The exsolution of chlorine-rich fluids plays a key role in porphyry Cu-Au deposits (PCDs) formation by transferring metals from the melt to the fluid, either directly or via breakdown of pre-existing magmatic sulfides. However, the relative roles of these two mechanisms of metal transfer to the magmatic-hydrothermal fluid remain unclear. In this study, amphibole composition is employed as a proxy to reconstruct magmatic evolution and fluid exsolution conditions favorable to the formation of PCDs. Our results show that magmatic Cl and Cu contents, Mg^#, and fO₂ values inferred from amphiboles exhibit coupled variations during magma evolution. We interpret these correlations to be due to Cl-rich fluid exsolution from a deep-seated PCD system which triggers an increase in fO₂ and the destabilization of previously formed sulfides in the middle to upper crust. This mechanism may be a key factor for the formation of Cu-rich PCDs that tend to be deeper and more oxidized than Au-rich PCDs. Our findings highlight amphibole composition as a potential indicator of magmatic-hydrothermal mineralization.