15

2.1 INTRODUCTION

This chapter outlines the geodynamic history of southern and central Africa and the regional and deposit scale geology at NKM. The chapter focuses on orogenesis and crustal growth, basin formation, deformation and intrusives events during the late Proterozoic to early Palaeozoic period. District scale stratigraphic and structural relationships are discussed using previously published data and unpublished historical data. The distribution of copper and cobalt across the region suggests that significant regionally extensive basin and structural controls were important during the mineralisation process.

The Neoproterozoic to earliest Phanerzoic Lufilian Fold Belt (LFB) is host to the Zambian and Congolese Copperbelts (ZCB and CCB). The LFB forms part of a series of linked Pan-African orogenic belts fringing the Congo and Kaapvaal-Zimbabwe cratons of southern Africa (Fig. 2.1a) (Porada, 1989; Porada and Berhorst, 2000; Selley et al., 2005). The tectonic evolution of southern Africa has been the focus of numerous studies (e.g. Bateman, 1930; Miller, 1983; Cahen et al., 1984; Daly et al., 1984; Daly, 1986; Cosi et al., 1992; Porada and Berhorst, 2000; Hanson, 2003; Johnson et al., 2005; Selley et al., 2005). The interpretation of the tectonic evolution is still controversial, however during the past decade advances in geochronology and field based studies have provided important new information (e.g. Porada and Berhorst, 2000; Hanson, 2003; Johnson et al., 2005). A comprehensive discussion of this research is beyond the scope of this study and readers are directed to the reviews of Porada and Berhorst (2000), Hanson (2003), Johnson et al., (2005) and Selley et al.,(2005).

The Neoproterozoic sedimentary and volcanic sequences that form the supra-crustal component of the fold belts record a history of crustal extension, subsidence and intraplate magmatism between 1000 and 600 Ma that are conventionally interpreted to relate to the dispersal of the Rodinia Supercontinent ( Wilson et al., 1997; Porada and Berhorst, 2000). The term Pan-African herein will only be used for the Palaeozoic collisional event forming Gondwana and the post-orogenic magmatism, shearing and uplift.

2.2 ARCHEAN AND MESOPROTEROZOIC BASEMENT IN THE LUFILIAN FOLD BELT

The regional geology of southern Africa is subdivided into three main Proterozoic orogenic mobile belts which enclose Archean and Palaeoproterozoic crustal fragments. The development of these belts was controlled by six Archean cratonic nuclei: the Kaapvaal, Zimbabwe, Tanzania, Bangweulu, Congo and Angola-Kasai Cratons (Fig. 2.1). These stable fragments form the core of the tectonic assemblage in southern Africa and include Archean fragments which were amalgamated with Palaeo- and Mesoproterozoic fragments to form two stable

Chapter 2

regional and distriCt geology

16

CongoCraton

KalahariCraton

LufilianFoldBelt

MwembeshiShear Zone

West CongoBelt

ZambeziBelt

GariepBelt

MozambiqueBelt

Fig 2.1(B).

DamaraBelt

fold belt foreland basin

Kibar

anBel

t

Irum

ide

Belt

KalahariCraton

BangweuluBlock

1.3-1.0Ga orogen

Archaean shield

Copper deposit

2.05-1.8Ga orogen

0.56-0.53Ga felsic province

0.76-0.73Ga mafic province

Foreland basin

External Fold and Thrust Belt

Domes Region

Synclinorial Belt

Katanga High

Zambezi Belt

Basement

Central African Copperbelt

Lufilian Fold Belt

MwembeshiShear Zone

CCBA’

A

ZCB

Fig 2.5.

250

150

ZIMBABWE

ZAMBIA

DRC

(B)(A)

Mozambique Belt

Zambezi Belt

20KM

1000KM

Fig 2.4.

Figure 2.1. a). The crustal architecture of southern Africa. Simplified geology map of the Pan-African system of central and southern Africa. The Lufilian Fold Belt (LFB) is situated between the Congo and Zimbabwe-Kaapvaal Cratons to the north and south respectively. The LFB hosts the Zambian and Congloese Copperbelts (modified from Kampunzu and Cailteux, 1999; Porada and Berhorst, 2000).b). The tectonic zoning in the LFB (from Selley et al., 2005). The LFB is divided into four separate tectonic zones and the copper deposits are distributed mainly within the External Fold and Thrust Belt, the Domes region and the Synclinorial belt. Selley et al. (2005) included the basement inliers of the Zambian Copperbelt within the Domes Region, rather than the External Fold and Thrust Belt, as have previous subdivisions of the LFB (e.g. Kampunzu and Cailteux, 1999).

blocks. In the north the Congo block includes the Angola-Kasai and the Tanzania cratons and the Bangweulu block, while in the south the Kalahari block includes the Zimbabwe and Kaapvaal cratons. The assembly of Archean and Paleoproterozoic cratons during the Mesoproterozoic (1300 to 1000 Ma) formed the Rodinia supercontinent (Hoffman, 1999; Rainaud et al., 2002).

Archean rocks are not exposed in the LFB, however a ~3.1 Ga detrital zircon population in the Neoproterozoic supracrustal assemblage implies that Archean rocks either comprise part of basement or contributed material during Proterozoic evolution (Hanson, 2003). The oldest rocks (i.e. ‘basement’) of the LFB consist of Palaeoproterozoic and volumetrically subordinate Mesoproterozoic meta-granites, migmatites, meta-volcanic and meta-sedimentary units (Hanson, 2003). They are predominantly exposed in the north-western (Kibaran Belt) and south-eastern (Irumide Belt) peripheries of the LFB, and as smaller inliers between these areas, in a belt known as the Domes Region (Fig. 2.1). Basements rocks in the Domes region and Irumide Belt consist of two lithologies and temporal distinct assemblages. The oldest group of rocks known as the Lufbu Schist are widespread and part of metamorphosed Paleoproterozoic (~1994 to 1873Ma) magmatic arc sequence of sedimentary and volcanic rocks (Master et al., 2002; Mendelsohn, 1961). Unconformably overlying these rocks is the ~1300 to 1100 Ma Muva Group, a meta-sedimentary succession of conglomerates, orthoquartzites and meta-pelites (Rainaud et al., 2002).

2.3 NEOPROTEROZOIC EXTENSION

The break-up of the Rodinia supercontinent occurred between ~1000 and 700 Ma (Miller, 1983; Munyanyiwa et al., 1997; Unrug, 1997). Rifting was extensive between the Kalahari and Congo cratons and formed a series

17

of eastward younging rift basins, now distinguished as separate orogenic belts including the Gariep, Damara, Zambezi, Lufilian and Mozambique belts (Hanson et al., 1993, 1994; Unrug, 1997). This sequence of meta-sedimentary and meta-volcanic rocks is known as the Katangan Supergroup. The supracrustal sequences of the Damara-Lufilian-Zambezi belts were previously amalgamated with the Brasiliano belt of South America (Hanson et al., 1993). The LFB is a record of intracontinental rift basins containing coarse-grained terrigenous and marine units. These were deposited within fluvial and alluvial fan environments and are overlain by carbonate and evaporitic strata, indicating a restricted marine or lacustrine environment with minor volcanic rocks (Porada and Berhorst, 2000; Selley et al., 2005). The relationships and architecture of the Neoproterozoic basins, originally deposited along the trend of Damara-Lufilian-Zambezi Orogen, are subjected to ongoing debate.

The rifting history of the Zambezi belt is recorded by multiple magmatic phases spanning from ~880 to ~740 Ma (Hanson, 2003; Hargrove et al., 2003). At the western end of the rift trend line in the Damara Belt Miller (1983), Porada (1989) and Hanson (2003) suggest that the deposition of the marine sequence of carbonates and turbidites were synchronous with continental rift sedimentation in the east. The Damara Belt records a complete Late Proterozoic Wilson cycle from intracontinental rifting and the opening of oceanic basins, to the deposition of >10 km thick package of fluviatile to turbidite siliciclastics, carbonates and igneous rocks, through to collision and development of a foreland basin (Miller, 1983; Stanistreet et al. 1991; Munyanyiwa et al., 1997; Hoffman, 1999;). Volcanism accompanied extension in the Damara Belt, with the deposition of thick alkaline rhyolitic ignimbrite sequences along the northern rift margin. Continental tholeiitic and alkaline basalts were deposited higher in the sequence (Miller, 1983; Hanson, 2003). The eastern limit of the Damara belt is marked by a major transform fault inherited from pre-existing crustal weak zone, which separated the Damara and Katangan rift basins.

Magmatism in the LFB is limited to sparse bimodal volcanic rocks and mafic to intermediate igneous bodies in the middle part of the Katangan Supergroup (Kampunzu et al., 2000). Basalts, pyroclastic and metagabbroic rocks are identified higher in the sequence and restricted to the western and northern sections of the LFB (Kampunzu et al., 2000; Key et al., 2001). Armstrong et al. (1999) reported a single U-Pb zircon age of 877 ± 11Ma for an extension-related A-type granite which intruded Palaeoproterozoic basement rocks in the ZCB prior to deposition of the Katangan Sequence (Kampunzu et al., 2000; Porada and Berhorst, 2000; Tembo et al., 2000; Hanson, 2003). Within the ZCB, gabbroic and dioritic intrusions predominate (Selley et al., 2005). The mafic and intermediate lavas and intrusive complexes in the western and central parts of the LFB are associated with a relatively short-lived magmatic event dated between ~765 and ~735 Ma (Key et al., 2001; Barron, 2003) (Fig. 2.3). The geochemical evolution of the mafic units ranges from earliest continental tholeiite, to alkaline and tholeiitic magmas, and finally to lavas with E-MORB affinities, suggest progressive continental rifting which resulted in an embryonic oceanic rift in the western LFB (Kampunzu et al., 2000). The northern border of rift basin was marked by a carbonate platform with a lagoonal basin developing to the south of the platform (Porada and Berhorst, 2000).

