Oxide mineral phases within high-grade metamorphic rocks are often largely ignored compared to silicate minerals, except for when constraining the redox state of a sample. It is becoming increasingly apparent that unusual concentrations of oxide phases (e.g. magnetite, ilmenite and spinel) are more common in granulite facies metamorphic rocks that previously thought. However, the mechanism of their formation remains poorly constrained. For example, it is currently unclear what process or combination of processes result in high (over 50% oxide concentration in a sample in some cases) concentrations. There is an ongoing debate if a single process can be applied across all protoliths, with the goal that these assemblages could be used to pinpoint particular crustal process(es). A number of mechanisms have been suggested to form such extreme concentrations of oxides within metamorphic rocks. These include melt fluxing in a deformation zone (Ghatak et al., 2022), partial melt loss (Morrissey et al., 2016), deformation related metamorphic reactions and protolith composition or a combination thereof. Within a collection of high grade metapelites from Rogaland, SW Norway, we see variations in mineralogy, including changes in orthopyroxene and cordierite content with oxide concentrations, variations in grain size, variable layering as well as variable signature of the amount of deformation. Using a combination of microstructures, EBSD, EDS, XCT and other data we will assess and illustrate the processes behind the generation of high oxide concentrations within metapelites and what this could mean for crustal processes during high-grade metamorphism.

Ghatak, H., Gardner, R. L., Daczko, N. R., Piazolo, S., & Milan, L. (2022). Oxide enrichment by syntectonic melt-rock interaction. Lithos, 414–415, 106617. https://doi.org/10.1016/J.LITHOS.2022.106617

Morrissey, L. J., Hand, M., Lane, K., Kelsey, D. E., & Dutch, R. A. (2016). Upgrading iron-ore deposits by melt loss during granulite facies metamorphism. Ore Geology Reviews, 74, 101–121. https://doi.org/http://doi.org/10.1016/j.oregeorev.2015.11.012

How to cite: Blereau, E., Piazolo, S., and Macente, A.: Constraining High Oxide Mineral Concentrations in High-Grade Metamorphic Rocks: Insights from Multidisciplinary Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15396, https://doi.org/10.5194/egusphere-egu23-15396, 2023.

Olivine is an abundant phase of ultramafic and mafic rocks in the earth's crust and mantle. Stony meteorites or stony-iron meteorites like pallasites also contain a lot of extraterrestrial olivines. During atmosphere entry olivine-containing meteorites experience different oxygen levels and intense heating for brief intervals, creating fusion crusts that are a few millimetres thick. As a result, various thermal pathways between the rim and the core are anticipated for meteoritic olivines. This shows different colours in natural pallasitic olivines. We are particularly interested in the effects of environmental variables on both terrestrial and interplanetary olivines, based on terrestrial olivines. Natural volcanic olivines from the 1959 Kilauea eruption in Hawaii, the Aheim mine, Norway, are employed and a stony-iron pallasite (collected 1822 – Atacama Desert). We generate two environments using a gas-tight tube furnace that produces CO-CO2 gas mixes—one in air and the second with a reduced atmosphere (fO₂10^-12 bar). The temperatures range from 950 to 1350 degrees Celsius (i.e. within the olivine stability field). After hand-picking single grains of olivines and putting them in Pt-Rh crucibles for an hour, the samples are lifted vertically out of the tube furnace and quenched in air. EPMA, SEM, RAMAN, and optical and laser microscopy are used to characterise and analyse the samples.

Preliminary findings, olivines show thermal stability and have a homogeneous chemical composition both before and after heating. A reduced environmental exposure causes a change in colour, similar to the stony-iron pallasite which will be discussed. In association with those observations, we also see Raman bands nearby 600 cm-1 vanish, and Raman bands show up at 800 cm-1. We will compare these effects in relation to the findings from tests involving air exposure and compare the observations obtained from naturally occurring pallasitic olivines.

How to cite: Brau, J., Schmitt-Kopplin, P., Kaliwoda, M., Scheu, B., and Dingwell, D. B.: Investigation of olivine's thermostability in an oxidized and reduced atmosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12907, https://doi.org/10.5194/egusphere-egu23-12907, 2023.

