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Synthesis of the structural evolution and associated gold mineralization of the Cadillac Fault, Abitibi, Canada

2016; Elsevier BV; Volume: 82; Linguagem: Inglês

10.1016/j.oregeorev.2016.11.029

1872-7360

Pierre Bedeaux, Pierre Pilote, Réal Daigneault, Silvain Rafini,

Geochemistry and Geologic Mapping

The Cadillac Fault Zone (CFZ) is a 250 km-long east-trending crustal discontinuity associated with numerous world-class gold deposits in the Archean Abitibi Subprovince. In Quebec, the fault follows the boundary between the Abitibi and the Pontiac Subprovinces and can be divided into four segments: 1) Rouyn, 2) Joannes, 3) Malartic, and 4) Val-d’Or. Each displays different attitudes and structural styles. The Malartic segment strikes SE, whereas the other segments are E-trending. Abrupt changes in strike or smaller-scale faults represent limits between the segments. Structural styles include four generations of foliation with numerous shear sense indicators and folding specifically related to each foliation. Structural features can be correlated from one segment to another, but display clear variations in attitude or expression. A stretching lineation signature is definitely associated with each segment. In the Malartic segment, the predominant E-trending schistosity displays an angular relationship with the contact between groups and bedding, suggesting that the SE-trending architecture of this segment was already emplaced prior to ductile deformation. The evidence suggests a model where the CFZ originates from several independent structures inherited from volcanism prior to Timiskaming deformation and Abitibi-Pontiac accretion. The proto-CFZ was then linked up during the Timiskaming deposition, forming high-strain zones. Inherited structures form the frame on which each deformation event was overprinted with different responses depending on segmentation. The structural styles of each segment can be integrated in a structural evolution model for the CFZ. The N-S shortening led to the development of a dominantly E-striking penetrative foliation and folding. During the subsequent extensional stage, the CFZ was reactivated with normal kinematics during the Pontiac uplift. A third deformation event is represented by the local development of NW-trending cleavage axial planar to the “S”-shaped minor folds. Finally, a late NW-SE shortening event produced a dextral strike-slip movement, with NE-striking vertical foliation and development of “Z”-shaped folds on bedding surfaces and anterior fabrics. Linkage of the CFZ had a major impact on hydrothermal activity in the southern Abitibi as it channeled fluids along large-scale pathways. Distribution of gold-bearing intrusions can also be related to segmentation and inherited structures of the CFZ. This association is expressed by gold mineralization styles present in several longitudinal fields reflecting fault segmentation.