| 1. |
- Alakangas, Lena, et al.
(författare)
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Min-North : Development, Evaluation and Optimization of Measures to Reduce the Environmental Impact of Mining Activities in Northern Regions
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Min-North (Development, Evaluation and Optimization of Measures to Reduce the Environment Impact of Mining Activities in Northern Regions) project was a trans-national cooperative project, with participants from the Geological Survey of Finland (GTK), University of Oulu (UO), UiT The Arctic University of Norway (UiT), Luleå University of Technology (LTU) and SMEs from Sweden, Finland and Norway. The project was funded by Interreg Nord and Norrbottens länsstyrelse. The participants have expertise in mine waste management, mine water treatment and geophysics. The overall aim of the project was to enhance the development of environmental protection technologies. An associated goal was to deepen cross-border cooperation by creating a larger critical mass of researchers in mine waste management and local SMEs in the Northern regions with greater capacities to disseminate and implement new methods, products and services. The project ran for 36 months from the 1st of January 2016 to the end of December 2018.
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| 2. |
- Hällström, Lina P.B., et al.
(författare)
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The geochemical behaviour of Be and F in historical mine tailings of Yxsjöberg, Sweden
- 2020
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Ingår i: Journal of Geochemical Exploration. - : Elsevier. - 0375-6742 .- 1879-1689. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- The speciation, mobility, transport, and fate of beryllium (Be) in the terrestrial environment is poorly studied even though it is considered to be one of the most hazardous elements in the periodic table. Historical tailings containing the unusual mineral danalite [Be3(Fe4.4Mn0.95Zn0.4)(SiO4)3.2S1.4] together with Fe-sulfides and fluorite has been stored open to the atmosphere for more than 50y. Environmental mineralogy, which combines geochemical and mineralogical techniques, was used to elucidate the weathering of danalite and fluorite. Danalite is unstable in oxic conditions due to the occurrence of Fe(II) and S-(II) in the crystal lattice and has oxidized at the same pace as pyrrhotite in the tailings. The acidic conditions generated from sulfide oxidation and the release of F from fluorite weathering have most likely enhanced Be mobility in the tailings. Secondary gypsum, hydrous ferric oxides and Al-oxyhydroxides are hypothesized to have played an important role regarding the mobility of Be in the tailings. The results indicate that Be released from danalite was first scavenged by these secondary minerals through co-precipitation. However, the dissolution of secondary gypsum due to changing geochemical conditions has also released Be to the groundwater. The groundwater at the shore of the tailings revealed the highest Be concentrations measured anywhere in the world (average: 4.5 mg/L) even though the water has a circumneutral pH. This extraordinary finding can be explained by high concentrations of F (73 mg/L), as F and Be have been shown to form strong complexes. The weathering of danalite and fluorite will continue for hundreds of years if remediation measures are not taken. Re-mining the tailings could be an appropriate remediation method.
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| 3. |
- Salifu, Musah, et al.
(författare)
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A simple model for evaluating isotopic (18O, 2H and 87Sr/86Sr) mixing calculations of mine : Impacted surface waters
- 2020
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Ingår i: Journal of Contaminant Hydrology. - : Elsevier. - 0169-7722 .- 1873-6009. ; 232
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Tidskriftsartikel (refereegranskat)abstract
- This study was aimed at identifying and quantifying mixing proportions in surface waters downstream of historical Cu-W-F skarn mine tailings at Yxsjöberg, Sweden, using 18O, 2H, and 87Sr/86Sr isotopes. In addition, a simple mathematical model was developed to evaluate the consistency of the mixing calculations. Hydrochemical and isotopic data from 2 groundwater wells, 6 surface water and 2 rainwater sampling sites, spanning 6 sampling campaigns between May and October were used. Three mixed surface waters downstream of the tailings were identified, namely: C7, C11 and C14. C7 was directly influenced by groundwater from the tailings whereas C11 was also subsequently influenced by C7. C14 on the other hand, had contributions from C11. Sequential mixing calculations indicated that the contribution of the groundwater to C7 ranges from 1 to 17%. The subsequent contribution of C7 to C11 varied from 49 to 91% whereas C14 had contributions of C11 ranging between 16 and 56%. A strong agreement between the model data (MD) and measured raw data (RD) for C11 and C14 indicated the accuracy of the mixing calculations. Variations between the MD and RD at C7, however, was mainly due to sorption and reductive processes underneath the tailings, which tend to attenuate the amount of dissolved ions reaching the surface waters, resulting in a low ionic contribution of the tailings groundwater to the surface water. The low ionic contribution of the groundwater to C7 suggested that although the tailings impoundment is of environmental concern, its impact on the downstream surface waters is small. The results of this study suggest that mixing calculations in surface waters involving a closed system such as groundwater (as an end-member) must be treated with caution. It is recommended that the interpretation of such mixing results must be coupled with detailed knowledge of the potential hydrogeochemical processes along its flow paths.
