2023-09-21 19:03:08
Diamonds are rare, and pink diamonds are even rarer. A new study, however, has revealed the mystery of these very precious crystals, which are found almost exclusively in Australia, in the Argyle mine.
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Iconic precious stones, diamonds owe their rarity to the extreme conditions necessary for their formation. These small crystals of exceptional hardness are formed at very high temperatures and very high pressures, around 140 to 190 kilometers below the earth’s surface. Their extremely slow growth, of the order of a billion years, and the very specific magmatic processes necessary for their rise to the surface only add value to these minerals so prized by jewelers. So, what regarding pink diamonds? Only one diamond in 100,000 would indeed possess this color, making it an exceptional mineral.
Argyle, pink diamonds (almost) in spades… but why?
Very few deposits in the world can boast of regularly extracting pink diamonds. However, this is the case for Argyle, which produces around 90% of the pink diamonds on the market. It must be said that this ancient volcano located in Australia has a particularity: the mine was in fact dug in the heart of a lamproite chimney and not kimberlite as is usually the case. If the geodynamic processes at the origin of this volcanic rock still remain mysterious, a new study nevertheless provides new data which might allow us to better understand the formation of this deposit.
A team of researchers has in fact carried out a new dating of these rocks. Published results in the magazine Nature communications thus suggest that the Argyle lamproite was formed around 1.3 billion years ago, or 100 million years earlier than previously thought. And that changes everything for understanding the formation of the site.
The tearing of one of the oldest supercontinents on Earth
We have known for a long time that Argyle is located at a suture zone between two very old continental blocks, the Kimberley craton and the Northern Australia craton. This collision occurred approximately 1.8 billion years ago during the formation of Nuna, one of Earth’s oldest supercontinents. This environment of very strong tectonic pressure seems to be an essential element for obtaining pink diamonds. It remained to be understood how these crystals then arrived on the surface.
The new dating, however, shows that the Argyle lamproites would have formed only 500 million years later. A date which corresponds to a very particular tectonic event: the continental opening. 1.3 billion years ago, the supercontinent began to fracture. But in the Argyle region, it is not entirely successful. The crust is then greatly thinned, allowing magma to rise to the surface. A magma carrying with it the famous pink diamonds formed at depth during the previous collision stage.
We now understand better how the incredible Argyle pink diamond deposit was formed. Results which might, perhaps, help identify new deposits elsewhere in the world.
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