Shallow water covers, typically less than 2 m deep, are commonly used to store tailings and minimize environmental degradation. Studies have, however, shown that wind induced waves can erode and resuspend tailings in areas where the water cover is much shallower than 1 m, possibly leading to oxidation of sulphide minerals, acid generation, and release of heavy metals. The present work investigated erosion and resuspension of co-disposed, cohesive mill tailings and lime neutralization sludge in a tailings pond located at the Heath Steele mine site, near Miramichi, New Brunswick, Canada. From measured wind data and published equations, suspended sediment concentrations were modeled for various water cover depths and compared to measured total suspended solids (TSS) values and the federal effluent discharge guideline of 25 mg L–1. The computed suspended sediment concentrations agreed with those measured at the effluent discharge point. The results show that winds blowing in the direction of the major axis of the pond contributed most to resuspension and elevated TSS. Key words: cohesive mine tailings and sludge, critical shear stress, wind-induced resuspension, effluent water quality.

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Flooding of tailings under shallow water covers is an effective method of decommissioning potentially acid generating mine tailings. The low diffusivity and solubility of oxygen in water are attractive features of this technology. However, wind-induced waves can resuspend flooded tailings and expose them to greater contact with dissolved oxygen, thereby increasing the potential for oxidation and acid generation. Field measurements of wind activity and waves under different water cover depths and associated resuspension for a mine tailings pond in Ontario are presented and discussed. The results show that wind speeds greater than 8 m/s above water covers that are shallower than 1 m create waves of height greater than 10 cm and bottom shear stresses greater than 0.2 Pa. Under these conditions the critical shear stress of the mine tailings was exceeded, resulting in erosion and subsequent resuspension.Key words: mine tailings, water cover, wind-induced waves, resuspension, wind speed, shear stress.

The use of shallow water covers for containing sulfide bearing mine tailings in non-arid climates has gained importance over the years due largely to their effectiveness as oxygen barriers. In spite of the numerous documented benefits of these covers, some fundamental questions on the application of the technology still remain; a major one being the contribution of the nature of the tailings particles to the overall performance of the cover. Many of the existing tailings ponds have been designed assuming cohesionless sediment behavior. Total suspended solids and sediment trap measurements at some existing water cover sites, designed using the cohesionless sediment approach, have indicated significant resuspension at these sites. The present study provides information on the cohesive nature of sulfide mine tailings particles using particle size and mineralogical data and results of laboratory erosion experiments. The results show that the erosion patterns for tailings particles are similar to those reported for cohesive natural sediments. A power law erosion equation is proposed for calculating erosion rates and estimating the optimal water cover depth for flooded mine tailings.Key words: sulfide mine wastes, subaqueous disposal, erosion character, cohesive sediments, erosion shear stress relationship.

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