Quantitative coal mineralogy of the Sydney Coalfield, Nova Scotia, Canada, by scanning electron microscopy, computerized image analysis, and energy-dispersive X-ray spectrometry

Abstract

Automated image and X-ray analysis, with a scanning electron microscope, has been used to "fingerprint" mineral particles in bituminous coals of the Sydney Coalfield and catalogue their chemical class and size distribution. Four seams (Hub, Harbour, Phalen, and Gardiner) were analyzed quantitatively for some 32 000 mineral particles; these analyses revealed particle-size and weight distributions for 27 chemical classes. Manual searches augmented the computer-automated scans, covering eight seams and recording a total of 35 mineral species, their paragenesis, and sites for 28 elements.Sydney seam mineralogy is dominated by pyrite and kaolinite, but illite, chlorite, siderite, ankerite, and quartz are locally prominent; these are accompanied by a large variety of accessory minerals (zircon, rutile, apatite, barite, gypsum, rare-earth phosphates, and ore minerals) and alteration products (goethite and hydrated sulphates). Individual column benches show geochemical fades with different mineral suites resulting from cyclic sedimentation, hydrologie conditions, and changes in pore-water chemistry during peat accumulation, coalification, and diagenesis. A sulphide facies and a siderite–chlorite facies are recognized within one seam (Harbour); these facies change vertically and laterally within lithotype bands.Stratigraphic correlation is precluded, but quantitative mineralogy can elucidate paleoenvironments and be applied to coal-cleaning technology (beneficiation) or environmental studies.