Calibration of the New Certified Reference Materials ERM-AE633 and ERM-AE647 for Copper and IRMM-3702 for Zinc Isotope Amount Ratio Determinations

ArticleinGeostandards and Geoanalytical Research 36(2):177-199 · June 2012with 359 Reads
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Abstract
The commonly used, but no longer available, reference materials NIST SRM 976 (Cu) and ‘JMC Lyon’ (Zn) were calibrated against the new reference materials ERM®-AE633, ERM®-AE647 (Cu) and IRMM-3702 (Zn), certified for isotope amount ratios. This cross-calibration of new with old reference materials provides a continuous and reliable comparability of already published with future Cu and Zn isotope data. The Cu isotope amount ratio of NIST SRM 976 yielded δ65/63Cu values of −0.01 ± 0.05‰ and −0.21 ± 0.05‰ relative to ERM®-AE633 and ERM®-AE647, respectively, and a δ66/64ZnIRMM-3702 value of −0.29 ± 0.05‰ was determined for ‘JMC Lyon’. Furthermore, we separated Cu and Zn from five geological reference materials (BCR-2, BHVO-2, BIR-1, AGV-1 and G-2) using a two-step ion-exchange chromatographic procedure. Possible isotope fractionation of Cu during chromatographic purification and introduction of resin- and/or matrix-induced interferences were assessed by enriched ⁶⁵Cu isotope addition. Instrumental mass bias correction for the isotope ratio determinations by MC-ICP-MS was performed using calibrator-sample bracketing with internal Ni doping for Cu and a double spike approach for Zn. Our results for the five geological reference materials were in very good agreement with literature data, confirming the accuracy and applicability of our analytical protocol.

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  • Thesis
    L'objectif général de cette thèse est de mieux comprendre l'influence d'anciens sites miniers sur la contamination en métaux (Cd, Hg, Tl, Pb, Zn) et métalloïdes (As, Sb) de l'hydrosystème aval. Une attention particulière a été portée à l'antimoine (Sb), dont le comportement dans les cours d'eau contaminés par les drainages miniers reste mal connu et dont la signature isotopique pourrait permettre de tracer différentes sources et processus. Le site d'étude est le bassin des Gardons dans le Gard ; ce cours d'eau Cévenol draine de nombreux sites miniers abandonnés (Pb, Zn, Sb, charbon). L'enrichissement en métaux et métalloïdes a été étudié dans les sédiments actuels et anciens du bassin des Gardons. Un historique de la contamination métallique a été reconstitué à l'aide d'une archive sédimentaire. Les sources prépondérantes de métaux et métalloïdes dans les sédiments ont été déterminées ainsi que la mobilité potentielle de ces éléments vers la phase aqueuse. En complément, les variations de concentrations en métaux et métalloïdes dans les phases dissoute et particulaire ont été étudiées lors d'un épisode de crue grâce à un échantillonnage à haute résolution temporelle. Dans leur ensemble, les résultats montrent que les anciennes mines du bassin des Gardons contribuent à l'enrichissement en métaux et métalloïdes du cours d'eau aval, particulièrement en période de crue. Plus spécifiquement, le comportement de l'antimoine a été étudié dans un affluent du Gardon impacté par du drainage minier acide en aval de l'ancienne mine de Carnoulès et la composition isotopique de l'antimoine a été déterminée dans des eaux prélevées sur le bassin des Gardons et de l'Orb amont, après mise au point d'un protocole de purification/pré-concentration de Sb. Les résultats mettent en évidence le potentiel des isotopes de l'antimoine pour tracer l'origine de cet élément et les processus qu'il subit au cours de son transfert dans les cours d'eau impactés par du drainage de mine.
  • Article
    Full-text available
    Long-term carbon cycling is a subject of recent controversy as new mass balance calculations suggest that most carbon is transferred from the slab to the mantle wedge by fluids during subduction, limiting the efficiency of carbon recycling to the deep mantle. Here, we examine the large scale mobility of carbon during subduction using new isotopic tracers sensitive to H-C-O-S-Cl fluids, namely iron and zinc stable isotopes, in samples interpreted to represent residual slab (Queyras, Western Alps) and sub-arc mantle (Kohistan, Himalaya). We show that during subduction there are several stages of carbonate precipitation and dissolution at metasomatic interfaces between metasedimentary and ultramafic rocks in the slab. During the early stages of subduction, before the slab reaches the 300-400 °C isotherms, the infiltration of sediment-derived fluids into ultramafic lithologies enhances carbonate precipitation in antigorite-bearing serpentinites. Carbonate storage in serpentinites therefore acts as a temporary reservoir of carbon in subduction zones. This episode is accompanied by a decrease in serpentinite iron isotope composition (δ56Fe), due to interaction with low-δ56Fe sediment-derived fluids, and an increase in the concentrations of fluid-mobile elements (e.g. B, Li, As). At higher temperatures (> 400 °C), carbonate is leached from the serpentinites by fluids. This is accompanied by a decrease in serpentinite zinc isotope composition (δ66Zn) which we interpret as the release of a carbonate-bearing fluid with an isotopically heavy δ66Zn signature. Thermodynamic modelling reveals that the sudden change in fluid carbon mobility is due to a decrease in the aCO2 of the fluids released during slab prograde metamorphism, which shifts from sediment- to serpentinite-dominated dehydration. This demonstrates that slab fluids bearing oxidized carbon (e.g. CO2), associated with isotopically light Fe, heavy Zn and fluid-mobile elements, can be released before the slab reaches eclogite facies P-T conditions. These observations provide strong evidence for the mobility of carbon in fluids during the early stages of subduction. Moreover, the fluids released will act as a potential metasomatic agent for the fore-arc mantle (or slab/mantle interface). The observation of carbonate-bearing metamorphic veins in the Himalayan sub-arc mantle with complementary light δ56Fe and heavy δ66Zn signatures provides further support for the large scale transfer of both sulphate- and carbonatebearing fluids during the early stages of subduction. This suggests that the fore-arc may have an important role in delivering water, sulfur and carbon to the source of arc-magmas.
  • Article
    Full-text available
    We investigated extent and direction of Zn isotope fractionation in secondary zinc minerals formed during low temperature hydrothermal and/or supergene oxidation of primary sulfide deposits. Zinc isotope data have been obtained from non-sulfide zinc mineral separates (willemite - Zn2SiO4, smithsonite - ZnCO3, hemimorphite - Zn4(Si2O7)(OH)2·H2O, hydrozincite - Zn5(CO3)2(OH)6, and sauconite - Na0.3Zn3(Si,Al)4O10(OH)2·4H2O) collected from several Zn deposits in Ireland, Belgium, Poland, Namibia, Peru, Yemen and Zambia. The data are compared with Zn isotope compositions measured on Zn sulfides collected in the same areas and/or derived from the existing literature, to establish the controls of direction and likely extent of any fractionations. We find that willemite has the greatest compositional variability, with measured δ⁶⁶ZnJCM-Lyon values ranging from −0.42 to 1.39‰, spanning the entire range of terrestrial variation in Zn isotopes recorded to date. Overall, significant fractionations in positive and negative directions are recorded relative to the precursor phase (primary sphalerite or an earlier secondary phase), with primary sphalerite falling in a relatively narrow range of isotopic values (approximately −0.1 to +0.4‰). Most of the data observed on willemite, hemimorphite and hydrozincite can be explained with a model of isotopic fractionation, in which partial dissolution of primary sphalerite is followed by precipitation of an initial secondary phase that preferentially incorporates heavy Zn isotopes. Smithsonite, instead, preferentially incorporates light Zn isotopes. This reflects the variation in the Zn-x bond strengths of these secondary phases with respect to the original sulfides. We also observed that isotope compositions do not depend only on the difference between the fractionation factors of the involved phases but also on the amount of the secondary mineral precipitated after dissolution of primary sulfide, and that the greatest fractionations occur when only small amounts of secondary mineral are precipitated. Progressive precipitation from migrating fluids that form phases enriched in heavy zinc isotopes would lead to a gradual decrease in the δ⁶⁶Zn values of such phases, and the fluids involved, in time and space. Strong negative isotopic shifts are almost only observed for late crystallizing phases, such as those in vugs. These are interpreted to reflect precipitation from residual, isotopically-light fluids that are the inevitable highly-fractionated product of the above-described process. Where a more complete replacement of primary sulfide has occurred, such as in the high-grade core of non-sulfide zinc orebodies, there is limited net isotopic fractionation because dissolved primary zinc is nearly quantitatively reprecipitated locally. In addition, in only one case (Yanque, Peru) we observed that the fringes of non-sulfide zinc deposit were characterized by isotopically fractionated compositions, with highly negative values implying extensive precipitation (earlier, or elsewhere) of isotopically heavy secondary phases. The higher-grade ore zones, where complete breakdown of primary sulfides and quantitative reprecipitation of zinc have occurred, show instead less fractionated compositions.
  • Article
    Full-text available
    Biological reference materials with well-characterised stable isotope compositions are lacking in the field of ‘isotope biochemistry’, which seeks to understand bodily processes that rely on essential metals by determining metal stable isotope ratios. Here, we present Zn stable isotope data for six biological reference materials with certified trace metal concentrations: fish muscle, bovine muscle, pig kidney, human hair, human blood serum and human urine. Replicate analyses of multiple aliquots of each material achieved reproducibilities (2sd) of 0.04–0.13‰ for δ66/64Zn (which denotes the deviation of the ⁶⁶Zn/⁶⁴Zn ratio of a sample from a pure Zn reference material in parts per 1000). This implies only very minor isotopic heterogeneities within the samples, rendering them suitable as quality control materials for Zn isotope analyses. This endorsement is reinforced by (i) the close agreement of our Zn isotope data for two of the samples (bovine muscle and human blood serum) to previously published results for different batches of the same material and (ii) the similarity of the isotopic data for the samples (δ66/64Zn ≈ –0.8 to 0.0‰) to previously published Zn isotope results for similar biological materials. Further tests revealed that the applied Zn separation procedure is sufficiently effective to enable accurate data acquisition even at low mass resolving power (M/ΔM ≈ 400), as measurements and analyses conducted at much higher mass resolution (M/ΔM ≈ 8500) delivered essentially identical results. Electronic supplementary material The online version of this article (doi:10.1007/s00216-017-0240-y) contains supplementary material, which is available to authorized users.
  • Article
    Full-text available
    Geochemical characteristics of arc magmas reflect incorporation of subducted materials to their mantle wedge sources in subduction zones. Subduction component addition has been proposed to modify the Zn isotopic budget of arc magmas. How- ever, the lack of a systematic study on Zn isotopic compositions of arc magmas hampers a better understanding of Zn isotope behavior in subduction zones. To address this issue, we have determined Zn isotopic compositions of 37 well-characterized arc rocks from the Kamchatka and Central-Eastern Aleutian arcs. These rocks record contributions of fluids and melts derived from altered oceanic crust (AOC) without overprints of sediment melts and thus allow focus on the potential effects of AOC-derived fluids and melts on the Zn isotopic budget of arc magmas. For comparison, nine basalts from the Gakkel, Mid-Atlantic and Southeast Indian Ridges, and the Lau Basin and nine adakites from Central America were also analyzed. Rocks from the Kamchatka-Aleutian arcs have d Zn from 0.16to0.31‰ that are mostly similar to those of mid-oceanridge basalts (MORBs), back-arc basin basalts (BABBs), and adakites (d Zn = 0.23–0.33‰), but a significant number of arc samples also display d66Zn higher than that of the depleted MORB-type mantle (DMM), indicating Zn isotope fractionation during magmatic processes and/or modifications of the mantle wedge Zn isotopic budget by incorporation of AOC-derived fluids and melts. The lack of correlations of d66Zn with geochemical indicators of magma differentiation (e.g., MgO, SiO , and Zn/Fe ) indicate that fractionation of olivine, pyroxene, and magnetite has a limited effect on the Zn isotopic compositions of arc magmas. Even though the mantle sources of arc rocks investigated here are strongly affected by AOC-derived fluids and melts that have higher d66Zn compared to the DMM, we observe no systematic variations of d66Zn with indicators of subduction components (e.g., Ba/La, Ba/Th, Sr/Y, Hf/Lu and 87Sr/86Sr). This suggests that insignificant transport of Zn from the subducting Pacific slab to the Kamchatka and Central-Eastern Aleutian mantle wedge. Our model calculations suggest that the observed offset of d66Zn between the mantle and arc magmas can be attributed to isotope fractionation during partial melting with no need for contributions from subduction components.
  • Article
    Full-text available
    This study investigates the double spike (DS) proportion effect on measurements of stable Zn, Mo, Cd, and Sn isotopes by multicollector–inductively coupled plasma–mass spectrometry (MC–ICP–MS). The effect of DS proportion values between 0.1 and 0.9 (i.e., 10% to 90% DS) on the compositions of measured references materials was determined. The ⁶⁶/⁶⁴Zn, ¹¹⁴/¹¹⁰Cd, and ¹²⁰/¹¹⁸Sn values positively correlate with the proportion of the DS within a mixture, whereas ⁹⁸/⁹⁵Mo values negatively correlate with the proportion of DS. Stable Mo, Cd, and Sn isotopes have a range of DS values around the optimum where the resulting delta values are insensitive to DS proportion values and reflect the values of the reference materials with the optimum DS proportion values. However, Zn isotopes do not have a stable DS proportion range, indicating that ⁶⁶/⁶⁴Zn values are much more sensitive to DS proportion values than the other three elements. The measured ⁹⁸/⁹⁵Mo values of a mixture of the IAPSO seawater reference with variable amounts of DS solution also show a negative correlation with DS proportions. This indicates that although it is difficult to explain why DS proportion values have a significant influence on isotopic analyses, we suspect that the iterative calculations involved in the three algebraic equations used to resolve DS data generate correlations between delta and DS proportion values. This study highlights the importance of assessing DS proportion effects when establishing analytical protocols for stable isotope measurement using the DS technique. Any correlation between the resulting measured isotopic compositions and the associated DS proportion values means that DS solutions must be precisely added to unknown samples to ensure that appropriate proportions of DS are used.
