Utilization of Landsat 7 ETM+ Multispectral Data and ASTER-GDEM in Geological Investigation and Alteration Mapping around Yankara-Dan Sabo-Takulawa Area within Wonaka Schist Belt, Northwestern Nigeria

Abstract

The study area forms part of the Precambrian to Early Paleozoic Nigerian Basement complex. ASTER-GDEM image draped on topographical map aided 3-D perspective view of physiographic features in the area. The Landsat ETM+ remote sensing data has suitable spectral and spatial properties that aided lithological and alteration mapping. Spectral transform approaches, consisting of band ratio (BR), principal component analysis (PCA), False Color Composition (FCC), and Feature Oriented Principal Component Selection (FOPC) were utilized. Prior to image processing, the ETM+ data were also subjected to image pre-processing. The results show that BR, PCA and FCC images discriminates the granitic rocks and metasediments. Color melange including ETM+ (7/4+4/3+5/7, 3/1+5/7+4/54 and 5/7+3/2+4/5) discerned highly altered zones and iron rich minerals. Colour composite (Kauffman ratio) and FCC show vegetation preponderance mostly on metasediments. Alteration of hydroxylated-silicate rocks are distinct with PCA. Hydroxyl minerals with marked oxidization and argillization are more recognizable with FOPC (Crosta technique) than PCA techniques. Structurally, the spectral responses distinctly show symmetrical M-shape fold pattern in granitic rocks that span within the southeastern part of the area.  The area also exhibit highest lineament density. Nearly N-S lineament trend corresponding to imprints of Pan-African Orogeny predominates.

Keywords: Alteration mapping, Band ratioing, Lineament density, lithology