Analyse des circuits mineralurgiques par cascadographie—Caracterisation de l'alimentation et evaluation de la fonction de selection

Cascadography is a generic, laboratory, instrumentational method of separating and characterizing mixes of mineral or particle species based on subtle physical and physiochemical differences. Like gas chromatography, cascadography characterizes a sample by the temporal separation of mineral species. Using a number of identical unit operations in series, the sample feed is injected into the first unit operation at time equals zero, and samples are taken at regular intervals from the last cell product. From the n-th cell, the product becomes the feed to the (n+1)th cell. Other than as a product, no material is removed from any cell—there is no circulating load or feedback. First to appear in the product are the rapidly moving particles followed by the more slowly moving particles. For example, if there exists a number of identical particles, then the particles will appear together in the output of the system. As the number of cells in series increases, so does the resolution between batches of particles with similar properties. If the system being studied is flotation, pure mineral species as well as locked particle assays can be made of the feed and waste streams, and from this information, the flotation cell selection function can be calculated.     

Application de la méthode des simulations croisées à l’analyse de tendances dans la relation pluie-débit à partir du modèle GR2M : cas du bassin versant du N’zi-Bandama (Côte d’Ivoire)

The study area is the N’zi watershed, sub-watershed of the Bandama River (Ivory Coast). The N’zi watershed is located between longitudes 3°49′ and 5°22′ West and latitudes 6°00′ and 9°26′ North and covers an area of 35,500 km². This study aims to identify trends in the rainfall-runoff relationship by using a monthly conceptual model. The methodology has consisted on the one hand in highlighting the existence of interannual climate and hydrological variability by using the method of segmentation of Hubert, and on the other hand, in applying the crossed simulations method by using the GR2M model, over several 7-year sub-periods. The results of the application of the method of segmentation of Hubert have demonstrated the presence of a hydroclimatic variability in the N’zi watershed. The modifications of the climate and physical conditions of the flow resulted in a modification of the hydrological response of the watershed translated by a non-stationarity in the rainfall-runoff relation.     

Une nouvelle méthode de cartographie de la région d’Oran (Algérie) à l’aide de la télédétection multispectrale

We have mapped the region of Oran, Algeria, using multispectral remote sensing with different resolutions. For the identification of objects on the ground using their spectral signatures, two methods were applied to images from SPOT, LANDSAT, IRS-1 C and ASTER. The first one is called Base Rule method (BR method) and is based on a set of rules that must be met at each pixel in the different bands reflectance calibrated and henceforth it is assigned to a given class. The construction of these rules is based on the spectral profiles of popular classes in the scene studied. The second one is called Spectral Angle Mapper method (SAM method) and is based on the direct calculation of the spectral angle between the target vector representing the spectral profile of the desired class and the pixel vector whose components are numbered accounts in the different bands of the calibrated image reflectance. This new method was performed using PCSATWIN software developed by our own laboratory LAAR. After collecting a library of spectral signatures with multiple libraries, a detailed study of the principles and physical processes that can influence the spectral signature has been conducted. The final goal is to establish the range of variation of a spectral profile of a well-defined class and therefore to get precise bases for spectral rules. From the results we have obtained, we find that the supervised classification of these pixels by BR method derived from spectral signatures reduces the uncertainty associated with identifying objects by enhancing significantly the percentage of correct classification with very distinct classes.     

L'érosion des chaînes de montagnes : influence de la sédimentation de piedmont

The applanation of mountain belts that results in peneplain is generally considered to be caused by the long-term activity of erosion. Peneplanation has been previously defined as the lowering of an elevated topography and the concomitant subduing of its relief. We propose a model following which piedmont sedimentation induces the base level rise, allowing applanation to develop at high elevation and resulting in an elevated ‘peneplain’. This model is illustrated by the morphological evolution of the southern flank of the Pyrenees during the Cainozoic. To cite this article: J. Babault, J. Van Den Driessche, C. R. Geoscience 337 (2005).     

