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79-529: After the discovery of gold on the Witwatersrand in November 1885, geologists found that the main reef spread to the east and west, but did so at great depth. At that period the technology to prospect or mine at such depth was not available, but a comparatively small influx of miners was still observed, growing Klerksdorp to a town with over 70 taverns and its own stock exchange. When the majority of

158-834: A continental divide , with 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

237-577: A 25 kilometres (16 mi) railway line from Johannesburg to Boksburg . The line was opened on March 17, 1890, with the first train being hauled by a 14 Tonner locomotive. It became known as the "Randtram", even though it was a railway and not dedicated to tram traffic. This was the first working railway line in the Transvaal . The discovery of gold on the Witwatersrand also created a super-wealthy class of miners and industrialists known as Randlords . Many Randlords built large estates and mansions on

316-662: 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,

395-615: A Witwatersrand gold reef in June 1884. He had prospected the area since the early 1880s, and operated the Kromdraai Gold Mine in 1883 in the NW of present-day Johannesburg with his partner Johannes Stephanus Minnaar in an area known today as the " Cradle of Humankind ". However, he found minor reefs, and today the consensus falsely holds that credit for the discovery of the main gold reef is attributed to George Harrison, whose findings on

474-499: A capital of £250 000 . His brother Thomas was the first chairman. Witwatersrand Gold Rush The Witwatersrand Gold Rush was a gold rush that began in 1886 and led to the establishment of Johannesburg , South Africa . It was a part of the Mineral Revolution . In the modern-day province of Mpumalanga , gold miners in the alluvial mines of Barberton and Pilgrim's Rest and local tribes had suspected

553-467: A common Dutch name, the city was named after. One theory is that it is named after two state surveyors who were sent to choose an area for the layout of the new town, Johann Rissik and Christiaan Johannes Joubert . Within 10 years, the town was the largest in South Africa, growing faster than Cape Town , which was more than 200 years older. The gold rush saw massive development of Johannesburg and

632-415: A depth of 1,200 m. The sample from the drill core yielded 62oz of gold per ton of processed ore, making it one of the richest reefs in the world. One of the companies found the hole drilled by Allan Roberts, cleaned it out and drilled deeper striking the same reef a further 122m on. From 1936 to 1947, an estimated 190 miles of drilling had been accomplished in the free state. This was largely made possible by

711-468: A large influx of companies and miners. Russian and Basotho gangs are known to have maintained close relationships with mineworkers in the area after the 1950s. With the opening of gold mines in the Free State, gangs diverted focus from the city of Johannesburg to a symbiotic relationship with miners, by which the gangs would provide women in exchange for money or gold smuggled from the mines. At

790-513: A reason to claim the gold fields for themselves. The Jameson Raid followed, which brought attention to Cecil Rhodes . The Jameson Raid was supported by Rhodes and led by Sir Leander Starr Jameson. Its intent was to overthrow the Transvaal government and turn the region into a British colony. There were 500 men who took part in the uprising; 21 were killed, and many were arrested, then trialed and sentenced. The mining village of Ferreira's Camp

869-471: 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

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948-451: 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

1027-516: 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

1106-405: 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

1185-624: The Anglo American Corporation of South Africa Ltd. was able to secure options for a large segment of the Klerksdorp district and subsequently carried out intense drilling in this land for prospecting. Using new technology and instruments he developed himself, the Hungarian geologist, Oscar Weiss, identified a favourable location on the farm St. Helena. In April 1938 he drilled into gold at a depth of 737m. The estimation

1264-598: The Cape Colony . Another find by Pieter Jacob Marais, who had dug gold in California, was recorded in 1853 on the Jukskei River but was subject to similar secrecy. He arrived at Potchefstroom on September 3, 1853. Marais explored the northern slopes of the Witwatersrand, a few kilometers from the future main reef, finding small gold samples while panning the Crocodile and Jukskei rivers and exploring

1343-543: The South African Republic (ZAR) by John Henry Davis, a Welsh mineralogist. Davis presented his gold find to President Andries Pretorius who feared what would happen to the new republic if the discovery became widely known. Davis was told to sell the gold, worth £600, to the Transvaal Treasury and was subsequently ordered to leave the country and escorted to the border, where he returned to

1422-588: The South African Republic (ZAR) worried that foreigners would outnumber the Boers and put in place measures to stop this. Kruger discussed the measures with Bantjes, whose father, Jan Gerritze Bantjes , had educated Kruger when he was a boy during the Great Trek . One of the measures placed heavy taxes on the sale of dynamite to foreigners to slow the momentum. This agitated the miners, and the British took this as

1501-710: The Suikerboschrand in the south during October and November 1853. On December 1, Marais sought approval from the Volksraad to look for gold, which was accepted with the provision that the Commission of the existing districts of the Republic would be notified if it was discovered. He was also warned that if he told any foreign power about any potential finds that caused a disturbance to the republic's existence, he would be punished by death. Marais then paddled

