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Dans le contexte de la construction du Pont sur le Larivot en Guyane cette étude minéralogique évalue l'importance du quartz dans les échantillons fournis. Les résultats de ces analyses serviront à une autre équipe à déterminer, la forabilité, l'abrasivité des roches.

Le programme « ABP, Amiante et bonnes pratiques », a proposé une étude intégrée et pluridisciplinaire depuis l’identification jusqu’au caractère pathogène des fibres issues des minéraux amiantifères présents en secteur minier néo-calédonien.- Au travers d’un échantillonnage d’un panel représentatif des asbestes présents (famille des serpentinites et des amphiboles), les minéralogies, les propriétés physico-chimiques et toxicologiques de ces minéraux amiantifères ont été caractérisées.- À noter que le programme ABP a apporté les premières données toxicologiques sur les fibres d’amiante néo-calédoniennes. Un intérêt particulier est porté sur l’antigorite, minéral fibreux très présent sur le territoire calédonien, notamment en secteur minier, mais non répertorié comme amiante dans la législation hors territoire.

Ce rapport présente la synthèse, issue du rapport scientifique final, des résultats du programme « ABP, Amiante et bonnes pratiques ».- Le programme ABP a proposé une étude intégrée et pluridisciplinaire depuis l’identification jusqu’au caractère pathogène des fibres issues des minéraux amiantifères présents en secteur minier néo-calédonien.- Au travers d’un échantillonnage d’un panel représentatif des asbestes présents (famille des serpentinites et des amphiboles), les minéralogies, les propriétés physico-chimiques et toxicologiques de ces minéraux amiantifères ont été caractérisées.- À noter que le programme ABP a apporté les premières données toxicologiques sur les fibres d’amiante néo-calédoniennes. Un intérêt particulier est porté sur l’antigorite, minéral fibreux très présent sur le territoire calédonien, notamment en secteur minier, mais non répertorié comme amiante dans la législation hors territoire.

Cette recherche menée dans le cadre d'un mémoire de master en archéologie préhistorique vise à comprendre les fonctionnements économiques et sociaux des sociétés de la fin du Néolithique et de l'âge du Bronze dans la Haute Vallée du Rhône. Pour cela, un total de dix céramiques issues de la nécropole dolménique du Petit-Chasseur à Sion (Valais, Suisse) a été mobilisé. L'étude minéralogique des céramiques à travers une machine performante, le Qemscan, a été utilisée. Celle-ci permet de mesurer le pourcentage de chaque minéral présent dans la céramique.

International audience; An old erg covers the northern part of the Lake Chad basin. This dune landform allowed the formation of many inter- dune ponds of various sizes. Still present in certain zones where the groundwater level is high (e.g. Kanem, southern Manga), these ponds formed in the past a vast network of lacustrine microsystems, as shown by the nature and the dis- tribution of their deposits. In the Manga, these interdune deposits represent the main sedimentary records of the Holo- cene environmental succession. Their paleobiological (pollens, diatoms, ostracods) and geochemical (δ18O, δ13C, Sr/ Ca) contents are often the basis for paleoenvironmental reconstruction. On the other hand, their sedimentological char- acters are rarely exploited. This study of palustro-lacustrine deposits of the Holocene N'Guigmi lake (northern bank of the Lake Chad; Niger) is based on the relationships between the sedimentological features and the climato-hydrological fluctuations. The mineralogical parameters (e.g. calcium carbonate content, clay mineralogy) and the nature of autoch- thonous mineralization (i.e. amorphous silica, clays, calcium carbonates) can be interpreted using a straightforward hy- dro-sedimentary model. Established to explain the geochemical dynamics of Lake Chad, this model is based on a bio- geochemical cycle of the main elements (i.e. silicium, calcium) directly controlled by the local hydrological balance (i.e. rainfall/evaporation ratio). All these results show that a detailed study of sedimentological features can provide impor- tant paleohydrological informations about the regional aridification since ca 6500 14C BP.

Clay minerals and K feldspars were evaluated as sources of K in a Norway spruce stand (Picea abies (L.) Karst.) from the Skogaby experimental forest in southwest Sweden. The soil, developed in a Quaternary glacial till, has only 3-5% clay, and more than 95% of its K resides in feldspars. Ratios of K/Rb were assessed in interlayers of 2: 1 clay minerals (extracted with hot (100 degrees C) 2 M HCl), biomass and the forest floor. These compartments had similarly low K/Rb ratios, whereas K feldspars were significantly poorer in Rb. A fractionation model indicated preferential retention of Rb in the biomass and forest floor, due to stronger adsorption of Rb than K in the humus, as well as preferential uptake of K from the exchange complex in the mineral soil. Preferential uptake of K may result from weaker adsorption of K by the cation exchanger, or preference for dissolved K over Rb by the roots. A quantitative mineralogical analysis revealed that loss from micas may account for half of the Holocene loss of K from the soil, which was approximately 22 Mg ha(-1). Exceptionally low K/Rb ratios in HCl extracts of the upper 60 cm of the profile indicated extensive loss of K from mica in the parent material and re-fixation of K and Rb at lower ratios. The results indicate that fixation in and release from clay minerals may be prominent in the cycling of K, even in a soil that is poor in clay minerals.

