Argyle diamond mine
Encyclopedia
The Argyle Diamond Mine is a diamond mine
located in the East Kimberley region in the remote north of Western Australia
. Argyle is the largest diamond producer in the world by volume, although due to the low proportion of gem-quality diamonds, is not the leader by value. It is the only known significant source of pink diamonds, producing over 90% of the world's supply. It additionally provides a large proportion of other naturally coloured diamonds, including champagne, cognac and rare blue diamonds. Argyle is currently transitioning from an open pit mine to an underground mine.
The Argyle diamond mine is also notable for being the first successful commercial diamond mine exploiting a volcanic pipe
of lamproite
, rather than the more usual kimberlite
pipe; much earlier attempts to mine diamonds from a lamproite pipe in Arkansas
, USA
were commercially unsuccessful. The Argyle mine is owned by the Rio Tinto Group
, a diversified mining company which also owns the Diavik Diamond Mine
in Canada
and the Murowa Diamond Mine
in Zimbabwe
.
An underground block cave mine is currently under development, and is likely to extend Argyle's diamond production until 2018.
region
in the far northeast of the Australia
n state of Western Australia
. It is located to the southwest of Lake Argyle in the Matsu Ranges, about 550 kilometres (341.8 mi) southwest of Darwin
. Because it is 185 kilometres (115 mi) kilometres by road from the nearest settlement (Kununurra
), a complete residential camp has been constructed on site. Most of the 520 workers commute from Perth
, over 2000 kilometres (1,242.7 mi) away, for alternating two week shifts at the mine. The mine has encouraged local employment and has a large number of indigenous local people working within the mine.
mining operations) not located on a kimberlite
pipe. The pipe is named "AK-1", although it is commonly simply called the "Argyle pipe".
The volcanic pipe is a diatreme
, composed of olivine
lamproite
, present as tuff and lava. Peripheral volcanic facies suggest the lamproite eruption formed a maar
. At the margins of the volcanic pipe the lamproite is mixed with a volcanic breccia
containing shattered wall rock fragments mixed and milled by the eruption. Minerals in the marginal facies include zeolite
minerals, mica
s, kaolinite
and clays, typical of post-eruption hydrothermal circulation.
Diamonds are found within the intact core of the volcanic pipe, as well as within some of the marginal breccia facies and maar facies. However, some diamonds are considered to have been resorbed during the post-eruption cooling of the pipe and converted to graphite
.
The diatreme pipe formed by explosive eruption of the lamproite magma through a zone of weakness in the continental crust
.
The diamonds found at the Argyle pipe have been dated to about 1.58 billion years of age, while the volcano which created the pipe is aged between 1.1 and 1.2 billion years old. This represents a relatively short period during which diamond formation could have taken place (around 400 million years), which may explain the small average size and unusual physical characteristics of Argyle diamonds. Diamonds found in the Argyle pipe are predominantly eclogitic
, meaning that the carbon is of organic origin (see Natural history of diamonds).
In addition to the pipe itself, there are a number of semi-permanent streams that have eroded away portions of the pipe and created significant alluvial deposits of diamonds. These deposits are also actively mined.
Most of Argyle's gem quality production is in brown diamonds. These diamonds are usually difficult to sell, although Rio Tinto has seen some success in a decade-long marketing campaign to promote brown diamonds as champagne and cognac toned. In contrast, the company has no problems selling diamonds in pink, purple and red tones, which are very rare and in high demand, therefore commanding premium prices. The pink diamonds are processed and sold as polished diamonds by a specialised team based in Perth to customers world wide.
The mine has ore processing and diamond sorting facilities on site. Once diamonds are removed from the ore and acid washed, they are sorted and shipped to Perth for further sorting and sale. A significant quantity of diamonds are cut in India
, where low costs of labor allow small diamonds to be cut for a profit; this is especially relevant to the Argyle mine, which on average produces smaller rough diamonds than other mines do.
), and have low levels of nitrogen
impurities, their colour resulting instead from structural defects of the crystal lattice. Argyle diamonds tend to fluoresce
blue or dull green under ultraviolet light, and blue-white under X-ray
radiation. The most common inclusion is unconverted graphite
, followed by crystalline inclusions of orange garnet
, pyroxene
, and olivine
.
