MOSCOW (Bloomberg) -- Oleg Deripaska's United Co. Rusal agreed to buy 25 percent of OAO GMK Norilsk Nickel, Russia's biggest mining company, and said it will pursue a takeover.

Rusal, the world's second-largest aluminum producer, will purchase the shares from billionaire Mikhail Prokhorov after his former business partner Vladimir Potanin waived the right to make a bid. The stake is valued at $13 billion, based on Moscow-based Norilsk's closing price.
A combination of Rusal and Norilsk would have $25 billion in sales, produce 12 percent of the world's aluminum and more nickel and palladium than anyone else. The company would be Russia's second-largest, after OAO Gazprom, and challenge BHP Billiton Ltd. and Rio Tinto Group as a diversified metals producer. Norilsk Chairman Andrei Klishas said Friday that “a merger is possible.”
“Rusal could not have bought this stake without specific Kremlin approval,” Chris Weafer, chief strategist at UralSib Financial Corp., said in a telephone interview from Moscow. “My guess is that will now extend to full control of Norilsk as part of the Kremlin's ambition to create a global Russian metals 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,” Rusal Chief Executive Officer Alexander Bulygin said in a statement.
---------------------French arrest Potanin and Prokhorov decided to end their business partnership in January after Prokhorov was arrested in the French ski resort of Courchevel on suspicion of pimping, for which he was later cleared. Their dispute over jointly owned stakes has hurt Norilsk, Morozov said last week after Prokhorov blocked plans to spin off a power unit worth $7 billion.
The two men are Russia's fourth- and fifth-richest, with fortunes of $13.5 billion each, Forbes magazine said in May. Deripaska is the second-richest with $16.8 billion.
It may take three months for Russian regulators to decide whether to approve Rusal's purchase of the Norilsk stake, according to Alexei Ulyanov, head of industrial supervision at the Federal Anti-Monopoly Service.
The country's antitrust authorities have frozen Deripaska's application to buy oil producer OAO Russneft, twice exceeding a deadline to make a decision. The billionaire also withdrew from a tender for OAO Power Machines last month, allowing rival bidder Alexei Mordashov to gain control, without giving a reason.
Rusal started syndicating a $4.5 billion loan to finance the purchase of the Norilsk stake, Interfax reported Dec. 19, citing unidentified bankers.
Rio Tinto is the world's largest aluminum maker.