Heavy Zn Isotopes Research Articles

Fluid-mediated Cu and Zn isotope fractionation in subduction zones and implications for arc volcanism: Constraints from high pressure veins within eclogites in the Dabie Orogen

High-pressure (HP) veins in eclogites are the products of fluid-rock interaction and provide insight into the composition and evolution of fluids in subduction zones. We here present the Cu and Zn isotope data for different types of HP veins and their host eclogites from Ganghe and Hualiangting in the Dabie Orogen to reveal the behavior of Cu and Zn isotopes during fluid-rock interaction and fluid evolution. The HP veins include omphacite-epidote (Omp-Ep), epidote-quartz (Ep-Qtz), and kyanite-epidote-quartz (Ky-Ep-Qtz) veins. The Omp-Ep veins first crystallized from eclogite-derived, solute-rich fluids with the Ep-Qtz and Ky-Ep-Qtz veins successively crystallizing from the residual fluids after the Omp-Ep vein formation. The early Omp-Ep veins have variably lower δ65Cu (−1.32 to −1.12‰ at Ganghe, −0.70 to −0.66‰ at Hualiangting) but higher δ66Zn (0.36 to 0.38‰ at Ganghe, 0.40 to 0.41‰ at Hualiangting) relative to the host eclogites (δ65Cu: −0.71 vs. 1.84‰, δ66Zn: 0.22 vs. 0.33‰), indicating CuZn isotope fractionation during slab dehydration in subduction zones with the lighter Cu and heavier Zn isotopes preferentially entering the vein-forming fluids from the eclogites. Systematic increase of δ65Cu from the Omp-Ep (−0.70 to −0.66‰) through Ep-Qtz (0.01‰) to Ky-Ep-Qtz veins (0.46 to 0.95‰) can be attributed to isotope fractionation induced by redox changes during the evolution of metamorphic fluids, as revealed by the negative correlations of δ65Cu with redox-sensitive ratios of Fe3+/ΣFe and (Eu/Eu*)N in those veins. Additionally, the higher δ66Zn of the Omp-Ep veins relative to the Ky-Ep-Qtz veins can be explained by equilibrium isotope fractionation between crystallized minerals and evolved metamorphic fluids. Our results thus demonstrate that CuZn isotope fractionation occurred during the evolution of slab-derived metamorphic fluids in subduction zones. Binary mixing calculations show that fluids derived from dehydration of mafic rocks in subducted slabs, represented by the multistage HP veins in the present study, cannot account for the heavier Cu and lighter Zn isotope compositions in most arc magmas than in mid-ocean ridge basalts. This offset can be resolved by addition of forearc serpentinite-derived fluids enriched in heavy Cu and light Zn isotopes into the mantle source of arc magmas.

Zinc Stable Isotope Fractionation Mechanisms during Adsorption on and Substitution in Iron (Hydr)oxides.

The Zn isotope fingerprint is widely used as a proxy of various environmental geochemical processes, so it is crucial to determine which are the mechanisms responsible for isotopic fractionation. Iron (Fe) (hydr)oxides greatly control the cycling and fate and thus isotope fractionation factors of Zn in terrestrial environments. Here, Zn isotope fractionation and related mechanisms during adsorption on and substitution in three FeOOH polymorphs are explored. Results demonstrate that heavy Zn isotopes are preferentially enriched onto solids, with almost similar isotopic offsets (Δ66/64Znsolid-solution = 0.25-0.36‰) for goethite, lepidocrocite, and feroxyhyte. This is consistent with the same average Zn-O bond lengths for adsorbed Zn on these solids as revealed by Zn K-edge X-ray absorption fine structure spectroscopy. In contrast, at an initial Zn/Fe molar ratio of 0.02, incorporation of Zn into goethite and lepidocrocite by substituting for lattice Fe preferentially sequesters light Zn isotopes with Δ66/64Znsubstituted-stocksolution of -1.52 ± 0.09‰ and -1.18 ± 0.15‰, while Zn-substituted feroxyhyte (0.06 ± 0.11‰) indicates almost no isotope fractionation. This is closely related to the different crystal nucleation and growth rates during the Zn-doped FeOOH formation processes. These results provide direct experimental evidence of incorporation of isotopically light Zn into Fe (hydr)oxides and improve our understanding of Zn isotope fractionation mechanisms during mineral-solution interface processes.

