Platinum Group Element Enrichment and Mobilization in the Mesamax and Expo Ni-Cu-PGE Magmatic Sulfide Deposits, Cape Smith Fold Belt, New Quebec

English Abstract:

The Expo and Mesamax Ni-Cu-PGE magmatic sulfide deposits are hosted within the Expo Intrusive Suite (EIS). The EIS consists of rocks of dunite to gabbronorite composition which have been metamorphosed by the Trans-Hudson orogen to the greenschist facies dominated by tremolite-actinolite, serpentine and chlorite. Both deposits consist of lenses of massive sulfides mainly composed of pyrrhotite-chalcopyrite-pentlandite-magnetite overlain by net-textured and disseminated sulfides. Palladium and platinum are significantly enriched at the vicinity of the contact between the net texture and the massive sulfide (Pt content as high as 236.1 ppm) and also in association with late talc- carbonate alterations. The scope of this study is to investigate PGE enrichment and mobilization mechanisms occurring in both deposits. Samples from the inner and outer zone of Mesamax and Expo were selected for geochemical assays at the onsite lab (Au, Pt, Pd, Ag, Rh, Cr, Cu, Fe, Mg, Ni, Co). A second selection was made for petrography, SEM, X-Ray mapping and LA-ICP-MS, based on the texture (massive sulfide, net texture, veins or alteration zones) and the PGE/ Cu+Ni ratio. From the preliminary results, there is an association between PGEs and carbonate alteration which suggests that CO2-bearing fluids mobilized PGEs during later events.