Geochimica et Cosmochimica Acta最新文献

{"title":"Chromium isotope fractionation during magmatic processes of island arc basalts","authors":"Li-Juan Xu, Chunyang Liu, Haibo Ma, Qianru Man, Ji Shen, Sheng-Ao Liu, Guochun Zhao, Gerhard Wörner","doi":"10.1016/j.gca.2025.04.008","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.008","url":null,"abstract":"We present the first stable chromium isotope dataset for a suite of island arc basalts (IABs) from Kamchatka to investigate chromium isotope fractionation during magmatic processes in a subduction setting. The chromium isotopic data (δ<ce:sup loc=\"post\">53</ce:sup>Cr) for Kamchatka arc magmas range from –0.09 ± 0.02 ‰ to –0.16 ± 0.02 ‰ (2σ, n = 22). These magmatic rocks exhibit a positive correlation between MgO content and Ni, Cr contents, as well as CaO/Al<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf> ratios, which suggests that they undergo olivine and pyroxene fractional crystallization. However, δ<ce:sup loc=\"post\">53</ce:sup>Cr shows no correlation with Cr, Ni, or MgO contents, nor with CaO/Al<ce:inf loc=\"post\">2</ce:inf>O<ce:inf loc=\"post\">3</ce:inf> ratios. Ionic modeling and Rayleigh fractionation modeling reveals minimal effects of fractional crystallization on the δ<ce:sup loc=\"post\">53</ce:sup>Cr factors in these arc magmas (Δ<ce:sup loc=\"post\">53</ce:sup>Cr<ce:inf loc=\"post\">crystal-melt</ce:inf>: +0.0001 ‰ to + 0.009 ‰), and probably IABs in general. Furthermore, the lack of correlation between δ<ce:sup loc=\"post\">53</ce:sup>Cr and the melting fraction suggests that partial melting also has a limited influence on Cr isotopic compositions. The δ<ce:sup loc=\"post\">53</ce:sup>Cr values also show no correlation with <ce:sup loc=\"post\">87</ce:sup>Sr/<ce:sup loc=\"post\">86</ce:sup>Sr ratios, chromium contents, or fluid-mobile elements (e.g., Ba/Th, B/Nb, As*/Ce), indicating that slab-derived fluids have a minimal effect on the chromium isotope composition of the mantle source of arc magmas. Notably, however, the majority of these samples show δ<ce:sup loc=\"post\">53</ce:sup>Cr similar to Bulk Silicate Earth, and are statistically higher compared to those observed in mid-ocean ridge basalts (MORBs) and ocean island basalts (OIBs). Melting and Rayleigh fractionation models suggest that the high δ<ce:sup loc=\"post\">53</ce:sup>Cr values in these arc magmas may be attributed to partial melting and fractional crystallization under higher magmatic oxygen fugacity conditions compared to those in MORBs and OIBs. This is consistent with their higher Fe<ce:sup loc=\"post\">3+</ce:sup>/Σ Fe ratios and Δ log fO<ce:inf loc=\"post\">2</ce:inf> (QFM) values, emphasizing the role of varying oxygen fugacity on chromium isotope fractionation in terrestrial basalts. This study highlights the potential of chromium isotopes as a powerful tool for tracing planetary oxygen fugacity environments.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"34 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143877859","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rubidium and potassium isotope compositions of enstatite meteorites: implications for the evolution of their parent body(ies)","authors":"Baoliang Wang ,&nbsp;Frédéric Moynier ,&nbsp;Yan Hu","doi":"10.1016/j.gca.2025.04.007","DOIUrl":"10.1016/j.gca.2025.04.007","url":null,"abstract":"<div><div>Enstatite meteorites, including enstatite chondrites and enstatite achondrites (e.g., aubrites), formed under highly reducing conditions in the solar system. Enstatite chondrites underwent progressive thermal metamorphism from petrologic type 3 to type 6, potentially leading to vaporization and redistribution of volatile elements. Coupled Rb and K isotopic analyses of enstatite meteorites could provide complementary insights into the inherent isotopic variability and volatile depletion processes. In this study, we present Rb and K isotopic compositions for a suite of enstatite meteorites, including sixteen enstatite chondrites spanning metamorphic grades from 3 to 6, as well as four aubrites. Type 3 enstatite chondrites exhibit isotopic compositions similar to those of Earth for both Rb and K, which further underscores the isotopic resemblance between Earth and enstatite chondrites. From type 3–4 to type 5–6, the examined enstatite chondrites generally show a trend towards heavier Rb and K isotopic compositions, indicating volatilization and redistribution of Rb and K during open system thermal metamorphism of the parent body(ies). One EH5 (St. Marks) and two EL6 (Pillistfer and Atlanta) samples deviate from this trend with light K isotope compositions, which may result from an interplay of evaporation, vapor transport and recondensation. On the other hand, the Rb and K isotopic variations in aubrites—which originated from the melting and fractional crystallization of enstatite chondrite-like parent body(ies)—likely reflect more complex processes, possibly involving a combination of plagioclase-bearing melt extraction, magmatic differentiation, core segregation, and the back-condensation of volatiles after impact volatilization.