Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa
Diamond-bearing gravels of the Lichtenburg-Ventersdorp area of the North West Province are associated with north-south orientated sinuous 'runs' that occur almost entirely on a flat erosional surface of the Malmani dolomites (Transvaal Supergroup) at some 1,500 m elevation. East to west, t...
Published in: | South African Journal of Geology |
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Language: | English |
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Geological Society of South Africa
2016
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Online Access: | http://hdl.handle.net/2263/63706 https://doi.org/10.2113/gssajg.119.4.585 |
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ftunivpretoria:oai:repository.up.ac.za:2263/63706 2023-05-15T16:41:36+02:00 Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa De Wit, M.C.J. (Mike) 2016-12 http://hdl.handle.net/2263/63706 https://doi.org/10.2113/gssajg.119.4.585 en eng Geological Society of South Africa http://hdl.handle.net/2263/63706 De Wit, M.C.J. 2016, 'Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa', South African Journal of Geology, vol. 119, no. 4, pp. 585-606. 1012-0750 doi:10.2113/gssajg.119.4.585 © 2016 December Geological Society of South Africa Pretoria Group Malmani dolomites Glaciation Stratigraphy Karoo Basin Evolution Gondwana Break-up Ferromanganese deposits Land surfaces Kaapvaal Craton Diamond-bearing gravels North West Province South Africa Article 2016 ftunivpretoria https://doi.org/10.2113/gssajg.119.4.585 2022-05-31T13:14:48Z Diamond-bearing gravels of the Lichtenburg-Ventersdorp area of the North West Province are associated with north-south orientated sinuous 'runs' that occur almost entirely on a flat erosional surface of the Malmani dolomites (Transvaal Supergroup) at some 1,500 m elevation. East to west, this dolomite plain measures 150 km, and northsouth it is on average 40 km wide. This unconformity, which first developed before the Pretoria Group sedimentation over a period of at least 80 Myr, is marked by siliceous breccias (palaeo-karst infill) and conglomerates (reworked breccias). It was exhumed in pre-Karoo and post-Gondwana times. Glacial pavements and remnants of thin Lower Karoo sediments are also found on this polyphase surface. The gravels that make up these 'runs' and sinkholes directly or indirectly linked to these runs, are coarse-grained, very poorly-sorted, and are best described as diamictites. The 'runs' are narrow, elongated, generally positive ridges that meander across the dolomite surface and are up to 30 km long and between 80 to 300 m wide. They have always been regarded as post- Cretaceous drainage features linked to southward-flowing river systems. Diamonds were discovered in these 'runs' and they have produced some 12 million carats. However, no Cainozoic fossils or artefacts have ever been found in almost 90 years of mining. From new field evidence, geomorphological studies, age dating from inclusions in diamond and zircon and clay analyses, it is proposed that these coarse-grained runs represent proximal palaeoeskers of the last deglaciation of the Dwyka continental ice sheet, that are preserved on this ancient 'palimpsest' surface. The age of the deposit is constrained by two populations of agate within the diamictites that are linked to two separate volcanic units of the Pretoria Group. In addition, the youngest crustal zircon ages from the gravels are 1 Ba, but mantle zircons from Lichtenburg suggest that these have been derived from Cambrian age kimberlites. Analysis of inclusions in diamond ... Article in Journal/Newspaper Ice Sheet University of Pretoria: UPSpace South African Journal of Geology 119 4 585 606 |
institution |
Open Polar |
collection |
University of Pretoria: UPSpace |
op_collection_id |
ftunivpretoria |
language |
English |
topic |
Pretoria Group Malmani dolomites Glaciation Stratigraphy Karoo Basin Evolution Gondwana Break-up Ferromanganese deposits Land surfaces Kaapvaal Craton Diamond-bearing gravels North West Province South Africa |
spellingShingle |
Pretoria Group Malmani dolomites Glaciation Stratigraphy Karoo Basin Evolution Gondwana Break-up Ferromanganese deposits Land surfaces Kaapvaal Craton Diamond-bearing gravels North West Province South Africa De Wit, M.C.J. (Mike) Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa |
topic_facet |
Pretoria Group Malmani dolomites Glaciation Stratigraphy Karoo Basin Evolution Gondwana Break-up Ferromanganese deposits Land surfaces Kaapvaal Craton Diamond-bearing gravels North West Province South Africa |
description |
Diamond-bearing gravels of the Lichtenburg-Ventersdorp area of the North West Province are associated with north-south orientated sinuous 'runs' that occur almost entirely on a flat erosional surface of the Malmani dolomites (Transvaal Supergroup) at some 1,500 m elevation. East to west, this dolomite plain measures 150 km, and northsouth it is on average 40 km wide. This unconformity, which first developed before the Pretoria Group sedimentation over a period of at least 80 Myr, is marked by siliceous breccias (palaeo-karst infill) and conglomerates (reworked breccias). It was exhumed in pre-Karoo and post-Gondwana times. Glacial pavements and remnants of thin Lower Karoo sediments are also found on this polyphase surface. The gravels that make up these 'runs' and sinkholes directly or indirectly linked to these runs, are coarse-grained, very poorly-sorted, and are best described as diamictites. The 'runs' are narrow, elongated, generally positive ridges that meander across the dolomite surface and are up to 30 km long and between 80 to 300 m wide. They have always been regarded as post- Cretaceous drainage features linked to southward-flowing river systems. Diamonds were discovered in these 'runs' and they have produced some 12 million carats. However, no Cainozoic fossils or artefacts have ever been found in almost 90 years of mining. From new field evidence, geomorphological studies, age dating from inclusions in diamond and zircon and clay analyses, it is proposed that these coarse-grained runs represent proximal palaeoeskers of the last deglaciation of the Dwyka continental ice sheet, that are preserved on this ancient 'palimpsest' surface. The age of the deposit is constrained by two populations of agate within the diamictites that are linked to two separate volcanic units of the Pretoria Group. In addition, the youngest crustal zircon ages from the gravels are 1 Ba, but mantle zircons from Lichtenburg suggest that these have been derived from Cambrian age kimberlites. Analysis of inclusions in diamond ... |
format |
Article in Journal/Newspaper |
author |
De Wit, M.C.J. (Mike) |
author_facet |
De Wit, M.C.J. (Mike) |
author_sort |
De Wit, M.C.J. (Mike) |
title |
Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa |
title_short |
Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa |
title_full |
Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa |
title_fullStr |
Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa |
title_full_unstemmed |
Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa |
title_sort |
early permian diamond-bearing proximal eskers in the lichtenburg/ventersdorp area of the north west province, south africa |
publisher |
Geological Society of South Africa |
publishDate |
2016 |
url |
http://hdl.handle.net/2263/63706 https://doi.org/10.2113/gssajg.119.4.585 |
genre |
Ice Sheet |
genre_facet |
Ice Sheet |
op_relation |
http://hdl.handle.net/2263/63706 De Wit, M.C.J. 2016, 'Early Permian diamond-bearing proximal eskers in the Lichtenburg/Ventersdorp area of the North West Province, South Africa', South African Journal of Geology, vol. 119, no. 4, pp. 585-606. 1012-0750 doi:10.2113/gssajg.119.4.585 |
op_rights |
© 2016 December Geological Society of South Africa |
op_doi |
https://doi.org/10.2113/gssajg.119.4.585 |
container_title |
South African Journal of Geology |
container_volume |
119 |
container_issue |
4 |
container_start_page |
585 |
op_container_end_page |
606 |
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1766032043675746304 |