HomeGoldSouth Deep Preparing for Next 50 years

South Deep Preparing for Next 50 years

Vishnu Pillay

Vishnu Pillay who heads
Gold Fields’ South African
operations

Gold Fields is one of the world’s largest mining companies, with production of some 3.5 million ounces of gold a year, but the 750,000 to 800,000 ounce a year contribution of its South Deep mine in South Africa when in steady state will be notable even in the context of such a group.

South Deep, which lies on the northern rim of the Witwatersrand basin, less than an hour’s drive (60 km) to the west of Johannesburg, is not a typical South African gold mine. Though its development has not been without the colourful incident that will please future mining historians, it is the mine that virtually guarantees South Africa will still be a gold producer in the second half of this century.

When the sinking of the South Deep main and ventilation shafts, the twin shafts, originally designed to extend some 3,000 metres and 2,750 metres below surface respectively, began in late 1995 the mine was owned by the then major mining house JCI. By the time the twin shaft complex was officially commissioned in early 2005 the mine’s ownership lay in the hands of Canadian mid-level group Placer Dome and the now deceased Brett Kebble’s Western Areas Gold Mining company.

After it began the twin shaft project JCI fell into the hands of mining entrepreneur Mzi Khumalo, who brought Kebble in as partner. At a later stage, Placer Dome became a 50% shareholder in South Deep before Placer was taken over by Canadian major gold producer Barrick. When Kebble was murdered revealing his group as bankrupt, and with the Canadians not interested in remaining involved the operation went into a form of curatorship with former politician and prominent business person Cheryl Carolus appointed as caretaker.

During this time the developing mine had a loaded skip, weighing some 28 tonnes and the 6.7 km of rope to which it was attached, fall 1.6 km down one of the twin shafts, damaging shaft infrastructure and setting back the project further.

However, shortly after that, in December 2006 Gold Fields took over Barrick’s 50% share of South Deep and in April 2007 acquired full control of the mine. South Deep, with its resource of 64 million ounces, was at last fully in the hands of a group that could do it justice.

South schematic

Schematic showing the South Deep operation, which includes the twin shafts as well as the already existing South shaft

“We are doing our planning to make sure South Deep fulfils its potential as one of the world’s greatest deep level mechanised mines,” head of Gold Fields South African operations Vishnu Pillay tells Mining Review Africa.

He says the anticipated working cost of R105,000/kg and R30,000/kg capital cost equates to a notional cash expenditure of R135,000/kg, which means South Deep is expected to be a very high margin high volume gold mine.

“The previous owners due to lack of funding did not invest in development and strategic items of infrastructure.” Gold Fields has rectified that situation and is spending about R1 billion a year on the project for the next six years, to ensure South Deep fulfils its potential. This includes deepening the ventilation shaft to 3,000 metres, and investment in key refrigeration infrastructure such as an ice plant on surface and a refrigeration plant at the mine’s 94 level.

Having the world’s best deep level gold orebody, Gold Fields also committed to itself to full mechanisation of South Deep with the introduction of additional mechanised fleets and manpower in strategic areas of the mine.

It initiated a major capital intensive long-inclined-borehole underground programme to provide geological structure and grade information, involving some 17.4 kilometres at a cost of over R15 million. In addition, Gold Fields has initiated a surface drilling programme at a cost of R151 million to evaluate the orebody in the areas to the east of South Deep, on the Uncle Harry’s property which the company has obtained from JCI and Randgold and Exploration.

Even though Gold Fields already held some of the South Africa’s and the world’s best gold assets, including the Driefontein and Kloof gold mines, and has a strong reserve base of 78 million ounces of gold, South Deep alone accounts for some 37% (29 million ounces) of the company’s reserves. This excludes the 16.5 million Uncle Harry’s resource. That resource could be converted to a reserve and would be mined from the South Deep infrastructure.

Yet, even after the Gold Fields takeover South Deep continued to be plagued by ill fortune. On the 1st of May 2008, coinciding with but unrelated to the first day Gold Fields’ new CEO Nick Holland took over from Ian Cockerel, nine people died at South Deep when the cable of their small service shaft cage snapped. Gold Fields management responded by saying that if they could not mine safely they would not mine at all, and the company has, together with the rest of South Africa’s gold sector, been working hard to improve the industry’s very poor safety record.

However, whereas the typical South African gold mine features a narrow tabular orebody where the economic seam width extends from a few centimetres to one – two metres, and involves very labour intensive mining, South Deep is different. South Deep is focused on two primary reefs, the Ventersdorp Contact Reef (VCR), and the stacked upper Elsburg reefs that subcrop with the VCR and form a wedge that attains a 130 metre thickness at South Deep’s eastern boundary. This wedge eventually thins to leave just the VCR to the west. The upper Elsburg reefs constitute 93% of South Deep’s reserves with the VCR accounting for the rest.

South schematic1

Schematic of a portion of the South Deep orebody (virtual scale exaggerated)

Gold Fields has divided the South Deep orebody into four packages for the mechanised mining that features automated loaders with the operator located away from the vehicle. The four packages from west to east are respectively 1.5-35 metres, 40-70 metres, 20-60 metres, and 20-30 metres in mining width. “In some cases the extraction will be total, and in others there will be selective extraction,” Pillay says.

