Duncan McLeish, PhD Student, McGill University


Duncan is a third-year PhD student working with Prof. Anthony. E. (Willy) Williams-Jones at McGill University where he is studying the genesis and geochemical evolution of epithermal gold deposits. After originally being inspired to study geology by spending summers as a canoe guide paddling through striking exposures of high grade metamorphic rocks in the Algonquin Park, Ontario, he completed a B.Sc. Honours degree in Earth Sciences at Dalhousie University in 2008. Excited by the prospect of working in the mountains of western Canada, he accepted a regional mapping assistant job with the BCGS in the summer of 2008.

The following fall he commenced an MSc at the University of Victoria studying the structural controls on a niobium-bearing carbonatite complex in the Rocky Mountains of northeast British Columbia. During his MSc studies he gained exposure to several collaborative industry-academic mineral exploration projects from which he caught the prospecting bug and developed a fascination with applying academic research to improving our understanding of how mineral deposits form and advancing techniques for their exploration. Following the completion of his MSc, he worked for several grassroots exploration companies as well as a major BC mining company before deciding to further his studies by taking on a PhD.

Project: The Nature and Origin of the Brucejack High-Grade Epithermal Gold Deposit, British Columbia, Canada

Epithermal gold deposits host a significant portion of the world’s total known near-surface gold endowment and are thus an important target in mineral exploration. Despite supplying a growing fraction of global gold production and receiving increased scientific attention from the mining industry in recent years, discovery rates for new epithermal gold deposits have been in decline since the 1990s. The reasons for this decline are manifold, but a reoccurring issue in many studies is that available genetic models, which are essential guides to exploration, still do not satisfactorily explain the formation of many epithermal and related hydrothermal gold deposits.

Pretium Resource’s Brucejack property in the Stewart-Eskay Creek mining district of northwestern British Columbia is host to one of the highest grade and best exposed intermediate sulphidation epithermal gold deposits in the world (individual electrum bearing quartz-carbonate veins grade up to 41,000 g/ton Au). My project aims to determine the origin of high-grade gold mineralization at Brucejack and produce a step-by-step reconstruction of the magmatic-hydrothermal history of the deposit by petrographically and chemically (including isotopically) characterizing the ore mineralization and associated hydrothermal alteration, determining the composition of the original mineralizing fluids through fluid inclusion analysis, and reconstructing the physicochemical conditions that controlled gold mineralization through thermodynamic analysis and quantitatively testing plausible models of ore formation (including testing whether boiling-mediated nanoparticle suspensions, or colloids, played a role in greatly increasing the capacity of the ore-forming fluid to carry gold). In addition, the well-explored nature of epithermal gold mineralization on the Brucejack property, combined with its close proximity to well-explored, world-class copper-gold-molybdenum porphyry deposits (Snowfields and Kerr-Sulphurets-Mitchell), will, through comparative study, allow for the testing of possible genetic links between epithermal and spatially associated higher-temperature porphyry deposits in general. If successful, my project will improve on existing models for the genesis of epithermal gold deposits and the strategies that guide their exploration.