Geology, Mineral Paragenesis, and Sequence Study of Bikilal Iron Mineralization in West Wollega; Western Ethiopia: Implication to Genesis.
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Date
2013-12-12
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Addis Ababa University
Abstract
Bikilal iron ore deposit is a Kiruna-type magnetite – ilmenite deposit in West Wollega Western Ethiopia. It is formed within syn-post tectonic intrusive gabbroic complex that intrudes the Precambrian gneiss. Bikilal gabbroic intrusion comprises olivine gabbro in the center, hornblende gabbro and hornblendite as dominant rock at the periphery of the intrusive as well as pegmatite, granite, migmatite, and anorthosite found as a minor lithology. Generally all lithological units are dipping SW with dip angles ranging from 350 ─ 750. The major structural trends in the study area are NW – SE following the regional lineament. Drill hole data shows that the rocks have layering. Hornblende gabbro and hornblendites with anorthosite are characterized by magnetite- ilmenite and apatite mineralization. Identification of different minerals and their textural relationships have been studied using ore and transmitted light microscope at the School of Earth Sciences, Addis Ababa University.
The iron ore bearing hornblendite is classified into upper zone in the northern, middle zone in the north- eastern, and lower zone in the southern part of the study area. Bikilal iron deposit consists of magnetite, ilmenite, hematite, sulphides, apatite and gold. The principal ore minerals are magnetite and ilmenite. Apatite is the second most abundant mineral in association with magnetite and ilmenite. The sulfide minerals present are pyrite, chalcopyrite, pyrrhotite and pentlandite. Gold grains are found as isolated free grain in association with other sulphide minerals but commonly it is found as hatched inclusion inside chalcopyrite.
The paragenetic sequence of mineralization was classified into four phases based on the microscopic study and existing geochemical data from previous works: Phase I = Silicates (olivine + pyroxene+ feldspar); Phase II =magnetite + massive- veinlet ilmenite + pyrite + pentlandite+ free gold; Phase III =exsolved ilmenite + hematite + pyrrhotite + gold; and Phase IV=chalcopyrite + geothite. In this work mineral association and paragenesis of Fe-Ti oxide-Py-Cu-Pyr-Ni-Au were identified and studied.
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Geology, Mineral Paragenesis, Sequence Study, Bikilal Iron Mineralization, West Wollega, Western Ethiopia, Implication to Genesis