Witwatersrand Basin

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Witwatersrand Basin and major goldfields Witwatersrand gold.png
Witwatersrand Basin and major goldfields
Carbon Leader Gold Ore, Blyvooruitzicht Gold Mine, Carletonville Goldfield, West Witwatersrand. The Carbon Leader is a blackened, hydrocarbon-rich stromatolitic interval richly impregnated with native gold and uraninite. This is a paleoplacer deposit, part of an ancient alluvial fan succession. Carbon Leader Gold Ore, South Africa 3.jpg
Carbon Leader Gold Ore, Blyvooruitzicht Gold Mine, Carletonville Goldfield, West Witwatersrand. The Carbon Leader is a blackened, hydrocarbon-rich stromatolitic interval richly impregnated with native gold and uraninite. This is a paleoplacer deposit, part of an ancient alluvial fan succession.
High-grade gold ore from the Witwatersrand near Johannesburg. Gold-rl-1293b.jpg
High-grade gold ore from the Witwatersrand near Johannesburg.

The Witwatersrand Basin is a largely underground geological formation which surfaces in the Witwatersrand, South Africa. It holds the world's largest known gold reserves and has produced over 1.5 billion ounces (over 40,000 metric tons), which represents about 50% of all the gold ever mined on earth. [1] The basin straddles the old provinces of Transvaal and the Orange Free State, and consists of a 5000–7000 m thick layer of Archean, mainly sedimentary rocks laid down over a period of about 260 million years, starting about 3000 million years ago. [2] The entire series of rocks, known as the “Witwatersrand Supergroup’’ consists of quartzites, banded ironstones, mudstones, tillites, conglomerates and some marine lava deposits. Most of the basin is deeply buried under younger rocks, but outcrops occur in Gauteng, the Free State, as well as in some of the surrounding Provinces. The outcrop in Gauteng forms the Witwatersrand ridge, from which the basin and its rocks derive their name. It was on the southern portion of this ridge that gold was first discovered on the farm Langlaagte in 1886, 5 km west of Johannesburg. [1] [3] Since this gold was embedded in a conglomerate, it was first assumed that this was alluvial gold in an old riverbed, that had been tilted as a result of earth movements. [1] [3] However, when it was found that, traced downdip, the conglomerate was not merely developed for the narrow width of a river, but continued in depth, there came the realisation that this conglomeratic zone was part of a sedimentary succession. [3] The conglomerate was quickly traced east and westward for a total continuous distance of 50 km to define what became known as the “Central Rand Gold Field”.

Witwatersrand mountain range

The Witwatersrand is a 56-kilometre-long (35 mi), north-facing scarp in South Africa. It consists of a hard, erosion-resistant quartzite metamorphic rock, over which several north-flowing rivers form waterfalls, which account for the name Witwatersrand, meaning "ridge of white waters" in Afrikaans. This east-west-running scarp can be traced with only one short gap, from Bedfordview in the east, through Johannesburg and Roodepoort, to Krugersdorp in the west.

Gold Chemical element with atomic number 79

Gold is a chemical element with the symbol Au and atomic number 79, making it one of the higher atomic number elements that occur naturally. In its purest form, it is a bright, slightly reddish yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal and a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the native element silver and also naturally alloyed with copper and palladium. Less commonly, it occurs in minerals as gold compounds, often with tellurium.

Tonne Metric unit of mass

The tonne, commonly referred to as the metric ton in the United States and Canada, is a non-SI metric unit of mass equal to 1,000 kilograms or one megagram. It is equivalent to approximately 2,204.6 pounds, 1.102 short tons (US) or 0.984 long tons (UK). Although not part of the SI, the tonne is accepted for use with SI units and prefixes by the International Committee for Weights and Measures.

