IOCG FLUIDS

UNICAMP
COMPOSITION AND POTENTIAL SOURCES OF OREBEARING FLUIDS IN IOCG SYSTEMS: CONSTRAINTS FROM
FLUID INCLUSIONS AND STABLE ISOTOPE SYSTEMATICS
Roberto Perez Xavier
Instituto de Geociências - UNICAMP, Campinas (SP), Brasil
XXVIII Curso Latinoamericano de Metalogenia
UNESCO-SEG-SGA
TECTONIC SETTINGS – Cu-Au DEPOSITS - FLUIDS
IOCG
IOCG
Magmatic CO2
– rich fluids +
brines; basinal
brines
Magmatic +
meteoric
fluids
Groves et al. (1998)
Kesler (2005)
Evolved
seawater
Metamorphic
CO2 – rich
fluids
IOCG DISTRICTS AND AGES
Great Bear (1,87 – 1,85 Ga)
Fennoscandinavia (Kiruna - 1,88 – 1,75 Ga)
Wernecke
(1,60 Ga)
Baja
N. Chile/Peru Candelaria,
Manto Verde,
Raul-Constable
(140 - 115 Ma)
Grenville
(mesoprot.)
015
Yunnan
Cloncurry
(Ernest Henry 1,5 Ga)
Carajás
(2,7 –
2,5 Ga?)
Lufilian
(710 – 530 Ma?)
Gawler
Craton
(Olympic Dam
Tennant Creek
– 1,6 Ga)
(1,83 Ga)
1% of the world Cu-Au production
Olympic Dam is the only U-producing IOCG deposit
Skirrow (2004)
IOCGs: what are the common features?
Hydrothermal ore deposits
characterized by abundant (> 10%)
hydrothermally precipitated iron oxide
(magnetite and/or hematite) with
associated copper-iron sulfides
(chalcopyrite – bornite) and gold
Disseminated chalcopyrite in both clasts and
matrix in hematite breccia. Olympic Dam
(Australia)
Cu, Au, U, LREE, Ag, F, P, Ba, Co, Ni, Te, Mo, Sn, Zn, Pb, V …  elements
of distinct geochemical affinity  depends on the chemistry of the host
rocks
Vast majority spatially and broadly coeval with felsic - mafic intrusions 
no specific magma composition related to deposits
Epigenetic – confined or close to regional-scale structures
IOCGs: what are the
common features?
Hydrolytic alteration (sericite –
hematite – carbonate – chlorite
- quartz) – epizonal systems
5 km
1 km
Potassic alteration (biotite –
K-feldspar – magnetite ) –
deposit scale
Sodic and/or sodic – calcic
alteration (albite – scapolite –
actinolite – diopside - magnetite)
- regional scale
IOCG deposit
Mgt-apatite deposit
Hitzman (2005)
IOCG : what are the common features?
CONTRASTING FLUID TYPES
High temperature (350°C – 500°C) hypersaline (up to 50 wt% NaCl eq.)
brines
Fsp = ferropyrosmalite
(Fe,Mn)8Si6O15(OH,Cl)10
Ccp= chalcopyrite
Cal= calcite
Olympic Dam – Gawler Craton (South Australia;
Bastrakov et al. (2005)
Lower temperature (150°C – 250°C) aqueous fluids of low to moderate
salinity
Many IOCG systems also contain CO2 – rich fluids
Why is salinity important in IOCG systems?
Chloride is an important complexing ligand for a wide range of metals,
including base metals, thus
CONTROLS METAL SOLUBILITY
400°C – 0,5 kb; hm+mgt+py (HMP) and mgt+py+po
(MPP)
Highly saline fluids can
transport metals far more
effectively than dilute fluids
Liu & Phail (2005)
CuClx1-x + 1/2 H2O + FeCly2-y + S2(g) =CuFeS2 + (x+y) Cl- + 3H+ + 0,75 O2
But sulphur contents are also important ...
