Occurrence of Key Chemical Elements in Late Cretaceous Adaville No. 1 Coal Seam, Kemmerer, Wyoming, Coal District: ABSTRACT

Abstract

The distribution of key chemical elements across an approximately 35 m-thick section of the Adaville No. 1 subbituminous coal seam near Kemmerer, Wyoming, has been examined, using instrumental neutron activation analysis (INAA) and x-ray fluorescence analysis of whole coal samples. In comparing the mean element concentrations for 28 western coals the Adaville No. 1 contains (1) significantly higher concentrations of Br, Ca, Ga, Rb, Sr, and Zr, (2) significant lower concentrations of Al, Ce, Cr, La, and Na, and (3) similar concentrations of Sc, Ti, and V. Scanning electron microanalysis (SEM) of low temperature ash (LTA) revealed the presence of abundant clays and plagioclase feldspar; minor hematite, pyrite, quartz, gypsum, sylvite, amphibole, pyroxene, and rutile; and trace amounts of delafossite (the first recorded occurrence in a coal seam), calcite, cuprite, cassiterite, K-feldspar, and sphene. The cross-seam distribution of these minerals, combined with the similarity of the concentration profiles of Al, Ce, Cr, La, V, Rb, Sr, and Sc to that of LTA, suggest that all of the elements, except Br, Ga, and possible Zr, have significant mineralogical associations with the Adaville No. 1 coal. The presence of authigenic quartz, sylvite, delafossite, gypsum, and pyrite, and crystal solution features, suggest considerablemore » ion mobility during peat deposition and coalification. The mineralogy and trace-element chemistry of the Adaville No. 1 coal seam are consistent with a wave-dominated deltaic depositional environment, long-lived saline conditions during peat accumulation, and a siliceous igneous rock source terrane.« less