Contents

It has since been established that the rocks that make up the Witwatersrand Ridge dip downwards and southwards to form the largely underground “Witwatersrand Basin” which covers an elliptical area with a 300 km long major axis from Evander in the north-east to Theunissen in the south-west, and 150 km wide stretching from Steynsrus in the south-east to Coligny in the north-west, [3] with a small subsidiary basin at Kinross. Gold occurs only along the northern and western margins of this basin, but not in a continuous band. The gold bearing rocks are limited to 6 sites where Archean rivers from the north and west formed fan deltas, with many braided channels, before flowing into the “Witwatersrand Sea” to the south, where the earlier sediments that form the older rocks of the Witwatersrand Supergroup had been deposited. Some of these gold bearing fan deltas are now at depths of 4 km below the surface. [1] [3] Although many of the older mines, around Johannesburg, are now nearly exhausted, the Witwatersrand Basin still produces most of South Africa's gold and much of the total world output. Silver, uranium, and iridium are recovered as gold-refining by-products. [4]

Strike and dip terms used to denote the orientation of a geologic feature

Strike and dip refer to the orientation or attitude of a geologic feature. The strike line of a bed, fault, or other planar feature, is a line representing the intersection of that feature with a horizontal plane. On a geologic map, this is represented with a short straight line segment oriented parallel to the strike line. Strike can be given as either a quadrant compass bearing of the strike line or in terms of east or west of true north or south, a single three digit number representing the azimuth, where the lower number is usually given, or the azimuth number followed by the degree sign.

Evander, Mpumalanga Place in Mpumalanga, South Africa

Evander is a town in the Mpumalanga, South Africa 8 km north west of Secunda.

Theunissen Place in Free State, South Africa

Theunissen is a small town that has the only wine estate, the Theunissen Wine Farm, in the Free State province of South Africa. It is located about 95 kilometers northeast of Bloemfontein and about 45 kilometers south of Welkom. It was founded by Boer War Commandant Helgaardt Theunissen. Theunissen has a small community which supports the local businesses.

Geological origin

The Witwatersrand basin was created during the Archean Eon, and is therefore amongst the oldest geological structures on earth. It was laid down in two stages, over the course of 260 million years starting just short of 3000 million years ago. The first phase, lasting 60 million years, consisted of sedimentary deposits in a shallow sea, conveniently named the “Witwatersrand Sea”. The resulting 2500–4500 m thick layer of sediments is termed the “West Rand Group” of Witwatersrand rocks. The second phase, which lasted for 200 million years, followed on from the first phase, with on-land deposits, resulting from the retreat of the Witwatersrand Sea, leaving a wide almost flat coastal plain over which rivers from the north formed wide braided river deltas, into some of which rich deposits of gold were deposited. The resulting 2500 m thick layer of rock is termed the “Central Rand Group”. The “West Rand Group” and “Central Rand Group” of rocks together form the “Witwatersrand Supergroup”, the full horizontal extent of which is termed the Witwatersrand Basin. [1] [2] [3]

Braided river A network of river channels separated by small, and often temporary, islands called [[braid bar]]s

A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in British usage, aits or eyots. Braided streams tend to occur in rivers with high sediment loads and/or coarse grain sizes, and in rivers with steeper slopes than typical rivers with straight or meandering channel patterns. They are also associated with rivers with rapid and frequent variation in the amount of water they carry, i.e., with "flashy" rivers, and with rivers with weak banks. Braided channels are found in a variety of environments all over the world, including gravelly mountain streams, sand bed rivers, alluvial fans, river deltas, and across depositional plains.