The invitation-only tender event is a highlight of the coloured diamond industry's calendar. Access to the collector's edition catalogue and website access in itself is highly sought after.
In March 2009, Argyle announced their first ever tender of rare blue diamonds. The "Once in a Blue Moon" collection was sourced over several years, and comprised a range of precious blue and violet diamonds, which weighed in total 287 carats (57.4 g).
In 1995, drilling samples taken from about 300 metres below the floor of the pit indicated the possible presence of about 100 million tons of ore, with an estimated grade of 3.7 carats (740 mg) per ton. In the mid-1990s part of the West Wall of the open pit mine, containing 25 million tonnes of waste rock, began to collapse. In 1998, the decision was made to remove or "cut back" the unstable part of the West Wall
which freed up further economic ore in the south part of the open pit.
An exploration decline was constructed at a cost of A$
70 million to evaluate the economics of mining diamond
s from the diamoniferous pipes below the floor of the open pit; these reserves would be mined underground (via block caving), rather than the open pit method currently used. In late-2005 Rio Tinto Ltd concluded that the operation was economically feasible. Pre-production construction of the underground mine commenced in early to mid 2006
and US$170 per carat (US$850/g) at the Ekati mine
, both in Canada.http://www.goldismoney.info/forums/showpost.php?p=6226&postcount=3 However, Argyle has two to four times the concentration of diamonds (ore grade) of these mines. This makes extraction economically feasible, as mine costs are mostly related to the amount of ore processed, not the amount of diamond extracted.
was given the go ahead to a future expansion project, moving it from an open pit to an underground mine. This plan was postponed; in September 2010 Rio Tinto announced fresh plans to develop an underground mine beneath the existing pit, increasing annual production to 9 million tonnes of ore.
The project is predominantly an underground construction requiring high quality development and engineering excellence. The Block Cave is expected to operate until 2018 using the latest in mining technology, including Sandvik
's auto mining technology. The project is due to be completed by 2013, two years later than first planned, after diamond prices slumped.
. However, no source volcanic pipe deposit was apparent. A systematic search of Western Australia for the source of these diamonds began in 1969. Tanganyika Holdings had employed Maureen Muggeridge
and formed a joint venture
called Ashton Joint Venture, after minerals which indicated the presence of diamonds were found in 1976. In 1979, Muggeridge discovered diamond samples in the floodplain
of a small creek that flowed in Lake Argyle. She soon traced the source of the diamonds to the headwaters of Smoke Creek. On 2 October 1979, the Argyle pipe was discovered.
Over the following three years, the deposit was assessed for economic viability, and in 1983 the decision was made to commence mining operations. Alluvial mining operations commenced immediately, while the open pit mine was constructed over a period of 18 months at a cost of A$450 million. The mine was commissioned in December 1985.
Several of this article's references contain excellent maps and photographs of the mine and examples of diamonds produced there, which cannot be placed in this article due to copyright limitations. The reader is especially directed to Shigley, Chapman, and Ellison's article, "Discovery and Mining of the Argyle Diamond Deposit, Australia" (Gems & Gemology, Spring 2001).
Diamond Mine
Diamond Mine is the second album by Blue Rodeo, released in 1989. It includes several instrumental interludes by Bob Wiseman between songs.-Track listing:All songs by Greg Keelor and Jim Cuddy.#"Swells"#"God and Country" – 3:32#"How Long" – 3:59...
located in the East Kimberley region in the remote north of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
. Argyle is the largest diamond producer in the world by volume, although due to the low proportion of gem-quality diamonds, is not the leader by value. It is the only known significant source of pink diamonds, producing over 90% of the world's supply. It additionally provides a large proportion of other naturally coloured diamonds, including champagne, cognac and rare blue diamonds. Argyle is currently transitioning from an open pit mine to an underground mine.
