The stratabound-type sulfide deposits in Japan are divided into two types; the Besshi-type deposit and the Kuroko-type deposit, on the basis of their geological and mineralogical aspects and isotopic characteristics.
The “Kuroko” deposit is a polymetallic sulfide-sulfate deposit genetically related to submarine calc-alkaline acid volcanic activity of Neogene Tertiary. All of the Kuroko deposits occur in the so-called Green Tuff region. The nature of deposits changes downward from the stratiform deposit to the disseminated and/or the stockwork deposits. Meanwhile, the Kuroko deposit can be generally divided into the following four zones according to the mineral assemblage of ores; Quartz-hematite zone, Kuroko (black ore) zone, Ôko (yellow ore) zone, and Keiko (siliceous ore) zone in stratigraphically descending order. The main hypogene minerals constituting the sulfide ore are pyrite, chalcopyrite, sphalerite, galena, minerals of tetrahedrite group, marcasite, bornite in decreasing order with quartz and barite as gangue minerals. Gypsum-anhydrite ores are well developed in the Kuroko deposit closely associated with sulfide ores.
Besshi-type deposit, that is to say, the bedded cupriferous iron-sulfide deposit, is well known in the Sambagawa metamorphic belt, and the deposits of allied type occur in the non-metamorphic Palaeozoic terrains and in the Shimanto belt. Besshi-type deposit is usually associated with submarine basic volcanic materials, and are modified by later metamorphism and deformation. The ore minerals consist chiefly of pyrite, chalcopyrite, sphalerite and of less amount of bornite. A negligible amount of galena is one of the most significant features of ore. Magnetite or hematite layers occassionally interbedded in the cupriferous pyrite layers, are worthy of notice of the connection with the fugacities of S₂ and O₂ during ore deposition.
Taro deposit, Kuroko-type deposit of the early Cretaceous age, occurs in the Taro belt of northeast Japan, being genetically related to submarine calcalkaline acid volcanic activity. The sulfide minerals consist chiefly of pyrite, chalcopyrite, sphalerite, and galena. Barite is rather less in amount than that in the Neogene Kuroko deposit. Small lenticular masses consisting of gypsum and calcite is poorly deleloped below the stratiform sulfide deposit. The ore deposit is comparatively monotonous in mineral assemblages, and variety of minerals is far less than that in the Kuroko deposit. However, alabandite occurring in the hanging wall side is noteworthy for studing the physico-chemical condition of ore deposition.
In this paper, all of the minerals from the above-mentioned deposits are listed up, and some of them are described about their chemical compositions, and also mineral assemblages, in order to offer useful information on the investigation of physico-chemical environments of ore formation. Moreover, the texture and structure of ores from the deposits are briefly summarized.