71-683: The Vaal River ( / ˈ v ɑː l / Afrikaans pronunciation: [ˈfɑːl] ; Khoemana : ǀHaiǃarib ) is the largest tributary of the Orange River in South Africa . The river has its source near Breyten in Mpumalanga province, east of Johannesburg and about 30 kilometres (19 mi) north of Ermelo and only about 240 kilometres (150 mi) from the Indian Ocean . It then flows westwards to its confluence with
142-461: A caron ), mid (no accent), and falling (notated with a circumflex ). Reports as to the number of Khoemana speakers are contradictory, but it is clear that it is nearly extinct. It was thought to be extinct until the discovery of four elderly speakers around Bloemfontein and Kimberley. A 2009 report by Don Killian of the University of Helsinki estimated that there were less than 30 speakers at
213-662: 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". There was no free oxygen in Earth's atmosphere until about 2 billion years ago, before the appearance and sufficient development of photosynthesizing cyanobacteria . The oxygen produced by these microorganisms rapidly reacted with, amongst others, Fe ions dissolved in water, precipitating insoluble red iron oxide ( hematite ). For various reasons,
284-556: A considerable amount of this section is also used for mining and industries, irrigation and power generation. The river regularly experiences pollution of its upper reaches, and this affects users downstream. During 2019 the Lekwa Local Municipality 's main water treatment plant in Standerton was in disrepair and was causing chronic pollution problems. To assist users downstream, clean water had to be pumped into
355-442: A hard, erosion-resistant quartzite metamorphic rock, over which several north-flowing rivers form waterfalls, which account for the name Witwatersrand, meaning 'white water ridge' in Afrikaans . This east-west-running scarp can be traced with only one short gap, from Bedfordview (about 10 km [6.2 mi] west of O.R. Tambo International Airport ) in the east, through Johannesburg and Roodepoort , to Krugersdorp in
426-471: 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
497-539: A significant impact on the heritage and culture of Khoemana speakers. Robust Khoemana (before more recent language attrition ) is principally recorded in an 1879 notebook by Lucy Lloyd , which contains five short stories; some additional work was done in Ponelis (1975). As of 2009, the EuroBABEL project is searching for remaining speakers. The people and their language first began to attract scholarly attention in
568-582: A three-phase construction that would augment water from Lesotho into the Vaal River, including four major dams. From 1954, the Natural Resources Development Council proposed that South Africa receive some water from neighbouring Lesotho . Negotiations between the two countries started in the late 1970s. A treaty for the development of the scheme was signed on 24 October 1987 by representatives of Lesotho, South Africa,
639-459: Is ǀHai!garib , drab river). Both Vaal and Tky (in modern orthography ǀHai ) mean "drab" or "dull", which alludes to the colour of the waters, especially noticeable during flood season when the river is laden with silt. In the upper reaches the river was named iLigwa ( Sindebele ), Ikwa or Igwa ( isiZulu ), ilikwa ( siSwati ), lekwa ( Sesotho ), or cuoa by the Khoikhoi, all referring to
710-414: Is a moribund Khoe language of South Africa. "Khoemana" (from khoe 'person' + mana 'language') is more commonly known as either Korana / k ɒ ˈ r ɑː n ə / korr- AH -nə (also ǃOrakobab, ǃOra, Kora, Koraqua) or Griqua (also Gri [xri] , Xri, Xiri, Xirikwa). The name 'Korana' reflects the endonym ǃOra IPA: [ǃoɾa] or ǃGora IPA: [gǃoɾa] , referring to
781-451: Is also one of the largest meteor impacts to have left its imprint on present-day Earth geology. 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
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#1732765226833852-516: 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
923-850: Is drawn from the Vaal to meet the industrial needs of the Greater Johannesburg Metropolitan Area and a large part of the Free State. In 1881 the Kimberley Waterworks Company, provided water from the Vaal to the Cape Diamond Fields at a cost of one shilling per 100 imperial gallons (450 L; 120 US gal). As a part of the Vaal-Hartz Scheme it is a major source of water for irrigation. Water drawn from
994-468: Is sometimes carried out at depths of 4 kilometres (2.5 mi) below the surface. The Witwatersrand Basin is a largely underground geological formation which surfaces in the Witwatersrand. It holds the world's largest known gold reserves and has produced over 40 000 tonnes (1.3 × 10 ozt), which represents about 22% of all the gold accounted for above the surface. The basin straddles
1065-560: The European Union , United Nations and the World Bank . It was then estimated to cost R9.1 billion for the first phase of the project alone. South Africa pays R150 million to Lesotho each year whether they use all of the water that is supplied or not. According to Hogan the headwaters portion of the basin supports high endemism in reptiles, and lower in the watershed are elevated levels of endemism for small mammals. Water
