| Geologic relationships and mineralization of peralkaline/alkaline granite-syenite of the Zargat Na＇ am ring complex, Southeastern Desert, Egypt |
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| 基金项目： | The author is deeply grateful to the Profs. A.H. Hashad, M.E. Ibrahim, H. Sato and S.A. E1-Nisr for providing the great facilities during the progress of this work. |
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| 摘 要： | The Zargat Na’ am ring complex crops out 90 km NW of Shalatin City in the Southeastern Desert of Egypt. The ring complex forms
a prominent ridge standing high above the surrounding mafic-ultramafic hills. It is cut by two sets of joints and faults which
strike predominantly NNW-SSE and E-W, and is injected by dikes, porphyritic alkaline syenites, and felsite porphyries. It
consists of alkali syenites, alkali quartz syenites, and peralkaline arfvedsonite-bearing granitic and pegmatitic dikes and
sills. The complex is characterized locally by extreme enrichments in REEs, wolframite and rare, high field strength metals
(HFSM), such as Zr and Nb. The highest concentrations (1.5 wt% Zr, 0.25 wt% Nb, 0.6 wt% Σ REEs) occur in aegirine-albite aplites
that formed around arfvedsonite pegmatites. Quartzhosted melt inclusions in arfvedsonite granite and pegmatite provide unequivocal
evidence that the peralkaline compositions and rare metal enrichments are primary magmatic features. Glass inclusions in quartz
crystals also have high concentrations of incompatible trace elements including Nb (750 ￠ 10−6), Zr (2500 × 10−6) and REEs (1450 × 10−6). The REEs, Nb and Zr compositions of the aegirine-albite aplites plot along the same linear enrichment trends as the melt
inclusions, and Y/Ho ratios mostly display unfractionated, near-chondritic values. The chemical and textural features of the
aegirine-albite aplites are apparently resultant from rapid crystallization after volatile loss from a residual peralkaline
granitic melt similar in composition to the melt inclusions.
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| 关 键 词： | 花岗岩 埃及 矿化作用 地质条件 |
Geologic relationships and mineralization of peralkaline/alkaline granite-syenite of the Zargat Na’ am ring complex, Southeastern Desert, Egypt |
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| Authors: | Gehad M Saleh |
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| Institution: | (1) Nuclear Materials Authority, P. O. Box: 530 EL Maadi, Cairo, Egypt |
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| Abstract: | The Zargat Na’ am ring complex crops out 90 km NW of Shalatin City in the Southeastern Desert of Egypt. The ring complex forms
a prominent ridge standing high above the surrounding mafic-ultramafic hills. It is cut by two sets of joints and faults which
strike predominantly NNW-SSE and E-W, and is injected by dikes, porphyritic alkaline syenites, and felsite porphyries. It
consists of alkali syenites, alkali quartz syenites, and peralkaline arfvedsonite-bearing granitic and pegmatitic dikes and
sills. The complex is characterized locally by extreme enrichments in REEs, wolframite and rare, high field strength metals
(HFSM), such as Zr and Nb. The highest concentrations (1.5 wt% Zr, 0.25 wt% Nb, 0.6 wt% Σ REEs) occur in aegirine-albite aplites
that formed around arfvedsonite pegmatites. Quartzhosted melt inclusions in arfvedsonite granite and pegmatite provide unequivocal
evidence that the peralkaline compositions and rare metal enrichments are primary magmatic features. Glass inclusions in quartz
crystals also have high concentrations of incompatible trace elements including Nb (750 ￠ 10−6), Zr (2500 × 10−6) and REEs (1450 × 10−6). The REEs, Nb and Zr compositions of the aegirine-albite aplites plot along the same linear enrichment trends as the melt
inclusions, and Y/Ho ratios mostly display unfractionated, near-chondritic values. The chemical and textural features of the
aegirine-albite aplites are apparently resultant from rapid crystallization after volatile loss from a residual peralkaline
granitic melt similar in composition to the melt inclusions. |
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| Keywords: | geologic relationship mineralization of peralkaline/alkaline granite-syenite Zargat Na’ am ring complex Southeastern Desert Egypt |
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