Stable sulphur and oxygen isotopes as indicators of sulphide oxidation reaction pathways and historical environmental conditions in a Cu–W–F skarn tailings piles, south-central Sweden
Document identifier: oai:DiVA.org:ltu-76207
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10.1016/j.apgeochem.2019.104426Keyword: Natural Sciences,
Earth and Related Environmental Sciences,
Geochemistry,
Naturvetenskap,
Geovetenskap och miljövetenskap,
Geokemi,
Skarn tailings,
Yxsjöberg,
Water-soluble sulphate,
Danalite weathering,
Sulphur isotopes,
Carbon-bonded sulphur,
Applied Geochemistry,
Tillämpad geokemiPublication year: 2019Relevant Sustainable Development Goals (SDGs):
The SDG label(s) above have been assigned by OSDG.aiAbstract: Improved remediation strategies or predictive modelling of acid mine drainage (AMD) sites, require detailed understanding of the sulphide oxidation reaction pathways, as well as pollutant-source characterisation. In this study, ore minerals, solids and water-soluble fractions of an oxidising Cu–W–F skarn tailings in Yxsjöberg, Sweden, were chemically and isotopically (δ34S and δ18O) characterised to reveal sulphate (SO42−) sources, sulphide oxidation reaction pathways and historical environmental conditions in the tailings. δ34S was additionally used to trace the weathering of danalite [(Fe,Mn,Zn)4Be3(SiO4)3S], a rare and unstable sulphur-bearing silicate mineral containing high concentrations of beryllium (Be) and zinc (Zn). Eighteen subsamples from a drill core of the tailings were subjected to batch leaching tests to obtain water-soluble fractions, which reflected both existing pore-waters and easily-soluble secondary minerals. The tailings were categorised into three geochemical zones: (i) oxidised zone (OZ), (ii) transition zone (TZ) and (iii) unoxidised zone (UZ), based on prevailing pH, elemental concentrations and colour. The upper OZ (UOZ) showed a sharp depletion of sulphur (S) and relatively higher δ18OSO4 values (−3.0 to +0.1‰) whereas the underlying lower OZ (LOZ) showed S accumulation and lower δ18OSO4 values (−4.6 to −4.2‰). The higher δ18OSO4 suggested the role of atmospheric oxygen, O2 (as oxidant), contribution of evaporated rainwaters and/or evaporation in the upper zones of the tailings. The lower δ18OSO4 values were indicative of ferric iron (Fe3+) as oxidant and the possible incorporation of 16O into SO42− during its formation, most probably from snow melt or depleted rainwater. The δ34SSO4 values in the OZ (+2.3 to +2.4‰) suggested SO42− from pyrrhotite oxidation in the UOZ which has been subsequently mobilised to the LOZ. Low δ34S fractionation (+0.2 to +1.9‰) between SO42− in the OZ and pyrrhotite, as well as the low δ18OSO4 values in the LOZ suggested the complete oxidation of pyrrhotite by Fe3+, signalling that previously, a low pH (<3) prevailed in the tailings. Mineralogical observations confirmed that pyrrhotite was completely oxidised in the UOZ, with the formation of hydrous ferric oxides (HFOs) coatings. The observed current high δ18OSO4 and pH (3.9–4.5) values in the UOZ were attributed to decreased oxidation rate and silicate buffering, limiting the availability of aqueous Fe3+ and subsequent formation of HFOs. The δ34SSO4 signatures of the water-soluble SO42− in the TZ and UUZ suggested the dissolution of gypsum which precipitated from a leachate from the weathering of danalite in the UOZ. In the middle UZ, the δ34SSO4 (−0.8 to +0.6‰) and δ18OSO4 (−1.8 to −1.0‰) signatures corresponded to SO42− from a mixture of pyrite, pyrrhotite and chalcopyrite oxidation by O2 at the LOZ (i.e. oxidation front). Negative δ34S fractionation values (−3.0 to −1.6‰) between these minerals and the water-soluble SO42− were attributed to the potential formation of intermediate S species, due to the partial oxidation of the sulphides. Consequently, the S accumulation in the LOZ could be due to the likely formation of the intermediate S species and secondary pyrite identified in this zone. The lower UZ coincided with the groundwater table and registered consistent negative δ34SSO4 (−2.6 to −1.8‰) and δ18OSO4 (−7.6 to −4.4‰) values. These signatures were hypothesised to be controlled by SO42− from the mineralisation of organic S in peat underneath the tailings and/or H2S oxidation, with possible contribution from sulphide oxidation in the tailings. This study highlights the usefulness of δ34S and δ18O as tracers of geochemical processes and environmental conditions that have existed in the tailings.
