UC BERKELEY MASTER NEGATIVE STORAGE NUMBER 03-67.15 (National version of master negative storage number: CU SN03067.15) MICROFILMED 2003 UNIVERSITY OF CALIFORNIA AT BERKELEY LIBRARY PHOTOGRAPHIC SERVICE REPRODUCTION AVAILABLE THROUGH INTERLIBRARY LOAN OFFICE MAIN LIBRARY UNIVERSITY OF CALIFORNIA BERKELEY, CA 94720-6000 COPYRIGHT The copyright law of the United States (Title 17, United States Code) governs the making of photocopies or other reproductions of copyrighted materials including foreign works under certain conditions. In addition, the United States extends protection to foreign works by means of various international conventions, bilateral agreements, and proclamations. Under certain conditions specified in the law, libraries and archives are authorized to furnish a photocopy or other reproduction. 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The manganese deposits of the Franciscan series 1913 BIBLIOGRAPHIC RECORD TARGET University of California at Berkeley Library Master negative storage number: 03-67.15 (national version of the master negative storage number: CU SN03067.15) GLADIS NUMBER: 184787999E FORMAT: BK AD:991012/FzB LEVEL:b BLT:am DCF:a CSC:d MOD: EL: UD:030604 /MAP CP:cau L:eng INT: GPC: BIO: FIC: CON: ARCV: PC:s PD:1913/ REP: CPI: FSI: ILC: II:0 CUScCU 040 090 100 245 260 300 502 610 690 20 0 SbDISS.BILLICK.GEOL 1913 Billick, Don C. The manganese deposits of the Franciscan series. Scl913. 61 p. :$bill. ;S$c29 cm. Thesis (B.S. in Geology)-- University of California, Berkeley, December, 1913. University of California, Berkeley.$bDept. of Geology and GeophysicsS$SxDissertations. Dissertations, Academic$xUCB$xGeology$y1911-1920. Microfilmed by University of California Library Photographic Service, Berkeley, CA FILMED AND PROCESSED BY LIBRARY PHOTOGRAPHIC SERVICE, UNIVERSITY OF CALIFORNIA, BERKELEY, 94720 DATE: 7/03 REDUCTION: 10 X PM-1 3%."x4” PHOTOGRAPHIC MICROCOPY TARGET NBS 1010a ANSI/ISO #2 EQUIVALENT = jl .0 = IZ 2 EA wn ll mn . om = 0 Il TEA = ws A ° ow [Ee l= eZ ne Le “- tn, | z 0 L. lo le, |v, le, [2, [1 SLE ELS Li TON CTO TOO YON OL A AOA DISS BILLICK Geol 1913 | Are TABLE OF CONTENTS page List of Illustrations 3 THE MANGANESE DEPOSITS OF THE FRANCISCAN SERIES Introduction 4 B Deposit at Fort Baker 5 y Deposit at Red Rock Island 24 Deposit at Manganese Ridge 29 DON C. BILLICK Deposits ih the Livermore-Tesla District 38 Cedar Mountain Ridge 38 Tesla 42 Summary of Facts 51 t Submitted as a thesis in fulfillment y of the requirement Lor ‘the degree of Probable Origin of the Deposits 53 Bachelor of Science,College of Mining, University of California . Berkeley,California December,1913, £'°* : L¢5 Department Beikeloy 4, Californig LIST OF ILLUSTRATIONS Chert Beds on San Francisco Peninsula Chert Beds on San Francisco Peninsula Chert Beds on Marin Seninsuls Contact Between Chert and Spheroidal Basalt Spheriodal Basalt at Hunters Point Spheriodal Basalt at ‘oint Bonita Metamorphdésed Chert at Fort Baker Hanging Wall of Fort Baker Deposit Fort Baker Manganese Deposit Foot Wall at Fort Baker Deposit Manganese Ridge Looking West From Manganese Ridge Outecrop at Manganese Ridge Boulder of Manganese Oxide Outcrop at Manganese Ridge Ore on Dump,Manganese Ridge Old Workings,0ld Ladd Mine Opén~Cut,01d Ladd line Qutcrop of Manganese Ore,Tesla 10 13 14 16 18 20 22 28 33 36 36 37 43 45 4% INTRODUCTION Numerous small deposits of manganese oxide occur in California,especially in the Coast Range mountains,but the origin of these deposits has never been determined. With a view of investigating their geological occurence and,if possible to arrive at some conclusion regard- ing their origin,a study of these deposits was under- taken. Only the following deposits were visiteds Fort Baker,on the Marin peninsula; Red Rock Island,in San Francisco bay;Manganese Hidge in Napa county; and those deposits in the Livermore-Tesla district,the latter being the most important in the Pacific coast region. The report is a presentation of the geological facts connected with the deposits and is not an exhaustive study of them. For much valuable assistance in his investigation, the writer is indebted to Mr.E.C.Harder's excellent re- port on the manganese deposits of the United States, found in United States Geological Survey Bulletin,num- ber 431 also to the report of the Challenger expedition of 1878;and especially to Mr.E.F.Davis of the University of California fer mmeth valuable information in connection with the study of the chert beds. FORT BAKER This deposit is located on the southern end of the Marin peninsula on the Fort Baker Military Reservation.The ridge on which the ore occurs is a spur of a larger ridge which terminates in Lime Point,the northern point of tlje Golden Gate. The deposit itself overlooks the Golden Gate at a dis- tance of one-half mile from the ocean,and has an elevation of five hundred feet .The ore is well exposed where an exca- vation was made in the construction of the military road which leads from Fort Baker to Fort Barry. Geological Relations The geology of the Marin peninsula is typical of those localities where Franciscan formations are found, the rocks consisting of sandstones and cherts with intrusive basalt. The sandstones are typical Franciscan and are distinguish- ed by the following characteristics: lack of bedding planes , coarseness of grains,lack of fossils ,and a scarcity of con- glomeratic material.The color varies from yellow to deep blue the unoxidized showing the blue color. The massiveness and lack of bedding planes show rapid accumulation as is common in turbulent streams.The grains are fairly coarse and angular showing that their transportation was only a short distance from the source,or that no attrition was suffered by wave or wind action. Chert Beds on San lrancisco Peninsula Showing folding of the Strata RETAKE OF PRECEDING FRAME Chert Beds on Marin Peninsula ~howing Comparative Thickness ofChert and Shale Strata Chert on San Francisco Peninsula,Showing Intricate Folding of the Strata RETAKE OF PRECEDING FRAME rt Zeds on Marin Peninsula ~howing _omparative Mmickness of. hert and "hale “trata | Ae } Ny LNe 7 hert on lan I'rancisco reninsula, howing Tntricate (0ldin; ol the trata Small patches of pebbly conglomerate,made up for the most part of chert pebbles,are found occasionally,but they are few and far between. No fossils have been found in the sand- stone. In a few localities thin partings of shale are found giving a bedded structure to the deposit. As all of the manganese deposits described in this treat- ise occur in the Franciscan cherts it may be well to describe them here in detail,as they present the same general character- istics in all localities. Hard,resistant,showing a variety of colors,having : excellent stratification ,their formation is of