DrMohamed Khedr | Kafrelsheikh University (original) (raw)
Papers by DrMohamed Khedr
Gondwana Research, 2023
Field geology, geochemical analyses and multi-sensor remotely sensed data of Landsat-8, ASTER and... more Field geology, geochemical analyses and multi-sensor remotely sensed data of Landsat-8, ASTER and
Sentinel-2 were used to detect various types of hydrothermal alteration and sulfide-gold mineralization
in Neoproterozoic metavolcanic and gabbroic rocks from Darhib and El-Beida areas in the South Eastern
Desert (SED) of Egypt. We also used RADAR data of Sentinel-1 using PCI Geomatica software to decipher
the structural lineaments that control this mineralization. Different styles of disseminated to massive sulfide
deposits include: 1) undeformed magmatic disseminated ores in Darhib gabbros, metavolcanic rocks
and metabasic dykes; 2) deformed (remobilized) massive ores mostly of a magmatic-hydrothermal origin
in Darhib tremolite talc rocks along E-W shear zones; 3) hydrothermal sulfide ores along El-Beida NW–SE
shear zones. Cu-Zn massive ores represent the main sulfides in the Darhib silicified tremolite-talc rocks
and meta-andesites, and occur as bands, veins and patches along Darhib E-W shear zones. Discontinuous
occurrences of sulfide ores-bearing tremolite-talc rocks indicate that major shear zones act as structural
controls on mineralization. Sulfide ores consist chiefly of chalcopyrite, sphalerite, pyrite and galena as
well as minor covellite and bornite. These ores are highly concentrated along E-W striking Darhib shear
zones and resulted from granite-derived hydrothermal fluids that form/and or accumulate sulfide minerals
from the sulfide-bearing metavolcanic rocks around shear zones. Two stages of hydrothermal alterations
are recorded in the Darhib talc mine including pre- (talcification, amphibolitization and
carbonatization) and syn- (silicification and chloritization) sulfide ore alterations. Disseminated sulfide
mineralization hosted in Darhib gabbros, metavolcanic rocks and metabasic dykes is of a magmatic origin,
similar to Cu-Ni sulfide deposits hosted in gabbroic varieties in worldwide mafic–ultramafic intrusions.
On the other hand, El-Beida gold-sulfide-bearing quartz and quartz carbonate veins are hosted
in ferruginated and silicified metavolcanics/ metavolcaniclastic rocks along NW–SE shear zones (Najd
Fault System trend). These are spatially associated with regional convergent structures (high-angle convergent
wrench structures), suggesting orogenic gold type mineralization. The E-W with minor WNWESE
shear zones in Darhib and NW-SE trending shear zones in El- Beida structurally controlled sulfides
and gold mineralization in the SED of Egypt. El-Beida sulfide mineralization occurs as disseminated ores
that consist mainly of pyrite, chalcopyrite, covelite and chalcocite with occasional occurrence of gold. The
spatial occurrence of native gold in ferrigenous alteration zones indicates the role of iron in gold precipitation
through buffering of gold-bearing complexes. Mineralogical and geochemical data of Darhib and
El-Beida sulfide-bearing rocks indicate that they crystallized from depleted mantle sources in a back-arc
basin setting, starting with the generation of arc-like volcanic rocks in a nascent BAB stage followed by
the emplacement of plutonic equivalent of MORB/OIB-like rocks such as gabbroic intrusions in a mature
BAB.
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Lithos, 2023
Gerf Neoproterozoic ophiolitic rocks in the Southern Eastern Desert of Egypt represent the larges... more Gerf Neoproterozoic ophiolitic rocks in the Southern Eastern Desert of Egypt represent the largest ophiolite
nappe in the Arabian-Nubian Shield and have been preserved as part of the N-S striking Allaqi-Heiani suture
zone. Landsat-8 OLI/TIRS, ASTER and Sentinel-1B data successfully discriminate the Gerf ophiolitic section and
the structural framework of the study area. This study has applied spectral transform approaches, consisting of
principal component analysis (PCA), band ratio (BR) and minimum noise fraction (MNF) for lithological and
structural mapping. NW-SE and N-S structural trends are dominant and control the distribution of talc‑carbonates
and ophicarbonates. The mantle section comprises dominantly harzburgites with subordinate dunites
and is rarely cut by dike-like bodies of clinopyroxenites; these peridotites have been partially to completely
converted to serpentinites and related rocks. The primary Gerf peridotites are low in TiO2 (0.01 wt%), Al2O3
(0.50 wt%), and CaO (0.44 wt%) content on average, but are rich in Ni (up to 2758 ppm) and Cr (2906 ppm)
relative to primitive mantle, suggesting their highly refractory residual nature after high degrees of partial
melting, similar to forearc peridotites. This is confirmed by chemistry of their relic primary minerals, namely
olivine (Fo: 91–93.7; NiO: 0.28–0.43 wt%), chromian spinel (Cr# 0.75 on average), orthopyroxene (Mg#:
0.92–0.93) and clinopyroxene (Mg#: 0.89–0.90). Gerf serpentinized peridotites also show ranges of oxygen
fugacity (Δlog ƒO2, FMQ + 0.2 – FMQ + 1.4) and equilibrium temperature (770–900 ◦C), consistent with those of
forearc peridotites. Bulk-rock analyses of ultramafic rocks and in-situ analyses of their pyroxenes reveal
enrichment of fluid mobile elements (FME: e.g., B, Cs, Pb, Sr) relative to high-field strength elements (e.g., Nb,
Zr, Ti, Ta), indicating intense metasomatism of Gerf peridotites by slab-derived fluids. The Gerf peridotites have
been subjected to intense CO2 input from the subducted slab to form carbonate-rich rocks beneath the arc-forearc
region. Carbonates (mainly magnesite) replace serpentine minerals and their formation synchronizes with the
transition from lizardite to antigorite at temperatures, ~250◦ to ~350 ◦C. The CO2-rich fluids increase the Au
content because of alteration and break down of Au-bearing sulphides, and this process formed Au mineralization
in carbonate-rich rocks. The maximum amount of CO2 expulsion from the subducted slab increases with
increasing mantle depth, and structural trends as ophicarbonates are abundant in thick parts of the ophiolite
sequence in the Gerf area that was highly dissected by NW-SE, N-S and E-W striking faults. This confirms that
structures control on distribution of the ophiocarbonate rocks in Gerf ophiolite. Calculated parental melts in
equilibrium with Gerf peridotite spinels have boninitic affinities, suggesting their generation during the forearc
stage, but parental melts of Gerf clinopyroxenite veins resemble N-MORB-like melts, indicating melt metasomatism
of sub-arc mantle by impregnated mafic melts during early subduction initiation.
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Geochemistry, 2023
Black sands in the southern Eastern Desert (SED) of Egypt contain substantial reserves of heavy m... more Black sands in the southern Eastern Desert (SED) of Egypt contain substantial reserves of heavy minerals (up to 5
%), and are found mainly in three basins namely: Hodein, Ibib and Diit between Shalateen and Halayeeb cities.
The heavy minerals in these black sands include ilmenite-leucoxene (31 %–44 %), magnetite (15–18 %), zircon
(11–21 %), garnet and green silicates (11–15 %), rutile (6–12 %) and monazite (2–4 %). Cassiterite, thorite,
uranothorite, gold, xenotime and chromian spinel are minor quantities (<1 %). Magnetite (FeO: 75–93.5 wt%)
and ilmenite (TiO2: 42.7–56.9 wt%), hosting high Mn, V, Zr, Zn, Cr, Nb and Co, were probably derived from
gabbroic rocks. The detrital chromian spinel composition (Cr#, 0.51–0.61; Mg#, 0.5–0.63; TiO2 < 1.0 wt%) and
its morphology are similar to those of spinels in fore-arc peridotites from the SED of Egypt, suggesting dominance
of fore-arc basins for peridotite emplacement. These basins were formed during arc-arc or arc-oceanic crust
collision and encolsed ophiolites, gabbroic rocks and I-type granites as sources of the SED black sands. The
studied garnets are mostly almandine in composition with few grossularite and spessartine; they might have been
derived from I-type granites and gneisses sources. The rutile and monazite show enriched LREE relative to HREE,
and display marked defeciency in Eu, suggesting highly fractionated granitic rocks as a main source. Two distinct
types of zircon are recorded: radioactive (Hf: 1578–8770, Y: 319–1335, U: 36–114 and Th: 40–64 ppm) and non
radioactive (Hf: 427, Y: 44, U: 2 and Th: 2 ppm); they were probably derived from different granitic sources.
