무극 금은 광상에 대한 유체포유물 및 안정동위원소 분석연구

Stable isotope and fluid inclusion studies of the Mugug Au-Ag mineral deposits

A couple of Au-Ag-bearing epithermal quartz veins of Cretaceous(87.9Ma) in age are developed in the Cretaceous(112Ma) granodiorite batholith which was emplaced in Mesozoic Baegyari sedimentary formation. Au minerals consist mostly of electrum with a 54.2-61.9 wt% Au and are closely associated with sulfide minerals including pyrite, chalcopyrite, pyrrhotite, galena and sphalerite. Homogenization temperatures of fluid inclusions in quartz, fluorite and calcite are 196-368℃(avg. 240℃), 74-176℃(ave. 115℃) and 75-200℃(ave. 119℃) respectively. Sulfur isotopic compositions(+5-+8‰) of ore sulfides indicate a deep-seated sulfur origin. Oxygen isotope compositions of different stages of quartz vary from +5.6 to +9.3‰ and calculated δ¹⁸O values of ore fluid at 250℃ range from -3.2 to +0.4‰, reflecting an isotopically evolved ore fluid mixed with a ¹⁸O depleted meteoric water under the variable mixing ratios between hydrothermal and meteoric waters. Isotopic data of calcite minerals support the above conclusions.