GMPV5.1

Solving geoscience problems using mineralogy

GMPV5.1

Solving geoscience problems using mineralogy

Convener: Jannick Ingrin | Co-conveners: Juraj Majzlan, Catherine McCammon, Elena ZhitovaECSECS

vPICO presentations

| Thu, 29 Apr, 13:30–15:00 (CEST)

vPICO presentations: Thu, 29 Apr, 13:30–15:00

Chairpersons: Catherine McCammon, Elena Zhitova, Jannick Ingrin

13:30–13:32

EGU21-13827

Interactions of ammonium and lattice of feldspar at high temperatures

Yan Yang

Nitrogen cycling between the Earth’s surface and interior influences atmosphere evolution, climate and habitability of our planet. Nitrogen transport process in the Earth’s interior is a key part of the cycling, which remains enigmatic. Silicate minerals are the main carriers of nitrogen mainly in the form of ammonium. Thus, untangling interactions of ammonium and lattice of the host minerals at the deep Earth’s conditions, is essential for understanding nitrogen transport process.

Feldspar, the most abundant mineral in the Earth’s crust, is a carrier of nitrogen to the deep Earth. Nitrogen is incorporated as ammonium in the M site of feldspar framework. To investigate interactions of ammonium and lattice at high temperatures, we conducted FTIR, Raman and XRD spectra measurements at high temperatures to 1000 ^oC on an ammonium-bearing feldspar, and revealed ammonium diffusivities and impacts on the lattice. The results show that diffusivities of ammonium at 800, 900 and 1000 ^oC are comparable to those of hydroxyl in feldspar, but much slower than structural molecular water. Importantly, ammonium in the M site of feldspar seems more stable than that in the layered site of phengite previously reported. Moreover, ammonium-bearing feldspar has smaller temperature-induced Raman mode wavenumber shifts and thermal expansion coefficients, as compared with ammonium-free feldspar.

The above results suggest interactions of ammonium and lattice of the silicate minerals at high temperatures. Thermal stabilities of ammonium depend on structure of the host silicates, and thermal stabilities of the host silicates are in turn affected by ammonium incorporated.

How to cite: Yang, Y.: Interactions of ammonium and lattice of feldspar at high temperatures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13827, https://doi.org/10.5194/egusphere-egu21-13827, 2021.

13:32–13:34

EGU21-13814

ECS

Topotaxial intergrowth and origin of antiperthite in monzogranite

Yueting Song and Shanrong Zhao

The crystallographic orientation of antiperthite (squared alkali feldspar inclusions grow inside plagioclase host) in Tiantangzai monzogranite from Dabie Mountain was investigated. The morphology of alkali feldspar inclusions is hexahedron, three pairs of parallel faces are controlled by the (010), (001) and (110) planes of the host plagioclase, respectively. Some plagioclase develops albite polysynthetic twin, defined the twinned individuals as Pl(1) and Pl(2), respectively; some alkali feldspar inclusions are related by Carlsbad twin, the twinned individuals are also defined as Kfs(1) and Kfs(2), respectively. Pl(1) is oriented similarly to Kfs(1). The topotaxial relationship between Pl(2) and Kfs(1) is similar to albite-twin. The topotaxial relationship between Kfs(2) and Pl(1) is similar to Carlsbad-twin. Kfs(2) and Pl(2) would form a topotaxial relationship similar to Carlsbad-albite-twin. Pl(1) generally becomes thinner or disappears in the regions where alkali feldspar inclusions developed. The development sequence of the alkali feldspar inclusions and the polysynthetic albite twin needs to be further investigated. Electron microprobe line scanning shows a homogeneous K, Ca and Na distribution in a single plagioclase grain with inclusions developed, suggesting that the origin of alkali feldspar inclusion may not be related to exsolution. The fractures in the host plagioclase are well developed, but most fractures do not pass through the embedded alkali feldspar. The precipitated alkali feldspar may be a result of alkali-bearing fluids penetrating through fractures and replacing plagioclase. The rim of some larger anhedral alkali feldspar inclusions has many voids, the local average misorientation map indicates there is a rectangular area with low misorientation difference inside the anhedral inclusions. The anhedral alkali feldspar inclusions are presumed to form by secondary replacement on top of the original rectangular inclusions.

How to cite: Song, Y. and Zhao, S.: Topotaxial intergrowth and origin of antiperthite in monzogranite, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13814, https://doi.org/10.5194/egusphere-egu21-13814, 2021.

13:34–13:36

EGU21-12665

Orientation relationships between magnetite micro-inclusions and plagioclase host

Olga Ageeva, Ge Bian, Gerlinde Habler, and Rainer Abart

Magnetite micro-inclusions in silicate minerals are important carriers of the remanent magnetization of rocks. Their shape orientation relationships (SOR) and crystallographic orientation relationships (COR) to the host crystal are of interest in the context of the bulk magnetic properties of the inclusion-host assemblage. We investigated the SOR and COR of magnetite (MT) micro-inclusions in plagioclase (PL) from oceanic gabbro using correlated optical microscopy, scanning electron microscopy, Electron backscatter diffraction analysis and Transmission electron microscopy.

In the mm-sized PL crystals of the investigated gabbros MT is present as equant, needle- and lath-shaped (sub)micrometer sized inclusions. More than 95% of the needle-shaped inclusions show SOR and specific COR to the plagioclase host. Most of the needles are elongated perpendicular to one of the MT{111} planes, which is aligned parallel to one of the (112), (1-12), (-312), (-3-12), (150), (1-50) or (100) planes of plagioclase. These inclusions are classified as “plane-normal type”. The needle elongation parallel to MT<111>, which is the easy direction of magnetization, ensures high magnetic susceptibility of these inclusions. The underlying formation mechanism is related to the parallel alignment of oxygen layers with similar lattice spacing across the MT-PL interfaces that are parallel to the elongation direction [1].

Apart from the SOR and the alignment of a MT{111} with one of the PL low index planes, the MT crystals rotate about the needle elongation direction. The rotation angles are statistically distributed with several maxima representing specific orientation relationships. In some cases one of the MT<001> axes is aligned with PL[14 10 7] or PL[-14 10 -7], which ensures that FeO₆octahedra of MT well fit into channels // [001] of PL, which are formed by six membered rings of SiO₄ and AlO₄ tetrahedra [2]. This COR is referred to as the “nucleation orientation” of magnetite with respect to PL. There are several other possibilities to fit FeO₆ octahedra into the [001] channels of PL, but the alignment stated above allows for the additional parallel alignment of one of the MT{111} with one of the above mentioned low index lattice planes of PL. MT crystals with one of these nucleation orientations can undergo directional growth to develop laths and needles. MT crystals with other nucleation orientations that do not allow for the parallel alignment of MT{111} with the above mentioned PL lattice planes, do not significantly grow and form the equant inclusions.

For some needles one or more of the MT{011} planes that are parallel to the needle elongation direction, are aligned with low-index planes of plagioclase such as PL (112), PL(150), PL(1-50) etc., and form MT facets. This situation corresponds to achievement of the best possible match between the two crystal lattices. This can either be generated during primary growth or during re-equilibration of the micro-inclusions and the plagioclase host.

Funding by RFBR project 18-55-14003 and Austrian Science fund (FWF): I 3998-N29 is acknowledged.

