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Chambishi |
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Zambia |
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Cu Co
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
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The Chambishi Main, West and Southeast sediment hosted copper-cobalt deposits are developed within the Lower Roan Group in the Zambian Copper Belt. They are located on the southwestern margin of the 'Kafue Anticline', approximately half way between the Nkana-Mindola and Nchanga mining complexes in northern Zambia. They are ~360 km north of Lusaka and 28 km NW of Kitwe. Chambishi Southeast is centred on a point ~10 km NW from the Mindola mine, while the Main and West deposits, which are separated by a narrow barren gap, are a further ~7 km to the NW (#Location: 12° 39' 36"S, 28° 3' 21"E).
The Chambishi Main deposit was discovered in 1902, with underground access being developed in 1927, although operations were suspended in 1931 due to depressed copper prices. Operations were not restarted until an open pit was initiated in 1963, with the first ore treated in 1965, to be supplemented by underground production from 1972. The open pit was closed in 1978, and the underground mining were suspended in 1987. Non-Ferrous Corporation Africa (NFCA) aquired the operation in 1998, and commissioned a new undeground mine in 2003. Construction commenced on the Chambishi West underground mine in 2007, with first production in 2010. Exploration at Chambishi Southeast has sporadically taken place since 1903, with the main discovery drilling from 1975 to 1982. Production was scheduled to begin in 2016.
Regional Setting
For details of the regional setting of Chambishi, the Chambishi-Nkana basin, the Central African/Zambian Copper Belt and the Lufilian Arc, see the separate Zambian Copperbelt record.
The Chambishi deposits are hosted by the Neoproterozoic Lower Roan Group Ore Formation of the Katanga Supergroup, within the Chambishi-Nkana basin, located on the mid-southwestern flank of the 'Kafue Anticline'. The 'Kafue Anticline' is a late-tectonic structural feature within the Domes Region of the Lufilian Arc, centred on a basement high of Palaeo- and Mesoproterozoic gneisses and schists, over which the Katangan sedimentary rocks were draped. The Chambishi-Nkana basin is essentially a NW-SE elongated, doubly plunging, structural basin, predominantly surrounded by pre-Katangan basement. The basinal structure cuts across the generally NW-SE trending facies boundaries within the Lower Roan Group. The Chambishi deposits lie on the northeastern and northern margins of the Chambishi-Nkana structural basin.
Geology & Mineralisation
The stratigraphy of the Lower Roan Group at Chambishi can be summarised as follows, from the base, where it unconformably overlies the Palaeo- to Mesoproterozoic basement complex, which is predominantly a grey, microcline-biotite-granite and numerous aplite dykes, with a few Lufubu schist xenoliths, overlain by Mesoproterozoic Muva conglomerate, quartzite and quartz-schist (after Garlick in Mendelsohn, 1961):
Mindola Clastics Formation or Footwall Formation, 0 to 150 m thick - at surface the Mindola Clastics Formation is thin, but thickens down-dip, and comprises:
Basal Conglomerate, 0 to 65 m thick - a sporadically developed boulder bed near the surface, where it is a metre or so thick, overlying Muva schist east of the orebody, increasing to 65 m in thickness above granite basement deeper in the basin, under the West Orebody.
Footwall Aeolian Quartzite, up to 33 m thick - quartzites with large scale cross bedding (most likely aeolian), with upper beds which are coarser grained, feldspathic to arkosic and with considerable small scale crossbedding suggesting a provenance from the SW. Includes a layer of anhydrite lenses. Laps against granitic basement highs in many places where the Basal Conglomerate is absent.
Footwall Transition Arenites, 0 to 18 m thick - arkose, grading upwards into argillaceous arenites and thin argillites. The unit contains local, thin zones of disseminated chalcopyrite and pyrite, and a few fekdspar, quartz and sulphide veins.
Cobble Conglomerate, 0 to 20 m thick - a conglomerate with granite and quartzite cobbles up to 8 and rarely 25 cm in diameter in a carbonate and anhydrite-rich sandy matrix which leaches to a porous manganiferous material near surface. A few drill holes intersected traces of disseminated bornite and chalcopyrite in parts of this member.
