Russia's Polyus Gold cuts reserves estimate of flagship project

* Natalka's gold reserves estimate cut by 49 pct

* Polyus says committed to take project forward

* Says in talks with potential partners for Natalka (Adds details, quotes, context)

MOSCOW, Feb 24 (Reuters) - Polyus Gold, Russia's biggest gold producer, is sticking with its flagship Natalka project despite a drop in its estimated gold reserves, and hopes to prepare an operating plan by mid-2015, it said on Tuesday.

Polyus put the challenging and costly project to develop one of the world's largest untapped deposits in the Russian far east on hold in November to review its reserves, jeopardising the country's ambitions to increase gold output.

The review showed the deposit based in the Magadan region had proved and probable gold reserves of 16.2 million troy ounces and measured, indicated and inferred resources of 36.8 million ounces, down 49 percent and 38 percent, respectively, from estimates made in 2011.

"This is a major decrease, although the company previously guided that it's likely to happen," said Vadim Astapovich at VTB Capital (Other OTC: CGHC - news) . Polyus said in November that Natalka's reserves could drop by 55-65 percent after the review.

"Now (NYSE: DNOW - news) , Polyus basically has to do the mining plan from scratch, based on new reserves estimates," Astapovich added.

Polyus, which had previously planned to start Natalka in mid-2015, said on Tuesday it was committed to pursuing the project "in a prudent and cost-effective manner".

"Despite the change in mineral resource and ore reserve estimates, Natalka remains one of the largest development projects in the gold industry," Polyus said in a statement, adding it was in talks with a number of potential partners.

The gold grade in ore resources was reduced by 14 percent to 1.5 grams per tonne.

"With such a low gold content and a remote place where Natalka is based, I would say that the project would not be economically viable at the current gold price of around $1,200 per ounce, if it was launched now," Astapovich said.

However, Polyus, controlled by businessman Suleiman Kerimov and his partners, has already invested $1.2 billion in Natalka, and has largely completed the first stage of the project, which means capital spending requirements will be much lower if it decides to go ahead, he added.

Natalka was previously expected to add 0.5 million ounces of gold, or 30 percent, to Polyus' current operations after the launch.

Polyus shares were up 0.9 percent on Tuesday, outperforming a 0.6 percent decline in the FTSE Gold Mines Index. (Reporting by Polina Devitt; Editing by Elizabeth Piper and Mark Potter)