Patrological, geochemical and strontium signature for a pan-african rare-etal zoume granite in the Tibisti assif , Southern Libya

الملخص EN

The Zouma stock is amazonite-bearing, epizonal granite intruded into the Middle to Late Proterozoic metamorphic belt of Lower Tibistian Series and the Super Tibistian Magmatic Series (STMS) on the northeastern fringe of the Tibisti Massif.

The stock is exposed over a circular area of about 2 km2.

The Zouma stock is comagmatic with other Cambrian (531-550 Ma) post-orogenic granites and their cogenetic volcanics of the Eghei Magmatic Series (EMS).

This stock is highly differentiated amazonite granite.

This granite is affected by a strong albitization, microlization, and amazonitization met somatic processes.

The Zouma granite is inequigranular, medium grained, contains quartz, green microcline (amazonite), an orthoclase and albite microlites (average An5) in the ground mass.

Accessory minerals include masuto-zinnwaldite, amblygonite, topaz, fluorite, beryl, rutile, cassiterite, zircon, apatite and opaques.

These minerals are the typical suite for such specialized granites.

The main alteration products are Seri cite and minor iron oxides.

The quartz and feldspars of the Zouma granite often contain multiple crystallographic ally aligned zones of albite microlites, which we informally called the " Zouma Texture ".

This texture suggests episodic pressure release and volatile flux during cooling.

The Zouma stock is without question represent geochemically distinct granite nearly in every respect from the remainder of the Eghei granites.

The Zouma is enriched in Al203, Na20, Be, Li, Pb, Rb, and Zn.

It is depleted in Ti02 Fe203 (total), MgO, CaO, K20, Ba, CI, Co, S, Sn, Y, Zr, and perhaps U.

An eight-point Rb / Sr isochron gives an age of 532 ± 7 Ma and an initial 87Sr / 86Sr ratio of 1.243 ± 0.14039.

In spite of the very low uncertainty in the initial ratio, this is a very high value for an initial ratio.

An estimate of the amount of Sn removed during the secondary alteration of the Zouma granite can be made from the correlation of Sn and Ti02 and with the Rb / Sr ratio in granites from tin districts worldwide.

We predict a tin content of at least 1.25 million metric tons of Sn were removed from the stock during post-magmatic hydrothermal activity.

The Zouma and Hoggar occurrences suggest that the post-orogenic plutons associated with the latest Pan-African event (500-600 Ma) may be very attractive exploration targets for Sn and other rare-metals of granitic affinities.

Other than that, the green and white color of this granite makes it a very attractive decorative stone, and the presence of amazonite pegmatite's with large crystals of amazonite, which can be used as gemstones.