Interestingly, there are significant differences between the Neoproterozoic Katangan Supergroup of the LFB and the Zambezi and Damaran belts. The Katangan Supergroup has a far greater metal endowment, is significantly thinner and contains limited igneous units within the basal portion of the succession (Selley et al., 2005). Selley et al. (2005) suggest that the absence of volcanism during deposition of syn-rift rocks indicates subdued crustal heat flow and low rate of crustal attenuation.

18

2.4 STRATIGRAPHY OF THE KATANGAN SUPERGROUP IN THE ZAMBIAN COPPERBELT

The interpretation of the basin evolution resulting in the deposition of the rocks of the Katangan Supergroup is still controversial (e.g. Binda, 1994; Porada and Berhorst, 2000; Selley et al., 2005). The ~1.5 to 3 km thick (pre-erosional thickness of ~5 to 7 km; Annels, 1989) Neoproterozoic Katangan Supergroup in the ZCB is a package of deformed and metamorphosed sedimentary rocks unconformably overlying the basement (Fig. 2.2). North of the ZCB exists the laterally equivalent and equally extensive Congolese Copperbelt (CCB) (Table 2.1).

Up

pe

rR

oa

nG

rou

pL

ow

er

Ro

an

Gro

up

Kit

we

Fm

.

CopperbeltOrebody Member

Ba

se

me

nt

Mw

ash

iaG

rou

pL

ow

er

Ku

nd

elu

ng

uG

rou

p

500m

Min

dola

Cla

stic

sFm

.

877+/-11Ma

~740Ma

Emplacementof mafic lavasand intrusivesin central andwestern DomesRegion ~765 Ma- 735 Ma

main ore-bearinginterval

GrandConglomerate

basement gneiss

Nchanga red granite

conglomerate

sandstone

mixed sandstone - siltstone-carbonate

gritty siltstone

mixed carbonate - siliciclastic

carbonate

breccia

diamictite

siltstone-shale

intrusive gabbro

eva

pori

tic

deposi

tion

alenvir

on

men

ts

Figure 2.2. Lithostratigraphy of the Katangan Supergroup, Zambian Copperbelt showing approximate average unit thickness (from Selley et al., 2005). The Nkana-Mindola Deposit (NKM) is hosted at the base of the Kitwe Formation. This chapter provides a description of the stratigraphy and basin architecture of the Lower Roan Group at the NKM deposit. The Katangan Supergroup is divided into a five-fold subdivision which includes (1) Lower Roan Group (siliciclastic rock dominated succession); (2) Upper Roan Group (platformal carbonates, chaotic breccia and subordinate siliciclastics rocks); (3) Mwashia Group (carbonates and generally fine grained siliciclastics rocks); (4) Lower Kundulungu Group (glacial diamictite overlain by carbonate and carbonate-bearing clastic rocks); and (5) Upper Kundulungu Group (basal diamictite overlain by carbonate). Gabbroic rocks mainly occur in Upper Roan and Mwashia Groups. The maximum age of sedimentation is constrained by the Nchanga Red Granite and the upper sedimentation is constrained by the Sturtian glaciation (Grand conglomerate diamictites), and mafic lavas and intrusive rocks in the Domes Region (from Selley et al., 2005).

19

Group Formation Member Clemmey (1976)

Nkana-Mindola

(mine termi-nology)

Chambishi Nchanga (Binda and Mulgrew,

1974)

Konkola Musoshi (Lefe-bvre, 1989)

Lubembe(Lefebvre,

1989)

Kundelungu(former Upper Kun-delungu)

Plateau (Ku 3)

Klubo (Ku 2)

Kalule Ku 1.3

Ku 1.2

Ku 1.1

Nguba(former-Lower Kun-delungu)

Monwezi Ng 1.2

Likasi Ng 1.3

Kakontwe (Ng 1.2)

Grand Conglom-erate (Ng 1.1)

Mwashia Upper Mwashia Mwashia Upper Mwashia

Middle Upper Roan

Lower Ultra Far Water Fm.

Lower Mwashia Mines Group (R.A.T.)

Upper Roan Bancroft Fm. Dolomite Fm. Upper Roan Kanwangungu Fm.

Kibalonfo Fm. Musoshi Fm.Lower Roan Kitwe For-

mationAntelope Antelope

Clastic Mbr.Far Water Sediments

Sandy talc schist

Shale with grit

Shale with grit

Kibalongo Fm.

Chambishi Chambishi Dolomite Mbr.

Far water DolomitesDolomite-Argillite Seq.

Cherty Dolo-miteInterbedded Argillite and Dolomite

Chingola DolomiteDolomitic schistUpper Banded shale

Hangingwall Aquifer

Chingola For-mation

Kitotwe Mbr.Kabemba Mbr.

Nchanga Nchanga quartzite Mbr.

Upper quartzite

Upper quartzite Feldspathic Quartzite

Hangingwall Quartzite

Pelitic-Arkosic Formation

Rokana Rokana Evaporites Member

Near Water Sediments

Interbedded Argillite and Dolomite

Banded Sand-stoneUpper Pink QuartziteShale markerBanded Sand-stoneLower chart marker

Copperbelt Copperbelt orebody Member

Ore Shale and Hang-ingwall Argillite

Ore Shale Lower Banded Shale

Ore Shale Ore Shale F.Q.

Mindola Kafue Kafue Aren-ites

Footwall Conglom-erate; Arkose and argillite; Lower Conglom-erate

Footwall Con-glomerate; Arkose and argillite; Lower Conglomerate

Transition ArkoseArkoseConglomerate

Footwall conglom-erateFootwall SandstonePorous sandstone

Mutonda formationKafufya Forma-tionChimfunsi Formation

Simbi

Lubembe

Konkola Basal Quartz-ite

Footwall Quartz-ite; Basal Conglom-erate

Footwall Quartzite; Basal Conglom-erate

Footwall QuartzitePebble conglom-erateBasal conglom-erate

Table 2.1. Stratigraphic nomenclature of the Katangan Supergroup on the Zambian Copperbelt and relationship between nomenclature used at different deposits. The Mindola Clastic Formation and the Kitwe Formations are the focus of this study at the NKM deposit (modified from Cailteux et al., 2005; Selley et al., 2005; Batumike et al., 2007).

20

900 Ma 800 Ma 700 Ma 600 Ma 500 Ma

877+/-11Ma

Lufilian Orogeny

Maxi

mum

age o

f Kata

ngan s

edim

enta

tion

Stu

rtia

n G

laci

ation ~

740 M

a

T1 T2 T3 T4 T5

Nchanga Red Granite

12

16

7

1

7

54,6

3 2

4

8,10,119

9

12

1212

9

916

14,15,1613

1,16

ZambianCopperbelt

U-Pb uraninite

U-Pb monazite

U-Pb rutile

Pb-Pb Cu sulfide

Re-Os molybdenite

Re-Os Cu-Co sulfide

(B)

1

2 3 45

6

7

89

10

11

12

1314

15

16

11°

27°

Congolese Copperbelt

m

Do es Region

DRC

ZAMBIA

(A)

Kamoto

Monwezi

Mindigi

Shinkolobwe

Kambove

Luisha

Luiswishi

Kawanga

Kansanshi

Kimale

Dumbwa

Musoshi

Konkola

Nchanga

Chibuluma West

Nkana-Mindola

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

Basement

Katangan Sgpand youngerstrata

Hook Massif

The interpretation of basin evolution and deposition of the Katangan Supergroup remains controversial (e.g. Binda, 1994; Porada and Berhosrt, 2000; Selley et al., 2005). Stratigraphic correlation between ZCB and CCB is a controversial issue based on the stratigraphic sub-division of the Katangan Supergroup. Within the ZCB, the Katangan Supergroup is preserved in several predominantly NW trending structural “basins” (a series of west-northwest- to north-northwest- trending synclines). These are separated by, or in some cases are entirely enclosed by, reworked Palaeoproterozoic crystalline basement including Mushi, Bwana-Ndola, Roan-Muliashi, Chambishi-Nkana, Nchanga and the Luwuishi Basins (Mendelsohn, 1961; Selley et al., 2005) (Fig. 2.4). However a regionally robust five-fold stratigraphic division has been defined for the Katangan Supergroup

Figure 2.3. Summary of geochronological data associated with Cu and U mineralization in the Lufilian Fold Belt (modified from Selley et al., 2005). This figure shows the relationship of mineralizing events to significant stages of basin development. The location of the samples shown in insert A. Thermal events include: T1 (765-735 Ma) extension-related magmatism (Key et al., 2001), T2 (614-570 Ma) eclogite facies metamorphism in the Zambezi belt (John et al., 2003) and greenschist facies metamorphism in the Zambian Copperbelt (Rainaud et al., 2002), T3 (577-532 Ma) felsic magmatism in the Katanga High (Hanson et al., 1993), T4 (534-521 Ma) whiteschist facies metamorphism in the central part of the Domes Region (John et al., 2004), T5 (510-460 Ma) post-collisional uplift and cooling throughout the Domes Region (Cosi et al., 1992; Rainaud et al., 2002; John et al., 2004).

