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The potential for
gold in Liberia
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Liberia — a major under-explored West African gold terrane:
▪▪ Recent exploration success and new mine development have led to a considerable
increase in activity.
▪▪ 90 per cent of Liberia is underlain by the Archean and Birimian, two of the most
productive gold-bearing terranes globally.
▪▪ These rocks host multi-million ounce gold deposits in neighbouring countries.
▪▪ Liberia has not been systematically explored using modern techniques and deposit
models, so the potential for new discoveries is great.
The geology of Liberia
Liberia is located within the Man Shield, part of
the West African Craton, which comprises two
major areas of Archean and Paleoproterozoic
rocks. Liberia was mapped during the 1970s in a
joint programme between the Liberia Geological
Survey (LGS) and the United States Geological
Survey (USGS). Aeromagnetic and aeroradiometric
9°W
10°W
8°W
gi
GUINEA
8°N
YA
M
B
ES L O
F
A
10 Mountains
6
9
13
" Gbarnga
1
e
" Karnplay
"
Ganta
12
5
7°N
ng
Sanniquellie "
" Sacleapea
" Tubmanburg
Robertsport "
St. John River
-Kokoya
15
8
Kakata
"
"
4
Buchanan "
T
O
D
C
14
Zwedru
20 "
23
E
S
T
O
I
Quaternary
Liberian age province
Supracrustals
17
ZO
JU A
River Cess "
Granitic rocks
Intermediate to basic
intrusions
Granitic to dioritic gneiss
!
"
Gayama
11
Kle Kle
12
Toto Mountain Range
13
Tortor Mountain
14
River Cess
15
Kokoya
16
Jueh-Bokon
17
Numon South
18
Sinoe
19
Dugbe F
20
Zw edru
21
Bukon Jedeh
22
Putu Range
23
Zia
24
Jolodah Village
COTE D'IVOIRE
BE
River "
Gbeh
19
21
Bukon Jedeh
24
" Pleebo
"
International boundary
0
25
Harper
!
!
Lucky Hill
22
Town
11°W
9
10
N
!
12°W
Mt Coffee
B
Greenville
Granitic to dioritic gneiss
"
Mandingo Hill
8
U
Supracrustals
18
Cestos River
Intermediate to basic
intrusions
Granitic gneiss
Gondoja
7
E
Granitic to dioritic gneiss
H
DUG
Supracrustals
Eburnean age province
Leopard Rock
6
D
Pan African age province
16
u
Fault
Pu
t
Gold occurrence
Alluvial gold belt
5
ge
6°N
Harbel
Putu Range
-Zwedru
Ndablama
Innis
an
11
Monrovia "
3
4
R
Atlantic Ocean
S
7
New Liberty
Weaju
5°N
3
Ra
Kpo
Bea Mountain
2
ba
EI
Ni
m
Bopolu-Wuesua
-Tawalata
Masawo-Zolowo
-Zorzor
" Zorzor
1
2
7°N
zi
R
" Foya
Mano River
-Wologizi Range
8°N
Bedrock gold occurrences
an
ge
"
SIERRA LEONE
5°N
7°W
Voinjama
6°N
11°W
Liberian age (2.5–3.0 Ga) Archean basement,
extending across central and western Liberia, is
characterised by a granite-greenstone association
W
olo
±
12°W
maps for the entire country, supported by field
checking, allowed the bedrock geology and main
tectonic divisions of Liberia to be defined.
10°W
9°W
8°W
50
75
100
Km
7°W
Simplified geology of Liberia showing the principal gold occurrences.
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dominated by granitoid gneisses and migmatites,
which are infolded with supracrustal metavolcanic
and metasedimentary rocks and intruded by a
younger igneous complex. The supracrustal rocks
form discontinuous narrow, elongate ‘schist belts’.
The metamorphic grade is generally amphibolite
facies with greenschist facies dominating the
schist belts.
The boundary between the Archean and
Paleoproterozoic age rocks (Eburnean age
province, 1.9–2.3 Ga) is not well defined in eastern
Liberia, but is generally considered to lie along
the north-east-trending Cestos Shear Zone. The
south-eastern part of the Eburnean age province
in Liberia, extending west from Côte d’Ivoire to
Greenville, consists of tightly folded paragneiss,
migmatite and amphibolite. The north-western
part of the province, to the north of Greenville,
has similar lithologies and geophysical
characteristics, but younger isotopic ages.
