The Mujeong au-Ag hydrothermal vein type deposits occur within the Teriary igneous rocks of the Janggi basin. Ore minerals consist of pyrite, pyrrhotite, sphalertite, chalcopyrite, galena, cosalite, lillianite, argentite and electrum, and associated with epidotization, sericitization and pyritization. Fluid inclusion studies reveal that ore fluids were low saline with a simple NaCl-H2O system. fluid inclusion data indicate that homogenization temperatures and salinities of fluid are 150 to 340℃ and 1.0 to 6.5wt.% NaCl equivalent, respectively. Sulfur isotope compositions of sulfied minerals (δ34S=6.2 to 9.6‰) indicate that the δ34‰SH2S value of ore fluids was about 10.4% This δ34‰H2S value is likely consistent with and hydrothermal sulfur, whereas the fluids were highly influenced by mixing with meteoric water. Measured and calculated oxygen and hydrogen isotope values (δ18OH2O=2.7 to 3.4‰, δDH2O=-83.6 to -52.7‰) of ore forming fluids suggest mixing with hydrothermal and meteoric water. Equilibrium thermodynamic interpretation by mineral assemblages and chemistry indicates that sulfur fugacities (-log fs2) ore forming fluids range from 9.0 to 12.6 atm stage II.
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