  • Article
    AimsRecent advances in mass spectrometry have demonstrated that higher plants discriminate stable Zn isotopes during uptake and translocation depending on environmental conditions and physiological status of the plant. Stable Zn isotopes have emerged as a promising tool to characterize the plants response to inadequate Zn supply. The aim of this review is to build a comprehensive model linking Zn homeostasis and Zn isotopic fractionation in plants and advance our current view of Zn homeostasis and interaction with other micronutrients. Methods The distribution of stable Zn isotopes in plants and the most likely causes of fractionation are reviewed, and the interactions with micronutrients Fe, Cu, and Ni are discussed. ResultsThe main sources of Zn fractionation in plants are i) adsorption, ii) low- and high-affinity transport phenomena, iii) speciation, iv) compartmentalization, and v) diffusion. We propose a model for Zn fractionation during uptake and radial transport in the roots, root-to-shoot transport, and remobilization. Conclusions Future work should concentrate on better understanding the molecular mechanisms underlying the fractionations as this will be the key to future development of this novel isotope system. A combination of stable isotopes and speciation analyses might prove a powerful tool for plant nutrition and homeostasis studies.
  • Article
    Full-text available
    Subduction zones modulate the chemical evolution of the Earth’s mantle. Water and volatile elements in the slab are released as fluids into the mantle wedge and this process is widely considered to result in the oxidation of the sub-arc mantle. However, the chemical composition and speciation of these fluids, which is critical for the mobility of economically important elements, remain poorly constrained. Sulfur has the potential to act both as oxidizing agent and transport medium. Here we use zinc stable isotopes (δ66Zn) in subducted Alpine serpentinites to decipher the chemical properties of slab-derived fluids. We show that the progressive decrease in δ66Zn with metamorphic grade is correlated with a decrease in sulfur content. As existing theoretical work predicts that Zn-SO42− complexes preferentially incorporate heavy δ66Zn, our results provide strong evidence for the release of oxidized, sulfate-rich, slab serpentinite-derived fluids to the mantle wedge.
  • Article
    Metal transfer from mantle wedge to primitive arc magmas and subsequent enrichment by magmatic fractionation and volatile exsolution are critical processes for mineralization in arc systems. Copper is one of the most important ore-forming elements whose behavior is sensitive to oxygen fugacity. Copper isotope composition (δ ⁶⁵ Cu) may provide valuable insights into Cu transfer and enrichment in hydrous oxidized arc magmas. However, the extent of Cu isotopic variation in arc systems and its link to Cu transfer and enrichment for ore mineralization have been poorly explored. Here we report the Cu isotopes in basalts, dacites and molten sulfur in Niuatahi volcano, Tonga rear arc to address the issue. These samples, as well as associated black smoker chimneys, represent products of magmatic fractionation and degassing of hydrous oxidized arc magmas with ore mineralization. Sulfide-undersaturated differentiation of basalts in the Niuatahi and their high water content and oxygen fugacity suggest complete exhaustion of sulfides in the mantle source during fluxed melting and transfer of nearly all Cu, Ag and other chalcophile metals to the primary magmas. The δ ⁶⁵ Cu of Niuatahi basalts thus reflect that of the mantle source. The basalts display δ ⁶⁵ Cu of 0.01‰ to 0.17‰ (n = 3; external uncertainty of 0.05‰, 2sd), similar to mid-ocean ridge basalts (MORBs), komatiites and the depleted mantle (0.06 ± 0.20‰, 2sd). These results, together with their Cu contents indistinguishable from MORBs, suggest that oxidized slab components are very likely to have limited influence on the Cu budget and mean δ ⁶⁵ Cu of the mantle wedge. The Niuatahi magma became sulfide saturated after magnetite crystallization during magma differentiation from basalt to dacite. Constant Cu/Ag in the basalts and dacites suggests segregation of immiscible sulfide melts instead of crystalline sulfides. The sulfide segregation significantly decreased contents of Cu and other chalcophile metals but hardly changed δ ⁶⁵ Cu in dacites (−0.01‰ to 0.35‰, n = 11 with a mean of 0.21 ± 0.24‰, 2sd), implying restricted fractionation of δ ⁶⁵ Cu during magnetite fractionation and sulfide melt segregation. Molten sulfurs, which are formed by intensive magmatic degassing of arc lavas and characterized by substantial enrichment of Cu and other metals, show δ ⁶⁵ Cu of 0.30‰ to 0.37‰. These values are indistinguishable from those of comagmatic dacites (0.34‰). Although the published δ ⁶⁵ Cu of sulfide chimneys in the Niuatahi appears slightly lighter (0.00‰ to 0.29‰ ± 0.18‰, 2sd), the overall limited range of δ ⁶⁵ Cu in molten sulfur and sulfide chimneys indicates that discharging magmatic volatiles and hydrothermal venting with significant removal of Cu hardly fractionates δ ⁶⁵ Cu. The δ ⁶⁵ Cu data from arc lavas, molten sulfur and sulfide chimneys thus reveal limited variations in δ ⁶⁵ Cu (within 0.35‰) during fluxed melting, magmatic fractionation, magma degassing and mineralization in arc systems. If these results represent general processes, they imply that the heavier or lighter δ ⁶⁵ Cu in other sulfide chimneys and associated deposits should result from the complex hydrothermal processes and/or low-temperature secondary reworking.
  • Article
    We have prepared a large volume of pure, concentrated and homogenous zinc standard solution. This new standard solution is intended to be used as a primary reference standard for the zinc isotope community, and to serve as a replacement for the nearly exhausted current reference standard, the so-called JMC-Lyon Zn. The isotopic composition of this new zinc standard (AA-ETH Zn) has been determined through an inter-laboratory calibration exercise, calibrated against the existing JMC-Lyon standard, as well as the certified Zn reference standard IRMM-3702. The data show that the new standard is isotopically indistinguishable from the IRMM-3702 zinc standard, with a weighted δ66/64Zn value of 0.28 ± 0.02‰ relative to JMC-Lyon. We suggest that this new standard be assigned a δ66/64Zn value of +0.28‰ for reporting of future Zn isotope data, with the rationale that all existing published Zn isotope data are presented relative to the JMC-Lyon standard. Therefore our proposed presentation allows for a direct comparison with all previously published data, and that are directly traceable to a certified reference standard, IRMM-3702 Zn. This standard will be made freely available to all interested labs through contact with the corresponding author.
  • Article
    The stable isotope signatures of zinc are increasingly used to study plant and soil processes. Complexation with phytosiderophores is a key process and understanding the controls of isotope fractionation is central to such studies. Here, we investigated isotope fractionation during complexation of Zn2+ with the phytosiderophore 2’-deoxymugeneic acid (DMA) - which we synthesised - and with three commercially-available structural analogues of DMA: EDTA, TmDTA and CyDTA. We used ion exchange chromatography to separate free and complexed zinc, and identified appropriate cation exchange resins for the individual systems. These were Chelex-100 for EDTA and CyDTA, Amberlite CG50 for TmDTA and Amberlite IR120 for DMA. With all the ligands we found preferential partitioning of isotopically heavy zinc in the complexed form, and the extent of fractionation was independent of the Zn:ligand ratio used, indicating isotopic equilibrium and that the results were not significantly affected by artefacts during separation. The fractionations (in ‰) were +0.33 ± 0.07 (1, n=3), +0.45 ± 0.02 (1, n=2), +0.62 ± 0.05 (1, n=3) and +0.30 ± 0.07 (1, n=4) for EDTA, TmDTA, CyDTA and DMA, respectively. Despite the similarity in Zn-coordinating donor groups, the fractionation factors are significantly different and extent of fractionation seems proportional to the complexation stability constant. The extent of fractionation with DMA agreed with observed fractionations in zinc uptake by paddy rice in field experiments, supporting the possible involvement of DMA in zinc uptake by rice.
  • Article
    The metabolic processes involving copper, such as cellular assimilation, electron transfer and protein formation, can partition copper isotopes in the body amongst different organs and bodily fluids. Systematic changes in copper isotopic composition in the body may assist in identifying regions where copper metabolism has been altered. The cellular prion protein (PrPC) is a copper-binding protein that is highly expressed in the brain. Its misfolded isoform PrPSc is required for the development of prion diseases, fatal neurological diseases including Scrapie and Creutzfeldt-Jacob's disease. As this protein is implicated in copper metabolism, we investigated how expression levels of PrPC could affect the distribution of copper isotopes in the body. We used a novel ion exchange method to isolate copper for stable copper isotope analysis of the liver, kidney, red blood cells, serum, and different regions of the brain of wild type, PrPC knockout (Prnp-/-) and mice in which the copper-binding sites of the octarepeat region were mutated (His → Ala, Cu-del). We found the liver, kidney and brain tissue samples to be enriched in ⁶⁵Cu compared to the food, but only in the liver were differences observed associated with genotype when considering the absolute δ⁶⁵Cu values. Characteristic isotopic shifts were identified between the serum and the liver (all genotypes, p = 0.022), and between the serum and the hippocampus, cerebral cortex, and brainstem (Prnp-/- and Cu-del only, p values were 0.002, 0.053, and 0.017 respectively). We have demonstrated that altering the gene expression of a single protein, in this case PrPC, can produce systematic changes in copper isotopic distribution in transgenic mice.
  • Article
    Iron, Cu and Zn stable isotope systems are applied in constraining a variety of geochemical and environmental processes. Secondary reference materials have been developed by the Institute of Geology, Chinese Academy of Geological Sciences (CAGS), in collaboration with other participating laboratories, comprising three solutions (CAGS‐Fe, CAGS‐Cu and CAGS‐Zn) and one basalt (CAGS‐Basalt). These materials exhibit sufficient homogeneity and stability for application in Fe, Cu and Zn isotopic ratio determinations. Reference values were determined by inter‐laboratory analytical comparisons involving up to eight participating laboratories employing MC‐ICP‐MS techniques, based on the unweighted means of submitted results. Isotopic compositions are reported in per mil notation, based on reference materials IRMM‐014 for Fe, NIST SRM 976 for Cu and IRMM‐3702 for Zn. Respective reference values of CAGS‐Fe, CAGS‐Cu and CAGS‐Zn solutions are as follows: δ⁵⁶Fe = 0.83 ± 0.06 and δ⁵⁷Fe = 1.20 ± 0.12, δ⁶⁵Cu = 0.57 ± 0.05, and δ⁶⁶Zn = ‐0.79 ± 0.12 and δ⁶⁸Zn = ‐1.65 ± 0.24, respectively. Those of CAGS‐Basalt are δ⁵⁶Fe = 0.15 ± 0.05, δ⁵⁷Fe = 0.22 ± 0.05, δ⁶⁵Cu = 0.12 ± 0.07, δ⁶⁶Zn = 0.17 ± 0.11, and δ⁶⁸Zn = 0.34 ± 0.21 (2s). This article is protected by copyright. All rights reserved.
  • Article
    Copper is a redox-sensitive trace element, which can be both, an essential micronutrient and a pollutant. We therefore analyzed Cu concentrations and stable isotope ratios (δ⁶⁵Cu values) in a drained Retisol to trace the response of Cu to a changing hydrological regime and enhanced clay eluviation. The study soil was artificially drained 16 years before sampling resulting in macroscopically visible pedogenetic changes and is thus a suitable site to investigate the influence of pedogenetic processes on the fate of Cu. Samples were collected from all horizons along a trench at four distances from the drain: 0.6 m, 1.1 m, 2.1 m and 4.0 m. In the E&Bt horizon, four different soil volumes (ochre, pale brown, white-grey and black) were sampled at all four distances from the drain. Furthermore, we analyzed soil solutions sampled with piezometer, porous cups, and at the drain outlet. The Cu concentrations were lowest in the surface (Ap) horizons (6.5–8.5 μg g− 1) and increased with depth to the clay-rich Bt horizons (10.5–12 μg g− 1), because of clay eluviation and associated Cu transport. The δ⁶⁵Cu values significantly decreased from the surface (Ap = − 0.25 ± 0.07‰) to the deeper horizons, but showed no significant variation among the deeper horizons (− 0.41 ± 0.28‰) and no correlation with the clay content, indicating that clay eluviation did not significantly affect δ⁶⁵Cu values. The isotopically heavier δ⁶⁵Cu values in the Ap horizons can probably be explained by agricultural management practices like sludge application and fertilization. Close to the drain (position 0.6 m), Cu concentrations were depleted and the lighter Cu isotope was enriched (− 0.91 ± 0.15‰) in the uppermost part of the E&Bt horizon. We attribute this to the changing redox conditions, caused by the lowering of the water level close to the drain. Copper concentrations in black and ochre volumes were significantly higher than in pale-brown and white-grey volumes. The black volume had significantly higher δ⁶⁵Cu values than the ochre volume indicating preferential sorption/occlusion of the heavy Cu isotope by Fe oxides. Enhanced clay eluviation in bulk soil close to the drain and in specific soil volumes did not affect δ⁶⁵Cu values. Cu concentrations (2.1–14 μg L− 1) and δ⁶⁵Cu (0.04–0.42‰) values in water samples showed no clear relation with redox changes along the trench perpendicular to the drain. The enrichment of the heavy Cu isotope in the solution samples (Δ⁶⁵Cu(soil-solution) = − 0.61 ± 0.41) indicates that reductive Cu mobilization is not the main driver of Cu leaching, because this would preferentially mobilize isotopically light Cu. We conclude that the eluviation of the < 2 μm fraction, strongly controlled Cu concentrations, but had no discernible effect on δ⁶⁵Cu values. The changing redox conditions did not seem to control Cu concentrations and the stable isotope distribution in most of the bulk soil, soil volumes and soil water. Instead, weathering, complexation of leached Cu, Cu application with fertilizers and sorption processes within the soil controlled its δ⁶⁵Cu values.
