Serpentinization reaction is known as one of the main sources of natural H2 at the Earth’s surface. Estimates of H2 production during this reaction require an in-depth understanding of the mineralogical processes leading to iron oxidation. The study of serpentinized peridotites collected at 13 localities at mid-ocean ridges, in ophiolites and ultramafic bodies reveals the development of an alteration sequence during reaction. At the olivine contact, a first reaction zone is composed of a fine-grained mixture of serpentine, Fe-brucite and awaruite (Reaction Zone 1). Thermodynamic modelling with the latest data for the Fe(OH)2 endmember indicates that awaruite formation limits H2 production with H2 concentrations comprised between 10-3 and 10-2 mol/kg. These values are consistent with the maximum values measured in fluids expelled at ultramafic-hosted hydrothermal sites. At the mesh rim, a second alteration zone composed of Ni-bearing magnetite, serpentine and Mg-brucite is found (Reaction Zone 2). Serpentine and Mg-brucite display a porous symplectite microtexture, indicating formation after Reaction Zone 1 by a dissolution-precipitation process. Magnetite formation in Reaction Zone 2 could not be reproduced with thermodynamic modelling by modifying, as previously thought, temperature or water to rock ratio. However, removing H2 from the system was found to reproduce both the mineralogy and the composition of Reaction Zone 2. This indicates that H2 diffusion is the main driver for magnetite formation during serpentinization. The H2, aq concentrations at the equilibrium with Reaction Zone 2 fall in the 10-7 - 10-3 mol/kg range. Based on the mineralogical observations and thermodynamic modelling performed here, two regimes for H2 production during olivine serpentinization can be proposed. If H2 diffusion is limited, the serpentinizing fluid contains between 10-3 and 10-2 mol/kg of H2 but the overall H2 production is one order of magnitude smaller than previous estimates. If H2 diffusion proceeds rapidly, the overall H2 production is comparable to previous estimates but the expected H2 concentration in the serpentinization fluid at the equilibrium with the reaction products is extremely low (10-7 to 10-3 mol/kg).
How to cite: Malvoisin, B., Dörfler, P., Auzende, A.-L., Brunet, F., Cannat, M., Austrheim, H., and Kaczmarek, M.-A.: RedOx gradient as the main driver for magnetite formation during serpentinization: implications for natural H2 production, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20851, https://doi.org/10.5194/egusphere-egu26-20851, 2026.
Serpentinization is a fluid–rock interaction process occurring in specific geodynamic settings, whereby aqueous fluids react with mantle-derived source rocks to produce serpentinite, ± magnetite, and native hydrogen (H₂). Among the key parameters controlling this process, the Fe²⁺ content of primary mantle minerals is directly linked to the capacity for H₂ generation. Because serpentine minerals themselves may incorporate Fe²⁺, serpentinites may retain a degree of “fertility” for continued H2production. In the context of the energy transition, this aspect is of fundamental importance, as zones potentially suitable for H2 extraction are commonly associated with partially to fully serpentinized mantle rocks. Such continental environments are typically suture zones, i.e. rift-inversion orogen that once hosted the subcontinental mantle exhumed along ocean–continent transitions (OCTs).
Several mountain belts worldwide preserve continental-margin ophiolites, consisting of subcontinental lithospheric mantle directly overlain by basaltic lavas and intruded by small gabbroic plutons and rare mafic dikes. However, only a few are sufficiently well constrained in terms of tectonic evolution and petrology. The Grischun–Malenco area (southeastern Swiss and northern Italian Alps) represents the type locality of a fossil OCT, whose history has been precisely reconstructed from pre- to post-rift stages through numerous fundamental studies. The Grishun–Malenco OCT developed along the Jurassic Alpine Tethys and facilitated the subcontinental mantle exhumation to the seafloor. These mantle rocks experienced variable degrees of serpentinization, whereas more proximal domains (present-day Malenco), remaining beneath the continental crust, may undergone only limited serpentinization. During subsequent Eo-Alpine convergence, the Grischun–Malenco area was buried within a potential serpentinization window above the subducting slab, i.e. within a supra-subduction zone located in the hanging wall of the compressional system. Finally, during Meso-Alpine convergence, the area was incorporated into the orogenic lid and tectonically emplaced onto the European plate. Tectonic reconstructions suggest that, structural inheritance, particularly Jurassic rift segmentation, facilitated the emplacement of large mantle bodies into the hanging wall, rather than their dismemberment into thin tectonic slices.
The Grischun–Malenco area therefore constitutes a natural laboratory for investigating serpentinization-driven H2production in continental settings. Integrated investigation of serpentinization processes in continental and supra-subduction environments; combined with constraints on the pressure–temperature conditions of multiple serpentinization events and assessments of source-rock fertility based on Fe²⁺/Fe³⁺ ratios; will provide critical guidance for future hydrogen exploration.
How to cite: Dimasi, F., Manatschal, G., Ulrich, M., Chenin, P., and Gasser, Q.: The Grischun-Malenco fossil Ocean-Continent-Transition: the fate of the subcontinental mantle in a Wilson cycle and its significance for H2 exploration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10175, https://doi.org/10.5194/egusphere-egu26-10175, 2026.
Hydrogen is expected to play a central role in the global energy transition, yet most industrial hydrogen production remains associated with significant CO₂ emissions. Natural hydrogen generated during serpentinisation of ultramafic rocks offers a low-carbon alternative, but its distribution, generation rates, and recoverability remain poorly constrained. To date, most research has focused on identifying naturally occurring hydrogen systems. Here, we explore a complementary approach: testing whether hydrogen-producing reactions in ultramafic rocks can be engineered to achieve economic production through subsurface stimulation. We present results from the Rock Hydrogen Project, a field-scale pilot experiment conducted in serpentinised peridotite in Oman, a globally recognised natural laboratory for ultramafic-hosted fluid–rock interactions. The project investigates the feasibility of enhancing hydrogen generation through controlled water injection into fractured peridotite at almost 1km depth. Downhole geophysical logging was used to characterise fracture distributions, providing a structural framework for interpreting pressure and flow responses. Then, a large-volume water injection, followed by a pump-back phase was completed. During this test, pressure, flow, fluid chemistry, and resulting gas compositions were monitored. Hydrological data outlines injectivity and pressure evolution, while recovered fluids and gases were analysed for major and trace elements, noble gases and major gas compositions using gas chromatography and noble gas mass spectrometry. This integrated dataset captures the coupled hydrological and geochemical evolution of fluids during subsurface circulation and the influence of stress-dependent permeability. Recovered fluids show pronounced chemical modification relative to injected waters, including increased salinity, alkaline pH (up to ~11.5), increased gas concentrations and highly reducing conditions. Measured gas compositions are dominated by hydrogen and small amounts of methane. Together, these observations indicate rapid fluid-rock interaction during injection and recovery. Ongoing work aims to test whether such stimulation can drive the production of hydrogen in fractured peridotite at relatively low temperatures. Next steps include the continued development of fracture network models based on downhole data, continued integration of hydrological and geochemical observations, and the drilling of an additional borehole to establish an injection–production array to test optimal rate of fluid circulation for hydrogen production. These efforts aim to quantify net hydrogen generation rates, evaluate scalability, and improve understanding of the coupled processes governing stimulated hydrogen systems in ultramafic reservoirs.
