Fractionation Of Trace Elements Research Articles

Large S isotope and trace element fractionations in pyrite of uranium roll front systems result from internally-driven biogeochemical cycle

Complex pyrite textures associated with large changes in isotopic and trace element compositions are routinely assumed to be indicative of multi-faceted processes involving multiple fluid and sulfur sources. We propose that the features of ore-stage pyrite from roll front deposits across the world, revealed in exquisite detail via high-resolution trace element mapping by LA-ICP-MS, reflect the dynamic internal evolution of the biogeochemical processes responsible for sulfate reduction, rather than externally driven changes in fluid or sulfur sources through time. Upon percolation of oxidizing fluids into the reduced host-sandstones, roll front systems become self-organized, with a systematic reset of their activity cycle after each translation stage of the redox interface down dip of the aquifer. Dominantly reducing conditions at the redox interface favor the formation of biogenic framboidal pyrite (δ34S from −30.5 to −12.5‰) by bacterial sulfate reduction and the genesis of the U mineralization. As the oxidation front advances, oxidation of reduced sulfur minerals induces an increased supply of sulfate and metals in solution to the bacterial sulfate reduction zone that has similarly advanced down the flow gradient. Hence, this stage is marked by increased rates of the bacterial sulfate reduction associated with the crystallization of variably As-Co-Ni-Mo-enriched concentric pyrite (up to 10,000′s of ppm total trace contents) with moderately negative δ34S values (from −13.7 to −7.5‰). A final stage of pyrite cement with low trace element contents and heavier δ34S signature (from −6.9 to +18.8‰) marks the end of the roll front activity cycle and the transition from an open to a predominantly closed system behavior (negligible advection of fresh sulfate). Blocky pyrite cement is formed using the remaining sulfate, which now becomes quickly heavy according to a Rayleigh isotope fractionation process. This ends the cycle by depleting the nutrient supplies for the sulfate-reducing bacteria and cementing pore spaces within the host sandstone, effectively restricting fluid infiltration. This internally-driven roll front activity cycle results in systematic, large S isotope and trace element fractionation. Ultimately, the long-time evolution of the basin and fluid sources control the metal endowment and evolution of the system; these events, however, are unlikely to be preserved by the roll front, as a direct result of its hydrodynamic nature.

Non-destructive identification of surface enrichment and trace element fractionation in ancient silver coins

A common issue in non-destructive surface analysis of historical silver coins is depletion of Cu from the near-surface areas, which in turn results in higher Ag content at a coin’s surface. This paper reports a non-destructive analytical strategy using µXRF for identification of Ag and Cu surface enrichments and depletions by comparing peak intensity ratios of Ag Kα/Ag Lα, Cu Kα/Ag Kα and Cu Lα/Ag Lα for coins and Ag-Cu standards of similar composition. Our characterization of coins from different contexts and chronologies shows that a multi-standard approach provides the most reliable identification of surface enrichment of Ag and depletion of Cu. Coins possessing Ag surface enrichment were further analysed with LA-ICP-MS to determine any differences in trace element composition between the cores and surface of the coins. We show that the near-surface regions of these coins are enriched in Au and depleted in Co, Ni, As, and Pt relative to their cores. These systematics allow for a more robust assessment of the degree of silver coin surface alteration critically important in measuring the original composition of historical silver coins.

Trace element fractionation through halite crystallisation: Geochemical mechanisms and environmental implications