Like all the alkaline complexes, feldspar exsolution texture is common within different rock types of Koraput Alkaline Complex (KAC), India. Both perthite and mesoperthite exsolution texture are common in this alkaline complex. The former is present within nepheline syenite and granite whereas the latter is observed within alkali gabbro, syenite, granite and nepheline syenite. Shapes of plagioclase feldspar lamellae of perthite and mesoperthite texture vary widely. Plagioclase feldspar lamellae in mesoperthite at places bifurcate and merge with each other forming anastomosing pattern. On the other hand, plagioclase feldspar lamellae in perthite are commonly needle-like. Using two-feldspar and one-feldspar thermometry we have estimated the temperature of formation of these textures. Compositions of exsolved alkali feldspar and the adjacent plagioclase feldspar pairs are used in two-feldspar thermometry. In one-feldspar thermometry, we have used the reintegrated compositions of exsolved alkali feldspars. In two-feldspar thermometry compositions of alkali feldspars immediately after exsolution in these rocks are also estimated. Here we quantify the shape of perthite and mesoperthite grains to objectively understand how effects of different factors (temperature and composition) determines lamellae shape. To solve this problem, we use a multivariate shape analysis approach via geometric morphometrics tool supplemented by statistical methods such as ordinations and statistical analyses [Principal Components Analysis (PCA) and Canonical Variates Analysis (CVA)]. Our result suggests that there is no influence of composition on the shape of plagioclase feldspar lamellae. On the other hand, a strong influence of temperature on the shape of lamellae is distinctly observed. Plagioclase feldspar lamellae showing anastomosing pattern formed at higher temperature. On the other hand, needle like plagioclase feldspar lamellae formed at the lower temperature.  Our data analytics-driven results provide a new perspective to understand the relation between the feldspar exsolution shape and formation temperature of the lamellae. The shape modification of the feldspar lamellae implies that the exsolution texture in alkali gabbro formed early followed by nepheline syenite, syenite and alkali feldspar granite. This finding is also coeval with the crystallisation history of the lithological units of this alkaline complex.

How to cite: Koley, M., Ghosh, B., Dhar, A., and Roy, S.: A multivariate approach to study the shape modifications of feldspar exsolution lamellae during cooling: A case study from Koraput Alkaline Complex, India, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-441, https://doi.org/10.5194/egusphere-egu23-441, 2023.

Kimberlites are the deepest and the most enigmatic magmas that reach the surface of the Earth. Their source, origin and even composition are a subject of debates. Kimberlites form hypabyssal sills and dykes but most often occur as explosion pipes, which comprise various volcaniclastic and magmatic units. Differences in the geological composition, shape and size of kimberlite pipes worldwide arise from the differences in the eruption processes and are the base for distinguishing three kimberlite classes. However, it is not clear if these differences result from the properties of the country rocks or from variable magma composition especially H2O : CO2 ratio.

During the ascent, kimberlites transport mantle fragments including diamonds to the surface and partially dissolve them. Previous studies have shown that dissolution features on diamond reflect the conditions in the host magma and especially presence and composition of fluid. Diamonds from volcaniclastic facies of different kimberlite classes all show very similar low-relief surface features indicating presence of fluid. Geometry of the trigonal etch pits on diamonds helps to deduce H2O:CO2 ratio of kimberlitic fluid. On the contrary, “corrosive” resorption styles of diamonds from hypabyssal kimberlite (HK) units are different between the three kimberlite classes allowing to examine differences in their crystallization conditions. This study aims to reproduce corrosive resorption of diamonds in controlled experiments in order to examine the composition of kimberlite magma in different kimberlite classes and its effects on magma emplacement.

Experiments were conducted in piston-cylinder apparatus at pressure 0.5 – 1 GPa and temperatures 1000 – 1200^oC using a range of volatile-undersaturated silicate and silico-carbonate melts. Experiments produced three specific resorption styles previously reported on natural diamonds from HK: (i) sharp pointy features common for diamonds from HK in class 3 kimberlites; (ii) corrosion sculptures common for diamonds from HK in class 1 kimberlite; (iii) deep channels – rare but prominent feature of natural diamonds. We compare our experimental results to the features of natural diamonds from HK units of class 1 kimberlites (Orapa kimberlite cluster, Botswana) and class 3 (Ekati Mine kimberlites, Canada) to compare magma composition and emplacement conditions of different kimberlite classes.

How to cite: Fedortchouk, Y.: Experimental study of dissolution style of diamonds from volcaniclastic vs. hypabyssal kimberlite facies: the effect of melt composition on kimberlite eruption and geology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10213, https://doi.org/10.5194/egusphere-egu23-10213, 2023.

The magmatic water content plays an important role in the evolution and explosivity of volcanic eruptions, due to the influence of water on magma density, viscosity, crystallization and melting temperatures. A reliable method for determining the pre-eruptive magmatic water content is to use nominally anhydrous minerals (NAMs) which can preserve various hydrogen configurations (as water proxy) in structural defects. This method allows to experimentally reconstruct the water lost during magmatic processes such as degassing and analyse it by infrared spectroscopy. Applying this to crystallographically oriented clinopyroxene crystals from lava samples collected in April 2021 from the Geldingadalir eruption, SW-Iceland, we obtain water contents of 0.69 ± 0.07 to 0.86 ± 0.09 wt. % H₂O. Because these values are higher than those expected for typical mid-ocean ridge basalts (MORB: 0.3 – 0.5 wt. % on average) it reveals a significant plume (OIB) contribution to the magma source. The implications of such water concentrations are that water saturation was attained only at very shallow levels within the plumbing system of the ascending Geldingadalir magmas. This can further explain the occurring pulsing behaviour of the lava pond and within the upper conduits, as the result of shallow, episodic, vapour exsolution.

