Sulphur isotopes and the early Archaean sulphur cycle

The early Archaean sulphur cycle continues to be discussed rather controversially on the basis of mass-dependent and -independent sulphur isotope fractionations in sedimentary sulphates and sulphides. Major debates are the ultimate sulphur source and the isotopic composition of seawater sulphate and the process(es) involved in the formation of sedimentary pyrite. New results for sedimentary pyrite from the Isua Greenstone Belt, SW Greenland are presented. Current views of the global sulphur cycle are evaluated which are based on these and additional published sulphur isotope records for southern Africa, Western Australia and India. In view of the absence of unequivocal evidence for a clearly biological origin, magmatic/hydrothermal processes are considered to be largely responsible for the precipitation of sulphides in sedimentary environments of early Archaean age. Sedimentary sulphides from the Warrawoona Group, Australia, could represent a possible exception.