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 63-74"},"PeriodicalIF":4.5,"publicationDate":"2025-04-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838916","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Biogenic iron minerals as a potential survival mechanism for nitrate-reducing iron-oxidizing bacteria","authors":"Han Li ,&nbsp;Kuan Cheng ,&nbsp;Ying Zhang ,&nbsp;Xiaomin Li ,&nbsp;Xiao Zhu ,&nbsp;Yundang Wu ,&nbsp;Guojun Chen ,&nbsp;Yang Yang ,&nbsp;Chao Guo ,&nbsp;Tongxu Liu","doi":"10.1016/j.gca.2025.04.010","DOIUrl":"10.1016/j.gca.2025.04.010","url":null,"abstract":"<div><div>Microaerophilic and phototrophic iron-oxidizing bacteria (FeOB) deal with the threat of cell encrustation by developing effective survival strategies, such as the production of extracellular organic structures for preferential nucleation. However, nitrate-reducing iron-oxidizing (NRFO) bacteria are not reported to have similar survival strategies. In this context, goethite and magnetite were chosen as biogenic iron minerals to evaluate their role in the survival mechanism of <em>Acidovorax</em> sp. BoFeN1. The NRFO kinetics results revealed that the added goethite and magnetite increased Fe(II) oxidation extent from 2.85 mM to 4.22 mM and 4.21 mM, while the extent of nitrate reduction was increased from 0.66 mM to 1.07 mM and 1.03 mM. The addition of goethite and magnetite did not promote microbial heterotrophic nitrate reduction without Fe(II), but accelerated the reaction between nitrite and Fe(II) in the chemodenitrification experiments. This suggested that goethite and magnetite facilitated the biological and chemical Fe(II) oxidation during the microbial NRFO process. Mineralogical analyses revealed that goethite and magnetite serve as nucleation sites for Fe precipitation. Electrochemical measurements revealed that goethite and magnetite elevated Fe(II) reactivity by decreasing its redox potential and corrosion potential. Therefore, goethite and magnetite promoted microbial NRFO process by mitigating cell encrustation and elevating Fe(II) reactivity. Since goethite and magnetite are typical secondary minerals of <em>Acidovorax</em> sp. BoFeN1, the production of biogenic iron mineral may be a survival strategy to prevent cell encrustation and maintain metabolic activity. The current findings provide novel insights into the survival mechanism of NRFO bacteria and related Fe-N cycling.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 53-62"},"PeriodicalIF":4.5,"publicationDate":"2025-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143838915","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Submicron-scale craters on Chang’e-5 lunar soils: records of complex space weathering processes","authors":"Lixin Gu, Yangting Lin, Yongjin Chen, Yuchen Xu, Xu Tang, Jinhua Li","doi":"10.1016/j.gca.2025.04.004","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.004","url":null,"abstract":"Hyper-velocity impacts are dominant agents in the physical and chemical alteration of lunar surface materials. Natural small-scale craters on lunar soils provide an opportunity to understand the impact process and specific space weathering effects on minerals, however, they have not been systematically studied. Here, we report the morphology and microstructure of submicron-scale craters on Chang’e-5 lunar soils. Craters are found only on a few soil grains. Most identified craters exhibit large diameter-to-depth (D/d) ratios (&gt;3) or are spatially clustered, indicating that they are formed by secondary ejecta rather than primary micrometeoroid impacts. Advanced electron microscopy investigations revealed that the microstructures of these craters are complex. Craters on the surfaces of two pyroxenes and one olivine have continuous nanophase iron (npFe<ce:sup loc=\"post\">0</ce:sup>)-bearing rims that extend over the crater and beyond over the crystal substrate, even when covered by an impact-produced redeposition layer. These features provide reliable evidence