The Potential for Diamonds in Liberia

NDS, MI LA NE F S O & Y GICAL SU E R LO RV N O E T E Y E S G I R

G N I

R E IA P R UB E LIC OF LIB

The potential for diamonds in Liberia

liberia diamond cover.indd 1 21/01/2016 09:33:29 Liberia — an under-explored West African diamond region:

▪▪ More than 160 known occurrences of kimberlite, with many part of a single province that includes diamondiferous kimberlites in neighbouring Sierra Leone and Guinea. ▪▪ A long history of alluvial diamond production in western and central Liberia. ▪▪ Potential for new alluvial and bedrock diamond discoveries in under-explored Archean terrane.

Diamonds in West Africa

Diamonds in West Africa are produced from (>300 kilometres), Archean crust with low both primary (bedrock) kimberlite sources and geothermal heat flow (c. 40 mW/m2), representing secondary (alluvial) placers in Ghana, Guinea, a favourable tectonic environment for economic Sierra Leone, Togo and Liberia. West African kimberlites (Kjarsgaard, 2007). It is host to diamonds account for approximately one per cent numerous kimberlite pipes and dykes, some of of the global production of diamonds (BGS, 2015). which are known to be diamondiferous. Published information about West African kimberlites is The Man Shield, that underlies a large part of generally sparse, with those in Sierra Leone being

central and western Liberia, is an area of thick the most studied. West African kimberlites can be

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! ! International boundary ! Harper "! 13°W 12°W 11°W 10 °W 9°W 8°W 7°W Simplified geology of Liberia showing the distribution of principal diamond occurrences in Liberia and neighboring countries. 2

liberia_diamond.indd 2 02/08/2016 15:50:11 broadly divided into two groups according to their to represent the entire production of diamonds age: in country due to the artisanal nature of the mining. Exports and imports of rough diamond 1. Precambrian kimberlites of Paleoproterozoic are overseen by the Government Diamond Office (2.1–2.3 Ga), Mesoproterozoic (1.15 Ga) and (GDO) within the Ministry of Lands, Mines and Neoproterozoic (700 Ma) age and Energy and by the Bureau of Customs. 2. Mesozoic kimberlites of late Jurassic (150 Ma) to late Cretaceous (80 Ma) age. The geology of Liberia

Notable Jurassic-age kimberlite deposits in the Liberia is underlain by the Man Shield, part of the region include the Tongo kimberlite (Sierra Leone) West African Craton, which comprises two major that has an estimated resource of about 1 million areas of Archean and Paleoproterozoic rocks, carats, and the Baoulé kimberlite mine (Guinea), with mapped during the 1970s in a joint programme an estimated resource in excess of 3 million carats. between the Liberia Geological Survey (LGS) and the United States Geological Survey (USGS). Diamond-bearing alluvial placers are frequently associated with kimberlite-rich areas in West The Precambrian Man Shield underlying Liberia can Africa, although in many cases their age, formation be subdivided into three age provinces (see map). and distribution are not clearly understood. Both The Liberian age province (2.5–3.0 Ga) extends industrial and gem-quality diamonds of varying size across central and western Liberia and is composed have been recovered from alluvial placers across of a suite of granitoid gneisses and migmatites the region. A small number of alluvial deposits which are infolded with supracrustal metavolcanic have been successfully mechanised (e.g. Mandala, and metasedimentary rocks and intruded by a Guinea), although most are worked on a small scale younger igneous complex. The Eburnean age by artisanal miners. In Sierra Leone, the diamond- province (1.9–2.3 Ga) of southern and eastern producing areas are concentrated in Kono, Kenema Liberia consists of tightly folded paragneiss, and Bo Districts and are mainly situated in the migmatite and amphibolite. It is separated from the drainage areas of the Sewa, Bafi, Woa, Mano and Liberian age province by the north-east-trending Moa Rivers. According to official figures, Sierra Leone Cestos Shear Zone. Rocks of the Pan African-age exported about 633 000 carats in 2013 (Kimberley province (c. 550 Ma) underlie an elongate, fault- Process, 2015). In Guinea, JORC-compliant inferred bounded zone along much of Liberia’s coastline. resources of 2.5 million carats at Droujba and They comprise metasedimentary and mafic meta- 2.9 million carats at Katcha have been reported. igneous rocks containing granitic bodies and subordinate norite intrusions. In Liberia, diamonds are produced solely from alluvial placers by artisanal miners located in the Mesozoic rocks in Liberia include extensive west and central parts of the country. Liberia has north-west-trending dolerite dykes emplaced a long history of alluvial diamond production, during a period of rift-related magmatism with an output of about 14 million carats (180–200 Ma). Reactivation of north-east- during the last 50 years. Output from small- trending Archean basement structures, and the scale operations peaked at about 600 000 carats subsequent emplacement of kimberlites, occurred per annum during the early part of the 1970s. during a later period of rifting (90–140 Ma). Historic diamond production was tarnished by Diamond-bearing kimberlites are restricted to the its association with conflict in the region. For this Liberian age province. Both the Eburnean and Pan reason diamond production between 2002 and African-age provinces were thought to be barren 2007 was depressed by export sanctions imposed (Haggerty, 1992). However, recent discoveries of by the United Nations, in an attempt to end alluvial diamonds in south-eastern Liberia cast illicit diamond mining in Liberia. In 2007 Liberia doubt on this assumption and highlight some became a Kimberley Process participant and, since uncertainty in the understanding of the tectonic then, diamond production has steadily risen to evolution of the region. approximately 80 000 carats in 2014 (Central Bank of Liberia, 2014). Reporting of diamond production The USGS/LGS documented about 160 kimberlite is compulsory under the Kimberley Process; occurrences in central and western Liberia. however, production figures are not guaranteed However, due to lack of bedrock exposure, poor 3

