GEOCHEMISTRY IN GEOTHERMAL
EXPLORATION
Argeo-C2 Conference
24th-28th November 2008
2
Role of Geochemistry in Geothermal Exploration
z Mapping, sampling & chemical analysis of
surface discharges
z Chemical data interpretation
z Discharges include: water (hot/cold),
fumarole steam
z Non- manifestation areas – Soil gas survey
z Soil gas survey include measuring chemical
components associated with geothermal
Objectives of Geochemical Work
z To gather enough geochemical data which
would be adequate to address the following questions:
z Availability and extent of a geothermal
resource
z Locate possible drilling targets
z Characterize geothermal fluids using the
chemistry
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Geothermal Manifestations
z Geothermal indicators occur in form of the
following:
¾ Fumaroles
¾ Hot (boiling) springs
¾ Mudpools
¾ Hot altered grounds
Steam jets
z Steam jets at L.
Bogoria which
sprout like geysers
z Found at the western
edge of the lake
z They are at local
boiling temp (98 oC)
z Famous tourist
attraction
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Fumarole occurrences
z Sometimes fumaroles occur in extremely difficult terrainz Strong fumaroles are
associated with mineral alteration products
Altered grounds
z Some areas are
characterized by hot altered grounds with no visible discharges
z Such areas could be
having buried
fumarolic activity
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Case example
z Surface exploration in Menengai Area in Nakuru
District – Kenya.
z Area characterised by very few surface geothermal
manifestations- only a few fumaroles inside the main Menengai crater and to the NW close to caldera rim
z Few boreholes produce warm water located to the
NW and SW of crater
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Geochemical Data Collection
z Field work started on 25th January 2004
z Work divided into three parts:
z Water sampling (B/holes, springs etc)
z Fumarole steam and condensate sampling
Fumarole /borehore location
180 170 160 9990 9980 9970 2 20 0 2 10 0 2 00 0 1 900 1 80 0 1 70 0 1 60 0 1 70 0 180 0 1 80 0 200 0 19 0 0 2000 18 001 800 1 80 0 1 80 0 1 80 0 18 00 18 00 1 90 0 20 00 2 10 0 2 16 0 21 00 2 200 2 000 2 00 0 2 10 0 2 0 00 19 00 1 80 0 1 9 00 1 90 0 1 90 0 2 000 20 00 21 0 0 2 200 2 30 0 2200 1800 1700 1 700 18 00 1 80 0 1800 1 700 1 70 0 1 600 1700 2 0 00 220 0 2200 L. NAKURU NAKURU TOWN LANET R. N jo r o KIA MU NY I ES TAT E N G A TA FA R M ME N E N G A I S T AT I O N KABARAK ESTATE MENENGAI CALDERA ENGOSHURA FARM KA BA TI N I C ra t e r s tr e a m BA H ATI S O L AI B AN I TA S IS AL ES TA TE O L B AN I TA S W AM P & P O N D Ol b an i ta str ea m kabaragi K IS A NA N A M AJ A N I MI NG I ES TA TE A TH IN A I SI SA L ES TA TE E L BO N W AL A O L ' R O NG A I H I LL S ME N EG A I H I L L FA R M KA MP I YA M O TO M O G O TI O 0 10KM LEGEND 0012
Soil gas survey sample points
180 170 160 9990 9980 9970 2 20 0 2 10 0 2 00 0 1 90 0 1 8 0 0 1 700 1 6 0 0 1 70 0 18 00 18 00 20 00 1 9 0 0 200 0 1 80 01 80 0 1 80 0 18 00 1 80 0 18 00 18 00 19 00 2000 2 10 0 21 60 2 100 2 20 0 2 000 2 00 0 2 10 0 2 000 19 00 1 80 0 1 900 1 90 0 1 90 0 2 000 20 00 2 1 00 2 2 00 23 00 2200 1800 1 7 00 1 70 0 1 800 1 800 1 800 1700 1700 16 00 1 700 2 00 0 0022 22 00 L. NAKURU NAKURU TOWN LANET R . N j or o KIA MU NY I ES TA TE N G A TA FA R M M EN E N G A I S T A TI O N KABARAK ESTATE MENENGAI CALDERA ENGOSHURA FARM K AB AT IN I C ra t e r s tr e a m BA H AT I S O L A I B AN I TA S IS AL ES TA TE O L B A NI TA S W AM P & P O N D Olb a nit a s t re am kabaragi KI SA N AN A MA JA N I MI N G I E STA TE A TH IN A I SI SA L ES TA TE E L B O N WAL A O L ' R O N G A I H I LL S ME N EG A I H I L L FA R M KA MP I YA M O TO M O G O TI O 0 10KM LEGEND
200 0 Contours in met ers
above sea level
Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center
Major (rift s carp) fault
Rift floor fault 00
Fumarole sampling
z Gases collected in
special gas sampling flasks after
evacuation and
charged with NaOH solution to absorb acidic gases
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Fumarole discharges
z Some manifestations
are too weak and
pumping is necessary
z Samples analysed for
gases and condensate analysed for volatile components in the lab
Why work in three Parts ?