Arkose and Argillite, 12 to 25 m thick - poorly bedded, white to pink arkose and layers of grey, generally schistose sandy argillite. Under the shallower parts of the Main orebody and farther east the argillite beds are absent.
Footwall Conglomerate, 0.5 to 10 m thick - this member has a variable composition and thickness. Where thickest it is a coarse arkose with pebbles and rare cobbles, and near the surface large fragments of granite and schist. In places there are scree like granitic deposits flanking granitic palaeo-hills. Elsewhere it is 1 to 3m thick and comprises light grey and rarely pink, poorly sorted, porous, pebbly arkose. In many drill holes, down dip this member is a thin gritty arkose or feldspathic quartzite, difficult to differentiate from the underlying quartzites of the 'Arkose and Argillite' and 'Footwall Quartzite' members.
Kitwe Formation, which commences with the:
Copperbelt Orebody Member, previously known as the Ore Formation or Ore Shale, 0 to 30 m thick - where fully developed, the basal 1 to 3 m of the Copperbelt Orebody Member is a dolomitic-schist, a rock rich in carbonate which is intensely contorted and schistose and cut by quartz-dolomite-anhydrite veins. The major part of the Copperbelt Orebody Member is a fine grained, biotite-quartz argillite, with well developed banding due to differences in grain size and the varying minor dolomite content. A pronounced flow-cleavage is parallel to the axial planes of small and large drag folds. In the west, the cleavage is less prominent. Over considerable areas small lenticules of dolomite, anhydrite and minor quartz, commonly with sulphides, are prominent in the upper parts of the Copperbelt Orebody Member. The upper 3 to 6 m is commonly more sandy, and may show graded bedding. Near the surface and near granitic promontories, cross bedded arkosic lenses in scours herald the approach of the hangingwall arenites. Down dip, a brownish vuggy dolomite bed up to 1 m thick occurs 2.5 m from the top. West of the Chambishi West Orebody, the Copperbelt Orebody Member becomes black, carbonaceous and pyritic.
In the folded section of the Main Orebody, and in the West Orebody, the Copperbelt Orebody Member averages close to 30 m in thickness, but down dip, thins to 20 m. Against resistant granite ridges, both east and west of the Main Orebody, the shale thins to 6 m, as the lower beds become sandy or arkosic, which in the absence of 'Footwall Conglomerate' may not be distinguished from footwall arenites. Rarely is argillite found in contact with granitic basement. East of the easternmost granitic promontory, the Copperbelt Orebody Member is 6 to 9 m thick for 1.5 km, beyond which it becomes sandy or quartzitic and may not be differentiated from the overlying or underlying arenites.
In the Main Deposit, where the Copperbelt Orebody Member is above the eastern granite ridge, it is barren and contains numerous arkosic layers, which thin down-dip and to the west, accompanied by the appearance of disseminated chalcocite in the lower third of the Copperbelt Orebody Member. Chalcocite gives way to bornite down-dip, while in the basal dolomite-schist, chalcopyrite appears, accompanied by abundant bornite. Coarse aggregates of both bornite and chalcopyrite are distributed along bedding planes, with associated cross-cutting quartz-dolomite veins carrying the same sulphides. The basal dolomitic-schist thickens down-dip and to the west, to become a 3 m thick layer with grades of up to 10% Cu. This high grade compensates for the progressive down-dip decrease in copper grade in the overlying argillite, as bornite passes into chalcopyrite. Further down-dip and to the west, chalcopyrite in the upper Copperbelt Orebody Member gives way pyrite. Bornite again appears as the western granite ridge is approached, and over which the Copperbelt Orebody Member thins to ~6 m, and is barren for a strike interval of ~200 to 300 m. Grades in the chalcopyrite, chalcopyrite-bornite and bornite zones generally average ~2%, 2 to 4% and >4% Cu respectively.
The Main orebody is laterlly limited by the two basement granite ridge. It has a strike length of ~800 m, expanding to 1500 m at a depth of ~300 m, with a thickness of up to 30 m, averaging 8 m, and an overall dip of 15 to 75°W with a series of drag fold-related reversals (Fleischer et al., 1976; SRK 2012).
