Abd El-Rahman, Y., "A remnant root of a Neoproterozoic island arc in the Northern Eastern Desert of Egypt: Evidence from the whole-rock and amphibole chemistry of the Gattar gabbro", Geochemistry, vol. 82, issue 2, pp. 126113, 2024. AbstractWebsite

The tectonic settings and petrogenesis of Neoproterozoic gabbroic rocks are critical to understand the formation and evolution of the Arabian-Nubian accretionary orogen. We present the whole-rock chemistry and amphibole chemistry of the Gattar gabbro in the northern Eastern Desert of Egypt to better understand the formation of this part of the orogen. The Gattar gabbro is composed of variable proportions of amphibole and plagioclase, which imply the hydrous nature of its parent magma. Trace element patterns of the gabbro and the calculated liquids in equilibrium with its amphibole show enrichment in large ion lithophile elements relative to high field strength elements, which indicate that the Gattar magma formed above a subduction zone. The low abundances of high field strength element in the gabbro are consistent with a depleted mantle source similar to intra-oceanic island arc rocks. However, the high Nb/La ratio of the Gattar gabbro (0.46–10.71) is reminiscent to Nb-enriched mafic rocks from subduction settings. The amphibole chemistry suggests that the hydrous magma of the gabbro crystallized at temperature and pressure estimates of 930 °C and 8 kbar and under oxidizing conditions. The Gattar gabbro is affiliated with the Tonian-Cryogenian arc-related mafic gabbro, which is rarely recorded in this northernmost segment of the Arabian-Nubian orogen. In terms of comparison with the Ediacaran post-orogenic gabbros from the northern Eastern Desert, the Gattar gabbro shows lower concentrations of incompatible elements and Ti/V ratio.

Abd El-Rahman, Y., "Petrogenesis of the late Tonian arc-related Um Balad gabbro-diorite complex (Egypt) and insight into its spatially related orogenic gold mineralization", International Geology Review, vol. 65, issue 1, pp. 89-113, 2023. AbstractWebsite

The gabbro-diorite complex of the Um Balad prospect hosts lode gold mineralization. The complex is dated at 723 ± 4 Ma using the LA-ICP-MS U-Pb zircon method and is correlated with the late Tonian-early Cryogenian subduction-related magmatic stage during the evolution of the Arabian-Nubian Shield. The gabbro-diorite complex evolved through the crystallization of a calc-alkaline magma and the subduction signature of this magma is verified by primitive mantle-normalized trace element patterns that show enrichment in large ion lithophile elements, U, and Th relative to high field strength elements as well as negative Nb and Ti anomalies. The high La/Ybcn (3.1–9.4) and Ta/Yb (0.12–0.41) ratios are consistent with a continental arc rather than an oceanic arc system. Amphibole chemistry indicates that this complex might have crystallized under a moderately oxidizing condition from a hydrous magma (>6 wt% water content) at temperature and pressure estimates of about 800°C and 3 kbar, respectively. Gold mineralization in the Um Balad prospect is confined to structurally controlled massive quartz±carbonate veins and surrounding alteration halos. Alteration in the prospect is represented by localized sericitization and carbonation as well as pervasive chlorite-sericite alteration. The alteration halos are characterized by enrichment in K and Rb and depletion in Ca and Sr compared to their host rocks. The veins of the prospect are related to lower order extensional fractures associated with the regional first order transpressional Najd Fault System. The high Fe contents of the gabbro-diorite complex represent a suitable chemical trap for gold through sulfidation of the host rocks. Supergene alteration resulted in the formation of goethite in association with atacamite and chrysocolla. Free mill gold is associated with these supergene phases, which were deposited in near neutral to slightly alkaline conditions.

Abd El-Rahman, Y., and V. Serneels, "Iron production in Ptolemaic Egypt: From the Abu Gerida specular hematite mines to the Hamama smelting workshop", Geoarchaeology, vol. 37, issue 2, pp. 245-266, 2022. AbstractWebsite

Although ancient Egypt has a firmly established record of mining and metallurgy of gold and copper, iron production in ancient Egypt is less well documented. Evidence of ancient iron manufacture in Egypt is to be found in the burnt plant remains, slag fragments, and a furnace-like structure discovered in the Hamama workshop in the Eastern Desert of Egypt. The iron ore required for iron production was delivered from the nearby specular hematite mines of the Abu Gerida area. This Egyptian specularite is geochemically distinguished from other Mediterranean varieties of specularite such as those in Elba, Tuscany, and Seriphos Island. The bloomery iron smelting process in the Hamama workshop produced two types of slags: furnace slags and tapping slags. These two types show different petrographic features and geochemical signatures. Some of the geochemical signatures of the slags, such as their high calcium contents, were derived from charcoal, while others were related to the ore used during the smelting process. Radiocarbon dating of the charred plant remains from the Hamama workshop suggests that the iron smelting activities took place in the early Ptolemaic era. Iron production was seasonal and was conducted by locals who most likely had dynamic socioeconomic ties with the urban centers of the Nile valley.

