56 Stratiform and Vein-type Deposits in the Pan-African Orogen in Central and Southern Africa Evidence for Multiphase Mineralisation

8/10/2019 56 Stratiform and Vein-type Deposits in the Pan-African Orogen in Central and Southern Africa Evidence for Multiphase Mineralisation

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GEOLOGICA BELGICA (2011) 14/1-2: 23-44

STRATIFORM AND VEIN-TYPE DEPOSITS IN THE PAN-AFRICAN

OROGEN IN CENTRAL AND SOUTHERN AFRICA: EVIDENCE FOR

MULTIPHASE MINERALISATION

Maarten HAEST1,2& Philippe MUCHEZ1

(7 gures)

1Geodynamics and Geouids Research Group, Department of Earth and Environmental Sciences, K.U.Leuven,

Celestijnenlaan 200E, B-3001 Heverlee, Belgium2Centre of Excellence for 3D Mineral Mapping, Earth Science and Resource Engineering, CSIRO, Dick Perry Avenue 26,

6102 Kensington, WA, Australia

ABSTRACT. Stratiform deposits in the Pan-African Orogen are of the Cu-Co type and are restricted to carbonates andsiliciclastic sediments that are stratigraphically close above the basement. The stratiform Cu-Co deposits formed during

early diagenesis (possibly around 820 Ma) and during late diagenesis/metamorphism and the Pan-African Orogeny (~580to ~520 Ma). The early diagenetic Cu-Co sulphides were partly remobilised into the second stratabound Cu-Comineralisation, with precipitation of Cu-Co sulphides in nodules, veins and as breccia cements.Vein-type Cu-Pb-Zn mineralisation occurs at two distinct levels, higher in the stratigraphy. The lower level vein-typedeposits occur in dolomite and are dominantly of the Zn-Cu type. The higher level vein-type deposits occur at the contact

between dolomite and sandstone and are dominated by Cu. The Cu-dominated deposits that have been dated, developedduring the waning stage of the Pan-African Orogeny (~530 to ~500 Ma). The Zn-dominated deposits for which amineralisation age has been established, formed after the Pan-African Orogeny. Some of these vein-type mineralisationhave been remobilised after their formation, with the precipitation of massive Cu(-Ag) sulphides.

KEYWORDS: Central and Southern Africa, Neoproterozoic mineralisations, Pan-African Orogen, Stratiform Cu-Co oredeposits, Vein-type Zn-Cu-Pb-Ag deposits,

1. Introduction

The Neoproterozoic rocks of the Pan-African Orogen inCentral and Southern Africa (Fig. 1) host numerous largeand rich base metal ore deposits of stratiform, strataboundand vein-type. Tenke Fungurume, Luiswishi and Konkolaare typical stratiform ore deposits of the Central AfricanCopperbelt in both the Democratic Republic of Congo(here after DRC) and Zambia (Fig. 2A). Kipushi and

Dikulushi in the DRC, Kabwe in Zambia and Berg Aukasand Tsumeb in Namibia are examples of stratabound orvein-type deposits (Figs. 2A&B). Several metallogenicmodels have been proposed for the origin of the stratiformdeposits in the Copperbelt (review in Cailteux et al., 2005and Selley et al., 2005). However, during these last years,results from several studies indicated mineralisationformed from early to late diagenetic processes and fromsyn-orogenic processes (e.g. Cailteux et al., 2005; Selleyet al., 2005; Dewaele et al., 2006c; Muchez et al., 2008).The typical vein-type deposits have a syn- to post-orogenicorigin and are also characterised by multiple mineralisation/remobilisation stages (Heijlen et al., 2008; Haest et al.,2009). In a preliminary study, Muchez et al. (2007) haveshown that the different mineralisation and remobilisationstages are related to the geodynamic evolution of theLulian Arc.

Recently Kampunzu et al. (2009) discussed in detailthe geological setting and mineralogy of the mostimportant sediment-hosted (i.e. vein-type and stratabound)Zn-Pb-Cu deposits in the DRC, Zambia and Namibia. Theaim of this paper is to review the most fundamental dataof typical deposits in order to present a metallogenicmodel framed in the geodynamic evolution.

2. Geological setting

The stratiform and vein-type Cu(-Co) ore depositsdescribed above are hosted by Neoproterozoic (meta-)sedimentary rocks of the Pan-African Lulian and DamaraOrogenic Belts (Fig. 1). These sedimentary rocks weredeposited in an intracontinental rift followed by a proto-oceanic rift system that nally evolved into a syn- to

postorogenic sequence (e.g. Kampunzu et al., 1991; Milleret al., 2009). The stratiform Cu-Co deposits and the vein-type deposits of Kipushi (DRC) and Kabwe (Zambia) aresituated in the Lulian Arc (Fig. 2A). The vein-typedeposit of Dikulushi (DRC) is located on the KundelunguPlateau to the north of this orogenic belt (Fig. 2A). TheBerg Aukas-type Zn-Pb stratabound ore deposits and the

Cu-dominated Tsumeb-type deposits are situated on theOtavi Mountain Land (here after OML), forming thenorthern foreland of the Damara Belt in Namibia (Fig. 2B,Pirajno & Joubert, 1993)


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24 M. HAEST& PH. MUCHEZ

The Lulian Belt is bordered by the Irumide Belt tothe east, the Kasai Block to the west, the Kibaran Belt tothe north and the Bangwelu block to the northeast (Fig.2A). The Bangweulu Block includes a basement ofgranitoids, overlain by a continental clastic successionthat contains minor volcanic intercalations near the base(De Waele et al., 2008). The Irumide Belt is characterised

by a metasedimentary succession of shallow marinequartzites and pelites that was deposited after 1.8 Gaaccording to U-Pb dating on detrital zircon (De Waele andMapani, 2002). Granitoids with a crust-dominatedgeochemical character intruded the Irumide Belt at 1664 4 Ma and at 1551 33 Ma (De Waele et al., 2006). Thesouthern part of the Kibara Belt consists of at least twoamphibolite grade meta-sedimentary successions. Theoldest succession was intruded by I-type plutons at 1.38 to1.37 Ga and deformed (Kokonyangi et al., 2004). A second

tectonic event affected both sedimentary successions andis dated at 1089 14 Ma based on a U-Pb zircon SHRIMPage of a syn-kinematic granitoid (Kokonyangi et al.,2004).

The (meta-)sedimentary succession that builds up theLulian Belt is called the Katanga Supergroup and issubdivided in the Roan, Nguba and Kundelungu Groups(Fig. 3; Cahen, 1954; Batumike et al., 2007; Cailteux etal., 2007). Deposition of the Katanga Supergroup startedafter intrusion of the Nchanga granite, which formed at883 10 Ma (zircon U-Pb SHRIMP: Armstrong et al.,2005). The Roan Group is separated from the Nguba by aconglomerate (Mwale Formation), which is related to theglobal Sturtian glacial epoch (Batumike et al., 2006). The

Nguba is separated from the Kundelungu by anotherconglomerate (Kyandamu Formation), which is related tothe Marinoan ice age (Batumike et al., 2006). TheKundelungu sedimentary rocks represent pre- to post-orogenic sediments (Kampunzu & Cailteux, 1999).

The Damara Belt is located between the Congo (to thenorth) and Kalahari (to the south) cratons, which both

consist of >1100 Ma rocks (Fig. 1, Frimmel et al., 1996).The Angola Block builds up the Congo craton to the northof the Damara Belt (Fig. 1). The southwestern part of theAngola Block consists of granitic to tonalitic-granodioritic

Fig. 1

Phanerozoic to recent cover

Undifferentiated Precambrian belts

Neoproterozoic-Cambrian belts

Mesoproterozoic belts

Paleoproterozoic belts

Archaean cratons, Archaean with Pprot overprintor Pprot with Archaean inliers/ possible unexposedArchaean basement

Possible extent ofunexposed Archaeancrust (Likasi Terrane)

Possible extent of

Congo Craton atca. 1.0 Ga

500km

Tanzania

Craton

BangweuluBlock

KasaiBlock

NE-Congo Block

Uganda Block

AngolaBlock

GabonBlock

SF Craton

ZimCraton

KaapvaalCraton

NatalBelt

KheisBelt

Gariepand

NamaquaBelts

West-CongoBelt

+Kimezian

Belt

Gab

.B

elt R. Belt

NEKib.Belt

Rus

Kibaran

Belt

LufilianBelt

Copperbelt

Irumid

eBelt

Southe

rn

Irumid

eBelt

MozambiqueBelt

LV

LT

Zambezi Belt

LimpopoBelt

CKB MB

LurioForeland

UbB+UsB

Fig. 2A

Fig. 2B

DamaraBelt

KaokoBelt

Figure1.Simplied geological map of Sub-Saharan Africa (map of Africa in the lower right corner outlines the region that is shown.CKB: Choma Kalomo Block; Gab. Belt: Gabon Belt; LT: Lake Tanganyika; LV: Lake Victoria; MB: Magondi belt; NE Kib. Belt:Northeast Kibaran Belt; R. Belt: Ruwenzori Belt; Rus.: Rusizian; SF Craton: Sao Francisco Craton; UbB: Ubendian Belt; UsB:Usagaran Belt; Pprot: Palaeoproterozoic; after De Waele et al., 2008)


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STRATIFORMANDVEIN-TYPEDEPOSITSINTHEPAN-AFRICANOROGEN 25

gneisses of 2.5 Ga (Delor et al., 2008). Inherited zirconsin adjoining Palaeoproterozoic formations give no agesolder than 2.71 Ga. The main part of the Angola Block iscovered with siliciclastic formations and interbeddedvolcanics that have been dated at 2.0 to 1.96 Ga (Delor etal., 2008).

The Damara Supergroup builds up the Damara Beltand is composed of the Nosib, Otavi and Mulden Groupsin the OML (Fig. 3; Frimmel et al., 1996). Deposition of

the Nosib Group started before ca. 756 Ma (Hoffman etal., 1996). However, no date for the onset of Nosib Groupsedimentation is known. By analogy with the similarStinkfontein Subgroup in the Gariep Belt, Frimmel et al.

(2001, 2004) assumed sedimentation started sometimearound 770 Ma, but Frimmel and Miller (2009) argue forthe Nosib Group being older and possibly contemporaneousto the Roan Group in the DRC and Zambia. The NosibGroup is separated from the Otavi Group by a conglomerate(Varianto Formation), which is related to the globalSturtian glacial period (Chetty & Frimmel, 2000) andcorresponds to the Mwale Formation in the KatangaSupergroup (Fig. 3; Cailteux et al., 2007). The Otavi

Group is subdivided in the Abenab and Tsumeb Subgroupsthat are separated by a conglomerate (Ghaub Formation)that was deposited during the Marinoan ice age (Hoffmannet al., 2004) and can be related to the Kyandamu Formation

Phanerozoic to recent cover

Late Neoproterozoic-Cambrian intrusions

Neoproterozoic-Cambrian belts

Mesoproterozoic belts

Archaean basement

DRC

Zambia

Angola

Zimbabwe

Mozambique

Tanzania

Zambia

Basementdomes

Dikulushi

Kipushi

Musoshi

Kabwe

Kengere

Lombe

Hook granite

LufilianArc

Kund

elun

gu

Platea

uKib

aran

Belt

Kasa BlockBangweulu Block

ZambeziBelt

Irumid

eBelt

Southern

Irumid

eBelt

Zimbabwe Craton

MSZ

Kansanshi

500km

N

A

B1730

1930

N

20km

Tsumeb

Berg Aukas

Kombat

Khusib Springs

Kamoto

Luiswishi

MuldenGroup andKombat Formation

Tsumeb Subgroup

Ghaub Formation

Abenab SubgroupNosib Group

Basement

Figure 2. A. Simpliedgeological map of theNeoproterozoic Lulian Arcand the Kundelungu Plateau tothe north, showing some of thestratiform and vein-type oredeposits in the region (MSZ:

Mwembeshi Shear Zone; CKB:Choma-Kalomo Block;modied after Porada andBerhorst, 2000). B. Simpliedgeological map of the OtaviMountain Land with location ofthe Berg Aukas and Tsumeb-type ore deposits (after Sehnge,1957).


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of the Katanga Supergroup (Fig. 3; Cailteux et al., 2007;Kampunzu et al., 2009).

Both the Lulian and Damara Orogenies occurredbetween ca 560 and 530 Ma (Hanson et al., 1993; Frimmel& Flling, 2004; John et al., 2004). Syn-to post-tectonicintrusives and rhyolites in central Zambia were dated byHanson et al. (1993). Synorogenic granites yielded U-Pbages of 566 5 Ma and 559 18 Ma. The age of the post-orogenic rhyolite is 538 1.5 Ma. SHRIMP U-Pb data of

metamorphic monazite from the Chambishi basin provideages of 592 22 Ma, 531 12 Ma and 512 17 Ma,which correspond respectively to the ages of eclogitefacies metamorphism, high pressure talc-kyanitewhiteschist metamorphism, and a regional metamorphicand mineralisation pulse (Rainaud et al., 2005). Post-orogenic cooling possibly started at ca 510 Ma (John etal., 2004; Rainaud et al., 2005). A post-orogenic magmatic

pulse in the Gariep Belt (southern Namibia) occurred at507 Ma (Frimmel, 2000).

Rocks from the Katanga Supergroup close to the coreof the Lulian Belt and from the Damara Supergroup inthe OML underwent greenschist facies metamorphism,

indicating peak temperatures between 300 and 400 Cwere reached in the region (Ramsay and Ridgeway, 1977;Frimmel et al., 1996).

3. Stratiform deposits in the Lulian Orogen

The aim of this overview is not to provide a detailedreview of the metallogenesis of the stratiform Cu-Co oredeposits in the Copperbelt, but to give relevant data andevidence for multiphase mineralisation. Detailed reviewson the Zambian and Katangan Copperbelt are publishedrespectively by Selley et al. (2005) and Cailteux et al.(2005). Recently, a detailed study of the uid inclusions at

Kamoto and Luiswishi (DRC) and a comparison with themicrothermometric data from both Zambia and the DRChas been carried out by El Desouky et al. (2009). A studyof the C, O, S and Sr isotopic composition of the two main

mineralisation phases in the DRC and a comparison withpublished data on the Copperbelt has been performed byEl Desouky et al. (2010).

The stratiform Cu-Co ore deposits in the LulianOrogen occur both in the DRC and Zambia. In the DRC,stratiform Cu-Co mineralisation is hosted in carbonatedominated allochtonous units at two levels of the MinesSubgroup (Cailteux et al., 2005; Fig. 3). Similar stratiformCu-Co deposits in Zambia are situated in more siliciclastic

units that belong to the Mindola and Kitwe Subgroups.These stratiform Cu-Co mineralisation will be discussedtogether and formed during two main phases, identied inZambia (Selley et al., 2005) and in the DRC (Cailteux etal., 2005; Muchez et al., 2008; El Desouky et al., 2009).Phase 1 Cu(-Co) mineralisation includes sulphides in

bands, in type I nodules and disseminated through thehost rock (El Desouky et al., 2010). Phase 2 Cu(-Co)mineralisation includes mineralisation in type II nodules,in veins and as cements in tectonic breccia. Type I andtype II nodules are based on the crystal size of the mineralsthey contain (El Desouky et al.,2010).

Frambodal and euhedral pyrite are found disseminatedin the host-rock around most deposits (Cailteux et al.,2005). Diagenetic pyrite at Nchanga (Zambia) has 34Svalues between -17 and -1 V-CDT, interpreted to beconsistent with low temperature open system bacteriogenicreduction of sea-water sulphate (McGowan et al. 2006). Arst generation of dolomite postdates the formation offrambodal pyrite, but predates the rst main phase ofCu(-Co) sulphides (Dewaele et al., 2006c; El Desouky etal., 2009). Phase I Cu(-Co) sulphides include carrolite,chalcopyrite, bornite and chalcocite and occurdisseminated, in bands or in nodules type I (El Desouky etal., 2009). The sulphides, dolomite and quartz replace the

initial anhydrite in the nodules (Muchez et al., 2008). Thenodules are surrounded by organic material. A diageneticorigin for both the stratiform ore deposits in Zambia andthe DRC was already proposed in the early 1970s (Annels,

Kundelungu

Nguba

Roan

635 Ma

LuseleKaniangaLubudi

MongweKiuboSampweNgule

Gombela

Bunkeya

Muombe

Mwashia

Dipeta

Mines

RAT

Biano

Subgroup FormationGroup

Katanga (DRC)

Katanga Supergroup

Age

Kyandamu

KipushiKakontweKapondaMwale

MonweziKatete

Deposit

Dikulushi

KipushiLombeKengere

750 Ma

756 Ma)

Figure 3. Stratigraphiccorrelation between theKatanga Supergroup inthe DRC and the DamaraSupergroup in Namibia(after Kampunzu et al.,2009).


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1974; Bartholom et al., 1972; Bartholom, 1974). Animportant part formed at the expense of anhydrite, whetherthis mineral was originally present in nodular form or

occurred as an interstitial cement replacing pyrite (Annels,1974; Bartholom et al., 1972; Haynes, 1986). Recent Re-Os dating of chalcopyrite at Konkola (Zambia) yielded anage of 816 62 Ma (Selley et al., 2005), which alsosuggests that Cu(-Co) sulphides precipitated during earlydiagenesis. At Kamoto (DRC), Luiswishi (DRC),Chambishi (Zambia) and Chambishi Southeast (Zambia),the early diagenetic sulphides precipitated from amoderately saline (11 21 eq. wt.% NaCl), low tomoderate temperature (Th = 115 220 C) uid, with aH

2O-NaCl composition (Annels, 1989; El Desouky et al.,

2007, 2009). The dolomite in the nodules has 18O and13C values of -9.79 to -11.50 V-PDB and -7.02 to

-9.93 V-PDB respectively, indicating (1) precipitationfrom a seawater-type uid at a maximum temperature of70C, and (2) incorporation of light 12C, produced duringoxidation of organic matter (Muchez et al., 2008). The

source of sulphur would be interstitial dissolved sulphatein the sediments, anhydrite cement or early diageneticanhydrite nodules (Annels, 1989). Sulphur was reducedthrough BSR, based on the low 34S values (Fig. 4A).However, BSR cannot have occurred during passage ofthe hydrothermal metal transporting uid and must have

started before the Cu(-Co) mineralisation or could haveoccurred intermittently between the hydrothermaldischarges (Muchez et al., 2008; El Desouky et al., 2010).Oxidation during BSR of the organic material included inthe rocks close to the nodules explains the light C isotopecomposition for the dolomite gangue (Muchez et al.,2008). Furthermore, BSR produced HCO

3-, which

precipitated in dolomite, and H2S, which precipitated in

the associated sulphides (Muchez et al., 2008). A decreaseof the pH during sulphide deposition led to the precipitationof quartz, always closely associated to the sulphidemineralisation (Muchez et al., 2008). 87Sr/86Sr ratios of

dolomite in type I nodules range between 0.71012 and0.73576 (Muchez et al., 2008), signicantly moreradiogenic than the strontium isotopic composition of

Neoproterozoic marine carbonates (87Sr/86Sr = 0.70560.7087, Jacobsen & Kaufman, 1999; Fig. 5A), suggestingintense interaction with siliciclastic sedimentary rocksand/or the granitic basement (Muchez et al., 2008). This

0

2

4

6

8

10

12

14

16

N

umberofsamples

Stratiform type IILufilian Arc (Dechow and Jensen, 1965; Lerouge et al.,2005)

Stratiform type ILufilian Arc (Dechow and Jensen, 1965;Muchezet al., 2008;Lerouge et al., 2005)

0

1

2

3

4

5

6

7

-21 -17 -13 -9 -5 -1 3 7 11 15 19 23 27 31

Delta34S

Numberofsamples

Berg Aukas-type (Hughes, 1987)Khusib Springs (Hughes, 1987)Tsumeb (Hughes, 1987)Kombat (Hughes, 1987)

0

5

10

15

20

25

Numberofsamples

Kabwe (Dechow and Jensen, 1965; Kamona and Friedrich, 2007)Kipushi (Dechow and Jensen,1965)Kansanshi (Dechow and Jensen, 1965)Dikulushi (Haest et al., 2009)

A

B

C

Figure 4. Compilation of the S isotope data of sulphides instratiform ore deposits in the Lulian Arc (Stratiform type I:Kamoto (Dechow & Jensen, 1965; Muchez et al., 2008),Luiswishi (Lerouge et al., 2005; Muchez et al., 2008); Stratiformtype II: Nkana and Mindola (Dechow & Jensen, 1965), Luiswishi(Lerouge et al., 2005)) (A), in vein-type ore deposits in theLulian Arc and on the Kundelungu Plateau (B) and in vein-typeore deposits in the Otavi Mountain Land (C).

Figure5.Compilation of Sr isotope data from carbonate gangueminerals associated with early diagenetic nodules in thestratiform deposits of Kamoto and Nchanga in the Lulian Arc(A) and from carbonate gangue minerals associated with vein-type ore deposits in the Pan African Orogen (B).

