Petrology, geochemistry, and isotopic composition of magmatic sulphide occurrences in the Montagnais Sill Complex, northern Québec, Canada

The Labrador Trough of northern Québec is a site of ongoing exploration for magmatic Ni-Cu-PGE (platinum-group element) sulphide deposits. The region is considered favourable for such deposits because it is host to voluminous mafic-ultramafic intrusive and extrusive rocks of the Montagnais Sill Complex (MSC) that are located proximal to trans-crustal faults and sulphidebearing country rocks. In addition, the MSC is the easternmost segment of the ∼ 1.88 Ga Circum-Superior large igneous province, which hosts world-class magmatic Ni-Cu-PGE deposits in the Thompson and Cape Smith belts. However, only a number of sub-economic magmatic sulphide occurrences have been identified in the MSC. In the present study, the newly discovered Idefix PGE-Cu and Huckleberry Cu-Ni-(PGE) prospects are used as case studies to evaluate ore-forming processes operating in the Labrador Trough as well as the prospectivity of the region regarding magmatic sulphide deposits. The Idefix PGE-Cu prospect represents a > 400-m-thick stack of aphyric gabbro sills (∼ 8- 14 wt.% MgO, ∼ 1-8 Cr/V) that contain disseminated sulphides (0.2-0.4 g/t Pd+Pt+Au, 0.1- 0.5% Cu and chalcopyrite > pentlandite ≫ sulpharsenides) and partially controlled by tellurides and electrum. Whole-rock compositions provided no clear evidence for crustal contamination (e.g., La/SmN < 1, Th/YbN < 1, and S/Sewr < 4,000), yet the sulphides, and particularly globular sulphides, hav