marked interest. The strata of the chert are from one to four inches thick,and are separated by partings of shale one-fourth of an inch to two inches thick,the beds of shale and chert al- ternating with almost mathematical precision. It is difficult to find any part of the chert beds that has not been folded or faulted. The beds as a whole have been twisted and folded to a remarkable degree,overthrust anticlines,dove-tailing,and a gener2l mixing being the resuly. The prevailing color of the chert is dark red but in many places one can find green,yellow,black,brown and white. Often several colors are found together giving a variegated appearance to the specimen or outcrop.On the igneous contacts a very dark red variety may be found but the prevailing color of the chert on these contacts is yellowish. On the igneous Contact Between Spheroidal Basalt and Chert ,Showing a Mass of Unmetamorphosed chert in a Mass of Metamorphosed Chert RETAKE OF PRECEDING FRAME contac a + Ww fia “etween [pheroidal a ss of Unmetamorphosed ‘etamorphosed Cher Vv ») cr (J) ~- poet [a =O te oa contacts all traces of the shale partings have disappeared and the chert has been metamorphosed into a hard massive bed.Though sometimes on the contacts we may find the hard massive chert and in it a mass of chert and shale that has not been metamorphosed and which still retains the bedded structure. These masses of hard massive metamorphosed chert are not confined to the igneous contacts alone,but may be found in other places in the chert beds. The metamorphic action does not seem to have been ef- fected by heat alone,as the masses are full of innumerable veinlets and small maeses of quartz and chalcedony,giving a hard,resistant rock made up of a large percentage of quartz. This action may be purely secondary to the metamorphism or may have resulted in metamorphosing the chert bed by leach- ing action alone. The chert is so sheared and broken by internal stresses that when a fairly large fragment is struck a blow it crumbles into small pieces . Deposition of quartz and chalcedony has taken place along the shearing planes and it is hard to find a hand specimen that does not show small seams of these min- erals. Remains of radiolaria« can be seen throughout the chert ;in some places they are thickly disseminated and in others they are not so abundant. 11 Spheroidal Basalt at Hunters Point,San Francisco "eninsula 12 RETAKE OF PRECEDING FRAME APY - ~ ~S a Spheroidal Basalt at Hunters Point,San Francisco Peninsula,Showing Comparative Size of the Pillows Spheroidal Basalt at Point Bonito Marin Peninsula RETAKE OF PRECEDING FRAME Probably the most interesting formation from a petrograph- ical standpoint is the basalt. When oxidized it presents the appearance of a very much broken up sandstone,being yellow in color,very soft and crumbly,and showing no grain what- ever.When unoxidized it is green in color and is very much fractured and broken ,due to internal stresses.The texture for the most part is aphanitic but occasionally a resemblance to diabasic may be seen. The pillow structure so characteristic of this basalt, especially on the San Francisco peninsula,makes it a strik- ing formation. The pillows vary in size from six inches to three or four feet in diameter and give the #ock a spheroid- al appearance. The pillows are potato shaped and seem to conform to one another though they usually are separated by basalt that has the appearance of being stretched and pulled around them. The pillow structure may be seen on the iarin peninsula at Point Bonito. The best exposure of this forma- tion is at Hunter's Point on the San Francisco peninsula, where the sea has cut a cliff several hundred feet high in the basalt. Pieces of chert and sandstone can be found in- cluded in the basalt mhowing it intrusive in these formations, and occasionally one can find basalt that has been injected along the contact planes of the chert and sandstone. By the grain and texture of the basalt we would expect Metamorphosed Chert at the Fort Baker Deposit i 2 = & Z a a Oo on oe a 3 © RS ~ < 2 or ranory 2 eo it to be a shallow intrusive,but it covers wide areas and is deepseated and it is strange that we find no texture so common to deep seated intrusives of this type.Slow cooling must have taken place,but we find a glassy to aphanitic texture seemingly disputing this fact. Several theories have been advanced to account for this peculiar action and the most probable one is that the chemical constituents were of such a nature as to retard the crystallization of the composite minerals. There is no evidence of surface flows and all evidence tends to show : it to.be a laccolith that never reached the surface. The roof of the laccolith was composed of the sand- stone and chert beds,and today chert and sandstone may be seen resting on the hill slopes of basalt or capping the crest of basalt ridges. This would seem to substantiate the theory of a laccolith. Structure Hanging Wall 6f the Fort Baker Deposit The chert exposed on the ridge on which the manganese deposit occurs has a general strike of N 40°E,and a dip of 40%°t0 thecsouthwest. The crest of the ridge is formed by a hard resistant outcrop of metamorphosed chert which varies from ten to fifty feet in thickness,and is in contact with the basalt on the east and the chert beds on the west. The bedding of the chert is parallel to the hard meta- morphosed stratum,and it in turn is parallel to the contact between it and the basalt. The metamorphosed chert seems to rest on the basalt and at the manganese deposit the basalt has been eroded away leaving the hard chert exposed as a small cliff. The ridge has a north and south trend seemingly parall- el to the strike of the chert. It is about one-half mile in length and terminates in a very steep slope or sea cliff,sever- al hundred feet high. Deposit The main deposit is about fifteen feet wide in the widest part and is traceable for a distance of ninety feet along the crest of the ridge where it seems to pinch out. The deposit is stratified and its dip and strike are the same as those of the chert.The deposit does not rest on the metamorphosed chert directly ,but is separated from it by a thin parting of shale about one inch thick.On the other side of the depos- it the ore grades into the chert. The stratification of the deposit shows all the characteristics of the chert beds,shale and chert being replaced perfectly by the manganese oxide. The ore body on first sight presents the appearance of a mass of black chert and shale . The ore is principally psilomelene with a large amount of wad,and a dark powdery oxide which may be pyrolusite. The best ore is free from silica for the most part,but small veins Fort Baker Manganese Deposit Showing Comparative Width of the Rich Ore of quartz may be