The Argyle Diamond Mine was a diamond mine located in the East Kimberley region in the remote north of Western Australia. Argyle was at times the largest diamond producer in the world by volume (14 million carats in 2018), although the proportion of gem-quality diamonds was low. It was the only known significant source of pink and red diamonds (producing over 90% of the world's supply), and additionally provided a large proportion of other naturally coloured diamonds, including champagne, cognac and rare blue diamonds.
Mining operations ceased in November 2020, after 37 years of operations and producing more than 865 million carats of rough diamonds. Mine operator Rio Tinto plans to decommission the mine and rehabilitate the site at least through 2025.
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, United States, 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.
Description
The mine site covers about , stretching in a mostly linear shape about long and wide. Argyle originally used open-pit techniques, reaching about 600 m deep at its deepest point. The open cut closed in 2010, and operations became fully underground in 2013 via block cave mining.
Location
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 south-west of Lake Argyle in the Matsu Ranges, about south-west of Darwin. Because it is by road from the nearest settlement (Kununurra), a complete residential camp was constructed on site. Most of the 520 workers commuted from Perth, over away, for alternating two-week shifts at the mine. The mine encouraged local employment and had a large number of indigenous local people working within the mine.
History
Small quantities of alluvially deposited diamonds have been known in Australia since the late 19th century, first found by prospectors searching for gold. However, no source volcanic pipe deposit was apparent. Following the discovery of several alluvial diamonds in the West Kimberley region along the Lennard River (Ellendale area) in 1969 a systematic search of Western Australia for the source of these diamonds was begun by a consortium of mining companies, collectively known as the Kalumburu Joint Venture. Tanganyika Holdings part of the Kalumburu Joint Venture (later to become the Ashton Joint Venture) had employed Maureen Muggeridge. 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.
Geology
The mine was the first successful commercial non alluvial diamond mine 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 were 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.