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International audience; The renewal of interest in Zn-Pb non-sulphide ores has been induced by mineral processing improvement and leads to new exploration and mining projects in the world. Although the mineralogy is often precisely known, and despite several studies linking ore deposition to regional tectonics, absolute dating of non-sulphide stages is rare and structure of ore bodies was largely disregarded. Geochronological data from non-sulphide ores are essential to timely constrain alteration episodes and to insert supergene ore genesis in the climate and tectonic evolution of the metallogenic province. The access to internal organization of ore could reveal post-mineralization episodes related to supergene evolution. Thus, a rock magnetism study combining anisotropy of magnetic susceptibility (AMS) and palaeomagnetism was performed on four non-sulphide deposits from the Moroccan High Atlas. AMS generally shows similar horizontal magnetic fabrics for ores and the clayey and carbonaceous internal sediments filling karstic cavities. The palaeomagnetic directions of ores and internal sediments are compatible, and the calculated poles are consistent with the last 30 Ma of the Africa apparent polar wander path, with an upper age at 0.78 Ma. The proposed three-step scenario is placed within the evolution of the Moroccan High Atlas belt. Deposition of primary sulphides is contemporaneous with opening of the Tethyan and Atlantic oceans. During the Tertiary, intracontinental deformation gave rise to the High Atlas fold-and-thrust belt and to regional uplift. Finally, Zn-Pb sulphides hosted in carbonates experienced oxidation under an arid climate to form karst-related Zn-Pb non-sulphide ores. These promising results pave the way for an efficient method to constrain the internal fabrics and age of Zn supergene deposits.

International audience; The demand in mineral resources is increasing rapidly, but there is a lack of transparency in the trade of concentrates raw mineral materials because of speculation and involvement in the finance of armed conflicts. Because of the distance between primary extraction and the final production sites it is difficult to check the origin of these products. An identity card is required for mineral commodities, so that trading in the industry can be verified and the traceability of concentrates ensured. This problem may be considered as an inversion process: studying the products sold to identify the original ore. The discriminant parameters are mineralogical composition, identification of textural microfacies of the target minerals (pyrite, sphalerite and chalcopyrite), " pseudo-paragenetic sequence " , and the contents and distributions of minor elements of target minerals. Statistical tests are used to compare the chemical composition of three target minerals. The application to Volcanic Massive Sulphide ore deposits shows that it is possible to distinguish target minerals between ore deposits in the Iberian Pyrite Belt province and from the Urals province using the selected characteristics. Ore deposits from different provinces may be discriminated using the identity cards, as well as different deposits in the same province.

International audience; Supergene non-sulfide Zn deposits offer high mineralogical diversity including clayminerals that can incorporate significant amounts of Zn like sauconite. Although clayeymaterial is commonly observed in such ore deposits, its nature and origin have beenrarely studied, especially in carbonate-hosting environments. However the role of clayminerals is essential for mineral processing because they usually have a negative impacton zinc recovery.In this work, we focus on the Bou Arhous Zn-Pb ore deposit in Eastern High Atlas,Morocco. This deposit is located in an anticline formed by Lower Jurassic limestoneand marl, with Upper Triassic shale in the core of the anticline. Zn-rich clayey materialfills karstic cavities and two types of clay rich deposits have been identified field: 1)white to ochre granular clay (kaolinite/smectite (K/S) irregular mixed layers, smectiteand illite) and 2) red smooth clay (kaolinite, chlorite, illite). The white to ochre granularclays are closely associated with supergene willemite (zinc silicate), one of the main Znbearing mineral phases of the Bou Arhous deposit. The red smooth clays fillkarst-related cavities cutting across the non-sulfide mineralized bodies. The red smoothclays present evidence of stratification that reflects internal sedimentation processesduring karst evolution. Bulk chemical analyses reveal that the Zn content is highlyvariable in all clayey samples and even can reach several percent. This enrichment maybe due to fine inclusions of zinc silicate or carbonate in the clayey material, or to theoccurrence of Zn clay minerals (i.e. sauconite).The mineralogy of clays and associated minerals in bulk powders and separated

International audience

Based on a combined geometrical and mineralogical analysis, a three-stage model of formation of the mineralized veins of the giant Imiter silver deposit (Anti-Atlas, Morocco) is herein proposed. A first episode is characterized by the development of quartz, pink dolomite and Ag-rich minerals veins formed during a dextral transpressive event. The second episode is associated with a normal left-lateral motion that re-opens previous structures, filled by pink dolomite gangue. Alteration stages contribute to a local Ag enrichment. Basé sur l'étude de nouvelles données géométriques et minéralogiques, un modèle de formation en trois stades des veines du gisement d'argent d'Imiter (Anti-Atlas oriental, Maroc) est proposé. Le premier stade est caractérisé par le développement des veines les plus riches, à remplissage de quartz puis dolomite rose, dans un contexte transpressif dextre associé à une direction de raccourcissement NW–SE à WNW–ESE. Le second stade, à remplissage de dolomite rose, est associé à un cisaillement senestre normal, contrôlé par une direction de raccourcissement nord–sud, réutilisant certaines des structures du stade 1. Des phénomènes d'altération contribuent à un enrichissement local en Ag.

