The boring billion: about Proterozoic porphyry copper ...€™sabout Proterozoic porphyry copper...
Transcript of The boring billion: about Proterozoic porphyry copper ...€™sabout Proterozoic porphyry copper...
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The "boring billion":
What’s about Proterozoic porphyry copper deposits ?
Anne-Sylvie André-MayerProfessor in Economic Geology
Université de Lorraine
GeoRessources
NANCY, FRANCE
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Precambrian porphyry deposits
Cooke et al., 2005
Sillitoe, 2010
25 largest porphyry copper-molybdenum deposits … Precambrian
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Goldfarb et al. 2010
Convergent margins
Meso- to Neoproterozoic
the Boring billion
Secular distribution of porphyry deposits
Paleoproterozoic porphyry deposits
Gaoua district, West African Craton
Scarcity of Proterozoic porphyry deposits
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“Most of the porphyry deposits
formed in the upper few kilometers
of crust, in tectonically active
environments and at plateboundaries.”
Richards, 2013
Meso- to Neoproterozoic : the Boring billion
Secular distribution of porphyry deposits
uneven preservation
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Jébrak et Marcoux, 2008
the supercontinent cycle,
the tectonic settings,
the depth of formation.
OROGENIC GOLD
Goldfarb et al. 2010
uneven preservation
Plate motions
Meso- to Neoproterozoic : the Boring billion
Secular distribution of porphyry deposits
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Jébrak et Marcoux, 2008
BEFORE AFTER
Goldfarb et al. 2010
long-term secular
changes in the Earth
System.
Modern-Style plate tectonics
Meso- to Neoproterozoic : the Boring billion
Secular distribution of porphyry deposits
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long-term secular
changes in the Earth
System.
dramatic reductions or
temporary cessations of
subduction
Mantle depletion rate
PROTEROZOIC
Meso- to Neoproterozoic : the Boring billion
Secular distribution of porphyry deposits
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long-term secular
changes in the Earth
System.
Secular distribution of porphyry deposits
Meso- to Neoproterozoic : the Boring billion
Richards and Mumim, 2013
Geochemical features
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Paleoproterozoic porphyry deposits
PROTEROZOIC
Secular distribution of porphyry deposits
Goldfarb et al. 2010
Convergent margins
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Secular distribution of porphyry deposits
Reddy and Evans, 2009
Paleoproterozoic in Earth evolution
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Paleoproterozoic porphyry deposits
India: 2.5 Ga
Malanjkhand
Sinclair, 2007
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Paleoproterozoic porphyry deposits
AITIK
The Fennoscandian shield: 1.8-1.9 Ga
SKELLEFTE
District: Tallberg
Sinclair, 2007
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Sinclair, 2007
GAOUA
GOREN
WAYEN
Paleoproterozoic porphyry deposits
The West African craton: 2.16 Ga
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Paleoproterozoic porphyry deposits
The Gaoua district
GAOUA
Le Mignot et al., 2017
SW Burkina Faso
Boromo-Goren
greenstone belt
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The Gaoua district
Copper-gold porphyry occurrences
Gold-only occurrences
Volta Resources, now B2Gold
22 Mt at 0.29% Cu and 0,33 g/t Au
Total resource estimate :
Gold : 98.6 t inferred and 7.5 t indicated
Copper: 912,000 t inferred and 64,000 t indicated
copper resources
(SRK Consulting Ltd., 2013).