How to cite: Shannon, J., Ellison, E. T., Al Mani, S., Matter, J. M., and Templeton, A. S.: Stimulating Hydrogen Generation in Serpentinised Peridotite: Field-Scale Injection Experiments in Oman, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3339, https://doi.org/10.5194/egusphere-egu26-3339, 2026.
Peridotite carbonation is an efficient process for carbon sequestration in Earth’s carbon cycle. This process is inevitably associated with serpentinization. However, the interplay of the two processes and the fluid-rock reaction details remain elusive. Here we present a ~330-meter-long fluid-peridotite reaction profile with a southward zonation of harzburgite, serpentinite to soapstone-bearing listvenite in the Luobusa ophiolite (Tibet). From harzburgite to listvenite, gradual decreases in whole-rock MgO, SiO2 and FeOT as well as nearly constant Al2O3 and trace-element patterns suggest a continuous reaction from serpentinization to carbonation. The H2O+ contents were rapidly elevated during serpentinization, and then abruptly dropped once the carbonation initiated as evidenced by a jump in CO2 contents. Such contrasting volatile behaviors indicate a competition between serpentinization and carbonation, which caused strong variations in H2 fugacity and redox states in the reaction system and controlled the compositional variations of involved fluids and crystallization of zoned magnesites. Clumped isotopes constrain the carbonation temperatures up to ~192-302 °C. In addition, thermodynamic modelling shows that the mineralogical, chemical and redox variations from serpentinization to carbonation are consistent with those observed in the Luobusa profile. C-O isotopic compositions suggest that the fluids were derived primarily from the mantle and added by those from surface reservoirs. Such CO2-rich fluids migrated along the trans-lithospheric thrust in Himalaya and reacted with the ophiolite, forming the studied profile. This study shows that the serpentinization-versus-carbonation processes may suppress the capacity of carbon sequestration, and calls for a reevaluation of the sequestrated carbon budget in ophiolite-rich orogens.
How to cite: Xiong, Q., Zheng, H.-D., Zhou, X., Chang, B., Dai, H.-K., Cai, H.-Z., Chen, M., and Zheng, J.-P.: Serpentinization versus carbonation: geochemical and thermodynamic constraints from an ophiolitic reaction profile , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3638, https://doi.org/10.5194/egusphere-egu26-3638, 2026.
Ocean basin basalt is well recognised as a potentially massive reservoir for CO2 removal via carbon mineralization due to the appropriate mineralogy and the presence of moderate porosity and permeability in these rocks. Similar mafic and ultramafic mineralogy reside terrestrially in exhumed oceanic crust, tectonically active continental margins, and even in stable cratonic settings. As disposal of the necessary volumes of carbon via mineralization requires injecting large volumes of CO2 in either supercritical or dissolved form, having sufficient permeability and porosity in the rock is critical to success. In the few studies that have been conducted on the hydrogeology of terrestrial ultramafics, fluid flow is largely governed by sparsely distributed fractures and faults, with little advection into the surrounding intact rock matrix. The process of carbon mineralization is therefore dependent on advective CO2 transport in the fractures but primarily relies on diffusion-driven transfer into the intact rock matrix. The process of matrix diffusion is well understood from detailed studies of contaminant transport in fractured rock, and robust analytical and numerical models can be used to demonstrate the process, evaluate the timing, and resolve the efficacy for commercial-scale carbon disposal in these settings. To illustrate the impact of fracture and rock properties on the success of carbon mineralization, an analysis is conducted with a radial transport model which can simulate CO2 injection in discrete fractures accounting for matrix diffusion. The analysis is based on a range of bulk permeabilities (1×10-17 m2 to 1×10-12 m2) and matrix porosities (1-4%) obtained from site investigations, and a range of fracture apertures, fracture spacings, and injection pressures. The cubic law is used to convert permeability to fracture aperture under given fracture spacings. Notwithstanding the geochemical reactions that will be involved, just the process of matrix diffusion illustrates that the matrix pore space can be largely filled with dissolved CO2 given the presence of sufficient fractures and enough time. Considering that the CO2 is also stripped via diffusion from the fractures over time/distance during injection and there is no significant form of CO2 egress from the matrix, there is no need for overlying caprock protection. As has been previously recognised, the largest potential limitation is the limited permeability of these rock types which constrains the volume of fluid that can be injected under acceptable pressure gradients. This is a very similar problem to that experienced in the geothermal industry, whereby hydraulic stimulation (without proppant) of healed fractures is successfully employed.
How to cite: Novakowski, K.: The importance of fractures and matrix diffusion to the success of carbon mineralization in terrestrial mafic/ultramafic rock bodies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15459, https://doi.org/10.5194/egusphere-egu26-15459, 2026.
A plug-flow reactor (PFR) with a 40-60 kg capacity for crushed rock at a targeted particle size range of 4.0-12.5 mm has been constructed to assess CO2-H2O-rock interactions and derive kinetic dissolution rates. By employing particle sizes significantly larger than those used in conventional laboratory dissolution experiments, this system aims to improve the accuracy of laboratory-derived rates relative to field behaviour. Preliminary testing has been conducted using three different mafic/ultramafic site samples from eastern Canada: feldspar-dominant samples from Tamworth, Ontario; forsterite-dominant samples from Thetford Mines, Quebec; and North Mountain Basalt samples from Nova Scotia. Deuterium and potassium chloride are used as conservative tracers to validate flow behaviour within the PFR, providing a baseline for reactive tracer experiments. Reactive tracers are implemented to estimate the effective surface area of the packed sample particles. Tracers with sorptive properties that have been preferentially explored include cesium chloride, strontium chloride, fluorescein, and rhodamine. Batch experiments were performed to characterize sorption kinetics and equilibrium behaviour across particle sizes. These results are compared to the breakthrough curves from flow-through experiments using a retardation factor to estimate the distribution coefficient. CO2-saturated water is prepared in a separate vessel at ambient temperature and a maximum pressure of 25 psi to produce a solution with a pH of ~4.6, comparable to the values during field-scale injections. Preliminary dissolution experiments recycled the CO2-H2O solution through the PFR to create semi-batch conditions and provide insights into the dynamic fluid chemistry as dissolution progresses. Temperature, pressure, pH, and conductivity are recorded at the inlet and outlet, while intermittent fluid sampling determined divalent cation and secondary metal concentrations over time. Steady-state concentrations were used to calculate dissolution rates normalized to the effective surface area. Transport behaviour was analyzed using an independent model based on the advection-dispersion equation accounting for retardation and permanent sorption coupled to mixing equations for the inlet and outlet zones of the PFR. PHREEQC was employed to predict reactive transport results from dissolution. Comparisons between experimental and modeled dissolution rates provide insight into scaling laboratory results to field conditions and improving predictions of mafic/ultramafic rock reactivity for mineral carbonation.