0.70560

0.71560

0.72560

0.73560

0.74560

0.75560

0.76560

0.77560

0.78560

10 20 30 40 50

1000/[Sr] (ppm)

87Sr/86Sr

Kamoto type I(Muchezet al., 2008)

Nchanga (Roberts etal., 2009)

Host-rock Nchanga (Roberts et al.,20 09)

0.70560

0.70760

0.70960

0.71160

0.71360

0.71560

0.71760

0.71960

0 5 10 15 20 25 30 35

1000/[Sr] (ppm)

87Sr/86Sr

Dikulushi Cu-Pb-Zn-Fe (Haestet al., 2009)

Dikulushi Cu-Ag (Haestet al., 2009)

Berg Aukas (Frimmel et al., 1996)

Kombat (Frimmel et al., 1996)

A

B


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supports the hypothesis that gneisses, magmatic rocks andschists from the Palaeoproterozoic basement, observed inthe Domes region and in the Zambian Copperbelt,

provided Cu to the mineralising uids (Voet & Freeman,1972; Ngoyi et al., 1991; Sweeney & Binda, 1994;Cailteux et al., 2005; Dejonghe & Ngoyi, 1995; McGowan

et al., 2006; Bernau et al., 2007). The origin of cobalt, thepresence of which is not revealed in these basement rocks,was postulated to be sourced from an alkaline magma

body at depth (Annels, 1974, 1989; Unrug, 1988) or fromthe Archean rocks of the Zimbabwe Craton (Cailteux etal., 2005).

A second main phase of Cu(-Co) sulphides is observedin type II nodules, veins and as cements in tectonic breccia(El Desouky et al., 2007, 2009). The main phase II Cu(-Co) sulphides are associated with coarse crystalline quartzand overgrown by dolomite. An identical Cu-Comineralogy for sulphides from both phases in the DRC

indicates that the late stratabound mineralisation probablyonly remobilised the early stratiform Cu-Co mineralisationin Katanga (Muchez et al., 2008; El Desouky et al.,2010).

This remobilisation has been related to metamorphismand deformation both in Zambia and the DRC (Annels,1989; Cailteux et al., 2005; El Desouky et al., 2009), asconrmed by radiometric dating at Musoshi (DRC),

Nkana, Chibuluma and Nchanga (Zambia), revealingmineralisation ages of 583, 526 and 514 Ma (Richards et

al., 1988a, b; Barra et al., 2004). These ages span theentire Lulian Orogeny and could all indicate individualremobilisation events of early diagenetic Cu(-Co)mineralisation into late diagenetic to syn-orogenic Cu(-Co) mineralisation (El Desouky et al., 2009). The age of583 24 Ma overlaps with the oldest biotite (~586 Ma)and monazite (~592 Ma) ages (Rainaud et al., 2005) andeven with the synorogenic magmatic rocks (560 Ma). At

Nkana, several successive mineralised vein generationsformed during the Lulian orogeny, i.e. layer parallelveins, irregular croscutting veins and massive veins(Brems et al., 2009). These vein generations respectively

formed during the initial phase of basin inversion, themain phase of deformation and a late phase of orogenesisor extensional tensions related to the collapse of the

36.5

41.5

46.5

51.5

56.5

208Pb/204Pb

15.2

15.4

15.6

15.8

16

16.2

17 18 19 20 21 22 23 24 25 26 27 28206

Pb/204

Pb

207Pb/204Pb

37.3

37.5

37.7

37.9

38.1

38.3

38.5

38.7

38.9

17.8 18 18.2 18.4 18.6

Up to 97.6;20.4

645M

a

514Ma

A

B

Up to 97.6;140.6

Stratiform Lufilian Arc (Walraven and Chabu 1994)

Musoshi (Richards et al. 1988a)

Kipushi (Kamona et al. 1999,Schneider et al. 2007)

Lombe (Walraven and Chabu 1994)

Kabwe (Kamona et al. 1999)

Berg Aukas (Hughes 1987)

Kengere (Walraven and Chabu 1994)

Tsumeb (Hughes 1987, Kamona et al. 1999)

Kombat (Hughes 1987)

Khusib Springs (Hughes1987)

Dikulushi Cu-Pb-Zn-Fe (Haest et al. Submitted)

Dikulushi Cu-Ag (Haest et al. Submitted)c

Figure6.Uranogenic and thorogenicplots for stratiform, stratabound andvein-type deposits in the DRC,Zambia (Kabwe) and Namibia (BergAukas, Tsumeb, Kombat and KhusibSprings) (A & B); C Detail of lessradiogenic Pb isotope data in the207

Pb/204

Pb vs.206

Pb/204

Pb space,indicated with dotted box in (A)(stratiform Lulian Arc: Kolweziand Kinsenda; after Kampunzu etal., 2009)


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orogen. Late hydrothermal alteration and veining atMusoshi is dated at 514 Ma 2 Ma, based on U-Pb rutile

dating and at 514 3 Ma, based on U-Pb uraninite dating(Richards et al., 1988a). Richards et al. (1988a, b) linkedthis hydrothermal phase to compressional deformationand metamorphism during the Lulian Orogeny or itcould be related to extensional tensions as a consequenceof collapse of the orogen.

The remobilised Cu(-Co) sulphides in the DRCprecipitated from a uid with a high salinity between 35and 45.5 eq. wt% NaCl, at a temperature between 270 and385 C (El Desouky et al., 2009). In Zambia, uidinclusions in late stage veins at Chambishi show a broadrange in homogenisation temperatures ranging from 200

to 430C (Annels, 1989). These uids have an aqueo-carbonic composition with a dominance of CH

4in certain

types (Greyling et al., 2005). Greyling (2009) proposedthe early orogenic uid inclusions were trapped nearhydrostatic conditions at a maximum temperature and

pressure of 260C and 800 bar. In an extensive study ofthe oxygen and carbon isotopic composition of wholerocks, veins and nodules, Selley et al. (2005) found a cleartrend in the isotopic signature, which has also beenobserved in earlier studies (Annels, 1989; Sweeney &Binda, 1989). The isotope data range from values typicalof Neoproterozoic marine carbonates (13C = -4 to +4

V-PDB and18

O = -8 to -4 V-PDB) in the non-mineralised host rock to isotopically light values (13C =-26 to 4- V-PDB and 18O = -25 to -8 V-PDB) incarbonates associated with the sulphide mineralisation. Arst and extensive study on the S isotopic composition ofthe sulphides in the Copperbelt in Zambia and the DRCwas carried out by Dechow and Jensen (1965). About 550sulphides and 10 sulphates were isotopically analysed.S-isotopic values range between -18 and +23 V-CDT(data from Nkana and Mindola have been incorporated inFig. 4A). Based on the quite similar 34S values ofstratiform sulphides and late stockwork sulphides atLuiswishi (DRC), Lerouge et al. (2005) suggested an in

situ recrystallization or a slight remobilisation ofstockwork sulphides without attainment of isotopicequilibrium between different sulphide phases. At Nkana(Zambia), an increase of the sulphur isotopic composition

occurs in the successive vein generations that formedduring the Lulian orogeny, going from -29 to +15 V-CDT, indicating the dominance of remobilised earlydiagenetic sulphides in the early veins and an increasingcontribution of newly formed S by TSR of dissolved

Neoproterozoic sulphates in the later vein generations

(Muchez et al., 2010).At Nchanga (Zambia), which is interpreted to be a

syn-orogenic Cu-Co deposit (McGowan et al., 2003),dolomites from the hanging wall show 87Sr/86Sr valuesfrom 0.711 to 0.7116, which are slightly enrichedcompared with Neoproterozoic seawater water (Fig. 5A;Roberts et al., 2009). Carbonates associated with the Cu-Co sulphides show more radiogenic 87Sr/86Sr, ranging

between 0.7136 and 0.7469 (Fig. 5A; Roberts et al., 2009).Also at Nkana, the strontium isotopic composition of thesyn-orogenic veins shows high 87Sr/86Sr ratios up to0.75407 (Muchez et al., 2010). These radiogenic values

are interpreted to indicate interaction of the uid thatprecipitates the vein cements, with the basement or withsediments derived from it.

The Pb isotopic composition of the stratiform Cu-Codeposits of Kolwezi, Kinsenda and Musoshi from theCAC has been measured (Richards et al., 1988a; Ngoyi etal., 1993; Walraven & Chabu, 1994). Richards et al.(1988a) divided the measured samples in groups based onre-crystallisation textures, grainsize and position (e.g.along veins). The strongly re-crystallised Cu(-Co)sulphides and the Cu(-Co) sulphides that have beensampled from veins that crosscut the stratigraphy might

belong to the second generation Cu(-Co) sulphidesdescribed above. Walraven & Chabu (1994) did not makeany distinction and the signicantly larger grain size ofthe second generation Cu(-Co) sulphides could indicatethat they only measured their Pb isotopic composition.The Pb isotopic signature of the stratiform Cu(-Co)sulphides from the CAC varies signicantly (Fig. 6). Thestratiform sulphides from Musoshi display a linear trendtowards highly radiogenic Pb isotopic compositions (Fig.6A). Richards et al. (1988a) interpreted this linear trend asa Pb-Pb isochron corresponding to an age of 645 15 Ma(Pb-Pb step-leaching of non-recrystallised sulphides;

Richards et al., 1988a) that was reworked during uraniniteformation around 514 3Ma (U-Pb dating of rutile anduraninite; Richards et al., 1988a, b; Fig. 6A). At Kinsenda,an isochron age of 725 Ma was based on Pb isotopic dataof sulphides and interpreted to reect remobilisation ofthe primary ore (Ngoyi et al. 1993). Kamona et al. (1999),however, interpreted the linear trend at Musoshi as theresult of mixing of Pb from different sources duringLulian metamorphism. In the 208Pb/204Pb vs. 206Pb/204Pbspace, the samples from the Musoshi deposit have 208Pbenriched values and are likewise linearly correlated (Fig.6B). The Musoshi mineralisation is hosted in shales thattypically have high Th/Pb ratios, explaining the 208Pb

enriched values. The U-Th-Pb system for the Musoshisulphides appears to be coupled and the 645 Ma age might

be considered consistent with respect to the localgeology.

15.57

15.62

15.67

15.72

15.77

15.82

15.87

17.8 17.9 18 18.1 18.2 18.3

206Pb/

204Pb

207Pb/204Pb

C


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Ngoyi et al. (1991) proposed on the basis of acombination of strontium and radiogenic lead isotopes onzircon that the Copperbelt granites at Kinsenda behavedas an open geochemical system during the Pan-Africanorogeny.

4. Vein-type deposits in the Lulian Orogen

4.1 Kipushi

The Kipushi deposit is located near the southern border ofthe Democratic Republic of Congo, with Zambia (Fig.2A). The mineralisation is situated in the northern limb ofa northwest-trending anticline, with an axial plane slightlyinclined to the south (see Kampunzu et al., 2009 andreferences therein). Both limbs of the anticline showconcordant successions from the Mwashya Subgroup,over the Muombe Subgroup, to the Bunkeya Subgroup(Fig. 3). The Muombe Subgroup is subdivided in theMwale, Kaponda, Kakontwe and Kipushi Formations(Batumike et al., 2007). The Kaponda, Kakontwe andKipushi Formations reach a thickness of 600 m at Kipushiand consist entirely of dolomite, although these formationsare normally characterised by an intercalation of thicklimestone beds and thin dolomite horizons. The KipushiFormation consists of gray to black dolomite, intercalatedwith some black cherts. The rocks are ne-grained andC-rich near the upper contact with the overlying KateteFormation at the base of the Bunkeya Subgroup (Fig. 3).The carbonaceous material is identied as shungite: anamorphous, ungraphitised organic substance. Shungite is

present as angular fragments in the sulphide ores and inthe barren rocks, but is also frequently observed inglobular forms (Francotte & Jedwab, 1963) and inllingssures and pores (de Magne & Franois, 1988). Thisfact strongly suggests that at least part of the carbonaceousmatter has been in liquid form (de Magne & Franois,1988). The sulphides partly replace the shungite (Francotte& Jedwab, 1963). The overlying Katete Formationconsists of an alternation of dolomites and dolomiticshales in the Kipushi region (de Magne & Franois,1988). The host-rock of the Kipushi deposit underwentregional, low-grade greenschist facies metamorphism.

