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Journal of African Earth Sciences 35 (2002) 107–121 www.elsevier.com/locate/jafrearsci

Structural controls on Neoproterozoic mineralization in the South Eastern Desert, Egypt: an integrated field, Landsat TM, and SIR-C/X SAR approach Timothy M. Kusky a

a,*

, Talaat M. Ramadan

b

Department of Earth and Atmospheric Sciences, St. Louis University, St. Louis, MO 63130, USA National Authority for Remote Sensing and Space Sciences, El-Nozha El-Gedida, Cairo, Egypt

b

Received 27 February 2001; received in revised form 11 June 2001; accepted 1 November 2001

Abstract The Arabian–Nubian Shield represents a complex amalgam of arcs and microcontinents assembled during Neoproterozoic closure of the Mozambique Ocean. The 750–720 Ma Allaqi suture is an arc/arc collision zone, formed when the Gerf terrane in the north overrode the circa 830–720 Ma Gabgaba terrane in the south, prior to closure of the Mozambique Ocean. Neoproterozoic rocks include ophiolitic ultramafic–mafic rocks, metasediments, intermediate metavolcanic rocks, intrusive gabbro-diorite rocks, granodiorites, biotite granites, and leucocratic granites. High-pressure/low-temperature metamorphism has been documented in rocks of the suture zone. Mineral deposits include nickel–copper–platinum and podiform chromite in ultramafic rocks, marble, gold-bearing quartz-veins in D2 and D3 shear zones, and radioactive mineralization associated with late leucocratic granitic rocks. Integrated field mapping and remote sensing techniques are used to distinguish and map the relationships between rock units, structures, and alteration zones associated with mineral deposits along the Allaqi suture of Egypt’s SE Desert. Landsat TM images processed using a band ratioing technique show different rock types remarkably well, and are able to distinguish between alteration zones associated with ultramafic rocks (listwaenites) and those associated with leucocratic granitic rocks (greisenization, silicification and albitization). Black and white L-band SIR-C/X SAR images outline foliations, faults and folds that control mineralization at several deposits in the area, whereas color composite multiband Chh-Lhh-Lhv SIR-C/X SAR images reveal some elliptical granitic bodies that host radioactive mineralization. E-trending, tight to isoclinal, gently dipping folds, thrust faults and subvertical shear zones related to the Allaqi suture are overprinted by N-oriented structures related to the Wadi Ungate shear zone, formed during collision of east and west Gondwana during closure of the Mozambique Ocean. The location of the Wadi Ungate shear zone in the Wadi Shellman area was previously unknown due to burial of basement rocks beneath thin dry sands. A new structural map was prepared using Landsat TM ratio images and SIR-C/X SAR imagery. SIR-C/X SAR data conveys considerably more information about rocks and structures beneath the thin sand cover than discernible from aerial photographs or Landsat TM images. Ó 2002 Published by Elsevier Science Ltd. Keywords: Precambrian; Proterozoic, Egypt, Remote sensing, Radar

1. Introduction In this contribution we integrate satellite remote sensing techniques and field data to decipher the structural geometry and evolution of the Wadi Shellman area along the Neoproterozoic Allaqi suture. The structural history of this critical area has implications for models of the evolution of the Arabian–Nubian shield, and crustal growth in the Neoproterozoic. We emphasize the *

Corresponding author. Tel.: +1-314-977-3132; fax: +1-314-9773117. E-mail address: [email protected] (T.M. Kusky).

integrated use of different satellite remote sensing techniques (TM enhancements and band ratioing, SIR-C/X SAR image interpretation; Fig. 2) and field studies as a powerful tool for structural and tectonic analysis. In the Wadi Shellman area, the suture is defined by deformed and metamorphosed supracrustal and intrusive rocks which host gold-bearing massive sulfide deposits and auriferous quartz veins. This work also attempts to map lithological and structural controls on mineralization in the Wadi Shellman area using Landsat TM and SIR-C/X SAR imagery. Interpretation of Landsat TM and SIR-C/X SAR imagery as well as field studies led to completion of new geological, structural

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T.M. Kusky, T.M. Ramadan / Journal of African Earth Sciences 35 (2002) 107–121

and mineral deposits maps (initially at a scale of 1:100,000) for the study area.

