Study: Selbaie Mine, Quebec, Canada

The Selbaie Mine site (‘the Site’) located in northern Quebec, Canada, is a former copper-zinc mine that operated between 1983 and 2004; rehabilitation works began in 2000 and were largely completed by 2006. A closure plan for the site was submitted to regulatory authorities in 1996 and updated in 2003. Two primary domains at the Site include a tailings management area (TMA) and waste rock dump (WRD), with most of the waste material being net acid generating. The 1996 Closure Plan included the following for the two primary domains: Waste rock piles (approximately 34 million tonnes at the end of mining) will continue to generate acid leachate for decades and even centuries, with or without a soil cover. The most cost-effective way to control this problem is to capture and treat the acid leaching products from the waste rock piles on a -term basis. The TMA contains a very large amount of sulphur and metals (40 million tonnes of tailings after operations), of which most remain saturated in the long-term and are therefore not prone to leaching acid or metal products. However, it is neither practical nor cost-effective to prevent the formation of local unsaturated tailings areas and unsaturated reactive waste rock areas on the perimeters of the dams that will be subject to acidic and metal product leaching. Therefore, the capture and treatment of acid leaching products from the tailings pond is necessary in the long-term. Ultimately closure covers were constructed over the TMA and WRD using a nominal 1 m thick soil cover comprised of local silty-sand till material followed by seeding the cover surfaces with a mixture of native grasses and legumes. The purpose of the TMA cover was to maintain saturated tailings to the extent practicable, while the cover on the WRD was intended to limit net percolation of meteoric water through water-shedding and store-and-release processes. Overall, the Site is underperforming due to the design and post-closure performance of the WRD and there is risk that additional desaturation of the TMA could result in acidic seepage from the TMA. Acidic seepage from the TMA would require additional effort and cost related to water treatment, maintenance, and surveillance activities at the Site. This paper describes the operation and performance of the Site with a focus on the TMA and WRD. The case study reinforces the need to use benchmarking, cover trials, and the fact that mine closure needs to start early and be progressive to avoid relatively high post-closure maintenance requirements and costs.

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