Provenance history of detrital diamond deposits, West Coast of Namaqualand, South Africa

Phillips, D., Harris, J. W., de Wit, M. C.J. and Matchan, E. L. (2018) Provenance history of detrital diamond deposits, West Coast of Namaqualand, South Africa. Mineralogy and Petrology, 112(S1), pp. 259-273. (doi:10.1007/s00710-018-0568-9)

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Abstract

The West Coast of Namaqualand in South Africa hosts extensive detrital diamond deposits, but considerable debate exists as to the provenance of these diamonds. Some researchers have suggested derivation of the diamonds from Cretaceous-Jurassic kimberlites (also termed Group I kimberlites) and orangeites (also termed Group II kimberlites) located on the Kaapvaal Craton. However, others favour erosion of diamonds from the ca.300 Ma Dwyka Group sediments, with older, pre-Karoo kimberlites being the original source(s). Previous work has demonstrated that 40Ar/39Ar analyses of clinopyroxene inclusions, extracted from diamonds, yield ages approaching the time(s) of source kimberlite emplacement, which can be used to constrain the provenance of placer diamond deposits. In the current study, 40Ar/39Ar analyses were conducted on clinopyroxene inclusions from two similar batches of Namaqualand detrital diamonds, yielding (maximum) ages ranging from 117.5 ± 43.6 Ma to 3684 ± 191 Ma (2σ) and 120.6 ± 15.4 Ma to 688.8 ± 4.9 Ma (2σ), respectively. The vast majority of inclusions (88%) produced ages younger than 500 Ma, indicating that most Namaqualand diamonds originated from Cretaceous-Jurassic kimberlites/orangeites, with few, if any, derived from the Dwyka tillites. The provenance of the Namaqualand diamonds from ca.115–200 Ma orangeites is consistent with Late Cretaceous paleo-drainage reconstructions, as these localities could have been sampled by the ‘paleo-Karoo’ River and transported to the West Coast via an outlet close to the current Olifants River mouth. At ca.90 Ma, this drainage system appears to have been captured by the ‘paleo-Kalahari’ River, a precursor to the modern Orange River system. This latter drainage is considered to have transported diamonds eroded from both ca.80–90 Ma kimberlites and ca.115–200 Ma orangeites to the West Coast, which were subsequently reworked along the Namibian coast, forming additional placer deposits.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Harris, Dr Jeff
Authors: Phillips, D., Harris, J. W., de Wit, M. C.J., and Matchan, E. L.
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Mineralogy and Petrology
Publisher:Springer
ISSN:0930-0708
ISSN (Online):1438-1168
Published Online:28 May 2018
Copyright Holders:Copyright © 2018 Springer-Verlag GmbH Austria, part of Springer Nature
First Published:First published in Mineralogy and Petrology 112(S1):259-273
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher

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