Pegmatite mapping using spectroradiometry and ASTER data (Zenaga,Central Anti-Atlas, Morocco)

摘要

The region of Angarf, located in the southern part of the Zenaga inlier (Central Anti-Atlas, Morocco), is known by the abundance of pegmatite veins, essentially constituted by quartz, muscovite and feldspar. These veins are hosted in the mica schists and granites of the Paleoproterozoic basement. Mapping of pegmatites was approached by using synergetic field data, spectroradiometric measurements, and ASTER data.Analysis and interpretation of the spectroradiometric data allowed the identification of an important sericitic alteration. The measured spectra of the pegmatites detected the presence of absorption bands at wavelengths of 900 nm, 1400 nm, 1900 nm, 2200 nm, 2350 nm, and 2450 nm, which allowed the selection of the most informative ASTER spectral bands for pegmatite mapping. After geometric, radiometric, and atmospheric corrections to ASTER data, some processing techniques were applied, including Principal Component Analysis (PCA), Minimum Noise Fraction (MNF), and Band Ratios (BR). Then, several RGB compound displays were analyzed using the results of these treatments. Three combinations of RGB were selected because of their potentials to extract the pegmatites outcrops. The first RGB combines the PC2, PC1, and PC3, it's suited to achieve good separation between geological facies allowing the identification of pegmatites. The second considers the MNF2, PC1, and 6/3; it has the same mapping potential as PC combination. The third combines 1/3, 1/4, and 2/5, it has allowed the identification of more pegmatites found in the field compared to the other two combinations. This last combination proved to be the most suitable for simply and rapidly identifying pegmatites. This result was validated using field and spectroradiometric data.The approach presented in this study gave satisfactory results in comparison with field data. It is a low-cost technique that highly applicable for pegmatite mapping and in the exploration of their minerals. The result could assist the development of pegmatite exploration in the other regions.