Geology, Petrography and Radioactivity of the Area between Wadi Dib and Wadi Mellaha, North Eastern Desert, Egypt

A varieties of rocks including metavolcanics, metagabbro-diorite complex, older granitoids, Dokhan volcanics, Hammamat sediments, younger granites as well as dyke swarms and veins are well exposed and studied in details at the strip enclosed between Wadi (W) Dib and W. Mellaha area. The metavolcanics is represented by the basic variety of metabasalt, intermediate variety of meta-andesite and acidic varities of meta-dacite and meta-rhyolites in addition to meta-pyroclastics. The metagabbro-diorite complex is shown intruding the metavolcanics and enclave rafts of then while this complex is intruded by both the older and younger granites and mainly have the composition of metamorphosed gabbros. The older granitoids in the area are seen extruded by the Dokhan volcanics and are intruded by the younger granites and generaly have the composition of quartz-diorite and granodiorites. The Dokhan volcanics in the study area are present and exposed at W. Dib, W. Abu Had and W. Mellaha while they are represented by successive sequences of lava flows ranging in composition from intermediate to acidic varieties with their related pyroclastics. A wide spectrum of different types of molasses rocks is represented by the Hammamat sediments which have conglomerates, greywakies, purple slate and siltstone. The younger granitic rocks which are considered the most important, from the radioactivity point of view, are classified into syenogranite and alkali feldspar granite varieties and are shown intruding all the rock units exposed in


INTRODUCTION
The study area is located in the northern part of the Eastern Desert of Egypt.It is situated in the Red Sea mountain ridges at about 80 km northwest of Hurghada City between latitudes 27º 30' 00" -27º 45' 00 N and longitudes 32º 50΄ 00˝ -33° 10' 00" E (Fig. 1).It covers an area of about 700 Km² and is mainly covered by Neoproterozoic basement rocks of a relatively rough mountainous topography such as G. Subir (or Zubir) (1398 m.a.s.l.), G. Melaha (1119 m.a.s.l.) , G. Abu Had (763 m.a.s.l.) , and G. Ladid al-ji`dan (1113 m.a.s.l.) and the area is accessible through wadies that drain toward the Red Sea coast which are W. Dib , W. Abu Had, W. Ladid al ji`dan and W. Melaha While W. Um Sitw is a southern branch of W. Dib (Fig. 2).

Fig. 1: Location map of the studied area, North Eastern Desert, Egypt
Remarkable differences in the lithology and structural patterns of the exposed ED basement made Stern and Hedge (1985) and El-Gaby et al. (1988) to subdivide ED into three tectonic provinces: North Eastern Desert (NED), Central Eastern Desert (CED), and South Eastern Desert (SED).The NED province comprises a number of granitic intrusions with some exposures of island arc metavolcanics, metasediments, Dokhan volcanics and Hammamat Molasse sediments.

Fig. 2: Landsat image (TM) of the study area showing main wadies
Many authors have been worked in the area in mapping, field description of the different rock units as well as the petrogenisses and tectonic evoluation of the area.These works include Francis (1971), Francis (1972), El Ramly et al. (1976) and Masoud et al. (1998) for mapping the different rock types in the area and environs and its structure evolution.Garson and Krs (1976), Sabet et al. (1977), Serencsits et al. (1979), El Sheshtawi et al. (1995), Hassanen et al. (1997) and Ghoneim et al. (1999) were interested in studying the ring complex of W. Dib and its evolution and different units constituting it.Mussa and Dardier (1982), Ressetar and Monrad (1983), Ahmed (1983), Heikal and Ahmed (1984), Heikal and Ahmed (1983), Ries et al. (1983) and Ragab (1987) were shed lights on the evolution of the Dokhan Volcanics in the area around G. Abu Had and its different lava flows and pyroclastics as well as the associated Hammamat Sediments.Rabie et al. (1994), Rabie et al. (1996), Hamoudah (1998), Ali (2001), Ahmed and Ali (2003), Ayoub (2003) and Hammad (2005) were caring about the younger granitic rocks from their geochemistry, petrography, radioactivity and hydrothermal activity points of view.