Zn isotope signatures in soil Fe[sbnd]Mn nodules with karst high geochemical background

Zn isotope has the potential to be used as an environmental tracer, due to its role in fingerprinting specific sources and processes. However, few studies have focused on Zn isotope system in terrestrial ferromanganese (FeMn) nodules, which is important on understanding the behaviors of Zn in soils. In this study, we analyse the isotopic composition in soil FeMn nodules and surrounding materials from a typical karst region in Guangxi Province, southwestern China and use advanced synchrotron-based methods to characterize Zn speciation. The Zn isotope compositions of the FeMn nodules range from 0.09 to 0.66 ‰, with an average value of 0.24 ‰. Pb isotope fingerprinting reveals that the major material sources contributing to the FeMn nodules are the surrounding soil (δ66Zn: ~0.36 ‰) and partly weathered carbonate bedrock (δ66Zn: ~0.58 ‰), which contain heavier Zn isotopes than the nodules. Synchrotron-based X-ray fluorescence (μ-SXRF) shows that Zn is well correlated with both Fe and Mn. X-ray absorption near edge spectroscopy (XANES) measurements reveal that Zn is associated with both goethite and birnessite phases, with goethite-sorbed Zn accounting for ~76 % of the total Zn and birnessite-sorbed Zn accounting for ~24 %. By combining these new results, the isotopically light Zn in the FeMn nodules compared to their sources can be explained by equilibrium sorption of Zn on goethite and birnessite, during which light Zn is preferentially sorbed. Our study provides important new data on Zn isotope compositions in terrestrial soil FeMn nodules and constrains associated mechanisms, and have implications for using Zn isotopes as environmental tracers.

Zinc Supply Affects Cadmium Uptake and Translocation in the Hyperaccumulator Sedum Plumbizincicola as Evidenced by Isotope Fractionation.

This study employs stable isotope analysis to investigate the mechanisms of cadmium (Cd) and zinc (Zn) interaction in the metal hyperaccumulating plant species Sedum plumbizincicola. To this end, the Cd and Zn isotope compositions of root, stem, leaf, and xylem sap samples were determined during metal uptake and translocation at different Cd and Zn concentrations. The enrichment of light isotopes of both elements in plants during uptake was less pronounced at low metal supply levels, likely reflecting the switch from a low-affinity to a high-affinity transport system at lower levels of external metal supply. The lower δ114/110Cd values of xylem sap when treated with a metabolic inhibitor decreasing the active Cd uptake further supports the preference of heavier Cd isotopes during high-affinity transport. The Δ66Znplant-initialsolution or Δ66Znplant-finalsolution values were similar at different Cd concentrations, indicating negligible interaction of Cd in the Zn uptake process. However, decreasing Zn supply levels significantly increased the enrichment of light Cd isotopes in plants (Δ114/110Cd = -0.08‰) in low-Cd treatments but reduced the enrichment of light Cd isotopes in plants (Δ114/110Cd = 0.08‰) under high Cd conditions. A systematic enrichment of heavy Cd and light Zn isotopes was found in root-to-shoot translocation of the metals. The Cd concentrations of the growth solutions thereby had no significant impact on Zn isotope fractionation during root-to-shoot translocation. However, the Δ114/110Cdtranslocation values hint at possible competition between Cd and Zn for transporters during root-to-shoot transfer and this may impact the transport pathway of Cd. The stable isotope data demonstrate that the interactions between the two metals influenced the uptake and transport mechanisms of Cd in S. plumbizincicola but had little effect on those of Zn.

A Mantle Plume Connection for Alkaline Lamprophyres (Sannaites) from the Permian Tarim Large Igneous Province: Petrological, Geochemical and Isotopic Constraints

AbstractThe origin of lamprophyres associated with large igneous provinces (LIPs) remains controversial, particularly whether they are derived by direct melting of mantle plumes, or from previously metasomatized domains in thermally perturbed subcontinental lithosphere. Here, we report the petrological and geochemical characteristics of a recently identified suite of alkaline lamprophyres (sannaites) that represent the final pulse of magmatism in the Permian Tarim LIP in NW China. The sannaites display porphyritic texture with phenocrysts of olivine, clinopyroxene, hornblende, phlogopite, and titanomagnetite in a groundmass of plagioclase, clinopyroxene, nepheline, hornblende, biotite, and titanomagnetite with minor pyrite and apatite. Carbonate ocelli and almost pure albite in the groundmass are interpreted to have crystallized from immiscible carbonate and hydrous fluids, respectively, produced by late-stage magmatic segregation. The rocks show low to moderate SiO2 (37.7–49.3 wt.%) and MgO (2.74–9.91 wt.%), together with high Fe2O3T (up to 22.7 wt.%) and alkali contents (up to 9.02 wt.% Na2O + K2O). They are characterized by high incompatible element abundances, especially a marked enrichment in large-ion lithophile elements (Rb and Ba) and light rare-earth elements (e.g. La and Ce) relative to P and high-field-strength elements (e.g. Ti). They show a relatively restricted range of δ66Zn values between 0.22‰ and 0.46‰ with an average of 0.37 ± 0.04‰ (2SE, n = 10), which is marginally heavier than that of MORBs (0.27 ± 0.05‰). Their (87Sr/86Sr)t values range from 0.7035 to 0.7061, εNd(t) from −0.97 to +5.62, and δ26Mg from −0.36‰ to −0.17‰ (n = 8), the latter being consistent with those of global MORBs. Based on the correlation between Zn isotopes and TiO2–FeO concentrations, we infer that the heavy Zn isotopes in some of the sannaites resulted from fractional crystallization of Fe–Ti oxide minerals. The whole rock geochemical features of these rocks (negative K anomalies and enrichment in large-ion lithophile elements) and rhyolite–MELTS simulations suggest that the primary magmas of the sannaites were derived from an amphibole-bearing enriched lithospheric mantle source. Metasomatism and related formation of amphibole-bearing metasomatized mantle may be linked to sublithospheric melts/fluids derived from the Tarim plume in the earlier stages of plume activity, rather than slab-derived fluids or carbonate melts as suggested in previous studies for other alkaline mantle-derived magmas. Partial melting may have been triggered by the thermal input from the Tarim plume during a later stage. This study suggests that exotic, alkali-rich magmas can be produced during the multi-stage evolution of large mantle plumes, involving complex cycles of lithospheric mantle metasomatism and later melting of previously enriched domains.

