Kinematic analysis of auriferous veins at the Sigma-2 gold mine, Louvicourt Township, Quebec

CIM Bulletin, Vol. 83, No. 941, 1990

C. Giguere, Departement des Sciences de la Terre, Universite du Quebec a Montreal, and J. Beland, Mineral Exploration Research Institute, Ecole Polytechnique, Montreal, Quebec

The auriferous mineralization at the Sigma-2 gold mine occurs in quartz-carbonate-tourmaline veins emplaced in a fractured grano-phyre layer in the upper part of a differentiated gabbro-diorite sill. Kinematic indicators show that fracture planes were active as strike-slip, dip-slip (reverse) and tensional faults. Measurements of attitudes of fractures and movement vectors indicate eight different sets that can be grouped into three systems: (1) an east-west oriented system includes a subvertical set and two other sets dipping north and south respectively; (2) a subhorizontal system of two conjugate sets bisected by a third tensional set; and (3) a system of subvertical conjugate northeast and north-northwest trending sets. Kinematic analysis indicates that the subvertical set of the east-west system was subjected to dextral strike-slip movement activated by a northwest-southeast compressive stress whereas the bulk deformation resulting from the remaining and subsequent seven sets can be explained by a protracted subhorizontal north-south compressive stress. The valuable gold mineralization is found principally in the fracture-filling veins of the subhorizontal system and subordinate-ly in the other sets; among these other sets, the NE trending subvertical one is slightly more favourable. The over-all tectonic picture is that of an early mild dextral strike-slip faulting in a ductile-brittle medium followed by a general flattening involving, first, a vertical and, later, a lateral extension by fracturing in a medium that had become brittle. The structural features are such that the differentiated sill could not be the source of the auriferous hydrothermal solutions.
Mots Clés: Sigma-2 gold mine, Gold mineralization.
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