Prospect Primary School Improvement Plan 2017 18 PROSPECT ...
Prospect, Kenya, from Fumarole Gas...
Transcript of Prospect, Kenya, from Fumarole Gas...
Characterization of Suswa Geothermal Prospect, Kenya, from Fumarole Gas
Geochemistry
By: Kipngok, J.K., Jill R.H., Malimo S.J., Ochieng L.A., Igunza G.M., Mwanyasi F., Bett E.K., Kangogo S.C. and Kanda I.K.
Date: 4th Nov., 2016 Venue: Addis Ababa
Outline
• Background Exploration Geochemistry of Suswa • Objectives for the 2015 work • Sampling and Analysis • Results: QA/QC • Non Condensible Gases • 3He/4He • Stable Isotopes of Water • Conclusion
Geological Setting
• S1 - Lavas and pyroclastics • S2 – Pyroclastics (trachyte,
carbonatite, and trachybasalt composition tuffs, ignimbrites, and ash deposits)
• S3 – Agglutinate (trachytes) • S4 – Pyroclastics (trachyte pumice
lapilli tuffs with thin trachyte agglutinate flows)
• S5 – Lavas (trachyte) • S6 – Lavas (aphanitic phonolite
lava flows and ash‐fall deposits) • S7 – Pyroclastics ( • S8a – Lavas (anorthoclase‐phyric
phonolite) • S8b1 - Collapse Breccia (pit crater) • S8b2 - Collapse Breccia (island
block)
Geological Setting
• S8c – Lavas (anorthoclase‐phyric phonolite lava flows and one or more scoria cones)
• S8d - Landslide Deposits • S9 - Lavas (anorthoclase‐phyric
phonolite; the feldspar phenocrysts show substantial magmatic resorption)
• 1986-1987-UNDP and GOK by Ármannsson (ISOR) • KPLC 1993 • GDC 2012/2013 • Regional Exploration provided local meteoric water
lines
Background Geochemical Exploration
• Most results reported only CO2 and air
• 2012/2013 campaign did not reach the inner caldera
• For the few samples with reported H2S or CH4, gas geothermometers 230 to 280C
• CO2 geothermometer >300C in the inner caldera, < 300C outside the caldera (1986/7) to over 350⁰C (2012/3)
• Stable isotopes explained two possible sources of water (1986/7)
Results of Previous Geochemical Surveys
• Resample the fumaroles (and additional new ones) in such a manner as to obtain gas chemistry and gas/steam measurements while minimizing the effect of air contamination.
• Sample available local groundwater • Evaluate the source of the Suswa Geothermal
Reservoir fluids • Evaluate the reservoir conditions indicated by fluid
chemistry • Provide geochemical contributions to the conceptual
model of Suswa
Objectives of 2015 Geochemical Work
• Sampled 20 fumaroles + 4 cold waters • Many low pressure and difficult to seal • Noncondensible gas in evacuated Giggenbach bottles
with NaOH and Zn acetate + CO and hydrocarbons (no NaOH)
• Analyzed 8 duplicate gas samples • Steam condensate for stable isotopes of water and
selected elements in bottles • Helium isotopes in copper tubes • 4 cold waters for stable isotopes and 3 for water
chemistry
Sample Collection
Results: QA/QC
• CO2 and H2 mole % dry gas in duplicate samples by GDC and GNS compare reasonably well, but H2S does not.
• RPD (relative % difference) of gas/steam are high and variable.
• Focus on compare dry gas or gas ratios because other units such as
• For H2S, 2015 GDC data is not used in any cases where there is 2015 GNS .
• Stable isotopes of water and condensate in 2015 comparable with 1986/1987.
