a comparison of fluid origins and compositions in iron … · 2015-04-16 · low salinity...
TRANSCRIPT
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
Low sulphidationepithermal deposit
Propyliticalteration
Propyliticalteration
PotassicalterationMetasedimentary
Basement
VolcanicRocks
Felsic intrusion
Limestone
Phyllicalteration
Intrusive Breccia
Breccia
Argillicalteration
High sulphidationepithermal deposit
Porphyry Cu deposit
Skarn & manto deposit~1 km
Barren interior
Barton et al., 2004, 2014
Potential genetic models leading to observed alteration zonation in iron-oxide-
copper-gold deposits
El Salvador Wood Camp, AZ
Alumbrera Butte
Vapor and brine inclusions are typical of porphyry copper deposits
Low salinity CO2-bearing fluids supply fluids from magma below to hydrothermal system above
Heinrich et al., 1999
Bajo de la Alumbrera
Rusk et al., 2004; Landtwing, 2010
Fluid unmixing in porphyry Cu deposits
Butte Henderson, CO El Salvador Climax, CO
Mineral Park, AZ Henderson, Porphyry-Mo, CO, USA
El Salvador, Porphyry-Cu-Mo, Chile
Mineral Park, Porphyry Cu-Mo, AZ, USA
Climax porphyry-Mo, CO, USA
El Teniente, Porphyry Cu-Mo, Chile
Los Pelambres, Porphyry-Cu-Mo, Chile
Yerrington, Porphyry-Cu, NV, USA
Chuquicamata, prophyry Cu-Mo, Chile
They are present in MANY significant porphyry-Cu-Mo deposits
B50 inclusions are common in many porphyry type deposits
Butte, Porphyry-Cu-Mo, MT, USA
IOCG Fluid inclusions (a few key differences from PCDs)
Hypersaline (multi-solid ) Halite-saturated (L-V-H)
Water-NaCl (L-V) CO2-only (CO2L)
The 4 types of fluid inclusions most common to IOCGs
Fluid inclusions in IOCG deposits
• Dominated by halite-saturated brines
• Vapor-rich inclusions are rare
• Salty fluids do not appear to be derived from fluid immiscibility
Time versus intensity
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.
Fluid inclusion LA-ICP-MS, Western Washington University
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Na/
Ca
(wt r
atio
)
Na/K (weight ratio)
IOCG fluids
porphyry fluids
Comparison of brines compositions
• Porphyry-Cu (Mo-Au) deposits: Bingham, Butte, Los Pelambres, Bata Hijau, and Yerington
• IOCGs: Sossego, Sequerino, Igarape Bahia, Alvo 118, Pista
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Na/
Ca (w
t rat
io)
Na/K (weight ratio)
IOCG fluids
porphyry fluids
Great Bear
Cloncurry IOCG
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Rb/
Sr (w
t rat
io)
Na/K (wt ratio)
IOCG fluids
porphyry fluids
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Sr (p
pm)
Ba (ppm)
IOCG fluids
porphyry fluids
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1000000
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K (p
pm)
Rb (ppm)
IOCG fluids
porphyry fluids
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).
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Sr (p
pm)
K (ppm)
IOCG fluids
porphyry fluids
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Cu (p
pm)
Fe (ppm)
IOCG fluids
porphyry fluids
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Zn (p
pm)
Mn (ppm)
IOCG fluids
porphyry fluids
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Zn (p
pm)
Pb (ppm)
IOCG fluids
porphyry fluids
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Zn (p
pm)
Fe (ppm)
IOCG fluids
porphyry fluids
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.
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Ave
rage
conc
entr
atio
n (p
pm)
Porphyry fluids
IOCG fluids
Na K Ca Mn Fe Cu Zn Rb Sr Ba Pb
Porphyry and IOCG brine compositions compared
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
Br/C
l
0.0001 Evaporite dissolution
0.001
0.01
0.0002
“magmatic”
Most porphyry-Cu brines
Next slide
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
Seawater evaporation curve
Xavier et al., 2009, next
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.
Halogens from Ernest Henry, Cloncurry, Australia
Br/C
l
0.0001 Evaporite dissolution
0.001
0.01
0.0002
“magmatic”
Most porphyry-Cu brines
chalcopyrite
pyrite
Quartz
Late carb
Barton et al., 2004, 2014
Potential genetic models leading to observed alteration zonation in iron-oxide-
copper-gold deposits
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
Transport TRAP Sources
e.g. Structural traps and fluid chemical changes: cooling, depressurization, fluid neutralization, fluid mixing, fluid boiling, fluid-rock reactions.
Fluids Physical transport: faults, fractures, breccias, porous sediments or tuffs, pressure and temperature evolution
Chemical transport: fluid composition, ligands, gases, metals, pH, redox state, etc
Other solutes
e.g. magmatic fluids, groundwater, seawater, bittern brines, metamorphic fluids, mantle fluids, evaporite dissolution
magmas, wall rocks, pre-existing ore deposits
Metals Ligands
• 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.
