Geology and Ore Deposits in the Vicinity of the Katsuraoka Mine, South-Western Hokkardo.

Abstract

The Katsuraoka mining district lies on the northern periphery of the Hiyama Palaeozoic massif which forms the core of the Oshima peninsula, Hokkaido. So-called Palaeozoic slates intercalated with limestone and thin layers of chert form the basement members of the district; they are covered by a Neogene Tertiary pyroclastic formation.
Among the basement members a narrow N 20°W trending mineralized zone is noticeable, in which small deposits of magnetite, pyrrhotite and pyrite are scattered. The deposits are found along the N-S trending sheared zone, and most of them are associated with diabase dykes.
The ore deposits can be classified into the following three types; 1) magnetite deposits, 2) pyrrhotite deposits, and 3) pyrite depasit. Pyrometasomatic êffects are indicated by a lime-silicate association produced upon the surrounding diabase. The alteration of wall rocks is succeeded, without exeeption, by later hydrothermal chloritization, sericitization or silicification. The pyrite mineralization corresponds to a hydrothermal candition, while the mineralization of magnetite and pyrrhotite corresponds to the earlier pyrometasomatic condition.
The geological circumstances and the character of mineralization of the ore deposits indicate that they belong to a cupriferous iron sulphide deposit.