New tailings impoundment feasibility design in Senegal

SRK completed the feasibility design of a tailings management facility (TMF) for the Oromin Joint Venture Group at the Sabodala Project in Senegal in 2010. To ensure a consistent water supply to the mine, the TMF facility will be used as a water reservoir during the rainy season to supplement a purpose-built water reservoir of 9.7 million cubic meters about 9 km from the mine site, which SRK also designed.

The TMF will contain about 17.6 million tonnes of tailings, with the capacity to expand up to 25.6 million tonnes. Two water-retaining earthen embankments provide containment. The dam will be constructed in phases, using a hybrid downstream-centerline method. The primary and secondary dams will have crest lengths of 550m and 214m, and maximum heights of 28m and 12m, respectively.

Beneath the dams, the foundation consists of a thin veneer of organic topsoil overlying silty clay saprolite that varies in thickness from 5 to 10m. These layers overlie weathered bedrock. The dams are homogenous earth-fill structures, constructed from compacted saprolite, which is sourced locally. Internal chimney and blanket drains are used to control the phreatic surface in the dams. Upstream and downstream dam slopes are 2H:1V and 2.5H:1V, respectively, and the crest widths are 9m. Upstream slopes will be clad with rip-rap for wave protection, and the downstream slopes will be seeded with erosion resistant vegetation. The dams will have a freeboard of 2m, and a 25m wide spillway, lined with rip-rap, capable of passing the Regional Maximum Flood (RMF), which is equal to a 1:7,000 year flood.

Tailings will be thickened to greater than 60% solids and deposited so that a pond will be maintained against the dam during the early stages of mine development. The pond surface area will be kept as small as possible to minimise evaporation. This pond will be supplemented by natural inflow from the TMF catchment during the rainy season.

Maritz Rykaart: mrykaart@srk.com



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