Halite is an important mineral for industry, agriculture and food production. It crystallises during water evaporation, and the progressive increase of dissolved metal ions in the brine occurs simultaneously. Thus, halite exploitation may deliver metal ions into the environment and the mechanism of this trace element accumulation has to be studied. In this work, we investigate the distribution of lanthanides and Y (hereafter called rare earth elements, REE), Zr and Hf between crystallising halite and brines in the Dead Sea as geochemical tools for recognising the mechanism of metal ion removal from brines and accumulation in halite. Halite forms cubic crystals where octahedral planes sometimes occur under particular thermal gradient conditions. Our findings indicate that crystal morphology influences the mechanism of metal ion removal from brines because octahedral surfaces are polar unlike those that are cubic. Accordingly, octahedra preferentially fractionate aqueous charged species such as [Hf(OH)5]−, compared to neutral species such as [Zr(OH)4]0. Cubic surfaces do not fractionate aqueous species. In crystal cores, positive Eu anomalies occur suggesting Eu substitution for Na in the lattice. This substitution is energetically justified by ab initio calculations. Hf enrichment relative to Zr also occurs in primary halite-rich evaporites. It is not found in cubic halite from saltworks. The results of this study suggest that primary halite kinetically crystallised from brines can concentrate dissolved metal ions onto crystal surfaces where dissolved charged species are adsorbed. Accordingly, the dissolution of halite due to human activity can release these metal ions to the environment.

Geochemical behaviour and risk assessment of trace elements in a tropical river, Northwest Borneo

By convention, dissolved trace elements in the river water are considered to be the fraction that passes through a 0.45 μm filter. However, several researchers have considered filtration cut-off other than 0.45 μm for the separation of dissolved trace elements from particulate fraction. Recent research indicated that trace elements could exist in particulate form as colloids and natural nanoparticles. Moreover, the trace elements in the continental dust (aerosols) constitute a significant component in their geochemical cycling. Due to their high mobility, the trace elements in the micron and sub-micron scale have biogeochemical significance in the coastal zone. In this context, this study focuses on the highly mobile fraction of trace elements in particulates (<11 μm) and dissolved form in the Lower Baram River. A factor model utilizing trace elements in the dissolved and mobile phase in the particulates (<11 μm) along with water column characteristics and the partition coefficient (Kd) of the trace elements indicated a more significant role for manganese oxyhydroxides in trace element transport. Perhaps, iron oxyhydroxides play a secondary role. The factor model further illustrated the dissolution of aluminium and authigenic clay formation. Except for Fe and Al, the contamination risk of mobile trace elements in particulates (<11 μm) together with dissolved form are within the permissible limits of the Malaysian water quality standards during monsoon (MON) and postmonsoon (POM) seasons.

Phoscorites of the Salitre I complex: Origin and petrogenetic implications

The Salitre I complex is a kidney-shaped alkaline-carbonatite-phoscorite complex part of the Late Cretaceous Alto Paranaíba Igneous Province, central Brazil. This complex is a key example where the phoscorite-carbonatite association was preserved from metasomatism by late-stage fluids and, thus, provides an opportunity to address the genesis of phoscorites. Salitre I is composed of two main coalescing intrusions: a) a northern one dominantly containing perovskite bebedourites (B1), with swarms of ring dykes of carbonatites and phoscorites and, b) a southern one containing melanite bebedourites (B2). Salitre I phoscorites can be subdivided into P1 and P2 based on modal abundance, mineral texture, chemistry and mode of emplacement. P1 phoscorites contain essential olivine, phlogopite and apatite, with accessory magnetite and traces of perovskite whereas P2 phoscorites are composed of the same essential phases but also contain carbonate-rich pockets, accessory pyrochlore and rare phlogopite. Carbonate C-O isotopes and whole-rock Sr-Nd show that Salitre I phoscorites crystallized from mantle-derived parental magmas, similar to other APIP carbonatite complexes. However, chemical and textural discrepancies between P1 and P2 suggest derivation from different magma sources and through distinct processes. For instance, P1 Al- and Ti-rich phlogopite, accessory perovskite and general trace element geochemical behaviour can be associated with the evolution of B1 perovskite bebedourites, i.e. genesis through fractional crystallization from a bebedourite magma. P2 phoscorites, on the other hand, have their evolution linked to a magmatic phase that underwent melt immiscibility, as suggested by trace element fractionation. Additionally, P2 contains pyrochlore, which is generally lacking in bebedourites. Therefore, whereas P1 phoscorites might have derived from a bebedourite magma, P2 phoscorites were generated from a carbonated magma enriched in phosphate and iron oxides.