The cadmium and zinc isotope compositions of the silicate Earth – Implications for terrestrial volatile accretion

Zinc and Cd isotope compositions are presented for a comprehensive suite of terrestrial rocks to constrain the extent of Zn and Cd isotope fractionation during igneous processes and better define the δ66Zn and δ114Cd values of the silicate Earth (the δ values denote per mille deviations of 66Zn/64Zn from JMC Lyon Zn and of 114Cd/110Cd from NIST SRM 3108 Cd). Analyses of spinel lherzolites provide a bulk silicate Earth (BSE) δ114CdBSE value of –0.06 ± 0.03 ‰ (2SD). For Zn, the peridotite data of the current and previous studies define a mean δ66ZnBSE = 0.20 ± 0.05 ‰ (2SD). Komatiite analyses of this and published investigations yield similar mean values, which suggests that the Zn and Cd isotope compositions of the mantle remained fairly constant since the Archean. Data for loess provide upper continental crust compositions of δ114Cd = 0.03 ± 0.10 ‰ and δ66Zn = 0.23 ± 0.07 ‰. The Zn isotope and abundance data for peridotites and oceanic basalts are in accord with the previous observation of a mantle array, with basalts having higher Zn concentrations and δ66Zn values than the peridotites. To a first order, this reflects slightly incompatible behaviour of Zn during mantle melting and melt differentiation with associated enrichment of heavy Zn isotopes in the melt phase. Cadmium is marginally more incompatible than Zn during igneous processes and the oceanic basalts also display a minor enrichment of heavy Cd isotopes relative to peridotites. However, secondary processes produce significant Cd isotope variability in both mantle melts and peridotites, obscuring the primary igneous array. The δ66ZnBSE estimates of this and previous studies resemble the Zn isotope compositions of CV and CO carbonaceous and some enstatite chondrites. In contrast, the BSE has a lower δ114CdBSE value than enstatite and carbonaceous chondrites. This implies that the Cd isotope composition of the BSE was either fractionated during accretion or that Earth’s Cd inventory was not exclusively acquired from material related to carbonaceous and enstatite chondrites. Importantly, delivery of Zn and Cd to the BSE solely by CI and CM chondrites is not in accord with the meteorite and terrestrial stable isotope data of these elements.

Environmental implications of land use change on the fate of Zn in agricultural soils: A case study of Puding karst soils, southwest China

Land use change threatens food security because it may cause the depletion and/or low bioavailability of micronutrients in agricultural soils. Therefore, it is significant to investigate the fate of micronutrients and predict the potential environmental problems. The zinc isotope technique is of particular interest in interpreting soil processes. In this study, Zn isotopic data of soil samples in five profiles based on different land uses were provided, and Zn behavior in different soils was discussed. The isotopic ratios of soil samples in the abandoned orchard, secondary forest, abandoned cropland, and cropland are similar, with the δ66Zn varying from 0.15 to 0.29‰. However, the samples in shrub grassland show a lower δ66Zn of 0–0.20‰, which may be affected by anthropogenic sources. For the vertical patterns, the non-cultivated long-rooted plants (i.e., abandoned orchard and secondary forest) show no significant difference in the distribution of δ66Zn, but the patterns of cropland and abandoned cropland samples are reversed. The cropland samples show positive correlations between δ66Zn and Fe2O3 (R2 = 0.90) and MnO (R2 = 0.75), indicating that Fe and Mn oxides preferentially adsorb heavy Zn isotopes on the mineral surfaces. The high affinity between Zn and oxides indicated that the concentration of bio-available Zn in cropland soils was getting lower. As a result, the supplies of micronutrients may be deficient and urged from fertilizer. This study provides a better understanding of Zn cycling in agricultural systems and gives improvements in soil management.

