Geochemical and industrial properties of the Kejal kaolin deposit, NW Iran

Abstract

The Kejal kaolin deposit, situated in the northwest of Iran, is considered a small part of the Hashtjin hydrothermal zone. Thekaolinization process in this deposit has occurred in ignimbritic and volcanic tuff parent rocks in different grades such that severelykaolinized samples can be found in the middle section of the kaolinization profile. Kaolinite is the most abundant clay mineral in thestudied samples. Quartz and cristobalite are the main minerals while anatase is the minor mineral of the kaolin samples. Among themajor oxides, SiO2, Al2O3, and TiO2 show the highest concentrations in kaolin samples. The mass change calculations based on Tishow enrichment of Si, Al, Sr, and LREEs and depletion of alkali and alkali earth elements, HREEs, and HFSEs. The evaluation of REEsnormalized to chondrite represents the higher concentration of LREEs comparing to HREEs. A remarkable positive Gd anomaly is seenin spider diagrams, which can be attributed to the primary CaO in the composition of ignimbritic precursor and also the Gd release dueto the decomposition of Gd complexes and adsorption by clay minerals. The Eu negative anomaly is the other obvious characteristicof the studied samples and is most likely related to the alteration of feldspars, decomposition of plagioclase, and Eu liberation from thesystem. The significant positive correlations between REEs and Al2O3, TiO2, and P2O5 demonstrate the important role of clay minerals,REE-bearing phosphate minerals such as monazite, and titanium minerals like anatase and rutile in the kaolinization process and REEtransport and establishment. The performed particle size test based on the hydrometer method shows about 20% of particles