1580-645: 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

1659-494: 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

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1738-484: 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

1817-413: 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 the northern scarp of the Witwatersrand plateau; the youngest (laid down 2.71 billion years ago) are those that form

1896-497: 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

1975-500: The Free State were located in the basal reef of the Main Bird series, which were the bottom parts of the reefs near the footwall contacts (boundary between two adjacent rock formations). It is therefore likely that sedimentary processes played a significant role in how the metal was distributed. However, the gold grains themselves and the layers where they are found don't always show clear signs of sedimentary processes. The metal and

2054-506: The Kimberley diamond discovery and the Witwatersrand goldfields. A 1946 census measured the urban population of the area at 5,320 individuals. By 1950, this total had multiplied over eight times to approximately 43,000 individuals. The mining sector in the Free State contributed 37.4% of the provinces GDP in 1981, making it the largest contributor at the time. By 1991, this dropped to 20.6%, and by 2001 it dropped further still to 14.3%. From

2133-469: The Knights Mine. On returning to his wagon, he discovered conglomerate rock that, when crushed, contained gold. Though there were smaller mining operations in the region, it was not until 1884 and the subsequent 1886 discovery at Langlaagte that the Witwatersrand gold rush got underway in earnest. Explorer and prospector Jan Gerrit Bantjes (1840-1914) was the first and original discoverer of

2212-666: The Rand or, less commonly, the Reef ) 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 '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

2291-722: The Sand and Dwars rivers in January 1854. His small gold finds were exhibited at the courthouse in Potchefstroom in January 1854. After submitting his final report to the ZAR government on April 7, 1855, he left the ZAR in 1855 to settle in Dordrecht , Cape Colony. In 1856, Lieutenant Lys travelled to Pretoria from Pietermaritzburg and became stuck crossing a marsh on the farm Driefontein , today's Germiston , which would become

2370-619: 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

2449-568: The Witwatersrand, and the area today is the prime metropolitan area of South Africa. One consequence of the gold rush was the construction of the first railway lines in this part of Africa. As a result of the rapid development of the goldfields on the Witwatersrand in the 1880s and the demand for coal by the growing industry, a concession was granted by the ZAR government to the Netherlands-South African Railway Company (NZASM) on July 20 , 1888 , to construct

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2528-463: 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

2607-625: The area was pronounced open. His discovery was recorded with a monument where the original gold outcrop is believed to be located and a park named in his honor. Harrison is believed to have sold his claim for less than 10 pounds before leaving the area. News of gold spread rapidly and reached Cecil Rhodes in Kimberley . Rhodes and his partner Robinson, with a team of companions, were curious and rode over 400 km to Bantjes' camp at Vogelstruisfontein, where they stayed with him for two nights near what would later become Roodepoort . Rhodes purchased

2686-582: 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

2765-437: The bringing to 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

2844-522: The declaration of 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

2923-501: The defunct Rand Afrikaans University (RAU, now part of 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

3002-478: The development of the use of diamonds for drilling purposes, an experimental effort largely led by the De Beers company. Diamonds were greatly preferable to the more expensive and rarer carbons that were previously in use. Use of diamond drills for prospecting work is important in obtaining information on the strike, dip, rake, and pitch of an ore-body, as well as tonnage, grade, and ore quality. The first gold bar

3081-443: The early 1930s Archibald Megson managed to interest Allan Roberts, an amateur geologist and dental technician, in the reef and entrance adit. Megson was bought out by Roberts who founded "Wit Extensions". In 1933 Roberts bored a hole of 1,263m near the adit on the farm Aandenk. It yielded nothing and the venture was discontinued. This effort was followed by others such as Western Holdings and a company owned by Hans Merensky . In 1933,

3160-485: The east, through Johannesburg and Roodepoort , to Krugersdorp in 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

3239-508: The end of the gold boom in 1989, many mines in the region became economically indefensible and were closed. From the mid 1980s to the early 2010s, mine employment in Matjhabeng fell from 180,000 to 30,000. Local legislators reacted to this decline by pushing for tax incentives and job-creation support in the mining industry. The Free State spans 129,825 km², approximately 10,6% of the total surface area of South Africa. The surface of

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3318-474: The existence of gold deposits. In 1886, gold was found in the Witwatersrand region. Scientific studies show that the "Golden Arc", which stretches from Johannesburg to Welkom , used to be a massive inland lake, and silt and gold deposits from alluvial gold settled in the area that formed the found gold. The first discovery of gold in the region was made in 1852 on the Pardekraal farm, Krugersdorp , in

3397-658: The farm Langlaagte were made in July 1886, either through accident or systematic prospecting. This was a British attempt to give credit for the discovery to the Anglo-Saxon sector to justify claiming the Witwatersrand fields as British. This move was one of the factors leading to the Anglo-Boer War of 1899-1902. Harrison declared his claim with the then-government of the South African Republic (ZAR), and