Chemical fractionation and risk assessment of trace elements in sewage sludge generated from various states of Pakistan.

In the developing world, rapid urbanization and industrialization produces an enormous volume of wastes daily. This study was aimed to explore the potential and risks associated with sewage sludge through the characterization and fractionation technique. Sewage sludge samples were collected from various wastewater treatment in five different cities of Pakistan. Considerable amounts of macro-elements were detected in all types of sewage sludge samples. The pHw of all sewage sludge were neutral to slightly alkaline in reaction. Total organic carbon (TOC) was maximum (18.73%) with Coca-Cola sewage sludge (CSS) while the minimum (14.69%) was with Water and Sanitation Agency (WASA) sewage sludge (WSS). Percent relative distribution of cadmium (Cd) was higher in residual fraction (F4) up to 52% in the Nestle wastewater treatment plant, Sheikhupura (NSS). The chromium (Cr) concentration in Kasur sewage sludge (KSS) was extremely in mobile fraction (exchangeable) as compared with all other sludge samples, therefore showing a higher level of risk assessment code. While in the case of Iron (Fe), mobility was less and its maximum portion was noted in residual fraction (F4) of all sewage sludge samples. Percent distribution of manganese (Mn) showed variable trends for different sewage sludge samples. Zinc (Zn) concentration showed high mobility (exchangeable fraction) in case of NUST wastewater treatment plant, Islamabad (NTS) (31.16%) and WSS (37.83%) as compared with other sewage sludges. The risk assessment code indicated that Zn and Ni had a medium level of risk with I-9 Sector wastewater treatment plant, Islamabad (ISS), CSS, KSS, and NSS whereas these pose a high risk with NTS and WSS. Based on physicochemical properties, nutrients, trace elements, mobility, and risk assessment code, it was concluded that KSS should not be recommended at any application rate while NTS and WSS may be used at low application rates whereas ISS, CSS, and NSS may be used for agricultural crop production.

Characterization, fractionation and mobility of trace elements in surface sediments of the Jequiezinho River, Bahia, Brazil.

The Jequiezinho River is a temporary river. In the urban stretch it is impacted, with perennial flow coming from domestic sewage and rainwater. This study evaluated the geochemical distribution and potential mobility of some metals (Pb, Co, Ca, Cr, Mg, Cu, Fe, Mn, Ni and Zn) in sediments of the Jequiezinho River. Sediment samples were collected at ten different sites along the river. The silt/clay fraction was submitted to acid digestion and sequential extraction with analysis by FAAS. The results indicated that, in the more densely populated region, there was an increase in concentrations of Cr, Ni, Cu, Co, Pb, and Zn. The contents found were compared with the guideline values of TEL (Threshold Effect Levels) and PEL (Probable Effect Levels)​​, not exceeding the maximum reference limits. The results indicated that Ca, Mg, Mn and Fe presented greater susceptibility to mobility and bioavailability suggesting the geochemical origin responsible for these high concentrations. The multivariate analysis showed that Cr, Ni, Cu, Co, Pb, and Zn presented a similar behavior, especially in locations with higher population density and the discharge of non-discriminated effluents, reflecting the anthropogenic contributions as responsible for the concentration increase.

