Abstract

Laser microprobe analysis of sulfide mineral pairs from several volcanogenic massive sulfide (VMS) stockwork feeder zones shows that greenschist to upper amphibolite facies metamorphism will reset sulfur isotope thermometers if the mineral grains are in direct grain-to-grain contact. However, discrete monomineralic sulfide grains that are completely encased in quartz matrix and that are not in direct grain-to-grain contact with one another, will preserve their original hydrothermal sulfur isotope compositions, because exchange during metamorphism is inhibited by the enclosing quartz. Calculated temperatures from three separate VMS systems range from 170 to 424 °C for sulfide pairs that are not in direct grain-to-grain contact, and are consistent with independently determined temperature estimates. Sulfide pairs that are in direct contact yield unreasonably low temperatures, indicative of reequilibration during metamorphism and subsequent slow cooling.

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