DEPARTMENT OF THE INTERIOR UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, DIRECTOR 4O7 GEOLOGY AND ORE DEPOSITS OF THE BULLFROG DISTRICT, NEVADA BY F. L. RANSOME, W. H. EMMONS AND G. H. GARREY . WASHINGTON GOVERNMENT PRINTING OFFICE 1910 CONTENTS. Page. INTRODUCTION, by F. L. Ransome........................................... 9 Situation and access................................................... 9 Field work and authorship............................................. 10 Literature............................................................ 11.1 History of mining development......................................... 12 Production............................................................ 13 Topography........................................................... 13 Preliminary outline of the geology and ore deposits...................... 14 PART I. General geology, by W. H. Emmons and G. H. Garrey ............. 19 Pre-Tertiary rocks...................................................... 19 Crystalline metamorphic formations................................. 19 General distribution........................................... 19 Schists south of Beatty........................................ 19 General character......................................... 19 Quartzite.................................................. 19 Quartz-biotite schist........................................ 20 Marble and calcite schist.................................... 21 Pegmatite and quartz veins................................. 21 Origin, stratigraphy, and age............................... 22 Complex south of the Original Bullfrog mine.....................' 23 General character......................................... 23 Quartz-biotite injection schist, pegmatite, and augengneiss... 23 Quartz schist and quartzite................................ 24 Marble................................................... 25 Sheared diorite............................................. 25 Quartz veins.............................................. 25 Quartz diorite dike........................................ 26 Diorite dike................................................ 26 Summary.........................................:............ 27 Silurian (?) limestone............................................... 27 Tertiary volcanic rocks......:.......................................... 29 Lava flows and tuffs................................................ 29 . Introductory statement......................................... 29 General character of the rhyolites................................ 29 General character of the basalts................................. 31 Detailed description............................................ 32 RhyoliteNo. 1............................................ 32 Occurrence and distribution............................ 32 General character..................................... 32 Microscopical character................................. 33 Limestone in rhyolite No. 1............................ 34 Age and origin........................................ 34 Rhyolite No. 2............................................ 34 Occurrence and distribution.....................'....... 34 General character..................................... 35 Microscopical character................................. 35 Age and origin........................................ 35 3 102S93 4 CONTENTS. PART I. General geology Continued. Tertiary volcanic rocks Continued. Lava flows and tuffs Continued. Detailed description Continued. Plagioclase basalt No. 1..................................... 36 Occurrence and distribution............................. 36 Petrography.......................................... 36 Age and origin........................................ 36 Rhyolite No. 3............................................ 36 Occurrence and distribution............................ 36 General character..................................... 37 Microscopical character................................. 37 Age and origin........................................ 37 Rhyolite No. 4............................................ 37 Occurrence and distribution............................ 37 General character..................................... 37 Microscopical character................................. 38 RhyoliteNo. 5............................................ 38 Occurrence and distribution............................ 38 General character..................................... 38 Distinguishing features................................. 39 Microscopical character................................. 39 Age and origin........................................ 40 Rhyolite No. 6............................................ 40 Occurrence and distribution............................ 40 General character..................................... 40 Microscopical character................................. 40 Basalt bodies in rhyolite No". 6.......................... 40 Plagioclase basalt No. 2..................................... 41 Occurrence and distribution............................ 41 Microscopical character................................. 41 Age and origin........................................ 42 Rhyolite No. 7............................................ 42 Occurrence and distribution............................ 42 Microscopical character................................. 42 RhyoliteNo.8............................................ 42 Occurrence and distribution............................ 42 Microscopical character................................. 42 Basalfacies............................................ 43 Plagioclase basalt No. 3..................................... 44 Occurrence and distribution............................ 44 Microscopical character................................. 44 Rhyolite No. 9.......................................... 44 Occurrence and distribution.......................... 44 Microscopical character. .............................. 45 Rhyolite No. 10........................'................. 45 Occurrence and distribution.......................... 45 General character..................................... 45 Microscopical character. .............................. 46 Plagioclase basalt No. 4................................... 46 Occurrence and distribution.......................... 46 Microscopical character............................... 47 Tuff No. 1.............................................. 47 Occurrence and distribution.......................... 47 Microscopical character................................. 48 Age and origin...................................... 48 CONTENTS. 5 PART I. General geology Continued. Tertiary volcanic rocks Continued. Lava flows and tuffs Continued. Detailed description Continued. Page. Rhyolite No. 11......................................... 49 Occurrence and distribution.......................... 49 General character..................................... 49 Microscopical character............................... 49 Rhyolite No. 12......................................... 50 Occurrence and distribution.......................... 50 General character..................................... 50 Microscopical character. .............................. 50 Age and origin...................................... 51 Rhyolite No. 13......................................... 51 Occurrence and distribution.......................... 51 General character..................................... 51 Microscopical character............................... 51 ; Rhyolite No. 14......................------------.------ 52 Rhyolite No. 15. ........................................ 52 Occurrence and distribution.......................... 52 Microscopical character............................... 52 Rhyolite No. 16........................................... 53 Plagioclase basalt No. 5...................................' 53 Quartz latite............................................ 54 Definition............................................ 54 Occurrence and distribution.......................... 54 General character..................................... 54 Microscopical character.. ............................. 54 Tuff No.2... ..............!.................,............' 55 Quartz basalt............................................. 55 Occurrence and distribution.......................... 55 Microscopical character. ...........^.................. 55 Age and origin........................................ 56 Intrusive rocks.................................................. 56 Rhyolite porphyry....................................... 56 Plagioclase basalt dikes.................................. 57 Occurrence and distribution.......................... 57 General character..................................... 57 Microscopical character. .............................. 58 Age, and relation to flows............................. 58 Leucite basanite.......................................... 58 Definition............................................ 59 Occurrence and distribution.......................... 59 Microscopical character................................. 59 Summary of the Tertiary eruptions................................. 60 Quaternary alluvium.................................................. 62 Geologic structure..................................................... 63 Outline........................................................... 63 Tilting and faulting............................................... 63 Terminology................................................... 63 Criteria for