We welcome contributions on all aspects of mineralogy, including environmental, soil science, metamorphic, plutonic, deep Earth, planetary, applied mineralogy, and so on. All approaches are welcome: analytical, experimental and theoretical.
Orals: Fri, 8 May, 14:00–15:45 | Room K1
Phase transitions in olivine are considered as a key mechanism for triggering faulting at depths greater than 300 km, leading to the nucleation of deep-focus earthquakes (DFEs), under conditions where ductile flow should dominate. Olivine phase transitions are characterized by three fundamental features thought to promote faulting: an exothermic reaction, a large negative volume change, and a strong mechanical contrast. However, it is unclear whether faulting at depth requires all three characteristics or can be triggered by just one.
To address this question, we conducted a series of deformation experiments using a large-volume press at the P61b beamline at DESY synchrotron (Hamburg, Germany). Experiments were performed on novaculite, while samples were transforming into coesite. This phase transition is dominated by a significant volume reduction but involves only minor latent heat release, allowing us to investigate the role of volume change. Throughout the experiments, we simultaneously collected X-ray diffraction patterns and images, together with acoustic emission (AEs) monitoring. Our results show that the growth rate of the high-pressure phase varies strongly with pressure–temperature (P-T) conditions and equilibrium overstep. All experiments were conducted under high differential stress. Thousands of AEs were collected in each experiment, whose locations were reconstructed using arrival times from six acoustic transducers placed around the sample assembly. In experiments characterized by lower transformation rates, AE locations mark fault planes that developed within initially intact sample volumes. Analysis of the AE catalogs reveals magnitude–frequency distributions spanning a wide range of b-values, which vary with P-T conditions and transformation kinetics. We observed that brittle faulting yields an expected b-value of about 1 and was related to the nucleation of coesite grains.
These experiments represent the first example of transformational faulting in deforming, polycrystalline quartz undergoing a high-pressure phase transition under elevated differential stress. Our findings indicate that a volume-changing phase transition with minor latent heat release can promote brittle failure at high pressure, providing new constraints on the mechanisms of deep faulting and expanding the range of mineral phase transitions potentially relevant to crustal and mantle seismicity.
How to cite: Mingardi, G., Gasc, J., Farla, R., Alvaro, M., and Schubnel, A.: Transformational faulting: Is olivine special? Evidence from quartz-coesite phase transition, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7996, https://doi.org/10.5194/egusphere-egu26-7996, 2026.
Quartz is a ubiquitous, durable mineral abundant in most lithologies and in sedimentary systems. Its stability during weathering and diagenesis makes it a robust provenance tracer. Quartz optically stimulated luminescence (OSL) sensitivity and electron spin resonance (ESR) signals have been empirically proposed as indicators for sediment provenance based on differences in quartz sensitivity. Sensitivity is defined as luminescence produced per unit dose (Gray: Gy) per unit mass (mg). The mechanisms driving OSL sensitisation during weathering from source rocks remain an open question in the luminescence community. While it is largely believed to be acquired by earth surface processes, recent studies bring evidence that sensitisation processes depend on source geology. Moreover, most studies focus on quartz grains deposited in the sink and infer possible sources rock by clustering.
The present study investigated a diverse suite of source rocks a wide range of geological settings, including granites, sandstones, volcanic and metamorphic rocks, and, where applicable, their derived sediments, independently dated from millions (Ma) to billions (Ga) of years. To understand the mechanism of OSL sensitivity we combined thermoluminescence (TL), OSL, ESR, cathodoluminescence (CL) and Raman spectroscopy measurements, with geochemical data obtained through laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Only in those quartzes that exhibited the [TiO4-Li+]0 paramagnetic centre in ESR, had notably high concentration of titanium and lithium impurities and had high blue emission in SEM-CL showed sensitisation following repeated cycles of laboratory dosing and bleaching. Samples lacking these centres did not show any laboratory OSL sensitisation by dosing and bleaching. We find a strong correlation of the degree of laboratory OSL sensitisation with the [TiO4-Li+]0 electron centre from ESR signal, and the titanium and lithium concentrations measured by LA-ICPMS. Our data on rocks of various ages and regions reinforce the idea that the potential for OSL sensitisation originates from specific lattice defect structures acquired by quartz during crystallisation. The results also highlight the role of Li⁺-ion impurities in forming paramagnetic centres such as [AlO₄/h]0 and [TiO4-Li+]0, advancing our understanding on interaction of radiations with specific defects in quartz.
This study is funded by the European Research Council Consolidator Grant - PROGRESS, (ERC-CoG-101043356) awarded to Prof. Alida Timar-Gabor.
How to cite: Constantin, D., Devi, M., Grecu, S.-C., Toth, Z.-R., Brezeanu, D., Barla, A., Nesterovschi, I., Cinta-Pinzaru, S., Ducea, M., Mojzsis, S., and Timar-Gabor, A.: Multi-spectroscopic characterisation of quartz from igneous, volcanic and sandstone rocks worldwide. Insights for provenance studies based on OSL sensitivity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10121, https://doi.org/10.5194/egusphere-egu26-10121, 2026.
Quantifying hydrogen incorporated via cation vacancies in nominally anhydrous minerals (NAMs) is essential for assessing its influence on mantle physical processes such as rheology. In addition, hydrogen partitioning between NAMs and hydrous melts has been proposed as a potential mechanism to explain the oxidised nature of arc magmas. Fourier-transform infrared (FTIR) spectroscopy is the most widely used technique for quantifying trace hydroxyl (OH) in NAMs due to its accessibility and cost-effectiveness. Moreover, FTIR spectroscopy can also constrain hydrogen-incorporation mechanisms and the orientation of the OH dipole within charge-balanced vacancy structures. These distinctions are critical for identifying defects that buffer or sense oxygen fugacity. However, because of the relatively low hydrogen solubility and the diversity of incorporation mechanisms, optimising analytical resolution, both in concentration and OH-dipole orientation, remains highly desirable but has traditionally been hampered in most minerals by the intrinsic anisotropy of the OH dipole. Most studies rely on unpolarised FTIR measurements of randomly oriented crystals to avoid pre-orientation biases, but this practice reduces both precision and accuracy because birefringent crystals show strong orientation-dependent absorbance. Polarised FTIR overcomes this limitation and provides access to OH speciation and bond orientation unavailable from unpolarised measurements. We present a method to recover the full crystallographic orientation of a crystal, expressed as Euler angles, from polarised FTIR spectra acquired at different angles relative to the polarisation direction by rotating the polariser. The method requires a reference standard and a single diagnostic wavelength within the silica overtone range, which allows selection of an optimal frequency for orientation recovery and makes the approach more flexible than spectrum-range methods (Asimov et al., 2006). We validate the method using numerical simulations and a comprehensive dataset of olivine crystals with known orientations based on EBSD measurements. Implemented in an open-source Python package (FTIRkit), the approach applies to any birefringent crystalline phase and can be extended to other polarised techniques, including Raman spectroscopy and optical microscopy.
References
Asimow, P.D., 2006. Quantitative polarized infrared analysis of trace OH in populations of randomly oriented mineral grains. American Mineralogist 91, 278–284. https://doi.org/10.2138/am.2006.1937
Funding: This project has been funded through the ERC project OZ (DOI: 10.3030/101088573).
How to cite: Lopez-Sanchez, M. A. and Padrón-Navarta, J. A.: A novel method for determining crystal orientation using polarised Fourier-Transform infrared spectroscopy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13627, https://doi.org/10.5194/egusphere-egu26-13627, 2026.
The ternary Pb5(XO4)3Cl system (X = P, As, V) comprises a key group of lead apatite minerals controlling the environmental behavior of toxic elements such as Pb, As, and V. Despite their closely related crystal structures, the three binary joins within this system exhibit contrasting miscibility patterns in nature, ranging from continuous solid solutions to compositionally restricted series depending on T.
Here, we investigate the thermodynamic origin of these differences by quantifying mixing behavior along the three binary joins: Pb5(PO4)3Cl pyromorphite – Pb5(AsO4)3Cl mimetite, pyromorphite – Pb5(VO4)3Cl vanadinite, and mimetite–vanadinite. Synthetic samples spanning the full compositional range (Xx = 0–1, Δx = 0.1) were analyzed using transmission infrared spectroscopy combined with autocorrelation analysis [1]. The δΔcorr parameter [1] was calculated independently for each binary join and used as a proxy for local structural heterogeneity related to strain induced by PO4–AsO4–VO4 substitution. The analysis focused on the high-frequency vibrational modes of tetrahedral groups in the ranges 600–1200 cm-1 (pyromorphite–mimetite), 640–1220 cm-1 (pyromorphite–vanadinite), and 500–1000 cm-1 (mimetite–vanadinite).
For the pyromorphite–mimetite series, excess enthalpies of mixing derived from δΔcorr (scaled to ΔHmix [2]) vary between −0.7 and +0.6 kJ/mol whereas density-functional theory (DFT) calculations using the single-defect approach [3] yield a symmetric distribution of ΔHmix function with a maximum of 3.8 kJ/mol at intermediate compositions XP=0.5. This discrepancy between spectroscopically and DFT-derived mixing enthalpies remains unresolved. However, the calculated vibrational entropy of mixing [4] stabilizes the solid solution, resulting in negative Gibbs free energies of mixing with a minimum of approximately -2 kJ/mol at XP=0.5. This thermodynamic behavior explains the absence of a miscibility gap at 300 K and the continuous nature of the pyromorphite–mimetite solid solution observed in nature [5].
