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

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DOI https://doi.org/10.36487/ACG_repo/2025_22

Cite As:
Desjardins, M, de Graaf, PJH, Beale, G & Rougier, M 2020, 'Geotechnical risk management for Victor Mine closure', in PM Dight (ed.), Proceedings of the 2020 International Symposium on Slope Stability in Open Pit Mining and Civil Engineering, Australian Centre for Geomechanics, Perth, pp. 399-414, https://doi.org/10.36487/ACG_repo/2025_22

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Abstract:
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

References:
de Graaf, P, Johnson, R & Beale, G 2018, Victor Mine – 2018 Geotechnical Review Board Report, unpublished report, April 2018.
Desjardins, M 2018, Victor Mine De Beers Canada Inc. Geotechnical Closure Report, unpublished internal report, 30 September 2018.
Itasca 2019, Closure of the Victor Diamond Mine: Infilling, Hydrodynamics, and Water Chemistry of the Pit Lake, Technical report prepared by Itasca Denver Inc. for De Beers Canada Victor Mine, May 2019.
Ontario Mines Regulation 2000, Mine Development and Closure under Part VII of the Act (Regulation 240/00).
Read, J & Stacey, P 2009, Guidelines for Open Pit Slope Design, CSIRO Publishing, Collingwood.
Rougier, M, Ruest, M, Gauthier, P & Horwitz, A 2015, ‘The use of head drilling and of structural data from digital photography obtained by drone survey to justify slope steepening at Victor Diamond Mine’, Proceedings of the International Symposium on Slope Stability in Open Pit Mining and Civil Engineering (Slope Stability 2015), The Southern African Institute of Mining and Metallurgy, Cape Town, pp. 485–504.
Rougier, M & Smith, J 2017, Results of the Updated Stability Analyses and Geotechnical Review of Victor Mine Ultimate Pit Slope Designs in Rock, Technical memorandum prepared for De Beers Canada Victor Mine, January 2017.
WA Department of Industry and Resources 1997, Safety Bund Walls Around Abandoned Open Pit Mines Guideline, Government of Western Australia.




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