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Luiswishi, Lukuni and Kiswishi |
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Katanga, Dem. Rep. Congo |
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Cu Co
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Super Porphyry Cu and Au
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The Luiswishi group of copper-cobalt deposits, which includes Luiswishi, Lukuni and Kiswishi are located ~20 km to the NNW of Lubumbashi, and 2 to 5 km NW of Lukuni in the Katanga province of the Democratic Republic of Congo and are part of the extensive Central African Copperbelt. Kiswishi is located ~700 m north of the Luiswishi pit, while Lukuni is ~2.5 km NW of the same pit (#Location: Luiswishi - 11° 30' 57"S, 27° 26' 22"E; Lukuni - 11° 30' 18"S, 27° 25' 14"E).
Regional Setting
For details of the regional setting and stratigraphy see the separate Central African Copperbelt - Congolese/Katangan Copperbelt record.
Geology
Copper mineralisation was discovered at Luiswishi in 1913. The three main deposits, Luiswishi, Lukuni and Kiswishi, are on the same structurally complex Etoile-Luiswishi, which extends to the SE, where it also envelopes the Rusahi and Etoile deposits. All three are deposits are hosted by a dolomitic sequence of Roan Group rocks on the overturned northern flank of the Ruashi anticline, close to the thrust contact between the Upper Roan and Lower Kundelungu Groups.
The preserved host Mines Subgroup sequence, overlying the R.A.T. Lilas of the R.A.T. Subgroup at Luiswishi, can be summarised as follows, from the base (after Cailteux et al, 2005):
Kamoto Formation, R-2.1 - which is up to 50 m thick, comprising a transgressive sequence, subdivided into,
• Roches Argilo Talqueuses Grises (Grey R.A.T., R-2.1.1) - a structureless grey-green silt rock that varies from 3.9 to 8.1 m in thickness at Luiswishi.
• Dolomites Stratifées (D.Strat., R-2.1.2a) - grey, laminated, magnesite rich, fine-grained, argillaceous and chloritic, dolostone beds.
• Roches Siliceuses Feuilletées (R.S.F., R-2.1.2b) - siliceous, finely bedded dolostones, laminitic stromatolites and chloritic-dolomitic siltstones, which together with the D.Strat., is 2.1 to 9 m thick at Luiswishi.
• Roches Siliceuses Cellulaires (R.S.C., R-2.1.3) - originally composed of massive, reefal stromatolitic dolostones, and lesser interbedded dolomitic siltstones, with casts after evaporite minerals, but now consisting almost exclusively of coarse dolomite and secondary quartz. It is distinguished from the underlying R.S.F. by the absence of banding, and at Luiswishi is 1 to 4.3 m thick.
Dolomitic Shale Formation, (S.D., R-2.2) - also a transgressive sequence, which is subdivided into,
• Schistes Dolomitiques de Base, (S.D.B. or S.D.-1a, R-2.2.1a) - a basal bedded dolomitic shale,
• Black Ore Mineralised Zone, (B.O.M.Z. or S.D.-1b, R-2.2.1b) - a band of dark, silty and chloritic dolostone, coarsely crystalline dolostone and dolomitic shales. Together the S.D.B. and B.O.M.Z. are 1.7 to 7.4 m thick at Luiswishi,
• Schistes Dolomitiques Supérieur (S.D.S.) - an alternation of pure dolostones and dolomite-poor, feldspar-rich and micaceous sandy pelites to sandstones. At Luiswishi, this sequence is 13.1 to 31.7 m thick, and has been split into,
- S.D.-2a - carbonaceous dolomitic shale,
- S.D.-2b and c - dolomitic shale and shaly dolostone,
- S.D.-2d - carbonaceous dolomitic shale,
- S.D.-3a - dolomitic shale and shaly dolostone,
- S.D.-3b - carbonaceous dolomitic shale.
Kambove Formation, Calcaire á Mineral Noir, or C.M.N., R-2.3 - a regressive sequence, which is 5.6 to 19.3 m thick at Luiswishi, where only the
• Lower Kambove Member, (R-2.3.1) is represented within the main deposit area. At Luiswishi it has been divided into three units,
- massive dolostone, stromatolites and dolomitic shale,
- laminated algal dolostone,
- massive stromatolitic dolostones, and crypto-algal and laminated talcose dolomite.