Compositions and P-T conditions (T: 655–970 ◦C, P: 1.18–9.53 kbar) of magmatic amphiboles are similar to those
derived from I-type granitoids. Bulk analyses of the economic heavy mineral assemblages show significant
concentrations of Fe (393 kg/ton), Zr (183 kg/ton) and Ti (129 kg/ton) with minor Cr (14 kg/ton), Ba (7 kg/ton),
Hf (4.9 kg/ton), Th (up to 3.34 kg/ton) and U (0.29 kg/ton). The elevated contents of Th and U could be related
to the occurrence of monazite and zircon with subordinate thorite, uranothorite and xenotime. The total REE
contents of these bulk analyses range from 1 to 4 kg/ton, where LREEs form 80–90 % of total REEs. Monazite
(ΣREEs: 443604 ppm on average), garnet, zicon (ΣREEs: 421 ppm) and rutile (ΣREEs: 309 ppm) are the main
host of REEs in the investigated black sands. Tonnages of raw sands, to a depth of one meter, are estimated per
10 km2 in each basin, giving 18 million tons for Ibib basin and 19 million tons for both Diit and Hodein basins.
Economic heavy minerals constitute 6–26 % of the total heavy minerals and around 1.0 % of total raw sands.
Calculated reserves of these economic minerals, per 10 km2 of black sands, range from 0.1 million ton in Ibib and
Hodein basins to 0.2 million ton in the Diit basin.
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Minerals 2024, , 2024
Based on new feld, petrographic, and whole-rock geochemistry data, we investigated three discrete... more Based on new feld, petrographic, and whole-rock geochemistry data, we investigated three discrete metagabbro-diorite complexes (MGDC) across the E-W Sinai to contribute to increasing knowledge of the evolution of the juvenile continental crust of the Neoproterozoic Arabian–Nubian Shield. The three MGDCs vary in the dominance of the gabbroic versus dioritic rock types among each of them. Gabbroids are distinguished into pyroxene-hornblende gabbros and hornblende gabbros, whereas dioritic rocks have been subdivided into diorites and quartz diorites. The studied MGDC rocks are almost metaluminous and possess prevalent calc-alkaline characteristics over subsidiary tholeiitic and alkaline affnities. The most distinctive feature in the profles of the investigated MGDCs on the N-MORB-normalized spider diagrams is the coincidence of stout negative Nb anomalies and projecting positive Pb spikes, which is typical of igneous rocks evolved in subduction zones. The three MGDC samples exhibit variably LREE-enriched patterns [(La/Yb)N = 4.92–18.55; av. = 9.04], either lacking or possessing weak to negligible positive and negative Eu anomalies. The calculated apatite and zircon crystallization temperatures reveal the earlier separation of apatite at higher temperatures, with the obvious possibility of two genetic types of apatite and zircon in the magma (cognate vs. xenocrystic) since both accessories have yielded very wide ranges of crystallization temperatures. The investigated MGDCs were formed in a continental arc setting, particularly a thick-crust arc (>39 km). The parent magmas comprised components derived from the melting of the mantle wedge, subducting oceanic lithosphere, and subducting overlying sediments. The mantle input was from a spinel–garnet transitional mantle source at a depth of ca. 75–90 km. The impact of slab-derived fuids was much greater than that of slab-derived melts, and so subduction-related fuids had a crucial effect on metasomatizing the partially melted mantle source. The parent mantle-derived magma has been subjected to substantial crustal contamination as a dominant mechanism of differentiation.
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Euro-Mediterranean Journal for Environmental Integration, 2024
The Hamama metavolcanics and their sulfide deposits are an important part of the Neoproterozoic S... more The Hamama metavolcanics and their sulfide deposits are an important part of the Neoproterozoic Shadli bimodal metavolcanics in the central Eastern Desert (CED) of Egypt and recently became a promising target for gold exploration in Egypt. Semi-massive to massive sulfide deposits occur in quartz-carbonate exhalite and as disseminated grains in metabasalt and metadacite. The Hamama prospect comprises polymetallic bimodal-mafic-type volcanogenic massive sulfide (VMS) deposits, particularly Zn-Cu-Ag-Au VMS deposits. Polybasite is a silver-bearing sulfosalt (65.17-71.81 wt% Ag). Arsenic-bearing framboidal pyrite is the main host of the precious metals (Au and Ag contents reach up to 0.12 wt% and up to 0.55 wt%, respectively). The arsenic-rich fluids likely promoted gold and silver accumulation in framboidal pyrite, which is hosted in the quartz-carbonate exhalite. This exhalite may have acted as a cap rock preventing the dissipation of the metal-rich hydrothermal fluids. Gold-and silver-bearing sulfides were possibly formed in a back-arc basin, which is considered as a suitable environment for VMS formation. The dominance of Zn and Ag reveals that the Hamama VMS deposits were generated at low temperature and a shallow water depth during rifting of the intra-oceanic island arc. Supergene processes formed secondary copper deposits in the upper part of the exhalite. Gold and silver are also accumulated in the gossan zone that is formed by low-temperature oxidized fluids. The factors controlling precious metal mineralization in the CED of Egypt are possibly related to the composition of the host rock and the hydrothermal fluid beside shear zones that act as channels for fluid circulation in an extensional tectonic setting.
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Geochemistry, 2024
The Rahaba layered intrusion in the Southern Eastern Desert of Egypt is mainly composed of pyroxe... more The Rahaba layered intrusion in the Southern Eastern Desert of Egypt is mainly composed of pyroxene hornblende-,
and hornblende gabbros. It hosts thick Fe–Ti oxide ore layers that are composed of titanomagnetite
with subordinate ilmenite and magnetite. To understand the petrogenesis of the Fe–Ti rich gabbroic rocks, the
nature of their parent high-Fe primitive mantle melts and condition of Fe–Ti oxide layer formation, we obtained
new mineral chemistry and whole-rock major and trace element compositions. The geochemical characteristics
of the gabbroic rocks resemble those of picro-basalts, suggesting generation from picritic basaltic-like melts of
tholeiitic affinity. Their high-Fe-Ti-Mg nature (TiO2, ~1.91 wt%; MgO, ~11.0 wt%; Fe2O3, ~14 wt%) probably
indicates elevated mantle potential temperatures due to upwelling of hot asthenospheric mantle. Rare earth
elements (REEs) of clinopyroxene show flat patterns with depletion in LREEs, similar to those of the host gabbros
and picritic basaltic lava, suggesting a mantle origin for their parental melts. Moreover, clinopyroxene compositions
show differentiation trends similar to low-pressure igneous intrusions, and reveal a rift-related origin.
Chemistry of plagioclase (An45–62), clinopyroxene (Wo38.4–45.3, En39.9–43, Fs14–19.3; Mg#: 0.71–0.92) and olivine
(Fo56–80) shows wide compositional ranges due to variable degrees of crystal fractionation. The calculated
equilibrium temperature for the Rahaba Fe-Ti-rich gabbros is mainly 820–1000 ◦C, at pressure below 5 kbar,
reflecting depth of rock solidification of <15 Km. These rocks show both subduction-like and rift-related
geochemical signatures comparable to other post-collisional layered intrusions in the Arabian-Nubian Shield.
