Chemical Geology最新文献

{"title":"Early stages impact of volcanism on sedimentary diagenesis: The case of the newly born volcano, Fani Maoré","authors":"Marine Manoux ,&nbsp;Christophe Rabouille ,&nbsp;Jean-Pascal Dumoulin ,&nbsp;Bruno Bombled ,&nbsp;Gaël Monvoisin ,&nbsp;Sandrine Cheron ,&nbsp;Audrey Boissier ,&nbsp;Yoan Germain ,&nbsp;Lucie Pastor ,&nbsp;Olivier Rouxel ,&nbsp;Cécile Cathalot","doi":"10.1016/j.chemgeo.2025.122674","DOIUrl":"10.1016/j.chemgeo.2025.122674","url":null,"abstract":"<div><div>Submarine volcanic eruptions impact ocean and sediment geochemistry by generating hydrothermal plumes, fluid expulsion, lava flows, and tephra deposition. The amount and impact of such inputs on the sediment composition and biogeochemistry, on short temporal scales, is yet to be quantified. To this end, the multidisciplinary GEOFLAMME cruise was conducted in May 2021 on board the R/V Pourquoi Pas? to study the Fani Maoré edifice, a newly born volcano located on the eastern submarine flank of Mayotte (Comoros archipelago, Indian Ocean). The strategy was to sample sediment cores along two eastward transects from this volcano towards the open ocean. This study aims for a comprehensive overview of the diagenetic alterations occurring within sediments in response to this volcanic event. Solid phase characterization using X-ray fluorescence and diffraction, particulate organic carbon (POC) content, carbon isotopic signature (δ¹³C-POC; ∆¹⁴C-POC) and pore water analysis (dissolved inorganic carbon-DIC; Alkalinity; NO³⁻ + NO²⁻; SO₄²⁻; dFe; dMn) reveals low organic matter mineralization and low volcanic material alteration throughout the area. However, close to the volcano and lava flows, DIC, alkalinity and Mg²⁺ in the sediment show a strong increase at depth while Ca²⁺ and Sr²⁺ show a strong depletion. We attribute these concentration gradients to the diffusion of a magmatic CO₂-rich fluid with a geochemical signature reflecting strong fluid-rock interactions as evidenced by carbon isotopic signature of DIC (δ¹³C-DIC; ∆¹⁴C-DIC) and ⁸⁷Sr/⁸⁶Sr ratio followed by carbonate precipitation at depth in the sedimentary pile. This study demonstrated that the interaction between magmatic CO₂ degassing and volcanic rocks leads to natural carbonation at depth, as evidence by vertical profiles that differ from those that can be described in more established volcanic systems. These findings enhance our understanding of the sediment biogeochemistry in a volcanic eruptive context, and offers perspective for a better use and development of new volcanic proxies in marine sediments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"680 ","pages":"Article 122674"},"PeriodicalIF":3.6,"publicationDate":"2025-02-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143478692","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Apatite and magnetite as probes into dissimilatory iron reduction in banded iron formations","authors":"Tianyang Hu ,&nbsp;Leslie J. Robbins ,&nbsp;Kurt O. Konhauser ,&nbsp;Lei Liu ,&nbsp;Brendan A. Bishop ,&nbsp;Guoxiang Chi ,&nbsp;Lijuan Xu","doi":"10.1016/j.chemgeo.2025.122676","DOIUrl":"10.1016/j.chemgeo.2025.122676","url":null,"abstract":"<div><div>Banded iron formations (BIFs) are ancient sedimentary deposits that provide critical insights into the evolution of Earth's early atmosphere, hydrosphere, and biosphere. This study focuses on the Ouyang BIF in the North China Craton (NCC), highlighting the substantial impact of dissimilatory Fe(III) reduction (DIR) on both the remobilization of iron from the primary iron precipitates and subsequent authigenic mineralization during diagenesis. This biological process is manifested in the light iron isotopes in magnetite (δ⁵⁶Fe values down to −2.1 ± 0.02 ‰) and distinct geochemical signatures in associated apatite. Specifically, the elevated Mn/U ratios (ranging from 467 to 1210) in apatite indicates redox cycling, while elevated concentrations of Sr (ranging from 15,453 to 20,466 ppm), and OH (33 % to 58 % in molar) in apatite are characteristic of biomineralization processes during BIF formation. The relationship observed between Sm/Nd ratios (and Nd isotopes) in apatite and δ⁵⁶Fe values in magnetite further suggests that iron was sourced to the Wuyang BIFs from both hydrothermal fluids and a benthic iron flux. Notably, the benthic Fe flux likely resulted from the DIR of ferric oxyhydroxide minerals in nearshore sediments, highlighting the essential role of continental iron and DIR in transporting Fe from the continents to BIF depositional centers. This study underscores the critical influence of microbial activity in iron cycling within ancient oceans. It further showcases how DIR was recorded by apatite and magnetite, offering insights into past DIR bacteria during BIF deposition.