2. Regional geological setting Neoproterozoic closure of the Mozambique Ocean sutured east and west Gondwana along the length of the East African Orogen (Stern, 1994), stretching from Mozambique and Madagascar in the south, to the Arabian Peninsula and Eastern Desert of Egypt in the north. An accretionary collage of arc and microcontinental terranes formed during closure of the Mozam-

bique Ocean is now preserved in the Arabian–Nubian shield (Stern, 1994; Abdelsalam and Stern, 1996; Dalziel, 1992; Shandelmeier et al., 1994; Greiling et al., 1994). Some of the arc terranes appear to represent juvenile additions to the continental crust during this time period (Reymer and Schubert, 1984), whereas others may have been built on older continental basement on the margins of the Mozambique Ocean (Vail, 1983; Kr€ oner et al., 1987; Stoeser and Camp, 1985; Stacey and Agar, 1985; Vail, 1985; Johnson et al., 1987; Unrug, 1996; Abdelsalam et al., 1998; Kusky et al., in press). The Wadi Shellman area in the southern part of the Eastern Desert of Egypt (Fig. 1). represents part of the

Fig. 1. Location map, showing structures and sutures of the Arabian–Nubian shield (modified after Abdelsalam and Stern, 1996). The Nile Craton is also known as the Saharan Metacraton (Abdelsalam et al., in review).


Neoproterozoic Allaqi-Heiani suture, separated from the Onib-Sol-Hamed suture by the Hamisana shear zone (Stern et al., 1989; Stern, 1994; Abdelsalam and Stern, 1996). The Allaqi suture separates the Gerf terrane (also known as the Aswan, Midyan, and South Eastern Desert of Egypt terrane (Kr€ oner et al., 1987; Greiling et al., 1994; Shackleton, 1994; Abdelsalam and Stern, 1996)) on the north from the 830–720 Ma Gabgaba terrane (also known as the Hijaz-Gebeit terrane (Abdelsalam and Stern, 1996)) on the south. The suture strikes roughly east, but swings to the southeast as it merges with and is overprinted by the NNE trending Hamisana shear zone (Fig. 1). The suture contains high pressure/low temperature metamorphic assemblages (Taylor et al., 1993), dismembered ophiolites (Berhe, 1990), and refolded recumbent folds, all consistent with a suture zone setting (e.g., Shackleton, 1994). Relatively high-grade gneissic rocks of the Gerf terrane on the north are interpreted as ensimatic island arc rocks and ophiolitic nappes uplifted on thrust faults as they were thrust over the Gabgaba terrane along the Allaqi suture (Greiling et al., 1994). The Gabgaba terrane to the south contains an island arc assemblage (ElNisr, 1997), including metavolcanic rocks and bands of marble, interpreted as deformed shallow water carbonates that originally fringed the arc volcanics (Greiling et al., 1994). The suture zone is interpreted as an arc/arc collision zone, formed prior to closure of the Mozambique Ocean. Younger N-striking folds and shear zones are interpreted to result from closure of the Mozambique Ocean, and collision of East and West Gondwana (Abdelsalam, 1994; Abdelsalam and Stern, 1996). The suture zone and Hamisana shear zones are cut by NW-striking faults and shear zones related to the Najd fault system, although the amount of displacement and extent of deformation associated with the Najd system is controversial (e.g., Sultan et al., 1988; Andre, 1989; Seng€ or and Natal’in, 1996; Smith et al., 1998; Kusky and Matsah, 2000, in press; Johnson, in press).

3. Methodology 3.1. Field mapping and geochemistry Reconnaissance-scale mapping was undertaken in the Wadi Shellman area to determine rock types and the structural attitude of primary layering, foliations, and lineations. These field studies were followed up with detailed petrographic and geochemical studies, in which rock types and structural associations were verified and reported (e.g., Yossief, 1995; Hassaan et al., 1996; Ramadan, 1997, Ramadan et al., 1998, 1999; Abu ElLeil et al., 1999).

