Diamond discovered from the Dongbo mantle peridotite in the Yarlung Zangbo suture zone, Tibet

Abstract: This paper reports the discovery of unusual mantle mineral group in the mantle peridotites of Dongbo ophiolite, which lies in the western part of the Yarlung Zangbo suture zone. The Dongbo ophiolite consists mainly of harzburgite, with a small amount of lherzolite and dunite, pyroxenite and gabbro dikes cutting across the harzburgite. Geochemical characteristics suggest that the Dongbo mantle peridotite was derived from mid-ocean ridge (MOR) but modified in a suprasubduction zone (SSZ) environment. Some grains of diamond and other unusual minerals, such as moissanite, were recovered by standard mineral separation techniques from a 693 kg sample of harzburgite. The presence of diamond, native Cr, Au, Fe, Si and Cu, together with the moissanite, indicates a strong reducing environment. The authors also found a lot of alloys, oxides, sulfides, silicates, fluoride and some other materials. These mineral assemblages recovered from the Dongbo harzburgite are very similar to those of Luobusa and Purang harzburgite, which gives evidence to the ophiolite-type diamond.