mineralogical and geochemical aspects of nubia sandstons ... · arab journal of nuclear sciences...

Arab Journal of Nuclear Sciences and Applications, 45(2)117-129(2012)

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Mineralogical and Geochemical Aspects of Nubia Sandstons at Gabel El Ghurfa, Southeastern Desert, Egypt

Ibrahim, M. E, Aly, G. M. and El-Tohamy, A.M.

Nuclear Materials Authority, Cairo, Egypt

[email protected]

ABSTRACT

Gabel El Ghurfa area is situated at the eastern part of Wadi Natash lies ~ 125 km ENE of Aswan and occupies some 130km2 of the exposed volcanics and Nubia sandstones. Gabel El Ghurfa forms a ring dyke (2km2) with a diameter of 1.2 km and composed mainly of normal and alkaline trachyte at the outer zone . The inner zone of the ring (600 m in diameter) is mainly represented by Lower Nubia sandstones (LNSS) and a minor trachyte plug. The LNSS is composed of conglomerate (at the base) followed by quartz arenite, greywacke and calcareous sandstone (at the top). The lower Nubia sandstones overlie the metasediments and overlain by the lower volcanic flows (alkali olivine basalt), whereas the Upper Nubia sandstones (UNSS) overlie the trachyte.

The lower Nubia sandstones are characterized by uranium minerals (metaheinrichite, autunite and uranophane ),sulfides and base metals (pyrite, galena, zincite, chromite , copper nickel, gold and silver) and accessories (e.g. zircon, monazite, spinel, sphene, fluorite, ilmenite, garnet, rutile and allanite) which confirmed by X-ray diffraction and ESEM analyses.

The geochemical data of the bulk LNSS samples reflect the enrichment of SiO2, CaO, Zr, Ba, Sr, Ti, Cr and Ni. The LNSS deposited in semi-arid to semi-humid climatic conditions .Total rare earth elemental concentration of LNSS vary between 50 and 295 ppm. From the rare earth elements (REE) data, the LNSS are characterized by (1) enrichment in light rare earth element (LREE), (2) depletion in heavy rare earth element (HREE) relative to the light and (3) negative Eu- anomaly.

1-INTRODUCTION

Gabel El Ghurfa area is situated in the southern part of Wadi Natash. The studied area lies ~ 125 km east- north east of Aswan and occupies some 130km2 of the exposed volcanic rocks and Nubia sandstones (Fig.1.a). The study area is delineated by longitudes 34° 07' 03? to 34° 17' 31? E, and latitudes 24° 26' 30? to 24° 32' 20? N. Geology of Wadi Natash has attracted many authors e.g. (1 ,2, 3and 4).

The aim of this study is to investigate in detail the mineralogical components and the geochemical relations of the Lower Nubian Sandstons in the core of Gabel El Ghurfa ring dyke.

2-GEOLOGIC SETTING

The exposed rocks at the study area comprise metasediments, lower Nubia sandstones, volcanic flows, volcaniclastic sediments and upper Nubia sandstones (Fig.1b). The lower Nubia sandstones (LNSS) overlie the metasediments (10 m thickness) and overlain by the lower volcanic flows (alkali olivine basalt). The UNSS overlie the upper volcanic flows (normal and alkaline trachyte), outside the western parts of the mapped area with thickness up to 20m (3).

Gabel El Ghurfa forms a ring dyke with a diameter of 1 km and consists mainly of alkaline and normal trachyte at the outer zone extruded LNSS. The inner zone (600m in diameter) of the ring dyke is mainly covered by Lower Nubia sandstone (LNSS) and minor plug of trachyte (10m in diameter) with low relief. The contact between the trachyte and the LNSS are sharp and dipping inward to the inner zone. Two major strike slip faults (WNW-ESE and NNW-SSE) with obvious displacement are common and show different degree of fault catacastics and breccias. These faults are good channel


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ways' for any incoming mineralization- bearing solution. The LNSS at the inner zone of Gabel El Ghurfa ring dyke is economically of great interest due to their high porosity and permeability and surrounded by trachyte from all sides (closed basin).

The LNSS are mainly composed of conglomerate (at the base), quartz arenite, greywacke and calcareous sandstone (at the top). The conglomerate (1 m thickness) is composed of angular to sub-angular quartz pebbles (up to 1 cm in length) with variable colors(vary from black through blood red to milky) embedded in fine – grained matrix.