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"678 ","pages":"Article 122676"},"PeriodicalIF":3.6,"publicationDate":"2025-02-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143378316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Calcium isotopes support spatial redox gradients on the Tethys European margin across the Triassic-Jurassic boundary","authors":"Ashley N. Prow-Fleischer ,&nbsp;Zunli Lu ,&nbsp;Clara L. Blättler ,&nbsp;Tianchen He ,&nbsp;Pulkit Singh ,&nbsp;Preston Cosslett Kemeny ,&nbsp;Jordan P. Todes ,&nbsp;Alexandre Pohl ,&nbsp;Tripti Bhattacharya ,&nbsp;Bas van de Schootbrugge ,&nbsp;Paul B. Wignall ,&nbsp;Simona Todaro ,&nbsp;Jonathan L. Payne","doi":"10.1016/j.chemgeo.2024.122530","DOIUrl":"10.1016/j.chemgeo.2024.122530","url":null,"abstract":"<div><div>The end-Triassic mass extinction was among the most severe biotic crises of the Phanerozoic. It has been linked with the global expansion of marine anoxia, and the prolongation of these conditions within epeiric seas has been proposed as a cause for the suppression of biodiversity during the early Jurassic Hettangian Stage. Testing this interpretation is complicated by spatially heterogeneous patterns of local marine redox conditions within the western Tethys European Epicontinental Shelf. In this study, we assess the redox state within this region by focusing on two carbonate successions in Italy, a peritidal platform at Mount Sparagio, Sicily, and an offshore ramp deposit at Val Adrara in the Southern Alps. Based on previously published I/Ca ratios, these locations record distinct local background redox conditions, with Val Adrara showing a notably lower pre-extinction oxygen saturation state than Mount Sparagio. Here, we measure δ¹³C and δ¹⁸O at Mount Sparagio and δ⁴⁴Ca and trace element ratios at both sites to identify the roles of mineralogical and diagenetic effects on the preservation of primary redox signals. A numerical framework of multiple elemental (Sr, Mg, Mn, I) and isotopic (δ¹³C, δ¹⁸O, δ⁴⁴Ca, δ²³⁸U, and δ³⁴S_CAS) ratios was constructed to recognize modes of carbonate diagenesis and source-mixing in the data. While diagenesis is impossible to completely rule out, our state-of-the-art approach provides robust evidence against common forms of diagenetic alteration as the main drivers of the overall paleoredox proxy trends.</div><div>Where the redox signals are largely preserved, we interpret differences in pre-extinction I/Ca between the two sites to reflect distinct local oxygenation states. Drawing from published Community Earth System Model simulations, we propose that ocean circulation and hydrological regime could have been important drivers of spatial heterogeneity in paleo-redox conditions across the European Epicontinental Shelf.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122530"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858014","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"On the coexistence of rift-related silica-undersaturated and silica-saturated alkaline rocks – The cretaceous Messum alkaline complex (Namibia) revisited","authors":"S. Jung ,&nbsp;R.L. Romer ,&nbsp;J.A. Pfänder","doi":"10.1016/j.chemgeo.2024.122479","DOIUrl":"10.1016/j.chemgeo.2024.122479","url":null,"abstract":"<div><div>The ∼132 Ma-old Messum igneous complex, a circular structure of ∼18 km diameter, belongs to the Damaraland intrusive complexes that intruded into the Pan-African Damara basement of Namibia. The plutonic rocks of the core of the complex comprise olivine-gabbro, biotite-gabbro, nepheline-syenite and quartz-syenite as