On the common occurrence of sulphate with elevated δ³⁴S in European mine waters: sulphides, evaporites or seawater?

The stable isotopic (δ³⁴S, δ¹⁸O, δ²H) composition of mine waters has been examined from coal and metal mines, of varying depth, in Spain (Asturias), the UK (north Derbyshire/Yorkshire) and Poland (Bytom, Upper Silesia). δ¹⁸O and δ²H data confirm a meteoric origin for all waters. The mine waters have elevated sulphate concentrations relative to recent meteorically-derived groundwaters and have elevated SO₄²⁻/Cl⁻ ratios relative to marine water. In the shallower mines and Markham No. 3, the dissolved sulphate δ³⁴S is low, suggesting the sulphate is derived from the oxidation of sulphide minerals. In most of the deeper mines, the dissolved sulphate δ³⁴S is too high (>15‰), to be derived from simple pyrite oxidation. In the deep Polish and Spanish mine waters, the source of sulphate may be evaporite mineral dissolution, but such a mechanism is problematic in the case of the Caphouse (UK) mine. Fractionation associated with sulphate reduction may have contributed to elevated dissolved sulphate δ³⁴S. Elevated sulphate in deep coal mine waters may not always be simply derived from pyrite oxidation. The consistent observation of elevated dissolved sulphate δ³⁴S in deep coal mines suggests a distinct genetic pathway, the origin of which as yet remains equivocal.