As below, so above
By Nechama Brodie
Before there were gold mines, there was grassland. Russet grass and red grass and giant spear grass, and occasional trees in sheltered outcrops and kloofs. This is Rocky Highveld Grassland, transitional vegetation that occurs between the true grasslands of the inland plateau and the bushveld; grasses that grow in rocky mountains, hills, ridges and plains of quartzite, conglomerate, shale, dolomite and andesitic lava.
Johannesburg sits on the edge of a 3,2 billion-year-old granite dome, formed at the same time as the earth's continental crust and extending 70 kilometres north to Tshwane. This is the oldest rock formation in Gauteng, and is the basement on which bands of younger sedimentary and volcanic rocks were later deposited.
The Boers named this place the Witwatersrand, white waters ridge, apparently because of the waterfalls running off the area's stony outcrops. In reality, there was no water, not in any great quantities; it is possible that quartz and iron pyrite deposits in the stone may have reflected light, giving the appearance of water. The city is, however, divided by a continental watershed. Streams to the north of Johannesburg flow into the Crocodile River then into the Limpopo, making its way to the warm Indian Ocean on the east cost. Water flowing on the southern side of the city ends up in the Vaal, joining the Orange River before travelling a thousand kilometres to reach the icy Atlantic Ocean on the west coast.
South of the city's centre lies the Witwatersrand Supergroup, a column of sedimentary deposits created between 2,7 billion and 3 billion years ago, then buried deep underground by the force of the impact of a giant meteor. The Witwatersrand Supergroup slopes away from the city in sequences of shale, quartzite and conglomerate. In Afrikaans the conglomerate was known as banket, named after a Dutch nougat-like confection studded with almonds. The conglomerate was studded with quartz, and in the surrounding rock there was gold.
Although there were several earlier gold finds on the Rand the first outcrop of the main reef was discovered by George Harrison in 1886, who received claim No.19 on the farm of Langlaagte as his zoekers or discoverer's claim. Harrison later sold his portion for just £10 and disappeared, rumoured to have been eaten by lions.
The reef horizons run several kilometres underground, extending from 65 kilometres east of Johannesburg to 145 kilometres west of the city, forming a crescent around the Witwatersrand basin. The gold-bearing rock bands are, in places, only centimetres thick – ranging from less than 20 centimetres up to 100 centimetres. This is a landscape of economic geography, defined in feet, metres, troy ounces and grams.
Early goldmines used large-scale versions of what was essentially a 400-year-old mining technique: the ore would be mined, crushed to a coarse powder (in this case by large battery stampers) then panned through water or solution to reveal the gold. The outcrops of surface conglomerate, weathered and oxidised from centuries of exposure, were extracted at such a rapid rate that within a few years miners had reached depths of 30 metres below the surface – where they found the gold ore was 'locked' inside sulphur-containing pyrites. This required a much more complex treatment, and the recovery rate from the ore dropped too low for mining operations to yield a profit. Modern science provided a timely intervention in the form of a newly patented process developed by three Glaswegians – the brothers RW and W Forrest, and JS MacArthur. The MacArthur-Forrest process updated an older method of treating crushed ore with a weak solution of cyanide; this dissolved the gold, very effectively, into the solution. The remaining rock particles would then be filtered off leaving the gold-heavy cyanide solution, to which zinc dust was added, causing fine specks of gold to precipitate. This gold could then be separated and refined, and the highly poisonous cyanide disposed of.
The reef that runs under Johannesburg contains relatively low-grade ore – it can take a ton of rock to yield just four grams of gold. The extent of the reef deposits and the high price of gold made continued mining operations viable, but required greater capital investment, specialised machinery and the work of thousands of labourers.
In the early surface and trench mines, black miners would throw ore up from level to level; as the depth of mines increased, the ore was hoisted by means of bullocks, and whips, then mechanical winches. As the mines got deeper, labourers were employed in the construction of supports – timber, concrete pillars or sand filling used to secure the workings against earth tremors and rockbursts. Miners drilled underground shafts and stopes using large jackhammers that could be operated by one person, drilling on average 24 metres a shift.
In this way, the mining companies operating along the Rand removed millions of tons of hard rock – Crown Mines alone removed 160 million tons of rock, from a depth of several thousand metres; by comparison, the excavation of the Suez Canal entailed the removal of just 130 million tons of soft material, from comparatively shallow depths.
On the Witwatersrand, some 5 000 million tons of waste material – rock milled to powder fineness and, after treatment, disposed of – was deposited on 247 slimes dams (consisting of finer sand) and 95 sand dumps. For years, these dumps caused severe air pollution problems particularly during the city's dry winter months. The mining industry tried various means of stabilising the surfaces of the dumps, including experimenting with resin, plastic, cement and bitumen. Attempts to establish natural plant growth on the dumps were initially unsuccessful; interestingly, it was not the presence of cyanide in the sand that created a problem, as the cyanide would naturally break down after being exposed to sunlight and air. Rather, the low pH levels and very fine quality of the sand, together with the high rate of erosion, discouraged vegetation. To encourage plant growth, lime was added to the sand to increase the pH, and reed windbreaks were planted to control the movement of the sand.
Mining operations in Johannesburg ceased in the 1970s, not because the gold reserves were depleted but because of a drop in gold prices combined with old mining technology, and growing political unrest. The names of the mines are largely forgotten: Langlaagte Estate, Crown Mines, Robinson Deep, Village Main Reef, City Deep, Geldenhuis Deep, Ferreira Deep. Left behind were the silhouettes of mining headgears; the Crown Mines village; a labyrinth of abandoned mineshafts criss-crossing the city centre; and the mine dumps, some of them 50 metres high. The most iconic of these is the Top Star, built in the early 1960s as a European drive-in movie theatre on top of the old Ferreira's Dump. Despite attempts by heritage agencies to protect the site, the Top Star is rapidly being demolished by reclamation company DRDGold, its bulldozers eviscerating the landmark like the farmers Boggis, Bunce and Bean in Roald Dahl's childhood classic Fantastic Mr Fox.
Advances in modern extraction processes mean that mine dumps are considered viable for reclamation when 0,4 grams of gold can be obtained per ton – some have yielded as high as 0,65 grams per ton. As long as the gold price remains above R80 000 a kilogram, the city's mine dumps will continue to be reclaimed; and with them, the face of Johannesburg will forever be altered.
Nechama Brodie is editor and co-author of The Joburg Book (Pan Macmillan and Sharp Sharp Media)