Download Read more - Geo-Data Information of Sierra Leone

Directorate of Geological Survey
Sierra Leone
This report summarizes a desk top study from
historic, published and unpublished sources. It is
intended to only hi-lights background information
with particular reference of Gold occurrences
relating to Sierra Leone.
Definition:
Gold is a chemical element with symbol Au (from
Latin: Aurum) and atomic number 79. In its purest
form, it is a bright slightly reddish yellow, dense
soft, malleable and ductile metal. Chemically, gold
is a transition metal and a group 11 element. It is
one of the least reactive chemical elements, and
is solid under standard conditions. The metal there
occurs often in free elemental (native) form, as
nuggets or grains, in rocks, in veins and in alluvial
deposits. It occurs in a solid solution series with
the native element silver (as electrum) and also
naturally alloyed with copper and palladium. Less
commonly, it occurs in minerals as gold tellurides.
Gold deposits in Sierra Leone are formed via a
wide variety of geological processes. In this
process the mineral is believed to exist initially in
a molten state in which it solidified to form the
deposit. But it is understood that the occurrence
of gold in the country is actually re-deposited by
circulating magma that cools as it reaches the
outer surface, and ends up in specific areas that
exhibit the correct conditions.
Intensely hot magma deep within the earth brings
element such as gold into a solution form during
eruption. As gold is moved and the magma cools,
gold nuggets and veins form as the metal
solidifies. Various deposits in the country are
classified as either primary, alluvial or placer and
residual or laterite. But some deposit within the
country contains a mixture of all three types of
ore.
The majority of primary gold deposits in the
country are purely referred to as lode gold
deposits. Lode gold deposits in the country are
generally high-grade, thin, vein and fault hosted.
They are primarily made up of quartz veins also
known as lodes or reefs, which contain either
native gold or gold sulfides or telluride.
January, 2016
Lode gold deposits in the country are usually hosted in
silicified banded ironstones and schistose quartzites
intercalated with amphibolites and intruded by muscovite
granite and associated tourmalinised pegmatites. Most
lode gold deposits are sourced from metamorphic rocks
because it is thought that the majority are formed by
dehydration of these rocks during metamorphism. The
gold is transported up faults by hydrothermal waters and
deposited when the water cools too much to retain gold
in solution as shown in the diagram below:
Figure 1 Primary Gold Formation
Table 1
Selected Properties of Gold
Symbol
Au
Atomic Number
79
Appearance
Metallic Yellow
Period
Period 6
Phase
Solid
Element Category
Transition Metal
Melting Point
Boiling Point
Density near r.t
Heat of Vaporization
Crystal Structure
( °C, °F)
3243 K
( °C, °F)
19.30 g/cm3
Heat of Fusion
Hardness
1337.33K
12.55
KJ/Mol
342
KJ/Mol
25.418J
Moh-K
Face Centered
Cube
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Placer or alluvial deposits are the most
commonly found gold in the country and are
sourced from pre-existing gold deposits and are
said to be secondary deposits. Almost all of the
gold mined in the country is from alluvial/placer
deposits. Placer deposits in the country are
formed by alluvial processes within rivers and
streams. The deposits are formed via gravity, with
the density of gold causing it to sink into trap sites
within the river bed, or where water velocity
drops, such as bends in rivers and behind
boulders.
Figure 3 Gold Bars
Figure 2 Primary Gold Formation
Gold Mineralization in Sierra Leone
Although gold mining activities in Sierra Leone has a long history but the occurrence of extractable gold was
first discovered in 1930 by Junner of SLGS in the Makoke River near Masumbiri. Present investigation coupled
with data obtained from previous works revealed that the country is a potentially significant gold country.
Gold deposit in the country exhibits a high degree of variability in form and distribution corresponding to
different lithological, geochemical and structural controlling aspects. Therefore, gold sulphide, gold-quartz
vein and gold ferruginous quartzite formations is hosted by intensely sheared and hydrothermal altered
granitoid rocks of the greenstone belt of the country.
Gold mineralization in the country is considered to occur in structurally controlled sites, commonly within
iron-rich garnet-cummingtonite schists. Potential ore zones develop in dilatants zones related to fold and
shear deformation of the schist and their wall rocks. Gold ores occur in a series of sub-parallel or en echelon
ore shoots and have been recorded in mineralized zone in silicified banded ironstones and schistose
quartzites, intercalated with amphibolites and intruded by muscovite granite and associated tourmalinised
pegmatite. From previous reports, Gold deposit is said to be a N-S trending, steeply dipping veins or zones
parallel to the axial plane of different folds. Subsequent evaluation of the arsenic geochemistry and the
geology led to the conclusion that the mineralization of gold in the country is structurally controlled.
The mineralization is generally confined to the more iron formation-rich portions of the garnet-cummingtonite
schist and the adjacent biotite quartzite and amphibolites. The main ore minerals are asenopyrite, pyrrhotite,
