Boron isotope composition of coals: a potential tracer of organic contaminated fluids

摘要

The B-content of coals from sedimentary basins is a function of the primary depositional environment and secondary enrichments. Boron has been used to infer paleo-environments of coal deposits, and environmental impact of coal burning power plants. To improve our understanding of B in organic matter, this study used secondary ion mass spectrometry to measure the B-isotopic composition of 25 coals and three kerogens (Type I, II and III).Results show that coal is B-10-enriched compared to most terrestrial waters. The delta(11)B values measured show large variability within a single 'homogenized' coal sample indicating that B is heterogeneously bound in various organic macerals. Of greater importance is the observation that all coal delta(11)B values are negative. The lowest delta(11)B measured was -70parts per thousand representing the lightest B-isotopic ratios ever reported for terrestrial materials. Bulk analyses of coals may not reveal isotope ratios this low because of the averaging of values from different organic macerals having different delta(11)B values.This discovery may be important for tracing organic contaminants in fluids. When organic matter is heated during burial, the isotopically light B partitions into fluid phases. The very low delta(11)B of organic products compared to most groundwaters may be useful in tracing fluids derived from organic sources. (C) 2004 Elsevier Ltd. All rights reserved.