Economic Geology of the Platinum Metals f-j 201;:3 - L'r:;vt riiA p& /■ c, 3,7eOsi»; 7sPt>«, 7sOs'«; «Ru™, «Pdi»*; iiRu™, 4ePdi»‘. The isotones are: 78Pt>“>, 7iAuW; 7nPt‘»‘, 77in«>, 7iOs>»*; 7sPtK®, 77Ir»i, 7aOs>»; 7sPt«°, 7«Os>si; 4ePdios, 47Agi°«; uRu™, «Pd‘“«, i7Agi»'; (4Rui°», «Rh‘»s, «Pd‘M; «Ru™; 4ePdi°3. The isodiaspheres are: 7sPt™, teOs*«; 7sPt»3, 77lr‘»3, 7iAu«'; 7sPt«*, 7eOs‘»°; 77lr'»>, 7aOs‘*»; 7»Ptw*, 7aOs>33; 7«Pt“», 7«Osi>«; uRu», 4aPdi»s; «Ru>»!, MPd™; «Ru“>, 4aRh>°3,47Ag‘»3; 44Rui“, 4aPdi»<; 44Ru*«, 4aPdi“. ECONOMIC GEOLOGY OF THE PLATINUM METALSPLATINUM METALS 9 ous gas OsOi. Therefore, the final product is shipped in bulk to the refiner, where it is analyzed and processed by chemical treatment. Every cleanup from the dredge of the Goodnews Bay Mining Co. is thus processed and separately analyzed. CHEMICAL PROPERTIES AND ANALYSES Pure platinum is not attacked by the common inorganic acids, but is dissolved, though less readily than gold, by aqua regia. On the other hand, pure iridium and rhodium are not appreciably attacked by aqua regia or other inorganic acids, and osmium and ruthenium are quite insoluble in such acids. Palladium is dissolved not only by aqua regia but also by hot nitric or hot sulfuric acid. This vulnerability of palladium to acids is reflected in its inferior ability to withstand the effects of weathering and consequently by its superior tendency to form natural mineral compounds. The platinum metals occur commonly in bedrock as two distinct alloys, which usually are intergrown in a pseudoeutectic fabric, but may also occur separately. As obtained from placer deposits, however, these two alloys are invariably mixed, and any chemical analysis of placer platinum therefore represents the sum of two different products, intermingled in an unknown ratio. Only rarely is it possible to obtain a pure sample of either alloy. Chemically, these alloys behave differently, in their reactions with acids and other reagents, than the purified platinum metals, and moreover, these reactions are not quantitatively predictable, because they depend upon the compositions of the alloys, which are inconstant. Hence, even the best analyses will fail to show either the composition of the individual alloys or their existing ratios, though certain guiding principles, hereafter enumerated in discussing different placers, may render possible a general understanding of the natural and proportions of the component alloys. Bulk samples of the platinum metals from placers are prepared for analysis, and also subsequently for refining, by dissolving them in hot aqua regia. In this procedure, most of the platinum, parts of the iridium and rhodium, and all the palladium are dissolved, but the osmium and ruthenium are unaffected and have to be gotten into solution by another method. The proportions of the soluble and insoluble fractions vary with different samples, according to the composition of the component alloys and their ratios, so that no general statement is warranted. In a typical sample of the platinum alloys recovered by the Good-news Bay Mining Co., Alaska, it was found that 98.1 percent of the platinum, 18.5 percent of the iridium, 66.7 percent of the rhodium, and all the palladium were dissolved in hot aqua regia. The remainder of the platinum, iridium, and rhodium and all the osmium and ruthenium constitute an insoluble fraction that is otherwise processed. The solubilities of the platinum metals in one another and in certain base metals has an important bearing upon the composition of their natural alloys. Gold and silver, in laboratory preparations, are miscible in all proportions, with well-defined solidus and liquidus curves, yet, the proportion of gold in native gold-silver alloys is rarely less than 60 percent, as shown by Mertie (1940, p. 93-124). The explanation of this phenomenon may be related to the formation of such alloys as hydrothermal rather than magmatic products. The platinum metals have different crystallographic properties that limit the amounts of these metals and the dross that constitute the two principal alloys. Thus the cubic platinum metals show continuous solidus and liquidus curves, but they appear not to be miscible in all proportions in nature, though the limits of natural miscibility have not been determined. Apparently, however, these limits are not dependent upon their mode of formation, as the natural alloys are dominantly of magmatic origin. Platinum and palladium have continuous solidus-liquidus curves for binary alloys of each of these metals with gold, silver, copper, iron, nickel and cobalt, so that the base elements may readily constitute the dross, if they were originally present in the magma. Other variations, however, result from local conditions in the bedrock sources, so that the compositions of the natural alloys are markedly inconstant. The platinum minerals are likewise variable in composition, but the variations are much smaller than in the alloys. Much less is known of the natural limits of miscibility of the hexagonal elements osmium and ruthenium with the other platinum metals and with the base metals. Melted mixtures of platinum or palladium with osmium or ruthenium show only partial solidus-liquidus curves, which give place at some point to more than two phases. Natural alloys of osmium and ruthenium contain amounts of iridium that commonly exceed those of the osmium, and such alloys also contain small amounts of rhodium and platinum. The amount of platinum, however, may range upward to 15 percent, though a tenor as great as this suggests that the analysis was made on a mixed sample of the two alloys. Palladium is generally absent or present only as a trace. The solubilities of the base metals in these hexagonal alloys is apparently slight, as alloys of osmiridium invariably contain small amounts of dross. In general, the limits of these ranges in mis-10 ECONOMIC GEOLOGY OF THE PLATINUM METALS cibility are different from those producible in the laboratory and have not yet been determined. The separation of the platinum metals into soluble and insoluble fractions for analysis has already been mentioned. The insoluble fraction is reduced by repeated treatments with alkaline oxidizing fluxes, and thereafter is gotten into solution. For scientific comparisons, these two fractions may be separately analyzed, as was done for the writer in 1945 by Johnson, Matthey and Co. with a sample of platinum metals contributed by the Goodnews Bay Mining Co., Alaska. Ordinarily, however, the soluble and insoluble fractions are combined for final analysis. The presence of black sand that cannot entirely be removed from placer platinum metals has already been noted. These remaining minerals go into solution at the refineries, either in the aqua regia, or along with the insoluble fractions that are treated with fluxes. Hence invariably there is given, even in superior commercial analyses, a percentage of “impurities.” This item includes the base metals that constitute the dross of the platinum alloys, the dross of any free gold that may be present, any lead shot, solder, or similar materials not recognized by the producer, and the base metals of the included black sand. Recent investigations have also shown that minute grains of chromite, chalcopyrite, and other minerals are intergrown in some of the natural platinum alloys. Thus in the platinum metals of the Goodnews Bay Mining Co., grains of chromite and chalcopyrite are clearly visible in polished sections at magnifications as low as 50 diameters. These facts lead to the conclusion that the true dross of natural platinum alloys, even in handpicked samples, is difficult to determine with precision. Chemical analyses of the natural platinum alloys are of different classes, with different degrees of dependability. Analyses are divided by the writer into two general classes, which are designated as superior and inferior analyses. Superior analyses are considered to be those wherein the percentages of all the component platinum metals are determined, with or without the base metals of the dross. Exceedingly few such analyses are available of the platinum metals produced in foreign countries. Numerous analyses of this kind have been made by the U.S. Bureau of Standards, and one was made by the U.S. Geological Survey. Most as-sayers are incapable of making high-grade analyses of the platinum metals and alloys, and concerns which are capable of doing such analytical work do not always do so, as the cost may be prohibitive. Another reason why such analyses, if made, are not published is that it may be to the advantage of either the producer or the processor, or both, that such results should not be generally known. The best analyses available to the writer are those made by Johnson, Matthey and Co., Inc., of Malvern, Pa., for the Goodnews Bay Mining Co. of Alaska. Few other superior analyses appear in this report. Inferior analyses include two general types. One type, which is the most prevalent, is essentially an analysis of only that part of the sample which dissolves in hot aqua regia. The insoluble fraction, whose total weight is known, is presented as osmium plus iridium, or perhaps as osmiridium. It commonly contains more iridium than osmium, as well as ruthenium and small amounts of platinum and rhodium. Therefore in such inferior analyses, the tenors of platinum, iridium, and rhodium are too low, and the tenor of ruthenium is neglected and rarely mentioned. Only the percentage of palladium is correct. The analyses of the platinum metals from Russia, because one part of the iridium is separately stated, whereas another part is reported as osmiridium, appear to be of this type; many other analyses in this report are of similar character. A second type of inferior analysis is one wherein only the soluble platinum and palladium are reported and the soluble iridium and rhodium are added either to the platinum or to the insoluble fraction reported as iridium plus osmium. This procedure is common practice where the alloy contains only small amounts of iridium, osmium, ruthenium, and rhodium. Such analyses have little value, but they cannot be ignored, because they show at least the tenor in palladium and a minimum tenor in platinum. Examples of these are shown by the two mean analyses of Colombian platinum published by Singewald (1950, p. 174). The problem thus arises how to present and interpret chemical analyses that are available in the literature. If, in addition to the percentages of some or all the platinum metals, the contents of copper, iron, and other base metals are specifically stated, the latter percentages cannot be ignored, and are stated as a part of the analysis with the implicit understanding that these tenors do not necessarily represent dross. If percentages of the base metals are not given, the gold (which is commonly free gold) is deleted, and the analysis is recomputed in terms of the platinum metals to total 100 percent. Even, however, if the tenors of the base metals are given, such recomputed analyses of the patinum metals alone serve a useful purpose in comparing different alloys with one another.PLATINUM METALS 11 MINERALOGY The platinum metals occur in nature in two forms: first, as natural alloys and intergrowths of alloys, and second, as chemical compounds in which the platinum metals function as cations. The alloys are solid solutions and have as wide ranges in composition as their crystallography and other factors permit. The chemical compounds also have variable compositions but within smaller limits, as these are controlled by substituions of cations and anions with comparable radii. Wright and Fleischer (1965, p. A5-A6) have tabulated as compounds, or mineral species, the platinum metals known to be chemically combined with oxygen, sulfur, arsenic, antimony, bismuth, tin, or tellurium, if these elements function as anions. Recognizing, however, the uncertainty that exists in a definite classification of the platinum metals, they have tabulated all nonminerals as “alloys and intermediate compounds.” The tabulation in this report is twofold, comprising alloys and minerals, with a reservation that a few of the so-called alloys may be partly or wholly minerals and vice versa. Moreover, in listing the alloys, preference is given to terms that indicate mixtures and inter-growths of platinum metals or alloys, as opposed to terms ending in “ite,” which connote platinum minerals. NATURAL ALLOYS OF PLATINUM METALS The native platinum metals, found mainly in placer deposits, consist generally of two principal alloys, which occur either separately or intergrown with one another. These alloys are designated commercially and generically as “platinum” and “osmiridium.” Platinum consists dominantly of that metal, but includes invariably the other five metals in variable amounts. Osmiridium consists dominantly of iridium and osmium, but includes also the metals ruthenium, rhodium, and platinum. Samples of the platinum metals taken from placers are heterogeneous for a number of reasons. First, the two alloys do not have constant compositions, but instead vary from one site in bedrock to another. Second, the proportions of one alloy to another vary from place to place, and if they are intergrown, as they commonly are, the ratios of the two alloys in grains and nuggets are inconstant. Third, it is commonplace that very minute grains of one alloy, measurable perhaps in microns, may be present in another, and this is one reason why it is almost impossible to obtain pure samples of either alloy for chemical analysis. Fourth, platinum-bearing minerals may also be included; in fact, laurite has been found in one of the alloys of the platinum metals in the Goodnews Bay district. Fifth, chromite is commonly either attached to or intergrown with the platinum alloys, and there are also minute inclusions of base minerals, wherein iron and copper are the principal cations, as exemplified by chalcopyrite. And finally, metallic iron and copper are invariably alloyed with the platinum metals, to form the dross. Bulk samples of the platinum metals recovered from placers therefore necessarily contain variable proportions of the six platinum elements, and chemical analyses, even superior analyses, have a limited value in deriving scientific conclusions regarding the compositions and interrelations of the alloys. Such analyses, however, may lead to important deductions relating to the origin and formation of the placers, and they are, of course, indispensable for commercial valuation of the platinum metals. It is virtually impossible, for the reasons stated, to obtain pure samples of either of the two alloys, and the closest approximations appear to be in their electromagnetic separations. Osmium, iridium, and ruthenium have small magnetic susceptibilities, as is evident from table 3; osmiridium, composed mainly of these three elements, likewise has a low paramagnetism. The separation of a placer sample in an intense magnetic field yields one product that is mainly osmiridum, though minute intergrowths and inclusions of the principal alloy may also be present. Naturally, this method is more practicable if the sample is first sieved, and grains of —200 mesh are selected for the electromagnetic separation. It follows, from the foregoing considerations, that specific mineralogical names of alloys, even of a single purified alloy, are not warranted, as an indefinite number of such terms could be applied. Nevertheless, numerous such designations have been used, according to the ideas of different writers. The better known of these names are shown in table 6, even though they include duplications and improper designations, and many of them do not conform to the definition of a mineral species. The six platinum metals are not specifically tabulated, as they do not occur in nature free of one another. The names platinum and palladium are used, however, as generic terms. It may be added that gold should also be used as a generic term, as pure gold, free of silver and dross, is not present in nature. The names osmiridium and iridosmium have been used by Palache, Berman, and Frondel (1944, p. 112) with meanings the reverse of those given in the preceding table. This has led to confusion, as the reader may be uncertain of the meaning intended by the writer. The products from the Witwatersrand and from Tasmania are alloys that contain more osmium12 ECONOMIC GEOLOGY OF THE PLATINUM METALS Table 6.—Alloys of platinum metals Platinum (generic term): Cuproplatinum, cupric platinum. Ferroplatinum. Ferric platinum with 10-30 percent Fe. Nickel platinum, nickelic platinum. Noril’skite, containing Pt, Pd, Ni, Fe, and Cu. Palladiplatinum, palladic platinum. Pd=Pt, approximately. Platinic iron. Platiniridium, platinic iridium, avaite. Polyxene. Platinum with less than 10 percent Fe, and therefore a synonym of platinum. Rhodic platinum. Stannic platinum, stannoplatinite. Unnamed alloys described by Genkin (1959) and Borovskii, Deev, and Marchukova (1959). A. Contains Pt, Sn, Ir, Pd, and Fo. B. Contains Pt, Pd, Sn, and Ir. C. Contains Pt, Fe, Ir, Ni, Cu, and Ag. Palladium (generic term): Allopalladium, eugenesite. Contains Pd, Pt, Ru, and Cu, and traces of other elements. Platinum amalgam, potarite. PdHg or Pd3Hg2. Unnamed alloy described by Genkin (1959) and Borovskii, Deev, and Marchukova (1959). D. Contains Pd, Pb, and Ag. Osmiridium, (Ir> Os): Auric osmiridium, aurosmirid, aurosmide. Contains up to 19 percent Au. Platinic osmiridium, platinosmiridium. Rhodic osmiridium, rhodosmiridium. Ruthenic osmiridium, ruthenosmiridium. Contains up to 21 percent ruthenium. Iridosmium, iridosmine (Ir< Os): Osmite, synonym of iridosmine. Platinic iridosmium, platiniridosmine. Rhodic iridosmium, rhodiridosmine. Ruthenic iridosmium, rutheniridosmine. Nevyanskite (Ir 50-80 percent): Varieties of nevyanskite, according to tenors of the other platinum metals. Siserskite, sisserskite, sysertskite, (Ir 20-50 percent): Varieties of siserskite, according to tenors of the other platinum metals. Alloys of gold and platinum metals: Platinic gold. Iridic gold. Rhodic gold, rhodite. Contains up to 43 percent rhodium. Palladic gold, porpezite. Contains up to 10 percent palladium. than iridium, and are therefore properly called iridosmine, if use is made of that term. A commercial designation is needed, however, for alloys consisting dominantly of iridium and osmium, regardless of the relative proportions of these two metals. For this purpose, the writer uses the term “osmiridium,” because the amount of iridium is generally greater than that of osmium, but for scientific descriptions, both osmiridium and iridosmine are employed. The terms “osmiridium” and “iridosmine” are not necessarily correlative with “nevyanskite” and “siser- skite,” because the numerical definitions of the two latter terms do not state whether they refer to analyses with dross or to analyses recomputed free of dross. Without this refinement, an alloy called nevyanskite may in fact be siserskite and vice versa. These names ending in “ite” are also objectionable because they suggest the definite compositions of minerals, whereas they are in fact alloys with widely divergent compositions. Osmiridium and iridosmine are preferable terms. CHEMICAL COMPOUNDS OF PLATINUM METALS The platinum metals also occur as chemical compounds, to which specific names have properly been applied. The platinum minerals may also include more or less copper, lead, tin, nickel and cobalt, and it is inferred that these elements substitute as cations for the platinum metals. If iron and chromium are reported, it is generally assumed that they are impurities resulting from an admixture with traces of other minerals, and even nickel and cobalt may sometimes belong in this category. The common base-forming elements are arsenic, antimony, bismuth, sulfur, tellurium, oxygen, and possibly other anions, such as selenium, but tin and lead may also function as anions instead of cations. The absence of a base-forming element indicates an alloy rather than a mineral, but as some elements may be either acid forming or base forming, it is sometimes difficult to decide whether certain combinations of elements represent alloys or minerals. A low percentage of tin or lead, however, suggests that these elements are present as cations. The platinum minerals differ from the platinum alloys in one important respect. The principal platinum alloy, designated generically as platinum, contains generally all six of the platinum metals, though osmium and ruthenium may be present only in small amounts. Osmiridium contains five of the platinum metals, and by careful analysis, palladium may also be identified. The platinum minerals, on the other hand, contain fewer of the platinum metals, and it has not been proven that all of them are ever present. Numerous platinum minerals have been discovered in recent years, notably since 1958. The principal investigators and discoverers, as shown in the accompanying bibliography, were J. E. Hawley, A. D. Genkin, E. F. Stumpfl, N. N. Zhuravlev, O. E. Zvyagintsev, and their several collaborators. Genkin (1959) recognized eight platinum minerals in the ores of the Noril’sk district, northwestern Siberia, which were identified by Borovskii, Deev, and Marchukova. Three of these proved to be platinum, alloyed with iridium, iridium and iron, or palladium, and a fourth was pal-PLATINUM METALS ladium, alloyed mainly with lead. The other four are listed as unnamed minerals. Stumpfl, in 1961, identified nine additional platinum minerals in the ores of the Driekop Mine, Transvaal, Republic of South 13 Africa, of which one was named geversite. The other eight are listed as unnamed minerals. The platinum minerals, as now known, are tabulated in table 7. Table 7.—Platinum minerals, named and unnamed Mineral Composition Reference Named minerals Arsenopalladinite____________ Braggite______________________ Cooperite____________________ Froodite_____________________ Geversite____________________ Hollingsworthite_____________ Ruthenian hollingsworthite Irarsite_____________________ Kotulskite___________________ Laurite______________________ Michenerite__________________ Moncheite____________________ Niggliite____________________ Palladinite (Palladite)_______ Sperrylite___________________ Rhodian sperrylite_________ Stannopalladinite____________ Stannoplatinite______________ Stibiopaliadinite____________ Vysotskite____________________ Zvyagintsevite_______________ (Zvyaginzevite)____________ Pd3As______________________________ (Pt, Pd, Ni)S______________________Bannister (1932a). (Pt, Ni, Pd)S______________________ Cooper (1928). PdBij______________________________ Hawley and Berry (1958). PtSb2______________________________ Stumpfl (1961). (Rh, Pt, Pd) (As, S),______________ Stumpfl and Clark (1965). (Rh, Ru, Pt) (As, S)2______________ Genkin, Zhuravlev, Troneva, and Muraveva (1966). (Ir, Ru, Rh, Pt) (As, S)___________ Do. Pd(Te, Bi)i_2______________________ Genkin, Zhuravlev, and Smirnova (1963). (Ru, Os)S2_________________________ Wohler (1866). (Pd, Pt) (Bi, Te)__________________ Genkin, Zhuravlev, and Smirnova 11963). (Pt, Pd) (Te, Bi)2_________________ Do. Pt (Te, Sn)?_______________________ PdO________________________________ PtAs2______________________________ (Pt, Rh, Ir, Pd) (As, S)2__________ Stumpfl and Clark (1965). (Pd, Pt, Cu)3 Sn2__________________ Pt3Sn2_____________________________ Mikheev, Kalinin, and Sal’dev. Pd3Sb______________________________ Adam (1927). (Pd, Ni)S__________________________ Genkin and Zvyagintsev (1962). (Pd, Pt)3 (Pb, Sn)_________________ Genkin and Korolev (1961); later Genkin, Muraveva, and Troneva (1966). Unnamed minerals Composition Reference Composition Reference PtBi2 (Not michenerite nor Hawley and Berry (1958). moncheite). Pt2Sn3___________________Ramdohr (1960). (Pt, Sn) As2_____________ Genkin (1959), Borovskii, Deev, and Marchukova (1959). (Pt, Os, Ru)As2______________ Do. PdS2_________________________ Do. (Pt, Ir)As2_______________Stumpfl (1961). (Pt, Ir, Os)As4______________ Do. PtSb_________________________ Do. Pt(Sb, Bi)__________________Stumpfl (1961). Pdj(Sb, As)2_______________ G. A. Desborough (written com- mun. 1969). Pd(Sb, Bi)_________________ Stumpfl (1961). (Pd2Cu)Sb______________________ Do. (PdsCuJSb,_____________________ Do. (Pt4Cu4)Sii3___________________ Do. PdBi________________________ Hawley (1962). Pd3 Pb_____________________Cabri and Traill (1966). Pd(Bi, Pb)_____________________ Do. Sperrylite, the most plentiful and widely distributed of the platinum minerals, is a tin-white brittle cubic mineral with a black streak, a hardness of 6-7, and a specific gravity of 10.58. Is is highly resistant to atmospheric weathering. Sperrylite consists mainly of platinum chemically combined with arsenic, but contains also a small percentage of rhodium. Three analyses of sperrylite are known to the writer. These analyses, recomputed free of gangue and other impurities to total 100 percent, are shown in table 8. The sperrylite from the Vermilion mine is very close to the theoretically computed values of platinum metals and arsenic. Two spectrographic analyses of sperrylite (Lewis, 1950) from the Falconbridge mine in the Sudbury Table 8.—Analyses, in percent, of sperrylite [N.D., no data] ABC Mean Theoretical composition Platinum______ 55. 77 56. 89 58. 06 56. 49 56. 58 Rhodium_______ . 76 1. 72 N.D. 1. 24________________ Palladium_____ Tr.______________________________________ Arsenic_______ 43. 47 41. 39 41. 94 42. 27 43. 42 Total___ 100. 00 100. 00 100. 00 100. 00 100. 00 A. Vermilion mine, Sudbury district, Canada, mean of two analyses (Coleman, 1905, p. 100). B. Tweefontein, Potgietersrust district, Republic of South Africa (Wagner, 1929, p. 17). C. Timpton Valley, Amur Province, southeastern Siberia (Quiring, 1962, p. 193). district are given in table 9. The nickel and copper may be contaminants. The principal item of interest14 ECONOMIC GEOLOGY OF THE PLATINUM METALS Table 9.—Spectrographic analyses of sperrylite from Falconbridge mine, Sudbury district, Ontario [The symbols indicate intensity of spectral lines according to the following arbitrary scale: Me, major constituent; Vs, very strong; S, strong; M, moderate; W, weak; Tr, trace. Cited from Lewis, 1950] S-57 S-78 Platinum. . Palladium. Arsenic___ Antimony.. Gold______ Tin_______ Bismuth___ Silver____ Zinc______ Copper____ Nickel____ Iron______ Silicon___ Magnesium Calcium___ Cadmium. _ Me Me Tr W Me .... Me Tr W W M Tr ____ W M S M s Tr Tr. Vs .... S Tr ... w W M M W M M ____ M .... Tr. in these analyses is the essential absence of palladium. This indicates that sperrylite is not a major source of palladium, and therefore that other palladium-bearing minerals are present in the ores of the Sudbury district, Ontario. Another noteworthy feature is the absence of rhodium in Lewis’s two analyses, whereas rhodium appears in two of the analyses in table 8. Sperrylite, in addition to its cited occurrences, has also been reported from the Broken Hill district, New South Wales, Australia; from the Great Eastern mine in Clark County, Nev., from the Rambler and Centennial mines, Albany County, Wyo.; from certain tributaries of the Little Tennessee River, Macon County, N.C., and from other localities. Cooperite, braggite, laurite, potarite, allopalladium, palladinite, stibiopalladinite, and niggliite are little known platinum minerals. Cooperite, braggite, and stibiopalladinite have been described from the Transvaal, Republic of South Africa. Laurite also occurs in the Transvaal and in Siberia but was first discovered in placer sands along the foothills of the Bobaris Mountains in Southeast Borneo. It later was reported from Colombia and Oregon. Potarite was described first from Guyana (formerly British Guiana), and was reported to be a chemical combination of palladium and mercury, but is classified in this report as a palladium amalgam. Allopalladium (eugenesite) is also included as an alloy. A surficial coating on a porpezite from Brazil was called palladinite and was assumed to be PdO, but no analysis is recorded. Niggliite is a rare mineral that was first found near In-sizwa, East Griqualand, Republic of South Africa, about 300 miles south of Johannesburg. The other platinum minerals that are listed have been dis- covered in recent years and have been described in papers cited in the accompanying bibliography. The list of platinum minerals presented above indicates that palladium is more prevalent than platinum in mineral compounds. This is expectable, as palladium is much less resistant to acid and alkali solvents than the other platinum metals. A large part of the palladium recovered at Sudbury and in the Transvaal is believed to occur as discrete minerals associated with the sulfides of the basic and ultrabasic host rocks. Mention should also be made of the fact that some of the platinum metals occur as atomic replacements of elements in the various ore minerals, and even in rock-forming minerals such as peridotite, perknite, gabbro, and their variants. Analyses of pyrrhotite, pentlandite, chalcopyrite, bornite, chromite, columbite, cassiterite, stannite, molybdenite, galena, freibergite sphalerite, sylvanite, hessite, and other minerals show that small amounts of the platinum metals may be present, if the atomic radii of the cations are not too different. The platinum metals may also occur as interstitial solid solutions in various minerals and ores. PLATINUM DEPOSITS DISTRIBUTION The platinum metals have been found as natural alloys in many countries, notably in the Russian Urals, in Colombia, and in Alaska, but few other countries have had significant productions. Platinum lodes are uncommon, yet the bulk of the world’s production is now coming from such deposits. The major sources are in the Union of Soviet Socialist Republics, in the Republic of South Africa, and in Canada; and the ores from these countries are described in considerable detail. The gold-platinum placers of Colombia have not been adequately described, but owing to their historical significance, they are treated as fully as the available data permit. The placers of the Goodnews Bay district, Alaska, are described in more detail than their size and production appear to warrant, for the following reasons. First, they are the only commercial platinum deposits in the United States, and are therefore of national importance; second, more statistical and genetic data on these placers are available than for any similar deposits elsewhere in the world; and third, an earlier report by the writer (1940) is now outdated and requires partial revision. The lithified placers of the Witwatersrand, Republic of South Africa, are given more attention than their production would appear to justify, because they are the world’s principal source of osmiridium. Deposits thatPLATINUM DEPOSITS 15 are small producers of the platinum metals, and others that were formerly productive but are now exhausted, are described in such detail as their scientific interest appears to warrant. Nonproductive deposits in the United States are given more attention than similar deposits in foreign countries. Table 10.—Distribution of platinum metals Albania Algeria Argentina Australia New Guinea (Australian) New South Wales Queensland Tasmania Victoria Brazil, 6 states Burma Canada, 10 provinces Alberta British Columbia Manitoba Newfoundland Northwest Territories Nova Scotia Ontario (principal deposits) Quebec Saskatchewan Yukon Ceylon Chile (Island of Chiloe) China (Mongolia) Colombia, 2 departments Choco Narino Cuba Czechoslovakia Dominican Republic Ecuador Egypt Ethiopia Finland (Lapland) France Germany Ghana Great Britain Cornwall Ireland Scotland Greenland Guatemala Guiana (French) Guyana Honduras Hungary India Assam Indonesia Borneo Java Sumatra Iran Italy Kenya Malagasy Republic (Madagascar) Malawi (formerly Nyasaland) Mexico New Caledonia New Guinea Papua Territory of New Guinea New Zealand Norway Panama Peru Philippine Islands Portugal Puerto Rico Republic of the Congo Katanga Republic of South Africa Cape of Good Hope Province Orange Free State Transvaal Rhodesia Romania Sierra Leone Somali Republic Spain Surinam Sweden Union of Soviet Socialist Republics Noril’sk district Petsamo district Ural Mountains Other districts United States (12 States) Alaska Goodnews Bay district Twenty-one other localities Arizona, 3 counties Arkansas California, 34 counties Colorado, 5 counties Delaware Georgia Idaho, 8 counties Maryland (Baltimore County) Missouri Montana, 5 counties Nevada, 3 counties New Mexico New York North Carolina, 3 counties Oregon, 13 counties Pennsylvania South Dakota Texas Utah, 2 counties Washington, 6 counties Wyoming, 3 counties Venezuela16 ECONOMIC GEOLOGY OF THE PLATINUM METALS Platinum metals have been found in 22 States of the United States, but only Alaska has become a major producer. In California and Oregon, platinum has been recovered in relatively small amounts as a byproduct of gold placer mining, and in several of the Rocky Mountain States, small gold-platinum or copper-platinum lodes have been mined, generally without a profit. Few of the occurrences of platinum metals in the United States merit description, but because such deposits exist in this country, all the principal ones are more fully described than similar deposits would be in foreign countries. The principal countiies in which platinum metals have been found are listed alphabetically in table 10, but most of these occurrences are so rare or freakish that they require no description in this report. Spectrographic research has greatly multiplied the known habitats of the platinum metals. In fact, traces of these elements in rocks and minerals are becoming so commonplace that it is difficult to learn and tabulate all the new occurrences. Minerals and rocks that contain traces of the platinum metals have been tabulated by Wright and Fleischer (1965, p. A9 and A1B). The platinum metals also occur in some meteorites and in the gases surrounding the sun, and they have been identified both in marine organisms and in sea water. CLASSIFICATION The platinum metals occur in workable deposits mainly as platinum minerals in nickel-copper and copper lodes and as platinum alloys in placers, but they occur also in other environments that are of more scientific than economic interest. The principal workable lodes are in Ontario and Manitoba, Canada, in the central Transvaal, Republic of South Africa, and in several areas of northwestern Siberia, U.S.S.R. To these should be added the lithified placers of the Witwatersrand, Republic of South Africa. Most of the workable lodes are characterized by platinum and palladium minerals, but some of them, notably in the Transvaal, also yield small amounts of the native metals or alloys. LODES The platinum metals occur as lodes in several different environments. The more significant deposits are related to the basic or ultrabasic rocks, but these metals are also found in ores that are related to granitic rocks, as shown in the following classification: CLASSIFICATION OF PLATINUM LODES A.—Platinum-bearing nickel-copper, copper, or copper-cobalt sulfides that are related genetically to basic or ultrabasic rocks, commonly the former, but are not magmatically segregated ores. The workable lodes occur principally as secondary concentrations of ore minerals rather than as magmatic minerals in situ, though the secondary ores appear to grade into disseminated ore minerals in the associated igneous rocks. The ore bodies occur either along the contact of the basic intrusives with country rock, or at variable distances up to 5 miles from the basic intrusives. These ores may or may not be associated with igneous rocks, of which some are considered to be related genetically to the parent basic rocks. By some geologists, the sulfides of these secondary deposits are thought to have originated as immiscible fluids of magmatic character; by others, these sulfides are considered to be epigenetic hydrothermal deposits. The ores of the Sudbury district, Ontario, exemplify such deposits. Native platinum metals or their alloys are commonly absent from deposits of this type. B. —Platinum-bearing nickel-copper ores that are magmatically disseminated or concentrated in gabbroic and ultrabasic rocks. Pyroxenite and anorthosite the principal source rocks are commonly associated with norite and all of these may have the outlines of dikes, sills, pipes, lenses, or schlieren. These rocks are petro-graphically homogeneous along their major structures for long distances but they vary locally and produce layers and lenses of peridotite and chromite. The platinum metals occur mainly in sperrylite, cooperite, and other platinum and palladium minerals, but smaller amounts of the native platinum metals or alloys are commonly present. The platinum minerals occur in the sulfides and in lesser amounts in the silicates and may be sufficiently plentiful to constitute the principal value of the ores, with byproducts of nickel copper, and other metals. The Merensky zone, in the Bushveld igneous complex of the Transvaal, illustrates this type of deposit. The ratios of platinum to palladium are significantly greater in the ores of class B than in those of class A. C. —Native alloys of the platinum metals that are magmatically disseminated in peridotites, less commonly in perknites, and rarely in gabbros. If concentrated, they are commonly intergrown with chromite. Most of these deposits are in dunites, which range in composition from hortonolite dunite to olivine dunite. The dunites at some localities may be partly or wholly altered to serpentinite. The platiniferous hortonolite or iron-rich dunites are exemplified by the Onverwacht and Mooiheep properties in the Bushveld igneous complex of the Transvaal. Platiniferous dunites, perknites, and their alteration products are the sources of the Uralian placers; dunite and serpentinite are the sole sources of the placers of the Goodnews Bay dis-PLATINUM DEPOSITS 17 trict, Alaska; and so far as known, similar peridotites and perknites are the sources of most placers that are known in the world. Platinum and osmiridium lodes have been discovered in dunite or serpentinite, principally in the Urals and in South Africa, but generally they have proven to be either too small or too low grade for profitable mining. Some masses of chromite, however, have been found in dunite that had high tenors in the platinum metals. D. —Platinum minerals or native platinum alloys in copper and related ores indigenous to contact meta-morphic and other types of ore bodies, including vein systems. E. —Native platinum metals in the gold ores of quartz veins and in other ores of free gold. Twenty-three examples of such deposits are listed on page 98. F. —Platinum-bearing meteorites. G. —Secondary platinum metals: 1. Recovered in purification of blister copper and copper mattes that produced on a large scale. 2. Recovered at the U.S. Mint and other mints, in the refining of metallic gold. The U.S. Mints make no payment to the producers of gold bullion for such platinum metals, claiming them as seignorage. 3. Recovered from industrial wastes and from jewelry. PLACERS Platinum placers consist of alluvial deposits that contain in workable amounts the alloys of the six platinum metals, and it is worthy of note that no analagous deposits of platinum minerals have ever been found. The platinum metals occur commonly in two alloys of variable composition, of which one consists dominantly of platinum with varying amounts of the other five elements, whereas the other consists dominantly of iridium and osmium, less ruthenium, still smaller amounts of platinum and rhodium, and with little or no palladium. Much of the placer platinum consists of two intergrown or intermixed alloys, each of variable composition, as exemplified by the product recovered in the Goodnews Bay district and described on pages 84-87. Some of the alluvial platinum comes from placers that yield both gold and platinum. The stream placers of Colombia and of California, later to be described, are excellent examples. Commonly the gold and platinum are separate alloys, one of gold and silver and the other of five or six platinum metals. This fact is not generally clarified by analyses of placer platinum, as small amounts of gold are reported merely as a part of the contained precious metals. Hence such analyses, in order to be comparable with others which show no gold, have to be recomputed free of gold as well as free of “impurities.” Examples will later be given, however, of placer gold with which small amounts of the platinum metals are alloyed. The densities of the platinum alloys found in placers and the sizes of their grains are generally similar to those of alluvial gold; hence, the geologic classification of platinum placers is exactly like that of the gold placers, as heretofore used by the writer: A. Residual and eluvial placers. B. Stream placers. 1. Present stream valleys. 2. Older stream valleys. a. Terrace deposits. b. Buried deposits. C. Beach placers. 1. Present beaches. 2. Ancient beaches. a. Elevated beach deposits. b. Buried beach deposits. D. Deltaic and outwash deposits. E. Glaciofluvial (glaciofluviatile) deposits. F. Aeolian deposits. G. Lithified placers. Placers of the platinum metals are commonly derived from dunite or serpentinite, less commonly perk-nite, in which these metals are sparsely and irregularly distributed. In nonglaciated regions, it may be inferred that the original lodes could be discovered by tracing the alluvial deposits upstream. Commonly the general country rock may thus be recognized, but workable lodes can rarely be located. This may result from one or more of the three following causes: 1. The original rocks from which the placers were derived may have been completely eroded, so that no platiniferous source rocks remain in the area. 2. The present country rock may be platiniferous, but may represent the uneroded low-grade roots of lodes that were much richer in their apical horizons. 3. All the original source rocks may have been of extremely low grade, and the placers may have been concentrated from such sources over a very long period of time. Under such circumstances, representative source rocks, even if preserved, would not constitute workable lodes and are not likely to be discovered. The formation of placers is possible under any of these conditions. But workable lodes can rarely be located in placer fields, and it is therefore concluded that the platinum metals in placers have been concen-18 ECONOMIC GEOLOGY OF THE PLATINUM METALS trated generally from source rocks wherein these metals were sparsely and widely disseminated. Heavy metals, such as platinum or gold, rarely migrate far downstream from their bedrock sources, unless they are so fine grained as to be moved by swift water or floated by surface tension. Flour gold, for example, may move downstream for many miles, in fact to the ocean. Generally, however, ordinary detri-tal grains of platinum or gold work rapidly downward through alluvial deposits, and come to rest either near, on, or within bedrock. If the bedrock has a well-developed cleavage or fracture, the precious metals may penetrate 10 feet or more. Only very high water that cuts to bedrock, or rejuvenation of a stream, will again move these metals, and even under these conditions, their downstream migration is not great. Hence, excepting some special environment, such as glaciation, placers of the precious metals may be assumed to lie within a few miles of their bedrock sources. If placer paystreaks are very long, it may be suspected either that several bedrock or proximate sources are present in a valley, or that the metals have been distributed downstream by repeated lowering of the base level of erosion or as result of glaciation. CANADA SOURCES AND PRODUCTION Native platinum and osmiridum appear to have been discovered in Canada by T. Sterry Hunt (1852, p. 120) in concentrates recovered from the placers on Riviere du Loup and Riviere des Plants, tributaries of Chavdiere River, in southern Quebec. Platinum metals were subsequently found in 10 of the 13 provinces of Canada, though only a few of these deposits are or have been significant producers. No workable lodes of native platinum metals are known to exist, but numerous platinum- and palladium-bearing base-metal lodes and platinum-bearing gold placers have been discovered. Platinum-bearing and palladiumbearing sulfides, mainly in nickel-copper lodes, have been located in Alberta, British Columbia, Manitoba, Newfoundland, Northwest Territories, Nova Scotia, Ontario, Quebec, Saskatchewan, and Yukon. The most important of these are the nickel-copper deposits of the Sudbury district, in south-central Ontario, and those of north-central Manitoba, though similar lodes in the other provinces may in the future yield considerable amounts of the platinum metals. Alluvial deposits containing the platinum metals are known in the provinces of Alberta, British Columbia, Quebec, and Yukon. In earlier years, the Tulameen district of British Columbia was an impor- tant producer of alluvial platinum, but these placers are now considered to be worked out, though certain fluvial deposits of greater thickness may sometime be mined. Small amounts of the platinum metals have also been recovered in other Canadian provinces, mainly as a byproduct of the mining of gold lodes and placers. The total production of platinum metals from Canada for 1965 and 1966 came mainly from the Sudbury district, Ontario, but since 1962 has included also an output from the nickel-copper mine at Thompson, Manitoba, and lately a small output from a similar ore body near Lynn Lake, Manitoba, together with a minor byproduct from gold placers. The total production of platinum metals from all Canadian sources, up to and including 1966, has been about 11,440,000 troy ounces, with a maximum annual output in 1960 of 483,604 ounces. ONTARIO SUDBURY DISTRICT DISCOVERY AND PRESENT MINING The basic rocks of the Sudbury area were first observed by A. P. Salter, a Canadian Government surveyor, in 1857; and Alexander Murray, of the Canadian Geological Survey, verified the presence of these rocks in the same year. Copper sulfides were discovered by Thomas Flanagan in a gossan outcrop west of Sudbury in 1883, along the right-of-way then being opened for the Canadian Pacific Railroad; and in the next few years, most of the larger ore deposits of the district were found. The production of nickel and copper began in 1887. The platinum metals are a byproduct of the production of nickel and copper in the Sudbury district. Other byproducts that are now recovered include selenium, tellurium, gold, silver, cobalt, and iron. Platinum, in the form of platinum diarsenide (sperrylite) was discovered at the Vermilion mine, in the Sudbury district, in 1885 by F. L. Sperry, a chemist of the Canada Copper Co., and this mineral was described and named by H. L. Wells (1889). As early as 1900, platinum was isolated in the ores of the Mond Nickel Co., and some platinum metals were extracted in subsequent years by Johnson, Matthey and Co., Ltd., in London. According to the Imperial Institute (1936, p. 62), the first recognized output from Canadian lodes was in 1919, when 25 ounces of platinum and 62 ounces of palladium were recovered. The nickel-copper lodes of the Sudbury district are the principal sources of the platinum metals in Canada. These ores lie along or close to the margin of a synclinal basin of the basic igneous and overlyingCANADA 19 sedimentary rocks, situated in south-central Ontario about 50 miles north of Georgian Bay, an arm of Lake Huron. Sudbury, which lies along the southeastern side of this basin, is a city of 35,000 people, which is reached by the Canadian Pacific and Canadian National Railroads as well as by first-class highways. An airport is located at the east side of the basin. The important operating mines lie along or a short distance outside the margins of this synclinal basin. Most of these are now owned and operated by two companies, the International Nickel Co. of Canada, Ltd., and the Falconbridge Nickel Mines, Ltd. The International Nickel Co. of Canada, Ltd. owns the Creighton, Frood-Stobie, Crean Hill, Garson, Levack, Murray, Clarabelle (opencut), MacLennan, Totten, Copper Cliff, Copper Cliff North, Coleman, Kirkwood, Little Stobie, Blezard, Evans, Vermilion, Worthington, Victoria, Whistle, Shepard, and other mines, of which the first nine were producers in 1965. This company has concentrators at Copper Cliff and Creighton; smelters at Copper Cliff and Port Col-borne, Ontario, and at Clydock, Wales; and precious metal refineries at Copper Cliff and at Acton, England (Mond Nickel Co.). The International Nickel Co. of Canada, Ltd. produces about 90 percent of the platinum metals recovered annually in the Sudbury district. The Falconbridge Nickel Mines, Ltd. owns the Falconbridge, Falconbridge East, Hardy, Onaping, Fec-unis Lake, Mount Nickel, McKim, Longvac, Longvac South, Strathcona, Lockberry, and other mines, of which the first five were productive in 1965. This company owns a smelter at Falconbridge, and the nickel-copper mattes are sent to their refinery at Kristiansand, Norway, for separation of the metals. The slimes from this process are refined, and the platinum metals recovered by the Englehard Industries, Inc., of Newark, N.J. GENERAL GEOLOGY The general geology of the synclinal basin, along whose margins lie the platinum-bearing nickel-copper ores, is difficult to interpret, as is indicated by the large volume of conflicting geological reports listed in the bibliography (p. 102-112). The synclinal basin is subelliptical in two-dimensional outline, with a spoonshaped three-dimensional form, a length of about 37 miles, and a maximum width of about 17 miles. The direction of the major axis is about N. 65° E. The rocks dip generally toward the center of the basin, but the basin is asymmetrical in that the dips are commonly steeper along its southeast than along its northwest side. Locally, however, the steeper north- westerly dips along the southeast flank are reversed to the southeast. In detail, the structure is by no means simple, as the syncline, particularly along its southeast flank, is modified by minor folds and faulting. Sur-ficially the central part of the basin shows low relief, but the igneous rocks that bound it cropout as low hills, which are designated locally as the north, east, south, and west ranges. The igneous part of the basin consists of two peripheral sill-shaped masses of intrusive rocks, separated by a narrow transitional zone, with a total thickness estimated by Knight (1923) along the east range of about 8,300 feet. The lower mass of “norite” has a thickness of about 1,800 feet; the upper mass consists of micropegmatite or granophyre with a thickness of about 6,000 feet; and the transitional zone has a thickness of about 500 feet. Associated with the norite along its basal margin are quartz diorite and other intrusive rocks which are considered by Hawley (1962, p. 10) to be phases of the norite, though this interpretation is not universally accepted. The total relative thickness of the norite and the granophyre vary on the different ranges, as shown by the dips of the rocks and widths of the outcrops. Thus on the south range (southeast flank of the basin), the thickness of the two principal units appears to be less different than on the north range. The width of the total outcrop of the igneous rocks ranges from a minimum of 1^4 miles on the north range to a maximum of H/2 miles on the south range. The average total width on the north range is 1.9 miles and on the south range is 3.1 miles. These igneous rocks that delimit the Sudbury basin are said by Canadian geologists to be of late Huronian (Animi-kie) age. The younger rocks inside the four ranges forming the central part of the basin, comprise a group of tuff-aceous and sedimentary rocks called the Whitewater series, which, according to Cooke (1948), Yates (1948), Thomson (1957a) and other Canadian geologists, consists of the Onaping tuff, the overlying Onwatin slate, and the superjacent Chelmsford sandstone. A basal member of the Onaping tuff is the Trout Creek conglomerate or agglomerate. The thickness of the White-water series, owing to lack of outcrops, is known only approximately, but the Onaping tuff has been estimated to have a thickness of 5,000 feet, and the two over-lying formations are believed to have a combined thickness of 3,700 feet. The Whitewater series is considered to be of late Huronian (Keweenawan) age. Older sedimentary and igneous rocks underlie the noritic and associated intrusives. The stratigraphic succession of these rocks has been given by Knight20 ECONOMIC GEOLOGY OF THE PLATINUM METALS (1943), Cooke (1946), Yates (1948), and other Canadian geologists. According to these geologists, a group of sedimentary and igneous rocks, called the Sudbury or Timiskaming series, and believed to be of early Hur-onian age underlies the noritic irruptive. The formations of the Timiskaming series, named from top to bottom, are the Mississagi quartzite, the McKim gray-wacke and the Copper Cliff arkose, underlain by the Frood series. An ancient greenstone, originally of intrusive origin, overlies in places the Mississagi quartzite. These two formations, subjacent to the norite, are of importance in relation to the genesis of the nickel-copper lodes. The oldest rocks of this district, underlying the Frood series, compose the Stobie group, which consists of metamorphosed andesitic and basaltic lavas and quartzites. The sequence above outlined is amplified by numerous intrusive rocks, notably by at least six types of granitic rocks. Two of these are granites, or granitic gneisses, that occur throughout the Sudbury series, and certain younger granitic rocks that intrude both the norite and the micropegmatite. Of special genetic interest is the quartz diorite that occurs at places along and near the contact between the norite and the underlying quartzite and greenstone. INTRUSIVE ROCKS The noritic rocks and associated intrusives, the over-lying transition zone, and the micropegmatite at the top of this igneous sequence constitute what is known collectively as the “nickel irruptive” because they have been interpreted as related genetically to the nickel-copper ores. The distribution of the “nickel irruptive” is shown in figure 1. No general agreement exists, however, as to the mode of formation of the “nickel irruptive” nor as to its influence in the formation of the ore bodies. Bell (1891) was the first to recognize a closure of the igneous ring and the existence of the Sudbury basin. Walker (1897, 1935) conceived the idea that the “nickel irruptive” was a homogeneous intrusive which after its original placement was differentiated gravitatively into three units; Barlow (1904, 1906) corroborated this interpretation; and Coleman, in several reports (1905, 1907, 1913, 1916, 1923), carried this hypothesis to its ultimate development. The hypothesis was also adopted by Adams, Kemp, Roberts, Longyear, and others. Along with the idea of differentiation by magmatic settling came the idea of enrichment of the nickel ores by gravitative action. This mode of ore genesis has now been abandoned, and along with this has come the interpretation that the norite and the micropegmatite were separate and distinct intrusives. The basin was interpreted first as a subsiding lopo-lith and later as a synclinally folded lopolith. But it has also been maintained that a basin of subsidence existed before the intrusion, and similarly that synclinal folding occurred before the intrusion. No agreement exists in regard to these hypotheses of placement. A recent highly speculative hypothesis by Wilson (1956) envisages the irruptive as the part of a funnel-shaped intrusive of which the bottom (concealed) consists of utrabasic rocks that underlie the norite. This seems to revert to the interpretation of magmatic differentiation by gravitative settling. The micropegmatite consists generally of intergrowths of potash feldspar and quartz, arranged radially around plagioclase, commonly oligoclase. The mafic minerals are hornblende with less biotite, both much altered to epidote. The most siliceous part of the micropegmatite is not at its inner boundary on the east range, as earlier reported, but according to Knight (1923) near its basal part. The norite has been studied petrographically by Phemister (1926), who concludes that this designation is a misnomer, because most of this intrusive contains little or no orthorhombic pyroxene. The common mafic mineral is hornblende, and though some of this is secondary, there is no evidence that it was derived from hypersthene. The plagioclase is a zoned labradorite, and some of the rock contains quartz. The so-called norite appears to lie petrographically between a mon-zotonalite and a granogabbro, and might be called a hornblende quartz gabbro. A more specialized designation would be bojite. The norite is most basic not at its base, but somewhere above its medial zone, close to the overlying transition zone. The quartz diorite, to which reference has been made, occurs sporadically at or near the base of the norite, without clean-cut contacts between those two rocks, but with well-defined contacts with the members of the Mississagi quartzite and associated greenstone. It appears from subsurface exploration to disappear downward in the adjacent country rocks, and this is used by Hawley (1962, p. 26) as one line of evidence that the quartz diorite is merely a phase of the norite. The quartz diorite is composed of plagioclase (ande-sine to labradorite), quartz, pyroxene, amphibole, biotite, and accessory minerals, mainly apatite. The mafic minerals are in various stages of alteration—the pyroxene to hornblende and the amphibole to shreds of trem-olite and actinolite. The biotite is bleached. As a whole, however, this rock is less altered than the norite near its basal contact.CANADA 21 81-30' 81”00’ Figure 1.—Geologic map of “nickel irruptive,” Sudbury district, Ontario. (Generalized from Geol. Soc. America, Toronto Field Trips Comm., 1953.) ORE DEPOSITS The nickel-copper ores occur along the north, south, and east ranges of the irruptive, but mainly along the south-southeast side. Most of the ore bodies are localized at two sites, one at or close to the basal contact of the norite with the underlying rocks and a second at distances up to 5 miles from the norite. These bodies are designated respectively as marginal and offset deposits. Some of the marginal deposits extend upward or laterally into the bounding norite, but very few lie entirely within the norite. The Falconbridge, Gar-son, Creighton, and Murray mines may be cited as examples of marginal deposits adjacent to norite, and the Levack mine as a marginal deposit that lies within but close to the base of the norite. The Copper Cliff, Worthington, and Frood-Stobie properties illustrate the offset lodes. A third type of deposit is represented by the Errington and Vermilion mines, where according to Thomson and others (1957, p. 85-86), the ore bodies are replacements of a chert-carbonate horizon that lies at the contact of the Onaping tuff and the overlying Onwatin slate. A description of all the cited ore deposits and mines of the Sudbury district is obviously beyond the scope of this report; and only general relationships are warranted and offered. The ore bodies are generally irregular in outline, but where unfaulted are commonly lenticular with an orientation parallel to that of the norite, plunging therefore toward the center of the synclinal basin. Where faulting and minor folding occur, this general orientation may be reversed. The ores, according to Thomson and others (19571. lie22 ECONOMIC GEOLOGY OF THE PLATINUM METALS within a variety of host-rocks, which include quartzite, greenstone, quartz diorite, gabbro, norite, granite, andesite, and breccias of these rocks. The principal structures which have been provided channelways for the ore solutions are faults, breccia zones, and less definite loci of shattering and brecciation. Regardless of the nature of the deposits and of the solutions that produced them, it is clear that the sulfide ores are secondary with regard to their present host rocks. These deposits have been classified by Hawley (1962, p. 32-38) into five types, designated as disseminated, massive, immiscible-silicate-sulfide, breccia, and vein stringer ores, of which the breccia ores are the most important. The primary minerals of both marginal and offset deposits, according to Hawley (1962, p. 41-128), are pyrrhotite, pentlandite, chalcopyrite, and cubanite, and the minor ore minerals are magnetite, ilmenite and pyrite. The rarer ore minerals comprise gersdorffite, niccolite, maucherite, heazlewoodite, bornite, valleriite, sphalerite, stannite, violarite, marcasite, native gold, silver, bismuth, and copper, tetradymite, hessite, chal-cocite, bismuthinite, nickelferous pyrite, parkerite, schapbachite, galena, molybdenite, tetrahedrite, small-tite, danaite, and hematite. The secondary supergene ore minerals include millerite, marcasite, limonite, chal-canthite, melanterite, morenosite, annabergite, and ery-thrite. The principal carriers of the platinum metals are pyrrhotite, pentlandite, and chalcopyrite, though these metals are known in smaller amounts in cubanite and pyrite and may also be present in some of the rarer ore minerals. The platinum-bearing minerals, inter-grown with or included in the ore carriers, include sperrylite, michenerite, froodite, and an unnamed palladium bismuthide, but work is in progress that undoubtedly will result in the discovery of other platinum and palladium minerals. The platinum metals also exist as molecular replacements within the cited carrier minerals. No native platinum metals or alloys exist in these ores. The ores at the Errington and Vermilion mines are quite different from those of the marginal and offset deposits. The ore minerals at the Errington mine, according to Thomson and others (1957, p. 85), consist of fine-grained pyrite, sphalerite, chalcopyrite, pyrrhotite, and galena in a carbonate matrix; and the metallic products are zinc, lead, and copper, with small amounts of gold and silver and mere traces of nickel. The ore deposit and minerals of the Vermilion mine are generally similar, though the geologic environment is much more complex; but this deposit, where sperrylite was first discovered, had a high tenor in gold and platinum. The geifeis of the Sudbury deposits has not been settled, but three principal hypotheses have been formulated. 1. The ores are magmatic sulfides that originated in the norite and were segregated petrographically or gravitatively at the base of the irruptive, whence they were distributed along the contact and in zones of fracturing. 2. The ores resulted from the injection of a magmatic sulfide melt along channelways in the norite and adjacent country rock, after the solidification or partial solidification of the norite. The ore deposits resulting from these magmatic injections are designated by Hawley (1962, p. 148-150) as primary ores, because they are considered to be of magmatic origin, but in relation to their host rocks, such deposits are secondary and nonsyngenetic. 3. The ores are epigenetic and probably hydrothermal, resulting from the introduction of sulfides into the norite and adjacent country rock. The ore-bearing solutions may have come from norite, quartz diorite, or from deep-seated sources of unknown origin. Knight (1923) has studied the norite throughout its thickness of 8,300 feet on the eastern nickel range and has found that the most basic part of the norite is not along its eastern edge but from 1,500 to 2,000 feet higher in the sequence. Also the most silicic part of the micropegmatite is not along its western edge but from 3,400 to 4,300 feet lower in the sequence. And finally, the country rock adjacent to the ore deposits may contain as much or more sulfides than the bounding norite. Hence, the first hypothesis no longer appears to be acceptable. The second hypothesis has been favored by many of the earlier writers and by Hawley in 1962. But the secondary nature of the sulfide ores and other lines of collateral evidence have led Dickson (1905), Knight (1917, 1920, 1923), Wandke and Hoffman (1924), Phemister (1926, 1937, 1956), Lockhead (1955), and other geologists to believe that the marginal and offset ore deposits are of epigenetic and hydrothermal origin. Thompson (1960) stated his belief that not only all the massive sulfides of the Sudbury district, but also the disseminated ores associated with them are of hydrothermal origin. The opinion is based upon the following criteria: 1. Spatial relationship of sulfide bodies to secondary structures, such as faults, folds, and fractures. 2. Wallrock alteration. 3. Well-defined paragenetic sequences of mineralization. 4. Different generations of sulfides.CANADA 23 5. Considerable variations in sulfide and metal content throughout the mineralized zones. 6. Irregular shape of mineralized bodies. PLATINUM METALS The tenors of all metals in the Sudbury ores are known to be variable, and maximum and minimum values for different mines are not commonly published. According to several authorities quoted by Hawley (1962, p. 116), the Ni:Cu ratio ranges from 1:0.5 to 1:3, but for the total production of the period 1947-57, this ratio was 1:0.8. The ratios pyrrhotite :clialcopyrite: pentlandite are estimated to be approximately 70:15:15. The tenors of the platinum metals, which depend upon the absolute and relative amounts of the sulfides, are correspondingly indefinite. In ores that contained 5 percent nickel and copper, O’Neill and Gunning (1934, p. 66), have shown a mean tenor for the period 1912-15 of 0.014 ounce platinum metals per ton. Allen (1961, p. 138) states that the average value is 0.02 ounce per ton. Hawley (1962, p. 122) presents a mean tenor of 0.019 to 0.026 ounce per ton—a value taken from a statement by the Ontario Department of Mines, based upon the recovery of platinum metals from the Sudbury ores for the period 1947-57. The nickel-copper ores at the different mines in the Sudbury district have different tenors in the platinum metals, so that the output of the platinum metals is not necessarily related to the output of the base metals. Thus by mining ores of higher or lower content of platinum, the output of the platinum metals may be increased or decreased without altering materially the production of nickel and copper. It is generally known that the tenor of platinum metals is higher in the offset deposits than in the marginal deposits. The relative amounts of the different platinum metals in the Sudbury ores is also indefinite, but the production of these metals over a long period of years gives an average ratio for platinum and palladium and some data on iridium, ruthenium, and rhodium. Among the available estimates are those by Rogers and Young (1929) for the period 1923-27, O’Neill and Gunning (1934) for the period 1923-32, corrected to apply only to the Sudbury ores, Tremblay (1946) for the period 1937-41, and Hawley (1962) for the period 1947-57. These are presented in table 11. The indefinite character of these percentages is emphasized by another set of figures, quoted by Hawley (1962, p. 122) that apply to the mines of the Falcon-bridge Nickel Mines, Ltd. These, in percentages, are platinum 36.6, iridium 4.7, ruthenium 9.9, rhodium 8.8, and palladium 40.0. Here the ratio of platinum to pal- Table 11.—Platinum metals in percent, in platinum minerals, Sudbury district Platinum Palladium Others Rogers and Young (1929). O’Neill and Gunning (1934) 49. 02 48. 97 2. 01 47. 99 45. 42 6. 59 Tremblay (1946)__ . ... 54. 26 41. 65 4. 09 Hawley (1962) 46. 00 41. 00 13. 00 ladium is approximately 1:1.1, which is the reverse of the four tenors shown above. For recent years, much confidence should be placed on Hawley’s estimate, which is based on productive data over a period of 10 years. Independent figures obtained by the writer from the U.S. Munitions Board and the War Production Board during World War II indicate that in general the amount of platinum exceeds that of palladium by 3 to 5 percent and that rhodium had the highest tenor of the minor elements, ranging from 8 to 12 percent. The tenor of ruthenium ranged from 2 to 3 percent and that of iridium from 1 to 2 percent. Osmium is rarely mentioned as one of the recovered elements, because it probably is lost by sublimation during smelting. The amounts of the precious metals in the ores of the Falconbridge mine are well shown in a paper by Lewis (1957), wherein are given the results of numerous chemical analyses of crude ores, pyrrhotite concentrates, and flotation concentrates. Neglecting the gold and silver in these determinations and recomputing to 100 percent, the mean tenors of the platinum metals are shown in table 12. Table 12.—Platinum metals, in percent, in ores from Falconbridge mine, Sudbury district Platinum Rhodium Palladium Crude ores _ 54. 1 14. 2 31. 7 Pyrrhotite concentrates 38. 5 29. 5 32. 0 Flotation concentrates. 54. 5 8. 3 37. 2 The percentages of platinum and palladium in the flotation concentrates agree fairly well with those heretofore presented and confirm the prevalence of platinum over palladium. The percentage of rhodium in the flotation concentrates agrees with the independent figures cited on page 24. The high percentage of rhodium in the pyrrhotite concentrates suggests a possible concentration of this metal in pyrrhotite; in any event it emphasizes the differences of tenors in different host minerals. Spectrographic data have been presented by Hawley, Lewis, and Wark (1951, p. 158) on the tenors of the platinum metals in the ore minerals pyrrhotite, chal-24 ECONOMIC GEOLOGY OF THE PLATINUM METALS copyrite, pentlandite, and pyrite, together with tenors from the mixed arsenides maucherite, niccolite, and gersdorffite. These are shown in table 13. Table 13.-—Spectrographic data, in ounces per ton, on platinum and palladium in ore minerals, Sudbury district Platinum Palladium Both Pyrrhotite_______________________ 0. 148 0. 472 0. 620 Chalcopyrite______________________ . 078 . 735 . 813 Pentlandite_______________________ . 935 . 440 1. 375 Pyrite________________________ .011 .009 . 020 Maucherite____________________ Tr. 7.223 7.223 More complete spectrographic data, however, have recently been published by Hawley (1962, p. 124-125). These are of particular interest in that they differentiate between the average run of ores and the ores from an offset deposit. Noteworthy are the higher tenors in platinum metals from an offset deposits. Changed slightly, so that platinum, rhodium, and palladium sum to 100 percent, these data are presented in tables 14 and 15. Table 14.—Mean tenors of platinum metals, in percent, in common ore minerals, Sudbury district Pt Rh Pd Total metals (ounces per ton) Pyrrhotite (mean of 37 samples). 57. 2 ii. i 31. 7 0. 035 Chalcopyrite (mean of 7 samples) .... 17. 7 . 9 81. 4 . 224 Pentlandite (mean of 3 samples). 33. 0 7. 5 59. 5 . 158 Pyrite (mean of 3 samples) 56. 2 2. 5 41. 3 . 055 Table 15.—Mean tenors of platinum metals, in percent, in minerals of an offset deposit, Sudbury district Pt Rh Pd Total metals (ounces per ton) Pyrrhotite .. ... 44.3 7. 0 48. 7 0. 055 Chalocopyrite . 28.3 . 2 71. 5 . 235 Pentlandite. ... 25. 1 10. 3 64. 6 . 307 Pyrite .. . ... 50.3 7. 5 42. 2 . 137 Mill average, 6 months . 31.7 4. 8 63. 5 . 155 Tables 13-15 do not entirely agree with one another, but table 15, because the data are more complete, affords a means of evaluating the relative amounts of platinum, rhodium, and palladium in pyrrhotite, chalcopyrite, and pentlandite. To accomplish this, the amounts of the three platinum metals are recomputed to ounces, neglecting the small amounts present in pyrite. But according to Hawley (1962), the mean ratios of pyrrhotite, chalcopyrite and pentlandite in the ores are respectively 70:15:15. Therefore, weighting the ounces of platinum metals respectively in pyrrhotite, chalcopyrite, and pentlandite are shown in table 16. Table 16.—Contents, in percent, of platinum, rhodium, and palladium in the principal ore minerals of marginal deposits, Sudbury district Platinum Rhodium Palladium Pyrrhotite______________________ 50. 44 56. 67 65. 20 Chalcopyrite____________________ 21. 41 6. 30 22. 96 Pentlandite_____________________ 28. 15 37. 03 11. 84 Pyrrhotite is clearly the principal carrier of the platinum metals, and chalcopyrite is the smallest, carrying little rhodium and less palladium. Pentlandite, according to these figures, contains comparable amounts of platinum and rhodium but less palladium. Analyzing similarly the figures of table 15, and neglecting as before the content of platinum metals in pyrite, the data shown in table 17 are derived. Table 17.—Contents, in percent, of platinum, rhodium, and palladium in the principal minerals of an offset deposit, Sudbury district Platinum Rhodium Palladium Pyrrhotite. . Chalcopyrite . . Pentlandite . 44. 20 25. 84 19. 96 35. 89 . 94 63. 17 25. 49 34. 19 40. 35 These two sets of data indicate that the pyrrhotite of the offset deposit contains less platinum, less rhodium, and much less palladium than the pyrrhotite of the marginal deposits. The chalcopyrite of the offset deposit contains a little more platinum, very much less rhodium, and more palladium than the chalcopyrite of the marginal deposits. And the pentlandite of the offset deposit contains less platinum, much more rhodium, and much more palladium than the pentlandite of the marginal deposit. This analysis, however, refers to relative proportions of the platinum metals in the three ore-bearing minerals, and does not at all vitiate the conclusion that the total amount of the platinum metals in the offset deposits exceeds that of the marginal deposits. Sperrylite, the diarsenide of platinum, is known to be present in most, if not all, of the nickel-copper ores, and it has been assumed to be the main source of platinum in the Sudbury district. But no quantitative data in favor of this interpretation have been presented, and in recent years this hypothesis has been questioned, notably by Lewis (1957, p. 1-5). In a letter (Oct. 18, 1960) to the writer, Mr. Lewis states: “In the examination of some hundreds of polishedCANADA 25 sections of Sudbury ore minerals, I have rarely seen sperrylite. On the other hand, almost any sample of pyrrhotite, pentlandite, or chalcopyrite, when treated by fire assay, with a spectrographic analysis of the resulting bead, will show evidence of the presence of platinum metals.” He therefore believes that sperrylite is not a major source of the platinum metals, but instead that they occur mainly as very dilute solid solutions in the major ore minerals, probably as substitutions in the crystal lattices. The recent discoveries, however, of new platinum minerals by Hawley and Berry, Genkin and collaborators, Stumpfl, Borovskii, and others suggest strongly that numerous platinum minerals exist as discrete intergrowths in the sulfide ores. In general, therefore, the present state of knowledge indicates that in deposits of the Sudbury type, the platinum metals occur mainly in pyrrhotite, chalcopyrite, and pentlandite, both as minute included minerals but also as molecular replacements. The proportions of total and individual platinum metals derived from these two sources have not been determined. OTHER LODES Production was begun in 1962 at another platinum-bearing lode at Gordon Lake, 55 miles north of Kenora, in the Kenora mining division, southwestern Ontario. This is the property of the Nickel Mining and Smelting Corp., Ltd. About 3 million tons of ore have been proven to the 1,000-foot level, but one shaft was sunk in 1962 to a depth of 1,817 feet, and other reserves will be established. The output is about 500 tons of ore daily. The nickel-copper concentrates are shipped first to Lac du Bonnet, Manitoba, and thence to Copper Cliff for smelting. This ore deposit has been described by Thomson and others (1957). The ore which dips steeply north and lies in an east-west fault zone, is bounded on the north by gneiss and on the south by massive granite. Along the fault zone are irregular bodies of chromite-bearing peridotite, which intrude the gneiss. These lenses of peridotite and the adjacent gneiss are mineralized by disseminated and massive pyrrhotite, pentlandite, and chalcopyrite. Joints in the peridotite and banding in the gneiss appear to control the placement of the ores. The tenors in nickel and copper are respectively 1.24 and 0.69 percent, and the gold and platinum metals add to 0.02 ounce per ton. The U.S. Bureau of Mines, however, reports the tenor in platinum metals to be about $3 (Canadian) per ton of ore. The Alexo mine is in east-central Ontario, about 3y2 miles southeast of Kelso, and more than 100 miles northeast of the nearest point on the north range of the Sudbury basin. This property, when owned by the Mond Nickel Co., was operated from 1912 to 1920, with a total production of about 51,860 tons of ore having a tenor of 4.2 percent nickel and 0.5 percent copper. The tenor in platinum metals was reported to be about 0.03 ounce per ton of ore. The property is now owned by the International Nickel Co. of Canada, Ltd., but has not been operated in recent years. A cross section of the west drift of this mine, as given by Baker (1917), shows that the ore body where it was worked had a thickness of 10 to 12 feet and plunged steeply northwestward. It is bounded on the northwest side by serpentinite and on the southeast side by pillow lava. The ore body is known to have a length of 700 feet and to extend to a minimum depth of 350 feet below the surface. Sulfides are disseminated in the adjacent serpentinite, but the workable ore consists of massive sulfides, mainly pyrrhotite and pentlandite, with small amounts of chalcopyrite and pyrite. Platinum metals have been recorded by O’Neill and Gunning (1934, p. 56-57 and 71-72) at five other sites in Ontario. These and six additional sites, taken from Thomson and others (1957), are listed below. 1. Shebandowan nickel-copper property, at Southwest Bay, lower Shebandowan Lake, Thunder Bay district, southwestern Ontario, about 73 miles west of Port Arthur. This property is now owned by the International Nickel Co. of Canada, Ltd. 2. Detroit-Algoma, mine, McTavish township, Thunder Bay district, southwestern Ontario. 3. Lode in Eby township, Timiskaming district, north of Sudbury. 4. Lode in Reaume township, Timiskaming district, north of Sudbury. 5. Cuniptau lode, in Strathy township, 4 miles northwest of Timagami and 60 miles northeast of Sudbury. Formerly owned by Ontario Nickel Corp., Ltd., now listed as property of Trebor Mines, Ltd. 6. Almo Lake, 4 miles west of Gordon Lake and 53 miles north of Kenora, Kenora Mining division, southwestern Ontario. Owner, Norpax Oils and Mines, Ltd. 7. Lode in Pardee township, about 50 miles southwest of Port Arthur, Port Arthur mining division, southwestern Ontario. Owner, Mattawin Gold Mines, Ltd. 8. Lode in Rathbun township, Sudbury mining division. Owner, Dolmac Mines, Ltd. 9. Milnet mine, Parkin township, Sudbury mining division. Property of Jonsmith Mines, Ltd.26 ECONOMIC GEOLOGY OF 10. Nickel Offsets mine, Foy township, Sudbury district, property of Nickel Offsets, Ltd. 11. Quinn claim, Munro township, Ontario. MANITOBA A number of lodes, mainly of nickel-copper and copper-zinc ores, are known in Manitoba, and some of these have become significant producers of the base metals, though most of them contain no platinum metals. The most important of these lodes, which is platinum bearing, is in the Thompson district of north-central Manitoba, between two forks of the Nelson River and about 890 miles north of Winnipeg. The newly built town of Thompson, where the Thompson mine is located, is about 2 miles south of Burnt-wood River, a tributary of the North Fork of Nelson River, and is connected southeastward by a 30-mile spur to the Canadian National Railroad. The discovery and development of this mine are well described in a magazine supplement of the “Northern Miner,” dated August 17, 1961. The geology and ore deposits were described briefly by Davis (1960) and more fully by Zurbrigg (1962). Zurbrigg has outlined a rectangular area trending northeast, with a length of 85 miles and a width of 15 miles, which includes the more important nickel-copper ore deposits. These, named from northeast to southwest, are the properties at Moak Lake, Mystery Lake, Thompson, Pipe Lake, Hambone Lake, Grass River, and Soab Lake. The mineralization, however, extends northeastward to Ospwagan Lake and southwestward to Setting Lake, for a total distance of about 200 miles. The International Nickel Co., of Canada, Ltd., beginning in 1948, prospected this area thoroughly and made the first discovery at Moak Lake in 1952; the deposit at Thompson was found in 1956. Two shafts were sunk on the Thompson deposit, of which the principal working shaft reached initially a depth of 2,000 feet, with operating drifts on the 200-foot levels; but this shaft was sunk to a lower level in 1964. A third operating shaft was completed in 1966 to a depth of 2,400 feet. The mill that was built to handle these ores has a daily capacity of 6,000 tons of ore, but is operated at 4,500 tons a day, yields annually 75 million pounds of refined nickel. The nickel refining plant at Thompson is the second largest in the world. Three new mines being developed at Soab Lake, Birch-tree, and Pipe Lake are scheduled to come into production in 1967. This mining is being done by the Canadian Nickel Co., Ltd., a subsidiary of the International Nickel Co. of Canada, Ltd. In 1962, the Thompson mine had 1,800 employees who live at Thompson, which has a population of 4,500 people. Electric power THE PLATINUM METALS is drawn from the Kelsey hydroelectric generating station on Nelson River, about 53 miles from Thompson. The ore reserves at the Thompson mine are estimated at 25 million tons, with a tenor of 2.8 percent nickel and 0.2 percent copper. The amount of palladium in these ores is comparable with that recovered at Sudbury, but the content of platinum and the minor platinum elements is lower. Besides the platinum metals, there are other byproducts of cobalt and sulfur. The deposit at Moak Lake probably contains ore reserves twice as great as those at the Thompson mine, but the content of nickel is only about 0.7 percent. The total reserves for the entire mineralized area are believed by Allen (1960) to be about 200 million tons and by the Northern Miner (1961) to be perhaps as much as 500 million tons. The nickel ores of the Thompson-Mystery Lake-Moak Lake area are stated by Wilson and Brisbin (1961) to be localized within an intensely deformed gneissic zone that lies between two great blocks of Precambrian rocks, of which the older lies to the southeast and the younger to the northwest, though both strike generally eastward. The older block consists dominantly of greenstone with less graywacke; the younger comprises limestone, quartzite, and conglomerate with a minor volume of lavas. The intermediate zone consists dominantly of gray and pink biotite gneiss which trends northeastward and is characterized by major thrust faulting along its length. This gneiss is believed to have been intruded as a granite into the sedimentary rocks and thereafter to have been greatly metamorphosed. Numerous other igneous rocks, mainly of intrusive character, occur within the gneissic zone; these include diorite, diabase, gabbro, and various peridotites, of which some are strongly ser-pentinized The metasediments include quartzite, subgraywacke, limestone, skam, an iron-formation, biotite schist, amphibolite, and minor amounts of greenstone. The peridotites are linearly arranged in zones parallel to the sheared metasediments and volcanics. The nickel deposits occur as massive ore bodies and stringers in schist, metasediments, and gneiss, and as disseminations and stringers in serpentinized peridotite. The nickel-copper ores of this district exist in two distinct environments. At the outset of exploration, these deposits were thought by geologists to consist of disseminated ores in the included and bounding peridotites, as at Moak Lake. Later, however, deposits of higher grade were found in the metasediments of the mineralized zone of faulting, and these are represented by the ore deposit of the Thompson mine. This deposit may be described as a sheet of sulfide breccia,CANADA 27 10 to 75 feet wide, which lies mainly in biotite schist and extends for a distance of 3y2 miles. Only a very small part of the ore breccia lies in peridotite. The structure controlling the ore is an anticlinal fold, and the locus of the ore is a zone of schist which is continuous over the length of the anticline. The greatest concentration of ore is along the east limb of the south-plunging anticline, along its nose, and in minor crenulations. The ore consists mainly of pyrrhotite, pentlandite, and pyrite, with less chalcopyrite and marcasite and traces of nickel arsenides. The sulfides occur as finegrained masses, lenses, and veinlets in brecciated schist and as stringers, veinlets, and disseminations in adjacent peridotite. Both the coarse and the fine-grained ores are termed “sulfide breccia,” as many inclusions and remnants of country rock are included in the ore. The other type of deposit is exemplified by the low-grade ores at Moak Lake, Mystery Lake, Pipe Lake, Soab Lake, and at other localities within the mineralized zone. Such ores consist of disseminated pyrrhotite and pentlandite in intrusive bodies of serpentinite, and are reported to have tenors in nickel ranging from 0.45 to 0.75 percent. These deposits are characterized by low tenors in chalcopyrite and therefore in copper. All these deposits are in varying degrees platinum bearing. A copper-nickel deposit, owned by the Sherritt-Gor-don Mines, Ltd., is on Lynn Lake, about 145 miles northwest of Thompson. This property is reported to have reserves of 13,820,000 tons of ore, and it was brought into production in 1953. The ore consists of pyrrhotite, pentlandite, chalcopyrite, and pyrite, which occur both in stockworks and in disseminated form. Small amounts of cobalt, zinc, gold, and platinum metals are also present. At the outset, the platinum metals were not recovered, because the chemical-leach method used in treating the concentrates was incapable of saving them. Improvements in milling practice, however, have resulted in a small output of platinum metals. An area of some interest where platinum metals are present has been recorded by Wright (1932). This is in the Oiseau (Bird)-Maskwa Rivers area, in southeastern Manitoba, where several copper-nickel replacement deposits occur in Precambrian rocks. The principal country rock comprises steeply folded andesitic lavas and quartzose tuffs which are intruded by dikes and stocks of peridotite and gabbro, as well as granitic rocks. The ores are copper-nickel replacement deposits which are localized in sheared zones in volcanic rocks close to and in part within marginal parts of the basic 329-505—69---3 and ultrabasic rocks. The principal ore minerals are pentlandite, nickeliferous pyrrhotite, chalcopyrite, and cubanite. At the Hititrite mine, in the Maskwa River area, the tenor of platinum metals was found to be 0.02 percent. Another area recorded by Uglow (1919) is near The Pas, in western Manitoba, about 75 miles south-southeast of Flin Flon. Here, in the shaft of the Northern Manitoba and Development Co., platinum was found in a gold-quartz vein, with a tenor alleged to have been $17 a ton. Another locality mentioned by O’Neill and Gunning (1934) is in the Star Lake district, in southeastern Manitoba. The deposit near The Pas is another occurrence of platinum in a quartz vein, in which gold occurs in pyrite and arsenopyrite; the tenor of platinum was determined to be 0.10 ounce per ton of ore. QUEBEC A nickel-copper ore deposit has recently been discovered in a Motte township, adjacent to Malartic, in southwestern Quebec. Operated by the Marbridge Mines, Ltd., this property is owned jointly by Falcon-bridge Nickel Mines, Ltd., and the Marchant Mining Co. Drilling has been done to a depth of 1,200 feet, and ore has been developed from a shaft at the 750-, 900-, and 1,050-foot levels. Production was begun in 1962, with a daily output of 400 tons of ore, from which 2,500 tons of concentrates is produced monthly. These are smelted at Falconbridge. The tenor in nickel is 2.11 percent. The ore is platinum bearing, but the tenor in platinum metals has not been announced. Another ore deposit containing nickel and copper has been found in the Belleterre district, Guillet township, of southwestern Quebec. This property is being developed by the Lorraine Mining Co., but 80 percent of the stock is owned by the Mclntyre-Porcupine Mines, Ltd. Drilling indicates ore reserves of 550,000 tons, and mining was planned to begin in 1965. The tenor in nickel is about 2.1 percent, and the tenor in platinum metals is reported to be about 0.05 ounce per ton of ore. Traces of platinum metals have also been reported by O’Neill and Gunning (1934, p. 55) in chromite ore from St. Cyr, Quebec. NORTHWEST TERRITORIES A platinum-bearing nickel-copper lode, originally called the Rankin Inlet deposit was discovered in 1928 at the top of a small peninsula, about 7 miles west of Falstaff Island. The literature has numerous references to this deposit, but the ones which form the basis of this description are principally those by Weeks (1932),28 ECONOMIC GEOLOGY OF THE PLATINUM METALS Drybrough (1932), O’Neill and Gunning (1934), the Imperial Institute (1936), Pelzer (1950), the U.S. Bureau of Mines Mineral Trade Notes (1961), and miscellaneous notes in Canadian and United States mining journals. The Rankin Inlet lode was prospected intermittently for nearly 30 years before production began in 1957. The property produced 460,000 tons of ore up to the time when operations ceased in 1962. The mean tenors of nickel and copper, according to the U.S. Bureau of Mines Mineral Trade Notes (1961, v. 53, p. 41), were 3.47 and 0.99 percents; and from other sources the tenors of platinum and palladium are known to have been respectively 0.03 ounce platinum and 0.06 ounce palladium per ton of ore. The platinum metals were not recovered. The local geologic features comprise a lenticular sill of serpentinized pyroxenite, from 200 to 300 feet thick, which lies between a sequence of overlying “upper volcanics” and an underlying sequence of Pre-cambrian sedimentary rocks. The ore is localized in the basal part of the pyroxenite and is interpreted as magmatic ore that resulted from a splitting of the magma into rock-forming and ore-mineral fractions before its cooling and crystallization. The ore minerals that have been identified, named in the order of their abundance, are pyrrhotite, pentlandite, chalcopyrite, magnetite, pyrite, violarite, marcasite, and gersdorffite. The platinum metals are included mainly in pentlandite and pyrrhotite and in smaller amounts in chalcopyrite. Another lode of a similar type has been found at Ferguson Lake, about 150 miles west of Rankin Inlet. Much drilling has been done at this property, but the results of this work are not known to the writer. A lode in which the platinum metals occur in a vein of quartz and pyrite was found by Wait (1910) in a sample collected from the northern part of Baffin Island on Strathcona Sound, an arm of Admiralty Island. A large layered basic pluton has recently been discovered in the Copper-mine area, in the northern part of Northwest Territories, and has been described by Smith and Kapp (1962). This mass, known as the Muskox intrusion, is dikelike in plan and funnel-shaped in cross section. It has four principal units which include a feeder, marginal zones, a central-layered series, and an upper border group. The overall length is 74 miles, of which 37 miles represents the feeder, which contains bronzite gabbro and picrite in zones parallel to a nearly vertical axis. The thickness of the feeder ranges from 500 to 1,800 feet. The marginal zones are parellel to the walls of the intrusion, which dip inward at an angle of 23° to 57°; these zones grade from bronzite gabbro at the contact through picrite and feldspathic peridotite to peridotite and in places dunite. The marginal zones range in thickness from 200 to 1,200 feet. The central zone is 8,500 feet thick and is known to consist of 38 principal layers of dunite, peridotite, pyroxenite, and gabbro. These layers are nearly horizontal and are discordant to the marginal zones. The upper zone, which is 200 feet thick, shows an upward gradation from gabbro to granophyre. Nickel-copper ores occur along the walls of the intrusion, and within one horizon of pyroxenite are ores containing disseminated chromite, copper-nickel sulfides, and platinum metals. A marked resemblance exists between this ore body and the Merensky zone of the Transvaal, and its great size suggest that another important copper-nickel-platinum deposit of the Sudbury type may have been discovered. BRITISH COLUMBIA LODES A platinum-bearing nickel-copper lode, owned by the Pacific Nickel Mines, is about 75 miles east of Vancouver and 7 miles northeast of Hope. The principal habitat of the ore is stated by Aho (1956), to be a stocklike body of pyroxenite that has a visible diameter of about iy2 miles and that has cores of peridotite and hornblendite. This mass appears to cut an adjacent diorite, but is itself cut by dioritic dikes—a fact suggesting approximate contemporaneity. The ore bodies are elongate, steeply pitching, parsnip-shaped structures consisting in part of sulfides with olivine-rich ores and in part of massive sulfide-silicate bodies. The principal ore minerals are disseminated and massive pyrrhotite with subordinate amounts of pentlandite and chalcopyrite. The ore has an average tenor of 1.4 percent nickel, 0.5 percent copper, and 0.01 ounce platinum metals per ton. The sulfides are considered to be of hydrothermal origin. A score of platinum-bearing lodes in British Columbia are mentioned by O’Neill and Gunning (1934), but none of these have been mined, or appear to have much chance of being developed. The more important ones, which include several occurrences of the platinum metals in siliceous gangue minerals, are summarized briefly below. Both Uglow (1919) and Vogt (1927) have listed the principal lodes in which platinum occurs in this environment. The list by O’Neill and Gunning follows: 1. Swede group of claims outside Lockeport Harbour, east side of Moresby Island, about 120 miles south-southwest of Prince Rupert. The lode is an immense deposit of low-grade copper ore, consistingCANADA 29 of small veinlets and disseminations of chalcopy-rite and bornite in diabase. A sample of the bornite assayed 0.01 ounce platinum and a trace of palladium to the ton. 2. Scottie Creek, about 140 miles north-northeast of Vancouver. The lode is a deposit consisting of disseminations, nodules, and lenses of chromite in serpentinite derived from an ultrabasic intrusive. Two assays of the chromite showed 0.02 and 0.10 ounce of platinum to the ton. 3. Mount Ida, about 50 miles east of Kamloops. The platinum occurs in quartz veins and in quartz stringers that lie in a wide shear zone and that contain copper, lead, and zinc sulfides. Assay show values ranging from 0.02 to 0.03 ounce platinum metals to the ton. 4. The Tulameen placer district, described on pages 29-31. The platinum-bearing streams head in areas of peridotite and pyroxenite. According to O’Neill and Gunning, platinum has been reported to occur in serpentinite dikes, masses of chromite, in replacement and vein deposits, in sulfides in greenstone, and in sheared and altered granodiorite. Assays ranged from 0.1 to 4.0 ounces per ton of ore. 5. Mother Lode claim, Burnt Basin, about 3 miles west of Coryell. The country rock consists of basic eruptive rocks, largely altered to serpentinite as in the Tulameen placer area. Platinum occurs with chalcopyrite, pyrite, galena, sphalerite, and molybdenite in gold-bearing quartz veins between two porphyry dikes. Assays show tenors in platinum metals ranging from 0.06 to 0.10 ounce per ton. 6. Nickel Plate mine, at Hedley. Platinum is reported to occur with auriferous arsenopyrite in metamorphosed limestone. One assay indicates a tenor of 0.5 percent platinum, which was thought to be present as sperrylite. 7. The old Sappho property, close to the international boundary between British Columbia and Washington and about 2y2 miles east of Midway. The country rock is argillite intruded by diorite, pyroxenite, and alkali-syenite dikes. Chalcopyrite close to the pyroxenite assayed 0.03 ounce platinum to the ton of ore. 8. Maple Leaf and several other properties in the Franklin Mining camp, about 135 miles east-northeast of Hope. A contact metamorphic deposit, called “The black lead,” occurs in impure quartzite and greenstone, near the contact with a shonki-nite, which is a marginal phase of an augite-syenite intrusive. The principal ore minerals are chalcopyrite, pyrite, a little bornite, and the acces- sory minerals apatite and sphene. Numerous assays show tenors in the platinum minerals ranging from 0.007 to 0.26 ounce per ton of ore. 9. Properties in the vicinity of Cascade, near the international boundary line, a few miles south of the Mother Lode claim. One of these is a chromite, deposit in serpentinized dunite, which contains platinum metals from traces up to 0.15 ounce per ton of ore. 10. Sullivan mine, about 60 miles east-northeast of Nelson. Palladium and a little platinum are recovered commercially from the lead-zinc ores of this property. 11. Cable claim and vicinity of Nome claim, in Ainsworth mining division. The ore at the Cable claim is auriferous pyrite in a quartz vein, with a tenor in platinum of 0.07 ounce per ton. The ore near the Nome claim came from a slide on Kaslo Biver, and the platiniferous rock, which resembles felds-pathic quartzite, is reported to have assayed 0.05 to 0.08 ounce platinum to the ton of ore. PLACERS The placers of British Columbia lie in the many tributary valleys of the Columbia, Frazer, Peace, and Liard Bivers, but the belt continues northwestward into Yukon, and veers thence westward into interior Alaska. Some of these Canadian gold placers also contained small amounts of the platinum metals which generally yielded no significant production. One area, however, known as the Tulameen district, had in earlier years an important output of the platinum metals; and because the geology of this area has genetic significance, it is briefly described in succeeding pages. TULAMEEN DISTRICT The Tulameen district, as mapped geologically by Camsell (1913) on a scale of 1:62,500, is an area of 13 miles square, with the southern boundary 31 miles north of the international boundary between Canada and the United States and the western boundary approximately at long 120° 58' W. A geologic map of a larger area, called the Princeton map area, was later prepared on a smaller scale by Bice (1947). The geography and geology of a part of the Tulameen district and some adjacent territory, taken from the maps by Camsell and Bice, are shown in figure 2. The platinum deposits of the Tulameen district are also-described by O’Neill and Gunning (1934, p. 89-98). The sedimentary country rock of this area consists principally of the Tulameen group of rocks, which are mainly andesitic flows and breccias, limestone, and30 ECONOMIC GEOLOGY OF THE PLATINUM METALS 121'00' 45' 120°30' EXPLANATION Peridotite ♦ + ±—±—— Pyroxenite and gabbro Contact X Placer Figure 2.—Gold-platinum placer deposits, Tulameen Valley, British Columbia. (Generalized from Oamsell, 1913, and Rice, 1947.) argillite, of Triassic or Carboniferous age. There are five igneous formations, all of which are believed to be of Jurassic age; those which bear particularly on the origin of the platinum metals are two formations of ultrabasic rocks, which are shown in figure 2. Also present are Oligocene sedimentary and volcanic rocks, capped by olivine basalt. Intense glaciation of this area during the Pleistocene epoch produced U-shaped principal valleys and hanging tributary valleys. Most of the placers are therefore of postglacial age, though some that lie in protected valleys athwart the main movement of the ice may antedate Wisconsin time. A large intrusive mass of pyroxenite and gabbro, with a length of 11 miles and a maximum width of 3 V2 miles is transected near its northwestern end by the Tulameen River and extends southeastward into the drainage of Granite Creek. A small body of peridotite occurs near the northwestern end of the pyroxenite and gabbro, and a dikelike body of peridotite is included near its southeastern limit. Some ultrabasic rocks are also reported in the upper valley of Lawless Creek. All the streams that carry platinum metals in workable quantities head in ultrabasic rocks, or in areas closely adjacent thereto; and the peridotite is considered to be more important as a source rock than the pyroxenite and gabbro. The streams that have yielded platinum metals are Tulameen River and Granite Creek with its three northern tributaries called Brake-burn, Newton, and Badger Creeks; Olivine (Slate) Creek, Cedar and Hines Creeks, respectively east and west of Olivine Creek, and Champion Creek; and Lawless (Bear) and Britton (Eagle) Creeks, which are northern tributaries of Tulameen River. Gold and platinum have also been found along Similkameen River, from 30 miles above to 20 miles below Princeton, where they were doubtless transported in glacial deposits. The deposits downstream from Princeton were worked intermittently, but not very successfully. The Tulameen River was generally productive from Princeton upstream to Coalmont, at the mouth of Granite Creek, a distance by stream of about 12 miles, though the deposits were not of very high grade. From Coalmont upstream to Olivine Creek, the deep glacialCANADA 31 gravels of Tulameen River have not been worked; but the stream and terrace gravels from Olivine Creek upstream to Champion Creek were found to constitute high-grade placers. The coarsest platinum on Tulameen River was also found within this stretch. The deep deposits downstream from Olivine Creek mav sometime be dredged successfully. The placers of Granite Creek, from the Tulameen River upstream to the mouth of Newton Creek, had the highest tenor in platinum metals of the district. Upstream from Newton Creek, the productive gravels are deeply buried under glacial deposits, and have not been successfully mined. Olivine Creek, for a distance of 4 miles from its mouth, also had high-grade gravel deposits. Gold is almost everywhere more plentiful in these placers than the platinum metals. The gold-platinum ratio was found to be variable, depending on the locations of the placers, ranging from 4:1 in the lower Tulameen valley to 1:1 in the valley of Olivine Creek. A mean value of this ratio can be obtained from the gold production (in dollars) and the platinum production in ounces for the years 1887-1899, 1901-1902, and 1904-1905, as given by O’Neill and Gunning (1934, p. 95). Regarding the dollars of the table for these years as representative of the value of pure gold (not gold bullion), and taking the fineness of the placer gold as 935, the mean gold :platinum ratio for the district appears to be about 2:1. The platinum metals occur as small, rounded, equi-dhnensional grains, many of which are pitted as a result of the weathering out of other minerals; and some have adhering grains of chromite or magnetite. These grains, in the upper valley of Tulameen River and its tributaries, ranged in size from less than one millimeter to 4 millimeters, and the largest recorded nugget weighed half an ounce. A sample, recently obtained by the writer, came from a right limit terrace, about 1% miles west of Princeton. This was found to have the following magnetic properties: Ferromagnetic________________________________32.9 percent Paramagnetic_________________________________64.2 percent Very weakly magnetic_________________________2.9 percent The heavy minerals recovered from the gold-platinum placers included magnetite, chromite, a little pyrite, and rarely native copper. The gold, judging from one assay given by O’Neill and Gunning (1934, p. 98) was of high grade, with a fineness of about 935. The principal source of most of the platinum metals found in this area is the peridotite, though the chemi- cal analyses recorded by Kemp (1902, p. 47-51) also indicate their presence in serpentinite, pyroxenite, and chromite. The platinum metals have also been reported in this district in other environments, at one place with pyrrhotite, chalcopyrite, pyrite, and sphalerite as a replacement deposit in limestone, at a second locality with copper sulfides in a greenstone dike, and at a third site in a shear zone in granodiorite. No superior analyses of the platinum metals from the Tulameen district are available, but one inferior analysis was made by Hoffman (1888), and another is inferred from a record of production in 1930. The analysis by Hoffman is shown both with and without base metals, as At and A2. The production record is given as analysis B. These analyses are shown as table 18. Table 18.—Composition, in percent, of platinum metals, Tulameen district Ai A 2 B Mean Platinum_________________ 73. 20 83. 33 86. 09 84. 71 Iridium____________________ 1. 16 1. 32 2. 78 2. 05 Osmium plus iridium_____ 10.68 12.16 10.14 11.15 Rhodium____________________ 2. 61 2. 97 . 60 1. 79 Palladium_______________ .19 .22 .39 .30 Copper__________________ 3. 44__________________________ Iron____________________ 8. 72__________________________ Total.............. 100. 00 100. 00 100. 00 100. 0 These two analyses are in general agreement in their tenors of platinum, and in the combined tenors of osmium plus iridium. Referring to table 37 of this report, it will be seen that the mean value of platinum in table 18 is quite similar to that recovered in the Good-news Bay district, Alaska, and if the mean value of iridium is added to that of osmium and iridium, it appears that the sum of these two metals is also comparable with that of the Alaskan product. The total output of platinum metals from the Tulameen district is not accurately known. According to Camsell (1913, p. 143), the production for 17 years in the period 1885-1909 was 9,860 fine ounces, but the output has not been recorded for the period 1910-32, after which mining practically ended. According to Quiring (1962, p. 93), the production of placer platinum from Canada for the period 1876-1930 amounted to about 18,775 troy ounces, most of which came from the Tulameen placers. There was a maximum production of 2,120 ounces in 1891. Poitevin in (1924) and O’Neill and Gunning (1934) agree that if proper records had been kept, the total production from the beginning to the end of mining should be approximately 20,000 ounces.32 ECONOMIC GEOLOGY OF THE PLATINUM METALS OTHER PLACERS Numerous other gold placers in British Columbia are known to contain small amounts of platinum metals, but none of these has yielded any significant production. O’Neill and Gunning (1934, p. 76-89 and 98-102) have described these deposits and have published sketch maps showing their locations in British Columbia. They also have given what is known of the gold and platinum tenors of the gravels. It suffices here merely to tabulate the known localities, as follows. Localities of platinum-hearing placers in British Columbia 1. Thibert Creek, a tributary of Dease River, Liard mining division. 2. Ruby Creek, Atlin mining division. 3. Graham Island, Queen Charlotte mining division. 4. Finlay River and tributaries, Omineca mining division. 5. Parsnip River and tributaries, Omineca mining division. 6. Dog Creek, a tributary of Stuart River, Omineca mining division. 7. Peace River, Peace River mining division. 8. Fraser River and tributaries, Quesnel mining division. 9. Government Creek, an eastern tributary of Fraser River, Cariboo mining division. 10. Quesnel River and tributaries, Quesnel mining division. 11. Bonaparte River and tributaries, Clinton mining division. 12. Tranquille River and tributaries, Kamloops min- ing division. 13. North Thompson River and tributaries, Kamloops mining division. 14. Deadman River and tributaries, Ashcroft mining division. 15. Coquihalla River and tributaries, Yale mining division. 16. Similkameen River and tributaries, Similkameen mining division. The Tulameen district lies in the drainage basin of Similkameen River. 17. Kettle River and tributaries, Greenwood mining division. 18. Okanagan River and tributaries, Osoyoos mining division. 19. Lardeau River and tributaries, Lardeau mining division. 20. Tributaries of Columbia River, Revelstoke mining division. 21. Tributary of Jervis Inlet, Vancouver mining divi- sion. 22. West Coast of Vancouver Island, Vancouver min- ing division. The following localities in Yukon are also mentioned by O’Neill and Gunning (1934, p. 108-111) : 1. Teslin (Hootalinqua) River and tributaries. 2. Kaskawulsh River and tributaries. 3. Kluane River and tributaries, Kluane mining divi- sion. Alluvial platinum is also recorded from the bars of the North Saskatchewan River, Alberta. YUKON The principal nickel-copper deposit of Yukon (Yukon Territory) is the Wellgreen lode, which was discovered in 1952 and which is owned by the Hudson-Yukon Mining and Smelting Co. This property is in the Kluane Lake district, about 150 miles west of Whitehorse, Yukon Territory. Reserves of ore are reported to range from 500,000 to 737,000 tons, with tenors in nickel of 2.04 to 2.14 percent and of copper from 0.74 to 1.42 percent. Platinum and palladium are reported to range respectively from 0.038 to 0.049 ounce and 0.27 to 0.32 ounce per ton of ore. A pilot shipment of 300 tons, on which these tenors are presumably based, was tested at Flin Flon in 1955. Another property in Yukon is that of the Canalask Nickel Mines, Ltd., in the Kluane Lake district. The ore reserves amount to 550,000 tons, with an average tenor of 1.68 percent nickel and 0.04 percent copper. The content of platinum metals has not been published. OTHER PROVINCES Other occurrences of the platinum metals are recorded by O’Neill and Gunning (1934, p. 54, 55, 75, 135) in the provinces of Nova Scotia, Saskatchewan, and Newfoundland. Two properites are mentioned in the eastern part of Halifax County, Nova Scotia, where small amounts of platinum occur in a scheelite-quartz vein. Platinum metals were found in two drill holes near the Rottenstone Lake, about 80 miles north of Lac la Ronge, northern Saskatchewan. The country rock at these sites is gneiss and schist, and the nickel-copper ores that contain platinum and palladium appear to occur in oxidized zones within these rocks. Small amounts of platinum are reported by Howley (1907, p. 783) to have been found in chromite in a ser-pentinized area in the vicinity of Mount Cormack, central Newfoundland.REPUBLIC OF SOUTH AFRICA 33 REPUBLIC OF SOUTH AFRICA The platinum metals are widely distributed in the Republic of South Africa, where they occur in the provinces of the Transvaal and Cape of Good Hope, in association with nickel-copper ores. In the same environment they extend northward into Rhodesia, and they are also recovered as a byproduct of the copper deposits in Katanga, Republic of the Congo, and in Zambia (formerly Northern Rhodesia). The platinumbearing lodes occur in various environments, and the platinum metals, though mainly in the form of platinum mineral compounds, occur at some places as native platinum alloys. The most important of the platinum lodes are related genetically to the noritic and pyrox-enitic formations of the Bushveld igneous complex (or series), of central Transvaal; and the principal productive areas are in the Rustenburg and Pilandsberg districts, at the southwestern and western sides of this complex. The gold fields of the Witwatersrand are in south-central Transvaal, contiguous to Johannesburg, and they extend southward into the Orange Free State. These are ancient lithified placers mined as lodes, from some of which are produced significant amounts of native platinum metals as a byproduct of gold mining. This output, though relatively small, represents the world’s largest production of osmiridium. The first definitely recorded discovery of platinum in the central Transvaal was made in 1923 by Adolph Erasmus, a prospector, who panned it from a termite mound at a site about 8 miles west-northwest of Naboonspruit. The first discovery of platinum within the norite belt was made less than a year later by A. F. Lombaard, wTho panned it from the gravels of a dry watercourse in the western part of the Lydenburg district. The lodes of the Waterberg, Potgietersrust, and Rustenburg districts were discovered, respectively, in 1924, 1925, and 1926. The mining of platinum was begun first in the alluvial and eluvial deposits, of which the most promising were in the Lydenburg district, though such deposits were also found at other localities. This mining proved to be unprofitable, because most of the platinum occurred in bedrock as very fine particles locked in sulfides, so that even if freed by weathering they were subject to downstream movement and dispersal. Mining of the lodes soon began in the Lydenburg, Pretoria, Rustenburg, Pilandsberg, Waterberg, and Potgietersrust districts. Wagner (1929) lists at various places in his book a dozen or more companies who undertook such mining, but practically all this work, except in the Rustenburg and Pilandsberg districts, was finally discontinued, either because it was unprofitable or because it was so much less profitable than the present mining at the west side of the Bushveld complex. The more promising of these deposits were eventually acquired by the Rustenburg Platinum Mines, Ltd., which now controls all lode mining in the Rustenburg and Pilandsberg districts. This company, in turn, is a subsidiary of a holding company known as the Johannesburg Consolidated Investment Corp., Ltd. Practically all the platinum metals now being recovered from the lodes of the Transvaal come from a specific zone within the norite belt, called the Meren-sky zone, described on pages 39-42. This is a very regular igneous sheet that has been traced for 250 miles in the Rustenburg, Pilandsberg, Lydenburg, and Potgietersrust districts. The platinum ores of the Meren-sky zone and other lodes of the Transvaal represent the greatest known reserves of platinum metals in the world. The production of platinum metals in the Republic of South Africa (other than osmiridium) has come largely from the nickel-copper lodes of the Transvaal, though a small but indeterminate part has come from placers and other sources. According to the data published by Quiring (1962, p. 96) and from other sources, the total production of the Republic of South Africa from 1925 to 1962, inclusive, has been 4,966,000 ounces, with a maximum output in 1957 of 603,700 ounces. The production of platinum metals from the Transvaal has been limited in recent years by the demands of the world’s metal markets. Since 1964, however, a program of expanded production has been in progress by the Rustenburg Platinum Mines, Ltd., and this has been corroborated by statements made by this company in the Platinum Metals Review, (v. 10, no. 2, p. 52-53, 1966, v. 11, no. 1, p. 9, p. 131, 1967; and v. 12; no. 4, p. 139). Permanent mining facilities are now being installed that will lead to a production of 1 million ounces by 1969. The ore reserves at Rustenburg alone are considered sufficient to maintain this output well beyond the year 2,000. TRANSVAAL AND ORANGE FREE STATE PROVINCES GENERAL GEOLOGY The general geology of the Bushveld igneous complex and of the surrounding rocks is similar in some respects to that of the Sudbury district, but markedly different in others. Both these areas are characterized by a synclinal basin floored by basic igneous rocks, and both areas are surrounded by Precambrian rocks; but most of the other characteristic features are dissimilar, though a tendency has existed to correlate34 ECONOMIC GEOLOGY OF THE PLATINUM METALS the geologic and petrographic features of the Bush-veld and Sudbury areas. The general stratigraphy adopted in this paper is that proposed by Hall (1932), who worked for more than 30 years in the Transvaal, though it is evident from a late geologic map of the Transvaal, compiled in 1955 by E. C. Truter and P. J. Rossouw, that new interpretations have been made. A recent memoir of the Geological Survey of South Africa, by Coetzee (1960, 198 p.), gives the systems, series, and smaller stratigraphic divisions now accepted by the Geological Survey of South Africa, with special reference to the Orange Free State. The oldest rocks of this region are the metamorphic rocks of the Swaziland system or Basal Complex. Unconformably above these are the sedimentary rocks of the Witwatersrand system; unconformably above these lie andesitic lavas, porphyries, and pyroclastics, together with the sedimentary rocks of the Ventersdorp system, and unconformably above these are the sedimentary and andesitic rocks of the Transvaal system, of which the Pretoria series is the uppermost division. The Basal Complex and the Witwatersrand, Ventersdorp, and Transvaal systems are of Precambrian age. The Transvaal system comprises rocks w7ith a maximum thickness of 25,000 feet. The Pretoria series, which constitutes the upper part of the Transvaal system, consists of sedimentary rocks, lava flows, and sills with a total thickness of about 13,000 feet; and within the Pretoria series lie the basic and ultrabasic intrusives and extrusives that compose the Bushveld igneous complex. The principal rocks of the Pretoria series are quartzite, shale, and conglomerate, of which the uppermost formation below the norite lopolith is the Magalies-berg quartzite, which at many places constitutes the floor of the norite. One feature of the Pretoria series, according to Hall’s classification, is the presence of three formations of basic amygdaloidal lavas, separated from one another by sedimentary rocks. Between the two younger of these lava sheets occur sills of the same petrographic character as those which intrude the Magaliesberg quartzite and underlying shales. These lavas and sills, together with the sedimentary rocks that separate them, are commonly included as a part of the Bushveld igneous complex, as they are regarded by some geologists as the earliest manifestations of the igneous activity that later produced the main noritic and associated rocks of the Bushveld complex. BUSHVELD COMPLEX The basal horizons of the Bushveld igneous complex have already been defined. Above the Magalies- berg quartzite, and commonly in contact with it, occurs a great intrusive mass of norite and associated ultra-basic rocks, which constitutes the part of the Bushveld igneous complex that is the principal source of the platinum-bearing nickel-copper ores. Where the noritic and associated rocks are not in contact with the Magaliesberg quartzite, they are floored by the Dull-strom volcanic formation, which overlies the quartzite at some localities, and is the youngest of the three volcanic formations cited above. The Bushveld complex also includes three younger formations. Above the noritic rocks, but at some places intruding them, is a formation generally called the Bed Granite. This does not usually rest directly upon the noritic rock, as it is more commonly separated by a band of felsite, granophyre, or quartzite. It has the general configuration of a sill, however, with a thickness measurable in hundreds, rather than thousands of yards, and is generally regarded as younger than the noritic rocks. Above the Bed Granite is a sheet of granophyre, with a thickness of about 1,200 feet, which is probably younger than the Bed Granite. The uppermost igneous formation of the Bushveld complex is a mass of felsite and derived pyroclastics, which are older than the norite lopolith. These felsites and related rocks, with a thickness of about 8,500 feet, are interpreted as the surficial equivalents of the underlying granophyre. They also are regarded as the basal part of the Booiberg group, which commonly forms the roof of the Bushveld igneous complex, and is considered to represent the uppermost part of the Pretoria series. The ages of the intrusive and extrusive rocks of the Bushveld complex, including the sedimentary rocks of the Booiberg group, are considered by South African geologists to be of late Precambrian age. The Booiberg group is overlain successively by the Waterberg and Karroo systems, though the geologic map by F. C. Truter and P. J. Rossouw (South Africa Geological Survey 1955), shows that these two systems have been replaced by five other systems which, named in order of decreasing age, are the Loskop, Waterberg, Kama, Kaap, and Karroo systems. The Loskop and Waterberg systems are now considered to be of Precambrian age; the Kama and Kaap are called Devonian to middle Carboniferous; and the Karroo system is regarded as Triassic to early Jurassic. None of these systems figures prominently in the geology of the Bushveld igneous complex, except that they overlap and therefore conceal parts of the norite lopolith and its included Merensky zone. Still later geologic maps by the Geological Survey of South Africa (1960 andREPUBLIC OF SOUTH AFRICA 35 1967) show further modifications of the stratigraphic sequence. The formation of noritic and associated rocks lies in an ovaloid synclinal basin which trends east-northeast, with major and minor axes respectively of about 280 and 110 miles. The surficial extent of these rocks, as shown in figure 3 including the eastern and northeastern area with the western and northwestern area, is about 20,000 square miles. This intrusive is regularly layered and dips inward toward its center at angles ranging from 5° to 50°. The maximum thickness of these basic and ultrabasic rocks varies from one locality to another, ranging from 5,000 to 18,200 feet, with a mean thickness taken from the data presented by Hall (1932, p. 268) of about 11,800 feet. This intrusive therefore has the general form of a gigantic sill. A thick central part of the noritic intrusive is generally believed to plunge to a great but undetermined depth and under this interpretation warrants the designation of a lopolith. There is, however, a zone north-northwest of Potgietersrust where only the upper part of the intrusive is present, as the lower zones were not developed in the form of a sill penetrating the country rock. Instead, this protuberance, which extends about 65 miles north-northwesterward from the projected rim of the lopolith, may best be regarded as a great dike that penetrated deeply into the country rock. West of Pilandsberg, only the lower part of the lopolith is present, and this is believed to have resulted from the erosion of the upper horizons. This lower zone includes inliers of quartzite and metamorphosed shale that indicate the irregular nature of the basal contact. The northern contact of the noritic formation with the rocks that underlie it is not exposed for about 130 miles, as it is overlapped in this stretch by younger sedimentary rocks. Owing to the same cause, a similar hiatus of about 90 miles exists along the southern contact. For these reasons, the minor axis of the lopolith, as given above, is materially different from that stated by Wagner and Hall, which applies to the noritic lopolith as a whole, and includes the intrusive branch that extends north-northwest from Potgietersrust. The norite and related rocks are divided by Wagner (1929, p. 44) into three principal zones, which named from bottom to top are the differentiated or critical zone, the main belt, and the upper zone. Wagner thus includes in his differentiated zone the chill zone, transition zone, and critical belt proposed by Hall (1926). A generalized section of the norite lopolith south and southwest of Pilandsberg has been presented by Wagner (1929, p. 45) as follows: 329-505—69---i Composite section across norite lopolith near Pilandsberg Upper zone Main belt.. Differentiated or critical zone. Approximate thickness (Jett) Norite, grading upward into gabbro and syenite. Diallage norite with stratiform segregations of titaniferous 8, 000 magnetite and labradorite-anorthosite. Diallage norite. ____do.............................. 1, 000 Bronzitite with bands of anorth-' osite and pseudo-porphyritic diallage norite (contains Merensky zone). Bronzitite with seams and lenses of chromitite. Bronzitite with isolated lenses of harzburgite, differentiated diallage norite, and chromitite. , Bronzitite with lenses of harzburgite and anorthositic norite containing bands of bytonite-anorthite and labra-dorite anorthosite (contains Vlakfontein nickel zone). Bronzitite with lenses of harzburgite. Pyroxenitic olivine-norite probably grading downward into the basal or chill zone of dia-basic quartz-norite. . 1,700 630-1, 000 3, 000 400 Minimum thickness in this area. 15, 100 ORE DEPOSITS Ore deposits that contain the platinum metals include numerous types with local variations, and the scattered over a great area along the periphery of the intrusive complex. The best understanding of these ores can be obtained by describing the petrography and mineralogy of type deposits, with emphasis upon the mode of occurrence of the platinum metals. This approach is much facilitated by a generalized genetic classification of the different ore deposits of the norite zone of the Bushveld complex. Emphasis is placed upon the productive ores of the Merensky zone, whereas the other types of deposits are only briefly described. A general classification of the platinum deposits related to the basic and ultrabasic rocks is as follows: Classification of platinum deposits of the noritic and related rocks A. Magmatic segregates: 1. Ores in which the platinum metals, mainly platinum and palladium, are associated with nickel-copper sulfides in norite and pyroxe-nite. 2. Ores of chromitite, containing native platinum metals. 3. Ores of dunite, containing native platinum metals. B. Pneumatolytic, hydrothermal, and contact meta- morphic deposits in sedimentary rocks subjacent to the basic and ultrabasic intrusives.36 ECONOMIC GEOLOGY OF THE PLATINUM METALS Figure 3.—Norite and differentiated ultrabasic rocks of the Bushveld igneous complex and the Witwatersrand System, Transvaal and Orange Free State, Republic of South Africa.REPUBLIC OF SOUTH AFRICA 37 EXPLANATION e—r—r Norite and differentiated ultrabasie rocks of the Bushveld igneous complex Unpatterned areas within unit indicate rocks of the Transvaal System Witwatersrand System Unpatterned areas within unit indicate rocks of Transvaal System .Contact, approximately located 10 0 10 20 30 40 MILES I i I______I____I________I---1 Figure 3.—Continued.38 ECONOMIC GEOLOGY OF THE PLATINUM METALS MAGMATIC SEGREGATES The mineral deposits formed by magmatic segregation have been divided by Wagner (1929, p. 49) into the seven following types. Classification of magmatically segregated 'platinum, deposits A. Upper noritic rocks: 1. Deposits in quartz-bearing anorthositic norite. 2. Deposits in a medium-grained feldspar-rich spotted norite. 3. Deposits in a rather coarse-grained feldspar-rich diallage-norite. B. Lower noritic rocks: 4. Deposits of the Merensky type that occur above and below the main Merensky zone. 5. The main Merensky zone, as developed in the Rustenburg, Pretoria, Lydenburg, Pieters-burg, and Potgietersrust districts. The mineralized rocks (are pseudoporphyritic pyrox-enitic diallage-norite, feldspathic harzburgite and chromitite. 6. Deposits in a fine-grained pyroxenitic diallage- norite, merging into coarse-grained feldspathic bronzitite and bronzitite. 7. Deposits in bronzitite. The first type of the magmatic differentiates is illustrated by a number of deposits about 35 miles north-northwest of Middleburg. The mineralized rock consists of irregular segregations of light-colored anorthositic quartz-bearing norite in a dark-colored diallage norite. The largest of these deposits has been proved by underground exploratory work to be of considerable size, but it has not been mined. Labradorite, the principal rock-forming mineral of the light-colored norite, is intergrown with diallage, a little quartz, and less chlorite. The ore minerals are chalcopyrite, pent-landite, and pyrrhotite, which appear as small specks scattered rather uniformly throughout the rock. Sper-rylite, the only recognized platinum mineral, occurs in minute, brilliant, cubo-octahedra. The tenor in platinum is given as a maximum of 0.65 troy ounce per ton of ore. The second type of magmatic differentiate is illustrated by the ores near the eastern limit of the noritic intrusive, southeast of the Steelport River. These deposits comprise at least five zones in the upper part of the norite which consists of irregular masses of medium-grained spotted feldspar-rich sul-fidic norites that either underlie or are enclosed in lenses of spotted anorthosite. The mineralized rock is dominantly a granular aggregate of labradorite, intergrown with some bronzite, and less hornblende and diallage. The sulfides occur interstitially as irregular intergrowths of pyrrhotite, nickeliferous py-rite, pentlandite, and chalcopyrite. These mineralized zones are rarely longer than 8 feet nor thicker than 18 inches, and conform structurally with the general attitude of the country rock, which dips 15° west-northwest. The tenor in platinum ranges from 0.02 to 0.12 ounce per ton, and the deposits lack economic value. The third type of ore deposit occurs in the same general vicinity as the one just described. The ores consist of small irregular bodies of coarse-grained feldspar-rich sulfidic diallage norite, enclosed in medium-grained spotted norite. The sulfide-bearing norite commonly encloses a thin seam of magnetite, and a great stratiform segregation of titaniferous magnetite lies a short distance higher in the sequence. The ore-carrier is a lustrous blue-green rock that consists of large tabular crystals of labradorite, anhedral grains of green diopside with rodlike inclusions, anhedral crystals of bronzite, and small grains of magnetite. Sulfides ranging in size up to 0.8 centimeter in maximum diameter are irregularly distributed in the rock. The character of the platinum minerals is not known, but they are believed to occur in the sulfides. A sample of the ore, taken over a thickness of 42 inches, had a tenor of 0.27 ounce of platinum per ton. This deposit is no longer worked. The fourth type represents ores similar to those of the Merensky zone, which occur in the igneous sequence above and below the latter zone. They differ from the true Merensky zone in being lenticular and in having lower tenors in the platinum metals. Some of these ores were formerly mined. A magmatic deposit of the sixth type occurs about 11 miles northwest of Potgietersrust, in association with the west-dipping dikelike extension of the noritic lopolith. This deposit is a thick sheet of finegrained pyroxenitic diallage norite, merging locally into coarse-grained bronzitite and feldspathic bronzitite, and was traced for 1,700 feet. The norite intrudes beds of ironstone and quartzite and includes xenoliths of these rocks. The sulfide mineralization is sporadic, and platinum is erratically distributed in the ores. For these reasons, the deposit has no economic significance. The seventh type of deposit, which occurs only in the Rustenburg district, consists of isolated pipe- and irregular-shaped masses composed partly of disseminated sulfides, partly of sulfides poikilitically intergrown with rock-forming minerals, and partly of massive sulfides. The enclosing country rock is bronzitite, with enclosed lenses of harzburgite and anorthositic norite. Small amounts of palladium and lessREPUBLIC OF SOUTH AFRICA 39 platinum are present in the sulfides, and also in sperry-lite. These deposits are not rated as important sources of the platinum metals. Merensky zone The Merensky zone is an exceedingly persistent igneous sheet that lies near the top of Wagner’s differentiated or critical zone. It therefore lies approximately 9,000 feet below the top of the lopolith in the Rustenburg district, and about 6,000 feet above its base. The Merensky zone has been traced intermittently for 140 miles in the Rustenburg and Pilandsberg districts, for 70 miles in the Lydenburg district, and for 40 miles in the Potgietersrust district. This zone has been prospected and proved to contain workable ore for 70 miles along its outcrop at the western end of the lopolith, where the Rustenburg and Union mines are located. Notwithstanding the general continuity of this sheet along its strike, marked differences exist in its thickness and petrographic cross section. A description of this zone throughout its entire length is far beyond the scope of this report, but such details, if needed, will be found in the volume by Wagner (1929). Another well-known zone, at stratigraphic distances of 400 to 1,000 feet above the Merensky zone, consists of an anorthosite which is particularly resistant to weathering, forming large residual boulders at the surface. This is regarded as a valuable horizon marker in prospecting. The Merensky reef, also called the Merensky platinum reef, where it exists as a distinct horizon, is a relatively thin sheet of coarsely crystalline pyroxenite with a pegmatitic habit that lies near the base of the Merensky zone. This reef, with a thickness of 1 to 2 feet, is the principal source of the platinum metals that are being recovered in present mining operations. The tenor in platinum metals, however, is somewhat higher in the upper than in the lower part of the reef. At the base of the reef is a seam of chromite, with a mean thickness of three-fourths of an inch, and at its top is a similar but thinner seam of chromite. These are called the lower and upper chrome bands and have high tenors in platinum, but are too thin to influence the average tenor greatly. Platinum metals extend upward from the Merensky reef for some inches into the over-lying pyroxenite, and similarly downward into an underlying anorthosite. The Merensky zone ranges in thickness from 2 to 35 feet. In general, this igneous sheet is a dark-colored norite, but the petrographic character varies both along the strike and across it. The relative amounts of pyroxene and feldspar are inconstant, and with an increase in feldspar the rock grades into anortho- sitic norite and anorthosite; with an increase in pyroxene it grades into pyroxenite. Locally the norite becomes peridotitic. The rock adjacent to the hanging wall is generally a light-colored spotted norite, composed of bronzite and diallage in a matrix of feldspar. Directly above the Merensky zone is a fine-grained pyroxenite, which by some writers is called the Merensky pyroxenite. This is overlain by anorthositic gabbro, which is overlain by a mottled or spotted anorthosite. These three sheets, with a combined thickness of 25 feet, are succeeded upward by another pyroxenite, with a thickness of 8 to 22 feet, which is called the Bastard reef. This well-known horizon resembles in several respects the Merensky zone, and even has a thin seam of chromite at its base. But it is either barren of platinum metals, or contains at most only very small amounts of them. Anorthosite commonly forms the base of the Merensky zone. Two platinum lode mines, controlled by the Rustenburg Platinum Mines, Ltd., are now being operated in the Merensky zone of the Transvaal. The older of these mines, called the Rustenburg (formerly the Waterval) mine, is about 7 miles east of Rustenburg; the other, called the Union mine, is about 48 miles N. 5°W. of Rustenburg. The geological and other data on these deposits, as presented below, have been obtained from papers by the technical advisers to the Rustenburg Platinum Mines, Ltd. (1957), by Coertze (1958), by Cousins (1959 a, b, c), by Beath, Cousins, and Westwood (1961), and by Beath, Westwood, and Cousins (1961). Certain minor discrepancies in these papers have been resolved by the writer, according to his best judgement. The ore body mined at the Rustenburg mine comprises the Merensky platinum reef with a thickness of about 12 inches, 8 to 9 inches of the overlying pyroxenite, and 8 to 9 inches of the underlying anorthosite making a total thickness of 28 to 30 inches. This platinum-bearing horizon is so regular that, over the last 10 years, the average stoping thickness of ore has been 281^ inches. The strike of the ore body is east-west, with a dip of 9°30'N., and mining has now reached a vertical depth of about 1,000 feet—a depth corresponding to about 6,000 feet down the dip. The extent of the mine along the strike is about 8 miles. Dikes and faults are rare, but at both mines there are roughly elliptical “potholes” of unknown origin that extend downward from the base of the Merensky reef, with diameters ranging from 20 to 100 feet and depths of 5 to 6 feet. Generally the ore at the bottoms of these potholes can be recovered. There are also subcircular dome-shaped masses, known as “kop-pies,” which project upward from the anorthosite on40 ECONOMIC GEOLOGY OF THE PLATINUM METALS the footwall, and may be high enough to replace entirely the Merensky reef, and rarely to extend upward into the overlying pyroxenite. The rocks bounding the potholes and koppies are unfolded. Potholes and koppies are more prevalent at the Rustenburg than at the Union mine. The ore body at the Union mine is markedly different from that at the Rustenburg mine. The pegmat-itic pyroxenite which constitutes the Merensky zone has a thickness ranging from 10 feet in the southwestern part of the property to 20 feet in the northeastern part. The ore body here strikes northeast and dips about 21° SE. Up to 1965, the mine had been worked to a depth of about 700 feet —a depth corresponding to a distance of 2,000 feet down the slope of the intrusive and for a distance of 2l/£ miles along its strike. The platinum metals occur both at the top and at the bottom of this thick sheet but are concentrated near its upper contact, so that it is generally unprofitable to work the leaner ore at its base. Potholes in the Union mine are larger than in the Rustenburg mine, with diameters ranging from 200 to 700 feet and with correspondingly greater depths. Any ore that occurs at their bases cannot readily be recovered. The platinum minerals at both mines are sperrylite, braggite, stibiopalladinite, and laurite, which occur as discrete grains and intergrowths in disseminated sulfides. The platinum metals probably occur also as molecular intergrowths replacing certain cations in the sulfides. Some native platinum metals are recovered, together with a little native gold. The platinum metals are mainly ferroplatinum, containing from 10 to 30 percent iron. Native ferroplatinum is more plentiful at the Union than at the Rustenburg mine, but the exact amounts or proportions have not been ascertained. The sulfides comprise chalcopyrite, pyrrhotite, pentlandite, nickeliferous pyrite, cubanite, graphite, millerite, and violarite. The tenor of the ore in platinum metals, in the stretch from Rustenburg to Brits, is reported to range from 0.25 to 0.35 ounce per ton. The tenors of similar lodes in the Lyndenburg and Potgietersrust districts are lower. These metals are strongly concentrated in the bounding chromite seams, particularly in the lower chrome band, where a tenor of 0.6 ounce per ton has been reported. The nickel and copper produced have a constant ratio to the amount of platinum metals recovered, but this ratio is higher at the Rustenburg than at the Union mine. In both mines, the ratio of nickel to copper is 1.8:1. The oxidation of the platinum-bearing sulfides is a matter of interest. The footwall of the Merensky zone is composed at many places of bronzite and less diallage, sparingly but rather uniformly included in a matrix of labradorite-bytonite. Within the zone of oxidation, beneath the present level of ground water, this rock is mottled by streaks of limonite for a depth ranging downward as much as 2*/^ feet below the Merensky zone. This weathered zone contains specks of sulfides and small amounts of platinum metals. At the Rustenburg mine the zone of oxidation extends about 700 feet down the dip, a distance corresponding to a vertical depth of about 120 feet in general, in the Rustenburg district, this depth ranges from 70 to 140 feet. The fact that the top of the present water table, however, is from 40 to 60 feet below the surface shows that the visible oxidation of the ore was accomplished when the water table was lower than at present, presumably during an earlier and more arid climate. The composition of the platinum metals in the sulfide ore and in the weathered ore are notably different. Two analyses from the Rustenburg district, which are the means of four analyses published by Wagner (1929, p. 110), have been recomputed to 100 percent to show these differences (table 19). The platinum: palladium ratios in these two analyses are respectively 3:1 and 5.7:1. It is clear that a part of the palladium, and possibly some of the rhodium, was dissolved by mineralized ground water. This process relatively enriched the more resistant platinum. Table 19.—Composition, in percent, of platinum metals in sulfide and oxidized ores, Rustenburg district [N.D., no data] Sulfide ore Oxidized ore Platinum..__________________________ 69.74 79.92 Iridium_____________________________ N.D. 1. 29 Iridium and osmium______________________ 3. 08 2. 84 Rhodium_________________________________ 4. 10 1. 92 Palladium______________________________ 23. 08 14. 03 Total--------------------------- 100. 00 100. 00 The preceding statements, which accept the origin of the platiniferous horizons in the Bushveld complex as differentiated igneous sheets, are now being reexamined more closely by workers at the Union and Rustenburg mines, and in nearby areas where data based upon drilling on a large scale is being done. Coertze (1958, p. 387-A00) has proposed that each of the basic types of the Bushveld igneous complex, including pyroxenite with chromite seams, anorthosite, norite, porphyritic, pyroxenite, pegmatitic pyroxenite, gabbro, ferrogabbro, dunite, and magnetite, represents a separate intrusion. More recently it has been stated by Beath, Cousins, and Westwood (1961, p. 2) that recent geophysical and collateral evidence tend to contradictREPUBLIC OF SOUTH AFRICA 41 the lopolithic concept of the noritic rocks of the Bush-veld igneous complex. Instead it is inferred that the eastern and western limbs of this intrusive represent separate T-shaped curved dikes that extend to great depths, and that basic and ultrabasic rocks do not underlie the central part of the basin. The cited authors appear to agree with the interpretation of Coertze, but also suggest as an alternative hypothesis that these rocks may be of extrusive origin, which would account for the phenomenal regularity of the successive sheets and for the absence of crosscutting by dikes. It is admitted, however, that the true genesis of the Bushveld igneous complex remains still within the realm of speculation. Chemical analyses The mean ratios of the platinum metals from the lodes of the Transvaal are much better known than the ratios from the Sudbury district. The sales of platinum metals, both from the lodes and from the Wit-watersrand lithifield placers, have been published regularly by the Department of Mines and Industries, of the Republic of South Africa, and have been quoted annually by the U.S. Bureau of Mines in the sequence of Minerals Yearbooks. The following data on the lodes comprise those of 20 years in the interval 1929-56, and therefore may include for a few years some of the platinum metals from mining operations now discontinued, but in general these data represent the production from the Rustenburg and Pilandsberg districts. These records, recomputed to simulate analyses, are shown in table 20. The ratio of platinum to palladium in the Merensky zone is reported by Wagner (1929, p. 129) to range from 6.5:1 to 1.6:1 and is shown in the Potgietersrust Table 20.—Composition, in percent, of platinum metals, mainly from Rustenburg district [N.D., no data] 1929 1930 1931 1934 1935 1936 1937 1938 1939 1940 Platinum_________________ 82.92 80.96 74.99 86.82 79.83 77.75 77.08 72.53 78.20 66.27 Iridium__________________ . 56 . 24 . 21 . 01 . 08 . 05 . 06 . 20 . 13 . 42 Osmium and iridium__________ .46 .45 .08 .01 .02 .14 .12 .08 .22 Ruthenium________________ .59 .47 1. 39 .41 .08 .91 . 51 1. 72 1. 20 2. 20 Rhodium ..... 1. 10 .64 . 15 N.D. N.D. N.D. N.D. N.D. N.D. . 64 Palladium_________________ 12.77 12.51 15.96 12.00 13.59 15.82 16.70 19.78 16.33 25.71 Total_______________ 98. 40 95. 27 92. 78 99. 25 93. 60 94. 53 94. 49 94. 35 95. 94 95. 46 1944 1945 1947 1948 1949 1951 1952 1954 1955 1956 Adjusted moan Platinum 63. 58 59. 72 77. 08 69. 17 61. 27 68. 89 66. 27 78. 18 60. 98 69. 50 75. 06 Iridium______________________ 38 .74 .06 .47 .30 .31 .13 N.D. N.D. N.D. . 27 Osmium and iridium_______ .03 .12 .14 .09 .10 .11 .11 .03 .08 N.D. . 13 Ruthenium _______________ 4. 39 4. 10 . 51 1. 29 1. 80 1. 51 1. 34 1. 62 .59 . 50 1. 41 Rhodium 1. 12 1. 79 N.D. 2. 57 3. 32 1. 79 2. 39 2. 66 2. 38 2. 30 2. 15 Palladium _ 27. 01 28. 59 16. 70 22. 03 29. 21 23. 14 26. 40 13. 81 33. 35 24. 30 20. 98 Total_______________ 96. 51 95. 06 94. 49 95. 62 96. 00 95. 75 96. 64 96. 30 97. 38 96. 60 100. 00 district to be as low as 1.3:1. Table 20 shows a ratio for the Rustenburg district of 3.6:1, which is substantially different from that at Sudbury, where it is about 1.1:1. The data on the relative prevalence of rhodium and ruthenium are not as dependable as could be desired, but according to table 20, the amount of rhodium exceeds that of ruthenium, though rhodium is much less plentiful than at Sudbury. The proportions of the metals recovered from the placers of Good-news Bay, Alaska, and from the Uralian placers, as shown respectively on pages 59 and 88, are markedly different from those recovered from the lodes of the Transvaal and Sudbury. This fact constitutes a significant difference that distinguishes the native platinum metals of the peridotites and perknites from the platinum metals recovered from the platinum minerals of lodes. CHBOMITITE ORES The more important platinum-bearing chromitite ores of the Bushveld complex are in the Lydenburg district, though similar bands have also been recognized in the Rustenburg district. Two principal zones of platiniferous chromitite, called the upper and lower chromitite horizons which lie in the lower fourth of the norite lopolith, are present in both districts. A third band, lying between the upper and lower horizons, has also been found in the Rustenburg district. These and other deposits of chromite are widely and persistently distributed along the strike of the intru-sives in both districts, ranging in length from 3 feet42 ECONOMIC GEOLOGY OF THE PLATINUM METALS to several miles and in thickness from 1 inch to 14 feet. The fact that a typical deposit in the upper horizon, about 50 miles N. 28° W. of Lydenburg, occurs about a mile east of the outcrop of the Merensky zone and about 1,200 feet stratigraphically below the latter indicates an areal dip of 13° westward. In this deposit are two lenses of chromitite, with thicknesses of 2 and 3 feet, separated by 17 feet of bronzitite and norite. The platinum-bearing chromitite consists generally of oval-shaped grains of bronzite crowded with minute poikilitic inclusions of chromite in a scanty matrix of larger included grains. Locally the rock is interspersed with irregular patches and streaks of coarse-grained chromite and picotite. The rock also contains minor amounts of diallage and calcic plagioclase. The content of Cr203 ranges in these deposits from 38 to 47 percent. Native platinum metals characterize the chromitite deposits. These commonly occur in very thin plates and in slender wires of which some have only the thickness of a hair. Analyses have shown that platinum predominates over palladium, but at one deposit in the Lydenburg district, palladium constituted 55 percent of the platinum metals. No analyses are available that give the tenors of iridium, osmium, ruthenium, and rhodium. Tenors of platinum metals in chromitite are stated by Wagner (1929, p. 93-95) to range from 0.06 to 5.75 ounces per ton, but no average tenor may be cited. These deposits were intensively prospected in 1925 and 1926, but since the discovery of the Merensky reef in the Rustenburg district, no further attention has been given to them. DUNITE ORES Platiniferous dunites and related rocks have been found at many sites in the Lydenburg and Rustenburg districts. These deposits have a stratiform range of 2,000 feet in the lower part of the noritic lopolith, mainly below the Merensky zone, but a few occur above that horizon in the Lydenburg district. The most important deposits, however, lie between the upper and lower chromitite horizons. These deposits are divided by Wagner (1929, p.51-52) into three types which depend primarily upon the nature of the olivine in the dunite. These varieties of olivine are, first, the normal type, wherein the ratio of MgO to FeO ranges from 12:1 to 2.5:1; second, hyalosiderite, with a MgO-FeO ratio ranging from 2.5:1 to 1.1; and third, hortonolite, in which the MgO-FeO ratio ranges from 1:1 to 1:2. The first type is characteristic of the dunites of the Ural Mountains and occurs only sporadically in the Transvaal; the second type is exemplified by only one important deposit, known as the Driekop deposit, which is about 32 miles N. 28° W. of Lydenburg; but more than 60 occurrences of ores of hortonolite dunite are known, both in the Lydenburg and Rustenburg districts. The two most important deposits of platiniferous hortonolite dunite, called the Mooihoek and Onverwacht lodes, occur about 3 and 6 miles respectively south of the Driekop deposit. The Driekop deposit is essentially an intrusive core of platinum-bearing hyalosideritic dunite, enclosed in a much larger pipe of nearly barren dunite. The workable surficial area measures approximately 80 by 60 feet, but narrows somewhat with depth. The dip of the dunite core and probably also of the dunite pipe is about 77° NE. The platinum-bearing core has been followed downward to a depth of 460 feet without any great constriction. The ore body consists dominantly of interlocking grains of hyalosiderite with a MgO :Fe0 ratio of 2.4:1, together with small amounts of large greenish-gray crystals of diallage and also small anhedral grains of magnetite. Locally the diallage is sufficiently plentiful that the rock becomes a wehrlite. A recent study of the Driekop deposit has been made by Heckroodt (1959, p. 59-71), and it is also from the dunite at this site that Stumpfl (1961, p. 833-847) identified the nine new platinum minerals that he described. In an area of 20 square miles surrounding this deposit, Heckroodt was able to recognize five successive phases in the basic and ultrabasic rocks, which were identified in the order of their intrusion as pyroxenite, norite and related rocks, pegmatitic feldspathic pyroxenite (Merensky zone), peridotite including dunite and ser-pentinite, and gabbroic rocks. The platinum metals occur mainly as native alloys, within small segregations, lenses, and irregular clumps of iron-rich dunite and wehrlite of markedly coarser grain, such that the olivine is particularly conspicuous by reflected light. Below water level, small amounts of sperrylite and cooperite are also present. Nine assays of average ore show a range in platinum metals from 0.02 to 0.53 ounces per ton, with a mean tenor of 0.17 ounce per ton. Picked samples, however, range upward to 2.7 ounces per ton. The ratios of platinum to palladium and other platinum metals have not been published. The Mooihoek ore deposit is a pipe of platiniferous hortonolite dunite, which is nearly circular in horizontal section, with a diameter of about 42 by 51 feet. This is enclosed in a layered cylindrical pipe of dunite and serpentinite, whose surficial horizontal measurements are 700 feet from north to south and 600 toREPUBLIC OF SOUTH AFRICA 43 850 feet from east to west. The larger pipe is bounded by coarse pegmatitic diallage and feldspathic pyrox-enite, which merge outward into olivine gabbro and spotted norite. The dimensions cited for the smaller pipe are those which delimit the workable ore, rather than dimensions based upon petrographic homogeneity, as the bounding dunite also contains small amounts of the platinum metals. The small platiniferous pipe of workable ore plunges N. 76° E. at an angle of 80°, and therefore lies nearly normal to the pseudostratification of the gabbroic country rock. This pipe is composed mainly of coarse-grained brown hortonolite dunite, which is interspersed with large clusters of black anhedral hornblende, books and aggregates of phlogo-pite ranging up to 6 inches in diameter, and clots and larger masses of lustrous titaniferous magnetite. Segregates of ilmenitite up to 3 feet in diameter are present. The hortonolite dunite merges rather gradually outward into the bounding olivine dunite. Pegmatitic veins composed of large crystals of diallage, phlogopite, hornblende, magnetite, and ilmenite in two systems of veins, with thicknesses from 1 inch to 4 feet, run parallel to the ore body. These veins appear to contain little platinum. Most of the platinum metals occur in the native state, but Wagner (1929, p. 219) records the fact that platiniferous sulfides occur in veins and chromitic schlieren along the hanging wall of the large pipe. Sperrylite and cooperite have also been identified in the main ore body below water level. The sulfides include pyrrhotite, pentlandite, and a little chal-copyrite. The tenor of platinum in the workable pipe of the Mooihoek mine ranged from 0.01 to 1.0 ounce per ton of ore, with an average tenor of about 0.13 ounce. The platinum metals occur throughout the workable pipe, but they increase from the margin of the pipe inwards to the center, where they are highest. Thus, a winze sunk down the middle of the pipe showed an average value of 2.1 ounces per ton, whereas the mean tenor for the 350-foot level of the mine was 0.34 ounce. The character and percentages of the six platinum metals have not been recorded. A section of the mine, published by Wagner (1929, p. 72), shows the underground workings down to the 450-foot level and crosscut. Mining has been discontinued. The Onverwacht mine was located on another pipe, similar to that at the Mooihoek mine. This pipe is an irregular but roughly parsnip-shaped segregate, or possibly intrusive, of hortonolite dunite and hortonolite wehrlite, within a much larger, steeply inclined pipe of olivine dunite that bears a transgressive or discordant relationship to the surrounding country rock. The olivine dunite at and near the surface is altered to serpentinite, which is cut by a network of veins and seams of magnesite. These secondary features disappear in the mine below a depth of 300 feet. The hortonolitic ore body crops out as a roughly circular area of coarse-grained rock with a radius of about 25 feet, surrounded by a finer grained shell of the same rock with a thickness of about 5 feet. This pipe plunges S. 28° E. at an angle of about 78° which is roughly normal to the stratiform sheets of bronzitite that constitute the country rock. Wagner (1929, p. 64) believes that these stratiform sheets were intruded in a horizontal position, and therefore that the pipes of olivine dunite, hortonolite dunite, and wehrlite had originally a vertical attitude. The radius of the hortonolitic pipe increased downward for a short distance, and then decreased to the 350-foot level of the mine, where it split into three smaller bodies. The largest of these roots continued downward to and below the 750-foot level, where it had a radius of about 11.5 feet. The other two roots disappeared below the 450-foot level. The principal or central part of the ore body consists of rather coarse-grained hortonolite dunite and wehrlite, wherein the hortonolite occurs as crystals that range in size up to a maximum diameter of 2 inches. Black anhedral crystals of hornblende are also present, and the rock is interspersed with patches and schlieren of phlogopite in leaves up to 8 inches in diameter. On the 200-foot level the ore contained clots of titaniferous magnetite, and on the 250-foot level and elsewhere in the mine, the ore included large xenoliths and slabs of chromitite. The platinum metals are so distributed that the tenors are highest in the central or axial zone of the pipe and decrease toward its periphery. In the upper levels the central part of the pipe had an average tenor of 1 ounce of platinum metals per ton of ore. Another zone of enrichment was in and along the borders of the bodies of chromitite; and along one such contact, ore was found that had a tenor of 55 ounces per ton. The best average ore was on the 250-foot level, where the mean tenor was 0.92 ounce per ton. With depth, however, the ore grew leaner; and between the 550-foot and 700-foot levels, the lode was barren, though workable ore was again found between the 700-foot and 800-foot levels. Mining has been discontinued. Native platinum alloys constitute most of the platinum metals recovered from the upper levels of the Onverwacht mine, but in the lower levels about 25 percent of these metals come from sperrylite and cooperite. The number and character of the platinum alloys have not been determined, but two inferior analyses of some of the native metals have been pub-44 ECONOMIC GEOLOGY OF THE PLATINUM METALS lished by Wagner (1929, p. 19). These samples were handpicked, and therefore the base metals may be regarded mainly as dross. The mean of these two analyses, with and without the dross, are shown respectively as A and B in table 21. Table 21.