Gold mining is the extraction of gold resources by mining. Historically, mining gold from alluvial deposits used manual separation processes, such as gold panning. However, with the expansion of gold mining to ores that are not on the surface, has led to more complex extraction processes such as pit mining and gold cyanidation. In the 20th and 21st centuries, most volume of mining was done by large corporations, however the value of gold has led to millions of small, artisanal miners in many parts of the Global South.
Like all mining, human rights and environmental issues are common issues in the gold mining industry. In smaller mines with less regulation, health and safety risks are much higher.
The exact date that humans first began to mine gold is unknown, but some of the oldest known gold artifacts were found in the Varna Necropolis in Bulgaria. The graves of the necropolis were built between 4700 and 4200 BC, indicating that gold mining could be at least 7000 years old. A group of German and Georgian archaeologists claims the Sakdrisi site in southern Georgia, dating to the 3rd or 4th millennium BC, may be the world's oldest known gold mine.
Bronze Age gold objects are plentiful, especially in Ireland and Spain, and there are several well known possible sources. Romans used hydraulic mining methods, such as hushing and ground sluicing on a large scale to extract gold from extensive alluvial (loose sediment) deposits, such as those at Las Medulas. Mining was under the control of the state but the mines may have been leased to civilian contractors some time later. The gold served as the primary medium of exchange within the empire, and was an important motive in the Roman invasion of Britain by Claudius in the first century AD, although there is only one known Roman gold mine at Dolaucothi in west Wales. Gold was a prime motivation for the campaign in Dacia when the Romans invaded Transylvania in what is now modern Romania in the second century AD. The legions were led by the emperor Trajan, and their exploits are shown on Trajan's Column in Rome and the several reproductions of the column elsewhere (such as the Victoria and Albert Museum in London). Under the Eastern Roman Empire Emperor Justinian's rule, gold was mined in the Balkans, Anatolia, Armenia, Egypt, and Nubia.
In the area of the Kolar Gold Fields in Bangarpet Taluk, Kolar District of Karnataka state, India, gold was first mined prior to the 2nd and 3rd century AD by digging small pits. (Golden objects found in Harappa and Mohenjo-daro have been traced to Kolar through the analysis of impurities — the impurities include 11% silver concentration, found only in KGF ore.) The Champion reef at the Kolar gold fields was mined to a depth of 50 metres (160 ft) during the Gupta period in the fifth century AD. During the Chola period in the 9th and 10th century AD, the scale of the operation grew. The metal continued to be mined by the eleventh century kings of South India, the Vijayanagara Empire from 1336 to 1560, and later by Tipu Sultan, the king of Mysore state and the British. It is estimated that the total gold production in Karnataka to date is 1000 tons.
The mining of the Hungarian deposit (present-day Slovakia) primarily around Kremnica was the largest of the Medieval period in Europe.
During the 19th century, numerous gold rushes in remote regions around the globe caused large migrations of miners, such as the California Gold Rush of 1849, the Victorian Gold Rush, and the Klondike Gold Rush. The discovery of gold in the Witwatersrand led to the Second Boer War and ultimately the founding of South Africa.
The Carlin Trend of Nevada, U.S., was discovered in 1961. Official estimates indicate that total world gold production since the beginning of civilization has been around 6,352,216,000 troy ounces (197,576.0 t) and total gold production in Nevada is 1.1% of that, ranking Nevada as one of the Earth's primary gold producing regions.
As of 2020, the world's largest gold producer was China with 368.3 tonnes of gold mined in that year. The second-largest producer of gold was Russia where 331.1 tonnes was mined in the same year, followed by Australia with 327.8 tonnes.
Despite the decreasing gold content of ores, the production is increasing. This can be achieved with industrial installations, and new process, like hydrometallurgy.
Main article: Placer mining
Placer mining is the technique by which gold that has accumulated in a placer deposit is extracted. Placer deposits are composed of relatively loose material that makes tunnelling difficult, and so most means of extracting it involve the use of water or dredging.
