Abstract The bonanza-grade, low-sulfidation epithermal Hishikari gold deposit is located in the Plio-Pleistocene volcanic area of southern Kyushu, Japan. The concealed veins were discovered in 1981 and the mine has since produced 5.462 million metric tons (Mt) of ore averaging 44.3 g/t Au (242 t Au) from 1985 to the end of 2018, at which time reserves were 7.98 Mt at 20.9 g/t Au. The Hishikari deposit consists of the Honko, Sanjin, and Yamada ore zones, which occur in a NE-trending area 2.8 km long and 1.0 km wide. The veins are hosted by basement sedimentary rocks of the Cretaceous Shimanto Supergroup and by overlying Hishikari Lower Andesites of Pleistocene age. Sinter occurs about 100 m above the Yamada ore zone. Temperature-controlled hydrothermal alteration zones occupy an area of >5 km long and 2 km wide. The Honko and Sanjin veins occur within a chlorite-illite alteration zone (paleotemperature >230°C), whereas the Yamada veins occur within an interstratified clay mineral zone (150°–230°C). The marginal alteration comprises quartz-smectite (100°–150°C) and cristobalite-smectite (<100°C) zones. Ore-grade veins are located between –60- and 120-m elev, with the paleowater table over the Honko-Sanjim veins at ~300-m elev. Overall, the Ag/Au wt ratio is about 0.6. Vein-forming minerals consist of quartz, adularia, and clay minerals plus truscottite, with electrum and minor pyrite, chalcopyrite, naumannite, galena, and sphalerite. The major veins formed from repeated episodes of boiling and strong fluid flow inferred from bands of quartz, adularia, and smectite with bladed quartz, columnar adularia, and truscottite.

Abstract The Hishikari high-grade low-sulfidation epithermal gold deposit is located in the Hokusatsu district, about 30 km north of the Kagoshima International Airport, Kagoshima Prefecture ( Fig. 1 ). In early 1981, a narrow (15 cm) but high-grade (290 g/t Au) vein was discovered 200 m below the surface by the Metal Mining Agency of Japan ( MITI, 1982 ), and subsequent development has proved Hishikari to have substantial reserves of high-grade ore. Production from July 1985 to March 2000 totaled 105 tonnes (t) of gold and 58 t of silver from 1.87 Mt of ore. The production plus total reserves are estimated to be 5.5 Mt, including 3.5 Mt at an average grade of 60 to 70 g/t Au in the Honko-Sanjin ore zone and 2 Mt at 20 to 25 g/t Au in the Yamada ore zone, for a total of approximately 260 t of contained gold. The Hishikari deposit, especially the Honko-Sanjin zone, is characterized by high gold contents in almost all veins and by a very high aluminum content in the veins due to abundant adularia and common smectite. This article presents a summary of the gold deposit at Hishikari and the detailed mineralogical description of a high-grade vein, the Hosen no. 1 vein, hosted by basement sedimentary rocks.