Rare earth mineralization in the Lala IOCG deposit, Southwest China: Insight from the mineralogy, geochemistry, and geochronology.

[Display omitted] • REE mineralization in the Lala deposit primarily formed at ca. 850 Ma. • The host rocks and contemporaneous felsic magmatic rocks serve as the primary sources of REE metallogenic materials. • Na, CO 2 , and F-rich magmatic waters aid REE mineralization, mixing with meteoric waters, leaching the REE from host rocks and early ores. The Lala deposit in the Kangdian metallogenic province is one of the most important iron oxide copper–gold (IOCG) deposits in South China. Rare earth element (REE) activation, migration, and redistribution occurred during late-stage Cu mineralization in the deposit. However, the geological characteristics of REE mineralization and the genetic mechanism of this deposit remain poorly understood. The goal of this study was to investigate REE mineralization and the ore-forming process in the Lala deposit by employing a comprehensive approach that included techniques in petrography, mineralogy, and geochemistry. Mineralogical analysis indicated that the REE-bearing minerals in this deposit include bastnäsite, monazite, parisite, xenotime, apatite, and fluorite. Apatite was observed to have high concentrations of REE (ΣREE ranging from 7,409 to 18,739 ppm). The results of U-Pb isotope dating of bastnäsite and xenotime suggest that the REE mineralization in the Lala deposit primarily formed at ca. 850 Ma, aligning with the Neoproterozoic magmatism in this region. The chondrite-normalized REE pattern of apatite is similar to that of host rocks and contemporaneous magmatic rocks; the ε Nd(t) values of bastnäsite and xenotime (calculated at ca. 850 Ma) ranged from −12.2 to −7.0, which is comparable to the values obtained for contemporaneous country rock (−8.7 to −6.4) and felsic intrusive rocks (−9.6 to 4.4). This similarity indicates that the host rocks and contemporaneous felsic magmatic rocks serve as the primary sources of REE metallogenic materials. The ∼ 850 Ma REE mineralization overprints the early stage Fe-Cu mineralization and is associated with a Neoproterozoic magmatic event. During this process, Na, CO 2 , and F-rich magmatic water mixes with meteoric water and leaches REE from host rocks and early-stage ores. Under the disintegration of REEs, F-complex in hydrothermal fluids, REE minerals (e.g., monazite, bastnäsite, parisite, and xenotime) precipitate together with apatite and fluorite in the Fe-Cu ores. [ABSTRACT FROM AUTHOR]