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Contribution to the study of radioactivity in younger granites in Southeastern Desert, Egypt
Journal of African Earth Sciences, Vol. 9, No. 2, pp. 297-301, 1989
0899-5362/89 $3.00 + 0.00 © 1990 Pergamon Press pie
Printed in Great Britain
Contribution to the study of radioactivity in younger granites in Southeastern Desert, Egypt A. F. KAMEL Nuclear Materials Corporation,Maadi Post Office Box 530, Cairo, Egypt. Abstract- The Egyptiangranites are the most dominantrock unit of the basementcomplex in EasternDesert. Several geologicalinvestigations and classifications were carried out on these granites. They were classified
according to relative age, dominantcolour, type locality and their apparent relation to orogeny. Most of the discoveredradioactiveoccurrencesare encounteredin the younger granites which are generally enriched in uranium than other rock types. The presentworkdealswith the distributionofradioactivityin youngergranitesrepresentedin the Southeastern Desert of Egypt and the identificationof these granites on aerial photographs and photomosaics in a trial to differentiatebetween granites with normal to moderateradioactivityand those having higher and anomalous radioactivity. The younger granites ha~,e a wide range of radioactivitywhich is from400 to 1000 count per second in the granites with normal to moderate radioactivitywhile it reaches 2000 count per second in the granites with abnormal radioactivityas givenin the radiometricmap constructedby Lockwoodin 1968. Someoutcropsof the second type are found with disseminateduranium mineralizations, and in certain localities field measurement of their radioactivitygave values of 10 000 count per second, and even more. Photogeologically,the younger granites are characterizedby lighter tone, coarser surface texture, angular to rectangular drainage pattern and the sharp contact against the other types of rocks. Granites with higher to anomalous radioactivityare highly fractured as comparedwith the other rocks of younger granites.
INTRODUCTION
O n e of t h e f u n d a m e n t a l p r o b l e m s of t h e b a s e m e n t r o c k s of E g y p t is t h e s t u d y of t h e g r a n i t e s . T h e gr an itic r o c k s ar e classified into two m a i n g r o u p s , n a m e l y t h e o l d e r S y n - t e c t o n i c to Latet e c t o n i c g r a n i t e s w h i c h ar e t h e g r e y g r a n i t e s , a n d y o u n g e r granites or Post-tectonic granites referred to a s p i n k g r a n i t e s (Akaad etal., 1960; E l R a m l y et aL, 1960; H u n t i n g , 1967; El Rarely, 1972; S a b e t , 1972; El G a b y , 1975; A k a a d et al., 1980 a n d H u s s e i n et al., 1982). El S h a z l y (1964) p o i n t e d o u t the presence of Post-orogenic plutonites referred to a s A s w a n g r a n i t e w h i c h h e c o n s i d e r e d y o u n g e r t h a n the normal pink granites. T h e y o u n g e r g r a n i t e s of t h e S o u t h e a s t e r n D e s e r t of E g y p t ar e c h a r a c t e r i z e d b y p r o n o u n c e d p i n k colour, b ein g essentially unfoliated a n d f or m m a s s e s w i t h c i r c u l a r to o v a l - s h a p e d o u t l i n e i n t r u d i n g into old g e o s y n c l i n a l s e d i m e n t s a n d volcanics. Most of t h e s e r o c k s a r e m e d i u m - g r a i n e d b u t few t e n d to be f i n e - g r a i n e d , while o t h e r s a r e p e g m a t i t e s . In t h e p r e s e n t s t u d y , c e r t a i n localities h a v e b e e n s e l e c t e d in t h e S o u t h e a s t e m D e s e r t of E g y p t (Fig. l ) .Th e s t r u c t u r a l l i n e a m e n t s w e r e i n t e r p r e t e d photogeologicaUy in e a c h locality. C o m p a r i s o n w a s c a r r i e d o u t b e t w e e n t h e hi ghl y r a d i o a c t i v e gr a ni t i c
r o c k s a n d t h o s e w i t h relatively low level of r a d i o a c tivity. Detailed s t u d y w a s c a r r i e d o u t in t h e localit i es w h e r e t h e g r a n i t e e x p o s u r e s a r e p r o m i n e n t a n d t h e i r r a d i o a c t i v i t y is well k n o w n . T h i s s t u d y w a s s u p p l e m e n t e d b y field c h e c k for a n u m b e r of these granite exposures. STRUCTURAL
SETTING
T h e y o u n g e r g r a n i t e s are c h a r a c t e r i z e d b y t h e p r e s e n c e of two s e t s o f j o i n t s p e r p e n d i c u l a r to e a c h o t h e r a n d a d i a g o n a l one. T h e r o c k s a r e d i s s e c t e d b y a n u m b e r of f a u l t s w i t h v a r i o u s t r e n d s a n d l engt hs. T h e different s t r u c t u r a l l i n e a m e n t s w e re i n t e r p r e t e d phot ogeol ogi cal l y u s i n g aerial p h o t o m o s a i c s scale 1:50000. T h e t r e n d a n d l e n g t h for e a c h s t r u c t u r a l line w a s r e c o r d e d in e a c h 10 ° f r o m n o r t h t o t h e e a s t a n d w e s t di rect i ons. Rose diag r a m s s h o w i n g t h e d i s t r i b u t i o n of t h e s e s t r u c t u r a l lines, w ere c o n s t r u c t e d f o r t h e S o u t h e a s t e m D e se rt in e a c h sel ect ed locality (Fig. 2). T h e i n t e n s i t y of f r a c t u r e s in e a c h locality w a s e s t i m a t e d b y m e a s u r i n g t h e t ot al l e n g t h of lineam e n t s in a u n i t a r e a of i k m 2. It w a s f o u n d t h a t in S o u t h e a s t e r n D e s e r t of E g y p t t h e s t r u c t u r a l lines h a v e t h e d o m i n a n t t r e n d s WNW-ESE, E-W, NWS E a n d ENE-WSW w h i c h c o n s t i t u t e 74. 7 % of t h e
AES 9:2-G
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298
A.F. KAMEL the granite with m o d e r a t e to lower level of radioactivity. Concerning the intensity of fracturing in the different localities, it w a s clear t h a t t h e highly radioactive y o u n g e r g r a n i t e s are d i s s e c t e d b y large n u m b e r of f r a c t u r e s with total length of 2-6 k m p e r unit area of 1kin 2 while t h e total length of f r a c t u r e s per unit a r e a is 1-2 k m in t h e g r a n i t e s of m o d e r a t e to low radioactivity. RADIOA~I'IVITY
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Fig. I. Index m a p of the study area.
