Fluid mixing and Zn-Pb mineralization in the Kushk ore deposit, central Iran, evidence from fluid inclusions

Kushk sulfide Zn-Pb ore deposit is located in the Posht-e-Badam block, in the central Iranian tectono-magmatic zone. The host rocks of the ore deposit include shale, sandstone and dolomite. In order to investigate the physicochemical condition controlling the formation of the sulfide ore, a number of fluid inclusions were gathered from silicic thin layers. The silicic contents of the samples have contemporaneously been deposited with shale and sulfide minerals mainly in the footwall and the main mineralized horizon. In this research, the general properties of fluid inclusions in the ore-forming system are taken into account and the interpretation of these data in terms of fluid evolution processes is discussed. Considering the syngenetic formation of the silicic thin layers and the mineralized shale, a similar formation condition can be considered for both of these units.  Based on the results, two types of fluids were involved in the formation of the silicic thin layers, including fluid 1 that is characterized by higher salinity (av. 38.8% NaCl.eq) and is thought to transport the metals chloride complexes and fluid 2 with lower salinity (av. 4.46% NaCl.eq) and is thought to carry sulfide species. Part of sulfide in this type of fluid could be originated from bacterial activity. Isothermal mixing of the two fluids sequencially resulted in destabilization of chloride complexes of chalcophile elements, the reaction between the elements and sulfur originated from the low salinity fluid and formation of the sulfide ore.