Pe en tents GD. ot Se, or Gros ‘dares We we eas th kel or as Soa. care rhy Areca ee Nakmty seme eae nett Ryne my BRST eon atote we ona nett eeyreen ams hee itp le lncaihjesag mms hewn Fey mgt rn Po ee mesa ee 74 mprenmates ues nara ene mute ie Ye Ati wy si | oe 4 1 ( f Mk | qt v Fath a j MOI 40 GVAH DEPARTMENT OF THE INTERIOR MONOGRAPHS OF THE UNITED STATES GEOLOGICAL SURVEY NAO Mn Xe WASHINGTON GOVERNMENT PRINTING OFFICE 1886 j : «+, Los ‘ary 2 UNITED STATES GEOLOGICAL SURVEY CLARENCE KING, DIRECTOR GC HOLG G x AND eee LNDUSTRY OF LEADVILLE, COLORADO WATE. Arias BY SAMUEL FRANKLIN EMMONS WASHINGTON GOVERNMENT PRINTING OFFICE 1886 FEDERER Or TRANSMITTAL. Unirep STATES GEOLOGICAL SuRVEY, Division oF THE Rocky Movunrains, Washington, D. C., October 1, 1885. Sir: I have the honor to transmit herewith the manuscript.of a report on the Geology and Mining Industry of Leadville, Colorado. To yourself, and to the Hon. Clarence King, under whose direction this investigation was commenced, I am greatly indebted for the facilities and kind encouragement that have always been afforded to those engaged in its prosecution. Very respectfully, your obedient servant, S. F. EMMONS, Geologist-in- Charge. Hon. J. W. PoweEtt, Director United States Geological Survey, Washington, D. C. PREFACE. The present work was undertaken at the instance of the Hon. Clarence King, first Director of the United States Geological Survey, in 1879. It was his intention that it should form part of a series of monographs which would in time include all the important mining districts of the country, and thus furnish an accurate and permanent record of the manner of occurrence and geological relations of the metallic deposits of the United States, as well as of all substantial improvements in the methods of obtaining the metals from their ores. In preparing such a monograph the general plan adopted was: first, to obtain an accurate knowledge of the geological structure of the region and of the various rocks of which it is made up; next, to study thoroughly the ore deposits in their varied relations to the inclosing rocks; and, finally, to investigate any methods of extraction or of reduction of the ores that pre- sented new or unusual features, without wasting time upon what was already so well known as to require no further comment. Various circumstances rendered such modifications of this plan necessary in the present case that the various stages of the work could not always be carried on in their log- ical sequence. ‘The great altitude of the region and consequent inclemency of its climate practically prevented surface work being carried on to ad- vantage during eight months of the year. The organization of the Survey was as yet incomplete, and assistants familiar with this class of work could not immediately be obtained; moreover, a year elapsed after the inception of the work before laboratory facilities could be obtained which rendered VII Vill GEOLOGY AND MINING INDUSTRY OF LEADVILLE. it possible to carry on the chemical investigations that form one of its most important and essential features. ‘The first want was accurate and detailed topographical maps, which are more than usually indispensable in the vicinity of Leadville, where the entire rock surface is covered by débris, and the geological structure had to be reconstructed by gathering into a con- nected whole the data derived from thousands of isolated shafts and tunnels which had penetrated below the surface accumulations. This want was supplied by Chief Topographer A. D. Wilson, the une- qualed accuracy and rapidity of whose work can only be adequately appre- ciated by those who have had occasion, as we had, to put it to the test of actual instrumental verification. The field work of the map of Leadville and vicinity was completed by him and his two assistants during the months ‘of August and September, 1879, and that of the map of Mosquito Range during part of July, August, and September, 1880. In December, 1879, I commenced the study of the ore deposits of Lead- ville. In this I received most invaluable aid from Mr. Ernest Jacob, grad- uate of the Royal School of Mines of London, who, working at first as volunteer, rendered most continuous and unwearied service during the whole continuance of the investigation To his keen insight into the intricacies of geological structure, his untiring energy in exploring every accessible prospect-hole in the region, and his accurate appreciation of the bearing of the data thus gathered, is attributable in great measure the successful unraveling of the complicated problem presented in the region represented on the map of Leadville and vicinity. So complicated a region, I make bold to say, it rarely falls to the lot of a geologist to study in detail. In July, 1880, it was first practicable to undertake the study of the high mountain region represented on the map of the Mosquito Range. Here geological and topographical field work went hand in hand, and my party worked together with that of Mr. Wilson until heavy snows at the end of September put an end to outside work. In this field work I had the assistance of Mr. Whitman Cross, who had made a special study of microscopical petrography under Professor Zirkel, of Leipzig, and of Prof. Arthur Lakes, of the School of Mines at Golden, Colo., who devoted his summer vacation to this work. To Mr. Cross, who, like Mr. Jacob, first ‘PREFACE. Ix joined the Survey as volunteer assistant, was intrusted the final petro- graphical determination of all the crystalline rocks of the region, and the great value of his subsequent investigations in the field of petrography and mineralogy have fully justified the confidence thus placed in his ability. In the autumn of 1880 the corps was increased by the addition of Mr. W. F. Hillebrand, who had already distinguished himself by his original investigations in inorganic chemistry in the laboratory of Professor Bunsen at Heidelberg; under his direction a laboratory was prepared at Denver in connection with the headquarter offices of this division of the Survey. During the summer I was fortunate enough to secure the services of Mr. Antony Guyard, a former pupil of the Ecole des Mines, and for twelve years chemist at the well known metallurgical works of Johnson & Mattey, London. At my request Mr. Guyard undertook the labor of making a chemical investigation of the processes of lead smelting as conducted at the various Leadville smelters. His sudden death at Paris, which was closely followed by that of his brother Stanislas, the distinguished French Orientalist, prevented the personal revision of his report which I could have desired him to make; and in that which was made by Mr. Hillebrand and myself we have not always felt justified in making modifications which might have been judged advisable could we have discussed the points with the author himself. Beyond the correction of a few clerical errors it is pre- sented substantially in the form in which it was left by him. In November, 1880, Messrs. Hillebrand and Guyard commenced their respective chemical investigations, the one of the rocks and ores, the other of the furnace products of Leadville, in the laboratory at Denver. Mr. W. H. Leffingwell, with the assistance of Mr. Jacob, completed the Leadville map during the latter part of 1880 by the accurate location of various shafts and tunnels, to the number of nearly a thousand, found necessary for the determination of the geological outlines, an extremely laborious undertaking, carried on as it was at times with 15 to 20 feet of snow on the ground. About the same time the topography and underground workings of the maps of Iron, Carbonate, and Fryer Hills were prepared under my direc- x GEOLOGY AND MINING INDUSTRY OF LEADVILLE. tion by Messrs. H. Huber & Co., F. G. Bulkley & Co., and George H. Robinson & Co., respectively. From June, 1880, to June, 1881, my time was partially taken up in the supervision and direction of experts employed under the authority of the Superintendent of the Census in making an investigation into the “Sta- tistics and-Technology of the Precious Metals” in the Rocky Mountains. From the close of field work in the summer of 1880 to May, 1881, I was mainly oceupied with Mr. Jacob in completing the examination of the mines and deposits of Leadville. In this work we received, with a single exception, the most courteous treatment from mine owners and superin- tendents, who not only opened their mines freely to our inspection and per- mitted the use of the maps of their underground workings, but also aided us materially in many cases by the information they furnished from their own every-day experience. ‘To these gentlemen, individually and collect- ively, I return my most hearty thanks, as well for the services above mentioned as for the confidence thereby displayed in the disinterestedness of our motives and our wish to be of service to the mining public in gen- eral without favoring unduly any individual or corporation. During the summer of 1881 the individual members of the corps, aided by Messrs. Morris Bien and W. B. v. Richthofen, were occupied in collating the results obtained, and in the preparation of the various maps and illus- trations for the engraver, and by autumn the work was so far completed that I was enabled to embody the principal results arrived at in an abstract published in the Second Annual Report of the Director of the Survey. During the time that has elapsed since the publication of that abstract the development of the Leadville mines has proceeded with rapid strides, and already the ores are changing from carbonates and chlorides to sul- phides. In other respects also these developments have afforded most gratifying confirmation of the general accuracy of the geological outlines given on the accompanying maps and sections. Even had it been other- wise, it would have been impracticable to have changed what had long since been engraved. In the press of other work it was not possible to attempt another examination of the field, and therefore in the final revision of this PREFACE. XI long-delayed material the changes have been mainly confined to condens- g and leaving out what has in a measure lost its value by the lapse of time. Where new facts have been obtained, they have been inserted in in notes. The report as it now stands is therefore essentially that which was prepared four years ago, and as such it should be criticised by those who have oceasion to read it. S. F. EMMONS. WaAsHINGTON, October 1, 1885. CONTENTS: Page LUTE OG! DEERE oScoo choose ceo0de Boe bbs 55 chSs06 SApsen e bdesKe eHoU Be pDduposooraceesous III DSRS EIDL coc ea cesses apodod bos Sos Sen beoTes deleao SeSeseeSedsASoED degosoqseese coos senaSncoees Vv MARTI OL" COINS 6 eo pbb ae cosbSs On OE0 DES SEO SESE SOOCEs BEEDEO HEOESO U4 5650 BReseb Bacoadsc XIII ILTGHP GY THLTOETERAY WON ah Sean SoDSSS SOS Ga UO0d HOD ONE IBEC OBIS SO SDUn EOSHOCOL Cob aEe Conn eAtenaee XXV ILTSH GID NTTAS SITS) = Sooclnasigoe coonoo Rep ossonEcen SASS betas DOUCI9 CObO SO CODD IDEE GU BEBE DOse XXVIL BRIEF OUTLINE OF RESULTS...-...---- Wgancado sobecor CoogabonsacoceGecs Cano sescoo rH aeSabegess XXIX PART I. GEOLOGY. CuHaPteR I. LEADVILLE—ITS POSITION, DISCOVERY, AND DEVELOPMENT ...--..----------------------- +++ 3 Teys oe ANG A GEREN ONO ojos cs3Qseeabecec poe doncs besose Soee-boobDd ageacuSeRccny BSucoosur ae 3 Routes|0f approwehes eee ene ee see) seen ae sobsecdo pacar cnodogsasoso saboes asdnsaeccoH 6 DISCOVERY Onetulo precious Mela Spm acias semi esae eee teem eae asset a= eee esiscetewessces 7 IDENGITOMAN: OF WMC Sons ose) Sbiooosstoce soo coeSeeose=oonssecs deduSs cones nooscesscoch Soon 10 EON De WONG BSS. meceacesube padenb BOE Cond SESS Heo RS bbAGODCCSs SIGDRCSSOS50 Hap aaa Same 14 PROG INCIO -ccoas conoce Sookce Ecaeo csccce Ste ses S0e0 coeese SsenSe ceosdn onee He See6 cence soses 15 CHAPTER II. GENERAL GEOLOGY OF THE MOSQUITO RANGE...-.... 0-022. --- 2-2-2 + 2-222 e eee ne eee ee eee eee 19 Rorellay Momo wa (COLO YGY seer She S oedsas Gece SSroneeeeos Senced caese0 nds ecebaaaemode 19 DIES Fne TPR he rose c donee mateo Obcoed ate See eared Gane Gece bp pase Sse Seeeopo Eoeceeoseese 20 DHOUPST ES eee ene eye art ee ies ara Seon ere ini sotctaides ceeesescedeoca stan 22 Vv@e et GOUT SS S556 Bese hagosen dose seb osS0 Sces cogs osca seeo Bebe Seep eSPeInScelces semen 23 NWOT RENTON, ooode pees SEeododug Besos SSOde0 Case adioeoS Soosgee Seeoce Eien CoSQeese 24 MonquitO ante LOpopraphysae mae eam =a = ane nee niet ee mmole ee omen wei = on ee 27 (CEG a GENUINE, o506 Sosere eeScoe Us ee ee SESS Se Os0e SeicOs SESS eso Seo Sse ocoseeese rare pest) WihaGntell GENO = concen oson Sol o5b Soon SMnsosou HoSnod OuceceRcrr Jace eeoscrcsserenese 33 Structural results of the dynamic movements .....--.-..----..----- -----------. ------- 34 Displacement —Voleanic rocks.-.-..--- ---- ---- ---- ---- «22+ +--+ 2 2 -- 22 cone oe ee eee eee 39 General erosion—Arkansas Valley erosion....-.----. = ~~~ 222 eee ee coon ne oe nee eee ee 40 (GUNG El GOS Cocke sedeele duoc so So oseS GSsads gS oe Soa SSNS CHocce ise Ses DeSE ae eeeasoertad 41 Sian CRN VEEN econ sao gseSeo sts 6b Sodse 2o85 Se SSB Eb0 Bal6 SESE Hose eooeeeEcemsee 42 XIV GEOLOGY AND MINING INDUSTRY OF LEADVILLE. CHAPTER III. ROCKRORMATIONS pas cose cee een cee ae me cnince es sa pewesclacesismice an ote c= seen eee Seen Senne iEMy NOE sags ce swew sence tonSah Seeneo Does BORO SOSH Sens DS SUSB eS eres Oadossos Seto nsee J SOTERA Rome tee SS easesN) Setbcos oe oe ce sosecd seacsesosec secre Sess sceese sos CR 2) os ae Sos Sen S KAOR Soo Se Sey se Sce ue eo Be Soosts Shes AsSons SegaSsacce sess sasossst (BhTETES Sos Se eoAcine abo AOS On ao Soo Deno Sn SoSso esos SoseoobSacse deca cecHasccens INT PIMOS $506 Someaeoseoacece 8 ea cesse0 Hoe sed Hace reocad cee boeee cocessenbacsces IRENA GE) Sa Soci Damen ace ScICOn dO S SOO SSO CE EE OS BSCS SHIOSOD IRSREOCCOGGssees HoSSEz5 RIERA AOA ORG) 2555 Geeee Seenorossee Geanop nsooc oscHesonossDeneecossce ceecancse= CORITOT ENT oosees Sonaen Sonesoeoqeos Ssgg soo GEES CO 56 GH o a Dee seoncses Gee acossasaassse TheGe GG PANIGY s cgesecec ae cobics se Ho pcoeaccno tees Cea Snesarecksocesa cee Socs Silurienits-s2--=-)- dla SomSae Cones oni EOS So aE Sean ogsase as Sedo sissbeses = VASLUI DINGS TONG sere Bene CHOb 600 eas DOES USE ODES OFRODS pac soac Sesec ssccs 25 TEN eye UTES eocsne Roas Babess cb oocb s- SSE coSO SSE OSease HSE cose BeScSso- Corresponding beds in Colorado Range......--..---.---- ---- -------- «++ ------ (Of rs DO EER ON i = Go BRS OSes SSH ES SAND BUC OSe SEOs IDNs EE Saco Cae esm ose Sicone cegcca.c Blue or ore-bearing limestone --.-- 2-2... enews e come wees ween ee mene ea=- INLD sos RES eo SeES soSeng CHOSHORSesoneode Iaesocos Atha: Within Siig ta ens .bch se gotecccbas sooste sae soo paso 6esecoabasse “Stesceso: V\WVEINGIe (GENE) SS e ee Gt bsodcockce < snag sosor sos SSondS SeSeacneeSeacuscosesssosesse WW tem (Ot UGS oe a6 ES Sobor cae rar Sees peesce scones Aosecopeedadsses MESOZOIC HOM AMOS = seem tece ssa iae ale ca setan cin main ininl=| ain minin amie 5) ml mine emis oie te Quatenaanyslorm atone tes aiacteae aie el oleae w lelare aioe met aeialal alae a owin ee loa ea Gingrllomiake Deus ese aseo a onc ee ete meee ae ae wate te alee alee ata cela sie Cnet eee TICE OSE WEN 985 555 sesSteseccsods Secs Naoonoeesss5 eese sss sSss ssh ac s- Distribution of sedimentary formations ......----. Se One en te secsonereonc ts Mruptive or igneous TOCKS - <2. 252.5 see ow ne wn we ween wenn hese wen iee wens owes naar Second Anyeno pUlte sre sama peat sete anata mime Sivas nam melee mete ole miele Mount Zion Porphyry — White Porphyry ...----. ..---- «200 20 --- enone wan cae -=- ibpieveey hn Teta WAY eso comb Sap cone or oreo Aeoees Secu cera posdeano Hao mccissons oc Gray On hiya yeaa acnt tas eee ia alm) wma a maw man ll al SHG QHD ERENEA? coca scons pon eaee ease so Heo Coc oS aon ese sao nese se aoscosses: Tied Tees) LEC EN AY cee oe saaeccous sedens «cos See Se OE MEA NGnAon cessicsoceOssosteenss Mosquito Porphyry —Green Porphyry —Silverheels Porphyry -......-.----.--------- IBY See bogs fa coe eee es Gece Deon ees one or | Os SS EeEOI SOO eS eS boases- 6550025: PDN 350 codsas dunce soso Sec ene Sao mR. cere SoBe emcee qUScoocneceeborssooolss Wien, GMM NINOS 5-65 aa oSse cotode dossee nd 250 conscosS nooses bone choo nao Satosescsc6 couscas MennuCresi MONUn OlsELanM Canu hed ies tanner soem celcice esse mioe= cle ae inert mimaa aime om Wel) WET oe oacede cobbe5 SancOae che Sd GOES DASH EHR DEER ESSEC ECO BESO OCB EC BRED aecsER acc NOKiM YW EStOrnMOUVISION es aes cite (ose ate nel clnieintee oie ple's/a)aisaa oaeyehemcm\s aeons se Brospect)Wountainy cae js cio) oat mec eee ae So eaten eeninoe cote eee ecree ema see Wkyyea nV Ia y MINAS Ge epee Cone S COSE09 SES EAD COA DIG SEE DOD GEOSn aS Hos GOEHeeOr SaOoHe Mike, YO S-- 5 eSadeces Goesacwbas S60 pode Teae nose Seere bso dedophoncy SSousono cegacees an NSDTO TER PRINS — oe copes SoS en odd 8SE G5 06066 5 CSOa SSC BRS BO bS0 HSSeS A OSeDs SasEo Smee se6 BSS GPA Kansasny wleve sen coe sscaie cnc ceincoowisccces se cecceocecoc codes mestcsecascseecszee lonely GTi ee eve me casa dase enbd Cond BOD ROO ESS OC CODD ECOP DEC Oo DATEAD SE Sa BED SCO OSERoe Cn aioe omnia nee eee eee sere eee ei ital ere Siena etnies enn spec mayoe ee eieiselehmiefens Je-sc'= m3 ppenshen=Winlen walle yi acters ae ear sem ele anes ajo ale phe ise eee Eretela cin jainininiee. MGSO Oto anil Ginette ee telas ate =e sfocece =) a croS ats [a'nin,cicieies Sam niece aim neta ane mn ==\- =e == XVI GEOLOGY AND MINING INDUSTRY OF LEADVILLE. CHAPTER V. Page. DESCRIPTIVE GEOLOGY: OF UEADVIELE) AND! VICINITY.9---- coccde sae mes ans ioe nee ele aenieeamaele 202 Goeneralistructure:25---s.-as22-escceneeces- oe SS SSE a Seo — rss ~ ASE 202 Distribution of porphyry. bodies: 22---2=-.-.-- + —< scons sece aeciodetes eae sacs =e 206 VARS JEG yy EL Geese ae Se cp ocmose Sees e ESS bee 56 Sono Shes Seb ASS SS SSaceseoccosesse 206 (Gray LGN IA yece as ocess coe ces eee coins RES ste SS See SSS Sec tosses ess ese 207 Pyritiferous Porphyry — Other porphyries....-...--....--....-----------=------------- 208 ATERLGASE OL PMOSQUICO TAU Mie a are ae orale oe am aan elena lel ie mleiale ele wena emia = i= imeem inet me de DAAC ich odes sccct, ca son8 Jone ge oe Seb se So es Sse SS SASS Ces sce Sate saceess sss 210 Mosquitomdanlt —— Minor tanita ess sease esa e ade e see See eles ewan an ceca ae eeiaee 211 West Sheridan — Dyer Moun LAINE. aes oe eee ss sales eeeine son se eee pen aate eae 212 WARS) EOE EY Gye eae ee eee eco, SRS eas GUT CoeD cob ese cess coos ence saocesece 214 IDE IAI Mem VS eek 8-5 So espe Sco secede Stones psec oS roceas sass esas sos es 215 Area between Mosquito and Ball Mountain faults.......-......-------. ---------- eee eee eee 215 Ball Mountain fault — Prospect Mountain Ridge........ ...--. ----. ---2 222. 2-22 eee eee 215 TitilesE ens nt MIM pul eIKOS ea =. ae elaenisie namnelse saan =eaener acee rene ate 216 Coal in Weber Shales— Blue Limestone....- .-.. ...2.. 02-222 222-2 e o-oo e enc nee seen ce 217 South slope of Ball Mountain..-.......----.---- BenbRec cas soo san Sa5n SsSH see Sssccsness- 219 Area between Ball Mountain and Weston faults ....-...---.----.----- ------------+----+--- 219 Wieston tau tee ee te pester seer meee sew ame ae ia a teiaret) birice Coe c todo Ie aROeCe aE ee esSeeeeE coe setemninacmacrnaas 244 Area between Mike and Iron-Dome faults..---. ..---- ede ce hose cee esece sees tea eee 244 Iintirel Dihityar a tinge ee ea Ser Bea a oe ensig Senco ate eo oa ree ce Scoemere se secs Sccn S220 244 Long and Derry Ridge — Josephine Porphyry -------------------------- Sestetsacasseese 245 Lake beds — Iowa gulch — Dome Ridge. --.---.----------.----. ------------------- ------ 246 South slope of Iron Hill...--. .----- ------ ------ -----+ -----+ +--+ +--+ -- +--+ eee ee eee eee 247 INGYEne Prone tll tac enee ee oe eee ar ae astm manana mom me foie ole om ee 248 Area between Iron-Dome and Carbonate faults...--...----..-.--. .----- ---- ---- ------------ 248 (Omir Plena sos nese oe esos nese oan ce cS aOe seneermmens tecenoreeces sss ose cn Soasce 248 South of California gulech—Proof of synclinal fold ----. Weenie soe eee eee 249 IDtip nae hPa (Ee awn) TEES Soe ee eocee ses Hobere Sates Hoopee Ste areseas Gere Co=See 250 California pulehes.--s2ee- = - ee eae a= = mem § Shoes oie ae Seen See eeeas eee 252 Carbonate Hill-.-----. Se Socks SSE DEES OSE See on Dans Se soeheipene se saea woe een eases 253, Little Stray Horse syncline...---.----. -------- +--+ +--+ ------ +--+ ee eee eee ee eee eee 253 astern, ViMise se oo ee See en iee eee rca eiee aiviatsia olla) lalate eins ime wee wie elo =) wanna ae eae 254 Genter of basin'— Wi esterm Mimisss see = etete ee a leeinisom oe oes a Ce ween eee ee eei ee 255 CONTENTS. XVII Descriptive geology of Leadville and vicinity — Continued. nee BEVOnsh thee eeecccesetes= DaSooro SanSct deseaoes She64eechn doncoten cpesanesSuoddocasenento aco 255 VERGE PET DMCA ISS cnggo co deansectee Tae aCe BEG 950 SEGOSS HOBBEGUICCOU SEO SED 8 BODCES COOSEsaoeE 257 (CES OE BG RA So5 soso So osee cencsa0ccbs0 daddies soodcu sodas csoccoDSss Gacu ses Geen Se 257 SOTTO cockA dagsobeoantnan sot coe cose dosoon chaos ouEebouocosatidens SSE sescCEesee 258 ITAA) DVL EY AMO Pca as Gop So a ene ge nooo SS BS ube COea65 COSC ECAC eeS Riscecien eee nae se es 259 Yankee Hill anticline — Little Stray Horse syncline — Big Evans anticline .-.--..----- 260 ATH VES TOMO ALOU ALOLan Ome ny ON ELI IS a aeisa!elalals wietalelatelaisieisleleeaey=ial taiciaicrisreem alam =e = lane = 261 GonorslestLucuulomemerarts cece oc stiscies elas cen coeia online tasers sees S cReSaCsaG 261 IDES Gras iad PET oo oe (OC OSS SSE COCIS ead BEL CO COC OSHS RES SRSaIbe: DEOnce Soemee ct EcOCon 262 \WERIGI), DiS =SSce ca so5e CoSgac Sate OK CE CaO S00 Beco. CoD BeOS Cone BUDGE OnO SHON COCO TSOOES 263 Explanation of transverse sections .....----. 022-2. 2-22 on ne eee eee ene ones cen nee n= 263 CuHaPTeER VI. PIISCUSBLON OF GEOLOGICAL PHENOMENA, -<--2<.cc2.secsescoceesesente--cecdeceses cansesencsee 276 PecimMentanyecoCks=seeee Seer isae caine aie croesistaisisiectaieicisicicic sj cit nie wlee aeatn/oeninslelseiceieeemipse'mjeisn= 76 Archoantoanssncsre-eaceeslcccsankosu eee sces aaa Su ectod> SSeS scocces caaa bcos Goncne sted soce 76 IRANIAN OS 35 see Sodio om SOSOSS GHC 66 BOOSEd GOI TDC CH OSHC BOOP ER ECECOO DEE BEN CooeeeEabeeso cose 77 IDMIGTIING GaG Meio ndcog Coc Se nocec SSE SO0s BOE CED Club BES OD DEBE SOSS AD CooS Heo DOSDEES 278 SE GTOUIAIG) sos Sa S59 CASS SES Jon SeSn SOS EEE DEO SEE IAS SO DS EO0Et SEO CHEN CeCe Ser Saesea sate 281 Oripinfof theysenpeniimne seas esses ses se ae ee alee sais es leal= eolneleeiiee nena nn elae eel === 282 Stir mnml le tr nT Oo Sao ookos oes ooe SSeS SDeSSeEb POSE EO COORC UE (Lip edti Corba tris ey 7G Nip se mene ee Boe cdo poSbas (eS Sop coocon sac SacaSne a ceded uc sSsd IIE aE OHIL ano Shey aces cuses6 CEU DOO BODO S Ann = CHCH OO HOR meas Bedondn Sen cseus seeccc WA Ihare qe Ie NC ES) oo. con sa0c og Dbn BS SoLieoe OSM COP SS OSOSn sa seecoc dar soseeencas Dabo a Renee ce ORO Ney 56 ooo Boa oded SAD SECHOS IIOSOd HONSSn) BOS SAS Abaresets SoS rAeS bocce Other thyolities se eecreeere mem ae see ietetele alee oles eistele ate lees lates ee oes eae ee ate ee Rhyolitie tufa—Dike in Ten-Mile amphitheater—Breccia .....--......----.---.--.. Quartziferonsitrachy tose a senmnerieesem eee meee seca secie er eee senee te aaa cleae ee nee JNIVE The) Bssecing go een JeoSCb soon bs necks or 0> Decide DEES Cains Os Sac Sono menOe aoc loobodc stents Pyroxene-bearing hornblende-andesite......-...---.- Boce Soscse a cesi Sarason sesacegsc Hypersthene-andesite— Tufaceous andesites.....--. .- 22. 22 eens eee ene wee een wenn ne UNOS Rw he a Ra Ee a 5 Aa SA cng cae sis SOG SCE SIS CO En AS I asHOnSe dp eScs SSSA AAS SE Rock structures observed—Individual rock types..-- ---- ....-. ---0.- eee conn een cena ee wees Mutual relations of rock types— Rock constituents — Their decomposition ..........--..--.. Negative observations —Chemical composition ...-.......-. ..-.-- -22- 22-2. eens cee eee wenn NOTESIUPON THE ELEN, MOUNTAINGROGKS! caja. male ie lenlew alan colaana eae ae sclera = sleiniaas tees Horn blend i¢ mock stem sateen orien ee ciasicin a= leh aceel-sslese Race aalaa0 ae eae ae eee PASI (EILIG TO GUS Ba teieta er oln cine alse loo a miste rats ialat= i faln into tn tml «n= mivin] en's nln Glolm lal o/steleipinie= eae ee ee eee INET NG) Ee eso See SE StS DOS OE SOD Ie Seba Tess cD GSS Ss Sap SeSac Eicon oSerarescGe seca e-rsc PART II. MINING INDUSTRY. CHAPTER I. (OVS IONS oc code cast os copebooeaochnred ho boda cb thc ese ce oeE a Ghesns cep eco ceorceinpessenceonc Classification of ore deposits in general ...-.-------.----. -----. ---- --- 2 eee ene wee WeadvalleidepOsts =< pstmi\eyateisia mie = ate lee ol Che ete mieelnielw lmieinte tm wleineleiels) elm = aie) o minieininl nim mee tet NE A LOM ao oseG0esoSs sors oooS SEI ISCMOU TOC CU OSeESe aso sen OSA cats Snes (COM PORTH ON Fase es see ate eter ietre es ie eae ee tel eae ee ei oh otto) Seo IDMe RAE RON, 5S 5 46 Sp Sdeo bsoods Sob sod abe SASSO HE Sen Soe SHH Sasso SSaagoSec5 Stosce- Secondary alteration—Mode of formation .................. ---.------ --2. --0- s00 eee Age of deposits — Origin of the metallic contents...... ..........-------- +--+. eo0e eee CHAPTER II. TRON GHEE GROUPIOR MINES lose sells aps sel ei = eal eee anemia tee = nel eee ae Tigi) 3 60) See ee en os eae ne ocd DOT a CO NODDED Soo EDOM RARER RARE CABO nON BOE eS ACS Som Generalideserip tion ens memerisemiee eae eeieatatsteeina mof tacit oars lolelae = ae eee Geological structure ....\---- -.-..--- =... O5E 4 O50 SHO SEECS Seegeeca Sack coece S OoSeere IEPA Ken aI Aes) OES eg 95 cae CFOS Em ob SH SD LODO Db SOGUso Be SAO HCO Ee coarapenscc OSth VWI OY NR iin na sey see nno Site doo SSS SoU Se hoE SSS DIS ooE OSS BORO SOTSO BS ECORI CHOSE Blue Limestone — Silurian—Cambrian —Iron fault ............-------- ---. eee eee 367 367 375 375 376 377 378 379 380 380 380 381 382 383 5a4 385 336, 388 CONTENTS. XIX Page. Trou Hill group of mines— Continued. Tron Hill— Continued. hiner Oniii seMeen ammenities se me Awaio maine ttt peace steel aee cele tow. scree x» 339 HOCK an dh OMG aparece mae eoesl em cniseec cu sicswe ceeeteconclncecs toce sacs 389 DiaiPlatay Stone andVas Vs ccc sac —2- fe sjnsctececeacnscwiccar esisccetssmesccet theseues 390 Ei yan ips elite eevee ee nse een evince ane e cer ceceminescclen aasctcuee ss oncivoc cc 391 South Bull’s Eye and Silver Cord Combination .......-.. 222-2... ---202.-ceneceeeee 392 INO URTATN ey PLO POL eee eee cee ae eeern nea omlocee, dee aes SH SSLO Gees COAREE cea Soon. 394 Relaionrof Iron faulpitorore POdes =e ee eee econ Se eerlecne case ceca= Secmc 399 NGnGMEITO MeL eeemeeta tee rare aioe ene lain San oacemew enn cesloanieaccecebeccereisee wes 2? 40% Gener cen oni calrstru Chure ema tie mteretseccccl oot coelaaeisan eerste one lscaccesan cece ae 401 Tron fault — Adelaide fault— Rock formations ............ 2-2. 22002. seclee cece eee 402 (ins GQ OSUG, Go eoe. cobb coe SAS Ao nse oon SSeS Soo TEAS Stn OBcn SERS Ee Mer rEs Ba He a eee se 404 WHNS SOE ESOS) 6.556 Ghos can PESO BeOS JOO RR OOOSa6 DESO SEOE aCe EOS SoBSEs peeitar obcocacr 405 JAM HS Nya) heey OT TEN eS 555 S35060 CESS DOS OUT HSER EE BE BEED SE DEO BoEeseeoSoe 405 NGO at 0 Otemmeniat tenses weielarelce es cavenis ciate te lein ci ciefeleispecle we cee ne aha crcievioeere meet 406 Wanye eckentesmase act meee ea esse Acts oeae mace sac oases cescedee eviecr be sets 408 CHAPTER III. CARBONATE EET GRO UPy ORMMIUNES eermieiasrietneect ete Sanne slain Mecints cele atte see e tsa aeimee hereon 409 (CrsrhGine ll VE OERD co. Soo bp omeSb GOCE OU S85 53 GROSSE CURR CEC COON DESCOR Stop Cee eSaen aaa onaeshaee 409 RACKS ORM atONS ee areata eae aa ane sea nate sine nn/an am eins ces semisaaecieeeancess tee ec 409 @anbonaertatl tee meeme meee ere ae ete ae altel ica estonia Weenies oS acetianis isso ee ee eat ane 410 Pendery fault — Morning Star fault — Ore deposits ...-...---..-..-..----2- --eeee eee eee “411 Southwest slope of Carbonate Hill ........-.- BERGHE LUOGUS PODER ORACbS HEaa eae cen pees 412 SOULE NOU pL Ote iin Sie sree mete eee pane cde mene ecmaioecios chat en See eae nloee = eee 414 (CER OREUID WO HISINT 56 a5060005 1 SHOCaU CUE OCOS SSAC BAGO nS CER E CS Hoe RBeneEeas conoos Beneese 416 Carbonatennelnoeemaa tac a cinenioe cases st qonnoereetisccaaelcaucoca dose SSoouSdn node coSonECe sa Snec aemedosoee Tenth GRALOGY Gots Hone Sees Hees Saeonocoee cadueodo oFes Soop Sono cpSEstescseconccso acad IGRI) Cent es coos 3S a SRS eCe COSOSe OSS EES Sas SDSciCos SEO Beeesber aa cronmoodm5e0ns Origin or source of the metallic minerals..-......--..-...--. .----- +--+ -2---- 22-2 ee eee : JAS ORR hr UGA EGO HO oe poo sonade acest essed COnU BEObSs Had Bees Busses ceSeemons SMOROE OMICS oo Sos Gocecs ed oo SOs Da C En Seno CIES DOCEECOCON CG SCO SOOODASUSSE ao EG Losers Motalliqicontenis of COUNLTy;TOCKSee ms selene alas an sees om onl aisen en aelane lena sie == emia Baryta determinations— Lead determinations........-....---. -----------+----- ------ Silverand gold determinations) oo. <<. 2 ooo. so ceee nonce cinmnn omen ec cansiccns cone uenlo==- Wossible;contents of porphyry DOdieS--<— secs. one mone orn n wcew snecisceniece= sere veene= APPENDIX B, By W. F. HILLEBRAND. CHEMISTRY. TABLES OF ANALYSES AND NOTES ON METHODS EMPLOYED ........--.-- e220 -2 02 2+ e000 cece eee ID STNWE HOES » Soc ss pon Sse cdios soacise soSeee SHoray Dobos coceno anoeeS dacs cosas cosbeeoae Table lp (Caray leet OIE sce padods oboe coo6 poedodse SeoboECOcolS baSeSrSserpcoacao Table, (1 Silicayand alkalideterminations)-.--2- =. <2... 0 sacs SHee XVII Cento ica WseC Mons esl Srea Sth oi) tenee seetatelowte) om sels eiieecmaisl eter eee maee ce eaecese eee XVIII (COWS CN BeOS. UMS AGEL TET cemateacaos Tee cEc oon eco Ue 0ob CECE SSSOREEOSD EAE BEtere XIX CCUCIQa CRI GemiGMg, MO GES WE pee Oo copce cecesceUCOSeCEES BUD SOD SeSkeosSeere case san se xX (Gracileateell seein, IN soscech hdaadeonsGcs doecdd Se GceSSobaes Hose SCS ene seen ecsese co aseee XXI Geological sections, V =-2-.-----.-.--5-.---7 Soh groase Sobscesosh ddan Gocdaomeueds esbe XXII Tron Hill: Geology and mine workings -....-.--. soseccouecds soot te oede segs odes moseeac ..senganbeee XXIII GeolomicnliseGilOus. we laeermer tec nny=slateisiereic eee oe Saleem cine] acini aeecae onibeoe Bros -Seece XXIV ESO EM BEGHOMS, Whoo eso seesescaquce: b¢ an50 oSsbeSocmee esos Sabo PeSOSURCOnES ManeeEaoe XXV North Iron Hill: : Geology and mine workings ..................-<..- soened JopcrenScSSs sé Coad sosasadsenSyonse XXVI Geological sections --.-......--.......5.....2 Sodosocesesocs SesonCnod Asecesnenceectiecmese XXVII Carbonate Hill: Ccalopypand nine amockine sersem asa enecnelnas lems a omieatea clear inn seiistew Soa wa aie scene sel- XXVIII Geological Becton, Mle seas oat (So Sroordsccrkge Secs adae deen aosase Stace sees ese XXIX (SEOIOPICAIUIRE CULO USM ecmmsiate senret Cee te ince Nata cer iccce bald cles stslbicsioe sSnSate seisiswe/sce's = XXX Fryer Hill: (Gahieay Pel ie Oneal sso) aocen6 ono see UBoy 6 DSc OU OO OOdd BREROs COUn proce EaOheTnEEeneae XXXI COOMA AB Mesh Ui easheq con sesoseScs. c558S9 400-0660 COCEES BACOOE Hae SbO ASECE Sb ROOeeD Eos XXXII (Samy nell ABE, Le Sanenieeeanegec ono CeCe 2e00 SHHSCCD DOCD DO BESS CONCEE Se Beorae RaeOcone XXXIII Gatien ening, WM soe sencco ecco donccoess vansss Socmen SCS ene EES oO es Bosereeese XXXIV INGER ALOIS Al SOMME AO VLCC Ake ol tateraintalisle sicisiete iriciciolsiciajsacoe) 2s 'atcisis wicicime e's e'eisc'eacle chee anecc XXXV XXVIII GEOLOGY AND MINING INDUSTRY OF LEADVILLE. ERRATA IN ATLAS SHEETS. SHEET VI. Blue section line BB should ron through the summit of Mount Lincoln and thence to sum- mit of Mount Cameron, instead of direct to latter from point on east spur. VII. The line of the Mike fault should not be continued south of Empire gulch. XII and XIV. The blue line, showing the course of the Starr ditch north of California gulch, has been omitted; the names give an approximate idea of its position. XIII. Color on small block of Blue Limestone at Comstock tunnel (L-38) has been left out. XV. “Ditch” just west of Sequa shaft should be “Little Evans gulch.” XXI. Section JJ, ‘‘ Iowa gulch fault,” should be ‘‘ Iowa fault.” XXIII. Parallel linings to denote ‘‘inclines” have been omitted on Silver Wave claim. XXV. Section FF, ‘‘ California fault,” should be ‘‘ Dome fault.” XXX. Section GG, “ White Porphyry ” color under drift east from upper shaft of Yaiked Doodle mine, Bhould have been that of ‘‘ vein material.” XXXI. Shaft ‘‘ Carboniferous No. 7” should be ‘‘ Carboniferous No. 1.” Shaft ‘‘ Little Chief No. 3” (southernmost) should be “ Little Chief No. 5.” Shaft “Little Pittsburgh No, 3” (near E, boundary line, and just north of dike), ‘No. 3” left out. Shaft Climax No. 2 (near E, boundary line, and line of section), ‘‘No. 2” left ont. XXXV. F-10 “ Leavenworth” should be ‘‘ Lawrence.” M-5 “Beecher” should be ‘‘ Belcher.” ee BRIEF OUTLINE OF RESULTS. GEOLOGY. The Mosquito Range, the study of whose geological structure formed a necessary basis for that of the ore deposits of the Leadville region, is the western boundary of the South Park, and has thus been considered from a topographical standpoint to form part of the Park Range. “Geology shows, however, that in Paleozoic times the boundaries of the depressions now known as the Parks were formed by the Archean land masses of the Colorado Range on the east and of the Sawatch and its continuation to the north, the Park Range on the west, and that the uplift of the Mosquito Range did not occur until the close of the Cretaceous. Prior to this uplift the various porphyry bodies, which now form a prominent feature among the rock formations of the region, were intruded into the sedimentary beds deposited during Paleozoic and Mesozoic times, spreading out between the beds and sometimes crossing them, but being most uniformly distributed at the top of the Lower Carboniferous or Blue Limestone. It was in this limestone that the greater part of the ores were deposited, and the original deposition must have taken place after the intrusion of the porphyry and before the uplift of the range. In the uplift of the range both eruptive sheets and sedimentary beds, with the included ore deposits, were plicated and faulted, and by subsequent erosion an immense thickness of rocks has been earried away, laying bare the very lowest rocks in the conformable series; the outcrops are, however, frequently buried beneath what is locally called ‘‘ wash,” a detrital formation of glacial origin. In the Leadville region, owing to the reduplication caused by faulting, a series of outcrops of easterly dipping beds of the Blue Limestone are exposed beneath the wash, of which all are metalliferous and a consid- erable proportion carry pay ore. ORE DEPOSITS. The principal ore deposits of Leadville occur, as above indicated, in the Blue Limestone and at or near its contact with the overlying bodies of porphyry. The ores consist mainly of carbonate of lead, chloride of silver, and argentiferous galena, in a gangue of silica and clay, with oxides of iron and manganese and some barite. These materials are mainly of secondary origin, and result from the altera- tion by surface waters of metallic sulphides. The study of these deposits has shown: 1, that they were originally deposited as sulphides, and probably as a mixture, in varying proportions, of galena, pyrite, and blende; 2, that they were de- posited from aqueous solutions; 3, that the process of deposition was a metasomatic interchange be- tween the materials brought in by the solutions and those forming the country rocks, consequently that they do not fill pre-existing cavities; 4, that the ore currents from which they were deposited did not come directly from below, but were more probably descending currents ; and 5, that these currents probably derived the material of which the ore deposits are formed mainly from the por- phyry bodies which occur at horizons above the Blue Limestone. PRACTICAL CONSIDERATIONS. Inasmuch as the ore currents did not come directly from below, it is not advisable to search for ore below the Blue Limestone herizon. This horizon, however, should be thoroughly prospected, and the maps and sections show its probable position in the as yet unexplored areas; the explorations, moreover, should not be confined to the upper surface of this limestone, but carried into its mass wherever there are indications of ore, and especially along the contact of transverse bodies of Gray Porphyry. The probabilities arethat very considerable bodies of ore remain as yet undiscovered, and the most promising areas for prospecting are indicated. It is also probable that as the distance from the surface increases the ores will be found less altered, and that they will therefore be less easily reduced by the smelting processes now employed. The petrography of the district is treated by Mr. Whitman Cross in Appendix A. The results of chemical investigation and the methods of research are given in Appendix B by Mr. W. F. Hillebrand, and in Appendix C Mr. Guyard has given a memoir on Jead smelting as conducted at Leadville, show- ing the character of the plant, the composition of ores, fluxes, and furnace products, and discussing the reactions which take place in the blast furnaces. XXIX GEOLOGY AND MINING INDUSTRY OF LEADVILLE. ACE oT. CoO Ong. ¥", MON. xlI——1 1 CHAPTER I. LEADVILLE—ITS POSITION, DISCOVERY, AND DEVEL- OPMENT. Topographical description The city of Leadville is situated in the county of Lake, State of Colorado, on the western flank of the Mosquito Range, at the head of the Arkansas Valley. Its exact position is in longitude 106° 17’ west from Greenwich and 39° 15’ north latitude. Its mean elevation above sea-level is 10,150 feet, taken at the court-house, in the center of the city." The most striking feature in the topographical structure of the Rocky Mountains in Colorado is, as is well known to those familiar with western geography, the fact that it consists of two approximately parallel ridges, separated by a series of broad mountain valleys or parks. The easternmost of these uplifts, the Colorado or Front Range, rises abruptly from the Great Plains, which form its base at 5,000 to 6,000 feet above the sea-level, to a crest of 13,000 to 14,000 feet. Itis deeply scored by narrow, tortuous gorges, worn by mountain streams, whose clear waters debouch upon the plains and become absorbed in the sluggish, turbid currents of the Platte and Arkansas Rivers. The trend of the range is due north and south, its highest portions being mostly included within the 1The datum point from which the levels of the map of Leadville were reckoned is the threshold of the First National Bank, a stone building at the southeast corner of Harrison avenue and Chestnut street. The altitude of this point, as determined by connection by levels with the bench-marks of the Denver and Rio Grande Railroad, is 10,135.55 feet; by levels with the bench-marks of the Colorado Central Railroad, 10,113 feet ; by depression angles from the top of Mount Lincoln, 10,112 feet. Asa mean, the contour passing through it is assumed to be 10,125 feet, greater weight being given to the first figure, since the leveling by which it was arrived at was probably more carefully done than in the case of the other two. A level-line had been run from Fairplay to the top of Mount Lincoln by the members of the Hayden Survey in 1872. 3 4 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. boundaries of the State, beyond which at either end it becomes gradually lower, and disappears as a topographical feature beneath the plains. To the west of this range lie the mountain valleys of the North, Middle, South, and San Luis Parks, in Colorado, and the Laramie Plains, in Wyoming, each of which possesses the same general feature of being nearly completely encircled by mountain ridges. On the other hand, each has distinet topo- graphical features of its own, which need not be entered upon here. Beyond the parks on the west, and separating them from the great basin of the Colorado River, is a second mountain uplift, to which the gen- eral name of Park Range has been given. It has by no means the regular structure of the Colorado Range, but is made up of a series of short ranges en échelon, from which offshoots connect with the latter, forming the ridges which separate the different park basins. In the latitude of Leadville this western uplift consists of two distinct ranges, the Mosquito or Park Range— the latter being the name given in the Hayden atlas of 1877, probably because it forms the boundary of the South Park——and the Sawatch Range, which forms the water-shed between the Atlantic and Pacific waters. The Mosquito Range is a narrow, straight ridge, about eighty miles in length, trending a little west of north, and is characterized by long, regular slopes scored deeply by glacial gorges on the east toward South Park and by an abrupt irregular inclination on the west towards the Arkansas Valley. The Sawatch Range, on the other hand, is a broader, oval-shaped mountain mass, divided by the deep gorges of its draining streams into a series of massives and wanting the continuous ridge structure of the Mos- quito Range. In this respect, as in its geological composition, which is the determining cause of the difference of its topographical forms, it resembles the Colorado Range. The culminating points of each range have a remark- ably uniform elevation of about fourteen thousand feet above sea-level. Between the two ranges lies the valley of the Upper Arkansas, a merid- ional depression 60 miles in length and about sixteen miles in width, measured from the crest of its bounding ridges. Its direction is parallel to that of the Mosquito Range, being a little east of south in its mean course, though more nearly north and south towards its head. From its southern end the Arkansas River, after receiving the waters of the South Arkansas, bends SITUATION OF THE CITY. 5 sharply to the east and cuts through the southern continuation of the Mos- quito and Colorado Ranges in deep canon valleys, the last well known to tourists as the Royal Gorge. About midway in the Upper Arkansas Valley the present bed of the stream is confined within a narrow rocky canon, called from the prevailing rock of the surrounding hills Granite Canon. Both above and below this canon the foot-hills of the bordering ranges recede again, leaving a valley bottom from six to ten miles in width. But little of this area is occupied by actual alluvial soil, its surface consisting mostly of gently sloping, gravel-covered terraces. In the area above the canon, which is about twenty miles long, the eye is at once arrested by its basin form. In the center is a relatively wide stretch of meadow land imme- diately adjoining the river, on either side of which mesa-like benches slope gently up to the foot-hills of the mountains, three or four miles distant, which rise abruptly from these terraces in broken, irregular outlines. The suggestion thus offered by its basin shape and terrace-like spurs that this portion of the valley was once filled by a mountain lake is confirmed, as will be seen later, by the geological facts developed during the present investigation. On the upper edge of one of these terraces, on the east side of the val- ley, is situated the city of Leadville. From the north bank of California gulch it extends along the foot of Carbonate hill to the valley of the east fork of the Arkansas, covering, with its rectangular system of streets and contiguous smelting works, an area of nearly 500 acres, while on the hill slopes immediately above are situated the mines which constitute its wealth. On Plate II is given the reproduction of a photograph of the city, taken from a point in its western outskirts on Capitol Hill ridge, near the junc- tion of the two branches of the Denver and Rio Grande Railroad and about west of the Harrison smelter. Although the plate leaves much to be de- sired in point of distinctness and the shape of the mountain spurs back of the town are necessarily obscured by foreshortening, it serves to give a general idea of the city and its surroundings. The square building with cupola, on the extreme left, is the court-house, back of which the wooded ridge in the middle distance is Yankee Hill; a similar building to the right toward California gulch is the high school. The chimney in the middle is 6 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. that of the Harrison Reduction Works, to the right of which is the Tabor mill. The slopes immediately back of the town are those of Carbonate hill, beyond which is seen the round summit of Ball Mountain, with Breece hill, as a wooded spur, extending northward from it. Still farther back the ridge slopes up in apparent continuity to Dyer Mountain, the highest point on the sky-line. To the left of Dyer Mountain is Mount Evans, 64 miles distant in a straight line, and on its rightis Mount Sherman, forming the eastern walls of Evans and Iowa amphitheatres respectively. Ona clear day the outlines of rock formations on these walls may be very distinctly seen. Routes of approach. The approach to Leadville, as may be seen from the above brief sketch of its topographical situation, was extremely difficult be- fore the development of its wealth had led to the building of railroads. Three routes of travel were available. The middle one, or that most used by travelers in coming from Denver, crossed the Colorado Range near the South Platte Carion, at an elevation of 10,000 feet, and skirting the northern rim of South Park, through the mining town of Fairplay, crossed the Mos- quito Range at Mosquito pass opposite Leadville at an altitude of 13,600 feet, or, making a detour of ten or twelve miles to the southward, at Weston’s pass, whose summit is only 12,000 feet above the level of the sea. This gen- eral route the Denver and South Park Railway follows, winding up the nar- row and tortuous gorge of the South Platte and passing over Kenosha pass at the head of its north fork into South Park; to cross the Mosquito Range, however, it is obliged to make a longer detour to the southward and pass down the valley of Trout Creek, a tributary of the Arkansas, which, heading on the east side of the Mosquito Range, debouches into the Arkansas Valley at Buena Vista, 40 miles south of Leadville. The southern route, before the time of railroads, generally crossed the Colorado Range at the Ute pass above Colorado Springs, and, traversing the lower end of South Park, passed into the Arkansas Valley either at Trout Creek or at Weston’s pass. The Denver and Rio Grande Railway, however, has located its line —a triumph of engineering skill — directly up the valley of the Arkansas, which it follows through canons and gorges that. before were practically impassable. a yy Lat :vs ‘ -_ i U. 5. GEOLOGICAL SURVEY EARLIEST EXPLORATIONS. ii The northern route starts from Golden, near Denver, and, following up the canon of Clear Creek, crosses the Colorado Range at an altitude of 12,000 feet, either by the Argentine or by Loveland’s pass. It then crosses the southern edge of Middle Park along the valley of Snake River and bends southward up the valley of Ten-Mile Creek, having thus gone around the northern end of the Mosquito Range. After crossing the relatively low divide of Frémont’s pass (11,300 feet), it reaches Leadville by descending the east fork of the Arkansas. At either end of this route railroads are already built, namely, up the valley of Clear Creek to Georgetown, and from Leadville across Frémont’s pass down Ten-Mile Valley to its junction with the Blue. But the advisability of completing the connecting link at such an altitude, in practical competition with the two already existing lines, seems under present conditions of development to be somewhat doubtful. Discovery of the precious metals— The discovery of the Leadville deposits presents so striking a picture of the life of the pioneer miner in the West, and of the large element of chance connected with it, that it seems proper to give its history with all the fullness of detail which the somewhat imper- fect data obtainable will allow. The earliest known exploration of the valley of the Upper Arkansas was that made by the expedition of Frémont in 1845. In his second expe- dition, in 1842, he had aimed at tracing the Arkansas River to its source, but, unwittingly leaving the main stream, had followed up the Fontaine qui bouille, now called Fountain Creek, probably passing near the present site of Denver, and struck into the mountains at some point nearly opposite that place. In 1845, however, as indicated by General Warren, he prob- ably entered the mountains near where Canon City now stands, and crossed the southern end of South Park, reaching the Upper Arkansas Valley through the valley of Trout Creek. Thence, following the Arkansas to its head, he crossed what was then called Utah pass and descended Eagle or Piney River to its confluence with the Grand or Blue. Jt seems proba- ble, therefore, that the name of Frémont’s pass, which is given to that of Ten-Mile Creek, would have been more appropriately applied to the 'Ten- nessee pass, which divides the Eagle River from the head of the Arkansas. to) GEOLOGY AND MINING INDUSTRY OF LEADVILLE. There is little doubt that this striking valley was afterward visited by trappers and individual explorers, but of such visits no record is left so far as is known to the writer. This region, like that of the parks, formed part of the debatable ground between the tribes of Arapahoes and Utes, who were constantly at war with each other and who made excursions to these mountain valleys simply for the purpose of hunting and without any per- manent occupancy. During the summer of 1859, at the time of the great Pike’s Peak excite- ment, a continuous stream of emigrant wagons stretched across the plains, following up the Arkansas River to the base of Pike’s Peak. As is gener- ally the case in such mining rushes, the golden dreams of a large portion of those attracted by the marvelous stories of the wealth that existed in the streams issuing from the mountains were never realized. Many of the wagons that had crossed the plains in the early summer, carrying the tri- umphant deviee ‘ Pike’s Peak or bust,” returned later over the same route with this device significantly altered to ‘“‘ Busted.” The more adventurous and hardy of these pioneers, although disappointed in their first anticipa- tions, pushed resolutely up through the rocky gorges towards the sources of the streams. Some of these found gold in Russell gulch, in the valley of Clear Creek, where the first mining developments were made within the State and where now stand the flourishing mining towns of Central City and Black Hawk. Others wandered across the Colorado Range into South Park, and found gold-bearing gravel deposits on its northern border, in Tarryall Creek and on the Platte in the neighborhood of Fairplay. This is, as far as can be learned, the extent of the explorations made in 1859. In the early spring of 1860 several small parties crossed the second range into the Arkansas Valley. Among the number were Samuel B. Kel- loge, now justice of the peace at Granite, and H. A. W. Tabor, later mill- ionaire and lieutenant governor of the State of Colorado. Mr. Kelloge had already had an experience of ten years in placer mining in California when he came toColoradoin1859. In February, 1860, he started with Tabor and his family, their wagon being the first that ever went as far as the mouth of the Arkansas. They pushed up the valley and about April 1 settled down at the site of the present town of Granite, about eighteen miles below Lead- DISCOVERY OF GOLD. 9 ville. Here, having discovered gold in Cash Creek, whose placer deposits are worked even at the present day, they whipsawed lumber to make sluices for washing its gravels. A few days after their arrival news was brought to them of the discovery of gold in California gulch. Two parties of prospect- ors had, it seems, already preceded them, though their route is unknown. Foremost among their names are those of Slater, Currier, Ike Rafferty, George Stevens, Tom Williams, and Dick Wilson, from the last of whom many of the following facts were obtained: The first hole dug in California eulch was about two hundred feet above the site of the present Jordan tun- nel, the second just below the present town of Oro. Owing to the richness of the ground and the number of the persons present, gold was discovered at an unusual number of points, and 14 discovery claims of 100 feet each were located. Kellogg and Tabor met the prospectors at the mouth of Iowa gulch, as they returned from locating the discovery claims, and agreed to prospect that gulch. They returned to Cash Creek for provis- ions, and went finally to California gulch on the 26th of April, 1860, as Iowa gulch had yielded little fruit to their labors — the geological reasons for which will be explained later. In spite of the difficulties of communication in this wild region, the news of the rich discovery of gold spread with amazing rapidity. The day after their arrival 70 persons came into the gulch from the Arkansas Valley; by July it was estimated that there were 10,000 persons in the camp. It is said that $2,000,000 worth of gold was taken out during the first summer. Prob- ably considerable deductions may be made from this estimate for the exag- geration that fills men’s minds in moments of such excitement. The record of claims located, however, shows enormous activity in mining during this summer. In California gulch alone, 339 claims, 100 feet in width, were located. Single individuals are said to have carried away from $80,000 to $100,000 each as the result of their first summer’s labor. ‘Tabor and Kel- loge worked their own claims and made about $75,000 in sixty days. he total production of the placer claims is generally stated at from $5,000,000 to $10,000,000, but a more conservative estimate places it at from $2,500,000 to $3,000,000. The climax was soon reached, and after the first year the population of this new district, whose post-office was then known as Oro 10 GEOLOGY AND MINING INDUSTRY OF LEADVILLE: City, rapidly decreased, until within three or four years the thousands had dwindled into hundreds. Kellogg, with the restless spirit of the western prospector, wandered away in the early part of the summer into the San Juan region and did not return. Tabor started the solitary store in the place, his wife being at the time the only person of her sex in the camp. When the product of the placers had gradually decreased and the prosperity of the camp was at its lowest ebb, he moved across the range to Buckskin Joe, which was then enjoying a fitful prosperity from the rich developments of the Phillips mine; but returned later, when the discovery of vein gold in the Printer Boy mine revived for a time the waning prosperity of the gulch. Development of mines—In 1861 a ditch was built from Evans gulch across the head of California gulch, by means of which sluice mining was carried on, but owing to the great cost of supplies, which had to be brought in on the backs of animals, only the very richest gravels could be worked with profit, and at that time little attention was paid to vein deposits. Among the early miners it is probable that few if any suspected the existence of the real mineral wealth that the region contained, although they were much annoyed in their working by worn, iron-stained fragments of heavy rock, which they had to throw out by hand from their sluices, the water not having sufficient force to carry them down. Report says that in August, 1861, C. M. Rouse and C. H. Cameron, of Madison, Wis., “struck carbonates,” of which a small quantity was shipped to George T. Clarke, of Denver; and that samples which he sent to Chicago yielded by assay 164 ounces of silver to the ton. The Washoe Mining Company is said to have been formed on the strength of these dis- coveries, but no work was done upon the claims, whose location, if they really existed, is now unknown. In June, 1868, the first gold vein, called the Printer Boy, was discov- ered by Charles J. Mullen and Cooper Smith, who were prospecting for J. Marshall Paul, of Philadelphia; and in August the Boston and Philadelphia Gold and Silver Mining Company of Colorado was organized, and a stamp mill was built at Oro, in California gulch, to treat the ore from this vein. A very considerable amount of gold is said to have been obtained from it, DISCOVERY OF CARBONATES. 