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ScienceDirect Russian Geology and Geophysics 55 (2014) 1367–1378 www.elsevier.com/locate/rgg

Mineralogy and geochemistry of clay fractions from different saprolites, Egypt: implications for the source of sedimentary kaolin deposits Hassan M. Baioumy * School of Physics, Universiti Sains Malaysia (USM), 11800 USM, Penang, Malaysia Received 12 September 2013; accepted 24 January 2014

Abstract The clay fractions of saprolites from granites, basalt, and schists in Egypt were subjected to mineralogical and geochemical investigations to examine the effect of source rock on the composition of the saprolites and the possibilities of these saprolites as a source of the nearby sedimentary kaolin deposits. The clay fractions of the studied saprolites show mineralogical and geochemical variations. Saprolites from the granites consist of kaolinite, while saprolites from the basalts are composed entirely of smectite. Schists-derived saprolites are composed of kaolinite in some cases and of a mixture of kaolinite, illite, and chlorite in the other. Saprolite from the basalt is characterized by relatively higher contents of TiO2 and Ni compared to the saprolites from granites. Saprolites from granites have higher contents of Ba, Li, Pb, Sr, Th, Y, and Zr compared to those of the saprolites from the basalts and schists. Saprolites from different schists show variations in the distributions of many constituents, such as TiO2, Cr, Ni, Ba, Y, and Zr. Although chondrite-normalized rare earth elements (REE) patterns are characterized by relative enrichments in the light rare earth elements (LREE) compared to the heavy rare earth elements (HREE) in all saprolites, granitic saprolites show negative Eu anomalies, while saprolite from basalt has no Eu anomaly. REE patterns of the saprolites from schists exhibit slight positive Ce anomalies and slight to moderate negative Eu anomalies. Weathering of saprolites from the basalt and metasediments is classified as the bisiallitization type, while weathering of saprolite from the granite is allitization type. Saprolites from schists vary from the bisiallitization (Aswan and Abu Natash) and allitization (Khaboba) types. Saprolites from the Khaboba schist can be considered the possible source of the Carboniferous kaolin deposits in the Hasber and Khaboba areas of Sinai, based on the similarity in the mineralogy and geochemistry of major, trace, and REE between the saprolites and the deposits. On the other hand, Carboniferous sedimentary kaolin deposits in the Abu Natash area, as well as the Cretaceous kaolin deposits in all areas of Sinai, might have been derived from the nearby schist saprolites, based on the similarity in the mineralogy and geochemistry between the saprolites and the kaolin deposits. Granites from the Arabian-Nubian Shield (ANS) and East Sahara Craton (ESC) are the possible sources of the pisolitic and plastic kaolin deposits in the Kalabsha area (Aswan), as indicated by the similarity in the mineralogy and geochemistry of the granitic saprolites and the kaolin deposits. © 2014, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. Keywords: saprolites; kaolin deposits; Egypt; mineralogy; geochemistry; source

Introduction Saprolite is isovolumetrically weathered bedrock that retains the original lithic fabric (Stolt and Baker, 1994). The features of saprolites are the result of weathering of the primary minerals, and of processes such as biological activity, illuviation and neoformation, including the accumulation of iron oxides and neoformed clays in voids. The resulting features are highly variable, both vertically and horizontally, as a result of differences in fabric and mineralogical composition of the parent rock, degree of weathering, and hydrological conditions (Scholten et al., 1997). The fabric of the * Corresponding author. E-mail address: [email protected] (H.M. Baioumy)

saprolite is related to the original lithology, which is most obvious in the coarse saprolite. As the primary minerals weather, voids develop and secondary minerals are formed, which can cause the break-up of the lithic fabric in the fine saprolites (Stoops and Schaefer, 2010). Most descriptions of saprolites deal with mineral transformations, especially in rocks composed of large crystals of feldspar, mica, hornblende, and quartz (e.g., Buol and Weed, 1991; Gilkes and Suddhiprakarn, 1979; Rebertus et al., 1986; Robertson and Eggleton, 1991; Wilson, 2004). Sedimentary kaolin deposits are widely distributed in Egypt covering different ages (Carboniferous and Cretaceous), localities (Sinai and Aswan), and types (pisolitic flint and plastic). Detailed mineralogical and geochemical (major, trace, and rare-earth elements) studies were performed at these

1068-7971/$ - see front matter D 201 4, V.S. So bolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rgg.201 + 4.11.001

