Shares of London-based

Rio Tinto

( RTP) were rallying 7% on news that aluminum giant

Alcoa

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and the

Aluminum Corp. of China

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would together buy a 12% stake in the company.

"This unsolicited development, of which we had no prior notice, reinforces our view of the long-term value of Rio Tinto," says Rio Tinto Chairman Paul Skinner.

Alcoa said it will contribute up to $1.2 billion to the roughly $14 billion total investment.

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The surprise move may throw a roadblock in the attempts by Australia's

BHP

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to follow through on its bid for Rio Tinto, made last November.

The mining patch has seen a flurry of merger activity over the past few years with

Freeport-McMoRan Copper & Gold

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purchasing Phelps Dodge,

Companhia Vale do Rio Doce

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gobbling up Inco and Rio Tinto buying Alcan.

Shares of BHP were rallying about 8%, while those of CVRD were ahead by 4.5%. Alcoa was adding 1%, and Aluminum Corp. of China was up 11%.