A timeline of the earth's geological history, with an emphasis on events in Southern Africa. W indicates when the Witwatersrand supergroup was laid down, C the Cape supergroup, and K the Karoo Supergroup. The graph also indicates the period during which banded ironstone formations were formed on earth, indicative of an oxygen-free atmosphere. The earth's crust was wholly or partially molten during the Hadean Eon; the oldest rocks on earth are therefore less than 4000 million years old. One of the first microcontinents to form was the Kaapvaal Craton. Earth's geolological timeline.svg
A timeline of the earth's geological history, with an emphasis on events in Southern Africa. W indicates when the Witwatersrand supergroup was laid down, C the Cape supergroup, and K the Karoo Supergroup. The graph also indicates the period during which banded ironstone formations were formed on earth, indicative of an oxygen-free atmosphere. The earth's crust was wholly or partially molten during the Hadean Eon; the oldest rocks on earth are therefore less than 4000 million years old. One of the first microcontinents to form was the Kaapvaal Craton.
An ashtray carved out of a soft form of banded ironstone. Note the alternating red and white layers that make up this rock. The red layers were laid down during the daylight hours when Archaean photosynthesizing cyanobacteria produced oxygen that immediately reacted with the dissolved iron in the water, to form insoluble iron oxide (rust). The white layers are sediments that settled during the night when there was no oxygen in the water . The earth's atmosphere was oxygen-free until about 2000 million years ago, when the rate of photosynthetic oxygen production began to exceed its rate of reaction with oxidizable materials (i.e. reducing agents). Iron banding 01.jpg
An ashtray carved out of a soft form of banded ironstone. Note the alternating red and white layers that make up this rock. The red layers were laid down during the daylight hours when Archaean photosynthesizing cyanobacteria produced oxygen that immediately reacted with the dissolved iron in the water, to form insoluble iron oxide (rust). The white layers are sediments that settled during the night when there was no oxygen in the water . The earth's atmosphere was oxygen-free until about 2000 million years ago, when the rate of photosynthetic oxygen production began to exceed its rate of reaction with oxidizable materials (i.e. reducing agents).
A diagrammatic representation of the position and size of the Kaapvaal Craton, outlined in red, in relation to present-day Southern Africa. The blue area depicts the portion of the craton that subsided below the "Witwatersrand Sea", about 3000 million years ago. It is in this sea that the sediments accumulated that would ultimately form the "West Rand Group" portion of the "Witwatersrand Supergroup" of rocks. The younger "Central Rand Group" of rocks accumulated on the low, flat coastal plain (see diagram below) after the Witwatersrand Sea had retreated southwards as a result of uplifting of the craton, especially in the north. CT indicates Cape Town, D Durban, B Bloemfontein, J Johannesburg, and K Kimberley. Cape-Vaal Craton.png
A diagrammatic representation of the position and size of the Kaapvaal Craton, outlined in red, in relation to present-day Southern Africa. The blue area depicts the portion of the craton that subsided below the “Witwatersrand Sea”, about 3000 million years ago. It is in this sea that the sediments accumulated that would ultimately form the “West Rand Group” portion of the “Witwatersrand Supergroup” of rocks. The younger “Central Rand Group” of rocks accumulated on the low, flat coastal plain (see diagram below) after the Witwatersrand Sea had retreated southwards as a result of uplifting of the craton, especially in the north. CT indicates Cape Town, D Durban, B Bloemfontein, J Johannesburg, and K Kimberley.
A diagrammatic presentation of the rivers that flowed into the Witwatersrand sea after 43000 m of sediment had already been deposited in the basin. The fast flowing rivers cascading down the mountains to the north now flowed over a wide flat coastal plain to form broad deltas of sluggish braided rivers, where the heavy materials (cobbles, gold, uranium and iron pyrite etc.) carried down from the mountains settled out, to form the gold bearing "Central Rand Group" deposits. Today's gold ore is confined to the fossil river deltas. Gold bearing braided rivers.jpg
A diagrammatic presentation of the rivers that flowed into the Witwatersrand sea after 43000 m of sediment had already been deposited in the basin. The fast flowing rivers cascading down the mountains to the north now flowed over a wide flat coastal plain to form broad deltas of sluggish braided rivers, where the heavy materials (cobbles, gold, uranium and iron pyrite etc.) carried down from the mountains settled out, to form the gold bearing "Central Rand Group" deposits. Today's gold ore is confined to the fossil river deltas.
The position of the Kaapvaal Craton (khaki coloured area) beneath the South African landscape, and the shrunken, shallow Witwatersrand Sea (light blue) at the time that gold was deposited in the broad, river deltas of six rivers that flowed into that sea, dropping all their heavier materials (cobbles, gold, uranium iron pyrite etc.) in the braided rivers of the deltas (see illustration on the left). Most of these gold deposits are deep under the South African surface, but form outcrops (exposures at the surface) along the Witwatersrand ridge. The six gold fields thus established are, in order from the west, moving clockwise, to the northern shore of the Witwatersrand sea, Welkom, Klerksdorp, Carletonville, West Rand, East Rand and Evander. Gold fields.jpg
The position of the Kaapvaal Craton (khaki coloured area) beneath the South African landscape, and the shrunken, shallow Witwatersrand Sea (light blue) at the time that gold was deposited in the broad, river deltas of six rivers that flowed into that sea, dropping all their heavier materials (cobbles, gold, uranium iron pyrite etc.) in the braided rivers of the deltas (see illustration on the left). Most of these gold deposits are deep under the South African surface, but form outcrops (exposures at the surface) along the Witwatersrand ridge. The six gold fields thus established are, in order from the west, moving clockwise, to the northern shore of the Witwatersrand sea, Welkom, Klerksdorp, Carletonville, West Rand, East Rand and Evander.

