Mode of occurrence of fluorite and some zinc sulphide minerals in the Tomiyasu gold mine (I)

Abstract

The gold veins of the Tomiyasu mine traverse granodiorite and basaltic tuffs and flows. They consist of crustified layers of quartz and some amounts of zincblende, galena, chalcopyrite and pyrite. The structure of the veins and their influence on the basaltic flows show that the veins have an epi-thermal origin. It is worthy of notice that fluorite occurs in the veins rather abundantly and that the zinc-sulphide minerals in the same veins occur in three different forms, namely, honey-coloured irregular grains, dark brown prisms and some fibrous aggregates. The last two types belong to the last stage of vein formation. The prismatic variety is zincblende, which is surrounded by forms {111}, {1 ?? 1} and {110}. and elongates in a direction parallel to an edge between {111} and {1 ?? 1}, It is quite different from the prismatic zincblende from the Asio mine, which elongates, as a result of repeated twinning, perpendicular to (111), or from that of the Ohmori mine, which is believed to be a Paramorphic pseudomorph of zincblende after wurtzite. The fibrous variety is anisotropic and may be regarded as wurtzite.