The core of the Kipushi anticline consists of a brecciaof silicied, talc-rich dolomites in a chloritic silty matrix,mainly derived from older Roan Group rocks, probably

belonging to the Dipeta Subgroup (Briart, 1948; Intiomale& Oosterbosch, 1974; Intiomale, 1982; de Magne &Franois, 1988; Kampunzu et al., 2009). The axial brecciais bordered by steeply dipping faults and de Magne &Franois (1988) propose it is a collapse breccia resultingfrom dissolution of an evaporitic diapir. A fault with anorientation of 295/80 to 295/55 cuts the northern ankof the anticline orthogonally and is called the KipushiFault. The Kipushi Fault contains a breccia and separatesthe concordant, 70 to 80 N dipping regular lithologic

succession to the east from the axial breccia to the west. Alarge slab of stratied shales, silty shales and sandstoneswith occasional irregular bedding, belonging to theMongwe and Kiubo Formations (Fig. 3), is located in the

hanging wall of the Kipushi Fault and is called the GrandLambeau (de Magne & Franois, 1988). This slab wouldhave sunk in the axial breccia during diapir collapse (deMagne & Franois, 1988).

The Kipushi mineralisation is located along theKipushi Fault, at the contact between the Kipushi and

Katete Formations and in pipes that crosscut the Kakontweand Kipushi Formations (Heijlen et al., 2008; Kampunzuet al., 2009). The Kipushi Fault and the contact betweenthe Kipushi and Katete Formations formed the two majorstructural features that controlled the position of themineralisation, with the highest Cu and Zn grades at theintersection of both (Heijlen et al., 2008). The position ofthe Kipushi deposit along a fault that crosscuts a WNWESE-oriented anticline indicates that the mineralisationdeveloped during or after the Lulian Orogeny. Recentlyobtained concordant Rb-Sr and Re-Os ages of 451 Ma onsphalerite-bornite and bornite-renierite assemblages from

the main sulphide mineralisation indicate it formed ca. 50Ma after the Lulian Orogeny (Schneider et al., 2007).See Kampunzu et al. (2009) for a more detailed descriptionand overview of the geology of the Kipushi deposit.

The main sulphide mineralisation at Kipushi overgrewthree generations of hydrothermal dolomite and ageneration of coarse-crystalline quartz. It is followed by aminor generation of sphalerite. The main sulphidemineralisation replaced the dolomite host-rock and itscements (Intiomale & Oosterbosch, 1974), whichcommonly resulted in banded ore (Heijlen et al., 2008).Pyrite and arsenopyrite precipitated at the start of the main

sulphide mineralising stage and they can be observed asrelicts in a groundmass of sphalerite and chalcopyrite(Heijlen et al., 2008), together with inclusions oftennantite, germanite, briartite and renierite. Sphaleriteshows chalcopyrite disease and smooth interlocking grain

boundaries between sphalerite and chalcopyrite indicatethat they are largely cogenetic. Bornite and chalcocite

precipitated at the end of the main sulphide mineralisationand they selectively replace chalcopyrite (De Vos et al.,1974; Heijlen et al., 2008; Kampunzu et al., 2009). Onequartz generation formed contemporaneously withsulphide deposition, as indicated by the commonoccurrence of euhedral quartz prisms in various sulphides

and, conversely, sulphide inclusions in quartz. A dolomiteformed after the main sulphide mineralisation and isovergrown by younger, minor pyrite-chalcopyrite-sphalerite mineralisation. The Cu-mineralogy changesfrom a cementing mass of chalcocite in the upper 100 mto chalcopyrite at depth, following this scheme: chalcocitechalcocitebornite bornite bornitechalcopyrite chalcopyrite (Intiomale & Oosterbosch, 1974). Ingeneral, Zn and Pb are preferentially hosted in impurecarbonate rocks, while Cu mostly occurs in fracturedrocks along the contact with the overlying KateteFormation (Heijlen et al., 2008; Kampunzu et al., 2009).

The main sulphide mineralisation at Kipushi,precipitated from halite-saturated, aqueous NaCl-KCl-CaCl

2brines (ca. 30-43 wt% NaCl equiv), with probably

excess carbonic vapour, based on decripitation of uid


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successive uid inclusion assemblages. These assemblagesrepresent an evolution towards a more oxidisedenvironment with possibly surface-derived meteoric uidsthat further dissolved evaporite-bearing strata, based onCl/Br and Na/Br signatures, higher than seawater,indicating a greater involvement of halite-dissolution

brines (Heijlen et al., 2008).

4.2 Kabwe

The Kabwe deposit is located in the central part of Zambia,in the south-eastern extension of the Copperbelt (Fig. 2A),in a region where Neoproterozoic metasedimentary rocksunconformably overlie a Palaeo- to Mesoproterozoic

basement. The basement consists of older granite-gneissand younger Muva schist and quartzite as well as maclavas of uncertain age. The metasedimentary cover rocksin the Kabwe region are considered time equivalent to the

Katanga Supergroup and are subdivided into theKangomba and Nyama Formations (Kamona & Friedrich,2007). The Kangomba Formation consists of a lowermember with arkose, quartzite and conglomerate and anupper member with metasiltstone, schist, phyllite anddolomite. The upper member could correspond to theBancroft Formation in the Zambian Copperbelt(Kampunzu et al., 2009), which is the lateral equivalent ofthe upper part of the Dipeta and the lower part of theMwashya Subgroups in the DRC (Cailteux et al., 1994).The Nyama Formation could be equivalent to the NgubaGroup or to the upper part of the Roan Group (Kamona &Friedrich, 2007) and consists in the Kabwe area of amatrix supported conglomerate at its base, a nely beddeddolostone alternating with carbonate-rich and carbonaceousshales, and a grey to dark grey bedded dolomite includinglenticular carbonaceous shales, and a light grey massivedolomite at the top (see detailed review and discussion inKampunzu et al., 2009). Rocks from the Kangomba and

Nyama Formations underwent greenschist- to amphibolite-facies metamorphism (Ramsay & Ridgeway, 1977).

The stratigraphic position of the massive Pb-Znmineralisation at Kabwe is unclear (cf. Batumike et al.,2006; Kampunzu et al., 2009). The Kabwe deposit is

hosted by massive dolomite, which is correlated by mostauthors to the upper member of the Kangomba Formation(Brancroft Formation, Upper Roan Group in theCopperbelt), while others correlate these massivedolomites to the massive dolomite at the top of the NyamaFormation (probably Kakontwe Formation, Lower Ngubain the Copperbelt). This uncertainty was not claried inthe most recent papers on the Kabwe deposit by Kamona& Friedrich (2007) and by Kampunzu et al. (2009) who

proposed both stratigraphic levels for the Kabwe deposit.Therefore the massive dolomite that hosts the Kabwedeposit is simply called the Kabwe dolomite, withoutcorrelation to the stratigraphy of the Katanga Supergroup.

The Kabwe dolomite forms part of a large NWSE-plunging syncline in the Kabwe region. The mineralisationat Kabwe consists of four main, epigenetic, pipe- to vein-like orebodies, controlled by NESW oriented faults

(Kamona & Friedrich, 2007). All orebodies haveassociated black organic matter (Kampunzu et al., 2009).

The sulphide mineralisation at Kabwe was precededby deposition of silica that replaced dolomite (Kamona &Friedrich, 2007). The main sulphide mineralisation startedwith massive pyrite and was followed by the Ge sulphides,

briartite and renierite that developed coeval withchalcopyrite, which contains exsolution intergrowths of

both (Kampunzu et al., 2009). The Ge sulphides werereplaced by a rst generation of sphalerite and galena thatcan be observed as inclusions in pyrite. Fractures in this

pyrite generation were healed by chalcopyrite and thepyrite is overgrown by a second generation of sphalerite(Kamona & Friedrich, 2007). These primary sulphideswere deformed, based on cataclastic textures, grainfracturing, lamellar twinning, bent cleavage planes andrecrystallisation (Kampunzu et al., 2009). A Pb-Pb modelage of ca. 680 13 Ma was provided by Kamona et al.

(1999), pre-dating the Lulian Orogeny, in accordancewith the observed deformed sulphides. However, Pb-Pbmodel ages are not robust and no conclusion should bemade about the age of mineralisation at Kabwe (cf.Frimmel et al., 2004).

The second sphalerite generation is commonlyovergrown by a second generation of galena that isintergrown with small amounts of covellite and chalcocite.These Cu sulphides are believed to be of secondary originand they selectively replace chalcopyrite and pyrite fromthe earlier massive sulphide mineralisation (Kamona &Friedrich, 2007). Most primary sulphide mineralisation is

observed as cores of massive sulphide ore, surrounded byoxide zones, with willemite, cerrusite, smithsonite,goethite and hematite that selectively replace sphalerite,galena and pyrite. Oxidation of sulphides persists down tothe deepest mining levels at 470 m (Kamona & Friedrich,2007).

Disseminated pyrite in the barren bedded dolostonebelow the Kabwe deposit has34S values from -7.5 to -5.1 V-CDT (Fig. 4B). These pyrites are with minimum 15 depleted in 34S relative to Neoproterozoic seawatersulphate (+10 to + 46 V-CDT; Claypool et al., 1980;Gorjan et al., 2000; Hurtgen et al., 2002, 2005) indicative

of BSR, in agreement with a diagenetic origin for thedisseminated pyrite. Galena, sphalerite and pyrite fromthe main sulphide mineralisation have lower, negative34S values of -17.75 0.28, -16.54 0.27 and -15.82 0.25 V-CDT respectively (Kamona & Friedrich, 2007;Fig. 4B). These sulphides are with minimum 25 depleted, compared to Neoproterozoic seawater sulphate,also indicative of BSR (Ohmoto, 1986). Comparison ofthe S isotopic composition of co-existing sulphide tripletsfrom the main sulphide mineralisation yields concordantisotopic temperatures in the range 227 to 356C, with a

probable temperature of 291+/-35C (Kamona &Friedrich, 2007). Thus the S from the sulphides must have

been reduced prior to the main sulphide mineralisation atKabwe, since BSR only takes place at temperatures below80 C (Machel, 2001). The reduced S was probably storedas disseminated pyrite in the massive dolomite host-rock


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and had lower 34S values, relative to the disseminatedpyrite in the barren bedded dolostone below the Kabwedeposit.

