A new clue will help reveal the locations of pink diamonds

The rare pink diamonds at Argyle

The Argyle diamond mine in Western Australia closed in 2020, but not before contributing more than 90 percent of all pink diamonds found in the world so far. Most diamond deposits in the world can be dated back to more than 2.5 billion years ago, but those in Argyle are relatively younger.

From the research so far, we know that the Argyle deposits sat at the juncture of two ancient continents. And around 1,800 million years ago, the northern and western continents collided, turning the diamonds in the deposits pink. What was not clear so far was how these diamonds made their way to the surface.

Hugo Olierook, a research fellow at Curtin University in Australia, along with other researchers from the UK, China, and Australia, analyzed the minerals from the Argyle mine to understand its origin.

Stretch: The missing ingredient

The researchers used laser beams that were smaller than the width of the human hair on rocks provided by Rio Tinto, a mining organization in their research. They found that the Argyle deposit was about 100 million years younger than previously estimated.

While this would not make much of a difference to us today, for geologists, it completely shifts the timescale and coincides with another major geologic event occurring in the area. Argyle is located in the region where Kimberley and the rest of northern Australia smashed many years ago and left a scar that could not heal.

Olierook and his colleagues now believe that the pink diamonds were brought closer to the surface by the breakup of the first supercontinent, Nuna. "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," said Olierook in a press release.

The researchers are of the view that diamond formation during the break up of continents might be prevalent but under-recognized. "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,’" Oliebrook added.

The research findings were published in the journal Nature Communications today.

Abstract

Argyle is the world’s largest source of natural diamonds, yet one of only a few economic deposits hosted in a Paleoproterozoic orogen. The geodynamic triggers responsible for its alkaline ultramafic volcanic host are unknown. Here we show, using U-Pb and (U-Th)/He geochronology of detrital apatite and detrital zircon, and U-Pb dating of hydrothermal titanite, that emplacement of the Argyle lamproite is bracketed between 1311 ± 9 Ma and 1257 ± 15 Ma (2σ), older than previously known. To form the Argyle lamproite diatreme complex, emplacement was likely driven by lithospheric extension related to the breakup of the supercontinent Nuna. Extension facilitated the production of low-degree partial melts and their migration through transcrustal corridors in the Paleoproterozoic Halls Creek Orogen, a rheologically-weak rift zone adjacent to the Kimberley Craton. Diamondiferous diatreme emplacement during(super)continental breakup may be prevalent but hitherto under-recognized in rift zones at the edges of ancient continental blocks.