Weathering Of Sulfide Minerals Research Articles

Peptide Bond Formation in Water Mediated by Carbon Disulfide.

Demonstrating plausible nonenzymatic polymerization mechanisms for prebiotic monomers represents a fundamental goal in prebiotic chemistry. While a great deal is now known about the potentially prebiotic synthesis of amino acids, our understanding of abiogenic polymerization processes to form polypeptides is less well developed. Here, we show that carbon disulfide (CS2), a component of volcanic emission and sulfide mineral weathering, and a widely used synthetic reagent and solvent, promotes peptide bond formation in modest yields (up to ∼20%) from α-amino acids under mild aqueous conditions. Exposure of a variety of α-amino acids to CS2 initially yields aminoacyl dithiocarbamates, which in turn generate reactive 2-thiono-5-oxazolidone intermediates, the thio analogues of N-carboxyanhydrides. Along with peptides, thiourea and thiohydantoin species are produced. Amino acid stereochemistry was preserved in the formation of peptides. Our findings reveal that CS2 could contribute to peptide bond formation, and possibly other condensation reactions, in abiogenic settings.

Shallow Groundwater Conveyance of Geologically Derived Contaminants to Urban Creeks in Southern California.

In California alone, there are currently over 200 instances on the EPA's list of impaired water bodies with unknown sources of excessive salinity or trace contaminants. This investigation focuses on Orange County, CA, a region that has undergone extensive hydrological modification, relies heavily on imported water for municipal supply, and has come under regulatory scrutiny for elevated TDS, sulfate, Cd, Ni, and Se. A survey of shallow groundwater weeps and springs, discharging directly to urban creeks, reveals high concentrations of TDS, sulfate, Cd, Ni, Zn, Cu, and Se that are often far in excess of water quality standards. Isotopic (δ(34)S and δ(18)O) and geochemical evidence indicate that the source of sulfate and TDS is weathering of sulfide minerals in the Capistrano Formation marine mudstone and dissolution of secondary minerals formed during past periods of sulfide oxidation, rather than anthropogenic inputs. The relative availability of carbonate minerals along the flow path appears to control pH, which then influences trace metal mobility to surface waters. Stable isotopes of H2O indicate that despite widespread use of imported water, meteoric recharge dominates shallow groundwater inputs with municipal sources contributing only 13-29% of discharge. These findings highlight the importance of understanding the hydrogeological setting to properly apportion contaminant sources and conveyances.

Sulfur sources of sedimentary “buckshot” pyrite in the Auriferous Conglomerates of the Mesoarchean Witwatersrand and Ventersdorp Supergroups, Kaapvaal Craton, South Africa

Large rounded pyrite grains (>1 mm), commonly referred to as “buckshot” pyrite grains, are a characteristic feature of the auriferous conglomerates (reefs) in the Witwatersrand and Ventersdorp supergroups, Kaapvaal Craton, South Africa. Detailed petrographic analyses of the reefs indicated that the vast majority of the buckshot pyrite grains are of reworked sedimentary origin, i.e., that the pyrite grains originally formed in the sedimentary environment during sedimentation and diagenesis. Forty-one of these reworked sedimentary pyrite grains from the Main, Vaal, Basal, Kalkoenkrans, Beatrix, and Ventersdorp Contact reefs were analyzed for their multiple sulfur isotope compositions (δ34S, Δ33S, and Δ36S) to determine the source of the pyrite sulfur. In addition, five epigenetic pyrite samples (pyrite formed after sedimentation and lithification) from the Middelvlei and the Ventersdorp Contact reefs were measured for comparison. The δ34S, Δ33S, and Δ36S values of all 41 reworked sedimentary pyrite grains indicate clear signatures of mass-dependent and mass-independent fractionation and range from −6.8 to +13.8 ‰, −1.7 to +1.7 ‰, and −3.9 to +0.9 ‰, respectively. In contrast, the five epigenetic pyrite samples display a very limited range of δ34S, Δ33S, and Δ36S values (+0.7 to +4.0 ‰, −0.3 to +0.0 ‰. and −0.3 to +0.1 ‰, respectively). Despite the clear signatures of mass-independent sulfur isotope fractionation, very few data points plot along the primary Archean photochemical array suggesting a weak photolytic control over the data set. Instead, other factors command a greater degree of influence such as pyrite paragenesis, the prevailing depositional environment, and non-photolytic sulfur sources. In relation to pyrite paragenesis, reworked syngenetic sedimentary pyrite grains (pyrite originally precipitated along the sediment-water interface) are characterized by negative δ34S and Δ33S values, suggesting open system conditions with respect to sulfate supply and the presence of microbial sulfate reducers. On the contrary, most reworked diagenetic sedimentary pyrite grains (pyrite originally precipitated below the sediment-water interface) show positive δ34S and negative Δ33S values, suggesting closed system conditions. Negligible Δ33S anomalies from epigenetic pyrite suggest that the sulfur was sourced from a mass-dependent or isotopically homogenous metamorphic/hydrothermal fluid. Contrasting sulfur isotope compositions were also observed from different depositional environments, namely fluvial conglomerates and marine-modified fluvial conglomerates. The bulk of the pyrite grains from fluvial conglomerates are characterized by a wide range of δ34S values (−6.2 to +4.8 ‰) and small Δ33S values (±0.3 ‰). This signature likely represents a crustal sulfate reservoir derived from either volcanic degassing or from weathering of sulfide minerals in the hinterland. Reworked sedimentary pyrite grains from marine-modified fluvial conglomerates share similar isotope compositions, but also produce a positive Δ33S/δ34S array that overlaps with the composition of Archean barite, suggesting the introduction of marine sulfur. These results demonstrate the presence of multiple sources of sulfur, which include atmospheric, crustal, and marine reservoirs. The prevalence of the mass-dependent crustal sulfur isotope signature in fluvial conglomerates suggests that sulfate concentrations were probably much higher in terrestrial settings in comparison to marine environments, which were sulfate-deficient. However, the optimum conditions for forming terrestrial sedimentary pyrite were probably not during fluvial progradation but rather during the early phases of flooding of low angle unconformities, i.e., during retrogradational fluvial deposition, coupled in some cases with marine transgressions, immediately following inflection points of maximum rate of relative sea level fall.

