FLAGSTAFF - The Navajo Nation is moving closer to getting into the coal mining business.

Tribal lawmakers voted Monday to form a limited liability company that would run the Navajo Mine near Farmington, N.M. The tribe said it will decide by July 1 whether to purchase the mine from Australia-based BHP Billiton for about $85 million.

Navajo President Ben Shelly also must sign off on the creation of the Navajo Transitional Energy Co. LLC. Lawmakers said it would be part of a transition to renewable energy production in the future, though critics of the mine purchase don't believe that.

The Navajo Nation signaled its intent in December to take over the mine that produces between 6.5 million and 8.5 million tons of coal each year, feeding the Four Corners Power Plant in northwestern New Mexico.

The plant's operator, Arizona Public Service Co., has said the production level will decrease when three of the units are shut down and it acquires majority ownership of the other two units.

Tribal lawmakers saw the formation of the company to run a mine as an opportunity to gain control of resources on the reservation and ensure that the jobs and revenue that come with them are protected. The mine's coal has generated more than $40 million for the Navajo Nation, Shelly said.

The Navajo Nation owns and operates about a dozen businesses on the reservation, including a utility company, a transit system, a housing authority, radio stations, an oil and gas company, and shopping centers.

Lori Goodman, of the environmental advocacy group Dine CARE, doesn't want to see a coal mining company added to the list. She said the tribe should await the results of a federal study on the environmental impacts of the power plant and the mine before making any further decisions.

"This is the first time in 50 years there will be an environmental assessment of everything," she said.