seen shot through it in many places. Only about one foot of pure ore is found because it grades off into the chert,the ore becoming more siliceous as the grada- tion proceeds into the chert. A freshly-broken surface of the hard variety of the ore is steel gray in color and has a decidedly metallic lustre; it has a hardness of seven and a high specific gravity. This ore is full of cavities which are filled with a brownish-black ocherous variety of manganese: nxide.The surface of the ore is covered with a black powdery form of the oxide that stains the hands black. Some of the ore shows a faint radiating structure, small crystals appearing more as a pattern on the surface than as a crystalline aggregate. This is rare as the ore gen- erally shows no crystalline structure whatever,being hard and massive or in a powdery or ocherous form. As the ore grades into the chert the transition is fairly gradual though the line between rich and poor ore is pleinly discernible. The good ore is about one and one-half feet wide and is bounded on the one side by the metamorphosed chert and on the other:side by the lean ore. The lean ore is composed of chert containing a high percentage of manganese oxide;it is black to brown in color and presents an appearance similar to some iron oresshaving a shiny lustre on the broken 21 Fort Baker Manganese Deposit Resting on the Foot Wall I'ort Daker surfaces.This lean ore grades off into greenish-yellow chert which is streaked and stained with manganese oxide.The hard variety of ore is confined to the chert bedsentirely,the shale appearing as the soft vapiety. The ore is separated from the metamorphosed chert by a thin parting of shale which is dark brown in color and con- tains many small seams of manganese oxide.The me tgmorphosed chert also contains innumerable seams of manganese oxide to the depth of a few inches. A red coating of iron appears as an fragments of the ore that have been weathered on the ex- terior surfaces.This is especially true on the surfaces that form the contact between the shale and the chert. Only about two feet of the ore is of a grade suitable for commercial purposes as it contains more than forty per manganese oxide. cent of / The ore was assayed and gave results from a mere trace to forty cents per ton in gold and no silver. That there may be other deposits farther down the crest of the ridge toward the Golden Gate is highly probable.Stains coating the hard chert and the outcropping déhert beds are very numerous .One hundred yards south on the crest of the ridge a small mass of good ore was found.It was not in place but was a large slab exposed along the side of the trail.In a large cavity in the metamorphosed chert a coating of man. ganese oxide was seen lining the cavity to depth of one-fourth 23 of an inch.Also where an excavation has been made for a . battery on this ridge the northern side of the excavation is stained black where percolating surface wabers have deposited manganese oxide. All of these signs tend to show the existence of one or more ore bodies south of the one exposed.in the road. RED ROCK ISLAND Red Rock Island lies in San Francisco Bay about one-half mile from Point Richmond. The island is about two hundred and fifty yards in length and from one hundred and fifty to two hundred yards wide,and it rises to a height of one hun- dred feet or more above the waters of the bay. It is fast being cut away by the waves and a landing can be accomplish- ed only on the eastern side where there is a small beach; the rest of the shore line is very precipitous. Rock Formations The formations composing the island are chert,shale, and basalt. The basalt occupies the northeastern portion of it and is the same kind that is found at Fort Bgker,having the same general characteristics throughout.That it is intrus- ive is shown by pieces of chert included in it. On the eastern side of the island above the basalt, is exposed a thick stratum of a dark red clay or shale. It 24 is fairly soft and weathers out in small nodular forms,a peculiarity of the pipe clays of the Sierra Nevada mount- ains. The chert which occupies the greater part of the island is well exposed in the sea cliffs ,and its dark red color gives the island its name. Some light colored chert is seen in connection with the ore deposit. The general strike of the cherts is N 60°E and the dip is about 80° to the south. in the chert here abundant remains of radiolaria can be. seen. Deposit The outcrop or exposure of the ore is about ten feet wide and extends across a small point of the island on the southwest for a distance of a hundred feet or more. It is well exposed on the west side of the point wherecthe steep slope has been blasted into a perpendicular wall. The deposit is tabular in shape and has the appearance of a vien;it follows the general strike of the beds. A great many faults have occurred in the region of the ore deposit but no large faults are apparent. In the open cut "slickensides can be seen on the walls ,and in some places small faults in the wall rock occur. The deposit is laminated rather than stratified,as thin laminae of chert occup interbedded with thin layers of chert and manganese ;these layers of chert and manganese vary in thickness from a fraction of an inch to an inch. No shale is visible in the deposit and it seems to have been replaced by the manganese oxide,but this can hardly be pos- sible for in one piece of ore-an inch in thickness twelve layers of chert and manganese were counted. The ore occurs for the most part in metamorphosed chert ,and on the walls it é@ither grades into stratified chert and shale or ends abruptly against the light colored metamorphosed chert. The ore is highly siliceous and of a low grade.Where it is not mixed with the chert it contains seams of quariz and chalcedony .0n the western end of the deposit huge . blocks of ore that have been blasted down from the cliff are piled up.Here all forme of it can be observed. The most common form is the laminated structure,long thin lenses or layers of chert interlocking with lenses of manganese oxide. The latter is not pure but is highly siliceous and,in most cases is brownish black:incolor in- stead of steel gray or black. Another form of the ore is a rather soft porous vari- ety containing innumerable small fragments of chert through- out. These fragments of chert are usually wholly enclosed in the manganese oxide and are pro¥ably residual pieces from chert beds that have not been wholly replaced. Another form of the ore is the hard pure psilomelane and in this ore the shale has been replaced by the mangan- ese oxide though in most of it the shale seems to be lack- ing. The metamorphosed chert is stained black and contains small seams and masses of manganese oxide where it is in contact with the ore. The ore assays about eighty cents Manganese Ridge,Napa Bounty,California in gold and sixty cents in silver.An analysis of it given by Penrose is as follows: | MnO 44,21 ™ 24.93 « 0 7.31 Fe 3.72 Fes0z 5 +32 p .27 . AlgCs 1.44 Si 0 35.32 2 Py Of .61 CoO Traces 84.51 The deposit was prospected in 1864 but the ore was too low in grade to justify any extensive exploration work.An open cut about ten feet deep opens up the deposit on the east end and a sheer wall fifty feet high exposes Looking West from Manganese Ridge it on the west.An incline of about 45° has also been run a distance of sixty ¢r more feet at the base of the slope. No good ore shows on the breast or the walls of this in- cline. 