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The Geochemistry and Mineralogy of the Gies Gold-Silver Telluride Deposit, Central Montana

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The Geochemistry and Mineralogy of the Gies Gold-Silver Telluride Deposit, Central Montana Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1992 The geochemistry and mineralogy of the Gies gold- silver telluride deposit, central Montana Xiaomao Zhang Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Geochemistry Commons, and the Mineral Physics Commons Recommended Citation Zhang, Xiaomao, "The eg ochemistry and mineralogy of the Gies gold-silver telluride deposit, central Montana " (1992). Retrospective Theses and Dissertations. 10164. https://lib.dr.iastate.edu/rtd/10164 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand corner and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6" x 9" black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. University Microfilms International A Bell & Howell Information Company 300 North Zeeb Road, Ann Arbor, Ml 48106-1346 USA 313/761-4700 800/521-0600 Order Number 9311645 The geochemistry and mineralogy of the Gies gold-silver telluride deposit, central Montana Zhang, Xiaomao, Ph.D. Iowa State University, 1992 UMI 300 N. Zeeb Rd. Ann Arbor, MI 48106 The geochemistry and mineralogy of the Gies gold-silver telluride deposit, central Montana by Xiaomao Zhang A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: Geological and Atmospheric Sciences Major: Geology Approved: Members of the Committee: Signature was redacted for privacy. Signature was redacted for privacy. Signature was redacted for privacy. For the MajiSr Department Signature was redacted for privacy. For the Graduate College Iowa State University Ames, Iowa 1992 ii TABLE OF CONTENTS page GENERAL INTRODUCTION 1 PAPER I. MINERALOGICAL, FLUID INCLUSION, AND STABLE ISOTOPE STUDIES OF THE GIES GOLD-SILVER TELLURIDE DEPOSIT, JUDITH MOUNTAINS, MONTANA 5 INTRODUCTION 6 GEOLOGY OF THE JUDITH MOUNTAINS 8 LOCAL GEOLOGY 12 PETROCHEMISTRY OF INTRUSIVE IGNEOUS ROCKS 13 MINERALIZATION OF THE GIES DEPOSIT 28 MINERALOGY OF THE VEIN SYSTEMS 32 FLUID INCLUSION STUDY 52 STABLE ISOTOPE STUDIES 57 DISCUSSION 66 PHYSICO-CHEMICAL CONDITIONS OF ORE FORMATION 71 GENETIC MODEL FOR MINERALIZATION 77 CONCLUSIONS 82 REFERENCES 84 APPENDIX. MICROPROBE ANALYSES OF MINERALS 112 iii PAPER II. AQUEOUS TELLURIUM SPECIATION AND THE STABILITY OF GALA VERITE AND HESSITE AT ELEVATED TEMPERATURES 119 INTRODUCTION 120 PREVIOUS STUDIES OF AQUEOUS TELLURIUM SPECIES 122 THE PRINCIPLE OF BALANCE OF IDENTICAL LIKE CHARGES 126 EQUILIBRIUM REACTIONS IN THE SYSTEM Te-O-H 129 STABILITIES OF GOLD AND SILVER TELLURIDES 137 APPLICATIONS TO THE CONDITIONS OF FORMATION OF THE GIES GOLD-SILVER TELLURIDE DEPOSIT, JUDITH MOUNTAINS, MONTANA 149 CONCLUSIONS 151 REFERENCES 153 PAPER III. MINERAL STABILITIES AND SULFUR ISOTOPE DISTRIBUTION IN log fOj-pH SPACE AT ELEVATED TEMPERATURES 166 INTRODUCTION 167 MINERAL STABILITIES IN log fOz-pH SPACE 169 SULFUR ISOTOPE DISTRIBUTION IN log fOj-pH SPACE 178 CONSTANT: EQUILIBRIUM CONSTANTS OF MINERAL-GASEOUS- AQUEOUS PHASE REACTIONS 181 REFERENCES 187 APPENDIX 1. PROGRAM LISTING 191 APPENDIX 2. USERS MANUAL 203 iv GENERAL SUMMARY 212 REFERENCES 215 ACKNOWLEDGEMENTS 217 1 GENERAL INTRODUCTION This dissertation focuses on the geochemistry and origin of gold and silver telluride mineralization at the Gies mine, Montana, where gold and silver telluride-bearing quartz veins occur along the contact between Cretaceous-Tertiary alkaline intrusive rocks and a sequence of sedimentary rocks of Cambrian to Cretaceous age. Gold and silver telluride mineralization is most common in mesothermal deposits of Archean age (e.g., Kalgoorlie, Australia (Markham, 1960; Nickel, 1977), and Sigma, Canada (Robert and Brown, 1986)), and epithermal deposits of Tertiary age (e.g., Cripple Creek, Colorado (Thompson et al., 1985), Emperor, Fiji (Ahmad et al., 1987) and Little Rocky Mountains, Montana (Wilson and Kyser, 1988)). Although most epithermal gold deposits