الفهرس 
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Abstract
Wadi Sabbagh area is situated at southern part of Sinai Peninsula, occupies about 469 Km2, embodied by moderate and high relief mountains of rugged topography such as Gabal Yahmid El Kebly (2274 m), Gabal Sabbagh (2266 m), Gabal Haleifiya (2247m), Gabal Umm Adawi (1740 m), Gabal Gindoll, Gabal Um Ikhlas. Gabal Umm Sulb, Gabal Homra and Gabal Barakat. The area dissected by a number of wadis such as Wadi Lithi, Wadi Abo Sommar, Wadi Gargar, Wadi Umm Adawi, Wadi Yahmid, Wadi Sabbagh, Wadi Haleifiya, Wadi Umm Meter, Wadi Umm Hamatta, Wadi Mahsh and Wadi Gindoll.
The detailed field studies of the exposed rock units revealed that Wadi Sabbagh area is covered mainly by granitoids and metamorphic rocks. According to field observations and relationships between the rock unites, aerial photographs, landsat images as well as petrographic investigations, it can be arranged the rock unites chronologically, beginning with the oldest as metamorphic rocks (gneisses and migmatites & metasediments), older granitoids (tonalite&granodiorite), younger granites (monzogranite, syenogranite and alkaline granite), pegmatites and dykes (microgranite porphyry, granophyre, porphyritic rhyolite, aplite, trachy-andesite, and basalt).
The present work directs to review the geologic setting, mineralogical, petrographic, geochemical and radiometric features of the granitic rocks and accompanying pegmatites exposed at Wadi Sabbagh area, and its environs. The younger granites are the most dominant rock unit exposed in the study area. The exposures of older granitoids are limited comparative to the younger granite. They cover small areas of Wadis Yahmid, Qasab and Qenaia occupying an area of about 23 km2 (about 5 % ) of the surface of the study area.
Two varites of older granitoids are present (tonalite and granodiorite). The tonalite consists of plagioclase, quartz, biotite, hornblende and minor amounts of potash feldspar. Apatite, zircon and opaques take place as accessory minerals while chlorite, kaolinite, epidote and sericite occur as secondary minerals. The granodiorites made principally of plagioclase, quartz, potash feldspar, biotite and hornblende. Apatite, zircon and opaques present as accessory minerals where chlorite and sericite are secondary mineral.
The studied younger granites cover about 93% (~436 Km2) of the land surface of study area. They appear as rather high-elevated mountains forming obvious high relief terrain. They are differentiated into monzogranite, syenogranite and alkaline granite.
The monzogranites occupy the great part of the mapped area, constitute about 55 % (~240 Km2) of the investigated younger granites, outcrops at Wadi Abou Sommar, Wadi Umm Adawi, Wadi Yahmid, Wadi Qasab, Wadi mahash, Wadi Mender and Wadi Lethi. They intrude the older granitoids with sharp contact. Conversely, they are intruded by the syenogranites and the alkaline granites with sharp contacts. They are traversed by many dyke swarms variable in composition from acidic to basic trending NE-SW and NW-SE. The monzogranites consists of plagioclases, K-feldspar and quartz as fundamentally minerals, while biotite and hornblende are the main mafic minerals. It’s considered by higher quartz content (34.7.7 vol. %), plagioclases content (32.8 vol. %) and potash feldspar content (27.5 vol. %). Accessory minerals are mostly represented by titanite, zircon, apatite and opaques. The monzogranites and syenogranites respected as subsolvus granite because they has two separate feldspars.
Both syenogranites and monzogranites are correlated to G.2 granites of (Hussein et al., 1982). They termed as phase III by (Higazy et al., 1992) and (Abd-Allah, 1995). The syenogranites cover about 100 km2 of the land surface representing about 20% (~87 Km2) of the studied younger granites. They invaded by pegmatite pockets and veins. They are expansively fractured, highly jointed and weathered, dissected by intermediate and basic dykes, which intrude the monzogranites with sharp contacts, and composed mainly of potash feldspar (42.7 vol. %), quartz (40 vol. %), plagioclase (14.5 vol. %), biotite and muscovite. Allanite, epidote, titanite, and zircon are the accessory minerals.
The alkaline granites correlated to G.3 granites of (Hussein et al., 1982). This type of younger granites shapes the mountains peaks of Gabal Umm Adawi. They cover about 25 % (~109 Km2) of the study younger granites. They intrude the monzogranites and syenogranites with sharp contact. The alkaline granites constituted principally of perthite, quartz, riebeckite, arfvedsonite, aegirine, acmite, biotite and plagioclase. The accessory minerals are zircon, titanite, monazite and opaques.