How to cite: Radu, I.-B., Skogby, H., Troll, V. R., Deegan, F. M., Geiger, H., Müller, D., and Thordarson, T.: A mineralogical approach to the 2021 Geldingadalir eruption of the Fagradalsfjall Fires,SW-Iceland – the study of water in clinopyroxene phenocrystals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16815, https://doi.org/10.5194/egusphere-egu23-16815, 2023.

The dominant phases of Earth’s upper mantle are commonly referred to as nominally anhydrous minerals (NAMs) but may contain significant amounts of water. The colloquial term “water” in NAMs is related to the presence of hydroxyl-bearing (OH^-) point defects in their crystal structure, where hydrogen is bound to lattice oxygen and is charge-balanced by cation vacancies. For this reason, the incorporation of even small amounts of water may substantially affect the physico-chemical properties of NAMs, such as their elasticity, rheology, and melting temperature. Olivine is considered the most abundant phase of Earth’s upper mantle and constitutes about 60 vol.% of a primitive upper mantle (pyrolite) phase assemblage. Although natural olivine samples originating from the shallow upper mantle are relatively dry (maximum H₂O concentrations of about 400 ppm), a plethora of experimental data indicate that olivine water storage capacity significantly increases to 0.2-0.5 wt.% H₂O at deeper upper mantle conditions.
In this contribution, we investigated the effect of water on the elastic properties and sound wave velocities of hydrous Mg_1.8Fe_0.2SiO₄ (Fo90) olivine samples with realistic water contents for deep upper mantle conditions with the aim of interpreting both seismic velocity anomalies in potentially hydrous regions of Earth's upper mantle and the observed seismic velocity and density contrasts across the 410-km discontinuity between the upper mantle and the mantle transition zone. To do so, we performed simultaneous single-crystal X-ray diffraction and Brillouin scattering measurements at room temperature up to ~12 GPa on Fo90 olivine with ~0.20 wt.% H₂O to constrain its full elastic tensor. Results were complemented with a careful re-analysis of all the available single-crystal elasticity data from the literature for Fo90 olivine to re-determine the elastic behaviour of the anhydrous phase. Our new data show that the sound wave velocities of hydrous and anhydrous olivines are indistinguishable within uncertainties at pressures corresponding to the base of the upper mantle. Therefore, if amounts of water were to be incorporated into the crystal structure of Fo90 olivine, its elastic and seismic behaviour at high pressure would likely remain unchanged. This suggests that water in olivine is not seismically detectable, at least for contents consistent with deep upper mantle conditions. Moreover, the incorporation of water in olivine is unlikely to be a key factor in reconciling seismological observations at the 410-km discontinuity with a pyrolitic mantle, but rather corroborates previous evidence of a deep upper mantle that is less enriched in olivine than the pyrolite model.

How to cite: Faccincani, L., Criniti, G., Kurnosov, A., Boffa Ballaran, T., Withers, A. C., Mazzucchelli, M., Nestola, F., and Coltorti, M.: Elasticity of hydrous olivine at high pressure and seismic detectability of water in Earth's mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14573, https://doi.org/10.5194/egusphere-egu23-14573, 2023.

The diffusion of atoms in minerals at high temperatures and pressures influences Earth’s lower mantle dynamic processes. This study aims to better understand the physical behaviour of Earth’s most abundant mineral with implications for lower mantle viscosity. Previous studies that measured Si-self diffusion coefficients in bridgmanite (Brg) showed a value at 25 ± 1 GPa and 1800 °C of Log₁₀(D_Si) = -18 ± 0.5 (based on units of m²/s). Our study revealed a significantly slower diffusion coefficient that may challenge previous calculations of lower mantle viscosity. We investigated Al, Si interdiffusion in Brg experimentally at 24 GPa and 1750 to 2000 °C using a multianvil apparatus using diffusion couples composed of bridgmanites that were pre-synthesised from 0-5 mol.% Al₂O₃-bearing MgSiO₃ enstatite. The Al diffusion profiles were analysed across the diffusion interface in the recovered samples using a scanning transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. The obtained diffusion coefficient for interdiffusion (volume diffusion) at 24 GPa and 1800 °C was Log₁₀(D_Al,Si) = -20.1 ± 0.7. The resulting data can be used to estimate deformational strain rates of Brg in the lower mantle from viscosity based on different creep mechanisms.

How to cite: Czekay, L., Miyajima, N., and Frost, D.: Al, Si diffusion in bridgmanite to estimate the Earth's lower mantle rheology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15214, https://doi.org/10.5194/egusphere-egu23-15214, 2023.

