THE KENTICHA RARE METALS-BEARING PEGMATITE FIELD (SOUTHERN ETHIOPIA)

ABSTRACT

The observed and mapped regional and local geological (structural in particular) features of the Kenticha pegmatite belt might be explained through the northwardly-directed expulsion of the dismembered ophiolites of the Kenticha formation accompanied and followed by warping of its heterogeneous rocks together with the intruded ultrabasics in the horizontal and vertical (upward) directions. This process is a regional-scale part of the general tectonic rearrangements and evolution of the southern Ethiopia and the northern Kenya.

The Kenticha ultrabasics have gone through intensive autometasomatic and superimposed hydrothermal-metasomatic alterations most probably and in the most prior to the emplacement of pegmatites the concentrically-zoned bodies of which are structurally controlled, in some cases are of gently dipping upper (roof) contacts and are of the unusual (for the pegmatitc bodies in general) morphological features.

The various acidic igneous rocks (in accordance with their geochemical specializations) are of different importance in creation of the geochemical background of the complex pegmatites of the pure line of the region.

The internal structure of pegmatites is formed due to the magmatic differentiation and to shear north-southwardly-oriented deformations and push-up stress of the underlying rocks. The latter led to development of gently dipping (in different directions) ring-like-distributed joints and local faults within them in addition to the regionally developed subvertical ones of different scales and orientations.

The complex (Ta, Nb, Hf, Zr, REE, U and Th) mineralization of commercial importance is superimposed on Be, Li, Cs, Rb-bearing and other zones of pegmatites and is related to the intensive metasomatic albitization and is structurally controlled.

The pegmatites and columbo-tantalite concentrates being extracted out of the pegmatitic ors are the complex raw materials with a number of possible by-products especially if a selective mining method is used.

The prospects of extracting gems of different ranks out of pegmatites within the area are high and are proven by the geological investigations carried out and by the data obtained so far.

Note: Copies of the final report are available at the Central Technical Library of
the ESTC.

(Final Report 1997)

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