The pegmatites broadly distributed in the examine area. They appear as irregular elliptical, rounded pockets and veins of various expansions invading the syenogranites. They are of the simple zoned type beginning by quartz at the central followed by alkali feldspar. The pegmatites consist of alkali feldspar, quartz and plagioclase, while zircon, xenotime and iron oxide are accessories.
The alkaline granites comprise the alkali minerals riebeckite, arfvedsonite and aegirine-augite, so this granite counted as anorogenic granite. Pegmatites give subsolvus texture as they have two separate feldspars. The subsolvus texture and the existence of hydrous minerals such as biotite point to a moderate richness of water through crystallization, and the existence of biotite advises the peraluminous character of studied pegmatites.
The study area is dissected by, numerous felsic and mafic dykes. These dykes vary in size from few meters to hundreds of meters striking N-S, NNE-SSW, NE-SW and E-W. The felsic dykes are represented by micrpgranite porphyry, granophyre, porphyritic rhyolite and aplite with N-S and NNE-SSW predominant trends. The mafic dykes are mostly basaltic in composition acquiring commonly NE-SW and E-W directions.
The studied older granitoids are respected as I-type granites because they have overdominance of plagioclase feldspars than potash feldspars, accordingly they give high Na/K ratio, along with, the presence of brownish green hornblende and brownish grass biotite. They resulting from hydrous magma so indicated by the presence of hydrous minerals for instance hornblende and biotite.
Geochemically, the studied older and younger granites show a small gap in the differentiation index (D.I.). In addition, D.I. of the younger granites proposes that they originated from highly differentiated magma origin, while the older granitoids are relatively less differentiated.
The older granitoids have higher value of the total iron oxide due to the high percentage of ferromagnesian minerals (hornblende and biotite), while the younger granites have a high percentage of Na2O and K2O contents that indicate enrichment in K-feldspars.
The absence of normative corundum in all older granitoids indicates metaluminous nature. On the other hand, the normative corundum in the younger granites is recorded in two monzogranite (av. =0.4%), two syenogranite (av. =0.1%) and four alkaline granite samples (av. =0.5%). This reflects their peraluminous nature, whereas the rest of the younger granite samples have no normative corundum (metaluminous nature)
Harker’s variation diagrams of the studied granites revealed that the contents of TiO2, Al2O3, FeOt, MgO and CaO decrease, while K2O contents increase with increasing the SiO2 content. This suggests a magmatic differentiation during the evolution of the studied rocks.
The plot of trace elements versus SiO2 of the studied granitoids shows that there is a recognizable silica gab between the older granitoids (tonalite and granodiorite) and the younger granites (monzogranite, syenogranite and alkaline granite), reflecting that, the two types of granites are different in their magmatic sources.
Values of both felsic and mafic indices show that older granitoids fall in the intermediate differentiation zone, whereas the younger granites fall in acidic and strong acidic differentiation zones. The older granitoids lie mostly in the tonalite and granodiorite fields, while the younger granites plot in the granite field. Data points of older and younger granites revealed that the former affected by a calc-alkaline character then the younger granites affected by alkaline affinity.
The different tectonic diagrams suggest the emplacement of the older granitoids during pre-plate collision tectonic formed in a volcanic-arc setting, whereas the younger granites indicate emplacement during a wide time span ranging from syn-collision to late-orogenic, within-plate and post-orogenic settings. The older granitoids are completely I-type granites originated at depth ≥30 Km, while the younger granites ranging from I-type and A-type granites, originated at depth limits 20-30 Km.
The field and geochemical investigation of the granitic rocks revealed that the monzogranite was subjected to hydrothermal alteration especially along a broad shear zone at Wadi Umm Adawi. Sericitization, hematitization and albitization are the main alteration phenomena. Chloritization and epidotization have lesser effects. In most cases, the observed hydrothermal alterations were accompanied by radioactive mineralization.
The sericitic granites show increase in TiO2, Al2O3, MnO, Na2O, P2O5, L.O.I., Rb, Sr, Y, Zr, Nb, Pb, Ga, Zn, Cu, Ni, V and Cr and decrease in SiO2, Fe2O3, FeO, MgO, CaO, K2O and Ba contents. The albitized granites exhibit an increase in SiO2, TiO2, Al2O3, Fe2O3, MnO, Na2O, P2O5, L.O.I., Rb, Sr, Y, Zr, Nb, Pb, Ga, Zn, Ni, V and Cr and decrease in FeO, MgO, CaO, K2O, Ba and Cu contents. On the other hand, the hematitized granites show enrichement in SiO2, Fe2O3, FeO, MnO, P2O5, L.O.I, Ba, Rb, Y, Zr, Nb, Zn, Cu, Ni, V and Cr and depletion in Al2O3, TiO2, MgO, CaO, Na2O and K2O Sr, Pb, Ga, and Cu contents related to fresh monzogranites.
