COPPER, SILVER, LEAD, VANADIUM, AND URANIUM ORES IN SANDSTONE AND SHALE.

WALDEMAR LIN DGREN'.

General Characteristics.--In widely separatedparts of the world and generallyfar away from igneousrocks ores of copper, lead, vanadiumand uranium appearin extensiveseries of sand- stone and shale under circumstances which indicate a common mode of origin. They are usuallyof low tenor and in the majorityof casescan not be utilized'. The primary ores are chalcocite, with small amounts of bornite, chalcopyrite and pyrite; galena;roscoelite, a vanadiummica; carnotite,a vana- dateof uranium. Smallamounts of nickel,cobalt, molybdenum, ' barium,and seleniumare often found. While all thesesome- timesoccur together, they are more commonlysegregated into separatedeposits in which one metal predominates.Gangue mineralsare conspicuouslyabsent or confinedto a little calcite, barite, and gypsum,the latter probablysecondary. Where exposedto the atmosphereoxidized minerals develop. The depositsare rather conspicuouslyconfined to certain formationsor memberswithin the Permian, Jurassic,or Trias- sic,but do not ordinarilyfollow a givenhorizon without frequent interruptions.Characteristic occurrences appear in fractured and brecciatedbeds or whereplant fossilsabound. More rarely the oresappear in fissuresin the sameformations where they wereevidently deposited by ascendingor descendingatmospheric waters. Occasionallythe ores have been leachedand carried down into the lower strata. They appearto have no connection with thermal springs. Oricjin.mlntheir presentform the oresare assuredlyepi- genetic,But the evidenceequally clearly points to theirhaving been'concentratedby atmosphericwaters from smallquantities 568 COPPER-ORES IN SANDSTONE AND SHALE. 569 of metals disseminatedin the rocks. It is believed,though the evidence of this is less direct, that the metals were carried down as sedimentsand solutions from older ore depositsin the adja- cent continental areas. The sedimentsare in many cases of shallowwater marine origin, but in part certainly land deposits, and often indicate arid conditions. The waters which concentrated the ores are believed to have beenmainly sodiumchloride and calcium sulphatesolutions con- taining sulphates and perhaps chlorides of copper and lead. Mineral associationand geologicalfeatures indicate low temper- ature depositionat shallowdepths, probably well below •ooø C., but below the zone'of direct oxidation. Very likely these ores havebeen forming continuously since the establishmentof active water circulation in the beds; in favorable placesbelow the sur- face concentrationmay now be in progress.

CO1'1'ER ANr• L•Ar• rmPOSITS • SAN•)STO•. European Occurrenceg.•--The European occurrencesare con- fined to the Permian and the Triassic, both largely agesof arid climate and saline deposits. The Russian Permian, extending far west from the Urals, consistsin its lower divisionof sandstones,marls, in part marine, and conglomerates. The sandstonesare rich in vegetable remains. Copperores are found over wide areas,but have not beenworked extensivelyof late years. They are saidto average 0.9 per cent. copper. The chalcociteores replace plant remains andtree trunks, or appearin the•cementof the sandstones.The minerals mentionedare (besidessecondary malachite and azu- rite): chalcocite,chalcopyrite, tetrahedrite (?), barite, vanadi- nite,volborthite (vanadate of copperand calcium). Much interesthas lately been taken in the copperdeposits of the Khirgiz Steppes2 betweenthe Urals and the Altai in the x For an excellent review of European localities, as well as complete index of literature, in part difficultlyaccessible, see Stelzner-Bergeat:Die Erzlager- stStten, I9o4, pp. 388-439. •Addiasseurch,A., "A Journey to Central Asia," Trans. Ir•st. Min. and Met., •7, •9o7-•9o8, pp. 498-522. 570 kV.'tLDEM.'tR LINDGREN.

