Modern Mining July 2019

COPPER/ZINC

of the workings via a pumping system to be installed in the Hutchings Shaft is planned, an exercise which will take 18 months. Water will be pumped into a 1 million m 3 vol- ume dewatering dam on surface, from where mechanical evaporators will be used to accel- erate evaporation. Examinations and testing of the shaft steel- work from surface down to 30 m below the water level, along with the use of video cam- era inspection down to 200 m below the water surface, as well as shaft probing and water qual- ity testing to within 100 m of the shaft bottom, indicate that the majority of the shaft is in good order. Sections of the shaft will be refurbished. A pre-owned Koepe rock winder and a dou- ble-drum men-and material winder with new ropes and equipment have been identified for purchase and installation. It is envisaged that the steelwork refurbishment will be carried out concurrently with the underground dewatering campaign to reduce the project construction time and make optimal use of the available con- struction crews. According to the DFS, the mineralisation of the Deeps resource shows considerable varia- tions in both thickness and dip resulting in the use of a variety of stoping methods to max- imise extraction and minimise dilution. Based on the analysis of the resource, it has been demarcated into four zones – the North-west Upper Zone, situated above the 957 Level; the North-west Lower Zone, situated below the 957 Level; the South-east Zone, situated

Left: Much of Prieska mine’s infrastructure, including the main 1 024 m-deep, 8,8 m-diameter hoisting shaft (Hutchings Shaft), remains intact. Below: The portal and main decline had been partially backfilled during mine closure in 1991. These have been re-excavated and rehabilitated.

of Prieska

this with an open-pit operation which will commence on the conclusion of underground mining in Year 9 of operations and run for roughly 17 months. The Deeps resource will be mined at a steady-state rate of 2,4 Mt/a and the open-pit resource at 1,2 Mt/a. Known as the +105 Level deposit, the open-pit resource consists of shallow supergene material left as part of the pillar supporting the upper levels of the mine. The combined project probable ore reserves amount to 13,62 Mt grading 1,1 % Cu and 3,2 % Zn, which translates to 143 kt of copper metal and 433 kt of zinc metal. These reserves make up 65 % of the Foundation Phase production target, with inferred and indicated mineral resources accounting for 21 %. Inferred and indicated mineral resources incorporated in Mine Stope Optimiser shapes and the Whittle pit optimisa- tion pitshell make up the remaining 14 %. The Hutchings Shaft and underground workings currently contain a volume of 8,7 million m 3 of accumulated water. Dewatering

July 2019  MODERN MINING  27