University of Nevada Reno Geology and Mineral Deposits of the Northern Half of the Mt. Tobin Mining District, ✓ Pershing County, Nevada P thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, by Richard Michael Perry Ppri 1, MINES UBRAJUC T K e & m The thesis of Richard Michael Perry is approved; University of Nevada Reno April, 1385 ii ABSTRACT The Northern half of the Mt. Tobin Mining District, 45 miles south of Winnernucca in the Tobin Range, produced 1073 flasks of mercury and minor silver and gold from deposits located near the northern margin of a late Tertiary vo1cano-tect oni c g ra ben. This graben is bounded to the north by a fault which juxtaposes complexly deformed sediments of the late Paleozoic Havallah sequence with Triassic sediments and Tertiary volcanics which fill the graben. Two types of mineralization are present; <1) Tertiary epithermal mercury—gold-siIver mineralization which is structurally controlled by the graben-bounding fault and <£> stratiform volcanogenic silver mineralization in the Havallah sequence. Analyses of 171 samples of Tertiary mineralized rocks indicate a vertical zoning of gold, silver, arsenic, antimony and mercury in vein and fossil hot springs deposits. i i i ACKNOWLEDGEMENTS The author is indebted to Larry Larson, Rich Schweickert and Dan Taylor for their critical reviews of this thesis. The not so subtle humor and threats of Dr. Larson were an inspiration to the author during the writing of this manuscript. Appreciation is also extended to Thomas Cudzilo, District Manager of Nicor Mineral Ventures, Inc., Sparks, Nevada, for approving funding for this thesis project. The Mt. Tobin District was suggested as a thesis by Tom Kuhi, Senior Geologist at Nicor. Bill Fuchs, also of Nicor, provided use of his ore microscope and many excellent suggest ions. Special thanks go to my wife Lisa, who provided love, understanding, and moral support during the span of this project. IV TABLE OF CONTENDS □age ABSTRACT . i i i ACKNOWLEDGEMENTS . LIST OF ILLUSTRATIONS LIST OF TABLES INTRODUCTION . PURPOSE ................................... .. 1 GEOGRAPHY .......... ................. 2 FIELD METHODS' AND LAB PROCEDURES. ....... 4 PREVIOUS WORK . ......... ......... 5 HISTORY AND PRODUCTION. ............ 7 GEOLOGIC SETTING........... 9 STRATIGRAPHY AND STRUCTURE .................. 12 SEDIMENTARY AND VOLCANIC UNITS. ........ 12 Havailah Sequence. ............ X•« o!— •J o Introduction and distribution, . X u_ Stratigraphic description. ........... IS Structure. ........... .. 19 Discussion of structural chronology. 27 China Mountain Formation .... ....... £8 Introduction and distribution. , £8 Stratigraphic description. ....... £8 Structure. 3£ Discussion of structural chronology. 36 Relation of Havailah to China Mountain structures . ............. 36 Matches Pass Formation .......... 40 Introduction and distribution. 40 Stratigraphic description. , 40 Caetano Tuff ........................... 42 Introduction and distribut ion. 42 Strat i graph ic description. ........... 43 Structure. ................. ...... 43 Andesite—Dacite Flows and Flow Breccias. 43 Introduction and distribution. ■ • § - ■ 43 Strat1 graphic description. ....... 44 Structure........... ..................... 44 Fish Creek Mountains Tuff. ........... 45 Introduction and distr ibut ion........... 45 Stratigraphic description. ....... 45 Structure........... ..................... 46 Basalt . ................................. .. 46 Introduction and distribution. 46 Strat igraphic description............... 48 Structure............................ - * 48 V INTRUSIVE R O C K S ........................ 49 Needle Peak Stock. ................... 49 Descript ion.............................. 49 Structure. ............. ........ 49 Dikes arid sills related to Koipato Group . 51?. Descript ion.............................. 50 Diabase Dikes. .......................... 52 Description........................ TOBIN VOLCANO-TECTONIC GRABEN................. .. 54 Introduction ........................ 54 Structure. ........... .. 54 ECONOMIC GEOLOGY INTRODUCTORY STATEMENT 60 TERTIARY EPITHERMAL MERCURY-GOLD SILVER MINERALIZATION.................................. 60 Gold-Bearing Veins ...................... > 60 Rockhouse adit ............. ...... Quartz-Barite Veins with Silver and Copper Sulfides. .................... .. 69 Blue Lead mine .......................... 69 Badger mine. ....... 73 Unnamed adits. .................... 75 Fossil Hot Spring Mercury Mineralization. 77 Mt. Tobin mine ............. 77 Last Chance mine . ................. S3 North Fork mine. ............ as Unnamed prospect ........... .. 91 Origin of mercury deposits ............. 94 EXHALATIVE STRATIFORM SILVER MINERALIZATION . 