Stratigraphic Distribution and Genesis of Gold Deposits, Bousquet Region, Northwestern Quebec

Special Volume, Vol. SV 24, No. 1982, 1982

The Bousquet region now contains three producing gold mines and has the potential of becoming one of the major gold producing regions of the Abitibi greenstone belt. Gold occurs in three distinct geological settings. Firstly, auriferous, stratiform and stratified quartz-muscovite-pyrite bodies or massive pyritic lenses such as at Dumagami, Bousquet and Silvers tack are situated along the north limb of the Cadillac syncline at the stratigraphic top of the Blake Riv_er Group, a predominantly volcanic assemblage of tholeiitic basalts overlain by increasingly felsic flows and fragmental rocks. Secondly, auriferous subconformable quartz veins and pyritic cherts of the Darius and Kewagama deposits occur within clastic sedimentary rocks and interlayered basalt flows of the Piche Group, probably along the zone where the volcanic and sedimentary rocks are intercalated and the former give way to the latter. The Piche rocks are on the south limb of the Cadillac syncline and represent the distal facies equivalents of the Blake River volcanic rocks. Thirdly, auriferous chalcopyrite- and pyrite-bearing quartz veins of Mooshla Gold Mines Ltd. occur within the Mooshla granodiorite stock, which intrudes the Blake River Group. The sequence of eveflts in greenstone belt and gold deposit development apparently began with submarine extrusion of the basalt that forms the base of the Blake River Group. This was followed by deposition of mafic and felsic pyroclastic rocks·and by emplacement of the Mooshla granodiorite stock. This stock represents a high-level magma chamber which fed felsic volcanic rocks that were extruded at the end of the volcanic cycle. Sea-water convection through the volcanic and plutonic rocks occurred during their cooling and transported metals upward, where they were precipitated both into fractures within the stock to form deposits of the third type and directly on the sea floor to form deposits of the first and second types. This leaching and redeposition of Au resulted in the formation of all three types of deposits during continuing volcanic-related hydrothermal activity. The later folding of strata about the Cadillac syncline separated the deposits into two geographic areas. The Dumagami, Bousquet and Silverstack deposits to the north are hosted by rocks deposited in a central and predominantly volcanic environment, whereas the Darius and Kewagama deposits to the south are hosted by rocks of more distal lithofacies of this same volcanic environment

Keywords: Gold, gold mining, stratisgraphy, Abitibi greenstone belt, volcanic environment.