II.
GEOLOGICAL SETTING A geological map at scale 1: 40,000 was prepared for the studied area (Fig. 3).According to the field relationships, the rock types exposed in the studied area can be arranged in the following geologic sequence according to the classification of the basement rocks of Egypt by El Ramly (1972):

Dykes and Veins … (youngest). Younger Granites Hammamat Sedimentary Rocks Dokhan Volcanics Older Granitoids Metagabbros-diorite complex Metavolcanics………... (oldest). II.1 METAVOLCANICS
The metavolcanics and related metavolcaniclastic sediments represent the oldest rocks of the studied area and are recorded in different localities forming highly weathered hills of low topography (Fig. 4).They are intruded by the older granites which carry them as roof-pendant (Fig. 5).These metamorphosed rocks are partially to completely altered due to secondary processes where the most common alteration features are chloritization and epidotization (Fig. 6).
In some localities the metapyroclastics show different grain sizes up to pebble size (Fig. 7).These pebbles are sometimes found as rounded to sub rounded clastics which solidified together forming the meta agglomerate (Fig. 8).It is important to state that the foliation is very clear in the metavolcanics (Fig. 9).In some localities, several dykes and Quartz veins are cutting the metavolcanics (Figs. 10 and 11).

II.2 METAGABBRO-DIORITE COMPLEX
The rocks of the metagabbro represent a major rock unit among the basement complex of Egypt, however several classifications were suggested for the Egyptian gabbroic rocks.Abu El-Ela (1985) stated that the metagabbro of the Eastern Desert of Egypt may be subdivided into ophiolitic metagabbro and metagabbro of island arc.
In the study area, the metagabbros are related to those of the Island Arc type and commonly called metagabbrodiorite complex.These rocks are well exhibited as small isolated and scattered hills at W. Ladid Al Jui'dan and to the south-east of W. Ladid al Ji'dan.They are pale to dark grey in colour, medium to coarse grained, massive and generaly weathered to spheroidal boulders (Figs. 12 and 13).These rocks intrude the metavolcanics and took xenoliths of different shapes and sizes from them.On the other hand they are intruded by the older granitoids and younger granites which send several offshoots into them.The thickness and intensity of these offshoots decrease gradually away from the contact.The microfractures of these rocks are sometimes filled with quartz and feldspar veinlets.
The older granitoids in the study area are well exposed at W. Milaha, and the western part of the area.They are characterized by low to moderate topography, exfoliation and bouldery weathering with characteristic huge bloocks (Fig. 14).
Generally, the older granitoids are represented by the quartz diorite and have grey to pale pink colour, medium to coarse grained and show marked variation in their composition.In some stations, the frequent presence of relics of metavolcanics as xenoliths is a characteristic feature in these rocks (Fig. 15).On the other hand the older granitoids are invaded by the dokhan volcanics and are intruded by the younger granites (Figs.16 and 17).
In some localities, the older granites are invaded by composite dyke which form from both acidic and basic composition in the same location (Fig. 18).In other localities, the older granite is overlain by the metavolcanics as a roof pendant which is resting on them (Fig. 19).affected by low grade metamorphism and alteration processes.The main alteration processes are chloritization and epidotization (Fig. 22).The pyroclastics are predominant than lava flows and are found associated with them.They are highly compact, hard, massive and represented by lapilli tuffs (Fig. 23).