21

(e.g. Mendelsohn, 1961; Clemmey, 1976; Annels, 1984; Cailteux, 1994; Kampunzu and Cailteux, 1999; Porada and Berhorst, 2000, Selley et al., 2005). At the deposit scale, a range of differing stratigraphic nomenclature exists for each Cu deposit on the ZCB (Table 2.1).

The major lithostratigraphic units, from base to top are the (Fig. 2.2):• Lower Roan Group (siliciclastic-carbonate package); • Upper Roan Group (platform carbonates, siliciclastics and chaotic breccias); • Mwashia Group (carbonates and generally fine-grained siliciclastics);• Nguba Group (formerly the Lower Kundelungu - glacial diamictite, carbonates and minor siliciclastic); and• Kundelungu Group (basal diamictite overlain by mixed carbonate and clastic rocks) is poorly defined in the

Democratic Republic of Congo (DRC) and only partially preserved, due to erosion in the ZCB.The Katangan Supergroup preserved in Zambia has previously been described by Jordaan (1961),

Clemmey (1976) and Binda (1994) and is summarised in the next section, including observations from this study.

2.4.1 Lower Roan GroupThe Lower Roan Group is subdivided into the basal Mindola Clastic Formation (MCF), consisting mainly of arenaceous strata, and the overlying siltstone-dolomite-shales of the Kitwe Formation (KF) (Clemmey, 1976) (Fig. 2.2).

2.4.2 Mindola Clastic Formation (MCF)The MCF is characterised by significant lateral and vertical facies variations involving texturally immature breccias, conglomerates and sub-arkosic sandstones, deposited in fluvial, alluvial fan, eolian and fan-delta environments. The MCF at NKM has an average thickness of 200-300 m and ranges from being absent in some areas to a maximum of 1 km at Konkola, northern ZCB. The MCF accumulated within sub-basins of limited strike extent and bounded by basement-cored topographic highs. The fault controlled origin of these basins is evidenced by their systematic west-northwest to north-northwest orientations, and the local preservation of cross-section half-graben cross-section geometries and the inverted axes of sub-basins coincide with synformal closures (Selley et al., 2005). Clemmey (1976) sub-divided the MCF into 2 members; however the classification is difficult to apply consistently, particularly where the MCF is deformed. At NKM, the Basal Sandstone Member (BSM) is distinguished from the overlying Kafue Arenite Member (KAM) by a widespread 5 to 15 m thick conglomeratic unit (Fig. 2.5).

2.4.3 Kitwe Formation (KF)The Kitwe Formation contrasts with the MCF and displays a well defined internal layer cake stratigraphic architecture. The Kitwe Formation consists of an approximately 200 m thick sequence of sandstone, marginal marine-evaporitic argillaceous sandstone, dolomitic siltstone-sandstone and massive dolomite. The formation occurs within a 125 km long and 13–25 km wide west-northwest trending belt, frequently referred to as the ‘Shale-belt’ (Fig. 2.6) and has been sub-divided in to five members (Fig. 2.5) (Binda and Mulgrew, 1974; Binda, 1994). The eastern edge of the ‘Shale Belt’ is poorly defined because lithostratigraphic equivalents exist on the eastern side of the Kafue Anticline (Binda, 1994). Binda and Mulgrew (1974) and Porada and Berhorst (2000) indicate that the western margin is defined by the pinch-out of the Copper Orebody Member (COM) with gabbro, dolomitic talc-schist and brecciated dolomites directly overlying the MCF. The MCF and KF occurring at NKM are the focus of detailed descriptions and discussion in Chapter 3.

The basal COM is the principal host to Cu-(Co) mineralisation (Clemmey, 1976). This unit is commonly referred to as the ‘Ore Shale’ west of the Kafue Anticline, and east of the Kafue Anticline, in the vicinity of

22

KatangaHigh

SynclinorialBelt

DomesRegion

External Fold &Thrust Belt

A A’

100km BasementKatangan Supergroup

upper

lower & middle

undifferentiated

overriding platePan-Africanage granite

overthrust plate

the Mufulira deposit, as the ‘Mudseam’ (Binda, 1994). Directly overlying the COM is the marginal marine sandstone-siltstone of the Rokana Evaporite Member (REM) (Clemmey, 1978). Higher in the sequence are the Nchanga Quartzite (NQM) and Chambishi Dolomite (Fig. 2.5 and 2.7).

2.4.4 Upper Roan GroupThe contact between the Lower Roan Group and the Upper Roan Group is poorly defined however it is historically distinguished by the predominance of carbonate strata (Mendelsohn, 1961) (Fig. 2.2). Selley et al. (2005) define the base of the Upper Roan Group by the appearance of >1m thick, regional extensive dolomite beds. The Upper Roan Group consists of laterally extensive decimetre to metre scale, upward fining cycles of sandstone, siltstone, dolomite, algal dolomite and patches of anhydrite. The preserved thickness of the sequence is variable, ranging from ~30 m to >800 m (Selley et al., 2005).

The Upper Roan Group at NKM consists of ~300 m thick sequence of interbedded argillites, dolomitic argillites, dolomites, dolomitic sandstone and argillaceous dolomites. All units are laterally continuous across the NKM area, however, no studies of the Upper Roan Group were undertaken as part of this research due to the poor nature of the exposures.

The Upper Roan Group may contain stratabound and discordant breccia units. These range from centimetres to hundreds of metres in scale, and appear to have accommodated much of the thickness variations in the Upper Roan Group (Wendroff, 2000; 2003; Selley et al., 2005). The breccias are composed of intraformational fragments within a matrix of carbonate, albite, quartz, anhydrite and/or chlorite (Annels, 1984). Selley et al. (2005) report that these breccias cross cut down stratigraphy to the south and west in the Mufulira, Konkola, Luanshya Basin and Chambishi Basin areas. The breccia bodies had developed along former evaporitic horizons, similar to the breccias occurring in the DRC described by Francois (1973) and Jackson et al (2003), however, Wendroff (1997, 2003) suggested the breccia formed as a molasse deposit.

2.4.5 Mwashia GroupThe Mwashia Group is a shale dominated sequence conformably overlying the Upper Roan Group (Fig. 2.2). Unlike the underlying Roan Group, relatively few Cu-Co deposits have been identified within the Mwashia Group rocks and consequently there are few published studies of the Mwashia Group and the overlying Kundelungu Group. Within the ZCB, Selley et al. (2005) describe the approximately 400 m thick Mwashia Group as consisting of a lower dolomite package overlain by a dolomite-siltstone-mudstone sequence capped

Figure 2.4. Schematic cross section (section A-A’) of the Lufilian fold belt showing the variation in the structural style between the tectonic zones (modified from Porada, 1989; Selley et al., 2005).

23

basement gneiss

Nchanga granite

conglomerate

sandstone

mixed sandstone - siltstone - carbonate

gritty siltstone

siltstone - shale

mixed carbonate - siliciclastic

carbonate

breccia

Min

do

laC

lasti

cF

orm

ati

on

Basement Complex

Kit

we

Fo

rma

tio

n

Bancroft DolomiteFormation

mainore-

bearinginterval

Kafue Arenites Member

Copperbelt Orebody Member(see associated diagram)

Rokana Evaporites Member

Nchanga Quartzite Member

Chambishi Dolomites Member

Antelope Clastics Member

Main

stra

tigra

ph

icpack

age

un

der

invest

igati

on

Stratigraphic Nomenclature(Modified from Clemmey, 1976)

Basal Sandstone Member(new terminology)

Basal Conglomerate/Breccia

Basal Quartzite

Basal Sandstone

Lower Conglomerate

Footwall Sandstone

Footwall Conglomerate

Mine Terminology atNkana-Mindola

Basement

(See associated diagram)

Far Water Formation

Far Water Sediments

Near Water sediments

Up

pe

rR

oa

nG

rou

p

Hangingwall Quartzite

Upper Quartzite

Ultra Far Water Sediments

10m

Lo

we

rR

oa

nG

rou

p

Ore Shale

Lo

we

rR

oa

nG

rou

pU

pp

er

Ro

an

Gro

up

Undulating unconformitysurface

by a siltstone-mudstone-carbonaceous mudstone sequence (Fig. 2.7). The base of the Mwashia Group is defined by the polylithic breccia in the DRC and the upper portion of the group is dominated by a clastic sequence (Cailteux, 1994). As with the Upper Roan Group, no exposures of the Mwashia Group were examined during this study at NKM.

2.4.6 Nguba and Kundelungu GroupsThe base of the Nguba Group (Ng 1.1 of Nguba - Cailteux and Kampunzu, 2002) is marked by the ~10–600 m thick Grand Conglomerate (Fig. 2.2). This unit is a regionally extensive sequence of debris flows and

Figure 2.5. Detailed lithostratigraphy sub-division of the Lower Roan Group at Nkana-Mindola. The local mine terminology is included for reference. The focus of this study is on the Mindola Clastic Formation and the basal portion of the Kitwe Formation, which hosts the majority of economic copper mineralisation.