Authors
Musah Salifu
Luleå tekniska universitet; Geovetenskap och miljöteknik
Other publications
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Thomas Aiglsperger
Luleå tekniska universitet; Geovetenskap och miljöteknik
Other publications
>>
Carl-Magnus Mörth
Department of Geological Sciences, Stockholm University, Stockholm, Sweden
Other publications
>>
Lena Alakangas
Luleå tekniska universitet; Geovetenskap och miljöteknik
Other publications
>>
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identifier: oai:DiVA.org:ltu-76207
datestamp: 2021-04-19T12:37:06Z
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10.1016/j.apgeochem.2019.104426
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lang: eng
title: Stable sulphur and oxygen isotopes as indicators of sulphide oxidation reaction pathways and historical environmental conditions in a Cu–W–F skarn tailings piles south-central Sweden
abstract: Improved remediation strategies or predictive modelling of acid mine drainage (AMD) sites require detailed understanding of the sulphide oxidation reaction pathways as well as pollutant-source characterisation. In this study ore minerals solids and water-soluble fractions of an oxidising Cu–W–F skarn tailings in Yxsjöberg Sweden were chemically and isotopically (δ34S and δ18O) characterised to reveal sulphate (SO42−) sources sulphide oxidation reaction pathways and historical environmental conditions in the tailings. δ34S was additionally used to trace the weathering of danalite (FeMnZn)4Be3(SiO4)3S a rare and unstable sulphur-bearing silicate mineral containing high concentrations of beryllium (Be) and zinc (Zn). Eighteen subsamples from a drill core of the tailings were subjected to batch leaching tests to obtain water-soluble fractions which reflected both existing pore-waters and easily-soluble secondary minerals. The tailings were categorised into three geochemical zones: (i) oxidised zone (OZ) (ii) transition zone (TZ) and (iii) unoxidised zone (UZ) based on prevailing pH elemental concentrations and colour. The upper OZ (UOZ) showed a sharp depletion of sulphur (S) and relatively higher δ18OSO4 values (−3.0 to +0.1‰) whereas the underlying lower OZ (LOZ) showed S accumulation and lower δ18OSO4 values (−4.6 to −4.2‰). The higher δ18OSO4 suggested the role of atmospheric oxygen O2 (as oxidant) contribution of evaporated rainwaters and/or evaporation in the upper zones of the tailings. The lower δ18OSO4 values were indicative of ferric iron (Fe3+) as oxidant and the possible incorporation of 16O into SO42− during its formation most probably from snow melt or depleted rainwater. The δ34SSO4 values in the OZ (+2.3 to +2.4‰) suggested SO42− from pyrrhotite oxidation in the UOZ which has been subsequently mobilised to the LOZ. Low δ34S fractionation (+0.2 to +1.9‰) between SO42− in the OZ and pyrrhotite as well as the low δ18OSO4 values in the LOZ suggested the complete oxidation of pyrrhotite by Fe3+ signalling that previously a low pH (<3) prevailed in the tailings. Mineralogical observations confirmed that pyrrhotite was completely oxidised in the UOZ with the formation of hydrous ferric oxides (HFOs) coatings. The observed current high δ18OSO4 and pH (3.9–4.5) values in the UOZ were attributed to decreased oxidation rate and silicate buffering limiting the availability of aqueous Fe3+ and subsequent formation of HFOs. The δ34SSO4 signatures of the water-soluble SO42− in the TZ and UUZ suggested the dissolution of gypsum which precipitated from a leachate from the weathering of danalite in the UOZ. In the middle UZ the δ34SSO4 (−0.8 to +0.6‰) and δ18OSO4 (−1.8 to −1.0‰) signatures corresponded to SO42− from a mixture of pyrite pyrrhotite and chalcopyrite oxidation by O2 at the LOZ (i.e. oxidation front). Negative δ34S fractionation values (−3.0 to −1.6‰) between these minerals and the water-soluble SO42− were attributed to the potential formation of intermediate S species due to the partial oxidation of the sulphides. Consequently the S accumulation in the LOZ could be due to the likely formation of the intermediate S species and secondary pyrite identified in this zone. The lower UZ coincided with the groundwater table and registered consistent negative δ34SSO4 (−2.6 to −1.8‰) and δ18OSO4 (−7.6 to −4.4‰) values. These signatures were hypothesised to be controlled by SO42− from the mineralisation of organic S in peat underneath the tailings and/or H2S oxidation with possible contribution from sulphide oxidation in the tailings. This study highlights the usefulness of δ34S and δ18O as tracers of geochemical processes and environmental conditions that have existed in the tailings.
subject:
@attributes:
lang: eng
authority: uka.se
topic:
Natural Sciences
Earth and Related Environmental Sciences
Geochemistry
@attributes:
lang: swe
authority: uka.se
topic:
Naturvetenskap
Geovetenskap och miljövetenskap
Geokemi
@attributes:
lang: eng
topic: Skarn tailings
@attributes:
lang: eng
topic: Yxsjöberg
@attributes:
lang: eng
topic: Water-soluble sulphate
@attributes:
lang: eng
topic: Danalite weathering
@attributes:
lang: eng
topic: Sulphur isotopes
@attributes:
lang: eng
topic: Carbon-bonded sulphur
@attributes:
lang: eng
authority: ltu
topic: Applied Geochemistry
genre: Research subject
@attributes:
lang: swe
authority: ltu
topic: Tillämpad geokemi
genre: Research subject
language:
languageTerm: eng
genre:
publication/journal-article
ref
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Published
4
Validerad;2019;Nivå 2;2019-10-02 (johcin)
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Salifu
Musah
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Luleå tekniska universitet
Geovetenskap och miljöteknik
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Thomas
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Luleå tekniska universitet
Geovetenskap och miljöteknik
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Mörth
Carl-Magnus
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affiliation: Department of Geological Sciences Stockholm University Stockholm Sweden
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Alakangas
Lena
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Luleå tekniska universitet
Geovetenskap och miljöteknik
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leal
0000-0001-7291-8505
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dateIssued: 2019
publisher: Elsevier
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1872-9134
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number: 104426
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