  • Article
    Full-text available
    Geochemical characteristics of arc magmas reflect incorporation of subducted materials to their mantle wedge sources in subduction zones. Subduction component addition has been proposed to modify the Zn isotopic budget of arc magmas. However, the lack of a systematic study on Zn isotopic compositions of arc magmas hampers a better understanding of Zn isotope behavior in subduction zones. To address this issue, we have determined Zn isotopic compositions of 37 well-characterized arc rocks from the Kamchatka and Central-Eastern Aleutian arcs. These rocks record contributions of fluids and melts derived from altered oceanic crust (AOC) without overprints of sediment melts and thus allow focus on the potential effects of AOC-derived fluids and melts on the Zn isotopic budget of arc magmas. For comparison, nine basalts from the Gakkel, Mid-Atlantic and Southeast Indian Ridges, and the Lau Basin and nine adakites from Central America were also analyzed. Rocks from the Kamchatka-Aleutian arcs have δ⁶⁶Zn from 0.16 to 0.31‰ that are mostly similar to those of mid-ocean ridge basalts (MORBs), back-arc basin basalts (BABBs), and adakites (δ⁶⁶Zn = 0.23–0.33‰), but a significant number of arc samples also display δ⁶⁶Zn higher than that of the depleted MORB-type mantle (DMM), indicating Zn isotope fractionation during magmatic processes and/or modifications of the mantle wedge Zn isotopic budget by incorporation of AOC-derived fluids and melts. The lack of correlations of δ⁶⁶Zn with geochemical indicators of magma differentiation (e.g., MgO, SiO2, and Zn/FeT) indicate that fractionation of olivine, pyroxene, and magnetite has a limited effect on the Zn isotopic compositions of arc magmas. Even though the mantle sources of arc rocks investigated here are strongly affected by AOC-derived fluids and melts that have higher δ⁶⁶Zn compared to the DMM, we observe no systematic variations of δ⁶⁶Zn with indicators of subduction components (e.g., Ba/La, Ba/Th, Sr/Y, Hf/Lu and ⁸⁷Sr/⁸⁶Sr). This suggests that insignificant transport of Zn from the subducting Pacific slab to the Kamchatka and Central-Eastern Aleutian mantle wedge. Our model calculations suggest that the observed offset of δ⁶⁶Zn between the mantle and arc magmas can be attributed to isotope fractionation during partial melting with no need for contributions from subduction components.
  • Article
    The copper (Cu) content and isotopic composition were studied in soils and in pine tree rings at locations close to and far from the Cu smelter, located at Kitwe, Zambia. The soil in the remote area contained 25-75mgkg-1 Cu, whereas the soil close to the smelter contained 207-44,000mgkg-1 Cu. The δ65Cu at the remote area and close to the smelter varied in the range -0.40 to -0.11‰, and -0.44 to 0.01‰ respectively. The δ65Cu of the surface soil at both profiles (-0.44 to -0.40‰) is similar to the isotopic composition of the concentrates processed in the smelter (-0.75 to -0.45‰), i.e. both locations are affected by Cu ore dust. The increase in the δ65Cu in the direction towards the centre of the profile is caused by the oxidative dissolution of Cu(I) from ore minerals, during which heavier Cu is released. In deeper parts of the profile, there is a slight decrease in δ65Cu because of easier mobilisation of the lighter isotope. The tree rings at the two locations differ in the total contents and isotopic composition. At the less contaminated site, the Cu contents equal 0.4 to 1.1mgkg-1 while, at the polluted site, the Cu contents vary in the range 3 to 47mgkg-1. Whereas, at the less contaminated location, the tree rings are substantially enriched in lighter Cu (δ65Cu=-0.76 to -2.2‰), at locations close to the smelter the tree rings have an isotopic composition (-0.31 to -0.88‰) similar to that of the contaminated soil or processed ore. The isotopic compositions of the tree rings close to the smelter are affected particularly by interception of dust containing Cu ore. The δ13C in tree rings demonstrate the interconnection of acidification and Cu mobility.
  • Article
    The use of Ni and Cu isotopes for tracing contamination sources in the environment remains a chal- lenging task due to the limited information about the influence of various biogeochemical processes influencing stable isotope fractionation. This work focuses on a relatively simple system in north-east Norway with two possible endmembers (smelter-bedrock) and various environmental samples (snow, soil, lichens, PM10). In general, the whole area is enriched in heavy Ni and Cu isotopes highlighting the impact of the smelting activity. However, the environmental samples exhibit a large range of d60Ni ( 0.01 ± 0.03‰ to 1.71 ± 0.02‰) and d65Cu ( 0.06 ± 0.06‰ to 3.94 ± 0.3‰) values which exceeds the range of d60Ni and d65Cu values determined in the smelter, i.e. in feeding material and slag (d60Ni from 0.56 ± 0.06‰ to 1.00 ± 0.06‰ and d65Cu from 1.67 ± 0.04‰ to 1.68 ± 0.15‰). The shift toward heavier Ni and Cu d values was the most significant in organic rich topsoil samples in the case of Ni (d60Ni up to 1.71 ± 0.02‰) and in lichens and snow in the case of Cu (d65Cu up to 0.06 ± 0.06‰ and 0.24 ± 0.04‰, respectively). These data suggest an important biological and biochemical fractionation (microorganisms and/or metal uptake by higher plants, organo-complexation etc.) of Ni and Cu isotopes, which should be quantified separately for each process and taken into account when using the stable isotopes for tracing contamination in the environment.
  • Chapter
    The foundations of stable isotope geochemistry were laid in 1947 by Urey’s classic paper on the thermodynamic properties of isotopic substances and by Nier’s development of the isotope ratio mass spectrometer (IRMS).
  • Article
    Full-text available
    The aim of this study was to improve our understanding of what controls the isotope composition of Cu, Zn and Pb in particulate matter (PM) in the urban environment and to develop these isotope systems as possible source tracers. To this end, isotope ratios (Cu, Zn and Pb) and trace element concentrations (Fe, Al, Cu, Zn, Sb, Ba, Pb, Cr, Ni and V) were determined in PM10 collected at two road sites with contrasting traffic densities in central London, UK, during two weeks in summer 2010, and in potential sources, including non-combustion traffic emissions (tires and brakes), road furniture (road paint, manhole cover and road tarmac surface) and road dust. The isotope signatures of other important sources (gasoline and exhaust emissions) were taken from previous published data. Iron, Ba and Sb were used as proxies for emissions derived from brake pads, and Ni, and V for emissions derived from fossil fuel oil. The isotopic composition of Pb (expressed using 206Pb/207Pb) ranged between 1.1137 and 1.1364. The isotope ratios of Cu and Zn expressed as 65CuNIST976 and 66ZnLyon ranged between -0.01 ‰ and +0.51 ‰ and between -0.21 ‰ and +0.33 ‰, respectively. We did not find significant differences in the isotope signatures in PM10 over the two weeks sampling period and between the two sites, suggesting similar sources for each metal at both sites despite their different traffic densities. The stable isotope composition of Pb suggests significant contribution from road dust resuspension and from recycled leaded gasoline. The Cu and Zn isotope signatures of tires, brakes and road dust overlap with those of PM10. The correlation between the enrichments of Sb, Cu, Ba and Fe in PM10 support the previously established hypothesis that Cu isotope ratios are controlled by non-exhaust traffic emission sources in urban environments (Ochoa Gonzalez et al., 2016). Analysis of the Zn isotope signatures in PM10 and possible sources at the two sites suggests significant contribution from tire wear. However, temporary additional sources, likely high temperature industrial emissions, need to be invoked to explain the isotopically light Zn found in 3 out of 18 samples of PM10.
  • Chapter
    Isotopes are atoms whose nuclei contain the same number of protons but a different number of neutrons.
  • Article
    Significant Zn isotope fractionation occurs during seafloor hydrothermal activities. Therefore, exploring variations in Zn isotope composition affected by hydrothermal fluids and oxidative processes would help to better understand hydrothermal fluid cycling and sulfide deposition on mid-ocean ridges. In this paper, the Zn isotope compositions of different types of sulfides and their oxidation products obtained from hydrothermal fields on the South Mid-Atlantic Ridge (13–15°S) were analyzed using a Neptune plus MC-ICP-MS. The δ⁶⁶Zn ratios range from –0.14‰ to +0.38‰, and the average δ⁶⁶Zn ratio is +0.12±0.06‰ (n=21, 2 SD) for all the studied sulfides and oxidation products. The Cu-rich sulfides have a slightly heavier Zn isotope composition (average δ⁶⁶Zn=+0.19±0.07‰, n=6) than the Zn-rich sulfides (average δ⁶⁶Zn=–0.02±0.06‰, n=5). The Zn isotope compositions of the oxidation products are similar to those of the Cu-rich sulfides, with an average δ⁶⁶Zn ratio of 0.14±0.06‰ (n=10, 2 SD). The Zn isotope compositions of all the samples are generally within the ranges of sulfides from hydrothermal fields on other mid-ocean ridges, such as the East Pacific Rise (9°N, 21°N) and the Trans-Atlantic Geotraverse. However, the average Zn isotope composition indicates the presence of significantly lighter Zn isotopes relative to those reported in the literature (average δ⁶⁶Zn=+0.39‰). The significant enrichment of the Zn-rich sulfides with light Zn isotopes reveals that kinetic fractionation likely occurs during mineral deposition. Furthermore, the Zn isotope compositions of the sulfides and their oxidation products (average δ⁶⁶Zn=+0.12‰) are significantly lighter than the average Zn isotope composition of the ocean (δ⁶⁶Zn=+0.5‰), which could further constrain the modern Zn isotope cycle in the ocean by serving as a sink for light Zn isotopes.
  • Article
    Full-text available
    Arc lavas display elevated Fe 31 /RFe ratios relative to MORB. One mechanism to explain this is the mobilization and transfer of oxidized or oxidizing components from the subducting slab to the mantle wedge. Here we use iron and zinc isotopes, which are fractionated upon complexation by sulfide, chloride, and carbonate ligands, to remark on the chemistry and oxidation state of fluids released during prograde metamorphism of subducted oceanic crust. We present data for metagabbros and metabasalts from the Chenaillet massif, Queyras complex, and the Zermatt-Saas ophiolite (Western European Alps), which have been metamorphosed at typical subduction zone P-T conditions and preserve their prograde metamorphic history. There is no systematic, detectable fractionation of either Fe or Zn isotopes across metamorphic facies, rather the isotope composition of the eclogites overlaps with published data for MORB. The lack of resolvable Fe isotope fractionation with increasing prograde metamorphism likely reflects the mass balance of the system, and in this scenario Fe mobility is not traceable with Fe isotopes. Given that Zn isotopes are fractionated by S-bearing and C-bearing fluids, this suggests that relatively small amounts of Zn are mobilized from the mafic lithologies in within these types of dehydration fluids. Conversely, metagabbros from the Queyras that are in proximity to metasediments display a significant Fe isotope fractionation. The covariation of d 56 Fe of these samples with selected fluid mobile elements suggests the infiltration of sediment derived fluids with an isotopically light signature during subduction.
  • Article
    Moldavites are tektites genetically related to the Ries impact structure, located in Central Europe, but the source materials and the processes related to the chemical fractionation of moldavites are not fully constrained. To further understand moldavite genesis, the Cu and Zn abundances and isotope compositions were measured in a suite of tektites from four different substrewn fields (South Bohemia, Moravia, Cheb Basin, Lusatia) and chemically diverse sediments from the surroundings of the Ries impact structure. Moldavites are slightly depleted in Zn (~10–20%) and distinctly depleted in Cu (>90%) relative to supposed sedimentary precursors. Moreover, the moldavites show a wide range in δ66Zn values between 1.7 and 3.7‰ (relative to JMC 3-0749 Lyon) and δ65Cu values between 1.6 and 12.5‰ (relative to NIST SRM 976) and are thus enriched in heavy isotopes relative to their possible parent sedimentary sources (δ66Zn = −0.07 to +0.64‰; δ65Cu = −0.4 to +0.7‰). In particular, the Cheb Basin moldavites show some of the highest δ65Cu values (up to 12.5‰) ever observed in natural samples. The relative magnitude of isotope fractionation for Cu and Zn seen here is opposite to oxygen-poor environments such as the Moon where Zn is significantly more isotopically fractionated than Cu. One possibility is that monovalent Cu diffuses faster than divalent Zn in the reduced melt and diffusion will not affect the extent of Zn isotope fractionation. These observations imply that the capability of forming a redox environment may aid in volatilizing some elements, accompanied by isotope fractionation, during the impact process. The greater extent of elemental depletion, coupled with isotope fractionation of more refractory Cu relative to Zn, may also hinge on the presence of carbonyl species of transition metals and electromagnetic charge, which could exist in the impact-induced high-velocity jet of vapor and melts.
  • Article
    Full-text available
    Metal ion-mineral surface interactions and the attendant isotopic fractionation depend on the properties of the mineral surface and the local atomic-level chemical environment. However, these factors have not been systematically examined for phases of the same composition with different levels of surface disorder. We present pH-dependent adsorption edges, x-ray absorption spectra, and isotopic measurements to illustrate the effects of surface disorder and surface coverage on zinc(II) (Zn(II)) surface complexation and isotope fractionation. Our results demonstrate that Zn(II) surface complexes on quartz and amorphous silica (SiO2(am)) transition from octahedral to tetrahedral coordination by oxygen as surface coverage increases. In low ionic strength solutions (I = 0.004 M) and at low surface loadings (Γ < 0.6 μmol m⁻²), Zn(II) adsorbs to the quartz surface predominantly as outer-sphere octahedral complexes (RZn-O = 2.05 Å) with no significant isotopic fractionation (Δ66/64Znaqueous-sorbed = -0.01 ±0.06‰) from aqueous Zn(II). In contrast, under similar chemical conditions and surface loading, outer-sphere Zn(II) adsorption complexes are not observed on SiO2(am) surfaces. At high ionic strength (I = 0.1 M) and low surface loading (Γ < 0.2 μmol m⁻²), inner-sphere, monodentate octahedral Zn(II) complexes (RZn-O = 2.05-2.07 Å) are observed on both quartz and SiO2(am) surfaces. At the same ionic strength (I = 0.1 M) and higher surface loading (Γ = 0.6-1.4 μmol m⁻²), Zn(II) forms inner-sphere, monodentate tetrahedral complexes (RZn-O = 1.98 Å) at the quartz surface. On the SiO2(am) surface under similar chemical conditions and surface loading, Zn(II) forms dominantly inner-sphere, monodentate tetrahedral complexes with shorter Zn-O bond distances (RZn-O = 1.94 Å). Despite different coordination numbers, the measured equilibrium isotope fractionation factors for inner-sphere octahedral and tetrahedral complexes versus dissolved Zn, under the same conditions and on the same silica substrate, are not distinguishable beyond uncertainties. However, there is a larger measured equilibrium isotope fractionation with preferential sorption of heavy Zn as inner-sphere complexes on SiO2(am) (Δ66/64Znaqueous-sorbed = -0.94 ±0.11‰) than on quartz (Δ66/64Znaqueous-sorbed = -0.60 ±0.11‰).The propensity for Zn(II) to occur in tetrahedral and octahedral coordination with oxygen may help explain these observations. We posit that the low energetic difference between octahedral and tetrahedral Zn(II) may be why changes in inner-sphere Zn(II) coordination numbers with increasing coverage do not manifest as distinguishable isotope fractionations or as an observable alteration to the macroscopic sorption edges. Thus, we attribute the larger magnitude of Zn isotope fractionation on SiO2(am) compared to quartz to differences in the bonding environments on the two types of silica surfaces rather than to a change in the coordination number of Zn(II).
