STRATIGRAPHIC CONSTRAINTS ON THE DEVELOPMENT OF AU-RICH VOLCANOGENIC MASSIVE SULFIDE SYSTEMS OF THE GOLDEN TRIANGLE, BRITISH COLUMBIA

The Golden Triangle of British Columbia represents a Jurassic-aged arc to back-arc succession that hosts gold-rich volcanogenic massive sulfide (VMS) deposits. Understanding of the paleoenvironmental evolution of these systems, from earlier arc evolution to extension, basin formation, hydrothermal activity, and later post-emplacement contractional deformation, is key for unraveling the factors that contribute to VMS deposit formation and exploration for their present-day distribution.

The highly prospective Scarlet Ridge area, located immediately east of the world-class Eskay Creek deposit, was mapped at 1:2000 scale to resolve questions relating to the stratigraphic controls on VMS mineralization. Representative samples from surface exposures and drill core were analyzed for their petrographic and geochemical signatures. Preliminary results indicate that bimodal volcanic centers hosting VMS formed due to late-stage back-arc development. These volcanic centers are characterized by abundant volcaniclastic deposits mantling felsic dome and flow complexes. Pyrite-rich stringer zones and abundant zones of sub-seafloor sulfide replacement within volcaniclastic rocks occur in the most prospective locations. Hydrothermally altered volcanic rocks are characterized by elevated Ishikawa alteration index values. The VMS mineralization is located in a proximal position to the volcanic vents.

In the study area, post-volcanic structural overprint is ubiquitous. This structural complexity relates to progressive, Cretaceous amalgamations of island arc terranes and suturing to ancestral North America. These events resulted in significant regional shortening and the formation of a thin-skinned fold and thrust belt. Structural blocks are bounded by anastomosing, brittle-ductile high-strain zones that juxtapose dissected volcanic packages with older, unmineralized arc-related units. Overall, these new results provide a framework for the exploration of VMS deposits in the Golden Triangle wherein understanding the primary Jurassic stratigraphic relationships must be viewed in the context of the Cretaceous tectonic overprint.