Chemical Geology最新文献

{"title":"Geogenic enrichment of dissolved phosphorus in a calcareous aquifer: Surface adsorption versus organic-matter mineralization","authors":"Wen Shao ,&nbsp;Yvonne Oelmann ,&nbsp;Yao Li ,&nbsp;Carsten Leven ,&nbsp;Harald Neidhardt","doi":"10.1016/j.chemgeo.2025.122944","DOIUrl":"10.1016/j.chemgeo.2025.122944","url":null,"abstract":"<div><div>Calcareous aquifers represent vital water resources and may critically influence the retention, release, and transport of phosphorus (P) within catchments. To address the limited understanding of P cycling in pristine calcareous aquifers, where both P retention and release processes remain poorly constrained, we conducted a hydrogeochemical field study in the Ammer floodplain catchment in Southwest Germany. Here, we combined groundwater hydrochemical analyses, sediment geochemistry data (e.g., P speciation by sequential extraction) and geochemical modeling to examine controls on total dissolved P (TDP) in a shallow calcareous aquifer. Inorganic orthophosphate (PO₄³⁻) dominated within the aqueous phase and correlated with reducing redox conditions (Eh), DOC, and NH₄⁺ concentrations (<em>p</em> &lt; 0.05, respectively), suggesting in situ microbial mineralization of sedimentary organic matter (OM) as a key mobilization mechanism. Sediment extractions revealed a strong positive correlation of surface-adsorbed PO₄³⁻ and organic P (P_org) with organic carbon (C) concentrations (<em>p</em> &lt; 0.05), indicating that OM constituted an important sink for both PO₄³⁻ and P_org. Distribution coefficients (Kd values) further suggested that P_org was preferentially adsorbed over PO₄³⁻. Supersaturation regarding calcite (saturation indices &gt; + 0.25) and a negative correlation between inorganic C and total P concentrations in the sediments (<em>p</em> &lt; 0.5) suggest a limited role for Ca-mineral precipitation in active P immobilization. In summary, our study advances mechanistic insights into P cycling in calcareous groundwater systems, thereby emphasizing the dual function of OM as both a sink and a source for P, a dynamic previously overlooked in floodplain aquifers.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122944"},"PeriodicalIF":3.6,"publicationDate":"2025-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144503873","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Optimized quantitative analysis of rare earth elements associated with typical secondary minerals in regolith-hosted deposits","authors":"Puqiu Wu ,&nbsp;Xurui Li ,&nbsp;Xiaoliang Liang ,&nbsp;Xiaoju Lin ,&nbsp;Jianxi Zhu","doi":"10.1016/j.chemgeo.2025.122942","DOIUrl":"10.1016/j.chemgeo.2025.122942","url":null,"abstract":"<div><div>Regolith-hosted rare earth element (REE) deposits are a major source of REEs, particularly the economically valuable heavy REEs (HREEs). Quantitative analysis of the various REE species is crucial for evaluating both the economic potential and mining efficiency of these deposits. The sequential extraction procedure (SEP) is widely used to quantify the speciation of heavy metals, but its applicability to REE analysis remains largely unexplored. Herein, SEP was optimized to quantify the occurrences of REEs associated with typical secondary minerals, specifically clay minerals and Fe (oxyhydr)oxides. The changes in mineral structure and morphology during extraction were examined using metal leaching experiments, transmission electron microscopy, and Mössbauer spectrum. These extractants demonstrated promising performance: 0.5 mol L⁻¹ (NH₄)₂SO₄ at pH 7 for ion-exchangeable REEs, 0.2 mol L⁻¹ (NH₄)₂C₂O₄ at pH 3 and 50 °C for amorphous Fe (oxyhydr)oxide–associated REEs; and a mixed solution of 0.2 mol L⁻¹ (NH₄)₂C₂O₄ and 0.1 mol L⁻¹ ascorbic acid at 90 °C for crystalline Fe (oxyhydr)oxide–associated REEs. This optimized protocol was successfully applied to separate REE fractions adsorbed on Fe (oxyhydr)oxide–clay mineral composites, the dominant REE carriers in regolith-hosted deposits. The results show that ion-exchangeable REEs, primarily associated with clay minerals such as kaolinite, constitute the main fraction, while Fe (oxyhydr)oxides such as goethite and hematite are preferentially enriched in HREEs. The efficiency and selectivity of the optimized SEP were further evaluated in relation to the chemical properties of extractants, mineral reactivity, and their relevance to geochemical applications.