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deposits to examine their source and origin (e.g., Baioumy and Gilg, 2011; Baioumy et al., 2012). Baioumy and Gilg (2011) suggested a mixture of medium- to high-grade metamorphic mafic, granitic, and alkaline rocks as a possible source of the pisolitic flint kaolin of the Kalabsha (Aswan) area. Baioumy et al. (2012) pointed out that the Carboniferous sedimentary kaolin deposits in Sinai area are heterogeneous in their mineralogical and geochemical compositions, which reflects local source areas for each deposit. The sources of these deposits range from a single mafic rock to a mixture of granitic, metamorphosed mafic, and alkaline rocks. On the other hand, the Cretaceous deposits are homogeneous in their mineralogical and geochemical compositions and were derived from a mixture of low-grade metamorphic and granitic rocks. Many of these crystalline (mafic, granitic, alkaline, metamorphic) rocks that belong to the Arabian-Nubian Shield (ANS) and East Sahara Craton (ESC) are located very close to the sedimentary kaolin deposits both in Aswan and Sinai areas. The weathering profiles of these rocks could be possible sources of the kaolin deposits in these areas. The clay fractions from the weathering profiles (saprolites) from some of these crystalline rocks such as metasediments, schists, granites, and basalts were investigated in the current study for their clay mineralogy and geochemistry (major, trace, and rare earth elements) to examine the possibility of these rocks as a source of the sedimentary kaolin deposits in Egypt. The mineralogical and geochemical variations among these saprolites were also discussed to illustrate the effect of parent rocks on the mineralogical and geochemical compositions of the saprolites.

Location and geology of studied saprolites The studied saprolites are located in two regions in Egypt that contain the sedimentary kaolin deposits, namely, Aswan and Sinai regions (Fig. 1). The Sinai Peninsula is located in the northeastern part of Egypt about 220 km from Cairo (Fig. 1A). Aswan area is located in the southern border of Egypt about 1000 km from Cairo (Fig. 1A). In Aswan area the basement rocks include the basement rocks of the East Sahara Craton, the Arabian-Nubian Shield, and the Mesozoic alkaline basalts. The ESC is composed mainly of gneiss and granites (e.g., Harms et al., 1990; Stern et al., 1994). The ANS is composed mainly of granites, granodiorites, quartz diorites, gneiss, gabbros, amphibolites, and schists (e.g., Ali et al., 2009; Hargrove et al., 2006; Hassanen, 1999; Hassanen and Harraz, 1996; Liégeois and Stern, 2009; Moussa et al., 2008; Stoeser and Frost, 2006; Sultan et al., 1990). The Mesozoic alkaline basalts include the ESC basalts (e.g., Lucassen et al., 2008) as well as the ANS basalts (e.g., Stein and Hofmann, 1992) (Fig. 1B). Two weathered profiles were sampled from the ANS in the Aswan area. One represents the granitic rocks from Wadi Allaqi area, and the other represents the metamorphic rocks (schist) from Wadi Abu Sobeira area. Along the floor of Wadi Allaqi, moderately weathered pink granites are commonly

observed. The progressive weathering of these granites led to the formation of a relatively thick horizon above the weathered spheroidal rocks (4–4.5 m thick). In the lower part of this zone, the parent rocks are present as isolated spheroidal masses. It generally occurs as medium- to fine-grained, pink, and highly exfoliated granites. The accumulation of residual debris is common along the closed joints and fractures. With progress the intensity weathering upward, the granitic masses are of white, moderately hard, and more kaolinitized with scattered green materials. The uppermost part of the profile is kaolinite-rich materials (0.5–1 m thick), less cohesive, white color, more kaolinitized with more quartz grains (Fig. 2A). The profile of weathered schist in the Wadi Abu Sobeira area appears as a thick horizon (up to 11 m). The lower part of the profile is characterized by a clay-rich zone (up to 7 m thick) with progressive highly weathered material of lower hardness, reddish yellow color due to the presence of some goethite and hematite. It represents the coarse saprolite of the profile. The upper part of the profile is generally kaolinitic (up to 4.5 m thick) and represents the fine saprolite of the profile (Fig. 2B). The weathering profile of the Mesozoic basalts was sampled in the Tushkey area along the asphaltic road between Aswan and Abu Simbel. Basalts occur as moderately high hills of fine-grained dark gray to yellowish gray materials. Mainly basalts are weathered at the bottom. The weathered parts are composed of whitish gray, yellowish white, and reddish white clayey materials with the abundance of coarser quartz grains, and gray rock fragments represent relicts of the original basalts. The clayey materials fill the fractures of the less weathered basalts (Fig. 2C). The weathering profile representing the ESC rocks west of Aswan was taken from granitic rocks from Um Shaghair area west of Aswan. The profile is composed of approximately 10 m of white and yellowish white to grayish white soft kaolinitic materials with abundance of visible coarse-grained residual quartz grains. The kaolinitized section is covered with a thick sequence of cross-bedded brownish yellow wellsorted sandstone of the Jurassic–Cretaceous Nubia Formation (Fig. 2D). In Sinai area the basement rocks belong mainly to the Arabian-Nubian Shield. Be’eri-Shlevin et al. (2009) classified the basement rocks of ANS in Sinai area that could be a possible source of the kaolin deposits in Sinai into four suites. Alkaline (Al) suite that is composed of syenogranites, alkalifeldspar granites and associated dike swarms and volcanics, and minor monzogabbros and monzodiorites; postcollisional batholithic calc-alkaline (CA2) suite that is composed of granodiorites and monzogranites, some quartz-diorites and minor gabbros; late/syn-collisional batholithic calc that is composed of variably deformed quartz-diorites, gabbros, granodiorites, and associated intermediate to felsic volcanics; and island arc complexes (IAC) that is composed of metasediments, metavolcanics, migmatites, amphibolites, orthogneisses, and paragneisses, and all rocks metamorphosed at greenschist to amphibolite facies conditions (Fig. 1C).