Karkaralinsk and Akmolinsk districts. Very rich copper ores have here been found in sandstones said to be Paleozoic, and they consistof malachite,azurite, bornite; little exact informa- tion is available. At Nankat, west of Kokand in Turkestan, new discoverieshave been made of metallic copperin sandstones and gypsiferousmarls of Tertiary age; fossil wood and chalco- cite are also found. 1 In Bohemia• the lower Permian (Rothliegende.)along the south slope of the Riesengebirgecontains similar ores. The lower bedscarry chalcocitewith a little silver, also somepyrite in several horizons of the arcosic rocks, which contain abundant plant remains. The Permian of the Palatinate in Germanyyields nodulesof chalcociteand chalcopyrite. Most important from an economicstandpoint and curiously connectedwith the mineralizationof the Permian is the "Kuper- schiefer,"or copper-bearingshale of Central Germany; this is describedon a subsequentpage (578). Over a large part of WesternEurope the Trias is a copper- bearing formation, and togetherwith the. coppermore or less lead is found. In England,at Alderley Edge and Mottram St. Andrews,g southof Manchester,copper ores have been mined. They occur in the cement of Triassic sandstones and conglomerates and consist of copper carbonates,galena, pyromorphite,and vanadinite;also some 'barite, manganese and cobalt. The ores are said to carry at most 1.4 per cent. copper. The mineral mottramite, a vanadate of copper and lead, was discoveredat this place. In Germanythe Trias is dividedin three parts: The lower variegatedsandstone (" Buntsandstein");the middleshell lime- stone (Muschelkalk); and the upper marls and sandstones (Keuper); of thesethe lower and upperdivisions contain lead and copper ores. • Beck, R., "Lehre yon den Erzlagerst/itten,"I9o9, 2, 172. a Gfirich, F., Z. f. prakt. Geol., I893, pp. 37o-37I. * Phillips,and Louis, "Ore Deposits,"I896, pp. 266-269. COPPER-ORES IN SANDSTONE AND SHALE. 571

