| Geochemistry of lamprophyres associated with uranium mineralization, Southeastern Desert, Egypt |
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| 作者姓名： | Mohamed E. Ibrahim Mohamed M. El-Tokhi Gehad M. Saleh Mamdouh A. Hassan |
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| 作者单位： | Nuclear Materials Authority P. O. Box 530 El Maadi Cairo Egypt，Geology Deprtment Faculty of Science United Arab Emirates University United Arab Emirates，Nuclear Materials Authority P. O. Box 530 El Maadi Cairo Egypt，Nuclear Materials Authority P. O. Box 530 El Maadi Cairo Egypt，Nuclear Materials Authority P. O. Box 530 El Maadi Cairo Egypt |
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| 摘 要： | Two brecciated shear zones (NNW-SSE) are found crosscutting cataclastic rocks. The cataclastic rocks (3.0 km2) occupy the core of the granitic pluton and enclose a roof pendant of mafic-ultramafic rocks. The NNW-SSE-extending lamprophyre dykes vary in thickness from 0.5 m to 1 m and up to 800 m long, cutting the cataclastic rocks and are composed mainly of plagioclases, amphiboles, relics of pyroxenes and K-feldspar phenocrysts embedded in fine-grained groundmass. They are characterized as being peraluminous, calc-alkaline in composition (chemical trap) and enriched in calcite, sulfide and P2O5. The lamprophyres were affected by hydrothermal alteration (chlorite-carbonate alteration) while the cataclastic rocks were affected by diagenetic alteration (K-feldspar-albite alteration). Uranium mineralization is the product of hydrothermal events and has been investigated by X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), involving primary uranium minerals (U3O8) and secondary uranium minerals (uranophane and beta-uranophane, kasolite, torbernite, autonite and meta-autonite) in addition to U- bearing minerals (astrocyanite, betafite and fergusonite). The presence of different mineral parageneses associated with clay minerals indicates that the lamprophyres were subjected to acidic and alkaline mineralizing solutions. Moreover, the U-Zr/U, U-Ce/U values show negative correlations, confirming U-enrichment in both cataclastic rocks and shear zones while the Th-eU/eTh, Th-Zr/Th and Th-Ce/Th values show negative correlations, indicating that the U-bearing solutions are rich in Th in the cataclastic rocks only.
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| 关 键 词： | 碎裂岩石 剪切区域 煌斑岩 热液蚀变 埃及 西南地区 沙漠地带 |
| 收稿时间： | 14 August 2006 |
| 修稿时间： | 2006-08-14 |
Geochemistry of lamprophyres associated with uranium mineralization,Southeastern Desert,Egypt |
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| Mohamed E. Ibrahim Mohamed M. El-Tokhi Gehad M. Saleh Mamdouh A. Hassan.Geochemistry of lamprophyres associated with uranium mineralization, Southeastern Desert, Egypt[J].Chinese Journal of Geochemistry,2007,26(4):356-365. |
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| Authors: | Mohamed E Ibrahim Mohamed M El-Tokhi Gehad M Saleh Mamdouh A Hassan Mohamed A Rashed |
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| Institution: | (1) Nuclear Materials Authority, P. O. Box 530, El Maadi, Cairo, Egypt;(2) Geology Department, Faculty of Science, United Arab Emirates University, United Arab Emirates |
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| Abstract: | Two brecciated shear zones (NNW-SSE) are found crosscutting cataclastic rocks. The cataclastic rocks (3.0 km2) occupy the core of the granitic pluton and enclose a roof pendant of mafic-ultramafic rocks. The NNW-SSE-extending lamprophyre dykes vary in thickness from 0.5 m to 1 m and up to 800 m long, cutting the cataclastic rocks and are composed mainly of plagioclases, amphiboles, relics of pyroxenes and K-feldspar phenocrysts embedded in fine-grained groundmass. They are characterized as being peraluminous, calc-alkaline in composition (chemical trap) and enriched in calcite, sulfide and P2O5. The lamprophyres were affected by hydrothermal alteration (chlorite-carbonate alteration) while the cataclastic rocks were affected by diagenetic alteration (K-feldspar-albite alteration). Uranium mineralization is the product of hydrothermal events and has been investigated by X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), involving primary uranium minerals (U3O8) and secondary uranium minerals (uranophane and beta-uranophane, kasolite, torbernite, autonite and meta-autonite) in addition to U- bearing minerals (astrocyanite, betafite and fergusonite). The presence of different mineral parageneses associated with clay minerals indicates that the lamprophyres were subjected to acidic and alkaline mineralizing solutions. Moreover, the U-Zr/U, U-Ce/U values show negative correlations, confirming U-enrichment in both cataclastic rocks and shear zones while the Th-eU/eTh, Th-Zr/Th and Th-Ce/Th values show negative correlations, indicating that the U-bearing solutions are rich in Th in the cataclastic rocks only. |
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| Keywords: | cataclastic rock shear zone lamprophyre hydrothermal alteration Southeastern Desert Egypt |
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