Glacial Dispersion at the Canadian Malartic Gold Deposit

Abstract

A novel drift prospecting approach detected components from previously established bedrock footprints at the world-class Canadian Malartic gold deposit within the site’s surrounding Quaternary sediments. The measured glacial dispersion of footprint components is significantly more extensive than the largest bedrock footprint. This new method could apply to similar high-tonnage disseminated gold deposits and other deposits with similar features. Drift prospecting methods included ice flow indicator mapping, surficial sediment sampling and characterization, particle size distribution analyses, till matrix geochemistry (major oxide, minor, and trace elements), glacial clast lithology, gold grain counts, and petrography. Our novel approach combined hyperspectral imaging analyses with petrographic analyses targeting glacial granules and pebbles. Within the study area, the direction of past ice flow phases evolves from ~210º to ~150º; it dominates towards ~170º. Multivariate analysis of till matrix major oxide geochemistry links clusters of samples to bedrock geology and postglacial processes. Till clast lithologies link to bedrock type. The spatial distribution of till matrix minor and trace element geochemical values reveals glacial dispersal trains for Au, Ag, Rb, W, and potentially Ba; however, glacial dispersal trains for Cs, Mo, Pb, and Sr are unclear (all listed elements have been previously reported as footprint components). Multivariate analyses of till matrix minor and trace element geochemistry link clusters of samples to footprint components (Mo has the highest first principal component positive loading in the relevant cluster), bedrock geology background values, and postglacial processes. Sand-sized gold grain counts from till and their morphology link to the phengitic white mica bedrock footprint associated with the deposit. Hyperspectral imaging analysis of bulk glacial clasts reveals dispersal extents that are significantly larger than the extent of the phengitic white mica footprint in bedrock (i.e, the most extensive bedrock footprint at the Canadian Malartic gold deposit). 4-8 mm tracer till clasts produce a dispersal extent 7.0-13.5 times larger while 2-4 mm tracer till clasts produce a dispersal extent 4.5-8.4 times larger than the bedrock footprint. Further, petrographic analyses of 42 highly phengitic 4-8 mm clasts classify 14 clasts as showing mineralogy and rock texture similar to the host quartz-monzodioritic, granodioritic, and meta-sedimentary rocks at the deposit. One of these clasts is mineralized with gold like the mineralization at the Canadian Malartic deposit, and this is the first reported instance of finding a mineralized clast using this novel technique. The Quaternary dispersion relative to the previously established bedrock footprints at the Canadian Malartic gold deposit is significant. Ongoing hyperspectral imaging and petrographic analyses of similar clasts may demonstrate numerous practical applications to exploration campaigns seeking other Canadian Malartic-type gold deposits or other deposits with similar characteristics.