Abstract

The breccia-hosted low- to intermediate-sulfidation gold-silver deposit of Chah Zard (reserves ~2.5 Mt at 2 g/t Au and 13 g/t Ag) is located in the Urumieh-Dokhtar magmatic arc, west central Iran. Gold and silver occur in hydrothermal vein and breccia with epithermal textures, including vug infill, crustiform, cockade and colloform. Fluid inclusion studies reveal that quartz from the cement of the Au-Ag-bearing polymictic breccia contains predominantly liquid-rich inclusions with homogenization temperatures ranging from 197 to 345ºC (mode 325ºC) and salinities varying from 10 to 14 wt.% NaCl equiv. The calculated pressure is ~95-98 bar, equivalent of hydrostatic depth of ~970 m. Fluid inclusions in sphalerite from late base metal-rich veins returned salinities ranging from 8 to 12 wt.% NaCl equiv, homogenization temperatures of 262-311ºC (mode 285ºC), and estimated hydrostatic depth of ~440-940 m. Calculated δ¹⁸O values of water in equilibrium with quartz range from +3.4 to +13.1‰ (avg. 10.1‰) suggesting involvement of both magmatic and meteoric fluids. The average calculated δ³⁴S values are −0.2‰ for pyrite; +0.2‰ for chalcopyrite; −1.0‰ for sphalerite and −0.2‰ for galena. The δ³⁴S_H2S values are consistent with a magmatic source for sulfur. The combined fluid inclusion and stable isotope data indicate that the hydrothermal fluids related to the Au-Ag deposition at Chah Zard are characterized by a mixture of magmatic fluids with meteoric water under epithermal conditions.