Rio Tinto said Feb. 23 that it is continuing to invest in the U.S. after recently approving a further US$368 million investment to advance its Resolution copper project in Arizona.

Resolution is a joint venture between mining giants Rio Tinto and BHP Billiton Group, through its Resolution Copper Co. and BHP Copper Inc. units, on a 55/45 basis, respectively.

"We are committed to a strong future in the U.S. through our existing operations and new projects like Resolution, one of the most significant and valuable undeveloped copper deposits in the world," CEO Jean-Sébastien Jacques said.

Permitting for the Resolution project was hit by multiple delays, including opposition from local indigenous peoples. Rio Tinto said it has invested US$1.3 billion in infrastructure, geological studies, and permitting.

Meanwhile, the company will also be opening a sales and marketing office in Chicago, Illinois, later this year, in addition to its previously announced commercial and marketing hub in Singapore.