Zoheir, B., Y. Abd El-Rahman, T. Kusky, and F. Xiong, "New SIMS zircon U-Pb ages and oxygen isotope data for ophiolite nappes in the Eastern Desert of Egypt: Implications for Gondwana assembly", Gondwana Research, vol. 105, pp. 450-467, 2022. AbstractWebsite

Ophiolite nappes, encompassing dismembered oceanic lithosphere sections, in the Eastern Desert of Egypt are mainly confined to Tonian-Cryogenian inter-terrane sutures. A cohesive geodynamic model of these ophiolites remains elusive in light of the variably obliterated field relationships and lack of ample geochronological information. Available geochemical data of the well-studied ophiolites lead to different interpretations of mid-ocean ridge, back-arc and/or fore-arc affinities. Relevant geochronological data are likewise heterogeneous in terms of methods and the dated lithologic units. Here, we attempt to constrain the timing and genesis of some Eastern Desert ophiolites by using new SIMS zircon U-Pb and oxygen isotope data of gabbros from four different ophiolites.

The new zircon U-Pb ages and oxygen isotope values integrated with available geochemical data constrain ages of 737 ± 6 Ma and 720 ± 6 Ma and fore-arc origin of the Wadi El-Sid and Gabal Abu Dahr-Abu Siayil ophiolites, respectively. The δ18O(Zrn) values of these fore-arc ophiolites (+2.5 to +8.5‰) deviate significantly from primitive mantle values, suggestive of substantial degrees of subduction-induced metasomatism. The Gabal El-Rubshi and Wadi Ghadir back-arc ophiolites returned younger and mutually similar ages (702 ± 5 Ma and 698 ± 4 Ma, respectively) and less heterogeneous δ18O(Zrn) values (+3.1 to +6.1‰). Excluding outliers, most measured δ18O(Zrn) values are indistinguishable from the unaltered MORB values and the restricted mantle-like δ18O range.

Results of the present study suggest multiple arc-fore-arc accretion events and an extensive late Tonian back-arc basin opening event in the evolution of the Eastern Desert accretionary belt. Subduction tectonics continued to stabilize the immature arc crust ∼750–720 Ma and a tapered back-arc spreading ridge engendered at ∼700 Ma. The final terrane accretion and suturing could have been associated with subduction-related melts that circulated and locally metasomatized back-arc ophiolites. This model is in broad agreement with the recently advocated ∼720 Ma plate reorganization in the closure of the Mozambique Ocean during the course of Gondwana assembly.

Abd El-Rahman, Y., "Weathering products at the historic Qulaan gold prospect, Eastern Desert, Egypt: Implication on the mobility and distribution of arsenic, gold and silver", Journal of African Earth Sciences, vol. 182, pp. 104276, 2021. AbstractWebsite

Gold mineralization of the historic Qulaan prospect is hosted in hydrothermally altered rhyolite. A variety of supergene minerals that includes arsenic, gold and silver phases were formed as a consequence of superimposed weathering on primary mineralization hosted in the hydrothermally altered rhyolite at the prospect. The arsenic-bearing phases are represented mainly by arsenic-rich ferric oxyhydroxides and Ca–Fe arsenates (arseniosiderite). Gold occurs in the form of native platelet and irregular grains that are commonly associated with ferric oxyhydroxide, while the Ag-phase, represented by iodargyrite, occurs in sericite-rich cavities. The formation of these minerals is related to oxidation of primary arsenian pyrite during the weathering process. Although pyrite oxidation results in an acidic condition, the presence of arseniosiderite as well as iodargyrite and the association between ferric oxyhydroxide and gold indicate an increase in the pH during the weathering process. Relict feldspar as well as hydrothermal chlorite and calcite in the host rocks are responsible for neutralizing the earlier acidic condition during the weathering of rhyolite.

