The gold-silver ores from the Kushikino mine, Kagoshima prefecture, Japan, with special reference to the occurrence of naumannite

Abstract

The Kushikino mine is an epithermal vein-type gold-silver deposit related to the Neogene volcanism, and is one of the largest gold mines in Japan. The microscopical and mineralogical studies of the gold-silver ores in the eastern part of the mine revealed the presence of electrum, naumannite and a mineral of polybasite group as main Au and Ag minerals, and pyrite, chalcopyrite, tetrahedrite, pyrargyrite, sphalerite, galena and three undetermined minerals as minor ore minerals, accompanied by quartz and a small amount of calcite as gangue minerals. The sequence of ore formation is reconstructed from the textures of veins as follows : 1. formation of siliceous altered rocks, 2. deposition of quartz and ore minerals, 3. deposition of calcite. The optical properties of the naumannite are discussed, with the results of etch reactions and X-ray powder data.