Mineralogy and the lanthanide elements geochemistry of the Baharieh kaolin deposit, east Kashmar, NE Iran

The Baharieh kaolin deposit (east Kashmar, Khorasan Razavi Province) is the product of alteration of dacitic rocks (Eocene) and is located in the Khaf-Kashmar-Bardaskan metallogenic belt. Field observations show that the development of this deposit was controlled by the tectonic system of the area and the presence of silica cap is the most important geological feature of this deposit. Mineralogical studies, using different analytic techniques (such as XRD, SEM-EDS, FE-SEM, DTA and TGA), indicate the presence of kaolinite, halloysite, illite, quartz, alunite, jarosite, muscovite, albite, gypsum, topaz, anhydrite, rutile, galena, zircon and hematite in the kaolin samples. Calculations of mass changes with the assumption of Al as index immobile element show that the development of the kaolinization process has been accompanied with intense enrichment of LREE relative to HREE. This phenomenon indicates the preferential adsorption of LREE by kaolinite, halloylsite, alunite, hematite, and jarosite and the relatively low activity of complexing ions in rock-altering fluids. Correlation coefficients between elements indicate that kaolinite, rutile, manganese oxides, and secondary phosphates have played an important controlling role in the distribution and fixation of lanthanides. Occurrence of Eu negative anomaly in relation to the alteration of feldspars by relatively high-temperature fluids along with the occurrence of positive Ce anomaly indicate the effects of low-temperature aqueous system on the Baharieh kaolin deposit.