Variations in elemental composition of macerals with vitrinite reflectance and organic sulphur in the Greta Coal Measures, New South Wales, Australia

The elemental composition of the individual macerals in the Early Permian Greta Coal Measures of the northern Sydney Basin and adjoining Cranky Corner Basin, New South Wales, including some seams with high to,,cry high organic sulphur contents, have been analysed in polished sections using light-element electron microprobe techniques, and the results evaluated in the light of vitrinite reflectance and other characteristics of the coals concerned. As with other Australian coals, the vitrinite macerals in each sample have the lowest proportions of carbon and highest proportions of oxygen, and the inertodetrinite and fusinite macerals the highest C and lowest O contents. Semifusinite and the liptinite macerals have intermediate C and O percentages. Organic sulphur and organic nitrogen are also highest in the vitrinite macerals of the individual samples, and lowest in the fusinite and inertodetrinite components. The vitrinite rnacerals in the Puxtrees seam of the Greta Coal Measures on the Muswellbrook Anticline, in the upper Hunter Valley, have similar elemental compositions (78% C) and similar reflectance values (Rv(max) around 0.7%) to vitrinites in the Late Pen-man bituminous coals in other parts of the Sydney-Bowen Basin. The vitrinites in the seams of the Cranky Corner Basin also have similar carbon contents to the Puxtrees seam material, suggesting a similar rank level, but have much lower vitrinite reflectance values(Rv(max) = 0.4-0.5%), probably due to marine influence associated with the depositional system. The vitrinites in the Greta seam on the Lochinvar Anticline, in the Lower Hunter region, have higher carbon contents (83%) than the Puxtrees material, suggesting a higher rank level, but similar to lower vitrinite reflectance values (Rv(max)=0.6-0.7%). Vitrinite carbon is also constant through the seam profile, despite upwardly decreasing reflectance values in the seam due to progressive increases in marine influence. The vitrinites in the upper Greta seam and the Cranky Corner Basin coals have high to very high organic sulphur contents, again probably due to marine influence on the depositional process. The vitrinites in the Cranky Corner Basin coals, which have particularly high organic sulphur contents, also have somewhat lower oxygen contents in relation to their carbon percentages than those of other Australian seams, suggesting that the additional organic sulphur has replaced oxygen in the macerals' molecular structure. The macerals, especially the vitrinites, in the coals with high organic sulphur and anomalously low vitrinite reflectance also have up to 0.5% Al and 1% Ca intimately associated with the organic matter. Similar organically associated inorganic elements are commonly found in lower-rank (e.g. sub-bituminous) coals, but are usually lost from the organic matter at higher rank levels. The coals of the Greta Coal Measures therefore have vitrinite carbon contents consistent with a high volatile bituminous rank, but those seams or parts of seams with high organic sulphur due to substantial marine influence appear to have preserved the vitrinite reflectance values and organically associated inorganic elements more typical of lower-rank, sub-bituminous materials. (c) 2006 Elsevier B.V. All rights reserved.