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| 4. |
- Salifu, Musah, et al.
(författare)
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A simple model for evaluating isotopic (O-18, H-2 and Sr-87/Sr-86) mixing calculations of mine - Impacted surface waters
- 2020
-
Ingår i: Journal of Contaminant Hydrology. - : Elsevier BV. - 0169-7722 .- 1873-6009. ; 232
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Tidskriftsartikel (refereegranskat)abstract
- This study was aimed at identifying and quantifying mixing proportions in surface waters downstream of historical Cu-W-F skarn mine tailings at Yxsjoberg, Sweden, using O-18, H-2, and Sr-87/Sr-86 isotopes. In addition, a simple mathematical model was developed to evaluate the consistency of the mixing calculations. Hydrochemical and isotopic data from 2 groundwater wells, 6 surface water and 2 rainwater sampling sites, spanning 6 sampling campaigns between May and October were used. Three mixed surface waters downstream of the tailings were identified, namely: C7, C11 and C14. C7 was directly influenced by groundwater from the tailings whereas C11 was also subsequently influenced by C7. C14 on the other hand, had contributions from C11. Sequential mixing calculations indicated that the contribution of the groundwater to C7 ranges from 1 to 17%. The subsequent contribution of C7 to C11 varied from 49 to 91% whereas C14 had contributions of C11 ranging between 16 and 56%. A strong agreement between the model data (MD) and measured raw data (RD) for C11 and C14 indicated the accuracy of the mixing calculations. Variations between the MD and RD at C7, however, was mainly due to sorption and reductive processes underneath the tailings, which tend to attenuate the amount of dissolved ions reaching the surface waters, resulting in a low ionic contribution of the tailings groundwater to the surface water. The low ionic contribution of the groundwater to C7 suggested that although the tailings impoundment is of environmental concern, its impact on the downstream surface waters is small. The results of this study suggest that mixing calculations in surface waters involving a closed system such as groundwater (as an end-member) must be treated with caution. It is recommended that the interpretation of such mixing results must be coupled with detailed knowledge of the potential hydrogeochemical processes along its flow paths.
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| 5. |
- Salifu, Musah, et al.
