Diamonds are found in volcanic pipes, known as kimberlites, in the oldest part of cratonic areas i.e. areas of thick continental crust that are more than 2.5 billion years. In southern Africa, the Kaapvaal Craton is riddled with kimberlite pipes, perhaps over 6,000, from which a small fraction is diamondiferous. Most of the mineralized kimberlite pipes were emplaced in the present day Orange and Vaal River drainage systems during the Early Cretaceous Period, 90 to 120 million years ago. Diamond grades in kimberlite pipes decrease towards the roots of the intrusions. With the greatest period of erosion during the Cretaceous diminishing with time through the Tertiary, it is estimated that the uppermost 1,400 meters of the pipes in the Orange/Vaal catchment area were removed and transported into the westward drainage systems. An estimated 3 billion carats of diamonds have been delivered to the sea, of which the majority lies north of the present day Orange River mouth off the shores of Namibia. The onshore deposits represent less than 10% of this total resource

Diamond deposits could only occur if at some time a shoreline and near-shore sedimentation occurred in the area. Present knowledge indicate that during the Tertiary Period, a large number of sea level fluctuations have taken place as seen by occurrence of marine terraces of varying elevations. Thus far at least eight terraces have been identified above the present day sea level north of the Orange River and many others have been reported down to water depths of 145 meters. Diamonds in marine areas are typically trapped in bedrock depressions eroded from various structures such as bedding planes, faults or joints in hard bedrock. These form gullies, potholes, basinal depressions, channels and other trapsites for diamondiferous

Only since the early 1990's mining technology has become available for the commercial exploitation of marine diamond deposits. De Beers were the first to develop the mining technologies known as the vertical and horizontal systems. The vertical system uses a 6-7 meter diameter drill head to cut into the seabed and suck up the diamond bearing material. The horizontal system uses remote-controlled vehicles, known as seabed crawlers, which moved across the sea floor pumping up gravel to the mothership to be processed. In both cases, the diamond bearing gravel is screened or sized and a diamond concentrate is recovered and sent to an X-ray recovery plant. Both NAMCO and Diamond Fields use variations of these two technologies that take into account the sea floor conditions of their mining concessions. With the commercial application of new mining techniques at increasing water depths, marine diamond production is expected to continue to grow in the future.