Trace element geochemistry and stable isotopic (d(13)C and d(15)N) records of the Paleocene coals, Salt Range, Punjab, Pakistan

The Paleocene coals of the Salt Range in the Punjab Province of Pakistan have great economic potential; however, their trace element and stable isotopic characteristics have not been studied in detail except for a few sporadic samples. In this study, a total of 59 coal samples of which 14 are obtained from open cast mines have been investigated for elemental composition and delta C-13-delta N-15 isotopic signatures. Average contents of trace elements such as Co, Cr, Cu, Pb, Sr, Th, U, V, and Zn are 7.4, 41.7, 11.2, 12.5, 90.2, 4.0, 1.9, 128, and 31.1 mg/kg, respectively. These values, when compared with the World Coal Clarke values, were relatively higher in low-rank coals in comparison with Clarke values for brown coals. Likewise, As (20.4 mg/ kg), Co (6.6 mg/kg), Cr (22.4 mg/kg), Cu (13.3 mg/kg), Pb (19.2 mg/kg), Sr (154.7 mg/kg), Th (2.5 mg/kg), V (47.8 mg/kg), and Zn (75.1 mg/kg) were significantly higher in the sub-bituminous to bituminous coals of the Salt Range. Mineralogical analysis, based on X-ray diffraction and energy dispersive X-ray spectroscopy, revealed that the studied samples contain illite, kaolinite calcite, gypsum, pyrite, and quartz. Elemental affinity with organic and inorganic phases of coals calculated by an indirect statistical approach indicated a positive association of ash content with Ag, Al, Co, Cr, Cs, Cu, Mn, P, Rb, Pb, Th, U, and V, suggesting the presence of inorganic components in studied coals. However, As, Fe, Sr, and Zn exhibit negative correlations that imply their association with the organic fraction. The delta C-13 and delta N-15 isotopic range and average-24.94 parts per thousand to-25.86 parts per thousand (-25.41 parts per thousand ) and-2.77 parts per thousand to 3.22 parts per thousand (0.96%), respectively, reflecting 3C type modern terrestrial vegetation were common in the palaeomires of studied coal seams. In addition, the trivial variations of 0.92 parts per thousand and 0.45 parts per thousand among C-13 and N-15 values can be attributed to water level fluctuations and plant assemblies.(c) 2022 Published by Elsevier B.V. on behalf of China University of Mining & Technology. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

The study of Paleocene coals in the Salt Range of Punjab Province, Pakistan revealed relatively high trace element contents and associated them with organic and inorganic phases. Isotopic analysis indicated the presence of modern terrestrial vegetation in the ancient peat deposits of the coal seams.