1136-641: The Griqua people . There exist (or existed) several dialects of Khoemana, but the details are unknown. Khoemana is closely related to Khoekhoe , and the sound systems are broadly similar. The strongly aspirated Khoekhoe affricates are simply aspirated plosives [tʰ, kʰ] in Khoemana. However, Khoemana has an ejective velar affricate, /kxʼʔ/ , which is not found in Khoekhoe, and a corresponding series of clicks , /ǀ͡xʼ ǁ͡xʼ ǃ͡xʼ ǂ͡xʼ/ . Beach (1938) reported that
1207-460: The Magaliesburg (although locals refer to segments of the scarp using area-specific names, such as Linksfield Ridge , Parktown Ridge or Observatory Ridge ). The entire plateau-like structure is also often called the Witwatersrand. The plateau's elevation above sea-level is between 1,700 and 1,800 metres (5,600–5,900 ft). The Witwatersrand plateau forms a continental divide , with
1278-735: The University of Johannesburg ), and to towns and regions such as the East Rand , West Rand and Randburg . The Witwatersrand plateau consists of a 5 000 -to- 7 000 -metre-thick (3.1–4.3 mi) layer of mainly sedimentary rocks laid down over a period of about 260 million years, starting approximately 2.97 billion years ago. The entire series of rocks, known as the "Witwatersrand Supergroup", consists of very hard erosion resistant quartzites , banded ironstones and some marine lava deposits, interspersed with softer, more easily eroded tillites , mudstones and conglomerates . The oldest rocks (laid down 2.97 billion years ago) form
1349-737: The Zuurbekom Wells in Gauteng 's West Rand. Eventually these would dry up and people would need a new source that could provide for their domestic, agricultural and industrial activities. Water schemes were initially established by the private sector to deal with the growing demand. These included the Braamfontein Water Company's Vierfontein Syndicate of 1893 and the Sivewright Concession of 1887 by
1420-806: The barrage (1914–1924). The Vaal River scheme was an initiative established to manage water distribution. The Rand Water board also established the Vereeniging Pumping Station (1924), the Zwartkopjes Pumping Station, the Vaal Dam (1938), the Zuikerbosch Pumping Station (1949) and the Lesotho Highlands Water Project (1998). Rain and underground water collects in pans, vleis and streams and where these connect,
1491-645: 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. The gold in the Witwatersrand Basin area was deposited in Archean river deltas having been washed down from surrounding gold-rich greenstone belts to
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#17327652268331562-418: The ǃOra people . Sometimes ǃOra is also known as Cape Khoe or Cape Hottentot, though the latter has become considered derogatory. The various names are often treated as different languages (called South Khoekhoe when taken together), but they do not correspond to any actual dialect distinctions, and speakers may use "Korana" and "Griqua" interchangeably. Both names are also used more broadly, for example for
1633-494: 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
1704-484: 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 (2.5 mi) below the surface. 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
1775-489: The 1660s, coinciding with Dutch colonial efforts in the Cape of Good Hope and the resulting armed conflicts. At the time, Khoemana was widely spoken throughout the coastal regions of South Africa. After years of attrition during the colonial era to the 1930s, and under apartheid from 1948 to 1994, the language has all but vanished. Currently, speakers of Khoemana are not only scarce but scattered, due to forced migrations during
1846-497: The Archean Eon, 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 3.9 billion years ago. Its size and position relative to Southern Africa today are indicated in the diagram on the left. About 3 billion years ago local cooling of the underlying asthenosphere caused subsidence of
1917-500: The Johannesburg Town Council, The Chamber of Mines and other local authorities within the Witwatersrand. Rand Water responded to water scarcity by imposing restrictions on Witwatersrand inhabitants in 1913. It also developed major water schemes that would respond to the growing demand. Between 1914 and 1998, the organisation partnered with various government and private entities to drive the Vaal River scheme and
1988-592: The Johannesburg Waterworks and Exploration Company. Water was expensive and largely inaccessible for most inhabitants. The Rand Water Board was established in 1903 to take over the operations of the private sector with a mandate to investigate sustainable water supply and sanitation services. The organisation would become fully operational in 1905, supplying water in bulk to the Witwatersrand . The organisation's members included officials from
