Abstract The Central African Copperbelt, including the Zambian Copperbelt, Congolese Copperbelt, and deposits in the North West Province of Zambia, is the world's largest and highest-grade sedimentary copper province, with approximately 200 Mt of contained copper and the world's largest cobalt reserves. It is hosted in Neoproterozoic metasedimentary rocks of the Katangan Supergroup (∼880 and ∼600 Ma) deposited in a series of intra-continental rift basins with abundant evaporite deposits. Early rift-stage continental rocks were overlain by a sequence of mixed evaporitic carbonate and clastic rocks, followed by a second period of renewed rift-stage clastic and mafic rocks. Widespread glacial and postglacial deposits covered this lower part of the basinal sequence, and mark an uppermost limit to the distribution of major copper deposits. Subsequent depositon of relatively monotonous, nonevaporitic basin fill clastic and lesser carbonate rocks preceded basin inversion during the Pan-African (∼590–500 Ma) Lufilian orogeny. The Copperbelt contains copper deposits in a range of rock units at a number of different stratigraphic levels. These deposits display differing styles and textures of mineralization and alteration types. Deposits may contain either or both disseminated, generally fine-grained sulfides and vein-hosted, generally coarse-grained sulfides. Nevertheless, there are shared characteristics among most deposits. Deposits are hosted at stratigraphic or structural redox boundaries. Where deposits occur in the stratigraphically lowermost reduced rocks, overlying reduced or favorable rocks generally were not mineralized. Although redox was a fundamental control for mineralization, the most carbonaceous rocks within an ore horizon are commonly not economically mineralized. Ore sulfide zonation within deposits occurs on multiple scales, with complexity of zoning broadly related to the complexity of the host-rock sequence. Macrostructural controls on deposit position suggest that extensional faults were important in controlling fluid flow, either directly or indirectly through influence on sedimentary and probably diagenetic facies variation. The stratigraphic section within which the deposits are located was affected by regional potassic, magnesian, silicic, and/or sodic alteration controlled partly by lithol-ogy and indicative of the passage of basinal brines. Mineralization in the Copperbelt appears to have occurred over a protracted period that spanned diagenesis, basin inversion, and metamorphism. This attests to the longevity of ore-forming brines resident within the Katangan basin and at least the upper part of its basement. The near-surface portions of deposits throughout the Central African Copperbelt have undergone oxidation and supergene enrichment and such enrichment has been important in upgrading the copper tenor of many deposits.

Abstract Sediment-hosted stratiform copper deposits comprise disseminated to veinlet Cu and Cu-Fe sulfides in sili-ciclastic or dolomitic sedimentary rocks. Sediment-hosted stratiform copper deposits are extremely common though economically significant deposits are rare. They account for approximately 23 percent of the worlds’ Cu production and known reserves in addition to being significant sources of Co and Ag. Three sedimentary basins (the Paleoproterozoic Kodaro-Udokan in Siberia, the Neoproterozoic Katangan in central Africa, and the Permian basin of central Europe) contain supergiant (>24 million metric tons (Mt) contained Cu) deposits. Sediment-hosted stratiform copper deposits are the products of evolving basin-scale fluid-flow systems that include source(s) of metal and S, source(s) of metal- and S-transporting fluids, the transport paths of these fluids, a thermal and/or hydraulic pump to collect and drive the fluids, and the chemical and physical processes which result in precipitation of the sulfides. Metal sources are undoubtedly red-bed sedimentary rocks containing Fe oxyhydroxides capable of weakly binding metals. Sulfur may be derived from marine or lacustrine evaporites, reduced seawater, or hydrogen sulfide-bearing petroleum. Metals appear to have been transported at low to moderate temperatures in moderately to highly saline aqueous fluids, with the temperature of the fluid largely dependent on the time of fluid migration in the basin’s burial history. These basinal fluids were focused to potential metal precipitation sites by thinning of the red-bed sequence at basin margins, by faults, by differentially permeable sedimentary units, by paleotopography within the basin, or along the margins of salt diapirs. Fluid movement produced widespread, basin-scale alteration that has commonly been overlooked but can form an important exploration guide. Sulfide precipitation occurred due to reduction, typically caused by reaction with carbonaceous rocks or petroleum. The amount of sulfides present at any deposit may be either metals or sulfide limited or could have been controlled by the amount of available reductant (e.g., petroleum). While understanding of sediment-hosted stratiform copper ore genesis at the deposit scale is relatively robust, there are still significant questions in regards its position in terms of basin evolution. A wide variety of basin architectures and processes can lead to the formation of sediment-hosted stratiform copper deposits. Despite general agreement that sulfides postdate sedimentation, the absolute age of mineralization in many deposits has been difficult to document and the available evidence suggests that deposits can form throughout a basin’s evolution from early diagenesis of ore host sediments to basin inversion and metamorphism. Supergiant and giant deposits formed in basins which underwent prolonged periods of fluid flow and in which unique conditions allowed for the accumulation of large amounts of metal-bearing fluid, sufficient reduced S, and large amounts of reductants.

