Authors: Desjardins, M; de Graaf, PJH; Beale, G; Rougier, M

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Desjardins, M, de Graaf, PJH, Beale, G & Rougier, M 2020, 'Geotechnical risk management for Victor Mine closure', in PM Dight (ed.), Slope Stability 2020: Proceedings of the 2020 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 399-414,

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The De Beers Canada Victor Diamond Mine is located in the James Bay lowlands of Northern Ontario. This case study presents the evaluation of geotechnical stability and pit lake filling. The work was used to support decisions that informed risk assessments and the closure plan for two key phases: Risk-based monitoring plans were developed along with Trigger Action Response Plans (TARPs) to ensure that closure of the pit proceeds safely and efficiently while satisfying regulatory requirements. Active mining operations in the open pit ceased in mid-2019 and pit filling is underway. The pit required the installation of a major dewatering system, with up to 94,000 m3/day, pumped mostly from dewatering wells. Considerations for closure included the site remoteness, safety, global and local stability, water quality of the pit lake, permitting commitments, and closure regulations in the province of Ontario. A major consideration was the rate of pit filling. Rapid pit lake filling using water from the nearby Attawapiskat River leads to more favourable stability and environmental outcomes. A simple hydrogeological model was used to predict the filling rate and the final pit lake level for a number of potential closure options. This was used to schedule a phased geotechnical monitoring approach to ensure the safety of the operators as the pit walls became increasingly pressurised. A trade-off study has informed the preferred approach for pit lake development. Active pit closure has recently been completed and closure reclamation is ongoing.

Keywords: mine closure, slope stability, geotechnical risk, pit lake, TARP, trigger action response plan

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