well as minor alkali gabbro and coexist with the Etendeka volcanic sequences of the Goboboseb Mountains, comprising basalts (Tafelkop and Tafelberg types) that are overlain by deposits of several quartz latite eruptions. New major and trace element and Sr, Nd and Pb isotope data are reported for nepheline-syenite and quartz-syenite. Major and trace element data are consistent with the development of nepheline-syenites through fractional crystallization processes. The nepheline-syenite samples have initial ⁸⁷Sr/⁸⁶Sr of 0.7046–0.7049 and initial εNd ranging from +0.53 to +1.47, indicating a mantle source with time-integrated lithophile element depletion. Initial Pb isotopes are rather uniform (²⁰⁶Pb/²⁰⁴Pb:17.89–18.14, ²⁰⁷Pb/²⁰⁴Pb: 15.56–15.58, ²⁰⁸Pb/²⁰⁴Pb: 37.78–38.00). Uniform initial Sr and Pb isotope ratios for nepheline-syenites suggest that the syenite magmas evolved through fractional crystallization from an inferred mafic alkaline magma without crustal contamination. However, the range in Nd isotope composition is too large to be related to crystal fractionation alone and imply a heterogeneous source with respect to the Nd isotope composition. The quartz-syenites show a large range in initial εNd (+1.0 to −4.4) and initial ⁸⁷Sr/⁸⁶Sr (0.7047–0.7115). Initial Pb isotope ratios are also heterogeneous (²⁰⁶Pb/²⁰⁴Pb: 18.29–18.74, ²⁰⁷Pb/²⁰⁴Pb: 15.60–15.65, ²⁰⁸Pb/²⁰⁴Pb: 37.43–38.49). These data, together with major and trace element constraints and results from AFC modeling substantiate the production of the quartz-syenites by fractional crystallization of clinopyroxene, amphibole and K-feldspar accompanied by assimilation of up to about 30 % pre-Pan African lower crust. Isotope and chemical data do not support derivation from a single batch of magma undergoing contamination, but suggest that a large magma body at depth evolved largely by fractionation with batches of melt extracted from this chamber being variably contaminated at lower crustal levels.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122479"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143168552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The use of combined CMg isotope compositions of carbonates from orogenic SbAu deposits as a tracer of fluid interaction with sea-floor altered crust","authors":"Andrea Agangi ,&nbsp;Axel Hofmann ,&nbsp;Takuya Echigo ,&nbsp;Robert Bolhar ,&nbsp;Daisuke Araoka ,&nbsp;Vincent Mashoene ,&nbsp;Lucia T. Ndhlovu ,&nbsp;Ryohei Takahashi ,&nbsp;Pearlyn C. Manalo","doi":"10.1016/j.chemgeo.2024.122442","DOIUrl":"10.1016/j.chemgeo.2024.122442","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The Mesoarchaean Murchison Greenstone Belt is composed of a strongly deformed volcano-sedimentary succession metamorphosed up to amphibolite facies and surrounded by metaluminous and peraluminous granitoids in the north of the Kaapvaal Craton of southern Africa. A circa 40 km-long shear-zone of strongly carbonatised rocks (the Antimony Line, or Sb-Line) oriented along the main trend of the greenstone belt (WSW–ENE) hosts important Sb deposits with accessory Au. These commodities mostly occur as stibnite and native gold hosted by quartz‑carbonate rocks at the centre of the Sb-Line, underlining the importance of CO&lt;sub&gt;2&lt;/sub&gt;-rich fluid flow for mineralisation during deformation and metamorphism.&lt;/div&gt;&lt;div&gt;In this study, we compare the elemental and stable isotope (C-O-Mg) composition of carbonates from the Sb-Line with regionally distributed carbonates hosted by the volcano-sedimentary succession distal to mineralisation. The carbonates of the Sb-Line and regional rocks have overlapping major element compositions. Both magnesite and dolomite in most Sb-Line samples have marked light-REE-depleted patterns with variable positive Eu anomalies. Carbon isotope ratios define two clusters, with marked δ&lt;sup&gt;13&lt;/sup&gt;C peaks at ca. -5 ‰ for Sb-Line rocks and ca. -2 ‰ for regional rocks, implying separate C-sources. The peak at ca. -2 ‰ likely represents early carbonatisation through sea-floor alteration, whereas the first peak at ca. -5 ‰ is indicative of deep CO&lt;sub&gt;2&lt;/sub&gt; (mantle, or magma-derived) introduced during tectonic activity of the Sb-Line. Magnesium isotope ratios of regional rocks reveal limited fractionation (bulk δ&lt;sup&gt;26&lt;/sup&gt;Mg = −0.27 ± 0.10 ‰) that overlap with mantle values, but some carbonate-bearing veins present &lt;sup&gt;26&lt;/sup&gt;Mg-depleted compositions (bulk δ&lt;sup&gt;26&lt;/sup&gt;Mg = −1.91 to −0.40 ‰). Sb-Line carbonated rocks have more fractionated Mg isotope compositions (bulk δ&lt;sup&gt;26&lt;/sup&gt;Mg = −0.8 to 0.0 ‰) and carbonates display marked negative &lt;sup&gt;26&lt;/sup&gt;Mg values (δ&lt;sup&gt;26&lt;/sup&gt;Mg from −1.46 to −0.31 ‰). We interpret these results in terms of preferential remobilisation of isotopically light Mg during fluid-rock interaction and dissolution of carbonate in the host-rocks. The lack of correlation between δ&lt;sup&gt;13&lt;/sup&gt;C and δ&lt;sup&gt;26&lt;/sup&gt;Mg indicates decoupling of these isotopic systems, implying contribution from isotopically distinct sources of C and Mg to the mineralised zone.&lt;/div&gt;&lt;div&gt;Similar to other structurally controlled Au&lt;img&gt;Sb mineralisation in Archaean greenstone belts, metal transport and ore deposition in the Murchison Greenstone Belt was closely related to the deep cycle of carbon, linking C-draw-down during sea-floor alteration, carbonate re-mobilisation during metamorphism and CO&lt;sub&gt;2&lt;/sub&gt; degassing from deep sources along major crustal discontinuities. In contrast to models for orogenic Au&lt;img&gt;Sb deposits invoking a purely intra-crustal, metamorphic origin of mineralising fluids, our results underline ","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122442"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143168553","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Evaluating the role of tectonic setting in new continental crust formation by U/Pb ratios","authors":"Xian Chen ,&nbsp;Zhengzhe Fan","doi":"10.1016/j.chemgeo.2024.122560","DOIUrl":"10.1016/j.chemgeo.2024.122560","url":null,"abstract":"<div><div>The role of tectonic setting in new continental crust formation remains enigmatic. A key to solve this issue is to determine which tectonic setting(s) are involved in the generation of new continental crust through time. Modern mantle-derived magmas that formed in intracontinental extension settings (U/Pb = ∼0.28–0.37) and in subduction settings (U/Pb = ∼0.1–0.16) have distinct mean U/Pb ratios. When shifting from subduction to intracontinental extension settings, the mean U/Pb ratios of new crust should define an increasing trend with time, whereas a decreasing trend will be observed when the converse transition is observed. Here we calculate U/Pb ratios of new crust [(U/Pb)_jc] of the Songliao Block from East Asia to determine the tectonic settings of new crust formation. Our results show that (U/Pb)_jc ratios have a decreasing trend from ∼1.55 to ∼1.2 Ga, followed by an increasing trend from ∼1.2 to ∼0.8 Ga, and changed to a decreasing trend again between ∼0.8 and ∼ 0.6 Ga. This implies that new crust formation of the microcontinent in a subduction setting during the middle-late Mesoproterozoic and the middle-late Neoproterozoic, however, in an intracontinental extension setting in the late Mesoproterozoic-early Neoproterozoic. Our method may provide a potential avenue to explore the regimes of new continental crust formation.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122560"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Surface acid alteration of juvenile Andean pyroclastic rocks: effect of glass composition on the development of surface fluoride-bearing minerals","authors":"J.A. Vila ,&nbsp;G.L. Bia ,&nbsp;S. Bengió ,&nbsp;C. Balbis ,&nbsp;L. Borgnino","doi":"10.1016/j.chemgeo.2024.122549","DOIUrl":"10.1016/j.chemgeo.2024.122549","url":null,"abstract":"<div><div>During eruption, sulphur dioxide gas interacts with glass shards, favouring the formation of sulphuric acid (H₂SO₄) aerosols and coatings enriched in hazardous elements such as fluorine (F). This study discusses the formation of F-bearing compounds during acidic weathering of Andean juvenile pyroclastic rock emitted from Puyehue and Lanín volcanoes and their potential to release F into aqueous reservoirs. Surface chemical composition and solid speciation of Si, Al, and O were performed by XPS. Batch experiments were carried out to understand the release of F from S-bearing compounds.