How to cite: Frappier, A., Kariminouroddin, M., and Novakowski, K.: Bridging Laboratory and Field Scales: A Plug-Flow Reactor to Assess Interactions Between Dissolved CO2 and Mafic/Ultramafic Rock, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14418, https://doi.org/10.5194/egusphere-egu26-14418, 2026.
Igneous rocks are gaining increasing attention as valuable natural resources in the energy transition. Among them, ultramafic and mafic lithologies are attractive because of their carbon mineralization potential. Another emerging aspect is abiotic hydrogen (H2) generation via the oxidation of reduced iron in the rock-forming minerals, a well-documented process for ultramafic systems known as serpentinization. However, the reaction pathway(s) for hydrogen generation from mafic rocks remain poorly understood. Compared to ultramafic rocks, mafic rocks have a more diverse mineralogy that may include Al- and alkali-bearing silicates, which may drive H₂ production in different reaction pathways. This study evaluates the H2 generation potential of Late Cretaceous silica undersaturated alkali basalt from the Balcones Igneous Province in Central Texas under different pressurized gas conditions (CO2 and Ar).
Static batch experiments were conducted to study rock-water-gas interactions and to assess the H2 generation potential of the basalt. We placed millimeter-sized rock fragments in teflon-lined Hastelloy reactors at elevated pressure (12-17 bar) and temperature (90°C), using both Ar- and CO2-saturated water. The effect of NiCl2, a potential soluble reaction catalyst, was also tested. Mineralogical and chemical changes resulting from rock-water-gas interactions were analyzed using optical microscopy, X-ray powder diffraction, and scanning electron microscopy. Headspace gas composition was measured with gas chromatography, and pH, conductivity, and solution chemistry were monitored throughout the experiment.
After 133 reaction days, the highest H2 yield was observed in the experiment with CO2-rich fluids containing added NiCl2. Comparable H2 production occurred in the Ar experiment, while lower H2 yield was observed in the experiment using CO2 alone. The results indicate that the addition of NiCl2 to CO2-rich fluids enhances the H2 generation. In addition to H2 generation, carbonate mineral precipitation was observed in CO2 experiments, further demonstrating concurrent carbon mineralization. The solution chemistry also reflects differences between settings: the CO2 experiments exhibited lower pH and elevated dissolved elemental concentrations, whereas the Ar experiment maintained higher pH and resulted in less dissolution of the original rock matrix.
Collectively, these findings demonstrate that silica undersaturated mafic rocks, such as the abundant intrusive bodies of the Balcones Igneous Province, have significant potential for both geologic H2 production and carbon sequestration.
How to cite: Gelencsér, O., Ukar, E., Fall, A., Zhang, T., and Larson, T.: Experimental assessment of H2 generation from Central Texas alkali basalts under CO2-coupled and high pH conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15365, https://doi.org/10.5194/egusphere-egu26-15365, 2026.
Hydrogen generation has been observed under conditions relevant to subsurface carbon mineralization, however, conditions that promote H2 production and its relevance to carbon mineralization remain understudied. In low-temperature (50°C) batch experiments with CO2-charged North-Atlantic-seawater and mid-ocean ridge basalt (MORB) glass, hydrogen and methane were produced and carbonates were formed. DNA extraction was attempted by 16S rRNA gene amplification was unsuccessful. Accordingly, no evidence was found for microbial presence that could explain formation of the reduced gases. Here, we quantify CO2 mineralization, H2 and CH4 production in experiments under mild conditions (50°C and 1.5 bar pCO2) relevant to subsurface carbon mineralization using the Carbfix method with MORB and seawater. Significant H2 production was not observed in higher temperature (130°C) experiments, conflicting with earlier studies. We provide evidence for H2 and CH4 production via water rock reactions (i.e., low temperature serpentinization) using aqueous cation concentrations, x-ray diffraction data and FTIR data of reaction products. Findings of this work have implications for pilot-scale studies injecting CO2-charged seawater into basalt formations, such as the Seastone project in southwest Iceland by Carbfix. This study highlights key variables to analyze in such studies to assess reduced gas formation, which can be sources of metabolic energy for microbial communities, a potential source of H2 for energy or feedstock use, or an additional reaction pathway for injected CO2. Findings from this work have implications for scaling carbon mineralization projects as they grow in importance in response to global warming.
How to cite: Phillips, E., Voigt, M., Baldermann, A., Mandon, C., Ólafsdóttir, Þ. L., Björnsdóttir, S. H., Marteinsson, V. Tor., and Gíslason, S. R.: Low-Temperature Carbon Mineralisation and Hydrogen Production in Basalt, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20378, https://doi.org/10.5194/egusphere-egu26-20378, 2026.
Natural hydrogen produced by fluid-rock interactions such as serpentinisation has recently been gaining traction as a potential source of carbon-free, green energy, that could go a long way towards mitigating the ongoing climate crisis1. This has led to accelerated efforts globally to identify geological sites at which hydrogen production can be stimulated, and the pressures, temperatures and fluid compositions at which hydrogen production can be optimised. Hydrogen production through serpentinisation involves a coupled redox transformation of Fe2+ to Fe3+ and H2O to H2, owing to which ultramafic lithologies are promising targets for stimulated hydrogen production, owing to their substantial Fe content2.
