Deciphering structures and deformation of the Obuom Gold Prospect, Central Ashanti Belt of Ghana: A lithostructural approach

The Obuom Gold Prospect is located in the central part of the Paleoproterozoic Birimian Ashanti belt of southwest Ghana. The prospect is approximately 45 km² and is underlain by basalt, andesite and dacite volcanic beds, graphitic and chlorite phyllites of sedimentary origin and granites. Published works on the Obuom geological terrane, using gravity models, showed that, the structures are more complex than previously thought and may involve multiple thrust slices. This research identified two deformational episodes; the first has a remarkable sinistral sense probably synchronous with an Eoeburnean event with the second, an overprint of dextral shearing during the Eburnean event. The first episode, Do₁ is characterized by NW-SE compression which resulted in subvertical NE-SW trending S₁ axial plane metamorphic foliation in tight to isoclinal F₁ folds with NW-SE trending L₁ lineations. The second episode, Do₂ indicates continuous shortening which produced nearly upright F₂ folds with east-west striking axial planes, slight plunging hinges and associated subparallel crenulation cleavages. The first deformational event Do₁ which represent NW-SE compression is observed affecting only the Sefwi Group. The Do₂ resulting from N-S compression affected both the Sefwi and Kumasi Groups.