</div><div>When pyroclastic rocks are partially altered in H₂SO₄, a mixture of S-bearing compounds precipitates on the surface of the rock grains. These compounds precipitate as a result of the weathering process of pyroclastic rocks after hydrolysis of the aluminate and silicate groups. The composition of the precipitated compounds is influenced by the magmatic source. Consequently, mafic particles exhibit precipitated compounds enriched in Al, Mg, Ca, and Fe and are more altered compared to felsic particles. The hydrolysis process also promotes the release of F, which was originally associated with the aluminosilicate network. Once released, a proportion of the dissolved F either precipitates or re-adsorbed onto S-bearing compounds, eventually being transported into the environment.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122549"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142858010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Molecular signatures of biomacromolecules at micron and submicron scales in Arctica islandica shells","authors":"Oluwatoosin B.A. Agbaje ,&nbsp;Qian Huang ,&nbsp;Michiel Op De Beeck ,&nbsp;Per L. Ambus ,&nbsp;Lisbeth G. Thygesen ,&nbsp;Bernd R. Schöne ,&nbsp;Karina K. Sand","doi":"10.1016/j.chemgeo.2024.122550","DOIUrl":"10.1016/j.chemgeo.2024.122550","url":null,"abstract":"<div><div><em>Arctica islandica</em> (Linnaeus, 1767) is a bivalve mollusk with a lifespan of up to 500 years. Its shell is a complex inorganic-organic nanocomposite, which is still not fully characterized. Here, we used Optical Photothermal Infrared (O-PTIR) microspectroscopy to characterize its organic phase, i.e. the hydrophobic insoluble extracts of both modern and fossil <em>A. islandica</em> shells. We compared the spectra from O-PTIR technique with those obtained from microRaman, microFTIR and ATR-FTIR spectroscopies. The structure of the shells was also studied using scanning electron microscope imaging. The spectroscopic techniques confirmed the presence of <em>β</em>-chitin and chitin-binding protein in the hydrophobic insoluble organic matrix. The results of element and light stable isotope analyses (δ¹³C, δ¹⁵N) from the hydrophobic insoluble extracts of both the modern and fossil shells were consistent with a shallow marine environment. The results demonstrate how O-PTIR can be applied in-situ for the study of biomaterials in shells, and points towards how it can be applied for the elucidation of intricate structure-function relationships. Furthermore, the approach of using the hydrophobic insoluble extracts to probe conditions and the nature of organic remains in fossil shells demonstrate an alternative to the use of soft tissues in isotopic studies and hence opens new possibilities for environmental reconstruction using fossil material when soft tissues are unavailable.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122550"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815870","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Using δ65Cu and δ34S to determine the fate of copper in stream waters draining porphyry mineralization: Implications for exploration targeting","authors":"James A. Kidder ,&nbsp;Christopher E. Beckett-Brown ,&nbsp;Alexandre Voinot ,&nbsp;Zhaoping Yang ,&nbsp;Pierre Pelchat ,&nbsp;Duane C. Petts ,&nbsp;Matthew Polivchuk ,&nbsp;John B. Chapman ,&nbsp;Scott Casselman ,&nbsp;Matthew I. Leybourne","doi":"10.1016/j.chemgeo.2024.122527","DOIUrl":"10.1016/j.chemgeo.2024.122527","url":null,"abstract":"<div><div>The fate of metals, such as Cu, in stream waters draining porphyry mineralization is commonly controlled by several natural processes such as sorption, microbial processes, and ligand availability. Isotopes of Cu offer a novel approach to understanding these processes and determining metal sources within complicated mineralogical systems. Drainages at the Casino Cu-Au-Mo porphyry deposit, Yukon, Canada exhibit circumneutral (pH &gt; 