Spectral X‐ray computed micro tomography : 3‐dimensional chemical imaging

We present a new approach to 3-dimensional chemical imaging based on X-ray computed micro tomography (CT), which enables the analysis of the internal elemental chemistry. The method uses a conventional laboratory-based CT scanner equipped with a semiconductor detector (CdTe). Based on the X-ray absorption spectra, elements in a sample can be distinguished by their specific K-edge energy. The capabilities and performance of this new approach are illustrated with different experiments, i.e. single pure element particle measurements, element differentiation in mixtures, and mineral differentiation in a natural rock sample. The results show that the method can distinguish elements with K-edges in the range of 20 to 160 keV, this corresponds to an element range from Ag to U. Furthermore, the spectral information allows a distinction between materials, which show little variation in contrast in the reconstructed CT image

Comportement du fer et d'autres ions échangeurs d'électrons en contexte de subduction

Subduction zones are the largest recycling systems of our planet. Subduction zones involve recycling of water from hydrated oceanic crust and lithosphere to the upper mantle. Water plays a key role in subduction zone processes, including plate tectonics, magma generation, elemental transport and earthquake generation. The chemical composition, H2O content of oceanic lithosphere sinking to the mantle, age and geometry of subducting oceanic slab are the main factors controlling subduction zone processes including dehydration.The principle aim of this dissertation is to investigate the regime of water release from subducting oceanic plate and the associated behavior of Fe and S in serpentinites, which are the main carriers of water into the slab. The experimental approach of my work allows one to compare chemical and mineral changes occurred during dehydration of serpentinites with different composition. A number of analytical techniques were applied to study the influence of bulk rock composition on the mineral chemistry of produced assemblages. The experimentally investigated pressure-temperature ranges, i.e. 2 GPa and 450-900C, are representative for hot subduction zones. The extrapolation to other common geothermal gradients was done through thermodynamic modeling. The investigated serpentinite compositions correspond to natural serpentinized peridotites described for oceanic lithosphere.Bulk Fe content was demonstrated to decrease thermal stability of antigorite by 25C on average. Dehydration of Fe-bearing serpentinites, consequently, occurs at lower temperatures compared to Fe-free assemblages. Dehydration reactions observed in Fe-free systems are univariant reactions, while in Fe-bearing systems, serpentinites dehydration appears over a range of temperature through divariant reactions. Moreover, the presence of Al in serpentinite stabilized clinochlore, which retains 15% water initial contain in serpentinite down to ~120km (820°C/2 GPa) within hot subduction. Such a dependence of serpentinite dehydration on bulk Fe and Al brings importance of considering not only geometry and the age of the slab, but also a composition of slab lithologies while modeling and interpreting processes in subduction zone. A comparison of the depths of serpentinite dehydration and seismicity revealed a strong correlation and therefore a potential contribution of water release to seismicity in the case of hot subduction zones (i.e., Chili type subduction).X-ray absorption spectroscopy measurements revealed a progressive reduction of Fe and S in investigated serpentinites. The bulk Fe3+/Fetotal ratio initially high in serpentinite is shown to decrease in anhydrous and higher temperature assemblages due to magnetite and Fe3+-bearing antigorite breakdown at <550°C and 700°C, respectively. The presence of pyrite in serpentinite, which transforms to pyrrhotite below 450°C, imposes a release of ¼ of initial sulfur, in H2S form. The presence of magnetite and pyrite in serpentinite, is crucial and responsible for the production of highly oxidized fluids and volatile sulfur