II.5 HAMMAMAT SEDIMENTS
The Hammamat sedimentary rocks in the studied area are exposed at both sides of W. Dib and at the northern side of W. Milaha as scattered masses of low to moderate topography.They are intruded by younger granites and locally intermixing with lava flows of Dokhan volcanics at the base of their sequences, which may be contemporaneous with the deposition of the basal parts of these sediments.
They are slightly metamorphosed and have different colours of light grey, greenish grey, deep green and black (Figs.24 and 25).
Generally these rocks are poorly sorted, compositionally and texturally immature due to their deposition in situ or by a very short distance of transportation and rapid rate of deposition as thick piles in deep basins.They are intercalated with Dokhan volcanics.In some cases these rocks are altered.
The conglomerates are poorly sorted, polymictic, massive and contain rounded to sub-rounded pebbles and cobbles of various rock types, cemented by fine matrix of greyish-green materials.These pebbles and cobbles are provided from the older rocks such as metavolcanics, metagabbros, Dokhan volcanics, older granitoids and reworked fine-grained Hammamat sedimentary rocks.They were subjected to different degrees of deformation as indicated by the development of schistosity in the matrix and elongation, flattening as well as the stretching of the pebbles.The conglomerate beds are ranging in colour from within the conglomerates and greywacke beds.They are grey in colour, fine grained and sometimes exhibit laminations and foliations.The microfractures dark green to greyishgreen depending on the type of rock fragments, composition of the matrix and alteration effects (Fig. 26).The slates are less common and occur as intercalations of these rocks are sometimes filled with quartz and feldspar veinlets (Fig. 27).
The greywackes have grey and greyish green colours depending on their compositions, source rocks and alteration effects.They are massive to slightly foliated, jointed and are intercalated with conglomerate beds.Some of the greywackes are pebbly, in which the grain size is ranging from 1 mm to 5 mm.They usually show graded bedding ranging from pebbly size grading upward to fine grain size (Fig. 28).In some localities, it is found that the younger granite is overlain by the Hammamat sediments with sharp contact as shown in (Fig. 29); this interpreted as they carried them during the ascending process.These granites are the youngest among all the described rock units in the studied area.They intrude the older preexisting rock units with typical sharp intrusive contacts (Fig. 30).
Generally, the younger granites are distinguished by their red to pink colours, massive appearance and by the absence of foliation but exfoliation and jointing are present (Fig. 31).Moreover, the marginal granitic parts are commonly fine grained exhibiting a notable amount of mafic minerals.
These rocks are altered in some parts due to secondary processes.The most common alteration features are hematitization, epidotization, chloritization and kaolinitization, especially, along joint planes (Fig. 32).
In most localities; the studied younger granites are represented by blocky-shaped masses with high topography and relatively high resistance to weathering and erosion.(Fig. 33).They are pink to pinkish white in colour and consist mainly of quartz and potash feldspar and some muscovite (Fig. 34).and Hedge, 1985).
In the study area, these dykes are penetrated and cut all the previously described rock types.They range in thickness from 0.5 m to10 m and extend for several kilometers in length.They run parallel to each other in swarms striking NE-SW to ENE-WSW.
They are arranged from oldest to youngest to three groups: Acidic, intermediate and basic dykes depending on their crosscutting relations (Hassan and Hashad, 1990).

ACIDIC DYKES
In the study area, acidic dykes are mainly represented by granite porphyry, granophyres, rhyolite and dacite dykes.They are generally fine grained, massive, fresh and hard displaying different shapes and various colours including red, reddish pink, buff to pale brown colours and more resistant to erosion than the enclosing rocks forming prominent spines and ridges.They are characterized by their sharp straight contacts with more or less vertical slopes.These dykes follow ENE-WSW direction.Some of them are rejuvenated by magma intrusion forming huge dykes (Figs.35,36 and 37).

META-ANDESITES
The meta-andesites are hard, massive, fine grained and porphyritic rocks.They are dark greyish green in color.
Microscopically, meta-andesites are commonly porphyritic and composed of plagioclase and hornblende phenocrysts embedded in fine-grained groundmass.Opaques are the main accessory minerals while chlorite, epidote and saussurite occur as secondary minerals.Sometimes, this rock type is fractured; some of these fractures are filled with secondary muscovite (Figs. 45,46,47and 48).

