Geochimica et Cosmochimica Acta最新文献

{"title":"Gold solubility enhanced by H2O in sulfur-bearing magma: Implications for gold partitioning and mineralization","authors":"Xingcheng Liu, Lanqin Li, Ting Xu, Xiaolin Xiong, Jintuan Wang, Zaicong Wang, Hugh St.C. O’Neill","doi":"10.1016/j.gca.2025.01.017","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.017","url":null,"abstract":"Most endogenic gold deposits are associated with H<ce:inf loc=\"post\">2</ce:inf>O-rich magmatism or their associated hydrothermal systems. However, the role that H<ce:inf loc=\"post\">2</ce:inf>O plays in the transfer and enrichment of gold remains elusive. Here we conducted piston cylinder experiments at 1 GPa and 850 or 950 °C on sulfur-bearing dacitic compositions with variable H<ce:inf loc=\"post\">2</ce:inf>O contents and under different controlled oxygen fugacity. Our results show that increasing the H<ce:inf loc=\"post\">2</ce:inf>O contents of the melts from 2 to 15 wt% enhances gold solubilities by up to 37-fold at moderate oxidizing conditions (approximately 2 log units above the fayalite-magnetite-quartz buffer). This dramatic increase results from H<ce:inf loc=\"post\">2</ce:inf>O-induced elevation of melt FeO content, which increases reduced sulfur concentrations, thereby promoting Au-S complexation in the melt. Under these conditions, H<ce:inf loc=\"post\">2</ce:inf>O-rich, near fluid-saturated melts exhibit gold partition coefficients between sulfide and silicate melt that are one order of magnitude lower than in H<ce:inf loc=\"post\">2</ce:inf>O-poor melts. Thus, H<ce:inf loc=\"post\">2</ce:inf>O content, combined with moderate oxygen fugacity, exerts substantial control on the gold fertility of primary magmas. These findings indicate that both partial melting of H<ce:inf loc=\"post\">2</ce:inf>O-rich sources and crystallization of H<ce:inf loc=\"post\">2</ce:inf>O-rich magmas can effectively mobilize and concentrate gold. The process is further enhanced when fluid exsolution occurs before gold sequestration into sulfides. In contrast, copper partitioning shows stronger dependence on oxygen fugacity than H<ce:inf loc=\"post\">2</ce:inf>O content, explaining the differing behavior of gold and copper during magmatic-hydrothermal evolution. These results provide new insights into the formation of gold-rich magmatic-hydrothermal ore deposits.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"29 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055250","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":"Discovery of Ge2+ in quartz: Evidence from EPR/XAS experiments and DFT calculations, and implications for Ge/Si systematics","authors":"Rudolf I. Mashkovtsev, Sanda M. Botis, Jinru Lin, Reza Deevsalar, Leo Ka Long Cheung, Eli Wiens, Ayetullah Tunc, Ning Chen, Roman Chernikov, Yuanming Pan","doi":"10.1016/j.gca.2025.01.025","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.025","url":null,"abstract":"The Ge/Si systematics as a biogeochemical tracer with diverse applications from paleo-climatic reconstructions to discrimination of magma sources and elucidation of Earth’s early evolution hinges on the coherent behavior of these elements in the tetravalent state. However, determination of Ge speciation in quartz and other silicate minerals is technically challenging because this element almost invariably occurs at several parts per million or lower concentrations. This contribution reports a detailed study of Ge speciation in quartz by combining single-crystal electron paramagnetic resonance spectroscopy, synchrotron X-ray absorption spectroscopy, and <ce:italic>ab initio</ce:italic> theoretical calculations. Our single-crystal and powder electron paramagnetic resonance spectra of artificially irradiated quartz reveal a suite of previously reported Ge electron centers (GECs) such as [GeHLi<ce:inf loc=\"post\">2</ce:inf>]<ce:sup loc=\"post\">0</ce:sup> and [GeHH<ce:inf loc=\"post\">2</ce:inf>]<ce:sup loc=\"post\">0</ce:sup> centers as well as a new GeHLi center. These multiply-compensated GECs in artificially irradiated quartz suggest that their precursors before irradiation involve the diamagnetic Ge<ce:sup loc=\"post\">2+</ce:sup> state. Ge <ce:italic>K</ce:italic>-edge X-ray absorption spectroscopic data of selected quartz samples further support the presence of Ge<ce:sup loc=\"post\">2+</ce:sup>. Theoretical calculations reproduce the experimental <ce:sup loc=\"post\">1</ce:sup>H and <ce:sup loc=\"post\">7</ce:sup>Li hyperfine constants of the [GeHLi<ce:inf loc=\"post\">2</ce:inf>]<ce:sup