11 though it is difficult to obtain actual data as to its production. Estimates place its total yield at 5600,000 to $800,000. The ‘5-20” vein was also opened at this time on the opposite side of the gulch, and also an extension of the Printer Boy, called the Lower Printer Boy. The working of these mines, which was carried on more or less continuously until 1877, imparted at times a fitful prosperity to the region. Meanwhile the location of the town of Oro had been frequently changed. It was first scattered along California gulch, then concentrated at the mouth of the gulch, near the present city of Leadville, and later moved up to the vicinity of the stamp mill, which still stands among the few cabins to which the name of Oro City is yet applied. During this time the Homestake mine in the Sawatch Range, near Homestake Peak, opposite the head of the Arkansas, had been opened and was yielding rich silver ore. In 1875 a smelter was built at Malta, west of Oro, to treat the ore from this mine and from.others which it was expected would be developed in that region. This smelter, like so many others built before any permanent production could be counted on for its supply, has never been successful. To Mr. A. B. Wood and his associate, Mr. W. H. Stevens, both experi- enced and scientific miners, is due the credit of being the first to recog- nize the value of the now famous carbonate deposits of Leadville. Mr. Wood came to Calitornia gulch first in April, 1874, to work the Star placer claim. While examining the gravel in the gulch he was struck by the appearance of what the miners call “heavy rock,” some of which he assayed. His specimens were not rich, yielding only 27 per cent. lead and 15 ounces silver to the ton; but the matter seemed to him worthy of investigation. He put prospectors at work to find the croppings of the ore deposits, and in June, 1874, the first ‘“‘carbonate-in-place” was found at the mouth of the present Rock tunnel, on Dome hill About the same time ore was discovered in a shaft sunk by Mr. Bradshaw near the bed of the gulch on the present Oro La Plata claim; but it is maintained by some that this ore was not in place, but simply ‘‘ wash,” accumulated from the abrasion of the adjoining croppings. Prospecting was quietly continued by Mr. Wood, but no claims were taken up, as the old placer claims — which, 12 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. though abandoned, would still be in force for another year — covered all the ground adjoining the gulch. Meanwhile he studied the occurrence of the mineral and the outcrops of the limestone on either side of California gulch. In the spring of 1875 he took Mr. Stevens and Professor H. Beeger, the latter then in charge of the Boston and Colorado Smelting works at Alma, to Iron and Dome hills, and showed them in the forest that then covered the slopes the outcrops, respectively, of the Lime, Rock, and Dome claims. Dur- ing this and the following summer the principal claims which constitute the valuable property of the Iron Silver Mining Company were located by Messrs. Wood and Stevens in the interest of Detroit parties. The first ore was extracted from the Rock mine, where a large mass of hard carbonate formed a cliff outcrop on the side of California gulch. This ore was rich in lead, but ran very low in silver. During the summer of 1876 ore was first taken from the croppings of Iron and Bull’s Eye claims, and some rich assavs, as high as 600 to 800.ounces to the ton, were obtained from it. The first working tests of Leadville ore were made by Mr. A. R. Meyer, a graduate of European mining schools, who first came to California gulch in 1876 from Alma, acting as agent for the St. Louis Smelting and Refining Company. In the fall of that year he shipped 200 to 300 tons of ore, princi- pally taken from the Rock mine, by wagon to Colorado Springs, and thence by rail to St. Louis. The freight to Colorado Springs cost $25 per ton and the ore averaged only seven ounces in silver to the ton; it contained, however, 60 per cent. lead, andin spite of the high cost of freight yielded a profit, owing to the high price of lead (seven cents a pound) then ruling. It having thus been proved that Leadville ore could be worked at a profit, prospecting was vigorously carried on, the next discovery being that of the Gallagher Brothers on the Camp Bird claim, supposed at that time to be the northern continuation of the Iron-Lime outcrop. This discovery was made late in the fall of 1876, and the claim now forms part of the property of the Argentine Mining Company. During this winter the Long and Derry mine was discovered by two prospectors of these names, who still own the mine and have become wealthy from its product. During the spring and summer of 1876 discoveries were made along what was then known as the CARBONATES ON FRYER HILL. 13 second contact, on Carbonate hill, the Carbonate and Shamrock mines being the first to yield considerable quantities of pay ore. In the following years the famous ore bodies on Fryer hill were discov- ered by a singular accident. At this point there is no outerop, the whole surface of the hill being covered to an average depth of 100 feet by detri- tal material. Tradition has it that two prospectors were ‘grub-staked,” or fitted out with a supply of provisions, by Tabor, half of all they discovered to belong to him. Among the provisions was a jug of whisky, which proved so strong a temptation to the prospectors that they stopped to discuss its contents before they had gone a mile from town. When the whisky had disappeared, though its influence might probably have been still felt, they concluded that the spot on which they had thus prematurely camped was as good a one to sink a prospecting hole on as any other. At a depth of 25 or 30 feet their shaft struck the famous ore body of the Little Pittsburg mine, the only point on the whole area of the hill where rock in place comes so near the surface. Discoveries rapidly multiplied in this region; immense amounts of ore were taken out, and the claims changed hands at prices which advanced with marvelous rapidity into the millions. A half interest in one claim which was sold one morning for $50,000, after being trans- ferred through several hands, is said to have been repurchased by one of the original holders for $225,000 on the following morning. The foundation of Mr. Tabor’s wealth was laid in the first discovery on Fryer hill, but its amount was materially increased in a singular way. When the fame of the rich discovery of Fryer hill had already become known at Denver, the wholesale house from which he was in the habit of buying his provisions commissioned him to buy for them a promising claim. On his return to Leadville, in accordance with this agreement, he purchased on their account, for the sum of $40,U00, the claim of a some- what notorious prospector known as Chicken Bill, on what is now Chryso- lite ground. Chicken Bill, in his haste to realize, had not waited till his shaft reached rock in place, but had distributed at its bottom ore taken from a neighboring mine, or, in the language of the miners, he had ‘salted ” his claim. After the bargain with Tabor had been concluded he could not resist the temptation of relating to a few of his friends the part he had 14 GECLOGY AND MINING INDUSTRY OF LEADVILLE. played in the transaction. The report of what he had done thus reached the ears of Mr. Tabor’s Denver correspondents before he himself arrived to deliver the property, when they not unnaturally declined to receive it, and Mr. Tabor was obliged to keep it himself. He, with his associates, under the title of Tabor, Borden & Co., afterward bought some adjoining claims and developed their ground, from which they are said to have taken out in the neighborhood of $1,500,000, and afterward to have sold their prop- erty to the Chrysolite Company for a like sum. In the spring of 1877, under Mr. Meyer's direction, the first smelting furnace was erected at Leadville by the St. Louis Smelting and Refining Company, now known as the Harrison Reduction Works, and: others fol- lowed in rapid succession. Growth of the city—'The nucleus of the present city of Leadville consisted of a few log houses scattered along the borders of the California gulch below the Harrison Reduction Works. In the spring of 1877 a petition for a post-office was drawn up by Messrs. Henderson, Meyer, and Wood, which necessitated the adoption of a name for the new town. Mr. Meyer proposed the names of Cerussite and Agassiz, both of which were rejected as being too scientific. Mr. Wood proposed the name of Lead City, to which Henderson objected that it might be confounded with a town of the same name in the Black Hills, and the name of Leadville was finally adopted as a compromise. The rapidity of the growth of this city borders on the marvelous. In the fall of 1877 the population of Leadville was esti- mated at about two hundred persons. The business houses of the town were a 10 by 12 grocery and two saloons. In the spring of 1878 a corpo- ration was formed, which was continued for six weeks, when the town’s growth justified its transformation into a city of the second class, Mr. W. H. James being the first mayor and John W. Zollars city treasurer. Within two years Leadville grew to be the second city in the State, with 15,000 inhabitants and assessable property of from $8,000,000 to $30,000,000. In 1880 it had 28 miles of streets, which were in part lighted by gas at an expense of $5,000 per annum. It had water-works, to supply all the busi- ness portion of the city, having over five miles of pipe laid. It had 13 schools, presided over by 16 teachers, and an average attendance of 1,100 METALLIC PRODUCTS. 15 pupils; a high school, costing $50,000; five churches, costing from $3,000 to $40,000; and three hospitals, in one of which 3,000 patients were treated during the year. In 1880 $1,400,000 were expended in new buildings and improvements. It had 14 smelters, with an aggregate of 37 shaft-furnaces, of which 24 were in active operation during the census year, and its produc- ing mines may be roughly estimated at 30. Production.—'I‘he amount that is annually added to the metallic wealth of the world by the Leadville district, the productive area of whose deposits as at present opened may be estimated at about a square mile, is truly remarkable. Its annual silver product alone is greater than that given by official estimates for any of the silver-producing nations of the world out- side of the United States except Mexico. Its lead product, on the other hand, though frequently neglected in estimating the total value of its out- put, is nearly equal to that of all England, and, of other nations outside of the United States, it is only exceeded by that of Spain and Germany. In the magnitude of its product Leadville has been only surpassed in the United States by the famous Comstock lode in the Washoe district of Nevada, and the surprising rapidity of its development in the few years of its existence has been even more remarkable than that of the latter, which produced forty-eight millions of gold and silver during the five years suc- ceeding its discovery. The third district of comparable importance in the magnitude of its product from a comparatively restricted area is the Eureka district of Nevada, which, according to Mr. Curtis, has, in the first fourteen years of its existence, produced sixty millions of gold and silver and 225,000 tons of lead." Owing to the want of any general law compelling producers to fur- nish an exact and sworn statement of the amount of their annual product, it is impossible to obtain anything more than an approximate estimate of the metallic production of a mining district like Leadville. Such an esti- mate varies necessarily in the closeness of its approximation, with the care with which it is made, with the accuracy with which the records of indi- vidual mines and smelters have been kept, and with the readiness shown ‘ ‘J. S. Curtis, Silver-lead Deposits of Eureka. Washington, 1524. 16 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. under varying circumstances to furnish these records to those who may be gathering statistics. The most trustworthy estimates of production are those that were obtained for the year ending May 31, 1880, by those engaged in collecting statistics of the production of the precious metals for the Tenth Census. This is due to the fact that not only was the force of experts sufficient to visit personally all the important mines and smelting works, but the law gave them the authority to demand, if necessary, an accurate tran- script of their records, and the data thus gathered were subjected to a crit- ical analysis during compilation by those technically familiar with the various branches of mining industry. Moreover, it was a most favorable epoch in the development of the district for obtaining an accurate record, since the larger mines were being systematically worked, the record of their product was kept with relative accuracy, and as yet but little ore was shipped out of the district for reduction and thus rendered difficult to trace. . The Census figures of production for this period are as follows: Leadville products during census year, 1879-30. Contents. Gross weight. = AES ican | Gold. | Silver. Lead. } == - } | Tons. Kilos. | Ounces.| Kilns. | Ounces. | Kilos. | Ounces. | Kilos. | I. Ore extracted .......... 152, 241 ] 138, 110, 797 | 1, 716 53. 36 | 10, 603, 331 H 329, 763. 5 (Ne (hear sis: II. Ore smelted..........-. 140,623 | 127,571,118 |3,913.7| 121.81 | 9,717,819 | 302,224 | (2) | Emteseseose | III. Bullion produced by | 28, 283 | 25, 657, 921 | 3,830.2 119.11 | 8,053,946 | 250, 478 | 28, 226 | 25, 606, 212 Leadville smelters. | | In the above table, I gives the amount of ore extracted from the vari- ous mines during the year and the contents of the same in silver and gold, as determined by assay at the mines. II gives the amount of ore smelted during the year and its assay value in silver and gold, including that sent out of the district for reduction, as determined by the returns from smelters and sampling works. III gives the bullion produced during the census year by the smelt- ers situated at Leadville and its contents in lead, silver, and gold. METALLIC PRODUCTS. ilieh It thus appears that the Leadville ores contained during the year an average of 694 ounces of silver per ton, and that the bullion produced therefrom contained an average of 285 ounces of silver per ton. The apparent discrepancy in the amount of gold given under the various heads may arise in part from the fact that it is generally present in such minute quantities in the ore that the assayers at the mines do not always make an estimate of it, and in part from small lots of gold-bearing ore either from Leadville itself or from adjoining districts that have escaped notice in making up the returns from mines, or in segregating outside ore in returns from sampling works and smelters. It was not possible to obtain an accurate esti- mate of the average percentage of lead contained in all the ores extracted. It appears, however, from data obtained from the eight principal smelters running at that time that the average yield per ton of ores treated by them during the year was 398.8 pounds or 19.94 per cent. of lead bullion, con- taining 65.64 ounces or 0.225 per cent. of silver. The various newspapers of Leadville have published monthly state- ments of the bullion product of the district, upon which the annual official statements made by the Director of the Mint and other estimates of the product of the district have been based. These figures often bear internal evidence of incompleteness or inaccuracy, and from want of any evidence .of the relative care with which they have been made, it is difficult to know, in cases of discrepancy between them, which is the most trustworthy. Nevertheless, in the absence of any other complete data, these must be assumed as the nearest approximation available. The following table of the product of the district, since the discovery of silver-lead deposits, has been compiled from these sources, using mainly the figures of the Leadville Herald, which have been the most continuously collected and published. In the case of shipments of ore to be reduced outside the district, of which only the price received is in many instances given, the weight of the metals contained in these shipments has been _ assumed arbitrarily to average the same as those in which the relative weights are known, which evidently cannot give the exact amount in every case, but which would be probably as nearly correct as an arbitrary assumption of probable averages for each year. The value of the total MON X1II——2 15 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. product is calculated according to the mint valuation ($1.2929 per ounce of silver), which, as is well known, is in the case of silver considerably higher than the fluctuating market value, and increases the value given for the total product by about seven million dollars above that which would be obtained by using the market value, if it were possible to obtain it in each case. The price of lead is assumed at 45 cents a pound as an aver- / age for the whole period involved: Production of Leadville mines from 1°77 to 1874, inclusive. Gold. Silver. Lead. Value. 7 ‘ : iin i aay Ounces. | Kilograms. Ounces. | Kiloyrams. Tons. Kilograms. Dollars. Reduced at Leadville. ........ 77,197 2,401 42,089,722 1,308,990 203, §31 184, 912, 426 | 74, 358, 395 Shipped out of the district. -- 25, 825 803 9, 012, 644 280,293 102, 867 93, 319, 399 | 21, 506, 343 —— —— — ns otilSencss—-—= eee 103, 022 3,204 | 51,102,3C6 | 1,589,283 | 306,698 | 278, 231, 825 95, 864, 738 | In the time that has elapsed since the census year, although, owing partly to decline in value of the metals and partly to a lower average tenor of the ore, the total value of the annual product has decreased, the amount of ore extracted from the mines of the district has very considerably increased, this having been in the census year (1879-1880) 152,241 tons, and in the year 1884, according to the report of the Director of the Mint, 232,000 tons. CHAPTER II. GENERAL GEOLOGY OF THE MOSQUITO RANGE. ROCKY MOUNTAINS IN COLORADO. The simplest expression of the geological structure of the Rocky Mountains in Colorado is that of two approximately parallel uplifts or series of ridges of Archean rocks, upon whose flanks rest at varying angles a conformable series of sedimentary formations extending in age from the earliest Cambrian to the latest Cretaceous epochs, the latter being locally overlaid by unconformable Tertiary beds. The eastern uplift is generally known as the Colorado or Front Range and the western as the Park Range, the series of depressions or mountain valleys between them having received the name of parks. The most prominent fact thus far recognized in the geological history of this region is that a great physical break or non-conformity in the strata is found between the Cretaceous and Tertiary formations; in other words, that at this period occurred the great dynamic movement which uplifted the Rocky Mountain region essentially into its present position. As the beds of the Paleozoic and Mesozoic systems have been thus far found to be practically conformable throughout the region, it may be assumed that no important dynamic movement took place during these eras, and that deposition went on continuously, except when continental elevations of the whole region may have caused a temporary recession of the waters of the ocean for a limited period, and thus produced a gap or gaps in the geolog- ical series without causing any variation in angle of deposition in the at present successive beds. 19 20 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Eastern uplft— The Colorado or Front Range is the more extensive and more important of the two Archean uplifts, and along its eastern flanks is exposed, by the denudation of the overlying Tertiary formations, an almost continuous fringe of upturned Paleozoic and Mesozoic beds. The most significant geological fact to be observed in connection with these exposures of upturned beds is that the formation which is immediately adjacent to the Archean varies from place to place. At one point Triassic beds, sloping away at varying angles from the flanks of the mountain, rest directly upon the Archean beds; at another point the lower beds of the Cre- taceous; at still another, and this more rarely, the Carboniferous limestones are exposed resting against the Archean, while above them, always con- formable, are found the Triassic, Jurassic, and Cretaceous formations as one follows the section in an ascending geological sense. At one or two points only along the eastern flanks Silurian beds are exposed beneath the Carboniferous. It has been customary with many of the early geological explorers to consider the uplift of these mountain ranges to be that of a simple anti- clinal fold in the sedimentary strata, which once arched over the underlying nucleus of crystalline rocks; this was, once considered the typical structure of a mountain range. In practical field geology, however, it is found that the symmetrical form resulting from this typical structure of mountain range is one of the rarest occurrences, at least in the Rocky Mountain region. The one great instance of such a perfect anticlinal range is that ot the Uinta Mountains, which presents exceptional features distinguishing it from the majority of mountain ridges of the Rocky Mountain system; this has a peculiarly normal anticlinal structure in the first place, and in the second place its trend is east and west, whereas all the other great mount- ain ridges of the Cordilleran system have a direction varying between north and south and northwest and southeast. The facts just noticed with regard to the sedimentary beds which rest against the eastern flanks of the Rocky Mountains, it will be readily seen, exclude the possibility of the typical anticlinal structure above mentioned. If we suppose a conformable series of sedimentary beds to have been folded into a long anticlinal fold and the crest of this fold subsequently planed THE COLORADO RANGE. yl off by erosion, so that the core of the fold is exposed, the projection or hori- zontal section made thus by the planing off of its crest would necessarily show a continuous line of outcrops along either side of the axis of the fold, in which the lowest bed of the conformable series would invariably be seen at the contact of the underlying rocks which, when these beds were depos- ited, formed the floor of the then existing ocean. In other words, if the Rocky Mountain uplift were a typical anticlinal uplift, the sandstones of the Cambrian period, which are the lowest beds of the conformable series exposed, would be found continuously along the eastern flanks of the Rocky Mountains wherever erosion had swept away the obscuring Tertiaries so that the edges of the folded rocks could be seen. Since it is evident, then, that the entire series of these beds could not at any time have arched over the present Archean exposures, the alternative presents itself that these exposures represent an ancient continent or island along whose shores they were deposited, a hypothesis which is borne out by the lithological character of the beds themselves, which bear abundant internal evidence, in ripple-marks, in prevailing coarseness of sediment, and in the abundance of Archean pebbles in the coarser beds, that they are a shore-line deposit. The varying completeness in the series of sedimentary beds exposed at different points would in this case be explained by unequal local erosion or elevation, by which the contact, now of a lower, now of a higher horizon, with the original Archean cliff would be laid bare. Inasmuch as the same evidence of shore-line conditions is found wher- ever the sedimentary beds adjoining the larger masses of Archean have been carefully studied, and as, moreover, in no part of the higher regions of these Archean ridges have relics of sedimentary beds been found, not even of the later Tertiary formations, as would be expected had they originally arched over these ridges, it is evident that these Archean islands have never been entirely submerged since they first appeared above the ocean level. The Colorado Range formed the most extensive of these ancient land- masses, and its outlines probably did not vary essentially from those of the present Archean areas. Extending from Pike’s Peak northward to the bound- ary of the State, its dimensions were approximately one hundred and fifty miles in length by about thirty-five to forty miles in width. To the eastward 22 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. it presented a continuous and regular shore line, broken only by a single narrow bay, separating the Pike’s Peak mass from the mainland, and now known as Manitou Park. On the west, toward the parks, its original out- lines are as yet less certainly known, but though less regular they probably had a general parallelism with the eastern shore line. North and south this line of elevation was continued by a series of islands and submerged reefs to the Black Hills of Dakota on the one hand and into the present Ter- ritory of New Mexico on the other. : The Parks—That the present valleys, known respectively as the North, Middle, and South Parks, have been more or less submerged in Paleozoic and Mesozoic and again in Tertiary times, and that at one time they formed a connected series of bays or arms of the sea, is proved by the sediments of those eras that are still found in them. Although the geology of the park region has not been studied in sufficient detail to afford complete data in regard to its past history, enough is known to furnish its general outlines. In some respects the present conditions of these depressions are those that prevailed in the earliest Paleozoic times; in others they have expe- rienced more or less change. Then as now the outlet or opening of the North Park was toward the north, of the Middle Park toward the west, and of the South Park toward the south. On the other hand, up to the close of the Cretaceous the North and Middle Parks were connected and formed a single depression; the present mountain barrier between the Middle and South Parks did not extend as far as their western boundaries, and a water connection existed between them, whose outlines cannot now be given exactly, owing to faulting and subsequent denudation; again, the waters of the South Park extended westward to the flanks of the land mass now form- ° ing the Sawatch Range. It seems probable that in earlier Paleozoic times only the North and South Parks were sufliciently submerged to receive the sediments that were washed down from the neighboring land masses, but that, as time went on, the waters became deeper or the sea bottom subsided, so that in Cretaceous times sediments were deposited continuously through the three valleys. In Tertiary times again, after they had been raised above the ocean-level, fresh-water lakes occupied the parks, and in their basins THE MOSQUITO RANGE. 23 sedimentary beds were deposited, which have since been so extensively eroded off that the age or extent of these lakes cannot readily be determined. Western uplift—The western boundary of the park area consisted of two or. more distinct ridges or islands, forming, however, a general line of eleva- tion nearly parallel with that of the Colorado Range. These are the Park Range proper, on the west side of the North Park, and the Sawatch Range, now separated from the South Park by the Mosquito Range. Between these was the Archean mass of the Gore Mountains, which formed, with the southern extremity of the Park Range, the western wall of the Middle Park, of whose geological relations but little is definitely known. The present topographical boundary of the South Park on the west is the Mosquito Range, which has for this reason been also called the Park Range. Geologically, however, this name is less appropriate than topo- graphically, since prior to Cretaceous times no Mosquito Range existed, but the rocks which now form its crest still rested at the bottom of the sea. The Sawatch range forms the normal southern continuation of the Park Range as an original Archean land-mass; hence it seems advisable to avoid the use of the name Park Range in this latitude. The Archean land-mass of the Sawatch in Paleozoic times, judging from the almost continuous fringe of Cambrian beds encircling it, as shown on the Hayden maps, which may be assumed to represent a tolerable approxi- mation to its original outlines, was an elliptical-shaped area, trending a little west of north, with a length of about seventy-five miles and an extreme breadth of about twenty miles. Through the eastern portion of this area, and parallel with its longer axis, runs the valley of the Upper Arkansas River, now an important feature in the topography, but which during Paleozoic and Mesozoic times did not exist. The relative height of these mountain masses above the adjoining valleys must have been far greater then than now, since the sedimentary beds which surround them must have been formed out of the comminuted material abraded from their slopes. It is probable, however, that they were not the only land masses at that time, and future geological studies in this region will doubtless decipher many yet unopened pages in its past history. The great area of volcanic rocks to the southwest, whose 24 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. culminating points are the San Juan Mountains, may very likely conceal the remains of a former land mass of equal, if not greater, dimensions than this. The present Archean areas to the south, in the Wet Mountain and Sangre de Cristo Ranges, may also, in part at least, have been land masses at those times. Moreover, the not infrequent occurrence of Cretaceous beds lying directly upon the Archean at points far away from any well- defined ancient shore line, suggest elevations and subsidences of which the geological studies thus far made in Colorado furnish no record. The areas already mentioned were, however, the most important elevations, since they are the only ones of which it may now be said with tolerable certainty that they have been permanent land surfaces through the long cycles that have elapsed since the commencement of the Paleozoic era. Their considera- tion, therefore, is all that is necessary for the purposes of the present study. Mountain structure. —It is no longer assumed, as it was in the early days of geology, that the elevation of mountains is the result of a vertically acting force or a direct upthrust from below. On the contrary, the gen- erally received contraction theory, which is the one that best accords with all observed facts of geological structure, supposes that it is horizontally acting forces that have uplifted them. According to this theory, during the secular cooling of the earth from a molten mass, a solid crust was first formed on its exterior. As cooling and consequent contraction of the whole mass went on, this first-formed crust, in order to adapt itself to the reduced volume of its nucleus, also contracted; but, as it was more or less rigid, this contraction resulted in the formation of wrinkles or ridges on its surface, which there is considerable evidence to show occupied essentially the same lines that the present mountain systems of the world do. Whatever the determining cause that originally fixed these lines, the earth’s crust along them would have been compressed, plicated, and probably fractured, and, in subsequent dynamic movements resulting from continued contraction, they would have constituted lines of weakness along which the effects of these movements would have found most ready expression. Whether the consolidation of the entire earth-mass is already com- pleted, or whether there still remains a molten nucleus towards its centre, is a purely speculative question, upon which geologists are not yet in entire EO ROCKY MOUNTAIN STRUCTURE. 25 accord, and whose discussion would not be appropriate in a memoir like the present, which has to do with observed facts and with theories only so far as they are necessary for a proper comprehension of these facts. It is an observed fact that in the great mountain systems are found the most intense expression of the compression of the crust, in plications and in great faults. It is also an observed fact that along these lines of elevation and of consequent fracturing of the crust, have occurred the most extensive extrusions and intrusions of molten or eruptive rock, whatever may have been their souree—whether from a fluid center or from a fluid envelope between a solid center and a solidified crust, or from subterranean lakes of molten rock at different and varying points beneath the crust. It may likewise be considered a fact of observation that the tangential or horizontal thrust which the contraction theory requires most readily accounts for the plication and faulting of the sedimentary beds which geological study discloses. This thrust may be best conceived as the expression of two forces of compression: a major force acting at right angles to the longi- tudinal axis of the mountain system, or east and west, and a minor force acting in a direction parallel with that axis, or north and south. The geological structure of the Rocky Mountains forms as marked a contrast to that of the regions adjoining it on either side as do its topo- graphical features. On the Great Plains, which stretch in an almost unbroken slope from their eastern base to the Mississippi River, or, it might be said, to the western foot of the Appalachians, the strata which form the surface lie in broad undulations, whose angles of dip are so gentle as to be scarcely perceptible to the eye, and which are apparently broken by no important displacements. | In the Colorado Plateau region, which extends from their western edge to the base of the parallel line of uplift of the Wasatch, the beds seem as horizontal as when they were originally deposited, but along certain lines abrupt changes of level are brought about by sharp monoclinal folds, aecom- panied by or passing into faults, and having great longitudinal extent. In the intervening mountain region the strata are compressed against the original land masses and flexed until the limit. of tension is reached, when by great displacements, often measured by thousands of feet, their 26 YEOLOGY AND MINING INDUSTRY OF LEADVILUE. edges are pushed past and over each other, the movement of both folds and faults showing that the force which produced them was acting from either side toward the center of the original land masses. As contrasted with the Basin region west of the Wasatch uplift, the folds of the Rocky Mountains show a greater plasticity in the sedimentary strata by their relative sharpness, the anticlines and synclines in the former having more gentle and equal slopes, while in the latter they often have the form of an S, with one member almost bent under the other into an isocline. Compared with the remarkably compressed folds of the Appalachians, on the other hand, where tie isocline may be considered the type structure, the flexures of the Rocky Mountains show that the sedimentary rocks are far from possessing the great plasticity and compressibility that they have in the former. The contrast between the eastern and western mountain systems, in respect to the relative plasticity of their strata, is so marked that it would seem that the reason therefor must be readily apparent. It is not that the beds in the former are thinner; on the contrary, the corresponding Paleozoic formations are many times thicker in the Appalachians than in the Rocky Mountains. It is to be remarked, however, that in the former eruptive rocks are com. paratively rare, especially those of Mesozoic and Tertiary age, while in the Rocky Mountains they are most abundant and in the western part of the Basin region they form the greater part of the surface; to this fact may probably be ascribed, as will be shown later, the less plastic condition of the earth’s crust in the latter regions. In the character of these eruptive rocks, again, there is a marked con- trast between the Rocky Mountains and the Basin region of Nevada. In the latter they almost exclusively belong to the Tertiary volcanics, approach- ing in character the lavas of modern voleanoes, the older and more crystal- line varieties, corresponding to the Mesozoic porphyries of Europe, having been rarely observed on the surface. In the Rocky Mountain region, on the other hand, while the Tertiary eruptive rocks are often developed on a very large scale, the earlier and more crystalline varieties seem to have an equal and even greater importance, if not in the actual amount of surtace —— THE MOSQUITO RANGE. 27 they occupy, certainly in the influence which they have had upon the con- centration of mineral formation. In that portion of the Rocky Mountain region under consideration there isa noticeable connection between the structural lines and those along which eruptive action has been most active. The latter correspond with the lines of weakness, of greatest folding and faulting. Leaving out of consideration the dikes which traverse the Archean rocks, which, though numerous, are of relatively small mass, the eastern uplift gives evidence of little eruptive activity, it being shown only by a few isolated outflows of Tertiary lavas. Along the line of the parks, on the other hand, both earlier and later erup- tions are so frequent that their outcrops form an almost continuous line from north to south parallel with the western uplift, while along the west base of the latter the Elk Mountains, the head of White River, and the Elk Head Mountains in Wyoming have apparently been the scenes of most violent and repeated eruptions during both Mesozoic and Tertiary times. MOSQUITO RANGE. Topography.— That portion of the Mosquito Range the study of whose geological structure was considered necessary for a proper comprehension of the ore deposits of Leadville is shown in relief on Atlas Sheet V. It comprises a length of 19 miles along the crest of the range, and in width includes its foot-hills, bordering the Arkansas Valley on the west and South Park on the east, a slope in the one case of seven and one-half miles and in the other of about nine miles in a direct line. This is essentially an alpine region, scarcely a point within the area of the map being less than 10,000 feet above sea level. In this area the range has a sharp single crest trending almost due north and south, the échelon structure being, however, developed on the northern and southern limits of the map respectively. To the west this crest presents abrupt escarpments, descending precipitously into the great glacial amphitheaters which exist at the head of almost all the larger streams flowing from the range. The spurs have extremely irregular, jagged out- lines, resulting from the numerous minor hills which rise above the average slope. Within a few miles of the valley bottom, however, their form sud- 28 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. denly changes, and from sharp serrated ridges they become broad, gently sloping mesas or table-lands. On the eastern side, though the descent into the glacial amphitheaters is almost as precipitous, the average slope is much less steep, and the spurs as a rule descend in long sweeping curves, widen- ing out gradually as they approach the valley. - The spurs on either side of the range are thickly covered with a forest erowth of alpine character, reaching from the valleys of the streams up to an average altitude of 11,700 feet, the upper limit varying somewhat with the more or less favorable conditions of the surface, and extending appar- ently somewhat higher on the western than on the eastern slopes. In the northern portion of this area, between the heads of the Arkan- sas and Platte Rivers, the main crest of the range, which has hitherto fol- lowed an almost straight line, takes a bend en échelon, and is continued on a line removed about two miles to the eastward, resuming, however, its orig- inal line just beyond the limits of the map. The massive formed by the three peaks, Mounts‘Cameron, Bross, and Lincoln, the last the highest point within the area mapped, lies still to the eastward of this crest and is topo- graphically an almost independent uplift. Sheep Mountain and the ridge which extends southeastward from it also form an apparently abnormal feature in the topography of the eastern slope. The sketch given in Plate III shows the general outlines of the eastern slopes of the Mosquito Range and the basin of the South Park, as seen from a western spur of Mount Silverheels. The sky-line of the western half is the crest of that portion of the range included inthe map which lies south of Mosquito Peak, the low gap is that of Weston’s pass, beyond which is the Buffalo Peaks group. The various gulches south of the Mount Lin- coln massive are indicated by name, and the lines of outcrop on their walls are somewhat strengthened to show the geological structure, which will be explained in detail in Chapter IV. Buffalo Peaks are 25 miles distant from the point of view, and the volcanic hill in the extreme left- hand corner of the sketch, seen across the South Park plain, is over 40 miles distant. The little hill on the edge of the plain, and on a line with the eastern spur of Buffalo Peaks, which forms the continuation of the Sheep Mountain ridge, is Black Hill, which lies just beyond the extreme Oe en eee = , T | i : t U.S .GEOLOGICAL SURVEY : = i . : ' ' ‘ | ~ } - South Park. F Buffalo Peaks. : i % ’ ee si aa. cas iii tc i wr wm We ita re Julius Bien & Co.lith. SOUTH PARK AND EASTER = GEOLOGY OF LEADVILLE, PL, Ml ~ | White Ridge. Gemini Peaks, Dyer Mt. \ i : | v + + a & te —— = A x Platte Valley BZ S.F. Emmons, Geologist-in- Charge. Buffalo Peaks. 7 agin White Ridge dexsittice a \ \ ~ . AN YY \ : WA Platte Valley MOSQuT Ty ) qi INTERDEPENDENCE OF TOPOGRAPHY AND GEOLOGY. 29 southeast corner of the Mosquito map. The base of this hill is 10,000 feet above the level of the sea. It were scarcely possible to select an alpine region more admirably adapted to illustrate the interdependence of topographical and geological structure than that chosen for this study. The gentle slopes of the eastern spurs follow the inclination of the easterly dipping beds of Paleozoic rocks which form their surface, and which remain in broad sheets, like the covering of aroof, to protect the underlying Archean schists from erosion. Where they have been cut through, first by the erosive action of glaciers and later by the corrasive action of mountain streams, to their stratified structure is due the formation of the almost perpendicular cliffs which form the canon wails of their streams. The generally abrupt slope immediately west of the crest is due toa great fault extending along its foot, in virtue of whose movement the western continuation of the sedimentary beds, which slope up the eastern spurs and cap the crest itself, are found at a very much lower elevation on the western spurs; while the jagged outline of the western spurs is due to a series of minor faults and folds, crossing them nearly at right angles. The secondary uplift of the Sheep Mountain ridge on the eastern slopes is the expression of a second great line of fault and flexure, whose direction, like that of the ridge itself, forms an acute angle with that of the main crest. The elevation of the Mount Lincoln massive is the result of a combination of the forces which have uplifted the Mosquite Range and of those which have built up the transverse ridge which sepa- rates the South from the Middle Park. In the later topography of the range the results of the action of a system of enormous glaciers are seen in the immense amphitheaters which form the heads of its main streams, and in the characteristic V-shaped transverse outlines of the valleys descending from them. Finally, the mesa- like character of the lower end of the western spurs toward the Arkansas Valley is due to the existence beneath their surface of comparatively undis- turbed beds deposited at the bottom of a lake formed at the head of that valley by the melting of the ice at the close of the first portion of the Glacial period. 50 GEOLUCGY AND MINING INDUSTRY OF LEADVILLE. The evidence furnished by the deposits of this lake affords an interest- ing confirmation of the deduction already made by geologists from the study of the glacial drift in Europe and in the Eastern States, and by Messrs. King and Gilbert from their study of the lake deposits of the Basin regions of Utah and Nevada; namely, that the Glacial period presented two maxima of cold, with an intervening warmer period during which the ice was partially melted and vegetation flourished. The general character of the stratified deposits of the Arkansas Lake shows that they must have been carried down during a time of great floods and that they are formed largely of rearranged moraine material. The thickness of these deposits proves the the existence during a long period of a lake which during part of the year was not frozen; their position shows that the shores of the lake extended several miles to the eastward of the Arkansas Valley. . Finally, the facts that these beds are deeply buried beneath surface accumulation of detrital material and that the moraines of now extinct glaciers extend out beyond the original shore-line of the lake and rest above its beds, prove that subse- quent to the draining of the lake another set of glaciers, formed during a later period of cold, covered the slopes of these mountains and carved out to a greater depth the present valleys. Geological history— Although now so prominent a feature in the topogra- phy of the Rocky Mountains, the Mosquito Range, from the sources of the Arkansas River to the southern end of the main Arkansas Valley, is geolog- ically a part of the Sawatch uplift. It was from the abrasion of the land surfaces exposed in the Archean island which occupied the present position of the Sawatch range that the sediments which constitute its stratified beds were doubtless in a great measure formed. In the seas that surrounded this island during Paleozoic and Mesozoic times was deposited a conformable and, as far as present evidence shows, an almost continuous series of coarse sandstones and conglomerates, alternating with dolomitic limestones and calcareous and argillaceous shales. The geology of the Rocky Mountains has not yet been studied in detail over a sufficiently extended area to afford data for tracing the history of the elevations and subsidences to which tke region asa whole may have been subjected, or of the alternate recessions and advances of ocean waters during this long lapse of time. The examination AGE OF UPLIFT. Bi of these beds made during the present investigation furnishes some evidence of a shallowing of these seas, and perhaps even of the existence of some land surfaces subjected to erosion during part of this time. Still, the absence of non-conformity in the successive strata deposited and their great uni- formity throughout the area studied show that no violent dynamic move- ment took place before the great disturbance at the close of the Cretaceous, which extended throughout the whole of the Rocky Mountain system and was doubtless the main factor in producing its present elevation. During this long period of conformable deposition there was an accu- mulation in this area of 10,000 to 12,000 feet of sedimentary beds. Toward the latter part of this period, possibly very near its close, there was an exhi- bition of intense eruptive activity, during which enormous masses of molten rock were intruded through the underlying Archean floor into the overly- ing sedimentary deposits, crossing the beds to greater or less elevations and then spreading out in immense sheets along the planes of division between the different strata. It is not possible at present to define all the points at which these eruptive masses forced their way up, although they were doubtless very numerous and widely spread throughout the region; but the negative evidence obtained proves that the intrusive force must have been almost inconceivably great, since comparatively thin sheets of molten rock were forced continuously for distances of many miles between the sedimentary beds. That the eruptions were intermittent and continued during a considerable lapse of time is proved by the great variety of erup- tive rocks now found and by the fact that a given rock in one place pre- cedes and in another follows a second. It might naturally be thought that this eruptive activity must have been coincident with or immediately sub- sequent to a great dynamic movement; but that it preceded the movement at the close of the Cretaceous, which caused the uplift of the Mosquito Range as well as of the other Rocky Mountain Ranges, is proved by the fact that these interbedded sheets of eruptive rocks, porphyries and porphy- rites, are found practically conformable with their bounding strata, and, like them, folded into sharp folds and cut off by faults. The intrusion between the strata of such vast masses of rock—which in some cases reached a thickness of from 1,000 feet to 2,000 feet, and of which in other cases suc- 32 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. cessive beds varying from 50 feet to 200 feet in thickness are now found intercalated between alternate strata to the number of 15 or 20 in a single section—must necessarily have produced great irregularities in the once level surface of the then existing crust; but these irregularities were largely obliterated by the dynamic movements which followed, and the only traces still remaining are variations in the strike of the inclosing beds, which show a tendency to curve around any concentration of eruptive masses. At some time during the long period which intervened between the final deposition of the latest sediments of the Cretaceous epoch and the succeeding deposition of Tertiary strata, and during which the waters of the ocean gradually receded from the Rocky Mountain region, the pent-up energy of the force of contraction of the earth’s crust, which had accumu- lated during ages of comparative geological tranquillity, found expression in intense and prolonged dynamic movements of the rocky strata forming the immediate crust of the earth in this region. These dynamic movements in their simplest form may be conceived as a pushing together from the east and from the west of the more recent stratified rocks against the relatively rigid mass of the already existing Archean land masses, and a consequent folding or crumpling of the beds in the vicinity of, the shore-lines, where, owing to the break in the continuity of the strata and the more irregular character of the floor upon which they rested, the conditions were more favorable to the crumpling movement than they would be, for instance, in the open plains, where a great thickness of level and hitherto undisturbed beds offers no lines of weakness to favor a commencement of folding. It is here a question only of the movement of the distinctly stratified beds, because it is in these alone that the resulting flexures can be accurately studied and mapped out; but it is evident that the crystalline and already violently contorted beds which formed the Archean land masses must have also partaken in the resulting movements, and their axial regions have been lifted up toa great elevation, of which the present height of the culminating peaks of the Rocky Mountains, formed as they are in the majority of cases exclusively of Archean rocks, is only a very much modified expressioa. Contemporaneously with the east and west movements (the expression of the major force of contraction in this region), there acted also a minor force MINERAL DEPOSITION. 