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
Résumé
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.