Hydraulic characterization of the kinsere geology, Democratic Republic of the Congo

Moswathupa, Hamilton Thabang Segana
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The Kinsevere mine operation extracts copper oxide ore that occurs within the Tshifufiamashi, Tshifufia and Kinsevere Hill fragments at the Mashi, Central and Kinsevere Hill pits, respectively. Copper oxide ore mining is expected to continue until 2021, following which, copper sulphide ore mining could be initiated and undertaken until 2027, entailing extension and deepening of the pits. Hydraulic tests were undertaken to determine and characterise hydraulic attributes of various siliceous and dolomitic rock units underlying the pits so as to understand the influence of mine progression on groundwater dynamics, inflows and pore pressures. From this, effective planning, safe mining and sound groundwater management may be undertaken. Hydraulic test data were acquired through pumping, airlift and slug testing of 39 boreholes intersecting the various rock units. The data were analysed using specified methods and characterised based on common hydraulic and lithologic attributes of the various rock units tested. Saprolite and saprock derivatives of the Kundelungu shale and siltstone units had a low hydraulic conductivity (K) of 8.0x10-3 – 2.6x10-2 m/d, while the derivative of the Mines Series shales dolomitiques (SD) unit had a K of 1.6x10-1 – 7.0x10-1 m/d. The RAT siltstone (RSL) and RAT breccia (RBX) units had a moderate K of 3.3x10-3 – 1.5x10-2 m/d and 1.7x10-2 – 5.4x101 m/d, respectively. The Mines Series SD and calcaire à minerais noir (CMN) units had a high K of 4.2x10-3 – 1.5x100 m/d and 1.3x100 – 1.6x102 m/d, respectively. Hydraulic and lithologic attributes influence the capacity of the various rock units to receive, store and transmit groundwater, thereby defining three aquifer units (siliceous, polymictic and dolomitic) at Kinsevere. Mine progression is expected to remove storage, increasing the groundwater sink towards the pits, leading to increased groundwater inflows via moderate to high permeability zones (RSL, RBX, SD and CMN) on the highwalls and pit floors under hydrostatic drive stemming from higher groundwater levels and upward pressures. Inflows into the Mashi Pit could increase from 125 L/s to 171 L/s, while the Central Pit could experience an increase from 545 L/s to 1 103 L/s when terminal depths are reached. Negligible inflows were observed in the Kinsevere Hill Pit. Projected inflows into the Kinsevere Hill North and South pits could be 27 L/s and 135 L/s, respectively. The inflows exceed dewatering discharge of 280 L/s. Most inflows stem from the highwalls, resulting in increased pore pressures that could compromise stability within rock units of low permeability and weakened self-retainability.
A Research Report submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfillment of the requirements for the degree of Master of Science in Hydrogeology June 2019