The role of digital airborne imaging spectrometer data in the discovery of the Arcopunco epithermal gold project; Huancavelica, Central Peru

The high Andes of Central Peru present significant logistical problems to mineral exploration and remote sensing is a valuable primary tool. Landsat TM data have been widely used but extensive clay-iron color anomalies need to be mapped in more detail to optimize follow-up exploration and land holdings. Major discoveries have little or no clay-iron anomalism and so it was decided to try airborne multi-spectral data using the GER Digital Airborne Imaging Spectrometer. The GER data were calibrated against field spectral data collected in advance of the survey. Simple band difference algorithms identified target zones with potential argillic, advanced argillic and phyllic alteration and gave field geologists a rapid means of identifying prospective ground. Arcopunco was identified within 10 km of existing mining operations as a large zone of advanced argillic alteration surrounded by argillic and phyllic alteration. The GER data were further processed using spectral feature fitting techniques to map the alteration mineralogy in detail. Fieldwork confirmed a quartz, alunite and pyrophyllite advanced argillic alteration assemblage associated with structurally controlled, mineralized volcanic breccias. The prospect was on open ground and subsequently claimed for exploration within 3 months of completion of the airborne survey. Drilling, commenced within one year of securing tenure, localized significant epithermal gold mineralization. The application of airborne multi-spectral data to mineral exploration in this area proved to be both cost and time effective and led to the identification of gold mineralization hitherto unrecognized in a well-known mineral district