Chemie Der Erde-Geochemistry最新文献

The Iberian Pyrite Belt (IPB) is a late Devonian – Early Carboniferous world-class polymetallic VMS province that includes significant Cu-(Sn)-Pb-Zn-(Ag) deposits of massive sulphides and feeder zones. The Aljustrel brownfield region contains one of the highest concentrations of ore in the IPB in 6 known deposits (Gavião, São João, Moinho, Algares, Estação and Feitais). To delve into the petrogenesis of the Aljustrel early Carboniferous (∼355 Ma) felsic-dominated bimodal volcanism, new whole-rock trace elements and SmNd isotopes, and UPb in zircon were obtained.

Based on Ga/Al and Y/Nb ratios, it is shown that Aljustrel felsic magmatism has the geochemical features of A2-type melts, typical of post-collisional and back-arc settings. UPb in zircon for a juvenile felsic volcanic rock point to antecrysts ages spanning from 387.9 to 366.6 Ma and a maximum emplacement age of 354.3 ± 2.6 Ma. These long-lasting melting events, present in both juvenile (ƐNdi = +1.79) and evolved felsic rocks (ƐNdi = −5.07), imply heterogeneous sources dominated by zircon-bearing igneous rocks. The SmNd model ages are in accordance with previous LuHf model ages in zircon, reinforcing that the isotopic variability is related to the same petrogenetic process.

Subordinated Aljustrel mafic rocks, coeval with the abundant felsic volcanism, show orogenic signatures, namely Nb-Ta-Ti negative anomalies and calc-alkaline affinities, whereas SmNd isotopic data (ƐNdi = +1.54 to +5.48) points to variable to no contamination with crustal material. These geochemical results suggest derivation from an enriched mantle source modified by subduction metasomatism. In addition, the mafic rocks did not provide zircons for geochronological analysis, with the exception of one sample, in which a Concordia age of 402.1 ± 15.5 Ma was obtained from a single grain.

The combined geochemical signatures of mafic and felsic volcanic rocks suggest asthenospheric rise, but this solely does not explain the abundance of zircon antecrysts in the felsic rocks. Therefore, a geodynamic model that includes a continuous evolution from Devonian to Carboniferous times is inferred. This more complex and broader geodynamic model for the Iberian Pyrite Belt in which successive metal remobilization occurred after successive melting events, fits the present geochemical data and is more likely to explain why the Iberian Pyrite Belt is a unique metallogenetic province.

The Zijinshan district, Fujian Province, southeastern China, is a globally renowned CuAu orefield and hosts a wide variety of ore deposits within the Zijinshan granite complex and surrounding volcano-sedimentary rocks. We performed FeS isotope analysis on pyrite separates from the Zijinshan high-sulfidation epithermal deposit, Yueyang intermediate-sulfidation epithermal deposit, Wuziqilong transition-type (from high-sulfidation epithermal to porphyry) deposit, and Jintonghu porphyry CuMo deposit, aiming to understand the formation process of Fe-sulfides and the evolution of ore-forming fluids in different deposits. Pyrites from the Jintonghu porphyry CuMo deposit show variations in δ⁵⁶Fe and δ³⁴S from −0.15 ‰ to 0. 45 ‰, and from 1.81 ‰ to 2.70 ‰, respectively. In contrast, pyrites from epithermal-type deposits (i.e., Zijinshan, Yueyang, and Wuziqilong) show a negatively shifted Fe isotopic composition from −1.74 ‰ to 0.45 ‰. The combination of Fe isotopic data from the Jintonghu porphyry CuMo deposit with published minerals-fluid fractionation factors and the use of a Rayleigh fractionation model allowed us to determine the δ⁵⁶Fe range of regional ore-forming fluids (−1.00 ‰ to −0.40 ‰), which is consistent with the previous “light fluid” hypothesis, suggesting that pyrite of porphyry CuMo deposits has isotopic compositions reflecting the isotopic value of the hydrothermal fluids. For the epithermal deposits, pyrite Fe isotopic composition is the result of a complex interaction of Rayleigh fractionation, rapid precipitation and kinetic fractionation, and δ⁵⁶Fe values of the initial fluids is difficult to estimate. Integrating the Fe and S isotope data for pyrite of different genesis, we found that porphyry CuMo deposits (δ⁵⁶Fe: −0.9 ‰ to 0.46 ‰; δ³⁴S: −4.06 ‰ to 3.9 ‰) can be distinguished from a non-magmatic/low-temperature region, while the transitional area of which may be a porphyry-related hydrothermal deposit (i.e., epithermal deposit). In general, we suggest that the Fe and S isotopic signatures of pyrite can effectively distinguish porphyry-type deposits from their associated hydrothermal deposits.