OLDER GRANITOIDS
The older granitoids are medium to coarse grained, hypidiomorphic and equigranular rocks.Q-A-P triangle (Streckeisen, 1976) is used for the nomenclature of older granitoids.In the present work, eight thin sections were chosen for modal analysis (table 1).According to the modal classification of Streckeisen (1976), quartz, plagioclase and potash feldspars were recalculated to 100% and plotted in Q-A-P diagram.The older granitoids were plotted within the granodiorite and quartz diorite fields (Fig. 57).Quartz diorites are characterized by low abundance of potash feldspars relative to granodiorites.
These rocks are composed of plagioclase, quartz, potash feldspars, biotite as essential minerals.Zircon, iron oxides and sphene are present as accessory minerals while chlorite and epidote as secondary minerals (Figs. From 58 to 65).

CRYSTAL TUF
They are massive, fine to medium grained and range from reddish grey to grey in colour.Microscopically, they consist of abundant crystals of plagioclase, quartz, biotite, hornblende and iron oxides (Fig. 69).

LITHIC CRYSTAL AGGLOMERATES
They are compact, poorly sorted, coarse grained and grey in colour.Microscopically, these rocks are mainly composed of angular fragments of porphyritic andesite and basalt as well as plagioclase, biotite and iron oxide crystals embedded in a fine grained groundmass.Porphyritic andesite and basalt are highly compacted and commonly cemented by very fine dark grey tuffs.
The fine grained matrix occurs in very thin screen filling the interstitial spaces between the rock fragments.Chlorite, sericite and epidote are found in the cement or associated with andesite as alteration products (Figs.72 and 73).

CRYSTAL AGGLOMERATES
Microscopically, these rocks are mainly composed of euhedral to subhedral crystals of altered plagioclase and hornblende embedded in a fine grained tuffeous groundmass composed of tiny crystals of plagioclase, actinolite, chlorite and iron oxides.

HAMMAMAT SEDIMENTARY ROCKS
Conglomerates and greywackes mainly represent the Hammamat sedimentary rocks at the studied area while siltstones are of limited distribution.In hand specimens, the Hammamat sedimentary rocks are mainly of green to dark grey colors.Some varieties show reddish tint.All Hammamat varieties are ill sorted, but the siltstones are rather sorted than the greywackes.

CONGLOMERATES
Conglomerates are polymictic constituting stretched, sub-rounded pebbly-size rock fragments, usually oriented in definite directions indicating that they were subjected to stress.The spherical pebbles are very rare.The pebbles are mainly represented by metavolcanics (metarhyolite and metabasalt), older granitoids (grandiorite), (Fig. 76) and reworked hammamat sedimentary rocks.The crystal fragments are plagioclase, quartz, perthite, iron oxides, actinolite and chlorite, where these crystals are highly brecciated.The matrix is mainly composed of quartz, plagioclase, iron oxides with subordinate amount of actinolite.The quartz grains commonly show undulose extinction and are corroded by plagioclase, actinolite and iron oxides.Plagioclase shows the lamellar twinning feature.Actinolites are highly chloritized.Sometimes, the matrix contains fragments of fine quartz (Fig. 77).

GREYWACKES
Greywackes are composed of crystals and rock fragments embedded in fine to very fine groundmass with no definite orientation.The crystals are mainly represented by quartz and plagioclase, orthoclase, carbonates and chlorite.Quartz shows undulose extinction and sometimes shows amoeboid shape due to corrosion by the matrix constituents.Plagioclase crystals are usually altered until they lose their identity.The less altered crystals show lamellar twinning.Orthoclase crystals show their simple twinning feature and corrode in the carbonate and quartz crystals.The matrix is mainly composed of clay minerals and iron oxides with subordinate amounts of quartz, feldspars, micas, epidote and chlorite.Carbonates and iron oxides are disseminated all over the rock (Fig. 78 ).The rock fragments are represented by metarhyolite, metaandesite and metabasalt and corrode in each other and by quartz, they have small inclusions of iron oxides and plagioclase.The greywackes are highly cracked and cracks are filled with carbonates, clay minerals and iron oxides (Fig. 79).