2059-545: The Khoekhoe of the time had a velar lateral ejective affricate , [k͡ʟ̝̊ʼ] , a common realisation or allophone of /kxʼ/ in languages with clicks, and it might be expected that this is true for Khoemana as well. In addition, about half of all lexical words in Khoemana began with a click, compared to a quarter in Khoekhoe. In Korana, [oe] and [oa] can be pronounced as [we] and [wa]. There are four tones in Khoemana: high (notated with an acute accent ), rising (notated with
2130-644: The Orange River southwest of Kimberley in the Northern Cape . It is 1,458 kilometres (906 mi) long, and forms the border between Mpumalanga, Gauteng and North West Province on its north bank, and the Free State on its south. It is the third largest river in South Africa after the Orange River (2200 km long) and the Limpopo River (1750 km long) and was established as
2201-564: The Vaal River before the Vaal Dam was built in 1938; now the water flows straight into the dam. Kromelmboogspruit joins the Vaal near the Vaal Barrage . Since the Vaal River's surface runoff is erratic, large dams have been built along its course to collect the water. In the past, before the river was established as the official source of water for part of the Gauteng , several small dams were built by farmers for irrigation . When
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2272-557: The Vaal River from other catchment areas between the 1970s and 1990s. These include the Lesotho Highlands Water Project and KwaZulu-Natal 's Tugela-Vaal Water Transfer Scheme. The Tugela-Vaal Transfer Scheme was completed in 1974 to transfer from the Tugela River in KwaZulu Natal via canals, pipelines and dams into the Vaal River system The Lesotho Highlands Water Project was finally launched in 1997 and would entail
2343-463: The Vaal supports 12 million consumers in Gauteng and surrounding areas. The majority of the Vaal River water upstream of the Vaal Dam is used for mining and industrial use such as coal mines and Sasol 's energy and chemical-related activities, as well as urban use and power generation. Further downstream of the dam, water is mostly dedicated to urban requirements and, although proportionally less,
2414-619: 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. Thus, it is possible that if it had not been for the Vredefort asteroid strike 2 billion 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
2485-463: The Witwatersrand, these were alluvial concentrates in contemporary rivers, or in quartz veins, in the form that gold had always been found elsewhere on earth. When George Harrison, probably accompanied by George Walker, found gold on the farm Langlaagte, 5 km (3 mi) west of what would become the city of Johannesburg, in an outcrop of conglomerate rocks, in February 1886, they assumed that this
2556-558: The apartheid era. This has rendered the language particularly vulnerable. Witwatersrand The Witwatersrand ( UK : / w ɪ t ˈ w ɔː t ər z r æ n d , - r ɑː n d / , US also / ˈ w ɪ t w ɔː t ər z -/ ; Afrikaans pronunciation: [ˌvətˌvɑːtəɾsˈɾant] ; locally the Rand or, less commonly, the Reef ) is a 56-kilometre-long (35 mi), north-facing scarp in South Africa . It consists of
2627-415: 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 . Since this gold
2698-512: The construction of the Vaal Dam was completed in 1938, the dam ensured the supply of water throughout each year even when the river was not full. The dam would receive water from different catchment areas through various projects. Two water transfer schemes were developed to supply the economic heartland of the country (then recognised as the Pretoria-Witwatersrand-Vereeniging complex) by channelling water into
2769-464: The first glaciation episodes on earth. 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. Uplifting of the north of the Kaapvaal Craton, in addition to orogenesis (mountain formation), towards the end of the deposition of
2840-475: 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 2.02 billion years ago. 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 among the oldest on Earth, but it
2911-445: 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. The kerogen , or bitumen , that is found in association with the gold deposits almost certainly represents what remains of these Archean photosynthesizing micro-organisms. It
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2982-677: The historic Witwatersrand Gold Rush . Harrison is believed to have sold his claim for less than £10 before leaving the area, and he was never heard from again. Harrison's original Zoekers' (in English: seekers', or prospectors') Claim No 19 was declared a national monument in 1944, and named Harrison's Park. The park is on the busy Main Reef Road, immediately west of Nasrec Road. In 1887 Cecil John Rhodes registered "The Gold Fields of South Africa" in London, South Africa's first mining house, with
3053-416: The impact centre. There are 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. In fact, apart from the Witwatersrand outcrops (i.e. where these rocks are exposed at the surface) in the immediate vicinity of
