Global mining giant Rio Tinto is putting an estimated $8-billion worth of assets up for sale across six countries but will hold on to its Kitimat operation in B.C.

Only four years after buying aluminum producer Alcan for $38 billion US, Rio Tinto announced Monday that it plans to sell 13 assets, including smelters and alumina refineries.

Observers interpreted the move as a way of diverting more resources to iron ore, which now accounts for nearly 80 per cent of earnings.

"It's all about returns, and these big miners, Rio included, are always reevaluating their businesses. And iron ore is currently a real cash cow for Rio Tinto," said Gavin Wendt, senior mining analyst for Mine Life in Sydney.

The sale, which would leave Rio Tinto's remaining aluminum business focused mainly on its more profitable operations in B.C. and Quebec, is designed to help the group more than double its aluminum earnings margins to 40 per cent by 2015.

"The only way they can achieve that is by getting rid of all these assets which can never be worldclass," said Peter Chilton, resources analyst at Constellation Capital Management.

Rio Tinto has been in aluminum since the 1950s. It ranks itself as the world's largest primary producer after the ill-timed Alcan deal in 2007 but could no longer ignore the business's big hunger for capital and relatively meagre returns.

Rio Tinto was careful not to appear overly keen to sell, making it clear that aluminum remained a core asset, saying global demand was relatively good and that it would consider making further investments in quality aluminum assets.

"We're going to be in no rush [to sell]," Rio Tinto Alcan CEO Jacynthe Cote said.

The company said it would look at various options for divesting the assets, which could include floating them as a separately listed company, spinning off shares in a new company to Rio Tinto shareholders or finding buyers for the assets.

Industry analysts said smaller buyers were more likely to be interested in these assets rather than other major producers. Aluminum prices have tumbled nearly 15 per cent in the past quarter. Financial services company UBS sees prices falling eight per cent more in 2012.

Rising Chinese aluminum output has been undermining global prices for the metal. "The aluminum industry has been suffering because of over-capacity coming from China," said Henry Liu of Mirae Asset Securities in Hong Kong. "This has led to very thin margins. It's very difficult to compete with Chinese producers."

Rio Tinto said it would sell assets in Australia, New Zealand, France, Germany, the U.S. and Britain to focus on its hydro-powered plants in Canada. It plans to keep its Weipa bauxite mine in Australia. Bauxite is used to make alumina, which is in turn used to make aluminum.

The group said a new unit, Pacific Aluminium, would hold the six Australian and New Zealand units being put up for sale, including Australia's Gove bauxite mine, alumina refinery and Tomago smelter and its New Zealand smelters.