Sulphur isotope variations within the Platreef Ni-Cu-PGE deposit: genetic implications for the origin of sulphide mineralisation.

Sulphur isotope studies of the Platreef, South Africa, indicated that magmatic signatures are preserved in early-formed sulphide droplets within the Platreef pyroxenites in the area from Sandsloot to Witrivier. These values are comparable to sulphide inclusions in diamonds in the nearby Klipspringer kimberlite and are considered to have a primary mantle origin. Later sulphides found in calc-silicate floor rocks at Sandsloot and Zwaltfontein and in xenoliths of calc-silicate throughout the section indicate an input of country rock S. Previous studies indicated that, in areas where the sedimentary floor rocks contain appreciable sulphides rather than sulphates, the Platreef sulphides are contaminated with country-rock S. Sulphur saturation in the Platreef magma took place before contamination, probably in a staging chamber prior to intrusion. A major pulse of magma entrained the preformed PGE- rich sulphides and was injected to form the Platreef, where assimilation of country-rock sulphides upgraded the S content on a local scale, and hydrothermal leaching introduced S from country-rock sulphates into later stage sulphides, also on a local scale.
Sulphur isotope studies of the Platreef, South Africa, indicated that magmatic signatures are preserved in early-formed sulphide droplets within the Platreef pyroxenites in the area from Sandsloot to Witrivier. These values are comparable to sulphide inclusions in diamonds in the nearby Klipspringer kimberlite and are considered to have a primary mantle origin. Later sulphides found in calc-silicate floor rocks at Sandsloot and Zwaltfontein and in xenoliths of calc-silicate throughout the section indicate an input of country rock S. Previous studies indicated that, in areas where the sedimentary floor rocks contain appreciable sulphides rather than sulphates, the Platreef sulphides are contaminated with country-rock S. Sulphur saturation in the Platreef magma took place before contamination, probably in a staging chamber prior to intrusion. A major pulse of magma entrained the preformed PGE- rich sulphides and was injected to form the Platreef, where assimilation of country-rock sulphides upgraded the S content on a local scale, and hydrothermal leaching introduced S from country-rock sulphates into later stage sulphides, also on a local scale.