Abstract

The gold deposits of the Yellowknife district occur in two distinct geological settings. The principal economic deposits occur in quartz-carbonate lenses in extensive chlorite schist zones (shear zones) cutting greenstone (amphibolite) rocks. The other deposits, of less economic importance, occur in quartz lenses in meta-sedimentary rocks.The deposits in the greenstones represent concentrations of silica, carbon dioxide, water, sulfur, arsenic, antimony, gold, and other metallic elements. Those in the sediments represent concentrations of silica, sulfur, boron, gold, and other metallic elements.For the deposits in the greenstones chemical evidence is presented to show that, under the influence of a strong thermal gradient, some of the carbon dioxide, water, sulfur, gold, silver, and other metallic elements in the original volcanic rocks was mobilized and migrated into the extensive shear zone systems. In the shear zones the chemical equilibrium was severely displaced, water and carbon dioxide reacted with the amphibolite rock producing extensive widths of chlorite and chlorite-carbonate schist, and silica, sulfur, gold, and numerous other elements present in the rock were mobilized. These mobilized constituents, together with those added by diffusion from the country rocks, migrated into dilatant zones, principally at shear zone junctions and flexures. In these sites they were precipitated as quartz, carbonates, sulfides, and gold.A similar process has operated to form the gold-quartz lenses in the meta-sediments. In these rocks silica, boron, sulfur, and various metallic elements were mobilized during the metamorphism of the sediments, and these migrated into and were precipitated in dilatant zones in faults, fractures, and drag folds in the rocks.

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