5) in Casino Creek and natural acid rock drainage (pH &lt; 3.5) in Proctor Gulch with the precipitation of schwertmannite (Fe³⁺). Isotopic systems δ⁶⁵Cu and δ³⁴S_sulfate indicate different metal sources, with signatures of both hypogene and supergene mineralization. Waters from Proctor Gulch contain δ⁶⁵Cu values (&lt; −0.5 ‰) consistent with supergene Cu sources from the leached or oxide portion of the mineralization. Comparatively, drainage in the upper part of Casino Creek contains a δ⁶⁵Cu composition (&gt; 0.5 ‰) characteristic of Cu sourced from hypogene sulfide mineral oxidation. Variation in metal sources is similarly supported by aqueous δ³⁴S_sulfate values in the stream waters, which suggest mixing of S derived from a sulfide mineral phase and a much heavier sulfate mineral (e.g., gypsum or anhydrite). Isotopic fractionation of Cu in the dissolved (&lt;0.45 μm) phase presents two predominant controls on Cu dispersion. The natural acid conditions in Proctor Gulch favor the preferential co-precipitation of ⁶³Cu with schwertmannite but could be influenced by intracellular assimilation or adsorption by microbes, which also has been shown to preferentially favor ⁶³Cu. Copper isotopic fractionation results in a gradient of increasing δ⁶⁵Cu values in waters downstream. In Casino Creek, higher pH conditions favor the precipitation of Fe(OH)₃ and the preferential adsorption of ⁶⁵Cu, resulting in decreasing δ⁶⁵Cu values downstream. Copper concentrations in stream waters remain elevated (up to 4.1 μg/L) above ambient background (1.9 μg/L) levels up to 11 km downstream of the deposit. Given the abundance of surface water in many parts of northern Canada, hydrogeochemical prospecting using broad scale stream water catchment analysis is clearly a viable greenfield exploration methodology.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122527"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"n-Alkanes δ13C and salinity correlation in mangrove Aegiceras corniculatum leaves and surface sediments from Zhanjiang estuaries, China","authors":"Guifang Cai ,&nbsp;Zhao-Wen Zhan ,&nbsp;Zhiguang Song ,&nbsp;Yao-Ping Wang ,&nbsp;Jia Xia ,&nbsp;Ding He","doi":"10.1016/j.chemgeo.2024.122552","DOIUrl":"10.1016/j.chemgeo.2024.122552","url":null,"abstract":"<div><div>Carbon isotope ratios (δ¹³C) in plant lipid biomarkers yield insights into historical climates by reflecting plant responses to environmental stressors. Previous research has established a correlation between increased salinity and elevated δ¹³C in <em>Avicennia marina</em> leaf wax <em>n</em>-alkanes, yet it remains unclear if these isotopic signatures are universally applicable across different species and regions or consistently preserved in sedimentary records. We investigated the influence of a 30 ppt salinity gradient on <em>Aegiceras corniculatum</em> in Zhanjiang, China, examining δ¹³C values in leaf wax <em>n</em>-alkanes and adjacent sediments. Leaf wax δ¹³C values ranged from −36.7 ‰ to −31.4 ‰, while sediment <em>n</em>-alkanes ranged from −35.6 ‰ to −28.2 ‰. Sediments consistently exhibited higher δ¹³C values than leaf wax, and their total lipid and <em>n</em>-alkane δ¹³C exhibited a positive correlation with salinity, increasing by 0.06 ± 0.02 ‰ and 0.1 ± 0.04 ‰ per ppt respectively. This positive correlation may be attributed to factors such as marine material input, seasonal variations in lipid synthesis, and plant community succession. In contrast, no significant correlation with salinity was observed in <em>A. corniculatum</em>'s bulk leaf tissues or total lipids. This lack of correlation can be attributed to the unique physiological conditions and varying salt exclusion mechanisms among mangrove species, which influence water use efficiency. Accordingly, while sediment δ¹³C values can indicate past vegetation, the variability necessitates caution in using mangrove sediment δ¹³C for paleoenvironmental reconstruction.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"673 ","pages":"Article 122552"},"PeriodicalIF":3.6,"publicationDate":"2025-02-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142815867","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}