First-principles study of sulfur isotope fractionation in sulfides

Isotope fractionation parameters for sulfur have been calculated using first-principles methods based on density-functional perturbation theory for sphalerite, galena, alabandite, greenockite and cinnabar in the temperature range of 0–1000°C. For comparison, the 10³ lnα value between sphalerite and galena, which appears to be well determined, is also calculated, and a good agreement between this calculation and other results is found. The calculations show that the order of heavy isotope enrichment is sphalerite > cinnabar > greenockite > alabandite > galena. The reduced partition function ratios of ³³S/³²S, ³⁶S/³²S in the temperature range of 0–1000°C are also calculated, and there exists a fixed proportion relation between sulfur isotope ³²S, ³³S, ³⁴S and ³⁶S in the calculated five sulfides, which can be expressed as δ³⁴S = 1:940 δ³³S and δ³⁶S = 1.891 δ³⁴S, in agreement with previously published relationships.