Basal conglomerate , microscopically, it is poorly sorted rock composed of pebbly grains with variable grain sizes (1 to 2 cm) embedded in a fine matrix of sand grain size (1mm). The grains are rounded to sub-round dominated by quartz and characterized by wavy extinction. The matrix is composed of sub-angular to sub-rounded grains of quartz and K-feldspars as microcline crystals characterized by cross-hatched twining. Quartz arenite is composed mainly of monocrystalline mature, well sorted grains (0.5mm) of quartz and feldspars of sand size. Quartz grains are medium to fine representing about 95% of the rock and occur as primary and secondary interstitial quartz grains. Greywacke, is pale brown to grey in color; medium to fine badly sorted grains, and composed of less than (75 in vol. %) grains and more than (25 in vol. %) matrix. It is highly porous, and porous is lined by chalcedony forming comb structure. Quartz grains are angular, sub-angular to sub-round with grain size ranging from (1mm to 6mm). It is badly-sorted occurring also as skeletal grains, polycrystalline quartz. Calcareous sandstone is black in color according to dominance of carbonate (up to 50 in wt %) and iron oxide (about 15%of the rock) representing the matrix while the grains are mainly quartz. Quartz grains are fine to medium less than 0.6mm; they are sub-rounded to sub-angular, milky white in color and characterized by wavy extinction.

Analytical Techniques

Twenty five surface samples representing the Nubia sandstones of Gabel El Ghurfa were collected. Eight samples were analyzed for the major oxides and a sizeable group of trace elements, including the 14 REE, in the ACME Labs, Vancouver, Canada, using the Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Seventeen samples were analyzed for major oxides SiO2, Al2O3 and P2O5 were determined by using Spectrophotometer. The Na2O and K2O were measured by the Flame Photometry technique. Total iron as Fe2O3, MgO and CaO were determined by titration method and L.O.I was determined gravimetrically. Trace elements concentrations of the collected samples were measured using X-ray Fluorescence. ESEM microscope (model Philips XL 30 ESEM) supported by a semi – quantitative (EDX) unit XRD (in Nuclear Material Authority, Cairo, Egypt) was applied for mineralogical investigations. The analytical conditions are 25 – 30 kv accelerating voltages, 1-2mm beam diameter and 60 – 120 second counting times.

3-MINERALOGICAL RESULTS

For studying the heavy fraction of the LNSS under investigation, composite samples from different LNSS types were collected. The collected sample was crushed, ground, quartered and sieved to the size fraction – 60 to +120 meshes which later was separated by bromoform. Some separated minerals were picked under binocular microscope and identified using ESEM supported by EDX and XRD. The fine fraction (< 60 mesh) was also investigated by the same techniques. The obtained data from both X-ray diffraction and ESEM analyses revealed the presence of the following mineral groups: 1- Radioactive minerals, 2-Niobate- Tantalite minerals 3- Sulfide and sulfate group 4-Base metals and sulfides and 5-Accessory minerals.

3.1- Radioactive minerals

The radioactive mineralization occurs as microfractures infilling or coating on joint surfaces and are represented by metaheinrichite, autunite, uranophane, kasolite and uranothorite.

3.1. a-Metaheinrichite [Ba (UO2)2(AsO4)2. 8H2O] is a rare secondary mineral derived by the weathering of primary uranium (Fig. 2a). It is one of meta-autunite group. Metaheinrichite was found associated to autunite mineral in calcareous sandstone.3.1.b-Autunite [Ca(UO2)2(PO4)2•10-12(H2O)] is the oxidation product of primary U- mineral (pitchblende and uraninites) and may also be


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derived from some other secondary minerals, like gummite and uranophane. Autunite is present as small aggregates grains in calcareous sandstone and conglomerate. The EDX analysis gives a Ca: U: P ratio 1.3:5.1:1, in calcareous sandstone (Fig. 2b).3.1.c-Uranophane [Ca (UO2) (SiO2)2(OH) 2. 5H2O] appears to be of supergene origin and present as small aggregates in calcareous sandstone of Gabel El Ghurfa (Fig.2c). The grains are very soft with different grades of yellow to waxy dull color.3.1. d- Uranothorite [(Th, U) SiO4] occurs as fine opaque grains. The ESEM analysis shows that it consists essentially of ThO2, and minor UO2compatible with (5). Other elements are present in small to minor amounts as Ca, S, Al, Fe and Y (Fig. 2d). Uranothorite was found in greywacke. EDX analysis gave Th: U: Si ratio 2.6:1:4.2 with considerable amounts of Y.

