Rio Tinto, the world’s third- largest mining company, will spend USD233 million to increase its holding in Ivanhoe Mines Ltd., its partner in the Oyu Tolgoi project.

Rio will buy 15 million shares, to lift its holding 2.7 percent to 22.4 percent.

The shares are being issued to Rio Tinto as part of an accord with Ivanhoe Mines in 2008 to finance equipment for the Oyu Tolgoi copper-gold complex. The mine, described by Rio as the world’s largest untapped copper and gold resource, is expected to start output in 2013, the company said.

Rio can increase its holding in Ivanhoe to about 44 percent by converting a USD350 million loan into stock and exercising all its share purchase warrants, Rio has said.