地理情報学と地球統計学: 概要

Geochemistry and Uranium Mineralization in Neoproterozoic Leucogranite of Gabal Homra Dom, SouthEastern Desert, Egypt

Gehad M Saleh, Ibrahim H Ibrahim, Ibrahim A Salem and Ibrahim B Abdel Kader

Gabal (G.) Homra Dom leucogranite crops out about 65 km south of Shalatin City, South Eastern Desert of Egypt. It is an elongated mass extending NNW-SSE, bounded by two major sinstral strike slip faults and mainly composed of monzogranite. They intrude amphibolites, metavolcanics and volcano-sedimentary associations. The southern eastern contact between G. Homra Dom leucogranite and the volcanosedimentary association is marked by a narrow sheared zone up to 5 m width. The sheared leucogranite samples are enriched with MgO, Na2 O, K2 O, Rb, Sr, Zr, Ba, V, Co in addition to Th and U and depleted in Al2 O3 if compared with the average of the fresh leucogranite. G. Homra Dom leucogranite exhibit calc-alkaline affinity and peraluminous to metaluminous compositions and could be generated by fractional crystallization of a granitic magma in lateto post collision granites. These are produced by circulation of fluids and alkali loss by vapor-phase transfer during late magmatic stage. The higher temperatures of the apatite model (950–1080° C) probably represent the initial temperature of the melt, whereas the lower temperature estimates from zircon suggests that these leucogranite was initially undersaturated with respect to zircon and hence the calculated temperature would not closely resemble original magmatic temperatures. The Homra Dom leucogranite were formed by partial melting of metagraywackes that are found in deeper part of the crust of the Arabian Nubian Shield. The relationship between eU versus eTh and eU/eTh ratio versus eTh and eU reflect strong positive relation along sheared leucogranite which means that eU/eTh ratio tends to increase with uranium mobilization and post magmatic redistribution. The minerals cassiterite, molybdenite and wolframite with the secondary uranium minerals (uranophane) are identified by Environmental Scanning Electron Microscope (ESEM) and XRD. These minerals are formed at the end of magmatic stage, where the mineralized fluids enriched with Bi, W, Sn, Mo and F rises as post magmatic hydrothermal episode along the south eastern contact.