Re–Os isotopic composition and PGE contents of proterozoic carbonaceous argillites, Virginia Formation, Northeastern Minnesota

Abstract Carbonaceous, sulfidic argillites from the Proterozoic Virginia Formation in Minnesota have been investigated in terms of platinum group elements (PGE) distribution and Re–Os isotopic signatures. Kerogen from protoliths and slightly metamorphosed equivalents is characterized by Re and Os enrichment factors relative to whole rock concentrations that range from 4 to 272. Re–Os isotopic values of kerogen in samples that show no evidence of extensive recrystallization fall near a 1.85 Ga reference isochron. This age is consistent with that estimated for the Virginia Formation, and suggests that dating of organic-rich Precambrian sedimentary rocks and the retrieval of data pertinent to the Os isotopic evolution of seawater may be possible using the Re–Os isotopic system.