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122942"},"PeriodicalIF":3.6,"publicationDate":"2025-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335527","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Changes in the global P cycle in the Neoproterozoic recorded by the compositions of arc lavas","authors":"Paul Sotiriou,&nbsp;Marcel Regelous,&nbsp;Karsten M. Haase","doi":"10.1016/j.chemgeo.2025.122937","DOIUrl":"10.1016/j.chemgeo.2025.122937","url":null,"abstract":"<div><div>The mafic lavas erupted at active subduction zones have higher P/Nd ratios than the bulk continental crust. This difference has been explained by the delamination of apatite-rich lower crust, transferring P from the crust to the mantle at subduction zones. Here we compile geochemical data from arc basalts (5.5–6.5 wt% MgO) that have formed in the last 2 Ga and show that Proterozoic arcs erupted basalts with lower average P₆/Nd₆ ratios than those of Phanerozoic fossil and active arcs. The P₆/Nd₆ ratios of active arc basalts are negatively correlated with Th₆/La₆ and positively correlated with Sr₆/Th₆, Ba₆/Th₆ and ¹⁴³Nd/¹⁴⁴Nd, indicating that high P₆/Nd₆ ratios in arc lavas are not inherited from subducted sediments, which generally have low P/Nd ratios. Phosphatised basaltic oceanic crust has high P contents and P/Nd ratios due to interaction with seawater, and metalliferous sediments deposited at active spreading ridges have very high P contents (2000–16,000 ppm) and P/Nd ratios (100–1456) due to coprecipitation of P with Fe-oxyhydroxides formed when reducing hydrothermal vent fluids mix with oxygenated deep ocean water. We propose that the lower P/Nd ratios of Proterozoic mafic arc lavas are the result of lower concentrations of P in seawater at that time. An increase in the P content of seawater at the end of the Proterozoic, coincident with the Neoproterozoic Oxygenation Event, is reflected in lower concentrations of P in marine sediments before 800 Ma, and in 1.3 Ga metalliferous sediments. The high P/Nd ratios of many young arc lavas are therefore not representative of those formed during most of Earth's history. Since most of the continental crust was formed before the end of the Proterozoic, less delamination of apatite-bearing lower crust may be needed to the explain the low P/Nd ratio of the bulk continental crust.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122937"},"PeriodicalIF":3.6,"publicationDate":"2025-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335528","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Corrigendum to “Zinc isotopic composition of oceanic crust: Insights from oceanic gabbro cumulates and MORBs” [Chemical Geology 670 (2024) 122443 1–13]","authors":"Xia Wang ,&nbsp;Zaicong Wang ,&nbsp;Jakub Ciazela ,&nbsp;Zongqi Zou ,&nbsp;Wei Li ,&nbsp;Yuanyang Yu ,&nbsp;Ming Li ,&nbsp;Yongsheng Liu","doi":"10.1016/j.chemgeo.2025.122934","DOIUrl":"10.1016/j.chemgeo.2025.122934","url":null,"abstract":"","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122934"},"PeriodicalIF":3.6,"publicationDate":"2025-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The impact of burial diagenesis on soil-formed minerals in paleosols using stable isotopes of phyllosilicates and carbonate clumped isotopes","authors":"Julia A. McIntosh ,&nbsp;Neil J. Tabor ,&nbsp;Isabel P. Montañez","doi":"10.1016/j.chemgeo.2025.122941","DOIUrl":"10.1016/j.chemgeo.2025.122941","url":null,"abstract":"<div><div>To understand the effects of burial diagenesis on the stable isotope geochemistry of soil-formed clay and carbonate minerals in paleosols, samples were collected from seven cores, spanning middle- to upper-Pennsylvanian strata of the Illinois Basin, with varied maximum burial depths of 1–3 km. Mixed-layer illite-smectite and kaolinite mixtures give δ²H and δ¹⁸O values of −83 ‰ to −36 ‰ and 11.9 ‰ to 21.1 ‰ (VSMOW), respectively. After carbonates were screened petrographically for diagenetic textures using transmitted light and cathodoluminescence, measured clumped isotope Δ₄₇ values range from 0.504 to 0.563 ‰ (I-CDES). Resulting mineral formation temperatures for phyllosilicate mineral mixtures are 28 to 66 °C (mean = 47 °C), whereas T(Δ₄₇) estimates for calcites are 36 to 61 °C (mean = 45 °C). Calculated δ¹⁸O_water values from which phyllosilicate minerals and calcites precipitated under isotopic equilibrium ranges from −7.1 to −1.2 ‰ and − 1.4 to +4.9 ‰, respectively. Closed and open-system phyllosilicate-fluid exchange modeling indicates that phyllosilicate alteration