SPECTROMETRY: APPLICATION TO MINERAL EXPLORATION USING SPACEBORNE MULTISPECTRAL SENSORS

Abstract Morro do Ouro, located near the town of Paracatu, Minas Gerais State, Brazil, is a world-class example of low-grade, high-tonnage, black shale-hosted gold deposit. Available geologic data coupled with reflectance spectrometry data were used to establish the “remote sensing signature ” of this type of deposit. Spectral classification techniques, usually employed with hyperspectral remote sensing data, were used to carry out spectro-lithological mapping of mineralized rocks, using a Landsat-5 TM scene covering the Morro do Ouro deposit and surrounding terrains. Reference spectra used for classification were obtained from field and laboratory measurements of selected samples from known gold occurrences in the area. The results show that all known mineralized zones in the study region are identifiable by the method, despite Landsat-5 TM spectral and spatial limitations, as well as the constraints imposed by the sub-tropical environment. The spectra of major lithologic types associated with Morro do Ouro type gold deposits were then modelled using the spectral resolution of Terra ASTER ((Advanced Spaceborne Thermal Emission and Reflection Radiometer), a newer generation spaceborne sensor developed for geologic applications that has higher spectral resolution than Landsat TM. A comparison of the spectra convolved to the spectral resolution of both sensors demonstrates the benefits that higher spectral resolution spaceborne sensors bring to mineral exploration and points out ASTER as a better choice than TM for gold exploratio