豊羽鉱床南域における多金属鉱化作用-定山渓豊羽地域精密地質構造調査の成果- Polymetallic mineralization at the Toyoha south district, Hokkaido, Japan.
The Toyoha mine is representative of the epithermal silver-lead-zinc-copper vein type deposits in Japan. Mineralization is divided into two stages, an earlier and later stage. In addition, the later stage is divided into two substages, first and second. Two veins named "No.1 vein" and "No.2 vein" were discovered by underground drilling in the southern periphery of the Toyoha mining area. Drilling was carried out under conditions of high rock temperature, during which new techniques for such conditions were developed. Temperatures reached a maximum of 215°C and hydrothermal fluids discharged from ore-bearing veins.<BR>Both veins are characterized by polymetallic mineralization accompanied by valuable trace components such as indium, tin, and bismuth, assumed to have formed during the later stage of polyascendant mineralization in the Toyoha deposits."No.1 vein" is inferred to exist about 300m south of the Soya-Iwami-Izumo veins with a WNW-ESE strike and dipping north. The vein is characterized by high In/Zn ratios and tin mineralization. This feature indicates the vein formed mainly during the "first substage" of mineralization. On the other hand, the "No.2 vein" is inferred to exist about 400m south of "No.1 vein" with an E-W strike and dipping north: The vein is characterized by low In/Zn ratios and high Pb/Zn ratios in comparison with the "No.1 vein". This may indicate that the vein formed mainly during the "second substage" of mineralization. The discovery of these probable extensions to the south and southeast increases the presently known area of mineralization at the Toyoha mine .<BR>The location of the two veins coincide with the GEOGAS anomalies detected by the orientation survey of MMAJ (1990b). This indicates that the method will be a useful technique for mineral exploration in and around the Toyoha south district and further to the south and southeast region adjacent to the geothermal center.
資源地質 46(2), 45-61, 1996-04-30
The Society of Resource Geology