The world's greatest deposit of gold is hosted by the Archaean Witwatersrand sedimentary basin, situated in the central portion of the Kaapvaal Craton of South Africa. The geological setting of this remarkable clastic sedimentary deposit, which has yielded more than one third of all the gold ever produced on the planet, is discussed. The stratigraphy and structure of the Witwatersrand Supergroup is reviewed together with the sedimentology, mineralogy and geochronology of the more important auriferous conglomerate (reef) horizons. Geophysical methods of exploration are discussed briefly. The Witwatersrand Basin was formed in response to a series of crustal plate movements from the north and west in a foreland basin setting. Deposition commenced in a shallow marine environment with quartzite and shale, including prominent iron rich shale horizons forming the West Rand Group (WRG). The overlying dominantly arenaceous Central Rand Group (CRG) was deposited in a basin which regressed as it filled. Important gold deposits formed on braided fluvial plains which sometimes terminated in a shoreline. Gold reefs at the base of the CRG show evidence of later marine reworking. Higher in the sequence, fluvial deposits become dominant. The focus of this paper is the Central Rand Group where most of the gold mineralisation occurs. Detrital gold (largely within sulphides) and uranium (as uraninite) were originally concentrated along with placer minerals such as chromite and zircon, at the base of fluvial cycles. In addition to the placer mineralisation, prokaryotic bacteria flourished and provided carbon-rich material that was highly effective in the concentration of non-detrital gold. Although most of the lithologies, including reef horizons, have great continuity and can be correlated across much of the Witwatersrand Basin, discrete entry points of reef material, with distributary channels and associated ore shoots, can generally be clearly defined. Three major events reshaped and metamorphosed the Witwatersrand. Lateral crustal plate movements caused severe faulting and folding, especially along the western and northern sides of the Basin. The second event was the catastrophic Vredefort meteorite impact which struck the centre of the basin. The resulting fluid movement which pervaded the Witwatersrand strata caused widespread metasomatic alteration. Localised alteration and remobilisation of the gold mineralisation is thought to have been in partial response to this event. The third major event was the emplacement of the Bushveld Complex, which is the largest layered igneous intrusion of its kind on Earth. The heat generated by this intrusion certainly exceeded that of the Vredefort event, also making it an important agent of mineral alteration and remobilisation, especially along the northern flank. The Great Debate on the origin of the gold has been the subject of heated discussions for decades. The three main points of view are a placer source, a hydrothermal source and a combination of the two called the modified placer theory. Recognition of the problem was realised soon after the discovery of the gold and continues to this day. Evidence has been presented in favour of all arguments, lending more credence for the modified placer process. Although the Witwatersrand is a mature goldfield with declining production, it is estimated that it still contains six times more gold than the world's second largest goldfield. Much of the remaining resource occurs at considerable depths; however, there are still opportunities for extracting some of this resource, as well as generally somewhat lower grade mineralisation, at moderate to shallow depth. The Basin thus remains a major exploration target. Gold mining in the Witwatersrand Basin has been responsible for the creation of the metropolis of Johannesburg and many thriving mining towns and has had a major influence in the shaping of South Africa. It still plays an important role in the country's economy.
Research Article| March 01, 1971 Reappraisal of Some Aspects of Precambrian Shield Geology: Reply CARL R ANHAEUSSER; CARL R ANHAEUSSER Economic Geology Research Unit, University of the Witwatersrand, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar ROBERT MASON; ROBERT MASON Economic Geology Research Unit, University of the Witwatersrand, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar MORRIS J VILJOEN; MORRIS J VILJOEN Economic Geology Research Unit, University of the Witwatersrand, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar RICHARD P VILJOEN RICHARD P VILJOEN Economic Geology Research Unit, University of the Witwatersrand, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar GSA Bulletin (1971) 82 (3): 805–806. https://doi.org/10.1130/0016-7606(1971)82[805:ROSAOP]2.0.CO;2 Article history received: 23 Jul 1970 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation CARL R ANHAEUSSER, ROBERT MASON, MORRIS J VILJOEN, RICHARD P VILJOEN; Reappraisal of Some Aspects of Precambrian Shield Geology: Reply. GSA Bulletin 1971;; 82 (3): 805–806. doi: https://doi.org/10.1130/0016-7606(1971)82[805:ROSAOP]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract No Abstract available This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Research Article| March 01, 2021 FOREWORD Morris Viljoen; Morris Viljoen Search for other works by this author on: GSW Google Scholar Richard Viljoen Richard Viljoen Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2021) 124 (1): 1–4. https://doi.org/10.25131/sajg.124.0018 Article history first online: 19 Apr 2021 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Morris Viljoen, Richard Viljoen; FOREWORD. South African Journal of Geology 2021;; 124 (1): 1–4. doi: https://doi.org/10.25131/sajg.124.0018 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietySouth African Journal of Geology Search Advanced Search It is both a pleasure and an honour for us to contribute the foreword to this special volume celebrating the illustrious geoscientific career of Carl Anhaeusser. We have had a longstanding association with Carl and our early careers in particular followed similar paths. We met as first year Geology students at Wits University in 1958. Here we became good friends and have remained so throughout our lives. Like ourselves, Carl was hooked on geology from the outset, and he has spent his whole life researching the nature of and the processes operating in the Early Earth. After completing BSc... You do not currently have access to this article.