In contrast, the pyromorphite–vanadinite join exhibits very small excess enthalpies of mixing derived from autocorrelation analysis, ranging from −0.23 to +0.18 kJ/mol (near 0), suggesting nearly ideal mixing and random substitution of PO4 and VO4 tetrahedra. Contrary, the mimetite–vanadinite series shows a slightly positive and asymmetric distribution of ΔHmix function with a maximum of ~0.9 kJ/mol at XAs≈0.35. This agrees with DFT-derived ΔHmix = 1 kJ/mol. Like the pyromorphite–mimetite, mimetite–vanadinite series is stabilized by the negative excess vibrational entropy term. This gives a negative Gibbs free energy of mixing oscillating about -3.5 kJ/mol at 300K.
These results demonstrate that subtle differences in local structural heterogeneity and the balance between enthalpic and entropic contributions govern miscibility in Pb-apatite solid solutions. Future work will extend this approach to the full ternary Pb5(PO4)3Cl–Pb5(AsO4)3Cl–Pb5(VO4)3Cl system to quantify mixing energetics and local structural heterogeneity arising from coupled P–As–V substitution. Financial support for BP was provided by the National Science Center, Poland [Grant No. 2025/57/B/ST10/02894].
References
[1] Salje, E. K. et al. (2000). Eur. J. Mineral., 12, 503–519. [2] Majzlan, J. et al. (2023). Eur. J. Mineral., 35, 157–169. [3] Benisek, A. & Dachs, E. (2020). Phys. Chem. Miner., 47, 15. [4] Benisek, A. & Dachs, E. (2012). J. Alloys Compd., 527, 127–131. [5] Markl, G. et al. (2014). Am. Mineral., 99, 1133–1146.
How to cite: Puzio, B. and Benisek, A.: Local structural heterogeneity and mixing energetics in the pyromorphite–mimetite–vanadinite system, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19035, https://doi.org/10.5194/egusphere-egu26-19035, 2026.
Scandio-fluoro-eckermannite (IMA 2024-002), a new Sc-dominant amphibole-supergroup mineral, has been discovered in the Bayan Obo REE-Nb-Fe polymetallic deposit, China. The new mineral was collected from banded Fe-REE ores that have formed due to the fenitization caused by carbonatite intrusion, in the Main and East open pits at Bayan Obo. Associated minerals include monazite, bastnäsite, magnetite, biotite, fluorite, bazzite, thortveitite, and magnesio-fluoro-arfvedsonite. The new mineral occurs as euhedral to subhedral crystals and aggregates, appearing both as inner zones of a crystallization sequence from scandio-fluoro-eckermannite to magnesio-fluoro-arfvedsonite as well as homogeneous fine-grained particles, reaching up to 350 μm in size and approximately 7 wt% in Sc2O3 contents.
Scandio-fluoro-eckermannite displays a light yellow to light blue color under plane-polarized transmitted light, with perfect cleavage on {110}, non-magnetic, and no fluorescence. The hardness is 5-6 by analogy to eckermannite and the calculated density is 3.097 g/cm3. Electron microprobe analyses obtained the main components (average value in wt. %): Sc2O3 6.39, SiO2 54.30, MgO 13.42, Na2O 8.38, Al2O3 1.29, MnO 1.47, CaO 1.21, K2O 0.47, FeOcalc 6.43, Fe2O3calc 3.80, F 3.01, H2O+calc 0.67, F≡O -1.27, total 99.74. The composition normalized on the basis of 24 anions (O, OH, F, Cl), with the assumption of (OH, F, Cl)=2 apfu, corresponds to the empirical formula A(Na0.52K0.09□0.39)S1.00 B(Na1.81Ca0.19)S2.00 C(Mg2.87Fe2+0.77Mn3+0.18Sc0.80Fe3+0.41)S5.03 T(Si7.78Al0.22)S8.00 O22 W[F1.36(OH)0.64]S2.00. It leads to the simplified formula (Na,□)(Na,Ca)2[(Mg,Fe2+)4(Sc,Fe3+,Mn3+)][(Si,Al)8O22)](F,OH)2and the ideal formula NaNa2(Mg4Sc)Si8O22F2. The crystal structure was refined in the monoclinic system, space group C2/m (#12). Its unit-cell parameters are: a = 9.8212(3) Å, b = 18.0866(5) Å, c = 5.3091(2) Å, β = 103.767(4)°, and Z = 2, with the a:b:c ratio of 0.543: 1: 0.294. The crystal-structure refinement indicates that the Na is the dominant cation at the A(m) and M(4) sites, Mg is the dominant cation at the M(1) and M(3) sites, Sc is the dominant trivalent cation at the M(2) site, and F is the dominant cation at the O(3) site. Therefore, this is the Sc-dominant variety of fluoro-eckermannite. The discovery of scandio-fluoro-eckermannite highlights the importance of amphibole in controlling Sc in this type of ore-forming system. Scandio-fluoro-eckermannite might also be used as a potential recorder to investigate the enrichment process of Sc in the Bayan Obo deposit.
How to cite: Liu, S., Fan, H.-R., Gu, X.-P., Butcher, A. R., Lahaye, Y., Michallik, R. M., Jolis, E. M., Lukkari, S., Li, X.-C., and Liu, X.: Scandio-fluoro-eckermannite, ideally NaNa2(Mg4Sc)(Si8O22)F2, a new Sc-dominant amphibole-supergroup mineral from the Bayan Obo deposit (China), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22633, https://doi.org/10.5194/egusphere-egu26-22633, 2026.
Arsenic is a toxic and widespread contaminant of waters and soils, originating from both natural geochemical processes and anthropogenic activities e.g. mining, metallurgy, and agriculture. Its removal remains as a global environmental challenge. Arsenic immobilization is commonly achieved through sorption, ion exchange, or precipitation, often involving iron-, aluminum-, or calcium-based phases. However, many of these methods suffer from limited capacity, sensitivity to water chemistry, or poor long-term stability.
In this study we present an approach for arsenate AsO43- removal from water based on reactive sorption on granulated Pb-zeolite. Arsenate is precipitated in the form of low-solubility solid phase - mimetite (Pb₅(AsO₄)₃Cl) - by reaction with Pb2+ desorbed from granulated Pb-zeolite (clinoptilolite). Pb-modified granulated zeolite was prepared by (1) sorption of Pb²⁺ from solution, (2) intensive washing to remove excess Pb and (3) granulation. For granulation, suspension of zeolite in sodium alginate solution was dropwise added to calcium chloride solution, resulting in formation of beads 2 - 4 mm in size. Dried beads provide with mechanically stable, porous and easy to handle sorbent.
Arsenate removal was investigated under static and dynamic flow-through conditions. In static batch experiments using [As] = 0.1 to 5 mg/L, arsenate removal exceeded 90% within minutes and approached 99% with increasing contact time, indicating that under well-mixed conditions the process is not limited by external mass transfer.
Column experiments were performed at varying flow rates, arsenate concentrations, sorbent masses, and column diameters in order to evaluate the effect on removal efficiency. Increased flow rate resulted in decreased arsenate removal due to shortened residence time, whereas higher sorbent mass enhanced removal by increasing the reactive contact area and the effective diffusion path length. Arsenic concentrations in the effluent increase gradually with time and the breakthrough curves follow a logarithmic rather than sinusoidal trend. This indicates sustained arsenate removal over extended periods (up to 6 days of continuous operation at the conditions of the experiment).
SEM/EDS analyses of reacted granules revealed the formation of a porous crust composed of mimetite needles on the granule surface. Mimetite precipitation does not passivate the reactive interface. The reaction front was located on the surface of granules indicating that precipitation kinetics was faster than lead desorption. Also, the porous structure of the alginate granules allowed for diffusion of Pb²⁺ from the interior outward. Comparison of arsenic removal and lead release rates indicates a gradual, approximately linear depletion of lead with time. Precipitation of Pb₅(AsO₄)₃Cl on the surface of granules created a Pb concentration gradient which was a driving force for further Pb desorption from zeolite in the interior of the granules: lead was consumed progressively from the outer regions of the granule inward. This mechanism likely governs the extended tailing observed in the breakthrough curves.
Proposed application of Pb-zeolite alginate granules enables efficient arsenate removal through induced mimetite precipitation under both static and flow-through conditions. The combination of high removal efficiency, long-term reactivity, and physical immobilization of lead highlights the potential of this approach for water treatment applications.
This research was funded by National Science Centre project No 2024/53/N/ST10/01763.
How to cite: Stępień, E., Manecki, M., and Bajda, T.: Pb-zeolite alginate granules for arsenate removal from water: static and dynamic studies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4922, https://doi.org/10.5194/egusphere-egu26-4922, 2026.
Kaolinite-to-illite transformation is a common clay-mineral reaction during sedimentary basin diagenesis and can be used to constrain fluid–rock interaction and the evolution of diagenetic environments. Here we integrate XRD, SEM/TEM, EDS/EPMA, numerical simulations, and physical simulation experiments to constrain the controlling factors, regional temperature thresholds, and mechanisms of kaolinite illitization. Results show that during early diagenesis under relatively open-system conditions, meteoric-water flushing and organic-acid activity enhance feldspar dissolution, providing Si and Al sources for kaolinite formation. With increasing burial depth and temperature, the diagenetic system evolves from open to semi-closed/closed conditions; restricted fluid circulation promotes the accumulation of K⁺ released by continued feldspar dissolution in pore waters, thereby providing the key prerequisite for illite nucleation and stabilization. The onset temperature of illitization differs significantly among regions. Illite precipitation is jointly controlled by temperature, K⁺ concentration, and pH, and the critical K⁺ concentration required for illitization decreases with increasing temperature and pH. Combined mineralogical and geochemical constraints indicate that kaolinite illitization proceeds predominantly via a dissolution–reprecipitation mechanism, and its extent is governed by the coupled effects of temperature thresholds, effective K⁺ supply, and the openness of the diagenetic system. These findings provide a basis for characterizing clay-mineral diagenetic behavior and reconstructing paleo-fluid conditions.