  • Article
    Full-text available
    Zinc (Zn) isotopes have shown promise for investigating biogeochemical processes and tracing sources of Zn for environmental studies. This study, the first in its kind, investigates Zn isotopic ratios in tree rings and soils of two sites in the Northern Athabasca Oil Sands Region (NAOSR) of Alberta, Canada. To this end, we have developed an appropriate protocol to analyze tree-ring δ⁶⁶Zn values by pooling year-equivalent tree rings of four individual trees for both sites. The results of combined tree-ring Zn concentrations show minimal variation in heartwood, with a statistically significant decrease after 1979 and 1986 for site 1 and site 2, respectively. For site 1, tree-ring δ⁶⁶ZnJMC Lyon ratios vary between 0.83±0.08 to 0.54±0.07‰ with a statistically significant decrease from 1877 to 2008. For site 2, δ⁶⁶ZnJMC Lyon ratios range from 0.78±0.02 to 0.59±0.07‰ with the lowest values obtained for the outermost ring closest to the bark. However, this site does not display statistically significant long-term trend. In comparison to the tree rings, adsorbed Zn within soil organic horizons is relatively enriched in heavy isotopes (δ⁶⁶ZnJMC Lyon of 1.00±0.20 to 1.12±0.10 and 0.81±0.10 to 0.86±0.06‰ for sites 1 and 2, respectively). Tree-ring and soil organic horizons δ⁶⁶Zn values are also substantially heavier than the value reported for adsorbed Zn in NAOSR tailing sands (δ⁶⁶ZnJMC Lyon =0.35±0.06‰). The heavy signature in the organic horizons may be a product of Zn biogeochemical cycling through soil processes and uptake by trees, although Zn atmospheric deposition from the NAOSR cannot be discounted. On the other hand, tree physiological processes, particularly radial translocation, could have potentially influenced the studied tree-ring Zn concentration and isotopic characteristics. However, this mechanism has not received substantial research. The δ⁶⁶Zn analyses in different wood components are required before its influence on δ⁶⁶Zn values can be properly assessed and tree-ring δ⁶⁶Zn can be used as environmental indicators.
  • Article
    We determined Zn isotopic compositions of 21 orogenic peridotites from the Baldissero and Balmuccia peridotite massifs in Ivrea-Verbano Zone, Italian Alps, to investigate Zn isotope behaviors during partial melting and melt percolation in the mantle. The samples include lherzolites, harzburgites, and dunites. Lherzolites are strongly depleted in light rare earth element relative to middle and heavy rare earth element with (La/Sm)PM from 0.009 to 0.265 and (La/Yb)PM from 0.003 to 0.125, which can be explained by 5-15% fractional melting of a primitive mantle source. Harzburgites and dunites with nearly identical Mg# (molar 100 * Mg/(Mg + Fe) = 90.2-91.0) have (La/Sm)PM and (La/Yb)PM higher than but Zn contents similar to or lower than those of the parental lherzolites, suggesting that they were influenced by Zn-depleted silicate melt percolation. Lherzolites have δ⁶⁶Zn from 0.13 to 0.27‰ showing no correlations with indicators of melt extraction (e.g., Al2O3, Mg#, and La/Yb) and Zn contents. Three sulfide melt-affected lherzolites show similar δ⁶⁶Zn to the other normal ones. These observations indicate that 5-15% partial melting and sulfide melt percolation cause limited Zn isotope variations in the mantle. The metasomatic harzburgites and dunites display high δ⁶⁶Zn (up to 0.46‰) negatively correlated with Zn contents. Such correlations are attributed to kinetic effect during silicate melt percolation, whereby ⁶⁴Zn preferentially diffuses out from mantle minerals (e.g., olivine) to the percolating silicate melts. A diffusion model suggests that the negative correlation between δ⁶⁶Zn and Zn contents in dunites can be explained by an empirical βZn (i.e., βZn-exponent in D66Zn/D64Zn = (m64Zn/m66Zn)βZn) of 0.05-0.06 in olivine.
  • Article
    This study reports spatial and temporal variability of Zn and Cu isotopes in atmospheric particulate matter (PM) collected in two major European cities with contrasting atmospheric pollution, Barcelona and London. We demonstrate that non-traditional stable isotopes identify source contributions of Zn and Cu and can play a major role in future air quality studies. In Barcelona, fine PM were collected at street level at sites with variable traffic density. The isotopic signatures ranged between -0.13±0.09 and -0.55±0.09‰ for d66ZnIRMM and between +0.04±0.20 and +0.33±0.15‰ for d65CuAE633. Copper isotope signatures similar to Cu sulphides and Cu/Sb ratios within the range typically found in brake wear suggest that non-exhaust emissions from vehicles are dominant. Negative Zn isotopic signatures characteristic for gaseous emissions from smelting and combustion and large enrichments of Zn and Cd suggest contribution from metallurgical industries. In London, coarse PM collected on the top of a building over 18 months display isotope signatures ranging between +0.03±0.04 and +0.49±0.02‰ for d66ZnIRMM and between +0.37±0.17 and +0.97±0.21‰ for d65CuAE633. Heavy Cu isotope signatures (up to +0.97±0.21‰) and higher enrichments and Cu/Sb ratios during winter time suggest important contribution from fossil fuel combustion. The positive d66ZnIRMM signatures are in good agreement with signatures characteristic for ore concentrates used for the production of tires and galvanised materials, suggesting non-exhaust emissions from vehicles as the main source of Zn.
  • Article
    An internal standard technique which gives more than a 5-fold improvement in the precision of an isotopic analysis made in a thermal ionization mass spectrometer is described. The technique developed has application in the following fields: certain half life determinations; geochemical age determinations; nuclear absorption cross sections and low isotopic burnup; and isotopic dilution analysis for the assay of uranium. To apply the technique, three or more isotopes of an element must be present so that two different isotopic ratios of the same element can be compared in such a manner as to eliminate almost completely mass discrimination (instrument bias). The flexibility of the internal standard technique to problems which are amenable to surface ionization mass spectrometry is clarified is discussions given on its application to uranium isotope abundance measurements and to a new determination of the half life of Cs/sup 137/. (P.C.H.)
  • Article
    Full-text available
    Spectral interferences originating from instrumental and sample-matrix components continue to present a major analytical challenge to high-precision isotope ratio measurements by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). This is particularly true when measuring stable isotopic variability of Cu and Zn, where instrumental and sample-matrix related spectral components may obscure the very small isotopic anomalies that typify these metals in terrestrial materials. We present a systematic characterisation and quantification of spectral interferences across the mass range Cu-63 to Zn-70 using two MC-ICP-MS instruments: a Micromass IsoProbe and a VG Axiom. Significant instrumental Ni backgrounds of up to 40 mV total Ni occur on the IsoProbe, reflecting streaming off the Ni-sampler and/or skimmer cones. This Ni contribution, however, is insufficient to account for the excess peak contribution at (64)amu, suggestive of an as yet unidentified interference contribution at this mass. By contrast, Ni backgrounds on the Axiom are roughly one order of magnitude lower, and no comparable interference occurs at (64)amu. High-resolution mass scans on the Axiom have identified (ArCO+)-Ar-40-C-12-O-16 and (ArNN+)-Ar-40-N-14-N-14 species at (68)amu and (ArNO+)-Ar-40-N-14-O-16 at (70)amu. Also, HNO3-related (HH)-H-1-H-1 (14)N(16)O(16)O16O(+) and (HH14)-H-1-H-1 (NOOO+)-O-16-O-16-O-18 species at (64)amu and (66)amu respectively were observed on the Axiom using solution nebulisation. None of these species were observed on the IsoProbe, possibly reflecting the effect of an Ar-bled hexapole collision cell that reduces molecular interferences through ion-molecule reactions. Instrumental backgrounds have been successfully corrected using an on-peak acid blank subtraction procedure. Zinc hydride adducts occur on the Axiom using solution nebulisation. These interferences are eliminated using a desolvated plasma, and have been corrected by monitoring the (ZnH+)-Zn-64-H-1/ Zn-64 ratio on a pure Zn solution and applying an offline peak subtraction. No Zn hydride interferences were observed on the IsoProbe, suggesting differences in instrument design influence the formation and/or persistence of these species. Matrix-induced interference contributions on the Axiom and IsoProbe show increasing significance from argides (NaAr+, MgAr+, AlAr+) to oxide/hydroxide (TiO+, TiOH+, VO+, VOH+, CrO+, CrOH+) to double-charged species (Ba2+, Ce2+). Switching from solution nebulisation to a desolvated plasma enhances argide. and double-charge species, and concurrently depresses oxides and hydroxides, reflecting changing conditions within the ICP-source. These results highlight the importance of removing problematic matrix components prior to. Cu and Zn MC-ICP-MS isotope ratio measurements.
  • Article
    In order to test the usefulness of stable zinc isotopes as an atmospheric source tracer, we analyzed the zinc isotopic composition of two sediment cores, taken at 1 km distance of the former zinc smelter in Lommel, Belgium. The peat bog lake sediments accumulate mainly atmospheric particles, have high organic matter contents (12–60 wt.%), are anoxic and highly contaminated with heavy metals (up to 4.7 wt.% Zn, and 1.1 wt.% Pb) with a sulfide mineralogical control on mobility. Down core variations in δ66Zn (relative to the JMC 3-0749L standard) were small, ranging from + 0.07‰ to + 0.39‰, but are nevertheless eight times the external reproducibility of 0.04‰. Good agreement was found between the two cores, and despite 30% Zn mobilization to deeper layers, no evidence of associated diagenetic Zn isotope fractionation was found. Sediments deposited in the early 20th century have δ66Zn of + 0.30‰ ± 0.05‰ (2SD, n = 5) and a shift takes place between 1945 and 1950 to δ66Zn values of + 0.14‰ ± 0.09‰ (2SD, n = 7) in the 2nd half of the century. In order to understand this shift in δ66Zn we analyzed 32 ore-grade sphalerite (ZnS) samples from African, Australian and European origin. Together with 29 published δ66Zn values for ore-grade ZnS, we find remarkably homogeneous isotopic compositions, which when averaged for mining location gives δ66Zn of + 0.16‰ ± 0.20‰ (2SD, n = 10 mines, n = 61 analyses). Early 20th century Zn deposition with δ66Zn of +0.30‰ is significantly different (p < 0.001) from average ZnS δ66Zn of +0.16‰. We suggest that this reflects the presence of an atmospheric smelting residue (slag) component, enriched in the heavy Zn isotopes due to Rayleigh type fractionation during Zn refining.
  • Article
    Full-text available
    In this paper, we present the copper isotope signatures of black smoker sulfides, massive sulfides, and their alteration products and provide new insights into mineralization processes and applications of copper isotope geochemistry to sea-floor hydrothermal systems on the Mid-Atlantic Ridge. The hydrothermal systems studied include the Lucky Strike field at 37°17′N on a basaltic substrate and the Rainbow and Logatchev fields, situated on ultramafic rock. Copper isotope variation in the hydrothermal precipitates was examined in conjunction with S isotopes and Se and Co concentrations. The comparison between δ 65Cu and Se contents shows that subsurface precipitation of Cu-rich sulfides does not control significantly the δ 65Cu values of the hydrothermal chimneys. It appears that the major cause of copper isotope fractionation in hydrothermal systems (up to 3‰) is the sea-floor oxidation of primary copper sulfides. Enrichment in the heavy copper isotope can be explained by processes occurring at the sea floor, such as hydrothermal reworking of previously altered sulfides by high-temperature fluid. Massive sulfides characterized by negative δ 65Cu values have undergone extensive recrystallization. In these mineralogical assemblages, isotopically heavy copper typical of altered sulfides has been leached and redeposited in the external zones or incorporated in hydrothermal fluids. Copper isotopes are therefore a promising tool for the study of supergene processes and the recycling of previously oxidized sulfides, as well as a means of characterizing the degree of hydrothermal reworking of large sulfide deposits. Further studies of copper isotope fractionation under controlled laboratory experimental conditions are required to identify copper isotope fractionation during sulfide alteration. In particular, the possible biological mediation of copper isotope fractionation during sulfide oxidation may be an important direction for further studies.
