Metal Zonation and Evolution of the Bronson Slope Porphyry Cu-Au-Mo Deposit in the Iskut Region of British Columbia, Canada

Bronson Slope is a Cu-Au-Mo porphyry deposit located within the Stikine Terrane in the Golden Triangle District of northwestern British Columbia, Canada. This deposit represents a complex, multistage magmatic-hydrothermal system emplaced into sedimentary and volcanoclastic rocks of the Triassic Stuhini Group. Bronson has an inferred resource of 517.3 Mt at 0.33 g/t Au, and 0.09% Cu. This study integrates detailed and quick logging from 20 drill holes, totaling 20,296m, SWIR spectral analysis, ICP-MS geochemistry, XRF analysis, magnetic susceptibility measurements, geochronology, and 3D models developed in Leapfrog Geo which define the stratigraphy, intrusive geometry, extension, alteration footprint assemblage, metal zonation, and evolution of the mineralizing system. The deposit is hosted by multiple monzonite to quartz monzonite intrusions emplaced in at least five pulses (pre-, early-, inter-, late-, and post-mineral). The pre-mineral monzonite and Stuhini group serve as the principal host for multiple intrusions, alteration and mineralization. Early-mineral quartz monzonite porphyries emplaced as swarm dikes into the monzonite triggered the first hydrothermal magnetite-rich phase, dominated by a strong pervasive magnetite alteration and multiple quartz-magnetite stockwork and sheeted veining events along porphyry sheets. Inter-mineral quartz monzonite porphyries host the main Cu-Au-Mo mineralizing event, characterized by quartz-chalcopyrite-magnetite stockwork and sheeted veining at the top and upper margins, and quartz-molybdenite sheeted veins at the lower and distal margins, overprinting earlier intrusions and alterations. Rhenium–osmium dating in quartz-molybdenite samples exhibits ages of 196.5 to 197.4 Ma, setting the main mineralization in the Early Jurassic. A broad white-mica alteration footprint, which developed at the top and margins of the porphyry, overprints early biotite-magnetite-K-feldspar alteration and is characterized by a muscovite to phengite halo. Chalcopyrite tensional veining is developed within the core of the porphyry versus dilational pyrite shear veining dominated by a broad phengite envelope in the margin of the porphyry. Polymetallic sphalerite-galena chalcopyrite veins developed at the south peripheries of the system. A late Cretaceous contractional faulting exhumed the deposit and marked a strong overprinting of the system by a structurally controlled pyrite shear vein system in a northwest-southeast trend.