GMPV5.1

EDI
Solving geoscience problems using mineralogy

Mineralogy is the cornerstone of many disciplines and is used to solve a wide range of questions in geoscience. This broad session offers the opportunity to explore the diversity of methods and approaches used to study minerals and how minerals behave and evolve in their many contexts. We welcome contributions on all aspects of mineralogy, including environmental, soil science, metamorphic, plutonic, deep Earth, planetary, applied mineralogy, and so on. All approaches are welcome: analytical, experimental and theoretical.

Convener: Jannick Ingrin | Co-conveners: Catherine McCammon, Elena ZhitovaECSECS, Juraj Majzlan
Presentations
| Fri, 27 May, 08:30–11:51 (CEST)
 
Room K1

Presentations: Fri, 27 May | Room K1

Chairpersons: Jannick Ingrin, Catherine McCammon
08:30–08:34
08:34–08:41
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EGU22-3511
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ECS
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Virtual presentation
Ching shiuan Hung and Yen Hua Chen

The Wanshan tribe is in the Maolin district of Kaohsiung City in Taiwan. This area belongs to the Chaochou Formation within the Lushan Slate Belt. Its terrain is hillslope and stream terrace with slate and argillite rock-composition. The geological features of this area include slope angle greater than 30 degrees, colluvium, and serious erosion, which had a debris flow during the Morakot typhoon (2009). The area is currently classified as a massive potential landslide region and is still in a slow slip (creeping).

In this study, mineralogical and microstructural techniques were applied to investigate the slope stability of this area, e.g. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), optical microscope (OM), scanning electron microscopy (SEM), and microcomputer tomography (micro-CT). A 40 m-depth rock-core was drilled at the field site and the core samples were prepared for related measurements and experiments. The rock-core composed of fresh slates and weathered slates.

Based on XRD and OM analyses, the mineral phases in this area included quartz, illite, chlorite, muscovite and feldspar. The weathered core-sample had a more content ratio of clay minerals compared to that in the fresh slate core-sample. The FTIR results exhibited that the weathered core-samples had a higher water content than that in the fresh slate samples. With the help of SEM and micro-CT, it can be observed that the weathered core-sample had many longitudinal fractures, however, the fresh slate core-sample just had the slate cleavage.

It is so interesting that the lithology of rock-core changed into a dense fresh slate at the depth of 20 m; it suggested that this rock-layer is more impermeable to water. The weathered rock is favorable for water infiltration and then induced rock weathering, which could weaken the mechanical strength of this rock-layer. It is known that the lithology variation/change of rock-layers preferred to accumulate water, and it was easy to become a weak interface-layer. Therefore, we should pay attention to the fluctuation of groundwater level in this area and the drainage system needs to be well done.

How to cite: Hung, C. S. and Chen, Y. H.: Study on slope stability of Maolin area in Kaohsiung (Taiwan) using mineralogical and microstructural techniques, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3511, https://doi.org/10.5194/egusphere-egu22-3511, 2022.

08:41–08:48
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EGU22-3992
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ECS
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Highlight
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On-site presentation
Tze-Yuan Chen, Li-Wei Kuo, Steven Smith, Ching-Shun Ku, Ching-Yu Chiang, Dennis Brown, and Marianne Negrini

Cloud-to-ground lightning can result in high-temperature metamorphism of rocks, forming rock fulgurite. Here, we characterize a rock fulgurite on granitic gneiss from Kinmen Island, Taiwan, and demonstrate that high-pressure metamorphic features can be also generated by lightning. With the lightning monitoring system, we detected a lightning event with a peak current of 162 kA and the associated fulgurite. We conduct microanalytical methods on rock fulgurite, including optical microscope, scanning electron microscope with electron backscatter diffraction (EBSD), focused ion beam-transmission electron microscopy, and in-situ synchrotron Laue diffraction analyses. The fulgurite is characterized by an up to 200 μm thick glassy crust overlying host rock for around 10 square meters. Within the glassy crust, typical high-temperature features, such as vesicles, relic mineral fragments, and reduced oxidation-state iron oxides spheres, can be recognized. Below the glassy crust, EBSD analysis documents phase transformation (from monoclinic to triclinic) and planar features (exsolution lamellae) of alkali feldspar (sanidine) grains. Synchrotron Laue diffraction analysis indicates that these planar features are parallel to the (100) plane and preserve residual stress of up to 1.57 GPa, well above the 0.38 GPa recorded in feldspar grains (reference sample from borehole cores) that are not affected by lightning. The findings, including glassy crust, phase transformation and planar features of alkali feldspar grains, and high residual stress, suggest that lightning can result in both high-temperature and high-pressure metamorphic features. Because these assemblages are reminiscent of shock metamorphic textures produced by meteorite impact, we interpret them to be shock-related features. Given that the recognition of shocked minerals (with planar features) and glasses are both parts of the set of diagnostic criteria for meteorite impacts, in the absence of a broader suite of criteria, we recommend caution, since our identification of the Kinmen Island fulgurite indicates lightning can result in low-level shock metamorphic features.

How to cite: Chen, T.-Y., Kuo, L.-W., Smith, S., Ku, C.-S., Chiang, C.-Y., Brown, D., and Negrini, M.: Low-level shock metamorphism induced by lightning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3992, https://doi.org/10.5194/egusphere-egu22-3992, 2022.

08:48–08:55
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EGU22-11558
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ECS
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Virtual presentation
Cilva Joseph

Nanoscale apatite inclusions in xenotime: witness of Pb mobility

Cilva Joseph1, 2, Denis Fougerouse1, 2, Steven M. Reddy1, 2, Aaron Dodd3, Steven Denyszyn4, David W. Saxey2, William D.A. Rickard2

1School of Earth and Planetary Sciences, Curtin University, Perth, Australia

2Geoscience Atom Probe Facility, John de Laeter Centre, Curtin University, Perth, Australia

3Microscopy and Microanalysis Facility, John De Laeter Centre, Curtin University, Perth, Australia

4School of Earth Sciences, University of Western Australia, Perth, Australia

Discordant ages as measured by 206Pb/238U and 207Pb/235U ratios in various geochronometers are common. Several mechanisms have been proposed to explain discordant ages in different minerals. These include loss of radiogenic Pb, mixing of different age domains within a mineral, and intermediate daughter radioisotope disequilibrium. Xenotime (YPO4) is a geochronometer used to date different geological processes, such as diagenesis, metamorphism, and hydrothermal events. However, xenotime commonly yields small degrees of discordancy (<3%) by high precision geochronology techniques. To investigate the mechanism responsible for slightly discordant xenotime analyses, two ~1000 Ma crystals (z6413 and Y1) from Ontario and Western Australia were analysed using atom probe tomography (APT) and transmission electron microscopy (TEM) which provide sub-nanometre scale chemical and crystallographic analysis of minerals. Both samples have not undergone significant metamorphism (T < 300°C) after crystallisation. Combined APT and TEM results revealed the presence of nanoscale apatite [Ca5(PO4)3(F,Cl,OH)] inclusions and crystal dislocations in the xenotime grains. APT data indicates that the apatite inclusions are rich in radiogenic Pb and that the dislocations are decorated with Ca, Cl and H. Nanogeochronology of xenotime by APT indicate that the apatite inclusions likely formed by exsolution during the cooling of crystals, capturing radiogenic Pb. Dislocations in the crystals may have acted as fast diffusion pathways leading to radiogenic Pb-loss and caused the U-Pb system disturbance.

How to cite: Joseph, C.: Nanoscale apatite inclusions in xenotime: witness of Pb mobility, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11558, https://doi.org/10.5194/egusphere-egu22-11558, 2022.

