Mohamed Hamdy

Tanta University, Geology, Faculty Member

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Papers by Mohamed Hamdy

Cr-spinel records metasomatism not petrogenesis of mantle rocks

Nature Communications, 2019

Mantle melts provide a window on processes related to global plate tectonics. The composition of ... more Mantle melts provide a window on processes related to global plate tectonics. The composition of chromian spinel (Cr-spinel) from mafic-ultramafic rocks has been widely used for tracing the geotectonic environments, the degree of mantle melting and the rate of mid-ocean ridge spreading. The assumption is that Cr-spinel's core composition (Cr# = Cr/(Cr + Al)) is homogenous, insensitive to post-formation modification and therefore a robust pet-rogenetic indicator. However, we demonstrate that the composition of Cr-spinel can be modified by fluid/melt-rock interactions in both sub-arc and sub-mid oceanic mantle. Metasomatism can produce Al-Cr heterogeneity in Cr-spinel that lowers the Cr/Al ratio, and therefore modifies the Cr#, making Cr# ineffective as a geotectonic and mantle melting indicator. Our analysis also demonstrates that Cr-spinel is a potential sink for fluid-mobile elements, especially in subduction zone environments. The heterogeneity of Cr# in Cr-spinel can, therefore, be used as an excellent tracer for metasomatic processes.

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Origin of dyke swarms in Wadi El Redi-Wadi Lahami area, southern Eastern Desert of Egypt

by Mohamed Hamdy and Mohamed Abd El-Wahed

Dykes predominate within the Neoproterozoic

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Garnierite-bearing serpentinite from the Central Eastern Desert of Egypt: A signature of paleo-weathering in the Arabian Nubian Shield?

by Mohamed Hamdy and Mohamed Abd El-Wahed

This paper records the garnierite in Wadi Dubur Neoproterozoic serpentinites from the Central Eas... more This paper records the garnierite in Wadi Dubur Neoproterozoic serpentinites from the Central Eastern Desert of Egypt. Garnierite (Ni-Mg hydrous silicates) occurs in two types (Type I and Type II) of infillings in the weathered serpentinite that was displaced sinisterly by NNW-SSE trending strike-slip faulting and dextrally with NE-trending shearing. All recognized garnierites are serpentine-likes (népouite/pecoraite) existing in mixtures with the hosting serpentines. The Type I garnierite is Fe-richer [Mg0.26-0.71 Ni1.22-1.79 Fe1.28-3.05 Al 0.0-0.02 Si1.11-1.73 O5(OH)4] showing zoning in a collomorph texture, while the Type II garnierite is homogenous with more Si and Mg [Mg0.54-0.94 Ni1.38-2.04 Fe0.38-1.29 Al 0.0-0.01 Si1.66-2.10 O5(OH)4]. Raman spectra indicate that the substitution of Ni for Fe formed a poorly crystalline goethite. The serpentinization of the Dubur peridotite protolith and the associated alteration of chromite and Ni-sulfides were important for the early individualization of Ni. It is proposed that the unweathered serpentinites represent the bedrock, while the altered garnierite-bearing ones represent the saprock. The early weathering of serpentinites contemporaneous with a faulting activation caused in situ precipitation of Ni and Fe in veins (Type I garnierite). With the faulting repetition and progressive alteration maintenance Ni, Si and Mg were transferred to the percolating meteoric solutions, and moved downward through the weathering profile precipitating the Type II garnierite in gouges. Although the studied Ni-rich rocks represent a narrow mineralogical occurrence, they are remnants of a former lateritic regolith mostly probably formed by tropical or sub-tropical weathering during Cretaceous at the expense of Wadi Dubur Neoproterozoic serpentinites. The formed regolith has been subsequently largely eroded, buried and recently exhumed in arid climate.

