Stripping-coal deposits on lower Lignite Creek, Nenana coal field, Alaska

Abstract

Stripping-coal reserves in an area of about 9.4 square miles extending from the Nenana River about 6 miles up the valley of Lignite Creek are estimated to amount to about 95, 000, 000 tons. The stripping-coal reserves are located in the lower and middle members of the Tertiary coal-bearing formation. Five continuous beds in the middle member range in thickness from 5 to 30 feet, and a discontinuous bed at the base of the lower member is about 60 feet thick. Analyses of outcrop samples, as received at the laboratory, show a heating content of 7,500--8,200 Btu, an ash content of 6 to 14 percent, and a moisture content of 25 percent. The reserve estimate is based on a maximum thickness of overburden of 200 feet. Coal below the level of Lignite Creek or its major tributaries was not considered as it was assumed that stripping would be by hydraulic methods. Uncertainties regarding the position of the coal outcrops and the extent of burning of the coal beds are the basis for a recommendation that, where possible, the stripping reserves be tested by drilling. Overburden consists largely of weakly consolidated sandstone and includes some coarse gravel and a few boulders 20 feet or more in diameter. Water for hydraulic mining can be obtained from the Nenana River. Lignite Creek does not appear to be a dependable source. Disposal of debris may affect the channel of the Nenana River causing damage to railroads and structures. Landslides are common in the valley of Lignite Creek and will affect mining operations and transportation routes.