—Analyses, in -percent, of platinum metals at Onverwacht mine A B Platinum________________________________ 84. 46 97. 40 Iridium plus osmium_____________________ 1. 63 1. 88 Rhodium_________________________________ .20 .23 Palladium_______________________________ .42 .49 Iron____________________________________ 12. 41---------- Copper__________________________________ .64------------- Nickel__________________________________ .24------------- Total............................ 100.00 100.00 PNEUMATOLYTIC, HYDROTHERMAL, AND CONTACT METAMORPHIC ORES Pneumatolytic and hydrothermal ores are best exemplified by a group of deposits in the Waterberg district, about 8 miles west-northwest of Naboonspruit. These consist of brecciated quartz lodes that lie in felsite and felsitic tuff, close to the Red granite, in the upper part of the Bushveld igneous complex. The principal one of these lodes and another lode branching from it were worked in 1924-26, but mining was finally discontinued because the platinum ores, though of high tenor, were erratically distributed with much ore of very low grade between the rich ore shoots. The principal lode has a thickness of 6 to 60 feet, and can be traced at the surface in a direction about N. 55° E. for 21/2 miles. The dip of the ore body is from 60° to 75° SE. A branch from the main lode has a thickness of 4 to 30 feet, and is traceable east-northeast for a distance of about 1,240 feet. Some of the richest ore came from this branch lode. Both the main lode and its branch consist of closely spaced stringers of quartz, separated by irregular bodies of felsite. The ore consists of opaque white quartz in a comb structure with the crystals oriented normal to the walls. Other phases of the ore led to the conclusion that there were at least four stages of brecciation and deposition of quartz and chalcedony. The ore minerals are specularite and other iron oxides, sericite, chromiferous chlorite, kaolin, and pyrolusite. Native platinum alloys occur in these ores in grains ranging in size from 0.04 to 0.6 millimeter. A part of the platinum metals are intergrown with specularite ; another part of later origin is embedded in iron oxide derived from the oxidation of pyrite. Chemical analyses indicate that the ratios of platinum to palladium in the main and branch lodes are respectively 13:1 and 1.6:1. The other platinum metals were appar- ently not identified, but may be present in small amounts. The tenors in gold range from 0.4 percent in the main lode to 3.0 percent in the branch lode, so that these are platinum ores with gold as merely a small byproduct. The tenor of the platinum metals in high-grade ore shoots was remarkably high. Ore taken over a stretch of 50 feet in the main lode, over a width of 20 inches, had a tenor in platinum metals of 5.4 ounces per ton, and for the same distance along the branch lode, over a width of 35 inches, the ore had a tenor in platinum metals of 51 ounces per ton. Picked samples had still higher values. The genesis of these siliceous platinum ores is problematical. The brecciation and the ore minerals led to a belief that they were formed at no great distance below the surface initially as pneumatolytic deposits and were followed in the waning stages of mineralization by hydrothermal deposition. Hot springs are still present in the vicinity of these lodes. The general character of the ores suggests their derivation from an underlying persilicic intrusive, but the presence of chromitiferous chlorite suggests that the ores may have come from basic or ultrabasic intrusives. A composite origin is strongly suggested. Siliceous lodes that contain platinum are known elsewhere in the world, and in fact, 23 such occurrences are tabulated on page 98 of this report. Most of these deposits, however, are gold-quartz veins, with a byproduct of platinum metals. A contact metasomatic deposit occurs near the magmatic deposit 11 miles northwest of Potgietersrust, that was described above. This ore body is in the so-called Dolomite series, which is that part of the Transvaal system which directly underlies the Pretoria series. The ore deposit consists of several zones of crushed dolomite in a thick bed of banded ironstone, which dips steeply west, and the ore comprises lenses, eyes, and irregular bodies of graphic granite and pegmatite that contain copper and nickel sulfides, with which are associated sperrylite and stibiopalladinite. This locality is the site of the original discovery of stibiopalladinite. The deposit is considered to be too low grade for mining. The Merensky reef has been traced intermittently for 25 miles north-northwest of Potgietersrust, and also for a short stretch south of that town. A platinum deposit that is genetically related to the Merensky reef, but not an integral part of the reef, is particularly well developed in the zone between Vaalkop and Zwartfontein, where it was formerly mined. This deposit is a sinuous lens about 11,000 feet long and about 145 feet thick, which conforms with the pseudostratification of the intrusive sheets, and strikes generallyREPUBLIC OF SOUTH AFRICA 45 north-northwest with a westward dip of about 55°. The ore body may be either of magmatic or contact metamorphic origin. In its southern part, where dominantly pseudomagmatic, the ore carrier is coarsegrained feldspathic pyroxenite and pegmatitic norite, with a hanging wall of coarse-grained anorthositic norite and a footwall of fine-grained rock of the same kind, but in its northern zone, the ore is composite, consisting in part of platinum-bearing bronzitite and in part of overlying and underlying silicated dolomite that is also platinum bearing. The true Mer-ensky reef in this area lies generally above the Vaal-kop-Zwartfontein body, and commonly contains few or no platinum metals. Platinum metals occur in the southern sector in concentrations of pyrrhotite, pentlandite, chalcopyrite, and cubanite, which commonly are intergrown with hornblende both in the principal ore carrier and in the contiguous hanging wall and footwall. The platinum minerals are reported to be sperrylite and coop-erite, but they include both platinum and palladium which are probably included in a number of different minerals. In the northern sector, where the ore of highest grade occurs, the sulfides that are contained in the intrusive rocks and dolomite are not uniformly distributed, but occur instead in irregular ore shoots, the locations of which require careful prospecting and sampling. Northern, central, and southern parts of the northern, or Zwartfontein, sector are described in detail by Wagner (1929, p. 168-182), and cannot very well be summarized. The central and most important ore body of this northern sector has a known length of 3,500 feet, a thickness of 90 feet, and an average dip of 70° westward. For the whole ore deposit the platinum-bearing sulfides are as given above, and range in size from 1.0 millimeter to 1.5 centimeters, but in the contact metamorphic ores, the average size is about 4 millimeters. The mean tenor is platinum metals for the entire ore body is about 0.35 ounce per ton of ore, but in picked samples is as large as 2 ounces. From the concentrates produced in the last quarter of 1928, the ratios of the platinum metals, according to Wagner (1929, p. Ill), are platinum 55.4 percent, iridium, osmium, ruthenium, and rhodium 2.4 percent, and palladium 42.2 per cent. This deposit was actively worked before the discovery of the Merensky zone in the Rustenberg district, but mining in later years has been discontinued. PLACEKS OF THE WITWATERSRAND DISTRICT Detrital platinum has been found at numerous localities in South Africa, but none of these deposits is of present commercial value. Reference has already been made to the placers of the Lydenburg district, where platinum mining was first begun, though soon discontinued. A well-known lithified osmiridium placer is the so-called Black Reef conglomerate which is a part of the Black Reef series, that constitutes the upper 15 percent of the Transvaal system. This deposit is the site of a mine operated by the Government Gold Mining Areas (Modderfontein) Consolidated, Ltd., north of Johannesburg. The tenor of osmiridium at this property is high. The principal commercial lithified placers, however, are those of the Witwatersrand, which occur in the southern part of the Transvaal and the northern part of the Orange Free State. HISTORY AND PRODUCTION The gold deposits of the Witwatersrand consist of lithified placers that are mined as lode deposits. Osmiridium in this area, according to Wagner (1929, p. 33), was first identified by William Bettel in concentrates from the conglomerate (banket) of the New Ri-etfontein mine, in Orange Free State, in 1892. The first published description of the osmiridium was given by Young (1907, p. 17-30), but additional data were soon published by other workers. No attempt was made to save this osmiridium from 1892 to 1920, because the gold was saved by amalgamation, which was unsuited to the recovery of platinum metals. Beginning in 1921, however, a preliminary concentration began to be made on corduroy and blankets. This process permitted a production of osmiridium. The East Rand Proprietary Mines, one of the largest goldmining companies in the world, controls 8,785 claims and has underground workings that extend 7y2 miles along the strike of the auriferous reef and 314 miles along its dip. These workings, as recently described by Anderson (1958, p. 321-325), underlie about 20 square miles of the municipalities of Germis-ton and Boksburg, southeast of Johannesburg. In May 1958, this mining had reached a depth of 11,000 feet, equivalent to about 1 miles below sea level. Much of the osmiridium produced in the Witwatersrand district comes from the different properties of the East Rand Proprietary Mines. The conglomerate of one of these, which is the site of the Modderfontein “B” mine, has been proved to have the highest tenor in osmiridium, as well as gold. Osmiridium is also recovered from properties in the West Rand. The search for deeper deposits continues, and in 1962 the Anglo-American Corp. of South Africa, Ltd., sank a drill hole to a depth of 14,100 feet. The site of this hole was about 120 miles southwest of Johannesburg, and about 5 miles east of Bothaville, Orange Free State. This probe passed through the Karroo. Trans-46 ECONOMIC GEOLOGY OF THE PLATINUM METALS vaal, and Ventersdorp systems to reach the gold-bearing conglomerates of the Witwatersrand system. The output of osmiridium from the Witwatersrand, in the Transvaal and Orange Free State, has remained sensibly constant since 1925, and is likely to continue so, because it is a byproduct of the regional production of gold, which changes little. In 1958 and 1959, however, the output of osmiridium decreased because the production of gold was curtailed, but both the osmiridium and the gold outputs are again increasing. The production of osmiridium from the Witwatersrand from 1921 to 1960 has been shown by Quiring (1962, p. 101) to be approximately 231,125 ounces. Adding to this the outputs for 1961-65, the total production from 1921 to 1965 inclusive is seen to be 248,625 ounces. A maximum production of 7,780 ounces was made in 1942. GENERAL GEOLOGY The Witwatersrand system, consisting of bedded rocks of terrestrial origin, rests unconformably upon the rocks of the Swaziland system, which is the basal complex of this region. The Ventersdorp system, over-lying the Witwatersrand system, consists dominantly of andesitic lavas and pyroclastics, and both systems are considered to be of late Precambrian age. According to Furon (1963, p. 341), the thickness of the Witwatersrand system is about 28,000 feet; and according to Coet-zee (1960, p. 31-92), the thickness of these two systems is about 40,000 feet. Many local disconformities and unconformities exist in the Witwatersrand system, and the beds therefore show divergent thicknesses at different localities. The auriferous conglomerates of the Witwatersrand are ancient lithified placers, which comprise numerous strata with an aggregate thickness of about 2,000 feet and a maximum individual thickness of about 65 feet. The rocks of the Witwatersrand system, in the Transvaal and Orange Free State, are folded into a large syncline with a major axis trending east-west, a length of about 110 miles and a width of about 45 miles. In the Johannesburg area, these rocks form the north flank of the syncline, and dip steeply south, though they flatten with depth to 30°. Near Parys, the synclinal structure is modified locally by a quaqua-versal anticline. Owing to erosion and to the cited dome, the rocks of the Witwatersrand system crop out mainly at four separated areas, that is, near Johannesburg, Heidelburg, Parys, and in an area between Ventersdorp and Klerksdorp. DEPOSITS The gold and platinum of the Witwatersrand occur in thin beds of conglomerate and grit, known as reefs, which form the upper part of the Witwatersrand system. Several groups of these reefs have been recognized, including the Main Eeef and Livingston group, near the base of the Upper Witwatersrand series, the Bird Eeef group 1,600 feet higher in the sequence, and the Kimberly or Battery Eeef group 5,000 feet strati-graphically above the Main Eeef group. The principal production comes from the Main Eeef group of reefs, which are mined in the Johannesburg area over an east-west extent of about 50 miles. The Main Eeef group includes three productive reefs, which named from bottom to top are the Main Eeef proper, the Main Eeef Leader, and the South Eeef. In the central part of the Johannesburg area, these three reefs are of equal size, but the Main and South Eeefs extend eastward only as far as Boksburg, and the Main Eeef extends westward about 11 miles. The Main Eeef Leader has the greatest overall extent, and has been the principal producer of gold. These reefs are locally persistent, but are nonper-sistent over great distances, and vary considerably in thickness. Individual ore shoots have east-west and north-south dimensions that range respectively up to 5,000 and 1,000 feet. The beds of conglomerate in the Upper Witwatersrand system range in thickness from an inch to 15 feet, and in the Main Eeef group from 1 to 10 feet, with thin intercalations of quartzite. The average thickness of the Main Eeef, the Main Eeef Leader, and the South Eeef are respectively 4, 2, and 3 feet. The platinum metals are exceedingly scarce, but are most prevalent in the Main Eeef Leader on the Far East Eand, less so on the West Eand, and are least plentiful in the Central Eand, where all the reefs of the Main Eeef group are thickest. Both the gold and the platinum metals are found to be most plentiful in conglomerates that have large pebbles. In the Main Eeef Leader, these pebbles have a mean diameter of 2 inches, and consist mainly of quartz, with less quartzite, chert, and slate. The sandy matrix, in which the noble metals mainly occur, contains a large volume of secondary pyrite, estimated in the Main Eeef Leader to constitute 3 percent of the ore. The gold occurs in minute angular crystalline aggregates, generally in direct association with the pyrite. Other ore minerals that are present in small amounts are pyrrhotite, galena, sphalerite, chalcopy-rite, cobalt arsenide, uraninite, and the platinum metals. The sandy matrix has been recrystallized, with the development of secondary quartz, sericite, chlorite, chloritoid, carbon, and calcite. Tourmaline, zircon, and rutile are also present, but these are probably original accessory minerals of the conglomerates. Less resistant accessory minerals, such as the iron ores, have been de-REPUBLIC OF SOUTH AFRICA 47 stroyed in the process of recrystallization, and probably constitute the sources of the pyrite. The gold is exceedingly fine grained, and has not in general retained its original detrital form. The platinum metals, however, have resisted recrystallization and show rounded outlines, or at least rounded edges of the crystalline grains, that indicate their detrital origin. The platinum metals are exceedingly fine grained and range in size at one mine, according to Wagner (1929, p. 36), from 0.04 to 0.19 millimeter in diameter. At a mean diameter of 0.12 millimeter, such particles would have a value of about 0.012 cent, meaning that it would take 800,000 particles to weigh a troy ounce. The tenor of platinum metals is almost unbelievably low. Thus in the Modderfontein “B” banket, which contains more osmiridium than at any other mine in the Witwatersrand, the recovery, according to Wagner (1929, p. 35-36), is from 1 ounce per 1,212 tons of milled ore to 1 ounce per 9,285 tons of milled ore, or from 0.000003 to 0.0000004 percent. These figures, however, represent the amounts recovered, which probably are only about half of those actually present in the conglomerates. The detrital origin of the gold and platinum metals of the Witwatersrand is favored by practically all South African geologists who have had a professional familiarity with these ores. The acknowledged fact of recrystallization, with solution and redeposition of the gold, however, has led some to believe that the noble metals are epigenetic and hydrothermal in origin, with sources extraneous to the conglomerate. Probably the most ambitious formulation of an epigenetic hypothesis was made by Graton (1930, 185 p.), who, notwithstanding his many contributions to the theory of ore deposits, was unfamiliar with placers. Consequently, he failed to evaluate the evidence for a detrital origin of these deposits; in particular, he overlooked the rounded and subrounded form of the grains of platinum metals. A few other geologists, in particular Davidson (1953 and 1955), have also accepted Graton’s interpretation. Evidently, owing to their great resistance to the chemical processes attendant upon weathering, the grains of osmiridium, unlike the detrital gold, have not been dissolved and redeposited, but instead have maintained their original form and character. It is generally admitted that the gold and osmiridium were deposited simultaneously. It therefore follows, without the cogent collateral evidence, that all the precious metals of the Witwatersrand originated as detrital deposits. The exact sources of the gold and platinum metals are not definitely known, though granitic intrusives within the Swaziland system, are known to be mineralized with gold, tin, and columbite, Most geologists familiar with these deposits believe that these metals were transported for a long distance from bedrock sources to the northwest or north-northwest that are now either eroded or overlapped by younger geological formations. It is certain that these bedrock sources are not directly related to the platinum-bearing intrusives of the Transvaal, as the former are millions of years older than the latter. Probably the noble metals of the Witwatersrand were contained in sediments that were transported by and deposited from a large river that built a delta close to the sea. CHEMICAL COMPOSITION Data are shown in table 22 on the composition of these platinum metals, which appear to be mainly osmiridium (iridosmine). It must be stated, however, that these chemical data are inferred from the records of production, and are not based directly upon chemical analyses. It is believed by Wagner (1929, p. 36-37), that two or more alloys are present, and as this is probably true, it follows that the cited compositions of the osmiridium are analogous to chemical analyses of bulk samples of unseparated alloys, like most analyses of placer samples. Table 22.—Composition, in percent, of osmiridium from W itwatersrand [N.D., no data] Plati- num Irid- ium Os- mium Ruthe- nium Rho- dium Ruthe- nium and rhodium Palla- dium Total Ai _ 13.02 32.00 37.24 17.21 0.53 N.D. 100.00 . 9.64 33.29 42. 57 14.28 .22 N.D. 100.00 . 7.67 37.54 42.46 12.19 .24 N.D. 100. 00 a4._ . 6.70 39.16 43.46 10. 51 .17 N.D. 100. 00 . 9.19 35.56 41. 46 13.50 .29 N.D. 100. 00 Bi- . 15.70 36. 55 41. 36 N.D. N.D. 15. 41 N.D. b2.. . 4.48 22.07 24.82 N.D. N.D. 10. 29 N.D. Bm- . 11.82 34. 35 38. 77 N.D. N.D. 15. 06 N.D. 100. 00 c... . 13.43 33.13 37.28 15. 63 .53 N.D. 100. 00 D... . 13.67 32. 58 37.09 15.82 .84 N.D. 100. 00 Ei.. . 18.99 40. 55 44.60 16.83 1.04 N.D. . 3.89 21. 33 24.13 8. 73 .34 N.D. Em-. . 12.68 34. 29 38.10 14.17 .76 N.D. 100. 00 Weighted mean . 12.86 33. 54 37.87 15.03 .70 N.D. 100.00 Ai, A2, A3, A4, and Am. Four analyses and their mean value that show variations in composition at four different mines (Wagner, 1929, p. 37). Bi, B2, and Bm. Two analyses and their mean value that show the maximum (Bi), minimum (B2), and mean (Bm) compositions at most of the large mines (Wagner, 1929, p. 38). C. The mean composition of the platinum metals sold in a period of 10 years during the period 1925-34 (Imperial Institute of Great Britain 1936, p. 60). D. The mean composition of the platinum metals sold in a period of 17 years within the interval 1927-49 (U.S. Bureau of Mines, Minerals Yearbooks 1928-50). E. Two analyses and their mean value that show the maximum (Ei), minimum (E2), and mean (Em) compositions of the platinum metals for 15 years prior to 1950 (U.S. Bureau of Mines, Mineral Yearbooks, 1950). The bulk composition of the platinum metal of the Witwatersrand is shown in table 22. Omitting Ai, A2, A3, A4, Bj, B2, E and E2, and weighting Am, Bm, C, D, and Em respectively at 4, 2, 10, 17, and 15, the weighted mean of the five metals are found to be as shown in table 22. The individual analyses conform fairly well48 ECONOMIC GEOLOGY OF THE PLATINUM METALS for iridium, osmium, and ruthenium, the three major constituents, but for platinum some significant differences appear. The tenors of osmium are consistently greater than those of iridium by values ranging from 2.75 to 9.28 percent, with an average value of 4.46 percent. Hence, this product may be called iridosmine, if use is made of that term. Euthenium, which commonly occurs with osmium, shows relatively consistent values. The values of platinum, however, range between limits of considerable magnitude, from 4.48 to 18.99 percent. This range suggests that a part of the platinum is alloyed with osmiridium, but that another part may be constained in a minor alloy of platinum that contains considerable iridium but little osmium. Palladium is not shown in these analyses, possibly because its tenor is of the order of mere traces. The ratios of the two postulated alloys could be learned only by determining the composition of one of them. CAPE OF GOOD HOPE PROVINCE Platinum has been found in widely separated areas in the Cape of Good Hope province, but only one of these deposits appears to have any possible significance. The recorded localities are as follows: 1. Dike in altered dolerite, near Cradock. 2. Dike in weathered dolerite and in derived elu- vial and alluvial beds near Cala, about 80 miles north of Queenstown. 3. Ocherous shale of the Witteberg series of the Karroo system, near Grahamstown. 4. Small bodies of basic and ultrabasic rocks near Tabankulu, in the district of Griqualand East. 5. A large sill of basic and ultrabasic rocks in Beau- fort volcanics of the Karroo system, near Insizwa, district of Griqualand East. The Insizwa deposit appears to be the most promising of these. According to du Toit (1911) and Wagner (1929, p. 255), this sill has a length of about 12 miles, dipping everywhere toward its center, and thus it simulates a lens-shaped body with a major axis that trends approximately north. This intrusive is mainly gabbro and norite, differentiated to yield at its base a thin sheet of fine-grained perknitic dunite, or picrite. The platinum-bearing minerals occur in the picrite, either in disseminated form, or in veins and tabular masses of massive sulfide ore. The sulfides include pyrrhotite, pentlandite, cubanite, and chal-copyrite, with smaller amounts of bomite, niccolite, and sphalerite. The average tenor of platinum metals, on the basis of exploration so far done, is between 0.025 and 0.05 ounces per ton of ore. The best available information indicates that palladium greatly pre- dominates over platinum. Considerable exploratory work was done on this deposit in 1962, by a large South African mining company. REPUBLIC OF THE CONGO (KATANGA) The province of Katanga, in the east-central part of the Eepublic of the Congo (formerly the Belgian Congo), and the adjacent part of Zambia (formerly Northern Rhodesia) have large deposits of copper and copper-cobalt ores from which significant amounts of the platinum metals, as well as gold, iron, nickel, lead and zinc are being recovered as byproducts. The total output of platinum metals from electrolytic refineries, in the period 1930-58, according to Quiring (1962, p. 97) was about 52,760 troy ounces, with a maximum output in 1936 of about 15,740 ounces. The copper and copper-cobalt mines lie within a parabolic belt with a northern axis and a total length of about 750 miles. The average width of the belt is about 35 miles. Most of the deposits are in Katanga and adjacent parts of Zambia. Seventeen lodes of copper and 10 lodes of copper-cobalt lie between lat. 10° and 14° S., and between long. 24°30' and 29°30' E. Four other copper lodes occur farther to the southeast. The production data on platinum metals from these mines, as given by Quiring (1962, p. 97), establish a platinum: palladium ratio of 1:4. RHODESIA Platinum was found in 1914 in a cobalt-nickelbearing chromite in the Selukwe district, between Gwelo and Fort Victoria, and in 1918 in a hematitic gossan of dunite near Indiva, about 15 miles east of Gwelo. These and other occurrences of the platinum metals, however, attracted little attention until after the discovery of platinum deposits in the Lydenburg district. Thereafter intensive prospecting was done in Rhodesia on the Great Dike (Great Dyke), an elongate mass of ultrabasic and basic igneous rocks which intrudes the granite that is the principal bedrock of the eastern half of Rhodesia. The Great Dike stretches continuously in a nearly straight line, trending S. 15° W. for about 320 miles from the headwaters of the Masin-gua River to the headwaters of the Bubi River. At its northern end, it terminates in a hook-shaped configuration, and beyond its southern end, it continues in intermittent outcrops for an additional 50 miles. The width ranges from 2 to 7 miles, with a mean width of about 4 miles. The layered sheets of this intrusive dip at gentle angles from both sides toward its center. This dike has been called a lopolith, but its structure and genesis have not been definitely proven. The petrographic succession of rocks, according to Swift (1961, p. 39), consists of a principal basal massETHIOPIA 49 composed of layers of pyroxenite and serpentinite. A drill hole at Wedza, bored to a depth of 5,000 feet, showed that the deeper part of this basal mass is entirely dunite, for which reason the surficial serpentinite is attributed to the effects of meteoric rather than magmatic waters. Small xenoliths of granite afford proof of the intrusive origin of the dike. Above the pyroxenite and serpentinite is a layered minor succession of gabbro and norite, with smaller amounts of pyroxenite, which therefore constitute the central part of the synclinal igneous structure. Two types of platinum-bearing ores have been found in the Great Dike. One consists of stratiform seams of chromite in the serpentinite, ranging in thickness from 4 to 6 inches, with a maximum recorded thickness of 14 inches. From five to 10 such seams crop out in different areas. They appear to be of no economic significance. The principal ores occur in a sheet of pyroxenite which lies 20 to 60 feet below the base of a feldspar-rich norite. These ores have been found at three principal localities. The most important of these lies in the Belingwe district, near the southern end of the intrusive, and includes the well known Wedza mine, about 15 miles west of Sha-bani. This deposit, which consists of a large volume of oxidized ore in pyroxenite, occurs in a reef 8 to 10 feet thick, of which the uppermost 3 to 4 feet showed tenors in platinum of 0.15 to 0.20 ounce per ton of crude ore. This property was mined in the period 1926-28, and 1,338 tons of concentrates, with platinum tenors ranging from 15 to 258 ounces per ton, were shipped to London. An examination of these concentrates proved the presence of minute octahedra of sperry-lite and very small flattened crystals of cooperite, which are believed to be enclosed in iron-copper-nickel sulfides. A second area is the Makwiro platinum field, about 165 miles north-northeast of the Wedza mine and about 18 miles west-southwest of Norton. The platinum at this locality occurs in a pyroxenitic sheet of the Merensky type, which lies about 30 feet below the feldspar-rich norite. The ore contains iron and copper minerals and is irregularly distributed, with a maximum tenor in platinum metals of 0.15 ounce per ton. A third area is in the Selundi Hills, about 45 miles north-northeast of the Wedza mine and a few miles east of Selukwe. The Great Dike has been shown by Cousins (1959, p. 186-188) to be merely one of a chain of basic and ultrabasic intrusives that lie approximately along a straight line that trends S. 20° W. from a short distance south of the Zambesi Diver, in Rhodesia, nearly to the Orange Diver, a distance of about 1,000 miles. This line passes through the Bushveld igneous complex west of Potgietersrust, and it may extend south of the Orange River to some of the occurrences of basic and ultrabasic rocks in the Cape of Good Hope Province. Cousins believes that this line marks the position of a fracture in the crust of the earth that may extend to a great depth. ETHIOPIA Platinum was first produced in Ethiopia by Europeans in 1925, but platinum is known to have been purchased long before that date by itinerant traders, who probably smuggled it through the Sudan into Egypt. From 1927 to 1940, Ethiopia was a rather important producer of the platinum metals, but in recent years the output has greatly diminished. Quiring (1962, p. 93-94) has estimated that the total output, from 1926 to 1959 was about 90,200 troy ounces, with a maximum production of 8,230 ounces in 1940. Platinum was produced in the early years from two general districts, in the valleys of the Didessa and Bir Bir Divers, and a declining production indicates that no new discoveries have been made and that these remain in the two principal districts. Information is lacking on the Didessa district, but the Bir Bir district was studied by Duparc and Molly (1927), whence come the only geographic and geologic data. The province of Wollega lies west of the province of Shoa, south of the province of Gojjam, and has an area of about 30,000 square miles. Wollega includes some smaller districts, whose names are no longer recognized. The Bir Bir River flows generally south-south-westward to the Baro River, which empties into the Sobat River, which is an eastern tributary of the Bahr el Abiad (White Nile) River; the Didessa River, against which the Bir Bir heads, flows northwestward into the Bahr el Azraq (Blue Nile) River. This platinum field is in a remote area, about 220 miles west-southwest of Addis Ababa, and is difficult to reach from Addis Ababa, or from the head of navigation on the Baro River. The productive area in the Bir Bir district is near Yubdo, which is on the west side of the Bir Bir River, on a plateau in which this stream is entrenched. This plateau consists of two well-defined ridges, the Yubdo ridge trending north and the Sodo Ridge trending northwest. The Yubdo ridge lies between the Bir Bir and Kobe Rivers, and its northern extremity is separated from the Sodo Ridge by a western tributary of the Bir Bir River, called the Alfe River. The plateau consists of a basement of ancient crystalline rocks, with may silicic and a smaller number of basic intrusives, mantled by basaltic, trachytic, and other volcanic rocks of Tertiary age. To the east, a sequence of Meso-50 ECONOMIC GEOLOGY OF THE PLATINUM METALS zoic rocks lies between the crystalline rocks and the Tertiary volcanics. The Yubdo and Sodo ridges consist mainly of dunite bordered by pyroxenite, which in turn is bounded discontinuously by gabbroic rocks. At some places where dunite forms the crests of these two ridges, there occurs a well-indurated brownish quartzite, which has been produced by the silicifica-tion of dunite. This rock, which contains 9 percent Fe203 and 1 percent Cr203, has been called a bir-birite by Duparc and Borloz (1927, p. 137-139). This weathered rock extends below the surface to a depth of 10 to 15 feet, and contains platinum, of which an analysis is later presented. Much of the platinum in this field, however, is recovered from deposits of red clay that mantle the tops and slopes of the hills over an area of about 100 square miles. This represents residual and eluvial material derived from the ultrabasic and basic rocks. Another part of the platinum is recovered from gold-platinum placers in the valleys of the Bir Bir and Didessa Rivers and their tributaries. Data relating to the character of the platinum are lacking, nor are the accessory minerals of the concentrates recorded. It is reasonably certain, however, that chromite is one of these, as the platinum metals resemble closely those from the Urals. The largest nugget found is said by O’Neill and Gunning (1934, p. 134) to have come from the Didessa River, or one of its tributaries, and to have weighed 0.48 troy ounce. Two analyses of the platinum metals are available. One, designated below as A, was made by Duparc of a cleaned sample from the birbirite, and this was republished by The Imperial Institute of Great Britain (1936, p. 96). A second analysis, designated as B, was made by Johnson, Matthey and Co., Ltd. These two analyses, and their mean value (C), recomputed to total 100 percent, are as follows: Analyses, in percent, of platinum metals, Bir Bir district, Ethiopia [N.D., no data] A B c Platinum _ . . _ 95. 82 94. 60 95. 21 Iridium _ _ _ _ .99 . 84 . 92 Osmium plus iridium 1. 70 3. 48 2. 59 Ruthenium. _ _ N.D. N.D. . 85 Rhodium .... .90 . 80 N.D. Palladium. _ _ .59 . 28 . 43 Total 100. 00 100. 00 100. 00 SIERRA LEONE Platinum was first discovered in Sierra Leone in 1926, and placer mining began in 1929 and continued until 1957, after which no production has been recorded. The total output from 1929 to 1957 is estimated by Quiring (1962, p. 93-94) to have been about 5,560 troy ounces, with a maximum production of about 740 ounces in 1935. The productive area has been confined to a small peninsular area that extends from Freetown, on the Atlantic coast southeastward for about 25 miles, with a maximum width of 8 or 9 miles. This peninsula is bounded on the northeast by an inlet from the ocean, on the south by Yawri Bay, and on the west by the Atlantic Ocean. The entire peninsula is a rugged and densely forested mountain mass that rises to an altitude of 3,000 feet, and is deeply dissected by numerous mountain streams with high gradients and boulder floors. Mining is impracticable during the wet season, and therefore is carried on from October to June. The peninsula consists of a large basin-shaped body of basic and ultrabasic rocks, of which the western part, adjacent to the ocean, has been removed by erosion. This is indicated by the fact that the same rocks crop out on Banana Island, which lies offshore to the southwest. These rocks have a well-defined primary banding of stratiform character. The lower part of the intrusive mass is mainly olivine norite or troctolite, whereas the upper part is somewhat less basic. Two large lenticular sheets of coarse-grained anorthosite and anorthositic gabbro have been recognized, and these are believed to be the sources of the platinum metals, as all streams which dissect them have platinum-bearing gravels. The platinum metals recovered from the placers are coarse grained, and numerous nuggets weighing between 0.25 and 0.52 ounce have been found. One nugget weighed 1(4 ounces. The larger nuggets are invariably waterworn, but small angular grains of crystalline character are also present. A part of the platinum is ferromagnetic. The principal minerals of the concentrates are titaniferous magnetite and ilmenite, and platinum is found adhering to grains of ilmenite. One chemical analysis of the platinum has been published by The Imperial Institute of Great Britain (1936, p. 42). This analysis, recomputed to total 100 percent, is platinum 93.14, iridium 1.01, osmium plus iridium 2.82, rhodium 1.29, palladium 1.74, ruthenium not determined. The absence of osmiridium is indicated. A geologic exploration has recently been made of this district by a large South African mining company, to determine if possible the bedrock sources of these platinum metals. This work failed in its principal objective, and led to an interpretation that the platinum metals occur in widely disseminated grains, which over a very long period have been concentrated by weathering and erosion to form the present placers.UNION OF SOVIET SOCIALIST REPUBLICS 51 UNION OF SOVIET SOCIALIST REPUBLICS HISTORY AND PRODUCTION Platinum was discovered in the stream gravels of the Ural Mountains, according to Sobolewsky (1835), in 1822, and production of the platinum metals began in 1824 and has continued to the present time. At the outset, ruthenium and palladium were not recognized, and even the analyses shown in table 23 do not mention the presence of ruthenium. These placers were slowly depleted, and a search was begun for platinum lodes. Primary ores were found in the Urals in 1890, but proved not to be of the kind that yielded large workable mines. Sometime in the thirties, however, lode deposits of nickel-copper ores containing the platinum metals were found in northwestern Siberia, in the vicinity of Noril’sk. As a result of the development of these and other lodes, and notwithstanding the lessened output from the Uralian placers, the platinum production of Russia has been increasing for some years. Other lodes and some smaller placers have also been found in the U.S.S.R. Among these are the lodes of the Petsamo district, a part of which formerly belonged to Finland. The production of platinum metals by the U.S.S.R. is approximately known, but it is impossible to separate the placer from the lode outputs. According to the figures presented by Quiring (1962, p. 93-94), the production from 1823 to 1960 has been 12,886,000 ounces, to which should be added 5,300,000 ounces credited to the U.S.S.R. in the years 1961-65. The total production is therefore about 18,186,000 ounces up to and including 1965, which is about 42^ percent of the world’s production. A maximum output of placer platinum, amounting to 241,125 ounces, was made in 1912. The largest production, coming from both lodes and placers, was 1,700,000 ounces and was obtained in 1965. URAL MOUNTAINS LODES Primary ores of the platinum metals were found first in the Mshniy-Tagil district, of the Ural Mountains. These consisted of relatively small segregates of chromite, which locally contained accumulations of the platinum metals. These ores have been investigated mainly by Inostranzev (1893), Karpinsky (1926), Duparc and Tikonowitch (1920), Zavaritsky (1928), Vysotsky (1933), and by Betechtin (1930, 1935, 1961). In addition to the publications cited, Betechtin published a series of papers in the Russian language, with no abstract in any other language. The Ural Mountains lie along the western margin of a belt of basic and ultrabasic rocks, mainly of gabbroic character, which have invaded a country rock consisting of Paleozoic sedimentary rocks and older cry- stalline schists. Figure 4 shows the localities of dunite in the Ural Mountains. The ultrabasic rocks occur in 11 ovaloid dome-shaped masses, with elongations roughly parallel to the axis of the Ural Mountains. These extend over a distance of about 300 miles, between lat 56° and 60°30/N., but the more important ones lie within a range of 190 miles. These rocks extend from a point 60 miles N. 30° W. of Sverdlovsk northward to about 20 miles In.15° W. of Severovral’sk, as shown in figure 4. The ultrabasic masses range in length from 4,000 feet to 6y2 miles and have areas from 300 acres to about 12 square miles. The principal platinum-bearing rocks are dunite, peridotite other than dunite, and pyroxenite, of which dunite is the most important source rock. The dunite is rarely completely unaltered but shows instead various stages of serpentinization. The unaltered dunite consists almost entirely of olivine in a panidiomor-phic fabric, but includes disseminated grains, pockets, stringers, and lenses of chromite. Native platinum is rarely visible in the average dunite, even under the microscope; but where present in ore deposits, it is commonly intergrown with chromite, rarely with olivine. The platinum metals, which include osmiridium, occur generally as minute isolated globules or crystalline grains; but as later described, large segregates of primary platinum have been found. Duparc and Tikonowitch (1920) estimated from the amounts of alluvial platinum metals recovered from the placers that the average tenor of these metals in the dunite of the Nishniy-Tagil area was about 0.13 grain per cubic yard. Obviously, only significant concentrations could be of economic value. The pyroxenites, which are rather constantly associated with dunite, are classified by Duparc and Tikonowitch as pyroxenite proper and koswite. The pyroxenite consists dominantly of monoclinic pyroxene, but includes also some olivine and accessory magnetite. The koswite (magnetite peridotite) is a more basic rock that contains olivine and magnetite, together with some hornblende. Hornblendite is also present. The gabbros, of which there are numerous varieties, are either barren of platinum metals or have exceedingly low tenors, amounting to mere traces. The dunites of the Urals were studied in great detail by Duparc and Tikonowitch (1920), and later by Zavaritsky (1928). These writers agree that the ultra-basic rocks of the Urals are segregates from, and not intrusives into, the gabbros. There are, however, a large variety of dike rocks which intrude both the basic and the ultrabasic rocks. The ultrabasic rocks were also affected by still later processes, such as the formation of minerals in miarolitic cavities, later by52 ECONOMIC GEOLOGY OF THE PLATINUM METALS Figure 4.—Dunite localities in the Ural Mountains. 1, Daneskin-Kamen area, drained by the Sosva and Souprei'a Rivers and their headwater affluents. 2, Gladkai'a-Sopka area, drained by the Wagram River and its tributary the Travianka River. 3, Kanja-kowsky area, drained by the Severney-Jow and the Pouloudniewa'ia Rivers. 4, Garewai'a area, drained by the Garewaia and the Jow Rivers. 5, Koswinsky-Kamen area, drained by the Kytlyn River and its headwater tributaries. 6, Sosnowsky-Ouwal area, drained by the Tilai' River and its headwater tributaries, and the Earkovka River. 7, Kamenouchky area, drained by the Niasma River and its headwater tributaries and the Sokolka River. 8, Weressowy-Ouwal area, drained by several headwater tributaries of the Iss River. 9, Swetli-Bor area, drained by the Iss River, and one of its tributaries called the Kossia River. 10, Tagil area, drained on the European side by the Wyssim, Syssim, and Martian Rivers and their affluents and on the Asiatic side by the Bobrowka and Tschauch Rivers and their affluents. 11, Omoutna'ia area, drained by the Omoutnai River, and a headwater tributary of the Tschoussowai'a River.UNION OF SOVIET SOCIALIST REPUBLICS 53 serpentinization, and still later by the formation of carbonates and other minerals of supergene origin. The dunite of the Nishniy-Tagil district is the largest intrusive of this type in the Urals and may be regarded as typical of the others. This mass, as described by Betechtin (1961) and as illustrated in figure 5, includes a discontinuous band of antigorite-serpentinite along its western side and is surrounded by pyroxenite (diallageite). The transition from dunite to pyroxenite is characterized by a rock of intermediate character called tilaite, which is composed of diopside, augite, orthopyroxene, olivine, and basic pla-gioclase feldspar. Eastward from the pyroxenite are successive gabbro, diorite (locally syenite), quartz diorite, and granite. All these rocks pass gradually into one another without sharp boundaries, and suggest complementary species resulting from magmatic or gravitative differentiation. The dunite of the Nishniy-Tagil district was thought originally to represent a batholith, but it was later proved by Zavarijtsky to be a relatively thin laccolith dipping gently eastward. This conclusion was established by gravimetric measurements, which showed that the dunite nowhere extended below a depth of 1.5 kilometers. Later, a drill hole, which was bored to a depth of 600 meters, showed no serpentinization below a depth of 450 meters. This was interpreted to mean that olivine, because it is denser than serpentine, had a superior stability at greater depth. Of possible interest with regard to genesis is the fact that a gas composed of hydrogen, nitrogen, oxygen, and the inert gases was discharged from this borehole for 2 weeks. The platinum metals of the Nishniy-Tagil district occur within the dunite in irregular masses of chromite, of which about 600 masses have been found. Many of these, however, contain little or no platinum. Generally, chromite occurs as an accessory mineral in the ((/unite, in amounts ranging from 1 to 2 percent. It is believed by Bethechtin that there existed in the silicate magma an unstable chemical compound of chromium, iron, and platinum, together with fluid components or mineralizers, which were gradually dissipated with falling temperature. The progressive disintegration of this chemical compound produced several other types of chromite deposits, which have different characteristics. The first and earliest type of ore deposit was formed by direct crystallization from the dunitic silicate magma. During this stage, the chrome ore crystallized in zones and irregular nonlinear aggregates that are characterized by indistinct boundaries and an absence of other accessory minerals. These deposits apparently were entirely of magmatic origin. In a second stage, the chromite accumulated in bodies which, though not entirely regular in outline, were distinct and sharply delineated from the adjacent dunite. These deposits were vein-like and miarolitic, and many of them showed bordering halos that contained chrome-garnet, chrome-chlorite, and dioside, rarely sulfides. These ores were found also to be related to crosscutting coarsely crystalline dikes that contained enstatite, diallage, and other minerals of a pegmatitic character. Such ores were therefore considered probably to be both hydro-thermal and pegmatitic and were believed to be contemporaneous with an early stage in the decomposition of the postulated chrome-iron-platinum compound. The third stage in the crystallization of the chromite and platinum metals yielded the more significant ore deposits. This stage apparently marked the final disintegration of the chrome-iron-platinum compound and took place when the dunite was partly congealed and was being subjected to structural dislocations. These conditions resulted in the formation of a brec-ciated but unaltered dunite with irregular cavities, which were filled with the chrome-iron-platinum compound that still retained a part of its fluid components. These deposits are sharply defined and are considered to be hydrothermal in origin. They are characterized by an abundance of accessory minerals such as chrome-garnet, chrome-diopside, and chrome-chlorite. Most of the chromite-platinum lodes of the Urals are believed to have been formed during this stage of crystallization. They range in length from 1 to 400 feet. Three such lodes, in the Nishniy-Tagil district, are called the Gosshakhta, Aleksandrovskii Log, and the Krutoy Log lodes. In the Krutoy Log property, a mass of high-grade chromite-platinum ore at the top of the ore body extended in one adit for a distance of 2 meters. From this deposit was recovered about 965 ounces of native platinum metals, of which the largest mass weighed 13%, troy ounces. Unfortunately such deposits were few and widely separated, and none of the numerous chromite ore bodies has been developed into a large producing mine. A fourth stage in the history of mineralization, contemporaneous with the final solidification of the dunite, resulted in serpentinization, together with the formation of native copper, nickel-iron, magnetite, calcium and magnesium carbonates, brucite, ferrobruc-ite, and related minerals. This late liypogene process produced only small amounts of platinum and insignificant amounts of iridium. A final stage was marked by exogenic processes whereby supergene solutions, acting upon the olivine, produced iron and magnesium hydroxides and carbonates.54 ECONOMIC GEOLOGY OF THE PLATINUM METALS EXPLANATION Alluvium Limestone Slate m Mica schist Tilaite Gabbro Pyroxenite Serpentine " \\ * * " o , Dunite Contact Figure 5.—Ni.shniy-Tagil dunite massif. (From Betechtin, 1961.)UNION OF SOVIET SOCIALIST REPUBLICS 55 Zavaritsky (1928, p. 87) has presented 15 chemical analyses of primary platinum metals collected from different parts of the Nishniy-Tagil district. These, recomputed to total 100 percent, are shown in table 23. Like all Russian analyses seen by the writer, a part of the iridium is included with osmium, and ruthenium has not been determined. Two mean values have been computed, one including copper, nickel, and iron, and the other without these elements. The ranges in the percentages of copper, nickel, and iron, are respectively 0.50 to 11.41, 0.30 to 3.70, and 10.76 to 15.55. It is uncertain whether these three base metals represent dross, or impurities resulting from unseparated heavy minerals, or both. Table 23.—Analyses, in percent, of primary platinum, Nishniy-Tagil district [Based on data from Zavaritsky, 1928, p. 37., N.D., no data] No. Platinum Iridium Osmium plus iridium Rhodium Palladium Copper Nickel Iron Total l--_ 72. 43 . 4. 22 1 6. 93 N.D. 0. 87 . 15. 55 100. 00 2... 74. 37 7. 14 5. 85 . 70 . 18 . 50 0. 50 10. 76 100. 00 3-.. 78. 50 1. 54 8. 87 N.D. N.D. N.D. N.D. 11. 09 100. 00 4 72. 49 7. 01 5. 75 1. 00 . 20 2. 00 . 30 11. 25 100. 00 5... 73. 56 1. 58 . 52 . 63 . 06 8. 62 . 15. 03 100. 00 6-.. 74. 88 1. 83 4. 67 . 54 Tr. 4. 81 . 95 12. 32 100. 00 7... 72. 01 1. 42 3. 54 . 23 . 20 8. 17 1. 54 12. 89 100. 00 8-.. 76. 27 3. 83 3. 62 . 60 . 12 2. 94 . 81 11. 81 100. 00 9 74. 45 1. 57 5. 03 1. 00 Tr. 5. 31 1. 01 11. 61 100. 00 10__ 73. 66 4. 10 2. 78 . 43 . 18 5. 13 1. 05 12. 67 100. 00 11.. 74. 69 1. 80 2. 42 . 74 . 05 4. 06 3. 70 12. 54 100. 00 12.. 55. 64 1. 08 14. 97 . 36 . 15 11. 41 1. 45 14. 94 100. 00 13. . 69. 84 4. 10 9. 49 . 74 . 11 3. 47 . 40 11. 85 100. 00 14.. 68. 67 6. 20 8. 21 . 98 . 10 3. 49 . 27 12. 08 100. 00 15.. 72. 61 4. 74 4. 54 . 54 Tr. 4. 67 . 93 11. 97 100. 00 Mean 71.93 3. 46 5. 62 . 65 . 14 4. 63 1. 07 12. 50 100. 00 Mean . .. 87. 94 4. 22 6. 88 . 80 . 16 . 100. 00 i Iridium plus rhodium. A comparison of the amounts of platinum metals in the Uralian lodes and placers can be made. The means of those that represent the placers of the Nishniy-Tagil district, computed free of impurities, are given in analysis C2 that is shown in table 24, on page 59 of this report. Comparing the mean values of Zavar-itsky’s analyses with analysis C2, it will be seen that the tenor of platinum in the former is about 4 percent less than in the latter, that the total iridium plus osmium is about 4y3 percent larger, that rhodium is about 1 percent less, and that palladium is about 0.5 percent smaller, that is, only about a fourth as large. Differences of the same order of magnitude result by comparing the mean of Zavaritsky’s analyses with analysis G2, of table 24, which represents the mean product from all the dunitic areas of the Urals. These differences may be explained in several ways, of which two will be stated. If the principal platinum alloy is intergrown with osmiridium, a possible inference might be that the placer samples represent metals that were eroded from apical horizons in the lodes, whereas Zavaritsky’s samples represent metals in different proportions that are characteristic of lower horizons in the lodes. If, on the other hand, the placer samples represent a detrital mixture of two distinct alloys, coming perhaps from different areas in the drainage systems, the discrepancy may be more readily explained by the assumption that the principal platinum alloy was mixed with osmiridium, in approximately a ratio of 20:1. The true explanation may be much more complex than the two above cited, and from studies in progress on the platinum metals of the Goodnews Bay district, Alaska, it seems that other interpretations are probable. PLACERS SOURCES The Uralian platinum placers are coextensive with the bodies of ultrabasic rocks of the Urals, as heretofore described. These rocks, and their resulting placers, are divided by Duparc and Tikonowitch (1920, p. 41-43), into 11 dunitic and five pyroxenitic centers. The dunitic centers and the principal rivers that drain this stretch of the Ural Mountains are shown in figure 4. The headwater tributaries, where most of the placers were mined, cannot be shown on a map of such a small scale, but most of these headwater streams are given in the figure caption. Figure 4 shows that eight of these dunitic centers are on the Asiatic side of the Urals, two are on the European side, and one, the Tagil area, is on both sides. The richest platinum placers of the Urals were in the Tagil area, and here the most important placers were on the European side of the divide.56 ECONOMIC GEOLOGY OF THE PLATINUM METALS Smaller amounts of the platinum metals were also eroded from pyroxenitic bedrock. Each of the dunitic areas is surrounded, or partly bordered by pyroxenite, but in addition to such sources, Duparc and Tikono-witcb (1920, p. 49-50) also mention five localities where platinum-bearing pyroxenite occurs without dunite. These are not shown in figure 4 but are located as follows: 1. Tokaisky area, which comprises a body of pyroxenite whose center lies about 14 miles S. 60° E. of the Koswinsky-Kamen dunite area. 2. Goussewi-Kamen area, about 10 miles east of the Swetli-Bor dunite area. 3 and 4. Sinaia-Gora and Kiedrowka areas, about 24 and 15 miles respectively north of the Tagil dunite area. 5. Obleiskaya-Kamenka area, which lies directly west of the Nishniy-Tagil dunite area. All these areas except the fifth are on the Asiatic side of the Ural Mountains. PHYSIOGRAPHY The physiography and hydrology of the Ural Mountains is briefly described by Duparc and Tikonowitch (1920, p. 1-6). The area is one of mature topography, and the rounded mountain tops in that part of the range where the placers occur have altitudes ranging from 1,300 to 3,500 feet. Timberline in the central Urals has a mean altitude of about 2,Y00 feet, so that much of the area is timbered. The western flanks of the Urals are more abrupt than the eastern flanks, which by Duparc and Tikonowitch is attributed to late tectonic disturbances. This condition is probably reflected in the character of the placer deposits. The streams on both sides of the Urals, and in large measure within the mountains, flow in silt-filled valleys through rolling country, and the water is normally clear, though the more sluggish streams are commonly stained a brownish color by dissolved vegetal matter. Most of the Urals and all the placer-bearing areas lie southwest of the regional belt of permafrost. Wisconsin glaciation, according to Suslov (1961, p. 6), extended southward in the Urals to some line between lat 59° and 60°, and as the placer fields lie between lat 56° and 60° 30', only the northern fourth of these fields was glaciated in Wisconsin time. Therefore, the placer loci 7 to 11 inclusive, as given above, are in unglaciated territory, and these include the rich placers of the Nishniy-Tagil area. The ice in the glaciated area, however, was rather sluggish, and apparently did not obliterate the placers. DEPOSITS The placer deposits have not been adequately described in detail, except perhaps in the Russian language. One early report that contained cross sections of numerous workings was published by Saytzeff (1897, 95 p.). This paper was written in Russian with a short resume in German. Duparc and Tikonowitch (1920, p. 264-282) have given a classification and general description of the placers. Compiled statements have also been published by O’Neil and Gunning (1934, p. 117-121) and by the Imperial Institute of Great Britain (1936, p. 90-93). Duparc and Tikonowitch have classified the Uralian placers into three principal types, to which they have added a fourth and subordinate type. Their classification is as follows: 1. “Lojok” alluvials, which comprise residual and eluvial deposits. 2. Stream placers in the present valley floors. 3. Low terrace deposits of fluvial origin. 4. Certain higher alluvium, to which a Tertiary age was assigned. Some generalized sections of these deposits are given. The residual deposits consist of weathered dunitic and pyroxenitic debris, mainly the latter if pyroxenite is present, because dunite disintegrates under weathering more rapidly than pyroxenite. Most of the weathered debris is unsorted, consisting of pyroxenitic fragments in a dunitic sand, but the platinum metals tend to be concentrated toward the base of the section. The rocks are deeply weathered, and the thickness of residual and eluvial deposits may be considerable. The eluvial deposits show some sorting of materials, and grade imperceptibly downstream into the headwater fluvial deposits. Typical stratigraphic sections through the “lojoks,” which range in thickness from 18 inches to 70 feet, include an ill-defined basal stratum of plati-niferous sand, with a thickness of 6 inches to 10 feet, overlain by sand and rock debris with a thickness of 6 inches to 50 feet. The uppermost part of the deposits consist of turf and vegetal material with a thickness comparable to the basal layer. The thick medial stratum contains a little platinum, but the bedrock, particularly if shattered, may contain considerable alluvial platinum, so that this broken debris has to be removed and cleaned in order to obtain a high recovery. This condition, however, is more prevalent farther downstream, where fluvial action has been marked. The stream placers range from narrow, shallow pay-streaks in the headwater stretches of streams draining areas of ultrabasic rocks to much wider and thicker bodies of alluvium in the lower valleys. Duparc andUNION OF SOVIET SOCIALIST REPUBLICS 57 Tikonowitch give a generalized section, that illustrates apparently the placers in the upper but not the headwater stretches of some of the streams. The section consists of a lower stratum of productive alluvium, ranging in thickness from 10 inches to 5 feet of argillaceous gravel, overlain by 1 to 13 feet of gray-green to yellow porous sands and gravels, in turn overlain by 20 inches to 5 feet of brown to gray clay. The uppermost layer consists of 14 inches to 31/3 feet of turf and vegetal material. The lower stratum is generally workable for its content of platinum metals, but the higher strata are virtually barren. The placers in the main valleys range in thickness from 10 to 60 feet. In the valley of the Iss River, according to Purington (1899, p. 10), the thickness below the surficial layer of turf and vegetal material ranged from 8 to 24 feet. The turf, which is stripped off before mining, has a thickness of 5 to 20 feet. No sections in the lower valleys are available, but it is known that most of the platinum metals are confined to a relatively thin basal stratum, which is overlain by a thick body of barren or very low grade sand and gravel, commonly interlayered with beds of silt and clay. The surficial stratum consists of turf and vegetal material. The principal bedrock in the main valleys away from the Urals is gabbro, which is deeply weathered to clay, so that the alluvial platinum penetrates into it to a variable depth. This fact makes it necessary for the dredges to dig considerable bedrock. This platiniferous clayey bedrock is difficult to decompose by water, and thus arises a problem in high recovery of the platinum metals. Kemp (1902, p. 75) records the fact that locally there are also beds of productive gravels in the medial overburden. It is probable that the basal platiniferous gravels are buried placers of Pleistocene age, overlain by Recent alluvium, in which the later paystreaks occur. The widths of these paystreaks, which are narrow in the headwater stretches of the streams, become very wide in the lower valleys. According to a statement by Kemp (1902, p. 70), the workable ground in the lower valleys had widths ranging from 400 to 1,600 feet and in places may have been as great as 2,500 feet. Most of these placers have been repeatedly worked, beginning in the early days with shoveling-in operations in the headwater stretches and culminating in the installation of large electric dredges. Some of the small headwater streams are still worked by hand methods, as are parts of the terrace deposits. Some of these placers extend a long distance down-stream, as for example, in the valley of the Iss River, where the paystreak was worked from the center of the Weressowy-Ouwal dunite area downstream to the confluence of the Iss and Tura Rivers, a distance by stream of about 50 miles. Thence the paystreak continued down the Tura River for at least 50 more miles. The same conditions apply on the European side of the Nishniy-Tagil area, where the Wyssim, Syssim, and Martian Rivers had paystreaks throughout their lengths and the platinum-bearing gravels continued from their mouths down the Chusovay River, though not in a measure comparable with the deposits on the Tura River. Similarly on the Asiatic side of the Nishniy-Tagil area, the Bobrowka and Tschauch Rivers had long paystreaks. The terrace deposits on the sides of the main streams evidently lie at no great distances above the valley floors, as it is recorded that they are flooded during periods of extreme high water. Most of the platiniferous sands at the base of the terrace deposits range in thickness from 2l/fj to 71/fj feet, and are overlain by clay ranging in thickness from 12 to 33 feet, rarely attaining a thickness of 130 feet. At some localities, two productive strata occur in the terrace deposits, as for example on the Iss River. Type sections of these terrace deposits are as follows: 1. Brown clay (top of section), thickness 12 inches to 33 feet. 2. Productive stratum, in part pebbly, in part argillaceous, thickness 8 inches to 5 feet. 3. Barren brown clay, thickness 22 inches to 28 feet. 4. Productive stratum, generally more clayey than the upper productive stratum, thickness 7% inches to 9% feet. 5. Sediments of variable character, but unstated thickness. Hence, the depth to bedrock is not known. It is evident from these sections that the base of the terrace deposits lies far below the level of the valley floor. The widths of the terrace paystreaks range generally from 33 to 165 feet, but some of them attain widths of 500 to 650 feet. The productive sands and clays of these deposits are apparently of Pleistocene age, as they contain numerous remains of Elephas primigenius. The original tenor of the platiniferous gravels and sands in the rivers draining the Urals is only of historical interest, as all the high-grade ground has been mined and deposits of far lower grade are now being worked. It is recorded that the Wyssim, Syssim, Martian, and Tschauch Rivers, which drain the Nishniy-Tagil area, had at the outset of mining some placers with tenors as high as 10 troy ounces per cubic yard, though this had diminished before the First World War58 ECONOMIC GEOLOGY OF THE PLATINUM METALS to tenors ranging from 0.01 to 0.85 ounce per cubic yard. The same conditions also applied to the placers of the Iss Eiver and its tributaries, that drain the Weressowy-Ouwal area, though these placers were not as high grade as those of the streams draining the Nishniy-Tagil area. It is not invariably clear whether the quoted tenors refer to the productive strata alone, though it is thought that generally this is true. Pur-ington (1899, p. 12) stated clearly, however, that his average value per cubic yard on the Iss Eiver, as of 1899, referred to the whole alluvial section of 10(4 feet. This overall tenor was about 64 cents per cubic yard, but the platinum metals at this time had only about a third of their present value. The tenors of the ground in the lower valleys, as for example on the Tura Eiver, are not known, but they must be approaching the value of marginal deposits that cease to be workable. Few data are available on the character and sizes of the noble metals of the stream placers. In the headwater stretches of streams draining the ultrabasic rocks, only the platinum metals occur; but in the downstream stretches, as in the Tura Valley, the ratio of platinum to gold, according to Purington (1899, p. 11), was about 5:1. The granularity of the platinum metals, throughout the length, width, and depth of the paystreaks, has not been recorded. Some very large nuggets, however, were found in the headwater stretches of some streams, and these were especially plentiful in the Nishniy-Tagil area. The largest recorded nugget, which was recovered from a tributary of the Martian Eiver, weighed 25% troy pounds. Nuggets were less common on the Iss Eiver and its tributaries, but two large ones from the Weressowy-Ouwal area weighed 22(4 and 10(4 troy pounds. Coarse gold and platinum do not commonly migrate any great distance downstream from their bedrock sources, and it is therefore inferred that the platinum recovered from the lower valley of the Iss Eiver and from the Tura Valley must be exceedingly fine grained—a feature engendering a problem of high recovery. These long paystreaks, however, also suggest either enrichment from local bedrock, or the existence of some geologic process, such as stream rejuvenation, that would distribute the precious metals so far downstream. CHEMICAL ANALYSES Numerous analyses of the platinum metals recovered from the Uralian placers are available, but they are all inferior analyses in which one or more of the components are not determined or are stated in combination with some other platinum metal. The tenors in gold are given, and these must be deleted, as the native gold is free, not alloyed with the platinum metals. Some of these analyses show components designated as sand, manganese, insoluble, and loss, all of which must likewise be deleted. Where tenors in copper, iron, or nickel are stated, however, it seems probable that a major part of these are alloyed elements of the dross, and the analyses are shown both with and without them, recomputed in both analyses to total 100 percent. Kemp (1902, p. 18-21) published 26 analyses of platinum, seven analyses of osmiridium, and one analysis of platiniridium from the Uralian placers, most of which came from the Nishniy-Tagil area. The analyses of osmiridium, which are known to have come from the vicinity of Syssertsk, were later republished by Duparc and Tikonowitch (1920, p. 189). The analyses of platiniridium, made in 1835, is omitted in computing a mean analysis, as no similar platinum alloy has been recorded from this area. The 26 samples of platinum are said by Kemp to have been nuggets, but it is not clear whether each sample was a single nugget, or an assemblage of small nuggets. Duparc and Tikonowitch (1920, p. 237-249) published 86 analyses of platinum metals from the Uralian placers, of which 79 came from the valleys of streams that drain areas of dunite and seven from valleys that head in pyroxenite. The two principal dunitic areas are one near Nishniy-Tagil, and a second area that includes the Weressowy-Ouwal and Swetli-Bor centers. In so far as placer platinum is concerned, it would be difficult to separate the two last-named centers, as the boundaries of their dunite masses are separated by only a mile and both are drained by tributaries of the Iss Eiver. Platinum analyses from four of the five pyroxenitic areas are separately tabulated by Duparc and Tikonowitch (1920, p. 247). It would be desirable to present mean analyses of the platinum metals from all 16 areas, as it appears that many of these yielded platinum metals with distinct characteristics. But most of the areas have too few analyses to yield dependable mean values. Thirty-seven analyses, however, are available from the Nishniy-Tagil area, and 26 from the Weressowy-Ouwal and Swetli-Bor areas, which are the two most productive centers. These analyses, as shown in table 24, are assembled in the seven sets. The analyses A2, C2, D2, and E2 are surprisingly uniform in their tenors of the platinum metals and dross, departing little from the proportions shown in G2, which is a weighted mean analysis of 168 samples from dunitic areas. The only other comparably large group of analyses, as shown on page 88 of this report, represent the metals derived from dunite at the placer mine near Platinum, Alaska. It is noticeable that the Uralian analyses show more platinum, butUNION OF SOVIET SOCIALIST REPUBLICS 59 Table 24.—Mean analyses, in percent, of placer platinum metals, Ural Mountains [N.D., no data; Tr., trace] Samples Platinum Iridium Osmium plus Ruthenium Rhodium Palladium Copper Iron Total iridium A, 77.99 2. 04 2. 45 a2 91.32 2. 39 2. 87 B, 2. 47 56. 07 33. 47 B2 2. 50 56. 72 33. 86 C, 77. 96 2. 49 2. 16 C2 92. 02 2. 94 2. 55 D, 83. 58 1. 31 3. 88 Ds 92. 94 1. 46 4. 32 E, 79. 79 2. 26 3. 60 E, 91. 46 2. 59 4. 13 F, 85. 66 1. 00 . 74 F2 95. 57 1. 12 . 83 G, 79. 69 2. 13 3. 15 G2 91. 79 2. 46 3. 62 N.D. 2. 40 0. 52 1. 38 13. 22 100. 00 N.D. 2. 81 . 61.................... 100. 00 4. 36 2. 48 Tr. .33 .82 100. 00 4. 41 2. 51 Tr._____________________ 100. 00 N.D. 1. 54 . 57 2. 04 13. 24 100. 00 N.D. 1.82 .67 .................... 100.00 N.D. .70 .45 .68 9. 40 100. 00 N.D. .78 .50 .................... 100.00 N.D. 1. 11 . 48 1. 44 11. 32 100. 00 N.D. 1. 27 . 55 ___________________ 100. 00 N.D. 1. 18 1. 05 . 72 9. 65 100. 00 N.D. 1.31 1. 17 .....-............ 100.00 N.D. 1. 34 . 50 1.45 11. 74 100. 00 N.D. 1. 55 . 58 ................... 100. 00 Localities of cited analyses Ai and Aj Mean of 26 analyses of platinum metals (Kemp, 1902), with and without the base metals. Bi and Bj Mean of seven analyses of osmiridium (Kemp, 1902), with and without the base metals. Ci and Cj Mean of 37 analyses of platinum metals from the Nishnly-Tagil area (Dupare and Tikonowitch, 1920), with and without the base metals. Di and Da Mean of 26 analyses of platinum metals from the W6ressowy-Ouwal and Swetli-Bor areas (Dupare and Tikonowitch, 1920), with and without the base metals. only half as much iridium plus osmium, as do the Alaskan analyses. On the other hand, the Uralian analyses show more rhodium and palladium than do the Alaskan analyses. Samples Fx and F2, from one of the Uralian pyrox-enic areas, probably represent a principal alloy of platinum containing little or no osmiridium. This is indicated by a tenor in platinum higher than those of Gi and G2, by the lower tenor in iridium plus rhodium, and by a distinctly higher tenor in palladium. On the other hand, analyses B2 and B2, as presented by Kemp, represent seven samples from the vicinity of Syssertsk, which are quite different. These show very low tenors in platinum, with nearly 90 percent iridium plus osmium and practically no palladium. Obviously such analyses represent osmiridium, with no intergrown platinum alloy of the ordinary type, though one of these seven samples contains nearly 10 percent platinum, which is sufficient to suggest a minor intergrowth of the ordinary platinum alloy. Areal mean analyses, however, from areas of dunitic and pyroxenic bedrock do not give a complete picture of the variable character of the platinum alloys. One example of a marked variation from the cited analyses is the mean analysis of a number of placer samples from the Kanjakowsky dunite area, which shows 62.50 percent platinum and about 24.30 percent “osmiure,” or combined iridium and osmium. Obviously such platinum metals represent two alloys, of which osmiridium constitutes an important, though not the major 329-505—69-----------5 Ei and E2 Mean of 79 analyses of platinum metals from dunitic areas of the Urals (Dupare and Tikonowitch, 1920), with and without the base metals. Fi and Fa Mean of seven analyses of platinum metals from the pyroxenitic areas of the Urals (Dupare and Tikonowitch, 1920), with and without the base metals. Gi and Ga Weighted mean of 168 analyses of platinum metals represented by Ai, Aa, Ci, Ca, Di, Da, Ei, and E2, with and without the base metals. component. Still greater variations in the proportions and compositions of the component alloys are apparent in individual analyses. The ratios between the different platinum metals have considerable interest and significance, not merely for interpreting the analyses of any one product, but also for comparing products from different regions. For the Uralian product, and in fact for most of the platinum metals elsewhere recovered, the establishment of certain useful ratios is not feasible, first because the contained iridium and osmium are usually not completely separated, and second because the content of ruthenium is rarely determined. Osmium and ruthenium occur mainly in osmiridium, and their ratio is generally nearly constant, so that the sum of these two elements may function as a fixed numerator or denominator in formulating distinctive ratios. Because platinum, iridium, and rhodium occur both in the principal alloy and in osmiridium, the ratios Pt: Os+Bu, Ir: Os+Bu, and Eh: Os+Bu are particularly significant and useful when they can be obtained. For the Uralian placers, however, all that may be safely stated is that the ratio Pt: Ir+Os+Bu is approximately 15:1, whereas for the Alaskan product the corresponding value is 6:1. The higher ratio indicates a large predominance of the principal alloy over osmiridium, and it is estimated that the ratio of these two alloys for the Uralian product is between 20:1 and 25:1, whereas the same ratio for the Alaskan product is believed to be about 12:1. This ratio, though doubtless variable in bedrock, tends to approach a constant mean value in the60 ECONOMIC GEOLOGY OF THE PLATINUM METALS placers and serves to characterize the placer platinum products in different parts of the world. The most distinctive feature of the placer platinum metals found in the Urals, Alaska, and elsewhere in the world is their low content of palladium, as compared with the platinum metals recovered from the lodes of Canada, Siberia, South Africa, and all other platinum-bearing lodes. Other differences exist in the Uralian platinum samples with regard to their included base metals, if these are interpreted as dross. The mean of the analyses of samples from the Nishniy-Tagil area (C2) and the mean of Kemp’s analyses (A2), thought likewise to have come from the same area, are nearly 5 percent higher in base metals than the corresponding mean analysis of samples from the Weressowy-Ouwal area, yet both these mean analyses represent samples from areas of dunite. On the other hand, the mean analysis of samples from areas of pyroxenite shows about the same amount of base metals as the mean analysis of samples from the Weresowy-Ouwal area. These facts suggest that none of these four means represent dross alone, but instead that all of them include undetermined amounts of extraneous impurities. It also is noteworthy that osmiridium, where it exists as a distinct alloy, constituting all the placer product, has a very low content of dross. Few data are available regarding the heavy minerals that constitute the concentrates recovered with the platinum metals, but it is recorded that numerous such minerals have been identified. The only heavy minerals noted by the writer in the published descriptions are magnetite and chromite, though doubtless ilmenite is also present. At some places cinnabar is specifically mentioned, but this is obviously derived, not from dunite or pyroxenite, but from veins in gold-bearing granitic rocks within the basins of the Uralian streams. NORIL’SK DISTRICT The geographic position of Noril’sk, the general geology of the Noril’sk district, and the drainage of the surrounding country are shown in figure 6. Mount Budnaya, also known as Budnaya Gora (ore mountain) , is the site of the original discovery of the platinum-bearing copper-nickel ores that are now being exploited. Its reported geographic position is approximately lat 69°20' N., long 88°8' E. A number of other similar deposits are also known in this area, of which some are being mined. Among them are the Sotnik-ovskol deposit, which is adjacent to Budnaya Gora; the deposit at Mount Barjernaja, east of Budnaya Gora; the Ugal’nyi Buckey deposit, about 1.6 miles south of Budnaya Gora; the Noril’sk II deposit, located approximately at lat 69°00' N., long 89°00' E., and the occurrence on the Bybnaja Biver, about 6.2 miles southeast of Budnaya Gora. Geologic environments similar to those near Noril’sk exist also about 250 miles to the east, and continue southward from Noril’sk for 400 miles or more, so that the prospect of new discoveries are excellent. Production of platinum metals from the Noril’sk district began in 1940, and by 1947 constituted 30 percent of the annual production. This percentage has continued to increase in recent years. The geologic environment of the ore bodies in the Noril’sk district resembles in some respects that at Sudbury, but differs markedly in others. Northwest and south of Noril’sk are numerous sedimentary formations, mainly of Paleozoic age, and southwest of Noril’sk is a large elliptic area of Triassic lavas of about 2,000 square miles. The Paleozoic rocks, from Cambrian to Carboniferous, include many limestones, but one Permian formation consists of sandstone and slate, with some beds of coal. Owing to the large area shown in figure 6, the Paleozoic sedimentary formations are not separately delineated. Numerous basic intrusives invade both the Paleozoic and the Triassic rocks, and these, though assigned an age of Carboniferous to Lower Mesozoic on Spizharskiy’s (1959) geologic map, must be in part Triassic or post-Triassic in age. They are probably related genetically to the Triassic trap-rocks. The ore bodies are localized at the contacts of the intrusives with certain of the Paleozoic rocks. Shimkin (1953, p. 79) mentions as the principal loci of the ore deposits the contacts between the intrusives and Silurian limestones or Permian and Carboniferous “sands and clays.” Genkin (1959) however, emphasizes the fact that the ores at Budnaya Gora and at certain other localities are localized at the contacts of the intrusives with the coal-bearing Tungusk (Permian) coal-bearing formation. The intrusives are mainly diabase (dolerite by transliteration from the Bussian) and gabbro-diabase but include differentiated rocks such as picrite, tschenite, labradorite prophyrite, titaniferous augite diabase, and other specialized types. These intrusives differ morphologically from those at Sudbury in that they occur as large dikes, sills, and less regular intrusive bodies. The essential minerals of the undifferentiated rocks are plagioclase feldspar (commonly labradorite), augite, hornblende, biotite, and olivine, with the secondary minerals chlorite, serpentine, sericite, prehnite, and the zeolites. The ore deposits at Budnaya Gora are of two principal types. The high-grade ores occur as veins and lenses; the low-grade ores occur as disseminated deposits lUNION OF SOVIET SOCIALIST REPUBLICS 61 o< ui >7 Platinum deposit lodes, classification........ 16 Platinum-gold ratios, Colombia................ 64 Platinum group of metals, components...... 5 Platinum lodes............................ 14,17 Platinum lodes in Alaska, search______________ 91 Platinum metals, Australia____________________ 69 detrital origin_________________________ 47 in gold ores..........................- 17 native state........................... 43 occurrence in conglomerates............... 46 other countries_______________________— 75 physical properties........................ 5 Sudbury district.......................... 25 Platinum metals and gold, Goodnews Bay district.......................... 84 Platinum nuggets, Goodnews Bay district— 81 Sierra Leone.............................. 50 Ural Mountains............................ 58 Platinum-palladium ratio for Noril’sk deposits....................................... 62 Platinum placers........................... 17 Platinum placers of the Urals................. 55 Pleistocene chronology, Goodnews Bay district........................................ 83 Plumbojarisite................................ 98 Pneumatolytic ore, Republic of South Africa. 44 Porpezite..................................... 14 Potarite....................................14,76 Potgietersrust district, Transvaal........39,41 Potgietersrust platinum lode, Transvaal... 33 Preparation of samples for analysis............ 9 Pretoria district, Transvaal, platinum mining_________________________________________ 33 Pretoria series, Transvaal................34,44 Processing of platinum metals.................. 7 Production, total, platinum in Republic of South Africa...................... 33 Production of ore and history of Witwatersrand......................................... 46 Production and sources of platinum in Canada. 18 Production of platinum, Ethiopia.............. 49 Oregon.................................. 99 world...................................... 4 Production of platinum metals from Tulameen district, B.C..................... 31 Pyrite, ore mineral.......................22,66 Pyrolusite ore mineral........................ 44 Pyroxenite.................................... 1, 16,28,29,30,33,35,39,40,42,43,49,50,51, 53,54,56,58,66,67,79 Pyrrhotite, ore mineral............. 22,24,40,45 Q Quebec platinum deposits...................... 27 Queensland, platinum deposits.............- 69 Quinn claim, Ontario.......................... 26 R Rambler mine, Albany County, Wyo..........14,101 Rankin Inlet lode, Northwest Territories, mean tenors of nickel and copper. 28 Rathbun township lode, Sudbury district--- 25 Reaume township lode, Ontario................. 25 Recovery of platinum metals from refineries.. 101 Red Granite, Transvaal....................34,44 Red Mountain, Goodnews Bay district, platinum metals in dunite...................... 84 Page Republic of South Africa, platinum deposits.. 85 production of platinum metals.......... 2,4 Republic of the Congo (Katanga)............ 48 copper deposits........................... 33 Rhodesia, platinum deposits................... 48 Rhodian sperry lite........................ 13 Rhodium, market prices......................... 3 relative amount in Sudbury ore............ 23 Richmond River district, New South Wales.. 72 Rooiberg group, Bushveld igneous complex... 34 Rudnaya Gora, Noril’sk district____________ 60 Russian production of platinum metals------ 4 Rustenburg district, Transvaal, platinum lodes...................... 33,39,41 Rustenburg mine, Transvaal_________________ 39,40 Rustenburg Platinum Mines Ltd. of South Africa.......................... 4,33 Ruthenian hollingsworthite.................... 13 Ruthenium, chemical analyses.................. 48 market prices.............................. 3 not determined in U.S.S.R................. 51 relative amount in Sudbury ore.......... 23 S Salt Chuck mine, Kasaan Peninsula, Alaska. 76 Sangamon Interglaciation, Goodnews Bay district........................ 84 Sappho property, British Columbia............. 29 Scottie Creek, British Columbia............... 29 Search for platinum lodes in Alaska. ......... 91 Secondary platinum metals____________________ 17 Selukwe district, Rhodesia................... 48 Selundi Hills, Rhodesia...................... 49 Separation of platinum metals................ 10 Sericite, ore mineral......................... 44 Serpentinite................................ 1, 16,17,27,29,42,43,49,51,53,54,70,72,73,74, 75, 79,91,99 platinum and osmiridium lodes............. 17 Shebandowan nickel-copper property, Ontario......................................... 25 Shi Shi Beach, Washington................... 101 Siberia, minor platinum deposits______________ 65 Sierra Leone, platinum deposits............... 60 platinum production........................ 4 Sinala-Gora and Kiedrdwska areas, Ural Mountains......................... 56 Siserskite.................................... 12 Smuggling of platinum from Colombia........ 4 Solidus curves for platinum metals............. 9 Solubilities of the platinum metals............ 9 Sosnowsky-Ouwal area, dunite locality...... 52 Sotnikovskol deposit, Noril’sk district...... 60 Sources and production of platinum in Canada........................................... 18 South African pro duction 0 f platinum metals. 4 South Reef, Main Reef group, Transvaal..... 46 Specularite, ore mineral...................... 44 Sperrylite_____________ 13,18,22,24,40,43,49,61,101 analyses................................ 13 spectrographic analyses................... 14 Stannopalladinite............................. 13 Stannoplatinite............................... 13 Stibiopalladinite..........................13,14,40 Stillwater Complex, Montana................... 95 Stobie group, Ontario......................... 20 Stream placers, gold-platinum, California and Colombia.......................... 17 Ural Mountains............................ 56 Sudbury basin, Ontario........................ 20 Sudbury deposits, genesis..................... 22 Sudbury district platinum deposits............ 18 Sudbury series, Ontario....................... 20 Sulfide breccia, Thompson mine, Manitoba... 27 Sullivan mine, British Columbia............... 29 Sumatra and Borneo, platinum deposits...... 75120 INDEX Page Superior chemical analyses of platinum.... 10 Swaziland system, oldest rocks of Transvaal.. 34, 46,47 Swede group of claims, British Columbia... 28 Swetli-Bor area, dunite locality............ 52 Ural Mountains........................56,58 T Tagil area, dunite locality................. 52 Takilma-Waldo district, Oregon-------------- 99 Tasmania, platinum deposits............... 69,71 Tasmanian osmiridium........................ 70 Tenor, ore at Onverwacht mine--------------- 43 ore at Thompson mine, Manitoba__________ 26 platinum in Humboldt County, California..................................... 94 platinum in Red Mountain................ 87 platinum metals, Gordon Lake, Ontario. 25 Insizwa deposit, Cape of Good Hope Province......................... 48 Sudbary ore......................... 23 Union mine, Transvaal............... 40 Salt Chuck ore, Alaska.................. 77 Terrace deposits, Ural Mountains............ 56 Thompson district, Manitoba................. 26 Thompson mine, Manitoba____________________ 26 Tilaite, Ural Mountains..................... 53 Timiskaming Series, Ontario............... 20 Tokalsky area, Ural Mountains............... 56 Total production of platinum from Canada.. 18 Totten mine, Sudbury district............... 19 Transvaal, first discovery of platinum....... 2 platinum deposits....................... 33 Transvaal and Orange Free State provinces, general geology.................. S3 Transvaal system....................... 34,44,45 Page Troctolite, Sierra Leone.................. 50 Trout Creek conglomerate, Ontario........... 19 Tulameen group of rocks, British Columbia. _ 29 Tulameen placer district, British Columbia.. 29 U Union mine Transvaal................... 39,40,98 Union of Soviet Socialist Republics, history and production of platinum____ 61 production of platinum.................. 4 United States, platinum metals. ............ 76 production of platinum metals........... 4 Upper Witwatersrand series, Transvaal_____ 46 Ural Mountains, discovery of platinum__________ 61 platinum placers........................ 2 Uralian placers, principal types............ 56 Uralian platinum lodes and placers.......... 55 Uralian platinum samples.................. 60 Use of platinum, earliest.................... 2 Uses of platinum metals...................... 3 V Vaalkop-Zwartfontein body, Transvaal...... 45 Ventersdorp system, Transvaal_____________34,46 Vermilion mine, Sudbury district.......18,21,22 Victoria, platinum deposits.............. 69 Victoria and Queensland.................. 72 Violarite, ore mineral................... 40 Vysotskite................................ 13 W Walhalla copper mine, Victoria______________ 72 Washington, platinum deposits.............. wi Waterberg district, ratio of platinum to palladium........................................ 44 Rage Waterberg platinum lode, Transvaal. Waterberg system, Transvaal........ Wedza mine, Rhodesia......................... 49 Wehrlite, Onverwacht mine, Transvaal...... 43 Wellgreen lode, Yukon........................ 32 Weressowy-Ouwal area, dunite locality..... 52 Ural Mountains........................56,58 West Point mining district, California....... 98 Whitewater series, Sudbury basin............. 19 Wisconsin glaciation, Ural Mountains......... 56 western Alaska.......................... 79 Witteberg series, Cape of Good Hope Province. 48 Witwatersrand, gold mining.................... 2 history and production.................. 45 placers.....................__....... 45 platinum placers........................ 14 production of platinum metals............ 4 Witwatersrand system......................... 34 general geology, Transvaal.............. 46 Wollastonite, Sumatra........................ 74 World production, compilation by country__ 5 World production of platinum.................. 4 World’s total production of platinum metals... 5 Worthington mine, Sudbury district........19,21 Wyoming, platinum deposits.................. 101 Y Yellow Pine mining district, Nevada........... 97 Yukon platinum deposits....................... 32 Z Zambia, copper deposits....................... 33 Zinc, byproduct from Katanga.................. 48 Zvyagintsevite................................ 13 Zvyaginzevite................................. 13 s &* ►* AA ► * A * UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 630 GEOLOGICAL SURVEY PLATE 1 161 °50' 45' 40' 161 ° 35' (1940b) GEOLOGIC MAP OF THE GOODNEWS PLATINUM DISTRICT, ALASKA SCALE 1:63 360 1 0 I—| |—I |—| | |—|~F 1 2 3 4 5 MILES 1 .5 0 1 H H H H H I =T 2_________3_________4_________5 KILOMETERS CONTOUR INTERVAL 50 FEET DATUM IS MEAN SEA LEVEL APPROXIMATE MEAN DECLINATION, 1969EARTH SCIENCES LiSRARY * ► r u. ujc. '=> T(p v. 631 7 DAY ANALYSIS OF A 24-YEAR PHOTOGRAPHIC RECORD OF NISQUAUY GLACIER S.S.D,*Analysis of a 24-Year Photographic Record of Nisqually Glacier, Mount Rainier National Park, Washington By FRED M. VEATCH GEOLOGICAL SURVEY PROFESSIONAL PAPER 631 A contribution to the international Hydrological Decade UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 71-602805 UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1969 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402CONTENTS Page Abstract____________________________________________________ 1 Introduction________________________________________________ 1 Purpose and scope______________________________________ 1 Reasons for the program___________________________ 1 Purpose of the report_____________________________ 2 Selection of study area___________________________ 2 Previous investigations________________________________ 4 Photographs_______________________________________ 4 Surveys and maps__________________________________ 4 Acknowledgments________________________________________ 4 Description of the area_____________________________________ 5 Physiography___________________________________________ 5 Climate______________________________________________ 5 The photographic program____________________________________ 5 Network of stations____________________________________ 5 Photographic series not published______________________ 6 Time of year and weather conditions____________________ 7 Camera equipment_______________________________________ 7 Light conditions_______________________________________ 7 Scale corrections on prints____________________________ 7 Quantitative interpretations from the photographs______ 7 Changes in ice thickness_______________________________ 7 Changes in lateral ice margins________________________ 13 Longitudinal slope of the ice surface_________________ 13 Snow lines and firn edges_____________________________ 21 Page Qualitative interpretations_________________________________ 22 Characteristics of the terminus________________________ 22 Debris cover and its distribution______________________ 22 Moraines_______________________________________________ 22 Crevassing and general character of the glacier surface__________________________________________ 34 Terminus to profile 1______________________________ 34 Profile 1 to about 1,000 feet (300 m) above profile 2________________________________________ 34 1,000 feet (300 m) above profile 2 to above profile 3________________________________________ 34 Erosion and deposition_________________________________ 44 Banks and lateral moraines_________________________ 44 Outburst floods____________________________________ 44 Flood of October 14, 1932_____________________ 44 Flood of October 24-25, 1934__________________ 44 Flood of October 25, 1955_____________________ 44 Natural changes below glacier from floods and other causes_____________________________________ 44 Conclusions_________________________________________________ 49 Recommended photographic procedures_________________________ 51 Photographic stations__________________________________ 51 Optimum light conditions_______________________________ 51 Selecting the view_____________________________________ 51 Equipment______________________________________________ 51 Recording the photographic data________________________ 52 References__________________________________________________ 52 ILLUSTRATIONS Page Plate 1. Map of Nisqually Glacier and vicinity, showing locations of the photographic stations and cross profiles._In pocket Figure 1. Map of south side of Mount Rainier and vicinity__________________________________________________________ 3 2-5. Photographs of Nisqually Glacier, from confluence with Wilson Glacier to the nunatak, as seen from station 7: 2. 1890 (date uncertain)___________________________________________________________________________ 8 3. August 1915_____________________________________________________________________________________ 9 4. August 22, 1945______________________________________________________________________________ 10 5. August 27, 1963______________________________________________________________________________ 11 6. Photograph showing ice margins for selected years in period 1890-1965__________________________________ 12 7-10. Photographs across glacier in series 14-W (profile 2) used to determine slope and changes in ice thickness: 7. August 21, 1942_________________________________________________________________________ 14 8. August 27, 1952______________________________________________________________________________ 15 9. September 8, 1960____________________________________________________________________________ 16 10. August 30, 1965_________________________________________________________________________ 17 11. Graph showing changes in ice-surface elevation, or glacier thickness, at profile 2 and above profile 3_ 18 12. Photograph of area where changes in ice thickness above profile 3 were measured on the photographs in series 15, showing minimum ice conditions in 1944___________________________________________________ 19 13. Photograph showing ice margins around the nunatak for selected years in the period 1942-65_____________ 20 14. Graph showing longitudinal slope of the glacier surface at profile 2___________________________________ 21 hiIV CONTENTS Page Figure 15. Photograph showing several areas of firn outlined on a 1955 view taken from station 13______________ 23 16-19. Photographs of the terminus in series 1-NE, taken from points at or near the old highway bridge: 16. 1903______________________________________________________________________________________ 24 17. 1908______________________________________________________________________________________ 25 18. July 5, 1929______________________________________________________________________________ 26 19. August 19, 1942__________________________________________________________________________ 27 20-25. Photographs showing the lower part of Nisqually Glacier, as seen from station 5: 20. August 31, 1942--------------------------------------------------------------------------- 28 21. August 22, 1951--------------------------------------------------------------------------- 29 22. September 1, 1954_________________________________________________________________________ 30 23. September 11, 1959________________________________________________________________________ 31 24. September 8, 1962_________________________________________________________________________ 32 25. August 30, 1965--------------------------------------------------------------------------- 33 26. Photograph showing patterns of small recessional lateral moraines on east bank in 1940, as seen from station 12------------------------------------------------------------------------------------------ 35 27-31. Photographs of Nisqually Glacier near the nunatak, as seen from station 6: 27. August 27, 1952___________________________________________________________________________ 36 28. September 1, 1954------------------------------------------------------------------------- 37 29. September 5, 1958_________________________________________________________________________ 38 30. September 6, 1961------------------------------------------------------------------------- 39 31. August 30, 1965--------------------------------------------------------------------------- 40 32-34. Photographs of upper reaches of Nisqually and Wilson Glaciers, as seen from station 13: 32. August 28, 1949___________________________________________________________________________ 41 33. August 30, 1957--------------------------------------------------------------------------- 42 34. August 30, 1965--------------------------------------------------------------------------- 43 35. Photographs showing erosion of old lateral moraine from 1947 to 1965--------------------------- 45 36-38. Photographs of Nisqually valley below the glacier, as seen from station 3: 36. 1934___________________________________________________________________________________ 46 37. August 25, 1947--------------------------------------------------------------------------- 47 38. August 31, 1965--------------------------------------------------------------------------- 48 39. Photographs showing river channel just above the highway bridge, as viewed downstream from station 2 in 1949, 1950, 1956, and 1965----------------------------------------------------------- 50 TABLE Page Table 1. Descriptions of the photographic series, 1890-1965________________________________________________________ 5ANALYSIS OF A 24-YEAR PHOTOGRAPHIC RECORD OF NISQUALLY GLACIER, MOUNT RAINIER NATIONAL PARK, WASHINGTON By Fred M. Veatch Abstract A systematic coverage of Nisqually Glacier by photographs taken from a network of stations on the ground was begun in 1942 to explore the value and limitations of such photographs as an aid in glacier study. Principles developed may be of value elsewhere, especially for the program “Measurement of Glacier Variations on a World-Wide Basis” of the International Hydro-logical Decade. Nisqually Glacier in Mount Rainier National Park, Wash., covers 2.5 square miles (6.5 square kilometers) (1961) and extends from an altitude of about 14,300 feet (4,400 meters) near the top of Mounit Rainier down to 4,700 feet (1,400 meters) , in a horizontal distance of 4.1 miles (6.6 kilometers). Analyses were made of the annual photographs taken by the writer for 24 years from about 20 stations. A number of pictures taken sporadically from 1884 to 1941 by others were also available for use in the study. Where possible, the results obtained from photographs were compared with those from the available engineering surveys. Such detailed analysis of an extensive photographic coverage of a single glacier may be unique. Photographs illustrating the retreat and advance of the glacier’s west ice margin in a reach extending for about a mile (1.6 kilometers) downstream from Wilson Glacier show that, by 1965, most of the ice thickness lost in that area between 1890 and 1944 had been recovered. Withering of the stagnant valley tongue down glacier from the nuntak is portrayed, as is iits spectacular reactivation in the 1960’s by a vigorous advance of fresh ice. Some of the visible characteristics of advancing and receding termini are noted. Annual values of the glacier’s surface slope (5 to 10 degrees) at a cross profile were measured on photographs with respect to a projected vertical line identifiable in each picture. The results were found to average about 2 degrees less than those obtained from the 5-year topographic maps, but they are thought to be a little more accurate owing to lack of a sufficiently small contour interval on the maps for this special purpose. Year-to-year variations in the surface slope and other characteristics from place to place along the glacier are portrayed by pictures to a degree not economically attainable by any other means. Annual changes in the glacier’s thickness at two locations were determined from photographs and found to agree well with the results of stadia surveys. A summary of conclusions reached in regard to other data or features of the glacier that were illustrated by annual photographs follows: 1. Toward the end of the ablation season, position of the annual snowline ranged between altitudes of about 5,800 and 7.300 feet (1,750 and 2,250 meters). The altitude limits within which fim was observed on the glacier were about 6,000 and 7.300 feet (1,850 and 2,250 meters). 2. Sources from which debris reaches the glacier are evident. 3. Medial moraines and other persistent patterns sometimes overlooked in the field are more noticeable in photographs. Ice-cored moraines and patterns of multiple lateral moraines are visible. 4. The extent, severity, and nature of crevassing in an area reflect the dynamic condition of the glacier at that location. 5. Erosion has caused certain bedrock areas or features on canyon walls to become unrecognizable within less than 15 years. 6. Effects of the 1932 and 1955 outburst floods on the stream channel and trees for a mile (1.6 kilometers) or so below the glacier are shown in comparison with ordinary, lesser floods. Visible effects include degradation, widening and changes in configuration of the channel, formation of small terraces, removal of vegetation from the flood plain, and the deposition of huge boulders on the stream banks and flood plain. Some photographic procedures recommended for use in a program of this type are described in the section on “Recommended Photographic Procedures.” INTRODUCTION PURPOSE AND SCOPE Reasons for the program Over the years, glaciers show marked changes. For their study and analysis a repetitive photographic program has obvious potential value because it is relatively quick and inexpensive and can include a wealth of information unobtainable by ordinary surveying techniques. Such a program graphically portrays the l2 ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD, visible characteristics and changes inherent in a fluctuating glacier. Since this has long been recognized, systematic photographic programs have been undertaken on many glaciers in many parts of the world. However, no such program, to the knowledge of the writer, has combined a fairly detailed photographic coverage over nearly the full length of a single glacier, a long period of annual record, and an analysis of the potential of a program such as is described in this paper. Published reports by Field (1932, 1937, 1947), Harrison (1954, 1956), LaChapelle (1962), Meier and Post (1962), and others have utilized glacier photographs, but the pictures for any one glacier did not include coverage or length of record as detailed as those available for Nisqually Glacier, nor did the reports indicate the many kinds of data obtainable from such photographs. Such an analysis is especially important now because a photographic record has been designated as a first, least costly step, in the new program “Measurements of Glacier Variations on a World-Wide Basis” of the Commission of Snow and Ice (International Association of Scientific Hydrology). This global-scale program is also part of the International Hydrological Decade. Thus, the findings and techniques described herein are thought to have possible application elsewhere. The idea that worthwhile benefits might derive from a long-term program of annual photographs of Nisqually Glacier was conceived by the writer in collaboration with Arthur Johnson of the U.S. Geological Survey when Mr. Johnson was mapping the glacier in 1941. Soon after the annual photographic records were begun, a marked thickening of the upper part of the glacier was noticed from the annual cross-profile surveys (Johnson, 1949). The thickening was followed over a period of two decades by one unusually large and several smaller kinematic (moving) waves of fresh ice advance. The effect of these was particularly impressive in the terminal area from 1963 to 1965. The waves probably resulted from the marked increases in precipitation on Mount Rainier as evidenced in the measurements at Paradise Ranger Station, situated less than a mile (1.6 km (kilometers)) from the glacier at an altitude of 5,430 feet (1,160 m (meters)). The climatic change of the late 1940’s, which subsequently was found to have caused the advance of glaciers in many parts of the world, apparently was first detected in 1946 and 1947 in glaciers on Mount Rainier. As a result, Nisqually Glacier became an object of considerable international scientific interest. A program of this kind is less expensive than one based on aerial or p'hototheodolite photography because it does not require trained photogrammetrists or as NISQUALLY GLACIER, MOUNT RAINIER, WASH. costly equipment. Furthermore, since it consumes relatively little field time its success is more certain during brief periods of cloudless weather. Purpose of the report The primary purpose of this report is to describe, and demonstrate by means of examples, what kinds of data usable in analyzing glacier characteristics can be obtained from a simple program of long-term photographic coverage from stations on the ground. It is not intended to be a detailed or complete report on the glacier’s physical characteristics. Secondary purposes of the report are to describe to interested workers the photographs available here and fo illustrate some of the spectacular changes that have occurred in this glacier. Examples are given of qualitative and quantitative data sought in regard to the glacier’s growth, depletion, movement, slope, moraines, crevassing, snow and fim lines, and debris cover. Some objectives that developed as the photographic program progressed were the illustration of some geomorpho-logical changes occurring in old moraines and the adjacent hills and valley, and the portrayal of erosion and other changes in the river channel below the glacier from outburst floods and other causes. The report presents photographs taken by the writer for 24 years from about 20 stations and some older photographs taken by others. Only a hand-held amateur camera was used, without photogrammetric instruments of any nature. Office techniques used included the interpretation and marking of ice margins and slope crest lines on photographs, and the performance of simple scaling, scale-ratio computions, and angle measurements. Selection of study area Nisqually Glacier on Mount Rainier, Wash., was chosen for the project because of its variety of features for such an experiment, the availability of data from previous investigations, the many concurrent topographical and profile survey data which could be used for checking, the superior accessibility of this glacier, and the practical local interest in it as an important source of the water supply of the Nisqually River. The general location and access to the glacier are shown in figure 1. Quantities of melt water coming from Nisqually Glacier vary with the amounts of snow and ice it contains and with external conditions such as air temperature and the amount of radiant energy received from the sun. Streamflow records show that the discharge of the Nisqually River is markedly affected by variations in the melting rates of headwater glaciers. Thus, because the river is used for the production ofINTRODUCTION 3 121°50' 121-45' s^Pketr &£ Figure 1.—South side of Mount Rainier and vicinity, showing location of Nisqually Glacier. Glacier margins and Dart of culture corrected to 1966. Scale 1 inch = 62,500 feet (approximately 1 inch ■= 1 mile).4 ANALYSIS OF 2 4-YEAR PHOTOGRAPHIC RECORD, power ait hydroelectric plants downstream from Mount Rainier National Park, any study of glacier fluctuations and related climatic changes is of important economic interest in connection with the long-range planning of water resource use. PREVIOUS INVESTIGATIONS Photographs Nisqually Glacier in Mount Rainier National Park long has been a favorite object of photographers, for it is a readily accessible subject for glacier research and is part of a high-altitude area of rare scenic grandeur. For many years (until 1936) its terminus remained less than half a mile (0.8 km) upstream from the former highway bridge on the road to Paradise Inn. The main body of Nisqually Glacier is visible from several vista points along its east side, accessible from the Paradise Inn area (pi. 1). Numerous random photographs, mostly confined to the area of the terminus, were taken in association with surveying activities. The first known photograph of the glacier was a view of the snout taken by Allen C. Mason in 1884. I. C. Russell (1898, p. 399^00), as a member of a U.S. Geological Survey group making a reconnaissance of Mount Rainier and its glaciers, recommended systematic photographic coverage and measurement of the position of the Nisqually Glacier terminus from permanent, marked locations. Russell also reported that Nisqually Glacier affords abundant opportunity for observation and study of the various features that glaciers possess, such as crevasses and moraines. No network of regularly scheduled photographs covering most of the glacier was established until 1942, nearly half a century later, when a program of annual photographs from about 20 stations was initiated by the writer, then district engineer, Water Resources Division, Geological Survey, Tacoma, Wash. Surveys and maps A definite location of the terminus of Nisqually Glacier was recorded first in 1857, by Lt. A. V. Kautz, and next in 1885, by James Longmire. Its approximate position in 1910 was determined on the small-scale planetable map of Mount Rainier National Park that was made in 1910-13 by the U.S. Geological Survey under the supervision of F. E. Matthes. Annual records of the position of the terminus, begun in 1918 by F. W. Shmoe, National Park Service, were obtained each year by that agency until 1961 and have been continued since then by the Conservation Division of the U.S. Geological Survey. In 1930 and 1931, Llewellyn Evans, superintendent of the Light Division, Tacoma Department of Public NISQUALLY GLACIER, MOUNT RAINIER, WASH. Utilities, made cross-profile and other surveys and compared the results with data taken from Matthes’ 1910 map. In 1931 a contour map was prepared cooperatively by the Tacoma [City] Light Division, the National Park Service, and the U.S. Geological Survey. A plan of contour mapping at 5-year intervals was then conceived by Llewellyn Evans, Owen A. Tomlinson, and Glenn L. Parker of those respective agencies. This has been done, beginning in 1936, first by planetable and later (covering a larger area) using photogrammetry from aerial photographs, by the U.S. Geological Survey in cooperation with the city of Tacoma and the National Park Service. At the request of the Tacoma Light Division a map of the same type was also made in 1940; it was not published but is on file in the office of the Conservation Division, U.S. Geological Survey, Tacoma, Wash. Nisqually Glacier was also mapped by terrestrial photogrammetry in 1952 and 1956 by Walther Hofmann of the Technical Institute in Munich, Federal Republic of Germany (Hofmann, 1958). Beginning in 1940, the Conservation Division of the U.S. Geological Survey, under the supervision of regional hydraulic engineers Arthur Johnson (to 1952), Fred A. Johnson (1953-62), and Gordon C. Giles (1963- ), has made annual surveys by stadia techniques of three cross-profiles of the glacier (locations on pi. 1). The Conservation Division also has made surveys of glacier movement and has reported on recession and volume changes (Johnson, 1960). The surveys have been carried out with the assistance and cooperation of National Park Service personnel and, in some years, with the financial assistance of the Tacoma Department of Public Utilities. The 1956 map used for showing locations of the photographic stations and cross profiles was prepared by the Topographic Division of the U.S. Geological Survey, which obtained the topography from aerial photographs by using a Wild A-8 plotter. ACKNOWLEDGMENTS This report was prepared under the general supervision of Mark F. Meier, geologist in charge of glacier research. The assistance of Austin Post and Donald Richardson was very helpful. Collaboration of several colleague reviewers, especially Arthur Johnson and Gordon C. Giles of the U.S. Geological Survey and W. O. Field of the American Geographical Society, is gratefully acknowledged. The Tacoma Department of Public Utilities furnished several photographs and assisted in the preparation of photographic illustrations for the report. Some photographs and the data on changes in ice-surface elevation at the cross profiles were supplied by the Conservation Division of the U.S. GeologicalPHOTOGRAPHIC PROGRAM 5 Survey. The cooperation of the National Park Service and the Washington State Historical Society in making their photographic files available is appreciated. DESCRIPTION OF THE AREA PHYSIOGRAPHY Nisqually Glacier extends from an altitude of about 14,350 feet (4,370 m) near the summit of Mount Rainier southward 4.1 miles (6.6 km) to a terminus (in 1966) at an altitude of 4,640 feet (1,410 m) for a total drop in elevation of about 9,700 feet (2,960 m). It is divided by Nisqually Cleaver into two channels from altitudes of 13,100 to 9,500 feet (3,990 to 2,900 m) in a horizontal distance of about 3,200 feet (980 m). Ice flow in the east channel is discontinuous at the steep cliffs opposite the upper part of Cowlitz Cleaver, where the ice stream is discharged in the form of intermittent avalanches or falls. If the glacier thickened sufficiently, the flow at that point would be continuous. The glacier is fed from the west between altitudes of 8,600 and 7,100 feet (2,620 and 2,160 m) by Wilson Glacier, as shown on the maps in figure 1 and plate 1 and in the photograph in figure 34. Wilson Glacier originates in a shallow cirque and occupies a short, wide basin on the south flank of the mountain. It is fed mainly by snowfall and snow avalanches, but it also receives a minor icefall or avalanche discharge from part of an upper lobe of Kautz Glacier. Nisqually Glacier has a surface width of approximately half a mile (0.8 km) from the foot of Nisqually Cleaver to profile 2 (pi. 1). Below profile 2 it tapers to a width of 500 feet (152 m) near the terminus. Its total area, including Wilson Glacier, was measured on the 1961 map as about 2.5 square miles (6.5 km2). The following tabulation augments the description of the glacier by providing basic data on the locations and altitudes of several features, as taken from the 1961 map, including rough approximations of the surface slope for the reaches between those features: Feature Distance above old highway bridge Midglacier altitude in 1961 Slope (degrees) Feet Meters Feet Meters Terminus in 1961 (crest of face) 5,830 1,780 4,800 1,460 25 Profile 1 6,870 2,100 5,290 1,610 17 Profile 2 9,380 2,860 6,050 1,840 13 Profile 3 Base of lower icefall and approximate 12,850 3,920 6,840 2,080 16 firn limit 1 Top of upper icefall (near top of Nis- 14,460 4,410 7,300 2,220 30 qually Cleaver) 24,400 7,440 13,100 3,990 27 Head 26,800 8,170 14,350 4,370 1 In this report, the term “snow” is restricted to that which fell during the most recent winter season, and "firn” designates granular snow that has survived one or more ablation seasons. Nearly 8,000 feet (2,440 m) up valley from the site of the former highway bridge and 1,200 feet (370 m) above profile 1, the glacier flows past and sometimes over a nunatak2 (fig. 27). The top of the nunatak is at an altitude of 5,670 feet (1,730 m). It currently diverts a major part of the east-half ice flow toward the west wall of the canyon; for more than 10 years, from the early 1940’s to the mid-1950’s, essentially all the ice flow was west of the nunatak. CLIMATE The Nisqually Glacier area receives most of its precipitation from moist, eastward-flpwing cyclonic storms which form over the Pacific Ocean on the south edge of the winter Aleutian low-pressure area. More than 80 percent of this precipitation falls as snow during the period October to May. Since the low-level winds normally flow from the southwest during these winter storms, Nisqually Glacier, lying as it does on the south side of Mount Rainier, receives nearly the full effect of the storms. A precipitation shadow lies to the northeast of the mountain. During the period 1920-59 the annual precipitation at Paradise Ranger Station (fig. 1), at an altitude of 5,430 feet (1,660 m), averaged 106 inches (269 mm) for the 24 complete but noncontinuous years of available record. On parts of the glacier, particularly at higher altitudes, the precipitation may have been greater. Snow depths at Paradise sometimes reach 30 feet (9 m). The range in annual precipitation recorded there during the 1920-59 period was from 64 to 138 inches (163 to 351 mm). THE PHOTOGRAPHIC PROGRAM NETWORK OF STATIONS Several of the photographic stations were established at sites from which miscellaneous earlier photographs had been taken—for example, the 1890 view that was published in the 18th Annual Report of the U.S. Geological Survey. Additional stations were selected to improve the overall coverage and to collect some views illustrating geomorphological changes in the hills and valley. The objective was to provide fairly complete coverage of the glacier and valley below, with at least two angles of view available for every area insofar as feasible. Along the east side of the glacier two “tiers” of stations were used—one as high as feasible and the other 2 This rock hill was termed a nunatak by Giles (1960), is locally known by this name, and is so termed herein. However, this knob does not always project above the surface of the ice, nor is it always surrounded by ice, so it does not always fit the accepted glaciological definition of “nunatak.” 352-693 0—69 26 ANALYSIS OF 2 4-YEAR PHOTOGRAPHIC RECORD not far above the glacier surface. The higher stations provide most of the information needed for study of the glacier, but the lower ones are especially useful in any analysis of longitudinal surface slope or in any photographic determinations of rates of surface movement (the latter subject was not studied in this report). The selection of photographic stations, except near the highway bridge, was restricted to the more -accessible east side of the glacier. An attempt was made to avoid hazardous areas, such as those too precipitous or subject to rolling rock, and sites where tree growth or rise of the glacier surface might later obstruct the view. A brief description of each photographic station, including its period of record, is given in table 1; the locations are shown on plate 1. The approximate direction of every panoramic view photographed from each station is indicated on plate 1. Each view series is given NISQUALLY GLACIER, MOUNT RAINIER, WASH. a serial number corresponding to the number of the station, with direction of the view added when necessary for differentiation between series. Footnotes explain the changes that have been made in the location of each station. PHOTOGRAPHIC SERIES NOT PUBLISHED Several of the photographic series shown on the map and in the description list are not discussed in this report but are included to indicate their availability in the files of the U.S. Geological Survey, Tacoma, Wash., should they later become of interest. These are series Nos. 1-SW, 2-NE, 4, 5-W, 8-W, 8-N, 9, 10, 12, 14-N, 16, 17-S, 17-NW, 18-S, and 18-NW. Some have been discontinued. Table 1.—Descriptions of the photographic series, 1890-1966 Years Altitude Geological Survey Direction of view Series Figures of ------------------------------- period of record relative Place from which photographs were taken record Feet Meters to glacier l-NE . 16-19 ' 20 3, 900 1, 190 1942, 1947, 1949- Up Highway bridge on Nisqually River. 1-SW 20 3, 900 1, 190 1942, 1947- Down Do. 2-NE 20 4, 300 1, 310 1943-50, 1952, 1953, 1956- Up Stone monument on cliff.2 2-S 39 17 4, 300 1, 310 1943, 1947-50, 1952, 1953, 1956- Down.. - Do. 3 _ 36-38 14 4, 150 1, 260 1941, 1942, 1947, 1952, 1956- do Viewpoint % mi (0.4 km) north of Ricksecker Point. 4 10 4, 250 1, 300 1944, 1955, 1958- Up Canyon Rim viewpoint.3 5_ _ 20-25 21 5, 240 1, 600 1940, 1942-45, 1949-52, 1954- Up Nisqually Vista, at trailside exhibit. 5-W 5 13 5, 240 1, 600 1943-46, 1949-57 Across. __ . Do.4 6 . 27-31 24 5, 560 1, 690 1942- Up Point on cliff.6 7 2-5 16 5, 760 1, 760 1890, 1940-42, 1945, 1948, 1951, 1954, 1958- Up Bend in trail to glacier (1890 station). 8-W 21 5, 580 1, 700 1941-46, 1951- Across.. .. . 18 ft (5.5 m) west of B.M. 5587, on old moraine. 8-N 27 5, 580 1, 700 1931, 1936, 1941- Up Do. 9 10 6, 040 1, 840 1915, 1943, 1955, 1958-60, 1962- Across.. 60 ft (18 m) west of old trail on ridge.7 10 19 5, 860 1, 790 1947- do Point on moraine trail. 11 35 16 6, 050 1, 840 1940, 1947, 1951-53, 1955- Down Do.3 12 13 6, 074 1, 850 1936, 1941, 1955- Across 0 B.M. 6074, on old moraine. 12-N 26 3 6, 074 1, 850 1940, 1955, 1956 Up Do. 13 . 32-34 17 6, 325 1, 930 >» 1949- Across and up. Point on bedrock beside Skyline Trail. 14-W _ 7-10 18 6, 165 1, 880 1942-44, 1951 Across . . B.M. 6165, on moraine. 14-N 20 6, 165 1, 880 1942-44, 1947, 1951- Up Do. 15 12 22 6, 293 1, 920 1943-46, 1948- Up B.M. 6293, on moraine. 16 17 6, 428 1, 960 1949-65 Across and up. B.M. 6428, on moraine. 17-S 2 6, 800 2, 070 1964- Down Large rock on a moraine.11 17-NW 2 6, 800 2, 070 1964- Across and up. Do.11 18-S 17 6, 882 2, 100 1943-44, 1946, 1948-55, 1958-62, 1964 Down B.M. 6882, on large imbedded rock.12 18-NW 17 6, 882 2, 100 1942-44, 1948-55, Across and up. Do.12 1958-62, 1964 * Used old bridge through 1960 and new bridge several hundred feet downstream and a little higher in elevation, 1959-65. Numerous photographs looking up glacier from station 1 are available in the files of other agencies. 2 Prior to 1964 this series was taken about 100 ft (30 m) farther up glacier, at old survey stake No. 1185. 3 1944 taken from road H mile (0.4 km) south; 1955 and 1959 taken from bend in road 0.7 mile (1.1 km) south of Canyon Rim viewpoint. 4 Prior to 1949 taken from bend in trail about 110 ft (30 m) northeast of Nisqually Vista. 5 After 1957 the terminus was photographed in series 5. • Prior to 1957 taken from site about 200 ft (60 m) west and 50 ft (15 m) lower in altitude. 7 1943 view taken from about 200 ft (60 m) north of 1915 site, and all views thereafter taken from new point about 400 ft (120 m) north of 1915 site. 8 Taken from 3 points with a radius of 25 ft (8 m). 9 Usually panoramas covering about 135° down, across, and up glacier. 10 The 1949 photograph was taken at or near B.M. tablet 4-1940 situated about 500 ft (150 m) up glacier from the bedrock point used thereafter. 11 This point established to supersede B.M. 6882 to obtain less hazardous access. » In 1943, 1944, 1948, 1951, and 1953 the views were taken from B.M. 6853 which is about 50 ft (15 m) west and 30 ft (9 m) lower than B.M. 6882.QUANTITATIVE INTERPRETATIONS FROM THE PHOTOGRAPHS 7 TIME OF YEAR AND WEATHER CONDITIONS To obtain information on annual accretion, wastage, and movement of ice in Ni squally Glacier, the photographs have been taken as late in the ablation season as thought safe before a heavy, fresh snowfall might occur. Early in the program the photographs were taken in late August, but more recently they have been taken during the first 2 weeks of September. Although the minimum mass of glacier ice and snow normally occurs in late September, photographs are taken earlier to avoid risk of a snowfall which would conceal features such as the firn line. The climate at Nisqually Glacier is characterized by rapid changes in weather which are difficult to predict owing to the paucity of weather data beyond the coastline. Such changes may seriously interrupt completion of the photography, and they sometimes necessitate a second trip to Mount Rainier. Weather variations make it much more difficult to schedule aerial photography or to spend a number of days in cumbersome (though more precise) phototheodolite procedure; this emphasizes the economy of using a hand camera in one quick trip that can take full advantage of a brief break in the weather. CAMERA EQUIPMENT Cameras used for taking the 1942-65 pictures mentioned in this report were: 1942-57—Kodak Model 3-A, film size 3% by 5y2 inches, focal length 170 mm, equipped with cable shutter release; 1958-65—Kodak Tourist, film size 21/i by 3% inches, focal length 105 mm. Exposures normally were for l/200th second at f-11 or f—16, and were all made with the camera handheld. In general, Kodak Super XX film (speed ASA 100) was used from 1942 to 1955 and Kodak Verichrome Pan (ASA 80) thereafter. The relatively low graininess of these films and their latitude to accommodate the contrasting lighting encountered in glacier scenes have been satisfactory. In this program, the experimental use of lens filters, particularly the K-2 (yellow) one, have shown no advantage over the unfiltered lens. LIGHT CONDITIONS An effort was made to take the annual view at each station at the same hour of the day, as well as at the same time of year, so that similar light conditions would minimize illusory effects and possible misinterpretations. This was not always feasible, but analyses made during preparation of this report emphasize the importance of following such a procedure. SCALE CORRECTIONS ON PRINTS The selected enlargements or prints in each photographic series utilized in the quantitative analyses in this report were reduced to the same scale by developing and applying scale-ratio coefficients. These were obtained by scaling the linear distances between identical fixed points (features in bedrock) common to all the prints, and determining the ratio between the value for each print with respect to the comparable value on a selected base print. The resulting coefficients were applied to any analytical data measured on those prints to reduce all measurements to the scale of the base print. QUANTITATIVE INTERPRETATIONS FROM THE PHOTOGRAPHS CHANGES IN ICE THICKNESS Annual photographs can readily be used for analyzing the approximate year-to-year changes in a glacier’s thickness. Three examples are described below, using lateral ice margins, the crest of the ice as seemin lateral views, and the crest of an ice bulge as viewed from down glacier. In the first example, on each annual photograph in series 7 (selected years of which are shown in figs. 2-5) a smoothed line was drawn for a few thousand feet along the west ice margin3 downstream from Wilson Glacier. The positions of several points on each marginal line were then defined by measuring down to them, on the pictures, from a series of fixed points (bedrock features) along the canyon wall identifiable on all the photographs studied. Next, the distances so measured were adjusted to the scale of the August 23,1951, view, which year was selected as the year of minimum ice in that area. The scale adjustment was done by means of scale-ratio measurements made between several fixed points identifiable on all the prints. Using the converted distances, the lines were transferred to the 1951 print (fig. 6). Most of these ice-margin lines are believed to be accurate to ± 20 feet (6 m) vertically or horizontally. The greatest source of error is in the subjective determination of the location of the margin of the active ice for each year because the margin is obscured in many places by varying amounts of remnant ice, snow, or rock debris. In the series 7 photographs, the valley wall is about 3,300 feet (1,000 m) away from the camera opposite the middle of the nunatak and 7,500 feet (2,300 m) away just below Wilson Glacier. The approximate 8 The margin is the apparent edge of the moving ice, whether it is obscured by detritus or not.ANALYSIS OF 2 4-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. Figure 2.—Nisqually Glacier, from confluence with Wilson Glacier to the nunatak, as seen from station 7 in 1 890 (date uncertain). (Figures 2-5 were photographed from the same viewpoint as was used for the photograph published in the Geological Survey’s Annual Report for 1896-97 (Russell, 1898).) Note some similarities to 1963 view in regard to extent of ice and patterns of crevassing,- note also the absence of a large moraine near the west canyon wall. Photograph is believed to have been taken in 1890 by W. O. Amsden, but may have been taken in 1896 by a member of the I. C. Russell (U.S. Geological Survey) reconnaissance party.QUANTITATIVE INTERPRETATIONS FROM THE PHOTOGRAPHS 9 Figure 3.—Nisqually Glacier, from confluence with Wilson Glacier to the nunatak, as seen from station 7 in August 191 5 by G. L. Parker, U.S. Geological Survey. This view was taken from a slightly different location than the others in series 7; it was higher on the hillside, with camera pointed farther to left. Note (as is graphically verified in fig. 6) how the conformation of the surface slope of the ice along the west canyon wall was different in 191 5 than in 1963 or 1965, and how during the intervening half century many changes in exposure of the rock formations occurred. Note also the two moraines near far edge of glacier, marked by debris lines.10 ANALYSIS OP 24-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. Figure 4.—Nisqually Glacier, from confluence with Wilson Glacier to the nunatak, as seen from station 7 on August 22, glacier is at about its lowest known ice mass, as evidenced by the exposure of bedrock. There is almost no crevassing in at profile 2 (location in fig. 20) is very flat and broken below there. Note the light-colored medial moraine approaching right. Sources of debris may be deduced. Note also large ice-cored moraine along west edge of glacier.11 QUANTITATIVE INTERPRETATIONS PROM THE PHOTOGRAPHS Figure 5.—Nisqually Glacier, from confluence with Wilson Glacier to the nunatak, as seen from station 7 on August 27,1963. Note transverse crevasses developing in east part of glacier above nunatak indicating the direct down-valley movement of that ice. Ice-cored moraine seen in figure 4 is now subdued because of the rejuvenated movement. Note that since 1945 the glacier has recovered much of the volume evident in the 1 890 view. > * > v1 12 ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD, NISQTJALLY GLACIER, MOUNT RAINIER, WASH. i ^96^- ^ \9&« Figure 6.—Ice margins for selected years in period 1890-1965 are indicated on the series 7 photograph taken August 23, 1951. Note that by 1965 the glacier had recovered much of the ice thickness it had lost since 1890. 1 < iQUANTITATIVE INTERPRETATIONS FROM THE PHOTOGRAPHS vertical scale of the valley wall on a photograph could readily be calculated from these distances and the camera’s focal length. In the second example of ice thickness analysis, data for the graphical plotting of the changes in ice-surface elevation at a single cross-profile axis were derived as follows. On each annual print of series 14-W (figs. 7-10) the distance was measured between a selected rock feature on the canyon wall directly opposite the photographic station and the ice margin directly below it. The results were converted to a common-scale basis with respect to the print for year of the lowest ice, 1951, as was described in the previous example, and the values were plotted graphically against time (fig. 11 A) and compared with the thickness changes indicated by the annual cross-profile surveys. The graph of thickness changes measured on the photographs could not be given a vertical scale in feet (or meters) unless it were obtained by comparison with field survey results, as is this case, or by geometrical computation using map data and the camera lens focal length. On the graph in figure 11A the scale of the photographic measurements was adjusted to closely fit the scale to which the field surveys were plotted. There are a few small inconsistencies between the field surveys and photographic measurements in figure 11 A, probably due to the low vertical angle between the camera viewpoint and the distant ice margin which is not always clearly visible. Still, such a graph for a valley glacier lying between steep canyon walls is roughly indicative of the changes in ice thickness in the entire cross section of the glacier opposite the point of measurement. A third example of a method of determining ice thickness variations from photographs utilizes the measurement reach indicated on the 1944 view in photographic series 15 (fig. 12) taken looking up glacier. In the annual photographs of series 15, distances were measured down from a bedrock feature to the crest, as seen from the photographic station, of a “standing” wave or bulge in the glacier surface nearly 4,000 feet (1,200 m) up glacier from profile 3 at an altitude of 8,400 ± 100 feet (2,560 ± 30 m). This bulge (fig. 12) occurs at the downstream end of a reach of relatively flat slope, and its crest is seen in profile when looking upstream from below. The distances so measured were plotted against time, using an estimated vertical scale, and thus their fluctuations were compared with the stadia surveys of profile 3 (fig. 11B). Though without a true vertical scale in feet (or meters), these results are indicative of the fluctuations in position of the ice surface at that site during glacier advance or recession. In this example the values are 13 believed to be accurate to within plus or minus 25 feet (8 m). It is most interesting that thickness changes were nearly synchronous at profile 3 and at the bulge 1.2 km above profile 3. The minor inconsistencies between the graphs in figure 115 may possibly be caused by differences in timing of the ice advances of Wilson Glacier with respect to those of Nisqually Glacier above Wilson Glacier. An attempt was made to check this timing, but the results were not satisfactory. The reason for this may be the small upward angle of view in the photographs of the top of any ice bulge on Wilson Glacier; they do not place the lip of the bulge sufficiently in outline or profile. Another source of inconsistency may be the irregular changing shape of the top of the ice bulge occurring from year to year. CHANGES IN LATERAL ICE MARGINS Some of the ice-thickness analyses in the preceding section also indicate changes in position of the lateral ice margins of the glacier. Such changes are further illustrated by lines around the nunatak as shown on an enlarged part of the August 22, 1951, view from series 6 (fig. 13). The ice margins for each of the selected years indicated were transferred by tracing from one single weight print to another, over a very bright light. All the annual prints used must be enlarged to the same scale. The maximum error incurred in figure 13 is estimated to be ± 30 feet (9 m) measured along the surface of the ground rather than vertically or horizontally; the average distance from the camera is 2,500 feet (760 m), varying from about 2,100 to 2,900 feet (640 to 880 m). It was found that the topographic maps and crossprofile survey results currently available for this glacier do not contain enough detail to permit the derivation of as accurate data on changes in the ice margins, in some areas, as can be determined from photographs. LONGITUDINAL SLOPE OF THE ICE SURFACE The photographs in series 14-W (figs. 7-10) were found suitable for obtaining measurements of longitudinal slope of the glacier surface at profile 2. On each annual print the angle of slope was measured by protractor with respect to a vertical line (figs. 7-10) projected on the canyon wall at far end of the profile. The position of this line was determined from a phototheodolite view that was taken by the Conservation Division of the U.S. Geological Survey and was checked from a photograph taken by the writer in which a plumb-bob line was suspended in front of the camera. It was interesting to find that the general slope of the glacier is deceiving to the eye; it is greater than it appears, and thus14 ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. i Figure 7.—View across glacier in series 14-W (profile 2) used to determine slope and changes in ice thickness,- photographed on August 21, C 1942. The vertical line used in measuring angle of slope of the ice surface is shown. Not indicated is the bedrock feature from which the changes in ice-surface elevation were measured. The apparent crest of the debris-covered ice (arrow), rather than the white ice, was averaged to compute slope and changes in thickness in this and all other views in this series. Note that the hand-held camera had been tilted, due to the deceptiveness of the true slope of the glacier.QUANTITATIVE INTERPRETATIONS FROM THE PHOTOGRAPHS 15 Figure 8.—View across glacier in series 14-W (profile 2) used to determine slope and changes in ice thickness; photographed on August 27, 1952. The vertical line used in measuring angle of slope of the ice is shown. Note the relief visible in the canyon wall, which is not at all apparent in the views that were taken in 1942, 1960, and 1965 under flatter lighting.16 ANALYSIS OF 2 4-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH Figure 9—View across glacier in series 14-W (profile 2) used to determine slope and changes in ice thickness; photographed on September 8,1960. The vertical line used in measuring angle of slope of the ice is shown. Note that glacier surface in this area has become much rougher since 1952 (fig. 8), and the streak of white (clear) ice is now hidden behind the thickened zone of crevassed, debris-covered ice.QUANTITATIVE INTERPRETATIONS from the PHOTOGRAPHS Figure 10. View across glacier in series 14-W (profile 2) used to determine slope and changes in ice thickness,- photographed on August 30, 1965. The vertical line used in measuring angle of slope of the ice is shown. Note that the crevassing is more pronounced than it was in the 1960 view (fig, 9), and there is less contrast between clear and debris-covered ice.18 ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. ALTITUDE OF CROSS PROFILE 1845 1840 - 1830 - 1825 1820 1815 - 1810 - 1805 DISTANCE ON PHOTOS 4.50 5.00 5.50 - 6.00 - 6.50 £ i o z - 7.00 - 7.50 - 8.00 - 8.50 - 9.00 - 9.50 2085 2080 - 2075 - V) cr “ 2070 - 2065 2060 2055 2.60 - 2.65 10 - 2.70 g; - 2.75 -J 5 - 2.80 -J2.85 B Figure 11.—Graphs showing changes in ice-surface elevation, or thickness, of the glacier. A, Changes in glacier thickness at cross profile 2 as measured on photographs are compared graphically with results of the annual stadia surveys. It should be noted that each stadia survey value used in the comparisons is the average ice-surface elevation along the cross profile, but each photographic measurement is made from a bedrock feature in the conyon wall down to only one point, selected in each photograph as either the apparent crest or a representative point useful for the purpose. B, Changes in ice-surface elevation as measured on photographs at an ice bulge nearly 4,000 feet (1,200 m) upglacier from profile 3 are compared graphically with the results of annual stadia surveys at profile 3. The values from photographs are obtained by measuring from a fixed point on bedrock down to the top of the ice bulge as it is seen in profile from down glacier at station 15 (fig. 12).Figure 12.—Changes in ice thickness occurring about 4,000 feet (1,200 m) up glacier from profile 3, were measured on the photographs in series 1 5 in the reach indicated on this September 3, 1944, ^ view from that series,- upper end of measurement is the base of a lava * flow and lower end is top of the ice. This 1944 view illustrates the general nature of the upper area after many years of recession had Ik •• occurred, just preceding the ice advance of the late 1940's. The ice discharge from Wilson Glacier is low, and large areas of bedrock near its mouth are exposed. The falls at far left are relatively large compared with their condition in later years (1957-65). Note the opposite directions of cleavage in crevassing patterns which are visible in midglacier at lower left. It is evident that the debris load comes from sources along both sides of Nisqually Glacier and from Wilson Glacier. Bedrock areas marked by small X's were inundated by ice as the glacier thickened and expanded (compare with fig. 34 which shows this area in 1965).Figure 1 3. Ice margins around the nunatak for selected years in the period 1942-65 are indicated on the August 22, 1951, photograph taken from station 6. The down-glacier parts of the 1942, 1961, and 1965 lines are indeterminate because the ice is obscured by debris. QUANTITATIVE INTERPRETATIONS FROM THE PHOTOGRAPHS 21 makes the photographer unconsciously tilt a hand-held camera a little in a down-glacier direction. A protractor was placed along the apparent crest of the dark ice in each picture on a reach 100-200 feet (30-60 m) in length. On a few of the annual prints, the top of the white ice near the far margin of the glacier may have been better than the dark ice as an index of the slope, particularly on the print for 1952 (fig. 8), where the white ice surface is especially prominent and is about 2 degrees steeper than the dark ice. However, in the photographs for most other years, the white ice either is too obscured or could be confused with the glacier’s margin, so it was not used. For comparison with the photographic results obtained from 1942 to 1965, slope values in the same period were determined from topographic maps for 1941,1946, 1951,1956, and 1961. (See fig. 14.) On each map a 200-foot (60-m) reach was used, drawn along the same ice ridge as appeared in the corresponding photograph to be the crest of the ice. Elevations between contours were interpolated. The results for 1951, 1956, and 1961 probably are more accurate than those for 1941 and 1946 because of the more refined procedures used in making the later maps. The results were used (Meier, 1968) in a study of 'the flow and stress in Nisqually Glacier. The slope values obtained from maps are somewhat greater, by about 2 degrees, than the corresponding values measured on photographs. This is believed due to a lack of sufficient detail in the maps for this kind of a study; they do not completely reflect the Short reach of flattened slope that occurs in the immediate vicinity of profile 2 in the east half of the glacier, which is discernible in some photographs. (See fig. 4.) See also the generalized slope values for the glacier given in the tabulation on page 5. One source of error in the measurement of glacier slopes on photographs, under conditions similar to those at profile 2, is the effect of varying vertical angles of camera view that result from the different stages of the glacier. During the 18 years covered by this analysis, the mean altitude of the glacier surface along profile 2 fluctuated below the camera viewpoint at station 14 by amounts ranging from 110 to 240 feet (34 to 73 m). Thus, because of the downward angle of camera view, the longitudinal ice-surface profile appearing on the prints to be the crest probably lies on the far side of the true crest. In addition, as the glacier surface rises and falls from year to year the crest seen on the photographs may Shift laterally toward and away from the camera or, by chance, may lie at an angle to the main flow lines of the glacier. The above factors create some relatively minor errors when glacier slopes measured on photographs are compared with those obtained from contour maps. However, the fact that the changes in slope obtained by the two methods are reasonably consistent with each other indicates that the photographic method, which is relatively low in cost, is accurate enough to be a useful and1 valuable accessory in a reconnaissance study of glacier slope. Additional comments on the slope of the glacier are contained in the section “Crevassing and General Character of Glacier Surface.” SNOW LINES AND FIRN EDGES Oblique photographs of a glacier taken from stations on the ground along only one side of a glacier were found to have but limited value for mapping and analyzing the boundaries of snow and firm These photographs give fairly satisfactory coverage for that purpose on the full width of the glacier up to an altitude of about 5,800 feet (1,800 m), and on its eastern half up to about 6,700 feet (2,000 m). However, at higher Figure 14.—Determinations of longitudinal slope of the glacier surface at profile 2, as measured on the annual photographs taken from station 14-W, are compared graphically with those measured on the 5-year series of topographic maps. 352-693 0—69-----i22 ANALYSIS OP 2 4-YEAR PHOTOGRAPHIC RECORD, altitudes some parts of the glacier surface are obscured by ice bulges or moraines or by slopes dipping away from the position of the camera. So, when these lines are to be mapped and it is not economical to have pho-tographic stations at rather high altitudes on both sides of a glacier, it would be better to obtain aerial photographs. In this report the lower edge of the snow is called the snow line, and the lower extremity or edge of the firn is called the firn edge. (See also footnote 1, p. 1.) The wide range in annual altitude of the snow line and firn edge on Nisqually Glacier from 1942 to 1965 and their extremely broken appearance are evident in the various photographs published herein. On a 1955 picture (fig. 15) taken from station 13 a few of the firn areas have been outlined to illustrate their scattered occurrence. Location of the firn edge ranged from about 6.000 to 7,300 feet (1,880 to 2,250 m) during the period covered by these photographs. Position of the snow line in late summer of each year has been found to range between about 5,800 and 7,300 feet (1,750 and 2,250 m). An example of a well-defined snow line on this glacier is seen in the 1942 view in series 5 (fig. 20), where but little snow remained below 7.000 feet (2,100 m). QUALITATIVE INTERPRETATIONS CHARACTERISTICS OF THE TERMINUS The terminus of Nisqually Glacier has been illustrated by photographs since 1884. These complement the field surveys by showing in more detail the irregularities of the terminal margin and by indicating its approximate position during periods when no surveys were made. For example, figures 16 and 17 show that the glacier terminus near the falls at left was in a more advanced position in 1908 than in 1903. The dynamic condition of a glacier’s snout also is revealed by photographs (Meier and Post, 1962). By its characteristic bulging, crevassed, “fat” appearance an advancing terminus (fig. 16) usually can be distinguished from a retreating terminus (figs. 17-19). If a glacier is receding or stagnant, the front has fewer crevasses and is more gently sloping; it may be segmented as is shown in the 1962 picture in series 5 (fig. 24) where the advance of fresh ice is visible upglacier but has not yet affected the dead-ice terminus. Ice hummocks on the glacier (fig. 17) also indicate a wasting condition. The “sliced-off” appearance of the terminal front shown in figure 18 has been typical of Nisqually Glacier’s stagnant terminus during its long recession. For further illustration of changes in the glacier’s terminus, see figures 20-25. NISQUALLY GLACIER, MOUNT RAINIER, WASH. The photographs in this report, when viewed in the light of contemporaneous field survey results, show that the appearance of a glacier’s terminus is roughly indicative of its dynamic state; however, the terminus does not reflect any condition upstream from the terminal area. Further, annual pictures of the snout do not necessarily reveal the presence or absence of movement of the terminus. For example, while photographs might illustrate the occurrence of a net recession of 30 feet (9 m) in a 12-month period, this could have resulted from 10 feet (3 m) of forward movement accompanied by 40 feet (12 m) of melting, or 70 feet (21 m) of forward movement offset by 100 feet (30 m) of melting. DEBRIS COVER AND ITS DISTRIBUTION Annual photographs are useful in a study of the changing patterns of debris carried on a glacier’s surface. Examples of information about debris readily observable on the Nisqually Glacier photographs are as follows. The 1945 view in figure 4 shows that the extensive load of debris carried on the east side of Nisqually Glacier between altitudes of 5,700 and 7,000 feet (1,740 and 2,130 m) originates from Nisqually Cleaver west of Gibraltar Hock, from the southwest slopes of-Gibraltar Kock and Cowlitz Cleaver, and from the down-glacier hillsides bordering the east side of the glacier. In years of above-average snowfall such as 1890 (fig. 2) and 1954 (fig. 22) this mantle of debris was obscured by snow as far down the glacier as about an altitude of 5,800 feet (1,800 m). The photographs in figures 20-25 also indicate that the insulating effect of debris was responsible for development of the debris-covered, high, morainelike ridge of ice which was visible for many years near the west edge of Nisqually Glacier downstream from Wilson Glacier; and they show how this ridge later became obscured during the new ice advance. Changes in debris conditions are also illustrated in figures 27-34, and described both in the picture captions and in the section “Crevassing and General Character of the Glacier Surface.” MORAINES Photographs may bring out some detailed moraine and erosion patterns not noticed by an observer on the ground because film can emphasize color values and relief otherwise not very apparent. The pictures for different years can readily be examined and compared with respect to subtle features, which may easily be forgotten if observed only during occasional field inspections. An example of such a feature is the light-colored band in the large medial moraine near the east sideQUALITATIVE INTERPRETATIONS 23 Figure 15.