Sulphur is necessary for precipitation of many metals, especially the
chalcophile elements, including Cu, Zn, and Pb
Without sufficient sulphur,
these metals will tend to
remain in solution
Barton & Jonson (1996)
CuClx1-x + 1/2 H2O + FeCly2-y + S2(g) =CuFeS2 + (x+y) Cl- + 3H+ + 0,75 O2
IOCG fluids: insights from fluid inclusions
and stable isotopes
What are the major components of these fluids?
How have these fluids evolved and deposited Cu
and Au?
What are the potential sources for these fluids?
Origin of high salinity of the ore-bearing fluids?
IOCG fluids: general composition
-10
NaCl= -21.2°C
-20
NaCl+KCl= -22.9°C
Tfirst melting (°C)
-30
NaCl+MgCl2= -35°C
NaCl+FeCl2= -37°C
-40
-50
NaCl+CaCl2= -52°C/-55°C
-60
-70
-80
Inclusion fluids are
characterized by CaCl2
– rich aqueous
solution, particularly
the highly saline brines
(A)
Other solutes seem to
be important in more
diluted inclusion fluids
(B)
(C)
Carvalho (2009); Torresi (2008); Xu (2000)
Carajás IOCG fluids – (A) – Igarapé Bahia; (B) Alvo 118; (C)
Sossego
Cloncurry IOCG fluids (Ernest Henry, Mount Elliott)
IOCG fluids: salinity versus temperature
60
Salinity (wt% NaCl eq.)
50
40
Tennant
Eloise
Creek
30
20
10
Olympic
Candelaria
Dam
0
0
100
200
300
Th (°C)
400
500
Modified from Skirrow (2000)
INVOLVEMENT OF DIFFERENT FLUID TYPES
Mixing of fluids could be important for precipitation and possibly metal
introduction
IOCG FLUIDS: THE CLUNCURRY
DISTRICT (AUSTRALIA)
INVOLVEMENT
OF DIFFERENT
FLUID TYPES
High T
hypersaline
brines
+
Aqueous fluids
of lower T
(100°C – 350°C)
and salinity
between 5 to 36
wt% NaCl eq.
+
CO2-bearing
fluids
Baker et al. (2008)
COMPOSITION OF INDIVIDUAL FLUID INCLUSIONS
10 m m
Spot size = 23 μm
LA-ICPMS =
spectrometry
laser
ablation
inductively
couple
plasma
mass
COMPOSITION OF INDIVIDUAL FLUID INCLUSIONS
PIXE = Proton – Induced X-ray Emission
(Heinrich et al., 1993)
A high energy (a few MeV) proton beam
from a nuclear microprobe passes easily
through minerals like quartz to depths of
more than 80 µm, and excites X-rays from
elements within trapped fluid inclusions
The X-rays emitted can be used to
identify each element within the
sample  individual fluid inclusions
can be analyzed non-destructively
IOCG FLUIDS:
COMPOSITION OF THE
INCLUSION FLUIDS
PIXE= individual fluid
inclusions can be
imaged and analyzed
non-destructively
Red, yellow to white colors reflect
increasing abundance
Blue to black represent low to zero
concentration
Baker et al. (2008)
IOCG FLUIDS: COMPOSITION OF THE INCLUSION FLUIDS
Element
Cl (wt%)
Lightning Creek
41
Element
Olympic Dam
Cl (wt%)
0.2 - 12.2
K
8.5
K
0.2 - 6.9
Ca
5.8
Ca
0.34 - 4.0
Mn
0.4
Mn
0.23 - 0.65
Fe
7.5 - 27.7
Cu
0.03 - 4.5
Fe
Cu
10
1.3
Zn (ppm)
595
Zn (ppm)
352 - 1,600
Br
839
Br
201 - 1,716
Rb
911
Rb
< 2,421
Sr
795
Sr
589 - 3,349
Ba
7,410
Ba
719 – 3,950
Pb
1,033 – 4,229
Representative results of PIXE analysis of elemental
abundances for highly saline inclusions. Note: high
levels of Cu and Fe
Perring et al. (2000); Bastrakov et al. (2007)
IOCG FLUIDS: WHERE DO THEY COME FROM?