8th International RILEM SIB Symposium, ANCONE, Italie, 07-/10/2015 - 09/10/2015; Clay fines are known to reduce the water resistance of bitumen-aggregates binding and cause stripping in Asphalt Concrete (AC) mixtures. To address this phenomenon, a better understanding of the mineralogical composition of aggregates is needed as well as an assessment of the bitumen-clay-water interactions. This paper contributes to reach this goal from a mineralogical perspective. The most common clays in natural aggregates, kaolinite, illite and montmorillonite, were used to prepare thin clay films and artificial clay-rich aggregates. The bitumen-clay interaction was studied using the sessile drop and the Oliensis spot tests on those thin clay films, whereas Duriez tests allowed measuring the stripping potential of AC mixtures containing the clay-rich aggregates. The results show that the water-bitumen-clay interaction and water resistance of the AC mixture are specific to the clay mineralogy. Furthermore, they show that the bitumenclay interaction may be captured upon determining the surface energy of bitumen, the chemical composition and pH value of the clay and the bitumen-clay compatibility. Hence, predicting the water resistance of clay rich AC mixtures from mineralogical properties of the bitumen-clay interaction seems feasible.

The magnetic fabric of the Pliocene Kızılkaya ignimbrite in the Central Anatolian Volcanic Province has been investigated by anisotropy of magnetic susceptibility (AMS) and isothermal remanent magnetization (AIRM). Seven sections were sampled at various stratigraphic heights within the devitrified portion of the ignimbrite. The magnetic mineralogy is complex: titanomagnetite occurs as magmatic grains, and as inclusions in other phenocryst and glass shards; an oxidized phase and hematite occur in deposit levels affected by alteration processes. The disturbance produced by lithic and pumice clasts has been reduced by discarding the specimens that deviate more than ±1σ from the site mean value of the density. The AMS fabric varies along each individual section. Neither the AMS magnetic lineation nor the magnetic foliation plunge clearly define a common area as the vent location. The AIRM fabric of low-coercivity minerals, mainly represented by free titanomagnetite grains of magmatic origin, is consistent between sites and the inferred flow directions converge on a region near Derinkuyu, in the Nevsehir plateau, previously reported as the Kızılkaya ignimbrite source area. This study shows that systematic use of the remanent fabric improves the results given by AMS and aids the identification of the primary magnetic fabric related to the ignimbrite emplacement dynamics.

Summary In the Ecuadorian Cordillera, the hardened volcanic ashes (cangahuas) account for 15% of the cultivated area. The soil resulting from the fragmentation of these materials, generally by heavy machinery, shows an apparent stable millimetric structure. However, this new structure is highly susceptible to disintegration under rain, because it contains no organic matter and little clay, and the material itself is readily eroded in consequence. We studied the evolution of soil aggregate stability in two factorial experiments during five cultivation cycles with two kinds of soil preparation and five fertilization treatments. The aggregate stability was not influenced by either kind of soil preparation, nor by large additions of cattle manure (80 t ha−1) or green manure (10 t ha−1), nor by growing a perennial grass. The variation in the aggregate stability seemed to depend on the components inherited from the original volcanic material: in the plots with larger clay content, and with swelling clay minerals, the aggregates were less stable than those composed of isometric fine silt particles.