Abstract The Zambian Copperbelt accounts for approximately 46 percent of the production and reserves of the Cen tral African Copperbelt, the largest and highest grade sediment-hosted stratiform copper province known on Earth. Deposits in the Zambian Copperbelt are hosted by the Neoproterozoic Katangan Supergroup, a rela tively thin (~5 km) basinal succession of predominantly marginal marine and terrestrial metasedimentary rocks that lacks significant volumes of igneous rocks. The stratigraphic architecture of the Katangan Supergroup in the Zambian Copperbelt is comparable to that of Phanerozoic rift systems. The basal portion of the sequence (Lower Roan Group) contains continental sandstones and conglomerates deposited in a series of restricted sub-basins controlled by extensional normal faults. These largely terrestrial sediments are abruptly overlain by a re gionally extensive, variably organic rich marginal marine siltstone/shale (Copperbelt Orebody Member, or “Ore Shale”) that contains the majority of ore deposits. This horizon is overlain by laterally extensive marine car bonates and finer grained clastic rocks that evolved through time into a platformal sequence of mixed carbon ate and clastic (Upper Roan Group) rocks with abundant evaporitic textures, including widespread breccias thought to record the former presence of salt, now dissolved. Rocks of the overlying Mwashia and Kundelungu groups are dominantly shallow marine in origin. Three significant tectonic events affected the basin. Extension associated with early rifting led to the devel opment of isolated fault-controlled basins and subsequent linkage of these basins along master faults at the time of Copperbelt Orebody Member deposition. A later period of extension occurred during late Mwashia to early Kundelungu time (~765–735 Ma) and is associated with limited mafic magmatism. Basin inversion and later compressive deformation (~595–490 Ma) culminated in upper greenschist-facies metamorphism (~530 Ma) in the Zambian Copperbelt. The majority of ore deposits in the Zambian Copperbelt occur within a 200-m stratigraphic interval centered on the rocks of the Copperbelt Orebody Member. Deposits are broadly stratiform and are grouped into argillite- (70% of ore) and arenite-hosted (30% of ore) types. The distribution, geometry , and size of deposits are fundamentally controlled by early subbasin fault architecture and the availability of both in situ and mobile reductants, the distribution of which is linked to basin structures. Argillite-hosted deposits occur within rela tively dark and locally carbonaceous siltstones and shales, suggesting the former presence of an in situ organic reductant. These deposits are laterally extensive with strike lengths up to 17 km. Arenite-hosted deposits occur in both the footwall and hanging wall of the Ore Shale and have maximum strike lengths of 5 km. They occur at sites that were geometrically favorable for mobile hydrocarbon or sour gas accumulation. Both argillite- and arenite-hosted deposits contain so-called barren gaps of weakly to unmineralized strata that are typically asso ciated with the fault-bounded shoulders of early subbasins. Two mineralization assemblages occur in the Zambian Copperbelt. The volumetrically dominant type con sists of prefolding disseminated and lesser vein-hosted Cu-Co sulfides. The most typical sulfide assemblage in the deposits is chalcopyrite-bornite with subsidiary chalcocite and pyrite. The Zambian Copperbelt is unusual among sediment-hosted stratiform copper districts in having abundant Co and low Ag, Zn, and Pb. The Cu-Co sulfide carrollite is widespread in the district, although cobalt is present in economic quantities in only some deposits on the western side of the district. The Zambian Copperbelt also contains ubiquitous, but volumetri cally minor, Cu-U-Mo-(Au) mineralization in postfolding veins. Cu-Co sulfides display complex textural relationships that are best explained by multistage ore formation. Diagenetic to late diagenetic mineralization is indicated by the typically nonfracture-controlled distribution of both sulfide and gangue phases, replacive textures of Cu-Co sulfides after diagenetic cements and pyrite, and an approximate 815 Ma Re-Os isochron age for sulfide precipitation at the Konkola deposit. Brines ca pable of mobilizing metals were most likely generated during development of evaporitic environments in units of the Upper Roan Group, and/or subsequent dissolution of these evaporites to form the Upper Roan Group breccias. Late diagenetic to early orogenic mineralization is recorded by prefolding bedding-parallel veinlets and tex turally and compositionally comparable disseminated Cu-Co sulfides. An Re-Os isochron age on Cu-Co sul fides from two arenite- and one argillite-hosted deposits of 576 ± 41 Ma is consistent with early orogenic hy drocarbon or sour gas production. The minor Cu-U-Mo-(Au) mineralization event occurred following postpeak metamorphism, at approximately 500 Ma. The Zambian Copperbelt ore province is characterized by stratigraphically and laterally widespread meta somatism that records a protracted history of basinal brine migration. Although the alteration history is com plex, it can be broadly categorized into an early Ca-Mg-SO 4 , anhydrite- and dolomite-dominant stage involv ing brine reflux below the level of Upper Roan Group evaporites; a second, K-dominant stage characterized by widespread and commonly intense development of K-feldspar and locally sericite, best developed in rocks of the Lower Roan Group and associated with ore; and a third, Na-dominant stage characterized by development of albite, commonly at the expense of earlier-formed K-feldspar. Albite dominates in Upper Roan Group brec cias and Mwashia-Lower Kundelungu strata. It is also locally associated with a late Cu-U-Mo-(Au) vein event. Although none of these alteration types are direct guides to ore, they demonstrate widespread brine circula tion within the lower parts of the Katangan Supergroup.