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L I N E A M E N T S IN S O U T H E R A S T E R N DESERT/EGYPT, ,
ROSE DIAGRAMS SHOWING THE MAIN TRENDS OF STRUCTURAL LINEAMENTS IN DIFFERNT LOCALITIES IN SOUTHEASTERN DESERT,EGYPT
Fig. 2. Rose diagrams.
total length of all lineaments. There are two less d o m i n a n t t r e n d s namely, t h e NNW-SSE a n d NESW trends, A n u m b e r of t h e s e l i n e a m e n t s were c h e c k e d in t h e field a s faults. The WNW-ESE a n d NW-SE t r e n d s d o m i n a t e in the granitic r o c k s with p r o m i n e n t radioactivity while t h e E-W a n d ENEW S W t r e n d s are t h e m a j o r t r e n d s of f r a c t u r e s in
The b a s e m e n t c o m p l e x in Egypt c o n t a i n s m o s t of t h e discovered radioactive o c c u r r e n c e s . Most of t h e s e o c c u r r e n c e s are e n c o u n t e r e d in t h e y o u n g e r granites. According to R a n k a m a a n d S a h a m a (1955), the c o n t e n t oflithophfle trace e l e m e n t s d e c r e a s e s with the geologic age of granite, therefore t h e Egyptian p i n k granite will b e m o r e radioactive t h a n grey granites w h i c h are older in age. Nishimori e t al. (1977) s t a t e d t h a t the E g y p t i a n g r a n i t e s are enriched in u r a n i u m mineralization t h a n similar granites in o t h e r p a r t s of t h e world. Field radiometric m e a s u r e m e n t s carried o u t on s o m e granite e x p o s u r e s of the E a s t e r n Desert s h o w e d t h a t the pink granites have n o r m a l radioactivity which r e a c h e s 2 0 0 c o u n t p e r second. The a n o m a l i e s have m a x i m u m radioactivity of 5 0 0 0 c o u n t p e r s e c o n d which b e c o m e s m o r e in t h e f r a c t u r e d g r a n i t e s a n d in t h e pegmatite d y k e s i n t r u d i n g t h e granitic rocks, w h e r e it r e a c h e s 10 0 0 0 c o u n t p e r second. Lockwood (1968) CalTied o u t aero-radiometric s u r v e y in a larger a r e a in t h e S o u t h e a s t e r n Desert of Egypt a n d c o n s t r u c t e d radiometric m a p s w h i c h s h o w that radioactivity is p r o m i s i n g in localities covered b y y o u n g e r granites. M a x i m u m radioactivity is 2 0 0 0 c o u n t p e r s e c o n d in t h e highly radioactive r o c k s while radioactivity is ranging b e t w e e n 4 0 0 a n d 1000 c o u n t p e r s e c o n d in the granitic r o c k s with m o d e r a t e to low radioactivity (Table I). S o m e of t h e s e radioactive localities were s e l e c t e d for t h e p r e s e n t study. Photointerpretation w a s carried o u t in each selected locality a n d the different s t r u c t u r a l l i n e a m e n t s were s t u d i e d photogeologically o n aerial photom o s a i c s scale 1:50 000. Detailed field radiometric s u r v e y w a s carried o u t in t h e localities with promising radioactivity. F r o m t h e p r e v i o u s w o r k a n d the p r e s e n t w o r k carried o u t on t h e y o u n g e r granites, it w a s noticed t h a t radioactivity varies with t h e variation of t h e grain size, relative age a n d degree of tectonic effect. The fine-grained g r a n i t e s are m o r e radioactive t h a n the coarse -grained variety including t h e A s w a n granite. G r a n i t e s w h i c h are d i s s e c t e d b y larger n u m b e r of f r a c t u r e s with t h e d o m i n a n t WNW-ESE a n d NW-SE t r e n d s are m o r e radioactive t h a n the
Contribution to the study of radioactivity in younger granites in Southeastern Desert, Egypt
299
Table 1. The main trends of radioactivity and structural lines in younger granites. Southeastern Desert. Egypt.