Gamal eldien et al., 2015-acgs12308_16(1).pdf

Neoproterozoic ophiolitic Serpentinites are common in the Arabian-Nubian Shield (ANS) of the East... more Neoproterozoic ophiolitic Serpentinites are common in the Arabian-Nubian Shield (ANS) of the Eastern Desert (ED) of Egypt, which were formed in arc stage in different tectonic setting. Thus they might subject to exchange with the crustal material derived from recycling subducting oceanic lithosphere. This caused metasomatism enriching the rocks in incompatible elements and forming nonresidual minerals. Herein, we present detailed mineral chemical and geochemical investigation of four ophiolitic serpentinite masses (from W. Mubarak, G. El-Maiyit, W.

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Garnet hornblendite in the Meatiq Core Complex, Central Eastern Desert of Egypt: Implications for crustal thickening preceding the 600 Ma extensional regime in the Arabian-Nubian Shield

by Mohamed Hamdy and Mohamed Abd El-Wahed

Dike-like bodies of garnet (Py 77.04–84.66) hornblendites were recorded, for the first time, in t... more Dike-like bodies of garnet (Py 77.04–84.66) hornblendites were recorded, for the first time, in the structurally lowest parts of the gneiss of Meatiq Core Complex in the Central Eastern Desert of Egypt. They are composed mainly of hornblende (pargasite to pargasitic hornblende), [depleted in LREE with flat HREE segments (normalized to CI-chondrite), and enriched in LILE (normalized to N-MORB)] and crystallized from sub-arc tholeiitic melt that derived from wet mantle wedge (615–600 Ma ago), at P = 23–27 kbar and T = 510–600 °C. Diapirism of hot mantle due to decompression caused partial dehydration melting (P = $12 kbar and T = 800–>1100 °C) of hornblende into pyrope-almandine garnet and diopside (Wo 49– 51 En 32–34 Fs 16–17.5). The clockwise P-T path continued by isothermal decomposition (10–11 kbar) of garnet into hercynite-rich spinel (XFe 2+ = 0.46–0.64) and quartz. By continuous cooling and probably by introduction of the Abu Ziran granite-related solutions, the hornblendites followed a retrograde greenschist facies hydration path, including transformation of diopside to tremolite (T = 280–420 °C and pressure > 5 kb) and garnet to chlorite (T = 190–345 °C). In addition, metasomatic minerals mainly of feld-spars and titanite, and minor ilmenite, rutile, topaz and calcite formed, as well as composition of the original amphibole changed having increases of FeO, TiO 2 and K 2 O and decreases of Al 2 O 3 , MgO and Na 2 O. Deep source of the Meatiq hornblendites implies for a probable local crustal thickening of Meatiq Core Complex by crustal shortening, while their exhumation was most probably accompanied the NW-SE extension and thinning of the previously thickened crust that occurred during oblique island arc convergence with the closure of the Mozambique ocean and the collision of East and West Gondwanaland.

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Neoproterozoic serpentinites from the Eastern Desert of Egypt: Insights into Neoproterozoic mantle geodynamics and processes beneath the Arabian-Nubian Shield

The assembly and disruption of Gondwana supercontinent involve several complex processes that ind... more The assembly and disruption of Gondwana supercontinent involve several complex processes that induce major changes in chemical structures of the Arabian-Nubian Shield mantle reservoir. These processes include melting, depletion and metasomatic refertilization of the upper mantle peridotites. The geody-namic evolution of these processes is addressed based on petrological, mineral chemistry and geochem-ical data from a selected set of ophiolitic serpentinized peridotites from the Eastern Desert of Egypt (G. El-Maiyit, Um El-Saneyat and W. Atalla). The examined rocks represent mantle residual harzburgites after different degrees of partial melting. The most intact Cr-spinel cores and whole-rock trace and rare earth elements data show that mantle protoliths of the studied peridotites underwent different partial melting degrees of $23% to 35% (G. El-Maiyit rocks), $15% to 20% (Um El-Saneyat rocks) and $18% to 25% (W. Atalla rocks). The variations of partial melting degrees between different areas suggested mantle hetero-geneity beneath the Arabian-Nubian Shield. The melt extraction took place under oxidizing conditions. All the studied samples are enriched in light rare earth elements (LREEs) relative to the middle (MREEs) and the heavy (HREEs) which is attributed most probably to induction of serpentinization-related hydrothermal fluids. The data conclude that the studied peridotites have different tectonic settings , including the forearc for G. El-Maiyit, mid-ocean ridge for Um El-Saneyat and mid-ocean ridge-arc transition setting for W. Atalla. The coexistence of the mid-ocean ridge peridotites with those of the supra-subduction zone reflects the transitional evolutionary history of the Neoproterozoic Mozambican oceanic lithosphere beneath the Eastern Desert of Egypt. A similar geodynamic evolution is recognized for the Mesozoic ophiolitic mantle peridotites which concludes that the construction of the Neoproterozoic mantle in the Eastern Desert of Egypt is might be similar to those of the younger age.

