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Eastern Desert (eastern + desert)
Selected AbstractsChemical and Isotopic Constraints on the Origin of Wadi El-Tarfa Ground Water, Eastern Desert, EgyptGROUND WATER, Issue 5 2000M. Sultan We evaluated the use of the renewable ground water resources of the Eastern Desert to develop sustainable agriculture in Upper Egypt, an alternative that could alleviate some of Egypt's dependence on water from the Nile River. Ground water from shallow aquifers in the Eastern Desert of Egypt, near the intersection of Wadi El-Tarfa and the Nile River, was analyzed for chemical compositions, stable isotope ratios, and tritium activities. The ground water has a range in total dissolved solids of 300 to 5000 mg/L. Values of ,D and ,18O range from -10 to +34 %o and -2 to +5.2 %o, respectively, and defines a line having a slope of 5.7 that intersects the meteoric water line at about ,D = -15 %o on a plot of 8D versus ,18O. These findings indicate that the water might have been derived by a combination of evaporation of and salt addition to regional precipitation. Only one sample could have been derived directly by evaporation and transpiration of modern Nile River water. Salinization of the ground water could have occurred through dissolution of marine aerosol dry fallout, carbonate minerals, gypsum, and other trace evaporitic minerals at and near the ground surface. Tritium activities ranged from 0.04 to 12.9 TU (tritium unite), indicating that all but one of the samples were derived at least partly from precipitation that occurred within the last 45 years. These data indicate that Nubian Aquifer paleowater is not a significant component of the shallow aquifers of this portion of the Eastern Desert. The most likely source of this ground water is sporadic flash flood events yielding locally voluminous recharge that accumulates in coarse sediments and fractured rock beneath alluvial channels. The magnitude of this renewable ground water resource and its potential for supporting sustainable agriculture require further investigation. [source] Exhumation during oblique transpression: The Feiran,Solaf region, EgyptJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2009T. S. ABU-ALAM Abstract The Feiran,Solaf metamorphic complex of Sinai, Egypt, is one of the highest grade metamorphic complexes of a series of basement domes that crop out throughout the Arabian-Nubian Shield. In the Eastern Desert of Egypt these basement domes have been interpreted as metamorphic core complexes exhumed in extensional settings. For the Feiran,Solaf complex an interpretation of the exhumation mechanism is difficult to obtain with structural arguments as all of its margins are obliterated by post-tectonic granites. Here, metamorphic methods are used to investigate its tectonic history and show that the complex was characterized by a single metamorphic cycle experiencing peak metamorphism at ,700,750 °C and 7,8 kbar and subsequent isothermal decompression to ,4,5 kbar, followed by near isobaric cooling to 450 °C. Correlation of this metamorphic evolution with the deformation history shows that peak metamorphism occurred prior to the compressive deformation phase D2, while the compressive D2 and D3 deformation occurred during the near isothermal decompression phase of the P,T loop. We interpret the concurrence of decompression of the P,T path and compression by structural shortening as evidence for the Najd fault system exhuming the complex in an oblique transpressive regime. However, final exhumation from ,15 km depth must have occurred due to an unrelated mechanism. [source] Evolution of the Pan-African Wadi Haimur metamorphic sole, Eastern Desert, EgyptJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2000H. Abd El-Naby By comparison with the general features of metamorphic soles (e.g. vertical and lateral extension, metamorphic grade and diagnostic mineral parageneses, deformation and dominant rock types), it is inferred that the amphibolites, metagabbros and hornblendites of the Wadi Um Ghalaga,Wadi Haimur area in the southern part of the Eastern Desert of Egypt represent the metamorphic sole of the Wadi Haimur ophiolite belt. The overlying ultramafic rocks represent overthrusted mantle peridotite. Mineral compositions and thermobarometric studies indicate that the rocks of the metamorphic sole record metamorphic conditions typical of such an