Stable isotope geochemistry of acid mine drainage from the Wiśniówka area (south-central Poland)

Abstract

This paper presents the results of a current isotopic study of pyrite mineralization, acid mine drainage (AMD), and nearby rivers and farmer's wells located in the western part of the Main Range, Holy Cross Mountains (south-central Poland). The principal source of dissolved sulfates in acid lakes, ponds and intermittent pools is the predominant microscopic-grained and locally framboidal pyrite (FeS2) that tends to oxidize rapidly on exposed quarry walls and unvegetated historic and current tailings piles. This process is expedited by the occurrence of arsenic in the pyrite crystal structure, which greatly decreases its resistance to weathering. The δ34S signature of pyrite from the Podwiśniówka quarry (mean of −24.0 ± 3.1‰) was different from that of the Wiśniówka Duża quarry (mean of −17.4 ± 7.2‰). These values fingerprinted two basic pyrite mineralization zones assigned to lowermost and middle Upper Cambrian rock series, respectively. The δ34S-FeS2 differences also were reflected in dissolved sulfates that displayed distinctly different δ34S values: −15.3 ± 1.0‰ (Podwiśniówka) and −10.0 ± 1.7‰ (Wiśniówka Duża). These negative δ34S values stand in contrast to their positive equivalents of the Cambrian Main Range, as well as in the examined rivers and farmer's wells unaffected by AMD processes. The acid water bodies also displayed diverse seasonal variations of δ34S-SO42–, δ18O-SO42– and δ18O-H2O that were linked to surface area, site topography, exposition to radiation, changing weather patterns, especially temperature and a periodical influx of rainwater or meltwater. The isotope data also suggest that evaporation occurred after pyrite oxidation without a direct contact with lake/pond waters, which is also evidenced by the occurrence of sulfate efflorescences on Podwiśniówka and Wiśniówka quarry faces. The stable S, O and H isotopes have been employed for fingerprinting different geochemical processes and for assessing a potential impact of AMD waters on nearby rivers and local perched aquifers, particularly in case of no visual indications. The S isotope signatures of ponds and pools have also been used for determining the provenance of historic and recent mine waste material.