The Anglo-Australian mining company is the third-largest producer of rough diamonds globally after Alrosa Co and Anglo American controlled De Beers, but is seeking to exit the industry. In a slide presentation released to the Australian Securities Exchange, Rio Tinto said it faced no time pressure for a transaction and it continued to review all options, including a sale of its diamonds portfolio.

The company said the US was expected to remain a key market for diamond jewellery, but it would be surpassed in market size by China by 2025. Other markets were expected to move in line with growth in gross domestic product, it said.

Supplies of rough stones, meanwhile, are likely to be flat to declining over the next decade as existing mines become older and deeper.

Bruce Cox, managing director of Rio Tinto Diamonds, in the presentation delivered in Montreal, Canada said there had been no new "tier 1" diamond discoveries in the last 17 years. As a result, Mr Cox said demand-supply imbalances were expected to widen.

Rio Tinto produced 11.7 million carats, generating revenue of $726 million, in 2011. But its diamonds business remains relatively small, with sales revenue last year topping $60.5 billion.

The company in late March said it had begun a strategic review of its diamonds business, which includes mines in Australia, Canada, Zimbabwe and a project in India. Rival BHP Billiton last November said it was reviewing its own diamonds operation and was considering the sale of its mine in Canada.

Rio Tinto said that trends in China were driving wealth in the country and a push toward consumer-driven economic growth that would underpin long-term demand for diamonds and other products, including titanium dioxide, borates and salt.