The Igla Sn-(W-Be) deposit, Egypt: Prolonged magmatic-metasomatic processes during the middle stage evolution of the Arabian-Nubian Shield
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| Authors: | Zoheir, Basem; Carr, Patrick; Xu, Xinyue; Zeh, Armin; Kraemer, Dennis; McAleer, Ryan; Steele-MacInnis, Matthew; Ragab, Azza; Deshesh, Fatma |
| Year: | 2025 |
| Journal: | Gondwana Research 142: 20-43 Article Link (DOI) |
| Title: | The Igla Sn-(W-Be) deposit, Egypt: Prolonged magmatic-metasomatic processes during the middle stage evolution of the Arabian-Nubian Shield |
| Abstract: | The Igla Sn-(W-Be) deposit in the Central Eastern Desert of Egypt is associated with a suite of granitic rocks, including monzogranite, granophyric granite, and porphyritic leucogranite. These rocks belong to a calcic to calc-alkalic series, characterized by low Mg# values and low Ti and P concentrations. Monzogranite and granophyric granite show features typical of fractionated volcanic-arc I-type granites, while the leucogranite, with its distinct Rb/Ba, K/Rb, and Ga/Al ratios, is classified as a highly evolved A-type granite. Mineralization at Igla mine includes cassiterite and wolframite, along with minor molybdenite, arsenopyrite, columbite, and tourmaline, mainly hosted in beryl ± topaz-quartz veins and miarolitic cavities within greisen and silica-rich stockwork. Zircons from the monzogranite show LREE enrichment, moderate positive Ce anomalies, and moderately oxidizing conditions (ΔFMQ ≃ 1.75), while granophyric granite zircons exhibit higher HREE enrichment and more oxidizing conditions (ΔFMQ ≃ 1.04). Leucogranite zircons have the highest REE concentrations, more pronounced negative Eu anomalies, and distinctly reducing conditions (ΔFMQ ≃ -0.06). U–Pb dating of zircon and xenotime reveals concordant 206Pb/238U ages of 708.7 ± 2.0 Ma for monzogranite, 701.3 ± 1.5 Ma for the granophyric granite, and a noticeably younger age for the leucogranite (605.1 ± 2.4 Ma). Petrography and microchemistry of cassiterite reveal two distinct stages: an earlier generation (Cst-I) with straight oscillatory zoning, and a later chaotically zoned generation (Cast-II) that overgrows and crosscuts the former. U-Pb dating confirms two discernable age populations: Cst-I, with a weighted mean 206Pb/238U age of 637.4 ± 1.4 Ma; and Cst-II ages scatter from 605 to 588 Ma, partially overlapping with the leucogranite formation. Wolframite, although less precisely dated at 615.3 ± 4.3 Ma, suggests rejuvenated tectonics, magmatism, and hydrothermal activities, culminating in the formation of Cst-II. Primary aqueous fluid inclusions in quartz indicate deposition from a low-salinity aqueous fluid with undetectable dissolved gas, while trails of aqueous-carbonic inclusions with slightly higher salinity and appreciable gas (CO2, CH4) contents occur together in the same crosscutting trails with arsenopyrite and bismite inclusions. The variable contents of CO2 and CH4 in these inclusions suggest that carbon redox equilibria within the ore-forming fluid may have played a pivotal role in linking redox potentials, facilitating the deposition of arsenopyrite, bismite, and Cst-II. The improved age constraints highlight the role of highly evolved transcrustal magmatism in mobilizing and upgrading early rare metal concentrations, coinciding with the ∼ 650–600 Ma geodynamic transition in the Arabian-Nubian Shield. Crustal thinning, partial melting of older granitoids, and prolonged magmatic-hydrothermal interactions were key in ore formation and upgrading. |
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