hide
Free keywords:
-
Abstract:
Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian–Nubian Shield (ANS), six samples from five rare-metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U–Pb ages and O-isotopic compositions as well as whole-rock Sr- and Nd- and alkali feldspar Pb-isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwing-shaped REE patterns and strongly negative Eu anomalies. Four granites gave mantle-like zircon 18OV-SMOW between 4.2 and 5.96‰ and yielded ages of 628–633 Ma. This is about when subduction-related magmatism began to be replaced by collision-related magmatism. Igla Ahmr granites are older, formed at 691.7–678.9 Ma with 18OV-SMOW c. 5.95‰. All have positive initial Nd values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared with unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and unmineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics
