About the first discovery of titanium–containing hydroxylclinohumite in podiform chromitite

For the first time in podiform chromitites, a mineral of the humite group, titanium–containing hydroxylclinohumite, belonging to natural dense water-containing magnesian silicates (DHMS phases), was found. The find was made in chrome ores of the Paity plateau, located in the northern part of the Voikaro-Synyinsky ultramafic massif of the Polar Urals. Chromitites are deposited in the dunite body, which is located at the contact of apoharzburgite amphibole-olivine-antigorite and amphibole-enstatite-olivine metamorphic rocks containing relics of non-serpentinized harzburgites. According to optical data and chemical composition, the mineral belongs to titanium-containing hydroxylclinohumite, since it contains TiO2 (up to 5.64 wt.%), in the complete absence of fluoride. The presence of OH-grouping in the mineral is confirmed by the Raman spectrum, which generally corresponds to the standard of hydroxylclinohumite. The results of geothermometry show that this mineral was formed in chromitites of the Polar Urals at a temperature of 668–740º with and, probably, a pressure of 20–25 kbar. It follows from this that the formation (or recrystallization) of chromite ores occurred under high-pressure conditions, i. e. ore occurrences of chromites in the northern part of the Voikaro-Synyinsky massif were formed, apparently, in a suprasubduction environment.