Geochemical Constraints on Petrogenesis of Homrit Waggat Rare Metal Granite, Egypt

Hany H. El Hadek¹, Mohamed A. Mohamed¹, Galal H. El Habaak¹, Wagih W. Bishara¹, Kamal A. Ali²

¹Geology Department, Faculty of Science, Assiut University, Assiut, Egypt

²Department of Mineral Resources and Rocks, Faculty of Earth Sciences, King Abdulaziz University, Jeddah, Saudi Arabia

Email address

Citation

Hany H. El Hadek, Mohamed A. Mohamed, Galal H. El Habaak, Wagih W. Bishara, Kamal A. Ali. Geochemical Constraints on Petrogenesis of Homrit Waggat Rare Metal Granite, Egypt. International Journal of Geophysics and Geochemistry. Vol. 3, No. 4, 2016, pp. 33-48.

Abstract

The Homrit Waggat granite is a composite granite pluton intruded in metamorphosed volcano-sedimentary association and the metagabbro-diorite complex to the east and north and tonalite-granodiorite suite to the south and northeast. Mineralogically and geochemically the granite phases change from subsolvus peraluminous granodiorite to hypersolvus metaluminous and highly evolved alkali feldspar granite, passing through biotite and mylonitized biotite granites. Late to post-magmatic processes are represented by marginal stockscheider amazonite pegmatite, marginal amazonite albite as well as greisen zone up to 30 m². Increasing of SiO₂, alkalis, Rb, F, Nb, Ta, Sn, Ga, HREEs and Y, and decreasing of Fe, Al, Mg, Ca, Mn, Ti, Sr, Ba, Zr, and LREEs from the biotite granodiorite to hypersolvus alkali feldspar granite reflects magmatic fractionation processes of Homrit Waggat granite phases. LREEs fractionation patterns as well as Eu anomalies decrease from granodiorite to the alkali feldspar granite and the latter displays flat patterns. In the hypersolvus alkali feldspar granite, Ga/Al ratio is typically of A-type granite, but not their Zr, Y, or Ce enrichments. In addition, the hypersolvus granite is characterized by low-P₂O₅ and the LREEs>>HREEs depletion which reflects the initial undersaturation of accessory mineral assemblage that resulted from high concentration of volatiles and/or alkali complexes. The behaviour of REEs and Zr in the mentioned phases is consistent with F- content as well as accessory minerals in the studied granites. Trace elements pattern in the spider diagram show significant depletion in Sr, Ba, P and Ti, and enrichment in Rb, Th and U. The Sr, Ba, P and Ti depletion could be related to fractionation of plagioclase, apatite and ilmenite. Zircon saturation temperature (Tzr) calculated from bulk rock composition for Homrit Waggat granites range between 809°C and 765°C. These values are consistent with low temperature granite which crystallized from a source melt saturated with zirconium concentrations via partial melting of I- type granite magma may be granodioritic in composition. The highly evolved alkali feldspar granite was formed from the initial granodioritic I-type melt via fractional crystallization. F-rich melt and F-complexing played an important role in the evolution and chemical characterization of the highly evolved hypersolvus alkali feldspar granite. Four stages of mineralization were detected in the Homrit Waggat granite. These stages are magmatic, pegmatitic, metasomatic and veins. Columbite, cassiterite, fluorite as well as undifferentiated rare earth minerals are detected.

Keywords

A-type Granite, Rare-Metals, Zircon Saturation, Mineralization, Fractionation, Melt

1. Introduction

Granitic rocks constitute a significant proportion of the continental crust of the Nubian Shield. They are classified into two groups: older and younger granites [3, 23]. The older group comprises calc-alkaline syn-tectonic (700-850 Ma) gabbro-diorite, tonalite, trondhjemite, and granodiorite intrusions, which was followed by late-to post-tectonic (650-520 Ma) younger group of granodiorites, granites, and alkali feldspar granites [7, 23, 32, 57, 61, 62] Some of the younger granite plutons show an A-type geochemical signature such as low CaO and MgO and high SiO₂, Na₂O + K₂O, Nb, Y, and REE [1, 27, 49, 50].

Regarding the origin of A-type granites in the Nubian Shield, one of the major unsolved problems is the difficulty of assessing the tectonic environment and the protolith of these granites [48]. Homrit Waggat area lies between latitudes 25° 7' - 25° 12' N and longitudes 34° 16' - 34° 22' E (Fig. 1), covering an area about 50 km². According to Moghazi et al. [48] Homrit Waggat rocks belong to an island-arc association (metagabbro-diorite complex), older granitoids (tonalite-granodiorite association) and younger granitoids (leucogranite) are represented. Leucogranites are characterized by a shallow level of emplacement and provide a useful case study of A-type granite in the Eastern Desert of Egypt.

Rare metal granites have been identified as those with high concentrations of normally dispersed elements such as F, Li, Rb, Cs, Sn, Ta, Nb, Zr and REE [41]. Christiansen et al. [14] distinguished two fundamentally different types of rare-metal granites: one peralkaline and the other metaluminous to peraluminous (F-Li). The peraluminous or metaluminous leucogranites probably include a major crustal component [5, 10, 51]. The peralkaline granites are extremely enriched in Zr, Nb and LREE, whereas the aluminous granites are enriched in Rb, Ta, U and Sn [14]. King et al. [40] stated that the aluminous A-type granites possess higher oxygen fugacity yet lower Zr content and crystallization temperature compared to the alkaline A-type granites.

The purpose of the present study is to declare the diagnostic characteristics which would be useful for the petrogenesis of the Homrit Waggat granites. So, geochemical behavior of major, trace and REEs are studied.

2. Geological Setting

The Homrit Waggat area comprises a volcano-sedimentary association and a metagabbro-diorite complex intruded by a granodiorite suite, which is in turn intruded by leucogranite (Fig. 2). The Homrit Waggat pluton displays elongated oval shape bodies in a NW-SE direction (long axis 9 km) separated by Wadi El Faliq. It covers an area of about 50 km² and rises about 1096 m above sea level. The pluton intrudes the metamorphosed volcano-sedimentary association and the metagabbro-diorite complex to the east and north and tonalite-granodiorite suite to the south and northeast (Fig. 2). The studied area is intersected by major sets of faults trending approximately northwest and due north (Fig. 2). The granitic rocks possess a system of jointing well developed in two main sets, trending NE-SW and NW-SE with less dominant N-S trends. These joints are gently to steeply inclined and sometimes are vertical.

