Simon Blancher - Academia.edu (original) (raw)

Papers by Simon Blancher

Industrial dusts are commonly agglomerated using empirical recipes with binders such as bentonite... more Industrial dusts are commonly agglomerated using empirical recipes with binders such as bentonite, while Sludges are agglomerated into mixes. Those materials contaminate the products, are expensive and generate significant amounts of slag. Achieving cold dust agglomeration with little or no binder requires understanding the controlling parameters in order to predict and optimize the process behavior. This in turn necessitates comprehensive dust characterization to base predictions on measurable characteristics. In the present work we collected 13 Mn-rich dusts over all the process chain: feed fines, smelting, and refining dusts, as well as ferromanganese alloy dust. This is the first systematic study of dusts along the Mn-processing chain for chemical, physical and mineralogical parameters. X-Ray Diffraction, Qemscan® and laser granulometry analyses show that the mineralogy, Particle Size Distribution (PSD) and morphology evolves from complex heterogenous to simple, homogenous along the process chain: The mineralogy of the primary ore dusts shows various hydroxides, oxides, carbonates, tectosilicates and phyllosilicates. The furnace dusts contain oxides, tectosilicates and carbonates with volatiles, while the refining dusts present only oxides and metal. Finally, the Metal dust is nearly pure metal. Particle morphologies and PSD vary from jagged, irregular particles with broad PSD (>1 mm to <0.3 µm) to smooth and spherical with narrow PSD (100 µm to <0.3 µm). The Metal dust is an exception with angular particles. The Cationic Exchange Capacities (CECs) of all samples range from 0 to 22 meq/100g. Specific surface areas (SSAs) range from <0.1 to 27m²/g, and seem to decrease with from ore feed to Metal dust. This may be due to the disappearance of hydrated and/or sheet-bearing minerals, since a smaller grain size usually implies an increased SSA. The zeta potential varies strongly over the range of the samples tested. However, beside the Gabon ore which has an Isoelectric Point (IEP) ~ 4.1, the other IEP ranges between 2 and 2.5. From previous studies, it is known that feed material dusts, with intrinsic properties close to that of binders, agglomerate better than process dusts. It may hence be interesting to test the process dusts as additives mixed into the feed material to fit specific agglomeration requirements.

Fe-Ti oxides concentrates produced from heavy mineral sand deposits are widely used for the produ... more Fe-Ti oxides concentrates produced from heavy mineral sand deposits are widely used for the production of titanium dioxide pigments that are critical components of white paint, plastics and paper. According to mining industry, the Fe-Ti concentrates mostly consists of three phases: ilmenite, leucoxene and rutile. However, a few mineralogical studies have shown that the variety of Fe-Ti oxides found in sand deposits is far more complex, mostly due to alteration processes. The aim of this contribution is to characterize in detail by means of Qemscan analyses the mineralogy of the three main concentrates (ilmenite, leucoxene and rutile) produced by the Grande Côte Operation (GCO) mineralurgical plant in Senegal. The ultimate goal is to characterize the different products and textures formed during the natural ilmenite alteration processes, to localize the phases carrying the main impurities (Cr and P), and finally to determine the physical properties of each mineral component to improve metal recoveries. Along alteration processes, Ti content increase. Ilmenite (FeTiO 3) is progressively transformed into pseudorutile (Fe 2 Ti 3 O 9) particles which could also be altered and transformed into hydroxylian pseudorutile [FeTi 6 O 12 (OH) 3 .3H 2 O] or complex blends of anatase microcrystals (TiO 2). These transformations are accompanied by significant changes in particle textures. Microporosity and fractures appear and the impurity content also increases. Anatase rich microcrystal assemblages, so far described as Leucoxene, could be identified to consist of grains with higher porosities, water contents and higher intrapore impurities. These particles are the main carriers of chromium and phosphorus. The observed mineral transition textures have a significant impact on the ore dressing processes. During these transformations, the physical properties of these phases change, the magnetic susceptibility as well as densities decreases, due to the increase in porosity. The separation of particles, especially those with high porosity will help improving the GCO mineralurgical plant performance and to reduce the impurity contents in finals products.