(författare)
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Biogeochemical Controls on 13CDIC Signatures from Circum-Neutral pH Groundwater in Cu–W–F Skarn Tailings to Acidic Downstream Surface Waters
- 2020
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 10:9
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Tidskriftsartikel (refereegranskat)abstract
- Regular features of ground and surface waters affected by drainage from mine waste include their acidity and elevated concentrations of dissolved metals, with their attendant negative effects on drinking water quality and aquatic life. One parameter that aids in buffering these waters against acidity and sustains aquatic life is dissolved inorganic carbon (DIC). In this study, the chemical and isotopic (δ13C) composition of primary calcite and DIC (δ13CDIC) in groundwater and surface waters within and downstream, respectively, of abandoned Cu–W–F skarn tailings at Yxsjöberg, Sweden, were used to trace the biogeochemical processes controlling their respective δ13CDIC signatures. In addition, the δ13C signatures of the inorganic (carbonate) fractions of the tailings were used to verify the formation of secondary carbonates within the tailings. Lower average δ13C values of the carbonate fractions (δ13Ccarb = −2.7‰) relative to those of the primary calcite (δ13C = +0.1‰) from the orebodies from which the tailings originated pointed to the precipitation of secondary carbonates. These lower δ13Ccarb signatures were assumed to represent mixed-source C signals involving isotopically light CO2 from the atmosphere, the degradation of organic matter in the upper part of the tailings and HCO3− from calcite dissolution. The groundwater δ13CDIC values (−12.6‰ to −4.4‰) were far lower than the hypothetical range of values (−4.6‰ to +0.7‰) for primary calcite and secondary carbonate dissolution. These signatures were attributed to carbonate (calcite and secondary carbonate) dissolution and the degradation of dissolved organic carbon (DOC) from various organic sources such as peat underneath the tailings and the surrounding forests. Downstream surface water samples collected in May had low δ13CDIC values (−16‰) and high DOC (14 mg C/L) compared to the groundwater samples. These signatures represented the oxidation of the DOC from the wash out of the mires and forests during the snowmelt and spring flood. The DOC and δ13CDIC values of the surface waters from June to September ranged from 6–15 mg·C/L and −25‰ to −8.6‰, respectively. These signatures were interpreted to reflect mixed C sources, including carbonate dehydration by acidity from Fe3+ hydrolysis due to the mixing of groundwater with surface waters and the subsequent diffusive loss of CO2 (g), aquatic photosynthesis, photooxidation, DOC degradation, as well as microbial respiration. Although the 13CDIC signatures of the downstream surface waters seemed to be seasonally controlled and influenced by variable groundwater contributions, the lack of data with respect to DIC concentrations, coupled with multiple potential biogeochemical processes that could influence the DIC pool and 13CDIC values, made it difficult to identify the major regulating process of the 13CDIC signatures. Therefore, other complimentary isotopes and elemental concentrations are recommended in order to decipher the dominant biogeochemical process.
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| 6. |
- Salifu, Musah, et al.
(författare)
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Sr/Ca and 87Sr/86Sr : A tracer for geochemical processes in mine wastes
- 2018
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Ingår i: RISK TO OPPORTUNITY. - South Africa : ICARD/IWMA. ; , s. 723-728
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Konferensbidrag (refereegranskat)abstract
- Understanding geochemical processes in mining environments are essential to waste management decisions including remediation. In an attempt to understand geochemical processes, chemical data have mostly been used but these have oft en led to inaccurate conclusions. Th erefore, in this work 87Sr/86Sr, Sr/Ca and other elemental ratios (Ca/K and Rb/Sr) in leachates were employed to constrain the geochemical processes in an abandoned tungsten (W) tailings in Yxsjöberg, South-Central Sweden. Th e results of this study indicate that coupling chemical ratios with 87Sr/86Sr ratios off er better insights in discriminating between diff erent geochemical processes in mine wastes
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| 7. |
- Salifu, Musah
(författare)
-
Stable and radiogenic isotopes as tracers for geochemical processes in mineralogically-complex mine waste environments : Insights from 13C, 2H, 18O, 34S and 87Sr/86Sr.