The low average Ce/Pb (8.3) and high Ba/Nb (391) ratios together with the enriched large-ion lithophile elements
(Cs, Ba, K and Sr) and depleted high-field strength elements (Th, Nb, Ta and Zr) reflect the contribution
from a preceding subduction event. The lineament map, structural lineament and lineament density map reveal
main WNW-ESE and NW-SE structural trends of the Najd System in the Rahaba area. The Rahaba Fe–Ti rich
gabbroic intrusion was likely formed by initial impact of a mantle plume head with Fe-rich streaks at the base of
metasomatized lithospheric mantle during an extensional phase associated with activity of the Najd-related
strike-slip faults, at the end of the East African Orogeny. The resultant mantle-derived melt compositions and
Najd-related structures possibly controlled the distribution of Fe–Ti ore deposits during this Orogeny. The
Rahaba gabbroic intrusion was emplaced during post-collisional extension after slab break-off and lithospheric
delamination following collision of accreted island-arcs with the Saharan Metacraton.
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Journal of the Geological Society, 2024
Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to... more Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian-Nubian Shield (ANS), six samples from five rare-metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U-Pb ages and O-isotopic compositions as well as whole-rock Sr-and Nd-and alkali feldspar Pb-isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwingshaped REE patterns and strongly negative Eu anomalies. Four granites gave mantle-like zircon δ 18 O V-SMOW between 4.2 and 5.96‰ and yielded ages of 628-633 Ma. This is about when subduction-related magmatism began to be replaced by collisionrelated magmatism. Igla Ahmr granites are older, formed at 691.7-678.9 Ma with δ 18 O V-SMOW c. 5.95‰. All have positive initial ε Nd values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared with unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and unmineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics.
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Journal of Asian Earth Sciences, 2022
Korab Kansi and Abu Dahr Neoproterozoic ophiolitic peridotites in the Southern Eastern Desert (SE... more Korab Kansi and Abu Dahr Neoproterozoic ophiolitic peridotites in the Southern Eastern Desert (SED) of Egypt, are parts of the largest ophiolitic nappes in the Arabian-Nubian Shield. They mainly comprise refractory harzburgites with minor dunites that are commonly altered to serpentinites and talc carbonates. Olivine relics in serpentinized peridotites of the two complexes have olivines with high forsterite (Fo 90.6-92.2) and NiO (0.39 wt%) and low MnO (0. 13 wt%) contents, similar to those of mantle olivines. High Mg# (0.91-0.95) of orthopyroxene is consistent with that of depleted harzburgites. Primary spinel Cr# (0.55-0.75) and TiO 2 contents (<0.04 wt%) of the two peridotite complexes are similar to forearc peridotite spinels. The estimated degree of partial melting of Korab Kansi peridotites (25-40% melting) is slightly lower than that of Abu Dahr (30-40% melting), consistent with modern forearc peridotites. Korab Kansi peridotites exhibit lower oxygen fugacity (Δlog ƒO 2 , FMQ + 0.7 on average) and equilibrium temperature (610-710 • C) than those of Abu Dahr (T, 750-900 • C at Δlog ƒO 2 , FMQ + 2.1), both suggesting subduction-modified peridotites. The low concentrations of incompatible elements, U-shaped REE patterns and high spinel Cr# of both peridotites indicate highly depleted mantle protoliths, reflecting multiple metasomatic and melting episodes in the mantle wedge. Enrichment of fluid mobile elements (e.g. B, Li, Th, U, Pb) relative to high-field strength elements (e.g. Nb, Ta, Ti, Zr) may reflect interaction between slab-derived fluids and peridotites. Calculated parental melts in equilibrium with Korab Kansi and Abu Dahr peridotite spinels have tholeiitic (MORB-like) and boninitic affinities, which were generated during protoforearc spreading to a mature arc stage. Variations in melt compositions suggest a transitional setting from early proto-forearc spreading of mantle beneath Korab Kansi to the mature arc stage of Abu Dahr peridotites. Subduction initiation possibly started in the W and/or SW with proto-forearc spreading, and progressed to the E and/ or NE where a mature arc stage with boninitic melts above an E-and/or SE-dipping subduction zone.
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Lithos, 2022
The geochemical compositions of minerals from the Moho transition zone of ophiolites potentially ... more The geochemical compositions of minerals from the Moho transition zone of ophiolites potentially can help to understand the magmatic evolution of the ophiolites, and subsequent mantle-melt interactions. The Jurassic-Late Cretaceous Makran ophiolite of south Iran comprises one of the most extensive tracts of oceanic crust which were scraped off and preserved in an accretionary complex. The Makran ophiolite records traces of MORB-OIB-type magmatism during the Jurassic, but mostly supra-subduction zone magmatic activity during the Late Cretaceous. Despite a few geochemical studies on the crustal rocks, the nature and geochemical signatures of the mantle rocks from this ophiolite remain controversial. The Sorkhband mantle-crust transition zone underlying crustal cumulates in the western Makran consists of stratiform chromitites, harzburgites, chromite-rich dunites and dunites, with crosscutting dikes of olivine websterite and olivine clinopyroxenite. Major-and trace-element compositions of clinopyroxene grains in olivine websterite and clinopyroxenite dikes indicate crystallization from melts similar to boninites and low-Ti fore-arc basalts. Spinel compositions in olivine websterite and clinopyroxenite dikes suggest crystal fractionation from boninitic or high-Mg# magmas have played a major role in the genesis these rocks. We propose a two-stage model for the formation of the Sorkhband dunites including (1) supra-subduction zone-related melt infiltrates through harzburgites in the mantle-crust transition zone to dissolve peridotite orthopyroxene and leave dunites with high forsterite-NiO olivines, and (2) boninitic melts accumulate and react with surrounding harzburgites to crystallize cumulate dunites with low-Mg# olivine and high-Ti spinels. We conclude that there have been temporal changes in the composition of mantle melts in the fore-arc mantle section of the Makran ophiolite during the initial subduction of the Neotethyan ocean beneath the Lut block during the Late Cretaceous.
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International Geology Review, 2020
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International Journal of Earth Sciences
The Wadi El-Hima Neoproterozoic I- and A-type granites in the Southern Eastern Desert of Egypt ar... more The Wadi El-Hima Neoproterozoic I- and A-type granites in the Southern Eastern Desert of Egypt are rich in garnets (up to 30 vol%) and are cut by NW–SE strike-slip faults, as confirmed from structure lineament extraction maps. These mineralized granites and garnet mineralization zones can be successfully discriminated using remote sensing techniques. Spectral angle mapper and matched filtering techniques are highly effective for mapping garnet-rich zones and show that the highest garnet concentrations occur along the intrusive contact zone of NW–SE striking faults. El-Hima granites have high SiO2 (73.5–75.1 wt%), Al2O3 (13.4–15.3 wt%) and total alkali (6.7–8.7 wt%) contents, suggesting that they were sourced from peraluminous (A/CNK > 1) parental magmas. Garnet-bearing trondhjemites are metasomatic in origin and formed after I-type tonalite-granodiorites, which originated in a volcanic arc tectonic setting. Garnet-rich syenogranites and alkali-feldspar granites are both post-coll...
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Arabian Journal for Science and Engineering, 2021
The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern D... more The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern Desert shear zones. They are hosted in talc- and tremolite-talc-rich rocks and also in meta-basaltic dykes and quartz-veins. The principal mineralization in Atshan includes sphalerite, pyrite, chalcopyrite, galena and pyrrhotite, whereas that in Darhib comprises chalcopyrite, sphalerite, pyrite, and galena with subordinate bornite and covellite. Darhib mineralization contains traces of altaite and electrum. Altaite has the highest Te concentrations suggesting crystallization under low f S 2 and/or high f Te 2 conditions, probably due to S budget consumption from the hydrothermal fluids in the late stage of deposition. Electrum has the highest Au contents with gold fineness value falling within the range of epithermal Au–Ag deposits. The dominance of recrystallized and replacement textures in the studied mineralizations suggests a secondary or post-depositional metamorphic overprint. The significant Cd contents in sphalerite from remobilized massive mineralizations hosted in tremolite-talc-rich rocks indicate crystallization at ~250–300 °C. Galena hosted in tremolite-talc-rich rocks is characterized by exceptionally high selenium and tellurium contents, indicating its generation from relatively Se–Te-enriched hydrothermal fluids. Pyrrhotite hosted in quartz-veins from Atshan was formed under lower sulfur activity ( a S 2 ) and oxygen fugacity ( f O 2 ). Covellite and bornite were formed due to chalcopyrite oxidation, revealing a role of supergene process. Shear zones, possibly produced during later thrust faulting, were acted as channel ways for hydrothermal mineralizing fluids that may have modified and/or precipitated the mineralization. Mineralizing fluids have probably resulted from dehydration during metamorphism and/or late-magmatic fluids from nearby granitic intrusions.