loc=\"post\">0</ce:sup> center and suggest the new GeHLi center to be a new variant of the multiply-compensated GECs with the second monovalent cation in a distant <ce:italic>c</ce:italic>-axis channel, again supporting the Ge<ce:sup loc=\"post\">2+</ce:sup> state. The presence of Ge<ce:sup loc=\"post\">2+</ce:sup> in sedimentary-diagenetic quartz, in particular, challenges existing thermodynamic data that Ge<ce:sup loc=\"post\">4+</ce:sup> is the only stable oxidation state in aqueous solutions under near-surface conditions. Incorporation of Ge<ce:sup loc=\"post\">2+</ce:sup> in quartz and other silicates can significantly affect Ge/Si fractionations, with important implications for their applications as a biogeochemical tracer from surficial environments to magmatic-hydrothermal systems, Earth’s core-mantle differentiation, and other planetary processes.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"59 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055426","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":"Processes controlling nickel and its isotopes in anoxic sediments of a seasonally hypoxic bay","authors":"Sarah Fleischmann ,&nbsp;Florian Scholz ,&nbsp;Jianghui Du ,&nbsp;Jan Scholten ,&nbsp;Derek Vance","doi":"10.1016/j.gca.2025.01.016","DOIUrl":"10.1016/j.gca.2025.01.016","url":null,"abstract":"<div><div>Nickel (Ni) is a biologically active metal whose reactivity and isotope fractionation in the marine realm are strongly influenced by biological and redox-related processes, giving the stable isotope system potential for studying past ocean environments. Reducing, organic-rich, sediments constitute an important sink of Ni from the modern ocean. Importantly, at open ocean upwelling margins, these kinds of sediment record the isotope composition of the modern deep ocean. Thus, records of their Ni isotope composition in the past have the potential to record the past deep ocean isotope composition and the oceanic isotope mass balance. However, the detailed processes controlling the upwelling sink are not fully understood. Here, we address this issue through data for sediments, porewaters and the water column of Kiel Bight in the Western Baltic Sea. This setting preserves sediments that have similar characteristics to those of open ocean upwelling margins, allowing us to study specific controlling processes in a well constrained setting.</div><div>In common with sediments from open-ocean upwelling settings, Ni is well-correlated with carbon in solid sediment, suggesting delivery of Ni via rain of organic carbon from the water column. Overall, porewaters at all sites studied show increasing Ni concentrations from around 10 nM near the sediment–water interface to as high as 50 nM at 25 cm depth. This increase is correlated with increases in ammonia concentrations, suggesting release of Ni from anaerobic respiration of organic matter. However, porewater Ni/NH₄ ratios are always lower than Ni:N of water column suspended particulate matter, suggesting an additional process that removes Ni from the porewater. Porewater sulphide also increases with depth, from as low as zero at the sediment–water interface to levels as high as 3 mM at 25 cm. Overall, porewater Ni isotopes become heavier with depth, from bottom water δ⁶⁰Ni around +0.5 to +1‰, to values as high as +2.3‰ at depth. All these observations strongly suggest that Ni is removed from porewater into a solid sulphide. Mass balance indicates that over 90% of the Ni delivered in organic material to the sediment–water interface is transferred from organic matter into solid sulphide. Upward diffusive fluxes lead to the loss of a small amount back to the water column via a benthic flux. Given the large proportion of Ni retained within the sediment, the loss of such Ni does not strongly impact the isotope composition of the buried pool. These data are crucial in clarifying the processes controlling the size and isotope composition of organic-rich sediments on upwelling margins.