Abstract

The Wyodak coal at Wyodak, Wyoming, is composed of the Lower Canyon bed and the overlying Anderson bed. A claystone parting separates the coal beds. Samples from a continuous 282-ft core of the Wyodak bed were analyzed for their maceral and major and trace element contents. Collinite is the dominant maceral in both beds; the collinite:telinite ratio is greater than 30:1. Abundant liptinites are also characteristic of the coal. Inertinites are much less common, though the Canyon bed has several zones enriched in inerts. The Anderson bed has no inertinite zones, but contains more carbonaceous shale beds and pyrite than the Canyon coal. The claystone parting is believed to have formed as lacustrine conditions temporarily caused destruction of the vegetation.

The Canyon bed apparently formed under marshy conditions characterized by fluctuating water levels, while the Anderson bed formed in a forested environment with a high water table; the abundance of dispersed pyrite in the Anderson bed is attributed to persistent reducing conditions caused by the high water levels.

Inductively Coupled Argon Plasma (ICAP) analysis of samples indicates minor enrichment of Sr, minor depletion of Fe, K, Mo, and Az, and significant depletion of Ba relative to average concentrations in coals of the Powder River Basin. New mine site occurrences of Ce and Nd are noted. Relative to overburden, the coal exhibits depletion of Ba, Ga, La, Mn, Mo, Nb, Pb, Sc, Th, Yb, and An, and no significant enrichment of any element; claystone samples are enriched in Cu and depleted in Mn. Twenty-one of twenty-nine elements display their highest concentrations in the Anderson bed, supporting the idea that high water levels and greater movement of fine-grained mineral matter existed during Anderson bed deposition.