Abstract

The Hemlo gold deposit (∼700 t Au; northwestern Ontario, Canada) is hosted in a shear zone in the Hemlo greenstone belt, which is a synclinal keel between two granitoid domes. The dome-and-keel structure formed by diapirism and sagduction (vertical tectonism) that was synchronous with regional horizontal shearing (horizontal tectonism). Mineralization occurred during shearing, and mineralizing fluids probably had a magmatic source that is interpreted to be related to syntectonic mantle-derived granodiorite (sanukitoid) intrusions. The gold deposit, the intrusions, and the hosting shear zone all developed within a regime characterized by synchronous vertical and horizontal tectonism. They were all possibly linked to a range of processes associated with the accretionary growth and stabilization of the craton, in particular slab breakoff and the associated extensional orogenic collapse following terrane accretion.

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