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Pink diamonds are extremely rare and coveted: a now-closed Australian mine was the source of 90% of the colored gemstones. The highest quality shiny pink specimens can sell for tens of millions of dollars. But a discovery made in the same area could help reveal new jewel deposits, researchers say.
Scientists studying the Argyle diamond deposit in Western Australia, where the mine was located, said they now have a better understanding of the geological conditions necessary for the formation of pink diamonds and other color varieties, according to a study published Tuesday in the journal Nature Communications.
Using lasers to analyze minerals and rocks extracted from the Argyle deposit, researchers found that the pink diamond-rich site was formed during the breakup of an ancient supercontinent, called Nuna, about 1.3 billion years ago.
“Although the continent that would become Australia did not break up, the area where Argyle lies expanded, including along the scar, which created spaces in the Earth’s crust for magma to rise to the surface, bringing with pink diamonds,” said the study’s lead author, Dr. Hugo Olierook, a researcher at the John de Laeter Center at Curtin University in Perth, Australia, in a press release.
Discovering pink diamonds
Most diamond deposits are found in the middle of ancient continents, within volcanic rocks that rapidly transported diamonds from deep within the Earth’s interior to the surface.
However, for diamonds to turn pink or red, they must be subjected to intense forces resulting from colliding tectonic plates, which twist and bend their crystal lattices. Most brown diamonds are also formed this way.
At Argyle, this process occurred about 1.8 billion years ago, when Western Australia and Northern Australia collided, turning once-colorless diamonds pink hundreds of miles beneath the Earth’s crust.
But how did these colored diamonds reach the surface? The research team found that the Argyle deposits date back 1.3 billion years, from a time when an ancient supercontinent, known as Nuna, was breaking into fragments.
Supercontinents, which form when several continents join together to form a single landmass, have emerged several times in Earth’s geologic history.
“Using laser beams smaller than the width of a human hair on rocks supplied by Rio Tinto (the company that owns the mine), we found that Argyle is 1.3 billion years old, which is 100 million years older than previously thought , meaning it would likely have formed following the breakup of an ancient supercontinent,” Olierook said.
The authors proposed that the breakup of Nuna may have reopened the old juncture left by colliding continents, allowing diamond-bearing rocks to travel through this region to form the large diamond deposit.
This chain of events, according to the study, suggests that the junctions of ancient continents could be important for the search for pink diamonds and could guide the exploration of other deposits.
“Most diamond deposits were found in the middle of ancient continents because the volcanoes that host them tend to be exposed at the surface for explorers to find,” Olierook said.
“Argyle lies at the suture of two of these ancient continents, and these edges are often covered by sand and soil, leaving the possibility that similar volcanoes containing pink diamonds are yet to be discovered, including in Australia.”
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