Reference

[1] Ageeva et al (2020) Contrib. Mineral. Petrol. 175(10), 1-16.

[2] Wenk et al (2011) Am. Min. 96, 1316-1324

How to cite: Ageeva, O., Bian, G., Habler, G., and Abart, R.: Orientation relationships between magnetite micro-inclusions and plagioclase host, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12665, https://doi.org/10.5194/egusphere-egu21-12665, 2021.

13:36–13:38

EGU21-10116

ECS

Using electron backscatter diffraction to determine the formation mechanism of mineral inclusions in garnet

Thomas Griffiths, Victoria Kohn, Rainer Abart, and Gerlinde Habler

Determining the origin of mineral inclusions is a key problem in petrology. Assuming different inclusion formation mechanisms can lead to dramatically different petrological interpretations. Crystallographic orientation relationships (CORs), systematic relationships between the crystallographic orientations of crystals sharing boundary segments, are sensitive to the mechanisms of inclusion formation. Electron backscatter diffraction (EBSD) in the scanning electron microscope yields highly spatially resolved information about host-inclusion CORs. EBSD point analyses allow collection of large COR datasets, while retaining a link to the location of every measured inclusion and any shape preferred orientation (SPO) relative to host crystallography and microstructures. Based on combined COR, SPO and location information, we can differentiate between multiple origin hypotheses where COR formation is predicted, and the large number of measurements achievable allows observation of the relative frequency of different CORs.

Acicular rutile inclusions in garnet with SPOs parallel to garnet crystal directions are often interpreted based on microstructures alone as products of exsolution, implying the existence of precursor Ti-bearing garnet. We studied rutile needles from metapegmatite garnets from two localities with separate geological histories. Rutile needles occur in zones that extend parallel to garnet {112} (both localities) and {110} (one locality) crystal planes. Needles are elongated parallel to <111> (both localities) and <100> (one locality) directions in the garnet hosts. The majority of needles show a “specific” (completely fixed) COR to the garnet host. Several different CORs can be found within a single garnet domain and the frequency of different CORs varies both between domains from the same locality and between localities. Despite the existence of several CORs, there is a systematic link between the rutile-garnet COR exhibited by a given needle inclusion and its elongation direction relative to the crystallography of both garnet and rutile.

A comparison with literature datasets of CORs from garnets with acicular rutile inclusions reveals that both the type and frequencies of rutile-garnet CORs found in metapegmatite garnets differ strongly from those found in garnets of purely metamorphic origin. CORs judged to result in a poor alignment between rutile and garnet structures are considerably more frequent in the metapegmatite samples.

In garnets from one locality, the SPO of rutile needles does not favour all crystallographically equivalent garnet <111> directions equally. Instead, needles are preferentially elongated parallel to garnet <111> directions at high angles to the garnet facets defined by inclusion zoning. SPO and COR of the rutile needles thus depend on the orientation of the growing garnet interface, which is incompatible with an exsolution origin for these inclusions. Oriented nucleation of rutile at the garnet interface and subsequent simultaneous growth of both phases can account for these observations.

These results show the power of combining spatially resolved COR data with SPO information. An exsolution origin for rutile needles cannot be proposed based on needle SPO alone, and specific CORs are not necessarily indicative of an exsolution origin for rutile needles even if they occur together with an SPO relative to the garnet host.

We acknowledge funding by the Austrian Science Fund (FWF): I4285-N37.

How to cite: Griffiths, T., Kohn, V., Abart, R., and Habler, G.: Using electron backscatter diffraction to determine the formation mechanism of mineral inclusions in garnet, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10116, https://doi.org/10.5194/egusphere-egu21-10116, 2021.

13:38–13:40

EGU21-5066

ECS

High-pressure crystal chemistry of four natural REE(As,P)O4 minerals from Mt. Cervandone, Italy

Francesco Pagliaro, Paolo Lotti, Alessandro Guastoni, Davide Comboni, G. Diego Gatta, Nicola Rotiroti, and Sula Milani

REE orthoarsenates and orthophosphates are common accessory minerals characterized by the general chemical formula REEXO₄, where REE represents one of the lanthanides (La-Lu series), Y, Sc, Ca or Th, whereas X stands for As, P or Si. In the framework of a long-term project on the high-T/high-P crystal-chemistry and phase-stability of REE-bearing minerals, the high-pressure behavior of chernovite-(Y) (nominally YAsO₄), xenotime-(Y) (nominally YPO₄) gasparite-(Ce) (nominally CeAsO₄) and monazite-(Ce) (nominally CePO₄), has been studied. Chernovite-(Y) and xenotime-(Y) show a HREE- (Gd-Lu series) and Y-enrichment, and the same tetragonal symmetry (space group I4₁/amd), whereas gasparite-(Ce) and monazite-(Ce) share the same LREE (La-Eu) enrichment and monoclinic cell (space group P2₁/n). All these minerals occur at Mt. Cervandone (Western Alps, Italy), a renowned Alpine REE-bearing mineral deposit. The crystal chemistry of the four minerals has been studied via EPM-WDS analysis. Excluding gasparite-(Ce), which formation is bound to the replacement of the mineral synchisite-(Ce) (CaCe(CO₃)₂F), a sensible enrichment in Gd and Ho is observed. Moreover, the majority of the chernovite-(Y) show a variable amount of ThO₂, up to 13 wt%, and phosphorous as substitute for arsenic in almost every proportion. In the case of the monoclinic series between monazite-(Ce) and gaparite-(Ce), no solid solution has been observed. Experiments at high-pressure were performed by in situ synchrotron X-ray diffraction using a diamond anvil cell. The high-pressure behavior of single crystals of xenotime-(Y), gasparite-(Ce) and monazite-(Ce) has been studied up to ~20 GPa, whereas that of chernovite-(Y) has been studied by powder diffraction up to 8.20(5) GPa. A II-order Birch-Murnaghan equation of state was fitted to the V-P data, within the phase stability field of the minerals, yielding the following bulk moduli: K_P0,T0 = 125(3) GPa (β_V₀= 0.0080(2) GPa^-1) for chernovite-(Y); K_P0,T0 = 145(2) GPa (β_V₀= 0.0069(1) GPa^-1) for xenotime-(Y); K_P0,T0 = 106.7(9) GPa (β_V₀= 0.0094(1) GPa^-1) for gasparite-(Ce), K_P0,T0 = 121(2) GPa (β_V₀= 0.0083(1) GPa^-1) for monazite-(Ce). K’ = ∂K_V/∂P = 4 (fixed) for all the minerals. Deformation mechanisms, at the atomic scale, were described on the basis of structure refinements.

Acknowledgments: This research was partly funded by the PRIN2017 project “Mineral reactivity, a key to understand large-scale processes” (2017L83S77).

How to cite: Pagliaro, F., Lotti, P., Guastoni, A., Comboni, D., Gatta, G. D., Rotiroti, N., and Milani, S.: High-pressure crystal chemistry of four natural REE(As,P)O4 minerals from Mt. Cervandone, Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5066, https://doi.org/10.5194/egusphere-egu21-5066, 2021.