24

diamictites, intercalated with minor, thin interbeds of siltstone and sandstone (Binda and Van Eden, 1972). Classical interpretations suggest the group is a chronostratigraphic equivalent of the oldest globally recognized Neoproterozoic Snowball Earth glaciation event and is correlated with the Sturtian diamictites deposited at ~740Ma (Hoffman, 1999). In the Democratic Republic of Congo (DRC), the Grand Conglomerate is up to 600m thick and has a broad temporal association with ~760 to 750 Ma mafic extensional igneous activity including gabbroic sills and mafic volcanic flows and tuffs (Armstrong et al., 1999; Key et al., 2001; Rainaud et al., 2002). Limited data is available for the Kundulungu Group at NKM. An intersection of black to grey limestones in the Mindola Central Dam Wall has been assigned to the Kakontwe Limestone Formation and is overlain by purple to grey-black argillites. The series occupies the synclinal hinge of the Nkana Syncline in the northern and central areas at NKM.

2.4.7 Intrusive Rocks Mafic and ultramafic intrusive rocks of the Upper Roan are of continental tholeiitic, alkaline and EMORB basaltic composition and comprise a minor proportion of the Katangan sequence. These intrusive bodies are in close spatially association with breccia units The bodies are generally discontinuous and are typically strongly altered, suggesting they were emplaced as sills, however, Porada and Berhorst (2000) suggest the bodies have been tectonically emplaced. Variations in the composition of the mafic rocks record different stages of continental break-up, from pre-continental rift to a continental rift system and then to an oceanic rift system (Kampunzu et al., 2000).

There are few documented intrusive rocks within the Nkana-Mindola area. Meta-gabbroic rocks have been identified east of the Mindola pit near the Mindola Dam and intrude the Upper Roan, Mwashia and Lower Kundelungu Groups (Mendelsohn, 1961). These rocks are medium to coarse-grained, dark-grey to greenish in colour with a high biotite composition (Jordaan 1961) and contain slivers of metasediments. The surface expression of the intrusive bodies broadly approximates the shape of the Nkana Syncline. Previous surface mapping of the NKM mining lease identified several gabbroic bodies. Outcrop pattern suggests the gabbroic rocks have been folded. According to Whyte and Green (1971), syenitic to gabbroic rocks at the Chibuluma Deposit have been extensively altered and metamorphosed to scapolitized amphibolitic rocks.

The most significant intrusive rock at Mindola are lamprophyre dykes. At approximately 2000 N at the Mindola Shaft, a 10m to 30m wide east southeast steeply dipping fine-grained, biotite rich dyke cross-cuts basement schists and the Lower Roan Group rocks. On the upper levels at Mindola Shaft the same dyke dips west-north-west at shallow angles (Jordaan, 1961). Jordaan (1961) classified the lamprophyre dyke as a kersantite, based on the petrographic and chemical analyses of eight samples. The dyke has poikilitic plagioclase laths set in a fine ground mass of quartz, mica and epidote. Biotite and chlorite grains impart an overall weak schistosity to the rock. Accessory minerals include skeleton crystals and spiral form ilmenite. The margins of the dyke are diffuse and the contact with the basement schist is difficult to recognise due to thermal metamorphism of the wallrock and the interfingering of dyke rock with argillaceous rocks (Jordaan, 1961). Minor copper sulphides, in the form of bornite and chalcocite, are associated with the margins of dyke when it cross cuts through basement lithologies and commonly where it is interfingered with the argillites of the COM. Other cross cutting dykes in the ZCB occur at River Lode, Nchanga and at the North Orebody Konkola (Mendelshon, 1961).

2.4.8 Correlation with the Congolese Copperbelt (CCB)To north of the ZCB exists the lateral equivalent and equally extensive CCB. Stratigraphic correlation between the CCB and ZCB are based on the stratigraphic sub-division of the Katangan Supergroup. Correlation of the

25

Basement

Lower Roan Group

Upper Roan and Mwashia Groups

Gabbro

Lower and UpperKundelungu Groups

Shale BeltM

okambo D

ome

KonkolaDome

ChililabombweDome

Kafue Anticline

Chambishi Basin

Luanshya Basin

28°

13°

Kitwe

Chingola

Ndola

20KM

B

B’

upper Mwashia and Kundelungu Groups have been documented (e.g. Binda, 1994; Cailteux et al., 1994; Porada and Berhorst, 2000), however correlation of the underlying Upper Roan and Lower Roan Groups between the CCB and ZCB remains partially unresolved. The most widely accepted correlation suggests the Kitwe Formation of the Lower Roan Group is equivalent to the Congolese Mines Subgroup (Table 2.1) (Cailteux et al., 1994; Binda and Porada, 1995; Kampunzu and Cailteux, 1999). The ‘Roches Argilo-Talqueuses’ (R.A.T) is the oldest unit and correlates to the siliciclastic rocks of the Lower Roan Group in the ZCB, however, tectonic displacement between the Mines Subgroup and R.A.T. generally blurs the relationship between the units. Porada and Berhorst (2000) suggest that many of the units are laterally equivalent facies stacked by northeast directed thrusting.

Figure 2.6. The distribution of the ‘Ore Shale’ belt on the Zambian Copperbelt (modified from Selley et al., 2005). See figure 2.7b for stratigraphic correlation along section line B-B’.

26

diamictite

siltstone and shale

polylithic and crackle breccia

sandstone dominant

carbonate dominant

200

m

A A’

Lower and Upper Kundelungu groups

Roan & Mwashia groups

basement

Upper Roan Gp

Mwashia Gp

LowerKundelungu Gp

Kitwe

Mufulira

A

A’

KLB

145

KW

24

KW

26

KW

22

LB

18

L62

L79

L80

MW

107

DH

218

DH

219

IT27

IT25

Konkola Nchanga Chambishi Nkana Luanshya Mufulira

Kafu

eA

nti

clin

e

Upper

Roan

Carb

on

ate

Kit

we

Form

ati

on

Low

er

Roan

Min

dola

Cla

stic

Base

men

t

75m

NW SE

Upper Roan

Roan AntelopeMember

Chambishi DolomiteMember

Nchanga QuarziteMember

Rokana EvaporitesMember

Shale

Copperbelt OrebodyMemberFootwall arenite andarkose

Footwall conglomerate

Mava Schist & quartzite

Basement granite

Basement LufubuSchist

Unconformity

B’B

B’

B

A

B.

27

2.5 PAN-AFRICAN OROGENESIS – DEFORMATION OF THE LUFILIAN FOLD BELT (LFB)

The Lufilian Fold Belt (LFB) is a north verging fold-thrust belt which formed during the closure of the Neoproterozoic basins. The LFB is defined on the northern margin by relatively undeformed uppermost Katangan Supergroup while the southern margin is marked by the sinistral, east-northeast trending Mwembeshi shear zone. Movement in the shear zone has resulted in the present juxtaposition of low-grade LFB rocks to high-grade rocks of the Zambezi Belt (Unrug, 1989). Recent research specifically documents the deformational events associated with the Pan-African orogenesis. The Pan-African orogenesis is manifested as major thrusting, backfolding and backthrusting in response to convergent tectonics (e.g. Daly et al., 1984; Daly, 1986; Unrug, 1987; Kampunzu and Cailteux, 1999; Hanson, 2003). Despite numerous significant studies (e.g. Daly, 1986; Unrug, 1989; Kampunzu and Cailteux, 1999; Porada and Berhorst; 2000; Hanson, 2003), the tectonic evolution remains unresolved and Table 2.2 is a summary of several different tectonic models for the LFB.

The Lufilian orogenesis is thought to span ~100 m.y. The oldest metamorphic ages of greenschist facies rocks in the ZCB are U-Pb monazite (592 ± 22 Ma) and Ar-Ar biotite (585.8 ± 0.8 Ma) (Rainaud et al., 2002). Hanson et al. (1993) constrained the main phase of orogenesis to between ~560 and ~530 Ma using U-Pb zircon dating of syn- to post-tectonic granites and rhyolites in the Katangan high. John et al. (2004) report U-Pb monazite ages of ~530 Ma for peak metamorphism for white schist facies rocks in the central and western Domes region. Postorogeneic cooling is recorded by the widespread 510 to 465 Ma Ar-Ar biotite, Rb-Sr muscovite ages (Cosi et al., 1992; Torrealday et al., 2000; Rainaud et al., 2002; John et al., 2004) (Fig. 2.3).

The LFB consists of four north verging tectonic domains. De Swardt and Drysdall (1964) suggested the LFB could be divided into four orogenic zones - the ‘External Fold and Thrust Belt’, the ‘Domes region’ the ‘Synclinorial’ belt and the ‘Katangan High’ (Fig 2.1b and 2.5). The ZCB occurs adjacent to the easternmost basement inlier of the Domes region while the CCB occurs within the External Fold and Thrust belt. The boundary between the two coincides with an abrupt southward increase in metamorphic grade and structural style (Ramsay and Rigdeway, 1977; Francois and Cailteux, 1981; Key et al., 2001; Selley et al., 2005).

