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R E IA P R UB E LIC OF LIB

The potential for gold in

liberia cover.indd 1 21/01/2016 09:28:22 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 , 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 maps for the entire country, supported by field the , which comprises two checking, allowed the bedrock geology and main major areas of Archean and Paleoproterozoic tectonic divisions of Liberia to be defined. rocks. Liberia was mapped during the 1970s in a joint programme between the Liberia Geological Liberian age (2.5–3.0 Ga) Archean basement, Survey (LGS) and the United States Geological extending across central and western Liberia, is Survey (USGS). Aeromagnetic and aeroradiometric characterised by a granite-greenstone association

12°W 11°W 10°W 9°W8°W 7°W

Voinjama Be drock gold occurrences

" ge 1New Liberty " Foya ± Mano River Ran 2Weaju zi -Wologizi Range gi 3Ndablama Wolo 4Innis N °N 5 Leopard Rock Masawo-Zolowo 8° 6Gondoja -Zorzor " Zorzor 7Mandingo Hill Bopolu-Wuesua A F -Tawalata O mba Range 8Mt Coffee L Ni 9 Lucky Hill YAMBESEIKpo Bea Mountain Mountains 10 Gayama 10 " Sanniquellie 11 Kle Kle " Karnplay 6 12 " 12 Toto Mountain Range 2 3 9 Ganta 13 Tortor Mountain 5 13 N8 " 14 River Cess N 7° Gbarnga " 1 Sacleapea 7° 15 Kokoya " Tubmanburg St. John River " -Kokoya 16 Jueh-Bokon Robertsport 15 17 Numon South 8 Kakata " 18 Sinoe 7 19 Dugbe F Putu Range Atlantic Ocean " 11 20 Zw edru Monrovia " -Zwedru Harbel 21 Bukon Jedeh Zwedru 22 Putu Range 20 " 23 Zia N °N S 23 4 6° O " T 24 Jolodah Village Buchanan T S O E D 14 C I Gold occurrence 16 22 Fault 17 Putu Range N H Alluvial gold belt Quaternary " Z O River Cess J U A Pan African age province Liberian age province COTE D'IVOIRE DUGBE Supracrustals Supracrustals River " 18 19 Granitic to dioritic gneiss Granitic rocks Cestos River Gbeh N6 " 21 N 5° Intermediate to basic Greenville 5° Eburnean age province E intrusions B Supracrustals U Granitic gneiss D Intermediate to basic Granitic to dioritic gneiss " intrusions Bukon Jedeh 24 Pleebo Granitic to dioritic gneiss " Town ! 0255075100

! " ! ! International boundary Harper Km

12°W 11°W 10°W 9°W 8°W 7°W Simplified geology of Liberia showing the principal gold occurrences.

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liberia GOLD.indd 2 21/01/2016 09:26:33 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 Drilling for gold in Sinoe County. Courtesy of Hummingbird Resources plc. 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 volcano- sedimentary sequence, the Birimian Supergroup, Gold prospecting in south-east Liberia. Courtesy of Ryan Langdon. 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 also trends north-east. The north-west-trending relationship between the Birimian sequence Todi Shear Zone marks the boundary of the elsewhere in West Africa and the Eburnean age Pan African province and comprises a series province of Liberia is unclear, they are generally of south-west-dipping faults associated with considered to be equivalent. intense zones of mylonite.

Pan African-age rocks (c. 550 Ma) underlie an Gold in Liberia elongate, fault-bounded zone along much of Liberia’s coastline. They comprise metasedimentary There is a long history of artisanal gold mining and mafic meta-igneous rocks containing in Liberia from alluvial placers with production granitic bodies and subordinate noritic intrusions. peaking at more than 30 000 ounces per annum Phanerozoic rocks in Liberia include extensive in the 1940s. Between 2008 and 2012 annual north-west-trending Jurassic-age dolerite dykes, production is estimated at about 20 000 ounces minor Paleozoic and Cretaceous sandstones and per annum (BGS, 2015). unconsolidated Quaternary deposits. The cratonic geological environment of Liberia is Multiple phases of deformation are present favourable for two main types of gold deposit: in the Precambrian rocks. The structural trend of the rocks in the Liberian and Eburnean age i) greenstone-hosted quartz-carbonate vein provinces is principally north-east, whereas deposits (a subtype of lode gold deposits) in that of the Pan African province is mainly a wide variety of host rocks; north-west. A number of major north-east- trending faults in eastern Liberia are extensions ii) alluvial placer deposits. of regional structures, which extend into Côte d’Ivoire, and include the economically important Nearly 600 gold occurrences have been recorded Cestos, Dugbe, Dube and Juazohn shear zones. in Liberia, with gold placer deposits accounting The Lofa River Shear Zone in north-west Liberia for almost 80 per cent of the total.

