Mineral chemistry aspects of radioactive mineralization associated with Zr-, Nb-, and REE-bearing minerals from felsic dikes at Abu Hawis, North Eastern Desert, Egypt

The exposed rocks in Abu Hawis area, North Eastern Desert (NED), Egypt, consist of tonalite-granodiorite and monzogranite, dissected by post-granite felsic (microgranite and rhyolite) and mafic (basaltic-andesite) dikes. The investigated radioactive minerals and Zr-, Nb-, and REE-bearing minerals were restricted to felsic dikes having E–W and NE–SW trends. Uraninite, uranothorite, and thorite occur as the main radioactive minerals in microgranite dikes, while thorite is represent in rhyolite dikes. Y2O3 and HREE are recorded in zircon crystals from rhyolite dikes whereas HREEs in zircon grains from microgranite dikes are below detection limit. Zircon crystals from microgranite dikes contain high values of HfO2 with up to 9.08 wt % owing to the effect of hydrothermal activity. Columbite from microgranite dikes has Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios ranging between 0.0052–0.0164 and 0.0549–0.7010, respectively, which point to manganocolumbite composition, except for two spots that show a ferrocolumbite composition. Fergusonite is recorded in microgranite dikes, with average values of Nb2O5, Y2O3, and HREE2O3 reaching 50.3, 22.93, and 17.68 wt%, respectively. Monazite is recorded in both microgranite and rhyolite dikes, with marked enrichment of ThO2, which reaches up to 12.52 wt% in the first one, while the total ΣLREE2O3 reached up to 68.5 wt% in the latter. Parisite and chevkinite are confined to rhyolite dikes with clear enrichment in LREE with averages ranging between 53.53 and 43.75 wt% ΣLREE2O3, respectively.


Introduction
The Arabian-Nubian Shield (ANS) is composed of basement rocks of Precambrian age along the Red Sea two flanks, located in western Arabia and northeastern Africa (Johnson and Woldehaimanot 2003;Liégeois and Stern 2010). The ANS was evolved in three stages, as follows: (a) Intra-ocean ridge subduction and arc magmatism ˃750 Ma, (b) collisional events and terrane amalgamation (˃750 Ma-˂620 Ma), (c) tectonic escape and extension ˂620 Ma (Farahat et al. 2011;Fathy et al. 2018). It consists of a large orogenic belt that extends from western Arabia to East African Orogen (EAO) (Fig. 1a), through Saudi Arabia, Yemen, Oman, Jordan, Egypt, Sudan, Eritrea, Ethiopia, and Somalia, whereas the southern belt occupies Mozambique segment.
Rare metal granites (RMG) are those enriched in one or more mineralization of the elements Zr, Nb, Ta, Rb, Cs, W, Sn, Li, F, Be, U, Th, REEs, and Y. RMG can be attributed either to magmatic and/or metasomatic processes (Abdalla et al. 1998;Gaafar et al. 2014;Dessouky et al. 2020;Ali et al. 2021;. RMG intrusion occurred between 530 and 620 Ma during post-orogenic magmatism in the Egyptian Nubian Shield (Abdel Karim and Sos 2000;Moussa et al. 2008;Eliwa et al. 2014;Ali 2015;Skublov et al. 2021;Abdel Gawad et al. 2021a). However, rare metal mineralizations are mainly restricted to granites, pegmatites, acidic volcanics, and mylonite rocks as well as quartz and jasper veins widely distributed in the Eastern Desert of Egypt (Fig. 1b) (Saleh 2007;Raslan et al. 2010;Abdel Wahed et al. 2012;Dawoud et al. 2018;Heikal et al. 2001;2019;Fawzy et al. 2020;Ghoneim et al. 2020;Surour and Omar 2020;Dessouky et al. 2020; Abdel Gawad et al. Fig. 1 a Geologic map of the Arabian Nubian Sheild (ANS); b geologic map of the basement rocks of Neoproterozoic age, Eastern Desert (ED), Egypt (Liégeois and Stern 2010) Rare earth elements (REE) are considered as critical and vital material to future development. They are having a great importance, such as cell phones, computer memories, DVDs, rechargeable batteries, cerium oxide used for polishing gemstones such as granite and marble as well as glass, medical devices, high-efficiency motors in hybrid electric vehicles, catalytic converters, metallurgy, FeB magnets, wind power turbines, catalysts, and metal alloys as well as high demand for green energy and military defense systems (German and Elderfield 1990;Mariano and Mariano 2012;Gambogi 2013;Zepf 2013;Liu et al. 2013). Life demand is expected to increase dramatically over the next 10 years, without increase in the total REE reserves, thus highlighting the need to exploit for more REE deposits to be discovered (Hoatson et al. 2011;Jaireth et al. 2014). According to the high economical use of REEs, global request for REE will rise continuously, which will put great pressure on the current REE supply chain.
Several studies were carried out on Abu Hawis area (NED), Egypt (Ahmed and Moharem 2002;Al-Boghdady et al. 2005;Ali 2007; El-Bialy and Omar 2015; Dawoud et al. 2017). This paper presents in terms of novel data and interpretations about the mineralization especially U-, Th-, Zr-, Nb-, and REE-bearing minerals from the studied felsite dikes at Abu Hawis. To achieve this goal, micro-chemical analyses of these mineralization were first carried out in order to obtain informative data about radioactive minerals as well as Zr-, Nb-, and REE-bearing minerals.

