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Article

Homrit Akarem Post-Collisional Intrusion, Southeastern Desert, Egypt: Petrogenesis of Greisen Formed in a Cupola Structure and Enrichment in Strategic Minerals

by
Mokhles K. Azer
1,*,
Adel A. Surour
2,3,
Hilmy E. Moussa
1,
Ayman E. Maurice
4,
Mabrouk Sami
5,6,
Moustafa A. Abou El Maaty
1,
Adel I. M. Akarish
1,
Mohamed Th. S. Heikal
7,
Ahmed A. Elnazer
1,
Mustafa A. Elsagheer
1,
Heba S. Mubarak
1,
Amany M. A. Seddik
8,
Hadeer Sobhy
9 and
Mohamed O. Osama
10
1
Geological Sciences Department, National Research Centre, Dokki 12622, Egypt
2
Department of Geological Sciences, Faculty of Science, Galala University, Suez 43511, Egypt
3
Geology Department, Faculty of Science, Cairo University, Giza 12613, Egypt
4
Geology Department, Faculty of Science, Helwan University, Cairo 11790, Egypt
5
Geosciences Department, College of Science, United Arab Emirates University, Al Ain 15551, United Arab Emirates
6
Geology Department, Faculty of Science, Minia University, El-Minia 61519, Egypt
7
Geology Department, Faculty of Science, Tanta University, Tanta 31733, Egypt
8
Geology Department, Faculty of Science, New Valley University, El-Kharga 72511, Egypt
9
Geology Department, Faculty of Science, Zagazig University, Zagazig 44519, Egypt
10
Nuclear Materials Authority, El Maadi, P.O. Box 530, Cairo 11742, Egypt
*
Author to whom correspondence should be addressed.
Geosciences 2025, 15(6), 200; https://doi.org/10.3390/geosciences15060200
Submission received: 6 April 2025 / Revised: 10 May 2025 / Accepted: 22 May 2025 / Published: 26 May 2025
(This article belongs to the Special Issue Advances in Analytical Chemistry for Mineralogical and Environmental Studies)
Browse Figures
Versions Notes

Abstract

The greisens discussed in the present study are associated with the Homrit Akarem post-collisional granites, which are exposed near the western edge of the Egyptian Nubian Shield in the Southeastern Desert of Egypt. The Homrit Akarem granites intruded into Neoproterozoic country rocks, with sharp intrusive contacts. The marginal parts of the Homrit Akarem intrusion underwent extensive post-magmatic metasomatism, resulting in the formation of albitized granite and greisens. The Homrit Akarem greisens occur as veins and stockworks, which can be classified into four types: muscovite-rich, cassiterite-rich, topaz-rich, and beryl-rich greisens. Based on petrographic inspection, we identified ore minerals (cassiterite, beryl, topaz, muscovite, Nb-Ta oxides, tourmaline, fluorite, and corundum) in the greisens using electron probe microanalysis. The Homrit Akarem mineralized greisens were formed in a magmatic cupola above A-type magma, where fluid–rock interactions played a significant role in their formation. The accumulation of residual volatile-rich melt and exsolved fluids in the apical part of the magma chamber produced albitized granite, greisens, and quartz veins that intruded into the peripheries of the granitic intrusion and its surrounding country rocks. The variation in the mineralogy of the studied greisens indicates the diverse chemical composition of both the hydrothermal/magmatic fluids and the host granites. The simultaneous decrease in temperature and pressure is considered a crucial factor that controlled mineralization in the apical parts of the magma chamber. The occurrence of cassiterite, beryl, topaz, tourmaline, muscovite, and Nb-Ta oxides in the studied greisens suggests a potential polymetallic deposit of industrial minerals.

1. Introduction

Greisens are metasomatic rocks that form through the hydrothermal alteration of granites and/or their country rocks during the late stage of granitic magma crystallization [1,2,3,4,5]. They are considered key to mineralization because the last hydrothermal fluids associated with granitic intrusions tend to concentrate incompatible metals, such as tin, beryllium, tungsten, molybdenum, niobium, and tantalum [6,7].
The Egyptian Nubian Shield contains voluminous granitoids of varying ages, geochemical characteristics, origins, and geotectonic settings (e.g., [8,9,10,11]). The authors of [11] classified the Egyptian granitoids into a three-fold petrological classification scheme, which includes synorogenic calc-alkaline granitoids, late-to post-orogenic calc-alkaline granitoids, and post-orogenic alkaline granites. Some post-collisional granitic intrusions are often modified by metasomatic processes, including albitization, silicification, and greisenization, which lead to their enrichment in certain rare metals of substantial economic significance, such as REE, Nb, Ta, Zr, U, and Th (e.g., [11,12,13]).
Greisens have been documented in various locations within the Eastern Desert of Egypt, including Homrit Akarem, Abu Dabbab, Nuweibi, Um Naggat, Mueilha, Homrit Waggat, Igla, and Abu Rusheid (e.g., [5,14,15]). The present study deals with the greisens associated with the post-collisional granites of Egypt; these greisens have not been thoroughly investigated to understand their formation from a petrological perspective. In the present work, we present new field data, a petrographic investigation, and the mineral chemistry of the greisens related to the Homrit Akarem intrusion. In addition, our aim is to discuss the greisenization that occurred during the hydrothermal processes and the mineralization in the cupola structure associated with post-collisional granites in the Egyptian Nubian Shield.

2. Geologic Setting

The study area is located at the western edge of the Egyptian Nubian Shield outcrop in the Southeastern Desert of Egypt (Figure 1), between latitudes 24°9′ and 24°13′ N and longitudes 34°1′00″ and 34°5′40″ E. It is primarily composed of metamorphosed island-arc rocks and intrusive granitoids (Figure 2). The island-arc rocks represent the oldest rock units in the mapped area and are highly deformed and metamorphosed. They include metasedimentary rocks with minor metavolcanics varieties. The intrusive granitoids are represented by granodiorite and post-collisional granites. The granodiorite contains various xenoliths of the metamorphosed island-arc rocks.
The post-collisional granites of the Homrit Akarem intrusion intrude into metamorphosed volcano-sedimentary successions, exhibiting sharp intrusive contacts. The core of the Homrit Akarem intrusion consists of alkali feldspar granite, which grades into muscovite granite and albitized granite. Alkali feldspar granite is the predominant rock type, while muscovite granite is less common and serves as the transitional zone between the pink granite and the whitish albitized granite that constitutes the marginal and the apical parts of the Homrit Akarem intrusion. The outer margins of the albitized granite are subjected to intense silicification and greisenization processes, and they are also penetrated by numerous pegmatite and fluorite veins.
In the study area, greisens are irregularly distributed along the margins of the albitized granite. They appear as pockets or as veins filling fractures and can also form extensive selvages surrounding quartz veins, occasionally extending into the surrounding country rocks. Greisens are easily identifiable in the field due to their bleached colors, and they are sometimes fragmented. The recorded greisen bodies associated with the Homrit Akarem intrusion can be classified into four types: muscovite-rich (Figure 3a), cassiterite-rich (Figure 3b,c), topaz-rich (Figure 3d), and beryl-rich (Figure 3e) greisens. The muscovite-rich greisen is prevalent as veins (~100 m long), cutting through the albitized granite and extending into the country rocks. Cassiterite-rich greisen occurs as clusters of subparallel veins that range from 10 to 40 cm in thickness and from 100 to 400 m in length. Topaz-rich and beryl-rich greisens are found as selvages around quartz veins in the country rocks adjacent to the granitic intrusion. Locally, greisens may be stained red or black due to impregnation with Fe or Mn oxides (Figure 3f) during the late stages of hydrothermal alteration. Several fluorite veins and pods have been observed cutting through the greisen bodies, confined to the same fracture trends that control the endogreisen bodies.