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"391 ","pages":"Pages 1-15"},"PeriodicalIF":4.5,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055247","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Equilibrium indium isotope fractionation in chloride-rich aqueous solutions using first-principles calculations","authors":"Haochen Duan, Fang Huang","doi":"10.1016/j.gca.2025.01.026","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.026","url":null,"abstract":"Aqueous indium (In) speciation and isotope fractionation factors are important to understand the origin and transport of indium during magmatic-hydrothermal and atmosphere-hydrosphere processes. Here, we investigate indium speciation in chloride-rich aqueous solutions and explore their reduced partition function ratios (10&lt;ce:sup loc=\"post\"&gt;3&lt;/ce:sup&gt;&lt;ce:italic&gt;lnβ&lt;/ce:italic&gt;) using first-principles calculations. The simulations with initial configurations of InCl(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;5&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2+&lt;/ce:sup&gt;, InCl&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;+&lt;/ce:sup&gt;, InCl&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt;, InCl&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;−&lt;/ce:sup&gt; and InCl&lt;ce:inf loc=\"post\"&gt;5&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt; were performed at 400 and 600 K, respectively. The results show that InCl(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;5&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2+&lt;/ce:sup&gt;, InCl&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;+&lt;/ce:sup&gt;, InCl&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;2.4&lt;/ce:inf&gt;, InCl&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;−&lt;/ce:sup&gt; and InCl&lt;ce:inf loc=\"post\"&gt;5&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt; are the stable In&lt;ce:sup loc=\"post\"&gt;3+&lt;/ce:sup&gt; species at 400 K, and their 10&lt;ce:sup loc=\"post\"&gt;3&lt;/ce:sup&gt;&lt;ce:italic&gt;lnβ&lt;/ce:italic&gt; decreases from 1.00 ‰, 0.89 ‰, 0.83 ‰, 0.75 ‰ to 0.66 ‰. At 600 K, the stable In&lt;ce:sup loc=\"post\"&gt;3+&lt;/ce:sup&gt; species are composed of InCl(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;5&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2+&lt;/ce:sup&gt;, InCl&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;3.7&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;+&lt;/ce:sup&gt;, InCl&lt;ce:inf loc=\"post\"&gt;3&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;1.7&lt;/ce:inf&gt;, InCl&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;−&lt;/ce:sup&gt; and InCl&lt;ce:inf loc=\"post\"&gt;5&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;2−&lt;/ce:sup&gt; with their 10&lt;ce:sup loc=\"post\"&gt;3&lt;/ce:sup&gt;&lt;ce:italic&gt;lnβ&lt;/ce:italic&gt; decreasing from 0.46 ‰, 0.42 ‰, 0.39 ‰, 0.35 ‰ to 0.31 ‰. These results indicate that 10&lt;ce:sup loc=\"post\"&gt;3&lt;/ce:sup&gt;&lt;ce:italic&gt;lnβ&lt;/ce:italic&gt; is negatively correlated with the coordination number and bond length of chlorine ligands in aqueous In&lt;ce:sup loc=\"post\"&gt;3+&lt;/ce:sup&gt; species. Meanwhile, water molecules are gradually removed from the first hydration shell gradually with increasing temperature, such as InCl&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;+&lt;/ce:sup&gt; and InCl&lt;ce:inf loc=\"post\"&gt;4&lt;/ce:inf&gt;(H&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;O)&lt;ce:inf loc=\"post\"&gt;2&lt;/ce:inf&gt;&lt;ce:sup loc=\"post\"&gt;−&lt;/ce:sup&gt; to ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"36 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055370","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":"Bulk silicate Earth-like 142Nd and 182W mantle component sampled by 2.0 Ga Onega Basin picrites, Fennoscandia","authors":"I.S. Puchtel, J.L. Hellmann, H. Rizo, J. Blichert-Toft, A.V. Stepanova, A.V. Samsonov, R.J. Walker","doi":"10.1016/j.gca.2025.01.013","DOIUrl":"https://doi.org/10.1016/j.gca.2025.01.013","url":null,"abstract":"In order to further evaluate the timing and possible mechanisms responsible for the transition from both positive and negative to no <ce:sup loc=\"post\">142</ce:sup>Nd and <ce:sup loc=\"post\">182</ce:sup>W anomalies in the Archean mantle, we obtained <ce:sup loc=\"post\">142,143</ce:sup>Nd, <ce:sup loc=\"post\">176</ce:sup>Hf, <ce:sup loc=\"post\">186,187</ce:sup>Os, <ce:sup loc=\"post\">182</ce:sup>W isotope and lithophile trace and highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd, and Re) abundance data for mantle plume-derived ∼2.0 Ga picrites and an associated differentiated mafic–ultramafic sill from the Onega Basin on the Fennoscandian Shield. The Onega Basin picrites share striking chemical similarities with the modern Kilauea picrites, featuring enrichments in light rare earth elements (LREE; La/Sm<ce:inf loc=\"post\">N</ce:inf> = 1.5 ± 0.2), depletions in heavy rare earth elements (HREE; Gd/Yb<ce:inf loc=\"post\">N</ce:inf> = 2.2 ± 0.1), positive high field strength element (HFSE) anomalies (Hf/Hf* = 1.2 ± 0.1, Nb/Nb* = 1.6 ± 0.1), and modern bulk silicate Earth (BSE)-like average W/Th = 0.20 ± 0.08 (2SD). Model calculations indicate that the parental picritic magmas were likely derived from 3 % equilibrium batch melting of a LREE-depleted garnet lherzolite PREMA-type mantle source containing a component of recycled oceanic crust.