The role of AMD secondary minerals in controlling environmental pollution: Indications from bulk leaching tests

Weathering of sulphide minerals produces a large variety of Fe-oxide-bearing ochreous, varicoloured precipitates and efflorescences of variably soluble sulphate salts. These secondary minerals play an important role in acid mine drainage processes and, more generally, for environmental pollution, since they can be either a sink or a source for acidity and toxic metals. At Libiola mine, eastern Liguria (Italy), the secondary minerals directly form through precipitation from acid sulphate waters within waste-rock dumps and outcropping mineralized bodies as well as within streams and runoff channels. Within waste-rock dumps they are present mainly as cement, filling the inter-clast porosity, and/or as coating and ephemeral efflorescences on the outcropping surfaces. Their stability represents a major environmental issue due to the potential importance of these phases in controlling metal distribution in the surface environment. This paper presents a detailed mineralogy and geochemistry characterisation of these materials, investigating the tendency for different types of secondary minerals (hardpans, ochreous consolidated precipitates, ochreous colloids, non ochreous colloids) to release metals after a simple mixing with deionised water for 12days. Within the different types of deposits, hardpans showed the lowest tendency to release metals, in contrast to ochreous colloids and ochreous concretions that gave the highest concentrations.Nickel was the element most easily extracted by this treatment, even from non-ochreous colloids, while iron was much less readily leached. Dissolution experiments carried out on efflorescent sulphate salts demonstrated that these materials have a strong acid producing affinity which led to their complete dissolution. These results indicate that secondary phases associated with acid mine drainage can play an important role in controlling trace metal mobility, acting either as scavengers, to remove metals, from solutions or also as secondary sources of metal contamination during the interaction of these materials with surface waters.

Determination of the long-term release of metal(loid)s from construction materials using DGTs

Long-term leaching experiments are crucial to estimate the potential release of dangerous substances from construction materials. The application of Diffuse Gradients in Thin film (DGT) in static-batch experiments was tested to study the long-term release of metal(loid)s from construction materials for hydraulic engineering, for half a year. Long-term release experiments are essential to improve calculations of the life-time release for this materials. DGTs in batch experiments were found to be a space and labour efficient application, which enabled (i) to study, in a non-invasive manner, the total release of nine metal(loid)s for half a year, (ii) to differentiate between release mechanisms and (iii) to study mechanisms which were contrary to the release or caused experimental artefacts in the batch experiments. For copper slag (test material) it was found that eight metal(loid)s were released over the whole time period of 184 d. Cu, Ni and Pb were found to be released, predominantly caused by (the) weathering of sulphide minerals. Only for Zn a surface depletion mechanism was identified. The results from the long-term batch experiments deliver new information on the release of metal(loid)s during the life cycle of construction materials with regard to river basin management objectives.