There were no continents during the early stages of the Archean Eon, [6] but island arcs did form. It was the coalescence of several of these island arcs that led to the formation of the Kaapvaal Craton, one of the first microcontinents to form on earth about 3900 million years ago. [2] Its size and position relative to Southern Africa today are indicated in the diagram on the left. About 3000 million years ago local cooling of the underlying asthenosphere caused subsidence of the south eastern portion of this microcontinent below sea level. [2] The floor of this newly formed “Witwatersrand sea” consisted of smoothly eroded granites. Sandy sediments brought in by rivers from the north started being deposited on the granite about 2970 million years ago. This sandy layer eventually became compressed to form the Orange Grove Quartzite, the lowermost layer of the Witwatersrand Supergroup. This quartzite layer can be seen lying on its granite base in Johannesburg, where it forms a 56 km long east-west ridge over which several rivers running to the north form waterfalls, giving rise to the name Witwatersrand, which in Afrikaans means “Ridge of White Waters”.

Kaapvaal Craton Archaean craton, possibly part of the Vaalbara supercontinent

The Kaapvaal Craton, along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga crust on Earth. Similarities of rock records from both these cratons, especially of the overlying late Archean sequences, suggest that they were once part of the Vaalbara supercontinent.

South Africa Republic in the southernmost part of Africa

South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by 2,798 kilometres (1,739 mi) of coastline of Southern Africa stretching along the South Atlantic and Indian Oceans; to the north by the neighbouring countries of Namibia, Botswana, and Zimbabwe; and to the east and northeast by Mozambique and Eswatini (Swaziland); and it surrounds the enclaved country of Lesotho. South Africa is the largest country in Southern Africa and the 25th-largest country in the world by land area and, with over 57 million people, is the world's 24th-most populous nation. It is the southernmost country on the mainland of the Old World or the Eastern Hemisphere. About 80 percent of South Africans are of Bantu ancestry, divided among a variety of ethnic groups speaking different African languages, nine of which have official status. The remaining population consists of Africa's largest communities of European, Asian (Indian), and multiracial (Coloured) ancestry.

Asthenosphere The highly viscous, mechanically weak and ductile region of the Earths mantle

The asthenosphere is the highly viscous, mechanically weak and ductilely deforming region of the upper mantle of the Earth. It lies below the lithosphere, at depths between approximately 80 and 200 km below the surface. The Lithosphere–asthenosphere boundary is usually referred to as LAB. The asthenosphere is almost solid, although some of its regions could be molten. The lower boundary of the asthenosphere is not well defined. The thickness of the asthenosphere depends mainly on the temperature. However, the rheology of the asthenosphere also depends on the rate of deformation, which suggests that the asthenosphere could be also formed as a result of a high rate of deformation. In some regions the asthenosphere could extend as deep as 700 km (430 mi). It is considered the source region of mid-ocean ridge basalt (MORB).