—Several areas of firn are outlined on this September 3, 1955, view taken from station 13. Note patchy, broken configuration of the firn edge.24 ANALYSIS OF 2 4-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. ***«. ' V V*' *: - . " ^ ^ V m {- .>■ * w r. m , , . . ,, . wir - , . rtC>ar the old highway bridge in 1903. Note bulging rigure 16.—Photograph of the terminus selected from series 1-Nb, taken trom a point at or 4 A . 4 , , < . . , , , , I .1 .. | ,, Those characteristics suggest that the terminus is, or has shape of terminus, steepness of downstream face, and the vertical crevassing pattern. ^ Service very recently been, advancins. Photographed by Eugene Ricksecker; furnished by the Natl0naQUALITATIVE INTERPRETATIONS 25 - BHaBK ~ -- ~ SI t-jVK -- 1 HflE. -1 »*■- - Hi v ] Hr . 1 ‘W - frmk &■> *_ ■ n ^hh L • ->»V’ , Vi ^P| H1 WBBF » i * mV - • ■«-% § ; JfW-' Figure 17.—Photograph of the terminus selected from series 1-NE, taken from a point just below the old highway bridge in 1908. Note changes in terminus with respect to 1903 photograph. At upper left the bulging ice has been replaced by ice hummocks,- the crevassing pattern on downstream face is no longer predominately vertical; ice surface now has the general appearance of being melted and eroded. These conditions suggest that the advance has ceased and the terminus has begun to recede. Photographed by Mr. Leftbetter of Seattle,- furnished by Tacoma City Light.26 ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. Figure 18.—Photograph of the rom ser'es 1-NE, taken from a point at or near the old highway bridge on July 5, 1929. In marked contrast to the 1 an . appearances, the noncrevassed, "sliced-off’’-looking terminal face and the generally concave, debris-covered condition o t e sur ace a ove indicate that the terminus is now definitely receding and is approaching a stagnant condition.QUALITATIVE INTERPRETATIONS 27 Figure 19.—Photograph of the terminus selected from series 1-NE, taken from a point at or near the old highway bridge on August 19,1942. The terminus is now more irregular and segmented than in 1929. This suggests stagnation, as there is little evidence of ice flow to the terminus from above. The rate of melting is probably reduced because of the extensive debris cover.28 ANALYSIS OF 2 4-YEAR PHOTOGRAPHIC RECORD, NISQTJALLY GLACIER, MOUNT RAINIER, WASH. Figure 20.—Lower part of Nisqually Glacier as seen from station 5 on August 31,1942. Approximate locations of the surveyed cross profiles are shown. Entire glacier is receding. Area down glacier from profile 1 (lower end of the white ice) is stagnant, as indicated by hummocky, debris-covered, noncrevassed ice. Note the long morainelike ridge of debris-covered ice immediately to left of the white ice. The nunatak is bare. Note debris load on right half of the glacier from profile 3 downstream.QUALITATIVE INTERPRETATIONS 29 *&/-', ' • ::. ;m , :• Figure 21.—Lower part of Nisqually Glacier as seen from station 5 on August 22, 1951. Since 1942 the glacier has thickened by about 80 feet (24 m) at profile 3 and 40 feet (1 2 m) at profile 2, but it still is thinning at profile 1. Note the lateral melting of ice ridge to left of the nunatak, as compared with the 1942 view, and the exposed river bed.30 ANALYSIS OF 21-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. Figure 22.—Lower part of Nisqually Glacier as seen from station 5 on September 1, 1954. This is the year of minimum ice mass at profile 1 where, according to surveys, the glacier surface has dropped 1 3 feet (4 m) since 1951,■ at profile 3 it has dropped 21 feet (6 m), but at profile 2 the glacier is now 42 feet (1 3 m) thicker than in 1951. Note steep front of the vigorous advance of fresh ice which is passing to left of the nunatak. Downstream from there the ice is "dead" and melting away—slowly, however, owing to its insulation by a thick mantle of debris. Surveys show that 1954 is the first year when a segment of the ice surface near the west end of profile 1 began to rise.qualitative interpretations Figure 23.—Lower part of Nisqually Glacier as seen from station 5 on September 11,1959. With respect to its 1954 condition the glacier now is 9 feet (3 m) thinner at profile 3,12 feet (4 m) thicker at profile 2, and 70 feet (21 m) thicker at profile 1 .The stagnant ice terminus now is visible at lower left. Fresh, white ice has nearly obscured the debris-covered ice ridge opposite the nunatak near the left (west) edge of the glacier.32 ANALYSIS OF 2 4-YEAR PHOTOGRAPHIC RECORD: NISQUALLY GLACIER, MOUNT RAINIER, WASH, Figure 24.—Lower part of Nisqually Glacier as seen from station 5 on September 8, 1962. Profile 3 is 7 feet (2 m) higher than in 1 959, and since then the glacier has thickened 22 feet (7 m) at profile 2 and 24 feet (7 m) at profile 1. The broad bulge of thickening is visible in midglacier in the vicinity of profile 2. The nunatak has been topped by flowing ice. Dead ice downstream has receded considerably since 1959, but now previously stagnant ice in midchannel is thickened and has been incorporated in the advancing terminus.QUALITATIVE INTERPRETATIONS 33 Figure 25. Lower part of Nisqually Glacier as seen from station 5 on August 30, 1965. With respect to its 1962 condition the glacier has gained 3 feet (1 m) in thickness at profile 3 and lost 5 feet (2 m) at profile 2; however, at profile 1 the thickness has increased 34 feet (10 m). The preliminary result now available for the 1966 survey shows that 1965 was a peak year at profile 1. The vigorous terminal reach and snout of the glacier have completely covered or incorporated all vestiges of stagnant ice. The nunatak is almost entirely engulfed.34 ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD of the glacier in figure 4. Another example is shown in the 1940 photograph taken from station 12 (fig. 26), which illustrates several small lateral moraines that had been deposited along the east side of the glacier at an altitude of 6,400 feet (1,950 m), suggesting a discontinuous rate of recession of the glacier. CREVASSING AND GENERAL CHARACTER OF THE GLACIER SURFACE In addition to the data presented in the preceding sections, some further examples of what photographs can show about glaciers are given below on the following subjects (all of which have not been studied herein in detail): 1. Crevassing patterns, from which the nature of the subsurface structure, the direction of ice movement, and changes in rates of movement can be interpreted. 2. Information of changes in surface slope, or the shape of its longitudinal profile, in areas not covered by surveys and contour maps. 3. Some details about advance, recession, debris load, contour, movement, thickness, and surface erosion. Terminus to profile 1 Photographic series 1-NE (figs. 16-19) and 5 (figs. 20-25) illustrate the gradual deterioration and shrinkage of the entire glacier downstream from the nunatak and profile 1, and its subsequent reactivation. This lower area was virtually stagnant from about 1944 to 1954, but a spectacular advance of fresh ice passed the nunatak in 1954-55 and reached the terminus in 1963. By 1965 it had given form to a new, vigorous-looking terminus. Profile 1 to about 1,000 feet (300 m) above profile 2 Captions for the photographs in series 6 (figs. 27-31), 7 (figs. 2-5), and 14-W (figs. 7-10) contain miscellaneous descriptive comments for this reach of the glacier. Certain features can be seen more clearly in one series than in the others. The following comments about the photographs in series 6 and 7, arranged in chronological order for each series, include most of the descriptive material that is contained in the captions: Photographic series 7 (figs. 2-5) 1890 The glacier above the nunatak is at the highest stage ever known to have been photographed. 1915 Note the debris-covered moraines along far side of glacier, which were not visible in 1890. The nunatak (at lower right) still is covered by ice. 1945 Nunatak is exposed. Slope at profile 2 is almost flat. Light-colored band of debris shows in medial moraine at right center; Wilson Glacier ice discharge is very low. There is almost no crevassing in middle reach. NISQUALLY GLACIER, MOUNT RAINIER, WASH. 1963 Crevassing in midglacier near profile 2 is extremely coarse or rough. Ice level at profile 2 is the highest in nearly 30 years. Direction of the crevassing pattern in east part of glacier above the nunatak, when compared with that in figure 27, indicates that as the nunatak becomes submerged a lesser proportion of the east-half discharge is diverted toward the west canyon wall. Photographic series 6 (figs. 27-31) 1952 White-ice stream at left has much more uniform slope than in 1945. This is first year since the early 1940’s when fresh crevasses have appeared in midglacier above the nunatak. Their direction, at a steep angle to the general direction of ice flow, indicates strong longitudinal shearing above the nunatak caused by more vigorous flow in the east half of the glacier. 1954 New ice front is passing the nunatak. Note severity of the crevassing upstream and its continued angling (since 1952) with respect to the valley axis. 1958 Ice level at profile 2 peaked in 1957; at profile 1 it remained constant for 4 years before again advancing in 1962. The slope at profile 1 appears rather steep. In this photograph there is a good portrayal of the ablation of crevasse walls. 1961 See large patch of debris at lower left which has greatly increased since 1958. A flat reach appears to be forming in white-ice slope above profile 2. Nunatak is being topped with ice. 1965 Profile 2 appears to be on a long reach of rather uniform slope, with flat slope occurring not far upstream from there. Nunatak is almost entirely engulfed with thick ice. This year the ice level at profile 1 is highest since about 1938. 1,000 feet (300 m) above profile 2 to above profile 3 For comments about this area, see captions of the photographs in series 15 (fig. 12) and 13 (figs. 32-34). Series 15 provides some coverage of upper part of glacier for the period prior to 1949, before series 13 was begun. A summary of the comments contained in the captions follows: Series 15 (fig. 12) 1944 Glacier is nearing the end of a long period of recession, and at this stage there is very little crevassing. The inflow of ice from Wilson Glacier is low; note the large exposures of bedrock. A heavy load of debris is being carried, contributed from both banks of Nisqually Glacier. Scries 13 (figs. 32-34) 1949 This picture was taken from a point about 500 feet (150 m) upstream from the station where remainder of the series was taken. Crevassing pattern has expanded since 1944, especially in areas nearest the camera station. Bedrock outcrops at lower end of Wilson Glacier are nearly covered. 1957 Glacier surface at profile 3 is 10 ft (3 m) higher than in 1953; ice field at top of cliff at left is much thicker. Crevassing now extends to east edge of the glacier. 1965 Surface of glacier in general appears a little smoother and slopes less steep. Firn can be seen in several areas. Ice on cliff at left appears about the same as in 1962.QUALITATIVE INTERPRETATIONS 35 Figure 26.—Patterns of small recessional lateral moraines on east bank at an altitude of about 6,400 feet (l ,950 m) are evident in this 1940 view taken looking up glacier from station 12. The patterns suggest that at times the recession progressed in a discontinuous manner, as in successive small steps interrupted by slight advances. Photograph by F. F. Lawrence, Conservation Division, U. S. Geological Survey, August 26, 1940. ►36 ANALYSIS OF 2 4-YEAE photographic record, nisqually glacier, mount rainier, wash. Figure 27.—Nisqually Glacier near the nunatak, as seen from station 6 on August 27, 1952. Note long reach of smooth-appearing, convex-upward slope of the white ice, terminating in smooth black ice. Effect of advancing new ice now has nearly reached the nunatak, as evidenced in midglacier by the pronounced new (sharp-edged) crevassing. Stream bed shows both to left and right of nunatak. <QUALITATIVE INTERPRETATIONS Figure 28.—Nisqually Glacier near the nunatak, as seen from station 6 on September 1,1954. Practically all the main ice flow from east half of glacier is being diverted to west side of the nunatak. Note steep front of the fresh ice advance.38 ANALYSIS or 24-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. Figure 29.—Nisqually Glacier near the nunatak, as seen from station 6 on September 5,1958, Note growth and movement of ice over peak of nunatak and along its east side which have occurred since 1954. Crevassing in midglacier in the vicinity of the nunatak has a very coarse pattern, and this photograph is a good portrayal of the ablation of crevassed walls. This was a summer of abnormally high ablation. The ice-cored, morainelike ridge noted at left in the 1942 view in series 5 (fig. 20) has nearly disappeared.QUALITATIVE INTERPRETATIONS 39 Figure 30.—Nisqually Glacier near the nunatak, as seen from station 6 on September 6, 1961. Note finer pattern of the crevassing in comparison with 1958, and the large patch of debris on ice at lower left. Slope at profile 2 appears reduced. This is the fourth consecutive year, beginning with 1958 (fig. 29), in which surveys show that the elevation and slope of the glacier surface from profile 2 to profile 1 have remained nearly constant.40 ANALYSIS OF 2 4-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH, Figure 31.—Nisqually Glacier near the nunatak, as seen from station 6 on August 30, 1965. Crevassing patterns this year are generally coarser than in 1961. This wave of ice advance which is engulfing much of the nunatak reached a peak at profile 2 in 1963 and at profile 1 in 1965. Photographs show that a substantial part of the east-half discharge is now continuing straight down glacier parallel to the valley margins, in contrast to the 1952-54 conditions of nearly complete diversion to the west. See also figures 5 and 25. The large patch of debris visible in 1961 has gone, but debris still is surfacing "i just to left of nunatak. Debris mantle again is continuous in reach along west canyon wall where an ice ridge formerly existed.i QUALITATIVE INTERPRETATIONS 41 Figure 32.—Upper reaches of Nisqually and Wilson Glaciers as seen from station 1 3 on August 28,1949, taken several hundred feet (say 1 50 m) up glacier from station 1 3. Location of profile 3 is shown. Along profile 3 the surface of the ice is 62 feet (19 m) higher than in 1944 (fig. 12); 19 feet (6 m) of this was added since 1948. Crevassing is becoming more extensive. Bedrock outcrops at the mouth of Wilson Glacier are nearly covered. Many of the bedrock outcrops noted with X’s in figure 12 (1944) are already covered by the expanding glacier. y4 Figure 33.—Upper reaches of Nisqually and Wilson Glaciers as seen from station 1 3 on August 30, 1957. Most of exposed bedrock areas marked in figure 12 (1944) are now covered by Wilson Glacier. Glacier surface at profile 3 is only 3 feet (1 m) higher than in 1949, but near left edge of picture it probably is about 60 feet (18 m) higher because at profile 2 the ice level rose 97 feet (30 m) from 1949 to 1957. The crevassing appears much coarser (rougher) now ^ and extends to the east edge of the glacier. Exposed face of the ice field above the cliff is thicker. The falls at far left are nearly dry , (compare with fig. 1 2). Note the different layers (ages) of firn exposed in the small area at lower right, which can be differentiated by various Y shades of sray. YI l QUALITATIVE INTERPRETATIONS 43 Figure 34.—Upper reaches of Nisqually and Wilson Glaciers as seen from station 1 3 on August 30,1965. The glacier from profile 3 downstream to where it leaves this view has now reached a steady-state condition, as determined by the annual surveys. In general the crevassing appears similar to that of 1957. Firn can be seen in many areas. Ice on cliff at left is much thicker than in 1957. r >44 ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD, EROSION AND DEPOSITION Banks and lateral moraines Annual photographs reveal the progress of erosion along the banks of a valley glacier and along old lateral moraines. The 1947 and 1965 views in series 11 (fig. 35) illustrate 18 years of erosion of west side of the old east-bank lateral moraine. Along this part of the moraine the average lateral recession of its crest over the 18-year period has amounted to a total of 10-15 feet (3-5 m). In regard to erosion of the banks of a glacier, the views in series 14-W (figs. 7-10) show how some of the bedrock areas on the steep hillside above the west end of profile 2 became unrecognizable within 20 years. Note changes in the lower rock formations seen in the 1942 and 1960 views, which wTere photographed under similar light conditions. Thus, on photographs of a canyon wall, it may be difficult to pick out bedrock features that will be usable as long-term landmarks for measurements in photographic studies. In the present study, a few usable points were found that could be identified on pictures throughout the 24-page period of record. Outburst floods Repetitive photographs also portray changes in topography and vegetation in the channel and valley below a glacier that result from outburst-type floods (jokulhlaups). Three such floods emanating from Nis-qually Glacier are described briefly below. Flood of October 14, 1932. This flood tore away the reinforced concrete arch bridge which had been constructed in 1926. A precipitation total of 6.90 inches (175-mm) fell at Paradise Ranger Station October 10-13, inclusive. It is interesting to note what apparently is the deck of that bridge clearly visible in the 1947 view (fig. 37) in series 3 (figs. 36-38), just below the tree-covered island near the center of the picture. Flood of October 24-25, 1934. A series of outburst surges from the glacier, according to the monthly report of the Superintendent, Mount Rainier National Park, dated November 5,1934, “completely plugged the bridge and piled rock and debris 15 feet deep on top of the arch. Approach roads on both sides of the bridge were washed out.” Precipitation of 8.92 inches (227 mm) occurred at Paradise Ranger Station October 20-25, inclusive. This bridge, less than 2 years old and situated at the same site as the bridge it replaced after the 1932 flood, was reconditioned and used until its washout in 1955. Flood of October 25,1955,. The flood occurred about noon and destroyed bridges and other property downstream. It was preceded by heavy rainfall (a total of 5.51 inches (140 mm) was measured on the 24th and NISQUALLY GLACIER, MOUNT RAINIER, WASH. 25th at Paradise Ranger Station) and was observed by a Park Ranger to flow in several large surges. The frontal wave of the first surge was estimated to be 20 feet (6 m) high, and the water carried many large rocks and chunks of ice that were visible at the surface. The first surge tore from its abutments the heavily reinforced 80-foot (24-m) span, concrete highway bridge. Natural changes below glacier from floods and other causes The 1934,4 1947, and 1965 pictures in series 3 (figs. 36-38) illustrate the removal of vegetation, channel widening, and subsequent killing of trees that occurred for a few thousand feet (500-1,000 m) below the bridge as a result of glacier floods of the early 1930’s and 1955. The flood channel in the vicinity of the highway bridge was widened by the 1955 flood, and some vegetation was removed, as illustrated by the 1949 and 1956 views in series 2-S (figs. 39A. C). Margins of the flood plain and vegetation as they existed a month before the flood are indicated by white lines in figure 396' (1956). Note also the automobile-size boulders that were cast up onto the parking area just to left of and above the bridge, and the much larger boulder deposited upstream. Many large trees downstream from the bridge were washed away. The annual photographs in series 2-S (only a few of which are shown in this report) show some interesting variations in the configuration of the low-flow channel between the glacier terminus and the highway bridge. They reveal how within one season the channel wyould change from meandering to straight, or vice versa, then retain one form for several consecutive years. An example is evident from a comparison of the photographs shown as figures 39.4 and 392?, for 1949 and 1950. Note also the new terraces visible in 1950 along the flood plain. Each subsequent annual view showed that the channel remained straight from 1950 until after 1953 (which was the last view taken until 1956). A tributary alluvial fan, first visible in 1960, was deposited on right-bank flood plain above the bridge; by 1965 (fig. 3922) it had become a little larger. The 1932-36 photographs taken by the National Park Service looking upstream from the bridge, which are not published here, indicate that the flood of October 1934 was very substantial and erosive above the bridge as well as in the vicinity of the island 1,000 feet (300 m) downstream. * This “1934” undated photograph closely matches the appearance of the glacier terminus in a National Park Service photograph dated September 5, 1934. The match is fair, but less perfect, with their 1933 photograph; it is clearly poor with their October 1, 1932 photograph. Thus it seems likely that this “1934” picture, upon which the large amount of downstream flood plain vegetation is visible, was taken after the 1932 glacier outburst flood and before the October 1934 flood, when denudation of that vegetation probably took place.QUALITATIVE INTERPRETATIONS 45 Fisure 35.—Erosion of old (pre-1 840) lateral moraine on east side of the glacier is shown by the series 11 photographs of August 25, 1947 (upper), and September 4, 1965 (lower). The total erosion during the period 1947-65, indicated by black line on the 1947 view, appears to have averaged between 1 0 and 1 5 feet (3 and 4 .5 m) horizontally.Figure 36.—Nisquolly valley below the glacier, as seen from station 3 in 1934 prior to October flood (date estimated,- see footnote 4, page 44). Photograph furnished by Conservation Division, U.S. Geological Survey. Note substantial stand of trees and brush on west part of flood plain, and river on east side of flood plain.QUALITATIVE INTERPRETATIONS 47 Figure 37.—Nisqually valley below the glacier, as seen from station 3 on August 25, 1947. West of the island of trees, most of the vegetation present in 1934 view is gone, due to glacier outburst flood of October 1934. The river now flows west of this island of trees. The deck of the concrete highway bridge used prior to the October 1 3, 1932, flood is visible on flood plain just below island of trees (arrow).48 ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. Figure 38.—Nisqually valley below the glacier, as seen from station 3 on August 31, 1965. Aggradation on the flood plain, caused by the outburst flood of October 25, 1955, is evidenced by altered topography and dead trees. A new bridge was constructed high above the flood-affected channels.ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. 49 CONCLUSIONS The information and data on glacier characteristics and changes contained in this report are believed typical of what can be derived from a long-term record of annual photographs. A summary of the findings follows: 1. Data on changes in ice margins are readily obtain- able from photographs. Likewise, changes in glacier thickness can be derived either from the positions of the ice margins along a canyon wall or from measurements made on the photographs of distances from a bedrock feature down to a bulge in the ice surface, with the latter photographed as a profile or “silhouette” from below. Both methods check well with the results of stadia surveys; values from the second method probably are accurate in this area to within plus or minus 25 feet (8 m). 2. Annual values of the surface slope at profile 2 were measured on photographs and are believed to be at least as accurate as those determined from the contour maps. Absolute values of the slope ranged from 5 to 10 degrees. A photographic analysis of slope can be made rather accurately from annual pictures provided there is established by field surveys the projection of a reference vertical line on the canyon wall directly opposite the picture station, identifiable on each print with respect to enduring landmarks. Also, the photographic station used must not be much higher than the glacier surface. 3. Position of the summer snow line on Nisqually Glacier was found to range between altitudes of about 5,800 and 7,300 feet (1,750 and 2,250 m), whereas the firn edges appeared to be between altitudes of about 6,000 and 7,300 feet (1,850 and 2,250 m). However, the snow lines and firn edges on this glacier usually are very irregular. Aerial photographs or a more complete coverage of ground photographs than is available for this project would be needed for an analysis of the snow and firn limits in relation to climatic fluctuations. 4. Photographs are helpful in analyzing the rates of retreat and advance of a glacier’s terminus and in distinguishing an advancing terminus from a retreating one, through illustration of the characteristic appearance of each. If advancing, the front of the terminus is steep, bulging, and cre-vassed; if receding or stagnant, it usually has a noncrevassed, more gently sloping appearance or it may become hummocky or segmented. 5. The pictures portray the appearance of a wasting glacier, including its stagnant lower reaches, during the latter part of a long period of recession. Later, they illustrate waves of fresh ice advance which engulfed the nunatak and replaced the segmented, stagnant terminus by a bulging, cre-vassed “fat” looking front. 6. Photographs illustrate the occurrence, nature, and changes in moraines and debris-covered ice ridges. They also show the sources, distribution, and general nature of the debris carried on a glacier’s surface. 7. The dynamic condition of a glacier is indicated quite well by the nature and pattern of the crevassing as well as by the general character of the glacier surface. During ice advances, the crevasses are larger and coarser in pattern than during a recession. A hummocky surface reflects the wasting and ablating condition of stationary or receding ice, as is shown on the photographs. 8. Information about the progress of erosion on the banks and lateral moraines of a glacier can be determined from annual photographs. Canyon wall bedrock features change more rapidly than might be supposed. 9. Some of the effects of glacier outburst floods, often more damaging than is realized, are illustrated by the photographs in this report. The removal or killing of many large trees and the deposition of enormous boulders are shown.50 ANALYSIS OF 24-YEAR PHOTOGRAPHIC RECORD, NISQTTALLY GLACIER, MOUNT RAINIER, WASH.RECOMMENDED PHOTOGRAPHIC PROCEDURES Figure 39.—River channel just above the highway bridge, as viewed downstream from station 2 on cliff. A, August 28, 1949. Channel conditions illustrated in this view are about the same as those shown in the unpublished 1943, 1947, and 1948 photographs. No major outburst floods occurred in this period. Scale in vicinity of bridge is indicated by cars on parking area at left. 8, August 27, 1950. The relatively minor channel changes occurring between 1949 and 1950 still are larger than noticed for any other 12-month period not having a large outburst-type flood. The low-flow channel has become straightened and slightly degraded since 1949, and a few terraces and bars have formed along the left flood plain. C, August 28, 1956. The October 25, 1955, glacier outburst flood has caused easily recognizable changes in the channel: 1, large (13 by 19 by 25 ft, or 4 by 5.8 by 7.6 m) boulder deposited at left; 2, wider swath cut through vegetation (edges of vegetation before flood indicated by white lines); 3, terrace formed along left side of flood plain; 4, many large boulders (one was 8 by 8 by 1 5 ft, or 2.6 by 2.6 by 4.9 m) deposited high on left bank above and below highway. Compare with fig. 39 A. D, August 31, 1965. In the 9-year interval since 1956 note the following: 1, exceptionally large boulder at left has not moved; 2, small terraces are visible at left, caused by moderate-sized floods; 3, an alluvial fan (first visible in 1960) has been deposited by a right-bank tributary this side of the bridge. RECOMMENDED PHOTOGRAPHIC PROCEDURES PHOTOGRAPHIC STATIONS When photographic stations are being selected, possible changes in the glacier and in nearby vegetation should be anticipated. Enough stations should be selected so that, if some should be destroyed or obscured, good views of all study areas including the terminus will still be afforded from other sites as the glacier advances or recedes. All parts of the glacier subject to analysis should be photographed from at least two different viewpoints, if feasible. Where a particular reach is subject to study, every part of each ice margin in that reach should be visible in at least one picture. For a study of surface slope from photographs, the station should be about the same elevation as the glacier surface and, if possible, where permanent features such as bedrock strata or outcroppings can be recognized in the background. If an ice advance should block the view from such a station, photographs taken at a higher altitude on an extension of the same cross-profile axis should be satisfactory for continuing the record of slope measurements. Where stations are not on bedrock, the possibility of encroachment by vegetation or destruction by erosion should be considered. The site should be located in reference to two or more witness rocks in the vicinity. Sta- 51 tions should be marked with monuments such as bronze tablets or steel stakes, which are easily recognized. When setting up a program of this kind it is better to establish too many rather than too few photographic stations. Some stations can always be dropped, but once any photographic records are missed they are lost forever. OPTIMUM LIGHT CONDITIONS Ideally, glacier -photography should be scheduled so that the same lighting conditions occur every year at each station. To accomplish this, the photographs should be taken at about the same time of day and on about the same date each year. Without such uniformity in lighting, the changes illustrated in a series of pictures are difficult to analyze, and interpretations may be misleading. At stations where photographs are taken in several directions, there may be no entirely satisfactory time of day for all of the views. Furthermore, the scheduling of photographs at a series of stations must be adjusted to fit the practicable time of travel from place to place, thus requiring some compromise with the desired light conditions. When a particular view is found to be blocked or shaded by fog or clouds, it still is advisable to take a picture even though another photograph might be obtained later under better conditions. The first picture may be of poor quality, but perhaps it could be used for study if none other should become available. SELECTING THE VIEW The best direction of view at a station should be selected the first year, taking into account the probable movements of the glacier, and then repeated each year without change. The exact site over which the camera is placed should be identifiable by a permanent marker, and the camera should be positioned within a foot of the same location each year. When pointing the camera, it is helpful to refer to an earlier photograph that shows the desired view at the station. Panoramic views should overlap 20 to 30 percent so that the photographs when trimmed will match satisfactorily. The transverse axis of the camera should be held in a level position, adjusting the view as necessary by raising or lowering the camera’s front but without tilting it sideways. EQUIPMENT The camera should be sturdy and equipped with a lens that permits high resolution over the entire image and a minimum of optical distortion toward the corners52 ANALYSIS OF 2 4-YEAR PHOTOGRAPHIC RECORD, NISQUALLY GLACIER, MOUNT RAINIER, WASH. of the picture. It is understood that, as a general guide, the best results from a good lens will be obtained when its aperture is closed two to four stops from its maximum opening. Therefore, under a condition of intense light such as is available at a glacier, a rather slow film is preferable so the middle range of lens openings can be utilized. A film with wide exposure latitude is needed for satisfactorily reproducing all the shades of contrast that are present in most glacier scenes. Color photography is superior to black and white in recording vegetation, which in the case of many receding glaciers is a very important change to be recorded. For this purpose 35 mm film should be satisfactory. If the photographic party is equipped with two cameras, it is believed worthwhile that the views at all the photographic stations be taken both in black and white and in color. A desirable format for the photographic image is 4 by 5 because of its ready adaptation to ordinary 8- by 10-inch (20- by 25-cm) enlargements. With any other proportion, part of the negative must be masked when an 8 by 10 print is made; selecting the part or parts of each picture to be masked out and placing the guide marks on each negative for use of the enlarger operator is a time-consuming and relatively unrewarding process. The rapid shutter speeds normally usable in this work make hand-held camera exposures generally satisfactory from the standpoint of negative sharpness. However, consistently better results, both as to sharpness and proper positioning and levelling of the camera, can be obtained with a tripod if enough time is available. As mentioned earlier, no advantage has been found in this program in the use of a lens filter—such as a K-2 (yellow) one. A haze filter for reducing the effect of ultraviolet rays on film at high altitudes is helpful in color photography. RECORDING THE PHOTOGRAPHIC DATA When the annual photographs of Nisqually Glacier are taken, data are entered on a looseleaf “Index to Photographs” form prepared for recording the following: Column heading Information indicated Negative No_________________ Serial file number, entered later in the office. Film No--------------------- Manufacturer’s exposure number, which is given on each film of a film pack. Cam. and F.L________________ Model and size of camera, and focal length of its lens. Film and Speed______________ Name of film, and its ASA speed. Column heading Information indicated By------------------------- Initials or names of each member of the party. Date----------------------- Month, day, and year. Station No----------------- Number of the photographic sta- tion. Direction__________________ With respect to points of the com- pass or to the glacier’s valley, like “up” or “across”. Hor. or Vert--------------- Enter H or V for position in which the film is held when exposed. Std. Time------------------ (Inadvisable to use Daylight Time.) Exposure 1/---------------- For example, enter “200” to indi- cate l/200th of a second. f-------------------------- Lens opening. Filter Remarks A print of each form sheet that has been filled out with the data on a season’s pictures is carried in the field for possible reference in succeeding years. REFERENCES Field, W. O., Jr., 1932, Glaciers of the northern part of Prince William Sound, Alaska: Geog. Rev., v. 22, p. 316-388. ------1937, Observations on Alaskan coastal glaciers: Geog. Rev., v. 27, p. 63-81. ------1947, Glacier recession in Muir Inlet, Alaska : Geog. Rev., v. 37, p. 369-399. Giles, G. C., 1960, Nisqually Glacier, Mount Rainier, Washington, 1959 Progress Report: U.S. Geol. Survey, Tacoma, Wash., open-file report, 31 p. Harrison, A. E., 1954, Glacier studies with a camera: Sierra Club Bull., v. 39, no. 6, p. 60-65. ------1956, Fluctuations of the Nisqually Glacier, Mt. Rainier, Washington, since 1750: Jour. Glaciology, v. 2, no. 19, p. 675-683. Hofmann, Walther, 1958, Der Vorstoss des Nisqually-Gletschers am Mt. Rainier, USA, von 1952 bis 1956: Zeitschr. Glet-scherkunde u. Glazialgeologie, v. 4, no. 1-2, p. 47-60. Johnson, Arthur, 1949, Nisqually Glacier, Washington, Progress Report 1946, 1947, and 1948: U.S. Geological Survey, Tacoma, Wash., report on file, 3 p. ------ 1960, Variation in surface elevation of the Nisqually Glacier, Mt. Rainier, Washington: Intemat. Assoc. Sci. Hydrology Bull. 19, p. 54-60. LaChapelle, E. R., 1962, Assessing glacier mass budgets by reconnaissance aerial photography: Jour. Glaciology, v. 4, no. 33, p. 290-296. Meier, M. F., 1968, Calculations of slip of Nisqually Glacier on its bed—No simple relation of sliding velocity to shear stress: Intemat. Assoc. Sci. Hydrology, Bern Assembly 1967. Pub. 79, p. 49-57. Meier, M. F., and Post, A. S., 1962, Recent variations in mass net budgets of glaciers in western North America: Internal Assoc. Sci. Hydrology, Obergurgl Symposium, Pub. 58, p. 63-77. Russell, I. C., 1898, Glaciers of Mount Rainier: U.S. Geol. Survey 18th Ann. Rept. 1896-97, pt. 2, p. 355-415. o US. GOVERNMENT PRINTING OFFICE: 1969 O 352-693UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 631 PLATE 1 121°46'15“ Base modified from U.S. Geological Survey Nisqually Glacier 1956 map, 1963 INTERIOR—GEOLOGICAL SURVEY, WASHINGTON, D.C.—1969—W69090 MAP OF NISQUALLY GLACIER AND VICINITY, MOUNT RAINIER NATIONAL PARK, WASHINGTON SHOWING LOCATIONS OF THE PHOTOGRAPHIC STATIONS AND CROSS PROFILES7 Dm* 75" 3X Mineral Resources of Glacier Bay National Monument, Alaska GEOLOGICAL SURVEY PROFESSIONAL PAPER 632 JUN 4 1971 [DOCUMENT tfSkaas. Mineral Resources of Glacier Bay National Monument, Alaska By E. M. MacKEVETT, Jr., DAVID A. BREW, C. C. HAWLEY, LYMAN C. HUFF, and JAMES G. SMITH GEOLOGICAL SURVEY PROFESSIONAL PAPER 632 A reconnaissance study of the mineral deposits and their geologic setting and a geochemical sampling program in one of our wildest, most beautiful, and most remote national monuments UNITED STATES GOVERNMENT PRINTING OFFICE, W A S H IN G T O N : 1 9 7 1UNITED STATES DEPARTMENT OF THE INTERIOR FRED J. RUSSELL, Acting Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 77—609017 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 2040239 40 40 40 40 40 41 41 41 42 42 42 43 43 43 43 43 44 44 44 44 45 45 48 48 50 50 50 50 51 51 51 51 51 52 52 52 52 52 52 53 53 53 54 54 54 54 54 54 54 CONTENTS Page Abstract and summary ____________________________________ 1 Mineral deposits ___________________________________ 1 Previously known deposits ..................... 1 Nunatak molybdenum prospect ---------------- 1 Brady Glacier prospect _____________________ 3 Fairweather Range ....------------------ 3 Alaska Chief prospect —----------------- 3 Placer deposits near Lituya Bay ____________ 3 Margerie prospect __________________________ 3 Reid Inlet gold area and Sandy Cove prospect -------------------------------------- 3 Other previously known deposits ..__________ 4 Deposits discovered during 1966 ........— 4 Geochemical anomalies .......................... 4 Favorable areas .................................. 5 Introduction ----------------------------------------- 5 Geographic setting Previous investigations Present investigation Acknowledgments Regional geology ................................ — 9 Stratigraphy .......................... — 10 Intrusive rocks .........—.................... 10 Structure .....................—-------------- 11 Geochemical studies ..................—.........— H Methods of analysis .......................... 12 Sampling and sample preparation ................. 13 Anomalous and background values ............... 13 Total heavy metals _________—.............. 13 Copper ...................................... 13 Lead ...................................... 13 Molybdenum ................................. 13 Chromium ................................. 13 Nickel ................................. 13 Other elements ............................... 14 Unaltered rocks .............................. 15 Causes of anomalous values ................ - 15 Results of geochemical studies .................. 15 Total heavy metals .......................... 10 Copper ..................................... 16 Lead .................................... — 16 Molybdenum .............................. 17 Chromium and nickel .......................... 17 Other elements.......................... 17 Areal descriptions .......................... 17 Western Dundas Bay area_________________ 17 Eastern Dundas Bay area ................. 20 Miller Peak-Sandy Cove area ____________ 20 Mount Merriam area .................... 22 Reid Inlet gold area .................. 22 Mineral deposits .................................... 22 Locality list keyed to maps and tables ------- 25 Metallic commodities ......................... 29 Base and miscellaneous metals ................ 29 Antimony ------------------------------- 29 Mineral deposits—Continued Metallic commodities—Continued Base and miscellaneous metals—Continued Arsenic _________________________1----- Bismuth ............................... Cadmium ______________,________________ Copper -------------------------------- Distribution---------------------- Types of deposits ................ Descriptions of deposits ...... Mount Young area _____________ East of Casement Glacier ----- North shore of Adams Inlet .... North of White Glacier ....... North of York Creek __________ Minnesota Ridge .............. Gable Mountain ...........— South of Rendu Glacier ------- West shore of Tarr Inlet ----- Margerie prospect ____________ Curtis Hills .............- North Marble Island __________ South Marble Island __________ Willoughby Island ____________ Francis Island ............... Alaska Chief prospect -------- East side of Dundas Bay Bruce Hills _______........... West of mouth of Rendu Inlet South of Tidal Inlet .. ...... Blue Mouse Cove .............. Southwest Gilbert Island and nearby unnamed island West of Shag Cove............. West arm of Dundas Bay ------- West of mouth of Tarr Inlet . . West of Tarr Inlet ........... North of Johns Hopkins Inlet South of Johns Hopkins Inlet East of Lamplugh Glacier Southwest of Lamplugh Glacier .. East of Reid Glacier ......... East of Hoonah Glacier........ Fairweather Range_____________ Southeast arm of Lituya Bay — Other deposits that contain copper _____________________ Lead __________________________________ Radioactive elements __________________ Tin ___________________________________ Zinc .................................. Distribution and types of deposits — Descriptions of deposits.......... Nunatak on Casement Glacier __ Mount Brack __________________ HIIV CONTENTS Mineral deposits—Continued Metallic commodities—Continued Base and miscellaneous metals—Continued Zinc—Continued Descriptions of deposits—Continued Southwest of Red Mountain ______ Southwest of Alaska Chief prospect __________________________ Hugh Miller Inlet _____________ Mount Cooper __________________ Northwest shore of Johns Hopkins Inlet ____________________ Other deposits that contain zinc .. Precious metals .................-......... Gold .....T............................ Distribution and occurrence ....... Lode deposits ..................... Reid Inlet gold area __________ Terry Richtmeyer prospect.... LeRoy mine ................ Rainbow mine .............. Sentinel mine ............. Monarch mines ............. Incas mine ..........,..... Sunrise prospect .......... Hopalong and Whirlaway claims .................. Galena prospect ___________ Highland Chief prospect ___ Rambler prospect .......... Other lode deposits in the Reid Inlet area ......... South of Lituya Bay ___________ Sandy Cove prospect ...........~ West of McBride Glacier ....... East of lower Brady Glacier---- West of Dundas Bay ............ Russell Island ................ Other lode deposits ___________ Placer deposits.................... South of Wood Lake ............ Dundas River __________________ Outwash of Brady Glacier ------ Oregon King Consolidated ...... Lituya Bay ____________________ Other placer deposits ......... . Platinum .............................. Silver ________________________________ Rendu Inlet prospect ................ Iron and ferroalloy metals .................. Iron .................................. Descriptions of deposits ............ East of Dundas Bay ............ West of Rendu Inlet............ Queen Inlet.................... Page 55 55 55 55 55 55 56 56 56 56 56 56 56 59 60 60 62 62 63 63 63 64 64 64 64 66 67 67 67 67 67 67 67 67 67 68 68 69 69 69 69 69 70 70 70 70 Mineral deposits—Continued Metallic commodities—Continued Iron and ferroalloy metals—Continued Iron—Continued Descriptions of deposits—Continued West of Blackthorn Peak ....... East of Brady Glacier _________ Fairweather Range.............. Placer deposits _________________ Chromium ______________________________ Cobalt ________________________________ Manganese _____________________________ Molybdenum ._-------------------------- Distribution ______________________ Types of deposits _________________ Descriptions of deposits___________ Casement Glacier ______________ Van Horn Ridge ________________ West side of Tarr Inlet ........ Nunatak prospect .............. Geology ___________________ Ore deposits ______________ Geochemical studies ....... Entrance of Adams Inlet________ Wachusett Inlet________________ Triangle Island ............... Geikie Inlet___________________ Lower Brady Glacier ___________ Ridge west of Rendu Inlet _____ Other molybdenum deposits _____ Nickel -------------------------------- Descriptions of deposits___________ Brady Glacier prospect, by H. R. Cornwall ________________ Geology ------------------- Ore deposits ______________ Possibilities of commercial ore deposits ............ Titanium ______________________________ Distribution ______________________ Descriptions of deposits .......... Fairweather Range _____________ Placer deposits near Lituya Bay .. Tungsten ______________________________ Vanadium ______________________________ Geologic influences on localization of metalliferous deposits ___________________________ Nonmetallic commodities________________________ Petroleum and coal, by George Plafker--------------- Petroleum _____________________________________ Stratigraphy_______________________________ Structure ................................. Potential _________________________________ Coal __________________________________________ References cited ___________________________________ Page 72 72 72 73 73 73 73 73 73 73 74 74 74 74 74 74 75 77 78 78 78 78 79 79 79 79 79 79 80 81 81 82 82 82 82 83 83 84 84 84 85 85 85 87 87 88 89CONTENTS V ILLUSTRATIONS [Plates are in pocket] Plate 1. Map showing bedrock lithology and locations of known metalliferous mineral deposits, Glacier Bay National Monument. 2. Map showing total heavy-metals concentration in stream-sediment samples. 3-7. Maps showing metal concentrations in stream-sediment samples: 3. Copper. 4. Lead. 5. Molybdenum. 6. Chromium. 7. Nickel. 8. Map showing anomalous values of arsenic, beryllium, bismuth, cadmium, silver, strontium, tin, tungsten, and zinc in stream-sediment samples. 9. Geologic sketch map showing sample locations at the LeRoy mine, Glacier Bay, Alaska. 10. Geologic sketch map, magnetic profiles, and generalized geologic section, Queen Inlet magnetite locality, Glacier Bay National Monument, Alaska. 11. Geologic map of the Nunatak molybdenum prospect. 12. Map of the Nunatak molybdenum prospect showing sample locations, extent of known mineralization, and bathymetry of adjacent parts of Muir Inlet. Page Figure 1. Map of Glacier Bay National Monument, Alaska, showing selected mineral deposits, geochemical anomalies, and outlines of some areas favorable for mineral deposits --------------------------------------- 2 2. Index map showing Glacier Bay National Monument, Alaska, and geologic provinces within the monument 6 3-7. Geochemical sampling maps: 3. Western Dundas Bay area --------------------------------------------------------------------- 18 4. Eastern Dundas Bay area _____________________________________________________________________ 21 5. Miller Peak-Sandy Cove area —---------------------------------------------------------------- 23 6. Mount Merriam area -------------------------------------------------------------------------- 26 7. Reid Inlet gold area ________________________________________________________________________ 28 8-15. Geologic sketch maps showing sample locations: 8. Francis Island prospect ____________________________________________________________________ 46 9. Alaska Chief prospect----------------------------------------------------------------------- 47 10. Bruce Hills copper-molybdenum deposit _______________________________________________________ 49 11. Rainbow adit __________________________________________________________;--------------------- 60 12. Monarch No. 1 mine ___________________________________________________________________________ 61 13. Monarch No. 2 mine ------------------------------------------------------------------------- 62 14. Incas mine __________________________________________________________________________________ 63 15. Sandy Cove prospect _____-___________________________________________________________________ 65 16. Geochemical map of Sandy Cove gold-copper prospect __________________________________________________ 66 17. Map showing magnetometer traverses west of Rendu Inlet ______________________________________________ 71 18. Generalized geologic map of Brady Glacier nunataks showing nickel-copper sulfide lodes ______________ 80 19. Geologic sketch map and structure section of Tertiary rocks in the Lituya district_____________________ 87 20. Tentative correlation of stratigraphic sections exposed in the Lituya district ..................... 88 TABLES Page Table 1. Average precipitation and average temperature for Cape Spencer and Gustavus ------------------------------ 8 2. Detection limits for some elements determined by the six-step and direct-reader spectrographic methods _ 12 3. Semiquantitative spectrographic analyses of representative unaltered rocks ____________________________ 14 4-8. Total heavy-metals and semiquantitative spectrographic analyses of stream-sediment samples: 4. Western Dundas Bay area ______________________________________________________________________ 19 5. Eastern Dundas Bay area ...................................................................... 22 6. Miller Peak-Sandy Cove area __________________________________________________________________ 24 7. Mount Merriam area ___________________________________________________________________________ 27 8. Reid Inlet gold area _________________________________________________________________________ 29VI CONTENTS Page Table 9. Semiquantitative spectrographic analyses and gold analyses of mineral deposits in the Glacier Bay National Monument ________________________________________________________________________________________ 31 10. Comparison of analytical results on soil samples from the Bruce Hills copper-molybdenum deposit .-— 50 11. Semiquantitative spectrographic analyses and gold analyses of samples from the Reid Inlet gold area - 57 12. Assay data on the LeRoy mine ------------------------------------------------------------------------ 59 13. Semiquantitative spectrographic analyses and colorimetric analyses for molybdenum of samples from the Nunatak molybdenum prospect --------------------------------------------------------------------- 76 14. Comparison of older and younger soils at the Nunatak molybdenum prospect in terms of molybdenum and copper content .................................................................................. 78 15. Semiquantitative spectrographic analyses of rocks and ore from the Brady Glacier nickel-copper prospect — 82MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA By E. M. MacKevett, Jr., David A. Brew, C. C. Hawley, Lyman C. Huff, and James G. Smith ABSTRACT AND SUMMARY The U.S. Geological Survey investigation of the mineral-resource potential of Glacier Bay National Monument was made during the summer of 1966 at the request of the National Park Service for its use in planning future development of the monument. The most important results of field tests and laboratory analyses are herein summarized. Background on the geography, geology, and study methods used is given in the “Introduction.” The chief metallic commodities of potential economic importance are copper, molybdenum, nickel, gold, silver, titanium, and iron. A few other metals might constitute byproducts or form deposits in some favorable areas that are as yet unexplored or concealed. The belt of Tertiary sedimentary rocks that borders the Gulf of Alaska and probably occurs offshore is a possible host for petroleum, but the potential is low. The economic potential for nonmetallic deposits known in the monument, such as coal, limestone, and dolomite, is minimal because of their low grade, impurities, cheaper availability elsewhere, and other limiting factors. The deposits considered to have the best economic potential include eight that were previously known and seven that were found during our investigations. The previously known deposits are the Nunatak molybdenum prospect; the Brady Glacier nickel-copper prospect; titanium, iron, and copper deposits associated with the layered mafic intrusive rocks of the Fairweather Range; the Alaska Chief copper prospect; gold- and ilmenite-bearing beach placers north and south of Lituya Bay; the Margerie copper prospect; and gold lodes in the Reid Inlet area and at the Sandy Cove prospect (fig. 1). The most attractive deposits found during our investigations include a copper-molybdenum deposit in the Bruce Hills; veins and altered zones north of White Glacier; base-metal lodes near Mount Brack; and copper deposits south of Rendu Glacier, near Gable Mountain, east of Dundas Bay, and west of Tarr Inlet (fig. 1). The previously known deposits are described in the order of their probable economic potential. The Nunatak molybdenum prospect and the Brady Glacier nickel-copper prospect are those most likely to be developed in the near future. The deposits of potential significance that we found cannot be ranked without additional data, and, at this stage, are considered to have about the same potential. They are all partly or largely covered by snow, ice, or surficial deposits, and satisfactory appraisals of their configurations and grades require physical exploration. These newly found deposits are of interest because of their inferred sizes, their grades, and the possibility that concealed parts of some deposit may be larger and richer than is apparent from surface examination. These deposits would be regarded as exploration possibilities by most mining companies, but remoteness and difficult access are limiting factors in most cases. Probably none of these newly found deposits will prove to be of major importance, but they cannot be eliminated from consideration without exploration. The investigations were thorough enough to conclude that most, if not all, sizable mineral deposits exposed in the Glacial Bay National Monument east of the Fairweather Range have been found. Some of the geochemical anomalies detected in stream-sediment samples from this same part of the monument may indicate the existence of concealed minor deposits. In the Fairweather Range itself, most of the planned fieldwork was prevented by bad weather, and only small parts of its eastern margin were examined; therefore, our appraisal of the deposits of the range is severely limited by lack of data. MINERAL DEPOSITS PREVIOUSLY KNOWN DEPOSITS Nunatak Molybdenum Prospect Deposits at the Nunatak molybdenum prospect (fig. 1, loc. 1) consist of abundant, closely spaced molydenite (M0S2)-bearing quartz veins, minor molybdenite disseminated in horn-fels, and a mineralized fault zone. The deposits have been described by Twenhofel (1946), and they were sampled and explored with two diamond-drill holes by the U.S. Bureau of Mines (Sanford and others, 1949). Mining companies have conducted limited exploration at the prospect. The deposits are mainly in hornfels, but locally, they occur in an intrusive igneous body mapped as quartz monzonite porphyry, which is exposed over a small area, and in a silicified zone near the edge of the igneous body. Pyrite (FeS2), pyrrhotite (Fei-iS), chalocopyrite (CuFeS2), and traces of silver are associated with the molybdenite in parts of the deposit. Satisfactory estimates of the grade of the deposits will require bulk sampling, and adequate estimates of the reserves are contingent upon determining the extent of the deposits. Our reserve estimate for the closely spaced molybdenitebearing vein network, or stockwork, above sea level near Muir Inlet is 2,247,000 tons of material averaging 0.067 percent M0S2 and 0.016 percent copper. Our estimate for the remainder of the stockworks and the fault zone deposit is 129,530,250 tons of material averaging 0.026 percent M0S2 and 0.018 percent copper. The grades are based on assays of chip samples collected during our investigations. In addition, about 18,000,000 tons of material similar to that in the second category above are inferred to underlie the steep cliffs near the southern end of the stockworks. Reserves that are comparable in tonnage and grade to those above sea level probably also occur below sea level. Twenhofel (1946, p. 17, 18) estimated that the whole stock-work contained 8,500,000 tons of material averaging 0.125 12 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Outline of zone of east-west trends and porphyritic intrusiveSj_-( > 'inferred location of Mt Fairweather stock GLACIER ~BAY Outline of Mt Crillon \ La Perouse stock Outline of Astrolabe-OeLangle stock Dundas Bay 20 MILES CHICHAGOF ISLAND KEY TO LOCALITIES SHOWN ON MAP 1. The Nunatak Muir Inlet 11. White Glacier 2. Brady Glacier 12. South of Rendu Glacier 3. Alaska Chief 13. Gable Mountain 4. Margerie Glacier 14. Altered zone east of Dundas Bay 5. Reid Inlet 15. West of Tarr Inlet 6. Sandy Cove A. Main arm of Dundas Bay 7. Lituya Bay placers B. West shore of Tarr Inlet 8. Mount Crillon gabbro C. Mount Merriam 9. Bruce Hills D. Miller Peak-Sandy Cove 10. Mount Brack E. Upper Berg Creek Figure 1.—Map of Glacier Bay National Monument, Alaska, showing selected mineral deposits, geochemical anomalies, and outlines of some areas favorable for mineral deposits. •, previously known deposits with economic potential; X, deposits of possible economic interest found by USGS investigations; ■, geochemical anomalies. percent MoSz and 91,500,000 tons of material averaging 0.080 percent MoS-z and that the fault-zone deposit contained 540,000 tons of material averaging 0.169 percent M0S2. Twen-hofel’s grade estimates are based mainly on channel samples and may be more representative than ours; none of his samples were analyzed for copper. Three diamond-drill holes drilled by the American Exploration & Mining Co. in 1966 explored parts of the deposits be- tween 400 feet above sea level and 300 feet below sea level. These cores are reported to indicate grades of M0S2 similar to those in our and Twenhofel’s samples. The Nunatak molybdenum prospect contains a large reserve of low-grade molybdenum ore, and if the current trends in price and demand for molybdenum continue, it may be minable in the near future.ABSTRACT AND SUMMARY 3 Brady Glacier Prospect The Brady Glacier nickel-copper deposits are exposed on two small nunataks in Brady Glacier (fig. 1, loc. 2). The prospect is covered by patented claims held by the Newmont Mining Co. Published descriptions of the deposits are based on meager information (Berg and others, 1964, p. 115; Cornwall, 1966, p. 37). The deposits are localized near the base of layered gabbro and in adjacent periodotite that forms part of the layered mafic and ultramafic igneous rock complex known as the Crillon-LaPerouse stock. They consist of pyrrho-tite (Fei-xS), pentlandite ( (Fe,Ni)sSs), and chalcopyrite (CuFeS2> that form disseminations, veinlets, and lenticular masses as much as 35 feet long and 5 feet in diameter). The prospect has been explored by 46 diamond-drill holes, many of which were drilled through several hundred feet of ice in the nearby glacier. The nunataks have not been systematically sampled, but examination of their rocks indicate that disseminated sulfides are present nearly everywhere. The amounts are small, and the overall average grade would probably be less than 0.5 percent each nickel and copper. Several of the sulfide masses in the nunataks have been sampled, and the assays shows 2-3 percent nickel, 1-1.4 percent copper, and 0.25 percent cobalt. Individual massive sulfide lenses are small; however, five such bodies on the nunataks have lengths ranging from 15 to 35 feet and average widths of about 6 feet. The vertical extents of the lenses are probably comparable to these dimensions. Diamond drilling thus far has shown that low-grade nickel-copper mineralization is widespread in the gabbro-peridotite complex, but more drilling is needed to establish continuity of the higher grade zones. By analogy with known commercial deposits of a similar nature elsewhere, it is possible that, as the basal contact of the layered complex is approached at greater depth, higher grades of nickel and copper mineralization will be encountered. The information available to us is inadequate for making any reserve estimates, but the results of exploration may be considered sufficiently favorable to encourage mining the deposits. Fairweather Range The layered mafic and ultramafic rocks of the Fairweather Range include the Crillon-LaPerouse and the Astrolabe-DeLangle stocks of Rossman (1963a) and an inferred intrusive mass near Mount Fairweather (fig. 1). These rocks have been little explored and prospected. Descriptions of them and brief accounts of their mineral deposits (fig. 1, loc. 8) are in Rossman (1963a) and in Kennedy and Walton (1946, p. 67-72). Some layers in the layered complexes are known to contain large amounts of ilmenite in low-grade concentrations and lesser amounts of titaniferous magnetite. These and similarly mineralized layers that undoubtedly occur elsewhere in the complexes are a potential resource of titanium and iron. Minor amounts of vanadium are associated with the ilmenite and magnetite and constitute a remotely possible byproduct. Pods and lenses of massive sulfides, chiefly pyrrhotite (Fei-xS) with subordinate chalcopyrite (CuFeS2), have been reported from some of the layers and contact zones of the complexes. By analogy with other layered mafic and ultramafic intrusive masses, the poorly exposed and apparently largely concealed ultramafic rocks of the lower part of the complexes are possible hosts for chromite and platinum deposits. The peripheral and lower zones of the complexes may also contain sulfide deposits rich in nickel and copper and possibly small amounts of platinum. The little-explored and prospected layered intrusive rocks of the Fairweather Range are potentially important because they contain known resources and are favorable hosts for a variety of mineral deposits. However, they occur largely in remote and rugged terrain where prospecting, exploration, and mining are difficult and costly. Alaska Chief Prospect The Alaska Chief copper prospect (fig. 1, loc. 3) consists of patented claims on a massive sulfide deposit in tactite, hornfels, and marble near a granitic mass. Workings at the prospect consist of a cleared and scraped area about 150 feet long and 55 feet wide and an adit 40 feet long. The deposit is exposed throughout the cleared area and less extensively in the adit. The lateral extent of the deposit could not be ascertained because its surface exposures are surrounded by densely vegetated steep hillsides that lack outcrops. Little is known of its subsurface configuration. The deposit consists of pyrite (FeS2), pyrrhotite (Fei-xS), chalcopyrite (CuFeS2), bornite (CusFeSi), and sphalerite (ZnS), and their oxidized derivatives. Chip samples from the cleared area contained about 1 percent copper, as much as 4.377 ounces of silver per ton, and lesser amounts of gold and zinc. Drilling or similar exploration will be required to determine the reserves of the deposits. The prospect has been briefly described by Reed (1938, p. 72, 73) and by the Wrights (1937, p. 221, 222). Placer Deposits Near Lituya Bay Placer deposits that contain gold and other heavy minerals are distributed irregularly along the beaches for about 20 miles northwest of Lituya Bay and 15 miles southeast of the bay (fig. 1, loc. 7). There may be similar placers just offshore beneath the Gulf of Alaska. The deposits consist of concentrations of heavy minerals in modern bare beach sands and in older beach sands whose surfaces are covered by vegetation. They have been worked intermittently since the early 1890’s. Between 1894 and 1917 they produced gold valued at about $75,000 (Mertie, 1933, p. 135). Their production since 1917 has been minor. A little platinum has been recovered from the deposits. The placer deposits also contain concentrations of ilmenite and, to a lesser extent, of magnetite. The deposits have been investigated by Rossman (1957) and by Thomas and Berryhill (1962, p. 37-40); both of these investigations stressed their ilmenite content. They could be worked under favorable economic conditions for gold, and they also constitute a potential resource of titanium, and possibly iron. Margerie Prospect The Margerie copper prospect (fig. 1, loc. 4) is in granitic rock and hornfels. Its deposits consist of pyrrhotite (Fei-xS)-chalcopyrite (CuFeS2> lenses, copper-bearing altered zones about 6 feet thick, and thin quartz veins. All the deposits examined appear to be too small or too lean to be exploitable; but the prospect has been little explored, and indications of mineralization are widespread in the general vicinity. The deposits were discovered in 1960, but they have not been described in the geologic literature. Reid Inlet Gold Area and Sandy Cove Prospect The gold lodes of the Reid Inlet gold area (fig. 1, loc. 5) and the Sandy Cove prospect (fig. 1, loc. 6) occur in narrow nonpersistent quartz veins and in the contiguous altered wall-rock. They are probably too small and too sporadically dis-4 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA tributed to be minable now, but they probably would be amenable to small-scale mining during more favorable economic conditions. The total value of gold production from mines in the Reid Inlet area was about $250,000 (Rossman, 1959, p. 39). The geology and ore deposits of the Reid Inlet area have been described by Rossman (1959). The Sandy Cove prospect was described by Reed (1938, p. 65-68). Other Previously Known Deposits Several other mineral deposits, such as those on Willoughby, Francis, and Marble Islands (Reed, 1938, p. 69-72), west of Rendu Inlet and on the southern part of Gilbert Island (Rossman, 1963b, p. K48-K50), have been reported in the monument. All of these probably have low potentials for mineral production. DEPOSITS DISCOVERED DURING 1966 Several localities that contain mineral deposits of potential significance were discovered during the 1966 fieldwork (fig. 1). No ranking is implied by the sequence of the descriptions that follow. Most of these deposits are poorly exposed and require additional work for their satisfactory evaluation. Our brief examinations and limited sample data indicate that they warrant exploration. The Bruce Hills deposits (fig. 1, loc. 9) are in and near a fault zone that cuts granitic rocks. They consist of stockworks of quartz veins, disseminations, and fracture coatings, and contain pyrite (FeS2), chacopyrite (CuFeS2), pyrrhotite (Fei-xS), molybdenite (M0S2), and malachite (Cu2Co3(OH)2). The deposits near Mount Brack (fig. 1, loc. 10) occupy veins and altered zones in metamorphic rocks. They consist of sphalerite (ZnS), galena (PbS), and probably a sulfosalt, and contain minor amounts of silver. Deposits north of White Glacier (fig. 1, loc. 11) are localized in small altered zones that cut limestone and marble and in large altered zones that cut mafic volcanic rocks. The altered zones in the limestone and marble contain chalcopyrite (CuFeS2), particularly near intersections with dikes that cut the zones, and some altered zones in the volcanic rocks carry as much as 2 percent zinc. A large mineralized altered zone is exposed in steep cliffs south of Rendu Glacier (fig. 1, loc. 12) near the contact between light-gray granitic rocks and metamorphic rocks. A sample of float from this zone contained 0.2 percent copper. Mineralized joint coatings of unknown extent occur in coarse-grained dioritic rocks at Gable Mountain (fig. 1, loc. 13). The copper minerals in the joints are malachite (Cu2C03(0H)2) and chrysocolla (CuSi03 • 2H2O). A composite grab sample from the deposit contained 0.1 percent copper and minor quantities of silver and molybdenum. Low-grade copper deposits occur in a large altered zone east of Dundas Bay (fig. 1, loc. 14). The altered zone, which is in quartz-rich metamorphic rock that locally is bounded by volcanic rocks, is as much as 300 feet wide and at least 1 mile long. Samples from the altered zone contained as much as 0.2 percent copper and traces of silver, molybdenum, and lead. Disseminated sulfides and quartz veinlets that carry copper minerals occur in siliceous lenses within light-colored granitic rocks west of Tarr Inlet (fig. 1, loc. 15). A sample representative of the lenses yielded 0.1 percent copper. Numerous other deposits, including a few that probably have potential equal to those described here, were found during our investigations. GEOCHEMICAL ANOMALIES The geochemical sampling program disclosed numerous areas with anomalous contents of metals. Five areas that contain significant anomalies were detected by examination of stream sediments, but most of the anomalies were revealed by analyzing mineralized rock samples. The geochemical sampling also provided information about “background” concentration of elements in geologically different terranes. Although some of the anomalous areas were revisited and resampled in detail, none have been thoroughly evaluated; almost all, the five significant anomalies in particular, deserve further sampling and search for the causes of the anomalously high metal contents. The data now available do not establish whether specific anomalies are derived from concealed mineral deposits with economic potential or from areas of widespread, but, nevertheless, insignificant mineralization. Comparison of the geochemical maps with the mineral-deposit maps shows that not all known mineral deposits have geochemical anomalies detectible by methods used in this study; the various factors causing this problem are discussed in the main part of this report. The discrepancy does not lessen the importance of the anomalies that were mapped. A significant geochemical anomaly (fig. 1, loc. A) with as much as 150 ppm (parts per million) tungsten and 30 ppm tin occurs in stream sediments derived from light-colored granitic rocks and adjacent metamorphic rocks near the main arm of Dundas Bay. These stream-sediment samples were collected late in the fieldwork, and there was no opportunity to resample the streams in the area. Geologically, the area is favorable for tungsten and tin deposits. Another unevaluated significant anomaly is on the west shore of Tarr Inlet (fig. 1, loc. B) not far south of a copper deposit. This anomaly contains 700 ppm copper, 200 ppm lead, 500 ppm tin, 1,000 ppm zinc, and anomalous amounts of other metals also. The anomaly is within a north-trending belt of mixed granitic and undifferentiated metamorphic rocks. The belt contains many small mineral deposits as well as the Reid Inlet gold area and appears favorable for base-metal deposits. Anomalously high total heavy-metal, molybdenum, and strontium contents characterize an anomaly in stream sediments derived from a complex geologic terrane near Mount Merriam (fig. 1, loc. C) Large iron-stained zones in hornfels and marble adjacent to intrusive granitic bodies there may be the source of the anomalous elements. In as much as these zones have not been sampled and the stream sediments have not been resampled in detail, the anomaly is unevaluated; it is considered significant, however. Sediments from several streams in the vicinity of Sandy Cove and Miller Peak (fig. 1, loc. D) have anomalous total heavy-metal, molybdenum, and strontium contents. These stream sediments have been resampled and the anomaly verified, but the source of the high metal content is not known. Granitic bodies intrude marble in this area, and there may be either widespread low-grade mineralization or hidden mineral deposits associated with the granitic rock-marble contacts. Anomalously high chromium and copper values occur in the sediments of upper Berg Creek (fig. 1, loc. E) near the monument boundary. This anomaly has not been resampled or evaluated, but the geology of the drainage area suggests that the metals may be derived from a volcanic terrane. The contiguous area outside the monument has not been examined.INTRODUCTION 5 FAVORABLE AREAS Specific areas in the Glacial Bay National Monument can be selected as being more favorable for mineral deposits than others from consideration of the distribution and characteristics of known mineral deposits, the results of geochemical sampling, and the geology. There is no certainty that these areas contain significant hidden mineral deposits, but they are liklier to than other areas. The contact zones between granitic intrusive bodies and marble and other metamorphic rocks constitute favorable areas for several types of mineral deposits. Such contact zones are abundant in the monument east of the Fairweather Range. Spatial and probably genetic relations exist between many of the known mineral deposits and granitic masses. In some places, such as the Alaska Chief copper prospect and the Queen and Rendu Inlet iron deposits, the indications of genetic relationships are strong. Another association between mineral deposits and granitic rocks may be exemplified by the light-colored unfoliated granitic rocks that occupy a northwest-trending belt from Dundas Bay (fig. 1, near loc. A) to beyond Johns Hopkins Inlet (pi. 1). With the possible exception of the Reid Inlet gold deposits, which are rather distant, only a few mineral deposits are known to be associated with this belt. However, many metallic elements are generally concentrated during the late evolutionary stages of similar granitic rocks, and such rocks are associated with deposits of tin, molybdenum, tungsten, beryllium, gold, and other metals. The layered gabbro and ultramafic rock complexes of the Fairweather Range and their border zones (fig. 1, Iocs. 2, 8) are favorable hosts for nickel, copper, iron, titanium, platinum, and perhaps vanadium deposits of various types. These complexes are probably more likely to contain significant undiscovered mineral deposits than any other favorable area in the monument. However, exploration and development problems caused by the extremely rugged terrain and severe weather would be great. The beach and possible submarine placers on the Pacific Ocean shore west of the Fairweather Range (fig. 1, near loc. 7) contain iron- and titanium-bearing heavy minerals derived from the gabbro and ultramafic rock complexes as well as some gold and platinum. This area probably contains very large low-grade placer deposits. A favorable belt of mixed rocks, including granitic intrusions and many kinds of metamorphic rocks, extends from the Brady Glacier northward past Reid and Johns Hopkins Inlets and along the west side of Tarr Inlet (fig. 1, south of loc. 5 north to 4). This belt contains many large iron-stained zones and many known mineral deposits, including those in the Reid Inlet gold area and the Margerie prospect. The marble and metamorphosed volcanic units are favorable hosts for deposits and are cut by at least two types of granitic intrusions. In the Muir Inlet area and in areas to the east and west of the inlet is a structural zone with east to west trends (fig. 1, near Iocs. 1 and 9), rather than the north-northwest to south-southeast trends which typify the monument as a whole. The cause of these aberrant trends is not known, but the east-west zone is congruent with an area characterized by dikes and plugs of porphyritic intrusive bodies whose compositions are similar to many of the granitic rocks in the monument. In places, as at the Nunatak molybdenum prospect, the country rock has been shattered by these shallow-depth intrusions. This area of congruent east-west trends and porphyritic intrusions contains most of the molybdenum deposits known in the monument and is probably the most likely area in which to find hidden molybdenum-copper deposits. A potentially favorable area (fig. 1, near loc. E) is included in the eastern end of the area just described. Granitic intrusive rocks, metamorphic rocks somewhat similar to those near Muir Inlet, and a generally higher background content of metals in stream sediments all suggest that the area on both sides of the boundary in the northeastern part of the monument may contain undiscovered mineral deposits of unknown size and significance. Glacier Bay National Monument contains a few mineral deposits that are likely to be minable in the near future; some that may be minable in the more distant future, but which are not well enough known to be evaluated; some that probably would be minable with economic or technologic changes; and many that are insignificant. The economic potential for petroleum, coal, and nonmetallic commodities in the monument is low. INTRODUCTION The U.S. National Park Service, in November 1965, requested that the U.S. Geological Survey study the mineral resources and mineral-resource potential of Glacier Bay National Monument, Alaska. The purpose was to provide factual information for the use of the National Park Service in planning the future development of the monument for the public. A Geological Survey field party investigated the mineral deposits of the monument and their regional geologic setting during the summer of 1966. Three concurrent methods of study were used. The most important method consisted of detailed field examination and a sampling of previously known deposits and of new deposits found during the course of the overall investigation. The second involved extensive collection and geochemical analysis of stream-sediment samples from all major drainages. About 2,700 stream-sediment and mineralized rock samples were analyzed. The third method was reconnaissance geologic mapping, which delineated the maj or rock units forming the host rocks of the mineral deposits, determined the bedrock compositions of the geochemi-cally sampled drainage basins, and revealed new mineral deposits and areas favorable for deposits. The investigation successfully covered almost all the monument, with only the high part of the Fair-weather Range (fig. 2) and the Pacific coastal strip west of that range left unvisited. Eighty-eight mineral deposits, both newly found and previously known, are described in this report. Of this number, 16 deposits considered to be of greater economic interest than the rest are described in detail. Many insignificant mineral deposits were visited and sampled; their locations are given in this report, although they are not described.6 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA MUIR PROVINCE Adams Inlet Johns Hopkins Inlet FAIRWEATHER > GLACIER ,,bay PROVINCE CHILKAT Geikie Inlet . Lituya\Bay PROVINCE GEIKIE PROVINCE Bartlett Cove ‘Ripple Cove Gustavus Dundas Bay ICY STRAIT 20 MILES CHICHAGOF ISLAND 138°00' 137”00' 136°00' 135-30' 59°00' 58“30' Figure 2.-—-Index map showing Glacier Bay National Monument, Alaska, and geologic provinces within the monument.REGIONAL GEOLOGY 7 The geochemical sampling and analysis defined several significant geochemical anomalies, including some in areas known to contain mineral deposits. Most of the amomalies have not been evaluated completely, although some were resampled in detail. The reconnaissance geologic mapping developed the regional framework of the mineral deposits and the background information essential to the interpretation of the geochemical data. The mapping also contributed greatly to the knowledge of the regional geology of this northern part of southeastern Alaska. The geochemical sampling program relied heavily on rapid analyses of the samples. All stream-sediment samples were dried and sieved to -80 mesh shortly after collection, and the total heavy-metals content (copper, lead, and zinc) was determined on a split by conventional field tests (Huff, 1951; see “Methods of analysis”). The samples were then airmailed to the Geological Survey laboratories, where spectro-graphic analysis for 30 elements was made. Results were airmailed back to the field, usually arriving within 2-3 weeks from the time the sample was collected. Mineralized rock samples were in some cases screened by the total-heavy-metals test in the field before being sent to the laboratory for spectro-graphic analysis or assay. Samples were analyzed spectrographically by Nancy M. Conklin, J. C. Hamilton, R. G. Havens, Harriet G. Neiman, and A. L. Sutton, Jr. D. A. Brew wrote the introductory material and regional geologic summary and prepared the lithology for the combined lithologic-mineral deposit location map. E. M. MacKevett, Jr., wrote all but one of the descriptions of the mineral deposits, incorporating geochemical material prepared by L. C. Huff. MacKevett was assisted by J. G. Smith in organizing data, by R. J. Wehr with laboratory studies, and by Susan R. Bartsch with drafting. H. R. Cornwall wrote the description of the Brady Glacier deposit. George Plafker is responsible for the summary of petroleum prospects in the Gulf of Alaska Tertiary province. C. C. Hawley prepared the maps showing the results of geochemical sampling and the discussions of geochemical anaomalies. Hawley and Huff wrote the section discussing the geochemical sampling program. MacKevett and Brew wrote the “Abstract and summary.” GEOGRAPHIC SETTING Glacier Bay National Moument, Alaska, is an area of rugged glacier-clad mountains and steep-sided fiords within the St. Elias Mountains physiographic province in the northwestern part of southeast Alas- ka (fig. 2). Scenically and glaciologically, it is one of the most spectacular parts of Alaska. The magnificent Fairweather Range culminates in Mount Fair-weather (15,300 ft) and forms an awe-inspiring de-vide between the Gulf of Alaska, only 12-15 miles west of the range crest, and the deep fiords of Glacier Bay proper, as close as 8 miles east of the crest. The rapid recession of the glaciers in Glacier Bay has not only provided an unparalled opportunity to study recessional glacial phenomena but has also exposed older glacial deposits and related features that are evidence for a complex sequence of relatively young glacial events. The monument is located some 100 miles west-northwest of Juneau, Alaska, (fig. 2) and is accessible only by water or air. Small boats can reach Glacier Bay from the Inside Passage waters by way of Icy Strait. Reaching the Pacific coastal part of the monument involves an exposed and often rough run through Icy Strait and around Cape Spencer into the open ocean. Boating within Glacier Bay itself is less difficult and conditions are generally good during the summer months, although strong tides and sudden winds can abruptly change conditions. Charter float-equipped aircraft from Juneau and Haines reach the Bay in about an hour and can land in most fiords, except where icebergs are numerous. Ski-wheel aircraft have landed on several of the large glaciers. Alaska Airlines maintains regular daily air service to the permanent community at Bartlett Cove (monument headquarters) during June, July, and August and to Gustavus (just outside the monument) all year. The monument has an area of about 3,900 square miles, excluding the water areas outside Glacier Bay proper. Of this area, 530 square miles (or about 14 percent) consists of the 50-mile-long Glacier Bay and its various arms and inlets. About 830 square miles (or 21 percent) is covered by glaciers. Much of the remaining 2,550 square miles is covered by snow all but 3 or 4 months of the year. The land areas in the monument are all mountainous, except for a few broad plains underlain by glacial outwash in the southern and east-central parts. Four general types of mountains are found, reflecting differences in total relief, glacial history, and vegetation development. Toward the north-northwest, the lower, rounded summits andt thickly forested steep slopes, typical of the Chilkat Range and the southern parts of the monument, give way to slightly higher, bare, serrated peaks and ridges that border steeply narrow steep-gradient valleys. Still farther north, coalescing valley glaciers and ice-8 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA fields convert similar peaks and ridges to nunataks. In the highest parts of the monument, the precipitous peaks of the Fairweather Range have impressive ice-fluted flanks that descend to heavily crevassed valley glaciers below. The glaciers in the monument range from small hanging types common on most peaks to ones of great expanse, such as the Brady Glacier Icefield, 240 square miles in area; but most are valley glaciers 1-3 miles wide, which head in cirques or icefields at an altitude of 4,000-6,000 feet and descend almost to tidewater. The glaciers are, in general, quite crevassed and are easily traversed only in early summer. The Brady Glacier and Takhinsha Mountain Icefields are snow covered in their higher parts during most summers and are therefore more easily traversed. At present, the ice in the glaciers may be as much as 1,000-1,500 feet thick in some of the deeper valley glaciers and as much as 1,000 feet thick on the broader and higher icefields. Adjacent to nunataks and valley walls the ice thickness increases rapidly, but the bedrock surface may be very irregular locally. Except for some stagnant ice at low altitude, all the glaciers in the monument are active, and there are signs that some are growing. The fiords of Glacier Bay are steep sided and deep, local depths being greater than 1,000 feet. Shallower areas are found only near the broad expanses of outwash deposits in the southern part of the monument and over the small deltas associated with tidewater glaciers and the larger streams. Most of the streams in Glacier Bay National Monument are small, have steep gradients, and drain areas of only a few square miles. In the southern part of the monument, however, several short, but vigorous, rivers drain relatively large areas. These rivers, most of their tributaries, and many of the other streams are swift and difficult to cross on foot. Almost all streams, regardless of size, were found to carry active stream sediment suitable for geochemical analysis. The climate of the monument is generally maritime in the southern and lower altitude parts. Increasing altitude in the Fairweather Range, the presence of many glaciers, and the rain-shadow effect of the Fairweathers tend to make the northern part of the monument less humid and more like interior regions. No weather data are available for the northern or higher altitude parts, but data are available for Cape Spencer and Gustavus (fig. 2). These data, summarized in table 1, show that the months from February through July or August have the least precipitation, that the fall and early winter months have the most, and that the temperatures, are, in general, mild in both summer and winter. Table 1.—Average precipitation and average temperature for Cape Spencer (1937-66) and Gustavus (19i0-66) [Data from U.S. Weather Bureau, 1937—66] Month Precipitation (inches) Temperature (degrees Fahrenheit) Cape Spencer Gustavus Cape Spencer Gustavus January .... 8.14 4.44 32.05 25.90 February .... ... 6.04 3.13 33.39 28.80 March .... 6.31 2.89 35.29 32.39 April .... 5.47 2.32 40.12 39.41 May .... 6.60 2.86 45.12 46.17 June ... 5.17 2.59 47.36 52.24 July ... 7.55 4.04 50.31 55.48 August .. 9.46 4.42 52.55 54.77 September . 14.33 6.95 48.97 49.75 October ...16,70 9.31 44.20 42.26 November _. ...13.28 6.19 37.65 33.38 December .. 10.12 5.01 33.68 28.23 Annual average 1 110.64 54.30 42.20 40.75 1 Through 1965. PREVIOUS INVESTIGATIONS Glacier Bay has attracted many geologists and glaciologists during the past 90 years, mainly because of the rapid recession of the glaciers. Few of the earliest explorers and scientists came with economic interests in mind, but by 1892 some prospectors were in the area (Rossman, 1963b). In 1906, F. E. Wright and C. W. Wright (1937) studied the Johns Hopkins Inlet area and other parts of the monument; in 1919, J. B. Mertie visited the area. Buddington (Buddington and Chapin, 1929) visited the monument in 1924. Somewhat later, several other Geological Survey geologists (Reed, 1938; Twenho-fel and others, 1949; Kennedy and Walton, 1946) visited specific mineral deposits then of interest or under development. Economic interest in the monument was lessened by prohibition of prospecting from 1924 to 1936. In 1942, Twenhofel (1946) studied the Muir Inlet Nunatak molybdenum deposit in detail, and the U.S. Bureau of Mines sampled the deposit (Sanford and others, 1949). In 1949, D. L. Rossman began geologic studies in the monument, which are summarized in three reports (Rossman, 1959, 1963a, b). In 1950-51, J. F. Seitz studied the geology around Geikie Inlet (Seitz, 1959). Don J. Miller studied the Gulf of Alaska Tertiary province for several years; his mapping within the monument was incorporated by Rossman (1963a) after earlier open-filing (Miller, 1961). Reconnaissance studies in the Juneau 1:250,000 quadrangle part of the monument were made during the period 1956-58 (Lathram andINTRODUCTION 9 others, 1959). A few mining companies, notably Fremont and Moneta-Porcupine, prospected in the monument during the late 1950’s and early 1960’s. PRESENT INVESTIGATION The Geological Survey party that made the studies reported herein was led by D. A. Brew and E. M. MacKevett, Jr., with Brew overseeing the operations and reconnaissance geologic mapping, and MacKevett, the studies of mineral deposits and the mineral-resource evaluation. In addition to Brew and MacKevett, the party consisted of Arthur B. Ford, Charles C. Hawley, Lyman C. Huff, A. Thomas Ovenshine, Arthur S. Radtke (until July 9), James G. Smith (after July 13), geologists, and Raymond J. Wehr, physical science technician. Huff and Hawley coordinated the geochemical studies throughout the project. Henry C. Cornwall joined the project temporarily early in August to study the Brady Glacier deposit. The USGS R/V Don J. Miller, a 105-foot power barge manned by Robert D. Stacey, master; Allen Z. Komedal, chief engineer; and John J. Muttart, cook-seaman, was used as base for the field operations. The project was supported by a helicopter operated by National Helicopter Engineering Co., with Dan Ellis, pilot, and Howard Grannell, mechanic. The party started fieldwork on May 24, 1966, and had excellent weather during May, June, and July. Frequent storms in August and early September hampered the studies, and the party left Glacier Bay on September 5,1966. The field studies were affected to a certain extent by the amount of snow cover present. Therefore, the sequence in which the different parts of the monument were studied is significant. In late May the investigations covered shoreline and island exposures along the west side of Glacier Bay from Ripple Cove to Blue Mouse Cove; in June, the northeastern and east-central parts of the monument; in July, the north-central, some of the northwestern, and the southeastern parts; and in August, the south-central part, the west-central, and some of the northwestern areas. In general, the amount of snow diminished rapidly through June and early July and slowly in July and August; in September the terrain above 4,000 feet was covered by new snow. The results of the field studies are also a function of the way the data were gathered. All shoreline exposures within Glacier Bay and most of those along Icy Strait were traversed by slow-moving outboard-powered skiff, and frequent stops were made to examine the outcrops and obtain stream-sediment samples. Ridges accessible by helicopter and suitable for walking were traversed by geologists and examined in detail. The rougher ridges were examined aerially from the helicopter, and spot landings for outcrop study were made wherever possible. Some streams were traversed on foot to gather sediment samples and bedrock information, but most were sampled during helicopter spot landings. ACKNOWLEDGMENTS The cooperation of the U.S. National Park Service staff at Glacier Bay National Monument contributed greatly to the efficiency of the field operation. We should like to thank, in particular, Robert B. Howe, Superintendent, Charles Janda, ranger, and Kenneth Youmans. We also thank the Newmont Mining Co. and American Exploration & Mining Co. for their cooperation in the appraisal of the Brady Glacier copper-nickel and the Muir Inlet Nunatak molybdenum deposits, respectively. L. F. Parker of Mount Parker Mining Co., visited the Survey geologists in the field on one occasion, as did Lawrence Duff, a private operator, both aided in locating prospects in the Reid Inlet area. REGIONAL GEOLOGY Knowledge of regional geology is important to this mineral resource appraisal in three ways: (1) the study of the rocks and their distribution aids in interpreting the geochemical data; (2) knowledge of the geologic framework of the known deposits leads to geologic insights about particular environments that need to be carefully evaluated in areas where no deposits are yet known; and (3) projection of known rock units from mapped areas into unmapped areas provides a basis for appraising the mineral potential of the unmapped areas. The emphasis in this report is on the gross lithic and structural framework of the monument, and no detailed stratigraphic information is presented. The lithologic map (pi. 1) shows the major rock types and indicates the general geologic associations of the mineral deposits. Glacier Bay National Monument consists of five distinct geologic provinces, each of which is characterized by specific structural and lithologic features. The Coastal province lies west of the Fair-weather fault (fig. 2). The Fairweather province is east of the Fairweather fault and extends eastward to the Brady Glacier. The Geikie province extends north-northwestward through the center of the mon-10 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA ument; at its northern end, it merges with the east-west-trending Muir province. The Chilkat province occupies the southeastern part of the monument. The features which characterize these provinces are discussed below. STRATIGRAPHY The bedrock stratigraphic section in the Glacier Bay National Monument ranges from Early Silurian through late Tertiary in age, with significant gaps in the late Paleozoic, late Mesozoic, and early Tertiary. The section is not well understood because of scanty fossil record, apparent abrupt facies changes, widespread metamorphism, and the disruption caused by intrusive bodies. The Paleozoic part of the section crops out through the east half of the monument and is particularly well exposed in the Chilkat province (fig. 2). A stratigraphic thickness of 20,000 to 30,000 feet is estimated to be present. Detrital clastic rocks, mostly graywacke and argillite, of Silurian and possibly Devonian age are dominant; some discontinuous nonfossiliferous limestones are also present. To the north, these rocks appear to grade into a comparable section that contains significant amounts of volcanic rocks. In the western and northwestern parts of the Chilkat province are exposures of thick reef limestones whose correlation with the rest of the section is uncertain. Carbonate and detrital clastic units of Middle Devonian age occur in the north-central and northwestern parts of this province, and also in the Muir province. The relations between the known Devonian rocks and the known Silurian rocks are obscured by structural complexities and poor fossil control. The Paleozoic rocks throughout most of the Chilkat province are not greatly metamorphosed, except adjacent to intrusions. In the Geikie and Muir provinces, these same rocks locally are highly metamorphosed, and it is difficult to correlate them with their less metamorphosed equivalents. Mesozoic strata are found in the Coastal and Fair-weather provinces along north-northwest trends similar to trends in the Mesozoic rocks of nearby Chichagof Island. They include three gross units of unknown thickness: (1) a low-grade metamorphic unit derived from mixed detrital clastic rocks and volcanic rocks, found only west of the Fairweather fault; (2) a biotite schist unit; and (3) an amphibolite unit. The schist unit is derived from a gray-wacke-shale sequence known to be of Jurassic and Cretaceous age on Chichagof Island, and the amphibolite may be equivalent to volcanic rocks of probable Triassic age in that same area. Tertiary strata unconformably overlie the metamorphosed Mesozoic strata in the Coastal province; they consist of at least 12,000 feet of Miocene and Pliocene sandstone, shale, and minor volcanic rocks and conglomerate. The Tertiary strata probably extend offshore onto the continental shelf. INTRUSIVE ROCKS Intrusive rocks of probable late Mesozoic and perhaps Tertiary age dominate the Geikie and Muir geologic provinces and occur in all the other provinces to a lesser extent. Some of the foliated granitic rocks discussed below may actually be metamorphic rather than intrusive, but they are closely associated with the intrusives. The distribution of the different intrusive rocks is shown on plate 1, from which it is apparent that most of the known mineral deposits are spatially related to intrusions. Most of the intrusives in the monument are meso-zonal foliated granitic rock bodies. Hornblende quartz diorite, hornblende diorite, and biotite-horn-blende quartz diorite are most common, but some biotite-hornblende granodiorite also occurs in foliated bodies. In general, foliation is parallel to that in the adjacent metamorphosed country rocks, but local divergences are present. This relation suggests that these bodies were intruded before the end of the episode in which the country rocks were deformed. Most of the foliated granitic bodies contain, and are locally bordered by, areas of hornblende quartz diorite gneiss, which commonly contains abundant inclusions and is in some places very heterogeneous. Most of the mesozonal to epizonal unfoliated granitic rocks in the monument are in the Geikie province, but isolated bodies also occur in the Fair-weather, Muir, and Chilkat provinces. Because these granitic bodies all lack well-developed foliation, their intrusion is considered to postdate deformation. Compositionally, the unfoliated granitic rocks range from hornblende-biotite granodiorite to biotite granite. These bodies generally are free of distinctive border zones, but they do contain large hornfels inclusions. The intrusion at Johns Hopkins Inlet (fig. 2; pi. 1) is unusual in that it is associated with very extensive and spectacular border zones of such inclusions. A variety of dike rocks, ranging from aplites to lamprophyres, with andesites and diabases the most abundant, were mapped in the monument. They are particularly common in the western and northwestern part of the Chilkat province and in the metamorphic rocks in the Muir province. Many of theGEOCHEMICAL STUDIES 11 dikes probably are relatively young, and in many places have mineral deposits associated with them. The majority of dikes strike east or northeast, and they tend to occur in subparallel swarms. A layered gabbro complex occupies a large part of the Fairweather province, and at least two other bodies of gabbro occur nearby. The gabbro in the synclinal structure of the largest complex is more than 30,000 feet thick. The regularly layered center of this mass is commonly bordered by a structurally complex zone of gabbro and ultramafic rocks that locally contains important sulfide deposits. Other mineral deposits are known to occur within the layered portion. STRUCTURE Each geologic province in the Glacial Bay National Monument has characteristic structural features, and two provinces—Muir and Chilkat—have unusual complications. Certain features, however, are common to the whole monument: (1) a dominant north to northwest strike of all units and planar structures within all units, (2) steep dips, and (3) repetition of section by large-scale folds. The major faults in the monument also strike north to northwest, although there are minor local divergences from this pattern. In the Coastal province the moderately to gently dipping Tertiary strata form two northwest-trending synclines and one anticline, which have been displaced vertically by northwest-striking faults. Structures in the underlying Mesozoic rocks are not well known but probably are similar to those in the adjacent Fairweather province. The Fairweather fault, which separates the Coastal and Fairweather provinces, is part of a high-angle fault system that extends for more than 280 miles from Yakutat Bay on the north to Chatham Strait and western Baranof Island on the south. The segment of the fault within Glacier Bay National Monument is near the central part of the system. The dominant fault movement is inferred to be vertical, with the west side down; but both historic displacement (Tocher and Miller, 1959) and inferred older movements farther south (Loney and others, 1967) suggest that a right-lateral component is also present. Steeply dipping north- and northwest-striking foliation characterizes the Fairweather province, and the map units apparently are repeated by large folds. The emplacement of the large gabbro bodies had little structural effect on the country rock, except close to the contact. The Geikie province is characterized by parallel north- and northwest-striking foliations in the country rocks and in the numerous granitic bodies. The distribution of country rock units implies complex folding, but the intervening intrusive masses make exact analysis difficult. In the northwestern part of the province, northwest strikes and steep westerly dips of contacts suggest that most of the rocks in the province may be stratigraphically below units mapped in the adjacent Fairweather province. Geikie province also contains a prominent north-northwest-striking zone of discontinuous faults. The structures in the Muir province are very similar to those in the Geikie province, but contacts and foliations strike west to northwest and dip moderately to steeply to the north. These attitudes in the country rocks may be related to the configuration of the major intrusive bodies, but they may also represent preintrusion attitudes in part. In any case, the abrupt change from northerly trends near Muir Inlet to westerly trends only a few miles to the north suggest that one or more major structural discontinuities are involved. The distribution of map units in some areas between intrusive masses suggests that large folds, overturned to the south, may be present. The same abrupt change in strike has been mapped in the northern part of the Chilkat province, near Tidal Inlet. There, the situation is complicated by an east-west fault zone and, farther to the east, by an important high-angle reverse fault that brings relatively simply folded Devonian strata over more highly folded Silurian (?) rocks. Outside the area of these complications, the rocks in the Chilkat province are characterized by northwest strikes, moderate to steep northeast dips, and large amplitude folds overturned to the southwest. GEOCHEMICAL STUDIES Geochemical studies in Glacier Bay National Monument consisted of the collection, analysis, and subsequent interpretation of more than 2,700 samples including (1) 1,200 stream-sediment samples, (2) 1,000 altered or mineralized rock samples, (3) 500 soil samples (4) 30 unaltered and unmineralized background level samples, and a few (5) panned stream-concentrate samples, (6) water samples, and (7) glacial-moraine samples. The resulting basic data and preliminary interpretations provide only a skeletal framework, and we believe that further geochemical interpretation of these data is possible. In particular, the relations between bedrock lithic types and metal content of locally derived stream sedi-12 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA ments should be considered in detail. The following interpretations are preliminary and inconclusive. Stream-sediment samples provide the greatest amount of available geochemical data on the composition of the rocks and surficial deposits and on abnormal accumulations of metals, which might indicate the presence of undiscovered buried mineral deposits. The density of stream-sediment samples varies greatly because large areas in the monument have glacial, rather than normal, stream drainage. In areas of normal drainage, there is more than one sample per square mile; in the glacier-covered areas, the samples are much more widely spaced. The results of the stream-sediment studies are given in figures 3-7, on plates 2-8, and in tables 4-8. The concentrations of total heavy metals, chromium, copper, lead, molybdenum, and nickel are shown on individual maps, and one map (pi. 8) summarizes other elements, such as arsenic, beryllium, bismuth, cadmium, silver, strontium, tin, tungsten, and zinc, which were detected in anomalous amounts. Complete analytical data are given for several promising areas on separate maps and in tables. The analytical data derived from other samples are incorporated in the sections on mine and prospect descriptions. METHODS OF ANALYSIS Most samples were analyzed twice, first by a field geochemical prospecting test for total heavy metals (hereafter referred to as THM) and then spectrographically in the laboratory. The results of the THM tests were available 1 or 2 days after sample collection and were used to guide further sampling. The results of the spectrographic analysis were available to the field party within 2-4 weeks. The THM field test was made in a portable laboratory aboard the R/V Don J. Miller. The test is of the type described by Huff (1951) in which the sample is digested by heating with acid, and the dissolved metal content determined by dithizone. This type of THM test extracts much more of the zinc, copper, and lead contained in the sample than does the commonly used cold citrate soluble THM test described by Hawkes (1963). The more complete extraction is of considerable importance at Glacier Bay because the oxidation of the rocks there varies widely, and more of the metal may be tightly bound than in a more temperate or thoroughly weathered region. It should be emphasized that the THM test samples only the acid-soluble part of the contained zinc, copper and lead. The spectrographic method, however, measures virtually all the metal present. Both the spec- trographic and THM tests are semiquantitative; but, within limits of error, comparison of the THM and spectrographic analyses permits assignment of some anomalies to copper, lead, or zinc. For example, the THM test is especially sensitive to zinc, an element that has a poor spectrographic sensitivity (table 2). Stream-sediment samples that have high values of THM and low spectrographic values of copper and lead are therefore believed to have anomalous concentrations of zinc. Table 2.—Detection limits, in parts per million, for some elements determined by the six-step and direct-reader spectrographic methods Spectrographic method Spectrographic method Six-step Direct-reader Six-step Direct-reader Ag i i Mo 3 10 As 2,000 2,000 Nb 10 40 Au 20 10 Ni 3 2 B 20 20 Pb 10 4 Ba 2 10 Sb 200 50 Be 1 1 Sn 10 20 Bi 10 9 Sr 5 10 Cd 50 50 Ti 2 10 Co 3 3 V 7 4 Cr 1 2 W 100 300 Cu 1 1 Y 10 5 La 30 20 Zn 200 200 Mn 1 5 Zr 10 10 The spectrographic method supplements the THM test because the latter does not detect elements such as chromium, molybdenum, nickel, tin, and tungsten. These and other elements are detected by spectrographic analysis if they are present in concentrations as high or higher than those given in table 2. The sensitivity for elements such as cobalt, copper, chromium, molybdenum, and nickel is low enough to detect minor concentrations of these elements, but the sensitivity for gold, tungsten, and zinc is high enough that these elements need to be markedly enriched to be detectable. Two slightly different spectrographic methods were used, referred to in table 2 as the six-step and direct-reader methods. The six-step method is similar to that described by Myers, Havens, and Dunton (1961) in that the concentrations are measured visually from photographic plates; it differs in that concentration are reported in the six-step geometrical array, 1, 1.5, 2, 3, 5, 7,..., instead of the three-step array, 1, 3, 7,.... The direct-reader method refers to a direct-reading spectrograph in which the concentrations are measured automatically by photomultiplier tubes. The two methods are comparable in sensitivity and accuracy for most of the elements sought (table 2). In addition to routine THM and spectrographic analyses, many mineralized rock samples were ana-GEOCHEMICAL STUDIES 13 lyzed for molybdenum and gold in the laboratory by sensitive chemical methods. SAMPLING AND SAMPLE PREPARATION Stream-sediment samples were collected from both large and small streams. Most of the streams sampled were flowing, but some samples were taken from the dry beds of intermittent streams. Clayey and silty sand was collected; this material is generally present in considerable abundance in the major streams, but may be very scarce in steep, small, or intermittent stream courses. However, some clayey and silty sand may be found even in small streams in pockets behind boulders. The samples were placed in water-resistant paper bags, then dried at about 100 °F. After drying, the sample was sieved at —80 mesh and that fraction was analyzed—first by the field THM test, then spectrographically. ANOMALOUS AND BACKGROUND VALUES Every region is characterized by a range of content values for each element; the average of these values is the background value. In many cases the median value is taken as background. Most samples have about this concentration, but a few will have much higher or much lower concentrations and these values are considered anomalous. High values are of special economic interest because they indicate areas of enrichment which may, in turn, be done to the presence of potential ore bodies. Most regions are underlain by many rock types, and because each rock type has a characteristic element content, background values are not constant. Therefore, any group of anomalous values must be interpreted with consideration of such variations. The results of this geochemical investigation are reported (pis. 2-8) in ranges of concentration, each range being identified by a specific symbol. The data shown on the maps suggest patterns of element distribution. TOTAL HEAVY METALS Analyzed stream-sediment samples from Glacier Bay National Monument contain from 20 to 1,000 ppm zinc, copper, and lead extractable in hot acid. The median THM concentration is about 25 ppm, based on results from a set of samples from 915 localities (pi. 2), which include the average values from some duplicate analyses. About 75 percent of the samples contain less than 60 ppm; 90 percent, less than 100 ppm; and 95 percent, less than 120 ppm. The samples with 120 ppm or more THM are considered markedly anomalous. COPPER Copper ranges from about 5 to about 700 ppm in stream-sediment samples from the monument. The median copper content is about 40 ppm, based on the set of 636 samples (pi. 3) analyzed by the six-step method. About 95 percent of the samples contain less than 100 ppm, and the samples that contained 100 ppm or more copper are considered markedly anomalous. LEAD Lead was not detected by spectrographic analysis in the majority of Glacier Bay stream-sediment samples. The median value is therefore less than the spectrographic detectibilities (table 2), although it may be approximately the detectibility of the direct-reader method (4 ppm). Based on 636 samples (pi. 4) analyzed by the six-step method, about 85 percent of the samples contain less than 10 ppm; and 94 percent, less than 15 ppm. The values above 15 ppm are considered markedly anomalous. MOLYBDENUM Molybdenum is not reported in the majority of spectrographic analyses, but its median value may not be much less than the 3 ppm detectibility of the six-step method. In some areas many samples showed values by the direct-reader method of 5-10 ppm; these values are below the general detectibility of the method and therefore were not considered in the statistical analysis. They may, however, indicate areas of slightly anomalous molybdenum content and are given on the detailed maps (figs. 3-7). In a group of about 1,000 samples, molybdenum exceeded 10 ppm in only 36 samples (pi. 5). All values above 10 ppm are considered anomalous. CHROMIUM The chromium content of stream sediments in the monument ranges from less than 5 ppm to about 2,000 ppm (0.0005-0.2 percent). Based on a group of 957 samples (pi. 6), the median concentration is about 60 ppm and about 90 percent of the samples contain less than 100 ppm chromium. About 98 percent of the samples contain less than 200 ppm chromium. Samples containing 200 ppm or more chromium are considered markedly anomalous. NICKEL Nickel ranges from about 3 to 700 ppm in stream sediments in Glacier Bay National Monument. Based on the 636 samples (pi. 7) analyzed by the six-step method, the median value is about 15 ppm nickel. About 90 percent of the samples contain less than 30 ppm, and about 95 percent, less than 40 ppm nickel. Values of 40 ppm or more are considered markedly anomalous.14 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA OTHER ELEMENTS Based on the 636 samples (pi. 8) analyzed by the six-step method, the median cobalt concentration in stream-sediment samples is between 10 and 15 ppm, and about 90 percent of the samples contain less than 20 ppm cobalt. Cobalt is not shown on the maps, as it generally tends to vary directly with nickel. Any tin and tungsten values detected by the spectrograph were considered anomalous and are shown on plate 8, along with any detected values of a group of rare elements including silver and arsenic. Values of strontium greater than 1,000 ppm were considered anomalous and are also shown on plate 8; although strontium is not very common in ore Table 3.—Semiquantitative spectrographic analyses in parts per million of representative unaltered rocks [O, looked for, but not found; . . . not looked for] Semiquantitative spectrographic analyses Lab. No. Field No. Ag B Ba Co Cr Cu Fe La Mn Mo Ni Pb Sc Sn Sr Ti V Y Zr A. Detrital sedimentary rocks 1 D125435 Hx279A 0 100 5 70 20 20,000 0 500 0 15 0 0 200 1,000 50 15 2 D125436 Hx279B 0 300 15 50 100 50,000 0 70 0 30 0 0 200 5,000 150 10 3 D126165 Ov931 0 100 7 30 30 20,000 0 500 0 15 0 0 500 1,000 70 20 B. Limestone 1 D125437 Hx289 0 5 0 7 3 200 0 30 0 0 0 0 200 0 0 0 2 D125438 Hx524 0 150 0 5 7 100 0 15 0 0 0 0 100 0 0 0 3 D126163 Hx681 0 15 0 15 20 500 0 150 0 5 0 0 70 50 0 0 4 D1261104 Hx682 0 100 3 30 20 1,000 0 200 0 15 0 0 500 50 0 0 C. Mafic dikes and sills 1 D125449 Hx540 0 70 20 150 70 70,000 0 700 0 50 0 0 200 5,000 200 20 2 ’D125938 Bd518B 0 50 10 0 7 > 100,000 70 500 0 0 0 0. . 5,000 15 7 3 D125441 Ov282 0 10 30 1,000 50 70,000 0 700 0 300 0 0 70 1,500 150 10 4 D126156 Hx567 0 300 20 70 20 50,000 0 200 0 20 0 0 700 3,000 300 20 5 D126157 Hx575 0 30 30 200 70 > 100,000 0 1,000 0 70 0 0 150 7,000 500 30 6 D126162 Sj52 0 100 30 70 200 > 100,000 0 1,000 0 100 0 0 500 7,000 500 30 7 D124941 Hx405 0 300 30 200 50 70,000 0 1,000 0 100 0 7,000 200 20 1 Also found 2 ppm Be, 10 ppm Nb. D. Diorite, quartz diorite, and quartz monzonite or granodiorite (field identification) 1 D125155 Hx565 0. . . . 500 15 20 10 70,000 0 1,000 0 5 0 0 500 3,000 150 30 2 D125158W HxG14 0. . . . 500 15 15 100 70,000 0 1,000 0 10 0 0 500 5,000 200 50 3 D125159 Hx654 0. . . . 700 7 30 30 50,000 0 700 0 10 0 0 500 2,000 100 10 4 D125439 Fa280 0. . . 500 10 10 30 50,000 0 700 0 3 0 0 300 3,000 150 20 5 D125442 Hx4f>0 0. . . 300 15 15 70 70,000 0 1,000 0 7 0 0 500 5,000 200 20 6 D125443 Hx464 0. . . . 150 15 1.5 30 50,000 0 1,000 0 0 0 0 500 5,000 200 20 7 D125450 Bd554 0. . . . 200 15 20 70 50,000 0 1,000 0 7 0 0 300 5,000 150 20 8 ‘D124685 Hx377 0. . . . 700 5 3 7 30,000 0 500 0 0 0 0. . 2,000 20 20 9 D124072 Hx211A 0. . . . . . 1,000 10 10 15 50,000 0 1,000 0 3 0 0. . 5,000 200 30 1 Also found 3 ppm Be. E. Granite or aplite 1 'D125440 Fa312 0. . . . 300 0 5 7 7,000 0 700 0 0 10 0 20 150 0 10. . 2 JD125160W Hx603B 0. . . 200 0 5 5 10,000 0 200 0 0 15 0 20 50 0 15. . 3 D125154 Hx564 0. .. . . . 3,000 0 1 7 10,000 0 100 0 0 10 0 500 500 15 0. . 1 Also found 7 ppm Be, Tr, Li. 2 Also found 1 ppm Be, 10 ppm Nb. F. Hornblende, garnetiferous rock of diorite composition and associated rocks 1 D125444 Hx491 0 100 20 30 150 30,000 0 1,000 0 20 0 0 300 1,000 200 10 2 D125446 Hx513A 0 15 20 20 100 70,000 0 700 0 15 0 0 500 5,000 200 0. . 3 D125447 Hx513B 0 30 50 50 150 > 100,000 0 500 0 70 0 0 150 2,000 500 10. . 4 D126152 Hx485 0 100 20 50 30 > 100,000 0 1,500 0 15 0 0 200 3,000 300 15. . Lithologic Unit Al. Pale-gray calcareous siltstone with ellipsoidal masses of limestone, Tidal Formation of Rossman (1963b). 2. Dark-gray slaty argillite, interlayered with Al. 3. Interlayed siltstone and calcareous siltstone, Tidal Formation of Rossman (1963b). Bl. Gray finely crystalline massive limestone, Willoughby Limestone of Rossman (1963b). 2. Gray finely crystalline thin-bedded limestone. 3. Dark-gray carbonaceous limestone, Black Cap Formation of Ross- man (1963b). 4. Limestone and argillite, interlayered, typical of Rendu Formation of Rossman (1963b). C 1. Mafic dike. 2. Mafic igneous rock, forms sill-like masses. 3. Mafic dike. 4...do...... 5. ... do. C6. Mafic dike. 7. do Dl. Biotite-hornblende granodiorite. 2. Biotite-hornblende quartz diorite. 3. Biotite-hornblende granodiorite or quartz monzonite. 4. Hornblede-biotite quartz diorite. 6. Biotite-hornblende diorite or granodiorite. 6. Hornblende diorite. 7. Hornblende-biotite diorite or granodiorite. 8. Biotite quartz monzonite. 9. Quartz monzonite or granodiorite. El. Leucogranite or quartz monzonite. 2. Leucogranite. 3. Aplite. FI. Hornblende-garnet "diorite.” 2. Gneissic diorite, disseminated sulfides visible. 3. Hornblendite associated with 2. 4. Hornblende-garnet "diorite.”GEOCHEMICAL STUDIES 15 minerals or in metal deposits, it is shown because it may indicate alteration or strontium metasomatism. UNALTERED ROCKS Rocks in Glacier Bay National Monument contain differing amounts of trace elements, depending on their origin, lithology, and major-element composition. Many samples would be required to define exactly the trace-element geochemistry of the bedrock units, but spectrographic analyses (table 3) of 30 apparently unaltered and unmineralized rocks provide a basis for some generalizations. Limestones probably have lower trace-element contents than any other rock type common in the monument. The range in concentraion in four analyzed samples is 0-3 ppm cobalt, 5-30 ppm chromium, 3-20 ppm copper, and 0-15 ppm nickel. No lead or zinc was detected. Streams draining unaltered limestone terranes should, therefore, have a low content of these metals. Three analyzed samples of de-trital clastic sedimentary rocks contain as much as 15 ppm cobalt, 70 ppm chromium, 100 ppm copper, and 30 ppm nickel, indicating that streams draining unaltered detrital clastic rock terranes should carry these metals in considerable abundance. Of the igneous rocks in the monument, the diorite-granodiorite-quartz diorite suite was the most adequately sampled and analyzed. The average (arithmetic mean) concentration of selected elements is compared below with values for similar rocks reported by Turekian and Wedepohl (1961): Ba Co Cr Cu Ni Sr High calcium granitic rocks: 1. Granodiorites and other granite rocks of Glacier Bay 506 12 14 40 5 443 2. Average of Turekian and Wedepohl (1961) 420 7 22 30 15 440 Based on only three samples, the leucocratic granitic rocks (which are mainly adamellites) have an appreciably different trace-element suite, including trace amounts of lead. Semiquantitative analysis shows that one sample contains 7 ppm beryllium and a trace of lithium, elements characteristic of some leucocratic granites that have associated ore deposits. More mafic rocks, such as hornblendite and gneiss-ic garnetiferous diorite, generally contain higher concentrations of the elements cobalt, chromium, copper, and nickel. Mafic dikes, including lamprophyres, locally contain very high concentrations of these elements, particularly chromium and nickel. The mafic dikes are locally abundant and probably contribute important amounts of these metals to stream sediments. CAUSES OF ANOMALOUS VALUES Anomalous concentrations of metallic elements occur in stream-sediment samples from various parts of Glacier Bay National Monument; some of these concentrations indicate the presence of mineralized rocks and are discussed in the following section. In a few places, similar anomalous concentrations indicate unusual amounts of metals contained in the country rocks or, directly or indirectly, the effects of glaciation. Swarms of mafic dikes are the probable source of anomalous concentrations of metallic elements in some parts of the monument. Such dike swarms make up as much as 40 percent of the bedrock in some areas. Some of the dikes contain unusual amounts of elements such as chromium and nickel, and most are bordered by thin selvages of baked and bleached rock with abundant thin carbonate veinlets. Erosion of the dike and contact-zone rocks provides material relatively rich in metallic elements; hence, the presence of anomalous nickel and chromium in the stream sediments probably indicates the presence of dike swarms rather than ore deposits. Aggrading glacial streams accumulated metal concentrates that may or may not be indicative of bedrock mineralization upstream. Some glacial outwash stream sediments show small, but real, concentrations of a suite of elements including iron, titanium, lanthanum, chromium, niobium, vanadium, yttrium, and zirconium. These concentrates were caused by a lag effect; the fast-moving glacial streams selectively carried off light minerals and left the heavy minerals that contain this suite of elements. That the same suite of metals was found in panning concentrates indicates the validity of the proposed mechanism. RESULTS OF GEOCHEMICAL STUDIES The geochemical studies show both many local concentrations of metals in stream sediments and systematic geographic distributions for individual elements. Some of the distribution patterns are related to mineral deposits in the bedrock, some to metal-rich country rocks, some to lag concentrates, and others are not clearly related to any of these. The distribution of anomalous values shown in figures 3-7 and on plates 2-8 are discussed below with reference to known geologic features. The interpretations given are necessarily brief, and further development of the detailed relations between stream-sediment metal contents and bedrock composition of the drainage basins involved is possible in some instances.16 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA TOTAL HEAVY METALS Anomalous THM values are widely scattered at Glacier Bay (pi. 2). Some of them cannot be assigned to any distinct mineralized zone and are interpreted to be the result of widely scattered, but individually small, centers of hydrothermal alteration and metallization. Inspection of the map shows that THM values are generally higher in the relatively unmetamorphosed and predominantly detrital clastic Chilkat province than in the predominantly metamorphic and granitic Geikie or Muir province (fig. 2). Within the Chilkat province there are noticeable concentrations of anomalous THM values near the head of Excursion River, near Miller Peak and Sandy Cove, and northwest of Tidal Inlet near Mount Merriam. The areas near Miller Peak-Sandy Cove and Mount Merriam are underlain by a variety of sedimentary rocks cut by small stocks and are discussed under “areal descriptions.” Anomalously high samples near the head of Excursion River are close to a prominent fault zone, which controls the north-northwest course of the river and are probably related to mineralization along the fault zone, such as that known at the head of Adams Inlet. Farther east, additional subparallel faults are suggested by prominent topographic alinements. Some of the anomalous samples, particularly those in uppermost Berg Creek, show high copper and chromium contents also. Isolated anomalous values scattered through the Chilkat province are probably related to additive contact metamorphism or related mineralization. Isolated anomalous THM values east, west, and south of Snow Dome are related to an abundantly iron-stained contact zone with small magnetite masses adjacent to a granodiorite stock. An isolated anomalous THM value north of the Nunatak molybdenum prospect probably reflects copper and zinc added during molybdenum mineralization. High THM values north and south of White Glacier probably result from the zinc and copper deposits (pi. 1, loc. 6) known in the area. In the Geikie province, high THM values are concentrated near Dundas Bay. Many of these values are due to high copper contents, and they are discussed either with copper deposits or in the descriptions of the geochemical results in the eastern and western Dundas Bay areas. The Reid Inlet gold area is not marked by any conspicuous THM anomaly, even though the gold deposits contain some sphalerite,which should contribute zinc to the streams. One anomalously high and several moderately high values of THM (60-119 ppm) are found in the Reid Inlet area, however. A very metalliferous stream sediment (1,000 ppm) was found north of the area in Tarr Inlet. Only a small number of stream-sediment samples were obtained from the Muir province because drainage is predominantly glacial. The region seems to have a low THM content. COPPER The copper distribution pattern (pi. 3) resembles that of the THM distribution, particularly in the generally higher metal values of the Chilkat province in comparison with the Muir and Geikie provinces. The pattern is not, however, identical with THM; part of the difference is due to test method: the THM test is most sensitive for zinc and less sensitive for copper and lead; hence, high THM does not necessarily indicate high copper. The difference between THM and copper values is very noticeable at the head of Excursion River and in the Miller Peak-Sandy Cove area. At both of these places, only part of the THM anomalies is due to copper and an appreciable part is due to zinc, as is shown by comparison of the THM and the copper, zinc, and lead spectrographic analyses. In other places, as in uppermost Berg Creek east of Adams Inlet, anomalies barely discernible in THM are better shown in copper. No copper anomalies were found in the Muir province, although it should again be noted that this area is extensively covered by glaciers and has few flowing streams. The Geikie province contains several conspicuous copper anomalies, even though the background copper content is lower here than the Chilkat province. The largest anomaly is east of Dundas Bay, where the copper content is as much as 300 ppm in streams draining a large altered and mineralized area (pi. 1). Near the head of Taylor Bay, copper and THM values are high in a small creek draining across a gold prospect (Rossman, 1963b, pi. 1). Most of the Reid Inlet gold area does not contain copper anomalies, but stream sediments collected east and west of the central part of the area do have anomalous copper contents. An isolated stream-sediment sample on the west side of Tarr Inlet contained 700 ppm copper. A single sample from near the south end of the peninsula between Tarr and Rendu Inlets shows a value that is barely anomalous, but may be significant, as the sample locality is near a locally magnetite-bearing batholithic contact zone. LEAD The distribution of lead resembles that of THM, but the correlation with the copper pattern is lessGEOCHEMICAL STUDIES 17 marked. The data indicate broad areas of anomalous lead concentration in the southern part of the Chil-kat province and in the northern and southern parts of the Geikie province (pi. 4). Lead is somewhat enriched in two samples south of Snow Dome, one of which was marked by an anomalous THM value; these high values are probably derived from mineralization in a nearby contact zone. Lead also furnishes one of the few geochemical clues to the Reid Inlet gold area; anomalous amounts of lead are present in drainages on the Lamplugh Glacier side of the area. Galena present in the gold deposits probably explains the anomalous values. A small lead and THM anomaly north of Marble Mountain may be related to hydrothermally altered limestone country rock. The highest lead value found (200 ppm) is from the west shore of Tarr Inlet and coincides with anomalous values in THM, copper, and other metals. Slightly enriched values of lead (16-24 ppm) occur in drainages entering the south side of Johns Hopkins Inlet and also east of the Tarr Inlet about due east of the 200 ppm anomaly noted above. At both places the streams drain leucocratic granitic rocks, the only unmineralized rocks in the monument which contain spectrographically detectable lead (table 3). MOLYBDENUM The largest area of anomalous molybdenum content is in the northernmost Chilkat province near Mount Merriam. Other areas of possible significance are near Miller Peak and Sandy Cove and at the head of Dundas Bay. Because of the relatively poor sensitivity (10 ppm), the spectrographic analyses indicated only markedly anomalous values of molybdenum. As a result, no regional molybdenum background was detected (pi. 5). Detailed soil sampling (pi. 12) disclosed anomalous molybdenum values near the Nunatak molybdenum deposit. The stream-sediment sampling program did not detect the deposit, probably because of the recent glacial erosion which stripped off all enriched soil and because of the diluting effect of the surrounding extensive outwash deposits. CHROMIUM AND NICKEL Chromium (pi. 6) and nickel (pi. 7) have a distribution pattern that generally resembles the pattern for copper (pi. 3). As is true of all the metallic elements discussed, chromium and copper are regionally most abundant in the Chilkat province. The largest chromium anomaly in the Chilkat province is in upper Berg Creek. This area, which is also the site of a copper anomaly, is underlain by mixed volcanic and detrital clastic rocks, and some iron-stained zones crop out nearby. The chromium anomaly may persist downstream to Adams Inlet. Another chromium anomaly traceable downstream was detected along a tributary on the west side of Queen Inlet in an area where limestone and limy sandstone are intruded by granitic rocks. Two anomalous and several moderately high chromium values near Mount Wright are apparently caused by a mafic dike swarm, and isolated values elsewhere may mark mafic dikes. Nickel is also markedly enriched near Mount Wright. OTHER ELEMENTS Anomalous amounts of tin, tungsten, strontium, silver, and other metals are recorded on plate 8. Tungsten was found in only two samples at the head of Dundas Bay, near exposures of leucocratic granitic rocks. High tin content was noted there and at several other places, the most significant being the 500 ppm content of the highly anomalous stream sediment sample in Tarr Inlet. Silver was found in amounts ranging from 1 to 10 ppm in samples from several scattered localities, including the Tarr Inlet sample and a sample found south of Margerie Glacier. Strontium is markedly enriched in two areas, the Miller Peak-Sandy Cove area and the Mount Merriam area. Both are also characterized by relatively high THM and molybdenum values. AREAL DESCRIPTIONS More detailed geochemical data are available for some of the areas of the monument in which mineral deposits are known or in which one or more geochemical anomalies were detected. Areas for which more complete data exist are western Dundas Bay, eastern Dundas Bay, Miller Peak-Sandy Cove, Mount Merriam, and Reid Inlet (figs. 3-7). WESTERN DUNDAS BAY AREA Scattered anomalous values of THM, beryllium, copper, molybdenum tin, and tungsten occur in the western Dundas Bay area (fig. 3). Some of the high THM values are caused mainly by anomalously high copper concentrations, others by zinc. Tungsten-tin-molybdenum anomalies occur in two streams entering the head of Dundas Bay (table 4 and fig. 3, samples 12, 13) The tungsten content of these samples is unusally high and molybdenum and tin are also noticeably enriched. The headwaters of the stream of sample 12 drain an area near the contact of older granitic rocks and a leucocratic pluton,18 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA 120 50 70 j 20 0 A77/01'; 60 20 50 20 100 70 20 20 0 WfWrn 20 20 30 0 10 0 o o is i/>/g 30 45 40 0 10 20 20 30 30 0 15 0 'em 7*: 20 30 30 0 10 0 50 50 50 5 15 10 60 30 30 40 30 JO 52 40 20 30 V) 160 20 15 56 <5 10 0 120 30 20 0 10 0 0 10 0 60 60 50 20 3 10 0 t ,____________§3, 10 80 50 50 3 10 10 60 30 50 0 7 0 —_ 40 30 50 0 10 10 7/1 40 50 30 70 0 15 15 40 50 50 0 15 0 30 50 70 0 15 15 136°40' 58°30 30' 136°20‘ 58° 20' Base from U.S. Geological Survey EXPLANATION THM Cr Cu Mo Ni Pb Stream-sediment sample convention For illustrating approximate concentration, in parts per million, of elements where THM stands for total heavy metals -------- #__ 20 100 70 30 Sn, 70 W 13 9n 9fi n Sample location and analysis Sample 13 contains, in parts per million, 20 total heavy metals, 100 chromium (Cr), 70 Copper (Cu ), 20 molybdenum ( Mo), 20 nickel (N i) but no lead ( Pb), and anomalous elements such as 30 tin ( Sn) and 70 tungsten (W ) i Mt. Fairweather 1:250,000, 1961 0 2 MILES 1 _______I_________I CONTOUR INTERVAL 200 FEET DATUM IS MEAN SEA LEVEL Figure 3.—Geochemical sampling map of the western Dundas Bay area.GEOCHEMICAL STUDIES 19 Table 4.—Total heavy-metals and semiquantitative spectrographic analyses, in parts per million, of stream-sediment samples, western Dundas Bay area [THM, total heavy-metals (Cu+Pb-f-Zn) field test; 0, looked for, but not found ; . . . , not looked for] Loc. Lab. No. Field No. THM Semiquantitative spectrographic analyses (fig-3) D125- 66- Ag B Ba Co Cr Cu Fe La Mn Mo Ni Pb Sc Sn Sr Ti V Y Zr 1 720 Fd365 20 0. . 300 15 50 30 50,000 30 1,000 0 15 0 0 300 3,000 200 30. 2 733 Bd643 80 0. . 300 20 50 70 70,000 30 1,000 0 20 10 0 500 5,000 200 30. 3 721 Fd366 120 0. . 300 15 50 50 70,000 100 700 3 15 0 0 200 3,000 300 30. 4 734 Bd644 120 0. . 300 20 50 70 70,000 30 1,000 3 20 0 0 300 5,000 200 30. 5 722 Fd367 100 0. . 300 15 30 30 50,000 70 700 7 15 0 0 200 3,000 150 30. 6 719 Fd364 20 0. . 300 15 70 30 50,000 30 1,000 0 15 0 0 500 5,000 200 20. 7 732 Bd642 60 0. . 200 15 20 50 70,000 30 1,500 0 10 0 0 200 5,000 300 50. 8 717 Ed362 20 0. . 200 20 100 50 50,000 30 1,000 0 20 0 0 500 5,000 200 30. 9 730 Bd640 60 0. . 300 15 50 30 70,000 30 1,000 0 15 0 0 300 5,000 200 30. 10 731 Bd641 20 0. . 300 15 30 50 70,000 30 1,000 0 15 0 0 300 5,000 200 30. 11 718 Fd363 20 0. . 300 15 20 30 50,000 0 1,000 0 10 0 0 200 3,000 200 30. 12 *723 Fd368 120 0. . 300 15 100 50 50,000 50 700 30 20 0 30 300 3,000 200 30. 13 2787 Bd646 20 0. 500 15 100 70 70,000 50 1,000 20 20 0 30 500 3,000 200 30. 14 3454 Bd563 40 0. . 300 7 20 20 50,000 50 700 3 5 15 0 150 2,000 100 50. 15 s453 Bd562 40 0. . 300 7 20 20 30,000 70 1,000 5 5 15 0 150 2,000 100 50. 16 716 Fd361 20 0. 300 20 30 30 70,000 30 1,000 0 10 0 0 300 5,000 300 30. 17 4455 Bd565 20 0. 200 0 5 7 20,000 150 500 0 0 15 0 100 1,000 30 30. 18 4456 Bd566 20 0. 200 3 10 10 15,000 50 1,000 0 0 15 0 100 700 30 30. 19 452 Bd561 20 0. . 200 15 20 50 70,000 30 1,000 3 7 0 0 200 5,000 300 30. 20 4457 Bd567 20 0. 300 0 5 7 20,000 100 700 0 0 15 0 100 1,500 30 50. 21 451 Bd560 20 0. 200 15 20 70 50,000 30 1,000 3 5 0 0 300 3,000 200 30. 22 474 Bd559 20 0. 200 15 20 30 50,000 0 1,000 0 7 0 0 150 5,000 200 30. 23 726 Bd636 40 0. 200 15 50 30 50,000 30 700 0 10 0 0 200 3,000 200 20. 24 727 Bd637 60 0. 200 20 20 70 70,000 0 1,000 0 15 0 0 200 5,000 200 30. 25 693 Fd356 20 0. 300 15 30 30 50,000 30 1,000 3 10 0 0 300 3,000 200 20. 26 694 Fd357 40 0. 300 15 15 30 50,000 30 1,000 0 10 0 0 200 3,000 200 30. 27 728 Bd638 60 0. 300 15 30 30 70,000 0 1,000 0 15 0 0 300 5,000 200 30. 28 695 Fd358 20 0. 200 20 20 50 70,000 0 1,000 0 10 0 0 200 3,000 300 30. 29 696 Fd359 20 0. 200 10 20 70 50,000 0 1,000 0 10 0 0 200 2,000 150 30. 30 729 Bd639 80 0. 200 15 30 50 70,000 30 1,500 0 15 0 0 200 5,000 200 30. 31 715 Fd360 20 0. 200 15 30 30 70,000 0 1,000 0 10 0 0 200 5,000 300 30. 32 473 Bd558 40 0. 200 15 15 70 50,000 0 1,000 0 7 0 0 200 5,000 200 20. 33 459 Bd569 40 0. 150 15 15 150 > 100,000 0 1,500 10 5 0 0 200 3,000 200 20. 34 862 OvlOll 20 0 0 290 14 18 28 67,000 0 1,100 0 10 16 27 0 470 6,100 270 38 370 35 474 Bd556 20 0. . 200 20 20 30 50,000 0 1,000 0 7 0 0 200 3,000 200 20. 36 471 Bd555 20 0. 150 10 15 30 30,000 0 700 0 3 0 0 100 2,000 100 15. 37 *460 Bd571 20 0. 200 10 15 30 50,000 30 700 0 5 0 0 200 2,000 150 30. 38 350 Bd552 20 0. 200 15 20 30 30,000 0 1,000 0 7 10 0 200 3,000 150 15. 351 Bd553 20 0. . 250 15 70 50 40,000 0 1,000 0 15 30 0 300 3,000 200 20. 39 742 Ovl612 20 0. . 200 15 20 20 50,000 0 1,000 0 7 0 0 200 3,000 150 30. 40 724 Bd634 60 0. . 200 15 20 30 70,000 0 700 0 10 0 0 200 3,000 200 30. 41 691 Fd354 20 0. 200 15 20 50 50,000 0 1,000 0 7 0 0 200 3,000 200 30. 42 725 Bd635 60 0. 300 15 70 30 70,000 30 1,000 0 15 0 0 300 5,000 300 30. 43 692 Fd355 20 0. 300 20 70 30 70,000 30 1,000 0 15 0 0 300 5,000 300 30. 44 347 Bd539 20 0. 500 15 70 50 70,000 30 1,000 0 15 0 0 300 3,000 300 20. 45 476 Sjl4 20 0. 300 15 30 30 100,000 30 1,000 0 10 10 0 300 5,000 300 30. 46 744 Ovl616 50 0. 300 15 50 50 50,000 0 1,000 5 15 10 0 200 5,000 200 20. 47 743 Ovl614 20 0. . 300 15 30 30 50,000 0 1,000 0 10 0 0 200 3,000 200 20. 49 482 Mk435 20 0. 500 15 15 50 50,000 30 700 0 10 0 0 300 7,000 200 20. 50 483 Mk436 20 0. 500 15 30 30 50,000 30 1,000 0 15 0 0 300 5,000 200 20. 51 484 Mk437 20 0. 300 15 20 50 70,000 0 1,000 3 10 10 0 300 3,000 200 30. 52 340 Fd287 40 0. 200 20 30 70 70,000 30 700 0 10 0 0 300 7,000 200 30. 53 485 Mk438 20 0. 300 15 20 20 70,000 0 1,000 0 5 0 0 200 3,000 200 30. 54 486 Mk439 40 0. 200 15 20 30 70,000 0 1,000 0 7 0 0 150 3,000 200 20. 55 487 Mk441 60 0. 500 15 30 30 50,000 0 1,000 0 7 0 0 300 3,000 200 20. 56 488 Mk443 160 0. 300 30 20 15 > 100,000 0 1,500 <5 10 0 0 300 3,000 200 20. 57 697 Hf330 20 0. 300 15 50 30 70,000 30 1,000 0 20 0 0 300 5,000 300 20. 58 698 Hf329 20 0. 300 15 100 30 70,000 30 2,000 0 20 0 0 500 5,000 500 30. 59 489 Mk444 120 0. 300 15 30 20 50,000 0 1,000 0 10 0 0 200 3,000 200 20. 60 490 Mk446 110 0. 300 15 30 30 50,000 0 1,000 0 10 0 0 200 5,000 200 20. 61 495 Mk452 60 0. 500 15 50 20 70,000 0 1,000 3 10 0 0 300 3,000 200 20. 62 494 Mk450 80 0. 200 15 50 50 50,000 0 1,000 3 10 10 0 200 2,000 150 20. 63 492 Mk447 80 0. 200 15 30 30 70,000 0 1,000 0 15 10 0 300 5,000 300 20. 64 342 Fd290 20 0. 200 20 70 70 70,000 0 700 0 30 0 0 300 3,000 200 20. 65 493 Mk449 200 0. 200 15 50 150 50,000 0 1,000 5 15 10 0 300 3,000 200 20. 66 496 Mk453 60 0. 150 15 30 50 70,000 0 1,000 0 7 0 0 150 2,000 150 20. 67 509 Bd609 40 0. 300 15 20 50 50,000 0 1,000 0 10 10 0 200 5,000 200 20. 68 *510 Bd610 200 69 512 Bd613 40 0. 300 15 30 30 50,000 0 1,000 0 10 0 0 200 3,000 150 20. 70 511 Bd612 40 0. 300 0 30 50 50,000 0 1,000 0 10 10 0 200 3,000 150 20. 1 Also found 150 ppm W. 2 Also found 70 ppm W. 8 Also found 3 ppm Be. 4 Also found 2 ppm Be. 5 Lost. 8 Sample contaminated by waste from old cannery.20 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Table 4.—Total heavy-metals and semiquantitative spectrographic analyses, in parts per million, of stream-sediment samples, western Dundas Bay area—Continued Loc. Lab. No. Field No. THM Semiquantitative spectrographic analyses (fig-3) D125- 66- Ag B Ba Co Cr Cu Fe La Mn Mo Ni Pb Sc Sn Sr Ti V Y Zr 71 513 Bd614 40 0 200 15 50 30 50,000 30 1,000 0 15 15 0 200 3,000 200 20 72 515 Bd617 40 0 300 15 30 50 70,000 30 1,000 0 15 10 0 300 3,000 200 20 73 514 Bd616 40 0 200 15 50 50 50,000 0 1,000 0 15 0 0 300 3,000 200 20 74 516 Bd618 30 0 150 30 30 50 70,000 0 1,000 0 30 0 0 200 3,000 200 20 75 517 Bd620 30 0 500 15 50 70 70,000 30 1,000 0 15 15 0 300 3,000 200 20 76 518 Bd621 30 0 300 15 30 30 50,000 0 1,000 0 10 0 0 300 3,000 200 20 64A 341 Fd289 20 0 150 15 15 20 50,000 0 1,000 0 5 0 0 150 2,000 150 15 Samples north of Taylor Bay 77 497 Mk456 160 0 150 30 150 200 70,000 0 1,000 0 50 0 0 300 5,000 300 20 78 498 Mk458 200 0 150 30 150 150 > 100,000 30 1,000 0 50 0 0 300 7,000 500 20 and it seems probable that the source of the anomaly is mineralization along or near the contact. The compositon of the leucocratic pluton itself is reflected in the beryllium and lead content of stream-sediment samples from areas underlain by the pluton (table 4, samples 14, 15, 17, 18, 20). The beryllium content of these samples is not high in terms of estimated crustal abundance, but because beryllium is generally present in the monument in concentrations of less than 1 ppm. the 2-3 ppm concentrations represent enrichment. Similarly, the lead content of these samples is only 15 ppm, a level that is not markedly anomalous around Glacier Bay, but is locally anomalous for the western Dundas, where lead content is generally low. Except for the 120 ppm THM value of nearby sample 12, the area with anomalous tungsten does not have anomalous THM content. Samples that show anomalous values of THM interpreted to be due primarily to zinc or copper are concentrated in a small area on the west side of Dundas Bay, near samples 56, 59, 60 , and 65 (table 4). The high THM values of samples 56 and 59 are probably caused by zinc, as spectrographic determinations show no lead and near background values of copper. One markedly anomalous sample (No. 68, 200 ppm THM) is related to an abandoned cannery, as also evidenced by 0.1 percent tin (not given in table 4). Anomalous THM and copper values are also found in an unnamed stream draining into the head of Taylor Bay (fig. 3 and table 4, samples 77, 78) from an area of gneissic rocks. Rossman (1963b) reported a gold prospect in the drainage. EASTERN DUNDAS BAY AREA A small area east of Dundas Bay and not far north of Icy Strait contains two THM anomalies (fig. 14). The first, near the shore, contains both high THM and copper values and occurs in an altered zone. The metal content of the zone ranges from 100 to 300 ppm copper and as much as 30 ppm lead (table 5, 2-5). This occurrence is described more completely under copper mineral deposits. The second anomaly, about 3 miles farther east, contains high THM values (table 5, samples 8-10, and possibly 18). The most metal-rich sample (No. 8) was taken from a stream-bed along the contact of an igneous pluton with limestone country rock. Near sample 18 on Icy Strait, limestone exposed along the beach contains jasperoid masses as much as a foot across. This THM anomaly is partly due to zinc, because the THM values in samples 8-10 are in excess of copper plus lead. MILLER PEAK-SANDY COVE AREA The Miller Peak-Sandy Cove area is on the east side of Glacier Bay, north of the mouth of Beartrack River and south of Mount Wright (fig. 5). The area contains the Sandy Cove gold-copper prospect, which is just to the east of sample locations 41 and 41A. In addition, there are several small areas of anomalous metal content, discussed geographically starting at the northwest part of the mapped area. Stream-sediment samples collected south of Mount Wright, particularly samples 1-13 and 19, 22, and 23 (table 6), are generally characterized by anomalous or relatively high values in THM copper, chromium, and nickel. The area is mainly underlain by fine-grained detrital sedimentary rocks, subordinate limestone, and amygdaloidal basalt or andesite, which are all cut by numerous mafic dikes. Our interpretation is that the anomalous metal value are probably derived from the dikes or small-scale vein mineralization in the baked and altered adjacent country rock.GEOCHEMICAL STUDIES 21 136° 15f 10' 136°05’ Base from U.S. Geological Survey Mt. Fairweather 1:250,000, 1951 Q 2 MILES I_________I__________I CONTOUR INTERVAL 200 FEET DATUM IS MEAN SEA LEVEL Figure 4.—Geochemical sampling map of the eastern Dundas Bay area. Streams farther east (table 6, samples 14, 15) drain a mixed sedimentary terrane which includes limestone, and the THM values may largely represent zinc from mineralized carbonate rocks like those known to exist near White Glacier (pi. 1). Similar mineralization may exist to the south and southeast of samples 28-38, where the anomalous or relatively high values of THM and trace amounts of lead may be derived from a mixed sedimentary terrane. A group of samples in a tributary stream east of the Beartrack River (particularly samples 56-59) show relatively high or anomalous values of THM22 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Table 5.-—Total heavy-metals and semiquantitative spectrographic analyses, in parts per million, of stream-sediment samples, eastern Dundas Bay area [THM, Total heavy-metals (Cu+Pb-(-Zn) field test; 0, looked for, but not found ; . . . ., not looked for] Loc. Lab. No. Field No. THM Semiquantitative spectrographic analyses (fig-4) D125- 66- Ag B Ba Co Cr Cu Fe La Mn Mo Ni Pb Sc Sn Sr Ti V Y Zr 1 528 Hf320 40 0 300 15 100 70 70,000 30 1,000 0 20 0 0 300 5,000 300 70 2 529 Hf321 160 0 300 15 50 150 50,000 0 1,000 0 20 30 0 150 3,000 150 15 3 530 Hf322 160 0 200 15 50 150 50,000 0 1,000 0 20 20 0 150 3,000 200 15 4 533 Hf325 125 0 200 15 50 300 70,000 0 1,000 5 15 20 0 150 5,000 200 15 5 745 Ovl631 60 0 300 20 30 50 70,000 30 1,000 3 15 10 0 200 5,000 200 20 6 735 Hx552 60 0 200 10 50 30 70,000 30 700 0 10 0 0 200 3,000 200 20 7 739 Hx556 40 0 300 15 50 50 50,000 0 1,500 0 15 15 0 200 3,000 150 20 8 749 Ovl635 300 0 700 15 30 50 50,000 30 1,000 0 20 30 0 200 3,000 200 15 9 748 Ovl634 160 0 700 15 50 50 50,000 30 700 0 15 20 0 200 2,000 200 15 10 738 Hx555 160 0 500 10 30 30 30,000 0 700 0 15 10 0 150 3,000 150 15 11 736 Hx553 80 0 300 15 50 30 70,000 30 700 0 15 0 0 200 3,000 200 20 12 737 Hx554 100 0 300 15 50 50 70,000 0 1,000 3 15 0 0 200 5,000 200 30 13 747 Ovl633 120 0 200 20 70 70 70,000 0 1,000 0 20 15 0 200 5,000 200 20 14 746 Ovl632 60 0 200 20 50 50 70,000 0 1,500 3 15 10 0 200 3,000 200 15 15 689 Hf327 20 0 200 15 50 100 70,000 50 1,000 5 15 0 0 200 5,000 300 30 16 690 Hf328 20 0 200 20 70 70 > 100,000 30 1,000 <5 15 0 0 200 5,000 500 30 17 467 Hx480 40 0 1000 7 15 10 50,000 30 700 0 10 0 0 200 3,000 150 20 18 468 Hx479 160 0 300 15 30 100 50,000 0 1,000 0 15 0 0 150 3,000 200 20 19 339 Fd284 20 0 300 10 30 15 70,000 0 700 0 15 0 0 150 5,000 200 30 20 338 Fd283 20 0 300 15 50 20 70,000 50 700 0 15 0 0 150 7,000 200 30 4 A 534 Hf326 20 0 300 15 70 100 70,000 30 700 0 20 10 0 200 3,000 200 15 and copper. The bedrock in the stream drainage is graywacke and argillite, and the origin of the THM and copper values is unknown. Samples in the southwestern part of the area locally show anomalous values of THM, copper, molybdenum, and strontium. These values are probably related to a pluton near Miller Peak. Samples 92 and 99 show anomalous concentration of copper and molybdenum, respectively. MOUNT MERRIAM AREA There are no mines or prospects in the geologically complicated Mount Merriam area (fig 6; pi. 1), but there are many stream drainages containing anomalous concentrations of THM and molybdenum and some outcrops of unprospected mineralized rock. The high THM values seem to be due to zinc, for neither lead nor copper is abundant. The area is similar to the Sandy Cove-Miller Peak area in having numerous high strontium values, suggesting the possibility of either alteration or additive contact metamorphism in the hornfelses and marbles around the granitic stocks. The highest concentrations of molybdenum are found in a small part of the area east of Composite Island (table 7, samples 8, 13, 14, 20, 21). Some of these samples also have high THM values, which are not confined to this small area, however. Molybdenum is present in greater-than-detectable quantities in all samples from the Mount Merriam area. REID INLET GOLD AREA The Reid Inlet gold area (fig. 7; pi. 1; tables 8, 11, 12) contains the main gold deposits of the monu- ment, but it is not well marked by geochemical patterns. The mixed greenstone and granite terrane west of Lamplugh Glacier has a distinct copper anomaly, and several of the samples, notably 8, 9 and 16 (table 8) east of Reid Inlet also contain anomalous amounts of copper. Most of the area, however, seems characterized by less than background amounts of copper. As the gold generally is accompanied by galena, lead might be expected to be abundant, but results show it to be only locally abundant (table 8, samples 1-4); a greater sample density might have given a stronger pattern. Since gold was found by panning in Ptarmigan Creek below the LeRoy mine and is visible in vein material elsewhere, the Reid inlet area seems to be an example of an area in which old-fashioned panning is more satisfactory than geochemical methods. MINERAL DEPOSITS Deposits of gold, silver, molybdenum, iron, nickel, titanium, copper, and other metals are known from Glacier Bay National Monument. Some of these deposits have been mined or explored on a small scale, but many of them are virtually unexplored. Two of the deposits, the Brady Glacier nickel-copper deposit and the Nunatak molybdenum deposit, have been investigated in some detail. The term “mineral deposit” is used broadly in this report to include anomalous concentrations of ore metals. The deposits described range from small insignificant mineral occurrences to some deposits that apparently are large or rich enough to warrant exploration.GEOCHEMICAL STUDIES 23 S8°45' 58° 40' EXPLANATION THM Cr Cu Mo Ni Pb Stream-sediment sample convention For illustrating approximate concentration, in parts per million, of elements where THM stands for total heavy metals 40 60 40 1000 Sr 0 13 5 Sample location and analysis Sample 77 contains, in parts per million, UO total heavy metals, 60 chromium (Cr), UO copper ( Cu ), no molybdenum (Mo), 13 nickel ( Ni ), 5 lead ( Pb),and anomalous elements such as 1000 strontium (Sr) Base from U.S. Geological Survey 1:250,000 Mt. Fairweather 1961 and Juneau 1962 2 MILES _l CONTOUR INTERVAL 200 FEET DATUM IS MEAN SEA LEVEL Figure 5.—Geochemical sampling map of the Miller Peak-Sandy Cove area.24 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Table 6.—Total heavy-metals and semiquantitative spectrographic analyses, in parts per million, of stream-sediment samples, Miller Peak-Sandy Cove area [THM, Total heavy-metals (Cu-f Pb-f-Zn) field test; 0, looked for, but not found not looked for] Loc. Semiquantitative spectrographic analyses (fig.5) Lab. No. Field No. THM ‘ 66— Ag B Ba Co Cr Cu Fe La Mn Mo Ni Pb Sc Sn Sr Ti V Y Zr 1 D126106 Hf355 100 0. 200 15 150 70 50,000 0 500 0 30 0. 0 200 20. 2 D126107 Hf356 120 0. 150 15 100 70 50,000 0 500 0 30 0. 0 150 3 D123511 Hx91 120 0 0 260 24 160 91 70,000 34 700 0 67 6 26 0 300 4 D126109 Hf358 80 0. 150 15 150 70 70,000 0 1,000 0 50 0. 0 100 25 100 5 D126108 Hf357 200 0. 150 15 150 70 70,000 0 1,000 0 30 0. 0 150 3,000 150 20. 6 D123512 Hx92 120 0 0 260 25 140 83 56,000 47 900 4 61 8 25 0 350 31 D126110 Hf359 100 0. 200 20 100 100 70,000 30 1,000 0 30 0. 0 150 100 7 D123528 Hxl05 80 0 0 150 42 330 44 41,000 42 800 9 66 5 30 0 420 8 D125304 Hx465 80 0. 200 30 150 100 70,000 30 700 0 50 0. 0 200 120 9 D125317 Bd517 40 0. 300 10 150 30 50,000 30 500 0 30 0. 0 300 5,000 150 20. 10 D125318 Bd518 60 0. 300 15 150 50 50,000 30 500 0 30 0. 0 300 20. 11 D123531 Hxl 19 80 1 0 460 18 110 40 40,000 42 990 10 42 0 22 0 600 D125305 Hx466 60 0. 200 15 70 50 70,000 30 700 0 30 0. 0 300 99 12 Hxl 18 40 0 0 810 25 150 70 49,000 29 800 8 59 15 28 0 330 D125319 Bd519 20 0. 700 20 150 70 70,000 0 1,000 0 50 20. . 0 200 3,000 200 20. 110 13 D123532 Hxl 20 40 1 0 590 26 220 60 38,000 52 700 11 71 14 27 0 290 4.300 14 D123964 Bdl50 160 0. 200 15 100 70 50,000 20 500 0 30 0. 0. 110 15 D124081 Hxl78 160 0 0 70 14 86 43 24,000 30 820 0 30 0 18 0 440 16 D125307 Hx468 40 0. 150 15 100 30 50,000 30 700 0 30 0. 0 300 15 60 17 D125306 Hx467 40 0. 150 15 100 50 50,000 30 700 0 30 0. 0 300 3,000 200 20. 18 Bd521 19 D125320 Bd520 0. 500 15 150 50 70,000 30 500 0 30 0. 0 300 "36! 20 D124082 Hxl 80 120 0 0 240 16 100 38 33,000 41 910 7 36 0 22 0 590 D125308 Hx469 40 0. 300 15 150 30 70,000 30 700 0 30 0. 0 300 100 21 D123965 Bdl51 120 0. 150 10 70 50 30,000 20 500 0 20 0 0 0. 2,000 100 15. D125321 Bd522 100 0. 150 15 100 70 30,000 30 700 0 30 0. 0 300 15. 22 D123513 Hx95 40 0 0 440 13 96 48 61,000 38 800 0 34 12 21 0 400 23 D123514 Hx97 40 0 0 310 21 140 100 45,000 47 800 6 51 0 23 0 300 120 24 D123522 Hx99 80 0 0 300 14 100 33 33,000 39 500 7 31 7 20 0 600 4.200 100 25 D124288 Ov867 40 0 0 220 15 86 71 43,000 30 500 5 34 10 18 0 300 4,100 200 20 130 100 26 D124289 Ov8G8 80 0 0 160 23 170 71 30,000 40 700 8 46 4 24 0 420 6.000 27 D123967 Bdl53 80 0. 