The Kipushi copper, zinc, lead deposit is located in the Democratic Republic of the Democratic Republic of Congo, 30 km to the WSW of Lubumbashi, and immediately adjacent to the border with Zambia.
It lies on the southern margin of the Congolese Copperbelt and to the NW of the Zambian Copper Belt, within the broader Central Africa Copper Belt. It occupies a steeply dipping fault zone on the margin of a larger 'mega-breccia' within carbonates of the Neoproterozoic Katanga Supergroup. The mine has been closed by civil un-rest, and due to poor mining practices.
Kipushi is the largest of three such deposits distributed across the southern margin of the Cupriferous Arc in Zaire. The other two, which are not economic, are Lombe and Kengere.
The Kipushi orebody comprises a transgressive tabular deposit developed within the immediate footwall of the north-south-trending Kipushi fault zone, where the fault cuts the core of a mega-breccia structure, which is itself on the thrusted northern limb of a regional, elongated, 25 km long, domal section of a regional anticline. The mega-breccia is developed within dolostone and interbedded dolostone and carbonaceous shale of the lower Nguba Group.
The Kipushi mine is located on the north eastern flank of the Kipushi Anticline, the southernmost of a number of NW trending, persistent, elongate, 'whaleback' anticlines that define the Congolese Copper Belt. The 'whaleback' form of these structures is due to the undulose nature of the reversal of plunge of the fold axis along these structures.
The core of the Kipushi Anticline is occupied by a chloritic-talcose dolomite breccia (or mega-breccia), known locally as the 'Axial' or 'Field' Breccia, which is apparently composed of clasts and matrix of the Upper Roan and Dipeta subgroup dolostones, with blocks of Kakontwe Formation dolomites also being recognised. This mega-breccia core is generally flanked by dolostones and silty dolomitic shales of the Mwashia Group passing upwards stratigraphically, into diamictite of the Grand Conglomérat of the basal Nguba Group, into dolostones of the Kakontwe Formation, dolostone and silty dolomitic shale of the Serie Recurrente and finally into silty dolomitic shale of the overlying upper Nguba Group.
However, in the western part of the dome, a large section of the northern limb of the anticline, including the sequence from the Mwashia to the Serie Recurrent, some 1800 m long and 2000 m deep, has been 'torn away' and replaced by mega-breccia. The contact between the mega-breccia and disclocated northern limb of the anticline is occupied by a discontinuity surface called the 'Kipushi Fault', which dips at 70°W. It cuts the steeply dipping sediments of the northern limb of the anticline at right angles.
The Kipushi 'Fault' and a similar parallel structure that bounds this block of breccia to the west, are most likely transform fault structures, accommodating differential deformation on the northern limb of the fold.
On the western margin of the 'Kipushi Fault', there is a north-south oriented slab of Nguba Group dolomitic siltstone which is elongated parallel to the fault (and at right angles to the strike of the limb to the east), known as the 'Lambeau'. This slab, which is about 500 m long extends from 160 to 1800 m below surface and is bounded above, below, laterally and to the west by the mega-breccia.
The orebody is copper rich to the north, where the footwall is shale, and zinc rich to the south, where it is dolomite, whilst there is also a general vertical trend from copper-rich at surface to zinc-rich with depth.
The Kakontwe Formation dolomitic rocks and to a lesser degree the Serie Recurrente, are irregularly invaded by the mineralisation, forming a tabular body generally parallel to, and bounded on its eastern margin by, the Kipushi Fault. This body extends from the surface to a depth of 1900 m (Francois and Coussement 1990). According to Francois and Coussement (1990) three types of ore have been recognised, as follows,
The Main Ore which is rich in Cu and Zn, with grades of around 20 to 30% contained metal, mainly as bornite, chalcopyrite and sphalerite. This occurs on both sides of the Kipushi Fault, with a horizontal length varying from 200 to 500 m. The zone may be up to 40 to 60m wide in the Kakontwe Formation.
Low Grade Copper Ore - with grades of around 2% Cu, mainly as chalcopyrite. This type penetrates into the Serie Recurrente, forming irregular stratabound lenses and 'fingers' which may extend up to 180 m eastward from the Kipushi Fault.
Very Rich Zn Ore - which contains around 40% Zn as sphalerite, occurring as elliptical pipes of 5 to 20 m in diameter that penetrate deeply into the Kakontwe Formation dolomites. These pipes are connected to the main ore, either laterally or upwards. The rich sphalerite cores are often surrounded by pyritic sheaths.
The dimensions and shape of the orebodies vary considerably from level to level, but an overall strike length of 600 to 800 m and width of 15 to 60 m is attained, while drilling has indicated that ore persists to at least 1900 m (Francois and Coussement 1990).