A schematic diagram of a NE (left) to SW (right) cross-section through the 2020 million year old Vredefort impact crater and how it distorted the contemporary geological structures. The present erosion level is shown. Johannesburg is located where the Witwatersrand Basin (yellow layer) is exposed at the "present surface" line, just inside the crater rim, on the left. Not to scale. Vredefort crater cross section 2.png
A schematic diagram of a NE (left) to SW (right) cross-section through the 2020 million year old Vredefort impact crater and how it distorted the contemporary geological structures. The present erosion level is shown. Johannesburg is located where the Witwatersrand Basin (yellow layer) is exposed at the "present surface" line, just inside the crater rim, on the left. Not to scale.

There was no free oxygen in earth's atmosphere until about 2000 million years ago, but there were photosynthesizing cyanobacteria. [5] The oxygen these microorganisms produced rapidly reacted with, amongst others, any dissolved iron compounds in the water, producing insoluble red iron oxide (rust), which precipitated out during the daylight hours. At night these reactions stopped. The result was alternating red and gray layers of mud which, when consolidated, became banded ironstones. [5]

Banded iron formation Distinctive layered units of iron-rich sedimentary rock that are almost always of Precambrian age

Banded iron formations are distinctive units of sedimentary rock that are almost always of Precambrian age.

As the sea deepened finer grained and muddy sediments accumulated. But changing geographical conditions resulted in the accumulation of a wide variety of sediments, ranging from mud, to sand, to gravel, and banded ironstones. Tillite deposits, dating from 2950 million years ago, are indicative of the first glaciation episodes on earth. [2] [7] Within 60 million years, up to 4500 m of sediment had accumulated on the granite base, to become the “West Rand Group” of rocks that contribute over 60% of the total thickness of the Witwatersrand Supergroup. [1] [2] [7]

Uplifting of the north of the Kaapvaal Craton, in addition to orogenesis (mountain formation), towards the end of the deposition of the “West Rand Group” of sediments caused the Witwatersrand sea to retreat. The area of the craton on top of which Johannesburg is now situated, became a vast riverine plain, which extended along the entire northern and western shoreline of the shrunken sea, in an arc extending from Evander in the east, through Johannesburg, Carletonville and then southwards to Klerksdorp and Welkom in the south-west. The rivers formed braided deltas with many interlacing, slow flowing channels where all the heavy materials brought down from the mountains were deposited: large pebbles, and heavy minerals, such as gold, iron pyrite, and uraninite. The gold was in its free elemental form. Cyanobacteria grew in relative abundance in these mineral rich waters. [1] [2] [7] The kerogen, or bitumen, that is found in association with the gold deposits almost certainly represents what remains of these Archean photosynthesizing micro-organisms. [2]

It is clear that for the next 200 million years the flood plain was repeatedly inundated, sometimes eroded, and sediments re-deposited. The result was a 2500 m thick layer of rock that is termed the “Central Rand Group”, which together with the “West Rand Group”, forms the “Witwatersrand Supergroup”. It is the younger Central Rand Group that contains most of the gold bearing conglomerates, locally referred to as banket, that are today of great economic importance.

The “Central Rand Group” of deposits was brought to an abrupt end by massive outpourings of lava, which form the Ventersdorp lavas which erupted 2715 million years ago. [2] The cause of these lava outpourings is a matter of speculation. It might be related to the collision of the Kaapvaal craton with the Zimbabwe craton, eventually to become knitted together to form a single continental unit.

