Integration of Airborne and Ground Geophysical Prospecting Applied to an Epithermal Gold Deposit in the Castro Basin, Southern Brazil

Abstract

The gold exploration in the Castro Basin, Brazil, has been hampered by complex geology, disseminated low-grade ore, and the subsurface nature of quartz-adularia veins. To address these challenges, this study applied airborne geophysical techniques (gamma-ray spectrometry and magnetometry) to identify hydrothermal alteration zones and related structures. Radiometric parameters and magnetic gradient variations were analyzed to correlate with gold occurrences. Results indicated a strong association between potassium enrichment and magnetic lineaments, which was confirmed by geochemical samples. Based on these results, the Torre Target was selected for ground geophysical surveys. Electrical resistivity, induced polarization and magnetometry data were collected and integrated with digital elevation models. Geoelectrical sections and maps delineated the main ore body characterized by high chargeability anomalies associated with argillic alteration and disseminated sulfides. Resistivity data highlighted potential vertical contacts and fault structures indicative of an epithermal system. Magnetic techniques identified areas of magnetite concentrations within breccias and rhyolite, suggesting a connection to the mineralization events. In addition, magnetic data helped differentiate chargeability anomalies associated with the ore body from those associated with residual soil from diabase dikes. Results were validated by drilling, confirming the accuracy of the targets identified. This study demonstrates the effectiveness of geophysical techniques for the exploration of challenging gold deposits in the Castro Basin.