Cogema Resources Inc. (Cogema) is currently developing the McClean Lake Project in Northern Saskatchewan. The development includes the mining of several uranium ore bodies and the construction and operation of an associated mill and tailings depository. The proposed tailings depository consists of tailings deposition into a mined out open pit, similar to the existing in-pit “pervious surround” method employed at Cameco’s Rabbit Lake mine. However, due to the high grade of the Project’s tailings, several modifications were made to the original design of the tailings facility and the tailings placement methodology. These modifications will provide the necessary radiation and environmental protection required for handling and placement of high grade tailings.
The modifications made to the “pervious surround” disposal concept include the deposition of tailings as a thickened (engineered) paste below a water cover and the incorporation of a unique groundwater pumping methodology which provides “hydrodynamic containment” of porewater expressed during consolidation. In addition these measures will ensure that tailings density is maximized and the hydraulic conductivity of the tailings mass is minimized by the end of operations. The provision of a water cover also eliminates consolidation problems associated with freezing. At the completion of milling activities, a soil cover will be placed above the tailings surface to consolidate the most recently deposited tailings and to provide a permanent barrier between the tailings and the terrestrial environment. At the time groundwater conditions are restored to pre-mining levels (flood back of the cone of depression), the tailings will be sufficiently consolidated, resulting in a low permeability tailings mass (ie. plug) contained within a higher permeability host rock. Contrasting permeability’s will cause groundwater to flow around the tailings mass rather than through it, similar to that of the pervious surround system. The subaqueous thickened tails deposition will ensure that decommissioning activities can proceed shortly after tailings placement with a minimal release of heavy metals and radionuclides to the environment.