Galena samples from the main sulphide mineralisationat Kabwe have a homogeneous, low radiogenic Pb isotopecomposition of 17.997 0.007 for 206Pb/204Pb, 15.713

0.010 for 207Pb/204Pb and 38.410 0.033 for 208Pb/204Pb(Fig. 6A-C; Kamona et al., 1999). Pb isotope data for theKabwe and Kipushi deposits have a similarly clustered Pbisotopic composition, but Pb isotope data from thesulphide mineralisation at Kabwe have slightly higher207Pb/204Pb and 208Pb/204Pb ratios (Fig. 6A-C). The Kabweand Kipushi deposits have similar geological settings,along a fault crosscutting a massive dolomite underlain bya thick sedimentary pile. Thus the Pb isotopic homogeneityof the Kabwe sulphides has probably the same origin asfor the sulphides from the Kipushi deposit.

The origin of the ore-forming brine at Kabwe is poorly

constrained, although Kampunzu et al. (2009) believethat, based on the speculative 680 Ma Pb-Pb model agefor Kabwe, the mineralising uids were the result ofdewatering of Katangan sediments during subduction atthe onset of the Lulian Orogeny. Whatever the age of themineralisation or the source of the mineralising uid, themineralisation formed from a high temperature uid (~300C) that probably acquired its metal content in muchthe same way as the mineralising uid at Kipushi, throughleaching of metals from suitable basement rocks. Whenthis metal-bearing uid migrated upward along NESWoriented faults, it precipitated its content as sulphideswhere it encountered signicant quantities of reduced

sulphur that were liberated from diagenetic pyrites on thesite of the current Kabwe deposit.

4.3 Dikulushi

The Dikulushi deposit is situated in the KundelunguPlateau region in the southeast of the Democratic Republicof Congo, close to the border with Zambia (Fig. 2A).Mineralisation at Dikulushi is hosted in a dolomite-sandstone sequence from the base of the KundelunguGroup (Fig. 3; Haest et al., 2007). The dolomites belongto the Lubudi Formation at the top of the Gombela

Subgroup and the sandstones are intercalated with shalesand conglomerates that form part of the MongweFormation, which is situated at the base of the NguleSubgroup (Fig. 3; Haest et al., 2007). A linear NNW-SSEoriented zone with shale that deformed in a ductile manneris located in the Lubudi Formation close to the contactwith the Mongwe Formation. This zone of shale is relatedto a detachment at depth, which caused its emplacementin the Lubudi Formation. It caused brecciation of thesurrounding parts of the Lubudi Formation and of thecontact zone between the Lubudi and Mongwe Formations(Haest et al., 2007). Similar vertical zones of shale areobserved in boreholes below the current excavation level

(Haest, 2009). On the surface, mineralisation is hosted inE-W- and NE-SW-oriented faults that crosscut theMongwe Formation and the brecciated contact betweenthe Mongwe and Lubudi Formations (Haest et al., 2007).

At deeper levels, mineralisation follows the borders of thevertical zones with shale (Haest, 2009).

Two kinds of mineralisation can be distinguished atDikulushi: a Cu-Pb-Zn-Fe mineralisation that isdominantly observed along E-W-oriented faults in thewest of the mine and as remnants along NE-SW-oriented

faults in the east, and a Cu-Ag mineralisation thatremobilised the earlier Cu-Pb-Zn-Fe mineralisation along

NE-SW-oriented faults in the east of the mine (Haest etal., 2007). The Cu-Pb-Zn-Fe mineralisation precipitatedduring the waning stage of the Lulian Orogeny at around520 Ma ago and was remobilised afterwards into the Cu-Ag mineralisation (Haest, 2009). Cu-Pb-Zn-Femineralisation at Dikulushi is dominated by galena,sphalerite, chalcopyrite, bornite and chalcocite, withassociated quartz, dolomite and calcite gangue that

precipitated in a reducing environment from a moderatetemperature (Th = 90-140 C), saline (20-25 eq. wt%

CaCl2) H2O-NaCl-CaCl2uid. The Cu-Ag mineralisationconsists almost entirely of an orthorhombic chalcocite,with a dense cleavage, post-dating barite, calcite andquartz gangue that precipitated in more oxidisingconditions from a low temperature (Th ~ 65 C), low tomoderately saline (19 eq. wt% NaCl) H

2O-NaCl-

KCl uid (Dewaele et al., 2006b; Haest et al., 2009,2010a).

Sulphides from the Cu-Pb-Zn-Fe mineralization andchalcocite and barite from the Cu-Ag mineralisation atDikulushi have similar 34S values between +10.0 and+14.1 V-CDT (Fig. 4B), in the range of Neoproterozoicseawater sulphate (+10 to +46 V-CDT; Claypool et al.,1980; Gorjan et al., 2000; Hurtgen et al., 2002, 2005).These sulphides and sulphates have a similar S isotopiccomposition as the sulphides in the discordant orebody atKipushi. The sulphur isotopic composition for thesulphides and sulphates at Dikulushi is probably also bestexplained by TSR, based on the narrow isotopic range,close to the isotopic composition of the proposed sourcesulphate (e.g. Ohmoto & Rye, 1979; Powell & Macqueen,1984; Naylor et al., 1989).

Calcite and dolomite associated with the Cu-Pb-Zn-Feand the Cu-Ag mineralisations at Dikulushi have a similarSr-isotopic composition between 0.71270 and 0.7161087Sr/86Sr (Fig. 5B; Haest et al., 2009). The 87Sr/86Sr ratiosof the carbonate gangue minerals are signicantly enrichedin 87Sr, compared to the strontium isotopic composition of

Neoproterozoic marine carbonates(87Sr/86Sr=0.70560.7087, Jacobsen & Kaufman, 1999),similar to the carbonates in the type I nodules at Kamoto(compare Figs. 5A&B).

Sulphides from the Cu-Pb-Zn-Fe and the Cu-Agmineralisation at Dikulushi have a clearly distinct Pbisotopic composition. CuPbZnFe polysulphides havea relatively unradiogenic and internally inhomogeneouslead isotopic composition (206Pb/204Pb=18.0718.49;Figs.

6A-C), most likely generated by mixing of Pb fromisotopically heterogeneous clastic sources (Haest et al.,2010b). Chalcocite samples from the Cu-Ag mineralisationcontain only trace amounts of lead and show mostly


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radiogenic Pb isotope signatures that fall along a lineartrend in the 207Pb/204Pb vs. 206Pb/204Pb diagram(206Pb/204Pb=18.6623.65; 207Pb/204Pb = 15.7216.02;Fig. 6A; Haest et al., 2010b). These anomalouscharacteristics reect a two-stage evolution involvingadmixture of both radiogenic lead and uranium during a

young uid event possibly c. 100 Ma ago (Haest et al.,2010b). The Pb isotope systematics of local host rocks tomineralisation also indicate some comparable youngdisturbance of their UThPb systems, related to the sameevent. They could have provided Pb with sufcientlyradiogenic compositions that was added to less radiogenicPb remobilised from precursor CuPbZnFe

polysulphides, whereas the U most likely originated fromexternal sources (Haest et al., 2010b).

Pb isotopic data for chalcocite from the Cu-Agmineralisation are less radiogenic than for sulphides fromthe stratiform Musoshi deposit, but on an uranogenic plot

these chalcocites lie along the 645 Ma isochron ofRichards et al. (1988a; Fig. 6A) and give an identicalapparent age. In the 208Pb/204Pb vs. 206Pb/204Pb space, thesamples from the Musoshi deposit deviate towards 208Pbenriched values, but are likewise linearly correlated (Fig.6B). This deviation can probably be attributed to the hostrocks since the Musoshi mineralisation is hosted in shalesthat typically have high Th/Pb ratios whereas the DikulushiCu-Ag mineralisation is hosted by sandstones that havelower Th/Pb. We suggest that the identical 207Pb-206Pbapparent ages for Musoshi and Dikulushi are a coincidence

because geological criteria clearly exclude a mineralisationage as old as ca. 645 Ma for the Dikulushi Cu-Ag

mineralisation and Haest et al. (2010b) showed that thelinear trend for the Cu-Ag mineralisation at Dikulushi can

be attributed to an admixture of radiogenic Pb and possiblyU at ca. 100 Ma.

4.4 Smaller vein-type deposits

A large number of smaller vein-type deposits occur in theCentral African Copperbelt. Most of them are of the Pb-Zn type, including the deposits of Kengere and Lombe inthe DRC. The vein-type deposit of Kansanshi in Zambiaforms an exception, being of the Cu-Au type. A recent,

detailed review of these deposits is given in Kampunzu etal. (2009). The Kengere deposit is located ca. 50 km to thesouth of Kolwezi and is the westernmost Pb-Zn deposit ofthe Copperbelt in the DRC (Fig. 2A). The mineralisationat Kengere is hosted in breccias and fractured rocks,associated with a NS trending fault, at the contact

between the Kaponda and Kakontwe Formations(Kampunzu et al., 2009). Both formations are characterised

by the occurrence of black amorphous organic matter. Thebarren Kipushi Formation overlying the KakontweFormation is locally affected by fracturing and minorquartz-carbonate precipitation. A major NESW trendingfault zone occurs to the north of the deposit and contains

a large breccia, which is sub-parallel to the axial foldplane (Kampunzu et al., 2009). The primary sulphidemineralisation at Kengere shows a paragenetic sequencefrom pyrite over dark brown, Fe-Cd-bearing sphalerite to

Ag-rich galena (Intiomale, 1982). Supergene alteration ofthe sulphide mineralisation produced secondary Zn-Pb-(Cu) oxide minerals, including cerussite, smithsonite,calamine and traces of chrysocolla.

The Lombe deposit is situated in the central-southernpart of the Copperbelt in the DRC (Fig. 2A). It is hosted

in carbonate units along a tectonic contact between theKipushi and Katete Formations (Batumike et al., 2006).The Kipushi Formation contains impregnations of blackamorphous organic matter. A large NESW trending faultis located south of the deposit and contains metabasicrocks from the Dipeta Subgroup (Kampunzu et al., 2009).Mineralisation at Lombe consists of a main orebody withmassive Pb-Zn sulphides, concordant to the dip of thehost-rock and a lenticular sub-economic zone ofdisseminated chalcopyrite and bornite mineralisation inthe upper beds of the Katete Formation. Precipitation ofthe main Pb-Zn sulphide orebody started with pyrite,

followed by sphalerite, tennantite, an unidentied Pb-Assulphide, galena, chalcopyrite and arsenopyrite (Intiomale,1982). The main sulphide mineralisation was oxidisedwith the formation of covellite, calamine, smithsonite,cerussite, malachite and azurite. The Pb isotopiccomposition of sulphides from Lombe and Kengere plotin a narrow cluster together with sulphides from theKipushi deposit (Fig. 6), except one sulphide from Lombethat shows a 206Pb enriched value. The deposits of Kengereand Lombe are also located along faults that crosscut theKakontwe Formation, above a thick sedimentary pile ofthe Roan Group. As described above for the Kipushi andKabwe deposits, their homogeneous Pb isotopic signaturemight be due to prolonged mechanical and geochemicalreworking and lateral transportation into zones favourablefor ore deposition, e.g. carbonate rocks.

