On the feasibility of imaging carbonatite-hosted rare earth element (REE) deposits using remote sensing

Rare earth elements (REEs), which are essential for many modern technologies such as batteries and wind turbines, have characteristic absorption features in visible to shortwave infra-red (VNIR-SWIR) reflectance spectra. Neodymium (Nd) has amongst the most prominent absorption features of the REEs and thus represents a key pathfinder element for the element group as a whole. Given that the world’s largest REE deposits are associated with carbonatites, we collected spectral, petrographic and geochemical data from a predominantly carbonatitic suite of rocks to assess the feasibility of imaging REE deposits using remote sensing. Rock samples were drawn from a number of sources including the Harker Collection in Cambridge, Cambourne School of Mines and the Natural History Museum in London. REE ores from the Bayan Obo (China) and Mountain Pass (USA) mines, as well as REE-rich alkaline rocks from the Motzfeldt and Ilímaussaq intrusions in Greenland were included in the sample suite.

Hand specimens of REE ores from Mountain Pass, USA.
Hand specimens of REE ores from Mountain Pass, USA. Samples from the Harker Collection.

By simulating the response of a number of remote sensing instruments, we demonstrated that hyperspectral instruments with capabilities equivalent to the operational Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) and planned Environmental Mapping and Analysis Program (EnMAP) instruments have the spectral resolution necessary to detect Nd absorption features, especially in high grade samples with economically relevant REE accumulations.

REE ore from Bayan Obo, China. The fibrous and equant bright phases are bastnäsite-(Ce) and monazite-(Ce) respectively. Sample from the Natural History Museum.

Unfortunatly, most REE-rich outcrops are too small to be detected by satellite-based platforms. However, Nd absorption features should be identifiable in high-quality, airborne, hyperspectral datasets collected at meter-scale spatial resolutions. Future deployment of hyperspectral instruments on Unmanned Aerial Vehicles (UAVs) could enable REE grade to be mapped at the cm-scale across whole deposits.

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Publication

Neave, D.A., Black, M., Riley, T.R., Gibson, S.A., Ferrier, G., Wall, F. & Broom-Fendley, S. 2016. On the feasibility of imaging carbonatite-hosted rare earth element (REE) deposits using remote sensing. Economic Geology 111, 641–665. <Open Access>