08:55–09:02
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EGU22-1195
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Virtual presentation
Irene Morales, José Francisco Molina, Pilar Montero, Fernando Bea, and Aitor Cambeses

Zircon derived from crustal rocks can survive dissolution into basic melt during rock assimilation and magma hybridization if shielded in mafic phenocrysts or minerals from non-disaggregated xenoliths. Under these conditions, zircon can be subject to thermal shock that triggers recrystallization of metamict domains and reaction with its hosted mineral inclusions. In this work, we simulate this process by performing thermal annealing experiments on zircon grains with a variable degree of metamictization. The results show recrystallization of metamict domains, melting of multi-phase mineral inclusions, nanopores formation, and microcracking propagation by thermo-elastic stress. Highly metamict zircon with elevated common-Pb and radiogenic-Pb loss, which were impossible to date with SHRIMP, lost all their common-Pb and some radiogenic-Pb upon annealing, producing well-fitted discordias with significant upper intercept age. The porosity enhances intracrystalline melt mobility, leaching out impurities. Baddeleyite was formed at temperatures below the thermal decomposition of pure zircon by two mechanisms: (1) incongruent zircon dissolution into molten mineral inclusions with a high CaO/SiO2 ratio (2) recrystallization of metamict domains aided by silica migration from the reaction site.

How to cite: Morales, I., Molina, J. F., Montero, P., Bea, F., and Cambeses, A.: Annealing experiments on zircons: influence of lattice orientation and metamictization., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1195, https://doi.org/10.5194/egusphere-egu22-1195, 2022.

09:02–09:09
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EGU22-6046
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ECS
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Virtual presentation
Ke Wu

The Yanchang Formation of the Upper Triassic in the Jiyuan area in the central and western parts of the Ordos Basin is one of the main oil and gas enrichment areas in the basin. However, the tight sandstones of the Yanchang Formation have long been controversial on mineral genesis, formation age and sediment source. The distribution and variation characteristics of detrital zircon ages were studied using LA-ICP-MS dating and geochemistry testing of the detrital zircons from sandstones. The source of detrital zircons of different age components is identified, and difference of tectono-paleogeographic environments is analyzed. The main conclusions can be drawn as follows. Cathodoluminescence images show that most detrital zircon have a zonal structure. Rare Earth Element distribution models show that the sandstone is rich in HREE and is short of LREE, and all of models are left-dipping patterns. The Th/U values of detrital zircon show that most of the values are greater than 0.4, and a few are less than 0.1.The above geochemical testing results show that the source of detrital zircon is mainly magmatic rocks, followed by metamorphic rocks, and the ages of detrital zircons are reliable.The age results show that there exist three age stages of the Yanchang Formation detrital zircons, i.e., 228- 379 Ma, 1650- 1915 Ma, 2400- 2560 Ma, corresponding to the tectonic movements of indosinian, Hercynin, middle- late Lüliang movement and early- middle Wutai movement.By comparing the isotopic ages for the plutons in and around research areas, the tight sandstone of the Yanchang Formation in the central and western parts of the Ordos Basin derive from the Daqing Mountains-Wula Mountains, Yinshan Mountains and Jining areas in the north-northeast of the Ordos Basin.The sedimentary rocks source from gneissic granite in the late Neoarchean, ancient TTG gneiss and granulite in the early Paleoproterozoic, the khondalite belt in the Lüliang Movement, and the magmatic rock in the Indosinian and Hercynian.

How to cite: Wu, K.: The study of detrital zircon geochronology, geochemistry and tectonic-sedimentary significance of Upper Triassic Yanchang Formation in  central and western Ordos Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6046, https://doi.org/10.5194/egusphere-egu22-6046, 2022.

09:09–09:16
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EGU22-3895
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ECS
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On-site presentation
Petra Schneider and Dražen Balen

The Late Cretaceous igneous rocks within the south-western part of the Pannonian Basin basement (Croatia) occur in two areas: at the north-western part of Mt. Papuk (Pp; covering the area of ~10km2) and at Mt. Požeška Gora (Pg; area of ~30 km2). The predominant rocks are rhyolites and basalts, with pyroclastic material to a lesser extent. Additionally, smaller granite body crops out on Pg. The specific magma geochemistry (A-type signature) and age (~82 Ma) recently refined on acidic varieties (granite and rhyolite) indicate the beginning of the tectonic transition in this area from compression to extension.

In the reconstruction of magma evolution, inclusions captured in zircon grains represent valuable material that provides additional information. Zircon grains extracted from the samples of acidic rocks (rhyolites and granites) are quite small, usually less than 100 µm in the longer axis, with an average aspect ratio of 2.1:1. The grains are euhedral, with an external morphology defined by {100} prisms and {101}>{211} bipyramids. Such a primitive external zircon morphology suggests a magma source in the lower crust or upper mantle. The high Zr-saturation temperature and Ti-in-zircon temperature (~780 °C for Pp, ~910 °C for Pg) also suggest a deep source processes and material. The zircon grains are colourless and highly transparent, comprising solid inclusions suitable for analysis with the Raman spectrometer. The inclusions are euhedral-subhedral, mostly less than 10–15 µm in diameter. They are randomly oriented with the respect to the host zircon crystal growth structure. The following inclusions in zircons were detected by Raman spectrometer: anatase, kokchetavite, kumdykolite, apatite and hematite. In respect to characteristics of magma crystallisation, we have found important that anatase represents a TiO2 polymorph formed at lower igneous temperatures, but its crystallisation compared to rutile is favoured by rapid crystallisation. The kokchetavite and kumdykolite are polymorphs of KAlSi3O8 and NaAlSi3O8, respectively. Recent research show that they represent metastable phases in melt inclusions as a consequence of rapid crystallisation. Apatite detected in zircon dominantly resembles F-apatite. A high F content is indicative of magma formed by partial melting of upper mantle material, while hematite inclusions indicate an oxidising environment for the magma at the time of hematite crystallisation. In addition to the inclusions, the rapid uplift of the Late Cretaceous acidic magma is supported by the occurrence of hematite with crystallographically oriented ilmenite exsolutions and perthite found in Pg granite as well as zircon aspect ratios.

In conclusion, the inclusions found in the zircon, which were protected from later equilibration with the melt or alteration by fluids, confirm a deep magma source (upper mantle/lower crust) and represent independent mineralogical evidence indicating rapid uplift and emplacement of a hot mantle/crust transition level magma with early-crystallised zircon into the upper crustal level. The rapid uplift was possible due to the formation of accompanying extensional deep-rifts in the course of the tectonic transition from compression to extension.

How to cite: Schneider, P. and Balen, D.: Rapid uplift of Late Cretaceous acidic magma from northern Croatia deciphered by studying inclusions in zircon using Raman spectroscopy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3895, https://doi.org/10.5194/egusphere-egu22-3895, 2022.

09:16–09:23
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EGU22-7905
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ECS
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On-site presentation
Julia Sordyl, Karolina Rybka, Klaudia Dziewiątka, Anna Jędras, Mateusz Skalny, Kacper Staszel, Adam Tomczak, Kamil Urbański, and Maciej Manecki

Synthetic REE-enriched Pb-apatites are potentially important materials in the industry. The size and morphology of the crystals can influence the physical properties, and therefore affect technological processes. The conditions of the synthesis can determine the size and morphology of the crystals. Lead apatite Pb5(PO4)3Cl (analogue of mineral pyromorphite) was chosen for this study because the morphology of its crystals shows particular sensitivity to changes in synthesis conditions or solution composition. The addition of REE elements was used because there are reports that the morphology of synthetic Ca-apatite crystals depends on the presence of REE elements. Therefore, in the present study, synthesis by solution mixing at room temperature was carried out and the change in morphology of the precipitated pyromorphite crystals was observed as a function of solution chemistry (presence or absence of La or Sm) and concentration, pH, and mixing parameters. Powder X-ray diffraction (XRPD) was used to identify the phase composition of precipitates, scanning electron microscopy (SEM) to examine the morphology of the crystals, and energy-dispersive X-ray spectroscopy (EDS) for analysis of the elemental composition of analyzed crystals.