Echantillons de Référence pour I Analyse Végétale

Lee réaultata interlaboratoires obtenus sur douze plantes destinées à servir d'étolons sont présentés. L'analyse porte sur les éléments N, P, K, Ca, Mg, Fe, Cu, Mn, Zn. Les résultats comprennent la moyerme calctulée arithmétiquement, la médiane, la distribution, I'éaart-type, le coefficient de variation et la valeur recommandée pour chaque élément.     

Distribution des thanatocénoses récentes de radiolaires dans l'Atlantique nord-oriental et le sud de la mer de Norvège

The relative abundance of five groups of radiolarian species (nasselarians and spumellarians) in the thanatocoenoses within the recent sediments from 64^oN to the Equator is described. Four types of thanatocoenoses of Radiolarians and several subtypes are distinguished and in the broadest sense four major faunal zones can be delimited: north of 60^oN, a subarctic zone, a boreal zone, a subtropical zone whose boundary runs approximately along 45^oN and, south of 13^oN, a tropical zone. The correlations between the faunal provinces and climatic belts are more gradual in the low and intermediate latitudes than in the high latitudes     

Ennoyage des mines de fer lorraines : impact sur la qualité de l'eau

The flooding of the abandoned iron mines of Lorraine leads to a degradation of the groundwater quality. Laboratory experiments allowed us to build a kinetic chemical model based on simple chemical mechanisms. During mining operations, pyrite oxidation and carbonate dissolution lead to the precipitation of gypsum. The local decrease of pH favours local dissolutions of minerals and releases ions that are fixed on cationic exchange sites. During the flooding of the mine workings, the dissolution of the newly precipitated gypsum, the precipitation of carbonates and cationic exchange reactions are responsible for the increase of the concentrations of sulphate, magnesium, sodium, potassium and strontium in water. Thereafter, these concentrations would decrease with the natural leaching of the mining reservoir. To cite this article: P. Collon et al., C. R. Geoscience 336 (2004).     

Apport de la gravimétrie à l'étude des structures profondes du Sahel de Tunisie (cas de la région de Kairouan–Sousse–Monastir)

The monotony of the surface and of the deep structure of the Sahel domain in eastern Tunisia (low topographic area covered by a Quaternary series) induces the possible existence of an important subsiding collapsed block and associated faulted zones. Gravity data analyses have permitted the reconnaissance of the crustal and gravimetric setting of the northern part of the Sahel domain and the discussion of main outlines of subsurface structures. The deep structure of a particular zone (Kairouan–Sousse–Monastir area) demonstrates the existence of an east-west en-doigt-de-gant crustal thinning confirmed by the gravity data. This deep structuring is perfectly showed by the high-resolution second-order enhanced analytic signal technique developed to image geologic boundaries such as contacts and faults. This technique, correlated with the distribution of all seismic events in the last century, has permitted to define an important east–west Kairouan–Sousse–Monastir tectonic corridor (CKSM). This corridor corresponds to major faults oriented east-west, were some folded structures can be developed. To cite this article: H. Gabtni, C. R. Geoscience 337 (2005).     

Évolution récente et actuelle de la côte basque française (analyse et perspectives)

A recent multidisciplinary study, comprising existing data analysis and geomorphological and geological fieldwork, has helped clarify marine erosion processes of Pyrenean formations along the Basque Coast. An important discovery was made during our study of an alterite of regional extent, which calls into question recent and present evolution of the Basque Coast and the processes leading to coastline retreat. Modelling these factors has made it possible to propose a predictive scenario for future coastal evolution. To cite this article: A. Genna et al., C. R. Geoscience 337 (2005).     

Anisotropie verticale de la perméabilité de l'horizon fissuré des aquifères de socle : concordance avec la structure géologique des profils d'altération

Pumping tests carried out in the fissured layer of a granitic hard-rock aquifer, interpreted at the observation wells by means of the analytical solution of Neuman and at the pumping wells with that of Gringarten show the existence of a strong vertical anisotropy of this layer of the aquifer; the horizontal permeability is clearly and systematically higher than the vertical one. These results agree perfectly with the geological observations, the fissured layer of the weathered granite profile showing the existence of many sub-horizontal fissures. It confirms that, within the fissured layer, the permeability of sub-horizontal fissures due to the weathering process dominates over that of sub-vertical fissures of tectonic origin. To cite this article: J.-C. Maréchal et al., C. R. Geoscience 335 (2003).To cite this article: J.-C. Maréchal et al., C. R. Geoscience 335 (2003).     