3476-430: The first batch of Witwatersrand gold from Bantjes for £3000. This purchase was the first transaction of the newly formed company, Consolidated Gold Fields of South Africa. News reached the rest of the world, and prospectors from Australia to California began arriving in masses, and settlers arrived in soon-to-be Johannesburg. The entrance of foreigners was going well, but a number of years later, President Paul Kruger of

3555-464: 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

3634-475: 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

3713-675: 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

3792-529: The goldfields is a flat expanse of sandy veld, averaging around 4,500 feet above sea-level, and seeing 15-20 inches of annual rainfall. Prior to the land's exploitation for gold mining, it was predominantly used for agricultural purposes. The following towns are part of the Free State Goldfields: In the 1890s the trader Gustav Furst had a small shop on the farm Zoeten Inval. It was 13 km from where Odendaalrus stands today. Furst showed

3871-445: 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

3950-677: 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

4029-416: 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

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4108-484: The mid 1980s to the early 2010s, mine employment in Matjhabeng fell from 180,000 to 30,000 as the production levels of many mines fell significantly. Local legislators reacted to this decline by pushing for tax incentives and job-creation support in the mining industry. The discovery of the reef led to the establishment of the city of Welkom and the town of Riebeeckstad , while neighbouring towns such as Odendalsrus, Allanridge and Virginia enjoyed prolonged growth. Water

4187-401: 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

4266-415: 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

4345-463: 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

4424-509: 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

4503-685: 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

4582-551: 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 is measurable in human hair. Sulfuric acid also erodes concrete and cement structures, resulting in structural damage to buildings and bridges. The majority of payable reefs in

4661-400: The prospector Archibald Megson a quartzite vein. Megson and his partners Donaldson and Haines sank an adit and found gold. However, it was in insufficient volumes to attract financiers. Donaldson and Haines took samples with them to London on the ship Drummond Castle . On 16 June 1896 the ship went down at Ushant and Furst disappeared from the scene, signaling the end of the initiative. In

4740-410: The reefs proved unrecoverable with the contemporary technology, these miners moved away throughout the late 1890s and the stock exchange was converted to a movie theatre by 1912. In the 1930s, new geophysical prospecting methods determined that deep gold reefs could be discovered. The mines in the Klerksdorp and Potchefstroom areas were started thanks to the success of these new methods, and the area saw

4819-424: The rock around it have been changed a lot by heat and pressure over time, which has made it harder to see how the metal originally got there. The gold particles have been rearranged in various ways, sometimes by being squished and stretched, and sometimes by dissolving and then reforming in a different shape. These changes were largely observed in situ . As a result, the original pattern of how sedimentary distribution

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4898-505: The scarp, overlooking the rest of northern Johannesburg with views up to 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

4977-535: 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

5056-647: 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

5135-468: 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 was first discovered here in 1886. This accounts for approximately 22% of all

5214-421: 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

5293-441: 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

5372-510: 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

5451-426: 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

5530-534: 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

5609-532: 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

5688-419: 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

5767-406: Was formalized into a settlement after people seeking gold settled in the area. Initially, the ZAR did not believe that the gold would last for long and mapped out a small triangular piece of land to cram as many plots onto as possible. This is the reason Johannesburg's central business district streets are so narrow. There is a dispute as to the origin of the name Johannesburg and to whom Johannes ,

5846-489: Was more than a half ounce per ton of processed ore. The Second World War broke out shortly thereafter and prospecting work came to a halt. After the Second World War various mining companies flooded Odendaalsrus and within a year over 50 holes were bored. On 16 April 1946 the great discovery was made on the farm Geduld. With the thirteenth hole he had drilled, a drill operator called "Lucky" Hamilton, struck gold at

5925-762: Was not affected significantly, but the individual gold particles were transformed into authigenic and major gold aggregates. Electron-probe microanalysis detected between 9.9% and 12.4% silver content in gold from the region. The following companies still operate gold mines in the Free State: VMR Harmony Gold Sibanye Stillwater Shaft Sinkers (PTY) Ltd. 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

6004-446: Was produced from these fields in 1951, 17 years after the first borehole had been sunk. Gold-bearing reefs were found only at the pre-Cambrian upper Witwatersrand sediments, where samples revealed nearly double the average grade of ore that was milled at the nearby Witwatersrand gold fields . The discovery of gold in the Free State is considered to be one of the most important events in the economic development of South Africa, along with

6083-548: 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

6162-497: 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

6241-507: Was supplied to the region from the Vaal Dam and new roads and railway lines were laid in order to service it. The following mines were established: Beatrix, Erfdeel-Dankbaarheid, Free State Geduld, Jeanette, Loraine, Oryx, President Brand, President Steyn, St. Helena, Welkom, Western Holdings. Apart from the obvious hollowing out of the rocks below southern Johannesburg, causing unpredictable sinkholes, surface instabilities and earth tremors,

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