Le Mignot et al., 2017
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Paleoproterozoic porphyry deposits
The Gaoua district
100
10
10 5 10 15 20 25 30
Nb/Th
Zr/
Nb
ARCN-MORB
OIB
Oceanic Plateau basalts
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Paleoproterozoic porphyry deposits
The Gaoua district
Brecciated diorite with triangular cavities
composed of Cp1
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Paleoproterozoic porphyry deposits
The Gaoua district
Brecciated diorite with triangular cavities
composed of Cp1Reworked mineralized
breccia affected by D1
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Paleoproterozoic porphyry deposits
The Gaoua district
Brecciated diorite with triangular cavities
composed of Cp1Reworked mineralized
breccia affected by D1
D1 shear band
with carbonate
alteration halo
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Paleoproterozoic porphyry deposits
The Gaoua district
Brecciated diorite with triangular cavities
composed of Cp1Reworked mineralized
breccia affected by D1Late oblique D2Ga shear bands
crosscutting the altered diorite
D1 shear band
with carbonate
alteration halo
2.48 g/t Au and low Cu
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Paleoproterozoic porphyry deposits
The Gaoua district
STAGE 1: PORPHYRY
STAGE 2: LODE-GOLD EVENT
Le Mignot et al., 2017
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Paleoproterozoic porphyry deposits
The Gaoua district
Cpy1Py1a
50 µm Anhydrite
Carbonates
STAGE 1: PORPHYRY
Re-Os age
2164±25
MSWD=1.3
Le Mignot et al. 2017
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Le Mignot et al. 2017
Paleoproterozoic porphyry deposits
The Gaoua district
Gold
solubility
limit
Au
(m
ol%
)
As (mol%)
1.E-02
1.E-03
1.E-04
1.E-05
1.E-06
1.E-07
1.E-08
1.E-09
1.E-10
1.E-11
1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00
Porphyry deposits
Orogenic deposits
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1000000
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1000000000
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Titre du graphique
S34 Fe57 Ni60 Cu63 As75 Se82 Sb121 Te125 Au197 Pb208 Bi209
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100000000
0 50 100 150 200 250
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100000000
Py1
Time (in s)
Time (in s)
LA-ICP-MS spectra
S
Fe
10
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10000000
100000000
1000000000
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S34 Fe57 Ni60 Cu63 As75 Se82 Sb121 Te125 Au197 Pb208 Bi209
PbCu
Au
Te
Sb
Ni
Fe
S
Bi
Se
Cu
Ni
FeS
As Se
Py2
PbAuTe SbBi
AsNi
Cu
Ni
Cu
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Superposition of Orogenic Gold
on a Porphyry Occurrence
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Paleoproterozoic porphyry deposits
The Gaoua district
Boromo-West geochronological constraints
Volcanic and plutonic rocks
Cu-Gaoua
Re-Os Pyrite
(This study)
Ore minerals
(1)
Gabbro
U-Pb Zircon
Diorite
U-Pb Zircon
(1)
2000 (2)
Rhyolite
U-Pb Zircon
(3)
Qz Diorite
U-Pb Zircon
Rhyolite
U-Pb Zircon
(4)
MORB/
within-plate
tholeiites
Arc volcanism
subduction
zones
WNW-ESE
compression
WNW-ESE
transpression
Synorogenic
(shear zone related)
basins local E-W
transtension
Deposition of Tarkwaian
(T) & Birmian (B)
sediments
2140
2120
2100
2080
2160
2180
Age
in MaD3
D2
N-S
compression
D1
?
?
?
S1
S0
F1
S0(B)
S0(T)
DExt
Bor-W
TH
TH
MT
RA
N/C
A
?
S2
S3
TF3
2140
2120
2100
2080
2160
2180
2200
Ma
(5)
Perkoa
Pb-Pb model age
Galena
Age
in Ma
Correlation between
the Boromo-West
greenstone belt
stratigraphy,
SW Burkina Faso
geodynamic
environment
deformation history
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Proterozoic porphyry deposits
Share the same features of Phanerozoic porphyry deposits
lower grade, lower tonnage, scarcity of alteration
Scarcity during Paleoproterozoic times, absent during Meso to
Neo-Proterozoic,
Primary features often obscured by later mineralization event(s)
Take home message
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The "boring billion":
What’s about Proterozoic porphyry copper deposits ?
QUESTIONS