3124-675: The main source of water for the great Witswatersrand area after the 19th century gold rush . The Vaal Dam lies on the Vaal River in Deneysville just south of the border between Gauteng and the Free State. The Vaal River is the longest river wholly within the borders of South Africa. Vaal is a Dutch name (later Afrikaans ), translated by the Griquas or Boers from an earlier Kora Khoekhoe or !Orakobab name, sometimes spelled as Tky-Gariep (in Khoekhoegowab orthography it
3195-401: The north and west. Rhenium - osmium isotope studies indicate that the gold in those mineral deposits came from unusual 3 billion year old mantle -derived intrusions known as komatiite , present in the greenstone belts. Apart from the obvious hollowing out of the rocks below southern Johannesburg, causing unpredictable sinkholes, surface instabilities and earth tremors, the bringing to
3266-415: 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. There were no continents during the early stages of
3337-463: The north-east to Theunissen in the south-west, and 150 km (93 mi) wide stretching from Steynsrus in the south-east to Coligny in the north-west, 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 six sites where Archean rivers from the north and west formed fan deltas, with many braided channels, before flowing into
3408-512: The northern scarp of the Witwatersrand plateau; the youngest (laid down 2.71 billion years ago) are those that form the southern edge of the plateau. Gold is found in the conglomerate strata of the younger members of the Supergroup, locally referred to as banket . The abundance of this gold is without a natural equal anywhere else in the world. Over 40,000 tonnes (44,000 short tons) have been mined from these rocks since this precious metal
3479-509: 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. 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
3550-746: The phenomenon is called, has become a major ecological problem, because it dissolves many of the heavy elements, such as the uranium , cadmium , lead , zinc , copper , arsenic and mercury found in the mine dumps, facilitating their passage into surface water and ground water. The tailings ponds contain an average of 100 mg/kg of U 3 O 8 , and uranium levels are measureable in human hair. Sulfuric acid also erodes concrete and cement structures, resulting in structural damage to buildings and bridges. Although gold had been discovered in various locations in South Africa, such as Barberton and Pilgrim's Rest , as well as at several sites near
3621-460: The plain it traverses. Historically, the river formed the northern border of Moshoeshoe I 's Basotho kingdom at its height in the mid-19th century, then became the boundary between two Boer republics : The South African Republic (later the Transvaal province) and the Orange Free State . The geographic name "Transvaal" comes from the name of this river, meaning "beyond the Vaal river". This
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#17327652268333692-503: The republic. Witwatersrand and the Rand are names for the conurbation that developed along the range , although the terms are falling into disuse and Witwatersrand was the "W" in PWV (Pretoria-Witwatersrand-Vereeniging), the initial name of Gauteng province. In this context, it has lent its name to institutions including the University of the Witwatersrand (Wits University) and the defunct Rand Afrikaans University (RAU, now part of
3763-615: The river to dilute its high salt levels, thereby wasting a large quantity of this scarce resource. In 2021, a report released by the South African Human Rights Commission found the river to be polluted beyond acceptable levels, including the flow of raw sewerage into the River. The Vaal River is made up of 50 km of navigable water. The river basin thus offers a range of leisurely water activities that attract local and international tourists throughout
3834-641: The run-off to the north draining into the Indian Ocean via the Crocodile and Limpopo rivers, while the run-off to the south drains via the Vaal into the Orange River and ultimately into the Atlantic Ocean . Because of the extraordinary quantities of gold that have been extracted from the Witwatersrand rocks, the South African currency was named the rand in 1961 upon the declaration of
3905-535: The sedimentation of the fine grain mud was affected by cyclic episodes with more or less precipitation of iron oxides. The result was alternating red and beige layers of mud which, when consolidated, became banded ironstones . As the sea deepened, finer grained and muddy sediments accumulated. 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 2.95 billion years ago, are indicative of
3976-647: The south eastern portion of this microcontinent below sea level. 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 2.97 billion 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
4047-421: The surface of rocks that had been laid down in oxygen-free conditions had unforeseen effects. Iron pyrite (FeS 2 ), which is relatively plentiful in the gold ores of the Witwatersrand, oxidises to insoluble ferric oxide (Fe 2 O 3 ) and sulfuric acid (H 2 SO 4 ). Thus, when mine waste comes into contact with oxygenated rainwater, sulfuric acid is released into the ground water. Acid mine drainage , as