Zn–S isotopic fractionation effect during the evolution process of ore-forming fluids: A case study of the ultra-large Huize rich Ge-bearing Pb–Zn deposit

The fluid evolution process is a key research subject in the field of ore deposit geology. An accurate inversion of the evolution history of ore-forming fluids (OFFs) can play a crucial role in the investigation of mineralisation processes and metallogenesis. In addition, analysing the combination of Zn–S isotopes eliminates the uncertainty and unilaterality of monoisotopic tracing and provides a more accurate interpretation of the evolution of OFFs during the mineralisation process. To trace the migration direction and evolution process of OFFs, based on a collected and tested batch of Zn–S isotope compositions, the characteristics of Zn–S isotopic fractionation and the type of metallogenesis were comprehensively analysed to determine the basis for building a metallogenic model of the Ultra-large scale Huize rich Ge-bearing Pb–Zn Deposit, composed of Kuangshanchang deposit and Qilinchang deposit. Previous studies have shown that OFFs migrate upward from deep sections, whereas stratum brine and atmospheric precipitation containing reduced S migrate downward from shallow sections. Rayleigh fractionation of Zn–S isotopes occurred during the migration and evolution of OFFs, resulting in the accumulation of the heavier isotopes of Zn and S present in the fluids. For example, from shallow to deep sections, δ34S values were 5–9‰ (2400–2200 m), 8.5–17.2‰ (1900–1400 m), and 13.6–15.2‰ (1274 m), the δ66Zn values of ore minerals in Qilinchang were 0.205–0.307‰ (1832–1840 m) and 0.203–0.247‰ (1261 m), while the δ66Zn values of ore minerals in Kuangshanchang were 0.290–0.424‰ (1752 m), 0.169–0.3157‰ (1463 m), and 0.033–0.123‰ (1274 m), respectively. Consequently, the isotopic composition of sulfides exhibited an obvious spatiotemporal zoning. Heavier Zn isotopes and lighter S isotopes gradually accumulated in the sulfides at increasingly shallow depths; temporally, the sulfides gradually enriched in heavier isotopes between the early and late stages of mineralisation.

Climate influence on zinc isotope variations in a loess–paleosol sequence of the Chinese Loess Plateau

Zinc (Zn) is an essential micronutrient, and its isotopes are increasingly applied to understand trace metal biogeochemical cycling. Atmospheric deposition from anthropogenic or natural origins can perturbate the nutrient supply globally. However, our understanding on Zn isotope variations in natural mineral dust and during dust–climate interaction is still rare. This study presents Zn isotope data and leaching experiments with ammonium acetate buffering solution (pH = 5) on a loess–paleosol profile (S0–L3) from the Yimaguan section in the central Chinese Loess Plateau. The loess–paleosol sequence records the contributions from Asian mineral dust accumulation and chemical weathering, and the response to glacial–interglacial climate changes. Bulk loess–paleosol samples display limited Zn/Al (3.5 × 10-4 – 4.5 × 10-4) and δ66Zn variations (0.17–0.30‰). The mean δ66Zn of paleosol (0.19 ± 0.01‰, 2SD/√n, n = 11) is slightly lower than that of loess (0.24 ± 0.01‰, 2SD/√n, n = 13). Correlations with magnetic susceptibility and grain size distribution suggest that bulk δ66Zn variations between loess and paleosol are not sensitive to glacial–interglacial source fluctuations or wind sorting, but could result from loess pedogenesis.The leachable Zn fractions have high δ66Zn values (0.80–1.29‰) and display good positive correlations with Ca, Sr, Mg, Fe and Mn (r > 0.7), suggesting that carbonates are enriched in heavy Zn isotopes. Although Zn contents in carbonates are low (<3%) and dissolution of carbonates alone cannot explain the bulk Zn/Al variations (∼7% of Zn loss), significant carbonate weathering and biotic activities during loess pedogenesis could modify soil conditions (pH) and provide dissolved bicarbonate ions and organic ligands, which may facilitate the transport of heavy Zn isotopes by soil liquids. Conversely, the bulk δ66Zn of loess developed during glacial times were not modified by the low degree of chemical weathering, and thus the mean value of 0.24‰ for loess can be regarded as the average composition of the upper continental crust.