Geologic setting
Field evidence shows that the exposed rock types are represented by tonalite-granodiorite, and monzogranite, which are cut by post-granite dikes and quartz veins (Figs. 2 and 3a-e).
The exposed rocks of Abu Hawis area are mostly composed of tonalite-granodiorite that have a huge batholith extending along the border of Qena-Safaga Road. They are medium-to coarse-grained rocks, form low relief, and vary from gray to whitish-gray colors. The pluton outcrops of these granitoids show marked intensive fracturing, jointing, exfoliation, and oval-like shapes, owing to the effect of weathering processes (Fig. 3f). They are strongly foliated and metamorphosed and occur as gneissose tonalite-granodiorite. Meanwhile, the other parts of tonalite-granodiorite occur as massive rocks. They are presented as smallsized plutons, without any deformed signatures. They are composed of quartz, plagioclase, K-feldspars, biotite, and hornblende.
The monzogranite pluton possesses circular to elliptical outlines and intrudes into tonalite-granodiorite of the studied area (Fig. 3f). It is frequently forming hard massive rocks,  Dawoud et al. 2017) high relief, pink to reddish brown in color, and medium-to coarse-grained. It is mainly composed of K-feldspar, quartz, plagioclase, muscovite, and biotite. Granitoids were dissected by basaltic-andesite dikes and quartz veins, striking in E-W, NW-SE, e).
Pegmatites occur as pockets and/or dike-like forms. They are very coarse-grained, red, buff to reddish brown in color, and essentially composed of K-feldspar, quartz, plagioclase, biotite, and muscovite. They occur in the latest magmatic stages in Abu Hawis monzogranite and/or along the contacts between tonalite-granodiorite and monzogranite. Some exposures of these rocks are affected by hematitization and considered as good sources of strategic rare metal mineralization.
The most significant U mineralization occupies about 5 to 10 m width and 500 m length, subvertical, and highly altered basic dikes, striking in the NE-SW direction along the main shear zone of Abu Hawis plutons. Argillization, hematitization, and silicification are the main alterations affecting the sheared basic dikes. Relatively, high radioactive anomalies recorded in the main shear zone reached . 3 a Microgranite dikes having E-W trend cross cut tonalitegranodiorite; b NE-SW strike-slip fault (right lateral) cross cut E-W microgranite dikes; c rhyolite dikes having NE-SW cross cut tonalite-granodiorite; d andesite dikes having NW-SE trend cross cut tonalite-granodiorite; e basaltic dikes having N-S trend cross cut tonalite-granodiorite; f tonalite-granodiorite rocks were intruded by the monzogranite (oval shape) with sharp intrusive contacts about 80 ppm for eU and about 45 ppm for eTh, with an eU/eTh ratio reaching about 1.75 (Ammar et al. 2007).
Felsite dikes are cut through the tonalite-granodiorite. They range between 1 and 6 m width and are buff, pale pink to reddish brown color, are mostly fine-grained textures, and dominated by microgranite and rhyolite dikes. These dikes are mainly composed of quartz, K-feldspars, and plagioclase with mica as well as iron oxides. They are striking in the E-W and NE-SW directions with steeply dipping or nearly vertical (Fig. 3a-c). These dikes were jointed and fractured, highly altered, and affected by hematitization in addition to dendritic manganese oxides.
For an argillic sample, heavy liquids separation technique using bromoform of specific gravity 2.85 gm/cm 3 was used to concentrate the clay minerals. The clay minerals were picked under a binocular microscope to obtain pure mineral samples for X-ray diffraction (XRD) investigation. The X-ray diffraction (XRD) technique was used to identify the clay mineral sample using a PHILIPS PW 3710/31 diffractometer. These analyses were carried out in the laboratories of the Nuclear Materials Authority (NMA) of Egypt.

