Rare earth elements distribution of tertiary phosphorites in Tunisia

REE concentrations and distribution have been established for the Upper Palaeocene-Lower Eocene sedimentary phosphorites, southern Tunisia. REE contents of phosphatic beds vary according to the paleogeographic environments, granulometry and grain types. Shale normalized REE patterns are characterized by a slight depletion in HREE and a negative Ce anomaly.The Ce/Ce* and La/ Yb indexes indicate Ce deficit and the LREE-HREE fractionation, range from 0.35 to 0.86 and from 11.7 to 17.1, respectively. These ratios are variable and reflect important variations from basin to basin. The high REE contents correlate with the high bulk porosity and the specific surface of cryptocrystalline apatite The REE content,the enrichment and depletion in HREE and the Ce-anomaly may reflect diverse environmental conditions of each basin.