The Coulon volcanogenic massive sulphide deposit, Northern Quebec: context, structure, alteration and zonation

English Abstract:

The Coulon volcanogenic massive sulphides deposit (14 mt @ 1.3% Cu and 3.9% Zn), located in Northern Quebec, has been strongly deformed and metamorphosed in high grade conditions, and its primary characteristics have been modified. Within the study area near lenses 08, 9-25, 44 and 16-17, five lithological units have been recognized: amphibolite, and sillimanite-, cordierite-sillimanite-, cordierite- and cordierite-anthophyllite-bearing schists. The schist that contains porphyroblastic sillimanite corresponds to the main unit and is characterised by a well-developed planar fabric. However, proximal to the sulphide lenses, cordierite and anthophyllite porphyroblasts overprinting the structural fabrics are observed; and these minerals are likely the metamorphosed equivalent of minerals formed by chloritization (cf. Mg-alteration). Using the TiO2 vs Zr diagram to characterize the main groups of volcanic rocks, basaltic, andesitic and two types of rhyolite were discriminated. The area is characterized by a steeply dipping foliation associated to a D1 event overprinted by regional and local folds related to a D2 event. The main fabric (D1) strikes north-south in the northern part of the study area and is NE-SW trending in the southern portion. A steep stretching lineation is especially visible in the southern area, but is completely obliterated by metamorphic recrystallization in the northern portion. The massive sulphide lenses exhibit a pyrite-pyrrhotite-chalcopyrite-sphalerite-galena paragenesis. Generally of metric to decametric thickness, lenses extend up to 300 meters horizontally and to 700 meters vertically. The project investigate the geometrical and textural changes that the orebodies underwent as a result of metamorphism and deformations, with particular focus on the remobilisation problematics in the perspective of adjusting exploration guides.