Geochemical and Geochronological Constraints on Mineralization

GEOCHEMICAL AND GEOCHRONOLOGICAL CONSTRAINTS ON MINERALIZATION

WITHIN THE HILLTOP, LEWIS, AND BULLION MINING DISTRICTS, BATTLE

MOUNTAIN-EUREKA TREND, NEVADA

CHRISTOPHER RONALD KELSON

(Under the Direction of Douglas E. Crowe)

ABSTRACT

The Hilltop, Lewis, and Bullion mining districts (northern Shoshone Range, Nevada) are

part of the Battle Mountain-Eureka trend and contain both vein- and porphyry-type deposits.

New geochronology data from igneous rocks, porphyry-style Cu-Mo mineralization, and vein-hosted minerals elucidate the relationship between magmatic activity, hydrothermal fluid flow, and mineralization. Mostly felsic intrusive rocks were emplaced throughout the area between 39.3 ± 0.4 and 38.1 ± 0.4 Ma and weak Cu + Mo porphyry-style mineralization is associated with some of the intrusions. Ages of igneous rocks are nearly coincident with molybdenite ages, supporting a relation between pluton emplacement and porphyry Cu-Mo mineralization. Ages of quartz vein-hosted gold (35.9 ± 0.1 Ma, Hilltop deposit) and base-metal minerals (38.3 ± 0.07 Ma, Gray Eagle mine), established via ages of associated gangue clay minerals, are younger than nearby intrusive igneous rocks and may suggest the vein mineralization formed during prolonged hydrothermal activity related to igneous rock emplacement. Quartz vein-hosted sulfide minerals from the northern Shoshone Range are isotopically

34 similar (δ SCDT range from -6 to +9 per mil) to sulfide minerals from other Cu-Mo porphyry

deposits and Cordilleran vein-type deposits, supporting a mostly magmatic sulfur source.

Carbon isotope data from vein gangue carbonate minerals also support a magmatic origin for

ore-forming fluids with variable contributions from host rock organic matter or carbonate rocks

13 (δ CPDB range from -0.2 to –11.6 per mil); carbonate oxygen was derived mainly from

18 magmatic fluids (δ OVSMOW range from –1.3 to +14.4 per mil). Primary fluid inclusion data

(salinity range from 0 to 6.4 equiv. wt. % NaCl; Th range from 109-425°C) and measured

18 δ OVSMOW data (-0.97 to +17.3‰) suggest the ore-bearing vein quartz formed from variable

18 amounts of meteoric and magmatic components (calculated δ OVSMOW -16.2 to +13.3‰).

Depositional temperatures of base metal minerals, calculated using sulfide sulfur isotope geothermometry, range from 249-502°C and agree with vein quartz primary fluid inclusion Th values.

Geochronology, stable isotope, and geothermometry data show that vein- and porphyry- type mineralization is genetically related to Eocene magmatism and that some vein mineralization temperatures exceeded relatively low-temperature epithermal conditions and were more closely related to higher temperature porphyry-style processes.

INDEX WORDS: Base Metals, Battle Mountain-Eureka Trend, Bullion District, Carbon, Carbonate, Copper, Cu, Eocene Magmatism, Epithermal, Fluid Inclusions, Geochronology, Geothermometry, Gold, Hilltop District, Hydrothermal, Lewis District, Mineralization, Mo, Molybdenite, Nevada, Oxygen, Porphyry, Quartz, Shoshone Range, Silver, Stable Isotopes, Sulfide, Sulfur, Vein

GEOCHEMICAL AND GEOCHRONOLOGICAL CONSTRAINTS ON MINERALIZATION

WITHIN THE HILLTOP, LEWIS, AND BULLION MINING DISTRICTS, BATTLE

MOUNTAIN-EUREKA TREND, NEVADA

CHRISTOPHER RONALD KELSON

B.S., University of Utah, 1994

M.S., Brigham Young University, 1999

A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial

Fulfillment of the Requirements for the Degree

DOCTOR OF PHILOSOPHY

ATHENS, GEORGIA

2006

Christopher Ronald Kelson

GEOCHEMICAL AND GEOCHRONOLOGICAL CONSTRAINTS ON MINERALIZATION

WITHIN THE HILLTOP, LEWIS, AND BULLION MINING DISTRICTS, BATTLE

MOUNTAIN-EUREKA TREND, NEVADA

CHRISTOPHER RONALD KELSON

Major Professor: Douglas E. Crowe

Committee: Robert B. Hawman Michael F. Roden Paul A. Schroeder Sandra J. Wyld

Electronic Version Approved:

Maureen Grasso Dean of the Graduate School The University of Georgia May 2006

DEDICATION

This dissertation, representing five years’ worth of being away from home and family while either working in the field or spending long days, weekends, and odd hours in the laboratory and office, is dedicated to my wife Christa. Without her love, support, and patience, I would not have made it through this.

ACKNOWLEDGEMENTS

This research would not have been possible without the generous support of the Cortez

Joint Venture, and very special thanks to Mr. Robert C. Hays, Jr., Technical Services

Superintendent, Cortez Joint Venture. This research was also funded by the Society of

Economic Geologists (Hugh E. McKinstry Grant), the Geological Society of America (Grant No.

7180-02), and the Department of Geology, University of Georgia. Permission of the Cortez Joint

Venture to publish this investigation is gratefully acknowledged. Thanks to: Dr. Kenneth A.

Foland (OSU), Dr. Matthew T. Heizler (NMT), and Mr. Thomas D. Ullrich (UBC) for their assistance and insight with the 40Ar/39Ar data. Dr. Chris Romanek (SREL) and Mr. Tom

Maddux (UGA) assisted with the organic carbon isotope data. Dr. Zachary D. Sharp (UNM) provided the silicate oxygen isotope analyses. Richard Markey (AIRIE, Colorado State

University) provided the Re-Os analyses. Ms. Julia Cox and Mr. Chris Fleisher (UGA) assisted with stable isotope and electron microprobe analyses, respectively.

I would especially like to thank the members of my dissertation committee for many informative discussions regarding every facet of this study, and for their review of this dissertation.

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS...... v

LIST OF TABLES...... viii

LIST OF FIGURES ...... x

CHAPTER

1 INTRODUCTION ...... 1

REFERENCES...... 9

2 GEOCHRONOLOGY AND GEOCHEMISTRY OF THE HILLTOP, LEWIS, AND

BULLION MINING DISTRICTS AND SURROUNDING AREA, BATTLE

MOUNTAIN-EUREKA TREND, NEVADA ...... 11

Abstract ...... 12

Purpose of Study ...... 13

General Geology of the northern Shoshone Range ...... 14

Description of Mines in this Study...... 14

Analytical Methods ...... 20

Results ...... 24

Discussion ...... 37

Conclusion...... 48

Acknowledgements ...... 49

References ...... 51

3 GEOCHEMICAL AND GEOCHRONOLOGICAL CONSTRAINTS ON

MINERALIZATION WITHIN THE HILLTOP, LEWIS, AND BULLION

MINING DISTRICTS, BATTLE MOUNTAIN-EUREKA TREND, NEVADA ..54

Abstract ...... 55

Introduction ...... 57

Regional Geologic Setting...... 62

Northern Shoshone Range and District Geology ...... 65

Battle Mountain – Eureka trend ...... 67

Northern Shoshone Range Mineral Deposits ...... 68

Methods...... 81

Intrusive Igneous Rocks ...... 87

Geochronology ...... 98

Relationship between Magmatism and Mineralization...... 105

Discussion: Northern Shoshone Range Vein-Hosted Mineralization ...... 116

Summary and Conclusion ...... 124

Acknowledgements ...... 125

References ...... 126

4 CONCLUSION...... 137

APPENDICES ...... 139

A Geochemical data and location information for northern Shoshone Range samples.139

B 40Ar/39Ar data ...... 188

C Quartz vein-hosted mineral species delineated by sample and deposit...... 208

vii

LIST OF TABLES

Page

Table 2.1: Molybdenite Re-Os data from Tenabo, Hilltop, and Park Saddle areas...... 21