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"59 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143055371","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":"Microstructural analysis of phosphorus (P)-bearing assemblages in type 3 chondrites: Implications for P condensation and processing in the early solar nebula","authors":"M.C. Benner ,&nbsp;V.R. Manga ,&nbsp;B.S. Prince ,&nbsp;L.M. Ziurys ,&nbsp;T.J. Zega","doi":"10.1016/j.gca.2025.01.012","DOIUrl":"10.1016/j.gca.2025.01.012","url":null,"abstract":"<div><div>As the limiting element in the development of living systems, it is crucial to understand the history of phosphorus (P), from its stellar origins to its arrival on planetary surfaces. A key component in this cycle is understanding the forms of P delivered to the presolar nebula and their subsequent evolution on planetary bodies, including meteorites. Here, we report on the P distribution in the Bishunpur (LL3.15), Queen Alexandra Range (QUE) 97008 (L3.05), and Allan Hills (ALHA) 77307 (CO3.0) chondrites to determine its origins and secondary processing in the solar protoplanetary disk and on meteorite parent bodies using a coordinated analytical approach. In support of the microstructural characterization, we used density functional theory (DFT) to calculate the Gibbs free energy of the Fe₃P – Ni₃P binary under non-ideal mixing conditions in its entire range of composition and temperature space and performed equilibrium condensation modeling. We identified 106 P-bearing regions in these petrologic type-3 chondrites and find that the major P-bearing minerals are schreibersite ((Fe, Ni)₃P) and merrillite (Ca₉NaMg(PO₄)₇). Bishunpur predominately contains merrillite, which occurs in rims on chondrules and as hopper crystals. QUE 97008 primarily contains merrillite in association with metal and sulfides. Microstructural evaluation of merrillite in Bishunpur suggests igneous origins within the chondrule-forming region, whereas merrillite in QUE 97008 formed via condensation. In comparison, the dominant P-bearing phase in ALHA 77307 is P-bearing metal, including two Ni-rich schreibersite grains that are composed of 45 and 52.5 at.% Ni, far higher than predicted by equilibrium condensation. The equilibrium thermodynamic model, including our newly described non-ideal schreibersite solid solution, predicts the formation of a miscibility gap where (Fe_0.63, Ni_0.37)₃P and Ni₃P form via nebular condensation. We therefore suggest that Ni-rich schreibersite formed through non-equilibrium condensation.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"392 ","pages":"Pages 207-222"},"PeriodicalIF":4.5,"publicationDate":"2025-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143020254","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":"Evaluating the crystallization and eruptive histories of low-titanium basalts with 2D and 3D studies","authors":"Z.E. Wilbur ,&nbsp;J.J. Barnes ,&nbsp;S.A. Eckley ,&nbsp;T. Erickson ,&nbsp;R.A. Zeigler ,&nbsp;K. Domanik","doi":"10.1016/j.gca.2024.10.018","DOIUrl":"10.1016/j.gca.2024.10.018","url":null,"abstract":"<div><div>Volcanic products returned from the Apollo missions over 50 years ago provide a unique perspective into the magmatic evolution of the Moon. However, questions<!--> <!-->remain regarding the volatile loss, crystallization, and emplacement histories of lunar lavas. To address gaps in our understanding of the eruptive histories of lunar lavas, we investigate phase chemistry and 3D morphologies of low-titanium Apollo 15 basalts belonging to the olivine-normative and quartz-normative suites. We report the 2D and 3D petrography, mineral chemistry, and 3D void space morphologies of 15499, 15555, 15556, and the lesser studied 15495 and 15608 basalts. Quantitative apatite chemistry shows a wide range of apatite volatile compositions and that low-Ti basalt 15495 may contain the most OH-rich compositions measured from the Moon. Analyses of metal grains within the low-Ti basalts have expanded the field of expected Ni and Co metal concentrations for Apollo 15 mare basalts and are used to determine the petrogenesis of two of the studied samples. Coupling 2D chemistry