XRPD results showed that pyromorphite was identified in all samples. No changes in the crystalline structure were observed (hexagonal system, P63/m space group, typical for apatites). Also, EDS analyses showed that the chemical composition remained unchanged despite the morphological differences and the studied REEs (La or Sm) were incorporated into the structure in similar amounts in all precipitates. SEM images indicated that both the size and morphology of the pyromorphite crystals were sensitive to small modifications of the synthesis conditions. The size ranged from 2 µm up to 500 µm. Stirring resulted in smaller crystals than precipitation in the still water column. Crystals appeared in the form of long hexagonal needles (both single and cross-twinned), or slightly rounded, elongated and spear-like rods, or flower-like forms and intergrowths. The presence of REE caused elongation parallel to crystallographic c axis and formation of long needles compare to stubby hexagonal rods in the control sample.

The variation in size and morphology of Pb-apatites synthesized by the precipitation in aqueous solutions in different conditions were reported for the first time. Further research is needed to explain the contributing factors.

Slight changes in the synthesis protocol strongly affect the size and shape of Pb-apatite crystals. Therefore, determining the optimal conditions for the synthesis of homogeneous and well-formed crystals could be of great importance in the potential future applications of these materials.

This research was funded by NCN research grant no. 2019/35/B/ST10/03379.

How to cite: Sordyl, J., Rybka, K., Dziewiątka, K., Jędras, A., Skalny, M., Staszel, K., Tomczak, A., Urbański, K., and Manecki, M.: The influence of the synthesis procedure on the morphology of REE-enriched Pb-apatite (pyromorphite) , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7905, https://doi.org/10.5194/egusphere-egu22-7905, 2022.

09:23–09:30
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EGU22-11489
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On-site presentation
Richard James Roberts, Tawnee Britt, and Callum Hetherington

The occurrence of apatite and its trace element geochemistry in a borehole core through the Upper Zone from the Western Limb of the Bushveld is reported here (BK1). Apatite displays cyclic behaviour in the upper portion of the Upper Zone, appearing and disappearing several times. Two “spikes” of apatite, where apatite appears in abundance and then disappears suddenly, occur below the magnetitite layer noted as Layer 21, and are marked by a pronounced negative Eu anomaly in the apatite REE profile. The apatite intervals above Layer 21 are marked by sudden appearance and gradual disappearance, and have no Eu anomaly. Previous studies on the UZ in the Eastern Limb have noted this difference in REE profiles and have explained it either as a consequence of the trapped liquid shift, or as an indication of massive liquid immiscibility in the chamber at the level of Layer 21. We propose an alternative solution, in which a rejuvenated magma is injected into the magma chamber at or just below the level of Layer 21. This new rejuvenated magma is likely genetically related to the previous magma but is much higher in Fe and depleted in V compared to the previous magma, and is responsible for the formation of Layer 21 (8m thick), a layer considerably thicker than any other magnetitite layer, including the Main Magnetite Layer. The influx of a new magma is clear in the largest compositional shifts in the Upper Zone across layer 21, shown in the compositions of orthopyroxene (Mg#=25 below; Mg#=49 above), plagioclase (An#=47 below; #An=58 above), and olivine (Mg#=20 below; Mg#=40 below), as well as in the occurrence of liquid immiscibility only in the magma above Layer 21. In this model, the Eu anomaly created by plagioclase fractionation in the apatite below Layer 21 has been diluted by the addition of new magma which has not experienced prolonged fractionation of plagioclase.

How to cite: Roberts, R. J., Britt, T., and Hetherington, C.: Apatite in the Upper Zone of the Bushveld (Western Limb)- evidence for a rejuvenated magma at the height of Layer 21?, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11489, https://doi.org/10.5194/egusphere-egu22-11489, 2022.

09:30–09:37
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EGU22-12289
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ECS
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On-site presentation
David Heuser, Elena Petrishcheva, Gerlinde Habler, Ge Bian, Christian Rentenberger, Christian Leopold Lengauer, and Rainer Abart

Alkali feldspar is one of the most common rock forming minerals in magmatic and metamorphic rocks. It forms a solid-solution between the sodium and potassium end members. At temperatures above about 600°C alkali feldspar shows continuous miscibility. Towards lower temperatures, a miscibility gap exists. When cooled from super-solvus temperatures into the two phase region of the phase diagram, alkali feldspar of intermediate composition exsolves forming coherently intergrown lamellae of Na-rich and K-rich alkali feldspar, a microstructure referred to as perthite. The compositions and the characteristic widths of the exsolution lamellae reflect the cooling history. For a quantitative retrieval of cooling rates the thermodynamics of the solid solution including the effect of coherency strain and Na-K interdiffusion, which determines the coarsening kinetics, must be known.

Four alkali feldspars with different degrees of Al-Si ordering were investigated, namely Madagascar Orthoclase, Volkesfeld Sanidine, Zillertal Adular and Zinggenstock Adular. For each feldspar a ther- modynamic mixing model describing the strain free solvus was derived from feldspar-NaCl-KCl salt Na-K partitioning experiments performed at 800°C, 900°C and 1000°C. The models show increasing non-ideality with increasing degree of Al-Si ordering. The corresponding coherent solvi and spinodes were calculated using the strain energy function of Robin (1974).

The coarsening kinetics was obtained from exsolution experiments. To this end, each alkali feldspar was shifted to intermediate compositions by exchange with NaCl-KCl melt at 900°C for 35 days and subsequently tempered at 440°C, 480°C, 520°C and 560°C for 4, 8, 16, 32, 64, 128 or 256 days. Analyses of the run products by pXRD revealed splitting of reflections of the lattice planes that are subparallel to the lamellae subparallel to (-801), a feature that is diagnostic for coherent exsolution in feldspar. TEM investigation of foils extracted perpendicular to the crystallographic b-axis revealed fully coherent lamellae and lamellar widths between 8 and 30 nm. Lamellae growth rates were obtained from the time series experiments. For a given annealing time and temperature Madagascar Orthoclase shows relatively sharp and thick lamellae as compared to the other three feldspars. The coherency strain was derived from a comparison of the lattice parameters determined for the Na-rich and the K-rich lamellae by pXRD measurements of the experimental products with those of strain free feldspar as given by Kroll et al. (1986). The strain energy density calculated for the coherent intergrowth is by a factor of two smaller than the one given by Robin (1974).

Kroll, H., Schmiemann, I., and Cölln, G. (1986). Feldspar solid solutions. American Mineralogist, 71:1–16.

Robin, P.-Y. F. (1974). Stress and strain in cryptoperthite lamellae and coherent solvus of alkali feldspars. Am Mineral, 59:1299–1318.

How to cite: Heuser, D., Petrishcheva, E., Habler, G., Bian, G., Rentenberger, C., Lengauer, C. L., and Abart, R.: Determining the coherent solvus for alkali feldspar, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12289, https://doi.org/10.5194/egusphere-egu22-12289, 2022.

09:37–09:44
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EGU22-3747
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Presentation form not yet defined
Arefeh Moarefvand, Julien Gasc, Damien Deldicque, Loïc Labrousse, and Alexandre Schubnel

Polymorphic mineral phase transitions play an important role in the dynamics of the Earth’s crust and mantle. The quartz α→β transition, one of the most common, is a displacive transition which has been studied for over a hundred year and has been detected up to 3 GPa by several experimental methods. In thermodynamics databases, the α→β phase transition of quartz is generally associated with a significant change in elastic properties, and a corresponding shift of seismic wave velocities. Several seismological studies have used the transition to estimate the temperature profile of the lower crust. However, the elastic properties of quartz at high-pressure and temperature remain poorly known, particularly within at β-quartz field. Indeed, because the transition is so called a lambda-transition, it is impossible to simply extrapolate room pressure measurements at high pressure and temperature.

Here, experiments were performed within a 3rd generation Griggs-type apparatus, equipped with active and passive acoustic monitoring (Moarefvand et al. 2021). In this set-up, two ultrasonic transducers (5-10 MHz) allow us to measure p-wave velocities at in-situ P-T conditions. Experiments were carried out on 10mm long cored rock samples of Arkansas Novaculite (grain size of 3-6 µm), under hydrostatic pressure conditions ranging from 0.5 to 1.25 GPa and temperatures from 200 to 900°C, i.e. effectively crossing the quartz α→β phase transition. The transition was directly observed as a minimum in p-wave velocities, preceded by an important softening of velocities as temperature was getting close to the transition temperature. However, the p-wave velocities measured beyond the transition, in the β-quartz field, were lower than that predicted by thermodynamic databases. Two additional experiments were carried out on Novaculite, at 0.5 and 0.8 GPa confining pressures, using the acoustic emission (AE) set-up, in order to investigate whether these low velocities could be related to damage (microcracking) triggered by the transition, but no significant peak of acoustic emission was observed near the transition temperature. Novaculite samples were then analyzed using Electron Back-Scatter Diffraction (EBSD) and a prevalence of Dauphiné twinning was observed on all the samples that underwent the transition at HP-HT.