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liberia GOLD.indd 3 21/01/2016 09:26:54 Gold grains recovered during exploration in Sinoe County. Courtesy of Hummingbird Resources plc.

Placer gold deposits Drilling for gold in Sinoe County. Courtesy of Hummingbird Resources plc.

Deep and intense weathering since the Pleistocene, and persistent erosion in areas Bedrock gold deposits of moderate to low relief, coupled with clay bottoms to most of the gravel deposits, favour Bedrock gold deposits in Archean and Proterozoic the development of gold placers across Liberia terranes in West Africa are highly varied in size although most are found in the eastern and and form but typically consist of mineralised shear western parts of the country. The deposits zones and structurally-controlled quartz veins, and worked by artisanal miners are generally less are comparable with granite-greenstone-hosted than two metres thick, and are narrow and lode-gold mineralisation globally. discontinuous in form. The gold grains have rounded edges and are moderately coarse in size, Archean lode-gold deposits with nuggets widely reported. Lode gold deposits in Archean rocks in Liberia A number of ‘gold belts’ have been defined based are found in a wide variety of greenstone-belt on the distribution of alluvial placer deposits: lithologies with metamorphic grade ranging from lower greenschist to upper amphibolite facies. ▪▪ Bea Mountain The mineralisation, which may comprise quartz ▪▪ Bopolu-Wuesua-Tawalata veins, breccia zones, stringers and disseminations, ▪▪ Masawo-Zolowo-Zorzor typically extends over widths of 10–20 metres and may have a strike extent of more than a ▪▪ Mano River-Wologizi Range kilometre. Structure exerts strong control on its ▪ St. John River-Kokoya ▪ distribution with north-east-trending zones of ▪▪ Cestos River intense shearing being particularly important. ▪▪ Putu Range-Zwedru Other favourable sites include zones of polyphase ▪▪ Bukon Jedeh deformation, fold limbs and closures, and competency contrasts such as sheared lithological Each of these includes a large number of contacts. The mineralisation comprises free alluvial placer deposits some of which have gold closely associated with a range of silicates, been worked in the past and others where including quartz, tourmaline, chlorite and sericite, significant resources remain. However, it and various sulfide minerals. is generally considered that major placers amenable to large-scale modern mining The gold-bearing mineralisation may be methods are unlikely to be found in Liberia. associated with local development of a range of The widespread occurrence of placer deposits alteration minerals including, most commonly, suggests significant potential for bedrock- chlorite, carbonate and sericite. In some deposits, hosted gold mineralisation and provides useful dependent on host rock lithology, the alteration guidance on exploration targetting. assemblages may include phlogopite, talc,

