Geology and structure of a sulfide-rich gold deposit; an example from the Mouska gold mine, Bousquet District, Canada

Abstract

The Mouska mine in the Bousquet mining district represents a sulfide-rich gold deposit hosted by the Archean mafic metavolcanites of the Blake River Group, southern Abitibi greenstone belt. Mineralization shows both lithological and structural control and coincides with variably oriented high angle-reverse ductile and brittle-ductile shear zones. Host shear zones are superimposed on the regional foliation, and both appear to have formed from the same bulk stress field. Gold mineralization is composed of sulfide and quartz lodes and is associated with three distinct ore zones; each differs from the others by its style of veining and the nature of tectono-metamorphic overprint. Sulfide mineralization in this area varies from semimassive to massive sulfide lodes and dissemination. The strain features and age relationships of ore-bearing rocks and vein material throughout the ore zones display evidence of earlier sulfide mineralization with gold. This mineralization is pretectonic (with respect to the development of the foliation) and is interpreted as hydrothermal-synvolcanic. The auriferous quartz sulfide veins correspond to a multistage syn- to late tectonic mineralization and clearly crosscuts massive sulfide bodies. In the Mouska deposit, strain features and structural setting of gold mineralization show interactions between lithological factors, such as contacts, competency contrast and rock-body geometry, and the presence of pretectonic sulfides. In several parts of the mine volcanic sequence, the shear zone nucleation and development were controlled by both rock heterogeneities and the presence of soft sulfide bodies. The sulfides, in particular, were responsible for the structural instability recorded in some volcanic contacts and their activation as shear zones. In other parts, the sulfides have variably influenced the local slip movement. The shapes of ore shoots throughout the ore zones are variable and interpreted as reflecting the initial geometry of anisotropic interfaces involved in the deformation history.