Etude physico-chimique des résidus de pyrolyse de la sporopollénine

Two parameters are chosen to characterize the pyrolysis residues of sporopollenin: the first one is the $\text{d}{}_{1600}\text{d}{}_{1700}$ ratio, where d₁₆₀₀ and d₁₇₀₀ are the optical densities of the absorption bands at 1600 and 1700 cm^?1, respectively; the second one is the paramagnetic susceptibility χ_p measured by E.P.R.Those two quantities increase rapidly above 300°C, which confirms previous results that the sporopollenin structure undergoes important modifications at this temperature. A striking similarity is observed between the properties of sporopollenin residues and those of natural kerogens.     

Apport de la gravimétrie à l'étude de la structure du bassin des Triffa (Maroc nord-oriental) : implications hydrogéologiques

Various techniques (horizontal and vertical derivatives, upward continuation, Euler deconvolution) have been applied to the gravity data from the Triffa's plain and the north flank of the Beni-Snassen massif to delineate various major geological structures such as faults and basins. These results allow the production of a structural map showing the fault systems for the survey area. This map forms the basis for planning future hydrogeological research in this region. To cite this article: D. Khattach et al., C. R. Geoscience 336 (2004).     

Stratigraphie séquentielle du Carbonifère inférieur du Haut Atlas central et des Jebilet (Maroc): un exemple de bassins à turbidites contrôlées par la tectonique

Marine deposits of Visean age are well exposed in the Marrakesh area. Two third order sequences are identified in the central High Atlas and Jebilet: SA, which is of Middle Visean age (CM); SB of Upper Visean age (Cf6αβγ); and a complex with olistoliths of Upper Visean-Lower Namurian age (Cf6δ-Cf7). The SA and SIB sequences consist of a relative low-lying system tract with turbidites, a retrograde transgressive system tract and a prograde high-lying system tract. The relative low level comprises a turbiditic fan fed by tectonic uplift, which does not strictly coincide with eustatic processes. The transgressive system tract retrogrades firstly on the slope during tectonic reactivation with slumps, channels and silty levees, secondly on the shelf edge with a mixture of turbiditic and storm deposits and finally on the shelf with storm deposits and reef building. The high level system tract progrades on the shelf by a delta fan. This model is similar to sequences described in Spain and Italy by Mutti (1992), where tectonism is dominant.Nevertheless, eustasy, as described by Vail et al. (1977) played a part, since the same sequences are found in the chart of Ross and Ross (1987): S1, which of Middle Visean age (Cf5) and S2 which is of Upper Visean age (Cf6αβγ). Only the comparison between regional sequences described in Morocco and the sequences of the European platform allow tectonics and eustasy to be taken into consideration.     

Vers une meilleure représentation de la distribution et de la variabilité de l'ozone atmosphérique par l'assimilation des données satellitaires

Data assimilation plays an important role in the analysis of atmospheric data, in particular for numerical weather prediction and the detection of climate variations. In the field of atmospheric chemistry, assimilation techniques have been recently developed to study the distribution of tracer species, with emphasis on the ozone content. The present work reports on assimilation experiments of vertical ozone profiles from the GOME instrument performed with MOCAGE, a chemical-transport model and a 3D-FGAT variational technique. It is shown that this technique is very well adapted for ozone assimilation and can be extended to various sensors or other trace species. To cite this article: S. Massart et al., C. R. Geoscience 337 (2005).     

