Digital Image Processing of Landsat 8 and Spectral Analysis of ASTER data for Mapping Alteration Minerals, Southern Hamisana, NE Sudan

Abstract

The study area lies in the southern part of the Hamisana Shear Zone (HSZ), within the Nubian Shield as a transitional area between Gebeit and Gabgaba terrains. The objective this work is to use remote sensing and GIS techniques for geological mapping and prospecting for gold mineralization in the study area. A set of four Landsat 8 scenes has been mosaicked and subset to obtain a full coverage of the study area, in addition to subset of ASTER (AST_L1T) as semi-hyperspectral data for spectral analysis. The geological mapping was carried out based on interpretation of enhanced satellite image and field work. The study area is dominated by metavolcanic assemblage ranging from basic to acid in composition. The Meta volcano-sedimentary include dacite, andesite, greywacke, meta-conglomerate, rhyolite and basalt, and mafic-ultramafic rock with less common other volcanic varieties. These layered meta-volcano-sedimentary sequences are intruded by the syn-to late-orogenic and post-organic igneous intrusions. Different digital image processing techniques (True and false color combinations and image ratio) have been applied in this work in order to increase the discrimination between various lithological units and to delineate alteration zones which represent possible target zones for gold mineralization. The Principal Component Analysis (PCA) yielded saturated images that are more interpretable than the original data, especially for discriminating between metavolcanic and metasediments. The sultan ratio image was used in this work for lithological discrimination to help in geological mapping. Mapping hydrothermal alterations products associated with gold mineralization has been conducted through the spectral analysis of semi-hyperspectral ASTER data, where the Spectral Angle Mapper (SAM) technique has been used to identify the alteration minerals related gold mineralization, such as kaolinite, muscovite, dolomite, hematite, and Buddingtonite. The result of the spectral analysis of ASTER data indicated the probable target zone of alteration related to mineralization existing in the study area. Moreover, many exploration targets have been identified within the study area on the basis of the results of the spectral analysis. The targets are represented mostly by gold-bearing quartz veins.