**6.1 Periodontitis**

*Periodontal Disease - Diagnostic and Adjunctive Non-surgical Considerations*

interproximal spaces of the area of interest [20] (**Figure 2**).

**4. Bone destruction in periodontal disease**

**4.1 Bone loss**

*4.1.1 Amount*

*4.1.2 Distribution*

different surfaces of the same tooth [23].

**5. Pattern of bone destruction**

through the contact areas of the teeth and perpendicular to the film. Thus the projection geometry of the bite-wing films allows the evaluation of the relationship between the interproximal alveolar crest and the CEJ without distortion. If the periodontal bone loss is severe and the bone level cannot be visualized on regular bite-wing radiographs, films can be placed vertically to cover a larger area of the jaws. More than two vertical bite-wing films might be necessary to cover all the

Early destructive changes of bone that do not remove sufficient mineralized tissue cannot be captured on radiographs. Therefore slight radiographic changes of the periodontal tissues suggest that the disease has progressed beyond its earliest stages.

The radiographic image tends to underestimate the severity of bone loss. The difference between the alveolar crest height and the radiographic appearance ranges

Radiographs are an indirect method for determining the amount of bone loss in periodontal disease; they image the amount of remaining bone rather than the amount lost. The amount of bone lost is estimated to be the difference between the physiologic bone level and the height of the remaining bone. The distance from the CEJ to the alveolar crest has been analyzed by several investigators. Most studies, conducted in adolescents, suggest a distance of 2 mm to reflect normal

The distribution of bone loss is an important diagnostic sign. It points to the location of destructive local factors in different areas of the mouth and in relation to

In periodontal disease the interdental bone undergoes changes that affect the lamina dura, crestal radiodensity, size and shape of the medullary spaces, and height and contour of the bone. Height of interdental bone may be reduced, with the crest perpendicular to the long axis of the adjacent teeth horizontal bone loss; or angular or arcuate defects angular, or vertical, bone loss; could form [24–26]. Radiographs do not indicate the internal morphology or depth of craterlike defects. Also, radiographs do not reveal the extent of involvement on the facial and lingual surfaces. Bone destruction of facial and lingual surfaces is masked by the dense root structure, and bone destruction on the mesial and distal root surfaces may be partially hidden by superimposed anatomy, such as a dense mylohyoid ridge. In most cases, it can be assumed that bone losses seen interdentally continue

in either the facial or the lingual aspect, creating a troughlike lesion [27].

The earliest signs of periodontal disease must be detected clinically [16].

from 0 to 1.6 mm, mostly accounted for by X-ray angulation [21].

periodontium; this distance may be greater in older patients [22].

**52**

Radiographic changes in periodontitis follow the pathophysiology of periodontal tissue destruction and include the following [29]:

1.Fuzziness and disruption of lamina dura crestal cortication continuity is the earliest radiographic change in periodontitis and results from bone resorption activated by extension of gingival inflammation into the periodontal bone. Depicting these early changes depends greatly on the radiographic technique, as well as on morphological changes. No correlation was found between

#### **Figure 3.**

*Radiographic changes in periodontitis. (A) Normal appearance of interdental bone. (B) Fuzziness and a break in the continuity of the lamina dura at the crest of the bone distal to the central incisor (*left*). There are wedgeshaped radiolucent areas at the crest of the other interdental bone. (C) Radiolucent projections from the crest into the interdental bone indicate extension of destructive processes. (D) Severe bone loss.*

lamina dura in radiographs and the presence or absence of clinical inflammation, bleeding on probing, periodontal pockets, or clinical attachment loss. Therefore it can be concluded that the presence of an intact crestal lamina dura may be an indicator of periodontal health (**Figure 3**).


The NNW-trending Wadi Khashab shear zone (Figure 9) and related splays cut across the southwest part of the area, and it dips moderately or steeply to the east. This shear zone is cut by WNW–ESE and ENE–WSW strike–slip faults. The Wadi Khashab shear zone hosts several occurrences of gold-bearing quartz veins that are commonly associated with sericitized and silicified rocks. Of these occurrences, the El-Beida and Wadi Khashab occurrences are heavily worked out by artisanal miners at present. The Wadi Urga occurrence is confined to highly sheared metavolcanic rocks with signs of hydrothermal alteration along their contacts with a large granodiorite–tonalite intrusion. The ~E–W Urga fault is a major, fault that dissects the Wadi Khashab shear zone and apparently displaces its trace ~1–2 km right-laterally. Similar parallel structures are abundant north and south of this major fault. A number of prospective targets, including Wadi Beitan, Wadi Urga Rayan, Um Teneidab and north Wadi Hutib, have been identified along similar, ~E–W trending faults, or where the main NNW structural trend is cut by WNW–ESE strike slip faults. To the north, it seems that this structure may host other unexplored occurrences, based on the widespread carbonate alteration in the footwalls of the ophiolitic blocks.

#### 4.1.2. Wadi Rahaba Shear Zone

The Wadi Rahaba shear zone (Figure 9) represents an intense NNW-trending, steeply dipping, brittle-ductile shear zone cutting a generally carbonated mafic–ultramafic rocks and volcaniclastic successions in the central and northern parts of the study area. The shear zone also extends to the south, where it hosts the Anbat mine and other scattered surface mining sites. Towards the east of the Wadi Rahaba shear zone, a major thrust fault boundary marks the base of a hanging wall block of metagabbro and meta-granodiorite; and varies significantly from NW-trending and moderately steeply east-dipping in the central-east to shallow south-dipping and easterly trending in its northeastern part. A number of parallel, NW-trending, shallow to moderately easterly dipping thrust faults (or splays) occur immediately west of the Wadi Rahaba shear zone. These thrust faults mark the western boundary of the gneissic domains and are spatially associated with a number

of prospective targets. Numerous significant, E–W to ENE trending late cross-faults appear to offset the major thrust-faults within this area.

**Figure 9.** Structural map of the Wadi Hodein shear belt.

#### 4.1.3. Wadi Beitan Fault Zone

The Wadi Beitan fault zone (Figure 9) is a major, steeply dipping, WNW-trending silicified breccia zone with a strike length of some +25 km and is traced across the Um Eleiga mine area and eastwards. This structure cuts rocks of variable types in the area, including the Um Eleiga gabbro, Abu Dahr ophiolites and Rahaba gabbro–diorite complex. This zone converges with a NNW-SSE shear zone to the east and delineates the eastern structure contact of the island arc and ophiolitic rocks. Hydrothermal breccia and silica alteration of the host rocks are common along this structure, and abundant zones of sulfide mineralization with local malachite occurrences are observed. In the vicinity of the Um Eleiga gold mine, albitization of the gabbroic host rocks are pervasive. Iron oxides and copper hydro-carbonate are observed in some localities within the Um Eleiga mine

area. Noteworthy, the Wadi Beitan fault zone could have been genetically linked with the extensive dike swarms spread over the large are between G. Handusa and G. Nukeiba northwest of the Abu Dahr ophiolitic massif. These dike swarms overprint the earlier NNW-SSE structural trend. Numerous basic dikes along the WNW–ESE direction cut the Um Eleiga gabbro–diorite intrusion and extend eastward to the Abu Dahr ophiolites.

#### *4.2. Deformation Events*

The Wadi Hodein shear belt (Figure 9) is a NNW-striking belt (~105 km-long), deformed greenschist metamorphosed ophiolites and island arc rocks. It was developed via four phases of deformation; (i) D1, NNE–SSW crustal shortening, (ii) D2: NE-SW oblique convergence and transpression, (iii) D3, E–W compressional regime and (iv) D4: extension tectonics. Lithological layering represents the primary bedding surface (S0) which is still locally recognizable in the ophiolitic metagabbros and bedded metamudstone as cm-scale alternating lighter and darker layers.