33 of contraction in a north and south direction, whose effects can now be seen along the eastern foot-hills in gentle lateral folds, their axes approximately at right angles to the trend of the range, and whose presence is indicated by a sudden bend or curve in the line of sedimentary outcrop, where at one point, owing to a local synelinal, the beds have been more or less preserved from erosion, and again where, owing to the crossing or coincidence of crests of the folds, like those of waves crossing each other, is found an otherwise unexplainable steepening in the dip of the strata. It must be borne in mind that, while this great dynamic movement is defined as occupying a certain lapse of geological time and its principal effects were brought about within that time, it is not to be regarded as a sudden convulsion, like that of an earthquake, though such disturbances may have occasionally occurred. On the contrary, it must be conceived to have been rather a slow and gradual movement, extending over a period of time of which human experience can form no adequate conception. Moreover, as will be shown in the detailed study of the region, it can be proved that in a modified degree this movement has been continued into so recent a period as that following the Glacial epoch, and may very probably be going on at the present day, although, owing to the great area involved, it has been impossible to obtain any demonstrable proof of its actual exist- ence. Mineral deposition — Jt was during the period which intervened between the intrusion of the eruptive rocks and the dynamic movements which uplifted the Mosquito Range that the original deposition of metallic minerals in the Leadville region took place. These original deposits were probably in the form of metallic sulphides, though as now found they are largely oxidized compounds, and therefore the result of a secondary chemical action; although during this secondary action they may have been to a slight degree removed from their original position, their relation as a whole to the inclosing rocks must remain essentially the same. heir manner of occurrence and the probability that they were derived, in great part at least, from the eruptive rocks themselves prove that they must be of later formation than the latter, while the fact that they have been folded and faulted together with the inclosing rocks, both eruptive and sedimentary, shows that they must have MON XII——3 34 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. been formed prior to the dynamic movements, and that they are therefore older than the Mosquito Range itself. These deposits were formed by the action of percolating waters, which, having taken up certain ore materials in their passage through neighboring rocks, deposited them in a more con- centrated form in their present position. This process may have taken place while the sedimentary beds were still covered by the waters of the ocean, and the waters therefore have been derived from it; whether this was actu- ally the case or not cannot be known until the age of the eruptive rocks is more exactly determined. However, as it is already known by the estua- rine character of its fauna that the latest Cretaceous formation must have been deposited in an already shallowing ocean, it seems probable that the area occupied by the Mosquito Range may have already emerged from the ocean at this time. Structural results of the dynamic movements.— Before proceeding to a detailed geological description of the region included in the Mosquito map (Atlas Sheets VI and VII), which represents the results of the dynamic movements and of subsequent erosion, it may be well to give a brief summary thereof, thus reversing the natural order, for the benefit of those readers who may not have time or inclination to follow all the details of Chapter IV. The average or major strike of the sedimentary beds and of the axes of the principal folds is northwest magnetic, or N. 30° W., but in some cases a strike due north and south is observed. In these two directions are seen the influence of the shore lines of the Sawatch island, against which the sedimentary strata were compressed; for, while this area lies mainly along the eastern shore line which has a north and south direction, in the north- ern part the beds had already commenced to sweep round to the westward along the northern shore line of the island. To the south of this area the crest of the Mosquito Range itself marks the eastern limit of Paleozoic beds, while from South Peak, near Weston’s pass, northward this limit bends to the northwest toward the mouth of the east fork of the Arkansas. Beyond this line to the west everything is Archean; to the east of it Archean exposures are found only where denudation has removed their previous cov- ering of Paleozoic and later beds; it may be assumed, therefore, to repre- sent approximately the original shore line of the Paleozoic ocean. RESULTS OF DYNAMIC MOVEMENTS. 30 The uplift of the Mosquito Range was not the simple pushing up of the beds into a monoclinal fold, as might appear at first glance from the seem- ingly regular dip of the beds from the crest down it» eastern slopes, but a somewhat irregular plication of them into anticlinal and synclinal folds, and their fracturing by faults, which have the same general direction as the axes of the folds without coinciding exactly with them, and which often pass into folds at their extremities. The anticlinal folds have as a rule a very steep inclination, sometimes nearly vertical, on the west side of the axis and a more gentle slope to the east, thus approaching the form of the isocline. It is along this steeper slope that the fracturing has generally taken place, and the fault may thus follow the axis of a syncline or of an anticline, according as it runs to the one side or the other of this steep slope. The north and south direction of the main crest of the range is evi- dently determined by the great Mosquito fault, which, starting at some as yet unknown distance beyond the northern boundary of the map, follows the foot of the steep slope west of the crest to the region of the Leadville map, where for a short distance it bends somewhat further to the westward and is thence continued southward in the Weston fault, which passes into a synclinal fold south of Weston’s pass. From the Mosquito fault just north of Mosquito Peak branches off the next most important fracture plane, the London fault, which runs in a south- easterly direction across the eastern spurs of the range. The line of this fault passes just east of the axis of a most pronounced anticlinal fold across London Mountain and Pennsylvania hill to Sheep Mountain, on the sides of which the folding can be most distinctly traced along the canon walls. To the south of Sheep Mountain it apparently coincides with the axis of the anticlinal fold which forms Sheep ridge, and with it gradually dies out and passes under the level plain of the South Park. The geological structure of the Mosquito Range is simplest toward the south and becomes more complicated as one goes north, reaching the ex- treme of complexity opposite Leadville. Near Buffalo Peaks, a few miles beyond the southern limits of the map, it seems to be a simple monoclinal fold, the western slopes being entirely of Archean granite, and the crest 36 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. formed by Cambrian quartzites dipping gently eastward and resting uncon- formably on the Archean. At the southern edge of the map an anticlinal and synclinal fold comes in to the east of the monocline. Here the range has a double crest en éche- lon, divided by the longitudinal valley of Weston’s pass, which runs north- west magnetic following the direction of the strike. The ridge of South Peak to the west of the pass is formed by a monocline of easterly-dipping Cam- brian and Silurian beds. The valley of the pass itself is formed by a com- pressed synclinal fold in Carboniferous strata, along the eastern side of which runs the Weston fault, bringing up the Archean and Cambrian on its east side. The ridge bounding the valley on the east, which is the south- ern end of the main crest of the Mosquito Range, is an eroded anticlinal fold, from whose crest the overlying Paleozoic strata have been almost en- tirely removed, leaving the core of Archean exposed. On the very sum- mit of Weston’s Peak a small patch of Cambrian quartzites is left, a remnant of the crest of this fold, and at its western base the same beds are found in a vertical position adjoining the fault, while on the more gentle slopes of the eastern spurs are found the regular succession of easterly-dipping Pale- ozoic beds belonging to the eastern member of the anticline. The ridge sinks to the southward, and over its southern end the arch of Paleozoic beds is still left entire, but the anticlinal fold also sinks to the southward and entirely disappears beyond the limits of the map. The same general structure continues northward as far as Empire Hill, but a short distance from the southern edge of the map a second anticlinal fold, that of Sheep Ridge, comes in at the extremity of the eastern slope of the range, while from its steep western slope erosion has removed all trace of the synclinal fold seen on Weston’s pass, leaving only the easterly-dip- ping Paleozoic beds belonging to the monocline on the west of the fault, and the Archean on its east side; the crest of the range is formed of east- erly-dipping Paleozoie beds, or, where these have been eroded away, by Archean schists and granite. This double anticlinal structure is best shown in Section G (Atlas Sheet IX), which is drawn at right angles to the strike, and in which the supposed form of the eroded synclinal is shown by dotted lines. The line of this section also crosses two secondary anticlinals or -— 2. o~w es + RESULTS OF DYNAMIC MOVEMENTS. 37 minor waves in the strata, which are the almost invariable accompaniments of the larger folds. In this southern area the older eruptive rocks are but little developed, their only representative being a thin but persistent sheet of White Por- phyry above the Blue limestone. This increases in thickness from about fifty feet at Weston’s pass to over a thousand feet at its supposed source in White Ridge, on the north side of Horseshoe gulch. In the middle region of the area mapped, through an east and west zone which includes the principal mines of Leadville and vicinity, the de- velopment of bodies of earlier eruptive rocks is so great that the structure of the sedimentary beds is obscured and not always easy to trace. On the eastern slopes the double anticlinal structure continues as far north as Mos- quito Peak, at the head of Mosquito gulch. The great Sheep Mountain fold, with the London fault cutting through its steeper western side, gradually converges toward the crest of the range. Views of the sections of this fault-fold afforded by the canons of Horseshoe and Big Sacramento gulches are seen in Plates XV, XVI, and XVIII. East of this fold the strata slope gently eastward, with a slight secondary fold traceable along the extreme foot-hills. Between the Sheep Mountain fold and the crest of the range the strata of the gradually narrowing syncline are cut across by the two great eruptive bodies of White Porphyry and of Sacramento Por: phyry, in White Ridge and Gemini Peaks, respectively, which are accom- panied by a slight displacement. The nearly horizontal Paleozoic beds forming the crest and eastern member of the main anticline extend some- what to the west of the topographical summit of the range, but the western member of the anticline and the succeeding syncline (if it extended so far north) are either removed by erosion or buried beneath sheets of porphyry, On the western slopes in this zone the sedimentary strata, now greatly augmented in thickness by interstratified sheets of porphyry and extend- ing nearly to the valley of the Arkansas, are flexed into a number of minor folds and broken by many shorter faults, most of which pass at either end into anticlinal or synelinal folds. This is the area which is included in the detail map of Leadville and vicinity and which is described at length in Chapter V. It is traversed by seventeen larger and smaller faults and has 38 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. many aovticlinals and synclinals, in which the prevailing dip of the beds is to the eastward and the throw of the faults is mainly an uplift to the east. The area west of the Mosquito fault and north of the Leadville region is mainly occupied by beds of the middle member of the Carboniferous and by porphyry sheets, flexed into gentle folds of varying directions, but appar- ently not broken by faults, This region is already at some distance from the ancient shore line, which is marked by the outcrops of Cambrian and Silurian beds. These bend to the westward around the head of ‘Tennessee Park, and reach well up on the north slopes of the Sawatch in the Eagle River region; but, while the sedimentary beds bend thus in eeneral strike to the westward, the Mosquito fault and the crest of the range which has been uplifted by its movement continue on unchanged in their trend. North of Mosquito Peak is a large area in the higher part of the range, including the splendid amphitheaters in which the Platte and Arkansas Rivers rise, where the overlying Paleozoic beds have been entirely removed and only Archean exposures, traversed by dikes of earlier eruptive rocks, now remain. Kast of this area the flanks of Loveland hill and the massive of Mounts Bross and Lincoln are occupied by easterly dipping Paleozoie beds, which evidently are the eastern member of a broad anticlinal fold; but of the actual structure of the beds which once arched over the Archean area there is nothing left to tell. It is probable that there were folds here simi- lar and more or less parallel to the Sheep Mountain fold, as has been indi- cated in a general way by the dotted lines in the sections which cross this region. : ~ E y Pes Tp 7 ; a 7 IVY aTAJG Sasivanas 70 YOS1OSD ie «& i i rca Setar peverea NE tet ANS Bea Re irs BLUE LIMESTONE. 65 The following complete analyses of typical specimens, taken from local- ities at considerable distances from each other in the vicinity of Leadville, are further proofs of the uniformity of composition. I, II, and III are from the upper of the Blue Limestone, IV from near its base, and V from the upper part of the White Limestone. i | II. I. Iv. We = } Hooalltyeekrc east Ne ote ee Se nee | Dagen quarry.) aes Lenders: | Montgomeny:) Carbonate bill | Chamistessceseee ea sane eae sere ecee (Hillebrand.) | (Guyard.) (Guyard.) (Guyard.) - (Hillebrand.) | | Mime@esssse==ss—n- 30.79 | 30. 43 29. 97 27. 26 26. 60 Magnesia ........- 21.14 20. 78 21. 52 20.05 | 17.41 Carbonic acid ..... 46.84 | 46. 93 47.39 43.79 40. 01 Protoxideiofiron.-ce.-----=-<=-i--55.- 0. 24 0. 38 0.13 0.57 | 0. 83 Peroxide ofirons2 was soe .vss0- 50-2522 0.21 0.11 0.22 0.10 | 1.51 Protoxide of manganese .-....-.--.----- Trace 0. 05 0. 20 Os, eee Scegacoas Alumina .......... notnSodosanscseceese 0. 27 0.17 0. 04 0.11 1. 66 Blt dete ee eect saree ine cae oseise nea 0. 21 0.70 0. 27 7.76 11. 84 Chioring(s sss so. ssessccecoe secesntesecs | 0. 10 0.143 0. 041 0. 062 0.05 (ROtARN eae etiae costs etcceaene insects 0. 03 0, 046 0. 013 0.017 0. 017 SOU Phin S SQ oC ROOD SEE CICA mae SoS CEE EEE 0. 062 0. 094 0. 016 0. 037 0. 029 Sulphuric: teid) seo e.rs-caaseaececece= = SETACCM Rowamstecoeceasne|Soonccsneseese =: Tracel*||-scon-eeetewse Phosphoric acid.-.......-.....---...-.- Trace 0. 12 0. 03 0 07 Trace Sniphidorofironeec. <7 2-2 scc sciences -c- Trace ER rACOUn =a cacisaseae- = FRPACE) || zoo tenses ese=e Organic matter. ..............-..--..--- | 0. 03 0. 025 0.015 O07 ||ceosse-ceisece Winters nrc te Soares heaven 0.22 0. 04 0.07 0.05 0.48 | Wotdlesse ances acisccates see eee 100. 142 100.018 | 99. 925 100. 006 100. 436 The coloring matter is in part evidently organic, but in part, as sug- gested by Mr. Guyard, may be due to the presence of salts of iron. He says that he finds an appreciable amount of sulphide of this metal which will produce a black color. A remarkable feature in this analysis, as well as in that of the White Limestone, is the presence of appreciable quantities of alkaline chlorides. Microscopical examination under very high power (1,136 diameters) shows that the dusty appearance is due to minute specks in the grains composing the rock, which are fluid inclusions, in some of which the rapid movement of a bubble is visible. As will be shown later, it seems fair to assume that the included liquid consists of alkaline chloride. The microscope also shows that the rock is very finely granular, the size of the grains varying from .05 to.10 of a millimeter in diameter. No twin crystals of calcite are observed, and very little quartz or ore particles could be detected. MON XlII——5 66 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. The characteristics which may serve in the field to distinguish the rock of the Blue from that of the White Limestone are as follows: 1. Color, which is darker. 2. Composition, the former being almost free from silica, the latter con- taining 10 per cent. and upwards. 3. Texture, the former being generally crystalline, while the latter is more compact. 4. Chert secretions, which in the former are always black and in the latter nearly white. 5. Structure, the Blue Limestone being generally more heavily bedded than the White. Fossils. —The only fossils obtained from this horizon were found in the extreme upper part of the formation, either in the limestone itself or in chert nodules, which are found scattered over its weathered surface. The following forms were obtained from five different localities : Euomphalus, closely resembling 2. Spergenensis, Wall, from Warsaw limestones of Spergen hill. Spiriferina, which is probably new, though somewhat resembling S. Kentuckensis. Athyris subtilita. Pleurophorus oblongus. Productus costatus. Spirifera (Martinia) lineata. Spirifera Rockymontana. Streptorhynchus crassus (crenistria). Cyathophylloid corals, resembling Zaphrentis. or Cyathaxonia cynodon. While most of these forms are common to the Coal Measures of the East, the first-mentioned is there found in the Lower Carboniferous. For this reason and because this form and the Spiriferina do not oceur in any of the higher beds, it seems justifiable to assume that this horizon represents the Lower Carboniferous of this district. The upper limit of this formation has been fixed at the top of the massive Blue Limestone, which is generally marked by the frequency of chert concretions, and in the mining districts has been followed by prefer- ence by the ore-bearing solutions. Locally, however, limestone formation seems to have continued somewhat intermittingly for some distance above this horizon. WEBER SHALES. 67 Weber Shales. —On the general map of the Mosquito Range, owing to its small scale, it was considered advisable to make no subdivisions of the Weber Grits formation, and the whole is therefore included under one color (g). On the more detailed maps, however, a subdivision of the Weber Grits, designated the Weber Shales, has been distinguished by a distinct color (/). The beds included under this name are extremely variable in lithological character and in thickness. They constitute a transition series between the massive limestones below and the characteristic coarse sandstones of the Weber Grits above. They consist of argillaceous and calcareous shales alternating with quartzitic sandstones. The former are generally carbona- ceous, and in their extreme type pass into an impure anthracite. The eal- careous shales, on the other hand, are locally developed into a considerable thickness of impure limestone, which is very rich in fossil remains. Owing to its variable character and to the fact that the dividing plane between this and the preceding is frequently occupied by beds of porphyry, it is difficult to assign a definite thickness to the formation. It may, however, be assumed as varying from 150 to 300 feet. ; i In Leadville itself a thin bed of quartzite is often found immediately above the Blue Limestone, and on Iron hill is a greenish argillaceous shale, called the Lingula shale, from the abundant casts of this fossil which it contains. The coal development attains a thickness in one case of seven feet, but is extremely impure and gives little promise of any economical value. Fossils. —The most common form is Lingula mytiloides, Meek, which is supposed to correspond to L. ovalis, Sowerby. Besides these were obtained from several different localities the following : Phillipsia, sp.? (P. major ?) Discina nitida. Productus cora. Macrocheilus ventricosus. Productus semireticulatus. Archeoccidaris. Productus pertenuis. EKoccidaris Halliana. Productus muricatus. Fenestella perelegans. Productus Nebrascensis. Ethombopora lepidodendroides. Spirifera cameratus. Myalina perattenuata. Aviculopecten rectilaterarius. Polyphemopsis, (like P. chrysalis), Orthis carbonarius. Pinna, sp.? Streptorhynchus crassus (crenistria). Polypora, sp. undet. Chonetes granulifera. Paleschara, sp. undet. 68 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Weber Grits —This formation, which, as its name implies, consists mainly of coarse sandstones passing into conglomerates, has an estimated aggregate thickness of 2,500 feet, although neither its upper nor its lower limits can in the nature of things be very sharply defined. The typical rock, which often forms massive beds of considerable thick- ness and constitutes a prominent feature in the sections afforded by canons, is a coarse white sandstone passing into a conglomerate, made up of well- rounded grains and pebbles, mainly of white and sometimes of pinkish quartz. In the coarser conglomerates feldspar can often be distinguished in fragments, and this mineral is often disseminated in fine grains throughout the sandstone, but fragments of recognizable Archean schists are not often seen. It would seem, therefore, that these beds are mainly formed by the abrasion of the coarser granites of the Archean. The sandstones often contain a considerable admixture of brilliant white mica, and in some cases, besides the mica, so large a quantity of carbonaceous material as to become quite black. This carbonaceous material, which is insoluble in ether, alcohol, or sulphide of carbon, is probably either graphite or anthracite. Next to the sandstones and conglomerates, the most important constitu- ents of the formation are quartzose shales and mica schists, generally coarse- grained and of a greenish hue. Their lamination is very regular and often parallel to the bedding-planes, so that they often weather out in slabs or flags of considerable size. The mica, which, as in the sandstones, is mostly potash mica or muscovite, seems to form but a subordinate part of the rock mass, but is generally very prominent in large brilliant flakes on the surfaces of the lamine. Microscopical examination shows that in the sandstones and schists feldspar is always present with the quartz, and in some cases the three varieties, orthoclase, plagioclase, and microcline, can be distinguished. It also shows that the muscovite is, in part at least, derived from the decom- position of the feldspars; at the same time the uniform occurrence of large brilliant flakes along the bedding-planes of the shaly material suggests the possibility that these may have been directly derived from débris of the Archean and have been deposited in this position by the action of water. At irregular intervals throughout the formation are found beds of fine UPPER COAL MEASURHS. 69 black mud-shales or carbonaceous argillites, generally very thin and some- times calcareous, passing into impure limestones. About the middle of the formation is a tolerably persistent develop- ment of limestone of the usual blue-gray color and dolomitic in composi- tion. Its thickness, however, varies very much according to locality. It was best observed in Big Sacramento gulch, a short distance above the Lon- don fault, where are- two beds of limestone with associated shales, about fifty feet apart and each about ten feet in thickness. Fossils —F rom the limestones in Big Sacramento gulch were obtained the following forms: Spiriferina Kentuckensis. Productus muricatus. Athyris subtilita. Aviculopecten interlineatus. Productus costatus. Meekella striccostata. From micaceous schists in the upper part of the formation between Lamb and Sheep Mountains were obtained abundant casts of Hquisetacece. Upper Coal Measures (h).— Less favorable opportunities were offered for studying this group than for either of the preceding, since its beds were found only at the extreme limits of the map and in regions where continu- ous outcrops are rare. It consists of alternating calcareous and silicious beds, tLe latter not being distinguishable from those of the Weber Grits at the base, but passing upward into reddish sandstones, which in their turn are sometimes difficult to distinguish from the overlying red sandstones of the Trias. Its lower limit is drawn at the base of the first important lime- stone bed above the Weber Grits. This limestone, locally called the Robin- son Limestone from the fact that it forms the ore-bearing horizon of an im- portant mine of that name in the Ten-Mile district, is remarkable for being the first true limestone observed among the calcareous beds of the region. All below this horizon are practically dolomites of varying purity. As developed in this mine, it is of drab color, conchoidal fracture, and of pecul- iarly compact texture, resembling a lithographic stone. Its purity and textural characteristics are apparently not persistent outside of the Ten-Mile district. In the upper horizons of this district are found mud-shales, resem- bling in lithological character the Permo-Carboniferous of the Wasatch. Their fossil remains are found, however, to be distinctly Coal Measure forms. 70 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. The upper sandstones of this group are distinguished from the overlying Triassic rocks by a deeper color, approaching a Venetian red, whereas in the latter the color is rather of a light brick red. Plate V (p. 60) shows a remarkably contorted specimen of impure limestone of this horizon from the outcrops on Empire hill, where abun- dant fossils were found. Fossils—Tossil remains were found in various beds of this formation in the Ten-Mile district; in a peculiar black limestone of the Hoosier ridge, to the northeast of Mount Silverheels; and on Empire hill, on the west side of the range, adjoining Weston fault. From ten different localities in these regions the following forms were obtained : Productus costatus. Pleurotomaria (like P. Greyvillensis). Productus Nebrascensis. Naticopsis (like N. Altonensis). Productus Prattenana. Macrocheilus (primigenius °). Productus cora. Nucula (ventricosa *). Spirifera Rockymontana. Nucula (like N. Beyriche). Spirifera (Martinia) lineata. Microdoma (nearly M. conica). Spirifera camerata. Euomphalus (sp. ?). Athyris subtilita. | Archeoccidaris (sp. 2). Streptorhynchus crassus. Astartella (sp. ?). Chonetes Glabra. Loxomena (sp. ?). Bellerophon crassus. Fenestella (sp. ?). Bellerophon percarinatus. | Murchisonia (sp. °). ' Bellerophon (sp. ?). | Synocladia (sp. 2). Microdon tenuistriatum (very small). | Nautilus (sp. ?). Microdon obsoletum. Entolium (sp. °%). Pleurophorus occidentalis. Amplexus (sp. 7) MESOZOIC. As Mesozoic beds do not occur within the area of the map, no attempt was made to study them systematically or to obtain a measurement of their thickness, which would have taken a great deal of time and probably been impracticable without a more detailed map than could be had. Their ageregate thickness has therefore been assumed to be not less than 6,000 feet, a safe estimate judging from the thicknesses given by the geologists of the Hayden Survey for various parts of Colorado. LAKE BEDS. 71 The red sandstones of Mount Silverheels, above the beds assumed to be Upper Coal Measures in this report, are noticeable for their coarse grain and for the abundant pebbles of Archean rocks which they contain. In some intercalated shaly beds just east of Fairplay, Professor Lakes found plant remains and fossil insects. The former were determined by Professor Lesquereux to be undoubtedly Permian and the latter by Mr. A. Hyatt to be as certainly of Triassic age. In such conflict of evidence it seems safer to trust to that of animal life, since it is already well established that in America plants came into. existence in Cretaceous time which in Europe have always been considered to have made their first appearance during the Tertiary. QUATERNARY. The Quaternary formations which have been designated by special colors on the maps and sections are the Glacial or Lake beds, and the Post-Glacial or recent detrital formations. As already shown, there is evidence of the existence, during the intermediate flood period of the Glacial epoch, of a large fresh-water lake at the head of the Arkansas Valley, in whose bed was deposited a considerable thickness of coarse and rudely-stratified beds of detrital material from the adjoining mountains. Glacial or Lake beds (q)—Owing to the limited opportunities afforded for observing these beds in place, it was impossible to obtain a complete sec- tion of them or an accurate estimate of their aggregate thickness. The maximum thickness observed is about 300 feet; their material is generally coarse, and, as might be expected, very much coarser along what is known to have been the shore line of the lake. The finest of the beds consist of a calcareous marl, whose development seems to have been extremely local. The prevailing beds are a loose friable sandstone, resembling granite decom- posed in place, consisting largely of grains of quartz and feldspar, and often somewhat iron-stained. These beds frequently alternate with those of coarser material, which form a rude conglomerate. The coarser beds contain both angular fragments and bowlders of the rocks which make up the range, and lithologically can hardly be distinguished from the Wash of the succeeding formation; but, where any considerable thickness of the {04 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. beds is cut through, the stratification lines are easily recognizable and serve to distinguish this formation from the latter. Along the immediate shore-line—as, for instance, under the Wash of Fryer and Carbonate hills—the upper portion of the Lake beds consists fre- quently of large angular fragments, a number of which are derived from the actual outcrops of ore bodies. Recent or Post-Glacial (r)— Theoretically this rubric includes all the beds of the Post-Glacial Quaternary formations, of which there have been recog- nized in the region under survey several subdivisions, namely: the glacial moraines, a sort of bowlder clay or rearranged moraine material which is prevalent in the immediate vicinity of Leadville, where it received the local name of ‘*Wash;” asort of terrace formation found in the larger valleys; and the actual alluvial stream bottoms. The time allotted to the work did not admit of a sufficiently complete study of these different subdivisions to justify their distinction by separate colors on the map. In practice, therefore, on the surface maps only the alluvial bottoms and the broader accumulations of the terrace gravel in the larger valleys and plains, which are sufficient to completely obscure the subjacent geology, have been indicated. In the cross-sections of the spe- cial map of Leadville, however, where the explorations of shafts have given unusually complete data, the Wash is also included under this rubric. On the surface maps of Leadville and of the various groups of mines both these formations have been left out, as they would have hidden an impor- tant part of the geological outlines of the actual rock surface; they have, however, been indicated to scale in the cross-sections. DISTRIBUTION OF SEDIMENTARY FORMATIONS. The superficial distribution of the various sedimentary formations, or the relative area covered by their outcrops, being a function of or depend- ent upon erosion, is intimately connected with the existing topographical structure of the region. Were erosion the only factor to be considered, the Archean rocks would be found exposed continuously on the west side of a line approximately representing the old shore-line and in the deeper drain- age valleys and anticlinal axes of the eastern side. The displacements of ee DISTRIBUTION OF SEDIMENTARY FORMATIONS. ies the numerous faults which run through the region have, however, consid- erably modified this normal distribution. In point of fact, the central por- tion in the latitude of Leadville is mainly covered by the outcrops of Pa- leozoic sedimentary beds and of intruded masses of porphyry, the Archean exposures being confined to deep glacial amphitheaters near the crest of the range, and to minor masses which represent the eroded crests of anti- clinal folds. In the northern portion of the area Archean rocks are exposed along the main crest of the range and in the deep canon valleys and glacial am- phitheaters of the streams which flow into the Platte, Paleozoic beds being found only on the eastward sloping flanks of the included spurs. On the western side of the range, owing to the displacement of the great Mosquito fault, the area adjoining the valley of the east fork of the Arkansas is cov- ered by beds of the Weber Grits formation, while a bordering fringe of outerops of Lower Quartzite and White and Blue Limestone beds is found on the northern and eastern rim of Tennessee Park. In the southern half of the map the western limit of Paleozoic beds is a line running southeasterly from the forks of the Arkansas to the crest of the range at Weston’s pass, and southward beyond the limits of the map along the crest, approximately in a north and south line. West of this line are found only the granites and schists of the Archean, and irregular dikes and intrusive masses of porphyry. In the area included between this line and the crest of the range are triangular zones of easterly dipping sedimentary beds, in some cases forming a continuous series from the Cambrian to the Upper Coal Measures, cut off abruptly by fault-lines and succeeded again on the east by Archean exposures. ‘On the east of the crest the Paleozoic beds slope regularly back beneath the floor of the South Park, the Archean rocks being found only in the deeper hollows at the heads of the streams Beyond the limits of the map the outcrops of the more resisting beds of Mesozoic age form parallel ridges, ramning across South Park from north to south. The Quaternary Lake beds are found only along the lower ends of the spurs extending out into the Arkansas Valley from Leadville south to the limits of the map. 74 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. ERUPTIVE OR IGNEOUS. The eruptive rocks of this region, besides the granites, which were erupted during Archean time, are of Mesozoic or Secondary and of Tertiary age. The most important of these, both in magnitude of development and in their relations to the ore deposits of the region, are the Secondary erup- tives; the time of their eruption cannot, as explained in the preceding chapter, be exactly fixed, but was probably toward the close of the Mesozoic. The Tertiary eruptives, on the other hand, are of comparatively limited de- velopment and have had no appreciable influence on the deposition of ore ; their age is determined as such, not by any direct crossing of Tertiary beds, of which no instances were found in the region, but from their lithological | character, their analogy to eruptive rocks of known Tertiary age outside of this area, and from the fact that they are later than the Secondary erup- tives. SECONDARY ERUPTIVES. The earlier eruptive rocks occur mainly in the form of intrusive sheets, often of great magnitude, which, having been forced up from below through some more or less vertical vent or channel, have spread themselves out be- tween the strata, generally following a definite horizon, but at times crossing the stratification. They aiso occur in the form of dikes, this form being most common in the underlying Archean rocks. There is no evidence that any of them were poured out upon the surface like the lavas of the present day, but they must have cooled and consolidated under a great weight of superincumbent strata, to which is doubtless in great measure due their unusually crystalline character. They are with unimportant exceptions porphyritic in structure; that is, they contain larger crystalline elements in a groundmass or matrix of finer grain, as distinguished on the one hand from the granitic structure, in which all the elements are crystalline and of comparatively uniform size, and from Tertiary eruptives on the other, in which, while the structure may be por- phyritic, the larger crystals have a somewhat different development and the groundmass is made up in great part of non-crystalline material. SECONDARY ERUPTIVES. ie These distinctions are those that were in force before the introduction of the use of the microscope in lithological study. The more intimate knowledge of rock structure obtained by the microscopical study of rocks has brought about many changes in preconceived ideas, which are increas- ing every year, so that it seems merely a question of time as to when anew system of classification may be required. Already the distinctions noted above are true only of the most typical varieties of each, while between these are transition members which often must be placed in the one cate- gory or the other by some other distinguishing characteristic, such as time of eruption, internal structure, etc. In the present work it has been judged best to preserve the prevailing usage of designating the Secondary porphy- ritic rocks in which the prevailing feldspar is orthoclastic as porphyries, and those in which plagioclastic feldspars decidedly predominate as porphyrites. When the porphyrite is entirely granitic or evenly granular it becomes a diorite. On the general map of the Mosquito Range only two colors are given to the porphyries, founded on two general divisions which have a geograph- ical as well as astructural value. In the first of these is included the White Porphyry and its closely allied form, the Mount Zion Porphyry, which are the older and more nearly granular rocks, and which occur, with unimpor- tant exceptions, only south of the north line of the Leadville map; the sec- ond includes all other varieties of the Secondary porphyritic rocks of the region, which are generally younger and less uniformly crystalline, and which do not occur south of the south line of the Leadville map. On the detailed map of Leadville and vicinity the principal varieties of porphyry are each designated by a special color, the division “ Other porphyries” including those which could not, with absolute accuracy, be brought into either of the other divisions. 1In the time that has elapsed since field work was completed and the maps colored, opportunity has been had for studying more comprehensively the various Secondary eruptives in the course of work carried on in neighboring districts, and it has been found that some of the varieties designated on the following pages as porphyry, viz, the Sacramento, Silverheels, and Green porphyries, should probably be classed as porphyrites. The reasons for this, as well as the detailed description of all the rocks from a microscopical point of view, deduced from their study under the microscope by Mr. Cross, will be found in Appendix A. 76 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. MOUNT ZION PORPHYRY. This porphyry, when fresh and unaltered, is a gray rock resembling fine-grained granite, and is made up mainly of quartz, feldspar, and mica; orthoclase being the predominant feldspar and biotite the original mica; ~ plagioclase feldspar is decidedly subordinate, and biotite but sparingly developed. It is rarely found in an unaltered condition, however, and in the various stages of alteration it passes through a rock in which the partly decomposed biotite produces a slightly spotted appearance into a white rock glistening with fine lustrous particles of muscovite which can hardly be dis- tinguished from the White Porphyry. The muscovite results mainly from the decomposition of the feldspar and also from that of the biotite. Larger individuals of quartz and feldspar, as porphyritic ingredients, can frequently be distinguished by the naked eye. Beside the above minerals the micro- scope also detects zircon, magnetite, and apatite as accessory constituents of the rock; it shows, too, that the texture of the rock is quite granular throughout, with no amorphous material. Occurrence— This rock is of comparatively limited development, being found thus far only on Mount Zion and on Prospect Mountain. It is gen- erally in a less altered and therefore more typical condition on Mount Zion, for which reason it has received that name; but the most entirely unaltered specimens were obtained from some deep shafts on Prospect Mountain. On the south slopes of Prospect Mountain it is generally very much decom- posed and apparently grades off into White Porphyry, so that it is difficult to draw a sharp dividing line between the two rocks. No rock that could be definitely classed with this variety has been found south of Evans gulch, and the body in the bed of the gulch above the mouth of South Evans has been assigned to it somewhat doubtfully. WHITE PORPHYRY. The White or Leadville Porphyry is a generally white or granular, compact, homogeneous-looking rock, composed of quartz, feldspar, and muscovite. The quartz and feldspar are so intimately mixed together that they can only occasionally be distinguished by the naked eye, the former in small, double-pointed, hexagonal pyramids, the latter in small, white, rect- WHITE PORPHYRY. 4 angular crystals. The muscovite as an original constituent occurs in spar- ingly distributed, dark, hexagonal plates, which were at first supposed to be biotite; their true character was learned only when a specimen was found containing enough of the crystals to be subjected to optical and chemical tests. (See Appendix B, Table I, Analysis IL.) A characteristic appear- ance of the rock is the frequent occurrence of pearly-white leaflets of mus- covite, often in star-like aggregations, resulting from the decomposition of the feldspars. Orthoclase is the predominant feldspar. No biotite has ever been detected in the White Porphyry; but, as the rock is always in a more or less advanced stage of decomposition and as biotite occurs in the Mount Zion Porphyry, which seems to pass into it, it may have been an original constituent, though it is rather remarkable that no traces of it exist even in the small dikes where the rock still retains a distinct porphyritic struct- ure and has a fresh conchoidal fracture. By means of the microscope are found zircon as a common and magnetite and apatite as rarer constituents of this rock. No glassy matter is found, either in groundmass or in inelu- sions. Chemical analysis shows an appreciable amount of BaO and PbO, substances common in the ores, in its composition. Among the miners it is known also as “block porphyry,” on account of its tendency to split up into angular blocks, which are often stained interi- orly in concentric rings by iron oxide; and also as “forest rock,” from the frequent deposition of dendritic markings of oxide of manganese on the cleavage surfaces. Occurrence—The principal development of the White Porphyry is con- fined to a zone about the width of the Leadville map, and running from the western boundary of that map south of east, instead of due east as the map itself does. In other words, its lines have the prevailing northwest and southeast trend of other larger features of the region. Within this zone it is developed on an enormous scale, and occurs mainly as an intrusive sheet directly overlying the Blue Limestone and in contact with the principal ore deposits. It is not, however, entirely confined to this horizon, but is also found at both lower and higher horizons and can sometimes be observed crossing a stratum, generally at a low angle, from one horizon to another, thus splitting the sedimentary bed into two wedge-shaped portions. This 78 GEOLOGY AND MINING INDUSTRY OF LEADVILLE, occurrence is most noticeable in the area of the Leadville map along an imaginary northwest and southeast line, on one side of which it is found both above and below the Blue Limestone, while on the other it occurs only above it. The main sheet has an average thickness of several hundred feet and varies in its extreme dimensions from 20 feet along the northeast edge of the zone to 1,500 feet at White Ridge, on the east side of the range, the point of its maximum development and supposed to be the locality of its principal vent. Although all these masses must have been originally forced up from below through the Archean, it is remarkable that no section has yet been found which would show the actual passage from the Archean dike to the interbedded sheet. The nearest approach to this has been at the head of Iowa gulch, on Empire hill, and in a bore-hole in South Evans gulch, where White Porphyry has been found in the Archean in probable dike form, and on White Ridge and Lamb Mountain, in Horse Shoe gulch, where it is seen cutting up nearly vertically across Carboniferous strata. South of the zone above mentioned, White Porphyry is found as a remarkably persistent sheet at the Blue Limestone horizon gradually thin- ning out and extending to the southward as far as Weston’s pass. North of the zone it is found only in small sheets at Little Zion, Mosquito Peak, and London hill, and in several small dikes in the Mount Lincoln massive, its place being occupied by other varieties of porphyry. LINCOLN PORPHYRY. The other forms of porphyry found (and which on the Mosquito map have been designated by one general color), though presenting a number of varieties in the field, have essentially the same general composition, both mineralogical and chemical. They consist mainly of quartz, two feldspars, and biotite, hornblende occurring as an essential ingredient only in one variety. The crystalline ingredients are easily distinguishable by the eye, and there is therefore no danger of confounding them in the field with White Porphyry, except in the conditions of extreme decomposition in which they may be found near the ore bodies. This crystalline structure, a NN eg LINCOLN PORPHYRY. , 19 on the other hand, is often so far developed that they are not readily dis- tinguished by the untechnical eye from granites; as such, indeed, they are frequently classed by the miners. A careful examination, however, readily reveals their structural difference, which is that in them the larger crystals are inclosed in a finer-grained groundmass, whereas between the crystals of granite there is no such intervening and apparently structureless material. The principal subdivision of this group has been called Lincoln Porphyry, from the fact that it is typically developed in the mountain mass around Mount Lincoln. Its most striking characteristic is the frequent occurrence of large crystals of pinkish orthoclase, from one inch upwards in size, with a peculiar luster like that of sanidine. Plagioclase is generally in small, white, opaque crystals. Quartz occurs in double-pointed hexagonal pyramids, which have a rounded outline on fracture surfaces and often a slightly roseate tint. Mica is found in small hexagonal plates, generally decomposed and of greenish color. The microscope discloses, in addition to the above minerals, allanite, zircon, magnetite, titanite, and apatite. No microfelsitic or glassy matter is found in any rock of this type and no glass inclusions occur in the Mount Lincoln rock. Orthoclase feldspar predomi- nates in the groundmass and in the rock as a whole, while among the porphyritic crystals of rocks, in which the characteristic large orthoclase are wanting, plagioclase is in relatively larger proportion. Owing to the size of the crystals, large masses of the rock have at a little distance a decidedly granitic appearance. On weathered surfaces, especially in the dry region of the mountain peaks, it is of light-gray color, somewhat bleached, and often slightly stained by hydrous oxide of iron. In mine workings, on the other hand, when freshly broken it has a decidedly greenish tint, from the change of biotite into chlorite. Occurrence. —The main development of the typical Lincoln Porphyry is in the neighborhood of Mount Lincoln, where it occupies the same position with regard to the ore deposits of that region that the White Porphyry does about Leadville. It forms the immediate summit of Mount Lincoln, where it is apparently the remains of a laccolitic body or head of a channel of eruption. It occurs as an interbedded sheet in the Cambrian and forms several large bodies, apparently interbedded sheets, in the Weber Grits 80 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. which form the wooded ridges on either side of the Platte Valley in that region. It also occurs in the form of narrow dikes, cutting through the Archean. On the west side of the range it forms many large bodies in the Weber Grits, the most important of which is the laccolite body of Buckeye Peak. These bodies in the northwestern part of the region pass into the closely allied variety called Eagle River Porphyry, with which they doubt- less connect, and which will be described in detail in a forthcoming report on the Ten-Mile district. GRAY PORPHYRY. This rock, which occurs only in the immediate vicinity of Leadville, is in its typical form apparently a decomposed Lincoln or Eagle River Por- phyry. It has the same mineral composition and frequently the large ortho- clase crystals that the former has, and can be traced as a continuous sheet through transition forms into the typical variety of the latter. It is almost invariably decomposed, and on or near the surface is generally a greenish- gray rock, showing numerous crystals in a prominent earthy-looking ground- mass; in the mines it is usually found bleached and often reduced to a white pasty mass in which the outlines of former crystalline constituents are but faintly traceable. It is of importance in connection with the ore deposits, as where it has crossed the Blue Limestone it has often played the same réle with regard to them as the White Porphyry. As distinguished from the Lincoln Porphyry the microscope detects traces of former hornblende in the rock and finds glass inclusions in the quartz and numerous fluid inclusions in the feldspar. Occurrence.