of solar wind exposure prior to the impact events that formed the craters. The possibility cannot be ruled out that the npFe<ce:sup loc=\"post\">0</ce:sup> particles present in these craters were previously produced by solar wind irradiation and not by impact. However, no clear signs are observed to establish the chronological order of formation of npFe<ce:sup loc=\"post\">0</ce:sup> particles in other craters studied. Furthermore, a crater on ilmenite has a minimum D/d value of 2.6, suggesting that this crater is likely formed by a primary micrometeoroid impact. Some unusual euhedral and elongated npFe<ce:sup loc=\"post\">0</ce:sup> particles observed on the crater floor may also have been produced earlier by solar wind irradiation and retained in the crater during subsequent impact. Shock melting and vapor deposition may also contribute to npFe<ce:sup loc=\"post\">0</ce:sup> formation by reduction during impact. Our findings imply that secondary impacts can also have a high velocity (1–2.38 km/s lunar escape velocity) and play a more crucial role in the microstructural and chemical changes of lunar soils than previously recognized. Moreover, the formation of npFe<ce:sup loc=\"post\">0</ce:sup> particles in submicron-scale craters may involve multiple processes, such as solar wind irradiation, shock melting, and vapor deposition, and their effects can be superimposed. These new formation processes of npFe<ce:sup loc=\"post\">0</ce:sup> particles are universal and fundamental to the evolution of materials on the Moon and other airless planetary bodies.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"24 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143877860","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Triple oxygen isotopes in eggshell carbonate as a proxy of late Cenozoic CO2 and primary productivity","authors":"Vincent J. Hare, Drake A. Yarian, J. Tyler Faith, Chris Harris, Julia A. Lee-Thorp, Benjamin H. Passey, Kathryn G. Sokolowski, Loïc Ségalen","doi":"10.1016/j.gca.2025.04.002","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.002","url":null,"abstract":"The triple oxygen isotope composition of biominerals is a promising recorder of changes in global primary productivity (GPP), as well as environment and animal physiology. However, application is largely unexplored, particularly in many regions of the world where eggshell is a common component of paleontological/archeological sites of the late Cenozoic. Ratites (ostriches and their relatives), as nonobligate drinkers, gain most of their oxygen from atmospheric O<ce:inf loc=\"post\">2</ce:inf> and leaves, meaning that their eggshell should carry a strong imprint of anomalous <mml:math altimg=\"si1.svg\" display=\"inline\"><mml:mrow><mml:msup><mml:mrow></mml:mrow><mml:mrow><mml:mn>17</mml:mn></mml:mrow></mml:msup><mml:mi mathvariant=\"normal\">O</mml:mi></mml:mrow></mml:math> in atmospheric O<ce:inf loc=\"post\">2</ce:inf> - which is ultimately related to GPP and CO<ce:inf loc=\"post\">2</ce:inf> levels. In this study, we analyzed fossil eggshells from different climate states of the late Cenozoic, notably the Middle Miocene, Late Miocene, and Last Glacial Maximum (LGM), as well as modern eggshell from the same region, southern Africa. We interpret our results using an existing animal body water model, which we modify for parameter estimation using Bayesian inverse methods. Our results show that the predominant signal in the triple isotopic composition of biomineral carbonate is that of global carbon cycling (i.e. the ratio of GPP:CO<ce:inf loc=\"post\">2</ce:inf>), meaning that with further refinement, a relatively common material can be used to reconstruct changes in planetary primary productivity for periods beyond the ice core record. During the Middle Miocene, we find that GPP was significantly lower than today, at 95% confidence. Comparison with box-model output of the atmospheric O<ce:inf loc=\"post\">2</ce:inf> budget shows that Middle Miocene GPP levels dropped to below 60% of modern values, assuming that Middle Miocene CO<ce:inf loc=\"post\">2</ce:inf> levels were between 441 and 472 ppm (95% confidence). The result is discussed, with potentially important implications for future climate change.