More than 90% of all pink diamonds in existence come from the recently closed Argyle mine in northwest Australia. But no one really knew why they were found there, on the edge of the southern continent, while most diamond mines are in continental environments, such as South Africa or Russia.
An Australian team explains in the journal Nature Communications that these rare minerals were formed by the breakup of Earth’s first supercontinent 1.3 billion years ago. The two “ingredients” needed to make a pink diamond are already known, the study’s first author, Hugo Olierook from Australia’s Curtin University in Perth, told AFP.
“Like a champagne cork”
The first component, carbon, is found at great depths. At less than 150 km deep, this carbon is common graphite, used to make pencil leads, and “which doesn’t look particularly nice on a wedding ring,” the researcher jokes. Second “ingredient”, enormous pressure, large enough to change the color of a transparent diamond but without applying too much pressure.
“Just press a little, it will turn pink. But press it a little more and it will turn brown,” explains the geologist. The Australian team’s discovery helps explain what caused pink diamonds to burst from the Earth’s crust close to the surface.
The Argyle Mine was originally thought to have formed 1.2 billion years ago, but it was not clear how the diamonds could have returned without an associated geological phenomenon. The researchers then refined the dating of the deposit by measuring the age of tiny crystal elements in a rock from the mine. And arrived 1.3 billion years ago.
This age corresponds to the rupture suffered by the first supercontinent, indifferently called Nuna or Columbia. The pressure that colored the diamonds came from the collisions of the landmasses of western and northern Australia 1.8 billion years ago.
That mass shattered 500 million years later, at which point the magma rose to the surface, carrying the pink diamonds to the surface “like a champagne cork,” Mr. Olierook said.