,._ ·_/ DEPARTMENT OF THE INTERIOR FRANKLIN K. LANE, Secretary UNITED STATES GEOLOGICAL SURVEY · GEORGE OTIS SMITH, Director Professional Paper 114 GEOLOGY AND ORE DE_POSITS OF THE YERINGTON DIST_RICT, NEVADA BY • ADOLPH KNOPF WASHINGTON GOVERNMENT PRINTING OFFICE 1918 ._,., .. .,... ... '· _.! ~ 1 • ~ :. •• ~ .... \, :'. ·CONTENTS. Page .. Pago. Preface, by F. L. Ransome ...................... :. 5 Part I. General features-Continued. Outline of report ................................ 7 Gener;,tl geology-Continued. Pttrt I. General features .................•....•.. 9 Epitome of the. geologic history of the Geography ........................ ·......... 9 district .....•......................... 29 Field work .................................. 9 Part II. The ore bodies ......................... 31 Bibliography ............................... 9 General features ............................ 31 . History of mining .......................... 11 Minerals of the ore deposits .................. 31 Production .................................. 12 Primary ·minerals ....................... 31 General geology ............................ 12 Secon'dary minerals .......... ~ .......... 33 'l'riassic rocks . ............ : ........... 12 Contact-metamorphic ore deposits ........... 34 Character ........................... 12 Geologic environment ................... 34 Age ............................... 12 Composition of the rocks inclosing the Volcanic rocks ...................... 13 ore deposits ....................... 34 Andesites ...................... 13 Relation of the ore deposits to faulting Soda rhyolite-felsite (keratophyre). 13 and brecciation ................... 35 General features ............. 13 Form and dimensions of the ore deposits. 38 Petrography ...... : .......... 14 Metamorphism by the ore-forming solutions 39 Sedimentary rocks ................... 16 :Mineral transformations ............. 39 Garnetites and allied rocks .......... 16 Composition of the ore-forming solu- Character and distribution ....... 16 tions ............................. - 41 Origin of the metamorphic rocks .. 17 Paragenesis ............................. 41 Gypsum ........................ .' .. 18 Time of ore deposition .................. 43 Correlation of the Trias!3ic rocks ...... 19 Origill. and classification ........... : ..... 44 Cretaceous(?) rocks ..................... 19 Oxidation and sulphide enrichment ..... 47 General relations . .' ....... : ......... 19 Fissm-e veins and other deposits ............. 49 Major ~ntn~~io~s .................... 20 Part III. Mines and prospects ..............· .... 50 Granochonte ................. , .. 20 Mines an'd prospects on contact-metamorphic Quartz monzo~1ite .............. ·.· 20 deposits ...... ~ ........ : . ~ ..........· ...... 50 ·General features ............. 2'0 Bluestone :mine ................ ·........ 50 Scapolitic alteration ........ 21 Mason Valley mine ...................... 51 Minor intrusions .................... 21 History and de;velopment ............ : 51 Aplite .......................... 21 Geologic featm-es ... ._, ............... 52 Quartz monzonite porphyry.·.... 22 _ Malachite mine ............ .' .......... ·.. 55 Occurrence and character .... 22 McConnell mine ........ : ............... 55 Petrographic details ......... 22 Western Nevada mine ................... 57 'fertiary rocks ........................... 23. Greenwood prospect ........... , ........ 58 Ludwig mine ........................... The section in general. .............. 23 58 General features ..................... Conglomerate at the base of the. Ter- 58 Details of the geology ................ 59 tiary section ........ : ............. 23 The ores ............................ GO Latite series .......................... ~ 23 Gypsum deposit .........•............ 62 Latite vitrophyre ............... 23 Douglas Hill mine ........................ 62 Quartz latites ...............· .... 25 Casting Copper mine ..................... 63 Rhyolite .. ·......................... ~ 25 Mines and prospects on deposits in igneous Andesite. breccia ................... 26 rocks .................................... 64 Hornblende andesite ................ 26 Montana-Y Jrington mine ................. 64 Conglomerate ...................... 26 Empire-Nevada mine .................... 64 Basalt ... : ......................... 27 Jim,Beatty prospect. .................... 65 Correlation of the Tertiary rocks ..... 27 Terry and McFarland prospect ........... 65 Quaternary deposits ............... , ..... 27 Blue Jay mine .......................... 65 Geologic structure ...............· ........ 28 Index ... ·.................. : ................... : .. 67 3 ILLUSTRATIONS. Page. Page. PLATE I. Geologic map of the Yerington district, FIGURE 3. Columnar section of the Tertiary rocks _ Nev ..