Sulfur isotopes in pyrite, pyrrhotite, alunite and anhydrite from steam wells in the Taupo volcanic zone, New Zealand

Hypogene pyrite and pyrrhotite show a narrow range for S ³⁴ /S ³² , with mean value a little higher than for most magmatic hydrothermal deposits, suggesting an origin in the upper crust rather than in the mantle. Anhydrite has a much higher S ³⁴ /S ³² ratio. These differences correspond to differences in ratios for sulfide and sulfate ions in the depositing geothermal fluid, but measured temperatures of solutions depositing a pyrite-anhydrite pair indicate that solid and aqueous phases do not have the same equilibrium constant. No isotope fractionation occurs when supergene alunite forms from pyrite.

This record provided courtesy of AGI/GeoRef.