Rocks in the ‘Domes region’ were metamorphosed at upper greenschist to amphibolite metamorphic grade. Upper greenschist facies rocks occur in the eastern part of the region, where high amplitude folding dominates the structural style (Daly, 1986). Basement involved deformation throughout the Domes Region implies thick-skinned style of deformation and the position of the basement inliers to reflect structural culminates developed above ramps that splayed off a deep crustal detachment (Daly et al., 1984; Daly, 1986). In the western and central Domes areas, Cosi et al. (1992) and Key et al. (2001) provide evidence of large-scale thrusting by the existence of basement-cored nappes emplaced within the Katangan strata and juxtaposition of units of different metamorphic grade.

OPPOSITE: Figure 2.7. a). Stratigraphic correlation of the Upper Roan Group on the eastern flank of the Kafue Anticline (modified from Selley et al., 2005). b). Stratigraphic correlation of the Lower Roan Group of the Katangan Supergroup on the western flank of the Kafue Anticline, including a comparison with the Mufulira deposit on the eastern flank (modified from Binda and Mulgrew, 1974; Binda, 1994).

28

De Swardt and Drysdall (1964) defined the External Fold and Thrust Belt portion of the LFB as a foreland facing outer zone and record fragmentation, repetition and inversion of the Katangan stratigraphy (Fig. 2.8). There is little evidence of basement involvement in the exposed structural pile suggesting a more thin-skinned structural style compared to the Domes Region to the south (Porada and Berhorst, 2000; Selley et al., 2005). Decoupling along evaporitic strata, positioned in the middle Katangan stratigraphy, accounts for the lack of basement involvement in this portion of the LFB (Porada and Berhorst, 2000; Jackson et al., 2003; Selley et al., 2005). The western portion of the LFB has complex structures that trend obliquely to the regional folds and thrusts. The Roan and Kundelungu sequences in this area are allochthonous and Jackson et al. (2003) proposed salt tectonics as the dominant mechanism for the formation of Roan gigabreccias, which are characteristic of the External Fold and Thrust belt.

The relationship of the Domes Region to the Synclinorial Belt is uncertain. One model suggests a major change in the basin architecture was coincident with thrust dislocation between the Domes region and Synclinorial belt (e.g. Cosi et al., 1992; Porada and Berhorst, 2000). This boundary is interpreted as an abrupt break on a southward attenuating passive margin (Porada and Berhorst, 2000). To the north, a succession of marginal marine platformal-lagoonal rocks were deposited, while on the southern side of the break, deeper water facies dominated, however, Selley et al. (2005) suggested there is no evidence for a deeper marine sequence in the Synclinorial belt.

2.6 METAMORPHISM

Detailed accounts of the metamorphic facies are presented in Ramsay and Ridgway (1977), Francois and Cailteux (1981), Cosi et al. (1992) and Tembo (1994). The Proterozoic to early Palaeozoic rocks of the LFB vary from low-grade to high-grade metamorphic mineral assemblages, in part reflecting the complex tectonic development of the region. Ramsay and Ridgway (1977) recognised two non-parallel metamorphic belts. Recrystallization of the rocks is extensive with the main metamorphic minerals observed being biotite and sericite, and lesser amounts of scapolite, tourmaline, chlorite, tremolite-actinolite, epidote and apatite. The Lufilian metamorphic belt curves along the southern margin of the broader scale LFB and the Luangwa-Kariba metamorphic belt covers the eastern and south-eastern region of the Zambia. Ramsay & Ridgeway (1977) concluded that all the rocks younger than the basement complex in the LFB were metamorphosed in a single metamorphic cycle of Pan-African age. The metamorphic isograds parallel the broad structural framework, and the degree of metamorphism increases from the outer zones of the External Fold and Thrust Belt and into the Domes region. Prehnite-pumpellyite facies assemblages are recorded in the outer areas of the External Fold and Thrust Belt, shifting to greenschist facies metamorphism in the inner portions of the External Fold and Thrust Belt and further grading into amphibolite facies in the Domes Region (Kampunzu et al., 2000). Whiteschist and high pressure eclogites occur to the south of the Domes Region (Cosi et al., 1992). The lowest grade of metamorphism on the ZCB occurs at Konkola and Mulfulira, and increases to upper greenschist to amphibolite facies towards the southeast. Within the Roan-Muliashi “basin” epidote-amphibolite facies grade is reached, while carbonate rich rocks at Nkana consist of tremolite and talc (Mendelsohn, 1961).

2.7 Cu-Co MINERALISATION OF THE ZCB

The major deposits in the ZCB are distinctly aligned parallel to the Kafue Anticline (Fig. 2.9) and have been interpreted as indicating the presence of a deep structural feature (e.g. Annels, 1989) or a palaeoshoreline (e.g. Clemmey, 1976). Two broad classes of sediment-hosted Cu deposits occur within the ZCB (e.g. Fleischer, 1976;

29

Up

pe

rR

oa

nG

rou

pL

ow

er

Ro

an

Gro

up

Kitw

e

Fm

.

ba

se

me

nt

Mw

ash

iaG

rou

pL

ow

er

Ku

nd

elu

ng

uG

rou

p

Copperbelt Orebody Member (and equivalents)

50

0m

Min

do

la

Cla

stics

Fm

.

Min

do

la

Nk

an

a

Ch

an

bis

hiS

E

Ch

an

bis

hi

Ch

ibu

lum

a

Ch

ibu

lum

aW

est

Ch

ibu

lum

aS

ou

th

Mw

am

ba

sh

iB

Mw

am

ba

sh

iA

Pita

nd

a

Sa

mb

a

Fitu

la

Mim

bu

la

Ch

ing

ola

A&

C

Ch

ing

ola

B

Ch

ing

ola

D

Ch

ing

ola

E

Ch

ing

ola

F

Nch

an

ga

Ko

nko

laN

ort

h

Ba

lub

a

Lu

an

sh

ya

Bw

an

aM

ku

bw

a

Nd

ola

We

st

Mu

fulir

a

Lu

an

so

be

Lu

be

mb

e

Lo

nsh

i

Fro

ntie

r

?

Mu

so

sh

i

Chambishi

Basin

Luanshya

Basin

Nchanga-

Chingola

district

Konkola

district

Eastern

Kafue

Anticline

"ha

ng

ing

wa

ll"d

ep

osits

"fo

otw

all"

de

po

sits

carbonate/breccia-hosted

diamictite/carbonate-hosted

argillite-hosted

arenite-hosted

mixed argillite-arenite

basement-hosted

Cu Co Mineralization±

granite, gneiss, schist

conglomerate

sandstone

sandstone-siltstone-carbonate

gritty siltstone

mixed carbonate-siliciclastic

carbonate

breccia

diamictite

siltstone-shale

Figure 2.8. Two broad categories of the sedimentary-hosted copper mineralisation on the ZCB can be defined. Mineralisation is either the ‘arenite hosted’ or ‘argillite hosted’ style, however within a single deposit both styles of mineralisation can occur (modified from Selley et al. 2005). The NKM deposit is primarily an ‘argillite’ hosted deposit, however mineralisation transgresses the contact between the Mindola Clastic Formation and the Copperbelt Orebody Member.

30

Selley et al., 2005): the “arenite-hosted” mineralised systems and the classical “argillite-hosted” deposits (Fig. 2.8) and mineralisation commonly is not confined to one specific stratigraphic horizon. However, the argillite-hosted deposits are generally confined to the lower portions of the COM (e.g. Nkana –Mindola and Nchanga orebodies) (Fig. 2.8), while the arenite-hosted systems are mainly recognised within the MCF (e.g. Chibuluma, Chibuluma West, Mwambashi B, and Chingola B). Argillite hosted Cu mineralisation also occurs at the higher levels of the Kitwe Formation and within the Mwashia and lower Kundelungu Groups. Table 2.3 summarises the key features of the major deposits of the ZCB.

The major orebodies are preserved in synforms within basement inliers (Unrug, 1989). These structures have been interpreted as former basins which controlled the deposition of the rocks of the Lower Roan Group and influenced the localisation of sulphide mineralisation (Mendelsohn, 1961; Selley et al. 2005). Cu mineralisation transgresses stratigraphy, however, each orebody has a grossly stratabound geometry. Within a single deposit several types of mineralisation maybe recognised, including disseminated, pre-folding vein-hosted, post-folding vein hosted, shear-zone-hosted and oxidation-supergene mineralisation. Significant vein hosted Cu mineralisation also occurs in the western ZCB at the Kansanshi Deposit, which is hosted at a higher level in the stratigraphic succession (Broughton et al. 2002). In addition to Cu mineralisation hosted within the Katangan Supergroup, significant disseminated Cu mineralisation occurs in basement lithologies (e.g. Lumwana, Samba deposits).