Diagramas de Estabilidad Multifases Modificados: Un caso de AMD en Northumberland, UK

The weathering of sulphide minerals within spoil heaps causes the release of sulphate and environmentally hazardous metal ions. Newly-formed species can subsequently precipitate as highly soluble, secondary sulphate minerals, which, in turn, might be flushed by dilute recharge water or eventually transformed into more stable minerals. These processes determine which components are retained in the spoil as immobile solid phases and which (and when) others are released into the wider aquatic environment. To elucidate this sequence of mineral formation and transformation, we studied mineral-fluid equilibria in a major abandoned coal mine spoil heap at the former Shillbottle Colliery, Northumberland, UK. The investigations focussed on stability of iron minerals produced during the acid mine drainage process. The multi-component Phreeplot-calculated pE/pH diagrams reveal that many post-mining secondary minerals may co-exist, in contrast to what is indicated by the more commonly used charts. Being able to visualize the mutual stability of these minerals under specific chemical and physical conditions might aid understanding of formation and transformation mechanisms.

Stable isotope (O and C) geochemistry of non-sulfide Zn–Pb deposits; case study: Chah-Talkh non-sulfide Zn–Pb deposit (Sirjan, south of Iran)

The study of oxygen and carbon isotopic ratios has gained importance to determine the origin of ore-bearing fluids, carbon origin, and also to determine the formation temperature of non-sulfide Pb and Zn minerals. In order to determine the origin of fluids and carbon existing in Zn carbonate minerals in Chah-Talkh deposit, initially the amounts of δ18OSMOW and δ13CPDB changes in various zinc minerals in important deposits in Iran and the world were studied, and then by comparing these values in Chah-Talkh deposit with those of other deposits, the origin of fluids responsible for ore forming, carbon, and formation temperature of Chah-Talkh deposit was determined. The range of δ18OSMOW changes in smithsonite mineral in non-sulfide lead and zinc deposits varies from 18.3 to 31.6 ‰, and δ18OSMOW in hydrozincite mineral varies from 7.8 to 27 ‰. Due to the impossibility of smithsonite sampling from Chah-Talkh deposit (due to it being fine-grained and dispersed), hydrozincite minerals which have high isotopic similarities with smithsonite are used for the isotopic analysis of carbon and oxygen. The range of δ18OSMOW changes in hydrozincite mineral of Chah-Talkh deposit varies from 7.8 to 15.15 ‰, which places in the domain of metamorphic water. The extensiveness of δ18OSMOW changes in Chah-Talkh indicates the role of at least two fluids in the formation of non-sulfide minerals. The obtained formation temperature of non-sulfide minerals (hydrozincite) in Chah-Talkh deposit is 70 to 100 °C, which indicates the role of metamorphic fluids in the formation of deposit. Complete weathering of sulfide minerals to a depth of 134 m confirms the role of rising metamorphic fluids in the formation of non-sulfide minerals. The δ13CPDB values of Chah-Talkh deposit are set in the range of atmospheric CO2 and carbonate rocks, in which the existence of atmospheric CO2 indicates the role of atmospheric fluids, and the existence of carbonate carbon rock indicates of the role of metamorphic fluids in the precipitation of non-sulfide Zn minerals.

Sources and impact of sulphate on groundwaters of Triassic carbonate aquifers, Upper Silesia, Poland

