Equilibrium sulfur isotope fractionations of several important sulfides

Copyright © 2021 by The Geochemical Society of Japan. sulfur isotope analyses have been applied to ore deposits; the pioneers of this subject area are Kulp et al. (1956) and Jensen (1957, 1959), among others. At present, sulfur isotopes are used in the fields of geology (e.g., Shanks et al., 1981), biology (e.g., Rees, 1973; Habicht and Canfield, 1997; Habicht et al., 1998; Bolliger et al., 2001; Brüchert et al., 2001; Detmers et al., 2001) and environmental science (e.g., Harris et al., 2013), etc. Notably, research on the mass-independent fractionation of sulfur is currently the most active topic in the field of sulfur isotope geochemistry (Farquhar et al., 2000, 2001, 2013; Savarino et al., 2003; Subrata et al., 2013). It is well known that equilibrium isotope fractionation can be used to estimate the formation temperature of minerals in geological systems (Urey and Greiff, 1935; Urey, 1947). Isotope geochemistry mainly focuses on the change in the isotope ratio between different species rather than on their absolute abundances. The general rule for isotope fractionation is that heavy isotopes tend to form more stable chemical bonds; for example, M34S is more stable than M32S (M stands for metal cations). When considering kinetic isotope effects, molecules with different isotopes have different reaction rates (O’Neil, 1986). In the case of sulfur, 34S/32S is the key point of interest. In most cases, isotope fractionation is relatively small, and most of the time, the δ notation is used to express isotope fractionation. In this article, only the ratio of 34S/32S is Equilibrium sulfur isotope fractionations of several important sulfides