GEOLOGY, GEOCHEMISTRY AND FLUID INCLUSION STUDIES OF THE VEIN-TYPE FATHABAD CU±AU DEPOSIT, KHAF-KASHMAR-BARDASKAN METALLOGENIC BELT, NE OF IRAN

ABSTRACT The Fathabad deposit is located in the village of Fathabad in the central district of Roshtkhar County, Razavi Khorasan Province, Iran. It is hosted by felsic to volcanic rocks including basaltic-trachyandesite, trachybasalt, trachyandesite, trachydacite and rhyolite in composition. The geochemistry of the Fathabad volcanics is consistent with high-K calc-alkaline to shoshonitic and metaluminous to peraluminous features, characterized by low to high SiO2 (47-74.70 wt.%), Sr/Y (4.5-161) and (La/Yb) N (3.99 to 37.06); An enrichment of LILEs and LREEs and a depletion of REEs and HFSEs. Hydrothermal alteration has produced a zone of silicification, propylitic and Fe-oxide and hydroxide alteration associated with minor sericite-argillic alteration. Field and mineralogical studies indicate that mineralization has occurred in the form of hypogene and supergene. Microthermometric measurements of the primary LV fluid inclusions in quartz and calcite indicate that the ore-forming fluids belong to the H2O+NaCl+CaCl2 system with low to intermediate temperature (85 to 210°C) and salinity (12.30 to 23.83 wt.% NaCl+CaCl2 equiv.) in quartz and a temperature of 135 to 208°C with a salinity between 17.33 and 23.05 wt.% NaCl+CaCl2 equiv. in calcite. Mineralization is related to the mixing and cooling of magmatic and meteoric fluids. The δ34S isotope values (-1.58 to -2.86‰) in the chalcopyrite minerals indicate the magmatic origin of the sulfur. Due to the structural control of mineralization and alteration, the moderate to low temperature and salinity of the ore fluid, and the petrogenesis of the volcanic rocks, the Fathabad Cu±Au deposit is similar to epithermal deposits. Keywords: Fathabad Cu±Au deposit, geochemistry, fluid inclusion study, Khaf-Kashmar-Bardaskan metallogenic belt, epithermal deposits.