3.2- Niobate- Tantalite group

3.2. a - Columbite [(Fe, Mn, Mg) (Nb, Ta) 2O6]also called niobate; it is black to dark brown tabular or prismatic crystals recorded in greywacke samples and confirmed by ESEM technique and contain (30%) Nb2O5,(21%)TaO, (2%)Y2O3, (1%) UO2, (6%) ThO2, (3%) Fe2O3 and (3%) ? REEs. Nb2O5/TaO ratio equal to 1.4 mol indicates enrichment in Ta (Fig. 2e).2.b - Yttrocolumbite [(Y, U, Fe++) (Nb, Ta) O4] is derived from its yttrium content and similarity to columbite. It was recorded in greywacke samples of Gabel El Ghurfa and confirmed by ESEM technique and contains (33%)Nb2O5, (0.34%)TaO, (15%)Y2O3, (1%)UO2, (1%)ThO2, (2%)? LREEs and (6%)? HREEs (Fig.2f). Nb2O5/TaO ratio is equal to 97 mol and LREEs/HREEs ratio about 0.3. The analyzed samples show depletion in Ta and LREEs and enrichment in HREEs .Another sample contains (16 %) TaO, (22%) Nb2O5, and (16%) Y2O3, (1.3 %) UO2, (1%) ThO2, (3 %) ? LREEs and (5%) ? HREEs. Nb2O5/ TaO ratio equal to 1.3 mol ratio whereas ? LREEs/? HREEs ratio equal to 0.6. The enrichment of HREEs and Y2O3 are indicator of the alkali metasomatizm.2.c- Yttrotantalite [ (Y, U, Fe++) (Ta, Nb) O4 ] contains (29%) TaO, (17%) Nb2O5, and (16%) Y2O3, (2%) Fe2O3,(6%) UO2 , (4%) ThO2, (3%) ? LREEs and (8%) ? HREEs. Nb2O5/ TaO ratio equal to 0.6 mol, and ? LRREs /? HREEs ratio equal to 0.4%. Both yttrocolumbite and yttrotantalite is carrier for uranium more than thorium compared with columbite more thorium than uranium.

3.3- Base Metals

3. a -Native gold (Au) occurs as nuggets associated with silver and copper in quartz grains in the greywacke. Native gold was recorded as spike on carbonate matrix associated with Cu in calcareous sandstone of Gabel El Ghurfa. Au was measured by fire assay and contains about 1.5 g/t. Also it was confirmed by ESEM technique (Fig. 2g) and associated with Ag and Cu.3. b- Brass alloy (Cu3Zn2) is a native elements and not officially recognized minerals as yet, although it has been proposed. Its color is yellow to brassy yellow, and associated with pyrite. It was recorded in calcareous sandstone and greywacke of Gabel El Ghurfa with Cu: Zn ratio equal to 1.7:1.Zincite (ZnO2) is the mineral form of zinc oxide and an important ore of zinc. Zincite was found in calcareous sandstone as white grains, containing (84%) of ZnO (Fig.2h).

4-SULFIDE GROUP

4.a- Argentite (Ag2S) is the most important silver ore. The name 'argentite' refers to the high-temperature form of silver sulfide; only stable over 177 °C. Under this temperature any samples of 'argentite' convert to acanthite. Argentite was recorded in greywacke .The EDX analysis (Fig. 2i) give an Ag: S ratio equal to 2.5:1.4.b- Galena (PbS) was found in greywacke of Gabel El Ghurfa with Pb: S ratio 3:1 and traces of Ni, Mg, Al, Ca, and Ti (Fig.2j). 4. c-Pyrite (FeS2) was recorded in conglomerate of Gabel El Ghurfa and its color range from yellowish grey to grey with metallic luster. ESEM analysis (Fig. 3a) shows the Fe: S ratio 1:4. 4. d- Hauerite (MnS2) is member of pyrite group and found in association with complex of iron and manganese in greywacke of Gabel El Ghurfa.

