Lithostratigraphy, basin development, base metal deposits, and regional correlations of the Neoproterozoic Nguba and Kundelungu rock successions, central African Copperbelt

Gondwana Research 11 (2007) 432 – 447 www.elsevier.com/locate/gr

Lithostratigraphy, basin development, base metal deposits, and regional correlations of the Neoproterozoic Nguba and Kundelungu rock successions, central African Copperbelt M.J. Batumike a,b,⁎, J.L.H. Cailteux c , A.B. Kampunzu d,1 a

b

c

Département de Géologie, Université de Lubumbashi, B.P.1825, Lubumbashi, Congo Department of Earth and Planetary Sciences, ARC National Key Center for Geochemical Evolution and Metallogeny of Continents (GEMOC), Macquarie University, NSW 2109, Sydney, Australia Département de Recherche et Développement,Groupe G.Forrest International, Lubumbashi, D.R.Congo (av. Pasteur, 9, B-1300 Wavre, Belgium) d Department of Geology, University of Botswana, Private Bag 0022,Gaborone, Botswana Received 29 June 2005; accepted 18 April 2006 Available online 14 August 2006

Abstract The Neoproterozoic Katangan Supergroup comprises a thick sedimentary rock succession subdivided into the Roan, Nguba, and Kundelungu Groups, from bottom to top. Deposition of both Nguba and Kundelungu Groups began with diamictites, the Mwale/Grand Conglomérat and Kyandamu/Petit Conglomérat Formations, respectively, correlated with the 750 Ma Sturtian and (supposedly) 620 Ma Marinoan/Varanger glacial events. The Kaponda, Kakontwe, Kipushi and Lusele Formations are interpreted as cap-carbonates overlying the diamictites. Petrographical features of the Nguba and Kundelungu siliciclastic rocks indicate a proximal facies in the northern areas and a basin open to the south. The carbonate deposits increase southward in the Nguba basin. In the southern region, the Kyandamu Formation contains clasts from the underlying rocks, indicating an exhumation and erosion of these rocks to the south of the basin. It is inferred that this formation deposited in a foreland basin, dating the inversion from extensional to compressional tectonics, and the northward thrusting. Sampwe and Biano sedimentary rocks were deposited in the northernmost foreland basin at the end of the thrusting. The Zn–Pb–Cu and Cu–Ag–Au epigenetic, hypogene deposits occurring in Nguba carbonates and Kundelungu clastic rocks probably originate from hydrothermal resetting and remobilization of pre-existing stratiform base metal mineralisations in the Roan Group. © 2006 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. Keywords: Copperbelt; Nguba-Kundelungu; Lithostratigraphy; Basin evolution; Zn–Pb–Cu

1. Introduction The Neoproterozoic central African Copperbelt is well known for its world-class disseminated stratiform Cu–Co (e.g., Kamoto, Nchanga) and massive Pb–Zn–Cu (e.g., Kipushi) ore deposits hosted within the Katangan sedimentary succession (Fig. 1). The belt is bordered to the northwest by the Archean Congo Craton and the Mesoproterozoic Kibaride belt, to the east-northeast by ⁎ Corresponding author. ARC National Key Center for Geochemical Evolution and Metallogeny of Continents (GEMOC), Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Sydney, Australia. Tel.: +61 2 9850 9676; fax: +61 2 9850 6904. E-mail address: [email protected] (M.J. Batumike). 1 Deceased.

the Paleoproterozoic Bangweulu block, and to the south-southeast by the Paleo-Mesoproterozoic Irumide belt and Mesoproterozoic Choma Kalomo block (Fig. 2). The lower part of the Katangan sedimentary succession (Roan Group) has been the subject of many detailed multidisciplinary studies because it hosts the important Cu–Co orebodies of the Katangan belt (e.g., Bartholomé, 1972; Binda and Mulgrew, 1974; François, 1974, 1987; Cailteux, 1994; Cailteux et al., 1994, 2005b, and references therein; Kampunzu and Cailteux, 1999; Kampunzu et al., 2000). In contrast, the middle and upper parts of the Katangan Supergroup (Nguba and Kundelungu Groups, respectively) are less documented, except in areas where they host Pb–Zn–Cu deposits, such as at Kipushi, Kengere and Lombe (Fig. 1; e.g., Intiomale and Oosterbosch,

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Fig. 1. The Katangan Belt with the main localities (modified from François, 1974; Cailteux et al., 1994).

1974; Intiomale, 1982, 1983; Cailteux, 1989) or where they are mined for cement and lime production, e.g., at Kakontwe in the Likasi area (François, 1973a) and at Lubudi, 80 km north of Tenke (Schellinck, 1946). Study of the Nguba and Kundelungu Groups is critical in order to understand the geological evolution of the whole Katangan belt, and therefore, the objectives of this paper are to (1) present petrographic and lithostratigraphic investigations of the Nguba and Kundelungu Groups; (2) provide preliminary sedimentological data related to these two units; (3) review the base metal mineralisations occurring in this sedimentary rock succession; and (4) interpret these data in terms of evolution of the Katangan sedimentary basin. Field data used in this study were collected from the Bunkeya, Luiswishi and Kipushi areas (Fig. 1). 2. Geological setting The Neoproterozoic Katangan Supergroup consists of an ∼10,000-m-thick sedimentary succession exposed in southern Democratic Republic of the Congo (hereafter Congo) and northwestern Zambia (Fig. 1). A basal unconformity between the Katangan Supergroup and the Mesoproterozoic Kibaride belt (ca. 1.4–1.0 Ga) occurs north (Mitwaba area) and north-west (Nzilo area) of the Katangan belt (Cahen, 1954; Moureau, 1960; Byamungu et al., 1979; Kokonyangi et al., 2004). Similarly, the basal unconformity with the Paleoproterozoic Ubendian belt (2.1–1.8 Ga) is observed in the “Domes region” (Unrug, 1988)

and within the Katangan belt (Cahen et al., 1970; Porada and Berhorst, 2000). Lithostratigraphic division of the Katangan Supergroup is based on the occurrence of two diamictites, which constitute regional stratigraphic markers. These are the Grand Conglomérat-tillite/diamictite at the base of the Lower Kundelungu Group and the Petit Conglomérat at the base of the Upper Kundelungu Group. This allowed subdivision of the Katangan Supergroup into three groups (Table 1; François, 1973b, 1974, 1987): Roan, Lower Kundelungu and Upper Kundelungu, in ascending stratigraphic order. In this paper, the names “Nguba” (code Ng) and “Kundelungu” (code Ku) have been adopted in place of “Lower Kundelungu” (code Ki) and “Upper Kundelungu” (code Ks) respectively, following the recent proposals made by François (1995) and Cailteux (2003). The name “Kundelungu” was used firstly by Cornet (1897) to designate the sub-tabular rocks forming the Biano Plateau (extrapolated later to the whole tabular succession of the Kundelungu Plateau by the same author). This name is now proposed in place of “Upper Kundelungu” because rocks forming the uppermost part of the Katangan Supergroup are well exposed in the plateaus area and neighbouring districts. In contrast, Lower Kundelungu lithologies are not exposed in these areas, and the name “Nguba” is preferred as rocks belonging to this group are well exposed in the Nguba area (Fungurume district). The Roan Group consists of clastic sedimentary rocks and carbonates, mainly dolomites and dolomitic shales (e.g.,

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Fig. 2. The Katangan belt, part of the Zambezi belt and surrounding crustal blocks (modified from Unrug, 1983; Kampunzu and Cailteux, 1999).

Oosterbosch, 1962; François, 1987; Cailteux, 1994; Cailteux et al., 1994). The Roan sediments of the Copperbelt were deposited in a basin that evolved from a continental rift through a protooceanic (Afar/Red Sea type) rift linked to the breakup of the Rodinia supercontinent (e.g., Kampunzu et al., 1993; Meert and Van der Voo, 1997; Tembo et al., 1999; Kampunzu et al., 2000). Late Roan rocks (Mwashya Subgroup; Cailteux et al., 2007-this volume) and the overlying Nguba and Kundelungu Groups are thick carbonate or siliciclastic sequences assumed to have been deposited in a wider basin corresponding to a major phase of extensional tectonics and normal faulting that marked the transition to a Red Sea-type proto-ocean (Buffard, 1988; Kampunzu et al., 1993). Katangan sedimentary sequences were folded and thrust to the north during the Lufilian orogeny (Kampunzu and Cailteux, 1999). This orogeny produced the ca. 700 km long and 150 km wide northward-convex orogen, named the “Lufilian Arc” (Fig. 2). Three major deformation phases have been identified (Kampunzu and Cailteux, 1999): (1) Kolwezian folding and thrusting (D1), with transport to the north; (2) left-lateral strike– slip faulting (Monwezian event; D2), which affected the deformed and thrusted terranes; (3) the Chilatembo (D3) deformation, which produced east–west folding perpendicular to the orientation of the Katangan belt. Observations indicate that the D1 deformation caused major shearing in the Roan succession (e.g., in RAT–“Roches Argilo-Talqueuses” and Dipeta Subgroups), allowing the detachment of the Roan rocks from the basement and enhancing their breakup (Cailteux and Kampunzu, 1995; Tshiauka et al., 1995; Cailteux et al., 2004, 2007-this volume). The displacement and stucking of the Katangan tectonic sheets