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Ore Geology Reviews, 2021
Abstract The Soghan-Sikhoran ophiolite in southeast Iran (Outer Zagros Ophiolite Belt) is a remna... more Abstract The Soghan-Sikhoran ophiolite in southeast Iran (Outer Zagros Ophiolite Belt) is a remnant of a series of Upper Triassic–Cretaceous supra-subduction zone (SSZ) ophiolites that formed along the Zagros suture zone, which is considered as the southern border of the Neo-Tethyan sea. These SSZ ophiolites are older than the Late Cretaceous Zagros ophiolites. The main part of the Soghan-Sikhoran ophiolite comprises layered ultramafic cumulates including dunites, wehrlites, and pyroxenites, and a tectonized mantle section including residual lherzolites, and depleted harzburgites with foliated/discordant dunite lenses. Podiform chromitites are common and are typically surrounded by thin dunitic haloes. Spinels in lherzolite–harzburgite are geochemically characterized by a low Cr# (42.0 to 52.6), and plot in an abyssal peridotite field on geochemical discrimination diagrams, whereas spinel in dunites and high-Cr chromitite spinels (Cr# = 52.4 to 76.4) show geochemical affinities to boninites. Lherzolites and harzburgites have low REE contents and experienced >17 vol% partial melting. The Soghan-Sikhoran ophiolite contains both high Cr# and low Cr# podiform chromitite types. Trace and REE element patterns of Soghan-Sikhoran rocks are similar to those in SSZ peridotites. The studied ophiolites show relatively moderate to high oxygen fugacities (ƒO2), with log units ranging from −0.4 to +0.4 for harzburgites, +0.2 for lherzolites, from − 0.7 to + 2.5 for pyroxenites, from +0.8 to +2.2 for dunites, and from + 0.6 to + 0.8 for chromitites. The moderate to high oxidation state of the studied upper-mantle ophiolitic complexes also suggests a boninitic source in the mantle wedge of the arc setting. The two-pyroxene thermometer yields mean equilibrium temperatures of 879 °C, 895 °C, 912 °C and 912 °C for harzburgites, lherzolites, dunites and pyroxenites, respectively. We therefore interpret that the spinels in the lherzolite-harzburgite crystallized from tholeiitic melt generated due to proto-forearc spreading and formation of the infant arc, whereas high-Cr# spinel in dunites and high-Cr# chromitite crystallized from boninitic melts during the mature arc stage, with an increasing contribution of slab-derived fluids at high ƒO2.
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Ore Geology Reviews, 2020
Abstract The concentrically zoned Dahanib Alaskan-type complex in the Southern Eastern Desert (SE... more Abstract The concentrically zoned Dahanib Alaskan-type complex in the Southern Eastern Desert (SED) of Egypt contains cumulate dunites associated with banded chromitites in the core, through harzburgites, wehrlites, and gabbroic rocks to the rim. Primary mineral inclusions hosted in chromian spinels of the banded chromitites are usually pargasite, orthopyroxene (Opx), aspidolite, phlogopite, edenite, olivine and PGE-bearing sulphides. The chromian spinel in Dahanib chromitites has a narrow range of Cr# (0.53–0.63) along with high Ti and Fe+3, like that in the host clinopyroxene-rich cumulate dunites. It resembles in chemistry to spinels in the Alaskan-type complex formed in an island arc setting. The early cumulus olivine in disseminated chromitites and host dunites (Fo88-91) shows a typical fractional crystallization trend. The interstitial clinopyroxene (Cpx) in chromitites is similar in chemical properties to Cpx crystallized from tholeiitic basalt melts, and traces a cumulate trend of arc-related Alaskan complexes. The peridotitic and gabbroic rocks contain primary amphiboles, which are pargasite and edenite with high Ti, Na and Al. The sulphide minerals are usually chalcopyrite, pentlandite and horomanite with subordinate Cu-pentlandite, cubanite, samaniite, heazlewoodite and pyrite. Pentlandite, horomanite and cubanite at temperatures between 900 and 1040 °C are rich in some platinum group elements (PGE: Os, Pt, Ir). They are classified into primary and secondary origins, which were crystallized from segregated sulphide droplets and from hydrothermal fluids at temperature
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Journal of Petrology, 2018
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GSA Bulletin, 2019
How new subduction zones form is an ongoing scientific question with key implications for our und... more How new subduction zones form is an ongoing scientific question with key implications for our understanding of how this process influences the behavior of the overriding plate. Here we focus on the effects of a Late Cretaceous subduction-initiation (SI) event in Iran and show how SI caused enough extension to open a back-arc basin in NE Iran. The Late Cretaceous Torbat-e-Heydarieh ophiolite (THO) is well exposed as part of the Sabzevar-Torbat-e-Heydarieh ophiolite belt. It is dominated by mantle peridotite, with a thin crustal sequence. The THO mantle sequence consists of harzburgite, clinopyroxene-harzburgite, plagioclase lherzolite, impregnated lherzolite, and dunite. Spinel in THO mantle peridotites show variable Cr# (10–63), similar to both abyssal and fore-arc peridotites. The igneous rocks (gabbros and dikes intruding mantle peridotite, pillowed and massive lavas, amphibole gabbros, plagiogranites and associated diorites, and diabase dikes) display rare earth element patterns ...
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Journal of African Earth Sciences, 2019
Abstract Gebel Abu Dabbab, which is located at 50 km NW of Marsa Alam city, represents an unique ... more Abstract Gebel Abu Dabbab, which is located at 50 km NW of Marsa Alam city, represents an unique and specialized stock-like felsic intrusion of rare metals and Sn bearing albite granite. This granitic stock was emplaced along two intersected major faults and/or tensional shear zones trending NE and NW-SE relevant to the Najd Fault system. Petrographically, the albite granite is composed mainly of albite, quartz and microcline-microperthite and muscovite, in association with accessories; cassiterite, tantalite-columbite, zircon, allanite and apatite. The studied albite granite is enriched in Na2O, HFSEs, Ta and Nb, but it is poor in MgO, CaO, Fe2O3, TiO2, Ba, Sr, rare earth elements and radioelements (U, Th). Geodynamic modelling reveals that Abu Dabbab albite granite was generated as a result of partial melting of oceanic crust due to the interaction of primitive basaltic melts-derived from the mantle source. The resultant hybride melts were subsequently fractionated to tonalitic melts giving rise to the A1-subtype granite, which was emplaced within the intraplate environment at the later phase of the Pan African Orogeny. Moreover, the fractional crystallization and reworking of plagioclase were suffered from alkali mtasomatism after extraction of alkali feldspar granite melts.
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Lithos, 2019
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Gondwana Research, 2023
Field geology, geochemical analyses and multi-sensor remotely sensed data of Landsat-8, ASTER and... more Field geology, geochemical analyses and multi-sensor remotely sensed data of Landsat-8, ASTER and
Sentinel-2 were used to detect various types of hydrothermal alteration and sulfide-gold mineralization
in Neoproterozoic metavolcanic and gabbroic rocks from Darhib and El-Beida areas in the South Eastern
Desert (SED) of Egypt. We also used RADAR data of Sentinel-1 using PCI Geomatica software to decipher
the structural lineaments that control this mineralization. Different styles of disseminated to massive sulfide
deposits include: 1) undeformed magmatic disseminated ores in Darhib gabbros, metavolcanic rocks
and metabasic dykes; 2) deformed (remobilized) massive ores mostly of a magmatic-hydrothermal origin
in Darhib tremolite talc rocks along E-W shear zones; 3) hydrothermal sulfide ores along El-Beida NW–SE
shear zones. Cu-Zn massive ores represent the main sulfides in the Darhib silicified tremolite-talc rocks
and meta-andesites, and occur as bands, veins and patches along Darhib E-W shear zones. Discontinuous
occurrences of sulfide ores-bearing tremolite-talc rocks indicate that major shear zones act as structural
controls on mineralization. Sulfide ores consist chiefly of chalcopyrite, sphalerite, pyrite and galena as
well as minor covellite and bornite. These ores are highly concentrated along E-W striking Darhib shear
zones and resulted from granite-derived hydrothermal fluids that form/and or accumulate sulfide minerals
from the sulfide-bearing metavolcanic rocks around shear zones. Two stages of hydrothermal alterations
are recorded in the Darhib talc mine including pre- (talcification, amphibolitization and
carbonatization) and syn- (silicification and chloritization) sulfide ore alterations. Disseminated sulfide
mineralization hosted in Darhib gabbros, metavolcanic rocks and metabasic dykes is of a magmatic origin,
similar to Cu-Ni sulfide deposits hosted in gabbroic varieties in worldwide mafic–ultramafic intrusions.