Paléoclimat des Petites Antilles depuis 4000 ans BP : l'enregistrement de la lagune de Grand-Case à Saint-Martin

A 2.5-m-thick sequence of lake sediments at the Étang de Grand-Case, Saint Martin (French West Indies) is studied here. Significant hydrological budget fluctuations allows distinction of three main climatic periods: (1) an overall dry period (4200 BP–2300 BP), characterised by carbonated mud, gypsum and storm sand layers; (2) a wet phase (2300 BP–1150 BP) dominated by organic mud; and (3) a more complex phase (1150 BP to present), with detrital inputs due to human activities. Comparison with other regional high-resolution records shows that similar climate modifications typify the whole Mesoamerican and Caribbean area. The climatic phenomena that are implicated in the variations of both precipitation and hurricane frequency over the Lesser Antilles are due to the latitudinal displacement of the inter-tropical convergence zone. These data give new support to the hypothesis of the existence of a correlation between peopling phases and climate variations in the Caribbean as previously proposed by some archaeologists. To cite this article: P. Bertran et al., C. R. Geoscience 336 (2004).     

Contribution du paleomagnetisme a l'etude des series volcaniques cenozoiques et quaternaires de sardaigne nord-occidentale : Le probleme de la derive de la sardaigne

A paleomagnetic study has been made about the calc-alkaline lavas (Late Oligocene-Middle Miocene age) and the Plio-Quaternary basaltic alkaline lavas of the Logudoro and Bosano (North West Sardinia). This study is based on the chronological scale of the volcanic phases of this part of Sardinia; this scale was established on field observations and K/Ar datings. Hence, the authors propose a sketch of paleomagnetic stratigraphy and discuss the problem of the drifting of Sardinia in the course of Cenozoic time. They are lead to the conclusion that the move of Sardinia terminated at the moment when the calcalkaline lavas flowed into the Logudoro and the Bosano.

Résumé

Une étude paléomagnétique a été réalisée sur les laves calco-alcalines (âge Oligocène terminal-Miocène moyen) et les laves alcalines basaltiques plio—quaternaires du Logudoro et du Bosano (Sardaigne nord-occidentale). Cette étude repose sur l'échelle chronologique des phases volcaniques de cette région de la Sardaigne établie à partir d'observations de terrain et de datations K/Ar. Les auteurs proposent ainsi une ébauche de stratigraphie paléomagnétique et discutent du problème de la dérive de la Sardaigne au cours des temps cénozoïques. Ils sont amenés à conclure que la rotation de la Sardaigne était achevée au moment où les laves calco-alcalines se sont mises en place dans le Logudoro et le Bosano, car le paléomagnétisme de ces laves ne permet pas de mettre en évidence une telle rotation.     

Apports des analyses chimiques et isotopiques à la connaissance du fonctionnement des aquifères plio-quaternaire et turonien de la zone synclinale d''Essaouira, Maroc occidental

The Essaouira synclinal zone is one of the Moroccan semi-arid zones with annual rainfalls not exceeding 300 mm yr⁻¹ and very high potential evapo-transpiration of about 920 mm yr⁻¹. This syncline with a Senonian axial zone is bordered by two diapiric structures of Triassic deposits: the Tidzi Diapir that outcrops in the east and south, and the hidden Essaouira diapir in the west, which was found by geophysics. This syncline contains two main superimposed aquifers. (i) The Plio-Quaternary aquifer consists of sands, sandstone and conglomerates and provides the main part of the water supply. This free-water table flows out towards the northwest and its surface is affected by significant piezometric variations. (ii) The calcareous dolomitic Turonian is a confined aquifer under the Senonian marls in the and in direct contact with the Plio-Quaternary. For a few years, the drinking water supply to the town of Essaouira has come from deep drillings.These two aquifers were sampled in June 1995 and in Januray 1996 after exceptional rainfalls. All waters have the same geochemical profile. The interpretation of the total dissolved solids and chloride content of Plio-Quaternary aquifers makes it possible to specify their origins. It emphasises, in particular, the source from the Ksob Wadi in the northeast and the role of the hidden Essaouira diapir. Nitrate levels were raised excessively, increasing at the same time as chloride concentrations during the rains of the winter of 1996, and underline the wells vulnerability to pastoral and domestic activities.The interpretation of O- and H-isotopes distinguishes two contrasting Plio-Quaternary and Turonian aquifers with an Atlantic origin for the rain recharge. A specific campaign was varried out in November 1996 to date water from the Turonian aquifer by ¹⁴C. Two boreholes draw water of several thousands years old.