150 10 70 50 50,000 20 500 0 20 15. 0. 100 28 D124084 Hxl82 120 0 0 170 13 90 63 34,000 28 790 0 36 13 19 0 330 3.200 29 D124085 Hxl83 120 0 0 200 9 76 57 38,000 21 630 0 31 9 16 0 200 82 30 D125324 Bd525 100 0. 200 15 70 70 30,000 0 500 0 20 0. 0 200 3,000 150 15. 85 D125326 Bd527 100 0. 200 15 100 50 50,000 0 300 0 30 10. 0 200 3,000 31 D125325 Bd526 120 0. 200 15 70 70 50,000 0 300 0 30 10. 0 70 D125310 Hx471 120 0. 200 15 100 50 70,000 0 300 0 30 10. 0 70 3,000 15. 32 D124087 Hxl85 120 0 0 220 10 98 63 44,000 23 820 0 36 13 16 0 240 3,700 33 D125327 Bd528 100 0. 150 10 70 50 30,000 0 300 0 20 10. 0 150 3,000 150 15. 98 D123968 Bdl55 80 0. 150 10 70 70 30,000 0 300 0 20 0. 0. 3.000 10. D124086 Hxl 84 120 0 0 180 10 84 47 32,000 34 700 0 35 5 18 0 280 34 D123969 Bdl56 80 0. 100 7 50 70 20,000 0 300 0 20 0. 0 1.500 95 D125311 Hx472 40 0. 150 15 100 50 30,000 30 300 0 30 0. 0 200 2,000 35 D124088 Hxl86 160 0. . 120 8 65 90 21,000 23 740 0 22 9 15 0 290 1,800 100 15 57 D125312 Hx473 100 0. 200 15 150 70 50,000 0 500 0 20 0. 0 200 15. 36 D123970 Bdl57 160 0. 150 15 100 70 30,000 0 700 0 30 15. 0 D125328 Bd529 160 0. 150 15 150 100 30,000 0 700 0 50 20. 0 150 3,000 37 D125329 Bd530 120 0. . 200 10 150 50 50,000 30 300 0 30 10. . 0 300 38 D125313 Hx474 160 0. 200 20 150 100 50,000 30 700 0 50 10. . 0 150 5,000 200 20. 39 D124093 Hxl81 120 0 0 230 8 140 24 29,000 37 990 0 28 0 17 0 620 3,100 40 D123966 Bdl52 40 0. 200 7 50 30 30,000 0 300 0 15 0. . 0. . 91 41 D124150 Ov691 20 0 0 370 9 73 36 31,000 29 870 4 27 0 19 0 620 42 D125323 Bd524 120 0. 200 15 100 70 50,000 0 200 0 30 10. . 0 100 3,000 43 D125309 Hx470 120 0. , 200 15 70 70 70,000 0 300 0 30 10. . 0 100 3,000 200 20. , 44 D125322 Bd523 60 0. 200 15 150 70 50,000 0 300 0 30 10. 0 200 15. 45 D124327 Fd05 40 0 0 250 9 82 77 48,000 21 900 5 32 15 15 0 140 4.000 46 D124290 Ov871 40 0 0 190 12 110 49 26,000 28 610 5 35 17 14 0 180 47 D124291 Ov872 40 0 0 200 11 89 60 35,000 26 780 5 33 8 16 0 290 98 48 D124328 Fd5G 8 0 0 200 20 130 80 49,000 31 700 8 43 6 23 0 400 5,000 270 17 110 120 49 D124292 Ov873 120 0 0 260 15 90 70 40,000 24 830 5 40 15 16 0 120 50 D124293 Ov874 40 0 0 170 23 150 60 33,000 43 700 7 40 11 21 0 430 4.500 120 51 D124329 FdG7 100 0 0 280 18 130 78 50,000 32 600 6 44 9 21 0 270 100 52 D124425 Ba310 40 0 0 210 12 71 60 36,000 22 870 5 43 9 14 0 370 24 130 53 D124426 Bd311 60 0 27 290 15 100 92 53,000 0 800 5 50 13 15 0 160 4,000 230 14 100 130 54 D124427 Bd312 40 0 22 300 11 100 89 44,000 0 760 5 50 22 15 0 150 55 D124428 Bd313 20 0 0 290 12 95 60 44,000 34 600 6 42 8 17 0 80 15 130 56 D124429 Bd314 160 0 0 360 19 98 100 45,000 30 730 7 60 23 18 0 190 120 57 D124431 Bd310 20 0 0 280 5 79 48 51,000 20 600 6 34 11 14 0 90 120 58 D124432 Bd317 20 0 0 300 6 92 38 32,000 24 870 5 31 12 17 0 130 3,700 210 26 110 120 59 D124433 Bd318 80 0 0 310 19 83 110 31,000 43 700 6 51 25 13 0 230 60 D124434 Bd319 80 0 0 330 23 95 140 63,000 22 1,000 6 61 30 20 0 80 19 88 61 •D124435 Bd320 20 0 0 300 9 79 60 41,000 0 60 0 40 14 16 0 100 130 62 D124436 Bd321 40 0 0 320 20 87 88 50,000 28 750 6 49 13 15 0 290 140 63 D124437 Bd322 80 0 0 360 28 89 190 60,000 35 810 5 68 25 16 0 270 3,900 210 17 110 100 64 D124438 Bd323 20 0 0 280 9 75 72 32,000 21 400 0 29 0 12 0 200 65 D124439 Bd325 80 0 0 290 13 100 60 35,000 29 720 6 40 14 15 0 260 5 120 66 D124440 Bd32G 40 0 0 330 9 110 54 40,000 25 680 6 40 6 17 0 210 no 67 ■D124534 Bd327 80 0 0 300 13 93 63 35,000 30 660 4 38 11 15 0 270 130 68 D124330 FdG8 120 0 0 300 11 98 60 46,000 25 750 6 40 15 15 0 230 3,900 210 16 100 no 1 Also found 1 ppm Be.GEOCHEMICAL STUDIES 25 Table 6.—Total heavy-metals and semiquantitative spectrographic analyses, in parts per million, of stream-sediment samples, Miller Peak-Sandy Cove area—Continued Loc. Semiquantitative spectrographic analyses (fig.5) Lab. No. Field No. 66— THM Ag B Ba Co Cr Cu Fe La Mn Mo Ni Pb Sc Sn Sr Ti V Y Zr 69 D124508 Bd328 160 0 0 330 38 89 170 52,000 59 620 7 75 27 15 0 260 3,100 170 20 150 70 D124297 Ov878 20 0 0 200 16 120 52 28,000 40 700 7 33 11 21 0 410 3,100 240 28 110 71 D124296 Ov877 40 0 0 160 8 78 60 30,000 0 660 0 30 9 12 0 280 1,800 110 9 97 72 D124295 Ov876 80 0 0 240 13 87 100 51,000 34 400 5 41 9 15 0 160 3,100 200 17 100 73 D124294 Ov875 80 0 0 220 12 90 60 35,000 30 400 6 32 19 17 0 300 3,100 200 20 94 74 D125331 Bd532 120 0. 500 15 100 70 50,000 0 300 0 20 15. 0 300 3,000 150 20. 75 D125315 Hx476 40 0. 200 7 70 30 20,000 30 300 0 15 0. 0 1,000 1,500 100 10. 76 D125316 Hx477 60 0. 200 15 30 50 50,000 30 700 0 7 0. 0 1,000 3,000 200 15. 77 D123971 Bdl58 40 0 0 150 5 50 30 20,000 0 300 0 10 0. 0. 1,500 70 10. D125301 Fd275 40 0. 200 10 70 50 30,000 0 300 0 15 10. 0 1,000 15,000 150 15. 78 D124089 Hxl87 160 0 0 170 15 100 52 36,000 26 860 0 43 30 16 0 290 2,200 120 11 73 D125302 Fd276 80 0. 200 15 100 70 50,000 30 700 0 30 20. 0 150 3,000 150 20. 79 D125332 Bd533 120 0. 100 7 50 50 15,000 0 500 0 15 15 0 0 200 1,000 70 15. 80 D125334 Bd535 20 0. 150 7 50 30 15,000 30 200 0 15 0. 0 700 2,000 150 10. 81 D125333 Bd534 20 0. 200 7 50 50 30,000 30 300 0 15 0. 0 500 3,000 70 15. 82 D123972 Bdl59 120 0 0 150 7 7 30 30,000 0 500 0 15 10. 0. 1,500 70 10. D125335 Bd536 20 0. 200 5 100 30 20,000 30 300 0 15 0. 0 700 3,000 100 15. 83 D125336 Bd537 20 0. 200 5 50 30 20,000 30 300 0 10 0. 0 700 2,000 70 10. 84 D124090 Hxl88 40 0 0 110 8 45 20 22,000 59 630 21 17 9 23 0 480 1,000 79 28 60 D125303 Fa277 60 0. 200 15 70 50 70,000 0 700 0 15 20. 0 2,000 3,000 200 20. 85 D125330 Bd531 120 0. 300 15 100 70 50,000 30 500 0 30 20. 0 500 3,000 150 15. 86 D125314 Hx475 80 0. 150 7 30 20 20,000 0 300 0 15 10. 0 3,000 1,000 100 10. 87 D125337 Bd538 20 0. 200 5 50 30 30,000 30 300 0 10 0. 0 700 3,000 100 15. 88 D124411 Fd98 40 0 0 220 12 99 30 36,000 39 800 9 21 0 19 0 590 4,400 290 20 190 89 D124412 FdlOl 40 0 0 200 14 76 37 31,000 44 400 12 29 0 19 0 830 2,000 160 25 92 90 D124413 Fdl02 80 0 0 240 0 96 48 11,000 9 500 0 16 0 7 0 1,000 1,200 150 0 35 91 D126082 Hf350 40 0. 300 15 100 70 50,000 0 500 0 20 0. 0 500 3,000 200 20. 92 D124414 Fdl04 120 0 0 300 17 100 210 58,000 43 700 7 34 8 17 0 430 4,500 210 23 150 D124313 Ov887 120 0 0 300 16 110 180 36,000 52 1,100 9 32 13 20 0 490 3,600 220 16 160 93 D126082 Hf349 40 0. 300 15 100 70 50,000 0 500 0 20 15. 0 300 1,500 150 20. 94 D126080 Hf348 80 0. 300 15 70 70 50,000 0 500 0 20 10. 0 500 3,000 150 30. 95 D125299 Mk433 40 0. 300 15 50 70 50,000 30 1,000 0 15 0. 0 300 3,000 200 30. 96 D124285 Ov864 40 0 0 200 8 100 45 38,000 30 500 6 29 12 15 0 300 3,800 180 19 100 97 D124324 Fd61 20 0 0 350 11 72 100 50,000 41 1,300 12 22 13 20 0 610 2,800 240 17 100 98 D124325 Fd62 80 0 0 240 7 95 60 42,000 20 700 5 24 10 13 0 310 3,100 180 11 120 99 D124287 Ov865 20 1 0 110 13 60 36 32,000 60 400 19 24 15 23 0 1,700 1,400 120 34 82 100 D124326 Fd63 40 0 0 240 6 74 39 42,000 30 600 6 23 6 14 0 500 2,500 170 12 95 101 D124288 Ov866 20 0 0 300 12 70 76 41,000 32 900 7 23 12 17 0 450 3,500 180 19 98 102 D125298 Mk427 40 0. 200 10 70 50 50,000 30 700 0 20 0. 0 300 3,000 150 20. 103 JD124312 Ov886 100 0 0 280 11 100 57 36,000 41 1,100 9 25 11 17 0 530 2,800 180 16 100 104 D124337 Fd75 20 0 0 390 9 75 45 47,000 43 1,100 7 22 0 17 0 530 4,300 240 26 160 56A D124430 Bd315 120 0 26 300 24 100 100 54,000 29 760 6 69 16 17 0 160 4,100 260 30 no 41A 2D126084 Hf352 20 0. 700 15 50 70 70,000 70 1,000 10 15 10. 0 500 2,000 200 30. 1 Also found 1 ppm Be. a 1.5 ppm Be. LOCALITY LIST KEYED TO MAPS AND TABLES All the deposits are listed alphabetically on page 30, together with the numbers that key them to figure 1 and plate 1, the commodity they are described under (listed as “Main commodity”), and references to tables and other figures and plates. Our field investigations stressed evaluation of deposits of metallic commodities and involved examining (1) all known mines and prospects, (2) the many deposits discovered during the current investigation, and (3) some of the mineralized areas found by geochemical sampling. The mines and prospects were sampled and, in most cases, mapped in detail. The discoveries made during the current investigation were sampled, and their apparent sizes and probable grades were appraised. We tried to establish the geologic setting of the geochemically anomalous areas. The current reconnaissance investigation provides information on the nature and distribution of the mineral deposits in the monument and a basis for delineating additional target areas favorable for ore deposits. The study is not detailed enough to provide evaluations as to the economic feasibility of developing and mining a specific deposit, either currently or in the future. Such evaluations would require more extensive investigation and physical exploration, metallurgical and cost-analysis surveys, and other studies necessary to establish the feasibility of present or future mining. The examinations were limited by such factors as time, difficult access, and the poor exposures of some of the deposits. Evaluating the mountainous 3,900-square-mile Glacier Bay National Monument in only 31/2 months necessitated cursory examinations of many deposits. Access was impeded by rough terrain that required time-consuming climbs and descents and by locally dense brush. Foul weather was an-26 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA other obstacle, and low clouds and inclement weather prevented much of the contemplated work in the higher parts of the Fairweather Range. Many of the deposits are partly covered and obscured by snow, ice, and vegetation, or by diverse postmetallization rocks and rock debris which prevent satisfactory 136°30' 25' 136-20' Mt. Fairweather 1:250,000, 1961 2 MILES _l CONTOUR INTERVAL 200 FEET DATUM IS MEAN SEA LEVEL Figure 6.—Geochemical sampling map of the Mount Merriam area.GEOCHEMICAL STUDIES 27 Table 7.—Total heavy-metals and semiquantitative spectro graphic analyses, in parts per million, of stream-sediment samples, Mount Merriam area [THM, Total heavy-metals (Cu-f-Pb-f-Zn) field test; 0, looked for, but not found ;.not looked for] Loc. Semiquantitative spectrographic analyses (fig.6) Lab. No. Field No. THM Ag B Ba Co Cr Cu Fe La Mn Mo Ni Pb Sc Sn Sr Ti V Y Zr 1 252 Bd264 40 0 0 180 17 90 38 49,000 31 1,000 7 24 0 23 0 600 4,200 260 28 100 2 282 Ov861 40 0 0 200 7 71 25 27,000 48 400 10 17 0 18 1,400 1,900 120 34 100 3 250 Bd262 160 0 0 160 13 69 27 32,000 42 200 11 30 0 19 0 1,600 2,300 210 30 120 4 251 Bd263 80 0 0 160 9 74 30 26,000 36 600 8 17 0 18 0 1,000 2,000 130 31 81 5 281 Ov859 20 0 0 130 7 69 25 35,000 51 500 7 20 0 17 0 420 3,300 150 61 240 6 512 Bd334 40 0 0 210 13 86 28 34,000 38 400 12 20 0 20 0 1,300 3,700 180 37 110 7 511 Bd333 40 0 0 200 11 87 30 37,000 48 600 8 20 4 17 0 330 4,900 150 47 250 8 510 Bd332 80 0 0 110 9 43 16 15,000 45 600 15 15 0 16 0 600 1,000 88 29 66 9 280 Ov858 180 0 0 130 3 36 13 14,000 48 570 14 15 7 18 0 590 1,000 86 30 60 10 1249 Bd261 120 0 0 270 9 77 45 27,000 30 700 6 23 13 18 0 340 2,700 160 32 120 11 (») Ov857 40. 12 247 Bd259 40 0 0 150 9 53 29 29,000 30 600 7 20 4 16 0 300 2,000 110 40 90 13 1248 Bd260 200 0 0 90 4 38 15 11,000 41 480 12 15 0 16 0 440 740 78 31 60 14 279 Ov856 120 0 0 200 6 56 21 23,000 60 630 19 24 0 17 0 1,700 1,200 150 26 73 15 238 Bd250 40 0 0 190 17 43 24 52,000 39 1,200 11 12 5 24 0 590 4,500 360 30 170 16 268 Ov844 120 0 0 280 14 75 46 60,000 37 1,000 9 20 0 23 0 800 5,700 390 29 140 17 267 Ov843 40 0 0 50 11 60 25 51,000 42 800 10 16 0 21 0 1,200 4,000 290 29 120 18 276 Ov853 120 0 0 140 13 60 15 56,000 45 1,000 12 20 4 23 0 600 4,000 440 36 100 19 424 Fdl 17 40 0 0 130 12 100 39 33,000 32 700 7 20 0 15 0 300 3,300 130 0 100 20 423 Fdll6 120 0 0 600 19 44 21 32,000 47 500 16 16 0 23 0 520 2,800 100 30 83 21 422 Fdl 15 40 1 0 70 11 60 18 25,000 48 300 16 17 0 19 0 590 5,300 100 28 76 22 239 Bd251 80 0 0 200 14 60 30 46,000 39 1,100 10 17 0 21 0 610 3,900 300 26 130 23 269 Ov845 120 0 0 840 8 84 48 41,000 43 500 8 30 5 18 0 1,100 2,800 490 23 95 24 240 Bd252 40 0 0 240 17 46 34 59,000 41 1,100 9 16 0 24 0 770 4,500 300 30 110 25 241 Bd253 20 0 0 300 14 50 23 63,000 44 1,100 9 15 0 25 0 510 6,400 380 37 360 26 270 Ov846 40 0 0 150 14 69 38 43,000 38 500 9 27 0 20 0 1,500 3,400 220 23 99 27 266 Ov842 20 0 0 500 4 19 10 48,000 33 700 6 7 4 12 0 490 3,900 160 17 100 28 237 Bd249 40 0 0 300 15 38 21 57,000 26 1,000 7 15 6 20 0 600 4,000 220 23 95 29 272 Ov848 40 0 0 300 11 59 32 57,000 46 900 10 20 0 24 0 1,000 5,400 390 33 150 30 271 Ov847 40 0 0 140 10 60 30 34,000 42 400 11 20 0 18 0 3,300 2,400 140 25 86 31 1242 Bd254 100 0 0 290 6 81 39 32,000 37 400 8 29 0 16 0 880 8,000 210 23 90 32 273 Ov849 120 0 0 360 9 110 48 45,000 43 600 9 30 0 19 0 1,600 3,100 290 24 100 33 >274 Ov851 120 0 0 300 5 74 50 37,000 45 600 8 18 0 18 0 1,800 2,600 170 20 87 34 244 Bd256 160 0 0 130 20 73 36 56,000 44 900 13 38 5 28 0 820 5,300 570 32 100 35 245 Bd257 100 0 0 130 17 64 30 48,000 47 1,000 12 21 0 24 0 600 4,200 390 35 96 36 277 Ov854 200 0 0 210 7 68 28 28,000 50 300 10 26 0 17 0 1,000 1,800 210 23 83 37 509 Bd330 40 0 0 230 10 62 27 26,000 32 950 9 19 0 16 0 600 1,900 120 19 67 38 246 Bd258 120 0 0 230 13 81 42 38,000 37 600 8 29 0 20 0 580 3,000 240 23 85 39 278 Ov855 40 0 0 170 14 61 26 38,000 40 500 10 25 6 22 0 650 3,200 310 29 100 40 275 Ov852 120 0 0 450 9 67 35 40,000 31 500 8 28 6 16 0 990 2,400 180 19 89 41 243 Bd255 120 0 0 120 8 60 29 15,000 38 610 8 19 13 14 0 280 1,000 94 24 50 41 405 Hx285 80 0 0 60 3 30 16 13,000 38 450 8 11 10 10 0 300 720 60 13 44 42 255 Bd267 20 0 0 300 7 68 16 49,000 31 1,000 7 24 0 23 0 590 3,400 250 26 160 408 Hx293 20 0 0 300 8 75 31 36,000 36 800 6 15 0 17 0 660 3,300 190 0 150 43 *421 Fdll4 60 0 0 180 15 74 26 42,000 45 1,000 12 23 10 24 0 690 5,300 310 36 120 44 407 Hx292 20 0 0 290 6 59 22 34,000 27 700 5 13 0 14 0 600 3,400 150 6 110 45 406 Hx287 60 0 0 200 5 60 17 21,000 31 690 7 14 0 12 0 300 1,400 120 14 110 46 404 Hx284 40 0 0 220 8 49 28 31,000 35 500 8 17 0 15 0 690 2,000 160 14 75 47 1403 Hx282 100 0 0 190 0 76 49 10,000 0 300 6 13 0 9 0 3,100 830 140 0 36 48 395 Hx273 30 0 0 330 8 67 31 61,000 37 900 6 18 0 17 0 990 4,300 210 20 120 1 Also found 1 ppm Be. estimates of their size and extent. Despite these limitations, the coverage for most of the monument is good, and we believe that most large or significant deposits that crop out east of the Fairweather Range were examined. The results of the geochemical sampling program provide a basis for evaluating the sizable tracts of the monument where bedrock is covered. However, significant undiscovered deposits that might be found by extensive and thorough prospecting, using modern geophysical and geochemical methods, may exist in the monument, particularly in covered parts or in the Fairweather Range. Exploration of some known deposits may reveal larger and (or) richer ore bodies than those indicated by the surface examinations. 2 Lost. Most of the known mineral deposits within the boundaries of the monument are described in this report. The exceptions are the ilmenite-rich deposits that are widely distributed in the mafic layered in-trusives of the Fairweather Range (Rossman, 1963a); these were not examined during the current investigations. Only a few ilmenite localities are discussed specifically because the limited geologic information concerning them indicates that they are similar. However, comparable ilmenite-rich deposits are probably extensive and widespread throughout the mafic layered intrusives. The following part of this report consists of descriptions of the known metal-bearing mineral deposits within the monument. These descriptions28 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA EXPLANATION |THM Cr Cu |Mo Ni Pb Stream-sediment sample convention For illustrating approximate concentration, in parts per million, of elements where THM stands for total heavy metals x 11 30 60 83 33 Sn 5 21 0 Sample location and analysis Sample 11 contains, in parts per million, 30 total heavy metals, 60 chromium (C r), 83 copper (Cu), 5 molybdenum ( Mo), 21 nickel (Ni) but no lead (Pb ), and anomalous elements such as 33 tin (Sn). ND stands for not determined Location of mine, prospect,or mineral deposit Figure 7.—Geochemical sampling map of the Reid Inlet gold area.MINERAL DEPOSITS 29 are based largely on field and analytical data obtained during the current project, but they also include pertinent information obtained from previous investigations. The parts of this report describing nonmetallic commodities and petroleum are based mainly on previous investigations. It should be emphasized that all deposits examined in detail are reported on here, and all field and analytical data obtained are given for each deposit. Many other occurrences of metallic minerals were also noted, sampled, and analyzed, but they were deemed wholly insignificant because of limited grade or size and are therefore not described. The locations of such samples also are shown on plate 1. We have neither included nor excluded data arbitrarily. METALLIC COMMODITIES Metallic commodities in the monument include the following groups: Base and miscellaneous metals, precious metals, and iron and ferroalloy metals. Locations of deposits that contain anomalous concentrations of one or more of the metallic commodities are shown on plate 1. Numbers or letters in the text refer to the deposit locality number or letter shown on plate 1 next to the circles. Each circle on plate 1 indicates a discrete deposit or a group of deposits. Analyzed samples that contain only background concentrations of ore metals are shown by solid dots or solid dots with a cross; their analyses are not included in this report. Individual deposits are described under the commodity that would most likely yield the major mineral values, and these descriptions are referenced in descriptions of other lesser commodities in the deposit. The most important known deposits in the Monument are: the Nunatak molybdenum prospect (loc. 21), the Brady Glacier nickel-copper prospect (72), the Alaska Chief copper prospect (29), the Margerie copper prospect (19), the gold deposits of the Reid Inlet gold area and the Sandy Cove prospect (7), the placer gold deposits on the beaches near Lituya Bay (87, 88), and several iron and titanium deposits associated with the layered intrusives of the Fair-weather Range. BASE AND MISCELLANEOUS METALS Anomalous concentrations of the following base and miscellaneous metals were found in the monument: Antimony, arsenic, bismuth, cadmium, copper, lead, tin, and zinc. Except for copper and zinc, none of these elements appear to occur in significant quantities, although a few, notably lead, may be considered possible byproduct metals. Minor occurrences of radioactive minerals have been reported from the monument, and these are also discussed briefly. ANTIMONY Antimony is a minor constitutent of several of the copper deposits, the Rendu Inlet silver deposit (loc. 37), and the silver-lead-zinc deposits near Mount Brack (12). Only two of our samples contained detectable antimony: one from the Mount Brack deposits contained 7,000 ppm antimony (table 9, loc. Table 8.—Total heavy-metals and semiquantitative spectrographic analyses, in parts per million of stream-sediment samples, Reid Inlet gold area [THM, Total heavy-metals (Cu-f Pb-f-Zn) field test; 0, looked for, but not found not looked for] Loc. Semiquantitative spectrographic analyses (fiK.7) Lab. No. Field No. THM Ag B Ba Co Cr Cu Fe La Mn Mo Ni Pb Sc Sn Sr Ti V Y Zr l D125012-3 Hf240 30 0. 300 15 50 50 40,000 40 1,250 0 15 00. 0. 4,000 175 25. 2 D125014-5 I If 241 20 0. 225 18 00 100 00,000 0 1,000 0 23 20. 0. 5,000 175 20. 3 D125010-7 Hf242 110 0. 750 23 100 150 70,000 0 1,000 3 40 18. 0. 5,000 200 20. 4 D125898 Ovl777 40 0 0 900 11 120 22 81,000 25 700 0 33 17 13 0 820 3,000 190 20 9G 5 D124740 Hf214 30 0 0 GOO 11 120 20 21,000 31 400 4 26 0 15 0 470 2,400 170 18 160 fi D124093 Ovl281 20 0 0 300 10 77 29 20,000 25 300 0 18 10 17 0 050 3,300 150 21 110 7 D124092 Fdl84 20 0 0 230 7 00 29 20,000 33 200 0 15 9 13 0 450 2,700 110 17 92 8 D120218 Hf372 40 0. 150 30 200 150 70,000 0 1,000 0 100 0. 0 500 5,000 500 30. 9 D124094 Ovl283 100 0 0 140 37 420 230 32,000 27 900 10 200 8 35 0 500 5,500 300 33 120 10 D 1240.98 Ovl294 20 0 0 470 0 70 1G 20,000 35 500 0 13 10 15 0 000 3,300 130 24 200 11 D124738 Fd201 30 0 0 300 11 00 83 23,000 0 400 5 21 0 20 33 320 4,200 200 21 200 12 D124737 Fdl99 40 0 0 270 18 90 110 33,000 0 700 8 36 9 29 0 280 0,700 320 27 120 13 D124730 Fdl98 100 0 0 180 28 130 150 32,000 0 900 7 59 8 30 0 280 5,700 310 28 89 14 D124097 Ovl293 20 0 0 400 9 110 19 30,000 59 700 0 15 8 17 0 070 4,500 140 30 370 15 D124095 Ovl285 00 0 0 270 17 130 87 33,000 28 200 4 38 0 18 0 000 3,100 180 10 110 lfi D120217 Hf371 100 0. 200 30 150 100 50,000 0 1,000 0 50 10. 0 700 3,000 200 30. 17 D124713 Hf344 40 0 0 270 24 170 0.0 31,000 47 500 0 38 0 19 0 000 3,500 210 17 110 18 D120210 Hf370 40 0. 300 15 70 70 30,000 0 700 0 30 0 0 0 500 3,000 150 30. 19 I) 124742 Ovl280 20 0 0 390 11 78 30 23,000 24 300 4 20 0 14 0 720 2,100 140 14 98 20 D125909 Ovl832 20 0 0 740 14 71 31 95,000 32 700 0 20 13 9 0 230 3,000 140 15 100 21 D124090 OvlL>92 20 0 0 430 7 75 22 31,000 39 500 0 18 0 13 0 500 2,700 130 15 120 22 D124745 Mk303 0 0 340 0 74 21 20,000 0 500 0 10 0 13 0 520 1,900 100 7 190 23 I) 120008 Ovl843 40 0. 300 15 70 30 30,000 0 500 0 15 0. 0 500 3,000 150 15. 24 D124744 Mk359 0 0 450 0 44 9 18,000 21 830 0 8 0 9 0 1,000 1,000 91 G 9730 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Locality list of deposits, Glacier Bay National Monument Name of locality Table giving No. on— Main analy- Detailed on— ----------------- com- tical Fig. 1 PI. 1 modity data Figure Plate Name of locality Table giving No. on— Main analy- Detailed on— —-------------- com- tical Fig. 1 PI. 1 modity data Figure Plate Adams Inlet 5 Cu 9. . Entrance of 22 Mo Alaska Chief 3 29 Cu 9 9. . Southwest of 30 Zn 9. . Blackthorn Peak, West of 51 Fe Blue Mouse Cove 42 Cu 9. . Brady Glacier 2 72 Ni 15 18. . , East of 54 Fe 9. . East of lower 55 Au 9. . Lower 56 Mo Outwash of 59 Au Bruce Hills 9 34 Cu 9, 10 10 Casement Glacier 9 Mo East of 4 Cu 9. . Nunatak on 3 Zn 9. . Charpentier Inlet 47 Mo 9. . Curtis Hills 23 Cu 9. Dundas Bay, east of 33 Fe East side of 14 31 Cu 9. . Do 32 Cu 9. . West arm of. 58 Cu 9. . West of 57 Au Dundas River 53 Au 8 73 Fe 78 Cu 79 Ti 80 Ti 82 Cu 83 Fe 86 Cu Francis Island 28 Cu 9 8. . . Gable Mountain 13 14 Cu 9. . Galena Prospect (Reid Inlet) J Au 11, Geikie Inlet, west of 50 Mo North shore of 48 Mo 9. . Gilbert Island, Southwest end of 44 Cu 9. Do 45 Cu 9. . Northern 43 W 9. , Highland Chief Prospect (Reid Inlet) K Au Hoonah Glacier, east of.. . . 75 Cu 9. . Do 77 Cu 9 Hopalong and Whirlaway claims (Reid Inlet) I Au 11 Hugh Miller Inlet 46 Zn 9. , Incas Mine, Reid Inlet G Au 11 14 . Johns Hopkins Inlet, 64 Cu 9 76 Zn 9 Johns Hopkins Inlet, South of 65 Cu 9, . South shore of 74 Mo 9. , Lamplugh Glacier, east of F Cu 11 67 Cu 9. West of head of 68 Ni 9. . Leroy Mine (Reid Inlet) B Au 9, 11 9 Lituya Bay 7 87 Au 88 Au Southeast arm of 84 Cu South of 85 Au Margerie 4 19 Cu 9 McBride Glacier, west of 10 Au 9 Minnesota Ridge 13 Cu 9 Monarch Mines (Reid Inlet) E Au 11 12, 13 Mount Abdallah 16 Ni 9 Mount Brack 10 12 Zn 9 Mount Cooper 66 Zn 9 Mount Young, near 1 Cu 9 Northwest of 2 Cu 9 North Marble Island 24 Cu Nunatak, The 1 21 Mo 13, 14 11, 12 Oregon King Consolidated 81 Au Queen Inlet 40 Fe 9 10 Rainbow Mine (Reid Inlet) C Au 11 11 Rambler Prospect (Reid Inlet) L Au 11 Red Mountain, southwest of 20 Zn 9 Reid Glacier, east of 69 Cu 9 Reid Inlet 5 A-L Au 11 11-14 9 Southeast of head of. . . 71 Mo 9 South end of ridge west of 70 Mo 9 Rendu Glacier, south of 12 15 Cu 9 Rendu Inlet 37 Ag 9 Ridge west of 60 Mo West of 39 Fe 9 17 West of mouth of 38 Cu 9 Russell Island 61 Au 9 Sand Cove 6 7 Au 9 15, 16 Sentinel Mine (Reid Inlet D Au 11 Shag Cove, west of 46 Cu 9 South Marble Island 25 Cu 9 Sunrise Prospect (Reid Inlet) H Au 11 Tarr Inlet, west of 15 63 Cu 9 West of mouth of 62 Cu 9 West shore of 18 Cu 9 West side of 17 Mo 9 Terry Richtmeyer Prospect (Reid Inlet) A Au Tidal Inlet, south of 41 Cu 9 Triangle Island 36 Mo Van Horn Ridge 1 1 Mo 9 Wachusett Inlet, near head of 35 Mo 9 White Glacier, north of 11 6 Cu 9 Willoughby Island, northeast side of 26 Cu West side of 27 Cu Wood Lake, south of 52 Au York Creek, north of 8 Cu 9 METALLIC COMMODITIES 31 Table 9.—Semiquantitative spectrographic analyses and gold analyses of mineral deposits 1 in the Glacier Bay National Monument, Alaska [Spectrographic analyses by J. C. Hamilton, Harriet Neiman, and A. L. Sutton. Jr. Gold analyses by Claude Huffman, Jr., J. D. Mensik, O. M. Parker, L. B. Riley, V. E. Shaw, J. A. Thomas, and J. E. Troxel. Au : A, analyzed by atomic absorption ; B, analyzed by fire assay atomic absorption method] Results are reported in parts per million, which for the spectrographic analyses have been converted from percent to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.15, and 0.1 ... , which represent approximate midpoints of group data on a geometric scale. The assigned group for six-step results will include more accurately determined values for about 30 percent of the test results. Gold and silver values in ounces per ton are shown in parentheses below their corresponding parts per million values. Symbols used: M, major constituent—greater than 10 percent; 0, looked for, but not detected ;.....not looked for; <, less than. Local- Sample Au A B Ag As Ba Bi Cd Co Cr Besides the elements shown in the table, the following elements were also sought in all of the analyses: Be, Hg, La, Li, Pd, Pt, Ta, and Ti. Reported values for these, except Be, La, and Li, were always O. Al. Ca, Mg, Si, and Sr were looked for and found in several of the analyses, but as they were not sought in most analyses, their values are not reported herein. Locations of the deposits are shown on pi. 1 ; individual samples are described at the end of the table. Cu Fe Mn Mo Nb Ni Pb Sb Sn Ti V W Y Zn Juneau quadrangle 1 Bd-130B Bd-130C 1 (0.029) 10 (0.292) 0 0 700 3,000 0 0 0 0 70 7 1,500 500 150 150 M 30,000 300 150 7 15 10 10 150 150 150 150 0 0 0 0 3.000 2.000 1,500 700 0 0 70 100 700 1,500 2 Mk-270 <0.05 <0.05 «0.0015) «0.0015) 0 0 50 0 0 15 0 300 30,000 300 0 0 3 0 0 0 1,500 0 0 30 0 Mk-273 0 0 700 0 0 30 0 70 30,000 500 10 0 0 0 0 0 2,000 15 0 20 0 3 Mk-309 ................. 0 0 70 0 0 5 15 15 30,000 3,000 0 0 5 0 0 0 300 30 0 10 300 4 Mk-310 ............... 0 0 70 0 0 15 70 300 70,000 700 5 0 50 0 0 0 3,000 100 0 30 0 Mk-311 ................. 0 0 70 0 0 20 30 300 70,000 700 5 0 50 0 0 0 3,000 150 0 30 0 5 Mk-156 0 0 300 0 0 30 150 150 70,000 700 0 0 30 0 0 10 3,000 150 0 30 0 Mk-157 0 0 300 0 0 150 150 150 M 300 7 10 150 10 0 0 5,000 300 0 30 0 Mk-159 0 0 300 0 0 150 150 150 M 700 7 10 150 30 0 0 5,000 150 0 30 0 Mk-160 (0.029) 0 70 0 0 300 150 500 M 700 30 15 300 15 0 0 3,000 150 0 30 0 Mk-162 0 0 200 0 0 100 150 300 M 700 15 10 200 15 0 0 3,000 200 0 30 0 Mk-164 0 0 150 0 0 150 150 150 M 300 30 10 150 30 0 0 3,000 150 0 15 0 6 Mk-253 Mk-254 Mk-256A Mk-256B Mk-257 Mk-258 Mk-259 <0.2 (<0.008) < .2 (0.006) .4 (0.012) .4 (0.012) < .2 «0.006) < .2 « 0.006) .2 « 0.006) <0.05 «0.0015) < .05 «0.0015) < .05 «0.0015) < .05 «0.0015) < .05 «0.0015) .05 «0.0015) < .05 «0.0015) 0 0 20 (0.583) 15 (0.338) 0 0 0 0 0 0 0 0 0 0 70.000 70.000 2,000 3,000 500 200 300 0 0 0 0 0 0 0 0 0 0 70 0 0 0 0 7 50 50 15 10 100 7 7 200 100 2 15 5 150 30 30.000 30.000 70 50 150 70.000 M 50.000 M 70.000 70.000 70.000 2,000 2,000 500 300 150 200 200 0 0 0 0 0 0 5 0 0 0 0 15 0 10 5 15 200 200 20 15 70 0 0 30 200 20 50 100 0 0 0 0 0 0 0 0 0 10 20 0 0 0 100 300 2,000 1,000 5.000 5.000 5.000 0 20 100 50 70 150 200 0 0 0 0 0 0 0 0 0 0 0 10 0 0 500 2020,000 20 0 20 0 7 Mk-224 0.2 0.1 0.5 0 1,000 30 0 5 1.5 500 20,000 500 50 0 0 15 0 0 2,000 100 0 15 0 (0.006) (0.003) (0.437) Mk-225 28 33 50 0 150 300 0 7 0 50,000 M 50 0 0 3 100 0 0 150 0 0 0 0 (0.816) (0.963) (1.460) Mk-226 3 3 2 0 700 50 0 10 15 1,500 M 500 0 0 7 100 0 0 1,500 70 0 10 0 (0.087) (0.087) (0.058) Mk-227 .2 .1 5 0 150 200 0 0 0 500 50,000 200 0 0 0 100 0 0 70 0 0 0 0 (0.006) (0.003) (0.1460) Mk-228 6 6 5 0 700 100 0 7 0 1,000 M 300 0 0 3 30 0 0 1,000 30 0 15 0 (0.175) (0.175) (0.1460) Mk-229 < .2 < .1 0 0 300 0 0 0 1.5 100 70,000 70 0 0 0 0 0 0 150 0 0 10 0 «0.006) «0.003) (0) Mk-415 23 17 30 0 300 500 0 10 0 30,000 M 300 30 0 5 70 0 0 1,000 50 0 30 0 (0.671) (0.495) (0.875) Mk-415A 27 27 30 0 300 300 0 15 0 30,000 M 50 <10 0 3 50 0 0 500 20 0 0 0 (0.788) (0.788) (0.875) Mk-416 14 14 10 0 50 150 0 7 0 7,000 M 100 <7 0 3 150 0 0 50 7 0 0 0 (0.403) (0.403) (0.292) Mk-417 1 1 10 0 50 100 0 15 3 20,000 M 200 <7 0 5 30 0 0 300 20 0 15 0 (0.029) (0.029) (0.292) Mk-418 < .1 0 0 3,000 0 0 10 1.5 70 50,000 500 10 0 0 10 0 0 2,000 150 0 20 0 (<0.003) Mk-419 < .1 0 0 2,000 20 0 7 5 50 50,000 150 20 0 0 0 0 0 1,500 70 0 10 0 «0.003) Hf-280B .4 0 0 200 0 0 0 1.5 1,000 10,000 100 50 0 0 0 0 0 150 10 0 0 0 (0.012) Hf-280C 2 2 20 0 200 200 0 0 0 M M 20 <15 0 0 50 0 0 10 0 0 0 0 (0.058) (0.588) (0.583) 8 Mk-431 <0.05 <0.1 0 0 150 0 0 150 70 1,500 50,000 1,500 <5 0 150 0 0 0 5,000 150 0 70 0 (<0.015) «0.003) Mk-434A < .1 0 0 150 0 0 7 100 50 50,000 1,500 15 0 15 0 0 0 2,000 150 0 15 0 (0.003) Skagway quadrangle 9 No analyses 10 Mk-411 3 (0.088) 3 (0.088) 0 7,000 1,000 0 0 15 7 150 70,000 2,000 0 0 20 0 0 0 300 20 0 0 0 Mk-412 .3 (0.0088) 0 0 100 0 0 7 2 100 50,000 3,000 0 0 15 0 0 0 20 0 0 0 0 Hx-251 1 (0.003) 1.5 (0.0045) 0 15,000 20 0 0 10 2 500 70,000 3,000 0 0 20 0 0 0 30 0 0 0 0 See footnotes at end of table.32 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Table 9.—Semiquantitative spectrographic analyses and gold analyses of mineral deposits 1 in the Glacier Bay National Monument, Alaska—Continued Local- Sample Au ity 66A— -------- A B Ag As Ba Bi Cd Co Cr Cu Fe Mn Mo Nb Ni Pb Sb Sn Ti V W Y Zn Skagway quadrangle—Continued 11 Mk-145A Mk-145B Mk-146 Mk-151 0 0 0 0 0 0 0 0 500 300 7 200 0 0 0 0 0 0 0 0 10 15 0 30 20 30 15 30 20 50 100 70 50.000 70.000 M 50.000 300 300 500 1,000 0 5 200 5 0 0 0 0 3 5 3 15 20 10 15 0 0 0 0 0 0 0 0 0 3.000 5.000 700 3.000 150 200 0 300 0 0 0 0 15 15 0 30 0 0 0 0 12 Mk-315 0.3 (0.0088) 15 (0.437) 7,000 15 30 300 20 3 150 M 3,000 5 0 20 150 0 0 300 15 0 0 15,000 Bd-280 3 (0.088) 30 (0.875) 30,000 15 30 150 30 1 70 70,000 3,000 0 0 r 7,000 7,000 0 150 0 0 10 3,000 Bd-283B 0 0 7 10 0 150 1.5 300 M 150 15 0 70 10 0 0 30 10 0 15 0 Hx-315A 0 0 70 0 0 30 30 150 70,000 1,500 0 0 30 15 0 0 700 150 0 30 700 Hx-316B 0 0 150 0 0 15 70 100 70,000 700 7 10 70 0 0 0 3,000 200 0 70 0 13 Bd-185B 0 0 300 0 0 15 10 700 70,000 150 0 0 10 0 0 0 2,000 100 0 10 0 14 Bd-466B <0.1 «0.003) <0.05 «0.0015) 1 (0.029) 0 500 0 0 50 10 1,000 50,000 700 15 0 7 0 0 0 5,000 200 0 20 0 15 Bd-723 0 0 30 50 0 7 30 2,000 M 300 0 0 70 0 0 0 300 20 0 0 0 16 Bd-746 0 0 1,500 0 0 15 150 100 50,000 500 3 0 70 20 0 0 5,000 300 0 30 0 17 Mk-560 <0.05 «0.0015) 0 0 1,000 0 0 10 50 100 30,000 500 100 0 30 10 0 0 2,000 100 0 15 0 Mk-562 < .05 (<0.0015) 0 0 1,000 0 0 20 20 100 70,000 1,000 0 0 3 0 0 0 3,000 300 0 15 0 Mk-563 0 5,000 300 70 0 50 7 200 70,000 700 0 0 5 0 0 0 5,000 200 0 15 0 18 Hf-360 0 0 70 50 0 7 30 1,500 M 1,000 0 0 15 0 0 15 3,000 150 100 15 0 19 Mk-550A 5 (0.146) 2 (0.058) M 50 300 0 100 1 2,000 70,000 20 5 0 5 0 0 0 200 0 150 0 30 Mk-550B 0.6 0 50,000 200 50 0 5 2 500 50,000 100 3 0 0 0 0 0 1,000 30 0 0 0 Mk-552A 0 0 500 0 0 10 30 150 70,000 150 5 0 7 0 0 0 3,000 300 0 15 0 Mk-552B 0 2,000 300 0 0 20 30 700 M 200 0 0 15 0 0 0 3,000 200 0 15 0 Mk-553 0 0 30 150 0 15 15 3,000 M 150 0 0 15 0 0 0 500 30 3,000 10 0 Mount Fairweather quadrangle 20 Mk-222 .................. 1.5 0 300 0 70 30 5 50 M 100 30 0 100 500 0 0 150 0 0 0 7,000 (0.044) 21 <*) 22" No analyses 23 Mk-185A ..................... 0 0 50 0 0 100 30 700 M 1,500 0 0 100 30 0 010,000 500 0 20 0 Mk-187 0 0 200 0 0 15 700 100 50,000 1,500 0 0 150 0 0 0 5,000 300 0 20 0 Mk-200 0 0 200 0 0 50 20 500 50,000 700 0 0 50 0 0 0 1,000 500 0 30 0 24 No analyses 25 Mk-36 Mk-38 Mk-339 Mk-41 26, 27 No analyses 28 Mk-17 Hf-183B Iif-183C 0 50 (1.460) 0 0 0 0 100 7 5 0 150 0 0 0 0 15 10 10 100 5 0 100 7,000 50 50.000 30.000 M 500 2,000 7,000 10 0 0 0 0 0 150 0 0 0 0 50 0 200 0 0 20 0 2,000 1,500 30 200 10 30 0 0 0 30 0 10 0 1,000 0 29 Mk-469 8 (0.234) 7 (0.205) 100 (2.917) 0 150 150 0 70 15 15,000 M 700 10 0 100 30 0 0 700 30 0 0 700 Mk-470 6 (0.176) 5 (0.146) 140 (4.377) 0 20 70 0 70 20 15,000 M 1,000 5 0 100 20 0 0 500 20 0 0 700 Mk-471 < .05 (<0.0015) < .05 «0.0015) 0 0 200 0 0 5 15 300 70,000 2,000 0 0 5 0 0 0 1,500 70 0 20 0 Mk-472 (0.021) .8 (0.023) 0 0 300 20 0 15 30 1,000 70,000 3,000 0 0 20 0 0 0 2,000 100 0 20 0 Mk-473 10 (0.292) 9 (0.263) 70 (2.043) 0 100 200 0 30 15 1,000 M 1,000 7 0 20 0 0 0 300 20 0 0 300 Mk-475 2 (0.058) 3 (0.088) 100 (2.917) 0 200 100 0 200 15 M M 1,000 5 0 150 0 0 0 500 20 0 0 1,000 Mk-474 3 (0.0015) (s) 50 (0.0015) 50 0 100 300 0 300 30 15,000 M 5,000 7 0 500 15 0 0 1,000 50 0 0 1,500 0 0 150 0 0 30 200 150 M 1,500 0 0 100 0 0 0 7,000 700 0 30 0 0 0 70 0 0 50 150 200 M 2,000 0 0 100 0 0 0 10,000 500 0 30 0 0 0 70 0 0 30 200 200 70,000 1,500 0 0 100 10 0 0 5,000 300 0 20 0 0 0 50 0 0 30 150 150 M 1,500 0 0 100 0 0 0 7,000 500 0 30 0 30 Hx-504B ................... 7 0 150 10 0 3 1.5 70 15,000 1,500 7 0 0 300 0 0 700 30 0 0 1,500 31 Mk-4S1 ........................... 0 0 300 0 0 30 10 500 M 150 20 0 10 0 0 0 1,000 100 0 0 0 Mk-482 0 0 300 0 0 20 7 700 30,000 300 20 0 5 10 0 0 1,000 70 0 0 0 Mk-483 0 0 500 0 0 15 10 1,500 30,000 300 3 0 7 15 0 0 1,000 70 0 0 0 11 x—543 1 0 500 0 0 10 20 1,000 50,000 500 0 0 20 30 0 0 3,000 200 0 15 0 (0.029) Hx-544 0 0 200 0 0 10 15 1,000 70,000 300 15 0 10 0 0 0 1,500 100 0 0 0 Hx-54411 0 0 150 0 0 30 10 2,000 70,000 300 20 0 10 0 0 0 1,000 200 0 10 0 32 Ilx-548 ..................... 0 0 150 0 0 10 7 1,000 50,000 700 300 0 10 0 0 0 1,500 700 0 0 0 33 No analyses See footnotes at end of table.METALLIC COMMODITIES 33 Table 9.—Semiquantitative spectrographic analyses and gold analyses of mineral deposits 1 in the Glacier Bay National Monument, Alaska—Continued Local- Sample Au ity 66A— ---------- A B Ag As Ba Bi Cd Co Cr Cu Fe Mn Mo Nb Ni Pb Sb Sn Ti V W Y Zn Mount Fairweather quadrangle—Continued 34 Mk-85A .................... 0 0 50 0 0 20 2 3,000 M 300 1,000 0 5 0 0 0 500 0 0 0 0 Mk-85B <0.05 <0.05 0 0 1,500 0 0 7 7 3,000 50,000 300 30 0 3 0 0 0 2,000 70 0 15 0 «0.0015) «0.0015) Mk-85C ........................ 0 0 700 0 0 7 7 2,000 50,000 150 7 0 0 0 0 0 2,000 50 0 10 0 Mk-86A ........................ 0 0 500 0 0 0 2 70 20,000 50 20 0 0 0 0 0 700 20 0 0 0 Mk-86B ........................ 0 0 500 0 0 5 1.5 100 20,000 50 30 0 0 0 0 0 700 20 0 0 0 Mk-178 0 0 1,500 0 0 7 15 1,500 30,000 150 30 0 3 0 0 0 2,000 100 0 15 0 Mk-179 0 0 3,000 0 0 7 15 300 30,000 150 15 0 3 0 0 0 1,500 70 0 15 0 Re-56 1 0 700 0 0 30 30 3,000 70,000 300 70 0 7 0 0 10 3,000 150 0 20 0 (0.029) 35 Bd-273D ...................... 15 0 30 10 0 70 1 15,000 30,000 150 7,000 0 15 0 0 0 200 15 0 0 700 (0.338) 36 No analyses 37 Mk-542 Mk-544 <0.05 . «0.0015) 0 0 0 0 1,000 200 0 0 0 0 3 3 3 2 7 20 15.000 50.000 700 1,000 0 15 0 0 3 0 0 0 0 0 0 15 50 700 7 50 0 0 0 15 0 0 38 Mk-558 0 0 200 0 0 10 300 15 30,000 150 0 0 30 0 0 0 2,000 150 0 10 0 Mk-559 0 0 30 0 0 700 20 1,500 M 300 0 0 1,000 0 0 0 500 50 0 0 0 39 Mk-548 0 0 70 0 0 15 15 30 50,000 500 0 0 3 0 0 0 3,000 150 0 15 0 Mk-549 0 0 10 0 0 3 0 7 M 3,000 0 0 0 0 0 0 700 50 0 0 0 Hx-626 0 0 15 0 0 7 0 3 M 3,000 0 0 3 0 0 0 700 30 0 15 0 40 Mk-298A 0 0 70 0 0 10 15 30 M 700 0 0 5 0 0 30 1,500 50 0 20 0 Mk-298B 0 0 100 0 0 10 20 50 M 500 20 0 5 0 0 30 1,500 50 0 20 0 Mk-299 0 0 15 0 0 300 0 300 M 700 15 0 15 0 0 15 7 0 0 15 300 Mk-303 0 0 7 0 0 7 0 15 M 1,500 5 0 3 0 0 0 70 0 0 50 0 Mk-305 0 0 30 0 0 70 30 150 M 1,500 0 0 70 0 0 30 3,000 150 0 30 200 Mk-321 0 0 10 10 0 50 0 200 70,000 50 7 0 0 0 0 0 700 0 0 50 0 Mk-323 0 0 30 0 0 5 0 300 M 200 0 10 0 0 0 0 1,500 0 0 70 0 Mk-324 0 0 30 0 0 30 1.5 30 M 300 7 0 0 10 0 30 3,000 15 0 150 0 41 Hx-260V <0.2 « 0.006) 0.1 (0.003) 0 0 30 0 0 300 10 1,000 M 500 0 0 300 0 0 0 1,500 70 0 0 0 42 Mk-48 1 (0.029) 0 500 0 0 0 15 200 15,000 300 0 0 0 300 0 0 3,000 100 0 10 700 43 Hx-659A 0 0 5 0 0 7 2 150 M 3,000 5 0 10 0 0 0 150 30 150 0 0 44 Mk-84A 0 0 20 0 0 0 7 3 15,000 700 0 0 0 0 0 0 500 70 0 0 0 Mk-84B 0 0 30 0 0 70 2 50 50,000 300 0 0 7 0 0 0 700 50 0 0 0 45 Mk-65 0 0 150 0 0 10 7 1,000 30,000 1,500 0 0 3 0 0 0 1,500 70 0 15 0 Mk-67 10 (0.292) 0 700 0 0 20 7 7,000 50,000 1,000 2,000 0 3 0 0 0 3,000 100 0 15 0 Mk-68 0 0 2,000 0 0 0 0 10 15,000 300 15 0 0 0 0 0 1,000 15 0 0 0 Mk-69 0 0 500 0 0 10 10 7 30,000 1,000 0 0 3 0 0 0 2,000 150 0 15 0 Mk-72 0 0 1,000 0 0 10 10 5 30,000 700 0 0 3 0 0 0 2,000 100 0 20 0 46 Bd-37B 0 0 1,000 70 0 150 15 15 M 300 7 10 15 0 0 0 1,500 70 0 15 1,500 47 Mk-423 <0.1 (0.003) 0 0 500 0 0 0 15 150 M 1,500 7 0 10 0 0 1010,000 500 0 30 0 48 Hx-67 0 0 100 0 0 20 100 150 M 700 10 0 30 0 0 0 50 300 0 30 0 49 Hx-32A 0 0 50 0 0 10 15 100 50,000 700 0 0 10 0 0 0 3,000 100 0 30 0 Hx-32B 1 (0.029) 0 15 0 0 200 1 3,000 M 700 0 0 10 0 0 0 70 15 0 0 700 50-53 No analyses 54 Mk-460A Mk-460B 0 0 0 0 30 7 0 0 0 0 30 70 7 7 1,000 1,000 M M 1,000 1,000 15 7 0 0 30 50 0 0 0 0 0 0 700 150 30 30 0 0 0 0 0 0 55 Mk-455 <0.05 (<0.0015) 0 0 70 0 0 7 10 100 30,000 300 0 0 5 0 0 0 5,000 200 0 10 0 56, 57 No analyses 58 Hx 484A 0 0 30 0 0 150 30 10,000 M 1,000 0 0 0 15 0 0 2,000 200 0 15 0 56, 60 No analyses 61 Ov-2041 23 (0.670) 29 (0.845) 1 (0.029) 0 50 0 0 0 1 20 10,000 300 0 0 0 50 0 0 150 15 0 0 0 62 Fd-428B <0.05 «0.0015) 0 0 70 0 0 100 0 2,000 M 200 0 0 15 0 0 0 1,500 70 0 0 0 63 Hx-391 1 (0.029) 0 500 0 0 15 10 1,000 50,000 1,000 0 0 3 0 0 0 2,000 50 0 10 300 See footnotes at end of table.34 METALLIC COMMODITIES Table 9.—Semiquantitative spectrographic analyses and gold analyses of mineral deposits 1 in the Glacier Bay National Monument, Alaska—Continued Local- ity Sample 66A— Au A B Ag As Ba Bi Cd Co Cr Cu Fe Mn Mo Nb Ni Pb Sb Sn Ti V W Y Zn Mount Fairweather quadrangle—Continued Mk-396 0.1 (0.003) 0 0 200 0 0 5 50 10 20,000 700 0 0 15 0 0 0 700 70 0 10 0 Mk-399 .1 0.09 (0.003) (0.026) (0.029) 0 2,000 0 0 15 10 1,000 70,000 700 0 0 3 30 0 0 2,000 150 0 15 0 Mk-521 < .05 < .05 «0.0015) «0.0015) 0 0 700 0 0 15 70 700 70,000 700 3 0 30 0 0 0 3,000 150 0 30 0 Mk-522 < .05 < .05 (C0.0015) «0.0015) 0 0 150 0 0 15 1.5 70 20,000 150 0 0 3 0 0 0 300 15 0 0 0 Mk-524 0 0 700 0 0 15 70 70 50,000 300 3 10 15 15 0 0 3,000 150 0 30 0 Mk-525 < .05 < .05 «0.0015) «0.0015) 0 0 300 0 0 20 30 70 70,000 700 3 0 15 15 0 0 1,500 150 0 15 0 Mk-527 0 0 70 0 0 30 150 300 70,000 700 15 0 30 0 0 0 7,000 300 0 30 0 Mk-528 0 0 700 0 0 20 30 150 70,000 700 7 0 15 0 0 0 7,000 300 0 30 0 Fd-397 <0.05 <0.05 0 0 300 0 0 15 3 1,500 70,000 300 30 0 7 0 0 0 1,500 150 0 30 0 «0.0015) «0.0015> 66 Bd-382B 0 0 15,000 0 0 15 100 300 70,000 300 15 0 50 0 0 10 3,000 150 0 20 300 67 Bd-433A <0.1 (C0.003) 0 0 50 0 0 30 10 300 M 1,000 <5 0 15 0 0 0 3,000 200 0 15 0 Bd-433B 0 0 30 0 0 20 1 50 M 10 50 0 3 0 0 0 500 15 0 0 0 68 OV-1903B <0.05 (C0.0015) 0 0 150 0 0 150 200 150 M 200 20 0 300 0 0 0 1,500 150 0 10 0 69 Mk-566 0 0 15 0 0 0 2 7 20,000 300 0 0 7 0 0 0 20 15 0 0 0 Mk-567 <0.05 «0.015) 0 0 150 0 0 20 15 300 70,000 300 7 0 20 0 0 0 3,000 100 0 10 0 Mk-568 < .05 «0.0015) 0 0 150 0 0 30 10 1,000 M 200 0 0 50 0 0 0 1,000 30 0 0 0 70 Mk-366 <0.1 (<0.003) 0 0 300 0 0 15 50 150 50,000 1,000 7 0 30 10 0 0 3,000 200 0 30 0 Mk-368 < .1 0 0 300 0 0 10 30 150 30,000 700 30 0 20 0 0 0 1,500 750 0 20 0 «0.003) 71 Mk-564 ................. 0 0 2,000 0 0 5 30 30 30,000 200 10 0 20 10 0 0 2,000 200 0 15 0 Mk-565 ................ 0 0 10,000 0 0 7 30 50 20,000 150 15 10 30 10 0 0 2,000 700 0 15 0 *72 (*) ........................................................................................................................................... 73 No analyses 74 Fd-400A 0 0 700 0 0 7 15 150 15,000 700 30 0 15 15 0 0 1,500 200 0 30 0 75 Fd-402 0 0 500 0 0 15 30 300 30,000 500 15 0 15 10 0 0 2,000 70 0 20 0 76 Mk-531 0 0 700 0 0 15 150 70 70,000 700 3 10 30 10 0 0 3,000 150 0 30 300 77 Bd-702A 0 0 70 0 0 70 150 300 M 1,500 5 0 70 0 0 0 7,000 700 0 30 0 Bd-702C <0.05 <0.05 0 0 70 0 0 70 150 700 M 1,000 3 0 70 0 0 0 7,000 300 0 30 0 «0.0015) «0.0015) 78-88 No analyses .............. 1 Excluding the Nunatak molybdenum prospect, copper prospect, and the Reid Inlet gold area. 2 Nunatak molybdenum prospect, see table 13. the Brady Glacier nickel- 3 Gold value from six-step spectrographic analyses. * Brady Glacier nickel-copper prospect, see table 15. SAMPLE DATA FOR TABLE 9 Sample Locality Geologic setting 66A- Description of sample 1 Juneau D-5 quadrangle, 1.8 miles N. 5° E. of Mount Young. Iron-stained altered zones as much as 10 ft thick and 100 ft long in meta-volcanic rocks, hornfels, and slate that are cut by numerous mafic dikes. Bd-130B Bd-130C Selected specimen of sulfides replacing meta-volcanic rocks. Grab sample of altered hornfels and slate. 2 Juneau D-5 quadrangle, 3.5 miles N. 27%° W. of Mount Young. Bleached and altered zone 20 ft thick in granodiorite. Irregular-trending iron-stained zones cutting metavolcanic ( ?) rocks. Mk-270 Mk-273 20-ft-long chip sample at 6-in. intervals across altered zone. Grab sample representative of iron-stained zones. 3 Juneau D-6 quadrangle, nunatak in Casement Glacier 2.1 miles S. 9° E. from northwest corner of quad- Quartz-ankerite-barite veins as much as 1 ft thick within 10-15 ft thick altered zone in thin-bedded hornfels. Mk-309 Selected sample of veins. rangle. 4 Juneau D-6 quadrangle, 5 miles S. 21^° E. from northwest corner of Altered granitic rock. Mk-310 Mk-311 Composite grab sample. Selected sample of most altered rock. quadrangle. 5 Juneau D-6 quadrangle, north shore Amygdaloidal basalt, weakly mineral- Mk-156 100-ft-long chip sample at 2-ft intervals. Adams Inlet near triangulation station “Upper.” ized. Mk-157 Mk-159 Mk-160 Mk-162 Mk-164 44-ft-long chip sample at 2-ft intervals. 100-ft-long chip sample at 2-ft intervals. Selected sample representative of zone 4 ft long. 100-ft-long chip sample at 2-ft intervals. 110-ft-long chip sample at 2-ft intervals.MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA 35 sample data FOR table 9—Continued Locality Geologic setting Sample 66A- Description of sample 6 Juneau D-6 quadrangle, north of White Glacier between 5 and 6 miles N. 30° E. from southwest corner of quarangle. Barite-bearing altered zone 10 ft thick, adjacent to dike that cuts limestone. 10-ft thick iron-stained shear zone cutting limestone; some dikes nearby. Altered zones between 1 ft and 200 ft thick cutting volcanic rocks. Mk-253 Mk-254 Mk-256A Mk-256B Mk—257 Mk-258 Mk-259 10-ft-long chip sample across altered zone at 6-in. intervals. Selected sample adjacent to north wall of dike. Selected specimens near dikes. Selected sample of richest-appearing part of shear zone. 6-ft-long chip sample at 6-in. intervals. 200-ft-long chip sample at 1-ft intervals. 50-ft-long chip sample at 1-ft intervals. 7 Sandy Cove prospect, Juneau C-6 quadrangle, 2.25 miles S. 29° E. from northwest corner of quadrangle. Steep quartz veins as much as 1 ft thick cutting quartz monzonite. Local wall-rock alteration adjacent to veins. (See fig. 15.) Mk-224 Mk-225 Mk-226 Mkr-227 Mk-228 Mk-229 10-ft-long chip sample across face; sample interval 6 in. 5- ft-long channel through high-grade zone in face. 6- ft-long chip sample at 6-in. intervals. Selected sample representing entire width of a 4-in.-thick vein. 5-ft-long channel sample across back of portal. Selected sample of 4-in.-thick pyrite-quartz Mk-415 Mk-415A Mk-416 14-in.-long channel sample in face. Selected sulfide-rich ore from high-grade zone in face. Selected sample representative of 6-in. of Mk—417 Mk-418 Mk—419 Hf-280B Hf-280C 1-ft-long channel sample across vein. Selected sample representative of altered wallrock. 18-in. chip sample across altered wallrock at 2-in. intervals. Selected sample of sulfide-rich ore. Do. 8 Juneau C-6 quadrangle, north of York Creek about 7.5 miles S. 22%° E. from northwest corner of quadrangle. Numerous pyrite-rich veins as much as 6 in. thick cutting hornfels. Iron-stained breccia zone cutting hornfels. Mk-431 Mk-434A Selected samples representative of pyrite-rich veins. 20-ft-long chip sample at 1-ft intervals across breccia zone. 9 Skagway A-3 quadrangle; location doubtful. Molybdenite-bearing float found on moraine of Casement Glacier by Ohio State Univ. glaciologists in 1965. 10 Skagway A-3 quadrangle, west of McBride Glacier 3.8 miles N. 65° W. of Coleman Peak. Sulfide-bearing ankeritic zones at facies change between phyllite and marble. Mk-411 Mk-412 Selected samples of richest-appearing sulfidebearing rock. 2-ft-long channel sample across ankeritic Hx-251 11 Skagway A-3 quadrangle, 2.7 miles N. 38° E. from southwest corner of quadrangle. Small prospect pits and trenches on iron-stained breccia and shear zones between 1 and 12 ft thick. Country rock is granodiorite and hornfels. Mk-145A Mk-145B Mk-146 Mk-151 Selected sample from shear zone. Selected sample from breccia zone. Iron-stained rock from shear zone, selected sample. Grab sample from iron-stained fault zone 12 ft thick. 12 Skagway A-4 quadrangle, approximately between 0.9 and 1.3 miles west of Mount Brack. Altered zones as much as 30 ft thick enclosing discrete ankeritic veins as much as 1 ft thick in limestone, silt-stone, shale, and graywacke; some mafic dikes. Mk-315 Bd-280 Bd-283B Hx-315A Hx-315B Sulfide-rich float, source probably nearby. Grab sample from sulfide-rich vein, about 8 in. thick, that cuts a mafic dike. Grab sample from pyritic vein about 1 in. thick. Selected, probably representative, samples of thin sulfide-bearing quartz veins. Grab sample from ankeritic shear zone 2 ft thick. 13 Skagway A-4 quadrangle, on Minnesota Ridge near Glacier Pass. Copper- and iron-stained tonalite or granodiorite. Bd-185B Float. 14 Skagway A-5 quadrangle. Gable Mountain north of Carroll Glacier. Joint coatings in dioritic rock throughout a large area. Bd-466B Composite grab sample. 15 Near southwest corner of Skayway A-5 quadrangle. Iron-stained altered zone about 100 ft thick near contact between hornfels and instrusive rock. Bd-723 Float, probably representative of altered zone. 16 Near southwest corner of Skagway A-5 quadrangle. Lens of copper- and iron-stained hornfels about 10 ft long and 6 ft thick. Bd-746 Grab sample from lens. 17 Skagway A-6 quadrangle, west of Tarr Inlet south of Margerie Glacier. Altered and brecciated zones in granodiorite, generally between 2 and 12 ft thick. Mk-560 Mk-562 Mk-563 Selected specimen. Composite grab sample from an altered zone about 12 ft thick. Grab sample representative of a 2-ft-thick altered zone. 18 Skagway A-6 quadrangle, west of Tarr Inlet south of Margerie Glacier. Altered hornfels with sulfides as much as 2 ft thick. Hf-360 Composite grab sample. 19 Margerie prospect, Skayway A-6 quadrangle, south of Margerie Glacier. Quartz veins as much as 2 ft thick, altered zones as much as 12 ft thick, in hornfels and granodiorite. Mk-550A Mk-550B Mk—552A Mk-552B Mk-553 1-ft-long channel sample of quartz vein. Do. Do. Chip sample at intervals of 4 in. across 5 ft of altered zone. Massive sulfide float, pyrrhotite rich. 20 Mount Fairweather D-l quadrangle, 3 miles S. 37° W. from northeast corner of quadrangle. Small pyrite-rich pods less than 6 ft long and 1 ft thick in limestone. Mk-222 Selected specimen from pyrite-rich pod.36 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA SAMPLE DATA FOR table 9—Continued Locality Geologic setting Sample 66A— Description of sample 21 Nunatak molybdenum prospect. Mount Fairweather D-l quadrangle, 3.6 miles S. 77° W. from northeast corner of quadrangle. Extensive stockworks of molybdenitebearing quartz veins mainly in horn-fels. Analyses are shown in table 13. 22 Mount Fairweather D-l quadrangle, north shore of Adams Inlet near entrance; locality not found. Molybdenite coating fractures in meta-morphic rocks (Smith, 1942, p. 178). No analyses. 23 Mount Fairweather D-l quadrangle, between 3.5 and 5.5 miles S. 45° E. from northwest corner of quadrangle. At north edge of Plateau Glacier. Iron-stained zones 1-2 ft thick contiguous to mafic dikes that cut hornfels; some thin quartz veins in altered zones. Mk-185A Mk-187 Mk-200 Selected specimen of pyritized and iron-stained hornfels. Grab sample representative of iron-stained zones. Selected sample representative of 6-in.-thick quartz vein. 24 Mount Fairweather C-l quadrangle. North Marble Island, about 5.8 miles S. 38° W. from northeast corner of quadrangle. Sulfides disseminated in marble near porphyritic dikes and also in the dikes (Reed, 1938, p. 69). Not found during present investigation. No analyses. 25 Mount Fairweather C-l quadrangle, south Marble Island about 7.4 miles S. 12V2° W. from northeast corner of quadrangle. Sulfides disseminated in mafic dikes and in silicified limestone and marble near dikes. Mk-36 Mk-38 Mk-39 Mk-41 Selected sample near lower contact of large dike. Selected sample a few inches below upper contact of large dike. Selected sample of sulfide-bearing mafic dike. Do. 26 Mount Fairweather C-l quadrangle, prospect on northeastern part of Willoughby Island about 8 miles N. 34° W. from southeast corner of quadrangle; location doubtful. Sulfide replacement in limestone (Reed, 1938, p. 70-72). Not found during current investigations. No analyses. 27 Mount Fairweather C-l quadrangle, prospect on west side of Willoughby Island; location doubtful, probably about 8 miles N. 38%° W. from southeast corner of quadrangle. Sulfide replacement of intersecting lamprophyre dikes that cut marble (Reed, 1938, p. 70-72). Not found during current investigation. No analyses. 28 Mount Fairweather C-l quadrangle, near southwest extremity of Francis Island. Sulfides and their oxidation products in tactite near quartz diorite. (See fig. 8.) Mk-17 Hf-183B Hf-183C Sulfide-bearing float. Grab sample of copper-stained metamorphic rock. Grab sample of sulfide-bearing contact rock. 29 Mount Fairweather B-l quadrangle, Alaska Chief prospect, 5.4 miles S. 42V&0 W. from northwest corner of quadrangle. Sulfide-rich replacements and disseminations in metamorphic rocks near contact wih granodiorite ; well-developed gossan. (See fig. 9.) Mk-469 Mk—470 Mk—471 Mk-472 Mk—473 Mk-475 Mk-474 51-ft-long chip sample at 1-ft intervals. 53-ft-long chip sample at 1 ft intervals. 6-ft-long chip sample, at 6-in. intervals, across back of adit near face. 6-ft-long chip sample, at 3-in. intervals, across back of portal of adit. 51-ft-long chip sample at 1-ft intervals. Grab sample from ore pile. Soil sample. 30 Mount Fairweather B-l quadrangle about 1 mile southwest of Alaska Chief prospect. Shear zone in granodiorite or quartz monzonite. Hx-504B Grab sample from shear zone. 31 Mount Fairweather B-l quadrangle, east side of mouth of Dundas River about 9 miles S. 11° E. from northwest corner of quadrangle. Altered zone, more than 100 ft thick, in metamorphic rocks. Mk—481 Mk—482 Mk-483 Hx-543 Hx-544 Hx-544B Grab sample from altered zone. 30-ft-long chip sample at 1-ft intervals. Selected sample of sulfide-rich rock. Selected sample of pyritic schist. 40-ft-long chip sample at 2-ft intervals across best appearing part of altered zone. Selected sample of copper-stained rock from altered zone. 32 Mount Fairweather B-l quadrangle, east shore of Dundas Bay, about 8 miles N. 17° E. of southwest corner of quadrangle. Copper-stained quartz veins in cataclas-tic quartz diorite. Hx-548 Selected sample representative of quartz veins and host rock. 33 Mount Fairweather B-l quadrangle, about 8.8 miles N. 41° E. from southwest corner of quadrangle. Iron deposit shown on unpublished map by Rossman. Probably along contact between quartz diorite and marble. No analyses. 34 Mount Fairweather D-2 quadrangle, in Bruce Hills 1.4 miles S. 30° W. from northeast corner of quadrangle. Narrow veins and extensive altered zones in fractured granodiorite with minor hornfels. (See fig. 10.) Mk-85A Mk-85B Mk-85C Mk-86A Mk—86B Mk-178 Mk-179 Re-56 Selected specimen of sulfide-rich float; source probably nearby. Selected specimen of granodiorite with sulfide-bearing veinlets. Grab sample of gossan. Sulfide-bearing float. Selected sample of pyrite-rich vein. Grab sample representative of 4-ft-thick altered zone in granodiorite. Channel sample across 6-in.thick quartz vein. 6-ft chip sample at 6-in. intervals across altered zone. 35 Mount Fairweather D-2 quadrangle, on Wachusett Inlet 3.7 miles S. 20° W. from northeast corner of quadrangle. Two molybdenite- and chalcopyrite-bearing quartz veins, 1-2 in. thick, in tonalite. Bd-273D Selected sample of richest-appearing material in vein.METALLIC COMMODITIES 37 sample data for table 9—Continued Location Geologic setting Sample 66A— Description of sample 36 Mount Fairweather D-2 quadrangle, on Triangle Island near north end of Queen Inlet. A few hundred pounds of molybdenite were reportedly (Rossman, 1963b, p. K49) mined from Triangle Island in one day. No molybdenite was found on the island during the present study. No analyses. 37 Mount Fairweather D-2 quadrangle, west of Rendu Inlet. Two patented claims on short adit that is caved at portal; not found with certainty. Probably represented by a badly caved working on 6-in.-thick calcite-rich vein. Dioritic dike in footwall, marble in hanging wall. Mk-542 Mk-544 Grab sample representative of vein. Selected specimen from a 6-in.-thick auxiliary vein. 38 Mount Fairweather D-2, quadrangle, west of mouth of Rendu nlet. Irregular iron-stained altered zones, less than 1 ft thick and about 20 ft long, in marble. Mk-558 Mk-559 Selected sample from altered zone. Selected sample from pyrite-rich lens, about 2 in. thick, near footwall of altered zone. 39 Mount Fairweather D-2 quadrangle, on ridge west of Rendu Inlet. Irregular masses of skarn near contact between diorite and marble; local py-rite-rich lenses and altered zones. (See fig. 17.) Mk-548 Mk-549 Hx-626 Selected sample representative of an altered zone, about 15 ft thick. Grab sample of skarn. Do. 40 Mount Fairweather D-2 quadrangle, east of Queen Inlet, northeast of Composite Island. Magnetic in skarn near felsic intrusive rocks. Some irregular pyrite-rich zones mainly in nearby metamorphic rocks. (See pi. 10.) Mk-298A Mk-298B Mk-299 Mk-303 Mk-305 Mk-321 Mk-323 Mk-324 18-ft-long chip sample at 6-in. intervals across skarn. Selected sample of magnetite and sulfides. Do. Grab sample of skarn and sulfides from 2-ft-thick skarn. Grab sample, sulfide-bearing altered zone. Selected sample of pyrite-rich vein 6 in. thick. Selected sample, pyrite-rich vein 4 in. thick. Grab sample representative of pyrite-rich pod 6 ft thick and 20 ft long. 41 Mount Fairweather D-2 quadrangle, 3.2 miles N. 11° W. from southeast corner of quadrangle. Near contact between metamorphic rocks, chiefly marble, and altered hornblende diorite. Hx-260V Grab sample float of sulfide-bearing quartz vein. 42 Mount Fairweather D-2 quadrangle, southern part of Gilbert Island, north of Blue Mouse Cove. Mineralized shear zones as much as 12 ft thick and a few quartz-calcite veins as much as 1% ft thick. Mk-48 Chip sample across the richest appearing 2 ft of an altered zone at 3-in. intervals. 43 Mount Fairweather D-2 quadrangle, north of summit of Gilbert Island. Sulfide-bearing tactite 1 ft thick in marble 3 ft thick. Hx-659A Grab sample representative of a 1-ft-thick sulfide-bearing tactite zone. 44 Mount Fairweather D-2 quadrangle, island south of southwest tip of Gilbert Island. Fractured quartz diorite that is cut by aplite and alaskite dikes and by thin veins and clay seams. Mk-84A Mk-84B Selected sample of quartz veins with minor sulfides. Grab sample of quartz veins with minor sulfides. 45 Mount Fairweather D-2 quadrangle, near southwest tip of Gilbert Island. Bleached and fractured quartz diorite that contains sockworks of quartz veins and veinlets, abundant clay seams, and a few aplite dikes. Altered zone is several hundred feet long and at least 50 ft thick. Mk-65 Mk-67 Mk-68 Mk-69 Mk-72 Selected specimen of a 6-in.-thick quartz vein. Selected specimen of auartz vein (float). Grab sample from aplite dike. 100-ft-long chip sample taken at 4-ft intervals. 52-ft-long chip sample taken at 4-ft intervals. 46 Mount Fairweather D-2 quadrangle, west of Hugh Miller Inlet near southwest corner of quadrangle. Three iron-stained pyritic quartz veins, each les than half an inch thick, in hornblende diorite. Bd-37B Selected sample of best appearing vein material. 47 Mount Fairweather C-2 quadrangle, about 0.7 mile northeast from the head of Charpentier Inlet. Flat-lying altered zone about 50 ft thick in fine-grained diorite. Mk-423 30-ft-long chip sample at 1-ft intervals over best appearing part of altered zone. 48 Mount Fairweather C-2 quadrangle, north shore, Geikie Inlet about 2 miles from entrance. Sulfide-bearing greenschist, apparently large. Hx-67 Selected sample. 49 Mount Fairweather C-2 quadrangle, west shore of Shag Cove near its entrance. About 7.2 miles S. 3° W. from northeast corner of quadrangle. Quartz-pyrite veins in sheared quartz-ose zone. Hx-32A Hx-32B 3-ft-long closely spaced chip sample of zone and quartz stringers. Selected sample typical of pyritic pod about 3 ft long and 6 in thick. 50 Mount Fairweather C-2 quadrangle, at a rather high elevation southwest of the head of Geikie Inlet; location doubtful. Not found during present investigation, Molybdenite associated with garnet in tactite (Smith, 1942, p. 178). No analyses. 51 Mount Fairweather C-2 quadrangle, west of Blackthorn Peak. Magnetic anomaly noted by Seitz (1959, p. 16). Not found during present investigation. No analyses. 52 Mount Fairweather C-2 quadrangle, south of Wood Lake; location doubtful. Gold placer in glacially derived gravels (Rossman, 1963b, p. K50). No analyses. 53 Mount Fairweather B-2 quadrangle; location doubtful. Gold placer claims on upper Dundas River. No analyses. 54 Mount Fairweather B-2 quadrangle, east of Brady Glacier, south of Abyss Lake. Several lenses of magnetite-rich skarn as much as 10 ft thick and 30 ft long ; minor sulfides. Mk-460A Mk—460B Selected sample of skarn. Grab sample of skarn.38 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT.. ALASKA sample data for table 9—Continued Locality Geologic setting Sample 66A- Description of sample 55 Mount Fairweather B-2 quadrangle, east of lower Brady Glacier. On faulted quartz veins as much as 8 in. thick. Probably at or near locality described by Rossman (1963b, p. K50). Mk-465 Composite grab sample from quartz veins. 56 Mount Fairweather B-2 quadrangle, on lower Brady Glacier. Float from molybdenite-bearing quartz veins reported by Smith (1942, p. 177) and by Buddington and Chapin (1929, p. 329, 330). No analyses. 57 Mount Fairweather B-2 quadrangle, south of West Arm of Dundas Bay. Gold-bearing quartz veins reported by Rossman (unpub. data) ; not found during current investigation. No analyses. 58 Mount Fairweather B-2 quadrangle, on island in West Arm of Dundas Bay. Copper-bearing hornblendite dikes cutting diorite. Hx-484A Grab sample of copper-bearing hornblendite. 59 Mount Fairweather B-2 quadrangle, outwash of Brady Glacier. Placer-gold deposits reported by Rossman (1963b, p. K50). No analyses. 60 Mount Fairweather D-3 quadrangle, west of Rendu Inlet. Molybdenite-bearing quartz veins, less than 2 in. thick, with minor chal-copyrite and pyrite. No analyses. 61 Mount Fairweather D-3 quadrangle on north side of Russel Island. Two quartz-calcite veins, 3-5 in. thick, within a 3-ft-thick altered zone cutting granodiorite. Ov-2041 Selected sample of quartz veins. 62 Mount Fairweather D-3 quadrangle, on west side of Tarr Inlet. Several copper-bearing quartz-calcite veins as much as 6 in. thick within a 6-ft-thick zone of hornblende diorite pegmatite. Fd-428B Grab sample of veins. 63 Mount Fairweather D-3 quadrangle, west of Tarr Inlet. Altered pale-green quartz monzonite with local disseminated sulfides and sulfide-bearing veinlets. Hx-391 Grab sample containing sulfides. 64 Mount Fairweather D-3 quadrangle, north shore of Johns Hopkins Inlet near west edge of quadrangle and extending into Mount Fairweather D-4 quadrangle. Altered zones between 3 and 100 ft wide in metamorphic, intrusive, and volcanic rocks. Mk-396 Mk-399 Mk-521 Mk-522 Mk-524 Mk-525 Mk-527 Mk-528 Grab sample from an altered zone about 100 ft wide. 8-ft-long chip sample at 6-in. intervals. 40-ft-long chip sample at 1-ft intervals. Selected sample of pyrite-rich part of altered zone. 75-ft-long chip sample at 1-ft intervals. Chip sample at 1-ft intervals across 10 ft of altered zone of Mk-524 nearest contact with granodiorite. 10-ft-long chip sample at 6-in. intervals. Grab sample representative of richest appearing part of a 30-ft-wide alteration zone. 65 Mount Fairweather D-3 quadrangle, south of Johns Hopkins Inlet west of Lamplugh Glacier. Altered granitic rocks with copper stained fractures; altered zone is about 200 ft wide and extends several hundred feet along strike. Fd-397 Composite grab sample. 66 Mount Fairweather D-3 quadrangle, west of Lamplugh Glacier. Hornfels containing disseminated pyrite, appears to be part of extensive iron-stained area on southwest flank of Mount Cooper. Fd-382B Composite grab sample. 67 Mount Fairweather D-3 quadrangle, southwest of Lamplugh Glacier. Copper-stained hornfels cut by a few quartz veins. Altered zone is more than a half mile long and a quarter of a mile wide. Fd-433A Fd-433B Selected samples of a pyritic quartz vein. Selected sample of copper-stained hornfels. 68 Mount Fairweather D-3 quadrangle, west of the head of Lamplugh Glacier. Altered zone 60 ft thick at contact between intrusive and metamorphic rocks. Ov-1903B Selected sample of best appearing material in altered zone. 69 Mount Fairweather D-3 quadrangle, east of Reid Glacier. Altered zones as much as 25 ft thick and a few narrow quartz veins in strongly folded metamorphic rocks, mainly marble. Mk-566 Mk-567 Mk-568 Grab sample representative of 10-ft-thick altered zone. Grab sample representative of a 15-ft-thick altered zone. Float from quartz vein. 70 Mount Fairweather D-3 quadrangle, near south end of ridge west of Reid Glacier. Altered zones as much as 6 ft thick in metamorphic rocks; a few quartz veins between 6 in and 4 ft thick. Mk-366 Mk-368 5-ft-long chip sample at 4-in. intervals. 2-ft-long channel sample across a quartz vein. 71 Mount Fairweather C-3 quadrangle, east of Brady Galcier, south of the head of Reid Inlet. Several widely spaced iron-stained alteration zones between 5 and 10 ft thick within a schist and hornfels sequence. Mk-564 Fd-400A Grab sample representative of an 8-ft-thick altered zone. Selected sample of best appearing mineralized part of alteration zone. 72 Brady Glacier nickel-copper prospect, on nunatak in Brady Glacier in the southwestern part of Mount Fairweather C-3 quadrangle. Layered mafic and ultramafic intrusive rocks with disseminated and massive sulfides. (See fig. 18.) 73 Mount Fairweather B-3 quadrangle, on Astrolabe Peninsula. Magnetite- and ilmenite-bearing layered mafic intrusive rocks, widespread but mainly throughout a stratigraphic interval of about 1,000 ft (Rossman, 1963a, p. F44) METALLIC COMMODITIES 39 sample data for table 9—Continued Locality Geologic setting Sample 66A- Description of sample 74 Mount Fairweather D-4 quadrangle, on south shore of Johns Hopkins Inlet west of Lamplugh Glacier. Oxidized pyrite-bearing igneous complex about a quarter of a mile wide. Mk-565 Composite grab sample. 75 Mount Fairweather D-4 quadrangle, south shore of Johns Hopkins Inlet east of Hoonah Glacier. Pyritic hornfels between 4 and 6 ft thick. Fd-402 Composite grab sample. 76 Mount Fairweather D-4 quadrangle, northwest shore of Johns Hopkins Inlet. Hornfels with disseminated sulfides throughout an extensive zone. Mk-531 Representative grab sample. 77 Mount Fairweather D-4 quadrangle, south of Johns Hopkins Inlet, east of Hoonah Glacier. Large altered zone (several hundred feet thick) in hornfels near intrusive contact. Bd-702A Bd-702C Composite grab sample of sulfide-bearing hornfels. Composite grab sample of hornfels with gray sulfides. 78 Mount Fairweather C-4 quadrangle, both east and west of North Cril-lon Glacier. Copper-stained amphibolite (Rossman, unpub. notes). 79 Mount Fairweather C-4 and questionably C—5 quadrangle, northwest edge of Crillon-LaPerouse stock adjacent to North Crillon Glacier. Layered mafic intrusive rocks in contact with schist (Rossman, 1963a, p. F42, F43; Kennedy and Walton, 1946, p. 67-72). 80 Mount Fairweather C-4 and C-5 quadrangles, near contact of Crillon-LaPerouse stock adjacent to South Crillon Glacier. Layered mafic intrusive rocks near contact with metamorphic rocks (Rossman, 1963a, p. F42-F43 ; Kennedy and Walton, 1946, p. 71). 81 Mount Fairweather B-4 and C-4 quadrangles ; location doubtful, Oregon King claims. 36 placer claims north of LaPerouse Glacier (Alaska Div. Mines and Minerals, written commun.) 82 Mount Fairweather B-4 quadrangle, about 3 miles northwest of Mount Marchainville. Large copper-stained zone in gneiss near intrusive contact (Rossman, unpub. notes). 83 Mount Fairweather B-4 quadrangle, about 2V2 miles north of Mount Marchainville. Iron-stained zones in layered mafic intrusive rocks near contact with metamorphic rocks (Rossman, unpub. data. 84 Mount Fairweather C-5 quadrangle, southwest shore of southeast arm of Lituya Bay. Sulfides replacing dike (Kennedy and Walton, 1946, p. 71). 85 Mount Fairweather C-5 quadrangle, southeast of Lituya Bay. Hydrothermally altered zones with minor gold values (Rossman, 1959, p. 57, 58). 86 Mount Fairweather C-5 quadrangle, moraine on North Crillon Glacier. Copper-bearing float in moraine (Kennedy and Walton, 1946, p. 71). 87 Mount Fairweather C-5 quadrangle, south of mouth of Lituya Bay. Beach placers (Rossman, 1963a, p. F45-F46; Rossman, 1957 ; Martin, 1933, p. 133-135). 88 Mount Fairweather C-6 quadrangle, north of mouth of Lituya Bay. Beach placers (Rossman, 1963a, p. F45-F47; Rossman, 1957; Martin, 1933, p. 133-135). 12, sample Bd-280), probably as a constituent of a lead-bearing sulfosalt; the other, from the Francis Island copper deposit (loc. 28, sample Hf-183B), contained 200 ppm antimony. Tetrahedrite has been reported from the prospect on the west side of Willoughby Island (loc. 27) (Reed, 1938, p. 72), from the Rendu Inlet silver prospect (37) (A. F. Buddington, unpub. data, 1924) (Rossman, 1963b, p. K48, K49), and from Blue Mouse Cove on the south shore of Gilbert Island (42) (Rossman, 1963b, p. K50). Buddington (1924, unpub. notes) also reported jamesonite from the prospect on the west side of Willoughby Island and noted that an ore sample from there contained 25 percent antimony. L. F. Parker (oral commun., 1966) states that one of his samples from the north side of Johns Hopkins Inlet near locality 64 that was assayed by the State (then Territorial) Division of Mines and Minerals contained several percent antimony. None of our samples from that general vicinity contained antimony. ARSENIC Arsenic was detected in samples from many localities in the monument. It is particularly abundant in the Reid Inlet gold area (pi. 1) as a constituent of arsenopyrite that is associated with the gold lodes. Arsenic was also found in the Mount Brack argentiferous base-metals deposits (loc. 12), the Margerie copper prospect (19), on the west side of Tarr Inlet (17), and at a locality west of McBride Glacier (10). Most of the accessible Reid Inlet gold deposits contain arsenic, which occurs commonly or entirely in arsenopyrite. The arsenic content of samples from the LeRoy mine (table 11, loc. B) is as much as 20,-000 ppm. Samples from the Rainbow mine (C) contained as much as 1,500 ppm arsenic, and those from40 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA the Monarch mines (E) the Incas mine (G), and the Rambler prospect (L), respectively, contained maxima of 7,000, 20,000, and 50,000 ppm arsenic. Minor amounts of arsenopyrite are reported from the gold quartz veins of the Sunrise prospect east of Reid Inlet (Reed, 1938, p. 64). An unidentified arsenic mineral was collected from a narrow vein on the eastern shore of Reid Inlet (Rossman, 1959, p. 57). Arsenopyrite is also a probable accessory mineral in the unsampled and inaccessible gold lodes near Reid Inlet, whose geologic settings are similar to those of nearby arsenic-bearing deposits. Two samples from the Mount Brack deposits (table 9, loc. 12) contained 7,000 and 30,000 ppm arsenic, respectively. These samples represent complex silver-bearing base-metal deposits, but the mineral host for the arsenic was not determined. A sample from a quartz vein at the Margerie copper prospect (19) carried more than 10 percent arsenic. Another sample from the same vein contained 50,000 ppm arsenic, and a sample from a nearby altered zone revealed 2,000 ppm arsenic. Arsenic at the Margerie prospect is incorporated in arsenopyrite. An altered zone on the west side of Tarr Inlet (17) south of the Margerie Glacier contained 5,000 ppm arsenic. Arsenic in quantities of 7,000 and 15,000 ppm was detected from a deposit localized at a facies change between marble and phyllite west of McBride Glacier (10). Lollingite, an iron diarsenide, was questionably identified from the prospect on the northeast side of Willoughby Island (table 9, loc. 26) (Reed, 1938, p. 70, 71). Minor amounts of arsenic are reported in spectrographic analyses of the tactite that crops out south of Mount Merriam in the Mount Fairweather D-2 quadrangle (Rossman, 1963b, p. K41). Many of the arsenic-bearing deposits are associated with gold and silver, and, as often is the case, the arsenic minerals may serve as useful indicators in prospecting for those precious metals. BISMUTH Small amounts of bismuth were detected in samples from 12 localities (pi. 1; tables 9, 11). The highest bismuth contents shown by the analyses were 500 ppm from the Sandy Cove gold-copper prospect (loc. 7), 300 ppm from the Margerie copper prospect (19), 200 ppm from the Alaska Chief copper prospect (29), and 150 ppm from the Francis Island copper prospect (28). No bismuth-bearing minerals were identified, but bismuth is probably a minor constituent of some of the sulfides or sulfosalts. CADMIUM Cadmium was detected from four localities in the monument (tables 9, 11): the Mount Brack argentiferous base-metal deposits (loc. 12), sulfide lenses southwest of Red Mountain (20), the LeRoy mine (B), and the copper-zinc deposits north of White Glacier (6). The most cadmium found, 1,000 ppm, was in a sample from the LeRoy mine. Cadmium proxies for zinc geochemically, and all the cadmiumbearing samples contained larger amounts of zinc than of cadmium. Probably most of the cadmium is a minor constituent of sphalerite, but possibly some of it forms the cadmium sulfide greenockite. COPPER DISTRIBUTION Copper minerals are widespread and locally abundant throughout the monument (pi. 1). Among the previously known deposits whose major commodity is copper are those on the west side of Tarr Inlet (loc. 18), at the Margerie prospect (19), on Willoughby Island (26, 27), on Francis Island (28), at the Alaska Chief prospect (29), and at several localities in the Fairweather Range (78, 80, 82). In addition, copper constitutes a potential byproduct at the Brady Glacier nickel-copper deposit (72), the Nuna-tak molybdenum prospect (21), the Sandy Cove gold-copper prospect (7), and the Rendu Inlet silver prospect (37). Most of the discoveries resulting from our investigations contain anomalous concentrations of copper. The most significant of these are north of White Glacier (pi. 1, loc. 6), near Gable Mountain (14), south of Rendu Glacier (15), near Dundas Bay (31), in the Bruce Hills (34), west of Shag Cove (49), and west of Tarr Inlet (62, 63). TYPES OF DEPOSITS The copper lodes occur in diverse types of deposits in several different geologic environments; they include (1) altered zones, mainly mineralized fault zones, (2) massive sulfide bodies, (3) veins, (4) fracture coatings, (5) local disseminations, (6) con-tact-metamorphic deposits, and (7) low-grade copper-bearing amygdaloid. A clear distinction of type is impossible for many deposits because of intergradation of types. Typical examples of these types are described below. Deposits in altered fault zones are best exemplified by those east of Dundas Bay (pi. 1, loc. 31). The massive sulfide deposits are diverse and include replacements in metamorphic rocks as at the Alaska Chief prospect (29), the nickel-copper lenses in gabbro at the Brady Glacier prospect, and the cupriferous pyrrhotite-rich lenses (?) at the Mar-METALLIC COMMODITIES 41 gerie prospect (19). The copper-bearing veins are widely distributed but are generally narrow. They are predominantly quartz veins, but some contain moderate quantities of calcite. The gold-bearing veins at the Sandy Cove prospect (7) carry good copper values, and many other veins in the monument are enriched in copper. Stockworks of closely spaced veins and veinlets in bleached and altered metamorphic and intrusive rocks at the Nunatak molybdenum prospect (21) form deposits that are similar to some porphyry copper deposits. Similar stockworks form parts of the Bruce Hills deposit (34) and parts of the deposits at and near the southwestern end of Gilbert Island (44, 45). Copper minerals coat fractures at the deposit at Gable Mountain (14) and at a few other deposits. Disseminated copper minerals were noted in granodiorite in the Bruce Hills (34), in siliceous lenses west of Tan-Inlet (63), in hornblendite dikes near Dundas Bay (58), and in hornfels at a few localities near Johns Hopkins Inlet (75, 76). Copper minerals are sub-ordinant constituents of some of the skarns, as at the Queen Inlet magnetite deposit (40) and the deposit south of Abyss Lake (54). A very lean copper deposit is localized in the amygdaloid on the north shore of Adams Inlet (5). In general, the deposits range in size from isolated veins and lenses only a few inches thick, through sulfide bodies a few tens of feet in minimum dimension, to extensive networks of veins and mineralized zones that are several hundred feet wide. The deposits are in many different geologic settings, but most of them are in or near intrusive rocks. Chalcopyrite is the predominant copper mineral in almost all the deposits. Bornite or tetrahedrite is the chief ore mineral in a few of the deposits and subordinate associates of chalcopyrite in several others. Secondary copper minerals, chiefly azurite, malachite, and chrysocolla, are sparsely distributed in a few of the lodes. DESCRIPTIONS OF DEPOSITS Mount Young Area Several small base-metal and silver deposits occur near Mount Young (pi. 1, loc. 1). Only two of our samples from these deposits showed anomalous amounts of metals, and in these the minor zinc and silver values outweigh those of copper. However, the deposits are discussed under copper because some of them contain chalcopyrite and because copper minerals have been reported nearby. The deposits are in a geologically complex area characterized by a variety of metamorphic rocks, small granitic plutons, and mafic dikes. The highest analytical results were from a sample consisting of sulfides, chiefly pyrite, replacing metavolcanic rocks and from a sample of altered hornfels and slate (table 9, loc. 1). These samples contained as much as 1,500 ppm zinc and slightly anomalous amounts of silver, chromium, copper, molybdenum, and lead. The deposits consist of short quartz veins that commonly are less than 6 inches thick and numerous altered zones, commonly about 2 feet thick, which were traceable for only a few tens of feet because of contiguous ice and snow. A few altered zones are as much as 10 feet thick and are exposed for about 100 feet. The altered zones transect metavolcanic rocks, schist, hornfels, slate, and marble; a few zones are localized along the margins of mafic dikes that cut the metamorphic rocks. The altered zones consist of hydrous iron sesquioxides, carbonate minerals, and quartz; subordinate pyrite, traces of chalcopyrite, probably a secondary zinc mineral, barite, and clay minerals are also present. The quartz veins are best developed in the schist. They also occur in the other metamorphic rocks, along the margins of dikes, and as ladder veins within the dikes. Commonly, the veins contain minor amounts of pyrite and, rarely, traces of chalcopyrite. Assays of samples from three of the quartz veins all showed less than 0.0015 ounce per ton gold. Several iron-stained ankeritic altered zones between 5 and 30 feet thick cut granitic rocks near locality 2, about 3.5 miles northwest of Mount Young (pi. 1). Samples from these zones contained slightly anomalous amounts of copper and molybdenum (table 9, loc. 2) and less than 0.0015 ounce per ton gold. Copper minerals have been reported near Mount Young and in samples taken a few miles west of Mount Young (Lathram and others, 1959, their Nos. 18, 20). The deposits near Mount Young which were examined are too lean to be of economic importance, but the abundant weak mineralization and concealment of much of the bedrock by snow and ice might warrant additional prospecting during a relatively snow-free summer or prospecting by geophysical methods. East of Casement Glacier Several altered zones cut the granitic rocks near the southeast edge of casement Glacier (pi. 1, loc. 4). These zones are 5-30 feet thick and probably are mineralized fault zones. They are best developed near contacts between the granitic rocks and hornfels. The zones contain scattered pyrite and an array of oxidized gangue minerals. Analyses of representative samples of these altered zones shows only42 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA slightly anomalous amounts of copper and molybdenum (table 9, loc. 4). Many conspicuous altered zones as much as 50 feet thick occur near Snow Dome, about 5 miles northeast of locality 4 (pi. 1). They are mainly localized near contacts between granitic rocks and hornfels. Samples collected from these zones were virtually barren of ore metals. North Shore of Adams Inlet Weakly mineralized amygdaloidal lavas are exposed for about 500 feet along the north shore of Adams Inlet (pi. 1 loc. 5). A few steeply dipping mafic dikes cut the lavas. The lavas are flows of amygdaloidal and vesicular altered basalt as much as 15 feet thick. They are prophyritic with plagioclase (labradorite) phenocrysts in a highly altered very fine grained groundmass that probably orignally was intergranular or intersertal. Phenocrysts constitute about a third of the rock and are as much as 6 mm long, but typically about 3 mm long. The altered groundmass is composed of epidote, actino-lite, and lesser amounts of calcite, dolomite, and chlorite. Minor amounts of pyrite are scattered throughout the lavas. All the lavas are weakly mineralized by sulfides, most of which are localized along fractures and generally are most abundant near the dikes. The sulfides, which probably formed during the low-grade metamorphism of the lavas, consist of pyrite and trace amounts of chalcopyrite and pyrrhotite( ?). Extensive sampling showed that the lavas are very low in metal content (table 9, loc. 5). All the samples contained slightly anomalous amounts of copper; one sample contained 300 ppm cobalt. Most samples contained trace amounts of molybdenum; one contained silver and tin. The mafic dikes are also altered basalts, but they are more intensely altered than the lavas. They are porphyritic and consist of medium-grained plagioclase phenocrysts in a highly altered, very fine grained groundmass. The phenocrysts are probably oligoclase, and their cores are generally more altered than their rims. The goundmass is predominantly epidote and actinolite, but it contains small amounts of calcite, chlorite, and leucoxene. Pyrite and subordinate ilmenite and magnetite are scattered throughout the dikes. North of White Glacier Many mineralized zones are exposed north and northeast of a northward protruding lobe of White Glacier (pi. 1, loc. 6). These zones cut both limestone and the structurally overlying volcanic rocks. Some zones are near mafic dikes and a small granitic cupola that cuts the limestone. The altered zones in the limestone are less than 10 feet thick and generally not traceable for more than 100 feet. Those in the volcanic rocks are less numerous but larger and range in thickness from 2 to 200 feet; some of them can be traced for long distances. The altered zones in the limestone contain abundant ankeritic carbonates and barite and lesser amounts of quartz, chlorite, pyrite, and copper minerals. Parallel sets of quartz veins between 1 and 4 inches thick transect some of the zones. Several zones are parallel to mafic dikes, and a few are cut by mafic dikes. The sulfide mineralization commonly is strongest near the borders of the dikes. Thin pyritic lenses occur on bedding surfaces in the limestone contiguous to the altered zones. Analyses of samples from altered zones that cut the limestone are shown in table 9 (loc. 6 Nos. 66AMk-253 through 256B). These zones locally carry significant amounts of copper and minor amounts of silver, zinc, and cadmium. Their gold content is negligible. The altered zones in the volcanic rocks are conspicuously iron stained. A few locally contain abundant pyrite. A 6-foot-long chip sample representative of one of these zones carried 20,000 ppm zinc (table 9, loc. 4 No.66AMk-257). The host mineral for the zinc was not identified. Gold values in samples from these zones were negligible. The deposits north of White Glacier appear to be locally rich enough and large enough to warrant prospecting. A few altered zones south of White Glacier south of locality 8 were examined, but samples from them yielded negative results. North of York Creek About 15 widely spaced pyrite-rich veins and altered zones containing pods of pyrite cut the hornfels country rock north of York Creek (pi. 1, loc 8). A sample representative of the hornfels consists mainly of quartz and tremolite and moderate amounts of plagioclase and minor biotite. Both the veins and the altered zones commonly strike betweeen N. 10° E. and N. 40° E. and dip steeply. They both consist mainly of quartz and smaller quantities of pyrite, pyrrhotite, and dolomite. Most of the veins are about 6 inches thick. A sample representative of one vein (table 9, loc. 8) contained 1,500 ppm copper and small amounts of cobalt and nickel. Some of the altered zones are brecciated, and some attain widths of about 50 feet. A chip sample across one of the altered zones (table 9, loc. 8) carried 15 ppm of molybdenum. The deposits north of York Creek are too small or too lean to justify exploration.METALLIC COMMODITIES 43 Minnesota Ridge Copper minerals were found on Minnesota Ridge in a small outcrop within an extensive snowfield (pi. 1, loc. 13). The outcrop is composed of coarse-grained biotite-hornblende granodiorite or quartz diorite that is cut by a 3-foot-thick porphyritic andesite dike. The deposit consists of pyrite, chalcopyrite, and secondary copper or iron minerals that were probably deposited as open-space fillings along narrow joints with subordinate replacement of the adjacent wall-rock. A sample of the richest appearing mineralized material contained 700 ppm copper (table 9, loc. 13). The size of the deposit is conjectural because of the snow cover, but the deposit is too low in grade to encourage exploration. Gable Mountain Outcrops of coarse-grained dioritic rocks, probably quartz diorite, are exposed irregularly in a largely snow-covered area near Gable Mountain north of Carrol Glacier (pi. 1, loc. 14). The deposits consist of joint coatings of unknown extent. The chief copper minerals are malachite and chrysocolla. A composite grab sample from the deposits contained 1,000 ppm copper and small amounts of silver and molybdenum (table 9, loc. 14). Remoteness, difficult access, and snow cover will inhibit the prospecting of these deposits. South of Rendu Glacier A mineralized altered zone is exposed at altitudes near 4,000 feet in the cliffs south of Rendu Glacier (pi. 1, loc. 15). The zone cannot be reached without a difficult rock climb, and, consequently, it was not examined closely. In aerial reconnaissance the altered zone appears to be in mixed rocks near the contact with a light-gray granitic pluton. It is exposed over a surface about 50 by 200 feet. The margins of the zone are partly concealed, and its actual dimensions may be much larger. A sample of float from the altered zone carried 2,000 ppm copper (table 9, loc. 15). A thorough examination of the deposit, including detailed sampling, is probably warranted despite the deposit’s inhospitable setting and remoteness. West Shore of Tarr Inlet Copper lodes occur on the west side of Tarr Inlet about a mile south of Margerie Glacier (pi. 1, loc. 18). The deposits are fairly extensive and consist of alteration zones between 1 and 8 feet thick and local disseminated sulfides in hornfels. Chalcopyrite is the predominant copper mineral; it generally is associated with more abundant pyrite. A sample indicative of one of the best mineralized outcrops contained 1,500 ppm copper and minor amounts of bismuth, tungsten, and tin (table 9, loc. 18). This lo- cality is probably at or near two lode claims for copper that are held by the Kenney Presbyterian Home, but no workings or claim markers were found in the vicinity. Claims on copper lodes were reportedly staked in the general area before 1906 (Wright and Wright, 1937, p. 221). A stream-sediment sample collected a few hundred feet south of locality 18 (see pi. 8) contained 700 ppm copper, 0.29 ounce per ton (10 ppm) silver, 10 ppm molybdenum, 10 ppm bismuth, 50 ppm cadmium, 30 ppm arsenic, 200 ppm lead, 500 ppm tin, and 1,000 ppm zinc. The mineralized zones are fairly widespread, and further exploration might be worthwhile. Margerie Prospect The Margerie prospect is in steep and rugged terrain south of Margerie Glacier at altitudes between 1,500 and 2,000 feet (pi. 1, loc. 19). The prospect is on several claims located in 1960 for the Moneta Porcupine Co. The deposits are in light-colored granodiorite and nearby high-rank metamorphic rocks, chiefly hornfelses. They consist of quartz veins, mineralized shear zones, and pyrrhotite-rich massive sulfide bodies. The quartz veins, which are as much as 2 feet thick, commonly strike northeast and dip gently south. Their chief sulfide minerals are arsenopyrite and chalcopyrite. Samples from the quartz veins carry as much as 2,000 ppm copper, more than 10 percent arsenic, minor amounts of bismuth, cobalt, and tungsten, traces of molybdenum, and as much as 0.145 ounce per ton (5 ppm) gold (table 9, loc. 19). The altered zones strike about N. 30° W. and dip steeply to the southwest. They are about 6 feet thick and strongly sheared. Many of the nearby joints are coated with the alteration products and probably contain minor quantities or ore minerals. The altered zones are profusely iron stained, and their constituent minerals were not identifiable megascopically. Samples from the altered zones contained as much as 700 ppm copper and 2,000 ppm arsenic and slightly anomalous amounts of barium (table 9, loc. 19). The massive sulfides were not found in place, but judging from float, they probably occur in the steep cliffs south of the prospect. The float is predominantly pyrrhotite associated with minor chalcopyrite, quartz, and an unidentified tungsten mineral. A sample of the massive sulfide contained 3,000 ppm copper and 3,000 ppm tungsten, the highest tungsten value of any of our samples (table 9, loc. 19). The examination of the prospect was brief because of inclement weather. The prospect and its environs warrant a more thorough examination.44 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Curtis Hills Several small mineral deposits were found in the recently deglaciated terrain west of the Curtis Hills (pi. 1, loc. 23). Hornfels is the predominant rock in the area; it is cut by a few steep mafic dikes and locally mantled by glacial drift and snow. The hornfels is composed largely of tremolite and lesser amounts of plagioclase, calcite, and quartz. The deposits consist of narrow quartz veins, commonly less than 6 inches thick, and of altered zones, generally less than 2 feet thick. Many of the quartz veins are joint fillings. Pyrite is the only sulfide mineral recognized in both the veins and the altered zones. Some of the deposits contain minor amounts of copper and chromium (table 9, loc. 23). Although the area is almost virgin because of its recent denudation, the deposits in it appear to be too small and too lean to encourage prospecting. North Marble Island North Marble Island (pi. 1, loc. 24) consists of massive white marble cut by a few mafic dikes. Most of the marble is fairly pure and consists of a mosaic of calcite crystals from 2-5 mm long. Some of the marble is dolomitic. The only sulfide mineral noted is pyrite that occurs disseminated in some of the dikes and in the silicified zones adjacent to the dikes. Reed (1938, p. 69) reports sulfide bodies as much as 11/2 feet thick and 15 feet long in the marble near some of the dikes and small deposits locally along the dikes and in joints within the dikes. He states that the sulfide deposits contain pyrite, pyrrhotite, chalcopyrite, and covellite. Buddington (unpub. data, 1924) reported a claim staked for nickel on North Marble Island. Rossman (1963b, p. K51) mentions a mass of sphalerite and magnetite which occurs in the limestone (marble) on North Marble Island. South Marble Island South Marble Island (pi. 1, loc. 25) is composed of medium-grained white marble cut by numerous mafic dikes. The marble is fairly pure and consists almost entirely of an interlocking network of calcite crystals. The dikes are more numerous and thicker than those on North Marble Island. Most of them strike northwest and dip northeast at moderate angles. The largest dike is about 50 feet thick and is characterized by very fine grained chilled basaltic borders and medium-grained gabbroic interiors. A thin section from the core of the largest dike reveals the rock to be equigranular with an average crystal size of about 2 mm. The thin section consists of about 55 percent labradorite and 30 percent pyroxene; the labradorite is slightly normally zoned. Both augite and pigeonite are present. Pyroxene rims are altered to green hornblende, which constitutes about 10 percent of the rock. Magnetite is a minor primary accessory mineral, and a little sericite is an alteration product of the plagioclase. The mineral deposits are associated with the largest dikes and consist of disseminated pyrite within the dikes and pyrite-rich impregnations in the silicified wallrock near borders of the dikes. A few barren calcite veins cut some of the dikes. Samples from the deposits were all low grade and contained only slightly anomalous amounts of copper and nickel (table 9, loc. 25). Reed (1938, p. 69) states that the sulfide mineralization on South Marble Island is similar to that on North Marble Island but appears to be less intense. Willoughby Island Willoughby Island is underlain by massive light-gray limestone that has been locally converted to marble and is cut by many mafic dikes and a few felsic dikes. Glacial drift mantles some of the northeastern part of the island. Both the mafic and felsic dikes are very fine grained. The mafic dikes are 2-30 feet thick and retain relict pilotaxitic textures, but their original glassy groundmasses have been devit-rified. They consist of labradorite microphenocrysts and andesine microlites associated with an array of very fine grained minerals including chlorite, potassium-feldspar (?), cristobalite(?), opaque dust, and calcite. Their primary mafic minerals have been obliterated. Reed (1938r p. 72) reports that one of the mafic dikes from a prospect on the west side of the island consists mainly of andesine with considerable chlorite, quartz, pyroxene, and magnetite, and a little calcite. The felsic dikes consist chiefly of quartz and plagioclase. Minor amounts of oxidized, hydrothermally altered material occupy thin breccia zones contiguous to some of the mafic dikes and in the limestone and marble. Two pi-ospects are reportedly on Willoughby Island (Reed, 1938, p. 70), but despite an intensive search, neither was found. One of the reported prospects is on the northeast side of the island at an altitude of about 750 feet (pi. 1, loc. 26); the other is on the west side of the island at an altitude of about 450 feet (pi. 1, loc. 27). The northeastern part of the island is covered with dense brush, and the western part is rugged and in places covered with slide debris. According to Reed (1938, p. 70, 71), the prospect on the northeastern part of the island (pi. 1, loc. 26)METALLIC COMMODITIES 45 is apparently a sulfide replacement of limestone; that is, the deposit consists of massive pyrite with subordinate chalcopyrite and lollingite( ?), exposed over an area 15 by 5 feet and for a height of 15 feet. One end of the deposit was covered with talus (Reed, 1938, p. 70, fig. 5). At least three other similar deposits have been reported from the northeastern part of the island. The prospect (loc. 27) on the west side of the island is ambiguously reported to be both about 2 miles and about l-% miles south of the northwest tip of the island (Reed, 1938, p. 70, 71). The prospect is in marble near two intersecting lamprophyre (mafic) dikes (Reed, 1938, p. 71, fig. 6). The ore forms irregular pods or kidneys along intersections of the dikes and thin veins along the dike contacts or along joints in the marble. It consists of chalcopyrite, pyrite, tetrahedrite, and an unidentified sulfide mineral. Reed (1938, p. 72) states that prospecting downward along the dike intersections might be justified. Buddington (unpub. data, 1924) reports that a sample probably from this deposit assayed 25 percent lead, 25 percent antimony, 1.74 ounces per ton gold, and 42 ounces per ton silver. It is not known whether this sample represents selected high-grade specimens or is representative of the vein material. Buddington (unpub. data, 1924) also reports jamesonite from an unspecified locality on the west side of Willoughby Island. Francis Island A copper-zinc-silver deposit is near the contact of quartz diorite and the predominantly marble country rock near the southwestern shore of Francis Island (pi. 1, loc. 28; fig. 8) near a prospect described by Buddington (unpub. data, 1924) that is now concealed by landslide debris. Outcrops are good in the nearshore cliffs but are sparse toward the interior of the island because of dense vegetation. The quartz diorite is a coarse- to medium-grained rock that is hypidiomorphic granular in texture. It consists largely of plagioclase with calcic andesine cores and calcic oligoclase exteriors. Reddish-brown biotite and green hornblende are characteristic accessory minerals, and quartz is a minor interstitial phase. Magnetite is a minor accessory mineral. Pyrite is sparsely distributed in some of the quartz diorite, and in places is altered to hematite. Narrow seams of tremolite are irregularly distributed in some of the marble, and its presence, together with the coarseness of the marble, indicates that a pluton probably underlies the island at shallow depths. The quartz diorite intrudes the marble, and its irregular salients cut the marble in a few places (fig. 8). A contact-metamorphic aureole consisting of tactite and hornfels as much as 5 feet thick has formed in the marble adjacent to the intrusive. The tactite consists largely of garnet and pyroxene, the hornfels, of tremolite and chlorite. A brecciated, sheared, and silicified fault zone separates the quartz diorite and the tactite at the site of the deposit (fig. 8). The fault zone is as much as 10 feet wide, but because of cover, it can be traced on the surface for only about 50 feet. The ore minerals are irregularly distributed along the fault zone and comprise chalcopyrite, bornite, malachite, sphalerite!?), tetrahedrite!?), and chalcocite(?); all are associated with pyrite, secondary iron minerals, and pyrolusite( ?). Samples from the fault zone contained as much as 7,000 ppm copper, 1,000 ppm zinc, 200 ppm antimony, 150 ppm bismuth, and 1.46 ounces per ton (50 ppm) silver (table 9, loc. 28). Buddington (unpub. data, 1924) visited the prospect and reported that a small pocket of bornite with gold and silver values was found in the garnet-rich contact rock and that a quartz diorite dike was locally impregnated with pyrite and pyrrhotite. A semiquantitative spectrographic analyses of an azonal soil sample collected during our initial examination of Francis Island contained abnormal amounts of copper, zinc, silver, and nickel and instigated the subsequent geochemical survey. Results of the survey are shown in figure 8. THM tests of soil samples collected during the survey (fig. 8) indicate that the ore mineralization is localized along the fault zone near the probable site of the prospect. Prospecting the shear zone might be warranted, but indications are that the deposit in small. Alaska Chief Prospect The Alaska Chief prospect is at an altitude of 1,150 feet in the mountains northwest of the mouth of Glacier Bay (pi. 1, loc. 29). The prospect was staked before 1906 and patented in 1924. It is on a densely vegetated steep hillside and formerly was accessible by a 2-mile-long trail from the beach, now badly overgrown and in disrepair. The prospect consists of a cleared and scraped area of about 150 by 55 feet in maximum dimensions and a short southtrending adit (fig. 9). Sulfide-rich bedrock has retarded reestablishment of vegetation in the cleared area. The Wrights (1937, p. 221, 222) report that a tunnel (adit) 130 feet long was driven from a point 60 feet beneath the surface workings, but neither the writers nor Reed (1938, p. 37), who examined the property in the 1930’s, was able to find the tunnel.46 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Fault, approximately located 161 P 20 Soil-sample site Number above line is sample number; number below line is total heavy-ntHal content (in parts per million). Tail on circle indicates slope of land surface. Semi-quantitative spectrographic analyses are given in table 9 Mapped by L. C. Huff and R. J. Wehr, July 1966 Figure 8.—Geologic sketch map of Francis Island prospect, showing geochemical sample locations. The prospect is in calcareous contact rocks east of a granodiorite pluton that is associated with subordinate diorite. The intrusive contact and the bedding in the metamorphic rocks strike about N. 30° W. and dip steeply to the southwest. The metamorphic rocks are chiefly hornfels with subordinate tactite and marble. The hornfels consists mainly of plagio-clase, quartz, amphibole, garnet, and chlorite. TheMETALLIC COMMODITIES 47 tactite contains a similar mineral assemblage, but its predominant constituent is a grossularite-rich garnet. Reed (1938, p. 72) states that the contact rock consists mostly of zoisite and epidote but includes chlorite and calcite, and that the marble carries considerable quantities of chlorite, orthoclase, and quartz. The Wrights (1937, p. 221) also report calcareous argillite in the vicinity of the deposits. The deposit is exposed over the entire extent of the cleared area and intermittently in the adit (fig. 9). It consists of massive sulfide replace- ments of the metamorphic rocks. The Wrights (1937, p. 221, 222) state that some of the mineralization consists of calcite veinlets along bedding planes and that the peripheral parts of the intrusive are locally mineralized. Reed (1938, p. 73) notes that mineralization less intense than that manifested in the cleared area extends over a wide area. Efforts to ascertain the extent of the deposit were unsuccessful because of the dense vegetation. The deposit’s surface exposures locally consist of a gossan. Sulfide minerals in the deposit are pyrite, pyrrhotite, Portal of adit i \ ' ■» 66AMk-471 MAP OF ADIT A % EXPLANATION Mapped by E. M. MacKevett, Jr., and H. C. Cornwall, August 6, 1966 Area covered chiefly by vegetation Metamorphic rocks, chiefly homfels Cleared area underlain by gossan and massive sulfides Contact, approximately located Rim of cut, locally coincides with contact 0 40 FEET 1 ____I I --------1-----1 CONTOUR INTERVAL 10 FEET DATUM IS APPROXIMATE MEAN SEA LEVEL 66AMk-473 Location of chip sample (Sample data are given in table 9) x 66AMk-475 Location of grab sample (Sample data are given in table 9) N Figure 9.___Geologic sketch map showing sample locations at the Alaska Chief prospect.48 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA chalcopyrite, sphalerite(?), and bornite. Oxidized parts of the deposit contain malachite and little azurite along with abundant secondary iron and manganese minerals. The gangue is predominantly calcite with lesser amounts of quartz. Chip samples from the cleared area contained as much as 15,000 ppm copper, 700 ppm zinc, 0.232 ounce per ton (8ppm) gold, 4.377 ounces per ton (150 ppm) silver, and minor to trace amounts of nickel, molybdenum, bismuth, and cobalt. A grab sample from the ore pile contained more than 10 percent copper, 1,000 ppm zinc, 2.917 ounces per ton (100 ppm) silver and minor anomalous concentrations of cobalt, molybdenum, nickel, and bismuth. A soil sample collected below the cleared area contained 15,000 ppm copper, 1,500 ppm zinc, 1.46 ounces per ton (50 ppm) gold, 1.46 ounces per ton (50 ppm) silver, 300 ppm cobalt, 300 ppm bismuth, and 500 ppm nickel (see table 9, loc. 29; fig. 9.) Reserve estimates at the prospect are contingent upon estimates of the deposit’s size and configuration, neither of which is known. The deposit is exposed throughout the cleared area, which is about 150 feet long and 30 feet in average width. Assuming that the deposit extends to 50 feet beneath the surface, which is a third of its exposed length, the deposit holds 225,000 cubic feet of indicated reserves (150 by 30 by 50). About 8 cubic feet of the sulfide-rich rock would weigh a ton, and therefore the indicated reserve is 28,125 tons. The grade of this reserve as inferred by the surface sampling is slightly better than 1 percent copper. If the deposit extends to a depth of 100 feet below the surface, an additional reserve of 28,125 tons could be inferred. Additional inferred reserves of unknown tonnage and grade exist beyond the lateral limits of the cleared area and beneath the 100-foot subjacent projection of the cleared area. Negative factors to be considered in the reserve and grade estimates are that the sample taken from the adit (table 9, loc. 29, sample No. 66AMk-471) was lean and that the surface samples consisted partly of gossan, which might be richer than the unoxidized ore. Adequate reserve and grade estimates require additional exploration and more thorough sampling. The deposit justifies exploration on the basis of its indicated grade and the possibility that it is large. An exploration program consisting of diamond drilling and geophysical and geochemical methods to locate targets in the concealed areas probably is warranted. East Side of Dundas Bay Two copper-bearing deposits were found on the east side of Dundas Bay (pi. 1, Iocs. 31, 32). One deposit (31) occupies an extensive altered zone in quartz semischist that has sharp contacts with adjacent metabasalt. The altered zone is between 100 and 300 feet wide and is traceable for at least 1 mile. It strikes approximately N. 20° E. and dips steeply, and contains sporadically distributed pods of sulfides within abundant secondary iron minerals and also a few quartz veins. The sulfides are mainly pyrite and minor chalcopyrite. Malachite stains a small part of the zone. Semiquantitative spectro-graphic analyses of samples from the deposit contain as much as 2,000 ppm copper and traces of silver, molybdenum, and lead (table 9, loc. 31). The apparent size of the deposit makes it an exploration target even though its grade is somewhat low. The Wrights (1937, p. 222) state that a number of mining claims were located east of Dundas Bay for copper, lead, zinc, and gold. The other deposit (32) is in cataclastic biotite-quartz diorite that has (laser structure. It consists of copper-bearing quartz veins between 1 and 2 inches thick which have formed along foliation planes. The extent of the deposit could not be determined because of poor exposures. A sample of the quartz veins contains 1,000 ppm copper and 300 ppm molybdenum (table 9, loc. 32), but the average copper and molybdenum contents of the deposit are much smaller, because the high values are in the quartz veins, which are 1 foot or more apart. Bruce Hills The Bruce Hills deposit is in the central part of the Bruce Hills north of Plateau Glacier (pi. 1, loc. 34). The deposit is in granodiorite near a steep fault zone that strikes N. 30° E. (fig. 10). Many of the rocks near the fault zone are shattered and brecciated, and several subsidiary faults diverge from the fault zone (fig. 10). The part of the deposit that was examined occupies a spur that trends southwestward from the crest of the Bruce Hills. Rocks underlain by the fault zone are intensely shattered, heavily iron stained, and probably mineralized, but they have not been tested by sampling. The granodiorite contains a few small roof pendants of hornfels and is cut by several andesite dikes that strike about N. 70 0 E. and dip to the southeast. Surficial deposits comprising glacial till and talus partly cover the bedrock (fig. 10). The heavily iron-stained mineralized rocks are mostly altered granodiorite containing numerous sulfide-bearing thin quartz veins, disseminated sul-METALLIC COMMODITIES 49 fides, and mineralized fracture coatings. The ore minerals are associated with pyrite and (or) pyrrho-tite and include chalcoyprite, molybdenite, malachite, and minor amounts of molybdite, sphalerite, and galena. Other minerals in the deposits include mont-morillonite, chlorite, hematite, and goethite. Samples from the deposit carried as much as 3,000 ppm copper and 1,000 ppm molybdenum (table 9, loc. 34). The summit regions and north slopes of the Bruce Hills were largely snow covered at the time of the examinations, and the extent of the deposit to the northeast could not be determined. Likewise, tracing the deposit to the southwest was precluded by cover, including snow and ice. A few small outcrops along the crest of the hills northeast of the area shown in figure 10 contain chalcopyrite and molybdenite and probably represent a continuation of the deposit. Probably the molybdenite occurrence in the north-central part of the Bruce Hills reported by Rossman (1963b, p. K49, K50) is a part of the deposit. Forty-four azonal soil samples were collected at 50-foot intervals along several traverses at and near the deposit. Some of the samples were analyzed by the citrate-soluble cold THM test at the sample site, Y 40»- * f. \ v * A f ci EXPLANATION Talus and glacial till, mapped separately Andesite dike, showing dip > i-‘ A -» Granodiorite Homfels Disseminated sulfides Contact, dashed where approximate, dotted where concealed APPROXIMATE SCALE Fault, dotted where concealed 44 P 40 Soil-sample site Number above line is sample number; number below line is total heavy-metal content (in parts per million). Tail on circle indicates slope of land surface. Semi-quantitative spectrographic analyses are given in table 9 Geology by L. C. Huff, A. S. Radtke, and R. J. Wehr, July 1966 Figure 10.—Geologic sketch map of Bruce Hills copper-molybdenum deposit, showing geochemical sample locations.50 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA and subsequently, all the samples were analyzed for THM by our usual test. In order to check the analytical results, 24 of the samples were also analyzed by semiquantitative spectrographic methods. These analyses show that copper and molybdenum are the only ore metals present in abnormal amounts. From a comparison of the analytical results (table 10), the THM methods is judged to be a satisfactory exploration guide for this geologic situation. Table 10.—Comparison of analytical results on soil samples from the Bruce Hills Copper-molybdenum deposit [Total heavy-metals test by L. C. Huff and R. J. Wehr; analytical methods described under “Geochemical studies.” Semiquantitative spectiographic analyses by R. C. Havens and Nancy Conklin] Sample Total heavy-metals test Semiquantitative spectrographic analyses (parts per million) Cold Hot (parts per million) Copper Molybdenum Re-31 20 73 0 32 Vi 20 57 0 33 20 84 0 34 1 200 120 0 35 1 40 73 0 36 1 100 170 7 37 1 40 180 15 38 1 100 150 5 39 2 160 320 15 40 40 26 0 41 3 120 100 5 41A 2 160 240 90 42 2 40 52 0 43 2 80 100 0 44 2 40 72 5 45 1 40 55 18 46 A 120 69 0 47 2 180 480 17 48 3 120 150 6 49 5 + 160 170 10 50 3 160 130 77 51 5 160 130 72 52 5 + 160 120 0 53 5 + 600 710 12 54 3 180 170 9 55 5 120 98 0 Figure 18 shows that the highest THM content, 600 ppm, was detected in a soil developed on talus about 20 feet west of a large dike. Many of the soil samples collected in this vicinity have a THM content between 160 and 200 ppm. Because of cover and limited access, little is known concerning its overall size and grade, but the results of our examination suggest that the deposit is worth exploring. West of Mouth of Rendu Inlet Several small altered zones crop out in bleached marble west of the mouth of Rendu Inlet (pi. 1, loc. 38). The altered zones strike northwestward and dip steeply. They are as much as 20 feet long and 1 foot thick, and contain scattered sulfides, chiefly pyrite, and abundant secondary iron minerals. A sample from one of the altered zones contained 1,500 ppm copper, 1,000 ppm nickel, and 700 ppm cobalt (table 9, loc. 38). South of Tidal Inlet Several thin quartz veins occur in marble near the contact with hornblende diorite on the eastern shore of Glacier Bay south of Tidal Inlet (pi. 1, loc. 41). The marble is white and massive, and near the contact it contains small amounts of wollastonite and garnet. Sulfide minerals in the veins include pyrite, chalcopyrite, and pyrrhotite( ?). A sample representative of the veins carried 1,000 ppm copper, 300 ppm nickel, and 300 ppm cobalt (table 9, loc. 41). Blue Mouse Cove Three mineralized areas were examined on the southeastern part of Gilbert Island north of Blue Mouse Cove (pi. 1, loc. 42). The country rock is a complex assemblage of quartz diorite and younger granodiorite that has been cut by aplite and andesitic dikes. The first area, which is northwest of the easternmost tip of the island, is in a shear zone, 12 feet wide, adjacent to an andesitic dike. The shear zone consists of abundant quartz and dolomite and less abundant muscovite, secondary iron oxides, and an unidentified zinc mineral. The only anomalous sample from this zone (table 9, loc. 42) contained 700 ppm zinc and a trace of silver. The other areas are on the south shore of Gilbert Island north of Blue Mouse Cove. They contain several nearly parallel calcite veins and a quartz-calcite vein. The veins strike about N. 80° W. and dip between 75° NE. and vertical. The calcite veins are as much as 6 inches thick, and the quartz-calcite vein is a maximum of IV2 feet thick. The veins contain minor amounts of pyrite and secondary iron minerals. None of the samples from the veins contained anomalous amounts of ore metals, and their analyses are not given. The quartz-calcite vein is probably the same vein that Rossman (1963b, p. K50) reports to contain tetrahedrite, pyrite, and some gold and silver. None of the three areas appears to be attractive for exploration. Southwest Gilbert Island and Nearby Unnamed Island Copper-molybdenum deposits are sparsely distributed in the southwestern part of Gilbert Island (pi. 1, loc. 45) and on the nearby small island to the south (44). The deposits have about the same potential for molybdenum as they do for copper. They consist of stockworks of numerous quartz veinlets in bleached and altered biotite-hornblende quartz diorite that is cut by alaskite dikes with minor apliticMETALLIC COMMODITIES 51 phases. The quartz diorite is medium grained and has a hypidiomorphic granular texture. It consists of about 45 percent plagioclase (andesine), 30 percent blue-green hornblende, lesser amounts of quartz and red-brown biotite, and traces of zircon, sphene, apatite, epidote, and clinozoisite. The alaskite is strongly altered. It contains mainly plagioclase and quartz in near-equal amounts and about 15 percent potassium-feldspar. Some of the plagioclase is albite. Other minerals form less than 10 percent of the rock and include chlorite, muscovite, biotite, and epidote. Numerous east-striking near-vertical faults with displacements of only a few inches transect the vein-lets and their host rock. Most of these faults contain gouge seams an inch or so thick. The veinlets generally are less than 3 inches thick. They commonly strike between N. 20° W. and N. 40° W. and dip northeastward at moderate angles. Minor amounts of chalcopyrite and molybdenite are localized near the borders of some of the veinlets. The bleached and altered zones are exposed in seacliffs as much as 60 feet high. The northernmost mineralized zone is exposed for about half a mile along the face of the sea-cliffs and the southernmost zone for about one-sixth mile. These deposits probably include the few molybdenite-bearing veins near the western shore of Gilbert Island that were cited by Rossman (1963b, p. K49). A selected specimen representative of the highest grade material from the northernmost altered zone contained 7,000 ppm copper, 2,000 ppm molybdenum, and 0.292 ounce per ton silver (table 9, loc. 45). More representative and more extensive samples from the stockworks of both altered zones were of much lower grade (table 9, Iocs. 44, 45). Despite the large size of the deposits, they probably are too low in grade to encourage exploration. West of Shag Cove A sheared and altered zone about 65 feet wide occurs in quartzose rocks on the west side of Shag Cove south of Geikie Inlet (pi. 1, loc. 49). The zone strikes N. 50° E. and dips 75° NW. It contains numerous thin quartz veins and several sulfide-rich pods that have the same general trend as the major structure. The quartz veins contain pyrite. A chip sample representative of part of the altered zone with abundant quartz veins yielded low values (table 9, loc. 49, sample 66AHx-32A). The largest visible sulfide pod is about 3 feet long and V2 foot thick. It consists of pyrrhotite and subordinate amounts of pyrite, chalcopyrite, azurite, and cuprite(?). A sample from this pod contained 3,000 ppm copper, 700 ppm zinc, 200 ppm cobalt, and a trace of silver (table 9, loc. 49, sample 66AHx-32B). The chances of finding minable quantities of ore in the altered zone are remote. West Arm of Dundas Bay A small island in the southern part of the west arm of Dundas Bay is composed of gneissic dioritic rocks cut by several hornblendite dikes as much as 10 feet thick (pi. 1, loc. 58). The dioritic rocks are locally garnetiferous. Some of the hornblendite dikes contain disseminations and impregnations of sulfide minerals, chiefly chalcopyrite. A sample of high-grade material from one of the dikes carried 10,000 ppm copper (table 9, loc. 58). The dikes might be worthy of additional prospecting, but the chances of finding minable deposits in them are poor. West of Mouth of Tarr Inlet A zone of pegmatitic hornblende diorite about 8 feet thick, cuts the predominant heterogeneous hornblende diorite west of the mouth of Tarr Inlet (pi. 1, loc. 62). In addition to the pegmatitic diorite, the zone contains quartz-calcite veins about 10 inches thick and a few thin aplite dikes. Besides abundant quartz and calcite, the veins carry chalcopyrite, pyrite, epidote, and chlorite. Fractures in the veins are coated irregularly with secondary copper minerals, chiefly chrysocolla. A sample of the veins contained 2,000 ppm copper (table 9, loc. 62). West of Tarr Inlet The leucocratic granitic rocks west of the medial part of Tarr Inlet (pi. 1, loc. 63) locally are altered and contain pale-pink to green siliceous lenses. The lenses carry abundant disseminated sulfides and sulfide-bearing veinlets. The sulfide minerals are pyrite and subordinate chalcopyrite. A grab sample from one of the lenses contained 1,000 ppm copper, 300 ppm zinc, and a trace of silver (table 9, loc. 63). North of Johns Hopkins Inlet Several altered and mineralized zones are exposed in the steep cliffs along the north shore of Johns Hopkins Inlet (pi. 1, loc. 64). They are distributed intermittently from near the point opposite Lam-plugh Glacier westward for about 4 miles. Because of their number, proximity, and similarity, they are represented by a single symbol on plate 1. The altered zones near the eastern part of Johns Hopkins Inlet occur chiefly in septa of metamorphic rocks, mainly marble, within a predominantly dioritic ter-rane. Those near the western part are in greenstone, phyllite, or granodiorite, generally near intrusive contacts. A few of the altered zones are near mafic dikes.52 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA The altered zones range in width from a few feet to several hundred feet and are exposed for lengths as much as 1,000 feet. They consist of assemblages of quartz, calcite and ankeritic carbonates, plagio-clase (including albite) amphibole, muscovite, chlorite, barite, epidote, and secondary iron minerals. The zones locally contain lenses of sulfides and are cut by quartz and calcite veins. The sulfides are pyrite and very small amounts of chalcopyrite. The content of ore metals in the altered zones is low. The highest values that were obtained in any of our several chip samples from the zones were 1,000 ppm copper and traces of molybdenum and silver (table 9, loc. 64). The altered zones were examined by Reed during the 1930’s (Reed, 1938, p. 58, 59). L. F. Parker (oral commun., 1966) reports that a sample from one of the altered zones contained several percent antimony. Although some of the altered zones are large, all of them appear to be too low grade to encourage exploration. South of Johns Hopkins Inlet A large altered zone has formed in the granitic rocks south of John Hopkins Inlet west of the Lam-plough Glacier (pi. 1, loc. 65). The altered zone is irregular in outline. It is as much as 100 feet wide and exposed for several hundred feet along its strike in the cliffs south of Johns Hopkins Inlet. The zone is cut by a few granitic dikes. Surfaces of the altered granitic rocks are coated by malachite, chrysocolla, and secondary iron minerals. A grab sample from the altered zone contained 1,500 ppm copper and 30 ppm molybdenum (table 9, loc. 65). East of Lampi.ugh Glacier A few sulfide-rich lenses are in hornblende diorite that crops out on the ridge east of Lamplugh Glacier in the Reid Inlet gold area (pi. 1, loc. F). The hornblende diorite contains abundant mafic inclusions and is cut by several aplite dikes. The lenses are as much as 10 feet long and 1 foot in diameter. They consist almost entirely of pyrite. Semiquantitative spectrographic analyses of a sample from the largest lens disclosed 1,000 ppm copper and traces of nickel, cobalt, and chromium (table 11, loc. F). Southwest of I.amplugh Glacier Pyrite-bearing quartz veins as much as 10 inches thick cut hornfels west of the upper part of Lamplugh Glacier (pi. 1, loc. 67). The veins strike about N. 22° W. and dip nearly vertical. Wallrock contiguous to the veins is heavily iron stained and sparsely copper stained. Samples from the veins and the adjacent wallrock contained only minor anomalous amounts of copper and molybdenum (table 9, 67). East of Reid Glacier Two altered zones, each about 10 feet thick, crop out east of the divide between Reid and Scidmore Glaciers at altitudes near 4,000 feet (pi. 1, loc. 69). The altered zones trend irregularly and cut fractured metamorphic rocks, mainly marble. A few quartz veins between 1 and 2 feet thick also transect the metamorphic rocks. The altered zones are conspicuously stained by reddish-brown secondary iron minerals, but they lack visible ore minerals. Samples from the altered zones carried negligible amounts of copper and molybdenum (table 9, loc. 69, samples 66AMk-566, 567). The quartz veins contain small quantities of sulfide minerals. A sample from a quartz vein yielded 1,000 ppm copper (loc. 69, sample 66AMk-568). East of Hoonah Glacier Two mineralized areas crop out east of Hoonah Glacier near the southeast shore of Johns Hopkins Inlet. The first of these, about three-quarters of a mile northeast of Hoonah Glacier (pi. 1, loc. 75), consists of disseminated pyrite in hornfels and appears to be extensive. The hornfels locally is faulted and brecciated. A sample from this deposit contained insignificant amounts of copper and molybdenum (table 9, loc. 75). The second area is contiguous to Hoonah Glacier (pi. 1, loc. 77). It consists of a large altered zone several hundred feet thick that has formed in metamorphic rocks near their contact with granodiorite. The altered zone contains abundant pyrite disseminations and impregnations, mainly in biotite hornfels, and is conspicuously iron stained. Only a small part of it was examined. Samples from the zone yielded minor amounts of copper and molybdenum (table 9, loc. 77). Although the analyses indicated low contents of ore metals, a more thorough examination might find richer parts in the altered zone. Fairweather Range Copper minerals have been reported from many localities in the Fairweather Range. Most of the known occurrences are in the southern part of the range near or in rocks of the Crillon-LaPerouse layered gabbro stock. Rossman and members of his 1952 field party (unpub. data) mention copper-stained outcrops on both sides of North Crillon Glacier (pi. 1, loc. 78), from about 3 miles northwest of Mount Marchainville (82) and from a few other localities in the range.METALLIC COMMODITIES 53 A 5-foot-thick layer of gabbro that is exposed for several thousand feet along the south wall of the valley occupied by North Crillon Glacier (pi. 1, loc. 80) contains between 2 and 3 percent pyrrhotite and chalcopyrite (Kennedy and Walton, 1946, p. 71). Kennedy and Walton ( p. 71) also report that many apparently similarly mineralized bands, including some much greater in thickness, crop out in the nearby cliffs. They also report (p. 71) that specimens collected by R. G. Goldthwait from the north wall of the South Crillon Glacier contained between 5 and 6 percent sulfide minerals, principally pyrrhotite and chalcopyrite. These specimens were from near the contact between the gabbro stock and schist. Many fragments of amphibole-quartz schist that are constituents of a moraine on North Crillon Glacier near altitudes of 2,000 feet are stained with copper carbonates (pi. 1, loc. 86) (Kennedy and Walton, 1946, p.71). The copper deposits in the Fairweather Range are in very rugged terrain, and they have not been examined in detail. Samples are not available from any of them, and little is known about their size and tenor. Probably the deposits merit additional prospecting, but their remoteness and difficult access are serious impediments to any contemplated prospecting or mining. Southeast Arm of Lituya Bay A gabbroic dike that cuts granitic rocks on the southwestern shore of the southeast arm of Lituya Bay (pi. 1, loc. 84) contains irregular veinlets and blebs of pyrrhotite (Kennedy and Walton, 1946, p. 71). Small amounts of chalcopyrite, which Kennedy and Walton (p. 71) estimate to constitute less than 1 percent of the rock, are associated with the pyrrhotite. Other Deposits that Contain Copper In addition to those deposits that contain copper as their principal potentially economic commodity, several other deposits in the monument are copper bearing. Among these are deposits at the Brady Glacier nickel-copper prospect (pi. 1, loc. 72), the Nuna-tak molybdenum prospect (21), the Sandy Cove gold prospect (7), and the Rendu Inlet silver prospect (37). Chalcopyrite is an important constituent of the pyrrhotite-rich lenses, disseminations, and impregnations at the Brady Glacier nickel-copper prospect (pi. 1, and table 15, loc. 72). It is a minor constituent of the sizable lodes at the Nunatak molybdenum prospect (pi. 1, loc. 2), and probably copper would be recovered from it if the deposits were mined on a large scale. Chalcopyrite and bornite are associated with gold-bearing quartz veins at the Sandy Cove prospect (7). Samples from this prospect contained as much as 5 percent copper (table 9, loc. 7). Argentiferous tetrahedrite is the chief ore mineral at the Rendu Inlet silver prospect (pi. 1, loc. 37) (A. F. Buddington, unpub. data, 1924; Rossman, 1963b, p.K48, K49). Chalcopyrite and subordinate secondary copper minerals are minor constituents of many other deposits in the monument, notably those of the Reid Inlet gold area (pi. 1), near the head of Wachusetts Inlet (pi. 1, loc. 35), and the skarns east of Queen Inlet (40), south of Abyss Lake (54), and west of Rendu Inlet (39). A reported copper occurrence at Beartrack Cove on the east side of Glacier Bay (Wright and Wright, 1937, p. 221) was not found during our investigations. The Wrights (1937, p. 221) also report finding large masses of pyrrhotite with some copper (chalcopyrite?) in moraine deposits near Adams Inlet. They also mention (p. 221) copper claims on the mountain between Queen and Tidal Inlets. LEAD The mineral deposits of the monument generally are low in lead content, and none of the known deposits could be worked for lead. Only two of the deposits, one reported from the west side of Willoughby Island (pi. 1, loc. 27) and the other near Mount Brack (12), contain lead in possible byproduct quantities. Buddington (unpub. data, 1924) reports jame-sonite from an undisclosed locality on the west side of Willoughby Island. One sample, presumably from this locality and presumably of selected high-grade ore, contained 25 percent lead (A. F. Buddington, unpub. data, 1924). A sample from the Mount Brack argentiferous base-metal deposits, described under “Zinc,” contained 7,000 ppm lead (table 9, loc. 12). Two other deposits whose principal commodity is zinc—the deposit southwest of Red Mountain (pi. 1 and table 9, loc. 20) and a deposit about a mile southwest of the Alaska Chief prospect (30)—contain minor amounts of lead. A few of the copper deposits contain trace to minor amounts of lead. Galena is a minor constituent of some gold-bearing quartz veins in the Reid Inlet gold area, notably those at the LeRoy mine (pi. 1, loc. B). A sample from the LeRoy mine carried 1,500 ppm lead (table 11, loc. B). However, the Reid Inlet gold deposits are too small to permit recovering their base metals at a profit. Samples from the Sandy Cove gold prospect contained minor to trace amounts of lead (table 9, loc. 7).54 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA RADIOACTIVE ELEMENTS No uranium or thorium minerals were found during our investigations, although radioactive minerals were looked for during the field examinations, and all samples were routinely checked with a Geiger counter. Rossman (1963b, p. K52) states that some of the altered zones near Sandy Cove contain between 0.001 and 0.003 percent U3O8. Seitz (1959, p. 116) reports that he checked the area that he mapped near Geikie Inlet for anomalous radioactivity, and that the results were negative. No favorable indications of uranium or thorium minerals were noted during the examinations. Possibly undetected deposits of these elements are in some of the leucocratic granitic rocks or in the altered zones. TIN No tin minerals were found, and no significant anomalous concentrations of tin were detected in the rock and ore samples that were analyzed. The largest amount of tin that was found in these samples was 30 ppm in a sample from the Queen Inlet magnetite deposit (pi. 1 and table 9, loc. 40). Smaller amounts of tin were detected in samples from several other localities (table 9). A tin and tungsten anomaly in stream sediments was revealed by geochemical sampling near the north end of Dundas Bay. Samples from this area contained 30 ppm tin and as much as 150 ppm tungsten (table 4, Iocs. 12, 13). The provenance of the streams that yielded the anomalous samples consists partly of leucocratic granitic rocks, which are considered favorable for tin deposits, and prospecting the area seems justified. Two stream-sediment samples collected in the northern part of the monument also contained anomalous amounts of tin. A sample collected on the west side of Tarr Inlet a few hundred feet south of locality 18 (pi. 1) contained 500 ppm tin, the largest amount of tin detected during the investigation, in addition to anomalous amounts of other metals. The second anomalous sample, from west of Lamplugh Glacier terminus, contained 33 ppm tin, but only ordinary concentrations of copper, lead, and molybdenum. ZINC DISTRIBUTION AND TYPES OF DEPOSITS Although zinc is fairly widespread in the mineral deposits of the monument, most of the deposits in which it is the principal commodity are in the eastern part. Seven zinc deposits discovered during the investigation are described below. Zinc also occurs in seven deposits described under “Copper”; in the Queen Inlet magnetite deposit, described under “Iron”; and in a few lodes in the Reid Inlet gold area. The zinc deposits are diverse in type, having formed in several geologic settings. They consist of veins, altered zones, disseminations, and local sulfide-rich replacements in a variety of host rocks. Sphalerite is the main zinc mineral in most of the deposits, but some deposits contain fine-grained encrustations of secondary zinc minerals. The best zinc deposits in the monument seem to be near Mount Brack (pi. 1, loc. 12) and in an altered zone north of White Glacier (6) (described under “Copper”) that carries 2 percent zinc. DESCRIPTIONS OF DEPOSITS Nunatak on Casement Glacier An iron-stained altered zone is exposed on a small recently denuded nunatak on Casement Glacier (pi. 1, loc. 3). The nunatak consists of thin-bedded limestone, argillite, and hornfels. The altered zone is about 30 feet thick and contains several quartz-ankerite-barite veins that are less than 1 foot thick. The veins and the altered zone strike N. 58° W. and dip vertically. Pyrite is the only visible sulfide mineral in either the veins or the altered zone. The deposit is low in grade, and its only anomalous ore-metal concentration consisted of 300 ppm zinc (table 9, loc. 3). Mount Brack The deposits near Mount Brack (pi. 1, loc. 12) consist of veins and altered zones in graywacke, limestone, hornfels, siltstone, and mafic dikes. The veins and altered zones strike north, and most of them dip east. Six veins were exposed at the time of our examination; others are probably concealed beneath the snow, which is widespread and perennial over much of the area. The veins are generally between 6 and 8 inches thick. They consist chiefly of quartz and calcite with, locally, abundant ankeritic carbonates, sulfides, and sulfosalts( ?). Samples from the veins yielded higher values in zinc and most other ore metals than those from the altered zones. The vein samples (table 9, loc. 12, samples 66AMk-315, 66ABd-280) contained as much as 15,000 ppm zinc, 0.875 ounce per ton (30 ppm) silver, 7,000 ppm lead, 30,000 ppm arsenic, 7,000 ppm antimony, and 0.087 ounce per ton (3 ppm) gold. The presence of sulfo-salts is inferred from the arsenic and antimony content of the samples. Altered zones as much as 30 feet thick are fairly numerous near Mount Brack. They are composed principally of heavily iron-stained ankeritic carbonates, chlorite, quartz, and calcite and minor plagio-clase and muscovite. Some of them enclose quartz-METALLIC COMMODITIES 55 carbonate veinlets. Samples from the altered zones were lean; their maximum zinc content was 700 ppm. Indications of mineralization are widespread, and the general area probably merits prospecting. Southwest of Red Mountain Small pyrite-rich pods and impregnations occur in the Black Cap limestone, of Middle Devonian age, near a granodiorite cupola about 2miles southwest of Red Mountain (pi. 1, loc. 20). The largest pod is about 10 feet long and 1 foot in diameter. It consists largely of pyrite and subordinate calcite and encrustations of a secondary zinc mineral, probably hydrozincite or smithsonite. A sample from the largest pod contained 7,000 ppm zinc, 500 ppm lead, 70 ppm cadmium, and a trace of silver. The deposits are too small to be of economic significance. Southwest of Alaska Chief Prospect An altered shear zone that cuts granitic rocks about a mile southwest of the Alaska Chief prospect contains minor zinc values (pi. 1, loc. 30). The altered zone is about 3 feet wide. Its attitude is N. 30° W., 80° SW. The granitic host rock at the deposit is granodiorite or quartz monzonite. A sample from the altered zone contained 1,500 ppm zinc, 300 ppm lead, and traces of molybdenum, bismuth, and silver (table 9, loc. 30). The deposit probably is too lean to encourage exploration. Hugh Miller Inlet Three thin pyrite-rich veins cut biotite-hornblende quartz diorite on the west side of Hugh Miller Inlet west of Gilbert Island (pi. 1, loc. 46). The veins strike between N. 40° W. and N. 55° W. and dip northeastward. A steep northwest-striking shear zone cuts the quartz diorite near the veins. The veins are heavily iron stained and consist of abundant pyrite and its alteration products and probably quartz, barite, and carbonate minerals. A sample from the veins yielded 1,500 ppm zinc, 70 ppm bismuth, and a trace of molybdenum (table 9, loc. 46). Possibly the veins represent a fringe zone of the previously described extensive low-grade copper-molybdenum deposits that are exposed on nearby parts of Gilbert Island (45). The veins probably are too small and too lean to warrant exploration. Mount Cooper Altered zones occur in iron-stained pyritic hornfels near a peak locally referred to as Mount Cooper, west of Lamplugh Glacier (pi., loc. 66). They are best developed near fine-grained porphyritic dikes that cut the hornfels. A sample from one of the zones contained 300 ppm zinc, traces of molybdenum, and 15,000 ppm barium (table 9, loc. 66). The dominant minerals in the altered zones are quartz, plagioclase, actinolite, and barite. A large altered zone north of the ones examined was not sampled because of difficult access, but its composition is probably similar to the zone that was sampled. Northwest Shore of Johns Hopkins Inlet Iron-stained hornfels crops out for several hundred feet along the northwest shore of Johns Hopkins Inlet and probably extends for many hundreds of feet to the northwest (pi. 1, loc. 76). The hornfels contains abundant finely disseminated pyrite, but apparently it lacks significant amounts of ore minerals. A sample of the hornfels carried 300 ppm zinc and traces of lead and molybdenum (table 9, loc. 76). Other Deposits That Contain Zinc Zinc is a constituent of several deposits whose major commodity is copper, gold, or iron, described elsewhere in this report. The zinc-bearing deposits that are described under “Copper” include those near Mount Young (pi. 1, loc. 1), north of White Glacier (6), at the Margerie prospect (19), on Francis Island (28), at the Alaska Chief prospect (29), near Blue Mouse Cove (42), and on the west side of Tarr Inlet (63). Sphalerite occurs in the gold-quartz veins at the LeRoy and Rainbow mines in the Reid Inlet gold area (B, C). Minor amounts of zinc are associated with pyrite in contact-metamorphic rocks at the Queen Inlet magnetite deposit (40). Samples from the Mount Young deposits contained as much as 1,500 ppm zinc (table 9, loc. 1). A sample representative of a 6-foot-wide altered zone north of White Glacier contained 20,000 ppm zinc (6). Quartz veins at the Margerie prospect carry traces of zinc (19). A selected sample from the Francis Island deposit yielded 1,000 ppm zinc (28). Chip samples from the Alaska Chief prospect contained as much as 700 ppm zinc, and a grab sample from the ore pile contained 1,000 ppm zinc (29). A sample from an altered zone near Blue Mouse Cove yielded 700 ppm zinc (42). Zinc is a minor constituent of siliceous lenses west of Tarr Inlet which contain disseminated sulfides (63). Samples from the LeRoy mine contained as much as 15,000 ppm zinc (table 11, loc. B), and a sample from the Rainbow mine carried 2,000 ppm zinc (C). Samples from the Queen Inlet magnetite deposit have a very low zinc content table 9, loc. 40). Conceivably, zinc constitutes a potential byproduct in a few of these deposits.56 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA PRECIOUS METALS Gold is the only precious metal that has been found in significant amounts within the monument. Silver is a constituent of several deposits, and small amounts of platium have been reported from a few of the placers. GOLD DISTRIBUTION AND OCCURRENCE Both lode and placer deposits of gold are widespread in the monument. The lode deposits are mainly in the Reid Inlet gold area, but a few are known from elsewhere in the monument, notably at the Sandy Cove prospect (loc. 7). The best known of the placer deposits are on the beaches north and south of Lituya Bay (87, 88). (See pi. 1) The lode deposits commonly occupy narrow non-persistent quartz veins in granitic or metamorphic rocks. A few of them are sporadically distributed in thin altered zones adjacent to the quartz veins. Minor amounts of gold occur in some of the larger altered zones in the monument, and gold constitutes the main commodity of economic interest in a few of the altered zones. Gold is a minor constituent of a deposit that is localized along a facies change between marble and phyllite west of McBride Glacier (pi. 1, loc. 10). It is also a subordinate metal in some of the base metal deposits, as at the Alaska Chief prospect. The placer deposits comprise beach sands, outwash gravels, river and stream sediments, and a few residual placers. LODE DEPOSITS Reid Inlet Gold Area The Reid Inlet gold area includes the ridge south of Glacier Bay which is bordered by Reid and Lamplugh Glaciers and by Reid Inlet (pi. 1). It also includes small parts of the terrain east of Reid Inlet and west of Lamplugh Glacier (pl.l). The area contains most of the gold lodes in the monument and also one small copper deposit. Gold has been produced at six properties that are designated as mines; there also are six prospects for gold in the area. The total value of the gold produced from the mines is about $250,000. The Reid Inlet gold area has been examined by several geologists and mining engineers and is the subject of a detailed report by Rossman (1959). Our studies were facilitated by the results of the earlier investigations, and in most instances, Rossman’s maps have been used as bases for our sample localities and geologic data. The Reid Inlet area is underlain chiefly by gran-odiorite and quartz diorite and by a few northwest-striking screens and septa of metamorphic rocks. Fine-grained mafic dikes are locally abundant in the area. Almost all the Reid Inlet deposits occupy thin nonpersistent quartz veins, the rest are sporadically distributed in narrow altered zones contiguous to the quartz veins. Iron stains on the veins and on altered rock near the veins permits them to be readily identified at a distance. None of the deposits appear to be amenable to large-scale mining. Terry Richtmeyer prospect A gold claim about 1,200 feet south of Glacier Bay and 2 miles west of Ptarmigan Creek is reportedly held by Terry Richtmeyer (Alaska Div. Mines and Minerals, written commun., 1966) (pi. 1, loc. A). We were unable to find the claim. It probably is on quartz veins in granitic rocks near their contact with hornfels. LeRoy mine The LeRoy mine, the largest mine in the Reid Inlet gold area, is a little less than 1 mile south of Glacier Bay, at altitudes between 950 and 1,000 feet (pi. 1, loc. B). The mineralized veins at the mine were discovered in 1938 by A. L. Parker and L. F. Parker (Rossman, 1959, p. 38). The mine workings consist of four southwest-trending adits with subsidiary raises and stopes and minor surface workings (pi. 9). The longest adit explores the LeRoy vein for about 240 feet. The gold is in thin nonpersistent quartz veins and less extensively in narrow altered zones adjacent to the veins. The veins transect northwest-striking metamorphic rocks that dip steeply and form a screen between granitic masses. The metamorphic rocks consists of schist, slate, hornfels, and argillite and are differentiated into three units on plate 9. Petrographic studies of thin sections reveal that many of the rocks mapped as schist are schistose granodiorite that has been intensely sheared. With few exceptions the veins strike about N. 30° E. and dip between 50° and 80° NW. About 15 veins are exposed on the property. Most of them are only 1 or 2 inches thick, but one of them, the LeRoy vein (pi. 9) attains a thickness of about 3 feet. The veins are characterized by pinching and swelling and by a lack of continuity that appears an intrinsic feature compounded by faulting. The LeRoy vein, which has yielded the most production, apparently terminates southwestward near its contact with argillite (which Rossman (1959) considered to be a finegrained mafic dike). The vein has been stoped throughout much of its extent both above and below the adit level. Some of the veins are strongly fractured and brecciated. Gold is distributed irregularly in the veins and uncommonly in the contiguous altered zones that generally are a few inches thick.METALLIC COMMODITIES 57 Table 11.—Semiquantitative spectrographic analyses and gold analyses of samples from the Reid Inlet gold area [Spectrographic analyses by J. C. Hamilton, Harriet Neiman, and A. L. Sutton, Jr. Gold analyses by Claude Huffman, Jr., J. D. Mensik, O. M. Parker, V. E. Shaw, J. A. Thomas, and J. E. Troxel. Au: A, analyzed by atomic-absorption cyanide method ; B, analyzed by fire assay atomic-absorption method] Results are reported in parts per million, which for the spectrographic analyses have been converted from percent to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.150, and 0.1 ... , which represent approximate midpoints of group data on a geometric scale. The assigned group for six-step results will include more accurately determined values for about 30 percent of the test results. Gold and silver values, in troy ounces per ton, are shown in parentheses below their corresponding parts per million values. Symbols used ; M, major constituent-greater than 10 percent; 0, looked for, but not detected ;...., not looked for; <, less than. The following elements were looked for, but not found : Be, Bi, Hg, La, Li, Pd, Pt, Sb, Sn, Ta, Tl, W. Locations of the deposits are shown on pi. 1; individual samples are described at the end of the table. Sample _____Au 66A— Ag A1 As Ba Ca Cd Co Cr Cu Fe Mg Mn Mo Nb Ni Pb Si Ti V Y Zn A B Locality A [Location: Mount Fairweather D—3 quadrangle, 1,200 ft south of Glacier Bay, 2 miles west of Ptarmigan Creek. Geologic setting: 1 claim ; uppub. data from Alaska Div. Mines and minerals] No analyses Locality B [Location: LeRoy mine, Mount Fairweather D—3 quadrangle between Lamplugh Glacier and Reid Inlet. Geologic setting: Gold in quartz veins and contiguous altered zones within metamorphic rocks. Sample localities are shown on pi. 9] Mk-326 0 10,000 20,000 70 10,000 0 7 1.5 3 7,000 1,500 150 0 0 0 0 M 300 15 0 0 0.3 (0.0088) Mk-328 0 10,000 7,000 100 7,000 0 5 1.5 7 10,000 1,500 150 0 0 0 0 M 700 20 0 0 0.5 (0.015) Mk-329 0 15,000 15,000 100 30,000 0 5 1.5 15 15,000 7,000 300 0 0 0 50 M 700 30 10 0 1.0 (0.029) 2.0 Mk-330 0 10,000 1,000 50 30,000 0 5 1.5 3 15,000 7,000 700 10 0 0 0 M 300 30 0 0 0.4 (0.012) Mk-332 0 7,000 70,000 70 3,000 0 0 1.5 3 15,000 700 70 0 0 0 20 M 300 15 0 0 10 (0.292) 15 (0.450) Mk-333 0 3,000 30,000 30 30,000 0 0 1 3 7,000 1,500 1,500 0 0 0 0 M 150 15 10 0 0.2 (0.006) Mk-334 0 30,000 0 300 70,000 0 10 3 7 30,000 15,000 1,500 0 0 2 0 M 1,500 70 30 0 0.3 (0.0088) Mk-383 1 (0.029) 20,000 2,000 200 7,000 70 5 2 50 30,000 5,000 200 0 0 0 1,500 M 2,000 30 0 500 11 (0.321) 8 (0.233) Mk-384 1.5 (0.045) 7,000 1,500 100 30,000 100 7 1 20 15,000 2,000 300 0 0 0 500 M 500 15 0 500 17 (0.495) 16 (0.466) Mk-385 10 (0.292) 30,000 7,000 200 30,000 300 7 2 70 70,000 7,000 500 0 0 0 7,000 M 1,500 50 0 2,000 12 (0.350) 13 (.379) Mk-386 15 (0.450) 20,000 0 100 30,000 1,000 10 7 70 50,000 7,000 700 0 0 3 7,000 M 1,500 30 1015,000 37 (1.079) 24 (0.699) Locality C [Location : Rainbow mine, Mount Fairweather D—3 quadrangle, west of Reid Inlet about 15 ft above mean high tide. Geologic setting: Intermittent quartz veins in an altered fault zone. Sample localities are shown in fig. 11] Mk-387 0 30,000 1,500 1,000 3,000 0 0 5 20 10,000 1,500 300 0 0 0 70 M 700 15 0 0 4 (0.116) 7 (0.205) Mk-388 10 (0.292) 30,000 5,000 300 20,000 0 0 2 20 15,000 3,000 500 15 0 0 500 M 700 20 10 0 52 (1.518) 58 (1.664) Mk-389 10 (0.292) 30,000 1,500 700 700 0 0 7 50 15,000 1,500 200 10 0 3 300 M 1,000 20 10 0 57 (1.635) (1.606) Mk-390 70 (0.020) 30,000 1,000 1,000 5,000 0 0 0 100 10,000 8,000 150 15 0 0 500 M 500 10 0 2,000 350 (10.208) 330 (9.624) Mk-391 0 50,000 0 500 10,000 0 0 1 7 15,000 5,000 300 0 0 0 0 M 1,000 15 10 0 .3 (0.0088) .3 (0.0088) Mk-392 0 30,000 0 500 30,000 0 7 100 15 20,000 10,000 700 0 0 15 0 M 1,500 50 10 0 .5 .3 (0.015) (0.0088) Locality D [Location: Sentinel mine, Mount Fairweather D—3 quadrangle, west of Reid Inlet. Geologic setting: Altered fault zone in granodiorite] Mk-393 0 30,000 0 1,000 30,000 0 10 50 50 30,000 10,000 700 0 0 5 0 M 2,000 50 10 0 4 3 (0.117) (0.0875) Locality E [Location: Monarch No. 1 and No. 2 mines, Mount Fairweather D—3 quadrangle, west of Reid Inlet. Geologic setting: Quartz veins and adjoining altered wallrock in granitic rocks. Sample localities are shown in figs. 12 and 13] Mk-337 0 70,000 0 200 30,000 0 10 10 30 50,000 30,000 1,000 0 10 15 0 M 3,000 150 10 0 0.08 <0.05 (0.0023) (<0.0315) Mk-339 0 M 0 700 7,000 0 0 20 7 15,000 5,000 300 0 0 3 0 M 1,500 20 10 0 .2 (0.006) .4 (0.012) Mk-340 0 70,000 1,000 500 1,500 0 0 5 7 20,000 5,000 700 0 0 0 0 M 1,500 30 10 0 .4 (0.012) .3 (0.0088) Mk-341 0 70,000 1,500 700 1,500 0 5 7 7 20,000 5,000 700 0 0 0 0 M 1,500 30 15 0 .2 (0.006) .2 (0 .006) Mk-342 0 70,000 1,500 700 1,500 0 0 2 15 20,000 3,000 500 0 10 0 15 M 1,500 20 15 0 1 (0.029) (0.029) Mk-343 0 70,000 7,000 500 1,500 0 0 0 7 20,000 3,000 300 0 10 0 100 M 1,500 20 15 0 1 (0.029) 1 (0.029) Mk-344 0 20,000 2,000 300 700 0 0 0 10 7,000 1,000 300 0 0 0 10 M 700 0 10 0 .9 (0.026) .8 (0.0233) Mk-345 0 30,000 1,500 700 10,000 0 0 1 10 10,000 2,000 700 0 0 0 0 M 500 10 0 0 .8 (0.023) .6 (0.017) Mk-346 0 10,000 0 150 20,000 0 0 10 10 7,000 2,000 500 0 0 0 0 M 300 0 0 0 .1 (0.0029) .1 (0.0029) Mk-348 0 70,000 1,500 500 2,000 0 7 20 7 20,000 10,000 700 0 0 5 10 M 2,000 50 15 0 .7 (0.020) .8 (0.023)58 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Table 11.—Semiquantitative spectrographic analyses and gold analyses of samples from the Reid Inlet gold area—Continued Sample Au 66A— Ag A1 As Ba Ca Cd Co Cr Cu Fe Mg Mn Mo Nb Ni Pb Si Ti V Y Zn A B Locality F [Location: Mount Fairweather D-3 quadrangle, west of Reid Inlet. Geologic setting: Pyrite-rich pods of < 10 ft long and 1 ft thick in hornblende-rich diorite] Mk-375 0 50,000 0 50 50,000 0 100 150 1,000 M 50,000 1,000 0 0 150 0 M 1,000 100 20 0 0.4 0.4 (0.012) (0.012) Locality G [Location: Incas Mine, Mount Fairweather D—3 quadrangle, west of Reid Inlet. Geologic setting: Quartz veins intermittently distributed in an altered zone within granodiorite. Sample localities are shown in fig. 14] Mk-350 0 70,000 2,000 700 1,500 0 5 15 7 20,000 3,000 700 0 10 3 10 M 1,500 30 15 0 0.4 (0.012) 0.4 (0.012) Mk-351 0 70,000 1,000 700 2,000 0 0 1.5 5 20,000 3,000 500 0 10 0 15 M 1,500 20 15 0 1 (0.029) .7 (0.020) Mk-352 0 30,000 20,000 2,000 30,000 0 5 100 7 20,000 3,000 1,500 0 0 15 0 M 1,500 30 0 0 1 (0.029) 1 (0.029) Locality H [Location: Sunrise prospect, Mount Fairweather D—3 quadrangle, east of Reid Inlet. Geologic setting: Quartz veins cutting marble; some lamprophyre dikes in vicinity] Mk-572 0 7,000 0 30 30,000 0 0 3 20 7,000 1,500 100 0 0 0 0 M 150 15 0 0 0.05 (0.0015) Locality I [Location: Hopalong-Whirlaway prospect, Mount Fairweather D—3 quadrangle, east of Reid Inlet. Geologic setting: Quartz veins in granitic rock] Mk-571 0 7,000 0 15 M 0 0 3 30 10,000 2,000 700 0 0 0 0 M 200 30 0 0 <0.05 «0.0015) Locality J [Location: Galena prospect, Mount Fairweather D—3 quadrangle, at an altitude of about 500 ft west of Reid Inlet. Geologic setting: Quartz vein] No analyses Locality K [Location: Highland Chief prospect, Mount Fairweather D-3 quadrangle, at altitude between 2,500 and 2,800 ft west of Reid Inlet. Geologic setting: Quartz veins in metamorphic rocks] No analyses Locality L [Location: Rambler prospect, Mount Fairweather D-3 quadrangle, east of Lamplugh Glacier. Geologic setting: Quartz veins in granitic rocks and uncommonly in metamorphic rocks] Sj-5 0 M 0 1,500 700 0 0 10 50 30,000 10,000 100 0 0 0 300 M 5,000 200 20 0 0.05 <0.05 (0.0015) (<0.0015) Sj—6 0 10,000 5,000 150 300 0 15 1 150 20,000 1,000 30 0 0 0 50 M 700 15 0 0 5 (0.15) 4 (0.012) Sj-7 0 3,000 2,000 50 7,000 0 30 1 200 70,000 500 150 <5 0 0 0 M 200 0 0 0 7 (0.204) 5 (0.15) Sj-8 0 2,000 0 50 150 0 10 1 200 20,000 100 15 0 0 0 0 M 200 0 0 0 9 (0.263) Mk-545 0 7,000 30,000 100 7,000 0 0 1.5 20 7,000 700 150 0 0 0 30 M 200 7 15 0 (0.029) Mk-546 0 30,000 50,000 1,000 70,000 0 7 30 15 20,000 15,000 2,000 0 0 3 0 M 1,000 70 0 0 .5 (0.015) Mk-547 0 10,000 0 150 30,000 0 0 5 7 7,000 1,500 300 0 0 0 0 M 300 15 10 0 < .05 «0.0015) DESCRIPTION Locality A : No analyses. Locality B: 66AMk-326 Chip sample 18 in. long at 2-in. intervals across quartz vein with minor horses. Mk-328 Selected sample of entire width of 4-in.-wide quartz vein. Mk-329 Selected sample representative of 3-in.-wide quartz vein. Mk-330 Channel sample across 6-in.-thick quartz vein. Mk-332 Channel sample across 8-in.-thick quartz vein. Mk-333 Channel sample across 5-in.-thick quartz vein at surface. Mk-334 Channel sample across 3-in.-thick quartz vein and 12-in.- thick adjacent altered zone. Mk-383 Channel sample 15-in. long across quartz vein with subordinate altered wallrock. Mk-384 Channel sample 8 in. long across quartz vein. Mk-385 Channel sample 12 in. long across quartz vein and altered wallrock. Mk-386 Selected sample representative of 1-in.-thick quartz vein and 1-in.-thick altered wallrock. Locality C: Mk-387 Grab sample from small ore pile near face. Mk-388 Channel sample 1 ft long. Mk-389 Grab sample from quartz vein. Mk-390 Channel sample 1 ft long. Mk-391 .............. do..................... Mk-392 do...................... Locality D : Mk-393 Channel sample, 1 ft long, near easternmost outcrop of altered zone. Locality E : Mk-337 Monarch No. 1, 29-in.-long channel sample. Mk-339 Monarch No. 1, 10-in.-long channel sample across altered zone. OF SAMPLE Locality E—Continued 66AMk-340 Monarch No. 1, channel sample 16 in. long. Mk-341 Monarch No. 1, channel sample 24 in. long. Mk-342 Monarch No. 1, channel sample 14 in. long. Mk-343 Monarch No. 1, channel sample 12 in. long. Mk-344 Monarch No. 2, channel sample 6 in. long. Mk-345 ............do......... Mk-346 do .................. ... Mk-348 Monarch No. 2, channel sample 8 in. long. Locality F: Mk-375 Grab sample of pyrite-rich pod. Locality G: Mk-350 Channel sample 10 in. long. Mk-351 Channel sample 18 in. long. Mk-352. Chip sample 4 ft long, at 4-in. intervals. Locality H : Mk-572 Selected sample representative of a 4-in.- thick quartz vein. Locality I: Mk-571 Grab sample representative of veins. Locality J : No analyses. Locality K : No analyses. Prospect concealed by snow during 1966. Locality L: Sj-5 Grab sample of sheared and altered granodiorite from con- tact with quartz vein (Sj_6). Sj-6 Selected sample of 1-in. massive white unstained quartz vein. Sj-7 Selected sample from sulfide-bearimr quartz vein. Sj-8 do Mk-545 Grab sample from quartz veins 1_4 in. thick. Mk-546 Grab sample from quartz vein 2 in. thick. Mk-547 do ..................METALLIC COMMODITIES 59 The veins consist mainly of quartz and minor amounts of feldspars, calcite, and clay minerals. The sulfide minerals arsenopyrite, pyrite, galena, sphalerite, and chalcopyrite are minor constituents of most of the veins. Subordinate amounts of silver are associated with the gold. The veins have been extensively sampled, and the locations and gold values in samples that were collected during the 1966 investigations and during a previous examination by the Territorial Department of Mines are shown on plate 9. Additional analytical and descriptive data germane to these samples are shown in tables 11 and Table 12.-—Assay data on the Leroy mine [From the Alaska Div. Mines and Minerals (formerly Territorial Dept. Mines and Mineralogy)] Loc. (pl. 9) Width (inches) Au Ag (ounces per ton) Surface samples 54-7 4 0.02 Nil 54-8 .. 6 2.12 0.80 54-9 6 10.34 7.40 54-10 6 1.37 Trace 54-11 16 .50 Trace Underground samples 54-12 12 0.22 Trace 54-13 3 .11 Nil 54-28 28 .38 Trace 54-29 36 2.63 Trace 54-30 4 .25 Trace 54-31 6 .10 Nil 54-32 - 1 .46 Trace 54-33 12 1.56 Trace 54-34 22 .42 Trace 54-35 24 .73 Trace 1 C) .14 Nil 2 - 8 .36 Nil 3 C') .50 Nil 4 6 .56 Nil 5 l1) .42 0.60 6 (') .26 Trace 7 (3) 2.90 .66 8* 12 .16 Nil 9 18 .70 1.80 10 (5) .26 Trace 1 Selected sample. 3 Fines. 8 8 in. of drill core. 4 Location not known. 6 Grab sample. 