In this contribution we present the results of modelled fluid-rock interactions between a serpentinised peridotite from the Lizard Ophiolite Complex, United Kingdom and an engineered brine of a composition similar to ones used for CO2 sequestration experiments. Models were constructed by utilising the PHREEQC suite of codes3 using the carbfix.dat database4, at pressures of 50, 100 and 200 bars, temperatures of 100⁰, 200⁰ and 300⁰C and mass of H2O in the solution varying from 0.05-200kg. 1 kg of an almost completely serpentinised peridotite, consisting of chlorite, serpentine and magnetite was chosen as the starting material and fluid injection models were simulated by reacting increasingly dilute solutions with the host rock in successive steps. The models predict hydrogen production to peak at 200 bar and 300⁰C, at which 5.73 mole/kgw hydrogen is produced at low water/rock ratios. The amount of hydrogen produced appears to have a positive correlation with temperature and increases rapidly with increasing temperature. On the other hand, hydrogen production is inversely correlatable with the mass of H2O in the solution and decreases with increasing amounts of H2O as the simulations proceed. The effect of temperature appears to be much more pronounced on the amount of hydrogen produced, compared to the effect of fluid pressure. Only minor increases are observed in the amount of hydrogen produced with increasing fluid pressure (5.68 mole/kgw at 50 bar and 300⁰C increasing to 5.73 mole/kgw at 200 bar and 300⁰C). Our results, although preliminary, highlight the potential of ultramafic lithologies such as the Lizard Ophiolite Complex to play an important role in natural hydrogen stimulation endeavours.
- Zgonnik, V. The occurrence and geoscience of natural hydrogen: A comprehensive review. Earth Sci Rev 203, 103140 (2020).
- Osselin, F. et al. Orange hydrogen is the new green. Nat Geosci 15, 765–769 (2022).
- Parkhurst, D., Appelo, C. A. J. & Survey, U. S. G. Description of Input and Examples for PHREEQC Version 3: A Computer Program for Speciation, Batch-Reaction, One-Dimensional Transport, and Inverse Geochemical Calculations. Techniques and Methods https://pubs.usgs.gov/publication/tm6A43 (2013) doi:10.3133/tm6A43.
- Voigt, M., Marieni, C., Clark, D. E., Gíslason, S. R. & Oelkers, E. H. Evaluation and refinement of thermodynamic databases for mineral carbonation. Energy Procedia 146, 81–91 (2018).
How to cite: Dobe, R. and Wheeler, J.: Evaluating the feasibility of stimulating natural hydrogen production from the Lizard Ophiolite Complex, UK, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10436, https://doi.org/10.5194/egusphere-egu26-10436, 2026.
Serpentinites formed in abyssal settings show large variations in boron concentration and δ¹¹B, even within similar tectonic environments. To explore the processes controlling boron incorporation and isotopic fractionation during oceanic serpentinization, we developed a stepwise reaction-path model simulating progressive water–rock interaction, using experimentally derived data for B partioning and isotopic fractionation between fluid and rock. The model tracks the coupled evolution of B concentration and δ¹¹B in the solid through multiple reaction loops, characterized by evolving temperature and decreasing water–rock ratios.
Model results indicate that B concentration and δ¹¹B evolve asynchronously during serpentinization. However, at given B contents, serpentinites show a variety of δ¹¹B values, reflecting its strong sensitivity to reaction history rather than equilibrium with a single fluid reservoir. Progressive reaction loops produce divergent isotopic trajectories, in response to the degree of fluid renewal and cumulative fractionation during serpentinization.
Comparison with natural samples shows that B systematics of serpentinites from the Atlantis Massif are best explained by multi-stage serpentinization under relatively restricted fluid conditions, during which progressive fractionation drives δ¹¹B toward lower values despite significant B enrichment. In contrast, serpentinites from the 15°20′N transform fault, Mid-Atlantic Ridge, consistently exhibit seawater-like δ¹¹B, more resembling open-system behaviors involving repeated interactions between fresh fluids and new rock volumes.
These results demonstrate that reaction-path modeling provides a robust framework for interpreting boron isotope systematics in abyssal serpentinites and highlight the critical role of fluid–rock interaction history, along with temperature and bulk composition, in controlling δ¹¹B signatures.
How to cite: Zhu, J., Bach, W., Hansen, C., Liu, C.-Z., Zhang, C., and Liu, T.: Temperature and Water–Rock Ratio Controls on Boron Behavior in Serpentinized Peridotites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19487, https://doi.org/10.5194/egusphere-egu26-19487, 2026.
Strategies of underground carbon sequestration by CO2 injection into ultramafic rocks at depth, inducing carbonation of Mg-silicates, face challenges to predict and monitor the evolution of reaction progress, fluid flow, and geo-mechanical responses. The fossil geological rock record of naturally carbonated mantle rocks allows to investigate the involved non-trivial coupling of thermal-hydrological-mechanical-chemical feedback processes across the necessarily large spatial and temporal scales.
To explore the interplay between carbonation reactions and deformation, we investigate the field- to micro-scale structures of a sequence of variably carbonated, serpentinized harzburgites from the Advocate complex of the Baie Verte Ophiolite, Newfoundland. The ultramafic rocks were progressively carbonated at 280 – 350 °C to brucite-magnesite bearing serpentinite, magnesite-talc rock and listvenite due to metamorphic fluid infiltration along a nearby fault zone [1].
Serpentinites show the recrystallization of lizardite to antigorite + brucite. This was related to semi-brittle fracturing and brucite-magnetite veins, together with oriented growth of antigorite. Incipient carbonation proceeded along the brucite veins and replacing remnant lizardite domains. Subsequently, reaction of antigorite with CO2 to magnesite–talc rocks led to talc-rich domains that develop a penetrative foliation. Magnesite shows continued growth of Fe-zoned magnesite, commonly with euhedral facets. In places, talc fringes develop in strain shadows of magnesite grains, indicating that ductile deformation was assisted by dissolution-precipitation.
In contrast, the carbonation reaction talc + CO2 to quartz–magnesite caused common semi-brittle deformation in listvenite. This is manifested by boudinage and sub-parallel sets of quartz extension veins mostly arranged normal to foliation and in oblique echelon arrays, consistent with syn-reaction shearing. At the outcrop scale, these veins cut listvenite layers and boudins, without continuation into talc-magnesite rock. At the microscale, similar quartz veins transect elongated magnesite porphyroblasts in magnesite-talc-quartz rock and foliated listvenite. Their termination at the porphyroblast rims together with co-precipitated magnesite along the vein-walls indicate that they formed synchronous to carbonation reaction. Strongly foliated transitions from talc-rich lithologies to listvenites further show apparent mylonitic fabrics with crystallographic preferred orientations with maxima of [001]Mgs normal and [001]Qtz parallel to foliation. This fabric is inconsistent with low-temperature (< 400°C) dislocation creep, but was likely caused by oriented growth under deviatoric stress. Fuchsite-filled stylolites in quartz-depleted listvenites further attest for prolonged deformation and permeability renewal by pressure solution. Our results indicate that, in line with with experimental evidence [2], carbonation is related to a changing deformation style with increasing reaction extent, from brittle veining in serpentinite, to ductile creep in talc and semi-brittle fracturing in listvenite, although dissolution-precipitation creep mechanisms are relevant during all stages. The studied case example underlines that deformation is a key factor for extensive carbonation. We further show that pressure solution can maintain permeability even in fully carbonated listvenites and may lead to nearly pure magnesite rocks.
