Study on wall rock alteration related to polymetallic vein-type deposits, with special reference to the Toyoha mine, southwest Hokkaido, Japan 多金属鉱脈鉱床の熱水変質作用 : とくに西南北海道豊羽鉱山について

博士論文

The Toyoha mine possessing a number of hopeful ore－veins is situated in the suburbs of Sapporo city． The mine has been exploiting polymetallic ores containing abundant lead, zinc, silver and accessory gold，copper，tin，tungsten and indium． Geology of the mining area was re－investigated and new stratigraphy has been accomplished by the present author. Country rocks of the deposits are extensively subjected to various grades of alteration, which were divided into two；diagenetic and hydrothermal origins， then the hydrothermal alteration halo enveloping the ore－veins were precisely studied， i．e． mode of occurrence of the halo， petrochemistry of the altered rocks, mineral chemistry of chlorite and other alteration minerals are reported in this paper． Using sericites KAr ages of the altered rocks were also verified． Results obtained were compared with some typical polymetallic deposits in Japan， and presence of common features in many respects has been confirmed between them． Thus the characterization of the wall rock alteration related to the formation of polymetallic vein－type deposits has been accomplished. Newly obtained informations regarding above－mentioned subjects led to a conclusion that the Toyoha deposits might have been formed by repeated activities of ascending hydrothermal solutions in the periods of Pliocene to Pleistocene．