Geochimica et Cosmochimica Acta最新文献

{"title":"Marine chemical sedimentary protoliths determined for ca. 3.71 Ga calc-silicate schists and quartzites from the Isua Supracrustal Belt","authors":"Mike J. Zawaski, Johanna Marin-Carbonne, Nigel M. Kelly, Alexey Ulianov, Anne-Sophie Bouvier, Stephen J. Mojzsis","doi":"10.1016/j.gca.2025.03.029","DOIUrl":"https://doi.org/10.1016/j.gca.2025.03.029","url":null,"abstract":"Foliated calc-silicate schists and quartzites from a ca. 3.71 Ga domain within the northeastern part of the Isua Supracrustal Belt (southern West Greenland) may be interpreted as either deformed layered “metasedimentary” rocks, or the metasomatic fluid alteration products of a deformed mafic igneous precursor (i.e., basaltic protolith). One important reason for protolith assignment in this case stems from the debated claim that these are originally clastic sedimentary rocks which host the oldest interpretable bio-mediated sedimentary structures (cf. “stromatolites”). To determine the protolith, we used correlated mineralogical, outcrop- and regional-scale structural, and in situ major-, minor- and trace-element geochemical analyses coupled with high spatial resolution Si, O, and S isotope measurements. We conclude the protoliths were sedimentary chemical precipitates with a minor detrital clay fraction. This interpretation is bolstered by the low levels of generally immobile elements (Zr, Cr, Y, Ti, and P) which rule out either a purely igneous or clastic sedimentary origin. Further evidence for a sedimentary origin includes heterogeneous Si and O isotopes and mass-independent S isotope values (Δ<ce:sup loc=\"post\">33</ce:sup>S &gt; 0, S-MIF), along with rare earth element (REE + Y) signatures that show light REE-depletion in PAAS normalized REE patterns and seawater-like Y/Ho. Pervasive deformation has masked or obliterated most if not all primary sedimentary structures, such that no chemical or physical features can be reliably used as indicators for (shallow) water depth at time of deposition. Although we conclude these rocks are of sedimentary origin we reiterate (viz. our previous work) that the nabla-shaped (∇) features found within them are not biogenic stromatolites. Instead, evidence points towards their formation as products of local and regional strain and recrystallization, long after deposition.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"31 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143877904","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":"Sulfur outgassing and in-gassing in lunar orange glass beads and implications for 33S “Anomaly” in the Moon","authors":"Xue Su ,&nbsp;Youxue Zhang ,&nbsp;Yang Liu","doi":"10.1016/j.gca.2025.03.026","DOIUrl":"10.1016/j.gca.2025.03.026","url":null,"abstract":"<div><div>Our recent investigations have discovered inward diffusion (in-gassing) of moderately volatile elements (MVEs; e.g., Na, K and Cu) from volcanic gas into volcanic beads/droplets. In this work, we examine the distribution of sulfur in lunar orange glass beads. Our analyses reveal that sulfur exhibits a non-uniform distribution across the beads, forming “U” or “W” shaped profiles typical of in-gassing. A model developed to assess sulfur contributions from different sources (original magmatic sulfur versus atmospheric in-gassed sulfur) in the orange beads indicates that atmospheric sulfur in-gassed during eruption contributes approximately 9–24 % to the total sulfur content of an orange bead, averaging around 16 %. This in-gassed sulfur is derived from the eruption plume, where atmospheric sulfur could undergo photochemical reactions induced by UV light, leading to mass independent fractionation and a distinct sulfur isotope signature.</div><div>Interestingly, a recent study discovered a small mass independent isotope fractionation of sulfur in lunar orange glass beads in drive tube 74002/1 and a lack of such mass independent isotope fractionation in black glass beads in the same lunar sample. This finding contrasts with sulfur in lunar basalts, which typically exhibit mass dependent fractionation. With our work, the observed mass independent fractionation signal in sulfur isotopes of orange beads can be attributed to the in-gassing of photolytic sulfur in the optically thin part of the eruption plume where UV light can penetrate. Using the sulfur isotope data of lunar orange beads, we estimate that the Δ³³S value of atmospheric sulfur is approximately −0.18 ‰. Our study provides new insights into the complex dynamics of volatile elements in lunar volcanic processes, highlighting the role of in-gassing in shaping sulfur isotope signatures in volcanic glass beads.