On the other hand, El-Beida gold-sulfide-bearing quartz and quartz carbonate veins are hosted
in ferruginated and silicified metavolcanics/ metavolcaniclastic rocks along NW–SE shear zones (Najd
Fault System trend). These are spatially associated with regional convergent structures (high-angle convergent
wrench structures), suggesting orogenic gold type mineralization. The E-W with minor WNWESE
shear zones in Darhib and NW-SE trending shear zones in El- Beida structurally controlled sulfides
and gold mineralization in the SED of Egypt. El-Beida sulfide mineralization occurs as disseminated ores
that consist mainly of pyrite, chalcopyrite, covelite and chalcocite with occasional occurrence of gold. The
spatial occurrence of native gold in ferrigenous alteration zones indicates the role of iron in gold precipitation
through buffering of gold-bearing complexes. Mineralogical and geochemical data of Darhib and
El-Beida sulfide-bearing rocks indicate that they crystallized from depleted mantle sources in a back-arc
basin setting, starting with the generation of arc-like volcanic rocks in a nascent BAB stage followed by
the emplacement of plutonic equivalent of MORB/OIB-like rocks such as gabbroic intrusions in a mature
BAB.
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Lithos, 2023
Gerf Neoproterozoic ophiolitic rocks in the Southern Eastern Desert of Egypt represent the larges... more Gerf Neoproterozoic ophiolitic rocks in the Southern Eastern Desert of Egypt represent the largest ophiolite
nappe in the Arabian-Nubian Shield and have been preserved as part of the N-S striking Allaqi-Heiani suture
zone. Landsat-8 OLI/TIRS, ASTER and Sentinel-1B data successfully discriminate the Gerf ophiolitic section and
the structural framework of the study area. This study has applied spectral transform approaches, consisting of
principal component analysis (PCA), band ratio (BR) and minimum noise fraction (MNF) for lithological and
structural mapping. NW-SE and N-S structural trends are dominant and control the distribution of talc‑carbonates
and ophicarbonates. The mantle section comprises dominantly harzburgites with subordinate dunites
and is rarely cut by dike-like bodies of clinopyroxenites; these peridotites have been partially to completely
converted to serpentinites and related rocks. The primary Gerf peridotites are low in TiO2 (0.01 wt%), Al2O3
(0.50 wt%), and CaO (0.44 wt%) content on average, but are rich in Ni (up to 2758 ppm) and Cr (2906 ppm)
relative to primitive mantle, suggesting their highly refractory residual nature after high degrees of partial
melting, similar to forearc peridotites. This is confirmed by chemistry of their relic primary minerals, namely
olivine (Fo: 91–93.7; NiO: 0.28–0.43 wt%), chromian spinel (Cr# 0.75 on average), orthopyroxene (Mg#:
0.92–0.93) and clinopyroxene (Mg#: 0.89–0.90). Gerf serpentinized peridotites also show ranges of oxygen
fugacity (Δlog ƒO2, FMQ + 0.2 – FMQ + 1.4) and equilibrium temperature (770–900 ◦C), consistent with those of
forearc peridotites. Bulk-rock analyses of ultramafic rocks and in-situ analyses of their pyroxenes reveal
enrichment of fluid mobile elements (FME: e.g., B, Cs, Pb, Sr) relative to high-field strength elements (e.g., Nb,
Zr, Ti, Ta), indicating intense metasomatism of Gerf peridotites by slab-derived fluids. The Gerf peridotites have
been subjected to intense CO2 input from the subducted slab to form carbonate-rich rocks beneath the arc-forearc
region. Carbonates (mainly magnesite) replace serpentine minerals and their formation synchronizes with the
transition from lizardite to antigorite at temperatures, ~250◦ to ~350 ◦C. The CO2-rich fluids increase the Au
content because of alteration and break down of Au-bearing sulphides, and this process formed Au mineralization
in carbonate-rich rocks. The maximum amount of CO2 expulsion from the subducted slab increases with
increasing mantle depth, and structural trends as ophicarbonates are abundant in thick parts of the ophiolite
sequence in the Gerf area that was highly dissected by NW-SE, N-S and E-W striking faults. This confirms that
structures control on distribution of the ophiocarbonate rocks in Gerf ophiolite. Calculated parental melts in
equilibrium with Gerf peridotite spinels have boninitic affinities, suggesting their generation during the forearc
stage, but parental melts of Gerf clinopyroxenite veins resemble N-MORB-like melts, indicating melt metasomatism
of sub-arc mantle by impregnated mafic melts during early subduction initiation.
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Geochemistry, 2023
Black sands in the southern Eastern Desert (SED) of Egypt contain substantial reserves of heavy m... more Black sands in the southern Eastern Desert (SED) of Egypt contain substantial reserves of heavy minerals (up to 5
%), and are found mainly in three basins namely: Hodein, Ibib and Diit between Shalateen and Halayeeb cities.
The heavy minerals in these black sands include ilmenite-leucoxene (31 %–44 %), magnetite (15–18 %), zircon
(11–21 %), garnet and green silicates (11–15 %), rutile (6–12 %) and monazite (2–4 %). Cassiterite, thorite,
uranothorite, gold, xenotime and chromian spinel are minor quantities (<1 %). Magnetite (FeO: 75–93.5 wt%)
and ilmenite (TiO2: 42.7–56.9 wt%), hosting high Mn, V, Zr, Zn, Cr, Nb and Co, were probably derived from
gabbroic rocks. The detrital chromian spinel composition (Cr#, 0.51–0.61; Mg#, 0.5–0.63; TiO2 < 1.0 wt%) and
its morphology are similar to those of spinels in fore-arc peridotites from the SED of Egypt, suggesting dominance
of fore-arc basins for peridotite emplacement. These basins were formed during arc-arc or arc-oceanic crust
collision and encolsed ophiolites, gabbroic rocks and I-type granites as sources of the SED black sands. The
studied garnets are mostly almandine in composition with few grossularite and spessartine; they might have been
derived from I-type granites and gneisses sources. The rutile and monazite show enriched LREE relative to HREE,
and display marked defeciency in Eu, suggesting highly fractionated granitic rocks as a main source. Two distinct
types of zircon are recorded: radioactive (Hf: 1578–8770, Y: 319–1335, U: 36–114 and Th: 40–64 ppm) and non
radioactive (Hf: 427, Y: 44, U: 2 and Th: 2 ppm); they were probably derived from different granitic sources.
Compositions and P-T conditions (T: 655–970 ◦C, P: 1.18–9.53 kbar) of magmatic amphiboles are similar to those
derived from I-type granitoids. Bulk analyses of the economic heavy mineral assemblages show significant
concentrations of Fe (393 kg/ton), Zr (183 kg/ton) and Ti (129 kg/ton) with minor Cr (14 kg/ton), Ba (7 kg/ton),
Hf (4.9 kg/ton), Th (up to 3.34 kg/ton) and U (0.29 kg/ton). The elevated contents of Th and U could be related
to the occurrence of monazite and zircon with subordinate thorite, uranothorite and xenotime. The total REE
contents of these bulk analyses range from 1 to 4 kg/ton, where LREEs form 80–90 % of total REEs. Monazite
(ΣREEs: 443604 ppm on average), garnet, zicon (ΣREEs: 421 ppm) and rutile (ΣREEs: 309 ppm) are the main
host of REEs in the investigated black sands. Tonnages of raw sands, to a depth of one meter, are estimated per
10 km2 in each basin, giving 18 million tons for Ibib basin and 19 million tons for both Diit and Hodein basins.