Lead isotopes are useful in determining the source of metals in environment, and studies on lead isotopic characteristics of mineral deposits have provided important insights for economic geologists, archaeologists and environmental scientists over the past 50 years. This study reports new Pb isotope and trace element data of sulfide minerals from 25 mineral deposits in Japan in order to partly update the data set reported in the 1980s, which have long been used for provenance studies. The analytical precision of the Pb isotope ratios, measured by multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) in this study, is an order of magnitude higher than the previous data set, allowing regional- and deposit-level discrimination of isotopic signatures. The Pb isotope ratios of vein-type or intrusion-centered Japanese deposits from this study (²⁰⁶Pb/²⁰⁴Pb = 18.151–18.545, ²⁰⁷Pb/²⁰⁴Pb = 15.552–15.642, ²⁰⁸Pb/²⁰⁴Pb = 38.389–38.918) are mostly within the range of data from Japanese deposits of the same type measured in previous studies but tend to have slightly lower ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios. This is likely be due to the differences in analytical instrumentation and isotopic variations within the deposit, which should carefully be considered in future regional-scale provenance studies. Data from the Sai, Ohizumi, Budo and Shiraita deposits in Northeast Japan as well as the Kishu and Tokoo deposits in Southwest Japan indicate a two-component mixing presumably involving magma and meteoric fluid. The isotopic variation within each of these deposit is much smaller compared to previously reported variations within volcanogenic massive sulfide deposits in Japan, indicating a relatively uniform metal source with only a small contribution from basement rocks. In contrast, Daira and Ani deposits in Northeast Japan have highly variable isotopic characteristics similar to volcanic rocks with lower crustal assimilation, indicating an additional input of material from the lower crust.

Proterozoic terrains of the Anti-Atlas belt (Morocco) represent one of the key areas for studying the Precambrian geodynamics of the northwestern West African craton (WAC). Voluminous Paleoproterozoic granitoids, which outcrop in the basement of the Precambrian inliers of the southern Anti-Atlas, are conventionally regarded as vestiges of a magmatic arc constructed during incipient subduction on Earth. However, except for their calc-alkaline, arc-like signatures, little evidence supports the existence of this arc system and the sources and tectonic context of these granitoids remain elusive. In this study, we present new whole-rock major- and trace-element, and Sr-Nd isotope composition, and in situ zircon U-Pb ages of the composite granitoid intrusions from the Bas Draa inlier. We obtained Rhyacian ages for the quartz-diorite (~2059 ± 6 Ma) and leucogranite (~2051 ± 6 Ma), and Orosirian age for the biotite-bearing granite (~2022 ± 7 Ma). The studied magmatic rocks are classified into three groups according to their petrographic features and chemical composition: a) layered, sanukitoid quartz-diorites, b) biotite-muscovite (i.e., two-mica) leucogranites, and c) biotite-bearing, hybrid granites. All three groups of magmatic rocks share a common geochemical composition with late Archean granites worldwide, including a high Mg# (52.9–64), and Ni (average 40 ppm), Cr (10–250 ppm) and V (139-238 ppm) content. The identification of mantle-derived sanukitoids and hybrid granites, combined with the absence of first-order evidence for subduction, obduction, and collision, as commonly observed in Neoproterozoic and Phanerozoic orogens worldwide (i.e., blueschist facies metamorphics, ophiolites, and accretionary prism units), contests the theory for the onset of plate tectonics during Early Paleoproterozoic in the Anti-Atlas. We instead propose that the available data rather suggests that vertical tectonics, characteristic of the Archean, still prevailed in this domain throughout the Early Proterozoic times.

