THE BARZAVAND AND NEYSIAN COPPER DEPOSITS, NW NAEIN, CENTRAL IRAN ZONE: CONSTRAINTS ON STYLES OF MINERALIZATION AND GEOCHEMICAL SIGNATURES OF HYDROTHERMAL ALTERATIONS

Field observations in the northwest of Naein (Central Iran zone) indicate various types of alteration products have extended into pyroclastic and volcanic units with Oligo- miocene age. It seems the Zefreh (with NW- SE trend) and Kachumesqal (with E-W trend) faults are effective factors in the formation of Neysian and Barzavand copper deposits respectively. Alteration in Barzavand copper deposit (with stratabound form) includes pyritization, propylitization, zeolitization, saussuritization, uralitization and silicification, while in Neysian (with oval form) include phyllic, advanced argillic, argillic and propylitic. Geochemical studies in Barzavand show the positive correlation between (La/ Lu)N, (La/Yb) N and (La/Sm) N and CaO (r= 0.70 to 0.96) related to propylitization of host rock basalt and increase in pH of fluids responsible for mineralization that play important role in differentiation of lanthanides in study area. The Barzavand copper deposit has submarine volcanism, diagenesis, burial metamorphism and weathering stages during its evolution. Remarkable geochemical features in Neysian include high (La/Lu)N, Ba and Sr values than La, Ce and Y. It seems that extensive alteration occurred along with hypogene and supergene processes in Neysian. According to alteration properties, mineralogy and the whole-rock geochemistry, the Barzavand and Neysian copper deposits are most similar to Manto- type and porphyry copper deposits respectively.