Cutifani stated in the latest Anglo American annual report.
Kumba CEO Norman Mbazima said Kumba’s ROCE was already well above 50 per cent but obviously any improvement would benefit Anglo American’s average. Sishen’s ore body dips in a westerly direction at 11 degrees. The old mining direction was from south to north, covering the full 14-kilometre strike length. Now, to more efficiently access ore, the mining direction has been switched by 90 degrees, from east to west, which means more waste has to be extracted.
In 2013, total tonnes mined at Sishen rose by 22 per cent to 208.8 million tonnes (Mt) (2012: 171.6 Mt). Of that, 167.8 Mt was waste, 26 per cent more than the previous year. This was reflected in the mine’s iron ore production falling by eight per cent to 30.9 Mt from 33.7 Mt in 2012.
Anglo American technical director Tony O’Neill said at the Group’s investor day in December 2013 that, if Kumba carried on mining as usual, it would see production rise from 30 Mt per annum (pa) in 2013 with 175 Mtpa of waste to 31 Mtpa in 2014 with 220 Mtpa waste, 33 Mtpa in 2015 with 255 Mtpa of waste and 34 Mtpa by 2016 with 270 Mtpa of waste.
“There would be a recovery. That recovery would be very slow. And, along with that very slow recovery in ore produced, there would be a rapid increase in the amount of waste that would have to be moved to try to get the speed of ore exposure back into some sort of balance, at least,” says O’Neill.
Management has devised a new mine plan, which will eliminate about 600 Mt of waste from the life-of-mine plan, and also introduces ways to work smarter, Mbazima says.
The new mine plan would target a faster increase in iron ore produced in relation to waste mined so that, by 2016, Sishen will be mining 37 Mt of ore with 270 Mt of waste. That is the level where waste will peak. Mbazima says it will remain at that level for three to four years, and then reduce.
Andrew Loots, executive head of operations at Kumba, says the pit constraints started to emerge in 2008 after Sishen commissioned its new jig plant to beneficiate a mix of ‘A’ and ‘B’ grade material. As the jig plant ramped up, the ‘B’ grade resource did not materialise as expected.
After detailed definition of more ‘B’ grade material, it became evident that about 800 Mt had to be written off from Sishen’s deeper resources. To feed the jig plant, Kumba had to actively mine more ‘B’ grade material, which complicated the execution of the mine plan, as well as add more ‘A’ grade material.
At the same time, the stripping ratio, which is the proportion of waste to ore, rose to 4:1 from 2:1. To expose more ore, the mine’s vertical rate of advance, which was around 35 metres a year, had to be accelerated to 80 metres a year.
O’Neill says in some areas the mining direction has been moved by 90 degrees to improve the rate of advance. Access routes out of the pit have been simplified, which can improve fleet productivity by up to 20 per cent.
Loots says the new plan for Sishen has several elements, the first step being to optimise the mine plan with a new understanding of the resource. He says production will be maximised in two ways: through optimal design of the pit so that mining is sequenced to get the best ore-to-waste ratio, and through greater efficiencies.
SUSTAINABLE FUTURE
“We have a huge commitment from the Sishen team to make this successful,” Loots says.
“Our new mine plan has given us more confidence about what we can produce, and at what cost,” Mbazima says. “We have also optimised that cost. Reducing the amount of waste we mine over the life of the mine will reduce our unit cost over time. We have made our production more efficient and therefore more cost-effective.”
Sishen’s new mine plan means employment will be retained at current levels, and improving productivity not only helps Sishen’s costs but also its sustainability, Mbazima says.
“We have done a lot of technical and geological work and are now confident this is the optimal way to return Sishen to delivering its full potential,” says Mbazima.