Summary Groundwater within the unconfined or semi-confined parts of Triassic carbonate aquifers in Upper Silesia (Poland) contains high concentrations of sulphate (up to 290 mg/L), sometimes in excess of drinking water limits (>250 mg/L). To assess the influence of different possible sulphate sources, isotopic analyses of S and O were performed on groundwater sulphate and potential sulphate sources and combined with literature data. Three dominant sources of sulphate were delineated, based on the geological and literature study and supported by the mixing relations between inverse concentration of sulphate and its isotopic compositions. These sources are: (i) sulphate from rainfall; (ii) weathering of sulphide minerals in ore deposits in the aquifer-forming carbonate rocks; (iii) dissolution of sulphate evaporites in the Triassic sequence. Fortunately these three sources have distinctive S and O isotope compositions and thus their contributions to the total dissolved sulphate could be estimated. The application of linear mixing models for three sources in the dual isotope system allowed the impact of the three different sulphate sources on particular parts of the aquifers to be calculated. The average isotopic composition of sulphate in abstracted groundwater indicates that the most important source of sulphate is sulphide weathering, contributing about 50% of total sulphate. The second most significant source of sulphate input is rainfall and it is characterised by a mean contribution of 30%. Application of Monte Carlo analysis that incorporates the full variability in distributions of isotopic compositions for the three sources and all mixing fractions between them gave the most probable ranges of the dissolved in groundwater sulphate. This analysis indicated that the proportion of sulphate derived by sulphide oxidation is comparable with the estimations based on linear models. This study has shown that the water quality of these important groundwater resources is under threat from both natural sources, i.e. metal sulphide oxidation and gypsum dissolution. Analysis of the mathematical models analysis shows that the first process is the predominant source of sulphate in groundwater. However, the highest concentrations of dissolved sulphate are positively correlated with the increasing proportion of sulphate derived from gypsum dissolution. Moreover, one should keep in mind that natural processes might be anthropogenically accelerated due to variable water demands and groundwater abstraction. Eventually, the statistically second-order source of sulphate – rainfall might contain surface-derived contaminants, and its contribution to the total load of sulphate might indirectly indicate the vulnerability of aquifers for the pollution.

Hydrogeochemical investigation in an arid region of Iran (Tabas, Central Iran)

Groundwater is the most important source of water supply in Iran and understanding the geochemical evolution of groundwater is important for sustainable development of the water resources in Tabas area. A total of 29 samples of groundwater in Tabas area have been analyzed for ions and major elements. Groundwater of the study area is characterized by the dominance of Na–Cl water type. Groundwater was generally acidic to high alkaline with pH ranging from 5.42 to 10.75. The TDS as a function of mineralization characteristics of the groundwater ranged from 479 to 10,957 mg/l, with a mean value of 2,759 mg/l. The Ca2+, Mg2+, SO42− and HCO3− were mainly derived from the dissolution of calcite, dolomite and gypsum. The Cu, Pb and Zn ions are not mobile in recent pH–Eh, but these conditions controlled dissolved Se, V and Mo in groundwater. The As is released in groundwater as a result of the weathering of sulfide minerals like arsenopyrite.

In-Lake Neutralization: Quantification and Prognoses of the Acid Load into a Conditioned Pit Lake (Lake Bockwitz, Central Germany)

The formerly highly acidic pit Lake Bockwitz south of Leipzig (Germany) has been repeatedly treated since 2004 with soda ash to meet water quality criteria for the lake effluent. Intense monitoring of water quality parameters showed that previous predictions underestimated the acid load into the lake. Field research and lab experiments were designed to identify and quantify the processes responsible for re-acidification. Monitoring data and key parameters from intermittent-flow column experiments were integrated in hydrogeochemical and physical transport models. The combined lake budget model indicated that re-acidification was dominated by leaching of acidic sulfide mineral weathering products from the Tertiary bank substrates. High inputs of iron, aluminum, and sulfate were generated by infiltrating rain water, interflow, and groundwater recharge. In contrast, acid loads from surface runoff and soil erosion were minor at this particular site. Based on this work, a methodology is proposed to obtain critical parameters from field and lab investigations and integrate those into hydrogeochemical and physical transport models. These process-based models offer tools to reliably predict the water quality of mining pit lakes, develop appropriate treatment measures for the rehabilitation period, and plan the requirements for cost-effective lake water conditioning.

Determination of mercury biogeochemical fluxes in the remote Mackenzie River Basin, northwest Canada, using speciation of sulfur and organic carbon

Abstract The Mackenzie River Basin (MRB) in NW Canada is one of the least human-impacted large watersheds in the world. The western and eastern sub-basins of the MRB are also marked by contrasting geology, geomorphology, hydrology, and biology. These remarkable differences in a remote river basin provide a unique opportunity to probe the biogeochemical processes governing the sources, transport, and bioavailability of Hg at the terrestrial-marine interface and ultimately in the Arctic Ocean. Based on a large dataset of the concentration and speciation of Hg, S and organic matter in surface sediments across the MRB, a source-apportioned budget was constructed for Hg in the MRB. The results indicate that the Hg flux in the basin originates primarily from the weathering of sulfide minerals in the western mountainous sub-basin (∼78% of the total), followed by the erosion of coal deposits along the mainstream of the Mackenzie River (∼10%), with the remainder split between atmospheric inputs and organic matter-bound Hg (6% and 5%, respectively). Although the Hg flux from the eastern peatland sub-basin only accounts for ∼10% of the total riverine Hg flux, Hg in this region correlates strongly with labile organic matter, and will likely have a much stronger influence on local biota.

