Noranda/Falconbridge Sistemas de Informação

Noranda/Falconbridge Sistemas de Informação

Non-magmatic versus Magmatic Fluids in the
Genesis of Archean and Palaeoproterozoic Iron
Oxide-Copper-Gold Systems of the Carajás Mineral
Province (Brazil)
ROBERTO P. XAVIER, Institute of Geosciences – University of
Campinas (UNICAMP), Campinas, Brazil
Lena V. S. Monteiro, Institute of Geosciences – University of São
Paulo (USP), São Paulo, Brazil
Carolina P. N. Moreto, Gustavo H. C. Melo, Erika S. B. Santiago
Institute of Geosciences – University of Campinas (UNICAMP),
Campinas, Brazil
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
THE CARAJÁS DOMAIN
Intrusions
Three events:
•2.76 – 2.74 Ga
•2.57 Ga
•1.88 Ga
Carajás Basin
~ 2.64 Ga
Aguas Claras
Formation
2.76 – 2.73 Ga
Itacaiunas
Supergroup
volcanosedimentary
sequence
Modified from:
Vasquez et al. (2008)
Basement rocks : orthogneiss (~3.07 Ga) + granulites +
felsic Intrusions (2.99 Ga to 2.84 Ga)
THE CARAJÁS DOMAIN
Bacajá Domain (Paleoproterozoic)
Cu
Diversity of
mineral
systems
Cu - Au
SYSTEMS
Iron Oxide – Copper – Gold
(IOCG):
Neoarchean
2.68 Ga – 2.71 Ga and 2.57 Ga
Paleoproterozoic
1.88 Ga – 1.90 Ga
Cu-Au
(W – Sn – Mo - Bi):
Paleoproterozoic
1.88 Ga
CARAJÁS Cu – Au SYSTEMS
Deposit
Tonnage
Grades
IOCG deposits
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/Alemão
219 Mt
1.4% Cu, 0.86 g/t Au
Alvo 118
170 Mt
1% Cu, 0.3 g/t Au
Gameleira
100 Mt
0.77% Cu
Cu-Au (W-Sn-Mo-Bi) deposits
Breves
50 Mt
1.22% Cu, 0.75 g/t Au
Estrela
30 Mt
0.5% Cu
The CMP contains the world’s largest known concentration
of high - tonnage IOCG deposits
Resources of Cu-Au ore is over 2 billion tonnes
THE CARAJÁS DOMAIN
Bacajá Domain (Paleoproterozoic)
Cu
Iron Oxide Cu - Au
SYSTEMS
Structurally controlled by regional-scale E–W and W–NWstriking shear zones.
Host rocks: volcano-sedimentary units of the Itacaiúnas
Supergroup (ca 2.73−2.76 Ga), mafic and felsic intrusions (ca
2.74 Ga) and basement granitoids (ca 3.0−2.83 Ga).
NEOARCHEAN CARAJÁS IOCG SYSTEMS
2.71-2.68 Ga and 2.56 Ga: Na, Ca-Na (Act-Ab),
magnetite-rich bodies, replaced by K (Bt – FK) and/or
chlorite alteration. Cu-Au ore: breccias; e.g., Sequeirinho,
Bacaba, Bacuri, Visconde.
Na alteration
(Albite)
Na-Ca alteration Ca alteration
(Apatite+
(Albite+
Actinolite)
Actinolite)
Monteiro et al. (2008)
Fe oxide
(magnetite)
stage
Cu-Au
(chalcopyrite)
Sequeirinho deposit
NEOARCHEAN CARAJÁS IOCG SYSTEMS
Basement Rocks (gneiss)
Distal Na-Ca:
ACTINOLITE, hastingsite,
scapolite, allanite, chalcopyrite
Iron silicate –
enrichment:
grunerite, turmaline,
almandine
K alteration = Biotite
Cu-Au ore
Salobo deposit
Melo (2014)
Post-ore alteration = K alteration (Kf + hematite)
NEOARCHEAN CARAJÁS IOCG SYSTEMS
Salobo deposit
Melo (2014)
Ore forms lenticular bodies; no breccias
Cu-Au mineralization is disseminated and in seams
NEOARCHEAN CARAJÁS IOCG SYSTEMS
Igarapé Bahia/Alemão deposit
Mafic dikes (diabasediorite) (~2.6 Ga)
Basalts + BIFs (~2.75 Ga)
Breccia: main ore host
Clastic sedimentary rocks: arenite,
siltite, argillite  turbidites
Águas Claras Formation
(2.64 Ga): siliciclastic rocks
Steeply – dipping (75o) ore breccia
VALE (2000)
NEOARCHEAN CARAJÁS IOCG SYSTEMS
Igarapé Bahia/Alemão deposit
Mineralization: Magnetite + chalcopyrite + bornite ± cobaltite
± molybdenite ± Au ± U and REE minerals
PALEOPROTEROZOIC CARAJÁS IOCG
SYSTEMS
1.90- 1.87 Ga: K-alteration and chlorite predominant,
calcic (chl-ep-cc) and hydrolitic (ser-hem). Cu-Au ore:
crackle breccias, veins; e.g., Sossego and Alvo 118.
