Document Type: Original Article

Author

Geological Survey of Ethiopia, P.O.Box 2302, Addis Ababa, Ethiopia,

Abstract

The Bikilal layered gabbro-complex is composed of zones/layers of olivine/ pyroxene gabbro and hornblende gabbro. Within the hornblende gabbro, repeated lens-like thin and elongated bodies of hornblendite are found intimately associated with massive and disseminated ilmenite-magnetite bodies, in places with apatite. Petrological examination of the hornblende gabbro shows 50-55% hornblende, 40-45% plagioclase, 5-7% opaque minerals/ilmenite + magnetite/, and 5-15% apatite and that of hornblendite shows 75% hornblende, 10-15% apatite, 10-15% ilmenite and rare sulphides, and traces of Uranium. Regardless of the type of lithological units, two main zones of phosphate mineralization ,the upper and lower zones, were identified and delineated entirely based on phosphate (P2O5) assay values of chip, channel and, core samples,The strike length of the upper zone is 1600m. There are two main layers of phosphate mineralization in the upper zone; the average thickness of each layer is 30m and 40m respectively. The strike length of the lower zone is 3000m having a thickness of 60m ─ 200m. The mineable reserve of Soji-Bikilal phosphate deposit is estimated to be 181 million tons, at a grade of 3.5% P2O5. Preliminary beneficiation trial reveals commercial grade concentrate, at which the overall weight recovery, is in the range of 3-5%. The Radioactivity of Uranium has not been determined and hence re-evaluation of the phosphate rock for Uranium content should be carried out. Similar Gabbro intrusions occur in Western Ethiopia and in East Africa which should be assessed for phosphate potential to develop the fertilizer potential of the East Africa Region.

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