Niyayesh Khorshidi, PhD

Tailings at the former Lake George Antimony Mine contain high concentrations of antimony (Sb) and arsenic (As) left over from the mining and milling of antimony-gold-tungsten-molybdenum veins from 1972 to 1996. Reprocessing the tailings could help to mitigate environmental risks and generate economic benefits from recovery of critical elements. A thorough characterization of the tailings is essential for accurately assessing the viability of reprocessing. This study used an Olympus Vanta™ portable X-ray fluorescence (pXRF) spectrometer to analyze the composition of the tailings and applied compositional data analysis (CoDA) techniques to interpret elemental relationships. The average concentrations of Sb (3800 ppm) and As (4500 ppm) exceeded the Canadian Soil Quality Guidelines by over 100-fold and 300-fold, respectively, with maximum concentrations reaching 0.7 wt.% for Sb and 1.1 wt.% for As. Antimony showed a strong association with As, S, and Ca, followed by Ti, Pb, and W, indicating potential co-occurrence and shared geochemical behaviour among these elements in the tailings. Three-dimensional models showing the spatial distributions of Sb, As, and S were developed using the 3D kriging method in Geosoft Oasis Montaj, a geostatistical interpolation technique that creates voxel grids by accounting for spatial autocorrelation. Isosurfaces generated from these voxel grids were employed to highlight elevated concentrations of these elements, providing a detailed visualization of their spatial distribution. 

The results show that Sb is concentrated in the northern part of the tailings storage facility (TSF), particularly in finer-grained tailings, suggesting enhanced retention or potential liberation of Sb in these materials due to their high surface area and reactivity, as well as potential losses of Sb during mineral processing. Arsenic showed high concentrations in both surface and deeper layers and is concentrated in the northwestern part of the TSF. Sulphur levels exceeding 1% were observed in the western portion of the TSF, indicating the presence of sulphide minerals, as confirmed by mineralogical studies, that could pose environmental risks, such as acid rock drainage. These findings highlight the geochemical behaviour and spatial distribution of Sb, As, and S in the tailings and the utility of 3D modelling in identifying areas with elevated concentrations. Further analysis and model refinement are needed to enhance spatial prediction accuracy and inform decisions on tailings reprocessing and targeted remediation strategies.