Argyle Diamond Mine Closing

Mike Rashleigh, who toured the Argyle Diamond Mine in 2019, writes about the mine, its unique coloured diamonds, its major market influence and its planned closure in 2021.

The Last of the Argyle Diamonds

by Mike Rashleigh

Argyle Diamonds

In July 2019, I had a personal tour of the Argyle Diamond Mine in the Northern West Australia. The Argyle Mine is 206km from Kununarra and the closest “town” is Warmun settlement 55km to the south.

Flying into the mine airstrip by small plane is the quickest way to get there.

Flying over the mine site

Most of the world’s diamond mines are found in volcanic pipes of kimberlite. Kimberlite is an igneous rock, which sometimes contains diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an 83.5 carat (16.70g) diamond called the Star of the South Africa in 1869 spawned a diamond rush and the digging of the open-pit mine called the Big Hole. Kimberlite occurs in the Earth’s crust in vertical structures known as kimberlite pipes.

Kimberlite pipes were first found near Kimberley in South Africa but since then they have been found on most continents. Not all kimberlite pipes are created equal and only a small percentage of them contain diamonds and for many years it was assumed that only Kimberlite hosted diamonds.

The discovery of the Argyle ore body, and hence the mine, marked the first time that a commercial diamond occurrence had been identified that is not hosted in kimberlite. The AK1 pipe at Argyle instead consists of olivine lamproite, from which diamonds have been formed and eroded to provide alluvial deposits nearby. The deposit was discovered in 1979 following some 12 years of exploration by various companies in the area. The discovery of alluvial diamonds led directly to their source, the AK1 Pipe.

Left: ore stockpiles. Right: processing plant
Coloured diamonds from the Argyle Mine for sale by Rio Tinto

Development of the Argyle Mine was a two-stage process. Alluvial diamond mining took place between 1983 and 1985, when the AK1 pipe came into production. Since then, this has been the principal source of ore and from this ore, the diamonds. The mine was converted from open cut to underground operations in 2013.

The Argyle Diamond Mine, 100% owned by Rio Tinto, is one of the largest suppliers of natural coloured diamonds, producing approximately 20 million carats each year. The Argyle Mine is primarily known for its expensive and much sought after pink diamonds, but it also supplies cognac, champagne, blue, violet and red diamonds. The mine’s less valuable brown diamonds (called commercially “champagne” diamonds) have also had a major influence on the global diamond market. These diamonds have played a significant role in making diamonds more affordable to consumers. Argyle has produced more than 825 million carats of rough diamonds since it began production in 1983 and has enough reserves to economically mine through to the end of 2020. Rio Tinto’s planned closure of the mine in 2021 is set to reduce Australia’s rough diamond output by 99%.

It is said that the Argyle Mine’s closure will represent the end of diamond mining in Australia, at least until new discoveries are made. The possibility of a new Argyle-like diamond is unlikely, and at this time no one is known to be currently pursuing exploration opportunities in Australia. If a discovery is made, it will be several years before the discovery is developed into an operating mine. And the price? At this time, quality Argyle pinks sell for upwards of $200,000.00 per carat. Most stones are small so a famous Argyle stone, “The Argyle Muse”, a 2.28 carat fancy purplish-red diamond, was sold to an anonymous buyer for an estimated $14 plus million.

Left: The famous pink in rough and cut. Centre: A selection of stones in rough - note the structure. Right: The Argyle Amari