liberia_diamond.indd 3 02/08/2016 15:50:31 the Liberian occurrences are small pipes (with sur- face areas less than 0.1 km2) and thin dykes (up to a few metres thick) (Thorman, 2006).

To date, Liberian kimberlites have not been com- mercially exploited for diamonds and the number of kimberlites with economic potential remains unknown. The recent increase in diamond production is linked to a rise in the number of alluvial diamond deposits being worked and the increased mechanisation of the production process. No Diamond exploration at the Camp Alpha pipe. ©Stephen E Haggerty [YDMC] modern estimates of diamond resources have been published for Liberia.

access and dense vegetation, this may not be Diamonds in Liberia — key areas an accurate reflection of the true number of occurrences. USGS and LGS regional surveys during the mid 1970s identified numerous alluvial placers and Diamond exploration kimberlite indicator minerals in central and western Liberia. On the basis of these surveys, together Liberia has a lengthy history of diamond explo- with previous exploration and small-scale mining ration, particularly in central and western Liberia. activity, extensive areas in central and western Between 1962 and 1966 the Diamond Mining Liberia with significant alluvial diamond deposits Company (Liberia) identified a number of kimber- have been defined. Another locality in south-east- lite dykes as part of a regional exploration pro- ern Liberia has recently been identified as an gramme. In 1972 the United Nations undertook a artisanal diamond mining area. mineral indicator survey over western Liberia and discovered the small Mano Godua kimberlite pipe. Lofa River In the late 1970s a number of companies were active along the Lofa River and Yambasi creek. Many The Lofa River is one of the largest rivers of the early exploration campaigns concentrated in the country draining a distance of about on the discovery of alluvial diamond deposits. 350 kilometres from the east of the Wologizi However, seasonal flooding, poor access and the Range. The Lofa River region, especially from erratic distribution of diamond-bearing gravels Weasua to the coast, is host to significant alluvial meant that many companies were ultimately diamond production, with numerous workings in unsuccessful in bringing Liberian alluvial diamond the Lofa and Yambasi River basins and associated deposits into commercial production. Neverthe- tributaries. Occurrences in these basins extend less, the discovery of alluvial diamonds alerted from Weasua to the coast at Bomboja. The companies to the possibility of discovering buried distribution of diamonds in alluvial deposits in the kimberlites in central and western Liberia. Lofa River area is highly erratic, although early exploration reports suggest that lower terrace Since the 1980s, exploration for diamond-bearing gravels, ancient alluvial river flats and deep- kimberlites has increased significantly leading to plunge pools within the active river channel are the recent discovery of diamond-bearing kim- the most prospective areas for diamond recovery. berlites in western Liberia. Three distinct clusters The high diamond potential of the Lofa River area have been recognised: Kumgbor, Mano Godua and is attributed to a number of factors, including the Weasua. Other kimberlite occurrences, identified known occurrence of kimberlitic source rocks and by the USGS and LGS, are found in Nimba County, close proximity to the highly prospective eastern central Liberia. Seven new discoveries were made diamond region in Sierra Leone (Dorbor, 2010). by Mano River Resources, near Weasua, between 2000 and 2006. In addition a series of kimberlite Mano, Kumgbor and Morro-Gbeya rivers dykes, and a single pipe, were discovered in the Camp Alpha area by the Youssef Diamond Mining The Kumgbor and Morro-Gbeya Rivers, which Company (YDMC) in 2013 (Haggerty, 2015). All of drain into the Mano River, are areas of intense 4

liberia_diamond.indd 4 02/08/2016 15:50:32 artisanal mining, with diamonds produced from and river-terrace gravels flanking Bee Creek, many of the creeks, particularly the Papaya Creek although little is known about their distribution, (Dorbor, 2010). Gem-quality diamonds, up to a morphology and grade. However, local reports maximum of 170 carats, and industrial diamonds suggest that diamonds up to 15 carats have been were recovered from this area in the late 1970s. recovered from the area (Dorbor, 2010).

