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South African Marine Diamonds - Namaqualand Coast |
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Northern Cape, South Africa |
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Diamonds
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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Marine placer diamond accumulations are mined offshore of the Atlantic Coast in South African waters over an interval from the mouth of the Orange River in the north to the Olifants River in the south.
These deposits, have a complex geological history, involving the interaction of fluvial, marine and aeolian systems. Diamonds were released onto the continental shelf from the Orange, Buffels, and Olifants Rivers and their precursors river systems which drained the interior of southern Africa.
During the Cretaceous to early Palaeogene, a southern "Karoo River", with the Kimberley area in its catchment basin, was a tributory of the current lower Olifants River. This system was subsequently captured by a northern "Kalahari River", which fed into the modern Orange River, changing the point of entry of diamonds onto the Alantic coast.
The diamondiferous marine deposits are the result of repeated episodes of reworking of material derived from the hinterland by repeated marine regressions and transgressions over the continental shelf. Cyclic sea-level movement without basin subsidence produced a condensed sequence of sea floor sediments. Nearshore, the basal sediment sequence is similar to that found onshore, overlying Precambrian schist, phyllite and gneiss, suitable for the formation of classic diamond trapsites such as gulleys, potholes, cliffs and caves. Some of these deposits are drowned versions of those found onshore.
The bedrock topography on the middle shelf however, is more subtle, comprising Cretaceous and Palaeogene sediments, with few trap sites. In this region the ore gravel includes abundant locally derived clasts of bedrock that were produced during regressive and transgressive shoreface erosion. These clasts genarally comprise variable quartz and quartzite cobbles as well as exotic clasts of epidote, agate, riebeckite, chalcedony, banded ironstone, and jasper. The latter are commonly associated with the Orange River and are thought to be derived from the Vaal/Orange river system between Kimberley and Prieska. The diamondiferous lag gravel is commonly overlain by a shell-rich Holocene transgressive lag, that fines upwards into a silt.
In 2002, 0.074 million carats were recovered from marine mines off the South African coast, about 10% of the countries diamond production.
The most recent source geological information used to prepare this decription was dated: 2003.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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