3. Methodology

3.1. Field Work and Sampling

The field work was carried out through different field trips to collect fresh samples on a systematic basis and field observations of lithological variation, contacts, and structural elements. Representative sampling was carried out using GPS locations and extensive photo-documentation of the sample sites. In order to discern the petrological characteristics of the studied granitoids and the types of alterations, 25 samples of the pegmatites and 20 samples of the country rocks were collected for the present study.

3.2. Petrographic Studies

Petrographic studies of freshest-possible samples along with altered samples were conducted, with the intent of characterizing the entire mineralized samples and selecting a subset for microprobe mineral analyses and whole-rock major element compositions. Representative thin and polished sections were prepared for the petrographical studies to determine mineralogical composition, including alterations, and textures. Special care was taken to note the abundance of important ore minerals.

3.3. Analytical Conditions

Mineral chemical analyses were performed using a JEOL JXA-8530F field-emission electron probe microanalyzer (EPMA; Madison, WI, USA) at the Department of Earth Sciences at the University of Western Ontario (Canada). The operating conditions were 20 kV probe current, 40–60 nA accelerating voltage, 1–2 μm diameter beam, a counting time of 5–10 s, natural and synthetic mineral standards, and a ZAF matrix correction routine. The standards were orthoclase for K, albite for Na and Al, anorthite for Ca, rutile for Ti, zircon for Si, forsterite for Mg, and fayalite for Fe. The low detection limits (LDLs) of all analyzed oxides are ~0.01.

4. Petrography

The petrographic study of the Homrit Akarem intrusion indicates that it consists of various types of leucogranite, including alkali feldspar granite, muscovite granite, and albite granite. The marginal parts of the intrusion have undergone several types of alteration, such as greisenization, albitization, and impregnation with secondary minerals. In this paper, we will present the detailed petrography and mineralogy of the greisen bodies. The mineralogical compositions of the studied greisen bodies are diverse, with several types identified, including muscovite-rich, cassiterite-rich, topaz-rich, and beryl-rich greisens. The feldspars are completely absent in all types of the studied greisens.
Muscovite-rich greisen primarily consists of quartz and muscovite, along with disseminated crystals of topaz, cassiterite, and fluorite. Quartz is predominantly represented by milky quartz, which exhibits undulatory extinction. Muscovite appears as large tabular crystals with a pale brown color that are invaded by veins filled with secondary minerals (Figure 4a).
Cassiterite-rich greisen primarily consists of cassiterite and quartz, with smaller amounts of muscovite and fluorite (Figure 4b). Accessory minerals include columbite, galena, corundum, tourmaline, topaz, fluorite, and xenotime. Cassiterite typically appears dark in color and can be nearly opaque. Most large cassiterite crystals contain few inclusions and display oscillatory and/or sector zoning when viewed in cross-polarized light (Figure 4c,d). Muscovite is found as anhedral crystals and flakes that occupy the fractures within the cassiterite. Columbite is present either as inclusions within the large cassiterite crystals (Figure 4e) or as disseminated fine anhedral grains. Locally, fissure-filling corundum is observed as fine anhedral aggregates (Figure 4e). Tourmaline is characterized by well-developed euhedral to subhedral crystals, exhibiting a brownish-grey color and high relief.
Topaz-rich greisen is recorded only in the country rocks adjacent to the granitic intrusion. This light-colored rock consists essentially of aggregates of topaz and muscovite (Figure 4f), with smaller amounts of quartz, cassiterite, fluorite, and carbonates. Highly corroded feldspar crystals that have been replaced by mica and fluorite are locally recorded. The presence of carbonates and cassiterite as fissure fillings are common features of the topaz-rich greisen. Topaz forms excellent stubby idiomorphic crystals, appearing colorless in plane polarized light and grey in crossed polar light, and can be distinguished from quartz by its higher relief. The topaz contains inclusions of muscovite and feldspars. Texture relations indicate that the topaz crystallized before the quartz. Fluorite occurs as small anhedral crystals interstitial among the other minerals or as veins that follow fractures.
Beryl-rich greisen consists essentially of beryl and quartz, along with accessory phases of tourmaline, muscovite, Nb-Ta oxides, xenotime, and fluorite. Beryl occurs as euhedral, elongated prismatic crystals that range in color from yellowish to greyish-white. Tourmaline is present as disseminated crystals, diffuse clots, or late-stage fracture fillings. Muscovite and fluorite are present as fissure fillings. Nb-Ta oxides are typically found as disseminated prismatic laths, commonly associated with xenotime and thorite.

5. Mineral Chemistry

A variety of minerals from the studied greisens were analyzed using the electron probe microanalysis technique. These minerals included cassiterite, muscovite, beryl, topaz, tourmaline, Nb-Ta oxides, corundum, and fluorite. The representative microprobe analyses are given in Appendix A (Table A1, Table A2, Table A3, Table A4, Table A5, Table A6, Table A7 and Table A8) at the end of manuscript, while the whole data set is given in Supplementary Tables S1–S7.

5.1. Cassiterite

The cassiterite crystals were analyzed from cassiterite-rich, muscovite-rich, and beryl-rich greisens, and their chemical compositions are presented in Table A1 (A, B, and C) and Supplementary Table S1. The results reveal that SnO2 (95.03–97.38 wt.%) is the only major oxide, accompanied by a small amount of CaO (0.65–1.05 wt.%). Other oxides, such as SiO2, TiO2, FeO, Na2O, and K2O are present in minor quantities.

5.2. Muscovite

The chemical compositions and structural formulae of the analyzed muscovites are given in Table A2 (A and B) and Supplementary Table S2. Utilizing the Ti-Mg-Na ternary diagram [17], the analyzed muscovites straddle the boundary between primary and secondary muscovites (Figure 5a). These muscovites contain appreciable amounts of F (up to 3.26 wt.%) and can be termed fluormuscovite.

5.3. Beryl

Some beryl crystals were analyzed in beryl-rich greisen, and their chemical compositions are listed in Table A3 and Supplementary Table S3. The major element compositions demonstrate remarkable chemical consistency. SiO2 ranges narrowly from 65.21 to 66.91 wt.%, while Al2O3 concentrations vary minimally between 16.55 and 18.03 wt.%. Notably, BeO is significantly elevated (11.45–14.12 wt.%), reflecting pronounced Be enrichment. Alkali elements such as Na2O (0.36–0.49 wt.%) and K2O (0.01–0.12 wt.%) occur at relatively low yet consistent concentrations. FeO values vary slightly from 0.33 to 0.60 wt.%, whereas MgO (0.09–0.18 wt.%) and CaO (<0.13 wt.%) contents are low, indicative of restricted substitution within the beryl structure. The data underscore the chemical homogeneity and purity of beryl formed in a Be-rich hydrothermal environment typical of greisen deposits.

