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The Implications of Overlooked Early E-W Neoproterozoic Structures on Gold Mineralization in Northern Ethiopia

Y. Admassu1, D. Holm1, and L. Friberg2
1Department of Geology, Kent State University, Kent, OH 44242
2Department of Geology, University of Akron, Akron, OH, 44325

Precambrian basement rocks of northeast Africa and western Arabia belong to the Arabian Nubian Shield, which formed by accretion of 800-700 Ma island arc/back arc complexes. The Arabian Nubian Shield and its southern extension, the Mozambique Belt, have been collectively interpreted as strongly deformed at 750-650 Ma during west northwest oriented closure of the north- South trending Mozambique Ocean. Suture zones in the southern Arabian Nubian Shield trend north to northeast. However, bedrock mapping and structural analysis in northern and western Ethiopia, belonging to southern Arabian Nubian Shield show that Neoproterozoic greenstone rocks were first deformed into north verging recumbent folds. Subsequent second deformation produced north to northeast - south to southwest oriented tight folds and a steep northwest dipping axial planar foliation. Younger third and fourth deformations resulted in formation of northeast and northwest oriented dextral shear planes.

First deformation related, east-west oriented folds, and sutures are not explained by the existing regional tectonic model. This mostly unreported first deformation event also controls epigenetic gold mineralization in the study areas. North verging reverse up dip shear zones control quartz veining and are later intensely deformed by the second deformation. Bias from regional tectonic models and the popularity of post second deformation structures as the most important gold hosting structures have contributed to the misinterpretation of gold mineralization related to the first deformation. This could also partly explain the failure of exploration companies to trace down dip extension of notable surface mineralization.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas