Average Crust Research Articles

A case study on pollution and a human health risk assessment of heavy metals in agricultural soils around Sinop province, Turkey

In the present study, the concentration levels of heavy metals such as Cr, Fe, Ni, Cu, Zn, As and Pb in soil samples collected from 88 sampling locations around Sinop Province, Turkey were measured using energy dispersive X–ray fluorescence spectroscopy (EDXRF). To interpret and to evaluate the pollution status and distribution of heavy metals in soil, metal pollution parameters such as enrichment factor (EF), geo–accumulation index (Igeo), pollution factor (CF) and pollution load index (PLI) and geo–spatial distribution patterns were used. The mean concentrations of Cr, Fe, Ni, Cu, Zn, As, and Pb were found to be 194.73, 39,848.57, 85.02, 43.19, 65.10, 5.66, and 17.01 mg/kg, respectively. Results indicated that the mean concentrations of Cr, Ni, As, and Pb exceeded the world crustal average, with the exception of Fe, Cu, and As. Multivariate analysis results showed that Cr, Ni, Zn, As, and Pb levels in the investigated region were highly influenced by anthropogenic inputs such as agricultural practices. According to the health risk assessment model introduced by USEPA to evaluate the human health risks, the non–carcinogenic risk for children was above the threshold level, but low for adults. Total potential carcinogenic health risks for both children and adults in the study area were in acceptable range. Overall, when health risks are evaluated, it shows that children are more susceptible to non–carcinogenic and carcinogenic health effects of trace metals compared to adults.

Evolution of coal-bed methane in Southeast Qinshui Basin, China: Insights from stable and noble gas isotopes

The late Carboniferous-early Permian coal seams of the Qinshui Basin in Shanxi Province are the most prolific producer of coalbed methane (CBM) in China. Methane formed in the late Triassic during deep burial and reheating in late Jurassic-early Cretaceous driven by magmatic underplating. Basin inversion brought the coal seams to 400–700 m from the surface in the mid-late Cenozoic. Here we present results of a study aimed at understanding the origin of the methane, and how it was affected by Cenozoic exhumation of the basin. Methane from a 12 km traverse perpendicular to the basin margin in the southeast part of the basin have stable isotope compositions (δ13C = −30.2 to −35.2‰, and δD = −155 to −194‰) indicating a thermogenic origin with limited biogenic input. They are, however, lighter than expected based on coal maturity, and C1/(C2 + C3) (>1000) are significantly higher than typical thermogenic methane (<50). This is due to diffusive fractionation during commercial gas extraction. He-Ne-Ar isotopes are a mixture of crustal-radiogenic gas with air-derived noble gases. 4He concentrations (0.52 to 33.25 ppmv) and 4He/40Ar⁎ ratios (0.06–1.74) are unusually low. He-Ne-Ar concentrations are consistent with the open system Rayleigh fractionation of noble gases derived from air-saturated water with 4He/40Ar⁎ = 1 during gas extraction. The low 4He/40Ar⁎, compared with average crust (5) or local production (13) values, implies that >90% of the radiogenic 4He produced in the coals has been lost prior to equilibrium between gas and water phase in the reservoir. This likely occurred in response to gas loss process during rapid exhumation in Cenozoic, showing that the He and Ar content of natural gases is a sensitive indicator of gas loss event caused by recent basin inversion. The event may have led to the loss of up to 44% of the methane from the coal seams. This study demonstrates the importance of basin inversion on gas preservation in shallow CBM, and shows that, in contrast to δ13CCH4, the light noble gases are essential for tracing such a process.

