Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1-1-2002 Petrological, mineralogical, fluid inclusion and stable isotope characteristics of the Tuvatu gold-silver telluride deposit, upper Sabeto River area, Fiji Nancy L. Scherbarth Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Recommended Citation Scherbarth, Nancy L., "Petrological, mineralogical, fluid inclusion and stable isotope characteristics of the Tuvatu gold-silver telluride deposit, upper Sabeto River area, Fiji" (2002). Retrospective Theses and Dissertations. 21314. https://lib.dr.iastate.edu/rtd/21314 This Thesis 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]. Petrological, mineralogical, fluid inclusion and stable isotope characteristics of the Tuvatu gold-silver telluride deposit, upper Sabeto River area, Fiji by Nancy L. Scherbarth A thesis submitted to the graduate faculty in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Major: Geology Program of Study Committee: Paul G. Spry, Major Professor Karl E. Seifert C. Lee Burras Iowa State University Ames, Iowa 2002 11 Graduate College Iowa State University This is to certify that the master's thesis of Nancy Lee Scherbarth has met the thesis requirements of Iowa State University Signatures have been redacted for privacy lll This thesis is dedicated in loving memory to my stepfather, Norman H. Rybka, who always showed support and interest in my educational and personal endeavors. iv TABLE OF CONTENTS CHAPTER 1. GENERAL INTRODUCTION 1 Thesis organization 2 References 2 CHAPTER 2. PETROLOGICAL, MINERALOGICAL, FLUID INCLUSION, AND STABLE 4 ISOTOPE CHARACTERISTICS OF THE TUV ATU GOLD-SIL VER TELLURIDE DEPOSIT, UPPER SABETO RIVER AREA, FUI Abstract 4 Introduction 6 Regional Geological Setting 7 Geology of the Tuvatu Area 10 Petrochemistry of Igneous Rocks 11 Petrography 11 Methodology and major and trace element geochemistry 11 Precious Metal Mineralization of the Tuvatu Prospect 15 Paragentic sequence 16 Tuvatu and H lodes 19 Murau and SKL lodes 19 Nasivi lodes 21 Upper Ridges lodes 21 Plant Site lodes 22 Nubunidike and Davui lodes 23 Mineral Compositions 23 Silicates 24 Sulfides and sulfosalts 25 Pyrite 25 Galena 27 Tetrahedrite group minerals (fahlores) 27 Native gold 27 Tellurides 28 Vanadium oxides 30 Fluid Inclusion Study 31 Nature of the inclusions 32 Heating and freezing experiments 33 Pressure correction 37 Stable Isotope Studies 38 Oxygen and hydrogen isotopes 39 Sulfur isotopes 40 Discussion 41 Source of the ore-forming fluids 41 Sources of sulfur and metals, and composition of the hydrothermal fluids 43 Comparison between the Tuvatu and Emperor ore systems 45 Genetic model for mineralization 47 References 49 Figures 1-26 58 Tables 1-12 86 v CHAPTER 3. GENERAL SUMMARY 102 APPENDIX A. SAMPLE DESCRIPTIONS AND MINERALOGY OF 104 INDNIDUAL SAMPLES APPENDIX B. ELECTRON MICROPROBE ANALYSES OF SULFIDES, 113 SULFOSALTS, TELLURIDES, AND NATNE GOLD APPENDIX C. ELECTRON MICROPROBE ANALYSES OF OXIDES 140 AND SILICATES ACKNOWLEDGMENTS 157 CHAPTER!. GENERALINTRODUCTION The spatial and genetic relationship between porphyry copper/molybdenum mineralization and epithermal mineralization has been widely recognized (e.g., Richards, 1995). This relationship occurs at the deposit scale where it can be demonstrated that one porphyry system was responsible for both the epithermal gold and porphyry molybdenum/copper mineralization. Examples of this relationship include: Emperor (Eaton and Setterfield, 1993), Golden Sunlight, Montana (Spry et al., 1996; 1997), Porgera (Richards and Kerrich, 1993), and Far Southeast-Lepanto, Philippines (Hedenquist et al., 1998). However, the spatial relationship between porphyry systems and epithermal systems can also be demonstrated on a regional scale. For example, the well-known Colorado Mineral Belt is host to porphyry molybdenum (e.g., Climax, Urad-Henderson) and epithermal gold-telluride deposits (e.g., Central City, Bessie G). In Fiji, several gold occurrences, hosted in alkalic rocks (e.g., Emperor, Mt. Kasi, Tuvatu, Kingston, Banana Creek), are localized along the >250 km northeast trending Viti Levu lineament. Eaton and Setterfield (1993) demonstrated that a genetic relationship exists between subeconomic porphyry copper-gold mineralization at depth in the Nasivi shear zone, near the center of the Tavua caldera. The Emperor deposit occurs at the intersection of the Nasivi shear and the Viti Levu lineament. A genetic and spatial relationship between epithermal gold telluride and porphyry copper mineralization is also likely in the upper Sabeto River