CONTRASTING STYLES OF GOLD MINERALIZATION OF COMMON TECTONIC ORIGIN AT THE LATE STAGES OF ARCHEAN CRATONIZATION
The Hemlo deposit is a disseminated and replacement style gold deposit that is spatially associated with a stratigraphic contact. The protolith is mainly a fragmental rock and a barite horizon occurring at the contact. The contact and the fragmental rock at the contact probably served as mechanical traps and the barite horizon as a chemical trap. The deposit is located in the Hemlo shear zone and mineralization occurred during shearing, before mid-amphibolite-facies peak metamorphism. Mineralization was occurring at ~2677 Ma and most likely had started earlier. Mineralizing fluids probably had a magmatic source, interpreted to be related to the 2682–2677 Ma granodioritic (sanukitoid) plutons abundant in the vicinity.
In spite of the obvious differences, the two deposits share many similarities. Both are genetically related to shear zones and late mantle-derived intrusions that are of similar ages, and the associated shear zones have similar kinematic history and probably have similar ages. The two deposits appear to share a common tectonic origin and their different characteristics may be due to variation in local geological settings. In particular, we suggest that the gold deposits, the intrusions and the hosting shear zones all developed within a regime characterized by synchronous vertical and horizontal tectonism at the late stages of Archean cratonization. They were all possibly linked to a range of processes associated with the accretionary growth and stabilization of the craton, in particular slab break-off and the associated extensional orogenic collapse following terrane accretion.