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.