How to cite: Lin, S., Yuan, G., and Xu, F.: Mechanism of Kaolinite-to-Illite Transformation in the Central–Southern Xihu Sag, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8650, https://doi.org/10.5194/egusphere-egu26-8650, 2026.
The kaolinitic clays of the Şile Neogene Basin (Istanbul, Türkiye), constitute an important raw material resource for the ceramic industry. In the study area, the Istanbul Formation, composed mainly of Miocene clay, sand, and coal sediments, unconformably overlies the Upper Cretaceous andesitic volcanics of the Garipçe Formation. In this study, the relative influence of the Atterberg limits (AL), mineralogical compositions, specific surface area (SSA), and grain size distributions of six clay samples taken from three vertical sections of the İstanbul Formation were investigated comparatively. X-ray diffraction analyses of the whole rock and clay fractions show that, the dominated clay mineral is kaolinite (30-70%), accompanied by variable amounts of illite (5-25%) and smectite (0-25%). The illite-mica phase is almost entirely illite. Mixed layered phases and chlorite are absent. Non-clay minerals are mainly quartz (10-55%) and trace feldspar, siderite and anatase. In the samples, SSA values range 1.24-1.76 m2/g, and the grain size distributions are; d(0.1): 1.33-2.15 µm, d(0.5): 6.186-11.051 µm and d(0.9): 26.73-97.07 µm. The total and half-material grain sizes are approximately smaller than 40 µm and 10 µm, respectively. According to grain size distributions, the clays of Şile contain very fine-grained quartz (<10 µm) and larger-than-expected (>2 µm) clay mineral particles. AL values of the Şile clay samples are; The liquid limit (LL) was found to be in the range of 38-72%, the plastic limit (PL) in the range of 19.1-31.3%, and the plasticity index (PI) was between 19.6-41.5 (results are the average of three repeated experiments for each sample). Samples containing 5-25% smectite (four samples) exhibit systematically higher LL (60%), PL (27.90%), and PI (32.10%) ratios compared to smectite-free samples, reflecting the high surface activity and water adsorption capacity of smectite. In contrast, kaolinite and illite rich samples without smectite (two samples) display moderate plasticity (LL: 47%, PL: 23.72%, and PI: 23.28%) despite comparable grain size characteristics. This result can be explained by smectite's high specific surface area and its structural ability to adsorb more water. On the other hand, it is understood that the finest-grained samples do not always exhibit the highest plasticity. The fact that some of the quartz found in the Şile clays are fine-grained, similar to the clay minerals, may also have influenced the results. High SSA values in some samples appear to be related to the total clay mineral content and, more specifically, the presence of smectite. However, samples with similar smectite content and similar AL values also have different SSA values. For example, two samples with similarly high LL, PL, and PI values will have significantly different SSA values. It has been observed that the AL values in Şile clay samples are partially related to grain size and SSA, but more significantly related to mineralogical composition. In addition to kaolinite, the presence and amount of smectite, and also very fine-grained quartz will affect the results in the engineering and ceramic performances.
Key words: Atterberg Limits, Clay Mineralogy, Kaolinite, Smectite, Şile Neogene Basin
How to cite: Gargacı, M., Kahveci, S. E., Ekinci Şans, B., and Şans, G.: Mineralogical Effects on Plasticity Characteristics of Ceramic Clays: Insights from the Şile Neogene Basin (Türkiye), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14581, https://doi.org/10.5194/egusphere-egu26-14581, 2026.
Posters on site: Thu, 7 May, 16:15–18:00 | Hall X2
The serpentinite quarry at Jordanów Śląski is known for the first documented occurrence of nephrite in Europe (Traube, 1885). The quarry operated until the early 1980s and remained inactive for almost 40 years. Small-scale serpentine extraction started again in 2022. Recently, mining activity has increased, exposing a 20-25 m wide zone of leucocratic rocks, approximately 100 m long and 20-30 m deep. This zone most likely consists of tectonically assembled fragments of serpentinite, calc-silicate rocks, and leucogranite with pegmatite veins and nests, as well as common aplites. The discovery of scattered Sc-bearing mineralization at the contacts between granitic pegmatite and serpentinite (Sc-bearing actinolite, Sc-bearing diopside, jervisite, cascandite, scandio-winchite, heflikite, dubińskite, bazzite, kristiansenite, kolbeckite) has made this quarry one of the most important occurrences of scandium minerals in the world and the only one associated with a supra-subduction zone (Pieczka et al., 2024a-c).
This mineralization is accompanied by numerous minerals from the epidote supergroup (1) scattered throughout the pegmatite itself [clinozoisite, allanite-(Ce), allanite-(Nd), allanite-(Sm), allanite-(Y), Cr-bearing allanite-(Ce)], (2) at contacts with blackwall schists [Sc-bearing clinozoisite, Sc-bearing allanite-(Ce), heflikite], (3) at contacts with diopside-bearing rocks [allanite-(Ce), allanite-(La), dissakisite-(Ce)], (4) in zoisite-bearing calc-silicate rock [Cr-bearing clinozoisite and Cr-bearing epidote], and (5) in metasomatic and hydrothermal zones in serpentinite and altered actinolite-diopside-bearing metasomatites [Cr-bearing clinozoisite]. All minerals from the epidote supergroup associated with the pegmatite, except for allanite-(Ce) and clinozoisite, occur in fine grains not exceeding 100 μm and are enriched in lanthanides. On the other hand, minerals associated with zoisite-bearing calc-silicate rock and altered actinolite-diopside-bearing metasomatites form large crystals, reaching 2-3 cm in length, as well as string-like aggregates; they are completely devoid of lanthanides, usually found with relict chromite + Cr-bearing grossular or Al-bearing uvarovite.
The chemical compositions of pegmatite epidotes were influenced by the local compositions of the hydrated pegmatite-forming melt; those enriched in Sc and Cr could crystallize under the influence of Sc- and Cr-bearing fluids, which were released during the rodingitization processes of the Ślęża ophiolite lithologies. Their enrichment in lanthanides may be related to the interactions of these fluids with pegmatite lithologies at their marginal parts and fractures.
References:
Traube, H. (1885) Neues Jahrbuch für Mineralogie, Geologie und Paläontologie, Beilage-Band, 2, 91–94.
Pieczka, A., Stachowicz, M., Zelek-Pogudz, S., Gołębiowska, B., Sęk, M., Nejbert, K., Kotowski, J., Marciniak-Maliszewska, B., Szuszkiewicz, A., Szełęg, E., Stadnicka, K.M., and Woźniak, K. (2024a) American Mineralogist 109, 174–183.
Pieczka, A., Kristiansen, R., Stachowicz, M., Dumańska-Słowik, M., Gołębiowska, B., Sęk, M., Nejbert, K., Kotowski, J., Marciniak-Maliszewska, B., Szuszkiewicz, A., Szełęg, E., and Woźniak, K. (2024b) Mineralogical Magazine 88, 228–243.
Pieczka, A., Stachowicz, M., Zelek-Pogudz, S., Gołębiowska, B., Sęk, M., Nejbert, K., Kotowski, J., Marciniak-Maliszewska, B., Szuszkiewicz, A., Szełęg, E., Stadnicka, K.M., and Woźniak, K. (2024c) American Mineralogist 109, 940–948.
How to cite: Woszczyna, M., Włodek, A., Gołębiowska, B., and Pieczka, A.: Epidote-supergroup minerals associated with disseminated scandium mineralization at Jordanów Śląski in Lower Silesia, Poland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-334, https://doi.org/10.5194/egusphere-egu26-334, 2026.
Coesite was first synthesized in the early 1950s, then discovered in nature in 1960, and first applied as an index mineral for pressure-temperature (P-T) metamorphic condition and tectonic setting in 1984 with applications in the Dora Maira Massif (Italy) and the Western Gneiss Region (Norway). Until today, several experimental studies have focused on the calibration of the coesite-quartz phase boundary, mostly at high-temperature (HT) and high-pressure (HP) conditions. Among the various studies, there is a general agreement with only small differences at HT-HP conditions. For example, at 1200 °C the coesite-quartz phase boundary ranges between 31 to 33.5 kbar. However, differences in the HT are amplified in extrapolations to lower temperatures that are relevant to several recent coesite discoveries. At 550 °C the coesite-quartz phase boundary ranges between 23 to 28 kbar, providing a wide spread of P conditions.
The increasing number of coesite discoveries from different terranes in recent years highlights the importance of precisely locating the coesite-quartz phase boundary at low-temperature (LT). This study aims to validate the coesite-quartz phase boundary at LT (550-750 °C) and HP (28-30 kbar). The chosen P-T conditions are typical for coesite crystallization in subduction zone settings. The experiments were conducted in end-loaded piston-cylinder apparatuses using 12.7-mm diameter experimental assemblies composed of MgO filler pieces, graphite heater tubes, borosilicate glass insulators, and NaCl. Silver capsules, with volumes varying from 20 to 15 mm3, were filled with amorphous SiO2 powder and deionized H2O (≈2:1 ratio). Ten experiments were successfully performed. The experiments were conducted along the 550 °C, 650 °C and 750 °C isotherms at 28, 29, and 30 kbar for 48-72 hours. In summary, at 750 °C, 100 % coesite formed at 30 kbar, and 100% quartz was obtained at 29 kbar. At 650 °C, we synthesized 100 % coesite at 30 kbar, 100 % quartz at 28 kbar, and both large crystals of coesite (>200 μm) and small crystals of quartz (<100 μm) at 29 kbar. At 550 °C, experiments resulted in 100 % of small coesite crystals (<70 μm) at 30 kbar, 100 % quartz crystals at 28 kbar, and both coesite and quartz at 29 kbar. Moreover, a reversal experiment was conducted from quartz to coesite. Quartz was crystallized experimentally at 700 °C and 10 kbar for 24 hours. Then, it was loaded in a new experiment at 650 °C and 30 kbar, resulting in a complete recrystallization of coesite; no quartz was left at the end of the experiment.