#### 4.2.1. D1: NNE–SSW Crustal Shortening

N–S shortening and terrane accretion occurred as a result of a collision between the Gabgaba and Gerf terranes over a ~N-dipping subduction zone [77]. D1 structures are mainly preserved in the Wadi Khuda gneisses and in the Wadi Khashab–Gabal Sirsir ophiolitic mélange. Wadi Khuda gneisses represent a small structural window later cut by tonalite-granodiorite and biotite granite intrusions. In the Wadi Khuda gneisses, quartz– feldspar-micas gneissosity (S1) strikes ENE–WSW, and dips toward the NNW and SSE (Figure 10a). The axial plane gneissosity is only evident in the hinges of F1 folds which represented by metrewide, high-amplitude isoclinal, near recumbent to shallowly dipping folds. Boudins (B1) are developed on the quartzo-feldspathic layers in banded amphibolites. They have a symmetric shape and their long axes are parallel to the gneissosity (S1), suggesting a coaxial strain. The largest F1 fold is an asymmetric, doubly plunging anticline extending for up to 8 km in the Wadi Khuda gneisses (Figure 9). The axis of F1 major anticline is displaced by a NNW-striking sinistral strike–slip fault and the southern limb is superimposed by a NNW-tending anticline (F2). The early thrusts are SSE verging and are folded during the D2 event. These thrusts are preserved in the Arais ophiolitic mélange, marking the contacts between Beitan gneisses belt and the ophiolite blocks, as well as the contact between serpentinites and volcaniclastic metasediments (Figure 9). These thrusts converge downwards onto a basal S-dipping decollement.

#### 4.2.2. D2: NE–SW Oblique Convergence and Transpression

The D2 deformation phase is manifested by regional foliation (S2), mylonitic foliation (S2m), major and minor folds (F2), stretching and intersection lineations (L2) and major thrusts (T2). The structures include small-scale, rootless intrafolial folds (Figure 10b), shearband boudins (Figure 10b), recumbent (Figure 10c,d), tight isoclinal and sheath folds along the first-generation ductile shear zone. These structures are largely preserved as decimetre-scale folds in a transposing and intrafolial foliation (S2) in the Beitan gneisses belt, schistose metavolcanics and volcaniclastic metasediments. The S2 in foliated metavolcanics and volcaniclastic metasediments is axial plane schistosity for the F2 folds and is defined by a strong preferred alignment of actinolite, chlorite and biotite. In the bedding-parallel quartz veins, asymmetrical "shearband-type" boudins (B2; Figure 10e) and asymmetrical "domino-boudinaged" quartz veins are common. The shearband boudins (B2) were only observed in shear zone close to the gold occurrences. Ptygmatic folding is widespread in the Beitan gneisses (Figure 10f). S2 planes have moderate to high dips predominantly toward the SW and NE. Around the synorogenic gneissose granites, ophioltic metagabbros and serpentinite mountainous blocks, the S2 foliations show important changes along strike or define different geometric patterns. In the central segment of Hodein shear belt, S1 traces strike NW–SE to NNW–SSE to NNE–SSW, whereas they curve back into a NW–SE orientation to the southwest of Gabal Dahr serpentinite's peridotites.

**Figure 10.** Field photographs of structural elements in the study area: (**a**) gneissosity (S1) in Khuda gneisses defined by the graiN–Shape preferred orientation of quartz–feldspar aggregates, hornblende and biotite; (**b–d**) NNW-plunging, reclined and overturned and recumbent F2 folds and refolded quartz vein in volcaniclastic metasediments of Wadi Rahaba; (**e**) asymmetrical "shearband-type" boudinaged quartz veins in volcaniclastic metasediments around Urga gold occurrence; (**f**) Ptygmatic folds in Beitan gneisses; (**g**) Major F2 asymmteric anticline in volcaniclastic metasediments, Wadi Rahaba; (**h**) SW-verging volcaniclastic metasediments thrust over Beitan gneisses belt, south of Gabal Arais; (**i**) NE-verging serpentinite thrust over volcaniclastic metasediments, Wadi Rahaba.

> The L2 lineation plunges have a N25–35◦ W or N40◦ E within the S2 gneissosity and schistosity and show all the characters of a mineral and stretching lineation. The hinge lines of microfolds in gneisses, schistose metavolcanics and volcaniclastic metasediments define a vertical crenulation lineation trending mainly NNW–SSW. A number of large-scale F2 folds have been mapped, and most of their axes are NNW- or NW-oriented (Figures 10g–i,11a–i). Other F2 axes may have resulted from later reworking by F3. Axial planar to these folds is a spaced crenulation cleavage (S2), which is commonly well developed. F2 folds range from centimeter- to kilometer-scale and are common in Beitan gneisses belt and the ophiloitic mélanges (Figure 11a–i). These folds are open, asymmetrical to isoclinal and their axes are nearly upright or plunge NNW or SSW. Some of the F2 fold axes plunge NNE or SSW, which may have resulted from later slight reorientation by the D3 open folding and/or the second-generation low-angle ductile shear zone. The axial traces of F2 folds strike mainly NW–SE or NNW–SSE. A doubly plunging asymmetric F2 anticline in the Wadi Khuda gneisses dips moderately to NW or SE. A series of WSW-verging thrust faults (T2) (Figure 9), parallel to the hinges of the largest F2 folds could have formed by progressive F2 folding in a compressional setting.

**Figure 11.** (**a,d,g**) Landsat-8 OLI band composites RGB-753, (**b,e,h**) Landsat-8 OLI band ratio RGB-7/6, 6/5, 4/2 highlighted the different folding types and trends, and (**c,f,i**) the resultant interpretation maps of the different fold generations (thin lines for foliation trajectories and red arrows lines are interpreted fold axial traces and major faults (black lines). Gn; gneisses, S; serpentinites, VCM; volcaniclastic metasediments, MV; metavolcanics, SG; syn-orogenic granites, GD; metagabbro–diorite complex, PG, post-tectonic granite.

The ophiolitic mélanges in the Wadi Hodein–Wadi Beitan shear belt are thrusted over each other and over the Beitan gneisses belt (infracrustal rocks) along three major imbricate thrusts (T2). Three imbricate thrusts are named in this study: the Sirsir–Rahaba thrust, the Arais imbricate thrust and the Hodein–Beitan imbricate thrusts (Figure 9). The geometry of Wadi Khashab–Gabal Sirsir ophiolitic mélange is controlled by the oppositely dipping Sirsir–Rahaba and the southern extension of Wadi Hodein–Wadi Beitan sinistral reverse shear zone, respectively (Figure 12a–c). Gently to moderately ENE- and WSW-dipping foliation (S2) forms the dominant fabric that intensifies into belts of mylonites associated with D2 ductile thrusts. The Sirsir–Rahaba thrust dips ENE and separates ophiolitic blocks of Gabal Sirsir and the volcaniclastic metasediments of Gabal Anbat (Figures 9 and 12a–c). The Wadi Hodein–Wadi Beitan imbricate thrust forms an imbricated fan (Figure 12a–c). Axial planar to tight-to-isoclinal, reclined F2 sheath folds have axes concentrated around the L2 mineral lineation. To the north of Gebel of Abu Dahr the thrusts mark the tectonic contacts between the ophiolitic slabs (serpentinites and talc carbonates) and the overlying metavolcanics and volcaniclastic metasediments. Additionally, Arais imbricate thrusts control the contact between Arais opoilitic mélange and the Beitan gneisses belt (Figure 9) and also mark the tectonic contacts between the ophiolitic slices. These NE-dipping thrusts constitute a backthrust to the WSW-dipping Hodein–Beitan imbricate thrusts.