PURPLE SLATES
Slates are characterized by its colour varying from purple to violet colour.They are very fine to fine grained, highly fissile and have welldeveloped slaty cleavages.Microscopically, these slates consist of quartz grains in silty and ash size (< 1/64 mm), muscovite, hematite and chlorite forming alternating light fine and dark very fine laminae.The light bands are mainly composed of detrital quartz of silt size having a reddish color in the polarized light.The dark laminae are composed of sericite, chlorite and hematite (Fig. 80).Generally the slates are invaded by calcite veinlet cutting all laminae (Fig. 81 ).
It is worth to mention that, the Hammamat sedimentary rocks have suffered from low-grade regional metamorphism where chlorite and epidote are present at the expense of other silicate minerals.

YOUNGER GRANITES
The younger granites in the study area could be classified into two phases; the first one is of greyish pink colour while the second phase is of red colour.Q-A-P triangle (Streckeisen, 1976) is used for the classification of the younger granites.In the present work, five thin sections were chosen for modal analyses.The results were tabulated in table (2).The greyish pink granites plot within the syenogranite field while the red granites plot within the alkali granite field (Fig. 82) due to very high content of potash feldspar in this phase of younger granites, accordingly this granite could be considered as alkali feldspar granite.

SYENOGRANITES
These rocks are generally equigranular, medium to coarse-grained with hypidiomorphic and graphic textures.They are mainly composed of potash feldspars, quartz and biotite with subordinate amounts of plagioclase as essential minerals.Zircon and iron oxide are the main accessory minerals.Sericite, muscovite and epidote are found as secondary minerals.The presence of two feldspars phases (potash feldspars and plagioclase) suggests that these granites are mostly subsolvus and crystallized under high water vapour pressure (Greenberg, 1981).
Potash feldspars are the most dominant minerals in these rocks.They form 43.65% to 44.7 % of the modal composition (table 2).They are represented by microcline perthites.Microcline perthite occurs as subhedral to euhedral crystals ranging in size from 0.5 to 3.4 mm across..They are often cracked; most of the cracks are filled with iron oxides, muscovite and epidote (Fig. 83).The microcline perthite is restricted to the syenogranite near the contact with alkali feldspar granite.
Quartz is less dominant than potash feldspars.It forms 28.2% to 31.61 % of the modal composition (table 2).It is found as medium to coarse anhedral crystals of various shapes ranging in size from 0.4 to 2.8 mm across (Figs. 84 and 86).
Plagioclase occurs as subhedral to euhedral albite-oligoclase (An 5-20 ) crystals ranging in size from 0.35 to 1.7 mm across.It forms 18.02% to 20.57 % of the modal composition (table 2).Plagioclase crystals are completely altered to sericite.These crystals show the antiperthite texture and are cracked (Fig. 85).

