SYDNEY, May 6 (Reuters) - Global miner Rio Tinto RIO.AX RIO.L and its partners on Friday gave the final approval to a $5.3 billion expansion of the Oyu Tolgoi copper mine in Mongolia, paving the way for development of what will become the world's third-largest copper mine.
The expansion into underground mining is regarded as one of the world's best undeveloped copper projects and will drive Rio Tinto's ambitions to become a major global copper producer.
Rio Tinto is operator of the mine, which is 66 percent owned by its Turquoise Hill TRQ.TO arm and 34 percent owned by the Mongolian government.