Abstract
The ca. 2680 Ma Upper Beaver deposit is an Archean intrusion-related gold–copper deposit located in the Abitibi greenstone belt, Ontario. The deposit is associated with the Upper Beaver Intrusive Complex, which was emplaced in the hanging wall of an extensional listric fault rooted in metavolcanic rocks of the ca. 2704–2695 Ma Blake River assemblage. The fault formed during the development of an overlying basin of fluvial metasedimentary and alkalic metavolcanic rocks of the ca. 2679–2669 Ma Timiskaming assemblage. The Upper Beaver deposit was subsequently rotated to its current position during the formation of a post-Timiskaming fold, the Spectacle Lakes Anticline, associated with the development of the Larder Lake–Cadillac deformation zone, located 7 km south of the deposit. The Upper Beaver deposit is overprinted by the axial planar cleavage of the anticline but is less deformed than other gold deposits located along the deformation zone. Alteration and other pre-existing planar anisotropies enhanced strain partitioning and the development of folds and fabrics in strained mineralized zones of the deposit. Steeply dipping, sericite-altered mineralized zones developed a continuous foliation surrounding boudinaged and recrystallized quartz–calcite–anhydrite veins, whereas strong, shallowly dipping, stratiform, and skarnoid mineralized zones developed a wavy disjunctive cleavage and deformed mainly by folding. The mineralized zones acted as pre-existing anisotropies during deformation and their orientation and composition were key factors in the development of structures at the Upper Beaver deposit, which can be used as a guide for interpreting the development of structures in similar but more complexly deformed deposits along major deformation zones.
Published Version
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