Dissolved sulfate δ34S and the origin of sulfate 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 similarδ18O andδ2H concentrations, indicating a derivation from Holocene recharge (average of −7.9 and −54‰, respectively, excluding two outliers). Most mine waters emerging by shallow gravity drainage have dissolved sulfateδ34S levels of <+10‰, suggesting a derivation of sulfate from the oxidation of pyrite. Deeper mine waters, pumped from boreholes or shafts, tended to be more saline with dissolved sulfateδ34S levels of >+14‰ and, in two cases, >+30‰. The sulfate in these latter waters cannot be readily explained as deriving from pyrite oxidation. Alternative hypotheses (evaporitic or marine brines, evaporite dissolution or partially-closed-system microbial sulfate reduction) can be invoked as explanations. A more general hypothesis proposes that deep groundwaters/mine waters can be regarded as saline ‘sinks’, whose sulfateδ34S concentration is controlled by a dynamic equilibrium between rates of sulfate mobilization from various sources and sulfate removal by precipitation or microbial reduction.Supplementary material: Supplementary Material A (a detailed description of sample sites and results) and Supplementary Material B (locations of sample sites) are available athttps://doi.org/10.6084/m9.figshare.c.6418981