In Bavaria the Keuper contains galena and chalcopyritein certain gypsiferousbeds, and this is associatedwith a little zinc- blende and barite. In Wiirttemberg galena with a little oxidized copperore and barite is generally distributedin the Corbula bed of the lower, gypsiferous Keuper. In the Palatinate, the littoral character- istics are plainly indicated and there is an abundanceof fossil wood; in two horizons the sandstonescontain galena and cerus- site and were formerly worked. In the "Buntsandstein" in Prussia and Lorraine, near Saar- louis and other places,a horizon known as the Voltzia sandstone, is particularly rich in lead and copperores, which at times have been worked. The bed contains abundant plant remains. The mineralsare cerussite,galena, chalcocite (?) and carbonates. The best known depositsof the Trias are thoseof Commern and Mechernich,not far from Aix-la-Chapelle, in Prussia. Lead ores have been mined here for several hundred years, but it is reported that the mines may soon be closed. The ores-are of low grade and are mined in opencuts by removingabout I3O feet of overburden. In I9O3 the ores averaged I. 5 per cent. lead (Stelzner-Bergeat). The ores are galena, cerussite,oxidized copperores, with a little chalcopyriteand barite, the latter filling veins and veinlets in the sandstone. A little silver, nickel and cobalt are present. The thicknessof the ore-bearingsandstone is about 20 meters. Very remarkableis the general occurrence of the galenain so-called"Knoten" or knotty concretionsoften enclosingseveral sand g/'ains and sometimesbounded by the crystalfaces of thegalena. The epigeneticcharacter of theore is beyond doubt. American Occurrences2--On the North American continent aDumble, E. T., First Ann. Rept. Geol. Surv. Texas, I889, p. •86. Schmitz, E. J., "Copper Ores in the Permian of Texas," Trans. Am. Inst. Min. Eng., 26, 1896,pp. m5•-m52. ' Emmons,S. F., "Copper in the Red Beds,"in Bull. U.S. Geol. Survey No. 260, 19o5, pp. 221-232. Emroohs,W. H., "The Cashin Mine," Bull. U.S. Geol. Survey No. 285, I9O6,'pp. 125-128. Jennings,E. P., Trans.Am. Inst. Min. Eng.,34, P- 839. (Footnote continued on following page.) 572 kV.4LDEM.4R LINDGREN. copperores are of widespreadoccurrence in the Red Bedsof the Southwest. They occur in Texas, Oklahoma,New Mexico, Arizona, Colorado,Utah and Idaho, always conspicuousby the colorsof malachiteand azurite, but rarely proving of economic importance. More successthan elsewherehas attendedtheir exploitation in New Mexico. The ore occursin arkose sandstone,conglomerate, and clay- shale usually associatedwith plant remains and fossil wood. These strata were accumulatedin shallow seasor as land deposits by a processof rapiddegradation of adjacentland areasof the RockyMountain region. They havebeen referred to the Upper Carboniferous,Permian, Trias andJura; in part the identification of horizons difficult on account of lack of fossils, but it seems certainthat they are presentboth in the Upper Carboniferous and the Jurassic. In Texas they appearover large areasin Permiansandstones and shalesat several horizons, in strata rich in plant remains; •ovellite,.chalcocite, chalcopyrite, and pyrite are the minerals mentioned.They are saidto extendfrom 33ø to 34ø in latitude and from 980 to •ooø in longitude. In Oklahomaoccurrences are notedby Tarr in red shalesand sandstonesof probablePermian age; in Stillwaterand Payne counties. Fossil wood is often converted to chalcocite, some- times with a shell of chalcopyrite;here unusuallyhigh silver valuesof 3• ouncesper ton are reportedand traces of gold. In Colorado these ores have been observed at several places, notablyat Red Gluch,Fremont County, from whereLindgren describesnodules of chalcocitewith barite in black carbonaceous shale;sections show that the copper sulphide actually replaces the Turner, H. W., Trans..din.Inst. Min. Eng., 33, P. 678. Lindgren,W., Graton,L. C., and Gordon,C. H., "The Ore Depositsof New Mexico,"'Prof. Pai;er U.S. Geol. Survey'No. 68. Gale,H. S., "Geologyof CopperDeposits near Montpelier,Idaho, Bull. U. S. Geol. Survey No. 430, •9o9, pp. •2-•2•. Lindgren,W., "Notes on CopperDeposits," Bull. U.S. Geol.Survey No. 340, •9o7, pp. •7o-474. Tarr, W. A., "Copperin the Red Bedsof Oklahoma,"E½oN. Gva:m., 5, •9m, pp. 221-226. COPPER-ORES IN SANDSTONE AND SHALE. 573 shale,the lamination of which continuesthrough the ore. Here also chalcocitereplaces the coal of vegetable remains. The horizon is probably the uppermostCarboniferous. In north- eastern Arizona, according to Gregory,• small quantities of oxidized copperores are frequently seen in the La Plata sand- stone. North of the Coloradothey appearin the Carboniferous of the Kaibab Plateau, probably leached from once covering Red Beds. South of the Colorado S. F. Emmons has described a depositof oxidizedores and chalcocitein the Aubrey limestone near Grandview, which he considershaving been leached from onceoverlying Red Beds and carried down into the limestoneby descendingwaters. In southwesternColorado copper is widely distributedin the La Plata sandstone(Jurassic) often with vanadiumores. W.H. Emmons has described the Cashin Mine in this formation near Placerville. The ores are here argentiferouschalcocite, covel- lite, and bornite,with somecalcite. No igneousrocks are present and Emmons believes the ores to be leached from the Red Beds. There is an active circulation of water in the formation and springswith salt, sulphates,and hydrogen sulphideabound. A productionof about 300,000 ouncesof silver and 700,000 pounds of copperis recordedfrom this mine. The greatestdevelopment of the copper-bearingsandstones is in New Mexico; considerableproduction from picked ore has been achievedat the Nacimiento depositsin the northern part of the Statewhere the Red Beds,considerably disturbed, rest on pre- Cambrian granitic rocks which contain much older copper deposits. The bedshave been referred to the Triassic on the evi- denceof fossilplants. Accordingto F. C. Schrader(in pp. 68, U.S. G. S., cited above) most of the copperores occur in the basal beds and are confinedwithin a thicknessof 25 feet in a reddishwhite' sandstone' rich in fossilwood, which is largely chalcocitized.A tree trunk 60 f•et longwith a basaldiameter of 2• feet is mentioned,which is ahnost wholly convertedto copperglance. Besidesmalachite, azurite, and chrysocolla,there x Gregory, H. E., oral communication. 574 I/VALDEMAR LINDGREN. is somebarite, and, at one place, cerussite. The low grade or•s have not been utilized. According to the same geologist,in the Zuni Mountains in northeasternNew Mexico the copper-bearingbeds again lie at the baseof the Red Beds,resting on pre-Cambriangneisses which containcopper veins. The sandstones,shales, and marls for 3ø to 60 feet just abovethe baseof the bedscontain oxidized ores and galenareplacing wood. L. C. Graton describes in detail the ores from Tecolote dis- trict, San Miguel County, which are partly in the Red Beds of the Upper Carboniferous (Abo formation), partly in a higher horizon, perhapsthe Dakota sandstone. The calcareouscement of the arkoseis replacedby chalcocite,bornire, chalcopyriteand pyrite, the replacementextending into the feldspargrains. In the Oscura Range red sandstones,probably also of the Carboniferous Red Beds, contain chalcocite, bornire and chalco- pyrite, in part as replacementof fossil wood. Turner mentions the occurrenceof plant remains from this place, said to have been identified as the Triassic Podozamites crassifolia, the same cycadwhich is characteristicQf the depogitsat Abiquit•first studiedby Newberry. Graton believes,contrary to Turner, that the copperores have been introduced into the strata from a number of dislocations cutting the sandstone. Finally, I-I. S. Gale describescopper ores from southernIdaho which occur in the Ankareh Maroon shales and sandstones of the Trias or Carboniferous (equivalent to the Permo-Carbon- iferous of the Fortieth Parallel Survey). A thick limestone (including the Meekoceras beds) underlying these shales is' believedto be Triassicby somegeologists. There are then at least two main cupriferoushorizons in the Southwest:(x) The Upper CarboniferousRed Beds,equivalent to the Permo-Carboniferous,or the Abo formation; (2) the undoubtedlyJurassic, La Plata sandstone. The silver depositsin the' supposedlyTriassic sandstonesof COPPER-ORESIN SANDSTONE AND SHALE. 575