were genetically related to the circulation of meteoric water (Taylor, 1979; Ohomoto, 1986), there is considerable evidence that some components of epithermal gold-silver telluride deposits were derived from igneous source(s) (Porter and Ripley, 1985; Saunders and May, 1986; Ahmad et al., 1987). The relationship between the supposed igneous source and gold mineralization, however, is unclear. In considering the potential source of the ore-forming fluids, the Gies deposit provides an excellent opportunity to evaluate the genetic relationship between magmatic alkaline intrusion and gold-silver telluride mineralization. The possible contribution of magmatic and/or other components (e.g., meteoric water) to the ore-forming fluid will be assessed, and the origin and the physical and chemical conditions of the gold-silver telluride formation will be determined. 2 These objectives have been accomplished by geological, mineralogical and geochemical studies. More specifically, a mineralogical study of vein and associated altered rocks (reflected and transmitted light microscope and electron microprobe) was done to identify complex minerals and mineral assemblages, and to establish their paragenetic sequence; a fluid inclusion study of quartz associated with mineralization was undertaken to determine the temperatures, compositions and salinities of the ore-forming fluids; sulfur, carbon, oxygen and hydrogen isotope studies of the ore and the vein minerals were obtained to determine sources and their origin; a major and trace element study of the alkalic intrusive rocks and the altered rocks was done to determine the geochemical nature and origin of the alkalic complex and to establish the geochemical relationship between intrusive rocks and mineralization; and a thermodynamic study of Au-Ag tellurides and Cu-Fe sulfîdes to determine physical and chemical conditions of gold-silver telluride mineralization at the Gies mine. Despite the relatively common occurrence of gold and silver in many types of deposits, studies concerning the geochemical behavior of aqueous tellurium species and the stability of gold-silver tellurides at temperatures appropriate to the formation of these deposits are limited (D'yachkova and Khodakovskiy, 1968; Ahmad et al., 1987; Jaireth, 1991). The present work employs the "principle of balance of identical like charges" method of Murray and Cobble (1980) and Cobble et al. (1982) to calculate equilibrium constants of reactions in the system Te-O-H at elevated temperatures. These constants are subsequently used to calculate equilibrium constants of the reactions in the systems 3 Au-Te-Cl-S-O-H and Au-Te-Cl-S-O-H for the temperature range 150°-300°C. Log f02-pH diagrams have been constructed for these systems and compared with those constructed previously by D'yachkova and Khodakovskiy (1968), Ahmad et al. (1987), and Jaireth (1991). Conditions affecting the precipitation of calaverite (AuTe2) and hessite (Ag2Te) are also discussed. Log f02-pH diagrams are commonly used to show sulfide mineral stabilities in the hydrothermal environment and to determine physical and chemical conditions of hydrothermal mineralization (Barton and Skinner, 1979). In an effort to facilitate the construction of these diagram, computer programs have been developed to: (1) calculate the equilibrium constants of the reactions involving mineral, gaseous and aqueous species at elevated temperatures; and (2) calculate equilibrium boundaries of mineral reactions in the system Cu-Fe-S-O-H, the solubilities of barite and calcite, and the sulfur isotopic distribution in log f02-pH space at elevated temperatures. These log f02-pH diagrams can be used to constrain conditions of formation of common minerals in the hydrothermal environment. Explanation of Dissertation Format The dissertation consists of three papers; (I) Mineralogical, fluid inclusion, and stable isotope studies of the Gies gold-silver telluride deposit, Judith Mountains, Montana; (II) aqueous tellurium speciation and the stability of
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