The Tazawa mine is located west of Tazawa Lake in Akita Prefecture, Japan. The mine is mainly developed in the "green tuff" formation which is correlated with the middle or lower Miocene epoch.
The ore deposits occur as fissure filling type veins, amounting to ten-odd in number, and the NE-SW and NW-SE systems are predominant. Such minerals as pyrite, chalcopyrite, sphalerite, galena, quartz, calcite, etc. are commonly found in each vein, but the mineral assemblage shows two group types, one consisting mainly of pyrite and chalcopyrite and the other of pyrite, sphalerite and chalcopyrite. The cause of the difference in the two assemblages may be attributed to the erosion of the sphalerite zone in the upper part of the ore deposits, judging from the location of the said deposits and the nature of the mother rocks, etc.