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3.2. Remote sensing data, image processing, and interpretation Landsat TM and SIR-C/X SAR images (Fig. 2) were used to distinguish and map the rock types, structures, and alteration zones. Interpretation of these images resulted in generation of the geological map shown as Fig. 3, and the structural map shown as Fig. 4. In the following section we briefly describe the image processing techniques used here, highlighting the difference between the imagery types using the Abu Swayel subarea (location shown on Fig. 3) as an example. Details of the image processing techniques are presented elsewhere (Abdelsalam and Stern, 1999; Ramadan et al., submitted for publication). In following sections we illustrate examples of how these techniques can be used for regional structural and map compilation and tectonic interpretation. We generated several different images using digital image processing of Landsat TM data. The images range from false color composite images (bands 3; 2; 1 and 7; 4; 2), to ratio images (e.g., bands 5=7, 5=1 and 5=4 3=4 in RGB). From these studies, it was found that the false color composite Landsat TM images are most-suitable for regional structural analysis. The ratio images (bands 5=7, 5=1 and 5=4 3=4) are used in lithological discrimination of different rock types as well as the alteration zones in the study area (Figs. 2–4). The band ratioing and multiplication technique we use follows the general methodology of Abrams et al. (1983), Sultan et al. (1986), and Abdelsalam and Stern (1999), who noted that certain band ratios are particularly useful for lithological discrimination. Band ratioing also suppresses variations related to topography, overall variations in reflectance, and brightness differences related to grain size, while it emphasizes differences in shape of spectral reflectance curves (Rowan et al., 1974; Abrams et al., 1983; Blodget and Brown, 1982; Sultan et al., 1986). The TM band ratioing and multiplication technique maximizes rock discrimination because certain band ratios are sensitive to specific chemical and mineralogical components of the rock. Sultan et al. (1986) found that an RGB image produced using the ratios of bands 5=1, 5=7, and bands 5=4 multiplied by band 3=4 revealed the most information for rock types of the Arabian–Nubian shield in a climate like the SE Desert. Band 5=1 intensity is inversely proportional to the content of opaque phases in the rock, so that mafic igneous rocks (with high contents of opaque phases) yield a lower reflectance than other igneous rocks. The band 5=7 ratio is sensitive to the hydroxyl mineral content of the rocks, such that areas of high 5=7 values have relatively high hydroxyl mineral contents (argillites, serpentinites, alteration zones). Sultan et al. (1986) found that bands 5=4 times bands 3=4 is useful to distinguish

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Fig. 2. Landsat TM ratio image (5=7, 5=4, 5=4 3=4, in R, G, B) with SIR C/X swath of the western part of the Allaqi suture, South Eastern Desert, Egypt. The TM ratio image reveals rock types remarkably well, whereas the SIR C/X imagery shows structures better than the TM imagery.

between mafic and non-mafic rocks, because it is sensitive to rocks that have high Fe-bearing aluminosilicate concentrations such as hornblende and biotite. Sultan et al. (1986) produced false color composite ratio images by assigning the band 5=1 data to red, 5=7 to green, and 5=4 3=4 to blue. In this contribution we use a variation of the basic methodology developed by Sultan et al. (1986), where we assign band 5=7 to red, 5=1 to green, and 5=4 3=4 to blue, which we found to be most useful for distinguishing rock types in the study area. With this processing, felsic and granitic rocks appear in hues of green, serpentinites appear red, and mafic rocks appear in hues of blues (Fig. 2). The red color of the ultramafic rocks is due to band 7 absorption by MgO- and OH-bearing minerals. Fig. 5 illustrates the differences between the different types of Landsat imagery used in this study, using the Abu Swayel area (see Fig. 3 for location) as an example. Typical exposures of bedrock and alluvium are illustrated in Fig. 6. Fig. 5a shows a standard Landsat TM band 3-2-1 (RGB, respectively) image, in which bedrock appears dark and Quaternary alluvium, wadi fill, and sand deposits have light tones. Two granodioritic plutons in the southern half of the area appear white, and a

mafic pluton with a dioritic core and a talc-carbonate/ serpentinite rim outcrops and is distinguishable in the SE part of the image area (Fig. 5d shows a geological interpretation based on the various imagery). The Landsat TM ratio image (Fig. 5b) highlights the talc carbonate/serpentinite rim of the mafic pluton in bright orange colors, and shows the more felsic plutons in dark green (granodiorite) and light green (granite) colors. Metavolcanic rocks show in intermediate green colors, and some bands of blue around the plutons are moremafic horizons in the volcanic sequence, and the yellow to orange bands are interpreted as marble and other metasedimentary bands in the volcanic sequence of the Gabgaba terrane (a detailed lithological interpretation of this image is shown in Fig. 3). SIR-C/X SAR images are represented by one strip covering most of the study area (Fig. 2). Black and white single-band images were combined, co-registered to produce the color-composite multi-band images shown in this contribution. In many cases the SIR-C/X SAR imagery reveals greater structural detail than the visible and near-infrared Landsat TM imagery, especially in areas of thin sand cover. The SIR-C/X SAR data may be combined in different ways for different purposes (e.g., Abdelsalam and Stern,


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Fig. 3. (a) Geological map of the western part of the Allaqi suture, South Eastern Desert, Egypt, based on our field mapping and interpretation of Landsat TM and SIR-C/X radar imagery. (b) Cross-section of the western part of the Allaqi suture.

Fig. 4. Structural interpretation map of the western part of the Allaqi suture. The map was made based on our field mapping and interpretation of Landsat TM and SIR-C/X SAR data. Inset is a lower hemisphere equal angle projection of foliation planes.

1996, 1999; Henderson and Lewis, 1998). Here, we use a combination of L-band (23.5 cm wavelength), and C-

band (6 cm wavelength) data with different polarizations for highlighting different structures. Data that is

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Fig. 5. Comparison of different types of imagery for structural interpretation, using the Abu Swayel area: (a) Landsat TM image of bands 3-2-1, (b) Landsat TM ratio image, (c) SIR-C/X SAR Chh-Lhh-Lhv image, (d) Structural interpretation of imagery shown in a, b and c.

vertically transmitted and vertically received is abbreviated vv (Lvv for L-band, Cvv for C-band), data that is horizontally transmitted and horizontally received is abbreviated Chh or Lhh, and data that is horizontally transmitted and vertically received is abbreviated as Chv or Lhv. The X-band has only one polarization (vv), and is referred to simply as X-band or X-imagery. We assign

Chh to red, Lhh to green, and Lhv to blue to generate the color composite multiband SIR-C/X SAR used here. We have found (after Abdelsalam and Stern, 1996) that combination yields an image with the most information for structural interpretation in the area. This is partly a function of the ability of radar of longer wavelengths being better-able to penetrate the thin sand veneer in


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Fig. 6. Field photographs from the study area (a) Photographs showing the structural contact between ultramafic rocks (u) and metasediments (m) in the Wadi Haimur area; (b) photograph showing pencil cleavage in metavolcanic-sedimentary rocks, east of Wadi Marahiq; (c) photograph showing Pharonic ruins and grinding stones at the Wadi Marahiq gold mine; (d) photograph showing copper mineralization associated with the alteration zone in the Wadi Um Rilan area.

parts of the area (penetration is proportional to wavelength, and cross-polarization also enhances penetration; Henderson and Lewis, 1998). These images recorded several features beneath thin dry sand that obscures the underling rocks from TM images. These benefits of the SIR-C/X SAR imagery are highlighted by comparing the radar with the TM imagery for the Abu Swayel area (Fig. 5). Fig. 5c shows the radar image of the same area as discussed above, and it clearly highlights the structural features such as fault, fold, and foliation patterns of the region much better than the Landsat TM 3-2-1 image, or the Landsat TM ratio image. Foliations and faults are clearly visible on the radar image, where they were barely visible to indiscernible on the 3-2-1 and band ratio images, respectively. The radar image also is able to differentiate between the granitic, granodioritic, dioritic and serpentinite rocks, but it is clearly not as good as differentiating between rock types such as mafic and felsic volcanics and metasediments as the TM ratio image. For this reason, we used a combination of different imagery for making the geological and structural maps shown as Figs. 3 and 4. Radar imagery was used for making structural and some lithological interpretations (as shown in Fig. 5d), and the Landsat TM ratio images were used most extensively for lithological interpretation. The Landsat TM ratio images and their corresponding detailed interpretations for select subareas are shown in Figs. 7–9.

4. Geology of the Wadi Allaqi area Analysis and interpretation of the satellite imagery described above was integrated with field observations and published syntheses to make the geological and structural maps shown as Figs. 3 and 4, and the detailed maps of key areas shown as Figs. 5, 7–9. These maps and the results of previous work provide the basis for the interpretations presented here. The Wadi Allaqi area is underlain by Neoproterozoic rocks, Cretaceous sandstones, and Mesozoic to Cenozoic volcanic and sub-volcanic rocks (Fig. 3). The Neoproterozoic rocks and associated structures are the focus of this study. These rocks include a mafic–ultramafic ophiolitic assemblage, at least two volcano-sedimentary-plutonic island arc assemblages, and late- to post-tectonic granitic intrusions (Kr€ oner et al., 1987; Greiling et al., 1994; Shackleton, 1994; Abdelsalam and Stern, 1996; Taylor et al., 1993; Berhe, 1990; Shackleton, 1994). 4.1. The ophiolitic assemblage Ophiolitic rocks form several structurally complex elongate belts in the central part of the Wadi Allaqi area and are made up of imbricate thrust sheets and slices of serpentinites, talc carbonate schist and metagabbros (Figs. 3 and 4). These were thrust from north to south over an assemblage of island arc rocks (Fig. 6a).

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Fig. 7. (a) Landsat TM ratio image showing the imbricated thrust belt in the Wadi Haimur–Wadi Um Ashira area. (b) Structural interpretation of area in (a).

Fig. 8. (a) Landsat TM ratio image showing folded metavolcanic rocks, east of Gebel Um Ara. (b) Structural interpretation of image shown in (a).

Massive sheets of serpentinite occupy high ridges such as those of the Wadi Haimur and Gebel Umm Shellman areas (Fig. 3). Small slices and streaks of serpentinites are found imbricated with the metasedimentary and metavolcanic units. These can be easily distinguished on the Landsat TM images by their characteristic red color in the 5=7-5=1-5=4 3=4 Landsat TM ratio image (Figs. 2 and 7) (Sultan et al., 1986). The talc carbonate schist

unit defines the contact between the serpentinites and the metasedimentary and metavolcanic units of the island arc assemblage. These are identified on the Landsat TM ratio image by their sugary white color (Fig. 2). The ophiolitic metagabbros are very limited in the present area represented only by small highly deformed masses in structural contact with the ultramafic rocks. Most of the intrusive gabbro-diorite rocks in the area were


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Fig. 9. (a) Landsat TM ratio image showing mylonite zone of the Wadi Ungate shear zone in metavolcanic rocks. (b) Structural interpretation of image shown in (a).

mapped by previous workers as ophiolitic metagabbros (e.g., Hussein, 1990). 4.2. The island arc assemblages There are at least two separate island arc sequences in the area (Figs. 1 and 3) including that of the Gerf terrane in the north, and that of the circa 830–720 Ma Gabgaba terrane in the south (Kr€ oner et al., 1987; Taylor et al., 1993; Greiling et al., 1994). The Gabgaba terrane is distinguished from the Gerf terrane in that it has carbonates interlayered with the arc sequence, whereas the Gerf terrane does not (Greiling et al., 1994). Also, the Gerf terrane has high-grade metasediments whereas the Gabgaba has only low-grade metatuffs and metavolcanic rocks, and has no known metasedimentary rocks in the area of Fig. 2. The two arc sequences are tectonically interleaved along the Allaqi suture, and are difficult to distinguish from each other using lithological or reflective criteria (Figs. 2 and 3). The island arc assemblages are represented by metasedimentary and metavolcanic layered units and

intrusive gabbro to diorite plutons (Fig. 3). The metasedimentary units are dominant in the Wadi Haimur and Wadi Abu Swayel areas (Fig. 3), occupy low lands, are strongly foliated with locally developed pencil cleavage (Fig. 6b), and range from greenschist to amphibolite facies metamorphic grade. In the Wadi Shellman area the volcano-sedimentary sequence shows local increases in metamorphic grade close to contacts with granitic intrusions. This is manifested by plagioclase and quartz re-crystallization, segregation banding and lamination of felsic and micaceous minerals and ribbon migmatitic texture. Layered gray marble bands are intercalated with the metasedimentary units of the Abu Swayel area. These marble bands are yellow in the 5=75=1-5=4 3=4 Landsat TM ratio images, whereas the metasedimentary units are purple (Figs. 2 and 7). The metavolcanic rocks dominate the central and southern parts of study area and they are of intermediate to mafic composition (El-Nisr, 1997). These metavolcanic rocks host the alteration zones associated with the pyrite bearing massive sulfide deposits in the Wadi Umm Garayat and Wadi Marahiq areas (Figs. 3 and 4).

