Fluid inclusions in gold mineralization in the Sarekoubu area of the southern Altai Mountains, Xinjiang, China

Abstract

The Sarekoubu gold deposit occurs in Devonian metamorphic rocks at the southern margin of the Altai Mountains, Xinjiang, China. The main mineralization stages are pyrite-quartz stage (II) and polymetallic stage (III). Both the quartz debris in volcanics and vein quartz contains abundant fluid inclusions, but they are very different in types and compositions. Primary fluid inclusions in quartz debris are mainly L-V type with t h =255∼270°C, and L-V-S type (They are usually decrepitated from 248°C to higher than 335°C). SEM/EDS analysis shows that many daughter minerals are calcic salts. Fluid inclusions in vein quartz are different, and are dominated by LCO2, LCO2-LH2O, and LH2O-LCO2 types; those in polymetallic stage are more complex, probably with CO2-CH4 system fluid. The t m of solid CO2 are −78.1∼−61.9°C, and the t hCO2 are −33.7∼−17.7°C. Pure CO2 fluid inclusions and CO2-rich fluid inclusions are widely developed in the Sarekoubu gold deposit. δ13C of CO2 inclusions ranges from — 10.725‰ to −21.151‰, which are similar to those from mantle minerals. CO2 fluids in the Sarekoubu gold deposit might originate from degassing of upper mantle during late Hercynian collisional orogeny, or from the geochemical recycling of subducted materials