27 RETAKE OF PRECEDING FRAME Jlanganese Ridge,lNapa Bounty,California Looking “est from Manganese Ridge MANGANESE RIDGE Manganese Ri ‘ge ,which takes its name from a deposit of manganese oxide occurring upon it,is in Napa county, about seven miles east of the town of St.Helena. It is a hogback about one mile in length and is spur of a large ridge that separates Moore Greek canon on th east from Conn valley on the west. It has an east and west trend and juts out into Moore Creek canon. The western portion of the ridge where it joins the main ridge is covered with pine,oak,and manzanita; the eastern portion is covered . with a thick growth of chaparral,and on the extreme east- ern end for a distance of one-fourth mile,there is a heavy growth of pine,fir, and oak. The deposit is located near the middle of the ridge and on the southern side just below the cfest of the ridge. Rock Formations The rocks forming Manganese Ridge are composed of volcanic tuff ,porphyry,basalt,serpentine,sandstone,glauco- phane schist, and chert. Beginning on the eastern end of the ridge where it ends in iioore creek the formations will be described in order of their occurrence as one passes west along the crest of the ridge. The cherts which are first found,have a strike of a about © 40° E and they dip 60°t0 the southwest. Nearly half aS ad SN. of ilanganese Ridge is composed of the chert beds, the line between them and the other formations being marked by a change in the vegetation and in the character of the soil. The eastern half of the ridge which is composed of chert is covered with chaparral and as one passes west into the other formations a heavy growth of oak,pinesyand manzanita is found. The cherts are very much weathered and broken up and it is veyy difficult to find an exposure in place. All traces of the shale partings are gone and the cherts on the whole are light colored though several pieces of the dark red variety were found. All the chert shows innumer- able seams of quartz in it,and a specimen on first sight peesents the appearance of a cemented brecciajit is all stained black in the vicinity of the deposit,by the man- ganese oxide. It is difficult to determine just what the chert was in contact with on its western side for within a dist- ance of one hundred feet one finds sandstene,schist,and intruded basalt all mixed together. The sandstone seems to have been in contact with the chert first and then ba- salt was intruded along the contact. The sandstone is typically Franciscan,having all the characteristics of that of the Fort Baker deposit. The san@istone near the chert deems to be surrounded by the. basalt. The basalt also has all the characteristics that dis- tinguish that of the Marin peninsula,except that it shows no pillow structure.In some places if can be distinguished from the sandstone with difficulty. It is intrusive and contains masses of chert and sandstone as though it had come up along the contact between these two formations. It occurs farther west along the #idge in several places and outcrops on the southern slope ,tending to show that the basal part of the ridge is made up of it; but this is undeterminable owing to the depth of the soil. The schists are composed largely of glaucophane and quartz; they are crystalline and have the appearance of a fine-grained gneiss. The schists and sandstones alter- nate along the crest of the ridge and several outcrops of basalt occur with them. The serpentine is exposed on the wastern portion of the ridge and occupies rather a large area compared to the other formations. Near the contact of the serpentine,which is not very well defined,can be found masses of chert and sandgtone included in it ,showing it to be intrusive. The serpentine is not very much decomposed,but in it may be found masses of magnesite and chalcedony. A large mass off chalcedony or opal embedded in ike ser- pentine was brown to green in color and had the appearance of volcanic glass. On the surface of the serpentine were found chert pebbles; they were not embedded in it but ap- peared to be the remnant of an old stream bed. The ser- pentine is the last formation on the western portion of the ridge as Manganese Ridge joins the main ridge here. It is lower: than the main ridge and ends against a steep bluff which forms a capping escarpment on the main ridge. Sand Stone 7 Hoore 2a £ : . and sehishh Serpentine West and Bast Section of Manganese Ridge The bluff,which is about one hundred feet high is com- posed of volcanic tuff,and at the foot of this bluff a dark porphyritic rock was found. The relation of the ser=s pentine and the porphyry was not determined. The latter is a dark colored rock with phenocrysts of feldspar and quartz in a glassy ground mass. The rock when weathered turns gray and has the appearance of a tuff. Inclusions of some foreign rock or mineral can be seen, but the frag- ments are not large enough for determination with a pecket lens;it is probably a rhyolite porphyry. The tuff overlies all and forms a cap for the main ridge at this place. The tuff is coarse grained and contains: many large fragments of pumice. Many large water-worn pebbles occur on the surface of the serpentine but are not imbedded in it. Manganese Ridge 1s the largest of three parallel ridges all having the same elevation. The presence of chert pebbles on the western end of the #idge would seem to indicate that Manganese Ridge is a remnant off Tisecien stream terrace. The only metamorphic rock found in this vicinity is the glaucophane schist. That hhese schists have been deriv- ed from the sandstone is highly probable as the schists wl geem to grade off into the sandstone. The Deposit The main outcrop of manganese oxide is about one hun- dred feet long and twenty feet wide,though for a distance of two hundred yards east and west and fifty yards north and south the chert is stained black with it. The pure ore occurs in this one ledge,but east along the south slope of the ridge a few hundred feet,two other small deposits of good ore are found. These small deposite consist of round boulder-like masses of manganese oxide that