Archean volcanism and sedimentation in the Bousquet gold district, Abitibi greenstone belt, Quebec: Implications for stratigraphy and gold concentration

Research on the nature and distribution of Archean rock types in the Bousquet gold district, Abitibi, Quebec, provides new constraints on deposition, stratigraphy, and gold concentration. Facies changes and textures indicate that within the Blake River Group of the district, basalt to the east is more proximal to an eruptive center which shoaled upward, andesite was deposited in relatively shallow subaqeuous conditions as pyroclastic flow deposits and turbidites around volcanic complexes formed on the basalt eruptive center, and dacite accumulated as lava which erupted into a very shallow subaqueous setting. Turbidites in the Kewagama and Cadillac groups originated from the volcanic complexes and accumulated in the form of subaqueous fans, whereas those in the Pontiac Group are from an unknown source and accumulated on an abyssal plain. In this context, the Cadillac-Larder break formed initially as a low-angle normal fault zone.

Field relations and petrography of the rocks in the district indicate that the stratigraphic section consists of generally well preserved and largely informable rock units. Opposing stratigraphic tops in the volcanic rocks of the Blake River and Piché groups suggest that they could be correlatives disposed on opposite limbs of a regional-scale syncline, the axial plane of which passes through the Cadillac Group. Accordingly, the rocks of the Blake River, Piché, and Cadillac groups may be part of a vast, largely subsided and reworked volcanic complex. The shallow subaqueous depositional environment of the andesite and dacite in the Blake River Group could have economic significance because boiling of hydrothermal fluid may have contributed to the concentration of gold in the Bousquet gold district.