The mineralogical and geochemical control on the distribution and mobilization of trace and rare earth elements during development of argillic alteration zone: A case study from northeast of Kharvana, NW Iran

Intrusion of tonalitic, granodioritic and quartz-dioritic igneous bodies of Oligocene age into Cretaceous andesite, andesi-basalt and carbonate rocks led to occurrence of widespread argillic alteration zone, along with skarnification in the northeast of Kharvana (East Azarbaidjan Province, NW Iran). Mineralogical studies indicate that argillic alteration zone includes kaolinite, quartz, alunite, pyrophyllite, rutile, chlorite, jarosite, hematite, goethite and pyrite minerals. Geochemical investigations revealed that factors such as low pH, high water/rock ratios, abundant complexing agents in the hydrothermal solutions, and suitable drainage system have played an important role in leaching of elements such as Ga, Sc, Hf, Nb, Th, Ta, Zr, Y and REEs during the development of this zone. The distribution pattern of REEs normalized to chondrite shows differentiation and enrichment of LREEs relative to HREEs and occurrence of negative Eu and Ce anomalies during argillization of andesites. Variations of Eu and Ce anomalies suggest destruction of plagioclase, potassium feldspar and hornblende by hypogene solutions and generation of H2SO4 originated from oxidation of pyrite by supergene solutions in development of this alteration system. The correlation coefficients between elements display the controlling role of Mn-oxides in concentration of Cu, Pb, Zn, Cd and Tl. Concentration of REEs was controlled by adsorption processes (kaolinite), scavenging by metallic oxides and hydroxides (hematite and goethite) and fixation in neomorphic pahses (rutile, jarosite and muscovite-illite) in this zone.