A critical evaluation of copper isotopes in Precambrian Iron Formations as a paleoceanographic proxy

Trace metals in Iron Formations (IF) have been widely used as proxies for oceanic redox processes and oxygen evolution leading to the Great Oxidation Event (GOE). Copper has hitherto received comparatively little attention, with a single study reporting variation in δ65Cu between pre- and post-GOE black shales. This is attributed to postulated isotope fractionation effects in the pre-GOE ocean during widespread iron oxide deposition in IF. Here we focus on the application of Cu isotopes in two classic IF-containing sequences of the Neoarchean-Paleoproterozoic, namely the Hamersley (Australia) and Transvaal (South Africa) Supergroups. We specifically targeted the oxide-rich Joffre and Kuruman IF, the carbonate-rich Griquatown IF, and the Mn-rich Hotazel IF, which collectively record over 100 Ma of sustained IF deposition in the pre-GOE ocean. The aim was to assess the utility of Cu isotopes in IF as a paleoceanographic proxy in view of existing oxygen evolution models. Iron formation Cu concentrations are low compared to average crust and modern oceanic Fe-Mn oxide deposits, with average values between 1 and 5 ppm for all four IF data sets. Copper concentrations show no systematic variability with mineralogy, no statistical correlation with bulk Fe and Mn contents, good correlations with Ti (rCu-Ti = 0.73) for the Joffre data set and with Cr, Ni, and V for the South African data sets, and shale-like Cu/Ti ratios. Isotopic results show statistically invariant average δ65Cu values very close to 0‰ for all but the Joffre IF which has a marginally negative average δ65Cu value (−0.24 ± 0.22‰). Combined with other trace transition metal systematics, the Cu isotope data point to a Cu source that was controlled largely by inputs of fine volcanic-derived particles (ash), thus placing limitations on its utility as a paleoceanographic redox proxy during IF genesis.

Mobilisation of arsenic, selenium and uranium from Carboniferous black shales in west Ireland

The fixation and accumulation of critical elements in the near surface environment is an important factor in understanding elemental cycling through the crust, both for exploration of new resources and environmental management strategies. Carbonaceous black shales are commonly rich in trace elements relative to global crustal averages, many of which have potential environmental impacts depending on their speciation and mobility at surface. This trace element mobility can be investigated by studying the secondary mineralisation (regolith) associated with black shales at surface. In this study, Carboniferous shales on the west coast of Ireland are found to have higher than average shale concentrations of As, Cd, Cu, Co, Mo, Ni, Se, Te and U, similar to the laterally equivalent Bowland Shales, UK. Groundwater penetration and oxidative weathering of these pyritic black shales produces oxide deposits, dominated by goethite and jarosite, which are significantly enriched in As (44–468 ppm), Se (12–184 ppm), U (6–158 ppm) and other trace elements, compared to concentrations in the parent shales. Major elemental abundances vary in composition from 3.5 to 29.4% sulphate, 0.6–9.1% phosphate and 36.6–47.2% iron-oxide. Phosphate substitution within jarosite is observed in these samples, formed under ambient pressure and temperature conditions.The major and trace elements forming these secondary deposits are predominantly sourced from the underlying black shales through mobilisation by groundwater. This discovery is critical for the environmental assessment of black shale lithologies during shale gas exploration and production, where the demonstrated mobility of in situ elemental enrichments may indicate a significant source of produced- and groundwater contamination during and after hydraulic fracturing processes. The proportions of the major oxide phases exhibit a clear control on the trace elemental enrichments within the secondary deposits, where increasing Se and As concentrations correlate with increasing phosphate content of the jarosite mineralisation. This has implications for the remediation of acid mine drainage seeps, where phosphate-rich jarosite phases could be utilised for more efficient trace element removal.

Geochronological and geochemical studies of adakites from Tethyan Belt, Western Pakistan: A clue to geodynamics and Cu-Au mineralization

