Search

The Cu ore of Ifri is a chalcopyrite stockwork hosted by Cambrian formations and was until now interpreted as a syngenetic massive sulphide deposit. Textural studies highlight two generations of pyrite early (Py I) and late (Py II) with respect to the regional deformation. The chalcopyrite stockwork overprinted Py II, outlining the epigenetic nature of the Cu mineralization. Regarding the origin of Cu-depositing fluids, the presence in the stockwork paragenesis of an U, W, Sn association and preliminary Pb/Pb dating of a brannerite belonging to this association suggest a contribution of the Tichka granite.

This study presents an attempt to use the Anisotropy of Magnetic Susceptibility (AMS) to trace hydrothermal flow directions. The Chaillac Basin is located at the contact between the Mesozoic Paris Basin and the Variscan Massif Central, (France). The basin has been formed along N-S normal fault that allowed the sedimentation of Hettangian sand (−203 Ma) on a metamorphic basement. Stratiform F-Ba-Fe rich deposits occur as syn-sedimentary mineralization within silicoclastic Hettangian sediments. The mineralization sequence is formed by the succession of fluorite-baritegoethite. It cements the sand and presents surficial sinter structures. The tectonics shows that sinter crusts have been fed by vertical E-W and N-S veins emplaced during a general E-W extension. This later is coeval with the subsidence of the Paris Basin. The principal magnetic carrier is the goethite that has been precipitated by hydrothermal fluids. Magnetic fabrics measured in goethite-rich veins and in proximate sandstones are dominated by a strongly inclined magnetic lineation (maximum axis). In sinter and in sandstone located far from the vein (>1 m) the magnetic fabric is dominated by horizontal lineation with an azimuth similar to the sedimentary direction. The textures indicate that goethite has a free crystallisation in an open media (vein or sand porosity). Thus no late deformation has affected this deposit and the magnetic fabric is primary. Image analyses, performed on goethite shape and spatial distribution, suggest that the magnetic fabric is the result of oriented goethite growth produced by hydrothermal fluid flow. This work proposes a new approach to constrain hydrodynamic model developed in geology by using the AMS method: textural study combined with efficient magnetic fabric measurements should be used for systematic investigation to trace flow direction in fissures and in sand porosity.

International audience

With respect to sustainable development, the leachability of trace metal from solid materials in contact with water has focused much attention over the years. Portland cements produced in industrial kilns generally contain from 10 to 300 mg/kg of trace metals. The behaviour of these endogenous metals has been, in this regard, the target of different leaching studies. Many of these researches concluded that heavy metals release are lower than analytical detection limits. Although satisfying from an environmental point of view, it induces a lack in the knowledge about the trace metals behavior during the leaching of cement based material. Accordingly, we designed the CTG-LEACHCRETE device, a dynamic leaching system (modified Soxhlet type) that overcomes this difficulty and allows long term monitoring. The experimental procedure is presented and preliminary results are discussed.

International audience; L'étude structurale et métallogénique (gîtologique) du gisement de cuivre d'Ifri (Haut Atlas occidental, Maroc) montre qu'une grande partie de la minéralisation est liée à un stockwerk, dont la formation est contrôlée par un cisaillement ductile tardi-hercynien à vergence NNW. Ce résultat significatif remet en question le caractère syngénétique jusqu'alors évoqué pour la minéralisation et permet ainsi de proposer un nouveau guide d'exploration pour ce type de gisement. Structural and metallogenic studies of the Ifri copper deposit (western High Atlas, Morocco) demonstrate that a great part of the mineralization was linked to a stockwork developed during a Late-Variscan NNW-verging shearing event. With this significant result, the until now accepted syngenetic character for this mineralization has to be reconsidered and allows to suggest a new guide of prospection for this kind of deposit.