4118-466: The time. Matthias Brenzinger reported in 2012 that one possible speaker remained, but that she refused to speak the language. The discrepancies could be because the language has multiple dialects and goes by several names, with scholars not always referring to the same population. Khoemana is listed as "critically endangered" in UNESCO 's Language Atlas . The loss of this endangered language would have
4189-441: The total world output. Silver , uranium , and iridium are recovered as gold-refining by-products. 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 3 billion years ago. The first phase, lasting 60 million years, consisted of sedimentary deposits in
4260-510: 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. 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
4331-426: The upper, younger layers of the Witwatersrand Supergroup of rocks, on the southern side of the Witwatersrand plateau. The Witwatersrand Supergroup strata which reach the surface in Johannesburg dip downwards to the south at an angle of about 30°. From there on they are almost everywhere, with very few exceptions (see below), covered by younger rocks. Gold mining in these buried portions of the Witwatersrand Supergroup
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#17327652268334402-488: The west (see the diagram at left below). The scarp forms the northern edge of a 7-to-10-kilometre-wide (4–6 mi) plateau (or ridge) which rises about 200 m (660 ft) above the surrounding plains of the Highveld . A number of picturesque Johannesburg suburbs, including Observatory , Linksfield Ridge and Upper Houghton are located along the scarp, overlooking the rest of northern Johannesburg with views up to
4473-660: The westward flowing Vaal River is born. The river flows west into the Grootdraai Dam near Standerton , Mpumalanga . On its course to the Vaal Dam in Vereeniging, the river is joined by a number of tributaries. The Little Vaal River starts in an escarpment near Ermelo. Near Memel in the Free State is where the Klip River begins. The Watervals River begins in Secunda, Mpumalanga . The Wilge River used to meet
4544-420: The year. Activities include boating , yachting and water skiing . Deneysville is a town on the Free State side of the Vaal River and is a popular water-centre where visitors can enjoy swimming , kiteboarding , yachting , boating , catamaran cruising, jet skiing , windsurfing , snorkelling and fishing . Khoemana ǃOrakobab or Khoemana , also known as Korana , ǃOra , or Griqua ,
4615-534: Was alluvial gold in an old riverbed, that had been tilted as a result of earth movements. 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. Harrison had stumbled on the Main Reef conglomerate (part of the "Johannesburg Subgroup" of rocks — see illustration above). The conglomerate
4686-532: Was brought to an abrupt end by massive outpourings of lava, which form the Ventersdorp lavas which erupted 2.715 billion years ago. 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 final event that had a major impact on
4757-419: 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. 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 . The conglomerate
4828-753: Was first discovered here in 1886. This accounts for approximately 22% of all the gold that is accounted for today. Not all the conglomerates contain gold, and of those that do (known as "reefs" by the miners), the gold is not uniformly distributed throughout the layer, but tends to occur in streaks, where the pebbles that make up the conglomerate are larger than elsewhere. Here the gold is associated with other minerals, especially iron pyrite and uraninite , as well as carbon rich materials such as kerogen , or bitumen , which occurs in small balls less than 1 mm (0.04 in) in size, called "flyspeck carbon", or as continuous layers about 10–20 mm (0.4–0.8 in) thick. The gold-bearing conglomerates occur chiefly in
4899-470: Was in respect to the Cape Colony and Natal , which were the main areas of European settlement at the time, and which lay south of the Vaal. During the late 19th century, there was an influx of people migrating to the Witwatersrand in search of gold . The Vaal River would eventually become the main water source for the Witwatersrand. The growing population initially used water from the groundwater of
4970-548: Was quickly traced east and westward for a total continuous distance of 50 km (31 mi) to define what became known as the "Central Rand Gold Field". Harrison declared his claim with the then-government of the Zuid Afrikaanse Republiek (ZAR), and in September 1886 President Paul Kruger issued a proclamation declaring nine farms public mining diggings, starting on 20 September 1886. This heralded
5041-497: Was quickly traced east and westward for a total continuous distance of 50 km (31 mi) to define what became known as the "Central Rand Gold Field". 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 (190 mi) long major axis from Evander in
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