species, which can be transported from the subducting slab into the mantle wedge. Application of results, obtained in the present study, to nature demonstrates that fluids rising from subducting slab are responsible for oxidation of overlying mantle, and in addition, magnetite and antigorite breakdown which occurs with at least 100°C difference may cause a release of chemically different fluids at shallow (low-T) and deep (high-T) parts of subduction.Les zones de subduction sont les plus grands systèmes de recyclage de notre planète. Elles permettent le recyclage de l'eau contenue dans la croûte océanique hydratée et de la lithosphère du manteau supérieur. L'eau joue un rôle clé dans de nombreux processus associés aux zones de subduction, comme la tectonique des plaques, la production de magma, le transport élémentaire et la génération de tremblement de terre. La composition chimique, le contenu H2O de la lithosphère océanique, l'âge et la géométrie de la plaque océanique sont les principaux facteurs contrôlant les processus de subduction, y compris la déshydratation.L'objectif principal de cette thèse est d'étudier le régime de la libération de l'eau depuis la plaque océanique subductante et le comportement du Fe et du S en contenus dans les serpentinites, qui représentent la principale lithologie de roche hydratées océaniques. L'approche expérimentale de ce travail permet d’étudier les changements chimiques et minéralogiques associés lors la déshydratation des serpentinites de différentes compositions. Un certain nombre de techniques d'analyse ont été utilisées pour étudier l’influence de la composition de la roche totale sur la composition des assemblages produits. Les intervalles de pression de température expérimentalement étudiés, à savoir 2 GPa et 450-900C, représentent des zones de subduction chaudes. L'extrapolation à d'autres gradients géothermiques communs a été faite par thermodynamique. Les compositions de serpentinite étudiées correspondent aux péridotites serpentinisées naturelles décrites pour la lithosphère océanique.Mon travail indique que la teneur en Fer contrôle a stabilité thermique d’antigorite. Déshydratation de serpentinites avec Fe, par conséquent, pasee à des températures plus basses par rapport aux assemblages Fe-libres. La déshydratation observée dans les systèmes sans Fer se fait le long d'une réaction univariante, alors que dans les systèmes contenant du Fer, la déshydratation se fait sur un domaine de température (réactions de déshydratation divariantes). De plus, la présence de Al dans serpentinite stabilise clinochlore, qui conserve 15% de l'eau initiale jusqu'à ~ 120 km (820°C/2 GPa) dans subduction chaud. Cette dépendance sur Fe et Al apporte importance de considérer non seulement la géométrie et l'âge de la plaque océanique, mais aussi une composition de lithologies lors de la modélisation et d’interprétation de subduction. Une comparaison entre la profondeur des séismes et la profondeur de déshydratation des serpentinites indique une possible contribution de la libération de l'eau à la sismicité dans les zones de subduction chaudes et à pente faible.La spectroscopie d'absorption des rayons X montre une réduction progressive de Fe et de S dans des serpentinites. Le rapport Fe3+/ Fetotal, de la roche totale, élevé dans la serpentinite, diminue dans les assemblages anhydres de haute température par décomposition de la magnétite (< 550°C) et de l’antigorite (700°C). La pyrite des serpentinites se transforme en pyrrhotite en-dessous de 450°C et induit une libération de ¼ de soufre initial, probablement sous forme de H2S. La magnétite et la pyrite présentes dans des serpentinites, sont des phases cruciales pour la production de fluides très oxydés et d’espèces volatiles soufrées qui peuvent être transportés depuis la plaque subductée vers le coin mantellique. Application des résultats montre que les fluides s’élevant de la plaque océanique sont responsables de l'oxydation du manteau; et décomposition de la magnétite et l’antigorite avec au moins 100°C différence peut provoquer une libération de fluides chimiquement différents à peu profond (basse-T) et profondes (T-élevé) parties de subduction

