INFLUENCE OF AN IGNEOUS INTRUSION ON THE INORGANIC GEOCHEMISTRY OF A BITUMINOUS COAL FROM PITKIN COUNTY, COLORADO

Although the effects of igneous dikes on the organic matter in coal ha ve been observed at many localities there is virtually no information on the effects of the intrusions on the inorganic constituents in the coal. Such a study may help to elucidate the behavior of trace element s during in situ gasification of coal and may provide insights into th e resource potential of coal and coke affected by the intrusion. To de termine the effects of an igneous intrusion on the inorganic chemistry of a coal we used a series of 11 samples of coal and natural coke tha t had been collected at intervals from 3 to 106 cm from a dike that in truded the bituminous Dutch Creek coal in Pitkin, CO. The samples were chemically analyzed for 66 elements. SEM-EDX and X-ray diffraction an alysis were performed on selected samples. Volatile elements such as F , Cl, Hg, and Se are not depleted in the samples (coke and coal) neare st the dike that were exposed to the highest temperatures. Their prese nce in these samples is likely due to secondary enrichment following v olatilization of the elements inherent in the coal. Equilibration with ground water may account for the uniform distribution of Na, B, and C l. High concentrations of Ca, Mg, Fe, Mn, Sr, and CO2 in the coke regi on are attributed to the reaction of CO and CO2 generated during the c oking of the coal with fluids from the intrusion, resulting in the pre cipitation of carbonates. Similarly, precipitation of sulfide minerals in the coke zone may account for the relatively high concentrations o f Ag, Hg, Cu, Zn, and Fe. Most elements are concentrated at the junctu re of the fluidized coke and the thermally metamorphosed coal. Many of the elements enriched in this region (for example, Ga, Ge, Mo, Rb, U, La, Ce, Al, K, and Si) may have been adsorbed on either the clays or the organic matter or on both. (C) 1998 Elsevier Science B.V.