* Polyus aims for up to 15 pct of global antimony market
* Metal used primarily in fire retardants, batteries
* Polyus says may increase free float in future (Adds comment about potential increase of free float)
MOSCOW/LONDON, March 20 (Reuters) - Russia's largest gold producer Polyus said on Tuesday it planned to start selling antimony, targeting up to 15 percent of global output of the metal, and was considering boosting its free float in future.
Its decision to start sales of the metal, used primarily to make fire retardants and batteries, coincides with rising prices of antimony <ANT-LON>, which is trading in Europe at its highest level since June, around $8,700 a tonne, due to tight Chinese supply.
Polyus, controlled by the family of Russian tycoon Suleiman Kerimov, said it will produce the metal at its large Olimpiada gold deposit in Russia which has reserves of high-content antimony ore.
"We are going to be a significant player in the antimony market," Polyus Chief Financial Officer Mikhail Stiskin told the company's capital markets day in London. China, Japan and South Korea are the world's top antimony consumers.
Polyus held its capital markets day at the London Stock Exchange (LSE) amid a deep crisis in relations between London and Moscow over a nerve toxin attack on a Russian double agent in Britain.
Polyus believes that it is currently undervalued due to a number of risks, including geopolitics, and may consider increasing its free float to 25-30 percent, which it sees as a more appropriate level, from the current 16 percent in the mid- to long-term, it said.
The company hopes such a move would increase liquidity of its shares and lead to a re-rating of its valuation. Polyus returned to the LSE in 2017, when it sold shares worth more than $800 million in Moscow and London.
However, there is no timing for the possible move and there have been no specific talks on this so far, Victor Drozdov, Polyus's head of investor relations, said.
Polyus said it has already signed sales contracts for all of its 2018 production of antimony concentrate and is preparing to make its first delivery, to China.
Global production of antimony was estimated at 150,000 tonnes in 2017, United States Geological Survey data shows. More than 70 percent of that was produced by China, which has been tightening environmental regulations and beefing up its monitoring capabilities.
Polyus said it plans to produce concentrate containing 200,000 troy ounces of gold annually and 15,000-20,000 tonnes of antimony. The total amount of high content antimony ore to be mined at the Olimpiada deposit between 2017 and 2026 is estimated at 11 million tonnes.
The antimony project will also allow Polyus to reduce its total cash costs by $10 to $15 per ounce, the company added.
Earlier on Tuesday the company said that its total cash cost would be below $425 per ounce in 2018 and below $450 per ounce in 2019-2020. (Reporting by Polina Devitt, Zandi Shabalala and Diana Asonova; Additional reporting by Nallur Sethuraman; Editing by Susan Fenton)