Deformation, alteration and implicit 3D geomodelling of deposit-scale controls of vein-hosted copper mineralization of the Frontier Mine, Democratic Republic of Congo

Abstract

The structurally controlled, vein-hosted copper deposit of the Frontier Mine is distinct from the vast majority of sediment-hosted, stratiform Cu(-Co) deposits of the Zambian Copperbelt. Successively emplaced vein sets document the close interplay between the progressive structural evolution of the deposit, recording northeast-southwest shortening, and associated hydrothermal fluid flow and alteration (albitization). The deposit is hosted by greenschist-facies metasedimentary rocks of the Mwashya Subgroup in the first-order hinge zone of a regional-scale, refolded, recumbent fold (F₁/F₂). Early bedding/S₁-parallel veins (Vein Set 1) formed during layer-parallel shearing and the onset of recumbent folding (F₁). This early vein generation is relatively poorly mineralized, but was associated with a near-pervasive, bedding-parallel albitization and replacement of the mainly metapelitic wall rocks. The reaction hardening process promoted brittle deformation during the subsequent upright refolding (F₂) of the rocks and the formation of a second generation of highly mineralized, saddle-reef type veins (Vein Set 2) in the hinges of particularly upright F₂ folds (F₁/F₂). The controls of Vein Set 2 by fold hinges defines the overall shoot-like geometry of the orebody, parallel to the SE-plunging folds. The subhorizontal orientation and brecciated textures of a subsequent Vein Set 3 underline the formation of veins through continued northeast-southwest shortening of the brittle wall rocks during the lock up of the refolded first-order fold. The overprinting and structural relationships between vein sets, alteration and the regional fold structures signify a syn-tectonic, long-lived, multi-phase mineralization history during the Lufilian Orogeny.