pyrite, and chalcopyrite; and two types of mineralization are observed, both of which may be of ore grade
with respect to gold:
1) Arsenopyrite-rich zones, +/- pyrhotite, in garnet-cummingtonite schists.
2) Pyrhotite/arsenopyrite-rich micaceous quartzite.
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Gold Occurrences in Sierra Leone
The overall geological setting, presence of extensive
artisanal gold workings, and evidence from historic
work and recent work by consultants demonstrates
the significant potential of host gold mineralization.
However, to date there appears to be little
understanding of the source area, style of
mineralization or conceptual exploration models.
Figure 4 Visible Gold embedded in Rock Matrix
However, some domains within the basement
complex rocks of Sierra Leone are well known as
host for substantial gold mineralization occurring in
different geological environment in the country.
Structures of gold in Sierra Leone display a northeast
trending lineament, locally cross-cut and offset by
small northwest-southeast and east-west trending
faults.
A number of primary gold occurrence as well as
alluvial or placer gold deposits were identified from
various areas in the country. In spite of the country’s
long exploration history, there are still many gold
occurrences
remain
undiscovered
due
to
inappropriate prospecting methods.
Primary gold mineralization in the country has been
historically
identified
in
quartz
veining
with
disseminated to massive sulphides within amphibolites
units. The country’s gold mineralization is hosted by
shear zones or their subsidiary structures with gold
precipitated preferentially in the presence of magnetite
rich lithologies as a result of the competency and
chemical boundaries that they form.
Gold mineralization in Sierra Leone occurs in
different styles corresponding to different geological
environment and is genetically associated with the
country’s schist belt. Most gold occurrences in the
country are linked to a hydrothermal activity that
accompanied emplacement of Proterozoic to early
Paleozoic calc-alkaline granitoid.
The occurrence of gold mineralization is in the
greenstone belt which is made up of metasedimentary pelites and amphibolites units as well
as some syn to late-kinematic granites. The gold
occurs in different styles corresponding to different
geological environment.
Some gold deposits were related to a shearing
episode that post-dated emplacement of major
intrusions and others are thought to have formed by
exhalative hydrothermal processes during the break
phases of submarine volcanic activity.
Greenstone related gold deposits are typically
proximal to regional in scale, deep seated faults,
lineaments and shear zones.
Gold mineralization often occurs in relation to
shoots and lenses on second and third order
structures at low angles to the main structure in the
country.
In Sierra Leone, Gold mineralization is also associated
with sulphides and follows the contact between
magnetite rich garnet-cummingtonite schists and
cordierite schists. The contact zone is somewhat
several km wide.
Gold is known to occur in all Schist belts in Sierra
Leone
e.g.
around
Kamakwie-Laminaia,
Sula
Mountains, Kangari Hills, Nimini Hills, Gori Hills, Kambui
Hills and Gola Forest. Gold was mainly mined from
placer deposits and only in two areas around Baomahun
in the southern Kangari Hills and Komahun in the
eastern Nimini Hills where gold has been discovered to
occur as potential underground workings from quartzveins. The two companies operating in the area have
since secured a large scale mining lease and are yet to
commence operation.
Gold was first discovered in 1926 in the Makoke River
near Masumbiri. Further prospecting between 1928
and1930 proved the existence of an extensive alluvial
gold field in the Sula Mountains/Kangari Hills.
Gold mining started in 1930 and it occurrence were
found in the following areas:
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Gold at Kangari Hills
The gravels of almost all of the streams and rivers
in the Kangari hills are gold bearing. In March 1929
Mr. J.D Pollet discovered gold in a tributary of the
kwifuifui stream west of Makong. Later in the same
year Dr. Junner and Mr. Pollet discovered gold at
Baomahun and Dr Fowler Lunn found gold in the
Mapoko stream at Makele. These are the three
main areas in the Kangari schist belt where gold
occur.
Gold at Makong
To the west of Makong in the upper reaches of the
kwifuifui stream somewhat sugary quartz of veins
has been found and contains megascopically visible
gold. Around 1962, largest nugget found was about
1oz and large excavation in the tremolite schist
remaining. Mr. Pollet observed that in the kwifuifui
stream the best values of alluvial gold were
obtained where granite contained patches of
tremolite schist. Soil sampling, pitting, trenching
and drilling have been carried out by Axmin Mining
(SL) Ltd. as they own the Makong Licenses.
Gold at Makele
The gold in this area was probably derived from
pegmatites and the area is tectonically disturbed
like the molybdenite occurrence. The main gold
locality was 276.9 arcs in area and includes the
Mapoko stream near Makole and deposits
appeared to contain in the present river beds.
Gold at Baomahun
The gold at Baomahun is associated with a
mineralized zone carrying sulphides and this area
is situated within a tectonically disturbed area
different in geology from that of Makong. The gold
