January 15, 2004
By Lucille Davie
NOTICED that the familiar mine dumps south of the city have gradually been disappearing? Well, some 170 million tons have so far been removed and the plan is to eventually remove all the dumps, and in the process, change the familiar face of south Joburg.
That is, so long as the gold price remains around R85 000 a kilogram, or more. If the price falls below R80 000 (the cost of processing one kilogram) and stays there, the operation would have to be re-considered, says Charles Symons, general manager of Crown Gold Recoveries.
The scattered mine dumps that are visible are the remains of mine workings from the birth of Johannesburg in 1886, and they're very much part of what makes up the look of the city. The dumps are actually crushed rock, and because the gold extraction processes were not very refined in those early days, there're traces of gold still in the dumps. Sophisticated modern processes are able to extract these residues.
A good deal of the dumps are covered in grass, shrubs and eucalyptus trees, camouflage that doesn't quite disguise what they are, but helps them to blend in with their natural surroundings. They break the flat monotony of the southern suburbs, and once removed, those residents are sure to welcome the removal of the dust pollution caused by them.
It's estimated that there're approximately 200 dumps in and around the city, in varying shapes and sizes, a good deal of them averaging 50 metres in height, consisting of fine cream-coloured sand. Crown Gold has the rights to 70 of those dumps and it's likely that they'll remove all of them. In total there're 438 million tons of mine dump soil, stretching from Boksburg on the East Rand right through to Krugersdorp, about 30 kilometres south-west of the city. About 40 percent of that has so far been removed.
Crown's operation started in the early 1980s, when they built their plant in Crown Mines. Initially it was thought the operation would last eight years. But now, 20 years on, the operation shows few signs of slowing down, although on present estimates it is expected to run until 2007.
Extraction
Some dumps contain more gold than others, depending on how old they are, and which process was originally used to extract the gold.
The early extraction process involved placing the rock in a stamp mill, which acted like a large hammer, breaking up the rock. But this process wasn't very efficient. These days a rotary mill is used - it's a large tube driven by a motor. Rock is fed into the mill, together with steel balls, and when the mill rotates, the action crushes the rock.
The process of extracting gold fragments starts with the evaluation of the dump. A sample is taken by drilling from the top of the dump right through to bedrock. These samples are tested to determine how much gold is present in the dump, and how much it will cost to extract it.
"Some have higher grades than others. Not all are viable," says Symons.
Two kinds of dumps
There are two kinds of dumps: sand dumps and slimes dams. The latter consists of finer sand, from which more gold was extracted, and are therefore less likely to yield much gold now.
A dump is considered viable when 0.4 grams of gold can be obtained from every ton. But some dumps yield more: Menell's dump, south-east of the city, has produced 0.65 grams a ton. Some 800 000 tons of sand are treated every month.
So, as the dumps are flattened, and the original landscape revealed, where is all that sand going? To three dumps being created alongside Nasrec. They're huge, and they're growing.
Dust pollution
And what about dust blowing off the dumps and polluting the surrounding suburbs? The major method of preventing dust pollution is to grow grass on the dumps.
The first step of this process is to install an irrigation system and spray the dump with a fine mist. This leaches out the salts. Compost is then dug into the sand, and wheat is planted. This grows quickly and spreads through natural germination. When this dies it forms a mulch, and in this rich base a mix of grasses is planted.
Many dumps have eucalyptus trees growing around their base. Symons stresses that no eucalyptus trees are planted as they drain the soil of water, being very thirsty trees. Those that are already growing, naturally seeded, are left to grow because they drain the water from around the dumps.
Wits University runs a dust monitoring programme, where a series of dust bucket monitors are placed on the top of buildings and factories, towers, and in residential backyards. Once a month these buckets are cleared and their contents analysed.
Symons concedes that during the dry winter months, dust is blown off the dumps. He says that the contribution of dust from dumps on the winter pollution cloud that hangs over the city is "quite small".
Quarterly dust monitoring meetings, which are open to the public, are held. "We like to believe that we have a good relationship with the local communities," says Symons. The communities most affected are those in Diepkloof, Diepmeadow and Meadowlands.
Water pollution
And water pollution? "There is a certain amount of run off of polluted water from the dumps." But there is "no seepage into the normal water course", because by paddocking off the dumps, this run-off is strictly controlled, says Symons.
With heavy summer rainstorms "every now and then accidents do happen". When they happen they are dealt with timeously, according to prescribed pollution codes of practice.
One of the elements used in the early days to remove the gold was cyanide. Symons says cyanide has a short shelf life and when subjected to sunlight, it breaks down, so now, 100 years later, there'll be no traces of it.
"We have a good relationship with the local authorities - EMS, the SAPS and Metro Police - and if a pollution incident occurs, we let them know and then we take the necessary action to clean the area. We're open and honest with people." Symons says five to six incidents happen every year.
"Spillages seldom get into the water course," he adds.
A certain amount of radiation is associated with rock, in particular radon gas. Symons says it is not sufficient to be considered a health hazard. Crown Gold works closely with the Department of Mineral and Energy Affairs and the National Nuclear Regulator (NNR), who issue certificates once they've satisfied themselves that the process is being conducted within certain health and safety criteria.
Real estate
And when the dumps are removed, what happens to that very valuable real estate? It's owned by two companies, I Prop, and the Witwatersrand Gold Mine Trust, on the East Rand. It can be built on, with no fear of subsidence. The reason for this is that the original mines in Johannesburg were not created alongside the dumps, so the land below the dump is not hollow.
The reclaimed land has to first be checked for radon gas. Once a certificate of clearance has been obtained from the NNR, the owners of the land have to apply to the City to incorporate the land into the local township, or proclaim a new township, a process that can take up to 18 months. Once complete, the use to which the land will be put can be decided.
Petro Heydenrych, CEO of I Prop, says they have successfully converted 65 hectares of reclaimed land to mixed use purposes, at Crown City, south of Edgardale. Current uses are for industrial, distribution and office space. The land is being sold at between R180 to R220 per square metre, which will increase the revenue base to the City from land tax.
"The land use will depend on what we find when the dump is removed," adds Heydenrych.
And for those who used to take the drive up the dump which was converted into a drive-in, called the Top Star, just beyond the M2 south of the city, you may want to take a last nostalgic trip up the winding road to see a movie. Feasibility studies are at present being conducted, and it seems very likely that the Top Star mine dump will be treated for its gold residue and flattened.
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