Hidden wealth - Sierra Leone

Materials World magazine
,
3 Jul 2011

Sierra Leone has a wealth of mineral resources, but exploration of the war-ravaged country is in its infancy. Michael Forrest reports.

This year marks the 50th anniversary of the Independence of Sierra Leone. A former British Colony, the country has now settled to democratic elections after a decade or more of civil war and strife. Part of that war was funded by the mineral wealth of the country and, in particular, alluvial diamond production, often under control of anti-Government rebels. In 2002, a return to democracy occurred following United Nations intervention.

The undoubted mineral wealth of the country was illustrated by Liv Carroll, Senior Business Analyst at Gemcom Software International, in a presentation at the House of Lords, London, UK, run by the London Association of Mining Analysts.

‘Sierra Leone is approximately the size of Ireland, but the similarities of geology stop at this point,’ says Carroll. The majority of the country (the eastern part) is underlain by the 3,800 million-year-old (3.8Ga) Man craton – one of the oldest Archean terrains in west Africa, in neighbouring countries hosts gold, iron ore and diamond deposits. It is a typical Archean granite/greenstone assemblage that has been reworked in two significant metamorphic events at 3.2 and 2.7Ga (the Leonean and Liberian respectively).

‘These events caused structural tears and faults within the craton to act as conduits for mineralisation,’ noted Carroll. The craton has significant gold, iron ore and diamonds as well as other minerals. Currently, there are a number of mines under development for gold and iron ore, although diamond production is from alluvial and hard rock resources, based on Jurassic/Cretaceous-aged kimberlites at Koidu. Other clusters have been identified, and, given the distribution of artisanal production, many more await discovery. The Archean shield is not the only target.

To the south and west lies the Pre-Cambrian Kasila amphibolites and granulites, and it is the weathering of these rocks that generated Sierra Leone’s extensive titanium sands. The titanium is found in ilmenite and rutile minerals, oxides that have resisted weathering, and now are present in the Bullom series of coastal sediments of Pleistocene age. This group (Kasila) also hosts extensive bauxite deposits, the source mineral for aluminium. It results from the tropical weathering of aluminium-rich minerals, such as feldspar. Platinum minerals are also found in the Freetown Complex, a 193Ma mafic to ultramafic intrusion related to the opening of the Atlantic.

Golden interest

‘Mapping geology and mineral deposits is only part of the development of a mining industry – the challenge lies in attracting investment,’ declared Carroll. ‘The first step is collating all available databases in a usable format. Although there is a wealth of data, both within the country and in those colonial bodies that carried out the initial surveys, the problem is one of integration.’

However, overriding these considerations is a competitive mining code, which Sierra Leone reviewed in 2009. This code gives security of tenure (on a use or lose basis), transparency and reasonable royalty rates based on profits of 6.5% for diamonds, five per cent for gold and three per cent for other commodities.

Peter Gardner, Financial Director of Cluff Gold plc, London, UK, echoed this mining code approval. ‘Cluff Gold is focused on West Africa as it offers unparalleled exploration opportunities and a favourable operating environment. In Burkina Faso, our Kalsaka operation produced more than 74,000oz of gold in 2010 realising an average price of US$1,221/oz. This cashflow has enabled Cluff to explore in Ivory Coast and Sierra Leone.’

He explained that the flagship exploration programme is located in Baomahun in central Sierra Leone. The geological host is a series of garnet-mica and quartz-mica schists that vary from a few metres to 40m in thickness. The mineralisation found in these metasediments is located adjacent to banded ironstones (BIF) varying in scale from a few metres to decimetres. These appear to act as rigid, more competent objects in localising the mineralisation, although they do not host except when they are sheared or occur as intercalation with the other rock types. They may also act as geochemical traps owing to their high iron content. Indeed, the BIF horizons have been used as marker horizons by local artisanal miners to locate mineralised zones within the oxidised areas normally within 20m of surface.

One of the best exploration tools, noted Gardener, is versatile time-domain electro-magnetic (VTEM) geophysics, which accurately maps subsurface conductors related to conductive sulphide minerals, which at Baomahun are usually associated with gold.

He added, ‘Many of these targets have now been drilled, and we have a measured and indicated resource of just over 1.4Moz at a grade of 2.9g/t. There is significant exploration potential at Baomahun. Gold is known to be associated with the pyrrhotite and arsenopyrite, and the delineated existing resource only covers three kilometres of a 12km prospective trend. Two drill rigs are completing the in-fill drilling programme as part of the feasibility work.’

Environmental options

In planning the mine, Cluff Gold is considering developing hydropower in the area to be complemented with a heavy fuel-oil generating plant. There is significant potential of excess power for national consumption, and mine construction will require investment in local infrastructure, including roads.

Infrastructural considerations are paramount in developing large-scale mining operations of bulk commodities, such as iron ore. Sierra Leone has massive iron ore deposits that, in the past, have contributed to economic development. One of these is the Marampa mine that was operated between 1933-75 by the Sierra Leone Development Company It reached peak production of 2.5Mt/y in the 1960s, before low prices, declining grades and old equipment forced closedown.

In 2006, London Mining plc, an AIM-listed company, acquired the mining licence. CEO Graeme Hossie explained that his company was planning to develop the mine in two phases. The first phase is under construction and relies on tailings from past operations (70%) and soft highly weathered ore (30%). The 26% iron-grade material will be concentrated by wet high intensity magnetic separation (WHIMS), to produce a 65% concentrate. The company plans to be in production by the third quarter this year, with the transport of concentrate by road to a new river port (Tawfayim) for barging to the deep water port of Freetown. They have an offtake agreement with Glencore for this material.

Phase 1 will produce 3.6Mt/y of concentrate for a mine life of seven years. Phase 2 is more ambitious, with a 16Mt/y production target over a 23-year mine life. The output will be 65% iron sinter concentrate and pellet feed, with first production slated for 2014. Marampa has a JORC-compliant resource of 906Mt hematite and 37Mt of tailings.

Mining contributes 10.7% of GDP (International Monetary Fund data), and, when the iron ore production comes on stream, this is likely to provide 10-12% of GDP, with total mining export revenues to reach US$370m by 2015. There are currently three mines in operation (one each of diamond, bauxite, and rutile), and iron ore and gold to follow shortly.

Further information

Emails:
lcarroll@gemcomsoftware.com
pete.gardner@cluffgold.com
ghossie@londonmining.co.uk

The Sierra Leone Forum was held in May at the UK House of Lords, in London, and addressed by Lord Falconer. The meeting closed with a discussion, including a contribution by Sierra Leone’s Deputy High Commissioner Tamba Ngegba. The event closed with a presentation by Planting Promise, a UK charity that is developing schools through business development in Sierra Leone. Website: www.plantingpromise.org.uk