of these deposits derived from the below
mentioned rocks, especially from a zone of heavy
asenopyrite
mineralization
with
garnet
cummingtonite schist intermingle with strips of
quartzite and magnetite quartzite. Gold was found
in the heavy mineral concentrates of a tributary
adjacent to the asenopyrite zone. Through drilling,
geochemistry and large scale mapping, three main
areas of gold mineralization occurred in the West,
Central and Eastern ridge.
Gold deposit at Baomahun suggested that the
mineralization in the country is associated with
disseminated sulphides and lithologies with
varying resistivity.
Figure 5 Topographical Sheets with Known Gold Mineralization (hi
lighted) in Sierra Leone – (Data Sources: GIMS- NMA- 2016)
Cluff Gold has raised its mineral resource at the
Baomahun Gold Project in Sierra Leone to over the 1million-ounce bracket and plans scoping study for
underground redesigning. Cluff Gold reported a 40%
increase in total mineral resources at its flagship
Baomahun gold project after an extensive drilling
campaign
with
investigation
into
possible
mineralization extensions set to be launched shortly.
Gold at Nimini Hills
Placer gold was discovered in 1930 near Titambaia in
the Wongo stream in the Nimini plateau west of
Njaiama Nimikoro. In 1958 to 1962 lode gold was
investigated near Komahun by Laing. Extensive
fracturing and minor faulting occur along the Wongo
River on the western margin of the schist belt, both in
gneisses and schist. Very extensive alluvial gold
mining operations have carried out in the Valley of
Wongo River. Bands of banded iron stone occur in the
ultrabasic schist, close to it contact with banded
amphibolite.
An extensive programme of geochemical sampling,
loaming, trenching and drilling are carried out at
Komahun by Axmin Mining (SL) Ltd. An assay of this
drilled holes proved that lode mineralization is in the
sulphide zone. The mineralization consists of
asenopyrite with some pyrite in banded iron stone.
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reliable on their banks if they have broken through
the duricrust but the main guides to mineralization
are boulders of lateralized gossan.
Molybdenite with galena and other metallic minerals
occurs in the kinematic pegmatite
Gold in the Gori Hills
Gold is common in streams gravels of the schist belt
which has several fairly wide bands of aluminous
mica-quartz gneisses with numerous bands of
quartzite. Gold is also present in some of the streams
on the Western side of the schist belt. Extensive
pitting and mining has been carried out with alluvial
gravels in the flood plains of the western flowing
streams between Koidu and Bendu along the upper
part of the Sunya River and its tributaries North of
Bendu.
Figure 6 Geology Showing Schist Belts (yellow circles) in Sierra
Leone (Data Sources: GIMS- NMA 2016)
Gold at Sula Mountains.
The first gold found in Sierra Leone was in this area
in 1926 in the Makoke River near Masumbiri by N.
R. Junner. In the 30s several companies under
went exploration in the area including Coastal
Exploration Syndicate Ltd., Maroc Ltd, Balia Gold
Mining company etc.
Gold at Dalakuru Area
Dalakuru is the major gold production area in the
Sula Mountain and valuable deposits of alluvial gold
occur here. The area lies to the Sende River and
north of the Fundiburu River. The ground surface is
cover by duricrust boulders and soil. Amphibolite
and late kinematic granite outcrop in the Sende
River and banded iron formation occur to the west
of this area.
Lake Sonfon Area
The lake Sonfon country produces most gold in the
Sula mountain, but intense laterization hinders the
recognition of mineralization outcrops. Outcrops of
un weathered rock around Lake Sonfon down to
Dalakuru are exceptional and loaming is
unsatisfactory on duricrust surface but fairly
The greenstone belt of the country also serves as a
source for alluvial gold.
Gold in the Gola Forest Area.
Between 1940 -1941 gold was mined near Nongowa
village and the Pepe-Yama village and lowrima village
between 1942 to 1945. All the rivers are drained from
the southern Kambui hills to the western side. Stream
near Beodu village which is about halfway between
Lahuhum and Beledu low gold values were found with
younger granite intruding the granulite and quartz
magnetite hypersthenes gneisses.
Gaura Chiefdom drained a band of pyritised
hypersthene granulite rich in quartz and magnetite
but sample contains silver but no gold. Low gold
values were seen fairly east of the Moa River draining
granulite and ironstone bands that are intruded by
younger granite.
YEAR
Quantity(Oz)
Export Value (Le)
2009
5,361.46
14,500,799,025.53
2010
8,690.22
34,445,337,511.41
2011
5,374.62
27,512,074,885.67
2012
4,534.54
24,694,746,147.75
2013
3,099.41
15,763,548,045.74
2014
1,474.99
7,496,114,636.69
2015
3,460.28
18,332,608,452.51
Table:2 Gold Export 2009 to 2015 – Data Courtesy of Precious
Minerals Trading (PMT) -NMA
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Uses of Gold
Of all the minerals mined from the earth, there is none with more practical uses than gold.
Its usefulness is derived from a combination of truly unique properties. One such example of
its exceptional flexibility comes from the fact that it is the most malleable and ductile of all
metals. Modern science techniques have discovered how truly important this precious
substrate is in helping solve age-old and future challenges.
The following is a list of Gold’s most popular modern day application and uses;