13:40–13:42

EGU21-10129

Nano-sized particles and semimetal-rich melts in PGE-rich magmatic mineral systems

José María González-Jiménez, Joaquín A. Proenza, Fernando Gervilla, and Rubén Piña

The results of several high temperature experiments predict that nanoparticles and nanomelts enriched in noble metals indeed exist in magmatic systems. Nanoparticles of Ru-Os-Ir or P-bearing sulfides alloys have been synthetized from S-free or S-undersaturated basaltic silicate melts at > 1000 °C at > 1000 °C. Pt-rich arsenide nanoparticles have also been synthesized in high-temperature sulfide melts well before the melt had reached a Pt–As concentration at which discrete Pt arsenide minerals become stable phases. More recently, the immiscibility of PGE-rich bismuthide melts within Ni-Fe-Cu sulfide liquids have also observed in high-temperature experiments, evidencing the key role played by nanomelts in controlling the PGE partitioning in magmatic mineral systems and their necessary existence for the formation of PGE-rich nanoparticles. However, many researches still remain convinced that these nanoparticles represent artifacts produced during quenching of experimental runs. The combination of focused ion beam micro-sampling techniques with high-resolution transmission electron microscopy (HRTEM) observations allowed the identification of PGE nanoparticles and nanominerals in magmatic base-metal sulfides from the PGE-Cr deposits from the Bushveld Complex in South Africa and the eastern Cuban ophiolites. Moreover, nanometer sized of all six PGEs (Os, Ir, Rh, Ru, Pt, Pd) are relatively frequent natural quenched silicate melts preserved in mantle xenoliths. Collectively, all these observations made on natural rocks confirm the predictions of previous experiments on the possible formation of PGE mineral nanoparticles in magmatic systems rather to be result of low-temperature subsolidus re-equilibrium of magmatic minerals.

How to cite: González-Jiménez, J. M., Proenza, J. A., Gervilla, F., and Piña, R.: Nano-sized particles and semimetal-rich melts in PGE-rich magmatic mineral systems, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10129, https://doi.org/10.5194/egusphere-egu21-10129, 2021.

13:42–13:44

EGU21-10025

ECS

Evaluating the effects of deformation on the chemistry of composite magnesioferrite-magnetite crystals by means of EBSD

Igor González-Pérez, Samuel Noval-Ruiz, Jose María González-Jímenez, Fernando Gervilla, Isabel Fanlo, and Fernando Tornos

Chemical signatures of magnetite are commonly used to track the evolution of mineralizing systems in many geological settings. However, the impact of deformation processes on magnetite chemistry remains still underexplored. Here, we report a rare case of composite crystals consisting of magnetite and magnesioferrite recording different degrees and styles of deformation in order to evaluate how deformation promotes chemical modification. The samples employed in this study come from two different Mg-skarn iron deposits (i.e., El Robledal and San Manuel) from the Serranía de Ronda (SW Spain). Chemical data acquired by Electron Probe Microprobe Analyzer (EPMA) and Field Emission Scanning Microscopy (FESEM) are contrasted against microstructural data obtained by using Electron Back-Scattered Diffraction (EBSD). Our results show that magnesioferrite crystals [Fe²⁺# (Fe²⁺/Fe²⁺+Mg²⁺) = 0.22-0.46 and Fe³⁺# (Fe³⁺/Fe³⁺+Al³⁺) = 0.99-1.00] from El Robledal deposit are characterized by a ductile deformation that led to different crystallographic orientation domains along with the replacement of magnesioferrite by magnetite (Fe²⁺# (Fe²⁺/Fe²⁺+Mg²⁺) = 0.51-0.99 and Fe³⁺ (Fe³⁺/Fe³⁺+Al³⁺) =0.98-1.00] via coupled dissolution – reprecipitation. A replacement of magnesioferrite [Fe²⁺# (Fe²⁺/Fe²⁺+Mg²⁺) = 0.43-0.64 and Fe³⁺ (Fe³⁺/Fe³⁺+Al³⁺) = 0.99-1.00] by magnetite Fe²⁺# (Fe²⁺/Fe²⁺+Mg²⁺) = 0.78-1.00 and Fe³⁺# (Fe³⁺/Fe³⁺+Al³⁺) = 0.98-1.00] via a coupled dissolution – reprecipitation mechanism is also preserved in the composite (i.e., zoned) crystals from the San Manuel deposit, which was additionally overprinted by an additional recrystallization event as a result of grain boundary migration recrystallization. Our results show that deformation in a fluid-assisted deformation regime has induced chemical modification of the original magnesioferrite aggregates as well as strain localization. This close physicochemical link offers new avenues of interpreting the chemical signatures of Mg-Fe oxides, utilizing their microstructurally controlled variation or lack thereof.

How to cite: González-Pérez, I., Noval-Ruiz, S., González-Jímenez, J. M., Gervilla, F., Fanlo, I., and Tornos, F.: Evaluating the effects of deformation on the chemistry of composite magnesioferrite-magnetite crystals by means of EBSD, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10025, https://doi.org/10.5194/egusphere-egu21-10025, 2021.

13:44–13:46

EGU21-61

ECS

Mechanisms of bastnasite formation: replacement of calcite by rare earth carbonates.

Adrienn Maria Szucs, Alexandra Stavropoulou, Claire O'Donnell, Seana Davis, and Juan Diego Rodriguez-Blanco

The interaction of rare earth bearing (La, Nd, Dy) aqueous solutions with calcite crystals at was studied at ambient and hydrothermal conditions (25-220 °C) and resulted in the solvent-mediated surface precipitation and subsequent pseudomorphic mineral replacement of calcite by rare earth carbonates. Calcite grains were replaced from their periphery inwards, and the newly formed REE-bearing carbonates follow the crystallisation sequence lanthanite [REE₂(CO₃)₃·8H₂O] → kozoite [orthorhombic REECO₃(OH)] → hydroxylbastnasite [hexagonal REECO₃(OH)]. The specific rare earth involved in these processes and the temperature have a significant role in the polymorph selection, crystallisation pathways and kinetics of mineral replacement. La- and Nd-bearing kozoite, grows oriented onto the calcite surface, forming an epitaxy, due to their structural similarities. This phase forms elongated crystals on [100], with the {011} and {0-11} as major forms. The epitaxial relationship is (104) [010]_cc║(001) [100]_koz and is strongly dependent on the ionic radius of the rare earth in the structure of kozoite. These results have strong implications for the understanding of mineralisation reactions occurring in REE-bearing carbonatite deposits, the most important resources of rare earths in the world.

How to cite: Szucs, A. M., Stavropoulou, A., O'Donnell, C., Davis, S., and Rodriguez-Blanco, J. D.: Mechanisms of bastnasite formation: replacement of calcite by rare earth carbonates., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-61, https://doi.org/10.5194/egusphere-egu21-61, 2021.

