Mineralogy and Geochemistry of stream Sediments at Wadi Um Nafey area, North Eastern Desert, Egypt.

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1 Current Science International Volume : 06 Issue : 02 April-June 17 Pages: Mineralogy and Geochemistry of stream Sediments at Wadi Um Nafey area, North Eastern Desert, Egypt. Osama M. Draz Nuclear Materials Authority, Cairo, Egypt, P.O.Box 530, El-Maadi. Received: 18 February 17 / Accepted: 30 March 17 / Publication Date: 08 April 17 Abstract Wadi Um Nafey area is located in North Eastern desert. The area is covered mainly by granodiorites, syenogrenites and rapakivi syenogranite with some dyke swarms of acidic and basic composition. The chemical analysis for anomalous stream sediments samples show that the average content of uranium is about 14.4 ppm, while thorium is about 38.6 ppm. Radiometric analysis revealed that the average equivalent uranium content (eu) is 24.6 ppm and the average equivalent thorium is (eth) is 35.8 ppm. On the other hand, the analysis and identification of several separated mineral grains of some stream sediments samples using a scanning electron microscope and X-ray diffraction revealed the presence of several economic minerals. These minerals include zircon, uranothorite, thorianite, monazite, cerite, apatite, fluorite, garnet and hematite. The present study proved that zircon, uranothorite, thorianite and monazite are the main radioactive minerals responsible for the radioactivity of the studied stream sediments and may control the geochemical enrichment of elements such as Th, U, Zr, Y, and Nb. Key words: Wadi Um Nafey, granodiorites, syenogrenites and rapakivi syenogranite Introduction Egyptian granitic rocks have been formed during the Pan-African age; occupy about 40% of the exposed Precambrian rocks in the Eastern desert. They can be subdivided into two distinct major groups, namely the older and the younger granites. The younger granite was previously mapped as Gattarian, red and pink granites, (Akaad and EL-Ramly, 1960), late-to post- orogenic granites, (EL- Gaby, 1975) and G-II to G-III granites, (Hussein et al. 1982). Wadi Um Nafey is located in North Eastern desert. It is bounded by Longitudes / 01 // and / 30 // E and Latitudes 27 o 01 / 01 // and 26 o 58 / 03 // N and covers about 83 km 2. Geology The studied area has moderate to high relief. Wadi Um Nafey runs N-S. The rock types in Wadi Um Nafey area are Granodiorite, Syanogranites and Rapakivi Syenogranite (Fig. 1) with some dyke swarms of acidic and intermediate compositions. According to Omar (07), Granodiorite forms N-S belt and older than syenogranite which it is directly cut it with sharp obvious contact, as well as rapakivi syenogranite. Usually along the contact, the granodiorite has some offshoots of syenogranite types and it becomes more reddish in colour and highly fractured (Fig. 2a). Syenogranite outcrops most of the study area, at Gabal Al-Thilmah and intruded granodiorite. Syenogranite cuts by sets of faults that cause a very distinctive rugged topography (Fig. 2b). In some places, it is associated with some quartz and feldspar bodies (Fig. 2c). Exfoliation, onion-skin texture and bouldery shape appearance are present (Fig. 2d). Syanogranite altered in some sheared parts due to hydrothermal processes, especially along the fault planes and contacts. The most common alteration features are, hematitization, silicification, chloritization and epidotization as well as manganese oxides. Rapakivi syenogranite occupies the west part of W.Faliq Al-Sahl, W.Faliq AL-Waar. It forms N-S belt invading the granodiorite. The emplacement of the granite was usually followed by the intrusion of dyke swarms of variable attitudes and varying thickness. The majority of dykes were intruded along the fractures and fault zones mainly trending N-E and E-W direction. (Omar, 07). Corresponding Author: Osama M. Draz, Nuclear Materials Authority, Cairo, Egypt. draz_o_m@ yahoo.com 278