An extensive Paleoproterozoic volcanosedimentary sequence, the Birimian Supergroup,
borders the Archean basement of the Man Craton
along its northern and eastern margins. The
supracrustal rocks are surrounded by a regionally
extensive granitoid complex. Although the genetic
relationship between the Birimian sequence
elsewhere in West Africa and the Eburnean age
province of Liberia is unclear, they are generally
considered to be equivalent.
Pan African-age rocks (c. 550 Ma) underlie an
elongate, fault-bounded zone along much of
Liberia’s coastline. They comprise metasedimentary
and mafic meta-igneous rocks containing
granitic bodies and subordinate noritic intrusions.
Phanerozoic rocks in Liberia include extensive
north-west-trending Jurassic-age dolerite dykes,
minor Paleozoic and Cretaceous sandstones and
unconsolidated Quaternary deposits.
Multiple phases of deformation are present
in the Precambrian rocks. The structural trend
of the rocks in the Liberian and Eburnean age
provinces is principally north-east, whereas
that of the Pan African province is mainly
north-west. A number of major north-easttrending faults in eastern Liberia are extensions
of regional structures, which extend into Côte
d’Ivoire, and include the economically important
Cestos, Dugbe, Dube and Juazohn shear zones.
The Lofa River Shear Zone in north-west Liberia
Drilling for gold in Sinoe County.
Courtesy of Hummingbird Resources plc.
Gold prospecting in south-east Liberia. Courtesy of Ryan Langdon.
also trends north-east. The north-west-trending
Todi Shear Zone marks the boundary of the
Pan African province and comprises a series
of south-west-dipping faults associated with
intense zones of mylonite.
Gold in Liberia
There is a long history of artisanal gold mining
in Liberia from alluvial placers with production
peaking at more than 30 000 ounces per annum
in the 1940s. Between 2008 and 2012 annual
production is estimated at about 20 000 ounces
per annum (BGS, 2015).
The cratonic geological environment of Liberia is
favourable for two main types of gold deposit:
i)
greenstone-hosted quartz-carbonate vein
deposits (a subtype of lode gold deposits) in
a wide variety of host rocks;
ii) alluvial placer deposits.
Nearly 600 gold occurrences have been recorded
in Liberia, with gold placer deposits accounting
for almost 80 per cent of the total.
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Gold grains recovered during exploration in Sinoe County. Courtesy of Hummingbird
Resources plc.
Placer gold deposits
Deep and intense weathering since the
Pleistocene, and persistent erosion in areas
of moderate to low relief, coupled with clay
bottoms to most of the gravel deposits, favour
the development of gold placers across Liberia
although most are found in the eastern and
western parts of the country. The deposits
worked by artisanal miners are generally less
than two metres thick, and are narrow and
discontinuous in form. The gold grains have
rounded edges and are moderately coarse in size,
with nuggets widely reported.
A number of ‘gold belts’ have been defined based
on the distribution of alluvial placer deposits:
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪
▪▪
Bea Mountain
Bopolu-Wuesua-Tawalata
Masawo-Zolowo-Zorzor
Mano River-Wologizi Range
St. John River-Kokoya
Cestos River
Putu Range-Zwedru
Bukon Jedeh
Each of these includes a large number of
alluvial placer deposits some of which have
been worked in the past and others where
significant resources remain. However, it
is generally considered that major placers
amenable to large-scale modern mining
methods are unlikely to be found in Liberia.
The widespread occurrence of placer deposits
suggests significant potential for bedrockhosted gold mineralisation and provides useful
guidance on exploration targetting.
Drilling for gold in Sinoe County. Courtesy of Hummingbird Resources plc.
Bedrock gold deposits
Bedrock gold deposits in Archean and Proterozoic
terranes in West Africa are highly varied in size
and form but typically consist of mineralised shear
zones and structurally-controlled quartz veins, and
are comparable with granite-greenstone-hosted
lode-gold mineralisation globally.
Archean lode-gold deposits
Lode gold deposits in Archean rocks in Liberia
are found in a wide variety of greenstone-belt
lithologies with metamorphic grade ranging from
lower greenschist to upper amphibolite facies.
The mineralisation, which may comprise quartz
veins, breccia zones, stringers and disseminations,
typically extends over widths of 10–20 metres
and may have a strike extent of more than a
kilometre. Structure exerts strong control on its
distribution with north-east-trending zones of
intense shearing being particularly important.