Behavior of iron, and other ions capable for electron exchange in subduction settings

Les zones de subduction sont les plus grands systèmes de recyclage de notre planète. Elles permettent le recyclage de l'eau contenue dans la croûte océanique hydratée et de la lithosphère du manteau supérieur. L'eau joue un rôle clé dans de nombreux processus associés aux zones de subduction, comme la tectonique des plaques, la production de magma, le transport élémentaire et la génération de tremblement de terre. La composition chimique, le contenu H2O de la lithosphère océanique, l'âge et la géométrie de la plaque océanique sont les principaux facteurs contrôlant les processus de subduction, y compris la déshydratation.L'objectif principal de cette thèse est d'étudier le régime de la libération de l'eau depuis la plaque océanique subductante et le comportement du Fe et du S en contenus dans les serpentinites, qui représentent la principale lithologie de roche hydratées océaniques. L'approche expérimentale de ce travail permet d’étudier les changements chimiques et minéralogiques associés lors la déshydratation des serpentinites de différentes compositions. Un certain nombre de techniques d'analyse ont été utilisées pour étudier l’influence de la composition de la roche totale sur la composition des assemblages produits. Les intervalles de pression de température expérimentalement étudiés, à savoir 2 GPa et 450-900C, représentent des zones de subduction chaudes. L'extrapolation à d'autres gradients géothermiques communs a été faite par thermodynamique. Les compositions de serpentinite étudiées correspondent aux péridotites serpentinisées naturelles décrites pour la lithosphère océanique.Mon travail indique que la teneur en Fer contrôle a stabilité thermique d’antigorite. Déshydratation de serpentinites avec Fe, par conséquent, pasee à des températures plus basses par rapport aux assemblages Fe-libres. La déshydratation observée dans les systèmes sans Fer se fait le long d'une réaction univariante, alors que dans les systèmes contenant du Fer, la déshydratation se fait sur un domaine de température (réactions de déshydratation divariantes). De plus, la présence de Al dans serpentinite stabilise clinochlore, qui conserve 15% de l'eau initiale jusqu'à ~ 120 km (820°C/2 GPa) dans subduction chaud. Cette dépendance sur Fe et Al apporte importance de considérer non seulement la géométrie et l'âge de la plaque océanique, mais aussi une composition de lithologies lors de la modélisation et d’interprétation de subduction. Une comparaison entre la profondeur des séismes et la profondeur de déshydratation des serpentinites indique une possible contribution de la libération de l'eau à la sismicité dans les zones de subduction chaudes et à pente faible.La spectroscopie d'absorption des rayons X montre une réduction progressive de Fe et de S dans des serpentinites. Le rapport Fe3+/ Fetotal, de la roche totale, élevé dans la serpentinite, diminue dans les assemblages anhydres de haute température par décomposition de la magnétite (< 550°C) et de l’antigorite (700°C). La pyrite des serpentinites se transforme en pyrrhotite en-dessous de 450°C et induit une libération de ¼ de soufre initial, probablement sous forme de H2S. La magnétite et la pyrite présentes dans des serpentinites, sont des phases cruciales pour la production de fluides très oxydés et d’espèces volatiles soufrées qui peuvent être transportés depuis la plaque subductée vers le coin mantellique. Application des résultats montre que les fluides s’élevant de la plaque océanique sont responsables de l'oxydation du manteau; et décomposition de la magnétite et l’antigorite avec au moins 100°C différence peut provoquer une libération de fluides chimiquement différents à peu profond (basse-T) et profondes (T-élevé) parties de subduction.Subduction zones are the largest recycling systems of our planet. Subduction zones involve recycling of water from hydrated oceanic crust and lithosphere to the upper mantle. Water plays a key role in subduction zone processes, including plate tectonics, magma generation, elemental transport and earthquake generation. The chemical composition, H2O content of oceanic lithosphere sinking to the mantle, age and geometry of subducting oceanic slab are the main factors controlling subduction zone processes including dehydration.The principle aim of this dissertation is to investigate the regime of water release from subducting oceanic plate and the associated behavior of Fe and S in serpentinites, which are the main carriers of water into the slab. The experimental approach of my work allows one to compare chemical and mineral changes occurred during dehydration of serpentinites with different composition. A number of analytical techniques were applied to study the influence of bulk rock composition on the mineral chemistry of produced assemblages. The experimentally investigated pressure-temperature ranges, i.e. 2 GPa and 450-900C, are representative for hot subduction zones. The extrapolation to other common geothermal gradients was done through thermodynamic modeling. The investigated serpentinite compositions correspond to natural serpentinized peridotites described for oceanic lithosphere.Bulk Fe content was demonstrated to decrease thermal stability of antigorite by 25C on average. Dehydration of Fe-bearing serpentinites, consequently, occurs at lower temperatures compared to Fe-free assemblages. Dehydration reactions observed in Fe-free systems are univariant reactions, while in Fe-bearing systems, serpentinites dehydration appears over a range of temperature through divariant reactions. Moreover, the presence of Al in serpentinite stabilized clinochlore, which retains 15% water initial contain in serpentinite down to ~120km (820°C/2 GPa) within hot subduction. Such a dependence of serpentinite dehydration on bulk Fe and Al brings importance of considering not only geometry and the age of the slab, but also a composition of slab lithologies while modeling and interpreting processes in subduction zone. A comparison of the depths of serpentinite dehydration and seismicity revealed a strong correlation and therefore a potential contribution of water release to seismicity in the case of hot subduction zones (i.e., Chili type subduction).X-ray absorption spectroscopy measurements revealed a progressive reduction of Fe and S in investigated serpentinites. The bulk Fe3+/Fetotal ratio initially high in serpentinite is shown to decrease in anhydrous and higher temperature assemblages due to magnetite and Fe3+-bearing antigorite breakdown at <550°C and 700°C, respectively. The presence of pyrite in serpentinite, which transforms to pyrrhotite below 450°C, imposes a release of ¼ of initial sulfur, in H2S form. The presence of magnetite and pyrite in serpentinite, is crucial and responsible for the production of highly oxidized fluids and volatile sulfur species, which can be transported from the subducting slab into the mantle wedge. Application of results, obtained in the present study, to nature demonstrates that fluids rising from subducting slab are responsible for oxidation of overlying mantle, and in addition, magnetite and antigorite breakdown which occurs with at least 100°C difference may cause a release of chemically different fluids at shallow (low-T) and deep (high-T) parts of subduction

