Heikal, Mohamed A.

Kabesh, Mahmoud Lofty

Salem, Abdel-Karim Ahmed

Salem, M. A.

English

Biotites from the granitoid rocks of El-Imra, Eastern Desert, Egypt have been examined. The chemical data of 8 new analyzed biotites are presented. The behaviour of major and trace elements in the examined biotites are discussed according to different variation diagrams. The chemical composition of biotites has proved a reasonable guide to the magmatic origin of the host granitic rocks

Salem Abdel-Karim Ahmed

Heikal Mohamed A.

Kabesh Mahmoud Lofty

Salem M. A.

University of Szeged

Acta Mineralogica-Petrographica, Szeged, XXIX, 47—56, 1987—1988 G E O C H E M I S T R Y O F B I O T I T E A N D I T S S I G N I F I C A N C E A S A G U I D E T O T H E O R I G I N O F T H E G R A N I T O I D R O C K S O F E L - I M R A AREA, E A S T E R N D E S E R T , E G Y P T By A . K . A . SALEM, M . A . HEIKAL, M . L. KABESH, M. A . SALEM Earth Sciences Laboratory, National Research Centre ABSTRACT Biotites from the granitoid rocks of El-Imra, Eastern Desert, Egypt have been examined. The chemical data of 8 new analyzed biotites are presented. The behaviour of major and trace el-ements in the examined biotites are discussed according to different variation diagrams. The chemical composition of biotites has proved a reasonable guide to the magmatic origin of the host granitic rocks. INTRODUCTION The present study deals with the geochemistry of biotites separated from some granitoid rocks of El-Imra area, Eastern Desert, Egypt (Fig. 1). The granitic stock of El-Imra consists mainly of pink, pinkish — white and grey granites. They comprise porphyritic and equigranular, non-porphyritic types. Biotite is generally the sole mafic mineral in these granites. The biotite is mostly pleochroic from straw - yellow to chestnut brown. It occurs largely as irregularly - sphaped flakes reaching 0.18 mm in length. In some varieties, biotite show subparallelism and is associated with clusters of minute epidote granules. Occasionaly it froms stout flakes with torn ends. Rarely muscovite also is present in the groundmass as marginal gradation around bioitite. The main inclusions present in biotite are zircon, apatite and iron ores. The work reported in this paper forms part of a continuing research program carried out in the Earth Sciences Laboratory National Research Centre, by Kabesh and co- workers (KABESH and SALEM, 1981, KABESH et al, 1982). ANALITICAL METHODS The samples of the host granitic rocks were crushed to pass through a 100-mesh and 120 mesh sieve (U. S.). The crushed fraction was individually separated with bromoform, followed by removal of magnetite by hand magnet. Biotite separated from heavy fraction was purified by using the FRANTZ isodynamic separator. Finally, the pure sample of biotite was pulverized in agte mortar under acetone untill all pass through 200-mesh sieve (U. S.). The chemical analysis was carried out by using volu-metric, gravimetric and colourimetric methods of silicate analysis according to BEN-NETT and READ (1971) and VOGEL (1968). Trace elements were determined by induc-tively coupled plasma emission spectrometry at the Nuclear Materials Corporation, Cairo using the technique described by WALSH (1980) and McLaren et al., (1981). Dokki-Cairo, Egypt. 