13:46–13:48

EGU21-11559

ECS

Tourmalinisation in peraluminous granitic context : from experiment to thermodynamic modelling

Julien Fort, Stanislas Sizaret, Michel Pichavant, Arnault Lassin, Johann Tuduri, and Olivier Blein

Tourmaline records the physico chemical conditions during its cristallisation, as its primary chemical zonations are generally unbalanced, its occurrence as alteration product could be used to decipher the physicochemical properties of mineralizing fluids. However, the role of the tourmalinisation in hydrothermal processes remains little studied, if not poorly understood. The complexity of its thermodynamic properties is related to the presence of four cationic sites allowing the accommodation of a wide variety of elements (Henry and Dutrow, 2018). Moreover the phenomena of deprotonation, Si-^IVB and valence state, make the approach of solid solution properties complex (Hughes et al., 2001; Henry et al., 2011; Bačík, 2015; Morgan, 2016). Thus, thermodynamic properties are most often estimated (Garofalo et al., 2000; Hinsberg and Schumacher, 2007) and only a few measurements could be carried out on a reduced number of near-endmembers crystals (Kuyunko et al., 1984; Ogorodova et al., 2012).

This study aims to investigate experimentally the stability field of schorl (Na-Fe) – dravite (Na-Mg) solid solution at 2 kbar total pressure between 400° and 600°C as a function of the boron content of the fluid and fO2 condition, using an internally heated gas apparatus. Those metasomatic experiments have been conducted on a mixture of naturals crystals of cordierite + albite, representing a peraluminous granite composition in a Na-Mg-Fe-Al-Si-B-O-H system, characterized by a high-Mg, low-Fe content. These experiments were performed in order to simulate a classic aluminous host of these tourmaline alterations in granitic context. The results will be studied, in terms of stability of the tourmaline species, chemistry variation and texture. They will be compared with thermodynamic models build using data from the literature (Korges et al., 2018; Pan et al., 2019 among others) . Ultimately, the objective is to characterize in a P, T, W/R space, the chemical evolution of fluids, the alteration sequence of rocks and the variations in volumes related to the successive reactions.

How to cite: Fort, J., Sizaret, S., Pichavant, M., Lassin, A., Tuduri, J., and Blein, O.: Tourmalinisation in peraluminous granitic context : from experiment to thermodynamic modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11559, https://doi.org/10.5194/egusphere-egu21-11559, 2021.

13:48–13:50

EGU21-16170

Multi-Element Correlation Analysis of Cu-bearing Tourmaline using LA-ICP-Time-Of-Flight-MS

Hao A.O. Wang, Michael S. Krzemnicki, Susanne Büche, Sarah Degen, Leander Franz, and Rainer Schultz-Guttler

Major, minor and trace element analysis using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has been applied to a broad range of mineral samples for characterization, mineral resources prospection, tracing and provenance determination, radiometric dating and studies on mineral formation conditions. In this study, we present a state-of-the-art LA-ICP-Time-Of-Flight-MS (LA-ICP-TOF-MS) technique for multi-element analysis of gem-quality Cu-bearing tourmaline from Brazil, Mozambique and Nigeria, with a special focus on elemental correlation among and within various provenances.

A TOF-MS obtains a full mass spectrum from ⁷Li⁺ to ²³⁸U⁺ simultaneously with an improved mass resolving power. These advantages over other conventional ICP-MS setups allow the TOF users to apply a novel concept of “first measure, then determine” which elements are of interest for the analysis of geological samples. Since the TOF-MS technique requires no/limited a priori knowledge about the sample before measurement, this technique can be beneficial for studying elements which occur infrequently in the minerals and for analysing full elemental composition in unidentified inclusions.

Multi-element composition of more than 400 Cu-bearing tourmaline samples (majority elbaite, Na-rich) was analysed using LA-ICP-TOF-MS that cover various colors, qualities and provenances available in the gem and jewellery trade. In order to investigate the elemental correlation, a non-linear unsupervised dimension reduction was performed on the high dimensional multi-element dataset using t-distributed stochastic neighbor embedding (t-SNE) algorithm. An unsupervised calculation works solely with the elemental concentrations and without labels of data points, for example color or provenance. The clusters in the geochemical data visualization indicates elemental similarity of various samples. We found that t-SNE algorithm is better than principle component analysis (PCA) algorithm in maintaining intrinsic elemental correlation from the original high dimensional space and embedding such information onto low dimensional datasets for visualization. Therefore, the t-SNE method excels in distinguishing within-group elemental similarities from between-group similarities. The separation of subgroups achieved with t-SNE is in agreement with the confirmed geographic provenances.

Additionally, a unique type of Cu-bearing liddicoatite (Ca and REE-rich) was recently discovered near Maraca in Mozambique (Nampula area). Since they have been reported so far only from this occurrence, this type of tourmaline is especially interesting to study how elements correlated during tourmaline formation. Applying t-SNE calculation on these samples, we have found two groups (or four subgroups) of these tourmaline samples. When multi-element concentration was plotted, it can be seen that light-REEs (La to Nd) have an apparent correlation with Ca concentration, however a negative correlation was observed between mid-REEs (Sm to Ho) and Ca. A correlation of Na to Bi and Th was also observed.

In a rare four-color (pink, purple, blue, green) Cu-bearing tourmaline sample from Quintos mine in the state of Rio Grande do Norte, Brazil, multi-element analysis was conducted along a profile across the entire color variation, from the core of the crystal (pink) to the rim of the crystal (green) to monitor elemental variations and correlations throughout the crystal growth process of this tourmaline within the pegmatite.

How to cite: Wang, H. A. O., Krzemnicki, M. S., Büche, S., Degen, S., Franz, L., and Schultz-Guttler, R.: Multi-Element Correlation Analysis of Cu-bearing Tourmaline using LA-ICP-Time-Of-Flight-MS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16170, https://doi.org/10.5194/egusphere-egu21-16170, 2021.

13:50–13:52

EGU21-16379

ECS

Magnetite (U-Th-Sm)/He dating: analytical challenges and application

Marianna Corre, Martine Lanson, Arnaud Agranier, Stephane Schwartz, Fabrice Brunet, Cécile Gautheron, and Rosella Pinna

Magnetite (U-Th-Sm)/He dating method has a strong geodynamic significance, since it provides geochronological constraints on serpentinization episodes, which are associated to important geological processes such as ophiolite obductions, subduction zones, transform faults and fluid circulations. Although helium content that range from 0.1 pmol/g to 20 pmol/g can routinely be measured, the application of this dating technique however is still limited due to major analytical obstacles. The dissolution of a single magnetite crystal and the measurement of the U, Th and Sm present at the ppb level in the corresponding solution, remains highly challenging, especially because of the absence of magnetite standard. In order to overcome these analytical issues, two strategies have been followed, and tested on magnetite from high-pressure rocks from the Western Alps (Schwartz et al., 2020). Firstly, we purified U, Th and Sm (removing Fe and other major elements) using ion exchange columns in order to analyze samples, using smaller dilution. Secondly, we performed in-situ analyzes by laser-ablation-ICPMS. Since no solid magnetite certified standard is yet available, we synthetized our own by precipitating magnetite nanocrystals. The first quantitative results obtained by LA-ICP-MS using this synthetic material along with international glass standards, are promising. The laser-ablation technique overcomes the analytical difficulties related to sample dissolution and purification. It thus opens the path to the dating of magnetite (and also spinels) in various ultramafic rocks such as mantle xenoliths or serpentinized peridotites in ophiolites.

Schwartz S., Gautheron C., Ketcham R.A., Brunet F., Corre M., Agranier A., Pinna-Jamme R., Haurine F., Monvoin G., Riel N., 2020, Unraveling the exhumation history of high-press ure ophiolites using magnetite (U-Th-Sm)/He thermochronometry. Earth and Planetary Science Letters 543 (2020) 116359.