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Al-compositional variation in ophiolitic chromitites from the south Eastern Desert of Egypt: Petrogenetic implications

Journal of Mining and Geology, Oct 1, 2011

Eastern Desert of Egypt. The composition of chromian spinel in most of the studied chromitite sam... more Eastern Desert of Egypt. The composition of chromian spinel in most of the studied chromitite samples has not changed significantly from its magmatic composition. However, the fractured and disseminated-textured ores were slightly metamorphosed under the lower greenschist facies (AR) to the transitional greenschist-amphibolite facies (MG). Alteration is recorded in individual chromite grains in the form of optical and chemical zoning. Core to rim chemical trends are expressed by MgOand Al 2 O 3 -decrease, mainly compensated by FeO and Cr 2 O 3 increases. The unaltered chromian spinel in these bodies displays a large range of Al estimating Cr# (Cr/Cr + Al) atomic ratio from 0.57 to 0.89. In AR chromitite, the Al-richer chromite interstitially occurs within the Al-poorer one, whereas in MG chromitite the variation of Al is between massifs. The calculated compositions of melts in equilibrium with chromian spinel of Al-richer and Al-poorer chromites are island arc low-Ti tholeiites and boninites, respectively. The formation of high-Cr chromitites is interpreted as a result of the extensive reaction of harzburgite with migrating island arc tholeiite melts of boninitic affinity. Melt-rock reaction produced boninitic melts and porous dunitic channels in which the mixing/mingling of melts promoted crystallization of monomineralic high-Cr chromian spinel. The presence of Al-richer chromite interstitially in the Al-poorer chromite in the AR ore was most probably due to metasomatism by Al-rich melts, which may be related to the intrusion of the Al-rich websterite. In MG, on the other hand, the wide distribution of Al in chromitites in small district most probably reflects temporal and/or spatial variations in the types of melt (boninitic and tholeiitic) that were generated from, and emplaced in, subarc mantle domains in a supra-subduction zone environment.

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Origin of Magnesite Veins in Serpentinites from Mount El-Rubshi and Mount El-Maiyit, Eastern Desert, Egypt

Serpentinite-hosted magnesite veins have been studied in Mt. El-Rubshi and Mt. El- Maiyit, Easter... more Serpentinite-hosted magnesite veins have been studied in Mt. El-Rubshi and Mt. El- Maiyit, Eastern Desert, Egypt, in order to elucidate the origin of this type of ore. The studied cryptocrystalline magnesite veins were formed as the fracture fillings from ascending CO2-rich hydrothermal solutions. These solutions were brought from deeper- seated horizons upwards to a shallower zone, where due to the decrease of partial pressure of carbon dioxide the supersaturation of the hydrothermal fluids took place causing the deposition of magnesite, most likely at temperature below 300ºC.

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Thermodynamic constraints on metamorphism of ultramafic rocks from different tectonic settings at Gebel Arais and Gebel Malo Grim, Eastern Desert, Egypt

Petrology and Geochemistry of ultramafic rocks from Wadi Alam, South Eastern Desert of Egypt: evidences for two Neoproterozoic mantle reservoirs?