environment. The highest P,T conditions (c. 700 °C and 6.5,8.5 kbar) are preserved in clinopyroxene amphibolites and garnet amphibolites from the top of the metamorphic sole, which is exposed in the southern part of the study area. The massive amphibolites and metagabbros further north (Wadi Haimur) represent the basal parts of the sole and show the lowest P,T conditions (450,620 °C and 4.7,7.8 kbar). The sole is the product of dynamothermal metamorphism associated with the tectonic displacement of ultramafic rocks. Heat was derived mainly from the hot overlying mantle peridotites, and an inverted P,T gradient was caused by dynamic shearing during ophiolite emplacement. Sm/Nd dating of whole-rock,metamorphic mineral pairs yields similar ages of c. 630 Ma for clinopyroxene and hornblende, which is interpreted as a lower age limit for ophiolite formation and an upper age limit for metamorphism. A younger Sm/Nd age for a garnet-bearing rock (c. 590 Ma) is interpreted as reflecting a meaningful cooling age close to the metamorphic peak. Hornblende K/Ar ages in the range 570,550 Ma may reflect thermal events during late orogenic granite magmatism. [source] Mineralogical and Geochemical Characterization of Beryl-Bearing Granitoids, Eastern Desert, Egypt: Metallogenic and Exploration ConstraintsRESOURCE GEOLOGY, Issue 2 2009Hamdy M. Abdalla Abstract Mineral chemistry and geochemical characteristics of beryl-bearing granitoids in Eastern Desert of Egypt, were examined in order to identify the metallogenetic processes of the host granitoids. The investigated Be-bearing granitoids and type occurrences are classified into two groups: (i) peraluminous, Ta , Nb + Sn + Be ± W-enriched, Li-albite granite (e.g. Nuweibi and Abu Dabbab); and (ii) metasomatized, Nb >> Ta + Sn + Be ± W ± Mo-enriched alkali feldspar granite (i.e. apogranite; e.g. Homr Akarem, Homr Mikpid and Qash Amir). In these two groups, beryl occurs as stockwork greisen veins, greisen bodies, beryl-bearing cassiterite ± wolframite quartz veins, dissemination, and miarolitic pegmatites. Beryl of the Be-granitoids, particularly those of miarolitic pegmatites, contains appreciable contents of Fe, Na, and H2O. An important feature of the Be-apogranites is the occurrence of white mica as the sole mafic mineral in the unaltered alkali feldspar granite in lower zones. Presence of white mica as volatile-rich pockets suggests that the melt underwent disequilibrium crystallization, rapid nucleation rates, and exsolving and expulsion of volatiles. [source] Alteration Patterns Related to Hydrothermal Gold Mineralizaition in Meta-andesites at Dungash Area, Eastern Desert, EgyptRESOURCE GEOLOGY, Issue 1 2001Hossam A. Helba Abstract: The hydrothermal alteration patterns associating with the gold prospect hosted by metavolcanics in the Dungash area, Eastern Desert of Egypt, were investigated in order to assign their relationship to mineralization. The metavolcanics of andesitic composition are generated by regional metamorphism of greenschist facies superimposed by hydrothermal activity. Epidote and chlorite are metamorphic minerals, whereas sericite, carbonates, and chlorite are hydrothermal alteration minerals. The auriferous quartz vein is of NEE-SWW trend and cuts mainly the andesitic metavolcanics, but sometimes extends to the neighbouring metapyroclastics and metasediments. Quartz-sericite, sericite, carbonate-sericite, and chlorite-sericite constitute four distinctive alteration zones which extend outwards from the mineralized quartz vein. The quartz-sericite and sericite zones are characterized by high contents of SiO2, K2O, Rb, and As, the carbonate-sericite zone is by high contents of CaO, Au, Cu, Cr, Ni, and Y, and the chlorite-sericite zone is by high contents of MgO, Na2O, Zn, Ba, and Co. Gold and sulphide minerals are relatively more abundant in the carbonate-sericite zone followed by the sericite one. The geochemistry of the alteration system was investigated using volume-composition and mass balance calculations. The volume factors obtained for the different alteration zones, mentioned above (being 1.64, 1.19, 1.17, and 1.07, respectively), indicate that replacement had taken place with a volume gain. The mass balance calculations revealed addition of SiO2, K2O, As, Cu, Rb, Ba, Ni, and Y to the system as a whole and subtraction of Fe2O3 from the system. Initial high aK+ and aH+ for the invading fluids is suggested. As