Name of the area
Maximum radioactivity in count per second
Main tnmd of radioactivity
Main trend of structural lines
The cotmtry rocks
G e b d El Hudi
2000
N45°W
N40 o . 50°W
Mica sl~st, older granims and Nubian ssndsr~nes
Highly
Wadi El Arab
2O00
N40°W
N50 ~ _ 60oW
Nubian smdstones
radioactive
Gebel Magal Gebnel
1600
N45°W
N50 ° - 60%%'
Met~odiments, metavolcmics
Gebel U m Ara
1800
N35°W
NS0° - 60"W
Me.u~.~ments, metavoloanics and serpeatinites
Gebel Nugms
1000
N30°W
N0 ° - 1 0 ~ /
Metasediments and metavolcanics
Gebel Abu Brush
1000
N55°E
N30 o . 40OE
Metavolcanics, diofitesand older granites
Wadi Abu Natash
1000
N45°E
NT0• . 80°E
Older granites
G e b d Kdat
1000
N25°W
N30 o . 40oW
M ~ e A i m e n u , metavolc~dcs and older granites
Gebel Dahiz
1000
N70°E
N60 o _ 70OE
Metascdiments, metavolcanics and older granites
Moderately ~dioactive
granites dissected by small n u m b e r of fractures with the d o m i n a n t E-W and ENE-WSW trends. There is a general orientation of the distributed radioactivity as s h o w n in (Fig. 3). REI~TIONSIIrP BETWEEN RADIOACTIVITY AND STRUCTURAL LINEAMENTS The structurally controned u r a n i u m mineralization is well k n o w n in several locallties in the E a s t e r n Desert of Egypt. Kamel (1983) correlated the structural c o n t o u r m a p with the radiometric m a p of E1 Mueilha area, Central E a s t e r n Desert a n d found t h a t the t r e n d of photolineaments responsible for radioactivity is the N50 ° - 70°W, while Hussein eta/, (1985) found that the distribution of radioactivity in U m Ara area, S o u t h e a s t e r n Desert, is structurally controlled by WNW-ESE a n d NW-SE trends. In the present work a comparison was carried out between the m a i n t r e n d s of the distibution of radioactivity in each locality as indicated in the radiometric m a p s of Lockwood (1968) and the m a i n t r e n d of structural lines dissecting the granitic rocks in the s a m e locality. It was f o u n d that the highly radioactive y o u n g e r granite exposures of Gebel Um Ara, Wadi E1 Arab, Gebel El Hudi and Gebel Magal Gebriel have the m a i n t r e n d s of radioactivity N35 ° - 45°W, while the m a i n t r e n d s of structural lines in t h e s e localities are N40 ° - 60°W. There is a notable relationship between the m a i n t r e n d s of radioactivity a n d fractures where the t r e n d s are more or less conformable (Fig. 3, A, B, C).
The y o u n g e r granites with m o d e r a t e to low level of radioactivity are exposed in Gebel Abu Brush, Gebel Nugrus, Wadi Abu Natash, Gebel Kelat and Gebel Dahiz which have their m a i n t r e n d s of radioactivity quite different. These trends are N55°E, N30°W, N45°E, N25°W a n d N70°E respectively. The structural lines dissecting these granite expos u r e s have the m a i n t r e n d s N30 ° - 40°E, NO° - 10°W, N70 ° - 80°E, N30 ° - 40°W a n d N60 ° - 70°E. Correlation between the m a i n t r e n d s of radioactivity a n d s t r u c t u r a l lines shows t h a t t h e y are not conformable except for Gebel Dahiz indicating that radioactivity in the granites with moderate to low radioactivity is not structurally controned in most of the exposures. The present work indicates t h a t the y o u n g e r granites in the S o u t h e a s t e m Desert of Egypt c a n be differentiated into two groups according to t h e i r radioactivity and distinctive feature: I) the first group is the highly radioactive granites forming larger exposures dissected by large n u m b e r of fractures with the dominant trends WNW-ESE a n d NW-SE. The high level of radioactivity (1000-2000 c o u n t per second) m a y be attributed to the presence of relatively high percent of accessory minerals carrying u r a n i u m and thorium, the presence of iron oxides which have the ability of capturing u r a n i u m leached from the surroundings, the presence of potassium-40 present in potash feldspars or the presence of s e c o n d a r y u r a n i u m m i n e r a l s s u c h a s U r a n o p h a n e a n d Soddyite-Prlmary uraninite was
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Fig. 3. Radiometric map of granite exposures in Southeastem Desert. Egypt (Modified after Lockwood, 1968). found in the localities of El Eradiya in the Central Previous work h a s been carried out on the E a s t e r n Desert a n d Urn Ara in the S o u t h e a s t e m localities, Um Ara, Magal Gebriel and Nugrus, Desert of Egypt. Hussein et aL (1966) and Kamel etal. (1985) carried out the field radiometric S c h u r m a n n (1966) attributed the high level of survey of U m A r a A r e a and found t h a t radioactivity radio-activity of some Egyptian granitic rocks to ranges between 350 - 4000 CPS in the fine-gralned the presence of accessory minerals like zircon, granite while it is not more t h a n 500 CPS in the monazite, thorite, uranothorite, allanite and medium- to coarse-grained granite. Hussein et al, xenotime. (1985) studied t h e g r a n i t e pluton of Uma Ara and The rocks in the first group are characterized by attributed the high level of radioactivity to the their finer grain size as compared with the rocks in presence of secondary u r a n i u m mineralization the second group. They have pink colour and are disseminated in the rocks and considered the highly dissected by fractures. There is a good granite as fertile granite. In 1986, Hussein et al. relationship between the dominant trends of stated t h a t radioactivity increases with the radioactivity a n d s t r u c t u r a l lines. increase of accessory minerals represented by 2- the second group h a s moderate to low level of topaz, monazite a n d uraninite. They added that radioactivity (400 - 1000 c o u n t per second) form- u r a n i u m mineralization is related to synorogenic ing smaller outcrops a n d is dissected by smaller and epigenetic o ~ s . n u m b e r of fractures. There is no relation-ship Zalata et al. (1986) found t h a t Um Ara between the m a i n trends of the d i s t r i b u t i o n of granite pluton forms a composite mass, the first radioactivity and the dissecting fractures, phase is represented by coarse-grained monzoThe rocks in the second group are reddish in granite and the second p h a s e by fine-grained colour, coarser in grain size and deficient in the alkali feldspar granite which is highly radioradioactive accessory minerals. active.
