ANATOMY OF THE NI-CU-(PGE) MINERALIZED EXPO-RAGLAN DIKE-SILL-LAVA CHANNEL SYSTEM IN THE EARLY PROTEROZOIC CAPE SMITH BELT, NUNAVIK, QUEBEC

The N part of the Circum-Superior belt is represented by the 2.0-1.9 Ga Cape Smith fold and thrust belt, which extends >300 km E-W across the Ungava Peninsula. Excellent exposure and low-grade metamorphism in the central part provide an ideal setting to study the evolution of a mineralized magmatic plumbing system. The volcano-sedimentary sequence in this area comprises (S to N): siliciclastic sediments and lesser tholeiitic basalt, iron formation, and carbonates (lower Povungnituk Gp); massive-pillowed tholeiitic basalts (middle Povungnituk Gp); siltstones-shales (upper Povungnituk Gp); and thick peridotite-(pyroxenite) lava channels and locally invasive channelized peridotite-(pyroxenite) to Ol pyroxenite\gabbro sheet flows (Raglan Fm), and massive-pillowed Ol-phyric, Pyx-phyric, and Plag-phyric komatiitic to tholeiitic basalts (Chukotat Gp). The entire section is variably folded and locally thrust faulted, but contact metamorphosed sediments and thermomechanically-erosive contacts at the base of the Raglan Fm (or in its absence a 1-3 m-thick regionally extensive ferruginous horizon) indicate that the sequence is broadly conformable. The volcano-sedimentary sequence contains numerous mineralized mafic ± ultramafic intrusions. Bladed Ol pyroxenite ± pyroxenite dikes in the middle-upper Povungnituk Gp (e.g., Expo-Méquillon) host Cu-Ni-(PGE) mineralization along their sides and keels. Gabbro, pyroxenite\gabbro, and Ol pyroxenite\gabbro sills intrude all parts of the Povungnituk Group, the latter of which locally contain stratiform PGE-(Cu)-(Ni) mineralization (e.g., Delta). Peridotite lava channels and the Ol pyroxenite channelized parts of sheet flows at the base of the Chukotat Group host Ni-Cu-(PGE) mineralization at or near their lower contacts (e.g., Raglan deposits). Relationships between various components of the magmatic plumbing system are being determined through field mapping, geochemistry, and geochronology. Preliminary data indicate that various components of the magmatic plumbing system are temporally and petrogenetically related, but bladed dikes and differentiated sills in the Expo and Delta parts of the system are derived from less magnesian magmas and do not represent feeders to lava channels and channelized sheet flows in the Raglan parts of the system.