Silver minerals from the Sanru mine, Hokkaido, Japan

Abstract

Silver minerals from the Sanru mine, which is gold-silver quartz veins of epithermal type, were studied. Veins are consist mainly of banding chalcedonic quartz with small amounts of silver minerals, pyrite, chalcopyrite, sphalerite, arsenopyrite, adularia, kaolinite, sericite and carbonates. As silver minerals in the ore from Honpi and Juji-hi, electrum, aguilarite, naumannite, stephanite, pyrargyrite, miargyrite, polybasite and silver bearing tetrahedrite (freibergite) were determined by ore microscope, electron probe microanalyser and X-ray powder camera.
Electrum is closely associated with naumannite or aguilarite and has chemical compositions from 60.7 to 82.5 atomic % Ag (Table 1). Pyrargyrite occurs as small single grain in quartz vein or aggregate with tetrahedrite and chalcopyrite in veinlets along the crack in quartz vein. Pyrargyrite contains small amounts of Se and As (Table 2), and its chemical composition is very close to ideal formula. Stephanite, miargyrite and polybasite are accompanied by pyrargyrite in quartz vein and their chemical compositions (Table 2) are also very close to their ideal formulae. Tetrahedrite is mainly found in the pyrargyrite-chalcopyrite veinlets cutting quartz vein. It has silver contents from 24.8 to 29.7 wt % (Table 4). Aguilarite and naumannite have chemical compositions from Ag₂Se_0.46S_0.56to Ag₂Se_0.71S_0.29 (Table 5), and form Ag₂Se_0.90S_0.10 to Ag₂Se_0.96S_0.04 (Table 6), respectively.