ALKALI FELDSPAR GRANITES
Alkali feldspar granites are generally equigranular, medium to coarse-grained with hypidiomorphic texture.They are composed of potash feldspars, quartz, plagioclase, biotite and muscovite as essential minerals.The main accessory minerals are zircon, epidote and apatite while the main secondary minerals are iron oxides and muscovite.Some samples are mainly composed of potash feldspars and quartz with very few or absence of plagioclase crystals, suggesting transsolvus to hypersolvus texture (Martin and Bonin, 1976).
Quartz is less dominant than potash feldspars where it forms 41.4% to 43.51% of the modal composition (table 2).It occurs as anhedral to subhedral crystals ranging in size from 0.3 to 2.9 mm across.Minute worm-like or fingerlike bodies of quartz form the myrmekitic texture (Figs.87,88 and 90).
Plagioclase occurs as subhedral prismatic crystals ranging in size from 0.4 to 3.4 mm across.It is composed of albite (An 5-10 ) and forms 1.6% to 1.9 % of the modal composition (table 2).They poikilitically enclose quartz and iron oxides, and have clear cracks which are filled with the secondary muscovite mineral (Fig. 89).
Biotite is present in minor amounts as flakes which are brown to yellowish brown in colour, pleochroic and mottled with iron oxides.They are corroded by quartz and perthite to different degrees until some islets are completely separated and surrounded by the other silicate minerals.Some biotite flakes poikilitically enclose iron oxides (Figs.87,88 and 90).
Muscovite occurs as small anhedral flakes growing in the interstitial spaces between silicate minerals.. Also it is encountered as secondary mineral filling the cracks or replacing feldspars.Muscovite flakes are corroded by feldspars and quartz (Fig. 89).From the previous characteristics, it could be concluded that the alkali feldspar granites has the same mineral composition and the same texture of the syenogranite with some differences which could be summarized as follows: 1-The potash feldspars of alkali feldspar granites are highly exceeding the plagioclase.In some samples, plagioclase become very rare or absent.
2-Microcline perthite in alkali feldspar granites is more dominant than orthoclase perthite.Biotite in alkali feldspar granites is found in large amounts.
3-Alkali feldspar granites, generally, show less deformation than the syenogranite.This could be interpreted by the less undulose extinction of quartz and less fracturing of feldspars.

POST GRANITE DYKES
They are classified into three groups: acidic, intermediate and basic dykes.

ACIDIC GRANOPHYRE DYKES
These rocks are hard, massive, fine grained and varying in colour from reddish pink, pink to red colour with smoky quartz grains and manganese dendritic shapes.
Microscopically, they are distinguished by graphic and granophyric textures.They are mainly composed of medium grained quartz, K-feldspars and plagioclase set in a fine grained granophyric, crystalline groundmass displaying micrographic texture.Biotite, muscovite, apatite, carbonates and opaques are accessories, whereas sericite, chlorite and clay minerals are secondary minerals (Figs.91 and 92).

BASIC DOLERITE (DIABASE) DYKES
Basic dykes are fine to very fine grained and melanocratic of grey colour with few white medium grained crystals.
They are medium to fine grained and melanocratic of greenish grey to grey colour.Microscopically, these rocks are characterized by doleritic texture (Fig. 93) and mainly composed of calcic plagioclase, clinopyroxene and hornblende.Apatite and opaques are the main accessory minerals.Chlorite, epidote and saussurite are secondary minerals as alteration products of mafics and feldspars (Figs.93 and 94).

III. RADIOACTIVITY
The emitted natural gamma radiation that transmitted from the rocks is a function of their radioelements content.These radioelements are Uranium, Thorium and Potassium (K 40 ), together with their decay series.Gamma rays are the most fundamental nuclear radiation, which detected because of its penetration ability in various media, as well as its long range.In the Uranium (U) and Thorium (Th) decay series, a number of intermediate isotopes are involved before reaching the steady point.In the Uranium series, the highest energy gamma ray emitter is Bi 214 in the same time the strongest gamma emitter in the Thorium series is the Tl 208 .For these radioelements detection, the measured intensity radiation principally resulted from these two isotopes.The concentration of Uranium and Thorium is proportional to the concentration of 214Bi and 208Tl, respectively, when reaching the state of stability and balance.

IV.1: Radioactivity of the Different Rock Unites
There is a general and marked relation between the age of the rock unit and its radioactivity from one side as well as the relation between the increase of the radioactivity and the increase of the acidity of the rocks (magmatic differentiation).This is to be expected because both U and Th are trace elements incompatible with the major rock-forming minerals.Hassan and Hale (1988) reached the same conclusion from their γ-spectrometric determination of eU, eTh and K in the uraniferous granites and rhyolites of Devonian-Carboniferous age in southern new Brunswick in Canada.So, Radiometric survey is conducted to this area due to the presence of abundant granitic rocks of different types, contacts with other older volcanic rocks and remarkable features of late magmatic pneumatolytic phase and post-magmatic hydrothermal products such as pegmatite and aplite formation and different wall rock alterations associated with these granites.The radioactivity of the different rock types cropping out in the area under consideration were measured for the equivalent uranium (eU) and equivalent thorium (eTh) in part per million (ppm) by using a portable gamma-ray spectrometer (RS-230).Results of the filed radiometric survey measurements and laboratory measurements of the reach up to 482 ppm and K% reaches up to 5.78 % for the anomalous pegmatite samples.