Finally, four additional experiments were realized on quartz single-crystals to investigate the effect of grain boundaries and the evolution of anisotropy during the transition. Again, the velocities observed in the β-quartz field, were lower than that predicted by thermodynamic databases. Microstructural analysis of these samples revealed the importance of cracking, in particular in the direction parallel to the c-axis.

Taken together, our results show that the velocity change due to the transition known at low pressure might be less important at higher pressure than that predicted by thermodynamic databases. If true, this important result needs to be confirmed using alternative methodologies, as it would imply that velocity changes related to the α→β quartz transition at lower crustal conditions might be lower than that observed by seismologists in thickened continental crust.

References:

Moarefvand, Arefeh, et al. "A new generation Griggs apparatus with active acoustic monitoring."
Tectonophysics816 (2021): 229032.

How to cite: Moarefvand, A., Gasc, J., Deldicque, D., Labrousse, L., and Schubnel, A.: Experimental measurement of P-wave velocities across the α→β quartz at lower continental crust pressure and temperature conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3747, https://doi.org/10.5194/egusphere-egu22-3747, 2022.

09:44–09:51
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EGU22-6398
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ECS
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On-site presentation
Ozge Ozgurel and Razvan Caracas

Noble gases are geochemical tracers, providing information about the formation of our planet and serving as a record of conditions in Earth history. Each noble gas has at least one stable non-radiogenic isotope, which is residue either of Big Bang or supernovas, and at least one stable radiogenic isotope, product of nuclear decay reactions from unstable heavier isotope of another element. The ratio of non-radiogenic and radiogenic isotopes of the noble gases arriving at the surface are essential to understand processes occurring on various timescale in the Earth interior.

The isotopic signature of the noble gases in the mid-ocean ridge basalts (MORBs) are different than in the ocean island basalts (OIB) such as in Iceland, Hawaii, Galapagos, Réunion, or Samoa. One such example is the high 3He/4He ratio observed in OIB, which are explained as a signature of the core, which in this case becomes a hidden geochemical reservoir. Here, we study the Helium partitioning between molten pyrolite and liquid iron, which represent proxies for the crystallizing magma ocean and the growing core, respectively. We employ molecular dynamics simulations based on the density functional theory as implemented in the VASP package. We perform the simulations at several temperatures and pressures that sample the magma ocean adiabat.

These calculations will allow to derive some trends on the preference of Helium on the silicate or iron melts. In the long term, they will confirm or inform the existence of a hidden reservoir deep inside the Earth, to position it in space, and to determine its formation in time.

We acknowledge support from the Research Council of Norway, project number 223272. RC acknowledges support from the European Research Council under EU Horizon 2020 research and innovation program (grant agreement 681818 – IMPACT) and access to supercomputing facilities via the eDARI gen6368 grants, the PRACE RA4947 grant, and the Uninet2 NN9697K grant.

How to cite: Ozgurel, O. and Caracas, R.: Helium partitioning between mantle and the core at the early Earth, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6398, https://doi.org/10.5194/egusphere-egu22-6398, 2022.

09:51–09:58
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EGU22-3168
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Presentation form not yet defined
Juraj Majzlan, Martin Števko, Alexandra Plumhoff, Edgar Dachs, and Artur Benisek

Minerals of the olivenite-libethenite [Cu2(AsO4)(OH)-Cu2(PO4)(OH)] group appear at many sites with secondary copper oxysalts. Their structural arrangement seems to be particularly stable and is also found in minerals in other classes, such as in andalusite or kieserite. Thermodynamic properties of the end members were investigated before and suggest that olivenite is the most stable Cu arsenate. In this contribution, we inspected in a detail the solid solution series between olivenite and libethenite.

Samples used in this work were synthetic, prepared from aqueous solutions with Cu(NO3)2, (NH4)H2PO4, and Na2HAsO4. Chemical composition of the members of the olivenite-libethenite solid solution were determined by ICP-OES. The relative proportions of the cations (As/P) differ little from the initial ratios in the parental solutions. For libethenite and a few solid-solution members, the orthorhombic space group Pnnm was taken for the refinement of the powder XRD data. For olivenite and the remaining, most solid-solution members, the monoclinic space group P21/n yielded slightly better results. Acid solution calorimetry in 5 N HCl showed that the solid solution is thermodynamically non-ideal, with positive enthalpies of mixing. The data indicate slight asymmetry and can be fit by a function Hex = Xoli·Xlib [A + B(Xoli – Xlib)], where Xoli and Xlib are the mole fractions of olivenite and libethenite component, respectively, and A = 6.27±0.16 kJ·mol–1, B = 2.90±0.5 kJ·mol–1. The asymmetry and positive excess enthalpies of mixing are confirmed by autocorrelation analysis of Fourier-transform infrared spectra. The results are interpreted as a local heterogeneity that arises from strain relaxation around cations with different sizes (As5+/P5+) in the intermediate members. The length scale of the heterogeneity corresponds to the wavelength of the phonons, on the order of one or a few unit cells. A distinct feature in the Hex data is the sudden drop of the mixing enthalpies between Xlib = 0.7 and 0.8. This feature can be explained by a subtle symmetry change in the solid solution from orthorhombic to monoclinic. The energetic difference between these two configurations is 0.9 kJ·mol–1. Excess entropies are zero within the uncertainties of the measurements, with one exception (at Xlib = 0.2). Excess volumes show a complicated, non-linear dependence on Xlib. Addition of PO4 into olivenite causes contraction of the unit cell, as expected for substitution of a smaller for a smaller cation. On the other side of the solid solution, addition of AsO4 into olivenite causes expansion of the unit cell. The variations of Vex are related to the interplay of cation-size differences and the small driving force between the two related (orthorhombic/monoclinic) structure. The olivenite-libethenite solid solution is non-ideal but the deviation from ideality is too small for a development of a miscibility gap. In nature, the As/(As+P) ratio in such minerals is controlled by geochemical rather than thermodynamic factors.

How to cite: Majzlan, J., Števko, M., Plumhoff, A., Dachs, E., and Benisek, A.: Thermodynamic analysis of the olivenite-libethenite solid solution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3168, https://doi.org/10.5194/egusphere-egu22-3168, 2022.

Coffee break
Chairpersons: Jannick Ingrin, Catherine McCammon, Juraj Majzlan
10:20–10:27
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EGU22-4407
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On-site presentation
Petr Drahota, Vojtěch Ettler, Adam Culka, Jan Rohovec, and Radim Jedlička

Humidity is an important factor in sulfide oxidation as it has been shown that sulfide minerals weather differently depending on the humidity. Arsenopyrite (FeAsS) and löllingite (FeAs2) concentrates were placed under six relative humidities (RH) between 75% and 100% for 40 months and then studied using XRD, EMPA, Raman microspectrometry, and chemical extractions. Results of our experiments showed that oxidative dissolution of arsenopyrite and löllingite concentrates led to formation of different mineral assemblages in different amounts. Oxidative dissolution of arsenopyrite concentrate led to formation of poorly crystalline ferric arsenate (PCFA) and minor elemental sulfur, while oxidation of löllingite concentrate resulted in formation of well crystalline scorodite (FeAsO4·2H2O) and arsenolite (As2O3). Our data indicated that high levels of sulfate in arsenopyrite concentrate (released from sulfide oxidation) triggered fast precipitation of PCFA and retarded its transformation to scorodite. Effect of the RH on the mineralogy of oxidation products was negligible; however, quantity of newly formed oxidation products was function of RH. The data indicated that oxidation kinetics of arsenopyrite and löllingite concentrates were relatively similar and low (corresponding up to 3.5 % of the sulfide/arsenide) at RH≤94%, but löllingite concentrate oxidized much faster (up to 10×) at RH levels close to 100%.

