Rio Tinto is reportedly looking to raise its stake in the company operating Mongolia's flagship copper and gold mine Oyu Tolgoi as the Anglo-Australian company prepares to spend $5.3bn on developing the mine.

London’s Sunday Times reports that Rio Tinto has hired Goldman Sachs to look for potential co-investors in New York-listed Turquoise Hill Resources, the Australian Financial Review reported on June 13. Rio Tinto owns 51% of Turquoise Hill Resources, which controls a 66% stake in Oyu Tolgoi with the remaining 34% in the hands of the Mongolian government.

Goldman Sachs has “sounded out potential buyers, including Chinese state-owned companies, trading houses and pensions funds” about taking a minority stake in Turquoise Hill Resources, according to Sunday Times report. Any buyout will not be cheap, as Rio Tinto and its potential partner would need to spend more than $3bn to buy out the minority shareholders. Both Rio and Goldman declined to comment.

Rio Tinto’s interest in gaining more control over Oyu Tolgoi comes as no surprise given that the miner approved last month a $5.3bn financing for the development of the mine. Mongolia’s government and London-based Rio Tinto struck a long-awaited deal on the multi-billion underground expansion of the mine in May 2015 ending nearly a two-year-long stalemate in talks.

In December, Rio Tinto secured a $4.4bn debt package for the mine expansion. Works on the project, which will more than double output at the mine, will start in mid-2016 after Mongolia’s government and Rio Tinto secure all necessary permits. First draw bell production from the underground mine is expected in 2020. California-based Jacobs Engineering has joined the project at the beginning of June.

The feasibility study for the project sees recoverable copper of 25bn pounds, 12mn ounces of gold and 78mn ounces of silver over 41 years. Following the completion of underground development, the Oyu Tolgoi mine is expected to produce an annual average of 560,000 tonnes of copper between 2025 and 2030, compared to the current annual output of 175,000-200,000 tonnes.