Unusual HREE enrichment and mineralization age in the Jialu deposit from the Qinling Orogen, central China

Abstract

The Jialu carbonatites (∼240 Ma) in the Qinling orogenic belt are characterized by the enrichment of heavy rare earth elements compared with typical global carbonatites. The carbonatites are dominantly comprised of calcite, quartz, sulfate, K-feldspar, minor sulfides, and rare earth minerals such as monazite, bastnäsite, parisite, and xenotime, with two mineralization stages including the early quartz-K-feldspar-calcite stage (Stage I) and the late sulfide-rare earth mineral-calcite stage (Stage II). The rare earth element contents of Stage I calcite are higher than those of the Stage II, especially heavy rare earth elements. Calcite from the different mineralization stages exhibits variable chondrite-normalized REE patterns, with the HREE and REE abundances (134–1023 ppm) decreasing from the early to the late stage owing to the crystallization of xenotime. The δ13C (−5.39 ‰ to −6.68 ‰) and slightly higher δ18O (10.77 ‰ to 12.60 ‰) values for calcite from the Jialu carbonatites generally deviate from the values observed in the primary carbonatite field, which may be a result of Rayleigh-type fractionation. LA–ICP–MS U–Pb dating shows the lower-intercept ages of 243.8±5 and 237.6±1.3 Ma for the monazite and xenotime, respectively, with the weighted average 206Pb/238U ages of 240.9±6 and 239.2±1.3 Ma. These results indicate that the Jialu REE deposit was concurrent with Triassic carbonatite magmatism and REE mineralization observed on the southern margin of the North China Craton. This implies that this region may have great REE mineralization potential.