the fluids migrated into wallrocks, they became more concentrated in Mg, Ca, and Na with increasing activities of CO2 and S. The calculated loss-gain data are in agreement with the microscopic observations. Breakdown of ferromagnesian minerals and feldspars in the quartz-sericite, sericite, and chlorite-sericite zones accompanied by loss in Mg, Fe, Ca, and Na under acidic conditions and low CO2/H2O ratio may obstruct the formation of carbonates and sulphides, and the precipitation of gold in these zones. The role of metamorphic fluids in the area is expected to be restricted to the liberation of Au and some associated elements from their hosts. [source] Geochemistry and Radioactive Potentiality of Um Naggat Apogranite, Central Eastern Desert, EgyptRESOURCE GEOLOGY, Issue 1 2000AFANDY, Adel H. EL Abstract: The northern part of Um Naggat granite massif (UNGM) has suffered extensive post-magmatic metasomatic reworking which results into the development of (Zr, Hf, Nb, Ta, U, Th, F), and albite-enriched and greisenized apogranite body (UNAP) of 600 m thick, and more than 3 km in the strike length. Albitization produced an enrichment in Zr (av. 2384 ppm), Hf (61), Nb (419), and U (43). The Th/U ratio ranges between 1. 33 and 1. 90. Extreme albitization (i. e. the albitite rock) is characterized by sharp decrease in the rare metals contents. However, extreme greisenization (i. e. endogreisen bodies) is characterized by a considerable enrichment in Zr (av. 5464 ppm), Hf (143), Nb (2329), Ta (152), U (66) and Th (178). The Th/U ratio ranges between 1. 57 and 3. 60. In contrast to extreme greisenization, it seems that extreme albitization does not apparently change the fluid pH and therefore poor amounts of rare metals are localized in the albitites. It is suggested that the presence of Na+, H+ and F - in the ore fluids was essential to stablize complexes of Zr, Hf, Nb, Ta, U, Th, and HREE during extraction and transportation. In contrast, contemporaneous decrease of temperature and increasing pH due to decreasing pressure are considered the essential factors for localization of disseminated mineralization of Zr and Nb in the apical parts of the UNAP. The enhanced uranium content in the alteration facies of UNAP coupled with the absence of significant uranium mineralization may indicate the metalliferous rather than mineralized nature for the UNAP. The high uranium contents are stabilized in refractory accessory minerals. However, with repect to Zr and Nb, the UNAP especially the albitized and greisen facies, can be categorized as a mineralized productive granite. [source] Quaternary paleoenvironments and potential for human exploitation of the Jordan plateau desert interiorGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2005Caroline P. Davies The physical, chemical, numerical, and radiometric analyses of a 31-m sediment core from the Qa'el-Jafr basin provide an important record of Quaternary paleoenvironments for the Jordan Plateau and evidence for several significant changes in climate regime. Cluster and PCA analyses of the geochemical data support the designation of major sedimentation regimes identified by stratigraphic and sediment analyses. Multiple cycles of alluvial deposition, lacustrine units, and erosional unconformities characterize the deepest sediments, followed by a period(s) of intense evaporation. Radiocarbon ages of charcoal in the uppermost 7 m place the aeolian/alluvial phase between 16,030 ± 140 yr B.P. and 24,470 ± 240 yr B.P. Deflation processes may explain the lack of a Holocene sequence. Despite lacking radiometric ages for the lower sediments, the thickness and degree of calcium-carbonate cementation suggest considerable age for the basal sediments, which suggests that a very long terrestrial record of Quaternary climate changes has been preserved in the Jafr basin. This new record of paleoenvironments provides important context to the archaeological record of the Jordan Plateau during the Quaternary. Several archaeological surveys demonstrate extensive human exploitation of lakes and springs of the major wadis along the western margin of the Rift Valley. However, little is known of human exploitation of the desert interiors. Qa'el-Jafr sediments demonstrate significant lacustrine and high moisture phases sufficient for human exploitation of the eastern desert during the Pleistocene. © 2005 Wiley Periodicals, Inc. [source] | ||||||||||