Production of Jewelry
Gold has been used in the production of ornamental objects for several years now. While
expert opinion varies on this point, many believe that this was probably the first use of gold.
Specifically, it is a combination of the following attributes or qualities that give it its elevated
status among other precious metals:




Very High Lustre
Desirable yellow color
Resistance to tarnishing
Ability to be manipulated into wires, hammered into sheets or cast into shapes.

In Electronics
A small amount of gold is used in almost every sophisticated electronic device as conductors
carrying tiny currents and thus remain free of corrosion. This includes: cell phones,
calculators, personal digital assistants, global positioning system units and other small
electronic devices. Most large electronic appliances such as television sets also contain gold.

In Computers
Like other electronic devices, gold is used in modern desktops or laptop computers. Its ability
to rapidly and accurately transmit digital information through the computer and from one
component to another requires an efficient and reliable conductor and gold meets these
requirements better than any other metal. The importance of high quality and reliable
performance justifies its higher cost.
Edge connectors used to mount microprocessor and memory chips onto the motherboard and
the plug-and-socket connectors used to attach cables all contain gold. The gold in these
components is generally electroplated onto other metals and alloyed with small amounts of
nickel or cobalt to increase durability.

Coinage, Currency and Bullion
Because gold is so rare and highly valued, this precious metal makes a natural currency, and
has for at least 6,000 years. The U.S. used to hold all its monetary currency to a gold standard,
and since the turn of the millennium, gold value has been on the rise in the stock market. In
an uncertain economy, gold has emerged as a possible financial staple. One of the most
common ways to hold or invest in gold is in gold coins, gold bars, also gold bullion
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
Space and Aeronautics
In the aerospace industry where reliable and effective technologies are key to survival, gold
plays an essential role. Gold is used to lubricate mechanical parts, conduct electricity and coat
the insides of space vehicles to protect people inside from infrared radiation and heat.

Environmental Uses
Due to its unique chemical and metallurgical properties, gold has a vital role to play in future
technologies including water purification, reducing pollution, energy consumption, and diesel
emission control.

Medals and Awards
As a highly esteemed precious metal, gold makes a natural appearance in crowns, awards
and religious statues. Because of its unparalleled beautiful qualities and rarity, gold is one of
the highest status symbols. In everything from Academy Awards to Olympic medals, gold is
recognized for its admirable qualities and it holds a permanent place of value in humanity’s
eyes.
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Further Reading and Selected References.
Useful Contacts for further information.
The Mineral Potentials of Sierra Leone by Dr Klaus Peter-Freitag (1974)
Mineral Potentials in Sierra Leone Vol 1 and 2.
Geology of sierra Leone
http://www.nma.gov.sl/home/library-services/
http://www.recyclefrog.com/resource-centre/modern-uses-of-gold/
This commodity profile was compiled by
Joseph Lebbie
for
Directorate of Geological Survey in Sierra Leone (January 2016)
For further information, please contact
Directorate of Geological Survey Library Sierra Leone
13 Wilkinson Road, Freetown Sierra Leone
+232 79 999980
+232 79 252455
[email protected]
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