Funding: RUSTED project PID2022-136471NB-C21 & C22 funded by MCIN/AEI/10.13039/501100011033 and ERDF – a way of making Europe. M.D.M further acknowledges ERC project OZ (grant: 101088573).
References:
[1] Menzel et al., 2018, Lithos, doi.org/10.1016/j.lithos.2018.06.001
[2] Eberhard et al., in review, Science Advances
How to cite: Menzel, M. D., López Sánchez-Vizcaíno, V., Jabaloy Sánchez, A., and Garrido, C. J.: Changing deformation style during natural serpentinite carbonation to talc-magnesite and quartz-magnesite, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10215, https://doi.org/10.5194/egusphere-egu26-10215, 2026.
Carbonated ultramafic rocks such as soapstones and listvenites provide natural evidence of extensive fluid-rock interaction between mantle-derived lithologies and CO2-bearing fluids and serve as natural analogues for carbon sequestration. Oxygen isotope fractionation represents a powerful tool for constraining both temperature conditions and fluid sources during the carbonation process. Here, we present preliminary results from an integrated study combining in situ oxygen-isotope analyses with microscale textural observations in a carbonated ultramafic sequence from the Point-Rousse Complex (Baie Verte Ophiolite, Newfoundland, Canada). In situ oxygen isotope measurements were performed using Secondary Ion Mass Spectrometry (SIMS) targeting five mineral phases: antigorite, talc, magnesite, dolomite, and quartz. Phase-specific reference materials [1,2,3,4] were analyzed during the same analytical session to correct for matrix effects and to monitor instrumental drift.
The studied Point-Rousse Complex sequence comprises ophicarbonates (≤ 5.4 wt% CO₂), antigorite‑bearing soapstones (antigorite–talc–carbonate rocks, 12.8–17.1 wt% CO₂), quartz‑bearing soapstones (quartz–talc–carbonate rocks; 19.5–34.9 wt% CO₂), and listvenites (28.6–46.1 wt% CO₂). Ophicarbonates display non-pseudomorphic textures, with δ¹⁸O values of 4.3–5.2‰ (VSMOW) in antigorite, 7.6–8.6‰ in talc, and 11.1–12.2‰ in magnesite. Antigorite‑bearing soapstones show massive to foliated textures, with recrystallized antigorite overgrowing large magnesite grains, dolomite veins, and talc defining foliated domains. These rocks exhibit similar δ¹⁸O values in antigorite (4.2–5.2‰) and magnesite (9.9–11.7‰), but distinct values in talc (4.3–7‰) and dolomite (10.1–10.7‰). Quartz‑bearing soapstones and listvenites show more complex textures, including Fe‑rich zones in magnesite and talc–quartz coronas around dolomite. Magnesite exhibits a wide range of δ¹⁸O (10.6–17.7‰) with variable values in Mg-rich cores (Fe# = 0.01) and Fe-rich rims (Fe# = 0.16). Talc, dolomite, and quartz show relatively homogeneous δ¹⁸O values (6.1–6.9‰, 10.5–12.8‰, and 11.1–13‰, respectively).
Preliminary oxygen isotope thermometry based on texturally equilibrated serpentine-magnesite and serpentine-talc pairs yields carbonation temperatures of 244 ± 21 °C for ophicarbonates and 309 ± 43 °C for the antigorite‑bearing soapstones. Calculated apparent δ¹⁸O values of the fluid at these temperatures range between 3.7 and 5.4‰, consistent with metamorphic fluids. These results suggest a multi‑stage carbonation at moderate temperatures involving a progressively evolving fluid composition.
Funding: We acknowledge funding for doctoral fellowship FPI2022/PRE2023_IACT_059 (IDG) and Grants PID2022-136471NB-C21 & 22 (RUSTED) by MCIN/AEI/10.13039/501100011033 and FSE+. JAPN, CJG & MDM further acknowledge funding from the ERC project OZ (DOI: 10.3030/101088573).
[1] Scicchitano et al. (2021) DOI: 10.1111/ggr.12359
[2] Scicchitano et al. (2022) DOI: 10.1016/j.gca.2021.11.025
[3] Scicchitano et al. (2025) DOI: 10.1111/ggr.70031
[4] Sliwinski et al. (2018) DOI: 10.1111/ggr.12194
How to cite: Garduño-Torres, I. D., Menzel, M. D., Padrón-Navarta, J. A., Sánchez-Vizcaíno, V. L., Scicchitano, M. R., Sieber, M. J., and Garrido, C. J.: In situ oxygen isotope thermometry of carbonate–silicate assemblages in carbonated ultramafic rocks from the Point-Rousse Complex (Newfoundland, Canada), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13709, https://doi.org/10.5194/egusphere-egu26-13709, 2026.
Natural carbonation of ultramafic rocks is a key process controlling the long-term carbon cycle, as exposed peridotites can directly sequester atmospheric CO2 through carbonation associated with chemical weathering. To constrain the conditions and sources of fluids involved in past natural carbonation processes and magnesite formation, isotopic analyses (δ18O, δ13C and 87Sr/86Sr) were conducted on massive magnesite veins (n = 37) hosted within the exhumed mantle section of the ophiolitic sequence of the Central Sudetic Ophiolite (SW Poland). Samples were collected from three tectonically dismembered ultramafic units: (1) Szklary; (2) Braszowice; (3) Wiry.
Oxygen isotope compositions are most variable in Szklary (δ18O = 22.4 to 31.0‰ SMOW), show a moderately narrower range in Braszowice (22.0 to 29.6‰ SMOW), and are relatively homogeneous in Wiry (27.3 to 28.8‰ SMOW). Carbon isotope values further differentiate the units: Szklary magnesites exhibit the lightest carbon (δ13C = -11.8 to -17.9‰ VPDB), Braszowice samples show consistently heavier values (-10.6 to -13.9‰ VPDB), whereas Wiry displays the widest range toward heavier carbon (-5.5 to -13.8‰ VPDB). Strontium isotopes also vary systematically, with uniformly low 87Sr/86 ratios in Braszowice (~0.7065), more variable values in Szklary (~0.7071 - 0.7117), and the most radiogenic signatures in Wiry (~0.710 - 0.721).