Contribution to the study of radioactivity in younger granites in Southeastern Desert, Egypt Magal Gebriel is l o c a t e d to t h e n o r t h of U m Ara. It h a s b e e n investigated in t h e field radiometrically b y Kamel et al. (1986). T h e y n o t i c e d t h a t granitic r o c k s in t h e a r e a are relatively m o r e radioactive t h a n t h e o t h e r t y p e s of rocks. The fine-grained granite is m o r e radioactive, giving r e a d i n g s u p to 5 0 0 CPS, t h a n t h e c o a r s e - g r a i n e d granite w h i c h h a s radioactivity a m o u n t i n g to 4 0 0 CPS. Anomalo u s radioactivity w e r e r e c o r d e d in t h e fine-grained g r a n i t e w h e r e r a d i o a c t i v i t y r e a c h e s u p to 2 0 0 0 CPS. Kamel (1987) f o u n d t h a t t h e r e is similarity b e t w e e n t h e granitic r o c k s in U m Ara a n d Magal Gebriel a r e a s w h e r e t h e radioactive granite in t h e two a r e a s is fine-grained containing u r a n i u m mineralization ( u r a n o p h a n e ) w h i c h is a s s o c i a t e d with g r e e n a n d violet fluorite. Chemical a n a l y s i s c a r r i e d o u t on s a m p l e s collected from U m Ara a n d Magal Gebriel indicated t h a t u r a n i u m c o n t e n t r e a c h e s u p to 711 p p m in U m Ara a n d 7 0 0 p p m in Magal Gebriel. S a d e k (1953) discovered t h e radioactive m i n e r a l allanite in t h e p e g m a t i t e v e i n s i n t r u d i n g t h e granite r o c k s in W a d i El G e m a l a r e a w h i c h is a d j a c e n t to Gebel N u g r u s . El Shazly a n d H a s s a n (1972) c a r r i e d o u t radiometric s t u d y o n Wadi Sikait - W a d i El G e m a l a r e a a n d f o u n d t h a t radioactivity r e a c h e s i 0 0 0 IxR/h (about 5 0 0 0 CPS). The radioactive m i n e r a l s are m a i n l y zircon a n d thorite. H a s s a n (1972) recognized few s p e c k s of s e c o n d a r y u r a n i u m m i n e r a l s in t h e highly radioactive rocks. El M a n h a r a w i (1977) s t u d i e d t h e geochronology of s o m e b a s e m e n t r o c k s in t h e Central E a s t e r n D e s e r t a n d s t a t e d t h a t all t h e granite s a m p l e s fall w i t h i n a b i n d i n g envelope r e p r e s e n t e d b y two i s o c h r o n s , a n u p p e r o n e c o r r e s p o n d i n g to a n age of 6 2 0 m.y. a n d r e p r e s e n t i n g oldest pink-rdd granite while t h e lower one c o r r e s p o n d s to a n age of 4 6 0 m.y. a n d r e p r e s e n t s y o u n g e s t p i n k - r e d granite. H a s h a d et aL (1981) f o u n d t h a t t h e age o b t a i n e d for a apogranite in Wadi N u g r u s is 6 0 0 + 2 0 m.y.
REFERENCES
Akaad, M.Kand E1Ramly, M.F. 1960. Geological history and classification of the basement rocks of the Central Eastern Desert of Egypt, Geol. Surv., Egypt, 9, 2 4 p .
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Akaad, A.K. and Noweir, A.M. 1980. Geology and lithostratlgraphy of the Arabian Desert orogenic belt of Egypt between latitudes 25035 . and 26030 ' N., AG. (Jeddah), Bull. 3, 4, 127-135. El Gaby, S. 1975. Petroehemistry and geochemistry of some granites from Egypt. N.Nb. M[ner.Abh, 124, 147189. El Ramly, M.F. and Akaad, M.K. 1960. The basements complex in the Central Eastern Desert of Egypt between latitudes 24030 , and 25°40 ', Geol. Surv. Egypt, 8, 24 p. El Rarely, M.F. 1972. A new geological map for the basement rocks in the Eastern and Southwestern Desert of Egypt, scale 1:1,000000, Ann. Geol-Surv., Egypt, 2, 1-18. El Shazly, E.M. 1964. On the classification of the Precambrian and other rocks ofmagmatic affiliation in Egypt. U.A.R. International Geological Congress, New Delhi. India, part 10, 88-101. Hunting Geology and Geophysics LTD 1967. Assessment of the mineral potential of the Aswan region, United Arab Republic. Photogeological Survey, United Nations Development programme. United Arab Republic Regional Planning of Aswan. Hussein, A.A., Ali, M.M. and El Ramly, M.F. 1982. A proposed new classifiation of the granites of Egypt, J.Volc. Geoth. Res. 14, 187-198. Hussein, H.A, Kamel, A.F. and Mansour, S.I. 1985. Disseminated type uranium mineralization in the granitic rocks of Um Ara, Southeastern Desert, Egypt. Arab. Journ. of Nuclear Scie. and Appl. Cairo, Egypt. Karnel, A.F. 1983. Relationship between photolineaments and radioactivity in Gebel El Mueilha, Central Eastern Desert, Egypt. Jour. of Afr. Eart. ScL, I, 3/4, 343-347. Printed in Great Britain. Lockwood Survey Corporation Limited 1968. Airborne geophysical survey conducted in collaboration with the United Nations Development programme. UNDP project, Assessment of the mineral potential of Aswan Region. Nishimori, R.K., Regland, P.C., Rogers, J.J.W. and Greenberg, J. 1977. Uranium deposits in granitic rocks. Report No. GIB,, X-13/27 prepared for Energy Research and development Administration, Canada, U.S.A. Rankama, K. and Sahama, Th.G. 1955. Geochemistry, The University Chicago Press, Chicago 37. Sabet, A.H. 1972. On the stratigraphy of the Egyptian Basement rocks, Annals, Geol.Surv., Egypt, 2, 97-102. Schurmann, H.M.E. 1966. The Precambrian along the Gulf of Suez and the northern part of the Red Sea. E.J. Brill, Leiden Netherlands.
