Home >>  Education >>  Diamonds

Diamonds

Diamond mining in South Africa

Formation

Diamonds were formed aeons ago deep in the mantle of the earth, about 150 kilometres below the surface. Molten magma in the mantle was forced upward through fissures to the earth’s crust to burst out as volcanoes. Free carbon particles in the mantle, which were caught in the upward volcanic strea,m were subjected to heat and pressure so intense that the particles were crystallised into diamonds - the diamondiferous magma becoming known as ’blueground’ or kimberlite.Further outpourings of kimberlitic magma occurred and when the magma eventually cooled, the diamonds remained trapped in the solidifying magma pipes.

Occurance

The first diamond to be discovered in South Africa was found in 1866 on a farm near Hopetown, south of Kimberley. This was followed by the finding of kimberlite bearing pipes and further discoveries of alluvial diamond fields in the drainage system of the Vaal River in Lichtenburg and Namaqualand, and eventually even on the shores of the Atlantic Ocean off the west coast.

Between 1870 and 1891 no less than six kimberlite pipes were discovered in Kimberley, while the Koffiefontein pipe, 130 kilometres south of Kimberley, was discovered in 1880. The Premier, the biggest pipe in South Africa and, geologically, by far the oldest, was discovered at Cullinan near Pretoria in 1902. The world’s largest gem diamond, the 3 106 carat Cullinan, was found here in 1905. Several other small but payable deposits were discovered elsewhere in the country in the early years of the century, though most of these have been worked out and abandoned.

At Kleinzee, south of Port Nolloth in Namaqualand, diamonds were found in marine terraces in 1925. These diamonds were brought down by the Buffels River system in an ancient bed a few kitometres from its present course. A year later, another deposit was found at Alexander Bay on the South African side of the Orange River mouth to the north of which, in Namibia, Consolidated Diamond Mines (now Namdeb Diamond Corporation) was mining diamond bearing marine terraces along the whole coastline to Lüderitz. Diamond deposits were found in 1927 around Lichtenburg in the North West Province, though today these are virtually exhausted.

A more recent discovery was made in 1961 when Allister Fincham discovered the Finsch pipe, which proved to be one of the largest on the continent, Finsch, in the Northern Cape, came into production in October 1965.

In the early ’80s a diamond bearing pipe was discovered at Venetia in the far north of the country close to the Limpopo River. In late 1989, De Beers Consolidated Mines Limited announced the go-ahead for the Venetia diamond mine at an estimated cost of more than R1 billion. The company is developing an opencast mine to treat 3,3 million tons of ore and produce 4 million carats of medium quality diamonds a year, The mine will have an estimated economic life of about 20 years.

Mining

In South Africa, volcanic kimberlite pipes are mined as both underground and opencast operations. TheDiamonds Kimberley mines and Premier are underground operations; Koffiefontein and Finsch , formerly mined by opencast methods, are now worked as underground mines. Venetia is an opencast mine. A variety of mining methods are employed ranging from blasting and then hauling the ore away by huge trucks in open-pit mines, to open-benching. block-caring, open-sloping and panel-retreat operations underground.

On the Atlantic coastline in Namaqualand, beach or marine alluvial diamond deposits are worked by surface sand-stripping methods, by gravel and pothole exploitation methods in shallow water, and by suction dredging in deeper water to considerable distances off the coast.

Industrials

Only 15 to 20 per cent of the world’s diamond production is gem quality; the rest is destined for industrial use. Natural-diamond ’industrials’ - ’boart’ - (along with synthetic diamonds) are required for their hardness in cutting; sawing; wire-drawing; drilling purposes, mainly in the masonry, mining and oil businesses; and for grinding and polishing in the engineering industry. In many applications diamonds are indispensable; without them many high-technology industries simply would not exist.