Geology and genesis of the Siahouki intermediate-sulfidation epithermal Cu–Au–Ag deposit, SE Iran: constraints from fluid inclusions and S–O–C isotopes

The Siahouki Cu–Au–Ag deposit is located c . 50 km NW of Bam in the southern Urumieh–Dokhtar magmatic arc. The mineralization is hosted by Eocene dacitic and andesitic tuffs that have undergone extensive silicic, argillic and propylitic alteration. Ore deposition primarily occurs in NW–SE-trending, fault-controlled quartz–carbonate ± sulfide veins. Based on field observations, petrography and microanalytical data, five hydrothermal stages are defined: stage I, early distal argillic–propylitic alteration; stage II, the principal Cu–Au–Ag stage; stage III, late Au enrichment; stage IV, mineralization dominated by calcite; and stage V, supergene oxidation and secondary enrichment. Fluid inclusions show homogenization temperatures of 112–331°C and salinities of 0.9–10.1 wt% NaCl equiv. Stable isotope constraints confirm a mixed magmatic–meteoric origin for the ore-forming fluids. The sulfur isotope compositions of pyrite, chalcopyrite and tetrahedrite ( δ 34 S = −5.4 to +0.5‰) indicate a dominantly magmatic sulfur source. The oxygen isotope values ( δ 18 O fluid = −1.4 to +1.8‰) calculated from quartz–water equilibrium indicate significant meteoric water mixing. The carbon isotopes ( δ 13 C = −0.8 to +0.0‰) from hydrothermal calcite further suggest limited carbonate wall rock interaction. Collectively, these data indicate that ore deposition was controlled by episodic boiling and fluid mixing during the transition from magmatic–hydrothermal to meteoric-dominated conditions, defining the Siahouki deposit as an intermediate-sulfidation epithermal system.