The Coyote Creek Mining Company, L.L.C. (Coyote), a subsidiary of The North American Coal Corporation (NACoal) is the owner and operator of the Coyote Creek Mine, an active lignite surface mining operation in production status. NACoal is a wholly-owned subsidiary of NACCO Industries (NACCO).
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Summary:
LOCAL GEOLOGY
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 the Bullion Creek Formation). The Golden Valley Formation, which is stratigraphically above the Sentinel Butte Formation elsewhere, is present near the permit boundary, but is gone in the permit 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 upper part of the formation in eastern Mercer County, however, has been removed by erosion, thus it is only about 350 feet thick. The thickening of this formation westward is due also to the increasing thickness of the upper sandstone unit to the west. This upper member is a fine to medium grained, yellowish-brown sandstone. Generally, it is poorly cemented, but locally it is moderately to well cemented. The cemented sandstone is dark brown and forms conspicuous ledges 5 to 10 feet in height, but these are laterally discontinuous.
The Sentinel Butte Formation incorporates a varying number of lignite coal beds. The major lignite bed within the mine area is the Upper Beulah bed, the only economical lignite deposit. This lignite horizon has a thickness of generally 10 to 12 feet, except near the edges of the glacial diversion channels, where some of the lignite bed has been removed by erosion. Also, along the glacial diversion channels are areas of soft lignite (Leonardite). Soft lignite is a result of areas of the bed being exposed to oxidizing conditions via erosion caused by glacial meltwaters. The soft or weathered lignite is of very poor quality and not economically recoverable.
The major lignite bed within the mine area is the Upper Beulah bed. This lignite horizon has a thickness of generally 10 to 12 feet, except near the edges of the glacial diversion channels, where some of the lignite bed has been removed by erosion. Located above the Upper Beulah bed are several thin beds of lignite (Figure 6.2). These include, in the order that they occur, the Harnisch, Twin Buttes, and Schoolhouse beds. The Harnisch is located in an isolated area in the high elevations in the southernmost part of the permit area and ranges in thickness from 1 foot to 6.5 feet. The Twin Buttes is located in the south and west portions of the permit area in the higher elevations and ranges in thickness from 1 foot to 3.5 feet. The Schoolhouse seam spans a large portion of the permit area and ranges in thickness from 1 foot to 3.5 feet. Interburden between the Harnisch and Twin Buttes ranges from 25 to 65 feet. Interburden between the Twin Buttes and Schoolhouse beds ranges between 15 and 50 feet, and interburden between the Schoolhouse and Beulah ranges from 15 to 60 feet.
Located below the Upper Beulah bed are several other beds of lignite. The two splits of the Lower Beulah exist in the permit area. The first split lies an average of 5-25 feet below the Upper Beulah and the second split lies 5-20 feet below the first Lower Beulah split. The major beds, in the order below the Lower Beulah beds that they occur, are the Jim Creek and Antelope Creek beds. These range from 40-50 to 60-75 feet below the Upper Beulah bed. The Jim Creek bed has an average thickness of 3 feet, and lies an average of 40-50 feet below the Upper Beulah bed. The Antelope Creek bed averages 2.5 feet thick, and lies an average of 20-25 feet below the Jim Creek bed. Other thin beds and splits of the two beds, typically less than 2 feet thick, are occasionally found above and below the Jim Creek and Antelope Creek beds. Below the Antelope Creek bed the Kinneman Creek lignite zone can be found. The Kinneman Creek in the area consists of up to four splits with varying thicknesses from 1 to 2.5 feet. Below the Kinneman Creek is the Hagel lignite zone, generally made up of two to three beds, and then below that is the Tavis Creek bed. Below the Tavis Creek bed is generally a long sequence of sands and clays before the next lignite (150-300 feet). The Lower Beulah splits, the Jim Creek, and Antelope Creek seams have all been eroded by glacial meltwater in the glacial diversion trenches and do not exist over the whole permit area. However, according to information gathered, the Kinneman Creek seam and seams below it do exist in the permit area.