Tourmaline breccia pipes of the Giant Copper porphyry system: Extending the Cascadia porphyry district into southern British Columbia, Canada

Abstract

ABSTRACT The A. M. breccia is part of the Giant Copper property of British Columbia, Canada. It is the only well-defined tourmaline breccia pipe (TBP) in the Canadian Cordillera. The A. M. breccia shares similarities with other TBPs, most notably those of South America. The A. M. breccia demonstrates concentric zonation with regard to breccia texture, consisting of an outer rim of shingle breccia surrounding a fragmental breccia core. Copper grades correlate to breccia zonation, with higher Cu grades within shingle breccias relative to the fragmental core. Hypersaline fluid inclusions were identified in quartz cement within the A. M. breccia, which reflects conditions expected in porphyry copper deposits. Breccia textures, mineralization, and fluid inclusions at the A. M. breccia are nearly identical to other well-studied porphyry-related TBPs. The strong similarities suggest the A. M. breccia is a porphyry-related TBP. This interpretation encourages deep drilling to identify further mineralization within the A. M. breccia pipe as well as discovery for conventional porphyry mineralization at depth. Similarities can also be drawn to Ancestral Cascadia arc porphyry copper deposits and associated TBPs. The proximity of Giant Copper to the Ancestral Cascadia porphyry district infers a genetic relationship and the interpretation that the Giant Copper porphyry system developed from magmatism related to the Ancestral Cascadia subduction. Classifying Giant Copper as an Ancestral Cascadia porphyry system extends the district into southern British Columbia, where Giant Copper marks its northernmost extent.