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 it is set to close by 2020. 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. On June 21, 2015, after more than 11 years and 42 kilometres of tunnelling, the Argyle underground block cave development was officially completed. In 2013, Argyle is estimated to produce 10.2 million carats with an average per carat price of $25/carat.
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.
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 closed in 2010. An underground block cave mine is currently under development, and is likely to extend Argyle's diamond production until 2018.
The Argyle diamond mine is located in the Kimberley region in the far northeast of the Australian state of Western Australia. It is located to the southwest of Lake Argyle in the Matsu Ranges, about 550 kilometres (340 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 2,000 kilometres (1,200 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.
The mine is the first successful commercial diamond mine (except alluvial 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, micas, 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. 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.
Argyle is the fourth largest diamond producing mine in the world by volume, averaging annual production of 8 million carats (1,600 kg). 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 750,000,000 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, where low costs of labour 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.