(Adds gold production, forecast, background)
July 15 (Reuters) - A project financing agreement for the underground expansion of Oyu Tolgoi, a massive copper and gold mine in Mongolia, is expected to be signed by year end, mine owner Rio Tinto's Turquoise Hill Resources unit said on Wednesday.
Oyu Tolgoi produced 52 percent more copper concentrate in the second quarter, or 55,300 tonnes, than in the same period a year ago, Turquoise Hill said. This is the highest quarterly concentrate production since operations began.
Gold concentrate production was 238,000 ounces, more than double the 113,000 ounces in the second quarter of 2014.
Turquoise Hill repeated its previous forecast for full-year output of 175,000 to 195,000 tonnes of copper and 600,000 to 700,000 ounces of gold in concentrates.
In May, Mongolia and Rio Tinto reached an agreement that paved the way for work to resume on the $5 billion mine that is expected to drive growth for the country and company. A crucial next step for the expansion is securing finance.
Oyu Tolgoi started production in 2013. (Reporting by Nicole Mordant in Vancouver; Editing by Toni Reinhold)