Sample CO2 H2S H2 CH4 N2
SWF-3-2015 67.4% 194% - 32.2% 168%
SWF-6-2015 136% - - 124% 47.7%
SWF-8-2015 33.7% 167% 3.9% 18.5% 104%
SWF-12-2015 79.1% 193% - 5.1% 10.3%
SWF-14-2015 191% - 180% 179% 27.6%
SWF-15-2015 59.1% 42.6% 45.3% 44.3% 16.7%
SWF-16-2015 119% 189% - 38.1% 14.6%
SWF-19-2015 123% 196% 198% 198% 118%
SWF-20-2015 49.3% - 55.2% 42.1% 30.7%
RPD Calcs 2015 GDC Data vs 2015 GNS Data
Results: QA/QC
• All gas samples contained air
• Used air corrections based on oxygen concentrations
• Did not use GDC 2015 H2S data
• Used GNS if available, or if not, GDC 2012/2013 results from the same fumarole
• Gas distribution indicates stronger geothermal signature within the inner caldera
• CO2/H2S
• <1000 within the inner caldera
• >10,000 at the outer rim of the outer caldera
• H2S, a more soluble gas, could be removed by condensation
Non condensable gas distribution
SWF-31158
SWF-8146
SWF-12706
SWF-15796
SWF-193579
SWF-16711
SSF-15910
SSF-24954
SSF-311567
SSF-43472
SSF-52399
SSF-63472
SSF-83987
SSF-96774
SSF-101381
SSF-116016
SSF-127671
SSF-134726
SSF-1410906
SSF-1512516
• Gas distribution indicates stronger geothermal signature within the inner caldera
• CO2/H2
• Not related to condensation
Non condensable gas distribution
• Both GNS and GDC data sets show CO2/CH4 lows in inner caldera, albeit a different order of magnitude.
Non condensable gas distribution
• Magmatic He strongest in inner caldera (SWF-19, -3 and -15)
Non condensable gas distribution
Ar
N2/100
10He
100
200
500
1000
2000
5000
10000
10
20
50
100
200
500
1000
1 0.2 0.1 0.05 0.02 0.010.5
GNS SWF-3 GNS SWF-12
GNS SWF-14 GNS SWF-15
GNS SWF-19 GNS SWF-6
GNS SWF-8 GNS SWF-16
GNS SWF-20N2/He N2/Ar
He/Ar
air
asw*
crust
*Note: "asw" denotes "air-saturated groundwater."
**Note: For samples with He concentrations reported below the detection limit (DL); half of the DL i s used for plotting. DL = 0.001 mmol/100molH2OSamples Below DL:GNS SWF-6GNS SWF-8GNS SWF-16GNS SWF-20
***Note: All Plotted Samples have been Corrected for Air Contamination
He-Ar-N2 Trilinear Plot (Giggenbach, 1991)
• 250-350C (GNS)-280-350C (GDC) inside the inner caldera: most likely 250-290⁰C and if you include CO2, 325C
• 120-250C (GNS) from fumaroles outside the caldera: most likely 190-225C
Gas Geothermometry
Sampling Site Lab
H2-CO2
(C)1
CO2-H2
(°C)4
H2S-CO2
(°C)1
H2-Ar
(°C)5
CO2-N2
(°C)3
CH4-CO2
(°C)4
Inner Caldera GNS 339 295 251 351 290 280
Outer Caldera GNS 189 213 248 116 226 336
Inner Caldera GDC (2015) 334 281 320 - 314 >350
Outer Caldera GDC (2015) - - - - 282 >350
Outer Caldera
GDC
(2012/13 - - 213 - 230 >350
1: Nehring and D'Amore, 1984 2: Giggenbach, 1980 3: Arnorrson, 1987, using air corrected data 4: Arnorrson and Gunnlaugsson, 1985 5: Giggenbach and Goguel, 1989, using air corrected data
Liquid/Vapor Equilibrium
SWF-3
SWF-8
SWF-12
SWF-14
SWF-15
SWF-19
SWF-20
SWF-6
SWF-16
• Developed by Giggenbach
• Focused on gas ratios
• Reviewed several gas/gas and gas/water reactions
• Most consistent included Ar, H2 and CO2
• Inside the caldera, fumarole gases in equilibrium with vapor and liquid 200 to 270C
Log CO2/Ar versus log H2/Ar (Giggenbach, 1991)
Liquid/Vapor Equilibrium
Possibilities
• Gas separation occurring at high temperatures (250-300C)
• Equilibration happening at two-phase conditions
Diagram of log(CH4/CO2) vs. log(H2/H2O) (from Marini and Fiebig, 2005)
Inferences from NCG Distribution
• Gases related to high temperature interaction with rock or gas-gas reactions CO2, H2S, H2, CH4 are present inside the moat area but only (predominantly) CO2 in the outer caldera
• Gases both more and less soluble than CO2, so condensation not only mechanism
• Upflow is in the eastern and western moat areas in the vicinity of SWF-8 and -15, and SWF-3 and -14
• Temperatures of the hydrothermal fluid source of fumarole discharges are most likely 250-290⁰C in the inner caldera and 190-225⁰C
• Gas ratios suggest that both vapor and liquid may be present in the hydrothermal system
