Abstract
The Saint-Honoré carbonatite complex hosts a rare earth element (REE) deposit traditionally interpreted as being produced by late-stage hydrothermal fluids that leached REE from apatite or dolomite found in the early units and concentrated the REE in the late-stage units. New evidence from deeper units suggest that the Fe-carbonatite was mineralized by a combination of both magmatic and hydrothermal crystallization of rare earth minerals. The upper Fe-carbonatite has characteristics typical of hydrothermal mineralization—polycrystalline clusters hosting bastnäsite-(Ce), which crystallized radially from carbonate or barite crystals, as well as the presence of halite and silicification within strongly brecciated units. However, bastnäsite-(Ce) inclusions in primary magmatic barite crystals have also been identified deeper in the Fe-carbonatite (below 1000 m), suggesting that primary crystallization of rare earth minerals occurred prior to hydrothermal leaching. Based on the intensity of hydrothermal brecciation, Cl depletion at depth and greater abundance of secondary fluid inclusions in carbonates in the upper levels, it is interpreted that hydrothermal activity was weaker in this deepest portion, thereby preserving the original magmatic textures. This early magmatic crystallization of rare earth minerals could be a significant factor in generating high-volume REE deposits. Crystallization of primary barite could be an important guide for REE exploration.
Highlights
China has practically monopolized the production of rare earth elements (REE) over the last decades [1,2]
As the main objective of this paper is to present the magmatic and hydrothermal associated with the REE mineral crystallization, the weathered uppermost section of the deposit is not components associated with the REE mineral crystallization, the weathered uppermost section of the considered further except for comparative purposes
REE deposition in carbonatites, such as quartz, hematite, barite and late calcite (Figure 5D); (4) in the late-stage polycrystalline clusters, REE mineralization overprints primary barite and crystallization occurs radially from the barite edges (Figure 4B); (5) mineralization occurred in the form of tiny needles (Figures 4B and 5B,D), suggesting a rapid lower-temperature crystallization (Figures 4B and 5B,D); and (6) La/Yb ratio are similar to hydrothermal REE deposits such as Bear Lodge (Figure 10) [59,62]
Summary
China has practically monopolized the production of rare earth elements (REE) over the last decades [1,2]. Future demand is expected to be strong as the market for green technologies, the main consumer of REE, is projected to increase [3,4,5,6]. Several geological processes or environments can produce economic REE concentrations [1,7,8,9]. Carbonatites are REE-hosting rocks in which extractive metallurgy is better understood. According to Chakhmouradian and Zaitsev [9], 20 of the 50 most advanced REE extraction projects outside of China are found within igneous carbonate rocks, whereas most present-day or historical production has been from carbonatites or their weathered components
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