Preliminary report on coal resources of the Otter Creek EMRIA site, Powder River County, Montana

Abstract

The Knoblock coal bed in the Otter Creek EMRIA (Energy Minerals Rehabilitation Inventory and Analysis) site--an area of about 1,177 acres (476 hectares)--contains estimated identified coal resources of about 126 million short tons (114 million metric tons). The area around and including the Otter Creek EMRIA slte--an area of about 2,975 acres (1,204 hectares)--contalns estimated identified coal resources of about 318 million short tons (289 million metric tons). All estimated coal resources in the Knoblock bed are categorized as measured and indicated resources, and all but about 62 million tons (56 million metric tons) are at depths of less than 200 feet (60 metres). The average thickness of the Knoblock is about 61 feet (18.6 metres) and the overall relationship of quantity of overburden to tons of coal in the area with 200 feet (60 metres) or less of overburden is about 2 cubic yards (1.5 cubic metres) of overburden per ton of coal. The coal is subbituminous C in rank, has an average sulfur content of less than 0.2 percent, and has an average ash content of about 5.5 percent. The major and minor element composition of coal, coal-ash, and rock samples from the area is similar to the average composition of other coals of the Northern Great Plains and to the average rock composition of the Earth's crust. Only the selenium content of the Knoblock coal is more than an order of magnitude higher than that in the continental crust.