SYNTHESIS OF THE STRUCTURAL EVOLUTION AND ASSOCIATED GOLD MINERALIZATION OF THE CADILLAC FAULT, ABITIBI, CANADA

The Larder Lake-Cadillac Fault (LLCF) represents a major fault in the Superior Province, ranging from Ontario to Quebec. Several deformation events are documented: thrusting, extension and dextral and senestral strike-slip movements. However, the integration and the chronological relationships of those events in a tectonic setting are still debated. Moreover, important gold mineralization is spatially associated to the LLCF but its temporal relationship with deformation is poorly understood. In Quebec, the LLCF symbolize the boundary between the Abitibi Subprovince in the North and the Pontiac Subprovince in the South. The fault can be divided into the Rouyn, Malartic and Val-d’Or segments depending on their orientation from West to East. Rouyn and Val-d’Or segments are East-striking while the Malartic segment is South-East-striking. Our project aims at synthesizing the structural signatures along the fault and integrating them in a structural model. During the summers of 2013 and 2014, several cross-sections through the fault were performed in order to establish variations in the structural signature of each segment.

The structural signature is dominated by a well-developed vertical East-striking schistosity associated with isoclinal folds and reverse shear zone, suggesting a thrusting event. The associated stretching lineation is generally down-dipping. In the Malartic segment, the schistosity curves parallel next to South-East-striking faults. Dip-parallel stretched objects recorded in the Rouyn segment along with a subhorizontal cleavage suggest an exhumation event postdating thrusting. This interpretation is also supported by normal shear zones in the Val-d’Or segment. Shear indicators observed next to the LLCF and several second-order faults, like Z-shaped interference folds, sigmoid objects, and shear relationships, along with subhorizontal stretching lineation, endorse a late dextral strike-slip movement postdating every other event. A NE-striking secondary cleavage associated with this event acts as an axial plan for the bend of the Cadillac Fault between Rouyn and Malartic segments.

Cross-cutting relationships between veins and structural features suggest mineralization occurred before and during the thrusting event as well as the late-dextral strike-slip event.