Bornite is enriched in the upper levels in association with Ag, Ge and Mo. Bornite disappears below level 850. At greater depth, the Cu grades decrease while Zn and Pb levels increase correspondingly. For example on the 1150 m level, grades are 4.3% Cu, 11.2% Zn, 0.5% Pb, while on the 1300 m level they are 2.7% Cu, 14.8% Zn, 0.8% Pb.
Broadly, sphalerite occurs within dolomitic shales, while chalcopyrite is within breccias. Francois and Coussement (1990) also note that the sulphides of the deposit in decreasing order of abundance are sphalerite, chalcopyrite, bornite, pyrite, arsenopyrite, tennantite, galena and renierite, with minor briartite, gallite, germanite, carrollite, brechtinite, molybdenite, stomeyrite, mawsonite, tungstenite and germanium bearing sulvanite (de Vos, et al., 1974).
According to Intiomale and Oosterbosch (1974), the Kipushi deposit represents sulphide mineralisation replacing Lower Kundelungu carbonates (mainly dolomite and dolomitic shale) along a transverse fault bordering the brecciated core of an anticlinal structure. The mineralisation spreads into the wallrock formations from the fault following bedding planes and along conjugate fractures. The mineralisation more abundantly follows the intersection of the fault and the lithostratigraphic contact between the dolomite and the dolomitic shale, as well as in pipes within the dolomite, connected to the faulted zone.
The paragenesis of the ore according to Intiomale and Oosterbosch (1974) comprises an early Zn bearing phase represented by pyrite-arsenopyrite-sphalerite-galena mineralisation with minor Cu, Cd, Bi, Ge and Ga. This is present in both the Main Ore and the Zn rich pipes. This phase was followed by a second, or Cu-Fe phase introduced in at least two stages, the second of which does not rise as high as the first one in the deposit. Each of these Cu bearing stages consists of two sub-stages; an early sub-stage responsible for the veins of cobaltiferous chalcopyrite with subordinate molybdenite and a later sub-stage responsible for the argentiferous bornite. The Cu bearing mineralisation has reworked the earlier Zn-Pb deposit by concentrating certain mineral phases and by forming new ones.
The deposit contains barium-rich celsian feldspar, hyalophane and Ba-muscovite, although it lacks significant barite (Chabu and Boulégue, 1992; Chabu, 1995). Ore textures include replacement of host-rock, pre-metamorphic folded sulphide veins, sulphides intergrown with metamorphic minerals and post-metamorphic vein-filling sulphides. Sulphides are locally intergrown with phlogopite and albite, suggestive of pre- or synmineralisation albitic and magnesian-potassic alteration. There are several stages of pre- and postore dolomite formation and an important, ore-stage quartz event (Heijlen et al., 2008). An amorphous, non-graphitic organic substance, which occurs locally with sulphides, is interpreted to have been derived by hydrothermal alteration of migrated hydrocarbons (Francotte and Jedwab, 1963; Melezhik et al., 1999; Heijlen et al., 2008). The mineralisation is thought to have occurred when oxidised, metal-bearing fluids encountered a reduced, carbon-rich reservoir that was constantly replenished by a large amount of H2S (sour gas), probably derived from thermochemical reduction of seawater-derived sulphate (Heijlen et al., 2008). Gabbro dykes occur within the mega-breccia just to the west of the deposit. This latter paragraph is paraphrased from Hitzman et al. (2012).
The Prince Leopold Mine at Kipushi commenced operation in 1925. Between then and 1986 it produced 3.8 Mt of Cu, 5.9 Mt of Zn, 0.4 Mt of Pb, 45 000 t of Cd and 120 t of Ge (Francois and Coussement 1990).
Published reserve and resource figures include:
reserves in 1974 - 14 Mt @ 10% Cu, 18% Zn, 1% Pb, 160 g/t Ag (Intiomale and Oosterbosch 1974);
reserves in 1989 - 13 Mt @ 2.9% Cu, 14% Zn, below the 1300 m level where Cu grades drop off (Francois and Coussement 1990).
Based on the production figures and grades above, the total deposit would have been of the order of:
40 Mt @ 10% Cu, 18% Zn, 1% Pb, 160 g/t Ag.
In 1988 and 1989 the production rate was 450 000 tpy (RTSA 1990).
The in-situ resources that remain at Kipushi in 2012 (Ivanplats, 2012) were:
~28 Mt @ >20% Zn, ~2% Cu, with associated Pb, Ag and Ge.
(Source: Porter Geoconsultancy, http://www.portergeo.com.au/, 2012)