12. The richest sample represents a 6-inch-thick vein that is exposed at the surface and assayed 10.34 ounces per ton gold and 7.40 ounces per ton silver (pi. 9; table 12). Samples representative of the LeRoy mine lodes contained as much as 0.0045 ounce per ton (15 ppm) silver, 70,000 ppm arsenic, 1,000 ppm cadmium, 70 ppm copper, 1,500 ppm lead, 15,000 ppm zinc, and 0.699 ounce per ton (24 ppm) gold (table 11, loc. B). About $100,000 in gold has been produced from the mine. The LeRoy mine and vicinity were studied by geochemical methods to determine whether soil sam- pling and analyses would aid in exploration for gold lodes in the Reid Inlet area. The original prospectors in the area relied heavily on panning to trace the gold-bearing veins. Where the veins are exposed, panning works well; but throughout much of the area the veins are covered by soil and galacial deposits. Most of the veins contain more sulfide minerals, including galena, than gold. Rather than analyze the samples for gold, it was decided to determine their THM content, which would reveal any abnormal amounts of lead. Eighteen azonal soil samples were collected at 50-foot intervals along two horizontal traverses near altitudes of the lower and upper portals (pi. 9). In addition, 13 samples were collected from near the caved stope above the LeRoy adit. All the samples were collected within 250 feet of known gold-bearing veins and 11 were collected within 50 feet of known veins. Analyses of the samples showed that none of them contained significant amounts of lead or more than 40 ppm total heavy metals. From these results it was concluded that the small amounts of lead in the ore could not be detected in soil diluted with glacial detritus, and that the soil-sampling methods used are not satisfactory for the Reid Inlet area. Rainbow mine The Rainbow mine is west of the mouth of Reid Inlet (pi. 1, loc. C). The mine workings explore an altered fault zone about 1 foot thick that contains vein quartz. The fault zone, which is traceable on the surface for about half a mile southwestward from sea level to altitudes slightly more than 1,000 feet, strikes about N. 30° E. and dips between vertical and 70° SE. The workings consist of a southwesttrending adit about 180 feet long, a short crosscut, stopes above the adit level, and a small pit near the south westernmost outcrops of the zone (fig. 11). The portal of the adit is in sea cliffs about 15 feet above high-tide level. The fault zone cuts granodio-rite and small masses of alaskite. A shattered and brecciated quartz-calcite vein a few inches thick occupies the fault zone. The vein contains gold and an assemblage of sulfide minerals similar to those at the LeRoy mine. The altered zone, which is marked by abundant secondary iron minerals and gouge, also contains widely scattered gold. Analytical results of samples from the Rainbow mine are shown in table 11, loc. C). The highest gold value found in any of our samples from the monument, 10.211 ounces per ton gold, was detected in one of the samples from the mine. Besides gold, samples from the Rainbow mine carried as much as 2.04360 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA ounces per ton silver, 1,500 ppm arsenic, 500 ppm lead, and 2,000 ppm zinc. The Rainbow mine probably is the second largest gold producer in the Reid Inlet area, but its production data are unavailable. The mine was worked during 1945 and shortly thereafter, and its ore was transported by barge and truck to the mill at the LeRoy mine. The Rainbow mine is similar geochemically to the LeRoy mine, and the soil conditions are comparable. The Rainbow mine was sampled for the same purpose as the LeRoy mine—that is, to find out if analysis of the soil for lead could help trace the veins where they are covered by soil and glacial material. Most of the 12 soil samples that were collected were from the hillside 10-50 feet below an outcrop of the vein, where detection of an anomaly seemed most likely. None of these samples contained more than 40 ppm THM. These results support the conclusions made for the LeRoy mine—namely, that the amount of lead in the soils is too small to be useful in tracing the veins. Sentinel mine The Sentinel mine is west of the mouth of Reid Inlet at altitudes near 900 feet (pi. 1, loc. D). Ore at the mine is localized along a northwest-striking steep altered zone that cuts granodiorite. The altered zone is about a foot thick and consists of intensely altered and comminuted granodiorite that contains sparse impregnations of sulfides, abundant secondary iron minerals, and erratically distributed gold. Several other altered zones that are similar in attitude and character to the one at the mine are exposed on the hillside northeast of the property. A sample from one of these (table 11, loc. D) yielded negligible gold values. The mine has yielded a small undisclosed production of gold. It was worked by shallow surficial workings that are now obscured by overburden and vegetation. Monarch mines The Monarch mines are on the steep hillside west of Reid Inlet (pi. 1, loc. E). The Monarch No. 1 mine is at an altitude of about 1,875 feet, and the Monarch No. 2 mine, at an altitude of about 1,500 feet. Both of the mines were worked from adits, and both probably produced minor amounts of gold. The adit at the Monarch No. 1 mine extends for about 210 feet southward from its portal (fig. 12). A small overstope was excavated about 70 feet from the portal. The adit explores an altered zone between EXPLANATION L M < r* Granodiorite with minor alaskite jo Inclined Vertical Quartz vein Occupies altered zone % to 1 % feet thick zzs Inclined workings; chevrons point downward Foot of raise x66AMk-392 (.01) Sample location Gold content (in ounces per ton) is shown in parentheses. Sample data are given in table 11 'l 'j Altitude of portal approximately 15 feet above mean high tide 3- to 4-inch-thick quartz vein in 1-foot-thick altered zone 66AMk-392 (.01) '66AMk-391 (.01) Altered zone approximately 1 foot thick; scattered quartz and much gouge 66AMk-389 (1.66) "Altered zone approximately 1 foot thick i chute 35 Timbered area 66AMk-388 (1.52) / \ n \ /*- a .i C -7 Probable location of face 40 FEET _l____l Mapped by E. M. MacKevett, Jr., and J. G. Smith; July 12, 1966 Figure 11.—Geologic sketch map showing sample locations at the Rainbow adit.METALLIC COMMODITIES 61 1 and 5 feet thick within granodiorite. The zone strikes northward and dips steeply to the west. It contains quartz veins and lenses a few inches thick and abundant gouge and breccia. The granodiorite wallrock is medium to coarse grained and hypidio-morphic granular in texture. It contains about 65 percent plagioclase, 15 percent quartz, and 10 percent potassium feldspar. The rock is cut by microfractures and is altered, resulting in the obliteration of its primary mafic minerals and replacement of the original plagioclase by oligoclase. Its minor constituents and alteration products consist of sphene, allanite, calcite, chlorite, epidote, and opaque minerals. The veins and lenses, and less commonly the altered zones, contain sparsely distributed arsenopy- rite, pyrite, galena, and gold. Calcite and clay minerals constitute the lesser gangue minerals. Samples from the mine showed low values in gold and other ore metals (table 11, loc. E, samples 66AMk-337 through 66AMk-343). Rossman (1959, p. 50) reports a few other gold-bearing veins near the Monarch No. 1 vein. One vein, a few hundred feet west of the Monarch No. 1 vein, crops out over a length of about 100 feet and is as much as 10 inches thick. Some of the partly decomposed weathered material at the surface of the vein has been mined. A small rich stringer vein about 5 inches thick is exposed several hundred feet west of the south end of the Monarch No. 1 vein. Altitude of portal approximately 1,875 feet Figure 12.—Geologic sketch map showing sample locations at the Monarch No. 1 mine.62 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Workings at the Monarch No. 2 mine consist of a westward-trending crosscut adit about 120 feet long and two short drifts (fig. 13). The workings are in granodiorite that is cut by a few quartz veins and by northward-striking mafic dikes and faults. The granodiorite at the Monarch No. 2 mine is less altered, but slightly more deformed, than its counterpart at the Monarch No. 1 mine. The quartz veins strike northward and dip nearly vertical. They are between 2 and 8 inches thick and are bordered by thin gougey selvages. The veins contain sparsely distributed calcite, sulfides, and minor amounts of gold (table 11, loc. E., samples 66AMk-344 through 66AMk-348). A few other small quartz veins are near the Monarch No. 2 property (Rossman, 1959, p. 51). Incas mine The Incas mine is west of Reid Inlet at an altitude of about 1,000 feet (pi. 1, loc. G). The Incas lode, one of the first discoveries in the Reid Inlet area, was staked by Joseph Ibach in 1924 (Rossman, 1959, p. 46). The mine consists of about 200 feet of underground workings (fig. 14) and several trenches that are now badly caved and sloughed. The deposits are localized in quartz lenses in an altered fault zone within granodiorite. The fault zone strikes northward and dips steeply. It is between 1 and 3 feet thick and is traceable intermittently on the surface for about 1,000 feet. The granodiorite is medium grained and hypidiomorphic granular in texture. It contains about 60 percent plagioclase (sodic andes- ine), 20 percent quartz, 10 percent potassium feldspar, and 10 percent alteration products, chiefly epi-dote and chlorite. Much of the granodiorite has been deformed cataclastically. The quartz lenses contain minor amounts of calcite and sulfides, chiefly arseno-pyrite, and sporadically distributed gold. The altered zone consists of hydrothermally altered granodiorite and traces of gold and sulfides. Our samples from the mine revealed only minor amounts of gold and ore metals (table 11, loc. G). Rossman (1959, p. 48) states that several other veins and altered zones crop out in the vicinity of the mine. He also believes that the mine has not been explored sufficiently for evaluation of its economic possibilities. The small production from the property was probably mainly from surficial workings. Sunrise prospect The Sunrise prospect includes several shallow pits and trenches on the hillside east of Reid Inlet at altitudes near 800 feet (pi. 1, loc. H). Rocks at the prospect are marble and hornfels that strike northward and dip steeply. Subordinate fine-grained diorite or quartz diorite is also present. Several northeast-striking lamprophyre dikes, as much as 30 feet thick, cut the other rocks. The gold occurs principally in several subparallel narrow quartz-calcite veins whose attitudes are similar to those of the metamorphic rocks. The veins are between 2 and 12 inches thick and are discontinuous. Generally, their outcrop lengths are between 20 and 40 feet. Pyrite is the only metallic mineral noted in any of the veins. EXPLANATION Mafic dike v < A V V 4 1 > A - r V Granodiorite ^80 Fault, approximately located, showing dip Quartz vein between 2 and 6 inches thick, showing dip X 66AMk-348 (.02) Sample location Gold content (in ounces per ton) is shown in parentheses. Sample data are given in table 11 Figure 13.—Geologic sketch map showing sample locations at the Monarch No. 2 mine.METALLIC COMMODITIES 63 Reed (1938, p. 64) reports that a 10-inch sample across one of the veins carried 0.08 ounce of gold per ton and 0.20 ounce of silver per ton. A sample from the largest vein at the prospect carried negligible values (table 11, loc. H). Thin altered zones are developed adjacent to some of the lamprophyre dikes; these zones and nearby parts of the dikes carry minor amounts of pyrrhotite, pyrite, and arsenopyrite. Rossman (1959, p. 56) reports minor amounts of scheelite from a quartz vein near the Sunrise prospect. Hopalong and Whirlaway claims According to Rossman (1959, p. 56), two claims were staked on the Whirlaway and Hopalong veins on the west side of the ridge east of Reid Inlet, at altitudes near 1,350 feet (pi. 1, loc. I). The veins cut fine-grained diorite or quartz diorite. They strike northward and dip vertical and are as much as 1 foot thick. The veins pinch and swell, and throughout most of their exposures are only a few inches thick. They can be traced for about 60 feet along their strike. Besides quartz, the veins contain abundant calcite, minor muscovite, uncommon pyrite and arsenopyrite, and probably erratically distributed gold. Our samples from them were virtually barren (table 11, loc. I). Rossman (1959, p. 56) states that a small amount of gold was recovered by sluicing the weathered surficial parts of the veins. Galena prospect The Galena prospect is west of Reid Inlet at an altitude of about 500 feet (pi. 1, loc. J). Its workings consisted of trenches that are now obscured by sloughing and overburden. The prospect was staked in 1936 or 1937. The rocks at the prospect are gran-odiorite, subordinate schist, and a few lamprophyre dikes. The prospect is on a vein between 4 and 18 inches thick that was exposed over a length of about 60 feet (Twenhofel and others, 1949, p. 33). The vein consists of banded and vuggy quartz with fairly abundant pyrite, sphalerite, and galena. A sample representing a 12-inch width of the vein contained 0.16 ounce per ton gold, 0.30 ounce per ton silver, and 0.79 percent zinc (Reed, 1938, p. 63). Highland Chief prospect The Highland Chief prospect is at altitudes between 2,500 and 2,800 feet west of the head of Reid Inlet (pi. 1, loc. K). Extensive snowfields, which persist throughout most summers, covered most of the prospect area during our examination. The rocks that were exposed consist of amphibolite, schist, and marble, locally penetrated by granodiorite salients. The metamorphic rocks form part of a northwesttrending screen and dip steeply. None of the reported quartz veins at the property were exposed. According to information quoted in Rossman (1959, p. 54), the main quartz vein at the prospect is as much as 6 feet thick and contains considerable free gold. Ross- EXPLAN ATION A V A A V ^ a -I -7 < > V Granodiorite Hydrothermally altered fault zone containing quartz lenses X66AMk-350 (.01) Sample location Gold content (in ounces per ton) is shown in parentheses. Sample data are given in table 11 Figure 14.—Geologic sketch map showing sample locations at the Incas mine.64 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA man (1959, p. 54) reports that other steep northwest-striking quartz veins near the prospect contain gold. These are alleged to be as much as 2 feet thick and traceable for as much as 700 feet along strike. The prospect probably is one of the most promising in the Reid Inlet area, but its exploration and development have been curtailed by the near-perennial snow cover. Rambler prospect The Rambler prospect is on the steep hillside east of Lamplugh Glacier (pi. 1, loc. L). It consists of a few small surficial pits on quartz veins, mainly within leucocratic granodiorite. The granodiorite contains a few small screens of metamorphic rocks and is cut by a few northeast-striking steep mafic dikes. The quartz veins commonly strike between N. 60° E. and east and dip steeply. They are mainly only 1 or 2 inches thick, but in places attain a thickness of 3 feet. Most of the veins pinch and swell conspicuously. Typically, the veins are exposed for less than 200 feet along their strikes and are bordered by narrow altered zones. The veins consist of quartz, cal-cite, feldspars, barite, scattered sulfides (mainly arsenopyrite, pyrite, and galena), and traces of gold. All our samples from the veins yielded low gold values (table 11, loc. L). High-grade samples rich in gold reportedly have been collected at the prospect (Rossman, 1959, p. 55; Lawrence Duff, oral com-mun., 1966). Other lode deposits in the Reid Inlet area Several other gold-bearing lodes have been reported from the Reid Inlet area, but they were not examined during our investigations. These include the A. F. Parker prospect and a few unexplored quartz veins. The A. F. Parker prospect is about two-thirds of a mile northwest of the LeRoy mine at an altitude of 850 feet. The prospect was staked in 1938 and was worked by a 20-foot-long adit; it had a production of 7 or 8 tons of ore (Twenhofel and others, 1949, p. 33, 34). The prospect explores irregular quartz vein-lets that are localized in a fault zone cutting granodiorite. The veinlets are between 1/2 and 1 inch thick within a gouge zone about 10 inches thick. The fault zone strikes N. 70° E. and dips 86° SE. At the face of the adit, the fault zone is truncated by a fault that strikes N. 66° E. and dips 64° NW. (Twenhofel and others, 1949, p. 34). The quartz veinlets contain galena, pyrite, and a little free gold. Rossman (1959, p. 55, 56) reports a few other quartz veins in the Reid Inlet area that probably contain gold. These veins are little explored, but they probably are similar to the better known quartz veins in the area. South of Lituya Bay Rossman (1959, p. 57, 58, and his fig. 9) reports zones of hydrothermally altered rocks south of Lituya Bay and west of Crillon Glacier (pi. 1, loc. 85). These zones are reddish yellow and are developed in Tertiary volcanic and sedimentary rocks. They are readily susceptible to erosion, and their best outcrops are in streambanks, ravines, or gulleys. Most of the zones are virtually barren, but some of them contain gold. Their highest analyzed gold content was 0.24 ounce per ton (Rossman, 1959, p. 58, and his fig. 9). The zones are numerous and extensive and have been scarcely prospected. Parts of them may carry gold of higher grade than indicated by Rossman’s samples; they probably merit additional prospecting. Sandy Cove Prospect The Sandy Cove prospect is northeast of Sandy Cove, an embayment of the eastern part of Glacier Bay, at altitudes near 110 feet (pi. 1, loc. 7). The prospect consists of three claims that probably were staked during the 1930’s. It was explored by a northeastward-trending adit about 110 feet long and by a few surficial workings. The prospect is on a southfacing hillside that is partly covered by vegetation and soil. The ore deposits are localized in a series of northward-striking steep quartz veins and in the contiguous altered wallrock (fig. 15). Surface exposures of the veins and the altered zones are strongly oxidized and colored reddish brown by widely dispersed hydrous iron oxides. Most of the veins are in monzonite or quartz monzonite that forms small masses in marble country rock. Reed (1938, p. 66) considered the intrusive rock at the prospect to be monzonite; our petrographic studies indicate it is a quartz monzonite. The rock is medium-grained hypidiomorphic granular and consists mainly of pla-gioclase that is zoned from sodic andesine to calcic oligoclase. It contains about 25 percent potassium-feldspar and 10-15 percent each quartz and green hornblende. Minor accessory minerals and alteration products in the rock include sphene, apatite, allanite, epidote, chlorite, muscovite, calcite, pyrite, and magnetite. The quartz monzonite and monzonite are locally silicified near the altered zones and quartz veins. The quartz veins range in thickness from 1 to 12 inches, and the altered zones are as much as 10 feetMETALLIC COMMODITIES 65 EXPLANATION Monzonite and quartz monzonite Locally silicifled near altered zone Altered zone, showing dip Contains gold- and sulfide-bearing quartz veins and lenses; scattered sulfides, clay minerals, chlorite, and secondary iron minerals |--|66AMk-226 (.09) Location of chip or channel sample X 66AM k-229 (.01) Location of grab or selected sample Gold content (in ounces per ton) is shown in parentheses. Sample data are given in table 9 0 40 FEET 1 ___l_,_1____l____I DATUM IS APPROXIMATE MEAN SEA LEVEL Figure 15.—Geologic sketch map showing sample locations at the Sandy Cove prospect. thick. Most of the quartz veins are lenticular and discontinuous; some of them are in an en echelon pattern. In addition to quartz, their gangue minerals include ankeritic carbonates and probably barite. Sulfide minerals which locally make up the bulk of the veins consist of pyrite, chalcopyrite, and bornite. In places the sulfide minerals have been oxidized to malachite, chrysocolla, and diverse hydrous iron minerals. Gold is distributed erratically in the veins. The altered zones carry minor amounts of gold and sulfides. Samples from the prospect contained as much as 0.96 ounce per ton (33 ppm) gold, 50,000 ppm copper, 1.46 ounces per ton (50 ppm) silver, 50 ppm molybdenum, 500 ppm bismuth, and 150 ppm lead (table 9, loc. 7). The richest samples were from near the face of the adit (fig. 15). The other veins and altered zones appear to be leaner in ore minerals than the ones exposed in the adit. Reed (1938, p. 68) reports gold and silver assay results for 39 samples that were cut in the adit. These samples contained as much as 0.51 ounce per ton gold and 2.4 ounces per ton silver. Their average content was 0.11 ounce per ton gold and 0.6 ounce per ton silver, and their median content was 0.04 ounce per ton gold and 0.3 ounce per ton silver. Reed (1938, p. 68) also reports that 4 tons of selected ore from near the portal of the adit contained 0.37 ounce per ton gold and 0.15 ounce per ton silver. Rossman (1963b, p. K52) detected between 0.001 and 0.003 percent U3O8 in samples from some of the altered zones near Sandy Cove. Soil samples were collected at the Sandy Cove prospect in an effort to trace the vein that is exposed near the portal of the adit. A soil sample from just west of the adit contained 220 ppm THM, whereas one from just east of the adit contained only 20 ppm (fig. 16). Samples collected across the trend of the vein both to the northwest and to the southeast contained only background concentrations of heavy metals. Glacial till from the hillside above the prospect dilutes the residual soil and interferes with the application of geochemical techniques. Despite this dilution, the soil samples collected close to, or just downhill from, mineralized areas seem to be geo-chemically anomalous. The lack of anomalous samples across the trend of the vein is interpreted as indicating that the veins pinches out near the surface both northwest and southeast of the adit. A sample collected downhill from the dump contained 480 ppm THM; this sample is believed to be contaminated by ore metals from the dump, however, and not to have any significance in prospecting. The sampling and mapping disclosed several other veins northwest of the adit; they appear to form an en echelon pattern that trends northwestward. Soil66 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA P120 / 320 110c Rock samples 66AHf-280B,280C^ -240 ,20 V P20 ' % ' ac>*/ drift .10 percent) of iron, as much as 300 ppm copper, 300 ppm cobalt, 30 ppm tin, and traces of molybdenum and nickel (table 9, loc. 40, samples 66AMk-298A, -298B, -299, -303). Similar analyses of pyrite-rich pods, veins, and altered zones contained abundant iron and as much as 300 ppm copper, 70 ppm cobalt, 30 ppm tin, and traces of molybdenum and lead (loc. 40, samples 66AMk-305, -321, -323, -324). Analyses of an 18-foot-long chip sample taken across the richest appearing magnetite deposit in the sea cliffs revealed 23.4 percent total Fe as Fe203, 38.5 percent Si02, 7.0 percent A1203, 0.11 percent P205, 1.54 percent S, 0.36 percent Ti02, and 30 ppm As.1 The known iron deposits east of Queen Inlet are too small and too lean to warrant economic interest, but intensive prospecting might lead to the discovery of larger and richer deposits near the known ones. West of Blackthorn Peak Seitz (1959, p. 117) reports a magnetic anomaly near the divide of Geikie Glacier west of Blackthorn Peak (pi. 1, loc. 51). The anomaly was detected from an airplaine from an altitude of about 2,500 feet above the ground. Outcrops are poor in the vicinity of the anomaly because of extensive ice and snow. Probably the anomaly indicates a magnetite-rich skarn deposit, but confirmation of the nature of the deposit and its size and grade would require drilling or other physical exploration. East of Brady Glacier Magnetite deposits were found in the hills east of the lower part of Brady Glacier about 3% miles 1 FejO:i determined by atomic absorption by W. D. Goss. SiO^, AL-Oa, and TiOj determined colorimetrically by G. T. Burrow. P^Or, determined volu-metrically by L. F. Rader. S determined by induction furnace by Dorothy Kouba. As determined colorimetrically by E. J. Fennelly. south of Abyss Lake (pi. 1, loc. 54). The deposits are at an altitude of about 1,350 feet. They consist of several steep lenses of magnetite-rich skarn that strike northwestward. The lenses comprise abundant magnetite and garnet, subordinate quartz and calc-silicate minerals, and minor pyrite and chalcopyrite, and are bordered by marble and small masses of leucocratic granodiorite. They are as large as 30 feet long and 10 feet thick. Semiquantitative spectrographic analyses showed that samples of the skarn contained major amounts of iron and 1,000 ppm copper (table 9, loc. 54). Magnetometer readings of as much as 5,000 gammas were obtained on some of the skarn outcrops. Although some of the skarn bodies are rich enough to constitute iron ore, they are too small to be exploited. Development of the deposits is contingent upon the unlikely possibility of discovering concealed skarn bodies that contain large tonnages of magnetite. Fairweather Range The layered mafic and ultramafic rocks of the Fairweather Range contain a large low-grade iron resource and appreciable amounts of other metals, notably titanium. These rocks form the Crillon-LaPerouse and the Astrolabe-DeLangle stocks of Rossman (1963a) and probably a similar, but unexplored, mass near Mount Fairweather. Four localities where the layered rocks are known to contain concentrations of iron minerals are shown on plate 1 (Iocs. 73, 79, 80, 83). Undoubtedly, many other localities in the Fairweather Range contain similar deposits, but the range has been only cursorily prospected, chiefly because of its formidable terrain and difficult access. The iron deposits in the Astrolabe-DeLangle stock are represented in a general way by locality 73 on plate 1. Rossman (1963a, p. F44, F45) reports that some layers in the stock contain concentrations of ilmenite and that other layers contain as much as 20 percent titanium-bearing magnetite. At most places the contact zones of the stock also contain titaniumbearing magnetite. Most of the layers that carry much magnetite or ilmenite crop over a “stratigraphic” thickness of about 1,000 feet near the top of the mountain that forms Astrolabe Penisula. The iron- and titanium-rich layers are at an altitude of 1,100-2,000 feet and appear to persist through the mountain. Rossman (1963a, p. F45, table 8) gives the magnetite and ilmenite contents of some rocks from the Astrolabe-DeLangle stock. Several iron-stained layers that are signaled by bright red outcrops have been reported from the Crillon-LaPerouse stock (Rossman, 1963a, p. F42,METALLIC COMMODITIES 73 F48) (Kennedy and Walton, 1946, p. 71). A few of these are represented on plate 1 (Iocs. 79, 80, 83). Most of these layers contain fairly abundant ilmenite and subordinate pyrrhotite and chalcopyrite. The layers have not been prospected thoroughly, and probably some of them and some of the other layers in the stock also contain concentrations of magnetite. The presence of layered mafic intrusive rocks near Mount Fairweather is indicated by float on the moraines of the Fairweather Glacier. Presumably, the magnetite and ilmenite content of these unexplored rocks is similar to that of the Crillon-LaPerouse and the Astrolabe-DeLangle stocks. Placer Deposits The beach placers north and south of Lituya Bay which were described under “Gold” contain concentrations of these heavy minerals in the monument are between 2 and 13 miles south of Lituya Bay (Rossman, 1963a, p. F46). Rossman’s samples (1957, table 1) from the beach placers contained as much as 10 percent magnetite and 21 percent ilmenite, but their average content of these minerals was considerably less. The probability of iron being recovered from these deposits is remote. CHROMIUM No chromium lodes are known to occur in the monument, but chromite float has been reported on glaciers in the Fairweather Range (Goldthwait, in Kennedy and Walton, 1946, p. 71, 72). The largely unexposed ultramafic rocks that are inferred to form the lower parts of the layered intrusive complexes of the Fairweather Range are potential hosts for chromite deposits. Trace amounts of chromium were found in almost all our samples from the monument, and anomalous quantities of chromium were found in a few of the samples (tables 9, 11, 13, 15). The largest amounts of chromium detected in the samples were 1,500 ppm from near Mount Young (table 9, loc. 1), 1,000 ppm from peridotite at the Brady Glacier prospect (table 15, No. CSN-1), and 700 ppm from the Curtis Hills (table 9, loc. 23). COBALT Cobalt is a potential byproduct of the nickel-copper deposits at the Brady Glacier prospect, but no discrete cobalt minerals have been identified in the deposits. Samples representative of the richest ore at the prospect contained an average of 0.25 percent cobalt. Cobalt probably is a minor constituent of similar sulfide deposits that may be associated with the layered mafic and ultramafic complexes of the Fair-weather Range. Minor amounts of cobalt were detected in almost all our analyzed samples from the monument, and anomalous amounts of cobalt were detected in a few of them (tables 9, 11, 13, 15). The anomalous concentrations of cobalt are as much as 2,000 ppm in massive sulfides from the Brady Glacier prospect (table 15, pi. 1, loc. 72); 700 ppm in samples west of the mouth of Rendu Inlet (table 9, loc. 38); 300 ppm north of Adams Inlet (5), the Queen Inlet magnetite locality (40), and the Alaska Chief prospect (29); and 200 ppm from Shag Cove (49). MANGANESE Manganese is widely associated with most of the mineral deposits, but no potentially exploitable manganese deposits are known from the monument, and the likelihood of discovering such deposits is remote. Manganese-stained oxidized zones are conspicuous in outcrops of several deposits, particularly the base-metal replacement lodes and altered zones. Samples from several of the deposits contained between 2,000 and 7,000 ppm manganese (table 9). The most notable of these are from Francis Island (loc. 28, No. HF-183C) and the Alaska Chief prospect (29, No. hk-474). MOLYBDENUM DISTRIBUTION Many mineral deposits that contain molybdenum are known in the monument. They include one important prospect, the Nunatak prospect (pi. 1, loc. 21); a few deposits, such as those in the Bruce Hills (34) and near the southwestern part of Gilbert Island (44, 45), that contain molybdenum and copper of near-equal potential; several small molybdenite deposits; and some deposits whose analyzed samples revealed trace to minor amounts of molybdenum. Molybdenum is widely distributed throughout much of the eastern and northeastern parts of the monument where widespread, but generally small, molybdenum content characterizes many of the metalliferous deposits. The molybdenum deposits are particularly abundant in parts of the Mount Fair-weather D-l and D-2 quadrangles (pi. 1). TYPES OF DEPOSITS The molybdenum deposits are commonly localized in metamorphic rocks near granitic masses or within the granitic rocks themselves. They form stock-works, disseminations, veins, mineralized fault zones and fracture coatings, and at some places are parts of contact-metamorphic zones, dikes, or amyg-daloidal lavas. The largest known molybdenum deposits in the monument consist of swarms of closely74 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA spaced veins and veinlets that are termed “stock-works.” Except for minor amounts of molybdite in the Bruce Hills copper-molybdenum deposit (pi. 1, loc. 34), molybdenite is the only molybdenum mineral in the deposits. DESCRIPTIONS OF DEPOSITS Casement Glacier Molybdenite-bearing float was found on lateral moraines fairly high on Casement Glacier (pi. 1, loc. 9) by members of the Ohio State University field party sponsored by the Institute of Polar Studies (Colin Bull, written commun., 1965). The float reportedly also contained some copper carbonates. Van Horn Ridge Numerous claims for molybdenum are on Van Horn Ridge east of the head of Muir Inlet (pi. 1, loc. 11). A few of the claims have been explored by shallow pits and trenches. The deposits are in iron-stained altered zones, both in steeply-dipping north-striking hornfels and in granodiorite. Most of the altered zones are along faults. Typically, they are a few feet wide and do not persist along strike. The altered zones are weakly mineralized. Samples from them contained as much as 200 ppm molybdenum and traces of lead (table 9, loc. 11). West Side of Tarr Inlet Many iron-stained altered and brecciated zones are exposed in the cliffs west of Tarr Inlet south of Margerie Glacier (pi. 1, loc. 17). These zones are between 1 and 5 feet thick and cut granodiorite or, less commonly, hornfels. A few of them are near the edges of felsic dikes. The altered zones are lean in ore metals. Samples from them contained as much as 100 ppm molybdenum, 5,000 ppm arsenic, and 1,000 ppm barium (table 9, loc. 17). Nunatak Prospect The largest known molybdenum deposits in the monument are at the Nunatak prospect east of Muir Inlet (pi. 1, loc. 21). The deposits are mainly in the northern part of “The Nunatak,” an isolated knob about 1,100 feet high which is surrounded by water and periglacial debris. Before regression of the nearby glaciers, “The Nunatak” was surrounded by ice and was a true nunatak. The deposits were located in 1941 (Twenhofel, 1946, p. 12), and since then, they have been explored intermittently. They were investigated and described by a Geological Survey field party under the direction of W. S. Twenhofel (1946) and by the U.S. Bureau of Mines (Sanford and others, 1949). During the summer of 1966, the de- posits were explored with three diamond-drill holes by the American Exploration & Mining Co. Our field examination consisted of checking Twenhofel’s geologic map and collecting numerous chip samples, soil samples, and a few pertinent rock and mineral specimens. Deposits at the prospect consist of stockworks of molybdenite-bearing quartz veins, uncommon disseminated molybdenite, and a mineralized fault zone. They are mainly in hornfels, but locally they occur in quartz monzonite porphyry and in silicified zones near the edge of the porphyry (pi. 11). Geology The following descriptions of the rocks at the Nunatak prospect are largely from Twenhofel’s report (1946). The oldest rocks are dark-blue thin-bedded limestone and subordinate shale that crop out in the southwestern part of “The Nunatak” (pi. 11). These rocks are conformably overlain by a thick sequence of hornfels, which Twenhofel (1946, p. 12) differentiated into three units (pi. 11). The hornfels consists chiefly of orthoclase and clinozoisite with some diopside, garnet, quartz, and oligoclase. The lower hornfels unit is characteristically thin bedded and contains a few limy beds. The middle unit is also thin bedded and contains many beds that are rich in clinozoisite. The upper hornfels unit is thick bedded. Small discordant masses of quartz monzonite porphyry cut the hornfelses (pi. 11). Numerous postmetallization andesitic dikes cut the hornfels, limestone, and quartz monzonite porphyry. Surficial deposits, chiefly of glacial origin, cover parts of “The Nunatak.” Outcrops of the quartz monzonite porphyry are locally bordered by siliceous zones as much as 15 feet thick. The rock mapped as quartz monzonite porphyry by Twenhofel (1946) consists of phenocrysts of oligoclase and less abundant hornblende, biotite, and quartz in a microcrystalline groundmass that contains potassium feldspar, quartz, and plagioclase. The phenocrysts commonly are euhedral and 3-4 mm long. Accessory minerals in the rock are magnetite and sphene. The alteration products include actinolite and epidote. Numerous quartz-rich veinlets cut the rock. Samples of the porphyry which were studied petrographically contained less potassium-feldspar than a normal quartz monzonite; this fact, along with the characteristic microcrystalline groundmass, indicates that the rock should be classified as rhyodacite porphyry. However, the term “quartz monzonite porphyry” is retained here for consistency with previous usage.METALLIC COMMODITIES 75 The andesitic dikes are predominantly hornblende andesite porphyry and some dacite porphyry. They are altered porphyritic rocks with pilotaxitic ground-masses. They contain between 50 and 60 percent plagioclase (sodic andesine), the dominant mineral in both their phenocrysts and groundmasses. Hornblende, both a phenocryst and groundmass mineral, forms between 10 and 15 percent of the rock. Other primary minerals that are minor constituents of the andesitic rocks include biotite, pigeonite, magnetite, and apatite. The secondary minerals include actinolite, chlorite, epidote, and calcite. The dominant structural grain at “The Nunatak” is shown by north-striking beds that dip eastward (pi. 11). In the western part of “The Nunatak,” the beds are folded into an open anticline. Bedding is obscure near the rock mapped as quartz monzonite porphyry. Several steep faults, apparently with minor offsets, are exposed at the prospect (pi. 11). These faults commonly strike north or northeast. The myriad fractures that developed in the quartz monzonite porphyry and the hornfels before the intrusion of the andesitic dikes were mineralized to form the stockworks of quartz-molybdenite veins. Ore deposits The ore deposits consist of stockworks of closely spaced quartz veins and veinlets that contain almost all the known molybdenum reserves, mineralized fault zones, and less common fracture coatings and disseminations. The stockworks are widely distributed throughout the northern part of “The Nunatak,” extending from near the summit westward and northwestward to Muir Inlet (pis. 11, 12). They consist of myriad closely spaced quartz veinlets less than 1 inch thick, and thin quartz veins that are as much as 18 inches thick but commonly are less than 6 inches thick. The stockworks are mainly developed in the hornfels, but they have formed in the quartz monzonite porphyry also, particularly in its partially silicified peripheral zones. The stockworks are best exposed in the cliffs contiguous to the shoreline of Muir Inlet throughout a lateral extent of about 800 feet (pis. 11, 12). There they consist of hundreds of quartz veins and veinlets that strike N. 70° W. to west and dip nearly vertical. The veins and veinlets are cut by many steep northeast-striking fractures that are occupied by clayey gouge as much as 2 inches thick and less common barren quartz and calcite. In places the transecting fractures offset the veins a few inches. Poorly developed near-horizontal fractures also cut some of the quartz veins and vein-lets. Many of the quartz veins and veinlets contain molybdenite, generally as selvages or thin films along their borders, but, unusually, as scattered disseminations within the quartz. Molybdenite also forms rare thin films along some joint surfaces near the stockworks. Diamond-drill cores reveal quartz-free molybdenite along fractures in some of the hornfels and as very fine disseminations in some of the quartz monzonite porphyry. Besides quartz and molybdenite, the veins contain minor to trace amounts of pyrite pyrrhotite, chal-copyrite, tetrahedrite, bornite, enargite, alunite, potassium feldspar, epidote, albite, malachite, and chlorite. The copper minerals occur mainly near the margins of the stockworks, and their distribution indicates a crude lateral zoning of the deposits. Thin altered zones that border some of the veins contain phlogopite, montmorillonite, calcite, and feldspars. Rossman (1963b, p. K49) reports that a grab sample of mineralized quartz-rich rock that was collected from a gulley on the northeast side of “The Nunatak” contained 0.04 ounce gold per ton and 7.07 ounces silver per ton. Silver was detected in only two of our samples (table 13). Minor amounts of both gold and silver were found in some of the cores from the American Exploration & Mining Co. diamond-drill holes (Robert Garwood, oral commun., 1966). The fault deposits are largely confined to the steep north-striking fault that extends northward from the lake north of Nunatak Cove (pi. 11), but they are also weakly developed in some of the lesser faults at the prospect. They differ from the stock-works mainly by containing molybdenite deposited along fractures within fault zones. Stockwork deposits are inherently difficult to sample, and a reliable grade estimate for the Nunatak deposits would require extensive bulk sampling. Adequate estimates of the reserves are contingent upon determining the configuration of the deposits. Indications that the deposits extend to considerable depths are: (1) they are exposed throughout a large vertical range; (2) the richest exposures of ore are in sea cliffs that border Muir Inlet; (3) a company diamond-drill hole was mainly in mineralized rock to its bottom, about 300 feet below sea level; and (4) a Bureau of Mines diamond-drill hole penetrated uniformly mineralized rock continuously to its bottom 158 feet below sea level. Twenholfel’s reserve estimates (1946, p. 17, 18) are based on the results of drilling and sampling by the U.S. Bureau of Mines during 1942 and on his geologic mapping. The Bureau of Mines program consisted of drilling two diamond-drill holes totaling 285 feet and collecting and analyzing a total of 24976 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Table 13.—Semiquantitative spectrographic analyses and colorimetric analyses for molybdenum of samples from the Nunatak molyodenum prospect [Spectrographic analyses by Harriet Neiman. Molybdenum determined colorimetrically by G. T. Burrow and E. J. Fennelly] Results are reported in parts per million, which for the spectrographic analyses have been converted from percent to the nearest number in the series 1, 0.7, 0.5, 0.3, 0.2, 0.1.......which represent approximate mid- points of group data on a geometric scale. The assigned group for six-step results will include more accurately determined values for about 30 percent of the test results. Symbols used : 0, looked for, but not detected ; <, less than. The following elements were looked for, but not found: As, Au, Be,1 Cd, Hg, La, Li, Nb, Pd, Pt, Sb, Tl, W, Zn. Sample locations and descriptions are shown on pi. 12. Sample GGA Mo (colormetric) Ag Ba Bi Co Cr Cu Fe Mn Mo Ni Pb Sn Ti V Y Mk-93 305 0 70 0 7 20 150 50,000 1,000 200 15 0 0 2,000 70 15 94 275 0 100 0 7 15 150 30,000 700 100 10 0 0 1,500 30 0 95 725 0 70 0 10 30 300 70,000 700 500 20 0 0 1,500 50 10 96 700 0 100 0 7 30 100 30,000 700 300 15 0 0 2,000 70 10 97 190 0 150 0 10 50 100 70,000 1,500 200 15 0 0 3,000 70 15 98 370 0 100 0 7 20 200 50,000 1,000 100 15 0 0 2,000 50 10 99 360 0 100 0 7 50 200 50,000 1,000 300 15 0 0 2,000 50 10 100 45 0 150 0 10 50 100 70,000 1,500 30 20 0 0 2,000 70 10 101 55 0 150 0 10 70 100 70,000 1,500 30 20 0 0 3,000 70 10 102A . . . . 1,370 0 100 0 7 20 500 70,000 2,000 1,000 10 0 0 1,500 50 0 102B 065 0 150 0 10 70 200 70,000 2,000 20 20 0 0 2,000 70 10 103 60 0 300 0 10 50 200 50,000 1,500 20 20 0 0 2,000 70 10 104 115 0 200 0 10 100 150 70,000 1,500 30 30 0 0 3,000 100 10 105 8 0 500 0 10 150 70 50,000 1,000 7 20 0 0 3,000 100 10 106 55 0 500 0 10 150 50 50,000 1,000 50 30 0 0 2,000 100 10 107 15 0 150 0 10 50 500 70,000 1,500 10 15 0 0 1,500 70 10 108 145 0 150 0 15 30 1,000 70,000 1,000 100 15 0 0 3,000 70 15 109 25 0 150 0 10 70 300 70,000 1,500 150 15 0 0 3,000 100 20 110 45 0 100 0 10 100 300 70,000 2,000 30 20 0 0 2,000 70 15 Ill <5 0 200 0 10 30 100 50,000 1,500 5 15 0 0 2,000 70 10 112 <5 0 200 0 7 30 300 50,000 1,500 <5 15 0 10 3,000 100 15 122 110 0 70 0 0 7 150 15,000 500 15 0 0 0 300 15 0 123 40 0 100 0 0 10 100 20,000 700 30 3 0 15 700 20 0 124 40 0 150 0 0 15 200 30,000 500 20 7 0 0 1,500 30 10 125 170 0 200 0 0 3 200 15,000 200 100 0 0 0 500 15 0 120 30 0 700 0 5 15 50 20,000 300 20 7 0 0 1,500 70 10 127 40 0 700 0 0 3 30 10,000 100 30 0 0 0 700 15 0 128 60 0 700 0 0 1 50 10,000 150 50 0 0 0 500 0 0 129 40 0 700 0 0 1 70 15,000 150 15 0 0 0 500 10 0 130 10 0 300 10 0 2 100 10,000 200 7 0 0 0 300 0 0 131 10 0 150 0 0 1.5 50 7,000 200 7 0 0 0 200 0 0 132 10 0 150 0 0 15 70 20,000 7,000 7 5 0 0 1,000 30 0 133 20 0 150 0 0 10 50 20,000 1,000 20 5 0 0 700 30 0 134 160 0 50 0 0 10 50 30,000 1,000 100 5 0 0 1,000 30 0 136 20 0 300 0 10 20 50 50,000 1,000 15 15 0 0 3,000 150 15 137 80 0 300 0 5 15 30 30,000 1,000 70 7 0 0 2,000 50 0 140 20 0 150 0 7 30 70 50,000 1,500 0 10 0 0 1,500 70 10 Re-1 100 0 70 0 15 30 50 70,000 3,000 100 15 0 0 3,000 100 15 2 70 0 100 0 15 50 100 50,000 2,000 30 20 0 0 5,000 150 15 3 815 0 50 10 7 30 50 30,000 2,000 500 10 0 0 2,000 50 10 4 2,480 0 70 0 7 20 30 30,000 1,500 1,500 10 0 0 1,500 70 10 5 900 0 100 0 7 30 50 50,000 1,500 500 20 0 0 1,500 70 10 6 1,290 0 150 0 7 20 50 50,000 2,000 1,000 15 0 0 1,500 70 10 1 810 0 150 0 7 30 100 5,000 1,500 700 20 0 0 1,500 100 10 8 1,665 1 100 0 7 20 200 30,000 1,500 700 15 20 0 1,000 50 0 \) 640 0 100 0 7 30 70 30,000 1,000 300 15 10 0 1,500 70 10 10 <5 0 100 0 15 70 15 70,000 1,500 0 30 0 20 2,000 100 15 11 145 0 100 0 10 30 30 50,000 1,500 100 15 0 0 2,000 100 10 12 1,080 0 70 0 10 50 50 50,000 1,500 500 20 0 0 2,000 70 10 13 60 0 150 0 10 30 50 50,000 2,000 50 15 0 0 1,500 70 10 It 735 0 70 0 5 15 50 30,000 2,000 300 10 0 0 1,500 50 0 15 815 0 150 0 7 70 30 50,000 1,500 500 20 0 0 2,000 70 10 16 985 0 200 0 15 100 100 50,000 1,000 700 30 0 0 3,000 100 15 17 415 0 150 0 20 200 50 70,000 1,000 500 100 0 0 3,000 200 15 18 10 0 150 0 10 30 100 50,000 1,500 7 15 0 0 3,000 100 15 20 880 0 50 0 0 3 30 10,000 500 500 0 0 0 300 10 0 21 1,500 0 30 0 0 3 20 10,000 500 700 0 0 0 200 0 0 22 1,500 0 30 0 0 2 100 7,000 200 700 0 0 0 200 0 0 23 3,000 0 30 0 7 15 70 50,000 1,500 1,500 7 10 0 1,500 50 10 24 2,900 1.5 100 0 0 15 700 20,000 1,000 1,000 5 0 0 700 30 0 25 80 0 100 0 15 30 1,000 50,000 1,000 30 15 0 0 1,500 70 10 1 2 ppm Be detected in sample 66AMk_102A.METALLIC COMMODITIES 77 chip, drill-core, and channel samples. Sixteen samples were from the fault zone and 238 from the stockwork (Sanford and others, 1949). The average molybdenum content of 177 samples from the part of the stockwork mapped as containing conspicuous molybdenite was 0.075 percent (Twenhofel, 1946, p. 17). Fifty-six samples that were collected from parts of the stockwork mapped as containing inconspicuous molybdenite contained an average of 0.048 percent molybdenum (Twenhofel, 1946, p. 17). The samples from the fault zone contained an average of 0.12 percent molybdenum (Twenhofel, 1946, p. 17). A summary of Twenhofel’s reserve and grade estimates (1946, p. 17, 18) follows.2 His grade estimates were based partly on channel samples. Surface area Projected de-pth Estimated Estimated grade ( percent fsquare feet) ._______ Fault Dashed where approximate; dotted where inferred. U, upthrown side. Arrows indicate relative sense of horizontal displacement Thrust or reverse fault Dotted where inferred or concealed. Sawteeth are on upper plate —f— — Anticline Syncline Dashed where approximate 50-80 Average strike and dip of beds 70-80 _f_ Average strike and dip of beds, top unknown Vertical beds, top unknown Strike and dip of overturned beds ©----- Location of measured sections, shown in figure 20 Figure 19.—Geologic sketch map and structure section of Tertiary rocks in the Lituya district. POTENTIAL The petroleum potential of the Tertiary sequence within Glacier Bay National Monument is poor within the area of outcrop on land. There are no oil or gas seeps such as those which occur abundantly throughout the coastal part of the western part of the Gulf of Alaska Tertiary province. Deformation of the older siltstones and a low organic content in the less deformed younger siltstones limits the source-rock potential. However, the reported occurrence of an oily film and petroliferous odor in sandstone at one locality near the top of the Cenotaph Volcanics (Miller and others, 1959, p. 44) suggests the possibility that at least some hydrocarbons may have been generated in the lower part of the section. A critical factor for petroleum accumulation is the availability of adequate reservoir beds. Sandstones in all units except the uppermost part of the Yakataga Formation are commonly argillaceous and probably have low permeability and porosity. Some of the stratigraphically highest sandstones in the Yakataga Formation are good potential reservoirs, but they are stratigraphically several thousand feet above the possible source rocks and are separated from them by one or more disconformities or unconformities. The anticline (fig. 19, section A-A') is a marginal prospect as a structural trap because (1) it probably does not have structural closure; (2) potential reservoir sands in the upper parts of the Cenotaph and88 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA EXPLANATION Topsy Formations are breached by erosion; and (3) the structure is cut by an axial fault and is probably complicated by faulting at depth. The offshore petroleum possibilities within the monument cannot yet be adequately evaluated, but there is no reason to believe that they will differ significantly from those landward. Structures may be more favorable, and the source-rock potential of the sequence may increase in a seaward direction away from the zone of intense deformation associated with the Fairweather fault. On the other hand, potential reservoir rocks are likely to become scarcer with increasing distance from shore, and drilling depths to objective horizons in the Cenotaph Volcanics and Topsy Formations could rapidly become excessive. COAL Reported occurrences of coal in the Glacier Bay National Monument are limited to the sequence of bedded sedimentary and volcanic rocks of TertiaryREFERENCES CITED 89 age exposed in the Lituya district and to a single specimen of float material of unknown origin found near the terminus of the Casement Glacier (E. H. Lathram, oral commun., 1966). In the Lituya district, coal occurs as thin stringers and beds less than 8 inches thick in conglomerates of the Cenotaph Formation at both the type section on Cenotaph Island and in the valley of Coal Creek just south of Lituya Bay. Thin beds of carbonaceous silt-stone and silty coal as much as 8 inches thick are also interbedded with sandstone and siltstone of the Topsy Formation at Clay Point. The one available analysis of the coal, which was made on a grab sample collected by Don J. Miller, from Coal Creek, indicates that it has a high ash content and is probably of subbituminous rank: Proximate analysis of coal from the Cenotaph Formation, Coal Creek [U.S. Bureau of Mines, lab. No. F-47643] As received Moisture free Moisture 2.4 Volatile matter ... 34.6 35.5 Fixed carbon 34.0 34.8 Ash 29.0 29.7 100.0 100.0 Sulfur 5 .5 The coal in the Lituya district has little or no commercial potential because of its low rank and its occurrence as thin discontinuous beds and stringers. REFERENCES CITED Berg, H. C., Eberlein, G. D., and MacKevett, E. M., Jr., 1964, Metallic mineral resources, in Mineral and water resources of Alaska: U.S. 88th Cong., 2d sess., Senate Comm. Interior and Insular Affairs, Comm. Print, p. 95-125; U.S. Geol. Survey in coop, with Alaska Dept. Nat. Resources. Buddington, A. F., and Chapin, Theodore, 1929, Geology and mineral deposits of southeastern Alaska: U.S. Geol. Survey Bull. 800, 398 p. Cornwall, H. R., 1966, Nickel deposits of North America: U.S. Geol. Survey Bull. 1223, 62 p. Hawkes, H. E., 1963, Dithizone field tests: Econ. Geology, v. 58, p. 579-586. Huff, L. C., 1951, A sensitive field test for detecting heavy metals in soil or sediment: Econ. Geology, v. 46, no. 5, p. 524-540. Kennedy, G. C., and Walton, M. S., Jr., 1946, Geology and associated mineral deposits of some ultrabasic rocks in southeastern Alaska: U.S. Geol. Survey Bull. 947-D, p. 65-84. Lathram, E. H., Loney, R. A., Condon, W. H., and Berg, H. C., 1959, Progress map of the geology of the Juneau quadrangle, Alaska: U.S. Geol. Survey Map 1-303, scale 1:250,000; supersedes 1-276. Loney, R. A., Brew, D. A., and Lanphere, M. A., 1967, Post-Paleozoic radiometric ages and their relevance to fault movements, northern southeastern Alaska: Geol. Soc. America Bull., v. 778, no. p. 511-526. Mertie, J. B., Jr., 1933, Notes on the geography and geology of Lituya Bay: U.S. Geol. Survey Bull. 836, p. 117-135. Miller, D. J., 1953, Preliminary geologic map of Tertiary rocks in the southeastern part of the Lituya district, Alaska, and correlated columnar sections of Tertiary rocks in the Lituya district, Alaska: U.S. Geol. Survey open-file report. Miller, D. J. 1961, Geology of the Lituya district, Gulf of Alaska Territory province, Alaska: U.S. Geol. Survey open-file report. Miller, D. J., Payne, T. G., and Gryc, George, 1959, Geology of possible petroleum provinces in Alaska, with an annotated bibliography by E. H. Cobb: U.S. Geol. Survey Bull. 1094, 131 p. Myers, A. T., Havens, R. G., and Dunton, P. J., 1961, A spec-trochemical method for the semiquantitative analyses of rocks, minerals, and ores: U.S. Geol. Survey Bull. 1084-1, p. 207-229. Plafker, George, 1967, Geologic map of the Gulf of Alaska Tertiary province, Alaska: U.S. Geol. Survey Misc. Geol. Inv. Map 1-484, scale 1:500,000. (1 in. equals about 8 miles.) Reed, J. C., 1938, Some mineral deposits of Glacier Bay and vicinity, Alaska: Econ. Geology, v. 33, no. 1, p. 52-80. Rossman, D. L., 1957, Ilmenite-bearing beach sands near Lituya Bay, Alaska: U.S. Geol. Survey open-file rept. 149, 10 p. --------- 1959, Geology and ore deposits in the Reid Inlet area, Glacier Bay, Alaska: U.S. Geol. Survey Bull. 1058-B, p. 33-59. --------- 1963a, Geology and petrology of two stocks of layered gabbro in the Fairweather Range, Alaska: U.S. Geol. Survey Bull. 1121-F, F1-F50. --------- 1963b, Geology of the eastern part of the Mount Fairweather quadrangle, Glacier Bay, Alaska: U.S. Geol. Survey Bull. 1121-K, K1-K57. Sanford, R. S., Apell, G. A., and Rutledge, F. A., 1949, Investigations of Muir Inlet or Nunatak molybdenum deposits, Glacier Bay, southeastern Alaska: U.S. Bur. Mines Rept. Inv. 4421, 6 p. Seitz, J. F., 1959, Geology of the Geikie Inlet area, Glacier Bay, Alaska: U.S. Geol. Survey Bull. 1058-C, p. 61-120. Smith, P. S., 1942, Occurrences of molybdenum minerals in Alaska: U.S. Geol. Survey Bull. 926-C, p. 161-210. Thomas, B. I., and Berryhill, R. V., 1962, Reconnaissance studies of Alaskan beach sands, eastern Gulf of Alaska: U.S. Bur. Mines Rept. Inv. 5986, 40 p.90 MINERAL RESOURCES OF GLACIER BAY NATIONAL MONUMENT, ALASKA Tocher, Don, and Miller, D. J., 1959, Field observations on effects of Alaska earthquake of 10 July, 1958: Science, v. 129, no. 3346, p. 394-395. Turekian, K. K., and Wedepohl, K. H., 1961, Distribution of the elements in some major units of the earth’s crust: Geol. Soc. America Bull., v. 72, no. 2, p. 175-192. Twenhofel, W. S., 1946, Molybdenite deposits of the Nunatak area, Muir Inlet, Glacier Bay, in Twenhofel, W. S., Robinson, G. D., and Gault, H. R., Molybdenite investigations in southeastern Alaska: U.S. Geol. Survey Bull. 947-B, p. 7-38. Twenhofel, W. S., Reed, J. C., and Gates, G. O., 1949, Some mineral investigations in southeastern Alaska: U.S. Geol. Survey Bull. 963-A, 43 p. U.S. Weather Bureau, 1937-66, Climatological data: U.S. Dept. Commerce, Environmental Sci. Service Adm., v. 23-52. Wright, F. E., and Wright, C. W., 1937, The Glacier Bay National Monument in southeastern Alaska, its glaciers and geology: U.S. Geol. Survey open-file report, 224 p. ☆ U.S. GOVERNMENT PRINTING OFFICE: 1971 O-399-330UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 632 PLATE 1 EXPLANATION OF MINERAL SYMBOLS As, Bi, Sb, Sn Mo Pb, Zn ApA Cu Ni, Cr, Co, Ti 'vCV Au Fe Ag Elements present are indicated by Solid fill in sector indicates main \ R. 53 E. 136°30v Jjfe EXPLANATION position of patterning in symbol a Mine or prospect Placer deposit approximately located commodities in deposits. Partial fill indicates commodities present in small amounts or low-grade anomalous concentrations. Numbers or letters are referred to in text and tables o Mineral deposit found during this investigation /■ \ ( i Reported prospect or mineral deposit not examined during this investigation Single sample Two or more samples Locations of analyzed bedrock samples that lack anomalous concentrations of ore metals T. 35 S\ T. 36 S.\ 58°45' R. 46 E.N T, 38 S> Surficial deposits Mainly glacial outwash and till, but include lake deposits, recent marine clays, colluvium, beach deposits, and alluvium , R. 58 E. Detrital clastic rocks Mainly graywacke, shale, siltstone, calcarenite, and minor conglomerate, metamorphosed to hornfels or to schist in some areas; include small amounts of carbonate and (or) volcanic rocks locally Carbonate rocks Mainly limestone, minor dolomite locally; metamorphosed to marble or calcsilicate hornfels in some areas; include small amounts of detrital clastic and (or) volcanic rocks locally Volcanic rocks Mainly mafic to intermediate lava flows and breccia; metamorphosed to hornfels or to greenstone, green-schist, or amphibolite in some areas; include some detrital clastic rocks locally Undifferentiated metamorphic rocks Base from U.S. Geological Survey Juneau, 1962, Mt. Fairweather, 1961, and Skagway, 1961. Grid labels (D— 1, D-2, etc.) indicate locations of 1.63,360 quadrangles Heterogeneous gneisses and mixed contact zones Gneisses mainly dioritic to tonalitic, commonly foliated, but with some massive breccia. Contact zones consist of abundant large hornfels masses surrounded by rock of adjacent intrusive body Foliated granitic rocks Mainly diorite, tonalite, and grano-diorite; form partly discordant plutons Unfoliated granitic rocks Mainly granodiorite, adamellite, and granite; form discordant plutons Geology by D. A. Brew, M. Churkin, Jr., A. B. Ford, C. C. Hawley, L. C. Huff, E. M. MacKevett, Jr., A. T. Ovenshine, J. G. Smith, and R. J. Wehr, 1966. Earlier mapping incorporated, modified from Rossman (1963a, b); Seitz (1959); Miller (1961); Lathram, Loney, Condon, and Berg (1959); and Twenhofel (1946) R. 54 E, MAP SHOWING BEDROGK LITHOLOGY AND LOCATIONS OF KNOWN METALLIFEROUS MINERAL DEPOSITS, GLACIER BAY NATIONAL MONUMENT, ALASKA Includes previously known deposits and deposits found during the current investigation. The term 'mineral deposits”as here used includes all anomalous concentrations of metallic commodities detected SCALE 1:250 000 10 15 20 MILES 5 0 5 10 15 20 KILOMETERS CONTOUR INTERVAL 200 FEET DOTTED LINES REPRESENT 100 FOOT CONTOURS DATUM IS MEAN SEA LEVEL DEPTH CURVES AND SOUNDINGS IN FEET—DATUM IS MEAN LOWER LOW WATER SHORELINE SHOWN REPRESENTS THE APPROXIMATE LINE OF MEAN HIGH WATER 1970 MAGNETIC DECLINATION OF SHEET VARIES FROM 29° TO 30° EASTUNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY r 59°15'... 59°15' EXPLANATION <10 ppm ® 10-15 ppm O 16-24 ppm • >25 ppm Value shown if >25 ppm T. 35 s: T. 36 S. if T. 31 S. •J- 33 S. R— 59°00 ' Base from U. S. Geological Survey Juneau, 1962, Mt. Fairweather, 1961, and Skagway, 1961 , 61 E. 135°30' R. 53 E R. 54 E. MAP SHOWING LEAD CONCENTRATION IN STREAM-SEDIMENT SAMPLES GLACIER BAY NATIONAL MONUMENT, ALASKA SCALE 1:250 000 5 0 5 10 15 20 MILES L---1 I-----1 .1-1 I . ■ ■ " 1 -t. I- —■ =3 5 0 5 10 15 20 KILOMETERS i 1 F—| | 1 | —i l— i CONTOUR INTERVAL 200 FEET DOTTED LINES REPRESENT 100-F00T CONTOURS DATUM IS MEAN SEA LEVEL DEPTH CURVES AND SOUNDINGS IN FEET—DATUM IS MEAN LOWER LOW WATER SHORELINE SHOWN REPRESENTS THE APPROXIMATE LINE OF MEAN HIGH WATER 1970 MAGNETIC DECLINATION OF SHEET VARIES FROM 29° TO 30° EASTUNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 632 PLATE 7 59° 15 T. 30 S. E. CANADA R. 52 E UNTTED STATES EXPLANATION <10 ppm -*OOG- v&^BIackl, yTOlQMountain -fV-Mount fK Brack j^Sitth-gha-ee .i ■ 10-19 ppm -Mount 'Barnard ■3000- 20-39 ppm Gable, Mountain; . ck—.Coleman TpSYPeak o >40 ppm Value shown if >40 ppm -McCoiirteii Rids*? f • glacier P3S§ Mount; feriti'nelSS; \ Peal*' • ijyMbdnt (Abdallah" ’Mt \-Elderi Snow -Dome” .Triangle,. Curtis uj : i/poo- < Mount V \ < ()/Quincy Adams V INDEFINITE Tomtit C^Glaacr ffe«.MouhtCN mY-Merriam Mount\\' Kloh Kutz jfnrw-^ferio' Composite Island H Klotz, '’“■Hills) Kas^tji Mt Young 5# Mount .alisbury ts.Cpvra m id 'a. l-Peak Endicott Gap 't. 35 S Sipi 'MounCAxV \ <%Mtn ■ Gi I be/f , Island ,MtAbbe Garforthjq > Mou n't is; EscuresW' Sebree .Island Mount/ ' .OrvilleUr Puffin' Island Sturgess. Island( Lone Contact Nunatak \ ^ Heathen Nunatak m Milled KC ‘JSSW^ Peak Hugh Miller ‘MounOiin M iGilbert 9 *T;M OCmtYo* W0 K Y13 /■% .'*< ®r*% f/S*Fossil .. K V fm?- .Red Bed v \ Peaks V c«Y* Mount ..(•F'Criilon $;( Drake ’ \ Island Lefand Or (Islands A __\Crilk $ .A'/Hrt Cenotaph^ ■j/f- Island' S Marble •^©■Island YY ■if;] Marble ;\ HarborYf Mount Dagelet Beartra'ckT 'vL«M°untt 'Vih'.Divide'. Willoughby .Island ArBlackthomY < ! PemMt m t Flapjack ‘Island < . ,«viount La Perdufe) f t, --'.kQ • is; North \ V_Doi)|e MV. - Link; Island. Mount Wood* -\Netland y, . .-.Lars Threesome Mountain ) rJ i')Kidney l-^"#Ylsland Beatdsleef J::d L Spider, ..4-y -A Island Y us ion Y— lyi idd IdfL’ *^s Dome Island, Island's1 U 7/Q Young Island h"3t0' Lagoon Mtiynt. .;Mai:cbainyillgtT? 13320/; Palma ThtHUH'l Boussole _..Head Small Truk Oi/.i Dunikis Ho y A . rrn - • ’ 1961, and Skagway, 1961 SugarioafT Island^5 Horn f-./i Mln«, ■/ Island^/V Polka" Peninsula Villalu^l'fe 58°30 ' MAP SHOWING NIGKEL CONCENTRATION IN STREAM-SEDIMENT SAMPLES GLACIER BAY NATIONAL MONUMENT, ALASKA SCALE 1:250 000 5 0 5 10 15 20 MILES 5 0 5 10 15 20 KILOMETERS i—i i^-i i—i......- i r i - 1 =i CONTOUR INTERVAL 200 FEET DOTTED LINES REPRESENT 100-FOOT CONTOURS DATUM IS MEAN SEA LEVEL DEPTH CURVES AND SOUNDINGS IN FEET—DATUM IS MEAN LOWER LOW WATER SHORELINE SHOWN REPRESENTS THE APPROXIMATE LINE OF MEAN HIGH WATER 1970 MAGNETIC DECLINATION OF SHEET VARIES FROM 29° TO 30° EASTUNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 632 PLATE 8 - 59° 15 T. 30 S. 136°00 _CANADA R. 52 E UNITED STATES '-r EXPLANATION HffilBlackl, !)XS'.^Mountain •Mount Barnard r\Sitth-gha-e'e' ■'Y'.DaaP 4 ■ :3000v-\ Gabl© Mountain; ’'^/...Coleman SSSTeak c McCprwTell Bids'? Y/lacier iPstg it Mount; VRice'1 Be ’ io bi 50 Cd I/.N unatakV / ).Knot)® . ?_»»» W 1: I Red Ui Mini ■: , Sentinel^; ■i\. PeaK*' ) TjiMBunt Mdallafr Ms 8 ;Dome- U •Mt 'Elder; iTViangl^ ICurtTs &HIIIS: 1300 Sr# - 1400 ^ XMoiintV■ /’Q\. TO/Quincy Adams V INDEFINITE •9jSW§ U Peak , , Island \ «.t • Hugh Miller ‘Mountain Mount- .Mount' Bertha 1000 St^f ; h 1000 Sr* / s 1000 Sr ;MoCmt Triable N Marble ■Island r Pf Mount uSTCrillon -ffW A Fist? $ ■ : Cenotaph^" ' Island Y" ^Fossil rstfjx ...Scrum S f Drake \ Island Leland T»% ■Islands • •IS Marble ^Island ■ (Jw July Fourth Mountain's^ t'tfl,Marble.\ .•kV.Mtn Y. VV?J mm two samples YSS^.Tiirfgit N '■'-I Peak J : 1 ■■ 0 X !' M E N V- 7 1 ‘ 1000 Sr* -J 'EKasMount.ii a. (Vis La ChausseewjT / Spity^f- Harbor Francis lOOO'Sr Mount Dagelet MfSi’ioum, JrasPivideC BeahrackT ..Willoughby ^..Island -5£“¥ A 'Blackthorn I PeaKth/H,- Mount T Skarn , Flapjack 'Island A , .X.../'t>iount La Perous& •North ’ ponie1 MYy .- Link! Island/ Mount; ■Wood. Threesome .Mountain' ■" , Kidney M ' Beatdsleei , Spider, -•!>/ Z' Island^ STirWS idd IdfeX Strawber Island Slatted Bartlett ' \Jjikc Islands Young Island I£Nopot vf Y TgWatchai nvi I leg^i >2718 “i«OA Palma 2606', BoussoleStl, P\/C> r$\? ....Bead d f\ 9$ypr,il.h Dundxis ' Bay ' :al Survey Juneau, 1962. and Skagway, 1961 .Horn! - Mtn- Libby /?;•; IslandiyT1 Polka Peninsula Villaluenj R. 53 E. - R. 54 E. 58°30' MAP SHOWING ANOMALOUS VALUES OF ARSENIC, BERYLLIUM, BISMUTH, CADMIUM, SILVER, STRONTIUM TIN TUNGSTEN AND ZINC IN STREAM-SEDIMENT SAMPLES, GLACIER BAY NATIONAL MONUMENT, ALASKA SCALE 1:250 000 5 0 5 10 15 20 MILES 5 0 5 10 15 20 KILOMETERS CONTOUR INTERVAL 200 FEET DOTTED LINES REPRESENT 100-FOOT CONTOURS DATUM IS MEAN SEA LEVEL DEPTH CURVES AND SOUNDINGS IN FEET—DATUM IS MEAN LOWER LOW WATER SHORELINE SHOWN REPRESENTS THE APPROXIMATE LINE OF MEAN HIGH WATER 1970 MAGNETIC DECLINATION OF SHEET VARIES FROM 29° TO 30° EAST'""mniiiiu, rl-2 in. quartz 2-3 in. quartz 66AMK-332 (.44) 8 in. quartz. ''Miiiiiiiiiminl? ^/ttiiilllliliiiiiilli///^ Alt 950 feet (assumed) 6 in. quartz, b6/AMk-330 (.01) /. && 54-12 (0.22) ^ \ •Vein approximately 18 in. thick locally with • a metamorphosed horse 6 in. thick Small veins at surface Quartz stringer^ 1 in. quartz.. . Quartz stringer. 2 (.36)"vA 1 (.14)%^' 7k ■ Alt 987 feet % A oi % M-2y>ln.'quartz % ; in.] quartz at|surface . *. t s • b ^ %6 A M k-333/"(,01) j? Quartz stringei Juartz lesi than • ] - kt 3 in. ‘ &- -Small quartz veins •Several branching quartz veins le generally 1-2 in. thick. Stope 85 \*66AMk-383 (.33) 66AMk-384 (.50) X 66AMk-385 (.35) J 66AMk-386 (1.08) 10 (.26) r \ 3 <-5°)/ \ 54-11 (0.50)® Y-'" *vP UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGIGAL SURVEY PROFESSIONAL PAPER 632 PLATE 9 Base from a tape and compass survey by H. M. Fowler, Geology modified from Rossman (1959, pi. 5) Territorial Department of Mines (Alaska Division of Mines and Minerals), 1951 GEOLOGIC SKETCH MAP SHOWING SAMPLE LOCATIONS AT THE LEROY MINE, GLACIER BAY, ALASKA 40 0 40 80 FEET I__I_I__I__I________I__________ I 10 0 10 20 METERS I..........................l___________I CONTOUR INTERVAL 50 FEET DATUM IS APPROXIMATE MEAN SEA LEVEL APPROXIMATE MEAN DECLINATION, 1970 EXPLANATION lv:-::::::Kvs^ zrl ABC Metamorphic rocks A, slate, horrifels, schist; includes intensely sheared granodiorite Bf black graphitic schist C, black argillite a*0 _____L__________ Contact, showing dip 80 Fault, showing dip 80 • • ■ i i ~ Quartz vein, showing dip IS] Foot of raise □ Ore chute l l l I l l l I I I I I I Opencut Portal and opencut JK Inclined workings; chevrons point downward Lagging or timbering tunnel ® 54-11 (0.50) Location of sample collected and assayed by the Territorial Department of Mines. Value for gold, in ounces per ton, is shown in parentheses. Sample data given in table 12 x 66AM k-386 (1.08) Location of sample collected during present investigation showing gold content, in ounces per ton (in parentheses). Sample data given in table 11UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 632 PLATE 10 GAMMAS GAMMAS EXPLANATION 100 0 100 200 300 FEET I I I I I___________|_________|__________| Alt 1,740 fe< and A. S. Radtke, Jr., July 1966 GEOLOGIC SIETCH MAR MAGNETIC PROFILES, AND GENERALIZED GEOLOGIC SECTION, QUEEN INLET MAGNETITE LOCALITY, GLACIER BAY NATIONAL MONUMENT, ALASKAUNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 632 PLATE 12 ► *- * t EXPLANATION ./ 66ARe- 20 (,05-.005)/^66ARe-^C01-.005) ;.3 (.05- 005) 66ARe-9 (.03- 007) 21 (.15- 002)^f0^1‘0°51)-003) /^V»^(o (.07-.01) • ..7f.Q7-.01)/I6 (07':01> 0S)A^ //' :V V / • 8 ( 07-.C2)/ ' / 15 (.05- 003/ / V (.05-.005) :01) 40 (G. .0005- 0028; T. .001- 0046) 10 ( 006 yC ^ ■ _ ■ 43 (.0007-.0032) ( ^ - 66ARell8 (.0007-.0D . ^ 13W " ©3 I f i66AMk-93 (402l?bl5)0029 J'45 (^.doo^oosi, T. .032- 029) )-7. : or.inr.Wa nnol n. . " m. 39 (.0075- 008) /94 (.01-.015) 66AMk-95 (.05-.03)/ 66AMk-122_(.0015-.015) \f 123 (.003-.01) V"'-\124 (.002- 02) 66AMk- 96 (,03-,01)/ ...P :/• 37 (0007-.fX)39)B 36 (.014.013) 49 (0-.003) ■ / ■ ■ 48 (.0005-.002)' 50 (.01- 01) ^ . . . . 97 (.02-.(jl) '- .125(.01-02) 98 (.01-.Q2) .126 (.002-005) 99 (.03- 02) 127 (.003- 003) 46 (.0-.0028) ,47 (.0015.-01) 51 (G, .0005-.003; T, .001- 015) 60 (.0004- 0034) 58 (.0006- 0031). \ 61 (G.0-.010; T, .0007-.023) ■ ■ ■ * 59 (0-.0032) \ 52 (.0007-.007. 100 (.003-.01} ^01 ((003-01) (V-05) (.002-.0 128 (.005-.005) f 102A 1 1026 129 (.0015-«07) 05) <132 (.0007-.007) 02) / I .30 ( 0007:01) y • " I33 005) : 131 C0007-.005)/ ■ 134 (.01- 005) 103 (.002-.02) 1 66AMk 104 (.003*015) <-136 ( 0015-,005) 53) (.003-.015) \ 91. 105 (.0007-.007) ) 106,(005-005) 54(0-.003), \ 1 \l<5? (.001-.05) 55 (.002-.01; B. 0-.005) B (08(.01-.l) _ .0042) \ i 14 (.0032-.0037) ,■15 (.0005-.0037) , 16 (.0006-.0035) ■ 17 ( 0007-.0048)r)137 (.007-.003) / ;18 (.0008-.0046)* , 20 ( 0014- 0049) 19 (.0013-0040) ■ B?1 ,0017..006^ 22 (.0021 -.0063) MmmWM Area of known molybdenum mineralization vlll (.0005-.01) 66AMk-112 (<.0005-.03) Location of chip sample Sample intervals range between 1 and 5 feet. Percentage of molybdenum and copper is shown in parentheses (Mo-Cu). Results of semi quantitative spectrographic analyses are given in table 13 45 (G, .0007-.0031; T, .032-.029) ■ Location of soil sample Percentage of molybdenum and copper is shown in parentheses (Mo-Cu). Results of semiquantitative spectrographic analyses are given in table 1U (B, G, and T refer to description of samples) ©1 Location and number of diamond-drill hole that was drilled in 1966 <$> Location of U.S. Bureau of Mines drill hole, 1942 Approximately 136°06' \ I 56 (0-.002) - 003- 03) '66ARe-24 (1-.07) Approximately 58°59' - J 62 (.001 -.0038) L 111 (.0005-.0te---—66ARe~23 (/15-.007) 66AMK-112 (< 0005- 03)., I 63 (0025-.0035) I \64 (.091- 027; B. 0005- 003) ■ 65 (.0015-.0068) | 66 (.0018- 014), '67 ( 0022-.045r ■ 24 (.001 -.0,13) ■ 25 (.0015- 019) / 26 (.008-.6,31) 27 (.(XH9-.024) 114 (0-.003) ■ 113(0-.002) ■ 112 (.001-.01) ■ 111 (0-.007) ■ 110 (0-.003) ■ 109 (0-.003) 108 (0-.002) 107 (0-.002; B, 0-.005) ■ 28 (.0021-.025) I 29 (.0024- 032) ■ 30 (.0029-.02^) 2-.0 i) 31 (.0012- 106 (0-.01) ■ 105 (0-.003; B, 0-.002) 32 (.0008-0049) 68(0011-0092) | 69 (0011-0059). 66ARe-25 (.003-.1) J * c=> 9/ 33 (0006-0078)/ 34 (.001-033)/ 104 (0-003) 103 (0-003) 82 (0-002)/ 83 (0-002) ■ 81 (0-003) 1 84 (0-002) 1 85 (0-002) ■ 80 (0-003) I 79 (0005-0027) I 70 (0008-.006)\ 71 (.0008-.0042)\ 76 (.0005-.0028)^-2 (0032-00^ I 102 (0-003; B. 0-003) 101 (0-002) 75 (-9009-0032) "77 (0-003) I 78 (0-0026) 73 (0013-0058) "74 (0009-0038 87 (0- 005) 88 (0-005) I 89 (.0005-015) I 100 (0-003) 99 (0-002) 98 (0-002) 97 (0-005) 90 (0-01) 91 (0-007)_ 96 (0-003) 92 (0-003) 1 , ■ 95 (0-003) 94 (0-007) /V u Ar T A K Base by W. S. Twenhofel and R. M. Mielke, 1942 (Twenhofel, 1946, pi. 2) Bathymetry by A. T. Ovenshine and R. J. Wehr, August 1966 MAP OF THE NUNATAK MOLYBDENUM PROSPECT SHOWING SAMPLE LOCATIONS EXTENT OF KNOWN MINERALIZATION, AND BATHYMETRY OF ADJACENT PARTS OF MUIR INLET - 200 0 1 1 1 1 1 1__ 200 400 600 800 FEET 100 0 1___1 1 1 1___1_ 100 200 400 METERS APPROXIMATE MEAN DECLINATION, 1970 LAND CONTOUR INTERVAL 250 FEET SUBMARINE CONTOUR INTERVAL 100 FEET DATUM IS MEAN SEA LEVEL632 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PRO FESSpLNATEP2APER 1 36°3oV R>5;3E- EXPLANATION <30 ppm ® 30-59 ppm O 60-119 ppm J>120 ppm Value shown if >120 ppm T. 35 S T. 36 S.' 58°45' ■ )38°00>\ ( T. 32 S. : S9°0Q ' Base from U. S. Geological Survey Juneau, 1962, Mt. Fairweather, 1961, and Skagway, 1961 R. 53 E. R. 54 E, MAP SHOWING TOTAL HEAVY-METALS CONCENTRATION IN STREAM-SEDlMFN'r GLACIER BAY NATIONAL MONUMENT, ALASKA SCALE 1:250 000 5 0 5 10 15 20 MILES 5 0 5 10 15 20 KILOMETERS CONTOUR INTERVAL 200 FEET DOTTED LINES REPRESENT 100-FOOT CONTOURS DATUM IS MEAN SEA LEVEL DEPTH CURVES AND SOUNDINGS IN FEET—DATUM IS MEAN LOWER LOW WATER SHORELINE SHOWN REPRESENTS THE APPROXIMATE LINE OF MEAN HIGH WATER 1970 MAGNETIC DECLINATION OF SHEET VARIES FROM 29° TO 30° EAST7 DAY 63? v "Geology of the Florence Area, Wisconsin and Michigan GEOLOGICAL SURVEY PROFESSIONAL PAPER 633 Prepared under the auspices of U.S. Department of the Interior, Geological Survey; University Extension — The University of Wisconsin Geological and Natural History Survey; Michigan Department of Conservation, Geological Survey Division 1 Geology of the Florence Area, Wisconsin and Michigan By CARL E. DUTTON GEOLOGICAL SURVEY PROFESSIONAL PAPER 633 Prepared under the auspices of U.S. Department of the Interior, Geological Survey; University Extension — The University of Wisconsin Geological and Natural History Survey; Michigan Department of Conservation, Geological Survey Division 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. 77-610426 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402CONTENTS Abstract______________________________________________ Introduction__________________________________________ Location and surface features____________________ Climate and vegetation___________________________ Accessibility____________________________________ Discovery and mining of iron ore_________________ Previous geologic work___________________________ Purpose and methods of this investigation________ Acknowledgments._________________________________ General geology_______________________________________ Stratified rocks______________________________________ Lower Precambrian rocks__________________________ Quinnesec Formation__________________________ Description______________________________ Amphibolite__________________________ Schist_______________________________ Quartzite____________________________ Felsic Metavolcanic rocks____________ Thickness and relation to adjacent formations____________________________________ Character of original rock_______________ Age and correlation______________________ Middle Precambrian rocks—Animikie Series_________ Baraga Group_________________________________ Hemlock(?) Formation_____________________ Michigamme Slate_________________________ Definition, distribution, and lithology. . Brule River block____________________ Keyes Lake block_____________________ Quartzite________________________ Strata younger than quartzite____ Pine River block_____________________ Slate, schist, and phyllite______ Quartz graywacke_________________ Amphibolite______________________ Grunerite iron-formation_________ Quartzitic conglomerate__________ Iron-f ormation__________________ Phyllite above quartzitic conglomerate____________________________ Greenstone agglomerate___________ Slate and metagraywacke__________ Thickness and conditions of deposition. Age and correlation__________________ Badwater Greenstone______________________ Definition, distribution, and general lithology— Greenstone___________________________ Amphibolite (metabasalt)_____________ Iron-formation_______________________ Slate, metaargillite, and quartz graywacke________________________________ Tuffaceous (?) rocks_________________ Page 1 2 2 2 2 2 4 5 7 7 9 9 9 9 9 9 10 10 11 11 11 11 11 12 12 12 13 14 14 17 18 20 20 20 21 21 22 23 23 23 23 23 24 24 24 25 25 26 26 Stratified rocks—Continued Middle Precambrian rocks—Continued Paint River Group____________________________ Dunn Creek Slate________________________ Definition and distribution_________ Description_________________________ Thickness and relations to adjacent formations_____________________________ Conditions of deposition____________ Age and correlation_________________ Riverton Iron-Formation_________________ Definition and distribution_________ Description_________________________ Thickness and relations to adjacent formations________________________ Conditions of deposition____________ Age and correlation_________________ Post-Riverton strata____________________ Distribution________________________ Description_________________________ Conditions of deposition____________ Thickness and relations to adjacent formations________________________ Age and correlation_________________ Cambrian (?) rocks_______________________________ Intrusive rocks_______________________________________ Metagabbro_______________________________________ Hoskin Lake Granite______________________________ Peavy Pond Complex_______________________________ Structural geology____________________________________ Brule River block________________________________ Commonwealth syncline________________________ Other folds__________________________________ Keyes Lake block_________________________________ Pine River block_________________________________ Popple River block__________________________ Foliation and lineation__________________________ Time of folding and faulting_____________________ Metamorphism__________________________________________ Chlorite zone____________________________________ Biotite zone_____________________________________ Garnet zone______________________________________ Staurolite zone__________________________________ Graywacke-shale suite________________________ Iron-formation_______________________________ Basic igneous rocks__________________________ Sillimanite zone_________________________________ Graywacke-shale suite________________________ Basic igneous rocks__________________________ Peavy node_______________________________________ Time of metamorphism and relation to deformation. Page 26 27 27 27 29 30 30 30 30 30 31 32 32 32 32 32 33 34 34 34 34 34 36 37 37 37 37 38 38 39 39 40 40 40 40 40 41 41 41 42 42 42 42 42 43 43 inIV CONTENTS Page Magnetic surveys_____________________________________ 45 Ground magnetic survey___________________________ 45 Aeromagnetic survey______________________________ 46 Brule River block____________________________ 46 Keyes Lake block_____________________________ 46 Pine River block_____________________________ 46 Popple River block___________________________ 46 Economic geology_____________________________________ 47 Iron-ore mines___________________________________ 47 Florence mine________________________________ 47 Badger mine__________________________________ 48 Buckeye mine_________________________________ 48 Commonwealth mine____________________________ 48 Page Economic geology—Continued Iron-ore mines—Continued Davidson mine__________________________________ 48 Ernst mine_____________________________________ 49 Explorations_______________________________________ 49 Nonmagnetic iron-formation_____________________ 49 Welch______________________________________ 49 Polderman__________________________________ 49 Spread Eagle_______________________________ 49 Magnetitic iron-formation______________________ 50 Guides to further exploration______________________ 51 References cited________________________________________ 51 Index__________________________________________________ 53 ILLUSTRATIONS [Plates are In poc ket] Plate 1. Map showing geology of Precambrian rocks in the Florence SE and Iron Mountain SW quadrangles, Florence County, Wis. 2. Map showing geology of Precambrian rocks in the Florence West and Florence East quadrangles, Florence County, Wis., and Iron County, Mich. 3. Geologic map showing lithology of the Riverton Iron-Formation and associated strata in Florence mine area, Florence County, Wis. 4. Generalized geologic map and sections showing major structural features of the Florence area, Wisconsin. 5. Generalized geologic map of Florence area, Wisconsin, and part of Michigan showing metamorphic zones. 6. Magnetic and geologic map of area near Keyes Lake, Florence County, Wis. 7. Aeromagnetic contour map of the Florence SE and Iron Mountain SW quadrangles, Florence County, Wis. 8. Aeromagnetic contour map of the Florence West and Florence East quadrangles, Florence County, Wis., and Iron County, Mich. Figure 1. Generalized geologic map of northern Wisconsin and northwestern Michigan____________________________ 2. Geologic map showing lithology of the Michigamme Slate at the Little Commonwealth exploration_______ 3. Map showing distribution and relation of the Michigamme Slate and Quinnesec Formation_______________ 4-12. Photographs: 4. Predominance of quartz pebbles in quartzitic conglomerate near the Pine River, Florence County, Wis..___________________________________________________________________________________ 5. Alinement of pebbles in quartzitic conglomerate____________________________________________ 6. Ellipsoidal (pillow) structure in the Badwater Greenstone__________________________________ 7. Pencil slate_______________________________________________________________________________ 8. Graphitic slate breccia____________________________________________________________________ 9. Chert breccia in Riverton or post-Riverton strata__________________________________________ 10. Small sills of metagabbro in hornblende schist of the Quinnesec Formation__________________ 11. Michigamme Slate___________________________________________________________________________ 12. Folded foliation in the Quinnesec Formation________________________________________________ Page 3 16 19 21 22 24 28 29 34 35 43 44 TABLES Table 1. Lithologic sequence of Precambrian rocks in Iron and Dickinson Counties, Mich________________ 2. Rock units in the Florence area______________________________________________________________ 3. Chemical analyses of specimens from the Dunn Creek Slate in Florence, Wis., area_____________ 4. Chemical analysis of interbedded siderite-chert from the Riverton Iron-Formation, Florence, Wis., area. 5. Chemical analysis of the Hiawatha Graywacke, Florence, Wis., area____________________________ 6. Chemical analyses and modes of three samples from the Michigamme Slate________________________ 7. Partial analyses of iron ores from Florence, Wis., area______________________________________ Page 6 8 28 31 33 43 47GEOLOGY OF THE FLORENCE AREA, WISCONSIN AND MICHIGAN By Carl E. Dutton ABSTRACT The Florence area, in northeastern Wisconsin and an adjacent tract of Michigan, is part of the Menominee iron-bearing “range” of the Lake Superior region. It is in the upland that lies between Lake Superior and Lake Michigan and has an average elevation of about 1,300 feet; the relief exceeds 100 feet only locally. Glacial deposits are extensive and form characteristic hummocky surfaces. Outcrops are commonly small and scattered, but quartzose metasedimentary rocks and mafic meta-igneous rocks are well exposed locally on a few ridges and hills and along streams. Exclusive of intrusive masses, metavolcanic rocks of early Precambrian age underlie much of the southern part of the area, and metasedimentary and metavolcanic rocks of middle Precambrian age are at the bedrock surface elsewhere. Metagabbro, metadiabase, and granite of late middle Precambrian age intrude the lower Precambrian rocks, but only the mafic rocks intrude the middle Precambrian formations. Two very small areas of sandstone of probable Late Cambrian age are present but are too small to be shown on the maps. The Precambrian formations of the Florence area are correlated with units in either that part of the Menominee range to the east, which is the Iron Mountain-Norway district of southern Dickinson County, Mich., or that to the northwest, which is the Crystal Falls-Iron River district of southern Iron County, Mich. The formations are, however, in various folded segments that have been terminated and displaced by three major northwest-trending faults. Lower Precambrian rocks are mainly metabasalt and metarhyolite that constitute the Quinnesec Formation of unknown thickness. Middle Precambrian rocks in the area are divided into two groups. The Baraga Group is composed of the Hemlock (?) Formation, Michigamme Slate, and Badwater Greenstone; and the Paint River Group is composed of the Dunn Creek Slate, Riverton Iron-Formation, Hiawatha Graywacke, Stambaugh Slate, and Fortune Lakes Slate. So far as is known, conformable relations are generally prevalent, except for a disconformity at the base of the Hiawatha Graywacke and the discontinuity of the Riverton in the northwest part of the area. The Hemlock(?) Formation is amphibolite formed from metamorphosed mafic pyroclastic material; its thickness is not known because no older strata are exposed. The Michigamme Slate is predominantly metaargillite and schist but also contains metagraywacke, quartzite, conglomerate, metaagglomerate, and amphibolite. The thickness of the Michigamme is probably from 5,000 to about 20,000 feet. The Badwater Greenstone is almost exclusively metabasalt with minor amounts of phyllitic metaargillite or metatuff and locally thin beds of magnetite-grunerite schist. The thickness of the formation may range from 2,000 to 15,000 feet. The Dunn Creek Slate is fine-grained quartz graywacke and slate in the lower part and massive and laminated graphitic rock in the upper part; its thickness is possibly 2,500 feet. The Riverton Iron-Formation is a thin-bedded sedimentary unit composed of alternate ferruginous and siliceous layers. The ferruginous layers are siderite, hematite, limonite, and grune-rite, in various combinations; the siliceous layers are chert or metachert. The total thickness is about 600 feet. The Hiawatha Graywacke is mainly a breccia in which small chert fragments are enclosed by massive quartz graywacke or by siliceous limo-nitic material and associated phyllitic quartz graywacke; its thickness is not known but in general is probably not more than 100 feet. The Stambaugh Slate is a moderately magnetic fissile slate with some graywacke and is about 200 feet thick. The Fortune Lakes Slate is gray slate and interlayered graywacke; its exposed thickness is 1,000 feet, but the total thickness is unknown because no younger strata crop out. Metagabbro and metadiabase intrusive rocks of late middle Precambrian age are mainly elongate bodies that are commonly parallel to foliation in lower Precambrian metabasalt; they also tend to parallel the metasedimentary rocks in the Badwater Greenstone but were not seen in contact with them. Few intrusive relations to country rocks are exposed. Granite dikes and pegmatites that cut metabasalt of the Quinnesec Formation are believed to be part of the Hoskin Lake Granite, which probably underlies most of an area where scattered exposures are exclusively granite. Age determinations of similar granite in the nearby area indicate that the probable age is late middle Precambrian. Three faults of northwesterly trend, each of which shows relative uplift on the southwest side, divide the area structurally into four units. The northernmost unit contains a northwest-plunging major syncline of which most of the southwest limb is missing because of faulting and erosion. The adjacent unit is mainly a steep inclined south-facing homocline but also contains two synclines and an anticline that plunge southeastward. The third unit is apparently also homoclinal with vertical to steep southerly inclination and top facing southward. The southernmost unit contains foliated metavolcanic rocks that have a northwesterly trend, vertical to steep inclination, and tops facing northward. The Hoskin Lake Granite and most of the metagabbro are in this part of the area. Metamorphism of the Precambrian rocks is mainly at chlorite grade along the central part of the plunging major syncline and rises to sillimanite grade to the north and to garnet grade to the south. Continuity of isograds has probably been interrupted by faulting. 12 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN Iron ore has been the only mineral resource produced, except for sand and gravel that is used locally. Iron ore was first shipped in 1880, and through 1960 a total of about 7,750,000 tons was obtained from six mines. The ore was derived from siderite-chert iron-formation by the oxidation of siderite to hematite or limonite or both and by decrease or removal of chert through leaching or replacement with iron oxide. Ore ranged from 48 to almost 51 percent iron, as mined, and from 52.5 to 56.5 percent iron, if dried. Areas along the projected strike of the Riverton Iron-Formation and along positive magnetic anomalies related to parts of the Badwater Greenstone and Michigamme Slate have been unsuccessfully explored for iron ore by test pits and drill holes. The potentialities for high-grade iron ore or for low-grade ore amenable to beneficiation are not believed to be favorable. The ore bodies that were mined were all small, and geologic features that might have been conducive to the formation of large ore bodies do not appear to be present. The amount of magnetic or nonmagnetic low-grade ore that is readily available is believed to be rather limited because of the small dimensions at the surface and the steep dip. INTRODUCTION LOCATION AND SURFACE FEATURES The mapped area includes about 170 square miles of Florence County in northeastern Wisconsin and about 40 square miles in the adjacent southeastern part of Iron County, Mich. (fig. 1). It consists of four 714-minute quadrangles between lat 45°45' and 46°00' N. and long 88°7'30" and 88°22'30" W. The Florence East and Florence West quadrangles constitute the north half of the area, the Iron Mountain SW and Florence SE the south half. The Florence area is in the eastern part of the extension of Precambrian rock south of Lake Superior and is closely related geologically to the Crystal Falls and Iron Eiver areas to the northwest in Michigan (fig. 1). These three areas constitute the western part of the Menominee iron-bearing “range” that differs from the eastern part in some characteristics of stratigraphy, structure, and iron ore. The surface of the mapped area lies generally between 1,200 and 1,450 feet above sea level. It is broadly undulating to somewhat hilly; local relief is commonly less than 100 feet. The lowest and highest parts of the area are about 1,040 and 1,580 feet, respectively. Glacial till and glaciofluvial deposits extend over most of the mapped area and locally are more than 400 feet thick. Hummocks, numerous swamps, and a few scattered lakes are present. In the east-central part of the area, numerous irregular pits occur in glaciofluvial deposits, and a few of the large depressions are occupied by lakes. The area is drained by the Menominee River and its tributaries—the Michigamme, Paint, Brule, and Pine Rivers. Dissection along these rivers and their tributaries has partly determined the distribution of outcrops; however, some outcrops that were formerly visible are now covered by artificial lakes. Several prominent interstream ridges and upland tracts have numerous outcrops. CLIMATE AND VEGETATION Information on climate and vegetation in Florence County is reported by Hole, Olson, Schmude, and Milfred (1962). The climate of the Florence area is the humid cool-summer continental type. The average of total annual precipitation from 1891 to 1932 was about 30 inches, which includes the average total annual snowfall of almost 60 inches. The 42-year extremes of monthly average temperature are about 80 °F in July and 3°F in January. Approximately 90 percent of the county is covered by forests in which aspen is abundant and northern hardwoods (mainly sugar maple, elm, yellow birch, and basswood) are common. Oak, pine, and swamp conifers are in limited stands. Forest products are mainly sawtimber, poletimber, pulpwood, and wood for a variety of miscellaneous uses. The annual sales total about $40,000. About one-half the farm area is in woodland, of which about one-half is pasture. There is cleared land in the vicinity of Florence and the southeast part of the mapped area. The available cropland is used for hay, oats, corn and grass silage, and Irish potatoes. ACCESSIBILITY The principal road through the mapped area, a combination of U.S. Highways 2 and 141, trends northwest through the northern part and passes through the village of Florence. Access to and through some of the western part of the area is provided by State Routes 70 and 101. County roads and the roads leading from them permit access to most of the area, and only a few localities are more than a mile from a road. The closest passenger service by bus or by plane is through Iron Mountain, Mich., 15 miles eastward. The area has about 2,000 inhabitants, half of whom live in three unincorporated communities. Florence has a population of about 800 and is the county seat. The population of Spread Eagle is about 120 and of Commonwealth about 115. DISCOVERY AND MINING OF IRON ORE Iron ore was discovered in the Florence area in 1873. The site was developed into the Florence mine, and ore was first shipped in 1880. Shipments from this mine continued through 1931 and totaled approximatelyINTRODUCTION 3 47° 46° 90° 89° 88° Figuke 1.—Generalized geologic map of northern Wisconsin and northwestern Michigan showing location of the Florence area.4 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN 3,700,000 tons. The second discovery of ore was south of the present village of Commonwealth, and here too ore was first shipped in 1880. The Commonwealth group of mines, which includes the Badger, Buckeye, Commonwealth, and Davidson operations, shipped ore through 1916, and stockpile ore was shipped from 1937 to 1943. The shipments totaled about 3,000,000 tons. More recent shipments, mainly from the Davidson mine in 1953,1955-57, and 1959-60 and some from the Badger mine in 1959-60, totaled about 342,000 tons. The Ernst mine, near Commonwealth, shipped about 700,000 tons of ore during intermittent operation from 1912 to 1929. A detailed account of the discoveries and early developments was prepared in 1910-12 by W. O. Hotchkiss and is in the files of the Wisconsin Geological and Natural History Survey. Most mining in the Florence area ceased long ago because of the relatively poor quality of ore, and companies went out of business. Therefore available records of operations are fragmentary at best, and significant geologic data related to the mining are very limited. PREVIOUS GEOLOGIC WORK Little previous work has been done in the specific area of the present investigation, but work begun in 1937 in the area adjacent to the east and in 1942 in the area to the northwest provided data on lithology, stratigraphy, and structure that were applicable to the Florence area. The first geologic reports of significance concerning Florence County, Wis., were by Brooks (1880), Wich-man (1880), and Wright (1880). Brooks and Wright studied and mapped the outcrops along the Menominee River and its principal tributaries in areas that are now Florence and Marinette Counties, Wis., and Dickinson and Iron Counties, Mich. Brooks and Wright described the hand specimens, and Wichman the thin sections. They also interpreted local stratigraphy, structure, and economic geology as related to the iron deposits. They divided the sequence of rock units into the Laurentian (granitic gneiss) System and the overlying Huronian (iron-bearing) Series. Rocks in the Florence area, included in the Huronian Series, were divided into three parts: Upper—Granite (eruptive?), gneiss, hornblende, actinolite, mica, chlorite and quartz schists, iron ores, clay and carbonaceous slates, quartzite, and conglomerate. Middle—Clay slate and quartzite. Lower—Dolomite, iron ore, and quartzite. Van Hise and Leith (1911) briefly described the geol-ogy of the Florence area and presented a geologic map based on an outcrop map that had been prepared by W. N. Merriam and assistants in 1904 and partly revised by Hotchkiss in 1910. All sedimentary rocks were included in a single map unit called the Michigamme Slate, a unit which occupies most of the area and within which is a discontinuous iron-bearing member. Areas of intrusives and extrusives exposed north and east of Florence were also shown as a discontinuous unit. This unit and those of granite and gneiss and Quinnesec Schist and other green schists in the south part of the area were all shown as younger than the sedimentary rocks. The granite and gneiss were designated the Keweenawan (?) Series, and all other rocks were included in the Upper Huronian (Animikie Group) of the Huronian Series. In 1910-11 the Wisconsin Geological and Natural History Survey prepared geologic and magnetic data sheets of township units at a scale of 4 inches per mile for much of Florence County but made no geologic map of the area. An incomplete manuscript in the files of the Wisconsin Geological and Natural History Survey contains lithologic descriptions of the principal rock types but refers to stratigraphy and structure mainly in relation to regional similarities instead of specific interpretations for the Florence area. The great value of these outcrop maps can be better understood after reading the comment of Brooks (1880, p. 445) : When facts are so scarce, one is so rejoiced in finding them that he almost forgets that he has perhaps waded swamps or clambered through wind-falls, at the rate, with intense labor, of not to exceed five miles a day, maybe for one or several days, and found only a single outcrop. He may have passed -within a few rods of others and not observed them, because of trees and brush and fallen timber. The same labor and time would have carried him a hundred miles comfortably on horseback in the far west, with a boundless view and uncovered rocks constantly before him, enabling him to select the points to visit, thus utilizing time and labor to the utmost. Furthermore, the solution of problems was not and is not assured even when data are locally abundant. Brooks (1880, p. 481) stated: I have rarely found so small an area presenting so many outcrops and magnetic attractions, and occupied by so few and well characterized rocks, the structure of which gave me so much trouble as has the district about Lake Eliza [now Keyes Lake], more especially to the N. [north] and W. [west]. Allen and Barrett (1915) described the geology of the iron-bearing areas of Michigan and Wisconsin and proposed a correlation of stratigraphic units. They assigned the formations of the Florence area to two parts of the Huronian Group. Their Middle Huronian Series contained, in ascending order, the Vulcan iron-Forma-tion, Hanbury Slate, Quinnesec Schist, and granite; their Upper Huronian Series contained quartzite and conglomerate.INTRODUCTION Leith, Lund, and Leith (1935) suggested revisions of the geology on the basis of compilations and interpretations made subsequent to 1911. Their geologic map of the Florence area has a general similarity to the present concepts, but interpretations of the stratigraphic sequence differ greatly. The formations, except for the younger acidic intrusives, were placed in the Huronian Series and arranged as shown. Upper Huronian Michigamme slate Upper slates Iron River iron-formation member Lower slates South belt of Quinnesee greenstone1 Breakwater quartzite1 Middle Huronian Iron-formation (Little Commonwealth area) Greenstones near Spread Eagle Lake1 Lower Huronian Saunders formation (dolomites and quartzites) Quartzite near Keyes Lake1 Lyons (1947) and Emmons and others (1953) investigated masses of medium- to coarse-grained hornblende and plagioclase in and adjacent to the southeastern part of the Florence area. They interpreted the “plagioclase hornblendite” as an intermediate stage in the transformation of basalt that lies to the north to granite that lies to the south. The “plagioclase hornblendite” is classified as metagabbro in the present report. Other reports contain information mainly about adjacent areas, and additional bibliographic references to previous work are given. James (1951) presented the description, composition, and conditions of sedimentation of an iron-rich sequence of graphitic slate, iron-formation, graywacke, and magnetic ironstone of “Upper Huronian (?) age” in the Iron River area of Michigan. The sequence continues into the Florence area. James (1954) dealt with the occurrence, description, composition, and distinctive features of sulfide, carbonate, oxide, and silicate facies of iron-formation and also discussed the depositional environments. James (1955) described mineralogic changes of the graywacke-shale suite, basic igneous rocks, and iron-formation in chlorite to sillimanite metamorphic zones in the northern peninsula of Michigan and part of northern Wisconsin including the Florence area. The extent of the zones was shown on an areal geologic map. Much of the Florence area is in the chlorite zone, and the metamorphic grade rises southward to the garnet zone and northward to the sillimanite zone. James (1958) discussed the geologic relations in Dickinson and Iron Counties, Mich., that led to the recognition and naming of the formations, groups, and 1 Stratigraphic position in doubt. 5 series shown in table 1. The nomenclature is in part also applicable to the Florence area (compare table 2). In James, Dutton, Pettijohn, and Wier (1959), a map shows distribution of outcrops, structural data, magnetic data, and indicated or inferred areal geology in the southern part of Iron County, Mich. Brief descriptions of stratigraphic units are given. The geology shown for the northwest part of the Florence area on plate 2 is from the southeast part of that map. Bay ley, Dutton, and Lamey (1966) prepared a comprehensive report on stratigraphy, intrusives, structure, metamorphism, and economic geology in parts of Michigan and Wisconsin east of the Florence area. They included data presented by Prinz (1959). This area is characterized by tracts of crystalline rocks to the north and south of a faulted homocline of northwest-trending and steeply dipping sedimentary rocks of middle Pre-cambrian age. Two faults that trend northwest divide the area into three blocks, relative uplift being on the southwest side of each. The northern block also contains a northwest-plunging syncline of metabasalt that over-lies the youngest Precambrian sedimentary formation. The faults, syncline, metabasalt, youngest Precambrian sedimentary formation, and the southern tract of crystalline rocks continue into the Florence area. Aspects of the stratigraphy and structure in the Florence area that contributed to the interpretation in this adjacent area were discussed. Dutton and Linebaugh (1967) published a map showing the geological relation of the Florence area to other parts of the Menominee range and to other nearby ironbearing areas in eastern Iron County and central Dickinson County, Mich. James, Dutton, Pettijohn, and Wier (1968) discussed the stratigraphy, intrusives, structure, and economic geology in part of Michigan north and west of the Florence area. They include a bibliography of previous work. Sedimentary rocks of middle Precambrian age occur in a complexly folded syncline that overlies the previously mentioned metabasalt. The overall structure is a large triangular basin; two of the apices are at Iron River and Crystal Falls, Mich., and the third is near Florence, Wis. PURPOSE AND METHODS OF THIS INVESTIGATION Investigation in Florence County, Wis., by the U.S. Geological Survey in cooperation with the Wisconsin Geological and Natural History Survey began in 1955. The purpose was to determine the general stratigraphy, geologic structure, and mineral resources, especially potentialities for iron-formation amenable to beneficiation.6 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN Table 1.—Lithologic sequence of Precambrian rocks in Iron and Dickinson Counties, Mich. System Series Rock unit Upper Pre- cambrian Middle Pre- cambrian Pre- cam- brian Lower Pre- cambrian Keween- awan Series Animikie Series Diabase dikes and sills (probable age about 1,100 million years) -Intrusive contact- Granitic intrusive rocks (probable age at least 1,400 million years) ----Intrusive contact----------- Metadiabase and metagabbro Paint River Group Baraga Group Menominee Chocolay Group Fortune Lakes Slate -Intrusive contact- Stambaugh Formation Hiawatha Graywacke Riverton Iron-Formation Dunn Creek Slate, with Wauseca Pyritic Member Badwater Greenstone Michigamme Slate Fence River Formation Amasa Formation Hemlock Formation, with Mansfield Iron-Bearing Slate Member and Bird Iron Bearing Slate Member Goodrich Quartzite -Unconformity - Vulcan Iron-Formation Loretto Slate Member Curry Iron-Bearing Member Brier Slate Member Traders Iron-Bearing Member Felch Formation Randville Dolomite -Unconformity- Sturgeon Quartzite Saunders Formation Fern Creek Formation -Unconformity - Gneissic granite and other crystalline rocks —Intrusive or replacement contact??- Dickinson Group Six-Mile Lake Amphibolite Solberg Schist, with Skunk Creek Member Granite gneiss East Branch Arkose —Unconformity- Hardwood Gneiss (position uncertain) -?? Quartzite and schist (small bodies included in granite gneiss) Quinnesec Formation (position uncertain) Margeson Creek Gneiss (position uncertain) The results of the examination of the area by the Wisconsin Geological and Natural History Survey in 1910-11 under the direction of W. O. Hotchkiss, State Geologist, are on file at the Wisconsin Geological and Natural History Survey and were of much help in the present study. The available materials include field notebooks, many rock specimens and thin sections, and township maps showing the location and classifi- cation of rock exposed or penetrated by test pits and drilling. During the present investigation, all known sources of field data—outcrops, test pits and trenches, and drill cores—were examined. Data points were located by plotting on aerial photographs or by compass and pace traversing, and control was related either to points readily identifiable on aerial photos or to known land sub-GENERAL GEOLOGY 7 divisions of the township system. Field data were compiled on base maps at a scale of 1:12,000 prepared from planimetric quadrangles of the area at a scale of 1:48,-000. Final compilation was on topographic bases of the four T^-minute quadrangles at a scale of 1:24,000. Petrographic descriptions are based on examination of about 350 thin sections from the 1910-11 survey and about 475 prepared for this investigation. Percentages of minerals are visual estimates; relative abundance is indicated by “common” if present in all or many parts of the thin section, “subordinate” if present in about half of the fields examined, and “minor” or “rare” if seen only in a few fields. Approximate composition of plagioclase was determined by common petrographic methods where favorably oriented sections of grains were present. Most determinations were made, however, by the use of a five-axis universal stage (Emmons, 1943); supplementary distinction between albite and andesine was made by reference of feldspar indices of refraction to the index of the embedding medium. Throughout the report, most petrographic descriptions have been set in small type. Thus they may easily be recognized by the reader. The adjacent southeastern part of Iron County, Mich., was investigated during cooperative studies with the Michigan Department of Conservation, Geological Survey Division. The northwestern part of the Florence West quadrangle was mapped intermittently over a period of years—the extreme northwest comer by Good and Pettijohn (1949), the adjacent area to the southeast by J. E. Gair in 1955, and the remainder of the Michigan part of the quadrangle by H. L. James and K. L. Wier in 1955. The geology of these areas as shown on plate 2 is from James, Dutton, Pettijohn, and Wier (1959). The brief description of geology is based on all the work listed above and James, Dutton, Pettijohn, and Weir (1968). The eastern part of the Florence area in Michigan was also mapped intermittently. The area adjoining Peavy Pond was mapped in 1950 by It. W. Bayley in connection with his study of the Lake Mary quadrangle to the north (Bayley, 1959). The course of the Michi-gamme River between Peavy Falls and Lower Michi-gamme Falls was mapped by James and Bayley in 1951, during a period in which the normal flow had been cut off to permit construction of the dam at the lower falls. The stretch of the river bottom, with abundant outcrop, is now covered by the water behind the new dam. The remainder of this Michigan part of the area was mapped by James and Wier in 1955, and magnetic surveys were made by Wier in 1955 and 1964. Geologic mapping was done on 1:12,000-scale enlarge- ments of the topographic base. All materials that concern this part of the Florence area are taken from a report prepared by James and Wier (unpub. data, 1965). ACKNOWLEDGMENTS Acknowledgements are gratefully expressed to G. F. Hanson, Director of the Wisconsin Geological and Natural History Survey, for helping initiate the project, for financial support and supplying records of previous work, and for review of the manuscript. The association with and contributions of R. W. Johnson, Jr. as a coworker in the field and office from August 1955 to June 1958 were very helpful, and he made a special study of the Little Commonwealth area as indicated in this report. The important contribution of K. L. Wier and R. A. Solberg, who made a magnetometer survey of about 4 square miles to help decipher local complexities of stratigraphy and structure, and the assistance in general field work by F. D. Effinger in 1955, Fred Peeren-boom in 1958, W. L. Emerick in 1959, and J. P. O’Connor in 1960-1 are greatly appreciated. The cooperation of the Michigan Department of Conservation, Geological Survey Division, and the use of unpublished data by W. R. Bayley, H. L. James, and K. L. Wier are gratefully acknowledged. The preparation of all drafted illustrations and also preliminary and interim base maps and compilations by Reta E. Bradley is acknowledged with sincere appreciation. R. W. Bayley and R. G. Schmidt reviewed the manuscript, and their constructive comments and suggestions were especially helpful. The assistance of G. L. LaBerge in some petrographic and X-ray determinations and especially the cooperation of the Department of Geology at the University of Wisconsin in discussions with staff members, use of X-ray equipment, and loan of optical equipment are acknowledged with gratitude. GENERAL GEOLOGY The Florence area is near the southeastern apex of a large mass of middle Precambrian rock in northern Michigan and northeastern Wisconsin (fig. 1); the formations are mainly metasedimentary rocks, including several iron-formations, that are complexly folded and faulted. Extrusive and intrusive igneous rocks are also present. Lower Precambrian rocks include schists, gneisses, and amphibolites that are adjacent to the southwest and to the northeast. Upper Precambrian rocks crop out 40 miles to the northwest as a series of north-dipping basalt flows overlain by clastic strata. Bedrock of early and middle Precambrian age (table 2 and pi. 4) underlies most of the Florence area but is generally mantled by glacial and glaciofluvial deposits8 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN Table 2.—Rock units in the Florence area System Series Rock unit Description Quaternary Pleistocene Glacial deposits Unconsolidated morainal and glaciofluvial deposits. Cambrian(?) Upper Cambrian (?) Sandstone Rounded quartz grains cemented by iron oxides. Peavy pond Complex Represented only by hornblende metagabbro. Hoskin Lake Granite Pink, gray, white or mottled granite and some quartz monozonite. Metagabbro and metadiabase Sill-like and irregular masses; now amphibolite. Fortune Lakes Slate Gray slate and graywacke; more than 1,000 feet thick.’ 3 o Stambaugh Slate Moderately magnetic fissile slate with some graywacke; 200 feet thick. Precambrian Middle Precambrian Animikie Series O fe > Hiawatha Graywacke Massive nonfeldspathic graywacke, locally few to many fragments of chert; generally 0-100 feet thick. 5 G Ph Riverton Iron-Formation Contains iron-rich minerals (siderite, hematite, li-monite, magnetite, or grunerite, and various combinations of these minerals) with interlayered chert; 600 feet thick. Dunn Creek Slate Upper part is laminated graphitic slate and massive graphitic breccia; lower part is phyllite and quartz graywacke; 2,500 feet thick. a Badwater Greenstone Mainly metabasalt with some phyllitic rocks and, locally, gruneritic schist; 2,000-15,000 feet thick. o (h O Cj bC Michigamme Slate Mainly metaargillite and schist with some quartzite, conglomerate, agglomerate, and amphibolite; about 20,000 feet thick. c3 00 Hemlock (?) Formation Amphibolite derived from pyroclastic material; thickness unknown. Lower Precambrian Quinnesec Formation Metavolcanic and minor amounts of metasedimentary rocks; may be 40,000 feet thick. 1 All thicknesses are estimates based on inferred width of formation as shown on geologic map. Post-Riverton sequence is undifferentiated in Wisconsin. of Pleistocene age. Two very small areas of sandstone of probable Cambrian age are present. Excluding intrusive masses, lower Precambrian meta-volcanic and minor amounts of metasedimentary rocks underlie the southwestern part of the mapped area; middle Precambrian metasedimentary and less abundant metavolcanic rocks occupy the remaining part. Late middle Precambrian metagabbro and metadiabase occur in moderate-sized masses in the southeastern part of the area and minor ones elsewhere. Late middle Precambrian granite underlies a tract near the southwest corner of the area and is believed to be present in the extreme southeast corner also. The distribution of stratigraphic units and the structural geology in the mapped area are determined by three inferred faults that trend northwest and divide the area into four structural blocks. Names given to the structural units, from north to south, are the Brule River, Keyes Lake, Pine River, and Popple River blocks. Much of the geology in this paper is discussed under these structural names. A major fold, the Commonwealth syncline, occurs in the Brule River block. This structure plunges northwestward and forms one apex of a large triangular basin that contains the Riverton Iron-Formation and associated strata; the other apices of the triangular basin are at Crystal Falls and Iron River (pi. 4). Two anticline-syncline pairs of lesser magnitude have been recognized in the Michigamme Slate in the north part of the block. Similar folding is probably present throughout the stratified rocks of the area, but outcrops are too few to define them. Data in the western part of the Keyes Lake block establish a vertical to steeply dipping homocline and several southeast-plunging folds. Data on attitudes are more limited elsewhere, but the Pine River block is interpreted to be a south-QUINNESEC FORMATION 9 facing homocline with a steep southwest dip, whereas the Popple River block contains ellipsoidal lavas the tops of which face northward in the few places where they are present. All the lower and middle Precambrian rocks have been metamorphosed. The metamorphism is mostly regional, and well-defined gradients have been recognized (pi. 5). The grade increases outward from the chlorite zone, which is in a belt roughly parallel to the central part of the Commonwealth syncline. The gradient southward is gradual—through a biotite zone to a garnet zone in the southwest part of the area; the gradient northward is more abrupt—through biotite, garnet, and staurolite zones to sillimanite along the northern edge of the area. Locally, faulting has displaced the zone boundaries. Granite bodies are believed to have retarded the metamorphism of gabbro sills in a few places, but this action had only slight effect on the general pattern. No bedrock is exposed in the northeast corner of the area. However, by extrapolation westward from the Felch trough of Dickinson County (James and others, 1961), it is believed that the tract is underlain by pre-Hemlock strata of the Animikie Series together with pre-Animikie crystalline rocks (table 1). This projection of the strata of the Felch trough is further suggested by a broad magnetic anomaly that extends westward to the east edge of the Florence area. STRATIFIED ROCKS LOWER PRECAMBRIAN ROCKS QUINNESEC FORMATION The name Quinnesec Schist was used by Van Hise and Bayley (1900) to designate greenstone schists and associated mafic intrusive rocks such as are found at Quinnesec Falls on the Menominee River in southern Dickinson County, Mich. Leith, Lund, and Leith (1935) changed the name to Quinnesec Greenstone. James (1958) applied the term Quinnesec Formation to the belt of greenstone, amphibolite, and schist in southern Dickinson County, Mich., and the adjacent part of Wisconsin. The geographic extent of this formation is not known. The Quinnesec Formation in the Florence area trends southeastward across the southern part for a length of about 14 miles and a width of about 3-8 miles (pi. 1). Outcrops of the formation have been mapped eastward for 12 miles (Prinz, 1959; Bayley and others, 1966), and the unit continues for an undetermined distance. Exposures that are probably part of the Quinnesec Formation are rare west of the Florence area, and the extent of the unit toward the west and northwest is not well substantiated or delimited by aeromagnetic data (pi. 7). DESCRIPTION The Quinnesec Formation in the Florence area is composed of metamorphosed volcanic rocks and minor amounts of sedimentary rocks. Amphibolite and hornblende schist are most common, some associated biotite-quartz schist and grunerite schist are present, and quartzite is exposed at two localities. Felsic metavol-canic rocks and associated sericite schist are prominent rock types in the Quinnesec Formation in Florence County, Wis., but are less prominent eastward along the Menominee River in Marinette County, Wis., and southern Dickinson County, Mich. This felsic rock was not mentioned by J ames (1958). AMPHIBOLITE Most exposures of amphibolite in the Florence area are massive, dark green, poorly foliated, and fine grained. Ellipsoidal structures occur at widely separated localities and range from 1 to 3 feet long and y2 to 1 foot wide. Their shape and arrangement in secs. 12 and 13, T. 38 N., R. 18 E., and secs. 15 and 26, T. 39 N., R. 17 E., indicate that the original upper surfaces of these metamorphosed basaltic flows now face northward. Ellipsoids in a similar structural position occur just east of the mapped area in the northern part of sec. 10, T. 38 N., R. 19 E. In the absence of specific evidence to the contrary, it is believed that the top of the Quinnesec Formation faces northward and that the mafic metavolcanic rocks are older than the felsn ones. Hornblende and andeslne are (he principal minerals in the amphibolite, and the ratio ranges from 70:30 to 50:50. The average grain size is about 0.50 mm (millimeter). The most common accessory minerals are magnetite and quartz. Others, which range from common to scarce in various thin sections, are oligoclase, carbonate, biotite, chlorite, clinozoisite, epidote, sericite, and spliene. The average composition of the plagioclase in 60 percent of the thin sections is An3o-3a and in 30 percent is An«-48. Oligoclase averaging An-s-ss occurs in 10 percent of the slides. Plagioclase grains are mostly anhedral, but a few relict phenocrysts are present. Twinned grains are not present in all sections but are a minor constituent in many. No zoned grains were seen. Pleochroism of most of the hornblende is X, pale yellow; Y, olive green; and Z, blue green. The intensity of color differs within individual thin sections and locally within individual grains. Maximum observed extinctions by common methods are 15° to 24° in two-thirds of the slides examined. Hornblende grains are subprismatic with irregular terminations. Twinned grains are generally absent or scarce but are common in several sections. Poikiloblastie texture is common to abundant. SCHIST Hornblende schist differs from amphibolite in having well-developed foliation that may or may not be accom-10 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN panied by an increased percentage of hornblende. Occurrences of hornblende schist in the Quinnesec Forma-tion are indicated on the geologic map (pi. 1) by foliation symbols. Grunerite schist is exposed in a small area along the west side of the Little Popple River in the northern part of sec. 12, T. 38 N., R. 18 E., and in the southern part of sec. 3, T. 38 N., R. 18 E. Several large angular blocks and a possible small outcrop of grunerite schist in the SE^4 sec. 15, T. 39 N., R. 17 E. are not shown on the map. Grunerite is predominant in thin sections; it is subprismatic, randomly oriented to moderately well alined, as much as 0.15 by 0.50 mm, but very fine grained and partly radiating at the boundary with lenses and laminae of quartz. The quartz probably represents recrystallized chert and, with crossed nic-ols, is resolved into a mosaic of grains that are approximately 0.20 mm in diameter and have relatively smooth simple boundaries. Subhedral bluish hornblende as much as 0.15 by 0.50 mm (but generally less) is cut by grunerite blades. Minor amounts of biotite are present. Biotite-quartz schist in secs. 27, 33 and 34, T. 39 N., R. 17 E., near the west side of the area shown on plate 1, forms rapids in the Popple River and is exposed nearby. This schist is about one-half quartz, with associated biotite and hornblende in evenly divided proportions. Quartz is anhedral and approximately 0.30 mm in diameter. Biotite is in well-alined elongate grains as much as 0.20 mm wide and 0.50 mm long. Blue-green hornblende may be alined or randomly oriented; grains are commonly elongate and are 0.25 mm wide and 0.75 mm in maximum length. Anhedral twinned plagioclase grains are minor constituents and are approximately An30. Scattered zircon grains are less than 0.05 mm in diameter and have enclosing halos in biotite. A layer of garnet-biotite schist about 3 feet thick crops out along Wisconsin Highway 101 in sec. 28, T. 39 N., R. 17 E., one-half mile west of the mapped area. The garnets are reddish brown and euhedral; most are less than one-half inch, but some are as much as 2 inches in maximum dimension. A pronounced banded appearance in the schist results from the relative abundance of garnets in some layers. QUARTZITE A bed of white to light-gray medium- to coarsegrained quartzite exposed along the north side of Wisconsin Route 101 in sec. 15, T. 39 N., R. 17 E., is approximately 6 feet thick and has hornblende schist on either side. A small irregular exposure of quartzitic rock nearby contains rodlike quartz masses that possibly represent elongate pebbles or lenses. A quartzite bed 8 inches thick was noted in the same roadside exposure that contained the garnet-biotite schist mentioned above. FELSIC METAVOLCANIC ROCKS Felsic metavolcanic rocks crop out in an area approximately 7 miles long and 1 mile wide, extending from sec. 15, T. 39 N., R. 17 E., southeastward to at least sec. 34, T. 39 N., R. 18 E. (pi. 1). Small amounts of amphibolite and hornblende schist associated with the felsic rocks are exposed locally in secs. 14 and 23, T. 39 N., R. 17 E. Felsic metavolcanic rocks are also present east of the mapped area in Wisconsin and Michigan along the Menominee River at and near Aurora and Niagara, Wis. The felsic metavolcanic rock ranges from medium gray with some brownish cast to dark gray on fresh surfaces and from light gray to almost white on weathered surfaces. It generally shows a slight foliation but may be massive or well foliated. Grains less than 1 mm in maximum dimensions predominate, but rounded quartz and subhedral feldspar grains are locally as much as 3 mm. Biotite, muscovite, sericite, and pyrite occur in many specimens. Typical thin sections consist mainly of anhedral grains of untwinned feldspar and quartz is approximately equal amounts. Classification of feldspar was generally impossible because most individual grains are small, and even in the larger grains the Becke line is very indistinct because of the abundant very fine grained sericite and opaque material, probably hematite. Some untwinned feldspars have at least two indices less than balsam and are believed to be orthoclase, but more grains have at least two indices greater than balsam. A few sections contain plagioclase phenocrysts that have albite or pericline twinning and compositions in the ranges of An2,-32 and Anra-m. Quartz grains range from subangular to rounded. Some quartz that appears to have originally been one grain is resolved into a few or many units when viewed with crossed nicols. The irregular elongation and extinction of feldspar suggests possible deformation, but quartz shows almost no granulation or overgrowth. Sericite, muscovite, and biotite are generally present, and chlorite and magnetite are less common; each ranges widely in abundance. Biotite, chlorite, and part of the sericite are moderately or well alined, the alinement contributing to the foliation of the rocks. Some sericite is scattered and randomly oriented in much of the feldspar. Epidote-clinozoisite, sphene, and leucoxene are rare. Felsic metavolcanic rock and associated mafic material are transitional in character and alternate near the contacts, especially in sec. 30, T. 39 N., R. 18 E., along the south shore of the reservoir in adjacent sec. 29, and near the center of sec. 23, T. 39 N., R. 17 E. (pi. 1). This relationship can even be seen in single thin sections; felsic parts composed of irregularly elongate feldspar and subtabular biotite contain lenses and layers in which hornblende is abundant. Some sections are a mosaic of very fine feldspar and quartz, scattered quartz grains as much as 0.5 mm across, and much irregular hornblende. Other sections that are predominantly hornblende with some feldspar and scattered sub-BARAGA GROUP 11 rounded quartz grains as much as 0.5 mm across seem to be amphibolites with clastic quartz. The character of these mineral assemblages coupled with the interlayered relationships suggests a possible sedimentary accumulation of felsic and mafic materials in transitional zones. Such occurrences might also result from metamorphic differentiation or from intrusion as, for example, in the NW1/4SW1/4 sec. 25, T. 39 N., R. 17 E. (not shown on pi. 1). These felsic metavolcanic rocks are probably metarhyolite and are included in the Quinnesec Formation in the Florence area. They are also present eastward along the Menominee River as already mentioned. The felsic metavolcanic rocks in the two areas are mineralogic and stratigraphic equivalents and resemble metarhyolites in other parts of the region. Analyses of the felsic rocks along the Menominee River correspond closely to calc-alkali rhyolite and rhyolite obsidian (Bayley and others, 1966, p. 15-16). Gray slate and phyllitic rock are locally associated with the felsic metavolcanic rocks, especially in sec. 30, T. 39 N., R. 18 E. The principal minerals of the slate are quartz and biotite with accessory chlorite, sericite, possibly some feldspar, and several very small garnets in one section. Phyllitic rock is also dominantly quartz and biotite with accessory chlorite and very incompletely developed poikiloblastic chloritoid. THICKNESS AND RELATION TO ADJACENT FORMATIONS The thickness of the Quinnesec Formation is not known. The northeast limit is believed to be along a fault, and the southwest limit is beyond the presently mapped area. To the south, outcrops are sparse and many are granite. The greatest thickness of the formation indicated by outcrops in the Florence area is about 40,000 feet, and although no evidence of folding or faulting is known in this part of the area, some duplication of beds may be present. No formations older than the Quinnesec have been recognized in the Florence area. Presumably, the relations to younger formations are structural rather than stratigraphic. CHARACTER OF ORIGINAL ROCKS The Quinnesec Formation formed principally as a series of massive basalt flows; some flows moved into water, and this resulted in ellipsoidal structures. Rhyolitic flows also were extruded. No pyroclastic material has been recognized, but mud and sand accumulated between periods of extrusions. Subsequent metamorphism changed the basalt into amphibolite and hornblende schist and the sediments into phyllite, biotite-quartz schist, grunerite schist, and quartzite. The felsic volcanic rocks were little changed except for sericitization of the feldspar. AGE AND CORRELATION Van Hise and Bayley (1900) assigned the Quinnesec Formation to the Archean (early Precambrian of present usage). Van Hise and Leith (1911) revised the age to late Huronian (late middle Precambrian). Leith, Lund, and Leith (1935) gave the age as possibly, but doubtfully, Huronian (middle Precambrian). James (1958) tentatively concluded that the formation was of early Precambrian age, which was presumably corroborated by structural data given in this present report on the Florence area. Banks, Cain, and Rebello (1967) suggested that the Quinnesec Formation may be of younger age. Correlation of the Quinnesec Formation with other formations has not been established. MIDDLE PRECAMBRIAN ROCKS—ANIMIKIE SERIES BARAGA GROUP In Iron and Dickinson Counties, the Baraga Group, named for Baraga County, Mich. (James, 1958), contains six formations; the ascending stratigraphic succession is Goodrich Quartzite, Hemlock Formation, Fence River Formation and the probably equivalent Amasa Formation, Michigamme Slate, and Badwater Greenstone. Only the Michigamme Slate, Badwater Greenstone, and rocks questionably assigned to the Hemlock Formation, are present in the Florence area. The Baraga Group is the most widely distributed unit in the Florence area. It underlies most of the Brule River and Keyes Lake blocks (pi. 2) and the entire Pine River block (pi. 1). It is not in the Popple River block. The Hemlock (?) Formation is mainly metamorphosed basaltic rocks and associated sedimentary rocks, some of which are iron-bearing. The exposed thickness of each formation in the Baraga Group in the three-county area ranges greatly, and each formation is discontinuous at least locally. The thickness of the Hemlock^) Formation in the mapped area is not known because it occurs only as the central unit along the axis of an anticline and the lower contact is not exposed. The Michigamme Slate is predominantly interbedded graywacke and slate or their metamorphic equivalents, but in some places the formation contains conglomeratic and quartzitic rocks, graphitic slate, and iron-rich strata. The Michigamme is about 5,000 feet thick in the northern part of the Florence area but is apparently12 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN about 20,000 feet thick in the southern part. The typical Badwater Greenstone is metamorphosed massive basalt, locally ellipsoidal; it contains some tuffaceous rock and some iron-rich strata. The Badwater Greenstone is probably as much as 15,000 feet thick. The relation of the Baraga Group to the underlying rock units is not known because the lower limit of the Hemlock(?) Formation is not exposed either in the mapped area or an adjacent one. The Baraga Group and the younger Paint River Group are probably conformable in the Florence area. The Baraga Group is part of the Animikie Series of middle Precambrian age and is probably correlative with the Virginia Argillite of Minnesota (James, 1958; Cotter and others, 1965). HEMLOCK (?) FORMATION The name Hemlock Formation comes from the Hemlock River in northeastern Iron County, Mich., and was given by Clements and Smyth (1899) to the volcanic rocks in that area. The amphibolite that forms the core of an anticline in the northern part of the Florence area (pi. 2) is questionably assigned to the Hemlock Formation and is the only occurrence known in the mapped area. The rock is well exposed in the southern part of sec. 6, T. 41 N., R. 31 W., along a prominent ridge 50 to 100 feet above the general level of the area. The amphibolite is black and varies somewhat in grain size and composition. Most of it is massive, and original layering is evident in only a few places. On weathered surfaces, particularly those that cross the foliation and lineation, the rock has the texture of an agglomerate or coarse tuff; irregular fragments weather out in relief from a less resistant matrix. On surfaces parallel to the strike, these “fragments” are seen to be pod- or pencil-shaped units parallel to the low-plunging regional linear structures of the area. Most of the rock is a foliated fine- to medium-grained aggregate of hornblende and andesine, with lesser amounts of biotite and quartz. Locally the rock contains pod-shaped masses of needlelike black hornblende several inches across, commonly in a matrix that contains much carbonate. The amphibolite is bounded on both north and south by iron-formation and gametiferous schist that are assigned stratigraphically to the Michigamme Slate. The contact is exposed at several places in the SW1^ sec. 5 and the SE*4 sec. 6, T. 41 N., R. 31 W. In general, the contact is sharp, without indication of unconformity, but there is some interbedding as indicated by a thin layer of amphibolite in the iron-formation at the north end of the large outcrop in the NW^NW^ sec. 8, T. 41 N., R. 31 W. A small wedge of iron-formation exposed approximately 1,000 feet north and 1,000 feet west of the SE comer sec. 6 (not shown on pi. 2) appears to represent a small infold in the amphibolite. The thickness of the amphibolite in this area is not known, inasmuch as it occurs only along the creast of a narrow anticline. The Hemlock Formation is locally well exposed to the north in the Lake Mary quadrangle (Bayley, 1959) and consists mainly of basaltic flows and pyroclastic rocks with associated slate and iron-formation. The amphibolite in the Florence area was presumably formed from similar extrusive and sedimentary rocks. The Hemlock Formation is apparently best represented in, and almost restricted to, eastern Iron County, Mich., except for possibly a small area in northwestern Dickinson County, Mich. It should be emphasized that the questionable assignment of the amphibolite in the Florence area to the Hemlock Formation is based on the assumption that it is in an anticlinal structure. The postulated west-plunging structure should require a progressive widening of the unit eastward, but evidently this does not occur. Two explanations can be invoked: first, that the structure is anticlinal and the Hemlock (?) Formation here originally was no more than a thin lens, that is that the lack of widening to the east is due to an original thinning of the unit; second, that the structural interpretation is incorrect and that the amphibolite and its bordering units are simply lenses within the Michigamme Slate. MICHIGAMME SLATE DEFINITION, DISTRIBUTION, AND LITHOLOGY The name Michigamme Formation was used by Van Hise and Bayley (1895, p. 598) to designate an extensive unit represented by exposures of slate and gray-wacke and their metamorphosed equivalents on islands in, and the mainland around, Michigamme Lake in the western part of the Marquette district. Van Hise and Leith (1911, p. 267) revised the name to Michigamme Slate. The principal occurrences of the formation in the Florence area are in two tracts (pi. 4). A north tract underlain by Michigamme Slate lies along and north of the Menominee and Brule Rivers (pi. 2) and continues northwestward and southeastward beyond the Florence area. Exposures in this tract are large and numerous in southeastern Iron County, Mich., but only small and scattered in Florence County, Wis., and rare in Dickinson County, Mich. A south tract extends northwestward across the south half of the mapped area (pi. 1) and is then split into two parts, one of which presumably continues beyond the west side of the Florence area (pis. 2 and 4). Exposures in these areas areMICHIGAMME SLATE 13 generally small and scattered, except for those of quartzite and conglomerate. The Michigamme Slate extends eastward from the south tract into Dickinson County, Mich., for about 20 miles. The bulk of the formation in the north tract consists of metagraywacke, slate, granulite, and schist; iron-formation is locally present at the base and the top. Probably the most abundant rocks of the formation in the south tract are similar to the sericitic slate that is only locally exposed along the Pine River but presumably underlies extensive intervening areas of thick overburden. The rocks most commonly exposed are, however, quartzite (near Keyes Lakes in the southwest quarter of pi. 2) and quartzitic conglomerate (near the reservoir on the Pine Kiver in the northwest quarter of pi. 1). Other kinds of rock exposed are metagray wacke, grunerite-magnetite iron-formation, amphibolite (metabasalt (?)), and mafic volcanic breccia. The recognition that the quartzites, conglomerates, and associated rocks in the vicinity of Keyes Lake and of the Pine Kiver are part of the Michigamme Slate is believed to be one of the more significant results of of this investigation. It is based on extension from, and probable continuity with, the Michigamme in the southern part of Dickinson County, Mich. The rocks in the Florence area may be interpreted as younger units than previously known in the Michigamme, as local facies in that formation, or as both. A thin bed of iron-formation and garnetiferous schist, possibly equivalent to the Amasa Formation elsewhere, separates the Michigamme from the underlying Hemlock( ?) Formation. The upper limit of the Michigamme is marked by exposures of the younger Bad-water Greenstone along the Menominee and Brule Rivers (pi. 2) and in the northeast comer of the southern part of the area (pi. 1); there is no evidence of erosion. The other areas underlain by Michigamme Slate are believed to be bounded by major faults, and consequently stratigraphic relations are not known. The thickness of the Michigamme Slate in Wisconsin may be as much as 20,000 feet in the Pine River block of the southern tract where there is least evidence of repetition by folding. The probable thickness of the formation in the northern tract is 5,000 feet, or possibly less. The Michigamme Slate is the most widely distributed formation in the mapped area, includes a great variety of rock types not previously recognized or described in this area, and exhibits best the effects of regional metamorphism. The discussion of this unit is therefore longer than that of other formations and is divided according to structural blocks from north to south. BRULE RIVER BLOCK The basal strata of the Michigamme Slate are exposed in the Brule River block in several places adjacent to the ridge of amphibolite (Hemlock(?) Formation) in secs. 5, 6, and 8, T. 41 N., R. 31 W. This rock consists of an iron-formation, which may be equivalent to the Amasa Formation in the Baraga Group, is no more than 10 feet thick, and does not appear to be continuous. It gives rise to strong magnetic anomalies on either side of the amphibolite ridge that die out to the west and to the east. Most of the exposed iron-formation consists of granular quartz, magnetite, and lesser amounts of grunerite in layers one-quarter to one-half inch thick, but locally it is a skarnlike aggregate of grunerite, green pyroxene, garnet, quartz, and magnetite in various proportions. The associated schist is micaceous and studded with pink garnets as much as one-quarter inch in diameter. At least 80 percent of the Michigamme Slate in the northern part of the mapped area consists of approximately equal proportions of metagraywacke and schist in beds ranging in thickness from a few inches to hundreds of feet. Graded bedding is common in the metagraywacke. It is best shown in layers 6 to 12 inches thick; commonly the beds grade from a mediumgrained graywacke at the base to schist at the top, but locally, as in the exposures at the dam at Lower Michigamme Falls, the grading is from coarse-grained graywacke to fine-grained graywacke. In many places, notably in the northernmost exposures below Peavy Falls Dam, the original grain size is reversed; that is, original fine-grained argillaceous material in the upper part of a unit now is reconstituted to coarse-grained mica and staurolite. The southernmost occurrence of graded bedding is in the southwestern part of sec. 12, T. 40 N., R. 18 E.; here, the top of the beds is southward, toward the adjacent younger Badwater Greenstone. The graywacke is light to dark gray and greenish gray. Sub-rounded to rounded quartz grains are abundant, and feldspar grains of similar shape and size are a minor accessory. These minerals, which constitute about one-half of a typical specimen, are accompanied by abundant fine-grained quartz and biotite and minor amounts of epidote-clinozoisite, magnetite, and feldspar. The uppermost part of the Michigamme Slate in the Brule River area consists chiefly of dark phyllite and slate and also a minor lens of iron-formation. Except for the iron-formation that was seen in pits in the NE1^ sec. 17, T. 41 N., R. 31 W., the rocks are best exposed in outcrops in Michigan along the east side of the Brule River in secs. 12 and 13, T. 41 N., R. 32 W., and in Wisconsin along the west side of the river in sec. 9, T. 40 N., R. 18 E. Graywacke and schist typical 407-694 0—71------214 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN of the main part of the Michigamme Slate form the northern end of the outcrops and are succeeded to the south by biotite-chlorite-quartz schist, dark garneti-ferous phyllite, and dark laminated slate. Minor amounts of interbedded graywacke crop out near the south limit on the west side of the river. The beds referred to the upper unit of the Michigamme dip steeply and are exposed for a distance of about 1,000 feet across the strike, but almost certainly the stratigraphic thickness is considerably less. The dominant rock type is garnetiferous phyllite. Where fresh, it is black or green, but in much of the area it is weathered and red. The phyllite is fissile; glistening cleavage surfaces parallel bedding and lamination, and garnets protrude from the surfaces. In thin section, brown or green biotite and quartz are the principal minerals; garnet, chlorite, muscovite, and hornblende are abundant in some layers. The garnets, which contain many inclusions, are much larger than the other minerals in the rock, and all show clear evidence of rotation. At the Wausau exploration in sec. 17, T. 41 N., R. 31 W., a bed of iron-formation occurs within the phyllite. The area has been explored by a number of pits and trenches, most of which encountered only oxidized garnetiferous phyllite. Banded magnetite-quartz iron-formation is abundant, however, in dump materials from the pit farthest to the northeast, and it is exposed 100 feet to the south in the walls of the pit farthest to the southeast. In the pit exposure, the iron-formation is bounded on the south by phyllite. Some of the iron-formation contains grunerite or its alteration products. The deepest pit, shown as a shaft on plate 2, is about 12 feet square and probably was more than 50 feet deep, but there is no indication of iron-formation, nor is there evidence of it in any of the pits and trenches to the west. Considering the east-west trend of the bedding, it seems likely that the iron-formation is a thin lens, probably no more than 10 feet thick, perhaps repeated by folding. Another occurrence of ferruginous rock, which is possibly iron-formation and is at or near the upper limit of the Michigamme Slate, is known, but does not crop out, at the Spread Eagle exploration (pi. 1) in secs. 8 and 9, T. 39 N., R. 19 E., on the south side of the Florence syncline. Records of exploration and fragments in dumps indicate that hematitic siliceous slate, or argillite with some chert, is present and was probably derived from gray-green slate or argillite. Solid hematitic material is rare. Records of limited underground workings indicate an iron content that ranged from 25 to 57 percent. The progressive metamorphism of the Michigamme Slate in this block is indicated by the presence of biotite in the few southernmost exposures along the Brule River, garnetiferous phyllite for about 1 mile north from the Brule River, then staurolitic rock to Peavy Falls Dam, and sillimanite schist to beyond the northern limit of the mapped area. KEYES LAKE BLOCK The Michigamme Slate is presumably the most widespread formation in the Keyes Lake block, but exposures are common only in the vicinity of Keyes Lake. These rocks are predominantly quartzite with associated slate and phyllite. The quartzite and a probable facies change at the southeast terminus will be discussed first, and then strata younger than the quartzite in areas east and northwest of Keyes Lake will be described. Quartzite The metasedimentary unit that probably has the greatest number of exposures in the northern half of the Florence area is a quartzite that crops out from sec. 32, T. 40 N., R. 18 E., northwestward for a little more than 4 miles to sec. 14, T. 40 N., R. 17 E. The thickness is mainly from 500 feet to 1,000 or even 3,000 feet locally (Nilsen, 1965). The highly resistant rock forms prominent ridges to the east and northwest of Keyes Lake and has many glacially polished surfaces. This unit is composed predominantly of massive, medium-grained, white to pink, vitreous quartzite with a few interlayers of conglomerate. Locally, thin layers of quartzose serici-tic phyllite occur. Pebble layers in the quartzite are as much as 12 inches thick and are composed of pieces of oval to rounded quartz or jasper about 1 inch in diameter. Red to brown diffusion color banding extends along or across joints and bedding and also occurs as small to large irregular patches. Crossbedding is common in secs. 24 and 25, T. 40 N., R. 17 E., and uniformly indicates that the top of the quartzite is to the southwest Examination of the quartzite in thin section shows mostly recrystallized quartz grains that range from subangular to well rounded and average about 0.20 mm but are as much as 1 mm in maximum dimension. Suturing of grains is slight to absent. Intergranular sericite is a common to minor constituent and in one thin section has an interpenetrating relationship with quartz at the boundary of the grains. In some thin sections subhedral fine-grained magnetite is a common accessory. Zircon and leucoxene are minor accessory minerals and are generally restricted to a few laminae in an otherwise homogeneous quartz-itic rock. This quartzite unit near Keyes Lake was studied in detail by Nilsen (1965) whose mapping indicates that the isolated area of quarzite shown east of the thickest part of the main belt is composed mainly of two discontinuous basal units. The maximum thickness of 3,000 feet is exposed at this location. Nilsen’s paleocurrentMICHIGAMME SLATE 15 analysis of crossbedding indicates that the predominant current direction was toward the southeast. He inferred that the site of deposition was a shallow, partly barred, nearshore basin. The quartzite is at least locally underlain by sericitic phyllite and minor amounts of interbedded sericitic quartzite; this unit is shown in figure 2 but not on plate 2. There are only a few small exposures in the NE^4 sec. 25, T. 40 N., R. 17 E., and the SE^NW1/^ sec. 31, T. 40 N., R. 18 E.; sericitic phyllite was penetrated by test pits in the SE14 sec. 31 and the SW14 sec. 32, T. 40 N., R. 18 E. The quartzite unit is overlain by a variety of strata that will be described later for areas east and northwest of Keyes Lake. A probable abrupt facies change at the southeast end of the quartzite belt is marked by poorly exposed martitic quartzite, quartzose phyllite, and associated strata. The martitic quartzite in secs. 31 and 32, T. 40 N., R. 18 E., encouraged exploration in the Little Commonwealth area, presumably so named in reference to the then active group of mines near the village of Commonwealth about 2 miles to the east. The geology of the area (fig. 2) was investigated in detail by R. W. Johnson, Jr. (1958, p. 24^33), and the following descriptions are taken from his report. The unit labeled martitic quartzite in figure 2 is a highly quartzose rock that locally contains an abundance of martite (oxidized magnetite). This quartzite unit and the associated ferruginous rocks into which it grades have previously been informally designated the Little Commonwealth iron-formation.1 Most of the rock is composed of thin laminations or lenses of quartzite delicately interbedded with layers of dark-brown argillite that generally contains large amounts of martite. However, some quartzite beds and lenses are more than 5 feet thick locally, and the quartz-itic rock that is fragmented and strewn within the associated material gives the appearance of an intra-formational breccia or a very angular conglomerate. Within the dark-brown argillaceous layers, isolated quartz grains are common. The distribution of the martite in the argillite is erratic, in some places being almost absent but elsewhere constituting nearly the entire layer. Minor constituents in the martitic quartzite are iron silicates, garnet, mica, martite, and a few tourmaline crystals. In thin section, microcrystalline platy mineral aggregates and mica flakes are commonly chaotically distributed within the rock, but these are restricted to certain laminae. The platy minerals are mainly chlorite; 1W. O. Hotchkiss, 1920, Wisconsin Geological and Natural History Survey unpublished report; H. R. Aldrich, 1932, unpublished report on the geology of the Little Commonwealth exploration. concentrations of sericite or muscovite and, rarely, pale-brown biotite are present locally. Crushed globular clusters of anhedral pale-pink to red garnet are common. Martite is most abundant near the exploratory shafts (fig. 2) and where best crystallized is in the form of octahedra. Some relatively unoxidized rock containing magnetite instead of martite has been found in the northwestern part of the Little Commonwealth area and has been penetrated at depth in the drilling. The occurrences of magnetite at depth and of an anomalous magnetic high in the general Little Commonwealth area indicate that the oxidation of the magnetite to martite is a surface feature. The unit labeled quartzose phyllite and garnet quartzite in figure 2, though gradational, differs sufficiently from the more ferruginous associated rocks to constitute a mappable unit within the Little Commonwealth area. The quartzose phyllite of this unit is largely restricted to the central part of the area and is exposed in several trenches and test pits. The fresh rock is gray, compact, finely laminated, very fine grained, and lustrous with a few thin scattered lenses of fine-grained quartzite. It weathers to a dull red or reddish brown. The rocks commonly show slaty cleavage and minor crenulations, but exposures are too small to allow study of cleavagebedding relationships. In thin section, the rock is a very fine grained mixture of roughly equal amounts of mosaic quartz and ragged flakes of chlorite. In some specimens sericite or muscovite takes the place of the chlorite. The more quartzose phases of the unit closely resemble the vitreous quartzite near Keyes Lake, except for noticeably more sericite. Phyllitic rocks containing abundant sericite are seen in thin section to contain blue-green tourmaline in well-developed small columnar crystals and a few small grains of zircon. The garnet quartzite part of the unit is abundant in the eastern part of the area shown in figure 2, but exposures are small. It is associated with the martitic quartzite and the stilpnomelane-garnet slate and may grade into these other rock types. The garnet quartzite is massive to poorly laminated, medium grained, gray, and weathers dark reddish brown or brownish gray. Isolated rounded glassy grains of quartz, generally about 0.1 to 0.5 mm in diameter, are common. Pale-red garnets are abundant. They occur as equant crystals and as irregular granular clusters that apparently follow bedding planes. Drill cores contain thin dark-green ferrostilpnomelane laminae that are most abundant near the base of the unit. Thin sections of the quartzite show a very fine grained quartz mosaic containing small plates, microcrystalline clusters, and schistose laminae of pale-green chlorite, clusters of green stilp-nomelane, and mashed porphyroblasts of red garnet Greenr ( 0) © CO co © Ol J I < s 5 bo s 2 o s V V [.yq . ] Vitreous quartzite EXPLANATION Green quartz graywacke K'gsa ; Gray siliceous graphitic argillite Martitic quartzite Quartzose phyllite and garnet quartzite Stilpnomelane-gamet slate Sericitic phyllite O Outcrop or group of small outcrops Contact Long dashed where approximately located; short dashed where gradational Dragfold Inclined Vertical Strike and dip of beds Top not known OOP Strike of pebble band . 