Morphology, physical properties and paragenesis of inclusion-bearing diamonds from Yakutian kimberlites

Abstract

Inclusions in diamond crystals from three kimberlite pipes of the Yakutia diamond province, Siberia, U.S.S.R., have been studied by scanning electron-microscopy with colour cathodoluminescence, by spectroscopy in the visible, ultra-violet and infra-red ranges and by electron microprobe analysis. The kinds and chemistries of mineral inclusions in the investigated diamonds define peridotitic as well as eclogitic mineral association. Their mutual relationships are different in the different pipes. However, in all kimberlite bodies diamond crystals of the eclogitic paragenesis are much more common than previously recognized. In single diamond crystals the replacement of eclogitic diamond by by peridititic diamond has been defected by coloured cathodoluminescence imaging and by electron microprobe analysis. It is marked by about change of cathodoluminescence colour and by the nature and chemical composition of mineral inclusions. For the first time, diamonds formed at depths of less than 100 km were discovered. They contain inclusions of troilite, pyrrhotine, wüstite, native iron and SiO 2 (coesite?), and were formed at the early stage of diamond crystallisation. These enclosed prisoner diamond are richer in the light carbon isotope than the host diamonds. Four main stages of crystallisation have been established, each being documented by a specific set of inclusions.