The West Deposit, occurs to the west of the 200 to 300 m wide barren gap over the western granite ridge. As the Copperbelt Orebody Member thickens again, the sulphide mineralogy is dominated by chalcopyrite disseminations, with only minor bornite appearing again. The deposit has a strike length of ~1800 m, persists down dip for ~600 m, varies from 2 to 17 m in thickness, averaging 8 m, and is lower grade, containing ~2% Cu. A small ore lense is also found in arkose below the Cobble Conglomerate where these beds abut the western granite ridge. While the eastern margin of the West Deposit is influenced by the barren gap over the western granite ridge, its western margin corresponds to a facies change within the Copperbelt Orebody Member to a thick pyritic and carbonaceous shale, that persists to the western margin of the Nkana-Chambishi structural basin (Fleischer et al., 1976; SRK 2012).
There is an ~20 km long, largely barren gap to the south, separating the Chambishi Main deposit and Mindola. Within the middle of this interval, the Chambishi Southeast resource has been outlined, comprising two orebodies distributed over an 8 km by 1 to 2 km NW-SE trending zone. The North body is 4500 m long, 570 to 1240 m wide, dips at 5 to 15°NW and is 1.4 to 23 m thick, averaging 10 m, with ~55 Mt @ 2.3 to 2.4% Cu, 0.074% Co. The south body is 3540 m long, 800 to 1600 m wide and lower grade, with ~50 Mt @ 1.6% Cu, 0.0125% Co. The deposits are flat lying to shallowly dipping, and completely blind. They are located on the flanks of a palaeo-hill over which the Ore Formation becomes dolomitic. Cobalt mineralisation appears within the Copperbelt Orebody Member on the flanks of the basement palaeo-hill. Away from the palaeo-hill, the Mindola Clastics Formation again comprises quartzites, grits and conglomerates, and the overlying Ore Formation consists of interbedded dolomite shale/siltstones and argillites with organic carbon. The mineralisation occurs as fine disseminations (5 to 1500µm, with most between 25 and 400µm) or concentrations of chalcopyrite, distributed along bedding planes with minor amounts of carrollite, cobaltiferous pentlandite and skutterudite, and bornite/linnaeite in certain areas. Beyond the copper mineralisation, sulphides are principally pyrrhotite and pyrite (Garlick, 1961; Fleischer et al., 1976; Fleischer, 1984; SRK 2012).
The remainder of the Kitwe Formation, above the Copperbelt Orebody Member, was previously known as the "Hanging wall Formation", which is 40 to 80 m thick, and is subdivided into,
Hangingwall Quartzite, 3 to 12 m thick - an eastward thickening unit of white feldspathic quartzite and arkose beds with streaks of detrital iron oxides and silty and argillaceous layers.
Interbedded Quartzite and Argillite, 25 to 35 m thick - over the Main and West Orebodies this comprises a 25 m thick argillite unit with two quartzite members near the middle, each of around 3 m thickness. Above these middle quartzites, there are 12 to 15 m of schistose shale and dolomite. To the east, the quartzites thicken at the expense of the intervening argillites.
Upper Quartzite, 12 to 25 m thick - a coarse white to pink feldspathic quartzite, with in places a few pebbles. Near the base and top there are some thin silty and argillaceous beds. Magnetite and other detrital minerals mark the cross bedding, with intense concentrations on lower foresets and bottomsets. Generally it is 14 to 15 m thick, but thickens to the east due to an increase in the arenaceous content of the underlying and overlying units. It is also characterised by a chalky white appearance from the weathering of its high feldspars content.
Upper Roan Group, averaging 350 m thick - comprising, ~25 m of interbedded schist and quartzite; 12 to 24 m of cherty dolomite, 75 to 90 m of sandy talc-schist, and up to 400 m of white to pink dolostone, that includes some cherty layers with talc, and shale bands with disseminated pyrite. Around 100 m above the base of the latter dolostone unit in the northern and western parts of the Nkana-Chambishi Basin, a ~170 m thick metagabbro sill is underlain by ~52 m of granophyre, ~8 m of magnetite-rich rock and a further 35 m of gabbro, enclosed within Upper Roan Group carbonates. Chlorite-amphibole shear zones within the gabbro, contain dolomite, sparse pyrite, pyrrhotite and minor chalcopyrite.
