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Facies Analysis and Biostratigraphy of the Miocene Sequence,Cairo-Suez District,Egypt

Journal of Earth Science 2017年第1期28卷 1-8页

作者： Abdelbaset El-Sorogy Mohamed Abd-Elmoneim Ahmed Mowafi Khaled Al-Kahtany hisham gahlan Department of Geology and Geophysics College of Science King Saud University Riyadh 11451 Saudi Arabia Geology Department Faculty of Science Zagazig University Zagazig 44519 Egypt

Miocene siliciclastic-carbonate deposits are widely exposed in Cairo-Suez District, Egypt. These deposits are underlain and overlain by continental sediments of Oligocene and post Miocene, respectively. Three stratigraphic sections were investigated at Gabals Geneife, Homeira and Gharra. Lithostrtigraphically, the Miocene sequence could be differentiated into two main rock units representing shallow deposits with relatively intermittent deep marine incursions. These are from base to top, Gharra Formation and Genefe Formation. Detailed macrofossils investigations led to the recognition of four macrofossil zones, namely Alectryonella plicatula-Crassostrea frondosa Range Zone, Echinolampas amplus-Scutella ammonis Range Zone, Chlamys（Macrochlamys） sardoa-Chlamys（Argopecten） submalvinae Range Zone, and Chlamys gentoni-Pecten（Oppenheimopecten） benedictus-Pecten（P.） ziziniae Assemblage Zone. Microfacies analysis and identified taxa indicated that the Miocene sequence was deposited in transgressive-regressive cycles ranged from near shore, warm shallow inner to middle shelf marine environments with storm influence during the accumulation of the oyster banks.

关键词： facies analysis biostratigraphy Miocene Cairo-Suez District Egypt.

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Geochemistry,Petrogenesis and Alteration of Rare-Metal-Bearing Granitoids and Mineralized Silexite of the Al-Ghurayyah Stock,Arabian Shield,Saudi Arabia

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Journal of Earth Science 2023年第5期34卷 1488-1510页

作者： hisham A.gahlan Mokhles K.Azer Paul D.Asimow Mansour H.Al-Hashim Department of Geology and Geophysics College of ScienceKing Saud UniversityRiyadh 11451Saudi Arabia Geological Sciences Department National Research CentreCairoEgypt Division of Geological&Planetary Sciences California Institute of TechnologyPasadena CA 91125USA

New data are presented for the rare-metal bearing A-type granitoids of the AlGhurayyah stock in the northwestern segment of the Arabian Shield, a composite pluton intruding metamorphosed volcano-sedimentary successions of the Silasia Formation. Metals in the granitoids are variably enriched, with up to 1 990 μg/g Zn, 7 680 μg/g Zr, 2 316 μg/g Nb, 232 μg/g Ta, 485 μg/g Hf, 670 μg/g Th, 137 μg/g U and 1 647 μg/g total rare earth elements(REE). The silexite is highly mineralized and yields higher maximum concentrations of several metals than the granitoids, including up to 1 860 μg/g Y, 9 400 μg/g Zr, 878 μg/g Hf, 1 000 μg/g Th, and 2 029 μg/g total REE. The Al-Ghurayyah stock has been assigned to an intraplate setting. Lithospheric delamination led to generation of mantle melts that supplied heat to melt the juvenile crust of the ANS. The fluorine and rare-metal enriched parental magma evolved by fractional crystallization. The quartz-rich silexite, distinct in character from ordinary hydrothermal vein quartz, is inferred to be co-genetic with the granitoids on the basis of their similar REE patterns;it is interpreted as a small volume of residual magma enriched in SiO2, volatiles, and trace metals. Mineralization took place both at the magmatic stage and later during a hydrothermal stage that concentrated these elements to economic grades.

关键词： Arabian Shield Al-Ghurayyah rare metals silexite peralkaline granite hydrothermal metasomatism

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