Structural geology of the Cadillac Group along the Malartic segment of the Larder Lake Cadillac deformation zone, Quebec, and implications for gold mineralization Available to Purchase

The gold-endowed Larder Lake Cadillac deformation zone (LLCDZ) in the Abitibi greenstone belt of the Archean Superior Province generally trends east but swings to the southeast along the Malartic segment in Quebec. Immediately north of the LLCDZ along this segment, deformation of the less than ca. 2687 Ma metasedimentary Cadillac Group began with the formation of isoclinal F₁ folds, which are overprinted by post-2676 ± 2.0 Ma regional F₂ folds with an axial planar S₂ cleavage oriented parallel to the trend of the Malartic segment. Auriferous quartz veins strike east–west (085°) anticlockwise to bedding and S₂. They are folded into sigmoidal S-shaped folds due to sinistral shear parallel to bedding. Later dextral shearing segmented the veins and folded the F₂ folds into Z-shaped F₃ folds. The veins are similar in structural chronology, fluid isotopic composition (calculated $δDH2O$ value between –9.5‰ and –3.4‰ and $δ18OH2O$ values of 12‰), and isotopic re-equilibration temperatures (469 and 498 °C, quartz–biotite oxygen thermometer) to the veins at the nearby Canadian Malartic deposit to the east. They possess comparable Au–As–Sb association and sericite-arsenopyrite alteration halo, as other Cadillac-Group-hosted veins at the Lapa mine to the west. Collectively, they constitute a vein field that extends across the entire length of the Malartic segment. Contrary to recent interpretations of the Malartic segment as an early accretionary structure that controlled the emplacement of gold deposits, its southeast trend is interpreted as the short limb of a broad Z-shaped flexure that formed during later F₃ folding of the LLCDZ.