• Upper Kambove Member, (R-2.3.2), which is generally 40 to 100 m thick distal to the Luiswishi deposit, and is divided into three units
- pink-brown to white massive dolomite,
- dolostone, stromatolites, talcose dolomite, evaporitic breccia and grey-green siltstone,
- pink-brown to white dolostone, talceous dolomite, evaporitic breccia and red siltstone.
The Kambove Formation is overlain by the Dipeta and Mwashya subgroups, and then by the Nguba and Kundelungu groups, as described in the separate Central African Copperbelt - Congolese/Katangan Copperbelt record (see link above).
Structure
The main Luiswishi deposit is hosted within a series of large folded and rotated fragments of Mines Subgroup rocks, which together form a megabreccia (after Cailteux and Kampunzu, 1995). These fragments define a north-verging isoclinal synform with an axial plane dipping ~40°SW, the hinge zone of which is occupied by an axial fault, parallel to the axial trace. The deposit covers an area of ~1 km2 (Cailteux et al., 2003, 2004). The blocks of Mines Subgroup rocks which comprise the limbs of the synform are sandwiched between external R.A.T. Subgroup rocks. The fold is cut by several faults parallel, oblique and perpendicular to the fold axis (Cailteux et al., 2003, 2004). The longitudinal fault zones define the Roan megabreccia bounding faults while the transverse fault zones divide the megabreccia into Roan-derived fragments. These fragments are considered as separate deposits, namely Luiswishi deposits 1, 2 and 3. The brittle fault zones that separate the mega-fragments occur parallel, orthogonal or inclined to the direction of the fold, suggesting a polyphase brittle history.
These Roan Group rocks form a core to the Ruashi antiform, a NE vergent nappe structure, the flanks of which comprise sedimentary rocks of the Nguba and Kundelungu groups. The antiform is bounded on its northeastern flank by a longitudinal, SW-dipping overthrust above which the Roan Group rocks override the dolomitic sandstones, siltstones and pelites of the Kundelungu group, Ku-2.1 Kiubo Formation. To the SW, the Roan megabreccia is progressively over-ridden via a series of SW dipping thrusts by rocks of the Mwashya Subgroup, the Grand Conglomerate and succeeding carbonate and clastic rocks of the Nguba Group.
Mineralisation
The Luiswishi ores13601360 occur as two main Cu-Co of the R.A.T. Grises, fine-grained stratified dolostone of the D.Strat., and silicified-stromatolitic dolomites alternating with chloritic-dolomitic silty beds of the lower R.S.F.. The Upper Orebody is found towards the base of the S.D. Formation, mainly in the S.D.B. and B.O.M.Z. members. The two are separated by the generally barren R.S.C.. Minor, discontinuous, low grade sulphide mineralisation is known in similar lithologies of the carbonaceous units of the Kambove Formation (the 'Third Orebody'), giving rise to oxide ores in the weathered zone, representing 9% of the total proved reserves in the deposit (El Desouky et al., 2010; Lerouge et al., 2005).
The hypogene mineralisation in the two main orebodies is mainly stratabound disseminated chalcopyrite and carrolite with minor pyrite and bornite (Cailteux et al., 2003). Co-Ni-bearing pyrite, siegenite, carrolite or polydymite also occur in the Lower and Upper orebodies in the eastern part of the deposit (Loris, 1996).
Hypogene sulphides essentially occur as early disseminated and bedding-parallel layers of chalcopyrite and carrolite, and late veinlets and stockwork sulphides cross-cutting the bedding and the early sulphide generation. The second generation of sulphides has a mineralogy quite similar to that of the first, and its emplacement is attributed to the Pan-African/Lufilian tectonometamorphic event (Kampunzu and Cailteux, 1999; Cailteux et al., 2005).
Chalcopyrite, carrolite and minor bornite hosted occurs as alternating millimetre- to centimetre-thick layers in silicified dolomite and shales of the R.S.F., arenitic dolostone of the D.Strat., and chlorite-dolomite-rich arenite of the R.A.T. Grises of the lower orebody (El Desouky et al., 2010).
Towards the base of the S.D. Formation, chalcopyrite, carrolite and minor bornite are also hosted in evaporitic dolomite (pseudomorphed after anhydrite) and dolomitic shale beds of the upper orebody in both the B.O.M.Z. and S.D.B (El Desouky et al., 2010).