The average of the REEs in the studied granitic rocks (210.3 ppm for tonalite, 233.3 ppm for granodiorite and 247.3 ppm for monzogranite) is below the average of the worldwide granites (250-270 ppm), whereas the syenogranite (270.6 ppm) and alkaline granite (278.1ppm) averages are relatively higher than the worldwide granites. The older granitoids exhibit fractionated REE patterns and in comparison with the chondrite indicated an enrichment of the LREE compared with the MREE and HREE, this enrichment of LREE-content be related to the presence of allanite and apatite. The older granitoids display positive Eu anomaly.
Most monzogranites and syenogranites have a relatively smooth, LREE enriched, chondrite-normalized REE profiles. Enrichment of the LREE in relation to HREE is probably caused by fractionation of zircon. Small negative Eu anomaly in some monzogranite and syenogranite samples give a sign of more differentiated rock types. The alkaline granites are characterized by slight rnrichement of the LREE relative to MREE and HREE with characterristic strong negative Eu anomalies. The negative Eu anomaly is due to the feldspar fractionation. The association of negative Eu anomaly with low Sr idicates that the feldspar fractionation has played an important role in the evolution of the studied granites.
The LREE/HREE average ratio in pegmatites is 4.78, which mean relative enrichment of HREE and characterized by mild negative Eu anomaly. The relative enrichment of the HREE in interpreted to be due to the presence of some accessory minerals such as xenotime and zircon, which traditioally known as HREE accumulator.
With respect to REEs, the sericitic and the albitized granites show enrichement in Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er and Tm and depletion in La and Lu content. The hematitized granites show enrichement in Ce, Sm, Gd, Tb, Dy, Ho, Er, Tm and Yb and decrease in La, Pr, Nd, Eu, and Lu content.
The field radiometric survey indicates that, the shear zone granites verify the highest values of radioactivity reflecting the role of post-magmatic alteration processes as well as fracturing and joints shearing in the enrichment of radioactivity. Two anomalous zones are recognizable. The first anomaly confind to the pegmatite bodies hosted in syenogranites. The laboratory radiometric measurements of pegmatites revealed that, the eU reachs up to 168 ppm with 117 ppm in the average, while the eTh reachs up to 257 ppm with 175 ppm in the average. The average values of Ra and K are 89 ppm and 1.7 wt percentage, respectively in the characteristic samples of this district; this means that the considered pegmatites are uraniferous. The eTh/eU ratios range from 1.1 to 2.4 with an average 1.6. The second anomaly restricted to the altered monzogranites at Wadi Adawi area, its eU reachs up to 305 ppm with an average of 126 ppm. The eTh reachs up to 382 ppm with an average of 166 ppm. The average values of Ra and K are 60 ppm and 2.93 wt percentage, respectively. The average values eTh/eU ratios in the examined anomalies monzgranites (1.56) and the average of the equilibrium factor P-factor (2.1) indicating addition of uranium. The post magmatic processes could explain the high value of uranium and thorium. Attribute the high eU and eTh contents to the secondary ascending hydrothermal solutions succeed the radioactive mineralizations to accumulation mostly along fractures, faults and shear districts. The variety of the inter-elements relationship recommends that the radioactivity of the concerned rocks most possibly linked to syngenetic and epigenetic foundations. The F-Parameter is a radiometric aspect performance the extent of the alteration of diverse rock units that have conditions of uranium mobilization and accordingly the possibility of U-enrichment, the extent of this parameter (0.54 - 1.91), reveals that the examined rock units show different degrees of alteration.
The considered granitic rocks and pegmatites develop P-Factor (eU/Ra) ratio values more than unity and eU/eTh ratio values exceed than 0.33, this means a state of radioactive disequilibrium attributable to restructuring of uranium. The positive relation between U-Th and the opposite correlation between eU/eTh and eTh proposes the function of magmatic differentiation in radioactivity, this means that radioactivity of the deliberate rocks is mostly controlled by both magmatic and post magmatic processes.
The recognized radioactive minerals in the considered pegmatites are thorite, uranothorite, zircon, fluorite, columbite, samarskite, monazite, xenotime and allanite, whereas thorite, uranothorite, zircon and fluorite are the chief radioactive minerals in the altered altered younger granites. Additional accessory minerals such as ilmenite, magnetite, hematite, pyrite and rutile were found in the studied pegmatites. Hematite, magnetite and pyrite are the foremost accessories accompanying with the radioactive minerals in the altered younger granites.