On the Uchinotai "Kuroko" Deposits, Kosaka Mine, Akita Prefecture

Abstract

The Uchinotai ore deposits which are typical "Kuroko" deposit were discovered in the summer of 1959. In the next three years all constructions required for development were completed, and regular production was commenced in July 1962.
With progress of geological prospecting by underground core-drillings and drifting in the deposits, geological structures and ore reserves became known much better. The ore deposits seem to be dis-continuous, comprising three main ore deposits. At least, three lava-domes of white rhyolite, accom-panied by volcanic breccia, are recognized. The ore deposits are generally distributed on the eastern slope of these lava-domes, partly on the western slope also. In these ore deposits, a zonal arrange-ment of "black ore" (sphalerite-galena-chalcopyrite-tetrahedrite-barite), "yellow ore" (chalcopyrite-pyrite), "gypsum ore" and "siliceous ore" (pyrite-chalcopyrite-quartz), in descending order, is gene-rally observed, but distribution of the ores is complex in detail.