Rio did not name the price of the "history-making global bid" for its Once in a Blue Moon Tender, a 24.88 carat collection of 41 lots, mined from Argyle in Western Australia's north which finished production a year ago.

With the closure of Argyle, "it is extremely unlikely that there will ever be another collective offering of iconic gems in this colour spectrum from a single mine," Rio said today.

Rio Tinto also said its 2021 Argyle Pink Diamonds Tender collection, of 70 rare pink and red diamonds mined in the final year of operations, had delivered the "most significant set of record-breaking results in its 38-year history".

The diamonds were fiercely contested and the 2021 collection "continued its trajectory of double digit price growth" with 19 successful bidders from nine countries, Rio said.

"We are delighted with these results that are a reflection of the beauty, rarity and unique provenance of Argyle pink diamonds," Rio Tinto minerals CEO Sinead Kaufman said.

"We are extremely proud of the Argyle Pink Diamonds business and its legacy will continue as we retain and manage the brand through a proprietary Argyle pink diamonds trading platform, certification processes and creative collaborations with our trusted partners."

Argyle was virtually the sole source of the world's rare pink, red and violet diamonds.

Rio is also operator and majority owner of the Diavik diamond mine in Canada, has an exploration agreement with Angola's national diamond miner Endiama and is in a legal stoush with junior Star Diamond over an exploration project in Canada.

The broader diamond market is continuing its post-COVID recovery, with De Beers last week citing strong US consumer demand for diamond jewellery and further robust demand for rough diamonds in its eighth sales cycle.

Rio Tinto shares closed down 1.43% yesterday in London to 4,657.5p, representing a drop of almost 12% year-to-date.

It's capitalised at GBP77 billion (US$106 billion).