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The Potential for Gold in Liberia

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The Potential for Gold in Liberia 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 gold in Liberia 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 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 maps for the entire country, supported by field the West African Craton, 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 GUINEA -Wologizi Range gi 3Ndablama SIERRA LEONE 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. 2 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. 3 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, 4 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.
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