Home – Home – Jornals – Russian Geology and Geophysics 2014 number 12

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. Schist-derived saprolites are composed of kaolinite in some cases and of a mixture of kaolinite, illite, and chlorite in the other. Saprolite from the basalts is characterized by relatively higher contents of TiO ₂ and Ni compared to saprolites from the granites. Saprolites from the granites have higher contents of Ba, Li, Pb, Sr, Th, Y, and Zr compared with those of the saprolites from the basalts and schists. Saprolites from different schists show variations in the distributions of many constituents, such as TiO ₂, Cr, Ni Ba, Y, and Zr. Although chondrite-normalized rare-earth element (REE) patterns are characterized by relative enrichments in light rare-earth elements (LREE) compared to heavy rare-earth elements (HREE) in all saprolites, granitic saprolites show negative Eu anomalies, while saprolites from the basalt have no Eu anomaly. The REE patterns of saprolites from the schists exhibit slight positive Ce anomalies and slight to moderate negative Eu anomalies. Weathering of saprolites from the basalt and metasediments is classified as bisiallitization type, while weathering of saprolites from the granite is allirization type. Saprolites from the schists vary from bisiallitization (Aswan and Abu Natash) to allirization (Khaboba) type. Saprolites from the Khaboba schist can be considered the possible source of the Carboniferous kaolin deposits in the Hasber and Khboba areas of Sinai, based on the similarity in the mineralogy and geochemistry of major, trace, and rare-earth elements 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 from the similarity in the mineralogy and geochemistry of the granitic saprolites and the kaolin deposits.