How to cite: Drahota, P., Ettler, V., Culka, A., Rohovec, J., and Jedlička, R.: Effect of the relative humidity on the oxidation of arsenopyrite and löllingite, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4407, https://doi.org/10.5194/egusphere-egu22-4407, 2022.

10:27–10:34
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EGU22-11602
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Virtual presentation
Pedro Álvarez-Lloret, Adriana Torres-Mansilla, and Luis Monasterio-Guillot

The study of mineral decarbonation mechanisms is of great interest for its application to various geological and industrial processes. Biomineralization is a phenomenon by which living organisms are able to produce mineral phases, the most abundant of which are calcium carbonates and phosphates. Among the more abundant polymorphs of calcium carbonate are calcite and aragonite, being the most thermodynamically stable structures under biological environments (Weiner & Addadi, 1997). In general, mineral phases formed by biologically controlled mineralisation processes have lower crystallinity characteristics than their geological analogues. In the current communication, the thermal degradation of biogenic calcium carbonates is comparatively studied with their respective ones of geological origin. During the transformation, chemical and microstructural alterations occur from the original polymorphs of biogenic calcite (eggshell; Gallus gallus) and aragonite (mollusc shell; Ruditapes philippinarum) to the final calcium oxide mineral phase. The samples were gradually heated from room temperature to 1100°C in order to remove the water content and organic matter components contained in the biogenic phases and to induce progressive mineral decarbonation. The kinetics of these compositional transformations were analysed by means of differential scanning calorimetry (DSC). Different analytical techniques, such as attenuated total reflectance infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM), were used for the chemical and structural characterisation of the mineral transformation of these phases. During thermal degradation, changes are observed in the molecular composition of these biogenic phases related to the distortion of the carbonate group and its association with the organic components. Furthermore, the mineral decarbonation process of calcium carbonates involves different structural transformation mechanisms that depend on the modification of unit cell parameters, thermal expansion coefficients and microstructural reorganisation (Rodriguez-Navarro et al., 2009). Accordingly, CaCO3 crystalline structures are transformed from the original calcite and aragonite phases to the cubic structure of lime, with a calcite-aragonite transformation prior to decarbonation explained by the reorientation of the CO3 group towards Ca and by changes in the packing of the Ca atoms, followed by the increase of the unit cell volume (Antao & Hassan, 2010). The results show some significant differences during mineral transformation depending on their geological or biological origin. The characterization of this mineral decarbonation process has important implications in natural and industrial processes (i.e., cement production, CO2 capture).

  • Weiner, S.; Addadi, L. (1997) Design strategies in mineralized biological materials. Journal of Materials Chemistry, 7(5), 689-702.
  • Rodriguez-Navarro, C.; Ruiz-Agudo, E.; Luque, A.; Rodriguez-Navarro, A.B.; Ortega-Huertas, M. (2009) Thermal decomposition of calcite: mechanisms of formation and textural evolution of CaO nanocrystals. American Mineralogist 94, 578–593.
  • Antao, S. M., Hassan, I. (2010) Temperature Dependence of the Structural Parameters in the Transformation of Aragonite to Calcite, as Determined from in Situ Synchrotron Powder X-Ray-Diffraction Data. Canadian Mineralogist 48, 1225– 1236.

How to cite: Álvarez-Lloret, P., Torres-Mansilla, A., and Monasterio-Guillot, L.: Thermal degradation of biological carbonates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11602, https://doi.org/10.5194/egusphere-egu22-11602, 2022.

10:34–10:41
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EGU22-9668
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ECS
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On-site presentation
Edgar Alejandro Cortes Calderon, Ben S. Ellis, and Peter Ulmer

Lithium (Li) is a key element in the production and development of high energy density storage technology. The boost in production of battery-powered vehicles has, as a result, increased Li demand. Felsic magma reservoirs are commonly linked to Li-bearing ore deposits as their major source of Li. Understanding the processes that may affect the Li inventory in magmas is, thus, crucial to improve exploitation of Li resources. We performed experiments using haplogranitic glass shards and quartz cores between 60-150 MPa and 750-950 ºC, involving fluids with salinities ranging 0.3 to 4.4 NaCleq m in externally heated MHC pressure vessels. Quartz cores were used in all experiments to trap synthetic fluid inclusions at equilibrium conditions by in-situ thermal-shock. Li partitions weakly into quartz, DLiquartz/melt ~ 0.02, with no apparent variation with studied pressures and temperatures within analytical error. LA-ICP-MS analyses on natural quartz from this study and published data show that Li concentrations in quartz from “hot and dry” rhyolites (e.g. Mesa Falls Tuff, Lava Creek Tuff, Weinheim Rhyolite) are higher than “cold and wet” rhyolites (e.g. Kos Plateau Tuff, Bandelier Tuff, Bishop Tuff, Young Toba Tuff, Oruanui Rhyolite), 25 ± 6 and 6 ± 5 ppm (n = 5300) in average respectively. Our DLiquartz/melt experimental results are one order of magnitude lower than natural dry-rhyolites but similar to the apparent DLiquartz/melt derived from natural samples in H2O-saturated systems, where hydrogen seems to play a more important role charge-balancing Al in point defects of quartz than Li. While Li is slightly incompatible with single-phase intermediate density fluids, Li partitions relatively strongly into hydrosaline fluids (HSF), DLiHSF/melt 5-12, within the two-phase fluids coexistence surface, with the highest values in the high temperature experiments. Although Li in HSF increases with temperature and, in turn, with chlorinity of the HSF, such a scenario does not affect greatly the inventory of Li in the run melts. The higher the temperature of the studied system at a given pressure, the lower the proportion of HSF with respect to low density vapor fluid (LDVF) in the system. Such topological consequence limits the “effective” extraction of lithium by fluids in felsic magma reservoirs to very constrained regions in pressure, temperature and fluid composition. As a result, extremely and ubiquitous high Li degassing from rhyolitic melts based on the Li concentration offset between re-homogenised melt inclusions and groundmass glass must be carefully revisited.

How to cite: Cortes Calderon, E. A., Ellis, B. S., and Ulmer, P.: Lithium element partitioning among haplogranitic melt, fluid and quartz, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9668, https://doi.org/10.5194/egusphere-egu22-9668, 2022.

10:41–10:48
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EGU22-2645
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Virtual presentation
Encarnación Roda-Robles, Idoia Garate-Olave, Jon Errandonea-Martin, Alfonso Pesquera, and Pedro Gil-Crespo

In the Castillejo de Dos Casas area (C2C) (Central Iberian Zone) different granitic (Villar de Ciervo granite) and pegmatitic units of Variscan age occur intruded into the Neoproterozoic-Cambrian metasediments of the Schist Greywacke Complex (SGC). These units include: (1) biotite-rich porphyritic granite; (2) two-mica granite; (3) muscovite ± tourmaline ± phosphates-rich, leucogranites; (4) barren to Li-rich aplite-pegmatite cupola; and, (5) Li-rich aplite-pegmatite dykes. Except (1), all these units are highly peraluminous (A/CNK in the range of 1.18-2.23), Ca-poor (0.09-0.87 wt% CaO), and P-rich (0.29-3.11 wt% P2O5). Units (4) and (5) are heterogeneous, showing different mineral associations. The most common consists of a fine-grained matrix of quartz, plagioclase and Li-mica, where coarser feldspar crystals grow perpendicularly to the contacts, and topaz, montebrasite, Fe-Mn-phosphates, petalite, elbaite, cassiterite and Nb-Ta oxides are accessory. A layered texture is also locally observed.

The origin of pegmatitic melts is somehow controversial. For decades they have been considered the residual portions originated by the fractional crystallization of granitic magmas (e.g. London, 2008). However, lately the anatectic model, which proposes that pegmatitic melts originate directly by low degrees of partial melting, is gaining more followers among pegmatite researchers (e.g. Simmons et al., 2016).