0899-5362/89 $3.00 + 0.00 © 1990 Pergamon Press pie
Printed in Great Britain
Contribution to the study of radioactivity in younger granites in Southeastern Desert, Egypt A. F. KAMEL Nuclear Materials Corporation,Maadi Post Office Box 530, Cairo, Egypt. Abstract- The Egyptiangranites are the most dominantrock unit of the basementcomplex in EasternDesert. Several geologicalinvestigations and classifications were carried out on these granites. They were classified
according to relative age, dominantcolour, type locality and their apparent relation to orogeny. Most of the discoveredradioactiveoccurrencesare encounteredin the younger granites which are generally enriched in uranium than other rock types. The presentworkdealswith the distributionofradioactivityin youngergranitesrepresentedin the Southeastern Desert of Egypt and the identificationof these granites on aerial photographs and photomosaics in a trial to differentiatebetween granites with normal to moderateradioactivityand those having higher and anomalous radioactivity. The younger granites ha~,e a wide range of radioactivitywhich is from400 to 1000 count per second in the granites with normal to moderate radioactivitywhile it reaches 2000 count per second in the granites with abnormal radioactivityas givenin the radiometricmap constructedby Lockwoodin 1968. Someoutcropsof the second type are found with disseminateduranium mineralizations, and in certain localities field measurement of their radioactivitygave values of 10 000 count per second, and even more. Photogeologically,the younger granites are characterizedby lighter tone, coarser surface texture, angular to rectangular drainage pattern and the sharp contact against the other types of rocks. Granites with higher to anomalous radioactivityare highly fractured as comparedwith the other rocks of younger granites.
INTRODUCTION
O n e of t h e f u n d a m e n t a l p r o b l e m s of t h e b a s e m e n t r o c k s of E g y p t is t h e s t u d y of t h e g r a n i t e s . T h e gr an itic r o c k s ar e classified into two m a i n g r o u p s , n a m e l y t h e o l d e r S y n - t e c t o n i c to Latet e c t o n i c g r a n i t e s w h i c h ar e t h e g r e y g r a n i t e s , a n d y o u n g e r granites or Post-tectonic granites referred to a s p i n k g r a n i t e s (Akaad etal., 1960; E l R a m l y et aL, 1960; H u n t i n g , 1967; El Rarely, 1972; S a b e t , 1972; El G a b y , 1975; A k a a d et al., 1980 a n d H u s s e i n et al., 1982). El S h a z l y (1964) p o i n t e d o u t the presence of Post-orogenic plutonites referred to a s A s w a n g r a n i t e w h i c h h e c o n s i d e r e d y o u n g e r t h a n the normal pink granites. T h e y o u n g e r g r a n i t e s of t h e S o u t h e a s t e r n D e s e r t of E g y p t ar e c h a r a c t e r i z e d b y p r o n o u n c e d p i n k colour, b ein g essentially unfoliated a n d f or m m a s s e s w i t h c i r c u l a r to o v a l - s h a p e d o u t l i n e i n t r u d i n g into old g e o s y n c l i n a l s e d i m e n t s a n d volcanics. Most of t h e s e r o c k s a r e m e d i u m - g r a i n e d b u t few t e n d to be f i n e - g r a i n e d , while o t h e r s a r e p e g m a t i t e s . In t h e p r e s e n t s t u d y , c e r t a i n localities h a v e b e e n s e l e c t e d in t h e S o u t h e a s t e m D e s e r t of E g y p t (Fig. l ) .Th e s t r u c t u r a l l i n e a m e n t s w e r e i n t e r p r e t e d photogeologicaUy in e a c h locality. C o m p a r i s o n w a s c a r r i e d o u t b e t w e e n t h e hi ghl y r a d i o a c t i v e gr a ni t i c
r o c k s a n d t h o s e w i t h relatively low level of r a d i o a c tivity. Detailed s t u d y w a s c a r r i e d o u t in t h e localit i es w h e r e t h e g r a n i t e e x p o s u r e s a r e p r o m i n e n t a n d t h e i r r a d i o a c t i v i t y is well k n o w n . T h i s s t u d y w a s s u p p l e m e n t e d b y field c h e c k for a n u m b e r of these granite exposures. STRUCTURAL
SETTING
T h e y o u n g e r g r a n i t e s are c h a r a c t e r i z e d b y t h e p r e s e n c e of two s e t s o f j o i n t s p e r p e n d i c u l a r to e a c h o t h e r a n d a d i a g o n a l one. T h e r o c k s a r e d i s s e c t e d b y a n u m b e r of f a u l t s w i t h v a r i o u s t r e n d s a n d l engt hs. T h e different s t r u c t u r a l l i n e a m e n t s w e re i n t e r p r e t e d phot ogeol ogi cal l y u s i n g aerial p h o t o m o s a i c s scale 1:50000. T h e t r e n d a n d l e n g t h for e a c h s t r u c t u r a l line w a s r e c o r d e d in e a c h 10 ° f r o m n o r t h t o t h e e a s t a n d w e s t di rect i ons. Rose diag r a m s s h o w i n g t h e d i s t r i b u t i o n of t h e s e s t r u c t u r a l lines, w ere c o n s t r u c t e d f o r t h e S o u t h e a s t e m D e se rt in e a c h sel ect ed locality (Fig. 2). T h e i n t e n s i t y of f r a c t u r e s in e a c h locality w a s e s t i m a t e d b y m e a s u r i n g t h e t ot al l e n g t h of lineam e n t s in a u n i t a r e a of i k m 2. It w a s f o u n d t h a t in S o u t h e a s t e r n D e s e r t of E g y p t t h e s t r u c t u r a l lines h a v e t h e d o m i n a n t t r e n d s WNW-ESE, E-W, NWS E a n d ENE-WSW w h i c h c o n s t i t u t e 74. 7 % of t h e
AES 9:2-G
297
298
A.F. KAMEL the granite with m o d e r a t e to lower level of radioactivity. Concerning the intensity of fracturing in the different localities, it w a s clear t h a t t h e highly radioactive y o u n g e r g r a n i t e s are d i s s e c t e d b y large n u m b e r of f r a c t u r e s with total length of 2-6 k m p e r unit area of 1kin 2 while t h e total length of f r a c t u r e s per unit a r e a is 1-2 k m in t h e g r a n i t e s of m o d e r a t e to low radioactivity. RADIOA~I'IVITY
l.G.Nugru$
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Fig. I. Index m a p of the study area.