ABSTRACT Large porphyry Cu-Au deposits are associated with Early Miocene intrusive rocks in Tethyan belt, discovered along Chagai magmatic arc in Western Pakistan, adjacent to Southeast Iran. Two types of rocks were discriminated as granodiorite and monzodiorite from Saindak area. The granodiorites are associated with regional large Cu-Au mineralization, while the monzodiorites are mostly ore-barren. LA-ICP-MS U-Pb dating yielded weighted mean 206Pb/238U ages of 22.16–24.2 Ma for granodiorites and ca. 22.6 Ma for a monzodiorite. These intrusive rocks in the Saindak area are all calc-alkaline rocks, with enriched LILEs and depleted HFSEs, and without Eu negative anomalies. The felsic granodiorites are characterized by high Sr contents and Sr/Y ratios, with intermediate to high (La/Yb)N ratios that identify them as typical high-silica adakites. In contrast, the basaltic-andesitic monzodiorites are just normal arc-related rocks, showing less fractionated REE patterns than the granodiorites, with systematically lower LREE and higher MREE and HREE. Low K2O/Na2O ratios and decoupled Sr/Y-(La/Yb)N ratios indicate the characteristics of slab-derived adakites for the granodiorites, most likely originated through partial melting of the subducted Neotethys oceanic crust beneath Eurasian continent followed by subsequent mantle interaction. The almost simultaneously melting of subcontinental lithospheric mantle induced by dehydration of Neotethys plate gave rise to the formation of the barren monzodiorites. These intrusive rocks in the Saindak area are characterized by similar Sr-Nd-Pb isotopes with high 87Sr/86Sri ratios, slightly negative εNd(t) values and radiogenic Pb isotopes, plotting in the field between the MORB and EM-II mantle endmembers or the Average Cadomian Lower Crust, suggesting subducting sediments or old continental crustal materials have contributed into the compositions of these rocks by source enrichment or crustal contamination. The slab-melting derived adakite is favourable for regional massive Cu-Au mineralization in the Saindak area.

The Record of the Transition From an Oceanic Arc to a Young Continent in the Talamanca Cordillera

AbstractThe Talamanca Cordillera in the Central America Arc (Costa Rica‐Panama) preserves the record of the geochemical evolution from an intraoceanic arc to a juvenile continental arc in an active subduction zone, making it a testbed to explore processes that resulted in juvenile continental crust formation and explore potential mechanisms of early continental crust generation. Here we present a comprehensive set of geochronological, geochemical, and petrological data from the Talamanca Cordillera that tracks the key turning point (12–8 Ma) from the evolution of an oceanic arc depleted in incompatible elements to a juvenile continent. Most plutonic rocks from this transition and postintrusive rocks share striking similarities with average upper continental crust and Archean tonalite, trondhjemite, and granodiorite. We complement these data with seismic studies across the arc. Seismic velocities within the Caribbean Plate (basement of the arc) show a relatively uniform lateral structure consistent with a thick mafic large igneous province. Comparisons of seismic velocity profiles in the middle and lower crust beneath the active arc and remnant Miocene arc suggest a transition toward more felsic compositions as the volcanic center migrated toward the location of the modern arc. Seismic velocities along the modern arc in Costa Rica compared with other active arcs and average continental crust suggest an intermediate composition beneath the active arc in Costa Rica closer to average crust. Our geochemical modeling and radiogenic isotopes systematics suggest that input components from melting of the subducting Galapagos hotspot tracks are required for this compositional change.

Mineralogical and Geochemical Features of Cretaceous Bauxite from San Giovanni Rotondo (Apulia, Southern Italy): A Provenance Tool

In this study, the mineralogical and chemical compositions of bauxite from San Giovanni Rotondo (SGR) on the Gargano Promontory (northern Apulia, Italy) are presented and discussed with the aim of assessing the nature of its source material. Bauxite from the SGR, which is known as the “Montecatini mine”, was exploited intensively until the 1970s to recover alumina. As with most of the autochthonous peri-Mediterranean bauxites, the studied deposit is a karst bauxite with a massive, matrix-supported texture and an oolitic structure. Boehmite and hematite are the main mineral phases, and anatase, rutile, and kaolinite are present in lesser amounts along with detrital zircons and monazite grains. Calcite is abundant only in the deposit’s lower portion, triggering a significant dilution effect on trace element concentrations. However, with respect to the average crust and chondrite compositions, strong enrichments of trace metals (up to 10X Upper Continental Crust’s (UCC)) and rare earth elements (REEs, up to 800X chondrite) exist throughout the studied deposit. The distribution of REEs, the (La/Yb)N and Eu/Eu* ratios, and an Eu/Eu* versus Sm/Nd diagram have been used for determining the bauxite’s provenance. These geochemical proxies point to a parental material consisting of a mixture of distant magmatic and siliciclastic components.

