The extensive deposits in the coastal areas north of the Orange River lie in marine terraces under a layer of from 30 to 60 feet of sand. The Consolidated Diamond Mines Company operate over a 50-mile stretch at Orangemund, and this is the richest producer of gems in the whole world. Further south they also mine extensively at Kleinzee. The whole project is a mighty earth-moving operation, easily the biggest earth-moving activity in the whole world, for the great 60-foot overburden of sand has to be removed to uncover the diamond-bearing gravels. At Kleinzee alone, the diamondiferous gravel itself which is handled amounts to half a million tons a year, and il diamonds won amount to 1 carat per 10 tons of gravel treated. This mass of material involved is in addition to the huge quantity of sand overburden bulldozed away.

These alluvial diamonds have been dispersed from former pipes and tend to be concentrated in river-beds and along beach gravels. They were probably brought to coastal sea regions by river, and the sand then deposited over them. The sea must have retreated or the sea-bed rose, leaving high and dry the diamond-bearing marine terraces. Drift sand accumulated to the extent of some 60 feet in most regions and has to be shifted first.

The first step in mining is to sink prospecting bore holes, which show the thickness of the sand overburden and also reveal the geological character of the sought-after diamondiferous gravel. Then comes the first major mining operation, that of removal of overburden. This is carried out by formidable teams of really massive bulldozers. As may be imagined, the moving of a 60-foot depth of sand is a big operation.

When the diamond-bearing gravels are exposed, prospecting trenches 1 yard wide and perhaps up to 1 mile long are then cut and from these the effective richness of the deposit is assessed by on-the-spot recovery of any diamonds present, J using simple direct hand-sorting. At this point in the proceedings the workmen are very carefully watched, for if they try to pocket some of the diamonds (a common practice) then a seriously low figure of richness may be assessed from what is in fact really a lucrative region.

Having decided that a region is to be worked, the formidable earth-moving operation begins. The giant bulldozers operate in teams of three, each shifting overburden sand at the rate of nearly 200 tons an hour. In some regions, where the sand is too soft to support such heavy machines, drag-line excavators are used. The removal of the sand exposes the gravel diamond-bearing terraces which are quite shallow in depth, usually being no more than a yard thick. That is all that is available for mining, a shallow but very extensive bed.

The gravel is completely removed and stockpiled. All gullys and pot holes below the average level need to be searched carefully by hand and by sweeping, since very often the heavy diamonds have concentrated in such pot holes in the past and the richest finds are made in these.
The gravels containing the diamond later used for manufacturing white gold engagement rings are screened in situ locally where mixed vibrating screens reject 80 % of the gravel as waste and the diamond-rich residue is taken by truck or train to a central treatment plant.