Study of fluid inclusions and characteristics of ore-forming fluids in the shear zone-type gold mineralization at Qolqoleh deposit, Southwest of Saqez

Category Economic geology & mineral exploration
Group GSI.IR
Location The 25 Symposium of Geosciences
Author F.Aliyari-E.Rastad
Holding Date 30 June 2007


Qolqoleh gold deposit is located in northwestern part of the Sanandaj-Sirjan zone, and hosted in a ductile and brittle shear zone, and is categorized in orogenic gold deposits. Based on petrographic and microthermometric results, two types of fluids were distinguished in both concordant gold-bearing quartz-sulfide veins and veinlets, and discordant gold-bearing quartz-sulfide and quartz-calcite veins and veinlets. In this basis, the type I include two-phase (L+V) primary fluid inclusions with melting temperatures from -۱۲ to -۱۵ ۰C and homogenization temperatures from ۳۵۰ to ۳۹۶ ۰C, the salinity values of these fluid inclusions ranges from ۵.۵ to ۱۰ %wtNaCl and density is ۰.۸۰-۰.۸۶ g/cm۳. Type II consists of two-phase (L+V) primary fluid inclusions, which melting temperatures ranges from -۱۲ to -۱۵ ۰C, homogenization temperatures fall in the range from ۲۱۰ to ۲۵۰ ۰C, salinity values ranges from ۲ to ۴ %wtNaCl and density is ۰.۶۵-۰.۷۱ g/cm۳. The presence of two distinctive fields of fluid inclusions densities indicating the mixing of a hotter and more saline fluid with a cooler and less saline fluid. Furthermore, the mean pressure of fluid inclusions is about ۲ kbar and the mean depth of mineralization is approximately ۷ km. These values indicate high correlation with total homogenization temperature and salinity of fluid inclusions.

Abundances of liquid-rich two-phase fluid inclusions, presence the negligible amounts of vapour-rich fluid inclusions, homogenization many of fluid inclusions to liquid, presence of Co۲ in most of them, relatively uniform and low salinity values and correlation between total homogenization temperatures and salinities clearly indicate that the mixing process occur in the gold-bearing fluids. In addition, the considerable range of homogenization temperatures in the fluid inclusions of Qolqoleh gold deposit indicating that simple cooling process (decrease of temperatures) is the one of effective processes in deposition of gold-bearing fluid. Based on these characteristics, the Qolqoleh gold deposit is categorized in orogenic (mesothermal) gold deposits.

Keywords: fluid inclusions, homogenization temperature, salinity, mixing process, metamorphic fluid, Saqez, Qolqoleh