The Kansanshi deposit is located in northern Zambia,150 km west of the Zambian Copperbelt (Fig. 2A). TheKansanshi deposit is hosted by metasedimentary rocksthat belong to the Katanga Supergroup and include quartz-

biotite schist, biotite-garnet schist, carbonaceous phyllites,impure marbles, and quartz-muscovite phyllites(Torrealday et al., 2000). The exact stratigraphic positionof these rock units is unknown, because they form part of

thick-skinned thrust sheets that contain slices of pre-Katangan basement (Coward & Daly, 1984). Themetamorphic grade is upper greenschist - loweramphibolite facies. A large sill of metamorphosed gabbrothat developed prior to tectonic activity and mineralisationat Kansanshi, is located to the north of the deposit. TheKansanshi deposit consists of three primary high-angle,sheeted, coarse-grained vein sets, with crosscuttingrelationships that could be used to constrain their relativeage. The rst set of veins consists of quartz-dolomite-chalcopyrite-pyrite-(molybdenite) minerals, withmoderate to intense albitic and ferroan dolomite alterationof schists and phyllites that resulted in the destruction of

metamorphic biotite (Torrealday et al., 2000). The secondset of veins contains ferroan dolomite-calcite-pyrite-

pyrrhotite-(chalcopyrite)-(molybdenite), with ferroandolomite alteration. Both vein sets are surrounded by


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envelopes of disseminated chalcopyrite. The third vein setcontains coarse-crystalline calcite-ferroan dolomitemonazitemolybdenite-(brannerite)-(chalcopyrite),without an alteration envelope.

Re-Os dating on molybdenite from the rst two veinsets yielded mineralisation ages that overlap within their

2 uncertainties, indicating that there is no discernabledifference in the ages of these veins at the 2 level.Combination of Re-Os data for both vein sets yielded anage of 512.4 1.2 Ma (Torrealday et al., 2000). The thirdmolybdenite-rich vein set yielded a Re-Os age of 502.4 1.2 Ma, which is consistent with the observed crosscuttingrelationship observed in the eld. These results indicatethat the Cu mineralisation at Kansanshi developed in theCambrian, after the Lulian Orogeny during two discretemineralisation pulses at ca. 512 Ma and ca. 502 Ma(Torrealday et al., 2000).

The sulphides at Kansanshi have a S isotopic

composition between +2 and +10 V-CDT, which islower than the 34S values for sulphides from Dikulushiand falls in the lower part of the range for the sulphidesfrom Kipushi (Dechow and Jensen, 1965). The sulphidesat Kansanshi have S isotope ratios that are lower than thatof the proposed sulphate source, i.e. Neoproterozoicseawater sulphate (+10 to + 46 V-CDT; Claypool et al.,1980; Gorjan et al., 2000; Hurtgen et al., 2002, 2005). The

presence of organic matter in the host-rocks produced13C-depleted pyrobitumen and a large amount of CO

2gas

(Kribek et al., 2005). The presence of CO2 gas during

mineralisation is conrmed by the observation of two-phase (L+V) CO

2

-rich inclusions in quartz gangue,associated with the mineralisation (Kampunzu et al.,2009). Interaction between graphitised organic matter andthe hydrothermal uid likely controlled the oxidation stateof the ore uid (Kribek et al., 2005) and could have beenthe controlling factor leading to ore precipitation at thecurrent site.

5. Sediment-hosted ore deposits in the Otavi

Mountain Land

More than 600 Cu-Pb-Zn-V deposits and occurrenceshave been recognised in the OML and these are subdivided

in two types, based on geological, mineralogical andgeochemical data (Frimmel et al., 1996): (1) strataboundPb-Zn dominated deposits of the Berg Aukas-type arehosted in platform carbonates of the lower AbenabSubgroup, which is interpreted to be time-equivalent tothe Bunkeya and Muombe Subgroups in the DRC and (2)Cu-Pb-Zn deposits of the Tsumeb-type are hosted in

platform carbonates of the Tsumeb Subgroup, which istime-equivalent to the Gombela and Ngule Subgroups inthe DRC (Fig. 3).

5.1 Berg Aukas-type deposits

The Berg Aukas deposit is situated close to the easternborder of the Otavi Mountain Land (Fig. 2B). Berg Aukas-type Zn-Pb-V deposits are stratabound and, in places,stratiform and are situated in the Berg Aukas Formation.

Discordant, brecciated, pipe-like ore bodies extend awayfrom the stratiform ore into the hanging wall. These ore

pipes are usually related to thrusts and faults along whichkarst chimneys were formed by solution collapse (Frimmelet al., 1996). Mineralisation in the stratiform ore bodiesand the karstic pipes is dominated by sphalerite and

galena, with only very little to no Cu minerals present.Dolomite is the most important gangue mineral. The oresin Berg Aukas-type deposits have been often oxidised,with the formation of willemite, smithsonite, cerrusite andother secondary minerals (Frimmel et al., 1996).

The main sulphide mineralisation precipitated from asaline uid (23 eq. wt.% NaCl), at a minimum temperature

between 100 and 200 C (Thav = 180 C; Frimmel et al.,1996). Frimmel et al. (1996) estimate the formationtemperature of the main sulphide mineralisation at 240C,taking the overburden into account. Crush leach analysisof uid inclusions in dolomite gangue indicate that the

main sulphide mineralisation at Berg Aukas precipitatedfrom a uid, with low Cl/Br and Na/Br values that pointto seawater evaporation as a process to acquire a moderatesalinity, rather than halite dissolution (Chetty & Frimmel,2000). The oxygen isotope composition of dolomiteassociated with the main sulphide mineralisation varies

between -9.1 and -5.6 V-PDB. Frimmel et al. (1996)calculated that this dolomite generation (18Oav= -7.1 V-PDB) must have precipitated from a uid, with a 18O-value of 13 V-SMOW at a temperature of 240C. Thismineralising uid was strongly enriched in 18O, relative toseawater or meteoric water, which supports an evolveddiagenetic/metamorphic origin of the uid (Frimmel etal., 1996). The 13C-value for all dolomite gangue that

precipitated before, during and after the main-sulphidemineralisation, is similar and varies between 1.3 and 4.5 V-PDB, in the range of Neoproterozoic seawaterdolomite (13C = -4.0 to +4.0 V-PDB; Veizer & Hoefs,1976).

Sulphides from Berg Aukas have 34S values between20 and 30 V-CDT (Fig. 4, Melcher et al., 2006). These34S values fall in the range of 34S values for

Neoproterozoic evaporites (+10 to + 46 V-CDT;Claypool et al., 1980; Gorjan et al., 2000; Hurtgen et al.,2002, 2005), which is conrmed by Hughes (1987) who

measured 34S values of 31 and 33 V-CDT for gypsumand anhydrite in an evaporite horizon in the Upper TsumebSubgroup. The correspondence in S isotopic composition

between the sulphides at Berg Aukas and the S isotopiccomposition of Neoproterozoic evaporites might indicatethe sulphides at Berg Aukas derived their S through TSRof sulphate released during dissolution of evaporites inthe sedimentary column.

Host-rock dolomites to the Berg Aukas deposit have87Sr/86Sr ratios that vary between 0.7078 and 0.7108(Frimmel et al., 1996), similar or slightly enriched relativeto Neoproterozoic marine carbonates (87Sr/86Sr = 0.7056

- 0.7087; Jacobsen & Kaufman, 1999). The dolomitegangue to the sulphide mineralisation has 87Sr/86Sr ratiosthat vary between 0.7039 and 0.7174 (Fig. 5B), similar orenriched relative to Neoproterozoic marine carbonates,


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indicating contamination of the mineralising uid with87Sr by interaction with 87Sr-rich host-rocks (Frimmel etal., 1996). Pb-isotope data for sulphides from the BergAukas-type deposits are slightly heterogeneous and plotat the less radiogenic side of the Pb isotopic cluster dened

by the Cu-Pb-Zn-Fe mineralisation at Dikulushi (Fig. 6C),

close to the homogeneous Pb isotopic eld of the sulphidesfrom Kabwe (Fig. 6C). Melcher et al. (2003) deduced alinear trend from these data, which they attribute to mixingof Pb from a hydrothermal end-member, with Pb from adifferent source and/or from the host-rocks along whichthe mineralising uids were channelised. Frimmel et al.(1996) consider the underlying volcanic rocks of theAskevold Formation (Nosib Group) as the geologicallymost sensible source of Pb. Their main centre of volcanismis in the south of the OML. They have been metamorphosedto greenschist facies and in places strongly altered asevidenced by intense epidotization and calcitization,indicating ushing of the Nosib Group by basinal brines(Frimmel et al., 1996). The Pb isotope composition ofthese sources and the host-rocks through which themineralising uids migrated have not been determined.

5.2 Tsumeb-type deposits

The deposits of Tsumeb, Kombat and Khusib Springs arethe most important Tsumeb-type deposits in the OtaviMountain Land (Fig. 2B). They are not strictly stratabound,

but are often hosted in brecciated zones in massivedolomite from the Maieberg, Elandshoek and HttenbergFormations (Fig. 3), with associated carbonic material

(Chetty & Frimmel, 2000). These brecciated zones havebeen identied as karst structures in the deposits ofTsumeb and Kombat, lled with feldspathic sandstonefrom the overlying Mulden Group (Lombaard et al.,1986). The deposit of Tsumeb formed at ca. 530 Ma, basedon the close relation between mineralisation and syn-orogenic structures (Frimmel et al., 1996) and based on a

preliminary Re-Os model age of 527 Ma (Melcher et al.,2003). These ages indicate the Tsumeb deposit formed atthe end of the Damaran Orogeny (Frimmel et al., 2004).

Mineralisation in the Tsumeb-type deposits isdominated by Cu, with lesser amounts of Pb and Zn and

an important enrichment in Ag, As, Ge, Ga and Cd. Thehypogene mineralisation assemblage at Tsumeb containspyrite, followed by chalcopyrite, bornite, germanite,sphalerite and gallite, enargite, tennantite and briartite,renierite and galena. Ore emplacement at Tsumeb post-dated much of the regional folding, but the ores bear theimprint of the waning stages of deformation (Lombaard etal., 1986). At Kombat, bornite precipitated rst, followed

by chalcopyrite and galena, with subordinate sphalerite,tennantite and pyrite (Frimmel et al., 1996). Footwallmineralisation at Khusib Springs contains sphalerite,chalcopyrite, pyrite and minor tennantite. Massive Cu orecrosscuts the footwall mineralisation at Khusib Springs

and consists of early chalcopyrite and bornite, overgrownby pyrite and sphalerite, which were replaced by enargiteand tennantite, with Ge-bearing colusite, pearceite-

polybasite, galena and some pyrite (Melcher et al., 2006).

