Abstract:

The Touquoy Gold Mine (Nova Scotia, Canada) ceased production in 2023 and has since transitioned into the closure and reclamation phase. Waste rock produced throughout the life of mine primarily comprises argillite and greywacke of the Meguma Terrane and was used for construction purposes (tailings dam, roads, etc.) across the site. Excess waste material is stored in a designated waste rock storage area or as backfill in the open pit. Arsenic is the primary water quality parameter of concern since it is enriched in mine rock, consistent with bedrock elsewhere in eastern Nova Scotia. Various geochemical investigations of waste rock were completed with the objective to better define As distribution and leaching behavior and to quantify short- and long-term effects on mine drainage quality. Under unsaturated conditions, As is oxidized and leached from arsenopyrite with its mobility under circum-neutral pH conditions governed by various factors including As content, the availability of Fe- and Mn-particles, pH and particle size. Comparison of kinetic test and water quality data suggests that in-situ attenuation of As is occurring via adsorption to or co-precipitation with hydrous ferric oxide (HFO) and Mn-oxides. Arsenic mobility increases as a result of saturation and decreasing redox potential in previously oxidized waste rock as would be expected in open pit backfill. A combination of reductive dissolution of HFO and Mn-oxides, associated As^V, and anion exchange are likely causes for this. The conceptual and numerical understanding of As release has helped inform material handling, water management, and reclamation decisions to minimize water quality impacts to the receiving environment.

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Christian Deveau