with nondestructive 3D morphologic analyses provides critical insights on the relative timing of volatile exsolution in low-titanium lavas. Through the analysis of vesicles and vugs from X-ray computed tomographic data, we report the first 3D void space volume percentages for a suite of low-Ti basalts and show that these basalts degassed before the onset of mesostasis (e.g., apatite) crystallization. We use calculated cooling rates and 3D morphologic analyses to show that the studied basalts crystallized at various depths in separate lava flows, and 15608 represents the quenched margin of a mare flow. Our work highlights the value of combining 2D and 3D analytical techniques to study the emplacement history of basalts that lack geological context.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 110-124"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142673574","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Adsorption pathways of boron on clay and their implications for boron cycling on land and in the ocean","authors":"Simon J. Ring ,&nbsp;Michael J. Henehan ,&nbsp;Roberts Blukis ,&nbsp;Friedhelm von Blanckenburg","doi":"10.1016/j.gca.2024.08.014","DOIUrl":"10.1016/j.gca.2024.08.014","url":null,"abstract":"<div><div>Reversible adsorption and isotope fractionation of boron on the surface of clay minerals is a key process that impacts boron isotope cycling in porewater, rivers and the ocean. However, the differences in boron isotope fractionation factors between various clay minerals and their dependence on fluid chemistry are not well known. We performed two sets of experiments, using solutions of pure water with added boron and seawater, to explore the isotope behavior during adsorption of boron onto kaolinite, smectite and illite. We found that the amount of sorbed boron increases with ionic strength of solutions and is proportional to the cation exchange capacity of a given clay mineral. Maximum adsorption is observed in alkaline seawater, which we attribute to the efficient fixation of magnesium-borate ion pairs onto negatively charged surface sites. Isotopic fractionation is modestly different between clays and demonstrates that clay surfaces preferentially sorb borate, even when the concentration of borate in solution is low. In both pure water and seawater, adsorbed complexes retain the isotopic composition of their dissolved precursors (borate or boric acid) with minimal isotopic fractionation. In other words, isotopic composition of adsorbed boron is set by the ability of clays to adsorb boron from an already fractionated boron pool rather than specific fractionation associated with the complexation reaction. Our experimental results allow us to provide revised constraints on the adsorbed boron being transported in terrestrial fluids and the ocean.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 74-83"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142090198","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"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":"Association of tungsten with aluminosilicate mineral colloids and silicotungstates in soil porewaters: Insights into the unexpectedly high tungsten mobility in soil","authors":"Lei Lu ,&nbsp;Jing Sun ,&nbsp;Yu Dai ,&nbsp;Yaoyu Zhou ,&nbsp;Haojie Cui ,&nbsp;Ming Lei ,&nbsp;Huihui Du","doi":"10.1016/j.gca.2024.11.032","DOIUrl":"10.1016/j.gca.2024.11.032","url":null,"abstract":"<div><div>As an emerging contaminant, tungsten (W) displays unexpectedly high mobility in soil despite its extremely low solubility, challenging current scientific understanding. This paradox underscores the limited knowledge regarding the specific W species responsible for its high mobility. In this study, a series of field and incubation experiments were conducted across multiple soil types to investigate the distribution and speciation of W in soil porewater, widely known as ″the most mobile fraction″. Ultrafiltration analysis revealed that W in soil porewater predominantly existed in colloidal-size (5 kDa–0.45 μm) phases rather than the ″truly-dissolved″ phase (&lt;5 kDa). Especially in deeper soil layers approaching shallow groundwater, colloidal W content exceeded 93 %. XANES spectra showed that colloidal W was mainly in the hexavalent state (W^VI), and insoluble W metal (W⁰) entering the soil could rapidly oxidize into W^VI through biotic or abiotic processes. Advanced characterizations, including STEM-EDS-SAED, SEM-EDS, and SR-XRF, identified aluminosilicate mineral colloids as the primary carrier for W in soil porewater. Within