have been exposed by small prospect holes. No manganese oxide is Outcrop of the lianganese Ridge Deposit posed by prosp g found on the north slope of the ridge. The outcrop of the main deposit is conformable to the general strike of the chert beds and also parallel to the line of contact between the chert and the basalt. The out- crop is made up of large ,rounded masses ,and shows no bed- dimg planes whatever. The deposit is about one hungred yards east of the contact between the chert and the basalt. The ore varies from pure steel gray psilomelane to the ocherous wad. None of it is free from silica,as it ap- pears as. small seams throughout the hard variety,and in bhe soft variety it is mixed with the oxide of manganese and forms an ore which is over fifty percent silica in . many places. Also some of the hard variety of ore which appears pure at fifst sight,upon close examination will be seen to be made up of a large percentage of crystalline quartz,the manganese oxide acting more as a coloring min- eral. The small seams of quartz and chalcedony in the ore are replaced part of their length by manganese oxide in many cases,or have been entirely filled with it and ap- pear as black lines in the ore. The greatest bulk of the ore is composed of a karge percentage of silica in some form as chert,quartz or chal- cedony. In one specimen flat tabular crystals of a white mineral were seen. The ore in the main outcrop does not appear to grade into chert as it does at the Fort Baker Boulder of Manganese Oxide at Manganese Ridge Outcrop Showing Boulder-like Masses RETAKE OF PRECEDING FRAME Boulder of lianganese Oxide at Janganese Ridge Cutcrop Showing Boulder-like lasses Ae deposit,though the enclosing rocks are full of seams of LIVERMORE-TESLA DISTRICT manganese oxide. Southeast of Livermore in a mountainous region is the Below the deposit the surface rocks-are all coated with Livermore-Tesla district. The area of this district in ~~ manganese oxide and many fragments of the chert were found which manganese oxide occurs is about thirty-five miles which were nearly entirely reblaced by it. long and fifteen miles wide. The district is in the Diablo The large round masses that were exposed by prospect range and consists of several parallel northwest-scutheast holes seem to have been weathered from the chertjthey are ridges including Rocky Ridge,Cedar Mountain Ridge and Crane not in place and their relation to the once enclosing chert Ridge. They are separated by long narrow canons as Arroyo could not be determined. ) Mocho,CorralHollow and others. The slopes are steep and Assays on the ore gave about twenty cents in gold and are usually covered with thick vegetation in the western no recognizabte trace of silver. part of the district,while in the eastern part the hills are more barren. The prevailing vegetation is chaparral, manzanita and live oak. Only two localities in this district were visited by the writer,one on Cedar Mountain Ridge and | one in Corral Hollow about six miles below Tesla. The deposits on Cedar Mountain Ridge are about six- teen miles from Livermore and one mile south of iliendenhall Springs on the ranches belonging to Mr.Friggel and Mr. Dew- Hirst. Owing to the inclemency of the weather at the time of the writer's visit it was impoesible to make a careful geological study of the deposits. The rock formations consist of sandstone,ghert and Ore on the Dump at Manganese Ridge a conglomeratic schist. The cherts are very much weathered and broken up. Their color varies from dark red to a clear white,the light colored predominating and the red being found only occasionally . Cne clear white specimen was 38 found which had the appearance of beautiful piece of opal. The dip of the cherts is abght 20°to the southwest and the general strike is N 60%E) Nearly all the shale is gone from the chebt beds though in some places the shale is still visible. The sandstones are the same as have been described at other deposits showing all the characteristics of the Franciscan formation. A shale-conglomerate formation was observed on the west slope of % sual} ridge west of Mr.Dewhirst's house. It consists of a shaly rock containing flattened water-worn pebbles of a rock of an igneous nature. Theis rock is sheet- ed as by pressure,and pebbles varying from a fraction of an inch to several inches in diameter are flattened out parallel to the sheeting planes. The pebbles are embedded in the shale and they sometimes break with it as though the shale and pebble were one solid rock. The relation of this formation tothe cherts was not determined though it appears to underlie the chert and sandstone. No basalt was seen in the vicinity though some serpen- tine is said to occur about one-half mile south. The Deposits The deposits occur along a zone parallel to the strike of the chert beds and about a mile long. The prevailing form seems to be small lentivular pockets varying from a few feet to fifty feet or more in length,and from one foot to fifteen feet in width. The deposits are wholly within the chert and near no contact.In some of them a gradation from the oxide of manganese into chert can be seen ,but in most of the deposits it cannot. On Mr.Friggel's ranch there are some small,highly siliceous ,bedded deposits that grade into the chert. Many quartz veins occur with the ore and in some places they form over fifty percent of the deposit content.The ore is the soft friable oxide. The largest deposit is found on Mr.Dewhirst's ranch and is about fifteen feet wide in the widest part and fif- ty feet long. The ore as a whole is of a fairly good qual- ity but some of it contains a high percentage of quartz in the form of small seams and patches.It is soft and friable and contains much of the brown oxide of manganese. Upon close examination a truce Seating can be seen in a few parts of the deposit.The ore is honeycombed and ap- pears to have been leached by surface waters. The ore body does not seem to grade into the chert as Xposed in the outcrop,but the chert here is not in place being very much weathered and broken up. The frag- ments of chert near the deposit are all stained black,and contain small seams of manganese oxide and quartz. About one-half mile from the Dewhirst house ,on the west,a stratified deposit of a good grade of ore occurs. It is about ten feet wide and twenty-five to thirty feet long and has been opened up to a depth of four or five feet by a small prospect cut. In this deposit gragation from chert to manganese oxide can be seen.The gradation is abrupt,occurring in a space of several inches to a foot in width. Many specimens of ore from these deposits show pieces of a white quartzose rock embedded in the ore. These frag- ments have all the characteristics of a mmnch leached and metamorphosed chert,and probably