Case study: geotechnical considerations for the conceptual littoral zone design supporting mine closure at the Ekati mine Pigeon Pit

Authors: Clayton, C; Blacklock, N; Koop, G; Estrada, M Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2615_146

Cite As:
Clayton, C, Blacklock, N, Koop, G & Estrada, M 2026, 'Case study: geotechnical considerations for the conceptual littoral zone design supporting mine closure at the Ekati mine Pigeon Pit', in AB Fourie, G Boggs, J Heyes & M Tibbett (eds), Mine Closure 2026: Proceedings of the 19th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1-14, https://doi.org/10.36487/ACG_repo/2615_146



Abstract:
Ekati is a diamond mine located approximately 300 km northeast of Yellowknife in the Northwest Territories in the low Arctic ecoclimate zone, Canada. The area is characterised by continuous permafrost reaching depths up to 320 m, boulder fields and numerous lakes. The closure plan for the Pigeon Pit at Ekati involves flooding of the open pit to form a freshwater lake as part of progressive reclamation outlined in the interim closure and reclamation plan for the mine. To facilitate this, designs of an outflow channel and 3 conceptual littoral zones for fish habitat restoration were developed to enhance aquatic habitat while achieving long-term geomorphic and geotechnical stability. Three conceptual littoral zones – the Northwest, Southwest and Ramp – were designed to provide productive shallow water habitat through a combination of bench excavation, fill placement and engineered substrate. This paper presents the technical basis for the conceptual littoral zone designs, focusing on geotechnical characterisation, stability considerations and construction requirements appropriate for mine closure in cold region environments. An assessment of the existing pit walls, overburden slopes and bedrock domains suggests that the risk of longterm geotechnical instability is low. Current bench-scale performance in the region of the proposed littoral zones is observed to be good to very good, with minimal ravelling and intact bench crests. Stability analyses show factors of safety exceeding the target design acceptance criteria for long-term stability for both static and pseudo-static loading. Anticipated permafrost thaw during lake filling is not expected to influence deep-seated pit wall stability or compromise littoral zone performance. This integration of progressive mine closure into the mine plan demonstrates the application of hydrotechnical and geotechnical engineering design to develop stable, habitat-supporting pit lakes in cold region mining environments.

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