Mineral Potential of Eritrea, and Fe-Oxide andSericite alteration mapping using the RemoteSensing and GIS Techniques

An Internship program in JapanSpace Systems

Girmay Iyassu Mekonnen
girmaybelai@gmail.com

17/03/2021

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Background• Bachelor of science in Geology, Asmara University• Exploration Geologist, Department of Mines, Ministry of Energy and Mines• Secondment Geologist in different foreign, junior and senior explorationcompanies within Eritrea• Master of Science in Environmental Geology, Shimane University (ABEInitiative scholarship)2

Contents
1. Mineral potential of Eritrea,Regional Geology
Geology of EritreaBisha VMS

2. Fe-Oxide and Sericite alteration mapping using the Aster satelliteimages3

1. Mineral Potential of Eritrea41. 1.1 Introduction
 Located in East Africa
 Area: 124,000sq.km Land, 55,000sq.km.
territorial water and 350 big andsmall Islands Independence: May 24, 1991
 Population: 5,000,000; 9 ethnic groups
 Language:
 Tigrinya and Tigre,
 Arabic English51.2 Geological Setting
4.1 Reginal Geology• Regionally Eritrea is part of the Arabian Nubian shield:
Lies on the Northern part of the Neoprotrerozoic East Africa Oregen (stern, 1994
cited in (Drury & DE Souza Filho, 1998)• The shield was formed by the collusion between the East and west Gondwana
upon the closure of the Mozambique Ocean during the Neoproterozoic PanAfrican orogenic cycle (Ca. 900-550) (stern, 2008), (Zhao, et al., 2019).
Arabian Shield
Nubian Shield6

1.3 Model for Arabian Nubian Shield Formation

Formation of Arabian Nubian Shield (PeterJohnson, 2010),
Erosion and rifting of Arabian Nubian Shield(Alasdair Smith 2017)7

1.4 Geology of Eritrea• The Neoproterozoic rock of Eritrea is divided into four lithological distinct
terranes, each of which extends N-S and are separated by tectonic boundaries(Drury & DE Souza Filho, 1998)• The terranes are
1. Barka Terrane (BT),
2. Hager Terrane (HT),3. Nakfa Terrane (NT),
4. Arag Terrane (AT)8

1.5 Mineral occurrence
Mineralization is associated with theShear zones, mainly the VMS and theOrogenic gold mineralizations.

• Base Metals: Cu, Zn, Pb• Precious Metal: Au, Ag• Ni, Cr, Pt (PGE)

VMS and Orogenic gold mineralization belts (Johnson,9et al., 2017; Alasdair, 2020)

1.6 Mining activities in Eritrea

Zara Mine
Share Company

Bisha Mine
Share Company

AsmaraMining
MiningAsmara
ShareCompanyCompanyShareColluli MiningShare Company10

1.7 Active and developmental stage mines• Mining Operations
Bisha Mining Share Company: (607,666oz gold), (34.1moz silver), (552mlb copper), (2,582mlbzinc) (Alasdair, 2018).
Zara Mining Share Company: (0.76moz @5.1g/t gold) (Alasdair, 2018). The gold is hosted within
the quartz stock works in a microgranite lensoid body the mineralized zone has a strike length of 650m.

• Developmental Stage
Asmara Mining Share Company: (1,130,000t of Zinc), (580,000t of Copper), (415,000 ozs of Goldand (11moz of Silver) (Alasdair, 2018).
Colluli Mining Share Company: (1,289Bt), with average grade of 11% K2O, containing 206Mt of SOP(potassium sulphate).

Bisha Open Pit

Zara Open Pit

Debarwa Nippon Mining adit

Colluli Mine11

1.8 Geology of Bisha VMS
 The Bisha deposits are located within the Arabian-Nubian Shield. The ArabianNubian Shield has a wide range of deposit types and settings, including volcanic
massive sulphide (VMS) deposits.
 The rocks are a collage of volcanic arcs, granitoid intrusions, volcanosedimentary basins, and shear zones.
 It is overturned fold VMS deposit, the west to east and the antiform were eroded
where as the synform persists.
 Hosted by Felsic and intermediate tuffs
 70m thick oxide gossan, diping 600 to 700 W 1200m along strike
12Bisha geological map

Bisha VMS cross section

Oxidezone
Masssive
sulfideStringerzone

Felsic and int tuff
Chloritized fel and Int tuff

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1.9 Bisha Bimodal Siliciclastic VMS Model Schematic

Exhalite / ironformation

Dacite /rhyolite tuffs,
siliciclastic
rocks

SecondaryHydrothermal

Hydrothermal
Upwellingalong
synvolcanicfault

141.10 Bisha volcanogenic massive sulphide N-S section

Soap Zone

Oxide Zone

Primary Zone
Supergene Zone

Bisha technical report
2014.