O trabalho trata da formação de solos arenosos hidromórficos com morfologia de Espodossolo, encontrados em extensas planícies, onde ocorrem áreas isoladas de Latossolos, em terrenos ondulados e bem drenados de colinas. O objetivo do estudo é elucidar a existência de relação pedogenética num sistema Latossolo-Espodossolo, verificando o possível desenvolvimento dos solos arenosos por transformação dos Latossolos. Para tanto, foram caracterizados a morfologia dos solos e seus atributos fisicos, químicos e mineralógicos. Os solos estudados apresentam desenvolvimento autóctone e filiação com a rocha granítica do embasamento, mostrando relação genética lateral entre si. Pode-se admitir transformação do Latossolo em areia branca, que se verifica numa escala métrica, de acordo com as condições de saturação hídrica crescente, provocando amarelecimento, seguido de gleização, na periferia da colina. Nesta zona, ocorre empobrecimento em argila em subsuperfície, que se estende lateralmente na planície, onde se encontram, de início, o material arenoso e, em seguida, os Espodossolos hidromórficos. Esta disposição evidencia o desenvolvimento dos Espodossolos posteriormente à formação das areias. O principal processo pedogeoquímico envolvido na perda de argila seria a acidólise, que provoca dissolução da gibbsita e caulinita. Nesse caso, a transformação dos solos teria papel preponderante na evolução do modelado com aplainamento geral do relevo. This paper deals with the genesis of hydromorphic sandy soils with spodosol morphology found in extensive flat surfaces, in which isolated zones with undulating relief emerge, containing well drained oxisols. The objective of this study was to explain the existence of pedogenetic relationship in an oxisol-spodosol system, and to verify the possible development of the sandy materials as a consequence of oxisol transformation. For this purpose, we characterized the morphology of the soils and their physical, chemical and mineralogical attributes. The studied soils showed autochthonous development and filiation to granitic rock of the crystalline basement, displaying lateral genetic relationship between them. Thus, we can admit the occurrence of oxisol transformation, verified in a metric scale, caused by increasing waterlogging conditions. As a result, soil yellowing was found, followed by gleization near the edge of the hill. In this zone, clay depletion was evidenced in the subsuperficial soil layer, extending laterally towards the plain, with the appearance of sandy materials (white sands) near the hill, followed by hydromorphic spodosol. This disposition suggests that evolution of the spodosol occurred after sand formation occurred later. The main pedogeochemical process involved in clay removal would be acidolysis, which causes gibbsite and kaolinite dissolution. Thus, soil transformation would probably have played a preponderant role in the landscape evolution resulting in overall relief planation.

International audience; Soils in boundary conditions of contrasting ecosystems generally show unique features. Transition often leads to changes in soil-forming processes, whereby the environment never comes to equilibrium and therefore the soil chemistry and mineralogy show different influences. Such an environment was analysed in the Saloum River basin, west-central Senegal. The objective was to identify the main pedogenic processes prevailing in this saline and acid pedoenvironment and to assess the influence of environmental factors (climate, topography, soil salinity and acidity) on local soil formation and mineral distribution. The terrace landscape is built up by a floodplain, a low terrace, which is still influenced by groundwater, and a middle terrace. The results show that soil properties are strongly influenced by hydrology, salinity and acidity in the entire toposequence: Gleyic Hyposalic and Hypersalic Solonchaks (Sulfatic) in the floodplain, Haplic Gleysols (Thionic) in the low terrace, and Endogleyic Arenosols in the middle terrace. The oxidation of pyrite followed by the redistribution of the main products (Fe2+ and SO42-) represents the major chemical process responsible for iron oxide and jarosite formation. Mineral distribution and crystallinity are linked to the landscape position, which controls the hydrological behaviour and reactions of Fe and S ions. Finally, we observed intrapedon processes such as gleysation, sulfidisation and sulfurisation, as well as interpedon processes such as salinisation, colluvio-alluviation and lateral eluviation. The combination of processes depends strongly on the landscape positions.

L'évolution cristallochimique de pyrochlores au cours de l'altération météorique a été suivie, au moyen de techniques classiques d'investigation minéralogique (microscopie optique, MEB, microsonde électronqiue), sur des sondages et tranchées recoupant l'épaisse couverture d'altération ferrallitique du complexe alcalino-carbonatitique de Catalao II (Sud-Est du Goias, Brésil). Une brusque transformation des pyrochlores primaires (pyrochlore s.s.) en des espèces secondaires du type bario- ou cériopyrochlore a ainsi pu être observée au niveau d'encroûtements siliceux de profondeur (30-40 m), d'origine pédologique. Le passage d'une espèce à l'autre revêt les caractères d'une pseudomorhose et résulte du lessivage préférentiel de certains cations (Na, Ca) et anions (F), partiellement remplacés par Ba ou TR et (OH). (Résumé d'auteur)

Suspended matter (SM) from the Nyong basin (Cameroon, Africa), a tropical watershed, was collected by tangential flow ultrafiltration to separate particulate (>0.45 μm) and colloidal ( 20 kDa) fractions. In this basin, two distinctive systems in a selected small catchment (Nsimi–Zoetele) of the Nyong river basin have been considered: (i) colourless water (groundwater and spring) with a low suspended load ( 10 mg/l) and contains higher amounts of SM (10–20 mg/l) than the colourless water. Freeze-dried samples of SM have been analysed by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), electron paramagnetic resonance spectroscopy (EPR), and visible diffuse reflectance spectroscopy (DRS). Colourless water mainly contains mineral phases, such as poorly ordered kaolinite, plus quartz and goethite in the particulate fraction, and euhedral kaolinite plus amorphous iron oxyhydroxides in the colloidal fraction. In contrast, the SM in coloured water is mainly organic in nature. The mineral phases in the particulate fraction are similar to those from clear water, but with additional phytoliths and diatom frustules composed of biogenic opal. In the colloidal fraction, complexation of Fe3+ and Mn2+ with organic matter is evidenced by EPR, together with significant occurrence of Fe oxyhydroxides associated with organic matter. The sites of Al, Si, Fe, Mn in colloidal fractions derived from spectroscopic analyses are discussed with reference to chemical analyses performed by inductively coupled plasma mass spectrometry. Most of the observed solid phases or species correspond to those expected from published thermodynamic calculations for the same hydrosystem, except the colloidal iron oxyhydroxides in the coloured water. The presence of such iron phases is emphasised since they are expected to have large sorption capacities for numerous trace elements. The crystal chemistry of SM is used to discuss the origin of the mineral particles transported from the soil to the main rivers in terms of mechanical and chemical erosion processes.

