Evaluation of Critical Elements in Carbonatites

Science Issue and Relevance

Identification and assessment of critical elements is a USGS and Department of the Interior priority because dependency on foreign sources creates a strategic vulnerability. 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 undertaken to 1) determine favorable environments for exploration, and 2) identify where these elements reside when enriched. 

Carbonatites are complex, poorly understood alkaline igneous rock defined by containing greater than 50 modal % primary carbonate minerals. Carbonatite-related ore deposits are the primary supplier of light rare earth elements (LREEs) and niobium (Nb) and the only current significant source of LREEs and Nb outside of China. Critical element enrichment is carbonatites is extremely complex and poorly understood. Determining why some carbonatites are enriched and why certain zones of these deposits are enriched is essential in the delineation and assessment of critical elements. 

Methods to Address Issue 

The project objective is to determine the processes responsible for critical element enrichment in carbonatites and to enhance our ability to identify and assess economic deposits. Work involves the integration of field, mineralogical, and chemical studies of key locations, deposits, and minerals and is conducted through four tasks.

Formation of giant, carbonatite-related ore deposits: objective is to conduct a petrogenetic study to understand how these giant deposits are formed to guide future exploration – focus study area is Mount Weld in Australia because it is the largest light rare earth element producer outside of China.

Evaluation of processes controlling critical element enrichment in alkaline complexes in Montana and Wyoming: objective is to investigate the source of critical elements and the processes responsible for the observed enrichments in alkaline igneous complexes in this region. 

Fate and transport of REEs in carbonatite systems through fluid inclusion studies: objective is to characterize the chemistry of fluids that transport and concentrate rare earth elements (REE) in high-grade and high-tonnage carbonatite complexes. 

Evaluation of compositional variations in barite as an exploration tool: objective is to investigate barite as a potential proxy for rare earth element mineralization and its use as a sensitive tool for identifying rare earth element deposits. Barite is a common mineral that forms during multiple stages of carbonatite emplacement and is an important gangue mineral in rare earth element mineralized zones.