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Pothole (geology) - Wikipedia

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A geological pothole is a natural depression in the rock filled with cooled magma, creating a fault. In horizontal section, potholes are roughly circular to elliptical and vary in diameter from 20 m to more than 1 km. In vertical section, their shape is generally dish-like and may be quite asymmetric.^[1]

Formation

Potholes are frequently encountered during mining operations in the Bushveld Igneous Complex in South Africa. The massive intrusion of molten magma, predating the nearby Vredefort impact by at least 30 million years,^[2] led to partial to complete melting of the cumulus floor already in place. Flow and turbulence, high temperatures, and chemical reactions sculpted and potholed the surface of the floor in a process similar to the erosion caused by running water that results in a riverbed pothole. With the end of the outpouring, when emplacement ceased, cooling of the magma started, leaving the potholes filled, and creating a fault surface at the interface of the pothole and the filling magma. The final phase was when crystallisation of chromitite was followed by that of pyroxene and plagioclase, while the contents of the potholes, also consisting of UG2 or Merensky Reef, but having followed a different cooling profile, showed little or no crystallisation of chromitite.

Mining

In the Bushveld Igneous Complex, two orebodies, the Upper Group 2 (UG2) and the Merensky Reef, host about 70% of the world's platinum group metals (PGM), and pose major extraction problems for the mining industry in their faults, dykes, joints, domes, iron-rich ultramafic pegmatoids, rolls and dunite pipes. The greatest mining problems, though, are presented by potholes.

The problems posed by potholes to mining operations are rooted in the fracturing and fragmentation of the material in potholes and their surroundings. These lead to ground instabilities, especially in the hanging wall, and serious safety hazards. Mining is generally abandoned when more than about 40% of the raise line is potholed. A crew for developing new raise lines is usually on standby for such cases, incurring considerable development and labour costs.

References

^ The morphology of potholes in the UG2 chromitite layer and Merensky Reef (pothole reef facies) at Union Section, Rustenberg Platinum Mines - K. G. Lomberg, M. A. Patterson, J. E. Venter, and E. S. Martin
^ Kamo, S.L; Reimold, W.U; Krogh, T.E; Colliston, W.P (1996), "A 2.023 Ga age for the Vredefort impact event and a first report of shock metamorphosed zircons in pseudotachylitic breccias and Granophyre", Earth and Planetary Science Letters, 144 (3–4): 369, Bibcode:1996E&PSL.144..369K, doi:10.1016/S0012-821X(96)00180-X

Predictability of Pothole Characteristics and their Spatial Distribution at Rustenburg Platinum Mine - Chitiyo, Schweitzer, de Waal, Lambert and Ogilvie (Journal of the Southern African Institute of Mining and Metallurgy - December 2008)

Geology of South Africa

Geological formations

List of fossiliferous stratigraphic units in South Africa

Palaeoarchaean	Bushveld Igneous Complex Fig Tree Formation Komatii Formation Moodies Group Onverwacht Group Transvaal Supergroup
Paleozoic	Carboniferous Dwyka Group Ganigobis Formation Devonian Bokkeveld Group Table Mountain Sandstone Permian Abrahamskraal Formation Balfour Formation Dwyka Group Ganigobis Formation Teekloof Formation Whitehill Formation Ordovician Soom Shale
Mesozoic	Cretaceous Uitenhage Group Buffelskloof Formation Enon Formation Kirkwood Formation Sundays River Formation Kalahari Deposits Jurassic Drakensberg Group Enon Formation Uitenhage Group Karoo Supergroup Beaufort Group Abrahamskraal Formation Balfour Formation Katberg Formation Middleton Formation Teekloof Formation Dwyka Group Ecca Group Whitehill Formation Stormberg Group Bushveld Sandstone Clarens Formation Elliot Formation Triassic Elliot Formation Katberg Formation Molteno Formation Normandien Formation
Cenozoic	Algoa Group

‎Tectonics and orogeny

Volcanism	List of volcanoes in South Africa Pilanesberg Pilanesberg Game Reserve Prince Edward Islands Diatremes Big Hole Finsch diamond mine Jagersfontein Mine Koffiefontein mine Barberton Greenstone Belt Drakensberg Karoo-Ferrar
Earthquakes	1620 Robben Island earthquake 1969 Tulbagh earthquake 2006 Mozambique earthquake 2014 Orkney earthquake
Impact craters	Kalkkop crater Morokweng impact structure Tswaing crater Vredefort impact structure
Meteorites	Bellsbank meteorite

‎Mineral deposits
Kimberlite Merensky Reef Witwatersrand Banket (mining term) Coal in South Africa Iron ore in Africa Platinum in Africa Titanium in Africa Uranium in Africa Minerals Council South Africa Department of Mineral Resources (South Africa) Department of Mineral Resources and Energy

Paleontology‎

Ordovician

Devonian

Carboniferous

Permian

Beaufort Group

Assemblages	Cistecephalus Assemblage Zone Daptocephalus Assemblage Zone Eodicynodon Assemblage Zone Pristerognathus Assemblage Zone Tapinocephalus Assemblage Zone Tropidostoma Assemblage Zone

Triassic

Assemblages	Cynognathus Assemblage Zone Lystrosaurus Assemblage Zone

Jurassic

Cretaceous

Paleogene

Nummulite

Neogene

Pleistocene

Other

Research and administration‎

Geologists	Hans Merensky
Paleontologists	Andrew Geddes Bain Lieuwe Dirk Boonstra Charles Kimberlin Brain Robert Broom Alfred Brown Anusuya Chinsamy-Turan H. Basil S. Cooke Alfred W. Crompton Daniel Rossouw Kannemeyer Andre Keyser James Kitching John Talbot Robinson George William Stow Eduard Meine van Zinderen-Bakker

Regional articles
Geology of Cape Town

Other
Pothole (geology) Steep structure Swazian

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