Mineralogical thallium geochemistry and isotope variations from igneous, metamorphic, and metasomatic systems

This study presents new thallium (Tl) concentration and isotopic composition data for potassium feldspar (K-feldspar), micas, sulfides, and other minerals using solution multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS). The samples studied represent a diverse set of igneous, metamorphic, and metasomatic rock types. Purified separates of minerals anticipated to be Tl-bearing were analyzed; in many cases coexisting minerals were measured to examine the distribution of Tl and its isotopes between coexisting phases. This study is the first of its kind to document mineralogical controls on Tl chemical and isotopic fractionation.Thallium contents in rock-forming minerals and common sulfides vary from below detection limit (here, approximately 0.2 ppm Tl in the mineral utilizing an IsoProbe MC-ICP-MS) to 3200 ppm. In this present study, mica and feldspar samples can reach Tl concentrations well over 20 ppm, compared to only 0.7 ppm in average crust. In contrast, only 14 of 38 common sulfide samples contain Tl at levels above the detection limit. Measured Tl isotope ratios, reported as ε205Tl relative to the NIST 997 standard solution, range from −12.1 ± 0.6 to +18.0 ±1.4 (2σ). Most samples analyzed fall within the published range of ε205Tl (−20 to +15) (Nielsen et al., 2017). Although most sulfides show limited Tl enrichment, they display the highest ε205Tl values among coexisting minerals, with Fe-rich micas having the lowest ε205Tl values.The patterns in enrichment are best interpreted to reflect crystal chemical differences and the incompatible, dominantly lithophile nature of Tl. In turn, isotopic fractionation also reflects control by the bonding environment as well as redox conditions. The preferential distribution of Tl into micas and K-feldspar found here is consistent with the similarity in charge and ionic radius of Tl+ and K+. The higher ε205Tl values in sulfides agree with previous observations and theoretical studies showing the tendency of covalent bonds, high bond strengths, and high oxidation states to favor heavy isotopes. This work highlights important areas for future research regarding the natural weathering of Tl-bearing substrates, understanding regional cycling of Tl, and potential bioremediation of Tl contamination.

English

Assessment and distribution of the concentration of potentially harmful trace elements (PHTEs) is important for environmental health management. The concentrations of thirteen PHTEs were determined in the stream sediments and rocks samples from the underlying bedrock with the use of inductively coupled plasma-mass spectrometry (ICP-MS). Multivariate statistics and principal component analyses were used to identify and characterize trace elemental associations in the system. Trace elements ranged from 0.01 mg/kg as found in Cd concentration to 1591.00 mg/kg as found in Mn. Trace element concentrations vary from one location to another. The geochemistry of the underlying rocks including granite, quartzite and banded gneiss were far lower in metal concentration compared to that of the stream sediments. The concentrations of U (0.40 – 14.40 mg/kg), Mn (51.00 - 1591 mg/kg) and La (7.10 – 364.90 mg/kg) were of great concern to the ecosystem because of their relatively higher values in the stream sediments compared with the control, which is the average earth crust values. The results of enrichment factor and ecological risk index showed that Cu, Pb, As and Cd did not raise any eco-toxicological concern. From the results of the other elements analysed, there were considerable lower metal enrichment in terms of contamination status when compared with the background values. Metals such as Cr, Mn, Pb, Zn, Cu, Ni, V, As, Th, Cd, and La were positively correlated with each other (r = 0.51 - 0.95), which indicated analogous sources of geochemical characteristics. However, from the result, it is seen that there is considerable input of the metal concentration in the stream sediments possibly from man induced activities of these PHTEs in the drainage system of the catchment areas. Key words: Harmful trace elements, ecological risk, ecosystem, Okemesi, Ijero, stream sediment.