are residual pieces of chert that have not yet been replaced by the manganese oxide. These fragments are not found in the hard variety of the oxide but in the soft friable variety. The highly siliceous ore shows a crystalline stmucture in the mangan- ese oxide ,especially on the fracture planes where the surface is bright,shining and crystalline .The crystalli- zation may be due to the high content of silica in the manganese oxide. In the porous ore one finds occasionally a-:red ocherous powder-lining the cavities which probably is an oxide of iron. The ore as a whole is a low grade one,and will probably never be worked profitably.An assay on some of that from the langest deposit on Mr.Dewhirst's farm, gave no trace of gold or silver. TESLA DISTRICT The deposit visited in the Tesla district is known as the 01d Ladd Mine. It is on the south side of Corral Hollow in San Joaquin county,about seven miles southeast of Tesla. The formations consist of crystalline schists, sandstone and cherts. There are several kinds of crystalline schists in the region ,and though the outcrops are abundant they do not occupy a very large area. The principal schists are chlor- ite and glaucophane. Many outcrops of the chlorite schists resemble at first sight an outcrop of serpentine.Near one of them a good deal of actinolite in crystalline ag- gragates was found. The glaucophane schists contain a high percentage of glaucophane ,and several large specimens were picked up that consisted of nearly pure glaucophane.The relation of the schists to the chert was not determined io a wil tainty,but they appear to underlie them. The chert beds have a general strike of N40 dip of 55°to the southwest. They have all the character- istics of the cherts heretofore described.Their color varies from dark red to green. 01d Workingé at the 0ld Ladd Mine,Tesla District 43 One interesting feature noticeable here is the thivk- ness of some of the shale partings and chert strata. In many places shale partings six to eight inches thick were seen and chert layers up to six inches were found. The chert is fairly well weathered and good outcrops occul on the crest of the ridges. Most of the sandstgone in the region of Tesla and Carnegie is of the Eocene age and is coal bearing;but in ‘the vicinity of the 01d Ladd Mine the Franciscan sandstone occurs. The latter i8- coarse-grained,showing feldspars and quartz ,and having the same characterizing features as have been descbibed elsewhere. No basalt or serpentine were found in the locality. | er hy oh § a The Deposit Many dutcrops occur along a zone about a mile in length afd parallel to the general strike of the chert veds (They vary from a few feet to one hundred feet in width and from fifty to several hundred feet in length. On the northwestern end of the zone a deposit has been worked by an incline sixty feet deep,and several stopes. An open cut twenty feet wide and fifty feet long shows the character of the hanging and foot walls. Judg- ing from the shape of the stopes and the open cut the de- posit appears to have had lenticular or elliptical form and to have been about fifteen feet wide and seventy-five 44 Open Cut at the 01d Ladd Mine,Tesla District feet long.An examination of the ore on th dump showed no traces 8f bedding planes . The deposit has a pitch in the general direction of the dip of the chert Beds,and its longer axis is parallel to the strike of the beds. The foot wall is composed of red chert and shale , the shale beds being exceptionally thick.Next to the ore is a bed of soft decomposed shale several inches thick, which has been partly replaced by manganese oxide; ;and the chert and shale in the foot wall are stained black and are full of small semms ofit. The chert in the footwall is very much leached and has a pinkish tinge in some places,especially near the ore body. The hanging wall is composed of hard metamorphosed chert,greenish in color and full of stringers and seams of manganese oxide and quartz. Judging from the appear- ance of it the gradation from ore to chert was either abrupt on the hanging wall side or the wall was clean cat from the ore. The ore shipped from this mine is of a high quality containing very little silicaj;but the ore now on the dumps is of a very poor quality owing to its high slica content. What at first sight appears to be a lump of good ore,when broken open is found to be only a fragment of chert coat- ed with the manganese oxide. All the good ore seen from Outcrop of Manganese Ore in the Tesla District 0ld Ladd Mine in the Distance this mine was on the platform beside the railroad track awalting shipment ,the dump of ore at the mine being waste. Very little wad or ocherous ore was seen excepting along the foot wall where shale and decomposed chert have been replaced. A small piece of the outcrop has been left on the surface and this also is of the soft friable variety. of the ore. About on mile southeast of this deposit and along the strike of the beds a large outcrop occurssAlong this zone small outcrops which are only a few feet in extent occur very frequently .The large outcrop mentioned above is on the southeast end of the ore zone,and is the largest outcrop of manganese oxide the writer has seen. This out- crop is several hundred feet in length and nearly one hundred feet wide in the widest part.An open cut exposes the north side of the deposit and a tunnel taps it lower down. The deposit seems to be series of lenticular masses joining one another to form the large ore body. The chert on the south side is red in color and the strata: of chert and shale are exceptionally thick.The shale here has been colored red and is very hardioand- rei: sistant-and‘not soft and crumbly as is characteristic of it. All the chert is either stained black or is full of seams of manganese oxide,that is ,where it is near the ore. The chert on the horth side of the deposit is green,yellow and white ,and is also stained with the manganese oxide. The ore exposed in the outcrop is of a fair quality in some places but for the most part it is highly silice- ous ,the silica being in the form of seams and small masses of quartz. .thickly disseminated through out the ore. On the southern border of the ore a gradation into chert can be plainly seen ,but on the northern border the open cut has destroyed all evidemces of it. It is probable that if there was a gradation it was very abrupt.The main ore body is not stratified. On the southern wall of the open cut there is a porous crustification of soft manganese oxide. In the cavities of this ore is a sort of red clay or decomposi- tion product .The cut has caved in now and 1t is difficult to secure evidence of the nature of the ore on the north- ern border.The chert is highly metamorphosed in many . places on the northern border of