The Argyle diamond mine is also notable for being the first successful commercial diamond mine exploiting a volcanic pipe
Volcanic pipe
Volcanic pipes are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes. They are considered to be a type of diatreme. Volcanic pipes are composed of a deep, narrow cone of solidified magma , and are usually largely composed of one of two...
of lamproite
Lamproite
Lamproites are ultrapotassic mantle-derived volcanic and subvolcanic rocks. They have low CaO, Al2O3, Na2O, high K2O/Al2O3, a relatively high MgO content and extreme enrichment in incompatible elements....
, rather than the more usual kimberlite
Kimberlite
Kimberlite is a type of potassic volcanic rock best known for sometimes containing diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond in 1871 spawned a diamond rush, eventually creating the Big Hole....
pipe; much earlier attempts to mine diamonds from a lamproite pipe in Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...
, USA
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
were commercially unsuccessful. The Argyle mine is owned by the Rio Tinto Group
Rio Tinto Group
The Rio Tinto Group is a diversified, British-Australian, multinational mining and resources group with headquarters in London and Melbourne. The company was founded in 1873, when a multinational consortium of investors purchased a mine complex on the Rio Tinto river, in Huelva, Spain from the...
, a diversified mining company which also owns the Diavik Diamond Mine
Diavik Diamond Mine
The Diavik Diamond Mine is a diamond mine in the North Slave Region of the Northwest Territories, Canada, about north of Yellowknife.It has become an important part of the regional economy, employing 700, grossing C$100 million in sales, and producing 8 million carats of diamonds annually...
in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
and the Murowa Diamond Mine
Murowa diamond mine
The Murowa diamond mine is a diamond mine located in Mazvihwa, south central Zimbabwe, about 40 kilometres from the asbestos mining town of Zvishavane in the Midlands province. The mine is majority owned and operated by the Rio Tinto Group, which also owns the Argyle diamond mine in Australia and...
in Zimbabwe
Zimbabwe
Zimbabwe is a landlocked country located in the southern part of the African continent, between the Zambezi and Limpopo rivers. It is bordered by South Africa to the south, Botswana to the southwest, Zambia and a tip of Namibia to the northwest and Mozambique to the east. Zimbabwe has three...
.
Description
The mine covers about 450,000 square metres (110 acres), stretching in a mostly linear shape about 1600 metres (5,200 ft) long and 150 to 600 metres (500 to 2,000 ft) wide. The mine is of open pit construction, and reaches about 600 metres (1,900 ft) deep at its deepest point. The open cut is nearing the end of its life and is due to close in 2010.An underground block cave mine is currently under development, and is likely to extend Argyle's diamond production until 2018.
Location
The Argyle diamond mine is located in the KimberleyKimberley region of Western Australia
The Kimberley is one of the nine regions of Western Australia. It is located in the northern part of Western Australia, bordered on the west by the Indian Ocean, on the north by the Timor Sea, on the south by the Great Sandy and Tanami Deserts, and on the east by the Northern Territory.The region...
region
Regions of Western Australia
Regionalisations of Western Australia are systems by which Western Australia is divided into distinct geographic regions. The most commonly known regionalisation is the governmental division of the state into regions for economic development purposes, of which there are nine.Other regionalisations...
in the far northeast of the Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n state of Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
. It is located to the southwest of Lake Argyle in the Matsu Ranges, about 550 kilometres (341.8 mi) southwest of Darwin
Darwin, Northern Territory
Darwin is the capital city of the Northern Territory, Australia. Situated on the Timor Sea, Darwin has a population of 127,500, making it by far the largest and most populated city in the sparsely populated Northern Territory, but the least populous of all Australia's capital cities...
. Because it is 185 kilometres (115 mi) kilometres by road from the nearest settlement (Kununurra
Kununurra, Western Australia
Kununurra is a town in far northern Western Australia located at the eastern extremity of the Kimberley Region approximately from the border with the Northern Territory. Kununurra was initiated to service the Ord River Irrigation scheme....
), a complete residential camp has been constructed on site. Most of the 520 workers commute from Perth
Perth, Western Australia
Perth is the capital and largest city of the Australian state of Western Australia and the fourth most populous city in Australia. The Perth metropolitan area has an estimated population of almost 1,700,000....
