Chemie Der Erde-Geochemistry最新文献

The Khan-Khatun ZnPb deposit is located in the southeast margin of the Tabas Block of the Central Iranian Microcontinent. The stratabound ZnPb mineralization is of epigenetic origin and hosted by the Late Cretaceous limestones. The ore deposition occurred in structural open spaces and much less as a disseminated replacement in carbonate rocks. The deposit consists of sulfide and non-sulfide base metal ore types. Sulfide ores include sphalerite, galena, and minor amounts of pyrite and chalcopyrite. Three paragenetic stages are recognized: pre-, hydrothermal, and supergene mineralization. Fine-grained pyrite and chalcopyrite (0.02 to 0.15 mm) precipitated during the early stages of hydrothermal mineralization. Galena formed with or sometimes after sphalerite. The δ³⁴S values of sphalerite and galena range from +10.4 ‰ to +13.7 ‰ and + 10.2 ‰ to +14.1 ‰, respectively, and are consistent with thermochemical sulfate reduction (TSR) of the Jurassic evaporites. Willemite is an abundant non-sulfide mineral characterized by red-brown to white colors. The red-brown willemite formed during the late stages of the hydrothermal mineralization. The δ¹⁸O values of red-brown and white-colored willemite vary from +14.3 to +16.1 ‰ and − 9.62 to −8.1 ‰, respectively. Differences in δ¹⁸O values between red-brown willemite and white-colored willemite are probably the result of hydrothermal and supergene processes. Homogenization temperatures of primary fluid inclusions in calcite coexisting with sulfide ores and red-brown willemite range from 110 to 210 °C and 112 to 177 °C, respectively. The salinities of aqueous fluid inclusions of calcite and red-brown willemite vary from 11.1 to 21.26 wt% NaCl equiv. and 10.61 to 16.15 wt% NaCl equiv., respectively. Microthermometric measurements, isotopic analyses, geochemical, mineralogical, and textural evidence indicate that the mineralization process at the Khan-Khatun ZnPb deposit is consistent with Mississippi Valley-type (MVT) deposits.

The lavas of the Mt. Somma volcanic epoch were erupted during the early stage of the Somma-Vesuvius volcanic complex. These lavas are mildly differentiated with the presence of plagioclase-clinopyroxene-olivine- ± leucite-bearing rocks (leucite tephrites, leucite-bearing shoshonites, latites), also characterized by low in MgO, Cr and Ni, with a Sr-Nd-isotope range (⁸⁷Sr/⁸⁶Sr = 0.706865–0.707861; ¹⁴³Nd/¹⁴⁴Nd = 0.51244–0.51258) that overlaps with lavas of the late stage Vesuvius erupted after 1631 CE (late stage of the Somma-Vesuvius volcanic complex). Differentiation is dominated by closed-system processes, with fractional crystallization of clinopyroxene, calcic plagioclase, olivine, magnetite, and leucite. Open-system differentiation processes are subordinate and associated with limited interaction with crustal rocks. Oxygen isotopes on clinopyroxene and olivine phenocrysts (δ¹⁸O = 6.5–7.9 ‰) are higher than typical uncontaminated mantle magmas, suggesting a crustal contribution to the melt. Although open-system assimilation + fractional crystallization certainly took place, this process alone does not adequately reproduce the chemical and isotopic composition of the Mt. Somma ultrapotassic magmas. Therefore, a contribution from a recycled crustal component in the mantle source is required, but probably dominated by sediment-derived fluids and melts. The Mt. Somma lavas are characterized by distinctly different geochemical features compared to the mafic products of the neighboring volcanic areas (i.e., Phlegrean, Procida and Ischia volcanic fields), where the recycled crustal component is less pronounced.

Glass manufacturing processes and recipes changed fundamentally after the 8th century CE. The earlier centralised production system diversified, primary production sites multiplied, and the scale of individual productions contracted. Mineral soda was no longer used and instead replaced by plant ash as the main fluxing agent, affecting the chemical composition and properties of the glass. In this work, LA-ICP-MS and Raman spectroscopy were used to investigate the compositional and structural characteristics of 68 glass fragments recovered during recent excavations at Bukhara in Uzbekistan, dating to the 9th to early 11th centuries CE. This is the most extensive systematically collected and studied glass assemblage from Central Asia to date. The glass can be attributed to different origins, confirming on the one hand the diversification of glass production during the early Islamic period and, on the other hand, regional variations in the chemical compositions and network structure of soda-rich plant ash glasses. As clear archaeological evidence for early Islamic glass production sites in Central Asia is rare, regional production groups are distinguished primarily on relative concentrations of Mg, K, P, Cl, Li and Cs in relation to the plant ash component, while variabilities in Al, Ti, Cr, Y, Zr, Th and REEs and their ratios indicate different silica sources. Raman spectra suggest variations in network connectivity and Qⁿ speciation that confirm compositional groupings and suggest structural differences between regional productions of plant ash glass. The results demonstrate a clear dominance of local or regional glass groups, while revealing the importation of Mesopotamian glass, notably a high-end colourless glass type from the region around Samarra in Iraq. The new analytical data allow further separation and characterisation of novel early Islamic plant-ash glass types and their production areas.