Petrographically, the pluton consists of four different granite phases. Biotite granodiorite forms a wide incomplete zone. It occupies the southern and northeastern parts of the study area. Biotite granite occupies the core of the pluton. It is hard, massive and homogeneous, and contains a few xenoliths of granodiorite with sharp intrusive contact. The third granitic phase is mylonitized granite which forms the northeastern part of the pluton and shows striking features of both brittle and ductile-plastic deformation. Hypersolvus alkali feldspar granite is the latest phase. It makes up the southeastern and western parts of the pluton. The contacts between hypersolvus alkali feldspar granite and both of biotite granite and mylonitized granite are sharp.

The late - to post-magmatic hydrothermal processes are represented by marginal stockscheider amazonite pegmatite pods as well as marginal amazonite albite granite at the northern contacts with metagabbro-diorite complex. Both contain columbite, cassiterite and other undifferentiated rare earth minerals. Fluorite veins trending NNW–NW (up to 2 m wide and 30 m long) were recorded close to the contact between biotite granodiorite and mylonitized granite. Greisen zone up to 30 m² composed mainly of muscovite, fluorite, cassiterite and Nb-minerals, occurs at the eastern contact between hypersolvus and mylonitized granites.

Fig. 1. Location map of the studied area.

Fig. 2. Geological map of Homrit Waggat area after Hassanen [30].

3. Analytical Methods

Chemical analyses were carried out in ALS lab, Loughrea, Ireland for 13 samples representing the different phases of the Homrit Waggat granites. The analyses of major oxides were carried out using ICP-AES technique with precision ± 5% and the contents of trace and REEs were analyzed using ICP-MS technique with precision ± 10%. Fluorine content was analyzed by Ion Selective Electrode in ACME lab, British Columbia, Canada.

4. Whole Rock Geochemistry

Major oxides and CIPW norm calculations as well as trace element contents of the studied granites are presented in (Table 1) after El Hadek [24]. The analyzed granites except biotite granodiorite phase show high fractionation, as indicated from the high contents of SiO₂ (> 70 wt.%). On the Streckeisen and LeMaitre diagram [63] and the R1-R2 multicationic classification of igneous rocks proposed by De La Roche et al. [18], the Homrit Waggat granites lie in the granodiorite, syenogranite to monzogranite and alkali feldspar granite fields (Figures not shown).

SiO₂, Na₂O, K₂O, F, Li, Cs, Rb, Zr, Ga, Zn, Nb, Ta, Sn and Hf show continuous increasing, whereas, Al₂O₃, Fe₂O₃, TiO₂, CaO, MgO, Sr and Ba, are decreasing from biotite granodiorite to hypersolvus alkali feldspar granite. Aluminum saturation index (ASI) decreases from 1.22 in biotite granodiorite indicating peraluminous nature to 1.03 in hypersolvus alkali feldspar granite indicating metaluminous or very slightly peraluminous nature. In the marginal albite granite ASI are 1.16 and 1.22 indicating mildly peraluminous to peraluminous nature (Fig. 3 and Table 1). The analyzed samples of Homrit Waggat granites show normative corundum values range from 0.03 to 2.9%.

In general, the mafic components (TFMM) decrease with progressive magma evolution, consequently modal albite increases with evolution [72]. Decrease of Fe₂O₃, TiO₂ and MgO contents in Homrit Waggat granites from biotite granodiorite to hypersolvus alkali feldspar granite is reflected in decreasing abundances of biotite and ilmenite in the more differentiated rocks. As TFMM decreases, Rb, Nb, Ga, Sn and Ta increase while Ba, Zr, K/Rb, Zr/Hf and Th/U decrease (Fig. 4). These variations probably reflect changes in accessory-mineral abundance; in particular variations in Zr, Hf, Nb, Ta, Th, U and HREE which may be mainly controlled by zircon and monazite [72].

Table 1. Chemical analyses and CIPW norms of the Homrit Waggat granites.

Bd: below the detection limit. The detection limits for Mo = 1 ppm and Cs = 0.5 ppm.

Fig. 3. Al₂O₃ / (CaO+Na₂O+K₂O) versus Al₂O₃ / (Na₂O+K₂O) diagram, field boundaries from Maniar and Piccoli [44]. + = biotite granodiorite, x = biotite granite, ∆ = hypersolvus alkali feldspar granite, *= marginal albite granite.

Fig. 4. Correlations of (TiO₂ + Fe₂O₃ + MgO + MnO) wt.% TFMM with Rb, Nb, Ga, Sn, Ta, Ba, Zr, K/Rb and Zr/Hf for Homrit Waggat granites. Symbols as in Fig. 3.

Fluorine contents in the studied granites increase from 200 ppm in granodiorite to 2300 ppm in hypersolvus alkali feldspar granite. Such increasing would suggest the progressive influence of fluorine in the late stage evolution of Homrit Waggat granitic magma [55, 71]. The contents of F in the latest granite phase are consistent with F-bearing granites of Pichavant and Manning [56]. Štemprok [60] stated that the F-rich melts are able to persist to late stage of magmatic differentiation. Therefore, they are able to concentrate incompatible elements such as (Rb, Li, Ga, Sn and Y) because these elements can form stable complexes with F or H₂O at magmatic temperatures [8, 39]. This behavior is supported from the positive correlation between Sn, Rb, Ga and Y with F shown in (Fig. 5).

