Aquatic Geochemistry

, Volume 7, Issue 3, pp 195–216

Sulphide-bearing Waters in Northern Apennines, Italy: General Features and Water-rock Interaction

  • Lorenzo Toscani
  • Giampiero Venturelli
  • Tiziano Boschetti
Article

DOI: 10.1023/A:1012941328028

Cite this article as:
Toscani, L., Venturelli, G. & Boschetti, T. Aquatic Geochemistry (2001) 7: 195. doi:10.1023/A:1012941328028

Abstract

Sulphide-bearing Ca-carbonate, Na-carbonate, Na-hydroxide, Na-chloride and Ca-sulphate waters from Northern Apennines were investigated in order to determine their main chemical and isotopic composition and draw inferences on water-rock interaction. δ2H and δ18O values suggest an origin mostly meteoric for the analysed waters but a well drilled in Miocenic sediments. The Na-carbonate and the Ca-sulphate waters are the most interesting geochemically. Na-carbonate type, which sometimes reaches extreme composition (Na/Ca up to 228, equivalent ratio), may have been derived through prolonged interaction of Ca-carbonate waters with rocks containing feldspar, montmorillonite and illite under calcite saturation/oversaturation; the high F and pH and the very low PCO2 agree with prograde dissolution of silicates and lasting water-rock interaction. However, Ca–Na ion exchange, involving clays of marine origin, cannot be excluded in addition. The Ca-sulphate waters, occurring in Messinian gypsum-bearing sediments, are saturated in gypsum and calcite and exhibit very high total H2S (up to 219 mg dm-3) and PCO2 (up to 0.32 bar). Mass balance of sulphate sulphur, sulphide sulphur and delta34S suggests sulphate – derived from gypsum – as source for H2S; CH4 and organic matter generate the reducing conditions and sulphate reduction is mediated by bacteria. One Na-chloride water from a well in Miocenic sediments has unusual composition, containing about 700 mgdm-3 of potential CaCl2 and having δ2H and δ18O (-47.5 and -4.9‰ respectively) which plot far from the meteoric water lines; probably it is derived by mixing of meteoric and formation waters. The Na-hydroxide water, with very high pH (11.2), is generated through protracted interaction of meteoric waters with ultramafites.

H2S-bearing waters water-rock interaction Northern Apennines Italy 

Copyright information

© Kluwer Academic Publishers 2001

Authors and Affiliations

  • Lorenzo Toscani
    • 1
  • Giampiero Venturelli
    • 1
  • Tiziano Boschetti
    • 1
  1. 1.Dipartimento di Scienze della TerraUniversitá di ParmaParmaItaly

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