The comments from Oyu Tolgoi LLC chief Armando Torres came as an outspoken investor in the struggling Mongolian project reduced its exposure, and as Rio and BHP's plan to build a new copper mine in the US state of Arizona took a step forward.
The busy time for Rio's copper division comes as Rio chief executive Jean-Sebastien Jacques travels to Western Australia this week to inspect efforts to recover from poor performance at the Brockman mines this year.
A $US5.3 billion ($7.8 billion) underground expansion of Oyu Tolgoi is now expected to cost between $US6.5 billion and $US7.2 billion on the back of major delays and a design rethink.
Rio and its partners in the mine have started talking to lenders about increasing the existing $US4.4 billion finance package for the project, but Mr Torres indicated that could be difficult amid the uncertainty created by a review of the project agreements by Mongolian parliamentarians.
The parliamentarians are examining multiple aspects of Mongolia's relationship with Rio and the mine, which was formalised in major agreements in 2009 and 2015.
Speaking at a press conference in Mongolia on Thursday evening, Mr Torres urged the parliamentarians to clarify their stance swiftly.
“Timing is of the essence because we need to go to markets,” Mr Torres was quoted as saying by Bloomberg.
''Without conclusions, it’s difficult to secure additional funds.”
Oyu Tolgoi LLC is a Mongolian company that directly owns the mine. It is 66 per cent owned by Canadian company Turquoise Hill
Resources, which itself is 50.79 per cent owned by Rio.
While Rio, Turquoise Hill and Oyu Tolgoi LLC are expected to make use of extra debt, the scale of the cost blowouts has raised fears that Turquoise Hill may have to conduct a dilutive equity raising.
Those fears have sparked a savage slump in Turquoise Hill Shares
, which have lost 81.5 per cent of their value over the past year, and on Friday were trading at their lowest price since December 2000.
Minority shareholders have been frustrated by the level of control Rio wields at Turquoise Hill, and the most outspoken minority shareholder, Sailingstone Capital, has been selling significant amounts of Turquoise Hill shares over the past year.
Regulatory filings suggest Sailingstone held 258.1 million shares in Turquoise Hill on August 31, 2018, but that stake had fallen to 146 million by July 31, with the bulk of the selling occurring within the past five months.
Sailingstone's stake in Turquoise Hill is now 7.26 per cent, according to Bloomberg data.
Rio is hoping to build a copper mine of similar size to the expanded Oyu Tolgoi mine in the US state of Arizona, and those plans took a step forward over the weekend with the publication of a long-awaited environmental impact statement (EIS) for the Resolution copper project.
Rio owns 55 per cent of Resolution, with BHP owning the other 45 per cent, and the project aims to mine a deep underground deposit close to the historic Magma copper mine that BHP acquired in 1996.
The EIS claimed the project would "increase average annual economic value added in Arizona by about $US1 billion", and said it would deliver annual revenues of about $US200 million to the US federal government.
Resolution is expected to produce 40 billion pounds of copper in concentrate over 40 years, including molybdenum byproducts, via a panel cave more than 2000 metres underground.
If the mine produced at a consistent rate over those 40 years, annual production would be about 450,000 tonnes per year.
The project will partially occur on lands that are sacred to traditional landowners in the region, and the EIS suggests some historical artefacts and human burial grounds could be disturbed by the mine.
US presidential hopeful Bernie Sanders has been a vocal opponent of the project, and earlier this year helped to introduce legislation that would reverse a land swap struck under the Obama administration that was crucial for the project to proceed.
Public hearings into the Resolution Copper EIS will begin next month, and US regulators are scheduled to deliver a draft decision in mid 2020.