The investigation of sulfidation state and hydrothermal fluid evolution on genesis of the quartz-sulfide ± gold veins in the Mouchesh deposit (southern Kurdistan): constraints on mineralization, fluid inclusions, and stable isotope of sulfur

Mouchesh gold deposit (0.7 Mt @ 1.3 g/t gold) is located in the Takab-Delijan gold belt. Mineralization with several 28 gold-bearing quartz-sulfide veins (N40E-trending, 1 to 10 m wide, and 5 to 200 m long) has been formed in the host of Lower Cretaceous andesite and andesitic lithic tuff units. Open space-filling, comb, and disseminated textures are important mineralization textures that were formed in quartz-sulfide±gold veins (vein I) and quartz-barite-galena (vein II), which and cut later by carbonate veins (vein III). The homogenization temperature (Th) and salinity of the fluid inclusions, respectively, with an average temperature of 180 °C and salinity of 0.2 wt% NaCl eq. (vein I), 155 °C and 1.6 wt% NaCl eq. (vein II), and 135 °C and 1.5 wt% NaCl eq. (vein III). The values of δ34S in sulfide minerals of veins I and II are between +0.1 to ‒3‰ (δ34SH2S between ‒0.3 to +0.4‰), which indicates a single magmatic source for sulfur. The results of this research reveal that the existence of hydrostatic conditions (e.g., boiling) in the Mouchesh deposit has caused H2S releasing from the hydrothermal fluid, the decrease in the solubility of the bisulfide complex Au(HS)‒2, and ultimately the gold instability.