• 1. Magmatic fluids -Direct exsolution from magmas following water-saturation 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.
What is the origin of these high salinity fluids?
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
Log (I/Cl)m
Log
(Br/
Cl)m
Columbian emeralds: high T ev aporite dissolution
Capitan granite: halite assimilation
SW England granites
Py renees: basinal brines, low grade metamorphism
Earth
Seawater
-2
-3
-4
-6 -5 -4
PIXE data
Bulk crush- leach data
Ernest Henry
Starra
Halogens in earth fluids
Chlorine, Bromine, and Iodine studies are increasingly being applied to the study of fluid inclusions to infer the origin of fluids. 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
Bubble sizes: 35-65% bubble 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% Homogenization temperatures ~320-420 degrees C
A less-recognized, but common inclusion type: B50s
B50 fluid inclusions from Climax porphyry Mo deposit
B50s
(Butte, Bingham, Mineral Park, Pelambres, Climax, El Teniente, Chuquicamata, Henderson) (Rusk et al, 2008, Redmond et al., 2004, Klemm et al., 2007)
• 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 unmixing
Fluid sources and geochemical footprints in
IOCG deposits
Brian Rusk
Western Washington University, Bellingham, WA, USA; [email protected]
Consultant: Advanced Geoscience Investigations
SEG short course on IOCG deposits, Cape Town, South Africa, February, 2015
How do IOCG deposits form and how do we recognize them? Fluids, fluid processes, genetic models and footprints
Brain Rock
USTs from Mineral Park, Arizona
USTs from Henderson, CO
Deep quartz veins from Butte
Quartz-aplite vein dike from Yerington, NV
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
How common are tHese “parental” fluid inclusions in otHer porpHyry cu (mo-au)
deposits?????
Fluid inclusion Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)
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.
Quartz
• 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?
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
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)
Fluid pressure and temperature
LA-ICP-MS signal of a B50 fluid inclusion from Mineral Park, AZ
Contamination and explosion of shallow fluid inclusion B50 fluid inclusion
Na
Si
K
Ti Cu
Zn Sr
Simultaneous determination of pressure, temperature, and composition
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70
100
200
300
400
500
600 am02C LV am02C LVS am39K LV am39K LVS am39L LV am39L LVS
TH (o C)
Salinidade (% p.e. NaCl)
0 5 10 15 20 25 30 35 40 45 50 55 60 65
100
200
300
400
500
600am. 319/133,36
ifs H2O-NaCl (LVS) ifs H2O-NaCl (LV)
ifs H2O-NaCl (LV) ifs H2O-NaCl (LVS)
TH(
o
C)
Salinidade (% p.e. NaCl)
am. 319/107,31
0 5 10 15 20 25 30 35 40 45 50100120140160180200220240260280300320340360380400
Inclusões Tipo II (L+V+S)
Inclusões Tipo I (L+V)Qtz em veio sulfetado
TH (C
o )
Salinidade (% em peso equiv. NaCl)
Sequeirinho
Sossego
Pista
Torresi (2009); Carvalho (2009) Sossego IOCG deposit
FLUIDS IN IOCG DEPOSITS OF THE CARAJÁS MINERAL PROVINCE, BRAZIL
Ti in quartz thermobarometer (Thomas et al., 2010)
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
Ti Concentrations Isochores
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)
V
Mag
Halite
S1
S2
S3
15 microns
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
Pollard, 2001
SUMMARY OF FLUID INCLUSION TYPES
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.
Si Cl K Ca
Mn Fe Cu Zn Ba Starra fluid inclusion: Williams et al., 2001 Econ. Geol.
Fluid metal concentrations: PIXE elemental maps
Ca-rich brines are common Elevated metal concentrations High Ba concentration suggests S-deficient fluid
World-wide porphyry copper deposits
Fe and Cu concentrations in Cloncurry IOCGs and regional alteration
Highest Cu concentrations found in magmatic-hydrothermal 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 Data of Baker, Mustard, Williams, Ryan, Fu and Mark
Cu-rich brines from the porphyry Cu deposit in El Salvador, Chile Such inclusions are rare in IOCG deposits
Where is the “C” in IOCG fluids?
Fluid inclusion Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)
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.
Quartz
Fluid inclusion Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)
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10000
100000
0 50 100 150 200 250 300Time (seconds)
Cou
nts
Na23
K39
Mn55
Fe57
Cu63
Zn66
As75
Rb85
Sr88
Mo95
Ag107
Ba137
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.
Compositions of hydrothermal fluids
.
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 CO2-rich 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)
Kendrick et al. 2008, Fisher and Kendrick, 2008
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
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 (5000-20000 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
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 ore-deposit above.
B50 inclusions trapped a single phase hydrothermal fluid at pressures greater than the unmixing solvus.
Bodnar (1995)
Modified from Lowell and Guilbert, 1970
Simplified alteration patterns in a porphyry Cu system
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