Africa is home to more than the Cradle of Humankind. It was the core of the ancient supercontinent Pangaea, and comprises some of the oldest and most extraordinary geology on planet Earth. This detailed and colourful book features 44 of the continent's most spectacular and interesting 'geosites', from Table Mountain in the south to the eroded necks and plugs of the Hoggar region in Algeria; and from the volcanic islands of the Atlantic Ocean to the continental fragments off the African east coast. Each site is authored by a geologist (or specialist in a related field) with in-depth knowledge about the particular feature or landform: how it formed and developed, its current geological status, ecological impact, and its archaeological and cultural interest. Supported with many photographs, maps, satellite images and explanatory illustrations, the text is accessible to geologists and lay enthusiasts alike, unpacking the hows and whys of Africa's most intriguing landforms, sites and geological features.
Research Article| November 01, 1969 A Reappraisal of Some Aspects of Precambrian Shield Geology CARL R ANHAEUSSER; CARL R ANHAEUSSER Economic Geology Research Unit, University of the Witwatersrand, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar ROBERT MASON; ROBERT MASON Economic Geology Research Unit, University of the Witwatersrand, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar MORRIS J VILJOEN; MORRIS J VILJOEN Economic Geology Research Unit, University of the Witwatersrand, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar RICHARD P VILJOEN RICHARD P VILJOEN Economic Geology Research Unit, University of the Witwatersrand, Johannesburg, South Africa Search for other works by this author on: GSW Google Scholar GSA Bulletin (1969) 80 (11): 2175–2200. https://doi.org/10.1130/0016-7606(1969)80[2175:AROSAO]2.0.CO;2 Article history received: 04 Mar 1969 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation CARL R ANHAEUSSER, ROBERT MASON, MORRIS J VILJOEN, RICHARD P VILJOEN; A Reappraisal of Some Aspects of Precambrian Shield Geology. GSA Bulletin 1969;; 80 (11): 2175–2200. doi: https://doi.org/10.1130/0016-7606(1969)80[2175:AROSAO]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Attention is drawn to some of the misconceptions regarding the ancient crystalline shields, and an attempt is made to clarify some of the ideas held on their geology. In Southern Africa, the Precambrian shield is well represented and exposed, and recent studies of it reveal a clear and well-defined pattern of events in its evolution.The very ancient, stable, cratonic nuclei incorporating the greenstone belts are termed “The Earliest Precambrian.” Traversing the shield areas and surrounding the cratonic nuclei are large, elongated, highly metamorphosed and granitized “Precambrian Mobile Belts.” Although younger than, and totally different in character to, the cratons which they tend to encircle, they nevertheless form an integral part of the crystalline shields.The fundamental elements of the geology of the greenstone belts within the cratonic nuclei, together with a distinctive pattern of relationships between the greenstone belts and their surrounding granitic terrain are repeated with remarkable consistency in other shield areas of the world, especially in Canada and Western Australia. The geological features which typify and contribute to the establishment of this highly distinctive pattern are outlined in the text and demonstrated with the aid of tables and diagrams. The world-wide uniformity of the stratigraphy, structure, metamorphism, mineralization, associated granites, and geotectonic setting of the greenstone belts is stressed.An attempt is made to reconstruct an evolutionary model of the development of the early Precambrian granite-greenstone belt terrain. This avoids direct comparisons with younger geological features and events, particularly the younger, Alpine-type orogenic belts with which early Precambrian geology has frequently been compared and equated. The mobile belts are briefly discussed, and again it is suggested that their evolution was not necessarily along the lines suggested for Alpine orogenesis. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
There is a lack of published literature on coal deposits in Madagascar. The Imaloto Basin is a sub-basin of the Morondava Basin, Southwestern Madagascar, and hosts the Sakoa Coal Measures. The aim of this study was to increase our understanding of the petrography, geochemistry, and mineralogy of coal deposits hosted in the Imaloto Basin. Three coal seams (from the bottom: Main Seam, Upper Seam, and Top Seam) were intersected during a drilling program conducted by the Lemur Holdings in 2019. Coal samples were characterized using organic petrography (type and rank determination); the ash chemistry was assessed (XRF), and the mineralogy was considered using X-ray diffraction. The depositional environment at the time of peat accumulation was considered. The Main Seam samples are of better quality compared to the Upper Seam and Top Seam samples in terms of calorific value (CV) and ash yield. The coals are borderline Sub-bituminous Low Rank A to Bituminous Medium Rank D. An abundance of inertinite macerals was determined in the Main Seam, while the Upper and Top Seams are more vitrinite-rich. An unusual mineral, possibly albite or analcime, was determined in samples with a high Na content. The Imaloto coal samples show varied depositional settings (dry forest swamp, wet forest swamp, and piedmont plain), which influences coal quality.
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