Summary:
The mineral deposits at Kipushi are an example of carbonate-hosted copper-zinc-lead mineralisation hosted in pipe-like replacement and tabular zones. This deposit type tends to form irregular, discordant mineralised bodies within carbonate or calcareous sediments, forming massive pods, breccia/fault-like fillings and stockworks (Trueman, 1998). They often form pipe-like to tabular deposits strongly elongate in one direction. Zinc-lead rich zones can project from the main zone of mineralisation as replacement bodies parallel to bedding, as is the case at Kipushi.
This deposit type is associated with intracratonic platform and rifted continental margin sedimentary sequences which are typically folded and locally faulted (Cox and Bernstein, 1986). The host carbonate sediments were deposited in shallow marine, inter-tidal, salt flat, lagoonal or lacustrine environments and are often overlain unconformably by oxidised sandstone-siltstone-shale units. The largest deposits are Neoproterozoic in age and occur within thick sedimentary sequences.
The Katanga Supergroup hosts a number of epigenetic zinc-copper-lead deposits developed within deformed platform carbonate sequences. While many of these are relatively small (e.g. Kengere and Lombe in the DRC; Bob Zinc, Lukusashi, Millberg, Mufukushi, Sebembere, and Star Zinc in Zambia), Kipushi and Kabwe in the DRC and Zambia respectively represent world class deposits with predominantly massive sulphide mineralisation contained within dolomitic limestone (Kampunzu, et al., 2009). These deposits are polymetallic with a typical Zn-Pb-Cu-Ag-Cd-V association and contain variable concentrations of As, Co, Mo, Rh, Ge, and Ga.
Mineralisation at Kipushi is spatially associated with the intersection of Nguba Group stratigraphy with the Kipushi Fault and occurs in several distinct settings:
• Kipushi Fault Zone (copper, zinc, and mixed copper-zinc mineralisation both as massive sulphides and as veins);
• Série Récurrente:
- Disseminated to veinlet-style copper sulphide mineralisation);
- A high-grade pod (massive copper and zinc sulphides);
• Copper Nord Riche (mainly copper but also mixed copper-zinc sulphide mineralisation, both massive and vein-style);
• Big Zinc (massive zinc sulphide with local copper sulphide mineralisation), and
• Southern Zinc (poly-metallic massive sulphide) mineralisation and replacement.
Mineralisation at the Kipushi Project is generally copper-dominant or zinc-dominant with minor areas of mixed copper-zinc mineralisation. Pyrite is present in some peripheral zones and forms massive lenses, particularly in the Fault Zone. Copper-dominant mineralisation in the form of chalcopyrite, bornite, and tennantite is characteristically associated with dolomitic shales both within the Fault Zone and extending eastwards along, and parallel to, bedding planes within the Série Récurrente and adjacent Upper Kakontwe Formations.
Zinc-dominant mineralisation in the Kakontwe formations occurs as massive, irregular, discordant pipe-like bodies completely replacing the dolomite host. These bodies exhibit a steep southerly plunge from the Fault Zone and Série Récurrente contacts where they begin, to their terminations at depth within the Kakontwe Formation. This southerly orientation, observed across all the mineralised zones, is oblique to the north-west plunging intersection of the Kakontwe Formations with the Fault Zone, inferring a persistent structural control at the Kipushi deposit.