47 CHEMISTRY OS BIOTITES Eight new chemical analyses of biotites from El-Imra granitoid rocks are used to elucidate the pedogenesis of these rocks. The major element compositions of the examined biotites are given in Table 1, in addition, one analysis of biotite from Kada-bora granitic mass (KABESH et ah, 1977) and one analysis from the granodiorite of Sierra Nevada Batholith (DODGE et. al., 1969) are given for comparison. The chemical data are plotted on GOKHALE variation diagram Fig. 2, showing the ternary diagram MgO, FeO and A1203. It is observed that all the examined bio-tites fall wihin the zone drown by GOKHALE (1968) for biotites of magmatic nature. Structural formulae of biotite The structural formulae of the examined biotites are given in Table 2. The calculation is based on 24 (O, OH) to the general mica formulae X3 M6 Z8 O20 (OH, F, CI) and the results are listed in the samé table. FIG. J shows the ternary diagram Mg (Fe3-1- +Ti/+AlV I ) and Fe2 + (FOSTER, 1960). It is clear from the diagram that all the analysed biotites fall within the field Mg-iron rich varieties. 48 o TABLE 1 Chemical analyses of biotices from granitoid rocks of El Imra Oxide 1 2 3 4 5 6 7 8 average A B C SiO, 35.15 35.67 35.53 30.06 35.53 35.00 35.64 36.11 35.59 35.40 35.99 36.90 AljOj 4.27 14.54 15.15 15.20 15.30 15.98 15.30 14.45 14.95 16.66 14.94 15.40 Fe,03 36.36 6.43 6.47 5.06 7.01 5.78 7.23 5.56 6.24 5.17 6.11 3.90 F e O 19.47 21.66 18.57 19.29 17.67 18.48 19.23 19.23 19.20 21.61 16.91 16.60 MnO 0.25 0.12 0.21 0.18 0.18 0.19 0.29 0.25 0.21 0.45 0.14 0.52 MgO 9.73 8.04 8.58 9.89 7.81 9.36 7.13 9.01 8.69 6.23 12.90 10.90 CaO 1.42 2.03 2.23 1.52 2.77 2.00 1.52 1.77 1.91 1.40 0.14 0.22 Na ,0 1.53 1.09 1.66 1.52 1.71 1.19 1.09 1.71 1.44 0.34 0.12 0.04 KjO 7.30 6.22 7.38 7.60 7.08 6.94 7.20 6.60 7.04 6.34 7.81 9.10 Ti Ot 1.89 1.24 1.01 1.05 1.83 2.10 1.68 2.09 1.61 2.18 2.73 2.90 HjO- 0.15 0.20 0.30 0.21 0.16 0.46 0.35 0.26 0.26 0.32 — 0.20 H tO+ 2.52 2.59 2.91 2.42 2.42 2.95 3.11 3.30 2.83 3.10 2.50 31.0 total 99.83 100 100 100 100 99.99 99.96 99.87 99.97 99.29 99.43 99.18 A — Biotite from Kadabora (KABESH and SALEM, 1981) B — Biotite from Ras Barud, Eastern Desert Egypt (KABESH et al„ 1977) C — Biotite from granodiorite from Sierra Nevada Batholith, California (DODGE et al., 1969). FeO tot AI2O3 Fig. 2. Plot of AljOa-MgO-FeOto, in the investigated biotites. • Analised samples, A The average of biotites (after GOKHALE, 1968). 