5-ACCESSORY MINERALS

Allanite [(Ca, Ce, La, Y) 2(Al, Fe) 3(SiO4)3(OH) ]also known as orthite, it is a member of the epidote group. Most allanite contains some thorium, up to 3 percent (6). It is black in color but can be brown to brownish with vitreous luster. The EDX analyses (Fig. 3b) give Ca: LREEs: Y: ratio equal to 6.5:5.2:1:7.5:2.5 in greywacke. Monazite [(Ce, La, Th, Nd, Y) PO4] is a primary ore of several light rare earth metals most notably thorium, cerium and lanthanum. Monazite is radioactive,


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sometimes highly radioactive, and specimens are often metamict. Uranium may occupy some of the REE sites in monazite (7).Its color is yellow to brown or orange-brown. Monazite here may be well rounded, prismatic, kidney shape or may occur as inclusions. The total ? LREEs in rounded monazite is greater than ? LREEs in other types. It has been identified by ESEM as separated mineral grain in conglomerate, greywacke and calcareous sandstone, of Gabel El Ghurfa. The EDX analyses (Fig. 3c) give P: LREEs: Th: Si ratio 4:4.5:1.7:1, with traces of U in greywacke.

Titanite (CaTiSiO5) is named for its titanium content, reddish brown, or yellow monoclinic crystals. These crystals are typically wedged shaped or sphenoid in habit. Ca may be partly substituted by Na or rare earth elements. Titanite was found in conglomerate as individual small grains. Many specimens show the presence of Fe, Al, and in some cases considerable quantities of LREEs. Apatite (Ca PO4) is a common accessory mineral in almost rocks. The intensity of the color increases with an increase of Mn- content of the apatite (8). It was found in the greywacke and has Ca: P ratio 3.1: 1 (Fig.3d).

Zircon (ZrSiO4) varies from rose, water clear, fracture and yellowish ones .zircon was recorded in conglomerate, greywacke and calcareous sandstone of Gabel El Ghurfa, as well as some zircon crystals show inclusions. The perfect prismatic bipyramidal crystals indicate magmatic or primary origin (>900co). Zr/Hf ratio equal to 47 in metamict (rose) zircon, 45 in short prism zircon, 33 in prismatic zircon (Fig. 3e) and 60 in muddy zircon. It contains (41%) ZrO2, (0.6%) Hf2O3, (57%) SiO2 and (0.1?%) UO2.

Fluorite (CaF2) was recorded in conglomerate of Gabel El Ghurfa as individual grains barren from U- minerals .Fluorite have Ca: F ratio equal to 1.6:1, with small amounts of Y. Xenotime (YPO4) crystals are similar to zircon and can easily be confused with the duller luster. It's recorded in greywacke with color brown but also gray. The crystals are translucent to opaque. The EDX analyses (Fig. 3f) give Y: P ratio 2.5:1 with amounts of HREEs and U in greywacke.

Taenite ?–(Fe, Ni) is a mineral found naturally on earth. It is an alloy of iron and nickel (Fig. 3g), with nickel proportions of 20% up to 65%. Taenite is recorded in greywacke and contains (88%)NiO, (5%)Fe2O3, and (3%) CdO with traces of Ca, Al and Si. Rutile (TiO2) is found in greywacke, calcareous sandstone and conglomerates of Gabel El Ghurfa. It has many shapes as prismatic and elbow. Rutile was confirmed by X- ray diffraction and ESEM technique and contains (99%) TiO2 and (1%) SiO2.

B - Geochemistry of Nubia sandstones

Major elements

The average distribution of the major oxides content for the lower Nubia sandstones are shown in table ( 1 ). The general features drawn from data are as follow: The highest CaO and the lowest content of SiO2 is recorded at the calcareous sandstone (Av=38 % &20%, respectively). Zr is higher in concentration in greywacke and quartz arenite (Av=2562, 716ppm) respectively than in the calcareous sandstone (Av=118ppm). The highest Sr content is recorded in the calcareous sandstone (Av=339ppm). While the calcareous sandstone have the lowest Nb, Zn, Ni, Cr contents (Av=7, 22, 17, 29 ppm, respectively) as compared with greywacke and quartz arenite.

