Editor’s Note
The Argyle mine in Australia was the world’s primary source of rare pink diamonds. Its closure in 2020 highlights the geological rarity and immense value of these gems.
The Argyle mine, located in the remote Kimberley region of northeastern Australia, holds the largest known deposit of pink diamonds on Earth. Unlike impure blue and yellow diamonds, pink diamonds acquire their color through geological processes. According to the International Gem Society, pink diamonds are extremely rare and can command prices of up to $2 million per carat (1 carat equals 0.2 grams or 0.007 ounces). The mine closed in 2020 due to declining diamond supply and rising operational costs. Rio Tinto, the company that owned the mine situated on the shores of Lake Argyle, stated that mining operations lasted for 37 years, yielding over 865 million carats (191 tons or 172 metric tons) of rough diamonds. These included white, blue, purple, pink, and red diamonds.
According to a Live Science report, the Argyle rock formation is an unusual location for diamonds as it sits on the edge of a continent. Diamonds are typically found in kimberlite rock formations, but the Argyle structure contains a type of volcanic rock called olivine lamproite. Researchers dated the rocks at Argyle shortly after the site’s discovery in 1979. Initial results indicated an age between 1.1 and 1.2 billion years, but a new study last year revealed the rocks are 1.3 billion years old.
New research suggests the Argyle formation originated during the initial breakup of the supercontinent Nuna, providing clues about how the diamonds formed and why so many of them are pink. Pink diamonds are created by specific heat and pressure conditions generated when tectonic plates collide. The sheer force of these collisions can distort the crystal lattice of pre-existing diamonds in a way that turns them into various shades of pink.
The supercontinent Nuna formed when two sections of Earth’s crust collided about 1.8 billion years ago. The area where they collided is believed to overlap with the present-day Argyle formation, suggesting the collision gave birth to Argyle’s pink diamonds, though the diamonds would have been buried deep within the crust at that time. Scientists believe that 500 million years later, when Nuna began to rift apart due to tectonic plates moving away from each other, the diamond-bearing rocks were brought to the Earth’s surface. Those rocks also contained abundant brown diamonds.