Critical Elements in Carbonatites: From Exploration Targets to Element Distribution

Science Center Objects

Critical elements are essential to the economy and have potential supply chain disruptions, but compared to most base and precious metals, little work has been done in understanding ore-grade enrichments. Carbonatites are the primary source of the worlds light rare earth elements and niobium, and a potential source for heavy rare earths, scandium, tantalum, and thorium. Project objectives are 1) to evaluate at a global scale the controls that determine whether a carbonatite is enriched in critical elements or not, 2) to determine which mineral(s) host the critical elements in an ore zone and controls on their distribution, and 3) to determine the fluid composition responsible for rare earth element transport and enrichment.

 

SEM image of carbonatite

SEM backscattered electron image of REE fluorocarbonates in barite beforsite unit of Elk Creek carbonatite. From Verplanck and others, 2015, BCGS Paper 2015-3.

(Public domain.)

Science Issue and Relevance

Critical elements are essential to the economy and have potential supply chain disruptions but compared to most base (common and inexpensive) and precious metals, little work has been undertaken to 1) determine favorable environments for exploration, 2) identify where these elements reside when enriched. Critical element enrichment in carbonatites is extremely complex and poorly understood, and 3) characterize the chemistry of fluids that transport and concentrate REEs in high-grade and high-tonnage carbonatite complexes.

Methodology to Address Issue

Our project's objectives are to determine the processes responsible for critical-element enrichments in carbonatites. Elements of interest include neodymium (Nd), dysprosium (Dy), terbium (Tb), yttrium (Y), niobium (Nb), scandium (Sc), and tantalum (Ta), with other elements included as needed. Three specific objectives are 1) to evaluate at a global scale why some carbonatites are enriched in an element of interest and others are not, 2) to determine where (and why) an element of interest resides in enriched zones, and 3) to determine the composition of the fluids responsible for hydrothermal transport and deposition.  This information is key to constraining enrichment processes and extraction requirements. Methods to achieve this include: integrated chemical petrographic, scanning electron microscopy, cathodoluminescence spectroscopy, mineral chemistry, isotopic characterization, fluid inclusion microthermometry, and laser Raman spectroscopy.