Chemical Geology最新文献

{"title":"Flash vaporization and migration of iodine in the oceanic plate subduction zone","authors":"Noriyuki Suzuki ,&nbsp;Jun Kameda ,&nbsp;Miki Amo","doi":"10.1016/j.chemgeo.2025.123031","DOIUrl":"10.1016/j.chemgeo.2025.123031","url":null,"abstract":"<div><div>Crustal fluids in subduction zones, such as subsurface aquifers, submarine seeps, and gas hydrate waters, are often rich in iodine (I₂) and methane (CH₄). Large-scale aquifers in the Kanto subduction zone, where the Pacific Plate (PAC) and the Philippine Sea Plate (PHS) are subducting, also exhibit high concentrations of I₂ and CH₄. However, the origin and behavior of I₂ in the subduction zone are unclear, and its coexistence with CH₄ remains unresolved. To investigate this, we compiled the I₂ phase diagram under high-pressure and high-temperature (P–T) conditions to predict its physicochemical properties in the subduction zone. We then applied the P–T paths of subducted PAC and PHS sediments to the I₂ phase diagram. Our findings reveal that I₂ can exist as a liquid in the young and hot PHS subduction zone. Transient decompressions during earthquake ruptures can cause liquid iodine to flash-vaporize and be expelled from subducted sediments. Along with I₂, thermogenic CH₄ and hydrogen (H₂) generated in the subducted sediments are also released and transported upward, likely by slab-dehydrated fluids. Additionally, H₂ may enhance microbial CH₄ production through hydrogenotrophic methanogenesis. In subduction zones of young and hot oceanic plates such as the PHS, crustal fluids are enriched in I₂ and coexist with CH₄ owing to the simultaneous expulsion of I₂, CH₄, and H₂ from the same subducted sediments and their migration via deep fluids. Large subsurface aquifers can act as traps and reservoirs for migrating I₂ and CH₄, forming large-scale I₂ and CH₄ deposits.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123031"},"PeriodicalIF":3.6,"publicationDate":"2025-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145027361","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":"Revisiting the genesis of Bi-Te-Au-S associations: Implications for the ore-forming processes in gold deposits","authors":"Gao-Hua Fan ,&nbsp;Jian-Wei Li ,&nbsp;Zhan-Ke Li ,&nbsp;Xue-Feng Yu ,&nbsp;Xiao-Dong Deng ,&nbsp;Jin-Hao Liu ,&nbsp;Hang-Jin Jiang ,&nbsp;Hong-Jun Sun ,&nbsp;Tian-Ming Zhang","doi":"10.1016/j.chemgeo.2025.123027","DOIUrl":"10.1016/j.chemgeo.2025.123027","url":null,"abstract":"<div><div>The enrichment of Bi in hydrothermal gold deposits is usually expressed by various Bi-Te-Au-S mineral assemblages, which are often used as mineralogical indicators for physicochemical environments and ore-forming processes. However, the genesis of these assemblages remains poorly understood, particularly the conditions under which S-bearing Bi minerals form and their potential to concentrate gold. The current prevailing proposal is that these S-bearing minerals represent secondary sulfide phases forming through hydrothermal sulfidation during interactions between late-stage, S-rich fluids and preexisting Bi minerals. Here, we conducted four annealing experiments over a wide temperature range (280 to 400 °C) and compositional analyses on natural Bi-rich gold ores from the large Wulong Au-Bi deposit in North China Craton to investigate the genesis of Bi-Te-Au-S associations. The mineral assemblages show a large variation in morphology, texture, and composition after the experiments. Notably, many euhedral bismuthinite, joséite-A and joséite-B mineral grains are observed, showing distinct differences in morphology and distribution from those pre-experiment mineral assemblages. These minerals commonly host many tiny grains of native gold and maldonite. Newly formed mineral phases after each run also include unnamed euhedral to anhedral unnamed Bi-S, Bi-Te-S mineral phases, and Bi-Ag sulfosalts, which are often found adhering to the surface of other Bi-bearing mineral phases. These characteristics show that Bi-Te-S and/or Bi-S minerals crystallized from Bi-Te-S melts at the experiment temperatures and these melts can act as agents for gold concentrations. Based on the results presented here combined with published data, we propose that the Bi-Te-Au-S metallic melts can be activated under the ore-forming conditions of structurally controlled gold deposits similar to the Wulong Au-Bi deposit. The different cooling rates of these melts may control the formation of various textures shown by Bi-Te-Au-S mineral assemblages. Our findings highlight that Bi-Te-Au-S mineral assemblages can form directly from metallic melts, rather than being exclusively linked to late-stage hydrothermal sulfidation during an overprinting event. The formation and crystallization of such melts represent a distinct mechanism for concentrating and cycling critical metals like Bi, Te, S, and Au within evolving ore-forming fluid systems.