Ultramafic rocks of the Neoproterozoic age are common in the Eastern Desert of Egypt. These rocks... more Ultramafic rocks of the Neoproterozoic age are common in the Eastern Desert of Egypt. These rocks are commonly considered as a part of the widely distributed dismembered ophiolite sequence. The studied ultramafic rocks from Wadi Alam are classified into two main domains: mantle slices and non-slice ultramafics with intrusive nature. The non-slice ultramafics are observed within the mantle slices. Petrological and geochemical studies of the Neo-proterozoic ultramafic rocks from wadi Alam in the South Eastern Desert of Egypt provided new evidences for possibility of two Neoproterozoic mantle reservoirs. The serpentinized ultramafic mantle slices have harzburgite composition. They underwent melting with 23.4 to 24% melt extraction. Following the melting, rocks suffered cryptic mantle metasomatism, including chemical enrichment of the incompatible elements (LILEs, HFSEs and LREE) relative to the primitive mantle compositions. Metasomatism in the mantle reservoir of the studied rocks too...

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Mantle spinel peridotites beneath the Arabian Nubian Shield (ANS) in the Eastern Desert (ED) of E... more Mantle spinel peridotites beneath the Arabian Nubian Shield (ANS) in the Eastern Desert (ED) of Egypt were formed in arc stage in different tectonic setting. Thus they might subject to exchange with the crustal material derived from recycling subducting oceanic lithosphere. This caused metasomatism enriching the rocks in incom-patible elements and forming non-residual minerals. Herein, we present mineral chemical and geochemical data of four ophiolitic mantle slice serpentinized peridotites (W. Mubarak, G. El-Maiyit, W. Um El Saneyat and W. Atalla) widely distributed in the ED. These rocks are highly serpentinized, except some samples from W. Mubarak and Um El-Saneyat, which contain primary olivine (Fo# = 90–92 mol %) and orthopyroxene (En# = 86–92 mol %) relics. They have harzburgite composition. Based on the Cr# and Mg# of the unaltered spinel cores, all rocks formed in oceanic mantle wedge in the fore-arc setting, except those from W. Atalla formed in nascent fore-arc. This impli...

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Metasomatic signatures in Neoproterozoic ophiolitic serpentinites from Wadi Igla, South Eastern Desert of Egypt

The ophiolitic serpentinites in the Wadi Igla area, south Eastern Desert of Egypt, represent a pa... more The ophiolitic serpentinites in the Wadi Igla area, south Eastern Desert of Egypt, represent a part of the widely distributed dismembered Neoproterozoic ophiolites of the Arabian-Nubian Shield (ANS) that formed in arc stage in different tectonic setting. Thus they might subject to exchange with the crustal material derived from recycling subducting oceanic lithosphere. This caused metasomatism enriching the rocks in incompatible elements and forming non-residual minerals. On the basis of mineral chemical and geochemical data, we present new evidences of metasomatic signatures in Wadi Igla serpentinites. These rocks have harzburgite composition. Based on the Cr# and Mg# of the unaltered spinel cores, all rocks formed in oceanic mantle wedge in the fore-arc setting. These rocks are restites formed after partial melting between 23.06-24 %. Melt extraction occurred mainly under oxidizing conditions except a few samples under reducing conditions. As all the studied rocks do not contain m...

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Westward prograding metamorphism in mantle peridotites from the Eastern Desert of Egypt: clues to the subduction polarity of the Arabian Nubian Shield intra-oceanic arc ophiolite

Neoproterozoic arc mantle beneath the Arabian Nubian Shield (ANS) in the Eastern Desert (ED) of E... more Neoproterozoic arc mantle beneath the Arabian Nubian Shield (ANS) in the Eastern Desert (ED) of Egypt exhumed due to intra-oceanic upthrusting are represented mainly by exposed ophiolitic peridotites serpentinized to different degree. Metamorphism is related to the Pan-African collision and the subduction of oceanic lithosphere. However, polarity of the Pan-African intra-oceanic subduction is still questionable. We here trace the variation of the degree of serpentinization and regional metamorphism of six serpentinite masses, widely distributed in the ED (from the east to the west: W (Wadi). Alam, W. Igla, W. Mubarak, G. El-Maiyit, W. Um El Saneyat and W. Atalla). This is based on their mineralogy, textures and mineral chemistry. The studied rocks have harzburgite composition and they all formed in oceanic mantle wedge in the fore-arc setting, except those from W. Atalla that formed in MOR-arc transition setting. Much difference in the degree of serpentinization is obvious among the...