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liberia GOLD.indd 4 21/01/2016 09:26:55 magnetite, hematite, iron sulfide, tourmaline and grade of 1.6 g/t Au was reported at Ndablama in tremolite. A range of metals may be enriched in December 2014. the gold-bearing ores including arsenic, tungsten, cadmium, copper, lead and zinc. Exploration in the Kpo Mountains area of Gbarpolu County has identified gold-bearing Perhaps the best known and economically most quartz veins. Mineralisation is thought to be important gold occurrences in the Archean related to sheared lithological contacts between greenstone belts are found in north-west Liberia granite, granitic gneiss and supracrustal rocks, associated with a series of major north-east- consisting of BIF, schist and amphibolite. To trending structural lineaments, principally shear the north of the Kpo Range gold-bearing veins, zones. New Liberty is a shear zone-hosted gold hosted in granite and granitic gneiss, occur in the deposit in Archean age rocks with a greenstone Lucky Hill (Gblita) area. Mineralisation appears to belt affinity. It is a fully financed project with be controlled by the lithological contact between planned annual production of 120 000 ounces granite and granitic gneiss. of gold which began in 2015. Further details are given in Deposit Profile 1. Numerous additional Gold mineralisation comprising brecciated quartz major gold occurrences occur along a structural stockworks in strongly sheared zones has been corridor extending north-east of New Liberty. located in the Mandingo Hill area in Bomi County. Prominent examples include Weaju and Ndablama A number of structurally controlled, quartz- where exploration continues and significant gold sulfide-bearing gold occurrences occur in the resources have been identified. At Ndablama, in Mount Coffee area of the Todi Shear Zone. Further an area of established alluvial gold mining, gold east along the shear zone at Kle Kle several broad mineralisation is hosted in sheared ultramafic zones of gold mineralisation have been defined. and mafic rocks intercalated in a gneiss sequence above a buried granite body. Gold is frequently Quartz vein-hosted and disseminated gold localised along sheared contacts between the mineralisation occurs in strongly sheared schists ultramafic and mafic units that are intruded by in the Toto Mountain Range area in Bong County. granitic dykes and breccias. Phlogopite, tremolite, In the south of Bong County a mineral resource chlorite and talc alteration is associated with the (indicated) containing 210 000 ounces of gold mineralisation. A mineral resource (indicated + at a grade of 3.5 g/t Au is reported at Kokoya. inferred) containing 901 000 ounces of gold at a The mineralisation is structurally controlled and hosted in a package of strongly deformed amphibolites and gneisses. Deposit Profile 1: New Liberty, Grand Cape Mount County, north-west Liberia Proterozoic lode-gold deposits Deposit style: Archean shear zone-hosted gold. Most West African gold production has been Local geology: footwall and hanging wall gneiss and banded derived from Birimian-age greenstone belt rocks migmatites, containing greenschist-amphibolite facies rather than from the Archean. ultramafic rocks that host the gold. Deposit geology: structurally-controlled mineralisation in a Little systematic modern exploration has been 100 metre-wide, steeply-dipping ultramafic unit. Mineralisation undertaken over the Birimian terrane in south-east is 10–20 metres wide, strike length 2 kilometres. Liberia and the geology has not been studied in Mineralogy and alteration: free gold associated with detail. However, as in the Archean terrane, alluvial silicates and sulfides (pyrrhotite, arsenopyrite, gersdorffite). gold occurrences are numerous and widespread Weak silicification, magnetite destruction and phlogopite and significant mineralisation in bedrock is alteration. known at several localities. Host rock lithologies Mineral reserve: 8.5 million tonnes @ 3.4 g/t Au. are varied but commonly include metavolcanic and metasedimentary rocks, mafic and granitic Mining: Continuity of mineralisation to 500 metres proven by intrusives, pegmatites and sulfide-rich schists drilling. Open pit to 220 metres planned. and gneisses. The mineralisation is commonly Exploration: mineralisation associated with enhanced S, As located at the host rock contact with banded and W and enrichment in Na, K, Rb and Ba along marginal iron formation (BIF). The mineralised bodies have zones; strong magnetic and induced polarisation responses. variable morphology, ranging from irregular

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liberia GOLD.indd 5 21/01/2016 09:26:55 Visible gold in drillcore. Courtesy of Hummingbird Resources plc.

Jueh-Bukon, Numon South) have been identified in the environs of the Cestos Shear Zone, which

Analysis of drillcore using a portable XRF. Courtesy of Hummingbird Resources plc. lies along the contact between Archean and Proterozoic rocks and represents a near-vertical, crustal-scale structure that has been compared sheets, to quartz-carbonate sulfide-bearing veins, with the Ashanti Gold Belt in . The Ity gold disseminated sulfides and sulfide stringer veins. mine in Côte d’Ivoire is located on the north- As in the Archean terrane geological structure eastern extension of this shear corridor. is a dominant control on the location of gold mineralisation. Particularly favourable sites include The Juazohn Shear Zone is another highly second-order structures to regional shear zones, prospective target on account of known bedrock structural intersections, lithological contacts, occurrences, extensive alluvial deposits and gold grain-size variations within sedimentary packages geochemical anomalies. BIF-associated gold and zones of polyphase deformation. The gold deposits are the principal target in the area. High occurs as free grains commonly closely associated grade mineralisation has been reported at several with sulfide phases, chiefly pyrite, arsenopyrite locations including Zia in the north, Zwedru to the and pyrrhotite. Hydrothermal alteration is present west and in the Putu Range area which straddles in some deposits, commonly with attendant the Juazohn Shear Zone. enrichment in arsenic, bismuth and silver. The regional Dugbe Shear Zone in south-east The most important bedrock gold deposits in Liberia has been the focus of increasing gold this terrane are spatially associated with major exploration in recent years. To date the most regional shear zones trending either north-east or significant discoveries are located at Dugbe 1 east-north-east. Numerous gold occurrences (e.g. 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. NW SE Approximately 12 kilometres to the south-east 150 drilling has intersected significant high-grade Surface 100 gold mineralisation at Bukon Jedeh. The intrusive contact with a granite is a favoured site for high 50 grade gold in this area. Along strike to the west of 0 the Dugbe 1 Project gold mineralisation has been

-50 identified in the Sinoe area, which is characterised Limit of by biotite and garnet-biotite schists, intruded by defined -100 ore sulfide-bearing quartz-feldspar-mica pegmatites

-150 and mafic and granitic intrusives. The highest gold concentrations appear to be associated with -200 pegmatitic zones.