Previous interpretations commonly assumed that magnesite formation was associated with weathering under tropical conditions, in which the oxygen isotopic composition of meteoric water can be approximated as δ18O = 0.0‰ (SMOW). This model is widely invoked for the formation of massive magnesite veins and is supported by evidence for intense weathering of the ultramafic host rocks, including the presence of laterites. Under this assumption, calculated crystallization temperatures range from ~46 °C in Szklary to ~100 °C in Braszowice. Carbon isotope data indicate a dominant contribution of soil-derived CO₂ in Szklary, with increasing influence of additional carbon sources in Braszowice and especially in Wiry.
For samples with low Rb/Sr ratios, variations in 87Sr/86 can be attributed primarily to differences in the isotopic composition of the fluids, indicating multiple Sr sources. The predominance of homogeneous, low 87Sr/86 values at Braszowice is consistent with a crustal fluid source, comparable to ratios reported for Variscan granitoids and nephrites hosted in ultramafic rocks [1]. This suggests that at least some magnesite bodies formed during the Variscan overprint of ophiolitic massifs, contemporaneously with serpentinite-related nephrite formation. This interpretation is supported by elevated ⁸⁷Sr/⁸⁶Sr ratios in samples with higher Rb/Sr from both Szklary and Braszowice, which likely reflect radiogenic ingrowth over hundreds of millions of years. In contrast, the high variability and generally elevated 87Sr/86 values observed in Wiry are more consistent with contemporaneous Sr isotope heterogeneity and may record Sr mobilization during Miocene tropical weathering of older crustal rocks [2].
[1] Gil, G. et al., 2020. Ore Geology Reviews, 118, 103335.
[2] Waroszewski, J. et al., 2021. Catena, 204, 105377.
Acknowledgements: Research financially supported by NCN PRELUDIUM project 2022/45/N/ST10/00879
How to cite: Cieślik, B., Pietranik, A., and Kierczak, J.: Stable and radiogenic isotopes (δ18O, δ13C and 87Sr/86Sr) as tracers of complex carbonation of ultramafic rocks: Evidence from three magnesite deposits, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13569, https://doi.org/10.5194/egusphere-egu26-13569, 2026.
Mineral carbonation represents a promising carbon capture and storage (CCS) approach, offering permanent CO2 sequestration via spontaneous reactions, abundant natural feedstocks, and low environmental impact. Mafic and ultramafic rocks, in particular, exhibit high carbonation potential due to their rich magnesium, iron and calcium content. This paper provides a systematically study of the reaction process, intrinsic mechanisms, and role of mineral carbonation in the carbon-hydrogen cycle. (1) Reaction process and mechanisms in mineral carbonation. Mineral carbonation is a dissolution– precipitation process involving Mg2+-, Ca2+-, or Fe2+-rich silicates (e.g., olivine, pyroxene) and CO2-rich fluids. It proceeds through three stages: CO2 dissolves to form carbonic acid, dissociating into HCO3- and CO32- (stage 1); the resulting acidity promotes silicate dissolution, releasing metal ions (e.g., Mg2+, Ca2+) (stage 2); and metal cations react with carbonates ions to precipitate stable carbonate minerals (stage 3). Carbonation in peridotite and pyroxenite is often coupled with serpentinization, leading to the co-formation of carbonates and serpentine minerals. Under certain conditions, abiogenic H2 and organic carbon are also produced, offering implications for astrobiology, early life origins, and clean energy. (2) Role of water in mineral carbonation. Water and H+ ions play a critical role in enhancing silicate dissolution, facilitating the release of Mg2+, Ca2+, and Fe2+. Carbonate ions from hydrated CO2 combine with these cations to form stable minerals. In aqueous supercritical CO2 systems, water content affects carbonation efficiency by influencing pore volume, while nanoscale water films regulate the types of carbonate mineral types formed. Silicate dissolution is typically the rate-limiting step, controlled by mineral structure and composition, and strongly influenced by pH, temperature, and water activity, etc. (3) Long-term reactivity and tectonic integration in carbon-hydrogen system. Effective reactivity is maintained through fluid overpressure, reaction-induced porosity, dissolution channels, and fracturing, which collectively enhance fluid infiltration and promote complete carbonation. Mineral carbonation across diverse tectonic settings and is closely linked to plate activity. It acts as a long-term carbon sink in oceanic and continental lithosphere, while subduction zones facilitate deep carbon and hydrogen transport into the mantle, driving the long-term global carbon-hydrogen cycle.
How to cite: Zhou, D., Cao, S., Li, X., Cheng, X., Liu, J., Dong, Y., and Jiang, S.: Mineral Carbonation: Processes, Mechanisms, and Its Role in the Carbon–Hydrogen Cycle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22497, https://doi.org/10.5194/egusphere-egu26-22497, 2026.
The serpentinization of ultramafic rocks occurs under some of the Earth's most extreme geochemical conditions, with strongly reducing fluids, extreme pH, and low silica activity, which contribute to unique element mobility, including the mobilization of aluminum in H2O-rich fluids. This study presents a petrographic and geochemical analysis of partially serpentinized ultramafic rocks from the dunite core of the Tulameen Alaskan-type mafic-ultramafic intrusion in British Columbia, Canada. Mineral composition and textural relationships are used to establish alteration conditions during serpentinization of the intrusion, identify evidence of fluid-mediated element mobility, and reconstruct element transport mechanisms during alteration. Fluid mobile components typically exhibit anisotropic length scales of equilibrium, with fluid-mobile components equilibrating on far greater length scales parallel to permeable pathways than perpendicular to them. Electron microprobe analyses of samples from the Tulameen Intrusion reveal high aluminum content in antigorite and lizardite after olivine (0.14- 2.01 wt% Al2O3). Thermobarometry, mineral composition, and textural analysis indicate that most serpentinization of the Tulameen intrusion occurred at 300-450°C in the antigorite+brucite stability field, and continued as the intrusion cooled. Fluids were H2O-dominated with high pH (>8), low oxygen fugacity (FMQ-4), low silica activity (less than 10−2.5 at the serpentinization front), and low salinity during serpentinization. Correlation between the occurrence of Fe-rich serpentine (2.12-5.45 wt% FeO) and relatively high chlorine levels (0.02-0.05 wt% Cl) implicates salinity in fluid-based iron mobility. Comparative analysis of the alteration conditions identified in the Tulameen and known mechanisms of aluminum mobility suggests that aluminum becomes mobile in H2O-dominated fluids at high pH via the formation of AlO2- anions. These discoveries have implications for ongoing research on serpentinite reactivity in carbon sequestration and on the remobilization of mineral resources during hydrothermal alteration.
