Ore Deposits in the Vicinity of the London Fault of Colorado
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UNITED STATES DEPARTMENT OF THE INTERIOR Harold L. Ickes, Secretary GEOLOGICAL SURVEY W. C. Mcndenhall, Director Bulletin 911 ORE DEPOSITS IN THE VICINITY OF THE LONDON FAULT OF COLORADO BY QUENTIN D. SINGEWALD AND B. S. BUTLER Prepared in cooperation with the STATE OF COLORADO and the COLORADO METAL MINING FUND UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1941 For sale by the Superintendent of Documents, Washington, D. C. -------- Price 81.50 CONTENTS Abstract. ____________-____-__----_--------_-_--______________--___ 1 Introduction. __________________-_-----_---_-.---___._______.___-__ 4 Location of the area.__-______-----_-------___--__-_________-__ 4 Scope of the paper.._--_-_-___----_____________________________ 4 Previous work ____________________________________________ 4 Acknowledgments. _____-_____-_---_--_----___-_________.._-____ 5 Geography _ ____________--___---_------_--_----__--__---_-_-__ 6 Routes of approach._____:^_-___-_---_-_---____________________ 6 Topography ______________--_--_----_-----_-_-________________ 6 Climate and vegetation___-__-_-------_------__---_-_____-__--_- 6 General geology-_____ ________---_-_ ______________________ 7 Pre-Cambrian rocks..__--___.-------.----_---___-___.___...._ 7 Paleozoic sedimentary rocks.____---_--..---.__-___._________.__ 7 General features ...-..-.-.-------..-.-__-.__..__-_.__._._ 7 Sawatch quartzite (Upper Cambrian)________________________ 10 Manitou limestone (Lower Ordovician)_______________________ 11 Chaffee formation (Upper Devonian)...______-__._.__._-_,-. 12 Parting quartzite member._____________________________ 12 Dyer dolomite member _______________________________ 12 Leadville limestone (Mississippian)_____.__.._._____.____-_-- 13 Weber (?) formation (Pennsylvanian)._______________________ 14 Maroon formation (Permian and Pennsylvanian?)_._.._______. 15 Tertiary (?) igneous rocks._____________________________________ 15 General features__________-----_-__-____-___________..____ 15 White porphyries. _ ___---_-_.___---_-________________ 17 White porphyry.. __._--_.___-.__-___.____________ 17 Later white porphyry.__-__--_-_________. .............. 18 Gray porphyry group._____________________________________ 18 Monzonitic diorite porphyry.___________________________ 19 Quartz monzonite porphyry..-..________________________ 19 Lincoln porphyry____--___-_-_-_._______.______________ 21 Structure___._.____-______.---__.-_-.__.___.___.________ 22 Regionalstructure-_--___--__--------_---_-_______________. 22 London fault____________________________J______________ 23 Quaternary geology._____--_-_-----_-------_-_____-_-__________ 27 Economic importance.____-__--___-_-_-___-______._________ 27 Areas affected_____-_--__---__-_-__--___-___..________.._ 27 Ore deposits.______--_--__----_--_------------_-_-____-___________ 28 Regional relations._-__----__-_-__------____-_-____-___________ 28 Deposits in the Alma district...-____________________________ 28 Distribution __________________________________________ 28 Classification. ...-______-----____.-___-__________._____ 29 Gold veins of the London type._________________________ 29 Silver-lead deposits in limestones________________________ 29 Gold deposits in the quartzites of the Sawatch formation___ 30 Mutual relations of the classes.__---._______.___________ 31 in IV CONTENTS Ore deposits Continued. Regional relations Continued. Page Ore facies at Leadville_____________________________________ 31 Relations of the ores at Alma to those at Leadville____________ 33 Local centers of mineralization at Alma ______________________ 33 Origin of ores at Alma._______---_-___---___-______________ 34 The London vein system.___ ____._-_________-_-___.___:________ 35 Location. __'____i___-___________-__-_-_-__-_______________ 35 London mine__------_-------------_--------__---_-_____-__ 36 History and production____________.____________________ 36 Geologic map.________________________________________ 37 Rocks_____________________-__-___________'_____ _____ 37 Pre-Cambrian rpcks________________________________ 37 Paleozoic sedimentary rocks.-___--_--_-____________ 37 Tertiary (?) igneous rocks._________________________ 37 "Yellow porphyry"__________________________ ______ 38 "Black graphitic" shale___---_----_______________ 39 Structure. ____________________________________________ 39 London fault_____________________________________ 39 Syncline west of London fault.-______________________ 39 Minor faults whose strike is nearly parallel with that of the London fault.__________________ _ __!_________ 40 Transverse minor faults___^___-_u__-______j_._______ 43 Summary of folding and faulting_,___________________ 43 Occurrence of ore____-___'___^i_^_____ ________!