Uranium evaluation and its recovery from

Uranium evaluation and its recovery from microgranite dike at G. El Sela area, South Eastern Desert, Egypt Ahmed E. Abdel Gawad, Ahmed H. Orabi & Moustafa M. Bayoumi

Arabian Journal of Geosciences ISSN 1866-7511 Arab J Geosci DOI 10.1007/s12517-014-1499-3

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Author's personal copy Arab J Geosci DOI 10.1007/s12517-014-1499-3

ORIGINAL PAPER

Uranium evaluation and its recovery from microgranite dike at G. El Sela area, South Eastern Desert, Egypt Ahmed E. Abdel Gawad & Ahmed H. Orabi & Moustafa M. Bayoumi

Received: 5 February 2014 / Accepted: 3 June 2014 # Saudi Society for Geosciences 2014

Abstract The present work aims at integrating detailed field studies to prospect for uranium ores associated with microgranite dike. The investigated El Sela area is covered by two types of granitic intrusion comprising biotite granite and two-mica granite. They are cut by microgranite, dolerite, and bostonite dikes, and quartz and jasper veins. U mineralization is observed along an ENE–WSW shear zone where quartz and jasper veins bounded the microgranite dike which is affected by successive brecciation and fracturing. Ferrugination, silicification, kaolinization, illitization, and fluoritization affected microgranite dike having visible U mineralization. Different fractures in two-mica granite acted as good channels for the ascending hydrothermal fluids and the percolating meteoric water that leached uranium from its bearing minerals disseminated all over the host two-mica granite and redeposited them in microgranite dike along the main shear zone trending ENE–WSW. Uranium was determined in the collected samples spectrophotometrically using arzenaso III as complexing agent. Uranium concentrations measured by chemical analyses are higher than the “gamma radiometric” determinations of the same microgranite samples, which can be explained by a state of disequilibrium in the uranium decay series. Sulphuric acid was used, in the present work, for leaching uranium from a representative mineralized sample of highly ferruginated microgranite. Conditions were briefly studied to achieve uranium recovery under optimum conditions. The acid-leaching operating conditions allowed us to obtain a uranium recovery of about 90 %. Ion exchange resin was used for the concentration and purification of our pregnant solution. A 75 % dry uranium concentration in final yellow cake product has been achieved. A. E. A. Gawad (*) : A. H. Orabi : M. M. Bayoumi Nuclear Materials Authority, P.O. Box 530, Maadi, Cairo, Egypt e-mail: [email protected]

Keywords Microgranite dike . Uranium evaluation . Uranium minerals . Alterations . Shear zone . Eastern Desert . Disequilibrium . Leaching uranium . Uranium recovery

Introduction Granites are considered as one of the most favorable host rocks for U mineralization in many parts of the world. Genetically, the economic U deposits associated with granites are mostly located in analectic melts or in strongly peraluminous two-mica granites (Cuney et al., 1984; Poty et al., 1986; Friedrich et al., 1989). In general, granites are rich in incompatible elements (Rb, Nb, Sn, Th, and U) (Rameshbabu, 1999; Pal et al., 2007). The genetic relationship between granite intrusions and associated U mineralization has been discussed for a long time. Uranium existing in granites can be divided into two categories—primary and secondary uranium (Jiashu and Zehong, 1982). Primary uranium is fixed in rocks during magma crystallization while the secondary one is precipitated in various geological events (hydrothermal alteration, absorbed in altered minerals as chlorite, limonite and montmorillonite, and microfructures fillings) later from dissolved and transported uranium, which in turn comes from the primary uranium (Ali and Lentz 2011). Granites are known to host the most interesting U mineralization in Egypt (Ammar 1973; El Kassas 1974; Bakhit 1978; Ibrahim 1986; Salman et al. 1990; Abdel Monem et al. 1998; Fouad, 1999; Ibrahim 2002; Abdel Meguid et al. 2003; Ibrahim et al., 2005; Abu-Deif and El-Tahir 2008; El-Afandy et al. 2008; Abdel Gawad 2011, etc). El Sela granites are considered as one of the highest U favorability areas for hosting U mineralization in Egypt (Abdel Meguid et al. 2003; Ibrahim et al., 2005; Gaafar et al. 2006; Abu Donia 2006; Abd Elaal, 2006; Ibrahim

Author's personal copy Arab J Geosci

et al., 2007; El-Afandy et al. 2008; Ali and Lentz 2011; Ali 2011; Bayoumi 2011). It is located in the southern part of the Eastern Desert between latitudes 22° 16′ 26″– 22° 18′ 38″ N and longitudes 36° 13′ 33″–36° 16′ 26″ E. The present work aims at studying uranium evaluation associated with microgranite dike and then acid leaching of uranium from such dike. Conditions were briefly studied to achieve uranium recovery under optimum conditions. Ion exchange resin was used for the concentration and purification of our pregnant solution.

England) was used for elements analyses (U, Fe, Si, Al, Ti, and P). Uranium in the collected samples was determined spectrophotometrically using arsenazo III (Sulcek and Sixta, 1971) after its separation using Dowex 1×8 (Folke, 1973). All the applied chemicals were highly pure for chemical analysis and supplied by Fluka and Prolabo products. Standard solutions were standardized using the conventional methods (Mendham et al., 2000). Geologic setting

Experimental Detailed gamma-ray spectrometric survey for the most promising locations was carried out using a high sensitive and well-calibrated RS-230 portable gamma-ray spectrometer. A double-beam spectrophotometer (UNICAM,

The detailed field works distinguished two main granitic intrusions at G. El Sela area. They are chronologically arranged from the oldest to the youngest by biotite granite and two-mica granite, respectively. These granites are dissected by three different types of dikes. Field

Fig. 1 Geological map of El Sela area, south Eastern Desert, Egypt modified after Ali (2011)


It is mainly composed of quartz, k-feldspar, plagioclase, and biotite. Iron and manganese oxides represented by hematite, magnetite, goethite, and pyrolusite minerals fill rock joints and fractures. It contains finegrained homogeneous enclaves of black color and oval to circular shape of metavolcanics. The biotite granite was intruded by two-mica granite with clear sharp intrusive contact.

investigations revealed that these dikes are chronologically arranged as microgranite, dolerite, and bostonite dikes in ascending manner. The latest event was the intrusion of quartz and jasperoid veins that dissected all rock types within the study area with different magnitudes (Fig. 1). Quaternary sediments mostly comprise unconsolidated sands and gravels which are broadly categorized as undifferentiated wadi alluvium on the map sheet. They include outwash deposits, channel fill, terraced piedmont sands, gravels, and rock fragments of biotite granite, two-mica granite with different dikes and quartz vein.

Two-mica granite Pink, reddish pink to pinkish gray two-mica granite covers most area of G. El Sela basement complex. It is represented by low to moderate relief masses, forming the remnants of circular and/or arc-shaped granitic plutons (Fig. 1). Furthermore, it is strongly weathered, cavernous, exfoliated, fractured, and jointed along the ENE–WSW, N–S, NE–SW, NW–SE, and NNW–SSE trends. It is composed mainly of quartz, kfeldspar, plagioclase, biotite, and muscovite minerals with medium- to coarse-grained textures.

Biotite granite Biotite granite is represented by small exposure at the northwestern part of the mapped area within the main shear zone (Fig. 1). It is pink to reddish pink in color, slightly leucocratic, massive, and exhibiting low to moderate relief with medium- to coarse-grained texture. Biotite granite masses imply cavernous, exfoliated, and jointed surfaces caused by weathering processes.

