GEOCHEMISTRY IN GEOTHERMAL EXPLORATION

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 terrain

z 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 B_{O N W} AL A O L ' R O N_G A I H I L_L 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 00

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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 W_{AL A} O L ' R O N G A I H I L_L 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 titration

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Fumarole gas analysis

(mmol/kg steam)

Fum No.

loc date Temp

o_C 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 o_{C pH/20} o_C 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 25

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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 (

o

C)

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 G_A 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 3700

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Ground temp (

o

C)

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 N_{W 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 meters

above 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 A_{L A} O L' R_O N G A I H IL_LS 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 ?