Geological overview

The Cape Smith Belt in Nord-du-Québec, from the Lower PaleoProterozoic Era, is composed of a belt of volcano-sedimentary rocks extending over 370 km in an E–NE direction. The area is divided into four main tectonic units (Figure 1):

1. the autochthonous Archean basement of the Superior Province;
2. the allochthonous accretionary belt, or Ungava Trough s.s., made up of tectonic slices with south vergence;
3. the Narsajuaq Terrane, from the PaleoProterozoic Era; and
4. the parautochthonous Archean basement, locally separating the allochthonous accretionary belt and the Narsajuaq Terrane along the Kovik Antiform.

The Cape Smith Belt is composed of seven tectonostratigraphic units divided into north and south lithotectonic domains separated by the Bergeron Fault (Figure 1). The South Domain contains three groups. From south to north these are: the Lamarche Group, composed of a proximal to distal sediment assemblage, is cut by several gabbro sills; the Povungnituk Group, composed of tholeiitic flows, lies in angular unconformity over the Archean basement; and the Chukotat Group, made up primarily of basalts, komatiites and tholeiites. The North Domain is composed of:

1. the Chassé Formation (parautochthonous detrital unit);
2. the Watts Group (sedimentary and metavolcanic rocks), cut by mafic (peridotite, pyroxenite and gabbro) to felsic intrusions, overlaps the Chukotat along the Bergeron Fault in the south and is separated from the Archean basement by a décollement zone (Deception Complex) in the north;
3. the Parent Group, made up of a tuff and tholeiite-flow assemblage associated with felsic tuffs and dacitic and rhyolitic domes;
4. the Spartan Group, composed of psammites, pelites, semipelites, sandstones, felsic tuffs locally, and thick layers of mudstone; and
5. the Perreault Group, composed of a detrital assemblage consisting of wacke, conglomerate, sandstone (feldspathic) and mudstone.

Several subdivisions for deposits containing Ni, Cu and/or PGE mineralization have been suggested. The subdivision proposed by Thériault et al. (2002) for the Ni–Cu–PGE mineralization map of Québec has been adopted here.