  • Article
    Multiple-collector magnetic sector ICP-MS affords the possibility of applying instrumental mass discrimination corrections using a reference isotope ratio of an element (dopant) other than the analyte. Much attention has focused on the use of this approach for lead isotope analysis using a thallium dopant and the technique has also been applied to copper–zinc isotope analysis. The most successful applications of the doping approach have established empirical mass bias relationships between dopant and analyte isotope ratios but this often has to be done for single analytical sessions. Insufficient intra-session variation in mass discrimination often leads to poor constraints on these relationships. Moreover, with the Tl–Pb system there is some doubt over whether samples and standards exhibit the same relationship. Here we show that for the Cu–Zn system, two improvements on previous approaches lead to precise and accurate isotope ratios for unknowns. Firstly, addition of Sr to mixed Cu–Zn standard solutions generates extreme variation in mass bias so that empirical mass bias relationships between analyte and dopant are much better constrained. Secondly, we show that inadequate chemistry, specifically the inefficient removal of matrix Fe and Ti, seriously compromises the Cu–Zn isotope analysis of samples but that with clean chemistry, samples with complex matrices demonstrably yield similar mass discrimination relationships between Cu and Zn isotopes to standards. We also document previously unreported aspects of Cu–Zn isotope analysis: (1) that Cu–Zn mass bias relationships depend critically on the Cu/Zn ratio of the solution; (2) that for an introduction system with a desolvating membrane, the behaviour of standards is highly variable, perhaps due to variations in the oxidation state of Cu in the solution, and that this can be overcome by the passage of standards through the ion exchange procedure used to purify samples. Finally, we document chemical separation and mass spectrometric techniques that permit the isotopic analysis of order of magnitude smaller samples than previously achieved and report values for BCR-1 basalt standard of δ66Zn = 0.20 ± 0.09‰ (n = 12) and δ65Cu = 0.07 ± 0.08‰ (n = 6) at the 95% confidence level.
  • Article
    Molybdenum (Mo) isotopes in ancient sediments are promising recorders of global ocean paleoredox conditions. Organic-rich black shales can be used to reconstruct ancient ocean Mo isotope compositions if these sediments record the isotopic composition of contemporaneous seawater. Comparison of δ98/95Mo in two Devonian shale sequences of similar age, the New York Oatka Creek and Geneseo Formations, reveals that this assumption cannot be applied to all organic-rich shales. Although both sequences contain laminated intervals, elevated organic carbon, and enrichments of redox-sensitive metals, the mean δ 98/95Mo differs systematically between the formations by ∼0.59%. Independent paleoredox indicators reveal that portions of the Oatka Creek Formation were deposited under pervasively euxinic (anoxic and sulfidic) conditions, whereas conditions during deposition of the Geneseo Formation were intermittently euxinic to suboxic (oxygen deficient but not sulfidic in the water column). We infer that reconstruction of ancient ocean δ98/95Mo from organic-rich shales requires independent verification of persistent local euxinia. With these considerations in mind, our data point to δ98/95Mo in the Devonian oceans ∼0.6‰ lighter than in today's oceans, consistent with expanded anoxia.
  • Article
    Molybdenum isotopic compositions are precisely determined by MC-ICP-MS measurements using a Mo double spike. The double spike is added prior to chemical purification, so that laboratory and instrumental mass fractionations are separated from natural mass-dependent fractionation. Fractionation is determined on four Mo mass ratios, providing an internal consistency check. The external standard reproducibility is at 0.06 per mil on the 98Mo/95Mo ratio (2 standard deviation)). Using a normal microconcentric nebuliser with a cyclonic spray chamber, the minimum quantity of Mo is ˜1 μg for high-precision results. A hydrothermal molybdenite shows fractionation of -0.3 per mil on the 98Mo/95Mo ratio relative to our standard (Johnson Matthey, 1000 μg/mL (±0.3%) ICP standard solution, lot 602332B). Fine-grained sediments show fractionation of 0.1 and -0.3 per mil on the 98Mo/95Mo ratio. The observed Mo isotope fractionation is small but resolvable with the presented high-resolution technique.
  • Article
    The standard addition method is evaluated to verify the accuracy and precision of Mg and Ca isotope data with complex matrices, using the standard-sample bracketing technique and analysis by MC-ICP-MS. The 44Ca/42Ca ratio of seawater (expressed as δ4442Ca relative to SRM915a) was determined as 0.93±0.03‰ (95% confidence), in agreement with estimates obtained by the double spike method. Using standard addition, the seawater 26Mg/24Mg ratio (expressed as δ26Mg relative to the DSM3 standard) was determined as −0.80±0.06‰ (95% confidence) in agreement with previous estimates. Four terrestrial silicate rocks (MORB, flood basalt, glacial flour, and granodiorite) and olivine mineral separates from an island basalt are shown to exhibit no scatter within the error of the method, averaging a δ26Mg of −0.20±0.05‰ (95% confidence). Although a number of silicate rock data for Mg isotope ratios have already been reported, this is the first detailed effort to validate the accuracy of such data and test for residual analytical artifact after chemical purification of samples. Data regressions were evaluated statistically using the mean square weighted deviate (MSWD), demonstrating that the uncertainty on individual data points are generally over estimated. The external two standard deviation uncertainty on individual data points is estimated by Monte Carlo simulation as
  • Article
    Multi-collector inductively coupled plasma mass spectrometry now provides for precise and accurate measurements of Cu isotope ratios. Copper minerals prepared by direct dissolution with and without chromatographic purification yield identical Cu isotope ratios within analytic precision of about 0.04‰ (1σ). Cu isotope ratios have been measured for copper minerals from worldwide magmatic and hydrothermal copper deposits, and for several weathered deposits. Natural variations in δ65Cu values, relative to NBS976, range over 9‰. Chalcopyrite samples from mafic intrusions lie within a narrow range of about 1.5‰, and most cluster tightly between −0.10‰ and −0.20‰. This range lies within the broader black smoker chalcopyrite and iron meteorite ranges, and possibly represents a bulk mantle Cu isotope ratio. Most values for hydrothermal native copper from the Michigan native copper district also show a narrow range just larger than 0.1‰ and suggest a common homogeneous source for Cu in this large hydrothermal system. Later copper sulfide and arsenide minerals from this district range to values more than 2‰ lower than native copper. Ratios for chalcopyrite and bornite from moderate to high-temperature porphyry, skarn, and replacement deposits as a group and within individual deposits exhibit a broad range of values. Variations of nearly 1‰ are observed over distances on the order of 1 m. In some cases, these variations may result from multiple mineralization events or copper remobilization during retrograde or later hydrothermal activity. Fractionations between chalcopyrite and bornite, where they occur in the same sample or in related samples, cluster near 0.4‰, suggesting equilibrium Cu isotope fractionation between them at moderate temperatures. In addition, weathering of hydrothermal copper minerals produces a wide range of values in secondary copper phases. In the supergene environment, cuprite typically has higher values than associated native copper. Therefore, redox states appear to exert a significant control over fractionation at low temperatures. Significant questions remain to be answered. Before the source of copper in hydrothermal environments can be fully addressed, source reservoir Cu ratios need to be determined, and chemical and physical factors that control Cu isotope fractionation must be quantitatively defined.
  • Article
    ε⁶⁵Cu ([⁶⁵Cu/⁶³Cusample/⁶⁵Cu/⁶³CuNIST-976 −1]*10,000) in chalcopyrite from the 3 three igneous intrusions that make up the Grasberg Igneous Complex (GIC) and associated skarn deposits range from 0.2 to 13.4. Chalcopyrite grains from each intrusion have a specific range of ε⁶⁵Cu that is isotopically heavier in each successive intrusion. These variations may be interpreted in two ways: (1) isotope fractionation during distillation of Cu from the underlying source and establishment of hydrothermal cells associated with each intrusion; (2) isotope fractionation as the ore ore-bearing fluid moved outward from a central core. Within each sample, the smaller disseminated chalcopyrite grains yield consistently lower ε⁶⁵Cu values than larger disseminated grains, suggesting multiple mineralisation events.
  • Article
    The stable isotope compositions of Zn and Cu in natural materials are newly available for measurement with the advent of multiple-collector inductively coupled mass spectrometry (MC–ICPMS). Although the oceans are prime scientific targets, no progress has been made as yet because of considerable analytical challenges involving the low concentrations of these elements in seawater. We present a procedure which allows isotopic analysis of Zn and Cu isotope compositions of seawater samples at least 1 L in size by MC ICPMS.
  • Article
    Analyses of sphalerite samples from shale-hosted massive sulfide and stratigraphically underlying vein breccia deposits in the Red Dog district in northern Alaska show a range δ66Zn values from zero to 0.60 per mil. The lowest values are observed in the vein breccia deposits, and the stratigraphically overlying (but structurally displaced) shale-hosted massive sulfide deposits show a systematic trend of increasing δ66Zn values from south to north (Main-Aqqaluk-Paalaaq-Anarraaq). The δ66Zn values are inversely correlated with sphalerite Fe/Mn ratio and also tend to be higher in low Cu sphalerite, consistent with precipitation of lower δ66Zn sphalerite closer to the principal hydrothermal fluid conduits. The most likely control on isotopic variation is Rayleigh fractionation during sulfide precipitation, with lighter zinc isotopes preferentially incorporated in the earliest sphalerite to precipitate from ore fluids at deeper levels (vein breccias) and close to the principal fluid conduits in the orebodies, followed by precipitation of sulfides with higher δ66Zn values in shallower and/or more distal parts of the flow path. There is no systematic variation among the paragenetic stages of sphalerite from a single deposit, suggesting an isotopically homogeneous zinc source and consistent transport-deposition conditions and/or dissolution-reprecipitation of earlier sphalerite without significant fractionation. Decoupled Zn and S isotope compositions are best explained by mixing of separate metal- and sulfur-bearing fluids at the depositional site. The results confirm that Zn isotopes may be a useful tracer for distinguishing between the central and distal parts of large hydrothermal systems as previously suggested and could therefore be of use in exploration.
  • Article
    Little is known about the range or controls on the zinc isotope composition of terrestrial materials and no systematic studies have been carried out on ore-forming systems. We have obtained zinc isotope data from 19 sphalerite samples, formed over a range of well-constrained precipitation conditions, from the Irish Zn-Pb ore field. The results reveal variation in delta(66)Zn (where delta(66)Zn = [(Zn-66/Zn-64)(sample)/(Zn-66/Zn-64)standard - 1] X 1000), from -0.17 to 1,33 per mil relative to the Lyon JMC 3-0749L zinc standard. This variation is significant compared to the external reproducibility (+/- 0.12 parts per thousand, 2 sigma), and the data show very good mass-dependency with delta(67)Zn and delta(68)Zn values. Thus, natural variations in the zinc isotope composition of these ore minerals can be resolved. Our results span the entire range of delta(66)Zn values measured on terrestrial geologic samples to date. The data suggest that variations in the primary source rock composition or precipitation temperature are unlikely to be important controls on the zinc isotope composition of sphalerite in the ore field. We suggest that the variation is most likely, due to a kinetic fractionation involving the preferential incorporation of light zinc isotopes in sphalerite precipitated rapidly under disequilibrium conditions. However, we cannot rule out the possibility of mixing of zinc derived from two isotopically distinct sources. The significant variation in zinc isotope compositions we have observed in the Irish ore field confirms that such fractionations can provide new insights into mineralizing processes in the Earth's crust.
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    Full-text available
    Two approaches to correct for mass discrimination effects associated with Cu and Zn isotopic measurements on two different MC-ICP-MS instruments (a Micromass IsoProbe and a VG Axiom) have been compared and assessed in detail: (1) sample-standard bracketing (SSB), and (2) the ‘empirical external normalisation’ (EEN) whereby a second element is used to simultaneously correct for mass discrimination. This has provided new insights into the mass discrimination behaviours of Cu and Zn under varying instrumental set-ups, and has allowed improvements to be made to the existing correction procedures. With the SSB approach, mass bias stability is a prerequisite, and matrix components must be removed from the analyte to avoid matrix-related mass discrimination effects. By comparison, the EEN approach requires a degree of mass bias instability, and automatically corrects for matrix-related mass discrimination effects. The EEN correction may therefore appear more robust. However, while the EEN correction yields high-precision 65Cu/63Cu and 66Zn/64Zn data, an as yet unidentified source of systematic drift in the 67Zn and 68Zn signals through time hinders analyses of ratios incorporating these isotopes. Using the EEN correction where analyte and spike ratios were measured sequentially within a peak-switching protocol led to a three-fold deterioration in precision relative to static measurements. This is consistent with mass bias drift on the scale of a single five-second-measurement integration. For relative 65Cu/63Cu and 66Zn/64Zn ratio measurements, the SSB and EEN corrections give long-term reproducibilities of less then ±0.07‰ (2SD) for pure Cu and Zn reagents. This is sufficient for resolving mass-dependent isotopic variability in natural and anthropogenic materials.
  • Article
    Multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has become the preferred method for precise and accurate measurements of the relative abundances of many radiogenic and stable isotopes in natural materials. Isotopic analyses by MC-ICP-MS require a correction for instrumental mass-dependent isotopic fractionation (“instrumental mass bias”). Two techniques have been used to correct for instrumental mass bias in the MC-ICP-MS: (1) standard-sample bracketing (SSB) or (2) double spiking. SSB is often cited as the preferred method, but it is more susceptible to matrix effects. Here we demonstrate that a matrix effect in the MC-ICP-MS may arise indirectly from the chemical separation and purification of molybdenum using anion exchange resin. The results of our experiments show that a Mo standard passed through a column of anion exchange resin or a Mo standard added to a Mo-free solution that had been collected from anion exchange resin appears to be isotopically lighter than expected from direct analysis of the same standard. Using amounts of Mo similar to what might be expected from most natural samples (∼3μg per column cut), these offsets span a significant fraction (∼10–60%) of the total known range of mass-dependent Mo isotopic variation in nature. This “column matrix effect” appears to be caused by organic material stripped from the resin. All of our attempts to eliminate or control this column matrix effect have failed, making it difficult (if not impossible) to obtain accurate measurements of mass-dependent Mo isotopic variations in natural materials using the anion exchange resin procedure described in this study and SSB techniques to correct for instrumental mass bias in the MC-ICP-MS. It is currently unknown if this type of column matrix effect will affect measurements of other stable or radiogenic isotopes by MC-ICP-MS when SSB is used to correct for instrumental mass bias.
  • Article
    The double focusing-Jeol Inductively Coupled Plasma Mass Spectrometer PLASMAX2 is used at different resolving powers, for the separation between zinc isotopes and their interfering ions. NIST standard solution samples of zinc as single and multielements are used in the analysis. Variation of different Zn isotopic abundances and their interfering ions are studied as a function of concentrations at low and high resolutions. The precision for different isotopic ratios in multielement solutions, after taking the experimental considerations, at high resolution are calculated and found to have a value between 0.19 and 0.42. While the accuracy for the isotopes can reach a value between 0.27 and 1.17, blood and serum samples in human are used as an application for this method in the biological samples. The obtained results are compared with that obtained by using flame atomic absorption spectrometer and it is found in the same range of concentration.
  • Article
    A method using multiple-collector inductively coupled plasma source mass spectrometry for the precise measurement of Ti isotope composition in natural materials has been developed. Instrumental mass discrimination is corrected using a “standard-sample bracketing” approach by expressing the isotope ratios of samples relative to those of the bracketing standard. Variations in 47Ti/46Ti,48Ti/46Ti,49Ti/46Ti and 50Ti/46Ti ratios of samples are expressed in ε units which are deviations in parts per 104 from the same isotope ratios of the reference material. The long-term repeatability at the 2 standard deviation level is 0.4, 0.6, 0.7 and 0.8 ε units in terms of 47Ti/46Ti,48Ti/46Ti,49Ti/46Ti and 50Ti/46Ti ratio measurements, respectively. The technique reported here makes it possible for the first time that both mass-dependent fractionation and isotope anomalies of Ti isotopes in natural materials can be measured to high precision.
  • Article
    We present the first comprehensive set of stable Cr isotope data for the major igneous silicate Earth reservoirs, Cr(III)-rich ores and minerals, and hydrothermal chromates. These were determined by MC-ICP-MS using a double spike technique. Mantle xenoliths, ultramafic rocks, cumulates, as well as oceanic and continental basalts share a common Cr isotope composition with an average δ53/52Cr value of −0.124±0.101‰ (2 SD) relative to the isotopically certified chromium standard NIST SRM 979. An isotopic difference between mantle xenoliths and basalts, as was reported for iron, was not observed for chromium. Thus, the change in oxidation state that is observed when solid mantle rocks, containing only trivalent chromium, partially melt to form basaltic melts, which predominantly contain bivalent chromium, does not cause any measurable Cr isotope fractionation. Chromite separates from major chromitite seams of the Bushveld and Great Dyke layered igneous complexes are invariable in their Cr isotope compositions and reproduce within uncertainties the average δ53/52CrSRM 979 value of igneous silicate Earth reservoirs. This is important for environmental stable Cr isotope studies, because it labels the approximate isotope composition of industrial Cr(VI) pollutants. The Cr isotope compositions of hydrothermal lead chromates (crocoites PbCrVIO4) from various localities yield δ53/52CrSRM 979 values between 0.640 and 1.037‰; these Cr isotope compositions are substantially heavier than those of igneous silicate rocks from which the chromium was leached. Precipitation experiments revealed an isotope fractionation of Δ53/52Cr(crocoite–Cr(VI)aq) of only ca. +0.10±0.05‰ at a temperature of 20 °C. Thus, the heavy Cr isotope signature of crocoites is most likely the result of repeated redox cycling of chromium in hydrothermal processes.
  • Article
    Silicon isotope ratios can now be measured to very high precision using high-resolution multi-collector ICP-MS. Based on this technique we report that the Si isotope composition of IRMM- 018 is significantly lighter than the NBS28 standard, in direct contrast to previously published results. Our data are also incon- sistent with recently published absolute Si isotope abundances for these standards by Valkiers et al. (2005) and Ding et al. (2005). Instead, our results are coherent with the certified values for NIST standard SRM990 that was used to determine the atomic weight of Si, with a 30 Si/ 29 Si ratio that is over 6 permil lower for the same atomic weight. In order to avoid problems with future assessments of stable Si isotope variations, the NBS28 silica sand standard (RM8546) should remain the zero point. Therefore, an inter-laboratory calibration of NBS28 and other references ma- terials is recommended to solve the observed discrepancies and establish a reliable scale for reporting Si isotopes.
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    A consistent set of internationally accepted atomic weights has long been an essential aim of the scientific community because of the relevance of these values to science and technology, as well as to trade and commerce subject to ethical, legal, and international standards. The standard atomic weights of the elements are regularly evaluated, recommended, and published in updated tables by the Commission on Atomic Weights and Isotopic Abundances (CAWIA) of the International Union of Pure and Applied Chemistry (IUPAC). These values are invariably associated with carefully evaluated uncertainties. Atomic weights were originally determined by mass ratio measurements coupled with an understanding of chemical stoichiometry, but are now based almost exclusively on knowledge of the isotopic composition (derived from isotope-abundance ratio measurements) and the atomic masses of the isotopes of the elements. Atomic weights and atomic masses are now scaled to a numerical value of exactly 12 for the mass of the carbon isotope of mass number 12. Technological advances in mass spectrometry and nuclear-reaction energies have enabled atomic masses to be determined with a relative uncertainty of better than 1 ×10
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    The isotopic composition of U in nature is generally assumed to be invariant. Here, we report variations of the 238U/235U isotope ratio in natural samples (basalts, granites, seawater, corals, black shales, suboxic sediments, ferromanganese crusts/nodules and BIFs) of ∼1.3‰, exceeding by far the analytical precision of our method (≈0.06‰, 2SD). U isotopes were analyzed with MC-ICP-MS using a mixed 236U-233U isotopic tracer (double spike) to correct for isotope fractionation during sample purification and instrumental mass bias. The largest isotope variations found in our survey are between oxidized and reduced depositional environments, with seawater and suboxic sediments falling in between. Light U isotope compositions (relative to SRM-950a) were observed for manganese crusts from the Atlantic and Pacific oceans, which display δ238U of −0.54‰ to −0.62‰ and for three of four analyzed Banded Iron Formations, which have δ238U of −0.89‰, −0.72‰ and −0.70‰, respectively. High δ238U values are observed for black shales from the Black Sea (unit-I and unit-II) and three Kupferschiefer samples (Germany), which display δ238U of −0.06‰ to +0.43‰. Also, suboxic sediments have slightly elevated δ238U (−0.41‰ to −0.16‰) compared to seawater, which has δ238U of −0.41 ± 0.03‰. Granites define a range of δ238U between −0.20‰ and −0.46‰, but all analyzed basalts are identical within uncertainties and slightly lighter than seawater (δ238U = −0.29‰).
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    This IUPAC study aims at formulating recommendations concerning the metrological traceability of a measurement result in chemistry. It is intended to provide the chemical measurement community with a consistent view of the creation, meaning, and role of metrological traceability and its underpinning concepts. No distinction is made between measurement results obtained in “high metrology” and in the “field”. A description is given of the calibration hierarchies needed in different circumstances to arrive at metrological traceability along a metrological traceability chain. Flow charts of generic calibration hierarchies are presented as well as a variety of examples. The establishment, assessment, and reporting of metrological traceability are discussed, including the provision of metrological references by a metrological institutional framework and the role of interlaboratory comparisons.
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    The modified sample–standard bracketing method (m-SSB) combines a sample–standard bracketing and an inter-element correction procedure to account for instrumental mass fractionation during multi-collector ICP-MS measurements. Precisions for Cu and Zn isotopes in plant and experimental granite leachate samples are in line with those obtained using other mass bias correction techniques. In addition, the inherent temporal drift of mass bias during the analytical session and the empirical linear relationship between dopant and analyte are used to apply independent correction schemes that rigorously check the accuracy of mass bias correction using m-SSB. Consequently, a very robust isotope data set is obtained. We further suggest the use of a matrix-element spike in inter-element doped standards to increase the mass bias variability. This improves the quality of the empirical relationship between dopant and analyte and enables cross-checking of the m-SSB method when instrumental mass bias is stable.
  • Article
    This second, revised and updated edition of a book first published in 1973 aims to provide a basic introduction to the subject. It comprises 3 main chapters. The first (22pp) provides a brief introduction to the theoretical and experimental principles by dealing with composition, isotopic fractionation, exchange, diffusion, and with mass spectrometry. Chapter 2 (46pp) describes in detail the isotopic properties of hydrogen, carbon, oxygen and sulphur, and briefly those of selenium, nitrogen, silicon, boron and alkaline and alkaline earth metals. Topics dealt with for each element include preparation techniques and measurement, standards, fractionation mechanisms and various interactions. The third and main chapter in the book (105pp) deals with variations of stable isotope ratios in a variety of natural situations. These include extraterrestrial materials, igneous rocks, volcanic gases and hot springs, ore deposits, the hydrosphere, atmosphere and biosphere, and sedimentary and metamorphic rocks. - I. McTaggart
  • Article
    Mass discrimination is a variable and unpredictable source of systematic error in mass spectrometric analysis using surface ionization techniques. A method of eliminating it through an internal standard technique is investigated. To simplify the algebra a method of describing mass discrimination has been developed (equations (11)) which is symmetrical with respect to all isotopes in a sample. A set of equations for mixtures of samples with different isotopic compositions is set up and solved for elements with three or four isotopes, four isotopes giving the simplest solutions. The solutions can be applied to quantitative analysis by the isotopic dilution technique, to the measurement of absolute isotopic abundances and to the measurement of relative abundances of samples of polyisotopic elements which have undergone isotopic fractionation. To make the most of these proposals the precision of measurement of ion current ratios from thermal ionization sources must be improved.
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    Isotope reference materials are essential to enable reliable and comparable isotope data. This article reviews the work in this field within the past years. The focus is on all stable elements, except for classical stable isotopes (H, C, N, O, S) and for radioactive elements. Currently available isotope reference materials are listed. The limitations of synthetic isotope mixtures being used to characterize these materials are discussed, as well as the limitations of the isotope reference materials, such as uncertainty and homogeneity. The needs for present research on isotope variations are being considered and are compared to the limitations of current isotope reference materials. This disagreement between both can only be solved by providing isotope reference materials defining a [small delta]-scale for each element of interest. Such materials should be provided with additional data on isotope abundances whenever possible. As an outlook a possible outline for a new program on isotope reference materials is discussed.
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    Full-text available
    We present the first measurements of vanadium (V) stable isotopes for six reference materials – USGS PCC-1, BHVO-2, BCR-2, BIR-1a, GSP-2 and AGV-2 – plus the widely available carbonaceous chondrite Allende. We present standard addition and matrix spiking tests to assess the robustness and reproducibility of our data. Standard addition utilised an enriched ⁵⁰V solution designated VISSOX (Vanadium Isotope Standard Solution OXford). We further assessed the veracity of the method by spiking collected sample matrices with the same amount of a V standard solution, whose isotopic composition was defined as 0‰. Standard addition and matrix spiking tests recorded no appreciable artificial isotope fractionation. We estimate that the best currently attainable long-term reproducibility of stable ⁵¹V/⁵⁰V isotope measurements in complex matrices is 0.15‰, which is in the same order as the reproducibility achievable with standard solutions. Finally, a large range of ∼ 1.2‰ in stable V isotopic composition was documented, with ∼ 0.5‰ of that variation in high temperature igneous materials alone. The range and resolving power of V stable isotopes, with respect to igneous material, compared favourably with the magnitude of fractionation reported for other non-traditional stable isotope systems, which bodes well for the utility of this new system.
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    Full-text available
    The present study evaluates several critical issues related to precision and accuracy of Cu and Zn isotopic measurements with application to estuarine particulate materials. Calibration of reference materials (such as the IRMM 3702 Zn) against the JMC Zn and NIST Cu reference materials were performed in wet and/or dry plasma modes (Aridus I and DSN-100) on a Nu Plasma MC-ICP-MS. Different mass bias correction methods were compared. More than 100 analyses of certified reference materials suggested that the sample-calibrator bracketing correction and the empirical external normalisation methods provide the most reliable corrections, with long term external precisions of 0.06 and 0.07‰ (2SD), respectively. Investigation of the effect of variable analyte to spike concentration ratios on Zn and Cu isotopic determinations indicated that the accuracy of Cu measurements in dry plasma is very sensitive to the relative Cu and Zn concentrations, with deviations of δ⁶⁵Cu from −0.4‰ (Cu/Zn = 4) to +0.4‰ (Cu/Zn = 0.2). A quantitative assessment (with instrumental mass bias corrections) of spectral and non-spectral interferences (Ti, Cr, Co, Fe, Ca, Mg, Na) was performed. Titanium and Cr were the most severe interfering constituents, contributing to inaccuracies of −5.1‰ and +0.60‰ on δ68/64Zn, respectively (for 500 μg l⁻¹ Cu and Zn standard solutions spiked with 1000 μg l⁻¹ of Ti or Cr). Preliminary isotopic results were obtained on contrasting sediment matrices from the Scheldt estuary. Significant isotopic fractionation of zinc (from 0.21‰ to 1.13‰ for δ⁶⁶Zn) and copper (from −0.38‰ to 0.23‰ for δ⁶⁵Cu), suggest a control by physical mixing of continental and marine water masses, characterized by distinct Cu and Zn isotopic signatures. These results provide a stepping-stone to further evaluate the use of Cu and Zn isotopes as biogeochemical tracers in estuarine environments.
  • Article
    This paper presents an adapted anion exchange column chemistry protocol which allowed separation of high-purity fractions of Cu and Zn from geological materials. Isobaric and non-spectral interferences were virtually eliminated for consequent multiple-collector ICP-MS analysis of the isotopic composition of these metals. The procedure achieved ∼ 100% recoveries, thus ensuring the absence of column-induced isotopic fractionation. By employing these techniques, we report isotopic analyses for Cu and Zn from five geological reference materials: BCR-027 blende ore (BCR), δ65Cu = 0.52 ± 0.15‰(n = 10) and δ66Zn = 0.33 ± 0.07% (n = 8); BCR-030 calcined calamine ore (BCR), δ66Zn = -0.06 ± 0.09‰ (n = 8); BCR-1 basalt (USGS), δ66Zn = 0.29 ± 0.12‰ (n = 8); NOD-P-1 manganese nodule (USGS), δ65Cu = 0.46 ± 0.08‰(n = 10) and δ66Zn = 0.78 ± 0.09‰(n = 9); SU-1 Cu-Co ore (CCRMP), δ65Cu = -0.018 ± 0.08‰(n = 10) and δ66Zn = 0.13 ± 0.17% (n = 6). All uncertainties are ± 2s; copper isotope ratios are reported relative to NIST SRM-976, and zinc isotope ratios relative to the Lyon-group Johnson Matthey metal (batch 3-0749 L) solution, JMC Zn. These values agree well with the limited data previously published, and with results reported for similar natural sample types. Samples were measured using a GVi IsoProbe MC-ICP-MS, based at the Natural History Museum, London. Long-term measurement reproducibility has been assessed by repeat analyses of both single element and complex matrix samples, and was commonly better than ± 0.07‰ for both δ 66Zn and δ65Cu.
  • Article
    Fumarolic gases, rocks and condensate samples from Merapi volcano (Indonesia) have been analyzed by multiple collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) for their Zn isotopic compositions. The variation observed, expressed as δ66Zn (δ66Zn = [(66Zn/64Zn)sample/(66Zn/64Zn)JMC 3-049L − 1] 103), ranges from + 0.05‰ to + 1.68‰. The overall reproducibility was found to be better than 0.10‰ (2SD). The δ66Zn of andesitic rock samples are homogeneous with a mean value of + 0.24‰, which is comparable to previously reported basalt data. δ66Zn in the Woro fumerolic field are ranging from + 0.05‰ to + 0.85‰ and + 1.48‰ to + 1.68‰ in fumarolic gases and condensates respectively. Upon cooling from 590 to 297 °C, gaseous Zn concentrations decrease and become increasingly enriched in the lighter Zn isotopes, while the condensates become increasingly enriched in the heavier isotopes. Gas and condensate isotopic compositions can be explained with a Rayleigh condensation model with temperature dependent isotope fractionation factor, α(solid/vapor). Over the 574 °C to 297 °C range of observations, 1000 ln(αsolid/vapour) = C1 + C2/T + C3/T2 (with C1 = 0, C2 =− 0.88 × 103, C3 = 1.00 × 106 and T in degrees Kelvin), which corresponds to α(solid/vapor) of 1.00033 to 1.00153 respectively at the indicated temperatures.
  • Article
    The stable copper isotope composition of 79 samples of primary and secondary copper minerals from hydrothermal veins in the Schwarzwald mining district, South Germany, shows a wide variation in δ65Cu ranging from −2.92 to 2.41‰. We investigated primary chalcopyrite, various kinds of fahlores and emplectite, as well as supergene native copper, malachite, azurite, cuprite, tenorite, olivenite, pseudomalachite and chrysocolla. Fresh primary Cu(I) ores have at most localities copper isotope ratios (δ65Cu values) of 0 ± 0.5‰ despite the fact that the samples come from mineralogically different types of deposits covering an area of about 100 by 50 km and that they formed during three different mineralization events spanning the last 300 Ma. Relics of the primary ores in oxidized samples (i.e., chalcopyrite relics in an iron oxide matrix with an outer malachite coating) display low isotope ratios down to −2.92‰. Secondary Cu(I) minerals such as cuprite have high δ65Cu values between 0.4 and 1.65‰, whereas secondary Cu(II) minerals such as malachite show a range of values between −1.55 and 2.41‰, but typically have values above +0.5‰. Within single samples, supergene oxidation of fresh chalcopyrite with a δ value of 0‰ causes significant fractionation on the scale of a centimetre between malachite (up to 1.49‰) and relict chalcopyrite (down to −2.92‰). The results show that—with only two notable exceptions—high-temperature hydrothermal processes did not lead to significant and correlatable variations in copper isotope ratios within a large mining district mineralized over a long period of time. Conversely, low-temperature redox processes seriously affect the copper isotope compositions of hydrothermal copper ores. While details of the redox processes are not yet understood, we interpret the range in compositions found in both primary Cu(I) and secondary Cu(II) minerals as a result of two competing controls on the isotope fractionation process: within–fluid control, i.e., the fractionation during the redox process among dissolved species, and fluid–solid control, i.e., fractionation during precipitation involving reactions between dissolved Cu species and minerals. Additionally, Rayleigh fractionation in a closed system may be responsible for some of the spread in isotope compositions. Our study indicates that copper isotope variations may be used to decipher details of natural redox processes and therefore may have some bearing on exploration, evaluation and exploitation of copper deposits. On the other hand, copper isotope analyses of single archeological artefacts or geological or biological objects cannot be easily used as reliable fingerprint for the source of copper, because the variation caused by redox processes within a single deposit is usually much larger than the inter-deposit variation.
  • Article
    Over 100 high-precision Fe isotope analyses of rocks and minerals are now available, which constrain the range in δ⁵⁶Fe values (per mil deviations in ⁵⁶Fe/⁵⁴Fe ratios) in nature from −2.50‰ to +1.5‰. Re-assessment of the range of δ⁵⁶Fe values for igneous rocks, using new ultra-high-precision analytical methods discussed here, indicate that igneous Fe is isotopically homogeneous to ±0.05‰, which represents an unparalleled baseline with which to interpret Fe isotope variations in nature. All of the isotopic variability in nature lies in fluids, rocks, and minerals that formed at low temperature. Equilibrium (“abiotic”) isotopic fractionations at low temperatures may explain the range in δ⁵⁶Fe values; experimental measurements indicate that there is a large isotopic fractionation between aqueous Fe(III) and Fe(II) (ΔFe(III)–Fe(II)=2.75‰). However, many of the natural samples that have been analyzed have an unquestionable biologic component to their genesis, and the range in δ⁵⁶Fe values are also consistent with the experimentally measured isotopic fractionations produced by Fe-reducing bacteria.
  • Article
    Full-text available
    First published as an Advance Article on the web 16th October 2003 Multicollector ICP-MS has been used for the precise measurement of variations in the isotopic composition of the isotopic standard of magnesium (SRM980) provided by the National Institute of Standards and Technology (Gaithersburg, MD, USA). The SRM980 consists of metal chips weighing between 1 and 50 mg and each unit delivered by the National Institute of Standards and Technology corresponds to a bottle containing about 0.3 g. Height units were analysed. Variations in sample 25 Mg/ 24 Mg, and 26 Mg/ 24 Mg ratios are expressed as d 25 Mg and d 26 Mg units, respectively, which are deviations in parts per 10 3 from the same ratio in a standard solution. The differences in d 25 Mg and d 26 Mg of the SRM980 are up to 4.20 and 8.19%, respectively, while the long-term repeatability of d 25 Mg and d 26 Mg are 0.09 and 0.16%, respectively, at 95% confidence. However, when plotted in a three-isotope diagram, all the data fall on a single mass fractionation line. Overall limits of error of the SRM980 reported here fall within the previously reported overall limits of error. The isotopic heterogeneity not only corresponds to differences among units but has been found at the chip-size level. This result, due to the precision of the MC-ICP-MS technique, makes the SRM980 inappropriate for the international isotopic standard of magnesium. The SRM980 can still be used to report the excess of 26 Mg, which is defined by the deviation from the mass-dependent relationship between 25 Mg/ 24 Mg, and 26 Mg/ 24 Mg ratios. Two large batches (around 10 g of Mg in each) of pure Mg solutions (in 0.3 M HNO 3) have been prepared and characterised. These 2 solutions (DSM3 and Cambridge 1) are suitable reference material because they are immune to heterogeneity. DSM3 and Cambridge 1 are isotopically different (by 1.3% per u) and are available upon request from the first author. In addition, DSM3 has an isotopic composition very similar to the Mg-isotopic composition of carbonaceous chondrites (Orgueil and Allende). Because of the lack of heterogeneity and the cosmochemical and geochemical significance of DSM3, we urge the use of DSM3 as the primary isotopic reference material to report Mg-isotopic variations.
  • Article
    Full-text available
    This review gives an overview of the literature on reference materials of geochemical and environmental interest for the two-year period 2008–2009. Reference materials play an increasingly important role in all fields of geoanalytical research. This is demonstrated by the large number of publications containing data on reference materials. Although many reference materials exist, there is still a great need for certified samples, so-called delta zero materials for stable isotopic work and homogeneous microanalytical reference materials. This review focuses on six topics: developments of certification processes of reference materials mainly postulated in ISO guidelines and the IAG protocol, new developments of the GeoReM database, investigations of powdered rock reference materials, Chinese reference materials published in Chinese journals, microanalytical reference materials and isotopic reference materials.
  • Article
    A compilation of δ 44/40Ca (δ 44/42Ca) data sets of different calcium reference materials is presented, based on measurements in three different laboratories (Institute of Geological Sciences, Bern; Centre de Géochimie de la Surface, Strasbourg; GEOMAR, Kiel) to support the establishment of a calcium isotope reference standard. Samples include a series of international and internal Ca reference materials, including NIST SRM 915a, seawater, two calcium carbonates and a CaF 2 reference sample. The deviations in δ 44/40Ca for selected pairs of reference samples have been defined and are consistent within statistical uncertainties in all three laboratories. Emphasis has been placed on characterising both NIST SRM 915a as an internationally available high purity Ca reference sample and seawater as representative of an important and widely available geological reservoir. The difference between δ 44/40Ca of NIST SRM 915a and seawater is defined as -1.88 ± 0.04‰ (δ 44/42Ca NIST SRM 915a/Sw = -0.94 ± 0.07‰). The conversion of values referenced to NIST SRM 915a to seawater can be described by the simplified equation δ 44/40CaSa/Sw = δ 44/40CaSa/NIST SRM 915a - 1.88 (δ 44/42Ca Sa/Sw = δ 44/42Ca Sa/NIST SRM 915a - 0.94). We propose the use of NIST SRM 915a as general Ca isotope reference standard, with seawater being defined as the major reservoir with respect to oceanographic studies.
  • Article
    The objective of this study is to determine for the first time the zinc (Zn) isotopic composition of different soil horizons, parent rocks, litter, and plants from a single pristine watershed.Three soil profiles from Nsimi–Zoétélé site (South Cameroon, Africa) have been investigated. The δ66Zn (δ66Zn = [(66Zn/64Zn)sample / (66Zn/64Zn)JMC 3–0749L) − 1] ⁎ 103) measured in the soils and rocks range from − 0.05 to 0.64‰. In a typical hillslope soil profile developed in situ from a granitic parent rock, we observe two important and systematic trends: i) a weathering regime in the saprolite horizon that involves strong Zn depletion, with no or slight fractionation compared to the fresh igneous rock, and ii) a shallower weathering regime with significant depletion in heavy Zn isotopes in the most superficial soil horizons. In contrast, the soil profile of the swamp zone does not exhibit isotopic fractionation between the soil and the parent rock.Six plants and two litter samples were analyzed for their Zn isotopic compositions. δ66Zn varied from 0.75 to − 0.91‰ among all samples. Plant roots and shoots are generally enriched in heavy isotopes (δ66Zn of + 0.42 to + 0.76‰) relative to the litter layer (0.12 to 0.25‰) and most superficial soils. Similar to the controlled plant growth study of Weiss et al. [Weiss, D.J., Mason, T.F.D., Zhao, F.J., Kirk, G.J.D., Coles, B.J. and Horstwood, M.S.A. (2005) Isotopic discrimination of zinc in higher plants. New Phytologist 165, 703-710.], negative δ66Zn values were obtained for tree leaves (the most aerial part of the tree). Based on biomass data for the tropical forest, vegetation is on average enriched in light isotopes compared to the litter and the superficial soil horizons which are the nutrients reservoirs.Due to the age of these soils and the complexity of pedogenetic processes, it is difficult to explain the isotopic composition of the soils at present. However, the transformation of the saprolite horizon into a ferruginous horizon is associated with an enrichment in light Zn isotopes. This observation may be due to the adsorption of Zn onto clays surfaces. The uptake of Zn by roots in the soils leads to an enrichment in heavy isotopes. Once the Zn is in the xylem, it will be transported within the plant. During this transport, both diffusion and active uptake of heavy isotopes by cells out of the xylem favour the mobility of light isotopes to the most aerial parts of the plants.The difference in Zn isotopic composition between the deep horizons and the superficial horizons of soils suggests that Zn isotopes can be used to discriminate the source of Zn and other metals leaving the catchment by river water.
  • Article
    Copper and Zn metals are produced in large quantities for different applications. During Cu production, large amounts of Cu and Zn can be released to the environment. Therefore, the surroundings of Cu smelters are frequently metal-polluted. We determined Cu and Zn concentrations and Cu and Zn stable isotope ratios (δ65Cu, δ66Zn) in three soils at distances of 1.1, 3.8, and 5.3 km from a Slovak Cu smelter and in smelter wastes (slag, sludge, ash) to trace sources and transport of Cu and Zn in soils. Stable isotope ratios were measured by multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) in total digests. Soils were heavily contaminated with concentrations up to 8087 μg g−1 Cu and 2084 μg g−1 Zn in the organic horizons. The δ65Cu values varied little (−0.12‰ to 0.36‰) in soils and most wastes and therefore no source identification was possible. In soils, Cu became isotopically lighter with increasing depth down to 0.4 m, likely because of equilibrium reactions between dissolved and adsorbed Cu species during transport of smelter-derived Cu through the soil. The δ66ZnIRMM values were isotopically lighter in ash (−0.41‰) and organic horizons (−0.85‰ to −0.47‰) than in bedrock (−0.28‰) and slag (0.18‰) likely mainly because of kinetic fractionation during evaporation and thus allowed for separation of smelter-Zn from native Zn in soil. In particular in the organic horizons large variations in δ66Zn values occur, probably caused by biogeochemical fractionation in the soil–plant system. In the mineral horizons, Zn isotopes showed only minor shifts to heavier δ66Zn values with depth mainly because of the mixing of smelter-derived Zn and native Zn in the soils. In contrast to Cu, Zn isotope fractionation between dissolved and adsorbed species was probably only a minor driver in producing the observed variations in δ66Zn values. Our results demonstrate that metal stable isotope ratios may serve as tracer of sources, vertical dislocation, and biogeochemical behavior in contaminated soil.