SSE

NNW

S

N

two-mica gr.

two-mica gr. Open cut microgranite dike

a

b ENE

c Fig. 2 Photomicrograph shows field investigation at El Sela area. a Microgranite dike invades two-mica granite crosscut by NNW-SSE sinistral strike-slip fault. b Open cut in microgranite dike. c Close up view

WSW

d of brecciated jasperoid vein cemented by white quartz in the main shear zone. d Sheared pegmatite pockets cut two-mica granite in the main shear zone


Postgranitic dikes and veins El Sela granites are dissected by microgranite, dolerite, and bostonite dikes along ENE–WSW, N–S, NE–SW, NW–SE, and NNW–SSE directions. Microgranite dike is the oldest one which strikes N-75° and dipping 70° to 80° S. It is very finegrained, highly altered, whitish pink, pale pink, reddish pink, grayish pink to grayish in color and ranges from 3 to 15 m in

Fig. 3 Photomicrographs of twomica granite and microgranite dike at El Sela. a Feldspars highly sericitized with minuet crystals of muscovite and opaques, two-mica granite. b Biotite altered to chlorite associated with radioactive halos of fine metamect zircon in two-mica granite. c Biotite crystal highly altered to ferrichlorite (pennite) and muscovite, two-mica granite. d Corroded muscovite flacks poikilitically enclose elongate opaques, two-mica granite. e Corroded muscovite flake by the adjacent feldspars and quartz, microgranite. f–h Uranophane in ferruginated, silicified, and kaolinized microgranite

a

thickness. It crosscuts two-mica granite plutons along the ENE–WSW main shear zone. It is dissected by the NW–SE dextral strike-slip faults, NNW–SSE, NNE–SSW, and N–S sinistral strike-slip faults (Figs. 1 and 2a). This dike extends over more than 5 km SW from the northern margin of El Sela plutons and enriched in visible U mineralization. So, many open cuts were made in order to evaluate their U contents (Figs. 1 and 2b).

100 µm b

100 µm

c

100 µm

e

200 µm f

200 µm

g

200 µm h

200 µm

d

100 µm

Author's personal copy Arab J Geosci Fig. 4 Photomicrographs of microgranite samples show different hydrothermal alteration and U-mineralization in El Sela area. a Uranophane in ferruginated microgranite. b Microfructures filled with uranophane in illitized microgranite. c Illitized and fluoritized microgranite associates deep violet to black fluorite

uranophane

a

b

Dolerite dikes are fine- to medium-grained grayish green to dark gray in color. They range in width from 1.5 to 5 m thick. On weathering, they yield onion-like boulders and essentially composed mainly of plagioclase with mafic olivine and pyroxene. They have ENE– WSW, NNW–SSE, NE–SW, and N–S major trends (Fig. 1). These dikes have important two mineralized trends, ENE–WSW and NNW–SSE, enriched by visible U mineralization and pyrite. The first trend in which dolerite strikes N-75° and dipping 70° to 80° S is adjacent to microgranite in some parts of the mapped area. The second mineralized trend of dolerite strikes N-112° and dipping 56° W. The microgranite and dolerite dikes are corresponded to major radiometric anomalies in the spectrometric maps than the ambient twomica granite (Gaafar 2005, Abu Donia 2006). Bostonite dikes display different colors ranging from pale brown, buff to reddish brown according to the intensity of iron oxides staining. They are very fine, to fine-grained, massive, fractured, and jointed, displaying compact appearance. They are of 0.5 to 2 m thickness occurring along the N–S and NE–SW trends. They are mainly composed of k-feldspar, plagioclase, little quartz, and iron oxides. They have a lower U content than biotite granite and two-mica granite. The main shear zone is characterized by the existence of three generations of quartz and jasperoid veins invade twomica granite and existing along ENE–WSW major trend.

c

They bound the microgranite and dolerite dikes and dissect them in concordant with successive fractures corresponding to repeated rejuvenations of the ENE–WSW major trend. Quartz veins are found as multiphases of different colors within the ENE–WSW and N–S tectonic trends (Fig. 1). The first phase is white, highly brecciated barren quartz (1 to 4 m thickness); the second is highly radioactive beige to gray jasper which sometimes changes to a red color along the fractures by ferrugination (20 to 80 cm thickness). These veins are, strongly jointed, fragmented, brecciated, and cemented by the third black jasper phase rich in U mineralization or by white quartz in other places (Fig. 2c). El Sela granitic plutons are affected by main sets of faults trending ENE–WSW, NNW–SSE, NNE–SSW, NW–SE, and N–S showing dextral and sinistral sense of movement (Fig. 1). The ENE–WSW and NNW–SSE are considered important tectonic trends which control the multi-injections and many alteration features in the study area. During reactivation, a simple shear parallel to the inherited ductile fabrics was responsible for the development of mineralized structures along the ENE– WSW and NNW–SSE trends. They can be considered as paleochannel trends for deep-seated structures and can act as a good trap for uranium and/or other mineral resources (Ali 2011). Unmappable pegmatite pockets were found as irregular bodies within biotite granite and two-mica granite. They are very coarse grained, buff to reddish pink in color, highly


Fig. 5

Sketch illustrates eU ppm, eTh ppm, and eU/eTh ratio contour maps of box cut 2, with geological background in the shear zone of El Sela area, South Eastern Desert, Egypt

sheared (Fig. 2d), and composed of k-feldspar, quartz, plagioclase, biotite with muscovite. They show higher content of total radioactivity than two-mica granite.

Petrography Two-mica granite is whitish to pale pink, buff, reddish brown colors, medium- to coarse-grained, highly fractured, and jointed. Microscopically, it is composed essentially of quartz (35 %), k-feldspar (31 %), plagioclase (26 %), and biotite and muscovite (5 %). Zircon, monazite, pyrite, fluorite, apatite uranophane, and opaques are accessories (3 %), while sericite, chlorite, muscovite, epidote, and kaolinite are secondary minerals. Quartz occurs as interstitial subhedral to anhedral crystals and shows wavy and undulose extinction. Some small anhedral quartz crystals poikilitically occur in perthite, plagioclase, and biotite. K-feldspar is represented by orthoclase microperthite. It occurs as subhedral to anhedral prismatic crystals showing simple twinning and shows patchy, string, and flame perthitic intergrowth. It encloses fine crystals of plagioclase, quartz, biotite, and highly altered into kaolinite. Plagioclase of albite and oligoclase composition (An8–14) occurs as subhedral to euhedral tabular crystals. It exhibits lamellar, percline, and simple twinning. Most crystals are highly altered to sericite and enclosing minute muscovite, opaques, and

Table 1 Statistical analysis showing radioelements distribution and their ratios in two box cuts at El Sela area, South Eastern Desert, Egypt T.C K% eUppm eThppm eU/eTh eTh/K (μR/h) Box cut 2 (microgranite dike altered into clay minerals (illitization) Minimum 10.70 2.00 4.80 3.40 0.31 0.83 Maximum 213 4.80 325.6 26.20 18.29 7.38 Mean 29.81 3.34 33.96 11.48 3.34 3.47 Standard Deviation 16.97 0.63 26.90 5.00 No. of readings 424 Box cut 8 (microgranite dike highly ferruginated) Minimum 12.90 1.00 11.40 1.30 Maximum 1723 6.80 1686 84.30 Mean 121.2 3.55 175.9 9.88 Standard Deviation 168.4 1.47 228.6 9.87 No. of readings 516

2.01

1.37

1.51 102.71 16.11 11.41

0.57 18.33 2.64 1.89


spatially associated k-feldspars and quartz grains whereas the secondary muscovite is formed after biotite (Fig. 3d). Zircon occurs as metamict zoned of prismatic or euhedral crystals associated with quartz, perthite, plagioclase, and biotite (Fig. 3b). Opaque minerals occur as cubic crystals, small irregular aggregates, or scattered grains as well as tiny inclusions in biotite and quartz. Microgranite dike is whitish pink, pale pink, reddish pink, grayish pink to grayish colors. It invades two-mica granite along the main shear zone trending ENE–WSW. Microscopically, it is composed mainly of quartz, k-feldspar, plagioclase, biotite, and muscovite (Fig. 2e). It is characterized by microperthite texture. It is also extremely enriched by accessories especially zircon, pyrite cubes, radial uranophane, and opaques. Secondary minerals are sericite, chlorite, epidote, and kaolinite. Microgranite highly ferruginated, silicified, and kaolinized associates uranophane (Figs. 3f–h).