**Figure 12.** (**a**,**d**) Landsat-8 OLI band composites RGB-753, (**b**,**e**) Landsat-8 OLI band ratio RGB-7/6, 6/5, 4/2 highlighted ENE–WSW strike slip faults dissected the island arc metavolcanics, (**c**) the resultant interpretation maps of the different fold generations (thin lines for foliation trajectories and red arrows lines are interpreted fold axial traces and major faults (black lines) and (**f**) Landsat-8 PC3 shows the ENE–WSW dextral strike–slip faults cutting across pre-existing structures and controlling the drainage system. S; serpentinites, VCM; volcaniclastic metasediments, MV; metavolcanics, SG; syn-orogenic granites, GD; metagabbro–diorite complex, PG, post-tectonic granite.

Most of the small-scale, tight to isoclinal, asymmetric F2 folds in the Wadi Hodein-Wadi Beitan imbricate thrusts show top-to-the-ENE thrusting. Many shear sense indicators, including mineral lineations, asymmetric shear folds, asymmetric porphyroblasts, shearband boudins, S-C fabrics and shear bands indicate that the ophiolite blocks along Sirsir–Rahaba thrust and Arais thrusts are moved top to WSW and those along Hodein– Beitan thrusts are moved up to ENE (Figure 13a–c). Each thrust zone comprises several thrust segments showing anastomosing morphologies and form WSW-dipping tectonic duplexes. S2 gneissosity in the Wadi Beitan gneisses occur as asymmetrical folds around these boudins. Migmatitization is common in the shadows of the rotated boudins. The boudins do not display any foliations but are surrounded by the S2 gneissosity, suggesting that they formed during the D2 deformation. Shearband boudins show a top-to the-WSW movement.

**Figure 13.** Field photographs of structural elements in the study area: (**a**) Foliation-parallel shearband boudins of quartz along S2 foliation in volcaniclastic metasediments,Wadi Rahaba, indicating sinistral transpressive shearing along thrust planes, (**b**) Metagabbro prophyroclast in volcaniclastic metasediments indicating top-to NE sense of movement along thrust planes, Wadi Beitan, (**c**) Asymmetrical folds and shearband boudins of quartz veins along S2 foliation in volcaniclastic metasediments, Wadi Rahaba, indicating top-to NE sense of movement along thrust planes, (**d**) Strike–slip shear zones appear as steep ductile zones in sheared metavolcanics which sheared the S2 foliation. S3 foliation strike N20–30◦ W with steep dip toward the SW, Wadi Beitan, (**e**) Crenulation lineation in metasedisment with a subhorizontal plunge to the NNW, (**f**) Asymmetric tight and reclined folds in volcaniclastic metasediments, south of Gabal Abu Darh, indicating sinistral sense of shearing, (**g**,**h**) Quartz and metagabbro asymmetric prophyroclast in volcaniclastic metasediments, Wadi Um Teneidab and Wadi Rahaba, (**i**) en-echelon folded quartz veins in schistose metavolcanics, Wadi Hutib, indicating sinistral sense of shearing.

#### 4.2.3. D3: E–W Shortening and Sinistral Shearing

D3 structures are related to transposition and reorientation of the D2 structures. S3 schistosity overprinted the pre-existing S2 schistosity. S3 foliation strikes N20–30◦ W and dips 60–70◦ to the NE or SW (Figure 12d). Mylonitic foliation in C3 shear zones is superimposed on the S2 foliation (Figure 13d). The spacing of the strike slip shear zones varies from a few centimeters to some meters. Kilometer scale NNW-oriented strike–slip shear zones are commonly developed in the Wadi Khashab–Gabal Sirsir ophiolitic mélange, especially along Wadi Khashab, along the main planes of Hodein–Beitan shear zone and Sirsir–Rahaba shear zone (Figure 9). The ophiolitic and metavolcanic rocks on both sides of the shear zone show S-shaped fault–drag folds (F3), consistent with the sinistral movement. Quartz veins showing signs of ductile shearing are sulfide-bearing and are associated with green malachite alteration in places.

The strike–slip shear zones in Hodein shear belt separate the Wadi Beitan gneisses from the overlying ophiolitic mélange (Figure 9). The mylonitized rocks are characterized by stretched quartz ribbons with an anastomosing pattern of intervening variably deformed lenses. The angle between S3 and C3 is often clearly visible and can reach 5◦, indicating strong shear values. Asymmetric boudins are developed in the Wadi Beitan banded gneisses and amphibolite. Mylonitic rocks exhibit subvertical to steeply dipping foliations (N20◦ W and N40◦ W) and dip steeply to the SW-dipping high-angle S3 foliations in the high strain zones along the main planes of the Beitan imbricate thrusts and Sirsir–Rahaba thrust. The S3 foliation is defined by kink bands or spaced cleavage that are parallel to the F3 axial planes. S3 kink bands are sharp deflections of S2. The high-strain zones with subvertical foliation planes are subparallel and are oriented NNW–SSW except in the central part of the Wadi Hodein–Wadi Beitan shear belt where they are deflected into NNE-SSW. In these high-strain zones, isoclinal and intrafolial folds with shallow plunging fold hinges and a subvertical axial planar foliation are abundant. Shallow NNW- or SSEplunging mineral and stretching lineations are present on the steep foliation planes in the NNW–SSE striking high-strain zones.

Two distinct types of mineral lineations L3 on the S3 foliations have been recognized by the measurement of the minerals that grew during D3. The first type, here defined as L3a, is a SW and SE-plunging mineral stretching lineation along the ENE-verging thrust (T3). L3a is marked by platy quartz, amphibole fish and feldspar rods. The second type, here referred to as L3b, is a b-type lineation orientated subparallel to the F3 fold axes. The L3b is a crenulation lineation with a subhorizontal plunge to the NNW or SSE (Figure 13e). The D3 deformation produced regional-scale NNW-trending folds (F3) defined by open folds with nearly vertical axial planes. Superposition of F3 on F2 folds resulted in extensive NNW-trending tight and reclined folds and NE-trending open folds. The most common macroscopic shear sense indicators include asymmetric tight and reclined folds (Figure 13f), sigmoidal porphyroclasts (Figure 13g,h), S-C fabrics, folded and en-echelon quartz lenses (Figure 13i), shearband quartz boduins and pop up structures. The lineation indicates that the tectonic transport took place while far-field compression progressed and switched to oblique thrusting.

#### 4.2.4. D4: Extension and Terrane Exhumation

D4 was a prolonged phase of brittle deformation associated with intrusion and emplacement of late-orogenic granitoid intrusions and terrane exhumation. During D4, the Wadi Hodein–Wadi Beitan shear belt was dissected by a number of dextral strike–slip faults, deformed the post-orogenic granites and the D1–D3 structures. These ENE–WSW right-lateral strike–slip faults occur in the central part of the Wadi Hodein–Wadi Beitan shear belt and along Wadi Khuda (Figures 9 and 12d–f). Another major sinistral strike–slip fault striking NNE-SSW controls the course of Wadi Urga El-Rayan. NW–SE oriented gold-bearing quartz veins were originated during D2 and were subsequently deformed by D3–D4 events.

#### **5. Gold Occurrences in the Wadi Hodein Shear Belt**

A number of gold occurrences in the Wadi Hodein shear belt are mainly associated with the high strain zones. The latter are confined to fault-bounded imbricated thrust sheets of allochthonous ophiolitic blocks. The Roman and Ptolemaic gold occurrences are confined to deformed granitoid and metagabbro–diorite complexes in the northern and central parts of the Hodein shear belt. In the following sections, we describe the internal structures of the mineralized quartz veins and the structural controls of several occurrences, namely: Wadi Khashab, the El-Anbat mine, the Um Teneidab mine, the Urga El–Ryan occurrence, the Hutit mine and the Um Eleiga deposit.

