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Ore Genesis of the Sediment-Hosted Cu deposits in the Central African Copperbelt based on a case study of the Cu-Co/Ag mineralization in the Kaoko Belt, Namibia

By Dr. A Nghoongoloka

Geological Survey of Namibia (GSN), Ministry of Industries, Mines and Energy, Windhoek, Namibia

newabner@gmail.com

The sediment-hosted Cu-deposits are 2^nd largest source of Cu (20-25%) after the porphyry systems. The Central African Copperbelt (DRC and Zambia) supply 16% copper and 73% cobalt. Mineralization occurs as Stratiform Cu-Co/Au and likely remobilized Vein-type Cu-Ag deposits hosted by the Katanga Supergroup, which is an analogue of the Damara Supergroup in the Kaoko Belt. The Kaoko Belt contains over 200 Cu mineral occurrences, including the Otuani deposit with 5 Mt, Okohongo deposit with 10.2 Mt, at grades of ca. 0.4 to 25 wt % Cu, and 55 to 93 g/t Ag. The Kaoko Belt mineralization has been described as structurally controlled, stratiform, sediment-hosted, Cu-deposits. This study characterized the mineral paragenesis and geochemistry and proposes genesis of the Kaoko Belt mineralization and compare with deposits in the Central African Copperbelt.   It was revealed that the Sediment-hosted deposits formed by syngenetic-diagenetic Cu-Co± Au mineralization and epigenetic Cu-Ag mineralization, followed by supergene enrichment process. The syngenetic-diagenetic process deposited stratiform ores, which are often overprinted by multistage syn- to post-orogenic veins. Ore forming fluids homogenized between 50 and 400 ^oC, with distinct salinity ≤ 25 and ≤45 wt% NaCl eq., for the vein-type and stratiform ores, respectively. Mineralization was formed due to mixing, cooling and reduction of predominant basinal fluids and seawater or meteoric water, as well as somewhat magmatic contribution. Multi-sources of sulfur include the magmatic sulfur, thermochemical sulfate reduction (TSR), microbial sulfate reduction (MSR) and sulfur from organic matter or traces of hydrocarbons in the Neoproterozoic sedimentary rocks. Silver can be leached from precursor sulfides and host rocks and incorporated into sulfides during the supergene process. The Kaoko Belt mineralization is the same type as the sediment-hosted Cu-deposits in the Damara Belt and Central African Copperbelt.