These results suggest that the coesite-quartz phase boundary at relatively low temperature may occur at higher pressure than previously extrapolated. The ongoing reaction reversals experiments from coesite stability field to quartz will better constrain the character of coesite-quartz phase boundary at LT-HP conditions typical for subduction zone settings, where coesite likely crystallized in natural rocks. Acknowledgements: This work was funded by the National Science Centre (Poland) through the project 2021/43/D/ST10/02305 to K. Kośmińska.
How to cite: Callegari, R., Thomas, J., and Kośmińska, K.: Experimental evaluation of the Coesite-Quartz phase boundary at low-temperature & high-pressure conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6476, https://doi.org/10.5194/egusphere-egu26-6476, 2026.
Anomalous high-conductivity layers (HCL) are a defining feature of subduction zones and play a critical role in global processes as water cycling, seismicity, and arc magmatism. Hydrous minerals, especially amphiboles (general formula AB2C5T8O22W2), are considered to be major contributors to these conductivity anomalies in the Earth crust, but the atomic-scale links between mineral oxidation, charge transport, and thermal stability are still not fully understood. Given their crustal abundance, the oxidation of Fe2+-bearing hydrous amphiboles has therefore been extensively investigated in recent years. Electrical conductivity measurements on several amphibole species have suggested the formation of polarons (conduction electrons coupled with longitudinal optical phonons) at high temperatures (HT). However, only recently direct evidence for the existence of polarons in Fe2+-bearing amphiboles has been provided by Raman spectroscopy [1,2,3]. In addition, reversible delocalisation of H+ cations has been detected [1,3,4].
Glaucophane (□Na2(Mg3Al2)Si8O22(OH)2) is a common amphibole in blueschist facies rocks; therefore, its HT behaviour should play an important role in geological processes occurring in subduction zones. The aim of our study is to elucidate the role of CAl in the formation of charge carriers in glaucophane at HT. We have analysed Fe2+-bearing glaucophane [(□0.91Na0.08K0.01)(Na0.87Fe0.07Ca0.06)2(Mg0.54Al0.34Fe0.12)5(Si0.99Al0.01)8O22((OH)0.98F0.02)2] from Pollone (Piedmont, Italy) by in situ HT Raman spectroscopy in air [5] and under vacuum. The results indicate that, similar to CAl-free amphiboles, glaucophane undergoes a multi-step process controlled by structural anisotropy and cation site occupancy. The first Fe2+ oxidation stage occurs between ~600 and 650 K. This stage is accompanied by shifts in Raman peaks linked to TO4 ring vibrations, indicating electron delocalization and topological reorganization of the tetrahedral framework, together with changes in the anisotropic local structure. A second oxidation stage develops between ~800 and 1000 K, where Fe2+ oxidation is localised in M(1) polyhedra. This stage is marked by strong intensity reductions in low-frequency lattice modes and further rearrangement of the TO4 rings. The final stage, preceding decomposition, occurs between ~950 and 1150 K and involves progressive H+ cations delocalization from OH groups, with incomplete recovery upon cooling, evidencing irreversible structural changes.
Under vacuum (~10-4 bar), both the oxidation stages and H+ delocalization occur at temperatures approximately 100 K higher than in air, indicating that the absence of oxygen raises the temperature required for these processes to take place. Hence, octahedrally coordinated Al does not suppressed the temperature-induced electron and H+ delocalization in either presence or absence of external O2.
Results from ongoing electrical-conductivity experiments combined with in situ Raman spectroscopy at different temperatures will also be discussed.
References
[1] Mihailova et al. (2021) Commun Mater 2, 57
[2] Mihailova et al. (2022) Condens Matter 7, 68
[3] Bernardini et al. (2025) Sci Rep 15, 14244
[4] Della Ventura et al. (2017) Am Min 102(1), 117-125
[5] Kei Yin Ngan (2025) Master thesis: Oxidation and thermal decomposition of Fe-containing glaucophane. University of Hamburg, Germany
How to cite: Baratelli, L., Ngan, K. Y., Schlüter, J., and Mihailova, B.: Temperature-activated charge carriers in Fe2+-bearing glaucophane revealed by Raman spectroscopy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10029, https://doi.org/10.5194/egusphere-egu26-10029, 2026.
To date, processes such as volatile-element cycling and redox reactions in subduction and the mid-crust zones are still not fully understood. Particularly, a better understanding of the redox processes in rock-forming silicate minerals is essential for developing a more accurate picture of lithospheric electrical conductivity. Amphiboles (AB2C5T8O22W2) are major constituents of subduction-zone lithologies and can store substantial amounts of water in the form of W-site hydroxyl groups, making them important contributors to the global water cycling. Recent Raman scattering studies have shown that Fe²⁺-bearing hydrous amphiboles can undergo reversible temperature-induced oxidation and dehydrogenation, leading to the formation of mobile charge carriers, polarons (delocalized e⁻ coupled with polar phonons) and delocalized H⁺, and hence, to polaronic conductivity and H+ diffusion (Della Ventura et al., 2018; Mihailova et al., 2022; Bernardini et al., 2025).
Magnesio-hornblende (nominally A⧠BCa2C(Mg4Al)T(Si7Al)O22W(OH)2) is of special interest in this context because it represents one of the most abundant amphibole groups, the hornblendes (TAl-containing Ca-amphiboles), but the influence of its tetrahedrally coordinated Al on the redox processes remains largely unexplored. Thus, the goal of this study is to investigate the atomistic mechanisms of charge-carrier activation and thermal stability in magnesio-ferri-hornblende by in situ high-temperature Raman spectroscopy in the range 300–1400 K. The exact chemical composition of the studied sample was determined by wavelength-dispersive electron microprobe analysis:
A(Na0.06K0.01)B(Ca1.94Na0.03Mn0.03)C(Mg3.54Fe2+0.8Fe3+0.54Mn2+0.11Zn0.02Cr0.001)T(Si7.42Al0.51Fe0.06Ti0.01)O22W((OH)1.92F0.05O0.02Cl0.01). Experiments were conducted under both oxidizing conditions (air) and vacuum (~ 10-4 bar) to evaluate the role of external O2 on the activation temperatures and reversibility of these processes.
First results obtained in air reveal that magnesio-ferri-hornblende is stable up to 1400 K. The observed temperature-induced anomalies in both framework vibrations and OH-stretching indicate the onset of oxidation of Fe²⁺ to Fe³⁺ coupled with delocalization of H⁺ next to Fe2+Fe2+Mg and Fe2+MgMg chemical species. These processes are expressed by the disappearance of the corresponding OH-stretching Raman peaks upon heating and characteristic Fe²⁺O₆-related Raman-active modes. At temperatures above 1150 K even H⁺ cations next to MgMgMg, but the corresponding OH-stretching peaks reappear on cooling, indicating mobile H+ cations in a large temperature range. Furthermore, after cooling down to room temperature, a strong direction-dependent resonance Raman scattering (RRS) is observed, demonstrating strong mutual alignment of the polaron dipoles, which is a precondition of highly anisotropic polaronic conductivity. As a next step, in situ high-temperature Raman scattering experiments under an applied external electric field will be conducted, allowing for the simultaneous monitoring of temperature-induced electron–phonon coupling, H⁺ delocalization, and the evolution of electrical conductivity.
References:
- Della Ventura, G., Mihailova, B., Susha, U., Guidi, M. C., Marcelli, A., Schlüter, J., Oberti, R. (2018): Am. Mineral., 103, 1103 -1111, https://doi.org/10.2138/am-2018-6382
- Mihailova, B., Della Ventura, G., Waeselmann, N., Bernardini, S., Xu Wei, Marcelli, A. (2022): Condens. Matter, 7, 68, https://www.mdpi.com/2410- 3896/7/4/68
- Bernardini, S., Della Ventura, G., Hawthorne, F.C., Marcelli, A., Salvini, F., Mihailova, B., (2025): Sci. Rep., 15, 14244, https://doi.org/10.1038/s41598-025-98025-9
How to cite: Fleischer, K. and Mihailova, B.: Atomistic insights into redox processes and conductivity phenomena in Hornblende, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13233, https://doi.org/10.5194/egusphere-egu26-13233, 2026.
Fe-bearing carbonates are increasingly recognized as key phases for iron and carbon storage in Earth’s deep interior, yet their physical properties at high pressure remain poorly constrained, particularly for compositionally complex and structurally disordered systems. In this study, we investigate the high-pressure behavior of ordered and disordered ankerite, Ca(Mg₁₋ₓFeₓ)(CO₃)₂ (0 ≤ x ≤ 0.7), to assess the influence of cation ordering on structural evolution, elastic properties, and Fe spin behavior[1,2]. The present work investigates the high-pressure (HP) behaviour of ankerite, Ca(Mg1-xFex)(CO3)2 (x=0.4, 0.7), crystallizing in the R-3 space group, and disordered ankerite with R-3c symmetry. Cation ordering and disordering influence on the physical properties and phase evolution of Fe-dolomite and ankerite [1,2], with important implications for their elastic behaviour, that might help in partially explaining the observed seismic anisotropic anomalies in the mantle wedge [3] as well as contributing in the carbonate’s detection in the inner Earth [4]. Particular attention is given to comparisions with the single carbonate magnesiosiderite, focusing on the Fe spin behavior at high pressure. The analysed P conditions reach 80 GPa, higher than the range typical of the Fe spin crossover in single carbonate magnesiosiderite, i.e., ~43 GPa at room temperatures [5][6]. The results obtained in this work confirm that neither ordered nor disordered ankerite undergo a high-spin to low-spin transition up to 80 GPa, independently on the Fe content.
