Mineral chemistry of banded migmatites from Hafafit and Feiran areas, Egypt

The migmatitic rocks exposed in Hafafit and Feiran areas exhibit some migmatitic structures as the banded, agmatic, boudinage and schlieren structures. The dominant type of these structures is the stromatic migmatites. Electron microprobe analyses of plagioclases, biotites and amphiboles from Hafafit and Feiran areas, in the Eastern Desert and Sinai, Egypt, are carried out and the metamorphic conditions are discussed. The present study revealed marked differences in the composition of plagioclases, biotites and amphiboles from Hafafit and Feiran localities. The obtained data indicated that plagioclases of the Feiran migmatites are of andesine and oligoclase composition, and display anorthite content from An₂₀ to An₃₈; whereas the Hafafit migmatites show a wider range of plagioclases from An₁₀ to An₆₀, and therefore plagioclases have labradorite, andesine and oligoclase composition. This may be due to the slow rate of the crystallisation processes. The analyses indicated that biotites of the studied areas are of metamorphic origin showing significant variation in Fe–Mg. It is worth mentioning that biotites from Hafafit migmatites have Mg–biotite composition while that of Feiram migmatites have Fe–biotite composition. High Mg and low Fe contents in biotite suggest higher crystallisation temperature. The composition of amphiboles in Hafafit migmatites is ferro-tschermakitic hornblende, while amphiboles from Feiram migmatites are magnesio-hornblende. High Ti content in the hornblende of Feiran migmatites suggests that they were formed at slightly higher temperatures and lower pressure than the Hafafit migmatites (i.e. Feiram migmatites and Hafafit migmatites were formed at granulite and amphibolite facies, respectively). Discrimination diagrams show that the muscovite is of secondary origin. Moreover, the present study confirmed that these migmatites are mainly formed by metamorphic differentiation via partial melting.     

Hydrodynamic behavior of Kangan gas-capped deep confined aquifer in Iran

The Kangan aquifer (KA) is located beneath the Kangan gas reservoir (KGR), 2,885 m below the ground surface. The gas reservoir formations are classified into nine non-gas reservoir units and eight gas reservoir units based on the porosity, water and gas saturation, lithology, and gas production potential using the logs of 36 production wells. The gas reservoir units are composed of limestone and dolomite, whereas the non-gas reservoir units consist of compacted limestone and dolomite, gypsum and shale. The lithology of KA is the same as KGR with a total dissolved solid of 333,000 mg/l. The source of aquifer water is evaporated seawater. The static pressure on the Gas–Water Contact (GWC) was 244 atm before gas production, but it has continuously decreased during 15 years of gas production, resulting in a 50 m uprising of the GWC and the expansion of KA water and intergranular water inside the gas reservoir. The general flow direction of the KA is toward the northern coast of the Persian Gulf due to the migration of water to the overlying formations via a trust fault. The KA is a gas-capped deep confined aquifer (GCDCA) with special characteristics differing from a shallow confined aquifer. The main characteristics of a GCDCA are unsaturated intergranular water below the confining layers, no direct contact of the water table (GWC) with the confining layers, no vertical flow via the cap rock, permanent uprising of the GWC during gas production, and permanent descend of GWC during water exploitation.     

Rate and budget of blown sand movement along the western bank of Lake Nasser,southern Egypt

Three sets of Landsat? satellite images for the years 1993, 1998, and 2003 show that the sand dunes at the southwestern Desert of Egypt are generally moving towards southeast direction with a mean annual creeping speed over ground attaining 15 m/year. The manual-stickled field measurements show that the net annual extension of the longitudinal dunes in the coastal area is between 4 and 5 m/year, while the inland longitudinal dunes showed a net movement ranging between 5 and 6 m/year. Seasonal variations of drift potential and sand movement refer to a strongly high energy wind desert environment in the spring season, high energy wind desert environment in the summer season, and relatively high to intermediate in the autumn and winter seasons, respectively. The total annual estimated volume of transported sand which falls down into Lake Nasser basin attains 16,225,808 m³ as calculated by Bagnold's equation and quantities of sand collected from the sand traps. Comparing this value with the total volume of Lake Nasser Basin, which attains 120?×?10⁹ m³, we can conclude that the sand sheets or sand accumulations may represent serious natural hazards to Lake Nasser in some locations. However, the sand drifting towards the lake may be obstructed by high contour topography hindrance, and the mean grain size of the sand sheets is bigger than 0.25 mm, which needs high wind velocity more than 4 m/s. In addition, the direction of the prevailing wind is N-NNW to S-SSE, and this direction sometimes is parallel to Lake Nasser in some places according to the meandering of the lake. The total lengths of hazardous areas along the western bank of Lake Nasser, which receive the most amounts of the drifted sands, attain 43.6 km only.     

