Origin of Diamonds in Chromitites of the Luobusa Ophiolite, Southern Tibet, China

Abstract

Diamonds and an extensive assemblage of associated minerals were discovered in podiform chromitites of the Luobusa ophiolite, southern Tibet, China. Thus far, 25 diamonds have been recovered from the mineral separates of samples collected in 1996.

All the diamonds are colourless and transparent. Most of them are euhedral crystals, showing sharp-edged octahedral morphology. Others are broken fragments. Both Raman spectra and X-ray diffraction techniques have been used to confirm the identification of the diamonds.

Minerals associated with the diamonds include chromite, forsterite, enstatite, Cr-diopside, PGE minerals, graphite, SiC (moissanite), gehlenite, Si-Fe and Cr-C alloys, zircon, sphene, rutile, apatite, corundum, sillimanite, plagioclase, K-feldspar, amphibole, biotite, phlogopite, chlorite, serpentine, sulphides, carbonates, celestite, uvarovite, almandine; wollastonite, quartz, and Fe-Ni and Au-Ag alloys. All the minerals were recovered from mineral separates and confirmed by either electron microprobe or X-ray diffraction studies.

The sampling and separation procedures were designed to minimize any possibility of natural or anthropogenic contamination of the samples.