The Tonkolili Iron Ore Deposits, Sierra Leone

The Tonkolili banded iron formations (BIF), Sierra Leone, host extensive iron ore deposits which are of economic signifi cance to the seaborne iron ore trade. The deposits are dominated by a strategic JORC compliant mineral resource of 11.6 Bt grading 30.1 per cent Fe comprised of primary magnetite mineralisation in the form of a fresh metamorphosed BIF featuring a uniform mineral assemblage of quartz-magnetite ± ferro-silicate minerals. Pilot plant metallurgical test work has demonstrated that the production of a magnetite concentrate is achievable using the established beneficiation techniques of magnetic separation and flotation. The concentrates arehigh-grade, and suitable for blast furnace or direct reduced iron pellet feed. The major challenge facing the development of such magnetite deposits at industry competitive production rates is the significant capital investment required for process plant and associated infrastructure.Two well-developed weathering zones exist within the deposits, and are associated with the progressive development of a tropical weathering profile overprinting the primary BIF. These zones feature a near surface hard indurated duricrust up to 60 m thick, and a soft progressively developed saprolite between duricrust and fresh BIF. These zones have been found to be amenable to producing iron ore products including DSO lump and sinter fines from the duricrust, and concentrate from the saprolite. Mineral resources sufficient to support commercial production of such iron ore products were defined by an intensive exploration program in 2010.African Minerals Limited has developed a three phase production strategy to progressively self fund the development of the Tonkolili strategic magnetite project by:• commencing a Phase I 12 Mt/a DSO operation in Quarter 4 2011,• increasing production in Phase II to 35 Mt/a with the commissioning of a saprolite beneficitation plant and associated infrastructure upgrades, and• developing a 45 Mt/a Phase III operation producing high-grade magnetite concentrate.The comparatively low capital and operating costs of a duricrust DSO lump and sinter fines operation coupled with its proximity to ground surface make it highly attractive for the generation of early cash flow for the Tonkolili project. Revenue from this early production may be used to selffund the subsequent development of phases requiring progressively more significant beneficiation plant and infrastructure.