G UM.ARA
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G.EL HUDI
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G-MU6RUS
W ABU N AT S:H
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L I N E A M E N T S IN S O U T H E R A S T E R N DESERT/EGYPT, ,
ROSE DIAGRAMS SHOWING THE MAIN TRENDS OF STRUCTURAL LINEAMENTS IN DIFFERNT LOCALITIES IN SOUTHEASTERN DESERT,EGYPT
Fig. 2. Rose diagrams.
total length of all lineaments. There are two less d o m i n a n t t r e n d s namely, t h e NNW-SSE a n d NESW trends, A n u m b e r of t h e s e l i n e a m e n t s were c h e c k e d in t h e field a s faults. The WNW-ESE a n d NW-SE t r e n d s d o m i n a t e in the granitic r o c k s with p r o m i n e n t radioactivity while t h e E-W a n d ENEW S W t r e n d s are t h e m a j o r t r e n d s of f r a c t u r e s in
The b a s e m e n t c o m p l e x in Egypt c o n t a i n s m o s t of t h e discovered radioactive o c c u r r e n c e s . Most of t h e s e o c c u r r e n c e s are e n c o u n t e r e d in t h e y o u n g e r granites. According to R a n k a m a a n d S a h a m a (1955), the c o n t e n t oflithophfle trace e l e m e n t s d e c r e a s e s with the geologic age of granite, therefore t h e Egyptian p i n k granite will b e m o r e radioactive t h a n grey granites w h i c h are older in age. Nishimori e t al. (1977) s t a t e d t h a t the E g y p t i a n g r a n i t e s are enriched in u r a n i u m mineralization t h a n similar granites in o t h e r p a r t s of t h e world. Field radiometric m e a s u r e m e n t s carried o u t on s o m e granite e x p o s u r e s of the E a s t e r n Desert s h o w e d t h a t the pink granites have n o r m a l radioactivity which r e a c h e s 2 0 0 c o u n t p e r second. The a n o m a l i e s have m a x i m u m radioactivity of 5 0 0 0 c o u n t p e r s e c o n d which b e c o m e s m o r e in t h e f r a c t u r e d g r a n i t e s a n d in t h e pegmatite d y k e s i n t r u d i n g t h e granitic rocks, w h e r e it r e a c h e s 10 0 0 0 c o u n t p e r second. Lockwood (1968) CalTied o u t aero-radiometric s u r v e y in a larger a r e a in t h e S o u t h e a s t e r n Desert of Egypt a n d c o n s t r u c t e d radiometric m a p s w h i c h s h o w that radioactivity is p r o m i s i n g in localities covered b y y o u n g e r granites. M a x i m u m radioactivity is 2 0 0 0 c o u n t p e r s e c o n d in t h e highly radioactive r o c k s while radioactivity is ranging b e t w e e n 4 0 0 a n d 1000 c o u n t p e r s e c o n d in the granitic r o c k s with m o d e r a t e to low radioactivity (Table I). S o m e of t h e s e radioactive localities were s e l e c t e d for t h e p r e s e n t study. Photointerpretation w a s carried o u t in each selected locality a n d the different s t r u c t u r a l l i n e a m e n t s were s t u d i e d photogeologically o n aerial photom o s a i c s scale 1:50 000. Detailed field radiometric s u r v e y w a s carried o u t in t h e localities with promising radioactivity. F r o m t h e p r e v i o u s w o r k a n d the p r e s e n t w o r k carried o u t on t h e y o u n g e r granites, it w a s noticed t h a t radioactivity varies with t h e variation of t h e grain size, relative age a n d degree of tectonic effect. The fine-grained g r a n i t e s are m o r e radioactive t h a n the coarse -grained variety including t h e A s w a n granite. G r a n i t e s w h i c h are d i s s e c t e d b y larger n u m b e r of f r a c t u r e s with t h e d o m i n a n t WNW-ESE a n d NW-SE t r e n d s are m o r e radioactive t h a n the
Contribution to the study of radioactivity in younger granites in Southeastern Desert, Egypt
299
Table 1. The main trends of radioactivity and structural lines in younger granites. Southeastern Desert. Egypt.
