Clifford Chance (CC) has won a high-profile mandate to advise the Aluminium Corporation of China (Chinalco) on its joint acquisition with Alcoa of a 12% stake in Rio Tinto for around $14bn (£7bn).

The deal marks CC's first instruction from the client and is thought to represent the largest-ever overseas investment by a Chinese company. The move could block the efforts of Anglo-Australian mining company BHP Billiton to buy Rio Tinto.

CC is fielding a team led by corporate partners Kathy Honeywood and Nigel Wellings in London and Rupert Li in Beijing.

Linklaters is acting for regular client Rio Tinto, with corporate partner James Inglis thought to be leading the team. The magic circle firm is advising the mining giant on BHP Billiton's £50bn approach for Rio, made late last year, and also acted for the company on its $34bn (£17bn) bid for Alcan last summer.

Alcoa has turned to Wachtell Lipton Rosen & Katz for corporate advice and Cleary Gottlieb Steen & Hamilton for competition, with Cleary partners Mark Leddy and David Gelfand (both Washington DC) and Nicholas Levy (Brussels) advising. Macfarlanes is advising the company on UK issues, with corporate partner Graham Gibb leading the team.

Last year, Alcoa instructed Skadden Arps Slate Meagher & Flom on its $33bn (£16.6bn) hostile bid for Alcan, using Cleary for competition matters.

Commenting on the deal, Honeywood said: "Chinalco is a significant and prestigious client of the firm and our work on this transaction demonstrates our ability to deploy international teams in support of their strategy."

The deal comes shortly after CC senior partner Stuart Popham was part of a delegation that traveled to China with Prime Minister Gordon Brown in an attempt to improve trade links between the UK and China.

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