Assessing heavy metal toxicity in sediments of Chennai Coast of Tamil Nadu using Energy Dispersive X-Ray Fluorescence Spectroscopy (EDXRF) with statistical approach.

The concentration of some heavy metals: Al, Ca, K, Fe, Ti, Mg, Mn, V, Cr, Zn, Ni and Co in sediments from Pulicat Lake to Vadanemmeli along Chennai Coast, Tamil Nadu has been determined using EDXRF technique. The mean concentrations of Mg, Al, K, Ca, Ti, Fe, V, Cr, Mn, Co, Ni, and Zn were found to be 1918, 25436, 9832, 9859, 2109, 8209, 41.58, 34.14, 160.80, 2.85. 18.79 and 29.12 mg kg-1 respectively. These mean concentrations do not exceed the world crustal average. The level of pollution attributed to heavy metals was evaluated using several pollution indicators in order to determine anthropogenically derived contaminations. Enrichment Factor (EF), Geoaccumulation Index (Igeo), Contamination Factor (CF) and Pollution Load Index (PLI) were used in evaluating the contamination status of sediments. Enrichment Factors (EF) reveal the anthropogenic sources of V, Cr, Ni and Zn Geoaccumulation Index (Igeo) results reveal that the study area is not contaminated by the heavy metals. Similar results were also obtained by using pollution load index (PLI). The results of pollution indices indicates that most of the locations were not polluted by heavy metals. Multivariate statistical analysis performed using principal components and clustering techniques were used to identify the source of the heavy metals. The result of statistical procedures indicate that heavy metals in sediments are mainly of natural origin. This study provides a relatively novel technique for identifying and mapping the distribution of metal pollutants and their sources in sediment.

Elemental and isotopic behaviour of Zn in Deccan basalt weathering profiles: Chemical weathering from bedrock to laterite and links to Zn deficiency in tropical soils

Zinc (Zn) is a micronutrient for organisms and essential for plant growth, therefore knowledge of its elemental cycling in the surface environment is important regarding wider aspects of human nutrition and health. To explore the nature of Zn cycling, we compared its weathering behaviour in a sub-recent regolith versus an ancient laterite profile of the Deccan Traps, India – an area of known soil Zn deficiency. We demonstrate that progressive breakdown of primary minerals and the associated formation of phyllosilicates and iron oxides leads to a depletion in Zn, ultimately resulting in a loss of 80% in lateritic residues. This residue is mainly composed of resistant iron oxides and hydroxides ultimately delivering insufficient amounts of bio-available Zn. Moreover, (sub)-tropical weathering in regions experiencing extended tectonic quiescence (e.g., cratons) further enhance the development of old and deep soil profiles that become deficient in Zn. This situation is clearly revealed by the spatial correlation of the global distribution of laterites, cratons (Africa, India, South America and Australia) and known regions of Zn deficient soils that result in health problems for humans whose diet is derived from such land.We also investigate whether this elemental depletion of Zn is accompanied by isotope fractionation. In the saprolitic horizons of both weathering profiles, compositions of δ66ZnJMC-Lyon lie within the “crustal average” of +0.27±0.07‰ δ66ZnJMC-Lyon. By contrast, soil horizons enriched in secondary oxides show lighter isotope compositions. The isotopic signature of Zn (Δ66Znsample-protolith up to ~ −0.65‰) during the formation of the ferruginous-lateritic weathering profile likely resulted from a combination of biotically- and kinetically-controlled sorption reactions on Fe-oxyhydroxides. Our findings suggest that oxide rich soil types/horizons in (sub)-tropical regions likely exert a control on riverine Zn isotope compositions such that these become heavier than the crustal average. This isotopic behaviour invites a broader study of global soils to test whether light isotope composition alone could serve as an indicator for reduced bioavailability of Zn.

