A Comparison of Fluid Origins and Compositions in Iron Oxide

A Comparison of Fluid Origins and Compositions in Iron Oxide

A Comparison of Fluid Origins and
Compositions in Iron Oxide-copper-gold
and Porphyry-Cu (Mo-Au) Deposits
Brian Rusk, Poul Emsbo,
Roberto Xavier, Louise
Corriveau, Nick Oliver and
Dexian Zhang
B50s
Magmatic-Hydrothermal System
• Common Alteration styles
High sulphidation
epithermal deposit
Low sulphidation
epithermal deposit
Argillic
alteration
Propylitic
alteration
Intrusive
Breccia
Volcanic
Rocks
Phyllic
alteration
Propylitic
alteration
Breccia
Porphyry Cu deposit
Metasedimentary
Basement
~1
Barren interior
Potassic
alteration
Limestone
km
Skarn & manto deposit
Felsic intrusion
Potential genetic models leading to
observed alteration zonation in iron-oxidecopper-gold deposits
Barton et al., 2004, 2014
El Salvador
Wood Camp, AZ
Vapor and brine inclusions are typical of
porphyry copper deposits
Alumbrera
Butte
Fluid unmixing in porphyry Cu deposits
Heinrich et al., 1999
Bajo de la Alumbrera
Low salinity CO2-bearing fluids
supply fluids from magma below to
hydrothermal system above
Rusk et al., 2004; Landtwing, 2010
B50 inclusions are common in many porphyry
type deposits
Butte, Porphyry-Cu-Mo, MT, USA
Henderson, Porphyry-Mo, CO, USA
El Salvador, Porphyry-Cu-Mo, Chile
Climax porphyry-Mo, CO, USA
Mineral Park, Porphyry Cu-Mo, AZ, USA
Chuquicamata, prophyry Cu-Mo, Chile
Los Pelambres, Porphyry-Cu-Mo, Chile
El Teniente, Porphyry Cu-Mo, Chile
Yerrington, Porphyry-Cu, NV, USA
They are present in MANY
significant porphyry-Cu-Mo
deposits
Butte
Mineral
Park, AZ
Henderson,
CO
El Salvador
Climax, CO
IOCG Fluid inclusions (a few
key differences from PCDs)
Hypersaline (multi-solid )
CO2-only (CO2L)
Halite-saturated (L-VH)
Water-NaCl (L-V)
The 4 types of fluid inclusions most common to IOCGs
Fluid inclusions in
IOCG deposits
• Dominated by halitesaturated brines
• Vapor-rich inclusions
are rare
• Salty fluids do not
appear to be derived
from fluid
immiscibility
LAICPMS analysis of fluid inclusion
Using a laser routed
through a petrographic
microscope, individual fluid
inclusions greater than ~10
microns can be analyzed for
~10-20 elements
simultaneously with
detection limits in the range
of a few ppm.
Time versus intensity
Fluid inclusion LA-ICP-MS, Western Washington University
Comparison of brines compositions
1000
1000
Na/Ca (wt
Na/Ca
(wtratio)
ratio)
100
100
10
10
IOCG fluids
IOCG
fluidsfluids
porphyry
11
• Porphyry-Cu (Mo-Au)
deposits: Bingham,
Butte, Los Pelambres,
Bata Hijau, and
Yerington
porphyry
fluids
Great Bear
Cloncurry IOCG
0.1
0.1
0.01
0.1
1
10
Na/K
ratio)
Na/K (weight
(weight ratio)
100
• IOCGs: Sossego,
Sequerino, Igarape
Bahia, Alvo 118, Pista
1000000
10
1
IOCG fluids
porphyry fluids
K (ppm)
Rb/Sr (wt ratio)
100
100000
IOCG fluids
porphyry fluids
10000
0.1
0.01
1000
0.1
1
10
100
1
Na/K (wt ratio)
10
100
1000
10000
Rb (ppm)
100000
IOCG fluids
100000
porphyry fluids
10000
1000
IOCG fluids
100
porphyry fluids
10
Sr (ppm)
Sr (ppm)
10000
1000
100
10
1
1
10
100
1000
Ba (ppm)
10000
100000
1
1000
10000
100000
K (ppm)
Fluids from IOCG depsosits are enriched in Ca, Ba and Sr relative to
magmatic fluids from porphyry deposits. Porphyry fluids have higher
K/Rb ratios, Rb/Sr ratios and lower Na/K ratios (More K).