The upper part of the S.D. Formation, the S.D.S., contains some chalcopyrite and carrolite, largely hosted in the carbonaceous S.D.-2a, S.D.-2d and S.D.-3a beds (El Desouky et al., 2010).
In the uppermost Kambove Formation, sulphides are very fine-grained disseminated pyrite with minor sphalerite, hosted in dolomite.
Isotopic studies (El Desouky et al., 2010) show a large range of δ34S values, from -14.4 to +17.5‰ for chalcopyrite and -10.2 to +13.6‰ for carrolite. The most negative values were obtained from the Upper Orebody S.D. Formation, and the most positive from the Lower Orebody in the Kamoto Formation, with the distribution having a lithostratigraphic control. There is a reversal of the trend, with a slight increase in δ34S values upwards into the S.D.S from the lowest in the base of that member (El Desouky et al., 2010).
In more detail, δ34S values of the first phase stratabound sulphides range from -14.2 to +17.5‰ for chalcopyrite and between -13.1 and +3.0‰ for carrolite, whereas those from the second phase veins and stockworks vary from +2.5 to +11.3‰ for chalcopyrite and from -13.1 to +13.6‰ for carrolite (El Desouky et al., 2010).
The similar, but wide range of the δ34S values, suggests the last stage involved development of new veining and substantial overprinting of, and redistribution of sulphur from, the earlier sulphides. El Desouky et al. (2010) conclude that petrological features combined with sulphur isotopic data of sulphides at Luiswishi and on nodules of anhydrite in the Mine Series, indicate a dominant origin of sulphides from seawater/lacustrine sulphates, precluding a possible hydrothermal introduction of the sulphur.
All Cu-Co minerals in the weathered superficial zone and most of the minerals in surface outcrops in the open pit mine are oxidized, with malachite, chrysocolla and azurite as the main supergene copper-bearing minerals, and heterogenite as the principal supergene cobalt mineral, and hematite is the predominant non-Cu-Co mineral. Supergene Cu-Co oxide minerals are mainly concentrated along bedding planes, in cavities, cracks, and in fracture zones associated with faults, and decrease in abundance with depth (Lerouge et al., 2005).
The Luiswishi orebody also carries cross cutting vein type uranium mineralisation, similar to that at Shinkolobwe and the other Congolese U deposits (Swambo, Menda and Kalongwe), which like in those deposits, is restricted to the Lower Ore Zone. Although visible uranium minerals are only found in the veins of the Lower Ore Zone, relatively high radiometric levels are also found in the totally weathered lower 2 to 3 m of the upper mineralised interval above the RSC. The uranium occurs in coarse to pegmatitic veins of magnesite and dolomite, with minor quartz and albite, close to and within the brecciated and folded Lower Orebody Zone in the thrust contact between the Roan and the Kundelungu. Primary uraninite and pitchblende in crystals up to 5 cm across occur together with linnaeite and minor chalcopyrite and pyrite. Disseminated monazite is also fairly common. The weathering of the veins does not produce secondary uranium minerals, while Co occurs as erythrite (rather than the more usual heterogenite) and Cu tends to be katangite rather than malachite.
Resources and Past Production
Published figures include:
Luiswishi
Production + reserves/resources 2012 - 12.4 Mt @ 4.32% Cu, 0.95% Co; (Hitzman et al., 2012 after J. Woodhead, unpub. data, 2012);
Production + resources - 8 Mt @ 2.50% Cu, 1.10% Co (USGS Scientific Investigations Report 2010-5090-J, 2010);
Lukuni
Production + resources - 2.7 Mt @ 4.30% Cu, (USGS Scientific Investigations Report 2010-5090-J, 2010);
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2010.
Record last updated: 31/12/2015
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Luiswishi Lukuni
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Selected References:
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El Desouky H A, Muchez P, Boyce A J, Schneider J, Cailteux J L H, Dewaele S and von Quadt A, 2010 - Genesis of sediment-hosted stratiform copper-cobalt mineralization at Luiswishi and Kamoto, Katanga Copperbelt (Democratic Republic of Congo): in Mineralium Deposita v.45 pp. 735-763
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Lerouge C, Cailteux J, Kampunzu A B, Milesi J P and Flehoc C, 2005 - Sulphur isotope constraints on formation conditions of the Luiswishi ore deposit, Democratic Republic of Congo (DRC): in J. of African Earth Sciences v.42 pp. 173-182
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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