A breccia-centered ore and alteration model for the Copper Canyon alkalic Cu-Au porphyry deposit, British Columbia

Abstract

Similar to the nearby Galore Creek deposit, the Copper Canyon prospect of northwestern British Columbia is a porphyry-type copper-gold-silver occurrence associated with alkalic intrusive rocks of the Late Triassic-Early Jurassic Copper Mountain Suite. A reevaluation of the prospect geology shows that, of the previously recognized orthoclase and/or pseudoleucite porphyry syenite intrusions, mineralization is spatially and temporally associated with a single intrusive phase (unit i5) and biotite-garnet stockworks. Further, a newly defined unit of pre-mineralization magmatic-hydrothermal intrusive breccia occupies the core of the prospect and is a favorable host for much of the prospect mineralization. Prospect alteration can be divided into two distinct styles. Calc-potassic alteration consists of K-feldspar, Mg and Fe³-rich (An₂₀) biotite, andradite-rich garnet, hematite, magnetite, chalcopyrite, pyrite, and sphalerite (Zn₉₄₋₉₉, Fe₀.₅₋₂, Cd₀.₄₋₁)S and is associated with copper-gold-silver mineralization. Ankerite-sericite-pyrite (± fluorite, albite, anhydrite, pyrite, and trace covellite and bornite) alteration adjoins this core, hosting gold mineralization and insignificant copper. Sulfide-electrum and biotite geothermometry suggest fluid temperatures decreasing from the core (<̲S 550°C) to distal gold mineralization (<̲361°C). Distal gold mineralization is most likely the result of higher than typical sulfur activity and bisulfide transport of gold.