Silver ReefI in Southern Utah (Harrisburg district), which created quite a boom about •88o, are now only worked on a small scale. The ores were silver chloride above the water level and native silver and argentire in depth; copperwas also present, and seleniumis reported. Plant remains were abundant. On the wholea secondaryconcentration from a primary argentifer- ous chalcociteis the most probableexplanation. It has already been emphasizedthat the chalcociteuniversally carries silver, though in the ordinary occurrencesthe tenor is rarely above •o ounces per ton. South .4merica.--The well known and long worked copper deposits of Coro-Coro2 in Bolivia, a series of standstones, believedto be of Permian age, here containseveral beds impreg- nated with native copperwith somenative silver, domeykiteand chalcocite,also much gypsum. The copper-bearinghorizons are muchlighter in color than the prevailing deepred sandstones. Accordingto Steinmannthe strata are of Cretaceousage and the copperwas introducedby hot waters derived from an intru- sion of diorite. Neverthelessthe descriptionssuggest strongly that the depositsbelong in a different class. .4frica.--Sufficient information is not at hand to decide whether the recentlyopen, ed Kata.nga a ores of southeastern BelgianKongo, near Rhode}ia, belong in this division. Large massesof high grade oxidized copperores are containedin sand- XRoelker, "The Silver Sandstone District of Utah," Trans. Am. Inst. Min. Eng., 9, I88i, pp. 21-33. Rothwell, "The Silver Sandstone Formation of Silver Reef," Eng. and Min..[our., 29, 188o, pp. 25, 48, 79. Newberry, "Report on the Property of the Stormont Silver Mining Company," 30, i88o, p. 269; 2•, I88I, pp. 4-5. Kemp, "Ore Deposits of United States," •9oo, p. 334. • Older literature: See Stelzner-Bergeat (I.), p. 4•9- Steinmann, G., RosenbuschFestschrift, I9O6, pp. 335-368. • Farrell, J. R., "The Copperand Tin Depositsof Katanga,"Eng. and Min. Iour., 85, April xx, I9O8, p. 564. Buttgenbach,I-I., "Les gisements de cuivre de Katanga," A. S. Geol. de Belge, 3I, I9o4, p. 515. Ball, S. H., and Shaler,M. K., "Mining Conditionsin the BelgianCongo," Trans. Am. Inst. Min. Eng., x9xo. 576 WALDEMAR LINDGREN. stones,shale, and limestone,probably of Paleozoicage. The ores are of high grade (8 to I2 per cent. copper) and are stated to contain a little gold and silver; some manganese,cobalt, and nickelare present. Barite and quartz appearas gangueminerals. A deposit at Ruwe, in the same general region describedby Ball, contains in a sandstone,a most curious associationof ores yielding gold, platinum, silver, palladium,vanadium, nickel. lead and copper,the last two metalsas vanadates. In someways this depositsuggests the type now under description.

