cu-co mineralization and geotectonic evolution of the ... · 1 cu-co mineralization and geotectonic...
TRANSCRIPT
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
3
Geotectonic Setting
Part of the 900kmlong Lufilian Arc a550-530Ma Fold Belt–formed during thecollision of theAngola-Kalahari andCongo- Tanzaniaplates
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
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
15
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
16
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
18
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).
19
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
20
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
21
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
24
Dominantly 1200 – 1400 Ma qtz – fs –bio gneisses schists and granites -similar to Kafue Anticline in ZambianCopperbelt. Includes thrust emplacedLower Roan and Upper Roanmetasediments.
25
342.5 million tonnes of oregrading 0.74% Cu, plus
inferred resources of 563.1million tonnes at 0.63% Cu.
Lumwana
29
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
30
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.
31
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
32
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
33
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
34
Schematic Geology of the Samba Deposit ( Wakefield, 1978)
Basement Mineralization inthe Copperbelt
36
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
38
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
42
Middle Clastics – NW Pit
Middle Clastics – Main Pit
Kansanshi Grade Maps
Courtesy of First Quantum Minerals
46
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
47
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
48
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
49
• 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