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Al-compositional variation in ophiolitic chromitites from the south Eastern Desert of Egypt: Petrogenetic implications

Journal of Geology and Mining …, 2011

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نتائج أولية لأول تسجيل للذهب واليورانيوم في صخور الرخام بوسط الصحراء الشرقية، مصر: شواهد على تمعدنات مصاحبة ولاحقة للتحول (؟) بالرسوبيات المتحولة

Nascent fore-arc

Zonation of primary haloes of Atud auriferous quartz vein deposit, Central Eastern Desert of Egypt: A potential exploration model targeting for hidden mesothermal gold deposits

Journal of African Earth Sciences, 2015

ABSTRACT The Atud gold mine located in the Neoproterozoic diorite and metagabbro of the Central E... more ABSTRACT The Atud gold mine located in the Neoproterozoic diorite and metagabbro of the Central Eastern Desert of Egypt has been initially excavated during Pharaonic times. Between 1953 and 1969, the Egyptian Geological Survey and Mining Authority performed underground prospection in the auriferous quartz vein and metasomatic alteration zones in the main Atud area, estimating a principal gold lode of 19,000 tones (16.28 g/ton), and 1600 tons of damp (1.24 g/ton). Yet the potentiality of the deposit has not been exhausted. However, for exploration of hidden ore, quantitative characterization using trace elements zoning of mineralization haloes with 280 samples from surface and three underground mining levels is applied. This was through multivariate statistical analysis (Factor analysis) of 11 selected trace elements. Axial (vertical) extents of primary haloes above and beneath gently dipping orebody are also visualized to interpret the level of erosion, determine the direction of mineralizing solutions as well as to examine whether the hidden orebody is promising at the Atud mine.

Multi-element association analysis of stream sediment geochemistry data for predicting gold deposits in south-central Yunnan Province, China

Geochemistry: Exploration, Environment, Analysis, 2006

The use of traditional statistical and new methods of spatial analysis can provide suitable indic... more

Interstratified vermiculite-mica in the gneiss-metapelite-serpentinite rocks at Hafafit area, Southern Eastern Desert, Egypt: from metasomatism to weathering

The Hafafit vermiculite in the Southern Eastern Desert of Egypt at the contact of the metapelite ... more The Hafafit vermiculite in the Southern Eastern Desert of Egypt at the contact of the metapelite and serpentinite rocks with the pegmatites and gneisses of the Hafafit uplift is the only known deposit in the Arabian-Nubian Shield (ANS) rocks of the Eastern Desert (ED). It is distinctively interstratified with mica. The mineralogy and mineral chemistry of this vermiculite at four sites (HV1, HV2, HV3 and HV4) were studied to better understand its origin, which might refers to a specific geologic setting retained to Hafafit area. The vermiculite at Hafafit forms with phlogopite, actinolite-tremolite, asbestos-anthophyllite-talc and talc zones that are arranged from pegmatite and gneisses to the metapelite and serpentinite rocks. These zones were probably formed by metasomatism that related to the intrusion of the granitoid rocks and the connected pegmatites in the upper Pan-African. The XRD and EMPA studies of the interstratified vermiculite-mica concluded that vermiculitization took place through a layer-by-layer transformation of original micas. This formed, in decreasing abundance, mixed-layer phases of biotite/vermiculite (hydrobiotite), phlogopite/vermiculite (hydrophlogopite) and chlorite/vermiculite (corrensite) and discrete phases of vermiculite, chlorite and smectite. A model is suggested, in which chemical weathering by the moving downward meteoric water led to replacement of the interlayer K, in biotite from gneiss and in phlogopite from metasomatic zones, by H2O molecules, Fe2+ was oxidized and (OH)- replaced O2- forming hydrobiotite and hydrophlogopite. By more K remove, Fe was replaced by Mg with the introduction of more layers of H2O molecules leading to formation of the vermiculite. Weathering formed corrensite mixed-layer and chlorite expandable minerals on the expense of chlorite. Formation of the incomplete smectite like layers and Al-hydroxy interlayers (13.97 Ǻ) took place at the expense of vermiculite, replacing the Mg interlayer cations (12.63 Ǻ). Weathering took place mostly by low-pH solutions and in warm environment and the most extensive degree of weathering was at the HV4 site, in which the lode of vermiculite is the biggest. We propose that vermiculitization at Hafafit occurred due to a specific integration between the geologic setting (including rock type and tectonics) of the area and weathering processes producing the only vermiculite deposit in the ANS rocks of the ED of Egypt.

