Low-Sulfide Mineralization with High Pd–Pt–Rh Tenor in Anorthosites from the Yoko-Dovyren Massif

During a geochemical study of taxitic platiniferous anorthosites of Reef I in the Yoko-Dovyren massif, a type of rock with a high ratio (tenor) of light platinum group elements (PGE) to sulfur has been described for the first time. Such rocks contain a total of up to 10.5 ppm Pd–Pt–Rh and <0.06 wt % S. They are associated in Reef I with already known anorthosites that have moderate PGE/S ratios and contain, according to our data, up to 6.5 ppm Pd–Pt–Rh in total and 0.3‒1.5 wt % S. The areas of high PGE tenor in anorthosites consist of plagioclase, may contain small amounts of olivine, and always contain orthopyroxene (several wt %), represented by xenomorphic segregations and amoeboid poikilitic crystals up to 10 cm in size. They contain intergrowths of Fe–Ni–Cu sulfides and hydrous minerals, usually smaller than 100 μm in size along with numerous submicron PGM grains. The extreme PGE/S ratio can be interpreted as the result of local accumulation of late fractions of a PGE-rich sulfide melt formed by crystallization of a sulfide liquid that was immiscible with silicate melt.