How to cite: Corre, M., Lanson, M., Agranier, A., Schwartz, S., Brunet, F., Gautheron, C., and Pinna, R.: Magnetite (U-Th-Sm)/He dating: analytical challenges and application, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16379, https://doi.org/10.5194/egusphere-egu21-16379, 2021.

13:52–13:54

EGU21-820

ECS

Stability relations of monazite-(Ce), gadolinite-(Ce), gadolinite-(Y), britholite-(Ce) and bastnäsite-(Ce) during late- to post-magmatic processes in nepheline syenite (Čistá pluton, Czech Republic)

Maciej Jaranowski, Bartosz Budzyń, Gabriela A. Kozub-Budzyń, Jiří Sláma, and Josef Klomínský

Stability relations of the REE-bearing accessory phases and alteration processes in the cancrinite-bearing nepheline syenite from the Čistá pluton (the center of the upper-crustal Tepla–Barrandian unit, Bohemian Massif, Czech Republic) were studied. Observations of rock microtextures, quantitative analyses of minerals and compositional X-ray mapping were performed using electron probe microanalysis (EPMA). The primary REE-bearing accessory minerals assemblage includes monazite-(Ce) associated with gadolinite-group minerals (i.e. gadolinite-(Ce) and gadolinite-(Y)), which were partially replaced by britholite-(Ce), bastnäsite-(Ce), aggregates of fine-grained REE-bearing phases (possibly fluorapatite and/or britholite-(Ce)) and, rarely, cerianite. K-feldspar and albite form intergrowths or symplectites with REE-phases in the investigated reaction microtextures. Furthermore, the zircon crystals demonstrate oscillatory zoning and/or extensive patchy zoning due to alteration processes. The alteration of accessory minerals are interpreted as driven by K- and Na-bearing alkali fluids with high CO₂ activity during late- to post-magmatic processes.

Acknowledgements: This work was supported by the National Science Centre research grant no. 2017/27/B/ST10/00813.

How to cite: Jaranowski, M., Budzyń, B., Kozub-Budzyń, G. A., Sláma, J., and Klomínský, J.: Stability relations of monazite-(Ce), gadolinite-(Ce), gadolinite-(Y), britholite-(Ce) and bastnäsite-(Ce) during late- to post-magmatic processes in nepheline syenite (Čistá pluton, Czech Republic), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-820, https://doi.org/10.5194/egusphere-egu21-820, 2021.

13:54–13:56

EGU21-9966

Role of P-T conditions and bulk rock composition in the mineralogical variations in millimeter scale: a study from South Maharashtra Shear Zone, western India

Pallavi Praharaj and Sukumari Rekha

The pressure-temperature conditions are transient in time and space during tectonic processes. To understand the complete P-T history of crustal domains examining the mineral paragenetic sequences and zoning profiles of minerals from diverse lithologies in the domain is necessary. But in highly tectonised crustal domains establishing time equivalence between far-spaced samples is difficult. To overcome this, a mylonite sample with closely spaced layers of different mineralogy collected from the South Maharashtra Shear Zone located along the north of Western Dharwar Craton (Rekha and Bhattacharya, 2014) was studied. The mylonite has four mineralogically distinct layers of few millimeters width containing garnet porphyroblasts of distinct zoning pattern separated by quartz layers. Layer-1 has two domains on the basis of the relative abundance of quartz; Layer-1A with more quartz and less flaky minerals and Layer-1B with less quartz and more flaky minerals. Layer-1A is composed of quartz>biotite>plagioclase>chlorite>K-feldspar with syn- to post-tectonic garnet porphyroblasts and the fabric is defined by shape preferred biotite-chlorite aggregates, recrystallized plagioclase and quartz ribbons.Layer-1B is relatively quartz poor and plagioclase>biotite>chlorite>K-feldspar aggregates rich domain as compared to L1A with biotite-chlorite aggregates and recrystallized plagioclase defined fabric.Prehnite elongated parallel to schistosity present but not very common. Layer-2 is very thin with amphibole-biotite±chlorite defined foliation and consists of plagioclase-K-feldspar-quartz with large garnet porphyroblast ofsyn to post-tectonic origin. Chlorites are mainly present near to garnet. Layer-3 is composed of biotite-calcite-plagioclase-chlorite-quartz with syn/post-tectonic garnet porphyroblast and the foliation is defined by biotite-chlorite aggregates, recrystallize plagioclase, calcite grains aligned parallel to the foliation and elongated quartz grains.Layer-3 is separated from the quartz layers on both sides by the formation of thin hornblende layers arranged parallel to the foliation. Very few hornblende grains found within the layer aligned parallel with the fabric defining minerals. Large pre-tectonic muscovite grains are preserved in Layer-3 and are altered to epidote along the margins of the grain. Layer-4 consists of hornblende, calcite, quartz with few plagioclase, K-feldspar and post tectonic garnet porphyroblast. The fabric is defined by the long axis of amphibole and calcite grains aligned parallel to it. Later biotite-prehnite grains formed at high angle to the fabric defining minerals. Conventional geothermobarometers were used for P-T estimation and it varies from 450-560°C and 6 kbar for Layer-1A, 445-550°C and 7 kbar for Layer-1B, 475-570°C and 6 kbar for Layer-2, 450-575°C and 7-8 kbar for Layer-3 and 450-5500°C and 7-9 kbar for Layer-4 at reference temperature of 500°C and pressure of 6kbar. Though different layers have distinctly different mineral assemblages there is hardly any variation in the P-T conditions which implies the original bulk rock composition was different for different layers not the P-T conditions of deformation.

Keywords: Mylonite, Western Dharwar Craton, Geothermobarometry

How to cite: Praharaj, P. and Rekha, S.: Role of P-T conditions and bulk rock composition in the mineralogical variations in millimeter scale: a study from South Maharashtra Shear Zone, western India, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9966, https://doi.org/10.5194/egusphere-egu21-9966, 2021.

13:56–13:58

EGU21-4392

ECS

Monitoring mineral precipitation sequence of Lake Magadi soda lake: A multi-technical approach

Melese Getenet, Juan Manuel García-Ruiz, Franziska Emmerling, Dominik Al-Sabbagh, Fermín Otálora, and Cristóbal Verdugo-Escamilla

Lake Magadi is a saline soda lake in East African Rift Valley, occupying the axial trough of Southern Kenyan Rift. Its fed by perennial saline hot/warm springs, which evolve into the soda and saline chemistry of the lake. The main processes thought to cause the enrichment of the lake in Na⁺, CO₃^2-, Cl^-, HCO₃^- and SO₄^2- are evaporative concentration, mineral precipitation and fractional dissolution [1]. Lake Magadi is considered an analogous environment to the early Earth [2]. The high pH, silica and carbonate content of Lake Magadi allows the formation of silica and carbonate induced self-assembled mineral structures [3,4]. Revealing the mineral precipitation sequence of Lake Magadi have implications in understanding the geochemistry of evaporative rift settings and soda oceans. We have experimentally investigated the mineral precipitation sequence during evaporation at 25 °C. The sequence of mineral precipitation was recorded by using in-situ video microscopy. The mineral patterns observed in video microscopies were identified by spectroscopic, diffraction and electron microscopy techniques. The mineralogy and elemental composition of the precipitates were determined by using Raman spectroscopy, powder X-ray diffractions and scanning electron microscopy coupled with energy dispersive X-ray analyser. The results of the ex-situ analyses were compared with the in-situ X-ray diffraction. In-situ X-ray diffractions were performed on acoustically levitated droplets in the μSpot beamline at BESSY II synchrotron (Berlin, Germany). Finally, thermodynamic evaporation simulation was performed by using PHREEQC code with Pitzer database. Ex-situ and in-situ experiments revealed that mineral precipitation begins with trona, followed by halite and finally thermonatrite. In PHREEQC simulations, natron was observed instead of thermonatrite, suggesting the role of kinetics in the mineral assemblages. This multi-technical approach of in-situ monitoring and ex-situ characterization is a powerful approach to unveil mineral precipitation patterns and the resulting geochemical evolution in evaporative rift settings.

