Abstract

Malawi has well developed carbonatites that display models for exploration of rare earths and host various economic minerals including monazite, synchysite, bastnaesite and apatite.

The carbonatites are part of the Chilwa Alkaline Province (CAP) that extends from Mozambique into Southern Malawi.

Introduction

Rare Earth Elements (REE) or sometimes called lanthanides are elements that have shaped modern life.  Modern life is dominated by the use of electronic materials made from these elements.

These REE are found in alkaline rocks associated with nepheline syenites and carbonatites. Southern Malawi host these rocks and have become subject for understanding the genesis of carbonatites and rare earths while also offering economic minerals for extraction (Figure 1).

Rare earths groups

There exist two groups of rare earths classified as light rare earths and heavy rare earths.

LIGHT RARE EARTH ELEMENTS: La, Ce, Pr, Nd, Pm, Sm, Eu, Gd

HEAVY RARE EARTH ELEMENTS:Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc

These elements are used in electronics, manufacturing, medical science, technology and renewable energy.

In electronics they are used in the manufacture of television screens, computers, cell phones, silicon chips, monitor displays, long-life rechargeable batteries, camera lenses, light emitting diodes (LEDs), compact fluorescent lamps (CFLs), baggage scanners, marine propulsion systems.

The manufacturing industry uses them to producehigh strength magnets, metal alloys, stress gauges, ceramic pigments, colorants in glassware, chemical oxidizing agent, polishing powders, plastics creation, as additives for strengthening other metals, automotive catalytic converters.

Medical Sciences have benefited from improvements in the application of portable x-ray machines, x-ray tubes, magnetic resonance imagery (MRI) contrast agents, nuclear medicine imaging, cancer treatment applications, and for genetic screening tests, medical and dental lasers.

Technology has improved through introduction of lasers, optical glass, fibre optics, masers, radar detection devices, nuclear fuel rods, mercury-vapour lamps, highly reflective glass, computer memory, nuclear batteries, and high temperature superconductors.

Hybrid automobiles, wind turbines, next generation rechargeable batteries, biofuel catalysts have been introduced in the renewable energy sector thanks to the application of rare earths.

Exploration for rare earths in Malawi

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

These 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) (Table 1).

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.

In conclusion 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

Mineral Resources of Malawi Carbonatites

Malawi carbonatites host rare earths minerals (mainly monazite, synchysite and bastnaesite), strontianite and apatite (Table 2). 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.

Table 2: Minerals Resources of Malawi Carbonatites

LOCATION	MINERAL	GRADE %	IMPORTANT OXIDES %	DELINEATED TONNAGE (MT)
Kanga nkunde	Monazite	10 Rare Earth Oxides (REO)	>1.4 Sm2O3 >0.10 Y2O3 >0.17 Eu2O3	0.294 30m depth
	Apatite
Tundulu (Nanthache hill)	Synchysite and Bastnaesite	7 REO		0.6 30m depth
	Apatite	15.0 P2O5		0.9 30m depth
Songwe	Synchysite	1.6 REO	>3 Sm	8.5 200m depth
Chilwa Island	Synchysite and Fluorencite	5.0 REO	1.4 Sm2O3 0.10 Y2O3 0.17 Eu2O3
	pyrochlore	0.95 Nb2O3

Conclusion

Malawi offers a model or natural laboratory for coming up with exploration models for carbonatite related economic minerals.  Opportunities for developing world class rare earths mineral deposits exist at Kangankunde, Tundulu, Songwe and Chilwa Island.

References                  

1. Dallas S. Laval M. and Malunga G. W. P. 1987. Evaluation of known mineral deposits. Rep. BRGM 87 MWI054
2. Garson, M. S. 1962.  The Tundulu carbonatite ring complex in southern Nyasaland. Mem. Geol. Surv. Nyasaland, 2.
3. Garson, M. S. 1965.  Carbonatites in southern Malawi. Bull. Geol.  Surv. Malawi, 15.
4. Garson, M. S. and Campbell S. W. 1958.  Chilwa Island. Mem. Geol. Surv. Nyasaland, 1.
5. Holt D. 1965. The Kangankunde Hill rare earth prospect. Results of an economic investigation. Bull. Geol. Surv. Depart. Malawi
6. 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.

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The piece “Technical File: Rare Earths in Malawi” featured above was initially published in Malawi’s Mining & Trade Review Issue Number 43 that is circulating this November 2016.

The full edition is available for download here. This monthly publication is edited by Marcel Chimwala.