was facilitated by evaporite-bearing beds and generated megabreccias with fragments derived from Roan, Nguba and Kundelungu Groups (Cailteux and Kampunzu, 1995). The timing of these orogenic events is constrained to between ca. 750 Ma, the age of the youngest extensional volcanic rocks, and ca. 525 Ma, the minimum age of U-mineralisations along D2 faults inferred to date the end of the movements (Kampunzu and Cailteux, 1999). Kampunzu et al. (2000, 2003) suggested that the Nguba–Kundelungu transition represents the inversion from extensional to compressional tectonics in the Katangan basin. Kundelungu sedimentary rocks exposed at the northern margin of the belt have horizontal to sub-horizontal attitudes. The contrasting structural patterns between the D1–D2 folded Kundelungu sedimentary rocks and unfolded tabular Kundelungu led to the division of the Katangan belt into a folded and metamorphosed zone forming the Lufilian Arc exposed in the south and a non-metamorphosed zone exposed in the north interpreted as an aulacogen (Unrug, 1988; noted “Tabular” in Fig. 2) or as a palaeograben (Hanon and Dumont, 1997). 3. Lithostratigraphy and petrography The lithostratigraphic subdivisions of the Nguba and Kundelungu Groups used in this paper are supported by new detailed mapping conducted in the Bunkeya and Luiswishi areas, and by logging of borehole cores from the Kipushi mine. A total of 115 samples (30 from Bunkeya, 50 from Luiswishi and 35 from Kipushi) were investigated using standard petrographic techniques. Modal compositions of the rocks were determined from thin sections stained for plagioclase and

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Table 1 Lithostratigraphy of the Katangan Supergroup in Katanga (modified from François, 1973b, 1987, 1995; Kampunzu and Cailteux, 1999; Cailteux, 2003; and according to Cailteux et al., this volume, for the Roan lithostratigraphy) Supergroup

±500 Ma

Group

Subgroup

Kundelungu Ku (formerly Upper Kundelungu)

Biano Ku 3

Ngule Ku 2

Gombela Ku 1 (formerly Likasi)

(±620 Ma) Nguba Ng (formerly Lower Kundelungu)

Bunkeya Ng 2

Muombe Ng 1

±750 Ma Roan R

Katangan

Formation

Former nomenclature (François, 1987)

Members and lithologies

Ks 3

Arkoses, conglomerates, argillaceous sandstones

Sampwe — Ku 2.3

Ks 2.2

Dolomitic pelites, argillaceous to sandy siltstones

Kiubo — Ku 2.2 Mongwe — Ku 2.1 Lubudi — Ku 1.4

Ks 2.1 Ks 1.3 Ks 1.2.4

Dolomitic sandstones, siltstones and pelites Dolomitic pelites, siltstones and sandstones Alternating pink oolitic limestone (“Calcaire de Lubudi”) and sandy carbonate beds

Kanianga — Ku 1.3 Lusele — Ku 1.2 Kyandamu — Ku 1.1 Monwezi — Ng 2.2

Ks 1.2.2 and 1.2.3 Ks 1.2.1 Ks 1.1 Ki 2

Carbonate siltstones and shales Pink to grey micritic dolomite (“Calcaire Rose”) Petit Conglomérat tillite/diamictite Dolomitic sandstones, siltstones and pelites

Katete — Ng 2.1

Ki 1.3

Kipushi — Ng 1.4

Ki 1.2.2

Dolomitic sandstones or siltstones in northern facies; alternating shale and dolomite beds (“Série Récurrente”) in southern facies Dolomite with dolomitic shale beds

Kakontwe — Ng 1.3 Kaponda — Ng 1.2

Ki 1.2.1

Mwale — Ng 1.1 Kanzadi — R 4.3 Mwashya (formerly Upper Mwashya) R4 Kafubu — R 4.2 Kamoya — R 4.1

Ki 1.1 Upper Mwashya R 4.2

Kansuki — R 3.4

Lower Mwashya R 4.1

Dipeta R3

Mofya — R 3.3 R 3.2

R.G.S. — R 3.1 Mines R2

Kambove — R 2.3 Shales Dolomitiques — R 2.2 Kamoto — R 2.1

R.A.T. R1

Carbonates Carbonate shales and siltstones; “Dolomie Tigrée” at the base Grand Conglomérat tillite/diamictite Sandstones or alternating siltstones and shales

Carbonaceous shales Dolomitic shales, siltstones, sandstones, including conglomeratic beds and cherts in variable position Dolomites including volcaniclastic beds Dolomites, arenitic dolomites, dolomitic siltstones Argillaceous to dolomitic siltstones with interbedded feldspathic sandstones or white dolomites; intrusive gabbros Argillaceous dolomitic siltstones (“Roches Gréso-Schisteuses”) Stromatolitic, laminated, shaly or talcose dolomites; locally sandstones at base; beds of siltstones at top Dolomitic shales including three carbonaceous horizons; occasional dolomites Stromatolitic dolomite (R.S.C.), silicified/arenitic dolomites (R.S.F./D.Strat.), grey argillaceous dolomitic siltstone at the base (Grey R.A.T.) Red argillaceous dolomitic siltstones and sandstones (“Roches Argilo-Talqueuses”)

Base of the R.A.T. sequence unknown <900 Ma

Basal conglomerate

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K-feldspar. About 1000 points were counted on each thin section using an Eltinor4 point-counter coupled to a petrographic microscope, following the Gazzi-Dickinson methodology (Dickinson et al., 1983). 3.1. Nguba Group The Nguba Group is subdivided into two major units, namely, the Muombe (formerly Likasi, code Ng 1) and Bunkeya (code Ng 2) Subgroups (Bellière, 1966; François, 1973b, 1987, 1995). The Muombe Subgroup begins with the regional stratigraphic marker of glacial origin (Cahen, 1954; Binda and Van Eden, 1972) known as the “Grand Conglomérat”, also named the Mwale diamictite (Dumont et al., 1997). Rocks of the Muombe Subgroup overlying the Grand Conglomérat display a regional facies change from clastic sedimentary rocks (sandstones, siltstones and shales) in the north to dominantly carbonate rocks (dolomite and limestone) in the south (e.g., at Kipushi). The Bunkeya Subgroup is mainly made up of clastic and dolomitic rocks characterized by abundance of detrital mafic igneous rock grains (Bellière, 1966; Batumike et al., 2006). 3.1.1. Muombe (formerly Likasi) Subgroup The Muombe Subgroup is divided into four formations: the Grand Conglomérat/Mwale, Kaponda, Kakontwe and Kipushi. 3.1.1.1. Grand Conglomérat or Mwale Formation. The Grand Conglomérat or Mwale Formation is generally a massive matrix-supported pebbly and cobbly conglomerate. François (1973b, 1987) described this unit in the western part of the Lufilian Arc (Kolwezi-Tilwezembe region, Fig. 1) as an unsorted grey or greenish grey conglomerate with a fine-grained phyllite–quartz matrix (50–80 vol.%) containing quartzite, quartz, granite, gneiss, diorite, mica schist, gabbro, shale and silicified oolitic dolomite clasts. These clasts are 0.5–500 mm in diameter, angular to rounded, and may be faceted or striated. In the western region, this formation contains a continuous horizon that grades from coarse-grained arkose to orthoconglomerate beds to the northwest (along the Kibaran rocks, in the Nzilo area), to fine-grained arkose with siltstone/shale beds to the east (Tilwezembe area), and to shale/pelite to the south (Kabolela area). Thickness decreases north to south from a maximum of 1300 m in the Nzilo area, down to 120 m in the Kyona area (Fig. 1). Cailteux (1991) described the same suite of clasts at Manfwe (Fig. 1) with 0.02–0.05 mm size detrital minerals (e.g., microcline, plagioclase, muscovite, tourmaline, ilmenite) occurring in a chloritic matrix, and the presence of decimetric to metric sedimentary cycles marked by orthoconglomerate beds (base) overlain by conglomerates, sandstones and bedded pelites (top). These pelites are characterised by thin chloritic layers (0.02– 0.2 mm) alternating with clast-rich layers. In the Bunkeya area, the Mwale unit forms an 80-m-thick (Fig. 3) massive, unsorted and greenish grey matrix-supported conglomerate containing randomly oriented, angular to rounded and faceted clasts (up to 35 cm). Quartz (16–20 vol.%), granite (12–15 vol.%), plagioclase and microcline (3–9 vol.%),

