Rare Australian pink diamonds emerged when a supercontinent broke up

Coloured diamonds from the Argyle Diamond Mine in Western Australia

Murray Rayner

Western Australia’s pink diamonds were brought to the surface from deep underground around 1.3 billion years ago when the former supercontinent Nuna broke up.

Pink diamonds are extremely rare and prized. More than 90 per cent of those found so far have come from the Argyle Diamond Mine in the Kimberley region of Western Australia.

Like other diamonds, Argyle pink diamonds initially formed at least 150 kilometres underground during Earth‘s ancient past and started out colourless.

Then, around 1.85 billion years ago, they are believed to have turned pink when two former continents – which now form northern and western sections of Australia – smashed together to become part of a supercontinent called Nuna that once incorporated 90 per cent of Earth’s land mass.

The collision deformed the crystal structures of diamonds caught in the middle and caused them to reflect light differently, becoming pink, says Hugo Olierook at Curtin University in Western Australia.

To find out how and when the pink diamonds later came to the surface, Olierook and his colleagues analysed samples of diamond-containing rock from the Argyle Diamond Mine.

They determined that the diamonds settled at the surface between 1.31 and 1.25 billion years ago by dating the surrounding rock using radiometric methods. This coincides with when Nuna started to break into smaller continents, suggesting the two are linked, says Olierook.

The northern and western sections of Australia held together at this time, but they were stretched apart enough for diamond-containing magma to well up between the former continents. “It’s like if you were to yank a sutured skin wound open, the stitches may hold, but a little bit of blood might trickle out,” says Olierook.

To date, most diamonds have been found in the middle of ancient continents, where they have formed at the base of the thick crust and later been shot up by volcanic activity. However, the unusual placement of the Argyle deposit suggests there may be more riches to be discovered at the edges of ancient continents, says Olierook, which have traditionally been overlooked.

The Argyle Diamond Mine closed in 2020 after all its pink and other diamonds were extracted over a 37-year period, meaning the search is now on for new deposits.

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