Bridgmanite and CaSiO₃-perovskite, respectively, are the first and third most abundant minerals in the Earth's lower mantle. The intersolubility of Ca and Mg between these two minerals is still under debate. Some studies indicated limited intersolubility, while others suggested a complete dissolution of CaSiO₃-perovskite into bridgmanite at lower mantle conditions. This controversy leads to different explanations of the physical properties of the lower mantle such as density, elasticity, and viscosity, accordingly modifying our understanding of the nature and dynamics of the Earth’s interior. Therefore, it is essential to determine the intersolubility of bridgmanite and CaSiO₃-perovskite.

The intersolubility of Ca and Mg between bridgmanite and CaSiO₃-perovskite can be affected by the temperature, pressure, and bulk compositions of the system. Previous studies showed an increase in intersolubility with temperature, but reported no robust pressure and composition dependence. Because FeAlO₃ is the second dominant component in bridgmanite, investigating the effect of FeAlO₃ content and pressure dependence is essential to clarify the phase relation of the Earth’s lower mantle.

This study determined the pressure and FeAlO₃ dependence on the intersolubility of bridgmanite and CaSiO₃-perovskite at pressures of 27 to 40 GPa at a constant temperature of 2300 K using a multi-anvil press. Two compositions of MgSiO₃:CaSiO₃ = 1:1 and MgSiO₃:FeAlO₃:CaSiO₃ = 3:2:5 were examined. SEM images clearly show the existence of two phases in all products. TEM-EDS analyses indicate a decrease in the CaSiO₃ content of bridgmanite in both systems with increasing pressure. The FeAlO₃ component only slightly enhances the CaSiO₃ content of bridgmanite: adding the FeAlO₃ component increases the CaSiO₃ content of bridgmanite from 0.04(2) to 0.3(2) mol.% at 40 GPa. The MgSiO₃ content of CaSiO₃-perovskite decreases with increasing pressure from 1.8(7) to 0.06(8) mol.% in the FeAlO₃-free system, and from 1.2(5) mol.% mol to an unmeasurably small value in the FeAlO₃-bearing system. We conclude that, even with the presence of a FeAlO₃ component in bridgmanite, the intersolubility is limited and remains nearly constant at different pressures. Thus, bridgmanite and CaSiO₃-perovskite should coexist in the lower mantle, and CaSiO₃-perovskite is the host mineral of large lithophile elements such as Ca in the lower mantle.

How to cite: Wang, L., Miyajima, N., Wang, F., Wang, X., and Katsura, T.: Limited intersolubility of Ca and Mg between bridgmanite and CaSiO3-perovskite in the lower mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6782, https://doi.org/10.5194/egusphere-egu23-6782, 2023.

Investigation of the reservoir lithology of Edremit geothermal field from western Anatolia is performed using the drill cuttings that belong to the reservoir levels. The samples are analysed in an attempt to determine the mineralogical and petrographical features, mineral compositions and whole rock geochemistry. The examinations include macroscopic and microscopic analyses, followed by the techniques of X-Ray Diffraction (XRD), Confocal Raman Spectroscopy (CRS), Electron Probe Micro Analysis (EPMA) and X-Ray Fluorescence (XRF). Dominant rock fragments and mineral phases are identified as granitic rocks and quartz, feldspars, micas, carbonates and amphiboles, respectively. Textural characteristics of the samples display the effects of cataclasm and alteration, indicating faulting and hydrothermal fluid activity. The changes in major and trace element concentrations along the well bore reveal three different concentration levels at depth intervals of 900-928 m, 930-974 m and 976-1038 m as well as an inverse relationship between SiO₂ and CaO. These three distinctive zones correlate well with the variations in grains sizes (coarse to fine) and textural features (cataclastic to mylonitic) with depth. Taking into account the reported water leakage zone around 930 m depth and the evidences for hydrothermal fluid effect (such as pyrite abundance, alterations, sulphur presence) observed along the well bore, possible fault zone and as a result, the likely pathway for the hydrothermal fluid is inferred to be in the middle section (930-974 m) of the identified three zones. It is also deduced from the lithogeochemical results that the fluid is potentially Si-rich in this zone and Ca-rich in deeper levels which are in line with the previously investigated hydrogeochemistry of the system. This study points out that mineralogical-petrographical studies integrated with geochemical analyses can potentially serve as significant indicators in determination of lithological variations that can be correlated with fault zones of deep systems for prospective exploration sites.

This study has been published in Applied Geochemistry in 2022 and complete work can be accessed from https://doi.org/10.1016/j.apgeochem.2022.105388

How to cite: Elidemir, S., Güleç, N., Deniz, K., and Kadıoğlu, Y. K.: Implications for Possible Fault Zones Deduced from Lithogeochemical Characterization of Reservoir Levels of a Geothermal Field: Edremit Example, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-545, https://doi.org/10.5194/egusphere-egu23-545, 2023.

