The Argyle Formation, located on the edge of a continent in Western Australia, was responsible for producing more than 865 million carats (172 tonnes) of rough diamonds over the course of 37 years. This includes 90% of the world’s pink diamonds. The mine closed in 2020 due to declining diamond supplies and unfavorable economic conditions.
Pink diamonds are extremely rare and valuable, with some fetching more than $2 million per carat. Unlike blue and yellow diamonds, which get their color from impurities, pink diamonds’ color comes from geological processes that deform the crystal structure. This uniqueness adds to their allure and value in the gem market.
Rio Tinto, the company that owned and operated the Argyle mine, was able to extract a large quantity of brown diamonds from the area in addition to the highly sought-after pink diamonds. Researchers have determined that the formation is around 1.3 billion years old, shedding light on the conditions under which pink diamonds are formed.
Pink diamonds are created when tectonic plates collide under intense pressure and temperature conditions, causing pre-existing diamonds to take on different pink tones. This process occurred as the Nuna supercontinent began to break apart 1.8 billion years ago, creating the perfect conditions for pink diamonds to form in the Argyle Formation. As diamond-bearing rock was pushed closer to the surface due to plate tectonics, it became accessible for mining by Rio Tinto for decades before it closed down in 2020 due to declining supplies and unfavorable economic conditions.