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mining and its related activities generate large volumes of mine wastes such as tailings that can have negative environmental implications. One of such mine wastes of potential environmental concern is the historical Yxsjöberg Cu-W-F skarn tailings in Sweden, which encompasses a complex mineralogy including sulphides, carbonates, silicates, oxides / wolframite and halides. Some of these minerals contain high contents of potentiallytoxic elements such as Be, Bi, Cu, F, Zn and W; hence posing a significant threat to surrounding soils, aquatic ecosystems and drinking water quality due to their weathering. Potential remediation strategies for this site require a detailed understanding of the mobilization and transportation of contaminants in and from the tailings to the surrounding environments. Therefore in this present work, chemical and isotopic (18O, 13C, 34S, 87Sr/86Sr) composition of minerals, tailings and water-soluble (WS) fractions of the tailings were used to gain comprehensive insights into geochemical processes including mineral weathering and precipitation, trace elemental sources and sulphide oxidation reaction pathways within the tailings. Furthermore, chemical composition and water mixing analyses, aimed at quantifying the elemental contributions of the tailings and tailings groundwater to the downstream surface waters were carried out using 18O, 2 H and 87Sr/86Sr isotope data of ground and surface waters collected during 6 different sampling campaigns from May to October 2018. Subsequently, the consistency of the mixing analyses was evaluated via a simple model. Biogeochemical processes regulating the stable carbon isotope signatures of dissolved inorganic carbon; DIC (δ13CDIC) of the ground and surface waters were also investigated. Three distinct geochemical zonation namely; oxidised (OZ), transition (TZ) and unoxidised zones (UZ) based on pH, elemental contents and colour, were observed in the tailings as a result of their long term storage and exposure to oxidising conditions. The OZ was characterised by a low pH (3.6 - 4.5), depletion of S as well as Be, Co, Cu and Zn in both the bulk tailings and WS fractions, particularly in the upper OZ (UOZ). On the other hand, the WS fractions of the lower OZ (LOZ), which included the oxidation front, recorded elevated concentrations of these trace metals and SO4 2- .Mineralogical observations and elemental contents of the tailings as well as the 34S and 18O signatures of SO4 2- ( 18OSO4 and 34SSO4) of the WS fractions in the OZ, TZ and upper UZ (UUZ) pointed to the historical and extensive weathering / oxidation of danalite and pyrrhotite by Fe3+ (i.e. at pH ≤ 3) in the UOZ, particular during their early stages after deposition when the sulphide surfaces were fresh. Very radiogenic 87Sr/86Sr ratios coupled with elevated concentrations of silicate-associated elements such as Al, Fe, K and Mg in the WS fractions of the OZ indicated the weathering of biotite, K-feldspar and muscovite. Weathering of Ca-bearing minerals as well as the dissolution of secondary minerals (e.g. gypsum) in the LOZ resulted in high Ca/K ratios. In the TZ and UUZ, the WS fraction 87Sr/86Sr and 34SSO4 values as well as consistent peaks of Ca, Be, Mn, SO4 2- and Zn suggested the dissolution of gypsum with a similar isotopic composition as danalite. Danalite was weathered in the OZ and hence Be was assumed to have been mobilised from this zone and trapped secondarily in gypsum in the UUZ. The 18OSO4 and 34SSO4 signatures of the WS fractions in the middle UZ suggested their mobilisation from the current oxidation front and represented mixed signals from the incomplete oxidation of pyrite, pyrrhotite and chalcopyrite via atmospheric oxygen (O2), resulting in the potential formation of intermediate sulphur species such as elemental S. Negative 18OSO4 and 34SSO4 signatures of the lower UZ were attributed to their probable release from processes such as carbon-bonded sulphur mineralisation and hydrogen sulphide (H2S) oxidation in the forests surrounding the mine site. Recorded negative δ13C signatures of some carbonates (average = -2.7 ‰) in the tailings compared to that of primary calcite (δ13C= +0.1 ‰)signaled the precipitation of secondary carbonates. The δ13C values of these secondary carbonates were ascribed to a mixture of C sources from atmospheric CO2, degraded organic matter and primary calcite dissolution in the tailings. The water mixing analyses indicated that the elemental contributions of the tailings groundwater to the downstream surface waters were small (1 -17 %), resulting in low dissolved concentrations of various elements in the latter relative to that of the former and thus a low negative environmental impact. The results of the mixing analyses and the model suggested that the low elemental concentrations of the surface waters were due to various potential retention mechanisms such as precipitation, sorption and reductive processes within the tailings and at the outlet of the tailings. The δ13CDIC values of the groundwater samples were attributed to mixed C signals from the primary calcite and potential secondary carbonate dissolution in the tailings as well as degradation of the vegetation and sewage sludge on the tailings, the peat underneath the tailings and the surrounding forests. The δ13CDIC signatures of the downstream surface waters seemed to be dependent on the climatic seasons and groundwater contributions. However, limitations with respect to unavailable data on DIC concentrations as well as a myriad of potential biogeochemical processes that could influence the DIC pool and δ13CDIC values of the surface waters made it difficult to pinpoint the major regulating process (es) of the δ13CDIC signatures. Nonetheless, the results of this study shows that the use of the 18O, 34S, 87Sr/86Sr and to a lesser extent 13C isotopes, coupled with the chemical and mineralogical data offer better insights into discriminating between various elemental sources and related geochemical processes, especially in mineralogical-complex setting such as skarn tailings. Furthermore, the results of the mixing analysis and the model data emphasises the importance of a thorough understanding of the hydrogeochemical processes along groundwater flow paths, as these processes can modulate the amount of dissolved elements reaching the surface waters.
