TRACE-ELEMENT GEOCHEMISTRY OF THE OBED MOUNTAIN DEPOSIT COALS, ALBERTA, CANADA

This study reports on the elemental concentrations and vertical variat ion of coal seams from the Obed Mountain deposit, Alberta Foothills, C anada. Results from two sections of Seam 1 show that the major element s (i.e. Al, Fe, Mg, K, Na, Ti, and Si) have high concentrations in int ervals having high ash content, with the only exception of Ca. Similar ities are apparent, in both sections, in the vertical variations of Th , U, Se, and Zn; Rb, Cs, and K; Sb, Mo, and W; Mn and Sr; and Ba, Cr, Co, Hf, and Sc. These similarities are also evident among the REEs, no tably between Ce and La; also between Dy, Eu, and Sm. Most elements, w ith the exception of Ba and Sr are slightly more concentrated in Secti on 2 of Seam 1, located approximately 1.5Fig. km away from Section 1. Compared to Seam 1, Seam 2 has lower mean concentrations of elements. Boron in the coal ranges from 27 to 100 ppmw, though most values are l ess than 50 ppmw. Boron concentrations suggest a freshwater deposition al environment. The element is depleted in the sedimentary partings (1 2-29 ppmw only) and is enriched in the coal interval near the roof and immediately beneath the partings. This enrichment shows possible down ward mobilization of boron. Vertical variations of elements are helpfu l in delineating the boundaries between coal and sedimentary partings in the succession. The Obed Mountain coals are ''clean'' by world stan dards and their elemental concentrations are comparable with those in coals of a lower rank from the same coal formation used for power gene ration in Alberta. All sedimentary partings have low concentrations of Ba, Hf, Sc, Sr, Ta, Th, U, and REEs; this, along with the absence of an Eu negative anomaly suggests a non-volcanic origin for the partings . (C) 1997 Elsevier Science Ltd.