Geology and Gold-Silver Mineralization of Dongjin Mine

동진광산의 지질과 금은광화작용

The Donjin deposits which is located in the Chinan Basin, are emplaced along $N10{\sim}40^{\circ}E$ trending fissure sets. So it is a sort of fissure-filling ore deposits. The results of paragenetic studies suggest two stages of hydrothermal mineralization; stage I: base-metal sulfides stage, stage II: late base-metal sulfides, electrum and silver-bearing sulfosalts stage. Au: Ag ratios of the electrums show that Ag atomic% are higher than that of Au. The temperature and salinity of the Donjin deposits estimated from fluid inclusion and sulfur isotope geothermometry are as follows; stage I: $240{\sim}315^{\circ}C$, 2.4~7.1 NaCl eq. wt.%, stage II: $190{\sim}268^{\circ}C$, 4.6~8.4 NaCl eq. wt.%. The estimated oxygen and sulfur fugacity during first stage mineralization, based on phase relation of associated minerals, range from $10^{-35}{\sim}10^{-39.7}$ atm. and$10^{-11}{\sim}10^{-13.4}$ atm., respectively. All these evidences suggest that the Dongjin deposits are polymetallic meso-epithermal ore deposits.