Summary:
The Kansanshi deposits (Main, North West and South East) are located within the deformed metasediments of the Nguba (formerly Lower Kundulungu) Group, which is part of the Katanga Supergroup in the Zambian Copperbelt. Locally, the deposits are situated within domal structures along the crest of a regional antiform. Deposit mineralization is closely associated with these domes and is localized to a structurally modified sequence of rock units comprised of dolomites, dolomitic marbles, various schists and phyllites. It is within these domed structures that the three major ore bodies (NW Pit, Main Pit and SE Dome) of the Kansanshi Mining License are located.
Mineralisation across each of the Kansanshi deposits occurs as shallower oxides and secondary copper minerals, with deeper underlying primary copper sulphides. Mineralisation is influenced by depth below surface, distance from the dome apexes, structural features (faulting, veins, and breccias) and lithological associations.
The dominant primary sulphide copper mineralization and geology may be summarized as:
• stratabound with mostly disseminated and veinlet style mineralization;
• sub-vertically dipping, quartz-carbonate-sulphide veins that crosscut stratigraphy;
• localized brecciated style of mineralization.
The primary sulphide mineralization is influenced by weathering and oxidation with:
• near surface weathering in the saprolitic zone resulting in residual copper styles of mineralization;
• around vertical veins, with oxide copper mineralization forming, such as malachite, tenorite and chrysocolla;
• transitional weathering zones with mixed primary and secondary copper sulphide copper mineral assemblages;
• pervasive shallow to deep weathering located along geological structures.
Primary sulphide copper mineralization is mostly chalcopyrite, with minor bornite. Oxide mineralization is mostly chrysocolla with malachite. The transition zone contains mixed copper oxides, primary copper sulphides, secondary copper sulphides and minor native copper and tenorite. Minor copper is hosted in clay and mica minerals, and is classified as refractory. Gold is generally positively associated with copper mineralization.
The Kansanshi copper mineralisation is believed to have originated from hydrothermally remobilised copper controlled by lithological and structural factors. Oxidised copper-enriched hydrothermal fluids are thought to have originated from magmatic sources, migrating upwards and acquiring significant mineral and metal content by leaching and scavenging elemental copper and gold from basement and/or overlying sedimentary rocks. Copper mineralisation across the Kansanshi deposits was precipitated within dome-shaped trap structures under prevailing reducing conditions within the host lithologies. Sulphide and associated metal deposition occurred at redox interfaces where oxidised copper-enriched fluids intersected reducing carbonaceous sediments such as the carbonaceous phyllites. The interaction between graphitic organic matter and hydrothermal fluid likely controlled the oxidation state of the ore fluid, leading to mineralisation.
The 4800E and 5400E structural zones exemplify potential fluid pathways. Mineralisation traps are clearly concentrated around the immediate apexes of domes, favouring specific lithologies as well as structural features and veins. This geological framework has informed the modelling approach and exploration work, particularly with multi-directional holes drilled at approximately 60° to 70° to maximise intersection angle with the antiformal shape of the lithological units and veins, thereby accounting for multiple vein and fold orientations. This approach optimises the angle of intersection, reducing the risk of sample assay results distorting the dimensions of true mineralisation volumes.
Stratabound mineralisation
Stratabound mineralisation hosts the majority of Kansanshi’s copper metal. Bedding-parallel disseminated chalcopyrite is dominant within phyllites and carbonaceous phyllites with a tendency for stronger mineralisation closer to larger veins. Organic carbon within the phyllites acts as a reducing agent, facilitating the precipitation of sulphides along specific strata horizons. Chalcopyrite is the dominant sulphide species, accompanied by lesser amounts of bornite and molybdenite, and with increasing pyrite and pyrrhotite more distal to the stronger chalcopyrite mineralisation. Oxide minerals (malachite, chrysocolla) and secondary sulphides (chalcocite) are more abundant in the shallower weathered and oxidised zones.
Vein mineralisation
Vein mineralisation hosts more than 30% of total copper metal across the three deposits. The veins are primarily composed of quartz/carbonate with accessory copper minerals, typically exhibiting subvertical orientations and ranging from centimetre to metre-scale widths. Chalcopyrite is the principal copper sulphide mineral while malachite, chrysocolla, and chalcocite are common in the shallower, more weathered parts of the veins. Veins are common within the clastic units but may extend into adjacent marble units. Concentration of vein mineralisation tends to be higher in the contact zone with its host rock.
Minor vein constituents such as anhydrite, magnetite, and trace uraninite are occasionally present. Molybdenite is notably common in calcite veins at the Main and NW deposits.
Breccia
Breccia mineralisation occurs where there has been brittle structural deformation, creating space to trap sulphide mineralisation. Although less common at Kansanshi, brecciated zones can exhibit strongly mineralised stockworks along with increased veins occurrences (Hanssen et al., 2010). Breccia mineralisation is most common in the Main deposit, also with localised breccia mineralisation associated with gabbroic intrusives and the 4800E and 5400E structural zones.
Oxide mineralisation
Most oxide copper mineralisation occurs closest to surface and is often semi-massive. Weathering and oxidation of primary sulphides has led to zones of enriched supergene copper oxide and secondary chalcocite mineralisation. The presence of oxide and secondary copper minerals is typically strongest at the apexes of the domes in the North West and Main deposits. In contrast, South East deposit has relatively underdeveloped oxide and secondary copper mineralisation. Oxide mineralisation, primarily malachite, tenorite, chrysocolla, and minor azurite, occurs within veins, alteration haloes, faults, fractures, breccias and strata.
Oxide mineralisation is dominant in the shallowest portions of deposits and is influenced by morphology, affecting the mobilisation and dispersion of copper minerals along complex weathering pathways. Weathering tends to be strongest along and down vertical structures and vein sets. As a result, oxidised mineralisation can occur at depths well below the average depth of weathering. Gangue minerals consist mainly of smectite clays, calcite, marble, iron oxides and hydroxides.
Mixed mineralisation
Mixed mineralisation forms broad transition zones between oxide and underlying sulphide mineralisation. These transition zones contain mixtures of primary copper sulphides (chalcopyrite), secondary copper sulphides (chalcocite) and copper oxide minerals. The ratio of single acid soluble copper to total copper is useful for determining the degree of mixing of these respective minerals and therefore which processing circuit will yield optimal copper recovery.
Sulphide mineralisation
Copper mineralisation across Kansanshi is mostly fresh (unoxidised) primary copper sulphides (chalcopyrite) with rare isolated occurrences of bornite. Other common primary sulphides include pyrite and pyrrhotite. Primary sulphide mineralisation is typically located below the oxidised and mixed mineralisation zones and is associated with both veins and along select strata horizons.