12

76

4

5

3

8

9

10

11

13

12

14

15

16

1718

20

21

22

23

24

25

26

2930

31

32

27

28

19

Basement

Lower Roan Group

Upper Roan and Mwashia Groups

Gabbro

Lower and UpperKundelungu Groups

Recent Discovery

Shale Belt

Cu-(Co) Deposit(surface projection)

Mokam

bo Dom

e

KonkolaDome

ChililabombweDome

Kafue Anticline

Chambishi Basin

Luanshya Basin

28°

13°

Kitwe

Chingola

Ndola

20KM

Figure 2.9. Geological map of the Zambian Copperbelt and the location of the major Cu-Co deposits hosted by the Katangan Supergroup (modified from Jordaan, 1961; Fleischer et al., 1976; Selley et al., 2005). 1 Luanshya, 2 Roan Extension, 3 Baluba, 4 Lufubu South, 5 Chibuluma South, 6 Chibuluma West, 7 Chibuluma, 8 Nkana-Mindola, 9 Chambishi SE,10 Chambishi, 11 Pitanda, 12 Mwambashi A,13 Mwambashi B, 14 Samba, 15 Fitula, 16 Mimbula, 17 Chingola A-F, 18 Nchanga, 19 Fitwaola,20 Konkola, 21 Konkola North, 22 Musoshi, 23 Lubembe, 24 Luansobe, 25 Kasaria, 26 Mufulira,27 Frontier (Lufua), 28 Mwekera, 29 Ndola West, 30 Itawa, 31 Bwana Mkubwa, 32 Lonshi,33 Mokambo.. (Sourced from Darnley (1960), Mendelsohn (1961), Annels (1984), Fleischer (1984), Sweeney and Binda (1989) and Selley et al., 2005).

31

International litho­strati graphic subdivision and orogenic cycle

Interpretations from Francois (1993); Cahen et al. (1984)

Interpretation from Kampunzu and Cailteux (1999) and Hanson (2003)

Event and Age Regional effect Event and Age Regional EffectPaleozoic Transverse folding -

~503 MaTransverse undulations to the main trend of the Lufilian arc

Chilatembo Late transverse folding

Neo

Pro

tero

zoic

(Lufi

lian

Oro

geny

)

Monwezian~ 602 Ma

E-W faulting

Monwezian

Strik-slip and escape bloack tectonicsLateral extrusion with cumula-tive displacement ~ 130kmClockwise rotation of crustal blocks and related development of convex structure of the Lufil-ian arc.

Kundelunguian~ 656 Ma

Folds with axial planes vertical or dipping N in the external folds of the Lufil-ian Arc

EpeirogenesisAge ?

Uplift in and near the Kundelungu Plateau

Kolwezian

Northward fold and thrust tec-tonics present day orientation of the Lufilian arc: E-W trend in the western sector and NW-SE in the eastern part.Major vergence to the N, back folding to S

Kolwezian656 Ma

Folds with axial planes dip-ping S. Nappes displaced several tens of km from S to N in southern DRC.

Lusakan FoldingLomamian Orogeny

Table 2.2. Summary of the recognized key structural events in Zambia during the Lufilian Orogeny (~600Ma to 500 Ma).

Supergene and oxidation ore minerals commonly overprint hypogene sulphides in the near surface environment. At NKM, a mixed oxide-sulphide assemblages occur within 100m of the surface Jordaan (1961). Malachite and chalcocite have been recorded at depths of > 600m in the Nchanga Lower Orebody and >1km at the Konkola North Deposit (McKinnon and Smit, 1961; Pollington and Bull, 2002).

2.7.1 Argillite-hosted Cu depositsThe argillite-hosted Cu deposits of the COM vary lithologically from dolomitic siltstones, siltstones and minor sandstones (e.g. Mindola and Roan Antelope) to black, carbonaceous shale orebodies (e.g. Nkana South). Unmineralised intervals occur at sites where the facies changes to either a massive arenaceous or carbonate facies (e.g. Annels, 1984).

2.7.2 Arenite-hosted Cu depositsThe arenite-hosted deposits account for approximately 30% of known Cu-Co mineralisation while argillite-hosted deposits comprise the remainder. The small high grade footwall arenite-hosted mineralisation occurs within condensed sections of the Mindola Clastic Formation such as at Mwambashi B (Selley and Bull, 2002; Selley et al. 2005) (Fig. 2.10). However, arenite-hosted Cu orebodies situated stratigraphically above the COM also occurs (e.g. Nchanga-Chingola, Mufulira) (McGowan et al., 2003; Selley et al., 2005). The mineralogical composition of the arenite-type deposit is complex and predominantly controlled by variations in feldspars, mica and organic carbon. The full spectrum of the two lithological end-members, hosting the different styles of mineralisation, can occur within a single copper deposit, forming a complex, transgressive mineralised system.

32

2.7.3 Chambishi ‘Basin’The Kafue Anticline dominates the regional structure in the central and southern corner of the ZCB (Fig. 2.11). To the east is the Mufulira Syncline while on the western flanks are the Chambishi and Roan-Mulashi Basins (synclines). Within the Chambishi Basin, the metasedimentary rocks of the Katangan Supergroup are enclosed by basement granites, the Lufubu Schists and the Muva metasediments, and intrusive, sill-like gabbroic bodies. Existing geological maps of the Chambishi Basin were used to define macroscopic structural domains. The southeastern corner of the basin is dominated by the NW striking Nkana Syncline, while in the northern area of the ‘basin’ WNW trending folds are common. The fold patterns exhibit evidence of ‘inheritance’ from pre-existing basement structures, including partitioning of strain, nucleation of folds parallel to inverted rift margins, and deflected orientations of the Lower Roan-Basement contact above inverted growth faults (Croaker and Selley, 2003; Selley et al., 2003, 2005). In the northern and western areas of the basin, the broad WNW striking synclines are separated by fault bounded basement inliers.

2.8 Cu-Co DEPOSITS OF THE CHAMBISHI ‘BASIN’

The Chambishi Basin has several significant copper deposits hosted within arenite and argillite sequences and comprises a significant proportion of the total copper resource on the ZCB. The Chambishi Basin is host to six significant Cu deposits with the largest being the Nkana-Mindola Mine. Four significant deposits occur

100 m

Copperbelt Orebody Mbr

sub-arkose

conglomerate

carbonaceous shale

argillaceous sandstone and siltstone

talus breccia

granitebasement granite

middle Kitwe Fm.

Upper Roan Gp

Mindola

Clastics Fm.

dolomite, sandstone and gabbro

W E

mineralized interval

MW 5 BN7 BN26 BN10 BN14

BN24

Figure 2.10. The stratigraphic-structural position of the Cu mineralization at the ‘arenite’ hosted Mwambashi prospect. Cu mineralization at the Mwambashi prospect is hosted in the MCF. There is a close relationship between basement geometry and the distribution of mineralization at both deposits (modified from Selley and Bull, 2003).

33

i eR v r

RIV

ER

bMwam

ashi

KAFUE

KITWE

CHAMBISHI WEST

PITANDA

MWAMBASHIB

CHIBULUMA WEST

CHIBULUMA EAST

CHAMBISHI SOUTHEAST PROSPECT

CHAMBISHI MAIN

CHIBULUMA SOUTH

MINDOLA

CENTRAL

SOUTH OREBODY

Lower and Middle Kundelungu

Basal Kundelungu - Kakontwe Limestone and Basal Tillite

Mwashia Group

Upper Roan Group

Lower Roan Group

Muva

Lufubu

Mines and known Ore Deposits

Granite

Gabbro

10KM

������

MWAMBASHI A

Lusaka

������

Figure 2.11. Geological map of the Chambishi basin. The NKM deposit is situated in the south eastern corner of the Chambishi Basin (modified from Garlick, 1961 and Jordaan, 1961).

34

DEP

OSI

TEs

timat

ed

Rese

rves

-Re

sour

ces

(~ 1

989

Mt

Gra

de~

Cu

%,

~ C

o %

~ A

g g/

t

Dep

osit

Type

Min

eral

isat

ion

Hos

t Li

thol

ogy

Foot

wal

lLi

thol

ogy

Alte

ratio

n-Ev

apor

ites

Zona

tion

Refe

renc

es

Konk

ola

500

4 %

Cu

2.7

g/t

AgAr

gilli

teSt

rata

boun

dBn

, Cpy

, Cc,

Py

and

Ag

Lam

inat

ed s

iltst

one

and

carb

onat

eH

emat

ite a

reni

tes

and

sand

ston

e, c

ongl

omer

ate

Dol

omite

and

anh

y-dr

ite p

seud

omor

phs,

K-

feld

spar

Brou

ghto

n, 2

003

Kirk

ham

, 198

9Sw

eene

y an

d Bi

nda,

198

4

Nch

anga

550

3.8

% C

u2.

7 g/

t Ag

Argi

llite

and

ar

enite

Stra

tabo

und

Bn, C

py, C

c, P

y an

d Ag

Silts

tone

; Fe

ldsp

athi

c qu

artz

iteSa

ndst

one,

qua

rtzi

tes

and

shal

esK-

fleds

par

and

seric

teCp

y+Bn

>Cp

y>Py

Voet

and

Fre

eman

, 197

6Ki

rkha

m, 1

989

Mck

inno

n an

d Sm

it, 1

961

McG

owan

et

al. 2

003

Muf

ulira

300

3 %

Cu

2.7

g/t

AgAr

enite

Stra

tabo

und

Bn, C

py, C

c, P

y an

d Ag

Feld

spat

hic

sand

ston

e an

d si

ltsto

neCo

nglo

mer

ate,

qua

rtzi

tes

and

sand

ston

e-si

ltsto

neAn

hydr

ite, K

-fel

dspa

r an

d se

ricite

Cc-B

n-Cp

yKi

rkha

m, 1

989

Scot

t, 2

003

Bran

dt e

t al

., 19

61

Cham

bish

i10

02.

