1

Cu-Co Mineralization and GeotectonicEvolution of the Zambian Basin.

Brussels 2010

GeologicalSocietyLondon

Steve Roberts1

School of Ocean and Earth Science, University of Southampton, Southampton, UK

Plus: Mike Richards; Ross McGowan; Robin Bernau; James Nowecki;Adrian Boyce; Bruce Nesbitt; Alistair Beach

2

The ZambiaCopperbelt andDomes Region

Lumwana

Nchanga

3

Geotectonic Setting

Part of the 900kmlong Lufilian Arc a550-530Ma Fold Belt–formed during thecollision of theAngola-Kalahari andCongo- Tanzaniaplates

4

Copperbelt

5

Geology ofNchanga Mine

Produced >500 Mt @3.6% Cu. Reserves inregion of 111 Mt @

3.8% Cu.

6

NchangaMine

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Feldspathic Quartzite

Ripple Marks

Phlogopite Rich Fault Zone

8

9

D

BC

B. Lower arkose in vicinity of mineralization,

Fe-oxide staining and development of malachite

A. Lower arkose, coarse feldspars with shear zones

evident within samples.

C. Sample of lower ore-body

D. Shale overlying lower orebody

A

2

1

Nchanga Mine

10

B

A C

B. Sample of weakly mineralised Pink

Arkose.

C. Carrollite bearing upperarkose with variable amounts ofdolomite

A. Biotite/phlogopite alteration front preserved

within arkose in lower section of NE511 Borehole

A

D

D. Sericite quartz alteration of

Upper Orebody in NE511

Nchanga Mine

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Ore Petrology andHydrothermal Alteration

2

1

12

Ore Grade Distribution andMetal Enrichments

Down-hole grades of copper and cobalt mineralization for borehole NOP741, Nchanga Open Pit (assay grades from mine data) and Grant Diagram.

0 5 10 15 20 25

400

360

320

280

240

200

0 1 2 3

400

360

320

280

240

200

‘Dolomite Schist’

‘UBS’

‘TFQ’

‘BSS’

‘LBS’

Arkose

Granite

Total Copper (%)

Depth (m)

Total Cobalt (%)

Depth (m)

Depleted

Enriched

13

PhlogopitePhlogopite

Phlogopite

0123456

0.5 0.75 1

Mg/Mg+FeW

t% F

ArkoseMin ArkosePQTFQMin TFQGranite SZDolSchist SZBandSS SZArkose MicaPQ MicaTFQ Mica

Key Points (1) Phlogopite replaces earlier “detrital”Muscovite. (2) Up sequence variation in Mg# Ratio. (3)Phlogopites are F-rich

14

B

C D

F

ANE511-6P NOP723-13P

NE532-1P NE511-5P

NOP723-19P NE554-6PE

50µm

100µm100µm

100µm 50µm

100µm

Dol

Dol

Dol

Mal

Mal

Dol

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Carbonate Stable Isotope Data

-10

-8

-6

-4

-2

0

2

4

6

8

10

0 5 10 15 20 25

!18O (SMOW)

!13

C (P

DB

)

Upper Roan Dolomites

Shear Zone dolomite

Upper Orebody dolomite alteration

From Selley et al. 2005

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0.7000

0.7100

0.7200

0.7300

0.7400

0.7500

0.7600

0.7700

0 50 100 1501000/Sr

87

86

Sr/

Sr

WR Arkose Malachite

Data from Muchez et al. 2008

Neoproterozoic seawater

0.77345>0.79364 Upper OrebodyDolomitic Schist

Intial Ratio at 880MaUpper OrebodyDolomitic Schist

Carbonate Sr Isotope Data

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Sulfur Isotope Data

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Fluid Inclusion Data

Nchanga study compared to fluid inclusion data from theChambishi and Musoshi deposits, Zambia (Annels, 1989;Richards et al., 1988), some Irish Pb-Zn orefield deposits,and classic Mississippi Valley Type fluids (Trude &Wilkinson, 2001).

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Geology of the Chingola C deposit where a NE-verging recumbent anticline structurehas developed where basement schists are thrust over Lower Roan stratigraphy

Geology – Chingola C

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The distribution of mineralization atChingola B (based on copper gradeboundaries) plotted on to the sectiongeology. Mineralization is strongly relatedto the fault-propagation folds andcontrolling thrusts, as well as basaldetachments.

The distribution of mineralization atChingola C (based on copper gradeboundaries) plotted on to the sectiongeology. High-grade mineralization isstrongly related to thrust structures.

Distribution of mineralization atChingola B & C

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Lithostratigraphic andstructural controls ondistribution of ore.

Giant geochemicalanomaly.

Characteristics of ore minerals as a result of initial mineralizationand subsequent oxidation.

Evidence for hydrothermal alteration (phlogopite/k feldspar/dolomite).

Passage through the system of highly saline brines

Evidence for thermochemical sulfate reduction in the generation ofore bodies.

Evidence for interaction of mineralized fluids with basement lithologies

Nchanga

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The ZambiaCopperbelt andDomes Region

Lumwana

Nchanga

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Lumwana

From Selley et al. 2005

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Dominantly 1200 – 1400 Ma qtz – fs –bio gneisses schists and granites -similar to Kafue Anticline in ZambianCopperbelt. Includes thrust emplacedLower Roan and Upper Roanmetasediments.

