The Anglo-Australian miner bought 3.7m shares of Ivanhoe for about C$73m (£46m), bringing its stake in the exploration and development company to the maximum level allowed under a pact between the two companies.
The move comes just days after the Mongolian government asked to renegotiate the terms agreed in 2009 on developing the mine – of which they own 30 per cent – demanding to speed up the timetable for its stake to rise.
It is the second time since June that Rio has increased its stake in Ivanhoe, whose share price has been under pressure as investors worry that Mongolian lawmakers will take more control of Oyu Tolgoi as part of a trend of resource nationalism in parts of Asia and Africa.
Ivanhoe discovered the gold-copper ore deposit in 2001 in Mongolia’s Gobi Desert and it currently owns 66 per cent. It is expected to be one of the largest mines in the world when it is developed.
Ivanhoe’s shares closed up 20 per cent at C$3.05 yesterday.