Mineral matter and trace elements in coals of the Gunnedah Basin, New South Wales, Australia

The concentrations of major and trace inorganic elements in a succession of Permian coals from the Gunnedah Basin, New South Wales, have been determin ed by X-ray fluorescence techniques applied to both whole-coal and high-tem perature ash samples. The results have been evaluated in the light of quant itative data on the minerals in the same coals, determined from X-ray diffr action study of whole-coal samples using a Rietveld-based interpretation pr ogram (SIROQUANT(TM)), to determine relationships of the trace elements in the coals to the mineral species present. Comparison of the chemical compos ition of the coal ash interpreted from the quantitative mineralogical study to the actual ash composition determined by XRF analysis shows a high degr ee of consistency, confirming the validity of the XRD interpretations for t he Gunnedah Basin materials. Quartz, illite and other minerals of detrital origin dominate the coals in the upper part of the sequence, whereas authig enic kaolinite is abundant in coals from the lower part of the Permian succ ession. These minerals are all reduced in abundance, however, and pyrite is a dominant constituent, in coals formed under marine influence at several stratigraphic levels. Calcite and dolomite occur as cleat and fracture infi llings, mostly in seams near the top and bottom of the sequence. The potass ium-bearing minerals in the detrital fraction are associated with significa nt concentrations of rubidium, and the authigenic kaolinite with relatively high proportions of titanium. Zirconium is also abundant, with associated P and Hf, in the Gunnedah Basin coal seams. Relationships exhibited by Ti, Zr, Nd and Y are consistent with derivation of the original sediment admire d with the seams from an acid volcanic source. Pyrite in the coals is assoc iated with high concentrations of arsenic and minor proportions of thallium ; no other element commonly associated with sulphides in coals, however, ap pears to occur in significant proportions with the pyrite in the sample sui te. Small concentrations of Cl present in the coal are inversely related to the pyrite content, and appear to represent ion-exchange components associ ated with the organic matter. Strontium and barium are strongly associated with the cleat-filling carbonate minerals. Ge and Ga appear to be related t o each other and to the coal's organic matter. Cr and V are also related to each other, as are Ce, La, Nd anti Pr, but none of those show any relation ship to the organic matter or a particular mineral component. (C) 1999 Else vier Science B.V. All rights reserved.