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 164-175"},"PeriodicalIF":4.5,"publicationDate":"2025-03-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824998","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":"Polymetallic Te-rich melts contribute to efficient enrichment and precipitation of Au in hydrothermal ore deposits","authors":"Gao-Hua Fan ,&nbsp;Jian-Wei Li ,&nbsp;Ri-Chen Zhong ,&nbsp;Sarah A. Gleeson ,&nbsp;Zhuo-Sen Yao ,&nbsp;Daniel E. Harlov ,&nbsp;Xiao-Dong Deng ,&nbsp;Hao Cui ,&nbsp;Chang Yu ,&nbsp;Wen-Sheng Gao","doi":"10.1016/j.gca.2025.03.027","DOIUrl":"10.1016/j.gca.2025.03.027","url":null,"abstract":"<div><div>Tellurides are abundant in a large variety of hydrothermal Au deposits. Previous studies have proposed that these phases crystallize from polymetallic Te-rich melts that may act as scavengers for Au to form high grade deposits. However, the conditions under which Te-rich melts form and whether such melts can act as agents to concentrate Au have not been directly assessed. Here, we present an experimental study using natural ore samples from a giant Te-rich Au deposit (Dongping, China) to show that tellurides in Au ores crystallized from polymetallic melts and these melts behaved as a critical agent for Au enrichment and precipitation. The samples investigated contain abundant polymetallic inclusions, which consist of various telluride-gold mineral assemblages as well as minor chalcopyrite. Individual inclusions typically comprise one micron-sized gold grain. Annealing experiments of these inclusions were carried out at 300, 350, 400, and 450 °C. The polymetallic inclusions had relatively subtle changes in morphology and texture at 300 and 350 °C, but changed markedly at 400 and 450 °C, accompanying with the formation of abundant droplet-like and/or vermiculate gold grains randomly dispersed in the telluride matrix. Three <em>in-situ</em> scanning electron microscopy heating–cooling experiments with different heating rates and durations revealed a eutectic temperature of 243 to 270 °C for polymetallic tellurides, at which native gold began to dissolve into molten tellurides. During the heating processes of the three experimental runs, changes in topographic contrast occurred, with the formation of transient holes in the tellurides and the appearance of tellurides on the surface of chalcopyrite. These observations are indicative of localized migration of the molten tellurides. Upon cooling in run #1 and #2, native gold recrystallized at ∼ 340 °C from the molten tellurides and subsequently regrew in a gradual manner. After these two runs, many newly-formed telluride-gold globules were observed occurring as fracture- and/or cavity-infillings within the host pyrite, further confirming molten state of the polymetallic minerals. Collectively, our new data demonstrate that polymetallic Te-rich melts with a complete melting temperature of ∼ 340 to 400 °C are responsible for the formation of telluride-gold mineral assemblages in natural Te-rich Au ores. Such melts can act as an important Au scavenger and facilitate Au precipitation. Our findings highlight the significance of polymetallic Te-rich melts as a key agent for concentrating Au to form high-grade Au ores worldwide.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 176-187"},"PeriodicalIF":4.5,"publicationDate":"2025-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824999","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":"Untangling the effects of crustal and source processes on the Mo isotope systematics of oceanic arcs: insights from the Tonga-Kermadec subduction system","authors":"R. Pontow ,&nbsp;R. Bezard ,&nbsp;M. Willbold ,&nbsp;S. Turner ,&nbsp;T. Di Rocco","doi":"10.1016/j.gca.2025.03.025","DOIUrl":"10.1016/j.gca.2025.03.025","url":null,"abstract":"<div><div>The Mo stable isotope system is a promising tracer of crustal recycling. As subduction zones play a major role in returning crustal material back to the Earth’s mantle, understanding the Mo isotope behavior during processes operating at these settings is paramount. The Mo isotope compositions of arc lavas are highly variable and despite recent advances in this field, questions remain about Mo isotope fractionation and mobilization during