Foreign Language Learning at a Technical University in the Modern Period

Abstract Introduction. The article is devoted to the problems of the foreign language learning at a technical university. The theoretical importance of the research is in the analysis of the existing language learning system at a technical university in light of a modern engineer’s professional activity model’s change. Grounding of certain corrections in the language learning system also provides the theoretical importance of the research. The practical importance of our research is in the modification of the existing language learning system based on the environmental and activity approaches. Materials and Methods. While carrying out the research we used a complex of methods; that is: literature analysis, empiric and praxymetric methods, and a modeling method. Results. 4 main types of an engineer’s professional activity are defined in the engineer’s activity model. These types correspond to the main activity types by M.S. Kagan’s concept – value-motivating, cognitive, reorganizing and communicative activities. An engineer’s activity results analysis led to discovering new features in the engineer’s personality structure lying in the communicative competence role increase. It was also found out that successfulness becomes a link between value-motivating and communicative activities. Consequently, we have made a conclusion on the increasing demands to the students’, masters’, post-graduates’ and academic researches’ language proficiency. Foreign language proficiency should provide for the ability to participate in the international conferences, to attend foreign professors’ lectures, and to take part in the students’ exchange programs. All of the above presupposes rather high foreign language proficiency and requires a foreign language learning system creation. The authors analyzed language learning courses at a technical university and carried out a post-graduates’ survey. As a result, lack of syllabuses being able to fill in the gaps in language proficiency and to support speech skills was found out. Basing on the conclusions mentioned above an extra multi-purpose and multi-level structure syllabus was worked out. This syllabus allowed to solve the existing programs, to increase foreign language learning and general learning motivation, to create conditions for self-development and self-realization in the professional activity. The article also describes in detail a foreign language learning system developed by the Department of Foreign Languages and Russian as a Second Language in the general learning environment of a technical university, which acquires for the modernization and reaching the education level corresponding to the leading universities’ level. Conclusion. The learning environment created by the Department of Foreign Languages and Russian as a Second Language of Samara National Research University named after academician S.P. Korolyov and including a compulsory language learning system and a system of extra language learning courses provides for the students’ individual needs in foreign language proficiency satisfaction at various levels. It also provides for their intellectual and moral self-development

