The Cupriferous Iron Sulphide Deposits of the Koryu Mine in Hidaka Province, Hokkaido

Abstract

Along the Hidaka metamorphic zone, which constitutes the geological back-bone of the Island of Hokkaido, several cupriferous iron sulphide deposits which indicate close connection to gabbroic or diabasic rocks are found. The Koryu mine described here is the representative. Around the mining area zonally arranged metamorphic and gabbroic rocks that resulted from the Alpine orogenic movements are developed.
The ore deposits consist of some variable small bodies which lie sporadically in a shear zone that has some peculiar alterations.
The ore bodies are divided into 1) massive ore body, 2) "Gari" or brecciated ore body and 3) impregnated ore body according to the nature of the ore. They are lenticular or layered in shape and are disposed en echelon in the shear zone. The constituent ore minerals are magnetite, pyrrhotite, chalcopyrite, and pyrite. Some silicate minerals such as bluish-green hornblende, diopside, anthophyllite, cummingtonite, chlorite, epidote, biotite and quartz are also present.
Mineralization of the deposits has proceeded under the influences of dynamic movement and closely related metasomatism. In an earlier stage, magnetite was formed; it was accompanied by Fe-Al metasomatism which is indicated by bluish-green hornblende in the wall rock. Formation of the succeeding sulphide minerals was associated with characteristic Fe-Mg metasomatism as suggested by the presence of anthophyllite and cummingtonite.
The differences between the ore types are probably due to the differing suscptibility of various areas in the shear zone resulting from dynamic movement accompanvinu the ore deposition.