49 s Mg Fig. 3. Relation between octahedral cations of the studied biotite (after FOSTER, 1960). Symbols are same as Fig. 2. Mg and granodiorite, (3) quartz-diorite, (4) nepheline syenite, (5) gneiss and schist, (6) pegmatite. Symbols are same as Fig. 2. The value of the Y - group cations; Mg, (Al I V+Fe3 + +Ti4+) and (Fe2+ + M n 2 + ) are plotted on FOSTER'S diagram Fig. 4. It is evident from the figure that the analyzed samples of biotite fall within the fields granite and granodiorite. Fig. 5 shows the relation between (Fe 2 + /Mg)x 100 and A1IVX100 of the exam-ined biotites. It is evident from the diagram that all the analyzed biotites fall in the field of the magmatic differentiation (SHIBATA et al., 1966). Fig. 6 shows that the division between phlogopite and biotite compositional field is arbitarily chosen to be where M g : F e = 2 : 1 (DEER et al., 1966). T h e examined biotites are plotted on this figure which shows that all the analyzed samples fall with-in. 50 Structural Formulate of biotites TABLE 2 1 8 average Si AIIV 5 .52 2 .48 5.63 2 .37 5 .56 2 .44 5 .57 2 .43 5 .53 2 .47 5 .56 2 .44 5 .55 2 .45 5 .63 2 .37 5 .57 2 .43 8.00 A1VI Fe8 + Ti Mg Fes+ Mn 0.16 0.75 0.22 2 . 3 0 2 .55 0 .03 0 .33 0 . 7 6 6 .02 0 .07 1 .90 3 .00 0.02 0.35 0 . 7 6 6.08 0.12 1.99 2 .42 0.02 0.33 0 . 5 9 5 .66 0 . 6 0 2 . 2 9 2 .48 0 .05 6 .34 0 .33 0.82 0.21 1.82 2 .29 0.02 5 .49 0 .43 0 . 5 9 0.21 2.23 2 .45 0 .03 5 .94 0 .35 0 .84 0.20 1.67 2 .49 0 . 0 4 5 .59 0.28 0.65 0 .24 2.11 2 . 5 0 0 .03 5.81 0 . 3 2 0 .73 0 .38 2 . 0 4 2 . 5 0 0 .03 6.00 Ca Na K 0 . 2 4 0 . 4 6 1 .46 0 . 3 4 2 . 1 6 0 .33 1.25 0 .37 1.92 0 .05 1.48 0 .25 1 .90 0 .46 1 .50 2.21 0 .46 0 . 5 2 1.41 2 .39 0 .36 0 .34 1 .40 2.10 0.25 0 .27 1.43 1.95 0 . 2 9 0.51 1.31 2.11 0 .32 0.22 1.41 1.95 OH 2 . 7 2 2 .72 3 .04 3 .06 3 .06 . 2.22 3 .42 2 . 3 4 2.86 58 .92 66 .43 61.51 57 .28 63 .08 57 .69 66 .60 59 .99 61 .29 Fe !+/Mg 220 200 -180 -160-140 -120 -100 -80-60-40-2 0 -GRANITE 200 220 —I— 240 260 280 —I— 300 —I 1— 320 340 ~T -I 360 380 AI1 Fig. 5. The Fe2+/Mg-AlIV relations in biotite-formuias of granitic rocks of magmatic origin and metamorphic origin (after SHIBATA el al., 1966). Symbols are same as Fig. 2. Annite 1.0 0,8" cn o 0,6 Ç I 0,U 0,2 -0,0 2,0 Phlogopite 2A Siderophyllite BI0TITES > V PHL0G0PITES 23 I 3,2 I 3,6 4,0 Eastonite Al atoms per Formula unit-Fig. 6. Composition of biotite in terms of Fetot/(Fetot+Mg)-Al. The division between phlogopite and biotite fields is arbitarily chosen to be where Mg:Fe,ot=2:l (DEER et al., 1966). Symbols are same as Fig. 2. , 52 TABLE 3 Minor elements in biotites from granitoid rocks of El Imra with some other localities for comparison 1 2 3 4 5 6 7 8 A B C Ga 20 27 31 19 33 133 29 121 95 90 44 V 211 253 227 220 333 103 212 109 90 100 180 Cr 44 53 72 47 55 127 60 133 130 80 10 Nb 27 33 37 44 28 19 30 17 — — 20 Co 18 17 18 22 19 33 27 40 60 4C 34 Cu 11 8 13 7 6 30 8 28 * 25 50 Zn 0.2 0.3 0.2 0.2 0.5 1.5 0.5 1.5 * * — Sc 7 5.5 3.5 5.5 4.5 33 4.5 4.1 * * 44 Sr 3 7 5 7 8 17 4 22 6 6 20 Ba 2440 2360 2010 2518 2500 1122 2019 1215 450 340 * Zr 62 57 70 50 73 40 60 33 * 57 60 Ni 13 22 19 30 25 62 .. 