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. They are believed to have turned pink around 1.85 billion years ago 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.
Olierook and his colleagues have now used radiometric methods to date diamond-containing rock from the Argyle Diamond Mine and say the diamonds settled at the surface between 1.31 and 1.25 billion years ago. This coincides with when Nuna started to break into smaller continents, 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.
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 pushed up by volcanic activity. The origin and location of the Argyle deposit suggest that the gems may also be found at the edges of these landmasses, says Olierook.
The Argyle Diamond Mine closed in 2020 after all its pink and other diamonds were extracted over a 37-year period. The search is now on for new deposits.