— The main sheet of Gray Porphyry, the only body which is distinguished by a distinct color on the Leadville map, occurs above the main sheet of White Porphyry in the northern half of the area shown on that map, and extends beyond it to Mount Zion. Other bodies which belong without question to this variety, as well as those which are more doubtful, have, for reasons to be given below, been included under the color of “Other porphyries” on this map. The most important of these is a sheet occurring in the Blue Limestone, cutting transversely upwards from its base to the overlying White Porphyry. Among those which are doubtful are er te ORS TERN or Satiow an nee atstnas ele ene ‘ SACRAMENTO PORPHYRY. 8i the Printer Boy and Josephine Porphyries, which occur the one on Printer Boy, the other on Long and Derry hill. Among rocks so thoroughly decomposed as are those in the immediate vicinity of the ore bodies it is often impossible to assign an occurrence with absolute certainty to a dis- tinct type; the miner can, however, in most cases distinguish these porphyries from the White Porphyry by the outlines of former crystals which the slight stain of iron oxide caused by their decomposition leaves. SACRAMENTO PORPHYRY. This rock in the hand specimen has the same general appearance as the variety of Lincoln Porphyry which has no large crystals. It is a dark- gray, granular, rather even-grained rock, in which the groundmass is decid- edly subordinate, and contains quartz, two feldspars, biotite, and horn- blende. It is distinguished from the former rock by carrying a much larger proportion of plagioclase feldspar, and hornblende as well as biotite. The microscope discloses the usual accessory minerals, with allanite and pyrite, and shows that the groundmass is holocrystalline and contains no glassy material. In the large masses of the higher mountain region it is usually a fresh-looking rock, but in mine workings and under a covering of soil and gravel capable of holding water it is usually much decomposed and bleached to a light-green, almost homogeneous-looking rock, with much epidote. The processes of decomposition in this rock, which are exceptionally interesting, are explained at length in Appendix A. Oceurrence— The main laccolitic body of Sacramento Porphyry is found under Gemini Peaks, between the heads of Big and Little Sacramento gulches. A fine cliff section of the body is also found on the face of Mount Evans towards Evans Amphitheater. It reaches a thickness of over a thousand feet in this region. Its main sheet occurs above the White Por- phyry, or, when this is wanting, with an interposition of Weber Shales between it and the Blue Limestone. East of the London fault it rests directly on the Blue Limestone, and in the neighborhood of the Sacramento mine it plays the same réle with regard to the ore deposits that the White and Lincoln porphyries do at other points. It also forms sheets higher up in the Weber Grits and less frequently in the lower Paleozoie strata In MON XII —6 82 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. a broad, general way it may be said that on the eastern slope of the range Lincoln Porphyry extends from the northern edge of the map to Mosquito gulch, Sacramento Porphyry from Mosquito gulch to the ridge south of Little Sacramento gulch, and White Porphyry from there south to the limits of the map. The only point observed which showed evidence of a feeding channel from below was at the head of Little Sacramento gulch. PYRITIFEROUS PORPHYRY. This rock, though an extremely important element in the geology of the immediate vicinity of Leadville, does not occur outside that region and, like most of the eruptive rocks in the vicinity of the great ore concentra- tions, is in such a universally decomposed condition that its original constitu- ents cannot be definitely determined. It is generally of a white color, with grayish-green or pinkish tints, comparatively fine grained, and with no traces of large crystals. In it can be distinguished small grains of white feldspar, quartz, biotite which is generally altered to a chloritic substance, and pyrite. The last ingredient, from which it derives its name, is found abundantly scattered through the rock in crystals, often so fine as to be undistinguishable by the naked eye. They occur at times within the crystals of quartz and biotite, and are hence supposed to be an original constituent of the rock. They are frequently concentrated along cleavage planes, sometimes associated with finely disseminated crystals of galena. Pyritif- erous Porphyry is readily distinguished from the White Porphyry by its crystalline constituents. It differs from the Sacramento and Gray Porphy- ries by a relatively small amount of plagioclase feldspar and from the former by the absence of hornblende Its most strikingly distinctive feat- ure is the amount of pyrites which it contains, which is estimated to con- stitute, on the average, 4 per cent. of its mass. The only further constitu- ents disclosed by the microscope are minute crystals of zircon. Fluid but no glass inclusions are found. Occurrence— The Pyritiferous Porphyry, as stated above, is confined to the area of the Leadville map, and is at present principally developed on Breece hill and the slopes of Ball Mountain. Its original extent previous to erosion was probably much greater than at present. It is a stratigraph- OTHER PORPHYRIES. 83 ical replacer of the Gray Porphyry on the north and of the Sacramento Porphyry on the east, occurring mainly above the Blue Limestone, but with either White Porphyry or Weber Shaies interposed between it and that hori- zon. In California gulch it is also found at lower horizons, but apparently cutting across them upwards. MOSQUITO PORPHYRY. This porphyry, a light-gray, fine-grained rock occurring exclusively in the form of dikes, is formed of quartz, two feldspars, and biotite. The quartz is very prominent, in clear, irregular grains; orthoclase feldspar is predominant over plagioclase; biotite occurs in small leaves and is not abundant. The occurrence of macroscopical apatite in glistening hexag- onal prisms is a noticeable feature of the rock. The microscope discloses aremarkable association of small ore grains (ilmenite, pyrite, specular hem- atite, and magnetite), together with zircon. Occurrence—The type rock was only observed in dikes in the Archean, viz, in the North Mosquito Amphitheater, on the north face of Mount Lin- coln, and in Cameron Amphitheater where it extends from the Archean up into the Paleozoic. . GREEN PORPHYRY. This is a fine-grained, almost compact rock, of light-green color, result- ing from the chloritic decomposition of its original constituents, which renders their identification difficult. Quartz, two feldspars, biotite, and hornblende have been identified; but the relative proportions of orthoclase and plagio- clase are not readily apparent. Muscovite and calcite are decomposition products of the feldspars. The groundmass is often so subordinate that the rock seems macrocrystalline. Occurrence—It is found as interstratified sheets on lower Loveland hill near the Fanny Barrett claim and in Cambrian quartzite on the north side of Mosquito gulch; also, as a dike running north across the Paleozoic beds from the lower edge of Bross Amphitheater. SILVERHEELS PORPHYRY. This rock forms important intrusive sheets on the mountain mass of Silverheels outside of the limits of the Mosquito map; it has not been so 84 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. carefuily studied as the other varieties. It is an extremely fine-grained, greenish-gray rock, which in the hand specimen is characterized by fine needles of what is apparently decomposed hornblende. It carries quartz in small amount, two feldspars whose relative proportions are hot readily apparent, with hornblende and biotite. These constituents are so very small as not to be readily distinguished. The microscope discloses the usual accessory minerals, including allanite and pyrite. The groundmass is holocrystalline and contains no glass. A porphyritic rock found on a south- ern spur of Mount Silverheels, at the forks of Crooked Creek, although of much coarser grain and more distinctly porphyritie habit, has essentially the same elements as the Silverheels Porphyry. DIORITE, Only three occurrences of granular plagioclastic rocks were found in the region, each of which was in the form of a dike cutting through the Archean in Buckskin gulch. The rock of each of these occurrences repre- sents a distinct variety of the type. Hornblende diorite——The normal diorite, which forms a broad dike cross- ing the head of the gulch, is a fine-grained, gray rock, in which the prom- inent constituents are plagioclase feldspar and hornblende, while a little quartz, brown biotite, yellow titanite, and dark ore grains can be detected by the naked eye. The microscope discloses also zircon and apatite, with chlorite and epidote as alteration products of the hornblende and biotite, and muscovite formed from orthoclase. A similar rock is found in French gulch, on the west side of the range Quartz-mica diorite—This rock occurs on the south side of Buckskin gulch, opposite the Red Amphitheater. It is a dark, even-grained rock, in which quartz and feldspar are more prominent than the small irregular leaves of biotite; hornblende is wanting. The microscope shows zircon, magnetite, apatite, biotite, plagioclase, orthoclase, and quartz as original constituents. Ang:tic diorite —This rock, which is darker and finer grained than either of the preceding, occurs in the Red Amphitheater, cutting up through the Archean into the base of the Cambrian. In the hand specimen only horn- blende, biotite, plagioclase, and a little quartz can be distinguished, but the - U.S.GEOLOGICAL SURVEY GEOLOGY OF EEADVINELE, PLATE VII Hornblende Porphyrites Heltctype Printing 6. 2ll Tremor : nes Py i > . eS [ae ee ae PORPHYRITE. 85 microscope detects also augite, orthoclase, zircon, titanite, magnetite, hema- tite, and apatite. PORPHYRITE. As compared with the quartz-porphyries, the type rocks of this class are distinguished at first glance by a great predominance of basic silicates (hornblende or biotite), by a comparative rareness of quartz, and by their rather younger field habit, as shown by the marked conchoidal fracture and generally fresher appearance. For the latter reason it was at first thought in the field that they might possibly be of Tertiary age, but the fact that they are folded and faulted with the inclosing Paleozoic rocks, as well as their internal structure, proves them to be, like the quartz porphy- ries, of Secondary age. In their manner of occurrence they are also distinct from the latter rocks, in that they do not form large bodies, neither dikes nor intrusive sheets being as a rule over twenty feet in thickness. The former often occur in the form of interrupted dikes; the latter, on the other hand, while occasionally crossing from bed to bed, have a most remarkable extent in one general horizon as compared with the thickness of the sheet. Although subordinate in amount to the quartz porphyries, these rocks occur with so many variations of internal structure and compo- sition that they afford a complete series, including almost all the possible varieties of the type, and a complete description and classification made by Mr. Cross from a lithological point of view will be found in Appendix A. Only the general features of the rocks will therefore be given here. The typical rock, both in composition and manner of occurrence, may -be taken as that which occurs interbedded in the Paleozoic beds along the cliff sections on either side of Mosquito gulch. A photograph of a hand specimen of this rock is reproduced in Plate VII, Fig. 2, which gives some idea of its general appearance; it is a rather dark greenish-gray rock, with dark weathered surface and clean conchoidal fracture. ‘The most promi- nent macroscopical constituents are well defined prisms of dark hornblende and small, white, opaque crystals of plagioclase. The microscope detects some biotite both among the porphyritic constituents and in the ground- mass, and both orthoclase and quartz in the groundmass No glass and but few fluid inclusions are found. 86 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Occurrence—The manner of occurrence of this rock in the region above mentioned is quite remarkable. It has been traced in practical continuity over an area of some four square miles, and probably has a much wider extent. It is regularly interbedded and rarely over twenty feet in thick- ness. It is easily traceable from a distance on the cliff walls, as a dark band between the lighter-colored sedimentary strata, and, while it appar- ently follows rigorously the same horizon, it is found, on close examina- tion, to cross from bed to bed at different points, so that its range in this area is actually from the upper part of the Cambrian to the top of the Silu- rian. ‘The manner in which it crosses the beds is shown in Plates XIII and XIV. It also occurs at various other points in narrow dikes in the Archean. This rock forms Type V of Division B of Mr. Cross’s classification, this division being that in which the hornblende and biotite are found both in the groundmass and as porphyritic constituents. His Division A includes rocks in which these basic minerals are entirely wanting in the groundmass, and which, in consequence, are of much lighter color than either of the other divisions. The rocks of his Division C, on the other hand, in which the hornblende and biotite are found only in the groundmass, are generally of darker color, and the arrangement of these minerals around the larger porphyritic crystals often shows a fluidal structure. Included fragments of pebbles of Archean rocks are more frequent in these than in any other eruptive rocks of the region, and in Plate VII, Fig. 1, is shown a specimen of a rock of Division A, from a remarkable dike in the Arkansas Amphitheater, in which the included fragments are large rounded crystals of orthoclase, whose presence in such form it has not yet been pos- sible to account for. TERTIARY ERUPTIVES. The Tertiary eruptives found in this region consist of rhyolites and one occurrence of quartziferous trachyte within the limits of the Mosquito map, and of an interesting occurrence of andesite just south of those limits. The quartziferous trachyte being a small body, and of no great importance as bearing on the subject-matter of this report, has not been designated by a special color, but is included on the map under the rhyolite color. The RHYOLITE. 87 eruption of these rocks had apparently no influence on the ore deposition of the region, since that, as well as can be determined, was pre-Tertiary, and no ore bodies have been found in connection with these rocks. Their interest is therefore chiefly lithological. RHYOLITE. The most important body, both in mass and in lithological interest, is that of Chalk Mountain, on the northern edge of the map, which, as the name of the mountain indicates, is prominent on account of its dazzling white color. It is a very crystalline rock, in which the groundmass is so subordinate as to appear in the hand specimen entirely wanting; it corresponds, therefore, to the generally accepted definition of Nevadite. Its prominent constitu- ents are sanidine, generally in large crystals and having a peculiar satiny luster, and smoky quartz. The microscope also detects some plagioclase, a little biotite, with magnetite, apatite, and zircon in relatively small propor- tion as compared with the quartz porphyries. The quartzes contain fluid inclusions. A careful study of this rock by Mr. Cross has developed the fact that the peculiar luster of these feldspars is due to an actual parting, analogous to cleavage, which has already been determined as that which gives the blue color observed in the feldspar of many rocks, notably labra- dorite and some rhyolites. He also found crystals of topaz in some of the druses of this rock, the first instance, so far as known, in which this mineral has been found in Tertiary rocks. On Plate VIII is the reproduction of a photograph of x hand specimen of this rock, in which the smoky quartz grains appear black; above this are two microsections which show the sim- ilar granular structure of this rock and of White Porphyry.' The next important body of rhyolite is that at the west base of Bart- lett Mountain, at the head of McNulty gulch, a tributary of the Ten-Mile Creek; it here cuts across porphyrite and quartz porphyry. ‘This rock, though generally light colored, is not as white as the Chalk Mountain rock, nor is it so decidedly of the Nevadite type, the groundmass being often quite prominent. It contains glassy feldspars, quartz, and biotite. In darker ‘In some of the plates, by an error in proof-reading, the title White Porphyry, which belongs to the left-hand section, has been placed below the right-hand section and vice versa. The reader will bear in mind that the section containing the large crystal is Nevadite. 33 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. portions of the rock biotite is quite abundant and some hornblende appears. The microscope shows glass, but no flnid, inclusions in both quartz and feldspar. The groundmass is cryptocrystalline. In general habit it is more like the recent volcanics than the Chalk Mountain rock, and yet, in some parts, it is with difficulty distinguished from a quartz porphyry. A third important body of rhyolite is that which forms Black hill, at the southeast extremity of the map. This is a light, often rather pinkish colored rock, of fresh habit and conchoidal fracture. It carries macroscopically two feldspars, smoky quartz, and some biotite. The microscope shows the groundmass to be granular, and that fluid inclusions occur in both quartz and feldspar and glass inclusions in the quartz. From the hand specimen alone the rock would be difficult to distinguish from an earlier quartz por- phyry, but the manner of its occurrence and its relations to the surround- ing rocks leave little doubt that it must be of Tertiary age. On the west slope of Empire hill a fine-grained, nearly white rock oc- curs below the White Limestone, which is distinctly orthoclastic and con- tains quartz and biotite. The fact that the quartz contains glass and no fluid inclusions points to a Tertiary age, but the occurrence has not been very carefully studied. A similar rock with larger crystals was found in a brecciated material from the Eureka shaft, in Stray-Horse gulch, which it has not yet been possible to account for. Trachyte.— At the head of Union gulch are small irregular bodies, in granite and White Limestone, of fine-grained, dark-gray rock, full of brown biotite, with small glassy feldspars and some rounded yellowish quartz grains. The microscope shows hornblende and about equal portions of orthoclase and plagioclase. The groundmass is microfelsitic and has a fluidal structure. The quartz grams seem rounded and worn, and are confined to macroscopic individuals, for which reason they are regarded as accidental rather than normal constituents, and as the rock contains only 61.22 per cent. silica it is considered a trachyte rather than a rhyolite. ANDESITE, The Buffalo Peaks form a double-pointed mountain mass, rising about a thousand feet above the main crest of the Mosquito Range, some ten miles U.S.GEOLOGIGAL SURVEY GEO}EOGy Ol EEADMIELE SPE ATIE Vill Nevadite, from Chalk Mt @ i © "0 . ; — er ~~ a =e a ANDESITE. 89 south of Weston’s Pass. They consist of a normal hornblende-andesite, which is the cap rock, with a black vitreous rock which was at first consid- ered an augite-andesite, and a great development of tufaceous and breccia beds. A careful study of the darker rocks led Mr. Cross to the conclusion that their characteristic mineral was hypersthene, and to the establishment of hypersthene-andesite as a normal pyroxenic variety of this class. These rocks are described briefly in Appendix A, and more fully in No. 1 of the Bulletins of the United States Geological Survey. CHAPTER IV. DESCRIPTIVE GEOLOGY OF THE MOSQUITO RANGE. Introductory— The following pages present a detailed description of the area included in the Mosquito map, summarized from field notes made during the summer of 1880. They contain the facts upon which have been founded the general conclusions drawn elsewhere with regard to the geol- ogy of this region, and therefore include many details that may not inter- est the general reader, but which will be of use to those who wish to use the maps on the ground or who desire to investigate critically the correct- ness of the generalizations. In preparing them it has been the aim of the writer to condense the description as far as could be done without omitting any essential observations. Circumstances made the time of field work extremely limited, and the detail in which it was possible to examine differ- ent parts of the region was necessarily unequal. The prime object of the work was to gather all information which might have bearing upon the origin and manner of formation of the ore deposits of the Leadville region. In the prosecution of this object much information of interest in other direc- tions has been collected, and many lines of investigation have suggested themselves which it would have been a pleasure to pursue further had time permitted. That such material be found incomplete is to be attributed, therefore, toa want of opportunity rather than of scientific zeal. In the following description the region has been treated in the general. topographical order in which it was examined; that is, following the east- ern slopes of the range from the northern edge of the map southward to Weston’s pass, and then along the west side in the inverse direction. Both geologieal and topographical structures lend themselves to this method of 90 SURFACE FEATURES. 91 treatment, and permit four general divisions of the area: 1. The northeast- ern, including the Mount Lincoln massive, which, as shown in Plate IX, stands out quite by itself. 2. The middle-eastern region, or from Buckskin to Horseshoe gulch, inclusive. 8. The southern, including both sides of the range south of the line of Horseshoe and Empire gulches. 4. The northwestern division, including the area on the west side of the range north of the line of the Leadville map; the middle area, which comes within the limits of this map, being described in a separate chapter. Each of these four divisions presents a general type of geological structure peculiar to itself, The numbers after rock descriptions are the catalogue numbers of the specimens in the Leadville collection of the United States Geological Sur- vey. . Surface features.— ‘he whole region treated of in this report may be divided as regards its general superficial characteristics into three belts or zones: (1) The bare summits and high ridges above timber-line; (2) the belt of forest growth covering the mountain slopes below timber-line; (3) the open erass-grown and treeless valleys. The elevation of timber-line can only be given in a most general way as the average height at which tree-growth stops on the spurs where sur- face conditions are favorable. The bare glacial amphitheaters in the in- terior of the range and the almost perpendicular walls of the canons present conditions unfavorable to tree-growth even at points below the timber-line, in spite of which the line is often well marked. Below an average elevation of 11,700 feet the flanks of the mountains are covered with coniferous trees of the more hardy Alpine varieties, such as the Douglas fir and Engelman spruce, which in favorable situations often form a dense forest by no means easy to traverse, owing to the abundance of dead and fallen trunks, relics of former forest fires. The lower limit of tree growth is even more sharply defined; not, however, by its elevation above sea-level, but by the change of surface slope to the low angle which characterizes the valleys. Whether it be the bottom of a little mountain stream, a hundred feet wide, or the broad expanse of the South Park, almost as many miles in extent, the down- ward spread of forest growth is arrested with equal suddenness, provided 92 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. only there be a sufficient thickness of loose detrital material, whether gravel or alluvial soil, accumulated over the hard rock surface. Along the alluvial bottoms of the streams, it is true, there is often a fringe of willow, alder, or cottonwood; but the sturdy pine, although delighting to face the mountain blasts on bare inaccessible precipices, seems afraid to trust himself where he cannot thrust his roots down to a base of firm rock, or around bowlders large enough to act as a counterpoise to the shaft he exposes to the force of the wind. The high mountain region, the forest region, and the valley region represent fairly three degrees of comparative difficulty in reading the geological story. In the former, except where covered by talus slopes at the foot of great cliffs, the rock surfaces are all laid bare and the geological structure is an open book, only needing an understanding and careful observer to be read correctly. In the forest region there is more or less accumulation of soil and decaying vegetable matter, and rock outcrops are often rare and widely spaced. The record has many gaps which time and care are not always sufficient to fill without resorting to hypothesis or analogy. In the larger valleys, however, whose surfaces are covered to unknown depths by gravel and soil, no outcrops are visible, and induction or analogy are the geologist’s only resources for determining the structure of the underlying rock formations. Glacial formations —In the Arkansas Valley, as already noted, there is dis- tinct evidence of the existence of a glacial lake, and the Arkansas Lake beds, composed of stratified sands, marls, and conglomerates, have been actually exposed in a thickness of several hundred feet. In the South Park, on the other hand, no such stratified deposits have been observed, nor is the topography such as to suggest the possibility of a local lake of any great extent having been formed there during the Glacial period. While the existence of such a lake in the South Park is therefore considered improb- able, the fact that the exigencies of this work admitted the examination of only a small portion of its surface, immediately adjoining the Mosquito Range, does not justify a positive statement to this effect. 5 sone ee GLACIAL DEPOSITS. 93 Post-Glacial formations. —The Post-Glacial deposits of unstratified gravels are equally prominent, however, on both sides of the range.’ They result in great part from the redistribution of glacial moraines by the floods which accompanied the melting of the ice at the close of the Glacial period. In the Arkansas Valley they were spread out over the already existing Lake beds, and reach a relatively high level on the mountain spurs. In the western portion of the South Park they form the flood-plain of the larger valleys, which they filled up to a very considerable depth, as has been shown by excavations made at Alma and Fairplay in washing them for gold. Depths of 60 to 100 feet have here been proved of coarse gravel con- glomerate, entirely without stratification. These points are comparatively high up and near the source of supply, and it may be assumed that finer material of the same origin extends to equal if not to greater depths well out on the bottom lands of the park. Within these flood-plains the streams run in alluvial bottoms which widen as one descends and often open out into broad meadows, partially drained lake basins, where some natural ob- stacle has caused a partial damming up of the earlier streams. Of actual moraines no inconsiderable remnants still remain. They can be most clearly seen along the steep sides of the canon gorges through which the mountain streams debouch into the more open valleys, where they often form gravel ridges several hundred feet in height; and on the lower spurs beyond these canons their existence under the forest growth may often be surmised by their characteristic topography of irregular ridges inclosing rounded hollows without exterior drainage, as well as proved by shafts and tunnels made by the misapplied energies of prospectors. Archean exposures.— I’ the lithologist no more favorable opportunity could be had for an exhaustive study of the older crystalline rocks which form the backbone of the Rocky Mountain system than that afforded by the exposures in the deep gorges and glacial amphitheaters of the interior of this range. The scope of this work did not admit, however, of any such exhaustive study, which would have required much more time than could have been devoted to the whole region. The utmost that could be done was to grasp the more salient characteristics of the series and to outline on the map such of the more important eruptive masses which intersect them 94 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. as fell under observation, without pretending to present them in any deter- mined degree of completeness. The special study of the Archean rocks in the field was assigned to Assistant Whitman Cross, to whom also was al- lotted the duty of examining them microscopically, and the greater part of the observations here recorded are derived from his notes. Granites and gneisses with accessory occurrences of amphibolite constitute, as already stated in Chapter III, the main components of the Archean in Mosquito Range. As seen from one of the commanding peaks of the range the most striking features of the rocks are the great irregular vein-like masses of white pegmatite, which form an infinitely intricate network on a background of darker gneiss. When examined more closely, however, the definite outline of these pegmatite bodies is no longer so apparent, and they are found to be intergrown in the surrounding rocks in a most intri- cate manner. It is only in the smaller veins, such as are shown in Plate IV, that their outlines can be definitely traced. Structure lines, as defined by relics of former stratification, are so seldom to be distinctly traced that no attempt has been made to co-ordinate the few facts observed into any -general structural system. Of eruptive rocks in the form of dikes and intrusive masses of irregular shape an almost infinite variety, both in form and composition, is found. The dikes are generally narrow, being rarely over 50 feet in width, and of limited continuous length. Those shown on the map are only the more prominent of those actually observed, and it must be borne in mind that a great portion probably did not come under observation at all. NORTHEASTERN DIVISION. Platte amphitheater—Like the Arkansas River, whose amphitheater adjoins this on the west, separated only by a single narrow, knife-like ridge, the Platte at its source flows first north and then bends round upon itself to take its main course in a diametrically opposite direction. A reason for this by no means uncommon occurrence in the glaciated regions of the Rocky Mountains may be found in the fact that on the northern sides of the higher peaks are the greatest and most permanent accumulations of névé ice, to whose erosive action, not yet thoroughly studied, are doubtless Ee U.S.GEOLOGICAL SURVEY Bross Amphitheatre ! j ‘ we atk eA, bg Papa aah ite yieenis ak As be age te KY O44 ‘ daddy cid data “art eat as aed 4S « AAAS W sates arate at y ea AL i * aya * ru Eve Yu wees Rye ty Seas ress = = SS $2.5 Julius Bien & Co.lith, GEOLOGY OF LEADVILLE, PL. IX i Mt Lincoln. 1 Lincoln Amphitheatre — Platte Amphitheatre. North Peak. : i | ns “he utd i, aay hy h | Se aT TR GE Montgomery S.P. Emmons, Geologist-in- Charge Bross Amphitheatre | aaa’ Mt Bross. . Eh yt ; yiata We ’ 4 , 4 , wy ym wl ee fyi ghat mre bath ge Quartzville Cameron Am phitheatre. Ms Lincoln Lincoln Amphitheatre ‘ 4 4 ‘ 4 wa hate ataa aaa aad a® net Me “aadeta 4 hing s ss + aga nary aha tine 44 aati as yun Wm gana ad nhs ——s = _—_ eri. aa as Platte Amphitheatre. + North Peak. | PLATTE AMPHITHEATER. 95 due the semicircular form and remarkable verticality of the upper walls of glacial amphitheaters or cirques. The main area of the Platte amphitheater lies directly west of Mount Lincoln, but a smaller northwest branch extends back of North Peak, hold- ing on its basin-shaped floor, which is about six hundred feet higher than the other, several pretty glacial lakes with characteristically emerald-tinted waters. The glacier formed by the confluence of the two immense névé masses that once filled these amphitheaters, which must have been about two thousand feet thick, flowed directly east, carving out a straight U-shaped valley in the crystalline rocks, whose general form remains essentially unchanged to the present day. On the upturned sedimentary beds which rest upon the Archean, how- ever, later erosion has acted more rapidly and irregularly, and at the little town of Montgomery the valley suddenly widens out into a broad, grassy bottom-land, with forest-covered hills sloping away more gently on either side. Immediately above Montgomery, as shown in Plate IX,' the present stream bends a little southward around a boss of Archean, composed chiefly of gneiss and amphibolite, penetrated by a fine-grained white granite, in which reticulated veins of white pegmatite stand out prominently. In the bottom of the valley, above this boss for a mile or more, extend glacier- worn hillocks (roches moutonnées) of typical form, evenly rounded and scored by very distinctly-marked grooves and strize on the upper side, but breaking off unevenly on the lower side toward the stream. On either side of the gorge, above the talus slopes of broken rock masses at their foot, steep walls of Archean rocks rise about two thousand feet, with a thin capping of nearly horizontal Paleozoic strata at the very summit. The structure planes of the Archean, which are unusually distinct in the Platte gorge, stand nearly vertical, with a strike south-southeast. The eastern portion of the Archean mass seems mainly composed of gneiss and crystalline schists, granite occurring only in subordinate masses. The granite near Montgomery is of the gray, fine-grained type, suggestive 1Tn this and the succeeding diagrammatic sketches, which are intended mainly to illustrate the geology of the various exposures shown, the letters on the outcrops are the same that are used on the geological maps to designate the different rock formations, i. e., a= Archean, ) = Cambrian, ¢=Silu- Tian, etc. 96 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. rather of an eruptive origin, and contains relatively more mica and quartz than that found in Buckskin gulch. The gneiss is of the normal gray type, generally rich in quartz and biotite. Its feldspar occurs often in large Carlsbad twins. The microscope detects plagioclase, microcline, and mus- covite; also, abundant fluid inclusions in the quartz, sometimes double and with salt cubes and moving bubbles. A schist found locally on the northern face of Mount Lincoln is of dark-green color and contains only biotite, muscovite, and tourmaline, with a little feldspar, which is scarcely visible, even under the microscope, and then appears in a stage of alteration into muscovite. The white pegmatite masses are specially prominent, as al- ready mentioned, on the faces of the spurs on either side of the gorge at Montgomery. Their color is due to the large proportion of white ortho- clase feldspar, which in the mass gives its tone to the quartz also, while the mica, generally muscovite, occurs in bunches of subordinate importance, growing between the crystals of the other constituents. The more prominent eruptive masses observed and which are indicated on the map are: i 1. Half a mile above Montgomery a dike of porphyry crosses the valley at right angles and can be traced for a considerable distance up either wall. It is a light-colored, felsitic-looking rock, in which only very small quartz grains and biotite leaves can be detected by the naked eye. It most nearly approaches the Mount Zion, or fresh variety of White Porphyry, and has a holocrystalline structure as seen under the microscope. 2. A mile above Montgomery is a wider dike of light-gray quartz- porphyry, whose distinguishing peculiarity lies in brilliant-green grains of epidote, which are scattered uniformly through the rock and which are, in part certainly, the result of the decomposition of biotite. Its ground- mass is also microcrystalline. 3. A third dike is particularly noticeable for its peculiar form, changing half way up the cliff from a vertical to a horizontal sheet. This change of form is not unusual in dikes which extend up into the Paleozoic or regularly bedded rocks; but this is the only instance in which it has been observed in the Archean. The rock belongs to the Mosquito Porphyry type, and is identical with that found (type No. 2) on the south face of Mount Lin- PLATTE AMPHITHEATER. 97 coln and at the head of the Cameron amphitheater. It is a light-gray, fine- grained rock, consisting of quartz, feldspar, and biotite crystals in a very scanty groundmass. The groundmass is a fine-grained mosaic of quartz, with some feldspar and muscovite, the latter resulting from decomposition of feldspar and probably in part also from fine biotite leaves, since this al- teration is visible in the larger individuals. 4. Just west of this is a very irregular body of quartz-porphyry, not shown on the map. It occurs at the base of the cliffs and is very variable in form and thickness, branching out irregularly and continually changing its direction. It is a dull-green rock and belongs to the Green Porphyry type. It is rich in feldspar, with a few grains of quartz, and what is prob- ably a decomposition product of hornblende which gives the color to the rock. On the cleavage-planes are coatings of epidote. 5. Still further up the valley, directly under the summit of Mount Lin- coln, is a dike of White Porphyry extending high up on the face of the cliff. It resembles closely the typical White or Leadville Porphyry, but is less decomposed. A few small crystals of quartz and feldspar are visible, also frequent light-green specks of partly decomposed biotite. It is almost identical with the similarly situated dike (dike No. 1) in Cameron amphi- theater, on the south face of Mount Lincoln, and with fragments found at the head of Buckskin amphitheater, for which this description will also apply. Its outer weathered surface is very white and homogeneous-looking; immediately under this is a dark zone, less than an inch in thickness, which apparently owes its color to the oxidation of some heavy metal originally contained in ore particles or in the biotite. It was impossible to obtain sufficient biotite for a chemical test to prove this assumption, which is founded on indications observed by the microscope. In the Cameron rock small crystals of pyrite could be detected, and in that from Buckskin a little galena also, whose decomposition would more directly account for the dirty-brown color alluded to. On the raised floor of the northwestern arm of the Platte amphitheater granite predominates among the Archean rocks. It is of the same variety as that found directly west in Bartlett Mountain and Clinton amphitheater, and has large and prominent crystals of feldspar disposed in regular order MON XII——7 98 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. throughout the mass. The associated gneiss also contains large orthoclase crystals, often two inches in length and usually Carlsbad twins. On the surface of this floor was observed an interrupted dike of hornblende-por- phyrite, which is figured on the map; also, small outcrops of other eruptive rocks, notably one of White Porphyry, whose outlines were not determined with sufficient accuracy to be there indicated. On the west wall of this amphitheater appears a dark line, which may probably be part of the same dike of porphyrite as is shown on the map to extend almost continuously along the west wall of the Arkansas amphitheater. Owing to their darker color and peculiar fracture in large masses, which is like that of a basalt or andesite, the porphyrite bodies can readily be distinguished at a consider- able distance. The North Peak ridge, which forms the northern wall of the Platte gorge, being lower than the corresponding spurs to the north and south, respectively, is composed almost entirely of Archean rocks, a proportion- ately smaller capping of Paleozoic strata being left onits crest. The actual outline of the remnant of Cambrian quartzite remaining on the ridge could only be determined with exactness by the expenditure of more time than it was possible to devote to this point, and the line given on the map is that determined by observation of the apparent stratification. lines from Mount Lincoln, Quandary Peak. — On the Quandary Peak ridge, which lies just north of the limits of the map, it is easily seen from a distance that a remnant of Lower Quartzite is left at the very summit of the peak, as shown in the sketch given in Plate X, which is taken from the summit of Mount Lincoln. The angle of inclination of these beds, which is 15°, is less than that of a por- tion of the ridge, in consequence of which they have been eroded off the saddle immediately east of the peak, and are found again lower down on the spur. At the timber-line, which reaches only the eastern end of this spur, the dip steepens to 25°. This line of steepened dip can be traced on all the prin- cipal eastern spurs of the range and corresponds very nearly with the mouth of the cation gorges which have been cut in the Archean. It is often accom- panied by some apparent dislocation of the strata, the amount of which, owing to discordant dip angles, it was not easy to determine. For pros- Se — cn eee tags gg NIOONIT DIN WOUd HIMON ‘RUTIVA UAAIM AOI GNV AONVY OLINOSON WNP) ¥ Vote syne Avepuengy MNS IVOIN0TOXS SO or QUANDARY PEAK. 99 pectors this line seems to have had especial attraction, and not without reason, since along it are the best exposures of the lower Paleozoic rocks, in which on this side of the range there has been a considerable concentra- tion of ore. The sketch given in Plate X is a view of the region adjoining the upper Blue River Valley, as seen from Mount Lincoln. To the left or west of this valley the hills are almost entirely Archean, with a few later sediment- ary beds resting against their eastern spurs. On Quandary Peak alone do they still extend up to the very summit. On the east of the valley are the hills surrounding the town of Breckinridge, made up of Mesozoic beds and numerous porphyry sheets, in which valuable ore deposits have been dis- covered and from the débris of which rich gold placers have been accumu- lated in the valleys. The Quandary Peak ridge is here described, although it does not come within the limits of the map, since it was the only point at which the search for fossils in the Cambrian quartzite was successful. On its eastern end, a short distance above timber-line and perhaps half a mile above the Monte Cristo mine, about fifteen feet of greenish argillaceous slates, belonging to the upper part of this formation, are exposed by a prospector’s tunnel which was run in on the north face of the spur. From these shales, after a dili- gent search, good impressions of the Potsdam species Dicellocephalus were obtained. Unfortunately the ground is too much covered by soil and forest to afford a continuous section; but, unless a fault intervenes, this shale bed should be below the quartzite and limestone in which the Monte Cristo deposit occurs, and not many feet from it. Lithologically it resembles the greenish shale beds observed in very many points throughout the region below the calcareous shales and sandy limestones of the upper portion of the Lower Quartzite series, but nowhere were any further traces of these fossils found. The exposures of the Cambrian or Lower Quartzite formation are never- theless those of the Paleozoic series which can be most clearly and con- tinuously traced, as they slope up in a U-shaped curve on either side of the valleys below the cation gorges of this portion of the range. In general the outcrops in the valley bottoms and along the lower slopes are concealed 100 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. by surface accumulations, either talus slopes or alluvial soil. In the rela- tively wider valley of the Platte, however, about half a mile below the town of Montgomery, a moraine ridge which crosses the valley once dammed up a shallow lake basin, now a bit of meadow-land; the present stream, which drains this basin, exposes as it cuts through this ridge the quartzites and shales of the Lower Quartzite formation and a considerable portion of the overlying White Limestone, striking N. 15° E. and dipping 20° to the east. Hoosier pass ridge—QOn the slopes of the Hoosier pass ridge, just above Montgomery, about one hundred feet of the Lower Quartzite are again ex- posed in section, with two parallel intrusive sheets of porphyrite, the one 10, the other 40 feet thick; the whole dipping 25° to 30° east, with a strike to the west of north. This rock is the mica variety, having for its chief con- stituents a white plagioclase feldspar, with a much altered biotite and a few scattering quartz grains, in a dull-green groundmass. The general line of contact of the Cambrian is traceable along the slope towards the crest of the North Peak ridge, but distinct outerops are first found again at the saddle between Montgomery and the Blue River, over which a horse-trail leads. This saddle marks the outcrops of the Blue Limestone, which consist of a dark iron-stained dolomite, weathering black and carrying thin seams of barite. On the east of the saddle its limits are somewhat loosely defined by outcrops of blue shales, carrying casts of Zaphrentis and corals, which form a little knoll on the ridge, and may be assumed to belong to the shale member of the Weber series. On the west of the saddle, outcrops of the Blue and White Limestones extend to the steeper slopes of the North Peak ridge, where their limits are defined by a bed of green, fine-grained, silicious shale, impregnated with cubes of pyrite which at times forms beds a foot in thickness. Only the Lower Quartzite beds extend west of this on to the higher portion of the ridge. The work- ings of the now abandoned North Star mine on the first shoulder of the ridge have, as shown by the dump, passed through this quartzite into the schists of the Archean. On the northeast face of the ridge, overlooking the valley of the west fork of Blue River, is a small amphitheater with a little lake in its basin, which the topography of the map shews but imperfectly. It is entirely in re ee HOOSIER PASS SECTION. 101 the Archean, with the exception of a thin rim of Cambrian quartzite around its upper walls, and was probably carved out by a tributary of the main Blue River glacier, which descended the gorge from the back of Quandary Peak. A section was made from this saddle eastward across Hoosier pass to Hoosier Ridge, which connects the Silverheels massive with the group of hills to the north that constitute the eastern boundary of the Blue River Valley. This ridge also forms the divide between the waters of the Blue and Upper Platte Rivers and those of Tarryall Creek. No satisfactory measurements could be obtained of the thickness of the members of the Carboniferous group above the Blue Limestone, as was hoped: first, because the line followed did not cross the strata at right angles, but at times almost followed the strike; secondly, because of the great number of beds of porphyry included in the section, whose thick- ness could not be determined; and, thirdly, because of the evidence of a syncline on Hoosier pass itself. Nevertheless, the data obtained are given here somewhat in detail, as it was one of the few opportunities offered during the investigation to follow continuously the ascending series of beds from the Blue Limestone up to the assumed top of the Carboniferous formation. From the saddle eastward to the grass-covered summit of the pass the outcrops may be assumed to indicate a thickness of about two thousand feet of beds. In this are included those of two prominent sheets of porphyry, which are apparently interbedded. On the first hill east of the saddle is an outcrop of shales, containing indistinct casts of fossils, apparently Zaphrentis and corals, which probably form part of the Weber Shales. The other outcrops are of the characteristic gritty rocks of this series (either micaceous, quartzose schists or coarse white sandstone, rich in muscovite and often passing into conglomerate) and one bed of black argillaceous shale, which all show a conformable dip to the east and north. The grass-grown glades which form the summit of the pass leave a gap about half a mile without outcrops. Towards the eastern side, and overlooking the head of Blue River,-a prospect shaft on the Ready-Pay claim has cut a body of light- gray limestone, which is probably one of the thin beds of limestone found in the middle of the Weber Grits series. This limestone, as well as an 102 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. outcrop of coarse white sandstone a little east of the shaft, has a dip of 30° to the westward, with a strike of about N. 25° W. On the slope of the pass towards the Platte Valley the Dead-Broke tunnel discloses what is probably the same bed of limestone, with sandstones dipping in the same direction. A body of light-colored mica-porphyrite is also cut in the end of the tunnel. The existence of a synclinal fold, as proved by these western dips, is in complete accord with the evidence, obtained farther south along the flanks of the ridge, of a secondary roll or minor fold in the strata parallel to the great fold of the center of the range, and explains the great thickness of exposures of Weber Grits beds. That the fold may have been accompanied by faulting is possible, but, as already stated, no direct evidence of a fault was found. Perhaps, had time permitted, a careful exploration of the ravine at the head of the Blue River and on the west face of Hoosier ridge might have afforded more definite proof. As it is, the geological outlines given on the map are generalized from observations made on the spur connecting it with Hoosier pass. The results of these observations are graphically shown in section A A, Atlas Sheet VIII, for the eastern end of which, beyond the Platte Valley, they furnished the data. The largest body of porphyry there shown, which forms the shoulder of the spur above Hoosier pass to the east, consists of typical Lincoln Porphyry (54). It contains the usual large pinkish crystals of feldspar, which in this rock, however, seem excep- tionally susceptible to alteration and, instead of being fresh and rather glassy in appearance, are opaque and often quite kaolinized. The micro- scope shows rather more plagioclase than in the type rock, which may be accidental. The quartz occurs in small, double-pointed, hexagonal pyramids showing also the development of the prism; and on the crest of the spur, where, owing to the gentle slope and accumulation of soil, decomposition seems to have gone on most freely, the rock surface is covered with a coarse sand made up almost entirely of such quartz crystals, often with well defined angles and facets. The steep north slope of the spur, facing the basin-shaped head of an eastern tributary of the Platte, shows a cliff wall of this rock with characteristic cross-jointings and vertical cleavage, almost amounting to a HOOSIER RIDGE. 