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Abstract

The Kitsault Valley is located near the southernmost tip of a region in northwestern British Columbia known as the Golden Triangle. A trend of epithermal, VMS, and hybrid VMS-epithermal Ag-Zn-Pb occurrences hosted by intermediate volcaniclastic rocks of the Toarcian-aged Kitsault Unit is observed within the valley, though the controls on their distribution and varied mineralization styles are not well-understood. The Torbrit and Wolf Ag deposits represent high-grade hybrid VMS-epithermal and epithermal mineralization along this trend, respectively. These deposits have been studied using graphic core logging, lithogeochemical analysis, micro-XRF analysis, thin section petrography, and SEM-EDS analysis to characterize their host lithofacies, alteration assemblages, mineral assemblages, and parageneses, informing new models for their formation. The Kitsault Unit is determined to represent a series of subaqueous pyroclastic flows or water-supported mass flows originating from shallow-water phreatic or phreatomagmatic eruptions. Torbrit represents fault-channeled hydrothermal venting of low- to intermediate-sulfidation magmatic and seawater-derived fluids into a shallow oxygen-stratified basin during a pause in local volcanism, which transitioned to epithermal veining upon deposition of overlying volcaniclastic rocks. Wolf represents similar fluids emplaced along a shallow fault which was already confined by overlying rocks, forming epithermal veins. Both deposits are overprinted by brecciation and subsequent cementation, as well as later fracture-filling veins. The initial exhalative and epithermal mineralization phases are coeval with deposition of the Kitsault Unit during Early to Middle Jurassic syn-volcanic growth faulting and subsidence. The depositional environment, timing, and mineralization styles of Torbrit and Wolf are similar to those of the high-grade Eskay Creek Au-Ag-Zn-Cu-Pb deposit within the nearby Eskay Rift structural trend, suggesting that the Kitsault Valley may represent a failed rift along a jog off of this trend. Differences in metal endowment between these two localities are attributed to lesser magmatic influence, shallower formational depths, and lower fluid temperatures and salinities within the Kitsault Valley area, all of which are linked to the failed rift environment.