5.4. Topaz

Some topaz crystals were analyzed in cassiterite-rich and topaz-rich greisens, and their chemical compositions are shown in Table A4 and Supplementary Table S4. The chemical composition for topaz grains indicates highly homogeneous compositions, characterized predominantly by SiO2, Al2O3, and F contents. SiO2 in topaz grains from cassiterite-rich greisen ranges from 28.99 to 30.08 wt.%, while in topaz-rich greisen, it shows slightly lower variability, from 27.78 to 30.69 wt.%. Al2O3 concentrations display limited variation, with values spanning from 50.04 to 52.50 wt.% in cassiterite-rich greisen and from 50.09 to 52.42 wt.% in topaz-rich greisen. Fluorine content exhibits significant enrichment (17.61–20.16 wt.%). Notably, the minor oxide components (e.g., FeO, MnO, MgO, CaO, Na2O, K2O, P2O5, and TiO2) are consistently low. The obtained data confirm the high purity and chemical uniformity of the topaz grains, reflecting their stable crystallization environment and the specialized hydrothermal conditions prevalent in greisen deposits.

5.5. Tourmaline

Some tourmaline crystals were analyzed in the cassiterite-rich and beryl-rich greisens. The chemical composition and structural formula of the analyzed tourmaline crystals are presented in Table A5 and Supplementary Table S5. The examined tourmaline crystals exhibit limited variation in their compositions, as the major components are represented by SiO2 (34.79–35.34 wt.%), Al2O3 (33.65–34.23 wt.%), FeO (11.98–12.46 wt.%), B2O3 (8.42–8.93 wt.%), and MgO (1.38–1.73 wt.%). Other oxides, such as TiO2, CaO, Na2O, and K2O, are present in minor amounts, each less than 1 wt.%.

5.6. Nb–Ta Oxides

The identification of Nb–Ta oxides under the microscope was refined and confirmed by EPMA. Some crystals of Nb-Ta oxides were analyzed in cassiterite-rich and beryl-rich greisens, and their chemical analyses and structural formulae are given in Table A6 and Supplementary Table S6. The analyzed crystals display very wide ranges of Nb2O5 (54.08–66.84 wt.%) and Ta2O5 (9.65–24.14 wt.%). They show a columbite composition with Mn# [Mn/(Mn + Fe)] values between 0.12 and 0.20 and Ta# [Ta/(Ta + Nb)] values ranging from 0.08 to 0.21. Plotting the data on the “columbite quadrilateral” diagram revealed that the analyzed points are akin to the Fe-dominant columbite (Figure 5b).

5.7. Fluorite

Fluorites were analyzed in the various types of greisens, and their chemical analyses are given in Table A7 (A and B) and Supplementary Table S7. The results indicate the presence of F (47.27–50.91 wt.%f) and CaO (47.77–51.39 wt.%) as the main components. Minor oxides such as FeO (up to 0.73 wt.%), MnO (up to 0.09 wt.%), SiO2, Al2O3, Na2O, K2O, P2O5, and TiO2 occur as traces to negligible quantities across all samples, generally below 0.5 wt.%. These results collectively highlight the remarkable chemical purity and limited compositional variability of fluorite, emphasizing its crystallization from relatively homogeneous, fluorine-rich fluids.

5.8. Corundum

Corundum was recorded only in the cassiterite-rich greisen, and its chemical analyses are listed in Table A8. EMPA data of corundum grains demonstrate a remarkably homogeneous composition dominated by Al2O3. Al2O3 contents consistently remain very high, ranging narrowly between 96.36 and 99.63 wt.%, indicating high purity and minimal substitution. Minor oxide constituents detected include SiO2 (0.01–0.57 wt.%), FeO (up to 0.11 wt.%), and MgO (up to 0.18 wt.%), along with trace amounts of CaO, Na2O, K2O, TiO2, MnO, and P2O5, each generally at or below 0.1 wt.%.

