Design and construction evolution of the Kemess Mine tailings dam

CIM Montreal 2007
Georgia Lysay, Scott Davidson,
Abstract The Kemess Mine tailings impoundment is retained behind an earthfill dam that, when complete, will measure about 110 m in height with a crest length in excess of 1 km. Due to weak foundation conditions, the dam must be raised at a very flat downstream slope approaching 7H:1V. This requires an enormous volume of fill to construct the downstream shell of the dam, which has a low permeability clayey till core and is raised via the centerline construction method.

For the initial years of annual dam raising, the downstream shell of the dam was constructed with non acid generating waste rock from the open pit, 7 km distant and requiring an uphill haul with obvious cost implications. To reduce costs, feasibility studies were initiated for raising of the downstream shell using cycloned sand. This required inclusion of flotation cells for removal of residual sulphides from the tailings to produce the non acid generating product required for the downstream shell of the dam. These studies were positive, and cycloned sand construction was initiated in December of 2002.

This paper describes the experience gained with cycloned sand construction for the dam. Unique aspects include environmental controls given the sulphide-bearing ores, preparation of the existing shell of the dam for subsequent placement of hydraulically placed cycloned tailings sand, on-dam settling ponds, water management issues, reclamation of the sand dam for erosion control given the wet climate, and use of the system to construct an above-water beach of non acid generating tailings to increase the closure security of the structure. A particularly unique aspect of the Kemess experience is hydraulic fill operations extending throughout the coldest winter months, as compared to other operations where such placement has traditionally been considered non-viable through the winter months.
Keywords: Tailings, dam, Hydraulic, cyclone, ARD
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