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"16 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143877999","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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 isotope fractionation in magnetite produced by the marine magnetotactic bacterium Magnetovibrio blakemorei","authors":"Vincent Busigny, François P. Mathon, Matthieu Amor, François Guyot, Nicolas Menguy, Christopher T. Lefevre","doi":"10.1016/j.gca.2025.03.028","DOIUrl":"https://doi.org/10.1016/j.gca.2025.03.028","url":null,"abstract":"Magnetotactic bacteria (MTB) possess the ability to precipitate intracellular nanosized magnetite. Their emergence may date back to the early Archean (e.g. 3 Ga) but evidence of such a long history has yet to be provided. MTB identification in the rock record relies on magnetofossils, the residual magnetite crystals that may survive in time to rock deformation and low-grade metamorphism. Several criteria such as size, shape and magnetic properties have been proposed to distinguish magnetofossils from other magnetite sources. Recent experimental work on the freshwater strain <ce:italic>Magnetospirillum magneticum</ce:italic> AMB-1 revealed that Fe isotope composition represents a promising additional criterion, but isotopic characterization of distinct MTB strains and of their magnetite needs to be provided to evaluate the robustness of iron isotope signatures for paleontological applications. In the present work, we investigate the marine strain <ce:italic>Magnetovibrio blakemorei</ce:italic> MV-1 under various conditions selected to examine the influence of Fe concentration (50, 100 and 150 μM) and redox state (Fe(II)-ascorbate or Fe(III)-citrate) on bacterial biomineralization and determine associated Fe isotope fractionations. Our results confirm the preferential incorporation of light iron isotopes into magnetite relative to the bacterial growth medium previously observed in AMB-1. Modeling the evolution of the growth medium and magnetite isotope compositions by Rayleigh distillation process yields iron isotope fractionations (<ce:italic>i.e.</ce:italic> Δ<ce:sup loc=\"post\">56</ce:sup>Fe<ce:inf loc=\"post\">growth medium-magnetite</ce:inf> = δ<ce:sup loc=\"post\">56</ce:sup>Fe<ce:inf loc=\"post\">growth medium</ce:inf> − δ<ce:sup loc=\"post\">56</ce:sup>Fe<ce:inf loc=\"post\">magnetite</ce:inf>) ranging between 0.2 and 0.9 ‰ with a mean value of 0.55 (±0.35) ‰. This isotope fractionation shows no clear relation with iron concentration or redox state. Importantly, the enrichment in light iron isotope of biological magnetite contrasts with the isotopic characteristics of magnetite formed by abiotic precipitation, the latter being enriched in heavy isotopes. This suggests that Fe isotopes could be used as a biosignature for magnetofossils identification in terrestrial or extraterrestrial samples. Finally, in contrast with previous results obtained on AMB-1, no specific enrichment of <ce:sup loc=\"post\">57</ce:sup>Fe (relative to <ce:sup loc=\"post\">54</ce:sup>Fe, <ce:sup loc=\"post\">56</ce:sup>Fe and <ce:sup loc=\"post\">58</ce:sup>Fe) could be detected in MV-1 magnetite, which we interpret by differences in iron budgets between the two strains.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"24 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143901830","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multiple episodes of serpentinite alteration revealed by progressive leaching experiments","authors":"Aled D. Evans ,&nbsp;Matthew J. Cooper ,&nbsp;Dave Craw ,&nbsp;Damon A.H. Teagle","doi":"10.1016/j.gca.2025.04.001","DOIUrl":"10.1016/j.gca.2025.04.001","url":null,"abstract":"<div><div>Serpentinized mantle rocks typically experience multiple alteration events, but to date, identifying distinct serpentinization episodes remains difficult because whole rock geochemical and isotopic analyses reflect the cumulative sum of fluid-rock interactions. Here we unravel the alteration history of serpentinized mantle rocks by undertaking multi-stage progressive leaching experiments to isolate distinct geochemical and ⁸⁷Sr/⁸⁶Sr signatures hosted within serpentinized peridotites from the Troodos Mantle Sequence and Limassol Forest Complex, Cyprus that have different geological histories. Whole rock powders underwent an initial 10 % acetic acid solution leaching step before a subsequent 3 M HCl treatment. The remaining residue was then completely dissolved and analysed following a standard HF and HNO₃ digestion. For comparison an untreated sample of whole rock powder was also completely digested and analysed. In the Troodos Mantle Sequence, an initial serpentinization event with relatively primitive ⁸⁷Sr/⁸⁶Sr ratios (0.705 to 0.706) is recorded by the rock residues and is consistent with alteration by fluids sourced from the dehydrating downgoing