Between 1948 and 2001, the extraction of Uranium (U) ores in France have produced a large quantity of waste (tailings, waste rock, etc.), still containing U-rich minerals and other trace elements (TE), that were associated to the initial mineralization. Some of those TE can be relatively mobile and redistributed with U in the various reservoirs of the critical zone, contaminating environmental compartments such as soils and sediments.

Wetlands correspond to areas where the physical and chemical conditions may greatly vary according to the variations of the water table. When these areas are contaminated by mining inputs, the presence of particulate organic matter (POM) in large quantity may influence the mobility of U and many various TE. Moreover, in recent years, the multiplicity of drought events can lead to the modification of the ability of such wetlands to sequestrate U and its co-occurring metals. The consequences of these events in terms of speciation and mobility of contaminants under oxidizing conditions need thus to be better understood.

For this purpose, wetland soils impacted by former U mining and milling activities in a site of the Massif Central (Rophin, France) were studied. Various analytical approaches (SEM, EPMA analyses and BCR chemical extractions) were deployed to determine the speciation of TE and understand their stability (leaching tests) under oxidizing conditions.

The pollution index Igeo, calculated along a soil core of 48 cm, highlights significant anthropogenic contributions in U, Pb and Cu the highest contamination levels in those elements being linked to a white layer, probably inherited from the former mining activities. For Cu and U, the solid speciation in this mining deposits is mainly governed by adsorption on surface particles and to a lesser extent, by precipitation of authigenic/inherited phases such as oxides for U (e.g. uranium dioxide - UO₂) and sulfides for Cu (e.g. chalcopyrite - CuFeS₂). Sorption processes onto the POM seems to mainly govern their speciation in ancient and recent POM-rich layers. Along the soil core Pb solid speciation seems mostly associated to stable phosphates e.g. plumbogummite (PbAl₃(PO₄)(PO₃OH)(OH)₆) inherited from the regional granite and U-Pb-rich mineralization. Again, mining deposits show differences with Pb adsorbed on surface particles and linked to other mineral phases such as sulphates e.g. anglesite (PbSO₄) and hokutolite ((Ba,Pb)SO₄). Additionally, refractory granite minerals contain U and Pb in variable quantities all along the soil core, (e.g. titanium oxides, REE phosphates, zircons). Eventually, minute amounts of Pb and U phosphates containing traces of Cu and As, with a stoichiometry close to parsonsite (Pb₂(UO₂)(PO₄)₂ 2H₂O), the prevailing U mineralization of the Rophin deposit, are also identified. The various U and TE-phases identified in this wetland outline different behavior and mobility according to environmental parameters modifications. Finally, leaching tests and chemical extractions highlighted a certain mobility for some elements, such as Cu and U, that may be hazardous for the environment.

How to cite: Darricau, L., Cucinotta, J., Gorny, J., Mangeret, A., Zebracki, M., and Courtin, A.: Reactivity of U and co-occurring metals from mine deposits in a wetland under oxidizing conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1127, https://doi.org/10.5194/egusphere-egu23-1127, 2023.

The Donegal mica crisis began in 2011 and was initially linked to the presence of excessive free mica in the binder of aggregate concrete masonry units (ACMU) used for construction of dwellings and commercial premises in the decade prior. Free mica was identified to be abraded from the muscovite rich aggregate source, a low-grade phyllite. This free mica increased the microporosity of the cement binder leaving it highly susceptible to secondary degradation processes, including moisture ingress, potential freeze-thaw degradation and internal or external sulphate attack. As well as weakening the binder overall strength the ability to adhere to the flakey mica-rich aggregate was also reduced. Further work since then has highlighted the presence of elevated levels of pyrrhotite within the predominant problematic aggregate, a highly reactive sulphide responsible for internal sulphate attack. Taken together, ACMU’s produced using phyllite aggregate has produced abundant defective concrete block within County Donegal. These ACMU’s have rapidly deteriorated producing the present crisis within County Donegal.

Whilst the most defective phyllite-bearing ACMU has typically already suffered critical deterioration, work undertaken as part of I.S. 465 has also highlighted other metasedimentary aggregates in use within County Donegal which are of lower or higher metamorphic grade. Sulphide abundance within these aggregates is lower and sometimes absent, depending on the grade and phases of deformation they have been subjected to. In addition, when sulphides are present pyrite tends to predominate, with pyrrhotite largely absent except for at the higher metamorphic grades transitioning from the problematic phyllite (i.e. schist, hornfels and amphibolite). These aggregates also produce slightly lower levels of free mica in the binder, either due to stronger annealing at higher metamorphic grades or less abradable mica and splaying along crenulations at lower grades. These aggregate types, and the houses built from the ACMU’s are nevertheless showing signs of degradation and point to the need to consider the longer-term impacts and risks of ACMU’s made from the different aggregate types that may be prevalent within County Donegal.