Fig. 3. Lithostratigraphic columns of the Nguba Group in Bunkeya and Luiswishi areas, and at Kipushi. ⁎S.R: Série Récurrente.

rhyolite (4–6 vol.%), quartzite (3–5 vol.%), mica schist (2– 3 vol.%), dolomite (0.6–1 vol.%) and jasper (0–0.6 vol.%) clasts are distributed in a dolomitic shale matrix. In the Luiswishi area, the Mwale Formation is ∼ 600-m-thick (Fig. 3), dominantly matrix-supported grey to darkish grey conglomerate. Clast-supported beds occur within its lower part and two finely bedded shale intercalations occur in its upper part. Angular to well rounded or faceted clasts that are randomly oriented in a dolomitic shale matrix range from 2 mm to 50 cm in diameter. These clasts mainly consist of quartz (14–17 vol.%), granite (10–13 vol.%), quartzite (5–10 vol.%), dolomite (4– 5 vol.%), sandstones (2–4 vol.%), shales (2–5 vol.%) and feldspar (0–0.5 vol.%). The lower part of this unit contains abundant sand-sized clasts and elliptical clasts that are distributed parallel to the bedding near the contact with the underlying Mwashya shales. The proportion of clast decreases upward. At Kipushi, the Mwale Formation is a 300–500-m-thick unsorted greenish grey matrix-supported conglomerate, which also contains interbedded siltstone and shale (Fig. 3). The laminated shales contain isolated clasts lying parallel to the bedding, and display basal flute and load structures, whereas graded bedding occurs in the siltstone beds with a gradual transition between shale and siltstone beds. Sulfides-rich (pyrite and chalcopyrite) carbonaceous beds and a 10-m-thick conglomeratic sandstone bed occur at the base and top of the formation, respectively. Quartz (11–12 vol.%), granite (7– 9 vol.%), dolomite (4–6 vol.%), quartzite (3–4 vol.%), sandstones (1–2 vol.%), feldspar (0–1 vol.%) and mica schist

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(0–0.6 vol.%) clasts are randomly distributed in a dolomitic or carbonaceous shale matrix. Clasts are rounded or angular and range in diameter from a few millimeters to 20 cm. In the Kipushi Pb–Zn–Cu mine, the Mwale contains sulphide-rich veinlets cutting across-bedding in shale beds. The Mwale/Grand Conglomérat diamictite in Zambia mostly occurs along the international border with Congo, in the Copperbelt (≤ 70 m thick) and in the Northwestern Provinces (≥ 200 m thick) north of Kansanshi and around Luswishi (Binda and Van Eden, 1972). Load deformation, erosion channels and intraformational breccias (Binda and Van Eden, 1972; Cailteux et al., 2007-this volume, and references therein) characterize the transition between the Grand Conglomérat diamictite and the underlying Mwashya Subgroup. In the western and northeastern districts (Kolwezi area, E-NE of Lubumbashi) in Congo, significant erosion surface affecting the Mwashya rocks marks the emplacement of the diamictite (François, 1973b, Cailteux, 1991; Cailteux et al., 2007-this volume). 3.1.1.2. Kaponda Formation. This unit was called Kaponda (Intiomale, 1982) from the name of the old village of Kipushi. It is marked by an important change of lithofacies, from detrital in the north to carbonate in the south. In the western part of the Lufilian Arc, the Kaponda Formation is up to 150 m thick and consists of yellowish grey, lilac or grayish-black finely grained banded marly or sandy shales, with locally irregular bedding and lenticular siltstone layers (François, 1973b). To the north (e.g., in the Lubudi, Mamfwe, Mwashya areas), this unit is thinner and grades into coarser sandy rocks (François, 1973b, 1987; Buffard, 1988). In the Bunkeya area, it consists of a 20m-thick greenish to grey laminated or massive siltstone. In the central part of the Lufilian Arc (e.g., Mulungwishi, Kabolela), it consists of banded shales containing alternating marly or sandy shale and dolomite beds (François, 1973b, 1974). To the south and south-east, the proportion of carbonate rocks increases, and a dolomite unit named “Dolomie Tigrée”, characterized by undulating layers (striped appearance), progressively appears at the base (François, 1973a). The Dolomie Tigrée is 0.4 m thick at Kakontwe (Likasi area), 25 m thick at Kakanda, and reaches 50 m in thickness at Mulungwishi. In the Luiswishi area, the Kaponda Formation is 80 m thick and consists of finely bedded carbonaceous siltstones (Fig. 3). These siltstones are composed of chlorite and sericite (up to 40 vol.%) distributed parallel to the bedding, silty quartz grains (12–15 vol.%) and rare plagioclase (< 1 vol. %) within a calcareous matrix. Alternating irregularly bedded reddish dolomitic shales and dolomite beds (banded shales) mark the uppermost part of the formation. At Kipushi, the Kaponda Formation is an ∼150-m-thick finely bedded, carbonaceous, fine-grained dolomite, containing carbonaceous grey to dark-grey dolomitic shale beds (Dolomie Tigrée; Intiomale, 1982), and whitish dolomite beds in places (Fig. 3). The dolomite consists of a dolomicrite with high content (∼ 8 vol.%) of detrital minerals including quartz, feldspar, muscovite and chlorite. Intiomale (1982) identified three units within this formation; from bottom to top: (1) predominantly dolomitic shale; (2) massive dolomite rich in

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limonite; (3) dolomite unit containing chert and sporadic lenticular beds of dolomitic shale. 3.1.1.3. Kakontwe Formation. The Kakontwe Formation draws its name from the Kakontwe village, which is located 6 km NW of Likasi (Fig. 1). At Kakontwe the formation is 245 m thick, and is mostly formed by limestone that are mined for cement and lime production. It consists of (1) 20-m-thick lightgrey massive dolomite (CaO = 29.37 wt.%/MgO = 19.33 wt.%); (2) 26-m-thick massive grey limestone (CaO = 48.20 wt.%/ MgO = 3.27 wt.%), locally with oncolites; (3) 45 m-thick massive limestone (CaO = 51.40 wt.%/MgO = 3.08 wt.%); (4) 119 m-thick bedded grey limestone showing an alternation of dark and light layers (CaO = 54.15 wt.%/MgO = 1.03 wt.%); (5) 23-m-thick massive light grey to black dolomitic limestone (CaO = 40.47 wt.%/MgO = 12.24 wt.%); (6) 12-m-thick bedded dark grey limestone with thin shaly layers (CaO = 46.59 wt.%/ MgO = 2.53 wt.%), from bottom to top (François, 1973a). In that region, total thickness increases from 25 m in Kakanda to the north up to 600 m in Tantara (Shinkolobwe area) to the south. Kakontwe rocks do not occur in the Mulungwishi and Bunkeya districts. Thickness of the Kakontwe Formation in the Kolwezi region also increases, from 10 m in the Tilwezembe area (north) up to 330 m in the Kyona area (south), but it does not occur north of Tilwezembe (François, 1973a). The rocks consist of a massive or stratified pinkish-beige finely grained dolomite, overlain by dark grey to massive dolomite in its southern facies (François, 1973b). At Kipushi, it is ∼ 340-m-thick, massive to bedded, mediumto coarse-grained dolomite unit (Fig. 3) containing calcite and iron oxides (up to 4 vol.%), and cemented by micritic dolomite. Three units were identified (Intiomale, 1980, 1983): (1) massive fine-grained light grey dolomite; (2) bedded dolomite containing algal structures and oolites; (3) irregularly bedded grey dolomite with fine carbonaceous layers and many black cherts, from bottom to top. 3.1.1.4. Kipushi Formation. This unit has been documented in the Kipushi, Lombe and Kengere deposits (François, 1973a; Cailteux, 1989) and was named the “Dolomie de Kipushi” (Intiomale, 1980, 1982). It is a 100-m-thick finely bedded black carbonaceous dolomite unit overlying the Kakontwe Formation (Fig. 3), characterized by white oolites and black chert lenses and containing lenticular grey-brown dolomitic shales (14– 49 vol.% dolomite; Intiomale, 1980) in its middle part. 3.1.2. Bunkeya Subgroup The Bunkeya Subgroup, newly proposed in this paper, is divided into two formations: Katete and Monwezi. Both formations are represented by sandstones in the northern part of the Katangan belt, and are well exposed and documented in the Bunkeya region (Batumike, 2004; Batumike et al., 2006). 3.1.2.1. Katete Formation. The Katete Formation (in Dumont et al., 1997), named from a village in the Lukafu area where this unit largely occurs (Van den Brande, 1936), is mainly clastic. In