IV.2: RADIOACTIVE ANOMALY IN THE AREA
This anomaly is located at the northern flank of W. Ladid Al Jiudan in alkali feldspar granites.The high gamma-radioactivity is linked to a pegmatite vein of 1.3m width and can be traced clearly for 10 -15meters length extending in nearly N-S direction (Fig. 95) .The granites surrounding the pegmatite vein are nearly nearly alterd with abundant hematitization and Mnoxides and are cut by basic dykes, and veins of quartz with slight hematitic staining on the walls of joints.Radiometric contour map is made for the anomalous pegmatite in W. Ladid Al-Jui'dan (Fig. 96).
The radiometric field measurements of the anomalous zone indicate the presence of elongated and stretched high radioactive zone strongly controlled by the pegmatite vein.The background gamma radioactivity of the alkali feldspar granites near the radioactive anomaly is 350 cps, while the pegmatite vein has a gamma radioactivity up to 3000 cps (table 3).The laboratory measurements for the grab sample which collected from this anomalous zone indicate that the equivalent uranium content equal 115 ppm, while the eTh is 482 ppm which indicates a Thorium Anomaly controlled by these pegmatites.

V. CONCLUSION
A varieties of rocks including metavolcanics, metagabbro-diorite complex, older granitoids, Dokhan volcanics, Hammamat sediments, younger granites as well as dyke swarms and veins are well exposed and studied in details at the strip enclosed between Wadi (W) Dib and W. Mellaha area.The metavolcanics is represented by the basic variety of metabasalt, intermediate variety of meta-andesite and acidic varities of meta-dacite and metarhyolites in addition to metapyroclastics.The metagabbro-diorite complex is shown intruding the metavolcanics and enclave rafts of then while this complex is intruded by both the older and younger granites and maily have the composition of metamorphosed gabbros.The older granitoids in the area are seen extruded by the Dokhan volcanics and are intruded by the younger granites and mainly have the composition of quartz-diorite and granodiorites when plotted on Streckeisen, 1976.
The Dokhan volcanics in the study area are present and exposed at W. Dib, W. Abu Had and W. Mellaha while they are represented by successive sequences of lava flows ranging in composition from intermediate to acidic varieties with their related pyroclastics.A wide spectrum of different types of molasses rocks is represented by the Hammamat sediments which have conglomerates, greywakies and purple slate and siltstone.The younger granitic rocks which are considered the most important, from the radioactivity point of view, are classified into syeno-granite and alkali feldspar granite varieties Streckeisen, 1976, and are shown intruding all the rock units exposed in the area.Numerous post-granitic dyke swarms and veins are recorded as basic and acidic dykes invading and cutting all the rock types exposed in the area.
The radioactivity of the rocks in the study area show an increase in their values from the older unites to the younger one which radioactivity is in harmony with the increase of the radioelement content.The younger granitic rocks show the highest values of radioactivity among the other rock units.An anomalous pegmatite body is located along a tributary branched from W. Mellaha has 157 ppm uranium content and 4350 ppm thorium content and 4.23 K% and is formed at the pnumatulitic stage of the alkali feldspar granites so one can conclude that it is thorium bearing pegmatite rather than uranium bearing pegmatite. IV.