The formation of sediment-hosted CuCo deposits remains controversial, in part due to the lack of a precise age for CuCo mineralization. The Dahenglu deposit is located in the eastern part of the Jiao–Liao–Ji Belt (JLJB), one of the famous sedimentary–metamorphic-type CuCo deposits in China, that is mainly hosted within Palaeoproterozoic epimetamorphic rocks. The orebodies occur as stratoid, lenticular and veined forms in conformity with the carbonaceous sericite phyllite. In this study, we present new ReOs and monazite UPb geochronological data for carbonaceous sericite phyllite, and zircon UPb geochronological data for diorite porphyry associated with the deposit. The ReOs geochronology on carbonaceous rocks from the Dalizi Formation provides a direct and reliable depositional age of 1967 ± 23 Ma. The UPb analyses of metamorphic monazite intergrown with cobaltite yield an age of 1812 ± 8 Ma. Magmatic zircon UPb dating from ore-bearing diorite porphyry yields a weighted mean age of 121.8 ± 0.8 Ma. These results constrain three periods of mineralization in the Dahenglu deposit. Syngenetic sedimentary mineralization and metamorphic mineralization occurred during the Palaeoproterozoic, and magmatic–hydrothermal mineralization occurred during the Early Cretaceous. We suggest that ReOs and UPb geochronology on carbonaceous-bearing epimetamorphic rock and metamorphic monazite can serve as robust chronometers to establish the age and temporal evolution of sedimentary hosted CuCo mineralization.

The Central Montana Trough is an important sedimentary basin for petroleum resources and as a record of North American tectonism. The thermal, overpressure, and tectonic histories of the trough are investigated through a study of beef calcite veins taken from the Heath Formation, the primary hydrocarbon source rock of the basin. Results from beef calcite analysis include petrographic characterization, U-Pb geochronology via LA-ICP-MS, clumped isotope thermometry, and conventional carbon and oxygen stable isotopes. U-Pb ages and clumped isotope temperatures are 121.8 ± 19.2 Ma at 43.1 ± 2.3 °C; 96.2 ± 25.9 Ma at 52.1 ± 3.7 °C; and 101.6 ± 24.2 Ma at 50.2 ± 2.4 °C. Large errors on U-Pb ages result from very low U contents (<0.03 ppm). Ages and temperatures indicate staged vein precipitation at burial depths between 600 m to 1.3 km during the major burial event of the basin and a normal geothermal gradient of 25 °C/km. Beef calcite emplacement and basin burial are the direct result of regional tectonism of the Sevier Orogeny. Calculated fluid δ¹⁸O using clumped isotope temperatures revealed δ¹⁸O values of 3–7 ‰ (SMOW), indicating beef calcite precipitation from connate formation brine. Analysis of median-symmetrical beef carbonate δ¹⁸O and δ¹³C values indicates precipitating fluids were diagenetically modified by bacterial sulfate reduction and methanogenesis of organic matter. A thin (0.1 mm) second generation of growth is found on the outermost vein margin by a sharp chemical boundary and a trail of inclusions. This second growth stage could not be dated separately, but significantly lower δ¹⁸O and δ¹³C values of −2 ‰ and −5.5 ‰, respectively, indicate precipitating fluids were hotter and further diagenetically altered by thermal organic matter breakdown.

Supplemental data: https://osf.io/39znd/.

Limited attention has been given to antimony present in detrital form in the different environmental compartments except for highly polluted systems related in some way to ore deposits. In highly polluted systems, the ultimate sinks of Sb may be the minerals tripuhyite (FeSbO₄) or perhaps schafarzikite (FeSb₂O₄) but how about Sb dynamics in the much more abundant, weakly polluted or ‘non-polluted’ systems? This deficiency in our knowledge is probably related to the perception that the element is mostly present ‘dissolved’ in waters and to a focus on the role of its binding to iron oxyhydroxides in solid phases. Here we evaluate the state of our knowledge in the Sb journey from geological matrices to detrital forms in soils and waters and identify key aspects that require further investigation. In high-temperature environments, Sb demonstrated its striking incompatibility by fractionation into aqueous fluids or sulfide/metallic melts, or by uptake in a few common minerals that accept this element (e.g., rutile or pyrite). In low-temperature environments, Sb enters the structures of minerals with different formation rates and solubilities, creating a confusing impression of being mobile and immobile at the same time. The estimates of Sb concentration in the upper continental crust are scattered and the Sb-bearing mineral(s) there have not yet been identified. Given that sedimentary rocks are consistently enriched in Sb, the carriers could be the clay minerals. In surface water bodies, Sb could be carried predominantly in the particulate fraction, despite the popular belief of the opposite. An important point to consider is the transport of Sb within the suspended particulate matter, not on its surface. In soils, many studies employed sequential extractions to show that Sb accumulates in the ‘residual’ fraction, without ever asking what the nature of this fraction is. Based on these facts (i.e., knowns), we have identified the unknowns regarding detrital Sb on our planet that should preferentially be addressed by future projects if our understanding is to improve.

Credible records of rifting and associated sedimentation and granitoid magmatism coinciding with the Columbia breakup event are not common in the Precambrian Indian continent. We report a 1322 ± 3 Ma concordia age for magmatic zircons from the granitoid rocks of the Sausar mobile belt, Central Indian Tectonic Zone (CITZ). The rocks exhibit geochemical characteristics of A-type granitoid rocks and were generated by the dehydration melting of shallow crust in an extensional tectonic setting. The predominantly negative ε_Hf(t) values and partial melting modelling imply their origin by the reworking of pre-existing granitoid crust. T_DM2 (Hf) model ages for these rocks range from 2856 Ma to 1885 Ma suggesting a prolonged period of crustal evolution and reworking of Archean to Paleoproterozoic basement rocks. The temperature for magma generation, determined from the calculated zircon saturation temperature of 874.2 °C is suggestive of melting of a thinned crust that was heated by the upwelling asthenosphere in an extensional tectonic setting. The obtained ages provide evidence for the existence of an extensional event during mid-Mesoproterozoic coinciding with the Columbia breakup event. The extension could also be argued as a local event related to far-field stresses generated due to the ca. 1.6 to 1.5 Ga subduction-collision event at the plate margin farther to the north of the studied region of the CITZ. The recrystallized margins of zircon grains yield ²⁰⁷Pb/²⁰⁶Pb ages between 0.95 Ga and 1.0 Ga implying their alteration during a metamorphic event that can be identified with the final amalgamation and stabilization of the northern and southern Indian blocks along the CITZ, coinciding with the Rodinia assembly, during which the regional structural fabric developed.

The metallogenesis of Li-rich pegmatites remains contentious and an innovative approach for exploring such deposits is needed. The well-known Koktokay pegmatites in the Altay Orogenic Belt exhibit various mineralization degrees and patterns. In this study, we conducted systematic elemental and boron isotope analyses on five tourmaline samples to decipher the metallogenic mechanism and prospecting indicators of rare metal pegmatites. KKTH2 and KKTH3 were collected directly from the magmatic stage and magmatic–hydrothermal stage of the No. 3 pegmatite, KKTH1 was collected from the Aikoz mine pit, and KKTH4 and KKTH5 were collected from a small operational mine near the No. 3 pegmatite. Unlike the No. 3 pegmatite, this mine produces gem crystals but lacks Li mineralization. All tourmalines belong to the alkali group, whereby KKTH1 and KKTH2 are classified as fluor-elbaite, whereas KKTH3 and KKTH4 are schorl. The tourmaline in KKTH5 shows high Al content (up to 45.30 wt%), classifying as mostly rossmanite–elbaite series, with minor amounts of olenite and liddicoatite.

A Rayleigh fractionation model yields a shift in △¹¹B value of 4.8‰ between Zone IV and VI involved more than just magma, as B-isotope fractionation between tourmaline and melt would be <1‰ when temperature drop from 650 °C to 500 °C. It further indicates that different parts of No. 3 pegmatite may have originated from diverse sources.

After comparing the δ¹¹B values of tourmaline in this study with other fertile and barren pegmatite globally, we suggest that δ¹¹B values of tourmaline higher than −10‰ is a potentially useful indicator for Li-rich pegmatites because of the likely relationship with marine evaporite or carbonate rocks in the source. Furthermore, we propose that tourmaline with a V/Sc value lower than 1 and a Li/Sr value higher than 100 can be used as indicators for Li exploration. The extent of Li migration from magma into the hydrothermal stage and mineralized in the residual melt correlates with the salinity of magma, which may reasonably explain the less intense wallrock alteration near the No.3 pegmatite. This finding provides new insight into the use of trace elements and boron isotope composition as a guide for exploring Li-rich pegmatites.