Geochemical classification (9) suggested that geochemical mapping system to allow reliable estimates of sandstone types from the geochemical data of ferruginous sandstone and shale using the parameters of log (SiO2/Al2O3) and log (Fe2O3/K2O) (Fig.4).Most of greywacke samples lie in Fe-sand and sublithic arenite to sub-arkose fields, whereas all samples of quartz arenite lies in quartz arenite field. Greywacke samples did not fall all in wacke field because of average SiO2 = 81 wt%, due to siliceous cement in the rock.

Silica enrichment is a measure of sandstone maturity and is a reflection of the duration and intensive weathering and destruction of other minerals during transportation. Abundance of alkalis characterizes immature sandstone such as greywacke, whereas the ratio of Na2O/K2O determines both the provenance and diagenesis of sandstone deposits (10 and11). Al2O3 and K2O contents may relate to the presences of potassium feldspars and mica. The source of Na2O is principally related to plagioclase


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feldspars. Rutile is the main holder of TiO2. Higher content of iron may be related to the abundance of iron oxide. MgO content is related mostly to the presences of spinel and garnet. Calcite cement and rock fragments are the main source for CaO.

Bivariant plot of SiO2 against total (Al2O3+K2O+Na2O) proposed by (12) (Fig.5), was used in order to identify the maturity of sandstone as a function of climate. This plot revealed the semi-arid to semi-humid climatic conditions for the samples investigated. According to (13), most of the lower Nubia sandstone samples fall in sodic sandstone field, and four samples lie on the ferromagnesian potassic sandstone field (Fig.6).

Trace elements

The behavior of trace elements during sedimentary processes is complex due to several factors such as physical weathering, sorting provenance and digenesis (14 and 15). Most of the trace elements for lower Nubia sandstones are given in (Table4.2). The average distribution of the trace elements content for the studied samples is shown in table (2). (16) stated that Rb is higher in marine shales (281ppm) than in fresh water (139ppm). The Lower Nubia sandstones gave Rb average (21 ppm) meaning that they were deposited in fresh water environment. Greywacke and quartz arenite show high U and Th contents (140-185 U ppm, 50-57 Th ppm) respectively, compared with the average concentration of the arenaceous sediments reported by (17) (U=0.5-2ppm and Th= 2-6ppm).The Uch

/eU ranges from 1.2 to 40 ,whereas eU/Ra varies from 1-4(18) manifesting addition and recent uranium. The ascending hydrothermal solutions carry the uranium as uranyl from the deep seated parts, where the (U+4 )gets oxidized into highly soluble uranyl (U+6) .The secondary uranium minerals were formed by the combination of the U-bearing solutions with other cations such as Ca, Pb, Ba and anions such as P2O5 and SiO2 (forming uranophane, kasolite, autunite, metaheinrichite) and deposit it mainly in the fractures and faults as well as in the porous and permeable LNSS.The heavy and sulfides minerals in the LNSS are of epithermal origin.

Rare Earth Elements (REEs)

Complete rare earth elements (REE) data for the lower Nubia sandstones are given in table (3) and the normalized rare earth element patterns are shown in (Figs. 7&8). Chondrite –normalized rare earth element of the lower Nubia sandstones are characterized by (1) enrichment in light rare earth element (LREE), (2) depletion in heavy rare earth element (HREE), extreme depletion of heavy REE relative to the light is most likely to indicate the presence of garnet in the source (3) negative Eu- anomaly, the removal of feldspars from a felsic melt by crystal fractionation or by partial melting of a rock in which feldspars is retained in the source will give rise to a(-ve) Eu anomaly in the melt. Total rare earth elemental concentration of greywacke varies between 68.4 and 295.8 ppm while in the calcareous sandstone varies between 50 and 278.7ppm.Three samples in greywacke (G2, G3, G4) exhibit strong negative Eu-anomaly (Eu/Eu* =0.39, 0.43, 0.4) respectively. The more probable mechanism of producing such Eu depletion is partial melting where feldspars (most likely plagioclase) are a residual phase.

