Geology and Ore Deposits of the Kinmei Mining District Asa-gun, Hiroshima Prefecture (Preliminary Report)

This district is located about 20 km north-east of Hiroshima city and is geologically situated in the intermediate non-metamorphic zone between the Sangun and Ryôke metamorphic zones. There are many ore deposits and outcrops in the district, but, at present, none of them other than the copper mine of Kinmei are workable. The Palaeozoic formations in this district consist of sheared slate, slate, chert, sandstone, and limestone, and are intruded by the upper Cretaceous biotite-granite, quartz-porphyry and hornblende-porphyrite. Palaeozoic formations, a part of quartz-porphyry and hornblende-porphyrite are thermally metamorphosed. In general, Palaeozoic formations are monoclinally dipping to north with EW trending. The Kinmei ore deposits consist chiefly of two series of veins, occurring along the both sides of a quartz-porphyry dike in slate and are formed by replacement of slate by the hydrothermal solution related to the post igneous activity of the upper Cretaceous biotite-granite. Each series of veins consist of many vertically elongated small lenses. As to the mineralizaiton, the writer can recognize two stages: The primary mineralization belongs to a hydrothermal type forming garnet, biotite, arsenopyrite, pyrrhotite, zincblende, chalcopyrite, galena, sericite, chlorite and quartz. The second mineralization belongs to a hydrothermal fissure-filling type forming calcite and quartz veins accompanying pyrite