95 Queenstake prospect........... .. 95 Origin of mineralization ........ 96 GEOCHEMISTRY. ................. 101 Contour Maps of Metal Values ....... 101 Correlation of Metal Values. ....... 108 Scatter gr a m s ........................ .. 110 Discussion of Geochemical Data ........... 111 CONCLUSIONS AND RECOMMENDATIONS. 119 REFERENCES CITED APPENDIX .................... INDIVIDUAL SAMPLE ASSAYS VI LIST OF ILLUSTRATIONS Plate Pa5e 1. Geologic map of the Northern half of the Mt. Tobin district............ > in pocket £. Cross sections. ................. .. in pocket 3. Sample location map ..... ......... in pocket Figure i. Location Nap. ........................ .. • ■ £. Stratigraphic Column........................ 13 3. Outcrop of Havallah in North-Central Nevada 14 4. Photomicrograph of Havallah Argillite . 15 5a. Isoclinal Fold in Havallah Chert........... £1 o 5b. Isoclinal Fold in Havallah Chert. ..... L— u. 6. Photomicrograph of cleavage in Havallah . £3 7. Pi Diagram of Fold in Havallah. ......... £4 8. Pi Diagram of Bedding Attitudes in Havallah £5 9. Contoured Pi Diagram . .................... £6 HZi. Photomicrograph of China Mountain Formation T u f f . ..................... ^ . 30 11. Photomicrograph of China Mountain Formation Pebble Conglomerate ............. 31 l£a. Photomicrograph of Cleavage in China Mountain Formation Tuff .......... 34 l£b. Isoclinal Fold in China Mountain Formation. 34 13. Asymmetric F3 Fold in China Mountain Formation ................. 35 14. Pi Diagram of Bedding and Foliations in Ch ina Mounta in Format ion.................... 37 15. Contoured Pi Diagram............. .. 38 16. Photomicrograph of Natchez Pass Biomicrite. 41 17. Photomicrograph of Fish Creek Mountains Tuff. ........... .. 47 18. Photomicrograph of Pyroxene basalt Flow . 47 19. Photomicrograph of Koipato Dike ...... 51 £0. Mao Showing East-West Volcano-Tectonic Depression in North—Central Nevada. .... 55 £1. Outcrop of gold-bearing quartz vein .... 61 ££. Polished section of gold—bearing quartz vein 63 £3. Geologic mao of Rockhouse adit ........... 64 £4. Photo of quartz vein underground at Rockhouse adit................. .. 66 £5. Thin section of quartz after calcite vein . 67 £6. Geologic map of Blue Lead mine........... .. 71 £7. Polished section of ore from Blue Lead mine 7£ £8. Geologic map of Badger mine ............... 74 £9. Geologic map of Unnamed adit............... 76 30. Geologic mao of Mt. Tobin mine. ...... 78 31. Geologic map of East workings .........- - 81 vii d i d . * Geologic map of Snake Pit adit. .... 82 . • B 86 C j L j * Geologic map of Last Chance mine. • 34. Polished section of cinnabar from Last Chance mine ....... ........... 87 35. Geologic map of North Fork mercury mine - - - 89 36. Mercury retort at North Fork mine . 90 37. Geologic map of Unnammed prospect . 92 38. Thin section of silicially altered tuff with hydrothermal barite ......... 93 39. Polished section of folded quartz stringer in Hava11ah argillite ...................... 97 40. Geochemical contour map of gold .... 41. Geochemical contour map of silver . ■ . ■ ■ - 103 42. Geochemical contour map of arsenic. a a 104 43. Geochemical contour map of antimony . ■ ■ * 105 44. Geochemical contour map of mercury. 106 45. Scattergram of gold vs. elevation . i 12 46. Scattergram of silver vs. elevation . a a ■ 113 47. Scatterqram of arsenic vs. elevation. B B B 114 48. Scattergram of antimony vs. elevation . a u B 115 49. Scattergram of mercury vs. elevation. B B B 116 50. Relative values vs. elevations for gold silver, arsenic, antimony and mercury . H 117 LIST GF TABLES i. Assay results from pyritic quartz veins . 62 65 CL a Assay results from Rockhouse adit . 3. Assay results from Blue Lead Mine . 70 4. Assay results from Badger Mine. 75 cr 75 -J b Assay results from Unnamed adit. 6. Assay results from West workings. 81 7. Assay results from Snake Pit adit . 81 6. Assay results from 1957 DMEA drilling at Mt. T.::>bin Mine. 84 9. Mercury production at Mt. Tobin Mine from 1936 to 1941................. .. ........... 84 10. Assay results from Last Chance Mine . 85 i i. Assay results from North Fork Mine......... 88 12. Assay results from Unnamed mercury prospect 94 13. Assay results from Queenstake prospect. 96 14. Assay resuIts from strati form sulfide­ bearing bed in Hava11ah ................... 98 15. Correlation coefficient matrix for 196 samples of Au, Aq, As, Sb, Hg ...... 110 VI11 1 INTRODUCTION! PURPOSE The primary objective of this study was to map the Northern Mt. Tobin district and each of the mines and prospects within the area to determine the relationship of mineralicat ion and alteration to the major structural features of the area— chief of which is a northwest trending vo1cano-tect on i c graben. Along