Study of the mobility of trace elements at the water-sediment interface in coastal and estuarine areas

In coastal and estuarine environments, trace elements trapped in sediments can be released back into the water column if resuspended during tides or floods. This is how this work is carried out to determine the mobility of trace elements when these phenomena occur on Senegalese coasts subjected to high energy tides. Sequential extraction carried out according to the European Community Bureau of Reference (BCR) was used to determine the mobilizable fraction of trace elements in sediments. Subsequently, laboratory sediment resuspension experiments were conducted to evaluate the ability of sediments to release trace elements into the water in order to better understand the natural effect of resuspension during tidal cycles and water movement on the coast. The release of elements into the water was monitored over a 24 h period along with redox potential (Eh), dissolved oxygen and pH. Bioavailability percentages of Cd, Ni, Pb and Zn showed a strong affinity with the acid soluble fraction, suggesting easy mobility of these elements. The results of the kinetic monitoring tests of the release of trace elements in water show that during the first minutes, desorption is very important with peaks that can reach 90‰ depending on the element that could potentially cause acute effects on aquatic organisms. However, the bioavailability of trace elements in contaminated sediments only influences mobility at the beginning of resuspension. Remobilization tests would therefore provide an indication of the ability of sediments to release trace elements during rapid changes in the physico-chemical conditions of the aquatic environment.

Garnet fractionation, progressive melt loss and bulk composition variations in anatectic metabasites: Complications for interpreting the geodynamic significance of TTGs

Tonalite-trondhjemite-granodiorite (TTG) suites constitute a large proportion of the Archean geological record; however, the geodynamic processes that generated them, and Archean continental crust in general, remain a subject of debate. The concentrations and ratios of Sr, Y, La, Yb, Nb, and Ta in TTGs are commonly used to determine the depth of melting of their metabasic sources. The trace element composition of melt produced by metabasic source rocks during anatexis is strongly affected by the presence and abundance of pressure-sensitive minerals, such as plagioclase (Sr-bearing), garnet (Y- and HREE-bearing), and rutile (Nb- and Ta-bearing). Elevated Sr/Y and La/Yb ratios and low concentrations of Nb and Ta in TTGs are generally considered to indicate melting at high pressures (≥2.0 ​GPa). The depth of melting is a key factor in determining the origin of TTGs as this provides critical information on the tectonic setting of their generation. We use phase equilibrium and trace element modelling to explore the effects of three potential influences on TTG trace element compositions: fractionation of trace elements into peritectic garnet cores, progressive melt loss from the source, and source bulk composition. We model three different compositions of Archean basalts along thermal gradients of 500 ​°C/GPa, 750 ​°C/GPa, and 1000 ​°C/GPa. The models produce major and trace element melt compositions that are generally consistent with measured compositions of TTGs. Although Sr/Y, La/Yb, Nb, and Ta exhibit pressure-dependent behaviour, other factors also affect these values. Garnet fractionation causes Sr/Y and La/Yb to reach much greater values and in this scenario, the values also increase with increasing temperature. Source bulk composition has an effect in all scenarios and most strongly influences La/Yb, Nb, and Ta. Overall, these results show that Sr/Y, La/Yb, Nb, and Ta can reach values generally considered to be indicative of high pressure melting at a range of P–T conditions including P ​< ​2.0 ​GPa. Consequently, trace element compositions of TTGs alone may provide a misleading impression of the depth of melting of metabasites and the geodynamic environment of Archean crustal growth and reworking.

Stepwise chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace element analysis of microfractured Hadean zircon

Abstract. The Hadean Jack Hills zircons represent the oldest known terrestrial material, providing a unique and truly direct record of Hadean Earth history. This zircon population has been extensively studied via high-spatial-resolution high-throughput in situ isotopic and elemental analysis techniques, such as secondary ionization mass spectrometry (SIMS), but not by comparatively destructive, high-temporal-precision (&lt;0.05 % two-sigma) thermal ionization mass spectrometry (TIMS). In order to better understand the lead loss and alteration history of terrestrial Hadean zircons, we conduct stepwise chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace element analysis (CA-ID-TIMS-TEA) on manually microfractured Hadean Jack Hills zircon fragments previously dated by SIMS. We conducted three successive HF leaching steps on each individual zircon fragment, followed by column chromatography to isolate U–Pb and trace element fractions. Following isotopic and elemental analysis, the result is an independent age and trace element composition for each leachate of each zircon fragment. We observe ∼50 Myr of age heterogeneity in concordant residues from a single zircon grain, along with a protracted history of post-Hadean Pb loss with at least two modes circa ∼0 and 2–4 Ga. Meanwhile, stepwise leachate trace element chemistry reveals enrichments of light rare earth elements, uranium, thorium, and radiogenic lead in early leached domains relative to the zircon residue. In addition to confirming the efficacy of the LREE-I alteration index and providing new insight into the mechanism of chemical abrasion, the interpretation and reconciliation of these results suggest that Pb loss is largely driven by low-temperature aqueous recrystallization and that regional thermal events may act to halt – not initiate – Pb loss from metamict domains in the Hadean Jack Hills zircons.

