Structural setting of the Young-Davidson syenite-hosted gold deposit in the Western Cadillac-Larder Lake Deformation Zone, Abitibi Greenstone Belt, Superior Province, Ontario

摘要

Within the southern Abitibi greenstone belt of the Superior Province, intrusion-related, in particular syenite-hosted gold deposits represent a significant type that is poorly understood. Whether the gold mineralization is genetically linked to the syenite intrusions (as in a magmatic model) or structurally associated with the development of subsequent shear zones remains very controversial. Our new structural data show that the multiply deformed Young-Davidson gold deposit and its surrounding Matachewan area occur along the western extension of the Cadillac - Larder Lake Deformation Zone (CLLDZ), a tectonically and economically important crustal-scale deformation zone in the southern Abitibi greenstone belt. Four generations (D1-D4) of deformation are recognized. The first part of the D_1 deformation (D_(1a)) records a NE-SW-oriented shortening and resulted in regional upright folding without penetrative foliation, whereas the subsequent D_(1b) generates regional penetrative foliations and top-to-NE reverse faults. D_2 occurs during a NW-SE-oriented shortening and produces asymmetric folds, oblique-slip thrusts and dextral strike-slip shear zones. D3 semi-brittle deformation refolds the D_1 and D_2 fabrics, whereas the latest D4 sinistral fault records a Paleoproterozoic brittle deformation. The Young-Davidson deposit is a lode-gold deposit that at least in part was structurally controlled. It is associated with the development of the CLLDZ and hosted in a syenite. Four main generations of veins are identified in the syenite. V_1 veins are characterized by folded and boudinaged quartz-ankerite veins， V_2 veins are represented by folded or en echelon quartz-pyrite veinlets, V_3 veins are comprised of en echelon quartz-carbonate veins with sulfide minerals, and V_4 veins consist of planar carbonate-quartz veins and minor hematite. Petrological studies reveal that the major phase of gold mineralization is associated with the V2 veins and partially with the V3 veins. Gold mineralization and emplacement of the associated veins appear to have occurred during regional D_(1b) NE-SW-oriented shortening and top-to-NE shearing and the syenite acted as a mechanical trap due to competency contrast to the wall rock.