Mineralogy, Geochemistry, and Genesis of Komatiite-Associated Ni-Cu-PGE Mineralization in the Thompson Nickel Belt, Manitoba
D. Layton-Matthews, C. M. Lesher, J. Liwanag, N. Halden, O. M. Burnham, L. Hulbert, D. C. Peck, R. R. Keays, 2011. "Mineralogy, Geochemistry, and Genesis of Komatiite-Associated Ni-Cu-PGE Mineralization in the Thompson Nickel Belt, Manitoba", Magmatic Ni-Cu and PGE Deposits: Geology, Geochemistry, and Genesis, Chusi Li, Edward M. Ripley
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The Ni-Cu-PGE ores in the 1.9 Ga Thompson nickel belt represent one of the worlds largest accumulations of mineralization associated with komatiites. Mineralization occurs as type I basal stratiform disseminated/net-textured/massive sulfides, type II internal strata-bound disseminated sulfides hosted by komatiitic dunite intrusions, type IVa Ni-rich sulfides, type IVb hydrothermal, and type V tectonically displaced breccia sulfides hosted by adjacent Pipe Formation sulfide facies iron formations, and metapelites. Although most of the ores exhibit a strong tectonometamorphic overprint, relict igneous textures in type II ores, the basal stratigraphic positions of type I ores, and the high Ni/Cu, low Pd/Ir ratios, and high S/Se ratios of type I and II ores indicate that they are derived by interaction of komatiitic magmas with sulfides incorporated from the enclosing iron formations at relatively low magma/sulfide ratios (R factors). The restrictive spatial association with type I ores, their high Ni-Pd-Cu, intermediate Co-Ru-Rh-Ir, and very low Cr tenors, and similarities to mineralization of this type in less deformed and metamorphosed areas suggest that type IVa ores formed via diffusion of metals into the metasedimentary rocks at the magmatic stage. Many ores are depleted in Pt > Cu > Au, which is interpreted to reflect preferential mobilization of these elements into wall rocks, most likely as bisulfide complexes, during polyphase deformation and middle-upper amphibolite facies metamorphism.