In order to study the effect of crystal structure on S isotope fractionation properties of sulfide polymorphs, the reduced partition function ratios of 34S/32S (103lnβ34–32) for FeS2, CoAsS, ZnS, CdS and MnS polymorphs are calculated in the present study. Our calculations show that 103lnβ34–32 decreases in the order of pyrite > marcasite > cobaltite > alloclasite > sphalerite ≈ wurtzite > γ-MnS > hawleyite ≈ greenockite > alabandite. The S coordination number exerts a strong influence on the equilibrium partitioning of S isotopes in these sulfides, and there exist significant S isotope fractionations between the sulfides with different S coordination numbers (CNS), such as alabandite (CNS = 6) and other sulfides (e.g., FeS2, CoAsS, ZnS and CdS polymorphs) (CNS = 4). There is a broad negative correlation between the average bond lengths of all the bonds formed by S and 103lnβ34–32 values. The compactness of atom packing plays an important role in determining S isotope fractionation properties of sulfides, and 34S generally tends to concentrate in the phases with higher atomic packing factor (APF). The linear correlation between APF and 103lnβ34–32 can predict the change of 103lnβ34–32 with increasing pressure, but pressure has a negligible effect on S isotope fractionation factors between sulfides.
First-principles investigation of the effect of crystal structure on sulfur isotope fractionation in sulfide polymorphs
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Shanqi Liu, Yongbing Li, Jie Liu, Tian Gao, Yang Guo, Jianming Liu, Yaolin Shi; First-principles investigation of the effect of crystal structure on sulfur isotope fractionation in sulfide polymorphs. European Journal of Mineralogy doi: https://doi.org/10.1127/ejm/2018/0030-2785
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