Polymetallic mineralization at the Shin-Ohtoyo deposit, Harukayama district, Hokkaido, Japan

The Shin-Ohtoyo Cu-Au deposit is located in the Harukayama district, 20 km west of Sapporo, Hokkaido, Japan. Both acid-type disseminated and adularia-quartz-type vein Au mineralizations have been recognized within a small distance of less than 500 m in the district. Mineralogical characteristics of sulfide ores from the Shin-Ohtoyo deposit have been proved to be polymetallic. Ore minerals containing Sn, V, Bi and Te are recognized. Nine ore types are recognized in terms of characteristic mineral assemblage; (I) chalcedonic quartz veinlets in silicified zone around the deposit, (2) bismuthinite, emplectite, +/-friedrichite and tetrahedrite, (3) an unnamed Cu-Sn-Fe-Zn sulfide, colusite-series minerals, +/-stannoidite, emplectite and tetrahedrite, (4) bournonite, Se-bearing galena and tetrahedrite, (5) luzonite/famatinite and Ag-bearing tetrahedrite, (6) colusite-series minerals, emplectite, aikinite and tetrahedrite/goldfieldite, (7) luzonite/famatinite, colusite-series minerals, mawsonite and tetrahedrite/goldfieldite, (8) enargite, luzonite/famatinite and tetrahedrite, and (9) colusite-series minerals and tetrahedrite. The first occurrence of friedrichite and stibiocolusite from Japan are reported. The chemical formula of the unnamed phase corresponds to Cu-6(Cu,Fe,Zn)Sn3S10. Sulfur isotopic ratios (delta(34)S) Of sulfides from the stockpile range from -0.5 parts per thousand to +1.9 parts per thousand, and those from drill cores recovered by Metal Mining Agency of Japan (MMAJ) vary from -2.7 parts per thousand to +0.8 parts per thousand. Sulfur isotopic ratio of barite in a cavity in the silicified tuff breccia collected from the stock pile yields +27.1 parts per thousand, while that of barite collected from MMAJ core is +21.7 parts per thousand. Sulfur isotopic thermometry applied for a pair of barite (+21.7 parts per thousand) and associated pyrite (+1.8 parts per thousand) indicates about 300 degrees C. High-Te tetrahedrite composition from both the chalcedonic quartz vein in the silicified zone around the Shin-Ohtoyo deposit and the polymetallic sulfide ores from the adit of the deposit, suggests that the Au mineralization in the former is attributed to a hydrothermal system marginal to the polymetallic mineralization.