Defining a Triassic carbonatite-related Mo-(REE) metallogenic belt along the southern margin of the North China Craton

Abstract

Carbonatites are important sources of rare metals (e.g., REE, Nb), but are not generally considered prospective for Mo mineralization. Numerous quartz-carbonate-rich vein-type Mo-(REE) deposits and prospects of enigmatic origin extend over 200 km along an E-W belt at the southern margin of the North China Craton (S-NCC). These veins commonly contain carbonates, quartz, sulfates, K-feldspar, sulfides, REE minerals, with minor aegirine-augite and pyrochlore occurring locally. This mineral assemblage is diagnostic of carbonatite-related hydrothermal systems. These veins also show alkali metasomatism, elevated REE contents, sulfate-bearing high-salinity fluid inclusions, and mantle-like isotopic compositions consistent with a carbonatite origin. Two Mo-(REE) mineralization events at ~ 238 Ma and ~ 220 to ~ 210 Ma are recognized based on monazite U-Th-Pb and molybdenite Re-Os isotopic dates acquired from representative deposits across the belt. Combined with previous geochronological data, we propose that these deposits define a Triassic carbonatite-related vein-type Mo-(REE) metallogenic belt in the S-NCC which formed during the syn-collisional to post-collisional period of the Qinling-Dabie Orogenic Belt. The carbonatite-related Mo mineralization formed via a synergistic interplay of three key mechanisms: (1) mantle metasomatism by Mo-rich crustal materials (subducted sediments/delaminated crust) generating fertile metallogenic mantle sources; (2) Mo dissolution and transport in mantle-derived volatile-rich carbonatitic melts and related hypersaline fluids; and (3) Mo enrichment/saturation through fractional crystallization of Mo-deficient phases (carbonates, K-feldspar, sulfates) combined with temperature and redox controlled precipitation processes.