Abstract: Rare earth elements and yttrium represent key strategic mineral resources in China, and the research on their metallogenic mechanisms hold significant scientific importance. Previous studies have confirmed the presence of large barite deposits accompanied by notable REY enrichment in the Cambrian Niutitang Formation black shales of the Southeastern Guizhou- Western Hunan region. But the sources, occurrence states, and enrichment mechanisms of REY remain poorly constrained. This study selected REY-rich layers from the Tianzhu barite deposit and systematically applied laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) mapping and micro-X-ray diffraction (μ-XRD) to investigate the origin, occurrence, and enrichment processes of REY. Integrated analyses reveal: (1) REY distribution patterns exhibit strong consistency with modern seawater-pore water systems, where elevated Y/Ho ratios, Ce/Ce*, and Eu/Eu* in high-REY zones indicate predominant seawater-derived signatures, with minor terrigenous inputs; (2) P-Ca-REY ternary correlation analysis demonstrates a significant positive relationship between Ca content and REY abundance (R2= 0.80), whereas no significant causal links exist between Ca-P or REY-P. Micro-XRD confirms that REY primarily reside in authigenic carbonate crystal lattices; (3) A“seawater sourcediagenetic enrichment” model is proposed, elucidating that sulfate radicals in barite oxidize organic matter during diagenesis, releasing carbonate ions that promote Ca2+-carbonate precipitation, thereby driving REY enrichment via isomorphic substitution in carbonate minerals. Through multidisciplinary approaches, this study proposes the seawater-derived origin, carbonate-hosted occurrence, and diagenetic activation mechanisms of REY in the Tianzhu deposit, providing new insights into the enrichment patterns of REY in black shale systems.

Key words: rare earth elements, black shale, barite, LA-ICP-MS mapping