Rodingite with Ti- and Cr-rich vesuvianite from the Sartuohai chromium deposit, Xinjiang, China

Abstract

Rodingite containing vesuvianite with the world's highest Cr₂O₃ and TiO₂ contents was found to occur in the ultramafic body of the Early to Middle Devonian Darbut-Sartuohai ophiolite zone belonging to the Sartuohai alpine-type ophiolitic melange, west Junggar district, Xinjiang, China. Many blocks of massive and vein rodingite were located at the Sartuohai chromium deposit in the serpentinized ultramafic body along the suture zone near Karamay. The rodingite is mainly composed of vesuvianite, grossular-andradite series garnet, diopside, and chlorite. The Cr₂O₃ content of the rodingite masses and veins is up to 0.2 wt% and 0.1 wt%, respectively. While the Cr₂O₃ content (wt%) of each mineral species in rodingite is up to 0.04 for vesuvianite, 0.4 for garnet and 0.4 for diopside, respectively. Tiny sporadic inclusions of vesuvianite and garnet of 5 μm to 35 μm in diameter also disseminate along the cleavage or in the grain of diopside of the massive rodingite. The vesuvianite inclusions are characterized by a high concentration in chromium of Cr₂O₃ = 6.21 wt% and titanium of TiO₂ = 7.43 wt% of all the reported data, in contrast to the low concentration in the host diopside. The garnet inclusions belong to the grandite series. The morimotoite and uvarovite components are 18% and 11% at most, respectively. The rodingite was considered to have been formed by two stages of metasomatism between gabbroic rock and a calcium-rich solution, which was probably produced in the process of serpentinization of peridotite under Cr- and Ti-rich, and Cr- and Ti-free environments.