Geology and Ore Deposits of the Central Kie Peninsula

Abstract

This area studied consists of two geologic elements, pre-Neogene geosynclinal sedimentary rocks, and Neogene sedimentary and igneous rocks. The older formations showing monoclinic zonal arrangement, parallel to the major Paleozoic structure in Southwest Japan, and contain many Kieslager ore deposits of small size, of which main mineral is fine-grained pyrite. In Neogene, granitic intrusion (Omine granite), sedimentation in small basins (Miyai formation) and acidic extrusive activities (Kumano acidic extrusive rocks) occured successively. At the last stage of the Neogene tectonics, numerous faults and fissures were formed allover the tectonic area. This was followed by the Kinan copper mineralization.
Ore deposits of the Kinan-type, the most important one in the area, are classified into two local types on the basis of mineral assemblages and texture of vein-forming minerals. Kitayama-type deposits, which are characterized by fine-grained pyrrhotite, represent a deeper phase of the Kinan mineralization, while the other, Kishu-type deposits, represent shallow one. Chalcopyrite-pyrite veins of the famous Kishu and Myoho mines belong to the latter group of the ore deposits.