The isotopic composition of groundwaters related to native sulphur deposits

Abstract

Native sulphur deposits of the Carpathian Foredeep contain hydrosulphuric groundwaters. The major components of hydrosulphuric waters (H₂O, HCO₃^-, SO₄^- and H₂S) have been analysed for stable isotope ratios in samples from Machów open-pit mine as well as from selected wells of the area adjacent to native sulphur ores collected in May 1993. The oxygen and hydrogen of recent water from the uppermost layer (at a water table occurring in the Tertiary rocks exposed at Machów) are isotopically very close to the recent infiltration waters. This means that these waters nearly completely replaced the original isotopically heavier waters. Nevertheless, a very high rate of bacterial reduction of sulphate to hydrogen sulphide (within the ore deposits) is indicated by the high concentration of H₂S (292 mg/l) and d³⁴S of SO₄^- (26.3‰) and H₂S (-7.9‰). This is further confirmed by high d¹⁸O of SO₄^-  (15.2‰ vs. SMOW).