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123027"},"PeriodicalIF":3.6,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145011026","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":"Microbial processes suppress antimony release during stibnite weathering under suboxic condition","authors":"Ting Lu ,&nbsp;Li Shao ,&nbsp;Aiwen Wu ,&nbsp;Zengping Ning ,&nbsp;Tangfu Xiao ,&nbsp;Enzong Xiao","doi":"10.1016/j.chemgeo.2025.123029","DOIUrl":"10.1016/j.chemgeo.2025.123029","url":null,"abstract":"<div><div>This study investigates the geochemical behavior of antimony (Sb) during the suboxic weathering of stibnite through both chemical and microbial processes. Our study revealed that microbial process suppresses the stibnite dissolution compared to chemical processes, contrasting with established models of Sb geochemical behaviors in oxic environments. In early stages, chemical weathering group (AS) and a microbial weathering group (BS) achieved comparable aqueous Sb concentrations (∼0.2 mM), yet through divergent mechanisms: AS formed passivating sénarmontite (Sb₂O₃) coatings via rapid surface oxidation, while BS established biofilms that physically decoupled Sb release from oxidative dissolution. In late stages, a paradigm shift occurred: AS exhibited 3-fold higher aqueous Sb (∼0.6 mM) compared to BS, with &gt;95 % Sb(V) due to Fe(II)/Fe(III) redox cycling. This process enhanced Sb(III) oxidation kinetics and promoted Sb(V)-Fe(III) oxyhydroxide coprecipitation, confirmed by XPS spectra. In contrast, BS maintained stable Sb levels (0.2 mM) with limited Sb(V) accumulation (58 %). Microbial consortia sequestered Fe(II) through enzymatic reduction, disrupting iron redox cycling and reducing Sb release. This “biogenic passivation” mechanism stabilized Sb, differing from oxic systems where biofilms typically accelerate Sb(III) oxidation. The findings improve predictions of Sb mobility in suboxic environments and suggest biofilm-mediated strategies for Sb pollution control.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123029"},"PeriodicalIF":3.6,"publicationDate":"2025-09-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144997442","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":"Iron isotopic systematics and ferric iron carriers of Phanerozoic continental red beds and implications for atmospheric oxygenation","authors":"Lukáš Ackerman ,&nbsp;Ondřej Bábek ,&nbsp;Tomáš Magna ,&nbsp;Franck Poitrasson ,&nbsp;Petr Novák ,&nbsp;Daniel Šimíček ,&nbsp;Hedvika Weinerová","doi":"10.1016/j.chemgeo.2025.123028","DOIUrl":"10.1016/j.chemgeo.2025.123028","url":null,"abstract":"<div><div>Continental red beds (CRB) are characteristic for their predominant red colour due to the widespread presence of ferric oxides (hematite or goethite) that might suggest distinctly oxygenated atmospheric conditions during their formation. Therefore, elemental and isotopic systematics of iron, a redox-sensitive element, can provide critical constraints on Fe cycling and possibly also palaeoredox conditions. However, our knowledge of the iron isotopic systematics (δ⁵⁶Fe) of CRB remains very limited. This prevents to evaluate whether these rocks are useful to trace past atmospheric oxygenation. To fill the gap, we present an extensive dataset of Fe elemental and isotopic data, paralleled by Mössbauer and diffuse reflectance spectra, for classic Phanerozoic examples of CRB supplemented by the analyses of colour detrital grain coatings. The data reveal goethite as the principal phase within grey-green siliciclastic lithologies and detrital grain coatings. These samples show a positive correlation between Fe³⁺/Fe_T and δ⁵⁶Fe (fine-grained lithologies) suggesting percolation of late-stage diagenetic fluids at variable redox and pH conditions connected with hematite dissolution. In contrast, the red facies are characterized by the predominance of hematite, largely variable Fe_T contents and δ⁵⁶Fe values overlapping with those estimated for the upper continental crust. The overall lighter and more homogeneous δ⁵⁶Fe values in Phanerozoic red beds compared to their Palaeoproterozoic (∼2.2 Ga) counterparts are consistent with more oxygenated atmosphere during the Phanerozoic. Therefore, the appearance of CRB may serve as an important marker of atmospheric oxygenation in the past.