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Fig. 1. A, Map of Egypt shows the location of the studied areas. B, Geological map of the southern part of Egypt (from Ali et al., 2009) showing the distribution of igneous and metamorphic rocks of the Arabian-Nubian Shield (ANS), East Sahara Craton (ESM), Mesozoic volcanic activity, and location of the studied saprolites as well as the pisolitic and plastic kaolin deposit in the Kalabsha area: 1, East Sahara Craton; 2, Phanerozoic volcanics; 3, metavolcanics and ophiolites; 4, granites; 5, gneiss and migmatites. C, Geological map of the Sinai Peninsula (after Shimron, 1980) showing the main igneous and metamorphic rock units, location of the studied saprolites, and the location of the Carboniferous and Cretaceous sedimentary kaolin deposits: 1, Phanerozoic sediments; 2, alkaline volcanics; 3, alkaline granites; 4, calc-alkaline granitoids; 5, metasediments; 6, gneisses.

Saprolite from the Babaa area occurs as a relatively thick profile (~70 m) of reddish to brownish soft clayey materials that overlie the less weathered yellowish gray metasediments that located at the entrance of Wadi Babaa (Fig. 2E). A few kilometers south to the Khaboba sedimentary kaolin deposits, hills of weathered schist are situated. The weathered profile is characterized by a clay-rich zone (up to 7 m thick) with progressive highly decomposed material of lower hardness, reddish yellow in color due to the presence of some Fe-oxides. Visible coarse-grained quartz grains and rock fragments showing the original foliation texture of the preexisting schist can be easily observed inside the clayey section. The weathered materials are in many cases overlain by a thick sequence of cross-bedded brownish yellow well-sorted sandstone of the Jurassic–Cretaceous Nubia Formation (Fig. 2F). At Wadi Abu Natash, east of the Carboniferous sedimentary kaolin of Abu Natash area, another weathered schist profile was measured. The profile is composed of approximately 15 m of whitish gray and yellowish gray clayey materials with the abundance

of visible coarse quartz grains as well as rock fragments showing the original foliation texture of the pre-existing schist. The weathered profile is also covered by a thick sequence of cross-bedded brownish yellow well-sorted sandstone of the Jurassic–Cretaceous Nubia Formation (Fig. 2G).

Materials and analytical methods Seven saprolite samples were collected from the two studied localities (three from the Sinai Peninsula and four samples from Aswan area). The clay fractions from the collected samples were subjected to detailed mineralogical and geochemical investigations. The clay fractions were separated from the saprolites treated with diluted HCl to dissolve any carbonates, then soaked in distilled water for ~2 weeks. During this period, the samples were ultrasonically treated three times (10–15 min each time) using a cleaning ultrasonic instrument and then

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Fig. 2. Macroscopic organization of saprolites developed upon different rock types in Aswan and Sinai areas. A, Saprolite from the Allaqi granite (Aswan); B, saprolite from the Abu Sobeirs schist (Aswan); C, saprolite from the Mesozoic basalts of the Tushkey area; D, saprolite from the ESC granites of the Um Shaghair area; E, saprolite from metasediments of the Babaa area (Sinai); F, saprolite from schist of the Khaboba area (Sinai); G, saprolite from schists of the Abu Natash area, Sinai.

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washed several times using distilled water till the formation of a suspension at pH ranging from 7 to 8. The clay fractions (