6. Discussion

Several petrogenetic models have been proposed for the origin of the Homrit Akarem intrusion [5,18]. Integrated data on the Homrit Akarem granites indicate that this intrusion was emplaced in a post-collisional setting during the final stage of the evolution of the Nubian Shield. The Homrit Akarem intrusion shares many features typical of A-type granites. The absence of mafic and intermediate igneous rocks within the Homrit Akarem intrusion suggests that it is unlikely to have originated from a mantle-derived mafic magma through extensive fractional crystallization. The available geochemical data indicate that the parental magma of the Homrit Akarem intrusion was generated through partial melting of a juvenile crustal source, followed by extensive fractional crystallization [5]. The gradational contacts between the different phases of the Homrit Akarem intrusion promote their emplacement within a very short time interval before the complete crystallization of the early phases. Although the main granitic phases of the Homrit Akarem intrusion are primarily magmatic, the influence of hydrothermal fluids and extensive replacement by secondary minerals became dominant in the marginal zones, resulting in the development of albitized granite and greisens.
In general, greisenization occurs during the final crystallization stage of granitic intrusions by interactions between granite and hot acidic fluids [7,19,20,21]. Greisenization and silicification are the products of magmatic volatiles while the magmatic system is still hot enough to power the formation of hydrothermal solutions. Greisens are commonly associated mineralization deposits that result from an intense pervasive metasomatic alteration involving a major fluid and mass transfer through albite granite [22,23]. The mineral replacement reactions lead to a decrease in the volume of the solid phases, which represents a potential process for creating pathways to enhance fluid flow [2].
In the Eastern Desert of Egypt, all greisens appear to be restricted to the granitic intrusions which are emplaced in shallow crustal levels [24,25,26,27], generally at a depth of less than 5 km. This limitation arises because the separation of hydrous fluid from granite to produce greisenization cannot occur deeper than about 5 km [5]. The present work indicates that the greisens associated with the Homrit Akarem granites represent a magmatic cupola situated above an A-type granite intrusion (Figure 6a,b). The hydrothermal fluids originated from a magmatic source and were exsolved from crystallizing granitic magma under lithostatic pressure. The hydrothermal solutions and the volatiles were concentrated in the upper part of the cupola before complete crystallization of the granitic melts. The pressure of these fluids increased until the overlying cupola ruptured, leading to wall-rock alteration or greisenization around the granite. During the greisenization process, the volume of the rock decreased due to mineral reactions, resulting in increased porosity and permeability [2,16,28,29]. In this study, the alteration halo surrounding the albitized granite is restricted to a narrow zone (up to 50 m), mostly limited to the fracture zones adjacent to the contact between the albitized granite and the country rocks, with some extension of a few meters into the country rocks.
The simultaneous decrease in temperature and pressure is considered the essential factor for the localization of mineralization in the apical parts of the magma chamber. During greisenization, primary minerals such as albite, K-feldspars, and muscovite are consumed, leading to the formation of a new generation of minerals, including quartz, mica, topaz, fluorite, and cassiterite. Fluid-driven subsolidus modifications are confined to the apex of the magma chamber, resulting in the formation of greisen and quartz veins along fracture systems. As the transition occurs from albitized granite to greisen bodies, sericite develops at the expense of K- and Na-feldspar, ultimately leading to the replacement of all original rock-forming minerals with the greisen assemblage. As the intensity of greisenization increases, different types of greisens are formed. The chemical homogeneity of topaz (SiO2: 27.78–30.69 wt.%; F: 17.61–20.16 wt.%) and fluorite reflects stable hydrothermal conditions, likely maintained by sustained fluid flow within the cupola. In contrast, oscillatory and sector zoning in cassiterite (SnO2: 95.03–97.38 wt.%) points to episodic fluid influx or fluctuations in pH, redox state, or metal availability during crystallization [27,30]. The presence of columbite inclusions within cassiterite (Fe-dominant; Mn# = 0.12–0.20) further links Nb-Ta mineralization to early magmatic stages, with subsequent hydrothermal reworking. The cassiterite of the present study was formed during the late hydrothermal stage in the newly formed fractures and contains Nb-Ta oxide inclusions that formed early in a magmatic stage. The Mg-Ti-Na systematics of muscovite, straddling primary and secondary fields (Figure 5a), suggest overlapping magmatic and hydrothermal origins, consistent with progressive fluid–rock interaction.
Whenever a mineral or mineral assemblage comes into contact with a fluid with which it is out of equilibrium, re-equilibration will tend to take place to reduce the free energy of the whole system [31]. During the greisenization process, silica and alumina transfer during the dissolution of feldspars, which leads to the growth of quartz, corundum, and topaz in aqueous fluids [32]. Some works demonstrate that the directions of silica and alumina transfer show no unambiguous correlation with the composition, PT conditions, pH, and density of the fluids [33,34,35,36,37]. This defines simultaneous spatially associated or separated growth of quartz, corundum, and topaz, as observed in the present study. In the present work, corundum formation in cassiterite-rich greisen (Al2O3: 96.36–99.63 wt.%) implies localized high Al activity, likely due to albite breakdown under acidic conditions. This aligns with experimental studies showing that greisenization consumes feldspars, releasing Al and Si into fluids, which precipitate as quartz, topaz, or corundum depending on fluid composition [28]. Similarly, beryl crystallization (BeO: 11.45–14.12 wt.%) in a Be-enriched environment highlights the efficiency of fluid-phase metal transport in A-type systems.
At the top and margins of the Homrit Akarem intrusion, the A-type granites were transformed into quartz–muscovite greisen through the replacement of feldspars with muscovite. This is supported by partial or extensive replacement of the albite crystals by muscovite (Figure 7a,b). This alteration, specifically the dissolution of albite, created some porosity. Near the veins, the newly formed muscovite was converted into topaz and quartz, resulting in a quartz–topaz greisen. The crystallization of cassiterite and beryl occurred simultaneously with the alteration of muscovite to topaz and quartz. The presence of fluorite veins and pods in various types of greisens indicates the availability of F in the interacting fluids during the different stages of greisenization [38,39]. Locally, greisenization was followed by either fluoritization or kaolinization, which was accompanied by localized impregnations of Fe- and Mn-oxides. The formation of tourmaline crystals in some greisen samples can be attributed to the interaction between B-bearing hydrothermal solutions and the host rocks in the apex of the cupola [40,41,42,43,44].
The polymetallic nature of Homrit Akarem greisens, hosting Sn (cassiterite), Be (beryl), Nb-Ta (columbite), and F (fluorite), positions them as prospective targets for critical metals. Cassiterite-rich veins (10–40 cm thick, 100–400 m long) represent high-grade zones, while disseminated Nb-Ta oxides in greisens may warrant bulk-tonnage evaluation. The association of fluorite veins with greisens further enhances economic potential, given the industrial demand for fluorite. However, the irregular distribution of greisen bodies necessitates detailed structural mapping to identify fracture-controlled mineralization.

7. Conclusions

  • Homrit Akarem granites represent a late Neoproterozoic post-collisional intrusion in the northern Nubian Shield. The Homrit Akarem intrusion has sharp intrusive contacts against the country rocks with gradational petrologic boundaries between its rock varieties.
  • The greisen bodies of Homrit Akarem intrusion are distinguished into muscovite-rich, cassiterite-rich, topaz-rich, and beryl-rich greisens. The occurrence of late impregnations of hematitic alteration in some greisen bodies may reflect the oxidized nature of the interacting fluids during the final stage of greisenization.
  • The Homrit Akarem granites represent A-type rocks that developed in a cupola structure. Accumulation of residual volatile-rich melt and exsolved fluids in the apical part of the magma chamber produced albitized granite, greisen, and quartz veins that cut the peripheries of the granitic intrusion and its surrounding country rocks.
  • The Homrit Akarem greisens were formed by the replacement of rock-forming minerals of the apical albitized granite, where the fluids that emanated through fractures were able to deposit greisen assemblages in the voids as well as pervasively greisenize the immediately surrounding country rocks.
  • Finally, further mineral exploration studies of the Homrit Akarem granites are recommended, especially the greisens and quartz veins that represent the most specialized and mineralized parts of the intrusion.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/geosciences15060200/s1.

Author Contributions

Conceptualization: M.K.A., H.E.M. and A.I.M.A.; validation: M.K.A., A.A.S., A.E.M., M.S., M.T.S.H., M.A.E., H.S.M. and A.M.A.S.; investigation: M.K.A., A.A.S., H.E.M., A.E.M., M.S. and M.A.E.; writing—original draft preparation, M.K.A.; visualization, M.K.A. and M.A.A.E.M.; writing—review and editing: A.A.S., H.E.M., A.E.M., M.S., A.I.M.A. and M.T.S.H.; data curation: M.A.A.E.M. and M.O.O.; project administration: M.A.A.E.M. and A.I.M.A.; formal analysis: M.T.S.H., A.A.E., H.S.M., A.M.A.S. and H.S.; software: A.A.E., M.A.E., H.S.M., A.M.A.S., H.S. and M.O.O.; methodology: H.S.M. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Science, Technology and Innovation Funding Authority (STDF), grant number 45905.

Data Availability Statement

Data from our research are available upon request.