The project was partially funded by the ‘’BMBF-Verbundprojekt 05K2019-Nanoextrem2” and “DFG core facility for high pressure research” (2018) and “SIMP Research Grant in Crystal ‐ chemistry, in memory of Prof. Fiorenzo Mazzi” (2022).
References:
[1] Zucchini A et al. (2014) Phys Chem Miner 41(10):783-793
[2] Zucchini A et al. (2017) Eur J Mineral 29:227-238
[3] Liu X and Zhao D (2017) Geophys J Int 210:1410-1431
[4] Chariton S et al (2020) Am Miner 105(3):325-332,
[5] Cerantola V et al. (2017) Nat Commun 8:15960
[6] Liu J et al. (2014) Am Mineral 99:84-93
How to cite: Pennacchioni, L., Sakrowski, R., Appel, K., Camarda, C., Mezouar, M., Sahle, C., Zucchini, A., Morgenroth, W., and Wilke, M.: ’Spin behavior of ordered/disordered ankerite at high pressures, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18658, https://doi.org/10.5194/egusphere-egu26-18658, 2026.
Magnetic properties of ferrimagnetic minerals have been studied in detail over the years. By contrast, the magnetic properties of paramagnetic minerals containing rare earth elements (REE) remain largely unexplored, even though the presence of particular rare-earth ions can give rise to complex magnetic behavior due to their unpaired 4f electrons. Consequently, filling this knowledge gap is becoming increasingly important in light of the enormous interest these minerals have attracted in recent years because of their economic value. The primary goal of this study is to characterize the intrinsic magnetic behavior of selected REE minerals at the grain scale and in relation to their crystal structures.
Six REE-bearing minerals from various Swedish localities were investigated: monazite-(Ce), xenotime-(Y), ferriallanite-(Ce), bastnäsite-(Ce), cerite-(CeCa) and fluorapatite. Electron microprobe analysis and X-ray diffraction methods were used to determine mineral chemistry and confirm crystal structures. Magnetic properties were characterized via field- and temperature- dependent magnetization measurements.
Field-dependent magnetization measured at 2 K revealed the absence of a hysteresis loop in all minerals except ferriallanite-(Ce), which exhibits a small hysteresis loop. This behavior is primarily attributed to the presence of Fe2+ and Fe3+ ions in ferriallanite-(Ce). The preliminary results show that the effective magnetic moments (μ_eff) obtained from temperature-dependent measurements are in good agreement with calculated free-ion magnetic moments (μ_calc), suggesting that paramagnetic rare-earth ions represent a major contribution to the observed magnetism.
These results provide fundamental knowledge of the intrinsic magnetic properties of selected REE-bearing minerals and improve our understanding of their crystal-chemical controls on their magnetism. Moreover, these insights form a basis for further interdisciplinary studies exploring the potential of designing novel functional materials inspired by naturally occurring compositions.
How to cite: Sordyl, J., Corona, A., Almqvist, B., Holtstam, D., Sahlberg, M., Cedervall, J., Sarkar, T., Herper, H., Vishina, A., and Eriksson, O.: Crystal-chemical controls on the magnetic behavior of REE-bearing minerals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13171, https://doi.org/10.5194/egusphere-egu26-13171, 2026.
The development of inexpensive and efficient methods for the recovery of critical raw materials is of increasing importance within the European Union, driven by the growing demand for rare earth elements (REE) in green technologies and electronic devices, as well as the strategic need to reduce limited reliance on external suppliers and maintain competitiveness. Recently, formation of a Pb–REE phosphate phase was reported alongside pyromorphite as a product of REE beneficiation by coprecipitation with Pb-phosphates (Sordyl et al., 2023).
Building on earlier observations, this contribution presents the results of the synthesis of mixed Pb–REE phosphates: La₂Pb₃(PO₄)₄·3.5H₂O, Ce₂Pb₃(PO₄)₄·3.3H₂O, Pr₂Pb₃(PO₄)₄·3.1H₂O, and Sm₂Pb₃(PO₄)₄·3.3H₂O, following the protocol of Staszel et al. (2023). They precipitate from aqueous solutions (pH 2-3, REE:Pb molar ratio of 3:2, at ambient temperature, open to the air) as poorly crystalline granular aggregates composed of rounded nanoparticles. The combined analytical approach including chemical analysis and microanalysis, synchrotron pair distribution function (PDF) analysis, and Raman spectroscopy confirms the incorporation of La, Ce, Pr, and Sm into the Pb phosphate structure in the same way as in the phases precipitated and described by Staszel et al. (2023). The composition of the precipitated phases is in agreement with previous reports by Staszel et al. (2023). Structural constraints derived from PDF analysis indicate that precipitated Pb-REE phosphates are similar to the rhabdophane REE(PO4)∙0.6H2O structure (space group P3121). This finding differs from the previously proposed orthorhombic crystal system (space group Cmmm) (Staszel et al. 2023). Additional techniques, such as extended X-ray absorption fine structure (EXAFS) and small-angle X-ray scattering (SAXS), will be applied to further resolve the periodic structure and the local distortions.
Resolving the crystallographic framework is essential for improving our understanding of the crystal-chemical role and structural position of REE within Pb phosphate phases. A thorough characterization of these newly described phases is therefore critical for refining the coprecipitation protocol and evaluating its applicability to REE recovery from phosphate-rich mineral sources or mining wastes, such as those associated with iron oxide-apatite deposits in northern Sweden. This work will be complemented by future in situ experiments to better monitor the nucleation processes governing the competitive formation of pyromorphite versus Pb–REE phosphate phases, with the aim of optimizing the recovery pathway toward the formation of the most effective REE-bearing phase.
The project is supported by the Wallenberg Initiative Materials Science for Sustainability (WISE) and Polish National Science Centre grant no. 2021/43/O/ST10/01282.
References
Sordyl, J., Staszel, K., Leś, M., & Manecki, M. (2023). Removal of REE and Th from solution by co-precipitation with Pb-phosphates. Applied Geochemistry, 158, 105780. https://doi.org/10.1016/j.apgeochem.2023.105780
Staszel, K., Jędras, A., Skalny, M., Dziewiątka, K., Urbański, K., Sordyl, J., Rybka, K., & Manecki, M. (2023). New synthetic [LREE (LREE = La, Ce, Pr, Sm), Pb]-phosphate phases. Mineralogia, 54(1), 58–68. https://doi.org/10.2478/mipo-2023-0006
How to cite: Ariza Acero, M. M., Staszel, K., Rzepka, P., Manecki, M., Sordyl, J., and Majka, J.: Synthesis and characterization of Pb–REE phosphate (REE₂Pb₃(PO₄)₄·nH₂O) for application in novel rare-earth element beneficiation methods, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15211, https://doi.org/10.5194/egusphere-egu26-15211, 2026.
Mycotoxins produced by certain fungi contaminate food, crops, and water, posing health risks and causing economic losses. Among the most prevalent, zearalenone (ZEN) and deoxynivalenol (DON) are difficult to remove with conventional adsorbents due to their relatively non-polar nature. Both toxins are associated with serious adverse effects, including endocrine disruption, immunotoxicity, and gastrointestinal damage. This study aims to develop a targeted removal approach for ZEN and DON and to elucidate the underlying mechanisms.
Knowing their large specific surface area, low cost, and good dispersibility, clay minerals have been employed as mineral supports. From this group, we focused on kaolinite-based materials, including a kaolinite-rich sample (M), synthetic calcined kaolinite nanotubes (MNC), halloysite purchased from Sigma-Aldrich (HS), and unpurified halloysite-containing sample (HD). The mineral supports were coated with approximately 20 wt% of TiO2, g-C3N4 (GCN), or a TiO2/GCN mixture for ZEN removal, and with TiO2, Fe2O3, or a TiO2/Fe2O3 for DON removal. For ZEN, a photodegradation approach using UV light was employed. In contrast, DON, being a more resistant toxin, required the addition of the oxidizing agent peroxymonosulfate (PMS, 2 mM) to achieve efficient degradation.
The GCN and TiO2/GCN materials were the most effective for ZEN removal, with the MNC-based samples achieving 98.8% and 97.7% degradation, respectively, after 25 min of UV exposure. The mechanisms of ZEN degradation varied with the composite, but for the majority of materials O₂•⁻ and •OH species played a major role. Importantly, incorporating an insulating clay mineral did not reduce photocatalytic efficiency; rather, the mineral interface appeared to enhance charge separation. Analysis of ZEN photodegradation pathways showed that oxidation and reactive oxygen species led to a breakdown of the carboxyl group and removed functional groups, forming various lower- and higher-mass intermediates [1]. Further degradation cleaved the aromatic ring, producing simpler oxygen-rich chains that can be ultimately mineralized to CO2 and H2O.
For DON removal, the MNC-based TiO2/Fe2O3 samples were the most effective, removing 98.8% of the initial concentration after 45 min, while MNC-based samples containing only TiO2 or Fe2O3 achieved 66.1% and 46.0%, respectively. Mössbauer spectroscopy and SEM confirmed the presence of the maghemite phase, showing that Fe2O3 loaded on the MNC support is nanosized, providing a large specific surface area for redox reactions and efficient PMS activation. Simultaneous ZEN and DON removal under UV light with PMS activation demonstrated that this approach is effective also for ZEN. Under visible light, DON was also efficiently removed, dropping below the detection limit within minutes using the MNC-based TiO2/Fe2O3 sample.
The results demonstrated the potential of mineral support in photocatalysis and photoinduced chemical oxidation for ZEN and DON removal. Future research will focus on expanding the study on DON, elucidating its degradation mechanisms and pathways.
Acknowledgements
This project was supported by the National Science Centre Poland, under a research project awarded by Decision No. 2021/43/B/ST10/00868.