A schematic diagram of the area surrounding the Vredefort Dome, where a massive meteor created an impact crater 300 km in diameter 2020 million years ago. The red dot represents the epicentre of the impact. The outer circle has a radius of 150 km, and indicates the approximate location of the crater rim. The inner circle marks the 100 km distance from the centre. Note that the outcrops (surface exposures) of Witwatersrand rocks (yellow areas) are located at 25 km from the epicentre of the impact and then again at about 80-120 km from the epicentre. The locations of important towns and cities in the region are indicate in the appropriate places. The red line in the detail of the Johannesburg region shows the location of the scarp/ridge that gave the "Witwatersrand" its name; the purple line the location where the main gold bearing reef is exposed at the surface, just south of Johannesburg. Witwatersrand outcrops 2.jpg
A schematic diagram of the area surrounding the Vredefort Dome, where a massive meteor created an impact crater 300 km in diameter 2020 million years ago. The red dot represents the epicentre of the impact. The outer circle has a radius of 150 km, and indicates the approximate location of the crater rim. The inner circle marks the 100 km distance from the centre. Note that the outcrops (surface exposures) of Witwatersrand rocks (yellow areas) are located at 25 km from the epicentre of the impact and then again at about 80–120 km from the epicentre. The locations of important towns and cities in the region are indicate in the appropriate places. The red line in the detail of the Johannesburg region shows the location of the scarp/ridge that gave the "Witwatersrand" its name; the purple line the location where the main gold bearing reef is exposed at the surface, just south of Johannesburg.

A final event that had a major impact on the geology of the Witwatersrand Basin and its exposure in the Johannesburg region, was a massive meteor impact 110 km to the south-west of Johannesburg 2020 million years ago. [1] [2] The epicentre of the impact was close to the present village of Vredefort, which has given its name to the geological remnant of this immense event: the Vredefort Dome. Not only are the remains of this impact the oldest on earth, but it is also the largest meteor impact that has left its imprint on the earth's geology of today. [1] [2] A meteor 10–15 km across created a 300 km diameter crater, distorting all the rock strata within that circle. Johannesburg is just within the outer edge of this impact crater. In the immediate vicinity of the impact all the subterranean strata were uplifted and upturned, so that Witwatersrand rocks are exposed in an arc 25 km away from the impact centre. There are unfortunately no gold deposits in these outcrops. The meteor impact, however, lowered the Witwatersrand basin inside the crater. This protected it from erosion later on; but, possibly more importantly, bringing it to the surface close to the crater rim, near Johannesburg. [2] In fact, apart from the Witwatersrand outcrops (i.e. where these rocks are exposed at the surface) in the immediate vicinity of the Vredefort Dome, virtually all the other outcrops occur in an arc approximately 80–120 km from the centre of the impact crater, to the west, north-west, north and north-east. [8] Thus, it is possible that if it had not been for the Vredefort meteor strike 2000 million years ago, we would either have never discovered the rich gold deposits beneath the Southern African surface, or they would have been eroded away during the uninterrupted removal of a several kilometres thick layer of deposits from the surface of the Southern African Plateau in the relatively recent geological past: i.e. the past 150 million years, but especially during the last 20 million years. [2]

Gold origin

The vast majority of the Earth's gold and other heavy metals are locked up in the earth's core. Evidence from tungsten isotope studies indicates that most gold in the crust is derived from gold in the mantle which resulted from a meteorite bombardment some 3900 million years ago (i.e. at approximately the time that the Kaapvaal craton formed). The gold bearing meteorite events occurred millions of years after the segregation of the earth's core. [9] The gold in the Witwatersrand Basin area was deposited in Archean river deltas having been washed down from surrounding gold-rich greenstone belts to the north and west. Rhenium-osmium isotope studies indicate that the gold in those mineral deposits came from unusual 3000 million year old mantle-derived intrusions known as komatiite, present in the greenstone belts. [10]

See also

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Geology of Ghana

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The geology of Sierra Leone is primarily very ancient Precambrian Archean and Proterozoic crystalline igneous and metamorphic basement rock, in many cases more than 2.5 billion years old. Throughout Earth history, Sierra Leone was impacted by major tectonic and climatic events, such as the Leonean, Liberian and Pan-African orogeny mountain building events, the Neoproterozoic Snowball Earth and millions of years of weathering, which has produced thick layers of regolith across much of the country's surface.