Acknowledgments

We acknowledge the Science and Technology Development Fund (STDF) of Egypt for supporting this work through the Applied Sciences Research Grant (Project No. 45905). The title of the STDF project is “Evaluation of highly fractionated granites as potential sources of economic-grade ore deposits in the Eastern Desert of Egypt”.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A

Table A1. (A) Representative microprobe analyses of cassiterite in cassiterite-rich greisen in Homrit Akarem intrusion. (B) Representative microprobe analyses of cassiterite in muscovite-rich greisen in Homrit Akarem intrusion. (C) Representative microprobe analyses of cassiterite in beryl-rich greisen in Homrit Akarem intrusion.
Table A1. (A) Representative microprobe analyses of cassiterite in cassiterite-rich greisen in Homrit Akarem intrusion. (B) Representative microprobe analyses of cassiterite in muscovite-rich greisen in Homrit Akarem intrusion. (C) Representative microprobe analyses of cassiterite in beryl-rich greisen in Homrit Akarem intrusion.
(A)
Rock TypeCassiterite-Rich Greisen
Sample No.CG15
Spot No.Cst1Cst3Cst5Cst10Cst12Cst14Cst22Cst25Cst31Cst38Cst46Cst48Cst51
SiO20.410.470.480.510.430.450.450.480.510.450.50.450.46
TiO2<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl
Al2O3<dl<dl<dl<dl<dl0.010.030.02<dl<dl0.08<dl<dl
FeO*0.060.090.020.040.120.170.150.070.260.070.090.050.04
MnO<dl0.010.01<dl0.02<dl<dl<dl0.01<dl0.03<dl<dl
MgO0.04<dl<dl<dl<dl<dl<dl<dl<dl<dl0.07<dl<dl
CaO0.670.980.881.030.880.990.991.010.980.990.981.011.03
Na2O0.080.080.040.09<dl0.080.050.080.260.170.050.080.11
K2O0.060.030.030.020.060.020.030.030.020.010.050.080.02
P2O5<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl
F0.320.230.240.180.070.040.320.130.070.530.230.350.41
SnO295.3997.0197.0296.9395.8796.7796.1896.6295.5196.1696.2295.5496.45
Total97.0398.998.7298.897.4598.5398.298.4497.6298.3898.397.5698.52
(B)
Rock TypeMuscovite-Rich Greisen
Sample No.MG12
Spot No.Cst1Cst3Cst4Cst5Cst7Cst8Cst9Cst10Cst11Cst12Cst13Cst14Cst15
SiO20.490.470.420.460.470.470.460.450.470.460.50.50.47
TiO2<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl
Al2O3<dl<dl<dl0.03<dl<dl0.02<dl<dl<dl0.020.04<dl
FeO*0.140.040.10.060.120.070.060.10.020.030.050.070.07
MnO0.03<dl0.03<dl0.02<dl0.01<dl0.04<dl<dl0.01<dl
MgO0.030.030.05<dl0.02<dl<dl<dl<dl<dl<dl<dl0.02
CaO0.980.790.910.940.781.021.050.870.980.860.890.930.96
Na2O0.020.160.090.050.060.10.080.910.080.070.140.140.05
K2O0.020.030.030.030.020.040.020.040.030.020.010.020.02
P2O5<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl
F0.180.160.290.190.140.210.170.210.070.170.060.060.15
SnO296.2196.6195.6396.2796.8897.0696.4796.1796.8196.7596.8895.7396.37
Total98.198.2997.5598.0398.5198.9798.3498.7598.598.3698.5597.598.11
(C)
Rock TypeBeryl-Rich Greisen
Sample No.BG9
Spot No.Cst1Cst3Cst4Cst5Cst6Cst7Cst8Cst9Cst10Cst11Cst12Cst13
SiO20.490.440.510.490.460.450.470.470.480.450.480.51
TiO2<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl
Al2O30.05<dl0.05<dl<dl<dl<dl<dl<dl<dl<dl<dl
FeO*0.030.040.050.050.160.150.070.170.070.140.10.03
MnO0.01<dl<dl<dl<dl<dl0.01<dl<dl0.03<dl0.04
MgO<dl0.010.010.02<dl0.05<dl0.03<dl0.01<dl0.02
CaO0.781.040.940.980.910.970.980.870.990.880.980.68
Na2O0.060.010.070.060.130.10.070.080.11<dl0.090.09
K2O0.060.06<dl0.030.010.040.030.050.070.040.030.04
P2O5<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl<dl
F0.080.160.230.190.540.130.10.130.090.140.140.23
SnO296.7195.9197.1296.1696.6896.7597.1197.3896.8296.1296.9997.33
Total98.2797.6798.9897.9898.8998.6498.8499.1898.6397.8198.8198.97
Table A2. (A) Representative microprobe analyses of muscovite in muscovite-rich greisen in Homrit Akarem intrusion. (B) Representative microprobe analyses of muscovite cassiterite-rich and beryl-rich greisens in Homrit Akarem intrusion.
Table A2. (A) Representative microprobe analyses of muscovite in muscovite-rich greisen in Homrit Akarem intrusion. (B) Representative microprobe analyses of muscovite cassiterite-rich and beryl-rich greisens in Homrit Akarem intrusion.
(A)
Rock TypeMuscovite-Rich Greisen
Sample No.MG12
Spot No.Ms1Ms7Ms10Ms11Ms14Ms16Ms19Ms20Ms22Ms23Ms26Ms27Ms28
SiO246.6945.4146.8446.7147.8646.7546.946.9949.2347.4246.2346.2547.02
TiO20.080.240.180.160.240.240.160.420.10.360.140.390.18
Al2O330.5230.7628.7929.1429.2331.6329.6130.5130.2730.5231.4630.6929.06
FeO*4.755.14.54.583.853.463.9651.681.993.583.84.42
MnO0.840.770.890.910.750.420.720.880.110.270.840.60.91
MgO0.390.491.091.170.960.631.080.361.220.860.391.060.95
CaO0.030.020.020.070.080.080.050.050.090.060.060.04<dl
Na2O0.230.240.220.210.270.270.20.250.240.210.220.210.18
K2O10.310.4210.3910.6710.3710.4910.3910.1810.1410.1310.4210.6210.65
P2O50.010.010.01<dl0.01<dl0.01<dl0.01<dl0.010.010.01
F2.572.872.932.662.511.912.582.21.981.642.432.612.97
Total96.4396.0195.7796.1596.295.7695.5796.5295.7393.6395.7396.3396.69
Structural formulae based on 22 oxygens
Si6.3806.2536.4596.4186.5236.3476.4386.3806.6316.5156.3226.3156.455
Al iv1.6201.7471.5411.5821.4771.6531.5621.6201.3691.4851.6781.6851.545
Al vi3.2953.2463.1393.1373.2183.4083.2293.2633.4373.4583.3933.2553.158
Ti0.0080.0250.0190.0170.0250.0250.0170.0430.0100.0370.0140.0400.019
Fe0.5430.5870.5190.5260.4390.3930.4550.5680.1890.2290.4090.4340.507
Mn0.0970.0900.1040.1060.0870.0480.0840.1010.0130.0310.0970.0690.106
Mg0.0790.1010.2240.2400.1950.1270.2210.0730.2450.1760.0800.2160.194
Ca0.0040.0030.0030.0100.0120.0120.0070.0070.0130.0090.0090.0060.000
Na0.0610.0640.0590.0560.0710.0710.0530.0660.0630.0560.0580.0560.048
K1.7951.8301.8281.8701.8031.8161.8191.7631.7421.7751.8181.8501.865
(B)
Rock TypeCassiterite-Rich GreisenBeryl-Rich Greisen
Sample No.CG15BG9
Spot No.Ms1Ms3Ms5Ms6Ms7Ms8Ms1Ms2Ms3Ms4Ms5Ms6Ms7
SiO240.5841.2541.4442.2942.2842.5143.8346.6345.1345.4846.3746.7646.92
TiO20.10.120.160.160.260.090.440.120.260.160.140.30.15
Al2O326.7328.4928.0127.8127.4427.8227.8631.0428.2329.2728.4730.1629.6
FeO*4.173.375.212.795.735.734.883.73.333.044.125.073.86
MnO0.760.630.910.290.971.040.830.60.450.740.750.950.56
MgO0.320.730.320.890.320.390.480.560.880.730.930.530.86
CaO0.690.060.010.030.020.020.420.130.060.030.070.040.08
Na2O0.260.230.230.190.240.250.230.250.210.160.190.210.22
K2O9.719.719.689.349.699.679.7910.3710.2910.1210.310.2410.2
P2O5<dl0.010.01<dl0.01<dl<dl0.010.010.01<dl0.01<dl
F3.262.152.542.412.952.712.692.122.622.342.52.642.4
Total86.5386.6888.3986.9689.6790.0691.2995.4791.8491.9593.896.6995.06
Structural formulae based on 22 oxygens
Si6.2766.2516.2406.3986.2986.2956.3646.3756.4746.4486.4986.3736.470
Al iv1.7241.7491.7601.6021.7021.7051.6361.6251.5261.5521.5021.6271.530
Al vi3.1493.3413.2123.3573.1163.1503.1313.3763.2473.3403.2003.2193.281
Ti0.0120.0140.0180.0180.0290.0100.0480.0120.0280.0170.0150.0310.016
Fe0.5390.4270.6560.3530.7140.7100.5930.4230.4000.3600.4830.5780.445
Mn0.1000.0810.1160.0370.1220.1300.1020.0690.0550.0890.0890.1100.065
Mg0.0740.1650.0720.2010.0710.0860.1040.1140.1880.1540.1940.1080.177
Ca0.1140.0100.0020.0050.0030.0030.0650.0190.0090.0050.0110.0060.012
Na0.0780.0680.0670.0560.0690.0720.0650.0660.0580.0440.0520.0560.059
K1.9151.8771.8591.8021.8411.8261.8131.8081.8831.8301.8411.7801.794
Table A3. Representative microprobe analyses of beryl in beryl-rich greisen in Homrit Akarem intrusion.
Table A3. Representative microprobe analyses of beryl in beryl-rich greisen in Homrit Akarem intrusion.
Rock TypeBeryl-Rich Greisen
Sample No.BG9
Spot No.Brl1Brl3Brl4Brl6Brl7Brl9Brl10Brl12Brl13Brl15Brl16Brl18Brl19
SiO266.9165.7966.2866.5465.2165.765.4166.465.8365.2766.0666.6465.87
TiO2<dl0.01<dl0.01<dl<dl0.020.010.01<dl<dl<dl0.02
Al2O317.9517.8116.8917.7217.7217.817.7417.6917.81818.0316.5517.74
FeO0.330.490.510.580.550.580.60.470.460.410.340.370.51
MnO<dl<dl0.01<dl0.02<dl<dl<dl<dl<dl0.01<dl<dl
MgO0.090.160.150.180.160.120.150.140.120.130.170.140.13
CaO0.030.020.040.030.070.040.030.030.040.060.080.130.03
Na2O0.360.450.480.490.440.440.430.410.410.360.360.410.43
