Trace elements in the Lower Pliocene fossiliferous Kangal lignites, Sivas,Turkey

The Kangal lignite basin, which is one of the most productive lignite basin s in eastern Anatolia-Turkey, includes two lignite seams containing abundan t gastropoda. shells in the Lower Pliocene Kalburcayiri Formation. The seam s are currently exploited in an open-cast mine in the Kalburcayiri field an d supply feed coal to a power plant with 300-MW capacity. The average thick ness of each of the two seams in this mine is about 10 m, and they are sepa rated by about 20 m of tuffaceous sedimentary rocks. A 15-20-cm thick tuff bed occurs within the upper seam. The purpose of the study was to understan d mineralogy and trace element concentrations of the two lignite seams in t he Kalburcayiri Formation which were affected by volcanic ashes. Fifty-nine core samples of the lignites from seven boreholes across the basin, and ei ght channel samples from the working lignite seams were collected and analy sed by proximate analysis, X-ray powder diffraction (XRD), inductively coup led plasma-mass spectrometry (ICP-MS), and scanning electron microscopy (SE M) with energy-dispersive X-ray microanalysis techniques. The samples show that the worked lignite seams, on an as-received basis, contain high moistu re contents (43.4-57.8%). All the samples on an air-dried basis have high a sh yields (from 19.5% to 81.7%) and a broad range of total sulfur contents (from 1.16% to TOM), and calorific values (684 to 4621 kcal/kg), except for two samples with no temperature rise due to high ash yield. The mineral ma tter of the studied samples is made up of calcite, quartz, feldspar, pyrite , opal-CT, clay minerals, gypsum and traces of aragonite. The trace element analyses, on a whole-coal dry basis, indicate that most of the borehole sa mples showed enrichment in specific elements, including Zn (15-1394 mug/g), Mo (13-368 mug/g), and U (5.5-131 mug/g), when compared to the range of th ese elements for most coals in the world. The contents of Zn, Mo, and U for the samples from the worked lignite seams are, respectively, 38-187, 54-16 1 and 28-55 mug/g. The SEM studies show that Zn is hosted mainly in. micron -sized. Zn-bearing mineral (sphalerite), but no Mo- and U-bearing minerals have been detected during these studies, except for monazites containing Th and U traces. The Mo and U concentrations are negatively correlated with t he ash yields, and these elements are contained mainly within organic matte r. (C) 2001 Elsevier Science B.V. All rights reserved.