Microgranite
Microscopically, microgranite shows equigranular texture and is composed mainly of K-feldspar, quartz, plagioclase, and muscovite (Fig. 4a). Zircon, pyrite, galena, sphalerite, and iron oxides are the most common accessory minerals, while sericite and kaolinite are the main alteration products. K-feldspar consists of microcline-and orthoclase microperthites. Microcline microperthite occurs as subhedral to euhedral crystals showing cross-hatched twinning (Fig. 4a). Orthoclase microperthite occurs as anhedral to subhedral crystals having simple twinning. Quartz occurs as interstitial grains between feldspar crystals as anhedral to subhedral crystals and fine grained. Plagioclase occurs as euhedral to subhedral tabular crystals. It exhibits simple and lamellar twinning (Fig. 4a, d). Muscovite occurs as anhedral crystals, corroded peripheries, and encloses opaques. Zircon crystals are coated by iron oxides, and occur as prismatic crystals enclosed in quartz and feldspars ( Fig. 4b-d). Microgranite affected by hydrothermal alterations include kaolinization, chloritization, and hematitization ( Fig. 4a-f).

Radioactive minerals
Uraninite is considered the main radioactive U-bearing mineral, while thorite and uranothorite are the main radioactive Th-bearing minerals in the studied microgranite and rhyolite dikes ( Fig. 5a-d and Table 1).
Uraninite is recorded in peraluminous granites and their pegmatites as well as dolerite dikes (Gaafar et al. 2014;Ali et al. 2021;Ghoneim et al. 2021 (Table 1). Thorite is a radioactive mineral. It is one of the most common Th-silicate minerals in felsic dikes of the area under investigation. It is enclosed as fine bright microinclusions in zircon crystals and shows intergrowth with zircon along its peripheries (Fig. 5b). It occurs as fine individual grains, subhedral to anhedral crystals (Fig. 5c).
Other minute grains of thorite occur adjacent to parisite crystals (Fig. 5d). The chemical composition of thorite shows that the means of ThO 2 concentrations attain 57.89 and 61.69 wt% in both microgranite and rhyolite dikes, respectively. The means of SiO 2 contents reach 18.76 and 17.11 wt% in thorite from microgranite and rhyolite dikes, respectively. Thorite in microgranite dikes shows high mean values of UO 2 , Y 2 O 3 , and ZrO 2 reaching 3.05, 3.39, and 0.51 wt%, when compared with thorite from rhyolite dikes. Dy 2 O 3 , Er 2 O 3 , and Yb 2 O 3 were recorded as minor amounts in the studied thorite, but with higher mean contents in microgranite than those in rhyolite dikes (Table 1). CaO, P 2 O 5 , and Fe 2 O 3 were recorded as minor constituents in the analyzed thorite (Table 1). Uranothorite is a common Th-silicate mineral in microgranite dikes. It occurs as subrounded, subhedral grains, and micro-inclusions in zircon crystals (Fig. 5a). According to EPMA, the chemical composition of uranothorite reveals that ThO 2 concentration ranges between 49.89 and 51.17 wt%, UO 2 from 27.01 to 27.42 wt%, and SiO 2 from 17.25 to 18.04 wt% (

