Scientists decipher the origin of REE deposits to guide exploration

Bastnäsite-(Ce) crystal with solid inclusions. (Image by ButtShark, Wikimedia Commons).

Scientists from Uppsala University, the Geological Survey of Sweden and the University of Cape Town were able to figure out the origin of the ‘Bastnäs-type’ REE deposits, such as those located in the Bergslagen ore province in south-central Sweden.

According to the researchers, these deposits originated in a sub-seafloor, shallow-marine back-arc setting where high-temperature magmatic fluids reacted with pre-existing limestone layers. The drastic changes in chemical environment experienced by the fluids during their interaction with the limestone led to localised skarn formation and magnetite-REE mineral precipitation.

The ‘Bastnäs-type’ REE deposits are Palaeoproterozoic, skarn-hosted magnetite-REE deposits that represent a large-scale (>100 km) feature of high-grade REE concentrations

To reach such a conclusion, the experts collected mineral oxygen and carbon isotope data from 10 of the classic central Swedish ‘Bastnäs-type’ deposits. The new isotope data allowed them to perform numerical models that, combined with existing geological observations, gave them clues on how the deposits came to be.

The ‘Bastnäs-type’ REE deposits were the first hard-rock ores ever to be mined for REEs and played a key role in the original discovery of several rare earth elements, for example, cerium and lanthanum, and REE minerals such as bastnäsite.

“An improved understanding of their origin could help to guide exploration for this type of REE mineralisation here and elsewhere to secure the future supply of these critical commodities,” the team of scientists said in a media statement. 

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