The carbonatite of Mabounié (Gabon), first described in 1988 [1], is a complex igneous intrusion ... more The carbonatite of Mabounié (Gabon), first described in 1988 [1], is a complex igneous intrusion approximately 2.3 km in diameter hosted in Paleoproterozoic fenitized gneisses and migmatites. Numerous mineralogical and geochemical studies were conducted in the twenty years following its discovery ([2-4], BRGM, pers. comm.) that led to the discovery of a polymetallic lateritic ore deposit above the intrusion. In the present work, new petrographic studies are reported on fresh drill core samples obtained within the framework of the Maboumine project. The carbonatite is heterogeneous sövite, crosscut by a few dikes of rauhaugite (dolomite-rich carbonatite). The mineralogy varies strongly along magmatic bedding, schlieren patches and hydrothermally recrystallized areas [4]. Apatite-sövite and phlogopite-sövite are common and intermixed with each other, and contain a variable amount of Ti-rich magnetite (in some cases, up to 40 vol.% of the rock). Other accessory minerals include rare-earth carbonates, ilmenite, pyrochlore, zircon, baddeleyite, calzirtite and zirconolite. In the lateritic profile developed above the carbonatite suite, the lowermost horizon consists of massive phosphates and is characterized by the dissoluion of carbonates; it is followed by “ribbon” laterites characterized by the breakdown of apatite, and finally by an iron-oxide-rich horizon at the surface of the deposit. Even though pyrochlore is affected by different processes and its composition changes slightly across the profile [3], this mineral remains the main carrier of rare metals (Nb, Ta) and rare earth elements, which are concentrated upward mainly in the “ribbon” ore.

International Journal of Geosciences

The heavy mineral sands of Senegal are exploited to extract titanium oxides and zircon. Mining is... more The heavy mineral sands of Senegal are exploited to extract titanium oxides and zircon. Mining is carried out first by means of a floating dredge and concentration plant which produces a heavy mineral concentrate (HMC) containing on average 78% titanium oxides, 11% zircon and a set of silicate and alumino-silicate minerals. This heavy mineral concentrate is then treated by gravity, magnetic and electrostatic separation to produce titanium oxide concentrates (ilmenite, leucoxene, rutile) and three varieties of zircon concentrates (Premium zircon, standard zircon and medium grade zircon standard). In this study, we describe the various mineral concentrates in terms of mineralogical assemblages, and textural variability within grains, using Qemscan and Scanning Electron Microscopy. The titanium oxide concentrates are differentiated by their TiO2 content and vary from ilmenite to rutile. The zircon concentrates are characterized by the presence of impurities in the zircons, which consist in numerous inclusions of titanium oxides and silicate minerals. The mineralogical characteristics determined by scanning electron microscopy and by Qemscan showed great variability within the grains themselves. Heavy minerals contain many mineral inclusions and show strong chemical zoning.

Separation and Purification Technology

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018

The objective of the SOLSA project (EU-H2020) is to develop an analytical expert system for on-li... more The objective of the SOLSA project (EU-H2020) is to develop an analytical expert system for on-line-on-mine-real-time mineralogical and geochemical analyses on sonic drill cores. As one aspect of the system, this paper presents the building of the hyperspectral library and its incorporation into sparse unmixing techniques for mineral identification. Twenty seven spectra representing 14 minerals have been collected for the library. Three sparse unmixing techniques have been investigated and evaluated using simulated data generated from our hyperspectral library, and real hyperspectral data acquired from a serpentinized harzburgite sample. Among the three techniques, the collaborative sparse unmixing by variable splitting and augmented Lagrangian (CLSUnSAL) method provided the best accurate results on the simulated data. In addition, the results of the CLSUnSAL method show high correlation with that of the QEMSCAN® analysis on the harzburgite hyperspectral data.

Journal of the Southern African Institute of Mining and Metallurgy, 2020

Mineralogical analyses and QEMSCAN ® process simulation were used to characterize a heavy mineral... more Mineralogical analyses and QEMSCAN ® process simulation were used to characterize a heavy mineral concentrate of celestine originating from the Beni Mansour deposit in Algeria, and to model a gravity separation process to remove Sr-, Ba-, and Ca-bearing impurity phases. By analysing the partitioning of Ba, it was shown that the very small amounts of barite present in the sample could not account for the chemically derived Ba concentration in the total sample. It was therefore decided to investigate the presence of Ba that could replace the Sr in celestine in the form of solid solution substitution. It was found that some celestine particles displayed zonation textures with respect to Ba, resulting in difficulties in meaningfully reducing the Ba content without a significant loss of Sr. It was shown that the removal of all barite would lead to a minimum of 0.65 wt% Ba in the final celestine concentrate. Density separation modelling by QEMSCAN® software showed that the 3.5-4.0 g/cm 3 density fraction had higher Sr and celestine concentrations, as high as 46.33 wt% Sr. In this particular fraction, the Ba and Ca contents could be reduced to 0.72 wt% and 0.49 wt% respectively.

