Hishikari Low Sulphidation Epithermal Gold Deposit: On the fourth day of the Tour in Japan, the group visited the Hishikari deposit, which is located in the Hokusatsu low sulphidation district of southwestern Kyushu, ~60 km northeast of the city of Kagoshima and 110 km northeast of Kasuga. On arrival, after changing into underground gear, Hiroshi Shimakura, a geologist from the Geology and Exploration section of the Sumitomo Metal Mining Co. Ltd., Hishikari operation, gave the group a brief overview of the mining operation and deposit, before taking us underground to visit two locations. The first was the Hosan 5 vein, in the Sanjin-Honko section of the deposit, which constitutes the northeastern half of the vein system, hosted by Cretaceous basement sedimentary rocks. The vein was relatively low grade at the location inspected, comprising a mining width of 3.6 m averaging 9 g/t Au (main image above). We were subsequently taken to the Yusen 1-3 vein in the southwestern Yamada section of the mine where a less impressive looking network of narrow veins (see lower central image, but note difference in scale), assayed an average of 350 g/t Au over a width of 3.3 m within Pleistocene andesitic hosts. After almost 2 hours studying these veins, the enclosing rocks and associated alteration, the group returned to the surface to discuss what we had seen with Hiroshi Shimakura and Koji Morimoto, Manager Geology and Exploration (fourth and third from the left respectively in the image above). We also had the opportunity to study ore textures in a variety of high grade ore samples (e.g., as shown in the lower left image above). The lower right image shows the surface above the northeastern (Sanjin-Honko) section of the deposit. The vein system is composed of sets that are developed below and sub-parallel to the main cultivated flat, while others cut obliquely through the hills to the right into the valley in the distance, although the top of the vein system is generally >100 m below the surface.
See the deposit description pages for details of the geology, controls on veining and alteration patterns. Photographs by Mike Porter.