In Rb-Sr-Ba ternary diagram (Figure not shown), the samples of biotite and hypersolvus alkali feldspar granites of Homrit Waggat are clustered in the field of strongly differentiated granite of El-Bouseily and El-Sokkary [22] and granite related Sn-W-Mo deposits of Biste [9]. K/Rb ratio is commonly used to characterize the evolution of granitic magma. In Homrit Waggat granites K/Rb ratios range between 78 and 57 in hypersolvus alkali feldspar granite, which is consistent with highly fractionated and evolved magma. The reduced K/Rb ratios may be due to the increasing fractional crystallization of biotite and K-feldspar [42]. The high Differentiation Index (DI) together with the strong depletion of Eu, Ba, and Sr in hypersolvus alkali feldspar granite may imply a considerable fractional crystallization (see, Mao et al., [46]). LILEs plot of Rb/Sr against both Ba and Sr, and Sr versus Ba (Fig. 6a-c) explained that Ba, Rb and Sr are controlled by fractionation trends of K-feldspar. Although the negative Eu anomaly was controlled by fractional crystallization of plagioclase, fractional crystallization of alkali feldspar seems more effective in controlling Ba abundances than that of plagioclase (Fig. 6d). The marginal albite granite shows K/Rb ratios between 31 and 35 <100 [15] or <150 [34] may indi­cate the interaction with an aqueous fluid phase or indicate mineral growth in the presence of aqueous fluids [59].

The biotite and hypersolvus alkali feldspar granites show Al/Ga ratios vary from 1720 to 3294, this is consistent with Al/Ga ratio in A-type granites < 3800 [17, 69], while biotite granodiorite shows higher ratios with average 4953. The increase of Ga implies that fluoride complexes are possible forms that made Ga stably preserved in the melt in the course of magma fractionation [28, 45]. The highest values of Ga (46-49 ppm) were detected in the marginal albite granite. According to Gu et al. [28] fluid fractionation is a possible mechanism to cause Ga enhancement in the marginal albite granite. The relation between Ga and Al contents is given in (Fig. 7).

REEs analyses of the studied Homrit Waggat granites are given in (Table 2). Chondrite normalized patterns after Anders and Grevesse [4] are shown in (Fig. 8). The average of ∑ REE increasing from 82.89 ppm in biotite granodiorite to 99.7 ppm in biotite granite and to 107.6 ppm in hypersolvus alkali feldspar granite. The marginal albite granite displays average of ∑ REE = 60.61 ppm.

The REEs fractionation as well as Eu anomalies decrease with fractionation in the studied granite. Biotite granodiorite has a considerable fractionated REE patterns ((La/Yb)_N = 9.62-9.89 and (Gd/Yb) _N = 1.85-2.18) and displays small negative Eu anomaly (Eu/Eu*)_N = 0.71-0.75 (Fig. 8a), biotite granite has a moderate LREE fractionated patterns ((La/Yb)_N = 1.93-2.96 and (Gd/Yb)_N = 0.51-0.76) and negative Eu anomaly (Eu/Eu*)_N = 0.29-0.46 (Fig. 8b), and hypersolvus alkali feldspar granite has a relatively enriched HREE patterns ((La/Yb)_N = 0.29-0.47 and (Gd/Yb) _N = 0.15-0.26) and large negative Eu anomaly (Eu/Eu*)_N = 0.02-0.06 (Fig. 8c). The REE patterns of biotite and hypersolvus alkali feldspar granites are consistent with REE patterns of A-type granites [21]. The albite granite has nearly similar REE patterns as hypersolvus alkali feldspar granite, but with lower total REE (Fig. 8d), the average of (La/Yb)_N = 0.39-49, and (Gd/Yb)_N = 0.22, and large negative Eu anomaly average (Eu/Eu*)_N = 0.03. Ahmadipour and Rostamizadeh [2]; Kaur et al. [37]; Zaraysky et al. [74] stated that albitizatiton process may lead to such REE depletion.

Fig. 5. Variation diagrams of Sn, Rb, Ga and Y versus F. + = biotite granodiorite, x = biotite granite, ∆ = hypersolvus alkali feldspar granite, *= marginal albite granite.

Fig. 6. Variation diagrams of (a & b) Ba and Sr vs. Rb/Sr, (c) Ba vs. Sr. Fractionation vectors (solid lines) and melting vectors (dashed lines) are redrawn from Inger and Harris [33]. Mu (VA) – vapour-absent muscovite melting; Mu (VP) – vapour-present muscovite melting and Bi (VA) – vapour-absent biotite melting. (d) Ba vs. Eu/Eu*, after Eby [19]. Pl = plagioclase, Kf = K-feldspar, Bt = biotite, Hb = hornblende, AF = alkali feldspar. Symbols as in Fig. 5.

Fig. 7. Plots of Ga versus Al₂O₃ for the studied granites. Symbols as in Fig. 5.

Fig. 8. Chondrite normalized patterns of biotite granodiorite (a), biotite granite (b), hypersolvus alkali feldspar granite (c) and marginal albite granite (d).

Table 2. REE (ppm) abundances of the Homrit Waggat granites.

5. Discussion

5.1. Petrogenesis

Fig. 9. Primitive mantle-normalized trace element patterns for Homrit Waggat granites. Normalizing values from Sun and McDonough [65]. + = biotite granodiorite, x = biotite granite, ∆ = hypersolvus alkali feldspar granite.

Homrit Waggat granite complex is formed of biotite granodiorite, biotite granite, mylonitized (highly sheared) pink granite and hypersolvus alkali feldspar granite. Increasing of SiO₂, alkalis, Rb, F, Nb, Ta, Sn, Ga, HREEs and Y, and decreasing of Fe, Al, Mg, Ca, Mn, Ti, Sr, Ba, Zr, and LREES from the biotite granodiorite to hypersolvus alkali feldspar granite reflects magmatic fractionation processes of Homrit Waggat granite phases. The behavior of REEs and Zr in the mentioned phases is consistent with F- content as well as accessory minerals in the studied granites. Trace elements pattern in the primitive mantle spider diagram (Fig. 9), shows significant depletion in Sr, Ba, P and Ti, and enrichment in Rb, Th, and U. The Sr, Ba, P, and Ti depletion could be related to fractionation of plagioclase, apatite and ilmenite.

