Geochemistry of lamprophyres associated with uranium mineralization, Southeastern Desert, Egypt

Mohamed E. Ibrahim, Mohamed M. El-Tokhi, Gehad M. Saleh, Mamdouh A. Hassan, Mohamed A. Rashed

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)356-365
Number of pages10
JournalChinese Journal of Geochemistry
Volume26
Issue number4
DOIs
Publication statusPublished - Nov 2007

Keywords

  • Cataclastic rock
  • Egypt
  • Hydrothermal alteration
  • Lamprophyre
  • Shear zone
  • South eastern Desert

ASJC Scopus subject areas

  • Geochemistry and Petrology

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