GEOCHEMISTRY IN GEOTHERMAL EXPLORATION

GEOCHEMISTRY IN GEOTHERMAL EXPLORATION Argeo-C2 Conference 24 th -28 th November 2008 Entebbe, Uganda James Wambugu KenGen

Role of Geochemistry in Geothermal Exploration Mapping, sampling & chemical analysis of surface discharges Chemical data interpretation Discharges include: water (hot/cold), fumarole steam Non- manifestation areas Soil gas survey Soil gas survey include measuring chemical components associated with geothermal activity (CO 2 gas, Hg, Rn-222 radioactivity) 2

Objectives of Geochemical Work To gather enough geochemical data which would be adequate to address the following questions: Availability and extent of a geothermal resource Locate possible drilling targets Characterize geothermal fluids using the chemistry Predict prevailing deep fluid temp. 3

Geothermal Manifestations Geothermal indicators occur in form of the following: Fumaroles Hot (boiling) springs Mudpools Hot altered grounds Geysers 4

Steam jets Boiling steam jets Steam jets at L. Bogoria which sprout like geysers Found at the western edge of the lake They are at local boiling temp (98 o C) Famous tourist attraction 5

Fumarole occurrences Discharging fumaroles Sometimes fumaroles occur in extremely difficult terrain Strong fumaroles are associated with mineral alteration products 6

Altered grounds Some areas are characterized by hot altered grounds with no visible discharges Such areas could be having buried fumarolic activity Altered grounds 7

Case example Surface exploration in Menengai Area in Nakuru District Kenya. 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 Few boreholes produce warm water located to the NW and SW of crater Cold water producing boreholes in the eastern side 8

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Geochemical Data Collection Field work started on 25 th January 2004 Work divided into three parts: Water sampling (B/holes, springs etc) Fumarole steam and condensate sampling Soil gas survey (for Rn-222, CO 2, temp) 10

2200 200 0 2 10 0 1 90 0 2 00 0 2 10 0 1 90 0 20 00 11 Fumarole /borehore location 1 70 0 00 KISANANA M OGOTIO 1 60 0 220 0 17 00 1600 1700 MAJANI MINGI ES TA TE kabaragi 1 70 0 2 000 1 700 SOLAI OLBANITA S W AM P & P ON D BANITA SISAL ESTATE O lb ani t a s t r ea m ATHINAI SISAL ES TA TE 17 0 0 2 0 0 E L BO N W ALA 1700 9990 2 30 0 2 20 0 210 0 1 90 0 1 8 00 1 8 0 0 9980 KA MP I YA M OTO 1 900 2 0 00 KABARAK ESTATE MENENGAI STATION MENENGAI CALDERA Crater stream BA HATI HILLS OL' RO NGAI ME NEGA I HILL FARM KA BA TI N I 2 0 0 2 16 0 200 0 2 000 2100 2100 NGATA FARM ENGOSHURA FARM 1900 2 2 00 19 00 KIA MUNYI ESTATE 20 00 9970 R. Njo ro NAKURU TOWN LANET 22 00 1 900 160 LEGEND Contours in meters above sea level Shopping center pyroclastic issue crates L. NAKURU 170 180 0 10KM 20 0 0 Roads Railway line Rivers Lava eruption center Major (rift scarp) Rift floor Lake, Pond inferred

22 00 20 00 19 00 21 60 2 20 0 19 00 23 00 12 Soil gas survey sample points 170 0 1 800 00 KI SA N AN A M OGOTIO 1 6 0 0 22 00 1 700 17 00 16 00 MA JA N I MIN GI ESTATE kabaragi 180 0 170 0 1 700 SOLAI OLB ANITA SWAMP & POND BANITA SISAL ESTATE O lba nit a s t r eam ATHINAI SISAL ES TA TE 1 800 1 7 0 0 2 20 0 E L BON W ALA 18 0 0 170 0 9990 18 0 0 2 2 0 21 00 1 90 0 200 0 1 8 00 2 0 00 9980 KA MP I YA M OTO 1 90 0 KABARAK ESTATE M ENENGAI STATION MENENGAI CALDERA Crater stream BA H AT I HILLS OL' RO NGAI ME NEGA I HILL FARM KABATINI 20 0 2 10 0 18 0 0 2 00 0 2 00 0 2100 2100 NGATA FARM ENGOSHURA FARM 1900 KIA MUNYI ESTATE 2 000 2 1 0 0 9970 1 90 0 R.Njoro NAKURU TOWN LANET 2200 19 0 160 LEGEND Contours in meters above sea level L. NAKURU 170 180 0 10KM 200 0 Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor

Fumarole sampling Gases collected in special gas sampling flasks after evacuation and charged with NaOH solution to absorb acidic gases Evacuated gas sampling flask 13

Fumarole discharges Some manifestations are too weak and pumping is necessary Samples analysed for gases and condensate analysed for volatile components in the lab Sampling pump 14

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 CO 2 in the soil gas are indicators of permeability and possible location of a reservoir. CO 2 may also be used in locating buried fumarolic activities where other evidence is lacking 15

Soil gas survey Gas absorption vessels CO 2 gas sampled from the soil gas in the field using an Orsat apparatus CO 2 absorbed in vessels containing KOH solution and measured in % 16

Chemical Analysis Equipments used for chemical analysis include: AAS, ICP GC, IC UV-VIS Titrpoprocessors etc 17

Chemical analysis Collected samples are analyzed in the lab Water samples analyzed for all the major & minor components Steam condensate analyzed for volatile components 18

Gas analysis Fumarole gases analyzed using a Gas chromatograph Gases analyzed by GC: N 2, H 2, O 2, CH 4 CO 2 and H 2 S analyzed by titration GC 19

Fumarole gas analysis (mmol/kg steam) Fum No. loc date Temp o C CO 2 H 2 S H 2 CH 4 N 2 O 2 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 20

Steam condensate chemistry Fum T o C ph/20 o C CO 2 H 2 S Cl SO 4 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 MF8 90 6.9 220 0.03 34.1 8.6 0.14 1.64 8 15 21

Gas ratios Fuma CO 2 /H 2 S CO 2 /H 2 H 2 /H 2 S H 2 /CO 2 CO 2 /N 2 MF1 282.8 94.3 3 0.011 14.4 MF2 8547.6 - - - 764.8 22

Gas geo temp ( o C) Fuma TCO 2 /H 2 TH 2 TH 2 S TCO 2 MF1 285.3 266.2 251.2 298.5 MF2 - - 265.5 371.6 23

18 0 2 200 18 0 2 16 0 20 00 2100 21 00 1 90 0 22 00 1 90 0 2 30 0 24 Carbon dioxide distribution 1 70 0 180 0 00 KISANANA MOGO TIO 1 6 0 220 0 17 00 1 7 00 1 60 0 MAJANI MINGI ES TA TE kabaragi 1 700 2 00 17 00 SOLAI OLBANITA SW AM P & PO ND BA N IT A SI S AL ES TA TE O l bani t a str e am AT HI N AI S I SA L ESTATE 180 0 17 0 2 0 0 EL BO N WA LA 1 7 00 9990 2 2 0 180 2 00 0 210 0 1 9 0 9980 KAMPI YA MOTO 190 0 1 9 0 0 2 0 0 20 0 0 KABARAK ESTATE MENENGAI STATIO N MENENGAI CALDERA Crater stream BA HATI HILLS OL' RONGAI MENEGAI HILL FARM KA B ATI N I 2 10 0 2 000 2 000 21 00 NG ATA FARM ENGOSHURA FARM 19 0 K IAMUNYI E STATE 20 0 9970 R. Njo ro NAKURU TOWN LANET 2 200 1900 160 LEGEND Contours in meters above sea level L. NAKURU 170 180 0 10KM 2 000 Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor Lake, Pond inferred 8.5 7.5 6.5 5.5 4.5 3.5 2.5 1.5 0.5