2 The aim of the present work is studying the mineralogy, geochemistry and radioactivity of the stream sediments of Wadi Um Nafey. Sampling and Methodology 15 samples representing the stream sediments of Wadi Um Nafey and samples representing the hard rock around Wadi Um Nafey were collected for petrographic studies. Samples of stream sediments are taken by digging a rectangular hole to a depth of 0.5 m. They are investigated mineralogicaly, chemically (for trace elements) and radiometrically. Trace elements were analysed using X-ray fluorescence (Phillips PW 14. Radiometrical analysis has been achieved using gamma-ray spectrometry with multi-channel analyzer" to determine uranium (eu) and thorium (eth). Uranium and thorium were measured chemically using coloremetric method. The sample was properly crushed, ground, and sieved before subjecting the liberated size fractions to heavy-mineral separation using bromoform (specific gravity = 2.85 gm/cm 3 ). From the obtained heavy fractions, pure mineral grains were manually picked and investigated under a binocular microscope.some of the picked mineral grains were subjected to X-ray diffraction analysis using a Phillips X-ray diffractometer (Model PW-5018) and an environmental scanning electron microscope (ESEM). This instrument includes a Philips XL 30 energy-dispersive spectrometer (EDS) unit. The applied analytical conditions were an accelerating voltage of 30 kv with a beam diameter of 1-2 μm for a counting time of 60-1 s and a minimum detectable weight concentration ranging from 0.1 wt% to 1 wt%. All these analyses were carried out at the laboratories of the Egyptian Nuclear Materials Authority (NMA). Fig. 1: Geologic map of the study area. (after Omar, 07). Petrography of syenogranite Syenogranite is massive, medium to coarse grained with red to pale pink colour. It is composed mainly of potash feldspars, plagioclase, quartz together with subordinate amounts of biotite and muscovite. The accessory minerals are zircon, sphene, epidote, fluorite and iron oxides. Secondary minerals are chlorite, sericite and calcite Potash feldspars is generally more abundant than plagioclase and occurs in subhedral to euhedral prismatic crystals (Fig. 3a). Potash feldspars occurring as euhedral crystals. They are represented by microcline with crosshatching. It encloses zircon, quartz, plagioclase and iron oxides (Figs. 3b & 3f). Quartz is medium grained and form anhedral crystals. It is characterized by irregular boundaries. It sometimes contains zircon and iron oxides (Fig 3c). Biotite occurs as flakes (Fig. 3d), it is partially altered to chlorite (Figs. 3e & 3f) with liberation of iron oxides. This alteration may be related to the later hydrothermal solution forming the secondary albite (Greenberg, 1981). It encloses iron oxides, quartz, apatite and zircon and is corroded by quartz and K-feldspars. Muscovite is found as pale 279

3 yellow, small to medium flakes interstitially between the other mineral constituents or filling the cracks of feldspar. Fluorite is found as small anhedral crystals of violet colour and usually associated with iron oxides. Zircon is abundant and occurs in different forms reflecting more than one generation. Opaques are mainly iron oxides. Fig. 2a: Granodiorite of wadi Um Nafey Fig. 2b: Faulting affecting in syenogranite, looking NE. Fig. 2c: Quartz veins in syenogranites, looking SW. Fig. 2d: Exfoliation, onion-skin and bouldery shape. 280

4 Fig. 3: Photomicrograph showing: a) Lamellar twinning of plagioclase with alteration. b) Cross hatching microcline with plagioclase and quartz. c) Quartz with chloritized biotite. d) Biotite occurs as flakes. e) Chloritized biotite. f) Cross hatching microcline Mineralogical Studies: For studying the heavy fractions of the stream sediments samples which collected from W. Umm Nafey, the samples were quartered and sieved which later separated by bromoform. Separated minerals were picked under binocular microscope and identified using ESEM supported by EDX. The 281

5 identification of these minerals is confirmed by XRD analysis when enough amounts of separated mineral grains were available. The average content of the heavy minerals in the studied stream sediments is % ranging from % and.112 % (Table 1 & Fig. 4). The content of heavy minerals in the studied stream sediments increase from south (upstream) to north (downstream). Table 1: Percentages of heavy minerals in the studied stream sediments of Wadi Um Nafey area. Sample No. Heavy minerals % Average Min..112 Max Heavy Light Fig. 4: The average content of the heavy minerals in the studied stream sediments The identified heavy minerals include: a) Zircon: It is common in the studied stream sediments. Most of the studied zircon occurs as excellent idiomorphic crystals. It displays various color appearance ranges from yellow to brown and cloudy. The obtained EDX and BSI are shown in (Fig. 5). Hf is known to be enriched with respect to Zr in the zircon of granitic pegmatites, especially in the late stages of pegmatite crystallization (Owen, 1987; Uher and Cerny, 1998). Zirconian hafnium and true hafnium have been identified only in granitic pegmatites (Finch and Hanchar, 03). This type of fractionation of Hf from Zr has been linked with the lower mobility of Hf (Gerasimovskiy et al., 1972; Smith et al., 1987). 282

