Supergene enrichment of Carbonatite REE Deposits (SCREED)

The rare earth elements (REE) are critical for the shift to renewable power and low carbon transport. These are the 15 elements from Lanthanum to Lutetium plus Yttrium and Scandium, and the huge increase in their usage drive by these factors means we cannot meet demand by recycling and must find new primary resources, preferably that can be extracted in the most equitable and environmentally benign way.

The main REE deposits are in carbonatites (igneous carbonate rocks) and weathered rock on top of granites. However, the weathered rock on top of carbonatites can be greatly enriched relative to bedrock (up to 100 times). The rock is already partly degraded, and the change in mineralogy on weathering may make processing to extract the REE easier.

In the Supergene enrichment of Carbonatite REE Deposits (SCREED) project, the research team examine weathered carbonatite deposits to understand how enriched deposits form, what minerals host the REE, and if the redistribution of the REE during weathering might provide beneficial changes in the element distribution in terms of the economically most useful elements, and in separation of the REE from environmentally problematic metals. Included in the study are examples in Finland, Southern Africa and Asia with the help of international academic and industry partners.

The aims of the project are:

1. To determine the controls on weathering of carbonatite REE deposits under different external conditions including climate, hydrology, biology and protolith.
2. To determine the absolute age of weathering in deposits, relative to the time of formation of the primary resources and current knowledge of changes in the climatic and hydrological regime.
3. To determine the distribution of the REE and actinides between residual and authigenic minerals and adsorbed onto the surface of clays, oxy-hydroxides and organic matter in order to investigate elemental fractions that may be beneficial
(enrichment in the mid- to heavy-REE; separation of REE from actinides) or detrimental (enrichment in actinides).
4. To link the data from 1-3 above into an overall genetic model incorporating the behaviour of REE and actinides under different conditions, allowing prediction of weathering style and impact on resource potential.
5. To develop a robust classification of the weathering products of carbonatite-hosted REE deposits that can be used to predict the resource potential and processing routes for a given system.
6. To link this classification to the bulk geochemical and mineralogical characteristics of deposits to provide information on increase in grade relative to bedrock, the presence of easily leachable (potential low energy of extraction) resources and the presence and mobility of actinides.
7. To communicate data and interpretations to industry and the public to raise awareness of the resource requirements of decarbonisation, and potential routes to increased extraction efficiency and reduced impact.