Some Considerations on the Mineralization in the Mikawa Mine, Niigata Prefecture

Abstract

The genesis of the copper-lead-zinc veins in the Mikawa mine, Niigata Prefecture is discussed mainly -from a physicochemical viewpoint.
The mineralization can be divided into two stages: The earlier stage is characterized by chalcopyrite, sphalerite, galena, pyrite, quartz and chlorite, and the later stage by hematite, dolomite-ankerite, siderite, kaolinite and chlorite.
The earlier ore shows a marked zonal distribution, that is, a galena-sphalerite-quartz assemblage occurs in the upper levels than a chalcopyrite-pyrite-quartz-chlorite assemblage. The distribution of these as semblages is closely related to the internal vein structure, and it has been concluded that narrower channelways for the flow of the ore solution were more favourable to the deposition of the latter assemblage than that of the former. Such a distribution of the mineral assemblages may be explained in terms of the evapor ation of the volatile components in the ore solution. Wall-rock alteration during the earlier stage of mineralization-silicification, sericitization, and kaolinization from the inner side, is ascribed to the outward diffusion of a weakly alkaline ore solution.
The later ore is accompanied by intense alteration characterized by kaolinitic clay and siderite. This ore and the accompanying alteration are ascribed to the acid and oxidizing characteristics of the solution.