UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, Director Bulletin 718 GEOLOGY AND ORE DEPOSITS OF THE ' CREEDE DISTRICT, COLORADO BY WILLIAM H. EMMONS AND ESPER S. LARSEN WASHINGTON GOVERNMENT PRINTING OFFICE 1923 ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OP DOCUMENTS GOVnRNMENT PRINTING OFFICE WASHINGTON, D. C. AT 40 CENTS PEE COPY PURCHASER AGREES NOT TO RESELL OB DISTRIBUTE THI3 COPT FOB PROFIT. PUB. BBS. 67, APPROVED MAY 11, 1922 CONTENTS. Page. Chapter I. Introduction.................................................. 1 Location and topography............................................. 1 Field work and acknowledgments...................................... 2 Hifltorj.............................................................. 3 Mining and treatment of ores.......................................... 6 General conditions................................................ 6 Humphreys mill.................................................. 6 Amethyst mill................................................... 7 Solomon mill.................................................... 7 Ridge mill....................................................... 8 Production.......................................................... 8 Bibliography......................................................... 11 Chapter II. Outline of the geology......................................... 12 Age of the rocks. ..................................................... 12 Potosi volcanic series................................................. 13 Alboroto group.................................................. 13 Piedra group..................................................... 13 Creede formation...................................................... 14 Fisher quartz latite.................................................. 15 Intrusive rocks........................................................ 15 Quaternary deposits................................................... 15 Geologic structure..................................................... 16 Chapter III. Rocks of the Alboroto group................................. 17 General features..................................................... 17 Outlet Tunnel quartz latite........................................... 18 General character and occurrence.................................. 18 Petrography...................................................... 18 Weathering and outcrops......................... '. ................ 19 Willow Creek rhyolite................................................ 19 General character and distribution................................. 19 Petrography...................................................... 20 Chemical composition;............................................ 23 Structure........................................................ 24 Weathering and alteration........................................ 24 Topography and scenery......................................... 25 Campbell Mountain rhyolite........................................... 25 General character and distribution................................. 25 Contacts........................................................ 26 Petrography...................................................... 27 Weathering and outcrops.......................................... 28 Distinction from other rhyolites................................... 29 Phoenix Park quartz latite........................................... 30 General character and distribution................................. 30 Petrography...................................................... 30 Outcrops and weathering......................................... 31 in IV CONTENTS. Chapter III. Rocks of the Alboroto group Continued. Page. Equity quartz latite................................................... 32 General character and occurrence.................................. 32 Contacts.......................................................... 32 Petrography...................................................... 32 Weathering and outcrops.......................................... 34 Chapter IV. Rocks of the Piedra group.................................... 35 General features..................................................... 35 Hornblende-quartz latite...................................... -^.... 36 General character and distribution................................. 36 Thickness....................................................... 36 Petrography...................................................... 37 Weathering and outcrops.......................................... 38 Windy Gulch rhyolite breccia......................................... 38 General character and distribution................................. 38 Petrography...................................................... 39 Weathering and outcrops.......................................... 40 Comparison with Campbell Mountain rhyolite...................... 40 Mammoth Mountain rhyolite......................................... .40 General character and distribution................................. 40 Character of contacts and thickness............................... 40 Petrography.. ...................................................... 41 Weathering and outcrops.......................................... 42 Comparison with Campbell Mountain rhyolite...................... 43 Rhyolite tuff......................................................... 44 General character and distribution................................. 44 Petrography...................................................... 44 Tridymite latite....................................................... 45 General character and occurrence.................................. 45 Thickness....................................................... 46 Petrography...................................................... 46 Tridymite, quartz, and cristobalite in volcanic rocks................ 47 Chemical composition............................................. 49 Flow near mouth of Deerhorn Creek................................ 49 Outcrops, weathering, and alteration............................... 50 Andesite............................................................. 51 General character and distribution................................... 51 Petrography...................................................... 51 Alteration and topography......................................... 53 Quartz latite tuff...................................................... 54 General character and occurrence.................................... 54 Thickness......................................................... 55 Petrography...................................................... 55 Massive rock in the tuff............................................ 55 Weathering and outcrops............................................ 57 Rat Creek quartz latite................................................ 57 General character and distribution................................... 57 Thickness......................................................... 58 Petrography...................................................... 58 Weathering, outcrops, and topography.............................. 59 Nelson Mountain quartz latite.......................................... 59 General character and distribution................................... 59 Thickness......................................................... 59 Petrography...................................................... 59 Weathering and outcrops............................................ 60 CONTENTS. Chapter V. Creede formation............................................... 61 Name, general character, and occurrence................................. 61 Structure and thickness. ............................................... 62 Subdivisions.......................................................... 62 Lower member......................................................... 63 General character................................................. 63 Petrography...................................................... 63 Interbedded travertine................................................. 64 Character and distribution......................................... 64 Origin............................................................ 64 Upper member........................................................ 65 General character and distribution................................... 65 Petrography...................................................... 66 Massive rocks..................................................... 66 Weathering and topography............................................ 68 Origin................................................................ 68 Position in the section................................................. 69 Age................................................................... 69 Chapter VI. Fisher quartz latite............................................ 71 General relations....................................................... 71 General character and distribution....................................... 72 Thickness............................................................. 72 Petrography.......^............................i..................... 72 Weathering and outcrops................................................ 73 Chapter VII. Intrusive rocks............................................... 74 Types................................................................ 74 Rhyolite porphyry....................................................