INSIGHT FROM STABLE ISOTOPES: diverse fluid sources
Olympic Dam, Gawler
Craton
Fluids of metamorphic origin
(Bastrakov et al. 2007)
Tennant Creek
Formation fluids (Hunt et al.
2007)
Cloncurry Cu-Au
Interaction of magmatic
fluids with surrounding
igneous/metamorphic rocks
(Mark et al. 2004)
Carajás IOCG deposits
(Sossego)
Deep seated
formational/metamorphic
fluids or magmatic +
meteoric waters (Monteiro et al.
2008)
IOCG FLUIDS: WHERE DO THEY COME FROM?
Halogen contents of fluid inclusions: conservative fluid tracers
Baker et al. (2008)
The data support a role for multiple fluids in the genesis of IOCG deposits
LOCATION OF THE CARAJÁS MINERAL
PROVINCE
Carajás Mineral Province
~200.000 km2
Equator
São Luis
Craton
Amazon Craton
Guianas Shield
Parnaíba
Basin
Central Brazil
Shield
Paraná
Basin
São Francisco
Craton
Craton Luís Alves
Craton Rio da
Plata
GEOLOGICAL MAP
OF THE CARAJÁS
MINERAL PROVINCE
Fe, Mn, Al, Au, Cu,
Cr, Ni deposits
IOCG
deposits
+
Intrusionrelated CuAu – (Mo W- Bi - Sn)
deposits
Docegeo, 1988
CARAJÁS MINERAL PROVINCE: STRATIGRAPHY
2.6 Ga
Diabase Dike/Sill
~2.65Ga - Xenocrysts
Paleoproterozoic A-type
alkaline granites:
Águas Claras
Fm
Cu-Au-(W-Bi-Sn-Mo)
Mn (Azul); Au-Pt-Pd
(Serra Pelada)
Carajás, Cigano, Breves,
Young Salobo,
Gameleira
2.76 Ga
Buritirama Fm (Mn)
Igarapé Bahia Fm (IOCG)
Syntectonic alkaline
granitoids
Grão Pará Fm
Ni- Cr-EGP
Giant Iron Deposits (18 Bt @ 66%Fe)
2.8 Ga
Basement
Rocks
Igarapé Salobo Fm (IOCG)
~2.74Ga
Igarapé Pojuca Fm (IOCG-Zn)
Plaquê
Suite,
Planalto,
Estrela,
Serra do
Rabo
~2.57Ga
Itacaiúnas
Supergroup volcanosedimentary
rocks
~1.88Ga
(minimum)
Luanga, Vermelho?
Old Salobo, Itacaiúnas
Complexo Xingu (~2.8 Ga)
Complexo Pium (~3.0 Ga)
Tectonic environment: rift zones in ensialic settings or intracratonic basins, pull-apart basin,
magmatic arc followed by extension and emplacement of A-type granites.
