This research work consists of petromineralogical analysis and infrared spectrometry to determine mineralization and hydrothermal alterations in the Limoncillo vein. This structure is located in the quartz-arenites of the Marcavilca Member of the Morro Solar in Lima and is associated with a dike and a sinestral fault of N-S direction. The mineral of economic interest is represented by native gold scattered on the hydrothermal quartz of the vein and, in greater concentration, on the quartz arenites adjacent to the Limoncillo Vein. Using infrared spectrometry it was possible to determine two types of hydrothermal alteration: 1) Argillic alteration represented by the mineralogical association of kaolinite, illite-smectite and potassium illite, which suggest a formation temperature between 150 ° and 200 ° C and a pH moderately acid, with a tendency to neutralize; and 2) sub-propylitic alte...