Other favourable sites include zones of polyphase
deformation, fold limbs and closures, and
competency contrasts such as sheared lithological
contacts. The mineralisation comprises free
gold closely associated with a range of silicates,
including quartz, tourmaline, chlorite and sericite,
and various sulfide minerals.
The gold-bearing mineralisation may be
associated with local development of a range of
alteration minerals including, most commonly,
chlorite, carbonate and sericite. In some deposits,
dependent on host rock lithology, the alteration
assemblages may include phlogopite, talc,
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magnetite, hematite, iron sulfide, tourmaline and
tremolite. A range of metals may be enriched in
the gold-bearing ores including arsenic, tungsten,
cadmium, copper, lead and zinc.
Perhaps the best known and economically most
important gold occurrences in the Archean
greenstone belts are found in north-west Liberia
associated with a series of major north-easttrending structural lineaments, principally shear
zones. New Liberty is a shear zone-hosted gold
deposit in Archean age rocks with a greenstone
belt affinity. It is a fully financed project with
planned annual production of 120 000 ounces
of gold which began in 2015. Further details are
given in Deposit Profile 1. Numerous additional
major gold occurrences occur along a structural
corridor extending north-east of New Liberty.
Prominent examples include Weaju and Ndablama
where exploration continues and significant gold
resources have been identified. At Ndablama, in
an area of established alluvial gold mining, gold
mineralisation is hosted in sheared ultramafic
and mafic rocks intercalated in a gneiss sequence
above a buried granite body. Gold is frequently
localised along sheared contacts between the
ultramafic and mafic units that are intruded by
granitic dykes and breccias. Phlogopite, tremolite,
chlorite and talc alteration is associated with the
mineralisation. A mineral resource (indicated +
inferred) containing 901 000 ounces of gold at a
Deposit Profile 1: New Liberty, Grand Cape Mount
County, north-west Liberia
Deposit style: Archean shear zone-hosted gold.
Local geology: footwall and hanging wall gneiss and banded
migmatites, containing greenschist-amphibolite facies
ultramafic rocks that host the gold.
Deposit geology: structurally-controlled mineralisation in a
100 metre-wide, steeply-dipping ultramafic unit. Mineralisation
is 10–20 metres wide, strike length 2 kilometres.
Mineralogy and alteration: free gold associated with
silicates and sulfides (pyrrhotite, arsenopyrite, gersdorffite).
Weak silicification, magnetite destruction and phlogopite
alteration.
Mineral reserve: 8.5 million tonnes @ 3.4 g/t Au.
Mining: Continuity of mineralisation to 500 metres proven by
drilling. Open pit to 220 metres planned.
Exploration: mineralisation associated with enhanced S, As
and W and enrichment in Na, K, Rb and Ba along marginal
zones; strong magnetic and induced polarisation responses.
grade of 1.6 g/t Au was reported at Ndablama in
December 2014.
Exploration in the Kpo Mountains area of
Gbarpolu County has identified gold-bearing
quartz veins. Mineralisation is thought to be
related to sheared lithological contacts between
granite, granitic gneiss and supracrustal rocks,
consisting of BIF, schist and amphibolite. To
the north of the Kpo Range gold-bearing veins,
hosted in granite and granitic gneiss, occur in the
Lucky Hill (Gblita) area. Mineralisation appears to
be controlled by the lithological contact between
granite and granitic gneiss.
Gold mineralisation comprising brecciated quartz
stockworks in strongly sheared zones has been
located in the Mandingo Hill area in Bomi County.
A number of structurally controlled, quartzsulfide-bearing gold occurrences occur in the
Mount Coffee area of the Todi Shear Zone. Further
east along the shear zone at Kle Kle several broad
zones of gold mineralisation have been defined.
Quartz vein-hosted and disseminated gold
mineralisation occurs in strongly sheared schists
in the Toto Mountain Range area in Bong County.
In the south of Bong County a mineral resource
(indicated) containing 210 000 ounces of gold
at a grade of 3.5 g/t Au is reported at Kokoya.
The mineralisation is structurally controlled
and hosted in a package of strongly deformed
amphibolites and gneisses.
Proterozoic lode-gold deposits
Most West African gold production has been
derived from Birimian-age greenstone belt rocks
rather than from the Archean.