103 columnar structure. The thickness of the body can be hardly less than five hundred feet, as roughly determined from the width of the outcrop on the spur. That it forms so regular a sheet as shown in the section is an assumption based only on analogy from other sheets of porphyry observed in the Silverheels massive. It apparently has its greatest thickness at this point, and thins out to the south and east, and in this respect has something of the laccolite form; but there is no evidence of any sudden steepening in the dip of the adjoining strata. On the contrary, the sandstone beds imme- diately overlying it, as shown in the outcrops on the crest of the ridge, have a regular dip eastward of about 10°. Only a few hundred feet of sand- stones and sandy shales separate this from the next succeeding sheet of por- phyry, which forms the cap of the first prominent shoulder about twelve hundred feet above the pass. This is a blue-gray rock, weathering yellow, of quite distinct habit, having a conchoidal fracture and a tendency to weather into sherdy fragments. It approaches the normal Silverheels Por- phyry, although coarser grained, showing few distinct crystalline ingre- dients when freshly fractured. On its weathered surface, however, fine needles of hornblende are easily distinguishable. Beyond another body of sandstone and shales, and a similar though not identical body of porphyry which caps a second shoulder, a body of argillaceous shales of green, red, and purple colors marks what is assumed as the base of the upper division of the Carboniferous group. From these to the main crest of Hoosier ridge are several outcrops of porphyry sheets and intervening gaps of shaly rocks; among which a bed of dark-blue limestone, about a hundred feet in thickness, stands out prominently on ac- count of its black weathered surface, opposite the head of the north fork of Beaver Creek. From this were obtained the following Coal Measure fossils : Athyris subtilita. Bellerophon, (sp. ?). Productus cora. Fenesteila, (sp. 2). Pleurotomaria, (P. Valvatiformis ?). And spines of an Archeoccidaris. Loxomena, (sp. °). On the crest of Hoosier ridge are the reddish sandstones which form the passage from the Upper Carboniferous formation into the overlying 104 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Trias, dipping 15° to 20° east and north. Two other beds of limestone at least are found in this formation, on the same line of strike southward along the western face of Silverheels and in the valley of Beaver Creek, and they may occur here in some of the numerous covered gaps in the section. Silverheels Massive—In order to complete the somewhat meager data obtained upon the upper member of the Carboniferous group on this side of the range, the observations made in the region west of the Platte Valley will be next recorded, comprising in this the eastern portion of Mount Silverheels and Beaver Ridge, with the included valley of Beaver Creek. In a general way the eastern half of Mount Silverheels may be said to be Mesozoic, in great part probably Triassic, while its western face be- longs to the Upper Coal Measures, and Beaver ridge to the Weber Grits. The included porphyry sheets in the former rocks have a more recent and trachytic appearance, like that found at the forks of Crooked Creek; those in the second group being rather of the Silverheels type, and those in the Weber Grits either identical with or similar to the Lincoln Porphyry. The number of these porphyry sheets is probably very much greater than is shown on the map, which represents a generalized outline of the more important bodies, deduced from observation made along three transverse lines only in the area represented east of the Platte; while in that portion of the mountain which lies east of the boundary of the map the porphyry bodies are, if anything, still more numerous. The swelling out of the strata, produced by the intrusion of such considerable masses of eruptive rock, is readily shown by the variations in the strike and dip. The steep north wall of Silverheels, as seen from the summit of Hoosier pass for instance, shows a fan-like arrangement of the easterly-dipping strata, which open out as it were to the west. In other words, the section shows strata on the west foot of the mountain, towards Beaver Creek Valley, dipping only 10° east; at the summit of the peak the dip has increased to 17°, while at the eastern extremity it is 22°, 25°, and even 35°. The divergence in strike produced by the bowing-out of the strata is less evident on the map, owing to the fact that at the point of greatest divergence the great elevation of Silver- heels above the surrounding valleys brings the outcrops, as projected on a a ee ie wi MOUNT SILVERHEELS. 105 map, so much farther west. A rough calculation of the difference in thick- ness of given east and west sections, taking the one on a line passing through Fairplay, the other through the summit of Silverheels, would give an increase in thickness in the latter case of 3,000 feet, which may be assumed as the aggregate mass of the intruded porphyry bodies at the latter point, since on the line through Fairplay they have very largely disappeared by thinning out. On a line eastward from Platte Valley to the summit of Silverheels the succession of rocks is as follows: Beaver Ridge, immediately adjoining the Platte Valley, whose steep slopes are covered with a thick forest growth which impedes observation, consists of the coarse grits of the Weber for- mation, with two principal and probably some minor bodies of Lincoln Porphyry. The valley of Beaver Creek, a straight depression in the line of strike, is apparently cut out of the softer shaly members at the top of this formation. From its bottom up the steep face of Silverheels are many porphyry bodies, whose débris often so obscures the outcrops that no con- tinuous section can be obtained. In this extent five sheets of porphyry and one bed of gray limestone were observed; these alternate with shales and micaceous sandstones, which pass at the summit of the peak into conglom- erates. A considerable number of these conglomerates outcrop on the ridge running eastward from the summit, alternating with purple and green shales and with sheets of porphyry, of which no less than eight were counted. The conglomerates contain an unusual number of rounded and sub-angular fragments of the more resisting Archean rocks, together with the rounded pebbles of pinkish milky quartz which are common in all the sandstones of a coarser nature. Beyond them the brick-red sandstones of the Trias become the prevailing rock, their dip steepening on the east slope to 25° and 35°. Along the west face of Silverheels the porphyry beds, which resist better the action of abrasion, can be traced in curving contours along the slopes, capping the more prominent shoulders of the spurs and disappearing from sight in the forests which clothe the lower spurs to the south. ; The type of the Silverheels porphyry (89), which is found at the sum- mit, is a fine-grained rock of slightly greenish-gray color, having a con- 106 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. choidal fracture, a sherdy habit, and a clear ring under the hammer. It is composed of feldspar, hornblende, and biotite, with a little quartz, and con- tains from 60 to 63 per cent. of silica. To the naked eye no groundmass is visible, although the crystalline ingredients are so minute (being gener- ally less than 1"™ in size) that they cannot readily be recognized. A com- mon variety (90) among the lower beds on the west and north is of coarser grain and more decidedly green color, due doubtless to the presence of chlorite. The most southern of the three transverse lines above mentioned runs eastward from a little south of Alma, crosses several low forest-covered ridges separated by small valleys, and shows only detached outcrops sep- arated by frequent covered gaps. In this section only one body of por- phyry and three distinct horizons of dolomitic limestone were found. The beds, moreover, have a strike somewhat east of north and a dip of 25° or more to the eastward, instead of a strike to the west of north and dips of 10° to 15°, which prevail opposite the summit of Silverheels. The low ridge bordering the Platte Valley is covered on the west side nearly to its sum- mit by the lateral moraine of the Platte glacier, which must therefore at one time have filled the valley to a level about 400 feet above its present bottom. Lincoln Porphyry, a continuation of one of the bodies seen in Beaver Ridge to the north, is disclosed by prospect holes. Various deep- red sandstones are crossed, alternating with limestone and shales, but the characteristic brick red of the Trias is first found at Crooked Creek, to the east of Fairplay, in the forks of which is another important sheet of por- phyry, probably the porphyritic trachyte of the Hayden map. This is in- teresting as being different in appearance from any of the other porphyries observed in the region and resembling that found in a railroad cut through a Cretaceous ridge near Como. Nevertheless it does not possess the char- acteristics of a Tertiary rock, unless a slightly rough feel may be consid- ered such. It is of light-gray color and contains abundant porphyritically disseminated crystals, mostly of white opaque feldspar, in a subordinated groundmass. Two feldspars, hornblende, altered biotite, and quartz in large but infrequent grains form its macroscopical constituents. Microscopically the groundmass is seen to be evenly granular and the rock to be simply a on wo a es MOUNT LINCOLN. 107 porphyritic or coarser-grained modification of the Silverheels type, with no glass inclusions or other characteristics of Tertiary volcanics Lincoln Massive —The Mount Lincoln massive, as is shown on the map and as may be seen in the sketch given in Plate IX (page 95), is divided by a deep glacial gorge, heading at the base of Mount Cameron, into two mountain masses: that of Mount Lincoln on the north and that of Mount Bross on the south. On the east face of either of these mountains are two smaller glacial amphitheaters, to which the names of their respective peaks have been given. The beds of each of these three gorges stand at a much higher level than the adjoining beds of the Platte and Buckskin gulches; and, if the glaciers which once filled them were ever directly connected with the main Platte glacier, later erosion has removed evidences of this fact. At all events, it is apparent that after the Glacial epoch, when the ice was eradually receding, these were separate glaciers or névé fields. This fact is more particularly manifest in the Lincoln amphitheater, in the middle of which stands a moraine ridge, outlined in the sketch above mentioned, which ends abruptly at the lower end of the amphitheater, about 700 feet above the level of Platte Valley. These amphitheaters have more signifi- cance geologically than their topographical importance would indicate, inasmuch as erosion, having once cut through the overlying and more resisting mantle of sedimentary beds, has carved deeply into the underly- ing Archean, leaving characteristic semicircular walls at their heads which afford most useful sections for studying the interior structure of the mount- ain mass. Mount Lincoln itself has three spurs stretching out to the eastward: a northeastern, an eastern, and a southeastern. Lincoln amphitheater is included between the two first. The surface of these spurs is covered by beds of the Paleozoic system, dipping eastward at an angle of 10° to 15°. This is the average inclination of the beds over the main portion of the mountain mass; but, as already mentioned in the case of Quandary Peak, the dip becomes steeper on the extreme eastern flanks. In general, how- ever, the slope of the spurs themselves steepens for a short distance more rapidly than the dip, in consequence of which there is a belt of lower beds exposed along the foot of the steeper slopes. 108 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. The eastern spur of Lincoln, a narrow straight ridge, being relatively much lower than the northeastern or southeastern spurs, is covered only by beds of the Cambrian formation, the White and Blue Limestones which still cap the other spurs having been removed by erosion. Section B B, Atlas Sheet VIII,’ passes through this spur and shows its profile and geo- logical structure as well as can be expressed on so small a scale. In addi- tion to the normal eastern dip, the beds have also a decided inclination to the south, so that the spur presents a perpendicular wall on the north towards Lincoln amphitheater, with a shallow ravine on the south sepa- rating it from the southeastern spur, the slope of the spur in that direction corresponding nearly with the dip of the beds. This southern dip is the relic of a lateral fold or slight corrugation produced by the forces of con- traction acting in a northerly and southerly direction at right angles to the major force. The Lincoln amphitheater is thus shown to have been cut out of the axis of an anticlinal fold, and in the sedimentary beds still re- maining on the northeast spur a slight inclination to the northward can still be detected, showing that they formed the northern member of this subor- dinate fold. The Cambrian quartzites which form the mass of the spur are of the characteristic white saccharoidal variety, thinly and evenly bedded, and contain a slight development of white limestone, which has been oceasion- ally observed elsewhere in this formation. At the eastern end of the spur is a cliff of quartzite, just above timber-line, below which the beds assume a steeper dip, so that the lower slopes are occupied by outcrops of succes- sively higher horizons. At the foot of this cliff are several prospect holes, following deposits of copper and iron pyrite near or in contact with a body of decomposed quartz-porphyry. A sheet of Lincoln Porphyry, which may be part of the same body, caps the spur above the cliff and is cut through by what seems to be a dike of porphyrite. The porphyrite contains both biotite and hornblende (the latter being, however, largely predominant) and is more decomposed than porphyrite rocks generally, both these minerals By an error in proof-reading, the line of this section, as given on the map in blne (Atlas Sheet VI), is partially wrong. It should pass from the summit of Mount Cameron to that of Mount Lincoln, and from there down the eastern spur, whereas on the map it passes directly from Mount Cameron to the spur. —<2 8 eS a oe MOUNT LINCOLN. 109 being mostly altered to chlorite. Its groundmass is crystalline and con- tains a considerable development of calcite. Magnetite is also plentiful and has been frequently changed into hydrated oxide of iron. Muscovite is frequently present as an alteration product of plagioclase. The rock as usual contains many fragments of Archean, in this case of muscovite-gneiss. The Lincoln Porphyry is like the normal type, but contains few large feldspar crystals. Besides these is a more compact rock, apparently a contact product, which in general differs from either rock; however, some specimens show its probable connection with the Lincoln Porphyry. Its biotite and hornblende are completely changed into chlorite and epidote. The groundmass is very fine and not resolvable into its elements. In ascending the regular slope of the ridge westward, as the dip of the formation is slightly steeper than this slope, successively lower beds of quartzite are crossed, and towards its upper end several interbedded sheets of porphyrite. These can be traced along the steep cliff wall overlooking Lincoln amphitheater, and are seen to follow the stratification lines for a considerable distance to the eastward and suddenly bend down into the underlying Archean, thus affording one of the few opportunities of observ- ing the change from a vertical dike into an interbedded mass. Owing to the contrast of the dark color of the porphyrite with the white including quartzite, these bodies can be distinguished from a great distance, and are distinctly visible from the opposite side of the Platte Valley, on the road which leads from Montgomery to the Hoosier pass. At its upper or western end, opposite the head of Lincoln amphithea- ter, this eastern spur merges into a basin-shaped valley with débris-covered slopes. On the east face of the northeastern spur, at the head of Lincoln amphitheater, a bare cliff wall affords a section of the lower sedimentary beds and included intrusive sheets, the whole mass much shattered and dislocated. Although time did not admit of the study of these cliff-sections in detail, as was done in the case of others which will be noticed later, the dark color of the intrusive masses and fragments obtained from the débris show that they are largely of porphyrite, and therefore are probably parts of the sheet already noticed on the east spur. 110 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. The upper surface of the northeastern and southeastern spurs of Lin- coln, respectively, is mainly formed of beds of Blue Limestone, which have been opened by innumerable prospect-holes and several considerable mines on either spur. On the steep cliff faces towards the Platte canon and the Cameron amphitheater, respectively, the limits of this formation and those which underlie it can be distinctly traced. On the more rounded interior slopes débris of Lincoln Porphyry obscure very largely the actual rock surface. For this reason and also owing to the small scale of the map, the outlines of the formations there indicated are somewhat generalized. The sharp summit of Lincoln itself is made up of a mass of typical Lin- coln Porphyry, projecting boldly above the sedimentary beds and noticeable for its vertical cleavage planes, producing a columnar structure which is best seen on its steep south face. Lincoln Porphyry is also found for a consid- erable distance down the east spur, and with it are associated shales and erits belonging to the Weber Shale formation. The short, sharp ridge directly west of the summit of Lincoln, and between it and the saddle that separates Mount Lincoln from Mount Cameron, is also composed of a series of beds which evidently belong to this horizon. They dip somewhat sharply to the east and consist of greenish, yellowish, and reddish shales and of micaceous quartzites, with a bed of black shale near the top, comprising in all a thickness of about two hundred and forty feet. Below this is a bed of Lincoln Porphyry, evidently interstratified, while on the saddle itself are outcroppings of Blue Limestone. A deserted mine on this saddle, known as the Present Help, the highest mine probably in the United States, is ap- parently at or near the contact of the Blue Limestone with the overlying porphyry ; its workings had been abandoned and were inaccessible. The intense metamorphism shown in all the sedimentary beds near the summit. of Lincoln and the columnar structure of its porphyry render it probable that the mass which forms the peak is directly above the channel through which this rock was erupted. There is evidence also that from this channel a sheet of the same rock was spread out over the surface of the Blue Lime- stone, which was probably the determining cause of the great concentration of mineral at this horizon. —— ee ae ee ee gee Lio aw eaw “se ~ MOUNT LINCOLN. 111 The typical Lincoln Porphyry, as found on the summit of Mount Lin- coln itself, is characterized by large orthoclase crystals, which sometimes reach two inches in length, of pinkish color, generally Carlsbad twins, and often so fresh and glassy in appearance as to remind one of the sanidine crystals of more recent rocks. There are five or six large crystals as a rule in an ordinary hand specimen. The smaller feldspars are white, and a large number show distinct strie. Quartz is very abundant and rela- tively large, in round grains, often of pinkish hue, and showing more or less plainly the faces of dihexahedral crystals. Biotite in darker or lighter green leaves, according to its condition of decomposition, is quite conspic- uous in the rock. A few specks of specular iron are sparingly scattered through the rock. The groundmass is light green or pinkish and is quan- titatively quite subordinate to the crystalline element. Under the micro- scope it is seen to be fully crystalline. Such is the typical Lincoln Porphyry, which projects in lofty columns from the summit of the mountain in a sharp apex which overtops all the surrounding peaks. Owing to its exposed situation it attracts the storm clouds from all the regions around, and even in midsummer scarcely a day passes without a slight fall of snow or hail on the summit. The very topmost rocks show traces of discharges of the electric fluid in the forma- tion of fulgurite, which encircles the little holes it has bored into the rocks. Around the base of this summit mass of porphyry its contact with the sed- imentary rocks is obscured by débris, the few outcrops that are seen being composed of rocks so much altered that their original character cannot be determined. Cameron amphitheater.—Qn the steep south face of Lincoln, a sketch of which is shown in Plate XI, a careful study was made of the various erup- tive masses. The Lincoln Porphyry of the eastern edge of the summit is of a much darker color than the normal rock and contains few or none of the larger feldspar crystals. It is so much decomposed that only in the center of large blocks is the original grayish color preserved ; but the round quartz grains are distinct throughout. The Blue Limestone, which here seems to have a brecciated structure, can be traced as a horizontal line across the face of the cliff, from the Present Help mine on the west to the 112 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Russia mine on the east, immediately below a bed of Lincoln Porphyry. Along the edge of the steep ravine which descends directly from the summit of Lincoln an irregular dike of porphyry crops out here and there, colored brilliant red and yellow on its surface, but so much decomposed that its original structure can no longer be determined. As shown in the sketch, it is only the Silurian (¢) and Cambrian (b) strata which form continuous out- crops across the cliff face, and these are somewhat broken by transverse dikes of eruptive rock. Within the Cambrian quartzite is an intrusive sheet of Lincoln Porphyry, whose darker color contrasts strongly with the bleached weathered surfaces of the summit rock. The base line of the Cambrian, where it rests on the Archean, appears more irregular in the sketch than it is in nature, but it is evident that the Cambrian sea bottom was not so smooth here as it is shown to be in other cliff sections. In the ravine next east from that already mentioned is a dike of White Porphyry, which can be traced, as shown in the sketch, from the gneiss of the Archean across the Cambrian quartzites into the White Limestone. This is dike No. 1, whose rock has already been described under that which oceurs on the north face of Lincoln. Its outline is extremely irregular, and its contact surfaces with sedimentary rocks, which are distinctly visible, show none of the contact phenomena supposed to result from the heat of a fused mass. In its upper portion it is rounded, and curves over one of the heavier beds of White Limestone in an oval mass. On its east side, near its summit, the thinner beds of limestone are bent upwards, as if displaced at the time of its intrusion, and the lower shale beds of the White Limestone belt are more or less serpentinized. It also sends out offshoots a few inches wide through the natural joints of the sedimentary beds. About fifteen to twenty feet above the base of the Lower Quartzite it crosses an interbedded mass of porphyry of a dark-green color, which is here some thirty feet in thickness. This interbedded porphyry is thoroughly decomposed, the only crystals visible being rounded quartz grains, which resemble those of the Lincoln Porphyry. All its cleavage planes are covered by a dark-green coating of chloritic nature, and it is crossed by thin perpendicular fissures, from one to two inches in thickness, containing pyrites and having a bright- yellow weathered surface. A comparatively fresh specimen was obtained GEOLOGY OF LEADVILLE PL xT U.S._GEOLOGICAL SURVEY oe marth rn pe iieee 'S.F. Emmons, Geologist-in- Charge. Julius Bien & Co lith. a en. SUMMIT OF MT LINCOLN AND NORTH WALL OF CAMERON AMPHITHEATRE {UPPER END| MOUNT LINCOLN. bis with some difficulty, which shows the characteristic large, pink, orthoclase feldspars of the Lincoln Porphyry. In this the green color is seen to be due to the alteration of biotite into a chloritie substance, which has been deposited on the surface of the smaller feldspars, so that they are scarcely distinguishable by the naked eye. Biotite is also no longer visible except under the microscope. Pyrite can be distinguished throughout the rock by the naked eye. The Archean rocks (a) at the base of this section consist almost en- tirely of dark-gray gneiss. In this the White Porphyry dike can be traced but a short distance, as it is soon lost under the steep talus slopes at the foot of the cliff. A few hundred feet east of this dike (to the right in the sketch) a second dike (No 2) can be traced, though less distinctly, from the gneiss entirely across the Cambrian and Silurian formations, apparently terminating at the base of the Blue Limestone. It is much narrower and straighter than dike No. 1, and like that seems to have a northeast and southwest direction. Its rock is a light-colored, fine-grained, highly-crystalline porphyry, belonging to the type designated as Mosquito Porphyry, which has already been de- scribed. There is an outcrop of the same rock in the Archean, on the west wall of the Cameron amphitheater directly under Mount Cameron, which may possibly be part of the same body, although the intermediate region is too much obscured by débris to trace any direct connection. Eastward of this cliff face the northern wall of the Cameron amphi- theater is much covered by débris for the distance of nearly a mile, in which extent, although the general dip of the sedimentary beds can be traced, no opportunity was presented for an examination of the intrusive bodies. Near the eastern end of the wall, however, is a second cliff section, which shows in a very instructive manner the position of the intrusive masses and dikes. It is graphically represented in Plate XII, which, like the preceding plate, is copied from sketches made on the spot by Prof. A. Lakes. The section was studied by Mr. Cross, from whose notes the following deserip- tion is largely taken. Here, as in the section just described, is an intrusive interbedded mass of porphyry in the Lower Quartzite (b), only a few feet above its base, MON XII——8 114 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. which is also crossed by a nearly vertical dike. This vertical dike, as may be seen on the left half of the sketch, can be traced from the Archean up to the base of the Blue Limestone. It is from fifteen to twenty feet wide at the bottom and branches at the top into five small arms, but does not spread out between the strata. Its rock isa White Porphyry, which differs from any of those observed elsewhere in carrying large orthoclase feldspars, sometimes an inch in length. They are Carlsbad twins, and have a pinkish tinge like those in the Lincoln Porphyry. Small rounded grains of quartz are also abun- dant, but no trace of hornblende or biotite could be seen, either by the naked eye or with the microscope. Under the microscope the feldspar is seen to be partly plagioclase, and in the quartz are many small fluid inclusions. The in- terbedded porphyry mass, like that on the south face of Lincoln, is prominent by its dark color; but on examination it is seen to consist of two distinct rocks, one of which seems to have pushed its way through the other after it had been already spread out between the beds. The later rock is a Lin- coln Porphyry, whose outlines can be distinguished from a little distance by its peculiarity of weathering, its fragments showing larger surfaces than that of the earlier rock. The earlier rock is of a light-green color, and shows, to the naked eye, scarcely any distinguishable crystals, feldspars being decomposed to a substance very like groundmass. Altered horn- blende, a few biotite leaves, and an oceasional quartz grain can be distin- guished by the lens; also, a few small specks of some metallic combination. Under the microscope the groundmass resolves itself into a fully erystal- line admixture of quartz, mica, and feldspar. Calcite is present in filmy particles and occasionally in grains. The larger quartz crystals contain fluid inclusions. The contact specimens of these two porphyries show a blending of the characters of the two in the tendency to the formation of large quartz and pink feldspar crystals in a base more like the older por- phyry. As shown in the sketch, the Lincoln Porphyry throughout the greater extent of the section is entirely included within the older mass. Towards the eastern end, however, it forms a distinct bed above the other, and each sends off a branch upward ina northeast direction across the strata, forming nearly parallel dikes which meet at the surface of the ridge. These a ee ee ee y U.S.GEOLOGICAL SURVEY Julius Bien & Co.lith =I GEOLOGY OF LEADVILLE, PL. XI. Geologist-in- Charge. S.F. Emmons, AMPHITHEATRE. ft 4 MOUNT CAMERON. 105 dikes are about fifteen feet in thickness each, while the combined beds have a thickness of from fifty to sixty feet. This intrusive sheet of Lincoln Porphyry at the Cambrian horizon, which seems continuous along the north wall of the Cameron amphitheater, was traced out to the end of the southeast spur of Lincoln; and what is apparently the same bed was also observed lower down the slopes, in the more steeply-dipping members of the same formation. Outerops of simi- larly situated bodies, as shown on the map, are also found on the south wall of the Cameron amphitheater and on either wall of the Bross amphitheater. Time did not permit of tracing any connection between these different out- crops; and it seems doubtful whether any exists, inasmuch as for some un- known reason there seems to have been much less tendency to spread out in extensive sheets at this horizon than at that above the Blue Limestone. Although this latter porphyry bed is only found to a limited extent above the Blue Limestone on Mount Lincoln, there is no doubt that it once covered that bed, forming a sheet comparable in extent to that of the White Por- phyry in the Leadville district. Cameron and Bross—The summit slopes of Mounts Cameron and Bross, except those on the cliff faces which are too steep to permit the lodgment of débris, are mainly covered by fragments of Lincoln Porphyry. Eruptive rocks under the action of atmospheric degradation split up into fragments whose shape and relatively small weight, as compared with their superficial area, render them more susceptible to being moved by melting snow, so that on mountain sides they generally cover a surface disproportionately large as compared with their actual outcrops. This is eminently the case on Mount Bross. where angular fragments of porphyry often cover the surface to a depth of ten feet or more and the character of the underlying rock can often only be determined by actual excavation. The porphyry of the summit of Mount Cameron is remarkable for the unusual development of large orthoclase crystals, often more than two inches in length, which weather out from its surface. Associated with the much-weathered fragments of porphyry are various brown quartzitic sand- stones, which may represent a bed of the Weber Grits formation not yet 116 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. eroded off the summit. No sufficient evidence was found, however, to justify its indication on the map. On Mount Bross the Lincoln Porphyry shows a still lighter color than that on Mount Lincoln, which seems due to the fact that the decomposed nica, instead of remaining as chlorite, has been entirely removed Frag- ments of shales and quartzitic sandstones of the Weber Grits formation are mingled with the porphyry débris of the upper slopes of Bross, and out- crops of these rocks are found on the ridge connecting it with Cameron, as well as to the south of its summit on the ridge overlooking Buckskin gulch- In the latter instance they stand at a much steeper angle than the lower series of Paleozoic beds, and give evidence of some local movement. In Section L, Atlas Sheet X, is shown the probable form of the Lincoln porphyry body on the summit of Mount Bross, as deduced from observed outerops. It is very possible that, like that of Mount Lincoln, it stands over a channel of eruption, but the evidence of this was not considered strong enough to justify its being indicated on the plane of the section. On the north face of Mount Bross, towards Cameron amphitheater, the base line of the Paleozoic formations can be traced with tolerable dis- tinctness. Of dikes crossing the formation, like those on the face of Mount Lincoln opposite, there are doubtless many, but only one was actually traced, which is cut by the western workings of the Moose Mine. In the Archean below this mine is a prominent mass of light-gray granite. The workings are in the Blue Limestone, which is exposed on the east spur of the mountain between the Cameron and Bross amphitheaters, forming the sur- face of the spur, until cut off by its steeper slope, whose angle is greater than that of the dip of the beds. This bed is completely honeycombed by abandoned mine workings, but the underlying White Limestone here, as in the Leadville district, seems to have yielded little or no ore. At the foot of the spur, erosion has exposed the quartzite beds of the Cambrian, in which is a prominent dike of porphyry running from the edge of Bross amphitheater a little north of east, in the direction of the summit of Mount Silverheels. It was traced as far as the secondary ridge bordering the Platte Valley into the White Limestone, where it was lost in the forest. MOUNT BROSS. TEA The rock (88) of which it is composed differs from any yet described. Its weathered surface is so white that at first glance it might be taken for the White or Leadville Porphyry. On a fresh fracture it has a light-green color and shows few macroscopical crystals. It has certain resemblances to porphyrite and also to the Silverheels Porphyry, but the microscope shows it to be identical with the quartz porphyry found on Loveland Hill and on the north wall of Mosquito Gulch, which has been described under the name of Green Porphyry. Bross amphitheater, like those of the other two peaks, lies nearly due east of the summit, but, owing to the steeper inclination of the Paleozoic beds which cap its walls, it has not been carved to so great a depth into the underlying Archean schists, whose outcrops are therefore of much less superficial extent. As in the others, the highest beds exposed in the cliff sections on its walls are those of the Blue Limestone. Shales, probably belonging to the Weber Shale formation, are disclosed in prospect holes along the road which curves round its head, and very possibly a consider- able portion of the area which has been given the color of porphyry on the map may prove by actual excavation to be underlaid by beds of this for- mation. The road which leads by the Dolly Varden and Moose mines, along the north face of Mount Bross and the west face of Mount Cameron, to the Present Help mine, on the south face of Mount Lincoln, is indicated on the sketch in Plate IX by a light double line, the location of the respect- ive mines being shown by the house outlines. The Dolly Varden mine, on the spur south of the amphitheater, finds its ore in the Blue Limestone adjoin- ing a dike of White Porphyry 40 feet in thickness, which crosses it at an angle of 60° with the horizon. Below the Dolly Varden mine the spur slopes more steeply than the beds, and at its base the Parting Quartzite of the Silurian is exposed. In the basin-shaped valley called Mineral Park, south of this spur, erosion must have exposed still lower beds than on the spur, and it is possible that the quartzite beds said to be exposed there may belong to the Cambrian. The ridge running south from Mount Bross, between Mineral Park and Buckskin gulch, is mainly covered by easterly-dipping beds of the Blue 118 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Limestone horizon. There are several bodies of Lincoln Porphyry, besides the main sheet near the summit, which are not shown on the map, as time did not admit a sufficiently detailed study to determine their outlines or whether they were remnants of this sheet or distinct bodies. The upper part of the Blue Limestone on this spur seems to have been particularly rich in black chert concretions, which now lie scattered over the surface of the ground, and from which Prof. Lakes obtained the following fossils : Spiriferina (sp. like S. Spergenensis). l Athyris subtilita. Spirifera Rockymontana. Streptorynchus crassus. Productus costatus. Pleurophorus oblongus. Buomphalus (sp. ?). These were mainly collected in a slight depression of the ridge, where the overlying porphyry had been eroded off, and therefore must have come from the upper part of the horizon. The lower Paleozoic beds are exposed in section at various points along the steep western wall of this spur, which faces Buckskin gulch. They were examined at two points. At the extreme southern end of the spur, just above the town of Buckskin Joe, where the steeper eastern dip of the formation comes in, several ore bodies have been discovered, and the now abandoned mines (the Excelsior, in White Limestone, and the Cri- terion, in Lower Quartzite) were once worked. At the Criterion mine a thickness of 150 feet of quartzites was measured between the Archean and the first bed of White Limestone. The ore bodies are accumulated here along vertical planes, running northeast and southwest, which seems to be. the direction of a dike of dark-green decomposed porphyrite, whose out- crops are found in the ravine below the mine, near the contact with the Archean. There is evidence also of a slight displacement along a plane running northeast and southwest, whose upthrow is to the west. At the Excelsior mine, which is about a quarter of a mile farther west, near the point of the cliff in the angle of the gulch, the ore bodies follow similar and nearly parallel planes. A section measured on the cliff near the mine gave the following thicknesses, in descending series : MOUNT BROSS. 119 Feet Blue Limestone, covering surface of spur ..........-.... 2 SHEAR, oil j Parting Quartzite (exposed in prospect holes) -....-.--. 2 ( White Limestone, partly covered by débris, estimated .. 200 @shalestandesa divglinGStOMGS erie eter are tee eta 35 | Gray quartzite, impregnated with metallic mineral ....-. 20 Massive nwhitevquamtziteysar- 2a <2 e- 4)e eee 6 Cambrian... .. -- J Greenish quartzite, with caleareous layers .......------ 8 Wihitesaccharoidaliiquantzite = oe 2-2-2 4.2.22 -522-5 12 - = 10- Greenish-white, compact, thiu-bedded limestone....-... 3 l \Wiltitetsaccharoidal quartzite 2222-4 2s5- 2-455 22-5. 4/2. 55 137 INTO NCHS SENS eidae BASE ora Re CORON IS REITER eR Sa ata eae eo a ? The limestone bed in this section is of interest as being the only one examined from this region which was not a dolomite. It contained 25.48 per cent. carbonate of lime, 4.03 carbonate of magnesia, with traces of chlo- rine, the residue being mainly silica. It has already been noted that the Cambrian beds in their upper part are often more or less calcareous, but generally resemble a sandstone on the surface, whereas this bed has the compact, even texture and clean fracture of a limestone. The strata at this point dip 15° to the east, with a strike a little east of north. Red amphitheater— Nearly under the summit of Mount Bross and high up on the east wall of Buckskin gulch is the Red amphitheater, a semi- circular recess in the cliff-wall nearly a thousand feet above the bed of the valley. ‘The scale of the map does not permit an adequate expression of the form of this remarkable basin, which is rendered still more prominent by the brilliant red and yellow coloring of its walls. This color comes from a thin coating of ocherous clay, which covers the rock fragments of débris piles, and which contains, besides oxide of iron, traces of arsenic, antimony, and sulphur. The rock fragments thus coated are so much decomposed that it is seldom possible to determine their original character, and it would have taken much more time than was available to thoroughly decipher the geological history of this remarkable locality, which has evi- dently been the scene of long-continued metamorphic action, probably a sequence of the eruption of the igneous rocks now forming dikes and intru- 120 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. sive sheets in the Archean and overlying Paleozoic beds. The results of the metamorphic action are shown, not only in the decomposition and coloring of the rocks above mentioned, but in the marbleizing of the limestones and the large development of serpentine within these limestones. The eruptive bodies developed here consist, besides the large body of Lincoln Porphyry near the summit of Mount Bross, first, of a considerable body of augite-bearing diorite (96), which cuts through the Archean from the valley below up into the bed of the amphitheater, and either spreads out along the base of, or extends into, the Cambrian beds under the talus slopes of débris; secondly, of a dike of White Porphyry, crossing Silurian and Carboniferous limestones in a vertical direction ; thirdly, of several thin intrusive beds of green and much-altered quartz-porphyry, parallel with the stratification. It is only on the south side of the amphitheater that a continuous cliff-section of the Paleozoic beds is exposed, and here the top of the Blue Limestone and the base of the Cambrian are each covered by surface accumulations. One principal and several smaller faults can be distinguished on the cliffs, in each of which the upthrow is to the west, but the amount of displacement is only slight. The Colorado Springs mine is opened on this cliff, near the base of the Blue Limestone, from which rich ore in small quantities has been obtained. The following section was made, by means of a pocket level, on the cliff just south of the mine and near the dike of White Porphyry above mentioned: Feet. Blackicherby limestones) .-s ee see eee 50 Blue-gray limestone --—2 -2e=- es. eee eee 50 Lower Carboniferous . < Light-blue limestone.-...............---..--. ) White marbleized limestone ..-....--.-.-.---.- 60 Light drab limestone with serpentine.........- ) — 160 Wihite'and greenish quartzite .-..-..---2.2--2-- 40 Wihiteslimestones. 2 2) 2). ee eases oe eee 10 nichts laishylimestOn Giese eee 40 Silurian =. 4 Green porphyry, 20 feet. Wihitedimestone ots seen EEN 52s Te Osc eee Sena seme | 3.56] 2.59 Nas Ogee sat taboos chee | 3.46| 2.29 150) eee er emcees | .90| 2.09 COg sera cmat sen cee seen oy eee 2.14 (6) (RS Rar pe ee eR ergot oes, Ba | Trace WeOsi essence kp eee asees None: |2=.-25=. Motalsa.sescos See 100.12 | 100.29 Specific gravity ..-.-..--. ezsseaioNGad) The specific gravity of Il was taken at 16°C. By special test in the White Porphyry a very small amount of lead was found, = 0.003 per cent. of PbO (Part II, Chap. VI). No CO, was found in I; that in fI, taken together with the increased percentage of CaO, indicates the presence of calcite, which is probably an infiltration product, as there aredolomite bodies in the neighborhood. The close agreement of these analyses is such as might have been expected from the preceding descriptions and confirms the views expressed as to the close relationship of the two rocks. PYRITIFEROUS PORPHYRY. This porphyry, so called on account of the remarkable amount of pyrite invari- ably found disseminated through its mass, owes its importance principally to its sup- posed connection with the ore deposits of Leadville. Its geographical extent is limited to the district shown upon the map of Leadville and vicinity, where it seems to occupy a stratigraphical position, which to the north is filled by the Gray and tothe east by the Sacramento Porphyry. From the latter it is distinguished in field appearance by its almost universally decomposed condition, and in its constituents by a relatively small proportion of plagioclase; from the for- mcr, in addition, by the absence of large crystals of orthoclase, and from both by the want of hornblende. Asa type, will be taken the unusually fresh rock occurring in White’s gulch between the Printer Girl and Golden Edge claims[87]. It has a distinet porphy- ritic structure, showing numerous white feldspar crystals, with quartz, biotite, and pyrite as other recognizable constituents. Altered feldspars are nearly indistinguish- PYRITIFEROUS PORPHYRY—MOSQUITO PORPHYRY. Beit able from the white groundmass, and plagioclase is but seldom identifiable with the naked eye. There are no large feldspar crystals, as in the Gray Porphyry. Quartz occurs most frequently in irregular fragments and rarely contains bays of the ground- mass. HBiotite appears in distinct leaves, usually altered to a green chloritic substance. Through a nearly parallel arrangement of its leaves a stratified appearance is pro- duced in some cases. Before disintegration of the rock, the place of the biotite is often occupied by ocher derived from the decomposition of pyrite. The latter mineral is scattered through the whole rock, but concentrated upon fissure planes by secondary processes. Galena appears locally in small quantity, but only on fissure planes. Some specimens contain irregular fragments of other rocks, chiefly quartzites of the Weber Grits formation. Microscopical.—No additional original constituent is shown by the microscope, with the exception of minute crystals of zircon. Apatite, so seldom wanting in rocks of this class, has not been identified in the Pyritiferous Porphyry. Pyrite takes the place of magnetite and seems to be an original constituent. Its particles are included in quartz and appear in arms of the groundmass, which penetrate or separate quartz grains. It is also seen imbedded in biotite and is scattered through the groundmass in the manner characteristic of the original ore minerals in similar rocks. Few of the feld- spars are entirely fresh and most of them are replaced by very fine aggregates of muscovite or kaolin. Plagioclase is identifiable in rare cases and was undoubtedly much subordinate to orthoclase in the fresh rock. In the freshest specimen obtained, chemical analysis showed 4.62 per cent. of potash and 2.91 per cent. of soda. Quartz appears in angular grains which are sometimes fractured and show parts of but slightly different optical orientation, separated by thin arms of the groundmass. Fluid inelu- sions are abundant in many grains, usually with but little fluid, while empty pores are also numerous; but none of glass was seen. Biotite is altered to chlorite or allied products, with a separation of yellow needles and tabular crystals, presumably rutile and anatase, respectively. The groundmass never reaches the coarseness of grain common in other porphy- ries of the region. It is always very finely and evenly granular, never allowing a dis- tinction of quartz and feldspar. MOSQUITO PORPHYRY. This type of quartz-porphyry, found in several distinet bodies and exhibiting in all a marked uniformity in structure aud composition, has been named from its princi- pal observed occurrence in the North Mosquito amphitheater [98]. All the bodies are dikes iu the Archean, and besides the locality mentioned the rock was seen upou the north wall of Mount Lincola [97] and in Cameron amphitheater [96], in the latter case penetrating sedimentary beds. It is a light gray rock of fine grain, whose most prominent constituent is quartz in clear, irregular grains, which seldom exceed 0.5°™ indiameter. Other recognizable elements are biotite in small leaves, not abundant, and minute feldspars, which can scarcely be distinguished from the light groundmass. A brilliant, black ore in small specks is abundant. Glistening hexagonal prisms of what the microscope proves to be apatite are often seen, upon close examination. 328 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Microscopical.—Zircon, ilmenite, pyrite, specular hematite, and probably magnetite are present in small quantity, a diversity in such constituents seldom seen in rocks of this region. Apatite, noticeable even macroscopically, is developed in stout prisms, with many minute inclusions, producing the dusty appearance often described. No other rock of the range exhibits a similar development of this mineral. Biotite is shown in various stages of decomposition, chlorite being the first product, which sometimes gives way to epidote, or, as is clear in many cases, to a micaceous min- eral apparently identical with the muscovite which is formed from adjacent orthoclase. Accompaniments of this change are yellow needles, presumably rutile, while the iron of the chlorite either is carried away or separates out in glistening black ore particles, thougbt to be specular hematite. Of the feldspars, orthoclase seems to predominate slightly. Plagioclase is pres- ent both in erystals and in the groundmass, where its small microlites are much more prominent than usual. Quartz is regularly but rather sparingly present in large grains, seldom showing crystal outline and containing numerous small fluid inclusions, while none of glass was observed. A microcrystalline, granular mixture of quartz and two feldspars, with but very little primary mica, makes up the groundmass. Chemical analysis shows 68.01 per cent. of silica, 4.36 per cent. of potash, and 4.26 per cent. of soda. The alkalies are rather more nearly balanced than one would suppose them to be from the microsc »pical examination. LINCOLN PORPHYRY. This rock is the most important of the varieties belonging to the second division: of the quartz-porphyries of the district, namely, those in which the porphyritic strueture: is macroscopically very plain. It has been called the Lincoln Porphyry from the facet that itis best developed in and about the mass of Mount Lincoln, forming the extreme summit of that peak, and in this once important mining district bearing approximately the same relation to the ore deposits which near Leadville is assumed by the White Porphyry. As will be shown later, it is very closely allied to the Leadville Gray Por- phyry and has intimate connection with the Kagle River Porphyry and other rocks of the adjoining district upon the north. In the following description will be con- densed the observations upon twenty specimens collected at different places. Devi- ations from the type rock of Mount Lincoln will be specially noted. Macroscopical_— The essential constituents are quartz, orthoclase, plagioclase, and biotite, all oveurring in distinct crystals and imbedded in a compact groundmass of varying importance. A part of the orthoclase appears in large, stout erystals, fre- quently two inches in length, usually pinkish in color, and so fresh and glassy as to resemble markedly the sanidine of younger rocks. They are often Carlsbad twins and contain noticeable inclusions of biotite leaves. For most occurrences of the por- phyry these large orthoclase crystals are eminently characteristic, though their devel opment has been hindered in some cases, particularly in dikes and small masses. In some of these instances small crystals of pinkish color are plainly more numerous- Sh a er ate eh tigi, LINCOLN PORPHYRY. 399 than in the type rock, but in others they cannot be well distinguished from the tri- clinic feldspar. Plagioclase is always very abundant in white individuals, seemingly less fresh than the orthoclase, although a striation can often be seen on the basal cleavage surfaces. Biotite occurs in small hexagonal leaves, which are sparingly but uniformly scattered through the whole. They are seldom fresh and usually appear to be changed into a green chloritic mineral. The quartz appears as a prominent macrc- scopical constituent, showing, as a rule, a development of pyramidal planes, to which the prism is occasionally added.' The groundmass is dense and homogeneous in appear- ance, usually grayish in color in fresh rocks, and very distinct. Only oceasionally does it become subordinate. Ore particles are plainly distinguishable in it. Specimens of the rock obtained from exposed surfaces of high mountains are usually bleached and light-gray in color, slightly stained by hydrous oxide of iron, while in tunnels and mine workings the rock is generally greenish through the chlo- ritic decomposition products of the biotite. Microscopical. The microscopical examination reveals the following as original constituents, named in order of formation, viz: Allanite, zircon, magnetite, titanite, apatite, biotite, plagioclase, orthoclase, and quartz. All the minerals named occur in more or less perfect crystal form and are imbedded in a granular groundmass, consist- ing of plagioclase, orthoclase, and quartz. The amount of plagioclase in the ground- mass is doubtless small, for it is so abundant in the form of imbedded erystals that but little substance could have remained for the second generation. The size of the grains in the groundmass is so small that one cannot well distinguish between quartz and orthoclase, but the holocrystalline nature is evident. No microfelsitic or glassy matter has been found in any rock of this type. Of the accessory constituents the most noteworthy is a/lanite, which appears very sparingly but constantly in this and other rocks of the Mosquito Range and adjoining regions. It is apparently the first mineral formed, or is perhaps contempo- raneous with zircon, these two minerals penetrating even magnetite and apatite. During the first study of these rocks the nature of this mineral was not determined, but, through the subsequent detailed investigation of a similar porphyry of the Ten- Mile mining district, enough was isolated by means of the Thoulet solution to allow of chemical analysis. The analysis, made by W. F. Hillebrand, was not completed, owing to accident, but it established the presence of Ce and La with the absence of Di, while Fe,O; and SiO, were the remaining constituents of note. Atabout the same time Mr. Joseph P. Iddings, of the U. 8. Geological Survey, determined the same mineral erystallographically in various rocks of the Great Basin in Nevada. As a rule the allanite is seldom macroscopically visible in the rocks of the Mosquito Range, while it is quite noticeable in those of the Ten-Mile region. It appears in small prisms of maximum length of about 5™", has a brilliant dark resinous luster, and when decomposed stains the surrounding zone in reddish-brown shades. The chance sections show a transparent, yellowish-brown mineral, with no distinet cleavage. The faces developed seem probably referable to w» P, » P4,0P,and+ Pa. It is often twinned, possibly parallel «Px, as by epidote, and in several sections which 1On the ridge east of Hoosier pass the outerop of a porphyry sheet is marked by quartz crystals which have weathered out of the underlying rock and which show both pyramid and prism. 