CONTROLS ON THE REGIONAL DISTRIBUTION OF IRON-NICKEL COPPER PLATINUM-GROUP ELEMENT SULFIDE MINERALIZATION IN THE EASTERN CAPE SMITH BELT, QUEBEC

Fe - Ni - Cu - platinum-group element (PGE) mineralization in the east ern Cape Smith Belt (Quebec) is hosted by ultramafic and differentiate d mafic-ultramafic bodies (high-level sills and dykes, lava lakes, or channelized lava flows). These units of Early Proterozoic age are asso ciated with both volcanic and sedimentary rocks (Povungnituk Group) th at accumulated during continental rifting and a transitional continent al to oceanic basalt sequence (Chukotat Group). Mineralization is foun d in two principal horizons. Important deposits occur in the Raglan ho rizon located near the tectonic boundary between the Povungnituk and C hukotat groups. A second mineralized zone, termed the Delta horizon, o ccurs within the Povungnituk Group and contains smaller sulfide showin gs. The distribution of proximal-distal sedimentary facies in the Povu ngnituk Group represents an important control on the localization, gra de, and size of the sulfide deposits and showings. Deposits in the Rag lan horizon are associated with relatively distal sedimentary units of the Povungnituk Group. In contrast, the Delta horizon occurs in a mor e proximal (quartz-rich) facies of the Povungnituk Group which is inte rlayered with volcanic rocks and marked by a profound decrease in the proportion of fine-grained, sulfidic beds relative to the Raglan horiz on. Regional mapping has shown that the Cape Smith Belt is a thin-skin ned thrust belt containing imbricates of Povungnituk Group and Chukota t Group rocks and thus controlling the regional extent of the minerali zed horizons. Critically, the along-strike continuity of the Raglan ho rizon (85 km) is determined by the three-dimensional structural geomet ry of a late thrust fault.