Iron reduction around gold-quartz veins, Yellowknife District, Northwest Territories, Canada

Gold deposits of economic importance are localized within domains of ductile shear zones in the Yellowknife greenstone belt. The oxidation state of primary iron has been determined in 78 samples comprising "background" metabasalts (Fe (super 2+) /Sigma Fe = 0.76), non-productive sections of the shear zones (Fe (super 2+) /Sigma Fe = 0.78), and ore-grade schists (Fe (super 2+) /Sigma Fe = 0.95).Statistical treatment of the data by analysis of variance reveals that a significant difference exists between the oxidation state of iron in ore-grade schists and the other groups of rocks, at a 95 percent confidence level.The results are discussed and evaluated quantitatively with reference to the fayalite-magnetite-quartz-H (sub 2) O buffer system. It is concluded that the observed reduction of iron in gold ore requires minimum water/rock ratios of about 3:1. Consideration of gangue mineral volumes leads to much higher water/rock ratios.An hypothesis for the ore-forming process is presented, based on data for the oxidation state of iron, and field observations, involving an inferred massive flux of hydrothermal solutions through high-permeability conduits within the shear zones, driven by an igneous energy source.