Economic heavy minerals constitute 6–26 % of the total heavy minerals and around 1.0 % of total raw sands.
Calculated reserves of these economic minerals, per 10 km2 of black sands, range from 0.1 million ton in Ibib and
Hodein basins to 0.2 million ton in the Diit basin.
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Minerals 2024, , 2024
Based on new feld, petrographic, and whole-rock geochemistry data, we investigated three discrete... more Based on new feld, petrographic, and whole-rock geochemistry data, we investigated three discrete metagabbro-diorite complexes (MGDC) across the E-W Sinai to contribute to increasing knowledge of the evolution of the juvenile continental crust of the Neoproterozoic Arabian–Nubian Shield. The three MGDCs vary in the dominance of the gabbroic versus dioritic rock types among each of them. Gabbroids are distinguished into pyroxene-hornblende gabbros and hornblende gabbros, whereas dioritic rocks have been subdivided into diorites and quartz diorites. The studied MGDC rocks are almost metaluminous and possess prevalent calc-alkaline characteristics over subsidiary tholeiitic and alkaline affnities. The most distinctive feature in the profles of the investigated MGDCs on the N-MORB-normalized spider diagrams is the coincidence of stout negative Nb anomalies and projecting positive Pb spikes, which is typical of igneous rocks evolved in subduction zones. The three MGDC samples exhibit variably LREE-enriched patterns [(La/Yb)N = 4.92–18.55; av. = 9.04], either lacking or possessing weak to negligible positive and negative Eu anomalies. The calculated apatite and zircon crystallization temperatures reveal the earlier separation of apatite at higher temperatures, with the obvious possibility of two genetic types of apatite and zircon in the magma (cognate vs. xenocrystic) since both accessories have yielded very wide ranges of crystallization temperatures. The investigated MGDCs were formed in a continental arc setting, particularly a thick-crust arc (>39 km). The parent magmas comprised components derived from the melting of the mantle wedge, subducting oceanic lithosphere, and subducting overlying sediments. The mantle input was from a spinel–garnet transitional mantle source at a depth of ca. 75–90 km. The impact of slab-derived fuids was much greater than that of slab-derived melts, and so subduction-related fuids had a crucial effect on metasomatizing the partially melted mantle source. The parent mantle-derived magma has been subjected to substantial crustal contamination as a dominant mechanism of differentiation.
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Euro-Mediterranean Journal for Environmental Integration, 2024
The Hamama metavolcanics and their sulfide deposits are an important part of the Neoproterozoic S... more The Hamama metavolcanics and their sulfide deposits are an important part of the Neoproterozoic Shadli bimodal metavolcanics in the central Eastern Desert (CED) of Egypt and recently became a promising target for gold exploration in Egypt. Semi-massive to massive sulfide deposits occur in quartz-carbonate exhalite and as disseminated grains in metabasalt and metadacite. The Hamama prospect comprises polymetallic bimodal-mafic-type volcanogenic massive sulfide (VMS) deposits, particularly Zn-Cu-Ag-Au VMS deposits. Polybasite is a silver-bearing sulfosalt (65.17-71.81 wt% Ag). Arsenic-bearing framboidal pyrite is the main host of the precious metals (Au and Ag contents reach up to 0.12 wt% and up to 0.55 wt%, respectively). The arsenic-rich fluids likely promoted gold and silver accumulation in framboidal pyrite, which is hosted in the quartz-carbonate exhalite. This exhalite may have acted as a cap rock preventing the dissipation of the metal-rich hydrothermal fluids. Gold-and silver-bearing sulfides were possibly formed in a back-arc basin, which is considered as a suitable environment for VMS formation. The dominance of Zn and Ag reveals that the Hamama VMS deposits were generated at low temperature and a shallow water depth during rifting of the intra-oceanic island arc. Supergene processes formed secondary copper deposits in the upper part of the exhalite. Gold and silver are also accumulated in the gossan zone that is formed by low-temperature oxidized fluids. The factors controlling precious metal mineralization in the CED of Egypt are possibly related to the composition of the host rock and the hydrothermal fluid beside shear zones that act as channels for fluid circulation in an extensional tectonic setting.
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Geochemistry, 2024
The Rahaba layered intrusion in the Southern Eastern Desert of Egypt is mainly composed of pyroxe... more The Rahaba layered intrusion in the Southern Eastern Desert of Egypt is mainly composed of pyroxene hornblende-,
and hornblende gabbros. It hosts thick Fe–Ti oxide ore layers that are composed of titanomagnetite
with subordinate ilmenite and magnetite. To understand the petrogenesis of the Fe–Ti rich gabbroic rocks, the
nature of their parent high-Fe primitive mantle melts and condition of Fe–Ti oxide layer formation, we obtained
new mineral chemistry and whole-rock major and trace element compositions. The geochemical characteristics
of the gabbroic rocks resemble those of picro-basalts, suggesting generation from picritic basaltic-like melts of
tholeiitic affinity. Their high-Fe-Ti-Mg nature (TiO2, ~1.91 wt%; MgO, ~11.0 wt%; Fe2O3, ~14 wt%) probably
indicates elevated mantle potential temperatures due to upwelling of hot asthenospheric mantle. Rare earth
elements (REEs) of clinopyroxene show flat patterns with depletion in LREEs, similar to those of the host gabbros
and picritic basaltic lava, suggesting a mantle origin for their parental melts. Moreover, clinopyroxene compositions
show differentiation trends similar to low-pressure igneous intrusions, and reveal a rift-related origin.
Chemistry of plagioclase (An45–62), clinopyroxene (Wo38.4–45.3, En39.9–43, Fs14–19.3; Mg#: 0.71–0.92) and olivine
(Fo56–80) shows wide compositional ranges due to variable degrees of crystal fractionation. The calculated
equilibrium temperature for the Rahaba Fe-Ti-rich gabbros is mainly 820–1000 ◦C, at pressure below 5 kbar,
reflecting depth of rock solidification of <15 Km. These rocks show both subduction-like and rift-related
geochemical signatures comparable to other post-collisional layered intrusions in the Arabian-Nubian Shield.
The low average Ce/Pb (8.3) and high Ba/Nb (391) ratios together with the enriched large-ion lithophile elements
(Cs, Ba, K and Sr) and depleted high-field strength elements (Th, Nb, Ta and Zr) reflect the contribution
from a preceding subduction event. The lineament map, structural lineament and lineament density map reveal
main WNW-ESE and NW-SE structural trends of the Najd System in the Rahaba area. The Rahaba Fe–Ti rich
gabbroic intrusion was likely formed by initial impact of a mantle plume head with Fe-rich streaks at the base of
metasomatized lithospheric mantle during an extensional phase associated with activity of the Najd-related
strike-slip faults, at the end of the East African Orogeny. The resultant mantle-derived melt compositions and
Najd-related structures possibly controlled the distribution of Fe–Ti ore deposits during this Orogeny. The
Rahaba gabbroic intrusion was emplaced during post-collisional extension after slab break-off and lithospheric
delamination following collision of accreted island-arcs with the Saharan Metacraton.
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Journal of the Geological Society, 2024
Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to... more Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian-Nubian Shield (ANS), six samples from five rare-metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U-Pb ages and O-isotopic compositions as well as whole-rock Sr-and Nd-and alkali feldspar Pb-isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwingshaped REE patterns and strongly negative Eu anomalies. Four granites gave mantle-like zircon δ 18 O V-SMOW between 4.2 and 5.96‰ and yielded ages of 628-633 Ma. This is about when subduction-related magmatism began to be replaced by collisionrelated magmatism. Igla Ahmr granites are older, formed at 691.7-678.9 Ma with δ 18 O V-SMOW c. 5.95‰. All have positive initial ε Nd values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared with unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and unmineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics.
