Diamonds Across Southern Africa

Diamonds have been transported across vast area of southern Africa. There are more than 3,000 kimberlite pipes -- many not bearing diamonds, of course -- in the craton drained by tributaries to the Orange River and its precursors, which end at the Atlantic coast. The rivers carried water, sediments, and diamonds to the ocean.

Over the past 100 million years up to 1,400 meters have been eroded from the land's surface, releasing billions of carats of diamonds on a trip to the sea. An estimate of diamonds eroded from the Kimberley mine -- the "Big Hole" -- alone is 500,000 carats. The rivers carried most of the eroded diamonds to the Atlantic Ocean, although about 10% of them were store in the alluvial deposits of the drainage systems. The rest are in the past and present beach deposits of the Atlantic coast, from Port Nolloth in Namaqualand to Luderitz in Namibia.
Because powerful ocean waves break the poorer quality diamonds, 90-95 percent of marine diamonds are of gem quality. The littoral zone, the area of wave action on the Atlantic coast where diamonds accumulate, has moved in and out with changes in sea level, but shore lines have been constant over long periods, resulting in wave-cut terraces with hollows and crevices in which diamonds concentrated. These terraces are preserved hundreds of meters both above and below sea level and are the focus of mining activity.