K2O0.020.020.040.010.050.040.030.020.050.030.030.080.05
BeO11.5112.413.6811.4513.8113.214.1212.4612.7711.9311.4612.313.31
Total97.297.1598.0897.0198.0397.9298.5397.6397.4996.1996.5496.6298.09
Table A4. Representative microprobe analyses of topaz in cassiterite-rich and topaz-rich greisens in Homrit Akarem intrusion.
Table A4. Representative microprobe analyses of topaz in cassiterite-rich and topaz-rich greisens in Homrit Akarem intrusion.
Rock TypeCassiterite-Rich GreisenTopaz-Rich Greisen
Sample No.CG15TG4
Spot No.Tpz1Tpz2Tpz3Tpz4Tpz1Tpz4Tpz6Tpz7Tpz9Tpz10Tpz13Tpz15Tpz16
SiO229.1628.9929.7130.0828.4729.3728.2127.7828.8629.3128.4929.1129.64
TiO2<dl<dl<dl<dl<dl<dl0.01<dl<dl0.020.010.01<dl
Al2O352.551.6150.0451.3852.1251.5451.7250.8551.1150.2652.0351.5752.01
FeO*0.020.020.020.020.03<dl0.020.030.03<dl0.030.040.03
MnO<dl<dl<dl0.01<dl<dl<dl<dl<dl0.010.01<dl<dl
MgO0.010.010.010.010.010.02<dl<dl0.010.010.01<dl0.01
CaO<dl0.03<dl<dl<dl0.04<dl<dl0.040.05<dl0.020.02
Na2O<dl<dl<dl<dl<dl0.04<dl<dl<dl0.03<dl<dl<dl
K2O0.010.010.010.010.010.030.010.010.010.020.010.010.01
P2O50.010.010.010.01<dl0.010.020.010.010.010.010.020.01
F18.3218.319.3718.3718.6219.4220.0219.9320.0418.8819.2619.3619.22
Total10098.9899.1799.8999.26100.510098.61100.198.699.86100.1101
Table A5. Representative microprobe analyses of tourmaline in cassiterite-rich and beryl-rich greisens in Homrit Akarem intrusion.
Table A5. Representative microprobe analyses of tourmaline in cassiterite-rich and beryl-rich greisens in Homrit Akarem intrusion.
Rock TypeCassiterite-Rich GreisenBeryl-Rich Greisen
Sample No.CG15BG9
Spot No.Tur1Tur3Tur4Tur6Tur7Tur8Tur9Tur1Tur2Tur4Tur5Tur6Tur7
SiO234.9353534.835.235353535.134.934.935.335.2
TiO20.150.10.130.160.110.120.140.140.090.160.140.120.11
Al2O334.233.93434.234.134.134.134.134.134.134.134.233.9
FeO12.312.312.512.11212.112.312.312.112.312.112.212
MnO0.520.530.510.530.480.540.520.530.480.510.510.520.49
MgO1.451.431.381.481.721.471.471.441.581.451.621.51.59
CaO0.170.10.130.160.120.120.150.150.090.170.140.130.11
Na2O2.0522.032.022.011.982.032.031.982.042.042.011.98
K2O0.030.030.030.040.030.030.030.030.020.040.030.030.03
B2O38.428.938.658.728.618.748.538.638.678.828.768.618.68
Total94.294.394.394.394.394.394.394.394.294.494.394.694.1
Structural formulae based on 29 oxygens
Si6.0456.0346.0596.0116.0696.0446.0506.0446.0666.0166.0266.0826.077
Ti0.0200.0130.0170.0210.0140.0160.0180.0180.0120.0210.0180.0160.014
Al6.9896.8976.9186.9666.9256.9416.9596.9416.9316.9256.9276.9326.905
Fe(ii)1.7821.7691.8021.7541.7271.7491.7791.7831.7451.7741.7461.7481.739
Mn0.0760.0770.0750.0780.0700.0790.0760.0780.0700.0750.0750.0760.072
Mg0.3750.3680.3560.3810.4420.3780.3790.3710.4070.3730.4170.3850.410
Ca0.0320.0180.0240.0300.0220.0220.0280.0280.0170.0310.0260.0240.020
Na0.6890.6690.6800.6770.6720.6630.6810.6800.6630.6830.6820.6710.663
K0.0070.0070.0070.0090.0070.0070.0070.0070.0040.0090.0070.0070.007
B2.5182.6602.5812.6012.5622.6042.5462.5742.5832.6272.6092.5572.589
Table A6. Representative microprobe analyses of columbite in cassiterite-rich and beryl-rich greisens in Homrit Akarem intrusion.
Table A6. Representative microprobe analyses of columbite in cassiterite-rich and beryl-rich greisens in Homrit Akarem intrusion.
Rock TypeCassiterite-Rich Greisen Beryl-Rich Greisen
Sample No.CG15BG9
Spot No.Clb1Clb3Clb4Clb6Clb7Clb9Clb11Clb1Clb2Clb5Clb7Clb8Clb9
SiO20.150.280.220.590.06<dl0.320.060.130.44<dl<dl<dl
TiO20.730.31.670.560.381.10.360.510.580.611.231.481.07
Al2O3<dl0.04<dl0.020.030.010.01<dl0.0100.010.050.01
FeOt17.115.515.115.31817.11617.716.214.716.516.716.7
MnO3.483.63.663.393.533.083.613.393.683.352.472.292.93
MgO3.483.63.663.393.533.083.613.393.683.352.472.292.93
CaO0.050.090.080.050.020.03<dl0.030.020.120.080.10.1
Na2O<dl<dl<dl<dl<dl<dl<dl0<dl<dl<dl<dl<dl
K2O<dl<dl<dl0.09<dl<dl<dl0.03<dl<dl<dl<dl<dl
P2O5<dl<dl<dl<dl<dl<dl<dl0<dl<dl<dl<dl<dl
Nb2O564.15960.560.467.466.361.864.264.158.66566.164.5
Ta2O511.615.513.115.710.49.9717.212.61121.412.412.811.3
Total97.294.494.396.199.897.599.398.695.799.297.799.496.7
Structural formula on the basis of 6 oxygen atoms
Si0.0090.0180.0140.0360.0040.0000.0190.0040.0080.0270.0000.0000.000
Ti0.0330.0140.0780.0260.0170.0490.0160.0230.0270.0280.0550.0650.049
Al0.0000.0030.0000.0010.0020.0010.0010.0000.0010.0000.0010.0030.001
Fe2+0.8700.8250.7770.7870.8950.8520.8070.9000.8340.7390.8180.8080.847
Mn0.1790.1940.1910.1760.1780.1560.1840.1750.1920.1710.1240.1130.150
Mg0.3160.3420.3370.3100.3130.2740.3240.3070.3370.3010.2190.1980.264
Ca0.0030.0060.0050.0030.0010.0020.0000.0020.0010.0080.0050.0060.006
Nb1.7651.6991.6891.6761.8121.7891.6821.7651.7821.5951.7451.7341.765
Ta0.1920.2690.2200.2620.1670.1620.2820.2080.1830.3510.2000.2010.186
Mn/(Mn + Fe)0.170.190.200.180.170.150.190.160.190.190.130.120.15
Ta/(Ta + Nb)0.100.140.120.130.080.080.140.110.090.180.100.100.10
Table A7. (A) Representative microprobe analyses of fluorite in muscovite-rich and cassiterite-rich greisens in Homrit Akarem intrusion. (B) Representative microprobe analyses of fluorite in topaz-rich and beryl-rich greisens in Homrit Akarem intrusion.
Table A7. (A) Representative microprobe analyses of fluorite in muscovite-rich and cassiterite-rich greisens in Homrit Akarem intrusion. (B) Representative microprobe analyses of fluorite in topaz-rich and beryl-rich greisens in Homrit Akarem intrusion.
(A)
Rock TypeMuscovite-Rich GreisenCassiterite-Rich Greisen
Sample No.MG12CG15
Spot No.Fl1Fl3Fl6Fl8Fl9Fl10Fl1Fl2Fl4Fl7Fl8Fl10Fl12
SiO20.040.040.030.020.020.060.120.030.130.080.010.010.04
TiO2<dl<dl0.01<dl<dl<dl<dl0.01<dl0.01<dl<dl<dl
Al2O3<dl0.03<dl0.01<dl0.020.060.030.110.02<dl0.070.02
FeO*0.10.060.060.130.080.030.070.070.020.090.090.140.05
MnO0.060.050.040.050.020.040.030.040.010.050.040.05<dl
MgO0.01<dl<dl<dl<dl<dl<dl0.01<dl<dl<dl0.010.02
CaO48.5249.9548.4150.8651.3749.8848.7149.7650.5449.6850.4149.2949.76
Na2O0.060.020.02<dl0.050.060.040.050.050.080.040.010.06
K2O0.030.080.020.03<dl0.030.020.040.030.060.070.120.02
P2O50.050.040.060.090.070.070.060.060.070.080.050.060.04
F50.8649.6450.9149.6948.3149.0350.4750.2449.6249.9648.6750.5250.34
Total99.7399.9199.56100.999.9299.2299.58100.3100.6100.199.38100.3100.4
(B)
Rock TypeTopaz-Rich GreisenBeryl-Rich Greisen
Sample No.TG4Bg9
Spot No.Fl1Fl4Fl6Fl7Fl9Fl10Fl12Fl1Fl2Fl4Fl5Fl6Fl7
SiO20.090.250.490.390.280.070.060.020.040.060.850.020.03
TiO2<dl<dl0.01<dl<dl0.01<dl<dl<dl<dl<dl0.01<dl
Al2O30.060.260.670.270.260.080.02<dl0.01<dl0.5<dl<dl
FeO*0.060.130.090.040.060.040.150.140.270.440.730.550.64
MnO0.010.060.040.040.040.050.040.050.040.090.020.050.05
MgO<dl0.07<dl0.01<dl0.040.120.01<dl<dl<dl<dl<dl
CaO51.0149.9647.7750.2951.251.3950.8350.1450.950.4349.8449.8249.46
Na2O0.040.020.020.010.050.09<dl0.070.01<dl0.03<dl0.04
K2O0.020.020.050.030.130.130.140.170.090.10.010.010.01
P2O50.080.040.050.060.050.060.080.070.030.050.050.060.03
F48.2448.4350.0648.8848.1347.6748.8449.1447.2948.9747.8248.7848.69
Total99.6199.2499.25100100.299.63100.399.8198.68100.199.8599.398.95
Table A8. Microprobe analyses of corundum in cassiterite-rich greisen in Homrit Akarem intrusion.
Table A8. Microprobe analyses of corundum in cassiterite-rich greisen in Homrit Akarem intrusion.
Rock TypeCassiterite-Rich Greisen
Sample No.CG15
Spot No.Crn1Crn2Crn3Crn4Crn5Crn6Crn7Crn8Crn9Crn10Crn11Crn12Crn13Crn14
SiO20.540.40.090.220.570.250.410.220.220.010.160.250.430.38
TiO2<dl<dl<dl<dl0.01<dl<dl<dl<dl0.01<dl<dl<dl<dl
Al2O396.3698.5196.8399.2298.5898.6599.6399.4697.9397.0699.1498.6898.3899.32
FeO*0.10.080.060.10.050.010.060.020.110.070.080.080.020.06
MnO0.030.020.010.02<dl<dl0.010.030.02<dl<dl0.010.010.01
MgO0.120.050.140.180.08<dl0.110.170.060.10.110.080.040.03
CaO0.10.010.05<dl0.04<dl<dl0.010.050.040.180.09<dl0.02
Na2O0.08<dl0.040.020.03<dl0.01<dl0.020.030.090.05<dl0.01
K2O<dl0.01<dl0.010.010.020.020.010.010.010.010.04<dl0.02
P2O5<dl0.01<dl0.02<dl0.020.01<dl<dl0.030.010.04<dl0.02
Total97.3399.0997.2299.7999.3798.95100.399.9298.4297.3699.7899.3298.8899.87