slab processes and the relative effect of magmatic differentiation on the Mo isotope compositions (<em>δ</em>^98/95Mo) of arc lavas. The Tonga-Kermadec arc is well suited to assess and disentangle crustal and source processes in intra-oceanic arc settings owing to widespread felsic volcanism and along-arc source variations, characterized by increasing proportions of a metasedimentary component from the northern Tonga to the southern Kermadec arc. In the pursuit of these objectives, we analyzed a set of basaltic to dacitic tholeiitic arc lavas from volcanoes covering the whole length of the Tonga-Kermadec arc and sediments from DSDP site 204. Tonga-Kermadec arc lavas have highly variable Mo concentrations (0.21 and 2.35<!--> <!-->µg/g) and <em>δ</em>^98/95Mo values (−0.29 to +0.34 ‰). At some volcanoes, considerable <em>δ</em>^98/95Mo variations in samples as primitive as basalt are correlated with indices of differentiation and Sr-Nd radiogenic isotopes, indicating an impact of crustal assimilation on Mo isotope compositions. However, the <em>δ</em>^98/95Mo of the most primitive lavas analyzed for each volcano appear to have preserved primary melt signatures, since they form an along-arc trend mirroring those of Pb isotope averages, a proxy that is controlled by source processes in the Tonga-Kermadec arc. Using these data, a north–south decrease in <em>δ</em>^98/95Mo of the sources of arc magmas is resolved. This is interpreted to reflect the competing signals of isotopically heavy slab-fluids (<em>δ</em>^98/95Mo higher than D-MORB values) with that of an increasing contribution of a metasedimentary component that is lighter than the DMM toward the south. Our data suggest that crustal assimilation can significantly distort primitive <em>δ</em>^98/95Mo even in mafic magmas from simple intra-oceanic arcs. The induced intra-volcano <em>δ</em>^98/95Mo scatter has the potential to obscure along-arc variability as well as systematics with typical chemical and isotopic proxies used to characterize arc lava sources (e.g., Ba/Th, radiogenic isotopes). However, we also show that a careful evaluation of these effects can, at least in the Tonga-Kermadec arc, allow the assessment of arc lava source compositions.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 13-36"},"PeriodicalIF":4.5,"publicationDate":"2025-03-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143817442","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":"Interaction of metal oxyions and phosphate with carbonate green rust: Insights into Earth’s modern and ancient environments","authors":"Ichiko Sugiyama,&nbsp;Itay Halevy","doi":"10.1016/j.gca.2025.03.018","DOIUrl":"10.1016/j.gca.2025.03.018","url":null,"abstract":"&lt;div&gt;&lt;div&gt;Carbonate green rust (GRCO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;) is often found in suboxic and anoxic environments, and is known to be highly reactive towards dissolved metals and other aqueous compounds. Though the reactivity of GRCO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; towards a variety of aqueous compounds has been determined in previous studies, its reactivity under conditions relevant to modern and ancient marine environments has not been systematically explored. Furthermore, the fate of the aqueous compounds upon aging of the GRCO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; remains almost completely unknown.&lt;/div&gt;&lt;div&gt;To inform the interaction of GRCO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; with oxyion-forming metals during the mineral’s precipitation and aging, we conducted a series of co-precipitation experiments of Cr&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;VI&lt;/mi&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt;, Mo&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;VI&lt;/mi&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt;, V&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;V&lt;/mi&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt;, U&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;VI&lt;/mi&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt;, and PO&lt;span&gt;&lt;math&gt;&lt;msubsup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;4&lt;/mn&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;mo&gt;−&lt;/mo&gt;&lt;/mrow&gt;&lt;/msubsup&gt;&lt;/math&gt;&lt;/span&gt; with GRCO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; in seawater-analog solutions, at pH 8.0, 