Foreign Language Learning at a Technical University in the Modern Period

Abstract Introduction. The article is devoted to the problems of the foreign language learning at a technical university. The theoretical importance of the research is in the analysis of the existing language learning system at a technical university in light of a modern engineer’s professional activity model’s change. Grounding of certain corrections in the language learning system also provides the theoretical importance of the research. The practical importance of our research is in the modification of the existing language learning system based on the environmental and activity approaches. Materials and Methods. While carrying out the research we used a complex of methods; that is: literature analysis, empiric and praxymetric methods, and a modeling method. Results. 4 main types of an engineer’s professional activity are defined in the engineer’s activity model. These types correspond to the main activity types by M.S. Kagan’s concept – value-motivating, cognitive, reorganizing and communicative activities. An engineer’s activity results analysis led to discovering new features in the engineer’s personality structure lying in the communicative competence role increase. It was also found out that successfulness becomes a link between value-motivating and communicative activities. Consequently, we have made a conclusion on the increasing demands to the students’, masters’, post-graduates’ and academic researches’ language proficiency. Foreign language proficiency should provide for the ability to participate in the international conferences, to attend foreign professors’ lectures, and to take part in the students’ exchange programs. All of the above presupposes rather high foreign language proficiency and requires a foreign language learning system creation. The authors analyzed language learning courses at a technical university and carried out a post-graduates’ survey. As a result, lack of syllabuses being able to fill in the gaps in language proficiency and to support speech skills was found out. Basing on the conclusions mentioned above an extra multi-purpose and multi-level structure syllabus was worked out. This syllabus allowed to solve the existing programs, to increase foreign language learning and general learning motivation, to create conditions for self-development and self-realization in the professional activity. The article also describes in detail a foreign language learning system developed by the Department of Foreign Languages and Russian as a Second Language in the general learning environment of a technical university, which acquires for the modernization and reaching the education level corresponding to the leading universities’ level. Conclusion. The learning environment created by the Department of Foreign Languages and Russian as a Second Language of Samara National Research University named after academician S.P. Korolyov and including a compulsory language learning system and a system of extra language learning courses provides for the students’ individual needs in foreign language proficiency satisfaction at various levels. It also provides for their intellectual and moral self-development

Evidence for syngenetic micro-inclusions of As3+- and As5+-containing Cu sulfides in hydrothermal pyrite

International audienceMost frequently arsenic is nominally monovalent (As 1-) in pyrite (FeS2) and substituted for S. Nominally trivalent arsenic (As 3+) has been reported previously in hydrothermal Peruvian pyrite and was considered to be substituted for Fe based on the negative correlation between the concentrations of the two elements. Here, we provide the first observation of the incorporation of As 3+ in goldfieldite (Cu12(As,Sb,Bi)2Te2S13) and As 5+ in colusite (Cu26V2(As,Sb)4Sn2S32) inclusions in As 1-pyrite from high-sulfidation deposits in Peru. This information was obtained by combining spatially-resolved electron probe (EPMA), synchrotron-based X-ray fluorescence (SXRF) and absorption spectroscopy (micro-XANES and micro-EXAFS) with new high energy-resolution XANES spectroscopy (HR-XANES). The two Cu sulfide inclusions range from several to one hundred micrometers in size and the As 3+ /As 5+ concentration varies from a few parts-per-million (ppm) to a maximum of 17.33 wt%, compared to a maximum of 50 ppm As 1-in pyrite. They also contain variable amounts of Sn (18.47 wt% max.), Te (15.91 wt% max.), Sb (8.54 wt% max.), Bi (5.53 wt% max.), and V (3.25 wt% max.). The occurrence of As 3+ /As 5+-containing sulfosalts in As 1-containing pyrite grains indicates that oxidizing hydrothermal conditions prevailed during the late stage of the mineralization process in the ore deposits from Peru

Revealing the chemical form of 'invisible' gold in natural arsenian pyrite and arsenopyrite with high energy-resolution x-ray absorption spectroscopy