#### *5.1. The Wadi Khashab Occurrence*

In the Wadi Khashab area (Figure 14a), the ophiolite slices are overthrust on the arc's metavolcanic rocks and volcaniclastic metasediments. The serpentinites of Gabal El Beida form a NW-elongated large belt and slices of different sizes tectonically incorporated in the volcaniclastic metasediments. The serpentinites form dissected elongated massive masses with sheared and foliated peripheries. These serpentinite bodies are altered to talc– carbonate rocks along the shear zones. Blocks and masses of ophiolitic metagabbros usually occur within the volcaniclastic metasediments. They locally exhibit weakly developed foliation and compositional layering. Ultramafic rocks are commonly associated with pillow and amygdaloid metabasalts. The metavolcanic rocks are represented by strongly foliated metaandesite, metabasaltic andesite and intermediate to acidic metatuffs [39].

Gold-sulfide mineralization is confined to discrete shear zones of highly silicified, ferruginated metavolcanics and volcaniclastic metasediments commonly associated with sulfide-bearing granophyric dikes and quartz± carbonate veins [39]. The Wadi Khashab zone is a major sinistral strike–slip shear zone, striking NNW–SSE and dipping steeply (65–75◦) towards the ENE. Rocks along this shear zone are carbonatized and consist mainly of highly sheared metavolcanics, serpentinites and volcaniclastic metasedimentary rocks. The wall rock alteration is present as strongly foliated flakes in quartz veins and is dominated by the silicification and chloritization associated with carbonate [39,78]. The silicified shear zone (SiO2 > 80%) of the pillow metabasalts is relatively enriched in Au (25–45 ppm) whereas the carbonatized shear zone (SiO2 < 50%) within the obducted area of the serpentinite rocks has a very low Au content (0.24–0.45 ppm) [78]. The samples analyzed by Zoheir [39] yielded 2.1–6.6 ppm Au, and the sulfidized granophyric dikes are also gold-bearing (0.2–2.1 ppm Au).

#### *5.2. The El-Anbat Deposit*

The Gabal El-Anbat–Gabal Sirsir belt consists mainly of heterogeneously sheared talc carbonate, carbonatized, serpentinite, ophiolitic metagabbro, pillow metabasalts, and arc metavolcanic and volcaniclastic rocks (Figure 14b). Syn-orogenic metagabbro–diorite, granodiorite and post-orogenic granitoid intrusions are widespread in the study area. The serpentinite occurs as large masses, forming the main body of Gabal Sirsir and small slices incorporated in the volcaniclastic metasedimentary rocks. The serpentinite is variably altered to talc-carbonate and its contacts with the neighboring volcaniclastic metasediments and ophiolitic metagabbro are highly sheared. The gold grade in the quartz-carbonate veins and hydrothermal alteration zones is ~0.3–46 g/t Au [79]. The metavolocanic succession of the Gabal El-Anbat–Gabal Sirsir area comprises variably sheared metabasalt, metabasaltic andesite, meta-andesite, metadacite, and metapyroclastic rocks [80].

In the El-Anbat mine area (23◦17 01 N, 35◦09 21 E), the alteration zones occur as sheets or lenses along the NW- and NNW-striking thrusts, between the carbonatized serpentinite and foliated intermediate metavolcanics (Figure 14b). S2 is a regional foliation in El-Anbat area striking NNW–SSW and dipping moderately or steeply to the ENE and less commonly to the WSW. The F1 folds are still preserved in ophiolitic metagabbros and mafic metavolocanics. The F2 folds are major NNW-trending asymmetric left-stepping folds in the volcaniclastic metasediments. Different styles of minor folds are recognized open concentric folds, closed tight folds, symmetric and asymmetric folds, isoclinal folds and chevron folds. During D3, Conjugate sinistral and dextral strike–slip faults and shear zones are apparently developed as a component of a major transpression system.

The mineralized shear zones and the bleached sheared host rocks are confined to the steeply dipping thrusts between carbonatized serpentinites and the underlying volcaniclastic metasediments. These zones are characterized by arrays of recrystallized quartz pods, fracture-filling ankerite, sulfidized granitic offshoots, boudinage of the granitic bodies, silicified listvenite masses and intermingling carbonate sericite and malachite veinlets [38], suggesting significant gold grades in the hydrothermally altered, sheared host rocks. The analyses indicate that gold is related to mineralized quartz veins (with up to 7.5 g/t Au) and to pervasively altered wall rocks (with up to 5 g/t Au) [38].

**Figure 14.** (**a**) Geological map of the Wadi El Beida–Wadi Khashab area (modified from Zoheir [39]); (**b**) geological map of Gabal El-Anbat–Wadi Hodein area (modified from [38]); (**c**) geological map of Um Teneidab area (modified from Hamimi and Sakran, [81]); and (**d**) geological map of Wadi Urga El Rayan area (modified from El Baraga, [48]).

#### *5.3. The Um Teneidab Deposit*

The Um Teneidab mine (23◦17 01 N, 35◦09 21 E) is located ~13 km to the southwest of the Hutit mine and to the west of Gabal Um Teneidab peak. The Um Teneidab area is underlain by gneisses and migmatites, serpentinite, volcaniclastic metasediments, and deformed mafic metavolcanic rocks. These rocks are cut by metagabbro–diorite complex (Figure 14c), as well as unmappable masses and offshoots of post-orogenic leucogranites [12,81]. Serpentinite constitutes the main mass of Gabal Um Teneidab and forms blocks and slices of variable sizes incorporated in the volcaniclastic metasediments. The mélange

blocks are randomly distributed, varying from cobbles to mountain size and usually oriented in the NWSE or NNW–SSE directions. The gabbroic rocks in the Um Teneidab mine area were mapped as island arc, synorogenic metagabbro–diorite complex [12,82] and as post-orogenic younger gabbros [81]. In the present work, we agree with Hassan and El-Manakhly [82] and Zoheir et al. [12] and consider the gabbroic rocks in the Um Teneidab mine area as a variably foliated, metagabbro–diorite complex.

The Um Teneidab metagabbro–diorite complex is dissected by a number of ENE–WSW and N–S dextral strike–slip faults and WNW–ESE major fractures with no obvious lateral displacement. The zones in which the leucogranites send offshoots into the gabbroic rocks (Figure 14c) are characterized by intense shearing and alteration as well as the presence of abundant quartz veins and felsic dikes. Shearing in the area is predominantly brittle, with little ductile deformation being experienced, with alteration zones and quartz veins that are generally controlled by NW–SE shear/fault sets. The subvertical NW- and NNWstriking milky quartz veins extend up to 250 m with 8 cm to 45 cm thickness and lensoid morphology. These veins are in part or completely recrystallized. The main lode is a zone of stockwork of veinlets (70 cm wide) bordered by hydrothermally altered wall rocks forming together a ~2-m-wide mineralization zone [12]. The gold in these veinlets and the hydrothermally altered wall rocks occurs as fillings in the microfractures and is scattered as sliver in altered pyrite and galena. The gold content ranges from 1 to 30 g/t in quartz veins, whereas the altered wall rocks locally contain ~8 g/t Au [12].

#### *5.4. The Urga El-Ryan Occurrence*

The Urga Ryan gold deposit (35◦5 0 E and 23◦21 23 N) is located at ~3 km to the south of the intersection between Wadi Urga Ryan and Wadi Hutib. The area around Wadi Urga El-Ryan (Figure 14d) is underlain by gneisses, volcaniclastic metasediments and mafic to intermediate metavolcanic rocks. The volcaniclastic metasediments include wide varieties of metagreywacke, metamudstone, slate, pelitic schists and metaconglomerate in decreasing order of abundance. They are strongly NW–SE foliated and less commonly NNE–SSW cleaved [48].