How to cite: Windsor, V. and Peacock, S.: Element mobility during serpentinization of the Tulameen Alaskan-type intrusion, British Columbia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16029, https://doi.org/10.5194/egusphere-egu26-16029, 2026.
Chlorite pseudomorphs in metaperidotites are not unusual in the Alps and are often in the vicinity of garnet peridotites, for example in the Ulten Zone of northern Italy (Pellegrino et al., 2021). If no garnet survives, then considering the important high-pressure and tectonic implications of garnet peridotite, it is important to demonstrate the former presence of garnet.
In Washington state, two similar ultramafic bodies inside the ~91-95 Ma Wenatchee Ridge Orthogneiss, a highly deformed tonalite pluton, contain cm-scale chlorite pseudomorphs consisting of Cr (1-6.5 wt%) clinochlore. The host rock typically contains Ol-Srp-Tr±Chl±En±Tlc±Cum±Chr±Mag. One body is typically foliated and contains highly flattened chlorite pseudomorphs with undeformed tremolite and cummingtonite, whereas the other body contains spectacularly deformed, including isoclinally folded, enstatite.
Chlorite occurs especially as relatively fine-grained randomly oriented flakes within the pseudomorphs. Rarely, chromite grains form s-shaped patterns inside. There is locally a slight core-to-margin variation in Cr content. These pseudomorphs are interpreted as a result of hydrous fluids accessing the rocks during cooling and decompression, resulting in chlorite replacing garnet.
Minor minerals present include ilmenite (minor geikielite or pyrophanite components), barite, pentlandite grains rimmed by awaruite inside magnetite grains, rare Ni-As grains (probably orcelite), chromite, and heazlewoodite in pentlandite.
A remarkable aspect of the chlorite pseudomorphs is the presence of late, thin (tens of microns), foliation-parallel calcite veins (no magnesite or dolomite). Normally confined to the pseudomorphs, they increase in thickness from margin to core, indicating a mechanical connection to the chlorite. Assuming countervailing volume expansion from decompression and volume decrease from cooling, a small volume loss, approximately consistent with the volume of the calcite veins, occurs for decreases of approximately 0.4 GPa and 400 °C. Lack of pre-existing carbonate indicates CO2 was introduced via fluid infiltration, whereas Ca may have been liberated from diopside or tremolite breakdown.
The veins are complex; some are composed purely of calcite, whereas others display fibrous, dilational characteristics and multiple minerals. A Fe-Ca-Si-O mineral (andradite?) is present locally. Small lozenges of probable lime, a rare and unstable mineral, occur. Lime has been reported from limestone xenoliths and pyrometamorphic settings, and is thought to form above 900 °C (Khoury et al., 2016), and readily reacts to portlandite. The veins must be late, forming from local Ca but an external CO2-rich fluid.
We tentatively propose a P-T path from the Grt-Ol-En field through the Di-Chl-En-Ol field, and into the Tr-Ol field, and finally into the Di-Atg fields of Lakey & Hermann (2022). This is consistent with the near absence of diopside but very late Di+Atg after tremolite, and indicates replacement of garnet by chlorite above about 2 GPa. This could indicate origin of these bodies at >2 GPa and ca. 800 °C, and a decompression and cooling path merging with that of the terrane at 600-650 °C and 1 GPa. Such pressures and the required tectonism would be a new twist on the Cordilleran Orogeny in the U.S. Pacific Northwest.
How to cite: Girot, D. L. and Magloughlin, J. F.: Evidence for retrogression of garnet peridotite in large ultramafic bodies, with late CO2-infiltration, and formation of heazlewoodite, orcelite, awaruite, andradite(?), lime, and pentlandite, and possible UHP metamorphism, Washington, USA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2258, https://doi.org/10.5194/egusphere-egu26-2258, 2026.
In eastern Taiwan, the metamorphic rocks of the Yuli Belt are mainly derived from subducted oceanic sediments, metabasite, arc-related volcanic rocks, and serpentinite bodies, which were subsequently exhumed from the subduction zone. This study focuses on serpentinites in Taiwan, including those from two distinct tectonostratigraphic units, the Yuli Belt and the Coastal Range, and aims to distinguish different types of serpentinites based on their mineral assemblages and geochemical characteristics. Based on mineralogy, microstructures, and geochemical features, serpentinites can be broadly classified into three major types in Taiwan. The first type, Eastern Taiwan Ophiolite serpentinites (ETO), is predominantly derived from oceanic crust, occurring as blocks within the mudstone of the Lichi Mélange. These serpentinites are mainly composed of mesh-textured fibrous chrysotile, sometimes containing incompletely serpentinized relict olivine. They lack subduction-related fluid signatures such as As and Pb, and display As/Ce ratios lower than 20. The second type located within the subduction zone of Yuli Belt. These serpentinites accompany with the schists, and are dominated by bladed antigorite. The subduction-related fluid metasomatism bring more As, Pb and Sb into serpentinite. Variations in As/Ce ratios reflect the shallower subduction depths in northern Yuli Belt and greater depths in the southern Yuli Belt. The third type comprises high-temperature metamorphic serpentinites. Their antigorite crystal morphology is distinctly different from the bladed form, having transformed into extremely fine-grained antigorite indicative of high-temperature recrystallization. New olivine porphyroblasts formed during high-temperature metamorphism, and magnetite aggregates developed around these olivine grains. They exhibit the lowest As/Ce ratios, and fluid-related elements such as As, Pb, and Sb are significantly depleted. The third type of high-temperature metamorphic serpentinite usually appears as large xenoliths in second type serpentinite in the northern part of the Yuli belt, while the metamorphic temperature of the surrounding schist is only 420-470°C, indicating that the third type of serpentinite was encapsulated and squeezed up in a state of plastic flow. This implies that the rheological behavior of serpentinites within the mantle wedge may be highly complex.
How to cite: Chen, H.-F., Pi, J.-L., Liu, C.-M., Li, Y.-H., and Huang, T.-H.: Geochemical characteristics of serpentinite types and their implications for tectonic environments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4134, https://doi.org/10.5194/egusphere-egu26-4134, 2026.
The natural carbonation of basalts has been extensively studied in recent years, as it helps us understand how this process develops and the factors that influence it, particularly in various geological settings and with respect to element mobility. The natural analog of Sverrefjellet in Svalbard remains largely unexplored, yet it presents an intriguing case due to its unique mineralogy. This study aims to correlate petrography, X-ray diffraction (XRD) results, scanning electron microscopy (SEM), cathodoluminescence, and elemental composition in order to gain insights into the mechanisms behind the carbonation sequence of basaltic rocks from the Sverrefjellet volcano in Svalbard.