CARAJÁS MINERAL PROVINCE: STRUCTURAL SETTING
N
50 Km
NW to ESE-NNW-striking sigmoidal structure with regional-scale strike-slip systems
(Cinzento and Carajás faults)
Regional metamorphism of greenschist to upper amphibolite facies (ca. 2.581-2.519 Ma)
Regional extensional regime at 1.9 – 1.88 Ga = intrusion of A-type granites
Cu-Au SYSTEMS IN THE CARAJÁS MINERAL PROVINCE
Deposits
Tonnage
Grades
IOCGs
Salobo
994 Mt
0.94% Cu, 0.52 g/t Au
Sossego
355 Mt
1.1% Cu, 0.28 g/t Au
Cristalino
+300 Mt
1% Cu, 0.3 g/t Au
Igarapé Bahia
219 Mt
1.4% Cu, 0.86 g/t Au
Alvo 118
170 Mt
1% Cu, 0.3 g/t Au
Cu-Au (Sn-Mo-W-Bi)
Breves
50 Mt
1.22% Cu, 0.75 g/t Au
Total Resources of the Belt ~ 2 Billion Tonnes Cu-Au Ores
Source: Tallarico (2003)
IOCG DEPOSITS OF THE CARAJÁS MINERAL PROVINCE
Supergrupo Itacaiúnas
metavolcano-sedimentary
sequences + intrusive
rocks of diverse
compositions
Similar sequence of hydrothermal alteration:
Na (albite + scapolite) Na-Ca (albite –
actinolite – epidote – magnetite - apatite) 
K (biotite – K-feldspar)  chlorite –
carbonate – sericite
Regional shear zones
granite
Different crustal
levels
Na
Na-Ca
Act + mgt
cpy
Sossego IOCG
(Sequeirinho
orebody)
Alvo 118 IOCG
gabbro
IOCG DEPOSITS OF THE CARAJÁS MINERAL PROVINCE
SOSSEGO IOCG
Sequeirinho ore breccia
Veins – Alvo 118
Igarapé Bahia
ore breccia
Sossego ore breccia
Pista ore breccia
Geochemical signature linked with Cu-Fe-Au:
Sossego IOCG: Ni, Co, Se, V, P, LREE, Th, U, Pd, Ag, Pb, Zn, Sn, Mo, Te
Alvo 118 IOCG: Sn, Te, Bi, Pb, Ag, HREE
Igarapé Bahia IOCG: LREE, Mn, U, Ba, F, Pb, Zn, Mo, P, Ag
FLUIDS IN IOCG DEPOSITS OF THE CARAJÁS MINERAL
PROVINCE
Sossego IOCG
Highly saline aqueous
fluids (35 to 70 wt% NaCl-CaCl2
NaCl eq.)
+
low to moderate
salinity (5 up to 30
wt% NaCl eq.)
aqueous fluids
K-Fe-Mg
chlorides
±
low salinity (< 6 wt%
NaCl eq.) CO2-rich
fluids (Salobo and
Igarapé Bahia only)
NaCl
K(Na)Cl
600
am02C LV
am02C LVS
am39K LV
am39K LVS
am39L LV
am39L LVS
500
Sossego IOCG deposit
o
TH ( C)
400
IOCG FLUID INCLUSIONS
Sequeirinho
300
200
100
0
5
10
15
20
25
30
35
40
45
50
55
60
65
15  m
70
Salinidade (% p.e. NaCl)
Carvalho (2009); Torresi 2005
600
500
am. 319/133,36
ifs H2O-NaCl (LVS)
ifs H2O-NaCl (LV)
am. 319/107,31
ifs H2O-NaCl (LV)
ifs H2O-NaCl (LVS)
400
Sossego
Inc lusõ e s T ip o I (L + V )
380
Q tz e m ve io sulfe ta d o
Inc lusõ e s T ip o II (L + V + S )
360
340
320
400
300
C)
oTH
( 300
o
TH (C )
280
260
240
220
200
200
180
160
Pista
140
100
120
100
0
5
10
15
20
25
30
35
40
Salinidade (% p.e. NaCl)
45
50
55
60
65
0
5
10
15
20
25
30
35
40
S a lin id a d e (% e m p e s o e q u iv . N a C l)
45
50
INTRUSION-RELATED BREVES Cu-Au- (Mo-W-Bi-Sn)
DEPOSIT
FR73
FR29
FR61
Supergene oxidation
zone
FR13
Cpy + py + po + aspy +
W + Bi + Sn
+
+
+
+
(1878 Ma and 1873 Ma)
50 Mt – 1.22% Cu + 0.75g/t
Au + 2.4g/t Ag + 1200g/t W
+ 70g/t Sn + 175g/t Mo +
75g/t Bi
+
+
+
episienito
+ Granite +
+ 1878 Ma + +
Quartz + white mica
+
+
biotite + chlorite
Modified from Tallarico (2003)
fluorita  tourmaline
+
+ ++
200 m
100
+ + + + +
+
0
Águas Claras Fm:
metasedimentary rocks
+

L800
INTRUSION-RELATED BREVES Cu-Au- (Mo-W-Bi-Sn)
DEPOSIT
Disseminated
VEINS
Fe-biotite + white
mica + Fechlorite 
tourmaline 
fluorite
Medium- to coarse-grained
metarenites strongly altered to chlorite
Chalcopyrite - arsenopyrite - pyrite  pyrrhotite  molybdenite 
cassiterite  scheelite  ferberite [(Fe,Mn)WO3]
INTRUSION-RELATED BREVES Cu-Au- (Mo-W-Bi-Sn)
DEPOSIT
LV-quartz-sulfide veins
LV-granite
LVS+LVMS-quartz-sulfide veins
LVMS-granite
LV-quartz in barren vein
LV-fluorite in barren vein
60
Salinity(wt% NaCl eq.)
