White mica alteration in porphyry systems is often directly associated with economic mineralization. White mica chemistry may record the evolution of the hydrothermal system and could represent an important vectoring tool for Cu-Mo mineralization. However, in such setting, macro to microscale variations in white mica chemistry are still poorly understood. Here, we focus on the white mica alteration in the Gaby porphyry copper district (Northern Chile), using automated mineralogy (QEMSCAN), short-wave infrared (SWIR), and electron microprobe (EMPA) analyses. The Gaby district consists of Late Carboniferous-Early Permian volcano-sedimentary rocks, the Permo-Triassic Pampa Elvira plutonic complex, and Eocene tonalite porphyries. Two main types of white mica alteration are identified: i) Early green Fe-Mg-rich sericite is observed in veins, halos, and as pervasive alteration, frequently intergrown with chalcopyrite-bornite and low amounts of pyrite; ii) Late grey Fe-Mg-poor sericite is found disseminated, locally as secondary alteration on green sericite, and in halos of pyrite-rich veins. In these veins, green sericite is also present as infill, as well as in their outermost zone. Correlation between portable SWIR (TerraSpec) analyses and variations of white mica composition at micrometer scale as determined with QEMSCAN and EMPA demonstrates the strengths and limitations of the SWIR spectroscopy in exploration for porphyry systems.