The most prolific lignite-bearing stratum in the state is the Sentinel Butte Formation of the Fort Union Group. The most prominent characteristics of the Fort Union Group formations are the cyclical deposition and lateral persistence of the lithologic units, especially the lignite seams. The Sentinel Butte Formation is a continental deposit comprising interbedded calcareous clays, sandy clays, and lignite beds, with isolated lenses of fine-grained sands, silts, and rare limestones, ranging in color from light gray to dark brown and black. Except for the limestones and an upper sandstone unit, the sediments are essentially nonindurated. The claystone and sandstones are generally thinly bedded and not jointed. These sediments were deposited mainly in swamps or in the floodplains of very slow, meandering rivers. The Sentinel Butte Formation conformably overlies the Tongue River Formation (also known as Bullion Creek Formation). The Golden Valley Formation, which is stratigraphically above the Sentinel Butte Formation elsewhere, is absent in the Freedom Mine area, due to postdepositional erosion; therefore, the younger glacial deposits of the Coleharbor Group unconformably overlie the Sentinel Butte Formation in the study area. Outcrops of the Sentinel Butte Formation are sporadic; bedrock is largely masked by residual soils, slopewash, and/or glacial drift. Where the entire Sentinel Butte Formation is present, as in western Mercer County, its thickness is approximately 500 feet ........

The lignite at the Freedom Mine surface mining operation is recovered using dragline and conventional truck and shovel mining methods due to the proximity of the lignite to the surface and the physical characteristics of the deposit. Mining operations includes; suitable plant growth material (SPGM) removal, replacement and storage, overburden removal, lignite production, and spoil backfill and grading. In the development phase, drainage and water control were established, and then the required infrastructure consisting of power, mine office and maintenance facilities, lignite stockpile facilities, and roadways were established.

The Freedom Mine is designed to supply approximately 14 to 16 million tons of lignite per year but generally produces between 12.5 million and 13.5 million tons of lignite coal annually.

TYPE AND GENERAL MINING METHOD
The Freedom Mine is a surface mining operation, which currently encompasses approximately 45,000 acres within the permitted areas. The mineable coal seam is known as the Beulah-Zap bed, ranging from 15 to 22 feet thick, with a weighted average thickness of approximately 18 feet throughout the permit area. The overburden directly above the Beulah-Zap bed ranges in thickness from 25 feet along the cropline, to more than 250 feet in the larger strip ratio areas.

Coteau utilizes standard surface mining techniques to extract coal from the proposed permit area. Mining operations will typically occur in a s ........

No mineral processing occurs at the Freedom Mine.

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