The Genesis of PGE Mineralization in the River Valley Intrusion, Ontario, Canada
The 2.48 Ga, mafic, River Valley Intrusion hosts contact-style Cu-platinum group element (PGE) mineralization. Magmatic sulphides comprise pyrrhotite ± chalcopyrite ± pentlandite whereas hydrothermal sulphides comprise chalcopyrite ± pyrite ± marcasite. The latter are more widespread, forming a halo up to 150 m from the mineralized zone, and are intimately associated with replacement assemblages comprising 1) amphibole ± chlorite ± epidote ± biotite ± quartz ± carbonate ± sodic plagioclase, and 2) K-feldspar + chlorite + quartz ± amphibole ± muscovite ± sodic plagioclase. Platinum group minerals (PGM) in magmatic sulphides are mostly moncheite and kotulskite. Most PGM, however, occur with hydrothermal silicates and sulphides and are dominated by kotulskite, isomertieite, sperrylite, and un-named Pd- and Pt-alloys. Fluid-rock interaction has caused widespread redistribution of base metals, sulphur and PGE. A lithogeochemical hydrothermal dispersion halo, best defined by Cu, extends well into the hanging wall of the mineralized zone.