GEOLOGICAL, GEOCHEMICAL AND SPECTROMETRIC STUDIES ON THE TRACHYTE DYKES OF WADI EL HORA AREA, SOUTH EASTERN DESERT, EGYPT

Wadi El Hora Phanerozoic alkaline trachyte dykes are located at the southern Eastern Desert of Egypt. These trachyte dykes are located between two strike-slip faults taking the N-S and NW-SE trend. The alkaline trachyte dykes consist essentially of feldspars (albite, oligoclase and sanidine), quartz, and alkali pyroxene (aegirine and aegirine-augite) with zircon, fluorite and opaques as accessory minerals, and finally kaoline and sericite as secondary minerals. The trachyte dykes are rich in high field strength elements Nb, Zr, and Y, they also exhibit typical extensional tectonic alkaline magmatisms and evolved in within plated environment. Rare earth elements (REE) patterns exhibit negative Eu anomalies and are largely uniform and heavily fractionated. These trachyte dykes could be considered as a good target for columbite and zircon exploration. According to a detailed spectrometric analysis, the radioelement concentrations are controlled by post magmatic redistribution since the eU/eTh ratio changed directly with eU concentrations and scattered with eTh. The radiometric measurements of trachyte dykes in the study area show a very wide variation in eU (0.6 – 197.1 ppm with an average 43.73) and eTh (2.4 – 626.3 ppm with an average 109.35) contents. The mineralogical study confirms the presence of kasolite, columbite, zircon, fluorite, molybdenite, monazite, pyrite and ilmenite minerals.


