The role of preexisting anisotropies in focusing deformation in an Archean intrusion-related Au deposit: a case study from the Upper Beaver Au-Cu deposit, Ontario, Canada

Abstract

The ca. 2680 Ma Upper Beaver deposit is an Archean intrusion-related gold-copper deposit located in the southern Abitibi greenstone belt between Kirkland Lake and Larder Lake, Canada. Mineralization is centered on the intermediate Upper Beaver Intrusive Complex which was emplaced in the hanging wall of an extensional listric fault early during Timiskaming basin formation. During subsequent deformation events, alteration, preexisting planar anisotropies, and the orientation and composition of the ore zones enhanced strain partitioning, controlling the development of folds, boudins and fabrics in strained ore zones. Steeply-dipping, sericite-altered ore zones, oriented parallel to cross-stratal dikes, developed a continuous foliation surrounding boudinaged and recrystallized quartz-calcite-anhydrite veins, whereas strong, shallowly-dipping, stratiform, garnet-epidote-amphibole skarnoid ore zones developed a wavy, disjunctive cleavage and deformed mainly by folding. The Upper Beaver deposit can be used as a guide for interpreting the development of structures in similar but more complexly deformed deposits along major deformation zones.