Local variations in carbon isotopes and nitrogen contents in diamonds from placers of the northeastern portion of the Siberian Platform

Variations in the isotopic composition of carbon and the nitrogen contents in diamonds from placers of the northeastern portion of the Siberian Platform have been examined. The results obtained indicate that there is no correlation between local variations in the isotopic composition of carbon and the nitrogen content and the degree of nitrogen aggregation. It has been demonstrated that changes in oxygen fugacity in the course of the growth of diamonds of the V variety do not affect the isotopic composition of carbon. The nature of the variations in the isotopic composition of carbon and the nitrogen contents indicate that there were at least two sources of carbon. The sources of lightweight and weighted compositions of carbon in the diamonds could be organic carbon and carbon in marine carbonates of the subducted crust of the Earth, respectively. Mantle carbon was involved in the diamond formation process at the final stages of the growth.