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 colorful 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 meters (m) and 2,750 m 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 fraudster Brett Kebble’s Western Areas Gold Mining Co.

After it began the twin shaft project, JCI fell into the hands of mining entrepreneur Mzi Khumalo, someone who has attracted controversy. It was 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 metric tons (mt), 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 was at last fully in the hands of a group that could do it justice.

“We are planning to make sure South Deep fulfills its potential as one of the world’s greatest deep level mechanized mines,” said Vishnu Pillay, head of Gold Fields South African operations, two years later. He said the anticipated working cost of about $330/oz and the $95/oz capital cost equates to a nominal cash expenditure of about $425/oz, which means South Deep is expected to be a very high-margin, high-volume gold mine.

Vishnu Pillay, head of Gold Fields’ South
African operations

Having the world’s best deep level gold orebody, Gold Fields also committed itself to full mechanization of South Deep with the introduction of additional mechanized fleets and manpower in strategic areas of the mine. It initiated a long-inclined-borehole underground program to provide geological structure and grade information, involving some 17.4 km at a cost of more than $1.65 million. In addition, the company has initiated a surface drilling program at a cost of $16.6 million to evaluate the orebody in the areas to the east of South Deep, on the adjacent Uncle Harry’s property which the company has obtained from JCI and Randgold and Exploration.

Before taking over South Deep, Gold Fields already held some of the South Africa’s and the world’s best gold assets. This included the Driefontein and Kloof gold mines. Altogether Gold Fields has a strong reserve base of 78 million oz of gold; nonetheless South Deep alone accounts for some 37% (29 million oz) of the company’s reserves. This excludes the 16.5-million-oz Uncle Harry’s resource, which 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 May 1, 2008, coinciding with but unrelated to the first day Gold Fields new CEO Nick Holland took over from predecessor 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.

Schematic showing the South Deep operation, which includes the twin shafts and the older existing South shaft

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

The suite of mining equipment includes low profile loaders, boom rigs and dump trucks, capable of maneuvering in 5- by 5.5-m 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 mechanized de-stressed long hole stoping. To undertake mechanized massive mining in an area at such depths, the relevant zone must first be de-stressed by mining a cut. This ensures a de-stressed window of 50 to 60 m above or below the associated stope. These stopes must be placed in horizons that minimize the lockup 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 m.

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 4 km distant is being explored. “We have completed scoping studies and decided we need more information. Considering the distance and investment involved we will wait until we have it to get better guidance before any decision is made,” Pillay said.

However, Pillay explained, there are other substantial synergies between Kloof and South Deep, which Gold Fields is looking to maximize. “This includes plant utilization, environmental management, stores buildings and yards, maintenance infrastructure, recreation and other facilities and accommodation for mining personnel,” Pillay said.

South Deep’s twin shafts and ground infrastructure; the operation will build production up to
some 750,000 oz of gold a year.

This will see the planned ramp-up of the twin South Deep shafts to their full capacity of 330,000 mt/month by July 2014. In addition, Pillay said 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 mt of ore per month and there are plans to expand it with the installation of an additional mill sometime between 2012 and 2014.

The cost per ton for South Deep will be less than that of a conventional mine with a $66/mt working cost estimated for when it is in full production. This compares with its current working cost of almost $100/mt and that of Gold Fields’ world class Driefontein mine where the working cost is just over $88/mt. The typical South African gold mine spends some 50% of its working costs on labor, another 15% to 20% in maintaining stores and some 10% to 12% on power. South Deep will avoid much of the labor and some of the stores costs.

Keeping Conditions Cool
South Deep has also been designed to minimize the use of water and power. The mine, which is ventilated to achieve a 28.5°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. Refrigeration plants on surface will provide 32 mw of cooling, supplemented with underground cooling and ice from surface. Some 1,120 l/sec of water will flow to the air coolers close to the workings.

South Deep has planned to secure its future by installing standby gensets to avoid reliance on
national utility Eskom for safety-critical mine dewatering and evacuation power.

As part of its dealing with both safety and critical functions at its deep level shafts, and to ensure that it is not dependent for these on the reliability of national utility Eskom, Gold Fields spent $15.5 million 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 dieselpowered 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.

If gold mining in South Africa is to be described as a sunset industry, South Deep at least will ensure it is a long time before twilight finally arrives.”