Composition of mineral inclusions and formation of polycrystalline diamondaggregates (Bort) from the Shengli kimberlite pipe, China

The growth features of four diamond aggregates (bort) of the variety VIII f rom the Shengli kimberlite pipe in China were studied using methods of scan ning (SEM) and transmission (TEM) electron microscopy. The inclusions of na tive iron and Fe-Cr intermetallides, sulfides (gersdorffite and siegenite), lizardite, phlogopite, apatite, barite, and potassic feldspar were found i n bort and bear significant genetic information. It was demonstrated that m icrocrystals composing these diamond aggregates show antisceletal faces (1 1 1) and present the transitional growth forms from octahedra to distorted rhombododecahedra. This fact can indicate a pressure decrease during the cr ystallization. The formation of the observed assemblages of mineral inclusi ons was interpreted using the hypothesis of diamond crystallization by inte raction of deep-source sulfur-bearing reduced fluids with mantle rocks.