30 72 95 25 10 Rb 930 1003 988 818 1111 630 1117 701 240 * * Li 150 165 140 111 159 277 172 301 310 * * Y 2 3 2 3 2 7 2 8 * * • * not detected A — Biotite from Kadabora (KABESH and SALEM, 1981) B — Biotite from Ras Barud, Eastern Desert Egypt (KABESH et al., 1977) C — Biotite from granodiorite from Sierra Nevada Batholith, California (DODGE et al., 1969). TABLE 4 Elemental ratios of the examined of biotites 1 2 3 4 5 6 7 8 Coxl03/Fe2 0.12 0.10 0.12 0.14 0.14 0.23 0.18 0.27 Nixl03/Fe2 0.09 0.13 0.13 0.20 0.18 0.43 0.20 0.47 Nixl03/Mg 0.22 0.46 0.37 0.51 0.53 1.10 0.70 1.39 CrxlOVFe 0.10 0.12 0.16 0.13 0.11 0.31 0.34 0.34 Vxl02/Fe 0.47 0.56 0.50 0.62 0.68 0.25 0.42 0.28 K/Rb % 51.5 65.2 62.0 77.0 53.0 91.4 53.5 68.2 Ni/Co 0.72 1.24 1.01 1.36 1.32 1.88 1.11 1.75 53 TRACE ELEMENTS Trace elements data of the analyzed biotites are listed in Table 3. Elemental ratios recalculated from the trace elements of the examined biotites are given in the same table. It is clear from Table 3 that the elements; Sc, Zn, Cu, Cr, Nb, Co, Cu, Sc, Sr, Zr, Ni, Rb, Li, and Y are concentrated in the biotites of the examined area. It is believ-ed that the trace elements: Sc, Zn, Cu, Co, Ni, Nb, Cr, V. and Ga substitute major elements in octahedral sites, although some Ga may substitute for A1 in tetrahedral coordination. Li is strongly concentrated in biotites. Li and Sc follow Mg according to various authors (DE ALBUQUERQUE, 1973). From the geochemical point of view bar-ium and rubidium dan be expected from their affinity to potassium to occur in high amount in the biotites. BO-BO-50-0-300-гоо-«о-о-1S0-Ga Cr 80-60-ад-го-40-30-20-10-Со Fig. 7. Variation diagram of trace elements of the biotites. Trace elements and elemental ratios are plotted on the following graphical rep-resentation : The values of the function Fetot/(Fetot+Mg) (Table 3) are plotted against V. Co, Ni, Ca (Fig. 7) and Cr. Ni, Co and Ga decrease with the increase of the value Fetot/(Fetot+Mg). Vanadium shows no definite trend. 54 The values of Fetot/(Fe lot+Mg) are also plotted versus some elemental ratios Fig. 8. It is clear from the figure that NiXlO^Fe^, NixKP/Mg, Co/Ni, CrXlO2/ Fe3+ and Vx l0 2 /Fe 3 + decrease with the increase of the value of the function, Fetot/(Fe tot + Mg). 0,2 0.1-0 0,1.-0,3-6.2-,0,1-0 3 2-R 0-• • CrxioW • • N¡x103/Mg • • • - • • * • C o / N i • • • • Ni« 10s/Fe1 • • • • — —. • • , Cox103/Fe* • Fig. 8. Variation diagram of some trace elemental ratios. 300 T 250 200-J=> oc ^ 150 100 50-I Biofite in metamorphic complexes Biotite in diffentiated granitic complexes i i 1 1 i 1 1 1 1 1 1 0,03 004 0,05 0,06 0,07 0,08 0,09 0,10 0,11 012 Rb % Fig. 9. Plot of K/Rb versus Rb% for the studied biotites (after STAVROV, 1971). 55 It is clear that the behaviour o f the trace elements o f the investigated biot i tes agrees fairly well with the expected behaviour o f trace elements o f biotites f r o m the granitic rocks, N o r t h Portugal (DE ALBUQUERQUE, 1973). Fig. 9 shows the relation between Rb% against the value o f K / R b o f biot i te according to STAVROV (1971). It is observed f rom the figure that all the biotites fall in the field o f magmatic differentiation. SUMMARY Biotites f rom the granitic rocks o f El-Imra mass have been investigated by geo-chemical