Continental shelves as potential resource of rare earth elements

International audienceThe results of this study allow the reassessment of the rare earth elements (REE) external cycle. Indeed, the river input to the oceans has relatively flat REE patterns without cerium (Ce) anomalies, whereas oceanic REE patterns exhibit strong negative Ce anomalies and heavy REE enrichment. Indeed, the processes at the origin of seawater REE patterns are commonly thought to occur within the ocean masses themselves. However, the results from the present study illustrate that seawater-like REE patterns already occur in the truly dissolved pool of river input. This leads us to favor a partial or complete removal of the colloidal REE pool during estuarine mixing by coagulation, as previously shown for dissolved humic acids and iron. In this latter case, REE fractionation occurs because colloidal and truly dissolved pools have different REE patterns. Thus, the REE patterns of seawater could be the combination of both intra-oceanic and riverine processes. In this study, we show that the Atlantic continental shelves could be considered potential REE traps, suggesting further that shelf sediments could potentially become a resource for REE, similar to metalliferous deep sea sediments.

Modèle de formation du gisement d'argent d'Imiter (Anti-Atlas oriental, Maroc). Nouveaux apports de l'analyse structurale et minéralogique. Model of formation of the Imiter silver deposit (eastern Anti-Atlas, Morocco). New structural and mineralogical constraints .

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

Typology of hard-rock Li-hosted deposits in Europe

International audienceLithium became a strategic metal in the last decade due to its widespread use in electromobility and green technologies. Consequently, demand has increased significantly reviving European interest in lithium mining and leading many countries to assess their own mineral resources/reserves to secure their own supplies. A compilation of European lithium hard-rock occurrences and a systematic assessment of metallogenic processes related to Li-mineralization have been produced. Accordingly, it appears that lithium is well represented through various deposit types related to several orogenies from Precambrian to Miocene ages. Thus, these deposits have been identified as mostly resulting from endogenous processes such as lithium-cesium-tantalum (LCT) pegmatites (e.g. Sepeda in Portugal; Aclare in Ireland; Läntta in Finland), rare-metal granites (RMG; Beauvoir in France; Argemela in Portugal) and greisens (e.g. Tregonning-Godolphin, Meldon in UK; Cinovec in Czech). Local exogenous processes may be related to significant Li-endowments such as jadarite precipitation in the Jadar Basin (Serbia) but are rarely related to economic grade and tonnage of lithium. Moreover, common parameters are identified in the Li endowment processes including: 1) a pre-existing Li-rich source; 2) a lithospheric thickening; and 3) an extensional regime

Rare earth elements as proxies of supergene alteration processes from the giant Imiter silver deposit (Morocco)

International audienceThe giant Imiter silver mine located at the northern edge of the West African craton in Morocco is assumed to be a late Neoproterozoic epithermal deposit mainly characterized by a hypogene paragenesis of Agrich sulphides and sulfosalts, and Ag-Hg alloys occuring preferentially in quartz-rich veins. The secondary enrichment zone at Imiter reaches a thickness of 50 to 150 m below ground surface. The upper levels, famous because of giant native silver crystals, grade up to 300 kg/t. Metallographic observations, SEM-EDS and XRD analyses reveal the presence of a quite complex secondary paragenesis made of acanthite, cinnabar, imiterite, perroudite, cerussite, mimetite, iron oxyhydroxides, synchisite and coronadite. Supergene alteration processes of the giant Imiter silver mine deposit consist of the remobilisation of the primary hypogene paragenesis by (i) deep and old basinal brines and (ii) downward infiltrations of surficial waters becoming progressively more reduced and F-enriched in response to fluid-rock interactions. Development of such a supergene mineralization strongly suggests prevalence of arid to semiarid conditions

No direct effect of F, Cl and P on REE partitioning between carbonate and alkaline silicate melts

This study presents new insights into the effects of halogens (F and Cl) and phosphorous (P) on rare earth element (REE) partitioning between carbonatite and alkaline silicate melts. F, Cl and P are elements that are abundant in carbonatites and alkaline magmatic systems and they are considered to play an important role on the REE behaviour. Nonetheless, their effect on REE partitioning between carbonate and alkaline silicate melts has not yet been constrained.Here we present new experimental data on REE partitioning between carbonate and alkaline silicate melts doped in F, Cl and P, in order to (1) test the Nabyl et al. [2020] REE partitioning model in F-, Cl- and P-rich systems, and (2) identify the possible role of F, Cl and P in carbonate melt REE enrichments during alkaline–carbonatite magma differentiation. The experiments were performed at 850–1050 °C and 0.8 GPa using piston-cylinder devices. Starting materials consisted of carbonatite and phonolite compositions ${\pm }$ doped in F, Cl and P. The experimental results show that REE partitioning is similar in F-Cl-P-rich and -poor systems. The silicate melt composition and its molecular structure (i.e. SiO$_{2}$ contents, the alumina saturation index and the alkali/alkaline-earth element ratio), which have already been identified as controlling REE partitioning in F-, Cl- and P-poor systems, still operate in doped systems. No direct effect of the F, Cl or P melt concentrations on REE partitioning has been identified. We also propose an application to natural systems