Mwashia Group, 550 m thick - comprising ~300 m of grey argillite, overlain by ~240 m of black carbonaceous argillites, with substantial disseminated pyrite and minor chalcopyrite.
Nguba Group, ~1000 m thick - diamictite, dolomite and shale.
Structure
The Lower Roan is strongly deformed in the vicinity of Chambishi Main and West, the main structure being the Chambishi Monocline, which parallels the Kafue Anticline margin in the vicinity of the western granite ridge. Conspicuous east-west drag folds associated with this structure are seen to the east of the ridge. The most intense folding is in the Ore and Hangingwall Formations, with the Upper Quartzite in the upper limb commonly thrust over the adjacent syncline. Fold geometries and plunges are influenced by the granite ridges also.
Published production, reserve and resource figures include:
Total production + resource as at 1988 - 240 Mt @ 2.3% Cu (Freeman, 1988);
Total production to 1988 - 33 Mt @ 2.88% Cu (Freeman, 1988);
Mineral resources at the end of 1997 (Northern Miner, Jan 26, 1998) were:
Chambishi Main Mine, proved reserves - 33.5 Mt @ 2.55% Cu;
Chambishi West Mine, resources - 47 Mt @ 2.27% Cu;
Chambishi Southeast Mine, resources - 69.7 Mt @ 2.59% Cu, 0.13% Co;
Total remaining ore reserves and mineral resources at 31 December 2011 (China Non Ferrous Metal Industries, 2012) were:
Chambishi Main Mine
sulphide, proved + probable reserves - 8.7 Mt @ 1.92% Cu;
sulphide, measured + indicated resources - 10.7 Mt @ 2.5% Cu;
sulphide, inferred resources - 8.1 Mt @ 2.42% Cu;
Chambishi West Mine
proved + probable reserves - 25.3 Mt @ 1.44% Cu;
oxide, indicated resources - 6.2 Mt @ 1.11% Cu;
sulphide, measured + indicated resources - 25.3 Mt @ 2.06% Cu;
inferred resources - 17.3 Mt @ 2.09% Cu;
Chambishi Southeast Mine
probable reserves - 29.7 Mt @ 1.44% Cu, 0.10% Co;
sulphide, indicated resources - 35.4 Mt @ 2.30% Cu, 0.12% Co;
sulphide, inferred resources - 125.6 Mt @ 1.82% Cu, 0.10% Co.
TOTAL measured + indicated resources - 77.6 Mt @ 2.16% Cu;
TOTAL inferred resources - 151.0 Mt @ 1.88% Cu.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 2012.
Record last updated: 9/8/2013
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.
Chambishi
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Annels A E 1989 - Ore Genesis in the Zambian Copperbelt, with Particular Reference to the Northern Sector of the Chambishi Basin: in Boyle R W, Brown A C, Jefferson C W, Jowett E C, Kirkham R V, (eds), Sediment-hosted Stratiform Copper Deposits: Geological Association of Canada Special paper 36 pp 427-452
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Fleischer V D 1984 - Discovery, Geology and Genesis of Copper-cobalt Mineralisation at Chambishi Southeast Prospect, Zambia: in Precambrian Research v25, no.1-3 pp 119-133
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Fleischer V D, Garlick W G, Haldane R 1976 - Geology of the Zambian Copperbelt (Exerpt covering Chambishi): in Wolf K H, (ed), Handbook of Strata-bound and Stratiform Deposits; II. Regional Studies and Specific Deposits Elsevier, Amsterdam v6, Cu, Zn, Pb and Ag Deposits pp 249-256
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Garlick W G 1961 - Chambishi: in Mendelsohn F (ed), Geology of the Northern Rhodesian Copperbelt McDonald, London pp 281-297
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Greyling L N, Robb L J, Master S, Boiron M C and Yao Y, 2005 - The nature of early basinal fluids in the Zambian Copperbelt: A case study from the Chambishi deposit: in J. of African Earth Sciences v.42, pp. 159-172,
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Selley D, Broughton D, Scott R, Hitzman M, Bull S, Large R, McGoldrick P, Croaker M and Pollington N, 2005 - A new look at the geology of the Zambian Copperbelt: in Economic Geology, 100 Anniversary Volume, Society of Economic Geologists, pp. 965-1000
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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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