龍化鑛山의 金銀鑛化作用

Gold and silver mineralization in the Yonghwa mine

The Yonghwa gold-silver deposits are emplaced along N15°~25°W trending fissures in middle Cretaceous porphyritic granite or Precambrian Sobaegsan gneiss complex. The results of paragenetic studies suggest that vein filling can be subdivided into four identifiable stages; state Ⅰ : the main sulfide stage, characterized by base-metal sulfide minerals, iron oxides and minor electrum, stage Ⅱ : electrum stage, stage Ⅲ : electrum and silver-bearing sulfosalts stage, stage Ⅳ : post ore stage of carbonates and quartz. The ore mineralogy suggests that depositional temperature of the formation of the gold and silver minerals are estimated as 200 to 250℃ and 140 to 180℃, respectively. Sulfur fugacity of the formation of the gold and silver minerals are estimated as 10-14.0 to 10-12.2 atm and 10-18.5 to 10-17.2 atm, respectively. A consideration of the pressure regime during ore deposition bases on the fluid inclusion evidence of boiling suggests lithostatic pressure of less than 180 bars. This range of pressure indicate that vein system lay at depth of 700m below the surface at the time during mineralization. Salinities of ore-bearing fluids range from 0.4 to 6.9 wt.% equivalent NaCl. The sulfur and carbon isotopic data reveal that these elements were probably derived from a deep-seated source. The δ¹⁸O of the hydrothermal fluid was determined from δ¹⁸O values of quartz and calcite. Oxygen and hydrogen isotopic studies reveal that meteoric water dominate over ore-bearing fluid.