Abstract

The Aqkand epithermal base metal deposit, located in the Tarom-Hashtjin metallogenic belt (THMB) of northwest Iran, is hosted by Eocene andesitic basalt lavas. Mineralization at Aqkand occurs as Cu-bearing quartz-fluorite breccia veins, and vug infill with comb, colloform, cockade, crustiform and plumose textures. The mineral assemblages are quartz, chalcopyrite, hematite, fluorite, and chlorite. Five stages of mineralized veins are distinguished at Aqkand, including: fluorite veins (stage-1), quartz-chalcopyrite stockwork and breccia veins (stage-2), hematite-bearing quartz veins (stage-3), quartz infilling veins (stage-4), and vug infill chlorite veins (stage-5). Hydrothermal alteration assemblages grade from proximal quartz and chlorite to distal sericite‒epidote‒calcite‒chlorite. Fluid inclusions data indicate trapping of medium-salinity (7.4–9.8 wt. % NaCl equiv.) fluids with homogenization temperature of 230 to 350°C. Laser Raman spectroscopy confirms that H2O is the main volatile in most of the inclusions; lesser amounts of CH4 is also present. The combined fluid inclusion microthermometric and laser Raman spectroscopy analyses show that the ore-forming fluids at Aqkand are trapped at medium- to high temperature as medium salinity, and low-density H2O–NaCl+CaCl2-bearing fluids. Based on fluid inclusion compositions, they can be classified into two end-members: magmatic fluid and meteoric water. Fluid boiling and subsequent hydraulic fracturing may have led to inflow and/or mixing of early magmatic fluids with circulating groundwater and finally to low-salinity fluid inclusions during cooling. Our data suggest that the mineralization at Aqkand is correlated with intermediate-sulfidation style of epithermal precious and base metal systems similar to other hydrothermal deposits of the THMB.