6 Fig. 5: EDX analysis, BSE image and microphotograph of zircon. b) Uranothorite: It is primary mineral of thorium and occurs as well formed tetragonal crystals with color vary from yellowish brown to brown. The BSI image showed that uranothorite sometimes found as discrete crystals in zircon. The obtained EDX, XRD and BSI are shown in (Fig. 6 a, b & c) The presence of Zr in the composition of uranothorite confirms the association between zircon and uranothorite, whereas uranothorite is iso - structural with zircon, such association suggests the limited solid solution series, which probably due to the low coupled substitution between Zr 4+ and Th 4+ (Wopenka et al., 1996 and Nasdala et al., 03 and El Balakssy, ). Fig. 6 a: EDX analysis and BSE image of uranothorite. Fig. 6 b: EDX analysis and microphotograph of uranothorite. 283

7 Fig. 6 c: XRD of uranothorite, ASTM card No c) Thorianite (ThO 2): It is rarely occurs as subhedral crystals. The obtained EDX and BSI of thorianite are shown in (Fig. 7). Fig. 7: EDX analysis and BSE image of thorianite. d) Monazite: Monazite is one of the REE minerals and occurs in the studied sediments in two types the first is hydrothermal monazite with poor Th and U contents and the second is magmatic monazite (normal) with normal Th and U contents. The obtained EDX are shown in (Fig. 8 a & b). Hydrothermal monazite or Th-poor monazite might be derivated from dissolution of allanite and fluorapatite (Pan, 1997). 284

8 Fig. 8 a: EDX analysis and BSE image of hydrothermal monazite. Fig. 8 b: EDX analysis and BSI image of magmatic monazite e) Cerite: It occurs as small crystals with EDX data showing Cerium content (78.05%). Cerite is a nesosilicate crystal structure (Moore and Shen, 1983), and the absence of SiO 4 polymerization suggests that it is formed from silica-under saturated fluids (Fig. 9). Fig. 9: EDX analysis and BSE image of cerite. 285

9 f) Apatite: It occurs as yellowish white crystals. The roundness and the pitted surface of apatite grains suggest its transportation. The obtained EDX and BSI are shown in (Fig. ). Fig. : EDX analysis and BSI image of apatite. g) Flourite: It was recorded in the studied sediments as irregular outline crystals with colorless to pale violet color. The obtained EDX and BSI are shown in (Fig.11). Fig. 11: EDX analysis and BSI image of flourite. h) Garnet: It occurs as euhedral crystals with red color. The obtained EDX and BSI are shown in (Fig. 12). 286

10 Fig. 12: EDX analysis and BSI image of garnet. i) Hematite: It occurs as cubic grains with reddish brown color. The obtained EDX and BSI are shown in (Fig. 13). Fig. 13: EDX analysis and BSI image of hematite. j) Biotite mica: Mica is a common mineral of stream sediments. It occurs as eubhedral to subhedral flacks. The obtained EDX and BSI are shown in (Fig. 14). 287

11 Fig. 14: EDX analysis and BSI image of biotite. Geochemistry of Trace Elements: Ten selective stream sediment samples were analyzed for the following trace elements: Cr, Ni, Cu, Zn, Zr, Rb, Y, Ba, Pb, Sr, Ga, V and Nb. The results are shown in Table 2. From the obtained results, it can be concluded that these stream sediments are slightly enriched in Zr, Co, Cu, Zn, Rb, Y, Sr and Nb (Compared with Upper Continental Crust (UCC), Rudinc and Gao, (03), and depleted in Cr, Ni, Ba, Pb and V. High Zr contents ( ppm), which is higher than the UCC (193 ppm) is attributed to the enrichment of the stream sediments in zircon. Cu and Zn are also slightly enriched (69.16 and ppm), which are higher than the UCC (28 and 67 ppm), this may reflect the contribution of some basic rocks in the source of the studied stream sediments. Sr content (774.7 ppm) which is higher than the UCC (3 ppm). Rb ( ppm) is also higher than the UCC (84 ppm) and this is related to the K bearing minerals (Mica), (Rose et al, 1979). Y is also enriched in these stream sediments with average (70.90 ppm), which is higher than that in UCC (21 ppm), Y is present in these sediments only within fluorite Fig Concentration ppm 1 Cr Co Ni Cu Zn Zr Rb Y Ba Pb Sr V Nb 0.1 Fig. 15: Trace elements concentrations in stream sediments of Wadi Um Nafey compared to UCC. 288