Ga/Al ratios in the hypersolvus alkali feldspar granite are particularly diagnostic for A-type granites where the samples fall in the A-type granite field according to Whalen et al. [69] (Fig. 10), within plate granite field of Pearce et al. [54] (Fig. 11a, b), and A2-type granite field of Eby [20] (Fig. 12). It should also be noted from Eby [20] that A1-types invariably are associated with true anorogenic (within plate) settings while A2-types are often emplaced in post-collisional, post-orogenic settings. Whalen and Currie [68] differentiate between large alkaline suites and other suites containing small amounts of A-type rock. They stated that crystal-liquid fractionation in the upper levels of large compositionally stratified I-type magma chamber can produce small volume of evolved magma with A-type characteristics [31, 43]. Large degree of fractional crystallization of I- or S-type granite magmas can also produce minor amounts of evolved magmas with high Ga/Al, very low Ba and Sr, and extreme variation in Rb/Sr and Rb/Ba [68]. Association of subsolvus to hypersolvus, peraluminous to metaluminous A-type granites found in the studied Homrit Waggat granite pluton is common and recorded also in many places of the world eg. Evisa complex, Cisica [11]; Flowers Bay, Labrador [16]; Mesoic Nigerian granites [12] and the Arabian Shield [35].

According to Collins et al. [17], such granite suites are restricted to crustal blocks, from which earlier orogenic (I- and S-type) granitic magmas were extracted, gives strong support to the model of a previously melted crustal source to produce the distinctive chemical signature of A-type granitic magma. Sawka et al. [66] concluded that the highly fractionated I- and S-type granite exhibit high Ga/Al ratios typical of A-type granite, but not their Zr, Y, or Ce enrichments. They also distinguished between S- and I-type granites by increasing P₂O₅ in S-type as well as the equal depletion of LREEs and HREEs (LREEs = HREEs). The Homrit Waggat studied granite is characterized by low-P₂O₅ and the LREEs>>HREEs depletion which reflects the initial under saturation of accessory mineral assemblage that resulted from high concentration of volatiles and/or alkali complexes.

A number of petrogenetic models have been proposed for the origin of A-type granites, including fractional crystallization of mantle derived mafic magmas, with or without crustal assimilation [38] and partial melting of crustal materials [17, 36, 70]. Using Zr versus Zr/Nb diagram (Fig. 13) of Geng et al. [26] indicates that Homrit Waggat earlier phase (granodiorite) samples match the partial melting trend. Based on Patiño Douce [53] diagram (Fig. 14), plotting of the major element ratios indicate the calc-alkaline granite (0.4 Gpa) source may be the primitive source of the Homrit Waggat granites.

The highly evolved hypersolvus alkali feldspar granite (the latest phase) was formed via fractional crystallization of I-type calc-alkaline magma. F-rich melt and F-complexing played an important role in the evolution and chemical characterization of the highly evolved hypersolvus alkali feldspar granite. Late magmatic fluid-melt played an important role in the formation of marginal amazonite pegmatite, while fluid-rock interactions are responsible for marginal local metasomatic albite as well as greisenization.

Chappell [13] distinguished two groups of I-type granites formed at high and low magmatic temperatures. The distinction is made on the absence or presence of inherited zircon. Zircon saturation temperature (Tzr) calculated from bulk rock composition for Homrit Waggat granites using Watson and Harrison [67] equation are ranging between 809°C to 765°C (Fig. 15a). These values are consistent with zirconium concentrations of inheritance – rich granites of Miller et al. [47], which range from 811°C to 730°C, with average value 766 ±24°C (1σ). This result is also confirmed from the highly felsic (SiO₂ range from 68 to 78 wt.%), mildly peraluminous to metaluminous, low Zr-contents (mostly < 200 ppm), and the negative correlation between Zr and SiO₂ (Fig. 15b). According to Miller et al. [47] zircon saturation temperature (Tzr) calculated from bulk rock composition provides minimum estimates of temperature if the magma was undersaturated, but maxima if it was saturated.

5.2. Mineralogical and Geochemical Specialization

The highly evolved hypersolvus alkali feldspar (SiO₂ = 74-78%), metaluminous to mildly peraluminous, enriched in Fe, Y, Nb, Rb, Zr and F, and depleted in CaO, MgO, Ba and Sr. These enrichments and depletions reflected their formation via fractional crystallization of I-type granite magma. According to Swaka et al. [66], the highly fractionated I- and S-type granites with A-type chemical characteristics are often mineralized.

Fig. 10. Discrimination 10000*Ga/Al diagrams [69] against: (a) Na₂O+K₂O, (b) Nb, (c) Y and (d) Zr. + = biotite granodiorite, x = biotite granite, ∆ = hypersolvus alkali feldspar granite.

Fig. 11. Plots of the studied granites on Ta versus Yb and Rb versus (Yb + Ta) diagrams [54]. VAG-volcanic arc granitoids, ORG-oceanic ridge granitoids, WPG-within plate granitoids and Syn-COLG-syn-collision granitoids. Symbols as in Fig. 10.

Fig. 12. Nb-Y-Ga*3 variation diagram [20] for the studied granites. x = biotite granite, ∆ = hypersolvus alkali feldspar granite.

Fig. 13. Zr versus Zr/Nb diagram [26] for the studied granites. + = biotite granodiorite, x = biotite granite, ∆ = hypersolvus alkali feldspar granite.

Specialization of rare-metal granites can be attributed to either magmatic or post-magmatic metasomatic processes [29, 58]. Therefore, this part will put emphasis on the hypersolvus alkali feldspar granite as the latest fractionated granite phase (magmatic stage), as well as late - to post-magmatic phases which represented by marginal amazonite pegmatite, metasomatic amazonite albite (pegmatitic stage), and greisens zone and veins (hydrothermal stage).