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Journal of Asian Earth Sciences, 2022
Korab Kansi and Abu Dahr Neoproterozoic ophiolitic peridotites in the Southern Eastern Desert (SE... more Korab Kansi and Abu Dahr Neoproterozoic ophiolitic peridotites in the Southern Eastern Desert (SED) of Egypt, are parts of the largest ophiolitic nappes in the Arabian-Nubian Shield. They mainly comprise refractory harzburgites with minor dunites that are commonly altered to serpentinites and talc carbonates. Olivine relics in serpentinized peridotites of the two complexes have olivines with high forsterite (Fo 90.6-92.2) and NiO (0.39 wt%) and low MnO (0. 13 wt%) contents, similar to those of mantle olivines. High Mg# (0.91-0.95) of orthopyroxene is consistent with that of depleted harzburgites. Primary spinel Cr# (0.55-0.75) and TiO 2 contents (<0.04 wt%) of the two peridotite complexes are similar to forearc peridotite spinels. The estimated degree of partial melting of Korab Kansi peridotites (25-40% melting) is slightly lower than that of Abu Dahr (30-40% melting), consistent with modern forearc peridotites. Korab Kansi peridotites exhibit lower oxygen fugacity (Δlog ƒO 2 , FMQ + 0.7 on average) and equilibrium temperature (610-710 • C) than those of Abu Dahr (T, 750-900 • C at Δlog ƒO 2 , FMQ + 2.1), both suggesting subduction-modified peridotites. The low concentrations of incompatible elements, U-shaped REE patterns and high spinel Cr# of both peridotites indicate highly depleted mantle protoliths, reflecting multiple metasomatic and melting episodes in the mantle wedge. Enrichment of fluid mobile elements (e.g. B, Li, Th, U, Pb) relative to high-field strength elements (e.g. Nb, Ta, Ti, Zr) may reflect interaction between slab-derived fluids and peridotites. Calculated parental melts in equilibrium with Korab Kansi and Abu Dahr peridotite spinels have tholeiitic (MORB-like) and boninitic affinities, which were generated during protoforearc spreading to a mature arc stage. Variations in melt compositions suggest a transitional setting from early proto-forearc spreading of mantle beneath Korab Kansi to the mature arc stage of Abu Dahr peridotites. Subduction initiation possibly started in the W and/or SW with proto-forearc spreading, and progressed to the E and/ or NE where a mature arc stage with boninitic melts above an E-and/or SE-dipping subduction zone.
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Lithos, 2022
The geochemical compositions of minerals from the Moho transition zone of ophiolites potentially ... more The geochemical compositions of minerals from the Moho transition zone of ophiolites potentially can help to understand the magmatic evolution of the ophiolites, and subsequent mantle-melt interactions. The Jurassic-Late Cretaceous Makran ophiolite of south Iran comprises one of the most extensive tracts of oceanic crust which were scraped off and preserved in an accretionary complex. The Makran ophiolite records traces of MORB-OIB-type magmatism during the Jurassic, but mostly supra-subduction zone magmatic activity during the Late Cretaceous. Despite a few geochemical studies on the crustal rocks, the nature and geochemical signatures of the mantle rocks from this ophiolite remain controversial. The Sorkhband mantle-crust transition zone underlying crustal cumulates in the western Makran consists of stratiform chromitites, harzburgites, chromite-rich dunites and dunites, with crosscutting dikes of olivine websterite and olivine clinopyroxenite. Major-and trace-element compositions of clinopyroxene grains in olivine websterite and clinopyroxenite dikes indicate crystallization from melts similar to boninites and low-Ti fore-arc basalts. Spinel compositions in olivine websterite and clinopyroxenite dikes suggest crystal fractionation from boninitic or high-Mg# magmas have played a major role in the genesis these rocks. We propose a two-stage model for the formation of the Sorkhband dunites including (1) supra-subduction zone-related melt infiltrates through harzburgites in the mantle-crust transition zone to dissolve peridotite orthopyroxene and leave dunites with high forsterite-NiO olivines, and (2) boninitic melts accumulate and react with surrounding harzburgites to crystallize cumulate dunites with low-Mg# olivine and high-Ti spinels. We conclude that there have been temporal changes in the composition of mantle melts in the fore-arc mantle section of the Makran ophiolite during the initial subduction of the Neotethyan ocean beneath the Lut block during the Late Cretaceous.
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International Geology Review, 2020
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International Journal of Earth Sciences
The Wadi El-Hima Neoproterozoic I- and A-type granites in the Southern Eastern Desert of Egypt ar... more The Wadi El-Hima Neoproterozoic I- and A-type granites in the Southern Eastern Desert of Egypt are rich in garnets (up to 30 vol%) and are cut by NW–SE strike-slip faults, as confirmed from structure lineament extraction maps. These mineralized granites and garnet mineralization zones can be successfully discriminated using remote sensing techniques. Spectral angle mapper and matched filtering techniques are highly effective for mapping garnet-rich zones and show that the highest garnet concentrations occur along the intrusive contact zone of NW–SE striking faults. El-Hima granites have high SiO2 (73.5–75.1 wt%), Al2O3 (13.4–15.3 wt%) and total alkali (6.7–8.7 wt%) contents, suggesting that they were sourced from peraluminous (A/CNK > 1) parental magmas. Garnet-bearing trondhjemites are metasomatic in origin and formed after I-type tonalite-granodiorites, which originated in a volcanic arc tectonic setting. Garnet-rich syenogranites and alkali-feldspar granites are both post-coll...
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Arabian Journal for Science and Engineering, 2021
The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern D... more The studied sulfide mineralizations of Atshan and Darhib areas are related to the south Eastern Desert shear zones. They are hosted in talc- and tremolite-talc-rich rocks and also in meta-basaltic dykes and quartz-veins. The principal mineralization in Atshan includes sphalerite, pyrite, chalcopyrite, galena and pyrrhotite, whereas that in Darhib comprises chalcopyrite, sphalerite, pyrite, and galena with subordinate bornite and covellite. Darhib mineralization contains traces of altaite and electrum. Altaite has the highest Te concentrations suggesting crystallization under low f S 2 and/or high f Te 2 conditions, probably due to S budget consumption from the hydrothermal fluids in the late stage of deposition. Electrum has the highest Au contents with gold fineness value falling within the range of epithermal Au–Ag deposits. The dominance of recrystallized and replacement textures in the studied mineralizations suggests a secondary or post-depositional metamorphic overprint. The significant Cd contents in sphalerite from remobilized massive mineralizations hosted in tremolite-talc-rich rocks indicate crystallization at ~250–300 °C. Galena hosted in tremolite-talc-rich rocks is characterized by exceptionally high selenium and tellurium contents, indicating its generation from relatively Se–Te-enriched hydrothermal fluids. Pyrrhotite hosted in quartz-veins from Atshan was formed under lower sulfur activity ( a S 2 ) and oxygen fugacity ( f O 2 ). Covellite and bornite were formed due to chalcopyrite oxidation, revealing a role of supergene process. Shear zones, possibly produced during later thrust faulting, were acted as channel ways for hydrothermal mineralizing fluids that may have modified and/or precipitated the mineralization. Mineralizing fluids have probably resulted from dehydration during metamorphism and/or late-magmatic fluids from nearby granitic intrusions.
