Vaesite from the Uchinotai deposits, Kosaka mine, Japan

The first occurrence of vaesite in Japan is described from the Kurokotype deposits of the Kosaka mine in Northeast Japan. Microprobe analysis showed its chemical composition to be very close to NiS2, though it con-tains small amounts of Fe, Cu, and Co. Sulfur fugacities at the time of deposition of thvaesite bearing ores were calculated to be 10-13.8, 10-11.0-10-11.7, and 10-8.7-10-9.9 atm. at 150°, 200°, and 250°C respectively on the basis of the observed mineral assemblage.