(IDEX Online) - Ultra-rare pink diamonds from the soon-to-close Argyle mine are expected to fetch $750,000 at auction in Australia.Rio Tinto's closure of the famed deposit in in Western Australia after 37 years is likely to boost demand and prices."This pink diamond is beyond rare and is in extremely high demand world-wide so we feel very privileged to see one a year but to have a few in the same auction is a privilege," said Lee Hames, chief operations officer for Lloyds Auctions."We predict that these pink diamonds will sell far exceeding their valuations due to the closure of the mine, and the interest we have had so far."Lots including two rings featuring pink diamonds (see picture) jointly valued at nearly $440,000 and a solitaire brilliant cut diamond worth over $260,000 go under the hammer on 7 September.The Argyle mine has been responsible for 90 per cent of the world's pink diamond production but is due to close early in 2021 when economically-viable reserves are expected to run out.The prices of Argyle Pinks have been insulated even from COVID-19 because of their rarity - less than 0.1 per cent of all diamonds - and the looming closure of the mine.