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the northern Kolwezi area, it is a 120-m-thick, predominantly sandy unit containing some arkoses or microarkoses, frequent shale beds, and intraformational conglomerates with shale clasts. In the central part of the Katangan belt, it is a massive pinkish-grey pelite, up to 1500 m thick (e.g., in the Kyona area; Fig. 1), marked in its upper part by hematite and typical centimetre-sized cavities plastered with carbonate–chlorite– hematite (François, 1973b). These cavities probably witness anhydrite concretions dissolution. The Katete Formation exposed in the Bunkeya area consists of 50-m-thick (Fig. 3), fine- to coarse-grained, cross-bedded or massive, purplish to dark grey sandstones. These sandstones are rich in plagioclase and lithic fragments including mainly purplish metapelite and rhyolite clasts. The quartz–feldspar–lithic compositional range of these sandstones is Q40–75F20–45L0–24, with volcanic fragments forming up to 65% of the lithic clasts population. In the Luiswishi area the Katete Formation consists of irregularly layered reddish siltstones composed of chlorite and sericite flakes (20–24 vol.%), angular to sub-rounded silty quartz grains (10–15 vol.%), iron oxides (4–5 vol.%), muscovite (∼ 2 vol.%), and plagioclase (∼ 1 vol.%), randomly oriented in a muddy matrix. Centimetre-sized cavities and hematite occur in the uppermost part of the formation. In the Kipushi mine, above the “Dolomie de Kipushi” occurs a 230-m-thick massive or irregularly bedded grey micaceous– chloritic–dolomitic shale or siltite (3–21 vol.% dolomite; Intiomale, 1980), alternating with metre-sized white to pinkish-grey micritic dolomite beds containing pseudomorphs after evaporite (millimeter-size gypsum crystals). These rocks, named “Série Récurrente” by the local mining geologists (François, 1973a), represents a lithofacies confined to the southern part of the Katangan belt characterized by Katete-type clastic deposition alternating with dolomite beds. Therefore, according to François (1973a) and Intiomale (1980, 1982), the “Série Récurrente” has to be considered as the lateral equivalent of the Katete Formation. Contrastingly, François (1973a, 1987) considered the Série Récurrente Formation as the uppermost unit of the mostly carbonate Muombe succession in the region. However, these rocks are related to the Monwezi sedimentation (Intiomale, 1980, 1982) and represent a new transgressive detrital sequence being marked by a significant input of coarse detritus to the north and by residual carbonate deposition to the south. 3.1.2.2. Monwezi Formation. The Monwezi Formation in the Kolwezi area generally consists of alternating purplish or greenish grey, finely bedded, dolomitic pelites and massive or irregularly layered siltstones (François, 1973b, 1987) with thicknesses ranging between 70 m (north) and > 1400 m (south). To the north, coarse feldspathic–dolomitic graywackes containing some conglomerate beds occur (François, 1987) and, to the south, the absence or paucity of dolomitic beds (Intiomale, 1982) makes easy the distinction between Monwezi and underlying rocks (Likasi Subgroup). In the Bunkeya area, the Monwezi Formation is made up of pinkish sandstones (180 m thick; Fig. 3) characterized by

graded- and cross-beddings. The sandstones are poorly sorted, immature, and consist of angular and rounded sand-sized quartz grains, quartzite and feldspar (mainly plagioclase), and some rhyolitic clasts, within a dolomitic matrix. In places feldspar is replaced by carbonate but well twinned plagioclase grains remain abundant. Petrographic compositions fall within the ranges of Q42–61F36–57L0–6. In the Luiswishi area, the Monwezi rocks consists of up to 500-m-thick greenish to purplish, massive or irregularly stratified, poorly sorted siltstones (Fig. 3). These siltstones are composed mainly of chlorite and sericite (22–28 vol.%), silty quartz grains (10–13 vol.%), plagioclase grains (< 1 vol.%), and abundant opaque minerals (up to 5 vol.%), contained in a muddy matrix. At Kipushi, the Monwezi Formation is represented by 100– 300 m of dolomitic pelites, and marly sandstones and siltstones, showing fine lamination or cross-bedding (Fig. 3). Chlorite flakes and pyrite grains are abundant, and white dolomite fills the fractures. Siltstones are very poor in K-feldspar (< 1 vol.%), and lenticular dolomite beds occur at the upper part of the formation. 3.2. Kundelungu Group The Kundelungu Group (Ku) is subdivided into three subgroups, namely, Gombela, Ngule and Biano in ascending order. The Gombela Subgroup begins with the Petit Conglomérat Formation, a regional stratigraphic marker of glacial origin (Cahen, 1954). The Ngule Subgroup is represented by the folded Mongwe and Kiubo Formations at the base, and by the undeformed Sampwe Formation at the top. Both the Sampwe Formation and Biano Subgroup consist of sub-tabular nonmetamorphosed rocks cropping out in the northern part of the belt. 3.2.1. Gombela Subgroup This subgroup was named Gombela (in Dumont et al., 1997) from a locality in the Mwashya district where the unit is well exposed and was firstly observed (Van den Brande, 1936). The name of Kalule, as recently proposed by François (1995), from both a village located on the Biano Plateau and a river flowing north of the Katangan belt, is not appropriate, as it is also used for a Permian basin in the Luena area to the north which host important coal deposits (Cambier, 1930). The Gombela Subgroup is divided into four units: the Kyandamu (“Petit Conglomérat”), Lusele (“Calcaire Rose”), Kanianga and Lubudi (“Calcaire de Lubudi”) Formations. 3.2.1.1. Petit Conglomérat or Kyandamu Formation. The Petit Conglomérat Formation, also named Kyandamu (Dumont et al., 1997), is a 30–50-m-thick, purplish to greenish grey, massive, unsorted matrix-supported conglomerate, showing a tillite facies to the north (e.g., in the Bunkeya region) and a marine facies in the southern areas (Cahen and Lepersonne, 1967). In the Kolwezi region, this conglomerate contains poorly sorted, subrounded and angular carbonate, quartz, quartzite, jasper, feldspar, shales, and granite clasts; it is characterized by

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the small size of the clasts (generally < 5 cm diameter) and remarkable abundance of clasts in 1–2 cm size range (François, 1973b). In the Bunkeya area, the Kyandamu Formation is an ∼50-mthick (Fig. 4), massive, unsorted matrix-supported conglomerate, which display locally weakly stratified beds containing elliptical clasts aligned parallel to the bedding. It contains rounded, angular, elliptical and faceted clasts of quartz (18–22 vol.%), quartzite (5–6 vol.%), carbonate (5–7 vol.%), feldspar (4–6 vol. %), granite (1–2 vol.%), rhyolite (1–2 vol.%), sandstone (0– 0.5 vol.%), and shale (0–0.5 vol.%). These clasts range from 1 mm to 10 cm in diameter and are randomly oriented in a calcareous or dolomitic sandy shale matrix. The Kyandamu Formation exposed in the Luiswishi area is a 60-m-thick (Fig. 4) sandy to muddy matrix-supported conglomerate containing poorly sorted and isolated millimetre- to decimetre-size clasts up to 20 cm of diameter. These rocks are generally massive, but locally contain interbedded shales and sandstones in the upper part of the unit. Clasts include elliptical, angular or rounded quartz (10–12 vol.%), carbonate (4–5 vol. %), granite (2–4 vol.%), quartzite (1–3 vol.%), sandstone (1– 2 vol.%), shale (0.4–1vol.%), jasper (0–1 vol.%), and plagioclase (0.4–1 vol.%). Shale, sandstone, and carbonate clasts are interpreted to have been derived from the Kakontwe Formation, with lesser representatives plagioclase and jasper derived from the Mwashya Subgroup (R 4). At Kipushi (Fig. 4), it is a 35 m-thick, greenish grey, matrixsupported conglomerate grading into a massive sandstone and a

Fig. 4. Lithostratigraphic columns of the Kundelungu Group in Bunkeya and Luiswishi areas, and at Kipushi.

