Tin-bearing chalcopyrite and platinum-bearing bismuthinite in the active Tiger chimney, Yonaguni Knoll IV seafloor hydrothermal system, South Okinawa Trough, Japan

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The active sulfide chimney ore sampled from the flank of the active Tiger chimney in the Yonaguni Knoll IV hydrothermal system, South Okinawa Trough, consists of anhydrite, pyrite, shalerite, galena, chalcopyrite and bismuthinite. Electron microprobe analyses indicated that the chalcopyrite and bismuthinite contain up to 2.4 wt. % Sn and 1.7 wt. % Pt, respectively. The high Sn-bearing chalcopyrite and Pt-bearing bismuthinite are the first occurrence of such minerals on the submarine hydrothermal systems so far reported. The results confirm that the Sn enters the chalcopyrite as a solid solution towards stannite by the coupled substitution of Sn 4+ Fe 2+ for Fe 3+ Fe 3+ while Pt enters the bismuthinite structure as a solid solution during rapid growth. The homogenization temperature of the fluid inclusions in anhydrite (220-310℃) and metasured end-member temperature of the vent fluids (325℃) indicate that the minerals are precipitated as metastable phases at temperature around 300℃. The Sn-bearing chalcopyrite and Pt-bearing bismuthinite expess the original composition of the minerals deposited from a hydrothermal fluid with temperatures of about 300℃.
2005-12-31