Gold panning, or simply panning, is a form of placer mining and traditional mining that extracts gold from a placer deposit using a pan. The process is one of the simplest ways to extract gold, and is popular with geology enthusiasts especially because of its low cost and relative simplicity.rocker box or large extractors, such as those used at the Super Pit gold mine, in Kalgoorlie, Western Australia, which has led to panning being largely replaced in the commercial market.
Using a sluice box to extract gold from placer deposits has long been a very common practice in prospecting and small-scale mining. A sluice box is essentially a man made channel with riffles set in the bottom. The riffles are designed to create dead zones in the current to allow gold to drop out of suspension. The box is placed in the stream to channel water flow. Gold-bearing material is placed at the top of the box. The material is carried by the current through the volt where gold and other dense material settles out behind the riffles. Less dense material flows out of the box as tailings.
Larger commercial placer mining operations employ screening plants, or trommels, to remove the larger alluvial materials such as boulders and gravel, before concentrating the remainder in a sluice box or jig plant. These operations typically include diesel powered, earth moving equipment, including excavators, bulldozers, wheel loaders, and rock trucks.
Main article: Gold dredge
Although this method has largely been replaced by modern methods, some dredging is done by small-scale miners using suction dredges. These are small machines that float on the water and are usually operated by one or two people. A suction dredge consists of a sluice box supported by pontoons, attached to a suction hose which is controlled by a miner working beneath the water.
State dredging permits in many of the United States gold dredging areas specify a seasonal time period and area closures to avoid conflicts between dredgers and the spawning time of fish populations. Some states, such as Montana, require an extensive permitting procedure, including permits from the U.S. Corps of Engineers, the Montana Department of Environmental Quality, and the local county water quality boards.
Some large suction dredges (100 horsepower (75 kW) & 250 mm (10 in)) are used in commercial production throughout the world. Small suction dredges are much more efficient at extracting smaller gold than the old bucket line. This has improved the chances of finding gold. Smaller dredges with 50-to-100-millimetre (2 to 4 in) suction tubes are used to sample areas behind boulders and along potential pay streaks, until "colour" (gold) appears.
Other larger scale dredging operations take place on exposed river gravel bars at seasonal low water. These operations typically use a land based excavator to feed a gravel screening plant and sluice box floating in a temporary pond. The pond is excavated in the gravel bar and filled from the natural water table. "Pay" gravel is excavated from the front face of the pond and processed through the floating plant, with the gold trapped in the onboard sluice box and tailings stacked behind the plant, steadily filling in the back of the pond as the operation moves forward. This type of gold mining is characterized by its low cost, as each rock is moved only once. It also has low environmental impact, as no stripping of vegetation or overburden is necessary, and all process water is fully recycled. Such operations are typical on New Zealand's South Island and in the Klondike region of Canada.
Also called a cradle, a rocker box uses riffles located in a high-walled box to trap gold in a similar manner to the sluice box. A rocker box uses less water than a sluice box and is well suited for areas where water is limited. A rocking motion provides the water movement needed for the gravity separation of gold in placer material.
Hard rock gold mining extracts gold encased in rock, rather than fragments in loose sediment, and produces most of the world's gold. Sometimes open-pit mining is used, such as at the Fort Knox Mine in central Alaska. Barrick Gold Corporation has one of the largest open-pit gold mines in North America located on its Goldstrike mine property in north eastern Nevada. Other gold mines use underground mining, where the ore is extracted through tunnels or shafts. South Africa has the world's deepest hard rock gold mine up to 3,900 metres (12,800 ft) underground. At such depths, the heat is unbearable for humans, and air conditioning is required for the safety of the workers. The first such mine to receive air conditioning was Robinson Deep, at that time the deepest mine in the world for any mineral.
