UNITED STATES DEPARTMENT OF THE INTERIOR Ray Lyman Wilbur, Secretary GEOLOGICAL SURVEY W. C. Mendenhall, Director Professional Paper 171 G EOLOGY AND ORE DEPOSITS OF THE PIOCHE DISTRICT, NEVADA BY LEWIS G. WESTGATE AND ADOLPH KNOPF UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON: 1932 For salo by the Superintendent of Documents, Washington, D. C. ------------------ Price 85 cents CONTENTS Page Abstract.. __.______...____________________________________.-_._____-__--__-__-------_____-. vn Part 1. General geology, by Lewis G. Westgate________--_________---_-_________-__--_-____--_-_-_____----------- 1 Introduction._ __.__________._____-_____-____________________-_-_---_-_______--__-___-___-______---------- 1 Location ____________________________________________________________________________________________ 1 Acknowledgments..._ ________________________________-_____-_______--____-_-__-_-_--_______--------- 1 Bibliography__ ____________________________-___________-___________-_-___-__-_--____-___-___-------- 1 Physiography._______________________________________________________________________________________ 1 Climate_.___..______________________-__---_________-_____---_-___-_______-_-__--__---_--__-------- 4 Water supply_______-_-______----____--__-_--_-_--__-___-___-_-_-l__---_---_-_-_-_-----__-___-----__- 4 Vegetation._ ______________-______-___--__-________-_________-______.-_--__-_-__----_-_---_-_-----_- 4 History _____________________________________________________________________________________________ 4 Geology...... ____________________ _-__--____._.__-___ ----_____-_____----__-_-------_--------- 6 Sedimentary formations.____-__-_-__________-__..___-----_____---____-__-___-_-__--__-__--_---_-------- 6 Cambrian system._____________________;.__________________________________________________________ 6 Lower Cambrian series.________________________________-_.___________-_-_-_-_-_-.__--_-_----_- 6 Prospect Mountain quartzite____-______-__-_____________-_______________-________-------_ 6 Pioche shale_____________________________________________________________________________ 8 Middle Cambrian series._-___--____-_-________--_____-_______-___-___-_---_-_-______-----_---. 10 Lyndon limestone________________________________________________________________________ 10 Chisholm shale-__________________________________________________________________________ 10 Highland Peak limestone__________________________________________________________________ 11 Upper Cambrian series._____________-_______--_________-__________-__--____-_------___------_- 13 Mendha limestone._______________________________________________________________________ 13 Ordovician system.________________________________________________________________________ _____ 14 Yellow Hill limestone-________________-_____-__-_____---_____--______--_________-__-_--------- 14 Tank Hill limestone_________________________________________________________________________ 14 Eureka quartzite_____________________________________________________________________________ 15 Ely Springs dolomite_____-___------_-_____-_-______-______-________-_-___---__-_-___--_---- 15 Silurian system____________________________ .____________-_____________________-_________-____^_ 16 Devonian system.________________________________________________________________________________ 16 Silverhorn dolomite and West Range limestone_________________________________________________ 16 Carboniferous system.____________________________________________________________________________ 19 Mississippian series._________------_--_-_____---_-____-______________________-_-______-__-_--_ 20 Bristol Pass limestone____________________-_-_____-_-_______-_--__-_-____--_____--__----__- 20 Peers Spring formation.____________________________________________________________________ 20 Scotty Wash quartzite--_____--_-___-____________---_____-__--_-_--__-___--___---_-------- 21 Mississippian and Pennsylvanian series___________________________________________________.______ 21 Bailey Spring limestone_-__-_____-_-_______________-_____-_____-___-_____--________----_-_ 21 Tertiary system._________________________________________________________________________________ 23 Pliocene (?) series_____________-____--_______-_______----____-_______-_-___-_-_-__-___----_--- 23 Panaca formation..._____________________________________________________________________ 23 Quaternary system._______________________________________________________________________________ 26 Valley alluvium______________________________________________________________________________ 26 Igneous rocks._..___.:____._..___________.__.______________.________________.________._______________ 26 Tertiary (?) lavas._________.___________________________._______________.-_-_.__ 26 General features__--___-----__-______---__-____--__-_-______-__-___-_-___-_-________----_--- 26 Condor Canyon section _______________________________________________________________________ 27 Black Canyon section.________________________________________________________________________ 29 Ely Springs and Delmues Well sections_______________________________________________________ 30 Northwestern area..._________________________________________________________________________ 31 Related dikes._________________________________________________________________________________ 32 Intrusive rocks...________________________________________________________________________________ 32 Quartz monzonite and associated porphyries at Blind Mountain____________________________________ 32 Quartz monzonite-_______________________________________________________________________ 32 7: Associated dike rocks__________--_______________________-________________________________ 35 ^ Granite porphyry dikes.______________________________________________________________________ 35 Minor occurrences of granitic rock____________________._________________________________________ 36 Lamprophyre._______________________________________________________________________________ 36 Diabase of the Ely Range________________________________._____________-__--_-.___ 36 m IV CONTENTS Part 1. General geology, by Lewis G. Westgate Continued. Geology Continued. Contact metamorphism, by Joseph L. Gillson.___________________________________________________________ 36 Blind Mountain area____________________________________________________________________________ 37 Size of area and rocks affected.________________________________________________________________ 37 Limestones ________________^______________________________________^___________.______________ 37 Pioche shale.________________________________________________________________________________ 37 Lavas and tuffs_______________________________________________________________________________ 38 Mixed rocks________________________________________.________________________________________ 40 Manhattan Gap area.____________________________________'______.___________________^______________ 41 Conclusions. ___________________.________________________________________________ _________________ 42 Structure_ _____-_--_-_-----_-_-______________.___________-_-_______-___-____-_____________.__-____- 42 Thrust faulting_______________________________________________________________________________ 42 Earlier normal faulting-___________________________________________________________________________ 43 Later normal faulting._-_-__-______^_________-____________-______-_-______________________________ 44 Brecciation ______________________________________________________________________________________ 44 Part 2. Economic geology, by Adolph Knopf____________________________________________________________________ 45 General features of the ore deposits...._________________________________________________:____________________ 45 Oxidation and water level.________________________________________________________________________________ 46 Mineralogy._____________________________________________________________________________________________ 47 Veins in quartzite.________________________________________________________________________________________ 48 Ore bodies in granite porphyry_-___________________________________________________________________________ 49 Replacement deposits in carbonate rocks-__________-_______________________.________________________________ 49 General features___.________________________________________________________________________________ 49 Fissure veins.________________________________________________________________________________________ 50 Tabular replacement deposits ("bedded ores")----------------------------------------------------------- 50 Silver-bearing jasperoid at Silverhorn.______________________________________________________________________ 51 Genesis of the ore deposits_______________________________________________________________________________ 51 Summary and conclusions.______________________ ________________________________________________________ 53 The mines.______________________________________________________________________________________________ 53 Combined Metals mine______________________________________________________________________________ 53 History.______-.___________;____________________________________-_-______________________________ 54 General geology._________________________________________________________________________________ 54 Ore bodies.________ _ ____________________________________________________________________________