GENESIS. The epigeneticcharacter of the copperdeposits in sandstone is provenbeyond reasonable doubt. The replacementof coal,car- bonaceousshale, and calcareoussandstone cement by chalcocite is proven. The gangue.minerals are few andquartz is conspicu- ouslyabsent. Baritein smallamounts is rathercommon. Irreg- ularity in disseminationis typical, though the ores often follow certain horizonsrather persistently. The entire independenceof the occurrenceof igneous rocks is marked. The difference between these depositsand the ordinary type of fissure vein is striking, and they can not have been formed in the samemanner. It is necessaryto explain why chalcociteis characteristicof the first and chalcopyriteof the secondtype. The occurrencesare mainly on the flanks of older continental areas containing pre-Cambrian copper deposits;the sandstones were rapidlydeposited as arkosesindicating a long epochof rock decay,the products of whichwere rapidly swept away during a following arid epoch. Consideringthe evidenceas a whole the sedimentarydeposits must contain finely divided copperores in part from solutionsderived from the land area, in part as cupriferousdetritus. When atmosphericxvaters charged with salt and gypsumsearched these beds they must have taken this copper into solution and concentrated it in certain horizons when reducingsubstances like coaly vegetablematter were avail- able. In most casesthe solutionprobably containedthe copper as sulphate,though where much salt was presentit might well COPPER-ORES IN SANDSTONE AND SHALE. 577 have been transformed into chloride; or xvhereH2S was avail- able it might have beencarried in solutionas sulphide. It doesnot follow that all depositsof copperores in sandstone and shalebelong to this classhere described,for an impregnation by ascendingthermal solutionsof foreign origin is a possible contingencyin someinstances. In the precipitation the most important chemical reactions were those between the carbonaceousmatter of plant remains and the calcareous cement or the kaolin in the sandstone on one hand and the cupriferoussolutions on the other hand.

v^•q^r)•u•4 ORES • S^•½DSTO2qES. The precedingpages show that the copperdeposits often carry some vanadium as vanadinite or volborthite. Lately vanadium with some uranium has been shown to be common in certain sedimentaryhorizons in Colorado and Utah. The depositsin Western Colorado are now worked and experimental plants for their reductionare being erectedat Newmire, near Placer- ville.• Some of the sandstonenear Placerville contained3.5 ø per cent. V2Oa and 0.05 per cent.UOa. Shipmentsare said to have containedas muchas • •.5 per cent.UaO 8 and 6.4o per cent. V205, but on the whole the grade is probablylow. In all these statesthe vanadium ores appear to occur in the Jurassiclimestone of the La Plata formation. The best known localitiesare near Placerville in the La Sal, Paradox, and Sindbad valleys. The ores follow certain horizonsor appearin fissures and brecciatedplaces; they are often associatedwith plant

• Hess, F. L., "Min. Res. U.S.," I9o7, p. 721. Merrill, G. P., "Non-metallic Minerals," I9o4, PP. 299-320. Hillebrand, W. F., and Ransome, F. L., "Carnotite, etc., in Western Colo- rado," Am. ]our. Sci., 4th Ser., xo, x9oo,pp. x•o-I44. In Bull. U.S. Geol. Survey No. 262, •9o5, pp. 9-•3. State Bureau of Mines, Colorado, Rept.

