The department, which in 2009 imposed an interim ban that is soon due to expire, now plans a 20-year moratorium on new mines. Western environmental groups have long sought such a measure.
In proposing an extended moratorium last year, the interior secretary, Ken Salazar, cited the potential for pollution in waterways and harm to wildlife, desert vegetation and air quality.
There is perennial dispute over whether uranium contamination detected in the area is natural or caused by humans.
The Center for Biological Diversity, an environmental group, says that at least one creek in Grand Canyon National Park, immediately below an old site known as the Orphan Mine, is contaminated with levels of uranium more than 10 times the federal limit.
Lee Allison, Arizona’s state geologist, citing his office’s work, questioned whether any Colorado River pollution from mining would be detectable, given that about 60 tons of natural uranium flow down the river each year.