Geochemical signature of surface water and stream sediments of a mineralized drainage basin at NE Chalkidiki, Greece: A pre-mining survey

The geochemical characteristics of surface water and stream sediments in Asprolakkas drainage basin, an area of Tertiary mineralization within amphibolite, located at NE Chalkidiki peninsula, Greece, were investigated in order to establish the geochemical baseline conditions prior to any type of new mining activities. The area represents the only example of active mining and processing of base metal sulfide ore in Greece and also includes an unmined porphyry Cu–Au ore deposit at Skouries. In a wider context, this research represents a pre-mining baseline geochemical study that can be used as an analog for similar metallogenetic provinces in areas with a Mediterranean type climate.Concentrations of dissolved major ions and trace metals displayed wide variability within the study area. Kokkinolakkas stream, draining the exploited Pb–Zn (±Ag) ore bodies, is strongly influenced by chemical weathering of sulfide minerals and presents elevated levels of SO4 (429–857mgl−1), Pb (4–64μgl−1), Zn (290–1350μgl−1), Mn (1680–7899μgl−1), Ni (12–50μgl−1), Cd (2–8μgl−1), As (8–45μgl−1) and Sb (9–16μgl−1). Stream water of unmined areas demonstrated a different chemical composition with elevated values mainly for Pb (up to 45μgl−1) and As (up to 141μgl−1). Hydrological conditions highly influence the behavior of major elements and metals. Stream bed sediments from Kokkinolakkas and Tsarkia Lakkos, located at the head waters of Asprolakkas basin, have anomalous values in Pb (1165–3439mgkg−1), Zn (1368–4538mgkg−1), As (964–2714mgkg−1), Sb (30–70mgkg−1), Cd (3.8–21.6mgkg−1) and Mn (6811 up to >10,000mgkg−1). Mobility of selected trace metals was investigated through the application of a 5-step sequential extraction procedure. Results show that, despite the high total metal content, the majority of analyzed elements are mainly bound to relatively immobile operationally defined geochemical phases of amorphous to poorly crystalline Fe and Mn oxides and the residual fraction. Considering the planned mining developments in the area, the results of this study may assist mine planners to set realistic goals for monitoring and remediation programs.

Sources and behavior of arsenic and trace elements in groundwater and surface water in the Poopó Lake Basin, Bolivian Altiplano

Water management in semiarid and arid catchments such as the Poopo Lake Basin requires improved understanding of the complex behavior of the various contaminants, which affect the drinking water quality and considered as crucial for sustainable development of the region. Mechanisms of arsenic (As) release in the surface and groundwater were studied. Hydrochemical data for surface water (4 samples) and groundwater (28 samples) were collected in a small watershed in the Poopo catchment at the highland of the Bolivian Andes (Altiplano). All of them show high electrical conductivity values and moderately oxidizing conditions. The surface water contains high concentration of sulfate and the trace elements As, Zn and Pb in the zone affected by acid mine drainage. There is a large variability of the concentration of As and of the trace elements in the groundwater in the five different regions within the Poopo catchment. The metal concentrations sensitive to changes of redox state and results of speciation modeling suggest that As (V) is a predominant aqueous species, which conforms to the prevailing oxidizing conditions in the shallow groundwater environment. Two generalized trends for As distribution were identified in groundwater: (a) high concentrations are found in the arid zone (100–250 μg/L) in the southern (region III) and in the northwestern (region V) regions, and (b) low concentrations (<50 μg/L) are found in the remaining part of the basin (region I, II and IV). However, the spatial distribution within these regions needs to be investigated further. A conclusion from the present study is that there are multiple sources of As as well as other trace elements (such as Cd, Mn and Zn) in the Poopo Lake Basin. Among the sources and the processes which led to the mobility of As and other trace metals in the region are: (a) weathering of sulfide minerals, (b) oxidation of pyrite and/or arsenopyrite in mineralized areas and (c) desorption from hydrous ferric oxide (HFO) surfaces. In non-mining areas, volcanic ash is suggested to be a significant source of As.

