الفهرس | Only 14 pages are availabe for public view |
Abstract The study area (W. El Gemal -W. Sikait area) is located at the southern part of the Eastern Desert of Egypt at about 50 km south of Marsa Alam coastal city. It is easily accessible through the Red Sea Highway (Marsa Alam-Halayb coastal asphaltic road) and then extends westward at the eastern entrance of W. El Gemal desert track and is included in the protected area. The main aim of this thesis is to study geology, geochemistry, and the application of remote sensing imagery for studying the potentiality of mineralization in the W. El Gemal-W. Sikait area. The area was not previously subjected to discriminating its lithology and mapping through remote sensing data. Consequently, Landsat-8 OLI data was chosen in the present study because the Swath width is 185 km and therefore it is useful in the regional mapping. Fieldwork was carried out at W. El Gemal-W. Sikait area for sampling, descriptions, photographs of the exposed lithological units, the different field observation relationships between the rock units, and verified remote sensing data for a good mapping. Moreover, the main rock units of the study area are arranged from older to younger as follows: The gneiss rocks, ultramafic rocks, ophiolitic metagabbros, ophiolitic mélange, metasedimentsmetavolcanics association, older granites, younger gabbros, and younger granites. All the previously mentioned rock types are mostly traversed by post-granite dykes and veins. Petrographically, the metagabbro rocks are composed of plagioclase, hornblende, actinolite, biotite, and quartz. Titanite and opaques are accessories. Epidote and chlorite are secondary minerals. The metasediments are represented by actinolite schist, hornblende schist, and biotite hornblende schist. Actinolite schist is composed of actinolite, hornblende, quartz, and plagioclase. Opaques and antigorite are the accessory and secondary III minerals respectively. Hornblende schist is composed of hornblende, plagioclase, quartz, and augite. Opaques and apatite are accessory minerals. Chlorite and saussurite are secondary minerals. Biotite hornblende schist is composed of hornblende, plagioclase, biotite, and quartz. Titanite and opaques are accessory minerals, whereas chlorite occurs as a secondary mineral. Metavolcanics are represented only by metadacite and are composed of plagioclase, quartz, K-feldspar, and biotite. Titanite and opaques occur as accessory minerals. Epidote is a secondary mineral. The granitic rocks are represented by older granites (quartz diorite and granodiorite) and younger granites (biotite granite). Quartz diorite is composed of plagioclase, quartz, biotite, and K-feldspar. Titanite, zircon, apatite and opaques are accessories. Chlorite and saussurite are secondary minerals. Granodiorite is composed of plagioclase, quartz, K-feldspar, biotite, and hornblende. Zircon, titanite, apatite, and opaques are accessories. Chlorite and sericite are secondary minerals. Biotite granite is composed of K-feldspar, quartz, plagioclase, and biotite. Zircon, titanite, apatite, and opaques are present as accessories. Chlorite existed as a secondary mineral. Geochemical characteristics were carried out through the analysis of 19 samples of the metagabbros, hornblende schist, metadacite, and granodiorite and biotite granite for major oxides, trace, and REEs. Geochemical studies indicated that the metagabbro rocks are tholeiitic to calc-alkaline either formed in the MORB setting modified by arc-related magmas or formed in back-arc environment and display subduction zone trace element signatures as a variable enrichment of LILE over HFSE, LREEs over HREEs and negative Nb anomalies. The investigated hornblende schist samples are Feshale immature material derived from andesitic arc source rock formed in oceanic island arc setting. The REE pattern of the hornblende schist samples shows approximately strong enrichment of the LREEs relative to HREEs with positive Eu anomaly. The metadacite are calc-alkaline metaluminous IV formed in the active continental margin setting. The REE pattern of metadacite samples displays a flat pattern with slight enrichment of the LREEs relative to HREEs and negative Eu anomalies. The investigated samples from older granites (granodiorite) are calc-alkaline peraluminous formed in volcanic arc setting, while the younger granites (biotite granite) are shoshonitic peraluminous formed in post-collision setting. The investigated granitic samples show enrichment of LREE relative to HREEs with positive and negative Eu anomalies for granodiorite and biotite granite respectively. The biotite granite REEs pattern shows less fractionated LREEs and HREEs relative to granodiorite. High abundances of LREEs in granodiorites are compatible with the presence of allanite accessory mineral observed petrographically contrary to high a bundances of HREEs observed in biotite granite which may be due to the presence of zircon-bearing HREEs. A Field radiometric survey has been carried out by “RS-230 gamma-ray spectrometer” for eU (ppm), eTh (ppm), and K%. The radiometric survey was greatly compatible with the alteration maps, where areas that significantly have higher iron oxides and hydroxides (hematite Fe2O3 and goethite FeO-OH) content. The gneiss rocks at W. Abu Rusheid have a higher radioactive content than granite rocks that appear at W. El Gemal and W. Abu Rusheid area. The radioactive content of granite rocks was natural, except the mineralized biotite granites at W. Abu Rusheid area show very high anomalies compared with other granite rocks at W. El Gemal and W. Abu Rusheid area. The heavy minerals were separated using heavy liquid (bromoform) separation technique from selected samples and picked under a binocular microscope and identified by Scanning Electron Microscope, energy dispersive spectrometry (SEM-EDX) technique. The identified minerals from the different anomalies in the rock types are gold, pyrite, ilmenite, galena, zircon, allanite, columbite, and apatite. The occurrence of gold V mineralization as fine-grained gold association with pyrite in metagabbro rocks suggests their formation as a result of chemical interaction between the hydrothermal solutions and the host rocks. where the interaction of the sulfur-bearing fluid with the iron-bearing host rocks form pyrite (FeS2) in cubic shape is an effective process, whereas the fined-grained gold was precipitated associated with pyrite at the contact between metagabbro rocks and metasediments-metavolcanics association |