In 37 years of operation, the Argyle mine produced over 865 million carats (172 tons) of rough diamonds, including 90% of the world’s pink diamonds.
The Argyle mine contains the largest deposits of pink diamonds ever discovered on Earth. Unlike blue and yellow diamonds, which derive their color from impurities such as nitrogen and boron, the color of pink diamonds comes from geological processes that distort their crystal structure. Pink diamonds are extremely rare and can be valued at over $2 million per carat (1 carat is equivalent to 0.2 g), according to the International Gem Society.
Pink diamonds mined from Argyle. (Photo: Rio Tinto).
The Argyle mine closed in 2020 due to a decrease in diamond supply and unfavorable economic conditions, including rising operational costs. The mine, located on the shores of Argyle Lake in a remote area of Western Australia, is situated 550 km southeast of Darwin. Its open-pit mining activities lasted for 37 years, providing over 865 million carats (172 tons) of rough diamonds, including white, blue, purple, pink, and red diamonds, according to Rio Tinto, the company that owns and operates the mine.
The Argyle geological formation is a unique diamond formation site because it is located at the edge of a continent rather than its center, where gemstones typically occur. Additionally, diamonds are usually found in kimberlite formations, but the Argyle formation contains a type of volcanic rock known as olivine lamproite.
Researchers dated the rocks at Argyle shortly after the area was discovered in 1979. Initial results indicated that the rock layer was approximately 1.1 to 1.2 billion years old, but a new study last year revealed that the rock layer is 1.3 billion years old. Thus, the Argyle formation emerged just as the supercontinent Nuna began to break apart, providing many clues about the diamond formation process and why there are so many pink diamonds.
Pink diamonds are formed under extraordinary temperature and pressure conditions when tectonic plates collide. The immense forces from these collisions can bend the crystal lattice of pre-existing diamonds in ways that result in various shades of pink. If the impact is too great, they can turn brown, according to Hugo Olierook, a researcher at Curtin University in Australia and the author of a 2023 study.
The supercontinent Nuna formed when two parts of the Earth’s crust collided about 1.8 billion years ago. The area where they collided corresponds to the current Argyle formation, demonstrating that the collision led to the birth of pink diamonds here. However, at that time, diamonds were buried deep within the Earth’s crust.
About 500 million years later, as Nuna began to break apart due to tectonic plates moving away from each other, the rock containing diamonds was pushed closer to the Earth’s surface. This layer also contained a substantial amount of brown diamonds, which Rio Tinto mined and sold in huge quantities.
