"Memory loss" during mineral processing: Application to base metals traceability

International audienceTraceability of concentrates is required to introduce transparency in the trade of raw minerals. In this context traceability may be considered as a kind of inversion process: studying the product sold (i.e. the concentrate) in order to identify the original ore, in terms of ore deposit-type and if possible, location. The difficulty of making this inversion from concentrate toward bulk ore corresponds to the "memory loss" of the crude ore which occurs during mineral processing. Based on textural characterization and the chemical composition of the material at different steps of processing, as well as the minimum residence corresponding to each step, an estimation of this "memory loss" is proposed and the relations between memory loss and global kinetic rate of flotation are established. "Memory loss" calculations are applied to the Neves Corvo plant. Throughout the process, the parameter of memory loss increases respectively from 0 to 195.06 for Cu; 0 to 46.15 for Zn and 0 to 0.43 for Fe. The "global memory loss", namely as the "experimental memory loss". For the Neves Corvo plant at the moment of the study this "experimental memory loss" was 14,146 min for Cu, 3408 min for Zn and 36 min for Fe. The results show that "memory loss" is greater for Cu than for Zn, thus emphasizing the importance of secondary elements for traceability purposes

Ex-situ mineral carbonation: resources, process and environmental assessment (Carmex project)

This article presents the main results of the Carmex project (2009-2012), whose purpose was to review the feasibility of ex-situ mineral carbonation in terms of resource availability, performance of the aqueous mineral carbonation process and life cycle analysis criteria. This collaborative project looked at a wide range of generic issues about this CO2 mitigation option, with particular views on assessing its potential in the context of New-Caledonia. Indeed, insularity and local abundance of 'carbonatable' rocks and industrial wastes (i.e. rich in MgO, CaO, if not Fe(II)O), coupled with significant GHG emissions from first-class nickel pyrometallurgical industries, make it a potential candidate for application of ex-situ mineral carbonation. The project conducted a worldwide analysis of the potential of ex-situ mineral carbonation using a dedicated SIG-based tool. Using a variety of materials the project also reviewed a number of critical issues associated with the aqueous mineral carbonatation process itself, with promising perspectives. Finally, through life cycle analysis of the system as a whole, ex-situ mineral carbonation was compared to mainstream CSC solutions. It was concluded that the viability of this CO2 storage option is located at the level of the process itself and lies with the optimisation of its operating conditions

Contrôle karstique de minéralisations nickélifères de Nouvelle-Calédonie

International audienceFracturing associated with the nickeliferous mineralisations of New Caledonia has been successively considered as pre-dating and then post-dating the metallogenic processes. On the basis of a study of the dynamics of karst contemporaneous with lateritisation, a new emplacement model is proposed for the mineralisation: a network of hydraulic fractures of the crack-seal type governs the emplacement of mineralisation, associated with a network of normal faults that controls the sinking and evacuation of the karst productsLa fracturation associée aux minéralisations nickélifères de Nouvelle-Calédonie a successivement été considérée comme antérieure, puis postérieure, au processus métallogénique. À la suite d'une étude des processus dynamiques du karst contemporain de la latéritisation, nous proposons un nouveau modèle de mise en place des minéralisations. Dans ce modèle, la minéralisation se met en place par l'intermédiaire d'un réseau de fractures hydrauliques de type crack-seal, associé à un réseau de failles normales qui guident l'enfoncement et l'évacuation des produits du karst

Formation de corrugations hydrothermales lors de l'altération des roches ultramafiques

International audienceDuring shallow subsurface (< 200 m depth) weathering processes, temperatures may reach several tens of °C as a result of exothermic chemical reactions, such as hydration of olivine in ultramafic rocks or chloritization of biotite in granitic rocks. These mineralogical transformations enhance mineral fracturing, and the growth of fracture networks leads to further reactions and increases the permeability. The subsequent deepening of the weathering front creates new reactions, thus self-maintaining the weathering process over several million years (Myr). For more than 20 Myr, the peridotite massifs of New Caledonia have undergone intense weathering that has produced thick lateritic weathering mantles. The observable undulations of the weathering front and the protrusions of unweathered peridotite, from several meters to several tens of meters high, attest to a corrugated bedrock topography, which may result from inhomogeneous fluid circulation patterns within the coarse, permeable and porous (30-50%) saprolite layer. Combined together, the excess heat (up to ≈ 100°C) and high permeability (10-14 to 2 10-13 m²) within lateritic weathering mantles could potentially trigger hydrothermal convection (buoyancy-driven flow). This was numerically modeled by accounting for temperature-dependent fluid density and viscosity, and for time-dependent and spatially varying parameters simulating the deepening of the weathering front. Modeling the transient evolution of the thermal and flow velocity fields over 10 Myr reveals that hydrothermal convection can be triggered in the weathering lateritic mantles of New Caledonia, even on sloped surfaces where topography-driven flow prevails. Convective cells develop above the weathering front, and the amplitudes of thermal undulations are enhanced when feedback mechanisms between permeability and temperature are accounted for. The models also allow definition of the most probable zones of mineralization and reveal two-dimensional corrugations below which weathering is no longer efficient

Ex situ mineral carbonation for CO2 mitigation: Evaluation of mining waste resources, aqueous carbonation processability and life cycle assessment (Carmex project)

This article presents the main outputs from the multidisciplinary Carmex project (2009–2012), which was concerned with the possibility of applying ex situ mineral carbonation concepts to mafic/ultramafic mining wastes. Focus points of the project included (i) matching significant and accessible mining wastes to large CO2 emitters through a dedicated geographical information system (GIS), (ii) analysis of aqueous carbonation mechanisms of mining waste and process development and (iii) environmental assessment of ex situ mining waste carbonation through life cycle assessment (LCA) methodology. With a number of materials associated with the mining sector, the project took a close look at the aqueous carbonation mechanisms for these materials and obtained unexpected carbonation levels (up to 80%) by coupling mechanical exfoliation and reactive carbonation. Results from this work support the possibility of processing serpentine-rich peridotites without applying the classical first step of heat activation. Perspectives are also given for the carbonation of Ni-pyrometallurgical slag available closed to ultramafic mining residues. LCA of the mining waste carbonation system as a whole made it clear that the viability of this CO2 storage option lies with the carbonation process itself and optimisation of its operating conditions. By combining the body of knowledge acquired by this project, it is concluded that New Caledonia, with its insularity and local abundance of ‘carbonable’ rocks and industrial wastes coupled with significant greenhouse gas (GHG) emissions from world-class nickel pyro and hydrometallurgical industries stands out as a strong potential candidate for application of ex situ mineral carbonation

Platinum-group-mineral inclusions in chromitites from the Oman ophiolite

Platinum-group-mineral (PGM) inclusions have been found in Al-rich chromitites from the southern part of the Oman ophiolite. Contrary to other ophiolitic complexes, laurites (RuS2) are the only PGM found. All of them are primary and are commonly associated with or included in a small silicate crystal, which seems to be a characteristic of the PGM from Oman. The presence of PGM in chromitites is explained by trapping during crystal growth. Relatively high fS2 and a parent liquid impoverished in Os and Ir with respect to Ru are required for their crystallization.Des minéraux du groupe du platine (PGM) ont été trouvés en inclusion dans des chromitites alumineuses du sud du complexe ophiolitique d'Oman. Contrairement aux autres complexes, on n'y trouve que des laurites (RuS2). Toutes sont primaires, fréquemment associées à un petit silicate (ou même incluses dedans), ce qui semble caractéristique de ce complexe. La présence de PGM dans les chromitites est interprétée par un piégeage lors de la croissance de cette dernière Les conditions de cristallisation impliquent une fS2 relativement élevée et un liquide parent appauvri en Os et Ir par rapport à Ru.Augé Thierry. Platinum-group-mineral inclusions in chromitites from the Oman ophiolite. In: Bulletin de Minéralogie, volume 109, 3, 1986. pp. 301-304

Organic and mineral characteristics of Kupferschiefer ore from Lubin mine (Poland): implications for bioleaching of the ore.

International audienceThe ore mineral and organic matter content of the Lubin black shale (LBS) are compared with copper concentrate (LC) obtained by flotation. Study of a mineralized profile shows a good correlation between the S, TOC and Cu, Co and Ag content, suggesting syngenetic bacterial sulfate reduction (BSR) accumulation. The presence of disseminated and fracture filling rather than framboidal Cu-minerals, suggests formation via diagenetic processes. Compared to the black shale, the LC shows a lower HI and a higher OI, and a much more diverse ore mineral content. The black shale ore is composed of 15 vol. % sulfide, this proportion reaches 27 % in the LC whereas the TOC is similar in the LC and LBS. The ore mineral diversity in the LC is due to the contribution of mineralized sandstone and dolomite adjacent the black shale ore

A double Fe-Ti oxide and Fe-sulphide liquid immiscibility in the Itsindro Gabbro Complex, Madagascar

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Evidence for Fe-sulfide and Fe-Ti oxide liquid immiscibility in the Itsindro gabbro Complex, Madagascar

International audienceThe petrology and mineralogy of the Itsindro complex, SW Madagascar has been investigated through samples coming from a borehole drilled, in the early 70’s, in a geophysical and Ni-,Cu-geochemical anomaly. The host rocks are represented by a pyroxenite unit with interbedded gabbro layers and a gabbro unit. A decrease of the Mg number of CPX, independent of the lithology, is observed from the deepest samples (316 m) up to 163 m suggesting a regular fractional crystallization process. The evolution of this parameter is more erratic in the upper part of the bore hole. The mineralisation consists in Fe-Ti-P oxides and Fe-(Cu-Ni) sulfides. The ilmenite-magnetite±apatite and pyrrhotite±chalcopyrite ±pent-landite assemblages are always observed in interstitial position. The contemporaneous character of the oxide and sulfide assemblages strongly suggests a two stages evolution of the tholeitic magma, a first immiscibility process between a Si-rich and a Fe-Ti-P liquids followed by a sulfide contamination of the latter giving way to massive Fe-rich over Cu- Ni sulphides