Table 2.2: Selenium-sulfide mineral associated with Hilltop molybdenite...... 27

Table 2.3: 40Ar/39Ar data from the northern Shoshone Range, Nevada...... 28

Table 2.4: Microprobe analyses of ore minerals from the northern Shoshone Range, Lander

County, Nevada...... 33

Table 2.5: Carbon and oxygen stable isotope data from carbonate minerals associated with base-

and precious-metal mineralization, northern Shoshone Range, Lander County,

Nevada ...... 35

Table 2.6: Sulfur stable isotope data from sulfide and sulfate minerals associated with base- and

precious-metal mineralization, northern Shoshone Range, Lander County, Nevada....36

Table 2.7: Sulfur isotope geothermometry data from four mines and prospects, northern

Shoshone Range, Lander County, Nevada...... 47

Table 3.1: Types and orientations of ore-bearing structures and Ag:Au ratios for northern

Shoshone Range vein deposits ...... 69

Table 3.2: Electron microprobe analyses of sulfide minerals from northern Shoshone Range vein

deposits...... 77

Table 3.3: Major and trace element chemical data for northern Shoshone Range igneous rocks .....

...... 82

Table 3.4: δ13C data for organic carbon-bearing rocks, breccias, and fault gouge, northern

Shoshone Range ...... 85

viii

Table 3.5: Summary of all K-Ar, Ar/Ar, and Re-Os geochronology data for northern Shoshone

Range igneous rocks, molybdenite (porphyry) mineralization, and vein-hosted

mineralization...... 100

Table 3.6: Salinity and homogenization temperatures for primary fluid inclusion as well as

oxygen isotope compositions of host vein quartz, northern Shoshone Range vein

deposits...... 107

Table 3.7: δ13C and δ18O data for carbonate gangue minerals and upper plate (?) limestone,

northern Shoshone Range vein deposits...... 112

Table 3.8: δ34S data for sulfide and sulfate minerals from northern Shoshone Range vein

deposits...... 115

Table 3.9: Calculated depositional temperatures based on sulfur isotope fractionation between

two coexisting mineral phases using fractionation equations of Kajiwara and Krause

(1971) ...... 118

LIST OF FIGURES

Page

Figure 1.1: Location of the Great Basin, Nevada, and mineral trends within north-central

Nevada...... 2

Figure 1.2: Location of study area with respect to the Golconda thrust and Roberts Mountains

thrust and major mining trends...... 3

Figure 1.3: Generalized stratigraphic column of the northern Shoshone Range in the vicinity of

Mt. Lewis...... 6

Figure 2.1: Back scattered electron images (BEI) of Betty O’Neal mine samples...... 16

Figure 2.2: Generalized geologic map of the northern Shoshone Range ...... 26

Figure 2.3a: 40Ar/39Ar age spectra and correlation diagrams for GM-3 biotite, DSC BXA clay,

and HT02-1 clay (analyzed by RIL)...... 29

Figure 2.3b: 40Ar/39Ar age spectra and correlation diagrams for GM-6 biotite and hornblende,

GM-15 biotite and hornblende, and T99413-570 biotite (analyzed by NMGRL) ...... 30

Figure 2.4: Carbonate and oxygen isotope data from four mineralized areas within the northern

Shoshone Range, Lander County, Nevada...... 41

Figure 2.5: Carbonate carbon isotope data from four mineralized areas within the northern

Shoshone Range, Lander County, Nevada...... 43

Figure 2.6: Sulfide and sulfate sulfur stable isotope data from six mineralized areas within the

northern Shoshone Range, Lander County, Nevada ...... 45

Figure 3.1: Location of the Lewis, Hilltop, and Bullion mining districts and mineralized areas

studied here, northern Shoshone Range, Lander County, Nevada...... 58

Figure 3.2: Simplified geologic map of the northern Shoshone Range study area, Lander County,

Nevada...... 59

Figure 3.3: Examples of northern Shoshone Range vein mineralization...... 71

Figure 3.4: Aeromagnetic map of the northern Shoshone Range study area and adjacent areas,

band pass filtered to emphasize m