Petrogenesis and evolution of the Nuweibi rare-metal granite, Central Eastern Desert, Egypt

Abstract

The Nuweibi rare-metal granite in the Central Eastern Desert of Egypt is highly evolved fine- to medium-grained leucogranite affected by pervasive albitization and greisenization. The intrusion holds an important tin–tantalum resource in the Egyptian Eastern Desert. Columbite–tantalite and cassiterite disseminations occur within the granite body, while the quartz ± feldspar veins cutting across the Nuweibi granite host only cassiterite disseminations. Microscopically, quartz and alkali-feldspar are the essential mineral constituents of Nuweibi granite, with minor mica (muscovite + rare biotite), while cassiterite, columbite–tantalite, zircon, allanite, beryl, tourmaline, titanite, and fluorite are accessories. Whole-rock geochemistry and micoanalytical data together with laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) dating of zircon and columbite have been used to constrain the evolution of the granite intrusion and associated mineralization. The Nuweibi granite is weakly peraluminous with extremely low MgO, CaO, TiO2, P2O5, Ba, and Sr contents and elevated Sn, Ta, Nb, and Rb contents. The REE patterns exhibit distinct tetrad effects, as well as negative Eu and Y anomalies. Also, the bulk rock Zr/Hf ratios are consistently < 10. The Nd isotopic system is disturbed and eNd values suggest a juvenile mantle and/or Neoproterozoic crustal source. The U–Pb system in zircon is disturbed and leaked continuously, while the U–Pb age of columbite is ~ 620 Ma. The geochemical and isotopic systematics of the Nuweibi intrusion reflect very advanced degree of fractionation combined with late magmatic fluid overprint which redistributed Sn and other mobile elements, while Ta still characterizes the igneous system.