The Murray & Roberts Cementation shaft sinking team responsible for delivering a new ventilation shaft at Palabora Copper Mine (PMC) recently celebrated the achievement of a major milestone – the reaching of the 800m mark. This represents two-thirds of the shaft’s final depth of 1 200m.
The ventilation shaft forms part of the copper producer’s Lift II project which will extend mine life by more than 15 years. Originally an open pit mine, the Palabora mine transitioned to being an underground block cave operation in the early 2000s when Lift 1 was commissioned.
Murray & Roberts Cementation’s contract to sink the 8.5 m diameter shaft was awarded in February 2019. According to Fred Durand, the company’s senior project manager, the shaft sinking is currently making good progress, with 40 or more lined metres of advance being completed on average each month.
Blasted face
“Shaft sinking operations should be completed by the end of this year with final handover of the shaft to our client, PMC, taking place at the end of the first quarter of 2024,” he says.
Ground conditions have presented a challenge on the project. This has resulted in the shaft lining being taken right down to the blasted face, says Jas Malherbe, Murray & Roberts Cementation’s on-site project manager.
Ground conditions have presented a challenge on the project. This has resulted in the shaft lining being taken right down to the blasted face, says Jas Malherbe, Murray & Roberts Cementation’s on-site project manager.
Unconventional approach
“Normally, we would line the shaft to within 12 to 18m of shaft bottom and support the sidewalls temporarily with split sets and mesh,” he explains. “In practice, this did not prove viable, prompting us to change our approach. The method we’ve adopted is unconventional but has proven to be highly effective.”
Drilling is undertaken by two twin-boom Komatsu electro-hydraulic jumbo drill rigs. These are slung down the shaft from surface and nested in the four-deck stage for drilling the shaft bottom, a procedure which is repeated for each 48-hour blast-to-blast cycle.
Lowering the excavator
Another key piece of equipment is a Komatsu excavator with a 0.3m3 bucket. It is lowered from surface through the stage to shaft bottom and is used for lashing. All the waste rock is loaded into a 11 tonne kibble which transports it to surface.
The ground conditions at the shaft are such that blasting tends to produce large rocks, which can be difficult to handle. “We break these up using the excavator which has a quick coupler which allows it be fitted with a hydraulic breaker within a few minutes,” says Malherbe.
Canadian method
The methods being used at Palabora are based on the Canadian shaft-sinking method that Murray & Roberts Cementation has pioneered in South Africa at its Venetia mine contract for De Beers Group.
“We have adapted the method because of the very different conditions we’re facing but many elements remain the same or are very similar,” says Jas. “In particular, the high degree of safety offered by the Canadian method has not in any way been compromised.”
