In some areas, the seabed is a source of diamonds, while beneath the seabed – sometimes at considerable depth – lie oil and gas, and perhaps other minerals. To find and recover diamonds or to prospect for and produce oil or gas from below the seabed present difficulties and require specialised ships and platforms. Indeed, offshore prospecting and production is extremely costly, especially as some of the vessel involved cost hundreds of millions of dollars to build and vast sums to operate.

Diamond recovery operations

Brought to the sea by the Orange River system from ancient eroded volcanic pipes inland in the Kimberley area, and also perhaps the product of the erosion of undersea volcanic structures, diamond deposits lie in gravel beds off the north-west coast of South Africa and the southern Namibian coast.

Although onshore diamond recovery has occurred along the coast to the north and south of the Orange River mouth since the early part of the twentieth century, offshore diamond recovery began in the late 1950s. A number of companies started the operations by using a vacuum recovery system, but DeBeers Marine Ltd was the first to employ specialised technology using vertically- or horizontally-operating equipment. The vertical technology involves lowering a large drill device to dig into the loose gravels and sand on the seabed. While the drill is boring into the seabed, the sediment is pumped up to the vessel where very sophisticated equipment recovers the diamonds.

 

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The vertical system of diamond recovery. A large, wide-based drill is lowered to the seabed and disturbs the sediment and gravels. The sediment is then suctioned to the ship for the diamonds to be recovered.  Diagram : De Beers

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The diamond recovery vessel Gariep that uses the vertical system of diamond recovery.

Another system that is used to recover diamonds from the seabed uses a remote vehicle onto which a suction dredger is attached. This is lowered to the seabed where it moves along the seabed, sucking up the sediment and gravels that are processed on board the vessel for diamonds to be recovered.

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This diagram shows of a remote vehicle with an attached suction device to recover diamonds from the seabed.  Diagram : De Beers