Lecture M1: Mineral Systems Overview Why a MS perspective ... · Slide after: A. Barnicoat. 3 ... Magmatic fluids. Meteoric fluids Surface derived needs rainfall and topography wide

Mineral Systems

Q3 Fluid reservoirs

1

predictive mineral discovery*Cooperative Research Centre

A legacy for mineral exploration science

2



A. Gradient inhydraulicpotential

B. Permeability

C. Solubilitysensitivity to P, T, C

D. Spatialgradient of P, T, C

E. Time (duration)

Key Parameter

is reflected in

ExplorationMineral System

scale-dependent translation

5 Questions1. Geodynamics2. Architecture3. Fluid

reservoirs4. Flow drivers &

pathways5. Deposition

Terrain Selection

Area Selection

Drill Targeting

Slide after: A. Barnicoat

3



Liebscher&Heinrich 2007

Potential fluid sources (basins?)

4



Meteoric water

Sea waterBittern

Metamorphic fluid

Mantle fluid

BasinEvaporites

Magmatic fluids

Meteoric fluidsSurface derived

needs rainfall and topography

wide range of chemistries anions: sulphate, bicarbonate, chloride or acetate

Sulphate: most important in shallow groundwaters

Bicarbonate: increases with depth

Acetate: may dominate in groundwaters at T ≈ 80-120 °C

Meteoric waters may be (largely) unmodified, may contribute to basinal waters or to magmatic fluids.

5



Meteoric fluids

6



SMOW

Basinal fluids

formation water water present in pores and fractures immediately prior to drilling

Connate water water trapped with the sediment and subsequently unmodified (meteoric or seawater)

modified meteoric water

Many basinal waters are of mixed origin with marine, meteoricand bittern components

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Basinal fluids - origins

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Meteoric origin

recent not recent

Basinal fluidsChemistry

major cations Na, K, Ca and Mg increase in general with increasing salinity (total dissolved solids)

The concentration of many cations is controlled by reaction withmineral phases including carbonates, feldspar, illite and chlorite

SiO2 is controlled by equilibration with metastable silica polymorphs such as opal at low temperatures, and with quartz at temperatures above about 80°C

pH increases with increasing salinity , a function of fluid rockinteraction as exemplified by the reaction

NaAl3Si3O10(OH)2 + 6SiO2 + 2NaCl = 3NaAlSi3O8 + 2H+ + 2Cl-

Chloride is the dominant anion in waters of seawater salinity and above

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Basinal fluids - salinity

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Salinity sources

• Dissolution of evaporites

• Descent of bittern brines from surface

Metamorphic fluids

‘Metamorphic’ fluids have mixed origin– Devolatilisation– External fluids reacting with metamorphic rocks

Devolatilisation– During heating, volatiles released– Constant temperature leads to no fluid generation– Decrease in temperature leads to resorption of residual

fluid by retrogression

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Metamorphic fluids

Devolatilisation

upflow & fluid focussing

increase in permeability

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Metamorphic fluids

13



tholeiiticbasalt

high-Cagranlite

Magmatic fluids

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Intrusion-related:CO2- H2O-NaCl

IOCG:NaCl-CO2- H2O Orogenic Au:

H2O- CO2- NaCl

Porphyry:H2O-NaCl

Orogenic Au: CO2- H2O-NaCl

Magmatic fluids

Ore deposits associated with magmatic-hydrothermal fluids:

• Porphyry Cu, Au and Mo deposits(A)

• High-sulphidation epithermal deposits associated with porphyries

• Intrusion-related gold and other

metal deposits, linked to reduced intrusions (B)

• Iron oxide – copper –gold (IOCG) deposits (C)

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A

A

B

B

B

C

C

C

C

Magmatic fluids – volatiles

Porphyries are characterised by H2O-NaCl fluids that are highin sulphur

Intrusion-related systems are associated with CO2-H2O fluidswith limited NaCl contents; sulphur contents of the depositsand by inference the fluids are relatively low.

IOCG systems are dominated by NaCl-rich melts and CO2-richfluids. Sulphur contents of the fluids are relatively low.

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Magmatic fluids – volatiles

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Mantle fluids

Possible source of reduced components

Subduction-related processes

CO2 used to be often considered to be mantle derived

Mantle redox more variable than initially envisaged- Possible source of (very) reduced fluid

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MantleMantle

Chlorine (HCl, NaCl)Chlorine (HCl, NaCl)Kendrick et al., 2008

40Ar/ 36Ar Constraints On Crust/Mantle Sources

Fluid reservoirs

3 end-member fluids:1) ambient crustal aqueous fluid, with

low concentrations of salt and volatiles

2) magmatic, dominated by CO2 and SO2

3) ‘deep-earth’, highly reduced CH4 -N2 - H2 - fluid - acid volatiles (H2S, HCl ±HF), - noble gases (Ne and Ar) of mantle origin,

- possibly metal hydrides (e.g. NaH, MgH2, AlH3 and SiH4)

- and probably Au

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(H, Na, N, C, Cl, metals)

10km

100 km

1000 km

H2 flux

seal

Melts &

CO2-SO2 fluids

Metal Province

Aqueous domain

Fluid 2

Fluid 1

Fluid 3

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-31

-30

-29

-28

-27

-26

-25

-24

-23

-22

-2.5-2.3-2.1-1.9-1.7-1.5-1.3-1.1-0.9-0.7-0.5-0.3-0.1log KCl/NaCl

log

fO2

Oxidize

d

Chlorite+

Magnetite

Tourmaline

Biotite+ Mt

Epidote

hmmt

mt am

CO2 aqCH4 aq

hm am

mt

Anhydritesaturation

HSO4 –

H2S aq

py

py

popoam

AlbiteAlbite + Qtz

H2S

aq

HS

-

am

am

ampy

400°CG G’

AmphibolePo

Pyrite

Amphibole

Amphibole+

BiotiteTa

lcS

atur

atio

n

Ca

–fe

ldsp

ar

pH >

~12

Increasing calcic component in albite

2

1 3

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Fluid 2: CO2 - SO2

– volatiles; potassicFluid 3: H2,H2S, CH4, N2, HCl, HF sodic

OxidizedAlkaline

ReducedAlkaline

Best Au grades

AcidAqueous

Fe-chlorite, magnetite, quartz, carbonate

Muscovite Paragonite

BiotiteK-feldsparAnhydriteCarbonate

Qtz, epidote, biotite, magnetite, anhydrite

Phengite, hematite

Tourmaline

Anhydrite,tremolite Pyrite, pyrrhotite, Albite, quartz

Biotite, amphibole, albite, quartz, carbonate, magnetite

Albite,Talc, AmphiboleCa-feldspar

Aqueous, neutral

Oxidized - Reduced

Fluid1: H20 ± NaCl ± CO2 ± H2S

Anhydrous Volatiles



Documents

Lecture M1: Mineral Systems Overview Why a MS perspective ... · Slide after: A. Barnicoat. 3 ... Magmatic fluids. Meteoric fluids Surface derived needs rainfall and topography wide