Rare earth elements are crucial for the global transition to a green and modern economy. Their economic occurrence is rare, and their production is concentrated geographically. Consequently, they are classified as critical minerals in many jurisdictions and require alternative sources to prevent potential disruption in the supply chain. Kimberlites, the main source of diamonds, can contain REE at levels comparable to some primary REE deposits such as the REE clay deposits of South China (Kynicky et al. 2012). In this study, we investigated whether processed kimberlites (tailings) at diamond mine sites could be potential secondary sources of REE. The research focused on REE deportment and their behavior during hydrothermal and supergene alteration of kimberlites, using samples of kimberlite core and tailings from the Snap Lake diamond mine (Northwest Territories, Canada). The study included petrography, mineral chemistry, and whole-rock geochemistry. Tailing samples are enriched in heavy (HREE) relative to the kimberlite core samples. In both core and tailings samples, REE are concentrated in monazite (up to 62 wt% REE2O3), apatite (up to 1.8 wt% REE2O3), and anatase (up to 3000 ppm REE2O3). Subordinate amounts of ancylite-(Ce) and allanite-(La) were found only in the tailings. Perovskite, a common mineral host of REE in kimberlites, was not observed in any of our samples. However, the size and shape of anatase-monazite intergrowths suggest they are possible pseudomorphs of perovskite. We propose a paragenetic sequence involving hydrothermal alteration of REE-rich primary perovskite by deuteric CO2-rich fluids, subsequently forming anatase-monazite intergrowths and monazite infillings in veins. The transformation of perovskite to monazite is economically significant because REE enrichment in monazite allows easier extraction than oxides.