75 Strike and dip of joint E Abandoned exploration shaft Trench X Test pit Dump GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN 88°17' Geology modified from R.W. Johnson, Jr., 1956-58 0 200 400 FEET 1 ________l_________l Base from compass and pace survey 1956-57 Figure 2. Geologic map showing lithology of the Michigamme Slate at the Little Commonwealth exploration.MICHIGAMME SLATE 17 stilpnomelane and, rarely, biotite are abundant in some thin beds. Thin stringers of saccharoidal vein quartz transect all structures in the rock. Stilpnomelane-garnet slate, which is most abundant north of the main road, consists mainly of dark-green to black ferrostilpnomelane and pale-red garnet. Locally, the slate is graphitic and cherty. A fibrous yellow amphibole occurs adjacent to the chert beds. The slate has distinct layers about y2 to 1 inch thick. Weathered outcrops are very soft and friable. The weathered slate is yellow brown to black and in places shows an iridescent coating which is presumably caused by iron or manganese oxides. Thin sections show a variety of mineral associations and textures. Most commonly the slate is porphyroblastic, showing bands of platy green ferrostilpnomelane and aggregates of red-brown garnet. In some specimens, chlorite and green ferrostilpnomelane are closely intergrown with minor amounts of biotite. Brown ferrostilpnomelane is developed locally as a feathery reaction rim near some chert fragments. Graphite is abundant in some of the slate; where it is present the grain size of the metamorphic minerals is relatively fine, and por-phyroblasts are nearly absent. The graphite seems to inhibit the growth of the metamorphic minerals. A thin belt of a related dark-reddish-brown fibrous slate extends westward some 700 feet beyond the main occurrence and appears to be interbedded and gradational with the martitic quartzite. The slate of the westward extension is less graphitic, and the dominant minerals here are well-developed ferrostilpnomelane and chlorite with some grunerite and chert. Strata Younger Than Quartzite Argillite and graywacke, younger than the quartzite near Keyes Lake, are present in small exposures and test pits along the south side of the quartzite throughout its length (pi. 2); the width of the belt within which the outcrops and pits are present is from 100 to 3,500 feet. The lithology of the strata younger than the quartzite in this area has not previously been described and is much more varied than the common slate-graywacke sequence that characterizes most of the Michigamme Slate. The principal rocks east of Keyes Lake are argillite, quartzite, and a massive garnetiferous chloritic rock; others west of Keyes Lake are phyllite, conglomerate, lean iron-formation, and a rock composed of medium-grained porphyroblastic chlorite. Thet strata east of Keyes Lake trend northwestward from the south side of sec. 32, T. 40 N., R. 18 E., and vicinity to the center of adjacent section 31, and the area of exposures widens southwestward into the NW^4 sec. 6, T. 39 N., R. 18 E. The succession of rock types southwest of the quartzite seems to be graphitic argillite, graywacke, graphitic argillite, garnetiferous chlorite rock, graphitic argillite, and quartzite. Graphitic argillite in the southwestern part of section 32 is in contact with the martitic quartzite that is a facies previously described (p. 15), and laminated-to-fissile graphitic argillite also occurs near the southwest edge of the quartzite at several places in the SE14SE14 and near the center of sec. 31, T. 40 N., R. 18 E. The adjacent graywacke is mainly greenish gray and is massive (SW14 sec. 32, T. 40 N., R. 18 E.); laminated to phyl-litic (SE14 sec. 31, T. 40 N., R. 18 E.); and massive, locally magnetic, and with or without small fragments of chert or quartzite (near the center of sec. 31). The second occurrence of graphitic argillite contains associated gray to black siliceous argillite. The chlorite rock is massive to poorly bedded, very dark green to black, and composed predominantly of fine-grained iron-rich chlorite and scattered subhedral reddish garnets as much as 2.0 mm in largest dimension. The graphitic argillite and associated phyllite in the third occurrence are dark gray to black, very fine grained, siliceous, and slightly garnetiferous. The adjacent quartzite is massive, medium to fine grained, and brownish gray to light red. These recurrences of similar lithologies may be a simple south-facing homoclinal sequence, but the repetition of graphitic and clastic rocks also suggest the possibility of three folds. If the graywacke is a facies change between the quartzite occurrences to the north and south, it is along an anticlinal axis. The northern occurrence of graphitic slate is along the axis of a syncline, and the chloritic rock is in another syncline. The problem has not been resolved because adequate structural data were not found. The sequence of Michigamme strata above the quartzite northwest of Keyes Lake could not be worked out in detail even though test pits are locally abundant and small exposures are scattered along its known length. The maximum width of the area indicated by test pit data to be underlain by these strata is approximately 2,000 feet in the NW)4 sec. 25 and the SWV4 sec. 24, T. 40 N., R. 17 E., but further discussion of the sequence refers to lower and upper parts because a median strip that is mainly from 500 to 1,000 feet wide is generally lacking in both exposures and test pits. The lower part of the sequence contains mostly metaargillite, lesser amounts of fine-grained to very fine grained metagraywacke, and a little phyllite. The amounts of very fine grained chlorite, graphite, quartz, and locally small garnets range widely. The oldest of four local units in the lower part of the sequence is a discontinuous conglomerate that lies adjacent to the south side of the most southeastern quartzite outcrop in sec. 25, T. 40 N., R. 17 E., and is also exposed approximately 200 feet northwest, at18 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN the Dunkel exploration, where it was penetrated by a test shaft and short adit. The rock is composed of pebbles of quartz (recrystallized chert or quartzite or both) in a matrix of rounded quartz grains, euhedral magnetite, and fine chlorite. The first mentioned occurrence of conglomerate extends for as much as 6 feet from the quartzite and is gradational into the second unit, which is a magnetite-bearing chloritic silty argillite that is about 4 feet thick. Graphic argillite, the third unit, extends from 10 to 20 feet south from the quartzite and contains porphyroblasts of chlorite; this rock also occurs on the crest of the ridge where it contains garnets about 0.50 mm in diameter. Highly contorted iron-formation, the fourth unit and from 20 to 30 feet south of the quartzite, is composed of chert layers about 1 to 2 inches thick and almost equal amounts of inter-bedded magnetite-grunerite containing some garnets. The iron-formation strikes northwest and can be followed for about 150 feet across part of the south end of the hill. This is the only known occurrence of magnetite-grunerite iron-formation in the Michigamme in the northern part of the Florence area. Massive magnetite, interlayed magnetite and quartz that is probably metachert, and brown-weathering carbonate with associated magnetite and pyritic chert are present in the dump at the Dunkel exploration. This small area of iron-formation causes a very local magnetic anomaly of about 15,000 gammas (pi. 6), which indicates the local concentration of magnetite. Iron-formation containing stilpnomelane, chert, and locally small amounts of magnetite was also penetrated by a few test pits along the trend of the quartzite, about 900 feet north of the Dunkel test shaft and adit. Another distinctive rock of unknown position in the sequence above the quartzite is composed almost exclusively of intergrown dark-green to black chlorite flakes as much as 1.0 mm in average dimension. Small euhedral garnets in the chlorite are common at some localities. Partings, generally coated with graphite, occur at intervals of to 1 inch. The decussate chloritic rock is generally underlain by argillite but locally, along the line between secs. 24 and 25, T. 40 N., R. 17 E., is adjacent to the quartzite. Chlorite porphyroblasts about 1.0 mm in average dimension are also common to abundant in some laminated argillite, and fine gray-wacke contains much chlorite, graphite, or both. A small amount of siderite containing scattered porphyroblasts of chlorite, with or without small fragments of chert, is exposed at the northwest corner of sec. 24, T. 40 N., R. 17 E. The highest part of the Michigamme strata for which data are available in the area northwest of Keyes Lake is known almost exclusively from the dumps of two exploratory shafts, several trenches, and numerous test pits in adjacent parts of secs. 23, 24, and 25, T. 40 N., R. 17 E. The order of abundance of these rocks is quartz graywacke, argillite, and stilpnomelane-bearing iron-formation. The quartz graywacke is medium to fine grained and greenish gray, weathering to various shades of red. The argillite is bedded or fissile and greenish gray or black, weathering to red. The iron-formation is composed of limonite or hematite, which appears to be pseudomorphous after radiating stilpnomelane; it is associated with chert, probably in layers or lenses. Very minor amounts of martite or magnetite are present locally. Exposures of iron-formation, penetrated during exploration, trend northwestward from the Dickey shaft in the SW14SW14 sec. 24, T. 40 N., R. 17 E., for a known distance of about 3,000 feet. The width of the area underlain by the explored iron-formation in section 24 ranges from 50 to 200 feet. A linear magnetic anomaly to the east of the Dickey and St. Clair shafts (pi. 8) may indicate that the iron-formation at the Dunkel shaft continues northwestward beyond the limits of the geologic map. PINE RIVER BLOCK The Pine River block contains only sparse outcrops, mainly along the Pine River (pis. 1 and 2), and the available data indicate that the area is probably underlain mainly by sedimentary rocks and some volcanic rocks. These strata are the westward extension of the Michigamme Slate from southern Dickinson County of Michigan since no interruption of continuity has been noted (pis. 1 and 4). Exposures of Michigamme Slate in Dickinson County are not large or numerous, but the dominant rock known is sericitic quartzose slate with minor amounts of gray vitreous quartzite and iron-formation consisting of interbedded siderite and chert (Bayley and others, 1966); the rock in the Pine River area is generally similar but locally is much more varied and has not previously been described. The Michigamme strata in this block are believed to be limited on the south by a major fault beyond which lies the northward-facing Quinnesec Formation of early Precambrian age. These relations also occur in southern Dickinson County (Bayley and others, 1966). The most common rock unit exposed in this block is quartzitic conglomerate in which crossbedding shows that top is southward (pi. 1), but the sequences of the older and younger rocks are still only partly known (fig. 3). To the north the quartzitic conglomerate is underlain by a distinctive and persistent assemblage that includes slate, dark-gray biotitic quartz graywacke, gruneritic iron-formation, and amphibolite. Farther north in a few widely scattered exposures is a gray well-bedded toLower Middle Precambrian Precambrian MICHIGAMME SLATE 19 45° 50’ EXPLANATION qsl Michigamme Slate \qsl, quartz slate. Locally includes minor conglomerate (cg\) a99. agglomerate and tremolite schist \ qc, quartzitic conglomerate. Locally includes gruneritic (gi) or magnetitic ('mil iron-formation a, assemblage of thin units. Locally includes graphitic slate (gs\), quartz-mica slate (si), quartz graywacke (gw), gruneritic schist (gru), and amphibolite Mam) 1233 Quinnesec Formation Metafelsic rocks-metarhyolite? and quartz-muscovite schist; locally includes in-terfoliated schist (sch) J o Outcrop or group of small outcrops Z < Contact 01 Long dashed where approximately lo-fi] cated; short dashed where inferred; ^ dotted where concealed; queried \yhere 5 doubtful <, _______________......... . O D • LU Probable fault 0- Dotted where concealed ; U, upthrown O. side; D, downthrown side; queried where doubtful , 75 Inclined Vertical Strike and dip of beds Strike and dip of beds Direction of top determined by graded bedding Strike and dip of beds Direction of top determined by cross bedding Strike and dip of foliation Strike and dip of bed and plunge of lineation Abandoned shaft x Test pit Figure 3.—Distribution and relation of the Michigamme Slate and Quinnesec Formation in secs. 20, 21, 28, and 29, T. 39 N„ R. 18 E.20 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN laminated sericitic slate or phyllite that probably is the oldest and most extensive unit in this part of the area. The stratigraphic position of iron-formation at and southeast of the quartzitic conglomerate exposures is not known; it is possibly a facies change of the conglomerate but is described separately. To the south the conglomerate is overlain by phyllite and farther south beyond a narrow covered interval by volcanic breccia and then quartz slate with minor beds of conglomerate. The lithology of the informal units in the Michigamme Slate will be described in geographic order from north to south. Slate, Schist, and Phyllite Slate along or generally near the Pine River is exposed in sec. 34, T. 40 N., R. 17 E., sec. 3, T. 39 N., R. 17 E. (pi. 2), secs. 27,28, and 29, T. 39 N., R. 18 E., and secs. 19, 20, and 21, T. 39 N., R. 19 E. (pi. 1). The rock is gray and well bedded in layers approximately one-fourth to one-half inch thick. The percentage of minerals in the rocks is approximated as quartz from 20 to 50; sericite and muscovite from 20 to 70; biotite from 10 to 25; and chlorite, if present, from 5 to 40. Hematite, carbonate, and tourmaline are minor constituents. A little magnetite and pyrrhotite are present locally. The size of the minerals is commonly less than 0.10 mm in diameter, but the micaceous minerals are locally por-phyroblastic and are as much as 0.50 mm. Most schist at these same localities is fine grained and is medium to dark gray and dark green. Chlorite or biotite or both are the principal minerals and are sufficiently abundant and well alined to produce some foliation. Dark red garnets are abundant in the schist near the quartzite; locally they are concentrated in layers and lenses, but they may be minor or absent. Some garnets have been rotated after formation as much as 25°, as shown by the angular discordance between general foliation and the layers of very fine opaque grains within the garnets. Deflected foliation at the boundary surfaces of the garnets also indicates direction but not amount of rotation. Some schist has alternate layers of light and medium gray and is composed chiefly of sericite and quartz. Porphyroblasts of chloritoid as much as 0.40 mm wide and 2.0 mm long have formed across the foliation in schist in the southeastern part of sec. 13, T. 39 N., R. 17 E. Lenticular to equant opaque grains (probably magnetite) about 0.02 mm across are commonly distributed parallel to the foliation in much of the schist. The phyllite is very fine grained, foliated, and medium to dark gray to dark green. Garnets range from abundant to absent. The composition and relationship of minerals are similar to those in schists, but most grains are about 0.05 mm or less in diameter. Quartz Graywacke Quartz graywacke is commonly massive but locally slightly fissile, mostly fine grained, and medium to dark gray. Some quartz graywacke grades toward or into finegrained quartz-biotite schist with only slight foliation. The graywacke is composed predominantly of anhedral to subangular quartz less than 0.10 mm in maximum dimension and some rounded quartz less than 0.50 mm generally, but as much as 2.0 mm in some sections. Associated intergranular minerals are biotite, chlorite, muscovite, and stilpnomelane(?) ; each is generally less than 0.10 mm. Very poikiloblastic chloritoid is present locally. Irregular to subhedral garnets occur in some sections and are as much as 3.0 mm in maximum dimension. Amphibolite The amphibolite is massive to irregularly layered, dark gray, and fine to medium grained; it is generally found 10 to 50 feet north of the quartzitic conglomerate. In some hand specimens radiating light-greenish-gray hornblende constitutes areas approximately 1.0 mm in diameter and may range in amount from a little to virtually 100 percent. In other specimens only biotite is readily identified with associated light and dark grains that are probably feldspar and hornblende, respectively; or biotite may enclose scattered hornblende porphyroblasts approximately 1.0 mm long. The weathered surfaces of some amphibolite commonly exhibit irregularly to well-developed, inter-layered, lenticular, or diagonally cross-cutting, mediumgrained, dark-green material in or with very fine grained light-gray rock, which contains relatively more feldspar. Layers are from 2 to 10 mm thick. Layering is also evident in fresh rock but is not so conspicuous as where weathered. Weathered surfaces of massive rock are uniformly medium to dark gray, mottled gray, or very light gray mottled with green. Foliated amphibolite has abundant chlorite or sericite on the partings. The amphibolite as seen in thin section is composed predominantly of hornblende and feldspar, but locally biotite predominates. Magnetite and quartz are commonly present, biotite and chlorite less often. Clinozoi-site, sphene, and garnet are found in some thin sections. Blue-green or olive-green hornblende in sheaves or subhedral grains (2.0 mm maximum) is the most abundant mineral present. Slender prisms in radiating or sheaflike bundles are characteristic ; single subprismatic grains are more common than irregular ones, and tooth are generally poikiloblastic. The hornblende in some sections is partly alined, but well-developed linea-tion is not characteristic. Most feldspar grains are less than 0.50 mm. irregularly anhedral, and untwinned, but determinations from albite and pericline twinning indicate a small amount of oligoclase and andesine with a composition ranging from Ana to An42 and an average of An., for a total of 25 grains in sections from five localities. Feldspar and hornblende seem to be present in about equal amounts in most thin sections, but the ratio differs greatly even in parts of the same thin sections.MICHIGAMME SLATE 21 Grunerite Iron-Formation The grunerite iron-formation is a poorly to welllayered gray rock that weathers brown. It is composed of radiating gray to brown grunerite masses from 1 to 2 mm in diameter, red to brown garnets, very fine grained quartz, and fine-grained magnetite. Some specimens are highly magnetic, but many are only slightly so or are nonmagnetic. Small amounts of limonite or hematite or both are present in weathered and oxidized specimens. Quartzitic Conglomerate The most prominent and best exposed unit in the Pine River block was considered a separate formation by Leith, Lund, and Leith (1935, p. 4) and was designated the Breakwater Quartzite. The unit appears, however, to be a lens in the Michigamme Slate and in this report is considered to be a part of that formation. The quartzitic conglomerate extends northwestward for about 3 miles from scattered exposures near the center of sec. 28, T. 39 N., R. 18 E., to the northeast corner of sec. 24, T. 39 N., R. 17 E. Outcrops are relatively numerous and individually are larger than those of any other sedimentary unit in the Florence area. Because dips are vertical or steeply southward, the 700-foot width of outcrop probably approximates the true thickness of the unit. Layers and lenses of quartzite containing a few or many flat pebbles generally predominate. The pebbles, and a few sporadic cobbles, are composed mainly of finegrained colorless quartz, which is mainly recrystallized chert. Some pebbles of iron-formation show laminae composed of very fine grains of specular hematite or magnetite or both, and a few pebbles are exclusively or predominantly composed of fine-grained hematite or magnetite or both. The pebbles and the plates of specular hematite are oriented in the bedding planes of the conglomerate which are also planes of foliation (fig. 5). A few pebbles are grayish-red jasper, and one cobble of jaspilite was found. The matrix of the conglomerate that contains the ferruginous pebbles is medium gray and composed of quartz, specularite, and magnetite. The matrix of other conglomerates generally contains little or no hematite or magnetite, but interstitial hematitic staining is common. The quartzite beds associated with the conglomerate are fine grained and range from white or pink with very little or no layering to reddish gray with moderately well developed stratification and much crossbedding. Although closely associated locally, the dark-colored quartzite is more abundant in the eastern part of the outcrop belt and the light-colored one in the western part. Figure 4.—Predominance of quartz pebbles in quartzitic conglomerate near the Pine River, sec. 28, T. 39 N., R. 18 E. In addition to the distinct pebbles and cobbles, there are lenticular forms that differ from the enclosing material in that they contain larger grains of quartz and very scarce intergranular iron oxide. The quartzitic conglomerate and associated strata in the Pine River area were mapped and described in detail by Nilsen (1965), who believes that these lenticular forms were originally clasts, rather than lenses of sand, inasmuch as (1) lamination within them commonly does not conform to overall stratification in the conglomerate, (2) cross stratification is absent in these forms although associated materials suggest fairly strong currents, (3) most forms are polygonal and angular rather than lenticular, and (4) platy minerals are virtually absent so that boundaries with the matrix are sharply defined. Nilsen (1965) showed that the quartzitic conglomerate consists of two conglomerate subunits separted by a quartzite and pebbly quartzite subunit. His paleocur-rent analysis based on crossbedding shows that the predominant direction of current flow was southeastward, and he inferred deposition in a shallow nearshore basin. In his opinion the quartzitic conglomerate near Pine River and the quartzite near Keyes Lakes are not correlative; however, the two units show many lithologic similarities even to the associated ferruginous rocks, so they may be the same unit. However, their age relations are insoluble on the basis of present knowledge. Quartzite in the western part of the outcrop belt has a generally massive appearance; but widely spaced22 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN Figure 5.—Alinement of pebbles in quartzitic conglomerate, NWy4 sec. 28, T. 39 N„ R. 18 E. partings, which possibly are bedding planes, trend approximately parallel to the base of the unit. Some differences in coloration have a similar trend but are discontinuous. The lower part of the quartzite in sec. 24, T. 39 N., R. 17 E., and sec. 19, T. 39 N., R. 18 E., has a 25-foot pebbly layer that is exceptional in that it contains a garnet-grunerite-magnetite assemblage as the matrix. This association indicates an unexpected contemporaneity of chemical deposition of iron-bearing material and accumulation of the pebbly layer. The quartzitic conglomerate rests conformably on the underlying strata as observed in sec. 24, T. 39 N., R. 17 E., in the northwestern part of sec. 19, T. 39 N., R. 18 E., and in section 20 of the same township. Strata younger than the quartzitic conglomerate lie conformably above it in sec. 28, T. 39 N., R. 18 E., at the only exposure seen. Another occurrence of younger strata immediately above the conglomerate is reported by Nil-sen (1965, pi. 1) to be in sec. 19, T. 39 N., R. 18 E. Iron-Formation A few outcrops of and test pits in iron-formation in the SW^NE^ sec. 28, T. 39 N., R. 18 E. (fig. 3), are 500 to 1,200 feet southeast of the most southeastern exposure of quartzitic conglomerate. The exposed rock appears to be a dense red hematite-quartz iron-formation; but thin sections reveal that the hematite is a secondary weathering product and that the fresh rock is metamorphosed iron-formation composed of gru-nerite, magnetite, and quartz. Before metamorphism the iron-formation was probably composed of siderite and quartz. Material in the dump of the test pit shown in figure 3 is unweathered and is predominantly magnetite and quartz. A linear positive magnetic anomaly crests over the occurrences of iron-formation (pi. 7) and, though interrupted at places, appears to extend southeast for 4 miles. Drill holes in the western part of sec. 27, T. 39 N., R. 18 E., passed through Michigamme Slate that locally contained veinlets of pyrrhotite, but the possible relation of the nearby high magnetic values and this mineral occurrence is not known. Exploration by drilling in the NE14, sec. 34., T. 39 N., R. 18 E., reported penetration of magnetic grunerite schist and associated quartz schist. Another drill hole near the eastern terminus of the anomaly, in the SE14SEI4, sec. 36, T. 39 N., R. 18 E., cut hematite-magnetite-quartz iron-formation, thus indicating that iron-formation probably causes the magnetic anomaly along much of or all its length. This ferruginous unit is probably cut out to the southeast by the fault that separates the rocks of middle Precam-brian age in the Pine River block from rocks of early Precambrian age in the adjacent Popple River block. The bedding of iron-formation exposed in sec. 28, T. 39 N., R. 18 E. (fig. 3), strikes northwest and, if extended, goes directly to the outcrop of conglomerate overlain by phyllite; and the northwestern continuation of the anomaly just described has similar relations to the outcrop. The probability of the iron-formation being a facies change of the quartzitic conglomerate is suggested by available data. An anomaly in sec. 19, T. 39 N., R. 18 E. (pi. 7), appears to be related to unexposed quartzitic conglomerate and possibly in part to unexposed material south of the contact as shown there and to the southeast in secs. 20 and 29, T. 39 N., R. 19 E. In contrast, however, the anomaly in the northeastern part of sec. 24, T. 39 N., R. 17 E., is related to the basal part of the quartzitic conglomerate that contains magnetite. The value and locally the trend of this anomaly change, but it continues to and beyond the northwest corner of the area shown on pi. 7. The characteristics of the outcrops north and south of the anomaly in secs. 10 and 15, T. 39 N., R. 17 E., are equiva-MICHIGAMME SLATE 23 lent or identical to those of outcrops in similar positions to the quartzitic conglomerate in its area of exposure. These relations of lithologies and magnetic values to the quartzitic conglomerate unit suggest that iron-formation at, southeast of and possibly northwest of the limit of outcrop may have formed as a facies somewhat comparable to that at the Little Commonwealth area (p. 15) east of Keyes Lake. Phyllite Above Quartzitic Conglomerate An exposure of phyllite, about 10 feet wide and 70 feet long, south of and in conformable contact with quartzite containing several pebble bands, occurs near the center of sec. 28, T. 39 N., R. 18 E. (pi. 1 and fig. 3). Most of the rock is laminated, color banded in various shades of gray, and composed chiefly of very fine grained alined flakes of sericite and chlorite and less abundant angular grains of quartz. Tabular masses of chlorite about 0.05 mm wide by 0.20 mm long are common, and a few altered garnets about 1.0 mm in diameter are present in some of the phyllite. Greenstone Agglomerate Greenstone agglomerate and associated green schist are exposed in the bluffs north of the Pine River in sec. 28, T. 39 N., R. 18 E., for a strike length of about 1,500 feet and a width of at least 200 feet (fig. 3). Several small exposures occur to the west and northwest in secs. 28 and 29, T. 39 N., R. 18 E. Also, near the north line of sec. 15, T. 39, N., R. 17 E., schistose material is predominant but lenticular fragments are present locally. The agglomerate is characterized by a predominance of lenticular to subangular greenish-gray fragments from 1 to 12 inches in maximum dimension with material of the same color but finer grain between the fragments. The agglomeratic texture is accentuated on weathered surfaces. Many fragments at this and other localities have small carbonate-filled areas that become pits filled with earthy limonite upon weathering. Much of the rock has been sheared locally, so that the fragmental texture has been partly or entirely destroyed. The principal minerals identified in the agglomerate are actinolite-tremolite, talc, chlorite, and carbonate. The actinolite-tremolite forms radiating clusters in the agglomerate but well-developed prisms in the schist. Slate and Metagraywacke Slate and fine-grained quartz graywacke are exposed in the channel and along the banks of the Pine River for about 2,000 feet downstream from the reservoir dam in sec. 28, T. 39 N., R. 18 E. (fig. 3). Most of the rock is well stratified and occurs in layers about 5 to 10 mm thick that differ in shades of gray and in grain size, the darker layers being of finer grain. Only quartz and locally garnet can be identified in hand specimens. Some layers are rich in garnet porphyroblasts that are as much as 6 mm in diameter. Coarse-grained metagraywacke beds a few inches thick occur locally; these contain abundant granules 2 to 4 mm in diameter. A few layers of coarser elastics that contain fine-grained quartzitic material in lenses and also lenticular particles of granule and pebble size were exposed in the canal from the dam to the power plant when the water was diverted in 1959. The slate contains a few ellipsoidal dark-green masses 1 to 3 inches long and rich in chlorite and amphibole; in thin section chlorite can be seen to fill the space between abundant clusters of colorless amphibole (probably tremolite-actinolite). These ellipsoids are probably metamorphosed concretions that were relatively rich in carbonate. The Michigamme Slate contains such concentrations in several localities in Michigan, for example, in the SE44 sec. 20, T. 45 N., R. 30 W. (James, 1955, pi. 2). THICKNESS AND CONDITIONS OF DEPOSITION The lower and upper contacts of the Michigamme Slate are exposed only in the northern part of the mapped area, where the thickness of the formation is about 5,000 feet or possibly less. Faults bound all other exposures of the formation except at its contact with the Badwater Greenstone in the northeast corner of the southern part of the area. The greatest inferred thickness is about 20,000 feet, in the Pine River block (pis. 1 and 4), where the formation may be least faulted and folded. The great thickness and the predominance of clastic deposits in the Michigamme Slate indicate probable deposition in a subsiding basin that received an abundance of disintegrated material from which slate, graywacke, and conglomerate formed. Two iron-formation units formed by associated chemical concentration and deposition. Minor vulcanism added fragmental material that is now greenstone agglomerate. The thickness and lithology of the sedimentary rocks and the presence of volcanic rock suggest a general environment of deposition in an orogenically disturbed area. AGE AND CORRELATION The Michigamme Slate is of middle Precambrian age and is the most widely distributed sedimentary unit in the Precambrian sequence of northern Michigan and adjacent areas of Wisconsin. From the Florence area the Michigamme extends eastward into Dickinson County, Mich., northward to the Marquette district, and presumably northwestward toward the Gogebic district.24 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN The formation is possibly the correlative of at least part of the Virginia Slate in Minnesota (James, 1958, table 2; Cotter and others, 1965). BADWATER GREENSTONE DEFINITION, DISTRIBUTION, AND GENERAL LITHOLOGY The Badwater Greenstone was named by James (1958, p. 37) for exposures of metabasalt near Badwater Lake in southern Dickinson County, Mich. The greenstone extends northwestward from the type locality across the northern part of the Florence area, with scattered exposures for a length of about 9 miles (pi. 2), and continues northward into Iron County, Mich. The greenstone unit has an apparent thickness that ranges from about 5,000 to 15,000 feet. Outcrops of Badwater Greenstone near the western edge of the northern half of the Florence area represent another part of the formation that trends northwestward for 3 miles beyond the mapped area and continues into Iron County (pi. 4); the western limit and probable thickness of this occurrence are not known. Outcrops of greenstone and associated metasedimentary rocks west of Keyes Lake are believed to belong to the Badwater Greenstone. These outcrops are within an area about 1 mile wide and iy2 miles long. The only known exposure of the Badwater Greenstone in contact with the underlying Michigamme Slate is in the NE%SE% sec. 18, T. 40 N., E. 19 E.; here the greenstone is conformable with garnetiferous phyllite. No contacts with the overlying Dunn Creek Slate are known in the mapped area, but a conformable relationship between these formations is assumed. One of the important results of the present investigation of the Florence area was the finding of field evidence which indicated the stratigraphic positions of the Badwater Greenstone and the Paint Kiver Group. The Michigamme slate-graywacke assemblage in the northern part of the mapped area has long been known to extend northwestward and then northeastward to the type locality of the Michigamme Slate at the middle of the west side of Marquette County, Mich. (fig. 1). The stratigraphic relation of the Michigamme Slate and the adjacent Badwater Greenstone was not proved until 1955 when graded bedding in quartz graywacke at or very near the top of the Michigamme was observed by H. L. James, K. L. Wier, and C. E. Dutton. The grading indicates that the tops of the beds are toward the nearby Badwater Greenstone in the SW(4 sec. 12, T. 40 N., R. 18 E., of Wisconsin (pi. 2). Furthermore, ellipsoidal (pillow) structures in the greenstone consistently indicate the tops to face south (as in secs. 14,22, and 23, T. 40 N., R. 18 E., and sec. 12, T. 40 N., R. 17 E.) toward the Paint River Group in the vicinity of Flor- ence (pi. 2). Thus the relative stratigraphic positions of the Badwater Greenstone and the Paint River Group were also clarified for Iron County, Mich. The most common rock in the Badwater Greenstone in the Florence area is massive greenish-gray metamorphosed flow basalt. In addition to typical greenstone and also amphibolite, derived from the highest grade of metamorphism of basalt, the formation contains some stratified rocks that are commonly argillaceous to arenaceous but locally are tuffaceous. Thin iron-rich beds are also present. GREENSTONE Greenstone, derived through low-grade metamorphism of basalt extrusives, is the most abundant rock type in the Badwater Greenstone. It is exposed in the Brule River block for almost 9 miles northwestward from sec. 20, T. 40 N., R. 19 E. Exposures are most numerous, steep, and rugged along the Menominee and Brule Rivers but are sparse, low, and rounded elsewhere. The maximum width of the outcrop belt is about 3 miles. Other outcrops of greenstone in this block form small scattered knobs in the southeast corner of the area shown on plate 2 and the northeast comer of the area shown on plate 1. Exposures of the greenstone in the Keyes Lake block occur in secs. 21, 27, 28, 35, and 36, T. 40 N., R. 17 E. (pi. 2). The greenstone flows are generally massive but locally ellipsoidal (fig. 6) or slightly foliated. Some exposures Figure 6.—Ellipsoidal (pillow) structure in the Badwater Greenstone, SWt4 sec. 27, T. 40 N., R. 17 E.BADWATER GREENSTONE 25 are agglomeratic. Ellipsoids are commonly 18 to 24 inches long and about 9 inches wide. The rocks are predominantly light greenish gray, but greenish gray or medium gray are local variations. The grain size is normally very fine but ranges to medium. In thin sections, texture is commonly a fine-grained mosaic that encloses amygdule fillings of quartz, clinozoisite, or carbonate. Actinolite or actinolitic hornblende and clinozoisite-epidote are the most abundant minerals in the mosaic. Twinned subhedral plagioclase, chlorite, sphene, and carbonate occur in subordinate amounts. Leucoxene, quartz, and biotite are minor constituents. The twinned plagioclase is albite with composition range of an9_o. Phyllitic and slightly schistose rocks that are locally associated with greenstone are composed of alined very fine grained chlorite and quartz and locally also biotite. The phyllites probably represent local thin accumulations of sedimentary or volcanic debris. AMPHIBOLITE (METABASALT) The Badwater metabasalts near the confluence of the Brule and Michigamme Rivers show the highest grade of metamorphism in the formation. Exposures are found in the sec. 12, and in the sec. 13, T. 40 N., R. 18 E. The rocks are amphibolite and are medium gray on weathered surfaces, dark gray to black if unweathered. They are fine grained, but granular hornfelsic texture is readily visible. The amphibolite is generally dense and uniform; locally, in sec. 13, it is amygdaloidal. The principal minerals in the amphibolite are hornblende and plagioclase; associated minerals are clinozoisite, epidote, biotite, quartz, magnetite, and leucoxene. The hornblende is the predominant constituent in the thin sections examined. The characteristic pleochroism is X, pale yellowish gray; Y, light grayish olive; Z, light grayish blue green. Extinctions (ZAc) range from 15° to 24°. Slender to stubby prismatic forms (0.5mm) with irregular terminations are prevalent. The plagioclase is andesine and is the second most abudant mineral in the amphibolite. The range in composition of plagioclase in two thin sections is from An2s to A1137. Clinozoisite and epidote or only epidote are present in about half the thin sections examined. Biotite is a subordinate or minor constituent in most sections, and in some appears to be an alteration product of hornblende. Quartz is present in minor amounts in most sections and is of anhedral form. Amygdule fillings are most commonly quartz, chlorite, biotite, and carbonate. IRON-FORMATION The most distinctive metasedimentary rock in the Badwater Greenstone is the grunerite-magnetite-quartz iron-formation that occurs in at least two discontinuous layered units approximately 10 to 50 feet thick in the western part of the Keyes Lake block. Exposures are few, scattered, and generally les9 than 10 square feet in area, but the position of the iron-formation at the bedrock surface is indicated by several old test pits and shafts and also by magnetic surveys (pis. 2, 6, and 8). The iron-formation is brown to reddish brown and moderately well stratified in alternate layers that differ in relative amounts of grunerite and quartz. Grun-erite and magnetite can readily be seen with a hand lens, but quartz grains are too small to be recognized. Associated minerals seen in thin sections are hematite, garnet, stilpnomelane, carbonate, brown biotite, green biotite, and, rarely, glaucophane. The grunerite is commonly in randomly oriented irregularly terminated prisms that average 0.10 mm wide and 0.50 mm long. A small amount of grunerite occurs in radiating or sheaflike aggregates that are 1.0 to 3.0 mm. Some grunerite has been partly or completely oxidized and replaced by pseudomorphs of hematite. Subangular quartz grains approximately 0.10 mm in diameter have formed by recrystallization of chert, but other quartz is pseudomorphic after grunerite and is chalcedonic. Magnetite grains are irregular to euhedral and commonly about 0.5 mm. Subhedral garnets, stilpnomelane needles, small sub-angular carbonate grains, and irregular flakes of brown and green biotite are minor constituents. Some biotite has been partly or completely altered to chlorite. The glaucophane is in blue blades about 0.15 by 0.50 mm long that have normal pleochroism and about 9° extinction (ZAc). The magnetic crestlines shown on plate 2 are based on a magnetometer survey of sec. 36, T. 40 N., R. 17 E., and adjacent areas (see pi. 6 and p. 45 of this report by K. L. Wier and R. A. Soliberg. Two approximately parallel magnetic anomalies caused by iron-formation trend northwestward through the western half of sec. 36 into sec. 26, T. 40 N., R. 17 E., and very similar trends occur in sec. 35, T. 40 N., R. 17 E., and sec. 1, T. 39 N., R. 17 E. Thinly stratified quartz-serioite slate crops out at several places between exposures of the iron-formations or the anomalies that result from them. Although the distribution of anomalies suggests possible repetition of iron-formation by simple anticlinal or synclinal folding, such interpretation seems to be contradicted in the southern part of section 26 because the projected trends of the paired anomalies converge as in a south-east-plunging syncline. Further consideration of this subject is given in the general discussion of geologic structure (see p. 39). Two thin discontinuous grunerite-magnetite-quartz iron-formation units separated by quartz-sericite slate also occur at the line between secs. 27 and 28, T. 40 N., R. 17 E. These units trend southeast, as shown by the magnetic crestlines, and the projection of the southern one converges in section 27 with another Crestline that trends southwest (pi. 2 and 8). The structure is interpreted as an anticlinal fold that is plunging southward.26 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN SLATE, METAARGILLITE, AND QUARTZ GRAYWACKE Most sedimentary rocks associated with the metabasalt of the Badwater Greenstone west and northwest of Keyes Lake consist of gray, very fine grained (less than 0.10 mm) material in which stratification, cleavage, or parallelism of platy and acicular minerals may or may not be present. “Slate” is the designation generally used for the rocks, but it is proper for only a few; most are metaargillite or fine-grained quartz gray-wacke. Quartz, chlorite, and biotite are commonly the dominant constituents. Sericite, garnet, hornblende, feldspar, pyrite, hematite, magnetite, and graphite range widely in abundance and generally are subordinate to rare. Most of the minerals have normal characteristics and relationships for rocks of this type, but a few distinctive features are present. Some garnets have been rotated during crystallization as indicated by the S-shaped distribution of inclusions from pre-existing foliation. Poikilitic hornblende porphyroblasts are as much as 1.8 mm wide and 4.5 mm long. The moderate to strong pleochroism of the mineral is X, pale straw; Y, pale-grayish green; and Z, grayish blue. Extinction in various sections ranges from 16° to 25°. The hornblende increases in abundance and grain size with proximity to metagabbro. One variety of slate has sericite and quartz as the principal constituents with subordinate or minor amounts of chlorite and biotite. This slate crops out in secs. 35 and 36, T. 40 N., R. 17 E., and lies between the two thin iron-formation layers mentioned previously. The slate is light to medium gray, well stratified in beds less than 1 inch thick, and has moderately developed cleavage that is at an angle of about 45° to the stratification. Poorly developed graded bedding is visible in some thin sections. Hornblende and chloritoid porphyroblasts in slates and slightly schistose rocks commonly have a random orientation, and adjacent foliation has been deflected. Foliation preserved in these minerals, as in the garnets, may be parallel to or rotated from the general trend in the rock. Another variety of slate examined contains minor to dominant amounts of quartz, amphibole (hornblende?), chlorite, and biotite; magnetite and epidote are minor constituents in a few specimens, and garnet is subordinate to dominant in a few others. The grain size in all sections of this slate ranges mainly from 0.05 to 0.2 mm, but many amphibole grains are 1.0 to 3.0 mm long. Most of the slate of this variety is in contact with or close to metagabbro in secs. 26, 27, 28, 35, and 36, T. 40 N., R. 17 E., and secs. 1 and 2, T. 39 N., R. 17 E. The known distribution of this variety of slate suggests that it is a metamorphic rock rather than a stratigraphic unit, but data are inconclusive. The slate is medium to dark gray and generally exhibits little stratification; locally foliation is moderately developed. In thin sections, amphibole is the most conspicuous component of this variety of slate; it is commonly present as radiating to sheaflike slender prisms, as poorly to well-developed porphyroblasts, or as irregular and stringy masses. Sieve structure resulting from included quartz is common. Foliation of the slate is interrupted by randomly oriented porphyroblasts and may be bent adjacent to them. Garnets interrupt foliation and deflect it, especially where they have been rotated. Garnets commonly are 0.5 to 1.5 mm in diameter and are subhedral to euhedral. Thinly bedded gray slate and black graphitic slate containing small garnets are exposed in the SW*4SE^4 sec. 26, the SE%SW^4 sec- 27, T. 40 N., R. 17 E., and at several places in the NW1/^ sec. 1, T. 39 N., R. 17 E. Quartz metagraywacke is locally present in the Badwater Greenstone and layers as much as several inches thick are interbedded with slate. The metagraywacke is grayish dark green, phyllitic, and contains fine (0.10 to 0.50 mm) grains of quartz that can be readily identified with a hand lens in bright light. In thin sections the metagraywacke is seen to be composed of scattered angular quartz grains and a small amount of rounded twinned and untwinned feldspar as much as 0.20 mm in diameter; but most grains are less than 0.05 mm and are anhedral quartz, biotite, chlorite, and some feldspar. Some chlorite- and stilpnomelane-bearing rocks, probably metasedimentary, are exposed along the line between secs. 22 and 23, T. 40 N., R. 18 E., and along the Brule River in secs. 7 and 8, T. 40 N., R. 18 E. Chlorite and stilpnomelane(?) are dominant; accessories are feldspar, epidote, leucoxene, and quartz. The rocks are almost phyllitic, but the chlorite and stilpnomelane do not have sufficiently well developed parallel orientation to produce good foliation. TUFFAGEOUS(?) ROCKS A gray phyllitic rock that probably was originally pyroclastic was found on a test pit dump near the Brule River in the SE)4NW% sec. 14, T. 40 N., R. 18 E., Wisconsin. The phyllite is a greenish-gray slightly foliated rock that contains very fine white grains and locally is altered to grayish maroon. In thin section the rock is seen to be composed mostly of very fine grained elongate chlorite less than 0.05 mm in length, angular quartz grains less than 0.10 mm, and scattered untwinned cloudy feldspar grains that are euhedral and anhedral and as much as 0.15 by 0.25 mm. The weathered maroon areas of the phyllite contain spots of hematite as much as 0.20 mm in maximum dimension and hematitic alteration of chlorite. PAINT RIVER GROUP The name Paint River Group was used by James (1958, p. 37) to designate the strata of middle Precam-brian age that are younger than the Badwater Greenstone in the Iron River-Crystal Falls area, Iron County, Mich. (pi. 4). The group comprises, in ascending order, the Dunn Creek Slate, Riverton Iron-Formation, Hia-DUNN CREEK SLATE watha Graywacke, Stambaugh Slate, and Fortune Lakes Slate. These formations lie within a triangular synclinal basin with apices at Iron River and Crystal Falls, Mich., and at Florence, Wis. The Paint River Group in the Florence area occurs only in the Commonwealth syncline and in a smaller syncline in the Keyes Lake block (pi. 2 and I). The Dunn Creek Slate is mainly gray metasiltstone and slate, but the uppermost part is a pyritic graphitic slate. The Riverton Iron-Formation is interbedded side-rite and chert where fresh, hematite-limonite chert where oxidized, and grunerite-magnetite chert where metamorphosed. The Hiawatha Graywacke is predominantly massive metagray wacke that commonly contains angular fragments of chert. The Stambaugh Slate is in part, and most characteristically, laminated cherty side-rite and magnetite in Iron County, Mich.; this type of rock is absent or very rare in the Florence area. The formation in Michigan also includes chloritic mudstone and slate. Similar rocks in Wisconsin are slightly magnetic and along the projected southeasterly trend of the formation are probably correlative. Rocks in the mapped area that are probably equivalent to part of the Fortune Lakes Slate are slate, associated with thin beds of graywacke, and locally minor amounts of chert-side-rite and sideritic slate. The Hiawatha Graywacke, Stambaugh Slate, and Fortune Lakes Slate are not sufficiently well exposed or explored in the Florence area to be mapped separately, except in the northwest corner, and elsewhere constitute a map unit of undifferentiated post-Riverton strata. On the basis of areal geology, the Paint River Group in the Florence area is estimated to be probably at least 3,000 feet thick. The group locally lies uncomformably on the underlying Badwater Greenstone in the Florence area and is locally unconformable on the Michi-gamme Slate near Crystal Falls, Mich. The only strata known to overlie the group are two small areas of sandstone of probable Late Cambrian age that occur near Commonwealth but are not shown on the map. The Paint River Group is composed predominantly of clastic materials (sand and mud) that accumulated in a basin characterized by widespread uniformity for relatively long intervals. Shorter intervals of widespread uniformity were characterized by stagnant and reducing conditions in which carbonaceous mud accumulated. Chert-siderite formed in clear water and a reducing environment of a barred basin or basins in which concentration by precipitation and settling exceeded overflow. Some chert-siderite of the Riverton Iron-Formation was subjected to erosion, probably by wave attack below water level, and fragments of chert were concentrated in place forming a residual breccia or 27 were swept into and embedded in the sandy mud from which the overlying Hiawatha Graywacke formed. The Paint River Group is of middle Precambrian age and is the youngest group of the Animikie Series known in Michigan. James (1958, table 2, p. 35) considered the Paint River Group to be younger than the Virginia Slate, the youngest formation of the Animikie Group in Minnesota. DUNN CREEK SLATE DEFINITION AND DISTRIBUTION The Dunn Creek Slate is at the base of the Paint River Group and was named for exposures of siltstone and slate near Dunn Creek south of Crystal Falls, Mich. (James, 1958). The Dunn Creek Slate in the Florence area is exposed in a few small outcrops, in open pit mines, and at test pits in four localities. 1. The formation is exposed at and near the Florence mine for at least iy2 miles in secs. 17,20, and 21, T. 40 N., R. 18 E. (pi. 2 and 3). 2. The next exposures are about 5 miles northwest, in Michigan, in sec. 31, T. 42 N., R. 32 W., which is 6 miles south of the type locality. 3. The Dunn Creek Slate extends southeastward from the Florence mine to exposures southeast of the village of Commonwealth, in secs. 34 and 35, T. 40 N., R. 18 E., near the Badger mine (pi. 2). The formation in this part of the area is in a northwest-plunging syncline. Exposures on the south limb of the syncline were present along county road N in the southwestern part of section 34 prior to widening of the road in 1967. 4. The Dunn Creek Slate is also exposed in parts of secs. 26, 27, 34, and 35, T. 40 N., R. 17 E. (pi. 2), as part of an isolated complexly folded south-plunging syncline. It extends northward into sec. 22, T. 40 N.,R. 17 E. DESCRIPTION Slate, metasiltstone, and metagraywacke are predominant in the type area of the Dunn Creek Slate and possibly also in the Florence area. The limited data suggest, however, that true slate is present only locally and that classification as argillite and phyllite is appropriate. Most of the exposures of the Dunn Creek Slate in the Florence area consist of graphitic rock. It forms the uppermost part of the formation close to the contact with the Riverton Iron-Formation and seems to be a direct correlative of the Wauseca Pyritic Member (James, 1958, p. 38) in Iron County, Mich. These graphitic rocks are laminated to thinly bedded, commonly pyritic, and in places complexly folded or con-28 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN torted. Locally they have well-developed cleavage (fig. 7). The laminated graphitic argillite previously exposed just below Riverton in a cut on the east side of county road N in the SW1^ sec. 34, T. 40 N., It. 18 E., is composed of graphite and limonite (after pyrite) and contains many altered porphyroblasts of chlorite approximately 0.10 by 0.40 mm. Table 3 (lab. No. 14999) shows a chemical analysis of this rock; it is one-half silica with organic carbon and iron oxides as the principal associated constituents. Laminated graphitic argillite, also not exposed now, on the west side of the cut along county road N is underlain by a massive graphitic breccia in which chips and fragments of graphitic slate or argillite less than one-half inch in maximum dimension are randomly scattered. The fragments commonly break along foliation, and the bright reflection of light from these surfaces contrasts conspicuously with the overall dull appearance of the very fine grained matrix (fig. 8). This breccia Figure 7.—Pencil slate produced by intersection of axial-plane cleavage and bedding-plane parting, Dunn Creek Slate, SW% SW}4 sec. 34, T. 40 N., R. 18 E. is exposed in roadside excavations to the south and west from the northwest corner of sec. 35, T. 40 N., R. 17 E., on the west side of the open pit exploration near that corner, and in a test pit 1,500 feet west and 250 feet north of that corner. This very distinctive breccia occurs throughout the Crystal Falls and Iron River areas to the north and west; its presence in the Florence area adds greatly to its known extent. A chemical analysis of the breccia from the roadcut is given in table 3 (lab. No. 15000); silica makes up slightly over half of the rock, and organic carbon is the only other abundant constituent. The fine-grained clastic rocks in the mapped area are mainly phyllite, but argillite, slate, and metasiltstone are also present. All have approximately the same mineral composition, so only the phyllite is described. Phyllite is generally some shade of gray or greenish gray and is laminated or thinly bedded. The principal minerals are fine-grained sericite, chlorite, and quartz. Differences in ratios and orientation of these minerals determine the color of the beds and the degree of foliation. The most common type of phyllite has dark-gray layers of very fine alined chlorite and sericite with alternate greenish-gray layers of very fine angular quartz and intergranular chlorite; the quartzose layers are about 2 mm thick, and the micaceous layers range from partings to 2 mm in thickness. Some phyllite is uniformly light gray, well foliated, and composed of very fine chlorite, sericite, and quartz. A third variety is predominantly green and chloritic when fresh but red and hematitic when weathered. Associated with gray phyllite are layers from y8 to 1 inch in thickness that Table 3.—Chemical analyses, in percent, of specimens from the Dunn Creek Slate in Florence, Wis., area [Lab. Nos.: 14999, laminated graphitic slate from roadcut, southwestern parts of sec. 34, T. 40 N., R. 18 E.; 15000, graphitic slate breccia from same roadcut as .lab. No. 14999; 15005, graywacke from test pit in the SW^NWH sec. 21, T. 40 N., R. 18 E. Analysts: P. L. D. Elmore, S. D. Botts, M. D. Mack. Rapid analysis method used] Lab. No. U999 15000 16005 Si02___________________________ 49.8 53.9 61.7 A1203____________________________ 6. 7 8. 3 17. 0 Fe203__________________________ 16. 9 .9 2. 2 FeO1___________________________ 1. 0 .22 6. 0 MgO_____________________________ 1. 0 .52 3. 0 CaO_______________________________ .10 .07 .17 Na20______________________________ .10 .29 .09 K20______________________________ 2. 1 2. 5 4. 3 Ti02______________________________ .28 .51 .84 P205____________________________ .02 .00 .05 MnCL. ___________________________ .03 .01 .04 H20 ________ . . 3. 2 1. 6 3. 6 C02___________________________ <.05 .08 .05 Organic carbon_________________ 15. 9 29. 4 -------- Total.._____________________ 97.18 98.30 99.64 1 FeO values may be in error because of the presence of organic matter in the samples.DUNN CREEK SLATE 29 Figure 8.—Graphitic slate breccia in the Dunn Creek Slate, SW^iSWti sec. 34, T. 40 N., R. 18 E. are minutely porous and predominantly quartz. Thin sections of this material show many angular quartz grains probably cemented by interstitial quartz containing very fine opaque material that is presumably graphite. The reason for the characteristic porosity is not known; it may be caused by the solution of interstitial quartz. Metagraywacke in the Dunn Creek Slate occurs inter-bedded with phyllite and is mineralogically the same except that it contains clastic quartz grains as much as 0.5 mm across and sparse altered feldspar grains. The fresh rock is medium gray; the weathered is grayish red to dark red. Locally, thin beds of quartzite not more than 1 inch thick are interbedded with the phyllite and metagraywacke. A chemical analysis of graywacke from north of the Florence mine is given in table 3 (lab. No. 15005); silica is the main constituent and alumina the principal associate. The Dunn Creek Slate in secs. 26, 27, 34, and 35, T. 40 N., R. 17 E., is more metamorphosed than at Commonwealth and Florence. Biotite is commonly present instead of sericite and chlorite and makes up 5 to 50 percent of the thin sections. Subrounded garnets are as much as 0.25 mm across, and irregular garnet areas that include biotite and quartz are as much as 0.5 by 1.0 mm. One specimen contained abundant hornblende, with many inclusions, in a wide range of sizes reaching 1.0 by 1.0 mm in maximum dimensions. The Dunn Creek Slate is exposed in the northwest comer of the mapped area (pi. 2). Most of the outcrops consist of gray to black slate with locally some chert. The northernmost outcrops are laminated graphitic slate. THICKNESS AND RELATIONS TO ADJACENT FORMATIONS The thickness of the Dunn Creek Slate can only be estimated from the areal pattern. The width of the formation northeast of Commonwealth is shown on the maps as 2,500 feet, which may approximate or exceed its average thickness. Increased width shown southeastward is probably due to repetition of beds caused by folding related to the major synclinal axis. The forma- 407-694 0—71-----330 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN tion apparently thins northwestward from Commonwealth and does not extend to the Brule River in sec. 12, T. 40 N., R. 17 E., but reappears in Michigan and is exposed in the northwest part of the mapped area. The limits of the formation south of sec. 34, T. 40 N., R. 18 E., and of its extension west of that section are not known. No contact of the Dunn Creek Slate and the underlying Badwater Greenstone was found in the Florence area. Gray phyllite occurs in a test pit 500 feet northwest of the greenstone outcrop in the northeast part of sec. 20, T. 40 N., R. 18 E. (pi. 3). This is the closest the two formations are known to come together. The Dunn Creek Slate is generally overlain conformably by the Riverton Iron-Formation, but northwest of Florence the Riverton is missing, and therefore post-Riverton strata rest unconformably on the Dunn Creek Slate. CONDITIONS OF DEPOSITION The Dunn Creek Slate marks the return to deposition of fine-grained clastic sediments after the volcanic eruptions that formed the Badwater Greenstone. The conditions of deposition further changed during Dunn Creek time as land-derived detritus decreased, circulation of water in the depositional basin decreased, and accumulation of pyritic black mud increased. Then either a very widespread submarine slump (James, 1958, p. 38), a turbidity flow, or a roiling by an earthquake tremor occurred. This disturbance formed the graphitic breccia with its chaotic character, wide extent, and absence of extraneous material. A return to quiescent conditions is indicated by subsequent deposition of laminated graphitic slate (argillite). AGE AND CORRELATION The stratigraphic unit that lies between the greenstone and the iron-formation in the Florence area is believed to be of the same age as the Dunn Creek Slate to the northwest in Iron County, Mich., because the stratigraphic position is similar to that in the type area. Furthermore, the pyritic graphitic slate and the distinctive graphitic breccia subunit in the sequences in the Florence area and the Crystal Falls and Iron River, Mich., areas are lithologically equivalent. RIVERTON IRON-FORMATION DEFINITION AND DISTRIBUTION The Riverton Iron-Formation was named (James, 1958) for the abandoned Riverton mine where the first mining in the Iron River area began in 1882. The Riverton Iron-Formation occurs in a major northwest-plunging syncline near Florence and Commonwealth, in an irregular southeast-plunging syncline 5 miles west of Commonwealth, and possibly in a few scattered outcrops to the north of this locality (pi. 2). From the Florence mine in secs. 20 and 21, T. 40 N., R. 18 E. (pi. 3), the iron-formation extends northwestward for only a short distance into the SW)) sec. 17, T. 40 N., R. 18 E., where the formation above the Riverton apparently lies directly on the Dunn Creek Slate. The Riverton Iron-Formation reappears northwestward in and beyond the northwest part of the mapped area (pi. 2.). Southeastward from the Florence mine the formation extends to the southeast corner of sec. 34, T. 40 N., R. 18 E., turns westward at the axis of a northwest-plunging major syncline, and then continues to a faulted and indefinite termination in the northern part of sec. 4, T. 39 N., R. 18 E. The westernmost exposures occur in parts of secs. 26, 27, 34, and 35, T. 40 N., R. 17 E.; this area is approximately 4 miles southwest of the Florence mine and the same distance west of the termination in section 4 (pi. 2). A small isolated occurrence of Riverton is found in the northwest corner of sec. 26, T. 40 N., R. 17 E., and the adjacent part of section 23. Smaller isolated exposures of iron-formation in the east-central part of secs. 22 and 27, T. 40 N., R. 35 W., are probably also part of the Riverton. DESCRIPTION James (1954) recognized four facies in the sedimentary iron-formations of the Lake Superior region: Sulfide, carbonate, oxide, and silicate. The carbonate facies consists of interbedded siderite and chert, and is known to be present at least locally in the Florence area (pi. 3). Alteration of this facies has produced three secondary types—oxidized iron-formation, iron ore, and grunerite-magnetite-quartz iron-formation. Chert in the primary and secondary types of iron-formation occurs generally as layers but may occur locally as lenses or rarely as fragments. In the carbonate facies, siderite and chert occur in approximately equal amounts, each being predominant in alternate layers that generally range in thickness from y2 k° 3 inches. Siderite is fine grained and banded in shades of gray that mark the stratification. Chert is mottled gray, lighter than the siderite, and has a finegrained sugary texture. This type of iron-formation is in a few very small exposures and test pits northwest of the Florence mine (pi. 3), in small amounts in the dumps of the Ernst mine and Welch exploration (pi. 2), and was very sparingly in the east side of a former excavation along county road N in the southwestern part of sec. 34, T. 40 N., R. 18 E. A chemical analysis of siderite-chert iron-formation from the Riverton Iron-Formation at the Welch exploration is given inRIVERTON IRON-FORMATION 31 table 4. The metallic iron content is 22.3 percent, and a common average for siderite-chert iron-formation in the Iron River-Crystal Falls area is 25 percent. The examination of thin sections of siderite-chert iron-formation indicates that siderite ranges from 0.02 to 0.05 mm across and chert from 0.05 to 0.10 mm; both are commonly subangular. Some sections contain scattered rectangular areas of chlorite as much as 0.15 by 0.07 mm in size. Scattered siderite areas in chert are about 0.15 by 0.10 mm. Hematite or limonite or both, with interbedded chert, have formed from the siderite-chert iron-formation by oxidation of the siderite. The iron oxides are generally fine grained, dull, soft, and compact; but locally they are relatively hard, somewhat glossy, and break with a conchoidal fracture. As in the unaltered iron-formation, the iron-rich and silica-rich layers occur in approximately equal amounts. This oxidized iron-formation averages about 35 percent iron. Siliceous limonitic or hematitic material with embedded angular chert fragments is in the upper part of the Riverton or basal part of the Hiawatha in small exposures across the southern part of sec. 27, T. 40 N., R. 17 E., and in the north-eastern part of sec. 4, T. 39 N., R. 18 E. Iron ore has formed locally from siderite-chert iron-formation by oxidation of siderite and by leaching of chert, or by a much more extensive replacement than took place when the hematite-limonite-chert iron-formation was formed. Iron ore shipped from mines in the Florence area ranged from 48 to almost 51 percent metallic iron as mined, and 52.5 to 56.5 percent if dried. The iron content of limonite is 60 percent and of hematite 70 percent, but admixtures of chert and argillaceous rock with the ore minerals lower the grade. Regional metamorphism of siderite-chert iron-formation has produced grunerite-magnetite-quartz iron-formation in secs. 26, 27, 34, and 35, T. 40 N., R. 17 E. The metamorphosed iron-formation is an aggregate of abundant grunerite and scattered red to brown garnets as much as 2.0 mm in size and euhedral magnetite as much as 1.0 mm. Metachert is generally present as layers Table 4.—Chemical analysis, in percent, of interbedded siderite- chert from the Riverton Iron-Formation, Florence, Wis., area [Location: Welch exploration, NW^ sec. 34, T. 40 N., R. 18 E. Analysts: P. L. D. Elmore, S. D. Botts, M. D. Mack. Rapid analysis method used. Lab. No.: 15004] Si02 45. 4 Ti02 .05 AI2O3 _ . _ 1. 8 p2o5 .41 Fe203 8. 4 MnO 1. 7 FeO' 21. 1 H20 .50 MgO 1. 9 C02 16. 7 CaO 1. 1 Na20 . __ __ .05 T otal 99 IS K20 .07 1 FeO values may be in error because of the presence of organic matter in the sample. or lenses but is not as distinctly separated as in other types of iron-formation because of the growth of grunerite at the interfaces. Metachert that ranges from scattered fragments to concentrations of randomly oriented pieces as much as 1 inch thick and 6 inches long is present locally. Gruneritic iron-formation in the northwestern part of sec. 35, T. 40 N., R. 17 E., has been altered and sufficient soft hematite and limonite formed to warrant exploration and shipment of some material from a small open pit. Grunerite is in small light-golden to brown blades that are commonly arranged radially in clusters about 2.0 mm in average diameter or randomly in decussate manner. The recrystallized quartz forms a mosaic of grains about 0.05 to 0.10 mm in diameter with smooth boundaries. Quartz at the margins of former chert layers and fragments is commonly elongate and divergent as if pseudomorphous after grunerite but has irregular extinction as in chalcedony. The silicate facies of iron-formation is probably represented by laminated to thinly bedded green-gray to dark-green layers composed of quartz, moderately iron-rich chlorite, chamosite, and some 2M, muscovite (S. W. Bailey, written commun., 1961). The layers range from dull argillitic to slightly phyllitic and are generally less than 1 inch thick. Lenses and interbedded layers of chert from one-quarter to one-half inch thick are commonly present. The only silicate facies seen has been in several of the open pit mines (the Florence, Badger, and Davidson open pits, pi. 2) and was as fresh or altered as the chert-siderite or oxidized iron-formation with which it was interbedded. Oxidation of the silicate facies has converted the silicate layers to very fine grained, compact, maroon to dark-gray-blue hematite. The silicate facies was not specifically recognized in the area of metamorphosed iron-formation. Data are too limited to determine satisfactorily the proportion of the Riverton that is silicate facies. However, because of the general similarity of the Florence area to the Iron River-Crystal Falls area, it seems likely that the probable silicate facies constitutes the upper part of the Riverton Iron-Formation or at least is more common in that part. Black partings and thin layers interbedded in the chert-siderite iron-formation and derivatives from it are pyritic and graphitic, may range from minor to locally abundant, and are generally near the base of the Riverton. THICKNESS AND RELATIONS TO ADJACENT FORMATIONS The normal thickness of the Riverton Iron-Formation can be only approximately but is believed to be about 600 feet.32 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN So far as is known, this formation is conformable with the Dunn Creek Slate as in Iron County, and inter-bedding is present at least locally. The Riverton is generally overlain, probably conformably, by younger strata of the Paint River Group except northwest of the Florence mine as previously mentioned. Local absence of the Riverton may be due to one or more of the following conditions: nondeposition, erosion, onlap of younger strata, facies change resulting from a much greater ratio of argillaceous material, or faulting. No field data specifically supported any one of these possibilities. CONDITIONS OF DEPOSITION The unaltered Riverton Iron-Formation consists mainly of interbedded siderite and chert. It was presumably deposited in a marine basin under conditions of restricted circulation when available oxygen was sufficient to yield carbonate but insufficient to produce ferric iron. -James (1954) suggested that deposition occurred in a marginal basin developed by broad offshore buckles during the change from earlier shelf environment to later geosynclinal conditions. The iron and silica were probably derived from deep weathering on land of low relief. The possibly argillaceous (“slaty”) nature of the upper part of the Riverton indicates an influx of very fine detritus, a change in the character of chemical reactions, and a transition to dominantly clastic deposition. AGE AND CORRELATION The iron-formation from which ore was formerly mined in the vicinity of the communities of Florence and Commonwealth occupies the same stratigraphic position, relative to the distinctive widespread graphitic slate breccia of the Dunn Creek, as the Riverton Iron-Formation in Michigan and is doubtless correlative. It is therefore in the Paint River Group of middle Precambrian age. POST-RIVERTON STRATA DISTRIBUTION The normal sequence of formations younger than the Riverton Iron-Formation can be identified only in the northwest corner of the mapped area (pi. 2) and is, from oldest to youngest, Hiawatha Graywacke, Stam-baugh Slate, and Fortune Lakes Slate. The Hiawatha Graywacke is massive, dark gray, and thin to locally absent. The Stambaugh Slate is mostly green to greenish-gray fissile slate with a few layers of graywacke, chert, siderite, or cherty siderite iron-formation; some parts are magnetic. The Fortune Lakes Slate is mainly gray slate with interlayered graywacke. These formations are fully described in the report on the Iron River-Crystal Falls area (James and others, 1968). Post-Riverton strata in other parts of the area cannot be individually recognized but are exposed in small outcrops and were penetrated by test pits along the south slope of the prominent ridge that extends southeastward from the Brule River in sec. 12, T. 40 N., R. 17 E., to the village of Florence. The strata have also been seen near and south of the village of Commonwealth, Wis., at numerous test pits and small outcrops and in several open pit mines. The strata possibly occur at a third locality that includes small parts of secs. 27, 34, and 35, T. 40 N., R. 17 E.; exposures are so small that these occurrences are not shown separately from the Riverton Iron-Formation on the geologic map. The inferred area of post-Riverton strata at this location is based on an assumed average width of outcrop of the Riverton. DESCRIPTION Most of the post-Riverton rocks in the area are argillite. They are mainly laminated to thinly bedded and composed of grains of sericite, chlorite, stilpnomelane, and quartz less than 0.05 mm in average dimension. They lack slaty cleavage but are locally phyllitic or fissile. The common color is green to grayish green, locally olive drab, olive green, gray, and black where graphite is the principal constituent. Many specimens weather to maroon, and many others have a dark-bluish coating on all weathered surfaces. Minor amounts of pyrite may be present. Interbedded chert is common in the argillite near the Brule River but decreases southeastward. Identification of the principal constituents and determination of their relative abundance is difficult, hut some approximations are informative. Quartz is commonly present and may be as much as 50 percent of a thin section. Sericite is found in about half of the sections and ranges from 50 to 85 percent. Stilpnomelane is present in most of the other sections and commonly ranges from 25 to 50 percent. Chlorite is in fewer sections than sericite or stilpnomelane and ranges mostly from 35 to 50 percent. Magnetite was not observed in any thin sections, but in some localities many small loose chips of fissile argillite are attracted by a magnet. Magnetite-bearing chips are present on the hill south of the Florence mine and other localities along the ridge to the Brule River in sec. 12, T. 40 N., R. 17 E. Magnetic surveying northwest of Florence (pi. 8; J. E. Gair, unpub. data, 1955) indicates a well-defined anomaly trending northwestward to outcrops of the typical Stambaugh Slate in Iron County, Mich., and suggests correlation. Magnetite-bearing argillite is also present at a few localities to the south and west of the village of Commonwealth but is not mapped separately.POST-RIVERTON STRATA 33 The second most abundant post-Riverton rock type is quartz metagraywacke. It is poorly bedded to massive, green to greenish gray, and commonly weathers to maroon. Ohert fragments are easily seen in most specimens of graywacke and are present in all thin sections. The size of fragments ranges greatly and may exceed several centimeters. Grains less than 0.05 mm in size constitute about 75 percent of the rock; the principal associated minerals are stilpnomelane (as much as 50 percent), quartz (35 percent), chlorite (30 percent), and hematite (50 percent). Quartz grains are easily visible to the unaided eye or with a hand lens; grains larger than 0.05 mm constitute about 15 to 20 percent of typical thin sections. The shapes of most quartz grains are. elliptical to subangular, and irregular grains are relatively uncommon. The ends of many elliptical grains are not sharply limited but are penetrated by blades of stilpnomelane. Slides commonly contain about twice as much quartz as chert, but the opposite relation was also observed. Growth of stilpnomelane into chert is generally much more extensive than into quartz. The chemical analysis of Hiawatha Graywacke from near Commonwealth is shown in table 5. The rock is predominantly siliceous and ferruginous. The iron-bearing minerals are stilpnomelane, hematite, and chlorite. The graywacke described is lithologically similar to the Hiawatha Graywacke of the Paint River Group in Iron County, Mich. It commonly has a chert breccia at the base, but the only known occurrence of basal breccia between the Riverton Iron-Formation and magnetite-bearing slate in the Florence area, is in outcrops in the NW^NE^ sec. 4, T. 39 N., R. 18 E. Most occurrences of Hiawatha Graywacke with chert fragments are, as stated previously, at open pit mines and outcrops in the vincinity of the village of Commonwealth and are adjacent to the Riverton Iron-Formation, but it has not been feasible to map the rock as a separate unit. Material that is probably also correlative with the basal brecchia of the Hiawatha Graywacke is exposed at a small open pit exploration in the northwestern part Table 5.—Chemical analysis, in percent, of the Hiawatha Graywacke, Florence, Wis., area [Location: South wall of small open pit in the NW^SE^ sec. 34, T. 40 N., R. 18 E Analysts: P. L. D. Elmore, S. D. Botts, M. D. Mack. Rapid analysis method used. Lab. No.: 15002] Si02 50. 2 Ti02 .49 A1203 10. 1 p2o5 .45 Fe203 3. 5 MnO 1. 6 FeO1 17. 9 H20 5. 6 MgO 5. 3 C02 3. 4 CaO_ .80 Na20_ .06 Total _ 99. 48 K20 .08 1 FeO values may be in error because of the presence of organic matter in the sample. of sec. 35, T. 40 N., R. 17 E. Chert fragments as much as by 2 inches in maximum dimensions are common locally in a garnetiferous dark-green matrix that becomes very limonitic or hematitic where weathered Quartz grains are generally rare to absent. This rock unit is associated with and is believed to overlie the Riverton, which at that place is weathered magne-tite-grunerite iron-formation. The breccia is not shown separately on the geologic map. Graywacke occurs in small exposures on both sides of the highway in sec. 12, T. 40 N., R. 17 E. It lies south of and stratigraphically above magnetite-bearing fissile argillite, possibly Stambaugh Slate, and may be correlative with part of the type Fortune Lakes Slate in Iron County, Mich. Graywacke with chert fragments, found at a test pit near the west side of sec. 21, T. 40 N., R. 18 E., has a similar stratigraphic position. Graywacke at the test pit in the northwestern part of sec. 20, T. 40 N., R. 18 E., and graywacke and argillite at the eastern pit in the southeastern part of sec. 19, T. 40 N., R. 18 E., are probably also correlative with the Fortune Lakes Slate. Several other types of rock are statigraphically younger than the Riverton Iron-Formation. Beds of buff to pink chert or porous silica-rich material in layers from one-eighth to one-fourth inch thick are locally interbedded with thinly bedded green-gray argillite. Massive to poorly laminated rocks composed of finegrained iron-rich chlorite are exposed or were penetrated by test pits at several places in secs. 33 and 34, T. 40 N., R. 18 E. A small amount of thinly interbedded siderite and chert was found in a few localities. CONDITIONS OF DEPOSITION Post-Riverton strata that were originally mainly mud and sandy mud indicate a marked change in the deposi-tional environment from the quiet water in which the Riverton Iron-Formation accumulated. Probable elevation of land near the site of accumulation for post-Riverton strata greatly increased the available amount of clastic materials, but iron and silica continued to concentrate in the depositional basin as is indicated by the presence of magnetite, stilpnomelane and chlorite, and bedded chert. The conditions preceding or during deposition of the early post-Riverton strata brought disturbance of the underlying Riverton Iron-Formation and at least locally broke up the chert layers into slabs or small fragments. Some slabs, as much as 2 by 18 inches and seen only in cross sections (fig. 9), were only slightly rearranged and buried in ferruginous mud, but more commonly small fragments were transported farther and incorporated in ferruginous sandy mud. Subaerial 407-694 0—71-34 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN Figure 9.—Chert breccia in Riverton or post-Riverton strata, sec. 27, T. 40 N., R. 17 E. erosion of the iron-formation is not necessarily indicated. Erosion to form the breccia could have taken place below sea level but above wave base, as on shelves, or in deeper water by slump. Subsequently, relative stability in the area of accumulation gave rise to deposition of mud with only small and local amounts of sand. THICKNESS AND RELATIONS TO ADJACENT FORMATIONS The thickness of the post-Riverton strata is believed to be several thousand feet. These strata generally over-lie the Riverton Iron-Formation disconformably, and the contact exposed for short distances at several abandoned open pits near the village of Commonwealth presumably marks similar relations. The Riverton is, however, not present at the bedrock surface northwest of sec. 17, T. 40 N., R. 18 E., near the village of Florence; and post-Riverton strata are believed to lie unconformably on the Dunn Creek Slate as far as sec. 12, T. 40 N., R. 17 E., and then on Badwater Greenstone to beyond the Brule River. Insofar as known, the post-Riverton strata are not overlain by rocks of Pre-cambrian age. AGE AND CORRELATION The post-Riverton strata in most of the Florence area are considered to be of middle Precambrian age on the basis of their stratigraphic relation to the Riverton Iron-Formation. Furthermore, the lithology and probable stratigraphic sequence of these strata are similar to individually recognized formations of the Paint River Group in the northwest corner of the mapped area from which they can be traced to the type area near Crystal Falls, Mich. CAMBRIAN (?) ROCKS Two small areas underlain by sandstone that is of probable Cambrian age are not shown on the map. Test pits along the west side of sec. 35, T. 40 N., R. 18 E., penetrated rock composed of well-rounded quartz, 0.25 to 0.75 mm in diameter, cemented by fine-grained bluish hematite. Angular blocks composed of well-rounded quartz about 0.25 mm in diameter cemented by finegrained dull limonite are abundant in an area 100 feet east and west by 25 feet north and south, on the south-facing slope in the NE!4 sec. 4, T. 39 N., R. 18 E. INTRUSIVE ROCKS Metagabbro and granite are the principal intrusive rocks in the Florence area, mostly in the Popple River structural block. Each intrudes the Quinnesec Formation but was not seen in contact with the other. Metadiabase occurs with metagabbro locally. A few pegmatites of quartz, feldspar, muscovite, and generally some tourmaline are present. Metagabbro and associated metadiabase are also found in the Keyes Lake and the Brule River structural blocks and very sparingly in the Pine River block. METAGABBRO Metagabbro is exposed in the southeastern part of the Florence area, especially in two large masses that presumably have generally sill-like relations to the Quinnesec Formation (pi. 1). The northern mass is exposed locally over a length of approximately 2y2 miles and width of half a mile through secs. 4, 5, and 6, T. 38 N., R. 19 E. The other mass is about 3 miles long, as much as 1 mile wide, and extends from secs. 13 and 24, T. 38 N., R. 18 E., through secs. 18, 19, 20, and into sec. 21, T. 38 N., R. 19 E. The metagabbro in sec. 9, T. 38 N., R. 19 E., represents the west end of a third sill about 2y2 miles long by as much as 1 mile wide and mainly east of the Florence area (Bayley and others, 1966). Small scattered occurrences of metagabbro in the Quinnesec Formation are present elsewhere, as indicated on the map. Isolated outcrops of metagabbro in areas believed to be underlain by Michigamme Slate occur in secs. 19 and 36, T. 39 N., R. 18 E., and sec. 19, T. 39 N., R. 19 E. Metagabbro commonly crops out as knobs that differ greatly in height, outline, and size. The outcrop areas indicated on the map represent groups of individual exposures that could be readily distinguished both on airINTRUSIVE ROCKS 35 photos and in field mapping. Some metagabbro areas in the Quinnesec Formation probably include small masses of Quinnesec, inasmuch as hornblende schist and amphibolite derived from basalt are not readily distinguishable from similar rocks that were once gabbro. The contacts of metagabbro with associated formations are not commonly exposed, so most limits and relations are inferred. The weathered surfaces of metagabbro are commonly dark green and rough, owing to the abundance, large size, and stability of the hornblende. The recessed areas are plagioclase that produces a gray mottling in the dark green (fig. 10). The metagabbro in the two sill-like masses in the southeastern part of the mapped area is medium to coarse grained and is generally composed of about equal amounts of plagioclase and hornblende, but the latter is as much as 75 percent in some specimens. The plagioclase is mainly labradorite (An50_66) and bytownite (An70_85) with minor andesine (An40_47). The relative abundance of andesine is less in the south sill (two of 26 determinations) than in the north (eight of 28 determinations) . This difference is interpreted as indicating that regional metamorphism of the southern mass was possibly less effective within the thermal aureole of the adjacent Hoskin Lake Granite. The hornblende has characteristic bluish-green pleochroism along Z, poiki-loblastic texture, and an extinction angle of about 24°. Accessory minerals are mostly small anhedral grains of chlorite, clinozoisite, epidote, untwinned feldspar mosaic, quartz, sericite, and sphene. The metagabbro in the small scattered exposures in the southern part of the area is similar to that in the large masses except that bytownite is generally absent and andesine is more abundant than labradorite. Metagabbro and metadiabase in the vicinity of Keyes Lake occur mainly in the Badwater Greenstone (pi. 2). Plagioclase in most of the rocks is andesine (An30.37), as in secs. 26, 27, and 36, T. 40 N., R. 17 E., and sec. 1, T. 39 N., R. 17 E. Texture and accessory minerals are similar to those described in the southern part of the area. Metagabbro just west and southwest of the quartzite and conglomerate in the Michigamme Slate in sec. 24, T. 40 N., R. 17 E., and sec. 31, T. 40 N., R. 18 E., occurs as small altered exposures that contain albite (An3_8) and the greenstone minerals commonly associated with this type of plagioclase. Metagabbro exposed in the northern parts of secs. 9 and 16, T. 40 N., R. 17 E., but just west of the mapped area, contains albite (An3_5). Some of the large outcrops of metamorphosed mafic intrusives in secs. 27 and 35, T. 40 N., R. 17 E., show a marked transition in grain size from metagabbro to metadiabase, but no systematic relation- Figure 10.—Small sills of metagabbro in hornblende schist of the Quinnesec Formation, sec. 26, T. 38 N., R. 18 E. Note tabular form and rough surface that results from differential weathering of hornblende and plagioclase. ships were evident. An outcrop 3,200 feet west and 350 feet north of the southeast corner of sec. 27, T. 40 N., R. 17 E., is mostly metagabbro but locally has vesiclelike cavities filled with calcite and a few small fragments similar to those in agglomerate. Another occurrence of agglomerate associated with metagabbro is 1,550 feet west and 1,900 feet south of the northeast corner of sec. 35, T. 40 N., R. 17 E. The amygdaloidallike and agglomeratelike rocks are probably masses of Badwater that are in, or at the margins of, the metagabbro. The area underlain by Badwater Greenstone along the Brule and Menominee Rivers (pi. 2) contains a few outcrops of mafic intrusive rock, but its relationship to adjacent rocks in Wisconsin was seen only in a small area in the northeast corner of sec. 13, T. 40 N., R. 18 E. Intrusive contacts are well exposed at this locality, but amygdaloidlike areas are also present. The texture and relation of hornblende and feldspar in other outcrops suggest derivation from diabase or gabbro. The intrusive rock near the northeast corner of sec. 13, T. 40 N., R. 18 E., cuts across and also follows the bedding of graywacke. The rock is massive and generally fine grained but has a few dark-gray feldspar laths. The principal mineral in a thin section is blue-green hornblende, in a mosaic of anhedral feldspar. Examination of six feldspar laths indicates a range in composition from An29 to An39. Minor minerals are chlorite, biotite, quartz, and magnetite. Rocks with ophitic texture in thin section are known only in two localities in this part of the area. The rock at the Brule River in sec. 12, T. 40 N., R. 17 E. (pi. 2), is36 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN massive, medium gray, generally fine grained but some amphibole grains are as much as 1.0 mm across; it is not visibly ophitic in hand specimen. The principal minerals identified in thin section are actinolitic hornblende, clinozoisite, and chlorite. A few altered feldspars are present. Saussurite pseudomorphs of feldspar prisms and sphene with cores of opaque material are common. Metadiabase in sec. 12, T. 40 N., R. 18 E., is massive, fine grained ophitic, and dark gray. The principal minerals in a thin section are blue-green hornblende and albite (An0_9) in approximately equal amounts. Minor constituents are epidote, biotite, quartz, and magnetite (?). Much of the plagioclase is lathlike, and albitic twinning is common. Metagabbro is also exposed in Michigan along and adjacent to the Brule River; in sec. 17, T. 41 N., R. 31 W., it forms an irregular sill-like body in the Badwater Greenstone. The texture is that of a medium-grained gabbro, but the rock is now an epidote amphibolite, characterized by pale-green hornblende (after pyroxene) and abundant epidote and sphene. The plagioclase is mainly oligoclase gradationally zoned to cores of andesine or labradorite. A narrow sill of amphibolitic metagabbro is exposed in sec. 6, T. 41 N., R. 31 W.; it is closely associated with amphibolite derived from the Hemlock (?) Formation and distinguished from it chiefly by the local gabbroic texture. The metagabbro and metadiabase in the Florence area are of post-Animikie age. HOSKIN LAKE GRANITE Prinz (1959,1965) gave the name Hoskin Lake Granite to a coarse-grained porphyritic rock for which the type locality is about 2 miles east of the southeast corner of the Florence area. The area of granite exposures does not extend from the type locality into the adjacent part of the Florence area, but a short western boundary is shown in sec. 21, T. 38 N., R. 19 E., because there are outcrops within 100 feet to the east and extending for 1,000 feet north of the southeast corner of the area (pi. 1). Exposures south of the area in secs. 28, 29, and 31, T. 38 N., R. 19 E., indicate a continuation of the granite southwestward for an undetermined distance. Additional less porphyritic granite outcrops scattered in an area 3 miles wide that extends approximately 5 miles northwest in the southwest part of the area shown on plate 1 are considered to be part of the Hoskin Lake Granite. Granite and pegmatite dikes in the Quinnesec Formation in the northwestern part of the area shown on plate 1 are present in secs. 15,22, 26, and 27, T. 39 N., R. 17 E. Granite west of the Florence area (not shown on the map) occurs as dikes in sec. 16, T. 39 N., R. 17 E., but as low scattered knobs of the only bedrock seen in an area about 1,300 feet long and 600 feet wide in the SEi/j SW14 and SW^SE^ sec. 20, T. 39 N., R. 17 E. These occurrences are also believed to be part of, or closely related to, the Hoskin Lake Granite. Granite in the southwest part of the area shown on plate 1 generally forms prominent rounded knobs that have well-developed joints and irregular outline. The granite is pink, gray, white, or mottled. The texture is coarse grained with at least a few, or locally many, feldspar phenocrysts. Other outcrops are fine grained and approach an aplitic appearance, especially in sec. 27, T. 39 N., R. 17 E. Structure is generally massive but may be locally streaked. The alinement of feldspar phenocrysts and the trend of slightly biotitic concentrations are due north in secs. 13 and 14, T. 38 N., R. 17 E. Similar features are found in the exposures in sec. 20, T. 39 N., R. 17 E., just west of the mapped area; however, the outcrops are smaller, less prominent, and less jointed. The coarse-grained texture also occurs in most of the granite dikes. Two-thirds of the measured strikes of joint systems are northwestward; approximately half of these trend N. 10° to 20° W., and 60 percent of them are vertical. Half of the northeast-trending joints strike N. 60° to 70° E., and dip from 70° S. to vertical. The granite is locally crossed by tourmaline-coated fractures, tourmaline-bearing pegmatites and quartz veins, and aplitic dikes. A pegmatite in the NE1^ sec. 22, T. 39 N., R. 17 E. (pi. 1) is mainly coarse gray to white feldspar and quartz but locally has up to 2-inch veins of quartz with pink tourmaline crystals mostly about 1 inch in length and 0.15 inch in diameter. Laths of striated feldspar and anhedral grains of unstriated feldspar can be readily distinquished in hand speci-ments of pegmatite; either type may be the more abundant in thin sections. The plagioclase is commonly albite (An0-S) or andesine (An43_53). The granite in the Florence area is about 75 percent very light buffi to orange-pink feldspar for which the maximum size is generally about 1 cm; phenocrysts are 2 to 4 cm long. Quartz is commonly light gray and less than 0.5 cm in maximum dimension. Biotite is about 1 mm across and uniformly scattered except for some local very thin discontinuous aggregates. Thin sections of nonporphyritic specimens consist mainly of anhedral to subprismatic twinned and untwinned feldspar and anhedral quartz with accessory biotite, chlorite, and sericite. Microcline is the common feldspar; untwinned feldspar is mainly oligoclase and some orthoclase. Plagioclase is generally less common than other feldspar but is equally or more abundant in some sections, which indicates that parts of the intrusive are quartz monozonite. Composition of plagioclase ranges from An0 to An«. Perthite and myrmekite are present. Some feldspar is cloudy and contains scattered sericite. Quartz has wavy ex-GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN 37 tinotion, and a cataclastic texture is common. Some parts show virtually a mortar structure. A few grains of epidote and clino-zoisite are present. No contact of the granite with adjacent rock was seen in the Florence area, and location of a boundary is inferred almost entirely from the aeromagnetic data (,pl. 7). A small outcrop of hornblende schist occurs within the granite in the SEj^NE^ sec. 3, T. 38 N., R. 17 E., but no contact is exposed. Dikes in the northwestern part of the area shown on plate 1 generally have sharp contacts with enclosing hornblende schist or amphibolite of the Quinnesec Formation, -but some dikes have transitional gneissic boundaries like those in sec. 20, T. 39 N., R. 17 E., just west of the mapped area. The granite is not known to intrude rocks younger than the Quinnesec Formation; it is probably younger than the metagabbro yet older than the regional metamorphism that affected the Animikie Series and the gabbro (except locally as mentioned on p. 35). Lead-alpha and isotopic lead methods placed the geologic age of zircons from the granite as 1,650 million years (Bayley and others, 1966, p. 75). This suggests a relation to the post-Animikie deformation and metamorphism in Michigan of 1,700 million years ago (Goldich and others, 1957, p. 550). PEAVY POND COMPLEX Exposures of metagabbro, in secs. 33 and 34, T. 42 N., R. 31 W., are part of the Peavy Pond Complex (Bayley, 1959), which occupies an irregular area of about 5 square miles in the adjacent Lake Mary quadrangle. The Peavy Pond Complex is composed mainly of metagabbro and metadiorite; but the northwest quarter has areas of predominantly metatonalite, granodior-ite, and granite arranged in order of decreasing basicity from the mafic area. Most of the complex is hornblende metagabbro that is described (Bayley, 1959, p. 78) as composed of 55 to 80 percent labradorite (An50.;o), 16 to 45 percent hornblende in a variety of colors, trace amounts of biotite and iron ore, and a few other associated minerals. Granitic rock in metasediments and in part of the complex in the Florence area is in thin lenslike bodies, few of which are more than 5 feet wide and tens of feet long. The rock, which ranges in texture from granitic to pegmatitic, is composed of quartz, microcline, seri-citized oligoclase, and muscovite. Most of the bodies are parellel to foliation in the enclosing rock, but a few cross the regional trend. In at least one occurrence, in the NE14 sec. 33, T. 42 N., R. 31 W., a cross-cutting pegmatitic granite has been sheared after emplacement and has a crude foliation parallel to that of the country rock. STRUCTURAL GEOLOGY The Florence area has four major structural units formed by three northwest-trending faults along which the blocks to the south have been relatively uplifted (pi. 4). Only major faults that caused profound dislocation of the normal stratigraphic succession have been shown; none of the fault surfaces have been seen in the field. The three faults appear to be the westward continuation of inferred faults in southern Dickinson County, Mich. (Bayley and others, 1966). These structural units, which will be described in sequence from north to south, are the Brule River block, the Keyes Lake block, the Pine River block, and the Popple River -block. Inasmuch as outcrops are scarce, structures within the blocks can rarely be defined solely on the basis of inclination of bedding top directions, especially as indicated by graded beds and crossbedding in the Michi-gamme Slate and ellipsoids in the Badwater Greenstone, help to decipher the fold patterns. Beds dip steeply throughout the Florence area, being vertical in many places and overturned locally. Minor folds are abundant. Foliation is generally nearly parallel to the bedding except at fold axes. Lineation is present in some places. BRULE RIVER BLOCK The Brule River block includes most of the area shown on plate 2. It is underlain by a sequence ranging from the Hemlock) ?) Formation to post-Riverton strata. These strata have been folded and form the Commonwealth syncline along the southern edge of the block, which is believed to be a fault because most of the southwest limb of the syncline is missing. More evidence of this fault is given in the discussion of the adjacent Keyes Lake block. The Brule River block extends northwestward into Iron County, Mich., southeastward into Dickinson County, Mich., and northward without limit in each of them. COMMONWEALTH SYNCLINE Commonwealth syncline is the name here proposed for the northwest-plunging fold in the Brule River block. This syncline forms one apex of a large triangular basin whose other apices are at Crystal Falls and Iron River in adjacent Iron County, Mich. (pi. 4). The general stratigraphic sequence in the group of northwest-trending formations is indicated by the following features: 1. Graded bedding in an outcrop of the Michigamme Slate in the SW1^ sec. 12, T. 40 N., R. 18 E., shows that the stratigraphic top of the beds very near the Badwater Greenstone is toward that formation.38 GEOLOGY, FLORENCE AREA, 2. The shape and arrangement of ellipsoids in the Bad-water Greenstone (in sec. 12, T. 40 N., R. 17 E.; secs. 14, 22, and 23, T. 40 N., R. 18 E.; and sec. 18, T 40 N., R. 19 E.) indicate that younger rocks are toward the south. These data are important because they have been the principal basis for recognition of not only the local position of the Paint River Group, but also the regional stratigraphic position. In the Florence area this group includes three units—Dunn Creek Slate, Riverton Iron-Formation, and post-Riverton strata. The Badwater Greenstone forms an outcrop belt that trends southeastward across the Florence area and continues into Dickinson County, Mich. Here the strike of the formation changes to westward, and the top of the beds is northward (Bayley and others, 1966). The areal distribution of the Riverton and associated formations also indicates a syncline (pi. 2). The strike of the beds trends from the northwest comer of the Florence area southeastward through the villages of Florence and Commonwealth to the pit of the Badger mine in sec. 34, T. 40 N., R. 18 E., turns sharply, and then trends generally westward for about a mile, to where the structure is believed to be interrupted by a major northwest-trending fault. Minor folding in which the predominant plunge is steeply to the northwest is common in the Riverton. The areal pattern shown for the Riverton northwest of Florence and at the southeast end of the syncline is indicated by the outcrops, but elsewhere the pattern is based on a general structural interpretation. OTHER FOLDS A series of five folds, all within Michigan, was noted in the northern part of the Brule River block. The main folds in the eastern half of the area shown on plate 2 are an overturned syncline, the axis of which lies immediately north of the Peavy Falls Dam, and a parallel anticline in which the Hemlock (?) Formation is exposed a little more than a mile to the south. The axes of these folds form broad south-facing convex arcs that are rudely symmetrical with the border of the Peavy Pond Complex to the north. This may represent an actual deformation of the fold axes, but more likely the structural trends resulted from the syntectonic emplacement of the igneous complex (Bayley, 1959). The fold axes plunge westward at an angle of about 20°, as estimated from measured values of lineation and minor folds. Three folds in the western half of the area shown on plate 2 extend for a short distance but do not seem to continue into the eastern half. In fact, it seems likely that none of the folds extend for more than a few miles, and that as a group they are arranged in an en echelon WISCONSIN AND MICHIGAN pattern that in some way is related to emplacement of the Peavy Pond Complex. One further aspect, probably also related to emplacement of the complex is that in the northern part of the quadrangle, beds are overturned to the north, whereas in the southern part they are overturned to the south. Doubtless many folds in the northern part of the Brule River block are intermediate in size between the two main structures and the small crumples that can be seen in outcrop. A minor synclinal axis certainly must be present a short distance north of the Michi-gamme Falls Dam because tops of beds are opposite each other. This in turn requires a second reversal between the outcrops at the dam and the Michigamme-Badwater contact. In a reconnaissance traverse of the Michigamme River below the damsite prior to construction of the dam, H. L. James and R. W. Bayley noted that tops of beds were toward the south; it has not been possible to reexamine the outcrops in order to verify these observations. Minor crumpling of beds is common, particularly near axes of major folds. Good examples may be seen in outcrops of staurolite schist in the SE14 sec. 31, T. 42 N., R. 31 W., and in the SW1/^ sec. 15, T. 41 N., R. 31 W. The pattern of the Michigamme-Badwater contact along the Brule and Menominee Rivers indicates a series of complex minor folds, and almost certainly the great range in outcrop width of an uppermost unit of the Michigamme Slate (not shown on the map) is due to folding. Outcrops of graywacke and slate along the Menominee River show much evidence of tight folding along axes that plunge south westward at angles of 25° to 50°. KEYES LAKE BLOCK Geologic structure in the Keyes Lake block is known only in the southwest part of the area shown on plate 2, where geologic data are virtually restricted to within a few miles of Keyes Lake. It is inferred, however, that the block continues eastward across the north part of the area shown on plate 1. In sequence from east to west, structures near Keyes Lake are a homocline of south-dipping Michigamme Slate, a southeast-plunging syncline of Badwater Greenstone, a fault trending north-northwest, a south-plunging syncline of Dunn Creek to post-Riverton strata, and a south-plunging anticline of Badwater Greenstone and Dunn Creek Slate. The best exposed part of the Michigamme Formation in this block is the quartzite near Keyes Lake; here crossbedding is common and uniformly indicates stratigraphic top to be toward the southwest. Consequently, so far as is known, the Michigamme strata constituteSTRUCTURAL GEOLOGY 39 a vertically or steeply dipping homocline. Furthermore, the structural and geographic relations of this quartzite to the Riverton Iron-Formation in the Brule River block are especially significant. The general trends at the east end of the quartzite and the west end of the iron-formation are approximately toward each other. Because the formations structurally face in opposite directions and appear to be terminated in approximately the same locality (pi. 2), a fault is inferred to lie between them. The area south of the fault was raised relative to the area north of it. A fault of similar relative motion in Dickinson County, Mich. (Bayley and others, 1966) has a northwesterly trend and presumably continues into northeastern Florence County, Wis. (pis. 2 and 4). The northwest end of the quartzite is marked by a progressive decrease in the number and size of exposures in sec. 14, T. 40 N., R. 17 E. The quartzite is shown on the map as continuing toward the same inferred fault that terminates its easterly extent, but it may simply lens out. One of the major structures in the Keyes Lake block is a southeast-plunging syncline of Badwater Greenstone west of Keyes Lake. As previously stated (p. 25), a fold is suggested by the arcuate areal distribution of two thin iron-formation units separated by a gray slate unit. A similar arcuate pattern of magnetic crests was indicated by a magnetometer survey (see pi. 6). The synclinal character of the fold is indicated by well-developed ellipsoids in metabasalt in the northeast limb that show that the top of the beds is to the southwest (pi. 2); no data to indicate top were observed in the southwest limb. Toward the southeast the structure is uncertain because of the absence of exposures beyond Keyes Lake and Loon Lake. It is likely, however, that the fold is cut off by the fault at the south edge of the Keyes Lake block. Another fault trending north-northwesterly is believed to extend along the west side of the southwest limb of the syncline because the adjacent structure to the west is another south-plunging syncline, and the normally intervening anticline seems to be absent. Two more folds in the southwest part of the Keyes Lake block lie between the two faults just described. One fold is a south-plunging syncline of Riverton Iron-Formation and Dunn Creek Slate. The other, which is mainly a mass of Badwater Greenstone to the northwest, is a plunging structure indicated by the southward convergence of magnetic crests. The anticlinal form is shown by the arrangement of ellipsoids indicating that the tops of the beds are to the northeast in sec. 21, T. 40 N., R. 17 E., and to the southwest in sec. 27, T. 40 N.,R. 17 E. (fig. 6). Folds and faults in the southwestern part of the area shown on plate 2 are believed to be related to the major fault along the southwest side of the Iron River-Crystal Falls-Florence synclinal basis. The sections and map on plate 4 illustrate a suggested interpretation of the development of the structure in this area. The Riverton Iron-Formation at this locality was part of a continuous layer that once extended along the side of the major basin (see reconstructed areal geology), but its present distribution resulted from faulting and subsequent erosion of the former anticlinal connections (sections on pi. 4). Termination of the three southeast-plunging folds in the Keyes Lake block relative to nearby exposures of Michigamme Slate along the Pine River to the southwest is interpreted to be the result of a northwest-trending fault with relative uplift on the south—a continuation of a fault in Dickinson County, Mich. This fault is a second one of major significance in Florence and Dickinson Counties. PINE RIVER BLOCK The Pine River block includes a small area shown in the southwestern corner on plate 2 and the continuing elongate area shown across the northern part of plate 1. This block is underlain almost exclusively by Michigamme Slate and extends westward and northward from Dickinson County, Mich. The scattered exposures are insufficient to determine the structure of all the Michigamme. However, the tops of the beds are toward the south in the crossbedded quartzitic conglomerate in sec. 24, T. 39 N., R. 17 E., to sec. 28, T. 39 N., R. 18 E., and in graded beds of graywacke in sec. 29, T. 39 N., R. 18 E. The uplift of this block is relatively higher than the Keyes Lake block but is relatively lower than the Popple River block to the south. POPPLE RIVER BLOCK The Popple River block includes slightly more than the southern half of the area shown on plate 1 and extends for undetermined distances to the east, south, and west. It is underlain by metavolcanic rocks of the Quinnesec Formation of early Precambrian age and by intrusive rocks of late middle Precambrian age. A fault along the north side is inferred because ellipsoids in the metabasalt of the Quinnesec Formation indicate a northfacing sequence, whereas the Michigamme Slate in the Pine River block faces south. The exact location of the fault is unknown except where the south-dipping graywacke in the Michigamme Slate is within 50 feet of the felsic metavolcanic rock that overlies the metabasalt in the Quinnesec Formation (fig. 3). The Popple River40 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN block has been uplifted at least several thousand feet relative to the Pine River block. The fault continues into southern Dickinson County, Mich., where the formations and relations are similar to those in the Florence area. FOLIATION AND LINEATION Argillaceous units within the Michigamme Slate and the Paint River Group show a well-developed foliation that typically is nearly parallel to the bedding except at fold axes. Foliation is also present locally in the Hemlock (?) Formation and Badwater Greenstone. This foliation is due to parallel orientation of platy meta-morphic minerals, notably mica and hornblende. Linea-tion due to mineral alinement is evident locally in schistose rocks and amphibolite but generally is not an obvious feature; the lineation is shown best by the axes of minor crumples. Both the major foliation and the lineation are clearly related to the principal westtrending axis of structural deformation. The strike of lineation in the northern part of the area also seems to be related to the northward arc of the major structures. Foliation is common in metarhyolite and metabasalt of the Quinnesec Formation. The strike is predominantly northwest, and the dip is steeply southwest. Only one outcrop of the Quinnesec Formation near the inferred contact with the Hoskin Lake Granite is known; foliation in the Quinnesec strikes northwest and is parallel to the contact, but this general direction is so common that it probably has no special significance. Only minor foliation was observed in the Hoskin Lake Granite. TIME OF FOLDING AND FAULTING The youngest strata—the post-Riverton beds—are folded and faulted, and the general parallelism of folds and faults in the Florence area presumably indicates early and late phases of a single deformation of postmiddle Precambrian time. Some metagabbro has foliation locally. The Hoskin Lake Granite has mortar structure locally, and cataclastic texture of quartz is common. METAMORPHISM The Florence area lies on the south side of the Peavy node and on the north side of the Florence County node of regional metamorphism (James, 1955). The meta-morphic grade decreases from sillimanite at the north edge of the area to chlorite along the Commonwealth syncline and then rises to garnet in the southern part of the area. The pattern (pi. 5) is generally similar to that shown by James, whose data included only a few localities in Wisconsin. As in Michigan, the grades in Wisconsin were determined on the basis of mineralogic changes in argillaceous rocks, mafic igneous rocks, and iron-formation. About 100 thin sections of specimens from 75 widely distributed localities were examined. A general systematic arrangement of grades is evident if a few local differences are minimized. CHLORITE ZONE The chlorite zone or equivalent grade of metamorphism is largely restricted to the Commonwealth syncline in the Brule River block but also extends into the adjacent part of the Keyes Lake block on the south. Chlorite and sericite are prevalent in the argillaceous rocks of the Paint River Group in the Brule River block; the ferruginous rocks are sideritic, hematitic, or limonitic. Much chlorite and saussurite are present in the metabasalt of the Badwater Greenstone at the locations shown on plate 5. Chlorite and sericite are also prevalent in argillaceous rocks of the Michigamme Slate in the Keyes Lake block, and albite-oligoclase (An2_13) is found in the metagabbro that intrudes the Michigamme in sec. 24, T. 40 N., R. 17 E., and sec. 31, T. 40 N., R. 18 E. (pi. 2) in the same block. A small area of quartz-magnetite iron-formation is exposed in secs. 31 and 32, T. 40 N., R. 18 E., and associated rocks have much chlorite and stilpnomelane and locally garnets. These rocks, however, are not considered an index to metamorphism because biotite is rare and much manganese is indicated by X-ray spectrograph (S. W. Bailey, written commun., 1961). Quartz-magnetite iron-formation is also exposed in a small area in the SE14SE14 sec. 25, T. 40 N., R. 17 E., associated with garnetiferous graphitic argillite and garnet-magnetite-grunerite with interbedded chert; this locality is an exception to the general low-grade metamorphism of the Michigamme here. Biotite is found in the exposure of Michigamme in the northwest comer of sec. 6, T. 39 N., R. 18 E., and delineates the limit of the chlorite zone in this part of the area. BIOTITE ZONE Information on the biotite zone or equivalent grade of metamorphism in the Brule River block is based on a few exposures at locations shown on plate 5. Most of the rocks are greenstone, but some are slate and metagabbro. All contain biotite, and the metaigneous ones, albite. Metabasalt at the north edge of the Badwater in the northeast part of T. 40 N., R. 18 E., contains oligoclase-andesine (An28-37), which is equivalent to normal garnet grade, and metadiabase 500 feet south has albite (Ano-9) accompanied by biotite. These characteristic differences establish the northern limit of the biotite zone at this locality.METAMORPHISM 41 Biotite in metamorphosed argillaceous rocks of the Michigamme indicates the location of the biotite zone in other parts of the Florence area. The boundary between it and the garnet zone in the western part of the Florence area may be drawn to show alternative interpretations. For example, the biotite zone might be considered to be a single unit that narrows sharply northwestward, and the two biotite localities near the north limit of T. 39 N., R. 17 E., would be either just local anomalies or a very small enclave in the garnet zone. In the interpretation shown on plate 5, however, the wide biotite zone in the eastern part of the area is believed to bifurcate toward the northwest, and the two apparently isolated biotite localities represent a southern branch. The biotite-bearing rocks in T. 39 N., R. 18 and 19 E., are predominantly slates composed of quartz and sericite in widely ranging proportions, whereas rocks in the adjacent part of the garnet zone are gruneritic iron-formation and schist. Similar lithologic, stratigraphic, and structural relations are found in T. 39 N.,R. 17 E. GARNET ZONE The northern garnet zone is in the Brule River block and is of small extent. The present study shows that the garnet and staurolite isograds must be approximately half a mile south of the positions shown by James (1955, pi. 1). Garnetiferous phyllite is present in the Michigamme Slate as far south as the contact with the Badwater Greenstone. Within the garnet zone, the typical graywacke and slate of the Michigamme, such as that exposed at the Michigamme Falls Dam, is nongarnetiferous; the graywacke, however, contains abundant epidote. At the north side of the zone, stauro-lite-bearing schist is exposed as far south as the center of sec. 8, T. 41 N., R. 31W. The principal garnet zone extends across the southwest half of the mapped area and through each of the known formations from the Quinnesec to the Riverton and younger metagabbro. The garnet zone in the Pine River and Keyes Lake blocks appears either to have divided or narrowed the biotite zone in the western part of the area. The data for each formation are discussed in stratigraphic sequence. The mafic rocks of the Quinnesec Formation are predominantly amphibolite, with minor amounts of hornblende schist; garnet-grunerite schist occurs in at least two localities. The feldspars in the amphibolite and hornblende schist are mostly andesine, but compositions range from An26 to An43. These rocks are part of an andesine-amphibolite facies that continues eastward beyond the mapped area (Bayley and others, 1966). The facies apparently also continues westward beyond the mapped area, and near the center of the west side on plate 1, biotite and garnet occur in a small area of metasedimentary rocks. This occurrence indicates that the andesine-amphibolite facies in mafic extrusive rocks is generally equivalent to the garnet grade in argillaceous rocks. The intensity of metamorphism in the felsic rocks of the Quinnesec is not indicated specifically but may be inferred by the composition of associated metagabbro. Rocks indicative of the garnet zone in the Michigamme Slate are garnet-magnetite-grunerite rock, garnetiferous quartz graywacke, and amphibolite containing oligoclase-andesine (An23-42). These rocks extend from the southeast corner of T. 39 N., R. 18 E., northwestward beyond the mapped area. Two thin discontinuous layers of grunerite with garnets and magnetite are in the Badwater Greenstone in T. 40 N., R. 17 E. Garnets are also present in some associated argillaceous strata. Interbedded garnet-magnetite-grunerite layers and sugary quartz (recrystallized chert) layers make up most of the Riverton Iron-Formation in the western part of the Keyes Lake block. The predominance of andesine (An30-so) and locally some bytownite (An85) in the gabbroic rocks that intruded all formations from the Quinnesec to the Dunn Creek indicates that most occurrences are within the limits of the garnet zone. The high anorthite content of plagioclase in the metagabbro near the Hoskin Lake Granite in the southeastern part of the area suggests that the granite intrusion occurred at nearly the same time as the regional metamorphism and locally retarded the widespread conversion that took place elsewhere in the metagabbro and metabasalt. Apparently no such relationship exists in the vicinity of Hoskin Lake Granite in the southwest part of the area, but very few data are available. STAUROLITE ZONE The graywacke-shale suite, iron-formation, and basic igneous rocks in the staurolite zone of regional metamorphism of northern Michigan are described by James (1955). His description is generally applicable to the rocks on the south side of the Peavy node along the eastern part of the northern edge of the mapped area and is quoted below. GRAYWACKE-SHALE SUITE [James, 1955, p. 1465-1466] The bulk compositional requirements necessary for formation of staurolite are such that this index mineral is found only in a few argillaceous rocks in northern Michigan. It is abundant in some beds, however, and not uncommonly it is present in the originally finer-grained upper parts of graded beds, thus in-42 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN creasing the contrast in grain size with the granulitic lower parts. * * * * * * » * The similarity in composition between staurolite and chlori-toid would suggest that the latter mineral would be equally common in a lower zone of metamorphism and that there might be a paragenetic relationship between the two minerals. Such, however, is not the case; chloritoid is a rare mineral in the region, and no evidence of development of staurolite from chloritoid has been seen in any of the sections studied. ***** Garnet is present in most rocks within the staurolite zone, and is exceedingly abundant in some layers * * *. The garnet commonly is a more deeply colored variety than that within the garnet zone proper but is similar in habit. Some of the biotite is molded around the garnets, but there is little or no evidence to indicate thrusting aside during growth, or rotation. Biotite is the predominant mica, though some muscovite is generally present. As in the garnet zone, the original graywacke layers are not notably different in appearance from those in the lower zones of metamorphism. The rock is massive, gray, and fine- to medium-grained, without schistose or gneissose structure. Original textures are entirely lost, however, and in thin section the quartz and feldspar (generally oligoclase) form an interlocking mosaic; the rock is a granulite, as that term is used by the British petrologists. * * * IRON-FORMATION Iron-formation in the staurolite zone consists of granular quartz, magnetite, and lesser grunerite, in layers one-fourth to one-half inch thick; but locally it is a skarnlike aggregate of grunerite, green pyroxene, garnet, quartz, and magnetite in various proportions. BASIC IGNEOUS ROCKS [James, 1955, p. 1472] Metamorphosed basic intrusive [and extrusive] rock within what is believed to be the staurolite zone is exposed at many places. It is now amphibolite. * * * Differences between the amphibolite of the staurolite zone and the epidote amphibolite of the main part of the garnet zone are not marked in outcrop but are clearly evident in thin section. The most obvious differences are the absence of epidote (except as a retrograde product) and the increase in anorthite content of the plagioclase. This transition from epidote amphibolite probably occurs within the upper part of the garnet zone. Texturally, most of the specimens studied are dominated by large hornblende plates, generally with irregular outline, which are set in a matrix of equigranular plagioclase and quartz with some biotite and sphene. The plagioclase typically is well twinned and of a composition varying from An35 to An«. The change from the sodic oligoclase of the garnet zone to intermediate or calcic andesine is abrupt and doubtless is related to the absence of epidote in the higher zone of metamorphism; in the sections studied, no plagioclase was found with a composition in the range Amo-Aibo. The hornblende plates are typically larger than associated grains; green is the dominant color, with strong pleochroism (X—yellowish; Y—green; Z—green, faintly bluish). Biotite is common as clear plates ranging in color from yellowish brown to reddish brown, the latter more common in the higher part of the zone. Other constituents of the rock are quartz, muscovite, sphene, and magnetite. * * * SILLIMANITE ZONE Eocks in the sillimanite zone were also described by James (1955), and some are present along the eastern part of the northern edge of the mapped area. GRAYWACKE-SHALE SUITE [James, 1955, p. 1466-1467] The only area in which sillimanite-bearing rocks are known to be exposed is at Peavy dam, in the southeastern part of Iron County. Most of the rock in the vicinity of the damsite is massive biotite granulite (graywacke) with interbedded micaceous sillimanite-staurolite schists; stratigraphically these beds are part of the Michigamme slate * * *. Three analyses of the Peavy dam rocks are given in Table 3 [table 6 of this report]. The modes of two thin sections for each of these analyzed rocks are tabulated in Table 4 [table 6 of this report]. The quartz and feldspar that form the ground-mass mosaic are equidimensional and about 0.2 mm in diameter. The feldspar is oligoclase (approximately Ani5) and only a few grains show twinning; in some slides, the plagioclase shows a slight but definite gradational zoning to a more albitic rim. The biotite is brown, forms large flakes about 0.5 mm in length with marked preferred orientation, and most grains show numerous dark haloes around tiny grains of zircon. The muscovite occurs as large clear flakes, 1 mm or more in length, that typically lie athwart the cleavage direction defined by the biotite. The garnet and staurolite form porphyroblasts of typical form and appearance; the garnets are rarely more than 0.5 mm in diameter, but the staurolite forms grains up to 10 mm in length. The sillimanite is most abundant in the more micaceous beds in association with staurolite. On cleavage surfaces it forms thin rods and lenses commonly oriented parallel to the regional linear structure. In thin section it appears as clusters of fine needles * * * The sillimanite bears no systematic paragenetic relationship to other minerals in the rock. ***** The rocks retain much of the outward appearance of the graywacke and slate in zones of lower grade. Bedding is well preserved and some layers show original gradational grain (now reversed, with staurolite in the originally finer-grained, more argillaceous “tops” of some layers). Originally calcareous concretions are visible in some beds ; at this particular locality they are strongly drawn out, with axial ratios of 10: 2:1. The concretions are considerably different in mineralogy from the matrix, most notably in the composition of the plagioclase, which is labradorite (approximately Ant>), as compared with oligoclase in the enclosing rock. Apatite is abundant as small grains. The texture, however, is much similar to that of the enclosing rock, and the boundaries are indistinct in thin section. BASIC IGNEOUS ROCKS [James, 1955, p. 1472] Few specimens of basic igneous rock from the sillimanite zone have been studied. Most are similar to the amphibolite from the staurolite zone—chiefly green hornblende and andesine. However, some specimens from the Peavy node in southeastern Iron County contain brownish hornblende, and some contain abundant pyroxene adjacent to gabbroic intrusive bodies (R. W.METAMORPHISM 43 Table 6.—Chemical analyses, in percent, and modes of three samples from the Michigamme Slate [ From James (1955, tables 3 and 4). Locality: SKJ4 sec. 32, T. 42 N., R. 31 W., Iron County, Mich. Analyst: Lucille M. Kehl] Analysis: Si02 .... 66.51 55. 90 60. 56 A1203 15. 31 19. 31 18. 43 Fe203 .50 . 95 2. 14 FeO 5. 22 7. 83 6. 40 MgO 2. 45 4. 01 3. 39 CaO 2. 00 1. 17 1. 33 Na20. _ _ _ .... 3.08 1. 73 1. 99 K20 2. 72 4. 91 3. 09 H20- .03 . 19 . 06 H20 + 1. 21 2. 77 1. 48 Ti02 .66 . 85 . 82 C02 . .01 None . 01 P205 . 15 . 18 . 18 MnO .06 . 04 . 04 Total.. _ _ 99. 91 99. 84 99. 92 Mode, in volume percent: Quartz. ... ... 62. 8 35. 9 46. 3 Biotite. _ . 21. 5 40. 7 33. 0 Muscovite ... ... 5. 6 7. 6 2. 0 Plagioclase (An16) _. _ . 8.5 9. 4 4. 3 Garnet . . . 1.6 3. 0 1. 0 Staurolite.. . 3 13. 3 Sillimanite. ._ Tr. 3. 1 Tr. Bayley, personal communication). The pyroxene-bearing rock is granoblastic, with irregular anhedra of nearly colorless diopside and scarce hypersthene in a matrix of andesine grains. Hornblende occurs as discrete grains or as replacements of the pyroxenes, and the rock apparently is a hornfels modified by regional metamorphism. PEAVY NODE The Peavy metamorphic node centers approximately on the Peavy Pond Complex described by Bayley (1959) as a syntectonic intrusion. The earliest, and quantitatively the major part of the complex presently exposed, is gabbroic in character. The gabbro was succeeded by later intermediate and granitic rocks. Locally rocks of the Hemlock Formation (in the Lake Mary quadrangle) were metamorphosed by the gabbro to the hornfels facies. Subsequently, both the gabbro and hornfels were metamorphosed to amphibolite in the same cycle. It is evident, therefore, that although the node of the thermal activity, as reflected by the zona-tion, is approximately centered on the complex, the source of metamorphic heat was not derived from that body at its present level of erosion. The now-metamorphosed gabbro may have formed a hood for a larger subjacent and possibly convecting body of magma; the relatively small bodies of granitic rock possibly represent offshoots from this deeper source. TIME OF METAMORPHISM AND RELATION TO DEFORMATION Metamorphism was regional in scope and possibly took place before the deformation. Several occurrences of rotated garnets indicate that some deformation was contemporaneous with, and possibly subsequent to, metamorphism. More positive evidence of possible pre-tectonic metamorphism, at least locally, consists of wrinkled foliation in schistose Michigamme Slate (fig. 11) in sec. 3, T. 39 N., R. 17 E. (pi. 2), in the Quinnesec Formation in secs. 4 and 9, T. 38 N., R. 18 E. (pi. 1), and especially in sec. 28, T. 39 N., R. 17 E., west of the mapped area, along the east side of State Route 101 (fig. 12). In the specimen shown in figure 11, stratification results from differences in the amount of biotite, and foliation results from parallel orientation of finegrained muscovite. Biotite flakes tend to be slightly elongate along the wrinkles of foliation. Examination of another thin section of the Michigamme Slate from the same location shows that biotite flakes, as much as 0.15 by 0.30 mm in size, are unaffected by and independent of the foliation of the muscovite and tend to be elongate parallel to the wrinkles in the foliation. Foliation and wrinkles are at angles of about 30° and 60°, respectively, to the bedding. The cataclastic texture of quartz and the mortar structure in the Hoskin Lake Granite are evidence that Figure 11.—Michigamme Slate in sec. 3, T. 39 N., K. 17 E. Foliation parallel to surface of photograph. Bedding represented by horizontal differences in color. Wrinkled foliation inclined to right. Piece of twig is 1 inch long.44 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN Figure 12.—Folded foliation in the Quinnesde Formation, sec. 28, T. 39 N., R. 17 E. Knife is 3% inches long.MAGNETIC SURVEYS 45 crystallization of the granite was accompanied or followed by some deformation. The isograds on plate 5 are drawn in accordance with the concept that metamorphism preceded deformation. Although alternative interpretations are possible, they do not seem to be especially more advantageous. MAGNETIC SURVEYS GROUND MAGNETIC SURVEY In 1958-59 an area of about 4 square miles near Keyes Lake in the southwestern part of plate 2 was surveyed by K. L. Wier and R. A. Solberg with vertical-intensity magnetometers. The instruments were temperature compensated and had sensitivities of about 30 gammas per scale division. Magnetic determinations were generally made at paced intervals of 100 feet along traverse lines generally 300 feet apart, but intermediate lines and stations were added in a few places. The traverse lines were controlled by the use of sundial compasses. Magnetic values above an arbitrary zero base are shown in tens of gammas on plate 6. The zero base has an approximate absolute vertical intensity value of 57,500 gammas, as established from magnetic base stations in southeastern Iron County, Mich., by the U.S. Bureau of Mines (Bath, 1951). The most prominent feature shown by the magnetic data is a concentration of high values in two pairs of discontinuous northwesterly trends that converge and join (pi. 6) like a plunging fold. Ellipsoidal structures in greenstone indicate that the top of lava flows associated with the northeast pair of anomalies is now toward the southwest, so the structure is interpreted as the northeast limb of a syncline plunging southeastward even though no data concerning the sequence in the southwest limb were found. Magnetic gruneritic iron-formation is exposed or was penetrated by test pits or shallow shafts at several places along each of the paired anomalies, except in the southeastern part of sec. 35, T. 40 N., R. 17 E., and the northwestern part of sec. 1, T. 39 N., R. 17 E. Discontinuity of the anomalies may indicate that the layers may be long lenses or that the magnetite content of layers is locally less because of the original composition or subsequent oxidation. Gray slate crops out at several places between the two magnetitic units and apparently separates them throughout the structure ; this relationship nullifies the possibility that the paired anomalies represent the limbs of a simple anticline or syncline. The abrupt termination of the anomalies toward the southeast is probably related to faulting. Termination of the greenstone outcrops is presumably due to deep preglacial erosion and subsequent extensive and thick accumulations of glacial deposits. Other features of the magnetic data appear to be less structurally significant. The anomaly in sec. 25, T. 40 N., R. 17 E., at the Dunkel exploration is caused by a local concentration of magnetite just above the upper part of a vitreous quartzite in the Michigamme Slate. The rocks underlying the anomaly near the center of sec. 31, T. 40 N., R. 18 E., are not especially magnetic, but their gross effect may have influenced the magnetometer; furthermore, these rocks are possibly the lithologic equivalent of those penetrated by the St. Clair-Dickey explorations in sec. 24, T. 40 N., R. 17 E. (pis. 2 and 8). Here small amounts of martite occur in radiating blades of limonite that is probably pseudomorphous after stilpnomelane or grunerite. The southward trend of a conspicuous anomaly outlined by the 1,000-gamma line near the southwest corner of Keyes Lake is possibly related to a dike of metagabbro. Most exposures of metagabbro are not noticeably magnetic, but some fracture surfaces in the outcrop northwest of the outlet of Keyes Lake contain scattered magnetite crystals as large as one-quarter of an inch. An anomaly with a northeast trend in the southwestern part of sec. 26, T. 40 N., R. 17 E., is not parallel either to the strike in the nearby outcrop of the Riverton Iron-Formation or to the areal pattern shown on plate 2. It may indicate a northeast extension of the small syncline of Riverton in the northwest corner of adjacent section 35 toward the outcrop mentioned above. However, a magnetometer traverse over the Riverton in a shallow syncline in the northwestern part of section 26 showed no anomalous magnetic values. A magnetic survey of the area without exposed bedrock in the northeast part of the mapped area (pi. 2) and the adjacent area eastward for 1 mile into Dickinson County, Mich., was made by Wier in 1964. Several anomalies were located, but the geology of the area remains largely unknown. A 2,000-gamma positive anomaly trending west-southwest crosses the north half of sec. 34, T. 42 N., R. 31 W., and is flanked on the south by a 600-gamma negative anomaly. A pair of closely spaced anomalies resemble each other: in the SV2SW1/) sec. 35, T. 42 N., R. 31 W., the ground plan is circular and about 1,300 feet in diameter, and the relief is 5,000 gammas; in the NW%NW)4 sec. 2, T. 41 N., R. 31 W., the ground plan is elliptical with dimensions of 1,300 by 900 feet, and the relief is 6,000 gammas. An anomaly in the NW(4 sec. 12, T. 41 N., R. 31 W., and extending a short distance westward into the adjacent section 11, has an area of about a square mile and relief46 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN of 3,000 gammas. Magnetic values just east of the mapped area increase rapidly in the eastern quarter of sec. 12, T. 41 N., R. 31 W., and the western part of sec. 7, T. 41 N., R. 30 W. An anomaly there is 3,600 feet wide, has 13,000-gamma relief, and is apparently related to the Felch Formation of the Felch trough in Dickinson County, Mich. (James and others, 1961). AEROMAGNETIC SURVEY The aeromagnetic maps (pis. 7 and 8) not only show a close relation to most of the areal geology based entirely on field data (pis. 1 and 2) but also show several significant features that would not have otherwise been apparent. The magnetic pattern generally agrees with the location and trend of the inferred faults that separate the structural blocks. The principal magnetic and geologic relations will be considered in each of the structural blocks. BRULE RIVER BLOCK The areas of high magnetic values related to the Michigamme Slate and the Paint River Group and low values for the Badwater Greenstone in the northeast limb of the Commonwealth syncline are well delineated by the magnetic pattern (pis. 2 and 8). The anomaly at the northwest corner of the mapped area is of special significance inasmuch as it is caused by the magnetite-bearing Stambaugh Slate. This slate is younger than the Riverton Iron-Formation and has been traced magnetically and by outcrops in the Crystal Falls and Iron River areas. It is, however, not a recognizable unit elsewhere in the Florence area, even though the southeastward continuation of the anomaly suggests that similar material is present in the lower part of the post-Riverton sequence. A prominent circular anomaly in the south-central part of plate 8 is centered above the axis of the Commonwealth syncline. Apparently it is caused by strata in the lower part of the post-Riverton sequence that are probably equivalent to the Stambaugh Slate. It is presumed that a steep northwestward plunge and extreme plication of magnetic strata are at this structural position. KEYES LAKE BLOCK The magnetic anomalies of the Keyes Lake block are a series of northwest-trending elongate areas (pis. 7 and 8). The anomalies on plate 8 are clearly related to the lithology and to a homoclinal structure in the Michigamme Slate, to a syncline and anticline in the Badwater Greenstone, and less clearly to a syncline in the Riverton Iron-Formation, as shown on plate 2. The cause of the anomaly near the north edge on plate 7 is not known. Drilling in that area (pi. 1) penetrated a variety of slates. PINE RIVER BLOCK The magnetic pattern and related geology in the Pine River block are shown on plates 1, 2, 7, and 8. The area is underlain by the Michigamme Slate, and the cause of most of the anomalies is not known. However, some are due to the magnetite-grunerite rocks exposed in sec. 2, T. 39 N., R. 17 E. (pi. 2), and penetrated by drilling in secs. 34 and 36, T. 39 N., R. 18 E. (pi. 1 and p. 22). The anomaly adjacent to the fault in the southwest corner on plate 8 continues across most of the area shown on plate 7 and possibly farther. The drilling in secs. 30 and 31, T. 39 N., R. 19 E., was reported to have penetrated gray slate in section 30 but graphite slate in the northern part of section 31 and greenstone in the two southernmost holes. A prominent anomaly along the southwestern part of the block (pis. 7 and 8) appears to be closely related to exposed magnetite-bearing quartzitic conglomerate but extends northwestward and southeastward into areas where there are no exposures. Drilling in sec. 27, T. 39 N., R. 18 E., near the maximum magnetic value (pi. 1) penetrated Michigamme Slate that contained some small veinlets and disseminations of pyrrhotite, but the possible relation of the anomaly and this mineral is not known. Drilling in secs. 34 and 36, T. 39 N., R. 18 E., cut magnetic grunerite schist and iron-formation, respectively. A prominent west-facing broadly convex anomaly shown along the eastern side on plate 7 constitutes the western end of a major anomaly that extends southeastward into Dickinson County, Mich., and is caused by the Vulcan Iron-Formation that is exposed there and was formerly mined for iron ore. The Michigamme Slate overlies the Vulcan in Michigan, but no Vulcan is known to crop out or to have been penetrated by drilling in Wisconsin. The western termination of the Vulcan is believed to be a steeply west-plunging anticline cut off just north of the axis by the fault that separates the Pine River and Keyes Lake blocks. POPPLE RIVER BLOCK The most striking feature in the magnetic pattern of the Popple River block (the southwest half on pi. 7) is its contrast and abrupt change from the well-defined northwestward trends in the Pine River block to few short, much less well defined trends, varied directions, and lower magnetic values. A large area of low values in the southwestern part of the block is presumably underlain by the Hoskin Lake Granite that crops out in a few places. The irregular contact between this rock and the surrounding Quin-ECONOMIC GEOLOGY nesec Formation (as shown on pi. 1) is based on the magnetic pattern. More than half of the area underlain by the felsic metavolcanic rock of the Quinnesec Formation is characterized by low magnetic values. The “bird’s-eye maple” pattern in the remainder of the Popple River block probably indicates variations in the mineral composition of metabasalt and metagab-bro that were not recognized during the geologic mapping. ECONOMIC GEOLOGY The possibilities of renewed mining in the area under present economic and technologic conditions do not appear to be favorable. The available iron-bearing material is not currently competitive in quality or quantity either as direct-shipping ore or as material amenable to beneficiation. The ore bodies that have been mined were all small, and geologic features that might have been conducive to the formation of large ore bodies do not appear to be present. The amount of low-grade magnetic or nonmagnetic ore that is readily available is believed to be very limited. Almost 8,000,000 tons of direct-shipping iron ore was mined locally from the Riverton Iron-Formation in the period from 1880 to 1960. The ore was predominantly soft hematite and limonite with a high phosphorus content, non-Bessemer grade; hard hematite with a con-choidal fracture was present locally but was not separated in mining. The composition of ore marketed prior to 1938 is given in table 7, but ore of similar grade is not known to be available in significant amount. Small nonmagnetic iron-bearing deposits associated with other formations have also been explored for direct-shipping ore but apparently have not been found to be of economic importance. Parts of the Riverton, Badwater, and Michigamme are magnetic, but neither the quantity nor quality of the iron-bearing rock appears to be suitable for possible beneficiation at this time. 47 Deposits of sand and gravel have been, and intermittently still are being, utilized for construction. IRON-ORE MINES The inaccessibility of all underground mines in the Florence area and the sparsity of critical geologic data on available mine maps make a detailed interpretation of the principal ore occurrences difficult. Data show that interbedded chert and siderite were associated with the ore and presumably were the source from which the ore was formed by oxidation of siderite and removal of much of or all the chert by leaching, replacement, or some combination of these processes. FLORENCE MINE The Florence mine is in secs. 20 and 21, T. 40 N., R. 18 E. (pi. 3). Production of ore began from a small open pit, but most mining was underground. Shipments of ore during the period of 1880 to 1931 totaled 3,680,-000 tons. Trend of the ore bodies was N. 45° W.; their general dip of 70° NE. indicates that the Riverton and associated strata are overturned. Ten levels were developed within a total depth of approximately 650 feet. Three ore bodies at the first level, about 132 feet deep, ranged from 400 to 750 feet long and from 70 to 250 feet wide. A fourth ore body, which was not distinct at the first level, was about 1,100 feet long and 150 feet wide at the third level. The four ore bodies were arranged in pairs; a small ore body was southeast of a large one on each side of a center line that trended N. 45° W. The southeast ore bodies did not extend below the seventh level (a depth of 425 ft), and the others had decreased considerably in size at this depth but extended to the tenth level. The southeast ore bodies were separated by pyritic black slate, according to the descriptions on available mine maps. This is presumably Dunn Creek Slate and forms the core of an anticlinal fold plunging northwestward. The northwest convergence of the north- Table 7.—Partial analyses, in percent, of iron ores from Florence, Wis., area IFrom Lake Superior Iron Ore Association (1938, p. 149,152)] Mine Sample Chemical composition Iron Phos- phorus Silica Manganese Alumina Lime Magnesia Sulfur Loss Moisture Commonwealth group ... Dried at 212°F 52.50 0.400 10.00 0.13 2.80 2. 75 2.72 0.500 5.00 . Natural2 48. 04 .366 9.15 .12 2.56 2. 57 2.54 .458 4. 58 8. 50 Dried at 212°F . 56. 52 .353 5. 73 . 26 2.56 3.06 2.90 .213 3.67 . Natural2 50. 65 .316 5.14 .23 2.29 2.74 2.60 .191 3.29 10.39 Florence ... Dried at 212°F_ 55.37 .267 6.95 .22 4. 43 1.63 2.79 .138 4.40 . Natural2 50. 06 .241 6.28 .20 4. 01 1.47 2.52 .125 3.98 9. 60 1 Commonwealth, Badger, Buckeye, and Davidson mines. 2 Basis for gale and use; recalculated from analyses of dried sample.48 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN west ore bodies is further evidence of the plunging anticline that must be accompanied on the north by a syncline or fault from which the Riverton continues along the general northwest trend. Other reported occurrences of pyritic black slate with iron-formation on each side indicate other anticlines, and a few occurrences of graywacke (classified as tuff in some places) flanked by iron-formation indicate synclines. However, no general pattern of folding was shown on the mine maps. Occurrences of tuff or black slate and tuff immediately northeast of the Riverton are mentioned in records of underground drilling and suggest the possibility that some faulting has locally cut out part of the normal sequence of Dunn Creek Slate. BADGER MINE The Badger mine is in the SE14SE14 sec. 34, T. 40 N., R. 18 E., and is at the southeast apex of the Riverton Iron-Formation in the Commonwealth syncline (pi. 2). This mine opened in 1891 and probably closed in 1901; approximately 700,000 tons of ore were shipped. Operations began as an open pit, which is now 600 feet in a west-northwest direction and 300 feet wide. Five levels, the lowest at a depth of 630 feet, were developed to mine an area about the same size as the open pit. It was reported that the ore body dips 70° N. and plunges westward. Graphitic phyllite of the Dunn Creek Slate is exposed in the northeast corner of the pit and was observed in the southeast end when the pit was partly dewatered in 1959. Fine-grained graywacke and argillaceous rock, also of the Dunn Creek Slate, crop out in several places east of the pit. A shallow northwestward extension of the pit exposes several thin lenses or wedges of graywacke containing a few chert fragments; these occurrences are believed to be Hiawatha Graywacke in small synclines. BUCKEYE MINE The Buckeye mine, in the southern limb of the Commonwealth syncline, is in the SW^SE1/^ sec. 33, T. 40 N., R. 18 E. (pi. 2); it was opened in 1909 as an underground operation and was closed in 1911. No record of the amount of ore produced was found. Eight levels were developed within a total depth of 825 feet. Drifts and crosscuts extended beneath an area approximately 1,400 feet north to south and 600 feet east to west, within which the ore-bearing area was about 560 feet north to south and 330 feet east to west. Mine maps show that two main ore bodies near the shaft were generally elliptical in horizontal section, elongate east and west, and vertical. The north one was 200 feet by 70 feet with a vertical extent from the third to the eighth levels. The south one had maximum measurements of 220 feet by 80 feet and extended from the first to the eighth levels. A small ore body 350 feet south of the shaft was 170 feet by 40 feet and extended vertically from the first to the fourth levels. The geology of the mine was mapped by W. O. Hotchkiss in 1910-11, and his maps are in the files of the Wisconsin Geological and Natural History Survey. A suite of 45 specimens is also available for examination. Strikes, dips, and some folds are shown on the maps; general lithologic descriptions for numerous localities are recorded, but no stratigraphic units or contacts are indicated. Prevalent strikes are east-west, and dips are steep, both north and south. Minor folds do not indicate the type of larger fold to which they are related. Graphitic slate, possibly the Dunn Creek, occurs east of the shaft and a few other localities. Much oxidized iron-formation lies adjacent to the ore bodies, but some cherty carbonate occurs in the northern part of the fourth, fifth, and sixth levels. North of the oxidized iron-formation, the mottled green and red, massive, bedded argillite with chert lenses is possibly the upper part of the Riverton. West and south of the iron-formation is a generally fine grained quartz graywacke that is graphitic throughout or has graphitic partings and is probably a part of the Hiawatha Graywacke. The distribution of these rocks and their strikes and dips suggest that the Buckeye ore bodies probably occurred mainly in the north flank of an anticline that plunges westward (pi. 2). COMMONWEALTH MINE The Commonwealth mine, in the NE14SWI4 sec. 34, T. 40 N., R. 18 E. (pi. 2), was opened in 1880 and closed in 1896. About 700,000 tons of ore were shipped. Mining began as an open pit operation, but later six levels within a total depth of 610 feet provided access for mining in an area 450 feet southeast to northwest and 400 feet across. Only the Riverton Iron-Formation is exposed in the open pit; no geology is shown on available mine maps. Field data in the vicinity of the pit indicate that this ore body was in the northeast limb of a major syncline and was possibly related to a local synclinal drag fold. DAVIDSON MINE The Davidson mine is in and also slightly east of the NE14SW14 sec. 34, T. 40 N., R. 18 E. (pi. 2); it was opened in 1889 and was probably operated until 1906 and again from 1953 to 1960. Approximately 800,000 tons of ore were shipped. Information concerning this mine is restricted mainly to the latest operation, by the Zontelli Mining Co., which produced a northwest-trending open pit 600 feet long, 350 feet wide, and about 100 feet deep. The southECONOMIC GEOLOGY 49 wall of the pit is pyrite-bearing graphitic rock of the Dunn Creek Slate, but elsewhere the opening exposes only Riverton Iron-Formation in which many minor folds are present, especially at the east end. This mine is in the north limb of an anticline in which Dunn Creek Slate is exposed. The south limb extends eastward through the small Field mine pit in which the Dunn Creek is exposed in the north wall, the Riverton is only about 100 feet thick, and the Hiawatha forms the south wall. ERNST MINE The Ernst mine is in the SW^4SW*4 sec. 27, T. 40 N., R. 18 E. (pi. 2). The mine was operated from 1912 to 1929, and 670,000 tons of ore was mined from six levels developed within a total depth of 500 feet. Main drifts extended N. 60°-75° W. for distances that ranged from 350 to 500 feet from the shaft. Width of the areas penetrated by crosscuts ranged from 170 to 240 feet. The single ore body began about 280 to 370 feet from the shaft, and horizontal sections at various levels ranged from circular at 75 feet in diameter to rectangular at 130 feet by 130 feet. No maps showing the geology of the mine are known to be available, and the structural setting of the ore is not known. Exploratory drill-hole data indicate that the ore was in an extensive area of oxidized iron-formation and interbedded chert-siderite. The record of one drill hole east and another north of the ore reported gray tuffaceous slate—probably graywacke in the Dunn Creek Slate. The ore occurrence at the Ernst mine is interpreted as being in a segment of the Riverton Iron-Formation on the northeast limb of the Commonwealth syncline. Exploratory drilling in the Ernst area in 1911-12 consisted of nine holes from the surface and four to possibly nine holes from underground locations. Holes from the surface were inclined from 60° to 80°, and drilled depths ranged from 175 to 679 feet. Most of the material penetrated by the holes from the surface was reported as some variation of iron-formation—ore, oxidized iron-formation, or cherty carbonate. Small amounts of gray slate, graphitic slate, and ferruginous slate were also reported. A vertical hole from the sixth level was recorded as being in hard blue and soft red ore of 50 to 65 percent iron for 500 feet, but the amount of sulfur generally exceeded 0.20 percent and locally 1.0 percent. EXPLORATIONS NONMAGNETIC IRON-FORMATION A few localities have been explored by shafts with limited underground workings or by test pits, and brief descriptions are given. Classification of materials in or from the shafts and test pits was a part of the field study, and information is recorded on a set of data sheets at the scale of 1:12,000 on file at the Wisconsin Geological and Natural History Survey. WELCH The Welch exploration in the NW^4 sec. 34, T. 40 N., R. 18 E. (pi. 2), had three levels. The deepest drift was at the 400-foot level, but the most extensive was at 300 feet, where crosscuts extended 250 feet southwestward, to a main northwest-southeast drift that was 600 feet long. No records of the geology at this exploration were found. The dump material is predominantly very fine grained hematite, limonite, or both, with interbedded chert. A very small amount of interbedded siderite and chert is also present. Oxidized quartz graywacke in the dump of a test shaft about 300 feet northeast of the Welch shaft is believed to be a part of the Dunn Creek Slate. POLDERMAN The Polderman exploration in the NW^SW1^ sec-33, T. 40 N., R. 18 E. (pi. 2), had only 120 feet of crosscut and 110 feet of drift at an unrecorded depth. The dump material is believed to be predominantly oxidized Hiawatha Graywacke. There are a few test pits in the vicinity of the shaft. SPREAD EAGLE The Spread Eagle explorations were in the N%. sec. 8 and near the center of the W*4 sec. 9, T. 39 N., R. 19 E. (pi. 1). A shaft in the SE^NW^ sec. 8 had workings designated as the 50-foot and 100-foot levels. The upper level had 165 feet of drift and 200 feet of crosscuts; recorded iron content of samples from the drift and from a zone 10 to 60 feet wide in the crosscuts ranged from 25 to 51 percent and averaged 40 percent. The lower level had 100 feet of drift and 170 feet of crosscuts; the iron content for 70 feet of the drift and 50 feet of a crosscut ranged from 27 to 47 percent and averaged about 41 percent. Rock associated with the iron-bearing material was designated as slate. A shaft near the center of the W(4 sec. 9 was 57 feet deep, and a crosscut northward for 85 feet penetrated two ferruginous zones that totaled 29 feet in thickness. The iron content ranged from 25 to 57 percent and averaged 36 percent. Associated material is recorded as greenstone. Drilling nearby is reported to have also penetrated satiny slates, tuffaceous slates, and tuffs. Numerous test pits and two additional shafts or cribbed test pits are also present. Exposures of Badwater Greenstone just north of this area of explorations indicate that the ferruginous material is probably part of the Michigamme Slate and near its upper limit—a part of50 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN the Michigamme that is transitional with the Badwater. Ferruginous material in the upper part of the Michigamme is present at the Wausau exploration in sec. 17, T. 41 N., R. 31 W., Iron County, Mich. (pi. 2 and p. 14), and at several localities in Dickinson County, Mich. Many other nonmagnetic localities have been explored by diamond drilling; the geologic data and other information are in the files of the Wisconsin Geological and Natural History Survey and have been compiled on the data sheets previously mentioned. Descriptions of materials penetrated were generally not helpful for determining the lithology, stratigraphy, or structure. However, reported occurrences of cherty carbonate or carbonate slate, which presumably was unoxidized Riverton Iron-Formation, were used locally in interpreting the areal geology. MAGNETITIC IRON-FORMATION In the southwestern part of the area shown on plate 2, magnetitic iron-formation is found in several types of occurrence. The localities have been known since at least 1879 and have been examined repeatedly. The Riverton Iron-Formation in secs. 26, 27, 34, and 35, T. 40 N., R. 17 E., consists of alternate layers of gar-net-magnetite-grunerite and chert that are complexly folded and presumably faulted. Oxidation in the NW(4 sec. 35 has produced soft limonitic and hematitic material that has been explored by several companies; a small amount of material from an open pit was shipped in 1948. The amount of magnetite is small as indicated by magnet tests, magnetic surveys, and visual inspection. A small concentration of fine-grained bluish hematite in the NW^4 sec. 35 was explored prior to 1910. The Badwater Greenstone in this group of sections and in several adjacent ones is predominantly metamorphosed basaltic rock with two thin discontinuous layers of garnet-magnetite-grunerite and interbedded chert. Magnetic values determined by an aeromagnetic sur-vey (pi. 8) are as high as, and locally higher than, those of adjacent Riverton; but the amount of magnetite and quantity of rock containing it are small. Several small areas have been explored by test pits or trenches. The St. Clair exploration shaft was in the SW(4 NW(4 sec. 24, T. 40, N., R. 17 E. (pi. 2). A drift and a crosscut at an unrecorded depth were each 240 feet long. The Dickey exploration, in the SW^SW^ sec. 24, was was just a shaft of unrecorded depth, so far as indicated by data in files. These explorations were in a thin oxidized layer of garnet-magnetite-silicate in the Michigamme. Limonite is more common than hematite, but both occur locally in radiating patterns and presum- ably were derived from stilpnomelane or, less likely, from grunerite. This area also was explored by many test pits. The Michigamme Slate in and just west of SW1/) sec. 32, T. 40 N., R. 18 E., contains a concentration of hematitic-magnetitic material at the Little Commonwealth exploration (p. 15 and fig. 2). A small deposit of magnetitic material in the Michigamme Slate in the SEi/4 sec. 25, T. 40 N., R. 17 E., occurs at the Dunkel exploration (p. 18 and pis. 2 and 6). This deposit was explored with two shallow shafts prior to 1910 and has been of recurrent interest to mining companies. Several explorations in the Michigamme Slate in secs. 27, 28, and 34, T. 39 N., R. 18 E., near the center of the area shown on plate 1, are along a prominent northwest-trending anomaly (pi. 7). The dump of a shallow test pit or shaft opened prior to 1910 in the SW1/4NE1/4 sec. 28, T. 39 N., R. 18 E. (fig. 3), contains predominantly iron-bearing rock that crops out nearby. In thin section the materials are translucent to opaque hematite, minor magnetite, garnets as much as 1 mm across, and quartz. The hematite is commonly arranged in a radiating pattern, as if pseudomorphous after grunerite or stilpnomelane, and spreads through adjacent areas of quartz. The quartz may be either approximately equigranular with unsutured boundaries and normal extinction or irregularly elongate with sutured contacts and wavy extinction. No definitely clastic quartz was recognized, so it is likely that the material is recrystallized chert. The dump of a shallow shaft, also in the SW^NE^ sec. 28, T. 39 N., R. 18 E., contains mainly somewhat quartzose but very magnetic iron-formation and some associated magnetic grunerite schist with a small amount of chert. The amount of magnetite-bearing rock is indeterminate from present data, but the highest known magnetic value in this area (6,750 gammas) is about 2,000 feet southeast along the prominent anomaly, and the area enclosed by the 3,000-gamma contour is 1 mile long and almost half a mile wide. The southwestern part of sec. 27, T. 39 N., R. 18 E., was explored in 1908 by two drill holes that were inclined 60° to the southwest and penetrated to depths of 605 and 833 feet. The core is quartz-sericite slate that presumably is part of the Michigamme Slate. Locally the core contains pyrite, magnetite, and pyrrhotite. Holes drilled in 1911 in the northeast part of sec. 34, T. 39 N., R. 18 E., were reported to have penetrated magnetite-grunerite iron-formation. A small magnetic crest indicated in the SE14 sec. 36, T. 39 N., R. 18 E., by the work in 1910-11 (pi. 7), created enough interest in 1958 so that a 265-foot holeREFERENCES CITED 51 was drilled. The material penetrated was opaque irregular hematite and minor amounts of magnetite inter-layered with quartz. The quartz was irregular to bladelike in form, as if pseudomorphous after grunerite, and characterized by wavy extinction, as in chalcedony. In summary, the possibility of utilizing the known magnetitic iron-formation in the Florence area is very remote because the deposits are small, thin, few in number, and of very low grade. GUIDES TO FURTHER EXPLORATION If renewed interest in direct-shipping ore should develop, several considerations should be taken into account. Previously, ore bodies were discovered at the bedrock surface and were then followed along strike and downdip as far as they were economically profitable, but today new procedures must be followed. 