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Archeological ruins and other artifacts such as grinding stones indicate that Umm Garayat and Marahiq gold deposits were mined by ancient Egyptians since the Pharonic ages (Fig. 6c). Ancient Egyptians extracted visible gold in quartz veins, but were not able to exploit the disseminated gold associated with massive sulfide deposits. Also, these rocks host Cu–Au-mineralization in the Wadi Um Rilan area (Fig. 6d). The gabbro-diorite intrusions are less abundant compared to the metasedimentary and metavolcanic rock units (Fig. 3). These intrusions are heterogeneous in composition and include gabbro, diorite, quartzdiorite, and tonalite. The gabbroic intrusions appear brown in color in the 5=7-5=1-5=4 3=4 Landsat TM ratio images (Fig. 2). Lenses of titano-magnetite mineralization are found east of Wadi Ungate within the gabbroic intrusions. 4.3. The late- to post-tectonic granitoids Late-tectonic (collisional) granites are widespread in the central part of the study area close to Wadi Shellman (Fig. 3). These are coarse-grained, enriched in mafic minerals and are mainly granodioritic in composition (El-Amin, 1995). They occur as deeply eroded circular features overlain by recent sand deposits and with a few isolated low-lying hills. The characteristically circular appearance of these granitic bodies makes them easy to distinguish in the Chh-Lhh-Lhv SIR-C/X SAR images (Fig. 2). In the northern part of the Wadi Marahiq area a large late-tectonic pluton intrudes into the metavolcanic rocks (Fig. 3). This pluton consists of medium to coarse-grained granite with disseminated pyrite, chalcopyrite and malachite. The pluton is surrounded by the Umm Garret, Wadi Marahiq and Wadi Um Rilan alteration zones and massive sulfide deposits (Fig. 4). Hence, this pluton might be related to the massive sulfide deposits in the study area (Ramadan et al., submitted for publication). Post-tectonic syenite and alkali granite bodies are widely distributed in the northern part of the study area (Fig. 3). They are massive, medium in grain size, and reddish in color with high to moderate relief. They intruded the above rock units and are cut by felsitic rocks as well as by acidic and basic dikes. At Gebel Filat, these rocks are dissected by several E–W dextral strike slip faults, with displacements of about 2 km (Figs. 3 and 4).

5. Structural geology Fig. 4 is a structural map of the area, based on our field work and interpretation of the satellite imagery. The structural sequence in the area is similar in general aspects to that established by Abdelsalam and Stern (1996) for the South Eastern Desert, and broadly similar

but different in detail from the structural sequence suggested by Greiling et al. (1994). Greiling et al. (1994) suggested that a group of old gneissic rocks in the SE Desert (Tier 1 gneisses) are tectonically overlain by the ophiolitic assemblage in the Gebel Muqsim area, and the northern boundary of the gneisses is truncated by an east-west striking shear zone. The steep attitude of the shear zone and related lineations is suggested to be due to folding about east-trending fold axes, which are related to northwest directed transpression (D2 ). Northward this trend gradually swings towards the northwest, and then continues in a west–northwest direction to the Abu Swayel area. Smith et al. (1998) suggested that in the southern part of the Eastern Desert thrusting is associated with flower structures that merge with and root into parallelism with the north-striking Gerf shear zone. The Gerf shear zone has the form of a flower structure bounded by steeply dipping strike-slip shears that enclose a large allochthonous slab of back-arc basin lithosphere. Our field and remote-sensing studies suggest that the western part of the Allaqi suture developed through four phases of Neoproterozoic deformation (D1 through D4 ). D1 and D2 are associated with early collisional stages between the Gerf terrane in the north with the Haya and Gabgaba Terranes to the south (Fig. 1), whereas D3 and D4 represent deformation associated with the later stages of collision (Abdelsalam and Stern, 1996), characterized by development of tight to isoclinal, gently inclined folds, and reactivation of some of the thrust faults in the E–W imbricate thrust zones (Fig. 4). D1 is characterized by development of an E-striking, steeply N-dipping planar fabric (S1 ) which represents the axial planar cleavage to E-plunging tight to isoclinal folds (Figs. 3 and 7). D2 produced regional thrusts as exemplified by shear zones preserved along Wadi Haimur (Fig. 2). These thrusts formed during the emplacement of mafic–ultramafic rocks of the ophiolitic assemblages over the metasedimentary and metavolcanic rocks of the island arc assemblage (Fig. 2). D2 -folds are dominantly EW-striking with W-plunging hinges, and steeply N-dipping axial planar cleavage. D2 folds affect the thrust surfaces (Fig. 3b). Major WNW–ESE and NW–SE shear zones and open folds (Fig. 4) formed during D3 . These shear zones are exposed in the Wadi Allaqi area as high-strain curvilinear zones that can be traced for tens of kilometers and are characterized by the presence of S–C fabrics, rotated porphyroblasts, sigmoidal foliation patterns, and crenulation cleavage (Figs. 5 and 7). These shear zones have sharp to gradational boundaries, wrap around lenses of less deformed rock and vary in width from a few meters to as much as 3 km across. Gold bearing quartz veins and alteration zones in the study area are located within D3 shear zones. D4 includes minor E-striking strike-slip faults, some of which are intruded by dike swarms.


