Bismuth-bearing Minerals from the Inakuraishi Ore Deposits, Southwestern Hokkaido, Japan

Two bismuth minerals, gustavite and "bismuthinite", were newly found in an ore from an outcrop of the Taisei vein, Inakuraishi mine. The ore occurs in strongly altered andesite as veinlets less than 5 cm in width and was cut by a manganese oxides vein, 10 to 20 cm in width. The manganese oxides were estimated to have formed by weathering of hydrothermal manganese carbonates. Vein minerals are quartz, pyrite, and chalcopyrite with accessary amounts of gustavite, "bismuthinite", galena, acanthite, sphalerite, hematite, and marcasite. The gustavite and "bismuthinite" occur in close association with each other, but they do not coexist with galena or acanthite which contains a few wt.% Bi. The possible temperature and sulfur fugacity during deposition of the bismuth minerals are estimated to be in ranges of 254•‹ to 280•Ž and 10-11.1 to 10-9.3 atm., respectively. These data suggest that the bismuth minerals had formed at the stage II of the Inakuraishi mineralization.