Geological interpretation of the northern flank of the Matagami camp, Quebec, using gravity and magnetic inversions

Abstract

The northern flank of the Galine anticline of the Matagami camp has been well known for decades for hosting polymetallic VMS deposits (mostly copper and zinc). In such an already explored area, sophisticated exploration tools must be used in the hope of generating new information. By integrating geophysical, petrophysical, and geological data into a three-dimensional (3D) common earth model to constrain gravity and magnetic inversions, our objective was to validate and improve the geological interpretations of the area and to highlight geophysical anomalies unexplained in the current geological model. Both 3D magnetic and gravity data inversions confirm the surface geometry and the steep dip of the geological units. The inverted gravity models indicate that units observable at the surface of the northern flank extend subvertically to several kilometres in depth. The pyroxenitic phase of the Bell River Complex is most certainly dipping steeply to the south, contrary to some surface measurements. The Olga pluton shows no significant decrease in width at depth, with the exception of the west end, which appears to be an apophysis. A major unknown mass, which may correspond to a synvolcanic mafic intrusion that is not outcropping, is revealed in the Allard River volcanic rocks. This improved geophysical model featuring geometrical constraints obtained by careful processing and inversion of the potential-fields data could contribute to new exploration targets.