Zircon
Zircon occurs as prismatic, subhedral to anhedral crystals, and varies from fine-grained to large crystals, reaching up to 200 μm in microgranite and rhyolite. It is associated with columbite, fergusonite, barite, rutile, ilmenite, hematite, and opaques ( Fig. 6a-d). The presence of fine-grained zircon as micro-inclusion in large zircon crystals indicates the presence of two zircon generations, which are encountered in the studied microgranite dikes.  According to EPMA (Table 2), zircon crystals from microgranite dikes are composed of ZrO 2 that ranges from 56.06 to 62.76 wt% and a mean reaching 60.09 wt%, SiO 2 from 30.76 to 34.29 wt% and a mean reaching 32.19 wt%, and HfO 2 from 1.03 to 9.08 wt% and a mean reaching 3.81 wt%. HfO 2 shows higher concentrations in the analyzed zircon crystals, reaching to 7.41, 9.08, and 6.12 wt% (Table 2). ThO 2 and UO 2 were recorded in zircon crystals and show low concentrations reaching up to 2.16 and 0.54 wt%, respectively. Only Yb 2 O 3 from HREE is recorded with low contents. Minor amounts of CaO, Fe 2 O 3 , and Al 2 O 3 were also recorded ( Table 2).
On the other hand, EPMA data show that zircon crystals from rhyolite dikes are composed essentially of ZrO 2 , ranging from 58.46 to 59.21 wt% and a mean reaching 58.72 wt%, SiO 2 from 29.73 to 30.29 wt% and a mean attaining 30.0 wt%, and HfO 2 from 0.98 to 3.09 wt% and a mean reaching 1.59 wt%. ThO 2 and UO 2 display low concentrations in the analyzed zircon crystals with mean values of 0.74 and 0.85 wt%, respectively. HREE (Dy 2 O 3 , Er 2 O 3 , and Yb 2 O 3 ) and Y 2 O 3 were recorded in the analyzed zircon crystals, with mean values reaching 0.54, 0.63, 1.06, and 4.03, respectively (Table 2). CaO and Fe 2 O 3 were also recorded in zircon crystals as minor constituents.

Nb-rich minerals
Columbite occurs as anhedral to subhedral crystals, up to 100 μm in microgranite, commonly enclosed in plagioclase, K-feldspar, and quartz crystals. Other columbite crystals are dispersed as fine-to medium-grained crystals enclosed in fergusonite (Fig. 6c). Some crystals of columbite enclose micro-inclusions of galena and opaque minerals (Fig. 6e). EPMA analyses reveal that the typical composition of manganocolumbite, according to the quadrilateral diagram of Černý and Ercit (1985), except two spots is ferrocolumbite composition (Fig. 7). EPMA data reveal that manganocolumbite is composed of  (Table 3 and Fig. 7). Fergusonite occurs as subhedral to anhedral and finegrained, while some crystals are strongly deformed and corroded along their peripheries. It is enclosed in zircon crystals as micro-inclusions and occurs along the peripheries of columbite as thin inclusions (Fig. 6b,

REE minerals
A. Monazite-Ce is a common REE-phosphatic mineral. It is always present in the studied felsic dikes. It occurs as anhedral to subhedral, fine-grained, micro-veinlets, and is observed as micro-inclusions in zircon and parisite crystals (Figs. 5a and 8a, b). The chemical composition of monazite  19, 9.17, 4.35, and 2.05 wt%, respectively. Gd 2 O 3 is the only heavy rare earth element, recorded in monazite, reaching up to 1.37 wt%. Monazite grains are enriched in ThO 2 concentrations ranging from 10.11 to 11.98 wt% and a mean reaching 11.29 wt%. SiO 2 , CaO, and Fe 2 O 3 occur in minor concentrations (Table 4).
On the other hand, EPMA data show that the chemical composition of monazite crystals from rhyolite is composed mainly of P 2 O 5 that ranges from 28.48 to 29.32 wt% and a mean reaching 29.08 wt%. The total ∑REE 2 O 3 content ranges from 67.82 to 68.50 wt% and a mean reaching 68.14 B. Parisite-(Ce) is always present only in rhyolite. It is a calcium REE-fluorocarbonate mineral and occurs as anhedral to subhedral large grains up to 100 μm ( Figs. 5d and 8b, c). Some corroded parisite crystals are in parallel intergrowth with monazite. Parisite occurs in association with fluorite, hematite, and thorite while the latter mineral, in some cases, occurs along the peripheries of parisite crystals (Fig. 5d). From the EMP analyses (Table 5), parisite shows a strong enrichment in LREE. It is essentially composed of CaO that ranges from 12.84 to 14.87 wt%, with a mean of 13.8 wt%. The total ∑REE 2 O 3 (La 2 O 3 + Ce 2 O 3 + Pr 2 O 3 + Nd 2 O 3 + Sm 2 O 3 + Gd 2 O 3 ) concentrations range from 52.28 to 55.21 wt%, with a mean of 53.53 wt%. Ce 2 O 3 is considered the most predominant LREE in parisite. It ranges from 22.09 to 23.91 wt% with a mean of 22.99 wt%. La 2 O 3 and Nd 2 O 3 show high concentrations in parisite, with mean values of 14 and 11.71 wt%, respectively, then Pr 2 O 3 followed by Sm 2 O 3 and then Gd 2 O 3 , in ascending magnitudes (Table 5). ThO 2 and SiO 2 are present in minor amounts, with mean values of 0.64 and 0.12 wt%, respectively. The empirical chemical formula of average parisite grains in rhyolite is as follows: Ca 1.02 (Ce 0.58 La 0.36 Nd 0.29 Pr 0.08 Sm 0.04 Gd 0.01 ) 2 (CO 3 ) 3 F 1.84 .
C. Chevkinite-(Ce) occurs as fine-grained crystals, up to 5 µm in length (Fig. 8d), subrounded to subhedral, and enclosed in quartz. It is recorded only in the rhyolite of the study area and has a limited abundance. It is a titanosilicate REE mineral. As a result of EPMA data, chevkinite crystals from the rhyolite are mainly composed of SiO 2 TiO 2 , and Fe 2 O 3 that reached up to 19.97, 20.35, and 13.11 wt%, respectively ( Table 5). The analyzed EPMA data indicate that chevkinite shows considerably higher ∑LREE 2 O 3 (La 2 O 3 -Sm 2 O 3 ) concentrations, reaching up to 44.21 wt% (Table 5). Chevkinite is enriched in LREE and Ce 2 O 3 is the main predominant REE that reaches 21.52 and 21.85 wt% corresponding to chevkinite-(Ce) in chemical composition. La 2 O 3 shows high concentrations reaching to 11.38 and 11.56 wt% and Nd 2 O 3 7.87 and 8.24 wt%, while Pr 2 O 3 and Sm 2 O 3 show low concentrations in the analyzed samples (Table 5). ThO 2 and UO 2 are present in minor amounts, up to 2.11 and 0.22 wt%, respectively. CaO and P 2 O 5 are recorded also in minor amounts, up to 1.65 and 0.09 wt%, respectively and/or not recorded.