The alkali feldspar granite of Homrit Waggat displays high Rb/Sr (27-84), Rb/Ba (9-49), low K/Rb (56-77), Y/Ho (22-47), Zr/Hf (12) and very low Eu/Eu* (0.02-0.06) all indicate that this granite is highly differentiated. The pronounced negative Eu anomalies indicate extensive fractionation of feldspar. The presence of strongly negative Eu, Sr, and Ba anomalies on the spider diagrams indicate fractionation of both plagioclase and K-feldspar (Fig. 9). This is further confirmed by the positive correlation between Sr and Ba versus Eu/Eu* (Fig. 16). The positive correlations between Nb and Ta, and U and Th (Fig. 17), indicates the magmatic behavior for these elements. On Zr/Hf versus Nb/Ta and SiO₂ diagrams (Fig. 18) the hypersolvus alkali feldspar granite lies in rare metal related granites and in leucogranites fields with Zr/Hf values ˂ 15, which is promising for Ta, Nb, Sn, W, Mo, and Be deposits.

According to Strong [64] granite related mineral deposits tend to occur as four main intergradational genetic types, viz. magmatic disseminations, pegmatites, porphyries, and veins, roughly reflecting stages of progressive decrease in temperature and pressure of deposition. These mineralization stages have been termed by Fersman [25] as follow: magmatic, pegmatitic, metasomatic and hydrothermal stages. In Homrit Waggat granite, the magmatic stage is represented by the hypersolvus alkali feldspar granite phase with specialized mineralogy and chemical composition. It contains disseminated cassiterite, fluorite, columbite and topaz in the mineral composition, and the high Ga/Al, low Ba and Sr, and high Rb/Ba and Rb/Sr, in addition to that high enrichment of F, Nb, Y, Ga, Th and U indicates highly evolved magma which formed the hypersolvus granite.

In the studied granite, the pegmatitic stage is represented by marginal stockscheider pegmatite which occupied the northern part of the studied area at the contacts of Homrit Waggat granite with metagabbro-diorite complex. These pegmatite pods are characterized by the presence of large crystals as well as veins of amazonite, and miarolitic cavities filled with quartz, topaz, and mica. Opaques are represented by columbite, cassiterite and other unidentified rare earth minerals.

Metasomatic stage is characterized by the coexistence of crystals and supercritical fluid. In the studied area, the effect of metasomatic stage is represented by local albitization and local greisenization. Albitization occupies the north western margin of the studied granite at the contact with metagabbro-diorite complex. Bulk chemical analysis and petrographic study of albitized rocks show that metasomatism increase the abundance of Na, Al, Nb, Ta, and Sn. Amazonite veins up to 5 cm thick cut the albitized rocks. Fluid inclusions study [24] reveals that the albitization had taken place at high temperature (350°C - 410°C), and vapor-rich aqueous fluid.

Fig. 14. Compositions of the studied granites compared to melts produced by experimental dehydration-melting of various lithologies [53]. Melt compositions produced by dehydration-melting of calc-alkaline granites at 0.4 and 0.8 Gpa [52]. Symbols as in Fig. 13.

Fig. 15. (a) Zr versus the cationic ratio M = (Na+K+2Ca)/(Al_*Si) diagram [67], (b) Zr versus SiO₂ variation diagram for the studied granites. Symbols as in Fig. 13.

Greisenization is also observed at the eastern part of the studied area at the contact between hypersolvus alkali feldspar granite and mylonitized granite. The zone of greisenization is up to 30 m wide, and composed mainly of muscovite, fluorite and topaz, with cassiterite and other opaques as accessories. Fluid inclusions study indicates the greisenization took place at temperature between 210°C and 330°C, from H₂O-CO₂ fluid. The latest stage of mineralization in the studied area is represented by fluorite veins as well as quartz veins, some of which are carrying cassiterite intersected the studied granite. Fluid inclusions study in vein fluorite on primary and pseudosecondary inclusions, liquid rich two-phase aqueous inclusions indicates that fluorite seems to be deposited at temperature ranges from 100°C to 270°C.

Fig. 16. Eu/Eu* versus Sr and Ba diagrams for hypersolvus alkali feldspar granite.

Fig. 17. (a) Plots of Nb versus Ta, (b) Th versus U for Homrit Waggat granites. + = biotite granodiorite, x = biotite granite, ∆ = hypersolvus alkali feldspar granite, *= marginal albite granite.

Fig. 18. (a) Nb/Ta versus Zr/Hf diagram differentiating the barren granites and granites hosting ore deposits [6] and (b) Zr/Hf versus SiO₂ diagram [73]. ∆ = hypersolvus alkali feldspar granite.

6. Conclusion

Homrit Waggat composite granite pluton consists of four main granite phases: Granodiorite, biotite granite, mylonitized granite as well as hypersolvus alkali feldspar granite. There are systematic changes from peraluminous to metaluminous as well as from subsolvus to hypersolvus granite. Late to post-magmatic processes are represented by marginal stockscheider amazonite pegmatite, marginal amazonite albite as well as greisen zone up to 30 m².

The behavior of major, trace and REEs as well as low zirconium saturation temperature are consistent well with the crustal origin of Homrit Waggat granite. Zr versus Zr/Nb diagram as well as REEs patterns indicate that the earlier phase (granodiorite) matches well with partial melting process of crustal source, while the latest phase (hypersolvus alkali feldspar granite) formed via fractional crystallization. This is also documented by the systematic increasing of SiO₂, alkalis, Rb, F, Nb, Ta, Sn, Ga, HREEs and Y, and decreasing of Fe, Al, Mg, Ca, Mn, Ti, Sr, Ba, Zr, and LREEs from the earlier phase (granodiorite) to the latest phase (hypersolvus alkali feldspar granite). Ga/Al and REEs patterns of the latest phase are corresponding with the within plate A-type granite. The lower contents of Zr and REEs relative to the within plate A-type granite as well as the metaluminous character are matching well with the post-orogenic highly fractionated I-type granite crystallized from highly evolved F–rich melt. F-complexing played an important role in the evolution and chemical characterization of the hypersolvus alkali feldspar granite.

Decreasing Zr versus SiO₂ as well as calculated zirconium saturation temperature (mostly < 800°C) for Homrit Waggat granite indicates low temperature granite formed from zirconium-saturated melt source. This source may be I-type granite of granodiorite-tonalite composition which had been formed via partial melting.

