The Egyptian Journal of Remote Sensing and Space Sciences (2013) 16, 199–210 National Authority for Remote Sensing and Space Sciences The Egyptian Journal of Remote Sensing and Space Sciences www.elsevier.com/locate/ejrs www.sciencedirect.com RESEARCH PAPER Application of remote sensing in exploration for uranium mineralization in Gabal El Sela area, South Eastern Desert, Egypt Talaat M. Ramadan a,*, Tarek M. Ibrahim b, Abu Deif Said c, Moustafa Baiumi b a National Authority for Remote Sensing and Space Sciences (NARSS), Cairo, Egypt b Nuclear Materials Authority, Cairo, Egypt c Faculty of Sciences, Zagazig University, Egypt Received 23 October 2013; accepted 3 November 2013 Available online 16 December 2013 KEYWORDS Abstract This research aims at integrating remote sensing data and field studies to prospect for Biotite granites; radioactive materials at Gabal El Sela area, South Eastern Desert of Egypt. This area is a part Landsat ETM+; of the Arabo-Nubian shield, which is constituted by Late Precambrian basement rocks and devel- Uranium mineralizations; oped during the Pan African tectono-thermal event. Geological interpretation of Landsat ETM+ Alteration zones; image and field studies revealed that the study area is mainly covered by ophiolitic ultramafic rocks, Quartz veins; intermediate metavolocanics, granodiorites, biotite granites and garnetiferous muscovite granites. Eastern desert These rocks are injected by pegmatitic and quartz veins and cut by acidic and basic dykes. The pro- cessed Landsat ETM+ data enable also to identify uraniferous alteration zones hosted in the gra- nitic rocks (using band ratio 5/7, 4/5, 3/1 in RGB, density slicing and supervised classification techniques). The measured reflectance values (DNs) of six spectral bands of Landsat ETM+ for all exposed rock types in the study area show that the alteration zones have the highest reflectance values. The study recorded the presence of uranium mineralizations in alteration zones associating with the granitic rocks occurring along ENE–WSW trending shear zones. Three uranium-bearing alteration zones hosted in granitic rocks were detected. These zones are characterized by ferrugina- tion, silicification, grizenization and kaolinitization. The most promising alteration zones (Site 1) occurs at the northeastern part of Gabal El Sela and is characterized by very high radioactive anom- alies (up to 5000 ppm eU). Microprobe analyses of samples collected from these alteration zones reveal the presence of uraninite crystals. It seems that the high fractures density of the granitic rocks acted as good channels for the ascending hydrothermal fluids and the percolating meteoric water, * Corresponding author. E-mail address: [email protected] (T.M. Ramadan). Peer review under responsibility of National Authority for Remote Sensing and Space Sciences. Production and hosting by Elsevier 1110-9823 Ó 2013 Production and hosting by Elsevier B.V. on behalf of National Authority for Remote Sensing and Space Sciences. http://dx.doi.org/10.1016/j.ejrs.2013.11.001 200 T.M. Ramadan et al. that leached the uranium minerals disseminated all over the rocks and redeposited them along the fractures of the shear zones. This study demonstrates the utility of orbital remote sensing data for finding unknown mineralized zones in the Eastern Desert of Egypt and similar arid regions. Ó 2013 Production and hosting by Elsevier B.V. on behalf of National Authority for Remote Sensing and Space Sciences. 1. Introduction of Egypt has been used in several ways by various authors e.g., El Shazly et al. (1975), Sultan et al. (1986), O’Connor et al. The Precambrian basement of the Arabian Nubian Shield, is (1987), El Baz (1990), Yousif and Ali (1998), Yousif and She- exposed in Egypt in the Eastern Desert, southern part of Sinai did (1999), Sultan et al. (1986), Ramadan et al. (2001) and Peninsula and the south western corner of the Western Desert. Ramadan and El Leithy, 2005. The study area is situated in the Halaib district, South Eastern The main objectives of the present work are to map in detail Desert, along the Red Sea coast between Lat. 22° 130–22° 200 N the basement rocks and to identify the uraniferous alteration and Long. 36° 080–36° 170 E(Fig. 1a). This area is located zones in Gabal El Sela area using Landsat Enhanced Thematic about 25 km west of Abu Ramad City on the coastal highway. Mapper (ETM+) data and field spectrometric measurements The investigated area is generally of moderate to low reliefs, and studies. where its highest peaks are Gabal Qash Amir (about 724 m.a.s.l) and Gabal El Sela (557 m.a.s.l). Main Wadis dis- 2. Materials and methodology secting the area are Wadi Eikwan, Wadi Eishimhai and Wadi Yoider. They all drain eastward toward the Red Sea. 2.1. Remote sensing data The general geology of the Halaib district was studied by several authors (e.g., Hume, 1937; El Ramly, 1972; Hussein, 1977; Kabesh, 