Sylvain Delchini

This study investigates the geochemical and mineralogical evolution of mine materials along the Nartau’s slope in order to understand post-depositional transformations and spatial heterogeneities. A systematic sampling campaign was conducted along a longitudinal transect of the dump, and samples were analyzed using X-Ray Diffraction (XRD), Scanning Electron Microscopy with Energy-Dispersive Spectroscopy (SEM-EDS), and Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). Results reveal distinct mineralogical zoning, with the progressive alteration of primary sulfide minerals and the formation of secondary phases such as iron oxyhydroxides and hydrous ferric arsenate. Geochemical data show increasing enrichment in trace metals (e.g.: As, Cu, Zn) downslope, consistent with mobilization and secondary immobilization processes. These findings provide valuable insights into the evolution of mine wastes and contribute to a better understanding of element redistribution within mine waste rocks.

Cette thèse présente la reconstruction de l’histoire tectono-thermique du massif varisque des Jebilet (Maroc) à fort potentiel minier, depuis son évolution pré-orogénique au Dévonien supérieur-Carbonifère inférieur jusqu’à sa structuration pendant l’orogénèse varisque-alléghanienne au Carbonifère supérieur-Permien inférieur. Pour répondre à cette problématique, ce travail s’organise autour de deux approches : (1) l’une métrologique appliquée à la géothermométrie Raman sur la matière carbonée (RSCM) et (2) l’autre intégrant une étude structurale, géochronologique et une analyse de la thermicité.L’approche métrologique a permis de valider l’applicabilité du géothermomètre RSCM (1) dans un contexte de métamorphisme polyphasé, (2) pour des roches carbonatées et des skarns des Jebilet et (3) de proposer un nouveau paramètre Raman RSA permettant de mieux préciser les températures supérieures à 500°C et d’étendre l’applicabilité de la méthode jusqu’à des températures maximales qui atteignent les 700°C.A partir de l’approche intégrée, trois épisodes tectono-thermiques ont été mis en évidence. Le premier épisode D₀ correspond à une tectonique extensive permettant l’ouverture du bassin des Jebilet au Dévonien supérieur-Carbonifère inférieur. Cette tectonique extensive est accompagnée par une anomalie thermique supérieure à 500°C déduites des mesures de géothermométrie RSCM (TRSCM) et par une importante activité magmatique bimodale et granodioritique datée dans ce travail entre 358 ± 7 et 336 ± 4 Ma. Au Carbonifère supérieur débute la phase compressive structurant le massif des Jebilet avec la mise en place de nappes superficielles au Namuro-Westphalien (D₁), suivie par la phase varisque majeure (D₂). L’analyse structurale a permis de montrer une évolution progressive du régime de déformation de D2 depuis une compression coaxiale à une transpression dextre compatible avec un raccourcissement horizontal WNW-ESE à NW-SE. D₂₁ est associée à deux événements thermiques, le premier syn-tectonique de moyenne température (300°<TRSCM<400°C), et le second syn- à post-tectonique de haute température (600°<TRSCM<660°C).Ce contexte tectono-thermique serait l’expression de processus géodynamiques impliquant à partir du Dévonien supérieur une délamination de la lithosphère rhéïque par « slab break-off » ou « slab roll-back » qui entrainerait (1) la remontée de courant asthénosphérique chaud, et (2) la rotation horaire de Gondwana et son amalgamation progressive avec Laurussia structurant au Carbonifère supérieur-Permien inférieur la chaine varisque-alléghanienne.

Ore variability remains a major challenge for grade control and metallurgical performance, emphasizing the need for detailed mineralogical characterization to support process optimization and quantitative assessment of ore deportment. This study evaluates a combined XRF-XRD approach (LuxREM solution) with field-adapted sample preparation for rapid, on-site chemical and mineralogical analysis of spodumene-bearing ores, addressing the technical challenge of fast lithium concentration assessment to guide process optimization. Proper sample preparation is essential, particularly for both XRF and XRD analysis, to ensure reliable results under on-site conditions where preparation is minimized. The Ball mill preparation method provides a balanced compromise compared with raw (As-It) and classical laboratory methods (Disc mill and Micro mill), sufficiently reducing particle size to minimize preferred orientation while avoiding excessive ultra-fine production. Analytical performance was compared to established chemical (ICP-OES) and mineralogical (QXRD and EMC) methods, confirming accuracy and robustness, particularly for quantifying spodumene and deriving lithium concentration. Phase-dependent discrepancies were observed, mainly reflecting inherent limitations of individual methods, highlighting the contrasting sensitivities of chemistry (EMC) and structure-based (XRD) approaches. Reconciliation of chemical and mineralogical data from a single sample provides a comprehensive understanding of its composition. The possibility of multiplying on-site XRF-XRD analyses by linking chemistry and mineralogy can enable verification of overall data consistency and ore variability providing rapid reliable information for operational decision-making, real-time process control, and enhanced resource management in lithium mining.

The present work aims at understanding the tectonic evolution of the Jebilet massif, Morocco, during the Late Paleozoic as constrained by structural, metamorphic, and geochronological studies. From Late Devonian to Early Carboniferous, bordering faults controlled the opening of the Jebilet intracontinental basin (D₀ stage) as shown by sedimentary infill. This episode was accompanied by a magmatic activity, newly dated between 358 ± 7 Ma and 336 ± 4 Ma. The first record of the Variscan event affected the Jebilet by the Late Visean‐Namurian and is represented by allochthonous superficial nappes emplaced at shallow depth in a moderately lithified sedimentary succession. D₁ also developed regional‐scale recumbent folds trending E‐W that may suggest N‐S crustal shortening not generating crustal thickening nor contributing to metamorphism. The main Variscan D₂ episode consists of a progressive evolution from bulk coaxial deformation to noncoaxial dextral transpression consistent with NW‐SE horizontal shortening, resulting in a moderate thickening. This episode was accompanied by HT‐LP metamorphism and syntectonic intrusions controlled by an inherited thermal anomaly in relation with the intracontinental rifting stage (D₀). Based on previous age determinations from syntectonic leucogranite and metamorphic rocks, D₂ is dated between 310 and 280 Ma. The tectono‐metamorphic evolution of the Jebilet massif can be correlated with a plate‐tectonic scenario evolving from, first a Late Devonian‐Early Carboniferous basin formation during stretching of the north‐Gondwana margin and initiation of the Paleotethys Ocean, and, second, to a Late Carboniferous‐Early Permian ocean closure (Rheic or Paleotethys Oceans depending of scenarios) that resulted in the final Variscan‐Alleghanian tectonics.