Little systematic modern exploration has been
undertaken over the Birimian terrane in south-east
Liberia and the geology has not been studied in
detail. However, as in the Archean terrane, alluvial
gold occurrences are numerous and widespread
and significant mineralisation in bedrock is
known at several localities. Host rock lithologies
are varied but commonly include metavolcanic
and metasedimentary rocks, mafic and granitic
intrusives, pegmatites and sulfide-rich schists
and gneisses. The mineralisation is commonly
located at the host rock contact with banded
iron formation (BIF). The mineralised bodies have
variable morphology, ranging from irregular
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Visible gold in drillcore. Courtesy of Hummingbird Resources plc.
Analysis of drillcore using a portable XRF. Courtesy of Hummingbird Resources plc.
sheets, to quartz-carbonate sulfide-bearing veins,
disseminated sulfides and sulfide stringer veins.
As in the Archean terrane geological structure
is a dominant control on the location of gold
mineralisation. Particularly favourable sites include
second-order structures to regional shear zones,
structural intersections, lithological contacts,
grain-size variations within sedimentary packages
and zones of polyphase deformation. The gold
occurs as free grains commonly closely associated
with sulfide phases, chiefly pyrite, arsenopyrite
and pyrrhotite. Hydrothermal alteration is present
in some deposits, commonly with attendant
enrichment in arsenic, bismuth and silver.
The most important bedrock gold deposits in
this terrane are spatially associated with major
regional shear zones trending either north-east or
east-north-east. Numerous gold occurrences (e.g.
NW
SE
150
Surface
100
50
0
-50
Limit of
defined
ore
-100
-150
-200
0
-250 m
Intrusive
Migmatitic gneiss
Oxide zone
Higher grade
ore
100 m
Life of mine
ore
Pit boundary at a gold price of US$1200 per ounce
Simplified section through the Dugbe 1 project Tuzon
Resource. (Modified from Hummingbird Resources plc).
Jueh-Bukon, Numon South) have been identified
in the environs of the Cestos Shear Zone, which
lies along the contact between Archean and
Proterozoic rocks and represents a near-vertical,
crustal-scale structure that has been compared
with the Ashanti Gold Belt in Ghana. The Ity gold
mine in Côte d’Ivoire is located on the northeastern extension of this shear corridor.
The Juazohn Shear Zone is another highly
prospective target on account of known bedrock
occurrences, extensive alluvial deposits and gold
geochemical anomalies. BIF-associated gold
deposits are the principal target in the area. High
grade mineralisation has been reported at several
locations including Zia in the north, Zwedru to the
west and in the Putu Range area which straddles
the Juazohn Shear Zone.
The regional Dugbe Shear Zone in south-east
Liberia has been the focus of increasing gold
exploration in recent years. To date the most
significant discoveries are located at Dugbe 1
about 40 kilometres east of Greenville in Sinoe
County. These foliation-parallel disseminated
gold deposits are hosted in high-grade, migmatitic
rocks. Further details are given in Deposit Profile 2.
Approximately 12 kilometres to the south-east
drilling has intersected significant high-grade
gold mineralisation at Bukon Jedeh. The intrusive
contact with a granite is a favoured site for high
grade gold in this area. Along strike to the west of
the Dugbe 1 Project gold mineralisation has been
identified in the Sinoe area, which is characterised
by biotite and garnet-biotite schists, intruded by
sulfide-bearing quartz-feldspar-mica pegmatites
and mafic and granitic intrusives. The highest
gold concentrations appear to be associated with
pegmatitic zones.
Potential for new discoveries
The wide distribution of placer gold deposits
across Liberia indicates the potential for new
major bedrock gold discoveries. Under-explored
areas of alluvial mining activity are priority
targets for future exploration.
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Deposit Profile 2: Dugbe 1 project (comprising 3
deposits — Dugbe F, Tuzon, Sackor), Sinoe County,
east Liberia
Deposit style: Proterozoic shear zone-hosted gold.
Local geology: migmatitic, feldspar-biotite-quartzothropyroxene gniesses.
Deposit geology: Dugbe F is a shallow-dipping, 8–15 metre
thick tabular mineralised body, with a strike length
>2.5 kilometres. Tuzon comprises a wider mineralised ‘folded
nose’ ore body.
Mineralogy and alteration: gold mineralisation associated
with increased sulfide content. Free gold occurs as very fine
grains along microfractures, grain boundaries and in quartzsulfide-bearing veins. Alteration is inconspicuous away from
the mineralised zone.