Cyprus slab. A more radiogenic ⁸⁷Sr/⁸⁶Sr (0.7086–88) signal, consistent with Cyprus Messinian seawater and evaporites, is mobilised by the initial leaching step. These contrasting signatures in the mantle rocks are similar to the Sr-isotopic compositions of Troodos Mantle Sequence groundwaters. Although previous field observations within the Limassol Forest Complex indicate some serpentinization by Cretaceous seawater, evidence from progressive leaching experiments of pervasive serpentinization on the Cretaceous seafloor is not forthcoming. Our results show that most samples from the Limassol Forest Complex yield a radiogenic ⁸⁷Sr/⁸⁶Sr signal (0.7087), most consistent with mid-Miocene Messinian seawater and broadly coeval with significant mid-Miocene uplift of the Limassol Forest Complex. These results demonstrate that progressive leaching approaches can reveal distinct alteration episodes with contrasting ⁸⁷Sr/⁸⁶Sr ratios and geochemical signatures that contribute to the overall integrated bulk rock signal.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 188-204"},"PeriodicalIF":4.5,"publicationDate":"2025-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143853635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Basin-scale production of hyperacidic brines is critical for the formation of high-grade and large-tonnage uranium deposits in sedimentary basins","authors":"Yumeng Wang ,&nbsp;Guoxiang Chi ,&nbsp;Sean A. Bosman","doi":"10.1016/j.gca.2025.03.031","DOIUrl":"10.1016/j.gca.2025.03.031","url":null,"abstract":"<div><div>Unconformity-related uranium deposits (URU deposits) in the Proterozoic Athabasca Basin (Canada) represent the largest and richest (with average grades ranging from 0.127 to 19.5 wt% U) U deposits in the world. Fluid inclusion studies and experimental data suggest that the ore-forming fluids of URU deposits are hyperacidic (pH &lt; 3.5), oxidizing basinal brines carrying high concentrations of U (0.2 to 3700 ppm), which are several orders of magnitude higher than ordinary basinal and basement formation waters. While the oxidizing conditions of these fluids are well established, the mechanism responsible for the basin-scale generation of hyperacidic brines remains unknown. This paper aims to address this problem and to explain why the Athabasca Basin is exceptionally endowed with high-grade and large-tonnage uranium deposits. Based on petrographic and infrared hyperspectral logging data indicating basin-wide coexistence of kaolinite and illite in quartz-dominated sandstones, and fluid inclusion data showing high potassium (K) concentrations in diagenetic and ore-forming fluids within the Athabasca Basin, it is proposed that the production of hyperacidic brines resulted from a pervasive diagenetic reaction between K-rich brines and kaolinite: 3kaolinite [Al₂Si₂O₅(OH)₄] + 2 K⁺ ↔ 2illite [KAl₃Si₃O₁₀(OH)₂] + 3H₂O + 2H⁺. Geochemical modeling of fluid-rock reactions demonstrates that the basin-scale production of hyperacidic brines is achievable when a combination of three specific conditions is satisfied: 1) the presence of a thick package of compositionally mature sandstones, characterized by quartz-dominated framework grains with minimal (&lt;1%) feldspar and the interstitial space filled with kaolinite; 2) the development of K-rich brines through seawater evaporation above the sandstone package; and 3) low fluid/rock ratios, which enable the reaction between kaolinite and K-rich brines to reach equilibrium and produce illite and H⁺. Recognizing the basin-scale development of hyperacidic brines and the specific conditions entailed offers insights into why the Athabasca Basin is exceptionally endowed with high-grade, large-tonnage U deposits. The conditions of hyperacidic brine production revealed in this study may be used for evaluating the U mineralization potential of other sedimentary basins.