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Figure 1. General geologic map of the central and southern sectors (dividing line after [16]) of the Eastern Desert of Egypt showing the location of the Homrit Akarem area.
Figure 1. General geologic map of the central and southern sectors (dividing line after [16]) of the Eastern Desert of Egypt showing the location of the Homrit Akarem area.
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Figure 2. Geologic map of the Homrit Akarem area (modified after [5]).
Figure 2. Geologic map of the Homrit Akarem area (modified after [5]).
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Figure 3. Hand specimens show the different types of greisens: (a) muscovite-rich greisen, (b,c) cassiterite-rich greisen, (d) topaz-rich greisen, (e) beryl-rich greisen, and (f) red hematitic and black Mn oxide staining of the greisen bodies.
Figure 3. Hand specimens show the different types of greisens: (a) muscovite-rich greisen, (b,c) cassiterite-rich greisen, (d) topaz-rich greisen, (e) beryl-rich greisen, and (f) red hematitic and black Mn oxide staining of the greisen bodies.
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Figure 4. Microphotographs of the studied greisens (a–f) are backscattered electron images, while c and d are images taken in plane-polarized transmitted light): (a) big muscovite crystals traversed by veinlets of secondary minerals; (b) cassiterite, muscovite, and fluorite in cassiterite-rich greisen; (c,d) oscillatory color banding and sector zoning in big crystals of cassiterite; (e) inclusion of columbite in cassiterite crystal; and (f) topaz, muscovite, and fluorite crystals in topaz-rich greisen.
Figure 4. Microphotographs of the studied greisens (a–f) are backscattered electron images, while c and d are images taken in plane-polarized transmitted light): (a) big muscovite crystals traversed by veinlets of secondary minerals; (b) cassiterite, muscovite, and fluorite in cassiterite-rich greisen; (c,d) oscillatory color banding and sector zoning in big crystals of cassiterite; (e) inclusion of columbite in cassiterite crystal; and (f) topaz, muscovite, and fluorite crystals in topaz-rich greisen.
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Figure 5. (a) Mg-Ti-Na ternary diagram plotting for the analyzed muscovites; “field primary muscovites” and “field of secondary muscovites” after [17]. (b) Chemical composition and nomenclature of the Ta-Nb oxides based on Ta/(Ta + Nb) vs. Mn/(Mn + Fe) ratios.
Figure 5. (a) Mg-Ti-Na ternary diagram plotting for the analyzed muscovites; “field primary muscovites” and “field of secondary muscovites” after [17]. (b) Chemical composition and nomenclature of the Ta-Nb oxides based on Ta/(Ta + Nb) vs. Mn/(Mn + Fe) ratios.
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Figure 6. (a) Schematic cross-section showing the outcrop-scale relationship between the Homrit Akarem pluton and greisens and their country rocks. (b) Schematic cross-section showing formation of albitized granite and greisens in the apex of a magmatic cupola above A-type granites.
Figure 6. (a) Schematic cross-section showing the outcrop-scale relationship between the Homrit Akarem pluton and greisens and their country rocks. (b) Schematic cross-section showing formation of albitized granite and greisens in the apex of a magmatic cupola above A-type granites.
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Figure 7. (a) Partial replacement of albite by muscovite with preservation of original crystal habit. (b) Extensive replacement of albite by muscovite without preservation of original crystal habit.
Figure 7. (a) Partial replacement of albite by muscovite with preservation of original crystal habit. (b) Extensive replacement of albite by muscovite without preservation of original crystal habit.
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Azer, M.K.; Surour, A.A.; Moussa, H.E.; Maurice, A.E.; Sami, M.; Abou El Maaty, M.A.; Akarish, A.I.M.; Heikal, M.T.S.; Elnazer, A.A.; Elsagheer, M.A.; et al. Homrit Akarem Post-Collisional Intrusion, Southeastern Desert, Egypt: Petrogenesis of Greisen Formed in a Cupola Structure and Enrichment in Strategic Minerals. Geosciences 2025, 15, 200. https://doi.org/10.3390/geosciences15060200