Name of the area
Maximum radioactivity in count per second
Main tnmd of radioactivity
Main trend of structural lines
The cotmtry rocks
G e b d El Hudi
2000
N45°W
N40 o . 50°W
Mica sl~st, older granims and Nubian ssndsr~nes
Highly
Wadi El Arab
2O00
N40°W
N50 ~ _ 60oW
Nubian smdstones
radioactive
Gebel Magal Gebnel
1600
N45°W
N50 ° - 60%%'
Met~odiments, metavolcmics
Gebel U m Ara
1800
N35°W
NS0° - 60"W
Me.u~.~ments, metavoloanics and serpeatinites
Gebel Nugms
1000
N30°W
N0 ° - 1 0 ~ /
Metasediments and metavolcanics
Gebel Abu Brush
1000
N55°E
N30 o . 40OE
Metavolcanics, diofitesand older granites
Wadi Abu Natash
1000
N45°E
NT0• . 80°E
Older granites
G e b d Kdat
1000
N25°W
N30 o . 40oW
M ~ e A i m e n u , metavolc~dcs and older granites
Gebel Dahiz
1000
N70°E
N60 o _ 70OE
Metascdiments, metavolcanics and older granites
Moderately ~dioactive
granites dissected by small n u m b e r of fractures with the d o m i n a n t E-W and ENE-WSW trends. There is a general orientation of the distributed radioactivity as s h o w n in (Fig. 3). REI~TIONSIIrP BETWEEN RADIOACTIVITY AND STRUCTURAL LINEAMENTS The structurally controned u r a n i u m mineralization is well k n o w n in several locallties in the E a s t e r n Desert of Egypt. Kamel (1983) correlated the structural c o n t o u r m a p with the radiometric m a p of E1 Mueilha area, Central E a s t e r n Desert a n d found t h a t the t r e n d of photolineaments responsible for radioactivity is the N50 ° - 70°W, while Hussein eta/, (1985) found that the distribution of radioactivity in U m Ara area, S o u t h e a s t e r n Desert, is structurally controlled by WNW-ESE a n d NW-SE trends. In the present work a comparison was carried out between the m a i n t r e n d s of the distibution of radioactivity in each locality as indicated in the radiometric m a p s of Lockwood (1968) and the m a i n t r e n d of structural lines dissecting the granitic rocks in the s a m e locality. It was f o u n d that the highly radioactive y o u n g e r granite exposures of Gebel Um Ara, Wadi E1 Arab, Gebel El Hudi and Gebel Magal Gebriel have the m a i n t r e n d s of radioactivity N35 ° - 45°W, while the m a i n t r e n d s of structural lines in t h e s e localities are N40 ° - 60°W. There is a notable relationship between the m a i n t r e n d s of radioactivity a n d fractures where the t r e n d s are more or less conformable (Fig. 3, A, B, C).
The y o u n g e r granites with m o d e r a t e to low level of radioactivity are exposed in Gebel Abu Brush, Gebel Nugrus, Wadi Abu Natash, Gebel Kelat and Gebel Dahiz which have their m a i n t r e n d s of radioactivity quite different. These trends are N55°E, N30°W, N45°E, N25°W a n d N70°E respectively. The structural lines dissecting these granite expos u r e s have the m a i n t r e n d s N30 ° - 40°E, NO° - 10°W, N70 ° - 80°E, N30 ° - 40°W a n d N60 ° - 70°E. Correlation between the m a i n t r e n d s of radioactivity a n d s t r u c t u r a l lines shows t h a t t h e y are not conformable except for Gebel Dahiz indicating that radioactivity in the granites with moderate to low radioactivity is not structurally controned in most of the exposures. The present work indicates t h a t the y o u n g e r granites in the S o u t h e a s t e m Desert of Egypt c a n be differentiated into two groups according to t h e i r radioactivity and distinctive feature: I) the first group is the highly radioactive granites forming larger exposures dissected by large n u m b e r of fractures with the dominant trends WNW-ESE a n d NW-SE. The high level of radioactivity (1000-2000 c o u n t per second) m a y be attributed to the presence of relatively high percent of accessory minerals carrying u r a n i u m and thorium, the presence of iron oxides which have the ability of capturing u r a n i u m leached from the surroundings, the presence of potassium-40 present in potash feldspars or the presence of s e c o n d a r y u r a n i u m m i n e r a l s s u c h a s U r a n o p h a n e a n d Soddyite-Prlmary uraninite was
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Fig. 3. Radiometric map of granite exposures in Southeastem Desert. Egypt (Modified after Lockwood, 1968). found in the localities of El Eradiya in the Central Previous work h a s been carried out on the E a s t e r n Desert a n d Urn Ara in the S o u t h e a s t e m localities, Um Ara, Magal Gebriel and Nugrus, Desert of Egypt. Hussein et aL (1966) and Kamel etal. (1985) carried out the field radiometric S c h u r m a n n (1966) attributed the high level of survey of U m A r a A r e a and found t h a t radioactivity radio-activity of some Egyptian granitic rocks to ranges between 350 - 4000 CPS in the fine-gralned the presence of accessory minerals like zircon, granite while it is not more t h a n 500 CPS in the monazite, thorite, uranothorite, allanite and medium- to coarse-grained granite. Hussein et al, xenotime. (1985) studied t h e g r a n i t e pluton of Uma Ara and The rocks in the first group are characterized by attributed the high level of radioactivity to the their finer grain size as compared with the rocks in presence of secondary u r a n i u m mineralization the second group. They have pink colour and are disseminated in the rocks and considered the highly dissected by fractures. There is a good granite as fertile granite. In 1986, Hussein et al. relationship between the dominant trends of stated t h a t radioactivity increases with the radioactivity a n d s t r u c t u r a l lines. increase of accessory minerals represented by 2- the second group h a s moderate to low level of topaz, monazite a n d uraninite. They added that radioactivity (400 - 1000 c o u n t per second) form- u r a n i u m mineralization is related to synorogenic ing smaller outcrops a n d is dissected by smaller and epigenetic o ~ s . n u m b e r of fractures. There is no relation-ship Zalata et al. (1986) found t h a t Um Ara between the m a i n trends of the d i s t r i b u t i o n of granite pluton forms a composite mass, the first radioactivity and the dissecting fractures, phase is represented by coarse-grained monzoThe rocks in the second group are reddish in granite and the second p h a s e by fine-grained colour, coarser in grain size and deficient in the alkali feldspar granite which is highly radioradioactive accessory minerals. active.