__________ 44 General features...,__._________ _________ __________ 44 London vein._____________:__-____________________ 44 McDonald vein _ __i'__:__!_:_:_____..________________ 46 Other ore bodies______-_-_-___--__-_-____^_______ 47 Relations of veins to enclosing rocks _________________ 47 General appearance of ore. _ ____________________________ 48 Detailed mineralogy of hypogene ore.____ _.______________ 49 Minerals in altered wall rock _______________________ 49 Gangue minerals.__.__________-______-__'_ _________ 50 Sulphide rnmerals---_-_--_-------------_-_-_-_-___- 51 Gold____-_-_ -_-_-__--_ '---._----,_------_-.-. 53 Summary of paragenesis_____---_.i!-^: --------_---. 54 Supergene alteration_______________.:__>-_____________-_- 54 Other mines of the London vein system.__ __'_________________ 56 American mine_______-___-_-___-----_-_-_-_________-_- 56 Havighorst tunnel-_------_---__---_---_ -__--_-____-- 56 Ophir mine. _______________________ _,_ _ ___!_____ _______ 57 Mosher tunnel_____-_----_,__--._---__- T -__;-__-_-___-__ 57 London-Butte mine___._-_______---__-:__.___-_-_____-__ 57 Deposits in London fault zone northwest of London Mountain...... 57 Area between London Mountain and New York Mountain _.____- 58 Extent of prospecting___________________ ___- j_____-_^_i_ 58 Venture shaft. ______-___-_.-_'_ _:_- ^ _ ^ _______'_-.___ _--- 58 Hard-to-Beat mine.________.___--_._.___-__i ___-_-L_-__-_- 58 Oliver Twist tunnel__----_-______.________ ___:_______--_ 59 New York Mountain________________^____________________ 59 Area northwest of New York Mountain.____j____i___-_--____ 60 Conclusions regarding deposits in London fault'zone north of Penn sylvania Mountain. _ _____________'___________"____ _________.___ 61 CONTENTS V Ore deposits Continued. Page Region south of Pennsylvania Mountain._______________________ 63 Extent of known mineralization.____________________________ 63 Sacremento mine.________--------___---__------_--_----___ 63 Mudsill mine__-.___-___---_-_---_----_----.------_---_-. 65 Sherwood mine.___________-_-_---__-__-_-_-_-___-___-_____ 66 Wagner mine.___.________-_--_---__---------------_-----_ 66 Barcoe tunnel__-_-__--___--------------____-__--_-----_--_ 66 Other mines and prospects..--------_-----__----_----------. 66 Conclusions regarding region south of Pennsylvania Mountain __ 69 Suggestions for prospecting.________________________________________ 70 Region north of Pennsylvania Mountain__._____________________ 70 Region south of Pennsylvania Mountain....._____________________ 71 Index..__._-.________________-__--_------_----------------_---__- 73 ILLUSTRATIONS PLATE 1. Geologic map of the Alma-Horseshoe district, Colorado. __ In pocket 2. Geologic sections of the Alma-Horseshoe district_---___._ In pocket 3. Generalized structure map of area near the London fault, showing relation of ore deposits to major structure...______ 26 4. Glacial map of the Alma-Horseshoe district._____________ In pocket 5. Glacial map of area west of Fairplay_-______.______________ 27 6. Plan and section of London mine. __-__-_-----________-_ In pocket 7. Level maps of London, American, and Ophir mines and Havig- horst and Mosher tunnels__________________________ In pocket 8. Sections A-A' to G-G' and section through South-side winze of London mine_--__--------_----------------_--__- In pocket 9. Photomicrograph of yellow Weber (?) shale ("yellow porphyry") _ 50 10-17. Photomicrographs of ore and gangue from London vein__ ___ 50 18. Index map of London-Butte mine showing relative position of various levels. _--_---------------_----------__---_-_ 58 19. Geologic map and sections of London-Butte mine showing Butte and Maumee tunnels _____________________________ 59 20. Geologic map of No. 3 and No. 4 levels, London-Butte mine. In pocket 21. Geologic map and section of Oliver Twist tunnel_ _ ______ In pocket FIGURE 1. Index map showing location of the Alma district____.______. 5 2. Age of ore deposits in relation to faulting and igneous intrusion. 31 3. Generalized columnar section at London Mountain________ 38 4. Sketch showing relation between London fault, McDonald No. 2 vein, and a minor reverse fault at the top of raise 203, London Extension mine, Alma district..._-_-_-_--___ 42 5. Idealized section at London mine showing faults and ore bodies before period of post-mineral faulting _____________ 44 6. Diagram of London Mountain showing southward-pitching syncline west of the London fault and stratigraphic and structural positions of veins before the post-mineral faulting. 45 7. Paragenesis of hypogene minerals in London vein.__________ 55 8. Sketch map of Sacremento mine___________-___--__-_-__-. 64 9. Geologic map and se.ction of Mudsill mine _________________ 65 10. Map of Sherwood mine.._----------_-----------------_--_ 67 11. Map of Barcoe tunnel......---------------_------------_.