the boring billion: about proterozoic porphyry copper ...€™sabout proterozoic porphyry copper...

The "boring billion":

What’s about Proterozoic porphyry copper deposits ?

Anne-Sylvie André-MayerProfessor in Economic Geology

Université de Lorraine

GeoRessources

NANCY, FRANCE

Precambrian porphyry deposits

Cooke et al., 2005

Sillitoe, 2010

25 largest porphyry copper-molybdenum deposits … Precambrian

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

“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


uneven preservation

Jébrak et Marcoux, 2008

the supercontinent cycle,

the tectonic settings,

the depth of formation.

OROGENIC GOLD


uneven preservation

Plate motions



Jébrak et Marcoux, 2008

BEFORE AFTER


long-term secular

changes in the Earth

System.

Modern-Style plate tectonics



long-term secular


System.

dramatic reductions or

temporary cessations of

subduction

Mantle depletion rate

PROTEROZOIC



long-term secular


System.



Richards and Mumim, 2013

Geochemical features


PROTEROZOIC



Convergent margins


Reddy and Evans, 2009

Paleoproterozoic in Earth evolution


India: 2.5 Ga

Malanjkhand

Sinclair, 2007


AITIK

The Fennoscandian shield: 1.8-1.9 Ga

SKELLEFTE

District: Tallberg

Sinclair, 2007

Sinclair, 2007

GAOUA

GOREN

WAYEN


The West African craton: 2.16 Ga


The Gaoua district

GAOUA

Le Mignot et al., 2017

SW Burkina Faso

Boromo-Goren

greenstone belt

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).



The Gaoua district

100

10

10 5 10 15 20 25 30

Nb/Th

Zr/

Nb

ARCN-MORB

OIB

Oceanic Plateau basalts


The Gaoua district

Brecciated diorite with triangular cavities

composed of Cp1


The Gaoua district


composed of Cp1Reworked mineralized

breccia affected by D1


The Gaoua district



breccia affected by D1

D1 shear band

with carbonate

alteration halo


The Gaoua district



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


The Gaoua district

STAGE 1: PORPHYRY

STAGE 2: LODE-GOLD EVENT



The Gaoua district

Cpy1Py1a

50 µm Anhydrite

Carbonates

STAGE 1: PORPHYRY

Re-Os age

2164±25

MSWD=1.3

Le Mignot et al. 2017

Le Mignot et al. 2017


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

10

100

1000

10000

100000

1000000

10000000

100000000

1000000000

1 6

11

16

21

26

31

36

41

46

51

56

61

66

71

76

81

86

91

96

10

1

10

6

11

1

11

6

12

1

12

6

13

1

13

6

14

1

14

6

15

1

15

6

16

1

16

6

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1

Titre du graphique

S34 Fe57 Ni60 Cu63 As75 Se82 Sb121 Te125 Au197 Pb208 Bi209

10

100

1000

10000

100000

1000000

10000000

100000000

0 50 100 150 200 250

0 50 100 150 200 250

10

100

1000

10000

100000

1000000

10000000

100000000

Py1

Time (in s)

Time (in s)

LA-ICP-MS spectra

S

Fe

10

100

1000

10000

100000

1000000

10000000

100000000

1000000000

1 6

11

16

21

26

31

36

41

46

51

56

61

66

71

76

81

86

91

96

10

1

10

6

11

1

11

6

12

1

12

6

13

1

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6

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1

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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

Superposition of Orogenic Gold

on a Porphyry Occurrence


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

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

The "boring billion":

What’s about Proterozoic porphyry copper deposits ?

QUESTIONS

the boring billion: about proterozoic porphyry copper ...€™sabout proterozoic porphyry copper...

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