A new estimate of detrital redox-sensitive metal concentrations and variability in fluxes to marine sediments

The enrichment and depletion of redox sensitive trace metals in marine sediments have been used extensively as paleoredox proxies. The trace metals in shale are comprised of both detrital (transported or particulate) and authigenic (precipitated, redox-driven) constituents, potentially complicating the use of this suite of proxies. Untangling the influence of these components is vital for the interpretation of enrichments, depletions, and isotopic signals of iron (Fe), chromium (Cr), uranium (U), and vanadium (V) observed in the rock record. Traditionally, a single crustal average is used asa cutoff for detrital input, and concentrations above or below this value are interpreted as redox derived authigenic enrichment or depletion, while authigenic isotopic signals are frequently corrected for an assumed detrital contribution. Building from an extensive study of soils across the continental United States – which upon transport will become marine sediments – and their elemental concentrations, we find large deviations from accepted crustal averages in redox-sensitive metals (Fe, Cr, U, V) compared to typical detrital tracers (Al, Ti, Sc, Th) and provide new estimates for detrital contributions to the ocean. The variability in these elemental ratios is present over large areas, comparable to the catchment-size of major rivers around the globe. This heterogeneity in detrital flux highlights the need for a reevaluation of how the detrital contribution is assessed in trace metal studies, and the use of confidence intervals rather than single average values, especially in local studies or in the case of small authigenic enrichments.

Assessment of Heavy Metal Contamination in Marine Sediments of East Coast of Tamil Nadu Affected by Different Pollution Sources

The aim of this study was to determine the concentration of heavy metals in the sediments of Periyakalapet to Parangipettai coast, east coast of Tamil Nadu, by using energy-dispersive X-ray fluorescence (EDXRF) technique. The average heavy metal concentrations in the sediment samples were found in the order Al>Fe>Ca>Ti>K>Mg>Mn>Ba>V>Cr>Zn>La>Ni>Pb>Co>Cd>Cu. The average heavy metal concentrations were below the world crustal average. The degree of contamination by heavy metals was evaluated using pollution indices. The results of pollution indices revealed that titanium (Ti) and cadmium (Cd) were significantly enriched in sediments. Pearson correlation analysis was performed among heavy metal concentrations to know the existing relationship between them. Multivariate statistical technique was employed to identify the heavy metal pollution sources.

Measuring the change under compositional data analysis (CoDA): Insight on the dynamics of geochemical systems

Geochemical systems are complex and the analysis of the shape of the frequency distribution of elements and chemical species often informs about the variability and dispersion related to the underlying dynamics. However, when compositional data are used it is incorrect to investigate concentrations in the Euclidean space. Distribution analysis is aimed at focusing on real coordinates, which can be obtained by applying some appropriate log-ratio transformation. In particular, distributional analysis for compositional data can be applied to isometric coordinates, called balances, obtained through partition of a multi-element data set. As an alternative the same investigation can be performed on indices such as the robust Mahalanobis distance after having ranked log-ratio compositions with respect to some reference composition (i.e. average Earth crust) and having obtained a sort of “measure of change”. By considering this second new perspective, the chemical composition of topsoils of the Campania Region (Southern Italy) was investigated by analysing the concentrations of Al, As, B, Ba, Ca, Co, Cr, Cu, Fe, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, Th, Ti, V and Zn, in mg/kg, determined on >3500 samples. Results reveal the presence of complex processes governed by interaction-dominant dynamics where self-organisation appears to play some role.

A record of igneous evolution in Elysium, a major martian volcanic province

A major knowledge gap exists on how eruptive compositions of a single martian volcanic province change over time. Here we seek to fill that gap by assessing the compositional evolution of Elysium, a major martian volcanic province. A unique geochemical signature overlaps with the southeastern flows of this volcano, which provides the context for this study of variability of martian magmatism. The southeastern lava fields of Elysium Planitia show distinct chemistry in the shallow subsurface (down to several decimeters) relative to the rest of the martian mid-to-low latitudes (average crust) and flows in northwest Elysium. By impact crater counting chronology we estimated the age of the southeastern province to be 0.85 ± 0.08 Ga younger than the northwestern fields. This study of the geochemical and temporal differences between the NW and SE Elysium lava fields is the first to demonstrate compositional variation within a single volcanic province on Mars. We interpret the geochemical and temporal differences between the SE and NW lava fields to be consistent with primary magmatic processes, such as mantle heterogeneity or change in depth of melt formation within the martian mantle due to crustal loading.

