PLATINUM-GROUP MINERALS IN PYROXENITE FROM THE BOSTON CREEK FLOW BASALTIC KOMATIITE, ABITIBI GREENSTONE-BELT, ONTARIO

The first occurrence of platinum-group minerals (PGM) in Abitibi belt volcanic rocks has been discovered in pyroxenite from the Boston Creek Flow basaltic komatiite, Ontario. The PGM observed are bismuthian merenskyite, merenskyite, bismuthian kotulskite, mertieite or stibiopalladinite, an unnamed Pd-Ag sulfide, sperrylite, and an unnamed Rh-Pt sulfarsenide. The grains are submicrometric to 15-mu-m in diameter, making in situ analysis difficult. The mineralization was observed in samples of clinopyroxenite and spinel (Fe-Ti oxide) clinopyroxenite collected at the margins of a 7-m-thick zone of altered pyroxenite. The platinum mineralization is characterized by spatial association with Cu-Fe sulfides, native gold, electrum, and a suite of silver minerals, and with secondary silicate alteration of Fe-Ti oxide and groundmass. There is an absence of nickel sulfide. Textural evidence and spatial associations indicate that the mineralization originated by hydrothermal processes. Hydrothermal fluid activity accompanying cooling of the flow or later greenschist-facies metamorphism appears to have mobilized and reconcentrated PGE during alteration of Fe-Ti oxide and brittle deformation.