Calcite and quartz are the dominant gangue minerals in allTsumeb-type deposits, with minor dolomite and hardlyany uorite or baryte (Frimmel et al., 1996). The oreswere enriched by supergene processes after theirformation, with the precipitation of massive oreassemblages that comprise chalcocite, digenite, covellite,

cuprite, native copper and silver.The main phase Cu mineralisation at Kombat, Tsumeb

and Khusib Springs precipitated from a uid, with asalinity between 17 and 23 eq. wt% NaCl at a minimumtemperature between 190 and 280 C (Frimmel et al.,1996; Chetty & Frimmel, 2000). Ga/Ge ratios of sphaleritesat Khusib Springs and at Tsumeb indicate mineralisationtemperatures of >260 10 C and close to 300 Crespectively (Melcher et al., 2006). Frimmel et al. (1996)estimated the effective formation temperature of the mainsulphide mineralisation in the Kombat and Tsumebdeposits, based on uid inclusion data and taking the

overburden in account, at 450 C. The formationtemperature of the main sulphide mineralisation at KhusibSprings was estimated at 370 C, also using uid inclusiondata (Chetty & Frimmel, 2000). The effectivemineralisation temperature for the Tsumeb-type depositsis taken between 300 and 450 C. Crush leach analysis ofuid inclusions in quartz, calcite and dolomite gangueindicate that these deposits precipitated from a uid, withlow Cl/Br and Na/Br values, indicative of seawaterevaporation as a process to acquire a moderate salinity,rather than halite dissolution (Chetty & Frimmel, 2000).

The calcite gangue in the Tsumeb deposit has 18O-values

between -12.1 and -6.4 V-PDB, with an average valueof -10.0 V-PDB. If calcite precipitated at a temperatureof 450 C, the mineralising uid had a 18O-value of ca.18 V-SMOW, which is signicantly enriched relativeto seawater (Frimmel et al., 1996). This uid probablyrepresents an evolved diagenetic or metamorphic uid.The same calcite gangue has 13C-values between -4.4and 4.0 V-PDB, which is in the range of Neoproterozoicseawater dolomite in Northern Namibia (13C = -5.0 to+5.0 V-PDB; Halverson et al., 2005). A calcitegeneration, pre-dating sulphide deposition at Kombat anda calcite generation post-dating sulphide mineralisation atTsumeb have 13C-values down to -7.2 and -9.5 V-PDB

respectively (Chetty & Frimmel, 2000), which couldindicate interaction with organic material

34S-values for sulphides from Tsumeb and KhusibSprings vary between +17 and +27 V-CDT and between+21 and +28 V-CDT respectively (Fig. 4C), similar tothe sulphides from Berg Aukas. Sulphides from theKombat mine cross this range with 34S-values between-11 to +26 V-CDT (Fig. 4C; Hughes, 1987). Melcher etal. (2003) relate the high 34S-values to derivation of Sfrom evaporite beds in the Damara Supergroup. Asdiscussed above for the Berg Aukas deposit, evaporite

beds in the Tsumeb Group are indeed characterised by34S-values between 31 and 33 V-CDT. Mobilisationof their SO

42- and reduction by TSR could explain the

observed 34S-values. The low 34S-values for sulphidesat Kombat, down to -11 V-CDT, correspond to a S


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isotopic fractionation of at least 21 between S fromNeoproterozoic seawater sulphates and sulphides,indicating BSR (Ohmoto, 1986). The BSR reduced S was

possibly stored in the Kombat deposit as disseminated,early diagenetic pyrite and dissolved during formation ofthe main sulphide mineralisation at Kombat to supply the

S. 87Sr/86Sr isotope ratio data for the carbonate host-rockof the Kombat deposit range between 0.7076 and 0.7086(Frimmel et al., 1996), in the range of Neoproterozoicseawater carbonates (87Sr/86Sr = 0.7056 - 0.7087; Jacobsen& Kaufman, 1999). Calcite gangue from the main sulphidemineralisation at Kombat is enriched in 87Sr, with 87Sr/86Srratios of 0.7101 to 0.7141 (Fig. 5B), indicating interactionof the mineralising uid with 87Sr enriched parts of the

basement or with other radiogenic rocks along the owpath of the mineralising uid. Pb isotope data for sulphidesfrom Tsumeb, Kombat and Khusib Springs are low

radiogenic and plot around the Pb isotopic cluster denedby the sulphides from the Dikulushi Cu-Pb-Zn-Femineralisation and to lower radiogenic values (Fig. 6C).Melcher et al. (2003) suggest Pb isotopic data for thedifferent Tsumeb-type deposits show mixing trends justlike for the Berg Aukas-type deposits that could be relatedto mixing of Pb from a common hydrothermal end memberwith Pb from different sources and/or aquifers (Hughes,1987). A comparison with Pb isotope data from the RoshPinah ore province made Frimmel et al. (2004) concludethat the common hydrothermal endmember for theTsumeb-type deposits likely represents Pb derived fromPalaeo- to Mesoproterozoic basement that was mixed

with Pb mobilised from the local host-rock by syn-orogenic uids.

6. Multiphase sediment-hosted mineralisation

model for the Pan-African Orogen

Sediment-hosted mineralisation in the Central andSouthern part of Africa developed during multiple phases

that likely span a period of over 400 Ma. Dolomitisationoccurred during early diagenesis in the Roan rift basin andis followed by a rst main phase of stratiform Cu-Comineralisation, dated at ca. 816 Ma (Selley et al., 2005;ca. 820 Ma in Fig. 7). The rst main phase of stratiformCu-Co mineralisation occurs in carbonates and

siliciclastics from the Lower Roan (Fig. 3). At ca. 816Ma, the Lower Roan was buried to not more than 1 kmdepth (Cailteux et al., 1994), which is still within limits ofan early diagenetic environment (600-1000 m in Machel,1999). As Annels (1974) suggested, early diagenetic Cu-Co mineralisation precipitated from a moderatetemperature, moderate saline uid that interacted withsedimentary rocks, the granitic basement and/or analkaline magma body at depth (Voet & Freeman, 1972;Annels, 1974, 1989; Unrug, 1988; Cailteux et al., 2005;McGowan et al., 2006; Bernau et al., 2007; Muchez et al.,2008; Fig. 7). Interaction with these different rock unitsand absence of complete mixing would explain thevariable Pb isotopic values of these deposits (Fig. 6). Swas partly derived from gypsum or anhydrite, previously

present in the evaporite nodules and reduced by BSR(Muchez et al., 2008).

The early main phase of stratiform Cu-Comineralisation was remobilised by a high temperatureuid in a second Cu-Co mineralisation during latediagenesis/metamorphism and during the LulianOrogeny (580 Ma to 520 Ma in Fig. 7). In the DRC, the2ndmain Cu-Co mineralisation occurs in nodules, veins oras breccia cements, within the Mines Subgroup (ElDesouky et al., 2007, 2009). In the Zambian Copperbelt,

precipitation occurred in multiple, successive veingenerations during and possibly after the Lulian orogeny(Brems et al., 2009).

The vein-type Cu-Pb-Zn deposits of Dikulushi andTsumeb formed in the front zone of the Lulian andDamaran Belts respectively, near the end of the PanAfrican Orogeny (530 Ma to 500 Ma in Fig. 7). The

Lufilian ArcKundelungu Plateau

??

?

?

?

?

?

?

AB

C?

Age (+ main event)

< 820 Ma

Mineralisation

580 Ma 520 Ma

5 30 Ma 5 00 Ma

- Roan sedimentation- Early diagenesis and

dolomitisation

1st stratiform Cu-Co mineralisation

- Disseminated, in bands andreplacing evaporite nodules

- Moderate saline, moderate T fluid- Basement interaction

- Late diagenesis to synLufilian Orogeny

- Major thrusting and foldingin the Lufilian Arc

2nd stratiform Cu-Co mineralisation- In veins, nodules and breccia- Remobilising 1st Cu-Co mineralisation- Highly saline, high T fluid

- Significant interaction with sed. pile- Moderate saline, moderate T fluid

- Waning stage of theLufilian Orogeny

B. Tsumeb (vein-type, Cu-Pb-Zn)(foreland of the Damara Belt in Namibia)

- Significant interaction with sed. pile

- Moderate saline, high T fluidC. Kansanshi (vein-type, Cu-Au)(west of Lufilian Arc in Zambia)

- uncertain stratigraphic position

A. Dikulushi (vein-type, Cu-Pb-Zn-Fe)

+ Kombat/Khusib Springs(vein-type, Cu-Pb-Zn, Namibia)??

Figure 7. Cumineralisation in theLulian Arc and on theKundelungu Plateau andits relation to thegeodynamic evolution.Reference is made toCu-Pb-Zn mineralisationin the Otavi MountainLand (geological crosssections after Dewaeleet al., 2006a). 1stand 2ndstratiform Cu-Co

mineralisation stages,respectively at


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Dikulushi deposit is situated at the level of the Gombelaand Ngule Subgroups in Katanga and the Tsumeb depositis situated at a stratigraphically equivalent position in

Namibia. Mineralisation at both localities precipitatedfrom moderate saline, moderate to high temperature uidsthat interacted with the basement and the sedimentary pile

below. Limited hydrothermal mixing produced internallyheterogeneous low radiogenic clusters in the 207Pb/204Pbvs. 206Pb/204Pb space. The sulphides from Dikulushi andTsumeb might have acquired their S from late

Neoproterozoic evaporite layers at depth or from inltratedseawater. The presence of Neoproterozoic evaporite layers

below the Kundelungu Plateau is however uncertain. S inboth deposits was reduced by TSR. The Kombat andKhusib Springs deposits in the OML show manysimilarities with the above deposits, which could indicate

a comparable origin. They are all situated at more or lessthe same stratigraphic level and their mineralogy isdominated by Cu, with minor amounts of Pb and Zn indolomite-rich lithologies. Their Pb isotopic compositionis internally heterogeneous and forms a 207Pb-enrichedcluster. However, S in the Kombat deposit was reduced byBSR and likely stored on site in the form of early diageneticdisseminated pyrite that was dissolved during the mainsulphide mineralisation. The vein-type Cu-Au deposit ofKansanshi developed in the same period, but itsstratigraphic position is uncertain and it contains Au inaddition to Cu, rather than Pb and Zn.

These vein-type deposits might have formed togetheror after the second main phase of Cu-Co mineralisation inthe Lulian Arc. Except for their partly overlapping ageand the fact that S in most of the sulphides from these

deposits was the result of TSR, they have little in common.The vein-type deposits all formed in the front zone of thePan-African Orogen, while the stratiform depositsdeveloped more towards the core of this belt. Thestratabound Cu-Co sulphides precipitated from a highersaline (in the DRC) and mostly higher temperature uid,relative to the vein-type ores in the front zone. Mineralisinguids in the core of the orogen locally recycled previousores, while the mineralising brines in the front zonetransported signicant quantities of metals from deeperlevels to the mineralisation sites, developing for examplethe world class Cu deposit of Tsumeb.