1. Fumaroles: results help in computing reservoir
temp at depth where the steam is being formed
2. Water analysis: results used to evaluate origin of
the fluids (use of isotopes), temp estimations at depth, predict scaling and corrosion problems
3. Soil gas survey : Rn-222 and CO2 in the soil gas are
indicators of permeability and possible location of a
reservoir. CO2 may also be used in locating buried
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Soil gas survey
z CO2 gas sampled
from the soil gas in the field using an Orsat apparatus
z CO2 absorbed in
vessels containing KOH solution and measured in %
Chemical Analysis
z Equipments used for
chemical analysis include: ¾ AAS, ICP ¾ GC, IC ¾ UV-VIS ¾ Titrpoprocessors
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Chemical analysis
z Collected samples are
analyzed in the lab
z Water samples
analyzed for all the major & minor
components
z Steam condensate
analyzed for volatile components
Gas analysis
z Fumarole gases analyzed using a Gas chromatograph z Gases analyzed by GC: N2, H2, O2, CH4 z CO2 and H2S analyzed by titration20
Fumarole gas analysis
(mmol/kg steam)
Fum No.
loc date Temp
oC CO2 H2S H2 CH4 N2 O2 MF1 E1724 N9975 29.1.04 60 28.28 0.1 0.3 - 1.97 0.722 MF2 E1753 N9977 6.2.04 91.2 3590 0.42 0 0.34 4.69 1.39
Steam condensate chemistry
Fum T oC pH/20 oC CO2 H2S Cl SO4 B F TDS Cond MF1 60 6.0 33 0.17 19.5 3.45 0.17 0.19 11 20 MF2 94 6.0 38 0.17 24.1 5.1 0.07 0.96 20 50 MF3 77 7.5 88 0.03 31.4 6.7 0.12 0.13 6 10 MF4 81 5.8 143 0.17 15.6 7.0 0.14 <0.1 4 10 MF5 88 6.7 77 0.17 16 5.43 0.05 0.214 6 10 MF6 84 6.7 33 0.7 16.3 6.74 0.2 <0.1 5.6 10 MF7 73 6.9 88 0.07 33 29 0.38 0.26 12 2522
Gas ratios
Fuma CO2/H2S CO2/H2 H2/H2S H2/CO2 CO2/N2
MF1 282.8 94.3 3 0.011 14.4
Gas geo temp (
oC)
Fuma TCO2/H2 TH2 TH2S TCO2
MF1 285.3 266.2 251.2 298.5
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Carbon dioxide distribution
180 170 160 9990 9980 9970 2 20 0 21 00 20 00 190 0 18 00 1 70 0 1 6 00 1 7 00 1 80 0 1 80 0 2 00 0 19 0 0 2000 18 00 18 00 1 80 0 1 80 0 18 00 18 00 18 00 1 90 0 2000 2 10 0 2 16 0 2 10 0 22 00 2 000 2 00 0 2100 20 00 1 90 0 1 80 0 1900 1 90 0 1 900 2 000 20 00 2 100 2 200 2 30 0 220 0 1800 1700 1 7 0 0 1 800 18 00 180 0 1 700 1 700 1 6 00 1700 2000 2200 220 0 L. NAKURU NAKURU TOWN LANET R . N jo r o KIAM UN YI ESTA TE NG ATA FAR M ME N E N G AI S TA T IO N KABARAK ESTATE MENENGAI CALDERA ENGOSHURA FARM KA B ATI N I Cr a t e r s tr e a m BA H ATI S O L AI BA N IT A SI S AL ES TA TE O L B AN I TA SW AM P & PO ND Ol ba ni t a s tre am kabaragi K IS AN A N A M AJ AN I M IN G I ES TA TE AT HI N AI S I SA L E ST AT E EL BO NWAL A O L' R O N GA I H IL LS M EN E G A I H IL L FA RM K AM PI Y A MO T O MO G O TIO 0 10KM LEGEND 2 000 Contours in meters
above sea level
Roads Railway line Rivers Lake, Pond Shopping center pyroclastic issue crat es Lava eruption center
Major (rif t scarp) fault Rift floor fault inf erred fault 00 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5
Radon-222 distribution