Iron-Copper-Zinc Isotopic Compositions of Andesites from the Kueishantao Hydrothermal Field off Northeastern Taiwan

The studies of iron (Fe), copper (Cu), and zinc (Zn) isotopic compositions in seafloor andesites are helpful in understanding the metal stable isotope fractionation during magma evolution. Here, the Fe, Cu, and Zn isotopic compositions of andesites from the Kueishantao hydrothermal field (KHF) off northeastern Taiwan, west Pacific, have been studied. The majority of δ56Fe values (+0.02‰ to +0.11‰) in the KHF andesites are consistent with those of MORBs (mid-ocean ridge basalts). This suggests that the Fe in the KHF andesites is mainly from a MORB-type mantle. The Fe-Cu-Zn isotopic compositions (δ56Fe +0.22‰, δ65Cu +0.16‰ to +0.64‰, and δ66Zn +0.29‰ to +0.71‰) of the KHF andesites, which are significantly different from those of the MORBs and the continental crust (CC), have a relatively wide range of Cu and Zn isotopic compositions. This is most likely to be a result of the entrainment of the sedimentary carbonate-derived components into an andesitic magma. The recycled altered rocks (higher δ56Fe, lower δ66Zn) could preferentially incorporate isotopically light Fe and heavy Zn into the magma, resulting in relative enrichment of the lighter Fe and heavier Zn isotopes in the andesites. The majority of the δ56Fe values in the KHF andesites are higher than those of the sediments and the local CC and lower than those of the subducted altered rocks, while the reverse is true for δ66Zn, suggesting that the subseafloor sediments and CC materials (lower δ56Fe, higher δ66Zn) contaminating the rising andesitic magma could preferentially incorporate isotopically heavy Fe and light Zn into the magma, resulting in relative enrichment of the heavier Fe and lighter Zn isotopes in the andesites. Thus, the characteristics of the Fe and Zn isotopes in back-arc and island-arc volcanic rocks may also be influenced by the CC and plate subduction components.

Copper and Zinc isotope signatures in scleratinian corals: Implications for Cu and Zn cycling in modern and ancient ocean

Metal stable isotopes in marine carbonates have been widely used as novel proxies for metal cycling through the geological past. Amongst these metals, copper (Cu) and zinc (Zn) have received great attention owing to their vital roles in metabolic processes. However, whether modern marine biogenic carbonates record the seawater isotope signatures of Cu (δ65Cu) and Zn (δ66Zn) and mechanisms and factors controlling isotope fractionation of these metals remain unclear, hindering applications of both isotope systems in paleoceanography. Here we present annually-resolved records of δ65Cu and δ66Zn in seven coral (Porites) cores sampled from different marine settings in the South China Sea and the Luzon Strait, western Pacific. We find that the aragonitic skeletons of corals are enriched in light Cu but heavy Zn isotopes relative to surface seawaters, with δ65Cu and δ66Zn in the range of −0.16 ± 0.06‰ to 0.40 ± 0.05‰ and 0.06 ± 0.04‰ to 0.46 ± 0.08‰ (2SD), respectively. The coral δ65Cu exhibits significant inter- and intra-colony variations, which are most likely controlled by Rayleigh-type fractionation in the calcifying fluids of corals rather than by changes in environmental factors or seawater δ65Cu. We thus suggest that δ65Cu in ancient carbonates may not be a direct record of Cu isotope compositions in coeval seawaters. In contrast, coral δ66Zn shows insignificant temporal variation, and the Zn isotope fractionation between individual corals and seawaters are relatively small and constant (0.10 ± 0.05‰, n = 33, 2SD). This limited Zn isotope fractionation is much lower than that determined during inorganic precipitation of calcite, which is likely due to pH up-regulation by the coral that changes aqueous Zn speciation, and preferential organic complexation of the heavy Zn isotopes in the calcifying fluids. Therefore, Porites corals are promising archives for tracking historical changes of surface seawater δ66Zn. Our new datasets of reef carbonates, particularly the coral δ65Cu values which are measured for the first time, could provide a better constrain on marine Cu and Zn geochemistry and their modern oceanic mass and isotope budgets.

Isotopic signatures reveal zinc cycling in the natural habitat of hyperaccumulator Dichapetalum gelonioides subspecies from Malaysian Borneo