Alteration and mineralizations

Fig. 6 Sketch illustrates eU ppm, eTh ppm, and eU/eTh ratio contour maps of box cut 8, with geological background in the arc zone of El Sela area, South Eastern Desert, Egypt

quartz crystals (Fig. 3a). Biotite occurs as subhedral flakes, which are commonly altered to chlorite, ferrichlorite (pennite), and/or muscovite along outer peripheries and cleavage planes (Figs. 3b, c). It is corroded by k-feldspar and quartz along the outer periphery. Muscovite occurs as minor irregular fine or medium flakes of seldom primary and little secondary origin. The primary muscovite grains were corroded by the

Due to the repeated magmatic activities, reactivated tectonic trends especially ENE–WSW and NNW–SSE and the associated fluids, many alteration halos are observed. Silicification, ferrugination, kaolinization, illitization, and fluoritization (with violet to black fluorite) were recorded. The ENE–WSW shear zone of the northwestern part of G. El Sela is occupied by massive, amorphous silica of light grey, red, to black colors of jasperoid vein and highly silicified microgranite dike. Silicified microgranite along the main shear zone has a noticeable amount of liberated secondary silica occurs as fine crystals associated with the large primary quartz crystals enriched by uranophane (Figs. 3f–h). Kaolinization indicates that the rocks were affected by acidic solution with low temperature varying from 200 to 250 °C (Helgeston 1974). Kaolinitization process causes an increase in alumina at the expense of the other major oxides. In shear zone, kaolinization affects microgranite dike which characterized by the formation of kaolinite associating with veinlet filled with uranophane (Figs. 3f–h). Ferrugination causes increase in total Fe2O3 content at the expense of other oxides. The strong alkaline solution may precipitate Fe +3 and U +6 within the microfractures in the form of iron oxy-hydroxides rich in uranium (Cuney, et al., 1984). Microgranite samples stained by Fe oxides adsorb U mineralization (uranophane) at the main shear zone of G. El Sela area (Figs. 3f–h and 4a). Ferrugination is represented mainly by hematite and goethite minerals.

Author's personal copy Arab J Geosci Fig. 7 Spectrophotometric calibration graph using standard pure uranium solutions with arsenazo III

Illite and fluorite alterations are observed mainly in arc-shaped granite (3.6 km in length). Microgranitealtered samples display clear illitization and the original textures nearly disappeared. The k-feldspar, plagioclase, and biotite are strongly altered to illite (k alteration) followed by fluoritization where the fluorite was emplaced through the fractures in this zone (Fig. 4b, c). This feature characterizes the plane of the ENE–WSW major fault. This indicates that the solution caused the alteration of the feldspars and biotite to illite according to the following reactions:

3ðK A1 Si3 O8 Þ þ ð2Hþ Þ→ðK A12 ðSi3 A1 O10 ÞðOHÞ2 þ 2Kþ þ 6ðSiO2 Þ

K feldspar acid solution

illite

quartz

This means that illite alteration of k-feldspar to illite is produced by an acidic fluid and it liberates silica and K+ according to Hemley and Jones (1964) and Pirajno (1992). The produced K+ liberated into solution can be used to alter plagioclase also to illite and produce some more quartz according to Hemley and Jones (1964) and Pirajno (1992): 6ðNa A1 Si3 O8 Þ þ 2Kþ þ 4Hþ →2 K A12 ðSi3 A1 O10 ÞðOHÞ2 þ 12ðSiO2 Þ þ 6Naþ Na plagioclase illite quartz

Table 2 Uranium concentrations compared with their equivalents of altered microgranite dike at G. El Sela. Two international standard samples using spectrophotometry Type

