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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IOCG fluids

porphyry fluids

Great Bear

Cloncurry IOCG

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Rb/

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t rat

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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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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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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; brian.rusk@wwu.edu

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

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TH (o C)

Salinidade (% p.e. NaCl)

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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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100000

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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