Enrichment process of phosphorite type REY based on the structure and geochemical features of the Zhijin Xinhua phosphorite in China.

In response to the insufficiently in-depth and systematic studies on the enrichment processes of phosphorite-type rare earths (REE), this study takes the recently discovered Early Cambrian Xinhua rare earth-phosphate composite deposit in Zhijin, Guizhou, as a case example. Building on detailed field investigations, this study conducts an in-depth analysis of the ore's structures. Employing a suite of analytical techniques, including X-Ray Fluorescence (XRF), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Total Organic Carbon (TOC) testing, and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), we meticulously delineate the sourcing, transportation, and storage processes of REE. The results demonstrate that the phosphorite-type rare earth ore has a typical particle structure. Biological waste comprises most of the particle composition, followed by sand debris, and agglomerates. There are two types of cementation and support, one is contact-pore cementation, particle support; the other is base-pore cementation, matrix-particle support. Phosphorite-type rare earth ore is classified into two types: phosphorus-rich rare earth ore and phosphorus rare earth ore. The ore minerals are all apatite, which highly concentrates rare earth elements and yttrium (REY), with average contents of 1187.16 ppm and 376.92 ppm, respectively. Rare earth elements may be mainly adsorbed by cryptocrystalline-amorphous collophane or exist in the lattice defects of microcrystalline-fine apatite in the form of isomorphism, which are concentrated in small shell organisms and shell walls, followed by sand debris, sand debris edges, and phosphate agglomerates, and are also enriched in phosphate cement. Following the extinction of small shell creatures in the shallow-water carbonate platform facies that thrived in the Early Cambrian, their cavities provided the ideal lodging space for rare earth element enrichment. Living creatures absorbed phosphorus to form shell walls while also enriching rare earth elements. Other significant rare earth transporters include agglomerates, sand debris, and some later pore water produced by the action of waves and tides. The paleogeographic conditions of bioclastic beaches on the platform's edge, the redox conditions of partial oxidation, and the superior conditions of biological organic matter are what regulate the enrichment of rare earth-phosphorus. Mineralization is more likely to occur when the environment shifts from oxidation to poor oxygen. The mineralization process has primarily gone through four stages: submarine jet + seawater mixing, phosphorus-rich-rare earth water mass formation stage; sea level rise, phosphorus-rare earth homogeneous migration stage; environmental changes, phosphorus-rare earth co-liberation stage; and diagenesis, phosphorus-rare earth coprecipitation stage.