Du River Sinoe River

Historic alluvial workings have been identified Alluvial diamond workings are found in the area in the Kakata area of the Du River basin. The around the Sinoe River in south-eastern Liberia, diamonds recovered from this area are generally but no information about these operations is small but mostly of gem quality. Kimberlitic rocks available (Dorbor, 2010). However, this is the first and associated minerals have not been found in evidence of diamond occurrences in this part of the Du River diamond area and, therefore, the source the country, generally thought to be underlain of the alluvial diamonds remains unknown, although by Proterozoic rocks of Eburnean age, which are it has been suggested that local conglomerates may considered to be barren. This highlights possible be a potential source (Dorbor, 2010). uncertainty over the tectonic evolution of this part of the country and the extent of the Archean Yaa River, Boe and Nzar creeks outcrop in Liberia (Haggerty, 1992).

The Gbapa-Bahn diamond area in Nimba County Kimberlite-hosted diamond deposits is relatively under-explored. It is largely confined to the margins of the Boe Creek, where kimberlitic The majority of Man Shield kimberlites are rocks were identified by the USGS and LGS in the geochemically classified as type-A, non- early 1970s. The area has a history of small-scale micaceous kimberlites (i.e. on-craton, basaltic alluvial diamond mining dating back to the 1950s. kimberlites) and typically occur as small pipes The diamonds are typically found in floodplain and abundant dykes. Liberian kimberlites occur in

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liberia_diamond.indd 5 02/08/2016 15:50:33 from Koidu in Sierra Leone (Tompkins and Haggerty, 1984) suggests that these kimberlites are highly prospective for diamonds. The presence of micro-diamonds in a kimberlite is another strong indicator of the macro-diamond potential of a kimberlite; the significant population of micro-diamonds recovered from kimberlites at Camp Alpha in Liberia is, therefore, encouraging.

Comparative studies of kimberlites in eastern

Pandanus candelabrum growing on the Camp Alpha pipe. ©Stephen E Haggerty [YDMC] Sierra Leone and western Liberia focussed on the KIM picroilmenite. This research identified kimberlites in Sierra Leone trending east–west. These lack a distinct magnetic anomaly as do three distinct clusters, two of which are Jurassic north–south trending kimberlites in Liberia. in age (Kumgbor and Mano Godua) and one older, Similar east–west trending kimberlites with no Neoproterozoic-age, cluster (Weasua) (Skinner clear magnetic signature may be present in Liberia et al., 2004). The Jurassic kimberlites are thought (Haggerty, 1978). to form part of single kimberlite province that extends into neighbouring Sierra Leone and Geobotany Guinea. Further evidence for the existence of a single kimberlite province is given by Taylor et al. Localised swampy conditions are a possible (1994) who suggest, on geochemical grounds, guide to the presence of kimberlites. This is due that Jurassic kimberlites from Liberia, Sierra to the clay-rich and hence impervious nature of Leone and Guinea are all type-A, non-micaceous the kimberlite bedrock. Furthermore it has been kimberlites. suggested that, a new species of palm, Pandanus candelabrum, may be restricted to the soils The recent discovery of a kimberlite pipe developed over kimberlite pipes but not kimberlite (2.5 hectares in area) in the Camp Alpha region in dykes (Haggerty, 2015), possibly diagnostic of Kumgbor (Haggerty, 2015) highlights the potential coarsely-brecciated kimberlite pipe eluvium. If this for bedrock-hosted diamonds in Liberia. The relationship is substantiated, it has potentially associated dykes have significant micro-diamond important implications for improving future populations, suggesting that the pipe may have exploration for kimberlite pipes in Liberia and economic potential. across West Africa.