INTRODUCTION
Wadi El Hora is found at about 8 km southwest of Darhib talc mine and about 40 km southeast of El Sheikh Shadli at the southern Eastern Desert of Egypt at latitudes 23 o 51 \ 48 \\ and 24 o 00 \ 51 \\ and between longitudes 34 o 50 \ 11 \\ and 34 o 58 \ 46 \\ with area about 225 km 2 (Fig. 1).This study deals with geological, geochemical and spectrometric studies of the alkaline trachyte dykes in the area which are located between N-S and NW-SE two strike-slip faults.These alkaline trachyte dykes consist essentially of feldspars (albite, oligoclase and sanidine), quartz, and alkali pyroxene (aegirine and aegirine-augite) with zircon, fluorite and opaques as accessory minerals, and finally kaoline and sericite as secondary minerals.
At the end of the Pan-African event (650-550 Ma), the calc-alkaline arc-related magmatism was replaced by calc-alkaline to alkaline post-orogenic magmatism (Abdel-Rahman 1995).The Arabian-Nubian Shield crust is thought to have formed during the Pan-African event (950-550 Ma) as a result of the rapid subduction of many island arcs, according to Kröner, 1985 andStoeser, 1986.This arc system stabilized as a result of its accumulation and subsequent sweeping together.According to Harris (1982), the Arabian-Nubian Shield was heavily invaded by plutonic to volcanic basic to acidic, and alkaline to peralkaline rocks.These igneous rocks are the surface manifestations of within-plate or A-type magmatism that occurred during the anorogenic tectonic-magmatic phase of the Arabian-Nubian Shield.El-Manharawy (1972), Hashad andMahfouz (1976), Hashad et al. (1981), Kamel et al. (1985), Akaad (1996), Ibrahim et al. (2002), Amer et al. (2002), Heikal (2003), and Saleh et al. (2021) are practically researchers who have previously studied the alkaline granitic complexes in the area.For the Paleozoic volcanics in Egypt, Meneisy (1990) proposed three primary volcanic episodes, encompassing the Late Carboniferous, Permian and Permo-Traissic periods.These volcanic rocks include a wide range of rock types, including latites, bostonites, andesites, basalts and rhyolites (Aly and Moustafa, 1984).
Long-lasting volcanic activity in Egypt demonstrates a shift in tectonic setting from ocean floor and subductionrelated volcanics in the Precambrian to intraplate volcanicity in the Phanerozoic.The effect of these complex tectonic regimes may be seen in changes in the composition of developed rocks throughout time.Numerous geochronological analyses of these Phanerozoic volcanics have shown three stages of activity in Egypt (El-Shazly, 1977, Hashad et al., 1978, Ressetar et al., 1981, Stairs et al., 1991).These are, Paleozoic  and .The tectono-magmatic events that had affected the Eastern Desert of Egypt during the Mesozoic Era are the causes of these dykes.
Generally, during the last two decades, a considerable investigation for the origin of continental intraplate alkaline rock series ranging from mildly alkaline or transitional basalts to peralkaline trachyte or rhyolites as i t i s a complex process (Saleh et al., 2004, 2007, 2015, 2021, El Tohamy, 2011, Hamdy et al., 2017, Ali et al., 2022, Abdalla et al., 2023).Numerous evolutionary and petrogenetic models have been suggested as: a) a crystal fractionation of mantle-derived magma (Price et al., 1985), b) a trachyte melts due to interaction of mantle-derived magmas with crustal materials (Davidson and Wilson, 1989), c) a process of magma mixing (Gourgaud and Maury, 1984) and d) injection of volatile-rich basic magma of mantle origin that induced partial melting of the lower crust (Bailey, 1980).The alkaline volcanic rocks emerge to host uranium are more than sub-alkaline and calcalkaline assortment (Leroy and Aniel, 1991).
GEOLOGIC SETTING AND PETROGRAPHY Gabal El Homur and Gabal El Silaia in Wadi El Hora area; are two distinct neighbors of younger granites that can be described as the main topographical landmarks in the study area.Hunting, (1967), Soliman, (1975), El Amin and Bassiony (1987) and Ghazaly (1996) had been described them in the previous literatures as two feldspars tectonic younger granites of intrusive character.There are many low relief older granites surrounding the two granitic intrusions, and exposed as scattered masses in wide sand plain.G.
El Silaia and Banat El Silaia (the associated small stocks) are described as pink coarse granites and are perhaps confined to one fault zone (El Ramly et al., 1971).Hashad and El Reedy (1979) determined the age of G. El Silaia as 221 ±12 m.y.age using an Rb/Sr isotope, confirming that it belongs to the alkaline suite of Egypt, that related to Mesozoic Era and agree with El Ramly et al., (1971).
Detailed field studies revealed that the area comprises the main lithologic rock types beginning from the oldest to the youngest as follow: metagabbros, metasediments, older granites, younger granites (monzogranites), and trachyte dykes.The metagabbros exhibit a wide variation of colors, varying from dark grey, dark green to lighter green due to variations in the relative proportions of felsic and mafic phases.These metagabbro show moderate relief and the most prominent topographic features are represented by the ridges that mainly oriented in NW -SE due to the NW -SE structure trend affecting this rock unit.A number of pegmatite veins (about 10 m length) are present as either parallel to or cross the layering planes intruding these rocks.
Biotite and hornblende schists are examples of the metasediments.They form relatively low relief terrain (about 250 m.a.s.l.), which extend NNW-SSE near the most upper stream of Wadi El Hora.These rocks are fine grained and greyish white in color, showing platy and/or fibrous crystals and extend beyond the mapped area in the SSE direction.The metasediments' foliations run parallel to the NNW-SSE right lateral strike slip fault (Fig. 2).Some acidic and basic dykes running ENE-WSW and cutting the metasediments.The older granites are generally low to moderate in topography (Fig. 3).They have a whitish grey tint and are medium to coarse-grained in hand specimens.They are sheared, especially around the faults affecting the extreme of the studied area.This shearing could be attributed to the intensive faulting affecting these masses.Also they are fractured, lineated with lineation and dipping steeply towards the east direction.Mullion structures and ribbing are very well marked on the foliation surfaces.
Numerous quartz and pegmatite veins, as well as basic dykes, cut and cross these rocks.These dykes are striking N45 o E and dipping 50 o toward NE.Several Schist xenoliths are found within these rocks.The trachyte dykes i n Wadi El Hora area are shown in Figure ( 5), as fine-grained rocks with a range of brown, greenish, or pinkish-gray colours.Petrographically, they are composed of quartz, alkali feldspars (sanidine) and alkali pyroxene (aegirine and aegirine augite) set in a fine grained groundmass which shows the characteristic trachytic texture (Fig. 6).Secondary minerals are represented by sericite, chlorite, muscovite and epidote, while zircon, fluorite and opaques are the accessories.Quartz is found as small anhedral to subhedral fine grains in the groundmass.It contains inclusions of zircon.Sanidine is subhedral and found as the main feldspar.Aegirine-augite occurs as black to greenish-black subhedral crystals associated with feldspars (Fig. 7).Aegirine is found as pale brown or brown subhedral crystal (Fig. 8).Zircon occurs as fine prismatic crystals in the groundmass and as inclusions in quartz.It occurs as minute crystals showing abnormal interference color.Pyrite is an euhedral crystal associated with K-feldspars as an abundant sulfides.Opaques are found as aggregates of anhedral crystals associated with feldspar.Fluorite is also present as minute cubic crystals, recognized by its isotropic character.ANALYTICAL METHODS This study involves the following: -Sampling of 16 rock samples from the studied trachyte dykes, and using the portable gamma-ray spectrometer (RS-230) to survey the area radiometrically.Preparation of thin sections for detailed petrographic studies.Sixteen representative samples were analyzed for major oxides and trace elements as well as rare earth elements for eight samples.Crushing, grinding, grain size analysis and heavy liquid separation were done to determine the heavy minerals content.In general, it is ocher-yellow to brownish yellow amber-brown, rarely lemon-yellow to green or reddish orange.It is occurred due to the oxidation of uraninite mineral.It is confirmed by ESEM and contains 44.55% U, 32.65% Pb, 9.12% Si and 4.14% K (Fig. 9).Monazite is a common light REEs bearing mineral and it is also an ultrastable mineral during weathering.It is bright rose-red in color.It sometimes makes a continuous series with huttonite (ThSiO 4) due to the coupled substitution between Th 4+ Si 4+ Ce 3+ P 5+ in the two minerals as an isostructural (Deer et al, 1992).It is confirmed by ESEM and contains 28.66% P, 17.57% Ce, 13.75% La, 4.18% Ce and 1.24% Sm (Fig. 10).

