Distribution and enrichment mechanism of critical metals in the Danping bauxite deposit, northern Guizhou (SW China)

Critical metals are indispensable for the global scientific and economic development, and their shortage has drawn attention to critical metal exploration in bauxite-related rocks. Bauxite deposits, especially karst-type ones, are usually enriched in critical metals like Li and REE (rare-earth elements La-Lu and Y). In this study, we analyzed the bauxite ore-bearing rocks at Danping (Guizhou, SW China) with a combination of XRF, ICP-MS, XRD, and SEM-EDS techniques, with the aims to investigate the distribution characteristics and enrichment mechanisms of the critical metals (e.g., Li, Ga, Zr, Sc, and REE). The bauxite ore layer at Danping is unconformably contacted with the underlying Huanglong Formation (Fm.) limestone or the Hanjiadian Fm. mudstone/ shale, and the overlying Qixia Fm. limestone or Liangshan Fm. carbonaceous shale. Lithium is mainly enriched in the top and bottom of the bauxitic clay strata (abbrev. OBC and UBC, respectively). Gallium is enriched in all the bauxite layers, OBC and UBC. Zirconium is moderately enriched in the bauxite layer, whilst Sc is more enriched in the UBC and its nearby wallrocks (e.g., compact bauxite). REE are locally enriched in/around the basement, with the total REE content of the bauxite ore host being 33.3 to 3082 ppm. In situ analysis indicates that the bauxite-bearing rocks contain REE minerals, including bastnasite and xenotime. Moderate to strong lateritization likely plays a vital role in the different enrichments of critical metals, especially in the bauxite and kaolinitic bauxite zone. Physicochemical conditions of the mineralization are very complex. The Li enrichment may have been closely linked to the clay formation and enrichment, especially during the pre-lateritization and late leaching stages. REE are mainly enriched in the lateritization stage, and then percolated downward via acidic leaching, where differentiation and re-enrichment occur. When REE migrate to an alkaline environment (caused by Huanglong Fm. limestone), bastnaesite precipitated readily, eventually forming REE-rich claystone and concentrated along the alkaline barrier of carbonate rock.