References
[1] K. Dziewiątka, J. Matusik, M. Herber, E.H. Hill, J. Kuc, G. Cempura, A. Jędras, Enhanced photodegradation of zearalenone with kaolin group-based nanotubular materials: Unveiling reaction mechanisms and pathways, Chemical Engineering Journal 506 (2025) 160198. https://doi.org/10.1016/j.cej.2025.160198.
How to cite: Dziewiątka, K., Matusik, J., and Błachowski, A.: Clay mineral-based materials for mitigating mycotoxin contamination: Two photoinduced removal approaches for zearalenone and deoxynivalenol, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18029, https://doi.org/10.5194/egusphere-egu26-18029, 2026.
In geological studies, the titanomagnetite series (Fe3-xTixO4) and the titanohematite series (Fe2-yTiyO3) are widely used for paleomagnetic identification, as variations in Ti content significantly affect their magnetic properties, thereby controlling the preservation of paleomagnetic signals. In this study, titanomagnetite and titanohematite series with different Ti contents were synthesized via a hydrothermal method to investigate their crystal growth mechanisms under varying Ti contents. Iron hydroxide precursors formed first and, upon heating, transformed into corundum or inverse spinel structures with Ti incorporated into the lattice. XRD results indicate that the precursor is an amorphous phase, and that the synthesized titanohematite samples consist of pure-phase titanohematite. XPS analysis shows that the relative ratio of Ti and Fe in titanohematite correspond to approximately y = 0.2, which the SEM–EDS analysis confirms the incorporation of Ti into the samples. SQUID measurements further demonstrate that low-Ti-content titanohematite exhibits antiferromagnetic behavior.
In addition, density functional theory (DFT) calculations were performed to optimize the structures and to evaluate the magnetic moments and band gaps of titanomagnetite and titanohematite series with different Ti contents. For the former series at x = 1, GGA calculations reveal that the inverse spinel structure is preserved, but with antiferromagnetic ordering while noting that the band gap was underestimated. When x = 0.5, Ti atoms partially occupy tetrahedral sites, leading to pronounced effects on the structural stability and magnetic properties. For the latter series, GGA+U calculations show that no significant structural changes are observed with increasing Ti concentration. However, a net magnetic moment emerges at y = 0.5, demonstrating that Ti incorporation beyond a critical proportion alters the cation distribution, consequently affecting the total magnetic moment.
Integrating hydrothermal synthesis parameters, crystal growth mechanisms, structural characteristics, and magnetic properties of both titanomagnetite and titanohematite series, this study provides new insights into the interpretation of paleomagnetic behavior and also offers a theoretical basis for potential applications in photocatalytic materials.
How to cite: Lee, Y.-H. and Chen, Y.-H.: Crystal growth and theorical calculations of titanomagnetite and titanohematite series, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16223, https://doi.org/10.5194/egusphere-egu26-16223, 2026.
The Niemcza Shear Zone (NSZ) represents one of the key structural elements of the Sudetic segment of the Variscan Belt, yet its tectonic significance remains under discussion. Several models have interpreted the NSZ as a major crustal boundary separating peri-Gondwanan domains. Here we present new insights into the metamorphic evolution of the NSZ based on a comparative analysis of two lithologies from its central domain: the strongly deformed Strach mylonite and the weakly deformed Buk graphitic quartzite.
An integrated approach combining white-mica and garnet–biotite geothermobarometry, Zr-in-rutile thermometry, Raman spectroscopy of carbonaceous material, and major- and trace-element zoning in tourmaline was applied. Both lithologies record similar medium-pressure, high-temperature metamorphic conditions within the greenschist- to amphibolite-facies conditions. Peak metamorphism is estimated at ~6–10 kbar and 630–710 °C, corresponding to the sillimanite stability field.
Tourmaline compositional zoning reveals two stages of prograde growth under predominantly internally buffered conditions, followed by retrograde rim formation linked to deformation-enhanced fluid infiltration, particularly within the mylonitic rocks.
Our results support interpretation of the NSZ as a long-lived, lithospheric-scale shear zone that focused deformation, magmatism and metamorphic re-equilibration during terrane amalgamation.
How to cite: Wicher-Jarząb, D., Szuszkiewicz, A., Szczepański, J., Lis, G. P., Korybska-Sadło, I., and Marciniak-Maliszewska, B.: Constraining the metamorphic evolution of the Niemcza Shear Zone, NE Bohemian Massif (SW Poland) using thermobarometry, Raman spectroscopy, and tourmaline zoning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20036, https://doi.org/10.5194/egusphere-egu26-20036, 2026.
The mining industry faces increasing demand for raw materials and stringent environmental regulations imposed by the European Union. These constraints promote the development of technologies that enable the reuse of industrial waste. Such approaches are consistent with the principles of the circular economy, which emphasize recycling and material recovery. The use of industrial by-products as partial substitutes for natural raw materials is well established in the construction sector.
Carbonate-rich flotation tailings from the Zn–Pb mining industry can partially replace sand in cement mortars. This study aimed to evaluate methods for limiting Pb release during the weathering of mortars containing such material as additive. In the experiments, cement mortars were prepared with 32 wt% of quartz sand replaced by flotation tailings from a Zn–Pb ore-processing plant. Two immobilization strategies were tested:
- Addition of phosphate ions (PO₄³⁻) utilizing Phosphate-Induced Metal Stabilization (PIMS), based on in situ precipitation of the low-solubility phase pyromorphite, Pb₅(PO₄)₃
- Amendment with natural zeolite (clinoptilolite) as a sorbent with a high affinity for Pb.
Mortars were prepared in accordance with EN 196-1. Two compositions were investigated:
(i) mortar containing flotation tailings, Portland cement (CEM I 52.5 N), and water enriched in PO₄³⁻ and Cl⁻;
(ii) mortar containing flotation tailings and clinoptilolite, with 20 wt% of the cement replaced by zeolite, mixed with deionized water.
After curing for 28 days, leaching tests were performed following PN-EN 12457-2:2006.
Phosphate addition did not reduce Pb mobility. The leached Pb concentration was at the order of 0.8 mg kg⁻¹, identical to that of the reference mortar without immobilizing additives. In contrast, zeolite amendment was fully effective. Lead concentrations in the leachate were below the detection limit (~0.05 mg L⁻¹).
These results demonstrate that cement mortars incorporating Zn–Pb flotation tailings can be produced with effective immobilization of Pb by minor additions of clinoptilolite. Further studies are required to optimize zeolite content with respect to the mechanical properties of the mortar. This approach offers a promising pathway for reducing mining waste and conserving natural mineral resources.
How to cite: Manecki, M. and Wrona, P.: Immobilization of Pb in calcite–dolomite flotation tailings used as a concrete additive, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20562, https://doi.org/10.5194/egusphere-egu26-20562, 2026.
Rare earth elements (REE) constitute essential critical raw materials, driven by their role in the ongoing evolution of high-technology and green energy sectors. Growing demand is driving the search for new sources and recovery technologies. A new technology for recovering REE via coprecipitation with lead apatite - pyromorphite Pb5(PO4)3Cl - has recently been proposed [1]. Different sources of REE with varying chemical compositions may contain anions that compete with Cl in the pyromorphite structure [2, 3] and potentially affect REE recovery. The aim of this study was to investigate the effect of F, Br, I, and OH, compared to Cl, on the incorporation of Ce (as a proxy for other rare earth elements) into the structure of pyromorphites.
Synthesis of pyromorphite analogs consisted of slow mixing of two solutions containing cations and anions in a reaction chamber, under atmospheric pressure, ambient temperature around 21°C and at pH=3, with vigorous stirring, and leaving the obtained suspensions for 48 hours for maturing. Ce-free phases were also synthesized as controls.
The precipitate comprises primarily appropriate anionic variety of crystalline pyromorphite: fluor-, chlor-, brom-, and hydroxyl-pyromorphite. Neither in the control experiment nor in the experiment with Ce was iodine pyromorphite formed. The crystal lattice got changed to accommodate Ce in the structure. It was expressed as change in unit cell parameters – dimensions a were elongated and the c dimensions were shortened, compared to each control. The extent of Ce substitution was not very sensitive to the anion used, with content measured at 0.44 (F), 0.57 (Cl), 0.52 (Br), and 0.43 (OH) atoms per formula unit (apfu). The precipitates of pyromorphites containing Ce were accompanied by small amounts of an additional phase, Ce2Pb3(PO4)4·nH2O [4].
For the first time, anionic substitution effects (F, Cl, Br, I, OH) on cerium incorporation in the pyromorphite-type lead phosphate apatite Pb5(PO4)3X has been studied. These will enable future optimization of REE recovery technologies from mineral materials of varying chemical composition, both qualitatively and quantitatively. Further extensive research is necessary to fully understand the details of REE substitutions in lead-apatites.
This research was funded by Polish National Science Center research grant no. 2021/43/O/ST10/01282.
[1] Sordyl, J., Staszel, K., Leś, M. & Manecki, M. Removal of REE and Th from solution by co-precipitation with Pb-phosphates. Applied Geochemistry 158, 105780 (2023).
[2] Pan, Y. & Fleet, M. E. Compositions of the Apatite-Group Minerals: Substitution Mechanisms and Controlling Factors. Reviews in Mineralogy and Geochemistry 48, 13–49 (2002).
[3] Hopwood, J. D. et al. The Identification and Synthesis of Lead Apatite Minerals Formed in Lead Water Pipes. Journal of Chemistry 2016, 9074062 (2016).
[4] Staszel, K. et al. New synthetic [LREE (LREE = La, Ce, Pr, Sm), Pb]-phosphate phases. Mineralogia 54, 58–68 (2023).
How to cite: Staszel, K. and Manecki, M.: Anionic substitution effects (F, Cl, Br, I, OH) on cerium incorporation within the pyromorphite-type lead phosphate apatite Pb5(PO4)3X framework, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7153, https://doi.org/10.5194/egusphere-egu26-7153, 2026.
