The Cretaceous, coal-bearing Corwin and Chandler Formations accumulated in two river-dominated deltas on the North Slope. The larger Corwin delta (Corwin Formation), in the western portion of NPRA, prograded northeastward and eastward, and the smaller Umiat delta (Chandler Formation), in the southeastern part of NPRA, prograded northward.

Ninety coal samples from these formations within NPRA were collected and analyzed in order to evaluate coal quality and elemental distribution. Their apparent rank ranges from lignite A in the northern part of NPRA to high-volatile A bituminous coal in the southern part. Mean vitrinite reflectance values range from 0.65 to 0.74%. Some Corwin Formation coal samples west of NPRA have coking potential with free-swelling indexes between 3.0 and 5.0. Compared to other western United States Cretaceous coal, NPRA coal is significantly lower in ash, volatile matter, 0, Si, Al, Ca, Fe, Ti, Cu, F, Li, Mn, Mo, Pb, Sb, Se, Th, and Zn. Statistical comparisons of element concentrations indicate that the mean content of Si, Al, K, Li, Sc, Y, and Yb increases as the mean ash content increases (correl tion coefficient at least 0.7). Sulfur values are extremely low (0.1%), and elements that normally show positive correlation with sulfur, such as Fe, As, Cd, Co, Cu, Mo, Pb, and Zn, are also low.

Therefore, coal from NPRA can be characterized by low ash and sulfur contents and low contents of elements of environmental concern, such as As, Be, Hg, Mo, Sb, and Se. The elements found to have positive correlations with ash content are probably present as aluminosilicate or stable oxide minerals. Variations in element content and quality of NPRA coal were probably influenced by the geochemical conditions that existed in the Corwin and Umiat delta systems.

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