The historic Craigmont Cu-Fe skarn deposit is British Columbia’s highest grade copper mine, producing 36.4 Mt of 1.29% Cu from 1961 to 1982. Although it is located on the southern margin of the Guichon Creek batholith, also home to the Highland Valley porphyry Cu-Mo district, the Craigmont skarn has not been definitively linked to a porphyry system. Through field observations, petrography, whole-rock and mineral chemistry, and integrated geochronology, Craigmont has been redefined as a porphyry-linked skarn system genetically tied to multi-pulsed Late Triassic magmatism within the batholith’s Border Phase. Three temporally and geochemically distinct intrusive pulses were recognized between ~220 to 209 Ma. Early dioritic Border Phase intrusions (~220 to 215 Ma) record unoxidized, hydrous magmatism that generated an initial stage of calc-silicate Cu-Fe skarn mineralization. Subsequent intrusions (~211 Ma) display fractionation trends indicative of magmatic differentiation but limited mineralizing potential. The youngest Border Phase intrusions (~209 Ma), crystallized from oxidized, hydrous magmas capable of producing Cu-bearing fluids, temporally overlapping with porphyry mineralization elsewhere in the Highland Valley district. Paired U-Pb garnet and zircon ages define two discrete hydrothermal stages: massive calc-silicate skarn alteration at ~215 Ma related to the earliest Border Phase intrusions (Stage 1) and overprinting, vein-hosted porphyry-type mineralization at ~209 Ma associated with later, oxidized intrusions (Stage 2). Although the extent of alteration within the New Craigmont property surrounding the Craigmont mine is relatively obscured by widespread cover, local expressions of potassic, phyllic, calc-potassic, and propylitic alteration styles indicate the presence of a larger porphyry system proximal to the skarn deposit. Epidote mineral chemistry from propylitic assemblages further supports this; New Craigmont epidote contains elevated porphyry indicator trace elements consistent with other porphyry deposits in British Columbia and worldwide. Finally, epidote mineral chemistry systematics within the Guichon Creek batholith reveal that New Craigmont contains a separate, porphyry center, unrelated to the distal propylitic and sodic-calcic signals of the Highland Valley district. This integrated analytical framework has direct implications for vectoring and fertility assessments in the underexplored margins of the Guichon Creek batholith and analogous porphyry-skarn systems globally.
Warren Wegener (Thu,) studied this question.