The end of production at Rio Tinto’s Argyle diamond mine is expected to trigger a bull run of at least a decade for pink diamonds, according to a leading broker. The increased rarity of the precious minerals and an expectation that no new sources of pink diamonds would be found for decades is contributing to the strong outlook, Australian Diamond Portfolio executive director Anna Cisecki said. Mining at Argyle ended last November, and this year’s pink diamonds tender is the last after Rio Tinto’s 37 years of operations. Releasing her firm’s annual pink diamond investment guide on Wednesday, Ms Cisecki said despite their rarefied nature, they were “still quite accessible”. “The average hold period is between five to 10 years,” Ms Cisecki said. “Prices are increasing and demand is very strong so we’re seeing fewer and fewer of them. We don’t expect them to be so readily available in 10 years.” Even if a new source of pink diamonds was found, Ms Cisecki said, it would take 10-15 years to develop into a producing mine. That should provide investors confidence, she said, given pink diamonds hold their value much more strongly than other investments. Ms Cisecki said blue diamonds were expected to be an instructive precedent: mined in South Africa, the peak of production was 15-20 years ago, and there was now an increase in price of about 10 per cent per annum. “That might be where pinks get to in about a decade’s time,” she said. Bids for Rio Tinto’s final pink diamonds tender closed earlier this month, with the outcome expected to be announced shortly.