Abstract:

Xiejiagou gold deposit is a newly found alteration deposit which occurred in Linglong granite at the Jiaodong area, Shandong. By analyzing the temperature, pressure and the component of the fluid inclusions in three mineralization stages, it is included that this gold deposit is an epithermal deposit and the gold-bearing fluid is salt-water solution. In the first mineralization stage, the homogenous temperature of fluid inclusions ranged from 320 ℃ to 350 ℃, with salinity from 2.7% to 6.6% NaCl equivalent and density from 0.498 g/cm³ to 0.886 g/cm³; in the second mineralization stage, the homogenous temperature of fluid inclusions ranged from 270 ℃ to 330 ℃, with salinity from 3.6% to 8.4% NaCl equivalent and density from 0.571 g/cm³ to 0.959 g/cm³; in the last mineralization, the homogenous temperature of fluid inclusions ranged from 250 ℃ to 290 ℃, with salinity from 5.8% to 10.6% NaCl equivalent and density from 0.724 g/cm³ to 1.158 g/cm³.So the evolution of goldbearing fluid was a process that temperature decreased and salinity and density increased. CO₂ and H₂O are the main components of the fluid, with CO, CH₄, H₂S, SO₂ and N₂ involved. There are some positive relationships between the content of CO₂ in the fluid and the grade of gold in the ores. The assemblage of different fluid inclusions and the evolution of fluid show that immiscibility is the key element for mineralization.

Key words: fluid inclusion, fluid immiscibility, geological significance, Xiejiagou gold deposit, Shandong