Geology and Ore Deposits of Geoje Dong-A Mine

거제(巨濟) 동아광산(東亞鑛山)의 지질(地質) 및 광상(鑛床)

The geology of the mine consists of Cretaceous lower andesitic breccia member, tuffaceous black shale, upper tuffaceous sandstone member and andesitic dike. Ore bodies are two parallel veins of breccia originated from hydrothermal activity of later acidic igneous intrusion. First two periods of mineralization, gold and silver, and copper, and later copper enrichment was identified. The first two might have been occurred during boiling of hydrothermal solution that formed breccia and copper enrichment was accomplished by enhancement of $CO_2$ fugacity from the organic material contained in the black shale. With all the geologic and mineralogic data and inferences attained from other investigators it was estimated that the optimum depth of the ore mineralization was between 500m and 300m below the surface of Kyong-Sang series.