The structural chemistry of gold in arsenian pyrite (FeS2) and arsenopyrite (FeAsS) is as yet unknown, despite the economic importance of this element and its potential recovery from low-grade ores and mine tailings. The systematic co-occurrence of Au and As poses a challenge for measuring the Au L-3-edge X-ray absorption spectra because the Au L alpha emission line is partly (pyrite) to totally (arsenopyrite) obscured by the intense As K alpha line. Utilizing a newly developed high luminosity multicrystal analyzer, in combination with the capabilities of a synchrotron-based microprobe, the Au L alpha and As K alpha lines were separated, and the Au L-3-edge X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra of chemically bound Au in arsenian pyrite and arsenopyrite from gold deposits were measured for the first time. High energy-resolution XANES (HR-XANES) shows that gold has a formal oxidation state of 1+ in the two sulfides, but a distinct bonding environment. In arsenian pyrite with a point Au/As atomic ratio of 0.14 (0.37 wt ratio) and lacking geochemical correlation between the concentrations of Au and As, Au occupies the Fe site and is bonded to six S atoms at 2.41 angstrom, as determined by HR-EXAFS. In contrast, in arsenopyrite with a point Au/As atomic ratio of 7.1 x 10(-3) (0.02 wt ratio) and exhibiting a Au-As correlation, octahedrally coordinated Au is bonded only to As atoms at 2.52 angstrom. The results reveal the atomic-scale structure of gold and its intricate geochemical association with arsenic in auriferous Fe sulfides. This work demonstrates that high energy-resolution X-ray absorption spectroscopy on synchrotron X-ray microprobes can illuminate the structural chemistry of trace elements in chemically complex Earth and planetary materials

Three-Dimensional Distribution of Platinum Group Minerals in Natural MSS-ISS Ores From the Norilsk One Deposit, Russia

The Mt. Rudnaya MSS-ISS (monosulfide and intermediate solid solution) fine-grained ores from a NE termination of Norilsk 1 deposit were analyzed using a combination of X-ray computed micro tomography, spectral X-ray computed micro tomography and scanning electron microscopy to achieve both, 2D and 3D data. The ores consist of ISS composed of tiny lamellar intergrowths of cubanite and chalcopyrite solid solutions, which form up to 4-mm distinct globules surrounded by an ISS-MSS matrix. Our X-ray computed micro tomography results may provide 3D textural evidence of a possible natural sulfide-sulfide liquid immiscibility between Cu-rich and Cu-poor sulfide liquids that occurred before MSS and ISS were crystallized. The platinum group minerals (PGM) distribution shows that 20.6 vol% of all PGM occur in the ISS-MSS matrix and 79.4 vol% in the ISS globules. We suggest that this distributional behavior is due to the fact that the platinum group elements (PGE) cannot be dissolved in ISS, which led to the formation of the large PGM grains, which are up to 120 μm on their longest axis. The initial enrichment of ISS in PGE was controlled by differences in the partition coefficients of platinum and palladium between Cu-poor and Cu-rich liquids

Chemical Forms of Mercury in Pyrite: Implications for Predicting Mercury Releases in Acid Mine Drainage Settings

International audiencePyrite (cubic FeS2) is the most abundant metal sulfide in nature and also the main host mineral of toxic mercury (Hg). Release of mercury in acid mine drainage resulting from the oxidative dissolution of pyrite in coal and ore and rock resulting from mining, processing, waste management, reclamation, and large construction activities is an ongoing environmental challenge. The fate of mercury depends on its chemical forms at the point source, which in turn depends on how it occurs in pyrite. Here, we show that pyrite in coal, sedimentary rocks, and hydrothermal ore deposits can host varying structural forms of Hg which can be identified with high energy-resolution XANES (HR-XANES) spectroscopy. Nominally divalent Hg is incorporated at the Fe site in pyrite from coal and at a marcasite-type Fe site in pyrite from sedimentary rocks. Distinction of the two Hg bonding environments offers a mean to detect microscopic marcasite inclusions (orthorhombic FeS2) in bulk pyrite. In epigenetic pyrite from Carlin-type Au deposit, up to 55 ± 6 at. % of the total Hg occurs as metacinnabar nanoparticles (β-HgSNP), with the remainder being substitutional at the Fe site. Pyritic mercury from Idrija-type Hg deposit (α-HgS ore) is partly divalent and substitutional and partly reduced into elemental form (liquid). Divalent mercury ions, mercury sulfide nanoparticles, and elemental mercury released by the oxidation of pyrite in acid mine drainage settings would have different environmental pathways. Our results could find important applications for designing control strategies of mercury released to land and water in mine-impacted watersheds