Stratigraphic framework and VMS mineralization potential of the Jurassic Hazelton Group in the Bear Pass, British Columbia

The Bear Pass area of northwestern British Columbia lies within the Golden Triangle, where Jurassic Hazelton Group volcanic, volcaniclastic, and sedimentary rocks host significant volcanogenic massive sulfide (VMS) deposits, including Eskay Creek, Granduc, and Anyox. Despite widespread hydrothermal alteration and stratiform sulfide mineralization in the Stewart Camp, the relationships between basin evolution, volcanic architecture, magmatism, and hydrothermal fluid flow in the Bear Pass area remain poorly constrained. This study integrates geological mapping, drill-core logging, whole-rock lithogeochemistry, petrography, micro-XRF, and short-wave infrared spectroscopy to establish a stratigraphic framework for Bear Pass and evaluate controls on mineralization at the BA Pb-Zn-Ag VMS occurrence. Geological mapping defines a four-unit stratigraphy consisting of pumiceous pyroclastic and volcaniclastic rocks with abundant coherent and pillowed flows, and younger overlying basinal strata. A key contribution of this study is the recognition of previously undescribed pumiceous and felsic volcaniclastic facies within Unit 1 (Unuk River Andesite Member of the Betty Creek Formation), which had previously been mapped as a comparatively homogenous andesitic succession. These porous volcaniclastic horizons, together with synvolcanic structures and intrusive contacts, are interpreted to have focused hydrothermal fluid flow and promoted replacement-style sulfide mineralization. Immobile element and rare earth elements indicate formation in a calc-alkaline volcanic-arc to incipient back-arc setting. At BA, three spatially associated mineralization styles are documented: laminated pyrite-sphalerite horizons hosted by silicified mudstone and siltstone; sphalerite-galena-pyrite replacement and breccia-matrix mineralization along the margins of an andesitic cryptodome; and chalcopyrite-bearing stringer systems cutting deeper volcaniclastic and coherent volcanic units. These styles define systematic metal and alteration zonation from deeper Cu-Ag rich feeder zones to cooler Zn-Pb-Ag mineralization along more distal fluid pathways. Collectively, these observations support the interpretation of BA as a hybrid VMS system in which seafloor exhalative, subseafloor replacement, and stringer-style processes operated within a structurally and lithologically heterogeneous volcanic basin. The results demonstrate that mafic-sedimentary contacts, permeable volcaniclastic facies, synvolcanic faults, and shallow intrusive margins are favourable exploration targets in comparatively immature arc-basin settings.