, over 2000 kilometres (1,242.7 mi) away, for alternating two week shifts at the mine. The mine has encouraged local employment and has a large number of indigenous local people working within the mine.
Geology
The mine is the first successful commercial diamond mine (except alluvialAlluvium
Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...
mining operations) not located on a kimberlite
Kimberlite
Kimberlite is a type of potassic volcanic rock best known for sometimes containing diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an diamond in 1871 spawned a diamond rush, eventually creating the Big Hole....
pipe. The pipe is named "AK-1", although it is commonly simply called the "Argyle pipe".
The volcanic pipe is a diatreme
Diatreme
A diatreme is a breccia-filled volcanic pipe that was formed by a gaseous explosion. Diatremes often breach the surface and produce a tuff cone, a filled relatively shallow crater known as a maar, or other volcanic pipes.- Word origin :...
, composed of olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
lamproite
Lamproite
Lamproites are ultrapotassic mantle-derived volcanic and subvolcanic rocks. They have low CaO, Al2O3, Na2O, high K2O/Al2O3, a relatively high MgO content and extreme enrichment in incompatible elements....
, present as tuff and lava. Peripheral volcanic facies suggest the lamproite eruption formed a maar
Maar
A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake. The name comes from the local Moselle...
. At the margins of the volcanic pipe the lamproite is mixed with a volcanic breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
containing shattered wall rock fragments mixed and milled by the eruption. Minerals in the marginal facies include zeolite
Zeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...
minerals, mica
Mica
The mica group of sheet silicate minerals includes several closely related materials having highly perfect basal cleavage. All are monoclinic, with a tendency towards pseudohexagonal crystals, and are similar in chemical composition...
s, kaolinite
Kaolinite
Kaolinite is a clay mineral, part of the group of industrial minerals, with the chemical composition Al2Si2O54. It is a layered silicate mineral, with one tetrahedral sheet linked through oxygen atoms to one octahedral sheet of alumina octahedra...
and clays, typical of post-eruption hydrothermal circulation.
Diamonds are found within the intact core of the volcanic pipe, as well as within some of the marginal breccia facies and maar facies. However, some diamonds are considered to have been resorbed during the post-eruption cooling of the pipe and converted to graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
.
The diatreme pipe formed by explosive eruption of the lamproite magma through a zone of weakness in the continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
.
The diamonds found at the Argyle pipe have been dated to about 1.58 billion years of age, while the volcano which created the pipe is aged between 1.1 and 1.2 billion years old. This represents a relatively short period during which diamond formation could have taken place (around 400 million years), which may explain the small average size and unusual physical characteristics of Argyle diamonds. Diamonds found in the Argyle pipe are predominantly eclogitic
Eclogite
Eclogite is a mafic metamorphic rock. Eclogite is of special interest for at least two reasons. First, it forms at pressures greater than those typical of the crust of the Earth...
, meaning that the carbon is of organic origin (see Natural history of diamonds).
In addition to the pipe itself, there are a number of semi-permanent streams that have eroded away portions of the pipe and created significant alluvial deposits of diamonds. These deposits are also actively mined.
Production
The Argyle diamond mine leads the world in volume production of diamond, averaging annual production of 35 million carats (7,000 kg), or about one third of global production of natural diamonds. Production peaked in 1994, when 42 million carats (8,400 kg) were produced. Of this quantity only 5% is considered gem-quality, with the rest being either near-gem quality or industrial grade; this is somewhat below world averages of about 20% of mined diamonds qualifying as gem-grade. (Author Janine Roberts contends that the "near-gem" quality rating is subjective and misleading because these diamonds can be cut into gems if desired.) Since operations began in 1983, Argyle's open pit mine has produced over 750000000 carats (150,000 kg) of rough diamonds.Most of Argyle's gem quality production is in brown diamonds. These diamonds are usually difficult to sell, although Rio Tinto has seen some success in a decade-long marketing campaign to promote brown diamonds as champagne and cognac toned. In contrast, the company has no problems selling diamonds in pink, purple and red tones, which are very rare and in high demand, therefore commanding premium prices. The pink diamonds are processed and sold as polished diamonds by a specialised team based in Perth to customers world wide.