these W-bearing aluminosilicate mineral colloids, W was primarily present as Al₂(WO₄)₃ precipitates with a W–Al distance of ∼ 3.64 Å, as confirmed by EXAFS. Additionally, a minor fraction of silicotungstates was also detected in the colloidal fraction using XAS and STEM-EDS-SAED. These two species were further substantiated through geochemical modeling and density functional theory (DFT) analysis. Importantly, this study hypothesizes that the associations of W with aluminosilicate mineral colloids and silicotungstates are widespread across different soil types. The finding suggests that colloid-associated W mobility is a dominant yet previously overlooked process, helping to explain why W, despite its low solubility, exhibits exceptionally high mobility in soils.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 1-13"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142804467","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":"Cadmium isotope fractionation and neutron capture effects in lunar samples","authors":"W. Abouchami ,&nbsp;F. Wombacher ,&nbsp;S.J.G. Galer","doi":"10.1016/j.gca.2024.12.001","DOIUrl":"10.1016/j.gca.2024.12.001","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Early pioneering studies of Apollo lunar soils revealed a geochemical dichotomy reflecting a dominance of mare and highland lithologies, with variable additions of Procellarum KREEP Terrane material. Here, we use the moderately volatile element cadmium to identify the sources and processes responsible for mass-dependent Cd stable isotope variations in the lunar regolith. In addition, capture of thermal neutrons by &lt;sup&gt;113&lt;/sup&gt;Cd, resulting from galactic cosmic rays (GCR) impacting the lunar surface, provides a means of reconstructing the exposure history of the regolith.&lt;/div&gt;&lt;div&gt;We report TIMS double spike Cd stable isotope data on samples from the Apollo 12, 16 and 17 missions, consisting of twelve soils of varying maturity, two ferroan anorthosites, and orange glass 74220. Cadmium abundances are generally lower in mare (12 to 79 ng/g) than highland soils (∼70 to 95 ng/g). Cadmium stable isotope compositions, expressed as ε&lt;sup&gt;112/110&lt;/sup&gt;Cd, display a larger range in mare (∼0 to + 106) than in highland (+60 to + 97) soils. The two anorthosites exhibit contrasting ε&lt;sup&gt;112/110&lt;/sup&gt;Cd values (−107 &lt;em&gt;vs.&lt;/em&gt; + 47) and Cd concentrations similar to those of highland soils. Orange glass 74220 is Cd-rich (290 ng/g) and has a light Cd isotopic composition (ε&lt;sup&gt;112/110&lt;/sup&gt;Cd = -27) due to condensation of Cd vaporized during lava fountaining.&lt;/div&gt;&lt;div&gt;A broad trend of decreasing Cd abundance and increasing heavy isotope enrichment with increasing maturity is observed for mare soils but is not apparent for the highland soils. These characteristics might arise from space weathering, including micrometeorite bombardment, but simple mass balance indicates that meteoritic addition has a negligible effect on the lunar regolith Cd. Likewise, neutron capture on &lt;sup&gt;113&lt;/sup&gt;Cd tends to increase with maturity in mare soils while being greater and relatively uniform in highland soils, reflecting a longer exposure history and more extensive reworking of the highland regolith. Neutron capture effects were not resolved for immature mare soils, orange glass and one anorthosite, indicating these samples experienced only short near-surface exposure to GCR.&lt;/div&gt;&lt;div&gt;The relationships between Cd abundances and isotope effects reveal three distinct correlations for the highland soils and the mature and immature mare soils, respectively. These are best explained by simple binary mixing between isotopically distinct components. The “heavy” Cd components of mare and highland soils have variable but overall low Cd contents while the cadmium-rich component is always isotopically “light”, and common, at least, to all mare soils. The strong correlation between Cd stable isotopic composition and neutron capture effects in mare soils constrains the ε&lt;sup&gt;112/110&lt;/sup&gt;Cd of the neutron capture-free component to be −4.9 ± 2.3, that is marginally lighter than that of the Bulk Silicate Earth (0.01 ± 0.94). This component is predominantly found in immature, K","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"389 ","pages":"Pages 43-58"},"PeriodicalIF":4.5,"publicationDate":"2025-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142841588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}