Inherent Errors in Using Continental Crustal Averages and Legislated Accepted Values in the Determination of Enrichment Factors (EFs): A Case Study in Northern Ghana in Developing Environmental Policies

Health problems related to geological and environmental processes often have been assessed using enrichment factors derived from global and legislated accepted values. The petrological studies and the analysis of soils in this study reveals elements storage and concentrations in the environment exposed to life depends on several factors which are not incorporated using the example the continental crustal averages and the accepted legislated values. The results from the study suggest the establishment of local background values particularly from more large-scale surveys where quality and statistically significant environmental data had been collected for local background value estimation for enrichment factors. The continental crustal averages and legislated values either overestimate or underestimate the enrichment or depletion factors hence making policies developed from them unreal. General name granite can be given to a suite of rocks but their mineralogical and modal compositions will vary. Same continental crustal average can be used for them whilst disregarding the local environmental activities. The study concludes from the results in the petrological studies of rocks in Bongo and environmental soil studies at Nadowli that EFs calculated from the local background values can be used appropriately to propagate the true environmental policy to clean up the environment against the related health issues connected with the geogenic and anthropogenic processes than continental crustal averages as well as the legislated accepted values that may have no relationship with the study environment.

Water contamination with heavy metals and trace elements from Kilembe copper mine and tailing sites in Western Uganda; implications for domestic water quality

The mining and processing of copper in Kilembe, Western Uganda, from 1956 to 1982 left over 15 Mt of cupriferous and cobaltiferous pyrite dumped within a mountain river valley, in addition to mine water which is pumped to the land surface. This study was conducted to assess the sources and concentrations of heavy metals and trace elements in Kilembe mine catchment water. Multi-element analysis of trace elements from point sources and sinks was conducted which included mine tailings, mine water, mine leachate, Nyamwamba River water, public water sources and domestic water samples using ICP-MS. The study found that mean concentrations (mg kg−1) of Co (112), Cu (3320), Ni (131), As (8.6) in mine tailings were significantly higher than world average crust and were being eroded and discharged into water bodies within the catchment. Underground mine water and leachate contained higher mean concentrations (μg L−1) of Cu (9470), Co (3430) and Ni (590) compared with background concentrations (μg L−1) in un contaminated water of 1.9, 0.21 and 0.67 for Cu, Co and Ni respectively. Over 25% of household water samples exceeded UK drinking water thresholds for Al of 200 μg L−1, Co exceeded Winsconsin (USA drinking) water thresholds of 40 μg L−1 in 40% of samples while Fe in 42% of samples exceeded UK thresholds of 200 μg L−1. The study however found that besides mining activities, natural processes of geological weathering also contributed to Al, Fe, and Mn water contamination in a number of public water sources.

Whole-rock Nd–Hf isotopic study of I-type and peraluminous granitic rocks from the Chinese Altai: Constraints on the nature of the lower crust and tectonic setting

The nature of the lower crust and tectonic setting of the Chinese Altai in the early to middle Paleozoic are still hotly debated. Decoupling between zircon Hf and whole-rock Nd isotopic systems for granites results in different interpretations for the above issues. In order to solve the problem, whole-rock Nd–Hf isotopic analyses were conducted on representative early to middle Paleozoic I-type granite and strongly peraluminous granites and rhyolites from the Chinese Altai. The I-type granites show metaluminous to weakly peraluminous feature and have εNd(t) values ranging from −2.2 to +0.8 and εHf(t) from +3.9 to +12.9, respectively. The strongly peraluminous granites and rhyolites have similar εNd(t) and εHf(t) values ranging from −3.0 to +1.7 and from +2.1 to +10.4, respectively. All samples plot above the Terrestrial Array on Nd–Hf isotopic diagram, indicating significant Nd–Hf isotopic decoupling in the magma sources. These samples show flatten HREE pattern and have Lu/Hf ratios similar to the average crust, suggesting that Nd–Hf isotopic decoupling was not originated from an ancient basement with elevated Lu/Hf ratios. The observed isotopic decoupling is similar to those modern island arcs, such as the Lesser Antilles and Sunda, where Nd selectively enriched over Hf due to metasomatism in the mantle wedge and consequently resulted in decoupling between the Sm–Nd and Lu–Hf isotopic systems. Our results, combined with the available data, show that prolonged subduction and crust–mantle interaction caused the Nd–Hf isotopic decoupling in the lithospheric mantle beneath the Chinese Altai. The crust of the Chinese Altai was extracted from the lithospheric mantle and inherited the Nd–Hf isotopic decoupling feature. Therefore, the Hf, rather than Nd, isotopic data more faithfully reflect the nature of the lower crust that was quite juvenile in the Paleozoic, and the Chinese Altai represents an early Paleozoic magmatic arc possibly built near western Mongolia.