area, eastern Viti Levu. Although a considerable amount is known about the geology of alkaline igneous rock-related gold telluride deposits (summary in Richards, 1995), exploration tools utilized in the search for these deposits are constrained by genetic models of ore formation. Such models depend on geological, petrological, and mineralogical data, as well as geochemical information derived from radiogenic isotope, stable isotope (S, C, 0, and H), and fluid inclusion studies. The present study enlarges on the data collected by Ashley and Andrew (1989), Corlett and Merchant (1996), Zhang 2 (1996), Hatcher (1998), and A-Izzeddin (1998) for the Tuvatu prospect. The goals of this project are: 1. To classify the various intrusive and extrusive rocks; 2. To characterize alteration assemblages associated with the various stages of gold-bearing mineralization (e.g .. silicification, sericitization, phyllic, potassic, etc.); 3. To determine the paragenesis and distribution of tellurides, sulfides, carbonates, and silicates throughout the deposit; 4. To determine the temperature of formation, composition, and source of the ore-forming fluids; and 5. To provide Emperor Gold Mining Company with substantial information that can be used to develop exploration strategies at the mine and regional scale. Thesis organization This thesis contains one manuscript entitled "Petrological, mineralogical, fluid inclusion and stable isotope characteristics of the Tuvatu gold-silver telluride deposit, Upper Sabeto River, Fiji," which will be submitted to Economic Geology. The manuscript has been formatted to comply with the requirements of the journal. Figures and tables referred to within the text are included at the end of the manuscript, following the reference section. Additional data appendices follow the General Summary. REFERENCES A-Izzeddin, D., 1998, The Tuvatu gold project, western Viti Levu: Pacific Exploration Technology (PET 98), Nadi, Fiji, September 1998, Abstract Volume, p. 29-30. Ashley, P.M., and Andrew, A.S., 1989, Petrographic, fluid inclusion and stable isotope investigation of a suite of samples from the Tuvatu prospect, Fiji: C.S.I.R.0. Division of Exploration Geoscience, Restricted Report 50R, 36 p. Corlett, G. and Merchant, R., 1996, Petrography of drill core samples from diamond drill holes 13 and 14, Tuvatu prospect, Viti Levu, Fiji: Terry Leach and Co. Consultants, Unpublished Internal Report to Geopacific Ltd./Emperor Goldmines Ltd., 52 p. 3 Eaton, P.C., and Setterfield, T.N., 1993, The relationship between epithermal and porphyry hydrothermal systems within the Tavua Caldera, Fiji: Economic Geology, v. 88, p. 1053-1083. Hatcher, R., 1998, Relation of structures, alteration and mineralisation at the Tuvatu gold prospect, Viti Levu, Fiji islands: Unpublished Bachelor of Applied Science Thesis, Brisbane, Queensland Institute of Technology, 151 p. Hedenquist, J.W., Arribas, A., Jr., and Reynolds, T.R., 1998, Evolution of an intrusion-centered hydrothermal system: Far Southeast-Lepanto porphyry and epithermal Cu-Au deposits, Philippines: Economic Geology, v. 93, p. 373-404. Richards, J.P., 1995, Alkalic-type epithermal gold deposits-review, in Thompson, J.F.H, ed., Magmas, fluids, and ore deposits: Mineralogical Association of Canada Short Course Series, v. 23, p. 367-400. Richards, J.P., and Kerrich, R., 1993, The Porgera gold mine, Papua New Guinea: magmatic hydrothermal to epithermal evolution of an alkalic-type precious metal deposit: Economic Geology, v. 88, p. 1017-1052. Spry, P.G., Foster, F., Truckle, J., and Chadwick, T.H., 1997, The mineralogy of the Golden Sunlight gold-silver telluride deposit, Montana, U.S.A.: Mineralogy and Petrology, v. 53, p.143-164. Spry, P.G., Parades, M.M., Foster, F., Truckle, J.S., and Chadwick, T.H., 1996, Evidence for a genetic link between gold-silver telluride and porphyry molybdenum mineralization at the Golden Sunlight deposit, Whitehall, Montana: fluid inclusion and stable isotope studies: Economic Geology, v. 91, p. 507-526. Zhang, L., and Merchant, R., 1996, Petrographic analyses of drill core from holes 36, 37, 41, 43, 45, 46, 47, and 48 Tuvatu prospect, Viti Levu, Fiji: Terry Leach and Co. Consultants Unpublished Internal Report to Geopacific Ltd./Emperor Gold Mining Company Ltd., 90 p. 4 CHAPTER 2. PETROLOGICAL, MINERALOGICAL, FLUID INCLUSION AND STABLE ISOTOPE CHARACTERISTICS OF THE TUVATU GOLD-SIL VER TELLURIDE DEPOSIT, UPPER SABETO RIVER AREA, FIJI A paper to be submitted to Economic Geology Nancy L. Scherbarth and Paul G. Spry Abstract The Tuvatu gold-silver