•........ _.. _.... _.... _. In pocket. in the Yerington district........... __ II. A, Garnetized Halobia; B, Photomicro- 4. Section through the glory-hole tunnel of - graph of latite vitrophyre. 16 the McConneli mine .... _... _.· _..... 29 III. Geologic sections across the. Yerington 5: Geologic section through tunnel No. 4, district; Nev. _. ___ .. __ .... __ . __ .. _. 28 Mason Valley mine ............. _. __ . 37 IV. A, Specimen showing junction of unre­ 6. Inclosure of an idiomorphic cross sec­ placed limestone with portion wholly tion of lamellar pyroxene in a clino- replaced by andradite; B, Garnetized, pinacoidal section of pyroxene ...... 41 silicified, and pyritized porphyry from 7. Geologic map of the area surrounding the Ludwig mine .... _. ____ ........... 36 the Mason Valley mine ............ 53 · V. A, Garnetite breccia in which the frag­ 8. Plan of the McConnell mine, showing ments have been partly replaced by the geologic relations ............. : . 56 epidote, Bluestone mine; B, Gangue of 9. Geologic section acr~ the Ludwig lode copper ore, in which andradite is inter­ at the vertical shaft.......... _ ....... 59 stitial between pyroxene crystals, 10.· Geologic section across the Ludwig lode, Western Nevada milie.. 40 320 feet southwest of the vertical FIGURE ~- Index map showing the location of the shaft_ ........... -- . : .............. __ 60 Yerington district, Nev......... 10 11. Areal geology of the Douglas Hill mine. 63 · 2. Geologic section extending N. 71°. W. 12. Diagrammatic map of the surface geology from the summit of Douglas HilL . 17 at the Casting Copper mine ......... 63 4 PREFACE. By.F. L. RANSOME. Y cringtOJl" is one of the smaller and less pro-· The fact that many of the ore bodies are not duct:ivc copper districts of the West, its· entire actually at the contacts between the plutonio . output frorp. the beginning of mining operations ·rocks and the invaded rocks leads to an inter­ being less than a third of the annual output of esting discussion of the essential characteristics the mines at Bisbee, Ariz. Nevertheless, its de­ of contact-metamorphic deposits. The conclu­ posits are exceptionally ifiteresting to the stu­ sion is reached that mineral composition and dent of ore deposition and differ from those of associations are of more weight than mere prox­ the larger and more productive districts of Utah, imity in deterniining the classification of a Nevada, New Mexico, and Arizona in ·being of deposit. contact-metamorphic origin and only slightly In describing the relation of enrichment to modified by enrichment. the adjacent limestone in the Lud~ig mine The relation of ore depos~tion to contact­ Mr. Knopf makes the important suggestion metamorphic. action has been discussed by Mr. that supergene sulphide enrichment is likelr to Knopf in a keen and suggestive way. He be an extremely wasteful process. This con­ shows that in this district, probably in early clusion, which accords with that presented ·in Cretaceous time, there were two plutonic intru­ my own paper on the ·copper deposits of the sions, the first of granodiorite and the second Ray and Miami districts, Ariz./ indicates that of quartz monzonite. These intrusions effected estimates of the thickness of rock eroded from intense contact metamorphism of the invaded above an ore body in the course of enrichment, rocks, both igneous and sedimentary. A nota­ based on a comparison between the copper ble contribution in the report is the recognition contents of pro tore and. ore, may be far under. of a time interval, marked by dike intrusions the mark. and fissuring, between this first metamorphism It is impracticable in a brief preface to call and the ore deposition, which nevertheless took attention to all the interesting features in the place at high temperatures and was accompa­ following pages. The report is an excellent nied by the formation of garnet and other sili­ example of a well-balanced, thorough study cates characteristic of contact metamorphism of a small mining district, in which the essen­ of the pneumatolytic type. It is clearly shown tial facts have been discriminatingly observed, that much iron and silica were introduced into the conclusions ably drawn, and the whole the ·limestones during the first metamorphism· pre$ented without superfluous or unrelated and that some of these same constituents and detail. large quantities of copper and sulphur were 1 U.S. Geol. Survey Prof. Paper 115 (in preparation). added during ore deposition. 5 . .. ~ . ,. - .' . ~ .. \ . : .· ~'. ,; . \,.· ~. ,." • ~ .J ~ • • ) ' • ~ • ·.I . !·; ~.. ·:1 ~ :. : ·OUT.LINE ·OF REPORT.' I : -.---. The Yerington district; which next t9. Ely i~ l of appro~imately upper