State of the Art of Carbonatites and Their Potential for Critical-Metal Deposits

Dear Colleagues,

Population growth and technological progress in the last 50 years have resulted in a 400% increase of global demand for mineral resources, which is expected to further double by 2050. Unprecedented market growth is particularly expected for critical raw materials (CRMs). This is boosting mineral exploration for carbonatites, which are one of the major sources of CRMs. Among CRMs are several chemical elements essential to high-tech and green-tech applications. Rare Earth elements (REEs) are among the most important of these, with a world mine production of just 210,000 t/yr., even though REEs are ubiquitous in modern technologies such as cell phones, TV screens, and electric cars. Intraplate regions have a favorable geological setting for carbonatite emplacement. Although the small size of the carbonatite outcrops makes them a difficult target, most of the carbonatites are associated with larger alkaline complexes. They also display larger lithological, geochemical, and mineralogical footprints, which can be expressed as potential mappable proxies and used as CRM ore vectors. The main CRMs occurring in carbonatites are light REEs (LREEs), Y, Nb, V, Zr, Hf, Ta, and fluorspar. There is a need for new sources of CRMs, which may host the most important ore-deposits of CRM-bearing minerals, such as bastnäsite, wakefieldite, britholite, monazite, vanadinite, perovskite, pyrochlore, zircon, Zr-garnet, wöhlerite, and baddeleyite. CRMs are typically associated with the sub-volcanic parts of the carbonatite system. In many cases, these sections are poorly exposed, but surficial indicators suggest their potential as CRM resources, and due to ever-increasing CRM demand, new mineral exploration at sub-surficial depths is realistic. Future ore-deposits are sub-economic due to small grain size, obstructing the separation of CRMs from contaminants, but this would be improved by the beneficiation and recovery of by-products. In many countries, a close relationship between geology and industry has significantly faded following the rapid discontinuation of mining activities in the second half of the 20th century. To reverse this trend, it is necessary to build new ore-deposit models and facilitate their uptake by industry stakeholders. Reducing uncertainties in the mineral prospecting of carbonatite-alkaline rock associations would be a significant step forward in exploration. Although a general model for carbonatites exists (Stoppa et al., 2016), data on the vertical extent of hosted ores are still lacking. Late hydrothermal activity in and around the magma chamber is known to be key in concentrating CRMs (Anenburg, 2018; Liu et al., 2018; Stoppa et al., 2019), but may also create complex mineralogy that is difficult to process industrially, thereby demanding more detailed mineralogical, microtextural, and geochemical characterization using the new mineral system-oriented approach (Banks et al., 2019). This approach, which is still underused in carbonatite exploration, will improve our understanding of CRM genesis in carbonatites and profoundly impact the estimation of resources associated with this unique rock type worldwide. Renewed links between industry and academic research may lead to the development of more efficient mineral processing techniques, allowing the extraction and concentration at acceptable cost and environmental impact, and thus increase deposits’ economic appeal.

Prof. Dr. Francesco Stoppa
Guest Editor

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• critical raw materials
• carbonatites
• mineral exploration
• mineralogical, microtextural, and geochemical characterization
• carbonatite subvolcanic model