occurred in the presence of a low temperature brine or meteoric water and is interpreted to occur in a layer-by-layer illitization transformation. Due to the lack of diagenetic textures and positively correlated T(Δ₄₇) and δ¹⁸O_water, calcites are interpreted to have undergone solid-state bond reordering. Despite low to moderate temperatures (&lt;125 °C) and varying depths of shallow burial (1–3 km), solid-state transformation of phyllosilicates and calcites indicates paleosols had prolonged exposure to burial conditions which has implications for the use of paleosol minerals for paleoenvironmental reconstructions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122941"},"PeriodicalIF":3.6,"publicationDate":"2025-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335531","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Compositional variability and alteration dynamics of chromitites under greenschist metamorphism in the Kızıldağ ophiolite, southern Türkiye","authors":"Recep Melih Akmaz ,&nbsp;Ibrahim Uysal ,&nbsp;Ben-Xun Su ,&nbsp;Ahmet D. Şen ,&nbsp;Wen-Jun Hu ,&nbsp;Hans-Michael Seitz ,&nbsp;Dirk Müller ,&nbsp;Alireza Eslami","doi":"10.1016/j.chemgeo.2025.122936","DOIUrl":"10.1016/j.chemgeo.2025.122936","url":null,"abstract":"<div><div>This study presents a complete alteration sequence in chromitites from the Kızıldağ ophiolite (southern Türkiye), documenting three distinct chromite types that record processes related to Neotethyan subduction. Chromitites exhibit predominantly lenticular forms and occasionally banded textures, embedded within mantle peridotites and the mantle-crust transition zone, specifically harzburgite and dunite. Our analysis categorizes chromite grains into three groups: fresh, altered, and porous. Fresh chromites are characterized by high contents of Cr₂O₃ ranging from 42.69 to 57.08 wt% and Al₂O₃ from 12.46 to 25.34 wt%. In contrast, altered chromites, typically located along fractures or at the edges of fresh grains, show significant variability in chemical composition, with Cr₂O₃ content between 43.34 and 63.94 wt% and Al₂O₃ between 2.91 and 14.84 wt%. Porous chromites, distinguished by their porous structure, present Cr₂O₃ contents from 44.58 to 52.66 wt% and Al₂O₃ from 3.00 to 8.38 wt%. Notably, altered and porous chromites demonstrate substantial enrichments in Fe and trace elements such as Mn, Ni, Zn, Co, and Ga, indicating a shift due to metamorphic processes. The observed high Cr# (0.68–0.93) and low Mg# (0.25–0.65) values in rims of the altered and porous chromite further illustrate the metamorphic influence on chromite, with greenschist-facies conditions indicated by the Cr–Al–Fe³⁺ diagram at temperatures below 450 °C. The alteration dynamics reflect a progression that initiates with the olivine matrix and advances through reactions involving fresh chromites. This progression results in mass loss, the formation of chlorite, and the porous structures. Our findings contribute to the understanding of metamorphic alteration processes in chromitites and provide a detailed account of the geochemical trends (such as Fe/Mg exchange and trace element enrichment) that reflect greenschist-facies metamorphism. The evidence of chlorite formation and the prevalence of porous textures highlight the influence of metamorphic fluids over serpentinization, offering a model for chromite alteration in supra-subduction zones. This research elucidates the metamorphic history of chromitites in the Kızıldağ ophiolite.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"692 ","pages":"Article 122936"},"PeriodicalIF":3.6,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335453","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Tracing CO2 and helium origins of mineral spring water of the Water Circuit of Minas Gerais in southeastern Brazil","authors":"Hendryk Gemeiner ,&nbsp;Hung Kiang Chang ,&nbsp;Larissa Neris Alcara ,&nbsp;Marcelo Martins Reis ,&nbsp;Peter H. Barry ,&nbsp;Amauri Antonio Menegário","doi":"10.1016/j.chemgeo.2025.122939","DOIUrl":"10.1016/j.chemgeo.2025.122939","url":null,"abstract":"<div><div>The Water Circuit of Minas Gerais, situated in the southeastern region of the Brazilian state of Minas Gerais, has garnered significant interest since the 19th century due to the abundance of mineral springs with heightened mineral compositions and high levels of CO₂. However, despite decades of research, the origins of this natural CO₂ enrichment phenomenon in these springs remain