Monteiro et al. (2008)
Sossego deposit
CARAJÁS IOCG SYSTEMS
Different crustal levels: vertical zoning of hydrothermal
alteration
1.90- 1.87 Ga: Shallow
Ig. Bahia/
Alemão
level IOCG systems
emplaced after exhumation
of the Neoarchean IOCG
systems formed under brittle
regime.
Salobo
2.71-2.68 Ga: structuraIy-
controlled, emplaced at deep
levels.
Monteiro et al. (2008), Xavier et al. (2012)
CARAJÁS IOCG SYSTEMS: fluid regimes
Neoarchean IOCGs
Paleoproterozoic IOCGs
Torresi et al. (2012)
Highly saline aqueous fluids (35 to 70
wt% NaCl eq.)
Carvalho (2009)
low salinity (< 6 wt% NaCl eq.) CO2-rich
low to moderate salinity (5 up to 30
wt% NaCl eq.) aqueous fluid
CARAJÁS IOCG SYSTEMS: fluid regimes
Neoarchean
Paleoproterozoic
Sequeirinho deposit
Paleoproterozoic
Sossego deposit
Neoarchean
Pista deposit
Involvement of multiple
fluid types = mixing?
Carvalho 2009; Torresi et al., 2012
ORIGIN OF IOCG ORE FLUIDS, METALS
AND SULPHUR?
Skirrow (2011)
CARAJÁS IOCG FLUID SOURCES: Hydrogen and
oxygen isotope compositions
Deepseated/magmatic
component
Participation
of externallyderived (nonmagmatic)
fluids:
Alvo 118
Meteoric?
Seawater?
Monteiro et al. (2008)
Basinal?
CARAJÁS IOCG FLUID
SOURCES: boron isotopes
Boron is
predominantly
of non-magmatic
origin
Lighter boron
isotopes (-8 to
11‰) → light
boron from
felsic intrusive
and volcanic
host rocks.
XAVIER et al. (2008)
IGARAPÉ BAHIA VS. BREVES TOURMALINES:
δ11B - δD COMPOSITIONS
Igarapé Bahia =
heavier than
expected for
magmatic-derived
fluid
Breves = mostly
consistent with
magma-derived
brines
XAVIER et al. (2013)
δDH2O values calculated at 400°C using the tourmaline-H2O fractionation factor of Kotzer
et al. (1993)
CARAJÁS IOCG FLUIDS: Cl-Na-Br SYSTEMATICS
Neoarchean and
Paleoproterozoic
IOCGs:
Paleoproterozoic
Evaporative
brines (bittern
fluids) modified
by fluid-rock
reactions +
magmatic fluid.
Xavier et al (2009)
CARAJÁS IOCG FLUID SOURCES: sulphur isotopes
Paleoproterozoic
Neoarchean
Neoarchean
Heavier sulphur than
expected for a
magmatic source
Surface-derived
meteoric fluids could
have introduced SO42Thermochemical
reduction of sulphate
might then have
produced isotopically
heavy H2S
Sulphur from leaching
of igneous sulphides
Monteiro et al. 2008; Pestilho 2011; Torresi et al. 2012
In Situ MULTIPLE SULPHUR ISOTOPE ANALYSES
Salobo
Sossego
1,2
5,6
3,4
10
9
19
18
17
16 15
7,8
13
14
1,2
3,4
5,6
9,10
7,8
CAMECA IMS 1280 ion microprobe – UWA (Australia)
Sossego
mantle
SULPHUR ISOTOPES AND THE MIF FACTOR
Neoarchean
Neoarchean
Neoarchean
Paleoproterozoic
mantle
Santiago et al. in prep.
Neoarchean IOCGs  non-zero Δ33S V-CDT values  mass independent
fractionation (MIF) = sulphur of the exogenic sulphur cycle.
Paleoproterozoic IOCGs also show mass independent fractionation (MIF) 
inherited from Archean sulphur.
CONCLUDING REMARKS
Carajás IOCGs have formed by multiple episodes of fluid
circulation and hydrothermal alteration in the Neoarchean
(2.71–2.68 Ga and 2.56 Ga) and Palaeoproterozoic (1.90–
1.87 Ga).
Neoarchean IOCGs tend to be deeper systems than
the Palaeoproterozoic IOCGs.
Neoarchean IOCG mineralisation (2.71–2.68 Ga and 2.56
Ga) show no overlap in time with any significant
magmatism recorded in Carajás.
Neoarchean IOCGs: closure of the Carajás Basin and
deep-seated circulation of non-magmatic brines, metal
leaching from the country rocks and Cu-Au mineralisation
along regional structures via fluid mixing (e.g., meteoric,
magmatic).
CONCLUDING REMARKS
Palaeoproterozoic deposits (1.90–1.87 Ga) display a
temporal link with 1.88 Ga A-type granite magmatism.
Paleoproterozoic IOCGs: 1.88 Ga A-type granitic
magmatism could have acted as source of heat to move
and mix non-magmatic brines with other fluid types (e.g.
magmatic, meteoric).
High T & high salinity enhance metal transport 
presence of evaporites is one of the key elements in well
endowed provinces.
Mixing of different fluid sources is a critical attribute to
the genesis of the IOCG systems worldwide.