Pan-African structural evolution of Paleoproterozoic basement gneiss and Cu-Co mineralized shear zones in the Domes Region of the Lufilian Belt, Mwombezhi Dome, Zambia

Abstract

In the Domes Region of the Lufillian Belt, world-class stratiform Cu (±Co, ±Ni, ±U, ±Pb, ±Zn) deposits are closely associated with tectonized pre-existing basement unconformities, viz. the pre-Katanga-basement décollement (KD). In the KD footwall on the Mwombezhi Dome, the Lumwana Mine exploits mineralization within <60 m thick, laterally-extensive shear zones beneath kilometer-scale thrust sheets of Paleoproterozoic gneiss and schist. New field data and structural analysis highlight preferential strain localization, kinematics and sequential reactivation of multiple shear zone generations (D1-3) under high- to medium-grade, metamorphic conditions and clockwise P-T-t path during the Lufillian Orogeny (ca. 550-500). Regional, progressive, top-to-the-NNE fore-thrusting is assigned to D1, while D2 represents localized, opposite, top-to-the-SSW kinematics attributed to under-thrusting by dome-scale fore-thrusted basement slivers. Subsequent D3 shear zones transposed D1-2 structures and represent overall top-to-the-NNE extensional detachment and NNE-SSW-elongation along a maximum principal extension axis (L3) which defines kilometer-scale shear- or asymmetrical-boudins of competent gneiss in the KD footwall. A pre-existing NNE-SSW prolate dome asymmetry (L1-2) dictates a downlimb-directed sense of shear on the short axes of D3 asymmetrical boudins (WNW-ESE). D3 shear zones are preferentially localized along relict pre-Katanga anisotropy and D1-2 mylonitic horizons, while Cu–Co bearing ore shoots are associated with passive fold hinges in these asymmetrical boudin necks.