50
40
CO2 (C)
30
L
S
20
20μm
L
10
V
0
20μm
0
100
200
300
400
500
Complex
mixture of Na,
K, Mg, Fe and
Ca chlorides
Tht (°C)
More saline members tending towards CaCl2-rich fluids
Cu – Au SYSTEMS OF THE CARAJÁS MINERAL
PROVINCE
IOCG DEPOSITS
vs.
INTRUSION-RELATED BREVES Cu-Au- (Mo-W-Bi-Sn)
DEPOSIT
WHAT ARE THE CONCENTRATIONS OF METALS AND
HALOGENS IN THESE ORE-BEARING FLUIDS???
Cu-Au FLUIDS IN THE CARAJÁS MNERAL PROVINCE
Na/K ratios are
similar
but
Carajás IOCG
brines have 5 to 10
times more Ca than
porphyry Cu-Au
fluids !!
Porphyry copper deposits:
Butte (Montana), Pelambres
(Chile), Yerrington (USA),
Mineral Park (a uneconomic
porphyry - USA), Bata Hijau
(Indonesia), Bingham (USA).
Xavier et al. (2008)
Cu-Au FLUIDS IN THE CARAJÁS MNERAL PROVINCE
Brine inclusions
from the Carajás
Cu-Au systems:
Ca-dominated
percent level of
Na, K and Fe
strongly enriched
in Mn, Sr, and Ba
tens to hundreds
of ppm of Pb and
Zn
Xavier et al. (2008)
Cu-Au FLUIDS IN THE CARAJÁS MNERAL PROVINCE
Cu-Au brines may have been
generated mainly from a
non-magmatic source !!!
Xavier et al. (2008)
Cu-Au FLUIDS IN THE CARAJÁS MNERAL PROVINCE
Cu-Au brines may have
been generated mainly
from a non-magmatic
source !!!
Even in the case of the
intrusion-related
systems ??
Xavier et al. (2008)
CARAJÁS Cu-Au BRINES: BORON ISOTOPIC COMPOSITION
10
Breves
Frequency
8
6
B source was mainly
non-magmatic !!!
Sossego
4
Igarapé Bahia
2
Salobo
0
-40
-30.1
-30
-20
-10
0
10
δ11B (o/oo)
non-marine evaporites
7.0
20
30
40
18.1
31.7
seawater
marine evaporites
oceanic crust
submarine hydrothermal
fluids
continental crust
sediments
granite and rhyolite
magmatic
Xavier et al. 2008
CONCLUSIONS
Brines associated with Cu-Au systems in Carajás are Cadominated + percent level concentrations of Na, K and Fe
Cu-Au fluids in Carajás are strongly enriched in Ba, Sr, Mn,
Pb and Zn
Compared to intrusion-related Cu-Au fluids, IOCG fluids are
more enriched in Ca, Ba, Sr, Zn, Pb
Intrusion-related fluids contain more Bi than IOCG fluids
No high salinity inclusions analyzed in any deposit contained
significant Cu  “spent fluids” ?
Cl/Br ratios indicate a NON-MAGMATIC SOURCE for the
brines in Carajás Cu-Au systems