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Pan-African (intraplate and subduction-related?) metasomatism in the Fawakhir ophiolitic serpentinites, Central Eastern Desert of Egypt: Mineralogical and geochemical evidences

Fawakhir serpentinites are the most western ophiolitic ultramafics relative to the Pan-African co... more Fawakhir serpentinites are the most western ophiolitic ultramafics relative to the Pan-African collision suture at the Qift-Quseir road in the central Eastern Desert (ED) of Egypt. Their location is the base for selecting them to examine the possible contribution of the westerly dipping subducted oceanic slab-related melt/fluid with the intraplate granitic intrusion-related melt/fluid in metasomatism of the Neoproterozoic ophiolitic serpentinites in the ED. Non-residual mineralogy and geochemistry of serpentinites (SF1) far from the post-collision A2-type Fawakhir granitoids and those of serpentinites (SF2) in the vicinity of the granitoid pluton were investigated. The Fawakhir serpentinites are harzburgitic in composition and the Cr# (0.66–0.80) and Mg# (0.32–0.50) of their unaltered spinel cores are indicators for their forearc setting, where they were formed in the oceanic mantle wedge. Based on the spinel C# and the whole rock Yb-V bivarite, the melt extraction from the primitive mantle is in excess of 18% up to 24%. The HREE pattern of the SF1 serpentinites refers to the fractional type of melting. Formation of non-residual mineral phases particularly in SF2 samples (amphibole, biotite, apatite thorite and monazite) and the enrichment of all serpentinites in trace incompatible elements (serpentinization is estimated as not governing budget of these elements) refer that these two serpentinite groups underwent modal metasomatism. It is suggested that viscous fluid/melt related to the Fawakhir granitioid emplacement metasomatized the SF2 serpentinites causing strong enrichment in LREE (display concave LREE; LaN/SmN = 3.32–6.25 and U-type HREE; GdN/YbN = 1.14–2.69) and slight enrichment in Zr (12–16.62 ppm and 1.6 × PM) by. All serpentinites are enriched in fluid-mobile elements by aqueous fluids, but the SF2 are more enriched in these elements. The spiked B compared to the other fluid-mobile elements (16.97–24.61 and 42.94–60.66 × PM in SF1 and SF2 samples, respectively) suggest that these elements were added to the obducted ophiolitic Fawakhir serpentinites through interference of subduction-related fluids at shallow depths with mafic melts from which the granitic melts were derived. Contribution of B from shallow-continental crust-related fluids is debated.
Hosting of the Fawakhir serpentinites for the gold deposit at Fawakhir Mine imply a possible genetic relation between gold mineralizations hosted in the ultramafic rocks of the ANS and the processes of recycling of the subducted oceanic slab and the interaction with the mantle. Detailed stable and radiogenic isotopic analyses of the mineralization zones are required to address this question.

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