On the recent exploration results at the Toyoha polymetallic vein-type deposits, Hokkaido, Japan

Abstract

The Toyoha ore deposits, which consist of more than fifty veins, are known as polymetallic vein-type deposits. The principal ore minerals are galena, sphalerite and pyrite with small amount of silver minerals, chalcopyrite, tetrahedrite, arsenopyrite, marcasite, pyrrhotite, magnetite, hematite etc. Tin, tungsten, indium, cobalt and bismuth as well as gold and silver occur as minor elements in the ore.
The authors recently proposed a poly-ascendant mineralization model, that is, such variety of ore minerals and elements was caused by the superimposed mineralization of at least seven stages (YOSHIE, et al., 1986) . In this paper, we have reviewed the poly-ascendant mineralization model with the latest knowledge and minor modification.
That model gives an effective guide for exploration. Since 1986, extensive and systematic underground diamond drillings have been carried out for the targets extracted from the model and have successfully resulted in a discovery of the giant new vein, "Sinano vein", which extends 600 meters long, with 30 meters maximum width, estimated more than three million tons of ore reserves at 250 g/t silver, 2% lead, 13% zinc and with considerable amount of copper, tin and indium.