Metallurgical slags of different ages resulting from Pb-metallurgy in the PImageíbram district (Czech Republic) have been studied. The chemical analysis (EPMA) of melilite, clinopyroxene, olivine and glassy matrix showed the following ZnO concentrations (in wt. %): 3.20-11.93 (melilite), 1.56 (clinopyroxene), 1.29-7.82 (olivine), 1.58-6.58 (glass). The Zn partition coefficient D = Cs / Cl between crystallized phases and coexisting glass was calculated. The values obtained are: 1.96-2.16 (melilite), 0.41 (clinopyroxene) and 0.79-1.19 (olivine). The distribution of zinc between the crystalline phases and glass depends on the phase assemblage, which reflects the blast furnace charge and temperature, as well as the cooling conditions of slags.

Experiments of dissolution of a soluble boro-silica glass were performed at 37°C in a saline solution without and with 50, 75 and 100 ppm of added silica. After reaction silica concentration was measured by AAS and colorimetry and fibers were investigated by SEM-EDS and XPS. The results give informations on the dissolution velocity of the glass and the factors controlling the formation rate of the gel layer and its composition. The dissolution velocity measured at the unaltered glass-gel interface is not significantly decreased by the silica concentration in solution whatever its origin (leaching of the glass fibres or initial addition). Accordingly, gel formation is controlled by the chemical reactions rate at, or near, the boundary of the unaltered core. The composition and the stucture of the gel layer are depending on the silica concentration in solution above a threshold of about 50 ppm. The framework of the gel appears to play the more important role in the dissolution velocity of the glass.

Thomassin Jean-Hugues, Touray Jean-Claude, Trichet Jean. Etude des mécanismes d'altération d'une obsidienne : les données de l'analyse de surface (spectrométrie de photoélectrons et microscopie électronique à balayage). In: Phénomènes de transport de matière dans l'écorce terrestre. ATP - CNRS. Action thématique Programmée du Centre National de la Recherche Scientifique. Résultats scientifiques. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1979. pp. 23-27. (Sciences Géologiques. Mémoire, 53)

The experimental alteration in water at 90°C of an andesitic glass and two basaltic ones has been investigated via X-ray photoelectron spectrometry (XPS) and electron microscopy. At the beginning of the reaction, the hydration of glass and the ion exchange with H+ of the solution take place. After a few days, one notices the growth of a superficial Fe-bearing layer. After one month duration, this layer becomes either non sticking (basaltic glasses) or sticking on the surface (ande¬ sitic glass) : it is made of iron-bearing phases, amorphous or poorly crystallized (ferrihydrite) . In all cases, a growth of sepiolite occurs at the interface preci¬ pitate-solution and, for the iron-richest glass, iron phyllosilicates growth in the inner part of the alteration layer., L'altération expérimentale dans l'eau douce à 90°C d'un verre andésitique et de deux Verres basaltiques artificiels a été étudiée par spectrométrie XPS et microscopie électronique. Au début de l'interaction, l'hydratation du verre et l'échange d'ions avec les H+ de la solution prédominent. Après quelques jours, on note la croissance d'une couche superficielle très enrichie en fer ; au bout d'un mois, cette couche devient faiblement adhérente (verres basaltiques) ou reste au contraire fixée au substrat (verre andésitique) ; il s'agit de phases ferrifères amorphes ou mal cristallisées (ferrihydrite) . Parallèlement, se forme dans tous les cas de la sépiolite à l'interface précipité-solution et, dans le cas du verre le plus riche en fer, des phyllosilicates ferrifères localisés à l'intérieur du microprofil d'altération., Thomassin Jean-Hugues, Touray Jean-Claude, Crovisier Jean-Louis, Ehret Gabrielle. Etude par analyse XPS et microscopie électronique des microprofils développés lors de l'altération expérimentale dans l'eau douce de verres basaltiques et andésitiques. In: Pétrologie des altérations et des sols. Vol. I : Pétrologie expérimentale. Colloque international du CNRS, Paris 4-7 juillet 1983. Strasbourg : Institut de Géologie – Université Louis-Pasteur, 1983. pp. 127-137. (Sciences Géologiques. Mémoire, 71)