Separation of nanoparticles from polydisperse environmental samples: comparative study of filtration, sedimentation, and coiled tube field-flow fractionation.

Nanoparticles (NPs) in the environment have a potential risk for human health and the ecosystem due to their ubiquity, specific characteristics, and properties (extreme mobility in the environment, abilities to accumulate of toxic elements and penetrate into living organisms). There is still a gap in studies on the chemical composition of natural NPs. The main reason is the difficulty to recover NPs, which may represent only one-thousandth or less of the bulk environmental sample, for further dimensional and quantitative characterization. In the present study, a methodology for the recovery of the nanoparticle fraction from polydisperse environmental samples was developed taking as example volcanic ashes from different regions of the world. For the first time, three separation methods, namely, filtration through a 0.45-μm membrane, sedimentation, and coiled tube field-flow fractionation (CTFFF), were comparatively studied. The separated fractions were characterized by laser diffraction and scanning electron microscopy and then analyzed by inductively coupled plasma atomic emission and mass spectrometry. It has been shown that all three methods provide the separation of NPs less than 400nm from the bulk material. However, the fraction separated by sedimentation also contained a population (5% in mass) of submicron particles (~400-900nm). The filtration resulted in low recovery of NPs. The determination of most trace elements was then impossible; the concentration of elements was under the limit of detection of the analytical instrument. The sedimentation and CTFFF made it possible to determine quantifiable concentrations forboth major and trace elements in separated fractions. However, the sedimentation took 48h while CTFFF enabled the fractionation time to be decreased down to 2h. Hence, CTFFF looked to be the most promising method for the separation of NPs followed by their quantitative elemental analysis.

Sulfides in the marbles of spurrite-merwinite facies: the Kochumdek River, East Siberia

In the marbles of the Kochumdek contact metamorphic aureole pyrrhotite, rasvumite, sphalerite, alabandite, wurtzite, galena, acanthite have been identified. Mineralogical diversity of sulphides is the consequence of the efficient crystal-chemical fractionation of trace elements under the PT‑conditions of spurrite-merwinite metamorphic facies. Trace element and isotope fingerprints of sulfides indicate that sedimentary parent rocks were the main source of sulfur and metals for sulfides mineralization.

Geochemical fractionation and risk assessment of trace elements in sediments from tide-dominated Hooghly (Ganges) River Estuary, India

The geochemical fractionation and potential mobilization of cadmium, chromium, copper, nickel and lead were studied in surficial sediments (top 0–10 cm; <63 μm grain-size) of the Hooghly (Ganges) River Estuary, eastern part of India, using a sequential extraction procedure. The risk assessment was evaluated at three specific levels; i.e., enrichment level (enrichment factor, geo-accumulation index), the availability level (elements bound to different fractions, risk assessment code, Individual and Global contamination factors) and biological toxicity level (Potential ecological risk index; sediment quality guidelines). Different geochemical phases indicated heterogeneities in TE distribution patterns as follows: (i) Cd was dominant in the exchangeable phase and significant proportion of Pb was bounded to the reducible fractions; (ii) the potential mobile fraction (ΣF1 − F3) in the sediments was higher for Cd and Pb (>46%), reflecting their adverse impact on benthic organisms as they are weakly bound to the sediment and can migrate to water; (iii) a minor fraction of Cu (<10%) was found in the oxidizable fraction suggesting less environmental risk to the aquatic biota and (iv) the dominance of the Ni, Cr and Cu in the residual fraction supports the assumption of their geogenic origin. Both Cd and Cu posed medium to high ecological risk values based on risk assessment code (RAC). Global Contamination Factor (GCF) values allowed to identify the “pollution hotspots” in the study area.

