ABSTRACT

Helium and argon isotopic data of diamonds suggest that the mantle where diamonds crystallised has remained almost a closed system for most of the Earth's history. The ³He/⁴He–³He evolution diagram implies that at least two diamonds studied are nearly as old as the Earth. Carbon isotopic compositions of the stones studied varied from -3.3 to -29.7‰, while older diamonds show less deviation from the generally considered average δ¹³C for diamonds.