菱刈鉱山山田鉱床周辺部の探鉱と開発の現況

抄録

The Eisen and Fukusen vein groups of the Hishikari Mine, a low-sulfidation epithermal quartz (-adularia) vein system, are newly developed as a result of consecutive and intensive exploration campaigns in the surrounding areas of the Yusen and Seisen vein groups of the Yamada deposit. Eisen vein group was thought to have much chalcedonic quartz than Yusen and Seisen veins have during the drilling phases. On the observation at the faces of Eisen No. 3 and No. 3-1 vein, however, chalcedonic quartz are cut by (high-grade) banded and/or clayey quartz veins. On the other hand, it was also revealed that bonanza zone of Eisen vein group is smaller than that of other vein groups of the Yamada deposit, and that many quartz veins ranging several strikes are hosted in the area. Therefore, it was required for execution of efficient exploration programs to understand the characteristics of bonanza zones of the veins.
Analysis of vein structures of the Yamada deposit suggests that vein width at striking N50°E tends to be wider than other strikes (N30°E and N70°E). This implies that N50°E might have been formed as a result of pull-apart structure, which could provide more sufficient open space or conduit for ascending mineralizing fluid than that of shear zone. High-grade Au mineralization also seems to have some relationship with the same strike.
Hydrothermal clay minerals were analyzed to delineate alteration zoning. It suggests that quartz-chlorite zone widely distributes in the northeastern part of the Yamada deposit, where high-grade mineralization is often confirmed. Since this zone is also distributed in undeveloped areas like north-westward of Eisen vein group and northeast extension of Fukusen vein group, Hishikari Mine will keep its exploration activities high in such peripheral zones.