Rare earths are found in alkaline and carbonatite rocks of the Chilwa Alkaline Province (CAP) in southern Malawi. These rocks are characterized by circular features of fenitised rocks with intrusions of carbonate rocks and rocks derived from nephelinitic lavas.

The rocks shows strong anomalies of thorium (>500 CPS). Yamada et al came up with pathfinder elements for exploration of rare earths in the CAP. These elements include Stibnite (Sb), Cadmium, Molybdenum (Mo), carbon and Fluorine (F).

Stream sediment mineralogy has shown that the presence of pyrochlore,zircon, rare earths minerals, pyroxene, alkali amphibole and apatite point to existence of carbonatites related rocks within the vicinity.

Geophysical methods (CPS especially Th), geochemical methods and stream sediment analysis can be a useful tool for rare earths exploration in the CAP.

Table 1: Pathfinder elements in the Chilwa Alkaline Province (CAP)

ELEMENT	CRUSTAL ABUNDANCE (PPM)	CAP ABUNDANCE (PPM)
Stibnite	0.10	1.40
Cadmium	0.10	4.00
Molybdenum	1.50	17.00
Fluorine	600.00	1080.00
Carbon	33,000.00	57,000.00
Ce	81.00	922.00
La	25.00	93.00
Europium	0.80	11.00
Neodymium	4.00	325.00
Tellurium	0.00	0.25
Neodymium	4.00	325.00
Terbium	0.00	0.25
Samarium	0.10	45.00

Malawi carbonatites host rare earths minerals (mainly monazite, synchysite and bastnaesite), strontianite and apatite Accessory minerals may include fluorite, manganese, pyrochlore, and barite These minerals are common at Kangankunde, Tundulu and Songwe. Recent studies have shown that even fenites and breccia contain valuable heavy rare earths emanating from late-stage hydrothermal activities.

Compared to all published data from carbonatites and granitoids, the fluorapatite compositions in the Songwe Hill carbonatite, determined by EPMA and LA ICP-MS, have the highest heavy (H)REE concentration of any carbonatite apatite described so far. A combination of this fluorapatite and the REE fluorocarbonates, synchysite-(Ce) and parisite-(Ce), which are the other principal REE bearing minerals at Songwe gives a REE deposit with a high proportion of Nd and a higher proportion of HREE (Eu–Lu including Y) than most other carbonatites. Since Nd and HREE are currently the most sought REE for commercial applications, the conditions that give rise to this REE profile is particularly important to understand. Multiple apatite crystallization stages have been differentiated texturally and geochemically at Songwe and fluorapatite is divided into five different types (Ap-0–4). While Ap-0 and Ap-1 are typical of apatite found in fenite and calcite-carbonatite, Ap-2, -3 and -4 are texturally atypical of apatite from carbonatite and are progressively HREE-enriched in later paragenetic stages. Ap-3 and Ap-4 exhibit anhedral, stringer-like textures and their REE distributions display a Y anomaly. These features attest to formation in a hydrothermal environment and fluid inclusion homogenization temperatures indicate crystallization occurred between 200–350 °C. Ap-3 crystallization is succeeded by a light (L)REE mineral assemblage of synchysite-(Ce), strontianite and baryte. Finally, late-stage Ap-4 is associated with minor xenotime-(Y) mineralization and HREE-enriched fluorite. Fluid inclusions in the fluorite constrain the minimum HREE mineralization temperature to approximately 160 °C. A model is suggested where sub-solidus, carbonatite-derived, (carbo)-hydrothermal fluids remobilize and fractionate the REE. Chloride or fluoride complexes retain LREE in solution while rapid precipitation of apatite, owing to its low solubility, leads to destabilization of HREE complexes and substitution into the apatite structure. The LREE are retained in solution, subsequently forming synchysite-(Ce). This model will be applicable to help guide exploration in other carbonatite complexes.

Mkango Resources Ltd. holds through its wholly-owned subsidiary Lancaster Exploration Limited a 100% interest in two exclusive prospecting licenses in southern Malawi. The Corporation's corporate strategy is to further develop the Songwe Hill rare earth deposit and secure additional rare earth element and other mineral opportunities.

Lindian Resources Ltd’s Kangankunde project is located in southern Malawi 100 km north of Blantyre and 25 km from the Nacala rail corridor. The carbonatite mineralisation was first discovered in 1907 however the importance of rare Earth mineralization within the deposit was not noted until the early 1950s. The project has had several phases of exploration with the most comprehensive geological and process test work completed between 1987 and 1990 by the French geoscience organisation Bureau de Récherches Géologiques et Minières (BRGM). The Kangankunde deposit is a large rare earth carbonatite system that rises up to 200 m above the surrounding plane over an area of 1.4 km by 1.7 km.

References

Broom-Fendley, Sam, Brady, Aoife E., Frances Walla, Gunn, Gus, Dawes, William: REE minerals at the Songwe Hill carbonatite, Malawi: HREE-enrichment in late-stage apatite

Dallas S. Laval M. and Malunga G. W. P. 1987. Evaluation of known mineral deposits. Rep. BRGM 87 MWI054

Garson, M. S. 1962. The Tundulu carbonatite ring complex in southern Nyasaland. Mem. Geol. Surv. Nyasaland, 2.

Garson, M. S. 1965. Carbonatites in southern Malawi. Bull. Geol. Surv. Malawi, 15.

Garson, M. S. and Campbell S. W. 1958. Chilwa Island. Mem. Geol. Surv. Nyasaland, 1

Holt D. 1965. The Kangankunde Hill rare earth prospect. Results of an economic investigation. Bull. Geol. Surv. Depart. Malaw

Malunga G. W. P. 1998. Rare earths exploration and reserve estimation strategies, the Malawi case. “Mining in Africa ‘98”. Johannesburg. South African Institute of Mining and Metallurgy. Pp 51-54.