3.c. Fluorite CaF 2
Fluorite is found as anhedral crystals that vary greatly in colour from colourless to deep purple depending on radiation from its inclusions, adjacent radioactive material, evidence of REEs, or the presence of Y in particular (Deer et al., 1992 andFayziyev, 1990).Fluorite is roughly pure, although traces of Y, Ce, and other rare-earth elements can replace the Ca (Berry et al., 2000).It has 88.33% Ca and 8.13% P according to ESEM (Fig. 11).Columbite is found as variable sized developed crystals with a black to brownish black color.It is confirmed by ESEM and contains 44.78% Nb, 18.42%Fe and 6.42% Mn (Fig. 12).Fig. 12: ESEM image and EDX analysis data of columbite, Wadi El Hora area, South Eastern Desert, Egypt.
Fig. 13: ESEM image and EDX analysis data of molybdenite, Wadi El Hora area, South Eastern Desert, Egypt.

3.f. Zircon ZrSiO 4
Colors of zircon include reddish brown, yellow, and grey.Occasionally, Hf can replace Zr in amounts ranging from 1% to 4%, but if Hf predominates over Zr, the mineral is known as hafnon.Additionally, most zircons may be radioactive due to the presence of U or Th, which can occasionally replace Zr (Berry et al., 2000).ESEM has verified its composition, which is 67.22 % Zr, 17.47% Si, and 1.86% Hf (Fig. 14).

3.g. Pyrite FeS 2
Euhedral crystals with a cubic habit make up pyrite.When new, it has a light brassy yellow color that distinguishes it; but, when changed, it may take on hues ranging from deep crimson to black.It is verified by ESEM to have 32.75% Fe and 63.45% S (Fig. 15).
Fig. 16: ESEM image and EDX analysis data of ilmenite, Wadi El Hora area, South Eastern Desert, Egypt.

GEOCHEMISTRY
Sixteen representative samples of trachytes from Wadi El Hora area were selected for chemical analyses of major oxides, trace, and rare earth elements using XRF technique at the Nuclear Materials Authority (NMA), Egypt.The results together with CIPW normative mineral composition as well as some geochemical parameters listed in Tables 1, 2 and 3. Classification, magma type and tectonic setting of the trachyte dykes in the studied area are denoted in these paragraphs according to some selected chemical variation diagrams.