330 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. seemed to lie approximately parallel to o P & extinction took place at 35° to 38° from the vertieal axis. Pleochroism distinct, the color varying from light to dark shades of yellowish brown. Zireon is abundant in minute clear crystals. Fig. 3, Plate X XI, shows two zircon crystals of characteristic form included in a quartz grain of a Lincoln Porphyry. Titanite was seen in but one or two specimens, and then very sparingly. Magunetite and apatite occur as usual in such rocks. Biotite frequently includes apatite and zir- con and may be penetrated by allanite. It is otherwise interesting from its altera- tion products, which will be discussed below. The plagioclase, which is so prominently developed in crystals, is probably an oligoclase, judging from the extinction in the zone perpendicular to the lamine, the direction being always within the limits of oligoclase. Orthoclase is seldom met with among the crystals of medium size, being present in larger individuals or in the irreg- ular grains of the groundmass, where it presents nothing noteworthy. The signifi- cance of this development is pointed out later. The large quartz grains and crystals contain a few fluid inclusions of irregular shape, and bays of granular groundmass penetrate them without any very marked change in texture of the mass. Glass inclusions are very rare in any specimens of the Lincoln Porphyry and never have been noticed in the type rock of Mount Lincoln. Quartz crystals have frequently exerted an influence upon grains of the same mineral in the adjoining groundinass, which have within a narrow zone the same optical orien- tation as theerystal. There is no regular relation of the quartz to the orthoclase within this zone. Alteration. — Biotite is usually more or less altered and presents different products under different circumstances. In a specimen from the head of Clinton gulch, Summit County, the chief product is a micaceous mineral, seemingly muscovite, which con- tains numerous needles of rutile. In other cases chlorite is first formed, and this is also accompanied by yellowish needles, or by irregular paler grains of undeterminable nature, which resemble titanite or at times anatase. Epidote seems to replace the chlorite, or in other cases to come directly from the biotite without any intermediate stage. The feldspars give place to an aggregate of muscovite leaves in most cases, but calcite is frequently seen as a product from plagioclase and epidote, also, may be often found resulting from the alteration of the triclinic feldspar. As in some of the other types to be described epidote is very commonly a result of alteration of pure feldspar, there appears no good reason for regarding it as induced by the preseuce of assumed inclusions in the case of the Lincoln Porphyry. Secondary chlorite is sometimes deposited throughout the groundmass, giving a green color to the rock. GRAY PORPHYRY, This rock, which occurs in the vicinity of Leadville, is the nearest relative of the Lincoln type. It is, however, directly connected with a porphyry which has its chief vent of eruption and largest masses in the adjoining region to the north, at the head- waters of the Eagle River. This latter type will be fully treated in the report upon the geology of the Ten-Mile district, and, as other allied rocks can there be drawn into the discussion, the present description will not go deeply into a comparison of types. GRAY PORPHYRY. 331 The Gray Porphyry is seldom fresh, as it occurs in the region adjacent to the ore deposits, where agencies of alteration have been active, and presents usually a greenish-gray rock, showing numerous crystals imbedded in a prominent groundmass. The minerals are the same as those of the Lincoln Porphyry, viz, large orthoclase, small and numerous plagioclase, and biotite crystals. In the mines the rock is so bleached that even with its original large crystals, it is not easily distinguished from the White Porphyry. The quartz contains large bays or penetrating arms of the. groundmass. Microscopical.— One never-failing and striking peculiarity of this, in distinction to the Lincoln'type, is the presence of outlines of a former constituent of the rock, which would seem to belong to hornblende, although no trace of that mineral in fresh condi tion could be found. These outlines are usually marked by dark grains, and inclose a fine-grained, grayish decomposition product, which acts very feebly in polarized light. They are not wauting in any slide examined, and are always of the same appearance, even when other minerals are entirely fresh. The feldspars of the Gray Porphyry, unlike those of the Lincoln Porphyry, con- tain numerous fluid inclusions, which are generally arranged parallel to the chief cleav- age planes. Besides these, there are many irregular interpositions, either devitrified glass inclusions or portions of the groundmass in a less crystalline state than it now presentsin the main mass of the rock, They are light reddish-brown in color, and plen- tiful in most of the small crystals. Distinct glass inclusions, although not noticed in any feldspars, are very characteristic of the quartz grains. They are often sharply negative crystalline in form, and sometimes show devitrification; others are spherical, and in these it can often be seen that from opposite poles, which probably lie in the vertical axis of the quartz grains, cracks penetrate the sphere in three planes, cutting each other at about 60°. If the sphere be cut by the section at right angles to the axis uniting these poles and near one of them, there results a delicate six-armed figure, which appears as if contained in the quartz itself. The groundmass, though holocrys- talline, is much finer-grained than that of the Lincoln Porphyry, and shows a tendency to an irregular intergrowth of quartz and feldspar. Occurrence. —Gray Porphyry is quite limited in distribution, being confined to the immediate vicinity of Leadville, and to the region northwest of that point. As has been described in detail (p. 80), it occurs chiefly in one large sheet, with numer- ous offshoots, and the large sheet has been directly traced to a connection with an immense body at the headwaters of the Eagle River. The hornblende of the Gray Porphyry is considered analogous to the crystals of that mineral observed in small dikes which are offshoots from the Hagle River mass. Chemical composition of the Lincoin and Gray Porphyries.— The following rock analyses were made by W. F. Hillebrand. I is of Lincoln Porphyry, summit of Mount Lincoln [75]. It is quite fresh in appearance, although showing some muscovite, calcite, and chlorite, when examined microscopically. B02 GEOLOGY AND MINING INDUSTRY OF LEADVIULLE.: II is of Gray Porphyry, Onota shaft, Johnson gulch, near Leadville [59a), fresh appearing, but somewhat altered, with the same products as in the former rock. ete I. GOH 5 sees aaa esse 66.45 | 68.10 yerVeoe sry gs = R=} © Cl resee ie ecrieeaee see 0. 05 | 0. 03 Total ..-.------------| 100.09 EE 100.11 2 636 Specific gravity, 16°C -- 1 i The relative amounts of soda and potash indicate an abundant soda-lime feldspar. The titanic oxide found corresponds to the suggestion that the yellow needles in the decomposed biotite are rutile, for the magnetite does not give signs of an intermixture of titanic iron through its alteration products. The presence of strontia in determina- ble quantities is unusual and worthy of note; it doubtless comes from the plagiocla:e. Instances of its determination in rocks are rare,! though it would probably be found in many cases if sought for. Although the large pink or white orthoclase crystals are characteristic of most of the occurrences referred to the Lincoln and Gray Porphyries, still a number of cases were found where the rock seemed identical with these types in every respect, except- ing that the large crystals wete wanting. In some bodies of rock, moreover, the large crystals were by no means equally distributed. It seemed therefore desirable to ascer- tain more defivitely the source of the alkalies in the rocks analyzed. In each case enough of the large orthoclase crystals had been included in the material used for analysis to give average results. In the mass of Mount Lincoln a dike of rock was found which was considered as a representative of the Lincoln Porphyry [78], although it was darker, more com- pact, and contained none of the large pink orthoclase crystals. Alkali determinations gave 2.42 per cent. of potash and 3.15 per cent. of soda, very nearly the same ratio as in the type rock. There was also found 64.16 per cent. of silica. The reduced amounts of all these are doubtless due to the increased quantity of biotite and of ore in this dike rock. In the next place the Gray Porphyry, of which the complete analysis had been He Gha was subjected to fae investigation. Alkali determinations were made in the 1 Streng Nene Jahrbuch fir Minerlopio, etc., p. 537, 1867. 5) DIORITE. 333 mass of the rock, carefully avoiding the large pink crystals, with the result of 2.95 per cent. of potash and 2.61 per cent. of soda. As small flakes were used for this purpose, it is probable that the groundmass was present in abnormal quantity, thus causing a relative increase in potash, even while excluding the large orthoclase crys- tals. Plagioclase was found to be much subordinate in the groundmass, as stated above. The large pink orthoclase crystals themselves were then analyzed, with the result: BiOa Ge cee sean eae oes ames) coe seks SeSaeene 62, 22 JNM ON Satece eet oeece RAS aati gseeeobsee Hn ae ene Se cae 20.33 OO Sab estes cesend Soteciessees odeosdaeeeseees 2.95 aan an dace cee icemracaiseeonates mons see aecie, chee 8.31 EH OV Sne tick o othe tee Doce oop ee eRe Em ars Soceoe 3. 45 ILO) Saks SSS secansee Ste onar OSSceab pecs Scagsces Trace Ti ~ceeessetocehat canes Sebo ceeses saeco song coer 1.90 Loss. - = ssone . 84 100, 00 | Careful examination of the material used showed only a few specks of biotite, but some soda-lime feldspar must have been present, judging from the large amount of lime found. A determination in another clear crystal chosen for its apparent purity gave nearly 3 per cent. of lime again. The loss is thought by the analyst, Mr. Hille- brand, to be chiefly soda. DIORITE. Of the distinctly plagioclastic rocks of the region but very few are granular in structure, the great majority being diorite-porphyries, or porphyrites, as they will here- after be designated. The three granular diorites found, represent three very distinct. varieties, one of them being the only pyroxene-bearing rock occurring within the area of the map. All occur, moreover, in the same gulch, and quite near each other. QUARTZ-MICA-DIORITE. This rock occurs on the south side of Buckskin guich, Park County, as a broad dike, forming for some distance the southeast wall of one of the elevated amphitheaters on Loveland Hill, and thence projecting as a knoll into the gulch opposite the Red amphitheater. It disappears under loose material before reaching the stream bed, and no continuation of the dike on the north side of the gulch was observed. The rock has a fine, evenly-grained structure, with feldspar and quartz strongly predominat- ing over the small, irregular leaves of. biotite. Microscopical examination shows zircon, magnetite, apatite, biotite, plagioclase, orthoclase, and quartz as original constituents. None of the essential minerals is well developed in crystal form and none shows noteworthy peculiarities. Plagioclase is largely in excess over the orthoclase and quartz is quite abundant. All are quite fresh, the biotite alone showing incipient decomposition [117]. HORNBLENDE-DICRITE. A broad dike crossing the head of Buckskin gulch from Democrat Mountain in a nearly east-and-west direction was found to consist of a very simple, normal diorite 334 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. {116}. It is fine-grained, yet shows distinctly to the naked eye all its prominent con- stituents. Feldspar, a large part of which is clearly plagioclase, subordinate quartz, hornblende in prisms with occasional terminations, a little brown biotite, yellow titan- ite, and dark ore grains are all easily recognized. The microscope shows zircon and apatite in addition, while chlorite and epidote are seen to result from the alteration of both biotite and hornblende. Muscovite forms in the orthoclase, which here seems much more attacked than the plagioclase. There is no groundmass and of the essential constituents only hornblende is developed in crystal form. A very similar dicrite was obtained from a prospect tunnel in French gulch, Lake County [115], in which pyrite replaces magnetite as the ore and zircon and titanite are very abundantly developed. SBiotite and quartz are even less prominent than in the preceding rock. AUGITE-BEARING DIORITE. In the Red amphitheater, on the northeast side of Buckskin gulch, there occurs a dike of a darker, finer-grained diorite than either of the preceding types [118]. Horn- blende, biotite, plagioclase, and a little quartz may be macroscopically detected. The microscope shows zircon, titanite, magnetite, hematite, apatite, biotite, augite, horn- blende, plagioclase, orthoclase, and quartz. Augite appears most abundantly in the freshest specimen, and certainly undergoes alteration to green hornblende, which, though not fibrous, like typical uralite, is still by no means so compact as the common dioritic hornblende. It is not possible, from the specimens examined, to say with cer- tainty that any of the hornblende is original, although the association of the minerals in the freshest specimens is such as to indicate a contemporaneous formation of bio- tite, augite, and hornblende. The latter two occur in irregular grains and the augite has none of the pinkish tinge common to it when appearing in diorite. This rock is remarkable as the only eruptive of the district in which augite has been found. Plagioclase appears abundantly in small grains, while orthoclase and quartz form the cementing material. Chlorite and epidote result from the alteration of hornblende and biotite; muscovite and calcite, from the feldspars. PORPHYRITE. Under this heading will be discussed a large number of distinct occurrences, which, unlike those of the quartz-porphyries, belong for the most part to small rock masses. There are in this group no markedly prevailing types to which the different rocks can be assigned, and the chief interest here lies in noting the great variations possible, both in structure and composition, in what are practically equivalent masses. One distinction, however, is feasible, viz, that between a variable subgroup, in which a triclinic feldspar is evidently strongly predominant, and a few rocks occurring in larger masses, in which orthoclase is also prominent and which seem at first glance more nearly related to the quartz-porphyries than to the marked plagioclase rocks of the first division. These latter types are referred to in the main report as quartz- porphyries, and are so represented upon the map. They are called by the local names Sacramento Porphyry and Silverheels Porphyry. Later investigation has shown them to be plagioclastic rocks, and as such they will here be treated. In describing them the general and variable group will first be considered and then the local types. : : ; : PORPHYRITE. 335 PRINCIPAL GROUP. The characteristic primary constituents of these rocks are the minerals zircon, allanite, apatite, magnetite, biotite, hornblende, plagioclase, orthoclase, and quartz. To these, as occasional accessories. may be added ilmenife and pyrite. All the common non-essential elements are developed in the ordinary way, and none is so abundant or so rare as to deserve comment. Allanite is not always present in the thin sections examined, but its observed distribution among different types is such as to warrant the belief that it is sporadically present in all the rock masses of this group. Feldspars. — All erystals of the first period of consolidation which have been identified are plagioclase, with but one possible exception, referred to later (p. 539). Orthoclase may be sparingly developed in this way in a few cases, but the freshness of the plagioclase in nearly all specimens collected and the ease with which the stria- tion can be seen upon the basal cleavage plane make it certain that a monoclinic feldspar must be very rare. In the groundmass, on the other hand, plagioclase is not visibly present at all in many cases, while orthoclase is very abundant. The plagioclase crystals are small, white, stout in form, and correspor.d exactly to those deseribed in the quartz-porphyries. They are chemically near oligoclase, judging from the optical properties, for the maximum observed extinction in the zone perpendicular to the usual twinning plane is but 20°. In a number of crystals twin- ning according to the Carlsbad law is apparently combined with that of the albite law, as, for example, in one section, falling at right angles to the brachypinacoid, there are 20 lamine, of which five pairs extinguish sharply at 8° 45’, the other five pairs at 6° from the twinning plane. In a few cases more than two directions of extinction were noticed in sections apparently lying in the macrodiagonal zone. In one crystal lamin were found extinguishing at 19°, 4° 30’, 8°, 13°, and 20°, several pairs showing the Jast two values. A satisfactory explanation for this action has not been found. It may be that lamine of different feldspars are here intergrown, but such a conclusion must be supported by further data than are here available. A delicate zonal structure is occasionally seen in plagioclase crystals, but the slightly varying angles of extinction do not indicate any pronounced changes in basicity of the different zones. Biotite.—_ Biotite appears as a constituent in three distinct forms: as macroscopic hexagonal leaves, in aggregates of small irregular flakes, and as minute leaflets in the groundinass. The large leaves are brown when fresh and often exhibit ragged edges when seen under the microscope, caused by the attachment of many flakes correspond- ing to those in the groundmass. Allanite, zircon, magnetite, and apatite penetrate the larger leaves. The tiny leaflets which enter at times richly into the composi- tion of the groundmass are irregular in shape and rarely over 0.05™™ in diameter, sometimes sinking to a minnteness requiring the highest power of the microscope to resolve them into separate flakes. They are greenish in color and at first glance it is not easy to discover their nature as mica; but their marked pleochroism and strong absorption in proper position renders their character certain. These flakes of green mica are often arranged one after another, partially overlapping, making needle-like aggregations, easily mistaken for hornblende with a low magnifying power. Hornblende.—.The hornblende is compact, of a green color in ordinary light, and generally presents quite well-defined crystals, the faces «P, «P %, OP, and P being 336 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. often visible on macroscopic crystals. It occurs either as a macroscopic element of the rock, in the form of minute needles in the, groundmass, or, lastly, in clusters of small irregular individuals, and then usually associated with biotite leaves. The small needles are sometimes well terminated (see Fig. 3, Plate XX). Still it is the rule to find the ends irregular, while the prism is sharply defined (see Fig. 4, Plate XX). The pleochroism is well marked, and the maximal angle of extinction in the prismatic zone is nearly 18°, measured from the vertical axis. Twinning parallel to « Pe is common and is frequently polysynthetic. The hornblende occasionally includes crystals of apatite, magnetite, rarely biotite, and clear microlites of zircon. It is commonly very fresh, and when decomposition has begun the first product is usually chlorite, from which epidote is formed. Quartz.— There are but few rocks of this kind in which quartz is prominent as a macroscopic constituent. In some of these, usually the more acid ones, it forms well- defined crystals, but it is more common to see it in rounded grains, seemingly quite variable in quantity, in occurrences which are otherwise nearly identical. These rounded particles undoubtedly represent partially remelted crystals of the first gen- eration, and their variability is here not remarkable. The chief development of the quartz is, as perfectly natural, in the groundmass, with orthoclase. Inclusions are not abundant in any of the crystals, though all earlier minerals do penetrate it in observed instances. Glass inclusions have never been found and those with fluid contents are rare. The groundmass seldom penetrates the large crystals. Groundmass.— The groundmass of those porphyrites which contain hornblende and biotite mainly as macroscopic elements is very uniform iu constitution and struct- ure. It consists of an evenly granular mixture of quartz and feldspar, with small octahedrons of magnetite scattered through it. The feldspar is seldom definitely determinable as such, but its presence is inferred from a formation of muscovite, where the rock is much altered, and because the quartz grains, through their stronger polarization, stand out in contrast to the rest of the colorless groundmass. « By far the greater part of this feldspar is monoclinic, for plagioclase was observed to enter into the composition of the groundmass in but few cases, and then in the form of thin plates, quite distinct from the irregular grains of orthoclase. The average size of the grains of quartz and orthoclase is 0.02™™, so that a complete separation of these minerals is never possible. There is never a trace of microfelsitic or glassy sub- stance, and only in contact specimens is the greater part of the groundmass crypto- crystalline. As has been mentioned above, biotite and hornblende enter into the con- stitution of the groundmass in very varying quantities, and only when present in great abundance do they render the mosaic of quartz and feldspar obscure. The quartz has a tendency to develop in clusters of irregular clear grains in certain cases. The distinguishing peculiarity of a certain minor subgroup lies chiefly in the character of the groundmass. This consists principally of an intergrowth of quartz and orthoclase, according to no discernible law, now the quartz, now the orthoclase being the inclosing mineral, and their relation is only made clear between crossed nicols, when it is seen that within the limits of certain irregular patches all the quartz and all the orthoclase has each its own optical orientation. The outline of the inclos- ing mineral has no relation to crystal form, and this intergrowth ucts throughout like the ordinary groundmass, filling the interstices between the large crystals. The macro- U.S.GEOLOGICAL SURVEY Fig.l 1 18 Fig. 3 Fig 4 STRUCTURAL TYPES OF PORPHYRITE. 337 scvpical effect of this structure is to render the groundmass much less distinet in con- trast with the crystals than is the case in the types of the main group. Flakes of biotite, grains of magnetite, &c., are scattered about in this groundmass with the same irregularity as in any other. A tendency to a micrographic-granite structure was noticed in two of the porphy- rites. It seems to have been induced by the presence of the rounded quartz grains above deseribed. Jach of these is surrounded by a zone in which quartz and orthoclase are more or less regularly intergrown. The appearance, as seen under the microscope, is that of alternate fibers of quartz and orthoc!ase, with a more or less distinct radiate arrangement about the large quartz grain, all the quartz substance, in both granule and groundmass, having the same optical orientation. A similar phe- nomenon was not observed in connection with large particles of feldspars, and those portions of the groundmass showing a regular intergrowth apparently independent of any crystal may have been formerly related to a quartz grain situated just above or just below the plane of the present section. In such a thoroughly erystalline rock a fluidal structure can only be expressed by the position of the hornblende needles or biotite leaves with reference to the large crystals. Such a relation is often observed, and it is also not rare to find hornblende crystals broken and biotite leaves folded and crumpled, attesting to movements in the partially solid rock. Structural forms.—The greater number of the rocks observed form a continuous series whose extremes are very dissimilar, and the relationship can be most easily understood and explained with the help of the subjoined table: | a SOoaey Subdivision. Macroscopic development. | In groundmass. | | # femtee wongogsc In hexagonal leaves -...--. | Entirely wanting. f a cee Hornblende... | Entirely wanting .......... Entirely wanting. Ae... | 11 f BioLiestee esse | In isolated leaves...-....... Entirely wanting. a |? Hornblende. ..-| In numerous crystals ...... Entirely wanting. Frit ened § Biogtiteree = Sparingly present ........ | Few minute leaflets. Hornblende ...) Abundant --.--....... .. | Entirely wanting. ah ae | Tyee. a Sena: pads ANN QUE a eee sacere Abundant. Hornblepde -. | Slightly predominant ......) ew small needles. | = Gblotiter: ==. ---- Rare or wanting ....... -- | Sparingly present. WE gee or ? Hornblende -..| Very abundant ............! Very abundant. VI f IBiotites.----—=- Numerous small leaves ..... Very abundant. { sae pg Hornblende ...) Rare or wanting. ..... .. | Entirely wanting. Sete | Vito GRE AO MUG Se meetin | PUAN G 2h erst stoic ole tees aicte - | Much snbordinate to hornblende. ? Hornblende -..| Very abundant -..... .... Very abundant. Under Division A are included rocks with a light, homogeneous-appearing groundmass, containing no microscopic individuals of the basic mineral which is so prominent in macroscopic crystals, this in the one case (I) being biotite, in the other (II) hornblende. Under C, at the opposite structural extreme, where the groundmass is filled with minute flakes or needles of a dark mineral, are also two modifications, one a biotite (VI) (Fig. 1, Plate XX), the other prevailingly a hornblende rock (Vig. 2, Plate XX). These are both dark and compact, showing comparatively few macro- MON XII——22 338 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. scopic elements, standing in marked contrast to those forms under Division A. Between these extremes, in regard to both structure and composition, are the forms embraced under B. In these the groundmass contains more or less of one or both of the dark basic minerals, and in proportion as these minerals enter into the composition of the groundmass the macroscopic elements become less distinct, thus forming a gradual transition to the Division C. Division A.— The plagioclase usually stands out very plainly in these rocks, and it is evident that no orthoclase is present in macroscopic individuals. Quartz occurs in good erysials and rather plentifully. The groundmass is microcrystalline and pos- sesses a very regular granular structure, its components being almost exclusively quartz and orthoclase. A dike in gneiss, near a little lake northwest of Mount Lincoln, rep- resents the typical hornblendie variety [120], while a similar dike in North Mosquito amphitheater is of the corresponding biotite rock [119]. Several occurrences at the head of Buckskin gulch are nearly allied to these type rocks. Division B.— By far the larger number of the porphyrites in the series fall within this division. In the three subdivisions of the table, one or both of the heavier sill- cates appear in the groundmass as well as in larger crystals. If the groundmass. minerals are regarded as belonging to a second phase of the rock’s existence, one of the striking peculiarities of this division is most natural, while from another point of view it might seem strange. The peculiarity referred to is the observed indepen- dence of the dark basic silicates occurring in the groundmass, of the species which may be developed as macroscopic constituents. The formation of hornblende in numerous iarge crystals during the first period of consolidation does not necessarily demand that the same mineral should be developed in the second period. The changed conditions attending the final consolidation may produce biotite or hornblende, or both of them, uninfluenced, or at least uncontrolled, by the earlier erystallizations. The table above shows this, but a study of the variations in the different rocks collected makes the facet much plainer. The rock most frequently met with in all the district belongs to Type V of this division. It is the one found in the intrusive sheets on the sides of Mosquito [127] and Buckskin gulches [126], on Mount Lincoln, or in dikes in the Archean, as on Bartlett Mountain [124] and Democrat Mountain [299]. The lower figure of Plate VII, page 84, shows the macroscopical appearance of this rock very well. Hornblende crystals are frequently well terminated in this modification, and owing to the minute size of many well-shaped prisms, while all intermediate stages. are also represented, it becomes difficult to decide whether there has or has not been a re- currence in the formation of hornblende prisms with good erystal form. Fig. 3, Plate XX, was designed to show both large and small prisms of hornblende with good ter- minal planes, but the imperfect execution of the prints leaves much to the imagination. In Fig. 4 of the same plate are shown needles of hornblende with the more common, irregular terminations. Division C.— The compact rocks of this division are not very numerous. The two occurrences illustrating best the micaceous and hornblendie varieties occur together in North Mosquito amphitheater. One of these, the biotite rock [260], was analyzed (p. 340), and its micro-structure is indicated by Fig. 1, Plate XX. Two other compact rocks deserve special mention under the next heading. - Ne er me we nS - PORPHYRITE. 339 The Arkansas Dike.— The long straight dike at the head of the Arkansas presents some remarkable phenomena, which cannot be explained satisfactorily from the data collected in the one short visit made to that area. Itis a special matter for regret that no time for further examination could be taken. This dike consists of what are re- garded as two eruptions of the same magma. The older rock is fine-grained and ex- hibits a few small feldspars and biotite leaves as sole recognizable macroscopic con- stituents [130]. The younger rock [129], which cuts irregularly through the former, now on one side, now on the other, or even running along the center, is also very dark and compact in the main, but is sharply distinguished by numerous large quartz erystals and by worn and well-rounded fragments of slightly pinkish orthoclase. A heliotype representation of this curious rock is given in the upper figure, Plate VII, natural size. These orthoclase fragments are all like pebbles, showing no trace of sharp angles. They reach a maximum observed diameter of over 5°, and none was noticed of less than 1. While never glassy, they seem quite fresh, represent but one erystallographic individual each, and are in no way related to anything seen in other occurrences of the porphyrites. The quartz crystals reach a diameter of over 1 in this rock and are always quite well-defined in crystalline form. Hornblende takes a prominent place beside the biotite in the microscopical constitution. Itis a eurious fact, commented upon later, that in spite of its large quartz crystals the younger porphyrite has but 59.26 per cent. SiO2, while the dark, compact, older rock contains 66.29 per cent. Repeated determinations for both rocks show similar results. The origin of these orthoclase pebbles is very problematic. To consider them as earlier secretions of the porphyrite magma is-to assume conditions to which no other rocks of the group have been subjected, judging from the total absence of such orthoclase in them. Inclusions of basic microlites would seem to be almost inevitable, if these orthoclase individuals had formed in the midst of the minerals which one must sup- pose to have reached consolidation before them. jeMount/Silyerheelscesaasreesassencmee) tees 2.70 | 4.08 |..-..-- al6| 126 | Porphyrite ...| Hornblende..----- | South wall of Buckskin gulch -....-..| 56.62 1.97 Be 00) | ease eae 17 TRIE BES pecenooca| pasa caccotoascess | Arkansas amphitheater --..--.--..-- HEY |ooc sec ey OO eereeeee Hornblende and | Ten-Mile amphitheater ......... --.. | 57.76 |.....---|.......-|-------- | biotite. | | Hornblende. ..---- | North Mosquito amphitheater ..-..... |imi54s SO Peas Seles een Perea ewemicn~ sctsc: Buckskinamphithenter 2--4-25. --s=--|) (G0s03i| ee cean| inane Seeeeree sen acheceoes | North Mosquito amphitheater. - 64. 80 1.43 3.98 | None acbassoossece Arkansas amphitheater ....--..--.-- 11665203) jcc seen eee sepscoateses Leet ecnictaeSeereceocorsesce ceecos|| SAB |leonoane:|| icasmads) neeeecn coe ! Chalk Mountain, eastern cdge........] 71-44 ]........|.-..... |-----.-- seeeconeosess | Northeast point of Chalk Mountain...; 74.45 4.53 3.97 | Trace Hocweesos* Southern end of Black Hill 69.54) |Ceo ee SeL aE OaECe ee South bank of Empire gulch .--. 68. 05 3. 50 | Near Granite, Chaffee County --.---.- 16:84: |\yco 52 ast acme ec | Little Ellen shaft. McNulty gulch ---.| 65.75! ....-..;........|........ ree ener oye se6 ec citigewsece csc ue casters) Gos 21h) ease eames eames : Five miles below Salt Works, South | 70.30 .... -. .--..-- | | Park. | . 32) 142 Trachyte - -..| Quartziferous --.- Head ofLittle Union gulch ----...-- N22 ee eee 33 143 | Andesite...... | Hornblende. .---- | Buffalo Peaks, northwest Peak ------- | 57.60 | Sosons-t| S=n eke] set ese 34 149 |.. Dacites=.---.- | Buffalo Peaks, central amphitheater..| 66.50 2.57 | 3.87 | None a35 144 .. Hypersthene......| Buffalo Peaks, northeast spur .---.--- 56.19 | 2.37 Hecros 96 None | 36 150) eed eee nl ore (UD seca asecete Buffalo Peaks, base of middle peak...) 60.36 | Seances | pSSs555e Weeeeee aComplete analysis in Table I. b Analyzed by L. G. Eakins. Note.—Blanks in the above table denote simply that no tests were made for the substance indicated. ERUPTIVE ROCKS. 591 TaBLe II1.—Determinations of lead, zinc, cobalt, and barium, chiefly in eruptive rocks. Coll F ‘ PbO in| PbO in No. : Rock. Variety. Locality. soluble insoluble) ZnO portion.| portion. | | | pi a ase le a ae a1 | 27p | Porphyry..-.| White ...... Quarry, California gulch...-............ 0.0030, | i ro On Bese GTS eoe Scie Dike in Dolly Varden mine, Mount Bross. 0.0028 |. \ CE) Mey Ne seutlin a seme Lincoln Summit of Mount Lincoln ......- Sr easiciee None. ) 43 [50a |e-.GO'- =. 2s Graynsee- Onota mine, Johnson gulch ........----- 0. 0024 | BY |aaraete ree Greate Eagle River.| From surface at E] Capitan mine, Ten- Trace. |........-.|-....---).--.---.).----- i nessee Pass. | g (i) ES Beat sees 55 SER cece From shaft of El Capitan mine, Ten- | Trace. |.......-. |..-..--. oscar eee | | nessee Pass. | | | \ i eerctatee | Limestone.. Blue.....-.-. Twelve feet below ore body, El Capi- | None. |.-.--...-.|.--..---|.....--. ease H tan mine. | | 8 | 130 | Porphyrite .| Biotite...... Arkansas amphitheater. -.....-.--.------ | WONOS |bsAtesqeas||onsssdee | baccnobal bosses | Q)) 24 eee CO) eee Hornblende | Bartlett Mountain ....--.......--.------ ORO00G {Sees ane cee | een erie estes coe ones and biotite. | | 10 |326 | Porphyry...| Eagle River) Main fork of Eagle River. -...-.........|......-. Joeeeeee eee | 0.0080 | 0.0008 |.....- t 11 | 269a | Rhyolite....)...-...--..--.| Little Ellen shaft, McNulty gulch ... .. |) catseée| seasetagea 0.0043 | 0.0010 |....-- | 12 | 90a | Porphyry--.| Pyritiferous | Hartford mine, Breece Hill........-.-... OSOU5R Nicene eta see | eee [ss5ee | VCD) | NO: | eG aR asses es CG Sesecee White’s Hill, west of Pilot fault --....-. OSUID GS ese eccdacn beanobad [ogonsmesteesees TEN) yf loca Gl) Boe cal) smgacee | White’s Hill, between Printer Girl and 0. 0013 0. 0029 |..-..... Joe seeese|essee= | | | Golden Edge. | | NeWWaltete ts ELE potest ce a eee ateei -mcie scene | White's Hill, Melvina tunnel -| Head of White's gulch .. Pyantereboy eH sane ete le Rebel Warrior mine, Ball Mountain | Wednesday tunnel, Ball Mountain...... | Sandstone ..|. Snow Bird claim, head California gulch..| 23 |120 | Pyrite ....-. | From Pyrit- | Lalla Rookh mine, Breece Hill...-....-. | iferous | Porphyry- | 24| 17 | Granite..... | Archean ....| Garden City shaft, California gulch. ..- p2asON7e Peso). cece (eas 00l. 2 2-tn , Northwest slope of Mosquito Peake sos: | aComplete analysis in Table I. N. B.—The blank spaces under the headings PbO, etc., do not indicate absence of the respective oxides. Where no results are given, no tests were made. REMARKS ON TABLES I, Il, AND III. Insoluble silicates were decomposed by fusing with alkaline carbonates for the determination of silica, titanie acid, and all bases except the alkalies. Ferric oxide and alumina were separated either by pure potassium hydrate, or more generally by ammonium sulphide, after addition of tartarie acid and ammonia. For the determination of ferrous oxide, treatment with sulphuric acid in sealed tubes at about 2009 C. was employed in cases where complete decomposition of the silicates could thus be effected, and the solution titrated with potassium permanganate. For the decomposition of refractory silicates, pure hydrofluoric acid, distilled from a platinum retort, was employed, the solution being effected in platinum vessels with careful exclusion of air. The iron was then determined as above. 592 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Barium and strontium were looked for in the precipitated calcium oxalate after ignition, and estimated by the method given by Bunsen in his treatise on Mineral Water Analyses; the purity of the resulting compounds of these elements was ascer- tained by means of the spectroscope. When a rock was examined merely to ascertain the presence or absence of barium, a considerable portion (10 grams) was decomposed with hydrofluoric and sul- phuric acids, the soluble salts were extracted with water after expulsion of the hydro- fluoric and excess of sulphuric acids, the residue was fused with sodium carbonate, extracted with water, and the insoluble part collected on a filter. After solution in hydrochloric acid, the barium, if present, was thrown down with sulphuric acid, the precipitate ignited and weighed, and after decomposition with sodium carbonate, tested spectroscopically.? For the estimation of the alkalies, decomposition was effected in the earlier anal- yses by hydrofluoric and sulphuric acids; in the later by heating in a platinum cruci- ble with calcium carbonate and ammonium chloride. The potassium was thrown down, after weighing the mixed chlorides, as potassium-platinic chloride, and caleulated from the weight of the latter, the sodium being found by difference. Lithium could never be detected spectroscopically in the potassium-platinic chloride, but occasionally in the sodium salt. Chlorine was determined by fusing with alkaline carbonate, extracting with water, acidifying the filtrate with nitric acid, and precipitating with silver nitrate. Phosphorus pentoxide was always determined in a separate portion of the pow- der, and water by ignition in a hard glass tube and absorption in a weighed calcium chloride tube. The loss in weight by treatment with acid in a suitable apparatus gave the carbon dioxide. For the detection and estimation of lead, large quantities (30-50 grams) were employed. Pyrite and other soluble salts were first extracted with nitric or nitro- hydrochloric acid; the filtrate, together with copious washings, evaporated nearly to dryness several times with nitric acid; the residue digested with dilute nitric acid, and the solution and undissolved matter separated by filtration. As the insoluble part might contain a trace of lead sulphate, a warm ammoniacal solution of ammonium tartrate was passed repeatedly through the filter, and to the filtrate ammonium sul- phide added. Through the previous nitric acid solution a strong current of hydrogen sulphide gas was passed for a considerable length of time, the precipitate, mainly sul- phur from reduction of iron salts, collected on a filter, well washed, dried, and ignited gently with the filter paper to volatilize the sulphur. A few drops of nitric acid were then added, and heat was applied to dissolve the lead, mostly reduced to the metal- lic state by the carbon of the filter paper. The solution was filtered onto a watch- glass, and to this was added the nitric-acid solution of any lead sulphide that might 1 Later investigation by the writer seems to indicate that baryta may be a far more frequent con- stituent of eruptive rocks than has hitherto been supposed. The failure to detect it in the ignited cal- cium oxalate, where it is usually looked for, cannot be regarded as a proof of its absence from the erup- tive rock examined. Experience in a number of cases has shown that where baryta and lime are in solution in as high a proportion as 1 of the former to 4 or 5 of the latter, in presence of considerable ammonium chloride, an almost complete separation of the two is effected by double precipitation of the lime by ammonium oxalate. The solubility of barium oxalate appears to be increased by the presence of magnesium salts. An ordinary spectroscope repeatedly failed to show the faintest evidence of baricm in the ignited calcium oxalate. This subject will be more fully investigated. (W. F. H.) ERUPTIVE ROCKS. 593 have appeared in the ammonium tartrate solution above mentioned. As a trace of lead sulphate might have been formed by the ignition of the precipitate by hydrogen sulphide and have escaped solution in the nitric acid added, the residue on the filter was exhausted with ammonium tartrate and tested with ammonium sulphide. The contents of the watch-glass were then evaporated with two or three drops of sulphuric acid, and finally gently heated to expel nitric acid. If lead was present it could now invariably be seen at the center as white powder. This was collected on the smallest possible filter, washed with alcohol, dried, ignited, and weighed as sulphate. The latter was then scraped as far as possible on charcoal, and carefully reduced with a very little soda. The yellow coating of lead oxide was invariably formed, and in the soda appeared minute metallic buttons, malleable and soluble in nitric acid. The solution, concentrated to a drop or two, showed a bluish-black precipitate with hydro. gen sulphide. The portion of the rock insoluble in nitric or nitrohydrochloric acids, composed of quartz and silicates, was decomposed with hydrofluoric and sulphuric acids purified by distillation from a platinum retort, and dissolved in slightly acidified water, after expulsion of the hydrofluoric and excess of sulphuric acids. Solution and possible residue were then treated as in the foregoing for the separation and estimation of lead. For the estimation of zine and cobalt, large quantities (30 grains) were taken and decomposition was effected by hydrofluoric acid. After evaporating with sulphuric acid and igniting to expel the excess of the latter, solution was effected in hot water slightly acidified; the solution saturated with hydrogen-sulphide; from the filtrate, after oxidation, alumina and iron thrown down by ammonia; the precipitate redis- solved in hydrochloric acid after filtration, and reprecipitated. This being repeated once more, the combined filtrates were evaporated to a moderate volume; the alumina still in solution was thrown down while boiling by ammonia, and this precipitate redis- solved and reprecipitated. To the again combined filtrates ammonium sulphide was added to throw down zinc, manganese, cobalt, and nickel, if present; the precipitate was treated on the filter with a mixture of one part hydrochloric acid of 1.12 sp. gr. and six parts solution of hydrogen sulphide. The zine and manganese in solution were thrown down again by ammonium sulphide, the manganese (being present in very small quantity) extracted by dilute acetic acid, while the zine sulphide on the filter was then brought into a weighed platinum crucible by means of hydrochloric acid, evaporated to dryness, and ignited with mercuric oxide in the manner recommended by Volhard. The oxide, after weighing, gave the characteristic green coloration on igniting with cobalt nitrate. The cobalt sulphide left on the filter after extraction of zine and manganese was ignited with the filter, digested with nitrohydrochloric acid; the solution rendered alkaline with ammonia; ammonium carbonate added; the slight precipitate separated by filtration and the cobalt thrown down by potassium hydrate. The ignited oxide tested by the method of Jorissen showed no trace of nickel. MON XII——38 594 TABLE 1V.—Gold and silver determinations. GEOLOGY AND MINING INDUSTRY OF LEADVILLE. et ee 1| 53 | White Porphyry...--- Buckskin amphitheater, débris slope..-.----.--. 0. 000, 024, 0 0. 007 2 “ Horseshoe,"’ south wali ------------.---------- 3 South base ot White Ridge -- 4 Summit of White Ridge ..........-.------------ 5 Four-Mile gulch 6 Head Four-Mile gulch i West end of Lamb Mountain u 8 Northwest slope of Sheep Mountain....--------|..--..-------- S=tdOjeceae= | 9| 47 |..---.do -...--.---.----].---- FO Gat eR RHE RO mn amSonS DOO DEOL COS BSS SnOSe Gad sacissenteO=css pect Ces eer | 10 Dolly Varden mine, west dike-. 0. 001, 269 0.37 | 11 | Dolly Varden mine, east dike .......-.----- ---- 0. 000, 481 0.14 { 12 .| Arkansas Valley, east side, above Howland.....'...........--- None | 13 (Clintonpnlchivese see see seee ne ee aaa 0. 000, 155 0. 045 \14 Mount Lincoln summit ..-.-.-.---- --------+--- 0. 000, 034 0. 01 15 Mount Lincoln summit, different specimen from | 0.000, 024 0. 007 above. {MG'|s178u0 |becuwloseecenseeeaees = Mount Lineoln, dike on south face....-..--..--- | 0.000, 017, 1 0.005 17) | 251a)|------ OU ss2 hen eseesaced East spur Mount Lincoln ..-.. --..---..-------- If kong = ets Trace 18 Onota shaft, Johnson gulch .-..-.----.----------| 0.000, 034, 3 0.01 \a19 | North of Onota shaft ' a0. 000, 137 0.040 20 | Lickscumdidrix bore-hole, Little Stray Horse | 0. 000, 137 0. 040 Park. | 21 | 84 | Sacramento Porphyry.) Between Sacramento and Pennsylvania gulches-' 0. 000, 034, 3 0. 01 22 | 98 | Green Porphyry.----- Mosquito gulch, north wall .-...- sronctoscsessss 0. 000, 017, 1 0. 005 23 | 90h Pyritiferous Porphyry Shaft west of Tribune, Breece Hill.--...--------- | 0. 008, 68 2. 533 | 24) 90e |....-- GO) eascessecsesees Hartford shaft, Breece Hill ..-..-.-------------- 0. 000, 275 0. 08 2 Montana shaft, Breece Hill ....-- --| 0.000, 045 0.013 .| South of Ace of Hearts, Breece Hill....-.---.--. 0. 008, 23 2. 400 |: | Shaft west of Ohio Bonanza, Breece Hill .....--. 0. 001, 34 0. 390 | South fork of White’s gulch.........----..-----| 0.000, 113 0. 033 | Comstock Tunnel, White’s Hill.-....---.--.--- 0. 000, 113 0. 033 | West of Pilot fault, White's Hill. 0. 000, 103 0. 030 | Head of White’s gulch ...... ....---.----------- | None .......| None | Above Pilot mine, Printer Boy Hill... .------. | 0.000, 034, 3 0. 01 Above Oro City, south side of California gulch..| 0. 000, 054, 8 0. 016 | Rebel Warrior shaft, Ball Mountain ---..-....-- 0. 000, 079, 1 0. 023 H . Red amphitheater, Buckskin gulch .....-.....-. 0. 000, 013, 7 0. 004 Bartlett Mountain, near summit ......--------.-| 0.000, 192,5 0. 056 37 | 119b |.----- do ............-..| Buckskin amphitheater, débris slope - - 0. 000, 048 0. 014 ET SR ol ee ea eee See rbsee leccece (i Was -8a See caisebosesincsacmecco easter sue Be BO ae EROTIC) =e | 39 266 ‘Horseshoe ”’ dike in limestone -.-..-.. ---.-----.|..--.-.---.--- Bar 0tY) oaeen 40 | 129 Arkansas amphitheater ..-..--------------.---- 0. 000, 017, 1 0. 005 41 | 131 ferseaeeerestchae iss Vacate (a astcoeenaesocces ‘Conese esbbecagon 0. 000, 006, 8 0. 002 | 42 | 140 | Rhyolite.........----- | Black Hill, South Park .... 0. 000, 068, 7 0. 020 | 43 142 | Trachyte Lead of Umioneulcheststsecee ssoetce tenes 0. 000, 092, 8 0.027 | 44 | 143 | Hornblende-andesite -| West slope of Buffalo Peaks .-.....----.----+--- 0. 000, 103 0. 030 Aoiloceson Granites=—sce—<—=eee Big Evans gulch.--.-- ...----.+-.-------200-20+|-22e eee ee eee None | AG) \.<2.<- | aaa C0ie-seee ee eae Yankee Hill, south of Logan shaft..--.-.--..--.|.------------- = Ot ees | a Complete analysis of this specimen in Table I. ERUPTIVE ROCKS. 595 REMARKS ON TABLE IV. For the estimation of such extremely small quantities of silver and gold as it was supposed some of the eruptive rocks from the Leadville region might contain, and even for their detection alone, a most extreme degree of care and precaution was imperative. It being necessary to operate upon large quantities of material, it was - decided to make the determinations by crucible assay, this process combining the greatest accuracy with the least expenditure of time. It was found, however, after a nuinber of tests, that none of the lead or litharge obtainable was sufficiently free from silver for the present purpose. The silver contained in the lead or litharge used for an assay was generally so largely in excess of that in the powdered rock mixed with it that the prills of silver obtained from the regular assay upon rock known to contain silver and from a check assay upon the lead or litharge alone frequently differed in weight only within the allowable limits of error. Recourse was then had to lead acetate, of which several lots were examined. These were all found much freer from silver than either of the substarces previously tested, and one lot of commercial acetate from Mallinckrodt & Co., of Saint Louis, Mo., was used for all the assays tabulated above. Preparatory to using, it was dehydrated by fusing in a large iron vessel till sudden swelling up and solidification of the whole mass took place, and then finely pulverized. This material, containing about 73 per cent. of lead by assay, was found by repeated tests, conducted, as given below, upon the same amounts as used for the rock assays, to carry 0.004 ounce silver per ton of 2,000 pounds, or 0.0000137 per cent., including a trace of gold far too small for estimation. The latter was left on solution of the silver in nitric acid as a minute black speck, indistinguishable without the aid of alens. By collecting into one button the silver from 500 to 600 grams of dehy- drated lead acetate, parting with great care, bringing the gold upon a sheet of white writing paper and flattening it out with a knife blade, the yellow reflection of gold could readily be observed by examination with a lens, and sometimes with the naked eye. The process of assay was as follows: Four Hessian crucibles, of suitable size, were each charged with one assay ton (29,166 milligrams) of the sample to be assayed. two and one-half assay tons of the dehydrated lead acetate, and a proportionate amount of a flux consisting of soda, borax, and a little argol. After mixing well, a layer of salt was placed on top, and, if much pyrite was present, an iron nail inserted, The four charged crucibles were then place covered in a wind furnace fired by coke, and left, with proper regulation and final strong increase of temperature, till fusion was complete. The contents were then poured into molds, the lead reguli, weighing each about 55 grams, reduced by scorification in a muffle to a smaller size, the reduced reguli united two and two and rescorified, and the two resulting therefrom again united and reduced by scorification to a single button of suitable size for cupellation. Toward the end of cupellation, which was always conducted with the greatest care and, as nearly as possible, under the same conditions of temperature for each assay, the button was poured from its cupel into another one immediately behind the first, in order that the cupellation might be finished upon a smooth bottom. If this preeau- tion was neglected, the silver button was occasionally not to be found in the roughened surface of the cupel. After a little experience, no loss need be apprehended in pour- 596 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. ing from one cupel to the other. The silver was then weighed upon an Oertling assay balance, indicating a difference in weight of 0.02 milligram with great exactness and of 0.01 milligram with tolerable accuracy. After deducting from the weight of silver found that due to the lead acetate, which, where ten assay tons had been used, would be 0.04 milligram, division of the remainder, if any, by the number of assay tons of rock taken gave directly the contents in ounces and decimal fractions of an ounce troy per ton of 2,000 pounds avoirdupois, since 29,166.6 ounces troy make one ton of 2,000 pounds avoirdupois and an assay ton contains 29,166.6 milligrams. The silver was then dissolved in nitric acid, but the presence of a trace of gold, derived from the lead acetate, rendered the detection of gold from the rock impossible, unless its amount considerably exceeded that of the lead salt. An example will best show the degree of accuracy attainable. Suppose rock and lead acetate to have been taken in the usual amounts: Four assay tons (116.66 grams) of the former to ten assay tons (291.66 grams) of the latter, and the final silver button to weigh 0.06 milligram. From this is to be deducted 0.04 milligram, and the remainder divided by 4, the number of assay tons of rock tested, gives 0.005 ounce per ton as the accurate result. Had the weight been 0.05 milligram, the correctness of the result, 0.0025 ounce, might be more open to doubt, as the balance cannot be counted upon to indicate differences of only 0.01 milligram with certainty. Hence, for the above quantities of sample and lead acetate, 0.005 ounce per ton is about the limit of accuracy. There will be noticed in the table occasional instances, notably in No. 41, where lower figures are given. In these cases the amount of rock assayed had been increased without at the same time increasing the lead acetate. In the case of No. 41 it was impossible to decide from 4 assay tons whether silver was present or not, though the weight seemed to slightly exceed 0.04 milligram. By doubling the amount of sample * and using still only ten assay tons of lead acetate, the weight of the silver sensibly increased, thus showing beyond reasonable doubt that the rock was argentiferous. It did not appear advisable, however, as a rule, to reduce the proportion between the weights of sample and lead acetate much below 4:10 for fear the reduced lead might not be sufficient to extract and collect the silver entirely. LIMESTONES. TABLE V.