Formation Conditions of Gold Mineralization in the Spokoininsky Ore Cluster, Aldan Shield, Russia

Abstract

The paper presents the first data on individual fluid inclusions hosted in quartz in the ores of three types (polysulfide, gold–silver–telluride, and gold–bismuth) of the Spokoininsky ore cluster with gold ore mineralization. The three ore types show differences in the physicochemical parameters and composition of their fluids. The fluid of the Spokoininsky cluster polysulfide ores are characterized by a relatively low initial temperature (180‒350°C), a higher CO₂ density (0.27‒0.71 g/cm³), and a higher fluid pressure (0.7‒1 kbar) compared to the fluids that formed the gold–silver–telluride ores (temperature 200–260°C, CO₂ density 0.28–0.56 g/cm³, pressure 0.7 kbar). The dominant salts in the fluids of polysulfide ores are Na and Mg chlorides, whereas the mineral-forming fluids of the gold–silver–telluride ores are simpler saline aqueous fluids containing Na chlorides. The fluids that formed the polysulfide ores have a H₂O–CO₂–N₂ composition, whereas the fluid of the gold–silver–telluride ores is mostly of H₂O–CO₂ composition. The gold–bismuth ores in the Mayskoe ore field were formed by H₂O–CO₂-bearing fluids with a salinity concentration of 4.0‒6.4 wt %-equiv. NaCl, a CO₂ density of 0.56‒0.61 g/cm³, at a temperature of 280‒335°C and a pressure of 0.7 kbar. The data led us to conclude that the ore-forming fluid of the Spokoininsky ore cluster was similar to the fluids of orogenic gold deposits.