Pink diamonds are among the rarest color variations of this gemstone.
Curtin University researchers studying diamond-rich rocks from Australia’s Argyle volcano have identified the missing geological process needed to bring valuable pink diamonds to the Earth’s surface where they can be mined, which could greatly help in the global hunt for new deposits.
Diamonds form deep in Earth’s mantle, at a depth of over 150 kilometers, where pressure and temperature force carbon atoms to form a densely-packed crystal structure. Impurities and traces of other elements can cause color variations in the crystal. Pink diamonds are among the most rare variation of this gemstone. Almost 90 percent of all mined pink diamonds come from just one locality–the Argyle volcano in the Kimberley region, Southwest Australia.
Diamonds are carried to Earth’s surface by powerful eruptions through volcanic conduits forming lamproite-dikes. Lamproite forming eruptions are still poorly understood despite their economic value. Studying rocks recovered from lamproite-dikes of the Argyle volcano, the researchers were able to reconstruct the history of the rocks hosting the diamonds.
“By using laser beams smaller than the width of a human hair on rocks supplied by Rio Tinto, we found Argyle to be 1.3 billion years old, which is 100 million years older than previously thought, meaning it would likely have formed as a result of an ancient supercontinent breaking apart,” lead researcher Dr. Hugo Olierook from Curtin’s John de Laeter Center, explains.
Over one billion years ago, the first proto-continents drifted together to form a supercontinent named Rodinia. At the time, the Kimberley region was located in the collision zone of three proto-continents–the future Australia, Antarctica and North America.
“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.”
Rodinia’s formation was just the first step to its inevitable break-up. The thick continental crust causes a build-up of heat inside Earth. Currents of partially molten material rising up will eventually tear up a supercontinent. When Australia started to drift apart from the landmass formed by Antarctica and North America, the crust between the two landmasses was stretched and weakened.
Video showing the movement of Earth’s tectonic plates over the past billion years.
The hot mantle currents brought the diamonds near the stretching continental crust and fueled powerful eruptions breaking through the surface. Cooling and solidifying in the volcanic conduits, the magma formed the lamproite-dikes of the Argyle volcano. Over time, erosion exposed the diamond-hosting rocks until humans started to mine them.
“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.”
By studying other areas with a similar geological history, the chance to find other pink diamonds could be significantly improved, so the conclusion of the researchers.
The study “Emplacement of the Argyle diamond deposit into an ancient rift zone triggered by supercontinent breakup” was published in the journal Nature Communications (2023). Additional material provided by Curtin University.
