ANDS, MIN L ES F O & Y GICAL SU E R LO RV N O E T E Y E S G I R G N I Y M 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 ¨ 13°W 12°W 11°W 10°W ¨ 9°W 8°W 7°W ¨ ¨ ¨ ¨ ¨ ¨ !¨ ¨ ¨ ! ¨ N Banankoro N ¨ ¨ Bouro 9° ¨ 9° ± Baoulé ¨ ¨ ! ¨ Koidu ! ¨ ! ! ! Mandala Droujba ! X! X ! ! Katcha X! " Voinjama¨ ! ! " ¨ Foya ! er To ngo ! ! ! ! fa Riv ! ! N Lo GUINEA N 8° 8° ! ! X ¨ SIERRA LEONE ¨ X Zorzor ! ! ¨ ¨ " ¨ ¨ X ! ! X! ! !¨ X ¨ ¨ ¨ X KumgborXXXX!X ! X ! ! X X X ! X ! X XX¨ Weasua X! X XX ! X X ! ! X ! X Sanniquellie " ! r ! ! "X eX ¨ Mano ! ! iv ! " Karnplay ! ! ¨ X R Godua Weasua ! o ! ! Kimberlite dyke n ! a N X ! ! M N 7° Kimberlite pipe " " ! ! Tubmanburg 7° X " Gbarnga Sacleapea X! COTE D'IVOIRE Diamond occurrence ! ! ! Robertsport " ! ! ! Quaternary ! " ! ! Kakata X ! ! Pan African age province " X ! Bomboja ! X r ! Supracrustals ! e X ! v X ! i ! ! ! ! ! "! R ! Granitic to dioritic gneiss ! Monrovia ! ! ! u ! Eburnean age province D Zwedru ! ! " ! N Supracrustals N ! 6° ! 6° Intermediate to basic " ! ! Buchanan ! ! intrusions ! Granitic to dioritic gneiss ! Du b ! ! e R Liberian age province ! iv ! er " ! Supracrustals ! Cestos City ! Granitic rocks ! ! ! Intermediate to basic Atlantic Ocean ! X ! ! intrusions ! N ! " N ! ! ! 5° Granitic gneiss 5° Greenville ! ! ! Granitic to dioritic gneiss ! " ! Town ! ! ! ! 0255075100 " ! ! Primary Rivers ! Pleebo ! ! ! Km ! ! ! 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 produc- tion 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 west- ern 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 ac- tive 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.