Boutwell, J. M., in Bull. U.S. Geol. Survey No. 260, I9o5, p. 205. Gale, it.-S., "Carnotite in Western Colorado,"in Bull. U.S. Geol. Survey No. 340, I9 O8. Gale, H. S., "Carnotite in Rio Blanco County, Colorado," in Bull. U.S. Geol. Survey No. 3I$, I9O6, pp. IIO-IIT. 578 I;VALDEMAR LINDGREN. remains. The occurrencesare all within the Great Plateau prov- ince of horizontalor gently inclinedstrata. The most prominent mineral is the bright yellow powdery carnotite, to which Fuchs and Cumenge give the formula 2U20•, V205, K•O, 3H•O, but Hillebrand doubtswhether the formula is as simple as this. Oneof hisanalyses of carnotite from Roe Cr.eek gave' UO ...... 54.89 PI;O...... o.x3 V20 ...... •8.49 CuO ...... o.15 CaO ...... 3.34 MoOa ...... o. 18 BaO ...... 90' H•O ...... 4.54 K20 ...... 6.53 CO ...... 0.56 Insolhble...... 7.•o Copperas greenstains of malachite,brochantite and azuriteis commonly present in the depositsand frequently also lead. Hildebrandalso found some rriolybdenum, arsenic, a seleniteof copper, and some manganese. Roscoelite,a vanadium mica developsin the calciticor kaoliniccement of someof the sand- Stonesin southwesternColorado. This mineral ca/-riesonly a small amount of oxide of vanadium, but is present in the richestolive-colored beds to the extent of 2o per cent. Lately a black mineral of doubtful composition,probably a vanadium oxide, hasbeen found in this region and it is indeedpossible that carnotiteis a secondaryproduct of an unknownprimary vana- dium mineral. The roscoelitehas probablynot beenaltered since its first deposition. In the Utah bedsBoutwell found vanadates of coppersuch as volborthiteand calcio-volborthite. Not similar to thesedeposits, yet perhapsof a similar origin, are the recently discoveredimportant vanadium depositsat Minasragra,v near Quisque, Province of Pasco,Peru, described by D. F. Hewett. The vanadiumsulphide, patronite, occurs here on a large scale as greenishblack massesassociated with a hydrocarbonand a • Hewett, D. F., "Vanadium Depositsof Peru," Trans. •lm. Inst. Min. Eng., 40, I9O9, pp. 274-299. Hillebrand, .W.F., "The Vanadium Sulphide Patronite," Your..4m. Chem. Soc.,29, 1907. Hillebrand, W. F., •lm. ]our. Sci., 4th Ser., 24, 19o7,p. 141. COPPER-ORES IN SANDSTONE AND SHALE. 579 peculiarnickel-bearing pyrite. An analysisof the patronitegave 58.79 per cent.sulphur, I9.53 per cent.vanadium, o.•8 per cent. molybdenum,•.87 per cent. nickel, and 3.47 per cent. carbon. The mineral forms a vein with much bitumenand clay in gently dipping cretaceousstrata. Igneous rocks are presentin abun- danceand may be responsiblefor the peculiardevelopment of a new type of ore. Genesis.--Tracesof vanadium are found, accordingto Hille- brand,in mostigneous rocks. Smallerquantities occur as oxida- tion products in many ore deposits,mostly as vanadinite or descloizite. More abundantlyvanadium occursin sedimentary rockssuch as claysand shales;it is alsoconcentrated in coal; the ashesof many varieties are rich in vanadium.x This peculiar relationshiphas not been fully explained;at any rate the proc- essesof weatheringand vegetationappear to be favorableto the doncentration of vanadium; and, to some extent, uranium sharesin this behavior. The associationof vanadiumand copper in the ore-bearingsandstones has already been emphasized,as 'wellas their frequentoccurrence with coalor vegetableremains. Viewing the evidence as ,a whole the vanadium deposits describedabove are probablyproducts of concentration,by sur- face waters of small quantitiesof the metal distributedthrough littoral bedsor land depositsof sandstoneand clays.

T•i• COPI'•I•-B•AI•NG S•AX.•S OF •XNSFV. X.X).•' Thecelebrated cupriferous shale (Kupfer schiefer) of Mans- feld in central Germany,though not identicalwith the deposits describedin this chapter, presentsmost interesting analogiesto them. A flourishingmini.ng industry is still basedon the "Kupfer schiefer,"the annualore productionbeing approximately 700,000 metrictons of ore containingbetween 2 and 3 per cent.of copper. ' xSee Clarke, F. W., "The Dataof Geochemistry,"I9O7, p. 611. A coal from the copper depositsin sandstoneof Red Gulch, Colorado,contained, according to Hillebrand, o.I8.per cent. vanadium. a Bestdescription with literature in Stelzner-Bergeat:"Die Erzlagerst•/tten," I, pp. 391-417. 58o W.4LDEM.4R LINDGREN.