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342.5 million tonnes of oregrading 0.74% Cu, plus

inferred resources of 563.1million tonnes at 0.63% Cu.

Lumwana

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Sulfide deformation andkyanite relationships

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Chimiwungu Malundwe

Hanging Wall Gneiss Hanging Wall Gneiss

Ore

Sch

ist

Ore

Sch

ist

Han

gin

gw

all Sc

his

t

Han

gin

gw

all Sc

his

t

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The prograde history of the Ile d’Yeu orthogneiss wasmarked by sharp strain localization along shear zones.During shearing, extensive fluid channelling led to achange from a Qtz+Pl+Kfs+Bt±Ms mineralogy to morealuminous micaschist assemblages made ofBt+Ms+Qtz±Ky. Mass transfers record gains in H2O, K,Mg, P, Rb, W, Sn, and losses in Ca, Na, Sr and Pb.

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2 4 6 8 10 12 14 16 18 20

Cou

nt

0

1

2

3

4

5

6

7

6 8 10 12 14 16 18 20

Cou

nt

0

2

4

6

8

4 6 8 10 12 14 16 18 20

Cou

nt

0 .0

0.5

1.0

1.5

2.0

2.5

Sulfur Isotope Data

Malundwe

Chimiwungu

Hangingwall Gneiss

D34Sδ34S

SulfideMineralogyand Isotopes

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Some Thoughts on Origin ofLumwana Mineralization

Discrete ore-horizonswithin shear zonesdeveloped within graniticgneiss host rocks.

Elemental mobility asanticipated for high gradeshear zones.

Thermochemicalreduction of sulfatephases.

Evidence suggestmineralization ofbasement to theCopperbelt ores ratherthan metamorphosed LRoan lithologies.

880-600 Ma

530 Ma

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Geological and Stratigraphic Setting ofOre

Lumwana + (Samba)

Nchanga + Nkana +Chambishi etc. etc.

Base

men

t

Low

er

Roan

U R

oan

Kata

ng

a S

up

erg

rou

p

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Schematic Geology of the Samba Deposit ( Wakefield, 1978)

Basement Mineralization inthe Copperbelt

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Sericite schistand foliatedporphyritic

rock at Samba

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Geological and Stratigraphic Setting ofOre

Lumwana + (Samba)

Nchanga + Nkana +Chambishi etc. etc.

Kansanshi, Frontier Base

men

t

Low

er

Roan

U R

oan

Kata

ng

a S

up

erg

rou

p

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Nkana

Brems et al. 2009

Tectonic Setting and Timingof Ore Formation 1

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Key Facts

Vein style deposit

Postdates metamorphism

Re-Os age of

From Torrelday et al. 2000

Kansanshi

Molybdenite within chalcopyrite VeinsRe-Os 511 +/- 1.7Ma

Tectonic Setting and Timing ofOre Formation 2

39Courtesy First Quantum Minerals

Kansanshi Mine

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Kansanshi – Qtz-Carbonate Veins in NW Pit

41Kansanshi Qtz-Carbonate Vein, NW Pit

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Middle Clastics – NW Pit

Middle Clastics – Main Pit

Kansanshi Grade Maps

Courtesy of First Quantum Minerals

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Veins at Kansanshi

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Luiswishi-Kamoto-Musonoi

From Muchez et al 2008

Cross section throughLuiswishi ore deposit

45From Muchez et al. 2008

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0.0

50.0

100.0

150.0

200.0

250.0

300.0

350.0

400.0

0.0 20.0 40.0 60.0Salinty Wt% Equiv. NaCl

T H

omog

. (oC

)

Kansanshi

Musoni/Kamoto

Kamoto Type1

Musoshi

Kamoto Type 2

High Angle VeinsLower OrebodyUpper Orebody

Chambishi

Nchanga

Copper Sulfides and FluidInclusions of the Copperbelt

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Schematic Geotectonic Setting of someZambian Copperbelt Ore Deposits

1

2

3

4

5

Basin Rift EventKonkola/Chambishi

Basin InversionNchanga

Basement Shear Zones.Lumwana/Samba

Modified by Compresional TectonicsNkana/Chibuluma

Post KinematicKansanshi

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Wessex Basin

Basin setting and the mechanism of regional exhumation exerted a fundamental controlon processes that determined fluid flow, heat flow and hydrocarbon formation anddistribution within a basin Bray et al. 1998

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• Recent mineral exploration and research has resulted in asubstantive expansion of the geological setting andcharacteristics of ore forming environments within theCopperbelt.

• These new data compel the development of an explorationparadigm which recognises this variety of settings and inparticular the importance of structures which facilitatesignificant amounts of fluid flow, wherever these occur inthe basin in terms of spatial location and timing.

• The timing and location of ore deposition ranges frombasement to lower Roan and it is increasingly evident thatworld class ore deposits can form within Basement, LowerRoan and even stratigraphy of the Upper Roan and above.

• This further enhances the exploration potential of theZambian Copperbelt.

Conclusions