REMOTE SENSING AND GIS APPLICATIONS IN GEOLOGICAL MAPPING, PROSPECTING FOR MINERAL DEPOSITS AND GROUNDWATER-BERBER SHEET AREA, NORTHERN SUDAN

Abstract

The geology of the East Bayuda Desert —Abiydia (Berber Sheet, NE-36-G) area in the north Sudan, has been investigated by means of remote sensing and Geo-Information System (GIS) techniques and limited geotraverses. Digital image processing of Landsat ETM+7 data and geo-spatial analysis were conducted to evaluate the use of remotely sensed data in geological mapping, mineral prospecting and hydrogeological investigation in such arid terranes. The study area represents a part of Bayuda terrane, and comprises Basement Complex rocks of Neoproterozoic age. The lithologies include the high-grade gneisses and migmatites, dismembered ophiolitic basic-ultrabasic rocks, metavolcanosedimentary sequence and supracrustal metasediments. These units have been intruded by syn- to late- and post-orogenic intrusions during and afler the Pan-African orogeny. Phanerozoic sedimentary Formations cover the Basement Complex rocks, which in turn have been covered by Cainozoic basaltic volcanics. Most of these units have been covered in parts by Quatemary Nile silts, alluvial deposits and / or aeolian sand sheets. The East African Orogen has been manifested in the study area. The collision between the west and east Gondwanaland continents resulted in at least five deformational phases, which can be traced in Satellite image. The three ductile and two brittle deformational phases result from the collision of the Bayuda terrane with Halfa and Gabgaba terranes. The first discemible deformational phase displayed by the isoclinal folds with E-W fold axis. These folds were refolded by close folds in NE-SW fold-axis fold. A third phase of open folds refolded the earlier fold with E-W fold axis. The ductile deformation has been followed by brittle deformational phase. The NE-SW trend Nakasib shear affected earlier structures, which in tum has been superimposed by N-S trend Keraf shear zone. Digital image processing was conducted to enhance the visual interpretation of the Landsat ETM+7 data. The IHS (Intensity-Hue —Saturation) transformation of the decorrelated stretched bands yielded an overall good lithologic discrimination. The two colour composite images 7, 4, l and 7, 5, 4 have been decorrelated stretched and then IHS transformed with the panchromatic band. The two colour composite images display well saturated hues and morphological signatures, which make them the best in discriminating various lithological units. The Principal Component transformations yield saturated images and resulted in a higher signal-to — noise ratio when standardized coefficients were used instead of the covariance matrices. Band ratioing images yielded geologically informative images, where both spectral and morphological information are preserved. Selective merged images were used by combined in the red-green-blue colour gun different and theless correlated images from various techniques. Colour composite images Litho-l, Litho-2 and drainage-image have been built. The Litho-1 colour composite image utilizes the PC2 (of the six bands) in red, band ratio 5/7 in green and DC2 (of bands 5, 4 & 3) in blue. The Litho-2 colour composite image utilizes PC2 (of the six bands) in red, DC2 (of bands 5, 4 & 3) in green and band ratio 3/1 *5/7 in blue. The drainage colour composite image utilizes band ratio 5/7, DC2 (of bands 5, 4 & 3), PC5 (of the six bands) in red, green and blue, respectively. These saturated and morphological expressed images display well discrimination ability of diverse lithological unit and structural elements. On the hand the drainage image created by selecting the band ratio 5/7, DC2 (of bands 5, 4 & 3) and PC5 (of the six bands) in the R, G and B, respectively. It was found that this image is superior in delineation the alluvial in the wadies, thus it was used mainly in mapping them. Geological map of Berber Sheet (scale of l:250000) has been produced utilizing the Geo- Berber database. The Geo-Berber includes the digitally processed remotely sensed data, field work and structural and petrographical data. These data combined with demographic data. The SRTM data provide the base for the elevation data in the geo-database. The extracted DEM render the 3D terrane visual image that assists the lithological discrimination by its morphological expression. The geo-spatially analysed lineaments data used in the Geo-Berber database have been produced by the spatial and structural analyses of the edge enha.nced- filtered Landsat images. Prospecting for mineral deposits has been exploited using the spectral criteria of the gossans and rock alteration associated with mineralization. The geo-spatially analysed- supervised classified colour composite images of Crosta (Feature Oriented Principal Components image) and Sabin’s ratio image proved to support the demarcation of the mineralization. The results are found to be controlled with the level of erosion as witnessed in the deeply eroded terranes as in the East Bayuda Desert and Abidiya areas. In the mineralized Ariab-NW Nakasib area that is characterized by low-level of erosion, the technique revealed optimum results in depicting the gossans. This malfunction in the remote sensing-GIS mineral prospecting model can be overcome by combining other geological and structural information in the geo-spatial analysis. A remote sensing-GIS model for depicting fractures and structurally-controlled aquifers in crystalline rocks prove to guide the prospecting of groundwater in Basement Complex terrane of the East Bayuda Desert. Digital image processing, lineament analysis and geo- spatial analysis combined with ground geophysical investigation gave best possible results as documented by the drilling activities.