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At Chinkuashih, an important Pleistocene copper-gold producing mine in Taiwan, the arsenical copper-gold ores are similar to those of Butte, Montana, in mineralogy, geochemistry, and temperature of formation. Electron microprobe analysis established the presence of antimony in the enargite (luzonite), as in the enargite at Butte. Octahedral pyrite crystals, characteristic of the ore zone, contain copper and arsenic in solid solution, producing anomalous areas of anisotropism. Sulfur isotopes for sulfides and sulf-arsenides yield values close to meteoritic and typical of magmatic hydrothermal deposits, but the equilibrium sulfate species barite is 250/00 heavier in S34. Data on the barite-pyrite pairs suggest temperatures of formation in the range of 255°C to 305°C (using Sakai’s 1968 geothermometric curve), a range compatible with fluid inclusion temperatures in barite (for the most part between 228°C and 305°C) and quite comparable to Meyer’s (1950) figures of 275°C to 335°C for the Butte deposit. Extensive chloritic, argillic, and silicic alteration preceded mineralization and suggest that large amounts of water, perhaps meteoric, were involved in the hydrothermal processes.

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