50 Ma after the Lulian Orogeny developed theKipushi Zn-Cu deposit close to the core of the LulianArc from a highly saline, high temperature uid (450 Main Fig. 7). This uid is less saline and warm than the uidfrom which the 2ndmain Cu-Co mineralisation precipitatedclose to the core of the Lulian Arc, but warmer and moresaline than the uids from which the Cu-rich vein-typedeposits on the Kundelungu Plateau and the OtaviMountain Land developed. The mineralising uid atKipushi acquired its high salinity by halite dissolution andits signicant metal content by interaction with theunderlying sedimentary pile and/or the basement. S wasderived from Neoproterozoic evaporites and maybe from

Neoproterozoic seawater and reduced by TSR on site,with coeval oxidation of the existing hydrocarbons. Someof this S probably mixed with diagenetic S produced by

BSR and stored in the host-rock.The Pb-Zn deposits of Kabwe, Lombe and Kengere in

the Lulian Arc and the deposit of Berg Aukas from theOtavi Mountain Land share many characteristics with the

Lufilian ArcKundelungu Plateau ?

?

?

?

?

A

A

450Ma A. Kipushi (vein-type, Zn-Cu)

- Significant interaction with sed. pile+ with basement

- Highly saline, high T fluid

- Post Lufilian Orogeny

< ca. 520 Ma (+ < 450 Mafor Kipushi)

A. Dikulushi (vein-type, Cu-Ag)

- Remobilisation of Cu-Pb-Zn-Fe- Mixing of low saline, low T fluid, with

moderate saline, low T fluid

B?

B?

+ Lombe/Kengere (vein-type, Pb-Zn)?

X

Biano Subgroup +upper part of the Ngule Subgroup

Upper part of the Gombela Subgroup +lower part of the Ngule Subgroup

Kyandamu Formation

Bunkeya Subgroup Mines Subgroup

Dipeta Subgroup

Mwashya Subgroup

Mwale Formation

Upper part of the Muombe Subgroup RAT Subgroup

Basement

Cu deposit

Cu(-Pb-Zn-Co) mineralisation (nodule or vein)

Dolomite

Mineralising fluid pathway

Evaporite nodule

Fault

B

B. Kabwe (vein-type, Pb-Zn) (age??)

- Large fluid circulation system- High T fluid

+ Berg Aukas (vein-type, Pb-Zn,Namibia)??

C

B. Kipushi (Vein-type ), Cu-Zn


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Kipushi mineralisation. They are all situated atapproximately the same stratigraphic level and hosted bymassive dolomite. These deposits are, however, dominated

by Pb and Zn, with minor Cu at the contact with theoverlying dolomite-shale sequence (cf. Lombe). Themineralising uid had the same high temperature at

Kabwe close to the core of the Lulian Arc, but had alower temperature in the Berg Aukas deposit in theforeland of the Damara Belt. S in the deposit of Kabwewas not the result of TSR from Neoproterozoic seawateror evaporite sulphate, but was reduced by BSR prior tointroduction of the mineralising brine. S from the sulphidesat Berg Aukas was reduced through TSR, similar to thedeposits of the Tsumeb-type in the same area. The sourceof the mineralising uids in these deposits has beenstrongly debated. Several authors propose a magmatic-hydrothermal origin (Thoreau, 1928; Taylor,1954;Intiomale & Oosterbosch, 1974; Walraven & Chabu,1994). Others believe the mineralising uids at Kipushiand Kabwe could also be evolved connate uids (Kortman1972) or uids produced by metamorphic dewatering(Unrug, 1988; Kampunzu et al., 2009). All these depositsare characterised by a low radiogenic, almost homogeneousPb isotopic cluster in the 207Pb/204Pb vs. 206Pb/204Pb space.The vein-type deposits of Kipushi, Lombe and Kengere inthe DRC cluster at lower 207Pb/204Pb values, compared tothe Berg Aukas and Kabwe deposits that have a 207Pb/204Pbisotope ratio in the range of the vein-type deposits ofTsumeb, Khusib Springs, Kombat and the Dikulushi Cu-Pb-Zn-Fe mineralisation (Fig. 6C). Pb isotope data for thedeposits of Kipushi, Lombe, Kengere, Kabwe and Berg

Aukas indicate Pb and perhaps other metals were derivedfrom several sources that may include the underlyingsedimentary pile and basement and their Pb washomogenised in large-scale hydrothermal systems, beforeinjection in dolomite horizons, favourable for oredeposition. The age of formation for the vein-type depositsof Lombe, Kengere, Kabwe and Berg Aukas is uncertain.

Nonetheless they are placed together with the Kipushideposit in Fig. 7, because these deposits show manysimilarities.

A low to moderate saline, low temperature uid

remobilised the Cu-Pb-Zn-Fe mineralisation at Dikulushiin a Cu-Ag mineralisation (< ca. 520 Ma in Fig. 7, possiblyat ca 100 Ma). This uid is the result of mixing amoderately saline uid that resembles the Cu-Pb-Zn-Femineralising uid, with a low saline uid that couldrepresent meteoric water saturating the host sandstone(Haest, 2009). The Cu-Ag mineralising uid likelyremobilised metals and S from the Cu-Pb-Zn-Femineralisation. Addition of radiogenic Pb from carbonateor sandstone host-rocks produced Cu-Ag sulphides with aPb isotopic composition that plots along a linear trend inthe 207Pb/204Pb vs. 206Pb/204Pb space. A late phase of minor

pyrite-chalcopyrite-sphalerite mineralisation at Kipushi

precipitated from a lower saline, lower temperature, moreoxidising uid, relative to the uid that precipitated themain sulphide mineralisation at Kipushi. This uid could

be of meteoric origin and acquired a high salinity by

dissolution of halite. The second mineralisation phase atKipushi is placed together with the Cu-Ag mineralisationat Dikulushi in Fig. 7, based on the possible contributionof meteoric water in the mineralising uid.

7. Conclusion

The stratiform Cu-Co ore deposits formed duringsuccessive periods in the evolution of the Lulian Orogen.Disseminated sulphides and sulphides cementing poresand replacing evaporites have an early diagenetic origin.This phase is related to a mineralising uid with a moderatetemperature and salinity, which most likely interactedwith the basement. S originated from the bacterialreduction of Neoproterozoic seawater sulphate. Oredeposition during diagenesis in Zambia and likely inKatanga was controlled by extensional faults cross-cuttingthe basement and Lower Roan Group. An important stageof mineralisation/remobilisation took place during

metamorphism and tectonic activity related to the Lulianorogeny between 580 and 520 Ma (El Desouky et al.,2009, 2010). High temperature uids were expelled withina compressional regime and mineral precipitation occurredin nodules, successive vein generations and tectonic

breccia.

The vein-type Cu-Zn-Pb mineralisation in the southernand central part of Africa have many commoncharacteristics. (1) They are hosted in massive dolomite(and sandstone), with associated organic material, at twodifferent levels in the Neoproterozoic stratigraphy. Thelower level Zn-Pb(-Cu) mineralisation are hosted by

massive dolomite and these mineralisation become Cu-rich near the contact with the overlying dolomite-shalesequence. The higher level Cu(-Zn-Pb) mineralisation arehosted by often brecciated sandstone and dolomite. (2)The higher level Cu deposits that have been dated, i.e.Dikulushi and Tsumeb, are syn- to late-orogenic, whilethe lower level Zn-Cu mineralisation of Kipushi is post-orogenic in age. (3) All deposits are associated with steepfaults that crosscut the stratigraphy, independent of theirage of formation. These faults could form conduits for themineralising uids. (4) The source of these mineralisinguids is unknown for the deposits in the DRC and Zambia.

Dewatering magma, deeply inltrating seawater, connatewater and metamorphic water have been proposed aspotential sources for the mineralising uids. Themineralising uid for the vein-type deposits in Namibia islikely seawater. (5) Syn- to post-orogenic Cu-Znmineralising uids at Dikulushi, Tsumeb and Kipushimigrated upward from depth, where they acquired a highsalinity from evaporated seawater or from the dissolutionof evaporites and a signicant metal content by leachingmetals from the basement and/or from the overlyingsedimentary pile. These mineralising uids disposed theirmetal content, when they mixed with a reducing phase onthe site of mineralisation in the form of hydrocarbons orH2S. The deposits of Lombe, Kengere, Kabwe, BergAukas, Kombat and Khusib Springs probably share thishistory of formation. (6) The syn- to postorogenic

polymetallic mineralisation are characterised by low


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radiogenic Pb isotopic compositions that are the result ofhydrothermal uid circulation systems, which scavengedand moderately homogenised Pb from different host-rocks. Pb isotope data from the lower level Pb-Zn depositsare more homogeneous than for the higher level Cudeposits. The more heterogeneous Pb isotopic composition

of these syn-orogenic Cu deposits could be attributed tosmaller scale uid circulation systems that did not succeedin completely homogenising the Pb isotope composition.

The mineralisation at Dikulushi and Kipushi wereremobilised afterwards by oxidised, less saline, lowertemperature uids that are at least partly meteoric inorigin. The Cu-Ag sulphides from the remobilisation

phase at Dikulushi have higher radiogenic Pb isotopicsignatures and display linear trends on both 207Pb/204Pbvs. 206Pb/204Pb and 208Pb/204Pb vs. 206Pb/204Pb diagrams.

8. Acknowledgements

This paper largely beneted from extensive, stimulatingand fruitful discussions with Hamdy El Desouky, StijnDewaele, Wouter Heijlen and Dieter Brems, (former)researchers at the Ore Geology and Geouids Researchunit of the K.U.Leuven, on various metallogenic aspectsof the Copperbelt. Constructive comments by JacquesCailteux and Hartwig Frimmel signicantly improved themanuscript. This research is nancially supported byresearch grants G.0585.06 and G.0414.08 of the FWO-Vlaanderen.

9. References

ANNELS, A.E., 1974. Some aspects of the stratiform oredeposits of the Zambian Copperbelt and their geneticsignicance.InBartholom, P. (ed) Gisements stratiformeset provinces cuprifres. Centenaire de la SocitGologique de Belgique,, Lige, 235-254.

ANNELS, A.E., 1989. Ore genesis in the ZambianCopperbelt, with particular reference to the northernsector of the Chambisi Basin. InBoyle RW et al. (eds)Sediment-hosted Stratiform Copper Deposits. GeologicalAssociation of Canada, 427-452.

ARMSTRONG, R.A., MASTER, S. & ROBB, L.J., 2005.Geochronology of the Nchanga Granite, and constraintson the maximum age of the Katanga Supergroup, ZambianCopperbelt. Journal of African Earth Sciences, 45: 32-40.

BARRA, F., BROUGHTON, D., RUIZ, J. & HITZMAN,M., 2004. Multi-stage mineralisation in the ZambianCopperbelt based on Re-Os isotope constraint

Documents

56 Stratiform and Vein-type Deposits in the Pan-African Orogen in Central and Southern Africa Evidence for Multiphase Mineralisation