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123028"},"PeriodicalIF":3.6,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145046922","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":"Colloidal and nanoparticle transport in a temperate river system: Hydrological controls and geochemical signatures in the Seine Basin","authors":"Francine Wang ,&nbsp;Mickaël Tharaud ,&nbsp;Antonio Moreda Piñeiro ,&nbsp;Marc F. Benedetti","doi":"10.1016/j.chemgeo.2025.123025","DOIUrl":"10.1016/j.chemgeo.2025.123025","url":null,"abstract":"<div><div>Colloids, including nanoparticles, play a significant role as contaminant carriers in surface waters due to their high sorption capacity for both metals and organic pollutants. However, the impact of hydrological regimes and land use patterns on colloid distribution and flux is not well understood, particularly at a large scale where major rivers receive cumulative inputs from numerous tributaries and a variety of land uses. The dynamics of colloids were explored in the Seine River and its tributaries, the Marne and the Oise Rivers, by single particle time of flight inductively coupled plasma mass spectrometry (spICP-ToF-MS). In addition to direct water analysis, <em>Dreissena polymorpha</em> was investigated for its potential as a colloid bioindicator, with promising results. Colloid concentration in river water appeared to be controlled mainly by the water discharge. Similar colloid populations and water chemistry have allowed conservative particle mixing between the Seine and its tributaries without undergoing significant aggregation, dissolution, or transformation. The impact of sporadic events such as flooding was also discussed. The comparable composition of suspended matter and colloids in the Seine River basin has suggested that colloids could be a finer subset of sediments, formed through similar processes. The export of colloids was significantly influenced by land use and erosion patterns, as well as agricultural activities. The rates of colloid export were estimated and aligned with the findings of previous studies despite differences between the studied areas.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 123025"},"PeriodicalIF":3.6,"publicationDate":"2025-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144933029","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":"Lithium isotopes in Palaeozoic stem-tetrapod bioapatite: Preservation, controls, ecology and oceanographic insights","authors":"Vincent Luccisano ,&nbsp;Jeremy E. Martin ,&nbsp;Romain Amiot ,&nbsp;Philippe Telouk ,&nbsp;Fanny Thibon ,&nbsp;Sébastien Olive ,&nbsp;Olivier Matton ,&nbsp;Christophe Lécuyer","doi":"10.1016/j.chemgeo.2025.123024","DOIUrl":"10.1016/j.chemgeo.2025.123024","url":null,"abstract":"<div><div>Major ecological changes in vertebrate evolution through geological times include transitions between aquatic and terrestrial environments. However, temporality and modalities of these transitions are poorly known, relying on fossil discoveries and their sedimentary context. Recently, the stable isotopic composition of lithium (δ⁷Li) in mineralised tissues of modern vertebrates has been proposed to finely discriminate aquatic environments. This new proxy has strong potential applications in the fossil record to better understand key ecological changes such as vertebrate terrestrialisation during the Late Devonian. However, the impact of diagenetic processes on the preservation of the original vertebrate δ⁷Li has never been studied to assess the usefulness of this isotopic system. Here we report the first in-depth analysis of δ⁷Li values <!--> <!-->of mineralised fossil vertebrate tissues, as well as of major and minor elements. The specimens come from the Late Devonian outcrop of Miguasha, known to have preserved stem-tetrapods corresponding to the first steps of the initial vertebrates terrestrialisation. We highlight the good preservation of the majority of the δ⁷Li values <!--> <!