Acknowledgments: We acknowledge funding from the European Research Council under grant agreement no. 340863, from the Ministerio de Economía y Competitividad of Spain through the project CGL2016-78971-P and Junta de Andalucía for financing the project P18-FR-5008. M.G. acknowledges Grant No. BES-2017-081105 of the Ministerio de Ciencia, Innovacion y Universidades of the Spanish government.

References:

[1] Eugster, H.P. (1970). Chemistry and origin of the brines of Lake Magadi, Kenya. Mineralogical Society of America Special Papers, 3, 213–235.

[2] Kempe, S.; Degens, E.T. (1985). An early soda ocean?. Chem. Geol. 53, 95–108

[3] Getenet, M.; García-Ruiz, J.M.; Verdugo-Escamilla, C.; Guerra-Tschuschke, I (2020). Mineral Vesicles and Chemical Gardens from Carbonate-Rich Alkaline Brines of Lake Magadi, Kenya, Crystals, 10, 467.

[4] García-Ruiz J.M., van Zuilen M.A., Bach W. (2020) Mineral self-organization on a lifeless planet. Phys Life Rev, 34–35,62–82

How to cite: Getenet, M., García-Ruiz, J. M., Emmerling, F., Al-Sabbagh, D., Otálora, F., and Verdugo-Escamilla, C.: Monitoring mineral precipitation sequence of Lake Magadi soda lake: A multi-technical approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4392, https://doi.org/10.5194/egusphere-egu21-4392, 2021.

13:58–14:00

EGU21-12619

Comparison of Microporous Minerals for Potential Contaminant Uptake

Marvin Osorio, Christopher Oze, and Aaron Celestian

14:00–14:02

EGU21-870

ECS

Reach of pollution and sediment correlation with the tailings in Šibenik Bay (Croatia)

Laura Huljek, Hana Fajković, and Željko Kwokal

To determine the influence of the historic factory of electrodes and ferroalloys on the Šibenik bay sediments, XRPD analysis were carried out. The factory was established in the city of Šibenik, on the coast of the Krka River estuary, and produced calcium carbide, and later electrodes and ferroalloys. It was active from 1900 until 1995 [1]. During that time, a large amount of produced tailings were stored nearby and on the shore of the estuary. Due to the presence of the strong winds (bora and sirocco), which can reach up to 130 km/h, the tailings material could be transported to long distances [2].

Samples of tailing were collected at the location of the former factory, which is a tailing hill today, samples of dust were collected from the rooftop of the factory in the 1980s. Other samples were taken on a 1 km distant beach in the Šibenik bay (Beach A) and a 19 km distant beach on the island in the outer Šibenik archipelago (Beach B). Both beaches are located south-west of the factory. The samples from the beaches were taken with a corer at different depths: 0 – 3 cm, 3 – 5 cm, around 5 cm. The sample from 3 – 5 cm depth was not analysed.

Bulk sample and a fraction <63 µm were analysed on X-Ray Diffractometer. The XRPD analysis of the sediments from Beach B in the outer Šibenik archipelago shows that calcite and quartz are the most abundant phases. This mineral composition shows that distant islands were not affected by aeolian transportation of the factory dust and tailing. In the bulk samples from Beach A, in the uppermost part (0 – 3 cm depth) mineral components are calcite, aragonite, calcium manganite, bustamite ferroan and carbon, while calcite, quartz, aragonite, calcium manganite and manganosite are present in the fraction <63 µm. The sample from the depth of 5 cm at the same beach, shows calcite, aragonite and Mn-oxide, while fraction <63 µm lacks in Mn-oxide.

A bulk sample of tailings shows mineral components: calcite, quartz, calcium manganite, bustamite ferroan and gypsum which corresponds to the previous research [3], and there is also manganese silicon, manganese silicide, carbon and amorphous phase [4]. A fraction <63 µm of the tailing, shows the following mineral phases: calcite, quartz, calcium manganite and bustamite ferroan, as presented in previous research [3]. Analysis of the rooftop dust shows three phases: carbon, bustamite ferroan and manganosite, which does not correspond to the data given from the factory [3].

From the presented results, it could be concluded that the historic factory influenced sediments in the Šibenik bay, however, its influence was not detected on the Beach B 19 km to the SW, which opens the question of reach and distance to which tailings can be transported by sea and/or wind.

This work has been supported in part (samples collection) by Croatian Science Foundation under the project lP-2019-04-5832.

How to cite: Huljek, L., Fajković, H., and Kwokal, Ž.: Reach of pollution and sediment correlation with the tailings in Šibenik Bay (Croatia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-870, https://doi.org/10.5194/egusphere-egu21-870, 2021.

14:02–14:04

EGU21-7462

ECS

Minerals of Bolshoi Semiachik geothermal fields (Central Kamchatka, Russia)

Elena Zhitova, Rezeda Ismagilova, Anastasia Sergeeva, Maria Nazarova, Anton Nuzhdaev, Ruslan Kuznetsov, Ilya Bolshakov, and Daria Bukhanova

The volcanic complex Bolshoi Semiachik is characterized by intensive hydrothermal activity which is expressed by presence of thermal fields with gas-steam jets (T up to ~ 140 ºC), boiling pots (T up to ~ 100 ºC), warm lakes (T up to ~ 90 ºC) and ground (T up to ~ 97 ºC) . The circulating hydrothermal solution is rich in ammonium, sulfate and locally in carbonate. To date, little is known about surface mineralogy that occurs at the geothermal fields of the volcanic complex Bolshoi Semiachik. The major geological expeditions were carried out there in the 1960`s, and there was also some additional research carried out in the 1980`s. The study of minerals occurring at the surface of geothermal fields is relevant for planetary science since similar minerals are suggested for Mars and Europa (Jupiter moon) and geochemistry since such environments of mineral formation are very specific.

In the summer 2020 the expedition of the Institute of volcanology and seismology has been organized in order to monitor thermal fields and to conduct mineral and water samples for study. Here we report the first data on mineral identification of processed samples (at about 50). At that moment, minerals have been identified by powder X-ray diffraction and electron-microprobe analyses.