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| 8. |
- Salifu, Musah, et al.
(författare)
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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
- 2019
-
Ingår i: Applied Geochemistry. - : Elsevier. - 0883-2927 .- 1872-9134. ; 110
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Tidskriftsartikel (refereegranskat)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 [(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.
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| 9. |
- Salifu, Musah, et al.
(författare)
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Strontium (87Sr/86Sr) isotopes: A tracer for geochemical processes in mineralogically-complex mine wastes
- 2018
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Ingår i: Applied Geochemistry. - : Elsevier. - 0883-2927 .- 1872-9134. ; 99, s. 42-54
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Tidskriftsartikel (refereegranskat)abstract
- Interpretation of geochemical data based primarily on elemental concentrations often lead to ambiguous results due to multiple potential sources including mineral weathering, atmospheric input, biological cycling, mineral precipitation and exchange processes. The 87Sr/86Sr ratio is however not fractionated by these processes. In this study, Sr isotope (87Sr/86Sr) ratios have been coupled with chemical data of Sr and Rb-bearing minerals, tailings and leachates (water-soluble) to gain insight into the geochemical processes occurring within the Yxsjöberg Cu-W mine tailings, Sweden. The tailings have been exposed to oxidizing conditions resulting in three geochemical zones namely (i) oxidized, (ii) transition and (iii) unoxidized zones. Leachates from the oxidized zone are acidic (pH = 3.6–4.5) and contain elevated concentrations of metals (e.g. Fe, Cu and Zn) and SO4. The low pH has also led to subsequent weathering of most silicates, releasing Al, Ca, Mg and Na into solution. The 87Sr/86Sr ratio in the tailings ranges from 0.84787 to 1.26640 in the oxidized zone, 0.92660–1.06788 in the transition zone, whilst the unoxidized zone has values between 0.76452 and 1.05169. For the leachates, the 87Sr/86Sr ratio ranges from 2.44479 to 5.87552 in the oxidized zone, 1.37404–1.68844 in the transition zone and 1.03697–2.16340 in the unoxidized zone. Mixing (between mineral weathering and atmospheric sources) was identified as the major process regulating the Sr composition of the tailings and leachates. The highly radiogenic signatures of the leachates in the oxidized zone suggests weathering of biotite, K-feldspar and muscovite. Despite the very radiogenic signatures in the oxidized zone, increments in Ca/K ratios, Be, Ce, Tl, Al, Fe and SO4 concentrations in the water-soluble phase were recorded in its lower parts which suggests the dissolution of amphibole, pyroxene, plagioclase, fluorite, gypsum, Al and Fe –(oxy) hydroxides as well as cation exchange by clay minerals. Presence of clay minerals has led to the partial retainment of radiogenic 87Sr/86Sr resulting in increased 87Sr/86Sr in the solid tailings material at these depths. The 87Sr/86Sr ratios of the water-soluble phase in the transition zone is similar to that of helvine and could indicate its dissolution. In the upper part of the oxidized zone, the 87Sr/86Sr ratios and trends of Be, Ca, SO4, Tl and Zn in the water-soluble phase suggest the dissolution of gypsum which precipitated from a leachate with the isotopic signature of helvine. In the lower part of the unoxidized zone, elevated concentrations of W were recorded suggesting scheelite weathering. But the 87Sr/86Sr ratios are higher than that expected from dissolution of scheelite and indicates additional processes. Possible sources include biotite weathering and groundwater. This study reveals that when interpreting geochemical processes in mine waste environments, 87Sr/86Sr should be considered in addition to chemical constituents, as this isotopic tracer offers better insights into discriminating between different solute sources.
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| 10. |
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