-->with the identification of a diagenetically altered endmember which constitutes a new reference framework to assess the preservation of δ⁷Li in the vertebrate fossil record. δ⁷Li variations of the well-preserved specimens are not controlled by biological factors, but by the environment setting as highlighted by strong correlations between contribution of detrital inputs on the chemical content of fossil bioapatites and their δ⁷Li values. Consequently, lithium isotope composition of vertebrate bioapatite can be used to finely reconstruct past aquatic environments and vertebrate palaeoeocology. The δ⁷Li value range of 20 ‰ to 23 ‰ in tetrapodomorphs indicates that they preferentially lived in the most distal and marine-influenced part of the estuary, confirming their euryhalinity and the complex environmental context of the vertebrate terrestrialisation. Tetrapodomorphs and placoderms have δ⁷Li comprised between 20 ‰ and 23 ‰, which are considered potentially valuable proxies for the δ⁷Li of the contemporaneous oceans.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"695 ","pages":"Article 123024"},"PeriodicalIF":3.6,"publicationDate":"2025-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145005079","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":"Preface for Chemical Geology VSI: Elemental salinity proxies","authors":"Wei Wei ,&nbsp;Geoffrey Gilleaudeau ,&nbsp;Yi Song ,&nbsp;Wolfgang Ruebsam ,&nbsp;Thomas J. Algeo","doi":"10.1016/j.chemgeo.2025.123023","DOIUrl":"10.1016/j.chemgeo.2025.123023","url":null,"abstract":"<div><div>This preface provides context for and summarizes the findings of the 20 studies contributed to the <em>Chemical Geology</em> VSI on “Elemental salinity proxies”. These studies are part of the recent renaissance of salinity analysis in paleoenvironmental research. Collectively, they provide key insights into the methodology and application of elemental salinity proxies for paleoenvironmental reconstruction that will serve as examples of ‘best practices’ in the future.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 123023"},"PeriodicalIF":3.6,"publicationDate":"2025-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145009047","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":"The protracted role of India-Eurasia collision in the uplift of the Gangdese terrane revealed by machine learning","authors":"Zhikang Luan ,&nbsp;Jia Liu ,&nbsp;Yantao Hao ,&nbsp;J. ZhangZhou ,&nbsp;Qunke Xia ,&nbsp;Cheng Su ,&nbsp;Eero Hanski ,&nbsp;Jingjun Zhou ,&nbsp;Tianting Lei","doi":"10.1016/j.chemgeo.2025.123022","DOIUrl":"10.1016/j.chemgeo.2025.123022","url":null,"abstract":"<div><div>The crustal thickening due to India-Asia collision was previously believed to play a key role in uplift of plateau. However, recent paleoaltimetry data indicates parts of the plateau reached high elevations earlier than previously thought. Accurate determination of crustal thickening history is critical to further constrain this issue. We applied machine learning to model crustal thickness using refined global geochemical datasets, addressing limitations in earlier approaches. The crustal thickness evolution history of Gangdese terrane in southern Tibet was recovered by the new machine learning model and compared with the paleoaltimetry data. Results show that at the initial stage of collision, the crust thickness was normal and decoupled with high paleoaltimetry, while the subsequent crustal thickening occurred after 41 Ma and kept the same path with the uplift of plateau. This challenges the notion of rapid uplift driven by crustal thickening and instead suggests a protracted uplift process, offering new perspectives on the geodynamics of southern Tibetan Plateau.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 123022"},"PeriodicalIF":3.6,"publicationDate":"2025-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144917632","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":"Linking low δ44/40Ca basalts to recycled carbonates through coupled chemical and Ca-Zn-Mg isotopic covariations","authors":"Hang Xu ,&nbsp;Xiao-Jun Wang ,&nbsp;Xiao-Yu Zhang ,&nbsp;Gang Zeng ,&nbsp;Jian-Qiang Liu ,&nbsp;Jian Zhao ,&nbsp;Fang Liu ,&nbsp;Li-Hui Chen","doi":"10.1016/j.chemgeo.2025.123019","DOIUrl":"10.1016/j.chemgeo.2025.123019","url":null,"abstract":"<div><div>Stable calcium (Ca) isotopic studies have revealed that some mantle-derived magmas, such as basalts, kimberlites, and carbonatites, generally exhibit varying degrees of lower δ^44/40Ca (δ^44/40Ca = [(⁴⁴Ca/⁴⁰Ca)_sample / (⁴⁴Ca/⁴⁰Ca)_{SRM 915a} − 1] × 1000) values compared to the peridotitic mantle. However, it remains controversial whether the low δ^44/40Ca signature can represent a fingerprint of isotopically light recycled carbonates in the mantle