Structural setting, textures, and timing of hydrothermal vein systems in the Val d'Or camp, Abitibi, Canada: implications for the evolution of transcrustal, second- and third-order fault zones and gold mineralization

In the Val d'Or camp, Archean Abitibi greenstone belt, Canada, numerous gol d-mineralized second- and third-order fault zones are spatially associated with the transcrustal Cadillac Tectonic Zone (CTZ). This situation is used to test whether fluid systems in the CTZ have a similar structural timing t o those in the gold-hosting structures, and hence the CTZ could represent t he main fluid conduit in the camp. The transcrustal CTZ at Orenada No. 2 co ntains structurally complex vein systems, with mineralized quartz-tourmalin e veins related to both D-2 oblique-reverse faulting and F-3 dextral asymme tric folding, both of which have been overprinted by unmineralized subhoriz ontal and subvertical quartz veins. Quartz +/- tourmaline veins within seco nd- and third-order shear zones at Paramaque and Riviere Heva also formed d uring D-2 deformation and have been, at least at Riviere Heva, deformed by F-3 asymmetric folding. In contrast, mineralized quartz vein systems at Car tier Malartic are controlled by F-3 folding and overprinted by late-stage D -3 faults which host late quartz-tourmaline veins. Quartz vein textures are consistent with these timing relations, because D-2-controlled veins conta in deformed quartz grains, whereas quartz in D-3-controlled veins is unstra ined. The D-2 and D-3 timing of mineralized quartz veins in the transcrusta l CTZ and in second- and third-order structures is consistent with the noti on that the CTZ represents the main fluid conduit and that mineralization o ccurred in linked second- and third-order structures. The different timing of quartz-tourmaline veins in different shear zones indicates that the vein s were probably hydraulically linked to the CTZ during at least two differe nt episodes. The location of Cartier Malartic structurally below the CTZ in dicates that fluids travelled either downward from the main conduit or that the shear zone was part of the CTZ.