Bauxite is a prominent constituent of the paleoweathering crust that formed during a ~ 150-million-year-long interval between the Ordovician and Late Carboniferous on the North China Craton, representing one of the largest karst bauxite deposits globally. Although critical metal-bearing minerals are found in this layer regionally, the mechanisms of their concentration are poorly known. In this study, samples of karst bauxite from five sites were studied using petrography, X-ray diffractometry (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM–EDS), and inductively coupled plasma mass spectrometry (ICP-MS) in order to explore the distribution of critical metals and their enrichment mechanisms. The karst bauxite consists of three lithologic components: (1) ferritic claystone, having total Fe₂O₃ content > 50% (main minerals: hematite and goethite); (2) clayey bauxite, having Al₂O₃ > 35% and clay content < 50% (main minerals: diaspore and boehmite); and (3) bauxitic clay, having Al₂O₃ > 35% and clay content > 50% (main minerals: clay minerals, with lesser amounts of diaspore). The mean contents of Li (892 ppm), B (327 ppm), and ΣREE (584 ppm) are relatively high, indicating industrial mining potential. Lithium is mainly in lithium-bearing chlorite (cookeite) and enriched in bauxitic clay, whereas B and REE are present mainly as adsorbed ions on the surfaces of diaspore, boehmite and clay minerals, although LREE also might exist as independent mineral phases (< 3 μm diam.). Processes of mineral evolution linked to weathering played an important role in the enrichment of these elements. Ferritic claystone is relatively enriched in HREE, clayey bauxite in LREE, and bauxitic clay in B and Li. This pattern of critical metal enrichment reflects a three-stage genesis of bauxite linked to in situ weathering and bauxitization, which provide insights into the weathering history of other bauxite deposits globally.

铝土矿是华北克拉通奥陶纪和晚石炭世之间约 1.5 亿年期间形成的古风化壳的重要组成部分，是全球最大的岩溶铝土矿矿床之一。尽管在该层中局部发现了关键的含金属矿物，但其富集机制却知之甚少。在本研究中，使用岩相学、X 射线衍射 (XRD)、扫描电子显微镜与能量色散光谱 (SEM-EDS) 和电感耦合等离子体质谱 (ICP-MS) 对来自五个地点的岩溶铝土矿样品进行了研究，以便探索关键金属的分布及其富集机制。岩溶铝土矿由三种岩性成分组成：（1）铁素体粘土岩，总Fe ₂O ₃含量>50%（主要矿物：赤铁矿、针铁矿）；(2)粘土质铝土矿，Al ₂ O ₃  > 35%，粘土含量< 50%（主要矿物：水铝石、勃姆石）；(3)铝土矿粘土，具有Al ₂ O ₃ > 35%，粘土含量> 50%（主要矿物：粘土矿物，含少量水硬石）。Li（892 ppm）、B（327 ppm）和ΣREE（584 ppm）的平均含量相对较高，表明具有工业开采潜力。锂主要存在于含锂绿泥石（库克石）中，并富集于铝土矿粘土中，而 B 和 REE 主要以吸附离子形式存在于硬水铝石、勃姆石和粘土矿物的表面，尽管 LREE 也可能作为独立矿物相存在（< 3直径微米）。与风化相关的矿物演化过程在这些元素的富集中发挥了重要作用。铁素体粘土岩相对富集重稀土元素，粘土质铝土矿相对富集轻稀土元素，铝土矿粘土相对富集B和Li。这种临界金属富集模式反映了铝土矿的三阶段成因，与原位风化和铝土矿化有关，