Geochemical and mineralogical dispersal in till from the Mount Polley Cu-Au porphyry deposit, central British Columbia, Canada

Abstract

The Quesnel terrane in the Interior Plateau of British Columbia, Canada, is highly prospective for locating new porphyry deposits; however, the bedrock in this region is obscured by a nearly continuous blanket of till, making mineral exploration challenging. Located within the Quesnel terrane is the Mount Polley deposit. It is an alkaline, silica-undersaturated, Cu-Au porphyry deposit mined by Imperial Metals Corporation. Eighty-six basal till samples were collected for geochemical and mineralogical analyses in the region of this deposit. Ore elements (Ag, Au and Cu), as well as pathfinder element (Hg and Zn) contents in till reflect detrital glacial dispersal from the Mount Polley deposit. The distribution of anomalous mineral counts of andradite garnet, apatite, chalcopyrite, epidote, jarosite and native gold also reflect glacial dispersal from the deposit. Outcrop-scale ice-flow indicators indicate a dominant ice-flow event to the NW that was preceded by a southwestward glacial advance. The element and mineral signatures of the Mount Polley Cu-Au porphyry deposit are dispersed in sub-glacial surface tills up to 12 km in the down-ice (NW) direction. We demonstrate that till geochemistry and mineralogy can serve for mineral exploration of Cu-Au porphyry mineralization in drift covered areas. Supplementary material: Complete data set for element and mineral results and ice-flow measurement is available at www.geolsoc.org.uk/SUP18828