©2015 Society of Economic Geologists, Inc. Economic Geology, v. 110, pp. 73–90 Geology and Hydrothermal Alteration of the Chapi Chiara Prospect and Nearby Targets, Southern Peru, Using ASTER Data and Reflectance Spectroscopy

Southern Peru contains several small- and medium-sized epithermal Au-Ag ( ± base metals) deposits related to Miocene-Pliocene metallogenetic belts. Specifically, the characterization of the geology and mapping of hydrothermal alteration zones of the Chapi Chiara prospect, Canahuire deposit, and Cerro Millo and San Antonio de Esquilache targets were done with data acquired by Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) spaceborne sensor. ASTER mapping techniques included (1) band ratio and principal component analysis (Crósta technique) applied to the visible and near-infrared and short-wave infra-red bands to produce a regional hydrothermal alteration map (alunite and/or kaolinite, illite-muscovite and/ or smectite, iron-bearing minerals) and (2) spectral indices and selective principal component analysis applied to the thermal infrared bands to detect quartz- and carbonates-bearing targets, respectively. These methods were used to establish a hydrothermal zoning pattern in paleostratovolcanoes, where the Chapi Chiara, Cerro Millo, and San Antonio de Esquilache targets are located. This zoning pattern was used to infer erosion condi-tions and the potential for metal deposits based on the mineralogy, which was also analyzed using reflectance spectroscopy and petrography. In addition, ASTER data were used to characterize the carbonate host rocks, the quartz-bearing units of the Yura Group, and the quartz-poor unit associated with the phreatic and phreatomag-matic breccias in the Canahuire deposit region. This characterization led to the development of a favorability model for the occurrence of “Canahuire-type ” deposits based on spatial analysis using the fuzzy logic technique