unclear. Here, we present the first noble gas isotope data from these spring waters combined with hydrochemical data. Calcium bicarbonate waters predominate in the spa town parks of Caxambu, Águas de Contendas and Lambari, whereas sodium bicarbonate and “mixed type” is found in the Cambuquira park. All samples display high He concentrations and elevated ⁴He/²⁰Ne values with respect to atmospheric values, indicating a deep origin and the gradual accumulation of radiogenic ⁴He in the waters. Spring samples show air-corrected ³He/⁴He (R_c/R_a) values between 0.55 and 3.39 R_a, suggesting an admixture of crustal and mantle volatile contributions. A consistent ³He/⁴He decrease with increasing distance from the Caxambu shear zone is observed, indicating that the release of deep fluids is fault controlled. We suggest that major fault segments within the Caxambu shear zone serve as continuous pathways for the ascent of mantle-derived CO₂ and He, enriching the springs of the Water Circuit region. Carbon isotope data indicates a significant contribution of carbonate-derived CO₂. We combined discharge estimates with carbon concentrations to quantify a CO₂ flux of 4.26 × 10⁶ mol year⁻¹ into the surface system from all springs in the four spa parks.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122939"},"PeriodicalIF":3.6,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144320887","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Post-depositional effects on chromium in black shales and implications for paleo-redox reconstructions based on chromium isotopes","authors":"Ziyao Fang ,&nbsp;Xiaoqing He ,&nbsp;Xi Yu ,&nbsp;Dandan Li ,&nbsp;Xiaolin Zhang ,&nbsp;Yanan Shen ,&nbsp;Liping Qin","doi":"10.1016/j.chemgeo.2025.122938","DOIUrl":"10.1016/j.chemgeo.2025.122938","url":null,"abstract":"<div><div>Chromium (Cr) is a redox-sensitive element, and its isotope system has been widely used as a paleo-redox proxy, providing insights into the evolution of oxygen in Earth's oceans and atmosphere. Black shales serve as an important archive for sedimentary Cr isotope data. The precise interpretation of Cr isotope records in black shales relies on a comprehensive understanding of the geochemical behavior of Cr throughout black shale formation and diagenesis. Here, we applied synchrotron-based X-ray spectroscopy, sequential leaching, and Cr isotope analysis to investigate the Cr species in sedimentary black shales from various sites and geologic periods. The results show that most of the authigenic Cr, which is the fraction of Cr precipitated from seawater, is not associated with the usual hydrogenetic phases (e.g., organic matter or iron-rich components) but rather resides in clay minerals. We further demonstrate that post-depositional diagenetic processes can induce redistribution of authigenic Cr in black shales, leading to enrichments of authigenic Cr in silicate minerals. Moreover, these processes were accompanied by significant Cr isotope fractionation, which substantially altered the Cr isotope compositions of the original phases. Similar effects can influence other trace elements, such as vanadium, in black shales. The findings imply that effectively separating authigenic and detrital fractions of these elements in black shales is unlikely. Instead, applying detrital corrections using the concentrations of typical detrital tracers (such as titanium and aluminum) after bulk isotope analysis is a more practical approach. This limitation affects the reliability of paleo-environmental interpretations derived from isotope data in black shales with high detrital contributions.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122938"},"PeriodicalIF":3.6,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144335452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Controls of sediment-bound and dissolved nutrient transport from a glacierised metasedimentary catchment in the high Arctic","authors":"Lukasz Stachnik ,&nbsp;Jon Hawkings ,&nbsp;Andrea Spolaor ,&nbsp;Katarzyna Stachniak ,&nbsp;Dariusz Ignatiuk ,&nbsp;Sławomir Sitek ,&nbsp;Krzysztof Janik ,&nbsp;Elżbieta Łepkowska ,&nbsp;Francois Burgay ,&nbsp;Marcin Daniel Syczewski ,&nbsp;Delia Segato ,&nbsp;Pablo Forjanes ,&nbsp;Liane G. Benning","doi":"10.1016/j.chemgeo.2025.122940","DOIUrl":"10.1016/j.chemgeo.2025.122940","url":null,"abstract":"<div><div>Rapid warming in polar and alpine areas is causing significant glacier mass loss and resulting in increasing freshwater