The LREEs/HREEs ratios in greywacke samples range from (3.9 ppm to 6.4 ppm), and lower than that of the calcareous sandstone (5.4ppm to 8.8ppm), also the range of Eu-anomaly (Eu/Eu*= 0.4 ppm to 0.76 ppm) for greywacke is lower than that of the calcareous sandstone (Eu/Eu*= 0.9 ppm to 0.82 ppm).There is a strong enrichment of the LREE with respect to the HREE. The principal carriers of REEs are the accessory minerals such as monazite, allanite, columbite, tantalite and xenotime. High enrichment of LREE in lower Nubia sandstone samples is controlled by the abundance of monazite mineral.


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Table ( 1 ): Results of the average and range of major oxides (%) of lower Nubia

sandstones, Gabal El Ghorfa area.

N = number of the samples

--= Not detected values

Calcareous sandstone

Greywacke Quartz Arenite

N=7??N= N=2

Rock Type

Oxides

20 (9 – 28)

81 (72 – 93)

95 (95 – 96)

SiOB2 B

2 (1 – 4)

8 (1 – 15)

0.5 (0.4 – 0.5)

AlB2 BOB3 B

0.33 (0.1 – 0.6)

1.4 (0.5 - 2.4)

0.07 (0.05 – 0.08)

TiOB2 B

3.5 (0.7 – 8.0)

3.2 (1.5 – 4)

1.04 (0.1 – 2)

FeO

3 (0.6 – 7)

4 (2 – 5)

1.2 (0.1 – 2)

Fe B2 BO B3 B

0.60 (0.0 – 1.3)

0.07 (0.01- 0.3)

0.04 (0.02 – 0.05)

MnO

38 (31 – 49)

1.3 (0.40 – 6)

0.6 (0.4 – 1)

CaO

1.5 (0.4 – 3)

0.6 (0.1- 0.80)

0.3 (0.1 – 0.5)

MgO

0.19 (0.01 – 0.4)

2.20 (0.1- 10)

0.60 (0.2 – 1.0)

NaB2 BO

0.05 (0.01 – 0.1)

0.42 (0.04 – 1)

0.45 (0.15 – 0.75)

K B2 BO

0.24 (0.04 – 1.02)

0.20 (0.04-0.34)

0.03 (0.03 – 0.03)

PB2 BO B5 B

33 (31 – 35)

1.15 (0.5 - 4.3)

0.75 (0.2 – 1.3)

L.O.I

99.64 (99.1 – 100)

99.2 (98.2-100)

99.6 (99.2 – 100)

Total


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Table (2): Concentration of trace elements (ppm) in lower Nubia sandstones.

Calcareous sandstone

Greywacke Quartz Arenite

N=7 N=16 N=?

Rock type Elements

?^? ??????

???? ?????±??`

??? (165 – 240) Ba

11 ???̄ ?

? ´ ??´¯?

?? (22 – 23) Cu

` ?^?̄ ?

? ´ ?̀ ?̄´ ?̄

? ` (15 – 18) Pb

?? (44-5.3)

` ´ ?^???

?? ??±?? Zn

?` ?^±?

´ ^ ????

??? ???±` ? Ni

??´ ??´??

???? ^ ` ` ????

` ? ? ^?????

Zr

?? ? ´?

?? ^??

?^ (25-53)

Y

´ (0.7-21)

?? ? `?

?? (7-19)

Rb

`¯? ???̄ ?

?? (3-155)

?? ( ???´ )

Nb

??^ ( ? ` `???

^? `?^??

´ ? ´ ^` ? Sr

? ´ ? ?^????

? ´ ? ?^????

??? ( ??????

U

?` ´ ???

? ` ^?`

?? ????

Th

?^ ???

? ´ (19-153)

?? ` ??? Cr

? `?̄ ?

^ ?^?

?? ???? Ga

?´ ??^??

? ´ ???

?? (30-34) V

? ??

? `?

un W

?̄ ? ?̄ ??̄ ?

? ?±?

un Sn

? ??

´ ???

un Be

? ??

? ??̄ ?

un Sc

?̄ ? ?̄ ??̄ ?

? ?̄ `?̄ ?

un Ta

?̄ ? ?̄ ??̄ ?

? `̄ ??̄ ?

un Cs

? ??̄ ?

? ^?

un Mo

? ???

? ??

un Co

? (0.2-4

? ??

un As

?̄ ? ?̄ ??̄ ?