Powder Technology

Fine particles (<3 mm) are important, environmentally hazardous wastes of the mining and metal... more Fine particles (<3 mm) are important, environmentally hazardous wastes of the mining and metallurgical industries that still contain valuable metals. Agglomeration, mainly using binders, is a common process to safely recycle those materials. This study aims at mastering cold agglomeration through understanding natural binder properties of the material. For the first time, a comprehensive physico-chemical characterization was performed on 13 samples from a manganese processing chain including ore fines. The main parameters to predict the agglomeration potential of the materials used in the present study are the presence of layer- and/or tunnel-structured phases along with the particle and grain size distribution, hardness and shapes, and particle surface charges. The Gabon ore fines show the best agglomeration potential. The soft, layer-structured plastic minerals (clays, lithiophorite) present naturally coat the hard grains (pyrolusite, cryptomelane) forming particles with enhanced binding potential. Blending these ore fines with low agglomeration potential dusts avoids binder use in the agglomeration process.

The fine fraction (< 2 mm) of the high grade Mn-ore from the world class Moanda deposit, Franc... more The fine fraction (< 2 mm) of the high grade Mn-ore from the world class Moanda deposit, Francevillan basin, in Gabon, contains up to 30 wt. % of manganese and about 0.4 wt. % phosphorous. A pilot study at laboratory scale integrating mineralogy and geochemistry before and after ultrasonic treatment was conducted on the fine fraction (< 2 mm) of oxidized Mn ore in order to reduce the phosphorous content and enrich this fraction in manganese. The fine fraction was dried, crushed at 2 cm and sieved at 2 mm. The two fractions (< 2 mm and 2 mm – 2 cm) were investigated by X-ray diffraction and scanning electron microprobe – electron dispersive spectroscopy analyses. Both fractions contain lithiophorite, cryptomelane and pyrolusite as Mn carrier, and goethite, muscovite, illite and quartz as contaminants. The Mn hydroxide nsutite was only found in the fraction 2mm – 2 cm.The < 2 mm fraction is significantly richer in goethite, muscovite/illite, and quartz. Phosphorous carrier...

Lateritic Mn ore from the southwestern border of the Francevillien Basin in southeastern Gabon co... more Lateritic Mn ore from the southwestern border of the Francevillien Basin in southeastern Gabon contains between 30 and 35 wt % Mn, accounting for about 250 Mt of estimated reserves. The phosphorous content can reach values of up to 0.5 wt % and significantly disturbs the ore beneficiation. A 15-kg ore sample was taken from the lower part of the laterite, close to the contact with the underlying black shales. It was crushed to 5 cm and then to 2 cm, homogenized, and quartered down to 2-kg samples. This sample contains 48 wt % Mn, 6.5 wt % Fe, and 0.25 wt % P. A 2-kg sample was sieved at 2 mm. This fine fraction (FF) (<2 mm), comprising about 30% of the total sample material, contains 28 wt % Mn, 0.4 wt % P, and 11 wt % total Fe, compared to coarse fraction (CF) (>2 mm) contents of 48 wt % Mn, 0.2 wt % P, and 5 wt % Fe. DRX and electron microprobe analyses indicate a similar mineralogical assemblage (goethite-quartz, muscovite, cryptomelane (KMn 8 O 16), lithiophorite (Al,Li)MnO...