Isotopes: Distribution of 3He/4He
• Inner caldera: R/Ra values >6 indicating magmatic influence
• Outer caldera dominated by air
SWF-61.23
SWF-36.50
SWF-86.25
SWF-12.19
SWF-51.30
University of Rochester R/Ra
Isotopes: Distribution of ẟD
• Distinguishes Inner and Outer Caldera Steam SWF-5
-30.9
SWF-1-36.1
SWF-2-23.9
SWF-3-21.6
SWF-6-84.5
SWF-7-21.2
SWF-8-12.3
SWF-11-32.3
SWF-12-12.2
SWF-14-28.7
SWF-15-23.1
SWF-16-51.7
SWF-4-36.1
SWF-9-56.5
SWF-10-74.5
Isotopes: Distribution of ẟ18O
• Distinguishes Inner and Outer Caldera Steam
SWF-5-8.09
SWF-1-8.25
SWF-2-6.53
SWF-3-6.02
SWF-6-15.89
SWF-7-5.81
SWF-8-3.25
SWF-11-7.50
SWF-12-5.58
SWF-14-6.83
SWF-15-6.15
SWF-16-10.85
SWF-4-8.15
SWF-9-10.88
SWF-10-13.08
Isotopes: ẟD vs ẟ18O
• Distinguishes Inner and Outer Caldera Steam
100 oC
140 oC
180 oC 220 oC
260 oC 300 oC
-90.0
-80.0
-70.0
-60.0
-50.0
-40.0
-30.0
-20.0
-10.0
0.0
-18.00 -16.00 -14.00 -12.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00
δD
eu
teri
um
δ Oxygen-18
Suswa - Stable Isotopes - 2015 Sampling (WETlab); 1986-1987 Sampling (ISOR)
2015: Outside Caldera 2015: Inside Caldera 1986-1987: Inside Caldera
1986-1987: Outside Caldera Meteoric Water Samples Global MWL
Central Kenyan Meteoric Water Line
Fractionation Trends↓ 100 oC to 300 oC ↓
Steam
Liquid
Water Source based on Stable Isotopes
1. Deep, approximately 260°C water that has risen to near surface in the moat and boiled at the surface (100°C), then condensed as it travels laterally;
2. Local meteoric water which has been heated to 260°C with minimal water/rock interaction, boiled in the reservoir, with steam moving to the surface in the vapor phase;
3. Mixtures of meteoric water and steam that is then re-boiled.
1. ≥260°C deep hot water has δ18O=-1.5 to +0.5 and δD=-2 to +6) (single stage or continuous boiling) boils at ~100°C, produces steam of east and west inner caldera
2. meteoric water (approximately δ18O=-4.5, and δD=-22), positive(+2) δ18O shift boiling in reservoir: steam δ18O ≈ -3, and δD ≈ -19 if the boiling occurred at 300C, and δ18O ≈ -5, and δD ≈ -26 if the boiling occurred at 200C, either indicate reservoir vapor
3. Range of isotopes in outer caldera to be related to different meteoric water sources: condensation more likely
Favored Model • Upflow at the east and western
ends of the Island Block • Reservoir extends below parts of
the ring fault zone and Island Block-throughout the inner caldera
• Outflow below buried lava in northern outer caldera in lava-tuff sequence along faults
• Similar outflow to the south but shallower
Models
Alternate Model • Upflow at east and west ends of the
Island Block • Reservoir extends below little or all
of the inner caldera • Hot northward outflow below deep
moderate conductor or cool outflow in or above the lava
• Alternates do not include a very small system narrowly restricted to upflows
Models
Conclusion
• Geothermometers (those based on ratios without air-related gases) suggest 250C to 290C.
• Reservoir fluids are two-phase, evidence of equilibrium with both liquid and vapor between 200 and 270C.
• A magmatic component in the eastern and western inner caldera fumaroles (3He/4He ratios). The source of noble gases in the rest of the fumaroles is air.
• Upflow occurs in the inner caldera: eastern (SWF-8) and western (SWF-3): lower CO2/H2S, lower CO2/CH4 values, higher ẟD and ẟ18O, high 3He/4He, evidence of sulfurous alteration.
Conclusion
• The source of the fumarolic steam at Suswa could be local meteoric water as sampled east of the project area, heated to ≥260°C by deep circulation with some relatively minor positive shift in ẟ18O, then boiled at relatively high temperatures (220 to 300C).
• Isotopic and gas/ratio data suggest that the steam discharging on the outer caldera and the outer rim could be the result of partial condensation (roughly 10% with continuous condensation) of steam similar to that discharging within the inner caldera (moat).