Sulfide Mineralization Hosted by Spurrite-Mervinite Marbles (Kochumdek River, East Siberia)

Marbles of the Kochumdek complex contain pyrrhotite, rasvumite, alabandine, wurtzite, galena, and acanthite. The diversity of sulfides is caused by efficient crystal chemical fractionation of trace elements under metamorphism of spurrite–merwinite facies. The isotopic–geochemical features of sulfides reveal their formation at the expense of trace elements and sulfur budget of the sedimentary parent rocks.

Occurrence, geochemical fractionation, and environmental risk assessment of major and trace elements in sewage sludge

Industrialization and accelerated population growth have created a huge amount of sewage sludge. Many studies have reported the sewage sludge as a sink of major and trace elements, but less is known about their geochemical fractionations. In order to assess the mobility, the distribution, bioavailability, and toxicity of those elements in sludge, we collected the sewage sludge samples from all the seven wastewater treatment plants in Xiamen City, China. Results revealed a strong spatial variation and the occurrence of 48 elements with concentrations ranging from 1.00×10-2 mg kg−1 (Re) to 9.03×101 g kg−1 (Fe) on the basis of dry sludge weight. Sequential extraction procedure showed that residual and oxidizable fractions were the main geochemical fractions of most studied elements. However, Ca, Mn, Sr, and Ni were mainly bound to acid-exchangeable fractions, while Fe, Zn, Cd, Cr, Co, and V were mainly distributed in the reducible fractions. The contamination factor and risk assessment code indicated that Ni, Cu, Zn, Cd, Cr, Co, Sr, Ca, Mn, Mo, Re, and W were highly mobile with less retention time and exerted high environmental risks through sludge land application. The sludge disposal strategy should consider not only the total concentrations of a broad range of elements but also their bioavailability.

Metal(loid)s inhalation bioaccessibility and oxidative potential of particulate matter from chromated copper arsenate (CCA)-contaminated soils

Field-collected chromated copper arsenate (CCA)-contaminated soils and associated particulate matter (PM) were characterized for their total metal(loid)s content (As, Cr, Cu, Fe, Mn, Ni, Pb and Zn) and physicochemical properties. Copper, Ni, Pb and Zn fractionation (using sequential extraction) and inhalation bioaccessibility (using two lung fluids) of trace elements were assessed in PM samples. In Gamble's solution (GS), low average bioaccessibility (up to 12%) was observed for As, Cu, Mn, and Ni. A strong correlation (r = 0.92, p < 0.005, n = 9) between the soluble and exchangeable fraction (F1) and bioaccessibility in GS was observed for Cu. Inhalation bioaccessibility in artificial lysosomal fluid (ALF) was higher for Cu (avg. 78.5 ± 4.2%), Mn (avg. 56.8 ± 12.1%), Zn (avg. 54.8 ± 24.5%) and As (avg. 45.4 ± 18.8%). Strong correlations between inhalation bioaccessibility in ALF and the mobile (i.e. F1+F2) metal fraction were observed for all tested metals (i.e. (Cu (r = 0.95, p < 0.005), Ni (r = 0.79, p < 0.05), Pb (r = 0.92, p < 0.005) and Zn (r = 0.98, p < 0.005)), n = 9). The oxidative potential (OP) of PM was also assessed using an ascorbate (AA) depletion assay (OPAA). Mobile Cu fractions were deemed to be the main factor influencing OPAA ((F1 (r = 0.99, p < 0.005), F2 (r = 0.97, p < 0.005)), n = 9) in PM samples. A strong correlation (r = 0.94, p < 0.005, n = 10) was also observed between Cu bioaccessibility in GS and OPAA.