Gold is also produced by mining in which it is not the principal product. Large copper mines, such as the Bingham Canyon mine in Utah, often recover considerable amounts of gold and other metals along with copper. Some sand and gravel pits, such as those around Denver, Colorado, may recover small amounts of gold in their wash operations. The largest producing gold mine in the world, the Grasberg mine in Papua, Indonesia, is primarily a copper mine.
A modest amount of precious metal is a by-product of sodium production.
Gold extraction refers to the processes required to extract gold from its ores. This may require a combination of comminution, mineral processing, hydrometallurgical, and pyrometallurgical processes to be performed on the ore.
Gold mining from alluvium ores was once achieved by techniques associated with placer mining such as simple gold panning and sluicing, resulting in direct recovery of small gold nuggets and flakes. Placer mining techniques since the mid to late 20th century have generally only been the practice of artisan miners. Hydraulic mining was used widely in the Californian gold rush, and involved breaking down alluvial deposits with high-pressure jets of water. Hard rock ores have formed the basis of the majority of commercial gold recovery operations since the middle of the 20th century where open pit and or sub-surface mining techniques are used.Once the ore is mined it can be treated as a whole ore using a dump leaching or heap leaching processes. This is typical of low-grade, oxide deposits. Normally, the ore is crushed and agglomerated prior to heap leaching. High grade ores and ores resistant to cyanide leaching at coarse particle sizes, require further processing in order to recover the gold values. The processing techniques can include grinding, concentration, roasting, and pressure oxidation prior to cyanidation.
Main article: Gold cyanidation
Cyanide extraction of gold may be used in areas where fine gold-bearing rocks are found. Sodium cyanide solution is mixed with finely ground rock that is proven to contain gold or silver, and is then separated from the ground rock as gold cyanide or silver cyanide solution. Zinc is added to precipitate out residual zinc as well as the silver and gold metals. The zinc is removed with sulfuric acid, leaving a silver or gold sludge that is generally smelted into an ingot then shipped to a metals refinery for final processing into 99.9999% pure metals.
Advancements in the 1970s have seen activated carbon used in extracting gold from the leach solution. The gold is absorbed into the porous matrix of the carbon. Activated carbon has so much internal surface area, that fifteen grams of it has the equivalent surface area of the Melbourne Cricket Ground (18,100 square metres (195,000 sq ft)). The gold can be removed from the carbon by using a strong solution of caustic soda and cyanide, a process known as elution. Gold is then plated out onto steel wool through electrowinning. Gold specific resins can also be used in place of activated carbon, or where selective separation of gold from copper or other dissolved metals is required.
The technique using dissolution with alkaline cyanide has been highly developed over recent years. It is particularly appropriate for low grade gold and silver ore processing (e.g. less than 5 ppm gold) but its use is not restricted to such ores. There are many environmental hazards associated with this extraction method, largely due to the high acute toxicity of the cyanide compounds involved. A major example of this hazard was demonstrated in the 2000 Baia Mare cyanide spill, when a break in holding pond dam at a mine waste reprocessing facility near Baia Mare in northern Romania released approximately 100,000 cubic metres (3,500,000 cu ft) of waste water contaminated with heavy metal sludge and up to 120 long tons (122 t) of cyanide into the Tisza River. As a consequence, most countries now have strict regulations for cyanide in plant discharges, and plants today include a specific cyanide-destruction step before discharging their tailings to a storage facility.
Historically, mercury was used extensively in placer gold mining in order to form mercury-gold amalgam with smaller gold particles, and thereby increase the gold recovery rates. Large-scale use of mercury stopped in the 1960s. However, mercury is still used in artisanal and small-scale gold mining (ASGM), often clandestine, gold prospecting.
While most of the gold is produced by major corporations, millions of people work independently in smaller, artisan operations, in some cases illegally. Artisanal mining refers to workers who use rudimentary methods to extract and process minerals and metals. Socially and economically marginalized communities mine to escape extreme poverty, unemployment and landlessness.
