義城地域의 金-銀 鑛化作用

Gold-silver mineralization of the Euiseong area

The Au-Ag deposits of the Euiseong area occurred in quartz veins which filled fissures in Cretaceous sedimentary and volcanic rocks. These ore veins can be classified in two types of deposits based on metallic mineral assemblages as follow: a pyrite type gold-silver deposit(Hoedong mine), characterized by Cu sulfides with Au-Ag alloy, and a Sb-rich silver deposit(Keumdongdo mine), characterized by base metal with Ag-bearing sulfosalts. Mineralogic and fluid inclusion evidences suggest that the ore minerals of these deposits was deposited from initial high temperatures (near 350℃) to later lower temperatures (200℃) with moderate salinity fluids ranging from 5.8 to 3.8 eq. wt.% NaCl. The gold-silver mineralization of the Hoedong mine occurred at temperatures between 300 and 200℃ from fluids with log fS₂ of -10~-16 atm. The antimony - silver mineralization of the Keumdongdo mine were deposited at the higher temperatures (350 to 250℃) and fS₂ (-10~-13 atm) than gold mineralization of the Hoedong mine. The calculated log fO₂ of fluids at 250℃ in two deposits are -32 to -34 atm and -36.5 to -38.5 atm, respectively. Boiling evidences indicate that the ore mineralization of the Hoedong mine occurred at more shallow depth (0.5 km) than that (1km) of the Keumdongdo mine. The above differences of depositional environments between two deposits caused the compositional changes of ore minerals such as electrum and sphalerite.