METAL-ORGANIC COMPLEXES IN ENVIRONMENTAL SOLID SAMPLES: ON THE SELECTIVITY OF PYROPHOSPHATE EXTRACTION

Sequential extraction procedures (SEP) have been widely used for the fractionation of trace elements in soils according to their physicochemical mobility and bioaccessibility. Potassium/sodium pyrophosphate in alkaline medium may be considered as the most appropriate extracting reagent for the recovery of amorphous metal-organic complexes, which play a very important role in biological, physical, and chemical processes in soil. However, the selectivity of pyrophosphate has been poorly studied. In the present work the ability of pyrophosphate to attack mineral inorganic phases of environmental solids was assessed using dynamic extraction, which allows one to minimize artifacts and mimic natural conditions. Samples of gabbro and granite containing nearly no organic compounds were taken as example. The eluents applied addressed exchangeable, specifically sorbed, bound to Mn oxides, and bound to metal-organic complexes fractions extractable by 0.05 M Ca(NO3)2, 0.43 M CH3COOH, 0.1 M NH2OH · HCl, and 0.1 M K4P2O7 at pH 11, respectively. As expected, pyrophosphate extraction leads to a partial dissolution of elements bound to inorganic compounds. The recovery of aluminum, iron, manganese, and rare earth elements by pyrophosphate is up to 4% of their total concentrations in samples. The results were discussed on the basis of coordination chemistry of pyrophosphate complexes. In general, pyrophosphate extraction could be further regarded to be sufficiently selective for the dissolution of metal-organic complexes while using SEP in environmental analysis, soil science, and biogeochemistry. Nevertheless, in the interpretation of the fractionation results, a partial dissolution of mineral inorganic phases should be taken into consideration, especially for soils with low content of organic compounds.

Melt‐Induced Fractionation of Major Ions and Trace Elements in an Alpine Snowpack

AbstractUnderstanding the impact of melting on the preservation of atmospheric compounds in high‐Alpine snow and glacier ice is crucial for future reconstruction of past atmospheric conditions. However, detailed studies investigating melt‐related changes of such proxy information are rare. Here we present a series of five snow pit profiles of 6 major ions and 34 trace elements at Weissfluhjoch, Switzerland, collected between January and June 2017. Atmospheric composition was preserved during the cold season, while melting toward the summer resulted in preferential loss of certain species from the snowpack or enrichment at the base of the snowpack. Increasing mobilization of major ions with meltwater (NH4+ &lt; Cl− ~ Na+ &lt; NO3− ~ Ca2+ ~ SO42−) can be related to their stronger enrichment at ice crystal surfaces during snow metamorphism. Results for trace elements show that less abundant elements such as Ce, Eu, La, Mo, Nd, Pb, Pr, Sb, Sc, Sm, U, and W were best preserved and may still serve as tracers to reconstruct past natural and anthropogenic atmospheric emissions from melt‐affected snow pit and ice core records. The obtained elution behavior matches the findings from another high‐Alpine site (upper Grenzgletscher) for major ions and the large majority of investigated trace elements. Both studies indicate that water solubility and location at the microscopic scale are likely to determine the relocation behavior with meltwater and also suggest that the observed species‐dependent preservation from melting snow and ice is representative for the Alpine region, reflecting Central European atmospheric aerosol composition.