Sverrefjellet, which erupted about one million years ago, consists of cinder cones, pillow lavas, and dikes formed under subglacial conditions (Treiman 2012). According to Pierozzi et al. (2025), the carbonate cement formed in relation to the alkali basalts of the volcano results from the carbonation process. These findings and new data from the carbonate cement can provide valuable insights into the sample's composition and evolution, the influence of the basaltic host rock, and the environmental conditions during carbonation. The carbonate cement sequence primarily consists of calcite-type carbonates within the magnesite-calcite-siderite compositional range. Various stages of carbonation are evident in the cements, indicating a shift in crystal chemistry from calcian proto-dolomite to Ca-poor magnesite, ultimately leading to a mixture of Fe-rich carbonates (siderite) and non-carbonate cements.
Throughout these stages, distinct behaviors of minor and trace elements are observed, revealing the conditions of the system during cement development. The findings emphasize the significant influence of the host rock's geochemistry on the composition and evolution of carbonate cements.
Treiman, A. H. (2012) ‘Eruption age of the Sverrefjellet volcano, Spitsbergen Island, Norway’, Polar Research. Norwegian Polar Institute, 31
Pierozzi, A., Faulkner, N., Szucs, A. M., Terribili, L., Maddin, M., Meloni, F., Devkota, K., Zubovic, K. P., Guyett, P. C., & Rodriguez-Blanco, J. D. (2025). Natural carbonation in alkali basalts: Geochemical evolution of Ca–Mg–Fe carbonates at Sverrefjellet, Svalbard. Carbon Capture Science & Technology, 17, 100510. https://doi.org/10.1016/j.ccst.2025.100510
How to cite: Pierozzi, A., Szucs, A., Drost, K., Meloni, F., Kele, S., Rinyu, L., and Rodriguez Blanco, J. D.: Mineralogical variation and elemental distribution within a natural carbonation cement sequence (Sverrejfellet, Svalbard): results and implications, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12133, https://doi.org/10.5194/egusphere-egu26-12133, 2026.
Abstract:
Quartz crystals containing garnet and rutile inclusions are found in the southwest of Kashan, Iran, adjacent to the Gohrood granitoid intrusive body. This area belongs to the Urmia-Dokhtar magmatic belt, located in the central part of the Iranian plateau with NW-SE trend. The intrusive body related to the garnet and rutile bearing quartzes shows granodiorite-tonalite composition with an age of 17 to 19 million years (Middle Miocene) which has intruded into Jurassic shales, sandstones, limestone, and also cretaceous and Eocene marls which have caused contact metamorphism in surrounding rocks and consequently the formation of typical skarn and hornfels in the area.
The studied quartz crystals show size ranges of 1-12 cm which have been formed inside cracks and fractures. The main alteration zones observed in the area consist of silicification, chlorite, epidote associated with hematite, and jarosite mineralization.
Different varieties of quartz crystals in terms of color and fluid inclusion characteristics are found in the study area: transparent and semi-transparent crystals, yellow crystals (citrine), dark crystals, smoky to reddish brown crystals (garnet inclusion), and rutile quartz.
The carried out fluid inclusion studies indicate that the mean temperature and salinity calculated for the transparent and semi-transparent quartzes are 308 °C and 7.5 wt.% NaCl and 360 °C and 1.6 wt.% NaCl, respectively, and generally, based on the carried out microthermometry studies, the estimated formation temperature ranges between 300-550 °C. The Hydrothermal fluid most likely reached the surface through the faults and joints of Gohrood granitoid with minimal contact with surface fluids, and near the surface mixing with meteoric waters, causing the loss of high temperature and salinity. During rising, these fluids have decomposed the minerals such as biotite, amphibole, and feldspars, which caused the alteration of the wall-rock. The performed microprobe and SEM studies on the inclusions containing garnet in the studied samples show the mineralogical composition of grossular.
How to cite: Fakheri, A., Masoumi, R., Asadzadeh Tarehbari, S., Panahi, M., and Rezapour, M.: Fluid inclusion and Mineralogical investigation of garnet and rutile quartz, Kashan, Iran, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2334, https://doi.org/10.5194/egusphere-egu26-2334, 2026.
Posters virtual: Thu, 7 May, 14:00–18:00 | vPoster spot 3
EGU26-6294 | ECS | Posters virtual | VPS25
Temperature-dependence of CO2 drawdown into Mg-bearing minerals.Thu, 07 May, 14:30–14:33 (CEST) vPoster spot 3
Mg-bearing minerals, including brucite [Mg(OH)2], lizardite [Mg₃(Si₂O₅)(OH)₄] and iowaite [Mg₆Fe³⁺₂(OH)₁₆Cl₂·4H₂O] are variably reactive with carbon dioxide (CO2) at Earth’s surface conditions and can be used to mineralize and sequester this greenhouse gas. Here, we assess the impact of temperature (5, 20 and 40 °C) on the rate of CO2 mineralization of these minerals. At each temperature, mineral powders (~100 mg ) were placed in a 7.5-litre flow-through reactor that was supplied with humidified laboratory air (0.042% CO2; 100% RH) at ~200 mL/min. Subsamples (n = 54) of each mineral were collected over 3 months and analyzed (XRD, TIC, BET) to ascertain the amount and rate of carbonation as a function of time, temperature, and mineral feedstock.
Preliminary X-ray diffraction (XRD) results show the formation of dypingite [Mg₅(CO₃)₄(OH)₂·5H₂O] and a decrease in the abundance of brucite over time. The 003 peak of iowaite shifted to smaller d-spacings, indicating replacement of chloride by carbonate ions and a transition to a more pyroaurite-rich [Mg₆Fe³⁺₂(CO₃)(OH)₁₆·4H₂O] composition. Total Inorganic Carbon (TIC) measurements were used to determine the amount and rate of carbonation as a function of time, temperature, and mineralogy.
The results of this study will help us estimate the carbonation kinetics of these minerals in ultramafic ores and mine tailings under different temperature conditions relevant to large-scale deployment of CO2 mineralization at mines across the globe.
How to cite: Sulemana, S. Z., Wilson, S., Moyo, A., Akhtar, S., Power, I. M., and Sleep, S.: Temperature-dependence of CO2 drawdown into Mg-bearing minerals., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6294, https://doi.org/10.5194/egusphere-egu26-6294, 2026.
