Using secondary minerals and hydrochemistry to

trace geochemical processes in the deep subsurface

Henrik DrakeLinnaeus University, Sweden

Co-workers: LnU/SKB: Mats Åström, Olga Maskenskaya, Changxun Yu, Frederic Mathurin, Tobias Berger, Linda Alakangas, Birgitta Kalinowski, Ignasi Puigdomenech, Elsewhere: Eva-Lena Tullborg, Johan Hogmalm, Martin Whitehouse, Christine Heim, Magnus Ivarsson, Bill Wallin, Curt Broman,

Thomas Zack, etc etc

Billion years of history

Present Groundwaters

Presently active bacteriaSRB, IRB etc

Deep Saline Glacial Marine Meteoric>~500ka 14ka 4-8ka present recharge

Past activity?Salinity?Redox?

?

Hydrothermal history Possible Quaternary

Start of mix with brine at 10 Ma

Methodology

Microscope/SEMFluid inclusionsTrace elementsBiomarkersGeochronologyFracture orientationsIsotopes

Drake et al., 2012, GCAMaskenskaya et al., submitted

Drake and Tullborg, 2009, AGDrake et al., in press, AG

Mathurin et al., ES&T (2012)

Hydrothermal

References:Drake et al. 2009 Lithos, Drake and Tullborg, 2009 Appl. GeochemDrake et al. 2012, GCA, 2013, GCAMaskenskaya et al., submitted x 2

Hydrothermal

Mathurin et al., in press GCA

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0

0 200 400 600 800SO4

2- (mg/L)D

epth

Drake et al., 2013 GCALaaksoharju et al., 2009

Berger et al., 2013

Low temperature minerals

Recent past conditions (0-10 Ma = minerals, and groundwater 0-0.5 Ma), 0-1000 m

• Near-surface redox front

• Fresh/saline interface and

• Trace element variation/Trace element uptake into calcite

• Activity of bacteria

– Sulphate reducers

– Methanogens

– Methane oxidation

– (Iron-reducers)

• Pre-drilling, undisturbed conditions (minerals)

Redox front

O2

Redox zoneRedox zone

Stable reducingconditions

Oxidisingconditions in fractures

Can be detected examining redox sensitive minerals and elements

Oxides

Drake et al., 2009, Appl.Geochem

CeIII CeIV

Drake et al., 2009 Appl.Geochem

Yu et al., in prep

Drake et al., in prep

Low temperature calcite and pyrite

TRACE METAL INCORPORATION (CALCITE)

Drake et al., (2012, GCA)

Maskenskaya et al., submitted

Also fracture-zone scale variabilityDrake et al., (2013, Appl. Geochem.)

Sulphur isotopes in pyrite (SRB-related)

This study

Samples: Groundwater(δ34S, SO4, DOC, HCO3)

Pyrite (δ34S)0 - >900 m depth

Mathurin et al., (2012)

Drake et al., 2013, GCA

Pyrite• intra-crystal δ34S pattern

Increase with growth

Drake et al., 2013, GCA

•huge variations across individual crystals (-32 to +73‰) •extreme minimum (-50‰) and•maximum (+91‰) values.•=>141‰ range!•SRB activity at all depths analysed, 0-900 m

δ34Srim- δ34Scentre vs.SO4

Drake et al., 2013, GCA

ONGOING/FUTURE STUDIES:

1. TRACES OF METHANE-OXIDATION/METHANOGENESISDrake et al., in prep

Calcite (δ13C, δ18O)0 - >900 m depth

SIMS 10 µm in situ analysis+ToF-SIMS/GC-MS

Drake et al.,in press Appl. Geochem

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-130 -110 -90 -70 -50 -30 -10 10δ13C ‰ (PDB)

Dep

th (

m.a

.s.l.

)

Methanogenesis(up to c. +5 per mil)

Small organic influence

Influence of organic C, e.g. from plants

Anaerobic oxidation of methane(biomarkers are SRB-specific of high AOM-specificity, ToF-SIMS+GC/MS data)

Min: -125‰

Drake et al., in prep

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0

-130 -110 -90 -70 -50 -30 -10 10δ13C ‰ (PDB)

Dep

th (

m.a

.s.l.

)

Methanogenesis(up to c. +5 per mil)

Min: -125‰

Drake et al., in prep

Similar study from Forsmark

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δ13C

Dep

th Not within range ofgroundwater (δ18O)

Within range ofgroundwater (δ18O)

Methanogenesis(to +12 per mil)

Anaerobic oxidation of methane

Stable isotope variation and trace element uptakein recent, <17y, precipitates at Äspö• Micro-variation of sulphur isotopes in pyrite

• Trace element uptake in calcite

PRECIPITATES ON BOREHOLE EQUIPMENT AT ÄSPÖ (-450 m)

Mathurin et al., ES&T (2012)Drake et al., in prep

MICRO-SCALE S-ISOTOPE VARIATION

Drake et al., in review

δ34Ssulphate +18 to +28‰δ34Ssulphide -29 to -1‰

Iron isotopes to be added, First SIMS results of fracture-coating pyrite δ56Fe -0.9 to +2.8‰

TRACE METAL INCORPORATION INTO CALCITE

0

0.02

0.04

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0.08

0.1

0.12

0.14

DMg

Laboratory DMe

This study

KA3385A-1

KA3105A-2

KA3105A-3

KA3105A-4

0.01

0.1

1

10

DFe

Laboratory DMe

This study

KA3385A-1KA3105A-2

KA3105A-3KA3105A-4

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

DSr

Laboratory DMe

This study

KA3385A-1KA3105A-2

KA3105A-3KA3105A-4

0

5

10

15

20

25

30

35

DMn

LaboratoryDMeThis study

KA3385A-1

KA3105A-2KA3105A-3

KA3105A-4

+Ba, LREEs(+Y, V)(not shown)

Drake et al., in prep

STABLE ISOTOPE VARIATION IN CALCITE

Drake et al., in review

Finally,this area has

• Most depleted δ13Ccalcite reported (-125‰)

• Largest δ13Ccalcite range within a single crystal (109‰)

• Largest range of δ13Ccalcite from single location (129‰)

• Largest δ34Spyrite range from single location (141‰; Drake et al., 2013, GCA)

Thank you!

δ13Cδ34S