methods. T h e behaviour of both major and trace elements are discussed according t o several variation diagrams, in which the values o f the funct ion Fe t o t / / ( F e l o t + M g ) increases with the decrease o f the values o f the elements; C o , N i , Cr,-G a as well as with elemental ratios. It is concluded that the biotites o f El-Imra confirm the magmatic origin o f the host granitic rocks. REFERENCES BENNET, H. and REED, R. A. (1971): A Handbook, Chemical Methods of Silicate Analysis. Acade-mic Press, London and New York. DE ALBUQUERQUE, C. A. R. (1973): Geochemistry of biotites from granitic rocks, Northern Por-tugal. Geochemica et Cosmochimica Acta. 37, 1779—1802. DEER, W. A. , HOWIE, R . A . and ZUSSAMANN, J. (1966): A n Introduction t o the Rock- forming Mine-rals. Longmans, London. DODGE, F . C. W. , SMITH, V. C. and MAYS, R . E. (1969): Biotites from granitic rocks of the Central Sierra Nevada Batholith, California. Journal of Petrology. 10, Part 2, 250—71. FOSTER, M. D. (1960): Interpretation of the composition of trioctahedral micas, U. S. Geol. Surv. Prof . Paper Washington. 354—B, S., 11—49. GOKHALE, N. W. (1968): Chemical composition of bioties as a guide to ascertain the origin of granites. Bull. Comm. Geol. Finlande. 40, 107—111. KABESH, M . L., HILMY, M . E., REFAAT, A . M. , ABDALLAH, Z. M . (1977): Geochemistry o f biot ite from Ras Barud granitic rocks Eastern Desert N. Jb. Miner. Abh. 12, №. 3, 201—210. KABESH, M. L., SALEM, A. K. A. (1981): Geochemistry of biotite from Kadabora granitic batholith, Eastern Desert, Egypt. Egypt-J. Geol. 25, №. 1—2, 37—47. KABESH, M . L., SALEM, A . K . A . and EL-NASHAR, E. R . (1982): Remarks o n the petrogenesis o f Samadai granitic complex, Eastern Desert, Egypt. Z., Geol. Wiss. Berlin. 10 H. 11, S. 1439— 1447. MCLAREN, J. W. , BERMAN, S. S., BOYKO, V. J. and RUSSEL, D . S. (1981): Simultaneous determination of major, minor and trace elements in marine sediments by inductively coupled plasma atomic emission spectrometry, Anal. Chem. 53, 1802—1806. STAVROV, O. D. (1971): Ore content in granite and geochemistry of rubidium — Geochemistry International. 8, 5, 739—754. SHIBATA, H. OBA, N. and SHIMODA, N. (1966): Bearing of aluminium in mafic minerals in plutonic and metamorphic rocks. Sc. Rep. Tokyo Univ. Education Sec. 9, №. 86, 89—123. VOGEL, A. I. (1968): A Text-book of Quantitative Inorganic Analysis 3rd ed. Longmans London. WALSH, J. N. (1980): The simultaneous determination of the major, minor and trace constituents of silicate rocks using inductively coupled plasma spectrometry. Spectrochimica Acta 358,107— 111. Maniscript received, 25 February, 1988 56 

Geochemistry of biotite and its significance as a guide to the origin of the granitoid rocks of El-Imra area, Eastern Desert, Egypt

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Geochemistry of biotite and its significance as a guide to the origin of the granitoid rocks of El-Imra area, Eastern Desert, Egypt

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