SPECTROMETRIC PROSPECTING
The natural radioactivity of rocks stems mainly from their contents of U, Th and K 40 .In the late magmatic stage, U and Th occur as U +4 and Th +4 .Th +4 is chemically stable, although oxygen fugacity regulates the stability and solubility of U +4 in silicate melts of different compositions.At lower oxygen fugacities, the stability of U +4 in silicate melts are higher (Finch and Ewing, 1992), and the uranium remains in the (+4) state like Th +4 , but when the oxygen fugacities increase U +5 and U +6 increase in magmatic silicate fluids and therefore the geochemical path of Th +4 and U +4 diverges.Rogers and Adams, (1969) stated that, in natural rocks the Th is three times as abundant as U, and the depletion or enrichment of uranium is illustrated according to this ratio.During differentiation of granitic rocks, generally; U and Th contents increase, although in some cases they decrease (Ragland et al., 1967) so the Th/U ratio can either increase or decrease as it is depending on the redox conditions, volatile contents, or alteration by endogens or supergene solutions (Falkum and Rose-Hansen, 1978).Rogers and Adams (1969) stated that the normal contents of U and Th in granitic rocks are 4 ppm and 11 ppm respectively.Uraniferous granites are defined according to Darnley (1982) as any granitic masses containing U at least twice the Clarke value (4 ppm) whether or not they are associated with U mineralization.Uranium also tends to form the relatively soluble uranyl ion (UO 2 ) +2 and mineralization may therefore arise through weathering and leaching of the host rock under oxidizing conditions with consequent removal of U and deposition elsewhere in fractures and faults (Gabelman, 1970).During fractionation, uranium may become enriched in the final fractions of magma, and the residual hydrothermal solutions may form U-rich veins (Goldschmidt, 1954).
The measurements are expressed in ppm for eU and eTh and % for K.In the field only gamma rays (which are of sufficient energy and have a long distance of penetration) could be detected.The instrument used in the ground γ-ray spectrometric survey measurements is RS-230.Ground γ-ray spectrometric survey can detect potassium (K%), equivalent uranium content (eU ppm), and equivalent thorium content (eTh ppm).Because U and Th are not gamma-ray emitters, the measurement of the gamma-rays released by their daughters is used to determine the eU and eTh using gammaray spectrometry.Uranium mobilisation (eU m) can be calculated as the difference between the measured eU and the expected original uranium, which is calculated by dividing the measured eTh by the average eTh/eU ratio in the crustal acidic rocks (original uranium = eTh/3.5according to Clark et al., 1966), to give the leaching values of uranium (eU m = eU-eTh/3.5).Positive values indicate uranium addition by mobilization, whereas negative values indicate migration of uranium by leaching.If the surface U distribution is less than that of the hypothetical U distribution, the mobilization of U should has negative values, which mean that U is leaching out (Cambon, 1994).
The eU content in the trachyte dykes range from 0.6 to 197.1 ppm with an average 43.73 ppm, while the average of eTh is 109.35ppm ranging from 2.4 to 626.30 ppm.The ratio of eU/eTh ranges from 0.25 to 0.31 with an average 0.40 and the eU mobilization is varying from -0.09 to 18.16 with an average of 12.49 as showing in (Table 4) and bar diagram (Fig. 27).The variation diagrams (Figs.28:34) of the trachyte dykes show moderately positive for K% relation with each of eU (Fig. 28) and eTh (Fig. 29), strong moderately positive for eU relation with each of eTh (Fig. 30) and eU mobilization (Fig. 33), low weak positive relation between eU and the ratio eU/eTh (Fig. 31), weak positive for the relation of eTh with eU mobilization (Fig. 34) and finally low weak negative for the relation of eTh and the ratio eU/eTh (Fig. 32).