AMA Style

Azer MK, Surour AA, Moussa HE, Maurice AE, Sami M, Abou El Maaty MA, Akarish AIM, Heikal MTS, Elnazer AA, Elsagheer MA, et al. Homrit Akarem Post-Collisional Intrusion, Southeastern Desert, Egypt: Petrogenesis of Greisen Formed in a Cupola Structure and Enrichment in Strategic Minerals. Geosciences. 2025; 15(6):200. https://doi.org/10.3390/geosciences15060200

Chicago/Turabian Style

Azer, Mokhles K., Adel A. Surour, Hilmy E. Moussa, Ayman E. Maurice, Mabrouk Sami, Moustafa A. Abou El Maaty, Adel I. M. Akarish, Mohamed Th. S. Heikal, Ahmed A. Elnazer, Mustafa A. Elsagheer, and et al. 2025. "Homrit Akarem Post-Collisional Intrusion, Southeastern Desert, Egypt: Petrogenesis of Greisen Formed in a Cupola Structure and Enrichment in Strategic Minerals" Geosciences 15, no. 6: 200. https://doi.org/10.3390/geosciences15060200

APA Style

Azer, M. K., Surour, A. A., Moussa, H. E., Maurice, A. E., Sami, M., Abou El Maaty, M. A., Akarish, A. I. M., Heikal, M. T. S., Elnazer, A. A., Elsagheer, M. A., Mubarak, H. S., Seddik, A. M. A., Sobhy, H., & Osama, M. O. (2025). Homrit Akarem Post-Collisional Intrusion, Southeastern Desert, Egypt: Petrogenesis of Greisen Formed in a Cupola Structure and Enrichment in Strategic Minerals. Geosciences, 15(6), 200. https://doi.org/10.3390/geosciences15060200

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