Sulfur isotope composition of secondary Ru-Os-Ir sulfides and sulfoarsenides from the Verkh-Neivinsk dunite-harzburgite massif (Middle Urals)

Limited data on the isotopic composition of sulfur of platinum-group minerals (PGM) are reported in the literature. The LA-ICP-MS method was used to study the S-isotopic composition of Ru-Os-Ir sulfides and sulfoarsenides forming secondary corrosion and superimposed PGM assemblages from placer deposit of the East Shishim river occurring within the Verkh-Neivinsky dunite-harzburgite massif. Sulfides from corrosion PGM assemblage (laurite, As-containing laurite) replace the grains of primary native Os and Ru minerals, forming rims on them. PGM from superimposed assemblage (laurite, irarsite, tolovkite, etc.) originated on the surface of laurite rims that form part of corrosion PGM assemblage. Variations in d34S values of secondary PGM (from -4.6 to 7.6 ‰) are more pronounced than those for laurite and erlichmanite from primary PGM assemblage (i. e., 0.2-2.3 ‰). The results are consistent with a model of the ultramafic massif ascending to the surface and subsequent water metamorphism during the tectonic flow and crust-mantle interaction. At the initial stage of metamorphism, mantle sulfur is present, isotopically lightened under oxidation conditions and temperature reduction. The final stage is marked by sulfur of the metamorphic fluid formed by the involvement of isotopically-heavy sulfur derived from the host sedimentary rocks.