Kimberlite indicator minerals Potential for new discoveries

The identification of resistant kimberlite indicator On the basis of favourable basement geology, the minerals (KIMs), such as garnet, spinel, ilmenite, wide occurrence of alluvial diamonds and the clinopyroxene, forsterite, orthopyroxene and known presence of kimberlites, there is considered zircon, in stream sediments and soil samples is a to be significant potential for the discovery of well-established exploration tool for kimberlites additional diamond resources, both in bedrock (Kjarsgaard, 2007). A number of these minerals and alluvium. The abundance of hypabyssal- have been widely identified in stream sediments in (root-zone) kimberlites relative to diatreme-facies Liberia. To date, indicator minerals have only been kimberlites in the Man Shield is indicative of analysed from a small number of kimberlites in extensive erosion across the region. Liberia. For example, the composition of garnet (a chromium-rich, calcium-poor variety) and spinel River systems in western Liberia are strongly (a chromium- and magnesium-rich variety) from influenced by the underlying geology and the Neoproterozoic Weasua kimberlites suggest structures. The river courses are irregular, that these pipes may be prospective for diamonds commonly leading to sporadic sedimentation. (Skinner et al., 2004). Similarly, the chemistry of In the case of the Lofa River this results in large ilmenite crystals recovered from kimberlites low overall volumes of gravel deposition but at Camp Alpha in Liberia (Haggerty, 2015) and produces small pockets of gravel rich in heavy

liberia_diamond.indd 6 02/08/2016 15:50:34 minerals (Leuria, 1966). Terraces along the river have suggested that the greatest quantity of are frequently the site of reconcentration of diamonds is located proximal to the source, such heavy minerals, although these are generally as at Koidu, Sierra Leone, where there has been difficult to identify as they are blanketed by thick extensive erosion, such as in Liberia, the potential lateritic overburden. Geomorphological mapping for distal transport should not be overlooked. The in the Koidu area of Sierra Leone, the Birim area estuary of the Lofa River at Bomboja is considered of Ghana and the Tortiya area of Cotê d’Ivoire to be a favourable target for the development of highlight the benefits of modern paleogeomorphic placer diamond deposits offshore. Attempts to studies for diamond exploration. This research begin mining in this area without the prerequisite emphasises the importance of understanding the exploration phase have not been successful. Quaternary evolution and hence the depositional environments in the region and the influence Historic diamond production in Liberia has that this has had on local diamond distribution. A been sporadic and has used primitive recovery similar approach could help to delineate the most techniques. Large areas of prospective ground prospective areas for alluvial diamond exploration have not been evaluated using modern methods. in west and central Liberia. Ground-based electromagnetic and magnetic surveys, successfully employed in Sierra Leone and The potential for offshore diamonds along the Guinea, should also be employed in conjunction Liberian coastline is high. Although studies with botanical surveys and KIM-chemistry.

Selected references

British Geological Survey (BGS). 2015. World Metallogeny, the Evolution of Geological Mineral Production 2009–2013. British Geological Provinces, and Exploration Methods. Eds. Survey, Keyworth, Nottingham. Goodfellow, W D. Geological Association of Canada, 245–271. Central Bank of Liberia (CBL). 2014. Annual Report 2014. Leuria, B. 1966. Notes on the geology of the Lofa River couth of Weasua, with a comment on Dorbor, J K. 2010. The regional geology and diamond dispersal and recovery. Diamond Mining mineral potential of the Republic of Liberia — a Corporation of Liberia, Ltd. summary. The Liberian Geological Survey, Ministry of Lands, Mines and Energy, Monrovia, Liberia. Skinner, E M W, Apter, D B, Morelli, C and Smithson, N K. 2004. Kimberlites of the Man Haggerty, S E, Hardie, R B and McMahon, B M. craton, West Africa. Lithos 76, 233–259. (1978). Kimberlitic ilmenite compositions from Western Liberia. Ministry of Lands, Mines and Taylor, W R, Tompkins, L A and Haggerty, S E. Energy, Monrovia, Liberia. 1994. Comparative geochemistry of West African kimberlites: Evidence for a micaceous kimberlite Haggerty, S E. 1992. Diamonds in West Africa: endmember of sublithospheric origin. Geochimica tectonic setting and kimberlite productivity. et Cosmochimica Acta 58, 4017–4037. Russian Geology and Geophysics 33, 35–49. Thorman, C H and Hoal, K O. 2007. Geological Haggerty, S E. 2015. Discovery of a kimberlite pipes assessment of Liberia's diamond producing regions, and recognition of a diagnostic botanical indicator diamond production potential and review of Liberia's in NW Liberia. Economic Geology 110, 851–856. production history, 107. Unpublished report. Kimberley Process, 2015. Statistics. http://www. Tompkins, L A and Haggerty, S E. 1984. The Koidu kimberleyprocess.com/en/liberia [accessed August kimberlite complex Sierra Leone: Geological 2015] setting, petrology and mineral chemistry. In: Kjarsgaard, B A. 2007. Kimberlite diamond Kimberlites and Related Rocks. Eds. Kornprobst, J. deposits, in: Mineral Deposits of Canada: A Elsevier Science Publishers, 83–105. Synthesis of Major Deposit-Types, District

liberia_diamond.indd 7 02/08/2016 15:50:34 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 Richard Shaw and Éimear Deady 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; rough diamonds ©iStock.com.

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

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/

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