The suite of mining equipment includes some low profile loaders, boom rigs and dump trucks, capable of manoeuvring in 5.0 by 5.5 metre ends, with Atlas Copco being the main supplier. Gold Fields will be the owner operator of the mining fleet, but the development work is being undertaken by contractor Murray & Roberts Cementation.

The mining method at South Deep is horizontal mechanised de-stressed long hole stoping. In order to undertake mechanised massive mining in an area at such depths, the relevant zone must first be de-stressed by mining a cut to ensure a de-stressed window of 50 to 60 metres above or below the associated slope. These destressed stopes must be placed in horizons that minimise the lock-up of reserves, while creating rock stress conditions similar to significantly shallower depths. Backfill is an integral part of the mining method, and is essential to both local and regional stability. The current mining depth at South Deep is about 2,700 metres.

The horizontal logistics of the operation are somewhat unique in that ore, personnel and material will be transported using conveyors and mono-rail systems.

Gold Fields was not the only group interested in taking over South Deep, and one of the reasons Gold Fields won out over other bidders are synergies with its adjacent Kloof mine. The possibility of accessing the bottom of the South Deep orebody from the Kloof No 4 shaft which is four kilometres distant is being investigated. “We have completed scoping studies and decided we need more information,” Pillay says. “Considering the distance and investment involved we will wait until we have it to get better guidance before any decision is made.”

However, Pillay says there are other substantial synergies between Kloof and South Deep, which Gold Fields is looking to maximise. “This includes plant utilisation, environmental management, infrastructure such as building stores and yards, maintenance infrastructure, recreation and other facilities and accommodation for mining personnel.”

Pillay says key factors in the buildup of production at South Deep include the rate of development build-up, the rate of destressing to open up the orebody, and the increase of the hoisting capacity of the twin-shaft system to reach the expanded target of 330,000 tonnes a month.

The hoisting capacity of the current winder at the South Deep twin shaft complex’s main shaft is 175,000 tonnes a month. The main shaft winder is a Blair multi-rope winder powered by two 6.0 MW motors with a payload per trip of 28.5 tonnes. The additional capacity to be provided by the twin shaft complex’s ventilation shaft winder will be 195,000 tonnes a month, powered by a winder similar to that of the main shaft with a payload of 31 tonnes per trip.

This will see the planned ramp up of the twin South Deep shafts to their full capacity of 330,000 tonnes a month by July 2014. In addition, Pillay says there are plans for the existing South shaft at the original Western Area operation to be used to haul waste rock to surface. This will free operational capacity at the twin shafts for hauling additional reef and could accelerate the ramp-up, and add flexibility to the operation. The South shaft was being used to haul personnel and materials and is being upgraded to haul this additional rock.

South Deep’s existing plant can process 220,000 tonnes of ore a month and there are plans to expand it with the addition of an additional mill sometime between 2012 and 2014.

The cost per tonne for South Deep will be less than that of a conventional mine, with a R600/tonne working cost estimated for when it is in full production. This compares with its current working cost of almost R900/t and that of Gold Field’s world class Driefontein mine where the working cost is just over R800/t. The typical South African gold mine spends some 50% of its working costs on labour, another 15% – 20% in maintaining stores and some 10% to 12% on power. South Deep will avoid much of the labour and some of the stores costs.

South Deep has also been designed to minimise the use of water and power. The mine, which is ventilated to achieve a 28.5O C wet bulb reject temperature, will use its three downcast shafts, namely the twin shafts and the South shaft, to provide 1,200 m3/s of cooled air. The twin shafts have four surface fans, three of which will operate, with one as a standby unit. The south shaft has two fans, of which one will be operating, the other being a standby unit.

Refrigeration will be based on surface bulk air cooling at these shafts with refrigeration plants on surface providing 32 MW of cooling, supplemented with underground cooling and ice from surface. Some 1,120 litres per second of water will flow to the air coolers close to the workings.

Power savings will be achieved in various ways including having the surface fans fitted with guide vanes to optimise power as the mine size increases. Ice supplied from surface to the 90 levels of the mine will reduce the amount of water pumped to the surface, and the size of intake and return airways have been designed at optimum cost to minimise electrical power cost. Energy recovery systems such as pelton wheels are to be installed at strategic locations. In addition, the use of fissure water generated underground will minimise electrical pumping costs and also minimise the use of national water resources. Because of mechanised mining, South Deep’s water consumption will be significantly reduced in comparison with conventional mining.

As part of its dealing with both safety and critical function at its deep level shafts, and to ensure that it is not dependent for these on the reliability of national utility Eskom, Gold Fields awarded Powertech Energy Solutions, a member of the Altron group, a R140 million contract to provide standby power generating facilities at South Deep, Kloof and Driefontein. Each of these standby power generator sets is designed to supply 10% of a mine’s power requirement. South Deep’s seven 2,250 kVA, 11 kV diesel powered Cummins generator units were commissioned in late January 2009.

These standby power facilities, which ideally as with all insurance investments will never have to be invoked, will ensure the safe extrication of underground staff and the continued de-watering of the shafts during power failures. All of the units can be brought on-line in about 30 seconds.

The South Deep mine currently uses 58 MW and has secured Eskom’s commitment for another 40 MW for the project. Once it reaches full operation, South Deep will use some 90 MW.

With its 64 million ounce resource base and in the process of overcoming its chequered history, South Deep is expected to be the reference point used to undermine the arguments of gold mining in South Africa being a sunset industry. If gold mining in South Africa is to be described as a sunset industry, at least it will be a long time before twilight finally arrives.

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