Geotechnical investigation for Kwatebala copper open pit, DRC

Kwatebala is located 12km west-northwest of Fungurume in the Katanga Province of the Democratic Republic of Congo. The topography of the area is characterised by gently rolling hills with pronounced ridges which are frequently associated with copper mineralisation. These ridges have areas of open grassland, known as copper clearances, but are mostly covered with moderately dense bush. Kwatebala is a 1900m long east-west trending ridge that rises from the surrounding valleys to an altitude of 1503m. Before mining began, the hill was covered in grassland with some surface exposure and trial pits, trenches and adits from previous exploration.

Extensive development now includes the construction of the plant, tailings storage facility, storm water dams, waste rock dumps, stockpiles and a mine slope consisting of three exposed benches.

The anticlinal ore body is mined using a Vermeer continuous miner and leaving a central waste portion as high walls; the waste rock is drilled and blasted. The ore material supplied to the plant is sufficiently well fragmented while reducing the disturbance to the rock mass.

The parameters of rock mass strength used in the stability analysis were derived from laboratory tests of representative samples of core taken from selected boreholes during the exploration drilling program. This data is continually updated as samples are collected and tested in ongoing quarterly audits.

The stability of the slopes were characterised “Dry” and “Wet” based on piezometric data gathered from the 2007 groundwater study.

The slope stability analyses were performed on representative sections of the slope with the Rocscience program Slide and Phase2. Factors of safety (FoS) were calculated using average Mohr-Coulomb parameters. The analysis yielded acceptable FoS and slopes with a low Probability of Failure. Kinematic analysis indicated that stability would be governed by structures rather than material strengths.

Noel Smith: nsmith@srk.co.za

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