This abstract proposes a three-fold metric for identifying the most defective ACMU’s at risk of premature deterioration dependent on the metamorphic grade and deformation characteristics of the aggregate used, the amount of free mica produced in the binder and the abundance of sulphides, particularly pyrrhotite.

How to cite: Brough, C., Staniforth, B., Garner, C., Strongman, J., Fletcher, J., and Colville, R.: The Donegal mica scandal, the tip of an iceberg?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-967, https://doi.org/10.5194/egusphere-egu23-967, 2023.

Talc and serpentine-group minerals are Mg-dominant trioctahedral layered silicates that are common in igneous and metamorphic rocks and can be found in a wide range of geological conditions. Hence, a precise physicochemical characterization of these phyllosilicates in intact mineral assemblies, e.g. in thin sections as prepared for polarization microscopy, can provide a better insight into the processes of mineral formation, magma differentiation, and alteration. Moreover, talc and serpentines are common mineral components in a variety of cultural-heritage objects such as engraved gems and old Babylonian cylinder seals. Hence, material profiling of artefacts can help understand their origin through crystallographic and crystallochemical markers that may advance provenance studies. Since sampling of such objects is mostly prohibitive, the development of non-destructive, non-invasive, and preparation-free analytical methods is desired.

To address this quest, a series of 18 serpentine-group minerals (nominally Mg₃Si₂O₅OH₄) and 10 talc samples (nominally (Mg₃)Si₄O₁₀OH₂) with different contents of Fe as a minor element was selected and studied by Raman spectroscopy and wavelength-dispersive electron microprobe analysis (WD-EMPA) to explore the potential of Raman spectroscopy as a truly non-destructive method for quantitative compositional characterization of these groups of phyllosilicates. The methodological approach is based on the already established quantitative relationships between the crystallochemical composition and the Raman signals of biotites (Aspiotis et al., 2022). The goal was first to verify whether the Raman scattering arising from the framework vibrations (15-1215 cm^-1) and OH-bond stretching (3500-3900 cm^-1) can assist in the identification of serpentine-group minerals and talc samples with various cationic compositions at the octahedral site. Secondly to establish quantitative relationships between the Raman signals (peak positions, integrated intensities, and full widths at half maximum) and the crystal chemistry of these phyllosilicates. We demonstrate that the quantification of ^MMg and ^M(Fe²⁺+Mn) contents in talc from the Raman spectroscopic analysis is as accurate as from EMPA. Regarding serpentines, ^MMg and ^MFe²+ amounts can be determined as well with a relative precision of ~ 2 and 5%, respectively.

How to cite: Aspiotis, S., Schlüter, J., and Mihailova, B.: Exploring Raman spectroscopy for crystallochemical analysis of talc and serpentine: application beyond geosciences, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14853, https://doi.org/10.5194/egusphere-egu23-14853, 2023.

Minerals are the oldest surviving materials from the formation of our solar system. They are time capsules that store and provide information about the evolution of Earth and other planetary bodies. In addition to being a cornerstone of geoscience research, minerals also have economic, industrial and commercial importance in many sectors of society. One of the fundamental questions in mineralogy and geosciences in general is “Where to find minerals?”. Due to the complex and intertwined nature of natural systems, it has been hard to predict the occurrences of minerals. However, with increase in the volume and accuracy of mineral data and rise of mineral informatics, data science and analytics methods can be developed to answer this fundamental question in mineralogy. 

In this contribution, we present “mineral association analysis”, a method to: 1) Predict the mineral inventory for any existing locality. 2) Predict previous unknown localities for any given mineral. Mineral association analysis is a machine learning method that uses association rule learning to find interesting patterns based on mineral occurrence data. Using mineral association analysis, we have been able to predict locations of critical minerals, such as minerals with Li- and Th-bearing phases, predict the mineral inventory of mars analogue sites, and even understand how mineralization and mineral associations changed through deep time.

How to cite: Prabhu, A., Morrison, S. M., Eleish, A., Fox, P., Golden, J. J., Downs, R. T., Perry, S., Burns, P. C., Ralph, J., and Hazen, R. M.: Mineral Association Analysis: Predicting unknown mineral occurrences and improving our understanding of mineralogy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10283, https://doi.org/10.5194/egusphere-egu23-10283, 2023.

The electron microprobe (EPMA) flank method can be used to determine in-situ the Fe2+/Fe3+ ratios in garnet [1], and potentially also in other minerals. It is a tool to reveal the redox history of rocks, especially when the garnet grain size or garnet homogeneity requires a microanalytical technique for Fe3+/Fe(tot) determination (e.g., [2,3,4]). The flank method is based on the accurate intensity measurement at two positions on the flanks of the FeLa and FeLb emission lines, and makes thus use of the systematic change of the intensities and wavelengths of the FeL lines with: (i) the iron oxidation state and (ii) the total iron content.  Data reduction of the obtained data so far required a complex combination of numerous Excel spreadsheets, and, for multiple linear regressions, the conversion to text files in combination with the Matlab clone Octave. This work-flow required a trained expert, and could quickly take up to even several days. 