In the case of C2C, the aplite-pegmatite cupola is located over the two-mica granite and close to the leucogranitic units, whereas the aplite-pegmatite dykes intrude concordantly into the SGC materials, over and close to the granitic/pegmatitic cupola. These spatial relationships strongly suggest the existence of a petrogenetic link between granitic and pegmatitic units. Whole-rock data show a gradual decrease in the Ca, Fe, Mg, Ti, Ba, Y and REE contents and K/Rb ratio with fractionation, from units (1) to (5), parallel to an increase in Al, Mn, P, Li, F, Rb, Cs, Sn, Nb and Ta. Similarly, chemical composition of main mineral phases shows gradual changes from the less evolved unit (1) to the most fractionated one (5). A continuum is observed for micas, with a progressive Li, F, Rb and Cs increase, parallel to a K/Rb decrease. Alkali feldspars show a gradual decrease of the K/Rb ratio for K-feldspar and of Ca for plagioclase; whereas tourmaline becomes Li-richer and Fe-poorer from (3) to (5) (it has not been identified in units (1) and (2)). Therefore, taking into account the spatial relationships of the 5 units, as well as their chemistry at whole-rock and mineral scales, the most feasible origin for the pegmatitic melts in the C2C area corresponds to the fractionation of a parental granitic melt that well could correspond to the unit (1) of the Villar de Ciervo granite, and that would evolve through the units (2), (3) and (4), up to the most fractionated unit (5) of the Li-rich aplite-pegmatite dykes.

 

London, D., 2008. Pegmatites. Canadian Mineralogist, Special Publication n° 10, pp. 347.

 

Simmons, W., Falster, A., Webber, K., Roda-Robles, E., Boudreaux, A., Grassi, L.R., Freeman, G., (2016): Bulk composition of Mt. Mica pegmatite, Maine, USA: implications for the origin of an LCT type pegmatite by anatexis. Can. Mineral. 54, 1053-1070.

How to cite: Roda-Robles, E., Garate-Olave, I., Errandonea-Martin, J., Pesquera, A., and Gil-Crespo, P.: On the link between granites and pegmatites: the case study of the Li-rich mineralization from Castillejo de Dos Casas (Salamanca, Spain), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2645, https://doi.org/10.5194/egusphere-egu22-2645, 2022.

10:48–10:55
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EGU22-5329
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ECS
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Virtual presentation
Idoia Garate-Olave, Encarnación Roda-Robles, Pedro Pablo Gil-Crespo, Jon Errandonea-Martin, Alfonso Pesquera, and Nora Santos-Loyola

One of the most characteristic attributes of pegmatitic rocks is their anisotropic fabric with a great variety of textures, including not only a broad range of crystal sizes, but also different types of unidirectional crystal growths such as the so-called Unidirectional Solidification Textures (UST). In the Tres Arroyos Pegmatite Field (Central Iberian Zone of the Iberian Massif), apart from comb-textures, the alternation of aplitic and pegmatitic layers (with variable modal proportions) parallel to the contacts with the host rocks occur commonly all across the pegmatitic dykes. The origin of the layering in these bodies is still enigmatic.

In the case of Tres Arroyos, the strong undercooling of the system could be produced by a combination of different factors, including a sudden drop of pressure favoring the exsolution of a fluxing components-bearing aqueous fluid from the pegmatitic melt, and a marked temperature decrease of the pegmatitic melt due to its intrusion into significantly colder host rocks. The reduced thickness of the studied dykes (average of 2 m) would promote to the development of nonequilibrium textures along the entire width of the dykes. The variation of the crystal size (≈2-3 orders of magnitude) through different layers constituting the dykes reflects changes in the nucleation density and crystal growth rate during crystallization. The occurrence of dykes with several alternating thin pegmatitic and aplitic layers could be the result of cyclical changes induced by the competition between crystal growth rate and nucleation rate. The simplest layering patterns observed in Tres Arroyos, with alternating quartz-rich and plagioclase-rich bands, or alternating lepidolite-rich and albite-rich layers, could be explained by a diffusion-controlled oscillatory nucleation model, whereas the understanding of more complex layering patterns would need a more comprehensive study.

How to cite: Garate-Olave, I., Roda-Robles, E., Gil-Crespo, P. P., Errandonea-Martin, J., Pesquera, A., and Santos-Loyola, N.: Preliminary results of Unidirectional Solidification Textures recorded by the aplite-pegmatites from Tres Arroyos (Badajoz, Spain) and the story they tell, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5329, https://doi.org/10.5194/egusphere-egu22-5329, 2022.

10:55–11:02
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EGU22-9288
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ECS
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On-site presentation
Edyta Waluś and Maciej Manecki

Libethenite and olivenite present itself as a particularly interesting candidates for a photocatalyst due to its unique structure. One of the features of copper hydroxy- phosphates and -arseniates is the presence of bridging hydroxyl (OH) groups shared between neighboring Cu atoms. In materials used in photoelectrochemical applications, the role of surface OH groups and OH-related defects is often variable and depends on the material system and reaction of interest. For instance, OH groups can improve photocatalytic activity by forming OH radicals or act as an important intermediate in the catalytic reaction. As such, the presence of the OH group inherent in the crystal structure of the material may lead to potentially interesting behavior. Seven compounds of the libethenite Cu2(OH)PO4 – olivenite Cu2(OH)AsO4  solid solution series were synthesized at 70 °C from aqueous solutions and characterized using XRD, SEM–EDS and FTIR and Raman. The substitution effect of [PO4]3- anions by [AsO4]3- on systematic changes in lattice parameters and spectral properties has been explained based on correlation between chemical composition and the peak positions. The substitution results in systematic linear increase in unit cell parameters and unit cell volume. Isomorphic substitutions are apparent in IR and Raman as a change in the position and intensity of bands derived from phosphates, arsenates and hydroxyl ions. Isomorphic substitutions of As for P in the solid solution series change the bond length and geometry. Investigation into materials that contain intrinsic OH groups may lead to better understanding of these processes and impact for photocatalytic properties. These studies will help determine the potential of libethenite Cu2(OH)PO4 – olivenite Cu2(OH)AsO4 isomorphic series as photocatalysts.

How to cite: Waluś, E. and Manecki, M.: Hydroxyl group of libethenite Cu2(OH)PO4 – olivenite Cu2(OH)AsO4 solid solution series - vibrational spectroscopic study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9288, https://doi.org/10.5194/egusphere-egu22-9288, 2022.

11:02–11:09
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EGU22-7167
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ECS
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On-site presentation
Marek Tuhý, Vojtěch Ettler, Juraj Majzlan, and Stefan Kiefer

For this investigation, biomass and soil samples from several smelter areas in sub-Saharan Africa were used. Grass samples and topsoils were collected in the Tsumeb area in northern Namibia (Cu-smelter, former mine), Selebi-Phikwe in Botswana (Ni-Cu mine and smelter), Luanshya in the Zambian Copperbelt (Cu mine and smelter), and Kabwe in central Zambia (Pb-Zn mine and smelter). Metal(loid)s concentration in soils and grass were generally in the order of hundreds to thousands mg/kg.

The surfaces of all the grass biomass samples contained a variety of geogenic (quartz, carbonates, clay minerals, feldspars) and anthropogenic (usually metal-bearing) particles directly attached to the biomass tissues. These smelter-derived particles are predominantly slag fragments enriched in various contaminants, droplets of metals/sulfides, and, in the case of the biomass from Kabwe, newly formed aggregates of submicrometric anglesite (PbSO4) crystals. Heavy mineral fractions were obtained from all biomass samples to better understand the solid-phase speciation of contaminants. In Tsumeb, the key metal-hosting minerals/phases on biomass were Cu-Fe sulfides, arsenolite (As2O3) and metal-bearing slag glass. In Selebi Phikwe pyrrhotite (Fe1-xS), pyrite (FeS2), pentlandite [(Fe,Ni)9S8] and chalcopyrite (CuFeS2) were predominant. Samples from Kabwe were composed of galena (PbS), pyrite (FeS2), sphalerite (ZnS), chalcopyrite (CuFeS2) and anglesite (PbSO4) and in Luanshya, the particulates were mainly formed by phases from the Cu-Fe-S ternary system. The mineralogy of particulates collected in the grass samples was similar to that in the corresponding topsoil samples. The knowledge of solid-phase speciation is of key importance for determining the fate of contamination in such environments.

This study was supported by the Czech Science Foundation (GAČR project no. 1-23794J) and a grant from the Endowment Fund of the Faculty of Science, Charles University, attributed to M. Tuhý. The Charles University team was partially supported by the institutional funding from the Center for Geosphere Dynamics (UNCE/SCI/006).

How to cite: Tuhý, M., Ettler, V., Majzlan, J., and Kiefer, S.: Mineralogy of particles deposited on biomass and in soils from various smelter-polluted sites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7167, https://doi.org/10.5194/egusphere-egu22-7167, 2022.

11:09–11:16
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EGU22-268
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ECS
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Virtual presentation
Mohamed Ghnahalla, Abderrazak El Albani, Ahmed Abd Elmola, Olabode M. Bankole, Claude Fontaine, Timothy W. Lyons, Chenyi Tu, Mohamed Salem Sabar, Alain Trentesaux, and Alain Meunier

Understanding and reconstruction of the paleo-condition dynamics linked to biological evolution in Earth history remain a big challenge because a majority of the ancient rocks have been affected by secondary modification processes, including tectonic, metamorphic, and hydrothermal activities. This study examines the influence of magmatic intrusion on sediment composition and paleo-environmental reconstruction from two drill cores (S1 and S2) drilled into the shallow-marine Mesoproterozoic (~1.1 Ga) El Mreiti Group of northeast Taoudeni Basin, Mauritania. Petrographic and mineralogical data show that the S1 drill core, intruded by dolerite sill, consists of a series of metamorphic minerals, including pyroxene, graphite, pyrrhotite, garnet, zeolite, talc, and saponite in sediments within the contact aureoles of the dolerite sill, indicating the influence of contact metamorphism and associated hydrothermal activities. The dominance of low-temperature minerals and the absence of metamorphic minerals in the S2 drill core sediments demonstrate that they are largely preserved and were only affected by high-grade diagenetic modifications. The anomalous enrichments of the Fe and redox-sensitive trace elements (RSTEs) in sediments within the vicinity of the dolerite sill coincide with increasing pyrrhotite contents, suggesting the transfer and remobilization of the RSTEs via thermal decomposition of pyrite to pyrrhotite during metamorphism and hydrothermal processes at elevated temperatures. This is supported by the absence of hematite, low Th/U ratios, and increasing Eu anomaly values in the dolerite sill and contact aureoles. This study reinforces the importance of screening and assessment of samples for post-depositional alteration effects before being used for the reconstruction of paleo-redox conditions in modern and ancient sedimentary rocks.

How to cite: Ghnahalla, M., El Albani, A., Abd Elmola, A., M. Bankole, O., Fontaine, C., W. Lyons, T., Tu, C., Sabar, M. S., Trentesaux, A., and Meunier, A.: Impact of post-depositional transformation on sedimentary rocks and implications for paleoenvironmental studies: Evidence from  Mesoproterozoic (1.1 Ga) sediments from the Taoudeni basin, Mauritania, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-268, https://doi.org/10.5194/egusphere-egu22-268, 2022.

11:16–11:23
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EGU22-9879
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ECS
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Virtual presentation
Arnab Kumar Pal, Siddharth Garia, and Archana M Nair

The shallow subsurface is prone to the dynamic influence of anthropogenic and environmental processes. To understand the influence, it is essential to quantify the rate of weathering across the depth profile. Chemical weathering rates for landscapes are difficult to quantify due to the non-uniqueness of the timescales over which weathering occurs. The rate of chemical weathering is generally observed to increase with physical erosion and weathering. Clay, a weathering product of rock mass, mainly contributes to this chemical weathering. Therefore, understanding the effect of clay mineralogy is significant in understanding this weathering environment. It is noticeable that intense rainfall in northeastern India mainly contributes to the weathering of the rock mass. Hence, the present study investigates the mechanism by examining the chemical weathering profile across the regolith depth. The primary objective of this study is to highlight that clay minerals have a significant role in the surface and subsurface weathering process across hillslope. Thus, for the analysis purpose, undisturbed soil samples were collected from the top 20 meters of the sediment column in a hillslope of northeastern India, inside IIT Guwahati campus, Assam at a regular 5-meter interval using the auger drilling technique. X-ray diffraction (XRD) was used to identify the clay mineralogy. Clay mineral was separated from the actual soil sample by following the USGS standard manual (extracting <2μm fraction) after treating with Hydrogen peroxide (H2O2) solution to remove organic matter. Organic matter was removed as it may cause background interference and prevent parallel orientation of clay minerals. It is observed that illite is the dominant clay mineral, followed by kaolinite and chlorite. Illite content decreases significantly with depth, while kaolinite and chlorite content increases slightly with depth. This variation may be attributed to climatic conditions, rainfall distribution across the year, resulting in deep infiltration. Mineral fluid interaction along with variation in climatic and environmental conditions subsequently causes clay mineral alteration. The accumulation of clay minerals and their alteration forms a zone of mechanical and chemical weakness, causing soil mass movement across hillslope. Thus, it can be concluded that mineralogical and geochemical analysis is essential for determining landscape sensitivity to erosion and weathering processes of hillslope areas.

How to cite: Pal, A. K., Garia, S., and Nair, A. M.: Effect of Clay Mineralogy on Hill Slope Weathering, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9879, https://doi.org/10.5194/egusphere-egu22-9879, 2022.

11:23–11:30
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EGU22-5274
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Virtual presentation
Pauline Moreau, Isabelle Duhamel-Achin, Blandine Gourcerol, Philippe Lach, Catherine Lerouge, Nicolas Maubec, Philippe Négrel, and Guillaume Wille

Long-term management of the mineral resource supply incorporating anthropogenic environmental impacts is crucial for sustaining human society. This is especially true for recovery of by-products and critical raw materials (CRM) whose production is often unable to respond quickly to rapid changes in consumption trends. As part of European H2020 research and innovation, the ION4RAW project aims at obtaining reliable estimates of by-products and CRM, and at developing ionometallurgy processes to improve their extraction from primary resources. Targeted metals are by-products (Te, Se, Re and Mo) and CRM (Bi, Ge, In, Co, Pt, Sb) in 5 selected Cu-Ag-Au ore deposits through the world (Cononish Gold mine, Scotland; Cobre Las Cruces and El Valle Boinas, Spain; El Porvenir and Cerro Lindo, Peru). The final objective of this study is to determine the carrier minerals of CRM and by-products, the variability of their chemistry, their distribution and quantification, in order to improve their recovery during ore treatment processes. We currently inventory by-products and CRM by characterizing ores and gangue, using a multi-technical approach (bulk chemistry and X-Ray diffraction, optical and scanning electron microscopic observations, µX-ray fluorescence mapping, EPMA spot analyses and laser ablation-ICP-MS). We present here the preliminary results of El Porvenir and El Valle Boinas that are two calcic skarn-related deposits defined by their garnet composition.

 

El Porvenir (Peru), owned by Nexa Resources, is a Pb-Zn ore deposit associated with andradite–bearing skarn, exploited in an underground mine located in the Western Cordillera of the Andes mountain range in central Peru.

El Valle-Boinas (Spain), owned by Orvana Minerals Corp, is a Cu-Au ore deposit associated with a grossular-bearing skarn, exploited in an underground mine located in Cantabrian Mountains, 60 km southwest from Aviles in Spain.

