Selenium-bearing Gold-Silver-Lead Ores of the Kato Mine, Fukuoka Prefecture

Abstract

The ore deposits of Kato mine, Fukuoka Prefecture, are probably mesothermal fissure-filling veins in the Mesozoic porphyrite. Minerals in the ores consist of quartz, sphalerite, chalcopyrite, and galena with minor amounts of hematite, pyrite, and klaprothite. The most characteristic feature of the ores is their high selenium content as well as that of gold and silver. Microscopic studies show that the silver content depends on silver-selenide, aguilarite Ag₄SeS, precipitated in place of argentite from the selenium-rich residual solution. Microscopically, the mineral has low hardness, probably Talmage's hardness A, light brownish grey colour, and weak anisotropism showing mimetic twinning. It always occurs as minute interstitial grains among sulphides.
Though native gold is mostly found penetrating sulphides as veinlets along minute fissures and other open spaces, some of them associating with galena and aguilarite occur as rosary and irregular aggregates of rounded granules, 1 to 10μ in diameter.