Other accessory minerals
Sulfide minerals including pyrite, galena, and sphalerite are recorded in the microgranite, whereas fluorite and fluorapatite are presented in the rhyolite.
Pyrite occurs as fine-grained, anhedral grains associated with fergusonite, columbite, and zircon in the microgranite (Fig. 6c). Other pyrite grains, associated with galena, are disseminated throughout plagioclase (Fig. 9a). EPMA data show that the chemical composition of pyrite is Fe reaching 47.03 wt% and S attaining 52.74 wt%. Quadrilateral diagram according to Černý and Ercit (1985) illustrating the chemical composition of columbite-tantalite from the microgranite, Abu Hawis area, North Eastern Desert, Egypt Galena is a lead sulfide mineral and occurs as very fine grains, thin films along the peripheries of sphalerite grains, and/or fine grains along zircon in microgranite ( Fig. 9a-d). EPMA data show that Pb concentration reached 85.22 wt% and S 12.73 wt%. Fe and Si are pre-sented as minor constituents, with mean values of 0.51 wt% and 0.89 wt%, respectively. Sphalerite is a zinc sulfide mineral and occurs as anhedral to subhedral grains and contains thin films of galena along its peripheries in the microgranite (Fig. 9d). EPMA data Fluorite occurs as anhedral to subhedral grains in the rhyolite. It occurs also as fine-grained and is associated with thorite, parisite, and hematite (Fig. 5c). EPMA data show that fluorite is composed mainly of Ca 52.23 wt% and F 45.72 wt%, with minor amounts of Si 0.19 wt%.
Apatite occurs as anhedral grains in the rhyolite and is associated with parisite and thorite (Fig. 5d). EPMA data show that the main constituents of apatite are CaO 55.03 wt% and P 2 O 5 42.07 wt%. SiO 2 occurs as minor constituent 0.41 wt% whereas F reached to 5.34 wt% designating fluorapatite.

The E-W and NE-SW control of rare metal mineralization
Felsite dike swarms are almost abundant and numerous in the North Eastern Desert of Egypt, having E-W and NE-SW (Ali 2007, Dessouky et al. 2020Waheeb and EL Sundoly 2020). The distribution of felsite dikes confirms that a gradual transition from N-S extension trend to NE-SW and NW-SE extension trends was occurred in Abu Hawis area (Ali 2007;Waheeb and EL Sundoly 2020). Ali (2009) states that a marked positive correlation was taken place between the extensional events and the NE-SW, NW-SE, and E-W trends. These events led to U-migration from Abu Hawis monzogranite to be deposited along the main shear zones trending in the NE-SW direction. These trends dominate on the mobility map (eU-eTh/3.5), and show NW-SE, NE-SW, and N-S extensional trends, respectively.
Abu Hawis granitoids are located to the northeast of El-Erediya granites enriched in U mineralization especially in jasper veins having NE-SW to ENE-WSW-striking fractures that dated 130-160 Ma for hydrothermal event (Abu-Deif 1992). Besides, the studied area is located in the western part of Ras Abda syenogranite. Age dating of the magmatic crystallization for Ras Abda mineralized syenogranite is 610 Ma (Dessouky et al. 2020;Abdel Gawad et al. 2021a, b, c), whereas the age of the hydrothermal event is 126.8 ± 2.0 Ma (Abdel Gawad et al. 2021a, b, c). These trends could have been reactivated many times at different ages. Therefore, they may be used as good indicators for the existence U mineralization that is associated with other rare metal mineralization.

Post-magmatic and hydrothermal processes controlling mineralization
The radioactive mineralizations -including uraninite, thorite, and uranothorite -are well recorded in felsic dikes. They could be of a syn-genetic origin during their emplacement along E-W and NE-SW structural trends. The sulfide The total analyses of thorite from both microgranite and rhyolite are often close to 90 wt% (Table 1) due to strong hydration or metamictization (Abd El-Naby 2009; Gaafar et al. 2014;. Some grains of thorite are enclosed in hematite, in which could be a good indicator of strong alteration. Zircon crystals incorporate micro-inclusions of uraninite, thorite, uranothorite, monazite, and zircon into their crystal lattice, which could enhance metamictization of zircon (Alekseev and Alekseev 2020;Levashova et al. 2021) (Fig. 4a). The presence of fine-grained zircon as inclusions in large zircon crystals indicates the occurrence of two zircon generations in the studied microgranite dikes. EPMA data show higher HfO 2 that reached 9.08 wt% in the analyzed zircon crystals from microgranite dikes. This could be a good indicator for the hydrothermal activities, according to Wang et al. (2010).
The calculated Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios of the analyzed columbite from microgranite range between (0.0052 and 0.0164) and (0.0549 and 0.7010), respectively, which indicate manganocolumbite composition. Fergusonite is the most dominated HREE-bearing mineral recorded in the microgranite with a mean ΣHRE 2 O 3 17.68 wt%. On the other hand, parisite and chevkinite are LREE minerals recorded in the rhyolite with means ΣLRE 2 O 3 53.53 and 43.75 wt%. However, monazite is a dominated LREE mineral in both microgranite and rhyolite with means ΣLRE 2 O 3 58.38 and 68.14 wt%.
High field strength elements (HFSE) Zr, Hf, Th, and Ti are generally mobile elements during magmatic stage, and/ or hydrothermal alterations containing complexing agents as F, S, and others (Keppler 1993;Ali 2012). Abu Hawis, Umm Tagher El Foqani, and Ras Barud monzogranites are enriched in HFSE (Zr, Hf, Th, and Ti), as well as rare metal mineralization. It is well known that F could have a prominent role during mobilization of Zr, Hf, Th, and Ti as well as REE (Moine and Salvi 1999) during hydrothermal alterations (argillic and hematitization). The reactivated structures are accompanied in association with succession fluid circulations leading to the injection of a series of microgranite, rhyolite, andesite, and basaltic dikes as well as quartz veins. Changes in host rock composition and mineralogy are used to decipher the type and extent of fluid-wall rock interactions during alteration. The physico-chemical conditions of these fluids were changing due to consequent reactions with the granitoids and post-granitic dikes with meteoric water.
Monazite, parisite, and chevkinite are associated with fluorapatite in the rhyolite dikes. These LREE minerals are poor in Th (Tables 4 and 5), with the absence of U and/or the presence with minor concentrations in chevkinite (up to 0.22 wt%). In this case of LREE minerals, the compositional features could suggest their formation as a result of fluorapatite metasomatism (Ziemann et al. 2005;Ali 2012). On the other hand, the chemical composition of monazite from the microgranite shows high Th contents, with a mean of ThO 2 11.29 wt%, which could indicate magmatic monazite.

Conflict of interest
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