Petrochemical characterization of Neoproterozoic Colomine granitoids, SE Cameroon: Implications for gold mineralization

Biotite granites and K-feldspar granites are the dominant intrusive rock types of the Colomine gold district in the Neoproterozoic terrain of SE Cameroon. The silica contents of these granitoids range from 68.93–75.39 wt% and Au contents from 0.6 to 32 ppb. They are weakly peraluminous (ASI = 1.0–1.2) I-type granitoids with high-K calc-alkaline to shoshonitic character, emplaced within a syn-collisional arc setting. They have fractionated trace element patterns (LaN/YbN: ~ 11–331) with enrichment in LREE compared to HREE and weak to strong negative Ba, Nb, Sr, P, Ti, Lu, and Eu (Eu/Eu* = 0.12–0.52) anomalies. The geochemical characteristics suggest that the granitoids formed by partial melting of crustal source rocks with some input from greywackes. Differentiation of the hydrous parent magma was characterized by fractionation of muscovite, biotite, hornblende, plagioclase, and K-feldspar with minor zircon, apatite and Fe-Ti oxide. Mafic garnet-bearing inclusions represent an early crystallization phase that was incorporated in the later felsic melt. The granitoids became emplaced into Proterozoic schist belts. Along the contacts, they became brecciated, sheared, foliated and sericitized. These “contact granites” have higher gold contents (5–32 ppb) than the fresh granitoids (0.6–3 ppb). Remobilisation of gold from early magmatic sulfide minerals by post-magmatic hydrothermal fluids enriched the shear-related granitoids. Hydrothermal alteration results to enrichment in Cu, Ni, Cr, Mo, Ga, V, Tl, and Au and depletion in LREE (e.g., La, Ce, Pr). Micro-shear and fault zones in the vicinity of the granitoids constitute favourable sites for exploration.

Mineralization and element redistribution in the Chah-Gheib Ni-laterite ore zone, Bavanat, Zagros Belt, Iran

Nickel laterites are supergene deposits derived from the weathering of ± serpentinized ultramafic rocks and they commonly accounts for over 70% of world land-based Ni resources. Serpentinized ultramafic rocks outcrop extensively in Iran as result of collision between Afro-Arabian and Iranian micro-plate during the Late Cretaceous. Two Ni-bearing laterite belts developed on the ultramafic rocks of the Neyriz ophiolite have been recently discovered in the Bavanat region (South Iran). The Chah-Gheib deposit, as the biggest Ni-bearing laterite in the Bavanat area, hosts a total estimated reserve mineralization of about 102,000 tons of ore at 0.92% Ni and 180,000 tons at 1.63% Cr.This study focuses on elemental fractionation and mineralogical control of major, trace and rare earth elements in a selected profile from the Chah-Gheib Ni-laterite, in order to assess the conditions of ore formation and its paleo-environmental significance.Four distinct horizons, including saprolite, lower limonite, upper limonite, and lateritic duricrust, have been recognized from the bottom to the top of the studied profile. Iron oxy-hydroxides are the dominant phases found in the laterite profile. Overall, Fe and other first raw transition metals (i.e. Cr, Ni, V, Co, Cu, and Zn) show abundances higher than those of the bedrock. The main Fe and Cr carriers in the laterite deposit are Fe oxy-hydroxides and chromite, respectively, although authigenic Ni- and Cr-bearing palygorskite is also common throughout the profile.Elemental mobility, estimated using Th as immobile element, showed that the major oxides are largely depleted with the exception of Fe2O3 and CaO. Among trace elements, Cr is the element resulting strongly enriched in those levels where large chromite crystals occurs while V, Co, Ni, and Zn are enriched only in some levels of the upper limonite horizon and in the lateritic duricrust, likely as adsorbed cations onto iron oxy-hydroxides and as a consequence of an alkaline pH environment. Alkaline pH conditions can also explain the Cu depletion observed throughout the profile. Such a condition during lateritization appears further supported by both the occurrence of carbonates and palygorskite and by the distribution of the Ba/Sr ratio. Carbonates and palygorskite, as well as secondary quartz, require dry climate to form and alternating wet-dry climate may allow lateritization. This study suggests that the Chah-Gheib laterite formed in a subtropical climate, possibly during the Late Cretaceous-Late Paleocene period, in a roughly 25°–35° latitude range, promoting Si and Mg mobilization during the wet season and carbonates, quartz, and Mg-rich silicate precipitation during the drier periods.