25 °C, and under anoxic conditions. The experimental results are provided as uptake percentages at different metal:Fe ratios and as a series of partition coefficients of the studied oxycation and oxyanions between aqueous solution and GRCO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt;. Additionally, aging experiments up to 13 months in duration were conducted at metal concentrations of 1 &lt;span&gt;&lt;math&gt;&lt;mi&gt;μ&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt;M and under the same experimental conditions, to quantify the retention or release of the metals associated with GRCO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; transformation to thermodynamically stable phases. Uptake of both V&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;V&lt;/mi&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; and Cr&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;VI&lt;/mi&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; was near-quantitative, and these metals were retained during aging. We identify reduction by the Fe&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;II&lt;/mi&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; in GRCO&lt;span&gt;&lt;math&gt;&lt;msub&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/math&gt;&lt;/span&gt; as the predominant mechanism of Cr&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;VI&lt;/mi&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; uptake, whereas in V&lt;span&gt;&lt;math&gt;&lt;msup&gt;&lt;mrow&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mi&gt;V&lt;/mi&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/math&gt;&lt;/span&gt; both reduction and adsorption are implied by our results. Up to &lt;span&gt;&lt;math&gt;&lt;mo&gt;∼&lt;/mo&gt;&lt;/math&gt;&lt;/span&gt;20% of ","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 96-112"},"PeriodicalIF":4.5,"publicationDate":"2025-03-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824982","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":"Changes in calcium ion concentration as the common driver for Na, K, S, and B incorporation during inorganic calcite precipitation in Mg-free artificial seawater","authors":"Joji Uchikawa, Szabina Karancz, Mariëtte Wolthers, Laura Pacho, Dustin T. Harper, Donald E. Penman, Lennart J. de Nooijer, Gert-Jan Reichart, Richard E. Zeebe","doi":"10.1016/j.gca.2025.03.022","DOIUrl":"https://doi.org/10.1016/j.gca.2025.03.022","url":null,"abstract":"Calcite is known to incorporate a range of non-constituent ions during its precipitation from aqueous solutions. Their concentrations (measured as <ce:italic>E</ce:italic>/Ca ratios, where <ce:italic>E</ce:italic> denotes the elemental forms of non-constituent ions) in calcite formed in seawater can serve as useful tools for paleoceanographic studies. But this requires concrete understanding of the incorporation patterns and their dependence to environmental factors at the time of mineral precipitation. Here, we present Na/Ca, K/Ca, S/Ca, and B/Ca ratios of inorganic calcite samples generated in laboratory experiments using Mg-free artificial seawater with systematic manipulations of pH, [DIC], and [Ca<ce:sup loc=\"post\">2+</ce:sup>]. The three parameters were varied both individually (the pH, DIC, and Ca experimental series) and in tandem (the pH-Ca and DIC-Ca series) to form calcites under variable versus near-constant precipitation rates (denoted as <ce:italic>R</ce:italic>). All measured <ce:italic>E</ce:italic>/Ca ratios showed a robust positive linear dependence to changes in [Ca<ce:sup loc=\"post\">2+</ce:sup>] in the Ca, pH-Ca, and DIC-Ca series, irrespective of changes in <ce:italic>R</ce:italic>. While K/Ca and S/Ca ratios changed almost exclusively with [Ca<ce:sup loc=\"post\">2+</ce:sup>], Na/Ca and B/Ca ratios showed an additionally strong increase with increasing pH and a more moderate increase with rising [DIC], when <ce:italic>R</ce:italic> changed accordingly in the pH and DIC series. While <ce:italic>R</ce:italic>-driven kinetic effects and/or formation of certain cation–anion pairs may be important for the elemental uptake in calcite under some circumstances, these mechanisms or processes cannot fully account for the observed trends in every experimental series for all <ce:italic>E</ce:italic>/Ca ratios considered here. We propose that the observed <ce:italic>E</ce:italic>/Ca trends can be comprehensively explained by simultaneously considering