-250 m 0 100 m Potential for new discoveries Intrusive Oxide zone Higher grade Life of mine ore ore The wide distribution of placer gold deposits

Migmatitic gneiss Pit boundary at a gold price of US$1200 per ounce across Liberia indicates the potential for new major bedrock gold discoveries. Under-explored Simplified section through the Dugbe 1 project Tuzon areas of alluvial mining activity are priority Resource. (Modified from Hummingbird Resources plc). targets for future exploration. 6

liberia GOLD.indd 6 21/01/2016 09:26:56 national aeromagnetic data. The relationship Deposit Profile 2: Dugbe 1 project (comprising 3 between bedrock gold and BIF in Liberia is deposits — Dugbe F, Tuzon, Sackor), Sinoe County, illustrated by the Innis prospect to the north of east Liberia the Cestos Shear Zone, where gold is associated Deposit style: Proterozoic shear zone-hosted gold. with disseminated and vein-hosted sulfides hosted by sericite-altered gneiss, BIF and garnet Local geology: migmatitic, feldspar-biotite-quartz- schist. Other areas with extensive BIF, coinciding othropyroxene gniesses. with major structural corridors, are highly Deposit geology: Dugbe F is a shallow-dipping, 8–15 metre prospective. Targets of this type associated with thick tabular mineralised body, with a strike length alluvial gold occurrences are located in the Nimba, >2.5 kilometres. Tuzon comprises a wider mineralised ‘folded Putu and Wologizi ranges. nose’ ore body. Mineralogy and alteration: gold mineralisation associated In north-west Liberia the under-explored north- with increased sulfide content. Free gold occurs as very fine east extension of the Archean-granite-greenstone grains along microfractures, grain boundaries and in quartz- terrane, bounded by the Lofa and Yambesei shear sulfide-bearing veins. Alteration is inconspicuous away from corridors, is a priority target for gold exploration, the mineralised zone. owing to the favourable geology, structure and Mineral resource: 43 million tonnes @ 1.28 g/t Au (Dugbe F, alluvial placer deposits. Inferred) + 41.8 million tonnes @ 1.51 g/t (Tuzon, Indicated). Mining: a Preliminary Economic Assessment (April 2013) Other areas that merit further investigation concluded the project is robust from a technical and economic include: the southern end of the Todi perspective, based upon a financial model spanning a 20 year Shear Zone in the River Cess area where mine life. Both Dugbe F and Tuzon can be mined as open pit. 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 The distribution of BIF, considered to be the in stream sediments have been reported; and source of much of the placer gold in the Archean the western end of the Dube Shear Zone in of West Africa, is relatively well known in Liberia the Jolodah Village area of Grand Kru County on account of the extensive exploration that where alluvial gold is widespread, although the has taken place for iron and the availability of bedrock source has not been identified.

Selected references Aureus Mining. 2014. www.aureus-mining.com Shannon, E H, and Sangmor, S S. 1982. Geology for development: a survey of the British Geological Survey (BGS), 2015. World principal mineral resources of Liberia and Mineral Production, 2009–2013. their exploration potential. Liberian Geological Hummingbird. 2014. www.hummingbirdresources. Survey, Monrovia. co.uk Thayer, T P, and Lill, G G. 1974. Mineral exploration Hedge, C E, Marvin, R F, and Naeser, C W. 1975. Age in western Liberia 1949–1950. Geological Survey provinces in the basement rocks of Liberia. U.S. Special Paper No. 4. Ministry of Lands and Mines Geological Survey Journal of Research, 3, 425–429. Republic of Liberia. Liberian Geological Survey. 1982. Summary of the Tysdal, R G, and Thorman, C H. 1983. Geologic Precambrian geology of Liberia — contribution map of Liberia. 1:1 000 000. US Geological Survey to IGCP project No. 108/144. Liberian Geological Miscellaneous Investigations Series Map I-1480. Survey, Monrovia, Liberia. Wahl. 2007. Geologic, Geophysical, and Sangmore S S, and Nair A M. 1985. Geology, Mineral Localities Map of Liberia — A Digital petrogenesis, gold and associated mineralization Compilation. USGS Open-File Report 2007– in the Tortor Mountain Range, Bong County, 1258, Sheet 1 or 4. Liberia. Liberian Geological Survey, Monrovia.

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liberia GOLD.indd 7 21/01/2016 09:26:56 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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