In Ghana, the galamseys are estimated to number 20,000 to 50,000. In neighboring francophone countries, such workers are called orpailleurs. In Brazil, such workers are called garimpeiros. The word garimpeiros is also used in Suriname and French Guiana, because many illegal gold prospectors are from Brazil.
There are an estimated 10 to 15 million artisanal and small-scale gold miners worldwide. 4.5 million of them are women. Miner's risks include persecution by government, mine shaft collapses, and toxic poisoning from unsafe chemicals used in processing.
The high risk of such ventures was seen in the collapse of an illegal mine at Dompoase, Ashanti Region, Ghana, on 12 November 2009, when 18 workers were killed, including 13 women. Many women work at such mines as porters. It was the worst mining disaster in Ghanaian history.
In order to maximize gold extraction, mercury is often used to amalgamate with the metal. The gold is produced by boiling away the mercury from the amalgam. Mercury is effective in extracting very small gold particles, but the process is hazardous due to the toxicity of mercury vapour.
Especially after the Minamata Convention has been ratified, there are initiatives to replace or reduce the use and emissions of mercury in the extraction of gold.
There are an estimated 600,000 children working in illegal artisanal gold mines.
For hours, children dig, crush, mill, and haul ore in the hot sun. Children stand in water, digging sand and silt from riverbeds. They carry heavy bags of mud with their heads to designated sieving and washing sites. Children suffer the effects of noise, vibration, overexertion, poor ventilation, and exhaustion. Children's lives are put at risk by rock fall, explosions, the collapsing of tunnels and mine shafts, falling into open shafts and pits, and breathing air polluted by dust and toxic gas. Having immune systems that are not fully developed makes children especially vulnerable to dust and chemical exposure. Injuries include serious respiratory conditions, constant headaches, hearing and sight problems, joint disorders and various dermatological, muscular and orthopaedic ailments and wounds.
There are different methods by which gold mining companies are ranked. One is by their annual production. Another is by their cash cost per ounce, that is, how much money it costs them to mine the gold. Since gold prices are the same everywhere, companies with lower costs per ounce make more profit. The most common method lists by market capitalization which considers the total value of capital holdings by that company. Also considered when comparing companies is their market capitalization per ounce of gold equivalent (sometimes abbreviated MV-GEO, EVO if the enterprise value is used) which takes the market value and total reserves and resources for each company as well as the price of gold into consideration. The figures for each company can be used to determine the value the stock market gives to each company's reserves on an ounce to ounce basis.
If the calculation is to exclude financial assets the enterprise value is used instead of market capitalization. EVO = Enterprise Value/Ounce (gold equivalent) = Enterprise Value divided by resources. The enterprise value is the difference between a company's market capitalization (product of the number of company shares and listed stock price) and its cash, investments less debt (amortization). Three of the 10 largest companies by market cap that engage in gold mining, Fresnillo, Buenaventura and Freeport-McMoran (copper/molybdenum) are not included in the first list because they are minor gold producers/most of their revenue comes from a metal other than gold (Fresnillo and Buenaventura rely more on silver, in some lists silver production is treated as gold production, converted to gold equivalent using the gold to silver price ratio; McMoran produced 32.375 tonnes of gold in 2013 (up 32% after falling by 31% in 2012) but gold accounted for only 8% of revenue (down from 10%).
World gold production in 2008 declined by 50 tonnes despite a strong showing in market price. Total production cash costs were up 4.1% industrywide in the third quarter of 2010 to US$585 per ounce of gold mined. The lower price of gold in 2013 is expected to impact gold production in the coming years; Barrick Gold is slowing construction at one of its largest gold projects Pascua Lama (18 m ounces of gold, 676 m ounces of silver) while in Australia mines are being shuttered by companies in an attempt to curb costs.