Fig. 3 :
Fig. 3: The Geological Map of the Area between W. El Dib and W. Mellaha

Fig
Fig. 9: displays the foliation in the Metavolcanics

Fig. 19 :
Fig. 19: shows the relation between the metavolcanics and older granite.II.4.DOKHAN VOLCANICS The Dokhan volcanics in the studied area are present at W. Dib ,W.Abu Had and W. Milaha.Generally, they are of moderate relief, very fine grained and grey to greyish pink in colour.The Dokhan volcanics are extrude in the metavolcanics, metagabbros and older granitoids On the other hand, they are intruded by the younger granites which took xenoliths of various shapes and sizes from them.The contact between the Dokhan volcanics and the metavolcanics is not clear due to the similarity of colour between them while the contact with the other rocks is sharp (Figs. 20 and 21).El Gaby (1983) and El Gaby et al. (1984 and 1988) believe that the Dokhan volcanics and Hammamat sedimentary rocks are penecontemporaneous.The Dokhan volcanics are represented by successive sequences of lava flows ranging in composition from intermediate to acidic varieties with their related pyroclastics.The lava flows are

Fig
Fig. 20: displays sharp contact between Younger granites and Dokhan volcanics

Fig
Fig. 24: shows the topography of the Hammamat Sediments comparing to the Younger granites.

Fig
Fig. 30: General view showing the relation between the younger granite and the pre-existing rock units.

Fig. 33 :
Fig. 33: General view of younger granites exposures II.7.PEGMATITES Pegmatites in the study area are granitic in composition.They are very coarse grained and occur as irregular forms and pockets.Some pegmatitic bodies at W. Ladid al-Ji , adan are associated with the younger granites.They are pink to pinkish white in colour and consist mainly of quartz and potash feldspar and some muscovite (Fig.34).

Fig
Fig. 34: shows the pegmatitic body in the younger granites.II.8:POST GRANITE DYKES: All the basement rocks of the NED are dissected by systems of dyke swarms which represent the youngest rock type ranging in age from 589 -543 Ma (Sternand Hedge, 1985).

Fig
Fig. 45: Phenocryst of plagioclase (Pl) corroded by the muscovite (Mu) and shows the porphyritic texture in metaandesite.

Fig
Fig. 63:Chlorite (Ch) containing iron oxide (Ir) as inclusions and is corroded by quartz (Q) in granodiorite.

Fig
Fig. 69: Crystal fragments of the plagioclase (Pl), hornblende (Hb), quartz (Q) and iron oxides (Ir) in crystal tuff.3.4.1.3.LITHIC CRYSTAL TUFFS These rocks are medium grained and consist of both crystal and lithic fragments.The crystal frgments are represnted by plagioclase and muscovite, whereas the lithic fragments are of andesitic and basaltic composition.Andesitic lithic fragments consist of plagioclase, quartz and mafic minerals.The basaltic fragments are composed of plagioclase and biotite set in a fine grained groundmass of the same constituents.These rocks are strongly welded and contain welded glass fragments of ash size (Fig. 70 and 71).

Fig
Fig. 70: Lithic fragments of the basalt and andesite and crystal fragments of the plagioclase (Pl) in lithic crystal tuff.

Fig
Fig. 72: Lithic fragments of the andesite and crystal fragments of plagioclase (Pl) in lithic crystal agglomerates.
albite.It is altered to sericite and epidote and contains inclusions of iron oxides.Hornblende occurs in two generations.The first generation is xenomorphic crystals enclosing relics of iron oxides.The second generation occurs as subhedral to euhedral crystals.Occasionally, the hornblende crystals of the second generation are altered to pale yellow actinolite and bluish green chlorite (Figs.74 and 75).

Fig
Fig. 74: Crystal fragments of altered hornblende (Hb) and plagioclase (Pl) with iron oxide inclusions in crystal agglomerates.

Fig. 83 :
Fig. 83:The growing of quartz (Q) grains on the outer rims of the perthite (Pr) crystal showing the graphic texture with inclusions of iron oxides (Ir) in syenogranite.

Fig
Fig. 84: The perthite crystal is fractured and corroded by the quartz (Q), muscovite (Mu) and iron oxides (Ir) in syenogranite.

Fig. 95 :
Fig. 95: To scale Sketch Map for the Anomalous zone of pegmatite in the Alkali feldspar granites along W. Ladid Al-Jui'dan.