the ore 8Body ,and the cut seems to have been excavated in the stratified chert, with metamorphosed chert and ore forming the southern or hanging wall of it. Not much soft ore was seen the outcrop appearing as big blocks and boulder-like massesfor the most part highly siliceous . The southeastern end of the ore zone is on the crest of the ridge where the outcrop is in the form of a manganiferous chert,not bedded and being very hard and resistant. ‘his end of the ore zone appears to be a mass separated from the main ore body described above, as there is a space of several hundred feet between these two outcrops where no outcrops occur s though the chert here shows stains of manganese oxide. SUMMARY The most noticeable facts observed in connection with these deposits is the intimate association of the mangan- ese ore with the chert beds. Not only the deposits here- tofore described but all the many manganese deposits in the Coast Range mountains occur in the chert beds. Their origin seems to be connected with that of the chert ,since no manganese deposits are found in the associated sand- stones and shales of the Franciscan series. another conspicuous feature is the proximity of the intrusive basalt to some of the deposits. At Fort Baker the contact between the chert and the basalt is only a few yards from the ore deposit .At Red Rock island it is about one hundred yards distant,and at “anganese Ridge the contact is about seventy-five yards away.At Cedar Mountain Ridge no igneous rocks were seen,but serpentine and basalt are said to occur one-half mile distant from the deposits. At Tesla where the largest deposit is found no basalt or other igneous rocks were found in the vis cinity . In all of the deposits except those at Cedar Mountain Ridge and Manganese Ridge the hard me tamorphosed chert forms one of the walls of the deposit. It varies in thick- ness from one foot to twenty feet or more. At Fort Baker it is more pronounced and forms a hard stratum between the basalt and the stratified chert,and is yellow to white in color. At Tesla it forms the hanging wall of the de- posit and is green in color. At Red Rock island it forms the hanging wall in one part of the deposit and is found also on the foot wall in another part.The color here is yellow to white. This hard,metamorphosed chert is made up of quartz for the. most part. An examination of the ore discloses a high content of silica. In some of the ore it is lacking but the great- er part of the ore in all the deposits is full of small seams and minute masses of quaeptz and chalcedony. This silica may be comtemporaneous in deposition with the maan- ganese oxide. When the ore reaches the metamorphosed chert wall it stops abruptly though the chert itself may contain seams of manganese oxide and be stained black.At Fort Baker there is a layer of shale between the metamorphosed chert and the ore. It contains some manganese as is shown by its brownish-black color. at Tesla also we find a bed of shale between the deposit and the foot wall of stratified chert. The shale here is not wholly replaced gid'd®es not seem to contain a very high percentage of manganese oxide. PROBABLE ORIGIN OF THEE DEPOSITS As manganese oxide is associated with the cherts ,one would suppose that they are the source of the ore,and that the source of the manganese would be intimately con- nected with the origin of the chertsjhence a considera- tion of the origin of the chert beds is pertinent at this time. | The presence of radiolaria in the chert beds at once suggests a deep marine origin,but the associated shale seems to disprove this theory. If a region on the floor of the ocean is thought of where silica is being continually deposited in a colloidal form or ooze,as 1s known to exist in abysmal depths ,and at certain times there is an influx of sediments ,as would happen in the spring of the year when the streams are heauily charged with the products of erosion ,the deposits of the silica would not be affected but would be disseminated through- out the sediment and a terrigenous deposit rich in sil- ica would be the result. This theory would explain the shale partings but the silica would have to be deposited at a more rapid rate than is common to the deposition of the oozes in the ocean today. Professor Lawson suggests that the sil- ica might come from siliceous springs on the ocean floor and the remains of radiolaria falling to the bottom of the ocean would become imbedded in the silica. Mr.E.F.Davis in a microscopic examination of the shale found evidences of radiolaria remains in it, and an analy=- sis showed it to be rich in silica. The~ fact thatsa large percentage of the silica in the chert is not composed of radiolarian remains,but ap- pears to be a chemical precipisate tends to disprove the theory of the silica's having its source in the remains of certain organisms that secrete siliceous skeletons from the sea maters,and would tend to substantiate the theory of siliceous springs. Another theory might be suggested for the source of the shale in that it might be a volcanic product and not a true terreginous product . Mr. Davis in his recent in- vestigation of the cherts,found the shale to contain p pieces of volcanic glass,and such material as might be present in the fine products of a volcanic outburst. Dredgings én the ocean floor,such as were made during the Challenger expedition reveal the fact that clays and fine sediments that are composed largely of volsganic material and its products of decomposition,such as kaolin, exist on the ocean floor. These deposits usually contain an abandance of animal remains,such as shark teeth and fish scales. But whatever the source of the silica may be,the chert is ge@tainly of marine origin. In explanation of the origin of the manganese deposits two theories suggest themselves :that the manganese was in small pockets originally and has spread by replacemant of the surrounding cherts,or that it was originally dis- seminated through the cherts and later was concentrated into pockets by a replacement of the chert. If we accept the hypothesis that the chert beds are of marine origin it is an easy matter to account for the manganese oxide. It is well known that manganese hydrates with ferric h hydrates are the most widely distributed Bodies in marine deposits,being especially abindant in abysmal regions . The manganese oxide occurs as a coating,a coloring,or as nodules. During the expedition of the Challenger the trawl brought up immense quantities of manganese nodules in nearly all depths below two thousand fathoms.Many s specimens of chocolate colored clays ,colored by man- ganese ,were brought up in the Pacific and Indian oceans, and objects such as rocks,coral branches,shark teeth,ete. were all coated with a dendritic black manganese oxide, The