International Journal of Geosciences, 2020

Journal of Geochemical Exploration

The association of ﬁne grained MgeNi silicates with oxy-hydroxides in laterites and saprolites re... more The association of ﬁne grained MgeNi silicates with oxy-hydroxides in laterites and saprolites represents challenges for ore processing, in particular, in nickel enrichment. The Weda Bay nickel deposit in Indonesia is a typical example of these complex ores, where clays such as nontronites develop on polyphase serpentinite as protolith. Thus, ores at Weda Bay have a very ﬁne textured and complex mineralogy, which requires a comprehensivemineralogical identiﬁcationthroughtheuseofaseriesofdiﬀerenttypesofanalyticalapproaches(i.e. macroscopic and microscopic methods including SEM equipped with energy dispersive X-ray spectrometry (EDS), Raman spectroscopy, Infrared and X-ray ﬂuorescence spectroscopy, and QEMSCAN® mapping). Nickel rich saprolites were found to be principally composed of several types of MgeNi serpentines, quartz, clays (nontronite in particular) and little amounts of iron hydroxides. Besides, some parts of the deposit were characterized by the development of nontronites at the interface between the saprolite and the limonite zone. Above this zone, the limonite zone is dominated by iron hydroxides as expected, which replace all earlier silicates including serpentine, and contains a signiﬁcant amount of nickel. The representative composite ore sample contains several nickel bearers with variable nickel grade of 2 to 3%. Exceptionally richer phases such as polygonal Fe (Ni)-rich serpentine were also found with nickel grade of 5 to 10%. Serpentine types as well as other newly formed silicates such as Fe-Mg-(Ni) smectites, are intimately mixed, preventing any mineral separation. Therefore, the only phases which can be separated are quartz and magnetite. This complicates the upgrading of nickel in Weda Bay laterite ore.

Geometallurgy, 2018

Increasing competition in the minerais industry and fluctuating coramodity prices require new way... more Increasing competition in the minerais industry and fluctuating coramodity prices require new ways of saving energy, lime, and general operational costs. A good understanding of physical processing or pre-processing streams that can potentially cut these costs requires detailed analyses of chemical and physical behaviours and processing responses during rainera]. processing. It is very useful to perform a detailed mineralogical and micro-textural characterization of materials (ore, tailings, and waste) that addresses, among other parameters, particle and grain sizes, as well as particle densifies. The choice and/or corabination of the 'best' processing approaches is crucial for processing efficiencies, and can be established and verified by using automated mineralogy with the associated software. A sample of low-grade iron ore from El Volcan, Mexico, serves as an example to demonstrate in a step-by-step approach how QEMSCAN® analyses provide processing information. Elements under consideration include iron, phosphorus, and sulphur.

Separation and Purification Technology, 2017

An innovative process was developed for the leaching of niobium- and rare earth elements-bearing ... more An innovative process was developed for the leaching of niobium- and rare earth elements-bearing pyrochlores ores and the subsequent separation of Nb from the REE. Compared to the conventional Nb hydrometallurgical methods, the proposed leaching process is based on a triphasic system: H2SO4(aq)-SO2(g)-activated carbon/ore. The implementation of this leaching step allows the selective dissolution of the non-valuable phases while signiﬁcantly reducing the H2SO4 consumption. The results obtained in continuous operation, at the pilot scale, show a reduction of the sulfur consumption by 48% when compared to the classical H2SO4 pasting-roasting process. The presence of activated carbon, at concentration as low as 0.4% (w/w), was found to considerably fasten the dissolution reactions and allows optimizing the SO2 utilization to a nearly quantitative rate. The triphasic leaching also aﬀords concentrating the Nb stream which decreases the energy consumption of the down-stream operations and especially for the subsequent Nb-REE-bearing pyrochlores roasting step. The process was optimized at the laboratory scale and then tested in continuous operation for 15 days at a ﬂow of 15 kg h−1 of dry equivalent of non-magnetic Nb-REE pyrochlore ore from the Gabonese Mabounié deposit and the equivalent of 8.25 kgh−1 of H2SO4 and 0.15 kgh−1 of activated carbon.

