Fluid Evolution and Stable Isotope Characters

Abstract

Fluid inclusions are particularly useful in documenting the temporal and spatial evolution of skarn-forming fluids, and provide evidence for the temperature and salinity shifts between skarn- and retrograde alteration stage. In the skarn stage of the Galinge deposit, ascending SiO₂-bearing NaCl saturated magmatic fluids separated to a hypersaline liquid and a vapor phase at 500~550°C and 300~400bar 1~1.5km paleodepth, at higher lithostatic pressure compared to hydrostatic pressure. Brine and vapor continued to ascend, and replaced the wall rock to form unmineralised skarns such as garnet, pyroxene etc with minor ore minerals. As they cooled to ~400°C in the retrograde stage, due to great consumption of SiO₂, the fluid predominantly consisted of saturated salty liquid. The residual fluid reacted with the earlier skarn to form epidote, amphibole etc with abundant ore minerals. This was followed by a decline in temperature to between 250~380°C at a hydrostatic pressure of 150~50 bar, corresponding a paleodepth of 0.5~1.5km as result of the mixing of magmatic water with lower-salinity meteoric waters. The overall hydrothermal cooling event took place during the geological background reversing, like mentioned above, the post-orogenic stage consists of a transition of compressional environment to extensional environment, while the magmatic fluids spread upward and outward on a larger scale.