The firststratum deposited in the subsidingbasin of the Upper Permianin centralGermany was a marineconglomerate of slight thickness. "Above it extends like a black shroud the thin bed of cupriferousshale, one of the most remarkableproducts of the geologicalages. Characterizedby its fauna as a shallow-sea deposit,full of plant remainscarried in from adjacentcoasts, the formationbears the stamp of an organicmud deposit admixed with an organicprecipitation. TM Above the cupriferousshale, which is lessthan • meter thick, extends a marine limestone (Zechstein), 8 to •o meters thick, and abovethat lie the greatgypsum and saltmasses of the upper- most Permian. Folding and faulting have since affectedthe beds,and the mining now follows the inclinedstrata to a depth of 500 meters. The cupriferousbed averages5 ¸ centimetersin thickness,but only the lower part of 20-30 centimetersis mined. The ores are sulphides,in minute distribution through the shalegiving it a bronzyappearance. Chalcopyrite predominates, but there is also bornite, pyrite, chalcocite,rarely galena and tetrahedrite. Small quantitiesof nickel, cobalt, selenium,vana- dium, and molybdenum have been recognized; there is also o.oto-o.ot 5 per cent. of silver. Zinc is presentand in the upper part of the bed, not mined, there is more zinc than copper. An averageanalysis is as follows:•'

AVERAGE ANALYSIS OF CUPRIFEROUS SHALE. (Dr. Haase, Analyst.) SiO, ...... 33.•5 Ag ...... o.oi4 AI•O, ...... •7.3 Ni ...... o.oi8 CaO ...... •o.4 S ...... 2.3• MgO ...... I .o CO2 ...... 9.24 Fe ...... 2.6 H20 ...... L7 Zn ...... x.276 Bitumen ...... 9.06 Cu ...... 2.75

There is about 3 per cent. K•.O and • per cent. Na•.O; lead amountsin place to •.5 ¸ per cent., manganeseto about 0.25 per cent.

xBeyschlag, F., In "DeutschlandsKalibergbau," •9o7, p. 4. a Stelzner-Bergeat, I, p. 396. COPPER-ORES IN S,4NDSTONE AND SHALE. 58I

There is practicallyno gangue,except veinlets of gypsumand barite. The bed is cut by faults, which in placescontain barite, anhydrite, calcite, niccolite, pyrite and chalcopyrite,and near these (the so-called"Rficken") the metal content is subject to enrichment, impoverishmentor removal upwards in adjacent beds. Bergeat assertsthat these changestake place on second- ary fissuresand cracks. There has beenmuch controversyabout the Mansfeld deposits. The majority of geologistsregard them as sedimentaryand syn- genetic: v. Groddeck, Stelzner, Freiesleben,and yon Cotta held this view, and it is sharedby Bergeat. Posepnyand Beck believe them epigeneticand probablyintroduced into the shale from the "Riicken." The "Kupfer schiefer" is certainly not an ordinary marine depositprecipitated from the sea water.• It was laid down in a shallow sea full of decayingvegetable and animal remains into which cupriferouswaters from the surroundinglittoral was dis- charged,most likely sulphatesolutions derived from the eruptives of the early Permiah epochs. No one can read the description of the great uniformity of distributionwithout being impressed with the very strongarguments for a syngeneticorigin. At the sametime it is properto call attentionto the character- istic presenceof nickel, cobalt, vanadium and selenium which recalls the epigeneticdeposits in sandstoneso abundantaround the shores of the Permian sea, in Bohemia and Russia, for instance. The Mansfeld basinwas simply then the final collect- ing placeof the solutionsderived from adjacentdesert shores. aIt is well known that sea water does contain a little copper, as shown among others by Dieulafait (Am. Chim. phys., 5th Set. I8, t879, p. 359; also C. R., 90, x573; PP. 96, 70, xox, •297), but it seems utterly insufficient to account for the Mansfeld deposits.