The world's largest pink diamond mine

The Argyle Formation contains 90% of the world's pink diamonds, formed when the first supercontinent broke up.

Pink diamonds mined at the Argyle mine. Photo: Jeweler Magazine

The Argyle Formation in western Australia has the largest reserves of pink diamonds on Earth. This is an odd location for diamonds to form, at the edge of a continent instead of in the center, where most diamond mines are located, in rock that is slightly different from the rock that normally contains diamonds. New research published on September 19 in the journal Nature shows that diamond color and strange geology most likely have the same origin from the planet's tectonic plates 1.3 billion years ago. Recent analysis by other scientists reveals that large-scale continental shifts played an important role in bringing colored diamonds to the surface.

"The breakup of continents is a key factor in bringing diamonds up from deep underground," said Hugo Olierook, a PhD student at Curtin University in Australia, lead author of a paper analyzing the origin of pink diamonds. , said.

Pink diamonds are different from blue and yellow diamonds, which are colored by impurities such as nitrogen and boron. In contrast, pink diamonds have their color because their crystal structure is bent. Argyle also contains more brown diamonds, which develop their color due to a more deformed crystal structure.

The Argyle diamond mine closed in 2020. Research from the 1980s dated the rock layer to about 1.2 billion years. But even the scientists who conducted the initial survey did not trust that number due to technical limitations. Olierook and his colleagues decided to retest using modern equipment, especially laser cutting technology that allowed them to carefully identify each crystal in the rock layer that needed to be dated.

New results reveal that the Argyle mine contains pink diamonds that are 1.3 billion years old, 100 million years older than previously thought. The mine was born when the supercontinent Nuna began to break up. First, about 1.8 billion years ago, two pieces of continental crust collided. The Argyle Formation lies right at this intersection. The impact of the shell can bend diamonds and turn them pink, according to Olierook.

The breakup of Nuna 500 million years later brought diamonds to the surface. The continent did not separate at Argyle, but the stretching forces likely weakened the vestiges of previous continental collisions, allowing an eruption of pink diamond-bearing rocks to continue over days or weeks.

Tracking the path of diamonds from deep underground to the surface will help understand how carbon enters and escapes from the Earth's interior because diamonds are mostly pure carbon). According to the research team, if pink diamonds form at the edge of the continent, they are likely buried under many layers of eroded rock and sediment.