Rio Tinto has increased its mineral resources at its Kennecott Utah Copper Bingham Canyon mine in the US by 20 million tons, the company has announced.

The rise in assets brings the total tonnage of resources at the mine to 106 million tons.

The resource addition, known as the North Rim Skarn, has increased the contained metal in mineral resources by 730,000t of copper, one million ounces of gold and 13 million ounces of silver over the 2010 year-end mineral resource estimate.

The North Rim Skarn deposit is located about 300m below the current Bingham Canyon pit and is expected to be developed by underground methods.

Rio Tinto will invest $165m to complete the next stage of exploration and development studies by 2014, which will include final shaft rehabilitation, an access decline from the pit and further underground exploration drilling.

The firm is also planning to further invest $238m to advance studies extending the open pit life to 2028 and the purchase associated long-lead time equipment.