Relations between chlorine in coal and the salinity of strata waters

Abstract

Studies of coal and strata water analyses have established that the distribution of chlorine in coal seams is closely related to the occurrence of brines in the deeper Coal Measures basins. The sodium and chlorine present in the coals are believed to have been adsorbed from the brines. Higher-rank coals, i.e. over 86% carbon dmmf, appear to be unable to adsorb more than very small amounts of these ions, rarely over 0.2% chlorine, even when brines are associated with them. Hypersaline brines with concentrations of dissolved solids up to 200 g/l occur in several of the Northern and Midlands coalfields; strata waters from the Southern coalfields of Britain have significantly lower salinities. The apparently anomalous occurrence of high-chlorine coals closely below the Permian unconformity in south-east Durham may be due to the presence of secondary brines derived in part from the overlying Permian beds. Several lines of evidence suggest that the ingress of chloride salts followed the imposition of the rank patterns upon the British coalfields, probably during the Hercynian orogenic movements.