The Kahramanmaras region (Turkey) is located between the Arabian Plate and the Tauride-Anatolide tectonic belt, making it a study area where lithological units of different ages and origins are found together. The petrography and geochemistry of ophiolitic complex units (Kocali Complex) located in northern Kahramanmaras and the sedimentary units (Karadut Formation) that tectonically overlie them were examined to reveal their roles within the tectonic system. Samples taken from the working area were examined under a polarizing microscope for their mineral composition, textural properties, and alteration degrees; major element contents were determined by XRF analysis, and trace and rare earth element contents were determined by ICP-MS analysis.
The basalts of the Kocali Complex are generally altered basalts, with some samples being almost completely carbonated. The conglomerates of the unit are predominantly composed of angular clasts, which include rock fragments of both magmatic and sedimentary origin. Petrographic examinations indicate that the serpentinites are rich in opaque minerals and locally contain ore minerals; in addition, they exhibit a pronounced sieve texture accompanied by carbonation-type alteration. The Cenozoic Karadut Formation consists of sandy and carbonate-rich limestones, marls, and mudstones. Carbonate limestones are fine to medium-grained and display a homogeneous fabric, whereas sandy limestones are distinguished by their light to dark gray coloration. These units commonly crop out as beds with variable dip angles and occur in alternation with marls. The marls are whitish to beige in color and locally characterized by manganese coatings. Microscopic observations reveal that the siltstones and mudstones of the formation contain feldspar and very fine-grained quartz, accompanied by iron oxide precipitation and opaque minerals.
Chemical analyses show that the SiO₂ contents of the Kocali Complex rocks range from 2.41 to 87.60 wt.%, Fe₂O₃ contents from 0.60 to 11.82 wt.%, and CaO contents from 0.32 to 42.92 wt.%. In contrast, the Karadut Formation rocks display SiO₂ contents between 61.31 and 95.24 wt.%, Fe₂O₃ contents of 0.42–3.02 wt.%, and CaO contents ranging from 0.33 to 16.59 wt.%. These results indicate that the units of the Kocali Complex exhibit considerable chemical heterogeneity. The SiO₂, Fe₂O₃, and MgO values are consistent with the characteristic geochemical signature of an ophiolitic mélange. In comparison, the Karadut Formation units are characterized by elevated SiO₂ and CaO contents, reflecting a carbonate-rich sandstone geochemistry. The observed chemical contrasts point to a genetic relationship between ophiolitic source rocks and sedimentary environments. In conclusion, the observed geochemical differences between the Kocali Mélange and the Karadut Formation reveal not only lithological and source-rock diversity but also provide important clues to the geodynamic evolution of the region. In this context, the study makes a significant contribution to the understanding of geodynamic processes by demonstrating the interaction between ophiolitic rocks and the sedimentary basin.
Keywords: Geochemistry; Mélange; Ophiolite; Petrography; Türkiye
How to cite: Erol, İ., Güngör, Y., Ürkkaya, C. S., Vurmuş, Z. D., Özdamar, Ş., and Sarıkaya, O.: Petrography and Geochemistry of the Kocali Ophiolitic Complex and the Karadut Formation (Kahramanmaras, SE Türkiye), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17703, https://doi.org/10.5194/egusphere-egu26-17703, 2026.
Expansive soils with high sulfate content pose a serious challenge to the pavement infrastructure due to the rapid formation of expansive minerals like ettringite. The conventional calcium-based stabilizers, like lime and cement, often accelerate the ettringite crystal growth and result in sulfate-induced heave. Therefore, an alternative stabiliser that prevents these adverse chemical reactions is required. This study evaluates the potential use of wollastonite powder (CaSiO3) as a sustainable stabiliser for sulfate rich soils. The research focussed on the physico-chemical and mineralogical changes of the wollastonite powder-treated soil matrix at varied curing periods and dosages. Atterberg limits were conducted to access the modification in plasticity properties of the stabilised sulfate-rich natural expansive soil. pH and EC of the treated expansive soil were measured at different time intervals to understand the balance between calcium and sulfate ions associated with wollastonite dissolution. X-Ray diffraction (XRD) analyses was performed at selected curing periods to study the minerological transitions and to detect the presence or absence of ettringite with time. These findings support the development of low-carbon sustainable binder as an alternative to the conventional stabilisers like lime in sulfate-rich environments.
How to cite: Murugan, G. and Talari, T.: Stabilisation of Sulfate-Rich Expansive Soils Using Wollastonite Powder: A Mineralogical Approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1249, https://doi.org/10.5194/egusphere-egu26-1249, 2026.
Modern aircraft engines might experience increased degradation when operating in regions with high contents of atmospheric mineral dust. Whilst not safety critical, this accelerated degradation might result in an increased maintenance burden. There are several distinct mechanisms of degradation caused by ingested dust in different engine parts. Particular focus has been on the damage caused by deposits on high pressure turbine (HPT) blades. Here deposits melt, infiltrate and chemically interact with porous thermal barrier coatings. This study examines the sensitivity of this kind of degradation to ingested mineral dust composition, which varies according to the geographical region of operation.
On exit from the compressor, minerals ingested into the engine can follow two different air flow paths. One is with air separated from the main flow, before entry into the combustor, which is used to cool the HPT blades. Minerals within this flow may be deposited in the HPT shank cavity and experience temperatures of ~800°C. The second pathway is with the main air flow through the combustor. Minerals following this route experience higher temperatures (>1200°C) and may be deposited on the HPT blade surface. A comparison of shank cavity with surface deposits isolates the effect that passage through the combustor and residency on the HPT blades has on the chemistry of the deposits. Here, we make this comparison for engines that have operated in different geographical regions.
We have analysed 8 shank cavity and HPT blade surface deposits from aircraft engines using XRD and SEM-EDS to obtain mineralogical and chemical compositions. Shank cavity deposits from a further 56 engines have also been analysed to obtain a sense of compositional variability across different operational regions. The mineral phases present in the shank cavity deposits are similar across all engines analysed and include several minerals, e.g., anhydrite and melilite, that formed in the engine from breakdown reactions of ingested dust. However, the relative abundance of these minerals varies, reflecting the likely composition of atmospheric dust in the regions of operation. The blade deposits are dominated by minerals formed by reactions between ingested minerals and thermal barrier coatings on the HPT blades, including garnets, spinels, and melilite. However, the relative abundance of these minerals also varies across regions.
Our ongoing work compares the chemistry of shank cavity deposits with HPT blade deposits using the minerals and textures to help constrain the processes causing the chemical changes. Concurrently, we seek to compare the chemistry of the shank cavity deposits with ingested dust composition. We aim to establish the extent to which the composition of the HPT deposits, and hence degradation, may be predicted from what is ingested at the front of the engine. With this knowledge, degradation mitigation strategies can then be tailored to operational region.
How to cite: Ownsworth, E., Jones, M., Pawley, A., Covey-Crump, S., Clarkson, R., Hughes, L., Bojdo, N., Dowling, J., and Liu, Y.: Mineralogy and reactions of aircraft engine deposits and relationship to geographical regions of operation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18893, https://doi.org/10.5194/egusphere-egu26-18893, 2026.
The complexity of hydrocarbon exploration in foreland thrust belts results from multiphase hydrocarbon charging, multistage thrusting, and complex pressure evolution. Based on fluid inclusion analysis, this study constrains the multiphase hydrocarbon charging history in Cretaceous strata in the Kela-2 gas field, Kuqa Depression. Paleopressure reconstruction was conducted using PVTsim modeling. By combining compositional data from fluid inclusions of varying origins and timing, the dynamic adjustment process of hydrocarbon has been systematically elucidated. Results show that both the Cretaceous Bashijiqike Formation(K1bs) and Cretaceous Yageliemu Formation(K1y) dry gas reservoirs in the Kela-2 gas field experienced two phases of hydrocarbon charging, consisting of blue-fluorescent oil and natural gas. The hydrocarbon accumulation process in the Kela-2 gas field can be divided into four stages. During 23 to 15 Ma, blue-fluorescent oil charged into the K1y reservoir. The ratio of the number of quartz grains with oil inclusions therein to the total number of quartz grains exceeds 5%, indicating the presence of a paleo-oil accumulation. During 15 to 5.3 Ma, thrust faulting triggered the upward adjustment of crude oil from the K1y to the K1bs reservoirs. Overpressure was absent in the reservoirs at this stage. The oil inclusions from both intervals exhibit similar geochemical characteristics, with MPI derived equivalent vitrinite reflectance (Ro) values of approximately 0.8, suggesting a common-source adjustment. During 5.3 to 2.5 Ma, intensified fault activity drove the charging of high-maturity coal-derived gas. The methane δ¹³C of gas inclusions in K1y is -29‰, lighter than that of its present-day gas reservoir (-25.7‰). Meanwhile, the current methane δ¹³C in K1bs is -28.3‰, which is lighter than that in the current K1y reservoir. It indicates sustained late-stage charging of high-maturity gas, with preferential migration into the K1y reservoir. A massive gas charging and oil displacement, triggering rapid pressurization of the reservoir to a maximum pressure coefficient of 2.0. From 2.5 Ma to the present, sustained fault activity and persistent gas charging led to the formation of a dry gas reservoir (dryness coefficient >0.99) and the continued development of overpressure. Integrated fluid inclusion analysis demonstrates a distinct temporal coupling among fault reactivation, hydrocarbon charging, and overpressure evolution, which collectively governed the final accumulation and preservation of the Kela-2 gas field.
How to cite: Li, X., Hao, F., Tian, J., and Cong, F.: Tracing hydrocarbon accumulation and adjustment in a thrust belt using fluid inclusions: A case study of the Cretaceous system in the Kela-2 Gas Field, Kuqa Depression, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8927, https://doi.org/10.5194/egusphere-egu26-8927, 2026.
