No part of this report may be circulated, quoted, or reproduced for distribution without prior written

approval from KenGen. All the information contained herein was prepared for information to the

ARGeo_C6 Technical Conference at Addis Ababa, Ethiopia

CONFIDENTIAL

Disclaimer:

• Geologists.

James A. Nyandigisi /Christine Nyamvula

NOVEMBER 2016

ARGeo C6, Addis Ababa, Ethiopia

HIGH TEMPERATURE HYDROTHERMAL ALTERATION IN ACTIVE GEOTHERMAL SYSTEMS

1

OUTLINE

Introduction 1

Geology Of Olkaria Domes 2

Hydrothermal Alteration Mineralogy

3

Alteration Vs Formation Temp

4

Conclusion And Recommendations 5

3

LOCATION OF OLKARIA - DOMES

Map of the location of the Olkaria geothermal and other Quaternary volcanoes along the rift axis (Omenda, 2003)

4

LOCATION OF OLKARIA - DOMES

Geo-sector Map of Olkaria Geothermal Field (KenGen, 2000)

Olkaria IV (140 MWe) Power Plant at DPF

One of the well head at DPF (OW 915 )

5

OBJECTIVES

Map the 1st occurrence and distribution of

HTAMs at Olkaria Domes Field

Compare 1st occurrence of HTAMs and the

formation temperature.

Delineate heating up, equilibrium and

cooling down areas

Determine optimal production casing depth

7

GEOLOGICAL SETTING

ROCK TYPES

Pyroclastics

Rhyolite

Tuffs,

Basalt,

Trachytes

Intrusive

Granite

Syenite Stratigraphic column of Olkaria Domes fields

(Omenda 1998)

8

STRATIGRAPHY OF OLKARIA

Plateau trachytes

Olkaria basalts

Pyroclastics Olkaria Volcanics

9

OW-805C to OW-922

PYROCLASTICS

OLKARIA

VOLCANIC OLKARIA BASALTS

PLATEAU

TRACHYTES

10

OW-39A to OW-923B

PYROCLASTICS

OLKARIA

VOLCANIC OLKARIA BASALTS

PLATEAU

TRACHYTES

11

STRUCTURAL MAP OF OLKARIA

Structural map of Greater Olkaria geothermal area (KenGen, 2000)

13

ALTERATION ZONES - SOUTH VIEW

Actinolite

(280oC)

Epidote

(250oC)

Chlorite

(230oC)

Below 180oC Quartz

14

ALTERATION ZONES - NORTH VIEW

Actinolite Epidote Chlorite Quartz

Below 180oC

15

OW-804B to OW-922

QUARTZ

CHLORITE

EPIDOTE

ACTINOLITE

16

OW-39A TO 923B

QUARTZ

CHLORITE

EPIDOTE

ACTINOLITE

17

ALTERATION MINERALOGY

19

COMPARISON X-SECTION: OW-805C TO OW-922

20

COMPARISON BTN FORM. AND ALT. TEMP

22

CONCLUSION

HTAMS (epidote) was encountered at

950 m.b.s.l or 1200 m.a.s.l.

Geothermal system of DPF is at

equilibrium and heating up at depth

HTAMs is structurally controlled at DPF

23

Equilibrium zones

OW-911 OW-915,

OW-923, OW-909,

OW-914

Cooling down zones

OW-901, OW-902,

OW-917, OW918,

OW-919, OW-922,

CONCLUSION

24

RECOMMENDATION

Recommended casing DPF is at 950 m

below the surface i.e.1200 m.a.s.l.

HTAMs data normalization to refined the

distribution & comparison Map

Fluid inclusion geothermometry study to be

conducted to ascertain the conclusions.

25