Reconnaissance geologic mapping in the Tapajos mineral Province, Brazilian Amazon, using spaceborne SAR imagery and airborne geophysics

The Tapajos Mineral Province lies within the Amazonian Craton, northern Brazil, and stands as one of the largest gold-producing provinces of the country. The geology; mapped at 1:250,000 scale, comprises Archean to Phanerozoic rocks, where numerous gold-rich placers of Quaternary alluvium provenance have been exploited and a few primary, deposits are known. No large primary deposit has been discovered thus far in the region. Spaceborne radar imagery (RADARSAT-1 and JERS-1) and airborne geophysics (magnetic and gamma-ray) surveys were used to produce a more complete geological map of a portion of the province and to provide guidelines for targeting potential primary gold mineralization. SAR imagery provided valuable textural information, related to bedrock geology; as well as structural information. Thorium and potassium gamma-ray data were most useful in the identification of lithologic units, allowing the recognition of distinct domains within the basement. Aeromagnetic data helped delineate regional structures. An integrated analysis and interpretation of these datasets allowed the definition of previously unrevealed lithologic domains within the basement, one of which encompasses most of the known primary and placer gold deposits. Furthermore, brittle structures interpreted from SAR and aeromagnetic data showed a spatial correlation with reported primary gold occurrences. These findings, obtained for a small portion of the Tapajos Province, demonstrate the importance of the synergistic use of spaceborne SAR and airborne geophysics for geologic mapping and mineral exploration activities in the entire province and elsewhere in the Amazon, where the geology is poorly known and the mineral potential is high.