Mineralogy and geochemistry of rare earth elements at the Dalir phosphate horizon, southwest of Chalous, Mazandaran province

The Dalir phosphate horizon is located ~57 km southwest of Chalous, Mazandaran province. The horizon developed as stratiform within upper shale of Soltanieh Formation (late Neoproterozoic - early Cambrian). According to mineralogical data, the major minerals of the phosphate horizon are calcite, fluorapatite, dolomite, quartz, pyrite, muscovite, and illite. Microscopic evidence such as existence of the fabric similar to grumeuse fabric indicates a vital role for diagenetic processes and dynamic pressures in the evolution of the horizon. The distribution pattern of Rare Earth Elements (REEs) normalized to PAAS reveals weak fractionation of Light REEs from Heavy REEs and negative Ce anomaly during phosphatization. Incorporation of the obtained results from mineralogical and geochemical studies suggests that the behavior and distribution of REEs were affected by the function of factors such as diagenesis, preferential sorption, presence and decomposition of organic matter, oxidation-reduction potential, and function of pore-waters. Further geochemical considerations show that fluorapatite, xenotime, muscovite, Mn-oxides and illite are the potential hosts for REEs.