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finely bedded shale in its upper part. It contains millimetre- to centimetre-size (up to 5 cm) poorly sorted clasts of quartz (11– 14 vol.%), quartzite (10–11 vol.%), carbonate (2–4 vol.%), granite (3–8 vol.%), mica schist (1–2 vol.%), chlorite (0.7– 1 vol.%), plagioclase (0.4–1 vol.%), shale (0–0.7 vol.%), sandstone (0–0.4 vol.%), and occasional chert and jasper. Abundant pyrite grains also occur (up to 3 vol.%). The clasts are angular to rounded and, in places, are elongated lying parallel to the bedding. Most of the clasts are intrabasinal and interpreted to have been sourced from the Nguba Group and Mwashya Subgroup. 3.2.1.2. Lusele Formation. In the Kolwezi region and Lukafu district, the Lusele Formation is a massive or finely bedded, pink or whitish grey, slightly calcareous, fine-grained dolomite. It is 5–15 m thick and contains quartz, scarce authigenic feldspar, muscovite, and iron oxide grains. Although commonly massive, fine and regular bedding can be observed in places (Van den Brande, 1936; Bellière, 1966; François, 1973b). It is a purplish grey dolomite in the Lubudi area, and the contact with the Kyandamu (Petit Conglomérat) Formation is gradual being marked by alternating dolomite and shale beds (Buffard, 1988). The Lusele Formation is a 9–10-m-thick, finely bedded, pinkish grey to pink micritic dolomite. The dolomite contains rare fine muscovite flakes (up to 1 vol.%), quartz (2–3 vol.%), feldspar (0–0.5 vol.%) and pyrite grains (2–3 vol.%) in the Bunkeya area; authigenic quartz (2–4 vol.%) and pyrite grains (1–2 vol.%) in the Luiswishi area, and rare coarse dolomite, calcite, pyrite and feldspar grains at Kipushi. 3.2.1.3. Kanianga Formation. The Kanianga Formation (defined in Grosemans and Jamotte, 1937) in the western part of the Lufilian Arc (Kolwezi region; François, 1973b) consists of alternating greenish or purplish grey, finely bedded dolomitic shales, and massive or coarsely bedded carbonate siltstones. Thickness varies from 300 m in the north to > 1000 m in the south of this area. Carbonate shales (10–30 m thick) overlain by carbonate siltstones occur at the base (François, 1973b, 1987). In the Bunkeya area, this unit is 300 m thick (Fig. 4) and is made up of alternating calcareous or dolomitic shales and siltstones. The transition between Lusele and Kanianga Formations is marked by a 1 m thick alternation of dolomite and shale beds. The Kanianga shales are pinkish grey and finely bedded, with phyllosilicate flakes (muscovite, sericite and chlorite) oriented parallel to the bedding. Siltstones are massive, well sorted, exhibit unidirectional cross-bedding and ripple marks, and show gradual transition with the shales. They contain angular to rounded quartz grains (22–27 vol.%), feldspar including plagioclase and microcline (4–7 vol.%), chlorite (7– 10 vol.%), and muscovite (0–1 vol.%) set in a calcareous matrix. Pinkish dolomite beds alternating with shale and siltstone occur at the top of this unit. This dolomite contains laminated or globular microbial structures characterised by alternating dark and light ondulating layers. In Luswishi area, the Kanianga Formation (up to 1600 m, Fig. 4) consists of massive or irregularly bedded, calcareous– dolomitic siltstone alternating with finely and regularly bedded

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(centimetre-size layers) or laminated dolomitic shale. Silty quartz grains (18–25 vol.%), chlorite (5–8 vol.%), plagioclase (up to 2 vol.%), dolomite grains (5–6 vol.%), sulphides (mainly pyrite, 2–3 vol.%), and subsidiary muscovite in siltstones are well sorted and cemented by dolomite. At Kipushi, Kanianga consists of 500–600-m-thick greenish grey dolomitic or calcareous massive siltstones alternating with laminated sandy marl or dolomitic shales (Fig. 4). In both the Luiswishi and Kipushi areas, the transition between Lusele and Kanianga Formations is marked by alternating dolomite layers within dolomitic shales. 3.2.1.4. Lubudi Formation. This unit was originally called the Calcaire de Lubudi (Grosemans and Jamotte, 1937), and marks the top of the Muombe Subgroup in the Lubudi and Lukafu areas. It consists of several 3–10-m-thick pink limestone beds containing occasional oolites, alternating with Kanianga-type sandy carbonate beds (Van den Brande, 1936; François, 1973b, 1987; Dumont et al., 1997). This formation may reach 80– 150 m in total thickness (Van den Brande, 1936). It has not been observed in the Bunkeya, Luiswishi and Kipushi areas. 3.2.2. Ngule Subgroup The Ngule Subgroup is subdivided into the Mongwe, Kiubo and Sampwe Formations. The name Ngule, newly proposed in this paper, comes from the Ngule river where these three units occur in a continuous section (François, 1973b, 1987). 3.2.2.1. Mongwe and Kiubo Formations. Grosemans and Jamotte (1937) designated the pelite–sandstone–quartzite complex overlying the Lubudi Formation in the Mokabe area as the Kiubo unit. Sandy pelites predominate in the lower part (named Mongwe by Dumont, 1967), whereas sandstone and quartzite are abundant in its upper part (François, 1973b, 1987). The name Kiubo, restricted to a quartzite–sandstone marker occurring at top of this complex by Cahen and Mortelmans (1939), is extended here to define the whole sequence with predominance of sandstones (Kiubo Formation). In the northern part of the Lufilian Arc the Mongwe and Kiubo Formations display similar lithologies (interbedded pelites and sandstones) and sedimentary structures (cross-bedding, intraformational conglomerates, etc.), meaning that both deposited in periodically energetic depositional environment. In the Kolwezi region, the Mongwe (up to 380 m) and Kiubo (up to 250 m) consist of alternating finely bedded dolomitic sandstones or siltstones and purplish-red pelite beds with some arkose (François, 1973b, 1987). The Kiubo Formation contains abundant hematite, and occasional cross-bedding and ripple marks in the sandstone beds. Several ∼1-m-thick pinkish arenitic limestone beds including centimetre-sized discoidal cherty nodules also occur, representing stratigraphic markers (François, 1973b, 1987; Cailteux, 1991). In the central part of the Katangan belt (e.g., Kolwezi, Mamfwe, Kambove, Luiswishi areas; Demesmaeker et al., 1963; François, 1973b; Cailteux and Kampunzu, 1995; Cailteux et al., 2004), a major tectonic discontinuity occurs 150– 250 m above the base of the Kiubo Formation. In these areas, the Kiubo rocks are overlain by thrusted nappes formed by the Nguba

and Kundelungu Groups, and by a breccia marking the discontinuity that contains blocs of the Roan, Nguba and Kundelungu Groups (Kampunzu and Cailteux, 1999). In the Bunkeya area, the Mongwe and Kiubo Formations have a total thickness of 200 m (Fig. 4) and comprise purplish to reddish, irregularly bedded pelites alternating with lenticular massive or layered siltstone to sandstone beds. Siltstones are marked by wavy beds, ripple marks and graded bedding, and contain intrabasinal purplish pelite clasts. A 3-m-thick pinkish massive dolomite unit including discoidal cherty nodules occurs within the Kiubo succession. Siltstones are well sorted and contain rounded to well-rounded quartz grains (25–30 vol.%), chlorite (9–12 vol.%), plagioclase (0–1.5 vol.%), and rare muscovite (0–1 vol.%) cemented by calcite or dolomite. Cahen et al. (1946) recognized lacustrine or marine plant and animal microfossils in these rocks in the Bunkeya-Lukafu region. The Mongwe and Kiubo sequences form a 500-m-thick alternation of greenish or reddish grey siltstones, and finely and irregularly bedded pelites in the Luiswishi area (Fig. 4). Lenticular carbonate sandstone beds displaying graded bedding and ripple marks occur within the succession. The top of the sequence shows pseudomorphs after evaporite (anhydrite) beds and irregular bedding, and siltstone beds containing angular purplish intrabasinal pelite clasts (intraformational conglomerates). At Kipushi, the Mongwe and Kiubo Formations cannot be frankly distinguished. The succession consists of ∼300 m in thickness irregularly bedded dolomitic sandy pelites containing massive dolomitic siltstone layers and 200–300 m in thickness finely bedded greenish grey to grey dolomitic pelites alternating with massive siltstones (Fig. 4). 3.2.2.2. Sampwe Formation. The Sampwe Formation is represented by an ∼ 1700-m-thick sub-horizontal sedimentary succession. It is well exposed only in the northern part of the Katangan belt (e.g., in Gombela and Sampwe areas), where it forms the base of the plateaus (Dumont, 1967; François, 1973b; Dumont et al., 1997). Rocks consist of alternating dolomitic pelite and argillaceous to sandy siltstone beds (François, 1973b, 1987). This formation is marked by cross-bedding, frequent graded bedding, and intraformational conglomerates. 3.2.3. Biano Subgroup The Biano Subgroup (François, 1995) is a sub-horizontal unit (≥ 400 m thick) conformably overlying the Sampwe Formation to the north of the Lufilian Arc (Fig. 1). Along with the Sampwe unit, Biano rocks form remarkable tabular relief (e.g., Kundelungu and Biano Plateaus). They consist of massive to irregularly bedded fine- to coarse-grained arkoses (frequently cross-bedded) and intraformational conglomerates. Some argillaceous sandstone beds also occur within the succession (Bellière, 1966; François, 1973b, 1987). The Biano rocks are distinguished from the Sampwe by the lack of carbonate (Bellière, 1966). Neither Sampwe and Biano are observed in the Bunkeya, Luiswishi, and Kipushi areas. The nature of the transition between folded (Kiubo at top) and tabular (Sampwe, Biano) rocks in the northern part of the Katangan belt (e.g., north of Fungurume) remains speculative.

