Stable isotopes in aqueous sulphate as tracers of natural and contaminant sulphate sources: a reconnaissance study of the Xingwen karst aquifer, Sichuan, China

Isotopic compositions of sulphate (δ 18 O and δ 34 S) have been analysed in groundwaters from a karst aquifer in Xingwen, China to assess their use as indigenous tracers of different pollutant sulphate sources. Sulphate δ 18 O is highly effective at distinguishing sulphate from atmospheric ‘acid rain’ sources (higher δ 18 O values) from sulphate produced by aqueous pyrite oxidation (natural or acid mine drainage), which always has lower δ 18 O. The range of sulphate δ 34 S produced by aqueous oxidation of different pyrite sources is sufficiently wide to enable different natural and pollutant sulphate sources to be distinguished. Despite the fact that streams containing processing fines and pyrite mine drainage both derive sulphate from oxidation of ore materials, there is still a clear distinction in their sulphate δ 34 S. A combination of sulphur and oxygen isotopic measurements is thus highly effective at discriminating between all the sulphate sources to the karst aquifer and this indigenous tracer provides a powerful tool for assessing the impact of acid mine drainage on karst groundwater.