Inference of minerals at Redondão kimberlite crater, Parnaíba Basin, Brazil, based on interpretation of airborne gamma-ray spectrometry and ASTER data

Abstract

This work reports how minerals at Redondão kimberlite pipe may be inferred through integrated interpretation of airborne gamma-ray spectrometry data and multispectral images derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Using several processing techniques (e.g. K, eTh, and eU concentration maps, K/eTh, K/eU, and eU/eTh ratio maps, K image inverse map, profile analysis for radiometric data and; spectral indexes and mineral distribution and abundance maps for ASTER data), it was observed that K concentrations within Redondão kimberlite intrusion are high enough to be distinct from the surroundings and at least three spectral signatures of endmembers extracted from ASTER images suggest that chlorite, diopside, and phlogopite minerals may be present within Redondão kimberlite crater and the near surroundings. Although the sources of K concentrations are unclear, it probably is composed of different minerals and phlogopite may be one of them. The spectral signatures of chlorite, diopside, phlogopite may be derived from clastic materials and products derived from ultramafic mineral weathered, but new studies are recommended to improve distribution and abundance maps of these minerals. These new studies may include hyperspectral sensor images and rock-spectra data. The results reported here be useful for further research whose goal is to map kimberlites using remotely sensed images not only in the study area, but also in other locations with similar geologic context.

Keywords

• Remote sensing
• Advanced spectral analysis
• Radiometric data
• K-bearing minerals
• Kimberlitic minerals
• Mafic intrusions