Contribution to the study of radioactivity in younger granites in Southeastern Desert, Egypt Magal Gebriel is l o c a t e d to t h e n o r t h of U m Ara. It h a s b e e n investigated in t h e field radiometrically b y Kamel et al. (1986). T h e y n o t i c e d t h a t granitic r o c k s in t h e a r e a are relatively m o r e radioactive t h a n t h e o t h e r t y p e s of rocks. The fine-grained granite is m o r e radioactive, giving r e a d i n g s u p to 5 0 0 CPS, t h a n t h e c o a r s e - g r a i n e d granite w h i c h h a s radioactivity a m o u n t i n g to 4 0 0 CPS. Anomalo u s radioactivity w e r e r e c o r d e d in t h e fine-grained g r a n i t e w h e r e r a d i o a c t i v i t y r e a c h e s u p to 2 0 0 0 CPS. Kamel (1987) f o u n d t h a t t h e r e is similarity b e t w e e n t h e granitic r o c k s in U m Ara a n d Magal Gebriel a r e a s w h e r e t h e radioactive granite in t h e two a r e a s is fine-grained containing u r a n i u m mineralization ( u r a n o p h a n e ) w h i c h is a s s o c i a t e d with g r e e n a n d violet fluorite. Chemical a n a l y s i s c a r r i e d o u t on s a m p l e s collected from U m Ara a n d Magal Gebriel indicated t h a t u r a n i u m c o n t e n t r e a c h e s u p to 711 p p m in U m Ara a n d 7 0 0 p p m in Magal Gebriel. S a d e k (1953) discovered t h e radioactive m i n e r a l allanite in t h e p e g m a t i t e v e i n s i n t r u d i n g t h e granite r o c k s in W a d i El G e m a l a r e a w h i c h is a d j a c e n t to Gebel N u g r u s . El Shazly a n d H a s s a n (1972) c a r r i e d o u t radiometric s t u d y o n Wadi Sikait - W a d i El G e m a l a r e a a n d f o u n d t h a t radioactivity r e a c h e s i 0 0 0 IxR/h (about 5 0 0 0 CPS). The radioactive m i n e r a l s are m a i n l y zircon a n d thorite. H a s s a n (1972) recognized few s p e c k s of s e c o n d a r y u r a n i u m m i n e r a l s in t h e highly radioactive rocks. El M a n h a r a w i (1977) s t u d i e d t h e geochronology of s o m e b a s e m e n t r o c k s in t h e Central E a s t e r n D e s e r t a n d s t a t e d t h a t all t h e granite s a m p l e s fall w i t h i n a b i n d i n g envelope r e p r e s e n t e d b y two i s o c h r o n s , a n u p p e r o n e c o r r e s p o n d i n g to a n age of 6 2 0 m.y. a n d r e p r e s e n t i n g oldest pink-rdd granite while t h e lower one c o r r e s p o n d s to a n age of 4 6 0 m.y. a n d r e p r e s e n t s y o u n g e s t p i n k - r e d granite. H a s h a d et aL (1981) f o u n d t h a t t h e age o b t a i n e d for a apogranite in Wadi N u g r u s is 6 0 0 + 2 0 m.y.
REFERENCES
Akaad, M.Kand E1Ramly, M.F. 1960. Geological history and classification of the basement rocks of the Central Eastern Desert of Egypt, Geol. Surv., Egypt, 9, 2 4 p .
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Akaad, A.K. and Noweir, A.M. 1980. Geology and lithostratlgraphy of the Arabian Desert orogenic belt of Egypt between latitudes 25035 . and 26030 ' N., AG. (Jeddah), Bull. 3, 4, 127-135. El Gaby, S. 1975. Petroehemistry and geochemistry of some granites from Egypt. N.Nb. M[ner.Abh, 124, 147189. El Ramly, M.F. and Akaad, M.K. 1960. The basements complex in the Central Eastern Desert of Egypt between latitudes 24030 , and 25°40 ', Geol. Surv. Egypt, 8, 24 p. El Rarely, M.F. 1972. A new geological map for the basement rocks in the Eastern and Southwestern Desert of Egypt, scale 1:1,000000, Ann. Geol-Surv., Egypt, 2, 1-18. El Shazly, E.M. 1964. On the classification of the Precambrian and other rocks ofmagmatic affiliation in Egypt. U.A.R. International Geological Congress, New Delhi. India, part 10, 88-101. Hunting Geology and Geophysics LTD 1967. Assessment of the mineral potential of the Aswan region, United Arab Republic. Photogeological Survey, United Nations Development programme. United Arab Republic Regional Planning of Aswan. Hussein, A.A., Ali, M.M. and El Ramly, M.F. 1982. A proposed new classifiation of the granites of Egypt, J.Volc. Geoth. Res. 14, 187-198. Hussein, H.A, Kamel, A.F. and Mansour, S.I. 1985. Disseminated type uranium mineralization in the granitic rocks of Um Ara, Southeastern Desert, Egypt. Arab. Journ. of Nuclear Scie. and Appl. Cairo, Egypt. Karnel, A.F. 1983. Relationship between photolineaments and radioactivity in Gebel El Mueilha, Central Eastern Desert, Egypt. Jour. of Afr. Eart. ScL, I, 3/4, 343-347. Printed in Great Britain. Lockwood Survey Corporation Limited 1968. Airborne geophysical survey conducted in collaboration with the United Nations Development programme. UNDP project, Assessment of the mineral potential of Aswan Region. Nishimori, R.K., Regland, P.C., Rogers, J.J.W. and Greenberg, J. 1977. Uranium deposits in granitic rocks. Report No. GIB,, X-13/27 prepared for Energy Research and development Administration, Canada, U.S.A. Rankama, K. and Sahama, Th.G. 1955. Geochemistry, The University Chicago Press, Chicago 37. Sabet, A.H. 1972. On the stratigraphy of the Egyptian Basement rocks, Annals, Geol.Surv., Egypt, 2, 97-102. Schurmann, H.M.E. 1966. The Precambrian along the Gulf of Suez and the northern part of the Red Sea. E.J. Brill, Leiden Netherlands.