BackgroundSome subspecies of Dichapetalum gelonioides are the only tropical woody zinc (Zn)-hyperaccumulator plants described so far and the first Zn hyperaccumulators identified to occur exclusively on non-Zn enriched 'normal' soils. The aim of this study was to investigate Zn cycling in the parent rock-soil-plant interface in the native habitats of hyperaccumulating Dichapetalum gelonioides subspecies (subsp. pilosum and subsp. sumatranum). We measured the Zn isotope ratios (δ66Zn) of Dichapetalum plant material, and associated soil and parent rock materials collected from Sabah (Malaysian Borneo).ResultsWe found enrichment in heavy Zn isotopes in the topsoil (δ66Zn 0.13 ‰) relative to deep soil (δ66Zn -0.15 ‰) and bedrock (δ66Zn -0.90 ‰). This finding suggests that both weathering and organic matter influenced the Zn isotope pattern in the soil-plant system, with leaf litter cycling contributing significantly to enriched heavier Zn in topsoil. Within the plant, the roots were enriched in heavy Zn isotopes (δ66Zn ~ 0.60 ‰) compared to mature leaves (δ66Zn ~ 0.30 ‰), which suggests highly expressed membrane transporters in these Dichapetalum subspecies preferentially transporting lighter Zn isotopes during root-to-shoot translocation. The shoots, mature leaves and phloem tissues were enriched in heavy Zn isotopes (δ66Zn 0.34–0.70 ‰) relative to young leaves (δ66Zn 0.25 ‰). Thisindicates that phloem sources are enriched in heavy Zn isotopes relative to phloem sinks, likely because of apoplastic retention and compartmentalization in the Dichapetalum subspecies.ConclusionsThe findings of this study reveal Zn cycling in the rock-soil-plant continuum within the natural habitat of Zn hyperaccumulating subspecies of Dichapetalum gelonioides from Malaysian Borneo. This study broadens our understanding of the role of a tropical woody Zn hyperaccumulator plant in local Zn cycling, and highlights the important role of leaf litter recycling in the topsoil Zn budget. Within the plant, phloem plays key role in Zn accumulation and redistribution during growth and development. This study provides an improved understanding of the fate and behaviour of Zn in hyperaccumulator soil-plant systems, and these insights may be applied in the biofortification of crops with Zn.

Zn isotope fractionation during the development of low-humic gleysols from the Mun River Basin, northeast Thailand

Zinc (Zn) is an essential micronutrient released into soils during rock weathering, and Zn isotope composition has been emerging as a powerful tracer involved in the Earth’s surface processes. To explore the soil development in dry tropical regions and evaluate the influence on the global Zn cycles, stable Zn isotope data were presented for the two pristine low-humic gleysol profiles from the Mun River Basin (MRB), northeast Thailand. The samples exhibit the δ66Zn (relative to JMC 3-0749L standard) from −0.69‰ to 0.32‰. Therein, the Fe nodule-containing soils exhibit a light shift of δ66Zn relative to parent red siltstones (Δ66Znnodule-containing soil–p of S1 = −0.60‰) and the other soils (Δ66ZnII-other zones = −0.66‰ – −0.50‰), indicating that the preferential retention of light Zn isotopes in residual soils is attributed to the adsorption of heavy Zn isotopes onto the surface of secondary Fe oxides. Due to the water insufficiency in the MRB, the redox conditions to control the oxide precipitation are driven by the seasonal alteration of groundwater levels. With the recession of groundwater, Fe oxides precipitate and adsorb heavy Zn isotopes. Besides, heavy Zn isotopes are also incorporated in clay fraction. On the contrary, the saturated water is likely to disrupt the interactions of Zn with Fe phases and clay minerals. In addition, low content of organic matter and Mn oxides and the absence of sulfides limitedly contribute to the light Zn pool in soils. Conclusively, the isotopic signature of Zn indicates that Fe oxide-rich soils are likely to control the heavier Zn isotope composition of dissolved load in rivers relative to continental rocks in dry tropical regions.

Mantle source of tephritic porphyry in the Tarim Large Igneous Province constrained from Mg, Zn, Sr, and Nd isotope systematics: Implications for deep carbon cycling

AbstractThe nature and source of magmatism associated with large igneous provinces (LIPs) remain disputed. Here we investigate the role of recycled materials that contributed to mantle heterogeneity in the Tarim Large Igneous Province (TLIP) in China through integrated Zn–Mg–Sr–Nd isotopes of a rare tephritic rock suite. The Sr–Nd isotopes [(87Sr/86Sr)i = 0.70368–0.70629; εNd(t) = −0.25–4.64] and δ26Mg values (−0.23&amp;#x89; to −0.34&amp;#x89;) of the tephritic porphyries are consistent with a normal mantle origin. In contrast, the whole rock and pyroxene phenocrysts yield δ66Zn values of +0.28&amp;#x89; to +0.46&amp;#x89; and +0.30&amp;#x89; to +0.39&amp;#x89;, which are slightly heavier than those of the terrestrial mantle (+0.16 ± 0.06&amp;#x89;) and mid-oceanic-ridge basalts (MORBs) (+0.27 ± 0.05&amp;#x89;). We exclude the possibility that the heavy Zn isotopes of the Wajilitag tephritic porphyries are caused by magmatic processes such as fractional crystallization and partial melting and correlate the isotopic features to the role of altered oceanic crust along with magnesite in the mantle source. The Wajilitag tephritic porphyry displays trace-element patterns similar to those of the melts from natural hornblendite, especially those of hornblendite + peridotite. Additionally, the geochemical characteristics such as enrichment in Nb and Ta, depletion in K, high TiO2, and constant Na2O/K2O ratios also suggest that the tephritic porphyries were derived from an amphibole-bearing source contributed by altered oceanic crust along with sedimentary carbonates. Our study provides insight into the contribution of subducted materials to the mantle heterogeneity beneath the TLIP and highlights the role of subduction in the deep carbon cycle and subducted slab-lithosphere-plume interaction in the generation of LIPs.

Zn-isotopic evidence for fluid-assisted ore remobilization at the Balmat Zinc Mine, NY

Shear zone-hosted ore bodies at the Balmat, NY, zinc deposit were remobilized at the kilometer scale during amphibolite facies metamorphism ca. 1180 Ma. Despite there being little evidence for interaction of hydrous fluids with ores during deformation, such translocation distances are considered unlikely without the assistance of fluids. Measurements of Zn isotopic composition of sphalerite from six Balmat ore bodies that originated from the same stratigraphic level (Upper Marble unit 6) reveal variation between ore bodies, as well as intra-orebody trends of isotopic lightening down plunge. In general, increasing distance of remobilization correlates with decreasing δ66Zn. The syn-tectonic isotopic fractionation recorded in Balmat sphalerite is interpreted to have resulted from the interaction between the ore and sulfide melts that were fluxed by H2S localized primarily in Upper Marble unit 7 (fetid dolomite). Lighter isotopes of Zn were enriched in the melt, leaving the residual ore enriched in heavier Zn isotopes. These observations support previous petrographic evidence for the presence of anatectic melts at Balmat and help to explain the unusual scale of translocation at Balmat by means of fluid-assisted remobilization during which intergranular melts decreased rock competency.

Assessment of coupled Zn concentration and natural stable isotope analyses of urine as a novel probe of Zn status.

Zinc is a common trace metal in the human body, present in about 10% of proteins. Despite numerous roles of Zn in health and disease, there is still a need for a robust biomarker of Zn status. Many parameters have been proposed, with varying levels of success, with plasma Zn often favoured. This study investigates if Zn status can be assessed from the natural stable Zn isotope composition of urine. To this end, 60 urine samples were analysed from ten healthy participants. Remarkably, samples with lower Zn concentrations are systematically enriched in heavy Zn isotopes. Most of the low-Zn urine originated from individuals who omitted dairy, meat or both from their diets. When data for blood serum from age-matched, healthy individuals are compared with the urine results, the former plot at the extension of the urine trend at higher Zn concentrations and lighter isotope compositions. The observed co-variation of Zn isotope compositions with concentrations is indicative of an isotope fractionation system where both properties are controlled by the same processes. It is interpreted as arising from filtration and/or reabsorption processes within the kidney, which are associated with absorbed dietary Zn. The data suggest that the Zn in blood serum that is bound to low molecular weight molecules has an isotope composition distinct from total serum, due to the different affinities of molecular Zn-binding residues to heavy and light Zn isotopes. This technique provides additional information into an individual's Zn status compared to urine or plasma Zn levels alone.

Zn isotope fractionation during uptake into marine phytoplankton: Implications for oceanic zinc isotopes

The extreme scarcity of zinc (Zn) in the euphotic zone, coupled to deep enrichments, is consistent with biological uptake at the surface and regeneration at depth. In the context of a nutrient-type depth profile so clearly shaped by uptake into phytoplankton, the growing dataset for Zn isotopes presents a challenge. These data either show very minor isotope effects associated with extreme depletion, or enrichment of the light isotopes in the upper ocean. In contrast, culturing of eukaryotes in the laboratory suggests that light Zn isotopes are preferentially taken up into diatoms and coccoliths, implying that Zn depletion at the surface should be associated with extremely heavy residual dissolved signals.Here we present the first Zn isotope measurements for cultured marine cyanobacteria and compare these data to those for eukaryotic diatoms grown under identical conditions. Of the four cyanobacteria cultured, belonging to the genera Synechococcus and Prochlorococcus, three preferentially take up light Zn into the cell, with a variability that is not fundamentally different between pro- and eukaryotic phytoplankton. We also observe only very subtle differences between Zn/P and Fe/P uptake ratios for these three cyanobacteria groups relative to diatoms grown under the same conditions. A fourth strain exhibits preferential uptake of heavy Zn isotopes, and very high Zn/P ratios. Overall, we speculate that the observed variability among cyanobacteria may be related to the molecular structure of their photosynthetic light harvesting apparatus, adapted to significantly different light niches.These new and published culture data support the hypothesis that cellular δ66Zn in culture might largely be controlled by the organic ligands that bind Zn in the medium. Given that the Zn-binding ligands in the ocean have thermodynamic stability constants that are orders of magnitude smaller than the EDTA used in culture media, the surprisingly subtle Zn isotope variability in some parts of the surface ocean may be reconciled with culture data by the lesser, near zero, preference of these weaker complexes for heavy Zn isotopes.“This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean - GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.”

