The origin of hypogene alteration and mineralization features in the Escondida 27porphyry Cu deposit resulted from intense overprinting related to three main hydrothermal 28stages. The beginning of each stage is recorded by deposition of bright quartz crystals on 29vein walls that precipitated from high-temperature fluids. In the deepest zones of the 30deposit, the earliest stage started with exsolution of intermediate-density fluids, which 31transported high concentrations of Cu, whereas Mo was not detected. However, in the 32shallow zones, the early stage began with depressurization and unmixing of intermediate-33density fluids, which generated both a hypersaline and vapour-rich fluid phase, producing 34an important geochemical segregation between both phases. The transitional stage also 35started with circulation of intermediate-density fluids but never experienced unmixing. 36These fluids transported the highest Mo concentrations in the deposit; however, Cu displays 37lower concentrations relative to intermediate-density fluids from the early stage. The 38beginning of the late stage was also associated with intermediate-density fluids; however, 39Cu and Mo were below the detection limits in most of the analysed fluids. During the 40evolution of the three stages, the fluids experienced gradual cooling, which promoted the 41precipitation of euhedral and zoned quartz crystals that overgrew the early high-42luminescence quartz generations. Sometimes, sulfide minerals display euhedral crystal 43boundaries with zoned quartz, suggesting that mineralization started during these phases.44The latest events detected in each main stage are linked to cooler and low-salinity fluids, from which dark quartz and hypogene sulfide sprecipitated along microfractures and 46interstitial spaces developed in the earlier quartz generations.