Journal of Geochemical Exploration, 2019

International Journal of Geosciences

Separation and Purification Technology

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018

Journal of the Southern African Institute of Mining and Metallurgy, 2020

Powder Technology

International Journal of Geosciences, 2020

Journal of Geochemical Exploration

Geometallurgy, 2018

Separation and Purification Technology, 2017

Journal of Geochemical Exploration, 2019

PARTEC, 2019

Fine particles are is one of the most important issues of the mining and metallurgical industry, ... more Fine particles are is one of the most important issues of the mining and metallurgical industry, due to its environmental and technological impacts. Companies cope with these materials through agglomeration, which is necessary to reintroduce them into the processing chain. These agglomerates have to answer to mechanical strength criteria. However, agglomeration trials are still hugely empirical, and there is little, if any, predictability in its success. This paper evaluates the impact of various parameters on agglomeration through a parametric study, using in the first step, four monomineralic samples. The parameters we chose are: the particles mineralogy and shape, the moisture of the sample, and the mean radius ratio of two populations of different grain sizes mixed together. Those parameters are chosen to fit the operating conditions of medium-pressure agglomeration systems. The moisture content is set to vary from 0 to 20 wt.% by 5% steps. Particle shape is considered either spherical or angular, analysed from optic granulometry measurements. The mean radius ratio changes between 1 (same particle size) to 0.1 (one population has a radius 10 times smaller than the other). Since the target materials are metallurgical manganese dust, the monomineralic samples were chosen accordingly: (1) pyrolusite (MnO2) and (2) haussmanite (Mn3O4) are the major manganese bearing phases, while (3) montmorillonite (known for its binder capacity in bentonite) and (4) kaolinite assess the importance of a foliated structure, with their other parameters (such as their swelling potential) differing. The resistance of the agglomerates to their storage, transportation and use in the metallurgical processing chain, is evaluated through drop tests, crushing tests and abrasion tests. A set of agglomerates with various performances will be investigated in more details to define the key parameters of agglomeration. This paper develops in further details how the parameters giving the best mechanical answers have been recognized and linked with their associated physical explanations, such as the optimal packing density and the ratio of the mean radius. Those parameters will be correlated with the main agglomeration forces (Van der Waals, electrostatic and capillary bridges) in order to explain and optimize the efficiency of the agglomeration processes.

EGU, 2018

On-line-real-time combined mineralogical and chemical analyses on drill cores are highly demanded... more On-line-real-time combined mineralogical and chemical analyses on drill cores are highly demanded by mining and metallurgical companies to speed up exploration and mining, as they provide more precise geomodels, and optimal definition of metallurgical parameters. The EU-H2020 SOLSA project (www.solsa-mining.eu), targets to construct an expert system coupling sonic drilling with an on-line-real-time analytical system combining systematic mineralogical and chemical analyses on drill cores. The analytical system comprises a profilometer, a high resolution RGB camera, VNIR (Visible Near Infrared)/SWIR (Shortwave Infrared) (Specim Ltd., Finland) hyperspectral cameras, and a XRF spectrometer. The objective is to reach real-time decision making through scanning of about 60 m drill cores per day. The system will be validated for nickel laterites, which represent 70 % of the Ni resources worldwide. SOLSA will provide open databases for combined analyses. Therefore, a hyperspectral open data base is built for nickel-laterite specific rocks and pure mineral samples. All these samples are also analyzed by conventional laboratory methods (XRD, Raman spectroscopy, SEM, EPMA and QEMSCAN ®). Currently, 27 spectra representing 14 minerals (i.e., asbolane, chromite, diaspore, olivine (forsterite), clay minerals (kaolinite, saponite, pimelite), magnesite, pyroxene (enstatite), serpentine (lizardite, nepouite, antigorite), talc, calcite) have been collected for our hyperspectral library. We plan to open it to public at https://solsa.crystallography.net/sod/. As the spectra of drill cores often contain a mixture of minerals, spectral unmixing techniques have been investigated and implemented. We employed sparse unmixing techniques, which have connections with the statistical and geometrical frameworks and have recently been demonstrated a great success in unmixing hyperspectral data for remote sensing applications. Sparse unmixing techniques aim at finding the optimal subset of signatures in a spectral library that can best model each mixed pixel. The methods exploit the fact that a spectrum always contains a mixture of a small numbers of endmembers, which is the case in our data acquired from the nickel-laterite samples. Among investigated unmixing methods, the collaborative sparse unmixing by variable splitting and augmented Lagrangian (CLSUnSAL) method provided the most accurate unmixing results on simulated data that were generated from our hyperspectral library. Hyperspectral data acquired from a serpentinized harzburgite sample (SOLSA label of ER-MB00-0012) on a polished surface, were processed by the CLSUnSAL method using our hyperspectral library. The same sample was analyzed by QEMSCAN ®. A good correlation was found for the mineralogy and mineral distribution (olivine, pyroxene, serpentine, chromite) between the results of the CLSUnSAL and QEMSCAN ® methods. These analyses will be cross-evaluated by the Raman spectroscopy mapping.