Two episodes of sulfide mineralization at the Yuhuang-1 hydrothermal field on the Southwest Indian Ridge: Insight from Zn isotopes

The newly discovered Yuhuang-1 hydrothermal field (YHF) on the Southwest Indian Ridge primarily contains two different sulfide distribution areas: the southwest sulfide (SWS) and the northeast sulfide (NES) distribution areas. In this study, Zn isotope compositions and element ratios of Zn, Fe, Cu, and Cd in the surface sulfides were analyzed to characterize Zn isotopic fractionation, ore-forming conditions, and mineralization processes of the YHF. The results indicate that sulfide-rich samples in the YHF exhibit intensive Zn isotopic fractionation, with δ66Zn values ranging from −0.43‰ to 1.24‰. These values are not only larger than those currently reported for seafloor sulfides but are also larger than the values reported for the deposits on land. Remarkably, the obtained δ66Zn value (−0.43‰) is the lowest one observed in seafloor sulfides (−0.26‰–1.17‰), currently. A study of Zn isotope systematics revealed that Zn isotope variations of sulfide-rich samples in the YHF were controlled by the sphalerite and pyrite content; the study also revealed that early minerals are rich in light Zn isotopes, but later minerals are rich in heavy Zn isotopes. A comparative study of previous data on Zn isotopes shows that Zn isotope fractionations in the YHF are likely attributed to Rayleigh fractionation, caused by mineral precipitation and multiple generations of pyrite. Further, Zn/Cd ratios of sulfide-rich samples indicate that the ore-forming temperature of the silicified sulfide-rich samples in the SWS probably formed under lower temperatures as compared with the silicified sulfide-rich chimney in the NES. Furthermore, sulfur and Zn isotope compositions in the SWS are significantly different from those in sulfide-rich samples of the NES, which suggests pervasively different metallogenic conditions, further indicating that they are probably products of separate mineralization episodes.

A global assessment of Zn isotope fractionation in secondary Zn minerals from sulfide and non-sulfide ore deposits and model for fractionation control

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.

Stable isotope fractionation of zinc and cadmium in soil-plant system: A review

Stable isotope fractionation provides a useful tool for tracing the transfer of zinc (Zn) and cadmium (Cd) in the soil-plant system. Isotope fractionation processes include equilibrium fractionation, e.g. dissolution, complexation, precipitation, and kinetic fractionation, e.g. diffusion and evaporation. Therefore, isotope fractionation of metallic element can be used to study the mechanisms of metal translocation in biogeochemical cycling. With the development of multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS), Zn and Cd isotopic composition in soil and plant samples can be accurately measured. The determination of Zn and Cd stable isotope ratios usually includes sample digestion, purification and mass discrimination correction. In the soil-plant system, plants are generally enriched with heavy Zn isotopes in comparison to soils, while roots are enriched with heavy Zn isotopes in comparison to shoots. For Cd, shoots are likely to be isotopically heavier than roots. The transport processes of Zn/Cd in the soil-plant system mainly involve transport in rhizosphere, root uptake and transport within plants. The adsorption and desorption of Zn/Cd by soil minerals can affect the metal mobility and the isotope fractionation between soil solid phases and soil solution. Heavy Zn isotopes are likely to be complexed, while light Zn isotopes are more mobile in soil solution. Conversely, soil minerals tend to adsorb light Cd isotopes, thereby resulting in an enrichment with heavy isotopes in the soil solution. Among the rhizospheric processes, the secretion of root exudates and the changes in pH also have an impact on the speciation and translocation of heavy metals, which lead to the release of heavy Zn isotopes into soil solution. Root uptake process is of pivotal importance for the determination of the isotopic composition of the whole plant. The diffusion of Zn2+ from the soil solution to the root surface leads to a light isotopes enrichment in plant. Heavy Zn isotopes are preferentially chelated or precipitated in the root apoplast. During the transport across the root cell membranes, the low-affinity transport leads to an enrichment with light isotopes in plant, while the high-affinity transport generates little or no isotope fractionation. Specific transporter of Cd in roots has never been found yet. Therefore, Cd may be took up mainly through low-affinity transport systems and thus be enriched in light isotopes in plants. The isotope fractionation between roots and shoots is related to the sequestration of Zn/Cd in roots and the xylem transport processes. The functional groups containing oxygen and nitrogen of organic acids in plant roots tend to chelate heavy Zn isotopes, with subsequent compartmentation in root vacuoles. The light Zn isotopes could be then loaded by the xylem and transferred to the aboveground parts. Interestingly, the intensity of isotope fractionation is mainly related to the transport distance in the xylem. Contrary to Zn, light Cd isotopes mainly bind to the thiol groups in roots, leading to the enrichment in heavy isotopes in shoots. The different behaviors between Zn and Cd in isotope fractionation in the soil-plant system could reflect the distinct accumulation and tolerance mechanisms of plants in response to Zn or Cd stress.