Mineral resources of Alaska, 1956

Abstract

The Jarvis Creek coal field lies on the north side of the Alaska Range, between latitudes 63°35' and 63°45' N., and longitudes 145°40' and 145°50' W. It is 3 to 6 miles east of the Richardson Highway. The coal field is about 16 square miles in area, the major part of which is a rolling plateau that slopes gently northward and is bounded on the east, south, and west by bluffs facing Jarvis Creek, Ruby Creek, and the Delta River. : The oldest rock is the Birch Creek schist of pre-Cambrian age, which is largely quartz-sericite schist with many quartz veins, and is locally intruded by rhyolite dikes. It is overlain by the Tertiary coal-bearing formation. Quaternary deposits include gravel, till, solifluctional debris, and windborne deposits. The coal-bearing formation of the Jarvis Creek coal field is correlated with the lower member of the coal-bearing formation on Healy Creek. In the south part of the coal field, it is divided into three stratigraphic units: (1) A basal lenticular toed, 500 feet in maximum thickness, consisting of micaceous sandstone and quartz conglomerate, derived from sources in Birch Creek schist southwest of the coal field; (2) a middle unit, 450 to 700 feet thick, of buff arkosic sandstone derived from areas north of the coal field, with interbedded shale and coal; and (3) an upper unit, about 900 feet thick, of dark-gray claystone, sandstone, and thin coal beds. The coal-bearing formation is warped into a north-trending structural basin. Dips around the border of the basin range from 5° to 10°. Thirty coal beds were found, but most are thin and discontinuous. Reserves total 5.9 million tons of indicated coal and 7.5 million tons of inferred coal. Stripping reserves are estimated to be between 100,000 and 300,000 tons. The greater part of the coal reserves is in a 50-foot zone of coal and shale at the base of the middle stratigraphic unit. The coal field potentif lly contains about 75 million tons of coal. Based on outcrop samples, the coal has a heating value of between 8,000 and 9,000 Btu (as received) and an ash content of 5 to 13 percent. It is classified as subbituminous C.