Mineral chemical studies on cobalt-nickel-bearing minerals in bedded manganese ore deposits

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Cobalt and nickel minerals from bedded manganese ore deposits in Japan are identified, and three species of them are compositionally specified. Parts of gersdorffite and cobaltite are crystallographically studied after the employment of newly obtained precession camera, and found to be cubic. The most important matters are the realization of a nickel-bearing pyrite reaching Ni 0.46% in weight in the materials from the Kashima mine, Tochigi Prefecture, the trace of distribution of nickel, and the consideration of the genesis. The conclusion is that nickel was originally contained in a nickel-bearing tephroite( <(Mn,Ni)_2SiO_4> ) and later concentrated in pyrite at the time of rhodonitization of tephroite. This conclusion is also applicable to the cases of the other nickel-cobalt minerals in the aggregates of rhodonite. In case of the presence of arsenic in nickel-cobalt minerals, the origin of arsenic can be ascribed to tephroite, too. In a rhodonite-dominant ore from Itaga, Tochigi Prefecture, the assemblage of siegenite( <(Co,Ni)_3S_4> )+cobaltite((Co,Ni)AsS) is found, and the ratio Co/(Co+Ni) is lower in the former than in the latter. In case of the Kashima mine, tirodite( <Mn_2Mg_5Si_4O_(11)(OH)_2> ) is found to contain minor NiO up to 0.18% in weight besides tephroite, which contains NiO up to 0.07% in weight. As to the origin of nickel and cobalt contained in these minerals, the most probable source is manganese nodules which were formed in the past geologic time in the same manner as currently precipitating in deep sea bottoms. Firstly, minerals of manganese dioxides precipitate after the capture of nickel and cobalt, and finally manganese silicates like above are formed, though the intermediate steps are still unknown. The geochemical behaviours of nickel and cobalt are considered to be similar in each through above processes.