Modern Mining January 2016

COPPER

The Lift 2 production level.

Lift 2 undercut level plan.

the need to move from point to point; they also need steady-state conditions and mature opera- tions teams.” While diesel-powered LHDs offer more reliability of tonnages, they generate heat and fumes into an already hot environment: Lift II will have to deal with virgin rock temperatures of over 57 deg Celsius. “The total heat load has been calculated at 30 MW, taking into account cooling and diesel fumes, should diesel-powered LHDs be used,” said Schoonbee. “We have three ammonium refrigeration plants on surface of 6 MW each, and two chiller plants underground of 3,5 MW each. Three more 3,5 MW units will be installed underground.” Such is the ventilation

first block cave conducted in rock of this hard- ness,” Fouche said. “Our implementation of Lift II will definitely benefit from that experience.” One of the issues tackled was the difficulty in getting sufficient fragmentation from blast- ing, leading to oversize rocks hanging up in the drawbells and interrupting smooth production flows. A range of innovations has resolved this, including water cannons and medium-reach rigs to dislodge hang-ups, and robot rigs to drill and break oversized material. “For Lift II, we are implementing design parameters that will optimise fragmentation,” said Fouche. “We have also modelled different fragmentation scenarios to prepare the breaking team for various conditions.” Continuing its pioneering ways, Palabora’s Lift II fleet includes the largest Sandvik load- haul-dumper currently working underground in Africa – the 12-m, 57-t LH621, boasting a 21-t tramming capacity. This choice makes a significant difference to the rate of moving rock, according to Fouche, and has been an impor- tant contributor to the project to date; apart from the larger payload, the long wheel-base enhances grip in muddy and rough conditions. In a departure from the Lift I configuration, the new project includes 30-t haul trucks, which are loaded by the LHDs, to take ore to the crusher. In what was probably another ‘first’ for the operation, the LH621 was transported under- ground via the vertical service shaft – requiring the partial dismantling of the vehicle and the use of a special ‘skeleton’ lift cage to reduce weight. There are currently three at work in the project, and there will be about 17 employed in full production; the question that now remains is: electric or diesel? “We are finalising the trade-off between electric and diesel LHDs,” said Underground Manager Aidan Schoonbee. “Electric units are slightly quicker, have a lower life-cycle cost and generate less heat – but they also have low predictability given their trailing cables and

challenge at Palabora that over 30 ventilation passes have been planned, with two passes being among the larg- est in the industry at 6,1 m diameter and 1 200 m deep – from the Lift II footprint to surface. Bored by Master Drilling’s largest raise borer yet – its 120-ton SA-designed

All time highs The Lift II project, like its predecessor, will register among the highest lifts in block caving. ‘Lift’is the vertical distance from the production level to the break- through point on surface or in the open pit above. Generally speaking, the high- er the lift, the lower the capital require- ment per vertical tonne of ore mined.

RD8 – the shafts benefit from cost, speed and safety advantages offered by this technology over the conventional blind-sinking methods. Connecting the 450-m gap between Lift I and Lift II are another five large-diameter raises – three forced-air passes and two return-air passes. Over 25 shorter raises will be drilled between the ventilation level and production level, contributing to better heat management as well as dust control – an important consid- eration in the context of underground crushers. The twin decline also plays a vital ventilation role, with one decline currently carrying air down to the workings and the other carrying air up to surface. The compound centrifugal chillers at Palabora are reportedly the first of their kind in Africa, and the first underground installations

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