Occurrence of Electrum from the Namseong Gold Mine

남성(南星) 금광산산(金鑛山産) 에렉트럼의 산상(産狀)

This paper describes the mode of occurrence and mineralogical properties of electrum from the Namseong Gold-Silver deposits, for the purpose of obtaining data on the characteristics of the ore deposits and the behavior of gold and silver during the mineralization. The gangue minerals are quartz, calcite, fluorite. Ore minerals are mainly composed of pyrite, sphalerite, chalcopyrite and galena with minor amount of argentite, electrum, pyrargyrite, native silver and unidenfied mineral(Cu-Fe-Ag-S series). Three stage of mineralization recognized are, from early to later, (I) pyrite-electrum stage (II) sphalerite-chalcopyrite-galena-argentite-electrum stage (III) sulfosalts stage. The filling temperature of fluid inclusions in quartz ranges from $225^{\circ}$ to $335^{\circ}C$. The value of sulfur fugacity estimated by means of electrum-tarnish method ranges from $10^{-11.5}$ to $10^{-14}$ atm. The compositional heterogeneity within a single grain with respect to gold concentration is common in the Namseong electrums Chemical composition of electrum ranges generally between 25~45 atom% Au. Its gold content decreases in late stages of mineralization.