International audience; Two sediment cores were studied from Comprido Lake, a black water floodplain lake located near Monte Alegre City, Eastern Amazonian Basin. The total organic carbon (TOC), nitrogen content (TN), δ13CTOC, sedimentary chlorophyll, diatom record and mineralogical composition revealed different hydrological and climatic regimes during the Holocene. Between 10,300 and 7800 cal yr BP, a dry climate was suggested by low values of TOC and chlorophyll derivatives concentrations that are related to the development of a C4 grasses on unflooded mud banks. A gap in sedimentation due to a complete dryness of the lake occurred between 7800 and 3000 cal years BP corresponding to the Middle Holocene dry phase. From 3000 cal years BP onwards a gradual increase of the TOC, chlorophyll derivatives and Aulacoseira sp. suggest an increase in the productivity and in water lake level due to the high water flow of the Amazon River and the catchment area as well. The Comprido Lake record indicates that the Late Holocene in this region was characterized by a wetter climate, as also observed in other records of the Amazonian Basin.

Thin section, XRPD, and SEM-EDS analyses were carried out on pastes and glazes of 12th-13th c. glazed cooking wares found out at Palazzo Ducale of Genoa (Liguria, NW Italy). Seven productions different in compositional, technical and typological characteristics were recognised. Imports from centres located in the northern Mediterranean sector included between Spain and the Aegean-Anatolian area, as well as an early local production (from Savona workshops), were identified. The comparison between all these specialised productions shows a fairly homogenous technical knowledge. Ca-poor (Fe-rich alluvial or kaolinitic) clays with quartz-rich temper were generally used for the body, which give the cooking wares a good resistance to thermal shocks. Firing temperatures were relatively high, while both single- and double-fired productions have been identified. All glazes are non-opacified and show Si, Pb-rich, low-alkali, low-Ca composition; no clear chemical clusters are generally recognisable. Fe is the only colouring agent of the glazes, but its presence could be unintentional in most cases. Les pâtes et les glaçures de céramiques culinaires (xiie-xiiie siècles) retrouvées au Palazzo Ducale de Gênes (Ligurie, Italie du Nord-ouest) ont été étudiées en lame mince au microscope polarisant, au microscope électronique (SEM-EDS) et par diffraction des rayons X (XRD). On a reconnu sept productions différentes par leurs composition, technique et typologie. À côté de plusieurs importations, dont les centres d’origine sont localisables dans la Méditerranée du Nord (entre l’Espagne et la région égéenne-anatolienne), on a découvert aussi une production locale (des ateliers de Savone) précoce. La comparaison entre les différentes productions montre un niveau technique relativement homogène. Généralement, les pâtes sont constituées d’argiles pauvres en calcium (alluviales, riches en fer, ou kaolinitiques) et de dégraissants riches en quartz, qui donnent une bonne résistance aux chocs thermiques. Les températures de cuisson sont relativement hautes, tandis que mono- et double cuissons sont évidentes. Toutes les glaçures sont transparentes, riches en Si et Pb et pauvres en Na, K, et Ca; aucun groupement compositionnel n’est bien visible. Le fer représente l’unique colorant, mais, dans la plupart des cas, sa présence n’est probablement pas intentionnelle.