The hypersolvus alkali feldspar granite is mineralogically and geochemically specialized. Four stages of mineralization were detected in the studied granite: magmatic represented by alkali feldspar granite, pegmatitic stage represented by marginal amazonite pegmatite, metasomatic stage represented by albitization and greisenization. The latest stage is represented by fluorite and quartz veins dissecting the granite.

Fluid inclusions study reveals that the albitization had taken place at high temperature (350°C - 410°C) vapour-rich aqueous fluid. The greisenization had taken place at temperature between 210°C and 330°C, from H₂O - CO₂ fluid. The fluorite veins were formed at temperature between 100°C and 270°C, from aqueous fluid.

References

1. Abdel Rahman, A. M., Martin, R. F., 1990. The Mount Gharib A-type granite Nubian Shield: role of metasomatism at the source. Contrib. Mineral. Petrol. 104, 173–183.
2. Ahmadipour, H., Rostamizadeh, G., 2012. Geochemical aspects of Na-metasomatism in Sargaz granitic intrusion (South of Kerman Province, Iran). J. Sci., Islamic Republic of Iran, 23 (1), 45-58.
3. Akaad, M. K., Noweir, A. M., 1980. Geology and lithostratigraphy of the Arabian Desert orogenic belt of Egypt between latitudes 25º 35 ʹ and 26º 30 ʹ N. Inst. Appl. Geol. Jeddah Bull. 3, 127–135.
4. Anders, E., Grevesse, N., 1989. The abundances of the elements: Meteoritic and solar. Geochim. Cosmochim. Acta 53, 197-214.
5. Baker, B. H., McBirney, A. R., 1985. Liquid fractionation. Part III: Geochemistry of zoned magmas and the compositional effects of liquid fractionation. J. Volcano. Geotherm. Res. 24, 55-81.
6. Ballouard, C., Poujol, M., Boulvais, P., Branquet, Y., Tartèse, R., Vigneresse, J-L., 2016. Nb-Ta fractionation in peraluminous granites: A marker of the magmatic-hydrothermal transition. Geology 44 (3), 231-234.
7. Bentor, Y. K., 1985. The crustal evolution of the Arabo-Nubian massif with special reference to the Sinai Peninsula. Precam. Res. 28 (1), 1–74.
8. Bhalla, P., Holtz, F., Linnen, R. L., Behrens, H., 2005. Solubility of cassiterite in evolved granitic melts: effect of T, f O₂, and additional volatiles. Lithos 80, 387–400.
9. Biste, M., 1982. Geochemistry of South Sardinian granites compared with their tin potential. In: Evans, A. M. (ed.), Metallizaion associated with acid magmatism. John Wiley and Sons Ltd., Chichester, England, 37-49.
10. Bonin, B., 1996. A-type granite ring complexes: mantle origin through crustal filters and the anorthosite–rapakivi magmatism connection. In: Demaiffe, D. (ed.) Petrology and Geochemistry of Magmatic Suites of Rocks in the Continental and Oceanic Crusts. ULB-MRAC, Bruxelles 201-217.
11. Bonin, B., Grelou-Orsini, C., Vialette, Y., 1978. Age, Origin and Evolution of the Anorogenic Complex of Evisa (Corsica): A K- Li - Rb- Sr Study. Contrib. Mineral. Petrol. 65, 425-432.
12. Bowden, P., Kinnaird, J. A., 1984. The petrology and geochemistry of alkaline granites from Nigeria. Phys. Earth Planet. Int. 87, 199-211.
13. Chappell, B., 2010. High- and low-temperature granites. The Ishihara Symposium: Granites and Associated Metallogenesis. 35-36.
14. Christiansen, E. H., Stuckless, J. S., Funkhouser-Marolf, M. J., Howell, K. H., 1988. Petrogenesis of rare-metal granites from depleted crustal sources: an example from the Cenozoic of western Utah, U.S.A. In: Taylor, R. P. and Strong, D. F. (eds) Recent advances in the geology of granite-related mineral deposits. Can. Inst. Min. Metall. 39, 307-321.
15. Clarke, D. B., 1992. The mineralogy of peraluminous granites: a review. Can. Mineral. 19, 3-17.
16. Collerson, K. D., 1982.Geochemistry and Rb-Sr geochronology of associated Proterozoic peralkaline and subalkaline anorogenic granites from Labrador. Contrib. Mineral. Petrol. 81, 126-147.
17. Collins, W. J., Beams, S. D., White, A. J. R., Chappell, B. W., 1982. Nature and origin of A-type granites with particular reference to south eastern Australia. Contrib. Mineral. Petrol. 80, 189–200.
18. De La Roche, H., Leterrier, J., Grand Claude, P., Marchal, M., 1980. A classification of volcanic and plutonic rocks using R1–R2 diagrams and major element analyses – its relationships and current nomenclature. Chem. Geol. 29, 183–210.
19. Eby, G. N., 1990. The A-type granitoids: A review of their occurrence and chemical characteristics and speculations on their petrogenesis. Lithos 26, 115-134.
20. Eby, G. N., 1992. Chemical subdivision of the A-type granitoids, petrogenetic and tectonic implications. Geology 20, 641-644.
21. Eby, G. N., 2011. A-type granites: magma sources and their contribution to the growth of the continental crust. In: Molina, J. F., Scarrow, J. H., Bea, F., Montero, P. (Eds.), Seventh Hutton Symposium on granites and related rocks, Avila, Spain, Abstracts Book with Attendees Addresses, 50–51.
22. El Bouseily, A. M., El-Sokkary, A. A., 1975. The relation between Rb, Ba, and Sr in granitic rocks. Chem. Geol. 16, 207-219.
23. El-Gaby, S., 1975. Petrochemistry and geochemistry of some granites from Egypt. Neus. Jahrb. Mineral. Abh. 124, 147–189.