7 %

Cu

15 g

/t A

gAr

gilli

teSt

rata

boun

dBn

, Cpy

, Cc,

Py

and

Ag

Biot

itic

argi

llite

, do

lom

iteAr

kose

s to

con

glom

erat

eAn

hydr

ite, K

-fled

spar

Cc>

Bn>

Cpy>

PyKi

rkha

m, 1

989

Anne

ls, 1

989

Cham

bish

i So

uthe

ast

502.

4 %

Cu

Argi

llite

Stra

tabo

und

Bn, C

py, C

c, P

yCa

rbon

aceo

us

Shal

e an

d ar

gilli

teQ

uart

zite

s, c

ongl

omer

ate,

sa

ndst

one-

silts

tone

Anhy

drite

, K-fl

edps

ar

and

dolo

mite

Kirk

ham

, 198

9An

nels

, 198

9Bu

ll an

d Se

lley,

200

3

Chib

ulum

a So

uth

124.

3 %

Cu

Aren

iteSt

rata

boun

dBn

, Cpy

, Cc,

Py

Seric

itic

sand

ston

es

and

quar

tzite

sSe

riciti

c ar

enite

s an

d qu

artz

ites

Seric

ite, a

lbite

Cc>

Bn>

Cpy>

PyKi

rkha

m, 1

989

Win

field

, 196

1

Chib

ulum

a Ea

st &

Wes

t25

4.9

% C

u0.

21 %

Co

2.7

g/t

Ag

Aren

iteSt

rata

boun

dBn

, Cpy

, Cc,

Py

Seric

itic

sand

ston

esSe

riciti

c ar

enite

s an

d qu

artz

ites

Seric

ite, a

lbite

Cc>

Bn>

Cpy>

PyKi

rkha

m, 1

989

Selle

y et

al,

2002

Nka

na65

02.

8 %

Cu

0.17

% C

oAr

gilli

teSt

rata

boun

dBn

, Cpy

, Cc,

Py

Dol

omite

, dol

omiti

c ar

gilli

te a

nd c

arbo

na-

ceou

s sh

ale

Cong

lom

erat

e, a

rkos

es,

feld

spat

hic

sand

ston

eAn

hydr

ite, d

olom

ite,

K-fe

ldsp

ar, a

lbite

Bn-C

py>

Ca>

Cpy

>Ca

>Py

Kirk

ham

, 198

9Jo

rdaa

n, 1

961

Balu

ba90

2.5

% C

u0.

15 %

Co

Argi

llite

Stra

tabo

und

Bn, C

py, C

c, P

yCa

rbon

aceo

us a

rgill

ite

and

shal

eCo

nglo

mer

ate,

are

nite

s an

d ar

gilli

teSe

ricite

Cc>

Bn>

Cpy>

Py>

CcKi

rkha

m, 1

989

Anne

ls e

t al

. 198

3Si

mm

onds

, 198

3

Luan

shya

230

2.7

% C

u2.

7 g/

tAr

gilli

teSt

rata

boun

dBn

, Cpy

, Cc,

Py

Carb

onac

eous

arg

illite

an

d sh

ale

Cong

lom

erat

e, q

uart

zite

an

d ar

gilli

tes

Py>

Cpy>

Bn>

CcKi

rkha

m, 1

989

Men

dels

ohn,

196

1

Lum

wan

a12

000.

7 %

Cu

0.05

5 C

oBa

sem

ent?

Stra

tabo

und

Bn, C

py, C

c, P

yG

ensi

s an

d sc

hist

Schi

st a

nd q

uart

zite

Seric

ite, q

uart

z,

phlo

gopi

teKi

rkha

m, 1

989;

Ber

nau,

20

07

Kins

ansh

i30

01.

17 %

Co

0.17

g/t

Au

Vein

hos

ted

Kund

elun

guD

isco

ncor

dant

&

con

cord

ant

Cpy,

Py

Schi

st a

nd c

arbo

nate

ve

ins

Schi

st a

nd q

uart

zite

Albi

teBr

ougt

on e

t al

. 200

3To

rrel

day

et a

l. 20

02

Mw

amba

shi

BAr

enite

Stra

tbou

ndCp

y-Bn

Sand

ston

eCo

nglo

mer

ate,

san

dsto

ne-

silts

tone

K-fe

ldsp

arSe

lley

et a

l. 20

03

Tabl

e 2.

3. T

he k

ey g

eolo

gica

l and

min

eral

isat

ion

char

acte

ristic

s of

the

rec

ogni

zed

copp

er d

epos

its o

ccur

ring

in t

he Z

ambi

an C

oppe

rbel

t.

35

within the northern sector of the Chambishi Basin (Fig. 2.11), however mining activity has only taken place at the Chambishi Deposit. Copper mineralisation at the Chambishi and Chambishi SE deposits is hosted within littoral argillite-siltstone facies of the COM. A small, high-grade Cu deposit is hosted within the footwall and separated from the COM by a barren argillaceous quartzite unit (Annels, 1984; Bull and Selley, 2003). Further west at the Pitanda and Mwambashi ‘B’ prospects and the Chibuluma deposit, copper mineralisation occurs within the arenite rocks of the MCF.

2.8.1 Chambishi DepositThe Chambishi Deposit is described in detail by Annels (1974, 1984) and Binda and Mulgrew, (1974). The deposit consists of two mineralised horizons separated by a low-grade zone (<1% Cu) directly overlying basement. The Ore Shale itself is a laminated biotitic argillite and calcareous argillite varying between 15 and 30 m thick and is coincident with changes in depth-to-basement. The Ore Shale contains carbonate-anhydrite-sulphide lenticles and changes from the argillite facies to slightly more arenaceous or carbonate facies over the basement highs. Most economic mineralization is found in the lower half of the Ore Shale, and locally within the upper footwall conglomerates and sandstones of the MCF. The orebodies pinch-out down dip corresponds to a change in the gradient of the footwall thickness. Chalcopyrite is the dominant Cu sulphide with minor bornite. Pyrite and pyrrhotite are typical co-existing gangue phases. Co mineralisation is unevenly distributed within the Cu orebody and present as Co-pyrite and carrollite.

2.8.2 Chambishi SE ProspectThe Chambishi SE prospect is a lateral continuation of the Chambishi Deposit. The two deposits are separated by a non-mineralised carbonate facies in the stratigraphic equivalent position to the mineralised host sequence. The position of the massive carbonate facies coincides with a basement high and it has been demonstrated that mineralisation occurs on the fringes of the basement high (Annels, 1984; Garlick, 1961).

2.8.3 Mwambashi B ProspectThe Mwambashi B arenite-hosted Cu prospect is located on the western margin of the Chambishi Basin (Fig. 2.9), northward of the WNW-trending Ore Shale pinch zone with low levels of mineralisation occurring within the upper MCF. Recent studies by Selley et al. (2002) suggested that disseminated chalcopyrite is grossly stratabound and generally partitioned into clean and heavy-mineral bearing arenaceous units and mineralisation is directly overlain by argillaceous rocks. The highest grades of mineralisation are restricted to more condensed intervals of MCF with a sharp well defined hangingwall being the COM. Pyrite is disseminated throughout the COM and minor chalcopyrite and bornite maybe present. The distribution of mineralisation is strongly controlled basin geometry, being localised to smaller, restricted sub-basins (Fig. 2.10) (Selley et al., 2002)

2.8.4 Chibuluma DepositTowards the SW margins of the Chambishi Basin, the high grade Cu and Co Chibuluma Deposit is hosted in the Basal Sandstone Member (BSM) of the MCF, immediately below by the KAM (Fig. 2.11). The Chibuluma orebodies are lower in the MCF sedimentary sequence when compared to Mwambashi B, however, the ore is hosted in small restricted basins similar to Mwambashi B. Garlick (1961), Whyte and Green (1971), Selley and Bull (2001, 2002) and Selley and Cooke (2001, 2002) have conducted detailed studies on this deposit. Copper mineralisation is mainly as bornite and chalcopyrite and the Cu orebody is grossly stratabound being confined to the margins of intrabasinal highs where strata pinch out against the basement highs. Mineralisation is partitioned into uppermost portions of the clean arkosic sandstones, while Co mineralisation is confined poorly sorted sub arkosic units consisting predominately of pyrite.

36

2.8.5 Nkana-MindolaThe NKM deposit is located in the SE corner of the Chambishi Basin and is predominately hosted in the lower portion of the COM (Fig. 2.11). The Chibuluma Mine lies on the south-west limb of the Nkana syncline and the Chambishi SE prospect is situated to the northwest of the NKM mine, along the eastern side of the Kafue Anticline (Fig. 2.11). The following section will briefly introduce the geological setting of the NKM deposit. Detailed surface mapping by ZCCM company geologists from 1950 to 1990 provides sufficient data on outcrop pattern and stratigraphic units occurring at NKM.

