ---------------- 149
Wythe County, Va-------------------------- 147
Y, Z
Yampa River, Colo------------------------- 102
Yavapai County, Ariz----------------------- 93
Yellow Creek mine, South Dakota--------	132
Yellow Pine mine, Nevada ----------------- 115
Yellowstone Basin -------------------------- 7
Yellowstone National Park -------------41, 46
Yerington, Nev---------------------------- 127
Yerington district, Nev------------------- 123
Yosemite Gulch, Utah---------------------- 138
Young, Ariz-------------------------------- 94
Yule Creek, Colo-------------------------- 102
Zinc deposits, Alaska --------------------- 89
Arizona ________________________________ 94
Arkansas ------------------------------ 94
California ____________________________ 96
Colorado ___________________  99,	101,	102
Idaho _________________________________ 104
Missouri _____________________________ 107
Nevada -------------------------- 110, 119
New Mexico __________________ 125,	127,	128
Pennsylvania -------------------------- 130
Tennessee ____________________________ 134
Utah ________________________ 142,	144,	147
Virginia ------------------------------ 147
Washington ---------------------------- 148
Zinc Hill mining district, California — 96, 97
Zionsville, Pa---------------------------- 131
Zircon ------------------------------------ 29
☆ U.S. GOVERNMENT PRINTING OFFICE: 1972 O—442-660﻿﻿