The metavolcanics are composed of repeatedly alternating and interfingered successions of basaltic flows together with layered andesite and subordinate dacitic flows and their corresponding metatuffs [48] as well as chlorite schists. The metavolcanic rocks are variably deformed by km-scale shear zones that led to intense shearing in the NNW–SSE direction (S2 and S3), overprinting the WNW–ESE schistosity (S1). The metagabbro is emplaced into both metavolcanics from the northern and western parts and volcaniclastic metasediments from the southern part [48]. The metagabbroic rocks are foliated and sheared, particularly along the shear zones. The syn-orogenic granites are slightly foliated and form an elongated intrusion (10 m × 2.5 m width) trending roughly N–S, which forms discontinuous hills. It is mainly tonalite in composition and is bounded from the west by the Wadi Beitan gneisses, and by metagabbro from the north. Volcaniclastic metasediments and metavolcanics border these rocks from the southeastern side. Xenoliths and roof pendants from metagabbro are enclosed within the syn-orogenic tonalite.

In the Urga El-Ryan occurrence (Figure 14d), the old mining houses spread along the main Wadi Urga Ryan and their tributaries, possibly reflecting significant mine activities. The mineralized regions are limited only to NNW–SSE striking and westward dipping zones of intense shearing in metavolcanic rocks. The quartz vein strikes N–S (355◦) concordantly with the shear zone system and dips at 80◦ E [83]. It was exploited in a deep mine down to a level of 15 m below the surface. These shear zones (up to 40 m in length and 5–30 cm in thickness) are strongly mylonitized and marked by recrystallized quartz lenses and asymmetric boudinaged quartz veins [12]. The narrow zones of sheared wall rocks are characterized variable degrees of hydrothermal alteration. The gold grade is 1 to 7g/t Au in the quartz veins from the Urga El-Ryan occurrence [84].

#### *5.5. Hutit Deposit*

The Hutit gold deposit occurs in the Wadi Huzama, which is a small tributary of the larger Wadi Rahaba (Figure 15a). The Hutit mine area is underlain by serpentinite, mafic metavolcanics, volcaniclastic metasediments, ophiolitic metagabbros, syn-orogenic metagabbros and post-orogenic granites (Figure 15a,b) [12,48,82,84,85]. Structurally, the Hutit deposit is controlled by the Rahaba–Sirsir sinistral shear zone and their kilometerscale imbricate thrust system (Figure 15b). The SW-directed thrusts bound the ophioltic blocks and dip moderately or steeply to the NE. Imbricate slices and sheets of serpentinite are tectonically overlying metavolcanics and volcaniclastic metasediments. The oblique thrust planes accommodate sinistral displacement and asymmetrical anastomosing and kinked fabrics. Asymmetric quartz lenses and drag folds indicate a sinistral sense of shear, whereas subvertical slickensides along the quartz vein walls document the reverse slip of the hanging wall block. Joints and fractures are abundant in the rock units mainly with NE–SW and NW–SE directions. Mafic to felsic dikes (basalt, basaltic andesite, andesite, rhyodacite and dacite) as well as granodiorite dikelike bodies strike NW–SE and less commonly NE–SW.

**Figure 15.** (**a**) Geological map of the Hutit gold mine and surroundings, (modified after from Hassan and El-Manakhly [82]; Zoheir et al. [12]), (**b**) Detailed geological map of the main lode in the northern mine and southern mine (modified after Zoheir et al. [12]). (**c**) Geological map of Abu Dahr ophiolite (modified from Ashmawy, [86]), and (**d**) Geological map of the Um Eleiga gold mine (modified from Zoheir et al. [41]).

Two main old mine workings (northern; 23◦27 26 N, 35◦11 34 E and southern; 23◦27 16 N, 35◦11 41 E) (Figure 15b) were mapped at the 1:1000 scale by Hassan and El-Manakhly [82]. The ruins of the separation and grinding plants are still observed in the northern old mine, whereas the loading station, leaching basins and crusher stages were observed in the southern mine. In both mines, a main entrance through a horizontal ~E–W adit leads to the veins at a distance of 20 m or 35 m [12]. The mineralized quartz veins occur along the thrust contact between the serpentinite masses and the mafic metavolcanics and volcaniclastic metasediments. Two types of anastomosing and undulating gold-bearing quartz veins were reported in the mine area, including bluish-gray (common in the northern mine) and milky quartz veins (dominant in the southern mine). Concerning the ore grade, Gabra [84] reported 1–36 g/t in samples from quartz veins the southern mine and 1–40 g/t in quartz veins from the northern mine. Takla et al. [85] reported an average of 20 g/t in samples from the two different types of quartz veins and 8 g/t Au on average in altered wall rocks.

#### *5.6. The Um Eleiga Deposit*

The Um Eleiga mine (24◦36 44" N, 35◦03 19" E) occurs ~50 km west of the Red Sea coast. Traces of placer gold workings during Roman–Byzantine and early Islamic times include hundreds of shallow pits, dumps, ancient mining camps, stone anvils, hammers, and grinding mills [12,41,83]. The geology of Um Eleiga area is dominated by a 7 km wide intrusive complex with a gabbroid core cutting the serpentinite-chromitite of Gabal Abu Dahr and the northern part of Wadi Rahaba–Gabal Abu Dahr ophiolitc mélange. The latter composed masses and blocks of serpentinized ultramafics, pillow metabasalts and mafic metavolcanics incorporated within highly tectonised matrix of pelitic and carbonaceous metasediments. The ophiolite fragments occur as NE-dipping slabs and sheets thrusted southwestward forming imbricate thrust system. Contacts of the serpentinized ultamfics with Um Eleiga metagabbros-diorite complex are sharp and irregular. In the upper part of the Abu Dahr massif, serpentinite contains large masses of serpentinized dunite, sills or layers of wehrlite, pyroxenite and gabbro [42,86].

The mafic metavolcanic rocks comprise blocks and thrusted slices of metabasalt and basaltic andesite [42,86]. These rocks structurally overlay the Um Eleiga intrusive metagabbros-diorite complex and Abu Dahr serpentinized ultramafics (Figure 15c). Pillow metabasalt occurs in the core of a major fault-propagation fold (Figure 15c) within the highly tectonized matrix with schists and sheared serpentinite. Pillow metabasalt forms ellipsoidal, globular and tabular shaped bodies, ranging between 10 cm to 1 m in diameter. The Um Eleiga intrusive metagabbro–diorite complex is approximately 7 km long and 4 km across, and encompasses a compositional continuum from gabbro to granodiorite through diorite and subordinate tonalite (Figure 15d). This complex exhibits a circular zonation, in which gabbro occupies the core and subordinate granodiorite forms the margin [41]. The Um Eleiga metagabbro and metabasalt have a tholeiitic to calc-alkaline affinity and are interpreted to have been formed in a forearc setting [42].

In the Um Eleiga mine, the mineralized quartz veins trend mainly NE–SW or ENE– WSW and cut the gabbroic rocks in the central part of the complex and extend beyond the gabbro–diorite boundary [12]. The fault/joint intersections are the main structural control of intensely hydrothermal alteration zones and high gold contents in the central part of the Um Eleiga complex [41]. Late barren quartz veins are confined to intersections of fault and tension gashes in the brecciated gabbro core and trend mainly N–S, NW–SE and E–W (Figure 15d). Sulfide-bearing quartz veins (5–40 cm thick) cut the metagabbro–diorite complex and are partially stopped out [12]. Analyses of quartz dumps in several pits gave gold values up to 28 g/t [82]. According to Takla et al. [85], most of the ancient workings in the mine area were confined to the old terraces (lithified wadi alluvium) within and adjacent to the intensely kaolinitised gabbro. Atomic absorption analyses of heavy concentrates of these old terraces indicated that gold contents were variable from barren to 10 g/t [85].