Nkana-Mindola mining area is situated on the eastern limb of the Kafue Anticline (Fig. 2.11). The mining area is dominated by the north-west plunging, asymmetric Nkana syncline with curved axial planes inclined steeply to the northwest in the hinge zone, but upright to westward dipping on higher structural levels (Fig. 2.12). The NKM deposit and dips at ~30o to the west in the northwestern most portion of the deposit, while in the southeastern corner of the deposit it is a complexly deformed orebody in the hinge zone area of the Nkana Syncline. The axis of the Nkana Syncline has an undulatory profile, with localised steepening and shallowing of fold plunges. Subtle changes in the fold geometry result from interference between northwest and west northwest fold geometries. Within the hinge zone of the Nkana Syncline folding is tight to isoclinal, while to the northwest the fold becomes more open and asymmetrical.

The NKM deposit is an argillite-hosted, primarily copper sulphide orebody consisting of chalcopyrite and bornite hosted in the upper portion of the MCF and the basal portion of the COM of the Kitwe Formation. Known economic mineralisation is confined to the northeast limb and the hinge zone area of the Nkana Syncline. It has a surface strike length of ~15 km and extends to a depth of ~1500 m beneath the current land surface. Sub-economic copper mineralization at the level of the COM is continuous for a further 17 km on the western limb of the Nkana Syncline (Fig. 2.12). ‘Barren Gaps’ truncate the mineralised system into two discrete zones; the northern dolomite-argillite hosted and the southern carbonaceous-carbonate argillite hosted areas (Fig. 2.13) Minor secondary oxide ore bodies of malachite, azurite, chalcocite and native copper occur at surface.

Basement Complex at the Nkana-Mindola DepositThe first classification of the basement was made by Gray (1932) with the division of the Lufubu System, now commonly referred to as the Lufubu Schist from the younger Muva System. The Lufubu rocks are gneissic to schistose in texture. At NKM the Lufubu rocks are quartz-biotite schists with minor interbedded sugary grey micaceous quartzites, graphitic schists, phyllites, semipelitic schist and migmatitic to banded gneisses. All rocks have a prominent northeast-southwest striking foliation. The granitic bodies occurring at NKM are interpreted as direct age and correlate with the felsic Nchanga Red Granite (877 ± 11 Ma; Armstrong et al., 1999). They are unconformably overlain by the basal Katangan strata (Garlick and Brummer, 1951; Armstrong et al., 1999; Master et al., 2002). At the SOB Shaft, granitic bodies have previously been described in association with ‘palaeohills’ (Mendelson, 1961). The granitic rocks (e.g. 1250 L SOB Shaft) are grey to pink with holocrystalline to porphyritic quartz-biotite. The edges of the intrusive bodies on the 1250L at SOB trend towards chlorite-biotite-sericite schist, which is related to post-intrusion shearing along the contact between the Lufubu Schist and the intrusive bodies.

Boundinaged quartz veins, confined to the Lufubu Schists, are parallel to the prominent foliation. Vein compositions are varied, with differing amounts of quartz, pink euhedral microcline, sericite, anhydrite and calcite. Minor ilmenite and tourmaline appear to have developed by metamorphic segregation. No visible sulphides have been identified in any of these veins. The contact between rocks of the basement and rocks of the Lower Roan Group is an unconformity, however considerable shearing and increased strain is focused at the this contact and in some areas the contact is faulted.. High strain zones within the gneisses are identified

37

MindolaPit

Todo

Nla

CITYOF

KITWE

MINDOLADAM

2KM

26 0

00m

E

34 000mN

26 000mN

42 000mN

30 000mN

38 000mN

30 0

00m

E

34 0

00m

E

38 0

00m

E

Basement Complex

Mindola Clastic Formation

Kitwe Formation

Upper Roan Group

Mwashia Group

Kundelungu Group

LowerRoanGroup

Mindola North Shaft(500L, 610L, 780L, 1050L)

Mindola Shaft(4180L, 4440L, 5510L)

Central Shaft(2320L, 2370L, 3130L)

SOB Shaft(790L, 1250L, 1810L, 2370L, 2880L, 3140L, 3360L)

Figure 2.12. Geological map of the Chambishi-Nkana area. The NKM deposit occurs in the northwesterly plunging Nkana Syncline. All economic copper mineralization occurs along the north eastern limb of the Nkana Syncline.

by the development of mica-boarded lenticles and separated by schistose layers consisting of biotite, sericite, chlorite, polycrystalline quartz and minor quartz. No outcrops of Muva Quartzite have been recognised at NKM, however to the south-west of NKM, mapped rocks of the Muva Quartzite exhibit fold axes parallel to the west-northwest striking folds within the overlying Katangan Supergroup (Mendelsohn, 1961).

38

IchimpeBarren Gap

KitweBarren

Gap

?

?

dolomitic siltstone facies carbonaceous facies

bn

No.3 shaftBarren Gap

Nkana Syncline

No. 4 shaftBarren Gap

bn

bn + cpy

cpy

cpy + py

bn

+cp

y

South OrebodyBarren Gap

foot

wall c

onta

ct

info

ldhi

nge

Kundelungu Gp

Mwashia Gp

Upper Roan

Kitwe Fm.

Mindola Clastics Fm.

Basement

arenaceous

dolomitic

Barren Gaps

2000 m

500

m

shaft

N

Gp

Figure 2.13. Plane of ore projection, modified from Jordaan (1961), and district scale map of the NKM deposit, showing broad down-dip and lateral (southward) sulfide mineral zonation from bornite (bn), to bornite and chalcopyrite (cpy), to chalcopyrite and pyrite (py). Orebodies are separated by arenaceous and dolomitic barren gaps. Dolomitic siltstone facies of the Copperbelt Orebody Member occurs only in the region of sediment input points (arenaceous barren gaps). In each case, barren gaps coincide with strike changes in the basement-Katangan Supergroup contact. These are most pronounced at the northern end of the system. The Kitwe barren gap overlies a subtle basement high and projects towards a major inflection affecting the trace of the Nkana Syncline. Coincidence of lithofacies variation and perturbations in fold geometry reflects inheritance of sub-basin geometry in Lufilian strain patterns (modified from Jordaan, 1961 and Selley et al., 2005).

2.8.6 BrecciasApproximately 1 km west of the Mindola Pit and waste dumps, surface mapping by NCCM geologists between 1960 and the mid-1980s identified the Mwashia and Kundelungu Groups in the hinge zone of the Nkana Syncline (Fig. 2.14). Importantly this mapping has identified an irregular, though recognisable synformal outcrop pattern of a breccia unit at the base of the Mwashia Group. Within this breccia unit gabbro, dolomite, sandstone, shale and skarn units have been identified during the mapping programme. No outcrop or drillcore of this portion of the stratigraphy was observed during the course of this study.

It is interpreted that this breccia is similar to the units that have been recognised at the Chambishi SE prospect to the NW and near the Chibuluma Mine on the western side of the Chambishi Basin (Fig. 2.15) (Annels, 1984; Binda, 1994; Selley and Bull, 2003; Wendroff, 2003). The breccia unit near the Chibuluma Mine is interpreted as cross-cutting down stratigraphy by Binda (1994) and coinciding with the pinch out of the COM. These units have been described as so-called ‘hydridised rock’ consisting of gabbro bodies and angular clasts of shale, sandstone and dolomite within a matrix of albite-dolomite cemented microbreccia (Annels, 1984; Tembo, 1994).

39

Figure 2.15. The geometry and relationship of breccia and gabbroic units at the Chibuluma Deposit (from Annels, 1984; 1989).

e

o

Bas

of Kitw

eFr

mation

c e pe I h m

Ba r n pr e Ga

NORTH SHAFT

MINDOLA PIT

Ga obbr

iaSalt brecc

S rka n

Ba m nse e taniteGr owe R an Gr upL r o o

Upper Roan Group

Mwashia Group

1 kmc

na Qu

Nha

g

artzite

ebe

Mm

r

Third orderscale F2 folds

To Ndola

CITYOF

KITWE

2KM

26 0

00m

E

34 000mN

26 000mN

30 000mN

38 000mN

30 0

00m

E

34 0

00m

E

38 0

00m

E

Mindola Shaft

S

l

Nkana ync ine

Basement Complex

Mindola Clastic Formation

Kitwe Formation

Upper Roan Group

Mwashia Group

Kundelungu Group

LowerRoanGroup

SOB Shaft

Mindola North Shaft

Central Shaft

42 000mN

NkanaPit

MINDOLADAM

Mining Licence Area

Stoped Out Area

MindolaPit

AREA OF ENLARGEMENT

26

0m

00

E

Mindola dam

Golf Club dambo

i

open t

Mndola

pi

NORTH SHAFT

MINDOLA SHAFT

Anticlinal Structure - basement high?

2 km

Ichempe Barren Gap

Bottom of Mwashia Group

Nkana Syncline

Bottom of Mwashia Group

aul

Zo

Ft

ne ?

Figure 2.14. Several significant breccia units have been previously mapped at NKM. They occur towards the top of the Upper Roan and appear from analysis of historic map datasets to be semi-conformable to stratigraphy. These units were not observed during this study and maps compiled from historic data at Mopani Copper Mines. The broader distribution of the gabbro rocks elsewhere in the Chambishi Basin is shown in Figure 2.11.

CHAMBISHI MINE

SSW NNE

AMPHIBOLITESILL

BASEMENT GRANITE

ORE-SHALE

ChertyDolomite

Hybrid Rocks/Breccias

Mine Levels×100m×100metres

0 2 4

2

4

6

8

10