1. Some tightly folded structures such as those at the east end of the Riverton Iron-Formation in the Commonwealth syncline may have ore that lies deep on the flanks of and along the axes of folds. To test this possibility will require additonal test pitting, trenching, and drilling in order to study the possible relations between structure and areas of enrichment. 2. The prominent circular magnetic anomaly near the community of Commonwealth is another area that warrants further study. The anomaly is probably due to the presence of complexly folded Stam-baugh Slate at depth (p. 46); the Riverton Iron-Formation and associated post-Riverton formations exposed here are generally only very slightly magnetic. The Michigamme Slate at the Little Commonwealth exploration and the Vulcan Iron-Formation, which is older than the Michigamme and in adjacent Dickinson County, Mich., contain ferruginous facies that are magnetic ; but neither is likely to be present at this site. Nevertheless, further detailed magnetic and geologic work may indicate that exploration is warranted. 3. Although the Riverton Iron-Formation is locally absent at the surface northwest of Florence, it may be present at depth and may have been enriched. Other sites to be considered for further geologic work and some exploraton to evaluate the possibilities of finding magnetic iron-formation are the iron-rich facies of the Michigamme Slate in the Little Commonwealth and Dunkel areas and the metamorphosed Riverton Iron-Formation in the Larsep exploration area (NW1/) NWy4 sec. 35, T. 40 N., R, 17 E.). If future circumstances cause increased interest in the carbonate facies of the Riverton Iron-Formation, places that should be investigated are the Ernst and Welch mines near Commonwealth, the Buckeye mine area south of Commonwealth, and the rock-cored ridge that extends northwest from the Florence mine. It seems likely, however, that the amount of carbonate iron-formation in the mapped area is small. If there is an increased interest in the oxidized iron-formation, studies should probably begin at the sites of inactive mines and extend along the strike and down the dip of the Riverton Iron-Formation. REFERENCES CITED Allen, R. C., and Barrett, L. P., 1915, Contributions to the pre-Cambrian geology of northern Michigan and Wisconsin : Michigan Geol. and Biol. Survey Pub. 18, Geol. Ser. 15. p. 13-164. Banks, P. O., Cain, J. A., and Rebello, D. P., Ages of Penokean granitic rocks in northeast Wisconsin [abs.l : Geol. Soc. America and associated societies, Ann. Mtg., New Oreleans, La., 1967, Program, p. 12. Bath, G. D., 1951, Magnetic base stations in the Lake Superior iron districts: U.S. Bur. Mines Rept. Inv. 4804,16 p. Bayley, R. W., 1959, Geology of the Lake Mary quadrangle, Michigan: U.S. Geol. Survey Bull. 1077.112 p. Bayley, R. W., Dutton, C. E., and Lamey, C. A., 1966, Geology of the Menominee iron-bearing district, Dickinson County, Michigan, and Florence and Marinette Counties, Wisconsin : U.S. Geol. Survey Prof. Paper 513, 96 p. Brooks, T. B., 1880, The geology of the Menominee iron region, Oconto County, Wisconsin, in Geology of Wisconsin : Wisconsin Geol. Survey, v. 3, p. 429-599. Clements, J. M., and Smyth, H. L., Jr., 1899, The Crystal Falls iron-bearing district of Michigan: U.S. Geol. Survey Mon. 36, 512 p. Cotter, R. D., Young, H. L., Petri, L. R., and Prior, C. H., 1965, Ground and surface water in the Mesabi and Vermilion Iron Range area, northeastern Minnesota: U.S. Geol. Survey Water-Supply Paper 1759-A, 36 p. Dutton, C. E., and Linebaugh, R. E., 1967, Map showing Pre-cambrian geology of the Menominee iron-bearing district and vicinity, Michigan and Wisconsin: U.S. Geol. Survey Misc. Geol. Inv. Map 1-466, scale 1:125,000. Emmons, R. C., 1943, The universal stage: Geol. Soc. America Mem. 8, 206 p. Emmons, R. C., ed., and others, 1953, Selected petrogenic relationships of plagioclase: Geol. Soc. America Mem. 52, 142 p. Fyfe, W. J., Turner, F. J., and Verhoogen, John, 1958, Meta-morphic reactions and metamorphic facies: Geol. Soc. America Mem. 73, 259 p. Goldich, S. S., Baadsgaard. Halfdan, and Nier, A. O. C., 1957. Investigations in A40/K40 dating: Am. Geophys. Union Trans., v. 38, no. 4, p. 547-551. Good, S. E., and Pettijohn, F. P., 1949, Magnetic survey and geology of the Stager area, Iron County, Michigan: U.S. Geol. Survey Circ. 55, 4 p. Hole, F. D., Olson, G. W., Schmude, K. O., and Milfred, C. J., 1962, Soil survey of Florence County, Wisconsin: Wisconsin Geol. and Nat. Hist. Survey Bull. 84,140 p.52 GEOLOGY, FLORENCE AREA, WISCONSIN AND MICHIGAN James, H. L., 1951, Iron formation and associated rocks in the Iron River district, Michigan: Geol. Soc. America Bull., v. 62, no. 3, p. 251-266. ------1954, Sedimentary facies of iron-formation: Econ. Geology, v. 49, no. 3, p. 235-293. ------1955, Zones of regional metamorphism in the Precam- brian of northern Michigan: Geol. Soc. America Bull., v. 66, no. 12, pt. 1, p. 1455-1488. ------1958, Stratigraphy of pre-Keweenawan rocks in parts of northern Michigan: U.S. Geol. Survey Prof. Paper 314-C, p. 27-44. James, H. L., Clark, L. D., Lamey, C. A., and Pettijohn, F. J., 1961, in collaboration with Freedman, Jacob, Trow, James, and Wier, K. L., Geology of central Dickinson County, Michigan: U.S. Geol. Survey Prof. Paper 310, 176 p. James, H. L., Dutton, C. E., Pettijohn, F. J., and Wier, K. L., 1959, Geologic map of Iron River-Crystal Falls district, Iron County, Michigan: U.S. Geol. Survey Mineral Inv. Field Studies Map MF-225, scale 1: 24,000. ------1968, Geology and ore deposits of Iron River-Crystal Falls district, Iron County, Michigan: U.S. Geol. Survey Prof. Paper 570, 134 p. Johnson, R. W., Jr., 1958, Geology of the Little Commonwealth area, Florence County, Wisconsin: U.S. Geol. Survey open-file report, 98 p. Lake Superior Iron Ore Association, 1938, Lake Superior iron ores: Cleveland, Ohio, Lake Superior Iron Ore Assoc., 364 p. Leith, C. K., Lund, R. J., and Leith, Andrew, 1935, Pre-Cambrian rocks of the Lake Superior region; a review of newly discovered geologic features with a revised geologic map: U.S. Geol. Survey Prof. Paper 184, 34 p. Lyons, E. J., 1947, Mafic and porphyritic rocks of the Niagara area: Madison, Wisconsin Univ. Ph. D. dissert. Nilsen, T. H., 1965, Sedimentology of middle Precambrian Animikean quartzites, Florence County, Wisconsin: Jour. Sed. Petrology, v. 35, no. 4, p. 805-817. Prinz, W. C., 1959, Geology of the southern part of the Menominee district, Michigan and Wisconsin: U.S. Geol. Survey open-file report, 221 p. (Results of investigation are included in Bayley, Dutton, and Lamey, 1966.) ------1965, Marinette Quartz Diorite and Hoskin Lake Granite of northeastern Wisconsin, in Cohee, G. V., and West, W. S., Changes in stratigraphic nomenclature by the U.S. Geological Survey, 1964: U.S. Geol. Survey Bull. 1224-A, p. A53-A55. Van Hise, C. R., and Bayley, W. S., 1895, Preliminary report on the Marquette iron-bearing district of Michigan, with a chapter on the Republic trough, by H. L. Smyth: U.S. Geol. Survey Ann. Rept. 15, p. 477-650. ------1900, Description of the Menominee special quadrangle, Michigan: U.S. Geol. Survey Geol. Atlas, Folio 62, 13 p. Van Hise, C. R., and Leith, C. K., 1911, The geology of the Lake Superior region; U.S. Geol. Survey Mon. 52, 641 p. Wichman, Arthur, 1880, Microscopical observations of the ironbearing (Huronian) rocks from the region south of Lake Superior, in Geology of Wisconsin: Wisconsin Geol. Survey, v. 3, p. 600-656. Wright, C. E., 1880, The geology of the Menominee iron region (economic resources, lithology, and westerly extension), in Geology of Wisconsin: Wisconsin Geol. Survey, v. 3, p. 665-734.INDEX Page Accessibility----------------------------- 2 Acknowledgments............................. 7 Aeromagnetic survey................48; pis. 7, 8 Age and correlation, Dunn Creek Slate.... SO Michigamme Slate------------------------ 23 post-Riverton strata...........-..... 54 Quinnesec Formation..................... 11 Riverton Iron-Formation------------------ 82 Amasa Formation, Baraga Group............ 11,13 Amphibolite, Badwater Greenstone_____________ 25 Hemlock Formation. --------------------- 12 Michigamme Slate ....................- - 20 Quinnesec Formation.--------------------- 9 Animikie Group------------------------------- 4 Animikie Series........................... 9 See also Baraga Group and Paint River Group. Argillite, chemical analysis..--------------- 28 Badger mine________________________ 4,27,31,38,48 Badwater Greenstone, Baraga Group............ 11 23, 24,30,35,37,48,48; pi. 2 Badwater Lake.............................. 24 Bailey, S. W., written communication-------31,40 Baraga County, Mich.......................... 11 Baraga Group, Animikie Series............... 11 See also Badwater Greenstone, Hemlock Formation, and Michigamme Slate. Bibliography................................ 51 B iotite metamorphism______________________ 40 Breakwater quartzite.-------------------- 5,21 Breccia, chemical analysis.................. 28 Brooks, T. B., quoted...................... 4 Brule River.............. 2,12,24,26,30,32,35,38 Brule River block________ 8, 11, 34, 37, 40, 41; pi. 2 aeromagnetic survey................... 48 Michigamme Slate_______________________ IS Buckeye mine-----------------------------4,48,51 Cambrian rocks____________________________ 8,84 Chemical analyses........................ 28,33,43 Chlorite metamorphism.................... 5,40 Climate------------------------------------- 2 C ommonwealth mine.......................... 4,48 Commonwealth syncline__________ 8,27,87,40,46,48 Crops....................................... 2 Crystal Falls............................2,8,30 Davidson mine............................4,31,48 Deposition conditions, Dunn Creek Slate__ SO Michigamme Slate______________________ 23 post-Riverton strata____________________ S3 Riverton Iron-Formation__________________ 32 Dickey exploration_______________________18,45 Dunkel exploration...................... 18,45,50 Dunn Creek Slate, Paint River Group............. 24, 26,87,38,39,41,47; pi. 2 Ernst mine........................ 4,30,48,51 Explorations................................ 48 Felch Formation__________________________ 46 Felch trough_____________________________ 9,46 Felsicmetavolcanic rocks_________________10,47 Fence River Formation, Baraga Group............. 11 [Italic page numbers indicate major references] Page Florence mine............................2,29,47 Forests...................................... 2 Fortune Lakes Slate, Paint River Group.. 27,32,33 Garnet metamorphism...................... 5,4/ Geology, economic------------------------- 47 general.................................. 7 previous work....................... 4 structural................... 8,25,37; pis. 1-4 See also individual structural blocks. Gogebic district.............- - -.......- - - 23 Goodrich quartzite, Baraga Group----------------- 11 Granite................................... 88 Graywacke, chemical analysis_________________ 29 Gray wacke-shale suite..................... 48 Greenstone, Badwater Greenstone.................. 84 Greenstone agglomerate, Michigamme Slate.. 88 Hanbury Slate-------------------------------- 4 Hemlock Formation, Baraga Group------------- 11, 12,38,40,43; pi. 2 Hemlock River.............................. 12 Hiawatha Graywacke, Paint River Group... 26, 31,33,48, 49 Hoskin Lake Granite................. 35,88,43,46 Huronian Series.............................. 4 Igneous rocks, basic......................... 48 Intrusive rocks............................. 84 Iron ore.................................8,46,47 Iron River iron-formation member, Michigamme slate................................. 5 Iron-formation......................5,7,15,18,45 Badwater Greenstone..................... 25 chemical analysis....................... 30 magnetitic............................... 50 Michigamme Slate............ 12,21,22,47,49,50 nonmagnetic............................. 45 staurolite zone......................... 4* James, H. L., quoted........................ 41 Keweenawan Series............................ 4 Keyes Lake block.... 8,11,24,34,37,88,40,41; pi. 2 aeromagnetic survey..................... 48 Michigamme Slate....................... 14 Lake Mary quadrangle......................... 12,43 Lake Superior................................ 2 Larsen exploration area.................... 51 Laurentian System____________________________ 4 Lineation.................................. 37,40 Little Commonwealth area................... 5,15 Little Commonwealth exploration............50,51 Little Popple River......................... 10 Location...................................... 8 Loon Lake................................... 39 Lower Michigamme Falls........................ 7 Lower P recambrian rocks................... 7,9 Magnetic anomalies..................9,13,18,22,25 Magnetic surveys................25,32,45; pis. 6,7,8 Marquette district........................... 23 Menominee range.......................... 2,5 Menominee River.................. 2,4,9,24,35,38 Page Metaargillite, Badwater Greenstone................ 88 Metagabbro........................................ 54 Metagraywacke, Michigamme Slate................... 88 Metamorphism............ 5,9,11,14,24,31,40; pi. 5 Methods........................................ 5 Michigamme Falls Dam........--------------38,41 Michigamme Lake........................... 12 Michigamme River..........................2,7,38 Michigamme Slate, Baraga Group-------------------- 4, 8,11,12,37,40,41,46; pis. 2,4 iron-formation............. 12,21,22,47,49,50 metagabbro. ................................ 34 structural blocks........................ 13,38 Middle Huronian Series_____________________________ 4 Middle Precambrian rocks______________7,11; pi. 4 See also Animikie Series. Mines................................ 2,4,88,47,51 Niagara, Wis________________________-..... 10 Paint River........................................ 2 Paint River Group, Animikie Series............... 12, 24,88,34,38,40,46 Fortune Lakes Slate___________________ 27,32,33 Hiawatha Graywacke_______________ 26,31,33,48,49 Riverton Iron-Formation----8, 26,80,47; pi. 2 Stambaugh Slate.................. 27,32,33,46,51 thickness............................... 27 See also Dunn Creek Slate. Peavy Falls Dam...........................15,38 Peavy Node, metamorphism_________________________ 48 Peavy Pond Complex......................... 37, 43 Phyllite, Michigamme Slate................. 80,23,41 Pine River..........................2,13,18,23,39 Pine River block................................ 8, 11,13,23,34,37,88,41; pis. 1,2 aeromagnetic survey......................... 48 Michigamme Slate____________________________ 18 Plagioclase, composition......................... 9 Pleistocene deposits............................... 8 Polderman exploration............................. 49 Popple River.................................... 10 Popple River block................................ 8, 11,22,34,37,58,48; pi. 1 Post-Riverton strata........................... 54 Purpose........................................... 5 Quartz graywacke.............................. 80,88 Quartzite..................................... 10,15 Quartzitic conglomerate, Michigamme Slate.. 21 Quinnesec Falls............................ 9 Quinnesec Formation....................... 9, 18, 34,36,39,43,46; pi. 1 Quinnesec Greenstone................. 5,9 Quinnesec Schist.......................... 4,9 Relations to adjacent formations, Dunn Creek Slate________________________________ 29 post-Riverton strata........................ 84 Quinnesec Formation......................... 11 Riverton Iron-Formation..................... 58 Riverton Iron-Formation, Paint River Group...............8, 26, SO, 47; pi. 2 Riverton mine..................................... 30 5354 INDEX Page St. Clair exploration....................18,45,50 Saunders formation..-------------------------- 5 Schist.----------------------------------9,12,20 Sillimanite zone------------------------- 5,42 Slate................................. 20,23,26 Spread Eagle exploration____________________14,49 Spread Eagle Lake______________________________ 5 Stambaugh Slate, Paint River Group_______ 27, 32,33,46,51 Page Staurolite zone---------------------------- 41 Surface features.............................. 3 Thickness, Dunn Creek Slate------------------ 29 Michigamme Slate_________________________ 23 Paint River Group_____________-....... 27 post-Riverton strata--------------------- 34 Quinnesec Formation--------------------- 11 Riverton Iron-Formation__________________ 31 Tuffaceous rocks, Bad water Greenstone____ 26 Page Upper Precambrian rocks_______________________ 7 Vegetation---------------------------------- 2 V irginia Argillite__________________________ 12 Virginia Slate----------------------------- 27 Vulcan Iron-Formation____________________4,46,51 Wausau exploration___________________________ 14 Wauseca Pyritic Member.--------------------- 27 Welch exploration_______________________ 30,49,51 U. -S. GOVERNMENT PRINTING OFFICE : 1971 O - 407 -694UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY UNIVERSITY EXTENSION-THE UNIVERSITY OF WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY 88°22'30" 45°52'30" f 5 O' 20' ^0 ■1 \Y V Seidel Lake 3375 IV NE i|FLORENCE 5 Ml. R 17 E. (FLORENCE WEST)]2.5 Ml. TO WIS 70 , mi TO WIS. lOlj 17'30" R. 18 E. Li-rr’j—^y. ICT7?------- 11 T *A?57 | 2 440 000 FEET 1 Y-' \--------- I COMMONWEALTH 2.8 Ml. ’l l Ml. TO HY. N 12'30" bm 7.C ,\ .21 gr o 0 c. gr' .....bb :LQ. j J 1" !<=> <• 1 e V© fX-; ©Qt \ | cimpgrtyna g V Xy| V-^V/isV'f........If?5/' 1300 >7 \ >>Al J350_^_ ' Gr^VQl Pi/ ^ r-FT---- V © \ } * IV \ i - W%> ° ipi 1111 Wk \t ■ V ■ mm f^OQ /JOO / \ ■ cJa . A4yy x yy- mMMmt mg- 19 '• \°©4 V." -*Q. v~_— x r WwMMM'v / \ -LL-■&■■■ •(Gravel Pit 11327 3375 / A/W (FLORENCE EAST) \U SPREAD EAGLE / Ml. / : 2 470 000 FEET ---------1---------i-- SPREAD EAGLE IU.S. 2& 141) 0s A/' R.18E. R .1£L 1 88°07'30" | XT'*——^-------------i 45°52'30" 0; y? f E Ac L T H " Sj •-V 77%77% Detail.of this area shown in figure 3 o - ik fi d/%i \ 5» o X Oo izQ5rlY-' :f^Xxx bm I200-.. : V «N W c~* 1 If M £ 1 o %- MJjf n\ jr T'Vofi' f Lake hi \\ 1 qmv / 1300 /- P *$>£ rnbj schist 47'30" a , 'uckskin H- 10 LSke z Z * *> * ’'t/w } l|||§i o 0~ XI 1.03. far A 1' qfv X. XX ? Halls \ Lake H'■343 A O LM.Xv! I© .0°' 7 220 000^ FEET A 24 xx, /<0. 45°45' 88°22'30" -CV- __ 2 420 000 FEET! Oi Base from U.S. Geological Survey, 1962 V-X/, - i j , .j / 7--H---•/ fAS' 1 IS 32: V tef/ /S£ r^O >34 :S\=*r=*==*r > f?8- \ Houseman ;Lake ,-cj: 6.,3«° -gravel Piti. BM J *! & i5 irror 13! ^4*44 !l- :j A 'V& frsrnestead ! / tP A? -^arkpH H..W ■fo | ^ ^//Boy Scq^ Camp qmv -4 l j \ /? r / n)j/J Z/o L\Z°° . y"' v ' / // ' 2 j - • I'-j/ /' y y / ;28/ vvyt ■j./A .A ^ /J089“ Tm ^ £SL, ' .c4V 1 MILE PROFESSIONAL PAPER 633 PLATE 1 EXPLANATION Dark tone indicates outcrop Light tone indicates concealed areas hgr 9rv aP^y peg^ Hoskin Lake Granite jranitt genei gray Granite, porphyritic and gr, granite dike generally pink, locally peg, pegmatite dike Intrusive rocks ir, granite ieg, pegmi ap, aplite Metagabbro and metadiabase sills and dikes pd Dunn Creek Slate INTERIOR GEOLOGICAL SURVEY. WASHINGTON. D.C. —1971 — G69I14 88°07'30" Geology by c.£. Dutton, 1955-62,and W.L. Emerick, 1959 4>0 I© .5 1 KILOMETER a bb Badwater Greenstone Greenstone and minor chloritic schist derived from basaltic lava flows bmq bm Michigamme Slate Mainly slate and quartz graywacke; some volcanic flows, pyroclastic rocks, and iron-formation 'y- bmq, quartzitic conglomerate r ... qfv aqfnvjT C CT3 qmv Quinnesec Formation Mafic and felsic metavolcanic rocks, locally alternating. qfv, felsic metavolcanic rocks; aphanitic to porphyritic metafelsite and sericitic schist qmv, mafic metavolcanic rocks; hornblende schist and amphibolite. Includes some metasedimentary rocks gru, gruneritic schist or iron-formation sch, quartz-biotite schist gn, gneiss Contact Long dashed where approximately located; short dashed where inferred; queried where doubtful. Most contacts covered by deposits of Pleistocene age D ? Probable fault Dotted where concealed. D, downthrown side; U, upthrown side-, queried where doubtful PLANAR AND LINEAR FEATURES (MAY BE COMBINED) JSL * X + Inclined Top determined by Top determined by Vertical graded bedding cross bedding Strike and dip of beds A Direction of top of layer, determined by ellipsoidal structure 35 | Inclined Vertical Strike and dip of foliation 75 A Bearing and plunge of axes of folded foliation Bearing and plunge of lineation 35 Inclined Vertical Strike and dip of joints 'k80 Strike and dip of joints in a system E Abandoned exploration shaft Vertical Inclined Inclined, showing hori- zontal projection of bottom of hole Diamond drill holes 88o22,30*’ 46° 00' |----- 52'30' d /a INDEX SHOWING QUADRANGLE LOCATION APPROXIMATE MEAN DECLINATION, 1970 CONTOUR INTERVAL 20 FEET DATUM IS MEAN SEA LEVEL GEOLOGY OF PRECAMBRIAN ROGKS IN THE FLORENCE SE AND IRON MOUNTAIN SW QUADRANGLES FLORENCE COUNTY, WISCONSINUNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 45°56 UNIVERSITY EXTENSION-THE UNIVERSITY OF WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY 88°16' PROFESSIONAL PAPER 633 PLATE 3 45°56‘ Long dashed where approximately located; short dashed where interred ,60 Inclined Vertical Strike and dip of beds B Abandoned shafts of Florence mine Trench X Test pit O- O Inclined Vertical Diamond drill holes Abbreviations bl black brc breccia cb carbonate ch chert, cherty OP graphitic grn green os greenstone gw graywacke ov gray hd hard hem hematite, hematitlc lim limonite, limonitic mag magnetic ox oxide PV pyrite, pyritic qt quartzite qz quartz ser sericitic sid siderite, sideritic si slate St siltstone tf tuttaceous vn vein Quotation marks indicate that description is from mining company reoords Base from U.S. Florence West, Geological Survey 1:24,000 1962 88°16' GEOLOGIC MAP SHOWING LITHOLOGY OF THE RIVERTON IRON-FORMATION AND ASSOCIATED STRATA IN FLORENCE MINE AREA, FLORENCE COUNTY, WISCONSIN 407-694 0 - 71Lower Middle Precambrian Precambrian k. r- 5* UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY R. 35 W. 34 33 PROFESSIONAL PAPER-633 PLATE 4 R. 32 W. Fault Long dashed where probable; short dashed where doubtful. D, downthrown side; U, upthrown side Anticline Syncline Showing approximate bearing and general plunge of axis Strike and dip of beds A Direction of top of layer determined from ellipsoidal structure R. 17 E. 18 Base from U.S. Geological Survey, 1955 R. 20 E. J____I___L 5 MILES BEFORE FAULTING AND EROSION BEFORE FAULTING AND EROSION GENERALIZED GEOLOGIC MAP AND SECTIONS SHOWING MAJOR STRUCTURAL FEATURES OF THE FLORENCE AREA, WISCONSIN 407-694 0-71UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY T. 42 N. T. 40 N. T. 39 N. T. 38 N. — X \ R. 32 W. T. 42 N. R. 30 W. T. T. T. 40 N. 39 N. 38 N. Base from U.S. Geological Survey 1:250,000 . „ „ Zones along Michigamme Iron Mountain, 1959; Iron River, 1961 "_________j_________-_________“________j MILES River from James, 1955 PROFESSIONAL PAPER 633 PLATE 5 EXPLANATION ;. , * h ** II H * \ PC* » // " H * *- » Peavy Pond Complex '^-hdrA/ -kiln's Hoskin Lake Granite Metagabbro and metadiabase r M ^ S ■ O e$ Paint River Group Riverton Iron»Formation shown in black Badwater Greenstone bm Michigamme Slate z < tr m o lu £E d Pre-Michigamme strata Vulcan Iron~Formation shown in black Quinnesec Formation Qfv, felsic metavolcanic rocks qmv, mafic metavolcanic rocks J Contact Fault Long dashed where probable; short dashed where doubtful. U, upthrown side; D, downthrown side + O • chlorite or Biotite or Garnet or equivalent equivalent equivalent Grade of metamorphism represented by one or more specimens Chlorite Biotite Garnet Staurolite Sillimanite Metamorphic zones GENERALIZED GEOLOGIC MAP OF FLORENCE AREA, WISCONSIN AND PART OF MICHIGAN SHOWING METAMORPHIC ZONES 407-694 0-71UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY UNIVERSITY EXTENSION-THE UNIVERSITY OF WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY PROFESSIONAL PAPER 633 PLATE 6 •429 131 •124 <2 •36 32 *\ 2. 12* •34 / / 17' / .22 *23 .23 .22 .46 > 27- \ / 71 V \ 71* \ \ EXPLANATION Outcrop or group of small outcrops Magnetic gruneritic iron-formation shown in red Contact Long dashed where approximately located; short dashed where interred; queried where doubtful D Probable fault U , upthrown side; D, downthrown side 97- •38 170 ■ 159* • 292 • 303 •200 •153 • 130 • 111 27 •148\ • 140 ' •135 • 132 • 135 •151 •159 •150 .135 •82 •80 •78 •72 •67 •63 •62 •60 •60 •78 .v •117 42 • 27 33 32 36 42 .46 .59 79 1142/' 147 in 18 98.1 100 117 •136 •39 1 •48 53- / / 56 •/ I >56 / -48 •50 , •636o ' §•657-•o *666 • 628 • 507 •110\-57*58 *71 '87 •296 •236 •78 .135. •191* •367. 141 241 *330’338283- *244 ^38 250' 234 • 250. •219 °o0 •71 > •142 •217 • 41 / .146 138.\ • 72 • 105 .203 353 370* -254 •3681 .>2000 ,222- (114. •244 -171 .365 •337' •298 •278 • 240 >375 •264 314, ,488- 402* • 291 .3761 -1364 454 •509 ■273 258 •309 •408 •437 •196472 •153 •125 .123 .104 >106 •291 •312 .233 *236 •204 •240 -202 '191 -167 •144 *140 >122 •122 •112 •190 •172 •155 .144 .133 .119 •398 ( 4 380 M26..I - - - 129\ 11* .119 •"&,, 541 4 593 .1 14 .116 1*15 1 •IOO4X0, (.192 .171 •151 •143 .151 • 189 •251 • 246 .119'' ?73 OOOl bool • 3181 • 430 ’ • 430 •#K Abandoned exploration shaft x Test pit Magnetic -determination Value in tens of gammas of vertical intensity above or below an arbitrary magnetic datum. Zero value is approximately equal to 57,500 gammas absolute vertical intensity ■1000- M ET A G /to B R O' .139^121 •240 •167 *204 .299 *245 •151 ^ .162 *119Y .100. 426 *173 .105 100 I •11 5\ I ►1051 • 125 .96, •142 •116 • 192 • 270 .147 1-283 644 ,•99 •312 • 480 .176 1 3* *74 x\ 186-' ■ 146\ • 234 • 205 •325 S11 • 1 365 • 304 .248 •775V 229 .274 196 .116 • 308 * • 359 • 201 ' 251 .212 .209/ •110 707 oP\ ,'V •354 .261 .330 $ 46°- ^>W,'12Vi0 A . * • ....................A l* ^ * . :<>• • - vsu: • 427 -184^25 \ <\0[\n1 62 38 25 JS9.X.7 Vj 35 .211 •49 \ 54 44. .19 18 21 23 21 22 18 .25 .63 \ 15 17 18 20 * 26 38 45 48 .50 .60 60 77 66 ’•123 166 .336/ 275* & ■A *> & y sr ~’ooo. .121 202. & •It^A - •58 co 572 .55 . 36 •• - , .61 .60 / -57 „ ,57 oV.57 85 50 47 43 43X43 46 0fc §S^ --------II II---«___a---s---*l 25 30 40 WISCONSIN 70 •57 36 31 ■m 9 104> «T I * NSSK* .71 181. •61 .123 *>*>**£- t 158-. • * * *j( 26 \ 126 • J f j ^V. %*)" ,0’ B I 006* •? fes 552- . \ l 18 '.2WJ160 .>& r?|218 •12^ •107 V103 •48 208 180 .1094 M 46 •637 127 cy>‘ .121 •42 *1 •S7n •35 .36 •2238 ^93 •769 -520 __ N *861 ^to-L327*. \ •A :>ei •63 •3 T*19 \ •24 lN y 8 4 •46 \( 00 •10J *61 23 i \ • 94* .129 \ •77 , ^<0 V y-24 0? nV-407 278 ^ .196 -309 •233 .co *197 •159 83> vSv T Ac 65* C\0 t\-Z- Ac^ ^\-51 V \ \ • 134 •161 •139 •337 •292 •314 •256 *224. •226 210 'b •345 .374 r*v-97 n£7206\ • •316 . 1 *1 •27 4f^'-,2\-6?48-27-'9( 440 *269 -115 "48 .15 263 *oL 292 *2f7 *49 ,13 4«6 .64 64 *13 •41 -2 N*c7 10 25 .31 ,29 *11 •15 •32 55- •35 •16 •7 *11 -15 .19 .23 *25 *28 -29 .33 -36 •9 .16 *32 o -28 !l63 / (•43 U l*74 \ •45 II If84 \ *55 II i r 64 ll •63 if83 •76 II |lS1 •89 II I *70 II •88 11 H / 1,63 / 85 40 ■43 37 35 33 36 37 81 ».-20 ,103 124 77 '•-8 V 159.’• •111 •52 -52 t 15 •30 .j •91 •76 .73 *76 .78 78 .62 •68 * •69 37. •90 ,'V * •72 • •153 .38 .22 .36 •53 .136 •160 •’.319, >.-4- 7 '3 • 54 •3s s -5 •28 •40 •17 ix • 6 •38 \ •1 CN •34 •24 X •52 s n-3 x •67 •68 •48 X . •69 Y J •18<. •92 •0% .80^1 26 • \ ATTP7.64 •< •188sc 54. *727N ' c . •54 •52 •41 •53 •63 •69 •71 63* •31 •29 •31 N •51 V5’258 -59 -63 .7 \ 78* .189 .181 .’220 •21 •42 .-7 r64 iCr '.232°°i •‘l72 .210 .138 .144 320- 460- •144 .23 •47 • 97 .227 t>2 \ .2^, .36 .50 ,61 • 70 81 >30 •67 •89 •53 \ \ >81 •66 \ \ 71* 63- >77 \ \ 63. •19 \-8 \q -10 *13 -21 •5l\.134*Y *36 *6 \ • 36. 3.6, •1 •6 x^* .-6 Vi4 •24 .3 jC-13 65 --0, .75 •21 fc-1 •-17 -'18J J’12 •-2Z nc *•71 •42 138 .57 *71 *54 *51 > •42 191 • .149 220- \ % -SX \ ^ -\ 3-^.1 -4 £ <447 ^ -154 °o -221 •117 .194 V; •169%1 -38 , poo -36 | -86 -200/. • 76 •391 .165'' 122 220. • 215 \072, T36i 149. 102' .102 • 186 -2 ,00°' 196 \ • 55 .6 *77 .87 ^1000-1 •192 -16 • 312 •82 •60 •37c -28 •399 •23 1 '•144'’.HI •272 •117 •401 72* •104 •32 •62 .53 •33 •(0 •57 •33 •47 •69 •39 •37 .69 •48 •4! MMf-31 •68 •53 •11 •89 • 51 .12 •43 •48 .12 103y 57 ' •45 •133" •81 •46 -8 .175.275 •74 -49 >150 >200 • 803 •45 SOS'1 .1021 '°On* 103 "70 40- I 133 .157 •38 •2000c •24 70o •64 • 28 -9 112 //i 5___.^*14 18 ,2^^V$4 LL 9 ^♦28.' h 373 s\/_ -9 *177 ,Y33.2?1, ,x .134 //242 .250/.X -38 .119 *170 .216/ \Q9 -32 .127 V142 .179/-260 .153 ft 121 .151/ 179>^.61 444 -190 *120 -125 L347 104, 470 .232 “134 ,126 l .222 302 .271 lj,66 .133 ' 341 \ •140 18 81 ■74 •94 *84 “63 *49 *39 "33 134 • 127 \11L48 - ; ‘T23_ \ •59 •13 •91 288 X •264 ►150 •239 U185 ns -187 n2i9 •280 •412 •138 ( •128 260 ^967 •150 173 205 •145 *199 1R,\ V84 *74 •162 \ \________ •135 „97 •161 \\227 • 177 'p.200 ** 334 78 *241 - 'll 64-261 -133-162 *230 14^N •138 •221 ,241\#^#V 13§ •58. •98 .17 •141 482 $. • • •208 )156 0317 •209 *362 ’84«V".241 V c"201 15B/*155.218 X283 168 138 •140 •32 •65 ™METAGA^2S \ i * T. 40 N. T. 39 N. 34 \ ,^A-440l .56 25 •89 .76 .-2 •39’. • 53 ill Oi r*-i8 407 16%q7 .212 -219 -I27 1/233 *237 2297 >(779 305/1*290 -324 -285 .159 546^84 433/235 ^•1890LV<. 4.JJ \o ,7'4V,556 ‘N° -221 \087 •185 , •317 •283 A \ •N AT •196 £> 1 •82X •120 1 •87^ •222 •336 \ •63 j •51 •181 •419 1 €0 4k •36 •142 •361 1 •48/ •226 •214 •86 105- *175 •119 • 89 72* •86 •192 138/ •54 •63 •48 197 l"? • 64 •37 KEYES LAKE 410 •65 •29 •19 •17 •22 •22 •24 i 1 «>JV *■’ .a’1 4* 12 4 •71 *78 -65 -64 -7- -1441' . 173^^ -15 •60 •28 •28 •33 •33 36 -41 „ 49- X31 79,^861 62 ’,*73 69 45; 31 24 ?3 22 21 •24 •27 * 32 * 38 *39 • 44, z •11 V •18 \420* 151- •92 •20 •13 V.\58 -36 -29 *31 -34 •135 •415 .1 25 320- •114 •156 •147 •140 \\ ^ V50 '\*388 ll ‘,33\ 4/>/i •3 54 n / .27k \ ) / 456 j •33 y/ • *2(17 •35 336 / 432 \ 335 105* •116 •127 •89 •96 10 82- . .V u u ,(>382 /' -429 II A02 >8 Aei gi50 u 'ft 122 V*113 161 \\ 151 135‘ \190 .114 •176 X^J43 nn^ ^ / & #*** 285 \128 121- 191 117 •93 •84 •81 •79 •77 •84 76 •40 •43 •61 •59 •69 •79 77* •24 | I •30 i •35 •41 I • 45 •29 •35 •42 •41 > 46* 52* •46 57* \ 62* •53 \ \ • 59 \ •52 *57 •61 68* 68* 67* •82 81 •69 •78 >\ 66 74 •64 ■ 6K 65- 98 94 99 92 94 93 Q1 88 ,61 •101 10S- 95* \ GRASS LAKE •95 102- 125 ■ 101- 111 120-V 183- .° n •207 e. 270 150. :140 \-i87 •145 •132 •136 •125 •112 .100 •100 114 109 \. 170 132* 117-113.- \ si 27 74 74- 89 \ VI28 80_ 79^ 75 . K69 r75 r109 7 85 45 51 55 •109 •245 •215 •166 •140 •120 •120 •128 ^*130 \ 126 119 nn* 129* ' *115 •123 •159 V„ 1 so- ies* 116* 1144 K<0 •78 •64 •74 •71 •76 •74 •80 •74 •79 •77 % 0 \ •89 •88 •109 •128 , 138 iC? .^0 # y • /AS! •149 •152 •176 •129 158- •99 •102 •108 •105 •99 *103 •104 •110 •110 •102 •111 *138 •153 •133 •76 70* 7138 •102 /131 •150 > •122 97* M02 yA0 |0°" •86 81* 113. 97 390* % 377 429 263 /317 183* 207 324 LOON LAKE •170 *175 •218 1177 •166 64 •225 225* VN# */189 •170 202* 223* •142 *150 158* O'n* •140 •129 •146 •135 •122 •140 163* N&l •112 •112 V120V 013 • \ •120 •124 •124 •134 123 •140 •127 •125 •121 •130 013 106 110 ■ •142 •134 •130 •132 •137 •150 •159 •164 •174 135* 125* *1 3? •75 118*1 60* \109 •120 •109 •118 •158 •270 •276 60* N 81* •1(13 •12l •133 •75. 71 •68 •73 70* •74 •70 *70v •67 •65 61 •59 •62 •66 ■67 •240 •190 450* -->r k149 130* •730 *36^ k194 .115 ier /76 -1150 -150 •75 •68 •75 •70 •70 •55 •53 •490 •68 •64 •66 •55 •56 •51 •52 •66 -52 11 2 1 11 12 •90 •81 *75 ■ 73 90> K.107 •92 •58 88^ 87 •83 •85 •80 •80 •72 A107 •212 004 004 •200 •130 •56 •212 •62 •60 •55 •50 •45 •40 •37 •37 •36 •47 •60 •68 •68 • 60 •54 •49 • 46 •42 •38 •36 •32 •38 •40 •52 •44 •50 •52 •54 •59 •62 •61 •62 •65 •68 •69 •69 86 -68 Ax •67 •' -68 •64 •71 •62 *711 •60 69* I •53 QG* •45 160 768 •40 •36 •33 •30 •33 •26 t62 751 ▼ 38 36c- •38 22- ■182 95* 85- 85* 80- \63 •\216 \ 308 -225 •74 J00 42- 49- /41 12 208 •238 -,4g> V2 •45s\>47 161*> 93- 95- 92* \ •150 63^> 67 v. 74^, 75 V' •124 •111 •108 •106 •91 •86 • 80 •76 •72 •74 Nl86, O./ \ 137*' •113 xn\56 125*, 116' 106 75^ 78 79 83 87 90 77 73 73 \ \ 150^ •175 •185 •67 •137 \ •1 20 \ •185 •297 .81 \ •143 85 •105 \ -1000- X 135 86 86 78 76 \ •91 •1 25 X •230 •222 •300 \ •60 •64 245 X •58 •158 X X •55 •53 74 *54 73 •120 •115 X •125 •145 \165> X •146s •123 •105 .56 .60 67 927 90* 84. • 61 •68 •72 >80 •83 •84 •82 •76 •83 •87 •89 •76 82 •/ 81* ,90 9, •91 85 86 107 85 •63 •66 •67 •60 •39 •69 5Y~'N\ 59 68 cc- \\ • 62 \\ •57 \\ Jt .Vfil •68 W •61 " •65 y/ = 63 •70 •70 •65 •71 •74 O j ) ! 68 •76 79-1 •81 867 •86 •89 • 92/ /90 *81 796 195 89" •99 797/ 88 , 96 •95 •99 •100 • 101 •103 •99 •84 •89 •94 •106 •107 •104 *102 •80 •83 •71 •79 •80 •80 •83 •85 •90 •96 •101 •101 •101 103 .73 .77 71 71 71 79 80 78 73 •81 •81 •83 *93 \ ll l9A 94Vn .93 8\\ .82 V6 \ rl 6 5 \73 71.\ •159 \ •88 •200 / •88 / / CD 00 •77 •84 \ •191 ' V 86 •93 •61 •77 ' •174 • 119 •87 •70 •75 1 *140 •158 x •50 •57 •74 \ *123 • 153 •127 \*106 • 144 •149 •62 •66 •164 •64 •130 •63 •61 00 CD ><113 •157 •G5 •62 •81 •95\ •135 •65 •64 •70 • 80 \"110 •66 •61 • 68 •71 •94' •65 •62 •64 •64 •80 •67 •62 •63 •60 •72 •70 •60 • 60 •58 •56 •66 •62 •68 •61 •56 •57 *62 •69 •55 •71 •63 •56 •54 •59 •71 •63 •54 •53 •57 •62 •52 •52 •73 • 53 67 *73 .63 .61 .58 •80 *37 •50 *51 •51 *56 •112 X >0\97 •10fcv •87 •76 * 128X •82 X '°o0 •96 X*126 •122 00 00 •122 •123 •96 % •169 •121 \ ^ 99 •122 •158 • 102 • 1 35 \*112 •112 •112 • 105 •1 iS'v. •101 •100 • 102 •92 •93 ^96l\ • 102 •87 •90 •93 \ • 101 •85 •92 •96 \ • 102 •84 • 93 •94 \ -102 •83 •93 • 97 \ *102 •86 •89 •96 \ *106 •82 • 87 • 94 \ 107 •83 •84 •90 •9fl •82 •82 •89 •94\ •79 •82 •84 •88 •81 • 81 •83 •87 •77 •79 •81 •86 •78 •71 •81 •87 •77 •79 •81 •82 •76 •79 •81 •83 •76 •79 CN CO 0 00 • 82 -82 T. 39 N. % % 500 500 2000 2500 FEET 300 400 500 METERS •84 78 •78 •78 •73 -60 •49 .43 •91 •87 *86*87 *89 -90.93 -95.97 *98 •"'°> .N<^ .N0<5 •85 •99 -97 -P* Y Base from U.S. Geological Survey Florence, Wise.-Mich., planimetric quadrangle, 1:48,000, 1939 Magnetic survey by K.L. Wier and R.A. Solberg, 1958-59 MAGNETIC AND GEOLOGIC MAP OF AREA NEAR KEYES LAKE, FLORENCE COUNTY, WISCONSIN 407-694 0-71UNIVERSITY EXTENSION-THE UNIVERSITY OF WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY 52'30" Jr \ vv ^ PROFESSIONAL PAPER-633 PLATE 7 EXPLANATION Magnetic contours Showing total intensity magnetic field of the earth in gammas relative to arbitrary datum. Hachured to indicate closed areas of lower magnetic intensity; dashed where data are incomplete. Contour interval 25, 50, and 250 gammas .1380 Location of measured maximum or minimum intensity within closed high or closed low Flight path Showing location and spacing of data NOTE Aeromagnetic data are obtained and compiled along a continuous line, whereas ground magnetic surveys are made at separate points. Errors within the normal limits of any magnetic measurement may cause slight discrepancies between flight lines in an aeromagnetic map, which would be more obvious than similar discrepancies between points in a ground magnetic map. For this reason as much care should be exercised in evaluating magnetic features that appear as elongations along a single aeromagnetic traverse as in interpreting an anomaly indicated by a single ground station NOTE: See plate 1 for explanation of geologic symbols 45°45' 88°22'30" 2 420 000 FEET qCT1 Bose from U.S. Geological Survey, 1962 (GOODMAN 148 000) R 17 £ R 18 E 3375 III V 15' SCALE 1:24 000 * V Vi 1 MILE % 1 KILOMETER APPROXIMATE MEAN DECLINATION. 1970 CONTOUR INTERVAL 20 FEET DATUM IS MEAN SEA LEVEL AEROMAGNETIC CONTOUR MAP OF THE FLORENCE SE AND IRON MOUNTAIN SW QUADRANGLES FLORENCE COUNTY, WISCONSIN 407-694 0 - 71^3>°v PROFESSIONAL PAPER-633 PLATE 8 Magnetic contours Showing total intensity magnetic field of the earth in gammas relative to arbitrary datum. Hachured to indicate closed areas of lower magnetic intensity; dashed where data are incomplete. Contour interval 25, 50, and 250 gammas Location of measured maximum or minimum intensity within closed high or closed low NOTE Aeromagnetic data are obtained and compiled along a continuous line, whereas ground magnetic surveys are made at separate points. Errors within the normal limits of any magnetic measurement may cause slight discrepancies between flight lines in an aeromagnetic map, which would be more obvious than similar discrepancies between points in a ground magnetic map. For this reason as much care should be exercised in evaluating magnetic features that appear as elongations along a single aeromagnetic traverse as in interpreting an anomaly indicated by a single ground station NOTE: See plate 2 lor explanation of geologic symbols APPROXIMATE MEAN DECLINATION, 1970 CONTOUR INTERVAL 20 FEET DATUM IS MEAN SEA LEVEL AEROMAGNETIG GONTOUR MAP OF THE FLORENCE WEST AND FLORENCE EAST QUADRANGLES FLORENGE COUNTY, WISCONSIN, AND IRON COUNTY, MICHIGAN 407-694 O - 71UNITED STATES DEPARTMENT OF THE INTERIOR 88°22'30" 46°00' GEOLOGICAL SURVEY ! 600000 FEET (MICH.) 2 O' ,RON RIVER (VIA US. 21 23 Ml I 3376 III SE IRON kivekjVtal pALts e Ml A (CRYSTAL FALLS) UNIVERSITY EXTENSION-THE UNIVERSITY OF WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY; AND MICHIGAN DEPARTMENT OF CONSERVATION, GEOLOGICAL SURVEY DIVISION 1 630 000 FEET (MICH.) 57'30" 36 X- f V psV. \V 1; *\4 \i MQ -M i 17'30" 2 440 000 FEET (WIS.) V bm V Pf „Dh' nss 4 ,51 j4Ule4nc&k^ km ix pd StageAXX) X i • -**->?* —10- 1 _ A ■*“ -*■ I < •X (P PS' • I w x\ 3 i in QV) \ , % . X. khz x 9 Ti.. -<► -_*KX ~=* 'Y -* ^ ,36°' v \ lrm R. 32 W R 31 W 63000° FEET (MICH.) 12'30" I pc 3376 II SW (LAKE MARY) 10' bm BM 1289 mg IX /ja& T v. -J \vkX= 1 v^oa 2 470 000 FEET (WIS.) U9 ■* -• hot O) Gravel X prts ^ 16 i'- «*- X^r; *,iva/c 55' 2.X (210 Li-. / , ■ \©» X 7 \ \‘V T. 40 N. 270 000 FEET (WIS.) T 39 N. “81 45°52'30" ►9“ ♦"*1 5 114 trV% /VAx ■ £ v^X\ Mb V X \ 7V77&S-- V ■ , %v, X%:)vXv & Kt fA \ ■ % mg , ^Lu ^ K \ X-x x . HTQr °o pH .\xxxT\y lie key \\ C •, bb /iSk * _•*- Float J Afud i. ~.«o\ j\l_ X - . 'K It T t4&C) x\s^ ( 5°«- ot/fp, X ’On /^Float 1 V < •- xq • 5. < S /^> o V^T^g>Ni4^97^.;: ' ■>,Vx rtk % "P'JiJp ,'V X X it&i- s-P ■ • r* 7 \ »-■-_____ ■ /' « - > ■0 l\ ( \ I, ^ oyj«> 0 j Yr^26, ;«f \ , j. -j ^ > X / / ^ JI^X r _ v J-'i L V n t*rv V °x Xvsx:jx Sr *1 r"N * \ v'X'sSjXs !< f\Vo ^j! V V 33 af i K “Ax ( | \ / U / *5 >4V v v, v i i J vs ■ ^fT'ing X Detail of this area ghoWn in plate'5(K[) ///y ( c_i38° \A ~'3So ' ) \ /\386X ( XT 5- / Ax XT- -* Ti A ^ )/ . -c‘ S ^ lix „-T f.i-337 k1380 bm ;/-3oT II 7X300 Power |>ro^ F^lls Qa£n ^>oo ST, -(300 X V \\ t5 v/« T v x?o; : 7 j--/X V - - / X-’j2r ; X mg W'-takO :j.6i7 -^,300'y ->3o°o44 q '*7 f\/,' © 'VOo- mg ■(^F bb X0' 14 T \ \ \ \ x \ .4 v ^9 Prv J ■ .-j: .-. oWatf ( j| v N.l TIN j[.;.-..li. tm4j .Wooaiawp. V TiSfci#7 sher Lake} 1276 bb COO%~: X*t'' A" Tm9 A c? \ X —r—^ - X X >i v X -a X i \X.xXk V « XCl /3«7' - , O _ -c \ .1300- •V • * \ --- ---- pd XT JP9 ' ■ 4T i .ass \ v V 4 T -^Xlfr ' >l3o° arloMl ake \ { W ! 0, 23 M F IL- 0 R XCE /> V^00 o >X3\>: sy "'r '*Oo I N T V X W’ "X2%-rl,g _ ;70 IT ro 2X X :TX*?^ y J;. ------------------1 ^k,,oov \ 7<00. \ \ 1} l^**04 W Par-X;/A0" v^l X Little C ommomvealflr7— ft bmq al o o < Poloerpian Jhnn w /259 88o22'30" Base from U.S. Gp^i - io*9 e°'°gical Survey, 1^02 Ol A, o/y uSb ~f, 7*00 7 Via... bm /joo -*4 H pru 19 I'El. %lx. Cohimonwealth [im.... • X. XIvXn1 g»XT sktWsT-Vx v X V NpnX M'e'c/’ 5\r '•> ,/4.00; r Buddie^ V TaWo^l 1\ Xi-XXXT'4'00 " ----- / Xt^t—*■— 11 Xi 00 on T ■ q Ktit T1 Michigamme Slate Mainly quartz graywacke and micaceous quartz slate bmq, quartzite and conglomerate bmi, gruneritic iron-formation and garnetiferous schist th Hemlock (?) Formation Amphibolite; mostly massive; some derived from agglomerate or coarse tuff -A-4___ Contact Long dashed where approximately located; short dashed where inferred; queried where doubtful. Most contacts covered by deposits of Pleistocene age D ““7 '"'7'.... Probable fault Dotted where concealed; queried where doubtful. U, upthrown side; D, downthrown side X iQx-’ 30 bb 55' 4 -n- -R- i 29 A 28 — T OMNFpNWEALTTH V ■' T4271I IX V ~ v “IT ::V t \ \ f *" pr "1320- X 30° Si 0 ; M- M 0 _jN (306 l, J27! ''tillin''-. 420 000 FEET (WIS.) 20' ___...._ .JirpxX . . (FLORENCE SE) i FERN 5 Ml. 3375 IV SE ' 18 Ml. TO U. V X '8- *«T8 9 "I, 9 :s(2); ==J-^r^. J1325 X" _~JL x—' m Lake / —Robbins j \X v / 4 aqx v i;(iT Middle Lake\t ^ (MICH.) Anticline Syncline Overturned Overturned anticline syncline Folds Showing approximate position of trace of axial plane and direction of plunge. Small arrows indicate direction of dip of limbs ragfo Minor folds, showing plunge Anticline Syncline Dragfold Closely spaced folds, showing generalized strike PLANAR AND LINEAR FEATURES (MAY BE COMBINED) Inclined Overturned Vertical Top determined by Top determined by Top determined by graded bedding graded bedding cross bedding Strike and dip of beds * Direction of top of layer determined by ellipsoidal structure 35 | Inclined Vertical Strike and dip of foliation Bearing and plunge of axes of folded foliation Strike and dip of cleavage --->25 Bearing and plunge of lineation • ________________ Magnetic crest ERNST m y Welch Abandoned shaft Capital letters indicate mine shaft; capi tal and lower case indicate exploration shaft W Trench x Test pit • •- Vertical Inclined Diamond drill holes Large circle, diamond drill hole; small circle, churn drill hole yr<7C 10. m mL %■ .C2_. < 88°22,30* 46° 00' 15' 88°07'30' MU Xx)' 1200 C2> 4 oV rM,iroE??!\ , \ | ...- a -- -i rjDiagenesis of Tuffs in the Barstow Formation, Mud Hills, San Bernardino County, California By RICHARD A. SHEPPARD and ARTHUR J. GUDE 3d GEOLOGICAL SURVEY PROFESS Physical properties, chemistry, and origin of silicate minerals formed in silicic tuffs of a lacustrine deposit ONAL PAPER 634 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1969UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 79-650237 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 50 cents (paper cover)CONTENTS Page Altered tuffs____________________________________________ 17 Field description_____________________________________ 17 Petrography_______________________■________________ 18 Nonanalcimic zeolitic tuff________________________ 19 Analcimic tuff____________________________________ 20 Potassium feldspar-rich tuff______________________ 20 Clinoptilolite-analcime-potassium feldspar relationships in the Skyline tuff____________________________ 21 Relationship of authigenic silicate mineralogy to thickness of tuffs__________________________________ 26 Genesis of the authigenic silicate minerals________________ 26 Interpretation of a saline, alkaline depositional environment for parts of the Barstow Formation___ 27 Correlation between salinity of depositional environment and authigenic silicate mineralogy_______ 27 Solution of glass to form alkali- and silica-rich zeolites________________.________________________ 28 Reaction of alkalic, silicic zeolites to form analcime_ 28 Reaction of zeolites to form potassium feldspar____ 30 Metasomatism during diagenesis of tuff_____________________ 32 References_________________________________________________ 32 Index____________________________________________________ 35 ILLUSTRATIONS Page Figure 1. Index map showing location of the Mud Hills________________________________________________________________ 2 2. Diagrammatic sketch showing X-ray diffractometer patterns of authigenic silicate minerals---------------- 3 3. Generalized geologic map of the Mud Hills and vicinity__________________________________________________ 4 4. Photograph of the Barstow Formation along the axis of the Barstow syncline_______________________________ 5 5. Generalized columnar section of the upper part of the Barstow Formation__________________________________ 6 6. Photographs of typical lacustrine mudstone of the Barstow Formation______________________________________ 7 7. Photograph of casts of mud cracks on bottom of Dated tuff________________________________________________ 9 8. Photomicrograph of altered tuff, showing analcime crystals______________________________________________ 10 9. Determinative curve for the anhydrous composition of analcime___________________________________________ 11 10. Histogram of the silicon content of analcime____________________________________________________________ 12 11. Photomicrograph of zoned clinoptilolite crystal_________________________________________________________ 13 12. Photomicrograph of oscillatory zoning in clinoptilolite_________________________________________________ 13 13. Photomicrograph of spherulitic phillipsite______________________________________________________________ 16 14. Electron micrograph of potassium feldspar_______________________________________________________________ 17 15. Photomicrograph of altered Skyline tuff, showing segregations of quartz in finely crystalline potassium feldspar________________________________________________________________________________________ 17 16. Photograph of hogbacks formed by altered tuffs______________________________________________________ 18 17. Photograph of clinoptilolite-rich part of Skyline tuff______________________________________________ 18 18-22. Photomicrographs: 18. Zeolitic tuff, showing pseudomorphs of shards_______________________________________________ 19 19. Zeolitic tuff, showing pseudomorphs of fibrous clinoptilolite_______________________________ 19 20. Zeolitic tuff, showing pseudomorphs of clinoptilolite and mordenite_________________________ 19 21. Plagioclase with potassium feldspar overgrowth______________________________________________ 21 22. Potassium feldspar pseudomorph after plagioclase____________________________________________ 21 23. Geologic sketch map showing the sampled locations of the Skyline tuff_______________________________ 22 ill Page Abstract_______________________________________________ 1 Introduction____________________-...................._ 1 Previous work_______________________________________ 1 Scope of investigation________________________________ 2 Laboratory methods................................. 3 Acknowledgments_____________________________________ 4 Regional geology___________________________________________ 4 Stratigraphy and lithology of the Barstow Formation.. 5 Conglomerate, sandstone, and siltstone________________ 6 Mudstone______________________________________________ 7 Carbonate rocks___________________________________ 8 Tuff................................................ 8 Authigenic minerals_______________________________________ 10 Analcime-__________________________________________ 10 Chabazite______________________________________ 12 Clay minerals________________________________________ 12 Clinoptilolite___________________________________ 12 Erionite________________________________________ 14 Mordenite__________________________________________ 14 Opal_______________________________________________ 15 Phillipsite__________________________________________ 15 Potassium feldspar. ............................... 16 Quartz_______________________________________________ 17IV CONTENTS Page Figure 24. Photograph of Skyline tuff, showing remnants of clinoptilolitic tuff surrounded by analcimic tuff___________________________ 25 25. Photograph of Skyline tuff, showing remnants of clinoptilolitic tuff surrounded by analcimic tuff and potas- sium feldspar__________________________________________________________________________________________________ 26 26. Plot showing the correlation between the silicon content of analcime and the precursor zeolite--------------------- 29 27. X-ray diffractometer traces of synthetic potassium feldspar, natural potassium feldspar, and natural clinopti- lolite_________________________________________---------------------------------------------------------------- 31 TABLES Page Table 1. Mineral content of the finer than 2/i fraction of five mudstones--------------------------------- 8 2. Chemical analysis of mudstone___________________________________________________________________ 8 3. Chemical analysis, molecular norm, and semiquantitative spectrographic analysis of shards from Hemicyon tuff_________________________________________________________________________________________ 9 4. Formulas of selected alkalic zeolites______________________________________________________________ 10 5. Chemical analyses and composition of unit cell of analcime and chabazite--------------------------- 11 6. Chemical analyses and composition of unit cell of clinoptilolite----------------------------------- 14 7. Chemical analyses and composition of unit cell of mordenite and phillipsite------------------------ 15 8. Mineralogic composition of the Skyline tuff as estimated from X-ray diffractometer patterns of bulk samples. 24DIAGENESIS OF TUFFS IN THE BARSTOW FORMATION, MUD HILLS SAN BERNARDINO COUNTY, CALIFORNIA By Richard A. Sheppard and Arthur J. Gude 3d ABSTRACT The Barstow Formation of Miocene age consists chiefly of lacustrine and fluviatile clastic rocks. Lacustrine rocks are mainly mudstone with interbedded tuff and carbonate rocks. The tuffs make up about 1-2 percent of the stratigraphic section and are the most conspicuous and continuous strata. Most tuff layers are less than 1 foot thick, but some are as much as 7 feet thick. All tuffs were originally silicic, and most were vitric and fine to very fine grained. This report summarizes the physical properties, chemistry, and genesis of those silicate minerals that formed in the tuffs during diagenesis. Zeolites, monoclinic potassium feldspar, silica minerals, and clay minerals now compose the altered tuffs ; parts of some tuffs, however, contain as much as 90 percent relict glass. The zeolites are chiefly analcime and clinoptilolite, but local concentrations of chabazite, erionite, mordenite, and phillipsite have also been found. The zeolites and potassium feldspar occur in nearly monomineralic beds or associated with other authigenic silicate minerals. The zeolites, except analcime, are locally associated with relict glass; analcime commonly is associated with the other zeolites; and potassium feldspar is associated with analcime as well as some of the other zeolites. Nowhere in tuffs of the Barstow Formation is either analcime or potassium feldspar associated with relict glass. Solution of silicic glass by moderately alkaline and saline pore water provided the materials necessary for the formation of zeolites and, subsequently, the potassium feldspar. The zeolites, except analcime, formed directly from the glass by a solution-precipitation mechanism. The observed paragenesis of zeolite minerals is attributed to variations in the activity of Si02, the activity of HzO, and the proportion of cations in the pore water during diagenesis. Much, if not all, of the analcime in the tuffs seems to have formed from alkalic, silicic zeolite precursors. Analcime in the Barstow Formation ranges in its Si: A1 ratio from about 2.2 to 2.8 and thus falls at the silica-rich end of the analcime series. The silicon content of analcime is believed to be inherited, at least in part, from the precursor zeolite—relatively siliceous analcime formed from a zeolite such as clinoptilolite, whereas relatively aluminous analcime formed from a zeolite such as phillipsite. Potassium feldspar, like analcime, has apparently not formed directly from the silicic glass. The formation of potassium feldspar from analcime and clinoptilolite is documented; however, feldspar may have also formed from the other precursor zeolites. Tuffs such as the Skyline tuff of informal use show a lateral gradation in authigenic mineralogy of nonanalcimic zeolites to analcime, and then to potassium feldspar. The chief factor responsible for this lateral gradation is probably a variation in the salinity of the pore water trapped in the tuff during deposition. Highly saline pore water during diagenesis favors the ultimate formation of analcime or potassium feldspar in the silicic tuffs, rather than the formation of zeolites such as clinoptilolite and phillipsite. INTRODUCTION The Mud Hills are in west-central San Bernardino County (fig. 1), Calif., mainly in T. 11 N., Rs. 1 and 2 W. The nearest principal town is Barstow, about 10 miles to the south. The Fort Irwin Road, a paved highway between Barstow and Fort Irwin, provides access to the Mud Hills by way of the graveled Fossil Bed Road. The area is shown on the 15-minute topographic maps of the Lane Mountain and Opal Mountain quadrangles by the U.S. Geological Survey. The Mud Hills are in the western part of the Mojave Desert, which is characterized by isolated mountain ranges surrounded by broad alluvial plains. The Mud Hills range in elevation from about 2800 to 4200 feet. Numerous canyons radiate southward from the north-central part of the Mud Hills and provide access to nearly continuous exposures of the Barstow Formation. PREVIOUS WORK The Barstow Formation contains rich vertebrate faunas that have received much attention since the pioneer work of Merriam (1911). Lewis (1964, 1968) reviewed the nomenclature of the Barstow Formation and discussed the faunas. As these topics will not be considered here, the reader is referred to Lewis’ reports. The rocks of the Barstow Formation, unlike the fossils, have received only cursory study except in recent years. Baker (1911, p. 342-347), Pack (1914, p. 145-150), and Knopf (1918, p. 257-259) briefly described the Tertiary deposits of the Mud Hills. These deposits include the Barstow Formation as well as the underlying formations. Durrell (1953) studied the stratigraphy of the Tertiary deposits during an investigation of strontianite deposits at the eastern end of the Mud Hills. Like most earlier workers, Durrell (1953, p. 24) 12 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. 117“ ______________________ ________________ 116" f — Slocum ^Mountain r T 30 S T 14 N Fort ^Irwin 1 / f < ^Baker Cuddeback Lake 31 13 / / m 32 47 TOT XI R4 IE Pee 42 k 43 M BlacA ountair 44 X xOpa Mou 45 nta n 46 12 R1E 2 3 X */** 5 6 7 \ 8 $odd : \ Lake f \ up N, Harper Lake Figure 23 MUD Lan ^-T^Mour HILLS e tain 11 f Cwotes \Lake::i -v./‘ A ramer Hinkley Z < q a LI CALICO 10 MOUNTAI NS OiKSP-—'' ..J" 0 1 i i , 11 ., il lli 1 , ll 1 1 1 , . i, Potassium feldspar n V i r i f 1 1 1 | 1 1 f | II 1 1 1 1 n i i i *1 r-n i i —1—1—l—i—| 1—l—i—l— 2.0 2.5 3.0 3.5 4.0 5.0 6.0 7.0 8.0 9.010 15 20 30 50 100 CuKa, IN ANGSTROMS Figure 2.—X-ray diffractometer patterns of authigenic silicate minerals. Copper radiation with nickel filter. Relative intensities indicated by height of lines above base line.4 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. from the bulk patterns until all lines are identified. This procedure made the identifications routine and helped the analyst recognize minor or trace amounts of constituents. Mordenite in samples that are chiefly clinoptilolite is difficult to detect on X-ray diffractometer patterns because these zeolites have many coincident peaks. The technique described by Sudo, Nisiyama, Chin, and Hayashi (1963, p. 10) was found useful for the discrimination. Powdered tuff is treated with 6A7 HC1 for 1 hour. This treatment causes decomposition of the clinoptilolite, but the mordenite persists. The “pure” mineral separates were prepared for chemical analysis from nearly monomineralic tuffs. The zeolites were separated by disaggregation followed by flotation in a heavy liquid mixture of bromoform and acetone, utilizing the equipment and technique described by Schoen and Lee (1964). ACKNOWLEDGMENTS Grateful appreciation is expressed to those in the Geological Survey who provided technical assistance during this investigation. Ellen S. Daniels, Harriet Neiman, and Elaine L. Munson performed the chemical analyses. Paul D. Blackmon determined the clay mineralogy of representative mudstones and altered tuffs. Melvin E. Johnson prepared the thin sections. We are especially grateful to Robert G. Schmidt, who suggested this investigation and who had recognized the occurrence of authigenic zeolites and potassium feldspar in the Barstow Formation as early as 1954. Thomas W. Dibblee, Jr., kindly provided us with his unpublished geologic maps of the Mud Hills and adjacent areas. REGIONAL GEOLOGY The generalized geology of the Mud Hills and vicinity is shown in figure 3, which is modified from Dibblee 117*15' 116*45' EXPLANATION £ Alluvium Playa clay Gravel and sand Basalt cc < < 3 O Nonmarine sedimentary and volcanic rocks >- a: < Marine sedimentary and metasedimentary rocks c/i 3 o I LU UJ o Cd < Q- h-LU Ui>a: Plutonic and hypabyssal rocks Includes gneiss and metavolcanic rocks _ 0 5 X 10 15 MILES J Contact Fault, showing relative movement Dashed where approximately located; dotted where concealed Figure 3.—Generalized geologic map of the Mud Hills and vicinity. (Modified from Dibblee, 1963, pi. 11.)STRATIGRAPHY AND LITHOLOGY (1963, pi. 11). Other generalized geologic maps of the area have been published by Dibblee (1961, p. B198) and the California Division of Mines and Geology (1963). The Tertiary deposits of the Mud Hills are about 6,000-7,000 feet thick and include in ascending order the following: Jackhammer Formation, Pickhandle Formation, and Barstow Formation. Both the Jackhammer Formation and the Pickhandle Formation consist of sedimentary and volcanic rocks. The Tertiary deposits are folded into the Barstow syncline, whose axis trends nearly east. The Barstow syncline is nearly symmetrical, and both limbs generally dip 20°-40° (fig. 4). Numerous faults, trending mainly northwest, cut the deposits. Movement along some of these faults has been predominantly right lateral (Dibblee, 1961). The Tertiary deposits are locally unconformably overlain by Quaternary alluvial deposits. Renewed movement on OF THE BARSTOW FORMATION 5 some faults apparently continued into Holocene time, because the Quaternary deposits are displaced. The hills north of the Mud Hills are underlain chiefly by granitic rocks and intermediate to basic plutonic rocks of Mesozoic age (McCulloh, 1960). The Calico Mountains, east of the Mud Hills, are underlain chiefly by sedimentary rocks, volcanic rocks, and silicic to intermediate intrusive rocks, all of Tertiary age (McCulloh, 1960, 1965). Paleozoic metasedimentary and metavolcanic rocks flank the Calico Mountains on the north. The hills south of the Mud Hills are underlain mainly by granitic rocks of Mesozoic age and a complex sequence of metamorphic rocks of probable Precam-brian age (Miller, 1944; Bowen, 1954; Dibblee, 1960; McCulloh, 1965). In the vicinity of Opal Mountain and Black Mountain, northwest of the Mud Hills, the rocks are chiefly Miocene silicic volcanic rocks and Pleistocene basalt. Figure 4.—View of the Barstow Formation eastward along the axis of the Barstow syncline at Rainbow Basin. The upper part of the Barstow Formation, shown in the photograph, is chiefly lacustrine mudstone and interbedded tuff. Gently dipping Pleistocene alluvial deposits unconformably overlie the Barstow Formation. STRATIGRAPHY AND LITHOLOGY OF THE BARSTOW FORMATION The Barstow Formation, of Miocene age (Lewis, 1964, 1968), consists chiefly of fluviatile and lacustrine rocks that are about 3,000-4,000 feet thick. The formation unconformably overlies the Pickhandle Formation (Bowen, 1954) and is unconformably overlain by sand and gravel of Quaternary age. An unknown thickness of the Barstow Formation was eroded prior to deposition of the Quaternary alluvium. The lacustrine rocks of the formation interfinger with relatively coarse clastic rocks of fluviatile origin. The lacustrine rocks are chiefly mudstones and interbedded carbonate rocks and tuffs. Fluviatile rocks include conglomerate, sandstone, and siltstone. Some sandstone and siltstone are tuffaceous. Sandstone and conglomerate have locally channeled into mudstone and, more rarely, into tuff. Areas underlain by thick mudstone units are commonly badlands; and differential erosion of the more resistant rocks, such as sandstone, conglomerate, carbonate rock, and altered tuff, has produced hogbacks. A generalized columnar section for the upper part of the Barstow Formation is shown in figure 5. Detailed measured sections of the formation have been 336-374 O—60- •26 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. Hemicyon tuff x X -x EX PLAN ATI ON -x-xx xx-Tuff Mudstone with local sandstone and conglomerate FEET r o - 50 X x x x xxxx - 100 X- -X- - 150 L 200 Dated tuff X X X X X X X Camel track tuff XX X X~ Skyline tuff x x x x x x \/ A7VV xxxx- Yellow tuff X-X x-: Figure 5.—Generalized columnar section of the upper part of the Barstow Formation. Five of the most persistent tuffs are assigned informal field names. given by Steinen (1966) and Sheppard (1967). Five of the most persistent tuffs in the upper part of the formation are assigned informal field names, in ascending order: Yellow tuff, Skyline tuff, Camel track tuff, Dated tuff, and Hemicyon tuff. The Skyline and Dated tuffs crop out the length of the Mud Hills, but the other tuffs are less extensive. The Yellow tuff crops out eastward from the western part of Rainbow Basin; the Camel track tuff crops out between Rainbow Basin and Owl Canyon; and the Hemicyon tuff crops out in about the western third of the Mud Hills. CONGLOMERATE, SANDSTONE, AND SILTSTONE Conglomerate, sandstone, and siltstone occur throughout the formation and throughout the Mud Hills; however, the thick accumulations are in the southwestern, south-central, and northeastern parts of the area. These coarse fluviatile rocks interfinger with mudstone of lacustrine origin. Highlands both north and south of the Mud Hills probably supplied detritus for these coarse clastic rocks. The conglomerate is green, brown, or red; medium to thick bedded; and poorly to moderately well indurated. The framework constituents of the conglomerate range in size from pebbles to boulders up to 3 feet in diameter. The pebbles generally are angular to subrounded, whereas the cobbles and boulders generally are subrounded to rounded. The composition of the fragments also is variable, but generally the fragments are medium- to coarse-grained granitic rocks, or granitic rocks with minor volcanic and metamorphic rocks. Fragments of quartz and pegmatitic, granitic rock also are present. Some conglomerates contain only volcanic fragments that include pink and green silicic or intermediate lavas and, rarely, pink lapilli tuff. The sandstone and siltstone are green, brown, gray, or red and generally poorly to moderately well indurated. Local cementation by brown-weathering calcite makes these rocks very hard and resistant. The sandstone is thin to thick bedded and fine to coarse grained; the siltstone is generally laminated or thin bedded. In addition to calcite, clay minerals and clinoptilolite locally are cements in the sandstone and siltstone. Primary sedimentary structures other than bedding are rare in the sandstone; however, the siltstone is commonly ripple laminated. The sandstone is locally crossbedded and, more rarely, ripple marked. The siltstone generally contains abundant spherical or irregular calcareous concretions. The framework constituents of the sandstone and siltstone consist of varying amounts of mineral grains and rock fragments. Sorting is generally poor; and the clasts have an estimated roundness of 0.2-0.6, although most are in the lower part of this range. The matrix is chiefly clay minerals and is less than 15 percent of the rock. The detrital minerals are mainly quartz and feldspar and lesser amounts of biotite, hornblende, epi-STRATIGRAPHY AND LITHOLOGY OF THE BARSTOW FORMATION 7 dote, clinopyroxene, muscovite, chlorite, zircon, magnetite apatite, and sphene. Generally quartz exceeds feldspar; and plagioclase exceeds alkali feldspar. Much of the plagioclase is sericitized. Biotite is very abundant in some of the sandstone. The rock fragments are chiefly granitic and volcanic rocks and lesser amounts of sedimentary and low-grade metamorphic rocks. Volcanic rock fragments include hyalopilitic and spherulitic lavas and sand-sized pumice or pseudomorphs of clay minerals and clinoptilolite. Following the classification of Pettijohn (1957, p. 291), these sandstones and silt-stones are termed arkose or subgraywacke, depending on whether feldspar or rock fragments predominate. MUDSTONE Mudstone, or a silty or calcareous variant, is the predominant rock in the lacustrine deposits of the Barstow Formation. The mudstone has an earthy luster and is pastel green, gray, brown, and, rarely, red. Calcareous concretions are common, particularly in the green mudstone. Most mudstone is even bedded and medium to thick bedded. Fresh mudstone breaks with a subconchoi-dal or conchoidal fracture (fig. 6A), and the fractures are commonly filled or partly filled with gypsum. Where weathered, the mudstone has a characteristic punky “pop com” surface coating that is several inches thick (fig. 6B). A white eiflorescence of thenardite (Na2S04) commonly coats weathered mudstone in the eastern part of Rainbow Basin and much of the mudstone to the east. In addition to clay minerals, most of the mudstone contains calcite, detrital silt and sand, authigenic silicate minerals, and, locally, angular fragments of charcoal. The silt and sand fractions make up as much as 15 percent of the rock, although they generally are less than 5 percent. Most of these relatively coarse grains are angular to subangular and are chiefly mineral fragments and rarely granitic rock fragments. Quartz, plagioclase, biotite, and hornblende compose most of the silt and sand fractions; and sanidine, zircon, muscovite, and epidote are minor constituents locally. Neither vitric material nor pseudomorphs after vitric material were recognized in the mudstone. The mineral content of the finer than 2/x fraction of five mudstones is given in table 1. Standard X-ray techniques were used to identify the clay minerals. After disaggregation in water and complete removal of soluble salts, the finer than 2/jl fraction was sedimented on tiles and oriented by suction. X-ray data were then obtained from untreated, glycolated, and heated (400°C and 550°C) samples. Montmorillonite and illite occur in all samples, and two samples also contain mixed-layer illite-montmorillonite. Neither chlorite nor kao- B Figure 6.—Typical lacustrine mudstone of the Barstow Formation. A, Small excavation showing contrast of fresh and weathered mudstone. Fresh mudstone breaks with a subcon-choidal to conchoidal fracture, but weathered mudstone has a punky “pop corn” coating several inches thick. Bedding dips toward right of photograph. B, Characteristic “pop corn” coating on weathered mudstone. finite was recognized. The clay mineral suite is presumably detrital, although the possibility that some of the clay minerals are authigenic cannot be rejected. Analcime and potassium feldspar in the mudstones are probably authigenic, although petrographic evidence is lacking. X-ray diffraction data of bulk samples indicate that the mudstone generally contains 10-20 percent analcime and 10 percent or less potassium feldspar. The analcime is anhedral to subhedral and ranges in size from less than 0.002 mm to about 0.4 mm. Clay minerals adjacent to large analcime crystals are alined parallel to the surface of the analcime. Possibly the clay minerals were pushed aside during growth of the analcime.8 DIAGENESIS OF TUFFS, BAR STOW FORMATION, SAN BERNARDINO COUNTY, CALIF. Table 1.—Mineral content of the finer than 2fi fraction of five mudstones [ Relative abundance expressed in parts of 10; Tr., trace;looked for but not found. Analyst: Paul D. Blackmon] Minerals Samples 1 2 3 4 5 Montmorillonite.................. Illite........................... Mixed-layer illite-montmorillonite. Analcime......................... Potassium feldspar............... Calcite.......................... Ferroan dolomite_________________ Quartz___________________________ Goethite........................ 2+ Tr. 4 3 i+ 3 6 3+ 4+ + 2 1 _ 2 2 <1 <1 i+ Tr. Tr. 1 <1 <1 Tr. Tr. Tr. Tr. . Tr. .. Tr. Tr. Tr. .. Tr. Tr. Tr. A chemical analysis of a typical mudstone is given in table 2. The K20 and Na20 contents of this mudstone are higher than generally reported for pelitic rocks (Shaw, 1956). However, the abundance of K20 and Na20 in this mudstone is similar to that of lacustrine mudstone in the Triassic Lockatong Formation of New Jersey (Van Houten, 1965). Authigenic analcime and potassium feldspar in the Barstow mudstone probably account for the high alkali contents. Some mudstone contains numerous disseminated cavities, 0.5-3.0 mm long, that are filled or nearly filled with calcite. Inasmuch as many cavities are bounded by planar surfaces, they may be crystal molds. The shape of some cavities resembles the morphology of crystals of gaylussite (CaC03 • Na2C03 • 5H20). Calcite occurs in the cavities as clusters of anhedral and subhedral crystals. Apparently the calcite precipitated in cavities that formed by solution of a readily soluble saline mineral. Table 2.—Chemical analysis of mudstone [Lab. No. D100507; field No. SM-1-31C. Locality: Rainbow Basin, SE1/4 sec. 24’ T. 11 N., R. 2 W., San Bernardino County, Calif. Analyst: Ellen S. Daniels] Si02 47.95 AI2O3 14.97 Fe203__ 4. 78 FeO .90 MgO _ 5. 08 CaO 5. 00 BaO_ . .05 Na20 2. 96 K20 4. 54 h2o+ 3. 97 h3o- 4. 53 Ti02 .58 P205--------------- . 13 MnO_________________ . 11 C02_ —______________ 3.70 S03_________________ . 30 Cl___________________ .03 F__________________ . 14 Subtotal________99. 72 Less O__________ .07 Total___________99. 65 CARBONATE ROCKS Carbonate rocks are locally common in the Barstow Formation and include limestone and dolomite, although the former is much more abundant. The limestone is light gray to light brown, finely to coarsely crystalline, and thin to thick bedded. Much of the limestone weathers dark brown. Some of the limestone is wavy bedded or vuggy or contains irregular segregations of dark-green to black opal. Most of the limestone contains some clastic grains, locally as much as 40 percent of the rock. Thin interbeds of green calcareous mudstone are common in the thick limestone units. Ostracodes are locally common in thin beds of finely crystalline limestone. Apparently some of the limestone is of algal origin (Knopf, 1918, p. 258-259). The dolomite is light gray, finely crystalline, and thin bedded. The beds characteristically weather light brown. Clastic material locally makes up as much as 20 percent of the rock. TUFF Tuffs in the Barstow Formation of the Mud Hills make up about 1-2 percent of the stratigraphic section and are the most conspicuous and continuous strata. At least 35 tuffs are recognized; most occur in the upper half of the formation, and most were deposited in lakes. The tuffs range in thickness from 0.25 inch to 7.0 feet, but most are less than 1 foot thick. The thicker tuffs generally are more continuous than the thinner ones. Thin tuffs commonly are single beds, but tuffs thicker than 6 inches generally are multiple bedded. Individual beds of multiple-bedded tuffs are 1/16 inch to 3.5 feet thick but generally are less than 6 inches thick. The original textural and structural features of the tuffs generally are preserved even though no vitric material remains. Most tuffs are even bedded, but beds of some thick multiple-bedded tuffs channel into lower beds as much as several inches. Individual beds of both single-bedded or multiple-bedded tuffs are commonly graded, being coarser at the base. The lower contact of a tuff generally is sharp, but the upper contact commonly is gradational into the overlying rock. Cross-bedding and ripple marks or ripple laminations are present but not common. Some tuffs show contorted laminations that probably formed after deposition by internal flowage. Casts of mud cracks (fig. 7) or vertebrate animal tracks are locally common on the bottoms of some tuffs. Accretionary lapilli are common in the lower part of basal beds of two thick tuffs, the Skyline tuff and the Hemicyon tuff. The lapilli are spherical or flattened slightly in the plane of the bedding and are 2-5 mm in diameter. Broken lapilli are very rare. Each accretion-ary lapillus characteristically consists of a structureless core surrounded by one or more concentric layers. The diameter of the core is generally more than half of the total diameter of the lapillus. Lapilli and matrix consist chiefly of vitric shards or pseudomorphed shards, and minor angular crystal fragments. The grain size of shards in the cores of the lapilli and in the matrix isSTRATIGRAPHY AND LITHOLOGY OF THE BARSTOW FORMATION Figure 7.—Casts of mud cracks on bottom of Dated tuff at Rainbow Basin. similar, but the shards of the concentric layers are distinctly smaller. Each concentric layer is graded outward from relatively coarse to fine material. In contrast to the shards of the structureless core, those shards of the concentric layers are oriented with their long dimension tangential to the core or concentric layers. This preferred orientation and fine grain size of shards in the concentric layers enables the lapilli to be recognized in thin section. Accretionary lapilli apparently form by accretion of moist ash in eruptive clouds and then fall as mud-pellet rains (Moore and Peck, 1962). The lapilli in the Barstow Formation probably fell directly into a lake, because prolonged, or perhaps any, transport by streams would disaggregate them. The source of the ash in the Barstow Formation is unknown, but the occurrence of accretionary lapilli suggests that the vent was nearby. Moore and Peck (1962, p. 191) found that, with rare exceptions, accretionary lapilli occur within a few miles of the vent. Most of the tuffs are vitric and fine or very fine grained. The vitric material commonly is of two types: platy bubble-wall shards that formed from the walls of relatively large broken bubbles; and pumice shards that contain small elongated bubbles. Most tuffs are composed of both types, but the platy shards are predominant. The index of refraction of unaltered shards ranges from 1.495 to 1.498. Crystal and rock fragments in the tuffs are generally angular and range from less than 1 percent to about 60 percent of the rock. Most tuffs, hpwever, contain less than 5 percent crystal and rock fragments. The crystals are chiefly plagioclase (An21_3t), quartz, sanidine, bio-tite, and hornblende. Minor amounts of any or all of the following are also present : Zircon, clinopyroxene, 9 apatite, magnetite, and, rarely, hypersthene. All these crystals are presumably pyrogenic. Rock fragments are chiefly volcanic and granitic but also include quartzite, chert, and schistose and gneissic metamorphic rocks. The volcanic rock fragments, mainly spherulitic and hyalopilitic lava, could have been torn from the vent area during the eruption of the ash. Although the other rock types could also have been derived from the vent during an eruption, some probably are epiclastic and were carried to the basin by streams or wind. The upper part of some tuffs, particularly thick tuffs, probably contains reworked ash mixed with epiclastic grains derived from highlands surrounding the basin. This part generally has an abundance of nonvolcanic rock fragments as well as grains of epidote, muscovite, chlorite, microcline, perthite, and altered plagioclase. Commonly, these constituents are subangular to subrounded. The only available chemical analysis of vitric material from the Barstow Formation is the one prepared for this study (table 3). The shards were separated from the other constituents of a relatively fresh part of Table 3.—Chemical analysis, molecular norm, and semiquantita-tive spectrographic analysis of shards from Hemicyon tuff [Lab. No. D100550; field No. M4-32B. Locality: tributary to Fossil Canyon, NEK SEK sec. 15, T. 11 N., R. 2 W., San Bernardino County, Calif. Chemical analysis by Ellen S. Daniels; semiquantitative spectrographic analysis by Harriet Neiman] Chemical analysis Si02 71.26 K20 2.68 Cl 0.11 AI363— 12.44 Fej03 65 FeO .31 MgO. - .. .35 CaO.... .65 Na20 ... 4.47 HjO+ 6.02 HjO- .75 Ti02 .15 P2Oj .. .02 MnO .06 co2 01 F - 05 Subtotal.... 99.98 Less O 05 Total 99.93 Molecular norm Q —- 33.14 C 1.20 hm ... 0.42 or 17.09 en 1.08 ap .05 ab 43.15 mt .18 3.45 il .24 ... 100.00 Semiquantitative spectrographic analysis 1 B 0.002 Ga... 0.003 V. 0.001 Ba__ 07 La 005 Y 002 Be .0003 Nb._ 001 Yb .0002 Cr 0001 Pb 002 Zr .01 Cu . 0007 Sr .01 1 Results are reported in percent to the nearest number in the series 1, 0.7, 0.5, 0.2, 0.15, 0.1, and so forth, which represent approximate midpoints of group data on a geometric scale. The original group for semiquantitative results will include the quantitative value about 30 percent of the time. The following elements were looked for but not found: Ag, As, Au, Bi, Cd, Ce, Co, Ge, Hf, Hg, In, Li, Mo, Ni, Pd, Pt, Re, Sb, Sc, Sn, Ta, Te, Th, Tl, U, W, and Zn.10 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. the Hemicyon tuff by disaggregation followed by flotation in a heavy-liquid mixture of bromoform and acetone. The shards were then “scrubbed” in an ultrasonic bath in an attempt to remove adhering authigenic chabazite and montmorillonite. This treatment was only partly successful, so the vitric material that was analyzed included about 3-4 percent impurities, chiefly montmorillonite. The analysis shows that the shards are silicic and hydrated. The K20:Na20 ratio of the glass is lower than expected from the Si02 content, but the ratio may have been modified during the secondary hydration (Noble, 1967). This hydrated glass could be classified as rhyodacite if the normative minerals (table 3) are applied to the rock classification of Nockolds (1954, p. 1008). Inasmuch as the original composition of the glass is unknown, the shards are considered rhyolitic in further discussions. On the basis of phenocryst content, the other tuffs in the formation probably also were rhyolitic. AUTHIGENIC MINERALS ANALCIME Analcime, commonly referred to as analcite, is one of the more abundant zeolites in sedimentary rocks. Since its discovery in the Green River Formation (Bradley, 1928) and in lacustrine tuffs near Wikieup, Ariz. (Ross, 1928), analcime has been reported in rocks that are diverse in age, lithology, and sedimentary environment (Hay, 1966). Analcime has an ideal formula of NaAlSi20G-H20, but the analcime of sedimentary rocks is generally more siliceous (table 4). Analcime is a very common zeolite in the tuffs of the Barstow Formation, where it ranges from trace amounts to nearly 100 percent. The analcime is associated with each of the other zeolites, but the association with chabazite is rare. Analcime is also commonly associated with authigenic clay minerals and potassium feldspar and Table 4.—Formulas of selected alkalic zeolites [Formulas are standardized in terms of a sodium end member that has one aluminum atom. Formulas are taken from Hay (1966, p. 7); however, the formulas for chabazite, clinoptilolite, and erionite are modified from the writers’ unpublished data] Name Dominant cations Formula Analcime Na NaAlSi2.o-2.8O5.o-7.6-l.O-l.3H2O Chabazite Na, Ca NaAlSi1.7-3.8O5.4-9.6-2.7-4.IH2O Clinoptilolite- Na, K, Ca NaAlSi4.2-5.0O10.4-12.0-3.0—4. OH2O Erionite . . _ Na, K, Ca NaAlSi3.o-3.708.o-9.4’3.0-3.4H20 Mordenite Na, Ca, K NaAlSi4.5-5.oOii.o-i2.o-3.2-3.5H20 Phillipsite Na, K Na AlSi,.3-3.<04.8-8.s-l. 7-3.3H20 less commonly associated with authigenic quartz. Unlike the other zeolites, analcime is not associated with relict glass. Analcime occurs in the tuffs as anhedral to euhedral crystals, although most are subhedral to euhedral (fig. 8). The crystals range from 0.006 to 0.3 mm in size, but most are 0.01-0.05 mm. Tire analcime is isotropic and could easily be overlooked in thin section except that it is generally pale tan in transmitted light but milky in reflected light due to abundant inclusions of opal. Commonly, the outer part of the analcime crystals is free of inclusions and is colorless and clear. The index of refraction of analcime from the Barstow Formation ranges from 1.484 to 1.487. Saha (1959, p. 302-303) showed that the index of refraction of synthetic analcimes decreases with increasing silicon content. The above indices are consistent with high silicon contents. A chemical analysis of an analcime from the Barstow Formation is given in table 5. The analcime was sep- Figxjbe 8.—Photomicrograph of altered tuff, showing subhedral and euhedral crystals of analcime. Unpolarized light.AUTHIGENIC MINERALS 11 arated from a nearly monomineralic tuff,; however, the analcime contained abundant inclusions of opal. Even so, the analysis shows that the analcime contains only minor amounts of cations other than sodium. Table 5.—Chemical analyses and composition of unit cell of analcime and chabazite [a, in column head, uncorrected analysis; b, analysis corrected for opal impurities] Analcime Chabazite aba Chemical analyses [Analyst of analcime: Elaine L. Munson. Analyst of chabazite: Ellen S. Daniels] Si02. AI2O3. Fe203 FeO. MgO. CaO_ Na20. K20__ h2o+ h2o- Ti02_ P205_ MnO. C02._ Cl... F____ 67. 68 60. 24 59. 68 14. 10 19. 75 13. 11 . 21 . 28 . 13 . 00 . 00 . 02 . 12 . 16 . 79 . 10 . 13 1. 13 8. 38 11. 15 5. 30 . 14 . 18 . 62 6. 12 1 • 8. 95 | 10. 25 2. 24 J 8. 76 . 06 . 08 . 04 . 01 . 01 . 02 . 00 . 00 . 00 . 01 . 04 . 05 _ . 01 . 01 . Subtotal - . . _. Less O _ _ . . ... 99.21 .01 99. 99 . 01 99. 86 . 00 Total __ __ ... 99.20 99. 98 99. 86 Molecular Si02:Al203+Fe203. — 5. 40 7. 68 Composition of unit cell [Fe«, Ti, P, and Mn were omitted in calculation of the unit cell] Si_________ A1_________ Fe+3....... Mg--------- Ca_________ Na_________ K__...... H20 +------ h2o-_______ o__________ Si-f Al+Fe+3 Si:Al+Fe+3-. 35. 00 28.53 12. 84 7. 39 . 12 . 05 . 14 . 56 . 08 .58 12. 56 4. 91 . 13 .38 17. 34 J16. 34 (13. 97 96. 00 72. 00 47. 96 35. 97 2. 70 3. 83 Analcime.—Lab. No. D100242; field No. M3-105A; separated from a thin tuff about 1,330 ft stratigraphieally below the Skyline tuff. Locality: south part of Rainbow Basin, SW1/4SE1/4 sec. 24, T. 11 N., R. 2W., San Bernardino County, Calif. Chabazite.—Lab. No. D100593; field No. M4-32F; separated from the upper part of the Hemicyon tuff. Locality: tributary to Fossil Canyon, NE1/4SE1/4 sec. 15. T. 11 N., R. 2 W., San Bernardino County, Calif. An attempt to correct for the opal impurities was made by utilizing the data of Saha (1959; 1961) on synthetic analcimes. Saha showed that the (639) peak of analcime falls at higher angles (degrees 20, CuKay radiation) for analcimes of higher silicon content. Displacement of this (639) peak was measured against the (331) peak of a silicon internal standard. The compositions and corresponding displacements of the (639) peak for the synthetic analcimes (Saha, 1961, p. 865) were replotted and are given in figure 9. The displacement of the (639) peak for the analyzed specimen was then measured and the Si02 content calculated from figure 9. Excess Si02 in the original analysis is assumed to be in the opal inclusions. Subtraction of this excess Si02 from the original analysis and recalculation of the analysis to 100 percent resulted in the corrected analysis that is given in table 5. This corrected analysis was recalculated into atoms per unit cell, on the basis of 96 oxygen atoms, and is also given in table 5. The composition of analcime from 24 other tuffs was determined by measurement of the displacement of the (639) peak (figs. 9 and 10). These analcimes show a compositional range of (NaA^ys^Sisz.sOge'AH20 to (NaAl)12,GSi35,4096-nHo0. Thus, the analcimes from tuffs of the Barstow Formation range in Si: A1 ratio from about 2.2 to 2.8. Coombs and Whetten (1967) studied analcimes from many sedimentary environments and determined a range in Si: A1 ratio of about 2.0-2.7. ATOMS PER UNIT CELL (0 = 96) Figure 9.—Determinative curve for the anhydrous composition of analcime from X-ray diffractometer data. Dots are replotted from the data of Saha (1961) for synthetic analcimes. A2fl is the 20 of the (639) peak for analcime minus the 20 of the (331) peak for the silicon internal standard. Radiation is CuKa,. The brackets show the compositional range of analcime from tuffs of the Barstow Formation.12 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. Figure 10.—Histogram showing the distribution of the silicon content of analcime in 41 samples from 25 tuffs of the Bar-stow Formation. Composition of analcime determined from X-ray diffractometer data by measurement of the displacement of the (639) peak of analcime. CHABAZITE Chabazite was unknown in sedimentary deposits prior to its discovery by Hay (1964, p. 1377) in tuffs and tuffaceous clays at Olduvai Gorge, Tanzania. Since then, authigenic chabazite has been recognized in tuffs from Arizona (Sand and Regis, 1966), Nevada (Hoover and Shepard, 1965), and Oregon (Gude and Sheppard, 1966, p. 914), as well as in the Barstow Formation. The physical properties and chemistry of these chabazites differ from that of the common chabazite that occurs in cavities of mafic igneous rocks. Chabazite has an ideal formula of Ca2Al4Si8024 • 12H20, but natural chabazites show considerable variation in cation content and Si: A1 ratio (table 4). The chabazite of the Barstow Formation rarely occurs in monomineralic beds. Generally it is associated with clay minerals and the following zeolites: Clinopti-lolite, erionite, mordenite, and, rarely, analcime. Au-thigenic quartz or opal are rarely associated with the chabazite in altered tuffs. Most of the chabazite-bear- ing tuffs in the formation also contain relict glass; however, the other authigenic zeolites of the formation are rarely associated with relict glass. The chabazite occurs as aggregates of anhedral crystals that are 0.002-0.05 mm in size. The mean index of refraction ranges from 1.461 to 1.468, and the birefringence is about 0.002. This compares with a range of 1.470-1.494 given by Deer, Howie, and Zussman (1963, p. 387) for chabazite from nonsedi-mentary environments. An analysis of chabzite from the Barstow Formation is given in table 5. The chabazite was separated from a nearly monomineralic part of the Hemicyon tuff. The analysis was recalculated into atoms per unit cell, on the basis of 72 oxygen atoms, and this is also given in table 5. Monovalent cations exceed divalent ones, and the Si: Al + Fe+3 ratio (3.83) is much higher than that for ideal chabazite. Gude and Sheppard (1966, p. 914) attributed the relatively low indices of refraction (a=1.460, y=1.462) and small cell dimensions (a= 13.712 ±0.001 A, c — 14.882±0.002 A) of this analyzed specimen to its high silicon content. CLAY MINERALS Most altered tuffs in the Barstow Formation contain authigenic clay minerals, and some consist predominantly of clay minerals. The clay mineralogy of the finer than 2/u, fraction for seven samples was determined by Paul D. Blackmon using the standard X-ray techniques described previously. Montmorillonite occurs in all samples, commonly with trace to minor amounts of mixed-layer illite-montmorillonite. A sample of the Yellow tuff also contains illite as well as montmorillonite and mixed-layer illite-montmorillonite. Montmorillonite is generally the predominant clay mineral reported in altered tuff; however, illite and mixed-layer illite-montmorillonite are known from tuffs subjected to diagenesis (Schultz, 1963). CLIN OPTILOLITE Clinoptilolite is a member of the heulandite structural group (Hay, 1966, p. 11). Although there is still some disagreement on the distinction between these closely related zeolites, most workers agree that clinoptilolite is the silicon-rich (Hey and Bannister, 1934; Mumpton, 1960) and alkali-rich (Mason and Sand, 1960) member. Indices of refraction (Mason and Sand, 1960, p. 350) and reaction to thermal treatment (Mumpton, 1960, p. 359-361; Shepard and Starkey, 1964) have also been used to distinguish clinoptilolite from heulandite.ATJTHIGENIC MINERALS 13 Clinoptilolite is a very common zeolite in tuffs of the Barstow Formation, where it ranges in content from trace amounts to nearly 100 percent. The clinoptilolite is associated with each of the other zeolites and with one or more of the following authigenic silicate minerals: Clay minerals, potassium feldspar, opal, and quartz. The clinoptilolite occurs as prismatic or platy crystals that are 0.005-0.25 mm long; however, most clinoptilolite is 0.01-0.02 mm long. The mean index of refraction ranges from 1.471 to 1.482 and is within the range considered by Mason and Sand (1960, p. 350) to be characteristic of clinoptilolite. Most clinoptilolites from tuffs of the Barstow Formation have a mean index of refraction less than 1.476. The birefringence is low, about 0.003. All clinoptilolites examined have parallel extinction and, except for the rims of some large zoned crystals, are length slow'. Large crystals, 0.04-0.25 mm long, in some tuffs are zoned. The zoned crystals generally consist of a uniform core and a progressively zoned rim (fig. 11). The core is length slow, but the rim is length fast. The index of refraction of the rim is as much as 0.010 higher than Figure 11.—Photomicrograph of large zoned clinoptilolite crystal, showing uniform core and progressively zoned rim. Crossed nicols. 336-374 0—60---3 that of the core. Electron microprobe analyses of two large zoned clinoptilolites by B. C. Surdam (written comm., 1967) showed that the rim contains 2.9-3.5 weight percent less Si02 than the core. Some large crystals show oscillatory zoning (fig. 12), but no attempt was made to study the differences in the index of refraction across the zones. Three chemical analyses of clinoptilolite from the Barstow Formation are given in table 6. The analyses were recalculated into atoms per unit cell, on the basis of 72 oxygen atoms, and these are also given in table 6. Monovalent cations exceed divalent ones, and the Si: Al + Fe+3 ratio is 4.20-4.37. Sodium exceeds potassium, as is generally true for clinoptilolite; however, potassium-rich clinoptilolites have been reported from other areas (Minato, 1964; Sheppard and others, 1965, p. 247). The BaO content of clinoptilolite 2 is unusual, and the barium may be present as barite impurities. The analyzed separate contained minor barite that was recognizable in immersion oil grain mounts. An attempt Figure 12.—Photomicrograph of zeolitic tuff, showing oscillatory zoning in relatively large crystals of clinoptilolite. Crossed nicols.14 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. Table 6.—Chemical analyses and composition of unit cell of clincrptilolite [a, In column head, uncorrected analysis; b, analysis corrected for C Oa plus equivalent CaO to make calcite or for SO3 plus equivalent BaO to make barite] 12 3 a a b a b Chemical analyses [Analyst; Ellen S. Daniels] Si02________________ 63. 69 64. 38 64. 70 64. 23 64. 71 A1203_______________ 12. 47 12. 37 12. 43 12. 20 12. 29 Fe203__________________ .62 .44 .44 .41 .41 FeO____________________ 02 .02 .02 .03 .03 MgO__________________ 1.42 .34 .34 .74 . 75 CaO__________________ 2. 25 1. 25 1. 26 1. 83 1. 64 BaO_________________________ .78 .53 ____________ Na20__________________ 2.46 4.30 4.32 3.17 3.19 K20__________________ 1. 80 2. 27 2. 28 3. 97 4. 00 H20 +_________________ 8.93 7.85 7.89 6.60 6.65 H20-__________________ 5.97 5.64 5.67 6.11 6.16 Ti02_________________ .07 .07 .07 .08 .08 P205___________________ .02 .01 .01 .02 .02 MnO____________________ .01 .01 .01 .00 .00 C02_________________________________________16_______ S03_________________________ . 13____________________ Cl_____________________ .03 .01 .01 .01 .01 F______________________ .02 .01 .01 .05 .05 Subtotal__________ 99. 78 99. 88 99. 99 99. 61 99. 99 Less O____________ .02 .00 .00 .02 .02 Total____________ 99. 76 99. 88 99. 99 99. 59 99. 97 Molecular Si02:Al203 + Fe203_________________ 8. 40_________ 8. 64__________ 8. 75 Composition of unit cell was made to correct the chemical analysis for the barite by subtracting the S03 content plus an equivalent amount of BaO to make barite. The excess BaO, 0.53 per cent, is presumed to be in the clinoptilolite. If the S03 content of the analysis is in error and is low, some, or perhaps all, of the excess BaO may be in additional barite. ERIONITE Erionite was considered an extremely rare mineral prior to the work of Detfeyes (1959a, b) and Regnier (1960, p. 1207), who showed it to be a common authi-genic zeolite in altered rhyolitic vitric tuffs in north-central Nevada. Since then, erionite has been recognized in altered tuffs from many of our Western States. Erionite in the altered tuffs of the Barstow Formation is associated with each of the other zeolites but is more commonly associated with clinoptilolite. The erionite is also commonly associated with authigenic clay minerals but rarely associated with authigenic quartz or opal. The erionite content of an altered tuff is generally 20 percent or less. Like most erionite of sedimentary deposits (Hay, 1966, p. 10), erionite of the Barstow Formation is acicular or prismatic. Individual crystals are 0.006-0.04 mm long. Erionite rarely occurs in aggregates of radiating crystals. Indices of refraction for erionite are <0= 1.461-1.465 and £=1.465-1.469. These indices are lower than those reported by Deer, Howie, and Zussman (1963, p. 398) and may be due to a relatively high silicon content of the Barstow erionite. Birefringence is 0.004, higher than that of the other associated zeolites. The erionite shows parallel extinction and is length slow. Inasmuch as erionite occurs in small amounts and [Fe+J, Ti, P, and Mn were omitted in calculation of the unit cell] Si________ A1________ Fe+A..... Mg-------- Ca________ Ba________ Na________ K_________ H20+______ h2o-______ o_________ Si+Al+Fe+3 Si:Al+Fe+3_ . 28. 99 _ _ _ 29. 19 ... ... 29. 09 . 6. 69 6. 61 6. 51 .21 ... . 15 ... . 14 . 96 - . 23 . 50 _ 1. 10 ... .61 .79 _ __ .00 - 2. 17 _ 3.78 . 2. 78 _ 1. 04 1. 31 ... 2. 30 13. 56 _. ... 11. 87 ... 9. 97 . 9. 06 _ ^. 8. 53 .. 9. 24 . 72. 00 ... 72. 00 ... 72. 00 - 35. 89 ... 35. 95 .. ... 35. 74 _ 4. 20 ... 4. 32 ... 4.37 1. —Lab. No. D100555; field No. SM-6-5C; separated from the Hemicyon tuff. Locality: tributary to Fossil Canyon, NW1/4NE1/4 sec. 15, T. 11 N., R. 2 W., San Bernardino County, Calif. 2. —Lab. No. D100554; field No. SM-4-4A; separated from the Skyline tuff. Locality; about 1 mile east of mouth of Owl Canyon, NW1/4NE1/4 sec. 29, T. 11 N., R. 1 W., San Bernardino County, Calif. 3. —Lab. No. D100594; field No. SM-4-11-I; separated from a tuff about 525 ft strati-graphtcally below the Skyline tuff. Locality: about 1 mile east of Owl Canyon, SW1/4SE1/4 sec. 20, T. 11 N., R. 1 W., San Bernardino County, Calif. invariably is associated with some other zeolite in the altered tuffs, no attempt was made to separate material for chemical analysis. Erionite is alkali-rich (table 4) and generally has a Si: Al + Fe+3 ratio range of 3.0-3.5 (Hay, 1966, p. 9). MORDENITE Mordenite has been confused with clinoptilolite or heulandite in sedimentary rocks because of their similar indices of refraction and chemistry (Coombs and others, 1959, p. 69; Shumenko, 1962). X-ray diffractometer techniques, fortunately, are adequate for positive identification (fig. 2). In recent years, mordenite has commonly been identified in Cenozoic tuffaceous rocks from several areas of the Western United States (Moi-ola, 1964; Sheppard and Glide, 1964; Curry, 1965; Hoover and Shepard, 1965; Surdam and Hall, 1968). Mordenite in the altered tuffs of the Barstow Formation is associated with each of the other zeolites, but itAUTHIGENIC MINERALS 15 is more commonly associated with clinoptilolite. Mor-denite is also associated with authigenic clay minerals and rarely with authigenic quartz, opal, or potassium feldspar. The mordenite content of an altered tuff generally is 20 percent or less and only rarely is as much as 40 percent. Mordenite crystals are acicular or prismatic and generally 0.01-0.04 mm long. They commonly are larger than the crystals of other associated zeolites. Indices of refraction for mbrdenite are fairly constant and are within the lower part of the range (1.472-1.487) given by Deer, Howie, and Zussman (1963, p. 401). The mean index ranges from 1.474 to 1.478 and the birefringence is low, about 0.003. All mordenites examined have parallel extinction and are length fast. An analysis of mordenite from the Barstow Formation is given in table 7. The mordenite was separated from a nearly monomineralic tuff about 4 feet above the Skyline tuff in the western part of the Mud Hills. The analysis was recalculated into atoms per unit cell, on the basis of 48 oxygen atoms and is given in table 7. Monovalent cations exceed divalent ones and the Si: A1 + Fe+3 ratio is 4.71. Sodium exceeds potassium as is true for most mordenites regardless of genesis. However, a potassic mordenite was recently found in tuffs of the Miocene Obispo Formation of Surdam and Hall (1968) in southern California. OPAL Opal is difficult to recognize in altered tuffs because of its isotropic and nondescript character. Opal is colorless to pale brown in thin section and has an index of refraction near 1.46. Most identifications of opal from the Barstow Formation are based on X-ray diffractometer powder data of bulk samples. The opal has characteristically broad peaks at the following d spacings: 4.26 A, 4.09 A, and 3.82 A. Opal is commonly associated with clinoptilolite and clay minerals and rarely associated with chabazite, mordenite, and erionite. Segregations containing as much as 70 percent opal are locally common. PHILLIPSITE Phillipsite has long been known to occur in deposits on the sea floor (Murray and Renard, 1891, p. 400-All). Since the discovery by Deffeyes (1959a) of phillipsite in altered rhyolitic tuffs of Nevada, this zeolite has been commonly reported as a rock-forming constituent of tuffs deposited in saline lakes (Hay, 1964). The phillipsite in tuffs of the Barstow Formation is commonly associated with clinoptilolite and analcime and less commonly associated with erionite and morde- Table 7.—Chemical analyses and composition of unit cell of mordenite and phillipsite [a, in column head, uncorrected analysis; b, analysis corrected for COj plus equivalent CaO to make calcite, and for SO3 plus BaO to make barite] Mordenite Phillipsite a a b Chemical analyses [Analyst: Ellen S. Daniels] Si02_________________________ 66.31 55.18 56.60 A1203_______________________ 11.52 14.97 15.35 Fe203____________________________ .67 .41 .42 FeO........................... .02 .00 .00 MgO____________________________ .54 .26 .27 CaO___________________________- 2.58 .20 .07 BaO...........................-....... 1.47.......... Na20__________________________ 3.09 6.77 6.95 K20____________________________ .96 3.39 3.48 H20 + _________________________ 8.46 9.40 9.64 H20-__________________________- 5.50 6.73 6.90 Ti02_____________________________ .12 .25 .26 P205____________________________ .00 .01 .01 MnO____________________________ .00 .00 .00 C02___________________________________ .10 ......... S03___________________________________ . 78---------- Cl_______________________________ .09 .04 .04 F____________________________ .02 .01 .01 Subtotal.................. 99.88 99.97 100.00 LessO_____________________ .03 .01 .01 Total______________________ 99. 85 99. 96 99. 99 Molecular Si02 :A1203 + Fe203___________________ 9. 42____________ 6. 15 Composition of unit cell [Fe+2, Ti, P, and Mn were omitted in calculation of the unit cell] Si________ A1________ Fe+3______ Mg-------- Ca________ Na________ K_________ H20+______ h2o-______ o_________ Si+Al+Fe+3 Si:Al + Fe+3- 19.78 4.05 . 15 .24 . 82 1.79 .37 8.42 5. 47 48. 00 23. 98 4.71 12. 06 3.85 .07 .09 .02 2. 87 .94 6. 85 4. 90 32. 00 15.98 3.08 Mordenite.—Lab. No. D100551; field No. M4-54B; separated from a tuff 4 ft strati-graphically above the Skyline tuff. Locality: about 1 mile north of Fossil Canyon, NW1/4SE1/4 sec. 9, T. 11 N., R. 2 W., San Bernardino County, Calif. Phillipsite.—Lab. No. D100592; field No. M4-5A; separated from the lower part of the Yellow tuff. Locality: west wall of Owl Canyon, NW1/4SW1/4 sec. 19, T. 11 N., R. 1 W., San Bernardino County, Calif.16 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. nite. The association of phillipsite with chabazite has not been recognized in these tuffs, although this association has been noted in tuffs from other areas (Hay, 1964, p. 1377; Sheppard and Gude, 1968). Phillipsite is also commonly associated with authigenic clay minerals and potassium feldspar and rarely associated with authigenic quartz. Most of the phillipsite occurs as spherulites in the altered tuffs, although prismatic crystals 0.01-0.02 mm long occur locally. The spherulites range in diameter from 0.04 to 1.0 mm, but most are 0.1-0.3 mm (fig. 13). Clusters of several mutually interfering spherulites are common, and many spherulites are malformed. Indices of refraction for phillipsite vary considerably, much more than for any other zeolite in the Bar-stow Formation. The mean index ranges from 1.448 to 1.476, and the birefringence is very low’, about 0.002. Most of the phillipsites have a mean index between 1.460 and 1.470. The spherulites generally are zoned; the outer part of the spherulite invariably has a higher index. A difference in index of as much as 0.018 has Figure 13.—Photomicrograph of spherulitic phillipsite in altered tuff. Matrix consists of clay minerals and minor potassium feldspar. Arrow indicates relict shard outlined by clay mineral. Crossed nicols. been measured between the interior and exterior parts. All phillipsites have parallel or nearly parallel extinction, and except for one specimen, are length slow’. The length-fast phillipsite has the highest (1.476) mean index of refraction that was measured. These indices of refraction for phillipsite from the Barstow Formation are similar to those of phillipsites from saline lakes (Hay, 1964, p. 1374), but are much lower than those of phillipsite from other environments. Deer, Howie, and Zussman (1963, p. 386) reported a range of 1.483-1.514 for presumably nonsediment ary phillipsites. A chemical analysis of spherulitic phillipsite that was separated from the Yellow tuff is given in table 7. The analysis was corrected for barite and calcite impurities associated with the phillipsite. The corrected analysis was then recalculated into atoms per unit cell, on the basis of 32 oxygen atoms, and is given in table 7. Monovalent cations greatly exceed divalent cations and sodium is greatly in excess of potassium. The Si :A1 + Fe+3 ratio is 3.08 and is much higher than the range of 1.3-2.2 given by Deer, Howie, and Zussman (1963, p. 393) for phillipsite. The high potassium plus sodium and silicon contents of this phillipsite distinguish it from phillipsites in nonsedimentary deposits. However, the analysis is very similar to analyses of phillipsites from altered rhyolitic tuffs in lacustrine deposits of southern California (Hay, 1964, p. 1375; Sheppard and Gude, 1968), and southeastern Oregon (Regis and Sand, 1966). Phillipsite from the Barstow Formation does differ from other similar phillipsites by its high sodium content. POTASSIUM FELDSPAR Potassium feldspar occurs as an authigenic mineral in sedimentary rocks that are diverse in lithology, de-positional environment, and age (Hay, 1966). The authigenic feldspar is a pure or nearly pure potassium variety and may occur as authigenic crystals or overgrowths or replacements of plagioclase. The authigenic potassium feldspar in tuffs of the Barstow’ Formation occurs chiefly as authigenic crystals and only rarely as overgrowths or replacements of plagioclase. The feldspar occurs in monomineralic beds or associated with one or more of the following authigenic minerals: Quartz, clay minerals, analcime, clinoptilolite, morde-nite, and phillipsite. The association of potassium feldspar with analcime and clay minerals is especially common. Nowhere in the Barstow’ Formation has authigenic feldspar been found associated with relict glass. Potassium feldspar occurs in the altered tuffs as low-birefringent aggregates of crystals that range in size from less than 0.002 mm to about 0.01 mm. Paul D. Blackmon, using electron microscopy, has shown thatALTERED TUFFS 17 the crystals are subhedral to euhedral and generally less than 0.005 mm in size (fig. 14). The feldspar is identical with authigenic potassium feldspar from sediments of Searles Lake, Calif. (Hay and Moiola, 1963, p. 323), and altered tuffs of Pleistocene Lake Tecopa, Inyo County, Calif. (Sheppard and Gude, 1968). The mean index of refraction is 1.518 which suggests nearly pure potassium feldspar. Other optical data could not be obtained because of the small size of the crystals. The feldspar is monoclinic inasmuch as X-ray diffractometer patterns of powders show only the (131) peak rather than the pair, (131) and (131), the criterion suggested by Goldsmith and Laves (1954, p. 3) for distinguishing monoclinic from triclinic potassium feldspar. The following cell constants were refined on a digital computer by least-squares analysis of X-ray diffractometer powder data: a= 8.593 ± 0.002 A 1=12.967 ±0.003 A c=7.165 ±0.001 A /J=116° 3.3'±1.0' Cell volume=717.25±0.19 A3 The structural state estimated from the i and c cell edges is that of sanidine, but the cell seems to be distorted (D. B. Stewart, 1965, written commun.). QUARTZ Authigenic quartz is a common constituent in the altered tuffs and is associated with all the other authigenic silicate minerals except opal. Quartz is commonly associated with analcime and potassium feldspar, less commonly associated with clay minerals and clinoptilo-lite, and only rarely associated with the other zeolites. Figure 14.—Electron micrograph of potassium feldspar, showing subhedral to euhedral outlines of crystals. Electron micrograph by Paul D. Blackmon. Some bulk samples contain as much as 80 percent quartz. The quartz occurs as veinlets and spheroidal or irregular segregations of anhedral crystals 0.005-0.2 mm in size. The spheroidal segregations are 0.25-2.0 mm in diameter (fig. 15). Some quartz is evidently chalcedonic, because it occurs in fibrous aggregates and has indices of refraction below 1.54. The X-ray diffractometer powder pattern of this material is identical with that of quartz. Figure 15.—Photomicrograph of sample from upper part of the Skyline tuff. Tuff has been replaced by finely crystalline potassium feldspar (gray) and spheroidal segregations of anhedral quartz (white). Unpolarized light. ALTERED TUFFS FIELD DESCRIPTION All tuffs in the Barstow Formation of the Mud Hills are altered, at least in part. Relict glass is rare, but parts of some tuffs contain as much as 90 percent relict glass. The altered tuffs are generally white to pale gray or pastel shades of yellow, brown, or green with a dull or earthy luster. Relict vitric material, if present, can be recognized by its distinct vitreous luster. Altered tuffs are resistant and form ledges (fig. 16). Original textures18 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. Figure 16.—View looking west along the north limb of the Bar-stow syncline at Rainbow Basin, showing resistant hogbacks formed by altered tuffs. Tuff near the center of the photograph is the Skyline tuff. and sedimentary structures, such as crossbedding and ripple marks, are generally preserved in the altered tuffs. Preservation of these features is convincing evidence that the present differences in composition and mineralogy of the tuffs are due to postdepositional processes. Authigenic silicate minerals in the altered tuffs generally cannot be positively identified in the field because of the very small size of the crystals. If the altered tuff is nearly monomineralic, certain gross physical properties of the rock may aid field identification. On this basis, then, the following tuffs generally can be recognized: Tuffs that contain a zeolite other than analcime, tuffs that are analcime rich, and tuffs that are potassium feldspar rich. Certain of the nonanalcimic zeolitic tuffs commonly can be further differentiated. Those tuffs that are nonanalcimic are relatively hard and generally show good preservation of the original vitroclastic texture'. Tuffs rich in clinoptilolite commonly are white to pale gray, very well indurated, and low in porosity, and they generally break with a blocky to conchoidal fracture (fig. 17). Phillipsite-rich tuffs are generally yellow and characteristically are spherulitic. Phillipsite is the only authigenic silicate mineral in the altered tuffs that is spherulitic. Tuffs rich in mordenite generally cannot be distinguished from clinoptilolite-rich ones; however, the former tend to be more porous and break with an irregular or blocky fracture rather than a conchoidal fracture. Tuffs rich in erionite or chabazite cannot be distinguished from one another; however, they commonly can be distinguished from clinoptilolite- or mordenite-rich tuffs by their greater porosity and irregular fracture. Figure 17.—Clinoptilolite-rich part of the Skyline tuff, showing typical blocky and conchoidal fractures. Tuffs that contain mostly analcime are porous, friable, and generally a pastel shade of green, yellow, or brown. Perhaps the most characteristic features are their sugary texture and poor preservation of the original vitroclastic texture. Individual euhedra of analcime commonly can be seen with a hand lens. Analcimic tuffs break with an irregular fracture or, more rarely, a blocky fracture. Tuffs replaced mainly by potassium feldspar are porous, very friable, punky, and white to pale green. If only minor authigenic quartz is associated with the feldspar, the tuffs can be disaggregated with the fingers. The feldspar-rich tuffs generally break with an irregular fracture and show poor preservation of the original vitroclastic texture. PETROGRAPHY The authigenic mineralogy of the altered tuffs was determined chiefly by study of X-ray diffractometer powder data of bulk samples, supplemented by thin-section and oil-immersion study. Thin sections were especially useful for determining the age relationship of the authigenic minerals; however, they generally were not examined until the mineralogy of the altered tuffs was known by X-ray methods. Optical identification of the zeolites is particularly difficult because of their small crystal size and similar optical properties and habits. Crystal fragments, unlike vitric material, in the altered tuffs generally are unaltered. However, plagio-clase locally is replaced by analcime or potassium feldspar; and plagioclase, biotite, and rarely hornblende are locally replaced by calcite. Hornblende and apatite locally show marginal solution.ALTERED TUFFS 19 NONANALCIMIC ZEOLITIC TUFF The vitroclastic texture is preserved in most tuffs that are chiefly zeolites other than analcime. Some zeo-litic tuffs lack relict texture or have only vague ghosts of shards where the zeolite is coarsely crystalline or where authigenic clay minerals are absent. Typcial pseudomorphs of bubble-wall shards consist of a thin marginal film of montmorillonite that is succeeded inward by crystals of one or more zeolites (fig. 18). The pseudomorphs may be either solid or hollow, and commonly both occur in the same specimen. The larger pseudomorphs commonly are the hollow ones. Hollow pseudomorphs characteristically consist of the marginal clay film succeeded inward by a single layer of zeolite (commonly clinoptilolite) crystals that are oriented perpendicular to the shard wall (fig. 19). The solid pseudomorphs are of two types: those in which the single layer of zeolite grew until crystals from opposite walls joined in the central part of the shard, and those which resemble the hollow pseudomorphs except that what was the central cavity is now filled with another zeolite, quartz, or calcite (fig. 19). The zeolite of the central filling is generally more coarsely crystalline than the marginal zeolite and is randomly oriented. Some pseudomorphs still have a small central cavity (fig. 20) even though a second zeolite grew on the marginal layer of zeolite crystals. Spherulites of phillipsite are characteristic of the Yellow tuff. The spherulites (fig. 13) resemble oolites except that they have a radial internal structure rather than a concentric structure that is so characteristic of 0.05mm Figure 18.—Photomicrograph of zeolitic tuff, showing pseudomorphs of platy bubble-wall shards that consist of an outer film of montmorillonite (light) and a filling of clinoptilolite (dark). Matrix is finely crystalline clinoptilolite and montmorillonite. Crossed nicols. oolites. The spherulites lack nuclei, but some have engulfed scattered pyrogenic crystals during their growth. Most spherulites are malformed. The spherulites commonly enclose ghosts of shards that are outlined by a continuous or discontinuous film of montmo- Figure. 19.—Photomicrograph of zeolitic tuff, showing pseudomorphs of fibrous clinoptilolite (cl) after shards. The bands in the clinoptilolite are due to variations in the index of refraction along the length of the fibers. The large pseu-domorph in the center of the photograph has a hollow interior. Other pseudomorphs are filled with calcite (ca). A thin outer film of montmorillonite surrounds the pseudomorphs but is not obvious. Matrix is finely crystalline clinoptilolite and montmorillonite. Unpolarized light. Figure 20.—Photomicrograph of zeolitic tuff, showing pseudomorphs of shards that contain a prismatic layer of clinoptilolite and an interior filling of randomly oriented mor-denite. Matrix is chiefly clinoptilolite with minor montmorillonite. Large crystal in lower part of photograph is a Pyrogenic feldspar. Unpolarized light.20 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. rillonite. Individual fibers of phillipsite pass undistorted through these relict shards. The same alinement of relict shards persists within the spherulites of a bed and attests to the formation of the spherulites during diagenesis rather than by direct precipitation on the lake floor. The stages of alteration of fresh vitric tuff to zeolitic tuff can be observed by thin-section study of the Hemi-cyon tuff. The earliest recognizable alteration is the development of a thin film of montmorillonite that envelops the shards. An advanced stage shows only the large vitric particles that are enclosed by a montmorillonite film and set in a matrix of finely crystalline zeolite and montmorillonite. The finer glass particles apparently alter before the coarser ones. Pumice shards commonly are altered to a greater degree than platy bubble-wall shards of comparable size, probably because of their greater porosity and surface exposure. A more advanced altered variant consists of ragged remnants of large glassy shards “floating” in a matrix of zeolite and montmorillonite. The small shards are pseudo-morphed by zeolite and montmorillonite. A final stage shows zeolite and montmorillonite pseudomorphs after shards in a finely crystalline matrix of the same minerals. The smaller pseudomorphs generally are solid, but the larger ones commonly are hollow. Thin-section study indicates that at least some of the zeolite pseudomorphs formed by crystallization of the zeolite(s) in cavities from which the glass had been dissolved. The hollow pseudomorphs, such as those illustrated in figures 19 and 20, are difficult to explain in any other way. Other zeolite replacements probably were formed contemporaneously with solution of the glass, but convincing evidence is lacking. The paragenesis of the authigenic silicate minerals in -the zeolitic tuffs can be ascertained by studying the sequence of filling of the shard cavities and by contrasting the mineralogy of the matrix with the mineralogy of the pseudomorphed shards, particularly the larger shards. Presumably, the mineral in the interior of a pseudomorph formed later than the minerals nearer the periphery of the pseudomorph. Those minerals in the finely crystalline matrix are presumed to have crystallized prior to the minerals that compose the large pseudomorphs. The following sequences of crystallization were determined using the above criteria: Paragenesis of authigenic silicate minerals [Earliest mineral listed on, left] Montmorillonite—chabazite—clinoptilolite Montmorillonite—chabazite—erionite Montmorillonite—phillipsite—clinoptilolite Montmorillonite—clinolite—mordenite Montmorillonite—clinoptilolite—quartz These relationships indicate that montmorillonite consistently was the earliest silicate mineral to form in the tuffs. Chabazite and phillipsite are early zeolites; but clinoptilolite, erionite, and mordenite are relatively late zeolites. The age relationship between erionite and clinoptilolite and between erionite and mordenite is unknown. According to X-ray diffractometer study, erionite occurs with each; but the critical textural relations were not recognized in thin sections. ANALCIMIC TUFF Analcime in the altered tuffs is characteristically sub-hedral to euhedral and isotropic. Most analcime is pale tan in transmitted light and milky in reflected light because of abundant minute inclusions of opal. Vitroclas-tic texture in analcimic tuffs is vague and is spotty if at all recognizable. Most nearly monomineralic analcimic tuffs lack any evidence of a relict vitroclastic texture. X-ray diffractometer study has shown that analcime is associated with each of the other zeolites, but para-genetic relationships could be observed in thin sections for only analcime and clinoptilolite, and analcime and phillipsite. Several specimens of the Skyline tuff clearly show clinoptilolite pseudomorphs after shards that have been replaced by analcime. In the Yellow tuff and a tuff about 750 feet stratigraphically below the Yellow tuff, analcime has replaced spherulites of phillipsite. Eemnants of the spherulites can be seen in some thin sections. Analcime has also replaced pyrogenic plagioclase locally in the Dated tuff. POTASSIUM FELDSPAR-RICH TUFF Authigenic potassium feldspar occurs in trace to major amounts and is associated with each of the zeolites except chabazite and erionite. The association of potassium feldspar with analcime in the altered tuffs is especially common. Similar to the analcime occurrences, the potassium feldspar is not associated with relict glass. These occurrences contrast with those of the other zeolites which are locally associated with relict glass. Potassium feldspar generally occurs as aggregates of minute subliedral to euhedral crystals. Kelict vitroclastic texture is vague or nonexistent in tuffs or those parts of tuffs where potassium feldspar is abundant. The vitroclastic texture is recognizable in the form of quartz pseudomorphs after shards, remnants of clinoptilolite pseudomorphs after shards, remnants of a clay mineral film that vaguely outline shards, and, rarely, hollow molds of shards. Thin-section study of tuffs that contain analcime and potassium feldspar shows that the feldspar has formed from the analcime. All stages of the replacement are recognizable: from marginal replacement, that commonly gives the analcime crystals a ragged appearance,ALTERED TUFFS 21 to complete pseudomorphs of finely crystalline potassium feldspar. Locally, the crystal outlines of the pseudomorphed analcime are noticeable because of clay minerals or irresolvable opaque material. Analcimic tuffs generally have a vague vitroclastic texture, and replacement by potassium feldspar causes further degradation or obliteration of the texture. Formation of potassium feldspar from zeolite precursors is clearly shown by the feldspar replacements of analcime and the occurrence of remnants of clinoptilo-lite pseudomorphs after shards in a finely crystalline matrix of potassium feldspar., The absence of associated relict glass and potassium feldspar in tuffs of the Bar-stow Formation strongly suggests that most, if not all, potassium feldspar formed from zeolite precursors rather than directly from glass. Feldspathic tuffs that have a vague vitroclastic texture probably formed from a tuff rich in a zeolite such as clinoptilolite which generally preserves the texture, whereas feldspathic tuffs that lack vitroclastic texture probably formed from analcimic tuffs. Authigenic potassium feldspar also occurs as over- growths on plagioclase or as replacements of plagioclase in some feldspar-rich tuffs. The overgrowths (fig. 21) are thin continuous or discontinuous sheaths that characteristically have an irregular outline but are in sharp contact with the plagioclase host. Replacement of plagioclase by potassium feldspar generally is complete, although rare partial replacements have been observed. These partial replacements consist of potassium feldspar surrounding isolated but optically continuous remnants of plagioclase. The complete replacements are generally hollow pseudomorphs; solid pseudomorphs are rare. The hollow pseudomorphs (fig. 22) retain the general shape of the plagioclase grain; however, the outline is very irregular rather than smooth. The hollow pseudomorphs consist of a boxwork of potassium feldspar that extinguishes uniformly. Potassium feldspar in the pseudomorphs, like that of the overgrowths, is untwinned. CLINOPTILOLITE—ANALCIME—POTASSIUM FELDSPAR RELATIONSHIPS IN THE SKYLINE TUFF The Skyline tuff is a relatively thick tuff that crops out from one end of the Mud Hills to the other (fig. 23). Figure 21.—Photomicrograph of plagioclase grain (P) with a partial overgrowth of potassium feldspar (K). The overgrowth is untwinned. Matrix is chiefly finely crystalline authigenic potassium feldspar. Crossed nicols. Figure 22.—Photomicrograph of a potassium feldspar pseudo-morph after plagioclase, showing typical boxwork structure. Matrix consists of finely crystalline potassium feldspar, clay minerals, and calcite. Crossed nicols.to to EXPLANATION UNCONFORMITY West half DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF.East half to 00 Figuke 23.—Geologic sketch map of the southern part of the Mud Hills, showing the sampled locations of the Skyline tuff. Mineralogy of samples is given in table 8. Geology mapped by R. A. Sheppard, 1964. Planimetric base from aerial photographs taken December 15, 1962. ALTERED TUFFS24 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. In the central part of the Mud Hills, the tuff is chiefly potassium feldspar or potassium feldspar and analcime (Sheppard and Crude, 1965a). The tuff at either end of the Mud Hills is zeolitic and consists chiefly of clinoptilolite (table 8). Minor erionite or mordenite, and rare phillipsite or chabazite, are locally associated with the clinoptilolite. As much as 30 percent relict glass occurs in parts of the tuff at the westernmost exposure. Table 8.—Mineralogic composition of the Skyline tuff as estimated from X-ray diffractometer patterns of bulk samples [___, looked for but not found; Tr., trace] X-ray analysis (parts in 10) Locality ----------------------------------------------------------------——--------—-——-----------—-------—-------------------- (fig. 23) Sample Sample taken Clay, Clay, Chaba- Phillip- Clinopti- Morden- Potassi- 10 A1 14 A2 zito site Erionite lolite ite Analcime um feld- Quartz3 Calcitc Other4 spar 2 CT.......At top....................... CB.......22 in. above base____________ B.........8 in. above base____________ A..........At base................... 3 D.........At top..................... C________Near middle................ A________Near middle, 4 ft west of C_ B_________At base.................... 6 A________8 in. above base............ 8 A________6 in. above base____________ 13 A________6 in. above base____________ 16 B........ At top...................... A......... 6 in. above base___________ 17 A_________At upper part_______________ 18 B_________Near top____________________ A.........Near base.................. 19 SM-4-4A.. At top...................... 4B._ Near middle................ 4C_. At base.................... 21 A_________Near top____________________ B__________Near middle_______________ 22 B.........New top..................... A......... Near middle_______________ 24 B........Near middle_________________ A........Near base.__________________ 26 C.........At top..................... B__________Near middle_______________ A_________At base____________________ 33 A........8 in. above base____________ 34 D_________At top..................... C........72 in. above base___________ B........40 in. above base___________ A.........At base.................... 36 C________42 in. above base___________ B........14 in. above base___________ A.........5 in. above base............ 37 B........12 in. above base___________ A.........At base.................... 38 C_________At upper part_______________ B........At lower part............... 39 B________10 in. above base___________ A_________At lower part_______________ 42 SM-6-2D.I At top 2C_. 36 in. above base_________ 2B_. 12 in. above base___________ 2A__ At base..................... 43 A________At lower part.............. 44 B.. _____At upper part________________ A.........At base...................... 45 B________18 in. above base__________.. A...______Atbaso----------------------- 50 B________Near top..................... A_________At base...................... 51 B________12 in. above base............ A_________At base...................... 52 A________14 in. above base............ 53 C________Near top................... B.........6 in. above base____________ A_________At base._____ ____________ 54 A________Near middle. ................ 55 C________At upper part................ B.........8 in. above base............ A......... At base..................... 58 SM-1-8A-. At top....................... A_________Near middle................. XT........ 10 in. above base......... XB________8 in. above base____________ SM-1-8C-. At base...................... 60 D_________Near top..................... C_________Near middle in septum________ A_________ At upper part of clinoptilolite remnant. B_________At lower part of clinoptilolite remnant. E_________At base...................... X_________At base, 2 ft west of E______ 62 A........At lower part_______________ X_________At base______________________ 63 A........6 in. above base_____________ 65 SM-3-9F" At top__________ 9C_. 44 in. above base 9B_ 20 in. above base 9A.. 8 in. above base. 9E._ At base....... See footnotes at end of table. Tr. Tr. Tr. Tr. Tr. 1 1 1 Tr. Tr. 2 1 Tr. Tr. Tr. Tr. Tr. Tr. 1 1 1 Tr. 1 Tr. Tr. Tr. Tr. Tr. Tr. 1 1 Tr. Tr. . .Tr. 5 . Tr. Tr. . 1 Tr. 1 1 Tr. Tr. 8 10 7 10 10 . 10 . 10 . 1 . 10 . Tr. ”io". 10 . 9 . 9 . 10 . 9 9 . Tr. 1 1 2 Tr. 1 Tr. 1 1 Tr. Tr. Tr. Tr. 1 Tr. Tr. 2 1 Tr. 1 3 2 5 Tr. 7 Tr. 10 7 1 1 9 Tr Tr. 2 3 1 1 Tr. 9 9 Tr. Tr. 8 2 9 Tr. 1 8 . Tr. 5 2 1 8 . 1 Tr. Tr. 10 9 1 10 9 10 .... 6 .. 2 9 . 1 3 7 8 .... 2 7 . 1 1 7 Tr. 10 .... 2 .. 7 Tr. 2 3 2 2 6 1 9 .. 1 4 .... 10 .... Tr. 4 2 Tr. 1 Tr. Tr. Tr. Tr. Tr. Tr. Tr. 9 5 ______ 8____________ 10 .... 10............ 1 1 3 Tr. 6 ________ 10_______ . 10___________ 9 . 10_______ Tr. ...... 3 Tr. Tr. Tr. Tr. Tr. 2 . Tr. 5 10 . 10 Tr. Tr. 10 1 Tr. 4 5 5 Tr. Tr. TrALTERED TUFFS 25 Table 8.—Mineralogic composition of the Skyline tuff as estimated from X-ray diffractometer patterns of hulk samples—Continued [___, looked for but not found; Tr., trace] X-ray analysis (parts in 10) Locality------------------------------------------------------------------------------------------------------------------------------------------------------------------- (fig. 23) Sample Sample taken Clay, Clay, Chaba- Phillip- Clinopti- Morden- Analcime Potassi- 10 A1 14 A2 zite site Erionite lolite ite um feld- Quartz3 Calcite Other4 spar 66 A..........6 in. above base............. 68 A.........Near middle.................. 69 B......... 30 in. above base........... A.........Near ndddle in clinoptilolite remnant. X.........Near middle, 7 ft north of A. _ C.........At lower part................ 70 C.........Near top..................... B_________Near middle............... A.........6 in. above base............. 95 A.........9 in. above base............. 96 B.........27 in. above base............ A.........6 in. above base............. 99 B.........12 in. above base............ A.........At base...................... 100 A_________6 in. above base______________ 101 B........12 in. above base........... A.........At base................... 103 C........At top..................... B........_ 18 in. above base........... A_________At base...................... Tr. 1 1 1 2.......... 2........... 2.......... ..... Tr. 1 ......... 2.......... ..... Tr. _____ Tr. ..... 1 ..... 1 ..... Tr. Tr.___________ Tr.__________ .... 5 Tr. ......... Tr. Tr. Tr............................. 9............................... Tr............ Tr. 8 .............................. .............. 7.................. 1.................. Tr. 6___________ 2................................................ .............. 3 1 4 .................... ........................ 10............................. ................................. 9............................. Tr_____________________________ 8_______________________________ ________________________ 10..................................... 10............................................................. 8_____________________________________________________________ 9 ............................................................ .............. 1 9.............................. ________________________ 10_____________________________________ ......... ... 9 1______________________________ ________________________ 10_____________________________________ .............. 2 3............................... ........................ 10................................... 10.............................. ........................ 10............................. 1 Authigenic illite and pyrogenic biotite. 2 Chiefly clay minerals with a basal spacing of 12-14 A. 8 Includes authigenic, pyrogenic, and detrital quartz. 4 Chiefly plagioclase. Sample A from locality 26 contains a trace of halite; sample A from locality 53 contains 4 parts opal; and sample C from locality 53 contains 3 parts glass. Parts of the zeolitic Skyline tuff between Fossil Canyon and Rainbow Basin commonly are analcimic. The analcime occurs in irregular discontinuous zones at the top and bottom of the tuff. The content of analcime ranges from trace amounts to about 90 percent. Locally, the Skyline tuff is analcimic throughout its entire thickness. Analcimic tuff can readily be distinguished from the predominantly clinoptilolitic tuff because it is light brown or yellowish green and granular in contrast to the white conchoidal-fracturing clinoptilolitic phase. Vitroclastic texture is obvious in the clinoptilolitic part but vague or absent in the analcimic parts. Remnants of zeolitic tuff occur locally in the predominantly feldspathic Skyline tuff at Rainbow Basin and the western wall of Owl Canyon. The remnants are in the middle part of the tuff and are generally analcimic. Contacts between the remnants and the potassium feldspar-rich tuff are irregular and gradational. At several localities, notably on the north limb of the Barstow syncline in the northwestern part of Rainbow Basin and on the south limb of the syncline near the top of the west wall of Owl Canyon, the remnants consist of one or more irregular clinoptilolitic cores (figs. 24 and 25) that are enclosed or nearly enclosed by an irregular sheath of analcimic tuff. The contacts are gradational and are not controlled by bedding within the tuff. The analcimic and clinoptilolitic remnants in the Skyline tuff are interpreted as relicts of a diagenetic alteration that preceded the formation of potassium feldspar. This interpretation is consistent with the parage-netic relationship observed in thin sections of the gradational zones. The sequence of formation was (1) rhyolitic glass to clinoptilolite to analcime to potassium feldspar, or (2) rhyolitic glass to clinoptilolite to potassium feldspar. Nowhere is there any evidence that analcime or potassium feldspar formed directly from the rhyolitic glass. Other tuffs of the Barstow Formation show a similar gradation of clinoptilolitic or phillipsitic tuff to analcimic tuff, and zeolitic (chiefly clinoptilolite and analcime) tuff to feldspathic tuff. The complete sequence from nonanalcimic zeolitic tuff, to analcimic Figure 24.—Skyline tuff, showing irregular remnants of clinoptilolitic tuff (white) surrounded by analcimic (gray) tuff. Uppermost part of tuff is not visible in photograph but consists chiefly of authigenic quartz and potassium feldspar. Base of tuff is generally analcimic; but locally the clinoptilolitic remnants extend to the base, or the base is potassium feldspar-rich. The tuff overlies brownish mudstone. Locality : south limb of syucline in southeastern part of Rainbow Basin; SE(4NE% sec. 24, T. 11 N„ R. 2 W.26 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. Figure 25.—Skyline tuff, showing irregular remnants of clinoptilolitic (cl) tuff that are surrounded by analcimic (A) tuff. Remainder of tuff consists chiefly of potassium feldspar (K). Note that potassium feldspar-rich tuff is locally in contact with the clinoptilolitic remnant. Locality: north limb of syncline in northern part of Rainboiv Basin; NW^ NE% sec. 24, T. 11 N., R. 2 W. tuff, and then to feldspathic tuff, however, has not been recognized in these other tuffs, probably because of their limited distribution. RELATIONSHIP OF AUTHIGENIC SILICATE MINERALOGY TO THICKNESS OF TUFFS In addition to the previously described vertical and lateral variations in authigenic mineralogy of the tuffs, there seems to be a relationship between the authigenic mineralogy and the thickness of the tuffs. Thin tuffs generally consist of analcime and (or) potassium feldspar, whereas thick tuffs consist of zeolites other than analcime. Analcime and (or) potassium feldspar occurs in 98 percent of the tuffs that are 6 inches or less thick. Ninety-four percent of those zeolitic tuffs that lack analcime or potassium feldspar are more than 6 inches thick. A similar relationship between the authigenic mineralogy and thickness of tuffs was recognized by Hay (1966, p. 43) at Olduvai Gorge, Tanzania. Pleistocene tuffs less than 1 inch thick generally are chiefly potassium feldspar, but thicker tuffs contain phillipsite or phillipsite and potassium feldspar. The tuffs were originally similar in composition and were deposited in a saline lake. GENESIS OF THE AUTHIGENIC SILICATE MINERALS Zeolites and feldspars of authigenic origin occur throughout the world in sedimentary rocks that are diverse in lithology, depositional environment, and age. Zeolites and feldspars are especially abundant in altered rhyolitic vitric tuffs of Cenozoic age. The zeolites, except analcime, formed during diagenesis by reaction of the vitric material with interstitial water (Deffeyes, 1959a), which may have originated as either connate water of a saline lake (Hay, 1964; Sheppard and Gude, 1968) or meteoric water (Hay, 1963). Most analcime and feldspar in the altered tuffs formed during diagenesis by reaction of precursor zeolites with the pore water (Sheppard and Gude, 1965a, p. 4; Hay, 1966, p. 90-98). Hay (1966) discussed those factors that may control the formation and distribution of zeolites and associated authigenic silicate minerals in sedimentary rocks. The authigenic mineralogy correlates with temperature, pressure, and chemistry of the pore water, and composition, permeability, and age of the host rock. Inasmuch as all the authigenic silicate minerals of the Barstow Formation occur within certain tuffs, differences in the composition, permeability, and age of the host rock cannot explain their distribution. The Barstow Formation was probably subjected to only shallow burial, and there is no evidence of hydrothermal activity ; thus, the temperature and pressure must have been relatively low during the formation of the silicate minerals. Comparison of the authigenic mineralogy of these tuffs in the Barstow Formation with the 'authigenic mineralogy of tuffs in relatively young saline-lake deposits suggests that the mineralogy reflects differences in the chemistry of the pore water during diagenesis. Experimental work by others indicates that the activity ratio of alkali ions to hydrogen ions and the activity of silica are the major chemical parameters of the water that control whether clay minerals, zeolites, or feldspars will form at conditions that approximate surface temperatures and pressures (Hemley, 1959, 1962; Garrels and Christ, 1965, p. 359-370; Hess, 1966). Zeolites and feldspars are favored over clay minerals by relatively high alkali ion to hydrogen ion activity ratios and by relatively high silica activities. The high alkali ion to hydrogen ion activity ratio necessary for the formation of zeolites in a tuff can be attained in the depositional environment of a saline, alkaline lake (Hay, 1964) or in the postdepositional environment by solution and hydrolysis of rhyolitic vitric material by subsurface water (Hay, 1963, p. 237-242). There is no direct indication of the chemical environment that existed during the deposition of the tuffs of the Barstow Formation. The chemistry of the water must be inferred from the sedimentary rocks of the basin. Most tuffs were deposited in lakes which probably varied in number, location, and size. The abundanceGENESIS OF THE AUTHIGENIC SILICATE MINERALS 27 of mammal tracks in lacustrine mudstones suggests that the lakes were, at least locally, very shallow. Mud cracks further suggest that the lakes occasionally desiccated. Inasmuch as relatively coarse clastic rocks locally intertongue with the lacustrine rocks, some lakes or some parts of the lakes were relatively fresh. Other lakes or parts of the lakes probably were alkaline and moderately to highly saline. INTERPRETATION OF A SALINE, ALKALINE DEPOSI- TIONAL ENVIRONMENT FOR PARTS OF THE BAR- STOW FORMATION The obvious evidence for a saline lake, bedded saline minerals, has not been found in the Barstow Formation at the Mud Hills, although bedded colemanite Ca2B60ii-5H20) occurs in contemporaneous lacustrine rocks on the southern flank of the Calico Mountains, about 10 miles southeast of the Mud Hills (Campbell, 1902, p. 12-13; Baker, 1911, p. 349-353; Noble, 1926, p. 59-60; McCulloh, 1965). Disseminated crystal molds that are filled or partly filled with calcite occur in mudstone and tuff of the upper part of the formation at the northeastern part of Rainbow Basin. The molds resemble the morphology of gaylussite (!0aC03 • Na2C03 • 5H20) and suggest saline conditions during deposition. The interbedded tuffs at this locality consist chiefly of analcime and (or) potassium feldspar. The common efflorescence of thenardite (Na2S04) on the surface of weathered mudstone, particularly at Rainbow Basin and eastward, suggests a depositional environment of moderate salinity. Although the conditions under which dolomite precipitates at nearly room temperature is not known, the beds of dolomite and dolomitic mudstone in the eastern part of the Mud Hills suggest a depositional or diagenetic environment of high pH and moderate salinity (Smith and Haines, 1964, p. P52-P53; Jones, 1965, p. A44). Dolomite occurs at Searles Lake in muds mainly near contacts with salines. A saline, alkaline depositional environment for parts of the Barstow Formation can be inferred from the occurrence of certain authigenic silicate minerals that have been found by other mineralogists to indicate saline waters. Zeolites such as clinoptilolite and morden-ite occur in altered silicic tuffs that were deposited in either fresh or saline waters; however, zeolites such as erionite and phillipsite in altered silicic tuffs are found almost exclusively in saline-lake deposits (Hay, 1964, p. 1384; 1966, p. 67). The common occurrence of analcime and potassium feldspar in the apparently non-tuffaceous mudstones of the Barstow Formation may also indicate a saline-lake environment, because these authigenic minerals are rare in nontuffaceous mudstones deposited in fresh water (Hay, 1966, p. 67). CORRELATION BETWEEN SALINITY OF DEPOSITIONAL ENVIRONMENT AND AUTHIGENIC SILICATE MINERALOGY Studies of tuffs deposited in relatively young saline lakes where water analyses are available have shown a strong correlation between salinity and the authigenic silicate mineralogy (Hay, 1964, 1966). Tuffaceous sediments deposited in fresh water still contain unaltered glass, but those deposited in saline water are altered and contain zeolites, potassium feldspar, or searlesite. Hay (1966, p. 68) found that potassium feldspar is a major constituent of tuffs saturated with sodium carbonate brine in Searles Lake, but potassium feldspar is absent and zeolites are common in equivalent deposits that contain mildly saline water at China Lake. Older lacustrine deposits that contain interbedded saline minerals also show a correlation between the inferred salinity of the depositional environment and the authigenic mineralogy of rhyolitic tuffs. In the Pleistocene deposits of Lake Tecopa, Calif. (Sheppard and Gude, 1968), glass is unaltered in tuff deposited in fresh water; however, the tuffs consist chiefly of phillipsite, clinoptilolite, and erionite where they were deposited in moderately saline water, and potassium feldspar and searlesite where they were deposited in highly saline water. Miocene tuffs at Kramer, Calif., contain potassium feldspar and analcime where they are associated with high concentrations of sodium borate but contain clinoptilolite and phillipsite where they are associated with rocks indicative of lower salinity (Hay, 1966, p. 68). Tuffs in the Eocene Green River Formation of Wyoming are altered to montmorillonite where they were deposited in fresh water; to clinoptilolite and mordenite (Goodwin and Surdam, 1967), in slightly saline water; to analcime, in moderately saline water; and to potassium feldspar and albite, in highly saline water (Hay, 1965; 1966,p.44-52). The diverse authigenic mineralogy of the tuffs in the Barstow Formation seems to have resulted from differences in pH and salinity of the lake water trapped in the tuffs during deposition. The lake water probably ranged from fresh water to water with a pH of 9 or higher and a moderate to high salinity. Those tuffs that consist of unaltered glass with minor zeolite and montmorillonite probably were deposited in relatively fresh water; whereas those tuffs that consist of zeolites exclusive of analcime, or of only analcime, or of potassium feldspar were deposited in water of relatively low, moderate, and high salinity, respectively. The gradational change in the areal distribution of authigenic silicate minerals in the Skyline tuff (fig. 23 and table 8) from chiefly clinoptilolite with minor28 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. relict glass to clinoptilolite plus analcime to analcime I plus potassium feldspar to chiefly potassium feldspar was probably due to a chemical zonation of the pore water during diagenesis. This zonation may have been inherited from the chemical zonation that existed in the lake during deposition of the Skyline tuff. Fresh water along shore may have been succeeded basinward by increasingly saline water. Such a mechanism seems the best explanation for a similar distribution of authi-genic silicate minerals in tuffs of Pleistocene Lake Tecopa, Calif. (Sheppard and Gude, 1968). At Lake Tecopa, however, the margin of the lake is readily discernible. An alternate explanation for the chemical zonation of the pore water in the Skyline tuff is post-depositional “freshening” by meteoric water. Uniformly alkaline and saline water trapped as pore water in the tuff during deposition may have been freshened along shore by the encroachment of fresh water after deposition (Eugster and Smith, 1965, p. 518). SOLUTION OF GLASS TO FORM ALKALI- AND SILICA-RICH ZEOLITES Solution of silicic glass by moderately alkaline and saline pore water provides the materials necessary for the formation of the zeolites. Deffeyes (1959a, p. 607) emphasized that zeolites form during diagenesis—not by devitrification of the shards but by solution of the shards and subsequent precipitation of zeolite from the solution. Tuffs in the Barstow Formation are generally inter-bedded with relatively impermeable mudstones and after deposition may have behaved as closed systems consisting of silicic glass and the connate lake water. The early formation of montmorillonite probably was favored by a relatively low Na+ + K+: H+ activity ratio (Hemley, 1962). This activity ratio would have been at its lowest value at the time of deposition. Subsequent solution of glass or the formation of montmorillonite by an initial marginal hydrolysis of the glass Would cause an increase in the pH and the concentration of alkali ions (Hay, 1963, p. 240), thereby increasing the Na+ + K+: H+ activity ratio of the pore water and providing an environment more suitable for the formation of zeolites rather than additional montmorillonite. Inasmuch as the zeolites of the Barstow Formation differ noticeably in chemical composition, the following factors may influence which zeolite will form: Activity of Si02, activity of H20, and the proportion of cations in the pore water. Where relationships are clear, the petrographic evidence indicates that phillipsite and chabazite formed before clinoptilolite, and clinoptilo- lite formed before mordenite. Phillipsite and chabazite contain more H20 and less Si02 than clinoptilolite. Thus, the formation of phillipsite or chabazite should be favored over clinoptilolite by a relatively high activity of H20 and (or) low activity of Si02. Such conditions may have prevailed in the silicic tuffs during early diagenesis. Continued solution of the glass coupled with the early formation of phillipsite or chabazite in a tuff probably has the effect of enriching the pore water in Si02 and cations. The activity of Si02 may thus increase and the activity of H20 decrease to levels suitable for the formation of clinoptilolite rather than phillipsite or chabazite. Mordenite rather than clinoptilolite probably formed when the activity of Si02 reached a maximum. That the Si02 concentration can effect which zeolite will form was demonstrated experimentally by Ciric (1967). At temperatures of 80°-90°C, Ciric synthesized zeolites with a range of Si: A1 ratios in a sealed Pyrex tube into which sodium aluminate had been added at one end and sodium metasilicate added at the other. A relatively siliceous zeolite formed at the silica-rich end, an aluminous zeolite formed at the aluminate end, and a zeolite of intermediate Si: A1 ratio formed in the middle of the tube. REACTION OF ALKALIC, SILICIC ZEOLITES TO FORM ANALCIME Analcime in some nontuffaceous lacustrine rocks apparently formed during diagenesis by reaction of aluminosilicate minerals with the pore water. For example, solution of plagioclase and quartz in sediments of Searles Lake probably supplied some of the silicon and aluminum for the formation of analcime, searlesite, and potassium feldspar (Hay and Moiola, 1963). Montmorillonite and kaolinite may also have reacted to form analcime in certain nontuffaceous sediments (Hay and Moiola, 1963, p. 330; Pipkin, 1967). Analcime in other nontuffaceous saline lacustrine deposits probably formed by direct precipitation from the lake water. The analcime in the Triassic Lockatong Formation either precipitated directly or formed at an early stage of diagenesis from a colloidal precursor or aluminosilicate mineral (Van Houten, 1960; 1965, p. 835-836). At Lake Natron, Kenya, analcime in nontuffaceous clays was precipitated from a sodium carbonate brine (Hay, 1966, p. 36-38). Ever since the discovery of analcime in tuffaceous sedimentary rocks, most workers have assumed that the analcime formed directly from vitric material. TheGENESIS OF THE AUTHIGENIC SILICATE MINERALS 29 presence of vitroclastic texture and pyrogenic crystals in some analcimic tuffs seemed sufficient evidence; however, Hay (1966, p. 91) showed that these criteria do not necessarily prove that the glass altered directly to analcime. Hay (1966, p. 90-93) concluded from a comparison of the authigenic mineralogy of tuffs in modern and ancient saline-lake deposits that analcime commonly formed at low temperatures by reaction of alkalic, silicic zeolite precursors. Furthermore, relict fresh glass has not been confirmed in analcimic tuff; thus, there is doubt that analcime ever has formed directly from glass. Much, if not all, of the analcime in tuffs of the Bar-stow Formation seems to have formed from alkalic, silicic zeolite precursors. These alkalic zeolites, because of their open structure (Smith, 1963) and large internal surface area, would seem to be particularly susceptible to alteration in the diagenetic environment. Experimental low-temperature work by other mineralogists, and theoretical considerations, indicate that the formation of analcime is favored over an alkalic, silicic zeolite such as clinoptilolite by a high Na+: H+ ratio (Hess, 1966), relatively low activity of Si02 (Coombs and others, 1959; Senderov, 1963; Campbell and Fyfe, 1965), and, perhaps, relatively low activity of H20. A comparison of chemical analyses of rhyolitic glass and clinoptilolite (Hay, 1963, p. 230; Sheppard and Gude, 1965b) suggests that sodium is lost from the glass during the formation of clinoptilolite. Perhaps this sodium, plus that originally in the pore water, was sufficient to provide an environment suitable for crystallization of analcime some place else. A relatively high salinity of the pore water would decrease the activity of H20 and thus favor the formation of the less hydrous analcime over any of the other zeolites in the Barstow Formation, all of which are much more hydrous than analcime. An increase in pH during diagenesis would decrease the activity of Si02 (Coombs and others, 1959; Senderov, 1963) and increase the Na+:H+ ratio. Both conditions should favor the formation of analcime over clinoptilolite. Quartz is more common in the analcimic tuffs than in the other zeolitic tuffs of the Barstow Formation. Crystallization of quartz in the tuffs would have lowered the activity of Si02. These arguments are based on the assumption that chemical factors alone are responsible for the formation of analcime; however, kinetic factors may be equally, or perhaps more, important. Analcime may simply form later than zeolites such as clinoptilolite and phillipsite. Studies of the composition of analcime in sedimentary rocks have shown a range in Si: A1 ratios of about 2.0-2.9 (Coombs and Whetten, 1967; Iijima and Hay, 1968). Coombs and Whetten (1967) studied analcime from rocks that are diverse in age, lithology, depositional environment, and geographic location and concluded that (1) analcime in the high part of the above compositional range formed by the reaction of silicic glass with saline water, (2) analcime in the intermediate part of the range formed by “burial metamorphic reactions” due to increased temperature and pressure, and (3) analcime in the low part of the range formed either by direct precipitation from alkaline water or by reaction of clay minerals and other materials with alkaline water. Analcime in tuffs of the Barstow Formation ranges in Si: A1 ratio from about 2.2 to 2.8 and, thus, nearly spans the compositional range known for sedimentary rocks. Unlike the analcimes studied by Coombs and Whetten (1967), these analcimes in the Barstow Formation formed in rocks that originally were similar in composition and were deposited in a similar environment. None of the tuffs were deeply buried; furthermore, there is no correlation between analcime composition and stratigraphic position. Analcime in the tuffs of the Barstow Formation formed from zeolite precursors and not directly from rhyolitic glass. Petrographic study showed that analcime formed from clinoptilolite and phillipsite; however, analcime probably formed from the other authigenic zeolites as well. Inasmuch as the zeolites have a wide range of Si: A1 ratios (table 4), it is tempting to suggest that the silicon content of analcime was affected by the silicon content of the precursor. To check the validity of this idea, the composition of analcime associated with phillipsite was compared with the composition of analcime associated with clinoptilolite. Figure 26 shows that analcime associated with phillipsite has 33.1-34.4 silicon atoms per unit cell, whereas analcime associated with clinoptilolite has 34.5-35.1 silicon atoms per unit cell. Inasmuch as phillipsite and clinoptilolite are relatively low’- and high-silicon zeolites, respectively, a correlation between the compositions of the precursor and analcime is suggested. Additional determinations, particularly from another formation, are needed for confirmation. ▲ • • ▲ A A AAAMt* M l—>—i—i—i—|—i—i—i—i—|—i—i—i—i—|—i—i—i—i | i i i i—| 33.0 33.5 34.0 34.5 35.0 35.5 SILICON ATOMS PER UNIT CELL Figure 26.