Mine drainage from the weathering of sulfide minerals and magnetite

Pyrite and pyrrhotite are the principal minerals that generate acid drainage in mine wastes. Low-pH conditions derived from Fe-sulfide oxidation result in the mobilization of contaminant metals (such as Zn, Cd, Ni and Cr) and metalloids (such as As) which are of environmental concern. This paper uses data from detailed mineralogical and geochemical studies conducted at two Canadian tailings impoundments to examine the mineralogical changes that pyrite, pyrrhotite, sphalerite and magnetite undergo during and after sulfide oxidation, and the subsequent release and attenuation of associated trace elements. The stability of sphalerite in tailings impoundments generally is greater than that of pyrrhotite, but less than pyrite. Dissolved Ni and Co derived from Fe sulfides, and to a lesser extent, dissolved Zn and Cd from sphalerite, are commonly attenuated by early-formed Fe oxyhydroxides. As oxidation progresses, a recycling occurs due to continued leaching from low-pH pore waters and because the crystallinity of Fe oxyhydroxides gradually increases which decreases their sorptive capacity. Unlike many other elements, such as Cu, Pb and Cr, which form secondary minerals or remain incorporated into mature Fe oxyhydroxides, Zn and Ni become mobile. Magnetite, which is a potential source of Cr, is relatively stable except under extremely low-pH conditions. A conceptual model for the sequence of events that typically occurs in an oxidizing tailings impoundment is developed outlining the progressive oxidation of a unit of mine waste containing a mixed assemblage of pyrrhotite and pyrite.

The Crystal Structure of Desulfovibrio vulgaris Dissimilatory Sulfite Reductase Bound to DsrC Provides Novel Insights into the Mechanism of Sulfate Respiration

Sulfate reduction is one of the earliest types of energy metabolism used by ancestral organisms to sustain life. Despite extensive studies, many questions remain about the way respiratory sulfate reduction is associated with energy conservation. A crucial enzyme in this process is the dissimilatory sulfite reductase (dSiR), which contains a unique siroheme-[4Fe4S] coupled cofactor. Here, we report the structure of desulfoviridin from Desulfovibrio vulgaris, in which the dSiR DsrAB (sulfite reductase) subunits are bound to the DsrC protein. The alpha(2)beta(2)gamma(2) assembly contains two siroheme-[4Fe4S] cofactors bound by DsrB, two sirohydrochlorins and two [4Fe4S] centers bound by DsrA, and another four [4Fe4S] centers in the ferredoxin domains. A sulfite molecule, coordinating the siroheme, is found at the active site. The DsrC protein is bound in a cleft between DsrA and DsrB with its conserved C-terminal cysteine reaching the distal side of the siroheme. We propose a novel mechanism for the process of sulfite reduction involving DsrAB, DsrC, and the DsrMKJOP membrane complex (a membrane complex with putative disulfide/thiol reductase activity), in which two of the six electrons for reduction of sulfite derive from the membrane quinone pool. These results show that DsrC is involved in sulfite reduction, which changes the mechanism of sulfate respiration. This has important implications for models used to date ancient sulfur metabolism based on sulfur isotope fractionations.

The Oued Mellègue: Mining activity, stream sediments and dispersion of base metals in natural environments, North-western Tunisia

In the Northwest of Tunisia, mining works have occurred in an area of vital water reserves and resources (Oued Mellègue and Oued Mejerda), which represent nearly 81% of total potential of water in the region. Demographic growth, insufficient drinkable water, agriculture and industrial plants are factors responsible for the strong demand of this resource. Water supply is done by an interconnected battery of dams built on the major watercourses, the first of which, the Mellègue dam, was erected in the 1960s. Nowadays, most of the mines are closed for almost two decades although one is still active: (Jerissa for Fe). It is important to emphasise the fact that there are millions of cubic metres of abandoned tailings, mainly from Pb–Zn–Ba mines, which are not surveyed, representing a serious threat to the environment. Exposed superficial mineralised tailings, weathering of sulphide minerals, and the presence of siderite and phosphorites as well, accelerate the oxidation and generate leaching solutions rich in toxic base-metals (Cd, Pb, Hg, Zn, U, among others, are the most important). Trace element analyses performed on tailings and stream-sediments samples and the use of “Principal Component Analysis” statistical method, helped to understand the processes of toxic metals circulation in the natural environment. It showed that the major and trace metals fate and transfer from contamination sources into the river systems are based on three main factors: i) a mineralogical component which is representative of regional rocks (shales, siliciclastics, limestones, and dolostones), ii) a residual assemblage concerning the ore mineral micro phases (phosphorites and common and complex sulphides of Pb and Zn) and iii) hydrated iron oxyhydroxide components representing the complex geochemical processes taking place, which are extremely active in scavenging toxic metals in either weathered tailing profiles or continuously reworked stream depositional systems. In addition, the superficial lime fraction and the Triassic-derived gypsum and halite could play a significant role in precipitating and thus fixing heavy metals in the proximity of various sources of contamination defined by tailing areas which are constantly being leached.

