Airborne radar data: Utility for geological mapping in tropical environments, Serra Pelada, Pará, Brazil

CIM Bulletin, Vol. 90, No. 1011, 1997

D.F. Graham, FirstMark Technologies, Ottawa, Ontario, and J.S. Moretzsohn, Docegeo, Rio Doce Geologia e Mineração S.A., Rio de Janeiro, Brazil

Airborne Synthetic Aperture Radar (SAR) was acquired over the Carajás Mineral Province, within the rainforests of the Amazon, which hosts the world’s largest Fe-ore deposit (Santos, 1986). Significant chemical weathering exists in this humid environment. Prevalent Au mineralization is thought to be generally associated with deformation zones in Archean schists. Radar data have proven to be very useful as an aid to geological mapping in the tropical rainforests of the Amazon Basin in Brazil. In these densely vegetated areas, a sense of regional structural trends is obtained as a consequence of the sensor/terrain geometry. The top forest canopy is the main terrain reflector of X-band radar energy, and consequently is the main terrain surface feature expressed in processed radar imagery. Radar is important for extending the continuity of mapped structural lineaments. Differential weathering is related to variations in radar image texture which is used to infer gross lithologic variations and relative age relationships of major rock units. Specifically, quartzites and banded iron formation are highlighted in the radar imagery due to their unique tonal and textural appearance, in contrast to schists, gneisses and metavolcanic rocks. As tropical areas are typically enveloped in cloud or mist, radar data are invaluable in providing information for logistical planning of field mapping activities.

Keywords: Geology, Geological mapping, Airborne Synthetic Aperture Radar (SAR)