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Mesothermal gold vein mineralization of the Samdong mine,Youngdong mining district,Republic of Korea
Authors:Chil-Sup So  Seong-Taek Yun  K L Shelton
Institution:(1) Department of Geology, Korea University, 136-701 Seoul, Korea;(2) Department of Mineral and Energy Resources Engineering, Semyung University, 390-230 Jecheon, Korea;(3) Stable Isotope Geology and Geochemistry Group, Department of Geological Sciences, University of Missouri-Columbia, 65211 Columbia, Missouri, USA
Abstract:Mesothermal gold mineralization at the Samdong mine (5.5–13.5 g/ton Au), Youngdong mining district, is situated in massive quartz veins up to 1.2 m wide which fill fault fractures within upper amphibolite to epidote-amphibolite facies, Precambrian-banded biotite gneiss. The veins are mineralogically simple, consisting of iron- and base-metal sulfides and electrum, and are associated with weak hydrothermal alteration zones (<0.5 m wide) characterized by silicification and sericitization. Fluid inclusion data and equilibrium thermodynamic interpretation of mineral assemblages indicate that the quartz veins were formed at temperatures between 425 and 190°C from relatively dilute aqueous fluids (4.5–13.8 wt. % equiv NaCl) containing variable amounts of CO2 and CH4. Evidence of fluid unmixing (CO2 effervescence) during the early vein formation indicates approximate pressures of 1.3–1.9 kbars, corresponding to minimum depths of ap 5–7 km under a purely lithostatic pressure regime. Gold deposition occurred mainly at temperatures between 345 and 240 °C, likely due to decreases in sulfur activity accompanying fluid unmixing. The delta34S values of sulfide minerals (-3.0 to 5.3 permil), and the measured and calculated O-H isotope compositions of ore fluids (delta18O = 5.7 to 7.6permil; delta = –74 to –80permil) indicate that mesothermal gold mineralization at the Samdong mine may have formed from dominantly magmatic hydrothermal fluids, possibly related to intrusion of the nearby ilmenite-series, lsquoKimcheon Granitersquo of Late Jurassic age.
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