#### **6. Discussion**

#### *6.1. Remote Sensing Targeting of New Gold Occurrences*

The Nubian Shield is a typical example of well-exposed crystalline basement rocks, and mafic–carbonate–hydrous mineralogical indices were used to extract the representative pixels in the satellite images. Zoheir et al. [12] used Landsat-8 OLI and ASTER band ratio images and successfully benefited from the effective absorption features of the mafic rock-forming minerals and their metasomatic products. Therefore, Landsat-8 OLI and ASTER data with comprehensive fieldwork were used for mapping geological structures, lithological units and alteration zones associated with orogenic gold mineralization in the study area. The image processing techniques of these remotely sensed data maximize the relatively small differences in the spectral responses of rock forming minerals within a specific wavelength range [87]. The applied approach includes false band combination (FCC), band rationing, principal component and mineralogical indices to the Landsat-8 OLI and ASTER data. It is evident that the band math of Landsat-8 (6/7) distinguished clay minerals, serpentine, and many alteration zones, whereas ASTER (7 + 9/8) demarcated carbonatized rocks, metavolcanics and metasedimentary rocks.

Landsat-8 FCC of Abrams ratio (RGB-6/7, 4/3, 5/4), Kaufmann ratio (RGB-7/5, 5/4, 6/7) and Chica-Olma ratio (RGB-6/7, 6/5, 4/2) characterized the contacts between the different rock units in the study area and upgraded the exciting geologic maps (see Figure 4). Moreover, they deciphered the structural elements especially folding and thrusting in the Wadi Hodein–Beitan shear belt as well as the ENE-dextral strike slip faulting. The RGB of the principal component analysis of Landsat-8 (PC2, PC1, PC4 and PC2, PC4, PC5) and ASTER (PC1, PC2, PC3 and PC6, PC3, PC1) discriminated the rocks consisting of high contents of Al and/or Mg-OH-bearing minerals and emphasized the contact between felsic and basic metavolcanics and volcaniclastic metasediments and gneisses along Wadis Hodein and Beitan (see Figure 5).

The mineralogical indices of Ninomiya [62] (OHI, KLI, CLI and ALI) were used to characterize the alteration zone in the study area using ASTER data. The resultant images highlighted effectively the zone of the hydrothermal alterations. In addition, they stressed the fact that the alteration minerals zones are found in both ductile and brittle deformation zones where the integration between the structural segments (density and direction) associated with the presence of the altered minerals may help to localize and predict new occurrences of gold mineralization. A false-color composite (FCC) ratio image (OHI, KLI, CLI) was generated. This RGB FCC image shows the OH-bearing rocks (metaultramafic–mafic ophiolites and island arc meta-basic rocks) and the clay-minerals (see Figure 6). The evaluation of the remote sensing alteration mapping results with field data using an error matrix approach and Kappa Coefficient shows a very good match, which indicates the overall accuracy of 88.33% and the Kappa Coefficient of 0.77 for Landsat-8 data and the overall accuracy of 74.10% and the Kappa Coefficient of 0.65 for ASTER data, respectively (Table 4A,B). It is noticed that the old working gold occurrences are associated with the high deformation and fracturing zones bounding the sheared ophiolitic belt and faulted contacts such as El-Beida, Urga Ryan, Hutit and Um Eleiga gold mines. Multisource datasets were selected to control factor layers indicating the distribution of gold mineralization potentiality zones such lithology, alteration zones, proximity to existing gold mines, proximity to favorable contacts, proximity to major structures (especially thrusts), faults density maps and lineaments density maps. The seven evidence layers were derived, analyzed, and integrated in a GIS platform to develop the gold mineralization model (see Figure 8).

**Table 4.** Error matrix for alteration mapping derived from remote sensing data versus field data. (**A**) Landsat-8 data; (**B**) ASTER data.

#### *6.2. Transpressional Tectonics in the Evolution of the Wadi Hodein Shear Belt*

The Wadi Hodein shear belt has evolved throughout a multistage deformation history (D1–D4), in which D2 and D3 were the most dominant. NNE–SSW crustal shortening (D1) led to development of early ENE–WSW striking S1 gneissosity and F1 doubly plunging anticline in the Wadi Khuda gneisses. D1 structures in the Wadi Khashab, Wadi El Beida and Gabal Anbat and Gabal Arais areas exhibit WNW-striking S1 schistosity, F1 minor tight, recumbent and overturned folds and T1 thrusts. NE–SW oblique convergence and transpression (D2) led to the development of NW–SE striking S2 regional foliation, S2m mylonitic foliation, F2 major kilometer scale anticlines and synclines (see Figures 10–13,16a–d) and minor open, asymmetrical to isoclinal folds, NW-plunging stretching and mineral lineations (L2) and WSW-verging major thrusts (T2). The major D2 fabrics are represented by a series of large-scale folds (F2) associated with northwest-vergent foliation (S2), indicating that the F2 folds formed in response to a NW–SE-oriented stress field.

**Figure 16.** (**a**–**c**) F2 folds superimposed by the upright open F3 folds in the Wadi Hodein shear belt (Wadi Hodein, Wadi El Beida and Wadi Khashab areas). (**d**) Sketch block diagram illustrating the structural evolution of the Wadi Hodein shear belt.

The Wadi Hodein–Beitan shear belt is cut by a suite of variably deformed granitic intrusions. Many of these intrusions occur in the vicinity of the major thrusts and are considered to have emplaced during the regional D2 deformation event. E–W shortening (D3) produced subvertical NNW-Striking foliation (S3), NNW–SSE thrust dominated strike slip shear zones (C3), NNW- and ENE-trending folds (F3). L3a is a SW and SE-plunging stretching lineation along the NNE–SSW T3 minor thrusts. L3b lineation is a crenulation lineation with a subhorizontal plunge. During D3, the major NNW-oriented shear zones rooted into a low-angle, deep crustal detachment, delineating the point at which oblique thrusting is partitioned into separate transpressional strike–slip and reverse-sense shear zones, i.e., Sirsir–Rahaba, Hodien–Beitan and Um Teneidab–Hutit shear zones. The sinistral porphyroclasts and NNW-plunging reclined and vertical folds as well as NE-trending open folds in sheared metavolcanics and volcaniclastic metasediments indicate a transpressive stress regime including both pure and simple compressional components. The latest extensional structures (D4) in Hodein shear belt include major brittle strike slip faults and microfaults and dikes associated with the intrusion of late to post-tectonic granites. Structures assigned to this deformation phase include ENE–WSW dextral and NNE–SSW sinistral strike–slip faults.

The newly produced structures map (see Figure 9) shows that the overall structural setting of the Wadi Hodein shear belt bears a resemblance to an asymmetric flower structures in which the ophiolitic mélange and the ophiolitie blocks are cut and bounded on both sides by reverse-slip faults, and strike–slip shear zones. The eastern (Sirsir–Rahaba and Um Teneidab–Hutit shear zones) and western boundary faults (Hodein–Beitan and Arais shear zones) correspond to a reverse-sinistral thrusts. The transpressional imbricate thrusts forming the Sirsir–Rahaba, Hodein–Beitan and Arais shear zones dip toward ENE, whereas those pertaining to the Um Teneidab-Hutit shear zones dip to WSW (see Figures 9 and 16d). All the shear zones show a moderately sinuous trace in map-view, up to 2 km-thick band of fine-laminated mylonites, developed in the footwall gneisses and volcaniclastic metasediments. The high-angle, NNW-oriented thrust-dominated, strike slip shear zones marked a near-vertical ductile deformation zone rather than an imbricate structure [88–90]. The thrusts show a typical sequence of propagation in the footwall of the previous thrust in a piggy-back model. Many kinematic indicators, including asymmetric porphyroblasts such as "σ-type" augens, and pressure shadows, indicate a sinistral sense of shearing. The predominance of reverse slip movement over the along strike shearing suggests a thrust-dominated transpression along the Wadi Hodein shear zone. The NW–SE to NNW–SSE subparallel Sirsir–Rahaba, Hodein–Beitan, Um Teneidab-Hutit and Arais strike–slip shear zones exhibit a consistently sinistral sense of shear.

#### *6.3. Structures Controlling Gold Occurrences*

The distribution of the gold occurrences is confined to the margins of the Wadi Hodein shear belt (see Figure 9) especially along the thrust-dominated transpressional major zones and their splays formed during D3. Conjugate sinistral (N) NW–(S) SE and dextral (E)NE– (W)SW strike–slip faults and shear zones apparently developed During D3 as a component of a major transpression system. These conjugate shear zones control the occurrence of gold in Hodein shear belt. Twisting and anastomosing S2 and T2 thrusts led to NE-trending F3 open folds and oblique sinistral shear zones on the pre-existing NW-striking thrusts. The S-C fabrics and asymmetric quartz lenses replicate left-lateral shearing, which resulted in widespread NE–SW-striking dilation bents within and around the shear zones. At the Hutit and El-Anbat mine areas, the mineralized quartz veins and the alteration zones occur along the NW- and NNW-striking thrusts between the carbonatized serpentinite and foliated metavolcanics and the metavolcanics and volcaniclastic metasediments. In the Um Eleiga mine, the mineralized quartz veins trend mainly NE–SW or ENE–WSW mainly along the fault/joint intersections. In the Urga El-Ryan occurrence, the mineralized regions are limited only to NNW–SSE striking and westward dipping zones of intense shearing in metavolcanic rocks. In the Um Teneidab deposit alteration zones and quartz veins are

generally controlled by NW–SE shear/fault sets. In the Wadi Khashab occurrence, the quartz veins occur as closely spaced swarms running parallel and subparallel to NNWtrending sinistral strike–slip shear zone of Wadi Khashab.

#### **7. Conclusions**

Detailed geological mapping of the Wadi Hodein area was successfully accomplished by employing different processing techniques, i.e., band combinations, band math (BM), Principal Component Analysis (PCA), decorrelation stretch and mineralogical indices, to Landsat-8 OLI, ASTER and ALOS PALSAR data. Field data were integrated with results of the remote sensing studies, which enabled an updated understanding of the structural evolution of the Wadi Hodein–Wadi Beitan shear belt. The structural framework of the Wadi Hodein–Wadi Beitan shear belt was shaped by the superposition of the NW–SE folds (F2) by the NNW-trending, km-scale tight and reclined folds (F3). The overall configuration of the investigated shear belt is identical to that of an asymmetrical flower structure in which the ophiolitic mélange and the ophiolitic blocks are cut and bounded on both sides by reverse slip and strike–slip shear zones. The field studies showed that most of the gold mineralization is mainly associated with quartz veins within extensive sinistral transpressional shear zones assigned to the last ductile deformation event (D3) in the evolution of the entire shear belt. This event was characterized by strong stretching and mylonitic lineation, abundant undulatory shear zones and shear foliation disturbance. The gold-bearing quartz veins are hosted by narrow, steeply SW- and NE-dipping NNW- and NW-trending mylonitic zones that are characterized by a steeply NNW-plunging mineral lineation. This may imply the important role of oblique convergence in the formation of the auriferous quartz veins.

The processing flow chart introduced in this study has identified areas with the potential for unexplored gold occurrences and helped to illustrate the controls of the distribution of gold mineralization sites. The processing results were classified into five categories, from very high to very low potentiality zones. Gold mineralization is here interpreted to show preferential distribution along the Wadi Hodein–Wadi Beitan shear belt. The most important conclusion of this study is that gold mineralization in the Wadi Hodein–Wadi Beitan shear belt was mostly confined to steeply dipping strike–slip shear zones in the marginal parts of the shear belt. The occurrence of gold-bearing quartz veins in central shear zone is not evident so far. A conceptual model for testing new and unexplored targets of gold–quartz veins in the region translates the coincidence of shear zones, alteration and acid dikes to highly potential zones for new and possibly important gold occurrences in the study area.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/min11050474/s1: Figure S1: Field photographs showing the different rock units in the study area; (a) and (b) hornblende gneiss alter-nating with bands of biotite gneiss forming ENE-trending ridges along Wadi Khuda, (c) banded amphibolite from Beitan gneisses belt, (d) contact between hornblende gneisses and gneissose granite from Beitan gneisses belt (e) car-bonated ophiolitic serpentinite enclosing small bodies of listivenitized ultramafites (dark ridges) from Wadi Rahaba, (f) small prophyroclast of ophiolitic metagabbro between volcaniclastic metasediment (lower) and serpentinite (up-per) from Wadi Rahaba; Figure S2: Field photographs showing the different rock units in the study area: (a) pillowed metabasalts from Wadi Khuda, northeast of Gabal Abu Dahr; (b) ellipsoidal Pillowed metabasalt from Wadi Hutib; (c) serpentinized peridotites of Gabal Arais thrusted over the Beitan gneisses belt and are intruded by a small mass of alkali feldspar granite; (d) syn-orogneic gabbro-diorite intruded the gneisses of Wadi Khuda; (e) post-orogenic biotite granite intrudes volcaniclastic metasediments along Wadi Rahaba; (f) syn-orogonic granodiorite intrudes volcaniclastic metasediments along Wadi Beitan, 3.1. Data and Processing Techniques; Figure S3: Flowchart of the remote sensing and GIS methodologies adopted in the present study; Figure S4: Lithological discrimination using (a) ASTER (RGB-431) and (b) grey scale ASTER band ratio (7 + 9/8); Figure S5: False-color composite of principal component analysis (PCA) of (a) Landsat-8 RGB-PC2, PC1, PC4 and (b) ASTER RGB-PC1, PC2, PC3; Figure S6: Model Builder of the geospatial thematic

maps used to locate the high potential zones for gold mineralization in the study area; Table S1: Eigenvector loadings of principal component analysis for Landsat-8 OLI data; Table S2: Eigenvector loadings of principal component analysis for ASTER data; Section S1: Data and Processing Techniques

**Author Contributions:** Conceptualization, M.A.E.-W., S.K. and B.Z.; methodology, S.K. and A.B.P.; software, S.K.; validation, S.K., M.A.E.-W. and B.Z.; data curation, S.K.; writing—original draft preparation, M.A.E.-W. and S.K.; writing—review and editing, B.Z. and A.B.P.; supervision, M.A.E.-W.; fieldwork, S.K. and M.A.E.-W., shaping and fine-tuning the conclusions, B.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** The present work has received no funding or grant.

**Data Availability Statement:** The data presented in this study are available on request from the corresponding author.

**Acknowledgments:** The authors appreciate the help of Mohamed Hamdy and Ismail Thabet (Tanta University, Egypt) during the fieldwork. Additionally, the Institute of Oceanography and Environment (INOS), Universiti Malaysia Terengganu (UMT) is acknowledged.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

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Tel: +41 61 683 77 34

www.mdpi.com ISBN 978-3-0365-6794-5


2.8 Backward compatibility

The software is constantly modified, and it is useful if the new version of software is able to read data saved by the older version. The backward compatibility can be achieved by storing archive version into stream and keeping deserializing code responsible for handling older versions. That leads to the newest code being the most littered with code for supporting previous versions, but such solution is probably the least memory consuming. Another approach is to use tagged fields, which also help with forward compatibility, as described below.

#### 2.9 Forward compatibility

Forward compatibility allows to use older version of modules when new version of data format is introduced. Supporting forward compatibility requires ability to skip unknown fields in input data. It is usually achieved by adding tags—unique identifiers and type information—to each field. This way during deserialization the software can read only those fields it is aware of. Such approach provides some additional memory footprint, but helps to maintain software in live environment where upgrades are not possible to be performed at once or at all on some instances. Still this solution does not fix all issues—not every type of change in future data format can be made. For example, consider removing field—question arises how older software will interpret missing data, which it still expects. Adding new field should always work, but adding a new type might be troublesome in languages which do not have runtime reflection and type definition capabilities (like C++). Keeping software forward compatible remains mostly the developer's responsibility.


