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Abstract Mineralogical and Geotechnical investigations were carried out on the weathered zones of the Basement rocks of Aswan Area, Egypt. The suitability of the composition of these zones in industrial applications were tested. The stratigraphic units recognized in the studied area comprise metamorphic (micaand hornblende-schists, amphibolites and gneisses) and igneous (minor intrusions, granites, granodiorite and epidiorites) rocks of Pre-Cambrian age; sandstones and clays belonging to the Nubian Sandstones Series of Upper Cretaceous age; gravels and sands and muds of Pleistocene and Recent ages. The most of weathering profiles developed on granitic rocks include the W2 (slightly weathered rock with discoloration in discontinuity surface), W3 (moderately weathered rock with less than half of the rock decomposed), W4 highly weathered rock with more than half of the material transformed to a soil) and W5 (completely weathered rock with all the material transformed to a soil but the original mass structure still largely intact) zones of weathering. The weathering profiles developed on the metamorphic rocks can be classified into two zones namely W4 and W5. The main petrographic alteration features recorded in weathered zones of granites of the studied area include: (1) fractured and fragmented quartz grains; (2) orthoclase coarse crystals with turbid surfaces; (3) microcrackes interspersed with clay minerals throughout the feldspar and mafic minerals; (4) potash-feldspar highly destroyed to fine grained of silica and clay minerals in the advanced stage of weathering process; (5) clay-filled vugs replacing plagioclase with progress weathering ; and (6) fissure systems characterized by inter-, intra-, and transgranular microcracks in plagioclase. The identified minerals in weathered materials (regoliths) can be categorized into two groups clay/phyllosilicate minerals and non clay minerals. The most dominant clay minerals are kaolinite, mica-illite, smectite, smectite-illite mixed layers and chlorite whilst the non-clay minerals are represented by quartz as the main mineral with remarkable amounts of feldspars (microcline, albite, anorthite and orthoclase, and with traceable amounts of iron oxides (hematite), alunite, anatase and calcite. Five types of clay minerals were identified throughout the clay fraction of the studied weathered materials, namely kaolinite, smectite, illite, smectite-illite mixedlayers and chlorite arranged according to their abundance. The non-clay minerals recorded include quartz, microcline, anatase, alunite and hematite. Kaolinite and quartz are the most abundant mineral in less than 2 micron fraction and the powdered whole samples of saprolite (regolith), SEM-EDX study confirms that (1) the feldspars (Plagioclase feldspar, K-feldspar), quartz, biotite, and muscovite are the main primary minerals in the studied regoliths, and (2) The main secondary minerals are kaolinite, illite, allunite and a smectitic material. The morphology of particles reveals irregular platelets, well-developed and irregular flakes, and booklets of kaolinite. The morphological features of some investigated samples give a good indication for a good crystallinity of kaolinite mineral. EDX analysis shows Al, and Si with nearly equal amounts and minor amount of K for kaolinite; K, Al, and Si for illite (or other mica); and Si, Al, K, and Ca for etched feldspar (orthoclase or plagioclase). EDX spectra of some samples indicate Fe, Al, Si, Mg and K present which are indicative of altered biotite or either goethite or hematite forming a thin coating on the kaolinite crystals. The textural disposition of the secondary minerals indicates important data about the processes of alteration undergone by the primary minerals. Mineralogical, chemical and microtextural analysis of the studied kaolin deposits showed that the progressive weathering of plagioclase and biotite of the parent rocks are the main source of kaolinite in the studied area. Well-preserved books and vermiform kaolinite characterize the studied kaolin deposits. The localized crystallization of kaolinite depending on the distribution of primary minerals strongly influenced the clay mineralogy of the studied weathering profiles. Excepting for SiO2, all the major element show a remarkable increase in content towards the top of these profiles. Trace and rare elements (Ba, Y, Sr, V, Eu, Zn, La, and Cr) tend to increase gradually upward. On the other hand, Ni, Nd, Sm, Ce, Yb and Zr show a general decrease towards the top of the profiles. The weathering indices values (CIA, CIW, PIA, V, WIP, R, SIT and MIA) of regoliths of these profiles correlated well with their mineralogy (i.e., the content of kaolinte as an indicator to intensive weathering of the regolith materials). The pH values of regolith samples show a wide range of values. LL ranges between 51 and 59; PL varies from 29 to 36 and the minimum of PI is 18 and its maximum is 29. The studied regolith can be characterized as medium expansive since the values of Atterberg limits for all samples fall within the range of medium degree of expansion. The plasticity charts show that studied regoliths belong mainly to the high plasticity inorganic clay groups. The general relationship between the clay content and the Atterberg limits show that the higher the clay content, the higher is the Atterberg limits. Also, these regoliths show that it is not sufficient to consider the liquid limit is a function of the smectite content but the other clay minerals need to be considered as well. The textural, chemical and mineralogical of whole rock data of the studied regolith have been evaluated by international standard specifications. The clays of Wadi Agabat, Wadi Abu Sobeira and West Aswan can be used for the production of cotto toscano (porous products), whereas the clays of Wadi Allaqi Road fall mainly in the red stoneware. Regarding the color (red, gray, purple) and the high iron oxide content, these kaolins cannot be used in fine ceramics. whereas, the clays of West Aswan regoliths only can be are suitable for paper filling and coating and paint filling. KEY WORDS: Granite; Mica schist; Weathering; Regolith; Texture; kaolinte ; Smectite;Illite; weathering indices; SEM analysis; EDX analysis; Atterberg limits; Plasticity, ceramic quality; Ceramics; Bricks; Paper coating, Paper filler. |