—Complete analyses. Dolomitic limestones. | | | | CaO MgO} MnO | FeO, CO: | SiOz AlO3| Fe203) K20 | Naz0 H20} SOs | P20s | Cl I Org.) FeS2 | Totals. (cae (cate | | | | i | eg 126.60) To 415 a 0. 83 40.91 11. 84 | 1.66 | 1.51 0.017 o. 029 0. AST hoories Trace0.05 |Trace a|.-...|.---.- ‘oo. 436 IL ... (20.79 21.14 ‘Trace | 0.24 46.84 | 0. 21 | 0. 27 | 0.21 (0.030 ie 062 0.22 Trace|Trace0. ili) ==--=5- 0. 03 | Trace 100. 142 | | | | | @.0.000,022, 5 per cent. I. Type of the Silurian or White Limestone. Coll. No. 164. From quarry in California gulch. Il. Type of the Lower Carboniferous or Blue Limestone. Coll. No.170. Silver Wave claim, Iron Hill. ——— LIMESTONES. 597 REMARKS ON TABLE YV. The carbon dioxide and the water of the above analyses were estimated as in the case of the eruptive rocks; the one by loss in weight upon treatment with hydro- chlorie acid in a suitable apparatus, the other by absorption in a calcium chloride tube. The organic matter of Analysis II was determined by an ordinary combustion analysis, after dissolving a considerable quantity of the rock in dilute hydrochloric acid and collecting and drying the insoluble matter upon an asbestus filter. The car- bon dioxide formed was caught in potash bulbs and weighed. For 58 parts of carbon found, 100 parts of organic matter were assumed, as recommended by Fresenius. The trace of iodine shown in Analysis I was detected and estimated by dissolv- ing one pound of the dolomite in nitric acid, precipitating the chlorine and iodine as silver salts, reducing the latter by zine and sulphuric acid, separating the iodine by addition of potassium nitrite, collecting it in carbon disulphide, and titrating with a dilute solution of sodium hyposulphite. Bromine could not be detected. The chlorine was determined on from five to ten grams of rock by precipitation with silver nitrate from a nitric acid solution. The alkalies were estimated by igniting twenty grams of the finely powdered rock in small portions in a platinum crucible to expel carbon dioxide, extracting with water and proceeding as in ordinary alkali determinations. As the amounts of alka- lies found did not exceed those required by the chlorine to form chlorides, but rather fell slightly below, due perhaps to partial volatilization during the preliminary calci- nation, it seems probable that the chlorine is combined with sodium and potassium, and possibly small quantities of calcium and magnesium. It was found that by boiling the powder with water without previous calcination a portion of the chlorine and alkali could be extracted, and that the amount increased as the pulverization was more perfect. The total amount of chlorine. thus capable of extraction never equaled that actually present in the rock, however. Microscopical ex- amination showed the dolomites to be full of extremely minute fluid inclusions. If the chlorine was derived from these inclusions, where it might be held as sodium and_po- tassium chlorides, a ready explanation is afforded for the incomplete extractibility of the chlorine by boiling water. By no mechanical pulverization could such a perfect subdivision of the particles be effected as to expose all the inclusions; a considerable proportion would still remain intact and retain a corresponding amount of chlorine. 598 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. TABLE VI.—Lime, magnesia, ard chlorine determinations. a | Coll. Heres. Locality. CaCOs | aMgCOs Cl 1| 153 | Cambrian......--. | Below Excelsior mine, Buckskin gulch -.-...--.-.------ 25. 43 4.03 Trace Monte Cristo Ridge, Quandary Peak..---..---.---.--. 46.05 36. 71 Do. Dyer Mountain, marbleized bed ...-.-.---------.----- 53.16 43. 43 Do. Quarry in California gulch........-..---..-----.------ 47. 50 36. 56 0.05 } Belo aes Mine, Dyer Mountain (light blue, com- 36. 27 21.73 Trace pact). | h-aped a> UO Sees Sse Hooo Below a mine, Dyer Mountain (pinkish, decom- 34. 30 20. 12 Do. | posed). Tel eelG | Pedowe eae ee Red amphitheater, Buckskin gulch............------- 49. 30 32. 49 Do. b8 | 170 | Blue Limestone...) Silver Wave claim, Iron Hill ...-...-.....-... .------ 54. 98 44.39 0.10 Oi SABC hee LO eeaee saan Dunkin mine, Fryer Hill (lime-sand) ..---. Se Aereconbese 55. 14 44.29 Trace 10 | 285 le Soles... see Chrysolite mine, Fryer Hill (lime-sand)..--..--..----- 54. 09 43.79 H Do. HO) Un) ree iG) Seance oe = et- ron pire A OS aa onan sem etn claim eee mine iene en aa atm el Do. 12] 170a (G0) Seecemoce scan Ridge south of Sacramento mine.--....-.-.--.---.---- 56. 80 41. 89 Do. ASh li eeecdO reese ees Sacramento mine, Spring Valley .....--..-.--.---.---- 54. 30 44, 33 Do. 14| 174 [hse lott Bacon South slope of White Ridge, Horseshoe gulch......... 52.77 36. 01 Do. UG} | Se |.---o ..-..-.------ London mine, London Mountain ...-..-.-.-----..----- 52. 86 Oy leesnscmonas 16 | 291 Weber Grits.--.-.. Ridge west of Mount Silverheels, Park County....... 54. 34 43, 82 Trace TW Ovales= doce as tees East bank of Beaver Creek -......-. --.------.------. 54. 32 43. 24 Do. HGH (heo09 cesar: seaeeee Beaver Creek, west base of Mount Silverheels......-- 53. 91 A313) |Sasepeioweaen 1@))) sees: Upper Coal Meas- | Robinson limestone, luwer bed -.--..---.-------.----- 87. 87 6593)|Seeeeneeeeer ure. 20) eso |----do See eee Robinson limestone, upper bed ..--..------..--------- Wo1l) || Virace; -2-c|ss-s-7)--eeee 21} 198| Trias (Con. fracture) Silverheels, between Fairplay and Como | 95. 78 WEG CRA ses 225058 22 198a, Se He (Con. fracture) first ridge west of Crooked Creek..... | 99.11 O03 36) Recetas 23) 416 |....do (Con. fracture) Jacque Mountain, near summit -----.- 7. 54 0:76 1|*24: = -onese 24 | o2.e. Trias ? Calcareous shale, near flume northeast of Fairplay-.. - 16. 18 EPEC ie meee on eae .--do mee = saan gb bos condcececciac Soc nsode SE SaeesosenSecec 34. 84 26. 35 ac 26) |=. < 55 Lake beds ......-., Marl from Greenback shaft, Graham Park .-...--.. _ 48. 63 42) eee eae aIncludes (FeMn)COs. bComplete analysis in Table V. N. B.—Blank spaces in above table denote that no tests were made. REMARKS ON TABLE VI. The above figures for calcium and magnesium carbonates have been calculated from the lime and magnesia actually found. With exception of two numbers indicated by b, the chlorine was determined only qualitatively and noted as “trace,” although generally present in quantity sufficient for estimation. TABLE VII.—Serpentine and amphibole from dolomitic limestones. | | | | j No. Bo | 810: ALO) Fe203 | FeO MnO} CaO | MgO | K20|Na20} HO | CO2 P.0s| Cl | Total, | | No. | | (aes (ene | Tal eessee 40.15 | 0.93] 1.28] 1.05 ].-.--- 2308)|(9'4003)|aesene| amen al2.88 | 1.60 |Trace)..... 100. 00 IL 161 {17.64 0.99] 0.62 | 0.18 |Trace) 32.24 | 19.01 |Trace) 0.07 | 3.72 | 25.33 | 0.05 0.08 | 99. 93 III | 16la eee 2.02] 0.38 3.19 | 0.20 | 13.50 | PERE bees Mrace| (i107 i\eeasae| seater | rae 98. 97 a By difference. I. A layer of pure serpentine on limestone from east side of Red Amphitheater, Buckskin gulch, Park County. Il. Limestone thoroughly impregnated with serpentine, producing a light-yellow rock. No pyroxene or amphibole visible under the microscope. Same locality. III. Amphibole with some pyroxene from limestone containing serpentine. Same locality. ORES AND VEIN MATERIALS. 599 REMARKS ON TABLE VII. In connection with the serpentine of Analysis I, it was found by treatment of the powdered rock with very dilute hydrochloric acid that the carbon dioxide was combined entirely with lime. That the rock is a true serpentine appears from a ¢al- culation of the oxygen ratios. | Oxygen percentages. Oxygen ratios. | SiOe = 21.413 | RO(FeOMg0O) : SiOz : H20 FeO = 0.233 i 16.245 1: 1.318 : 0.705 | MgO = 16.012 3:3.95 :2.11 | H:O = 11.449 H Required by theory 3: 4 72 | Analysis IJ, after deducting calcium carbonate, shows the residue to have a com- position approximating to that of serpentine. The mineral of which III is the analysis was obtained in an apparently pure state by treatment with dilute hydrochloric acid, whereby 164 per cent. of the whole went into solution and was found to consist chiefly of calcium carbonate, with a little mag- nesia, ferrous oxide, and phosphorus pentoxide. ORES AND VEIN MATERIALS. TABLE VIII.—Sand carbonates. Te Il. I. Adelaide. | Little Chief. | Waterloo. 80. 352 75. 408 0. 444 1.415 0. 467 1. 940 Op 290 N ean ean 0.137 0. 074 sectasacesc ss 1.386 Trace Trace spenasescberes 0. 095 0. 303 0. 335 0. 068 0. 056 0. 651 1. 972 aceokescagscé 0.121 Trace Trace 1. 532 Trace Trace 0. 486 14. 700 | 14. 251 0. 255 0. 288 0. 395 1. 140 0. 009 0.777 Trace Trace Total..........| 99.612 99. 744 |... Less O for Cl .- O57) || eeeee ioasat ne PORTA) | eee seca L Sand Carbonate, Ore Coll. No. 36, Adelaide mine, North Iron Hill. Il. Sand Carbonate, Ore Coll. No. 33; Little Chief wine, Fryer Hill. I. Sand Carbonate, Waterloo mine, Carbonate Hill. 600 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. REMARKS ON TABLE VIII. Consideration of Analysis I shows that the carbon dioxide is insufficient for eom- bination with all the lead oxide, and that the chlorine (entirely soluble in nitric acid) and the phosphorus pentoxide bear to one another the exact ratio of chlorine and phosphorus pentoxide in the mineral pyromorphite; 3(3PbO, P2O;)+PbCl.) Caleu- lating from the chlorine there is found to be 9.75 per cent. of this mineral. The carbon dioxide is, then, somewhat more than sufficient for the remaining lead oxide, forming 86.60 per cent. of cerussite, PbCO3. The silver exists in the state of chloride, as shown by extracting it from a large amount of ore with ammonia. A portion of the ferrous oxide is presentas magnetite. The slight excess of car- bon dioxide above that required for the lead is probably combined with ferrous, man- ganous, and calcium oxides. Analysis II shows plainly that pyromorphite is practically absent from the spec- imen of ore from the Little Chief mine. The lead exists mainly as carbonate, with a little sulphate, and probably a small amount of antimoniate. A yellow substance left unattacked with the silica and silver chloride ore, on treating with nitric acid, gave reactions for lead and antimony. ‘The silver exists altogether in the state of chloride and could be completely extracted by ammonia. The total chlorine, found by fusion with alkaline carbonates, extraction with water, and subsequent precipitation with silver nitrate, is slightly in excess of that required by the silver, but it was found that a few hundredths of 1 per cent. was present in a combination soluble in water. Only the chief constituents from the ore in the Waterloo mine (Analysis III) were estimated. Starting from the chlorine, which represents that soluble in nitric acid alone, the ore is found by calculation to contain 52.07 per cent. of pyromophite and 61.78 per cent. of cerussite, the carbon dioxide exactly sufficing for the lead oxide left after combining the elements of pyromorphite. An excess of 1.44 per cent. phos- phorus pentoxide is probably combined with alumina, of which a considerable amount was found to be present. TABLE IX.—Chloro-bromo-iodides of silver. ie | Soe III. Ci 13.78 9. 80 99. 925 I. Ore Coll. No. 39. Robert E Lee mine, Fryer Hill. Brees S5N63))|9 189.90! use e Esch 0.59 | 0 21 0.075 | } 100.00 | 100.00, 100.000} IT. Ore Coll. No. 30c. Amic mine, Fryer Hill. | AgCl....| 21.50/ 15.75! 99.966 AgBr..... 77. 99 | 94509) |e. oe = III. OreColl. No. 37. Big Pittsburgh mine, Fryer Hill. Apr 22 0.42| 0.16] 0.034 | 100. 00 100. 00 109. 000 ORES AND VEIN MATERIALS. 601 REMARKS ON TABLE IX. The figures in the upper series represent the relative proportions of Cl, Br, and I; those in the second series, the percentages of the corresponding silver salts. The ore specimens, having first been treated with nitric acid to extract any solu- ble chlorine salts, were then subjected to the reducing action of zine and sulphuric acid, whereby the silver salts were entirely reduced. To the filtered solution, contain- ing all the chlorine, bromine, and iodine, potassium nitrite was added, the liberated iodine collected in carbon disulphide, separated with the latter by filtration, and esti- mated by titration with dilute sodium hyposulphite solution. The chlorine and bro- mine were then thrown down by silver nitrate, the precipitate was washed thoroughly by decantation, brought entirely into a tared vessel, fused, and weighed. As _ suffi- cient material had been taken to insure several grams weight of mixed chloride and bromide, the estimation of the halogens by entire conversion into silver chloride in a current of chlorine gas was repeated on different portions with very closely agreeing results, of which the above are the mean. In Analysis [Ila qualitative test failed to indicate the presence of a trace of bromine, and the fused silver chloride, when heated in chlorine gas, showed no change whatever in weight. The silver in the ore, reduced by the action of zine and sulphuric acid, was not estimated. The figures in the second horizontal series above are therefore obtained by calculation from the chlorine, bromine, and iodine found. In Analysis I the proportion of AgCl:AgBr is 4:11, while in Analysis IT it is 1:4. 602 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. TABLE X.—Various ores and vein materials. N. B.—With the exceptions noted, blanks in the table denote ‘‘no tests.” 1. ‘‘Hard carbonate,’ Scooper mine, Yankee Hill. 2. ‘‘Silicious ore,” El Capitan mine, Taylor Hill. 3. “Gold ore,” Ore Coll. No. 60, El Capitan mine, Taylor Hill. 4. Silicious hematite, Ore Coll. No, 84, Chrysolite mine. 5. ‘Iron ore,” Ore Coll. No. 90, Kenosha mine, Long and Derry Hill. 6. Altered limestone (jight material), Garden City mine. 7. Altered limestone (dark material), Garden City mine. 8, 9, and 10. Specimen showing pyrite altering to alight ocherous mass. Ore Coll. No. 44, No Name gulch, Lake Co, 8. Nucleus of pyrite. 9. Dark zone. 10. Light outer zone. 11. White filling in chert nodule from porphyry, Ore Coll. No. 300b, Ben Burb shaft. 12. Chert nodule, Ore Coll. No. 299, El Paso shaft. 13. Breecia with ore cement, Ore Coll. No. 53, Evening Star mine. 14. Chert under ore body, Little Pittsburgh mine. 15. Granular quartz under ore, Ore Coll. No. 3a, Waterloo mine. 14 15 Tusoluble.| 60.00 |-..-----|.------- Gh Iscoceesllsssqesoeleasecce 7.36 | 16.36 | 54.28 |.-...-..|..-.-- ete TA eR aaron OL) WEP) CbONte ORB --554)) Sssscos)|esocacolsseSacd| beeostd||panaced biseessoc||seesiolfonsss PAC emeaintate Trace | 0.011] 0.0004) None |...----|.------ |------- E Totals. .|100. 000 |100. 000 |100. 000 |100. 000 |i78.90 | 100.72 |100.78 |j95.41 |100. 00 |100.00 |..-...-.| -.-.- a Remainder Fe203 and Al203, no water. b Remainder Fe203 and AloOz. Of the SiOz 3.06 per cent. was soluble in a moderately strong solution hydrate. c Cementing material chiefly pyromorphite, with some galena and cerussite, also a little calcite. of potassium d Remainder chiefly PbCO3 and Fe2Os; of the silica 3.93 per cent. was soluble in a moderately strong solution of potassium hydrate. e By difference. Ff Calculated. g By difference; includes some PbO and Sb20;. h By difference; includes a little Sb20;. i Remainder chiefly SiOz. j Remainder is SO3 and H20. REMARKS ON TABLE X. The analyses of the above table were made without view to completeness, the object being in the majority of cases to ascertain merely the general nature of the ore or material under hand. As this appears at a glance from the tabulated results, fur- ther remarks are unnecessary except in the case of 8,9,and 10. The specime n showed a nucleus of granular pyrite in process of decomposition, ferric oxide being observable throughout the mass. This very irregular nucleus was inclosed in an envelope of dark- ORES AND VEIN MATERIALS. 603 brown hydrated ferric oxide, the boundaries being in places rather sharply defined, in others indistinct. The dark zone was in turn surrounded by a zone of light-brown oxide, tbe line of demarcation being very regular and sharply defined. The dark oxide was compact and flinty; the light oxide also compact, but less hard. TABLE XI.—Alteration products of porphyry. Ore | | | | No. Coll. Local name. | SiOz | Ale: | Fex0s | FeO) ZnO | CaO | MgO | K:0 |Na:0 | H20 | SOs | Totals. | 0. | | ‘ | | 1 55b | Kaolin.-.-... 48.72 34.01 | 0.56 | USUT5! |b eonsSasl Seanenad 1.11 | 9.88 | 0.67 | Oe Pees | 100. 03 | 2 55a.| Chinese talc} 43.36 | 37.78 |......-.]..----|----... 0. 22 0. 30 Trace 17.95 | Trace | 99. 91 3 56c | Kaolin.--... 4.55 | 35.60 PAO Ti eee 55) eS Trace | Trace 2.73 | 5.28} 15.05) 34.55 | 100.00 | H | | | | H 4 56 Chinese tale| 24.47 38.05 0.93) 0:77 |---..--- 0. 23 0.30 2.72 | 1.30 16. 67 15.48 101. 15a 5 SBD ae CO lees soe PUREE Ie BERTON ae eee) oscese| Se hooaee 0. 53 1.14 | 2.83 | 1.56 | B16. 51 15.75 100.00 | | | | | 6 105a | -.- 35288))| 10:88) |) 222.2. Ieee | 33.05 1. 62 OR 7s ee rng ea 19:/06'))) -3-25- 100. 15 al) mel Oba eee 35. 97 GE ee elbcesns 35. 40 1. 87 O28} Penn eeoeee | UTS46) sa. aes 100. 31 | 8 105b |... 37. 54 24.76 | c0,64 |...... 18, 43 0. 63 0.71 | 0.66 | 0.36 | WDB feesecdios 100. 10 | | | a Includes 0.23 P20s. b By difference. ce Present as a visible impurity. 1. Amie mine, in ore body. Ore Coll. No. 55b. 2. New Discovery mine. Ore Coll. No. 55a. 3. Big Pittsburgh, contact of Gray Porphyry. Ore Coll. No. 56b. 4. Morning Star mine. Ore Coll. No. 56. 5. Swamp Angel tunnel, contact of White Porphyry. Ore Coll. No. 56b. 6. Lower Waterloo mine. Ore Coll. No. 105a. 7. Lower Waterloo mine. Ore Coll. No. 105a. 8. Lower Waterloo mine. Ore Coll. No. 105b. REMARKS ON TABLE XI. Owing to the indefinite nature of the greater part of the peculiar products of alteration represented by analysis in the above table, it is impossible to ascribe to them distinctive names. Notwithstanding the great external similarity of all but the first of the specimens examined, they have been found to differ most widely in composi- tion, though, aside from the above exception, three distinct groups may be recognized, namely: First, simple hydrated aluminium silicates allied to kaolinite; second, mixed aluminium silicates and aluminium and alkali sulphates, likewise hydrated; and, third, certain hydrated aluminium and zine silicates, also mixtures. In the following are given the distinctive physical and chemical characteristics, accompanied by brief discussions of the analytical results: No. 1, grayish white; compact, but of hardness considerably less than 1, rubbing off on the fingers; luster, pearly; insoluble in hydrochloric acid. Evidently derived directly from porphyry, since honeycombed remnants of feldspar crystals, and even large crystals, an inch in length, showing rough faces, occur imbedded in the mass. Under the microscope it appears to consist of crystalline scales without definite form. In order to obtain material for analysis free from undecomposed feldspar, it was slightly crushed and stirred with water in a beaker, whereby it became thoroughly dis- integrated, the fine matter floating and imparting to the water a beautiful satiny appearance similar to that frequently observable in streams receiving the tailings from 604 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. stamp mills, while the gritty particles fell to the bottom. By pouring off the sus- pended matter, allowing to settle, decanting the supernatant liquid, and drying the slimy deposit, an apparently pure matter was obtained, showing the pearly luster of the original mass, and containing, like that, when air-dried, about one-quarter of 1 per cent. of hygroscopic moisture. This is not included in the above analysis. No further loss occurred on prolonged heating until a temperature considerably above 100° C. was reached, while a strong red heat was requisite for complete expulsion of the water. No altogether satisfactory formula can be deduced from the figures in the table. On dividing the molecular value by that for water, as being most accurately deter- mined, the ratio is found to be SiO, : Al,O; : R(R)O : H,O 9.93 4.09 1.87 3.00 or, approximately, IC) eee: Bas ey oes, As no other specimens of a similar nature, from the Amie or other mines, have been observed, by analysis of which it could be ascertained whether the above ratio remains constant or not, it would be rash to aftirm that the material analyzed repre- sents a distinct mineral species, the final product of the alteration of the porphyry from which it is derived. No. 2, pure white, veined with manganese dioxide ; compact, hardness about 2, rubbing off on the fingers when dry. When fresh and moist, frequently greenish in color, opaline in appearance, and semi-transparent, especially on the thin edges, becom- ing opaque on exposure. Insoluble in hydrochloric acid. Portions free from MnO, taken for analysis. It was found that after two or three years’ exposure to the air a large amount of water, 3.36 per cent. of that given in the analysis, was still retained in a very weak state of combination, apparently as hygroscopic moisture, since it escaped over sul- phurie acid. No further loss occurred on heating at 100° C., nor below 160° C. to 170° C., although blackening took place, due to carbonization of organic matter. Dried over sulphuric acid or at 100° C., the powder was so extremely hygroscopic that it was deemed advisable to make the analysis upon air-dried material. The percentage of loosely combined or hygroscopic water was found to decrease slowly on long exposure of lumps to the air, so slowly as to be perceptible only at intervals of a month or more. Deducting all water driven off at 100° C., the molecular ratio SiO, : Al,O; : H,O is 1.98 : 1.00 : 2.20, thus showing the substance to be closely allied to kaolinite.' Nos. 3, 4, and 5. In general appearance 4 and 5 differ little from the substance last deseribed. Color, white, streaked frequently with iron and manganese oxides; hardness, after long exposure, in case of 5, about 24. Practically insoluble in hydro- chlorie acid. No.3 is pure white, and resembles 1; it contained no hygroscopic water. No. 4 contained but 1.23 per cent.; while No. 5 retained 4.58 per cent. of the same (included in the analysis), after long exposure to the air in the form of lumps. ' The same is found in the Morning Star consolidated group of mines according to L. D. Ricketts, one of whose published analyses (The Ores of Leadville, Princeton, 1883) shows a ratio SiO, : Al,Os : H,0 =2: 1: 3, probably including hygroscopic or weakly combined water. A Ua a igs alas cs ORES AND VEIN MATERIALS. 605 The air-dried material of 4 and 5 was analyzed, since, when dried over sulphuric ‘acid or at 100° C., the hygroscopicity was such as to render accurate weighing out of the question. In very few hours No. 5 reabsorbed, when exposed in the air, over half of the 4.58 per cent. of moisture lost at 100° C. Consideration of the analyses, coupled with the observed insolubility in hydro- chloric acid, shows beyond reasonable doubt that these bodies are mixtures of alunite, K,S0,+ (Al,)S;0;.+ 2H¢(Al,)Og, corresponding in formula to the jarosite of the following table, or of an allied mineral, with different indefinite hydrated aluminium-calcium- magnesium silicates. If the supposed alunite is caleulated on the basis of the sul- phuric acid, the residual amounts of silica, alumina, lime, magnesia, alkalies, and water are found to have widely different and not very definite molecular ratios in each analysis. : From the fact of No. 3, which is mainly an aluminium-alkali sulphate, containing no weakly combined or hygroscopic water, the hygroscopicity appears to be a prop- erty of the hydrated aluminium silicates. Nos. 6,7, and 8. Similarin appearance to the simple hydrated aluminium silicates represented by analysis 2. Nos. 6 and 7 were taken by Mr. L. D. Ricketts from one locality in the mine, No. 8 from another. The fi:st and second were not to be distin- guished from each other by the eye, being brilliantly white (greenish under certain conditions of light), opaline and semi-transparent, while the third was veined with iron and manganese oxides and possessed in a Jess degree the pronounced conchoidal fracture of the others. On exposure they became opaque, and after some months possessed a hardness of about 3. Nos.6and7 were entirely and readily decomposed by strong hydrochloric acid when finely pulverized, while upon 8 the action of the acid was not so marked, though still energetic. The hygroscopicity of these substances, especiall’ of the first and second, is extraordinary. Over sulphuric acid No. 6 lost 11.64 per cent. of water, while No. 7 lost 10.26 and No. 8 but 5.30 per cent., these amounts being included in the tabulated results of analysis. Exposure to a tempera- ture of 100° C., and even 15t° C., occasioned no further loss in weight, but the presence of organic matter made itself manifest by the blackening of the powder. The dried material reabsorbed moisture with great rapidity. It was at first supposed that these were, mixtures of calamine with some hydrated aluminium silicate. But if from the molecular values those for zine oxide are eliminated and proportionate amounts for silica and water subtracted, on the supposition that calamine is present, the ratios between the remaining molecular values are not the same as should be the ease if the mixture consisted in all these cases of calamine and one other definitely constituted mineral. Moreover, on decomposing with hydrochloric acid no gelatinization takes place, and not even a trace of silica goes into solution, an argument against the pos- sibility of the presence of either calamine or willemite. The molecular values, con- sidered altogether for each analysis, do not present relations sufliciently definite to allow of supposing any one of the specimens to represent a single mineral species. 606 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. TABLE XII.—Alteration products of galena and pyrite. No. | Gol. SiO2| Fe.O3 | Al:Os | CaO, MgO a NaO | HO | PbO} Bi2xOs; As20s | P20s| SOs Cl | Totals. Yo. | | | | | | | | oe 1 | 106a|None| 46.70 | None | 0.06 0.06 | 5.33 1.68 | 10.54 | 4.27 | 0.08 0.46 | 0.08 | 30.53 | 0.02 | 99.81 2 | 106b} 0.30 | 42.98 0.20 | 0. 64 | None | 6.31 0.83 | 10.12 | 8.27 | None 0.42 | 1.58 | 27.81 | 0.26 | 99.72 3 | 106c | 0.36 | 44.40 0.23 |None! None! 0.15 | 0.37) 899 19.50 | None 0.39 | 0.11 | 25.07 | 0.04) 99.1 Pl bate eee eee aaa) POE Lian 2.12 | 0.57 5 | 106e ae eta a Va as (0.36 | 0.77 (GAN TCG) GA Ree ESaen er bso ll beet 1.96 | 0.18 7| 106g | Wp ee ae eee (Era eee oe | 4.04) 0.57 | | 1 1. From Maid of Erin mine, under White Porphyry. Contains 0.0048 Ag and trace of Au. 2. From Morning Star (1 orsaken) mine, under Gray Porphyry. Contains 0.0036 Ag. 3. From Lower Waterloo mine, under Gray Porphyry. Contains 0.075 Ag. 4. From Morning Star (Forsaken), under Gray Porphyry. 5. From Morning Star (Forsaken), under Gray Porphyry. 6. From Morning Star (Forsaken), under Gray Porphyry. 7. From Silver Cord mine, under White Porphyry. REMARKS ON TABLE XII. Notwithstanding the great similarity in appearance of all the specimens of which the above are analyses they are rather complex mixtures in very varying proportions of several mineral substances. They all show a similar chemical behavior. Heated in a cPosed tube, water is first evolved, the substance then changes from an ocherous, or sometimes brownish yellow, to dark brown, and later sulphuric and sulphurous acids escape. Thesame changes occur in an open tube. On charcoal with soda there appears sometimes a slight coating of arsenic trioxide, accompanied by a smell of arsenic and the reaction for lead. Entirely insoluble in boiling water. Nitric acid in the cold extracts part of the lead oxide; also, arsenic and phosphorus pentoxides and usually chlorine. Continued boiling with nitric acid seems to decompose the iron minerals completely. Warm hydrochloric acid effects complete decomposition, and no trace of a ferrous salt can be detected, even if solution has been effected in an atmosphere of carbon dioxide. Caustic alkalies also decompose them completely, all the sulphur trioxide and arsenic and phosphorus pentoxides going into solution, whereby the analysis is materially sim- plified. Various tests, combined with a consideration of the three complete analyses, show that the lead is present as anglesite and pyromorphite!: in No. 2 as the latter mineral alone, the lead oxide, phosphorus pentoxide, and chlorine being in the exact proportions required for the formula (3PbO, P,0;)+PbCl. The As,O; is not present in the corresponding chloro-arseniate of lead, as shown by the fact that the proportion of P,O; to that part of the Cl not combined with silver is always the same as in pyromorphite, and that there is insufficient lead for both phosphorus and arsenic pentoxides together, as in No. 2, where it exactly suffices for the phosphorus pentoxide. The arsenic pentoxide is therefore undoubtedly present as a hydrated ferric arseniate. By combining in the first place chlorine and phosphorus pentoxide with lead oxide and the remainder of the latter with sulphur trioxide, definite conclu- sions may be reached as to the composition of the remainder of the mixture. Analyses 1The pyromorphite is sometimes visible in bunches of small crystals. oe ae oe = ORES AND VEIN MATERIALS. 607 land 2 (especially the latter) show that the chief constituent in these cases is probably jarosite, K,SO.4+ (Fe.)S;0,.+2H6(Fe.)Os. As there remains a slight excess of SO; and Fe,O; after combining the constituents of this mineral on the basis of the alkalies present, a basic ferric sulphate is to be assumed as a further constituent of the mixture. Analysis 3 shows little pyromorphite, much anglesite, little jarosite,and much hydrated basic ferric sulphate, of which latter it is impossible to determine the formula definitely, since it is not known how much ferric oxide and water may be combined with the arsenic pentoxide. The remaining partial analyses were made to ascertain whether or not the alkalies were constant constituents of this class of products of alteration of the original vein material. Qualitative tests showed that pyromorphite and anglesite were occasionally present in greater amount than shown in analyses 1,2, and 3. Arsenic pentoxide was found in very considerable quantity in the material from the Silver Cord mine (7). TABLE XIII.—WMiscellaneous alteration products. | I ; | | No. Rock. Locality, Sid. | Feig?} | K.0 Bie SoHE | eosKOy | Totals. eaaceewn | i aConsists of calcium carbonate, with a little magnesium and less manganese carbonate. b Specific gravity at 18}°-C. = 2.570. Hardness, 6. e Soluble in strong solution of potassium hydrate after four to five hours’ digestion = 65.73 per cent. d Specific gravity at 164° C. = 2.023. Hardness 5.5. eSoluble in strong solution of potassium hydrate after four to five hours’ digestion = 97.42. 608 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. TABLE XIV.—Assays of orcs, vein materials, and country rocks. Ore No. Coll. Name. Mine. Remarks. No. Ores. eee Sand carbonate -.-.--- Matchless, near Hibernia-.----.---- Crystals of cerussite - . Dalle © S5Difeanse0 Mone sae sescvene Morning Star, fourth level north ...) Compact....--...----- 3 abd5}es-— 22 CE pa aeaceeconace Morning Star, first level south .....- White sande eee. 89.10, equivalent to chlorine ..........- 82. 45 Bromide Oh siliverie-ss--t- oe oe 10. 45, equivalent to bromine .-.--.----- 16, 83 Iodide of silver ................ 0.45, equivalent to iodine ............- 0.72 100. 000 100. 000 Special stress has been laid upon the composition of the chloride ores, for the reason that they play an important part in lead smelting in Leadville. To chlorine, bromine, and iodine is due a great part of the loss in lead, not only because chloro- bromo-iodide of lead is a very volatile compound, but also because chloro-bromo-iodo- phosphates and sulphurets of lead are found which are also remarkable for their great volatility. Average of ores.— Mr. Th. Fluegger, assayer of the Harrison Reduction Works, in Leadville, has published in the Engineering and Mining Journal of March, 1880, an analysis of a sample from 1,000 tons, representing specimens from every producing mine in Leadville. This analysis, made with probably insufficient means in the lab- oratory of one of the smelters, has evidently no pretension to scientific accuracy, since some of the elements—sulphur, arsenic, antimony—are left uncombined and since all the rare elements are not indicated. Itis given here, however, because upon it have been based the main features of the chemical discussion of the blast furnace. If it is assumed that the quantity of silver reported in this analysis is correct, it represents an average quantity of silver of nearly 90.5 ounces to the ton. This figure appears exaggerated, for the reason that the proportion of silver to lead is one ounce to five pounds, while in practice mixtures aimed at contain one ounce of silver to six pounds of lead. But the average percentages of lead (23), iron (18), and silica (22.5) agree precisely with the general composition of the smelting charges in Leadville. ANALYsIs VI.—Average ore. Carbonicacid soso oR jase Sores fates ane ee Ses ieee aweeae Sek aes eee 5.58 Oxidelofilead feiss ser ayseleee ees ees etee cee eee cae shcaicrs inv Sees 24.77 SUIT arriel a ore eleven eetesintors aie eae rere stale a are eater ate aie re ieee Sees ee Coe eee 22.59 Salphurs A552 se ese ots ere eet Oana Se ates nee ome meseicin Baa tucemicatne vee 0. 90 PTOUOKIGC LOL MONE Sane eee ee rae Sane eter ao Pace ee ree ee eer ona 0. 89 MEFORId 6, OF ITON oe ienmal Soa remo aeeae ase ein ere Se neee eee coe se nee eee 24, 86 brotoxidelofiman ganese)i moose aceon atsiclals os seetsep os cle cine eee eels 4, 03 Silvers Fences eyaeets viarigeavsia lets apse ase ta ce ston Sesion = Saye eee 0.31 IU RRS e AS ROO CAO RSE Cae COB Sad CARS S Ree GEC CEE Cpa EEC ea eenanacaass 2. 36 Magnesia) (22 esate sseiser eae sete ser seer oo nae once eae ea eee 3. 04 ATBONICH Son societies aaene ieee Soe eae ae Cee eae Sie we ea oe sar ee 0. 01 ATILIMOWY <2 =e ieocrare aniater eye ce seats ee oe ae ean ran se Giea eros els eisie eee eiee ene 0. 02 Potash; and:s0d a oo2- ses.a- cena cctocec eacie nes eek aor eels oaks Sonate eee 0. 98 Chlorine: 2 22h eaea rasan ee ee eee ieee eens eh ieee ee een 0.09 Waiter. Sons ise nermceitane se sacs Cee oe eRe eae ccae Gee oe oe eee eee 5. 53 Alumina. .i encase issscse os che oe ear ee oaee aioe eae oe as tae mcrae ae eee es eee 3.99 Gold) \copperszimce sec mactwecebcce acces hose ececesece nen ene cores aes Trace 99, 95 Silver, 90.5 ounces to the ton; lead, 23 per cent.; iron, 18 per cent.; silica, 22.59 per cent. ASSAYS OF LEADVILLE ORES. 621 Assays of various ores.—The assays of the first division of the following table were made by the writer in June, 1880, for one of the smelters. The silver assays present a certain interest, since they were made in crucibles, whereas the ordinary method of silver assay at Leadville is that by scorification; the lead assays, however, are the ordinary fire assays usually made in the region. The assays given in the rest of the table were made by the different assayers attached to the respective smelting works. TABLE II. I.—ORE ASSAYS. Name of mine. Lead. Sieede the Galas the Per cent. | Ounces. | Ounces. 15.00 47.70 | None | 15. 00 30. 00 | 0. 85 | 26. 45 } 8. 80 0. 05 54.909 | 12.60 | 0.10 21.45 12. 00 0.10 9.45 34.15 | oN05) 9) 45, 80 28580 tilesescece ces | 0. 50 BURGM) SScacssbesbens 11. 30 78. 00 \eGrocstheososs Amie (special lot) ........-...--------- poiS1570 ai el TSOn TOL = |Seee-cecses ace Amie (black lumps) ----.---- = : 1.70 O15 40 mee lence eee ae PAMIG| WUMPR) sae aa eee ee | 1.50 STS 20 eee eee een Amie 42. 00 PAN GE WeSaS=mdentotes Do 7.00 OAV Shin Mt eee cere | Do 2.00 BTGSbme a Makeer cone Amie (lumps) 5. 80 PARE 4 eye eesoretes | Amie 6.70 VCC mE bpceeer cee 0. 50 WO: S08s Hen. senasen ee ok Do 17. 00 2305909 ecta cose ee Do 1. 90 | BPAY Weacecasesoosos Belcher .. 5. 65 | SRE AA | Wese Ses enone Doras. o 5 6. 50 SELEY! lorossaconcsoe! Ghrvaolite-cssp soe scons cone =~ ee 19. 30 PEEEEI |leeeosccnercone Wo seaneceee ses acces oie 27. 50 ChE O)) ae osccstosd Evening Star 44.35 GONO5! || boss cee vets Hibernia: (clayish) -~.--....--..<<..--- 1.80 SBME Na oeooceseccced | Blttle Gian teem sete ais 28. 00 PAIGTUY oe Remo ses osese 40, 00 OPE eer A ctlebecssog 54. 00 SISTO) w lseeereaseosee | 25.20 | BAO MAN | eserceeee ss | 84. 50 D2E SOM esoee kos e = 3 | SMELTER, AUGUST, 1880. PAT eSeace secosde > anc csiGan ese bes 14. 00 TSOAO0R ey anos eeneies | kG yy it ss SSS ea SOEs 46.00 TPAC) oy ese Sz onedhisse | Carhonateyesseeseaeaedens-eerabccack = | 30. 00 | LOTAOC Mn enone em eco Catal patos: seen ss caret eee | 33.00 | SONOOwy lees secs sce eee HiVGnin Stat penenea ne ee ower | 37. 50 55. 00 -| ERO) ree ere nan Aeyciatciniece sqaeee 33.70 45500" |) \SsSeccen scene | Mite @ Wiehe eee creme nla alee soca ce sicinm= 35. 00 CEAU Be BSescodee es Ho velan deere awe tee nannies ene 46. 50 S500) eas So-eteese Morning Star 48. 00 Wa | GGasegansceces Pine .-.- 28. 00 12. 00 | seeeeetaascc R. E. Lee None TESORO |e wtece natweece 622 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. TABLE I] —Continued. IlI.—ASSAYS MADE AT MESSRS. CUMMING & FINN’S SMELTER, JULY, 1880. | ilices = Name of mine. | ‘Lead. Sante nie | Sole ae ig Per cent. Ounces. Ounces. Adelaide.....-.....-....-.------------ 22 to 44 12 to 20 0.5 to 0.75 PAINE) -f= ai=\almn intent elm wim niel=iel-i'=Ilminiei= = in 2 to 10 20 to 1,100 Chrysolite <..-..----.---<----------- | 27. 00 40 to 80 RiveningiStariesese sess sees 22. 00 51.00 REG DOL Domes sees iaeieeite === | .5to 1 60 to 180 | Little Giant ....----.----+-+--+------- | 12 to 40 14 to 80 Morning Star.........--- Bees | 40 to 55 35 to 40 Virginius.-........- He denee sss esancees 25 to 35 8 to 32 IV.—ASSAYS MADE AT CUMMING & FINN’S SMELTER, AUGUST, 1880. Amie (lumps) .-.--..-------.---------- 3.00 | 40. 00 Amie (screenings) None | 100. 00 Hibernia (clayish) None | 33. 00 DOS sean sceseeseaeeee eee se None | 60. 00 Homestake .-...--.-------------- None | 70. 00 BD) 0 Seeatte tet eae elsif sie | 8.00 | 60. 00 | Morning Star (sand) | 55.00 | 38.00 Morning Star (hard) | 40.00 | 32. 00 TOT Geese Boma eaC EOE OO TOI ASR OSS | 40. 00 36. 00 Morning Star (sand) -...-..----------- 47. 00 EURO || segseseasncns LO is panei SSe co seasenosOseao ga 55. 00 BERNE [lh--Seaceascase | | Agassiz.....--.---------- 14. 00 401600 ei -eeeeeee eee 45. 00 141. 00 0.50 23. 50 165. 00 Basco shahas | | 48.70 PAC) etal Boers eeceaee | Carbonate ...------------------------- 27. 00 218. 00 | Ghiettatni-sss-ss==eee nese ene vou 7.00 76.00 . Chrysolite ------.--------------------- 29. 00 97. 50 Colorado Prince. ----- | None 15. 00 Double Decker..-...--.---------------- | None 35. 50 IRB assactmencoescosss CoM Roe ss | 8.00 119. 00 Monsakente-s-24ses22-6 sasaeee coca | 18. 50 62. 00 General Shields (Sawatch Range) --- None | 53. 50 | Gold Cup (Sawatch Range). .--------- None | 110. 00 | Gold Ore (Sawatch Range) -.--------- | None | 6. 70 | Independence (Sawatch Range) ------| None 8. 60 ro mass taet ete ite oie lati 40. 50 79. 00 Long and Derry .....-.--------------- 16.00 | 73. 00 | Mhittle Chiefs senesreanen nese eaten 16.00 | 56.50 Little Pittsburg 36. 40 266. 00 | Morning Star 65. 00 61. 00 Nevad seers cee eee eee ener 23.70 16. 00 | WPinetes-eesse eneeae eee I 31. 00 BPAY Ree bsgecisasc Ready Cash-..-..--.-----..- - 3.70 125. 00 | 9. 20 | Robert E. Lee None 146. 50 | Beare cre Bere | | At the smelters, silica, or rather that mixture of silica and refractory silicates insoluble in acids, and known as gangue, is determined, as well as the per cent. of iron. ee ea Se ae ASSAYS OF LEADVILLE ORES. The following will give an idea of their relative proportions: TaBLE I]—Continued. VI.—ASSAYS MADE AT THE CALIFORNIA SMELTER, JULY, 1880. Name of mine. Lead. Silver to ton. Tron. | Gangue. | | Per cent. Ounces. | Per cent. Per cent. WAU e\aasScapeeee siete owak seen eaaes 5.00 40. 00 | 40.00 20.00 BrlanpBOrUl ses sess aoeh ease eee: 40. 00 40.00 | 6.00 12. 00 Tego hehe eee ee ee eee | 24. 00 30. 00 24. 00 46. 00 Morning Stares------ced-scess--s2<: | 55. 00 40. 00 5. 00 16. 80 | Robert Emmet..-<..<-2-2-0-< a 5 21 25 These rates are subject to constant fluctuation, according to— 1. The price of fiuxes. 2. The amount of fluxes required in smelting. 3. The price of charcoal and coke. 4. The character of the ore: whether large lumps or sand; whether highly sul- phureted or highly silicious; whether rich or poor in lead; whether rich in oxide of iron or without it. The cost of treatment has varied during the year ending June 1, 1880, from $15 to $30 per ton of ore. The price paid for silver and lead in the ore varies naturally with the New York market. During the year ending June 1, 1880, the variation for silver has been from full New York quotations and no discount to a discount of 10 per cent., the average discount having been about 5 per cent. off silver quotations. Lead is bought by the unit, i. e., 1 per cent., or 20 pounds in the ton; and its price has varied from 15 cents to 45 cents per unit during the year 1879~80. The price per unit of lead depends on individual agreement, and also on the contents of the ore in lead. At some smelting works the cost of treatment will be $16 to $25, with a deduction of 5 per cent. off silver, and the price of lead 20 cents to 25 cents per unit when the ore contains above 30 per cent. At others, the cost of treatment will equal $20, the deduction off silver 5 per cent., aud the price for lead 15 cents per unit when the ore contains above 5 per cent. Gold is paid for at the rate of $18 per ounce, but only when its amount exceeds one tenth of an ounce per ton of ore. : Cost of transportation.— When the ore is bought direct from the mine, its trans- portation is paid for by the mine owners, and the cost of handling varies from $1 to $1.85 per ton of ore, according to distance; but when the ore is purchased at the sampling works, the smelters have to pay for its transportation to their bins at the above rates. SAMPLING. : Method.— The general method of sampling carried on in the camp is the follow- ing: In shoveling the ore from the ore-wagon to the ore-bin, every tenth shovelful is thrown aside into a wheelbarrow. Thence the sample thus obtained is wheeled to the sampling floor and passed through the crusher. It is then well mixed with the shovel, SAMPLING AND CRUSHING. 629 laid in a thin layer on the floor, and quartered down very carefully until small enough to be dried easily. The amount of moisture is determined by desiccation of this sample, previously weighed. When dry it is passed through Cornish rolls set to one- eighth of an inch or through small mills. It isonce more well mixed and quartered down until small enough to be ground on the buek-plate or in the mortar, and passed through fine sieves, about 70 meshes to the linear inch. This done, the sample is once more well mixed and divided into three parts, one of which is assayed by the smelter, the other at the mine, and the third by an independent assayer, or more generally kept in reserve for reference in case of dispute. Sometimes the bulk of the sample ob- tained from every tenth shovelful from the wagon is reduced by setting apart every fifth shovelful. This reduced sample is afterwards subjected to the treatment which has just been described in detail. Sampling works.—Hvery smelter in Leadville possesses a sampling floor, with ore-beds, crushers, and ore-bins; but there are besides three large sampling works, which are independent of the smelters and where the buying, assaying, crushing, drying, sampling, and selling of ore only are carried on. These works belong to Messrs. A. R. Meyer & Co., Eddy & James, and Gillespie & Ballou. The sampling works are provided with a large number of bins for the preparation and classification of ores of every grade and from every mine; and, as at the smelters, the machinery, crushers, Cornish rolls, and mills are driven by steam-power. Large open spaces are kept for the accumulation of ore-dumps and the preparation of ore- beds of a given composition. These are made by spreading layer upon layer of ores of known weight and contents in silver and lead. Drying is carried on on a large scale, the driers consisting of large parallelopipedic cuts in the ground, about six feet wide and twenty feet long, provided with a coal fire-place at one end, connected with a sheet-iron stack at the other, and covered over on a level with the ore floor with sheet-iron, upon which the ore to be dried is spread in layers. The advantages offered by these works are twofold. The prospectors and small miners can always dispose of their small lots of ore, and the large ones of those ores which are in any way exceptional or out of the usual run. On the other hand, the smelters can always find their supplies of ores of a given composition ready for the furnace, or special ores to modify or complete the composition of their own ore-beds or mixtures. CRUSHING. Sand ores do not require crushing; in fact, they are already in dust or pieces too smali for the furnace, and require mixing in convenient proportion with crushed ore in order to be fit for use. But hard ore and sand ore in lumps require crushing, as well as the limestone, iron-stone, and old slags which are used as fluxes. This is effected, both at smelters and at sampling works, by means of compact but powerful stonebreakers or crushers, always driven by steam-power. Machines used. —The crushers mostly used in Leadville are Blake crushers manu- factured by the Blake Crusher Company, New Haven, Conn., and by the Farrel Foundry and Machine Company, Ansonia, Conn. At the sampling works one or two Alden crushers manufactured by E. T. Copeland, New York, are also in use. 630 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. The table below gives the principal types used, their numbers, nominal lorse- power required, and capacity. Capacity numbers of | HEiween of Ay-wheel |powerre-| eapacity per, \ : jaws. per minute. | quired. hour. | | | Inches. | Tons. | 10 by 4 300 4 4 10 by 7 | 275 6 64 | 10by 4) 300 4 4 15 by 9 | 275 9 93 10 by 4 | 300 | 4 4 10 by 4 300 4 4 Blake crushers.—The crushers manufactured by the Blake Crusher Company belong to two styles: (1) The older style or eccentric pattern and (2) the Challenge Rock-Breaker, or Sectional Cushioned Crusher. Of the eccentric pattern, a horizontal and vertical section will be found in Plate XLI, Figures 1 and 2; the drawing given isa copy of that furnished by the company for a No. 2. The circle D is a section of the fly-wheel shaft, which should make from 225 to 250 revolutions per minute. The dotted circle H is a section of the eccentric. Fis a pitman or connecting-rod, which connects the eccentric with the toggles G G, whose bearings form an elbow or toggle- joint. #H is the fixed jaw; this rests against the end of the frame A. P P are chilled iron plates, between which the rock is crushed. When worn at the lower end they can be inverted and thus present a new wearing surface. The cheeks I J fit in recesses on each side and hold the chilled plates P P inplace. By changing the posi- tion of the cheeks from right to left when worn, both will have anew surface. J is the movable jaw. It is supported by the round bar of iron A, which passes freely through it and forms the pivot upon which it revolves. JZ is a spring of india-rabber, which is compressed by the forward movement of the jaw and assists its return. Jf I are bolt- holes. Bis the fly-wheel. Cis the driving-pulley. QQ QQ are oiling tubes; Rk Rk KR, steel bearings; O, the toggle-block; N, the wedge; Y, the wedge-nut; S, set-screws ior tightening toggle-block; 7, bush and key. The frame A A and supports Z Z are made of cast iron. This crusher is being gradually superseded by the Challenge Rock- Breaker, manufactured by the same firm, which has many points of superiority over the preceding, and is not quite so delivate in construction or so apt to get out of order. The Challenge or sectional cushioned crusher is represented in perspective and vertical section in Plate XI, Figures 3 and 4, which are copied from the company’s drawing of a No. 5 crusher. Its crushing capacity per hour is 9 tons when the jaws are set 14 inches apart and when its speed is 275 revolutions per minute. Flint, hard ores that break with a snap, dolomite, hematite, and old slags go through the crusher at that rate in the same conditions, but with sand or soft ore the capacity is sensibly diminished. The 9 horse-power indicated as being necessary to drive this crusher is purely nominal, and represents, so to speak, an average; in practice the driving engine should have greater power, in order to overcome irregular or unexpected resistance. The Challenge crusher consists of a three-sided frame-work F’, of cast iron, witha broad flanged base, holding the movable jaw in suspension, which forms the front part of the machine, between the upright convergent jaws of which the stone is crushed. CRUSHING MACHINES. 631 The jaw-shatt A is held in place by wrought-iron or steel clamps C, which serve to take part of the strain due to crushing in the upper part of the jaw space, and also serve as walls thereof. In the lower part of the three-sided frame, or front part of the crusher, and on each side of it are holes in the casting to receive the main tension rods FR, which connect the front and rear part of the machine. The rear part B is called the main toggle block. It is also provided with holes to receive the main ten- sion-rods & R, corresponding to those in the front casting. The tension-rods R R are provided with screw-threads and nuts NV N, by means of which their length, and in consequence the opening between the jaws, are readily adjusted to crush coarse or fine, The front and rear castings are supported on parallel timbers G G, to the under side of which are bolted the boxes carrying the main eccentric shaft, provided with fly- wheels and pulley. These timbers take the transverse strain, which comes upon the pitman connecting the main shaft and the toggle-joint, situated in the rear of the mova- ble jaw, and between it and the main toggle-block. Between the broad flanged bases of the front and rear castings and the timbers on which they rest are placed flat rubber cushions C’ O’, one-fourth to three-eighths of an inch thick. Every revolution of the shaft brings the toggles more nearly into line and throws the movable jaw forward. It is withdrawn by the rod provided with rubber spring Z. In this way a short vibratory movement is communicated to the movable jaw. The pitman Rk’ H is constructed so that it can be lengthened or shortened, and thus change the inclination of the toggles O O, and consequently the length of the movable jaw J. The great advantage: of this machine over the old style is that of possessing elastic parts, rigid enough to allow the performance of the work desired, but giving way under accidental strains, such as the introduction of a steel hammer between the jaws. The frame A is made of timber. The best method of setting up this stone- breaker is to place its frame on four timbers 15 by 15 inches, disposed as is shown at Y X’ and Y. These timbers are pinned or bolted together. The following are the main parts of the machine and the letters used to indicate them in the drawing: A, timber frame. L, rubber spring. B, main toggle-block. L’, spring rods. C’ C’, rubber cushions. M, pitman-rod nuts. D, fly-wheel. N N’, main tension-rod nuts. E, main pulley. O, toggles. F, main cast-iron frame. P, jaw (chilled plates). G, timber supports. R, main tension rods. H, pitman half-box. R’ H, pitman. I, cheeks. R’, pitman-rods. J, movable jaw. S, main eccentric shaft. K, jaw shaft. T, toggle bearings. The Farrel Foundry and Machine Company’s Blake crusher is used a good deal in Leadville. It is constructed on very nearly the same principles as the Blake Crusher Company’s eccentric pattern. It presents the same appearance, it requires the same amount of power to produce the same quantity of work in the same time, and a complete description of 1t would be superfluous, since it answers exactly to the description of the eccentric pattern. It differs from it, however, in one respect, namely the substitution of a crank shaft for the eccentric shaft. 