Seasonal and event variations in δ34S values of stream sulfate in a Vermont forested catchment: Implications for sulfur sources and cycling

Stable sulfur (S) isotope ratios can be used to identify the sources of sulfate contributing to streamwater. We collected weekly and high-flow stream samples for S isotopic analysis of sulfate through the entire water year 2003 plus the snowmelt period of 2004. The study area was the 41-ha forested W-9 catchment at Sleepers River Research Watershed, Vermont, a site known to produce sulfate from weathering of sulfide minerals in the bedrock. The δ 34S values of streamwater sulfate followed an annual sinusoidal pattern ranging from about 6.5‰ in early spring to about 10‰ in early fall. During high-flow events, δ 34S values typically decreased by 1 to 3‰ from the prevailing seasonal value. The isotopic evidence suggests that stream sulfate concentrations are controlled by: (1) an overall dominance of bedrock-derived sulfate ( δ 34S ~ 6–14‰); (2) contributions of pedogenic sulfate ( δ 34S ~ 5–6‰) during snowmelt and storms with progressively diminishing contributions during base flow recession; and (3) minor effects of dissimilatory bacterial sulfate reduction and subsequent reoxidation of sulfides. Bedrock should not be overlooked as a source of S in catchment sulfate budgets.

Sulfuric acid as an agent of carbonate weathering constrained by δ13C DIC: Examples from Southwest China

Abstract Rock weathering by carbonic acid is thought to play an important role in the global carbon cycle because it can geologically sequestrate atmospheric CO 2. Current model of carbon cycle evolution usually assumes that carbonic acid is the major weathering agent and that other acids are not important. Here, we use carbon isotopic evidence and water chemistry of springs and rivers from the Beipanjiang River basin (Guizhou Province, Southwest China) to demonstrate that sulfuric acid is also an important agent of rock weathering. The δ 13C of dissolved inorganic carbon (DIC) in the water samples ranges from − 13.1‰ to − 2.4‰, and correlates negatively to [HCO 3 −]/([Ca 2+] + [Mg 2+]) ratios and positively to [SO 4 2−]/([Ca 2+] + [Mg 2+]) ratios. These relationships are interpreted as mixing diagrams between two reactions of carbonate weathering, using carbonic acid and sulfuric acid as a proton donor, respectively. Mixing proportions show that around 42% of the divalent cations in the spring water from Guizhou are originated from the interaction between carbonate minerals and sulfuric acid. It is shown that 40% of this sulfuric acid is derived from the atmosphere and has an anthropogenic origin. The remaining 60% are derived from the oxidative weathering of sulfide minerals in sedimentary rocks. Our results show the positive action of sulfuric acid on the chemical weathering of carbonate. Particularly, we show that sulfuric acid generated by coal combustion has increased by almost 20% the weathering rates of carbonate in Southwest China. This is a clear evidence that human activities are changing the weathering rates of rocks and demonstrates a negative feedback on the acidification of the ocean by greenhouse gases. Because of the involvement of sulfuric acid in weathering reactions, 63% of the alkalinity exported by rivers is derived from carbonate, instead of 50% when atmospheric CO 2 is the only acid involved in chemical weathering of carbonate. In the Guizhou Province, the weathering of carbonate is thus, at least transiently, a net source of CO 2 to the atmosphere. When extrapolated at global scale, sulfuric acid-induced carbonate weathering could counterbalance a significant part of the CO 2 consumed by silicate weathering. This paper highlights the competition between silicate weathering by carbonic acid and carbonate weathering by sulfuric acid for the regulation of the atmospheric CO 2 level.

Temporal variation and the effect of rainfall on metals flux from the historic Beatson mine, Prince William Sound, Alaska, USA