the nonequivalent influence of changes in solution [Ca<ce:sup loc=\"post\">2+</ce:sup>] and [CO<ce:inf loc=\"post\">3</ce:inf><ce:sup loc=\"post\">2−</ce:sup>] on step-specific kink formation dynamics and the size difference between the respective non-constituent ions (K<ce:sup loc=\"post\">+</ce:sup>, Na<ce:sup loc=\"post\">+</ce:sup>, SO<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">2−</ce:sup>, and B(OH)<ce:inf loc=\"post\">4</ce:inf><ce:sup loc=\"post\">−</ce:sup> and B(OH)<ce:inf loc=\"post\">3</ce:inf>) relative to Ca<ce:sup loc=\"post\">2+</ce:sup> and CO<ce:inf loc=\"post\">3</ce:inf><ce:sup loc=\"post\">2−</ce:sup> that constitute the calcite lattice.","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"23 1","pages":""},"PeriodicalIF":5.0,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824993","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":"Towards building a unified adsorption model for goethite based on variable crystal face contributions: II. Pb(II), Zn(II) and phosphate adsorption","authors":"Mario Villalobos,&nbsp;América Xitlalli Cruz-Valladares,&nbsp;Alan U. Loredo-Jasso,&nbsp;Paola Villar-Nava,&nbsp;Fernanda López-Castilla,&nbsp;Luis Fernando Huerta-Hernández","doi":"10.1016/j.gca.2025.03.023","DOIUrl":"10.1016/j.gca.2025.03.023","url":null,"abstract":"<div><div>Following the first series of this work, where the acidity constants of the two surface proton-reactive sites of goethite were found, as well as the capacitance values for each of the four previously well-characterized goethites, in this second part we report the successful simulation of the adsorption of two heavy metal cations [Pb(II) and Zn(II)] and an oxyanion (phosphate) of high affinity for the goethite surface. All experimental data were freshly generated with the same four previously characterized goethites with independent crystal surface composition determinations and calculations of the corresponding surface site densities, to maintain complete self-consistency and avoid unwanted interfering variables. Three experimental pH adsorption edges at different total concentrations were constructed for each cation on each goethite, and four adsorption isotherms at different pH values for phosphate. Two surface complexes bound to singly-coordinated surface oxygens were found for both types of ions to optimally describe the experimental data: In the case of the cations, a bidentate complex with the unhydrolized cation and a monodentate complex with the hydroxylated cation. For phosphate a bidentate complex with the deprotonated phosphate moiety and a monodentate complex with a mono-protonated phosphate yielded the optimal results (a small contribution of a protonated bidentate complex was also found necessary to describe the data at pH 4). The values of the optimized goethite affinity constants for Pb(II) were <em>ca</em>. two orders of magnitude higher than those of Zn(II), and the optimized values of Charge Distributions were different for each metal cation, but most of the charge for the bidentate complexes occurred at the 1-plane, while that for the monodentate hydroxylated complexes occurred mostly at the 0-plane. In the case of phosphate, the same three stoichiometries as those found previously for arsenate described all adsorption isotherm data, but their affinity constants were found to be higher (less than one order of magnitude) than those for arsenate; and their charge distributions were slightly different as well.</div><div>The results of this work contribute to progressively build a unified model that describes the geochemical behavior of goethite towards adsorption of species of environmental interest. This endeavor may eventually be of aide to describe more complex systems and the interactions occurring among different component species as related to the presence of goethite.