12 Table 2: Trace Elements Concentrations in Wadi Um Nafey stream sediments. S.NO Average UCC Cr Co Ni Cu Zn Zr Rb Y Ba Pb Sr Ga V Nb UCC = Upper Contenintal Crust (Rudinc and Gao, 03). Radioactivity: The chemical and radiometric measurements of uranium and thorium contents reveal that the studied stream sediments are much enriched in thorium over uranium (Table 3). The average content of chemicaly U is about 14.4ppm, while chemical thorium about 38.6ppm, Also, the average radiometric eu is 24.6ppm and the average eth is 35.8ppm.The enrichment of thorium than uranium is due to the high leachability of uranium than thorium which is more stable and for the presence of thorium bearing minerals. Additionally, the calculated eth/ eu ratio is mostly more than unity (Av. 1.5) revealing that a selective leaching of uranium content compared with the increase of stable thorium (Hansink, 1976). The obtained resultes of calculating D factor (Uc/eU) and P factor (Ra/eU), which show average 0.6 and 0.65 respectively, these ratios which are less than unity are coincide with Hansink (1976) which revealed recent uranium loss. Table 3: U, Th, Ra and K contents in stream sediments of Wadi Um Nafey. γ- ray spectrometry Chemical measurments Calculated ratios S. No. eu ppm eth ppm Ra ppm K% U c Th c eth/eu U c/eu D factor Ra/eU P factor Av Uranium has high strong correlation level with thorium, which is (+0.93), Fig. (16). This may due to the presence of zircon, uranothorite, monozite and deep violet fluorite beside thorite minerals. Uranium has moderate degree of correlation with potassium (+ 0.57), (figure. 17.), This is attributed to slightly leaching of uranium from stream sediments due to its great mobility. While thorium gave 289

13 high moderate positive correlation ( ) with potassium (figure. 18), due to high stability of thorium minerals. realation between eu & eth in studied stream sediments eth eu eu K Fig. 16: A scatter plot diagram between uranium and thorium (ppm) for stream sediments. Fig. 17: A scatter plot diagram between uranium (ppm) and potassium (%) for stream sediments. eth K Fig. 18: A scatter plot diagram between thorium (ppm) and potassium (%) for stream sediments. Conclusion Wadi Um Nafey is located in north of the East Desert of Egypt. Data points to the homogeous distributions of the heavy minerals content along the stream sediments. These sediments appear to be slightly favorable delivery pools for thorium rather than uranium which is probably due to either the abundance of thorium bearing minerals or selective leaching of uranium through supergene processes. The Uc/eU and Ra/eU ratios are mostly less than unity, reveal the disequilibrium state of uranium and confirm uranium leaching. The present study proved that zircon, uranothorite, thorianite and monazite are the main radioactive minerals responsible for the radioactivity of the studied stream sediments and may control the geochemical enrichment of elements such as Th, U, Zr, Y, and Nb. References Akaad, M.K. and M.F. El-Ramly, Geological history and classification of the basement complex in the Central Eastern Desert of Egypt. Geo. Surv. Egypt, 9:

14 El Balakssy, S.S.,. Zircon zonation from Egyptian coastal sediments as genetical indicator, J. the Mineralogical Society of Egypt. The Egyptian Mineralogist, National Research Center, Cairo, Egypt. (in press). El Gaby, S., Petrochemistry of some granites from Egypt. N. Jb. Mineral. Abh., 124: Finch, W.I. and A. Hanchar, 03. Uranium provinces of North America: their Definition, Distribution and Models, U. S. Geol. Surv. Bull 2141, p: 18. Greenberg, T.K., Characteristics and origin of Egyptian granites. Geological Society of America Bulletin, part II, 92: Hansink, J.D., Equilibrium analysis of a sandstone rollfront uranium deposit, Proceedingd Intr.Symposium on exploration of uranium ore deposits, AEA, Vienna, p: Hussein, A.A., M. Ali and M.F. El Ramly, A proposed new classification of the granites J. Volcan., 14: Moore, P.B. and J. Shen, Occurrence cerite occurs in alkaline pegmatites, 68: Nasdala, L., H.J. Massone, 03. Characterization of an early metamorphic stage through inclusions in zircon, 33: Omar, M.A., 07. Some geological, geochemical and mineralogical studies on some pan African rock, north east of Gabal Gattar, North Eastern Desert, Egypt, Ph. D. thesis, Faculty of Science, Al Azhar University. Pan, Yu, Zircon and monazite forming metamorphic reactions at Manitouwedge, Ontario. Canadian Mineralogists, 35: Rudinc & Gao., 03. Government Auditing Standards and revision 162. Wopenka, B., et al., High-pressure assemblage in shock melt vein in Peace River, American mineralogist, 81: