Summary:
The Kwale Project initially comprised three areas that contained concentrations of heavy minerals. They were the South Dune, Central Dune (now totally depleted by mining and currently the repository for sand tailings from the South Dune) and the North Dune deposits, with the Bumamani deposit being discovered subsequently.
THE NORTH DUNE
The North Dune is part of the extensive Kwale Dune systems comprising of reddish, windblown Magarini sand formations that overlie a sequence of mineralised clay-rich fluviatile units, which in turn overlie a Mesozoic sandstone Base, known as the Mazeras formation. These three units are separated by lateritic paleo-surfaces which signify a time-gap between the geological formations. The Mazeras Sandstone, derived from the disintegration of the Mozambique Belt metamorphic rocks, has likely provided the supply of heavy minerals to the Magarini sand dunes and the fluviatile formations. Exploration of the Kenyan coastline is yet to be successful in terms of mineralised paleo-strandlines related to fossil marine terraces, as these are likely buried beneath recent barren fluvial overburden or were just not developed owing to reduced energy levels from a fringing coral reef that has acted as a barrier to effective winnowing and reworking of HM deposits.
The uppermost zone at Kwale North, referred to as Ore Zone 1, is a dark brown, predominantly fine grained, well sorted silty sand with very little induration. It is also characterised by a clean, high value heavy mineral assemblage. Ore Zone 4 lies below Ore Zone 1 with a clear lateritic boundary observed in the field with slightly difficult bit penetration, and in HM sink logs, exhibiting elevated iron oxides. Ore Zone 4 is lower in valuable heavy mineral content, often dominated by iron oxides and Al2SiO4 polymorphs (kyanite, andalusite and sillimanite). It is considered a fluvial deposit based on the difficulty of wash and the poor grain sorting. Ore Zone 5 lies below Ore Zone 4 and is separated from that zone by a lateritic paleo-surface. It is unique mineralogically due to an increased amount of almandine garnet that reports to the mag fraction, significantly increasing the magnesium, manganese, aluminium and silicon in the oxide chemistry.
Kwale North Dune Mineral Resources estimate is approximately 6,300m along strike and about 1,200m across strike on average, The average thickness of Ore 1, Ore 4 and Ore 5 are approximately 10m, 7m and 5m respectively.
THE BUMAMANI
The Bumamani deposit is part of the extensive coastal Plio-Pleistocene Magarini Formation, which comprises aeolian dunal sands and clay-rich fluviatile units that overlie down-faulted Jurassic and Tertiary formations. The presence of a thin, discontinuous laterite layer seen at the base of the dune sands is considered to indicate a change of climate in contradistinction to the underlying fluviatile sediments. These units are locally enriched with heavy minerals, primarily ilmenite, rutile and zircon as well as significant silicate gangue in the lower fluviatile units. The hinterland ‘Mozambique Belt’ metamorphic formations are considered the likely HM feed source for the Kwale deposits. Exploration along the Kenyan coastline is yet to be successful in terms of mineralised paleostrandlines related to fossil marine terraces, perhaps due to low wave energy levels caused by the fringing reef acting as a breakwater, thus preventing effective HM winnowing and trapping.
The uppermost zone at Bumamani, referred to as Ore Zone 1, is a dark brown, predominantly fine grained, well sorted silty sand with very little induration. It is also characterised by clean, polished HM with minimal gangue minerals. Ore Zone 4, underlying Ore Zone 1 is a sandy-clay fluviatile unit with low-level sorting and common lateritic fragments. The HM from this zone contains more lateritic aggregates. The Basement zone is a low-grade, clay rich, fluviatile unit with a difficult to impossible washability. The HM from this zone is notably enriched in gangue silicates.
The Bumamani Mineral Resource is approximately 1,600m along strike and 500-700m across strike on average. The deposit thickness averages 10m.
THE SOUTH DUNE
The Kwale South Dune deposit is an aeolian detrital heavy mineral sand deposit.
Kwale Operations’ deposits sit on top of an erosional high which is dissected by streams. The extent of geological and mineralised zones is constrained by the erosional surface surrounding the basement high. Heavy mineral grade and geology is consistent within mineralised horizons, typical of aeolian deposits. Grade and geological continuity in the lower mineralised horizon (Ore Zone 4) is compromised by variable induration.
The Kwale South Dune deposit is approximately 6.5km long, 300-1,000m wide and approximately 12-20 m thick on average. Mineralisation is present from surface over the majority of the deposit.