In the world of coloured gemstones, pink diamonds are particularly rare. For that, investors have never hesitated to pay a king’s ransom to own one – notably the huge 59.6 carat Pink Star (re-named the CTF Pink Star), which set the world auction record for any jewel when Hong Kong jeweller Chow Tai Fook bought it at US$71.2 million (S$96.9 million) in April 20­­17. Now that the only mine responsible for 90 per cent of the pink rocks worldwide is closing next year, prices will only skyrocket.

While pink diamonds have occasionally been mined at South Africa and Russia, the Argyle mine – located in a remote region in Western Australia – is the only known reliable producer. Yet, of its entire output of 800 million carats of diamonds over 36 years, only a meager 0.01 per cent has been fancy pinks, fancy vivid being the priciest grade. Today, it’s nearly exhausted the pinks it has yielded since 1983.

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When the fabled Argyle door finally closes, the supply of pinks is likely to dry up, although this has its upside. Says Singapore-based Simone Ng of Simone Jewels: “Our brand invested in a small lot of pink Argyle diamonds more than five years ago. Most have been sold and this is the moment our customers have been waiting for.”

Even those that weigh less than the CTF Pink Star command astounding prices. On Oct 7, Sotheby’s Hong Kong sold a 10.64 carat fancy vivid purplish pink diamond for US$19.9 million. In comparison, an 88.22 carat flawless D-colour diamond was sold by Sotheby’s Asia in April for just US$13.8 million.

(Related: Why coloured diamonds are good investments despite the hefty price tag)

Gemologist Paige Parker, who recently designed an Argyle-pink ring for Phillips’ Hong Kong jewellery sale set for Nov 25, says: “Argyle pinks will become major collectibles, like Golconda colourless diamonds.” One of those storied rocks was the famous Hope Diamond, from a 16th-century India mine that has since closed. Only time will tell, but she probably isn’t too far off the mark.

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(Photos: Sotheby’s Hong Kong, Phillips)