GEOCHEMISTRY IN GEOTHERMAL EXPLORATION

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

2 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

fumarole steam Non- manifestation areas Soil gas survey Soil gas survey include measuring

3 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

extent of a geothermal resource Locate possible drilling targets

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

5 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

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

7 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

8 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

inside the main Menengai crater and to the NW close to caldera rim Few boreholes

9 9

10 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

sampling (B/holes, springs etc) Fumarole steam and

11 Fumarole /borehore location KISANANA M OGOTIO MAJANI MINGI ES TA TE kabaragi 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 E L BO N W ALA KA MP I YA M OTO KABARAK ESTATE MENENGAI STATION MENENGAI CALDERA Crater stream BA HATI HILLS OL' RO NGAI ME NEGA I HILL FARM KA BA TI N I NGATA FARM ENGOSHURA FARM KIA MUNYI ESTATE R. Njo ro NAKURU TOWN LANET LEGEND Contours in meters above sea level Shopping center pyroclastic issue crates L. NAKURU KM Roads Railway line Rivers Lava eruption center Major (rift scarp) Rift floor Lake, Pond inferred

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

12 Soil gas survey sample points KI SA N AN A M OGOTIO MA JA N I MIN GI ESTATE kabaragi SOLAI OLB ANITA SWAMP & POND BANITA SISAL ESTATE O lba nit a s t r eam ATHINAI SISAL ES TA TE E L BON W ALA KA MP I YA M OTO KABARAK ESTATE M ENENGAI STATION MENENGAI CALDERA Crater stream BA H AT I HILLS OL' RO NGAI ME NEGA I HILL FARM KABATINI NGATA FARM ENGOSHURA FARM 1900 KIA MUNYI ESTATE R.Njoro NAKURU TOWN LANET LEGEND Contours in meters above sea level L. NAKURU KM Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor

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

13 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

14 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

15 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

16 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

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

18 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

19 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

20 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 N MF2 E1753 N

E1724 N9975 29.1.04 60 28.28 0.1 0.3-1.97 0.

21 Steam condensate chemistry Fum T o C ph/20 o C CO 2 H 2 S Cl SO 4 B F TDS Cond MF MF MF MF < MF MF < MF MF

22 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 MF MF

23 Gas geo temp ( o C) Fuma TCO 2 /H 2 TH 2 TH 2 S TCO 2 MF MF

24 Carbon dioxide distribution KISANANA MOGO TIO MAJANI MINGI ES TA TE kabaragi 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 EL BO N WA LA KAMPI YA MOTO KABARAK ESTATE MENENGAI STATIO N MENENGAI CALDERA Crater stream BA HATI HILLS OL' RONGAI MENEGAI HILL FARM KA B ATI N I NG ATA FARM ENGOSHURA FARM 19 0 K IAMUNYI E STATE R. Njo ro NAKURU TOWN LANET LEGEND Contours in meters above sea level L. NAKURU KM Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor Lake, Pond inferred

25 Radon-222 distribution KISANANA MO GOTIO MAJANI MINGI ES TA TE kabaragi 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 E L BON W AL A KAMPI YA MOTO 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 NGATA FARM ENGOSHURA FARM KIAM UNYI ESTATE R. Njo ro NAKURU TOWN LANET LEGEND Contours in meters above sea level L. NAKURU KM Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor Lake Pond inferred

26 Ground temp ( o C) KISA NANA M OGOTIO MA JA NI MINGI E STA TE kabaragi OLBANITA SWAMP & POND SOLAI O lba nit a s tr eam ATHINAI SISAL ES TA TE BANITA SISAL ESTATE E L BON W AL A KA MP I YA M OTO KABARAK ESTATE M ENENGAI STATION MENENGAI CALDERA Crater stream BA H AT I HILLS OL ' RONGAI ME N EGA I HILL FARM KABATINI NGATA FARM ENGOSHURA FARM KIA MUNYI ESTATE R.Njoro NAKURU TOWN LANET LEGEND Contours in meters above sea level L. NAKURU KM Roads Railway line Rivers Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor inferred

27 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

28 220 0 MENENGAI STATION R. Njoro Proposed drill sites KISANANA M OGOT IO MAJANI MINGI ESTATE kabaragi 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 EL B O NW ALA KAMPI YA MOTO HILLS O L' RONGAI 18 0 Proposed Site 3? BAHATI Proposed Site Crater stream KABATINI KABARAK ESTATE MENEGAI HILL FARM MENENGAI CALDERA Proposed Site NGATA FARM ENGOSHURA FARM KIAMU NYI ESTATE NAKURU TOWN LANET LEGEND Contours in meters above sea level Roads Railway line Rivers Lake, Pond L. NAKURU KM Shopping center pyroclastic issue crates Lava eruption center Major (rift scarp) Rift floor inferred 1 900

29 Menegai Caldera floor 29

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