Rio Tinto has announced an investment of $652 million (Rio Tinto's share $341 million) to support continued pre-feasibility studies on a large, tier-one copper deposit at its Resolution Copper Mining LLC (RCML) operation in Superior, Arizona.

Resolution Copper Mining (RCM) is jointly owned by Rio Tinto and rival BHP Billiton through their subsidiaries.

Rio Tinto's Resolution Copper Company, owns a 55-per cent stake in RCML and is the manager of the operation. BHP Billiton's subsidiary BHP Copper, Inc, owns the remaining 45 per cent. The project is located in the historic mining district about five kilomotres east of Superior, Arizona.

Pre-feasibility studies are expected to be completed by 2012 with production at the new mine expected to start by 2020, eventually ramping up to 500,000 tonnes per annum of copper.

Rio Tinto is a significant global copper producer with high quality assets and an interest in four of the world's ten largest undeveloped copper deposits, including Resolution. In 2007, copper was the biggest contributor to Rio Tinto with underlying earnings of $3.479 billion.

"Rio Tinto's copper operations are in the first quartile of the cost curve and we are well positioned to take advantage of strong global demand, driven by continued growth in China and other emerging economies, " said Bret Clayton,  chief executive, Rio Tinto Copper. "Resolution is an exciting prospect with an expected long mine life."

Resolution Copper announced on 29 May  that it had completed sufficient drilling on the deep porphyry copper deposit to report an Inferred Resource of 1.34 billion tonnes containing 1.51 per cent copper and 0.040 per cent molybdenum.

Pre-feasibility work scheduled over the next four years includes dewatering a former mine site and sinking an exploratory shaft to 2170 meters below the surface, as well as preparing numerous studies to evaluate technical, legal and environmental issues and to prepare a mining plan. The plan will include an examination of geohydrology, transportation and infrastructure needs, and will confirm the best approach to constructing the proposed underground mine.

The total cost to complete studies of the deposit,  determine the safest and most efficient mine development approach and evaluate all associated costs will be about 1 billion. Before these studies can be completed and the mine developed, Resolution Copper needs to own and manage surface lands above the mine and in the immediate surrounding area. In return for this land, Resolution Copper will transfer to the US government over 5,500 acres of high-priority conservation lands.

Passage of the Southeast Arizona Land Exchange and Conservation Act, currently under review in the US Congress, will accomplish this goal, and will also benefit the Town of Superior, the region and the state of Arizona.

The other three major undeveloped copper resources in which Rio Tinto has an interest are La Granja in Peru, Oyu Tolgoi in Mongolia and Pebble in Alaska.