Niyayesh Khorshidi, PhD
N. Khorshidi1, M.B. Parsons2, D.R. Lentz1
1Department of Earth Sciences, University of New Brunswick, Fredericton, New Brunswick, Canada
2Geological Survey of Canada (Atlantic), Natural Resources Canada, Dartmouth, Nova Scotia, Canada
Mine wastes in Canada are both an environmental liability and a potential source of critical minerals, but gaps in geochemical and mineralogical understanding limit their reprocessing. The Lake George Antimony Mine operated intermittently between 1876 and 1996 and was once the largest primary antimony (Sb) producer in North America. Mineralization occurs as a vein-type, intrusion-related system hosted by greenschist-grade metasedimentary rocks, with antimony as the dominant commodity and associated W, Mo, and Au. Tailings generated from on-site milling of Sb–Au–W–Mo ores (1972–1996) are stored in an unlined tailings storage facility. These tailings contain elevated Sb and As concentrations, raising concerns about metal(loid) mobility and potential impacts on surface and groundwater, while also representing a potential secondary resource for critical minerals due to historically low processing efficiency. Approximately 100 tailings samples were analyzed using ICP-ES/MS following four-acid digestion for near-total element recovery, and INAA for total metal(loid) concentrations. Compositional data analysis (CoDA) was applied to interpret elemental relationships. The tailings contain median concentrations of 2750 ppm Sb (400–7140 ppm), 4330 ppm arsenic (As; 240–13,200 ppm), and 370 ppb gold (Au; 1–1500 ppb). Particle size analysis indicates that most tailings are sandy silt (Folk classification). Major minerals include quartz, mica-group minerals, and mixed-layer clays (illite–smectite), with minor carbonates such as calcite and ankerite–dolomite, and sulphides including pyrite, arsenopyrite, and stibnite in deeper, unoxidized samples. Oxidized surface samples contain secondary antimony oxides and Sb–Fe oxides, with fewer sulphide and carbonate minerals. Antimony shows strong geochemical associations with silver (Ag), Au, As, and bismuth (Bi), followed by thallium (Tl) and sulfur (S), suggesting potential co-occurrence and shared geochemical behavior within the tailings. To evaluate potential environmental risks, acid-base accounting (ABA) was conducted on ten bulk samples collected from oxidized and reduced zones, representing different grain sizes and depositional environments. The results indicate the presence of potentially acid-generating (PAG) material, although on-site drainage from the tailings is currently circumneutral. Integration of mineralogical, particle size, and geochemical data offers a robust approach for assessing environmental risks, guiding monitoring strategies, and evaluating the potential for tailings reprocessing to recover critical minerals.