**6. Conclusions**

Studies have shown that, just like any physical system, projects have entropy that must be managed by spending energy, and this process of energy is called project management. In order to manage the project uncertainty, accurate estimates for activity duration are crucial in order to make informed decisions. This paper presents a new statistical method to better estimate the average and variability of the activity duration distributions in order to help project manager to better manage the project uncertainty (entropy) with the lowest possible effort (energy).

The new statistical calibration method extends two existing calibration methods using an automatic partitioning heuristic. The main objective of such an extension is to improve the ability to define distribution profiles for a project's activity duration that represent as accurately as possible the stochastic nature of the activities. The underlying assumption is that the lognormal distribution is the most appropriate distribution for modelling activity durations, but the parameters for this distribution cannot be easily extracted from empirical data due to hidden earliness and rounded values for the reported activity durations. These procedures were utilized as a starting point for developing a much more extensive calibration procedure, which has programmed in *C* + + and empirically validated on the dataset consisting of more than 5000 activities. These input data come from the real-life project database created by [21] and is freely available at www.or-as.be/research/database.

The previous calibration methods have shown promising results, but also some limitations, and these are also discussed in the current study. First, the original calibration procedure of [19] did not allow the project to be divided into partitions of activities that intrinsically adhere to the same distribution profile. For this reason, [20] have proposed an extended calibration method by introducing the ability of managerial partitioning using human input such as planned duration, the structure of the work breakdown structure or the risk profiles defined for each activity. This extended calibration method proved extremely favourable and confirmed that partitioning is a promising direction for proving the realism of the lognormal distribution for activity duration. Despite this improvement, managerial partitioning is based on criteria defined by the project manager, and, as the project manager is a human being, these criteria are susceptible to bias in human judgement.

To bypass this problem, we developed a completely new approach in the current study which we called the *statistical partitioning heuristic*. It is foremost a *statistical* procedure in contrast to the managerial procedure that requires human input. Moreover, the *partitioning* approach, which was shown to be promising in the extended calibration study, is kept as a *heuristic* tool (i.e., there are other ways of doing the partitioning) in the best possible—but not necessarily optimal—way. Consequently, in statistical partitioning, well-chosen activities that do not fit within a certain partition are eliminated from that partition and assigned to another, which is then also adapted until a fit is reached. The results obtained from this are very good, and almost perfectly match those from performing managerial partitioning in the extended calibration method.

This observation is certainly advantageous, as it suggests that equally adequate partitions can be obtained through the proposed statistical procedure without being susceptible to human bias or, moreover, requiring the definition of managerial criteria. Since project managers are now always

able, or willing, to define values for the managerial criteria for all activities, an automatic procedure can replace their cumbersome task. It is therefore advised to perform the statistical partitioning heuristic with the incorporation of advanced selection and stopping strategies for receiving the most appropriate and trustworthy distribution profiles for the activity durations. However, when it is certain that the managerial criteria have been properly defined, managerial partitioning can be executed in combination with (in fact, prior to) the statistical partitioning. Despite the promising results in this study, future research topics can be derived from Section 5.3, since addressing the limitations of the current automatic partitioning heuristic could indeed further advance our research.

**Author Contributions:** M.V. and J.B. conceived and designed the experiments, performed the experiments and analyzed the data; M.V. wrote the paper.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.


**Fusarium Wilt: A Killer Disease of Lentil**

**Fusarium Wilt: A Killer Disease of Lentil**

Neha Tiwari, Seid Ahmed and Ashutosh Sarker Neha Tiwari, Seid Ahmed and Ashutosh Sarker Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72508

#### **Abstract**

Lentil (*Lens culinaris* Medikus subsp. *culinaris*) is an important dietary source of protein and other essential nutrients in South and West Asia, North and East Africa. Lentil crops are vulnerable to a number of diseases caused by fungi, viruses, nematodes, insect pests, parasitic plants and abiotic stresses. Among them, the most significant and serious soil-borne disease is Fusarium wilt (*Fusarium oxysporum* f.sp. *lentis*: *Fol*). Fusarium wilt causes yield loss up to 50% in farmers' fields. The pathogen showed high levels of phenotypic and genotypic diversity in India, Algeria, Syria and Iran. The disease thrives at 22–25°C temperature and affect lentil either at seedling and vegetative or the reproductive stages of the crop. To minimize yield losses, an integrated management strategy comprising resistant/partial resistant cultivars, adjusting sowing time, bio-control and chemical seed treatments is the best approach to reduce the incidence of the Fusarium wilt of lentil. This review covers past achievements in managing the disease, pathogen diversity and identify gaps in managing Fusarium wilt to improve productivity and production of the crop.

DOI: 10.5772/intechopen.72508

**Keywords:** lentil, *Fusarium oxysporum* f.sp*. lentis*, Fusarium wilt, disease management

#### **1. Introduction**

Lentil (*Lens culinaris* Medikus subsp. *culinaris*) is a cool season, diploid (2n = 2X = 14) selfpollinating grain legume with genome size of approximately 4 Gbp [1]. It is an ancient crop originated in the Near East and after that rapidly spread all through the Mediterranean Basin, Central Asia and later to the New World including Latin America. It is one of the oldest grain legumes domesticated about 10,000 years ago [2–4]. Production and consumption of lentil involve more than 100 countries. The total world lentil production is about 4.8 million tons from an estimated area of 4.5 million ha with an average yield of 0.11 t/ha [5]. The cultivated *L*. *culinaris* sub spp. *culinaris* includes two physio-morphological cultivated lentil types: small

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© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

seeded (microsperma) and large seeded (macrosperma) [6]. Lentil is recognized as one of the most nutritious pulse crops ranking next to chickpea among cool-season food legumes. It contains 57–60% carbohydrate, 24–26% protein, 3.2% and 1.3% fiber. It is also a rich source of minerals containing calcium (69 mg per 100 g), phosphorus (300 mg per 100 g) and Iron (7 mg per 100 g) of seed [7, 8]. Lentil seed contains lysine, an essential amino acid, found only at low levels in cereal protein. Lentil is a valuable human food, mostly consumed as dry seeds as well as used as fodder, and generally grown as a crop rotation after cereals to enrich the soil by their nitrogen fixing ability [9]. In South East Asia, lentil mostly grows on residual soil moisture after post rainy season under rainfed conditions. The inclusion of lentil as a crop rotation can benefits the succeeding crops by improving the soil health through biological nitrogen fixation and carbon sequestration. The amount of nitrogen fixed by plants varies from 0 to 192 kg total N/ha around a mean of 80 kg total N/ha [10]. This estimate of N fixation is similar to the quantities fixed by chickpea and dry bean.

Since 1970s there have been significant achievements in national and international lentil programs in developing phenologically adapted, stress resistant and high-yielding cultivars [11]. During the past three decades, different national agricultural systems released more than 90 improved cultivars from germplasm developed by the International Centre for Agricultural Research in the Dry Areas (ICARDA) [11]. Therefore, the current review covers past achievements in managing the disease, pathogen diversity and identify gaps in managing Fusarium wilt to improve productivity and production of the crop.


**2.3 Dynamic yield stress**

Yield stress (0) is defined as the force a fluid must be exposed to in order to start flowing. It reflects the resistance of the fluid structure to deformation or breakdown. Rheograms from rotational viscometer measurements are used as a means to calculate yield stress. It can also be obtained by applying rheological mathematical models (section 2.6; Spinosa & Loito 2003). Yield stress is important to consider when mixing reactor materials, since the yield stress is affecting the physico-chemical characteristics of the fluid and impede flow even at relative low stresses. This might lead to problems like bulking or uneven distribution of material in a reactor (Foster, 2002).