Basin development and halokinetic structures in the Kalindi- Kipushi area (Zambia-DRC): an investigation into the structural controls of lithofacies, alteration and mineralisation in the ‘Southern Congolese Copperbelt’ region

The Central African Copperbelt (CACB) is the most well-endowed sedimentary hosted copper and cobalt province globally and contains additional Zn, Pb, Ge, Ni, U and Au resources. The Neoproterozoic-Cambrian Katangan Supergroup is composed of the Roan, Nguba and Kundelungu group siliciclastic and carbonate metasediments. The Roan Group contained significant amounts of evaporites which underwent halokinesis in the Congolese copperbelt (CCB). The study area within the southern CCB contains the Zn-Cu-Pb-Ge Kipushi mine, hosted in the Nguba Group carbonate rocks. Recent exploration near the Kipushi Zn-Cu-Ge-Pb deposit led to the discovery of the Phoenix Cu deposit hosted in the Kundelungu Group metasediments. Additional exploration in the area is hampered by limited outcrop and poor understanding of the stratigraphy and basin architecture. This study addresses this problem by creating a new geological base map from high-resolution geophysical and soil geochemistry surveys to identify lithologies, basin structures, and unconformities. The suprasalt stratigraphy from the Kansuki Formation of the Roan Group to the Kanianga Formation of the Kundelungu Group is described in detail using a lithofacies approach. Considerable lithofacies variability occurs within the Nguba Group, and the published Kipushi Mine stratigraphy was found to be unrepresentative of the study area. Basin analysis identified extensional normal faults with throws of ~600m active during deposition of the Mwale Formation glacially influenced diamictites at the base of the Nguba Group, resulting in a basement high at Kipushi. This extensional event coincided with the Sturtian Glaciation and resulted in the development of a separate subbasin from the central Congolese Copperbelt.
A combination of thermal subsidence, salt withdrawal, and global eustatics controlled accommodation development during deposition of the Bunkeya and Gombela subgroups. Halokinesis initiated during the deposition of the Mwashya Subgroup sediments. Isolated minibasins developed between diapiric salt structures during the deposition of the Katete Formation, then widened and joined during the deposition of the upper Monwezi Formation of the upper Nguba Group. Salt withdrawal continued through the Marinoan glaciation at the start of the Kundelungu Group deposition and appears to have waned during the deposition of the Kanianga Formation. A salt canopy domain is interpreted which could have contributed to early diapir collapse and welding along sub-basin margins, thus affecting hydraulic connectivity within the basin. The Lufilian inversion related to the Gondwana assembly reactivated and reversed salt and suprasalt structures. Structurally controlled Cu-Zn mineralisation occurred along the margins of the Kipushi diapiric anticline. The Kipushi and Phoenix deposits are located above basin-bounding normal faults that were active during the deposition of the Mwashya Subgroup and Mwale Formation. The Kipushi and Phoenix deposits occupy structural/stratigraphic hydrocarbon and sour gas traps adjacent to the diapir structure. The structurally controlled edge of the Kipushi diapiric complex allowed access to base metal-bearing brines into the upper sections of the Katangan Supergroup stratigraphy. The results of this study significantly expand our knowledge of the southern CCB. This work confirms the presence of an extensional event during the deposition of the Mwashya Subgroup and Mwale Formation and evidence of early halokinesis during the deposition of the Mwashya Subgroup. It confirms the presence of minibasin development during the deposition of the upper portion of the Nguba Group into the Kundelungu Group. The latter part of the study links basin development to the mineralisation system at the Pheonix and Kipushi deposits and provides insights into their relative location and tenor, focusing on the underlying basin architecture and fluid pathways responsible for the deposits' formation.