The First Finding of Ti-Bearing Hydroxylclinohumite in Podiform Chromite.

A humite group mineral, Ti-bearing hydroxylclinohumite, referred to natural compact water-containing magnesian silicates (DHMS phases) was found for the first time in podiform chromitites. The finding was made in chrome ores of the Paity Plateau located in the northern part of the Voikar–Synya ultramafic massif of the Polar Urals. Chromitites deposited in the dunite body located at the contact of apoharzburgite amphibole–olivine–antigorite and amphibole–enstatite–olivine metamorphic rocks containing nonserpentinized harzburgite relics. According to the optical data and chemical composition, this mineral belongs to Ti-bearing hydroxylclinohumite, because it contains TiO2 (up to 5.64 wt %) and is absolutely devoid of F. The OH-group in the mineral is confirmed by the Raman spectrum generally corresponding to the hydroxylclinohumite standard. According to the geothermometry results, this mineral was formed in chromitites of the Polar Urals at a temperature of 668–740°C and, probably, a pressure of 20–25 kbar. Hence, chromite ores were generated (recrystallized) under high-pressure conditions. In other words, the chromite ore occurrences in the northern part of the Voikar–Synya massif developed, apparently, in the suprasubduction environment. [ABSTRACT FROM AUTHOR]