—Plot showing the correlation between the silicon content of analcime and the precursor zeolite. Composition of analcime determined from X-ray diffractometer data by measurement of the displacement of the (639) peak of analcime. ▲, composition of analcime associated with phillipsite; • , composition of analcime associated with clinoptilolite.30 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. REACTION OF ZEOLITES TO FORM POTASSIUM FELDSPAR The formation of potassium feldspar by the reaction of zeolite precursors in tuffs that were never buried deeply was well documented by the studies of Hay (1966, p. 93-98) and Sheppard and Gude (1968). Analcime is replaced by potassium feldspar and al'bite in tuffs of the Green River Formation in Wyoming (Hay, 1965, 1966; Iijima and Hay, 1968) where the formation of feldspar can be correlated with high salinities of the depositional environment. Phillipsite is replaced by potassium feldspar and searlesite in rhyolitic tuffs of Pleistocene Lake Tecopa, Calif. (Sheppard and Gude, 1968), where high salinities prevailed. Some zeo-litic tuffs of Lake Tecopa contain abundant clinoptilo-lite and erionite as well as phillipsite; therefore, these zeolites could also have been precursors for the potassium feldspar. Petrographic study of the feldspathic tuffs in the Barstow Formation has shown that potassium feldspar replaced analcime and clinoptilolite. Other zeolites such as chabazite, erionite, mordenite, and phillipsite may also have been precursors for the feldspar, but the textural evidence was not observed. Relict glass is nowhere associated with the potassium feldspar; thus, the direct formation of feldspar from rhyolitic glass seems unlikely in these tuffs. Zeolites, because of their open structure (Smith, 1963), apparently are particularly susceptible to alteration in the diagenetic environment. The initially high salinity of the pore water trapped in the tuffs during deposition probably was the major factor that controlled the alteration. A relatively high salinity would lower the activity of H20 and favor the formation of anhydrous potassium feldspar from the hydrous zeolites, including analcime. Other factors such as the K+: H+ ratio and the activity of Si02 also affect the formation of potassium feldspar (Hemley and Jones, 1964; Hess, 1966). Hydrolysis experiments by Garrels and Howard (1959, p. 87) suggested that potassium feldspar will form at 25 °C in environments with a K+: H+ ratio greater than about 109 5. Potassium feldspar may form at near surface conditions where the K+: H+ ratio is as low as about 105"° and the pore water is saturated with amorphous Si02 (Orville, 1964). The zeolitic tuffs of the Barstow Formation that are rich in clinoptilolite commonly contain opal which may have contributed a favorable chemical environment for the formation of potassium feldspar. However, feldspathic tuffs in the formation now contain quartz or chalcedonic quartz but lack opal. If the activity of Si02 was controlled by quartz rather than by opal, rela- tively high concentrations of K+ would have been necessary for the formation of potassium feldspar. Unfortunately, the relative ages of potassium feldspar and quartz are unknown. Studies by Iijima and Hay (1968) on the composition of analcime in tuffs of the Green River Formation showed that analcime associated with authigenic potassium feldspar is less siliceous than that not associated with potassium feldspar. Iijima and Hay concluded that siliceous analcime became partly desilicated during the reaction to form feldspar. Analcime in the tuffs of the Barstow Formation show about the same compositional range whether associated with authigenic potassium feldspar or not. Unlike the analcime in the Green River tuffs, the Barstow analcime seems to be crowded with inclusions of opal. Thus, a highly reactive form of Si02 was nearby when the analcime reacted to form potassium feldspar. Desilieation of analcime was unnecessary. Although silicate reactions are generally regarded as sluggish at low temperatures, potassium feldspar has been synthesized from aluminosilicate precursors at temperatures no higher than 250°C. Gruner (1936) synthesized potassium feldspar from montmorillonite in a 10 percent solution of KHC03 heated to 245°C for 42 days. Barrer and Hinds (1950) synthesized potassium feldspar from leucite in a solution saturated with K2C03 and Na2C03 and heated to 195-200°C for 16 hours. The leucite had been prepared from analcime by cation exchange in a solution saturated with KC1 at 150°C. Nemecz and Varju (1962, p. 425) reported the synthesis of potassium feldspar from clinoptilolite in a solution containing potassium ions and heated to not more than 250° C for 12 hours. The authors, unaware of the work by Nemecz and Varju (1962), independently synthesized potassium feldspar from clinoptilolite. Clinoptilolite from the Barstow Formation was ground finer than 100 mesh and then heated over a steam bath in a saturated solution of KOH at about 80°C for 44 hours. After repeated washings followed by drying, the material was X-rayed. The diffractometer pattern (fig. 27) showed that the clinoptilolite was converted to potassium feldspar. This synthetic feldspar is compared in figure 27 with the natural potassium feldspar that occurs in the Barstow Formation, and the similarity is obvious. Although the synthetic feldspar was prepared at a higher temperature than that which probably prevailed during diagenesis and was prepared in a chemical environment that probably did not even closely approximate the diagenetic environment, the simple experiment demonstrates the rapidity of the reaction of clinoptilolite to form potassium feldspar in a favorable environment.GENESIS OF THE AUTHIGENIC SILICATE MINERALS 31 Figure 27.—Comparison of X-ray diffractometer traces of synthetic potassium feldspar with those of natural clinoptilolite and natural potassium feldspar from the Barstow Formation. A, Clinoptilolite. B, Synthetic potassium feldspar prepared from clinoptilolite (A) in a saturated solution of KOH at about 80 °C for 44 hours; peak marked by query is unidentified. C, Natural potassium feldspar from the Skyline tuff. Radiation is CuKa.32 DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. METASOMATISM DURING DIAGENESIS OF TUFF The transition of rhyolitic glass to an alkalic silicic zeolite, then to analcime, and finally to potassium feldspar is well documented for the Barstow Formation and other Cenozoic formations (Hay, 1966). Formation of alkalic silicic zeolites from rhyolitic glass results mainly in losses of silicon and potassium, and gains of calcium and H20 (Hay, 1963, p. 230-231; 1964, p. 1382-1383; Sheppard and Gude, 1965b). The reaction of alkalic silicic zeolites to form analcime involves mainly losses of silicon, calcium, potassium, and H20, and a gain of sodium. The final transformation of analcime to potassium feldspar results in losses of sodium and HaO, and gains of potassium and silicon. These metasomatic changes apparently are mostly restricted to the tuff bed and take place between the solid phases and the pore fluid. Except for H20, a chemical balance is probably maintained for a given tuff if the entire extent of the tuff is considered. Gains and losses of constituents between the tuff and the enclosing strata probably are slight; however, the metasomatic changes within the tuff bed must be considerable. The changes that involve silicon are not too difficult to understand because most altered tuffs, whether zeolitic or felds-pathic, contain free silica. The most puzzling aspect of the metasomatic changes is the “plumbing” that permits the drastic removal of potassium to form analcime, and then the subsequent addition of potassium to form potassium feldspar. REFERENCES Baker, C. L., 1911, Notes on the later Cenozoic history of the Mohave Desert region in southeasten California : California Univ. Pubs. Geol. Sci., v. 6, p. 333-383. Barrer, R. M., and Hinds, L., 1950, Hydrothermal synthesis of potash feldspar in the range 195-200°C: Nature, v. 166, p. 562. Bowen, O. E., Jr., 1954, Geology and mineral deposits of Barstow quadrangle, San Bernardino County, California: California Div. Mines Bull. 165, p. 1-185. Bradley, W. H., 1928, Zeolite beds in the Green River Formation : Science, v. 67, p. 73-74. California Division of Mines and Geology, 1963, Geologic map of California, Trona sheet. Campbell, M. R., 1902, Reconnaissance of the borax deposits of Death Valley and Mohave Desert: U.S. Geol. Survey Bull. 200, 22 p. Campbell, A. S., and Fyfe, W. S., 1965, Analcime-albite equilibria : Am. Jour. Sci., v. 263, p. 807-816. Ciric, Julius, 1967, Synthetic zeolites—growth of large single crystals: Science, v. 155, p. 689. Coombs, D. S., Ellis, A. J., Fyfe, W. S., and Taylor, A. M., 1959, The zeolite facies, with comments on the interpretation of hydrothermal syntheses: Geochim. et Cosmochim. Acta, v. 17, p. 53-107. Coombs, D. S., and Whetten, J. T., 1967, Composition of analcime from sedimentary and burial metamorphic rocks : Geol. Soc. America Bull., v. 78, p. 269-282. Curry, H. D., 1965, Geology of rock-forming sedimentary zeolites [abs.], in Abstracts for 1964: Geol. Soc. America Spec. Paper 82, p. 38. Deer, W. A., Howie, R. A., and Zussman, J., 1963, Framework silicates, v. 4 of Rock-forming silicates: New York, John Wiley & Sons, Inc., 435 p. Deffeyes, K. S., 1959a, Zeolites in sedimentary rocks: Jour. Sed. Petrology, v. 29, p. 602-609. ------1959b, Erionite from Cenozoic tuffaceous sediments, central Nevada: Am. Mineralogist, v. 44, p. 501-509. Dibblee, T. W., Jr., 1958, Tertiary stratigraphic units of western Mojave Desert, California : Am. Assoc. Petroleum Geologists Bull., v. 42, p. 135-144. ------1960, Geologic map of the Barstow quadrangle, San Bernardino County, California: U.S. Geol. Survey Mineral Inv. Field Studies Map MF-233. ------1961, Evidence of strike-slip movement on northwesttrending faults in Mojave Desert, California, in Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-B, p. B197-B199. ------1963, Geology of the Willow Springs and Rosamond quadrangles, California: U.S. Geol. Survey Bull. 1089-C, p. 141-253. ------1967, Areal geology of the western Mojave Desert, California : U.S. Geol. Survey Prof. Paper 522, 153 p. Durrell, Cordell, 1953, The Solomon and Ross strontianite deposits, Mud Hills, San Bernardino County, California, in Geological investigations of strontium deposits in southern California: California Div. Mines and Geology Spec. Rept. 32, p. 23-36. Eugster, H. P., and Smith, G. I., 1965, Mineral equilibria in the Searles Lake evaporites, California: Jour. Petrology, v. 6, p. 473-522. Garrels, R. M., and Christ, C. L., 1965, Solutions, minerals, and equilibria: New York, Harper and Row, 450 p. Garrels, R. M., and Howard, P. F., 1959, Reactions of feldspar and mica with water at low temperature and pressure, in Swineford, Ada, ed., Clays and clay minerals: Sixth Natl. Conf. on Clays and Clay Minerals Proc., p. 68-88. Goldsmith, J. R., and Laves, Fritz, 1954, The microcline-sanidine stability relations: Geochim. et Cosmochim. Acta, v. 5, p. 1-19. Goodwin, J. H., and Surdam, R. C., 1967, Zeolitization of tuffaceous rocks of the Green River Formation, Wyoming: Science, v. 157, p. 307-308. Gruner, J. W., 1936, Hydrothermal alteration of montmorillonite to feldspar at 245°C and 300°C [abs.] : Am. Mineralogist, v. 21, p. 201. Gude, A. J., 3d, and Sheppard, R. A., 1966, Silica-rich chabazite from the Barstow Formation, San Bernardino County, southern California: Am. Mineralogist, v. 51, p. 909-915. Hay, R. L., 1963, Stratigraphic and zeolitic diagenesis of the John Day Formation of Oregon: California Univ. Pubs. Geol. Sci., v. 42, p. 199-262.REFERENCES 33 ------1964, Phillipsite of saline lakes and soils: Am. Mineralogist, v. 49, p. 1366-1387. ------1965, Pattern of silicate authigenesis in the Green River Formation of Wyoming [abs.], in Abstracts for 1964: Geol. Soc. America Spec. Paper 82, p. 88. ------1966, Zeolites and zeolitic reactions in sedimentary rocks: Geol. Soc. America Spec. Paper 85,130 p. Hay, R. L., and Moiola, R. J., 1963, Authigenic silicate minerals in Searles Lake, California: Sedimentology, v. 2, p. 312-332. Hemley, J. J., 1959, Some equilibria in the system K2O-AI2O3-SiCL-HiO: Am. Jour. Sci., v. 257, p. 241-270. ------1962, Alteration studies in the systems NasO-ALOj-SiOs- H20 and K20-Al203-Si02-H20 [abs.], in Abstracts for 1961: Geol. Soc. America Spec. Paper 68, p. 196. Hemley, J. J., and Jones, W. R., 1964, Chemical aspects of hydrothermal alteration with emphasis on hydrogen metasomatism: Econ. Geology, v. 59, p. 538-569. Hess, P. C., 1966, Phase equilibria of some minerals in the K2O-Na20-Al203-Si02-H20 system at 25°C and 1 atmosphere: Am. Jour. Sci., v. 264, p. 289-309. Hey, M. H., and Bannister, F. A., 1934, Studies on the zeolites; pt. VII, “Clinoptilolite,” a silica-rich variety of heulandite: Mineralog. Mag., v. 23, p. 556-559. Hoover, D. L., and Shepard, A. O., 1965, Zeolite zoning in volcanic rocks at the Nevada Test Site, Nye County, Nevada [abs.]: Am. Mineralogist, v. 50, p. 287. Iijima, Azuma, and Hay, R. L., 1968, Analcime composition in the Green River Formation of Wyoming: Am. Mineralogist, v. 53, p. 184-200. Jones, B. F., 1965, The hydrology and mineralogy of Deep Springs Lake, Inyo County, California: U.S. Geol. Survey Prof. Paper 502-A, 56 p. [1966]. Knopf, Adolph, 1918, Strontianite deposits near Barstow, California : U.S. Geol. Survey Bull. 660, p. 257-270. Lewis, G. E., 1964, Miocene vertebrates of the Barstow Formation in southern California, in Short papers in geology and hydrology: U.S. Geol. Survey Prof. Paper 475-D, p. D18-D23. ------1968, Stratigraphic paleontology of the Barstow Formation in the Alvord Mountain area, San Bernardino County, California, in Geological Survey research 1968: U.S. Geol. Survey Prof. Paper 600-C, p. C75-C79. McCulloh, T. H., 1960, Geologic map of the Lane Mountain quadrangle, California: U.S. Geol. Survey open-file report. ------1965, Geologic map of the Nebo and Yermo quadrangles, San Bernardino County, California: U.S. Geol. Survey open-file report. Mason, Brian, and Sand, L. B., 1960, Clinoptilolite from Patagonia, the relationship between clinoptilolite and heulandite : Am. Mineralogist, v. 45, p. 341-350. Merriam, J. C., 1911, A collection of mammalian remains from Tertiary beds on the Mohave Desert: California Univ. Dept. Geol. Sci. Bull., v. 6, p. 167-169. Miller, W. J., 1944, Geology of parts of the Barstow quadrangle, San Bernardino County, California: California Jour. Mines and Geology, v. 40, p. 73-112. Minato, Hideo, 1964, Two zeolites in zeolitic rocks in Japan (potassium clinoptilolite and powdery mordenite) [abs.], in Program of Zeolite Symposium: Internat. Mineralog. Assoc., New Delhi, India, 1964, p. 3. Moiola, R. J., 1964, Authigenic mordenite in the Esmeralda “Formation,” Nevada: Am. Mineralogist, v. 49, p. 1472-1474. Moore, J. G., and Peck, D. L., 1962, Accretionary lapilli in volcanic rocks of the western continental United States: Jour. Geology, v. 70, p. 182-193. Mumpton, F. A., 1960, Clinoptilolite redefined: Am. Mineralogist, V. 45, p. 351-369. Murray, John, and Renard, A. F., 1891, Report on deep-sea deposits, in Report on the scientific results of the voyage of H.M.S. Challenger during the years 1873-76: London, 520 p. Nemecz, E., and Varju, G., 1962, Sodium bentonitization, clino-ptylolitization, and adularization in the rhyolitic tuffs of the Szerencs piedmont area: Acta Geologica, v. 6, p. 389-427. Noble, D. C., 1967, Sodium, potassium, and ferrous iron contents of some secondarily hydrated natural silicic glasses: Am. Mineralogist, v. 52, p. 280-286. Noble, L. F., 1926, Borate deposits in the Kramer district, Kern County, California: U.S. Geol. Survey Bull. 785, p. 45-61. Nockolds, S. R., 1954, Average chemical compositions of some igneous rocks: Geol. Soc. American Bull., v. 65, p. 1007-1032. Orville, P. M., 1964, Is K-feldspar stable in a near-surface environment? [abs.], in Abstracts for 1963: Geol. Soc. America Spec. Paper 76, p. 126. Pack, R. W., 1914, Reconaissance of the Barstow-Kramer region, California: U.S. Geol. Survey Bull. 541, p. 141-154. Pettijohn, F. J., 1967, Sedimentary rocks [2d ed.] : New York, Harper and Bros., 718 p. Pipkin, B. W., 1967, Mineralogy of 140-foot core from Willcox Playa, Cochise, Arizona [abs.]: Am. Assoc. Petroleum Geologists Bull., v. 51, p. 478. Regis, A. J., and Sand, L. B., 1966, K-Na phillipsite, Crooked Creek, Oregon [abs.] : Am. Mineralogist, v. 51, p. 270. Regnier, Jerome, 1960, Cenozoic geology in the vicinity of Carlin, Nevada: Geol. Soc. America Bull., v. 71, p. 1189-1210. Ross, C. S., 1928, Sedimentary analcite: Am. Mineralogist, v. 13, p. 195-197. Saha, Prasenjit, 1959, Geochemical and X-ray investigation of natural and synthetic analcites: Am. Mineralogist, v. 44, p. 309-313. ------1961, The system NaAlSiOi (nepheline)-NaAlSi3Os (al- bite)-H20: Am. Mineralogist, v. 46, p. 859-884. Sand, L. B., and Regis, A. J., 1966, An unusual zeolite assemblage, Bowie, Arizona [abs.], in Abstracts for 1965; Geol. Soc. America Spec. Paper 87, p. 145-146. Schoen, Robert, and Lee, D. E., 1964, Successful separation of silt-size minerals in heavy liquids, in Geological Survey research 1964: U.S. Geol. Survey Prof. Paper 501-B, p. B154-B157. Schultz, L. G., 1963, Nonmontmorillonitic composition of some bentonite beds, in Bradley, W. F., ed., Clays and clay minerals : Eleventh Natl. Conf. on Clays and Clay Minerals, Proc. p. 169-177. Senderov, E. E., 1963, Crystallization of mordenite under hydro-thermal conditions: Geochemistry, v. 1, p. 848-859. Shaw, D. M., 1956, Major elements and general chemistry, pt. 3 of Geochemistry of pelitic rocks: Geol. Soc. America Bull., v. 67, no. 7, p. 919-934. Shepard, A. O., and Starkey, H. C., 1964, Effect of cation exchange on the thermal behavior of heulandite and clinoptilolite, in Short papers in geology and hydrology : U.S. Geol. Survey Prof. Paper 475-D, p. D89-D92.DIAGENESIS OF TUFFS, BARSTOW FORMATION, SAN BERNARDINO COUNTY, CALIF. 34 Sheppard, R. A., 1967, Measured sections of the Barstow Formation, Mud Hills, San Bernardino County, California: U.S. Geol. Survey open-file report, 29 p. Sheppard, R. A., and Gude, A. J., 3d, 1964, Reconnaissance of zeolite deposits in tuffaceous rocks of the western Mojave Desert and vicinity, California, in Geological Survey research 1964: U.S. Geol. Survey Prof. Paper 501-C, p. C114-C116. ------1965a, Potash feldspar of possible economic value in the Barstow Formation, San Bernardino County, California: U.S. Geol. Survey Circ. 500, 7 p. ------1965b, Zeolitic authigenesis of tuffs in the Ricardo Formation, Kern County, southern California, in Geological Survey research 1965: U.S. Geol. Survey Prof. Paper 525-D, p. D44-D47. ---—1968, Distribution and genesis of authigenic silicate minerals in tuffs of Pleistocene Lake Tecopa, Inyo County, California : U.S. Geol. Survey Prof. Paper 597, 38 p. Sheppard, R. A., Gude, A. J., 3d, and Munson, E. L., 1965, Chemical composition of diagenetic zeolites from tuffaceous rocks of the Mojave Desert and vicinity, California : Am. Mineralogist, v. 50, p. 244-249. Shumenko, S. I., 1962, Varieties of authigenic sedimentary heulandite in the upper Cretaceous of the Ukraine: Akad. Nauk SSSR Doklady, v. 144, p. 1347-1350. Smith, G. I., and Haines, D. V., 1964, Character and distribution of nonclastic minerals in the Searles Lake evaporite deposit, California: U.S. Geol. Survey Bull. 1181-P, 58 p. Smith, J. V., 1963, Structural classification of zeolites : Mineralog. Soc. America Spec. Paper 1, p. 281-290. Steinen, R. P., 1966, Stratigraphy of the middle and upper Miocene Barstow Formation, San Bernardino County, California : California Univ., Riverside, unpub. M.A. thesis, 150 p. Sudo, Toshio, Nisiyama, Tsutomu, Chin, Kenshin, and Hayashi, Hisato, 1963, Mordenite and clinoptilolite in glassy tuffs of Japan: Geol. Soc. Japan Jour., v. 69, p. 1-14. Surdam, R. C., and Hall, C. A., 1968, Zeolitization of the Obispo Formation, Coast Ranges of California [abs.j, in Abstracts for 1966: Geol. Soc. America Spec. Paper 101, p. 338. Van Houten, F. B., 1960, Composition of upper Triasic Locka-tong argillite, west-central New Jersey: Jour. Geology, v. 68, p. 666-669. ------1965, Composition of Triassic Lockatong and associated formations of Newark Group, central New Jersey and adjacent Pennsylvania: Am. Jour. Sci., v. 263, p. 825-863.INDEX Page Acknowledgments_________________________________ 4 Alteration, stages, fresh vitric tuff to zeolitic tuff.______________________________ 20 Analcime...................................... 10 composition________________________________ 11 formation__________________________________ 26 formed from reaction of zeolites with water............................... 28 in mudstones............................... 7 indicator of saline-lake environment____ 27 replacement by potassium feldspar------- 20 Analcite. See Analcime. Analyses, chemical, analcime.................... 11 chemical, chabazite........................ 11 clinoptilolite.......................... 14 mordenite............................... 15 mudstones............................... 8 phillipsite............................. 15 mineral content, mudstones.................. 8 mineralogic, Skyline tuff.................. 24 shards, Hemicyon tuff----------------------- 9 unit cell composition, analcime ------------ 11 chabazite.............................. 11 clinoptilolite......................... 14 mordenite............................. 15 phillipsite........................... 15 Animal tracks.............................. 8 Barite________________________________________ 13 Barstow Formation, chemical environment-. 26 depositional environment................... 27 fossils.................................. 1,8 stratigraphy and lithology-------------- 5 topographic features----------------------- 5 Barstow syncline________________________________ 5 Blackmon, Paul D., analyst______________________ 8 Calcite, in cavities in mudstone............... 8 Camel track tuff, outcrop extent---------------- 6 Carbonate rocks_________________________________ 8 Chabazite___________________________________ 12 composition________________________________ 11 Chemical parameters controlling formation of silicates__________________________ 26 Clay minerals................................. 12 in mudstones________________________________ 7 Clinoptilolite______________________________ 12 analyses___________________________________ 14 zoning.................................... 13 Colemanite.................................. 27 Conglomerate................................... 6 Crystals in tuffs.............................. 9 Daniels, Ellen S., analyst-------------8,9,11,14 Dated tuff, outcrop extent..................... 6 Dolomite____________________________________ 8,27 Erionite..................................... H Feldspar, formation--------------------------- 26 Formulas of selected alkalic zeolites---------- 10 [Italic page numbers indicate major references] Page Fossils in Barstow Formation_________________ 1,8 Gaylussite___________________________________ 8,27 Geology, regional_______________________________ 4 Glass, solution to form zeolites________________ 28 Gypsum........................................... 7 Hay, R. L., zeolite formulas.................... 10 Hemicyon tuff, accretionary lapilli______________ 8 analyses of chabazite.................. 11 analyses of clinoptilolite_____________ 14 analyses of shards..................... 9 outcrop extent.___________________________ 6 states of alteration..................... 20 Laboratory methods........................... 8 Lapilli, accretionary, in tuffs______________ 8 Limestone--------------------------------------- 8 Lithology, Barstow Formation____________________ 5 Location of area................................ 1 Mammal tracks----------------------------------- 27 Metasomatism during diagenesis__________________ 82 Mineral associations, analcime------------------ 10 chabazite________________________________ 12 clinoptilolite............................ 13 erionite................................ 14 mordenite.................................. 14 opal..................................... 15 phillipsite______________________________ 15 potassium feldspar_____________________ 16,20 quartz................................ 17 relationship to depositional environment.. 27 Montmorillonite________________________________ 20 Mordenite------------------------------------ H detection method......................... 4 Mud cracks----------------------------------- 8,27 Mudstone______________________________________ 7 Munson, Elaine L., analyst------------------- 11 Neiman, Harriet, analyst------------------------- 9 Opal.........................................15,30 in analcime.............................. 11 Ostracodes...................................... 8 Paragenesis, authigenic silicate minerals....... 20 zeolites................................ 28 Petrography, altered tuffs--------------------- 18 pH, relation to mineral formation.............27,28 Phillipsite.................................. 15 spherulites.............................. 16 in Yellow tuff........................ 19 Plagioclase feldspar, replacement by potassium feldspar--------------------------------- 21 Potassium feldspar. -------------------------- 16 factors affecting formation--------------- £0 formation from zeolitic precursors........ 21 formed by reaction of zeolites with water. 80 in mudstones............................ 7 indicator of saline-lake environment--- 27 synthesized........-....--------------- 30 Page Previous studies------------------------------ 1 Quartz_______________________________________ 17,30 References....................-.............. 32 Regional geology ............................ 4 Rock fragments in tuffs------------------------- 9 Salinity, correlation with silicate minerals_ 27 Sampling------------------------------....... 3 Sandstone__________________________________ - 6 Scope of study................................... 2 Searlesite------------------------------- — 27 Shards........................................... 9 Silicate minerals, authigenic, paragenesis___ 20 genesis................................ 26 Siltstone........................................ 6 Skyline tuff, accretionary lapilli........... 8 analyses of clinoptilolite ............. 14 effect of chemical zonation of pore water during diagenesis_______________ 27 mineralogic composition—................. 24 outcrop extent---------------------------- 6 sequence of formation................... 25 variations in authigenic mineralogy----- 21 Spherulites, phillipsite.........t...........- - 16 Stratigraphy, B arstow Formation................ 5 Strontianite..................................... 1 Thenardite.................................. 7,27 altered, field description—............ 17 analcimic_________________________________ 20 composition. _______________________________ 8 distinguishing characteristics of types- 18 metasomatism during diageneis.............. 82 nonanalcimiczeolitic .................... 19 original texture and structure------------- 8 petrography----------------------------- 18 potassium feldspar-rich--------------- — 20 relationship between authigenic mineralogy and thickness------------------------- 26 salinity-silicate mineralogy correlation- 27 Vitric material in tuffs....................... 9 Water, pore, relation to analcime formation- 29 pore, relation to potassium feldspar formation------------------------------------- 30 Yellow tuff, analyses of phillipsite____________ 15 clay minerals........................... 12 outcrop extent............................. 6 phillipsite spherulites................... 19 Zeolites, alkalic, formulas_____________________ 10 factors controlling type formed------------ 28 formation--------------------------------- 26 formed from solution of glass______________ 28 paragenesis-........,................... 28 reaction with water to form analcime---- 28 reaction with water to form potassium feldspar.__________________________ 80 Zoning, in clinoptilolites______________________ 13 35 U. S. GOVERNMENT PRINTING OFFICE : 1969 O - 336-374 " ■ . . ' - > •' . . >••• * 4'tit/t TC> . v. 6>55 7 D*v ✓ r CES .iW Uppermost Cretaceous and Tertiary Stratigraphy of Fossil Basin, Southwestern Wyoming GEOLOGICAL SURVEY PROFESSIONAL PAPER 635 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN Fossil Butte, world-famous source of extraordinarily well preserved Eocene fresh-water fish, rays, hats, birds, plants, and insects and the type locality for the new Fossil Butte Member of the Green River Formation, is in sees. 5 and 6, T. 21 N., R. 117 W., and sec. 31, T. 22 N., R. 117 W., about 10 miles west of Kemmerer, Wyo. Dark exposures in the lower part of the butte are of the red, purple, yellow, and brown main body of the Wasatch Formation. The light cliffs and talus slopes mark exposures of the overlying brown, yellow, and white Fossil Butte Member of the Green River Formation. Above the cliffs and at the top of the butte are pale bands of the yellow to buff Angelo Member of the Green River Formation. The top of the vegetation band, at the base of the cliffs, marks the contact between the Wasatch and Green River Formations. The contact is the source of numerous springs. The aquifer commonly forms a bench above hummocky slumped topography. The buildings in the right foreground mark the site of Fossil, along an abandoned part of the Union Pacific Railroad. The curved road climbing the left (west) side of the butte leads to a quarry from which hundreds of fossil fish have been removed. A closer view of the hill of Wasatch strata on the left is shown in figure 10.Uppermost Cretaceous and Tertiary Stratigraphy of Fossil Basin, Southwestern Wyoming By STEVEN S. ORIEL and JOSHUA I. TRACEY, JR. GEOLOGICAL SURVEY PROFESSIONAL New subdivisions of the J ,000-foot-thick continental Evanston, Wasatch, Green River, and Fowkes Formations facilitate understandi?ig of sediment genesis and Wyoming thrust-belt tectonic events PAPER 635 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director Library of Congress catalog-card No. 70-604646 i. For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 65 cents (paper cover)Addenda and Errata: Uppermost Cretaceous and Tertiary stratigraphy of Fossil Basin, southwestern Wyoming: U.S. Geological Survey Professional Paper 635, 1970. Page 12, column 1, line k, and index (page 52): Konoletes should be Monolites. Page 12, column 2, line 20, and index (page 52): It should be Tricolporopollenites kruschi subsp. contortus. Page 13, column 1, and index (page 51): Araucariacidites should be Araucariacites. Page 13, near bottom of column 1, and index (page 52): It should be Tricolporopollenites microreticulatus. Page 13, column 2, paragraph beginning "The Cretaceous and Paleocene ages of the Evanston While the report was in press, vertebrate remains from another Evanston exposure within the Fossil Basin were described in print by Gazin /Gazin, C. Lewis, 1969, A new occurrence of Paleocene mammals in the Evanston Formation, southwestern Wyoming: Smithsonian Contributions to Paleobiology No. 2, p. The fossils are assigned a Torrejonian or middle Paleocene age, partially filling the gap in ages of previously reported collections. Nevertheless, the early and early middle Paleocene (Puercan and Dragonian) gap in age data remains. * Page 15, figure 8. The exposure north of the center of sec. 29, T. 23 N., R. Il6 WT., should be labeled Keh, rather than TKe. Page l6, column 1, last paragraph: Should read as follows: West of Almy in the bluffs on the sec. 3 and sec. 10, T. 23 N., R. 118 W., where three thin tongues of limestone wedge out into the Tunp Member (fig. 15Z?). The two lower limestone tongues are traceable eastward into the Fossil Butte and the Angelo Members of the Green River Formation, and the upper limestone bed is traceable into limestone beds in the Bullpen Member of the Wasatch Formation. Thus, the Tunp Member is equivalent in age to the whole Wasatch Formation in Fossil basin and is likely of early Eocene age, although parts may be slightly younger (table 4). No fossils have been found in the Tunp Member. ORIGIN The complex heterogeneity in composition of rocks assigned to the Wasatch Formation suggests a marked range in continental depositional environments. Most of the formation is of alluvial origin. At least some of the detritus, however, has barely been transported, if at all, and seems to be the product of residual weathering. Large volumes of detritus moved as mudflows and rock-slides rather than as saltating or suspended particles in a stream. Still other detritus may have been transported by streams and deposited within the lake in which the Green River Formation was deposited. The alluvial origin of much of the Wasatch is shown by many exposures of the main body. Extensive brightly colored bands of mudstone, which were deposited on flood plains, are cut by lens-shaped channels now filled by well-sorted conglomerate deposited as well-rounded and fairly clean gravel. Exposures are too discontinuous in the northern Fossil basin to permit mapping of these ancient stream courses. The basal conglomerate member illustrates deposits that formed after little or no transport. The rocks consist almost entirely of Nugget detritus now resting on the Nugget Sandstone. The conglomerate matrix consists of disaggregated Nugget sand grains. Coarser clasts are rounded, but this rounding may reflect spher-WASATCH FORMATION 29 oidal weathering in a more humid climate than at present rather than abrasion during transport. Around the periphery of the basin, other parts of the Wasatch also grade outward from the basin from well-sorted detrital beds through conglomerate to poorly sorted sedimentary breccia. At several places, this sedimentary breccia resembles a talus slope formed on an old surface of Mesozoic rocks; in a sense the talus represents a glimpse of an exhumed Eocene landscape. Interstices between the talus blocks are filled with red mud or pink sand like that elsewhere in the Wasatch Formation; in a few places the talus blocks are cemented by Green River limestone, thus preserving an old shoreline of the Eocene lake. Gravitational sliding and splifluction were probably the chief agents of transport for the Tunp Member (Tracey and others, 1961). The lack of sorting and rounding, the presence of large blocks scattered in sandy mudstone, the absence of bedding, and the steep topographic slopes along which the deposits accumulated suggest that, gravity predominated over running water. The deposits appear to have formed from mudflows and slides of both weathered material and fresh blocks of older rocks on steep slopes bounding the basin. The in-tertonguing relation between the Wasatch-Tunp diamic-tite and Green River limestones suggests that at least some of the mudflows may have swept into the Eocene lake as large deltas. Abundant water acting as a lubricant is likely, and inferred periods of heavy rainfall are consistent with the savanna climate commonly interpreted for the region. At least some of the strata assigned to the sandstone and mudstone tongues of the Wasatch may also have been deposited within the lake, possibly as deltas, offshore bars, and blanket bottom deposits, but an alluvial origin can also be inferred from the available data. Numerous green mudstone beds suggest possible local reducing environments. Thin and extensive limestone beds in the Bullpen Member indicate that the flood plains on which most of these strata were deposited were, during brief intervals, flooded by the Eocene lake. Whether these intervals of lake expansion reflect periods of especially heavy rainfall or abrupt sinking of the Fossil basin is not known. Tlie evidence from rock composition and fossils supports a very wet warm temperate to semitropical climate' (Van Houten, 1961, p. 122) for the region during Wasatch deposition. Red upland soils formed in moderately wooded areas giving way downslops to savattna environments (Va/i Houten, 1964, p. 83) with abundant streams and ponds. The paucity of coal mdi-cates that the area was moderately well drained. TECTONIC IMPLICATIONS The presence of considerable relief around the periphery of the Fossil basin is amply documented by the great ranges in sorting and grain size of Wasatch detritus, by the overlap of higher strata over lower strata onto older rock formations, and by channeling, as well as by observed local facies of Wasatch strata. Movement on all the thrust faults exposed north and west of the Fossil basin had ceased before Wasatch deposition, for the formation unconformably qverlies traces of the faults; gross elements of present topography, reflecting structure of the western Wyoming thrust belt, had already formed by earliest Eocene time. Many of the present topographic features are exhumed elements of an early Eocene landscape. Some, however, are not. The Tunp Member on Boulder Ridge, north and south of Sage, for example, records an apparent reversal of relief. Boulder Ridge is bounded on the west now by the wide valley of the Bear River. Yet the Tunp Member on the ridge contains enormous blocks, as much as 600 feet in maximum diameter, of Paleozoic carbonate rocks and fragments of Cretaceous rocks. The source of these clasts must have been a moderately high and steep mountain to the west, which was capped by the upper plate of the Crawford thrust fault. Post-Wasatch normal faulting likely down-dropped this mountain after Tunp deposition; erosion alone could not account for the present topography because of the greater resistance of formations above the Crawford fault than below it. Data are inadequate to date the normal faulting. Other localities at which Wasatch detritus now stands considerably higher than the source formations include Rock Creek Ridge, where blocks of conglomerate in the Tunp Member Jie on the crest of the ridge, 1,500 feet higher than present exposures several miles to the west of the Ephraim Conglomerate from which they were derived. The large exposures of Tunp diamic-tite that form rounded prominences on Dempsey Ridge are 800 feet or more higher than those on Rock Creek Ridge. Deformation during the Eocene, presumably associated with block faulting, is recorded along the east side of the Tunp Range where the main body overlies the lower unnamed member of the Wasatch with angular-unconformity. Some block faults of Eocene age have also been recognized farther east in the Fort Hill quadrangle.(Oriel, 1969). The mudflows and’rockslides believed to have formed the diamictite facies may have been triggered by earthquakes as well as by heavy rainstorms. Broad open and gentle folds have been recognized locally in Wasatch strata. Regionally the structure of30 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING Wasatch and Green River strata in the Fossil basin is a synclinorium to which the name Fossil syncline was applied by Yeatch (1907, p. 110, pi. 4). Mapping and drilling in the Sage, Kemmerer, and adjoining quadrangles indicate that structures in Tertiary strata do not reflect deeper and tighter structures in older rocks; rather, they reflect differential compaction and draping over buried topography and, in places, primary sedimentary dips. GREEN RIVER FORMATION NAME AND USAGE DEFINITION The Green River Formation was named by Hayden (1869, p. 90-91) for the sequence * * * composed of thinly laminated chalky shales * * *, best displayed along Green River. They are evidently of purely freshwater origin, and of middle tertiary age. The layers are nearly horizontal, and, as shown in the valley of Green River, present a peculiarly banded appearance * * *. One of the marked features of this group is the great amount of combustible or petroleum shales * * *. Despite widespread usage, the name is still used mainly in the original sense for - the light-colored laminated calcareous beds between the red-hued beds of the underlying Wasatch Formation and the green -hued beds of the overlying Bridger Formation. LITHOLOGIC HETEROGENEITY The Green River Formation in the Fossil basin is a heterogeneous sequence whose unity is principally in primary structure and somewhat in color. Its heterogeneity is best expressed by an inventory of rock compositions including: white, buff, and brown aphanitic relatively pure to clayey limestone; white indurated ostracode and gastropod coquina; algal limestone; marl-stone; light- to dark-gray, green, and brown mudstone and claystone; light- to medium-gray and tan siltstone; white- and brown-weathering gray sandstone, which has claystone and chert fragments in places; oil shale and petroliferous marlstone and mudstone; silicified limestone and chert; volcanic ash and tuff. Nevertheless, the sequence constitutes a mappable formation. The light shades of tan, yellow, white, green, and brown contrast markedly, even from a distance, with the more vivid shades of reds predominating in both the underlying and overlying units. Closer examination shows the overwhelming dominance throughout the unit of the thinly laminated structure and argillaceous strata mentioned by Hayden in his first published description (1869). SUBDIVISIONS USED HERE The Green River Formation of the Fossil basin is here divided into two units: a lower or Fossil Butte Member, characterized by tan to buff ledge-forming limestone, marlstone, and brown oil shale in which are the principal fish-bearing beds; and an upper or Angelo Member, characterized by white-weathering limestone that contains much nodular and slabby chert and by grayish-green claystone. FOSSIL BUTTE MEMBER NAME AND TYPE The Fossil Butte Member of the Green River Formation is here named for the excellent exposures on the south side of Fossil Butte (frontispiece) and along the north and east sides of Fossil Ridge, 10 miles west of Kemmerer, where the most extensive fossil fish quarries have been worked. The beds near the southeast end of the butte, in the SW14NW14 sec. 5, T. 21 N., R. 117 W., have been selected as the type section of the member (see p. 43-44). ROCKS INCLUDED The Fossil Butte Member at the type section consists of four units, each characterized by several dominant rock types. A basal mudstone unit about 45 feet thick consists of beds of light-gray fine-grained to very fine grained calcareous sandstone, mudstone, and siltstone. Above this unit is a tannish-gray limestone unit about 75 feet thick, containing light-gray to tan limestone, shaly limestone, siltstone, and chocolate-colored paper shale capped by a 6-foot bed of dark-yellowish-brown mudstone. This is overlain by a buff shale unit 45 feet thick consisting of predominantly buff-weathering laminated limy shale beds, organic paper shale, and thinly laminated oil shale, alternating with beds of white to buff marlstone. Thin ash beds % to 2 inches thick are scattered throughout. The main bed quarried for fossil fish is 10 feet below the top of this unit. The uppermost unit, 40 feet thick, is marked by the presence of several bands made up of thin beds of rich oil shale that weather a characteristic light-grayish white that seems bright blue in sunlight. This unit is capped by a ledge-forming limestone that weathers orange yellow, speckled by rusty spots. Several of the oil shale beds contain scattered to packed small crystals of calcite pseudomor-phous after evaporite minerals, and these give the beds a coarse sugary texture. Ash beds 1-5 mm thick are common, and beds as much as 20 mm thick are present in the upper half of the member. Some of these beds, near the fish beds, are characteristic enough to be traced over a fairly large part of the Fossil basin, but as yet we have not been able toGREEN RIVER FORMATION 31 correlate sequences of ash falls with those in the Fort Hill quadrangle in the Green River Basin. A tongue of crossbedded sandstone which we assign to the Wasatch Formation separates the lower mudstone section of the member from the upper part in the south end of the Kemmerer and Sage quadrangles. The tongue reaches a maximum thickness of about 50 feet, and it pinches out to the north and east within Fossil Ridge. North and east of the limits of the sandstone tongue, the lower mudstone unit of the Fossil Butte Member contains only minor amounts of organic shales or laminated limestone beds. In the headwaters of Clear Creek, however, in sec. 33, T. 21 N., R. 118 W., about 40 feet of laminated carbonaceous shale, including oil shale, and buff laminated limestone with fishbearing beds similar to those in the upper part of the Fossil Butte Member lie beneath a 40-foot ledge of the sandstone tongue. In the Roy Steele 1 Government well 4 miles to the south-southwest, in the NE14 NF14NF14 sec. 29, T. 20 N., R. 118 W., 323 feet of the Green River type of shale was reported in the interval 560-883 feet, above mudstone of the Wasatch Formation and below a 65-foot bed of sandstone that we interpret as the sandstone tongue of the Wasatch. Apparently the lower part of the Fossil Butte Member thickens to the south, along the trend of the Fossil synclinal axis of Veatch (1907), although very little of the lower part of the member is exposed south of the Kemmerer and Sage quadrangles. Facies changes within the Fossil Butte Member are similar to those described for the Green River Formation in other basins. Organic-rich limestones and shales near the central, deeper parts of the Fossil basin grade laterally through ostracodal and gastropodal limestones to algal limestones, marking the near-shore shallow-water lacustrine deposits of the Green River Formation (Bradley, 1926, p. 125-126). DISTRIBUTION AND THICKNESS The Fossil Butte Member is the most extensive part of the Green River Formation in the Fossil basin. This member extends farther toward peripheries of the basin than other parts of the formation. Thin limestone units observed in the southern part of the basin probably represent tongues of the Fossil Butte Member that extend into detrital rocks shed by the ancient Uinta Mountains (Anderman, 1955; Lawrence, 1963). The Fossil Butte Member is 267 feet thick in the valley of the South Fork of Twin Creek 3 miles south of the Kemmerer quadrangle. It is 208 feet thick on Fossil Butte (frontispiece) near the center of the Fossil basin. Buff-weathering laminated limestone ledges extend northward and northwestward from the center of the basin and remain fairly uniform. Interbedded tan, brown, and gray claystone and mudstone, however, grade through shades of green into red mudstone and coarser detrital rocks of the Wasatch Formation. On Tunp Range, west of Dempsey Basin and several miles north of the Kemmerer and Sage quadrangles, the limestone ledges thin from 50 feet to an edge in red clay of the Tunp Member of the Wasatch; the horizon of the limestone is recognizable even beyond its edge for it is marked in the Wasatch Formation by a surface of abundant algal logs (fig. 12), as on the north side of Pink Butte in sec. 28, T. 24 N., R. 117 W., and east of Hams Fork along the northern part of the Kemmerer quadrangle. LOWER CONTACT The contact of the Green River Formation and the main body of the Wasatch Formation is apparently sharp and conformable in most places. Commonly, it is marked by a bench or by numerous slump blocks heading at the contact (frontispiece). The slumps result from water seeping down through the more permeable siltstone and sandstone beds of the Green River and through block fractures of the jointed shale and limestone of the Green River into the less permeable mudstone of the Wasatch. In a few places, the contact at the base of the Green River is also gradational vertically. Within a few feet red mudstone below the Green River grades upward to very calcareous green mudstone, gray marlstone, and limestone. The regional relation between the two units, however, is far more complex. Because the two formations are known to grade into one another in part laterally, the lower contact of the Green River Formation is not isochronous. Moreover, individual limestone beds of the Green River Formation overlap the lower unit of the Wasatch Formation, and in places, rest directly on Mesozoic and Paleozoic rocks with angular unconformity. The irregularity of this unconformable surface indicates a moderate amount of topographic relief around the edges of the Fossil basin even during deposition of the Green River Formation. ANGELO MEMBER NAME AND TYPE Between the mudstone tongue and the Bullpen Member of the Wasatch Formation is a sequence of strata here named the Angelo Member of the Green River Formation for the excellent exposures high on the buttes overlooking the Angelo Ranch along the South Fork of Twin Creek, about 2.7 miles south of the Kemmerer quadrangle. Exposures in the type area are on these buttes and on spurs of Fossil Ridge, in the south-32 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING east corner of the Sage quadrangle. A section measured in the NW^4 sec. 1, T. 20 N., R, 118 W., is here designated the type section (see p. 14 -15). ROCKS INCLUDED The Angelo Member consists mainly of white- to blue-white-weathering limestone, marlstone, and mudstone, but includes siliceous limestone, chert, light-to medium-gray marly mudstone and claystone, and some sandstone beds and lenses. In general, very light tan to buff limestone is dominant in the northern parts of the Sage and Kemmerer quadrangles, whereas the member is whiter and more siliceous southward. A few thin to moderately thick units of low-grade oil shale that weather to brown papery shale are in the central part of the Fossil basin. The moderately organic shales and limestones and the subaphanitic marly limestones within the basin grade laterally through ostracodal and gastropodal limestone to algal limestone near the periphery of the basin, as in the Fossil Butte Member. DISTRIBUTION AND THICKNESS The Angelo Member is well represented in the buttes and mesas of the Hams Fork Plateau in the central part of the Fossil basin, from about the north edges of the Sage and Kemmerer quadrangles southward. The southern limits of the member have not been determined. Reconnaissance traverses suggest that the member intertongues with conglomerates shed by the Uinta Mountain uplift in the south-central part of the Fossil basin as observed by Veatch (1907, p. 97). The Angelo Member is about 200 feet thick in the central part of the basin but thins markedly and pinches out near the edges of the basin. FOSSILS AND AGE The Fossil Butte Member contains one of the best preserved and most extensive fossil assemblages known in North America. Fish, insects, and leaves abound, and even rays, bats, and birds are represented. Yet the precise age of the unit is not known. This reflects partly the absence of comparable forms in the standard and reference sections used to subdivide the North American continental Tertiary and partly the neglect, until very recently, of modem studies of the faunas and floras. Fossils previously reported from strata here assigned to the Fossil Butte Member include several forms of fish (Cope, 1877,1878,1884; Leidy, 1873; Thorpe, 1938; Hesse, 1939), a sting ray (Schaeffer and Mangus, 1965), bats (Jepsen, 1966), snakes (Schaeffer and Mangus, 1965), birds (Wetmore, 1933), insects (Scudder, 1890; Cockerell, 1920), and plants (Lesquereux, 1883; Brown, 1929, 1934), as well as abundant fresh-water mollusks, ostracodes, and alga] deposits. Fragments of similar fossils (fish, birds, insects, plants, mollusks, and ostracodes) have been found by us in the overlying Angelo Member, but these are far less abundant and more poorly preserved than in the Fossil Butte Member. Mollusks found by us in both members at numerous localities include Physa pleromatis White, Elimia? nodulifera (Meek), Bellamy a palvdinaeformis (Hall), Oreoconus n. sp. b, and Plesielliptio? (D. W. Taylor, written commun., Apr. 11 and 20,1960). In addition, the fresh-water snail Biom/phalarm pseudoammonius (Schlotheim) was found in several exposures of the Angelo Member. Ostracodes found in both members at several localities have been identified (I. G. Sohn, written commun., Apr. 15, 1959, Feb. 12, 1964) as “Hemicyprinotus” watsoensis Swain, Procyprois ravenridgensis Swain, and Pseudocypris sp. undescribed. Despite the abundance of well-preserved fossils, age assignments of the Green River Formation have been based on mammalian faunas from Wasatch strata that intertongue with the formation (Gazin, 1959, p. 135). The absence of diagnostic fossils from the overlying Bullpen Member of the Wasatch Formation precludes a precise age assignment for the Green River Formation in the Fossil basin. Although it commonly has been assigned a late early Eocene age (Gazin, 1959; McGrew and Roehler, 1960; Schaeffer and Mangus, 1965), the topmost strata may be younger or older than Lost Cabin. ORIGIN The lacustrine origin of the Green River Formation, recognized by Hayden (1869), has been amply demonstrated by the studies of Bradley (1926, 1929a, 1929b, 1930, 1931, 1948, 1959, 1963, 1964, 1966) in his notable contributions to paleolimnology. The abundance of varves, organic matter, and oil shale and the excellent preservation of abundant fish in exposures near the central part of the Fossil basin indicate that the lake in which the strata accumulated, named Fossil lake by Jepsen (1966, p. 1338), was thermally stratified and possibly deeper than 100 feet (Bradley, 1930, p. 101-103; 1963, p. 636). The abundance of algal, gastropodal, and ostracodal limestones, indices to shallow-water shore phases of the lake (Bradley, 1926), indicates that the shores of Fossil lake were along the present margins of the Fossil basin, although the lake mav have been connected briefly with the Eocene Gosiute lake in the Green River Basin (tig. 16). Eocene talus deposits of older rocks cemented by Green River limestone preserve the ancient lake shore at several lo-FOWKES FORMATION 33 Figure 16.—Locations of the Eocene lakes (showing maximum extent of each) in which the Green River Formation was deposited. (Modified from Schaeffer and Mangus, 1965.) calities. Fluctuations in the lake size are recorded in intertongues of Green River beds with Wasatch strata around the margin of the basin. The Wasatch tongues indicate (a) drops in lake level, (b) mudflows and rock-slides into the lake, and (c) several “floods” of detritus that may have been deposited within the lake as deltas and bottom sediments. Although Green River strata are now more than 1 mile above sea level, they were likely deposited at elevations of 1,000 feet or less (Bradley, 1930, p. 93—95; 1963, p. 633). The climate was humid subtropical to tropical (Bradley, 1966) and had a mean annual temperature of about 65°F and a rainfall of about 40 inches (Bradley, 1930, p. 93-95; 1963, p. 633). The paucity of evaporites (Fahey, 1962) indicates that Fossil lake did not undergo as great a saline cycle as did nearby lakes Uinta and Gosiute; whether this reflects continuous replenishment of the smaller lake by abundant streamflow or the ending of lacustrine deposition in the Fossil basin before the onset of a somewhat drier climate is not known. TECTONIC IMPLICATIONS The moderate depths at which the varied organic-rich fish-bearing strata near the middle of the Fossil basin must have been deposited indicate a continued down warp of this part of the earth’s crust. Fossil basin, formed by latest Cretaceous time, continued to sink through the middle and late early Eocene. Gentle folds and moderately steeply dipping strata along the flanks of the basin do not necessarily indicate postdepositional compressional deformation. Observed structures probably reflect, as in the Wasatch, differential compaction, draping over buried topography and, in places, primary dips. The overlap of underlying strata by Green River beds, which in places rest directly on older rocks, as well as other observed relations along the periphery of the basin, indicates that the area continued to be one of moderate relief. FOWKES FORMATION NAME AND USAGE DEFINITION The Fowkes Formation was named and defined by Veatch (1907, p. 90) as a thick series of light-colored beds composed largely of rhyolitic ash and containing thin layers of white limestone. These beds are well exposed [2 miles east of Almy] in the valley east of the Almy Hills and thence northward to the Narrows [of the Bear River]. This formation is named for the Fowkes ranch, about 9 miles [north] from Evanston, around which these beds are well exposed. Veatch (1907, p. 88) defined the Fowkes Formation as the middle formation of the Wasatch Group. He believed it was underlain by the dominantly reddish yellow beds of the Almy Formation and overlain by the dominantly reddish yellow beds of the Knight Formation, all of the Wasatch Group. SUBSEQUENT USAGE Since Veatch’s definition of the Fowkes, the unit has been a source of perplexity, if not confusion, to geologists working in the region. Almost nowhere has such a unit been found to subdivide the Wasatch Formation (or Group). For this reason and possibly because of the limited areal extent of the unit, the name has not been used except in brief reviews of Veatch’s report. An exception was the erroneous use of the name for another unit in the northern Wasatch Range (Eardley, 1944). SUGGESTED USAGE Because of the structural complexity of the Almy area along the east side of the Bear River, Veatch failed, in his reconnaissance study, to recognize all the faults in the vicinity of his type locality. He therefore emerged with an erroneous interpretation of the stratigraphic sequence. Detailed study of Fowkes exposures farther north and reconnaissance studies in the type locality have established beyond question that rocks assigned by Veatch to the Fowkes Formation overlie, and are therefore younger than, rocks assigned by him to both the Almy and the Knight, as well as to the Green River. The34 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING Fowkes Formation is, in fact, the youngest formation of unquestioned Tertiary age (Tracey and Oriel, 1959, p. 130) mapped by us in the region. The name Fowkes is retained, despite Veatch’s erroneous interpretation of the position of the formation in the section, because the rocks assigned to the formation constitute a rock-stratigraphic unit easily distinguished from others on the basis of lithologic characteristics. SUBDIVISIONS USED HEBE The Fowkes Formation is here divided into three new members: the Sillem Member at the base, consisting of pale-gray and pinkish-gray mudstone and gray conglomerate; the Bulldog Hollow Member in the middle, consisting of green tuffaeeous mudstone and sandstone ; and the Gooseberry Member at the top, consisting of light-gray to white calcareous and tuffaeeous puddingstone. SILLEM MEMBER NAME AND TYPE Directly above the Bullpen Member of the Wasatch Formation is a distinctive rock unit that was not mapped consistently by Veatch (1907, pi. 3) in the few places in which it is exposed. Some exposures were assigned to the Fowkes Formation, others to the Almy, and still others to Quaternary units. The composition of the rocks differs from that of the typical Fowkes. However, because we have studied the unit only locally, because the upper part of the unit grades upward into typical Fowkes strata, and because Veatch included the unit, in at least a few places, in his Fowkes Formation (as in the NE^4 sec. 8, T. 17 N., R. 120 W.), it is assigned here to the Fowkes Formation. The unit is here named the Sillem Member of the Fowkes for the best exposures seen on Sillem Ridge and in the badlands 1-2 miles north-northeast of Sage, here designated the type area. The type section was measured north of Sage, from about the center of sec. 5, T. 21 N., R. 119 W., to about the center of sec. 33, T. 22 N., R. 119 W. (see p. 46). ROCKS INCLUDED The Sillem Member consists of a basal conglomeratic unit and an upper pale mudstone unit. The conglomerate is absent from some sections examined by us, and in a few others its lithologic distinctiveness is equivocal. The most extensive, though rather poor, exposures of the unit are along butte and ridge tops, as on the crest of Sillem Ridge, where the concentration of pebbles probably is exaggerated by the ablation of finer particles. The basal conglomeratic unit includes conglomerate, sandstone, mudstone, and claystone. The conglomerate consists dominantly of very well rounded pebbles and boulders, some of which exceed 1 foot in diameter although most are less than 8 inches. The composition of the pebbles is distinctive and differs from that of the conglomerates in underlying and overlying formations. In the Sillem, they are largely medium- to dark-gray, in part black-flecked conglomeratic quartzite, dark-colored chert, and dark-colored Paleozoic limestone, at least some of which was derived from the Madison Limestone. The source of the conglomeratic quartzite may be the Brigham Quartzite in southeastern Idaho. Sandstone in the unit ranges from crossbedded coarse- to medium-grained very calcareous light-gray “salt-and-pepper” (dark-gray and black chert is the “pepper”) beds to very poorly indurated muddy pale-tan, pink, and light-gray beds that may contain some volcanic ash. The mudstone and claystone is also pale pink, tan, and gray. The upper unit of the Sillem Member consists dominantly of mudstone and claystone that grade from very pale pink, yellow, and gray in the lower part through predominantly pale gray in the middle to pale green and gray in the upper part. Green and purple mottling and thin bands are common, as are reworked chips of volcanic ash. The upper part of the unit includes some coarser volcanic debris comparable to that in the over-lying unit, such as scattered biotite flakes, magnetite, ampliibole laths, glass, and secondary silica in the form of opal. Interbedded with the mudstone and claystone are thin beds of marlstone, ostracodal and algal limestone, and pale-gray to greenish-gray and brown sandstone, containing lentils of chert conglomerate locally. Beds of poorly indurated pale-pinkish-tan sandstone with angular pebbles and chips of white to very light gray ash are abundant. The lower part of the middle unit also includes scattered lentils, at different stratigraphic horizons, of conglomerate comparable in pebble composition to the basal conglomeratic unit. DISTRIBUTION AND THICKNESS The Sillem Member is 100-400 feet thick in the Sage quadrangle. Remnants of the member have been observed, but not measured, at many other localities. The unit is exposed along the east side of Boulder Ridge in a south-southeastward-trending belt and on Sillem Ridge. The member is also present west of the Bear River, along the east side of the Bear Lake Plateau, and it has been recognized near the mouth of Acock Canyon, about 14 miles north of Evanston. The exposure at Acock Canyon is only a few hundred feet thick.FOWKES FORMATION 35 LOWER CONTACT The basal contact of the Fowkes Formation is not well exposed in most of the formation’s area of distribution. It is moderately well exposed at four localities where the position of the Fowkes Formation on beds within the Bullpen Member of the Wasatch Formation can be demonstrated. These localities include the northeastern part of sec. 5, T. 21 N., R. 119 W.; the central part of sec. 22, T. 21 N., R. 119 W.; sec. 19, T. 21 N., R. 119 W.; and the northeastern part of sec. 8, T. 17 N., R, 120 W. At all these localities, the basal beds of the Fowkes Formation seem to rest conformably on Bullpen strata. The contact, however, may be a disconformity and the stratigraphic range of beds directly beneath the contact may be considerable for the region. The contact between the Fowkes and Almy Formations as mapped by Veatch (1907, pi. 3) was examined by us in several reconnaissance traverses along the belt on the east side of the type Almy exposures. Because Veatch’s implied conformable stratigraphic contact truncates individual beds on both sides of it, we tentatively interpret the contact as a fault. BULLDOG HOLLOW MEMBER NAME AND TYPE The middle part of the Fowkes Formation, here named the Bulldog Hollow Member for extensive exposures along Bulldog Hollow, includes most of the rocks assigned to the Fowkes by Veatch (1907, pi. 3) and most exposures in the formation’s type locality. It is the most extensively exposed and probably thickest part of the formation. The section here designated (with some misgivings) as the type section for the Bulldog Hollow Member is that measured in the western part of sec. 33, T. 22 N., R. 119 W. (see p. 46). The member is thinner and more poorly formed and exposed in this section than at many other localities along Bulldog Hollow, south of Sage, and along the east side of the Crawford Mountains; however, the member has both a base and a top in the selected unfaulted section, whereas structural relations have not been determined farther south. ROCKS INCLUDED The member is dominantly pale- to dark-green, blue-green, and white tuffaceous and ashy mudstone and green to buff and brown tuffaceous calcareous sandstone. These rocks contain amphibole laths, biotite plates with well-preserved crystal faces, minute feldspar crystals, quartz, and glass. Both tuff and ash are of rhyolitic composition. Disaggregation of the poorly to moderately indurated sandstone facilitates the testing of the grains with a magnet. All samples examined in this unit contain at least some magnetite; a few contain 5, possibly as much as 10, percent, in sharp contrast to all underlying formations which contain virtually no magnetite. In addition, the matrix of some sandstone beds weathers to a distinctive blue efflorescence; the composition of the matrix was not determined. In a few places, tuffaceous sandstone contains an opaline cement. The Bulldog Hollow Member also contains some lenses of light-gray calcareous conglomerate similar to that in the overlying Gooseberry Member. DISTRIBUTION AND THICKNESS The Bulldog Hollow Member is more extensively exposed than the other two members of the Fowkes Formation. It has been mapped in a south-southwest-ward-trending belt from the west-central part of the Sage quadrangle to its southern edge. It has also been recognized in discontinuous belts along the east side of the Bear River almost as far south as Evanston. Almost all the exposures mapped as Fowkes by Veatch (1907, pi. 3) are assigned to the Bulldog Hollow Member ; the exposures on the west side of the Bear River, west of the old Almy settlement, however, are here assigned to the Green River Formation. The member is only 200 feet thick north of Sage but thickens greatly southward. It may be as much as several thousand feet thick (Veatch, 1907, table opposite p. 50) south of the Sage quadrangle. LOWER CONTACT The base of the Bulldog Hollow Member is apparently gradational downward into the underlying Sillem Member. The proportions of volcanic tuff and ash in sandstone and mudstone decrease downward, and the greens and whites of the Bulldog Hollow Member grade to pale gray and very pale greenish gray. The base of the Bulldog Hollow Member is placed at the base of the lowest moderately tuffaceous sandstone that contains observable biotite, amphibole, and magnetite grains. GOOSEBERRY MEMBER NAME AND TYPE The uppermost part of strata provisionally included in the Fowkes Formation is a puddingstone4 here named the Gooseberry Member for exposures near Gooseberry Springs in the west-central part of the Sage * The term “puddingstone” is used here for conglomerate that differs from all others in the Fossil basin sequence. The rock consists of very well rounded and spherical pebbles and cobbles so sparsely packed in a matrix of white ashy marl that very few are in contact with one another. Pebbles and cobbles in all the other conglomerates, In contrast, are tightly packed and have numerous points of contact. Diamictite differs from puddingstone in the extreme angularity and lack of size sorting of coarse clasts.36 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING quadrangle. The unit is tentatively retained in the Fowkes Formation because the underlying Bulldog Hollow Member contains lenses of somewhat similar conglomerate. However, it is possible that the Gooseberry puddingstone is an easternmost remnant of the Salt Lake Formation. The type area of the Gooseberry is the conglomerate ledge exposures about 2 miles northeast of Sage. The section here designated the type section is that measured in the N1/^ sec. 33, T. 22 N., R. 119 W. (see p. 45), although the section is incomplete. SOCKS INCLUDED The Gooseberry Member consists of light-gray to white puddingstone, calcareous rhyolitic ash, and tuff and ash bearing very finely crystalline to subaphanitic limestone. The puddingstone consists of sparsely to moderately tightly packed cobbles and pebbles in a matrix of white to pale-buff silty and tuffaceous highly calcareous sandstone, marlstone, and sandy limestone. Most clasts are 6 inches or less in diameter, but a few are as much as 1 foot. Packing of the well-rounded to subangular coarse clasts in most beds is so poor that few cobbles are in contact with others; most beds, therefore, are pudding-stone. The cobbles and pebbles are mainly of quartzite, chert, and limestone from Paleozoic formations but are also volcanic rocks of unknown derivation that range in composition from rhyolite to vesicular basalt. The presence of volcanic pebbles, the poor packing, and the white to light-buff calcareous matrix distinguish this conglomerate from those in all other stratigraphic units. DISTRIBUTION AND THICKNESS The extent of the Gooseberry Member as mapped by Rubey, Tracey, and Oriel (1968) is confined to the area northeast of Sage that was mapped as the Almy Formation by Veatch (1907, pi. 3). Rocks of similar composition, however, have been observed at many localities to the west on the Bear Lake Plateau (fig. 1). Somewhat similar rocks have been noted southward at some localities mapped as Fowkes by Veatch (1907, pi. 3), but whether they are exposures of the Gooseberry or simply conglomerate lenses in the Bulldog Hollow Member has not been ascertained. The member, though incompletely represented (it has no stratigraphic top), is about 200 feet thick in the Sage quadrangle. LOWER CONTACT The nature of the base of the Gooseberry Member has not been ascertained. Where examined locally, the upper part of the underlying Bulldog Hollow Member apparently grades into the Gooseberry. Moreover, the pres- ence in the Bulldog Hollow Member of Gooseberry-like conglomerate lentils also suggests a gradational contact. However, a moderately great range in thicknesses of the Bulldog Hollow Member suggests that the base of the Gooseberry may be an angular unconformity. Regional dips of the members of the Fowkes Formation (the Bulldog Hollow Member south of Sage, dips mainly south, whereas the Gooseberry exposures north of Sage dip gently northward) also make an angular unconformity likely. FOSSILS AND AGE The Fowkes Formation in the Fossil basin is of Eocene and possible early Oligocene age. The uppermost part, however, may be as young as Pliocene. Only ostracodes and gastropods have been found in the Sillem Member. Ostracodes were collected in the NEI/4NW14NE14 Sec. 5, T. 21 N., R. 119 W. (Tertiary loc. 21741), and in the NW)4 sec- 4, T. 21 N., R. 119 W. (Tertiary loc. 21704), and were identified as “Hemicy-privotiosv toatsoemis Swain, Procyprois ravenridgensvt Swain, and Pseudocyprisl sp. undescribed (I. G. Sohn, written commun., Apr. 15, 1959, Feb. 12, 1964); these fossils indicate only an Eocene age. The gastropods, though too poorly preserved to be useful for age determinations, included three forms of fresh-water snails and were collected from TTSGS Cenozoic localities 22621 and 22622 in sec. 12, T. 24 N., R. 120 W.; the first is 650 feet west and 550 feet south of the northeast corner of the section, and the second is 2,000 feet west and 1,000 feet south of the northeast corner. On the basis of fossils and stratigraphic position, the age of the Sillem Member is more probably middle than late Eocene. Both gastropods and leaves have been collected from the Bulldog Hollow Member. The gastropods have been identified as Bionvphalaria pseudoaw/monius (Schlo-theim) and Oreoconus ylanispira Taylor (McKenna) and have been assigned a late middle to late Eocene age (D. W. Taylor, written commun., May 29,1957; McKenna and others, 1962). The collections were made at the following localities: USGS Cenozoic loc. 20082, 300 ft E., 1,900-2,400 ft N. of SW cor. sec. 20, T. 21 N., R. 119 W. 20083, 250 ft W., 600 ft N. of SE cor. sec. 19, T. 21 N., R. 119 W. 20084, NWK sec. 16, T. 20 N., R. 119 W. 20146, north side, Fowkes Canyon, sec. 33, T. 17 N., R. 120 W. 22198, NEfiNE^NE>i sec. 29, T. 16 N., R. 120 W. The leaves were collected near the top of the Bulldog Hollow Member in sec. 4, T. 21 N., R. 119 W-, and wereFOWKES FORMATION 37 identified as Equisetum, sp. and Lygodivm kandfussi Heer, to which an Eocene age is assigned (R. W. Brown, written commun., Sept. 23, 1958). The age of the member, therefore, is middle or late Eocene. The radiogenic age of the hornblende in a sample of the Bulldog Hollow Member has been determined, by means of the potassium-argon method, by Richard Lee Armstrong (written commun., Mar. 5, 1967) of the Kline Geology Laboratory at Yale University. The sample was collected in the SE^NE^SE^ sec. 19, T. 21 N., R. 119 W. The following data were furnished by Armstrong: Percent K: 0.72, 0.72 Ar: 1.39X10-6 cc radiogenic Ar40 70 percent air Ar in analyzed sample Constants used: £TXj3=4.72X Kk^yr-1 KXe = 0.584X 10~10yr Ki0/K= 0.0119 atm (atmosphere) percent Date: 47.7 m.y. (million years)±1.5 m.y., or middle Eocene (Evernden and others, 1964, p. 165,189) The result probably should be considered a maximum possible age because of possible contamination by older material, although such contamination seems unlikely in this sample. Although the Bulldog Hollow Member may be as young as late Eocene, it probably is of middle Eocene age. Fossils have not been found in the Gooseberry Member within the Sage quadrangle. Reconnaissance west of the quadrangle in the Bear Lake Plateau, however, resulted in a collection of some fossil bones west of Pe-gram Creek in the NE14NE14 sec. 29, T. 15 S., R. 45 E., in Idaho, from puddingstone similar to that in the Gooseberry, despite the previous assignment of these rocks to the Wasatch Formation (Mansfield, 1927, pi. 9). The bone fragments included Leporidae teeth identified (Mary Dawson, written commun., Mar. 31, 1967) as probable Hypolagus of possibly late Miocene or early Pliocene age. This fossil from strata that can be assigned only with uncertainty to the Gooseberry and the inferred angular unconformity at the base of the member in the Sage quadrangle suggest that the Gooseberry may be considerably younger than the Sillem and Bulldog Hollow Members of the Fowkes Formation. Perhaps Gooseberry strata should be assigned to the Salt Lake rather than to the Fowkes Formation or established as a new formation. Tentative assignment here of the Gooseberry Member to the Fowkes Formation is based on the close association areally of the Gooseberry with other members of the Fowkes and on the similarities in composition of the conglomerates in both the Bulldog Hollow and the Gooseberry Members. The apparent disparity in ages for members of the Fowkes, suggested by the tenuous available data, closely parallels that determined for the Salt Lake Formation in its type locality in northern Utah. A lower tuff unit there, which closely resembles the Bulldog Hollow Member in composition (Eardley, 1959, p. 167), is also considerably older than other Salt Lake strata. This tuff unit, named the Norwood Tuff and assigned an early Oligocene age by Eardley (1944), contains vertebrates which, when reexamined, were assigned (C. L. Gazin, written commun., Nov. 9, 1959) a late Eocene age. The overlying Salt Lake strata, in contrast, are assigned a Pliocene and possibly a late Miocene age. Geologists working in the region have found the contact between the two formations extremely difficult to map because of similarity in composition. ORIGIN The Fowkes Formation probably was deposited mainly as alluvium but also in small lakes and ponds during a time of increasing volcanic activity in the region. Heterogeneity of detrital fragments, moderately good size sorting and rounding of coarse clasts, and sedimentary structural features suggest that the bulk of the material was deposited in fresh water. The poorly sorted puddingstone in the Gooseberry Member may have been deposited as a mudflow. Some interbedded ash layers in the formation may have been deposited subaerially. The source and direction of transport of the great volume of volcanic debris are not known. TECTONIC IMPLICATIONS The Fowkes Formation is limited in distribution to a belt along the western part of the Fossil basin (Yeatch, 1907, pi. 3). Although deposition of the unit may possibly have been confined to a downwarp or trough formed within the Fossil basin in middle or late Eocene time, the evidence suggests otherwise. Faults that cut underlying Tertiary strata also cut the Fowkes Formation, and gentle folds of both are concordant. The present distribution, therefore, seems to reflect post-depositional normal faulting that dropped Fowkes strata, thereby preserving them. Strata that formerly were more extensive and that remained elevated were no doubt removed by erosion. This erosion probably also accounts for extensive lag concentrates of pebbles and cobbles that were assigned a Quaternary age by Veatch (1907, pi. 3), both north and south of Sage. The relations of the units assigned here to the Fowkes to those mapped farther west, such as Norwood Tuff and38 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING Salt Lake Formation, are too imperfectly known to permit detailed tectonic reconstructions. In general, however, deposition of these units seems to have reflected basin-and-range faulting, particularly farther west, and extensive volcanism. The composition of the Sillem Member in exposures both west and east of Boulder Ridge suggests that the mountain of Paleozoic and Cretaceous formations (p. 28) that supplied detritus for the Tunp Member of the Wasatch was downfaulted by middle to late Eocene time. SOME REGIONAL RELATIONS The precise relations of the Fossil basin rock units to comparable units in adjoining areas remain somewhat enigmatic. Most of the units cannot be traced continuously from this basin to others. Although almost all the units seem to have lithologic counterparts in the stratigraphic sequences of nearby areas (table 3), current age assignments deny or make questionable precise temporal equivalence. The age assignments, however, are not unequivocal, for they are based in large part on different fossil forms in the different areas. Table 3.—Dominant rock types and sequences of Upper Cretaceous and Tertiary stratigraphic units in the Fossil basin and adjoining areas [Most of the units are not temporal equivalents] Dominant rock types Northeastern Utah, Echo Canyon area Fossil basin, northern part Green River Basin, Fort Hill area Light-gray and buff tuffaceous conglomerate. Salt Lake Formation. Gooseberry Member of Fowkes Formation. White to green tuffaceous and ashy sandstone, mudstone. Norwood Tuff of Eardley (1944). Bulldog Hollow and Sillem Members of Fowkes Formation. Bridger Formation. Unconformity Red and salmon mudstone and gray and brown sandstone, thin buff limestone. Bullpen Member of Wasatch Formation. Laminated marlstone and limestone, algal limestone. Angelo Member of Green River Formation. Upper tongue of Green River Formation. Gray-green and pink mudstone. Mudstone tongue of Wasatch Formation. Upper tongue of Wasatch Formation. Laminated organic marlstone, limestone, oil shale, ash. Fossil Butte Member of Green River Formation (upper part). Middle tongue of Green River Formation. Brown sandstone and green mudstone. Sandstone tongue of Wasatch Formation. New Fork Tongue of Wasatch Formation. Light-gray and buff laminated limestone and marlstone. Fossil Butte Member of Green River Formation (lower part). Fontenelle Tongue of Green River Formation. Red, purple, and tan, banded and variegated mudstone. Wasatch Formation. Main body of Wasatch Formation. La Barge Member of Wasatch Formation. Angular unconformity Boulder conglomerate and gray sandstone and mudstone. Evanston(?) Formation. Evanston Formation. Chappo Hoback(?) Member of Wasatch Formation. Formation. Red conglomerate and sandstone. Echo Canyon Conglomerate of Williams and Madsen (1959). Basal part, Chappo Member of Wasatch Formation. Angular unconformity Tan sandstone, gray mudstone, some coal. Wanship Formation of Eardley (1952). Adaville Formation. Adaville (?) Formation. Dark-gray marine mudstone. Hilliard Shale. Hilliard Shale. Gray sandstone and mudstone and coal. Frontier Formation. Frontier Formation. Frontier Formation.SOME REGIONAL RELATIONS 39 In general, the Fossil basin units seem to be intermediate in age between somewhat older comparable units to the southwest, in northeastern Utah, and younger units to the east, in the western Green River Basin (table 4). There being a progressively younger age, from west to east, for analogous rock units in the region both is predicted by and supports the conclusion that orogeny and thrust faulting in the cordilleran region progressed from west to east (Oriel and Armstrong, 1966, p. 2619). The generalization, however, is by no means true for all the units. LOWER STRATA OF THE WASATCH Progressively younger ages from west to east are perhaps best illustrated by strata that have been assigned to the Wasatch Formation beneath the Green River Formation. The main body of the Wasatch Formation is well dated in the Fossil basin. The base of the main body is no older than earliest Eocene (Gray Bull) and the top no younger than middle early Eocene (Lysite). Comparable rocks in the Green River Basin, where they are assigned to the La Barge Member of the Wasatch (Oriel, 1962, p. 2168-2170), are younger. Although most of the La Barge Member is late early Eocene (Lost Cabin age), the basal part may be as old as middle early Eocene (Lysite). West of the Fossil basin, strata formerly assigned to the Wasatch Formation in part of its extended type locality at Echo Canyon, Utah (Hayden, 1869, p. 91), are now subdivided into several units in northeastern Utah (Mullens and Lara way, 1964; Williams and Madsen, 1959). A basal unit of red conglomerate, sandstone, and shaly sandstone underlies with angular unconformity other strata previously assigned to the Wasatch. The red strata beneath the unconformity are now assigned to the Echo Canyon Conglomerate; they contain Cretaceous fossils of late( ?) Niobrara age near the base (Williams and Madsen, 1959, p. 123). The Echo Canyon Conglomerate is overlain by brown conglomeratic sandstone and gray sandy siltstone assigned to the Evanston (?) Formation (Mullens and Lara way, 1964). These beds are overlain by other mainly brownish red beds still assigned to the Wasatch Formation and to the Eocene. Thus, the deposition of the Wasatch-like strata began earlier (in the Late Cretaceous) in the Echo Canyon area than it did in the Fossil basin area and seems to have continued until well into the Eocene. RELATIONS OF LOWER UNITS The Evanston Formation, too, has lithologic counterparts both to the east and to the west. Evanston strata in the Fossil basin are of latest Cretaceous to late, but I not latest, Paleocene (Tiffany) age. Similar strata assigned to the Evanston(?) Formation in the Echo Canyon area in Utah (Mullens and Laraway, 1964) are probably also of very late Cretaceous age, according to pollen identified by E. B. Leopold (written commun. to T. E. Mullens, Mar. 27, 1963). Drab-colored, mainly gray to pale-green-gray, strata are also extensive to the east, in the Green River Basin. Extensive exposures in the Hqback area were initially assigned to the Evanston Formation (Schultz, 1914, p. 69, pi. 1) but are now included in the Hoback Formation (Eardley and others, 1944; Dorr, 1952, p. 64—71). Similar strata have been drilled farther south, in the La Barge area and southward, where they are assigned to the Hoback (?) and are believed to intertongue with the Chappo Member of the Wasatch Formation, which underlies the La Barge Member with angular unconformity (Oriel, 1969). The drab-oolored Hoback strata in the Green River Basin are, in general, somewhat younger than the Evanston in the Fossil basin. The Hoback is assigned a middle to late Paleocene and very early Eocene age (Dorr, 1952, p. 68; 1958, p. 1229-1232). The Chappo Member of the Wasatch, with which the Hoback intertongues, is assigned a latest Paleocene (Clarkforkian) 5 and earliest Eocene (Gray Bull) age (Oriel, 1962, p. 2168). RELATIONS OF TONGUES OF THE WASATCH AND GREEN RIVER FORMATIONS Subdivision of the Green River Formation by two Wasatch tongues in the Fossil basin, as in the western part of the Green River Basin, raises the question of possible contemporaneity.' Although the tongues resemble each other in stratigraphic position and lithology, available fossil evidence indicates that the Fossil basin tongues probably are older. The sandstone tongue of the Wasatch in the Fossil basin is similar in both composition and apparent stratigraphic position to the New Fork Tongue of the Wasatch in the Green River Basin (table 3; Oriel, 1961). Moreover, the Wasatch mudstone tongue in the Fossil basin somewhat resembles the upper tongue in the Green River Basin. The analogous Green River Formation units, therefore, are the lower and upper parts of the Fossil Butte Member and the Angelo Member in the Fossil basin and the Fontenelle, middle, and upper tongues, respectively, in the Green River Basin (table 3). 5 Although the validity of the Clarkforkian as the latest Paleocene provincial age has been questioned (Wood, 1967 ; D. W. Taylor, written commun., 1967), a generally accepted revision of the classification of the North American continental Tertiary is not available. Even if rocks previously dated as Clarkforkian prove to be of Gray Bull age, the fact that the Chappo and parts of the Hoback are younger than the upper part of the Evanston is not invalidated.40 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING Table 4.—Approximate ages of the stratigraphic units in the Fossil basin and adjoining areas Paleontologic dates are indicated by vertebrates; mollusks; _, leaves; Q » pollen; * , other forms Note: T., TongueTYPE SECTIONS FOR MEMBERS DEFINED IN THIS REPORT 41 The Fossil basin and Green River Basin are separated by the moderately continuous Oyster Ridge barrier. At one locality, however, in the west-central part of T. 15 N., R. 118 W., Wasatch strata can apparently be traced from one of the basins into the other (Veatch, 1907, pi. 3). We have noticed a few thin Green River limestones in this area. It seems likely that detailed mapping of these limestones northward along both sides of the Oyster Ridge barrier will determine their positions within the established stratigraphic sequences in the two basins. In the Green River Basin, the various tongues are moderately well dated. The Fontenelle Tongue is of latest early Eocene age, for the underlying La Barge Member and overlying New Fork Tongue of the Wasatch both contain mammals of Lost Cabin age (Gazin, 1952, 1962). Upper strata of the Green River intertongue with the Bridger Formation of middle Eocene age (Bradley, 1964). In the Fossil basin, the tongues are not as well dated. The presence of Lysite age mammals in Wasatch strata just a few feet below Green River strata suggests that the basal part of the Fossil Butte Member may be of Lysite or middle early Eocene age. Although available fossil control does not require it, the topmost Green River strata have been regarded as probably older than middle Eocene (Gazin, 1959, fig. 1; Schaeffer and Mangus, 1965, p. 12-13). This interpretation is supported by the presence of Wasatch strata above the highest Green River beds, although these Wasatch beds are not dated more precisely than as latest early or middle Eocene. Current interpretations, therefore, though better supported by the dating of units below the Green River than by the dating of those above, suggest that the Green River tongues in the Fossil basin are somewhat older than those in the Green River Basin. FOWKES-NORWOOD-BRIDGER RELATIONS The abundance of tuff and ash in strata above the Wasatch and Green River Formations in northeastern Utah and in the Fossil basin and Green River Basin suggests that the tuff and the ash reflect the same period of volcanic activity in the region. Yet the available bases for dating the several units are both intriguing and perplexing. Although the Fowkes Formation, the Norwood Tuff, and the Bridger Formation may prove to be of the same age, the likelihood now is that they are not. The relations of these units are among the least understood. The Bulldog Hollow Member and underlying Sillem Member of the Fowkes in the Fossil basin resemble strata assigned to the Norwood Tuff in Utah. Mollusks from the Bulldog Hollow Member indicate a middle or late Eocene age; leaves, an Eocene age; hornblende, an age of 47.7±1.5 m.y. (middle Eocene), from a potassium-argon determination. The similar Norwood Tuff contains vertebrates of late Eocene age (Gazin, 1959, p. 137), gastropods of late early to middle Eocene age (D. W. Taylor, written commun., to T. E. Mullens, Jan. 16,1963), biotite of 37.5 m.y. at the type locality (Evernden and others, 1964, p. 161,183), and biotite of 68±8 m.y. and 74±8 m.y. at the south end of Cache Valley (Williams, 1964, p. 271; Heylmun, 1965, p. 13). The Bridger Formation in the Green River Basin differs in appearance and composition from the dominantly rhyolitic Bulldog Hollow Member of the Fowkes. It is considerably darker in color, ranging from neutral-gray to dark-green and chocolate-brown tuffaceous mudstone and gray to brownish-gray tuffaceous mudstone. Moreover, it consists dominantly of andesite tuff, although it also includes rhyolite (Bradley, 1964, p. A49). Abundant fossil mammals establish the age of most of Bridger as middle Eocene, although the upper part may be younger (Bradley, 1964, p. A48). Biotites have not been dated from the Bridger Formation, but some from approximately correlative beds elsewhere in Wyoming are 45.4-49.0 m.y. old (Evernden and others, 1964, p. 165). Thus, our earlier belief that the Bulldog Hollow Member of the Fowkes is equivalent to the Norwood Tuff and is younger than the Bridger Formation is not well supported. Conflicts among the data remain to be resolved. The probably younger age of the Gooseberry Member of the Fowkes Formation and the possible equivalence of the Gooseberry to many strata assigned to the Salt Lake Formation are discussed on a previous page. The range in ages of strata that have been assigned to the Salt Lake Formation and other stratigraphic problems are discussed by Heylmun (1965). TYPE SECTIONS FOR MEMBERS DEFINED IN THIS REPORT Evanston Formation at type section for Hams Fork Conglomerate Member l Measured near middle of eastern part of sec. 36, T. 21 N., R. 117 W., miles northwest of Elko] Wasatch Formation (partial): Main body: Ft >» Mudstone, sandy and silty; mottled red, green, light gray, and yellow; partly covered at top of hill by blocks of Green River limestone float______________________________________ 62 Sandstone, medium-grained, light-gray; calcareous with salt-and-pepper texture; forms dark-brown crossbedded ledge------------- 1442 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING Evanston Formation at type section for Hams Fork Conglomerate Member—Continued Wasatch Formation (partial)—Continued Main body—Continued Sandstone, medium- to fine-grained, clayey, Ft in yellow; forms yellow slope________________ 16 Angular unconformity. Partial thickness, Wasatch Formation 92 Evanston Formation: Main body: Claystone, slightly to moderately silty, light-gray to pale-pinkish-gray; yellow stains along fractures______________________ 15 Sandstone, fine- to medium-grained, very calcareous, dark-brown to very dark gray; forms ledge________________________-______ 1 6 Claystone, light-gray___________________________ 9 Claystone, slightly silty, dark-gray------------ 5 Claystone, silty, light-gray-------------------- 3 Siltstone, light-pinkish-gray__________________ 20 Sandy siltstone and silty very fine grained to fine-grained sandstone; light gray with random yellow streaks__________________________ 3 Sandstone, clayey, fine-grained to very fine grained, yellow; interbedded with mottled light-gray, pinkish-gray, and yellow siltstone_____________________________________________ 6 Claystone, medium- to dark-gray and partly silty; grading downward to light-gray siltstone______________________________________ 10 Sandstone, fine- to medium-grained, light-gray salt-and-pepper; very thinly cross laminated with abundant carbonaceous streaks in some cross laminae__________________ 3 6 Siltstone, light-gray to pinkish-gray; yellow to orange mottling and bright-orange laminae of clayey siltstone__________________ 15 Claystone and silty and clayey siltstone, light- gray---------------------------------...... 10 Sandstone, mainly fine to very fine grained; contains some medium sand grains and silt; noncalcareous, carbonaceous; fossil leaves, limonite concretions, and yellow staining______________________________________ 2 6 Claystone, medium-gray; grades downward to light-gray siltstone______________________ 18 Sandstone, fine-grained, silty, noncalcareous, light-gray; weathers to light gray and yellow with dark-red-brown ferruginous layers; contains some limonite nodules_____ 3 Claystone, slightly silty in part, medium- to light-gray___________________________________ 13 Siltstone, somewhat clayey, light-gray; yellow splotches____________________________________ 10 Mudstone, light-gray; yellow and yellow-brown mottling__________________________________ 8 Evanston Formation at type section for Hams Fork Conglomerate Member—Continued Evanston Formation—Continued Main body—Continued Sandstone, fine-grained, very calcareous, salt- Ft in and-pepper; light gray but weathers to mottled brown, yellow, dark gray and purplish gray______________________________ 1 Siltstone and slightly to very silty claystone, light- to medium-gray; yellow and yellow- brown mottling; forms small badland______ 40 Siltstone to very fine grained sandstone with scattered medium sand grains, noncalcareous, salt-and-pepper, light-gray; some yellow along bedding and joints_________________ 5 Siltstone, poorly indurated, pinkish-gray; yellow and yellow-brown splotches; grades downward to slightly silty light- to medium- gray claystone_____________________________ 8 Lignite, very thinly laminated to papery___ 2 Conglomerate, containing well-rounded clasts as much as 8 in. in diameter; mainly light-gray quartzite; some black to gray chert and pink conglomeratic quartzite___________ 5 Siltstone, quartzitic, light-gray; contains scattered dark-gray chert grains_________________________ 4 Interbedded yellow-brown siltstone and light-gray mudstone; yellow and brown mottling___________ 14 Interbedded light- to medium-gray, yellow-weathering claystone and pinkish-gray clayey siltstone; laminae of red-mottled dark-gray and dark-brown silty claystone..___________________ 8 Claystone, black, very slightly to moderately silty; weathers light to medium gray_________________ 15 Thickness, main body of Evanston_____________ 257 6 Hams Fork Conglomerate Member: Sandstone, poorly sorted, medium-grained to very fine grained; thin layers of coarsegrained to conglomeratic sandstone; very light gray; weathers to yellow orange; forms prominent ledge________________________ 13 Sandstone, fine- to medium-grained; some gritty beds and highly carbonaceous to lig-nitic laminae near middle; poorly indurated; greenish gray_______________________________ 15 Claystone, medium-gray; tan-weathering streaks and layers of light-gray siltstone_15 Claystone, slightly silty, black_______________ 8 Interbedded light-gray mudstone, tan siltstone, and light-gray to brown fine-grained to very fine grained sandstone, partly covered______________________________________26 Ironstone, dark-chocolate to reddish-brown; weathers to purple_________________________ 6 Claystone, medium- to dark-gray________________ 1TYPE SECTIONS FOR MEMBERS DEFINED IN THIS REPORT 43 Evanston Formation at type section for Hams Fork Conglomerate Member—Continued Evanston Formation—Continued Hams Fork Conglomerate Member—Continued Sandstone, very fine grained, buff to gray; Ft in weathers yellow to tan; very calcareous and thinly crossbedded___________________________ 4 Interbedded very dark gray claystone, brown slightly silty claystone, and tan to gray silt- stone_______________________________________ 40 Covered, probably claystone and siltstone as above_______________________________________ 85 Sandstone, fine- to medium-grained; cross-bedded with abundant conglomeratic cross laminae; most well-rounded clasts are less than 1 in. in diameter but a few are larger- 30 Interbedded fine-grained sandstone and conglomerate with well-rounded quartzite and chert pebbles as much as 3 in. in diameter in matrix of medium- to coarse-grained sandstone____________________________________ 5 Sandstone, medium- to fine-grained, light-gray salt-and-pepper; lenses of coarse-grained to gritty sandstone; thinly laminated and cross laminated___________________________________ 35 Covered, probably fine-grained to very fine grained sandstone______________________________ 4 Sandstone, poorly sorted, coarse- to finegrained, crossbedded; weathers olive light brown with abundant irregularly shaped calcareous nodular light-gray sandstone___ 6 Covered_____________________________________ 6 Sandstone, moderately well sorted, mediumgrained, salt-and-pepper, crossbedded, yellow to yellow-brown___________________________ 5 Covered, probably tan to light-brown finegrained sandstone_____________________________ 5 Sandstone, very well laminated, tan; weathers to light brownish gray; forms ledge_________ 1 Covered, probably sandstone__________________ 14 Sandstone, fine-grained, salt-and-pepper, very light gray; abundant scattered medium and coarse grains; moderately well laminated with 2-inch layers of cross laminae_________ 7 6 Covered, probably sandstone__________________ 13 Sandstone, medium- to coarse-grained, partly gritty, crossbedded_________________________ 3 Covered, probably sandstone and conglomerate with pebbles and cobbles of well-rounded quartzite__________________________________ 70 Sandstone, medium-grained, and boulder conglomerate with quartzite clasts, crossbedded; weathers yellow, olive, and brown. 10 Boulder conglomerate; consists mainly of light-gray quartzite but includes boulders of medium- to dark-gray quartzite, pink conglomeratic quartzite, black chert, and dark-gray limestone_______________________ 18 Evanston Formation at type section for Hams Fork Conglomerate M ember—Continued Evanston Formation—Continued Hams Fork Conglomerate Member—Centinued Boulder conglomerate as above; matrix of Ft in medium- to coarse-grained sandstone; weathers light olive drab______________ 15 Total thickness, Hams Fork Conglomerate Member_________________________________455 Total thickness, Evanston Formation______712 6 Adaville Formation (partial): Covered, probably interbedded yellow to greenish-yellow sandstone and medium- to dark-gray mudstone________________________ 43 Mudstone, medium-gray; abundant chips of ironstone_________________________________ 10 Covered, light-gray- to yellow-gray-weather-ing slope, probably sandstone and siltstone. 10 Interbedded gray mudstone, yellow siltstone, and very fine grained light-gray, brownweathering salt-and-pepper sandstone_______ 25 Coal_________________________________________ 1 Covered_____________________________________ 44 Mudstone, medium-gray; capped by iron- stained yellow-brown sandstone_____________ 5 Interbedded dark-gray mudstone, dark-brown-stained sandstone with leached calcareous nodules, and light-yellow to tan sandstone; thin interbeds of reddish-brown ironstone.. 40 Total measured thickness, Adaville Formation_________________________________ 178 Base of measured section. Wasatch Formation (partial) at the type section for Bullpen Member [Measured in the NWM sec. 1, T. 20 N., R. 118 W.] Wasatch Formation: Bullpen Member: Top of butte. Limestone, finely crystalline, buff; weathers to yellow, tan, and brown chips and slabs Ft in on tan silty slope at top of butte__________ 10 Limestone, finely crystalline to sublitho-graphic, tan; contains sparse ostracodes; forms ledge__________________________________ 1 Claystone, green, partly marly; some interbeds of mudstone; green with tan and brown mottling______________________________ 13 Mudstone and claystone, mottled brownish red, brown, green, and tan------------------ 14 Claystone, green; contains thin layers of green mudstone and very calcareous claystone and light- to medium-gray marlstone and calcareous claystone_____________________ 1144 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING Wasatch Formation (partial) at the type section for Bullpen Member—Continued Wasatch Formation—Continued Bullpen Member—Continued Siltstone, brown; grades downward to tan Ft in and brown limestone and upward to brown mudstone______________________________________ 6 Limestone, chalky, white to pale-yellow; thinly laminated to 3-inch-thick beds; forms ledge_ 1 Mudstone and claystone, green___________________ 4 Mudstone and claystone, red and brown; thin layers of green and gray______________________ 9 Mudstone and claystone, mainly green but partly yellow and brown mottled_______________ 9 Limestone, buff, tan, and brown; weathers to small chips in brown silty soil____________ 4 Limestone, grading downward from tan, well indurated, very finely crystalline, and partly algal to white and chalky_______ 4 6 Mudstone, green; contains green and tan slightly silty claystone and tan marly mudstone______________________________________ 9 Mudstone, maroon; a little green and purple mottling______________________________________ 4 Mudstone, brown; some layers of brown-and green-mottled claystone and very thin layers of tan limestone______________________ 25 Sandstone, fine-grained to very fine grained, very calcareous, light-gray; forms tan spheroidally weathering ledge_________________ 1 Limestone, mainly very finely crystalline; some ostracodal coquinas in tan, brown, and buff laminae; forms brown silty slope with abundant limestone chips_____________________ 10 Limestone, recrystallized ostracodal coquina, tan; forms ledge______________________________ 1 Mudstone and siltstone, brown___________________ 6 Sandstone, ranging from brown, very fine grained, and very calcareous to medium gray, slightly calcareous, fine grained, and poorly indurated________________________________ 7 Sandstone, brown, medium-grained, moderately well sorted; contains scattered dark chert; moderately well and evenly laminated and cross laminated; forms ledge_____-_______________________________ 6 Sandstone, brown, fine-grained and muddy; poorly exposed____________________________ 8 Claystone, partly silty, shaly, mainly dark brown; some yellow with thin seams of purple______________________________________ 14 Wasatch Formation (partial) at the type section for Bullpen Member—Continued Green River Formation—Continued Angelo Member (partial)—Continued Limestone; forms brown, orange, and yellow Ft in chips in brown silty soil_________________ 4 Limestone, very finely crystalline and thinly laminated, medium-brown; fossil fish fragments_________________________________ 6 Limestone, very finely crystalline, tan to purplish-tan; abundant flat gastropods____ 7 Oil shale, low-grade________________________ 6 Partial thickness, Angelo Member (185 ft thick at this locality) of Green River Formation__________________________________ 17 Green River Formation at the type section of the Fossil Butte Member [Measured at the east end of the south-facing scarp of Fossil Butte, SWJiNWH sec. 5, T. 21 N„ R. 117 W.] Green River Formation: Angelo Member (partial): Top of butte. Ft in Limestone, marly, light-gray to white, thin-bedded; contains chert nodules; thin as bed 2 feet above base of unit___________________ 7 Shale, limy, grayish-tan, laminated; contains some oily beds________________________________ 9 Limestone, marly, light-gray, thin-bedded----- 1 Shale, silty, greenish-gray and rust-colored; contains plant fragments______________________ 1 Limestone, marly, and calcareous shale, light-gray to white; contains chert nodules and evaporite crystal cavities_______________ 10 Oil shale, laminated__________________________ 8 Limestone, shaly, light-gray____________________ 2 Shale, greenish-gray, crumbly___________________ 3 6 Limestone, shaly, light-gray, massive to laminated; ash beds near top________________________ 3 Shale, green- and olive-gray, mottled___________ 1 6 Partial thickness (rounded), Angelo Member__________________________________ 39 Fossil Butte Member: Limestone, chalky to white, pale-orange-yellow; laminated in top foot; marly; weathers to yellow below, grayish tan on fresh fracture; contains small ironstone blebs that weather to rusty spots_______:____________ 6 6 Shale, marly, grayish-tan, laminated________ 5 3 Oil shale, brown; weathers bluish gray at top and light tan below; contains evaporite crystal pseudomorphs of calcite_________ 4 6 Chalk, white, soft__________________________ 6 Shale, marly, and siltstone, tan to light-gray_ 4 6 Incomplete thickness, Bullpen Member.- 177 6 Green River Formation: Angelo Member (partial): Thinly interlaminated claystone and marl-stone, tan, yellow, and pink, and limestone, finely crystalline, well-indurated, light-gray and buff_____________________________________ 5TYPE SECTIONS FOR MEMBERS DEFINED IN THIS REPORT 45 Green River Formation at the type section of the Fossil Butte Memh er—Continued Green River Formation—Continued Fossil Butte Member—Continued Oil shale, brown, soft to limy and hard; con- Ft in tains beds with abundant evaporite pseu- domorphs_____________________________________ 5 Shale, limy, pink to tan____________________... 2 Limestone, porous; contains ash bed____________ 1 6 Shale, light-tan, varved_______________________ 1 6 Oil shale; weathers light bluish gray; fissile. .. 1 Marlstone, light-grayish-tan, soft_____________ 1 Shale, light-tan to buff, papery; and blueweathering oil shale; thin ash beds____________ 7 6 Oil shale, low-grade; weathers light gray___ 1 6 Shale, laminated, buff-weathering______________ 1 6 Ash, calcareous, pink______________________________ 6 Shale, laminated, buff-weathering______________ 4 Ash, calcareous, pink-weathering; bright yellow on fracture_____________________________________ 8 Shale, laminated; contains fossil fish_________ 2 Limestone, chalky, pinkish-tan_________________ 2 Shale, laminated, calcareous, buff; thin ash beds_________________________________________ 5 6 Limestone, chalky, light-buff; rust-colored ash zone at base; unit is very irregular__ 2 Shale, limy, laminated, carbonaceous; in beds 1-3 ft thick alternating with 6-in. beds of carbonaceous siltstone______________________ 10 Shale, light-tan, papery; contains thin beds of dark-brown oil shale_________________________ 7 Shale, light-tan to light-gray, laminated___ 7 6 Limestone, chalky, white___________________________ 6 Shale, laminated; limy at top__________________ 2 6 Limestone, buff, chalky, massive, irregular; fish fragments____________________________ 2 6 Mudstone, calcareous, dark-yellowish-brown to gray; thin gypsum veins___________________ 6 Shale, papery; chocolate colored on fresh surface 9 Limestone, chalky, yellow-weathering___________ 2 Shale and shaly limestone, rusty-tan to gray, laminated____________________________________ 6 Limestone, light-gray, bluish-gray-weather- ing, massive, fossiliferous__________________ 3 6 Limestone, light-gray to buff, chalky to blocky, brecciated__________________________ 21 6 Limestone, shaly, light-gray to buff___________ 3 Limestone, shaly, rusty-tan, brecciated_____ 4 Limestone, light-tan, hard, silty, medium- bedded_______________________________________ 5 Siltstone, shaly, light-bluish-gray; purplish gray at top__________________________________ 4 Limestone, silty, pale-buff, brecciated_______ 3 6 Siltstone, shaly, buff to gray, yellow-weathering, oolitic_________________________________ 1 6 Limestone, light-tan to buff, chalky, sandy_ 6 Siltstone, light-bluish-gray to greenish-gray, oolitic; gypsum veins------------------------ 6 6 Sandstone, light-gray to tan, fine-grained__ 4 Green River Formation at the type section of the Fossil Butte Member—Continued Green River Formation—Continued Fossil Butte Member—Continued Siltstone, limy, light-gray, ledge-forming, Ft in massive to brecciated; veined with gypsum. 1 Siltstone, medium- to light-bluish-gray______ 4 Mudstone, sandy, light-gray; rusty colored near base; calcareous_________________________ 5 6 Sandstone, light-gray, fine-grained to very fine grained, calcareous______________________ 1 Siltstone and claystone, gray to pale-olive- gray; muddy partings__________________________ 5 Covered zone above terrace (assumed top of Wasatch Formation)_____________________________ 17 Total thickness (rounded), Fossil Butte Member of Green River Formation__________208 Green River Formation at the type section of the Angelo Member [Measured on blufl overlooking the Angelo Ranch, west of South Fork Twin Creek, In the NWJi sec. 1, T. 20 N., R. 118 W.] Wasatch Formation: Bullpen Member (partial): Covered at top of butte; tan slope of weathered Ft in marlstone and thin-bedded yellow, brown, and tan limestone__________________________ 10 Limestone, brown, blocky______________________ 1 Interbedded chalky-white marlstone and greenish-gray claystone_____________________ 9 Claystone, green, soft________________________ 4 Claystone, mottled brownish red, brown, green, and tan; forms reddish band________ 14 Claystone, greenish-gray___________________ 8 Claystone, silty, brown to red_____________ 5 Marlstone, tan; and greenish-gray claystone. 4 Limestone, tan, flaggy, thinly laminated; forms 1-ft ledge above chalky-white marlstone__________________________________________ 3 Claystone, green______________________________ 4 Claystone, mottled red, brown, and green; forms pink band____________________________ 13 Mudstone, buff-weathering_____________________ 4 6 Limestone, tan, aphanitic, hard; 6-in ledge at top of white marlstone___________________ 3 6 Claystone, greenish-gray, soft____________ 12 Claystone, maroon; green and purple mottling. 4 Covered; brown soft slope; variegated purple, brown, and green claystone_________________ 25 Sandstone, quartz, calcareous, thin-bedded— 1 Covered; mudstone_____________________________ 7 Limestone, sandy, thin-bedded; ostracode coquina grading down to brown sandy mudstone____________________________________ 3 Covered; brown mudstone and fine-grained poorly indurated sandstone__________________ 9 Sandstone, brown, laminated___________________ 146 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING Green River Formation at the type section of the Angelo Meml) er—Continued Green River Formation at the type section of the Angelo Member—Continued Wasatch Formation—Continued Bullpen Member (partial)—Continued Sandstone, brown, coarse-grained; crossbedded Ft in in places___________________________ 15 Partial thickness, Bullpen Member of Wasatch Formation___________________________ 160 Green River Formation: Angelo Member: Oil shale, low-grade, brown, papery; and brown claystone___________________________ 10 Limestone, yellow- to buff-weathering, thinly laminated_________________________________ 6 Covered; brown soil; yellow, brown, orange limestone chips on surface__________________ 4 Limestone, brown, petroliferous, thinly laminated; fish fragments_____________________________ 6 Covered; purplish-tan limestone fragments; flat gastropods______________________________ 6 6 Oil shale, low-grade, brown_________________________ 6 Claystone, brown________________________________ 2 6 Claystone, greenish-gray________________________ 2 Limestone, shaly, soft______________________________ 6 Claystone, greenish-gray; thinly bedded limestone that weathers to orange, brown, and dark-brownish-gray chips_____________________ 9 6 Limestone, tan, buff-weathering, ledge-forming------------------------------------------- 1 Covered; tan and greenish-gray banded slope; alternating green claystone and tan calcareous shale with thin beds of sandy limestone_________________________________________ 23 Covered; white slope containing chips and slabs of tan limestone____________________ 14 Marlstono, hard, dark-brown, ledge-forming; weathers orange; banded______________________ 1 Covered; white to light-tan slope with abundant limestone chips; mostly fissile greenish-gray calcareous shale_____________________ 23 Limestone, light-brown, hard, crystalline; weathers tan_________________________________ 2 Claystone, olive-brown, hackly, hard___________ 17 Sandstone, gray, fine-grained, poorly sorted; grains of angular chert and clay_____________ 1 Covered; tan slope; fissile limy grayish-white shale with thin beds of brown hard limestone_________________________________________ 30 Limestone, algal or concretionary, slabby to thin-bedded, white-weathering; hard, ledge forming to soft, covered____________________ 10 Oil shale, papery, brown________________________ 1 Green River Formation—Continued Angelo Member—Continued Shale, calcareous, white-weathering; contains Ft in chalky limestone and chert_______________ 4 Limestone, tan to brown; weathers white____ 1 Mudstone, gray, calcareous___________________ 4 Limestone, tan, thin-bedded__________________ 5 Mudstone, bluish-green; and claystone; gray to white limestone chips_____________________ 15 Total thickness, Angelo Member of Green River Formation_____________________________ 194 Fossil Butte Member (top only): Shale, calcareous, buff- to white-weathering... 10 Oil shale, dark-brown; weathers blue; 3-cm beds of “sugar oil shale,” filled with 1-mm calcite pseudomorphs after evaporite crystals______________________________________ 1 Fowkes Formation at type sections for its members [Measured from the SEyi sec. 5, T. 21 N., R. 119 W., to the NEK sec. 33, T. 22 N., R. 119 W.] Fowkes Formation: Gooseberry Member (incomplete): Covered interval at top of hill; loose gravel Ft in float; possibly puddingstone conglomerate._ 60 Covered interval on hillslope; limy sandstone and silt in float____________________________ 60 Puddingstone; pebbles as much as 4 in.; light-gray chert dominant, set in white sandy limestone matrix; flat pebbles parallel bedding. 1-ft lenticular calcareous sandstone bed____________________________________ 8 Limestone, light-gray to white, very sandy to calcareous sandstone; biotite and dark mineral grains abundant. Forms rounded weathered surface. Contains five lentils of “puddingstone” about 2 in. thick, 1 ft to several feet in length; lentils grade later- ally and vertically into limestone_________ 6 Puddingstone; conglomerate in sandy limestone matrix_________________________________ 1 6 Limestone, white; contains thin layers of sparse granule-and-pebble conglomerate 1-3 in. thick near base. Upper 3 ft is white. Massive limestone with beds as much as 1 ft thick of laminated pinkish-tan limestone. Cross laminated and contorted in places; separated in others to form calcite-filled vugs as much as 1 in. high and 1 ft long. Resembles travertine________________ 5REFERENCES CITED 47 Fowkes Formation at type sections for its members—Continued Fowkes Formation—Continued Gooseberry Member (incomplete)—Continued Puddingstone, coarse-grained; light-gray at a Ft in distance; white limestone matrix. Contains crude beds 2-6 in. thick of finer and coarser pebbles floating in a limestone matrix. Pebbles well rounded and cobbles to as much as 4 in. of white, gray, black, and tan quartzite; brown, black, and gray chert and pinkish-white porcellenite(?); sparse volcanic pebbles; flat to well-rounded pebbles of dark-gray limestone_________________________ 9 Approx, thickness (incomplete; rounded), Gooseberry Member of Fowkes Formation____________________________________ 150 Bulldog Hollow Member: Sandstone, light-green to olive-brown, medium- to fine-grained; clayey matrix; abundant biotite, magnetite, dark chert grains; interbedded very fine grained sandstone, mudstone, and coarse-grained sandstone. Topmost beds crossbedded, dipping 20° E; 3-ft pebble conglomerate 20 ft below top; white tuffaceous claystone bed 50 ft above base________________________________ 131 Sandstone, medium-green to dark-green, very fine grained to medium-grained; dark-green clay matrix; very abundant magnetite_____ 5 Sandstone, light-green to olive-brown, medium- to coarse-grained; biotite and magnetite_______________________________________ 48 Sandstone, light-grayish-green, mediumgrained_______________________________________ 5 Covered interval; unit consists chiefly of soft dark-green sand that contains magnetite grains_______________________________________ 40 Gravel, black, tan; and gray chert and quartzite pebbles to as much as 6 in. in diameter; broken limestone-indurated puddingstone with pebbles floating in sandy limestone matrix_______________________________________ 2 Sandstone, greenish-tan, very fine grained to medium-grained; magnetite, chert grains and black mineral grains_____________________ 3 Gravel, as above______________________________ 5 Total thickness, Bulldog Hollow Member of Fowkes Formation________________239 Sillem Member: Mudstone, clayey, pale-tan to greenish-gray; pink mottling; thin beds of white tuffaceous claystone__________________________________ 15 Claystone, calcareous silty, light-gray; brown calcareous concretions________________________ 1 Sandstone, pale-gray to pale-tan, fine-grained, poorly sorted, clayey; moderately abundant dark grains and mica; angular fragments of claystone_______________________________________ 5 Fowkes Formation at type sections for its members—Continued Fowkes Formation—Continued Sillem Member—Continued Claystone, pale-green to pale-tan, silty; Ft in biotite flakes________________________________ 9 Mudstone, pale-tan to light-greenish-gray; weathers to gray and pink bands; silty and sandy; micaceous 10 ft above base_____________ 14 Mudstone; pale-greenish-gray siltstone and fine-grained muddy sandstone; weathers to gray with pink mottling__________________________ 15 Sandstone, muddy, very fine grained, pale-greenish-gray; contains brown and tan beds. Very silty and muddy at top of unit. Slope weathers to an encrusted mud surface______________________________________ 20 Mudstone, shaly; and siltstone, pale-greenish- gray------------------------------------ 1 Sandstone, light-greenish-gray; fine grained grading down to coarse grained____________ 2 Mudstone, silty, shaly; mottled pink, tan, and brown_______________________________ 6 Sandstone, olive-drab, green to light-green, coarse-grained; clayey matrix; grains dominantly quartz and black chert_____________ 4 6 Sandstone, coarse-grained, crossbedded, light-gray “salt and pepper”; about 10 percent dark grains, black chert, minor magnetite, and interbedded thin mudstone and conglomerate beds; lenticular conglomerate as much as 2 ft thick; granules and pebbles of chert and quartz; some clay balls as much as 6 in. in diameter________________________ 21 Covered below. Total thickness, exposed Sillem Member of Fowkes Formation__________________ 108 Total thickness (rounded), exposed Fowkes Formation________________________497 REFERENCES CITED Anderman, G. G., 1955, Tertiary deformational history of a portion of the north flank of the Uinta Mountains in the vicinity of Manila, Utah, in Wyoming Geol. Assoc. Guidebook 10th Ann. Field Conf., Green River Basin, 1955: p. 130-134. Armstrong, F. C., and Oriel, S. S., 1965, Tectonic development of Idaho-Wyoming thrust belt: Am. Assoc. Petroleum Geologists Bull., v. 49, no. 11, p. 1847-1866. Bradley, W. H., 1926, Shore phases of the Green River formation in northern Sweetwater County, Wyoming: U.S. Geol. Survey Prof. Paper 140-D, p. 121-131. ----— 1929a, Algae reefs and oolites of the Green River Formation : U.S. Geol. Survey Prof. Paper 154-G, p. 203-223, pis. 28-48 [1930]. ------1929b, The occurrence and origin of analcite and meerschaum beds in the Green River formation of Utah, Colorado, and Wyoming: U.S. Geol. Survey Prof. Paper 158-A, p. 1-7, pis. 1-3.48 UPPERMOST CRETACEOUS AND TERTIARY STRATIGRAPHY OF FOSSIL BASIN, WYOMING ------1930, The varves and climate of the Green River epoch: U.S. Geol. Survey Prof. Paper 158-E, p. 87-110, pis. 11-14. ------1931, Origin and microfossils of the oil shale of the Green River formation of Colorado and Utah: U.S. Geol. Survey Prof. Paper 168, 58 p., 28 pis. ------1948, Limnology and the Eocene lakes of the Rocky Mountain region: Geol. Soc. America Bull., v. 59, no. 7, p. 635-648. ------1959, Revision of stratigraphic nomenclature of Green River formation of Wyoming: Am. Assoc. Petroleum Geologists Bull., v. 43, no. 5, p. 1072-1075. ------1963, Paleolimnology, Chapter 23 of Frey, D. G., ed., Limnology in North America: Wisconsin Univ. Press, p. 621-652. ------1964, Geology of Green River Formation and associated Eocene rocks in southwestern Wyoming and adjacent parts of Colorado and Utah: U.S. Geol. Survey Prof. Paper 496-A, 86 p. [1965], ------1966, Tropical lakes, copropel, and oil shale: Geol. Soc. America Bull., v. 77, no. 12, p. 1333-1338. Brown, R. W., 1929, Additions to the flora of the Green River formation: U.S. Geol. Survey Prof. Paper 154-J, p. 279-292 [1930]. ------1934, The recognizable species of the Green River flora: U.S. Geol. Survey Prof. Paper 185-C, p. 45-77 [1935], ------1962, Paleocene flora of the Rocky Mountains and Great Plains: U.S. Geol. Survey Prof. Paper 375, 119 p. Cockerell, T. D. A., 1920, Eocene insects from the Rocky Mountains: U.S. Natl. Mus. Proc., v. 57, p. 233-260. Cope, E. D., 1877, A contribution to the knowledge of the ichthyological fauna of the Green River shales, in Hayden, F. V., Bulletin of the United States Geological and Geographical Survey of the Territories: v. 3, no. 4, p. 807-819. ------1878, Descriptions of fishes from the Cretaceous and Tertiary deposits west of the Mississippi River, in Hayden, F. V., Bulletin of the United States Geological and Geographical Survey of the Territories : v. 4, p. 67-77. ------ 1884, The Vertebrata of the Tertiary formations of the West: U.S. Geol. Survey Terr. (Hayden), Rept. 3, 1009 p. Culbertson, W. C., 1965, Tongues of the Green River and Wasatch Formations in the southeastern part of the Green River Basin, Wyoming, in Geological Survey research 1965: U.S. Geol. Survey Prof. Paper 525-D, p. D139-D143. Dorf, Erling, 1955, Paleobotanical correlations of Late Cretaceous deposits in southwestern Wyoming, in Wyoming Geol. Assoc. Guidebook, 10th Ann. Field Conf., Green River Basin, 1955: p. 96-99. Dorr, J. A., Jr., 1952, Early Cenozoic stratigraphy and vertebrate paleontology of the Hoback Basin, Wyoming: Geol. Soc. America Bull., v. 63, no. 1, p. 59-93. ------1958, Early Cenozoic vertebrate paleontology, sedimentation, and orogeny in central western Wyoming: Geol. Soc. America Bull., v. 69, no. 10, p. 1217-1243. Eardley, A. J., 1944, Geology of the north-central Wasatch Mountains, Utah: Geol. Soc. America Bull., v. 55, no. 7, p. 819-894. ------1952, Wasatch hinterland, in Geology of the central Wasatch Mountains, Utah: Utah Geol. Soc. Guidebook to the Geology of Utah, no. 8, p. 52-60. ------1959, Review of geology of northeastern Utah and southwestern Wyoming, in Intermountain Assoc. Petroleum Geologists Guidebook 10th Ann. Field Conf., Wasatch and Uinta Mountains transition area, 1959: p. 166-171. Eardley, A. J., Horberg, Leland, Nelson, V. E., and Church, Victor, 1944, Hoback-Gros Ventre-Teton [Wyo.] field con- ference: Michigan Univ., Rocky Mtn. Field Sta., 2 map sheets. Evernden, J. F., Savage, D. E., Curtis, G. H., and James, G. T., 1964, Potassium-argon dates and the Cenozoic mammalian chronology of North America: Am. Jour. Sci., v. 262, no. 2, p. 145-198. Fahey, J. J., 1962, Saline minerals of the Green River formation, with a section on X-ray powder data for saline minerals of the Green River formation, by M. E. Mrose: U.S. Geol. Survey Prof. Paper 405, 50 p. Flint, R. F., Sanders, J. E., and Rodgers, John, 1960, Symmic-tite—A name for nonsorted terrigenous sedimentary rocks that contain a wide range of particle sizes: Geol. Soc. America Bull., v. 71, no. 4, p. 507-509; addendum—Diamictite, a substitute term for symmictite, v. 71, no. 12, pt. 1, p. 1809. Gazin, C. L., 1952, The lower Eocene Knight formation of western Wyoming and its mammalian faunas: Smithsonian Misc. Colin., v. 117, no. 18, 82 p. ------1956, The occurrence of Paleocene mammalian remains in the Fossil Basin of southwestern Wyoming: Jour. Paleontology, v. 30, no. 3, p. 707-711. ------ 1959, Paleontological exploration and dating of the early Tertiary deposits in basins adjacent to the Uinta Mountains [Utah-Wyo.-Colo.], in Intermountain Assoc. Petroleum Geologists Guidebook, 10th Ann. Field Conf., Wasatch and Uinta Mountains transition area, 1959: p. 131-138. ------ 1962, A further study of the lower Eocene mammalian faunas of southwestern Wyoming: Smithsonian Misc. Colin., v. 144, no. 1 (Smithsonian Inst. Pub. 4474), 98 p. Granger, Walter, 1914, On the names of the lower Eocene faunal horizons of Wyoming and Mexico: Am. Mus. Nat. History Bull. 33, p. 201-207. Hayden, F. V., 1869, Preliminary field report [third annual] of the United States Geological Survey of Colorado and New Mexico: 155 p. ------ 1870, Sun pictures of Rocky Mountain scenery, with a description of the geographical and geological features and some account of the resources of the Great West: New York, Julius Bien, 150 p. Hesse, C. J., 1939, Fossil fish localities in the Green River Eocene of Wyoming: Sci. Monthly, v. 48, no. 2, p. 147-151. Heylmun, E. B., 1965, Reconnaissance of the Tertiary sedimentary rocks in western Utah: Utah Geol. and Mineralog. Survey Bull. 75, 38 p. Jepsen, G. L., 1966, Early Eocene bat from Wyoming: Science, v. 154, no. 3754, cover, p. 1333-1339. Lawrence, J. C., 1963, Origin of the Wasatch Formation, Cumberland Gap area, Wyoming: Wyoming Univ. Contr. Geology, v. 2, no. 2, p. 151-158. Leidy, Joseph, 1873, Contributions to the extinct vertebrate fauna of the Western Territories, in Hayden, F. V., U.S. Geol. and Geog. Survey of the Terr., Ann. Rept. 1, 1867: 358 p. Lesquereux, Leo, 1883, Contributions of the fossil flora of the Western Territories—Part 3, The Cretaceous and Tertiary floras in Hayden, F. V., U.S. Geol. and Geog. Survey of the Terr., Ann. Rept. 8,1874 : 283 p. McGrew, P. O., and Roeliler, H. W., 1960, Correlation of Tertiary units in southwestern Wyoming, in Wyoming Geol. Assoc. Guidebook, 15th Ann. Field Conf., Overthrust belt of southwestern Wyoming and adjacent areas, 1960: p. 156-158. McKenna, M. C., Robinson, Peter, and Taylor, D. W., 1962, Notes on Eocene Mammalia and Mollusca from Tabernacle Butte, Wyoming: Am. Mus. Novitates, no. 2102, 33 p.REFERENCES CITED 49 Mansfield, G. R., 1927, Geography, geology and mineral resources of part of southeastern Idaho, icith descriptions of Carboniferous and Triassic fossils, by G. H. Girty: U.S. Geol. Survey Prof. Paper 152, 453 p. Masurslcy, Harold, 1962, Uranium-bearing coal in the eastern part of the Red Desert area: U.S. Geol. Survey Bull. 1099-B, 152 p. Mullens, T. E., and Laraway, W. H., 1964, Geology of the Devils Slide quadrangle, Morgan and Summit Counties, Utah: U.S. Geol. Survey Mineral Inv. Field Studies Map MF-290. Oriel, S. S., 1961, Tongues of the Wasatch and Green River formations, Fort Hill area, Wyoming, in Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-B, p. B151-B152. ------1962, Main body of Wasatch Formation near La Barge, Wyoming: Am. Assoc. Petroleum Geologists Bull., v. 46, no. 12, p. 2161-2173. ------1969, Geology of the Fort Hill quadrangle, Lincoln County, Wyoming: U.S. Geol. Survey Prof. Paper 594-M, 40 p. Oriel, S. S., and Armstrong, F. C., 1966, Times of thrusting in Idaho-Wyoming thrust belt—Reply : Am. Assoc. Petroleum Geologists Bull., v. 50, no. 12, p. 2614r-2621. Oriel, S. S., Gazin, C. L., and Tracey, J. I., Jr., 1962, Eocene age of Almy Formation, Wyoming, in its type area: Am. Assoc. Petroleum Geologists Bull., v. 46, no. 10, p. 1936-1937. Peale, A. C., 1879, Report on the geology of the Green River district [Wyoming], in Hayden, F. V., U.S. Geol. and Geog. Survey of the Terr., Ann. Rept. 11, 1877: p. 509-646. ------1883, [Geologic map of] parts of western Wyoming, southeastern Idaho, and northeastern Utah, in Hayden, F. V., U.S. Geol. and Geog. Survey of the Terr., Ann. Rept. 12, 1878. Pipiringos, G. N., 1962, Uranium-bearing coal in the central part of the Great Divide Basin: U.S. Geol. Survey Bull. 1099-A, 104 p. [1962], Ruliey, W. W., and Hubbert, M. K., 1959, Overthrust belt in geosynclinal area of western Wyoming in light of fluid-pressure hypothesis, part 2 of Role of fluid pressure in mechanics of overthrust faulting: Geol. Soc. America Bull., v. 70, no. 2, p. 167-205. Rubey, W. W., Oriel, S. S., and Tracey, J. I., Jr., 1961, Age of the Evanston formation, western Wyoming, in Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper. 424-B, p. B153-B154. ------1968, Preliminary geologic map of the Kemmerer quadrangle, Lincoln County, Wyoming: U.S. Geol. Survey open-file map. Rubey, W. W., Tracey, J. I., Jr., and Oriel, S. S., 1968, Preliminary geologic map of Sage quadrangle, Lincoln County, Wyoming: U.S. Geol. Survey open-file map. Schaeffer, Bobb, and Mangus, Marlyn, 1965, Fossil lakes from the Eocene: Nat. History, v. 74, no. 10, p. 10-21. Schultz, A. R., 1914, Geology and geography of a portion of Lincoln County, Wyoming: U.S. Geol. Survey Bull. 543, 141 p. Scudder, S. H., 1890, The Tertiary insects of North America, in Hayden, F. V., U.S. Geol. Survey of the Terr. Rept. 13, 734 p. Sears, J. D., and Bradley, W. H., 1924, Relations of the Wasatch and Green River formations in northwestern Colorado and southern Wyoming with notes on oil shale in the Green River formation: U.S. Geol. Survey Prof. Paper 132-F, p. 93-107. Spieker, E. M., 1946, Late Mesozoic and early Cenozoic history of central Utah: U.S. Geol. Survey Prof. Paper 205-D, p. 117-161. Thorpe, M. R., 1938, Wyoming Eocene fishes in the Marsh Collection : Am. Jour. Sci., ser. 5, v. 36, no. 214, p. 279-295. Tracey, J. I., Jr., and Oriel, S. S., 1959, Uppermost Cretaceous and lower Tertiary rocks of the Fossil Basin [Wyoming], in Intermountain Assoc. Petroleum Geologists Guidebook, 10th Ann. Field Conf., Wasatch and Uinta Mountains transition area, 1959: p. 126-130. Tracey, J. I., Jr., Oriel, S. S., and Rubey, W. W., 1961, Diamic-tite facies of the Wasatch formation in the Fossil basin, southwestern Wyoming, in Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. Paper 424-B, p. B149-B150. Van Houten, F. B., 1961, Climatic significance of red beds, Chapter 5 of Nairn, A. E. M., ed., Descriptive palaeocli-matology : New York, Interscience Publishers, Inc., p. 89-139. —-----1964, Tertiary geology of the Beaver Rim area, Fremont and Natrona Counties, Wyoming: U.S. Geol. Survey Bull. 1164, 99 p. [1965]. Veatch, A. C., 1906, Coal and oil in southern Uinta County, Wyoming: U.S. Geol. Survey Bull. 285-F, p. 331-353. ------1907, Geography and geology of a portion of southwestern Wyoming, with special reference to coal and oil: U.S. Geol. Survey Prof. Paper 56,178 p. Wetmore, Alexander, 1933, Fossil bird remains from the Eocene of Wyoming—Condor: v. 35, no. 3, p. 115-118. Williams, J. S., 1964, The age of the Salt Lake Group in Cache Valley, Utah-Idaho: Utah Acad. Sci., Arts, and Letters Proc., v. 41, no. 2, pt. 2, p. 269-277. Williams, N. C., and Madsen, J. H., Jr., 1959, Late Cretaceous stratigraphy of the Coalville area, Utah, in Intermountain Assoc. Petroleum Geologists Guidebook, 10th Ann. Field Conf., Geology of the Wasatch and Uinta Mountain transition area, 1959: p. 122-125. Wood, H. E., 2d, chm., and others, 1941, Nomenclature and correlation of the North American continental Tertiary: Geol. Soc. America Bull., v. 52, no. 1, p. 1—48. Wood, R. C., 1967, A review of the Clark Fork vertebrate fauna : Breviora, no. 257, p. 1-30.INDEX [Italic page numbers indicate major references] A Page Absaroka fault 10,14 Acknowledgments - - 2 Page Distribution and thickness, Evanston Formation, Hams Fork Conglomerate Adaville Formation 6,10,14,23 Algal logs 21 Fowkes Formation, Bulldog Hollow Member 35 Almy Formation 6,9,16,17,19,33 Amerada Petroleum Co. 1 Chicken Creek unit well 19 Angelo Member, Green River Formation 20, 28,30, S/,39 Angelo Ranch 20,31 Armstrong, R. L., written communication— 37 B Badland buttes 10 Green River Formation, Angelo member.. 32 Fossil Butte Member 31 Wasatch Formation, Bullpen Member 22 lower member 18 Tunp Member 24 Dunkle, D. H., written communication 28 E Earth quakes 29 Basal conglomerate member, Wasatch Formation 17,27 Bear Lake Plateau 34,37 Echo Canyon Conglomerate... 39 Eli Hill 24 Elk Mountain 10,17,19,20,21,27 Bear River 16,19 Bear River Range - 9 Bear River valley 24 Big Park 24 Boulder conglomerates 6 Boulder Ridge 22,29,34,38 Bridger Formation .. 16,30,41 Brigham Quartzite 9,34 Hams Fork Conglomerate Member 6,16 Brown, R. W., written communication 13,37 Bulldog Hollow 35 Bulldog Hollow Member, Fowkes Formation 34,35,36,41 distribution and thickness - 7,9 fossils and age 12 lithology 9 Bullpen Creek 21,22 Bullpen Member, Wasatch Formation . 17, 21,28,29,31,32 C Cache Valley 41 lower contact 10 lower member— - 6 fossils and age - 11 main body - 6,9 color - - 9 Carter 16 Chappo Member, Wasatch Formation 39 lithology - - 9 Coal 6,10,29 Cokeville quadrangle 2,6,9,10,24 Collett Creek 10,13,18 origin IS Color, Evanston Formation 5,6,9 Wasatch Formation, basal conglomerate member .. 17 Exposures, Evanston Formation - 6,10 Green River Formation, Angelo Member.. 31 lower member 17 main body 18 F Faulting 6,9,10,14,22,24,29 Commissary Ridge 6,7,23,24 Fontenelle Tongue 41 Crawford Mountains 5.23,35 D Dawson, Mary, written communication 37 Dempsey Basin 24,31 Fossil basin 5 Fossil Butte - 19,28,30,31 Fossil Butte Member, Green River Formation 20,28, SO, 39 Fossil Ridge - ---- 30,31 Diamictite 29 Dip, Evanston Formation, Hams Fork Conglomerate Member 6 Fossils: Abiespollenites 12 Alnus 12,13,26 Fossils—Continued AlsophUidites.... Amerianna________ Anemia........... Appendicisporites. Aquilapollenites... Araucariacidites... Page 12 j 12 26 12 12 13 Araucariacites australis..................11,26 Asineops.................................... 28 bats........................................ 32 Bellamy a paludinaeformis................... 32 Betula stevensoni........................... 13 Biomphclaria pseudoammonius...... 26,28,32,36 birds....................................... 32 bones and scales............................ 28 Car piles................................... 13 Cary a....................................13,26 antiquora.............................. 13 CedreUa..................................... 26 charophytes...............................26,27 Cicatricosisporites......................... 12 dorogensis............................. 12 Cinnamomum affine........................... 12 linifolium................................ 11 Classopollis classoides..................... 12 Cleopatra................................... 12 condylarth.................................. 27 Coryphodon.................................. 28 Cyathidites............................... 12 Beltoidospora............................... 12 dicots...................................... 12 Dinoflagellata.............................. 12 dinosaurs................................... 12 Discus..................................... 26 Dombeyopsis obtusa......................... 11 Drepanotrema---------------------------- 28 Dryophyllum subfalcatum...................11,12 Elimia nodulifera..................... 26,28,32 Engelhardtia................................ 13 Ephedra..................................... 12 Equisetum................................... 37 Erdtmanipollis............................12,26 Eucommia -.................................. 26 Eucommiidites............................... 12 Fagus....................................... 13 Ficus.....................................12,13 planicostata.......................... 12 fish......................................30,32 Fremontia................................... 26 gastropods................ 12,16,26,27,28,36,41 Oleicheniidites senonicus.................13,26 Olypterpes veternus........................ 26 Or anger ella............................... 26 Outhbrlisporites............................ 12 Haplomylus speirianus....................... 28 Harrisichara................................ 26 Hemicyprinotus watsoensis................32,36 Hymenozonotriletes reticulatus.............. 12 Hypolagus................................... 37 Hyracotherium vasacciense................... 28 insects..................................... 32 Juglans..................................... 26 Kurtzipites................................. 13 Laurophyllum................................ 13 leaves..............................11,16,32,36 Lepisosteus...............................26,28 5152 INDEX Fossils—Continued Page Leporidae..................................... 37 Lyjodium kaulfussi............................ 37 Maedleriella.............................. 26,27 mammals................................... 6,41 Meniscotherium................................ 27 priscum............._ _............... 26 Metasequoia occidentalis...................... 13 mollusks............................... 28,32,41 Momipites..................................... 13 tenuipolus........................... 13 Monocolpopollenites......................... 13 Monoletes................................... 12 major................................. 12 Monosulcites minimus.......................... 12 Multiporopollenites_________________________ 12 Myrica torreyi................................ 12 Neoraistrickia............................. 12 Nyssoipollenites............................. 13 Omalodiscus.............................__ 26 Oreoconus.............................. 26,28,32 planispira................................ 36 Osmundacidites................................ 12 ostracodes........................... 26,27,32,36 Pachysandra.................................. 13 Paleoaster inquirenda....................... 12 Parasporia.................................... 26 Periporopollenites............................ 13 Physa.......................................12,28 bridgerensis............................. 26 pleromatis.............................26,32 Picea......................................... 13 Pinuspollenites................._......... 13 labdacus................................ 12 Pistillipollenites........................ 26 Pityosporites...............................12,13 labdacus.................................. 12 Planorbidae........................_...... 28 Platanus raynoldsi........................... 13 Platycarya................................. 26 Plesielliptio................................ 32 Podocarpidites biformis....................... 12 pollen...................................11,26,27 Pollenites (Tricolporopollenites) cognitus.. 12 Procyprois ravenridgensis...................32,36 Proteacidites................................. 12 callosus................................. 11 retusus.............................. 11,12 Protophyllocladus subintegrifolius..........12,13 Pseudocypris........................... 26,32,36 pagei..................................26,27 Pterocarya.................................... 26 Quercoipollenites henrici.................... 12 rays........................................ 32 Retitricolpites............................. 26 vulgaris................................. 26 Rhamnus....................................... 13 Salicoidites.................................. 13 Schizaeoisporites pseudodorogensis.......... 12 Selaginellites ariadnae...................... 12 Sequoia reichenbachi......................... 12 Smilacipites................................. 12 snakes...................................... 32 Sphagnumsporites setereoides................. 12 spores......................................11,26 Sporites arcifer.............................. 26 Sporopollis................................. 12 Sterioisporites............................. 12 Taxodiaepollenites hiatus.................... 12 Taxodium..................................... 26 teeth......................................... 27 Triceratops................................ 12 Tricolpopollenites kruschi contortus......... 12 microhenrici............................. 13 microreticulatum......................... 13 Tricolporopollenites kruschi................. 13 kruschi pseudolaesus..................... 12 Triletes.................................... 12 Triplanosporites sinuosus.................... 12 Triporopollenites robustus................... 13 Page Fossils—Continued Trivestibulopollenites betuloides....... 12 Ulmaceae............................... 26 Ulmipollenites undulosus................. 13 Ulmus................................... 26 Valvata................................. 28 vertebrates...................... 12,26,37,41 Zelkova-------------------------------- 13,26 Fowkes Formation........................ 16, 55,41 Bulldog Hollow Member________________ 34,36,41 distribution and thickness........... 35 lower contact....................... 35 rocks included...................... 35 type section......................... 35 fossils and age...________________________ 86 Gooseberry Member___________________ 34,55,41 distribution and thickness............ 36 rocks included...................... 36 type section....................... 36 name and usage__________________________ 55 origin.................................. 87 Sillem Member.....................22,84,37,41 distribution and thickness____________ 34 rocks included...................... 34 type section-------------------------- 34 subdivisions used here------------------- 54 tectonic implications.................... 57 Frontier Formation..........- -............ 10,23 G Gannett Group...........................— 11 Gazin, C. L., written communication.........27,37 Gooseberry Member, Fowkes Formation... 34,55,41 Gooseberry Springs.......................... 35 Green River Basin........... 2,5,12,26,31,32,39,41 Green River Formation......................... 2, 5,14,16,18,19,20,27,28,35 Angelo Member................ 20,28,30,81,39 distribution and thickness............ 32 type exposure......................... 31 Fossil Butte Member............... 20,28,80,39 color.................................. 30 distribution and thickness........... 31 lower contact....................... 31 rocks included..................... - 30 type section and exposures............. 30 fossils and age........................... 88 lithologic heterogeneity.................. SO name and usage........................... 80 origin..................................... 88 subdivisions used here..................... 80 tectonic implications................... 55 Gros Ventre Range...........-.............. 2 H Hams bench mark................................ 7 Hams Fork.......................5,6,7,10,14,23,31 Hanis Fork Conglomerate Member, Evanston Formation......................6,12,16 Hams Fork Plateau....................... 20,22,32 Hayden, F. V., quoted....................14,16,30 Highara Grit.................................. 17 Hilliard Formation............................ 10 Hoback........................................ 39 Hoback Formation............................ 5,39 Hogback ridges................................. 7 Hoxsey Oil Co. 1 Government test............10,11 I Idaho-Wyoming thrust belt...................... 2 Introduction.................................. 8 K Kemmerer....................................2, 30 Kemmerer quadrangle... 2, 6, 13, 20, 22, 28, 30, 31, 32 Knight........................................ 28 Knight Formation...............10, 16, 19, 26, 33 La Barge Member, Wasatch Formation...... 39 Lake Creek................................ 24 Lance Formation........................... 12 Lazeart syncline....................... 14 Lens-shaped channels.................... 28 Lenses..................................... 6 Leopold, E. B. written communication.........12, 14, 26, 39 Lewis Formation......................... 12 Lignite.................................... 6 Lithology, Evanston Formation, Hams Fork Conglomerate Member............. 9 main body........................... 9 Green River Formation................. SO Wasatch Formation, basal conglomerate member........................ 17 Bullpen Member..................... 21 lower member....................... 17 main body......................... 18 mudstone tongue.................... 20 sandstone tongue.................... 20 Tunp Member...................... 23 Little Muddy Creek...................... 10 Lower contact, Evanston Formation......... 10 Green River Formation, Fossil Butte Member......................... 31 Wasatch Formation, Bullpen Member.. 22 main body........................... 20 Lower member, Evanston Formation........ 6,11 Wasatch Formation....................17,87 M Madison Limestone........................ 34 Magnetite................................. 35 Main body, Evanston Formation..........6,0,12 Wasatch Formation................ 17,18,87 Medicine Butte fault....................... 6 Morely bench mark.......................... 7 Morgan Canyon............................. 17 Moyer...................................... 7 Mudflows.................................. 29 Mudstone tongue, Wasatch Formation...17,80,88 N National Cooperative Refinery Association, 1 Arthur H. Linden oil test.. 9,11 1 Government-Larsen oil test......9,11,18 New Fork Tongue, Wasatch Formation.....39,41 North Bridger Creek..------------------17,18 Norwood Tuff------------------------ 37,41 Nugget............................... 13,17 Nugget Sandstone......................2,17,18,23,28 O Origin, Evanston Formation............. 18 Hams Fork Conglomerate Member... 9 Fowkes Formation................... 57 Green River Formation.............. 88 Wasatch Formation.................. 88 sandstone tongue................ 20 Oyster Ridge........................... 5 Oyster Ridge barrier.................5,10,41 P Paris thrust fault...................... 9,14 Peck, R. E., written communication........ 27 Phosphoria Formation...................... H Pink Butte................................ 31 Pole Creek................................ 24 Preuss Redbeds............................ 23 Purpose of report.......................... 2INDEX 53 Relations, general............................ 5 regional................................ 88 Evanston, Hoback, and Wasatch Formations..................... 89 Fowkes Formation, Norwood Tuff, Bridger Formation............... 41 lower strata of the Wasatch......... 89 tongues of the Wasatch and Green River Formations................ 89 Rock Creek Ridge...................... 24,27,29 Roy Steele 1 Government well ..............19,31 Rubey, W. W., oral communication............. 17 S Sage........................... 2,16,22,29,35,36 Sage quadrangle...... 2,11,18,20,22,30,31,32,35,37 Salt Lake Formation.......................37,41 type locality........................... 37 Sandstone tongue, Wasatch Formation___17,20,28 Sillem Member, Fowkes Formation.......22,5^,37,41 Sillem Ridge................................. 22 Sohn, I. G., written communication........32,36 Sorting, Evanston Formation................... 6 Wasatch Formation, basal conglomerate member........................... 17 Tunp Member......................... 23 South Fork, Twin Creek....................28,31 Spring Creek................................. 12 St. Charles Limestone, Worm Creek Quartzite Member............................ 9 T Taylor, D. W., written communication........ 12, 26,32,36,41 Tectonic implications, Evanston Formation.. 14 Fowkes Formation....................... 87 Green River Formation................... 88 Wasatch Formation....................... 29 Thaynes Formation.......................... 17 Thaynes Limestone.....................- - - 23 Thickness, Evanston Formation................. 6 Evanston Formation, main body........... 10 Wasatch Formation....................... 19 basal conglomerate member............ 17 sandstone tongue..................... 20 Trail Creek.................................. 12 Page Tunp Member, Wasatch Formation________________ 17, 19,20,22,28,29,38 Tunp Range---------------------- 5,10,19,20,22,31 Twin Creek, South Fork..................... 28,31 Twin Creek Limestone..................... 10,17,23 Type area, Wasatch Formation, Tunp Member. .......................................... 23 Type exposure, Green River Formation, Angelo Member.................... 31 Type locality, Salt Lake Formation_____________ 37 Type sections.................................. 41 Evanston Formation, Hams Fork Conglomerate Member............................ 7 Fowkes Formation, Bulldog Hollow Member...................................... 35 Gooseberry Member................... 36 Sillem Member----------------------- 34 Green River Formation, Fossil Butte Member............................ 30 Wasatch Formation, Bullpen Member_____________ 21 U Uinta Mountains........................5,20,31 uplift.................................. 32 Unconformity, Evanston Formation............... lo Wasatch Formation, lower member____________ I7 V Varves......................................... 32 Veatch, A. C., quoted..................5,16,21,33 W Wasatch........................................ 19 Wasatch facies of Spieker....................... 5 Wasatch Formation................2,5,6,9,14,31,37 basal conglomerate member.................. 17 color.................................. 17 fossils and age....................... 27 lithology.............................. 17 sorting...........*................. 17 thickness.............................. 17 Bullpen Member............... 17,21,28,29,31,32 bedding................................ 22 color.................................. 21 distribution and thickness............. 22 faulting............................... 22 fossils and age....................... 28 lithology.............................. 21 Page Wasatch Formation— Continued Bullpen Member—Continued lower contact........................ 22 type section.......................... 21 Chappo Member............................. 39 La Barge Member......................... 39 lower member.............................. 17 color................................. 17 distribution and thickness............ 18 fossils and age............-....... 27 lithology............................. 17 unconformity.......................... 17 main body..............................17,18 color................................. 18 distribution and thickness............ 19 fossils and age..................... 27 lithology........................... 18 lower contact......................... 20 mudstone tongue.........-..............17,20 color................................. 20 fossils and age....................... 28 lithology............................. 20 name and usage............................ 14 New Fork Tongue................-.......39,41 origin................................... 28 sandstone tongue.......................17,20 fossils and age............- - -... 28 lithology..................-....... 20 origin................................ 20 thickness............................. 20 subdivisions used here.................... 16 tectonic implications..................... 29 thickness-................................ 19 Tunp Member............. 17, 19, 20, 22, 29, 38 channels.............................. 24 distribution and thickness............ 24 fossils and age....................... 28 lithology............................. 23 sorting............................... 23 type area............................. 23 Veatch’s subdivisions..................... 16 Wells Formation.....................11, 17. 20, 23 Whitney Canyon.................................. 6 Wolfe, J. A., written communication.........11, 14 Worm Creek Quartzite Member, St. Charles Limestone........................... 9