The results highlight a difference in swell-shrink behaviour between the two studied soils and stress the importance of the presence and the nature of clay minerals and the microstructure of the soil on the swelling and shrinkage phenomenon as well as on the accompanying microstructural transformations. They also reveal the role played by carbonates, cementation and initial conditions on intact or remoulded soils during moisture changes. Finally, the influence on the hydromechanical behaviour of wetting-drying cycles was analysed. The experimental results show that during the successive wetting-drying cycles, while the soil samples show an increase in the cumulative swelling deformation, a stabilization of swell strain of each cycle is reached at the end of the third or fourth cycle. These results are compatible with a reorganization of the microstructure as highlighted by the microstructural (SEM, porosimetry) analysis.; La présence de plusieurs formations argileuses affleurantes ou sub-affleurantes en région parisienne classe cette région parmi les plus vulnérables au phénomène de retrait-gonflement. Deux formations sont plus particulièrement concernées : les Argiles vertes de Romainville et les Marnes bleues d'Argenteuil. Ce mémoire est consacré à l'étude du comportement du retrait-gonflement de ces sols à partir d'une analyse menée au laboratoire, des caractéristiques minéralogiques, microstructurales, géotechniques et hydromécaniques. Les résultats obtenus mettent en évidence une différence de comportement entre les deux sols étudiés et soulignent l'importance de la présence et de la nature des minéraux argileux et de la texture du sol, sur le phénomène de retrait-gonflement et sur les transformations microstructurales qui en découlent. Ils montrent aussi le rôle joué par les carbonates, la cimentation et les conditions initiales sur les sols intacts ou remaniés lors des échanges hydriques. Enfin, l'influence des cycles de séchage/humidification sur le comportement hydromécanique des sols étudiés a été analysée. Les résultats montrent qu'au cours des cycles successifs de sollicitations hydriques, alors que les échantillons de sol présentent une augmentation du taux de gonflement cumulé, une stabilisation des déformations de chacun des cycles est atteinte au bout du troisième ou quatrième cycle. Ces résultats sont en relation avec une réorganisation de la microstructure mise en évidence par l'analyse microstructurale (MEB, porosimétrie).

The results highlight a difference in swell-shrink behaviour between the two studied soils and stress the importance of the presence and the nature of clay minerals and the microstructure of the soil on the swelling and shrinkage phenomenon as well as on the accompanying microstructural transformations. They also reveal the role played by carbonates, cementation and initial conditions on intact or remoulded soils during moisture changes. Finally, the influence on the hydromechanical behaviour of wetting-drying cycles was analysed. The experimental results show that during the successive wetting-drying cycles, while the soil samples show an increase in the cumulative swelling deformation, a stabilization of swell strain of each cycle is reached at the end of the third or fourth cycle. These results are compatible with a reorganization of the microstructure as highlighted by the microstructural (SEM, porosimetry) analysis.; La présence de plusieurs formations argileuses affleurantes ou sub-affleurantes en région parisienne classe cette région parmi les plus vulnérables au phénomène de retrait-gonflement. Deux formations sont plus particulièrement concernées : les Argiles vertes de Romainville et les Marnes bleues d'Argenteuil. Ce mémoire est consacré à l'étude du comportement du retrait-gonflement de ces sols à partir d'une analyse menée au laboratoire, des caractéristiques minéralogiques, microstructurales, géotechniques et hydromécaniques. Les résultats obtenus mettent en évidence une différence de comportement entre les deux sols étudiés et soulignent l'importance de la présence et de la nature des minéraux argileux et de la texture du sol, sur le phénomène de retrait-gonflement et sur les transformations microstructurales qui en découlent. Ils montrent aussi le rôle joué par les carbonates, la cimentation et les conditions initiales sur les sols intacts ou remaniés lors des échanges hydriques. Enfin, l'influence des cycles de séchage/humidification sur le comportement hydromécanique des sols étudiés a été analysée. Les résultats montrent qu'au cours des cycles successifs de sollicitations hydriques, alors que les échantillons de sol présentent une augmentation du taux de gonflement cumulé, une stabilisation des déformations de chacun des cycles est atteinte au bout du troisième ou quatrième cycle. Ces résultats sont en relation avec une réorganisation de la microstructure mise en évidence par l'analyse microstructurale (MEB, porosimétrie).

International audience; Brazilian Latosols are characterized by low activity clay, little horizon differentiation, a weak macrostructure and a strong microgranular structure. The development of the latter that was reported as being possibly related to the fine material mineralogy, location in the landscape, parental material and biological activity is still under discussion. The aim of this study is to discuss the origin of the microgranular structure of Latosols located in the Brazilian Central Plateau. Ten Latosols (L) developed in different parent materials were selected along an approximately 350-km long regional toposequence across the South American Surface (SAS) (L1 to L4) and Velhas Surface (VS) (L5 to L10). The structure of the Latosols was studied in the field and samples of the diagnostic Bw horizons were collected for laboratory analyses. Basic soil characterization was performed on the

