ABSTRACT

On the basis of a model chloride-complex solution with the same metallic abundances as the present-day oceanic water, the physicochemical factors controlling the ore-zoning observed in the Kuroko type mineralization in Japan have been examined. The result reveals that the ore-zoning can be explained by the oxidation and/or neutralization processes of the model ore-forming solution. This is in complete harmony with the interpretation expressed in the recent sulfur isotope studies of this type of mineralization. The hypothesis that the Kuroko ore-forming solution might have been derived essentially from the coeval seawater (KAJIWARA, 1973) appears to be acceptable. Extending the hypothesis, it is suggested that many of the hydrothermal systems in the earth's crust probably represent the circulating coeval seawaters. With this view, the natural hydrothermal mineralizations may be divided into two types, (A) mineralizations due to the reduction processes of the incorporated seawater and (B) those due to the oxidation processes of the once reduced circulating seawater. The deposits formed in shallow environments such as Kuroko and those formed in relatively deep environments such as contact metasomatic deposits may represent the oxidation- and the reduction-type mineralizations, respectively. It is also probable that the generation of silicate magmas in the orogenic belts is closely related to the availability of such circulating seawater in the earth's crust and possibly in the upper mantle.