Rare Earth Element Mineralisation in Carbonatites of Mozambique (4952)

As society moves from fossil fuels to low-carbon energy, demand for the raw materials that are critical for this energy transition is rapidly increasing. Among these, the rare earth elements (REE) are particularly important as they are essential ingredients in high-strength permanent magnets used in wind turbines and most electric vehicles. The largest and highest grade REE deposits are hosted in carbonatites (igneous rocks with >50% carbonate minerals) and alkaline rocks (igneous rocks with exceptionally high contents of sodium and potassium), which are commonly closely associated.

These alkaline-carbonatite complexes are relatively rare (with 609 known carbonatites globally), compositionally diverse, and occur as plutonic, sub-volcanic and extrusive rocks. The characteristics needed to form a REE-rich carbonatite are generally recognised to be emplacement at relatively shallow crustal levels, with sufficient melt differentiation to form REE-enriched ferrocarbonatites, followed by some degree of hydrothermal alteration.

However, this generalised conceptual model is based upon a relatively small number of well-studied alkaline-carbonatite complexes. The links between carbonatites and alkaline rocks remain deeply debated and the exact evolutionary path from a carbonatite magma to a REE ore deposit is not well constrained. In-part, this obscurity stems from the challenges of mapping carbonatites in the field, the multi-phase complexity of alkaline-carbonatite complexes, and the (probable) formation of alkaline carbonate minerals, which are poorly preserved in the rock record owing to different degrees of hydrothermal overprinting and the propensity for carbonatites to weather in the surface environment.

This project focusses on the Monte Muambe carbonatite and the surrounding Lupata volcanics, Mozambique, both of which are the southern-most expression of the Chilwa Alkaline Province (a highly prospective area of carbonatites and alkaline igneous rocks in Malawi and Mozambique). Monte Muambe is an exceptionally large carbonatite complex comprising REE-rich and REE-poor carbonatites intruded into Karroo-age sandstones.

Preliminary field studies indicate that Monte Muambe occupies a conceptual knowledge gap between shallow-sub volcanic carbonatites, which are more likely to be mineralised in REE, and extrusive rocks. Existing studies on genetically similar complexes have been carried out elsewhere in the Chilwa Alkaline Province to the north, but occur at deeper emplacement depths, while extrusive (relatively unmineralized) carbonatites of a similar age occur to the west in Zambia.

Despite occupying this interesting knowledge gap, the complex is poorly studied, with work limited to a small number of exploration reports. Through the CASE partnership with Altona Rare Earths, this project presents the first opportunity to study these localities in detail since they were discovered in the 1920s.

This PhD project builds on existing and ongoing research at Camborne School of Mines on the architecture and genesis of carbonatite-hosted REE deposits. Monte Muambe offers an exceptional opportunity to investigate the relationships between intrusive and extrusive alkaline silicate rocks, carbonatites, and REE mineralisation at a previously little-studied structural level.

The locality is only partially mapped, and the project will build heavily on initial field observations to categorise different intrusive events, and their stratigraphic relationships. Follow-on work will be flexible depending on the interests of the student, but will involve some degree of whole-rock geochemistry, mineralogy, and isotope geochemistry and/or geochronology.

The supervisory team has already visited Monte Muambe and has an understanding of the logistical requirements of work in the area.