Geology, Alteration, Geochemistry and Element distribution in Alteration Zones of Nughdoz- Zaylik Area, Arasbaran Magmatic Zone

The study area is located in 25 km SE of Ahar and 40 km NW of Meshkin-Shahr around Naqadouz village. Hydrothermal alteration has resulted in the developing of Argillic, Argillic - Silicic, Silicic and propilitic zones in this area. Based on petrographic studies, the altered rocks are basaltic andesite, andesite, dacite, rhyolite and lithic tuff in composition, with porphyry, glomeroporphyry, hyalomicrolithic and microlithic porphyric textures. The XRD analysis of altered samples show cristobalite, natrilite, kaolinite, quartz, albite, sanidine and orthoclase as the main minerals. Geochemical studies indicate that the alteration fluid has hydrothermal source and supergene processes are more important than hypogene processes. In this study, we use the immobile element method to calculate mass-changes and trace elements transmission amount during hydrothermal alteration. The Eu/Eu* ratio is higher in altered samples than relatively unaltered samples and the ratio of Ce/Ce* is more than 1for the relatively unaltered and most altered samples. The ratio of (La/Yb) n indicated that the depletion of HREE in altered samples is more than LREE, and LREE enrichment can increase this ratio. The lower ratio of (Tb/Yb) n in altered than unaltered samples indicate less depletion of HREE relative to MREE. Considering the distribution pattern of REE’s in alteration zones, it seems that the behavior of elements are controlled by pH, T & P changes, Eh, preferred absorption by clayey and iron oxide minerals and ligands frequency including SO2-4 , PO4+3 , CI-, F-, CO2-3 .