Negotiations with the Mongolian Government over the development of the Oyu Tolgoi mine are still not complete, and as Fairfax Media reported last month, funding commitments from at least 15 commercial banks for the $US5 billion ($5.3 billion) expansion of Oyu Tolgoi expired on March 31.
The Rio subsidiary that is building Oyu Tolgoi - Turquoise Hill Resources - said on Tuesday that it had now asked for extensions of those funding commitments out to September 30.
Rio hopes it will not take that long to strike an agreement with Mongolia, with a agreement mid-year more likely.
Rio shares last traded at $63.26.
After problems with rake blades in the tailings thickeners during the March quarter, sales of copper concentrate from Oyu Tolgoi are now matching production rates.
Rio's annual meeting of shareholders in London will take place later tonight, with the Australian AGM set to be held in May.