The present study copes with the environmental impact assessment of municipal solid waste incineration bottom ashes (MSWI BA) re-used as aggregates in road construction. The methodology involves the following steps: characterization of bottom ashes (physical properties, chemistry and mineralogy), experiments at laboratory scale, field study and geochemical modeling. Quantitative data for trace elements in primary glasses obtained by Secondary Ions Mass Spectrometry (SIMS) microanalysis show that these glasses are likely a main sink for Zn. In the cemented calcite admixture, lead seems to be mainly sorbed on iron oxy-hydroxides according to SIMS imaging and Extanded X-ray Absorption Fines Structure analysis (EXAFS). Except for SO4, low concentrations and alkalinity have been measured in leachates from a 10~year-old road built with MSWI BA (fast attenuation during the first years). No significant transformation of bottom ashes (such as an advanced carbonation state) has been observed after 10 years of utilization. Lateral preferential flowpaths (edge effects) are likely responsible for the difference between alcaline pore water and dilued leachates. Based on characterization and experimental data, an common model have been built to simulate leaching and mineralogical evolutions using the transport reactive code HYTEC. Simulations of batch and dynamic leaching tests, as well as of two roads (French and Swedish) built with bottom ashes show fair agreement with respect to the experimental data.; La présente étude traite du comportement de mâchefers d'incinération des ordures ménagères (MIOM) en scénario de valorisation (sous-couche routière), dans l'optique d'évaluer l'impact environnemental. La démarche mise en oeuvre associe des approches de caractérisation physico-chimique et minéralogique, d'expérimentation à différentes échelles (laboratoire et sites réels), et de modélisation hydro-géochimique. L'utilisation conjointe de différentes techniques d'investigation cristallochimique (microscopie optique, DRX, MEB, XRF, SIMS, EXAFS) ont permis d'apporter de nouvelles informations sur les teneurs en éléments traces des verres primaires et sur la spéciation de Pb dans une phase dite scoriacée. Le suivi des percolats issus d'une portion de route construite avec des mâchefers dix ans après la mise en service ainsi que l'observation des MIOM prélevés dans la sous-couche a fourni un retour d'expérience inédit tout en mettant en évidence le rôle prépondérant de l'hydrodynamique sur la stabilité du matériau et l'atténuation du caractère alcalin et chargé des eaux de percolation. Un modèle géochimique de MIOM a été élaboré à partir des données issus de l'étape de caractérisation, des résultats expérimentaux des essais de lixiviation et des informations recueillies lors du suivi de sites réels. Ce modèle a été appliqué pour simuler, via le code de calcul couplé géochimie-transport HYTEC, le comportement des éléments inorganiques et l'évolution minéralogique inhérent aux différents essais en laboratoire, à la portion de route suivie durant cette thèse et à un autre site réel faisant l'objet d'une étude suédoise.

The present study copes with the environmental impact assessment of municipal solid waste incineration bottom ashes (MSWI BA) re-used as aggregates in road construction. The methodology involves the following steps: characterization of bottom ashes (physical properties, chemistry and mineralogy), experiments at laboratory scale, field study and geochemical modeling. Quantitative data for trace elements in primary glasses obtained by Secondary Ions Mass Spectrometry (SIMS) microanalysis show that these glasses are likely a main sink for Zn. In the cemented calcite admixture, lead seems to be mainly sorbed on iron oxy-hydroxides according to SIMS imaging and Extanded X-ray Absorption Fines Structure analysis (EXAFS). Except for SO4, low concentrations and alkalinity have been measured in leachates from a 10~year-old road built with MSWI BA (fast attenuation during the first years). No significant transformation of bottom ashes (such as an advanced carbonation state) has been observed after 10 years of utilization. Lateral preferential flowpaths (edge effects) are likely responsible for the difference between alcaline pore water and dilued leachates. Based on characterization and experimental data, an common model have been built to simulate leaching and mineralogical evolutions using the transport reactive code HYTEC. Simulations of batch and dynamic leaching tests, as well as of two roads (French and Swedish) built with bottom ashes show fair agreement with respect to the experimental data.; La présente étude traite du comportement de mâchefers d'incinération des ordures ménagères (MIOM) en scénario de valorisation (sous-couche routière), dans l'optique d'évaluer l'impact environnemental. La démarche mise en oeuvre associe des approches de caractérisation physico-chimique et minéralogique, d'expérimentation à différentes échelles (laboratoire et sites réels), et de modélisation hydro-géochimique. L'utilisation conjointe de différentes techniques d'investigation cristallochimique (microscopie optique, DRX, MEB, XRF, SIMS, EXAFS) ont permis d'apporter de nouvelles informations sur les teneurs en éléments traces des verres primaires et sur la spéciation de Pb dans une phase dite scoriacée. Le suivi des percolats issus d'une portion de route construite avec des mâchefers dix ans après la mise en service ainsi que l'observation des MIOM prélevés dans la sous-couche a fourni un retour d'expérience inédit tout en mettant en évidence le rôle prépondérant de l'hydrodynamique sur la stabilité du matériau et l'atténuation du caractère alcalin et chargé des eaux de percolation. Un modèle géochimique de MIOM a été élaboré à partir des données issus de l'étape de caractérisation, des résultats expérimentaux des essais de lixiviation et des informations recueillies lors du suivi de sites réels. Ce modèle a été appliqué pour simuler, via le code de calcul couplé géochimie-transport HYTEC, le comportement des éléments inorganiques et l'évolution minéralogique inhérent aux différents essais en laboratoire, à la portion de route suivie durant cette thèse et à un autre site réel faisant l'objet d'une étude suédoise.