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 1-12"},"PeriodicalIF":4.5,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143739901","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":"Localized versus distributed dissolution in carbonate rocks: The key role of microstructure","authors":"Theo Briolet ,&nbsp;Elisabeth Bemer ,&nbsp;Olivier Sissmann ,&nbsp;Jerome Fortin","doi":"10.1016/j.gca.2025.03.019","DOIUrl":"10.1016/j.gca.2025.03.019","url":null,"abstract":"<div><div>Carbonate rocks are widespread and highly reactive, making their study a key topic for various environmental and anthropogenic issues. Dissolution of carbonate rocks is controlled by different factors, related to the fluid (chemical composition, pH, flow velocity) or the rock (mineral content, porosity, permeability, microstructure), and results in different dissolution patterns. To investigate the specific impact of microstructure on dissolution pattern, we perform controlled dissolution experiments under identical experimental conditions on two nearly pure calcite limestones (Euville and Lavoux) characterized by different grain and pore structures. Two distinct dissolution patterns are evidenced by the integration of CT-scanner and thin section observations, implying significant microstructural control. For Euville samples, dissolution is distributed across the entire width of the sample, whereas for Lavoux samples, dissolution is localized in wormhole-type channels. These contrasting responses are explained by differences in pore connectivity, reactivity and accessible specific surface areas. Conventional expressions of Péclet and Damköhler dimensionless numbers fail to differentiate the two studied limestones in a <em>Pe</em>-<em>Da</em> diagram despite their different behavior. Specific expressions are then defined to account for the specific accessibility to the intragranular microporosity and the associated specific surface area. The proposed approach allows a clear positioning of both limestones in areas of <em>Pe</em>-<em>Da</em> diagram consistent with the observed dissolution patterns.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 113-133"},"PeriodicalIF":4.5,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824983","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":"Nickel hydroxide–nickel carbonate competitive growth on carbonate surfaces","authors":"Winnie Liu ,&nbsp;Nabajit Lahiri ,&nbsp;Sebastian T. Mergelsberg ,&nbsp;Shawn L. Riechers ,&nbsp;John S. Loring ,&nbsp;Mark E. Bowden ,&nbsp;Sebastien N. Kerisit","doi":"10.1016/j.gca.2025.03.020","DOIUrl":"10.1016/j.gca.2025.03.020","url":null,"abstract":"<div><div>The thermodynamic and kinetic factors controlling the competitive heterogeneous nucleation and growth of ubiquitous metal carbonate and hydroxide phases are poorly understood. In this work, calcite (CaCO₃) and magnesite (MgCO₃) powders were reacted with NiCl₂ (0–600 μM) for 7 days at 22 °C and 5 °C. The reacted powders were analyzed with X-ray photoelectron spectroscopy (XPS), scanning electron microscopy, and energy-dispersive X-ray spectroscopy to characterize the Ni surface precipitates formed. Evidence from these techniques pointed to the formation of mixed Ni carbonate-Ni hydroxide amorphous surface precipitates. On calcite, XPS detected primarily Ni(OH)₂ despite the initial solutions being more supersaturated with respect to gaspéite (NiCO₃) than to theophrastite (Ni(OH)₂) by a factor of 17–18. In contrast, NiCO₃ was the dominant component detected by XPS on magnesite in the same conditions. Decreasing the temperature had the effect of increasing the proportion of NiCO₃ to the detriment of Ni(OH)₂. The experimental observations were consistent with low lattice/cation size mismatch favoring NiCO₃ nucleation and temperature most influencing Ni(OH)₂ nucleation. Comparison to previous work on Co-reacted powders indicated the differences in lattice/cation size mismatch and/or water exchange rate impacted the composition of the surface precipitates more than the relative thermodynamic stabilities of the competing minerals. This work explored the heterogeneous growth regime of Ni carbonate and hydroxide phases on carbonate surfaces and shed light on the factors that control the competition between surface precipitates when mineral surfaces are in contact with aqueous solutions supersaturated with respect to multiple mineral phases. These results contribute to geochemists’ efforts toward interpreting data from geochemical systems with elevated Ni concentrations, improving Ni environmental remediation and recovery strategies, and predicting the fate and transport of Ni in geochemical systems.