Rusal, the Russian aluminium giant, is to buy a 25 per cent stake in Norilsk Nickel in an attempt to become one of the world’s largest diversified mining companies.

Rusal will buy the stake from Mikhail Prokhorov, a Russian oligarch, and is then expected to make a full bid for Norilsk.

This would turn Rusal into not only the world’s largest aluminium producer but also a diversified resources company to rival BHP Billiton, CVRD, of Brazil, and Rio Tinto.

A merged Rusal-Norilsk would be the world’s fourth-biggest miner and have an estimated market capitalisation exceeding $100 billion (£49.8 billion), making it bigger than Anglo American.

Rusal is acquiring the Norilsk stake after Vladimir Potanin, Mr Prokhorov’s partner and co-owner in the nickel miner, failed to raise $15.7 billion to buy the shares.

Mr Potanin hired Citigroup last month to raise $10 billion from banks in London but this plan was scuppered by turmoil in the credit markets.

Mr Potanin is thought to have raised about $5 billion from two Russian banks, but this was insufficient to buy out his partner.

He announced on Friday morning that he would not exercise his option to buy Mr Prokhorov’s shares.

Mr Prokhorov’s investment vehicle, Onexim, will sell his shares to Rusal in return for 11 per cent of the enlarged company and a cash bonus.

Alexander Bulygin, chief executive of Rusal, said: “We intend to create Russia’s first global diversified metals and mining company.

"Our company will join the ranks of the world’s top five mining giants, providing significant growth for the company to its shareholders and reinforcing the international reputation of Russia as a strong industrial state.”

ABN Amro, BNP Paribas, Credit Suisse and Merrill Lynch will provide financing to Rusal to pay for the cash component of the consideration.

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