Mineral resource: 43 million tonnes @ 1.28 g/t Au (Dugbe F,
Inferred) + 41.8 million tonnes @ 1.51 g/t (Tuzon, Indicated).
Mining: a Preliminary Economic Assessment (April 2013)
concluded the project is robust from a technical and economic
perspective, based upon a financial model spanning a 20 year
mine life. Both Dugbe F and Tuzon can be mined as open pit.
The distribution of BIF, considered to be the
source of much of the placer gold in the Archean
of West Africa, is relatively well known in Liberia
on account of the extensive exploration that
has taken place for iron and the availability of
national aeromagnetic data. The relationship
between bedrock gold and BIF in Liberia is
illustrated by the Innis prospect to the north of
the Cestos Shear Zone, where gold is associated
with disseminated and vein-hosted sulfides
hosted by sericite-altered gneiss, BIF and garnet
schist. Other areas with extensive BIF, coinciding
with major structural corridors, are highly
prospective. Targets of this type associated with
alluvial gold occurrences are located in the Nimba,
Putu and Wologizi ranges.
In north-west Liberia the under-explored northeast extension of the Archean-granite-greenstone
terrane, bounded by the Lofa and Yambesei shear
corridors, is a priority target for gold exploration,
owing to the favourable geology, structure and
alluvial placer deposits.
Other areas that merit further investigation
include: the southern end of the Todi
Shear Zone in the River Cess area where
limited sampling has revealed elevated gold
concentrations in the laterite; the northern
extremities of the Dugbe Shear Zone and the
Dube Shear Zone, where anomalous gold values
in stream sediments have been reported; and
the western end of the Dube Shear Zone in
the Jolodah Village area of Grand Kru County
where alluvial gold is widespread, although the
bedrock source has not been identified.
Selected references
Aureus Mining. 2014. www.aureus-mining.com
British Geological Survey (BGS), 2015. World
Mineral Production, 2009–2013.
Hummingbird. 2014. www.hummingbirdresources.
co.uk
Shannon, E H, and Sangmor, S S. 1982.
Geology for development: a survey of the
principal mineral resources of Liberia and
their exploration potential. Liberian Geological
Survey, Monrovia.
Hedge, C E, Marvin, R F, and Naeser, C W. 1975. Age
provinces in the basement rocks of Liberia. U.S.
Geological Survey Journal of Research, 3, 425–429.
Thayer, T P, and Lill, G G. 1974. Mineral exploration
in western Liberia 1949–1950. Geological Survey
Special Paper No. 4. Ministry of Lands and Mines
Republic of Liberia.
Liberian Geological Survey. 1982. Summary of the
Precambrian geology of Liberia — contribution
to IGCP project No. 108/144. Liberian Geological
Survey, Monrovia, Liberia.
Tysdal, R G, and Thorman, C H. 1983. Geologic
map of Liberia. 1:1 000 000. US Geological Survey
Miscellaneous Investigations Series Map I-1480.
Sangmore S S, and Nair A M. 1985. Geology,
petrogenesis, gold and associated mineralization
in the Tortor Mountain Range, Bong County,
Liberia. Liberian Geological Survey, Monrovia.
Wahl. 2007. Geologic, Geophysical, and
Mineral Localities Map of Liberia — A Digital
Compilation. USGS Open-File Report 2007–
1258, Sheet 1 or 4.
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Authorship and acknowledgements
This minerals brochure was produced by the British
Geological Survey in association with the Liberian
Geological Survey, Ministry of Lands, Mines and Energy.
It was compiled by Paul Lusty and Gus Gunn with the
assistance of Kathrine Linley and Deborah Rayner.
Photographs on the front cover:
waterfall courtesy of Ryan Langdon;
drill rig courtesy of Hummingbird Resources plc.
The brochure forms one of a series produced during a
project providing support to Liberia Ministry of Lands,
Mines and Energy for effective management of land-based
minerals funded by the UK Government.
BGS Project Leader: Joseph Mankelow
Courtesy of Hummingbird Resources plc
For further information please contact:
The Director, Liberian Geological Survey
c/o The Ministry of Lands, Mines and Energy,
P.O. Box 10-9024, Capitol Hill, Monrovia, Liberia
http://www.molme.gov.lr/
© Liberian Geological Survey
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