The chemical weathering of ultramafic rocks has resulted in eluvial concentration of Pt-group minerals (PGM) in lateritic weathering profiles of southern New Caledonia. The Pt mineralization interpreted as being primary consists of Pt-group minerals included within chromite crystals. The oc- currence of PGM as free particles in the weathering profile results from the supergene dissolution of Pt-bearing chromite (Traore et al. 2008). Following their release in the profile, supergene dissolution processes variably affect the PGM particles. The behavior of Pt-group elements in the weathering profile is characterized by significant loss of Pd and relative enrichment of Pt indicating that Pd is more mobile than Pt in the exogenous cycle. Unstable Pt-Fe-Cu-Pd alloys and PGE oxides undergo chemical and mineralogical changes to acquire the chemical configuration of isoferroplatinum (Pt3Fe), which is the most stable Pt phase in a lateritic environment. The isoferroplatinum phase may also be dispersed throughout the weathering mantle and/or accumulated in the lower parts of profiles ac- cording to a translocation mechanism of residual Pt-rich fine particles driven by percolation of water through the connected pore spaces.

This paper focuses on the mineralogical and petrographic characterisation of ceramic fabrics rich in glauconitic pellets, found out in a few local productions of European and Mediterranean sites dated from Prehistory to the Middle Ages. The main distinguishing features of glauconitic inclusions are their rounded shape, dark colour and peculiar chemical composition. During the firing – as also evidenced by a few preliminary experimental tests on glauconitic sediments – the pellets change in colour (from green to red or black in thin section) because of the oxidation of divalent iron and their texture becomes more homogeneous, up to the partial or complete vitrification at moderately high temperatures. Dans cet article, on présente la caractérisation minéralogique et pétrographique des pâtes céramiques riches en pellets glauconitiques, trouvées dans quelques productions locales de sites européens et méditerranéens d’age préhistorique à médiéval. Les plus importants éléments discriminants des pellets glauconitiques sont leur forme arrondie, leur couleur rouge ou noire et leur composition chimique particulière. Durant la cuisson, comme quelques tests préliminaires sur sédiments glauconitiques l’ont confirmé, les pellets changent de couleur (de vert à rouge ou noir en lame mince), à cause de l’oxydation du fer bivalent, et leur texture devient plus homogène, jusqu’à la vitrification partielle ou totale à des températures relativement hautes.

In the Alps, debris flow deposits generally contain < 5% clay-size particles, and the role of the surface-charged < 2 mu m particles is often neglected, although these particles may have a significant impact on the rheological properties of the interstitial fluid. The objective of this study was to compare debris flow deposits and parent materials from two neighbouring catchments of the Swiss Alps, with special emphasis on the colloidal constituents. The catchments are small in area (4 km(2)), 2.5 km long, similar in morphology, but different in geology. The average slopes are 35-40%. The catchments were monitored for debris flow events and mapped for surface aspect and erosion activity. Debris flow deposits and parent materials were sampled, the clay and silt fractions extracted and the bulk density, < 2 mm fraction bulk density, particle size distribution, chemical composition, cation exchange capacity (CEC) and mineralogy analysed. The results show that the deposits are similar to the parent screes in terms of chemical composition, but differ in terms of: (i) particle size distribution; and (ii) mineralogy, reactivity and density of the < 2 mm fraction. In this fraction, compared with the parent materials the deposits show dense materials enriched in coarse monocrystalline particles, of which the smallest and more reactive particles were leached. The results suggest that deposit samples should not be considered as representative of source or flow materials, particularly with respect to their physical properties.

The Brazilian Central Plateau is constituted of the two main geomorphic surfaces: the South American surface and the Velhas surface. These surfaces were developed during the Cretaceous Superior and Tertiary and are covered by deeply weathered Latosols. The South American surface is the oldest and occupies the highest position in the landscape (950 to 1,200 m altitude) with smoothly convex plane portions. The Velhas surface is composed by irregular and slightly sloping planes and occupies in the landscape (750 to 950 m altitude). It is connected to the South American surface by areas of steep hillsides.

The geochemical development of laterites, a very common superficial formation in the tropics, is still a matter of debate. To determine the main steps of their formation, and to interpret lateral geochemical variations often observed within laterites, we studied the Kaya ferricrete in northern Burkina Faso by analysing two profiles in contrasting topographic positions. We determined the mineralogy and the composition in major and trace elements of whole rocks and of < 0.2 mu m granulometric fractions. The nature and proportion of relictual primary minerals and of secondary clays and Fe-oxyhydroxides control the distribution of major and soluble trace elements. The distribution patterns of Fe, transition metals, lanthanides, U and Th in the two profiles require (i) an initial accumulation in the top ferruginous horizon during its formation and (ii) a secondary redistribution downwards in the underlying horizons. Lanthanides, Ni and Co were remobilized to a much greater extent than Cu and Sc, whereas Fe, V, Cr and Th accumulated in the ferruginous horizon. The uphill better drained profile showed more intense redistribution than the downhill profile. Uranium in particular is poorly redistributed in the downhill profile, whereas it was redistributed like the lanthanides in the uphill profile. Remobilizations are also more intensely recorded in the fine fractions than in the whole rocks. These results allow us to propose a scenario for the formation of the Kaya laterite that accounts for both vertical and lateral chemical distributions. They also highlight the potential of multimethod geochemical studies to uncover the sequence of evolution of weathering profiles.

