Geothermal Exploration in Eritrea

Short Course Iv on Exploration for Geothermal Resources
November 16, 2009, Naivasha, Kenya

TABLE OF CONTENTS
1. Introduction
2. Regional Tectonic Setting
3. Geologic and Geothermal Setting
4. Hydrogeology of Alid
5. Alid Geothermal System: Lineamentassessment
6. Alid Geothermal system: Resistivity
survey7. Conclusion

Introduction- Previous works
Geothermal assessment was initiated during 1902 by Angelo
Marini (Marini, 1938).
UNDP sponsored work was carried out a reconnaissance survey
in 1973 by a Geological Survey of Ethiopia team (UNDP, 1973).
In 1992, the late Prof. Giorgio Marinelli and a staff member fromthe Department of Energy visited Alid area.
 In 1994, Mikhail Beyth of the Geological Survey of Israel
surveyed the Alid hydrothermal area.
A team of staff from the United States Geological Survey (USGS)
and the Ministry of Energy and Mines of Eritrea (MEM) carried out
a geological and geochemical investigation at Alid and its
surroundings during in 1996 (Clynne et al., 1996).
Reinterpretation of the chemistry of water and gas samples(Yohannes, 2004).
Fault and fracture analysis (Yohannes et al., 2006), resistivity
survey (Goitom et al, 2006) and hydrogeological investigation(Andemariam et al., 2006) was carried out on Alid andsurroundings.
An assessment of Resisistivity survey (MT and TEM) wasconducted on 2008 (Eysteinsson et al, 2009).

Regional TectonicSetting•zone of crustal extension•Down dropped crustal
sections, bounded by deeprooted normal faults(forming grabens) that cut
into the basaltic lavas,
extruded in the resulting
depressions.

Low temperature areas - springs

SAMOTI SPRING WITH
HIGH FLOWOutline geologyof Nabro-Dubbiarea•••••••Nabro Lies 2218m asl and
600m above Mabda
Trachytic lava flows andpyroclastic emplace
primarily on the Nabro
WNW faults and fractures
dissects the horst
Dubbi – the largest
reported historical 1861
eruption in Africa
Extensive basaltic lava
fields cover wide area
The major transverse
structure separates theDanakil blocks into two
geological set up•••Nabro Lies 2218m asl and 600m above
Mabda
Trachytic lava flows and pyroclastic
emplace primarily on the Nabro
The major transverse structure
separates the Danakil blocks into two
geological set up

Geological and Geothermal Setting-Alid•112 Km from Massawa and 30 Km south of Irafaile village•600 – 900m asl and 700 m uplifted from surrounding•Arid to semi-arid climate 350 – 400C

Geological setting:•Consists of rifted andfaulted young deposits ofsediments and volcanic flows.
•Bounded by metamorphic
basement and Stratoid basalt

A SECTION OF THE WESTERN SIDE OF ALID CRATER

PumiceLava Shell

Sedimentary Sequence
Rhyolitic flow
Vent

PumiceGeothermal Setting

Geothermal setting•Hot mineralized fluids discharge from many locations.
•Precipitates in the form of sulpho-salts and clays.
•Steaming grounds are common.

Assessment from Lineament

Contour plot of Alid area using FFD analysis. Note the highvalues lie on the Darere-Illeghedi line.

Resistivity map at 3500 metres below sea level.

Yellow line shows the location of the vertical resistivity boundary between ½ and 2 km depth.
The brown contour lines outline the low resistivity body west of Mt. Alid at about 2 km depth.

Conclusion
The tectonic setting and geological make up of the Danakil
depression provides a suitable environment for the occurrence ofgeothermal energy.
Alid and Nabbro-Dubbi are the notable prospect
A high temperature reservoir (2500C) is predicted on the Alidprospect.
Maximum lineament zone defined by ENE strike is well marked
on the FFD analysis inline with the major fracture set of the area.
Two high values depicted on the contour map are wellaccompanied with the thermal manifestation.
The resisitivity survey carried out at and around Alid dome
depicted a new anomaly at the rift floor, paving a way to look fora wider perspective.

The current study recommends the following detail works
on Alid:•Conduct CO2 and other trace element mapping of thearea to clearly identify zones of heat flow.
• worth to commence gravity and microseismicity tocomplement the MT and TEM geophysical survey.
•Collect samples for isotopic analysis to exactly constraint
the genesis and construct reaction paths.
Perform prospect investigation on Nabbro Dubbi including:•Conduct geological mapping•Collect water and gas samples and perform geochemicalinterpretation.

Conceptual model of Alid geothermal fieldRose diagram plots of a) Illeghedi, b) Darere, c) Asa-ila, d) Humbebet, e) Abakri,f) Debra Docholo, g) Aerole or Miski-Merehada , and h) Synoptic of the whole area.