Mineralization and Associated Structures of Okote Prospect (Southern Ethiopia)

Abu, Wube (2005) Mineralization and Associated Structures of Okote Prospect (Southern Ethiopia). Masters thesis, Addis Ababa University.

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Abstract

Okote prospect area is the southern extension of the N-S striking auriferous structure, the Megado graben-syncline. Only a few of the numerous primary gold indications are identified in this structure. In the Okote area sulfide rich auriferous quartz veins of mesothermal mineralization occur along highly fracture contact zone between massive amphibolites and amphibole schist and to a minor extent along the schistosity planes of the chlorite carbonates schist. Lithologically, the Okote prospect area is constituted of transitional to basic metavolcanics in contrast to the northern half of the Megado graben-syncline, where both metasediments and metavolcanics occur. The Okote metavolcanics are bounded by granitic gneisses both in the eastern and western side and exhibit alterations comprising chloritization, silicification, epidotization, sulphidization and carbonetization. Within the Okote prospect five main lithologic units are recognized: - Epidote Quartz Chlorite Schist, Chlorite carbonates schist, Talc tremolite actinolite schist, Meta gabbro and Metagranodiorite. They are structurally overlain by mafic and ultramafic rocks consisting of mainly Meta gabbro & Talc tremolite actinolite schist. The granitoids occur in the form of lenses intruding in to the foliated metavolcanics. Four phases of deformation are described. The earliest D1, deformation has produced a pronounced local S1, schistosity. D1 deformation produced a regional S1 schistosity. The S1 is well developed parallel to the compositional banding in the epidote quartz chlorite schist and variably developed in the ultramafic rocks. Moderately to steeply NE and SW doubly plunging folds produced close to tight S1 schistosity. It was followed by the formation of NW trending faults, which characterized by sinistral brittle shear zones (D2). The D3 is open E-W sinisoidal F3 folds with N-S axial planes and D4 is linear E-W fractures. The D1 and D2 phases of deformations produced dilatational zone of intersection, which is most important for mineralization of gold. The auriferous veins are distributed in the Adola group of the upper complex, which is with in the axial trough of the geosynclines that gave rise to the Mozambique belt during the upper Proterozoic Generally the rocks of Okote prospect show characteristic of green schist facies metamorphism. Geochemical evidences showed that the rocks of Okote prospect are intermediate to basic composition. Chondrite normalized graph shows less fractionation of the host rocks. The gold occurred in quartz vein and alteration zones, the nature of the gold is very coarse that can be seen with the naked eyes. Visible gold particles are commonly encountered in boxwork association of fractured and limonitized pyrite structure. Two phases of mineralization have been recognized in Okote prospect, Gold-sulfide-quartz and sulfide-carbonate-quartz. The mineralization is controlled by shearing, with pinch and swell structures both along the strike and down dip. Okote prospect can be evaluated and falls in ordinary workable deposit or it is open to doubt. Gold and sulphides are the most common minerals in the area. The association of gold with sulfides in the quartz veins at Okote may be taken as the evidence of gold transport as bisulfide complex.

Item Type:	Thesis (Masters)
Subjects:	Q Science > Q Science (General) Q Science > QE Geology
Divisions:	Africana
Depositing User:	Selom Ghislain
Date Deposited:	18 Jun 2018 12:38
Last Modified:	18 Jun 2018 12:38
URI:	http://thesisbank.jhia.ac.ke/id/eprint/4393

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