Biogeochemical prospecting for gold at the Yellowknife City Gold Project, Northwest Territories, Canada: Part 2 - Robust statistical analysis

Abstract

The Yellowknife City Gold Project (YCGP) is a promising Au district located in proximity to the city of Yellowknife, Northwest Territories, Canada. Positive results of a short biogeochemical survey in 2015 over the Crestaurum and Barney shears (Part 1) resulted in a broad survey over the early and advanced Au targets across the YCGP (Part 2). This survey uses a systematic two-phase statistical approach, including process discovery and process validation, to evaluate the multi-element biogeochemical dataset and identify the geochemical process controlling elemental occurrence and distribution in black spruce needles. To achieve these objectives, 2788 black spruce needle samples were collected across the Northbelt and Eastbelt of the YCGP and analyzed by ICP-MS using a multi-element determinations package for unashed vegetation. Following that, a biogeochemical dataset including Au, As, Ag, As, Bi, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Ni, P, Pb, S, Sb, Se, Tl, and Zn were prepared and analyzed using univariate and multivariate statistical analyses, including principal component analysis (PCA) and inverse distance weighted (IDW) interpolation method. The univariate statistical analysis showed that the average Au value in the black spruce needle is higher than the background level in all targets. Contiguous anomalous Au values were identified in needle samples collected proximal to the Ptarmigan & Tom mines (∼10 ppb) and Ryan Lake target (3.8 ppb). According to the robust RQ mode-PCA, PC1 and PC2 control the distribution pattern of elements in black spruce needles. PC1 includes two sets of elements indicating geochemical/mineralization factor (Au, As, Sb, Fe, Pb, and Mo) and physiological factor (Cu, Ca, Zn, K, S, P, and Mg). On the other hand, PC2 differentiates these two factors with more emphasis on the influence of the geochemical/mineralization factor. The IDW interpolation method indicates zones of Au enrichments at the YCGP are associated with different sets of pathfinder elements based on the bedrock composition and mineralization style. According to the IDW, elevated Au values associated with shear zones hosted within mafic/ultramafic bodies are accompanied by As, Sb, Pb, and Cu, while those located proximal to late felsic bodies are accompanied by Ag, As, Se, Hg, and Tl. Zones of Au enrichment located along the faulted contacts between the felsic-intermediate metavolcanics and sulphide metasediments are accompanied by Bi, Se, Hg, and Zn. The results of this study attest to the robustness of multivariate statistical analysis in detecting zones of Au enrichment using biogeochemical exploration.