Ressources for Future Generations, 2018

Mabounié polymetallic deposit originates from a carbonatite intrusion intensively weathered in eq... more Mabounié polymetallic deposit originates from a carbonatite intrusion intensively weathered in equatorial climate conditions. The laterite profile, covering the carbonatite complex, is composed of a 15 m high phosphated horizon at the bottom overlain by 30 m of banded and superficial horizons. The mineralogical characterization of the Mabounié deposit led to the definition of these different mineralogically homogeneous layers. In this study, the use of QEMSCAN®'s quantitative and automatic mineralogical analysis method made it possible to compare the results obtained within each drill core, and to interpolate the results vertically in order to observe the mineralogical variations from the deepest horizons of the alteration profile to the surface. Mineral phases bearing valuable elements (niobium and rare earth elements) have been identified and localized. For niobium, these are mainly niobates, goethite and ferrihydrite, with two major changes along the profile: 1) appearance of ferrocolumbite by alteration of the other niobates (pyrochlore and aeschinite), and 2) alteration of niobates inducing niobium transfer into iron hydroxides (goethite and ferrihydrite). Granulometric repartition of niobates decreases from the phosphate horizon (d50 >30 µm), to the upper level of superficial horizon (d50 = 10 µm) For the rare earth elements, hosts are primarily carbonates, followed by phosphates (apatite and monazite), crandallite, iron hydroxides and niobates. The very large number of hosts indicates an increasing complexity of the remobilization history of the rare earth elements during alteration process. Furthermore, hosting minerals are major phases, concentrate them by beneficiation is therefore hardly possible. This geometallurgical modelling study brings new concepts for the treatment of this complex orebody. Rare earth elements are in high concentration but no route of concentration by beneficiation can be easily founded; niobium can be concentrated in phosphate and banded horizons, but not in superficial one.

Geochemical cycle of Ni, Nancy, 2017

Mineral quantifications are challenging on Ni-laterites: XRD analyses provide useful information ... more Mineral quantifications are challenging on Ni-laterites: XRD analyses provide useful information on mineral species present in samples but with limitations in the precise quantification of complex mineral assemblages containing different particle and grain sizes. The quantification of clay mineral rich samples presents particular challenges as described by Pevear (1989) and Reynolds (1989). Automated-SEM systems including MLA, Qemscan, and TIMA show also limitations with respect to the distinction of Mg-silicates with close chemical compositions (olivine, serpentine, talc, nontronite, saponite, pyroxene,…). MLA and Qemscan, and the associated software, provide analytical results as count proportions acquired by their respective detectors. These results are presented as element wt%. It should be noted, though, that these results are far from precise and need to be laboriously calibrated and converted in order to ascertain precise element wt% information that are necessary to calculate a structural formula of a mineral. The Mineralogic system allows very fast EDS analyses that provide element and oxide analyses that are acquired from Zeiss SEM analyses and are presented as precise element and oxide wt%. This Mineralogic methodology is a step change to methods employed by QMESCAN, MLA and TIMA. Mineralogic allows for each acquired EDS spectrum to have a matrix correction and peak deconvolution applied before a spectrum quantification. This methodology thus allows for accurate and precise elements quantification, which is subsequently classified using the designed mineral library. In contrast to MLA and Qemscan systems, Mineralogic data can be directly used to establish precise phase compositions, structural formulae, and to even distinguish mineral phases of very similar chemical compositions. The Mineralogic system enables the user to group mineral populations of minor chemical variation. The distinction and quantification of clay minerals and minerals that are grouped within the smectite group is only one field of application. An extensive database is currently under construction that allows a high-precision identification and distinction of minerals including those that were hitherto regarded as problematic with respect to their identification and, even more, quantifications.

