Immiscibilty between silicate magma and aqueous fluids in Egyptian rare-metal granites: melt and fluid inclusions study

Mohamed, Mohamed Abdel-Moneim

doi:10.1007/s12517-012-0664-9

Cited by 14 publications

(12 citation statements)

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“…Interpretations of the ADAG genesis in particular are diverse and are not yet adequately addressed. Mohamed (1993Mohamed ( , 2013 adopted a metasomatic-hydrothermal model for modification of a highly fractionated primary granite. Renno et al (1993), by contrast, proposed a magmatic model emphasizing an enriched parental magma derived from remelting of lower crust.…”

Section: Source Magma and Geodynamic Modelmentioning

confidence: 99%

Geochemistry and Petrogenesis of Late Ediacaran Rare‐metal Albite Granites of the Arabian‐Nubian Shield

Amarah

Azer

Asimow

et al. 2021

Acta Geologica Sinica (Eng)

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The Abu Dabbab albite granite (ADAG), in the central Eastern Desert of Egypt, hosts the most significant rare metal ore deposit in the northern part of the Neoproterozoic Arabian-Nubian Shield. Here, we report detailed field, petrographic, mineralogical and geochemical investigation of the ADAG, an isolated stock-like granitic body with sharp intrusive contacts against metamorphic country rocks, probably emplaced at about 600 Ma. The fine-grained porphyritic upper unit is a preserved remnant of the shallowly-emplaced apex of the magma chamber, whereas the medium-grained lower unit crystallized at deeper levels under subvolcanic conditions. The peraluminous leucocratic ADAG shares common geochemical characteristics with post-collisional intraplate A-type magmas. In addition to the conspicuous enrichment in Na 2 O, the ADAG is remarkable for its anomalous concentrations of Ta, Nb, Li, Hf, Ga, Sn, Zn and heavy rare-earth elements. Nb-Ta minerals in the ADAG are mixed with Fe-Mn oxides, forming black patches that increase in abundance toward of the base of the intrusion. Columbite-tantalite, cassiterite and wolframite are the most important ore minerals. Pronounced negative Eu anomalies (Eu/Eu * = 0.10-0.24) reflect extreme magmatic fractionation and perhaps the effects of late fluid-rock interaction. The ADAG was most likely generated by partial melting of the juvenile middle crust of the ANS as the geotherm was elevated by erosional uplift following lithospheric delamination and it was emplaced at the intersection of lineations of structural weakness. Although formation of the ADAG and its primary enrichment in rare metals are essentially due to magmatic processes, late-stage metasomatism caused limited redistribution of rare metals. Fluid-driven subsolidus modification was limited to the apex of the magma chamber and drove development of greisen, amazonite, and quartz veins along fracture systems.

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Section: Source Magma and Geodynamic Modelmentioning

confidence: 99%

Geochemistry and Petrogenesis of Late Ediacaran Rare‐metal Albite Granites of the Arabian‐Nubian Shield

Amarah

Azer

Asimow

et al. 2021

Acta Geologica Sinica (Eng)

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“…Generally speaking, during the crystallization of magma, there are at least three main stages: the orthomagmatic stage, the pneumatolitic stage (or magmatic-hydrothermal transition) and the hydrothermal stage. Previous studies carried out on rare-metal mineralization in Egypt revealed that columbite, tantalite and topaz are mainly crystallized as magmatic minerals from the residual interstitial melt at the late orthomagmatic stage at temperatures between 450°C and 550°C (Mohamed, 2013;Emam et al, 2018), some cassiterite also potentially forming in this orthomagmatic stage.…”

Section: Crystallization Of the Magmamentioning

confidence: 99%

“…Among the Younger Granites in the Eastern Desert of Egypt, and particularly the third phase of these granites, rare-metal mineralization occurs in many districts such as Sn-Ta-W mineralization in the Abu Dabbab albite granite (Mohamed, 1993(Mohamed, , 2013; Sn-Ta-W mineralization in the Nuweibi albite granite (Mohamed, 2013); Sn, Mo, Be and F mineralization in the Humr Akarim and Humrat Mukbid alkali granites and a subordinate roof facies of albite granite (Ali et al, 2012a); Sn-W and Fat Igla (Sabet et al, 1976a), Mo mineralization in the pink granites of Gabel Qattar (Dardir et al, 1983); F mineralization in the El-Ineigi alkali feldspar granite (Sami et al, 2017); U mineralization in Um Safi (Abouelnaga et al, 2015), etc.…”

Section: Intrusion-related Rare Metal Deposits (Irrmds) In the Eastern Desertmentioning

confidence: 99%

“…Pneumatolitic processes occur during the final stages of crystallization, where the melt-volatile-rich phase (boronbearing and fluorine-bearing vapours) escapes at a temperature of 400°C from the cooling silicate magma along joints and fractures, producing greisen selvages along the mineralized quartz veins (Hussein, 1990) with a mineralization assemblage represented by quartz, beryl, topaz, cassiterite, fluorite, and white mica (Mohamed, 2013).…”

Section: Crystallization Of the Magmamentioning

confidence: 99%

“…The late hydrothermal stage in intrusion-related raremetal mineralizations in the Eastern Desert of Egypt took place at temperatures between 200°C and 350°C, being dominated by homogenous H 2 O-CO 2 -NaCl fluid, the mineralization associated with this stage being represented by quartz veins with cassiterite ± wolframite + chalcopyrite and fluorite (Mohamed, 2013;Emam et al, 2018).…”

Section: Crystallization Of the Magmamentioning

confidence: 99%

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Intrusion‐related Gold Deposits in Egypt

Botros

2021

Acta Geologica Sinica (Eng)

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Intrusion‐related gold deposits (IRGDs) occur in the Eastern Desert (ED) of Egypt within magmatic districts that are exploited for tungsten and tin mineralization. IRGDs and intrusion‐related rare metal deposits (IRRMDs) are almost invariably linked with the late to post collisional Younger Granites (YGs) that have three successive phases (I, II and III). At ∼635–630 Ma, the ED underwent a transition in deformation style from compressional to extensional and a switch from subduction with crustal thickening to delamination with crustal thinning. This transition was concurrent with the emplacement of a short magmatic pulse (∼635–630 Ma) that represents a transition between orogenic gold deposits and IRGDs. K‐rich calc alkaline granites (phase I and II of the YGs) hosting IRGDs like the Hangalia deposit were emplaced during the time span 630–610 Ma. Alkaline magmatism began at 610 Ma, coexisting with the K‐rich calc‐alkaline magmatism over the 610–590 Ma time span, where the Fawakhir (598 ± 3 Ma) and Um Had (596 ± 2 Ma) granites that host the IRGDs were emplaced. In time, the alkaline magmatism became more alkaline giving rise to phase III of the YGs that hosts IRRMDs. A distinct metallogenic epoch comprising both IRGDs and IRRMDs, was undergoing extreme growth at ∼600 Ma.

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