CONCLUSIONS
Wadi El Hora area Phanerozoic alkaline trachyte dykes are located at the southern Eastern Desert of Egypt.They are located between two strike-slip faults trending N-S and NW-SE.They consist essentially of feldspars (albite, oligoclase and sanidine), quartz, and alkali pyroxene (aegirine and aegirineaugite) with zircon, fluorite and opaques as accessory minerals whereas kaoline and sericite as secondary minerals.Wadi El Hora trachyte dykes could be considered as a good target for exploration of columbite and zircon.Detailed spectrometric analysis showed that the eU/eTh ratio fluctuates directly with eU concentrations and arbitrarily with eTh, showing that the radioelement concentration is controlled by post magmatic redistribution and also showing very wide ranges.The mineralogical study of the samples revealed the presence of kasolite, monazite, fluorite, columbite, molybdenite, zircon, pyrite and ilmenite minerals.

Fig. 2 :
Fig. 2: View showing the foliation in metasediments is parallel to the strike of the NNW -SSE right lateral strike slip fault.The older granites are generally low to moderate in topography (Fig.3).They have a whitish grey tint and are medium to coarse-grained in hand specimens.They are sheared, especially around the faults affecting the extreme of the studied area.This shearing could be attributed to the intensive faulting affecting these masses.Also they are fractured, lineated with lineation and dipping steeply towards the east direction.Mullion structures and ribbing are very well marked on the foliation surfaces.Numerous quartz and pegmatite veins, as well as basic dykes, cut and cross these rocks.These dykes are striking N45 o E and dipping 50 o toward NE.Several Schist xenoliths are found within these rocks.

Fig. 3 :
Fig. 3: View showing the older granites are characterized by relatively low to medium topography.The younger granites (monzogranites) (Fig.4) are exposed at the southwestern and northeastern sides of the mapped area (Fig.1).They are represented by G. El Homur and G. El Silaia.G. El Silaia is moderate relief, covering about 20 km 2 , and form

Fig. 4 :
Fig. 4: View showing younger granites (monzogranites) are characterized by low to medium topography.The trachyte dykes are the youngest rock type in the studied area.The Gabal El Homur and Gabal El Silaia comprise two significant masses (approximately 1.5 km 2 ) with few sheets and dykes.The trachyte dykes dip outward in all directions and always makes sharp contact with the metagabbros.Along the northerly directions of Gabal El Homur and Gabal El Silaia, other minor trachyte dykes are dispersed.The trachyte dykes intrude the two monzogranites, having a NE-SW

Fig. 6 :
Fig. 6: Photomicrograph showing trachytic texture, Wadi El Hora area, South Eastern Desert, Egypt.Quartz is found as small anhedral to subhedral fine grains in the groundmass.It contains inclusions of

Fig. 8 :
Fig. 8: Photomicrograph showing subhedral crystals of aegirine, Wadi El Hora area, South Eastern Desert, Egypt.ANALYTICAL METHODS This study involves the following: -Sampling of 16 rock samples from the studied trachyte dykes, and using the portable gamma-ray spectrometer (RS-230) to survey the area radiometrically.Preparation of

Fig. 9 :
Fig. 9: ESEM image and EDX analysis data of a) kasolite, Wadi El Hora area, South Eastern Desert, Egypt.3.b.Monazite (Nd, La,Ce)PO 4Monazite is a common light REEs bearing mineral and it is also an ultrastable mineral during weathering.It is bright rose-red in color.It sometimes makes a continuous series with huttonite (ThSiO 4) due to the coupled substitution between Th 4+ Si 4+Ce 3+ P 5+ in the two minerals as an isostructural(Deer et  al, 1992).It is confirmed by ESEM and contains 28.66% P, 17.57% Ce, 13.75% La, 4.18% Ce and 1.24% Sm (Fig.10).

Fig. 10 :
Fig. 10: ESEM image and EDX analysis data of monazite, Wadi El Hora area, South Eastern Desert, Egypt.3.c.Fluorite CaF 2Fluorite is found as anhedral crystals that vary greatly in colour from colourless to deep purple depending on radiation from its inclusions, adjacent radioactive material, evidence of REEs, or the presence of Y in particular(Deer  et al., 1992 and Fayziyev, 1990).Fluorite is roughly pure, although traces of Y, Ce, and other rare-earth elements can replace the Ca(Berry et al., 2000).It has 88.33% Ca and 8.13% P according to ESEM (Fig.11).