, "Ediacaran Sedimentary Rocks “so-called Hammamat” of the Egyptian Shield", The Geology of the Egyptian Nubian Shield: o Springer Nature Switzerland AG, 2021. Abstract

Ediacaran sedimentary rocks are widely distributed in the central and northern segments of the Eastern Desert of Egypt and in Sinai. These sedimentary rocks are considered syn- and/or post-orogenic molasse-type deposits that were accumulated in either foreland basins and in intramontane basins related probably to Najd strike-slip fault system. Ediacaran sedimentary rocks are commonly referred to as “Hammamat Sediments,” after the well-exposed historic exposure of such immature sediments at the Hammamat area in the central Eastern Desert. Ediacaran sedimentary rocks from other areas from the Eastern Desert and Sinai are different from the one described in Hammamat in terms of composition, tectonic setting, and rocks association and provenance of the sediments as delineated by recent work detrital zircon. In the central Eastern Desert, Ediacaran sedimentary rocks from Igla basin are characterized by its red color compared to the one in the Hammamat area, while the Ediacaran sedimentary rocks of the Kariem basin were deposited in intramontane strike-slip-related, while the equivalent sediments of the Hammamat area were deposited in a foreland setting. Unlike the Ediacaran sedimentary rocks of the central Eastern Desert of Egypt, the one in the northern segment of the Eastern Desert and in Sinai are commonly intercalated with volcanic rocks. However, the detrital zircon age patterns for the Ediacaran sedimentary rocks from the northern Eastern Desert and Sinai are different, which support the isolated nature of the Ediacaran basins. The deposition of the Ediacaran sedimentary rocks in isolated basins is not consistent with considering the Wadi Hammamat area as the type locality of these sedimentary rocks and so identifies them as “Hammamat Sediments.” The Ediacaran sedimentary rocks from each basin are expected to have unique features, which may be obscured by just identify these sediments as “Hammamat Sediments.”

, "Stream sediment geochemical survey of rare elements in an arid region of the Hamadat area, central Eastern Desert, Egypt", Ore Geology Reviews, vol. 117, pp. 103287, 2020. AbstractWebsite

The present work deals with the possibility of conducting orientated geochemical survey exploration in an arid area using stream sediments. These sediments were drained from the Neoproterozoic metavolcanic and granitic rocks of the Hamadat area, Egypt. The fine size fraction of <63 µm, which is most appropriate for the exploration in the arid desert conditions, has been considered. Fourty four samples, including 35 clay and silt fractions and three size fractions of three samples, were analyzed by ICP-MS for major and trace elements. The heavy mineral content was separated from the stream sediments and identified. Based on the geochemical and mineralogical features, the catchment area of the studied stream sediments is split into two primary domains: namely first and second. The first domain drains monzogranite and associated pegmatite and quartz veins, whereas the second domain drains a metasomatized riebeckite granite. The stream sediments of the first domain are enriched in LREE (and ΣREE), Th, Zr and Hf, whereas the second domain has a clear signature of Nb, Ta, Th, U, Y and HREE. These rare metals are predominantly accommodated in the structure of detrital minerals representative of the clastic aureole around the source rocks and are absorbed to a lesser extent. The obtained data are utilized for constructing high-resolution geochemical maps to show the distribution of different rare metals. The anomaly aureoles have been delineated for Y, Yb, Nb, Th and U on a base map of the catchment area. The distribution maps propose possible potential mineralization of rare metals, especially REE, Nb, Ta, Zr, and Hf, in the study area. The HREE + Y appear to be prospective in the second domain, whereas Th, Zr and LREE are possible resources in the first domain. Further studies to authenticate the potentiality of these resources are strongly recommended.

, The Geology of Egypt, , Chapm, Springer Nature Switzerland AG, 2020. AbstractWebsite

This richly illustrated book offers a concise overview of the geology of Egypt in the context of the geology of the Arab Region and Northeast Africa. An introductory chapter on history of geological research in Egypt sheds much light on the stages before and after the establishment of Egyptian Geological Survey (the second oldest geological survey worldwide), Hume's book and Said's 1962, 1990 books. The book starts with the Precambrian geology of Egypt, in terms of lithostratigraphy and classifications, structural and tectonic framework, crustal evolution and metamorphic belts. A dedicated chapter discusses the Paleozoic-Mesozoic-Cenozoic tectonics and structural evolution of Egypt. A chapter highlights the Red Sea tectonics and the Gulf of Suez and Gulf of Aqaba Rifts. Subsequent chapters address the Phanerozoic geology from Paleozoic to Quaternary. The Egyptian Impact Crater(s) and Meteorites are dealt with in a separate chapter. The Earth resources in Egypt, including metallic and non-metallic ore deposits, hydrocarbon and water resources, are given much more attention throughout four chapters. The last chapter addresses the seismicity, seismotectonics and neotectonics of Egypt.

