Mineralogy, geochemistry and age dating of shear zone-hosted Nb-Ta-, Zr-Hf-, Th-, U-bearing granitic rocks in the Ghadir and El-Sella areas, South Eastern Desert, Egypt  

作　　者：Ali M.A. Lentz D.R.2 

机构地区：[1]Nuclear Materials Authority [2]Depatment of geology,University of New Brunswick

出　　处：《Chinese Journal Of Geochemistry》2011年第4期453-478,共26页中国地球化学学报

基　　金：supported by a NSERC Discovery grant to Prof. Dr. David Lentz at Geological Department,University of New Brunswick (UNB),Fredericton,New Brunswick,Canada

摘　　要：The rare metal minerals of mineralized altered granites within the Ghadir and El-Sella shear zones, are represented by betafite, U-minerals (uraninite and uranophane), zircon, monazite, xenotime, and rutile in the Ghadir shear zone. While they are columbite-tantalite minerals as ferrocolumbite, pyrochlore, and fergusonite, Th-minerals (cheralite, uranothorite, and huttonite monazite), Hf-zircon, monazite and xenotime in the El-Sella shear zone. Hf-zircon in the El-Sella and Ghadir shear zones (increasing from the core to the rim) contains high inclusions of U-Th, and REE minerals such as cheralite, uranothorite, huttonite monazite and xenotime especially in the El Sella shear zone. The rare-metal minerals, identified from peralkminous granites of the shear zones are associated with muscovite, quartz, chlorite, fluorite, magnetite, and biotite that are restricted to the two shear zones. Uraninite (low Th content) occurring in the Ghadir shear zone indicates the hydrothermal origin, but there are thorite, uranothorite, cheralite, and Hf-zircon in the El Sella shear zone, also indicating the hyrothermal proccess after magmatic origin. Compositional variations of Ta/(Ta+Nb) and Mn/(Mn+Fe) in columbite from 0.07-0.42 and 0.04-0.33, respectively, and Hf contents in zircon are so high as to be 12%, especially in the rim in the El Sella shear zone. This feature re-flects the extreme degree of magmatic fractionation. Four samples from the altered granites of the Ghadir shear zone also are very low in TiO2 (0.04 wt%-0.17 wt%), Sr [(82-121)×10-6], and Ba [(36-380)×10-6], but high in Fe2O3T (0.46 wt%-0.68 wt%), CaO (0.64 wt%-1.23 wt%), alkalis (8.59 wt%-8.88 wt%), Rb [(11-203)×10-6], Zr [(98-121)×10-6], Nb [(9-276)×10-6], Ta [(2-139)×10-6], U [(14-63)×10-6], Th [(16-105)×10-6], Pb [(13-32)×10-6], Zn [(7-8)×10-6], Y [(15-138)×10-6], Hf [(3-9)×10-6], and ∑REE [(81-395)×10-6, especially LREE [(70-322)×10-6]. They are very high in Zr/Hf (15.07-85.96) and Nb/Ta (7.17-21.48), and low in Rb/Sr (2.56-3.36) and Th/U (The rare metal minerals of mineralized altered granites within the Ghadir and E1-Sella shear zones, are represented by betafite, U-minerals （uraninite and uranophane）, zircon, monazite, xenotime, and rutile in the Ghadir shear zone. While they are columbite-tantalite minerals as ferrocolumbite, pyrochlore, and fergusonite, Th-minerals （cheralite, uranothorite, and huttonite monazite）, Hf-zircon, monazite and xenotime in the El-Sella shear zone. Hf-zircon in the E1-Sella and Ghadir shear zones （increasing from the core to the rim） contains high inclusions of U-Th, and REE minerals such as cheralite, uranothorite, huttonite monazite and xenotime especially in the El Sella shear zone. The rare-metal minerals, identified from peralkminous granites of the shear zones are associated with muscovite, quartz, chlorite, fluorite, magnetite, and biotite that are restricted to the two shear zones. Uraninite （low Th content） occurring in the Ghadir shear zone indicates the bydrothermal origin, but there are thorite, uranothorite, cheralite, and Hf-zircon in the E1 Sella shear zone, also indicating the hyrothermal proccess after magrnatic origin. Compositional variations of TaJ（Ta＋Nb） and Mn/（Mn＋Fe） in columbite from 0.07-0.42 and 0.044）.33, respectively, and Hf contents in zircon are so high as to be 12%, especially in the rim in the E1 Sella shear zone. This feature re- flects the extreme degree of magmatic fractionation.

关 键 词：剪切带 矿物学 花岗岩 钽矿物 锆石 钽铌 地球化学 蝶 

分 类 号：P597.3[天文地球—地球化学]