Abstract:

Obtaining regulatory approvals for mine closure designs requires demonstration that mine waste disposal plans will remain environmentally-protective over long timeframes and under varying environmental and climatic conditions. For sub-aqueous mine waste disposal, testing deposition plans at full scale prior to approval is generally not feasible. Therefore, numerical model simulations often provide the best means of understanding the long-term resilience and sustainability of some mine closure solutions.

Diavik Diamond Mine, located in the Northwest Territories, Canada, have mined diamonds from three relatively narrow open pits with connecting underground mine tunnels that extend several hundred metres below the lake bottom of Lac de Gras. During mine closure, the open pits will be refilled with water from Lac de Gras and reconnected to the lake by breaching the dikes around the pit lakes to restore fish habitat. As well as accommodating ongoing mine-affected site runoff, groundwater, and pit wall leachate, one of these pits will be used to dispose an estimated of 4.2 Mm³ million cubic metres of process kimberlite (PK) which will continue to release a relatively high-concentration pore-water for several hundred years after mine closure.

Given the complexity of the pit lake geometry that includes dykes that will be breached, interconnected mine tunnels, consolidating PK with associated pore-water release and Lac de Gras mixing zones, a comprehensive three-dimensional hydrodynamic model of Lac de Gras was developed and linked to one- and two- dimensional models of the pit lakes to simulate the interaction of mine water and the environment.

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Ms. Marta Lopez-Egea