The surface of Bolshoi Semiachik geothermal fields is covered by clay minerals with montmorillonite that is rich in disseminated pyrite being the most abundant. Among salt minerals the common phases are sulfates: halotrichite-, copiapite and voltaite-group minerals, alunogen, gypsum and native sulphur. The SiO₂ polymorphs: tridymite, cristobalite are also found at the geothermal field surface. In the zone called Central Crater chalcantite has been found in association with rhomboclase and tridymite. Some samples with zeolite-group mineral - laumontite were also found, which at the moment is identified less reliably. The central (high temperature) part of deposits around steam-gas jet is composed of dickite in association with sulphur and quartz covered by alunogen and halotrichite efflorescent. The rim (at about 1 meter from the center) is composed of smectites, marcasite and natroalunite. This zonation is likely caused by pH which is lower at the central part where the steam unloads and increases at the peripheral area around the steam-gas jet.

Acknowledgment. The study has been supported by RFBR project # 20-35-70008. We are grateful to Volcanoes of Kamchatka for letting us to conduct the field works at Bolshoi Semiachik thermal fields. Experimental works on mineral identification have been carried out using Analytical Centre of IViS and Research Park of SPbU.

How to cite: Zhitova, E., Ismagilova, R., Sergeeva, A., Nazarova, M., Nuzhdaev, A., Kuznetsov, R., Bolshakov, I., and Bukhanova, D.: Minerals of Bolshoi Semiachik geothermal fields (Central Kamchatka, Russia), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7462, https://doi.org/10.5194/egusphere-egu21-7462, 2021.

14:04–14:06

EGU21-14392

ECS

Ca, Cu and Pb solubilization and biomineralization by microorganisms: case study from Kamchatka, Russia

Irina Chernyshova, Oleg Vereshchagin, Zelenskaya Marina, Himelbrant Dmitry, Vlasov Dmitry, and Frank-Kamenetskaya Olga

The role of microorganisms (lichens, micromycetes and bacteria) in the formation of biominerals is widely known (Purvis, 2008; Vlasov et al., 2020). In the fall of 2019, we organized an expedition to the area of Tolbachik volcano (cones 1, 2, 3 and Mount 1004), Kamchatka, Russia, and collected 120 samples of volcanic rocks with biofilms. The volcanic cones of Tolbachik concentrate a wide variety of elements and are a type-locality of more than 300 minerals (Vergasova and Filatov, 2012; Siidra et al., 2017; Pekov et al., 2018). Lichen species are widespread in the volcanic fields of Kamchatka, Russia (Kukwa et al., 2014). The goal of this work was to search for and study biominerals associated with lichens.

As a result of our research, calcium oxalates (whewellite and weddellite) and copper oxalates (moolooite) associated with lichens were found. Whewellite was found in the lichens Psylolechia leprosa and Sarcogyne hypophaea. Whewellite and weddellite were found together in the lichen Rinodina gennarii. Pyroxene (diopside) and plagioclase (anorthite) sourced calcium for the oxalates formation. Whewellite accumulates in apothecia in the form of whitish masses, consisting of lamellar crystals of 5-6 microns in size and their stacked intergrowths. Weddellite forms bipyramidal crystals of 2-10 microns in size. Moolooite was found in lichens Acarospora squamulosa and Lecanora polytropa (together with whewellite). The source of copper is tenorite, atacamite and copper-rich silicates (products of basalt processing by fumaroles). Moolooite forms lamellar crystals and intergrowths up to 5-6 microns in size. An interesting feature of oxalate formations in the Lecanora polytropa lichen is a high lead content, which has never been previously recorded in natural oxalates. Linarite and pyromorphite are most likely the source of lead. Chemical analysis showed that "nests" of calcium oxalates can contain up to 6 wt% PbO, while "nests" of copper oxalate - no more than 1 wt% PbO. The results obtained indicate the possibility selective sorption of lead and suggest the possibility of replacing calcium with lead in the oxalates. The studies of the location forms of lead in biofilms are in progress. The exact form of lead has not yet been established. Linarite and pyromorphite are most likely the source of lead. This research was supported by Russian Science Foundation grant (19-17-00141) and performed at the resource centers of St. Petersburg State University (MM, XRD, Geomodel).

Fedotov S.A. (ed.). Great fissure Tolbachik eruption (1975-1976, Kamchatka) // Moscow: Nauka. 1984. 637 p.

Kukwa M. et al. // The Lichenologist. 2014. 46. 1. P. 129–131.

Pekov I.V. et al. // Acta Cryst. 2018. B74. P. 502–518.

Purvis O.W. et al. // Mineralogical Magazine. 2008. 72. 2. P. 607–616.

Siidra O.I. et al. // European Journal of Mineralogy. 2017. 29. 3. P. 499–510.

Vergasova L.P. and Filatov S.K. // Volcanology and Seismology. 2012. 5. P. 3–12.

Vlasov D.Yu. et al. In: Aspergillus niger: pathogenicity, cultivation and uses, Nova Science Publishers, New York. 2020. P. 2-121.

How to cite: Chernyshova, I., Vereshchagin, O., Marina, Z., Dmitry, H., Dmitry, V., and Olga, F.-K.: Ca, Cu and Pb solubilization and biomineralization by microorganisms: case study from Kamchatka, Russia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14392, https://doi.org/10.5194/egusphere-egu21-14392, 2021.

14:06–14:08

EGU21-6901

ECS

Influence of temperature on the hydrothermal clay soils' shear strength of the Nizhne-Koshelevsky and Verkhne-Pauzhetsky thermal fields.

Ruslan Kuznetsov, Mikhail Chernov, Victoria Krupskaya, and Ruslan Khamidov

Nizhne-Koshelevskoe and Verkhne-Pauzhetskoe thermal fields are located in the south of Kamchatka, the first - within the Koshelevsky volcanic massif, the second - on the territory of the Pauzhetsky geothermal field. The first horizon from the surface in these fields is formed by clayey soils, that have been formed as a result of hydrothermal alteration of volcanic rocks. And in the natural conditions clayey soils are at temperatures reaching 100 °C.

Samples of undisturbed clay soils were taken within the thermal fields. The samples are characterized by a density of 1.29 - 1.42 g/cm³, rather high values of the weight moisture (90-110%), and temperatures of 50 - 70 °C.

The samples are dominated by clay minerals: kaolinite and mixed-layer - kaolinite-smectite, their content is about 75%. The other 25% are microcline, cristobalite, anatase, gypsum, pyrite, marcasite, quartz and alunite.

For samples of undisturbed clay soils, direct shear tests were carried out at a temperature of 20 °C and at a temperatures of the samples close to their natural temperatures (50–70 °C). Thus, the values of cohesion and the angle of internal friction of the samples were determined.

The obtained results can be interfered as follows: as a result of an increase in the temperature of clayey soils, the thickness of electric double layer on the surface of clay particles decreases. On the one hand, it leads to a decrease of cohesion value between the clay particles and the beginning of shear deformations at lower vertical loads. On the other hand, a smaller thickness of electric double layer brings particles closer to each other, which is the reason for an increasing angle of internal friction and shear resistance at higher vertical loads.

How to cite: Kuznetsov, R., Chernov, M., Krupskaya, V., and Khamidov, R.: Influence of temperature on the hydrothermal clay soils' shear strength of the Nizhne-Koshelevsky and Verkhne-Pauzhetsky thermal fields., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6901, https://doi.org/10.5194/egusphere-egu21-6901, 2021.