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Options include (1) progressive evolution from folded to tabular, or (2) a younger tabular succession overlying the folded formations. The first hypothesis is based on observations in the Nynga valley (Mwenda Mukosse area), ∼ 30 km NNE from Fungurume. In this area folds affecting the thrusted sheets (Kiubo and underlying units) decrease in amplitude to the north, and dips of the folded succession reveal an antiform structure, evolving from moderate dips in the south to gentle in the north; Sampwe rocks apparently lie conformably on Kiubo rocks to the north (Demesmaeker et al., 1963; François, 1973b; IGCP450 field trip, Lubumbashi, 2003). In contrast, a compilation of many detailed descriptions, air-photographs and satelliteimagery in several areas indicate that horizontal sedimentary rocks of the plateaus (Sampwe and Biano) discordantly overlie the folded Katangan units (Dumont et al., 1997; Kampunzu and Cailteux, 1999). 4. Sedimentary and tectonic evolution of the Katangan basin Old and new lithological and petrographic data documented in this paper suggest the following evolution of the Nguba and Kundelungu basins. 4.1. Nguba Group deposition The Mwale/Grand Conglomérat Formation, the marker unit at the base of the Nguba Group, shows several features of diamictites (Schermerhon, 1974), including a wide variety of clasts of different sizes contained in a mud matrix, and coexistence of poorly sorted rounded, angular, striated and faceted clasts (Cahen and Lepersonne, 1967; François, 1973b). Oversized clasts and isolated pebbles cutting the bedding in finely laminated shales (e.g., in Zambia, Binda and Van Eden, 1972) have been interpreted as dropstones or lonestones signifying the presence of floating ice in the depositional environment (Crowell, 1983, 1999; Edwards, 1984; Eyles, 1993). The load deformational structures or erosion basal contact with the underlying Mwashya Subgroup (Cailteux, 1994; Cailteux et al., 2007-this volume), coupled with the above features, are indicative of a glacial sedimentary environment (Selley, 1994). Shale or sandstone beds are also known in Palaeoproterozoic/Neoproterozoic glacial deposits, e.g., Port Askaig Tillite in Scotland (Panahi and Young, 1997), Gowganda Formation in Canada (Young and Nesbitt, 1999), Mineral Fork Formation in Utah (Young, 2002), and the Witvlei Group in Namibia (Gorjan et al., 2003). Mudrocks interbedded with diamictite beds may display turbidite features including graded bedding, flute and load casts, and fine lamination (e.g., in the Mineral Fork Formation), similar to those observed in the Grand Conglomérat (Binda and Van Eden, 1972; Cailteux, 1991). The occurrence of shale beds noted in the Mamfwe area (Cailteux, 1991) and in the southern part of the Katangan belt (François, 1973b; Buffard, 1988) is interpreted to relate to the increasing thickness of this formation (Fig. 3). Deposition of this diamictite is constrained by maximum/ minimum ages of 765/735 ± 5 Ma (Key et al., 2001) corresponding to the global Sturtian glacial event. It is the

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equivalent to the (1) Chuos/Varianto Formation in the Damaran Belt, Namibia (Kamona and Günzel, 2007-this volume), giving minimum ages of 746 ± 2 Ma west of the Otavi Mountain Land (Hoffman et al., 1996) and 741 ± 6 Ma in the Gariep belt (Frimmel et al., 1996), and (2) Jequitai Formation 740 ± 22 Ma at the base of the Bambui Group in Brazil (Dardenne, 1978; Babinsky and Kaufman, 2003). The overlying Kaponda Formation displays a progressive north-to-south decrease in grain size in its northern siliciclastic facies, and the deposition of a more carbonate facies to the south (e.g., Dolomie Tigrée). Similarly, the Kakontwe carbonate Formation is unknown in the northern part of the belt, but well developed to the south (Fig. 3). An identical situation occurs within the Katete Formation, with a coarser siliciclastic facies to the north, pelites in the central part of the Katangan belt, and carbonates (Kipushi and Série Récurrente Formations) to the south. This clearly suggests a basin open to the south and characterized by a proximal clastic facies in the north. The Kaponda, Kakontwe and Kipushi Formations are regarded as the cap carbonate to the Mwale/Grand Conglomérat diamictite and signal the beginning of the post-glacial period characterized by influx of weathered material (e.g., Young, 2002). The Katete and Monwezi rocks deposited at top of the Nguba Group form a new generalized transgressive clastic sequence prograding over the carbonates. They are marked by shallowwater carbonate pelites to the south and coarser immature sandstones in the northern part of the Katangan belt (e.g., graded- and cross-beddings in the Bunkeya area), indicating the persistence of the proximal facies to the north. 4.2. Kundelungu Group deposition The Kundelungu rock succession represents a new sedimentary cycle, starting with a matrix-supported conglomerate similar to that at the base of the Nguba Group. This conglomerate contains poorly sorted angular to well-rounded and faceted clasts, as well as isolated clasts (lonestones), supporting a glaciogenic origin (Cahen and Lepersonne, 1967; Selley, 1994; Eyles and Januszczak, 2004). The matrix shows a north– south facies variation from sandy to pelitic, and the bedding in upper beds suggests glacio-marine deposition (e.g., in Luiswishi and Kipushi areas). The lithological composition of the clasts also varies from north to south. Extra-basinal Paleoproterozoic rhyolitic clasts originating from the Bangweulu block occur in the northern part of the Lufilian Arc, but are absent in the south. Feldspars are also more abundant in the north than in the south (4–6 vol.% versus 0–1 vol.% respectively). In contrast, the southern region contains intrabasinal clasts from Roan (Mwashya Subgroup) and Nguba Groups rocks that are unknown to the north. The occurrence of these Roan and Nguba clasts indicates exhumation and erosion of the folded Roan and Nguba Groups during and possibly before the deposition of the Kyandamu/Petit Conglomérat Formation. The muddier nature of the matrix in the southern part of the belt results from the contribution of more weathered Nguba and Roan Groups detritus whereas fresh plagioclase and volcanic clasts were deposited in the northern part.

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The Kyandamu/Petit Conglomérat Formation is tentatively correlated with the ∼ 620–600 Ma Marinoan/Varanger glaciation (e.g., Germs, 1995; Bodiselitsch et al., 2005) although there are no geochronological data to constrain this age. Bodiselitsch et al. (2005) found that this glacial episode lasted between 3 and 12 my. It may be correlative with the Ghaub Formation in the Damaran Belt, Namibia (Kamona and Günzel, 2007-this volume) containing volcanics dated at 635.5 ± 1.2 Ma (Hoffmann et al., 2004), and with the Puga Formation in the Paraguay Belt of Brazil (Alvarenga et al., 2004). The Kyandamu rocks are overlain by a regional pinkish dolomite or limestone (Lusele Formation) displaying relatively constant thickness and lithological character. This unit may represent a cap carbonate signifying the quiet period characterized by extreme weathering following the glacial events (e.g., Cahen, 1954; Germs, 1995; Young, 1995; Saylor et al., 1995; Gorjan et al., 2003). Succeeding the Lusele dolomite, the Kanianga Formation shows a north–south increase in thickness, but without major lithological variation through the Katangan belt with the depocentre, that is located on the central part of the basin (Luiswishi area; Fig. 4). Graded bedding, cross-bedding, and alternating carbonate siltstone–mudstone beds suggest turbidite deposition. Pink oolitic limestone beds at the top of the sequence in the north of the belt indicate a shallow-water proximal deposition. The Mongwe and Kiubo Formations display shallow-water conditions ending the Kundelungu sedimentation in the southern depocentre of the Katangan Basin (e.g., it is upward coarsening and includes intraformational breccias, crossbedding, ripple marks, wavy bedding, and pseudomorphs after evaporite anhydrite-like beds, layers and nodules). In the central part of the belt (e.g., in Kakanda, Kambove, Luiswishi areas), the Kiubo Formation is overlain by allochthonous Roan, Nguba and Kundelungu rocks forming nappes, which were overthrust from the south (Kampunzu and Cailteux, 1999). Sub-horizontal Sampwe Formation and Biano Subgroup were only deposited on Kiubo rocks in the northernmost part of the belt. Deposition of this latest sequence in the Katangan basin is constrained by the tectonic events, and probably occurred between 540 and 460 Ma (Kampunzu and Cailteux, 1999). The question of conformable or unconformable position of Sampwe rocks on the folded Kiubo Formation, and the detailed lithostratigraphic transition between these two units is beyond the scope of this paper and should be the subject of further study and debate. 5. Base metal occurrences and deposits The Mwale, Monwezi, Lusele and Mongwe Formations in Congo contain stratiform low-grade copper (< 0.5 wt.% Cu) occurrences, as disseminated chalcopyrite and pyrite, forming a few decimetre-thick orebodies (François, 1974). These mineralisations are interpreted as syngenetic deposition in the Nguba and Kundelungu foreland basins. The Nguba and Kundelungu Group successions are also marked by numerous Zn–Pb–Cu or Cu–Ag–Au epigenetic deposits occurring in carbonates (Nguba) and clastic (Kundelungu) rocks.

