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ABSTRACT: Occurrences and Characteristic of Coals, Western Arctic Alaska

Christopher N. Gibson, T. Mowatt

The major coal-bearing units in western Arctic Alaska occur in two sedimentary rock sequences, the Nanushuk Group of Early to Late Cretaceous age and the Colville Group of Late Cretaceous age. The Nanushuk Group in the western Arctic is composed of the Kukpowruk Formation, consisting of delta front sandstone and shale, and the Corwin Formation, comprised of shale, sandstone, and conglomerate deposited in delta plain and alluvial plain environments. Most of the identified coal-bearing units are in nonmarine rocks of the Nanushuk Group. Interpreted data from shallow geophysical logs (natural gamma ray and gamma-gamma density) of seismic shot holes and other information enable correlation of coal beds in specified areas in the foothill and coastal plain regions of the wester Arctic. Coals in the Colville Group are apparently thinner, less abundant, and of inferior quality.

The coal rank ranges between high volatile bituminous and subbituminous. The bituminous coals (moisture free) have low sulfur (0.1-0.5%) and ash (4-15%) content, with heating value approximately of 10,000-14,500 Btu/lb. Some of the coals in the foothills region are of coking quality. The subbituminous coals (moisture free) have 0.2-0.8% sulfur and 3-20% ash, with heating value of between 7000 and 10,700 Btu/lb. The Nanushuk Group may underlie 30,000 mi2 of northern Alaska, where coal resource estimates range from 400 billion to 4 trillion tons.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990