In 2016, five of the world's 10 largest producing regions recorded growth in output, they are: China (450 tons +5), Russia (250 +8 tons), USA (209 tons +9), Canada (170 tons +10), Mexico (125 tons +5) and Indonesia (100 tons +25); In 2015 only Australia, Peru, Mexico, Uzbekistan and Indonesia produced more than the year before.In 2013, nine of the world's 14 major producing regions recorded growth in output, they are: Australia, Brazil, Canada, Chile, China, Indonesia, Mexico, Papua New Guinea and Russia; In 2012 only Canada, China, Ghana, Mexico, Peru and Russia produced more than the year before. In 2013, the world's five leading gold producers, in order of total production were China (420 tons +17), Australia (250 tons +5), US (227 tons -8), Russia (218 tons +2), South Africa (145 tons -15). In 2011, all of the world's 14 major producing countries recorded growth in output except for Peru, Indonesia and Brazil (global primary production up 5.5%); list was led by China (355 tons), Australia (270 tons), USA (237 tons), Russia (200 tons), South Africa (190 tons). South Africa's drop in output (down 10% from 2010 to 2012) is not a result of resource depletion but rather high production costs.
|Part of a series on|
Gold mining can significantly alter the natural environment. For example, gold mining activities in tropical forests are increasingly causing deforestation along rivers and in remote areas rich in biodiversity. Other gold mining impacts, particularly in aquatic systems with residual cyanide or mercury (used in the recovery of gold from ore), can be highly toxic to people and wildlife even at relatively low concentrations.
However, there are clear moves by many in the non-governmental organization community to encourage more environmentally friendly and sustainable business practices in the mining industry. The primary way this is being achieved is via the promotion of so-called 'clean' or 'ethical' gold. The aim is to get all end users/retailers of gold to adhere to set of principles that encourage sustainable mining. Campaigns such as 'No Dirty Gold' are driving the message that the mining industry is harmful (for the reasons noted above), and so must be cleaned up. Also, NGOs are urging the industry and consumers to buy sustainably produced gold.
Human Rights Watch produced a report in 2015 that outlined some of challenges faced globally. The report notes that
Thousands of children in the Philippines risk their lives every day mining gold. Children work in unstable 25-meter-deep pits that could collapse at any moment. They mine gold underwater, along the shore, or in rivers, with oxygen tubes in their mouths. They also process gold with mercury, a toxic metal, risking irreversible health damage from mercury poisoning.
Along with many other reports and articles, this has had the effect of spurring retailers and industry bodies to move toward sustainable gold. Indeed, the World Jewellery Confederation insists that it does all it can to "Deliver a Sustainable and Responsible Jewellery Industry".
Fairtrade and Fairmined dual certification for gold was launched across the United Kingdom on 14 February 2011, a joint scheme between The Fairtrade Foundation and The Association for Responsible Mining. The Fairmined mark ensures that the gold has been extracted in a fair and responsible manner.
The Fairtrade Standard for Gold and Associated Precious Metals for Artisanal and Small-Scale Mining was adopted in 2013, and the Fairtrade Foundation reports on a number of technical uses and responsible suppliers of Fairtrade Certified Gold. The Fairtrade Foundation launched a free course aimed at sales staff responsible for selling gold jewellery in 2017.
Within the United States, the Mine Safety and Health Administration (MSHA) has set noise exposure limits for those within the mining industry. These noise exposure guidelines state that the "Permissible Exposure Level" (PEL) of noise is 90 dBA as an 8-hour time-weighted-average. Mine workers exposed to a time-weighted average of at least 85 dBA fall into the "Action Level" in which workers with exposures exceeding that level are placed into a hearing conservation program. The National Institute for Occupational Safety and Health (NIOSH) has examined noise exposures of gold mine workers. One study found that gold mine workers noise exposures ranged from 165 to 261% of the MSHA PEL. Haul truck operators, load-haul-dump operators, single boom drill operators, and roof bolter operators represented the occupations with the highest noise exposures within gold mines.
Gold mining by country:
((cite journal)): CS1 maint: multiple names: authors list (link)