Resume Quatre unites ignimbritiques sont reconnues dans la region d'Arequipa : (1) celle de « rio Chili » a 13,33 Ma ; (2) l'ignimbrite « La Joya », la plus etendue, qui a 4,9 Ma ; (3) l'ignimbrite « aeroport d'Arequipa », qui s'est mise en place vers 1,65 Ma a partir de la zone ou s'est edifie le volcan Chachani ; (4) enfin, les « Tufs de Yura », vers 1,02 Ma, qui affleurent a l'ouest du Chachani. Il s'agit de rhyolites calco-alcalines a plagioclase, biotite, quartz, sanidine et opaques. La presence d'amphibole caracterise les ignimbrites de rio Chili et La Joya. Les elements en traces indiquent une contamination crustale plus forte pour les ignimbrites anciennes. Pour citer cet article : P. Paquereau et al., C. R. Geoscience 337 (2005).

Geochemical and mineralogical data from ancient sedimentary strata can be reliable indicators of the provenance of sediments. The heavy mineral assemblages and the major and trace element contents of sedimentary rocks from the Neogene continental successions of the Central Depression in Chile and the Mauri and Corque Basins in the Altiplano of Bolivia reflect volcanic source rocks with different degrees of magmatic differentiation and alkalinity. These results indicate that the source rocks of the Central Depression were less differentiated (andesite to rhyodacite) than those of the Altiplano basins (rhyodacite to rhyolite). The low concentration (cations per formula unit) of total Al ( 0.15 pfu) and [Ca+Na] (f0.92 pfu), the variable Ti content (0.01–0.04 pfu) of the clinopyroxenes and the high [Nb/Y] (>0.7) in whole-rock analyses of sandstones from the Mauri Basin indicate erosion of alkaline rock sources. Locally, the low concentration of total Al (

The purpose of this study was to investigate the impact of redox-induced changes in the organization of the clay fraction of a bulk vertisol using transmission electron microscopy. Chemical and X-ray powder diffraction (XRD) analyses indicated that the oxidized clay was composed of 32% kaolinite and 68% non-pure smectitic material, mostly a dioctahedral beidellite with octahedral Fe, according to Quantarg2 and DecompXR models.The cation exchange capacity of the soil increased from 26.1 to 65 cmolc+ kg-1 due to structural iron (FeStr) reduction and dissolution of oxide coatings. Transmission electron micrographs revealed dramatic changes upon reduction. Oxides were dissolved and the smectite increased in particle darkness, lateral extension, thickness, compactness and stacking order. These changes were interpreted to be a consequence of sorption of ferrous Fe and reduction of FeStr, as found in previous studies on pure Fe-bearing smectites.

International audience

The sources and potential availability of chromium (Cr) on soils formed on ultramafic rocks were investigated with mineralogical studies and selective chemical extractions. Soil solutions were collected in the field (i) along a soil toposequence under natural vegetation with ceramic cups; (ii) under grass in a mandarin trees plantation with tension-free tube lysimeters. On selected soil solutions, the Cr(VI) was determined colorimetrically with the s-diphenylcarbazide method and total Cr by ICP-AES and speciation of Cr(VI) was performed with the MINEQL+ V 4.5 software. The main mineralogical sources of Cr were Cr-substituted goethite and chromite. Up to 90 mg kg(-1) of Cr was extracted by KH(2)PO(4), whereas KCl extractable Cr was very low, indicating that exchangeable Cr was mainly in the highly toxic Cr(VI) form in these soils. Under natural vegetation, the Cr concentrations in the soil solutions remained relatively low (20 microg l(-1)) due to the high retention of the Cr(VI) anions by Fe-oxides. The Cr concentrations were larger in well aerated colluvial soils, where high levels of Mn-oxides are able to oxidize Cr(III) to Cr(VI), than in piedmont soil where the Mn-oxide content is lower, or in alluvial soils from the lowlands, where waterlogging occurs. Cr concentrations reached 700 microg l(-1) in the field that was fertilized with high amount of phosphorus, due to the exchange of Cr(VI) with phosphate. In such conditions, toxicity phenomena for crops can be expected.

22 ref.; International audience