Numerous studies and observation have been made on the influence of flow to crystal growth in solution. Previous observations of growth bands in natural galena suggests that upstream crystal faces possess a higher growth rate (Kessler et al. 1972). Flow control on crystal growth is complex and different approaches have therefore been considered. Studying at very thin scale focuses on crystal face behaviour with effect of flow on crystals defects (e.g. step bunching; Chernov 1992 and 2004). At crystal scale several observations and models propose to link crystal shape and growth kinetics to fluid flow. Experiments showed that in case of volumic diffusion, the bulk crystal growth rate is proportional to the inverse of the square root of the flow kinetics (Garside et al. 1975). By experiments on ammonium-dihydrogen phosphate (ATP) (Prieto & Amoros 1981) and This work concerns a very simple and well-defined geological situation: calcite-rich precipitate formed in a horizontal pipe channelling hot water (82°C) of hydrothermal spring in Chaudes-Aigues city (French Massif Central). Shape preferred orientation statistics were performed on 563 calcite sections in the (0001) calcite plane, shows elongated shapes with a general orientation parallel to the pipe axis. The mean shape orientation is the average of two distinct sub-populations that deviated slightly from the pipe axis. Observation on calcite shapes and the direction of the magnetic lineation are coherent, and suggest that it is possible to track hydrothermal paleo-circultion using magnetic lineations and petrographic fabrics. The proposed crystal growth model is based on the work of Gilmer et al. (1971). These authors consider two kinds of processes: diffusion of solute through a volume of unstirred liquid (i.e. boundary layer) to the crystal surface and reactions at the surface leading to the incorporation of molecules in the lattice. When the boundary layer is thicker, the diffusion process becomes slower and controls the crystal growth rate. Thus, it is possible to establish a quantitative link between growth rate and fluid velocity. Such equation has been only demonstrated in the case of crystal face parallel to fluid flow (Carlson 1958; Gilmer et al. 1971). This work proposes to estimate crystal growth rate in flowing solution based on diffusion through the boundary layer thickness. This latter is defined by a combination of diffusion law with fluid dynamical equation simplified for high Reynolds number and for crystal faces orientated from 90° to –18° as function of the flow. The proposed growth rate equation depends on two main parameters: (a) the position along the face and (b) the angle made by flow with the crystal face. The growth rate equation is proportional to the square root velocity and is in agreement with the Garside et al. experiments (1975). More over, this model is applied to calcite growth rate in 2D section perpendicular to the axis. The calcite shape reconstruction is similar to the texture observed at Chaudes Aigues. The differential growth rate with exposition allows to explain the elongated shape of the calcite crystal observed in the pipe. This approach may be applied for various geological setting, from deep metasomatism to flowing on the earth surface.

The textural description of a solid can be seen as a two stages job. The first one consists in determining the mineralogical composition and the size of the components. Information collected during this step will be named Granularity Parameter (GP). The second stage is a study of the spatial distribution of the components, called below Distribution Parameter (DP). The proposed method quantifies GP and DP by respectively constitution heterogeneity (HC) and distribution heterogeneity (HD). HC and HD are functions defined by P. Gy, 1982 and 1988 in his “Theory of particule material sampling”.

In deformed massive sulfide deposits, it is commonly difficult to distinguish between primary stockwork mineralization and remobilized sulfides that occupy late cleavages and deformation structures, and the mechanism of formation of the deformation veins is not always clear. An analysis of sulfide vein networks associated with two massive sulfide deposits of the Iberian Pyrite Belt is presented as an example of this complexity. Variscan deformation has affected the massive sulfide-related stockworks at La Zarza and Tharsis and led to the formation of sulfide-bearing deformation veins. The primary feeder stockwork has a complex mineralogical composition with pyrite-rich veins rimmed by narrow Co-As assemblages (e.g., cobaltite and arsenopyrite). Interstitial galena, chalcopyrite, and sphalerite minerals are also observed. The vein set developed during deformation was emplaced within cleavage and shear planes characteristic of the regional south-verging tectonics. Away from massive sulfides, the characteristic minerals of the syntectonic veins are pyrite and quartz. However, deformation veins developed in contact with primary feeder veins and massive sulfide have Co-As–rich rims and base metal sulfides similar to the primary feeder veins. The development of the complex vein paragenesis within the stockwork zones is explained in terms of regional-scale deformation models.

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.

International audience

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.