We converted this process into a web-application with a simple and intuitive graphical user interface (GUI), with which the entire work-flow can be completed within minutes to hours. The web-application uses the 2-dimensional linear regression fit to determine Fe2+ from its dependency both on the intensity ratio FeLb/FeLa and the total Fe content, based on eq. 2 in [1].  The web-application allows the visual examination of all data using a large variety of plots for in-depth data inspection. Video tutorials embedded on the website explain not only how to use the website, or how the data reduction itself works, but also the flank as well as the EPMA method itself. Own data can be uploaded and reduced, and an available demo dataset allows training and exploring the web-application.

The entire web-application is realised using Python, Streamlit and a public GitHub repository. We will present what the flank method is, how it works using the EPMA, how the data reduction process works, and demonstrate how to use the web-application from the raw dataset to the final results.

[1] Höfer H. E. and Brey G. P. (2007) The iron oxidation state of garnet by electron microprobe: Its determination with the flank method combined with major-element analysis. Am Mineral 92, 873–885.

[2] Wang C, Tao R, Walters JB, Höfer HE, Zhang L (2022): Favorable P–T–ƒO2 conditions for abiotic CH4 production in subducted oceanic crusts: A comparison between CH4-bearing ultrahigh- and CO2-bearing high-pressure eclogite. Geochim. Cosmochim. Acta 336, 269-290

[3] Tang M, Lee C-TA, Costin G, Höfer HE (2019): Recycling reduced iron at the base of magmatic orogens. Earth and Planetary Science Letters 528, 115827. doi.org/10.1016/j.epsl.2019.115827

[4] Aulbach S, Höfer HE, Gerdes A (2019): High-Mg mantle eclogites from Koidu (West African craton): Neoproterozoic ultramafic melt metasomatism of subducted Archaean plateau-like oceanic crust. Journal of Petrology 60, 723-754

How to cite: Hezel, D. C., Höfer, H. E., and Fichtner, A.: A new web-based and open data reduction application to determine Fe2+/Fe3+ ratios using the electron microprobe flank method., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16233, https://doi.org/10.5194/egusphere-egu23-16233, 2023.

The wide range of colored wastewater from industries in the aquatic environment poses a great threat to human and animal health and poses a great obstacle to the ecological ecosystem. Therefore, an effective, efficient, and environment-friendly treatment methods are being sought. Hydroxyl- phosphate and arsenate compounds have recently attracted attention for magnetic and photocatalytic applications in photoreactions with visible light.  They can be a promising alternative to TiO₂, in which the photoabsorption spectrum is in the range of ultraviolet (UV) light owing to its large bandgap, which accounts for only 5% of the sunlight.

Here, we present a detailed analysis of the properties of libethenite Cu₂PO₄OH - olivenite Cu₂AsO₄OH solid solution series, and their photocatalytic activities under visible light. Seven compounds of the solid solution series were successively synthesized by the wet chemical method at 70°C according to the results of Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) tests. The photocatalytic performance of the samples was thoroughly investigated for the degradation of methylene blue MB solutions under visible light and measurements by UV-vis spectroscopy.

We demonstrated the useful photocatalytic activity of these complex structures for the degradation of methylene blue (MB) dye under visible-light irradiation. The substitution effect of [PO₄]³⁻ anions by [AsO₄]³⁻ results in changes in the bonds of the OH group, which are the origin of the photocatalytic properties of this material, altering the bond length and geometry.  In addition, these substitutions affected the morphology of the precipitating solids, which changed the surface area of the material. This way the substitution of As with P in the solid solution series affected the photocatalytic properties The MB degradation efficiency after 6h declines from ~ 84 % for the Cu₂AsO₄OH and Cu₂PO₄OH down to ~81% for intermediate member.  The present work provides insights leading to a better understanding of the photocatalytic performance of Cu₂PO₄OH and Cu₂AsO₄OH. Thanks to these results it may be beneficial to prepare more efficient photocatalysts based on this material for sunlight photocatalysis, which will also be helpful in designing and preparing novel technologies.

This research was funded by NCN research grant no. 2021/41/N/ST10/03566

How to cite: Waluś, E. and Manecki, M.: Photocatalytic properties of libethenite Cu2PO4OH - olivenite Cu2PO4OH  solid solution series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9209, https://doi.org/10.5194/egusphere-egu23-9209, 2023.

