GEORG Geothermal Workshop 2016 Session A3 Upstream

1. SOURCES AND REACTIONS OF VOLATILES IN
ICELANDIC THERMAL FLUID
Andri Stefánsson, Sæmundur A. Halldórsson, David Hilton, Árný E.
Sveinbjörnsdóttir, Jaime D. Barnes, Shuhei Ono, Jan Heinemeier, Jens Fiebig,
Finnbogi Óskarsson, Peter Torssander, Stefán Arnórsson

2. Volatiles
• Volatiles are a group of elements and compounds that
typically have low boiling points and are commonly found
within planetary crusts and the atmosphere.
• In thermal fluids, volatile elements include for example: H,
O, C, S, Cl, F, N, B, He and other noble gases
• Use isotopes to understand sources and reactions
• Sampling
• Analysis
• Isotope geochemical modeling

4. Sampling

5. Sampling

6. Analysis

7. Hekla 1980
• Cl <10 to >20,000 ppm
• 5-450°C
• Hot springs, fumaroles
and wells
Thermal fluids

8. Hekla 1980
• 5-450°C
• Hot springs, fumaroles
and wells
• S <1 to >1500 ppm
Thermal fluids

9. Hekla 1980
• 5-450°C
• Hot springs, fumaroles
and wells
• S <1 to >1500 ppm
• CO2 <10 to >10,000
ppm
Thermal fluids

10. Hekla 1980
• 5-450°C
• Hot springs, fumaroles
and wells
• S <1 to >1500 ppm
• CO2 <10 to >10,000
ppm
• Meteoric and
seawater water
source
• Dominated by H2O
(>95 mol%)
Thermal fluids

11. • Trace sources and reactions of
volatiles
• Approach
• Conceptual geological and
geochemical models
• Data collection and
analysis
• Simulations of chemical
and isotope behavior of
the conceptual models
• Comparison of the two
Isotopes of volatile elements

12. Sulfur isotopes and low-temperature SO4
• Multiple oxidation states (S-II
to S+VI)
• Four stable isotopes (32S, 33S,
34S and 36S)
• SO4 in low-T water on the
Southern Lowlands
• Three trends:
• Meteoric water SO4
source
• Water-rock interaction
and SO4 in rocks
• Seawater mixing

13. Sulfur isotopes and low-temperature SO4
• Multiple oxidation states (S-II
to S+VI)
• Four stable isotopes (32S, 33S,
34S and 36S)
• SO4 in low-T water on the
Southern Lowlands
• Three trends:
• Meteoric water SO4
source
• Water-rock interaction
and SO4 in rocks
• Seawater mixing

14. Hekla 1980
Sulfur isotopes and low-temperature SO4
Chlorine δ34S (sulfate)

15. Carbon in low- and high-temperature fluid
• Multiple oxidation
states (C-IV to C+IV)
• Two stable isotopes
(12C, 13C)
• Both as gas phase and
liquid phase
• Fluid-rock interaction a
major source of CO2
• Melt (mantle) CO2 input
on- and off-rift

16. Carbon in low- and high-temperature fluid
• Multiple oxidation
states (C-IV to C+IV)
• Two stable isotopes
(12C, 13C)
• Both as gas phase and
liquid phase
• Fluid-rock interaction a
major source of CO2
• Melt (mantle) CO2 input
on- and off-rift

17. Hekla 1980
Carbon in low- and high-temperature fluid

18. Helium isotopes
• 3He dominates the
atmosphere where 4He is
produced by decay of heavy
elements in Earth
• He is non-reactive (as well as
other noble gases) – can be
used to look at source(s) and
source(s) heterogeneity
• Values given relative to air, RA
• MORB is ~8
• Higher values indicate
primordial mantle (early
earth) input
RA
0 5 10 15 20 25 30
Count
0
20
40
60
80
100

19. Hekla 1980
Helium in low- and high-temperature fluid

22. Sæmi A.
Halldórsson
Andri Stefánsson
Shuhei Ono
David R.
Hilton
Árný E.
Sveinbjörnsdóttir
Jaime D. Barnes
Jan Heinemeier Jens Fiebig Finnbogi
Óskarsson
Peter
Torssander
Stefán Arnórsson