632 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Alden crusher.—The Alden crusher and pulverizer, is not in use at smelters, which, when they have any pulverizing to do, use Cornish rolls; but it is used at the samp- ling works, where a considerable amount of pulverizing is done. The jaws of this crusher differ essentially from those of the others in this respect —that their grooves are perpendicular to the length.of the jaws, while in the others these grooves are par- allel to the length. Fig. 1, Plate XLV, gives a perspective view of the Alden crusher, in which portions of the jaws and jaw-faces are shown in section. The jaws are hung upon wrought-iron trunnions, the ends of which project through and are supported by the sides of the frame. Motion is imparted by links connected with the trunnion ends, and driven by studs prejecting from a sliding yoke beneath. This yoke is connected with a crank-shaft by a pitman. The rotation of the crank moves the yoke to and fro on a nearly horizontal plane, alternately moving and pushing the movable ends of the two jaws, and imparting a rubbing motion, which is the main feature of the machine. The jaws may be adjusted at varying distances, so as to obtain a product of varying degrees of fineness. The Cornish rolls, used by both the smelters and samplers for grinding their samples, consist of two steel cylinders, 12 inches long and 6 inches in diameter, con- nected by cog-wheels, driven by pulley and transmission belt, and fed by means of a thin sheet-iron funnel, having the shape of an inverted truncated pyramid. These rolls are usually set one-eighth of an inch apart. ASSAYING. In Leadville assaying is quite an important branch of the mining and smelting industries. In addition to the assayers attached to all the smelting and sampling works and to the principal mines, there are no less than twenty independent assayers residing in the city and having their own assay offices. Besides being employed as referees and experts in cases of dispute between mines and smelting works, the latter are patronized by the prospectors and small miners. The chief assays made in the camp are silver, gold, lead, iron, and gangue assays, and at some smelters specific-gravity determinations of slags. Furnaces.— The laboratories are generally provided with permanent crucible and muffle furnaces, made of common brick, lined with fire brick, and placed side by side, as is shown in Plate XX XIX; but very often the two furnaces are separate. By means of the dampers D/ and D/ in the chimney, the assayer can regulate the draft and the intensity of heat in the furnaces. The apertures A B C D are closed by means of sheet-iron plates, easily removed by tongs. Occasionally, portable clay furnaces, of American and English manufacture, are used for cupellation. Pulverization.— The ores and slags are, first of all, coarsely pounded in a cast-iron mortar (Fig. 12, Plate XLIII), a form of mortar that is not well adapted for this use, since it is too thin and very often breaks before the stone does. The coarsely pounded material is then ground on the buck-plate. This consists of a cast-iron plate (Figs. 9 and 10, Plate XLIII), about an inch thick, faced cn one side, and provided or not with flanges on each side. It rests on a firm table or timber support. The ore is laid on the plate and ground with the bucker. The bucker (Fig. 11, Plate XLIII) is a mass of cast iron, with a cylindrical lower surface, faced on the plate side, and fixed to a ph Sion eens ee ASSAYING. 633 wooden handle. Grinding is performed by placing the left hand on the bucker, hold- ing the handle in the right band, and moving the bucker forwards and backwards, at the same time lifting and lowering the handle, and exerting a slight pressure with the left hand. While all this is going on the bucker is also moved from the left to the right side, and inversely, so as to increese the grinding surface. All this is much more easily performed than described. The pulverized ore is then passed through sieves of 70 tc 80 meshes to the linear inch, represented in Fig. 8, Plate XLIII, in elevation. The metallic cloth of the sieve is made of brass. It is adjusted to a tinned-iron cireular frame, b, fitting in a cireular tinned-iron box, or dust-receiver, @. This is a very convenient arrangement, the loss in dust is very small, and the mixing of the dust takes place at the same time as the sifting. Crucibles and scorifiers.— Figs, 3, 4, and 5, Plate XLIII, represent the crucibles, scorifiers, and gold-annealing cups, which are manufactured by the Denver Fire Clay Company. The gold-annealing cups and scorifiers are similar to the European ones in appearance, but greatly inferior to them in quality. The assay crucibles, three-six- teenths of an inch thick, are probably the thinnest clay pots used in assaying in any country. They are very convenient for the reason that, with a low temperature in the furnace, the assay fluxes become easily fluid, but they never stand more than two runs in the erucible furnace. Cupels.— Cupels are always made in the assay laboratories in brass molds, the process being too well known to demand description. Their form and size are shown in Fig. 6, Plate XLIII. Muffies.— The mufiles made by the Denver Fire Clay Company are good. They are generally large enough to hold from 12 to 16 scorifiers, enabling the assayer to assay three or four samples of ore at the same time. Tools.— The scorifier tongs, cupel tongs, crucible tongs, raking rods, anvils, ham- mers, chisels, ete., are similar in every respect to those universally used in assaying. Slag molds.—The molds into which are poured the crucible and scorifier slags are peculiar, and are represented in Figs. 1 and 2, Plate XLII. They consist of a sheet of cast iron, divided into 12 conical molds. They are very convenient, the lead buttons and slags cooling rapidly on account of the thinness and large surface of the mold. Fuel.— Coke is used in the erncible furnaces and charcoal in the muffle furnaces, but sometimes coke and charcoal are mixed in the muffle furnaces. Balances.— Balances capable of weighing from four pounds to one-sixteenth of an ounce are used for the estimation of moisture in the ore; balances weighing from 100 grams to 1 milligram, for the weighing of scorifying and crucible assays; and those sensitive to the tenth of a milligram, for the weighing of silver prills and gold part- ings. These balances are generally manufactured by Becker & Sons, of New York. They offer no peculiarity in construction. The weights used in assaying are gramme weights for lead, iron, and gangue assays, and silver prills, or gold partings; but the ore, slags, and bullion are weighed in assay tons, whose symbol is A. T., or its subdivisions. The weight boxes contain one-tenth of an assay ton, or +5 A. T., 73; A. T., 3 A.T.,1 A.T., 2 A.T. Some boxes contain besides .j; A. T. and 5 A. T. The system of assay-ton weights introduced by Prof. C. F. Chandler, of the School of Mines, Columbia College, New York, is as simple as it is ingenious. The ton of 2,000 pounds avoirdnpois is equal to 32,008 ounces 634 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. avoirdupois, or to 29,166 ounces troy, or to 907,180,000 milligrams. The weight of the assay ton is 29,166 milligrams, consequently each milligram represents one ounce troy, and 29,166 milligrams represent one ton. When the material to be assayed for precious metals is weighed by the assay ton or its multiples, the weight of the precious metals in milligrams, or multiples of the milligram, corresponding to those of the assay ton, expresses in troy ounces the weight of gold or silver contained in one ton of ore or bullion. A few examples will illustrate this: 1. Twenty-nine thousand one hundred and sixty-six milligrams of bullion, or one assay ton, give after cupellation a button of silver weighing 205.5 milligrams. This shows that one ton of this bullion contains 205.5 ounces troy of silver. 2. One-half an assay ton of slags gives, after assaying, a button weighing 13 willigrams; this shows that one ton of slag contains 3 ounces troy of silver. 3. One-tenth of an assay ton of ore contaius 3 milligrams of silver; this shows that one ton of ore assays 30 ounces troy of silver. The laboratories are provided also with sand-baths, flasks, beakers, dishes, bu- rettes, and a few of the principal reagents used in assaying by the wet way. Tron and gangue assays are regularly made in the wet way, and occasionally the ore is assayed for sulphur and arsenic, the slags for lead, the ores and fluxes for lime and magnesia. Silver assays.— The general process used by common consent in Leadville for ore assays is the scorification process, arapid and accurate method. Some mines, however, require crucible assays. The scorification process is so well known and so fully de- seribed in text-books that it will not be insisted upon. The assays of each sample are made in three or four scorifiers. One-teuth of an assay ton is weighed for each scorifier, and then mixed with ten timesits weight, or one assay ton, of pure granulated lead, or rather with a granulated lead whose contents in silver are known and subsequently subtracted from the silver buttons obtained. The silver-prills are weighed to the tenth of a milligram, and each of these divisions corresponds to au ounce to the ton. A little borax is always used to scorify the oxide of iron and other bases. Slag, like ores, is assayed by scorification; but this process ought to be abandoned and the crucible process substituted for it, chiefly for the reason that in the crucible the assay may be made with one assay tonif necessary, this quantity not being excessive for the estimation of 1 or 14 ounces of silver to the ton. The crucibles used in crucible assays are those drawn to scale in Figs. 3 and 5, Plate XLII. A mixture of Pon gitresel OS) soso oackss mse seatencgeses seges sore ssoduEedtesdcosses Er GSSHAY TID. Tnitharge .- 2-2-2 22 22 ee ne ne cen enn nn ne nl 1 assay ton. Bicarbonate Ol S00 ogee eee sar sera eee ere elmer enn Mein 4 assay ton, lyon b< qempris Sosa cee acmconbtoo wobbomeueboU Aer eeplonoserSuyes> Hasso ¢ assay ton. INPRO poacodbaopnedas baoa Soaqso Bescleson sus coker gescmeobepasss saeco sng GEE UON, or some similar mixture, for each assayer has his favorite flux, is fused in them, in the presence of an iron nail or rod, which, however, some assayers dispense with altogether. The mixture is generally covered with a layer of borax or common salt. Bullion assays.—The assays are generally made on a car-load sample, representing 10 tons. Two pieces of lead are detached from the top and bottom part of each bar of bullion forming the car-load (in general 400 bars); all these are melted together in a plumbago crucible, under a cover of live charcoal; the charcoal and scum are then removed; the sample, well mixed by stirring, is poured into an ingot mold (a bullion ee ASSAYING. 635 one); the bar obtained is about one inch thick (Fig. 7, Plate XLV). Four pieces are detached from it with chisel and hammer, as shown in a, Fig. 7. One-half an assay ton is weighed from each piece, and cupelled, and the assay carried on as usual. Gold assays.— Gold assays are made by dissolving the silver buttons in weak nitrie acid, as usual. Lead assays. — Ores and slags are assayed for lead in the crucible. Five grams of the pulverized ore or slag are mixed with 15 grams of a flux composed of INOTTRR con dices SonCEbOTogSs SescbsS0o0e JES ASS ose. casc espa asso sddessss 1 part. Bi OOAID OH OCS) oo Sone sas osoceser ey cabo pens odes osSene Sees eSSecesens 4 parts. JANSON soscos es0cnn chocsn esos gesSo0 Gone chad ceoo ee sceece Sonos eecesorcod 1 part IM Re soto cecobe compad snepaco.cebenc ache ode cone ceoUeecOR dats ECE SscaSe + part or some analogous flux. The mixture is fused, with or without the addition of an iron nail or rod, either in the crucible or the muffle-furnace. When the muffle is used, the crucibles, represented in Fig. 5, Plate XLII, are placed in it, toeether with large pieces of charcoal, to produce a reducing atmosphere, and the front of the muffle is kept closed. In both crucible and scorification assays the lead buttons and slags, when taken out of the furnace, are rapidly poured into the molds, shown in Figs. 1 and 2, Plate XLII. In lead assaying the button of lead, detached from the slag after cooling, is weighed in grams and its fractions, and the result, multiplied by 20, gives the percentage. Iron assays.—The ores are assayed for iron by Marguerite’s well-known burette process, with a standard solution of permanganate of potash. Estimation of gangue.— Gangue is determined by dissolving the ore in strong hydro- chlorie acid, or aqua-regia, collecting the insoluble residue on a filter, washing well, calcining, and weighing. Some assayers evaporate the solution to dryness at 100° C. before filtering, in order to estimate both gangue and soluble silica. Estimation of moisture.— Moisture is determined in the ores by desiccation of one pound of ore placed in a copper pan over the muffle-furnace, or over a sand-bath heated by a kerosene lamp. Specific gravity determinations. —This operation is performed every day at a few smelters on the slags of each furnace. It seems an unnecessary operation, first, because superintendents ought to rely solely upon careful assays for Jead and silver; second, because, with a little practical experience, the mere appearance of the slag is more reliable than its specific gravity ; third, because those who determine daily the specific gravity of slags and their contents in lead and silver have never been able to find a relation between the three data. In the analytical study on the slags made specially for this report it will be seen that there is no relation whatever between the contents of lead and silver; and at the smelters it is admitted that the specific gravity of slag may be raised by other substances than lead—by iron, for instance. The specific gravity determinations are carefully made by means of the Jolly specific gravity spring-balance, represented in Fig. 2, Plate XX XVIII. This instru- ment consists of a wooden gallows-frame, at the end of whose horizontal beam is sus- pended a delicate wire spring, provided with a small ivory index, J, and a small brass pan, P, suspended from the spring by three wires. On the face of the vertical beam, looking towards the spring, is a mirror, carefully graduated in millimeters. A beaker, three-fourths filled with distilled water, is placed ona stand, 8, which is provided with a set-screw, and moves up and down the vertical bean. 636 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. To make a specific gravity determination the eye is placed in front of the mirror in such a position that the pupil of the eye, the upper part of the ivory index, the graduation on the mirror, and the image of the pupil in the mirror are brought into line. The number of divisions at this point is 2. A small piece of slag is then placed in the pan P; the division to which the ivory index is lowered is then carefully noted; let this be called 2; then a/—a# represents the weight of the slag in the air, expressed in divisions. The stand S is then raised until the slag dips into the water and the index rises. ‘The number of divisions is once more carefully noted ; let it be expressed by w’/; a/—x"’ represents the weight of the volume of the water displaced by the slag, consequently the specific gravity will be given by the formula a'—x —F xv!" +a; # being the number of divisions lost by the pan when immersed in water. The writer has devised a little instrument, easy to carry, easy to construct, and self-correcting, for the determination of specific gravity. It consists of a test-tube ballasted with distilled water and floating in a proof-glass filled with distilled water (see Fig.7, Plate XLII). The test-tube is carefully graduated; the level of the water a, outside of the tube, is noted, as well as the level of the water y, inside of the tube. A small piece of slag or mineral is introduced into the tube, which sinks a certain number of divisions 2; «! represents its weight. The water is raised inside of A little correction is necessary with this instrument; a” should in reality be vie vf the tube a certain number of divisions y/; y/ represents its volume ; “ gives its spe- y cific gravity corrected for temperature. One of the great advantages of this instru- ment is that specific gravity determinations can be made with almost as much accu- racy with common water as with distilled, the weight and volume of water being self- correcting. SECTION II. MATERIALS USED IN SMELTING, GENERAL CONSIDERATIONS. Smelting is conducted on exactly the same principle by all the smelters through- out the camp. Ab uno disce omnes. The ore is invariably smelted in blast furnaces lined with fire-brick, and provided with water jackets at the zones of agglomeration “and fusion; dolomite, hematite, and old slag being used as fluxes, and a mixture of chareoal and coke as fuel. Im one sinelter only a little metallic iron (old horse- shoes) is used for the reduction of galena when present in certain proportions in the ore, but even at this smelter it is an accidental rather than a nermal operation. The facilities afforded to the smelters by nature in the Leadville region are really very great; there smelting is practically reduced to its elementary principles. The ore is, so to speak, “roasted by nature,” since cerussite is evidently in all cases the result of the oxidation of galena; it requires no preliminary preparation save crush- ing, and for about one-fifth of the ore, which comes out of the mine in the state of sand, this is, of course, dispensed with; the quantity of matte and speiss formed is small; a good quality of hematite is found on Breece Hill, though it is used but in MATERIALS USED IN SMELTING. 637 small quantity, owing to the fact that the ores themselves often contain the requisite quantity of iron to form slag, and to reduce arsenical, antimonial, and sulphuret com- pounds of lead. Dolomite, as will be seen later, forms as good a flux as carbonate of lime; its chief defect is that the slag formed is less fusible than pure lime-and-iron slag. Before the railroads reached Leadville the smelters were compelled to use dolomite. Since that time it is said that a smelting firm has adopted the use of limestone with good results and that its use is likely to become general in the camp. Smelting in Leadville at the present day is never badly performed, chiefly for the reason that all the furnaces are constructed on the same principles and are pro- vided with the latest improvements. The imperfections in smelting are generally intentional, and are based on economical grounds which are in themselves unattack- able and render criticism useless. Still, if must be stated that a few smelting firms have brought smelting in Leadville to actual practical perfection, and in their economic results these are the most successful. STATISTICS OF LEADVILLE SMELTERS. In Table LV will be found the following information, compiled from data gathered by special experts for Mining Statisties of the Tenth Census and by the writer, for the year ending June 1, 1880, each smelter being designated by a letter: I. Annual consumption of ore. Il. Annual consumption of fluxes; their nature and cost. Iil. Annual consumption of fuels; their nature and cost. IV. Annual production of bullion; its contents, and cost of transportation. V. Relations between ore, fuel, fluxes, bullion, and silver. VI. Plant of each smelter. VIL. Labor; amount, time employed, and cost. TABLE IV. I. ORE. | | De pe TN oe 1S Spe a as a a | ed ae cea | Bees) | eee eee ed | | | | | Tons... 10, 236 38,000 | 18, 590 | 4, 200 | 8, 411 | 5, 793 25, 464 | 12, 000 | (a) | | | | a No data. Il. FLUXES. 1. Dolomite. 2. Hematite. 3. Average price of dolomite per ton. 4. Average price of hematite per ton. ed eel = a ies | aes B c Dz Be ih ur Gib dhe teers we | (3 | | | » (cee eaTy | l= | | | | 1. | Tons ..| 232 5, 312 4,170 | 250 440 | 964 | 2,467| (a) (a) | | PB || Gli ceeel 280 143 | 1,774 | 292 587 1, 162 | 2, 968 | (a) (a) | | 3 Dollars | 2.80 4.00 | 3.50 4.00 | 3.50 3.50 b1.25 | 3.50) (a) | | 4 fede 8.00 | 10. 00 | 9.50 11.50 | 6to7 | 9. 00 8.50 | 10.00, (a) | a No data. : b Cost of hauling. 638 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Charcoal, in bushels. Charcoal, in tons. Coke, in tons. Proportion of charcoal to coke at each smelter. Il. FUELS. Average weight of cord of pine wood used. Cost of charcoal per bushel. Average price of charcoal per ton. Cost of coke per ton. 1. Z 3. 4, 5. Pine wood, for boilers, in cords. 6. 7. 8. 95 10. Cost of pine wood per cord. Nene dally atk (i, D. E. F. a. H. I. | Average a) ao 1. Bushels | 188, 760 iI, 094,870 | 506,558 | 76, 791 200, 000 279, 498 563, 087 (a) (2) eee 2.| Tons...} 1, 3424 7, 664 3, 546 5374 1, 400 1, 9564 3, 9414 (a) (OO) oescsocese by ee (ee 3, 309 4, 890 2, 810 263 700 810 2, 550 (a) (2) eee Ae 2d Ones C.4:1 reuyen IEP AG ay 2:1 2:1 2.4:1 TBE (a) (a) 1.33 :1b 5.) Cords - 1, 040 3, 600 1, 200 400 760 750 (c) 1, 200 S00 Ue seemetaes 6.| Poruds.| 3, 000 2, 800 3,000 | 3,000 | 3,000 to 3,500; 2,000 to 3,200) 2,000 to 2,800 2,000 to 2, 800) (a) |.......... 7.| Cents ..| 10 to 15 10 to17 | 10 to 15 /12 to18 10 to 18 10 to 18 13 10 to 12 | (2) | eee 8.| Dollars.| 18.57 18. 57 18.57 | 18.57 18. 57 18. 57 18. 57 EAST) iG) ll eetnee ees 9.|.--do....; 28.60 25. 58 30.45 | 30.56 | 28. 60 25. 60 25. 56 | PHBE ((.))) Vesossances- On| eae One 4.50 4.75 5.00 4.75 | 4.50 4. 00 4.50 | 45°50)! 1(@) | eewete mee aNo data. b Proportion for whole camp obtained from 2 and 3. ec Charcoal screenings, but little wood. IV. BULLION. 1. Tons of builion produced. 2. Average tenor of bullion in silver (ounces per ton). 3. Average tenor of bullion in gold (ounces per ton). 4. Total amount of silver in ounces. 5. Freight to the East per ton of bullion. j 7 | | A. | B | C. D. E. BF. G. H. ir | | = | S| @ons .-. i 1, 752 | 6, 200 4, 436 503 1, 240 1, 321 4,012 5, 000 (a) 2. | Ounces. | 404.5 328. 53 | 250 250 300 300 450 300 (a) FH ant ca | 2.08 None | None None 15 None | None «16 (a) 4. |-- Ados-ee. 708, 684 | 2,036, 886 | 1, 109, 000 125, 750 | 372, 000 396,300 } 1, 805,400 | 1,500, 000 (a) 5. | Dollars - 40 to 45 | (b) (b) (b) 27 to 35 35. 00 35. 50 (b) | I I | i aNo data. b Paid by refiner. ee ee ee ee MATERIALS USED IN SMELTING. 639 N V. PROPORTIONAL RELATIONS. Parts of dolomite to 100 parts of ore. Parts of hematite to 100 parts of ore. Parts of fuel to 100 parts of ore. Parts of fuel to 100 parts of smelting charges. Bullion extracted to 100 parts of ore. Percentage of lead extracted in smelting. Percentage of silver extracted in smelting. Charges for smelting per ton of ore, in dollars. Cost of smelting per ton of ore, in dollars. : Average assay of slag, in ounces of silver per ton. Average assay of flue-dust, in ounces of silver per ton. SNNANE Hw ne SS A. B. C. D. E. F, G. H. iG Average. 2. 27 13. 98 22. 43 5. 95 5. 23 16. 64 9.69 | No data | No data a0. 88 2.73 37. 9. 54 6.95 6. 98 20. 06 11.65 | No data | No data as. 3 45.35 33. 04 34.19 19. 06 24.96 47. 76 25.49 | No data | No data a32. 83 36. 25 23. 33 22. 60 15. 33 19. 33 32. 50 19.00 | No data | No data a24. 03 5 17.11 16. 31 23. 86 11. 98 14.74 | 23.8 15. 75 41.66 | No data a20. 53 Uyt-SeS5cssase oss 85 to 88 | 86 to 91 88 85 to 95 | 85 to 90 | 90 to 93 87 90 85 to 90 88 100 95 to 97 97 88 to 95 | 95 97 98.5 97.5 96 96. 5 15 to 30 | 15to30 | 15to30 | 12to25| 16to30) 15 to30| 15to30| 15 to 30! 15 to 30 22. 00 12to18 | 18to23 10to15| 13to16/ 15to18 13. 00 13. 68 15. 00 16 to 18 15. 25 2 4 | 0.5 1.5 a5 1.5 1.5 4 | 1.5 | 2 36 Eile ||| PERM RSS ieee aan | ce 36 a These five averages were obtained by dividing by seven the sum of the respective proportions given for each snielter from which data were obtained. This gives a true average of the proportions for each smelter, but it might be considered that a truer average for the camp would be obtained directly from the totals of ore, fluxes, and fuel consumed during the year by these seven smelters. Calculated in this way, the average proportions are, respectively, dolomite to ore, 12.50; hematite to ore, 6.51; fuel to ore, 31.99; fuel to charge, 23.31 ; bullion to ore, 19.94. VI. PLANT OF SMELTERS. ‘ | } | | Smelter. ZG Pay ae C. DG alee ce |e aes aly Gans |b Ee Th | | E } B 1. Furnaces: | | { | (a) Number in use -.... | 2 | 68 2 2 2eodlewet ne We ete il eiaat: ely 2 (Gy Shapey-oe-2--e see Round. | Round- | Square Square. Round. | Square. | Square. | Round- | Round. | square. | y square. | | (c) Working capacity: | 35to40| 180 | 70 40 50 | 60 | 120° | 100 | 50 tons per 24 hours. | | ?. Steam-engines: | | | j (a) Number in use ...-- 1 | seat 1 1 t 1 | 1 2 1 | 1 | (b) Horse power .-.... | 40. | 160 ! 50 40 5 40 | 50 70 and 50 100 60 (c) Average steam 60 70 60 65 | 70 | 65 60 80 70 pressure, pounds. | | 1 3. Stone-breakers : | | \ (a) Number in use ...-. | 2 3 3 1 2 | 2 2 1 | 1 (b) Capacity numbers A No.5. | Nos.A,2,|Nos.A,2,! No. A. |Nos.land; Nos.0 Nos.2and| No.5. No. A. PaGormusheolle: | and5. | and 5. | 5. and 4. 5. Number in use None. | 3 | 3 i il | 1 | None. 2 1 None. 5. Other ernshers ..-..-. sees) 3stamp- Pulver- | None. | None. | None. | Small None. None. None. battery. | izer. | | | mill. 6. Blowers: | | | | (a) Number in use .. | 2 | 9 | 2 | 2 | 2 2 | 4 | 4 | 2 (b) Capacity numbers...) No.5. | Nos. 4,44,| No. 5%. | No.5. | Nos. 44 No.5. | Nos. 4, 5, |Nos.5and| No. 5h. 7. Dust chambers: and 5. | | and 54. | 54, and 6. | 53. (a) Number in use ..... at SYN I tea | gs Te | Te a 1 2 (b) Construction mate- | Bricks. | Sheet- | Lime- | Sheet- | Bricks. | Sheet- | Bricks. Sheet- Sheet- rial. | iron. stone. | iron. | ) iron. | | iron. | iron. | | | | | ' i 640 VII. LABOR. GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 1. Number of each class of employees per 24 howrs, when works are in full blast. A. B Cc. D eee: Re) i eGo H. 16 Diaih peseceeees === aaeine soem General foremen | Foremen ----- Head smelters | Slag wheelers Reeders ee =n een Hel persyes= see ee nea Engineers .-.-------------- MU Ger, Sepesacnadeo se soa pSososacer| laneeeesee lencssascah|ibessseeees|je" edn leSsosenoden ensprnccod| rest eees||secctetces Day laborers ..-.-..--.------ pceaneecss 81 60 to 70 ; 10 to15 12 20 20 to 25 10 20 | 2. Length of shift for employees (in hours). 2 General foreman ....--.----- Reeeeeecce | ease emer lhtectcsuel Be semeseee ee Sheu beeeeececs 13) ieweoteas Su/ Pees oremant=ssiee.e-ceee ee 12 8 12 | 12 12 8 12 12 Head smelter -...-.-.-.-.-:- 12 8 12 12 12 ie} 8 12 12 Slag wheeler | 12 12 | 12 125) 12 | 12 8 12 a2 Reeders: 22<.s2teesseose~ceeet 12, | Gh ie he The || SB = 8 12 12 Helpers) paeese re ee eaen eae apy || see | 8 ike ee Jf RES a ae wy | 3B} 12 Day laborers ......---------- 12 el 10 TOW |e 10 items 0 TOME FERTO 10 Engineers 12 alk eae) 12 1D ee 12 12 | Fuel men .- 12 8 | 12 12 12 12 | 8 12 12 3. Wages per shift of employees. i | = | | | = | General’ foremaniose encase emi iacicties 50, 03 (CER OME Or TGS CO sens Socqacsnos hand Be sSdee ae Cou POCOpUSCSb SEO ocre 35. 16 Sate ee eee on area ncahnin niaisi am tainisiny satin Greia wiclel swsicinise vets atanete 1,14 ProLoslo oom nOnmessere eee reise, salece a. selleaccicie aye (stasis oki sin ee ini isieiclo Se 0,41 JAI cosabe Gost poe Bec dooO Sc SEN e DOO DIODE ASCE Seer Be SDS bT Heads SESE neoG 2. 62 MOINGUNR eee e re eee sence criss cecsserics) ercccsc es co- cen tceccens veo ccen LONGE 100. CO 646 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. Analyses of dolomites made in the Grant Smelting Works by Dr. M. W. Iles. XIV. | XV. XVL XVII. | XVUOL xIx. | | | | | | Carbonate of lime .--.--------- 66. 50 | 54. 94 49. 57 57. 95 51. 60 | 55.35 | Carbonate of magnesia-..-.--.-..-- 25.10 | 41.95 | 37. 08 39. 65 39.77 39. 35 | Carbonate of iron..--...------- None | None | 6.23| None None | None | Sil Cases sealant tes 2.70 | 0. 93 4.22 0. 76 2.50 | 2. 80 | Alumina and peroxide of iron... 6.40 | 1.31 | 3. 53 1.65 6.13 | 2.50 Oreanicumattenr- pense ae None | 0. 21 None None None None | | | ae | ene —- otal Gesseeee eerste 100.7 | 99.32 | 100. 63 100. 01 100. 00 100. 00 | i | Norr.—Analyses XIV and XV, locality not given; XVI, Glass mine dolomite ; XVII, Carbonate mine dolomite, said to contain from two to six ounces of silver to the ton; XVIII and XIX, Glass-Pendery dolomite, said to contain from one to two ounces of silver to the ton. The superintendents in Leadville do not like dolomite as a flux. It is probable that before long limestone will be substituted for it. Already Messrs. Billing & Hilers have experimented at their smelter with perfectly pure arragonite from the Duncan quarry, Arkansas Valley, close to Leadville, and the results have been most satisfactory. Limestone.— Should limestone be used instead of dolomite, it might be brought from Robinson, in the Ten-Mile District, 16 miles distant, or from Canon City, about one hundred and thirty miles south of Leadville, on the Rio Grande Railroad. These lime- stones are similar in appearance to lithographic limestone. That from Robinson (Upper Carboniferous) contains 97.11 per cent. of carbonate of lime, as determined by Dr. W. I. Hillebrand. The following analysis of the Canon City limestone (Cretaceous) was made by Dr. M. W. Iles. ANALYSIS XX. CANON CITY LIMESTONE. Garhbonate OfMime tence no= ken Se csses Ae ache e bs Sos ceases as aajae eet 88. 90 (CRIA NMI Ole MIEKA AY SO be coea colts Sapees Gee ey De Soe Saeaec rageebeccencenc 6. 30 Silica 3.10 PMiibravayy oH Morals) Olt INGE mecinee nea de dara Tce ccecdcncnanccrcereacae.cdeeace 1.50 99. 80 Hematite._The hematite used as a flux at the smelters is chiefly extracted from the Breece Iron mine, on Breece Hill, but at cne smelter some Silver Wave mine iron ore is also much used asa flux. This ore was not, however, examined. The sample of Breece Hill hematite, which was examined in the laboratory of the Survey, was made from specimens collected on the hematite heaps of the following smelters: American, California, Elgin, Harrison, and Billing & Eilers. The following is the description of the specimens and the color of their streaks: 1. Black, submetallic luster; red spots; reddish violet streak. Red and yellow; silicious appearance; deep brick-colored streak. . Very compact ; submetallic luster; magnetic; black streak. . Compact; dull luster; light brick-colored streak. . Black; submetallic luster; brownish streak. 22 of In Analysis XXI the decimals are carried to six fgures, in order to introduce both gold and silver, HEMATITES USED AS FLUXES. 647 ANALYSIS XXI. BREECE IRON ORE. Elementary analysis. MWR 5 GSka sep ce ROAD E EDO SES ROU D EOE: SS RSet eS OOs Sect eee ee mee 66. 443392 MERGE NNO oc aceo sapeemenoeds ee cesaossSSo nesens conesonscene been eSSose 0. 007280 Nickelvandeobalte.< oc neces assoc. cee eee: sciscc Sea cencaecectnccre Trace EAT Ogee enh oe tre mie te etsrais (a ae cei issn iieiaieiaie'e chee Mee ee oe eee cet ae eatinnes oe 0, 025201 (CO PGwa seca nScs seoenseneb en swede oo euee mea csocee eoaene eases Eaee eee 0, 022597 Golde eee saeco = tare asia sh ee mieicete sees wae Goebanicw sesie eee mea oeteds 0. 000102 By Clemente aa eth atis cite epee aaimeoe Seles ee eee oe Nees 0. CO0404 AV SQDNLG tremecrscee oem latee ie Oem ien Sepsis byte ce cise wee Cie stalclcis once cislea seve 0. 007174 JNDUTMODMY 355525 s6a098 Seoecd nodal edee sen ae eo case eere sce sou Soso= Trace ORGY ccs Zoodeto sont Sea0ca0 SSabeuSne ssbaSs -Seqgce seaebe addacsss 27. 430173 Chigrme; (traces:calonlated) sis cec sme ceeetune eine lecieceaiece niece 0. 000132 WWI OT Rance eee merte mci: Aaa oo baee cies Scenes be cw cece cee cowie tes 0, 290000 Carhorni Cla Cidierey asics aie see ale sfapsl tenes ade Saco seiseas Sa aten owe 2. 444655 HOS PNOLICIOC] Open etemrenio eect ae eee dee ol eee e Sao oes eases 0. 100740 BP UGANIC: UCL eee eeictee wel set aia a cso aye esis cintae sae ceca sceeccedoccel: 0. 052250 2. 388500 0. 121800 LET GR Eh Socee io aae em ab MeeSon Sacbus Soy esa DnoEobes SeecieS Sc eDaaBo Ecos 0. 619900 AU MIN Bese anyecctstias Sue oer seins Sosa eelonic seen neces miseees she Leese 0. 045000 NOSE ein a Sen eneedeactde Sen Gan es CeSOcS OSONE ESO men oon DES eMesae Ede cose 0, 000700 100. 000000 Silver, 0.13 ounce to the ton. Gold, 0.06 ounce to the ton. Rational analysis. IPETOXICeS OM INON ee oe clei seis = = eee se@ledan ate: ccerea sete ye ase ets 71. 843540 Marnenctoxide Onuron(WMesO4). ms ceric cmasioanalaeise Seis sjs0 oe nie eee 18. 009740 Chr onaverOtir Olimewer = sere asa es Sn Saalalac Gas. cuee Wace seme e 6. 445000 OiOnid Gio fasts ores rae aces ee eae roe eA cine cine ee nie Rissiemsieineis Sse ees 0. 000536 (NG! 6455, GeeeEn HBOS SR FACS eee Ene are GnSHOeS OnE SESE eAac Bapaoec eens 0. 000102 Arsenic acid (combined withwkesOs)n-ce saee- see 225 sme cae seeew eben oe 0. OL1C00 (OMSVG Cli GON hs, Scenes cosasoee Bee] ee ao bec Uerce EMSS BS SaSErePessenne 0. 028300 Oxi lOmin Ce ees See amine a Sem as cya oe min) oe sie ieee leeiceelo a ciciseae 0, 031400 JP eep aks) Ot GAN ER TGR) Sore Sosa ea seae secu SeuSou Uoeeon SHES oscasoorssco 0. 011500 Osidesiof-covalt, nickel and antimony, .-2==---25-- -sces= cee meee -- Trace Phosphate of lime ...-...-.--- Soros zenbaseesesheeas cand ese de Gonos = EMIRIAD Titanic acid (in thle state of titanate of iron)-.-. ..2--- 2 ..--.----..-. e 225 RSTO eee tots oe oe a eset eta ae SOc Rise A cece adniee ao teenidee ILA - 3 Se caches cece dindcoto succob ens) CHOU CCCOA DIDS Sp peOsOEee pEb BeaoED 0. 004400 IY ROT VES eRenine GaSecaee see SSe ES Sh SEES, SB OBOOSOL ISS RAC EAS eEceer cree 0, 619900 IMIG TONY, - So saS ROR SSSaeGA care SUOs BESS SB EDC ooeIEsoned apa eee ee avaee sss 0. 045000 Water =25..-7.--. s2oé weed HES oe BS bas Shs S55 Seg bes54 Sbacodsoesse 0. 290000 MUSES 5 = pets agian Seis eg CA Ea os 6 Mee eri Se a ai Se 0. 000692 100. 000000 Discussion. —The hematite was not examined either for bromine or iodine, with which silver is generally combined in Leadville. Chromium, tungsten, molybdenum, and vanadium were carefully sought for, but no traces of these metals could be detected. Titanium could only be found by a method which was specially devised for its detection, and which is the following: The hydrochloric solution of hematite is reduced to the minimum of oxidation by sulphureted hydrogen and then boiled to expel the excess of this gas. The solution is then as nearly as possible neutralized with an 648 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. alkali and boiled with an excess of hyposulphite of soda, which precipitates titanic acid, alumina, and a little soluble silica. The precipitate collected on a filter, washed thoroughly and calcined, is treated in a platinum vessel with a mixture of sulphuric, hydrochloric, and hydrofluoric acids, and the whole is evaporated to dryness. The res- idueis fused with bisulphate of potash, and titanic acid is extracted, as usual, by boil- ing the dilute solution. Although magnetic oxide of iron is reported in the analysis with the formula Fe,0,, this is not exact. The writer succeeded in isolating this oxide in a state of great purity by alternately extracting it with the magnet and rubbing it with the finger on fil- ter paper until it no longer soiled the paper, to which the non-magnetic oxides remained attached. It was then analyzed, and its composition is represented by the formula Fe )0.,=6(FeO)+7(Fe.O;), instead of 7(/FeO)+7(Fe.O;), which would be equivalent to the formula Fe,O,. It is only quite natural that magnetic oxide formed in the midst of peroxide of iron should contain an excess of this oxide. The writer assumes that the force of adhesion was used for the first time in this instance for the mechanical sep- aration of substances. It has been employed since in connection with the use of the magnet in investigations on the nature of different metallurgical products, and in each case it has led to interesting results. ORE-BEDS. Smelting charges consist of mixtures of ore with fluxes and fuel in definite but somewhat varying proportions, previously determined, so as to produce a desired chemical combination. The ore entering into the smelting charge may be an unmixed ore of known composition, or a previously-prepared mixture of ores, called an ore-bed, or a combi- nation of the two. Cre-beds are prepared by superposing layers of different ores of known weight and composition in such proportion as to produce mixtures of known contents in lead, silver, iron, and silica. Composition of ore-beds.Ore-beds are generally made to contain equal parts ot metallic iron, metallic lead, and silica or gangue, or from 20 per cent. to 25 per cent. of each. The relation between Jead and silver is about six pounds of lead to one ounce of silver; but this relation often varies, as well as the percentage of lead, while, on the contrary, the percentage of iron and gangue remains pretty constant. The great advantage derived from the preparation of ore-beds, besides giving mixtures of known composition, is that of drying the ore, an operation which if carried on in the furnace would absorb an enormous amount of heat. In Table V will be found the following particulars in regard to seven different ore-beds: 1. Humid weight of each ore-bed in pounds, 2. Average percentage of moisture for each ore-bed. 3. Dry weight of each ore-bed in pounds, 4, Percentage of silica or gangue for each ore-bed. 5. Total weight of silica in pounds for each ore-bed. 6. Percentage of iron for each ore-bed. 7. Total weight of iron in pounds for each ore-bed. 8. Average tenor of silver in ounces to ton for each ore-bed. 9. Total weight of silver in ounces for each ore-bed. 10. Percentage of lead for each ore-bed. 11. Total weight of lead in pounds for each ore-bed. wee oe ee Eee eee a oe SMELTING CHARGES. 649 TABLE V.—Composition of ore-beds. Ore. | Silica. Tron. | Silver. Lead. Number of ore-bed. : | | | 0 | | Humid | Moist- | Per Total | Per | Total ;S22C°8) Total Per | Total Dry jweight.| ure. | weight. | cent. ‘weight.| cent. |weight. euene weight. | cent. weight. | Ce | | Lbs. P. ct. Lbs. Lbs. Lbs. Ounces. Lbs. 410,355 10.2 | 368,430 | 21.54 | 79,375 | 21.48 | 79,160 | 42.94 7,912 19. 50 | 71, 868 340,915 10.8 | 304,099 | 26.50 | 80, 840 23.20 | 70,779 | 39.12 5, 946 19.60 | 59, 875 302,690 10.7 270, 257 | 22.30 | 60, 354 22.10 | 59, 975 35.03 | 4,734 20.00 | 54,105 283,000 9.4 | 256,358 | 22.00 | 56,475 26.40 | 67,876 | 61.62 | 7,898 21.00 | 54, 135 279,475 12.0 | 245,902 | 20.00 | 49, 321 16.60 | 40, 841 66. 02 | 8, 146 28. 2 69, 437 330,805 10.2} 296,920 | 25.40] 75,556) 21.86 | 64,696} 65.03] 9,690 19.00 | 56, 267 Seances |SseaArnae 235, 340 17. 35 | 40,881 | 24.78 | 58, 321 56. 53 6,651.9 | 23.45 | 55, 239 | Totals and averages..| -...--.]..-.---- 1,977,306 | 22.40 \442,752 | 22.30 |441,648 | 51.56 | 50, 977.9 | 21.30 1490, 926 | No. 1 is made at Smelter H of ore from the Amie, Hibernia, Homestake, and Morning Star mines. Wo. 2 is made at Smelter H of ore from the Amie, Chrysolite, Evening Star, Morning Star, and Virginius mines. No. 3 is made at Smelter H of ore from the Amie, Evening Star, Hibernia, Homestake, Little Giant, Morning Star, ete. No. 4 is made at Smelter H of ore from the Amie, and Evening Star. No. 5 is made at Smelter H of ore from the Amie, Adelaide , and of flue-dust. No. 6 is made at Smelter H of ore from the Araie, Morning Star, ete. No. 7 is made at Smelter B of ore from the Catalpa, Evening Star, Henriett, Hibernia, Highland Chief, Morning Star, and Silver Wave mines. A consideration of Table V shows— 1, That the ore beds vary a good deal in weight; in the examples given, from 117 to 189 tons. 2. That the mixtures contain on an average about the same quantity of silica, iron, and lead. 3. That on an average the relation of silver to lead by weight is as 1 to 120.4, or one ounce of silver to 8¢ pounds of lead. 4, That the amount of moisture is pretty constant. SMELTING OHARGES. By smelting charges will be designated the combined weights of ore, fluxes, and fuel thrown at the same time into the furnaces, and by charges, the weights of ore and fluxes entering into the composition of the smelting charges. The word ore embraces ore beds and unmixed ores, and the word fluxes, dolomite, hematite, and old slags. The weights of smelting charges differ a good deal, according to the capacity of the furnaces. The term fuel will always be used for the mixtures of coke and charcoal used in Leadville. Although the amount of fuel used in smelting will always be given in weight, it must be remembered that coke and charcoal are not weighed at all smelters, but are as often measured by the shovel or the barrow; the volume has been converted into weight for comparison. SMELTER A. The information obtained at this smelter is not very satisfactory. The smelting charges are made up of — Ore, 150 pounds. | Flux, 50 pounds. Fuel, 35 pounds. | | | | Oretbed)—2. 100 | Dolomite ..-....-.-- 84 | Charcoal ....-....-.- Rock Mine ore .... 100 | Hematite -- 4 | Cokeand screenings. 30 | Evening Star ore... 44 | Old slags -.----..-- 60 Rock Mine ore .... 71 | Charge, 463 pounds. Smelting charge, 563 pounds. No. 3. Ore, 332 pounds. | Flux, 127 pounds. | Fuel, 95 pounds. ° | Ore-bed No.1 ....-. 106 | Dolomite ...-.-..--. 64 | Charcoal ..-..--.---- 50 | Ore-bed No, 2 -....- 53: |’ Hematite... .. <-<.. 3 Cokeandscreenings. 45 Dunkin Mine ore.. 40 | ola SINGS! 22> oo enon 60 | Rock Mine ore..--- 133 Charge, 459 pounds. Smelting charge, 554 pounds. At Smelter C the above charges are smelting charges according to our definition, but they are called semi-charges. The slags are not weighed, but measured by the ore-shovel; they are not mixed with the ore and flux, but with the fuel. Fuel is meas- ured by the fuel-shovel in the proportion of two shovels of charcoal for one of coke. One shovel of charcoal (fuel-shovel) is equal to seven pounds, and one shovel of coke (fuel-shovel) to 14 pounds. One shovel of slags (ore-shovel) weighs about 15 pounds. In smelting charges Nos. 1, 2, and 3, the average proportions are— IVES 1) Chica cece 6506 covone SoseSs OSeseelosaS CoO HEoS Hono Been bead boSa ase 454 RH Wi G0) (aS ene e SC BORO RAO BE OSes SeCead SAao GooaEEoS GUnEenicoceocEsooSs 31 JE (0) OTR.) 6 pono oo0 ond 6 ch nion Oa55 Gao BasopdnoRadoosso RoOdnaAHeRe Seas 214 At Smelter C the smelting charges are model ones, like everything else connected with this smelter. The slags obtained from the above smelting charges have the com- position of singulo-silicates. They are very fluid at a relatively low temperature, and carry less lead and silver than any others in the camp; and the average charge repre- senting the work done during a whole year will show with what regularity work is carried on at this smelter. “sna eee aes SMELTING CHARGES AT INDIVIDUAL SMELTERS. 653 The average charge, deduced from data given in Table IY, is as follows: | Ore, 310 pounds. | Flux, 157.6 pounds. | Fuel, 105.9 pounds. | ——— — ~ =} — a ——| Oreste see: 310 | Dolomite ........ 69.53 | Charcoal.......-- 59.10 | | | Hematite ... Seo oie |l COkeieenn em yaooe 46.80 | | | Old slags ........ 58. 50 | | Charge (ore and flux), 467.6 pounds. Smelting charge (ore, flux, and fuel), 573.5 pounds. In the average charge the proportions are— I ATED Cob tak poetic eR eS So ee aN Ee ES a ee ae 50% Mitel TOMOLeS esas < oe sore ie sens ea seme closes bor een caste se lLeee ce eee coca 344 BreWconchano Greece emcee aera eels site ais we cree lok cine wast ce cece sce 222 Being in possession of data obtained at Smelter C for the month of July, 1880, these data will be discussed, for in the opinion of the writer everything connected with Smelter C is worth recording. Oreusmeltedmmr Nitya Qe a-axis metal c ae tsetse sane stesecerhos xs Dolomite smelted in July, 184 Hematite smelted in July, BullronsprodwucedmndmlyseleS0 see sey neeie ise ea oe = aie aleatn ene ees ee 4354 The bullion produced in twenty-four hours is equal to 14 tons, assaying 136 ounces of silver to the ton. The average charge for the month of July, 1880, is as follows: | Ore, 310 pounds. | Flux, 144 pounds. Fuel, 105 pounds. sree pa eS So Le aS = a a Orés)-ssayee se ===. 310)| Dolomite --.-.25---- (yf Oat oe ene Seeoecne 105 | Hematite .......---. 17 Oldislaes een. sta5: 60 | Charge (ore and flux), 454 pounds. Smelting charge (ore, flux, and fuel), 559 pounds. In the preceding charge the average proportions are — = > D> IMIEEM OORT 432555 ob See ete ed decease U2 GEer Be SESE tee Cee Se eae ees Sees area 463 IN WAL GY CRB ca sie Re AGC) oe Deco doe se BoeS ER SOne RS Se Recon ae Se eee ae iSeiseias 3 Hbeletorelarmanes eye ae sae eee sia nero eienn- Seelaincin scheme ese ore cas cine 23 Produetion of bullion per charge, 90 pounds. As has previously been stated, the mixture of ore, dolomite, and hematite, weigh- ing about eight hundred pounds, is called the charge. It is made to contain about 20 per cent. of lead, of which about 88 per cent. is extracted in the state of bullion. Consequently each charge will contain 160 to 161 pounds of lead, of which 141 to 141.5 pounds are extracted in the state of bullion. This quantity of bullion requires 200 pounds of fuel for its extraction, showing that one part of bullion requires about one and one-half parts of fuel for its reduction. As the quantity of material to be smelted in each charge weigsis about 920 pounds, from which 141 pounds are extracted in the state of bullion, the remaining 779 pounds 654 GEOLOGY AND MINING INDUSTRY OF LEAPVILLE. constitute the slag, containing about 2 per cent. of lead, or 15 pounds, and the loss in fumes is equal to about four pounds of lead per charge. Each charge gives about 5.67 parts of slag for one part of bullion. The furnaces run about two hundred charges in 24 hours, yielding: Bullion, 16 tons; slag, S50 tons; and consuming: Rich ores, 634 tons; fuel, 20 tons; charges, 143 tons. SMELTER D. Smelting charges made in August, 1880. Ore, 700 pounds. | Flux, 330 pounds. | Fuel, 160 pounds. Ore-beds-.--.----- 500 | Dolomite .--.....-. 80 | Charcoal.......----- 95 | Various ores. ...--- 200 | Hematite .......... 170) | Cokepesssen tees sealon | | | Old slags --.-.-.--. 80 1 Charge (ore and flux), 1,030 pounds. Smelting charge (ore, flux, and fuel), 1,190 pounds. In the preceding smelting charges the proportions are— Biv OROS aa oe y= Se acai espa cicicicisidisis se esis ioalseiaenateeinle seieeeoa sees Sales 47 HnelliTOrOresso ce ease tess Se ses Soa ec2) ecioee tees ose nee ee ae lean aa tinn Aeree meer 228 IQinee CURES 5= Se conc cqonad ea ceno edsnadacdsene Agss Great onuogoshy sy SansEaisons 154 The composition of this smelting charge is a normal one. The composition of the average smelting charge, calculated from the data given in Table IV, is the fol- lowing: 1 | | | Ore, 700 pounds. Flux, 170.3 pounds. Fuel, 133.4 ponnds. | = os —— = ——— a | Various ores....-. 700 | Dolomite ..-..--. 41.65 | Charcoal......-.-. 89.6 | | | Hematite -....-.. 48.65 | Coke .---.2--=.--- 43.8 | Old slags ........ 80 | Charge (ore and flux), 870.3 pounds. Smelting charge (ore, flux, and fuel), 1,003.7 pounds. In the average smelting charge the proportions are— Hlnxtororatase-asee see cee ase sbobassonsds sched ce5ehs lone Stee ee ee 244 Ju RO ay sare aes aap COSC EMOA SA Sone OEE SHE or Ease Bane Can seen oeer osc apo cette 19 Buel torcharsersss acecctaces Se coe ae ee = eae avis eco ea oie Sepia eee eee 15t The percentage of fuel is the smallest which has been yet observed, and this last smelting charge would prove the most perfect if it were not for the important ele- ment, time, which has been purposely neglected. The question will be discussed after exhausting the composition of smelting charges of the various smelters, and it will be seen whether it is advisable to aim at the lowest percentage of fuel in smelting charges. SMELTER E. Smelting charges made in August, 1880. Ore, 300 pounds. Flux, 80 pounds. Fuel. 73 pounds. One-bedeees-.o-s-- 200 | Dolomite ...--...... 15 | Charcoal......---. 36.5 Various ores.....-. 100.| Hematite .. -...... 15')\\COKG}-=- se neeeeene 36.5 | Oldislage:<<- 224.365 ~ 50 | Charge (ore and flux), 380 pounds. Smelting charge (ore, flux and fuel), 453 pounds. we et Te oie et ee eT ne ' ScousnaE SED FcOMEEE come OnocmesD or eocHaaacd: 22 INO ONO. Vee Sac Hoodcoodbn Ke aeen ence anes bopooe cocosy saeendedeoccouscos meet 212 TIEN H NA LSS sects cro boe ac Sherartone atom sooo su.oUbonce d cone peansanaecenans= 74 Average charge deduced from data given in Table IV. | Ore, 600 pounds. | Flux, 203 pounds. | Fuel, 153 pounds. Pp | | | IE: Saute | | | Various ores...---. 600 | Dolomite .-.....-.. 58.1 | @harcont seer 92 | Hematite -......-- 69. 9 | Cokes ee reees so 61 | | Old slags .--.- -.. 75 | Charge (ore and flux), 803 pounds. Smelting charge (ore, flux, and fuel), 956 pounds. In the average charge the proportions are— IM etn soee Sa Seeeen esoobecesedassee =eancbe se rose sosgcecosd cacopenee ssc 334 eli fO Ones ela ae eee ee Ee AR orcs sive cn rosy ea wie aaa es anette 254 LOLI ye Rae cee Sones ooes soe sao 2oceae see endsoe seecoresoSasosesAgoosc 19 At this smelter the fuel is measured by the shovel. SMELTER H. Smelting charges made in August, 1880. No. 1. | Ore, 530 pounds. Flux, 175 pounds. Fuel, 130 pounds. | ' | |—- — - - - | = =|| | Ore:bed'=-22s--- = 500 | Dolomite -..--- Sea ol ONATCON:. onaan ese 110 | | Adelaide ore....... 30 | Old slags ..---..--- 120 Coke =e 20 | Charge (ore and flux), 705 pounds. Smelting charge (ore, flux, and fuel), 835 pounds o No. 2. | Ore, 550 pounds. | Flux, 155 pounds. | Fuel, 130 pounds | | | =e \- _ E | Ore-bed.....-..---- 500 | Dolomite .-.-..----- 85] Charcoal) ....-..... 110 | Adelaide ore. ...-.- 50 | Old slags .--..----- 120] Coke...--.-_.. aeeeeteO) Charge, 705 pounds. Smelting charge, 835 pounds. 4 . e 2 we Sh oe SMELTING CHARGES AT INDIVIDUAL SMELTERS. 657 No. 3. Ore, 480 pounds. | Flux, 160 pounds. Fuel, 120 pounds. | Ore-bed ............ 480 | Dolomite ......-.-- 60 | Charcoal........... 100 | Old slags ...-.- PoceeOUI i Coke@recsereateena- 20 Charge, 640 pounds. Smelting charge, 760 pounds. No. 4. Ore, 500 pounds. | Flux, 135 pounds. Fuel, 120 pounds. | Ore-bed......-...-.. 450 | Dolomite .--...-.-.-- 35 | Charcoall=="-,----< 100 Adelaide ore-.--.--- 50 Oldialacs ease pasa 100 | Cokes eecere eco cas 20 Charge, 635 pounds. Smelting charge, 755 pounds. In the preceding smelting charges the proportions are— | Fuel to charge. ----- No. 1. | No. 2. | No. 3. | no. 4. | | ez i |i | | | | | | | Flux tocre........-- | 33 | 282 | 384 | 27 Fuel toore ....-.-. | 243 232 |° 25 | 24 | 182 182] le) 19 | 1 | Data relative to the consumption of ore, fluxes, and fuel not being obtainable at this smelter, one of the most important in the camp, the construction of an average smelting charge is impossible; but the general rule observed at the works in the com- position of the smelting charges is the following: The ore-beds are made to contain equal parts of gangue and metallic iron, 20 to 25 per cent. of each, and from 16 to 25 per cent. of lead, about six pounds of lead for one ounce of silver. When the propor- tion of gangue and iron is equal in the ore-bed, the ore is mixed with 10 per cent. of dolomite; but when gangue is in excess hematite is added in sufficient quantity to make the balance. At this smelter the slags obtained are called acid slags. The fuel- shovels used at this and other smelters are drawn to seale in Pigs. 1, 2, and 3, and the ore and slag shovels are shown in Figs. 4 and 5, Plate XLIV. SMELTER I. Smelting charges made in August, 1=80. {At this smelter the ore-bed was made with Morning Star, Dunkin, Iron mine, and Agassiz ore.] | Ore, 526 pounds. Flux, 273 pounds. | Fuel, 147.5 or 137 pounds. | | is rie