- © The Mineralogical Society Of America
Sulfur, the 10th most abundant element in the universe and the 14th most abundant element in the Earth’s crust, is the defining element of sulfide minerals and provides insights into the origins of these minerals through its stable isotopes. The insights come from variations in the isotopic composition of sulfide minerals and related compounds such as sulfate minerals or aqueous sulfur species, caused by preferential partitioning of isotopes among sulfur-bearing phases, known as fractionation. These variations arise from differences in temperature, or more importantly, oxidation and reduction reactions acting upon the sulfur. The oxidation and reduction reactions can occur at high temperature, such as in igneous systems, at intermediate temperatures, such as in hydrothermal systems, and at low temperature during sedimentary diagenesis. At high temperatures, the reactions tend to occur under equilibrium conditions, whereas at low temperatures, disequilibrium is prevalent. In addition, upper atmospheric processes also lead to isotopic fractionations that locally appear in the geologic record.
Sulfur isotope geochemistry as a subdiscipline of the geological sciences began in the late 1940s and early 1950s with early publications by Thode et al. (1949) and Szabo et al. (1950) on natural variations of sulfur isotopes, and Macnamara and Thode (1950) on the isotopic composition of terrestrial and meteoritic sulfur. Sakai (1957) presented an early scientific summary of sulfur isotope geochemistry, with a particular emphasis on high-temperature processes. Thode et al. (1961) also presented an early summary, but with an emphasis on low-temperature processes. Both of these summaries outlined salient aspects of the global sulfur cycle. Sulfur isotope geochemistry understandably has had a long history of application to the study of sulfide-bearing mineral deposits. Early noteworthy papers include those by Kulp et al. (1956) and Jensen (1957, 1959). Similarly, there is also a legacy of contributions to understanding …