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Location: 86 km S from Gillette, Wyoming, United States
Caller Box 3035GilletteWyoming, United States82717-3035
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The Wasatch Formation and local Quaternary age deposits comprise all of the overburden lithologies at the mine site. The Wasatch consists of alternating, lenticular deposits of sandstones, siltstones, claystones, coal, and carbonaceous shales. Coal has been mined exclusively from the Wyodak-Anderson (WA) Seam. The remaining coal is 50-87 ft thick and 180 to 460 ft deep within the leased area. The WA seam is in the uppermost section of the Paleocene Fort Union Formation. The coal is thickest on the northwest side of the lease. There are two main geologic features at NARM. The first is a monocline that exists in a northwest to southeast trend over the middle portion of the mine. The lower 12-14 feet of the WA seam splits off as a hanger seam (Lower Wyodak-Anderson, or LWA) and has a steeply dipping gradient after it splits. The LWA seam is not mined because of poor quality and an increasingly high strip ratio. The mineable WA coal thickness averages 80 feet in the west and 60 feet east of the monocline. The second geologic feature is a ribbon split occuring in the southwest portion of the lease and trending northwest to the southeast. The WA splits into two nearly equally thick (30-35 ft) mineable seams: WA1 (upper split) and WA2 (lower split). The midburden between the WA1 and WA2 increases to a maximum of 120 ft thick. Structurally, the WA2 seam remains relatively flat, whereas the WA1 rides up over the parting and has a dipping structure. In conclusion, several thin rider seams (1-4 feet in thickness) occur within the overburden. They are quite consistent throughout the eastern portions of the lease but become more sporadic west of the splitline. The rider seams are not mined due to poor quality. The WA in the northern half and the WA1/WA2 in the southwest are the only seams mined at NARM. There are no known faults within the controlled coal area.NARM is on the eastern flank of a regional syncline. The bedding inclination is gentle with dips less than three degrees toward the west. Because of the undulating character of the coal beds, there can be localized dips toward the east. Many of the coal beds in the Fort Union and Wasatch formations have been oxidized and burned along their outcrops producing clinker (locally referred to as the scoria). The clinker is the baked or thermally altered shale and sandstone in the strata overlying the burned-out coal bed.Mineralization and Deposit Type The mined coal at NARM is high volatile sub-bituminous C as defined by ASTM coal rank. The coal seam has very low sulfur content and is marketable as thermal coal for power generation. The heating value of the coal seams ranges from 8400 to 9250 BTU per pound over the remaining project area and the heating content generally increases with increasing depth.The area is categorized as having low geologic complexity based on the following factors: - The Wyodak-Anderson (WA) seam is laterally continuous and can be correlated using geophysical logs across large distances with high confidence. - The seam is generally flat-lying and gently dipping towards the west with minor undulations. The depth of cover to the WA seam is generally shallow from the outcrop along the east to a maximum of 450 ft and averaging 320 ft for the remainder of the reserve. - There are no major geologic anomalies across the area except for two well-defined seam split areas: a ribbon split in the southwest and a monocline with a hanger seam toward the east. - The WA seam is currently mined across most of Campbell County and the northern portion of Converse County. - Local quality variations are small and regional quality trends have been established from a long mining history.
