New disposal techniques for reactive mine wastes to improve stability and facilitate site reclamation upon closure

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The complex challenges raised for the safe management of large quantities of reactive mine wastes require innovative approaches to address various geo-environmental concerns and ensure the geotechnical and hydrogeochemical stability of the disposal sites. Recent work has shown that waste rock inclusions (WRI) placed along selected paths within tailings impoundment can be used to improve their stability and performance by accelerating drainage and consolidation and providing reinforcement. This innovative technique, initially proposed by the Applicant (and collaborators), has been applied efficiently on a large scale at the Canadian Malartic gold mine site (western QC, Canada) for over 7 years. The successful field application of this technique has also raised additional questions that have not yet been addressed (or even considered), including the effect of WRI on the degree of saturation of adjacent tailings, their influence on oxygen ingress and generation of acid mine drainage (AMD) from sulphide minerals, and  how these may impact the reclamation work upon site closure. These issues will be investigated through the proposed Discovery Grant program (Project A). The disposal of reactive waste rock in piles exposed to natural conditions is another critical issue for mining operations, as these may become a major source of contaminated waters. Preliminary laboratory and field work has shown that it is possible to control the generation of contaminated seepage waters in piles by limiting surface infiltration with the addition of flow control layers (FCL) on the top and inside the pile. These layers are placed during pile construction on the surface of each bench (and lift) to limit infiltration and deep percolation toward the reactive core of the pile. Laboratory tests on physical models, numerical simulations and a recently built large scale experimental waste rock pile at the Tio mine (RTFT, Eastern QC) have shown that this technique has a great potential. But the studies also revealed other key aspects that need to be looked at more closely, including three-dimensional effects, localized water flow in the coarse-grained waste rock below the FCL, and ways to define optimum conditions to maximize the efficiency of FCL in terms of material properties and layer thickness, inclination, and vertical position in the pile. These aspects will also be investigated  through the proposed Discovery Grant research program (Project B).