Evaluation of a single-layer desulphurized tailings cover

Abstract

The potential effectiveness for long-term closure of a desulphurized tailings cover placed on reactive tailings at the Detour Lake Mine was assessed. The single-layer cover was aimed at reducing oxygen ingress using high water saturation to limit oxygen diffusion and consumption of oxygen in the cover by residual sulphide minerals. The cover was 1.0 to 1.5 m thick and met desulphurization targets, but was coarser grained than the design. One-dimensional unsaturated flow and oxygen diffusion modelling was used to predict water content profiles, depth of oxygen penetration, and diffusive oxygen fluxes. Effective diffusion and reaction rate coefficients estimated from field data matched laboratory measurements. Depth to water table was identified as the most important factor for reducing tailings oxidation. The deeper (4 m) water tables measured at the cover edges led to a lower degree of saturation and higher oxygen flux. Finer grain size and higher air-entry values in the cover materials helped maintain saturation, and a capillary break (fine over coarse) cover reduced oxygen fluxes to <5% of fluxes to uncovered tailings. The as-built cover (coarse over fine) reduced oxygen influx by at most 50% and as low as <1% of uncovered tailings.