While it is known that for diamonds to form there needs to be carbon deep in the Earth, and for these diamonds to turn pink they must be subjected to forces from colliding tectonic plates, Curtin University researchers have found the third ingredient needed for the presence of pink diamonds at surface level, which is continents that were ‘stretched’ during continental break-up approximately 1.3 billion years ago.
Plate tectonic reconstructions showing the position of Argyle within the McArthur-Yanliao Gulf. Image credit: Olierook et al., doi: 10.1038/s41467-023-40904-8.
“The vast majority of primary economic diamond deposits are hosted in kimberlite diatremes located in Archean cratons, with characteristically old and thick continental lithosphere thought to be necessary for sustained diamond growth,” said Curtin University researcher Hugo Olierook and his colleagues.
“However, the largest source of natural diamonds discovered to date, the Argyle mine in the Kimberley region of Western Australia, is one of only a few economic deposits found within a Paleoproterozoic orogen adjacent to cratonic regions underlain by Archean basement.”
“Moreover, Argyle is hosted in olivine lamproite, rather than kimberlite, and has yielded over 90% of all pink diamonds discovered,” they added.
“The discovery of Argyle in 1979 resulted in a paradigm shift that led to diamond exploration in non-Archean terranes.”
“Despite its importance, the geodynamic drivers responsible for the emplacement of such an unusual diamond-bearing complex remain unclear.”
By using laser beams smaller than the width of a human hair on Argyle rocks, Dr. Olierook and co-authors found Argyle to be 1.3 billion years old, which is 100 million years older than previously thought.
“Argyle is located at the point where the Kimberley region and the rest of northern Australia smashed together many years prior, and that sort of collision creates a damaged area or ‘scar’ in the land that will never fully heal,” Dr. Olierook said.
“While the continent that would become Australia didn’t break up, the area where Argyle is situated was stretched, including along the scar, which created gaps in the Earth’s crust for magma to shoot up through to the surface, bringing with it pink diamonds.”
“As long as these three ingredients are present — deep carbon, continental collision and then stretching — then we think it will be possible to find the ‘next Argyle,’ which was once the world’s largest source of natural diamonds.”
“Even with the knowledge of these three ingredients, finding another trove of pink diamonds will not be without its challenges,” he said.
“Most diamond deposits have been found in the middle of ancient continents because their host volcanoes tend to be exposed at the surface for explorers to find.”
“Argyle is at the suture of two of these ancient continents, and these edges are often covered by sand and soil, leaving the possibility that similar pink diamond-bearing volcanoes still sit undiscovered, including in Australia.”
“The Argyle volcano has produced more than 90% of the world’s pink diamonds, making it an unparalleled source of these rare and coveted gems,” said Murray Rayner, a geologist at the global mining group Rio Tinto.
“Knowing the Argyle volcano’s age, at 1.3 billion years old, and situated where some of Earth’s earliest continents fragmented, we have significant further insights into the formation of these diamonds.”
The findings were published in the journal Nature Communications.
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H.K.H. Olierook et al. 2023. Emplacement of the Argyle diamond deposit into an ancient rift zone triggered by supercontinent breakup. Nat Commun 14, 5274; doi: 10.1038/s41467-023-40904-8