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 1-12"},"PeriodicalIF":4.5,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143817441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rapid crystal growth promotes the precipitation of nanoscale fluid inclusions rich in halogens and metals in colloform sphalerite","authors":"Kai Luo, Alexandre Cugerone, Denis Fougerouse, Jia-Xi Zhou, Haiyang Xian, Yiping Yang, David W. Saxey, Vincent Motto-Ros, Xiao Sun, William D.A. Rickard, Steve M. Reddy","doi":"10.1016/j.gca.2025.04.003","DOIUrl":"https://doi.org/10.1016/j.gca.2025.04.003","url":null,"abstract":"Trace elements in sulfides are commonly used to determine the physicochemical conditions of ore deposit formation. The thermodynamic models underpinning these studies rely on the assumption that trace elements are incorporated into the mineral’s crystal structure, however recent atomic-scale investigations suggest that this assumption may be erroneous, especially in metamorphosed environments. Here, in primary undeformed colloform sphalerites from two Pb-Zn deposits in South-China, we study the microstructural, geochemical, and nanoscale distribution of trace elements. Our results show that colloform sphalerite hosts trace elements such as Ge (up to 5671 ppm) and Ga (up to 16307 ppm) in nanoscale polyphase inclusions (mainly 10–20 nm), comprising an aqueous solution and solid phases such as galena and pyrite. These Ge(-Ga) polyphase inclusions are rich in light elements and halogens (H, Li, Na, Cl, K) and heavier metals such as Mn and Pb, accounting for 5 %-78 % of the trace element budget in bulk sphalerite. We propose a model whereby the rapid crystallization of colloform sphalerite favors the preservation of elevated trace element concentrations in nanoscale fluid inclusions (i.e., Ga, Ge, Pb, Mn) that are in apparent thermodynamic disequilibrium with sphalerite. A nucleation mechanism is proposed involving the entrapment of dense liquid composed of an intermediate high-density disordered state under supersaturation conditions. Based on a global geochemical data compilation of colloform sphalerite, we show significant enrichment of Pb in colloform sphalerite and multiple positive correlations between Pb and Ge. This suggests that Pb-Ge-rich nanoscale dense-liquid inclusions may be a prevalent carrier for trace elements observed in colloform sphalerite textures. Similar colloform textures resulting from supersaturated solutions in minerals such as pyrite or quartz may also contain trace element-rich nanoscale inclusions. Presence of these nanoscale inclusions appears to have a minimal effect on the estimated formation conditions derived from sphalerite chemistry (temperature, <ce:italic>f</ce:italic>S<ce:inf loc=\"post\">2</ce:inf>). This study highlights the value of chemical mapping in revealing temperature variations in sphalerite.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"49 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143853639","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Strong and persistent mineral-specific lithium isotope fractionation: no discernable kinetic isotope effects during inorganic calcite and aragonite precipitation","authors":"Corinne Hite ,&nbsp;Joji Uchikawa ,&nbsp;Sambuddha Misra ,&nbsp;I.V. Satya Chanakya ,&nbsp;Pratyusha Chanda ,&nbsp;Richard E. Zeebe","doi":"10.1016/j.gca.2025.03.030","DOIUrl":"10.1016/j.gca.2025.03.030","url":null,"abstract":"<div><div>Stable lithium isotopes (δ⁷Li) of CaCO₃ minerals have increasingly been used as a tracer for changes in silicate weathering processes. However, there is limited understanding of the influence of physical and chemical conditions on δ⁷Li values of CaCO₃ minerals during their formation in aqueous solutions. Here, we examined Li isotope fractionation in inorganic calcite and aragonite precipitation experiments with systematic manipulations of solution pH and concentrations of total dissolved inorganic carbon species ([DIC] ≈ [HCO₃⁻] + [CO₃²⁻]) and calcium ion (Ca²⁺). Calcite and aragonite samples had δ⁷Li values lower than those of dissolved Li in solutions by about 3‰ and 16‰, respectively, indicating preferential uptake of the lighter ⁶Li isotopes. Aragonite consistently had δ⁷Li values lower than those of calcite by ∼13‰, likely due to differences in Li coordination and thereby the strength of bonds formed by/with Li within the respective mineral structure. We observed no statistically significant changes in aragonite nor calcite δ⁷Li values in response to changing solution pH, [DIC], [Ca²⁺], and CaCO₃ precipitation rates, indicating our solution chemistry manipulations imposed little effect on Li isotope fractionation. These findings lead us to argue that the observed Li isotope fractionations in calcite and aragonite with respect to dissolved Li in solutions are dominated by equilibrium isotope effects, and that kinetic effects for δ⁷Li values in CaCO₃ are either non-existent or too small to be expressed under our experimental conditions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 37-52"},"PeriodicalIF":4.5,"publicationDate":"2025-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143823313","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}