Structural analysis of the southern Ashanti Belt, Ghana, using airborne geophysical data

Abstract

The southern Ashanti Greenstone Belt, in Ghana, is an area of major economic importance for West Africa, where many companies are actively mining and exploring for gold. As a consequence, a significant geological data set has been collected over the years, but it has not always been subjected to an integrated interpretation, especially away from the main Ashanti fault system and the Tarkwaian portion of the belt, such as around the Wassa Mine. Using geophysical data and field observations, we have revised the geological and structural map of the south of Ashanti Belt, and have produced a new map around the Wassa mine. Crosssections built against potential field data give insights into the third dimension. This new information, combined with previous studies in the area, suggest the presence of 5 deformation events, corresponding to the Eburnean orogeny and associated with plutonism between 2200 and 2000 Ma. The first phase of shortening (D1), prior to the deposition of the Tarkwaian sediments, is followed by the main tectonic sequence (D2-D3), at around 2.1 Ga, characterized by large folds oriented NE-SW in the Birimian and in the Tarkwaian. After D3, two other deformation events occurred: D4 with sub-horizontal cleavage and recumbent folds and then, D5 with a NE-SW shortening. Gold mineralization and associated sulphids could be correlated with D1, D2 and D3 deformations.