Mineralogical investigations indicate that the major ore consists of chalcopyrite, galena, sphalerite, pyrite with minor pyrrhotite, tennantite-tetrahedrite–series minerals and tellurides. The electron microprobe allows analyzing micron-sized metal-carrier minerals, including electrum, Bi-Pb sulfosalts, hessite [Ag2Te], stannoidite, determining the composition of tennantite-tetrahedrite-series minerals (argentotennantite containing up to 12 wt% Ag and 5 wt% Bi) and detecting traces in major ore at a detection limits of 200-1000 ppm (for example, galena significantly contains Ag, Sb and Te). The laser ablation-ICP-MS was tested at maximum power of the laser and at different beam diameters adapted to the grain sizes (from 85 to 10 µm). Laser ablation-ICP-MS analyses with a beam diameter of 10 µm confirms EPMA data and allows detecting lower metal contents, such as Se, Rh, Pd, In, Te, in main ore minerals at detection limits of the ppm.

How to cite: Moreau, P., Duhamel-Achin, I., Gourcerol, B., Lach, P., Lerouge, C., Maubec, N., Négrel, P., and Wille, G.: ION4RAW: Improving metal recovery in Cu-Pb-Zn-(Au-Ag) ore deposits through inventory of by-products and critical raw materials, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5274, https://doi.org/10.5194/egusphere-egu22-5274, 2022.

11:30–11:37
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EGU22-206
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ECS
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On-site presentation
Valeria Ramirez Juya, Camilo Andres Betancur, Javier Garcia Toloza, and Luis Angarita

Colombian emeralds are widely recognized for their unique gemological and geological features; The first one involves color, which depend on the proportions of their minor and trace elements. The latter is associated with its genesis, which implicates hydrothermal brine fluids affecting the sedimentary host rock. Thus, to propose an emerald finger-print for each belt, we use geochemical methods as Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), ternary and binary diagrams, and principal component analysis (PCA) in 258 emerald samples; 117 from the eastern emerald belt (EEB) and 141 from the western emerald belt (WEB).

The chromophores elements relation (Cr, V, and Fe) is used to differentiate emeralds from different geographical proveniences, that approach is valid with Colombian emeralds. Besides, in this study, we notice differences betwixt the V/Cr relationship in both belts: in the EEB, the proportion is lower than 0.75, and in the WEB, this proportion is upper than 0.75, and in most of the cases is over 1. This tendency is also remarkable in the ternary plot that includes iron.

Furthermore, other chemical elements have a particular behave depending on the belt, is the case of Na and Mg; in this study, we introduce a binary plot as a new method where the linear relation between those elements permit expressing a mathematical equation to distinguish each belt (Na=0,8Mg+362), where there is a cut-off point in Mg=3225 and Na=2940, the data lower of that point represent samples of the EEB, and the data upper come from the WEB.

In detail, the basin environment of each belt controlled the abundance of heavy metals; in the WEB, the quantity of those elements is higher. Evidence of this is the higher volume of sulfides and oxides. Except for the Cr content, this variant could be due to a previous stage of mineralization that includes Cr-rich muscovites. In the EEB, the Na and K content in the emeralds is lower because the rock suffers feldespatic enrichment in layers (Santa Rosa and Chivor formations). Owing to that, the temperature is enough to generate a massive albitization process affecting the original lithology of the stratigraphic sequence.

How to cite: Ramirez Juya, V., Betancur, C. A., Garcia Toloza, J., and Angarita, L.: Geochemistry of emerald from the Colombian Emerald belts: Genetical implications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-206, https://doi.org/10.5194/egusphere-egu22-206, 2022.

11:37–11:44
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EGU22-210
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ECS
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On-site presentation
Javier Garcia Toloza, Andrés González, James Day, Valeria Ramirez Juya, Camilo Betancur, and Luis Angarita

In Colombia, emerald deposits are sediment-hosted in two parallel belts (Western and Eastern Emerald Belt). Host rocks are calcareous mudstones and limestones of Lower Cretaceous age. The emerald genesis is associated to the flow and mixing of basinal and evaporate derived fluids; a process that took place in organic-rich beds, the leached and released elements like beryllium, chromium, vanadium essentials for emerald formation were present there. The mineralization is found in veins and hydrothermal breccias, frequently includes carbonates, pyrite, albite; less common minerals as: emerald, parisite, apatite, fluorite. In the host rocks is common to find trace minerals such as pyrite, rutile, and, remarkably, the REE carrier monazite.  Parisite —Ca(Ce,La)(CO)F— was first and only described in Colombian emerald mines associated with sedimentary rocks. The Western Emerald Belt is the one where parisite and emerald have been found together. Nevertheless, we report the occurrence of parisite-(Ce) and synchysite-(Ce) —Ca(Ce,La)(CO)F—  in Eastern Emerald Belt. Both minerals have similar Ce/La ratios. Chondrite normalized REE patterns show a relative enrichment in the light-REE and a subtle negative europium anomaly; no significant difference with authigenic monazite REE patterns was observed, thus suggesting a genetic link. The fluorocarbonates were found in emerald-bearing veins consisting of albite, dolomite, pyrite, and apatite. The mineral assemblage suggests that fluorocarbonates were formed under similar P-T conditions ≈ 250-350ºC and 0.8-1.2 kbar (Giuliani et al 1993; Cheilletz et al 1994; Romero et al 1999; García-Toloza et al 2017) of emerald-bearing fluids with approx. composition: Na-Ca-K-Fe-Be-Cl-F-CO-N-CH (Banks et al 2000).  It is proposed that monazite-bearing black shales are the likely source for the REE, and the interaction with F-CO -rich saline hydrothermal fluids led to the dissolution of monazite and eventual precipitation of REE as fluorocarbonates in veins.

How to cite: Garcia Toloza, J., González, A., Day, J., Ramirez Juya, V., Betancur, C., and Angarita, L.: REE fluorocarbonates within rocks and emerald-bearing veins in eastern emerald belt, Colombia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-210, https://doi.org/10.5194/egusphere-egu22-210, 2022.

11:44–11:51
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EGU22-217
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ECS
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On-site presentation
Camilo Andrés Betancur Acevedo, Valeria Ramirez Juya, Javier Garcia Toloza, and Luis Angarita

The Colombian emerald deposits are confined in both flanks of the eastern Cordillera. Those deposits are referred to as; the eastern emerald belt (EEB) and the western emerald belt (WEB). The formation conditions of the Colombian emeralds are unique in the world considering the differences in the host rock and the hydrothermal fluids. They are hosted in sedimentary rocks with a significant amount of Cr, V, and organic matter. Besides, the fluids are not linked with a magmatic source. Indeed, they are the result of basinal fluids combined with brines. Two main processes define the typical mineralization: albitization and carbonatization influencing the major crystalization of minerals like calcite, dolomite, quartz, albite, pyrite, emerald, and minor minerals as fluorite, apatite, rutile, tourmaline, and zircon.
We observed three trace minerals not typical in emerald mineralization. Those are two phosphates (Monazite and Xenotime) and a fluoro-carbonate (Parisite). To them, we make petrographic analysis to identify their paragenetic relation in the sequence, and with the use of an Electron Probe Microanalyzer in 93 samples (50 Monazites, 36 Parisites, and 7 Xenotimes), we suggest formation condition features. Those minerals determine different moments in the mineralization process. Before the mineralization, monazite crystallized in the host rock, displaying euhedral crystals with wedge shapes not correlated to detrital formation. Latter, the first stage of mineralization takes place on the rock-vein contact. Where the albitization plays an important role and the xenotime crystallized in a tabular-elongated habit. This stage is proceeding for a carbonatization phase, it is usually linked with the emerald production and the crystallization of parisite, which exhibits a subhedral shape determined by a double pyramid like a pseudo-rhombohedral habit.
The hydrothermal fluids originated from the salt diapirism in the processes of albitization and carbonatization leached and released the REE elements from the oldest part of the basin. Besides, each mineral is linked with different hydrothermal pulses, and paragenesis implying an evolution in pressure and temperature conditions.

How to cite: Betancur Acevedo, C. A., Ramirez Juya, V., Garcia Toloza, J., and Angarita, L.: Geochemical analysis of REE minerals and their relation with the Colombian emerald belts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-217, https://doi.org/10.5194/egusphere-egu22-217, 2022.