By MEAD GRUVERCHEYENNE, Wyo. (AP) â¿¿ Wyoming's newest uranium mine could account for a substantial portion of the state's uranium production in a couple years. Production began Monday at Cheyenne-based Cameco Resources' North Butte Mine, which is west of Wright in southwestern Campbell County. Cameco Resources is a subsidiary of Saskatoon, Saskatchewan-based Cameco Corp., one of the world's largest uranium producers. The new mine is part of an aggressive expansion program by Cameco amid a soft uranium market. Uranium prices are about $40 per pound, down from about $70 just before the Fukushima, Japan, nuclear disaster two years ago revived fears about nuclear energy as a safe power source. Cameco plans to open five more uranium mines â¿¿ two in Wyoming and three in Nebraska â¿¿ over the next few years. "It's not a strong market and there are a lot of factors influencing that. But we are moving ahead with our growth projects in the U.S. because we're optimistic about the future of nuclear power," Cameco spokesman Ken Vaughn said Tuesday. Cameco officials expect the North Butte mine to produce 300,000 pounds of uranium ore this year, with production ramping up to 700,000 pounds in 2015. Wyoming produces more uranium than any other state â¿¿ about 1.6 million pounds a year, or close to one-third of all U.S. production. North Butte is an in-situ mine, where wells pump uranium-bearing solution from sandstone aquifers. At North Butte, the sandstone is about 600 feet below ground. Other wells at in-situ mine sites inject a solution called a lixiviant â¿¿ typically water mixed with oxygen and/or hydrogen peroxide, and sodium carbonate or carbon dioxide â¿¿ to release the uranium. Equipment at the surface processes the solution into yellowcake, an intermediary ore that can be processed into nuclear fuel. North Butte is a satellite mine of Cameco's Smith Ranch-Highland Mine north of Glenrock in Converse County. Cameco will truck uranium-bearing resin from North Butte to Smith Ranch-Highland for processing into yellowcake.