Geochemistry and radioactivity of mineralized pegmatite from Abu Rusheid area, South Eastern Desert, Egypt

الملخص EN

The mineralized pegmatite of Abu-Rusheid area, S.

Eastern Desert, has quartz core and feldspars and mica margins.

This pegmatite was analyzed by the Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) to determine the content of the major and trace elements including the rare earth elements (REE).

The mineralized pegmatite vein trends NNW-SSE with dip of about 10-30˚ due WSW.

It is emplaced parallel to foliation and banding of the cataclastic country rocks.

The studied pegmatite is classified as rare metals-enriched and shows a zonal distribution from the barren core to the mineralized wall-zone in the metals ; Nb, Ta, Zr, Hf, Th, U, Y and Ga.

The main carriers of the trace metals are zircon, rutile, columbitetantalite, Samar skite and other REE and Th-U minerals.

Cassiterite, chlorite, deep violet fluorite, calcite, goethite, hematite, pyrite, magnetite, zinnwaldite, and phlogobite, are the main accessory minerals.

The studied pegmatite is highly differentiated, NYF-type and characterized by high FeO / MgO ratio with high concentration of Nb, Y, Zr, Th, U, REE (except Eu), and Ga.

It is derived from Fenriched Proterozoic crustal source depleted in Cs, B and P.

The rock is per aluminous and highly fractionated and had been affected by hydrothermal alteration.

The pegmatite displays clear M-type tetrad effect of the REE.

The calculated tetrad effect in the pegmatite of Abu-Rusheid demonstrates clear tendency towards the ratios of the common isovalents such as Zr/Hf, Nb / Ta and Y / Ho.

However, the tetrad effect seems not to be mutual with the content of Na2O and Rb / Sr.

The absence of coherence between tetrad effect and soda content may indicate insignificant role of the Na-metasomatism in developing the tetrad effect.

The pegmatite has a prominent negative Eu anomaly and excessively low K / Rb ratio.

The radioactivity of the studied pegmatite is related to a) uranium mineral (autunite), b) thorium minerals (thorite, thorianite and uranothorite) and c) accessories minerals (zircon, allanite, xenotime, monazite, fluorite, columbite and samar skite).

The potential anomalous radioactivity in the pegmatite of Abu Rusheid is attributed to both magmatic and hydrothermal processes.