Mineralogical and geochemical characterization of Thanetian-Ypresian Phosphatic Layers in the Djemi-Djema Deposit

The Jebel El Onk region presents a complex geological history, starting with Maastrichtian limestones. Early Paleocene subsidence intensified, leading to the deposition of thick marly horizons and black marl shales during the early Thanetian. This was followed by the formation of a significant phosphate sequence during the late Thanetian to early Ypresian, comprising interbedded marls, phosphorites, and dolomites, and concluding with lagoonal gypsum marls and phosphate-rich clays, subsequently overlain by Miocene sediments. This study focuses on the Jebel-Onk phosphate deposit, with a particular emphasis on characterizing diverse phosphate facies and assessing their implications for resource management. Using X-ray Diffraction analysis, the apatite group minerals and associated rock components from the Djemi-Djema-East deposit were identified. To further elucidate the deposit’s morphology and surrounding lithology, the study integrated geochemical data and lithological succession derived from core drilling. An automatic mapping of the Paleo-Eocene stratiform phosphate body highlighted spatial irregularities in thickness and established correlations with the supra-layer cover, consisting of Ypresian and Lutetian flint limestones and Miocene sands. Chemical element analysis revealed content variations between the two dominant phosphate types, beige and dark gray, with isotener maps illustrating geochemical heterogeneities within the phosphate layer. Bi-variable statistical analyses provided additional insights, demonstrating strong positive correlations between P2O5, CaO, and SiO2, while MgO showed a negative correlation. Principal Component Analysis (PCA) further identified three distinct geochemical associations, corresponding to the phosphate material, the organic and dolomitic matrix, and the clay material. These findings offer valuable insights for optimizing selective phosphate exploitation. By identifying spatial thickness variations, geochemical properties, and facies transitions, the study enables precise targeting of high-grade zones, reduces waste, and supports strategic planning for sustainable resource management at the Djemi-Djema Est deposit.