The mine has ore processing and diamond sorting facilities on site. Once diamonds are removed from the ore and acid washed, they are sorted and shipped to Perth for further sorting and sale. A significant quantity of diamonds are cut in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, where low costs of labor allow small diamonds to be cut for a profit; this is especially relevant to the Argyle mine, which on average produces smaller rough diamonds than other mines do.
Diamond characteristics
The diamonds produced at the Argyle diamond mine are of an average low quality. Only 5% of mined diamonds are of gem quality, compared to a worldwide average of 20%; of the remaining 95%, they are about evenly split between classifications of "near gem quality" and industrial grade. 80% of Argyle diamonds are brown, followed by 16% yellow, 2% white, 2% grey, and less than 1% pink and green. Despite the low production volume of pink and red diamonds, the Argyle mine is the only reliable source in the world, producing 90 to 95% of all pink and red diamonds. Most Argyle diamonds are classified as type 1a (see material properties of diamondMaterial properties of diamond
Diamond is the allotrope of carbon in which the carbon atoms are arranged in the specific type of cubic lattice called diamond cubic. Diamond is an optically isotropic crystal that is transparent to opaque. Owing to its strong covalent bonding, diamond is the hardest naturally occurring material...
), and have low levels of nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
impurities, their colour resulting instead from structural defects of the crystal lattice. Argyle diamonds tend to fluoresce
Fluorescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...
blue or dull green under ultraviolet light, and blue-white under X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
radiation. The most common inclusion is unconverted graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
, followed by crystalline inclusions of orange garnet
Garnet
The garnet group includes a group of minerals that have been used since the Bronze Age as gemstones and abrasives. The name "garnet" may come from either the Middle English word gernet meaning 'dark red', or the Latin granatus , possibly a reference to the Punica granatum , a plant with red seeds...
, pyroxene
Pyroxene
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...
, and olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
.
Annual Diamond Tender
Each year, a small collection of the best pink diamonds are offered in an exclusive sale known as the Argyle Pink Diamond Tender. For every 1000000 carats (200 kg) of rough pink diamonds produced by the mine, only 1 carat (0.2 g) polished will be offered for sale at the tender.The invitation-only tender event is a highlight of the coloured diamond industry's calendar. Access to the collector's edition catalogue and website access in itself is highly sought after.
In March 2009, Argyle announced their first ever tender of rare blue diamonds. The "Once in a Blue Moon" collection was sourced over several years, and comprised a range of precious blue and violet diamonds, which weighed in total 287 carats (57.4 g).
Reserves
Initial proven reserves of the Argyle mine were 61 million tonnes of ore, with an average ore grade of 6.8 carats (1.36 g) per or tonne, about 400 million carats (80,000 kg). Further estimated reserves of 14 million tonnes of ore, at a grade of 6.1 carats (1.22 g) per tonne (85 million carats, 17,000 kg), also existed. As of 2001, reserves and resources in the open-pit mined area contain 220 million tonnes of 2.5 to 3.0 carat (500 to 600 mg) per tonne graded ore, sufficient to sustain current production rates until 2007. The ore grades at the Argyle mine are unusually high, with most commercial diamond mines averaging grades of 0.3 to 1.0 carats (60 to 200 mg) per metric ton. Alluvial deposits of diamonds are believed to have been exhausted.In 1995, drilling samples taken from about 300 metres below the floor of the pit indicated the possible presence of about 100 million tons of ore, with an estimated grade of 3.7 carats (740 mg) per ton. In the mid-1990s part of the West Wall of the open pit mine, containing 25 million tonnes of waste rock, began to collapse. In 1998, the decision was made to remove or "cut back" the unstable part of the West Wall
which freed up further economic ore in the south part of the open pit.
An exploration decline was constructed at a cost of A$
Australian dollar
The Australian dollar is the currency of the Commonwealth of Australia, including Christmas Island, Cocos Islands, and Norfolk Island, as well as the independent Pacific Island states of Kiribati, Nauru and Tuvalu...
