Geology and Genesis of Gold Mineralization in Burikaro and Ejersa Areas, Guji Zone, Oromia National Regional State, Southern Ethiopia
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Date
2014-05-30
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Addis Ababa University
Abstract
This study deals about geology and genesis of gold mineralization in Burikaro and Ejersa
areas, which are located in the Neoproterozoic Adola gold field of southern Ethiopia. The
area is not well explored and almost no research work has been done so far. Detailed
review of the geodynamic evolution and mineralization history of the region, field
description and geological mapping, rock and ore petrography, and surface sample
chemical analysis were conducted. Secondary data from trench sample chemical analysis
were also utilized in the study.
The area comprises highly weathered and variably deformed upper greenschist to
epidote-amphibolite facies metamorphic rocks like amphibolite, talc-tremolite-actinolite
schist, graphite-quartz-mica schist, meta-conglomerate, and meta-sandstone. Intermediate
to mafic meta-plutons such as meta-dolerite and meta-gabbro are also present intruding
the amphibolite rock. A major N-S and two minor NW-SE and E-W trending shear
zones; early- and late-tectonic quartz (± calcite) veins; and hydrothermal alterations like
silicification, carbonatiztion, tourmalinization, and chloritization were observed.
Besides its occurrence as a free gold, the gold mineralization of the study area is mainly
associated with the hydrothermally altered major N-S trending shear zones containing
late-tectonic quartz (± calcite) veins with associated sulfides and present mainly in the
graphite-quartz-mica schist and meta-conglomerate/meta-sandstone. The ore minerals
associated with gold are dominantly pyrite, magnetite, and ilmenite; minor amounts of
hematite and chalcopyrite, and accessory mounts of sphalerite, covellite, and limonite
chiefly occurring as open-space filling and replacement type mineralization. Based on
texture, mineral association, and alteration a paragenetic sequence is suggested.
The presence of not mineralized higher grade mafic metamorphic rocks at the base, the
association of the gold mineralization with the lower grade meta-sediments, and the
negative correlation between gold and metals like cobalt and nickel suggest that the
possible source rocks of the gold are the underlying mafic rocks and metamorphic
dehydration is the probable source for the hydrothermal fluids and leaching of gold from
the mafic rocks. The association of gold mineralization with sulfides suggest that HS--or
H2S-complexes were responsible for gold transport in the area.
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Keywords
Geology and Genesis, Gold Mineralization, Burikaro and Ejersa Areas, Guji Zone, Oromia National Regional State, Southern Ethiopia