In order to present a new petrological approach to quantify mass transfer redistribution, especially regarding chemical zonation, published data of a centimeter sized aluminium-rich clinopyroxene from the Bergen Arcs in Norway is used. The sample comes from the island of Holsnøy where the dry granulite-facies protolith underwent hydration reaction under amphibolite-facies conditions. This aluminium-rich clinopyroxene developed kinks during deformation along which fluid has been introduced. It reacted in two different ways: to garnet plus a less aluminous pyroxene along kinks and to chlorite along cleavage planes. Compositional maps from electron probe microanalyzer (EPMA) were coupled to the mass balance equation of Gresens (Gresens, 1967) to quantify for each pixel present in a studied surface area, element gains and losses, density changes and solid volume variations. This new method allows to estimate the solid volume variation associated with the reaction by assuming minimal mass transfer, or by considering an immobile element i.e. aluminium immobile or by preserving the mass during the reaction. Results demonstrate that for all three assumptions made, the actual mass behaviour does not change significantly for major elements as opposed to the solid volume variation and the actual sum of mass transfer. In the high strain domain (kink) the element losses and gains in replacing the aluminium-rich clinopyroxene by garnet, are balanced by the opposite gains and losses associated with the less aluminous clinopyroxene. This implies that the local fluid chemical composition required for the formation of one mineral is equal to that in equilibrium with the second one after the reaction. The same observation can be made regarding solid volume variation that is balanced between garnet and the less aluminous clinopyroxene. Considering now the specific reaction in the kink and outside the kink (chlorite), mass transfer and redox conditions (Fe³⁺ and Fe²⁺) tend to behave in the same way supposing a temporal relationship between these two parageneses.

The eastern flank of the Talesh range of western Alborz, northwestern Iran, exposes volumetrically significant Late Cretaceous volcanic and volcaniclastic associations as well as cross-cutting dykes and minor subvolcanic equivalents. The volcanic units appear as massive to pillowed flows interlayered with volcaniclastic beds and subordinate limestones. We present new field data, zircon UPb ages, bulk-rock major and trace element geochemistry, and SrNd isotopes on the igneous rock suite. Geochemical data show that the lava units and dykes are mainly basaltic in composition with minor basaltic andesites and trachytes. They form two contrasting series of arc-related calc-alkaline (Group 1) and OIB-like (Group 2) rocks. The zircon UPb age of Group 1 rocks is 95.6 ± 1.8 Ma (2σ), whereas for Group 2 rocks, cross-cutting relationships and stratigraphic constraints indicate a somewhat younger age. Group 1 rocks have ⁸⁷Sr/⁸⁶Sr_(i) varying from 0.7038 to 0.7070 and ε_Nd(t) values ranging from +0.5 to +5.0. Group 2 rocks have ⁸⁷Sr/⁸⁶Sr_(i) = 0.7040–0.7065 and ε_Nd(t) from −3.0 to +3.7. Trace element and isotopic modelling shows that the primitive Group 1 magmas were derived from a metasomatized mantle source enriched by the addition of ∼6–10 % sediment melt component, while Group 2 rocks are consistent with melts of an asthenospheric mantle source enriched by ∼1–5 % EMII component. Trace element modelling indicates that Group 1 rocks formed from ∼6–13 % partial melts of a spinel-garnet lherzolite with garnet:spinel ratios of 45:55 to 10:90, whereas primitive Group 2 melts were generated through ∼1–3 % partial melting of a garnet-spinel-lherzolite with garnet:spinel ratios of 90:10 to 80:20. We propose a geodynamic model in which a north-dipping Neotethyan slab beneath the western Alborz (Talesh area) continental margin produced arc assemblages of Group 1 rocks and subsequent slab rollback led to the upwelling of an asthenospheric mantle to generate OIB-like magmatism of Group 2 rocks in an extensional intra-arc to back-arc setting.

