PRELIMINARY STRUCTURAL ANALYSIS OF TIMISKAMING BASINS ALONG THE LARDER LAKE-CADILLAC DEFORMATION ZONE, ONTARIO AND QUEBEC, CANADA: A RECORD OF ARCHEAN DEFORMATION IN THE SOUTHERN ABITIBI GREENSTONE BELT

The Abitibi greenstone belt in Ontario and Quebec represents one of North America’s largest gold producing districts. Timiskaming assemblage sedimentary and volcanic rocks host the majority of orogenic gold deposits in the region. These rocks were deposited into extensional basins developed along long-lived deformation zones late during the greenstone belt evolution. Characterizing the structural evolution of these basins is essential to understand the late stage tectonic evolution of the Abitibi, and the relationships between deformation and gold mineralization. Some of the economically most important Timiskaming assemblage basins in the southern Abitibi occur along the ~300 km long Larder Lake-Cadillac deformation zone (LLCdz). Structural analysis was carried out in a selection of representative areas along the LLCdz: the Vigrass Lake and Gull Lake areas near Kirkland Lake in Ontario, and the Rouyn area in Quebec.

The study areas display common structural characteristics including an E-trending fabric and an overprinting NE-trending fabric associated with dextral shear structures. These structures are interpreted to represent post-depositional N-S shortening followed by localized dextral shear. However, local variations exist, probably due to rheologic and geometric variations. The Vigrass Lake area displays low strain, preservation of primary structures, and contains no major orogenic gold deposits. The Gull Lake and Rouyn areas show strong fabrics in relatively wide and narrow deformation zones, respectively, and contain several zones of high economic potential. In the Rouyn area, the LLCdz separates the Abitibi greenstone belt to the north from the Pontiac subprovince to the south, and shows extensive pre-dextral shear top-to-the-north normal fabric. N-S shortening and dextral movement has been documented elsewhere along the LLCdz and along a deformation zone of comparable scale to the north (the Porcupine-Destor deformation zone). These deformation zones are probably related to late stage tectonic amalgamation and subsequent modification of the Abitibi greenstone belt. Normal movement is limited to the Quebec segment of the LLCdz and may be related to the exhumation of the Pontiac subprovince.