Samples from box cut

Spectrometry uranium concentration Number Depth μg/ml (ppm) (m)

Radiometric equivalent uranium (eU) ppm

Microgranite dike highly altered into clay minerals (illitization)

1

2 3 4 5 Microgranite dike 6 highly ferruginated 7 8 Standard sample DL-1aa DH-1ab

3

187

51

3.5 1.2 1.5 1.2 1.5 2.5 3.5

230 100 90 213 1,860 2,000 2,265.5 111±0.043 2,566±0.024

58 15 8.7 63 1,036 1,299 1,700

Acidic alteration of albite produces illite quartz and Na+ ions dissolved in the hydrothermal fluid. Similarly, the anorthite component of plagioclase is transformed to illite (Hemley and Jones 1964; Pirajno 1992) and free Ca2+ ions transported also by the hydrothermal solution as follows:

Table 3 Repeated measurements of uranium in a selected sample

RSD for DL-1a=5.5 %, RSD for DH-1a=1 %. Accuracy for DL-1a= 0.043, accuracy for DH-1a=0.024 a

Certified value=116 ppm

Mean=X=0.1054

b

Certified value=2,629 ppm

RSD=±0.8 %

Measurements

Absorbance

1 2 3 4 5 6

0.105 0.107 0.104 0.105 0.105 0.106

7 8 9 10

0.105 0.106 0.106 0.105

Author's personal copy Arab J Geosci Table 4 The chemical analysis of microgranite dike recovered sample no. (8) at G. El Sela shear zone, South Eastern Desert, Egypt

Element oxides

Concentration (Wt%)

SiO2 TiO2 Al2O3 Fe2O3 CaO

73.10 1.05 14.50 4.35 0.53

MgO Na2O K2O P2O5 U3O8

0.77 4.42 0.85 0.43 0.2265

Table 5 Results of conventional acids used for leaching uranium and iron from microgranite dike Leaching acid

Uranium in the leach liquor (g/l)

% Leaching efficiency of uranium

Iron in the leach liquor %

Cold water Hot water (70 °C) Hydrochloric acid Sulphuric acid Nitric acid

0.34 0.56

15 25

0.09 0.11

1.93

85

1.25

2.04

90

0.165

2.15

95

1.05

3½Ca A12 Si2 O8 þ 2Kþ þ 4Hþ →2 K A12 ðSi3 A1 O10 ÞðOHÞ2 þ 3Ca2þ þ 4A13þ þ 3Si4þ Ca plagioclase illite

The excess of released quartz can migrate as colloidal silica to precipitate later in the tension fractures as jasperoid vein at upper structural levels under low temperature

condition (Figs. 5a–c) or caused silicification for the granite near the illite zone. The free Al+3 increase the alumina in the illite.

3 KðMg; FeÞ3 ðA1Si3 O10 ÞðOH; FÞ2 þ 2Hþ →KA12 ðSi3 A1010 ÞðOHÞ2 þ 2KðOHÞ þ 9ðMg; FeÞ2þ þ 6SiO2 þ 2H2 O þ 8O2− ↑ þ 6 F− Biotite

illite

Acidic alteration of biotite produces illite+quartz while magnesium, iron, oxygen, and fluorine are dissolved in hydrothermal fluids (Pirajno 1992). Oxygen may combine with Fig. 8 The “Mean-Chart” representing 10 replicates for the analysis of uranium in an aliquot volume, 1 mL, from leaching solution of selected sample (10). Mean=0.1054, standard deviation (SD)=0.00084, upper control limit (UCL)=0.108, lower control limit (LCL)=0.1028, upper warning limit (UWL)= 0.1071, lower warning limit (LWL)=0.1037

iron to produce hematite forming hematitic alteration. Some magnesium may be substitute in illite alteration. The released 3Ca2+ and 6 F− during illitization of the anorthite and biotite

Author's personal copy Arab J Geosci Table 6 Leaching of uranium from microgranite dike using different sulphuric acid concentrations