Hydrogeological and hydrogeochemical conditions, the concentrations of major and some minor ions and ²²²Rn were determined in the Kamenskoye hydro-radon occurrence in the Southern part of West Siberia. Two different aquifer systems were revealed in the hydrogeological section: the Quaternary sediments with pore waters and the Upper Paleozoic granites including the waters of regional fracturing zone and fracture-vein waters. They are located in a common mixing area and are affected by flooding and anthropogenic pollution. Mineral radon fracture-vein waters in granites, not affected by anthropogenic impact, have been revealed in two boreholes. These waters are cool, fresh (TDS 613.4 to 689.9 mg/L) and Si⁴⁺ content within a range from 10.3 to 13.6 mg/L_. The pH of these waters is neutral to weakly alkaline (6.9–7.8), the gases dissolved in the waters are oxygen and nitrogen. The determined activity of ²²²Rn varies within the range from 1101 to 1570 Bq/L; ²³⁸U concentration varies between 5.6·10⁻³–6.5·10⁻³ mg/L, while ²²⁶Ra ranges from 2.7·10⁻⁹ to 1.8·10⁻⁸ mg/L. The relative fractions of cations (Mg²⁺, Ca²⁺, Na⁺, Sr²⁺, Ba²⁺) decrease with an increase in TDS value due to the formation of poorly soluble carbonate and sulphate compounds. The forms of Fe(II) are represented by Fe²⁺, FeHCO₃⁺, FeCO₃⁰, and Fe(III) migrates in the forms of hydroxo complexes Fe(OH)₂⁺ and neutral species Fe(OH)₃⁰. Manganese migrates mainly as a cation, while other forms (MnHCO₃⁺, MnCO₃⁰) are less abundant, and MnSO₄⁰, MnCl⁺, MnOH⁺ are minor. The chemical forms of nickel and copper migration are free cations, as well as hydrocarbonate and carbonate complexes. Copper, as well as beryllium, also migrate as hydroxo complexes. The forms in which chemical elements migrate and their migration coefficients provide evidence that the equilibrium minerals become more complicated when passing from surface waters (greenalite, siderite, and ferrihydrite and greenalite) to the fracture-vein waters in the Upper Paleozoic granites saturated with dolomite, calcite, talc, magnesite and rhodochrosite.

