Project: District-wide geodynamic controls on porphyry and epithermal-style mineralization in the Stewart area (northwestern British Columbia): The role of reactivated basement structures.
Most porphyry Cu-Au deposits are generated in volcanic arc environments under broadly contractional stress regimes marked by crustal thickening, surface uplift and rapid exhumation (Sillitoe, 2010). The 170 km-long mineralised Stewart District in northwest BC is host to the Early Jurassic Kerr-Sulphurets–Mitchell Cu-Au deposits, the Brucejack epithermal gold deposit, and numerous other porphyry and epithermal deposits. The district has experienced significant Cretaceous contractional deformation that obscures the original structural and depositional setting in which these mineral deposits formed. Recent detailed studies suggest that the supergiant Cu-Au Mitchell-Snowfield deposit was emplaced in an Early Jurassic, fault-bounded, pull-apart basin (Febbo, 2016), rather than in a contractional environment. Nelson and Kyba (2014) initially proposed that fault-bounded Jurassic basins were subsequently reactivated (inverted) as thrust/reverse and tear faults during mid-Cretaceous contraction. If this model is correct and is applicable on a regional scale, the recognition of this environment of porphyry formation will lead to the development of new exploration models for porphyry mineralisation both within the Canadian Cordillera and globally.
In order to test this model, and its applicability to the region as a whole, this project will be focused on structural and stratigraphic mapping of two sites, the Big Bulk Au-Cu porphyry, and the Red Mountain Au epithermal deposits, which are along strike and to the south of the better studied Sulphurets district deposits. The goal of the project is to define the Early Jurassic basin geometry, structural architecture and stress regime that are associated with the deposits in the mapped region. It will assess whether the intrusives were emplaced along syn-sedimentary growth faults and will address the mechanisms of formation of permeable pathways for magmatic and hydrothermal fluids. It will be focused on developing and comparing deposit-scale models of the structural regime of the Early Jurassic at these sites, and its control on mineral deposit formation.