Role of colloidal transport in the formation of high grade gold veins at Brucejack, British Columbia

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Gold deposits can take many forms. The distribution of gold within a deposit may be relatively systematic, in which case it is possible to accurately estimate the resource with minimal data. In other cases, the distribution of gold in the deposit may be very irregular (known as "nuggety") and difficult to estimate. This difficulty delays mine permitting and creates challenges for resource extraction. I hypothesize that a fundamental difference in the way gold is transported and deposited by fluids may help explain the differences between deposit styles and provide tools for understanding the structural controls on gold grade. The Brucejack deposit is one of these cases, where extremely high grade veins (up to >41 kg/ton) cut through barren wall rock. The irregular distribution of gold and the very high grades lead us to hypothesize that the gold was transported within the vein system in the solid state as nanoparticles. Due to post-mineralization deformation and metamorphism, the primary nanoparticles have been recrystallized into larger nuggets and flakes, and the microstructural record of transport and deposition may not be preserved. Solid nanoparticle transport has been observed in both ancient and active hydrothermal systems. In order to understand the role of nanoparticle transport in creating rich, nuggety gold deposits, we will be studying opal and quartz vein deposits from active hydrothermal systems where gold enrichment is currently underway. We will characterize the microscopic textures which form when gold nanoparticles form and are locked up in silica veins. We will relate these microtextures to the preserved structures in the Brucejack deposit and determine what role nanoparticle concentration plays in creating a rich, nuggety gold deposit. We hope a structural understanding will contribute to exploration and accurate estimation of this type of resource.