Genetic environment of germanium-bearing gold-silver vein ores from the Wolyu mine,Republic of Korea |
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| Authors: | Seong-Taek Yun Chil-Sup So Sang-Hoon Choi Kevin L Shelton Ja-Hak Koo |
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| Institution: | (1) Department of Geology, Korea University, 136-701 Seoul, Republic of Korea;(2) Stable Isotope Geology and Geochemistry Group, Department of Geological Sciences, University of Missouri-Columbia, 65203 Columbia, Missouri, USA;(3) Center for Mineral Resources Research, Korea University, 136-701 Seoul, Republic of Korea;(4) Present address: Department of Mineral & Energy Resources Engineering, Semyung University, 390-230 Jecheon, Republic of Korea |
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| Abstract: | The Wolyu mine is one of the largest vein-type gold-silver-bearing epithermal systems in the Youngdong district and is the first gold-silver deposit in Korea found to contain significant germanium, in the form of argyrodite (Ag8GeS6). Mineralized veins (78.9 ± 1.2 Ma) crosscutting Late Cretaceous hostrock tuff and quartz porphyry (81.5 ± 1.8 Ma) consist of three stages of quartz and carbonates, the first of which contains pyrite, basemetal sulfides and Au-Ag-minerals. Stage I Au-Ag-Ge-mineralized veins show a systematic variation of mineral assemblage with time: (1) quartz + pyrite; (2) quartz + pyrite + sphalerite + electrum + argentite; (3) carbonate + quartz + sphalerite + electrum + argentite; (4) carbonate + native silver + argentite + Ag-sulfosalts + argyrodite + sphalerite. Calculated values of temperature and sulfur activity are: assemblage (1), 360-280°C and 10–7-10–10; (2), 280-210°C and 10–10-10–14; (3), 210-180°C and 10–14-10–16; (4), 180-155°C and 10–17-10–18. These data, the frequent association of gold with sulfides, and the abundance of pyrite in alteration zones indicate that decreasing sulfur activity and cooling were important in triggering gold deposition. Hydrogen and oxygen isotope compositions of ore fluids display a systematic variation with increasing time. Within the main Ag-Au-Ge mineralization,  D and
18O values decrease with the transition from quartz to carbonate deposition (from -78 and –2.8% to –90 and –8.7%., respectively), indicating increasing involvement (mixing) of less evolved meteoric water which resulted in progressive cooling and dilution of ore fluids in the shallow ( 370–600 m) Wolyu epithermal system. |
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