Material flow analysis applied to rare earth elements in Europe

International audienceThis paper explores flows and stocks, at the scale of the European Union, of certain rare earth elements (REEs; Pr, Nd, Eu, Tb, Dy and Y) which are associated with products that are important for the decarbonisation of the energy sector and that also have strong recycling potential. Material flow analyses were performed considering the various steps along the value chain (separation of rare earth oxides, manufacture of products, etc.) and including the lithosphere as a potential stock (potential geological resources). Results provide estimates of flows of rare earths into use, in-use stocks and waste streams. Flows into use of, e.g., Tb in fluorescent lamp phosphors, Nd and Dy in permanent magnets and Nd in battery applications were estimated, for selected reference year 2010, as 35, 1230, 230 and 120 tons respectively. The proposed Sankey diagrams illustrate the strong imbalance of flows of permanent magnet REEs along the value chain, with Europe relying largely on the import of finished products (magnets and applications). It is estimated that around 2020, the amounts of Tb in fluorescent lamps and Nd in permanent magnets recycled each year in Europe, could be on the order of 10 tons for Tb and between 170 and 230 tons for Nd

Material flow analysis for identifying rare earth element recycling potentials in the EU-27

International audienceRare earth elements (REEs) are essential for high-techology industrial sectors. This paper presents research on material flow analysis (MFA) applied to REEs in the EU-27. Innovative aspects of this research pertain to (i) considering potential lithospheric stocks of REEs in the EU and (ii) accounting for incomplete and imprecise information in MFA data reconciliation. Results obtained to-date provides a history of EU-27 raw rare earth imports and exports and a methodology for data reconciliation which constitutes an alternative to the classical least-squares method

Internal vein texture and vein evolution of the epithermal Shila-Paula district, southern Peru.

The epithermal Shila-Paula Au–Ag district is characterized by numerous veins hosted in Tertiary volcanic rocks of the Western Cordillera (southern Peru). Field studies of the ore bodies reveal a systematic association of a main E–W vein with secondary N55–60°W veins—two directions that are also reflected by the orientation of fluid-inclusion planes in quartz crystals of the host rock. In areas where this pattern is not recognized, such as the Apacheta sector, vein emplacement seems to have been guided by regional N40°E and N40°W fractures. Two main vein-filling stages are identified. stage 1 is a quartz–adularia–pyrite–galena–sphalerite–chalcopyrite–electrum–Mn silicate–carbonate assemblage that fills the main E–W veins. stage 2, which contains most of the precious-metal mineralization, is divided into pre-bonanza and bonanza substages. The pre-bonanza substage consists of a quartz–adularia–carbonate assemblage that is observed within the secondary N45–60°W veins, in veinlets that cut the stage 1 assemblage, and in final open-space fillings. The two latter structures are finally filled by the bonanza substage characterized by a Fe-poor sphalerite–chalcopyrite–pyrite–galena–tennantite–tetrahedrite–polybasite–pearceite–electrum assemblage. The ore in the main veins is systematically brecciated, whereas the ore in the secondary veins and geodes is characteristic of open-space crystallization. Microthermometric measurements on sphalerite from both stages and on quartz and calcite from stage 2 indicate a salinity range of 0 to 15.5 wt% NaCl equivalent and homogenization temperatures bracketed between 200 and 330°C. Secondary CO2-, N2- and H2S-bearing fluid inclusions are also identified. The age of vein emplacement, based on 40Ar/39Ar ages obtained on adularia of different veins, is estimated at around 11 Ma, with some overlap between adularia of stage 1 (11.4±0.4 Ma) and of stage 2 (10.8±0.3 Ma). A three-phase tectonic model has been constructed to explain the vein formation. Phase 1 corresponds to the assumed development of E–W sinistral shear zones and associated N60°W cleavages under the effects of a NE–SW shortening direction that is recognized at Andean scale. These structures contain the stage 1 ore assemblage that was brecciated during ongoing deformation. Phase 2 is a reactivation of earlier structures under a NW–SE shortening direction that allowed the reopening of the preexisting schistosity and the formation of scarce N50°E-striking S2-cleavage planes filled by the stage 2 pre-bonanza minerals. Phase 3 coincides with the bonanza ore emplacement in the secondary N45–60°W veins and also in open-space in the core of the main E–W veins. Our combined tectonic, textural, mineralogical, fluid-inclusion, and geochronological study presents a complete model of vein formation in which the reactivation of previously formed tectonic structures plays a significant role in ore formation