Fig. 11 :
Fig. 11: ESEM image and EDX analysis data of fluorite, Wadi El Hora area, South Eastern Desert, Egypt.3.d.Columbite (Fe,Mn)Nb 2 O 6Columbite is found as variable sized developed crystals with a black to brownish black color.It is confirmed by ESEM and contains 44.78% Nb, 18.42%Fe and 6.42% Mn (Fig.12).

Fig. 14 :
Fig. 14: ESEM image and EDX analysis data of zircon, Wadi El Hora area, South Eastern Desert, Egypt.3.g.Pyrite FeS 2Euhedral crystals with a cubic habit make up pyrite.When new, it has a light brassy yellow color that distinguishes it; but, when changed, it may take on hues ranging from deep crimson to black.It is verified by ESEM to have 32.75% Fe and 63.45% S (Fig.15).

Fig. 15 :
Fig. 15: ESEM image and EDX analysis data of pyrite, Wadi El Hora area, South Eastern Desert, Egypt.

Fig. 22 :
Fig. 22: Na 2 O+K 2 O vs. SiO 2 (after Irvine and Baragar, 1971; the line shaded area represents the continental oversaturated volcanics from the Cameroon (Fitton, 1987), magma type diagrams, Wadi El Hora area, South Eastern Desert, Egypt.The binary relations of Nb vs. Y and Rb vs. (Nb + Y) of Pearce et al., 1984; indicate that the trachyte rocks of the studied area plot in the within plate field (Figs.23 & 24).

Fig. 24 :
Fig. 24: Log Y-Log Nb, (after Pearce et al., 1984) tectonic setting diagrams, Wadi El Hora area, South Eastern Desert, Egypt.On the chondrite-normalized diagram (Fig. 25), the trachyte rocks of Wadi El Hora area exactly show depletion in Eu and high enrichment of light REEs (660.5 ppm) according to the heavy REEs (61.59 ppm).Also, the chondrite-normalized trace elements diagram (Fig. 26) shows that, the trachyte rocks of W. El Hora area exhibit enrichments in Rb, Nb, light REEs and Zr and exhibit depletion in Ba and Sr due to consumption of these elements during the fractionation of plagioclase.

Fig. 26 :
Fig. 26: Spider diagram of REEs and trace elements patterns, (normalization values are after Sun and McDonough, 1989), Wadi El Hora area, South Eastern Desert, Egypt.SPECTROMETRIC PROSPECTINGThe natural radioactivity of rocks stems mainly from their contents of U, Th and K 40 .In the late magmatic stage, U and Th occur as U +4 and Th +4 .Th +4 is chemically stable, although oxygen fugacity regulates the stability and solubility of U +4 in silicate melts of different compositions.At lower oxygen fugacities, the stability of U +4 in silicate melts are higher(Finch and Ewing,  1992), and the uranium remains in the (+4) state like Th +4 , but when the oxygen fugacities increase U +5 and U +6 increase in magmatic silicate fluids and therefore the geochemical path of Th +4 and U +4 diverges.Rogers and Adams, (1969) stated that, in natural rocks the Th is three times as abundant as U, and the depletion or enrichment of uranium is illustrated according to this ratio.During differentiation of granitic rocks, generally; U and Th contents increase, although in some cases they decrease(Ragland et al., 1967) so the Th/U ratio can either increase or decrease as it is depending on the redox conditions, volatile contents, or alteration by endogens or supergene solutions(Falkum and Rose-Hansen, 1978).Rogers and Adams (1969) stated that the normal contents of U and Th in granitic rocks are 4 ppm and 11 ppm respectively.Uraniferous granites are defined according toDarnley (1982)  as

Fig
Fig. (27): Bar diagram showing the Min., Max., and aver. of K%, eU, eTh, eU/eTh, eTh/eU and eU mob. of radiometric reading in the trachyte rocks, Wadi El Hora area, South Eastern Desert, Egypt.

Table 1 :
Major oxides and trace elements obtained from the chemical analysis of trachytes, Wadi El Hora area, south Eastern Desert, Egypt.

Table 2 :
Norm obtained from the chemical analysis of trachytes, Wadi El Hora area, south Eastern Desert, Egypt.

Table 3 :
REEs obtained from the chemical analysis of trachytes, Wadi El Hora area, south Eastern Desert, Egypt.