1994; Assaf et al., 1998; Ramadan, 2003). The Landsat ETM+ data were processed at the Image Processing mineral deposits of the district were also investigated by Laboratory of the National Authority for Remote Sensing and numerous authors (e.g., Bassiuny, 1957; El Shazly and Saleeb, Space Sciences (NARSS), using the ERDAS Imagine 8.3 software 1959; Basta and Saleeb, 1971; Takla et al., 1976; Hussein, on a Sun Spark workstation. One scene (Path 172/ Row 045, ac- 1990; Dardir et al., 1992; El AIfy et al., 1994; El Gammal quired in 2005) covering the investigated area, has been geometri- and Cherif, 1999; Ramadan, 2003). Airborne geophysical data cally corrected and radiometrically balanced. The remote sensing have been often used for geological mapping and regional data for the study area were processed for geological and struc- exploration (Reeves, 1985; Ramadan and Sultan, 2004). The tural mapping with the particular aim of discriminating uranifer- radioactive mineralizations of the Egyptian Eastern Desert ous granites and associated alteration zones. Several products have been studied by many authors (e.g. El Ghawaby, 1973; including false-color composite image (7, 4, 2 in Red (R), Green El Shazly and El Ghawaby, 1974; El Kassas, 1974; Ammar (G), Blue (B), Fig. 1a) and band ratio image (5/7, 5/4, 3/1 in R, et al., 1991; Ammar, 1997; Ramadan and Sultan, 2004). Re- G, B, Fig. 1b), as well as density slicing and supervised classifica- mote sensing application to the geology of the Eastern Desert tion images (Fig. 1c and d)wereobtained. Figure 1a False color composite Landsat ETM+ image (Bands 7, 4, 2 in R, G, B) for the study area. Application of remote sensing in exploration for uranium 201 Figure 1b Landsat ETM+ ratio image (5/7, 4/5, 3/1 in RGB) for the study area. The false-color composite image has been interpreted where each corresponding to a specific range of digital numbers geological and structural maps have been produced. The band (DN). Different density slices are shown as separate colors that ratio image was used for the lithological discrimination of can be draped over background images. We used this tech- different rock types, as well as to distinguish and map the ura- nique to create a clay alteration index map of Gabal El Sela niferous alteration zones in the study area. Density slicing con- alteration zones using band-ratio 5/7 (Fig. 1c). Landsat verts the 256 shades of gray in an image into discrete intervals, ETM+ band-ratio 5/7 maps clay alteration because the clay Figure 1c Clay alteration index map draped over 5/7 Landsat ETM+ ratio image for the study area. Red color reveals the enrichment zones with clay minerals. 202 T.M. Ramadan et al. Figure 1d Supervised classification image for the study area. Yellow color reveals the enrichment zones with clay minerals. minerals, such as kaolinite, montmorillonite, illite, and alunite, 2.2. Field study have reflectance maxima within band 5 and reflectance minima within band 7 (Sabins, 1997). Analysis of Landsat TM images A geological-structural map of the study area at scale 1:50,000 with supervised classification techniques helped in identifying was constructed using the Landsat ETM+ image and field previously unknown alteration zones in the study area observations. More than 150 rock samples representing the dif- (Fig. 1d). The measured reflectance values (DNs) of six spec- ferent rock units in the study area were collected. In addition, tral bands of Landsat ETM+ for all exposed rock types in radiometric survey for the study area was carried out by using the study area were used to distinguish between different rock a high sensitive and well calibrated 256 channel portable gam- units in the study area (Fig. 2). ma-ray spectrometer (GS-256). This spectrometer internally Figure 2 The spectral signatures of the exposed rock units in the study area. Ul (Ultramafic rocks), Mv (Metavolcanics), Gb (Gabbros), Gt (Granodiorites), Gr (Granites) and Al (Alteration zones). Application of remote sensing in exploration for uranium 203 stores data of conversion/correction constants to allow the dis- are in their turn, intruded by biotite granites. They are charac- play of data in conventional counts/time period or directly in terized by exfoliation texture and contain xenoliths of various ppm eU, ppm eTh and K%. The obtained data are used to dis- sizes and compositions. Petrographically, these rocks are cuss the distribution, mobilization and U-potentiality of the mainly composed of potash feldspars, quartz, plagioclase, studied granitic rocks. The data also enabled to define the char- hornblende and biotite. Chlorite, sericite and epidote represent acteristic features of the high radioactive zones in the study area. the secondary minerals. Opaques, sphene and zircon are the accessory constituents. The biotite granites are widely distrib- 2.3. Laboratory work uted in the eastern and central parts of the study area.