Structural controls of gold mineralisation in Birrimian structures, Western Mali: insights from magnetic data analysis

Abstract

This study is devoted to a subsurface structural model based on suitable applications on the reduced to pole aeromagnetic anomaly map of the Kossanto area. Integrative analysis and interpretation of available geologic and high-resolution aeromagnetic data help reconstruct the subsurface geologic trends controlling gold mineralisation in Western Mali and guide toward gold-mine exploration. The apparent magnetic susceptibility, directional derivatives, analytical signal and 3D Euler deconvolution allow for inferring the organisation of the underlying structures and better identifying the Birrimian deep-seated geological structures (faults, dikes and magmatic and metamorphic events), directed NE-SW, NW-SE, N-S and E-W. The NE-SW trending and major dextral shear that relates to the D3 tectonic phase controlling gold deposits in the West African Craton constitute a large corridor. This regional tectonic trend frames the majority of Artisanal mine sites. The Euler deconvolution makes it possible to distinguish rooted faults with notable differences in depths and helps identify many tectonic discontinuities of low intensity magnetic signals. Linear faults oriented N-S to NNE-SSW dominate not only terrain in the major central zone, the Senegalese-Malian shear, but also its ramifications along NE-SW, NW-SE and E-W during the strike. The magnetic signatures testify to Birrimian formations associated with these tectonic discontinuities of basement.