Table 7 Leaching of uranium from microgranite dike at different temperatures with 1 M H2SO4

% Leaching Dissoluted Dissolution Sulphuric acid Leached efficiency concentration, uraniuma (g/l) efficiency of Feb, % uranium of Fe, % M

Temperature, Leached °C uranium, (g/l)

% Leaching efficiency of uranium

Dissoluted Dissolution Fe, % efficiency of Fe, %

0.5 1.0 1.8 2.8 3.6

25 40 50 60

90 93 95 96

0.165 1.200 1.300 1.800

1.65 2.04 2.08 2.13 2.17

73 90 92 94 96

0.093 0.165 0.320 1.250 1.820

a

Input uranium content was 2,265.5 μg/g (2.265 g/l)

b

Input iron metal content was 2.3 %

4.04 7.17 13.91 54.34 79.13

may combine together forming fluorite 3CaF2 which is observed within the illite zone (Fig. 4c). This kind of alteration by acid solution is responsible for leaching of uranium from the hosting two-mica granite and redeposited in altered microgranite dike which acts as a good trap for U mineralization. The illitization and fluoritization of El Sela microgranite are compatible with the data by Ibrahim et al. (2004) for illite and fluorite alterations from El Missikate granite at the central Eastern Desert of Egypt.

Radiometric investigation Detailed radiometric survey for the most anomalous locations was carried out using a high-sensitive and well-calibrated RS230 portable gamma-ray spectrometer. This spectrometer internally stores data of conversion/correction constants to allow the display of data in conventional counts/time period or directly in μR/h T.C, % K, ppm eU, and ppm eTh. Field measurements were taken in order to define the extensions of the highest radioactive zones in microgranite dike to evaluate their uranium potentiality (Table 1; Figs. 5 and 6). Fig. 9 Effect of sulphuric acid concentration on uranium leaching efficiency and dissolution of iron from microgranite dike. Solid/liquid ratio=1:5, and stirring time is 4 h at room temperature

2.04 2.11 2.15 2.17

7.17 52.17 56.52 78.26

The selected two sites at the El Sela microgranite dike were chosen according to the highest radioactive anomalies. Altered microgranite dike affected by different alterations as ferrugination, silicification, fluoritization, kaolinization, and illitization which play important role in the redistribution of U mineralization and considered as a good environment/or trap hosting U mineralization (Figs. 5 and 6). The eU contour map of the studied box cut 2 shows that the eU content ranges from 20 to 45 ppm associated with two-mica granite (Fig. 5a). Grey, black, and reddish brown jasper vein stained by Fe oxides in microfructures shows that eU level ranges from 40 to 260 ppm along ENE–WSW and NW–SE mineralized trends. The level of U content ranges from 30 to 60 ppm eU associated with microgranite dike which altered into clay minerals (illitization). Ferruginated microgranite dike in box cut 8 (Fig. 6a) represents the highest U level ranging between 80 and 1,700 ppm eU content along ENE–WSW and NW–SEmineralized trends which associates with visible U mineralization (Fig. 4a, b). On the other hand, a reddish brown quartz vein has eU ranging from 40 to 60 ppm. The content of thorium, which is an immobile element, usually reflects the original composition of rock varieties. The eTh content contour map in box cut 2 (Fig. 5b) shows well discrimination between two-mica granite (high eTh content from 20 to 30 ppm eTh) while microgranite dike and jasper


vein (low eTh content from 8 to 18 ppm eTh). On the other hand, the highest spot in box cut 8 reaches 80 ppm eTh mostly coincides with microgranite dike due to the presence of thorite and uranothorite minerals (Fig. 6b). According to Clarke et al. (1966), eU/eTh ratio is about 0.33 as the crustal average. This ratio depends mainly on the content of U (mobile element) so, eU/eTh ratio is important for U exploration through the determination of U-rich areas. Therefore, in granites, U enrichment can be indicated by high ratio (>0.33), while U depletion (