  • Article
    Whether transition element isotopes can be fractionated at equilibrium in nature is still uncertain. Standard solutions of Cu and Zn were eluted on an anion-exchange resin, and the isotopic compositions of Cu (with respect to Zn) of the eluted fractions were measured by multiple-collector inductively coupled plasma mass spectrometry. It was found that for pure Cu solutions, the elution curves are consistent with a 63Cu/65Cu mass fractionation coefficient of 0.46‰ in 7 mol/L HCl and 0.67‰ in 3 mol/L HCl between the resin and the solution. Batch fractionation experiments confirm that equilibrium fractionation of Cu between resin and 7 mol/L HCl is ∼0.4‰ and therefore indicates that there is no need to invoke kinetic fractionation during the elution. Zn isotope fractionation is an order of magnitude smaller, with a 66Zn/68Zn fractionation factor of 0.02‰ in 12 mol/L HCl. Cu isotope fractionation results determined from a chalcopyrite solution in 7 mol/L HCl give a fractionation factor of 0.58‰, which indicates that Fe may interfere with Cu fractionation.Comparison of Cu and Zn results suggests that the extent of Cu isotopic fractionation may signal the presence of so far unidentified polynuclear complexes in solution. In contrast, we see no compelling reason to ascribe isotope fractionation to the coexistence of different oxidation states. We further suggest that published evidence for iron isotopic fractionation in nature and in laboratory experiments may indicate the distortion of low-spin Fe tetrahedral complexes.The isotope geochemistry of transition elements may shed new light on their coordination chemistry. Their isotopic fractionation in the natural environment may be interpreted using models of thermodynamic fractionation.
  • Article
    Techniques for the high precision measurement of 65Cu/63Cu ratios by multiple-collector plasma-source mass spectrometry has been developed. Two approaches, namely Zn-doping and “sample-standard bracketing”, have been exploited. By using the “sample-standard bracketing” technique, a range of samples including native copper, Cu-carbonate and Cu-sulphides from terrestrial and marine environments have been analysed. An overall variation in 65Cu/63Cu of 22 parts per 104 (22 ε units) is observed. This is more than 30 times the 2 σ analytical uncertainty of the technique employed, and thus demonstrates the great potential for using stable Cu isotopes as tracers in geological and planetary processes. The variations in ε65Cu values observed in this study display some regularity. Those samples involving formation through low temperature aqueous solutions display large differences in ε65Cu values even at a single locality, whereas chalcopyrite samples hosted in igneous rocks show similar Cu-isotope compositions worldwide. This indicates that the ε65Cu variations arise principally through mass fractionation in low temperature aqueous processes, rather than through source heterogeneity. In contrast to continental sulphides, chalcopyrites from black smoker sulphide chimneys on the ocean floor show large variations in ε65Cu values. Relative to active high temperature hydrothermal vents, the old inactive vent deposits are enriched in 63Cu and show smaller variations in ε65Cu values. Within in a single active chimney, Cu isotopes become lighter from bottom to top. This variation pattern is explained tentatively by means of a two-stage-process model, which involves: (1)the preferential leachin65g of 65Cu by hydrothermal processes, and (2)subsequent isotopic exchange between the early formed Cu-sulphides and 65Cu-depleted late-stage hydrothermal fluids. This new capability for Cu-isotope measurement is expected to have a major impact across disciplines ranging from cosmochemistry and geochemistry through biogeochemistry to biochemistry and alimentology.
  • Absolute values have been obtained by means of thermal ionisation mass spectrometry for the iron isotope abundance ratios of a sample of metallic iron of natural isotopic composition. This was achieved by calibrating the mass spectrometric measurement procedure using five different synthetic isotope mixtures, prepared from carefully characterised enriched isotope carrier compounds, viz. ⁵⁴Fe2O3 and ⁵⁶Fe2O3. These mixtures were made up at three different n(⁵⁴Fe)/n(⁵⁶Fe) ratios, covering a ratio range of more than two orders of magnitude, in order to determine the extent of the isotope fractionation in the ion source. Two mixtures bracket the natural ratio, two mixtures have ratio values approximating to unity, and one mixture has a ratio of about 10. The total relative uncertainty on the ratio values of the mixtures varies between 2 and 7 × 10⁻⁴ (2s).
  • Article
    Zinc isotope ratios were measured in the top sections of dated ombrotrophic peat cores in Finland to investigate their potential as proxies for atmospheric sources and to constrain post depositional processes affecting the geochemical record. The peat deposits were located in Hietajärvi, a background site well away from any point pollution source and representing ‘background’ conditions, in Outokumpu, next to a mining site, and in Harjavalta, next to a smelter. Measured total concentrations, calculated excess concentrations and mass balance considerations suggest that zinc is subjected to important biogeochemical cycling within the peat. Significant isotopic variability was found in all three peat bogs, with heavier zinc in the deeper and lighter zinc in the upper sections. Isotope ratios and concentrations correlated in the two peats located next to dominant point sources, i.e. the smelting and mining site, suggesting that zinc isotopes trace pollution sources. Concentration and isotope peaks were offset from the period of mining and smelting activity, supporting migration of zinc down the profile. The δ66ZnJMC (where δ66Zn = [(66Zn/64Zn)sample/(66Zn/64Zn)JMC-standard − 1] × 103) of the top section sample at the remote Hietajärvi site was 0.9‰ and we suggest this represents the regional background isotope signature of atmospheric zinc. The deeper sections of the peat cores show isotopically heavier zinc than any potential atmospheric source, indicating that post depositional processes affected the isotopic records. The large variations encountered (up to 1.05‰ for δ66Zn) and Rayleigh modelling imply that multiple fractionation of zinc during diagenetic alterations occurs and nutrient recycling alone cannot explain the fractionation pattern.
  • Article
    Full-text available
    This contribution reports our preliminary work to determine Cu isotope ratios for various granite rocks and examine the Cu isotope systematics within granite suites. A chemical procedure, modified from Maréchal [Maréchal, C.N., Télouk, P. and Albarède, F., 1999. Precise analysis of copper and zinc isotopic compositions by plasma-source mass spectrometry. Chemical Geology, 156(1–4): 251–273.], was used to separate Cu from rock matrix. Quantitative recovery (100.6 ± 1.6%), with a low total procedural blank (2.65 ± 0.66 ng) for Cu, has been achieved, allowing Cu isotopic measurements on samples with as little as 10 ppm Cu. The Cu isotope ratios (δ65Cu relative to NIST SRM 976) of 32 rock samples, ranging from mafic to felsic compositions, from 3 batholiths (2 I-type, 1 S-type) from the Lachlan Fold Belt in southeastern Australia, vary from − 0.46‰ to 1.51‰. Most of them cluster around zero, with mean values for the I-type and S-type granites of 0.03 ± 0.15‰ and − 0.03 ± 0.42‰ (2 sigma) respectively. These data, together with Cu isotope ratios of two loess samples, provide preliminary evidence that the baseline Cu isotopic composition of the crystalline part of upper continental crust is close to zero. The tight clustering of Cu isotope ratios of rocks from the I-type suites suggests that high-temperature magmatic processes do not produce significant Cu isotope fractionation. However, two granites with abnormally heavy Cu isotope signatures (up to 1.51‰) appears to be the result of localized hydrothermal alteration. Measurable variation in Cu isotopic composition of the S-type granite may reflect isotopic heterogeneity in the sedimentary source region as a result of redox processes or may be due to hydrothermal overprinting. Thus, Cu isotope geochemistry may be a useful tracer for studying hydrothermal alteration and source heterogeneity of granitic rocks.
  • Article
    The measurement of Cu, Fe, and Zn isotopes in natural samples may provide valuable information about biogeochemical processes in the environment. However, the widespread application of stable Cu, Fe, and Zn isotope chemistry to natural water systems remains limited by our ability to efficiently separate these trace elements from the greater concentrations of matrix elements. In this study, we present a new method for the isolation of Cu, Fe, and Zn from complex aqueous solutions using a single anion-exchange column with hydrochloric acid media. Using this method we are able to quantitatively separate Cu, Fe, and Zn from each other and from matrix elements in a single column elution. Elution of the elements of interest, as well as all other elements, through the anion-exchange column is a function of the speciation of each element in the various concentrations of HCl. We highlight the column chemistry by comparing our observations with published studies that have investigated the speciation of Cu, Fe, and Zn in chloride solutions.
  • Article
    We have developed a method for iron isotope analysis by multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) using a 58Fe–54Fe double spike. A 20 min analysis produces mass-bias-corrected iron isotope data with an external reproducibility of ±0.05 (2 SD) on δ56Fe, which represents a decrease in analysis time compared to sample-standard bracketing techniques. The estimation of external reproducibility is based on replicate analysis of the ETH hematite in-house standard. The double spike method has two advantages. First, matrix effects during MC-ICP-MS analysis are decreased with tests showing that accurate iron isotope data can, in some cases, be obtained even when matrix levels exceed iron concentration (Na/Fe, Mg/Fe, and Ca/Fe up to 5, 2, and 0.1, respectively). Because chemical separation reduces matrix/Fe to levels more than three orders of magnitude lower than this, measured Fe isotope compositions are unlikely to be compromised by matrix effects. Second, it is possible to spike samples before chemical purification, which enables any isotopic fractionation effect because of incomplete recovery of iron from a sample to be accounted for. This may be important where obtaining quantitative iron yields from samples is difficult, such as the extraction of dissolved iron from water samples. Fe isotope data on a set of standard reference materials (igneous rocks, ferromanganese nodules, sedimentary rocks, and ores) are presented, which are in agreement with previously published data considering analytical uncertainties. Mantle-derived standard rock samples that are the source of iron for surficial, (bio)geochemical cycling yield a mean δ56Fe of 0.041 ± 0.11‰ (n = 8; 2 SD) with reference to IRMM-14. Hydrothermal and metamorphic calcium carbonate rocks with a relatively low iron content (100–4000 ppm) have δ56Fe = −1.25 to −0.07‰. Structural Fe(II) in hydrothermal calcites has δ56Fe = −1.25 to −0.27‰. The light iron in this range of carbonate minerals may reflect the iron isotope composition of the hydrothermal fluids from which the carbonate precipitated, or the presence of Fe(III) and/or organic material in the hydrothermal fluids during calcite precipitation.
  • Article
    We used ICP–MS to measure the elemental concentrations and isotopic abundances of Cu and Zn in: nine Ti-rich lunar basalts (10017, 10022, 10024, 10057, 70215, 71055, 74255, 75055, and 75075); size-separated samples prepared by sieving of pyroclastic black glass 74001, orange glass 74022, and the lunar soils 15021, 15231, 70181, and 79221; a basalt from the Piton des Neiges volcano, Reunion Island; two samples of Pele’s hairs from the Nyiragongo volcano, Democratic Republic of Congo, and the martian meteorite Zagami.
  • Article
    A new 2 kg batch of SiO2 crystals, IRMM-018a as well as the existing NBS28 silica sand (or RM 8546, obtained by I. Friedman from U.S. Geological Survey) have been characterised for their “absolute” silicon isotope composition and molar mass. The amount-of-substance measurements needed for that purpose were performed on the IRMM amount comparator (Avogadro II) on samples from these batches, which were converted to gaseous silicon tetra-fluoride (SiF4). The isotope amount ratio measurements were calibrated by means of synthesized isotope amount ratios realized in the form of synthetic Si isotope mixtures, the measurement procedure of which makes them SI-traceable.IRMM-018a is intended to be used as Isotope Reference Material for isotope amount measurements in geochemical and other isotope abundance studies of silicon. It is distributed in samples of about 0.1 mol and will replace IRMM-018 (exhausted).
  • Article
    Tektites are terrestrial natural glasses of up to a few centimeters in size that were produced during hypervelocity impacts on the Earth’s surface. It is well established that the chemical and isotopic composition of tektites is generally identical to that of the upper terrestrial continental crust. Tektites typically have very low water content, which has generally been explained by volatilization at high temperature; however, the exact mechanism is still debated. Because volatilization can fractionate isotopes, comparing the isotopic composition of volatile elements in tektites with those of their source rocks may help to understand the physical conditions during tektite formation.
  • Article
    Copper and Zn isotope ratios of well-characterized samples from three ore facies in the Devonian Alexandrinka volcanic-hosted massive sulphide (VHMS) deposit, southern Urals, were measured using multi collector ICP-MS (MC-ICP-MS) and show variations linked to depositional environment and mineralogy. The samples analysed derived from: a) hydrothermal–metasomatic vein stockwork, b) a hydrothermal vent chimney, and c) reworked clastic sulphides. As the deposit has not been significantly deformed or metamorphosed after its formation, it represents a pristine example of ancient seafloor mineralization. Variations in δ65Cu (where δ65Cu = [(65Cu / 63Cu)sample / (65Cu / 63Cu)standard − 1] * 1000) and δ66Zn (where δ66Zn = [(66Zn / 64Zn)sample / (66Zn / 64Zn)standard − 1] * 1000) of 0.63 and 0.66‰, respectively, are significantly greater than analytical uncertainty for both isotope ratios (± 0.07‰, 2σ). Very limited isotopic fractionation is observed in primary Cu minerals from the stockwork and chimney, whereas the Zn isotopic composition of the stockwork varies significantly with the mineralogy. Chalcopyrite-bearing samples from the stockwork have lighter δ66Zn by ∼ 0.4‰ relative to sphalerite dominated samples, which may be due to equilibrium partitioning of isotopically light Zn into chalcopyrite during its precipitation. δ66Zn also showed significant variation in the chimney, with an enrichment in heavy isotopes toward the chimney rim of ∼ 0.26‰, which may be caused by changing temperature (hence fractionation factor), or Raleigh distillation. Post-depositional seafloor oxidative dissolution and re-precipitation in the clastic sediments, possibly coupled with leaching, led to systematic negative shifts in Cu and Zn isotope compositions relative to the primary sulphides. Copper shows the most pronounced fractionation, consistent with the reduction of Cu(II) to Cu(I) during supergene mineralization. However, the restricted range in δ65Cu is unlike modern sulphides at mid oceanic ridges where a large range of Cu isotope, of up to 3‰ has been observed [ [24] and [36]].