流体包有物研究による秋田県深沢鉱床の生成環境
1982 年 98 巻 1132 号 p. 477-482
詳細
1982 年 98 巻 1132 号 p. 477-482
The Fukazawa Kuroko deposit is situated in the almost central part of the Hokuroku basin. The Tsunokakezawa ore body dealt in this paper is the largest in the Fukazawa deposit and consists mainly of typical stratiform Kuroko ore body with several outlets of ore fluids forming siliceous ore bodies. The stratiform Kuroko ores are composed largely of sphalerite, galena and barite with pyrite, chalcopyrite, tetrahedrite, bornite, calcocite and covelline. Chalcopyrite and pyrite are commonly found in the coarse grained stratiform Kuroko ores which are distributed mainly in the western part of the Tsunokakezawa ore body. On the other hand, tetrahedrite, bornite, chalcocite and covelline are found in the fine grained ores with barite, and are commonly in the eastern part of the ore body. Colloform and framboidal textures are frequentry observed in the fine grained ores.
Filling temperatures have been measured for 104 fluid inclusions in sphalerite. barite and calcite. They range from 209°to 370°C. Most of them are ranged between 250°C and 340°C. The higher temperature values are obtained largely from the western part of the ore body and the lower values from the eastern. Inclusions in the Kuroko ores formed near the outlets of ore fluids yield higher filling temperatures than those in the outskirts of them.
From these temperature data, the depth of sea in the central part of the Hokuroku basin at the formation of the Fukazawa deposit is estimated to have been about 1440 meters at least. It is deeper than that proposed by SATO (1968). However, it is shallower than that supposed from the foraminiferal assemblage by GUBER and OHMOTO (1978).