? ??̄ ?

un Cd

0.1 (0.04-0.1)

0.7 (0.1-1)

un Sb

0.1 (0.04-0.18)

0.2 (0.1-0.3)

un Bi

? ??̄ ?

?? (2-78)

un Hf

^ ???

?? ????

un Li

N= number of analyzed samples, un= unmeasured values.


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Table (3): Rare earth elements (REEs) data of lower Nubia sandstones.

Calcareous sandstoneGreywacke

^? ^? ^? 66 G4 G3 G2 G1

Rock Type

Sample No

??¯?`???^????¯?????La

???????` ? ?̄` ???¯?´ ´ ?̄? ` ?̄Ce

?̄ ??`??^̄ ???¯?^̄ ???¯??̄ ?Pr

? ´ ?̄` ?̄??¯???´ ? ?̄??¯????¯???¯?Nd

?̄ ´?̄ ???̄ ?´ ?̄??¯???¯`??¯`?̄ `Sm

?̄ ??̄ ??̄ ^?̄ ??̄ ??̄ ??̄ ^?̄ `Eu

?̄ ??̄ ???¯?´ ?̄??¯??`??¯??̄ ^Gd

?̄ ??̄ ??̄ ??̄ ??̄ ^?̄ ´??̄ ?Tb

?̄ `?̄ ???¯??̄ ???¯`` ?̄´ ?̄?̄ ?Dy

?̄ ´?̄ ??̄ ??̄ ??̄ ??̄ ??̄ `?̄ ?Ho

??̄ ´??̄ ??̄ ??̄ ´?̄ ??̄ ?Er

?̄ ??̄ ??̄ ´?̄ ??̄ ??̄ ??̄ ??̄ ?Tm

?̄ ??̄ `?̄ ´?̄ ^?̄ ´?̄ ^?̄ ??̄ ?Yb

?̄ ??̄ ??̄ ´?̄ ??̄ ??̄ ??̄ ??̄ ?Lu

^?¯? ??¯? ? ` ´ ¯̀ ? ´^ ?̄ ? ` ? ?̄ ?^?¯` ?^?¯´ ? ´ ?̄ ?REEs

` ? ?̄ ??¯^ ???¯? ???¯´ ? ? ´ ?̄ ? ? ` ¯́ ???¯` ?^¯? ?LREEs

??¯? ?̄ ? ??¯? ??¯? ??¯^ ??¯^ ??¯? ^̄ ? HREEs?

?̄ ? ´ ¯́ ?̄ ? ?̄ ´ ?̄ ^ ?̄ ` ?̄ ? ?̄ ? ?LREEs /?HREEs

?? ?? ^ ?? ? ? ` ?? La/Yb

?̄ ? ?̄ ^ ? ?̄ ? ?̄ ` ?̄ ^ ?̄ ^ ?̄ ? La/Sm

?? ?? ?´ ¯̂ ??¯´ ??¯? ??¯? ?? ??¯? Gd/Lu

?¯`? ?¯?^ ?¯?? ?¯´? ` ¯?? ?¯`^ ?¯?? ?¯?? Gd/Yb

?̄ ^ ?¯´? ?¯´? ?¯̂ ?̄ ??¯?? 0.4 ?¯`? Eu/Eu*


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Fig. (1 ): Geologic map of Wadi Natash and Gabal El Ghorfa Southeastern Desert, Egypt,

(modified after Crawford et al, 1984 and Ibrahim, 2010)

b

a


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Fig. 2: (a) XRD pattern of metaheinrichite and EDX analyses showing (b) autunite, (c) uranophane, (d) uranothorite, (e) columbite, (f) yttrocolumbite, (g) gold, (h) zincite, (i) argentite and (j) galena of Gabel El Ghurfa.

a b

c d

e f

g h

i j


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Fig. 3: EDX analyses showing (a) pyrite, (b) allanite, (c) monazite, (d) apatite, (e) zircon, (f)xenotime and XRD pattern of taenite of Gabel El Ghurfa.

a b

c d

e f


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Fig. (4): Geochemical classification of the studied sandstone samples based on the scheme proposed by Herron, (1988).

Fig. (5): Chemical maturity of the lower Nubia sands tones Fields after Suttner & Dutta, (1986).

