Critical raw material potential of porphyry copper-gold deposits in the Golden Triangle, northwest British Columbia, Canada

Abstract

Porphyry deposits are major sources of copper, gold, molybdenum, and silver globally. However, the potential for critical raw materials (CRM) to be mined as by-products (e.g., antimony, bismuth, platinum group elements, and tellurium) at these deposits is poorly understood. Herein we present results from a lithogeochemical survey (n = 331), detailed mineralogy, and trace element mapping to characterize the concentrations of CRM and their deportment within the Golden Triangle, northwest British Columbia, Canada. We demonstrate that the host rocks to porphyry copper-gold (i.e., Galore Creek, Copper Canyon, KSM, Dok, Yeti, and Burgundy) and epithermal gold-silver (i.e., Brucejack) deposits were derived from oxidized and water-rich parental melts that suppressed sulphide crystallization, resulting in the pre-enrichment of CRM relative to other arc rocks globally. The structural juxtaposition, local thickening, and preservation of these prospective source rocks is likely one of the factors contributing to the mineral district’s exceptional gold and CRM endowment. Multiple analytical methods (e.g., aqua-regia, four-acid, fusion) for the same samples further demonstrate that the highest Bi (39 ppm), Pd (460 ppb), Sb (375 ppm), and Te (15 ppm) concentrations are associated with sulphide and/or other non-resistate minerals within the most hydrothermally altered samples. Detailed mineralogy and trace element mapping by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) reveals that CRM within the Golden Triangle are hosted by at least 58 different minerals. We apply these results to estimate the contained CRM at the Galore Creek and KSM deposits and to discuss their potential to be recovered as by-products. Lithogeochemical results are also applied to predict the mineral potential of different igneous suites within the Golden Triangle based on their CRM concentrations.