Geothermal Exploration in EritreaGeothermal Exploration in Eritrea

Ermias Yohannes, Eritrea Ministry of Energy and Mines, Department of Mines

Regional Geothermal Working Group Meeting Kampala, Uganda, 19-23 September 2011

1. Introduction

2. Regional Tectonic Setting

3. Geologic and Geothermal Setting

4. Recommendation

TABLE OF CONTENTS

The African Rift ValleyThe African Rift Valley

Introduction- Introduction- Previous worksPrevious works• Geothermal assessment was intiated during 1902 by Angelo

Marini from the Italian Institute for Military Geography on Alid geothermal manifestations (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 from the Department of Energy visited Alid area and prepared proposal for detail study.

• In 1994, Mikhail Beyth of the Geological Survey of Israel surveyed the Alid hydrothermal area for the possibility of epithermal gold deposition.

• 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 (Berhe et al, 2006) and hydrogeological investigation (Tesfalidet et al., 2006) was carried out on Alid and surroundings.

Regional Regional Tectonic SettingTectonic Setting

•zone of crustal extension

•Downdropped crustal sections, bounded by deep-rooted normal faults (forming grabens) that cut into the basaltic lavas, extruded in the resulting depressions.

• The tectonic setting and geological make up of the Danakil depression provides a suitable environment for the occurrence of geothermal energy.

• Alid and Nabbro-Dubbi are the notable prospect

Location map of Alid and Nabro-Dubbi geothermal areasLocation map of Alid and Nabro-Dubbi geothermal areas

High temperature prospects:Geological and Geothermal Setting

• 112 Km from Massawa - 30 Km south of Irafaile village

• 600 – 900m asl and 700 m uplifted from surrounding

• Arid to semi-arid climate 350 – 400C

Geological and Geothermal Setting-AlidGeological and Geothermal Setting-Alid

n.a.: not analyzed; H and O isotopes analyzed using mass spectrometry.

Alid geothermal prospectAlid geothermal prospect

• A high temperature reservoir (2500C) is predicted on the Alid prospect.

• Lineament analysis carried out in Alid justify the presence of fracture conducive for reservoir and fluid pathways.

• The resistivity survey carried out both MT and TEM signify an anomaly deep at Alid but need more survey points.

BudgetBudgetOutline geology of Outline geology of Nabbro-Dubi areaNabbro-Dubi area

• Nabro Lies 2218m asl and 600m above Mabda

• Trachytic lava flows and pyroclastic emplace primarily on the Nabro

• Dubbi – the largest reported historical 1861 eruption in Africa

• Extensive basaltic lava fields cover wide area

• The major transverse structure separates the Danakil blocks into two geological set up

Nabro-Dubbi: An active site of geothermalNabro-Dubbi: An active site of geothermal

•Reconnaissance survey was conducted•Geothermal manifestations include both fumarole and spring with alteration zones.•It was the site for the current volcanic eruption

Nabro volcanic eruption, June 2011Nabro volcanic eruption, June 2011

Lava flowLava flow

The current study recommends the following detail works on Alid:The current study recommends the following detail works on Alid:Conduct COConduct CO2 2 mapping of the area to clearly identify zones of heat flow.mapping of the area to clearly identify zones of heat flow. worth to commence MT and TEM geophysical surveyworth to commence MT and TEM geophysical survey Drill slim hole to map temperature gradient of the area. Drill slim hole to map temperature gradient of the area. Collect samples for isotopic analysis to exactly constraint the genesis Collect samples for isotopic analysis to exactly constraint the genesis and construct reaction paths.and construct reaction paths.

Perform prospect investigation on Nabbro Dubbi including:Perform prospect investigation on Nabbro Dubbi including:Conduct geological mapping.Conduct geological mapping.Collect water and gas samples and perform geochemical interpretation.Collect water and gas samples and perform geochemical interpretation.

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