Nick Holland
Photo by: Duane Daws
JOHANNESBURG (miningweekly.com) – South Deep gold mine’s 42% production increase, which last week helped spark Gold Fields’ 29% share price increase, was the result of the company getting better at its “plan the mine, mine the plan” approach – and in particular the execution of long-hole stoping.
The Johannesburg- and New York-listed company’s share price last Thursday took it highest single leap in 16 years after the release of third-quarter results that followed a strategic mine design change in the destress methodology.
This involves a conversion of the low-profile 2.5 m vertical height at the South Deep mine, west of Johannesburg, to a high-profile 5 m vertical height, which is making mining simpler. (Also watch Creamer Media video attached).
While this is underpinning much future promise, Gold Fields CEO Nick Holland puts the direct reason down to an improving set of basics.
“We’re just getting better at ‘plan the mine, mine the plan’,” he said in response to questions put by Creamer Media’s Mining Weekly Online.
The long-hole stopes, where improvement was most pronounced, are 17 m to 20 m vertical cavities that stretch 40 m to 60 m in length – “a big block of ground” that is mined in a special way.
“You don’t take it all at once. You do five rings at a time, which is in essence about 7.5 m, and you take out that rock and then you carry on, on a retreat basis to take out the rest,” Holland explained.
Some 6 000 t to 8 000 t are broken in a blast and these tonnes have a grade of 6 g/t to 7 g/t.
In the three months to September 30, total reef tonnes broken increased 37% to 333 000 t.
Longhole stoping accounted for 40% of total ore tonnes mined, support improved by 14% in the quarter to 1 584 m and backfill cubes increased by 42% to 113 m3, improving mining flexibility.
South Deep, a fully mechanised mine, spent time improving execution, making sure that it did not mine offline and remained within the contours of the grade.
Safety statistics were 40% better year-on-year and the number of injury-free days was at unheard of levels.
It also replaced fleet, bringing in 27 new pieces of category-one gear, including drill rigs, trucks and loaders that provided improved availability.
It has recruited 87% of a complement of 180 skilled positions in the trackless area of the mine, where 1 000 of South Deep’s total of 3 500 employees are active.
“All these things are starting to show results. But there is still a long way to go and I don’t think we should declare victory at this stage,” Holland commented to Mining Weekly Online.
He is expecting an improvement in the current quarter and for 2016 to be better than this year.
Production for the full year is expected to be 193 000 oz at the outside.
Total all-in cost in the third quarter was $961/oz.
It is expected to take about 18 months more to get the entire mine up to the new high-profile status.
Meanwhile, the bigger vertical cuts with the same 4.5 m horizontal dimensions for every metre blasted mean that even with the same rate of advance, more tonnes result.
The entire mine is set to be converted by early 2017, making it easier and simpler to access the orebody in the open stopes.
Global specialists were brought in to avoid the same area having to be mined several times, a negative aspect of low-profile distress.
The other problem with the low-profile destress is the mining sequence leads to deformation.
The high-profile environment opens the way for conventional jumbo drill rigs to mine, support and gain access to the open stopes; mine the stopes, backfill them and then move on.
Extensive modelling and algorithms had to be used to work out all of the structures.
In the three months to September 30, the outflow of cash from South Deep fell to R266-million and development increased 58% to 1 486 m.
The target for break-even is the end of 2016 and long-term guidance from February 2017.
Gold Fields took the long-term targets off the table at the start of this year and once the basics improve, long-term forecasting will return.
“For us to give three- to five-year views while we’re still fixing a lot of the basics I don’t think would be useful. I’d rather give a long view later,” said Holland.
The one consistent theme over the seven years that Gold Fields has owned the mine is that the orebody resolution is good.