A mining company plans exploratory work beginning this spring on private property within Montana's Crow Indian Reservation that's estimated to hold 400 million tons of coal.
The proposal from Signal Peak Energy adds to a spate of recent interest in the region's huge coal reserves despite flagging domestic demand for the fuel.
Signal Peak operates the Bull Mountain mine north of Billings and exports much of its coal to customers in Asia.
The exploration area on the reservation is just a few miles from the neighboring Northern Cheyenne Indian Reservation, and about 30 miles north of Wyoming.
Federal officials have given initial approval to the work, but it remains subject to appeal through March 22.
Crow attorney Bill Watt says the tribe has held preliminary discussions with Signal Peak.