14:08–14:10

EGU21-5432

ECS

Awaruite (Ni3Fe) as a platinum-group elements concentrator: Preliminary data

Anton Kutyrev

The most famous of natural occurring iron-nickel alloys are kamacite, taenite and tetrataenite, forming iron meteorites. Normally, they have significant platinum-group elements (PGE) content being a result of high siderophile behaviour of the latter. In spite of native iron and nickel having been described in terrestrial rocks, the most abundant Fe-Ni mineral in Earth’s crust is awaruite (Ni₃Fe). Current work represents the preliminary results of testing the ability of awaruite to concentrate PGE.

Awaruite is a widespread accessory mineral of ultramafic complexes. Its formation is usually assessed to the serpentinization of olivine which produces reductive fluid. The latter reacts with nickel sulfides and produces awaruite. Several reports of awaruite occurring together with platinum-group minerals (PGM) are present in the literature. In the Ural-Alaskan type complexes of Koryak Highlands (Far East Russia), such cases are abundant. Textural investigations of such complexes discovered a diverse array of serpentine–related mineralization, including isoferroplatinum in chlorite matrix, isoferroplatinum–amphibole intergrowths, and a wide range of PGE, Fe and Cu alloys formed in serpentine veinlets together with awaruite and base metal sulfides. This provides evidence of the relation between awaruite and platinum mineralization.

LA-ICP-MS has been used to reveal the PGE content in awaruite and coexisting sulfides. Grains from the placers related to the Galmoenan complex of Ural-Alaskan type were used for this study. The analysis revealed that sulfides may bear significant PGE admixture. Unexpectedly, the most abundant impurity is Os. Its content varies from 0.7 to 538 ppm. The shape of the time-resolved spectra of some samples indicates the possible presence of solid inclusions which concentrate Os. However, most of them, including those with 538 ppm Os, exhibit plain time-resolved spectra suggesting homogeneous Os distribution. Contents of other PGE are moderate: up to 8.3 ppm Pt, 1.4 ppm Pd, 4.3 ppm Ru, 0.25 ppm Rh and 2.6 ppm Ir.

Some awaruite grains also show relatively high Os content (up to 89 ppm), but time-resolved spectra of them exhibit clear evidence of mineral inclusions presence. In one case, Os spike coincides with the S spike, suggesting that Os is incorporated into the sulfide phase. In the case of spikeless spectra, Os content is always below the detection limit (b.d.l.). Rhodium content also is always b.d.l., while Ru content reaches 0.44 ppm, Ir – 0.08 ppm, and Pt – 0.03 ppm. The only element explicitly showing significant and homogenous presence in the awaruite is Pd, that content reaches 5.8 ppm in one analysis and 0.2–1.1 in many others.

These data indicate that in the studied case, awaruite mineralization is accompanied by the formation of PGM, while its role as a direct PGE concentrator is moderate and restricted to the first tenths ppm of Ru and Pd. Sulfides have shown much more impressive ability in concentrating PGE. Their selective enrichment in Os is a novelty and demands explanation.

Author thanks Evgeniy Sidorov and Dima Kamenetsky for the assistance. CODES of UTAS is greatly acknowledged for the LA-ICP-MS analyses. This work was supported by the Russian Foundation for Basic Research (RFBR) grant No 20-05-00290 A.

How to cite: Kutyrev, A.: Awaruite (Ni3Fe) as a platinum-group elements concentrator: Preliminary data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5432, https://doi.org/10.5194/egusphere-egu21-5432, 2021.

14:10–14:12

EGU21-160

ECS

Geochemical specialization of geological complexes in the northern part of the Kamchatka Peninsula

Liubov Kononova, Marina Ladygina, and Angelina Maltseva

The study area (4350 km²; 58°00'-58°40'N 161°00'-162°00'E) is located within the Kamchatka-Olyutorsk integumentary fold zone. The eastern part of the area is occupied by structures of the Litken rift; formations of the superimposed Neogene-Quaternary Central Kamchatka volcanic belt are developed in the central and western parts. Volcanic rocks of the Umuvayam complex (N₁um; α, ζ, λζN₁um) are widespread in the study territory, Tolyatovayam (N₁-₂tl; λζ N₁-₂tl), Veemgetver (N₂vm; ζN₂vm), Emiyayam ( νδ,δ,qδ, δπ, μ-γδ, qμ, qμ-qδ, γδ, εγ-δ N₁e) volcanic complexes, lava sheets and intrusions of the basic composition of the Quaternary age spread to a less extent. Geological formations and associated ore objects were developed during three mineragenic epochs: Late Cretaceous-Middle Paleogene (volcanic intraoceanic sediments and terrigenous complex of the oceanic shelf), Middle Paleogene-Neogene (terrigenous complex of the oceanic shelf) and Quaternary (andesite complex of the back-arc rift zone, island-arc complex and terrigenous complex of the back-arc basin of the active continental margin). Mineragenic epochs correspond to five structural-facies zones: Mid-Kamchatka-Koryak, Litken-Central-Kamchatka (Q_E-I-Q_H), Central Kamchatka, Litken (₽₂-Q), Kamchatka-Olyutorsk (K₂-₽₂).

In order to identify geochemical criteria for the ore content and potential metallotects for all geological formations.

In general, the structural-material complexes show the chalcophilic type of geochemical specialization. Mid-Kamchatka-Koryak structural-facies zone has a spectrum W_5,0Ag_4,4Bi_2,8Mo_2,5Sn_2,2Zn_2,0Cu_1,8, Litken-Central-Kamchatka As_11,0Mo_5,0Ag_2,9Co_1,5, Central Kamchatka Ag_6,0W_5,2(Bi,Mo)_3,3Cr_2,2Cu_1,9(PbSeSn)_1,8V_1,7Zn_1,6, Litken (SnV)_3,0Cr_2,4Sc_2,0Cu_1,9(SeZnGa)_1,8Ag_1,7Pb_1,6(CoGe)_1,6, Kamchatka Olyutorsk Ag_4,2Cr_3,8V_2,5Sc_1,7Cu_1,6(ZnGa)_1,5.

The following metallotects can be distinguished in the study area:

The rocks of the Umuvayam, Emivayam, and Tolyatovyam complexes are part of the Central Kamchatka structural-facies zone, which occupies the largest central part of the study area. Epithermal silver-gold objects of the adularia-quartz formation are formed due to the invasion of intermediate and acidic phases of these complexes, postmagmatic activity, and metasomatic transformations of rocks. The averaged spectrum of accumulation of chemical elements, derived for the rocks that make up the Central Kamchatka structural-facies zone, is characterized by a wide range and demonstrates the siderophilic-lithophilic-chalcophilic type of geochemical specialization. Silver, copper, lead, and zinc included in the spectrum are indicators of the known and predicted mineralization of silver-gold adularia-quartz and polysulfide formations, and the presence of molybdenum indicates the possibility of detecting copper-molybdenum-porphyry ore objects. Thus, the geochemical data fully confirm that the Central Kamchatka structural-facies zone is highly promising.

How to cite: Kononova, L., Ladygina, M., and Maltseva, A.: Geochemical specialization of geological complexes in the northern part of the Kamchatka Peninsula, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-160, https://doi.org/10.5194/egusphere-egu21-160, 2021.

14:12–15:00

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