1985 Volume 35 Issue 189 Pages 17-29
The mineral deposits of the Hitachi mine are divided into two groups, Fujimi and Fudotaki, according to their stratigraphical position: the deposits of the Fujimi group occurring between lower acidic and upper basic schists and those of the Fudotaki group in a thick pile of the basic schists. Chemical natures of sulfides and ores were compared between the deposits of two groups, mainly between the Fujimi and Fudotaki deposits.
Cobalt and nickel contents of pyrite are higher in the Fudotaki deposits than in the Fujimi deposits. Selenium contents and sulfur isotope ratios of pyrite differ also remarkably between these two deposits. Galena is more frequently observed under microscope in the Fujimi ores than in the Fudotaki ores. Barite occurs only in the sphalerite rich ores of the Fujimi deposits and not in the Fudotaki deposits. Such chemical differences of sulfides and ores between the two deposits are attributed to the chemical differences of hydrothermal solutions responsible for the two deposits, not to the physico-chemical differences of mineral deposition.
The observed differences in chemical natures between the two deposits are virtually the same as those between the Besshi type deposits, which are associated with basic schists derived from basaltic volcanics, and the Kuroko type deposits with genetical affinity to felsic volcanics. It is suggested that the hydrothermal solutions responsible for these deposits were once nearly in equilibrium with underlying volcanic rocks (having genetical connection with deposits) in respect to the exchange of chemical constituents.