delivery to the oceans. Recent research indicates that higher meltwater water runoff is likely to increase solute and sediment transport, which will include nutrients, to downstream environments. This enhanced delivery may drive a negative feedback effect on atmospheric CO₂ concentrations by stimulating primary production in fjords and near-coastal regions. Labile sediment-bound nutrient species constitute a high proportion of the total nutrient yield from glacierised catchments, but studies that investigate their source and behaviour are sparse. Here we determine sediment-bound and dissolved nutrient (Si, Fe, P) delivery from a polythermal glacier in SW Spitsbergen. Suspended sediment and dissolved samples were collected from subglacial outflows and a downstream site. Our results show high spatial variability in chemical weathering processes resulting in differences in sediment-bound nutrient concentration. Sulphide oxidation and carbonate dissolution appear more important in a channelised system underlain by rocks metamorphosed in green schist facies, and silicate mineral weathering appears more important in smaller subglacial outflows underlain by rocks undergone intense metamorphism in amphibolite facies. Sediments from the channelised outlet have two times higher content of sediment-bound highly reactive iron (∼0.29 % dry weight, hereafter d.w.) than the minor subglacial outflows. In contrast, sediment-bound amorphous silica (ASi) is almost double in the minor subglacial outflows compared to the channelised outlet (∼0.17 % d.w. vs ∼0.10 % d.w.). The yield of sediment-bound Fe and Si (2.3 and 1.3 10³ kg km⁻² yr⁻¹, respectively) was several times higher than the dissolved flux of those elements. Sediment-bound Fe yields were in the range of values noted previously for the Greenland Ice Sheet. Our data reinforces the critical role of sediment-bound nutrients on elemental cycling in glacierised basins of the high Arctic.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122940"},"PeriodicalIF":3.6,"publicationDate":"2025-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144330231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dating multiple fractionation trends in pegmatites – Implications for the genesis of a large lithium pegmatite province in West-Africa","authors":"Marieke Van Lichtervelde ,&nbsp;Oscar Laurent ,&nbsp;Prince Ofori Amponsah ,&nbsp;Isaac Iwan E. Williams","doi":"10.1016/j.chemgeo.2025.122935","DOIUrl":"10.1016/j.chemgeo.2025.122935","url":null,"abstract":"<div><div>The race for lithium supply for the green energy transition has brought Li pegmatites, the primary source of Li in the world, to the forefront. Their origins and mechanisms of formation are still debated, and geochemical tools to distinguish granite-related from anatectic pegmatites are still needed. In the current study, we combine two classical approaches, i.e., alkali fractionation in micas coupled to Nb-Ta-oxide geochronology, to date multiple fractionation trends in pegmatites from a large lithium pegmatite province in Ghana. We investigated distinct fractionation trends in the different pegmatites and we timeframed these trends by dating columbite-group minerals associated with primary magmatic micas. Distinct Rayleigh-type Rb/Cs fractionation paths were modeled using different starting Rb and Cs melt compositions that can be attained by direct partial melting of the meta-sedimentary country rocks. Columbite-group mineral dating reveals that each of these fractionation paths occurred at different ages spanning ca. 140 Myr. Moreover, our data shows that the oldest pegmatites correspond to poorly fractionated, Li-rich, Nb-Cs-Ta-Sn-poor pegmatites, whereas the youngest are the most fractionated, Cs-Ta-rich pegmatites (up to levels of the major Lithium-Cesium-Tantalum pegmatites worldwide). The proposed model of formation for this large Li-bearing province involves at least three distinct stages of partial melting and melt extraction at ca. 2170, 2080 and 2030 Ma. The produced melt batches evolved independently through fractional crystallization, the spodumene-bearing pegmatites being the least fractionated, and the “true LCT” pegmatites the most fractionated.</div></div>","PeriodicalId":9847,"journal":{"name":"Chemical Geology","volume":"691 ","pages":"Article 122935"},"PeriodicalIF":3.6,"publicationDate":"2025-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144289932","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}