الفهرس 
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Abstract
In the basement rocks, the distribution of the opaque minerals (OM) and their intergrowths are controlled by their chemical composition and physical properties, as well as by the rate of cooling of the parent magma. Recently, OM have been experimentally shown to be very sensitive to changes in temperature and pressure even those prevailing under surface conditions. In the present study, OM assemblages of some selected basement rock units from Southern Sinai were defined and studied in order to be used as a tool to differentiate between these different rock types. Polished sections were prepared from the selected rock units following their study in the field and in thin sections. The units selected included the gneisses and related rocks, continental margin volcanics and associated sediments, more than one suite of granites and some intraplate gabbroic intrusions. OM were identified by the ore microscope and SEMEDAX. Each rock type dealt with here is characterized by a specific OM assemblage. Gneisses are characterized by homogenous ilmenite, hematiteilmenite and rutileilmenitehematite exsolution. The second mineral is magnetite, either as homogenous magnetite or as ulvospinelmagnetite exsolution. Volcanics are characterized by containing magnetite (common) and ilmenite in quartzandesite, and magnetite, ilmenite and some ilmenitemagnetite exsolutions, in rhyodacite, whereas the rhyolite is characterized by containing only magnetite. As to the granites; GI granites contain titanomagnetite, exsolved magnetite (ilmenitemagnetite exsolutions) and ilmenite, exsolved ilmenite (hematiteilmenite and ilmenitehematite exsolutions), GII granite hosts an increasing amount of titanomagntite, while very few grains of ilmenitemagnetite exsolution is found in GIII granite. The intraplate gabbroic rocks are rich in magnetite, (ilmenitemagnetite exsolutions), ilmenite, (hematiteilmenite and ilmenitehematite intergrowths), rutile and some appreciable amount of sulphides, mainly chalcopyrite and pyrite. Some samples were taken from two rock types at Wadi Feiran to perform microprobe analyses of irontitanium oxides; a) The basic dykes cutting through the gneisses and migmatites and b) The amphibolites. Results are here presented. In conclusion, opaque mineralogy could be used as a simple and specific petrogenetic too1.