5.1. Kipushi deposit Kipushi is the most significant Zn–Pb–Cu deposit in Congo, totalling >12 Mt Zn mined ores and ore reserves. It is characterized by a suite of major (Zn, Cu, Pb), minor economic (Cd, Co, Ge, Ag, Re) and sub-economic (As, Ni, Mo, Ga, Bi, Se) metals (Intiomale and Oosterbosch, 1974). The deposit has been proven to extend from the surface up to ca. 1800 m depth. The structure hosting the deposit is a NW–SE-trending anticline with faulted axial plane. A heterogeneous layer parallel breccia containing well rounded fragments of Roan and Nguba Group rocks occurs along this axial fault (Briart, 1948; Intiomale, 1982). This tectonic breccia is connected to those underlying the Katangan thrusts (Demesmaeker et al., 1963; Intiomale and Oosterbosch, 1974; Cailteux and Kampunzu, 1995) The Zn– Pb–Cu primary sulphide mineralisation forms sub-concordant minor orebodies and discordant major orebodies. The subconcordant orebodies are hosted in rocks of the Kipushi Formation and in dolomitic shale alternating with dolomites of the Katete (Série Récurrente) Formation. The discordant orebodies are mainly hosted in carbonates of the Kakontwe Formation (Table 1), but also in a breccia cross-cutting the axial breccia and post-dating the axial fault (Intiomale and Oosterbosch, 1974; Intiomale, 1982). This second-generation Breccia contains Kaponda and Kakontwe Formation dolomite fragments. It is interpreted as a collapse breccia related to a discordant paleokarst: (1) developed during periods of emergence and sub-aerial exposure before folding of the host rocks, the primary mineralisation being contemporaneous to the karst formation (Chabu, 1990; Walraven and Chabu, 1994); or (2) closely linked to the emplacement of hydrothermal mineralisation during the orogenic event (Intiomale, 1982). The primary sulphide minerals form five distinct categories of ores (Intiomale and Oosterbosch, 1974; Intiomale, 1982): (1) Zinc-rich ore (> 30 wt.% Zn; < 0.3 wt.% Pb; < 0.5 wt.% Cu) containing Cd-rich sphalerite, pyrite, arsenopyrite, gallite, tennantite, chalcopyrite, galena; (2) Zn–Pb-rich ore (> 20 wt. % Zn; > 4 wt.% Pb; < 0.5 wt.% Cu; up to 400 ppm Ag in Zn–Pb veins) formed by brown to dark brown sphalerite (3.6–6.7 wt.% Fe), pyrite, galena, gallite, tennantite, chalcopyrite; (3) Cu-rich ore (> 10 wt.% Cu; < 2 wt.% Zn; < 0.3 wt.% Pb) which contains chalcopyrite, bornite, sphalerite, tennantite, renierite, pyrite, ± arsenopyrite, ± galena, ± tungstenite; (4) Zn–Cu–Pb or mixed ore (> 2 wt.% Zn; > 2 wt.% Cu; > 0.3 wt.% Pb), showing a complex mineralogy that reflects the combination of the Cu rich and Zn–Pb rich ores described above; and (5) massive pyrite ore which is the earliest mineralisation in the deposit. The Ge- and Ga-rich ores occur locally in Cu rich and mixed ore types. The different types of ores display a zonal distribution giving strong evidence of upward movement and successive mingling of three (Zn-rich, Zn–Pb and Cu-rich) separate mineralizing brines, the end product being reflected by Zn–Cu mixed ores. 5.2. Kengere and Lombe deposits Kengere (< 100,000 t metal) and Lombe (∼ 11,000 t metal) are two other small Zn–Pb deposits known in Congo (François,

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1974; Cailteux, 1989). The local lithostratigraphy of the mineralized field includes the Kaponda–Kakontwe and Kipushi–Katete (Série Récurrente) Formations, respectively (Table 1). The ore deposit is hosted in breccias and fractured rocks developed in carbonates of the Kaponda Formation along the contact with the Kakontwe Formation and related to faulting parallel to the axial planes of NE–SW-trending folds (Kengere), or in carbonates of the Kipushi Formation along the tectonized contact with the Katete (Série Récurrente) Formation (Lombe). The Kengere orebody (27 wt.% Zn; ≤ 1 wt.% Cu; < 5 ppm Ag, < 10 ppm Ge, < 50 ppm Ga) intersected in drillholes shows Znrich primary ore consisting of dark brown sphalerite, pyrite, and galena (Intiomale, 1982; Cailteux, 1989). Sulphide parageneses indicate the early formation of pyrite, followed by a later Fe– (Cd)-sphalerite and Ag–galena deposition (Intiomale, 1982). The Lombe orebody (31 wt.% Zn; 5.4 wt.% Pb; < 1 wt.% Cu; < 200 ppm Ag; < 40 ppm Ge, < 30 ppm Ga; up to 1 800 ppm Cd) contains sphalerite, galena, pyrite, minor tennantite, arsenopyrite, bornite, and covellite (Intiomale, 1982; Cailteux, 1989).

associated with breccia bodies characteristics of karstic origin (Whyte, 1966; Kortman, 1972). There are 13 Zn–(Cu–Pb–Ag–V) other small deposits or occurrences listed in Zambia (e.g., Lukusashi, Lukali, Kaungashi, and White Rock; Freeman, 1988). Commonly, the sulphide mineralisation contains sphalerite–galena–pyrite and subsidiary chalcopyrite. Some of these deposits contain silver. The most important is Lukusashi containing a Zn-rich ore (158,000 t grading 6.4 wt.% Zn, 0.98 wt.% Pb, 0.15 wt.% Cu and 19.4 g/t Ag), and a Zn–Cu rich ore (730,000 t grading 1.55 wt.% Zn, 1.47 wt.% Cu, 0.62 wt.% Pb and 39.4 g/t Ag; Freeman, 1988). The lithostratigraphic position of the host rocks is generally poorly constrained. However, the most important deposits are hosted by sequences including massive dolomites, bedded dolomite, shales, and conglomeratic dolomitic sandstones or tillite that are reminiscent of the Muombe Subgroup rocks. Related breccias were also documented in some deposits.

5.3. Dikulushi

Kansanshi is a Cu–Au low-temperature deposit (∼ 2.1 Mt metal; Freeman, 1988) located in the Domes area (Zambia), and hosted in metamorphosed (greenschist grade) and hydrothermally altered carbonate rocks of the Muombe Subgroup (Baron, 1999; Cailteux and Kampunzu, personal observations, 1999). The ore mineralisation consists of both vein-hosted and finely disseminated stratiform sulphides that include pyrite, pyrrhotite, chalcopyrite, bornite (supergene digenite, chalcocite), and brannierite, molybdenite, silver, and gold as traces.

Dikulushi is a low-temperature, hydrothermal Cu, Zn, Pb, Ag deposit (>167,000 t Cu and 517 t Ag; Lemmon et al., 2003) located 20 km to the west of the lake Mweru in Congo, in the extreme northeast of the Katangan belt (Fig. 2). The main copper-vein mineralisation is hosted in interbedded sandstones, argillites and intraformational breccias of the Mongwe Formation and is related to a fault zone that occurs along the contact with carbonates of the Lubudi Formation (Lemmon et al., 2003; Kanda Nkula et al., 2003, and references therein). These ores include dominantly massive chalcocite nearest the footwall, and less massive to disseminated chalcocite further into the hanging wall (Lemmon et al., 2003). Separate Zn–Pb sub-economic ores occur within carbonates of the Lubudi Formation and consist of massive iron-rich (copper) sphalerite, with lesser galena, chalcopyrite, and pyrite. 5.4. Kabwe deposit and other Zambian Zn, Pb occurrences Kabwe is the most significant Zn–Pb deposit in Zambia (3.1 Mt Zn, 1.3 Mt Pb). The primary massive sulphides have a simple mineralogy consisting of sphalerite, galena, pyrite, minor to trace chalcopyrite, rare briartite and renierite (Notebaart and Korowski, 1980; Kamona et al., 1991; Kamona, 1993). Massive pyrite mineralisation occurs marginal to some orebodies and seems to have been deposited at an earlier stage of the massive sulphides emplacement (Kamona, 1993). These sulphide orebodies are surrounded by oxide zones that include numerous secondary minerals as silicates, vanadates, phosphates and carbonates of Zn, Pb, V and Cu. The ores are mainly hosted in massive dolomite that has been correlated with the Upper Roan (Kamona, 1993; Burnard et al., 1993; Kamona et al., 1999). This contrasts with interpretation of other workers (e.g., Intiomale, 1982) who identified strong evidences that the hosting rocks are the Muombe carbonates overlying the matrixsupported “Grand Conglomérat” diamictite (Table 1), similarly as for the Zn–Pb deposits of Congo. The Kabwe deposit is