22 00 180 0 20 00 2 00 0 2 10 0 19 00 2 16 0 2 20 0 1 90 0 230 0 25 Radon-222 distribution 170 0 1 800 00 KISANANA MO GOTIO 16 0 0 22 00 1 700 17 00 16 00 MAJANI MINGI ES TA TE kabaragi 1 70 0 1 700 SOLAI OLBANITA S W AM P & P ON D BANITA SISAL ESTATE O lb ani t a str ea m A TH IN A I SI SA L ES TA TE 17 0 0 2 2 0 0 E L BON W AL A 17 0 9990 2 2 0 1 800 21 00 1 9 0 0 9980 KAMPI YA MOTO 19 00 1 90 0 2 000 2 00 0 20 00 KABARAK ESTATE MENENGAISTATION MENENGAI CALDERA Crater stream BA H AT I HILLS OL ' RO NGAI ME NEGA I HILL FARM KA B ATI N I 2 10 0 2 000 2100 2100 NGATA FARM ENGOSHURA FARM 190 0 KIAM UNYI ESTATE 20 00 9970 R. Njo ro NAKURU TOWN LANET 2200 190 0 160 LEGEND Contours in meters above sea level L. NAKURU 170 180 0 10KM 200 0 Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor Lake Pond inferred 3700 3000 2300 1600 900 200

22 00 20 00 2 00 0 19 00 21 60 2 20 0 1 90 0 23 00 26 Ground temp ( o C) 170 0 1 800 00 KISA NANA M OGOTIO 16 0 0 22 00 1 700 1 600 17 00 MA JA NI MINGI E STA TE kabaragi 180 0 170 0 1 700 OLBANITA SWAMP & POND SOLAI O lba nit a s tr eam ATHINAI SISAL ES TA TE BANITA SISAL ESTATE 17 0 0 2 200 E L BON W AL A 17 00 9990 2 2 0 1 800 21 00 1 9 0 0 200 0 9980 KA MP I YA M OTO 1 900 1 9 00 200 0 1 8 00 20 00 KABARAK ESTATE M ENENGAI STATION MENENGAI CALDERA Crater stream BA H AT I HILLS OL ' RONGAI ME N EGA I HILL FARM KABATINI 2 10 0 200 0 2100 2100 NGATA FARM ENGOSHURA FARM 190 0 KIA MUNYI ESTATE 2 000 2 10 0 9970 R.Njoro NAKURU TOWN LANET 2200 190 0 160 LEGEND Contours in meters above sea level L. NAKURU 170 180 0 10KM 200 0 Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor inferred 79 71 63 55 47 39 31 23 15

Conclusions & Recommendations A geothermal resource exists in Menengai caldera with reservoir temp in the range of 250ºC The high values of CO 2 measured to the NW part of the caldera could suggest a possible resource area. 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. Deep drilling is recommended to proof the resource 27

220 0 MENENGAI STATION R. Njoro 2100 2100 2200 Proposed drill sites 00 17 00 KISANANA M OGOT IO 1 600 1 700 1 6 0 0 1700 2 200 MAJANI MINGI ESTATE 17 00 kabaragi 200 0 17 00 SO LAI ATHINAI SISAL E STA TE Ol bani t a str eam OLBANIT A SWAMP & POND BA N ITA SI SA L E ST AT E 1 7 0 0 180 0 9990 1 70 0 EL B O NW ALA 1 800 2 2 00 23 00 KAMPI YA MOTO HILLS O L' RONGAI 18 0 Proposed Site 3? 2 20 0 BAHATI Proposed Site 2 2 00 0 Crater stream KABATINI 9980 1 90 0 KABARAK ESTATE MENEGAI HILL FARM 19 0 0 180 0 MENENGAI CALDERA Proposed Site 1 19 0 0 2 00 0 2 0 00 21 00 21 60 20 00 NGATA FARM 21 00 20 00 ENGOSHURA FARM 9970 21 00 200 0 KIAMU NYI ESTATE 1 90 0 2 2 00 1 900 NAKURU TOWN 19 00 LANET 28 2 000 160 LEGEND Contours in meters above sea level Roads Railway line Rivers Lake, Pond L. NAKURU 170 180 0 10KM Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor inferred 1 900

Menegai Caldera floor 29