How to cite: Demirçalı Özmen, H.: The Role of Natural Clays and Fining Agents in Food Processing and Health: Fruit Juice Clarification, Toxin Removal, and Safety Assessment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2103, https://doi.org/10.5194/egusphere-egu26-2103, 2026.
The Santamu area, located in the Tabei Uplift of the Tarim Basin, is characterized by multi-stratigraphic accumulation and multi-stage charging. Integrating fluid inclusion petrography and microthermometry, in-situ U-Pb dating of calcite veins, and 1D burial history modeling, this study systematically reveals the cross-stratigraphic hydrocarbon adjustment processes and differential accumulation mechanisms within the Ordovician, Carboniferous, and Triassic reservoirs. The charging histories are precisely constrained: the Ordovician experienced three oil-charging phases (Late Caledonian–Early Hercynian, Late Hercynian, and Yanshanian) and one late gas charge, with the Late Hercynian being dominant; the Carboniferous and Triassic T3 subunits received oil during the Yanshanian and Himalayan periods, followed by gas; while the Triassic T1 subunit records only a single Himalayan oil charge. Critically, the study elucidates that the hydrocarbons in the Carboniferous and Triassic strata are not directly sourced from coeval Ordovician oils, but are products of vertical transfer and mixing. Specifically, early-charged (pre-Yanshanian) Ordovician hydrocarbons migrated upward along faults during the Yanshanian and Himalayan periods, with the T1 oil specifically derived from the vertical spillage of hydrocarbons originally trapped in the T3 subunit. The multi-stage differential activity of the NEE-trending strike-slip and Santa Mu fault systems is identified as the key controlling factor, where the opening, activity, and sealing of these faults dictated the vertical migration pathways, charging timing, and final accumulation. Consequently, a composite accumulation model is established for the area, characterized by "multi-stage generation from the Cambrian Yuertusi source rocks, fault-controlled migration, and cross-stratigraphic vertical adjustment," which deepens the understanding of hydrocarbon enrichment in complex cratonic fault zones and provides critical guidance for exploration in analogous regions.
How to cite: Peng, G. and Tian, J.: Cross-stratigraphic Hydrocarbon Adjustment Controlled by Fluid Inclusions: A Case Study of the Santa Mu Area, Northern Tarim Uplift, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2534, https://doi.org/10.5194/egusphere-egu26-2534, 2026.
The Wenchang A Depression in the Pearl River Mouth Basin is a confirmed area with abundant oil and gas resources. The exploration breakthroughs of some wells have revealed the exploration prospects of the deep clastic rock reservoirs in the Wenchang A Depression. Previous studies have focused more on the reservoir research results of individual blocks, but there has been a lack of comparative research among different blocks, and the differences in the dissolution effects and formation reasons of the reservoirs in each block have not been clearly identified. Through the comparative study of the Zhuhai Formation reservoirs in Zones 9 and 10 of Wenchang A Sag, this paper clarifies the differences in the dissolution effects of the reservoirs between the two blocks. Based on rock thin section identification, scanning electron microscopy, trace element analysis, and fluid inclusions homogenization temperature testing, combined with seismic data and formation water data, the study of the differences in the dissolution effects of the Zhuhai Formation reservoirs in Zones 9 and 10 was carried out. The key conclusions are as follows: (1) Feldspar grain dissolution is the dominant dissolution process in the study area. In Zone 10, intense feldspar dissolution is observed in the thick-bedded sandstones in the middle part of the braided river delta front, whereas weak dissolution effects are noted in the fan delta and braided river delta plain reservoirs within the same zone. In Zone 9, vertical variations in dissolution intensity are insignificant; however, dissolution is enhanced in the fault transition zone horizontally, accompanied by weak authigenic kaolinite precipitation. Near the No. 6 Fault Zone, the dissolution effect is attenuated, while authigenic kaolinite extensively fills intergranular pores. (2) Elements associated with feldspar, such as Al, are detected in authigenic quartz overgrowths in Zone 10. Combined with fluid inclusion thermometry of quartz overgrowths, the results demonstrate that dissolution in Zone 10 occurred relatively late, primarily driven by organic acid derived from the thermal evolution of organic matter. (3) Elements including K, Ca, Fe, and Al are identified in quartz overgrowths in Zone 9, with the Al content significantly higher than that in Zone 10. During the deposition of the Zhuhai Formation, the Zhu III South Fault and the Fault No. 6 entered their peak activity. The dextral rotation of the stress field triggered a series of strike-slip faults, transitioning the strata from a closed system to a semi-open system. Faulting, characterized by stronger intensity in the southern segment and weaker in the northern segment, facilitated the migration of deep CO2 fluids into the reservoirs. Integrated with numerical simulation experiments, the results demonstrate that the secondary faults associated with oil-source faults connect organic acids derived from the thermal evolution of source rocks and CO2 fluids. This combined fluid action induces extensive dissolution of feldspar grains and enables effective migration of kaolinite within the semi-open system.This study provides a critical foundation for understanding diagenetic fluid evolution and reservoir development mechanisms in the study area, with implications for future hydrocarbon exploration in similar geological settings.
How to cite: Fang, R. and Yuan, G.: Analysis of the Differences in Feldspar Dissolution in Different Zones of Sandstone Reservoirs: A Case Study from the Zhuhai Formation, Wenchang A Sag, Pearl River Mouth Basin, China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8687, https://doi.org/10.5194/egusphere-egu26-8687, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 3
EGU26-8505 | ECS | Posters virtual | VPS25
Study on the Source of Ore-Forming Materials of the Sangmuchang Barite Deposit in Northern GuizhouThu, 07 May, 14:27–14:30 (CEST) vPoster spot 3
Abstract: The study of fluid inclusions and sulfur isotope characteristics of barite deposits is crucial for tracing the source of ore-forming materials and predicting prospecting targets. Current research indicate that the Sangmuchang barite deposit in northern Guizhou is primarily hosted within the joint fractures of dolomites in the Sinian Dengying Formation and Cambrian Qingxudong Formation. The contact between ore bodies and surrounding rocks is distinct, with the orebodies occurring as veins and lenticular. The ore textures are mainly veinlets, stockworks, massive, and banded, while the ore structures consist of inequigranular tabular-columnar blastic, fine-crystalline, and arenaceous texture. Fluid inclusion studies reveal that the inclusions are single-phase aqueous inclusions. Microthermometric measurements of 33 inclusions show that their homogenization temperatures range from 81°C to 182°C, with an average of 132°C; Salinity values vary from 9.61 wt.% NaCl eqv to 20.63 wt.% NaCl eqv, with an average of 17.53 wt.% NaCl eqv. Ten sulfur isotope analyses from the deposit show that the δ³⁴SV-CDT values range from 40.89‰ to 46.95‰, with a mean of +44.51‰.The characteristics of fluid inclusion salinity, temperature and sulfur isotopes suggest that the ore-forming fluids of this barite deposit are characterized by moderate-low temperature and moderate-high salinity. These ore-forming fluids were mainly derived from basin brines, with contributions from meteoric water. The significant enrichment of heavy sulfur isotopes and homogeneous sulfur isotope composition reveal that the sulfur source of ore-forming materials in this barite deposit is a relatively singular source for the sulfur in the ore-forming materials, which is similar to the δ³⁴S characteristics of Sinian marine evaporites, suggesting a close genetic relationship between the sulfur source and evaporites. Therefore, the Sangmuchang barite deposit is interpreted as a moderate-low temperature hydrothermal deposit. It was formed by the migration of moderate -low temperature hydrothermal fluids in the sedimentary basin, which leached ore-forming materials from underlying and surrounding barium-rich evaporite sequences, followed by precipitation within structural fracture zones under the mixing of meteoric water. The structural fracture zones and areas indicative of fluid migration pathways along the basin margin are important targets for exploration prediction. Keywords: ore-forming fluid; fluid inclusion; sulfur isotope; barite; northern Guizhou
How to cite: Chen, Y., Wang, J., and Liu, Z.: Study on the Source of Ore-Forming Materials of the Sangmuchang Barite Deposit in Northern Guizhou, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8505, https://doi.org/10.5194/egusphere-egu26-8505, 2026.
EGU26-13441 | Posters virtual | VPS25
High-Temperature phase transitions in serpentineThu, 07 May, 15:15–15:18 (CEST) vPoster spot 3
Serpentines are widely used to investigate lithospheric strength, subduction-zone processes, and the cycling of carbon and water in the Earth. In this work we have investigated the high-temperature phase transitions in natural serpentine with respect to the time of heating. The starting material was obtained by grinding natural serpentine sample and verified using powder X-ray diffraction (λ = 1.5406 Å). The powder was heated at temperatures from 300 to 1000 °C in 100 °C increments for durations ranging from 30 minutes to 24 hours, using 1–6 hour intervals. No phase changes were observed up to 400 °C. Two forsterite (Mg2SiO4) peaks at 35.993° and 36.857° first appeared in the XRD pattern at 500 °C after 3 hours of heating. The first appearance of enstatite (MgSiO3), marked by peaks at 28.1880 and 31.2890 were observed in the XRD pattern at 6000C starting at 8 hours of heating. Our work provides a robust temperature-time (T-t) phase diagram. The systematic T-t framework shows that serpentine breakdown and forsterite/enstatite formation depend on both temperature and duration of heating, rather than temperature alone. This can have implications for subducting slabs; where mineral transformations, fluid release, and associated changes in rheology may be governed by slab thermal histories and residence times at depth. These effects can influence interpretations of slab strength, seismic structure, and volatile cycling in subduction zones.
How to cite: Divya, R. V. and Dutta, R.: High-Temperature phase transitions in serpentine, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13441, https://doi.org/10.5194/egusphere-egu26-13441, 2026.
