Abstract

Initial data on the hydrogen and oxygen isotopic compositions of water in fluid inclusions in pyrite and chalcopyrite from some of the Kuroko deposits in the Hokuroku district of Japan fall within a narrow range: delta D = -- 26 to --18 per mil and delta 18 O = --1.6 to -0.3 per mil, relative to SMOW.These data together with geologic and other geochemical data indicate that the Kuroko ore fluids were predominantly of sea-water origin. A small proportion (less than 25 percent) of magmatic and/or meteoric water may have been mixed in the ore fluids.A model for the formation of the ores by convective circulation of sea water through high-temperature volcanic rocks is presented.

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