Geology of Tanzania

The geology of Tanzania began to form in the Precambrian, in the Archean and Proterozoic eons, in some cases more than 2.5 billion years ago. Igneous and metamorphic crystalline basement rock forms the Archean Tanzania Craton, which is surrounded by the Proterozoic Ubendian belt, Mozambique Belt and Karagwe-Ankole Belt. The region experienced downwarping of the crust during the Paleozoic and Mesozoic, as the massive Karoo Supergroup deposited. Within the past 100 million years, Tanzania has experienced marine sedimentary rock deposition along the coast and rift formation inland, which has produced large rift lakes. Tanzania has extensive, but poorly explored and exploited natural resources, including coal, gold, diamonds, graphite and clays.

The geology of Uganda extends back to the Archean and Proterozoic eons of the Precambrian, and much of the country is underlain by gneiss, argillite and other metamorphic rocks that are sometimes over 2.5 billion years old. Sedimentary rocks and new igneous and metamorphic units formed throughout the Proterozoic and the region was partially affected by the Pan-African orogeny and Snowball Earth events. Through the Mesozoic and Cenozoic, ancient basement rock has weathered into water-bearing saprolite and the region has experienced periods of volcanism and rift valley formation. The East Africa Rift gives rise to thick, more geologically recent sediment sequences and the country's numerous lakes. Uganda has extensive natural resources, particularly gold.

The geology of Eswatini formed beginning 3.6 billion years ago, in the Archean Eon of the Precambrian. Eswatini is the only country entirely underlain by the Kaapvaal Craton, one of the oldest pieces of stable continental crust and the only craton regarded as "pristine" by geologists, other than the Yilgarn Craton in Australia. As such, the country has very ancient granite, gneiss and in some cases sedimentary rocks from the Archean into the Proterozoic, overlain by sedimentary rocks and igneous rocks formed during the last 541 million years of the Phanerozoic as part of the Karoo Supergroup. Intensive weathering has created thick zones of saprolite and heavily weathered soils.

The geology of Nunavut began to form nearly three billion years ago in the Archean and the territory preserves some of the world's oldest rock units.

References

  1. 1 2 3 4 5 6 7 8 9 Norman, N., Whitfield, G. (2006) ‘’Geological Journeys’’. p. 38-49, 60–61. Struik Publishers, Cape Town.
  2. 1 2 3 4 5 6 7 8 9 10 11 12 13 McCarthy, T., Rubridge, B. (2005). ‘’The Story of Earth and Life.’’ p. 89-90, 102–107, 134–136. Struik Publishers, Cape Town
  3. 1 2 3 4 5 6 7 Truswell, J.F. (1977). ‘’The Geological Evolution of South Africa’’. p. 21-24, 27–28, 33–36, . Purnell, Cape Town.
  4. ↑ http://www.goldsheetlinks.com/production.htm
  5. 1 2 3 Margulis, L., Sagan, D. (1995). ’’What is Life?’’. p. 81-83. Weidenfeld and Nicolson, London.
  6. ↑ Stanley, S.M. (1999). Earth System History. pp. 297–301. W.H. Freeman and Company, New York. ISBN   0-7167-2882-6.
  7. 1 2 3 Tankard, A.J., Jackson, M.P.A, Erikson, K.A., Hobday, D.K., Hunter, D.R., Minter, W.E.L. (1982). Crustal Evolution of Southern Africa. 3.8 Billion Years of Earth History.pp. 118–139. Springer-Verlag, New York.
  8. ↑ Geological map of South Africa, Lesotho and Swaziland (1970). Council for Geoscience, Geological Survey of South Africa.
  9. ↑ Battison, Leila; Meteorites delivered gold to Earth, BBC News, Science & Environment, 8 September 2011
  10. ↑ Kirk, Jason; Joakin Ruiz; John Chesley and Spencer Titley; The Origin of Gold in South Africa, American Scientist, Vol 91, Nov.-Dec 2003, pp. 534–531

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