Le groupe minier français ERAMET cherche à exploiter le gisement de Bafoula, un gisement latériti... more Le groupe minier français ERAMET cherche à exploiter le gisement de Bafoula, un gisement latéritique manganésifère situé dans la région de Moanda au Gabon. Contrairement au gise-ment historique de Bangombé, il s'agit d'un gisement pauvre, un procédé d'enrichissement du minerai semble donc nécessaire. Afin de définir ce procédé et de vérifier le caractère économique du gise-ment, une étude géometallurgique est donc nécessaire pour car-actériser la minéralogie du gisement. ERAMET Research a choisi pour ce faire d'utiliser une méthode d'analyse minéralogique quantitative et automatisée grâce à un MEB. Il est possible avec un tel outil d'analyser rapidement un grand nombre d'échantillons permettant l'analyse géostatistique représentative de la réalité du terrain. Pour atteindre ce but, le logiciel Qemscan R automatise le fonctionnement des détecteurs EDS/BSE, et construit une carte minéralogique de l'échantillon dans laquelle chaque pixel est en-registré avec une chimie, une minéralogie, et donc une densité. Chaque particule est associée à une composition (minéralogique et chimique), une forme et une taille. Pour cette étude, une base de données spécifique a été construite pour modéliser le meilleur traitement minéralurgique à mettre en oeuvre. À teneur constante en manganèse, la proportion de pyrolusite (MnO2), cryptomélane (KMn8O16) et lithiophorite (Al2Mn3O9.3H2O) change, ce qui a un impact fort sur le traitement du minerai. Les minéraux de la gangue comme les phyllosilicates (illite, kaolinite, muscovite) et les hydroxydes (goethite, diaspore, gibbsite) contiennent aussi une part du manganèse dans leur structure. Les associations fines entre lithiophorite et minéraux de la gangue rendent sa récupéra-tion complète difficile à envisager. Le manganèse récupérable est donc essentiellement celui porté par les minéraux pyrolusite et cryptomélane. Sur une échelle régionale, l'interprétation et l'extrapolation verticale et horizontale de ces résultats permettent de montrer des variations minéralogiques locales (texture et composition) au sein d'un gisement et donc d'anticiper les change-ments de comportement du minerai dans un procédé en cours d'exploitation. Cette approche méthodologique à l'aide d'un MEB automatisé est donc un outil extrêmement efficace pour la carac-térisation géometallurgique d'un projet minier.

The carbonatite of Mabounié (Gabon), first described in 1988 [1], is a complex igneous intrusion ... more The carbonatite of Mabounié (Gabon), first described in 1988 [1], is a complex igneous intrusion
approximately 2.3 km in diameter hosted in Paleoproterozoic fenitized gneisses and migmatites.
Numerous mineralogical and geochemical studies were conducted in the twenty years following its
discovery ([2-4], BRGM, pers. comm.) that led to the discovery of a polymetallic lateritic ore deposit
above the intrusion. In the present work, new petrographic studies are reported on fresh drill core samples
obtained within the framework of the Maboumine project.
The carbonatite is heterogeneous sövite, crosscut by a few dikes of rauhaugite (dolomite-rich
carbonatite). The mineralogy varies strongly along magmatic bedding, schlieren patches and
hydrothermally recrystallized areas [4]. Apatite-sövite and phlogopite-sövite are common and intermixed
with each other, and contain a variable amount of Ti-rich magnetite (in some cases, up to 40 vol.% of the
rock). Other accessory minerals include rare-earth carbonates, ilmenite, pyrochlore, zircon, baddeleyite,
calzirtite and zirconolite.
In the lateritic profile developed above the carbonatite suite, the lowermost horizon consists of
massive phosphates and is characterized by the dissoluion of carbonates; it is followed by “ribbon”
laterites characterized by the breakdown of apatite, and finally by an iron-oxide-rich horizon at the
surface of the deposit. Even though pyrochlore is affected by different processes and its composition
changes slightly across the profile [3], this mineral remains the main carrier of rare metals (Nb, Ta) and
rare earth elements, which are concentrated upward mainly in the “ribbon” ore.

Nepheline can be described as a four end-member solid solution between Ne (NaAlSiO4), Ks (KAlSiO4... more Nepheline can be described as a four end-member solid solution between Ne (NaAlSiO4), Ks (KAlSiO4), An (Ca1/2□1/2AlSiO4) and Qz (□Si2O4), where □ is a vacancy in the structure. Few studies have explored its compositional variations, considered by most authors to be small and hardly related to magmatic evolution. In the Messum complex, an alkaline silica-undersaturated series is well exposed from