To understand the mobility of heavy metals during oxidative weathering of sulfides, we investigated weathering processes of tetrahedrite [(Cu,Fe,Zn,Hg)₁₂(Sb,As)₄S₁₃] in an oxidation zone with abundant siderite (FeCO₃) and baryte (BaSO₄) at Rudňany (Slovakia). The focus of this work lied in the isotopic (δ⁶⁵Cu, δ²⁰²Hg, δ³⁴S) variations of the minerals during weathering and the interpretation of such changes. In the studied oxidation zone, Hg-rich tetrahedrite converts in situ to pockets of powdery cinnabar (HgS) and an X-ray amorphous mixture rich in Sb, Fe, and Cu that slowly re-crystallizes to Cu-rich tripuhyite (FeSbO₄). Copper is mobile and precipitates as malachite [Cu₂(OH)₂(CO₃)], azurite [Cu₃(OH)₂(CO₃)₂], or less abundant clinoclase [Cu₃(AsO₄)(OH)₃]. The isotopic composition (δ⁶⁵Cu) of tetrahedrite correlates well with the degree of weathering and varies between 0.0 ‰ and −4.0 ‰. This correlation is caused by isotopic changes during dissolution and subsequent rapid equilibration of δ⁶⁵Cu values in the tetrahedrite relics. Simple diffusion models showed that equilibration of Cu isotopic values in the tetrahedrite relics proceeds rapidly, on the order of hundreds or thousands of years. Abundant secondary iron oxides draw light Cu isotopes from the aqueous solutions and shift the isotopic composition of malachite and azurite to higher δ⁶⁵Cu values as the distance to the primary tetrahedrite increases. Clinoclase and tripuhyite have lower δ⁶⁵Cu values and are spatially restricted near to the weathering tetrahedrite. The Hg and S isotopic composition of tetrahedrite is δ²⁰²Hg = −1.27 ‰, δ³⁴S = −1.89 ‰, that of the powdery secondary cinnabar is δ²⁰²Hg = +0.07 ‰, δ³⁴S = −5.50 ‰. The Hg isotopic difference can be explained by partial reduction of Hg(II) to Hg(0) by siderite and the following evaporation of Hg(0). The S isotopic changes indicate no involvement of biotic reactions in the oxidation zone, probably because of its hostility owing to high concentrations of toxic elements. This work shows that the Cu isotopic composition of the primary sulfides minerals changes during weathering through self-diffusion of Cu in those minerals. This finding is important for the use of Cu isotopes as tracers of geochemical cycling of metals in the environment. Another important finding is the Hg in the oxidation zones evaporates and contributes to the global cycling of this element through atmospheric emission.

The lava domes of the Cixerri half-graben (SW Sardinia) are part of the subduction-related igneous activity that developed in Sardinia during the Upper Eocene-Middle Miocene (38–12 Ma), with calcalkaline and high-K calcalkaline affinity. The investigated rocks are porphyritic basaltic andesites and andesites, with amphibole, plagioclase and minor clinopyroxene phenocrysts included in a groundmass composed of the same phases together with feldspar, quartz and opaque oxides. ⁴⁰Ar/³⁹Ar analyses of plagioclase and amphibole separates from an andesite indicate a crystallization age of 21.31 ± 0.05 Ma. The high abundance of amphibole in the Cixerri rocks, unlike andesites from the neighboring Sardinian districts, could be explained with the high calculated oxygen fugacity (NNO+1–NNO+2) and H₂O content (up to 9 wt%) in the Cixerri magmas. Bulk-rock major and trace element variations, and mass balance calculations are consistent with a magma evolution mainly driven by fractional crystallization of amphibole and plagioclase, which occurred in a polybaric plumbing system, as highlighted by the calculated pressure of amphibole crystallization (2–4 kbar and 6–9 kbar). Bulk rock isotope variations (⁸⁷Sr/⁸⁶Sr_i = 0.70701–0.70786 and ¹⁴³Nd/¹⁴⁴Nd_i = 0.512328–0.512436) indicate that the magma evolution took place in open-system conditions with a low degree of crustal assimilation. The HREE flat patterns point to a magma source in the spinel stability field located in a mantle wedge depleted in incompatible elements and metasomatized by slab and sediment derived fluids and melts.

Calamine susceptibility to dissolution requires a detailed experimental evaluation to uncover an alternative management option for these materials. This study aimed to investigate the (bio)leaching behaviours of Zn/Pb-bearing calamines to quantify their potential as a Zn resource. Chemical treatments, including the application of mineral (H₂SO₄, HCl and HNO₃) and organic acids (citric and oxalic acids), along with biotic treatments involving the bacteria Acidithiobacillus thiooxidans and Pseudomonas fluorescens, were used to analyse the mobilisation mechanisms, namely acidification and complexation. The results showed that HCl and HNO₃ were the most efficient chemical agents, with an extraction efficiency as high as 39 % (Zn). A. thiooxidans extracted the largest amount of Zn (40 %), which proves that the efficiency of the biotic process can be nearly the same as that of the chemical process. However, the main mechanism governing element mobility was the pH factor. This study shows the potential of calamines as prospective materials for the recovery of Zn and other elements (Ge, Tl), even in those treatment conditions that require further optimisation.