Population exposure to trace elements in the Kilembe copper mine area, Western Uganda: A pilot study

The mining and processing of copper in Kilembe, Western Uganda, from 1956 to 1982 left over 15 Mt. of tailings containing cupriferous and cobaltiferous pyrite dumped within a mountain river valley. This pilot study was conducted to assess the nature and extent of risk to local populations from metal contamination arising from those mining activities. We determined trace element concentrations in mine tailings, soils, locally cultivated foods, house dust, drinking water and human biomarkers (toenails) using ICP-MS analysis of acid digested samples. The results showed that tailings, containing higher concentrations of Co, Cu, Ni and As compared with world average crust values had eroded and contaminated local soils. Pollution load indices revealed that 51% of agricultural soils sampled were contaminated with trace elements. Local water supplies were contaminated, with Co concentrations that exceeded Wisconsin (US) thresholds in 25% of domestic water supplies and 40% of Nyamwamba river water samples. Zinc exceeded WHO/FAO thresholds of 99.4mgkg−1 in 36% of Amaranthus vegetable samples, Cu exceeded EC thresholds of 20mgkg−1 in 19% of Amaranthus while Pb exceeded WHO thresholds of 0.3mgkg−1 in 47% of Amaranthus vegetables. In bananas, 20% of samples contained Pb concentrations that exceeded the WHO/FAO recommended threshold of 0.3mgkg−1. However, risk assessment of local foods and water, based on hazard quotients (HQ values) revealed no potential health effects. The high external contamination of volunteers' toenails with some elements (even after a washing process) calls into question their use as a biomarker for metal exposure in human populations where feet are frequently exposed to soil dust. Any mitigation of Kilembe mine impacts should be aimed at remediation of agricultural soils, regulating the discharge of underground contaminated water but also containment of tailing erosion.

Geochemical records of anoxic water mass expansion in an oligotrophic alpine lake (Yunnan Province, SW China) in response to climate warming since the 1980s

In order to elucidate the effect of recent warming, we studied lipid biomarkers and trace elements in a dated sediment core from Lake Heihai, a small, deep, and ultraoligotrophic alpine lake in Yunnan Province (SW China), being only marginally affected by anthropogenic activities. The variation in lipid biomarkers (such as 10-methyl-C16:0fatty acid (FA), iso-branched C15( i-C15) and anteiso-branched C15( ai-C15) FA, and tetrahymanol) suggests a rapid productivity increase in sulfate reducing bacteria and ciliates since 1980, likely reflecting expansion of the hypolimnion anoxia and a prolonged duration of an oxic–anoxic chemocline in the water column. The concentrations of element molybdenum (Mo) in pre-1980 sediments approach the values in average crust. After 1980, the concentration increased, reaching levels approximately sixfold higher than the initial abundances. This likely reflects a high authigenic Mo deposition when the bottom water was more anoxic and enrichment in H2S. The suggested spatial and temporal expansion of the anoxic bottom water since 1980 was probably a response to the regional climate warming, resulting in stronger water column stratification and terrestrial grass inputs to the lake, and thus higher dissolved oxygen (DO) loss in hypolimnion.