6. Mineral deposits Several mineral deposits are associated with different rock units and structures in the study area. Copper– nickel–platinum mineralization, podiform chromite, and gold–quartz veins are associated with ultramafic rocks. Marble, gold-bearing quartz veins and alteration zones possibly associated with massive sulfides are associated with metavolcanics, and zones of radioactive mineralization are associated with leucocratic granitic rocks. Landsat TM and SIR-C/X SAR images as well as field studies indicate that these mineral deposits are structurally controlled, as well as being associated spatially with the late granites.

6.1. Mineral deposits associated with D1 , D2 (imbricate thrust belt) Fig. 7 shows a detailed Landsat TM ratio image and interpretation of the fold-thrust belt in the northwestern part of the area (Fig. 2). This area hosts the Abu Swayel and Haimur mines (Fig. 4), and the detailed image interpretation shown in Fig. 7 reveals the complexity of the structural setting. The mafic volcanic rocks stand out as blue colors on the TM ratio image, and the intermediate to felsic rocks are green. The ultramafic rocks form prominent orange streaks (Fig. 7). Discontinuous belts of serpentinite, talc schist, mafic and felsic volcanic rocks, and metasediments are repeated along imbricate thrusts, and folded about generally EW axes (Fig. 7). Most contacts between the different belts of rocks are thrust faults. Similarly, Fig. 8 from the Wadi Murra area (Fig. 3) shows how the TM ratio image highlights different mafic-intermediate volcanic units folded about a NS axis, and cut by NS oriented faults. The ultramafic rocks in the study area host copper– nickel–platinum mineral deposits, as well as chromite, talc deposits and gold-bearing quartz veins and listwaenites. Copper–nickel–platinum sulfides are associated with the ophiolitic ultramafic rocks in the Wadi Abu Swayel area (Fig. 4). The main deposit is located at about 185 km south of Aswan, near the head of Wadi Haimur. A number of smaller occurrences are known in the vicinity along Wadi Haimur (Figs. 3 and 4). This area was worked by the ancient Egyptians for copper and malachite, as shown by ancient ruins in this area. The ore body includes both massive and disseminated mineralization hosted in lenses of amphibolites, 500 m long and 30 m wide, striking NW–SE with dips at 60– 80° NE. The ore minerals include pyrite, pyrhotite, chalcopyrite, pentlandite, bravoite, chalcanthite and malachite in the oxidation zone. Ore reserves were estimated at 85,000 tons of ore containing 2.8% Cu and 1.53% Ni as well as minor amounts of Co (Hussein, 1990).

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We have used radar imagery to attempt to map the possible continuation of these deposits beneath wadi gravels and recent sands. Chh-Lhh-Lhv SIR-C/X SAR data recorded several features at this area, beneath the thin dry sand that obscures the underlying rocks from Landsat TM images and aerial photographs (Fig. 5). They convey considerable structural information such as faults, folds and foliations beneath a dry sand cover in the Wadi Shellman area. Interpretation of this imagery suggests that the ore-bearing rocks may extend in the NE and SW directions from the Abu Swayel mine (Figs. 4 and 5). Gold-bearing quartz veins and listwaenites are located along the northern limb of a major anticlinal fold at Haimur gold mine, where they are associated with ophiolitic ultramafic rocks (Fig. 3). The talc carbonates and associated listwaenites have sugary white textures easily visible on the Landsat TM ratio images (Fig. 4). These rocks are highly faulted and folded. The veins reach up to 25 m in length, 30 cm in width and strike NE–SW. Chemical analyses of 15 samples of these quartz veins revealed that they contain gold values ranging between