UNLV Retrospective Theses & Dissertations 1-1-2001 The geochemistry of gold-bearing and gold-free pyrite and marcasite from the Getchell gold deposit, Humboldt County, Nevada Kelli Diane Weaver University of Nevada, Las Vegas Follow this and additional works at: https://digitalscholarship.unlv.edu/rtds Repository Citation Weaver, Kelli Diane, "The geochemistry of gold-bearing and gold-free pyrite and marcasite from the Getchell gold deposit, Humboldt County, Nevada" (2001). UNLV Retrospective Theses & Dissertations. 1344. http://dx.doi.org/10.25669/rwv9-1zgy This Thesis is protected by copyright and/or related rights. It has been brought to you by Digital Scholarship@UNLV with permission from the rights-holder(s). You are free to use this Thesis in any way that is permitted by the copyright and related rights legislation that applies to your use. 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Further reproduction prohibited without permission. THE GEOCHEMISTRY OF GOLD-BEARING AND GOLD-FREE PYRTTE AND MARCASITE FROM THE GETCHELL GOLD DEPOSIT, HUMBOLDT COUNTY, NEVADA by Kelli D. W eaver Bachelor of Science Ohio Wesleyan University 1992 A thesis submitted in partial fulfillment of the requirements for the Master of Science Degree Department of Geoscience College of Sciences Graduate College University of Nevada, Las Vegas November 2001 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number 1409054 UMI UMI Microform 1409054 Copyright 2002 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Leaming Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Thesis Approval UNTV The Graduate College University of Nevada, Las Vegas November 21 2001 The Thesis prepared by Kelli D. Weaver- Entitled The Geochemistry of Gold-bearing and Gold-free Pyrite and Marcasite from the Getchell Gold Deposit, Humboldt County, Nevada is approved in partial fulfillment of the requirements for the degree of Master of Science ____________________________________ i . H Exiiminatum Coniimttee Chair Dean of the Graduate Cotkge W#" A v Examination Committee Member V g ( ___ Examination Committee It^einber Cradnate College Faculty Reprefentative PR/101-53/H«) 11 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT The Geochemistry of Gold-Bearing and Gold-Aee Pyrite and Marcasite from the Getchell Gold Deposit; Humboldt County, Nevada by Kelli D. Weaver Dr. Jean S. Cline, Examination Committee Chair Professor of Geoscience University of Nevada, Las Vegas Pétrographie and geochemical investigations of pyrite and marcasite from the Getchell Carlin-type gold deposit show that elevated concentrations of a characteristic suite of trace metals correlate with ore-stage pyrite morphology. Secondary ion mass spectrometry analyses revealed a significant positive correlation between As and Au in ore-stage Fe-sulfide minerals. High-resolution transmission electron microscopy analyses revealed that gold-bearing Fe-sulfide crystals are arsenic-rich marcasite, rather than pyrite. These analyses failed to identify gold as microinclusions in ore-stage pyrite/ marcasite, and support the conclusion that gold is present in solid solution. Analyses reflect the chemistry of fluids responsible for precipitation of the pyrite and marcasite. Near stoichiometric, pre-ore pyrite precipitated fi'om fluids tfiat were not saturated in Hg, Tl, As, Cu, Au and Sb. Ore-stage pyrite textures suggest rapid precipitation ftom fluids that contained Tl, As, Cu, Au and Sb. Late-ore stage marcasite indicates that late fluids continued to transport significant As. m Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS ABSTRACT...........................................................................................................................iü LISTOFHCURES................................................................................................................. vi LIST OF TABLES................................................................................................................ viü ACKNOWLEDGMENTS..................................................................................................... ix CHAPTER 1 INTRODUCTION.............................................................................................1 CHAPTER 2 CARLIN-TYPE GOLD DEPOSITS..................................................................4 Characteristics of Carlin-Type Gold Deposits ........................................................... 4 CHAPTER 3 THE GETCHELL GOLD DEPOSIT................................................................. 7 Location and General Regional Geology ..................................................................7 Getchell Stratigraphy ................................................................................................ 9 Granodiorite Intrusion............................................................................................ 12 Structural Controls of the Getchell Au Deposit..................................................... 13 Carlin-Type Gold Mineralization at Getchell ......................................................... 13 CHAPTER 4 SAMPLING AND ANALYTICAL METHODS............................................ 16 Pétrographie Analyses ............................................................................................ 18 Electron Microprobe Analyses ................................................................................ 18 Secondary Ion Mass Spectrometry ..........................................................................19 High-Resolution Transmission Microscopy ........................................................... 21 Cathodoluminescence ............................................................................................. 22 Statistical Analysis .................................................................................................. 22 CHAPTER 5 MINERAL PARAGENESIS...........................................................................23 Stage 1 — Pre-Ore Stage Mineral Assemblage ........................................................ 24 Discussion of Pre-Ore Paragenesis.........................................................................31 Stage 2 - Ore-Stage Mineral Assemblage ...............................................................31 Discussion of Ore-Stagp Paragenesis ......................................................................44 Stage 3 - Late-Ore Stage Mineral Assemblage ....................................................... 46 Discussion of Late-Ore Stage Paragenesis .............................................................. 56 IV Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 6 TRACE ELEMENT STUDY AND STATISTICAL EVALUATION.............. 61 Pyrite Geochemistry ..................................................................................................61 Discussion of Trace Element Analyses.................................................................... 69 Statistical Analysis of Sulfide Geochemistry ........................................................... 70 C luster Analysis of Sulfide Geochemistry ............................................................... 83 CHAPTER 7 GOLD QUANTIFICATION AND LOCATION...........................................