Research on rare earth elements (REE) is currently of high importance due to these elements being considered as critical raw materials. Particularly REE phosphates are the subject of laboratory experiments since they have various applications resulting from their structural diversity. In crystalline rocks REE phosphates occur as monazites and xenotimes (REEPO₄, monoclinic and tetragonal, respectively). Secondary phosphates precipitate out of aqueous solution usually in the form of rhabdophane or churchite (REEPO₄·nH2O, trigonal and monoclinic). Their formation results in immobilization of REE which plays a significant role in controlling the solubility of REE in nature, in beneficiation processes, and in technological applications.

The precipitation of rhabdophanes is usually studied experimentally in pure systems. However, it is recognized that the presence of other solution components can significantly affect the processes and the final product. Since both Pb and REE readily form phosphates that precipitate out of aqueous solutions, it has been hypothesized that the precipitation of REE-phosphates in the presence of Pb would result in the formation of mixed phosphate phases (containing both Pb and REE) or a mixture of two phases: phosphoschultenite PbHPO_4­ and rhabdophane REEPO₄·nH₂O. Despite the difference in ionic charge between Pb²⁺ and REE³⁺, formation of either phosphoschultenite PbHPO_4­ partially substituted with REE, or rhabdophanes partially substituted with Pb was also considered.

Synthesis of La-, Ce-, and Sm-rhabdophanes was attempted in the absence (control) and in the presence of Pb²⁺ ions in the solution (at ambient conditions, pH between 2 and 4). The final solutions were analyzed with inductively coupled plasma optical emission spectroscopy (ICP-OES) for Pb and REE concentrations, while solids were filtered, dried, and analyzed with powder X-ray diffraction (PXRD), scanning electron microscopy (SEM/EDS), Raman spectroscopy, and differential thermal analysis (DTA/TG).

As expected, monoclinic analogs of rhabdophanes precipitated in the absence of Pb: LaPO₄·0.67H₂O, CePO₄·0.67H₂O, and SmPO₄·0.67H₂O. However, at the presence of Pb²⁺, distinct new phases were formed. This precipitation removes REE elements from the solution very efficiently. The product forms extremely fine (<1 mm) crystalline precipitate in the form of globular aggregates. XRPD patterns of each of them are nearly identical, shifted towards higher angles as the ionic radius decreases in the order La – Ce – Sm. At this stage of research, the structure of these phases could not be identified conclusively. Chemical composition was approximated using SEM/EDS microanalysis (the precipitate is too fine for a microprobe). Raman spectrum indicates that the phases are hydrated and DTA analysis allowed to estimate the water content. At this stage of research, the chemical formula has been determined as La₂Pb₃(PO₄)₄ · nH₂O, Ce₂Pb₃(PO₄)₄ · nH₂O, and Sm₂Pb₃(PO₄)₄ · nH₂O, where n is between 3.3 and 3.5. Such unexpected results provide better insight into the new recovery pathways currently being explored for these critical raw materials. The results of these preliminary experiments open up new avenues for exploring as yet unknown crystalline phases composed of Pb-REE phosphates with potentially interesting practical applications.

This research was partly funded by NCN research grants no. 2021/43/O/ST10/01282 and 2019/35/B/ST10/03379.

How to cite: Staszel, K., Jędras, A., Skalny, M., Dziewiątka, K., Urbański, K., Sordyl, J., Rybka, K., Majka, J., and Manecki, M.: Impact of Pb2+ presence on precipitation of REE phosphates (analogs of rhabdophane) from aqueous solutions., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8801, https://doi.org/10.5194/egusphere-egu23-8801, 2023.

Zircon is an invaluable accessory mineral found in a wide range of crustal rocks. It can faithfully record its host rock’s composition, over long periods of geological time, leading to its wide use in studies of continental evolution. Detrital zircons collected from Earth’s modern rivers provide a representative sample that can be used to study the evolution of the continental crust on a large scale, aided by long-time sediment-sediment recycling, which results in the efficient mixing of zircons from source rocks of diverse origins.  

We use the Lu contents in zircons to identify those that come from the high-pressure zones of the deep mountain roots. By applying this technique to our global data base of zircon from major rivers, we show that Nuna and Gondwana were periods when Earth’s topography was dominated by high, Himalayan-type mountains, whereas Rodinia was not. The dramatic difference between Rodinia on one hand, and the amalgamation of Nuna and Gondwana on the other, is also manifested in other geological proxies, such as peaks in the average metamorphic pressure, seawater Sr isotope and S-type granite abundance. The two periods of extensive high mountain (supermountain) formation coincide with two major changes in Earth’s evolution: (i) postulated increases in atmospheric oxygen, and (ii) major biological advances. We argue that the big evolutionary changes that occurred during these two periods were potentially driven by dramatic increases in the supply of bio-limiting nutrients into the oceans, which resulted from the rapid erosion of Earth’s two supermountains.

How to cite: Zhu, Z. and Campbell, I.: Earth’s supermountains as revealed by detrital zircon from modern rivers linked to biological evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10435, https://doi.org/10.5194/egusphere-egu23-10435, 2023.