24. El Hadek, H. H. 2016. Rare-metal granites and their related mineralization, Central Eastern Desert, Egypt . PhD thesis, Geology Department, Faculty of Science, Assiut University. (in press.)
25. Fersman, A. E., 1931. Les pegmatites, leur importance scientifique et pratique, Academy of Science U. S. S. R., Lenningrad: Translation in French by J. Thoreau, Louvain, 3 vols., 1951.
26. Geng, H., Sun, M., Yuan, C., Xiao, W., Xian, W., Zhao, G., Zhang, L., Wong, K., Wu, F., 2009. Geochemical, Sr–Nd and zircon U–Pb–Hf isotopic studies of Late Carboniferous magmatism in the West Junggar, Xinjiang: Implications for ridge subduction? Chem. Geol. 266, 373–398.
27. Greenberg, J. K., 1981. Characteristics and origin of Egyptian younger granites: Summary. Geol. Soc. Amer. Bull. 1. 92, 224-232.
28. Gu, L. X., Zhang, Z. Z., Wu, C. Z., Gou, X. Q., Liao, J. J., Uang, H., 2011. A topaz- and amazonite-bearing leucogranite pluton in the eastern Xinjiang, NW China and its zoning. J. Asian Earth Sci. 42, 885–902.
29. Haapala, I., 1995. Metallogeny of the rapakivi granites. Mineral. Petrol. 54, 141–160.
30. Hassanen, M. A., 1997. Post-collision, A-type granites of Homrit Waggat complex, Egypt: petrological and geochemical constraints on its origin. Precam. Res. 82, 211-236.
31. Hildreth, E. W., 1981. Gradients in silicic magma chambers; implications for lithospheric magmatism. J. Geophys. Res. 86, 10153-10192.
32. Hussein, A. A., Aly, M. M., El-Ramly, M. F., 1982. A proposed new classification of the granites of Egypt. J. Volcano. Geotherm. Res. 14, 187-198.
33. Inger, S., Harris, N., 1993. Geochemical constraints on leucogranite magmatism in the Langtang Valley, Nepal Himalaya. J. Petrol. 34, 345-368.
34. Irber, W., 1999. The lanthanide tetrad effect and its correlation with K/Rb, Eu/Eu*, Sr/Eu, Y/Ho, and Zr/Hf of evolving peraluminous granite suites. Geochim. Cosmochim. Acta 63, 489–508.
35. Jackson, N. J., Walsh, J. N., Pegram, E., 1984. Geology, geochemistry and petrogenesis of late Precambrian granitoids in the central Hijaz region of the Arabian Shield. Contrib. Mineral. Petrol. 87, 205-219.
36. Jung, S., Hoernes, S., Mezger, K., 2000. Geochronology and petrogenesis of Pan-African, syn- tectonic, S-type and post-tectonic A-type granite (Namibia). — products of melting of crustal sources, fractional crystallization and wall rock entrainment. Lithos 50, 259–287.
37. Kaur, P., Chaudhri, N., Hofmann, A. W., Raczek, I., Okrusch, M., Skora, S., Baumgartner, L. P., 2012. Two-stage, extreme albitization of A-type granites from Rajasthan, NW India. J. Petrol. 0, 1-30.
38. Kebede, T., Koeberl, C., 2003. Petrogenesis of A-type granitoids from the Wallagga area, western Ethiopia: constraints from mineralogy, bulk-rock chemistry, Nd and Sr isotopic compositions. Precam. Res. 121, 1-24.
39. Keppler, H., Wyllie, P. J., 1991. Partiontiong of Cu, Sn, Mo, U and Th between melt and aqueous fluid in the systems haplogranite – H₂O – HCl and haplogranite – H₂O – HF. Contrib. Mineral. Petrol. 109, 139-150.
40. King, P. L., White, A. J. R., Chappell, B. W., Allen, C. M., 1997. Characterization and origin of aluminous A-type granites from the Lachlan Fold Belt, Southeastern Australia. J. Petrol. 38 (3), 371–391.
41. Kovalenko, V. I., 1978. The genesis of rare metal granitoids and related ore deposits: In: Štemprok, M., Burnol, L. and Tischendorf, G. (eds.), metallization associated with acid magmatism. Czech. Geol. Surv., Prague 3, 235-248.
42. Li, H., Watanabe, K., Yonezu, K., 2014. Geochemistry of A-type granites in the Huangshaping polymetallic deposit (South Hunan, China): Implications for granite evolution and associated mineralization. J. Asian Earth Sci. 88, 149-167.
43. MacDonald, R., Smith, R. L., 1987.Relationshipsbetween silicic plutonism and volcanism; Geochemical evidence, in the origin of granites, Abstracts; A symposium: Royal societies ofEdinburghand London, 1-2.
44. Maniar, P. D., Piccoli, P. M., 1989. Tectonic discrimination of granitoids. Geol. Soc. Amer. Bull. 101, 635–643.
45. Manning, D. A. C., Hamilton, D. L., Henderson, C. M. B., Dempsey, M. J., 1980. The probable occurrence of interstitial Al in hydrous, F-bearing and F-free aluminosilicate melts. Contrib. Mineral. Petrol. 75, 256–262.
46. Mao, W., Li, X., Wang, G., Xiao, R., Wang, M., Li, Y., Ren, M., Bai, Y., Yang, F., 2014. Petrogenesis of the Yangzhuang Nb- and Ta-rich A-type granite porphyry in West Junggar, Xinjiang, China. Lithos 198, 172–183.
47. Miller, C. F., McDowell, S. M., Mapes, R. W., 2003. Hot and cold granites? Implications of zircon saturation temperatures and preservation of inheritance. Geology 31 (6), 529–532.
48. Moghazi, A. M., Mohamed, F. H., Kanisawa, S., 1999. Geochemical and petrological evidence of calc-alkaline and A-type magmatism in the Homrit Waggat and EI-Yatima areas of eastern Egypt. J. Afri. Earth Sci. 29 (3), 535-549.
49. Mohamed, F. H., 1993. Rare-metal-bearing and barren granites, Eastern Desert of Egypt: geochemical characterization and metallogenetic aspects. J. Afr. Earth Sci. 17 (4), 525-539.
50. Mohamed, F. H., Hassanen, M. A., Matheis, G., Shalaby, M. H., 1994. Geochemistry of the Wadi Hawashia granite complex, northern Egyptian Shield. J. Afr. Earth Sci. 19, 61–74.
