Decrée, S.; González, F.J.; Marino, E.; Santofimia, E.; Magalhães, V.H.; Coint, N.; Mansur, E.T.; Baele, J.-M.; Deloule, E. Genetic Model Variability of Deep-Sea Phosphorites Along the Iberian–North African Margins Evidenced by In Situ Geochemistry and Isotopic Signatures. Minerals 2026, 16, 661. https://doi.org/10.3390/min16060661
Abstract
Phosphorites are a vital source of phosphorus for agricultural and industrial applications and are increasingly recognized for their potential as secondary repositories of critical raw materials (CRMs) such as rare earth elements plus yttrium (REYs). This study investigates deep-sea phosphorites from the Galicia Bank, Madeira, and Canary Seamounts, in the NE Atlantic Ocean, which are spatially associated with ferromanganese (Fe-Mn) mineralization. Through integrated petrographic, geochemical, and in situ isotopic analyses (O and Sr), we assess the timing, processes, and paleoenvironmental conditions of phosphogenesis and its implications for CRM enrichment. Rare earth element patterns in apatite reflect a predominant seawater-derived signature with variable Ce anomalies. Nevertheless, variable Y/Ho ratios point to evolving fluid sources including a hydrogenous component (directly derived from seawater), modified porewaters and, locally, volcanic or possibly hydrothermal inputs. Oxygen and strontium isotope compositions constrain phosphogenesis to several episodes ranging from the Upper Cretaceous to the Middle Miocene, with distinct isotopic shifts identifying both primary formation and later overprinting processes mostly linked to Fe-Mn oxyhydroxide growth or volcanic–hydrothermal activity. These findings highlight the dynamic and multiphase nature of phosphorite formation in deep-marine settings. The integration of high-resolution geochemical and isotopic tools proves essential for reconstructing genetic histories, defining metallogenic context and evaluating CRM prospectivity in complex submarine systems.
Keywords
Galicia Bank; Tropic Seamount; Seine Seamount; phosphorite; phosphogenesis; apatite; post-depositional processes; rare earth elements; Sr and O isotopes