source or is merely a result of isotope fractionation during mantle partial melting. In this study, we further explore this issue by presenting the coupling of chemical and Ca–Zn–Mg isotopic compositions in a suite of Cenozoic intraplate basalts (Abaga and Dalinor) from Northeast China. These basalts exhibit strong correlations among various chemical indices indicative of a carbonated mantle source; specifically, the samples with low SiO₂ contents (e.g., ≤ 45 wt%) are characterized by high CaO/Al₂O₃ (≥ 0.8) and low Hf/Hf* (≤ 0.6) and Ti/Ti* (≤ 0.8) values. This observation indicates that such basalts may have been variably contributed by a carbonated mantle source. Notably, the δ^44/40Ca values (0.63–1.04 ‰) of the studied samples display positive correlations with SiO₂, Hf/Hf*, and Ti/Ti* values, while showing a negative correlation with CaO/Al₂O₃ ratios. These correlations cannot be explained by potential effects of secondary alteration or magmatic processes, such as magma differentiation and partial melting, but should also be attributed to varying extents of contributions from a carbonated mantle source. Furthermore, the δ^44/40Ca values exhibit a positive correlation with δ²⁶Mg (−0.50 ‰ to −0.34 ‰) and a negative correlation with δ⁶⁶Zn (0.34–0.50 ‰) values. Such tightly coupled covariations of Ca, Mg, and Zn stable isotopes demonstrate that recycled carbonates in the mantle source have contributed to the low δ^44/40Ca basalts. Binary mixing calculations indicate that adding 5–10 % dolomite to the peridotitic mantle can explain the Ca–Zn–Mg isotopic compositions of most samples in this study. Therefore, this study suggests that the low δ^44/40Ca signature of some mantle-derived magmas can be regarded as a fingerprint of recycled carbonate in the mantle source, rather than being exclusively attributed to the effects of partial melting. The integrated application of Ca–Zn–Mg isotopes can provide deeper insights into the origin of the low δ^44/40Ca signature in mantle-derived magmas and deep carbonate recycling.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 123019"},"PeriodicalIF":3.6,"publicationDate":"2025-08-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144921178","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":"Transformation of triclinic birnessite induced by vermicompost-enriched soil organic matter","authors":"Oluwadunsin Oyetunji ,&nbsp;Oliver A.H. Jones ,&nbsp;Suresh Subashchandrabose ,&nbsp;Edward D. Burton ,&nbsp;Dane Lamb","doi":"10.1016/j.chemgeo.2025.123021","DOIUrl":"10.1016/j.chemgeo.2025.123021","url":null,"abstract":"<div><div>Birnessite commonly co-occurs with other manganese oxy(hydr)oxides and may serve as a precursor to their formation in natural environments. Here, we assess the structural stability of triclinic birnessite (TcBi) in vermicompost-enriched soil systems under alkaline conditions. Triclinic birnessite was introduced to the soil at Mn:C ratios of 1:2 and 2:1, and reacted for 35 d. Mineral speciation and transformation in the mineral-associated and particulate organic carbon (POC) fractions, collected on days 1, 15, and 35, were assessed at the Mn K-edge using X-ray Absorption spectroscopy (XAS). Based on XAS, in the POC fraction, Mn(III) increased by 39 % by day 35, while in the mineral-associated organic carbon (MAOC) fraction, Mn(III) increased by ∼21 % and 46 % at Mn:C 1:2 and Mn:C 2:1, respectively. Triclinic birnessite was more stable at Mn:C 2:1, with the minimal formation of other mineral phases. At Mn:C 1:2, TcBi underwent increased transformation to hexagonal birnessite, with the formation of Mn(III) phases. By day 35, XAS indicated TcBi decreased by up to ∼31 % in both POC and MAOC fractions, with the emergence of additional Mn phases, including manganite, lithiophorite, and Mn(III) phosphate, particularly in the MAOC fraction. Notably, manganite was observed in both soil fractions, while bixbyite and lithiophorite were only observed in the POC and MAOC fractions, respectively. Using XAS, our findings show that organic C interactions with TcBi under alkaline conditions drive redox cycling of Mn, leading to the recrystallisation of diverse Mn phases, highlighting TcBi's role in Mn mineral transformations in natural environments.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"694 ","pages":"Article 123021"},"PeriodicalIF":3.6,"publicationDate":"2025-08-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144908781","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}