Dissolved sulphate δ 34 S and the origin of sulphate in coal mine waters; NE England

Abstract

Coal mine waters have been sampled during a reconnaissance study in the East Midlands, South Yorkshire and Tyneside areas of England. Almost all the mine waters had similar δ 18 O and δ 2 H indicating a derivation from Holocene recharge (average -7.9‰ and -54‰, respectively, excluding two outliers). Most mine waters emerging by shallow gravity drainage have dissolved sulphate δ 34 S of < +10‰, suggesting a derivation of sulphate from oxidation of pyrite. Deeper mine waters, pumped from boreholes or shafts tended to be more saline with a dissolved sulphate δ 34 S of >+14‰ and, in two cases, >+30‰. The sulphate in these latter waters cannot be readily explained as deriving from pyrite oxidation. Alternative hypotheses (evaporitic or marine brines, evaporite dissolution, closed-system microbial sulphate reduction) can be invoked as explanations. A more general hypothesis proposes that deep groundwaters / mine waters can be regarded as saline “sinks”, whose sulphate δ 34 S is controlled by a dynamic equilibrium between rates of sulphate mobilisation from various sources and sulphate removal by precipitation or microbial reduction. Supplementary material: https://doi.org/10.6084/m9.figshare.c.6418981