The geochemistry of sulphur in a mixed allogenic-autogenic karst catchment, Castleton, Derbyshire, UK

Analyses are presented of anion chemistry and sulphur isotopic compositions of sulphate in sinking streams and groundwaters in a mixed allogenic-autog enic karst catchment. Using the sulphur isotopic data, sources of sulphate from agriculture and the effects of sulphate reduction arising from slurry application can be distinguished from natural rock weathering sources. With in the aquifer, sulphate in known autogenic waters has isotopic composition s distinct from allogenic waters, the autogenic waters being dominated by s ulphate from rainfall and rock weathering in these low agricultural intensi ty catchments. On this basis, water rising at low flow from Whirlpool Risin g, Speedwell Cavern, has been identified as dominantly autogenic. Groundwater flow between the sinks and risings in Speedwell Cavern is belie ved to be along conduits following mineralized faults (rakes). During trans it SO42-/Cl- in the water increases. Isotopic mass balance shows that this must be due to addition of sulphate from the oxidation of ore minerals by g roundwater. Mass balance considerations show that the present rate of sulph ide oxidation must be the result of enhancement by lead mining operations o n the rakes. Copyright (C) 2000 John Wiley & Sons, Ltd.