, "Not all Neoproterozoic iron formations are glaciogenic: Sturtian-aged non-Rapitan exhalative iron formations from the Arabian–Nubian Shield", Mineralium Deposita, vol. 55, pp. 577-596, 2020. AbstractWebsite

Neoproterozoic iron formations are exposed in the Wadi Hamama area (Egypt) in the northwestern part of the Arabian–Nubian Shield. Mafic and felsic volcanic and volcaniclastic rocks of an intra-oceanic island-arc setting host multiple, thin iron-formation units. Major element compositions of the iron formation confirm a low detrital input, whereas the rare-earth elements and Y data suggest deposition related to an influx of low-temperature hydrothermal fluids. Unlike most Neoproterozoic banded iron formations, but similar to other iron-formation occurrences from the Arabian–Nubian Shield, the Nd isotopic compositions of the Wadi Hamama iron formations are predominantly mantle-like. SIMS U–Pb zircon ages of the host volcaniclastic units indicate that the age of iron-formation deposition is ca. 695 Ma, which is within the Sturtian epoch that is presumed to be a glacial event of global extent. Nevertheless, there is no robust evidence of any influence of Sturtian glaciation in the Arabian–Nubian Shield. Our results rather suggest that the iron formations in the area may have formed as low-temperature exhalites on the floor of an island-arc basin. The iron formations were deposited during periods of volcanic quiescence, with metals having been derived during low-temperature pervasive hydrothermal alteration of volcanic and volcaniclastic rocks exposed at the seafloor–seawater interface. Precipitation took place due to mixing of metal-bearing hydrothermal fluids and cold, oxygenated seawater. There is no need to invoke possible effects of global glaciation to explain the origin of the Sturtian-aged iron formations in the shield. Our study thus suggests that not all Neoproterozoic iron formations are necessarily linked to glacial events as the Hamama deposit represents a non-Rapitan exhalative iron formation.

, "Origin of chert within the Turonian carbonates of Abu Roash Formation, Abu Roash area, Egypt: Field, petrographic, and geochemical perspectives", Geological Journal, vol. 55, pp. 2805-2833, 2020. AbstractWebsite

This paper tries to elucidate the origin of the siliceous rocks (cherts) within the Turonian flint-bearing chalky limestone member of Abu Roash Formation, Abu Roash area, north Western Desert, Egypt. Understanding the formation mechanism of the studied chert was gained through field and petrographic investigations, supplemented by geochemical analyses of both cherts and host Turonian carbonates. The field observations reveal that the chert is found in two forms: banded and nodular. The microscopic investigation determined that the cherts exhibit two types of silica: replacive silica (cryptocrystalline and microcrystalline quartz) and silica cement (length-fast chalcedony and megaquartz). The chert texture corroborates that the examined authigenic silica was formed diagenetically by the replacement and void-filling of the host carbonate rocks. The silica was most likely derived from the biogenic opal-A of the siliceous radiolarian tests. The silica-phase transformation started with the dissolution of the biogenic opal-A and precipitation of opal-CT. Subsequently, opal-CT was recrystallized into crypto- and microquartz at low pH and high temperature. The length-fast chalcedony and megaquartz occur later as infill to the cavities and pore spaces. The formation of chert is interpreted to be a result of mixing marine–meteoric waters. The effect of the freshwater diagenesis on carbonates is manifested by the dissolution of the allochems, precipitation of granular, drusy, and blocky calcite (meteoric cements), aggrading neomorphism of matrix, and calcitization of the skeletal particles. Geochemical analyses of the host carbonates indicate nearly flat REE patterns and absence of a negative Ce anomaly. This confirms the deviation from the typical seawater and supports the effect of phreatic meteoric water in the chert formation. The paragenetic relationships reveal that the chertification process was performed after dolomitization and before the carbonate meteoric cementation.

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