Petrographic, Microstructural and Geochronological Constraints on the Polyphased Cu Mineralization in the High-Grade Western Zambian Copperbelt of the Lufilian Belt: Implications for the Nature of the Protolith and the Metallogenic Model

Abstract : The Lufilian orogenic belt contains world -class copper deposits distributed in two distinct zones: the Congolese Copperbelt (North: external zone) and the Zambian Copperbelt (South: internal zone). Two Cu mineralizing events are preserved in the Congolese Copperbelt: (i) syn- to late-diagenetic of these sequences, and (ii) synchronous with the Pan-African metamorphism (greenschists facies) affecting the Lower Roan sequences in the vicinity of the Zambian Copperbelt. Western Zambian Copperbelt Cu occurrences are hosted by kyanite micaschists (amphibolite facies). The timing of the Cu mineralization and the nature of the protolith of the micaschists remain unclear. We present petrographic, deformation relative chronological and geochronological evidence for: - a sedimentary protolith for the Lumwana mineralized host rocks; - a polyphased Cu mineralization through the Lufilian orogenic evolution marked by a sedimentary copper mineralization overprinted by a syn-metamorphic mineralization associated with a first kyanite generation (Kyi). Sulfides are reworked during retrogressive P -T path (i) associated with the Soino foliation (ductile deformation) and with a second kyanite generation (Ky2), between ca. 580-630 C (geothermometry on rutile) and ca. 540-510 Ma (Th-Pb ages on retrogressive monazite); and (ii) associated to later shear bands and microfolds, between ca. 510-500 Ma (Th-Pb ages on monazite) in brittle deformation domain.