H1 gold output down 14 pct to 477,000 oz

* H1 unaudited revenues down 13 pct to $440 mln

* Keeps 2009 output forecast at 1.3 mln oz, up 5 pct

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MOSCOW, July 29 (Reuters) - Polyus Gold (PLZL.MM), Russia's largest gold miner, said on Wednesday output fell 14 percent to 477,000 ounces in the first half of the year due to lower metal content in the ore at its main mine, dragging down revenues.

Polyus said in a statement the average gold content in ore at the Olympiada mine in the Siberian region of Krasnoyarsk fell to 3.5 grams per tonne from 4.1 grams a year ago.

The company's unaudited revenues fell 13 percent year-on-year in the first six months of 2009 to $440 million.

Gold sales volumes fell to 477,000 ounces in the first half of 2009 from 559,000 ounces in the first half of 2008, although the average sale price rose to $922.5 per ounce from $908.7.

Polyus retained its full-year 2009 output forecast at 1.3 million ounces, which would be a 5 percent increase on 2008.

Onexim Group, the investment vehicle of Russian billionaire Mikhail Prokhorov, holds a little under 30 percent in Polyus Gold stock and associated shareholders another 10 percent.

The other main shareholder is tycoon Suleyman Kerimov, with 37 percent. (Reporting by Aleksandras Budrys, Editing by Peter Blackburn)