5.5. Kansanshi deposit

6. Interpretation and conclusion The Nguba and Kundelungu rock successions are both marked by deposition of glacial diamictites at their base, which are chronostratigraphic markers correlated, respectively, with the 750 Ma Sturtian and (supposedly) 620 Ma Marinoan/Varanger glacial events also observed in Namibia, South America and Australia. Carbonate rocks overlying these diamictites (the Kaponda, Kakontwe and Kipushi carbonates, and the Lusele dolomite, respectively) are interpreted as cap-carbonates, but no isotopic data constrain this proposal at present. The Nguba sedimentary basin is marked by a transgressive shallow-water sequence overlying the cap-carbonate, which contains clasts derived from the northern areas. The Kyandamu (Petit Conglomérat) rocks at the base of the Kundelungu Group in the southern areas contain clasts derived from the underlying Roan (Mwashya) and Nguba successions and probably represents the first foreland basin. The occurrence of these clasts to the south, indicate exhumation and erosion of the Roan and Nguba rocks during Bunkeya and Kyandamu deposition and suggests a south-to-north progression of the orogenesis which is compatible with the northward vergence of thrusting during the Kolwezian (D1) orogenic event in the Lufilian Arc (Kampunzu and Cailteux, 1999). Therefore, deposition of the Kyandamu rocks dates the inversion from extensional to compressional tectonics in the Katangan basin. Observations also suggest that Mongwe-Kiubo Formations were deposited in

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a shallow-water foreland basin advancing to the north, pushed by the northward thrusting of the Lufilian Arc. The Sampwe Formation and Biano Subgroup were deposited in the northernmost foreland basin at the end of the thrusting. In a re-interpretation of the Katangan lithostratigraphy and orogenesis, Wendorff (2000a,b) stated that (1) thrust sheets were moved towards the foreland region in the north as a result of gravitational transportation; (2) the megabreccias are olistostrome/debris-flow syntectonic conglomerates rather than tectonic breccias; (3) Red and Grey RAT are syn-orogenic sedimentary rocks younger than the Roan Group and deposited in the Katangan foreland basin after the deposition of the Nguba Group. More recently, Wendorff (2003, 2005) proposed a new stratigraphy of the Katangan succession and concluded that Congo-type Roan sedimentary rocks (RAT, Mines and Dipeta Subgroups) were deposited in a foreland basin at the end of the Lufilian orogeny and are partly coeval with the Biano/Ku 3 (Plateaux) Subgroup. The data documented in this paper combined with other previous structural, lithologic, petrographic, geochemical, and dating studies (e.g., Demesmaeker et al., 1963; Cailteux et al., 1994; Cailteux and Kampunzu, 1995; Kampunzu and Cailteux, 1999; Kampunzu et al., 2005; Cailteux et al., 2005a; Batumike et al., 2006) do not support this interpretation. The sedimentary rocks deposited in the foreland basins are part of the Kundelungu rocks, and are not the megabreccias as interpreted by Wendorff (2000a,b, 2003, 2005). It has been demonstrated by stratigraphic, petrographic, and geochemical observations that RAT sedimentary rocks are in lithostratigraphic position below the Mines Subgroup and therefore cannot represent synorogenic deposition younger than Mines Subgroup (Cailteux et al., 2005a; Kampunzu et al., 2005). Red RAT, Grey RAT and overlying Mines Subgroup rocks differ from the Kundelungu lithologies (Oosterbosch, 1962; François, 1973b, 1987; Cailteux, 1994) and are cut by uraninite veins yielding ages in between 620 and > 690 Ma (e.g., at Kalongwe, Luishia, Luiswishi, Shinkolobwe, Swambo; Loris et al., 1997, and references therein) whereas Kundelungu rocks (from the Kyandamu/Petit Conglomérat) were deposited between <630 and ∼ 500 Ma (Kampunzu and Cailteux, 1999). Therefore, RAT and Mines Subgroup rocks cannot be coeval with Kundelungu rocks and particularly with the Biano (Plateaux) Subgroup as proposed by Wendorff (2005). The Zn–Pb–Cu deposits hosted in the Nguba and Kundelungu rocks are hypogene hydrothermal, fault-related, breccia pipes and veins. The distribution of the orebodies along fault zones developed during the (D1) contractional phase of the Katangan orogenesis (Kampunzu and Cailteux, 1999), the flattening of the ore minerals and pressure shadows at the edges of the deformed sulphides (Intiomale, 1982; Chabu, 1990; Kamona, 1993), suggest a pre-kinematic or syn-kinematic (hydrothermal) emplacement of the mineralisation during this < 850 to >710 (D1) contractional phase. Contrastingly, based on Pb istopic compositions, model ages of 681 Ma for Kabwe (Kamona, 1993) and 454 ± 14 Ma for Kipushi (Walraven and Chabu, 1994) were proposed. A possible hypothesis on the origin of the metals is the remobilisation of pre-existing strat-

iform mineralisation in the Roan Group that has been strongly involved in the orogenic process and its resetting in Nguba and Kundelungu rocks. This hypothesis is supported by the occurrence of important copper deposits and positive anomalies of the other metals, especially in the Mines Subgroup (Kampunzu et al., 2005), that represent potential sources for these metals. The Zn–Pb–Cu deposits in the central African Copperbelt have to be compared with the Bamba–Kilenda (Cu, Pb, Zn, V, Ag) deposit hosted in the Neoproterozoic West Congolian belt (Kanda Nkula et al., 2003), and with the Berg Aukas (Zn, Pb, V), Khusib Springs (Cu, Pb, Zn), Tsumeb (Pb, Cu, Zn, Ge), and Kombat (Cu, Pb, Zn) deposits hosted in the Damaran belt, Namibia (Kamona and Günzel, 2007-this volume). Acknowledgements This paper is dedicated to the late Professor Henri Ali Basira Kampunzu who initiated the work and participated in discussions on the first drafts. Forrest and Gécamines Mining Companies (Lubumbashi, Congo), University of Lubumbashi and the Tectonic Special Research Center (late Prof. McPowell) are acknowledged for their financial and logistic support. Thanks are due to P. Dumont, M. Hanon, S. Bull and A.F. Kamona for their constructive comments and remarks on the manuscript. J. Batumike expresses gratitude to J. Kokonyangi for discussions in the early stages of the study. This research is a contribution to the UNESCO-IUGS IGCP 440 and 450 Projects. References Alvarenga, C.J.S., Santos, R.V., Dantas, E.L., 2004. C–O–Sr isotopic stratigraphy of cap carbonates overlying Marinoan-age glacial diamictites in the Paraguay Belt, Brazil. Precambrian Research 131, 1–21. Babinsky, M., Kaufman, A.J., 2003. First direct dating of a Neoproterozoic postglaciogenic cap carbonate. Proceedings of the IV South American Symposium on Isotope Geology, Short Paper, Salvador, pp. 321–323. Baron, J., 1999. Kansanshi Mine. IGCP 419 field trip. Cyprus Amax Kansanshi, unpublished report. Bartholomé, P., 1972. Metallotectes du gisement de Kamoto (République du Zaire). Bulletin de l' Académie Royale des Sciences d'Outre-Mer, Bruxelles, vol. 3, pp. 586–598. Batumike, M.J., 2004. Geochemistry and petrography of the Nguba and Kundelungu Groups, Neoproterozoic Katangan Supergroup, southeast D.R. Congo: Tectonic setting, paleoweathering conditions and sediment provenance. M.Sc. thesis, Department of Geosciences, Shimane University, Japan. Batumike, M.J., Kampunzu, A.B., Cailteux, J.L.H., 2006. Petrology and geochemistry of the Neoproterozoic Nguba and Kundelungu Groups, Katangan Supergroup, southeast Congo: implication for provenance, paleoweathering and geotectonic setting. Journal of African Earth Sciences 44, 97–115. Bellière, J., 1966. Les sédiments Kundelungiens dans l'Arc Mwashya— Bunkeya. Annales de la Société Géologique de Belgique 89, 357–373. Binda, P.L., Mulgrew, J.R., 1974. Stratigraphy of copper occurences in the Zambian Copperbelt. In: Bartholomé, P. (Ed.), Gisements Stratiformes et Provinces Cuprifères. Centenaire de la Société Géologique de Belgique, Liège, pp. 215–233. Binda, PL., Van Eden, J.G., 1972. Sedimentological evidence on the origin of the Precambrian Great conglomerate (Kundelungu tillite), Zambia. Palaeogeography, Palaeoclimatology, Palaeoecology 12, 151–168. Bodiselitsch, B., Keebert, C., Master, S., Reimold, W.V., 2005. Estimating duration and intensity of Neoproterozoic snowball glaciations from Ir anomalies. Science 308, 239–242.

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