Russia's Natural ResourcesMinistry on Tuesday extended until June 11 a deadline for accepting bids forthe rights to a huge Siberian copper field, saying potential bidders neededmore time to prepare documents.

Rosnedra, the federalsubsoil agency within the ministry, said in a separate statement the contestfor the Udokan deposit would now take place on Aug. 14, nearly a month laterthan the July 17 contest that had originally been planned.

Neither the ministry norits subdivision said whether any bids had already been made for the field, oneof only two untapped metals deposits large enough to be declaredstrategic by the government. The other is the Sukhoi Log goldfield.

Udokan, in the Chita region of eastern Siberia, will require investment of around$1.6 billion, the ministry said. It will be able to produce 187,000 tonnes ofcopper annually, equivalent to 15 percent of Russia's total copper production today.

Russian billionaire OlegDeripaska, state railway monopoly Russian Railways and mining giant NorilskNickel have all expressed their interest in bidding for Udokan,estimated to contain 13.4 million tonnes of extractable copper metal.

Russian media reported lastmonth state conglomerate Russian Technologies, whose wide-ranging assetportfolio includes titanium producer VSMPO Avisma , was alsoplanning to bid.

(Reporting by PolinaDevitt, writing by Aleksandras Budrys; editing by Chris Johnson)

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