Paleoenvironmental and environmental implications of the boron content of coals

The concentration of boron in Australian and Canadian coals was determined in order to assess the variation of boron in coal with respect to rank, age, geological setting and the degree of paleosalinity of the coal-forming environment. The study indicates that relations between boron and rank are either very complex or non-existent, and the boron content of coals is not governed by the age of the coal. The boron content of seams is sensitive to the environment of deposition and may show the variation in the same seam laterally due to changes to the environment of deposition and/or the enrichment of boron by a secondary source. It is proposed that the following ranges of values for boron in coal indicate the degree of marine influence during the early stages of coalification: 1. Up to 50 ppm boron - coal formed in a freshwater environment; 2. 50 to 110 ppm boron - coal formed in a mildly brackish water environment; 3. >110 ppm boron - coal formed in a brackish water environment. The vertical variation of boron in a coal-bearing section or strata is related to the depositional environment. There is often little variation in boron content for coal layers as compared to the partings (dirt bands). The boron content of parting(s) in a coal-bearing strata may vary greatly as compared to the coal seams. The variation of boron in heat-affected coal seams indicates that the behaviour of boron during the natural heating/burning of coal is dependent on the temperature of the system and the nature of the process.