The sulphur isotope geochemistry of carbonatites and associated silicate rocks from the Superior Province of the Canadian Shield

Abstract

Thirty-five sulphur isotopic analyses have been obtained from six carbonatite-alkalic rock complexes ranging in age from 1906 Ma to 1008 Ma located within the Ontario portion of the Superior Province. Pyrrhotite, chalcopyrite and pyrite mineral separates were used. The overall range of delta 34SCDT values are from +3.4 to -4.5‰. Each complex shows its own distinct range and mean sulphur isotopic composition. The overall range in the sulphur isotopic composition in conjunction with carbon and oxygen isotopic data suggests that these carbonatites and associated silicate rocks were derived from a relatively primitive mantle source. This is consistent with previously published Sr and Nd isotopic data that suggest that the mantle source underlying the Superior Province has remained essentially a closed system from about 2700 Ma to at least 1008 Ma. The sulphur isotopic data reported here is the first ever for carbonatites from the Superior Province. (Abstract shortened by UMI.)