1000000
1000000
100000
10000
IOCG fluids
1000
Cu (ppm)
Zn (ppm)
100000
porphyry fluids
10000
1000
100
IOCG fluids
10
100
100
1000
10000
1
100000
100
Pb (ppm)
1000
10000
100000
1000000
Fe (ppm)
1000000
1000000
IOCG fluids
100000
100000
porphyry fluids
Zn (ppm)
Zn (ppm)
porphyry fluids
10000
10000
IOCG fluids
1000
1000
100
100
100
1000
10000
Fe (ppm)
100000
1000000
porphyry fluids
100
1000
10000
100000
1000000
Mn (ppm)
Nearly all analyzed IOCG brines from Carajas contain <200 ppm Cu, 1 to 2
orders of magnitude less Cu than in porphyry Cu brines. Porphyry brines
are also enriched in Zn, Mn, and Pb, but contain similar Fe concentrations.
Porphyry and IOCG brine compositions compared
Average concentration (ppm)
100000
Porphyry fluids
IOCG fluids
10000
1000
100
0
Na
K
Ca Mn Fe Cu Zn Rb Sr Ba Pb
12
IOCG brines are strongly enriched in Ca and Sr and Ba and strongly depleted
in K, Cu, Zn, and Mn relative to porphyry brines.
Halogens in ore fluids
0.0001
Cl/Br ratios
differentiate
source of
salinity. They
most clearly
differentiate
basinal bittern
brines (and
metamorphic
fluids) from
magmatic fluids
from fluids that
have dissolved
evaporites
Most porphyry-Cu brines
“magmatic”
Seawater evaporation curve
Next slide
0
.
0
0
0
2
0.001
0.01
Br/Cl
Evaporite
dissolution
Halogens from the Carajas District
Mixing between magmatic fluids and bittern brines
suggested to form the range of deposits in Carajas. Each
one with its own individual signature.
Xavier et al., 2009, next
Halogens from Ernest Henry,
Cloncurry, Australia
0.0001
Most porphyry-Cu brines
chalcopyrite
“magmatic”
pyrite
0
.
0
0
0
2
Quartz
Late carb
0.001
0.01
Br/Cl
Evaporite
dissolution
Potential genetic models leading to
observed alteration zonation in iron-oxidecopper-gold deposits
Barton et al., 2004, 2014
Conclusions
• Unlike salty fluids in porphyry copper deposits,
hypersaine brines in IOCG deposits do not appear
to be generated by fluid immmiscibility.
• IOCG brines are compositionally distinct from
porphyry copper brines and contain more Sr, Ba,
and Ca, and less metals
• Whereas halogens in PCDs are compatible with
dominantly magmatic fluid sources, halogen data
suggests widely variable fluid sources in IOCGs,
typically including a significant component of
basinal brines.
Questions???
Hydrothermal fluids in the
formation of IOCGs
Ligands
Metals
Sources
Fluids
Other
solutes
magmas, wall rocks, preexisting ore deposits
e.g. magmatic fluids,
groundwater, seawater,
bittern brines, metamorphic
fluids, mantle fluids,
evaporite dissolution
Transport
Physical transport: faults,
fractures, breccias, porous
sediments or tuffs, pressure and
temperature evolution
Chemical transport: fluid
composition, ligands, gases,
metals, pH, redox state, etc
TRAP
e.g. Structural traps and
fluid chemical changes:
cooling,
depressurization, fluid
neutralization, fluid
mixing, fluid boiling,
fluid-rock reactions.
• Butte fluid unmixing diagram
• Fluid inclusions in IOCG deposits
13 minutes. 15 slides.
• Set up the problem….Understanding the origin
of fluids that form IOCG deposits. Simple
models of PCD formation, well understood,
magma derived-not so simple for IOCGs
• To make IOCG genetic models
• Compare fluids from porphyry systems where
we understand the fluid systems quite well
with IOCG systems where we understand less.
contents
• Summarize fluid inclusion characteristics
• Talk about fluid unmixing in porphs to
generate vapor and brine flincs
• Then talk about abundant brines in IOCGs, but
general lack of vapors and evidence for
unmixing.
• So calling into question the validity of magmas
as salty fluid sources in IOCGs.
Intro set the stage
• Many models of IOCG formation, but porphyry
models are easy….
• Include some images of the samples from
Carajas that we analyzed.
What is the origin of these high
salinity fluids?
• 1. Magmatic fluids -Direct exsolution from magmas following watersaturation during ascent or crystallization (700->1000°C) or
generated by fluid immiscibility leading to the production of vapors
and brines
• 2. Evaporite dissolution Waters - derived from sea water (+- other
sources) waters trapped in sedimentary basins, which acquired high
salinity due to dissolution of sedimentary evaporite sequences
• 3. Bittern brines – brines trapped in sedimentary basins that derived
their salinity by evaporation of H2O
• 4. Metamorphic Waters - Fluids of variable salinity and CO2-content
that have equilibrated with rocks during metamorphism at T>300°C.
B50 Fluid compositions
• Rare double bubbles, but
CO2-H2O clathrates are
common
• Most contain 2-10 mol%
CO2
• Mostly 2-5 wt% NaCl
equiv.
• Homogenize between
~325 and 400
• Densities between ~0.5
and 0.7
B50 fluid inclusions from Climax
Halogens in earth fluids
PIXE
data
Bulk crushleach data
Py renees: basinal brines,
low grade metamorphism
Starra
-2 Ernest
Log (Br/Cl)m
Henry
Earth
Seawater
Chlorine, Bromine, and
Iodine studies are
increasingly being applied
to the study of fluid
inclusions to infer the
origin of fluids.
-3
SW England
granites
Columbian emeralds:
high T ev aporite
dissolution
-4
Capitan granite:
halite assimilation
-6
-5
Log (I/Cl)m
-4
Cl/Br ratios differentiate
source of salinity. They
most clearly differentiate
basinal bittern brines (and
metamorphic fluids) from
magmatic fluids from fluids
that have dissolved
evaporites
A less-recognized, but common inclusion type: B50s
Bubble sizes: 35-65% bubble
B50s
CO2 clathrates common, double
bubbles rare:
Clathrate melting: +5 -+9
Ice melting temperatures: -2 to -6
Salinities in the range of ~2-9 wt %
NaCl equiv
CO2 concentrations of up to ~15 mol%
B50 fluid inclusions from Climax porphyry
Mo deposit
(Butte, Bingham, Mineral Park, Pelambres,
Homogenization temperatures ~320Climax, El Teniente, Chuquicamata, Henderson)
420 degrees C
(Rusk et al, 2008, Redmond et al., 2004, Klemm et
al., 2007)
Fluid unmixing
• Porphyry Cu deposits
are dominated by
inclusions containing
brine and vapor
• These fluids form from
unmixing of a
“parental” fluid of
“magmatic” origin
• The parental fluid has
been identified as a low
salinity CO2- bearing
fluid in several deposits
B50s
Redmond et al., 2004, Klemm et al., 2007, Rusk et al., 2008
Fluid sources and
geochemical footprints in
IOCG deposits
How do IOCG deposits form and how do we recognize them?
Fluids, fluid processes, genetic models and footprints
Brian Rusk
Western Washington University, Bellingham, WA, USA; brian.rusk@wwu.edu
Consultant: Advanced Geoscience Investigations
SEG short course on IOCG deposits, Cape Town, South Africa, February, 2015
How common are these “parental” fluid
inclusions in other porphyry Cu (Mo-Au)
deposits?????
Brain Rock
Quartz-aplite vein dike from Yerington, NV
USTs from Mineral
Park, Arizona
USTs from
Henderson, CO
Veins formed at high pressures and
temperatures: Deep veins formed under
lithostatic pressures at near magmatic
pressures and temperatures. Cu-Fe sulfide
poor and quartz-rich with potassic
alteration or no obvious alteration
Deep quartz veins from Butte
Fluid inclusion Laser Ablation-Inductively Coupled
Plasma-Mass Spectrometry (LA-ICP-MS)
Quartz
Using a laser routed through a
petrographic microscope,
individual fluid inclusions greater
than ~10 microns can be analyzed
for ~10-20 elements
simultaneously with detection
limits in the range of a few ppm.
• Maybe even a Ti in quartz versus isochore
diagram
• Yeah maybe a PT diagram showing PT
conditions at butte or similar. And then
something showing the Cu-rich nature of B35
inclusions too?
Fluid pressure and temperature
Even though they homogenize ~350
degrees C, a number of lines of
evidence suggest that many B50s are
trapped at temperatures closer to
550-650 degrees C.
For example:
S-isotopes (Field et al., 2005)
Ti in quartz (Rusk et al., 2006)
Common presence in brain rocks
and vein dikes
Dominance in deep sulfide-poor,
quartz rich veins with potassic
alteration (Redmond et al., 2004,
Rusk et al., 2008)
Combining quartz trace elements with fluid
inclusion analysis to determine pressure,
temperature, and composition of hydrothermal
fluids: An example from brain rock from Mineral
Park, AZ
Simultaneous determination of pressure,
temperature, and composition
Contamination and explosion of
shallow fluid inclusion
LA-ICP-MS
signal of a
B50 fluid
inclusion from
Mineral Park,
AZ
B50 fluid inclusion
Na
K
Si
Ti
Cu
Zn
Sr
Sequeirinho
600
am02C LV
am02C LVS
am39K LV
am39K LVS
am39L LV
am39L LVS
500
TH (oC)
400
FLUIDS IN IOCG
DEPOSITS OF THE
CARAJÁS MINERAL
PROVINCE, BRAZIL
300
200
100
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
Torresi (2009); Carvalho (2009)
Salinidade (% p.e. NaCl)
Sossego IOCG deposit
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
380
Sossego
Qtz em veio sulfetado
Inclusões Tipo I (L+V)
Inclusões Tipo II (L+V+S)
360
340
320
300
400
280
TH (Co)
C)
oTH
( 300
260
240
220
200
180
200
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
Salinidade (% em peso equiv. NaCl)
45
50
Ti Concentrations
Ti in quartz thermobarometer (Thomas
et al., 2010)
Isochores
Isochores for a ~3.5 wt% NaCl equiv, ~6
mol% CO2 fluid; density=~0.62-0.65
g/cm3 (calculated using data of Bowers
and Helgeson, 1984)
The intersection of calculated
isochores with isopleths of Ti
concentrations 100-130 ppm Ti gives
temperatures between 560 and 610 C
and pressures between ~1.7 and ~2.2
kbars
Introduction
• Porphyry Cu deposits
are dominated by
inclusions containing
brine and vapor
• These fluids form from
unmixing of a
“parental” fluid of
“magmatic” origin
• The parental fluid has
been identified as a low
salinity CO2- bearing
fluid in several deposits
B50s
Redmond et al., 2004, Klemm et al., 2007, Rusk et al., 2008
Multi-solid fluid inclusions: L-V-Halite ±
multiple solid duaghter minerals
• Th = 200-520° C
• 32-55 wt% NaClequiv.
– ± ferropyrosmalite
((Fe,Mn) 8Si 6O 15(OH,Cl)10
– ± sylvite
– ± Fe chloride
– ± magnetite
– ± hematite
– ± calcite
– ± kutnahorite
(Ca(Mn,Mg,Fe++)(CO3)2)
15 microns
S1
Halite
V
S2
Mag
S3
Mark et al., 2006
Variable fluid salinities and temperatures
Fluid inclusion data, multiple sources-see references
At least 3 and possibly 4 or 5
separate fluids identified
SUMMARY OF FLUID
INCLUSION TYPES
Pollard, 2001
Fluid bulk composition summary:
• High salinity (30-60 wt% NaCl equiv) Ca-rich brines
trapped at temperatures between 200 and 550°C
• Multi-solid inclusions more common in ore deposits
than in regional alteration
• More dilute fluids common- possible
mixing/dilution
• CO2-rich fluids common, but significance unclear
Fluid compositions and
metal contents
• SO that brings us to the goal of this
presentation to compare fluid characteristics
in porphyry and IOCG deposits to help to
constrain the ore genesis models of these
deposit types.
Fluid metal concentrations: PIXE
elemental maps
Ca-rich brines are common
Elevated metal
concentrations
High Ba concentration
suggests S-deficient fluid
Si
Cl
K
Ca
Cu
Ba
Fe
Mn
Zn
Starra fluid inclusion: Williams et al., 2001 Econ. Geol.
Fe and Cu concentrations in Cloncurry
IOCGs and regional alteration
Worldwide
porphyry
copper
deposits
Data of Baker, Mustard, Williams, Ryan, Fu and Mark
Highest Cu
concentrations found
in magmatichydrothermal
magnetite deposit with
NO Cu mineralization
Most IOCGs contain
between ~50 and 300
ppm Cu
Porphyry Cu
brines typically
10 to 100 times
more Cu than
IOCG brines
Where is the “C” in IOCG fluids?
Cu-rich brines from the
porphyry Cu deposit in El
Salvador, Chile
Such inclusions are rare in IOCG
deposits
Fluid inclusion Laser Ablation-Inductively Coupled
Plasma-Mass Spectrometry (LA-ICP-MS)
Quartz
Using a laser routed through a
petrographic microscope,
individual fluid inclusions greater
than ~10 microns can be analyzed
for ~10-20 elements
simultaneously with detection
limits in the range of a few ppm.
Compositions of hydrothermal fluids
Fluid inclusion Laser Ablation-Inductively Coupled Plasma-Mass
Spectrometry (LA-ICP-MS)
100000
Na23
K39
10000
Mn55
Counts
Fe57
1000
Cu63
Zn66
100
As75
Rb85
Sr88
10
Mo95
Ag107
1
0
50
100
150
Time (seconds)
200
250
Ba137
300
Pb208
With a 193 nm eximer laser shot through a petrographic microscope, individual
quartz-hosted fluid inclusions greater than ~10 microns can be analyzed for ~10-20
elements simultaneously.
Significance to IOCG deposits
 Did we analyze the wrong brines in all of the Carajas deposits?
How about Ernest Henry, Osborne, SWAN and Eloise? Are ore fluids
that form IOCGs less Cu-rich than ore fluids that form porphyry
deposits?
.
 CO2 (and S)-rich fluids have been implicated in transporting Cu,
Au, and As in magmatic porphyry Cu systems, when fluids unmix into
vapors and brine.
 Could CO2-rich fluids that are commonly observed in IOCG
deposits transport metals (especially Cu, Au, and As)? Although CO2rich fluids are observed in the vast majority of IOCGs, as far as I know,
no chemical analyses of these fluids exist
• Maybe a chart showing compositions of
porphyry fluids from various deposits…
ALL OF THE ABOVE FLUID SOURCES
HAVE BEEN IMPLICATED IN IOCG
MINERALIZATION- EVEN WITHIN A
SINGLE DEPOSIT
Halogens in Mantoverde IOCG
Mixing of magmatic fluids with bittern brines likely at Mantoverde as well
Marschik et al., 2011 (SGA)
Noble gas isotopes
40Ar/36Ar ratios imply that the
source fluids for Ernest Henry are
distinctly different than the source
fluids for Osborne and Eloise. Ernest
Henry has a distinct magmatic
component that mixed with
metamorphic fluids and basinal
brines. Osborne and Eloise formed
from basinal brines and show no
magmatic component to their noble
gas signatures
Kendrick et al. 2008, Fisher and Kendrick, 2008
Fluid metal and trace element
composition summary
• Fluids in IOCG deposits are Ca-enriched
brines and have distinctly different
compositions to magma-derived porphyry
Cu brines.
• The Ca-Ba-Sr-(Pb)-rich nature of these fluids
likely results from extensive interaction
between brines and wall rocks, altering
feldspars to albite
• IOCG Cu concentrations of <100 to ~500 ppm
are far less than is typical in porphyry Cu
brines, however a few Cu-enriched (500020000 ppm) fluids have been identified
Butte, Montana porphyry Cu geology
Rusk et al., 2004 (Chemical Geology)
Rusk et al.2008 (Economic Geology)
Bingham Canyon, Utah
Redmond et al., 2004 (Geology)
Trapping conditions of B35 and B60 fluid inclusions
B50 inclusions
trapped a single
phase hydrothermal
fluid at pressures
greater than the
unmixing solvus.
Bodnar (1995)
In many porphyry deposits, B50 fluids are the
original magmatically-derived “parental” source
fluid by which volatiles and metals were
transported from the magma below to the oredeposit above.
Simplified alteration patterns
in a porphyry Cu system
Modified from Lowell and Guilbert, 1970
Pre-Main Stage geology
Rusk et al., 2004 (Chemical Geology)
Rusk et al.2008 (Economic Geology)
Trapping conditions of B35 and B60 fluid inclusions
Bodnar (1995)
Show the data for halogens in PCDs