Marine placer diamonds, with particular reference to Southern Africa
Garnett, R.H.T. (2000). Marine placer diamonds, with particular reference to Southern Africa, in: Cronan, D.S. (Ed.) Handbook of marine mineral deposits. CRC Marine Science Series, 17: pp. 103-141
In: Cronan, D.S. (Ed.) (2000). Handbook of marine mineral deposits. CRC Marine Science Series, 17. CRC Press: Boca Raton. ISBN 0-8493-8429-X. 406 pp., more
In: Kennish, M.J.; Lutz, P.L. (Ed.) CRC Marine Science Series., more
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| Abstract |
Diamonds were discovered on the coast of Namibia in 1908. They had been fluvially transported to the southem Atlantic after their erosion from kimberlites hundreds of kilometers inland. Longshore currents, combined with high-energy wind and wave action during periods of considerable sea level changes, concentrated the diamonds in trap sites on paleo coastlines and other marine geological features. The host gravels generally exist as a thin veneer on an irregular bedrock. Discontinuous deposits lie on the inner and middle sections of the continental shelf along the South African and Namibian coastlines. The same sea conditions that created these unique deposits contribute to very difficult marine operating conditions. Half a century elapsed before the first diamonds were mined from offshore. lntermittent, small-scale mining, including a spectacular success in the early 1960s, has continued to the present day in both Namibian and South African waters. Large-scale marine diamond mining started a decade ago, the outcome of many years of exploration. Government encouragement and important technological developments, notably in positioning and geophysical exploration, contributed. Operations in waters as deep as 200 m have necessitated the successful development of new sampling and mining systems. A recent trend has been toward the deployment of seabed-mounted equipment. Higher production, lower grades, and increased throughput with new mining systems are expected in future. The principal marine diamond producer is Namdeb, for which De Beers Marine acts as a contractor. Four smaller but significant public companies are in various stages of development, ranging from sustained, profitable production to trial mining. Marine operations are more capital intensive, with higher unit costs, than equivalent onshore activities, but the grades are higher with little overburden. Total southern African, marine diamond production for 1998 is expected to be 0.7 to 0.8 Mct. Namibian production represents about 80% of the total, worth around US$170 million, and equals that from the country's onshore sources. Exploration has also been conducted offshore West Africa, Australia, and lndonesia, but without economic success. |
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