Abstract
The paper presents the results of determinations of stable S and O isotopes of dissolved sulfates and O and H stable isotopes of waters from three ponds, that is, Marczakowe Doly acid pond, Marczakowe Doly fish pond and Podwiśniowka acid pit pond, located in the Holy Cross Mountains (south-central Poland). The δ34SV-CDT and δ18OV-SMOW of SO4 2− in waters of three ponds (n = 14) varied from −16.2 to −9.5 ‰ (mean of −13.6 ‰) and from −8.1 to −3.2 ‰ (mean of −4.8 ‰), respectively. The mean δ34S–SO4 2− values were closer to those of pyrite (mean of −25.4 ‰) and efflorescent sulfate salts (mean of −25.6 ‰), recorded previously in the Podwiśniowka quarry, than to sulfates derived from other anthropogenic or soil and bedrock sources. The SO4 2− ions formed by bacterially induced pyrite oxidation combined with bacterial (dissimilatory) dissolved sulfate reduction, and presumably with subordinate mineralization of carbon-bonded sulfur compounds, especially in both Marczakowe Doly ponds. In addition, the comparison of δ18O–SO4 2− and δ18O–H2O values indicated that 75–100 % of sulfate oxygen was derived from water. Due to the largest size, the Podwiśniowka acid pit pond revealed distinct seasonal variations in both δ18O–H2O (−9.2 to −1.6) and δD–H2O (−29.7 to −71.3) values. The strong correlation coefficient (r 2 = 0.99) was noted between δ18O–H2O and δD–H2O values, which points to atmospheric precipitation as the only source of water. The sediments of both acid ponds display different mineral inventory: the Marczakowe Doly acid pond sediment consists of schwertmannite and goethite, whereas Podwiśniowka acid pit pond sediment is composed of quartz, illite, chlorite and kaolinite with some admixture of jarosite reflecting a more acidic environment. Geochemical modeling of two acid ponds indicated that the saturation indices of schwertmannite and nanosized e-Fe2O3 (Fe3+ oxide polymorph) were closest to thermodynamic equilibrium state with water, varying from −1.44 to 3.05 and from −3.42 to 6.04, respectively. This evidence matches well with the obtained mineralogical results.
Highlights
Acid mine drainage (AMD) is typically produced by the weathering of pyrite, marcasite (FeS2) and other iron-bearing sulfides brought to the surface by mining, mineral processing or other human activity (e.g., Taylor and Wheeler 1994; Plumlee et al 1999; Knoller et al 2004; Edraki et al 2005; Butler 2007; Nordstrom 2009, 2011a, b; Szynkiewicz et al 2011)
The mineralogical composition of this ochreous precipitate is characteristic of AMD/acid rock drainage (ARD) sites throughout the world (Edraki et al 2005)
The results derived from other studies have shown that the d34S of dissolved sulfates should be identical to parent sulfide minerals under quantitative disequilibrium oxidation (Taylor and Wheeler 1994).These results suggest that the only potential source of sulfates in the pit pond water is pyrite derived from the exposed pyrite mineralization zone and pyritaceous clayey shales
Summary
Acid mine drainage (AMD) is typically produced by the weathering of pyrite, marcasite (FeS2) and other iron-bearing sulfides brought to the surface by mining, mineral processing or other human activity (e.g., Taylor and Wheeler 1994; Plumlee et al 1999; Knoller et al 2004; Edraki et al 2005; Butler 2007; Nordstrom 2009, 2011a, b; Szynkiewicz et al 2011). The oxidation of pyrite or marcasite and subsequent conversion to sulfuric acid occurs through several reactions, with simplified equations as follows: FeS2 þ 7=2O2 þ H2O ! As a result of this reaction, the pH decreases to below 3 triggering the consecutive reaction (4) These processes are catalyzed primarily by iron-oxidizing bacterium species Acidithiobacillus ferrooxidans or A. thiooxidans, increasing reaction rates by several orders of magnitude (Nordstrom and Southam 1997). Some glacier studies suggest that sulfide oxidation might be very efficient under limited oxygen condition due to microbial activity (e.g., Wadham et al 2004)
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