* Deal between Polyus, Polymetal long been speculated
* Prokhorov's stake sale could be catalyst
* UK panel to rule on Polyus ownership change
* Natalka mine, ownership structure pose hurdles
MOSCOW/LONDON, Feb 14 (Reuters) - Doubters have long said it would make no sense to attempt a mega-merger of Russia's top gold miners - the country is too big, its reserves too far flung, the politics too tricky.
But with billionaire Mikhail Prokhorov quitting Russia's largest precious metal miner Polyus, talk has turned to how 40 percent shareholder Suleiman Kerimov could forge a deal with Polymetal, the silver miner he once owned, to create one of the world's largest gold companies.
The prize would certainly be huge: A merged company would be worth around $17 billion and could help Russia break into the world's top three gold producers by mid-decade. It could also be first in line to develop the country's untapped deposits such as Siberia's Sukhoi Log, one of the world's largest virgin gold deposits which is likely to be put up for tender soon.
Kerimov is seen as equal to the task. An ambitious and daring dealmaker, he led a party of investors that took over potash producer Uralkali in 2010 and merged it with rival Silvinit in a $24 billion deal.
Observers say he is unlikely to pass up the opportunity to deal with the new owners of Prokhorov's 38 percent stake to combine Polyus' huge reserves with their management know-how.
"He's a businessman and a real go-getter so I'd assume he'd have something in the back of his mind to do with Polyus, not sit still," said one Russian gold industry executive who declined to be named. "Having one management with a large Russian gold company makes a lot of sense."
Kerimov, who has connections to the Kremlin, owned Polymetal between 2005 and 2008 and invested with Polymetal shareholder Alexander Nesis in Uralkali.
However a source with knowledge of Kerimov's thinking said he may not interested in a merger. Numerous barriers stand in the way, and the doubters could still be right.
While the change of ownership at Polyus is fuelling merger talk, it could also be a hurdle to any wider tie-up.
Prokhorov's Onexim holding company is expected to sell its $4 billion stake to retail boss Zelimkhan Mutsoyev, who also joined Kerimov as a co-investor in Uralkali, and to fruit juice magnate Gavriil Yushvayev.
But the sale needs approval from the UK Takeover Panel, which is expected to rule in the next few weeks. At issue is whether the new owners are working together or with Kerimov, as opposed to operating individually, sources with direct knowledge of the sale procedure have said. If they are deemed to be working in concert that could force them to make an offer to buy out minorities which could scupper the sale.
Nafta said in September it was in talks with one potential buyer of Onexim's stake with a view to providing financial support. Analysts have speculated that Kerimov may be involved in the transaction or financing it. However a source with knowledge of the circumstances of the stake sale said that Nafta was not now involved in the process.
A Plan B could see the stake buyers make an offer based on the share price's six month average: 205 pence per share, said Alfa Bank analyst Barry Ehrlich. That looks unattractive to minority investors, given merger talk has boosted Polyus shares 14 percent since the end of January. They now trade around 226p.
Should Prokhorov's buyers instead take on debt to pay for the stake, Polyus could end up with less cash to spend on a potential merger given the need for buyers to pay off that debt.
"(A merger) isn't consistent with the idea of a leveraged transaction cutting down Polyus' scale, shedding assets and milking the company for dividends," said Alfa's Ehrlich.
MEGA-DEALS LOSE CHARM
More fundamentally, mining mega-deals have lost their charm for investors who have seen several destroy value and lead to billions of dollars of writedowns this year at big miners including Rio Tinto and Barrick Gold .
The latter, the world's largest gold miner, booked a $3.8 billion impairment charge to write down the value of its Lumwana copper mine, acquired through its C$7.3 billion takeover of Equinox Minerals in 2011.
There's also the issue that Polyus and Polymetal's assets are thousands of kilometres apart, spread over empty tracts of the largest country in the world. "They are far apart. There's no synergy," said one gold investor.
Another sticking point could be the value put on Polyus' vast Natalka gold mine project in Russia's far east. Polyus has said it expects to start commissioning a processing plant by the end of 2013 but a source close to Polymetal said that company expects the project to take longer to set up and come on line.
The biggest hurdle, as that of so many proposed mergers, would be ownership. A share deal could leave Polymetal's main shareholders overshadowed by Kerimov and his partners, while the lack of liquidity could make it tough for them to sell out.
"The strategic shareholders of Polymetal...will have far less control of the company," said Ehrlich. "It would be an exit into a Kerimov-controlled company they may never exit from."