Permalink : http://hdl.handle.net/2115/36735

Study on massive sulfide ores of the Shimokawa mine disclosed that the ores have been created by two distinctive phases of mineralization; One is characterized by precursory cubic-colloform pyrites (py(I)) probably related to the formation of pillow lavas in a fore-arc basin. The other is marked by presence of chalcopyrite-pyrrhotite-sphalerite assemblage associated with accessory cubanite, cobalt-pentlandite, mackinawite and pyrite (py(II)). Lead isotope data on the Shimokawa pillow lava, diabase and copper dominant ore, and gabbros in the Hidaka metamorphic belt suggest that copper dominant ore from the Shimokawa mine is not consanguineous with the Shimokawa pillow lava, but with the gabbros of the Hidaka metamorphic belt. From the lead isotope data, the Shimokawa ore deposits have been regarded as a composite type related to magmatic activities in both a fore-arc basin and an island arc system. Based on the geologic and geotectonic relationships of the Shimokawa diabase complex and the adjacent Nisama igneous complex it is concluded that the Shimokawa diabase complex is a slab obducted onto the island arc system represented by the Nisama igneous complex. The ore solution related to the formation of Shimokawa copper dominant ores might have been created in relation to the magmatism forming the Nisama gabbroic mass possessing nickeliferous pyrrhotite deposits.