Pumping Out South Africa's Deep Gold Mines
Mines in South Africa are having to go deeper and deeper to reach the country's rich reserves of gold, which presents quite a pumping challenge. Gold mines, such as the Beatrix, rely on ITT Flygt pumps to do this.
South Africa's status as an industrial power owes much to the vast mineral wealth buried beneath it soils. In addition to being the world's largest producer of gold, South Africa also leads in production of platinum group metals, vanadium, alumino-silicates and ferro-alloys as well as being the third-largest exporter of coal.
When diamonds were discovered in the 1870's in the town of Kimberly in South Africa's Northern Cape province, prospectors from around the world flocked there in search of an easy fortune. Among them was legendary mining baron, Cecil John Rhodes, who aspired to colonize Africa for Great Britain. The De Beers Diamond Company, created by Rhodes, grew into a global monopoly which, despite occasional break-aways by renegade producers, remains largely intact.
The discovery of huge gold deposits in Witwatersrand in 1886 drew prospectors away from Kimberly in search of even easier fortune. It was here that the Main Reef penetrated the earth's crust and disgorged its fabulous spoils. Surface gold had never before been found in such quantities. But once the surface gold was gone, prospectors sold their underground rights to larger mining companies capable of funding underground mining development.
Going DeepAs the shallower and more accessible gold deposits were mined out, mining companies were forced to dig deeper and deeper. Some of the deepest mines in the world are found in South Africa, where gold is mined at depths up to four kilometers (2.4 miles). This presents a host of operational problems, such as ambient underground temperatures of 50 degrees Celsius or more, occasional rock bursts, groundwater seepage and ever present danger of flooding.
The logistics of mining at ultra-deep levels necessitated development of a raft of new technologies. These include sturdier cables, mammoth air refrigeration systems capable of cooling hundreds of kilometers of underground tunnels, and devices to detect seismic activity, allowing miners to be evacuated before a rock burst.
At the Beatrix Gold Mine in South AfricaOs Free State province, owned by Gencor, South Africa's second largest mining house, thousands of miners must be conveyed each day to working areas as deep as one kilometer beneath the surface. From there, they proceed along tunnels and Ûstopes,Ó exposing new gold-bearing rock seams for blasting and clearing. The blasted rock is conveyed to the central shaft by locomotive-driven hoppers, where it is hoisted to the surface for processing into raw gold.
A massive underground infrastructure is required to keep this mine functioning safely 24 hours a day. Huge surface fans blow refrigerated air through the latticework of tunnels below, keeping temperatures to a workable range between 17 and 29.5 Celsius. The mine comprises two shafts at depths of 960 meters and 912.5 meters, while a third shaft currently under construction will descend to nearly 1.5 kilometers (almost 1 mile). Tunnels radiate from the shafts at various depths. Scores of ÛdrivesÓ and stopes branch out from these tunnels, providing access to the gold-bearing seam, often just a few feet thick. As the gold is mined out, the tunnels and stopes stray farther from the shaft. The shaft is the lifeline of the mine, delivering men and materials to the working areas below - and gold-bearing ore to the surface, all by way of large lifts.
Pumping Water Down and UpSeven thousand cubic meters of water are pumped into the mine each day to operate the rock-drilling machines and another 200 cubic meters are required as drinking water for the thousands of miners below. This spillage water mixes with mine seepage water and flows down tunnel drains to numerous sumps where it is pumped to two large storage dams on Level 16, situated 796 meters below the surface.
These storage dams provide the flooded suction required by the large multistage pumps at the main pump station some 18 meters below Level 16. From here, the water is pumped 814 meters direct to the surface.
The Beatrix mine uses six Flygt 90kW BS 2400 pumps. These pumps are capable of operating at submerged depths of 70 meters. One of the BS 2400 pumps is permanently situated at shaft bottom as an emergency stand-by pump. In the event of flooding (a rare occurrence at Beatrix), the BS 2400 pumps any shaft bottom water 144 meters vertically to the storage dams on Level 16 where multistage pumps take over again and pump the water to the surface.
Some 836 meters further down the mine, at a gradient of eleven degrees, two more Flygt BS 2400 pumps are used as emergency stand-by pumps, pumping any flood water back to the storage dams on Level 16 - a static head of 143 meters.
A major advantage of these pumps is their ability to pump aggregate of up to ten millimeters in diameter. Several other smaller Flygt pumps are in use elsewhere in the mine.
The construction foreman at the Beatrix gold mine, Saai Rabie, is responsible for overseeing construction of the new "decline" shafts and pump installation. "The pumps we use here must be capable of working under extremely trying circumstances," he says. "Working at depths of one kilometer or more in an underground mine, the pumps must be reliable and require minimal maintenance. Some of the Flygt pumps at Beatrix have been in operation since 1982. Service is excellent and parts are readily available from the ITT Flygt service agent in the nearby town of Welkom."
South Africa produces 495 tons of a gold a year, about 30 percent of the world's total. South Africa still accounts for more than half of the world's known gold reserves, though much of it lies at depths of five kilometers or more. Beatrix's production target is 1,333 kilograms of gold a year at an average grade of about five grams per ton of processed rock. Reprinted with permission from Minett Media.