The U.S. Congress has cleared the way for global miners Rio Tinto (RIO.L) (RIO.AX) and BHP Billiton (BHP.AX) (BLT.L) to swap land with the government, which will allow them to build a long-delayed $6 billion copper mine in Arizona.

The land swap, first proposed nine years ago, was tucked into the annual defense policy bill passed by the Senate on Friday and the House last week. The bill will now be sent to President Barack Obama to sign it into law.

The Resolution copper mine, 55 percent owned by Rio Tinto and 45 percent owned by BHP, could produce more than 1 billion pounds of copper a year at its peak, which would make it the largest copper producer in North America and one of the biggest in the world, according to its website. (www.resolutioncopper.com)

Rio and BHP need the land exchange, long opposed by environmental and native American groups, to develop the massive underground mine, where the companies have already spent more than $1 billion on drilling and digging a 1.3-mile (2 km) shaft.

The mine development plan, submitted a year ago, has yet to be approved by the government.

The Resolution project was picked up by BHP in its disastrous acquisition of Magma Copper in 1996, on which it lost A$3.2 billion.