source of the manganese according to Sir John Murray is in the basic volcanic rocks and minerals with which the nodules are associated in deep sea deposits. The manganese of these rocks and minerals is transform- ed into a carbonate and subsequently into axides which 55 on depositing in the ooze take a concretionary form around various nuclei. Buchanan,in 188l1,suggested that the manganese was derived by the reducing influence of organic matter on the sulphates in sea water,suplhides being produced and subsequently oxidized. .mbel had in 1878 already advanced a theoty that manganese oxide could be precipitated from waters of sub- marine springs on the ocean bottom. Diewlefait and Baussingoult in 1883 suggested that the manganese oxide could be derived from compounds of manganese dissolved in the sea water,in the form of a bi-carbonate,and then transformed at the surface of the sea into oxides which are precipitated in a permanent form on the sea bottom. The first theory,that of Sir John Murray,is accepted as most probable,as on the surfaceof the earth similar reactions occur as is shown by the black dendritic coat- ings on rocks. So it can be seen that in deep sea depos- its manganese may occur sparsely through the deposit or may make up a large percentage of it. Analyses of the cherts by Davis showéd that about one percent of the manganese oxide ,with iron oxide and silica as the main constituents of the chert. An examin- ation of the chert microscopically ,revealed in some of 56 the slides,small veins of manganese oxide. The minute veins werepartly filled with quartz,and the manganese oxide formed the middle portion of the vein or else filled the vein éntirely,being replaced by quartz farther along the vein. It is very common also to find innumerable stains and markingd of manganese oxide on the chert in places far remote from any deposit of the ore. From the analyses,microscopic examinations and the presence of coatings and stains of manganese oxide on the cherts,it is safe to say that the manganese oxide is sparcely disseminated throughout the chert beds. If the manganese deposite were laid down comtempor- aneously with the chert one would expect to find remains of radiolaria in the manganese oxide.A piece of pure ore from the Fort Baker deposit,wagihhighly polished and the surface examined with a high power microscope ;the polish- surface being highly illuminated with reflected light from a small arc . No traces of radiolaria were seen . The surface was then etched with acids with no results. This is not a conclusive proof that the manganese was not laid down at the time of the deposition of the chert beds,as all of the deposits have been leached mare or forms less and all trace of original silica/could be destroymdyed. Whatever the original form of the manganesd was,the deposits today are clearly secondary concentrations.This is shown by the prefect replacement of the chert beds, and the contemporaneous deposition of the silica and man- ganese oxide. If the manganese was laid down in small pockets originally it has spread by the replacement of the chert and all traces of its original) character have disap- peared,That the deposite have been leached is shown by the powdery, honeycombed,appearance of the ore. At:rlian- ganese Ridge the chertis are stained black for nearly fifty yards,the percolating surface waters having leach- ed the exterior portion of the outcrop and deposited tke sahfianese oxide farther down the slope. This is also noticeable at the Fort Baker deposit as has been describ- ed. The above principle might be applied to account for the secondary concentration of the ore from an original ore bodysfor as the cherts are worn away the mamganese oxide could be redeposited by the surface waters,thus affecting the concentration in the deposit itself. In explaining the action of solutions in concentrat- ing the manganese oxide,if it was spapcely disseminated in the cherts,the thermo-chemical arguments that L.Dieu- lafait put forward to explain the separation of irom from manganese in solutions,might well be used. These drguments rest on the principle that when several reactions can take place that one attended by the greatest evolution of heat will occur. Dieulafait found the following: 2 Fe 04 O = Fep03+26.6 Cal. 2 Mn O + 2°0 = 2Mn Oy + 21.4 Cal. Mn O 4 COp = Mn COs + 6.8 Cal. So when oxygen acts on a mixture of tron and manganese oxideg,or substances equivalent to them,ferric oxide will be formed first. When carbon di-oxide unites with these oxides then manganese carbonate will be formed first,and will be more stable. If oxygen and carbon dioxide act together in considerable excess ,Fe,0zand Mn COz can be formed at the same time. The=manganese carbonate then can be separated from the iron oxide by leaching and will be deposited as a carbonate or be oxidized to Mn 0, and CO, later. So if waters containing COg and oxygen were to act on a chert the manganese oxide would be leached out and the tron left behind in another state of oxida- tion,and the Mn COz being oxidized would be deposited as manganese dioxide. If the chert was leached the solutions probably would contain some silica,and this silica might be the source of the chalcedony and quartz seams in the manganese Ore. The metamorphosed chert forming a wall of the depos- it shows signs of having been leached as the chert is made up largely of quartz and chalcedony and the yellow and green color is due to the iron constituents. The metamorphism of the chert is due probably in some Gases to _eaching action alone,butat Fort Baker and other pl places where an intrusive is near, Hest combined with solutions probably brought about the results. At first sight it would seem that the hard,metamor- phosed chert controlled the flow of the solttiong,as it is impervious; but if we take the hypothesis thatiit is formed by leaching with the solutions that deposited the manganese ore this cannot be the case. At Fort Baker metamorphosed chert may be due to the action of an intrusive magma,as has been stated,and the ore deposit may have originatedaat the asme time or at a time when the effects of the intrusive were still ac- tive. The curious feature at Fort Baker is the thin strat- um of shale between the ore and the metamorphosed chert. This stratum may have contained a very high percent of manganese oxide at one time but it has been leached out again by solutions acting along the surface of the me ta- morphosed chert. At Tesla thick beds of shalé® may have been a factor in controlling the solutions due to their imperviousness, but in nearly all deposite we find the shale replacedd with manganesecaxdde. The best example of replacement action seencwas at Red Rock Island,which has been describ- ed in a description of the ore of that locality. END OF TITLE