</div></div>","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"396 ","pages":"Pages 182-194"},"PeriodicalIF":4.5,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143821320","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":"Bayesian calibration of the 40K decay scheme with implications for 40K-based geochronology","authors":"Jack N. Carter ,&nbsp;Caroline E.J. Hasler ,&nbsp;Anthony J. Fuentes ,&nbsp;Andrew J. Tholt ,&nbsp;Leah E. Morgan ,&nbsp;Paul R. Renne","doi":"10.1016/j.gca.2025.03.024","DOIUrl":"10.1016/j.gca.2025.03.024","url":null,"abstract":"&lt;div&gt;&lt;div&gt;The K/Ar and &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar geochronometers are based on the naturally occurring radionuclide &lt;sup&gt;40&lt;/sup&gt;K. Their precision and accuracy are limited by uncertainties on the &lt;sup&gt;40&lt;/sup&gt;K decay constants and, in the case of the &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar geochronometer, the isotopic composition of neutron fluence monitors. To address these limitations, we introduce a Bayesian calibration of the &lt;sup&gt;40&lt;/sup&gt;K decay scheme. We formulate robust priors for all model parameters including partial &lt;sup&gt;40&lt;/sup&gt;K decay constants, &lt;sup&gt;238&lt;/sup&gt;U and &lt;sup&gt;235&lt;/sup&gt;U decay constants, and age offset parameters to account for phenomena that can perturb apparent U-Pb and &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar ages. We then harness a set of complementary &lt;sup&gt;40&lt;/sup&gt;Ar/&lt;sup&gt;39&lt;/sup&gt;Ar, &lt;sup&gt;238&lt;/sup&gt;U/&lt;sup&gt;206&lt;/sup&gt;Pb, and &lt;sup&gt;235&lt;/sup&gt;U/&lt;sup&gt;207&lt;/sup&gt;Pb data from well- characterized geological samples with ages from 1.919 ka to 2000 Ma to derive Bayesian estimates of the &lt;sup&gt;40&lt;/sup&gt;K decay constants. Posterior values for the partial &lt;sup&gt;40&lt;/sup&gt;K decay constants are &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;β&lt;/mi&gt;&lt;/mrow&gt;&lt;mo&gt;-&lt;/mo&gt;&lt;/msup&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;= (4.9252 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.0054) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−10&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt;, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;β&lt;/mi&gt;&lt;/mrow&gt;&lt;mo&gt;+&lt;/mo&gt;&lt;/msup&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; = (5.6658 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.1543) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−15&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt;, &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mi&gt;EC&lt;/mi&gt;&lt;/mrow&gt;&lt;mrow&gt;&lt;mo&gt;∗&lt;/mo&gt;&lt;/mrow&gt;&lt;/msup&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; = (5.7404 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.0053) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−11&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt;, and &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;msub&gt;&lt;mrow&gt;&lt;mi&gt;EC&lt;/mi&gt;&lt;/mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/msub&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;= (4.9060 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.2942) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−13&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt; (uncertainties reported at the 68 % (1&lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;σ&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;) credible interval). These combine to a total &lt;sup&gt;40&lt;/sup&gt;K decay constant &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;msub&gt;&lt;mi&gt;λ&lt;/mi&gt;&lt;mrow&gt;&lt;mi&gt;tot&lt;/mi&gt;&lt;/mrow&gt;&lt;/msub&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;= (5.5042 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.0054) &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 10&lt;sup&gt;−10&lt;/sup&gt; yr&lt;sup&gt;−1&lt;/sup&gt;. Model estimates of the &lt;sup&gt;238&lt;/sup&gt;U and &lt;sup&gt;235&lt;/sup&gt;U decay constants are statistically indistinguishable from those reported by &lt;span&gt;&lt;span&gt;Jaffey et al. (1971)&lt;/span&gt;&lt;/span&gt;. Posterior values of the &lt;sup&gt;40&lt;/sup&gt;K decay constants and the &lt;sup&gt;40&lt;/sup&gt;Ar*/&lt;sup&gt;40&lt;/sup&gt;K isotopic composition of Fish Canyon sanidine (FCs) define a K/Ar FCs age of 28.183 &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mo&gt;±&lt;/mo&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; 0.017 Ma (1&lt;span&gt;&lt;math&gt;&lt;","PeriodicalId":327,"journal":{"name":"Geochimica et Cosmochimica Acta","volume":"397 ","pages":"Pages 149-163"},"PeriodicalIF":4.5,"publicationDate":"2025-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143824994","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}