180 170 160 9990 9980 9970 2 20 0 2 10 0 2 00 0 19 00 18 00 1 7 00 1 6 0 0 1 7 0 0 180 0 1 80 0 20 00 19 00 2000 18 00 1 80 0 1 80 0 18 00 18 00 18 00 18 00 1 90 0 2 000 2 10 0 2 16 0 2 100 2 20 0 2 000 2 00 0 21 00 2000 19 00 1 80 0 1 900 1 90 0 1 90 0 2 00 0 20 00 2 1 0 0 2 200 230 0 2 2 00 18 00 17 0 0 1700 1 800 18 00 1 800 1 700 1700 160 0 1 700 2 00 0 0022 22 00 L. NAKURU NAKURU TOWN LANET R . N jo r o KIAM UN YI EST AT E N G AT A FA R M ME N E N G A I S T AT I O N KABARAK ESTATE MENENGAI CALDERA ENGOSHURA FARM KA B ATI N I C ra t e r s tr e a m BA H AT I S O L A I B AN I TA S IS AL ES TA TE O L B AN I TA S W AM P & P O N D Olb an ita str ea m kabaragi K I SA N AN A M AJ A N I MI NG I ES TA TE A TH IN A I SI SA L ES TA TE E L BO N W ALA O L' R O N G A I H I L LS ME N EG A I H IL L FA R M K A MP I Y A M O TO MO G O TI O 0 10KM LEGEND 00 200 900 1600 2300 3000 370026
Ground temp (
oC)
180 170 160 9990 9980 9970 2 20 0 2 10 0 2 00 0 1 900 18 00 1 70 0 16 00 1 70 0 18 00 18 00 20 00 19 00 200 0 1 80 01 80 0 1 80 0 18 00 18 00 18 00 18 00 19 00 2000 2 10 0 21 60 2 100 2 20 0 200 0 2 00 0 21 00 2 0 00 19 00 1 80 0 1 90 0 1 90 0 1 90 0 2 00 0 20 00 2 1 00 2 200 23 00 2200 1800 170 0 1 700 1 800 18 00 1 800 170 0 1700 16 0 0 1 700 200 0 0022 22 00 L. NAKURU NAKURU TOWN LANET R . N j or o KIA MU NY I E ST AT E N G A TA FA R M M EN E N G A I S T A TI O N KABARAK ESTATE MENENGAI CALDERA ENGOSHURA FARM K AB AT IN I C r a te r s tr e a m BA H AT I S O L A I B AN I TA S IS AL ES TA TE O L B A NI TA S W AM P & P O N D Olb a nit a s t re am kabaragi KI SA N AN A MA JA N I MI N G I E STA TE A TH IN A I SI S AL ES TA TE E L BO NW AL A O L' R O N G A I H I L LS ME N EG A I H I L L FA R M KA MP I YA M O TO M O G O TI O 0 10KM LEGEND 200 0 Contours in metersabove sea level
Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center
Major (rift scarp) fault Rift floor fault inferred 00 15 23 31 39 47 55 63 71 79
Conclusions & Recommendations
z A geothermal resource exists in Menengai caldera
with reservoir temp in the range of 250ºC
z The high values of CO2 measured to the NW part
of the caldera could suggest a possible resource area.
z From the geochemical data obtained during this
study, the area to the south and SE of caldera do not seem to be attractive at all.
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Proposed drill sites
180 170 160 9990 9980 9970 2 20 0 21 00 20 00 1 90 0 1 800 17 00 16 00 1 700 1 800 18 00 2 00 0 1 9 00 2000 180 0 18 00 18 00 1 80 0 18 00 1 80 0 1 80 0 19 00 2000 21 00 21 60 2100 22 00 2000 200 0 21 00 2 000 1 90 0 18 00 19 00 19 00 1 9 00 2 0 0 0 2 00 0 21 00 2 200 23 00 2 2 0 0 1 800 1 70 0 1 7 00 1 800 18 00 1800 17 00 17 00 1 6 0 0 1700 2 000 22 00 2 200 L. NAKURU NAKURU TOWN LANET R . N j or o KI AM UN YI E STA TE N G A TA F AR M ME N EN G A I S TA T IO N KABARAK ESTATE MENENGAI CALDERA ENGOSHURA FARM K A BA TIN I C r a te r st r e a m B AH A TI SO L AI BA N ITA SI SA L E ST AT E O L BA N IT A SW A MP & P O N D O lb an it a st re am kabaragi K IS AN A N A MA J AN I M IN G I E S TAT E ATH I N AI S IS AL E STA TE EL BO NW AL A O L' RO N G A I H ILLS M EN E G AI H IL L F AR M K AM PI Y A MO T O M O G O T IO 0 10KM LEGEND 2 000 Contours in meters
above sea level
Roads Railway line Rivers Lake, Pond Shopping center pyroclastic issue crates Lava eruption center
Major (rift scarp) fault Rif t floor fault inferred fault 00 Proposed Site 2 Proposed Site 1 Proposed Site 3 ?