The influence of geological factors on the concentration of boron in Australian and Canadian coals

Abstract The concentration of boron in Australian and Canadian coals determined using atomic emission spectrometry (AES), inductively coupled plasma spectrometry (ICP-AES) and prompt gamma-ray spectrometry is summarized in order to assess the variation of B content in coal with respect to rank, age, geological setting (in-seam and stratigraphic) and the degree of paleosalinity of the coal-forming environment. This study indicates that no/or very complex relations exist between boron and rank (subbituminous to anthracite). Variations of B with ash content for Canadian coals of different age (Devonian to Oligocene-Eocene) indicate that the B content of coals is not governed by the age of the coal. There is some evidence of variation of B with maceral content in Canadian coals, particularly as related to the inertinite and vitrinite content of coals. The B content of coal seams is sensitive to the environment of deposition, with B contents remaining relatively stable and within the range of values designated for each depositional setting. However, B values may show variation in the same seam laterally due to changes of the environment of deposition and/or the enrichment of B by a secondary source. The vertical variation of B in a coal-bearing section or strata is related to depositional environment and lithology of rock. There is often little variation in B content for coal layers as compared to the partings (dirt bands). The B content of partings in a coal-bearing strata may vary greatly as compared to the coal seams. After reappraising earlier work, and on the basis of more recent studies on Australian and Canadian coals, it is proposed that the following ranges of values for B in coal indicate the degree of marine influence during the early stages of coalification: • up to 50 ppm B: freshwater-influenced coals • 50–110 ppm B: mildly brackish water-influenced coals • >110 ppm B: brackish water-influenced coals. Using these criteria, assessments are given for the degree of marine influence on Canadian and Australian coals.