Origin of Neoproterozoic ophiolitic peridotites in south Eastern Desert, Egypt, constrained from primary mantle mineral chemistry

The ophiolitic peridotites in the Wadi Arais area, south Eastern Desert of Egypt, represent a part of Neoproterozoic ophiolites of the Arabian-Nubian Shield (ANS). We found relics of fresh dunites enveloped by serpentinites that show abundances of bastite after orthopyroxene, reflecting harzburgite protoliths. The bulk-rock chemistry confirmed the harzburgites as the main protoliths. The primary mantle minerals such as orthopyroxene, olivine and chromian spinel in Arais serpentinites are still preserved. The orthopyroxene has high Mg# [=Mg/(Mg + Fe²⁺)], ~0.923 on average. It shows intra-grain chemical homogeneity and contains, on average, 2.28 wt.% A1₂O₃, 0.88 wt.% Cr₂O₃ and 0.53 wt.% CaO, similar to primary orthopyroxenes in modern forearc peridotites. The olivine in harzburgites has lower Fo (93?94.5) than that in dunites (Fo_94.3?Fo_95.9). The Arais olivine is similar in NiO (0.47 wt.% on average) and MnO (0.08 wt.% on average) contents to the mantle olivine in primary peridotites. This olivine is high in Fo content, similar to Mg-rich olivines in ANS ophiolitic harzburgites, because of its residual origin. The chromian spinel, found in harzburgites, shows wide ranges of Cr#s [=Cr/(Cr + Al)], 0.46?0.81 and Mg#s, 0.34?0.67. The chromian spinel in dunites shows an intra-grain chemical homogeneity with high Cr#s (0.82?0.86). The chromian spinels in Arais peridotites are low in TiO₂, 0.05 wt.% and Y_Fe [= Fe³⁺/(Cr + Al + Fe³⁺)], ~0.06 on average. They are similar in chemistry to spinels in forearc peridotites. Their compositions associated with olivine’s Fo suggest that the harzburgites are refractory residues after high-degree partial melting (mainly ~25?30 % partial melting) and dunites are more depleted, similar to highly refractory peridotites recovered from forearcs. This is in accordance with the partial melting (>20 % melt) obtained by the whole-rock Al₂O₃ composition. The Arais peridotites have been possibly formed in a sub-arc setting (mantle wedge), where high degrees of partial melting were available during subduction and closing of the Mozambique Ocean, and emplaced in a forearc basin. Their equilibrium temperature based on olivine?spinel thermometry ranges from 650 to 780 °C, and their oxygen fugacity is high (Δlog ?O₂?=?2.3 to 2.8), which is characteristic of mantle-wedge peridotites. The Arais peridotites are affected by secondary processes forming microinclusions inside the dunitic olivine, abundances of carbonates and talc flakes in serpentinites. These microinclusions have been formed by reaction between trapped fluids and host olivine in a closed system. Lizardite and chrysotile, based on Raman analyses, are the main serpentine minerals with lesser antigorite, indicating that serpentines were possibly formed under retrograde metamorphism during exhumation and near the surface at low T (<400 °C).     

Isotopic composition of some egyptian galena by thermal emission mass spectrometry

Summary The present paper contains some lead isotope analyses on galena specimens occuring in the central part of the Eastern Desert of Egypt. Thermal emission mass spectrometric technique is applied to these analyses. Recent methods of calculations for galena dating are used in determining the geochronological significance of the data. The lead isotopic composition of the samples has revealed the possible existence of two orogenic events accompanied with metallization that took place about 1000 m.y. and 600 m.y. ago.     

Mass spectrometric study of some selected galenas from the Eastern Desert of Egypt

Summary Thermal emission mass spectrometric technique is applied to the determination of the lead isotopic composition of some selected galenas from the Eastern Desert of Egypt. Recent methods of calculations for galena dating are used in determining the geochronological significance of the data. A correlation is made between the data obtained and the modes of occurrences of the deposits to enter any processes that cause their isotopic variations.     

Identifying sources of salinization using hydrochemical and isotopic techniques, Konarsiah, Iran

Konarsiah salt diapir is situated in the Simply Folded Zone of the Zagros Mountain, south Iran. Eight small permanent brine springs emerge from the Konarsiah salt body, with average total dissolved solids of 326.7 g/L. There are numerous brackish to saline springs emerging from the alluvial and karst aquifers adjacent to the diapir. Concerning emergence of Konarsiah diapir in the study area, halite dissolution is the most probable source of salinity in the adjacent aquifers. However, other sources including evaporation and deep brines through deep Mangerak Fault are possible. The water samples of the study area were classified based on their water-type, salinity, and the trend of the ions concentration curves. The result of this classification is in agreement with the hydrogeological setting of the study area. The hydrochemical and isotopic evaluations show that the groundwater samples are the result of mixing of four end members; Gachsaran sulfate water, Sarvak and Asmari carbonate fresh waters, and diapir brine. The molar ratios of Na/Cl, Li/Cl, Br/Cl, and SO₄/Cl; and isotopic signature of the mixed samples justify a groundwater mixing model for the aquifers adjacent to the salt diapir. The share of brine in each adjacent aquifer was calculated using Cl mass balance. In addition, concentrations of 34 trace elements were determined to characterize the diapir brine and to identify the possible tracers of salinity sources in the mixed water samples. B, Mn, Rb, Sr, Cs, Tl, and Te were identified as trace elements evidencing contact of groundwater with the salt diapir.