1

10

100

400

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er TmYb Lu

Sam

ple/

Cho

ndri

te

Fig. ( 6 ): classification of the studied lower Nubia sandstones (After Blatt et al., 1980), 1=Ferromagnesian potassic

sandstone, 2=Sodic sandstone, 3=Potassic sandstone

Fig. (7): Normalized REE patterns of the greywacke of Gabel El Ghurfa area.

1

10

100

400

La Ce Pr NdSm Eu GdTb Dy Ho ErTmYb Lu

Sam

ple/

Cho

ndri

te

Fig. (8): Normalized REE patterns of the calcareous sandstone of Gabel El Ghurfa area.


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6-REFERENCES

(1) Abu El-Gadayel, A. A. (1974): Contribution to geology and geochemistry of Wadi Natash lava flows. M. Sc. Thesis. Faculty of science, Cairo Univ., Cairo, p.212.

(2) Mohamed, F. H., (2001): The Natash alkaline volcanic field, Egypt: geological and mineralogical inference on the evolution of a basalt to rhyolite eruptive suit. J. Volcan & Geotherm. Res., V.105,p. 291 – 322.

(3) Crawford, W. A., Coulter, D. H. and Hubbard, J. H. B.,(1984): The aerial distribution, stratigraphy and major element chemistry of the Wadi Natash Volcanic series, Eastern Desert, Egypt. J. Afr. Earth Sci.V. 2, p. 119-128.

(4) Ibrahim, M. E. (2010): Laterites Bearing- REEs, Wadi Natash, Southeastern Desert, Egypt. Journal of Rare Earth, Vol., 28, No.3, 471-476p.

(5) Heinrich, E.W.(1958): Mineralogy and geology of radioactive raw materials McGraw Hill Book company, New York.

(6) Berry,L.G., Mason.B, and R.V.Dietrich,(2000): Mineralogy CBS publishers and Distributors , New Delhi, India. P. 561.

(7) Hughes, J. M., Cameron, M. and Mariano, A. N(1991): “Rare earth ordering and structural variations in natural rare earth bearing apatite”. Amer. Miner., V. 76, p.1165-1173.

(8) Deer, W. A., Howie , R. A. and Zussman, J. (1992): An introduction to the rock forming minerals ELBS second edition. 696p. Longman, UK.

(9) Herron , M.M.(1988): Geochemical classification of terrigenous sands and shales from core or log data. Jour.sed.petrol., V.58,p. 820-829.

(10) Akinmosin, A. and O.O. Osinowo. (2008): Geochemical and mineralogical composition of ishara sandstone deposit. SW Nigeria Cont. J. Earth Sci.,V. 3: p.33-39.

(11) Ibe , K.K. and C.C.Z. Akaolisa, (2010): Sand class classification scheme for ajalli sandstone units in Ohafia area. SE Nigeria J. Geol. Min. Res., 2(1):p.16-22.

(12) Suttner L.J. & Dutta P.K. (1986): Alluvial sandstone composition and paleoclimate, I. Framework mineralogy. J. Sed. Petrol.,V.56, p.329-345.

(13) Blatt, H., Middleton, G., Murray, R., (1980): Origin of Sedimentary Rocks: Prentice-Hall, New Jersey.N.J., p. 782.

(14) Garrels ,R.M. and Mackenzie ,F. T.,(1971): Evolution of sedimentary rocks. Norton, New York.

(15) Nesbitt, H.W., Markovies, G. and Price, R.C.,(1980): Chemical processes affecting alkalies and alkaline earths during continental weathering Geoch. Cosmoch. Acta,V.44: p.1659-1666.

(16)Degens , E.T., Williams, E.G. and Keith, M.L., (1957): Environmental studies of Carboniferous sediments part 1, geochemical criteria for differentiation marine and fresh water shales. Bull. Am. Ass. Petro. Geol., 41:2427-2455.

(17) International Atomic Energy Agency (IAEA) (1979): Gamma-Ray Surveys in Uranium Exploration, Technical Report Series, No.186 Vienna, 89p.

(18) Ibrahim ,M. E, Mehanna, M.A, Zohair, A.B, Qurany, Abu Zeid, E, and El-Tohamy. M.A (2011):Geology and Mineralogy of Cretaceous volcanic Rocks, east Wadi Natash, South Eastern Desert, Egypt. Natural Science (in press).

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