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1.11 Bisha deposit alteration patterns

Nevsun technical report
201416

2. Fe-Oxide and Sericite alteration using the Remotesensing and QGIS techniques( Airborne Spectral Thematic Emission andReflection Radiation, Aster)17

2.1 Downloading Satellite images and Digital elevation
modelMethodology• SRTM from USGS• QGIS data analysis• DIVA GIS for Spatial administrative data
• Aster image from MADAS• Extacting files using the 7 zip and processing in QGIS 3.418

2.2 Bisha Mine Area gossan, and geological map

Bisha Mine from google earth image

Bisha geological map

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2.3 Fe-Oxide Minerals Reflectance and Band Combination
Normal RGB false
color image (VNIRand SWIR)Fe-oxide the band
rationing 6 is red
gossan, 3 green
vegetation and 1 isblue the host rocks(Masoud, et al.,2014).
Source from the internet

202.4 Bisha Mine Fe-Oxide alteration mapping
Aster image band RGB (631)Green is Vegetation

Red is Fe- Oxide
Dark colours are chlorites (Gabbro and Basalts)
Light white to yellow arekaolinite (Felsics)

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2.5 Phyllic Minerals Reflectance and Band Rationing
Band Rationng (SWIR)
The sericite alteration band rationing of(RGB=4/6:5/6:5/8), 4/6 is argillic alteration,
5/6 is phyllic alteration and 5/8 is propylitic
alteration (Yojima, 2014).
The argillic alterations are the kaolinite,
smectite and illite; the phyllic alterations areassemblages of quart-sericite-pyrite; and thepropylitic alterations are the Fe and Mg bearinghydrothermal fluids altering the biotite oramphibole to epidote-chlorite-albite alterations.

The band reflectance and absorption of sericite
and kaolinite are indicated in the Figure.

spectral reflectance and ASTER simulated spectral patterns of alteration (Yojima,2014).

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2.6 Aster Band Rationing (4/6,5/6,5/8) For the whole country
Procedures
Downloading Aster image(from 2000-2008 duration)
Extracting files using 7 zip
Raster calculator
Virtual raster building
Merging

Clipping raster23

2.7 Bisha Main and Harena area Sericite alteration mapping

Aster image Band Rationing(4/6, 5/6, 5/8)

Red is vegetation
Green to Blue is Chlorite
Yellow is Sericite

242.8 North and South of Bisha Identified Targets
Sericite alteration zones, Aster band (4/6, 5/6,5/8)

North of Bisha

South of Biha25

2.9 Emba Derho VMS Mineralizations area

Emba Derho Aster image,
Sericite alteration band ration (4/6, 5/6, 5/8)

Emba Derho area Google earth image26

2.10 Debarwa and Adrasi Mineralizations, Targets

Debarwa and Adraesi Aster image,
Sericite alteration band ration (4/6, 5/6, 5/8)

Debarwa and Adraesi Google earth image27

2.11 Telegimja VMS mineralization target

Telegimja sericite alteration zone

Telegimja Google earth image28

2.12 Northern Eritrea Sericite alteration and Fe-oxide signatures

Rgbat Area band rationing (4/6, 5/6, 5/8)

Rgbat Area google earthimage indicating Fe-oxide
sgnatures29

3.0 Conclusion• Aster image Band rationing (4/6, 5/6, 5/8) is meant for porphyry copper, in addition tothat it is best for VMS targets as it has identified the Bisha and other mineraloccurrences (gossans).
• Aster image Band RGB(631) is very helpful to identify the hematite alteration zones, incase of Bisha’s gossan outcrops it provides valuable information and it delineates thealteration zones including the disseminated Fe-Oxide bearing outcrops.
• According to some publications green represents the sericite or smectite but in thecase of Eritrea, mainly in the central part and southeastern part of the country green
color lies on the tertiary basalts so the ratio band 5/6 is for an intermediate
composition, chlorites or epidot alterations to mafic composition.

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3.1 Acknowledgment• Japan International cooperation Agency (JICA)• Japan international cooperation Center (JICE)• Japan Space Systems (JSS)• Shimane University, Faculty of Natural Science and Technology• JOGMEG of the East African desk
• Embassy of the state of Eritrea to Japan• Ministry of Energy and Mines (MoEM), The State of Eritrea

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Arigatogozaimasu

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QGIS DEM data analysis

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Bisha Main cross-section

Bisha Main Cross section

Harena Cross section

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