51. Nardi, L. V. S., Bonin, B., 1991. Post-orogenic and non-orogenic alkaline granite associations: the Saibro intrusive suite, southern Brazil – a case study. Chem. Geol. 92, 197-211.
52. Patiño Douce, A. E., 1997. Generation of metaluminous A-type granites by low-pressure melting of calc-alkaline granitoids. Geology 25, 743–746.
53. Patiño Douce, A. E., 1999. What do experiments tell us about the relative contributions of crust and mantle to the origin of granitic magmas? In: Castro, A., Fernandez, C., and Vigneresse, J. L., eds., Understanding Granites: Integrating New and Classical Techniques: Geol. Soc. London, Spec. Publ. 168, 55–75.
54. Pearce, J. A., Harris, N. B., Tindle, A. G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J. Petrol. 25, 956–983.
55. Pérez-Soba, C., Villaseca, C., 2010. Petrogenesis of highly fractionated I-type peraluminous granites: La Pedriza pluton (Spanish Central System). Geol. Acta 8 (2), 131–149.
56. Pichavant, M., Manning, D. A. C., 1984. Petrogenesis of tourmaline –granites and topaz-granites, the contribution of experimental data: Phys. Earth Planet. Int. 35, 31-50.
57. Rogers, J. J. W., Greenberg, J. K., 1981. Trace elements in continental-margin magmatism: Part 3. Alkali granites and their relationship to cratonization. Geol. Soc. Amer. Bull. pt. 1, 92, 6-9.
58. Schwartz, M. O., 1992. Geochemical criteria for distinguishing magmatic and metasomatic albite-enrichment in granitoids—examples from the Ta-Li granite Yichun (China) and the Sn-W deposit Tikus (Indonesia). Mineral. Deposita 27, 101–108.
59. Shearer, C. K., Papike, J. J., Laul, J. C., 1985. Chemistry of potassium feldspar from three zoned pegmatites, Black Hills, South Dakota: implications concerning pegmatite evolution. Geochim. Cosmochim. Acta 49, 663-673.
60. Štemprok, M., 1982. Tin- fluorine relationships in ore-bearing assemblages. In: Evans, A. M., (ed), Metallization associated with acid magmatism. John Willy and sons Ltd, Chichester. England, 321-337.
61. Stern, R. J., Hedge, C. E., 1985. Geochronologic and isotopic constraints on late Precambrian crustal evolution in the Eastern Desert of Egypt. Amer. J. Sci. 285, 97–127.
62. Stern, R. J., Gottfried, D., 1986. Petrogenesis of a Late Precambrian (575-600 Ma) bimodal suite in northeast Africa. Contrib. Mineral. Petrol. 92, 492-501.
63. Streckeisen, A., LeMaitre, R. W., 1979. A chemical approximation to the modal QAP classification of the igneous rocks. Neus. Jahrb. Mineral., Abh., 136, 169-206.
64. Strong, D. F., 1988. A review and model for granite-related mineral deposits. In: Taylor, R. P. and Strong, D. F. (eds) Recent advances in the geology of granite-related mineral deposits. Can. Inst. Min. Metall. 39, 424–445.
65. Sun, S. S., McDonough, W. F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A. D., Norry, M. J. (Eds.), Magmatism in Ocean Basins. Geol. Soc. London, Spec. Publ. 42, 313–345.
66. Swaka, W. N., Heizler, M. T., Kistler, R. W., Chappell, B. W., 1990. Geochemistry of highly fractionated I- and S-type granites from the tin-tungsten province of western Tasmania. In: Stein, H. T. and Hannah, T. L. (eds.), Ore-bearing granite systems, petrogenesis and mineralizing processes. Geol. Soc. Amer. Spec. Pap. 246, 161-179.
67. Watson, E. B., Harrison, T. M., 1983. Zircon saturation revisited: Temperature and composition effects in a variety of crustal magma types: Earth Planet. Sci. Lett. 64, 295–304.
68. Whalen, J. B., Currie, K. L., 1990. The Topsails igneous suite, western Newfoundland; Fractionation and magma mixing in an ‘orogenic’ A-type granite suite. Ore-bearing granite systems; petrogenesis and mineralizing processes. Geol. Soc. Amer. Spec. Pap. 246, 287–299.
69. Whalen, J. B., Currie, K. K., Chappell, B. W., 1987. A-type granites, geochemical characteristics, discrimination and petrogenesis: Contrib. Mineral. Petrol. 95, 407-419.
70. Wu, F. Y., Sun, D. Y., Li, H., Jahn, B. M., Wilde, S., 2002. A-type granites in northeastern China: age and geochemical constraints on their petrogenesis. Chem. Geol. 187, 143–173.
71. Xiaolin, X., Zhenhua, Z., Jinchu, Z., Bing, R., Mingyuan, L., 1998. Partitioning of F between aqueous fluids and albite granite melt and its petrogenetic and metallogenetic significance. Chin. J. Geochem. 17, 303-310.
72. Yu, J. H., O’Reilly, S. Y., Zhao, L., Griffin, W. L., Zhang, M., Zhou, X., Jiang, S.-Y., Wang, L. J., Wang, R. C., 2007. Origin and evolution of topaz-bearing granites from the Nanling Range, South China: a geochemical and Sr–Nd–Hf isotopic study. Mineral. Petrol. 90, 271–300.
73. Zaraisky, G. P., Aksyuk, A. M., 2005. Petrogenesis of rare metal calc-alkaline granites. In: Proceedings of 10th All-Russia Petrographic Conference. Petrography of the 21th Century. Petrology and Ore Potential of CIS Regions and the Baltic Shield, Apatity, Russia, (Apatity, 2005), 93–95.
74. Zaraysky, G. P., Alfereva, J. O., Udoratina, O. V., 2007. Geochemical features of the Etyka tantalum deposit in Eastern Transbaikalia. Stellenbosch University (South Africa), Sixth International Hutton Symposium, 232-233.