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Ore Geology Reviews, 2021
Abstract The Soghan-Sikhoran ophiolite in southeast Iran (Outer Zagros Ophiolite Belt) is a remna... more Abstract The Soghan-Sikhoran ophiolite in southeast Iran (Outer Zagros Ophiolite Belt) is a remnant of a series of Upper Triassic–Cretaceous supra-subduction zone (SSZ) ophiolites that formed along the Zagros suture zone, which is considered as the southern border of the Neo-Tethyan sea. These SSZ ophiolites are older than the Late Cretaceous Zagros ophiolites. The main part of the Soghan-Sikhoran ophiolite comprises layered ultramafic cumulates including dunites, wehrlites, and pyroxenites, and a tectonized mantle section including residual lherzolites, and depleted harzburgites with foliated/discordant dunite lenses. Podiform chromitites are common and are typically surrounded by thin dunitic haloes. Spinels in lherzolite–harzburgite are geochemically characterized by a low Cr# (42.0 to 52.6), and plot in an abyssal peridotite field on geochemical discrimination diagrams, whereas spinel in dunites and high-Cr chromitite spinels (Cr# = 52.4 to 76.4) show geochemical affinities to boninites. Lherzolites and harzburgites have low REE contents and experienced >17 vol% partial melting. The Soghan-Sikhoran ophiolite contains both high Cr# and low Cr# podiform chromitite types. Trace and REE element patterns of Soghan-Sikhoran rocks are similar to those in SSZ peridotites. The studied ophiolites show relatively moderate to high oxygen fugacities (ƒO2), with log units ranging from −0.4 to +0.4 for harzburgites, +0.2 for lherzolites, from − 0.7 to + 2.5 for pyroxenites, from +0.8 to +2.2 for dunites, and from + 0.6 to + 0.8 for chromitites. The moderate to high oxidation state of the studied upper-mantle ophiolitic complexes also suggests a boninitic source in the mantle wedge of the arc setting. The two-pyroxene thermometer yields mean equilibrium temperatures of 879 °C, 895 °C, 912 °C and 912 °C for harzburgites, lherzolites, dunites and pyroxenites, respectively. We therefore interpret that the spinels in the lherzolite-harzburgite crystallized from tholeiitic melt generated due to proto-forearc spreading and formation of the infant arc, whereas high-Cr# spinel in dunites and high-Cr# chromitite crystallized from boninitic melts during the mature arc stage, with an increasing contribution of slab-derived fluids at high ƒO2.
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Ore Geology Reviews, 2020
Abstract The concentrically zoned Dahanib Alaskan-type complex in the Southern Eastern Desert (SE... more Abstract The concentrically zoned Dahanib Alaskan-type complex in the Southern Eastern Desert (SED) of Egypt contains cumulate dunites associated with banded chromitites in the core, through harzburgites, wehrlites, and gabbroic rocks to the rim. Primary mineral inclusions hosted in chromian spinels of the banded chromitites are usually pargasite, orthopyroxene (Opx), aspidolite, phlogopite, edenite, olivine and PGE-bearing sulphides. The chromian spinel in Dahanib chromitites has a narrow range of Cr# (0.53–0.63) along with high Ti and Fe+3, like that in the host clinopyroxene-rich cumulate dunites. It resembles in chemistry to spinels in the Alaskan-type complex formed in an island arc setting. The early cumulus olivine in disseminated chromitites and host dunites (Fo88-91) shows a typical fractional crystallization trend. The interstitial clinopyroxene (Cpx) in chromitites is similar in chemical properties to Cpx crystallized from tholeiitic basalt melts, and traces a cumulate trend of arc-related Alaskan complexes. The peridotitic and gabbroic rocks contain primary amphiboles, which are pargasite and edenite with high Ti, Na and Al. The sulphide minerals are usually chalcopyrite, pentlandite and horomanite with subordinate Cu-pentlandite, cubanite, samaniite, heazlewoodite and pyrite. Pentlandite, horomanite and cubanite at temperatures between 900 and 1040 °C are rich in some platinum group elements (PGE: Os, Pt, Ir). They are classified into primary and secondary origins, which were crystallized from segregated sulphide droplets and from hydrothermal fluids at temperature
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Journal of Petrology, 2018
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GSA Bulletin, 2019
How new subduction zones form is an ongoing scientific question with key implications for our und... more How new subduction zones form is an ongoing scientific question with key implications for our understanding of how this process influences the behavior of the overriding plate. Here we focus on the effects of a Late Cretaceous subduction-initiation (SI) event in Iran and show how SI caused enough extension to open a back-arc basin in NE Iran. The Late Cretaceous Torbat-e-Heydarieh ophiolite (THO) is well exposed as part of the Sabzevar-Torbat-e-Heydarieh ophiolite belt. It is dominated by mantle peridotite, with a thin crustal sequence. The THO mantle sequence consists of harzburgite, clinopyroxene-harzburgite, plagioclase lherzolite, impregnated lherzolite, and dunite. Spinel in THO mantle peridotites show variable Cr# (10–63), similar to both abyssal and fore-arc peridotites. The igneous rocks (gabbros and dikes intruding mantle peridotite, pillowed and massive lavas, amphibole gabbros, plagiogranites and associated diorites, and diabase dikes) display rare earth element patterns ...
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Journal of African Earth Sciences, 2019
Abstract Gebel Abu Dabbab, which is located at 50 km NW of Marsa Alam city, represents an unique ... more Abstract Gebel Abu Dabbab, which is located at 50 km NW of Marsa Alam city, represents an unique and specialized stock-like felsic intrusion of rare metals and Sn bearing albite granite. This granitic stock was emplaced along two intersected major faults and/or tensional shear zones trending NE and NW-SE relevant to the Najd Fault system. Petrographically, the albite granite is composed mainly of albite, quartz and microcline-microperthite and muscovite, in association with accessories; cassiterite, tantalite-columbite, zircon, allanite and apatite. The studied albite granite is enriched in Na2O, HFSEs, Ta and Nb, but it is poor in MgO, CaO, Fe2O3, TiO2, Ba, Sr, rare earth elements and radioelements (U, Th). Geodynamic modelling reveals that Abu Dabbab albite granite was generated as a result of partial melting of oceanic crust due to the interaction of primitive basaltic melts-derived from the mantle source. The resultant hybride melts were subsequently fractionated to tonalitic melts giving rise to the A1-subtype granite, which was emplaced within the intraplate environment at the later phase of the Pan African Orogeny. Moreover, the fractional crystallization and reworking of plagioclase were suffered from alkali mtasomatism after extraction of alkali feldspar granite melts.
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Lithos, 2019
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Springer Publishing Partner, 2022
Neoproterozoic granites from the Umm Naggat and Homrit Waggat areas, Central Eastern Desert (CED)... more Neoproterozoic granites from the Umm Naggat and Homrit Waggat areas, Central Eastern Desert (CED),Egypt, form part of the Nubian Shield and on the basis of textural and chemical characteristics, resemble highly fractionated rare metal-bearing A-type granites. Decorrelation Stretch (DS) and Band Rationing (BR) techniques of Sentinel-2 and Landsat-9 remote sensing data were successfully used in the spectral identification of lithological units, and particularly mineralized zones in A-type granites. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) were successfully processed and analyzed to discriminate the spatial and spectral extent of the hydrothermal mineralized alteration zones related to the rare metal-bearing granitic plutons. Structural features associated with hydrothermal alteration minerals may control the distribution of rare earth element (REEs) and rare metal mineralization, which have been successfully identified by Sentinel-1enhanced Soble directional filter images, using automatic lineament extraction techniques. The predominant structural feature directions in rare metal-bearing granitic plutons are N-S and NW-SE trending. These plutons mainly comprise biotite granites, syenogranites and alkali feldspar granites. Rock-forming minerals are quartz, K-feldspar (Or94-99), plagioclase (An0-7) and biotite, with subordinate chlorite, muscovite and fluorite.. Zircon, Fe-Ti oxides, rutile, apatite, epidote, titanite, columbite and thorite are the main accessory phases. The investigated granitoids are enriched in Rb, Nb, Y, Ta, Hf, Ga, Zr and rare earth elements (REE = 170-558 ppm) in contrast to low contents of CaO, MgO, Sr, and pronounced negative Eu anomalies (Eu/Eu* = 0.01-0.29), similar to postcollisional rare-metal bearing A-type granites. Based on mineral and whole-rock chemistry, these A-type granites crystallized from highly fractionated I-type tonalite-granodiorite magma, followed by extensive fractional crystallization in the upper crust during lithospheric delamina-2 tion. Rare-metal minerals of both magmatic and hydrothermal origin such as zircon, rutile, xenotime, thorite, cerite-(Ce), parasite, uranothorite, columbite, ishikawaite and bastnaesite are mainly disseminated. Integration of the enhanced images and geochemical analysis data are promising in discriminating lithological units and potential areas enriched with rare metals in the study areas.
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