Diamond Discovered in High‐Al Chromitites of the Sartohay Ophiolite, Xinjiang Province, China

Abstract

AbstractIn recent years diamonds and other exotic minerals have been recovered from mantle peridotites and high‐Cr chromitites of a number of ophiolites of different age and different tectonic environments. Here we report a similar collection of minerals from the Sartohay ophiolite of Xinjiang Province, western China, which is characterized by having high‐Al chromitites. Several samples of massive podiform chromitite with an aggregate weight of nearly 900 kg yielded diamonds, moissanite and other highly reduced minerals, as well as common crustal minerals. Thus far, more than 20 grains each of diamond and moissanite have been recovered from heavy mineral separates of the chromitites. The diamonds are all 100–200 μm in size and range in color from pale yellow to reddish‐orange to colorless. Most of the grains are anhedral to subhedral octahedra, commonly with elongate forms exhibiting well‐developed striations. They all display characteristic Raman spectra with shifts between 1325 cm−1 and 1333 cm−1, mostly 1331.51 cm−1 or 1326.96 cm−1. The moissanite grains are light blue to dark blue, broken crystals, 50–150 μm across, commonly occurring as small flakes or fragments. Their typical Raman spectra have shifts at 762 cm−1, 785 cm−1, and 966 cm−1. This investigation extends the occurrence of diamonds and moissanite to a Paleozoic ophiolite in the Central Asian Orogenic Belt and demonstrates that these minerals can also occur in high‐Al chromitites. We conclude that diamonds and moissanite are likely to be ubiquitous in ophiolitic mantle peridotites and chromitites.