Abstract Several abandoned Cu mines are located along the shore of Prince William Sound, AK, where the effect of mining-related discharge upon shoreline ecosystems is unknown. To determine the magnitude of this effect at the former Beatson mine, the largest Cu mine in the region and a Besshi-type massive sulfide ore deposit, trace metal concentration and flux were measured in surface run-off from remnant, mineralized workings and waste. Samples were collected from seepage waters; a remnant glory hole which is now a pit lake; a braided stream draining an area of mineralized rock, underground mine workings, and waste piles; and a background location upstream of the mine workings and mineralized rock. In the background stream pH averaged ∼7.3, specific conductivity (SC) was ∼40 μS/cm, and the aqueous components indicative of sulfide mineral weathering, SO4 and trace metals, were at detection limits or lower. In the braided stream below the mine workings and waste piles, pH usually varied from 6.7 to 7.1, SC varied from 40 to 120 μS/cm, SO4 had maximum concentrations of 32 mg/L, and the trace metals Cu, Ni, Pb, and Zn showed maximum total acid extractable concentrations of 186, 5.9, 6.2 and 343 μg/L, respectively. With an annual rainfall of ∼340 cm (estimated from the 2006 water year) it was expected that rain water would have a large effect on the chemistry of the braided stream draining the mine site. A linear mixing model with two end members, seepage water from mineralized rock and background water, estimated that the braided stream contained 10–35% mine drainage. After rain events the braided stream showed a decrease in pH, SC, Ca + Mg, SO4, and alkalinity, due to dilution. The trace metals Ni and Zn followed this same pattern. Sodium + K and Cl did not vary between the background and braided stream, nor did they vary with rainfall. At approximately 2 and 3 mg/L, respectively, these concentrations are similar to concentrations found in rainfall on the coasts of North America. High concentrations of total acid extractable Al and Fe were found at near-neutral pH in most of the waters collected at the site. Equilibrium solubility simulations, performed with PHREEQC, show that the stream waters are saturated with respect to Al, Fe and SiO2 solid phases. Because the “dissolved” sample fractions (acid preserved and filtered to 0.45 μm) show significant concentrations of Al and Fe it is presumed that these are present as colloids. The relationship between concentrations of Al and Fe, and rainfall was the opposite of that observed for the major ions Ca + Mg, SO4, and alkalinity, in that Al and Fe concentrations increased with increasing rainfall. Concentrations of Cu and Pb followed the same pattern. Adsorption calculations were performed with Visual MINTEQ, using the diffuse double layer electrostatic model and surface complexation constants for the ferrihydrite surface. These results suggest that 30–93% of Cu and 58–97% of Pb was adsorbed to ferrihydrite precipitates in the stream waters. Ni and Zn showed little adsorption in this pH range. Flux calculations show that the total mass of trace metals transported from the mine site, during the 60 day study period, was ranked as Zn (196 kg) > Cu (87 kg) > Pb(1.9 kg) ≈ Ni(1.9 kg). Nickel and Zn were transported mostly as dissolved species while Cu and Pb were transported mostly as adsorbed species. pH control on adsorption was evident when Cu and Pb isotherms were normalized by ferrihydrite flux. Decreased stream water pH due to periods of frequent and high volume rain events would cause desorption of Cu and Pb from the ferrihydrite surface, thus changing not only their speciation in solution but also their mechanism of transport.

Primary Geologic Sources of Arsenic in the Chianan Plain (Blackfoot Disease Area) and the Lanyang Plain of Taiwan

The area that includes Beimen and the immediate surrounding villages of southwestern Taiwan is recognized as the home of the world's only well-documented Blackfoot Disease (BFD) occurrence—where extremely high concentrations of arsenic (As) have been found in the artesian wells from the Chianan Plain that were previously used as a drinking water supply. In the past decade, very high levels of arsenic have also been discovered in the potable water from the Lanyang Plain of northeastern Taiwan, but BFD does not occur there. From regional geological/geophysical field investigations in these two areas and a literature survey of arsenic problems in the drinking water of other countries, we have identified five potential primary geologic sources of the As for the BFD area and six sources for the Lanyang Plain. We also report measurements of arsenic in two "new" areas: (1) the sea water west of the BFD area (three samples with As levels of 2.32, 7.46, and 9.71 μg/L; and (2) stream bed deposits east of the BFD area (two samples with As concentrations of 0.00485 wt% and 0.23000 wt%). With the current information available, it seems most plausible that the primary source of the arsenic in the BFD area is from fluid escape from the accretionary prism of Taiwan or from in situ formation of arsenic-laden sulfide minerals in the water-rich coastal sediments, whereas the most likely sources of the high concentrations of arsenic in the Lanyang Plain are hydrothermal venting in the Okinawa Basin and/or weathering of sulfide minerals associated with gold and copper ores along the Lishan fault to the south. Although oxidation is known to play a role in the formation of some arsenic compounds, most of these 11 primary sources and their associated rocks and minerals are originally related to reducing environments; however, continued research is necessary to fully explain each source's expulsion mechanism (mobility), transport (if any), and final concentration or enrichment of arsenic in the groundwater of Taiwan.