70 million to evaluate the economics of mining diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
s from the diamoniferous pipes below the floor of the open pit; these reserves would be mined underground (via block caving), rather than the open pit method currently used. In late-2005 Rio Tinto Ltd concluded that the operation was economically feasible. Pre-production construction of the underground mine commenced in early to mid 2006
Economics
The Argyle diamond mine is economically feasible because its large reserves and high grade ore offsets a low average diamond value. The estimated value of Argyle diamond production is only US$7 per carat (US$35/g); this compares to values of 70 USD per carat ($350/g) for diamonds produced at the Diavik mineDiavik Diamond Mine
The Diavik Diamond Mine is a diamond mine in the North Slave Region of the Northwest Territories, Canada, about north of Yellowknife.It has become an important part of the regional economy, employing 700, grossing C$100 million in sales, and producing 8 million carats of diamonds annually...
and US$170 per carat (US$850/g) at the Ekati mine
Ekati Diamond Mine
The EKATI Diamond Mine is Canada's first surface and underground diamond mine. It is located north-east of Yellowknife, Northwest Territories, and about south of the Arctic circle, near Lac de Gras. EKATI is a joint venture between BHP Billiton Canada Inc...
, both in Canada.http://www.goldismoney.info/forums/showpost.php?p=6226&postcount=3 However, Argyle has two to four times the concentration of diamonds (ore grade) of these mines. This makes extraction economically feasible, as mine costs are mostly related to the amount of ore processed, not the amount of diamond extracted.
Underground expansion
In 2005, Rio TintoRio Tinto Group
The Rio Tinto Group is a diversified, British-Australian, multinational mining and resources group with headquarters in London and Melbourne. The company was founded in 1873, when a multinational consortium of investors purchased a mine complex on the Rio Tinto river, in Huelva, Spain from the...
was given the go ahead to a future expansion project, moving it from an open pit to an underground mine. This plan was postponed; in September 2010 Rio Tinto announced fresh plans to develop an underground mine beneath the existing pit, increasing annual production to 9 million tonnes of ore.
The project is predominantly an underground construction requiring high quality development and engineering excellence. The Block Cave is expected to operate until 2018 using the latest in mining technology, including Sandvik
Sandvik
Sandvik is a Swedish company founded in 1862 by Göran Fredrik Göransson in Sandviken. It is a high-technology engineering group and a world-leader in tooling, stainless steel alloys and materials technology, mining and construction...
's auto mining technology. The project is due to be completed by 2013, two years later than first planned, after diamond prices slumped.
History
Small quantities of alluvially deposited diamonds have been known in Australia since the late 19th century, first found by prospectors searching for goldGold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
. However, no source volcanic pipe deposit was apparent. A systematic search of Western Australia for the source of these diamonds began in 1969. Tanganyika Holdings had employed Maureen Muggeridge
Maureen Muggeridge
Maureen Muggeridge was a niece of Malcolm Muggeridge but made her name in a very different field. After graduating in Geology from the University of St Andrews, she made her own way to Perth, Western Australia, with support from her family...
and formed a joint venture
Joint venture
A joint venture is a business agreement in which parties agree to develop, for a finite time, a new entity and new assets by contributing equity. They exercise control over the enterprise and consequently share revenues, expenses and assets...
called Ashton Joint Venture, after minerals which indicated the presence of diamonds were found in 1976. In 1979, Muggeridge discovered diamond samples in the floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
of a small creek that flowed in Lake Argyle. She soon traced the source of the diamonds to the headwaters of Smoke Creek. On 2 October 1979, the Argyle pipe was discovered.
Over the following three years, the deposit was assessed for economic viability, and in 1983 the decision was made to commence mining operations. Alluvial mining operations commenced immediately, while the open pit mine was constructed over a period of 18 months at a cost of A$450 million. The mine was commissioned in December 1985.
External links
Several of this article's references contain excellent maps and photographs of the mine and examples of diamonds produced there, which cannot be placed in this article due to copyright limitations. The reader is especially directed to Shigley, Chapman, and Ellison's article, "Discovery and Mining of the Argyle Diamond Deposit, Australia" (Gems & Gemology, Spring 2001).