Seminar

A major issue in the study of gold deposits is how some of them attain extraordinarily high concentrations of this metal (up to many kilograms per ton), albeit on a local scale. This is particularly an issue for epithermal (low sulphidation) deposits for which the gold concentration of the ore-forming fluid has been shown to be very low, on the order of 10 - 30 parts per billion. A hypothesis that has been proposed but never adequately tested or taken seriously is that instead of being transported in solution to the site of deposition, the gold is transported mechanically as a colloid or even as flocculated (aggregated) bodies, thereby opening the possibility of local accumulations of large masses of the metal. After an introduction that briefly covers the nature of colloids, the history of their discovery and their application, mainly in the field of medicine, the presentation launches into a discussion of the Brucejack epithermal gold deposit in northern British Columbia Canada, in which some of the veins figuratively drip with gold. This is a new discovery (the mine opened in March 2017) that has offered an unprecedented opportunity to test the hypothesis that gold colloids actually exist in nature. Evidence will be presented to show that not only do they exist, but without them Brucejack would be another run-of the-mill gold deposit rather than the hyper-enriched gold giant that it is. Finally, a case will be made that colloidal processes have been too long overlooked and that like other ore-forming processes they deserve their day in the Sun.