REE mobility and Ce anomaly in bauxite deposit of WZD area, Northern Guizhou, China

Abstract The rare earth element (REE) behavior and the related Ce anomalies of two profiles in bauxite of the Xinmo Syncline from Wuchuan–Zheng'an–Daozhen (WZD) area (Northern Guizhou, China) have been studied. The bauxite has diaspore as its main ore mineral, with lesser amounts of boehmite. Clay minerals, including kaolinite, chlorite, illite and smectite, are a minor mineral constituent. Furthermore, a significant Ce-bearing mineral parisite (Ce 2 Ca(CO 3 ) 3 F 2 ) is found near the bottom of the profiles. The bauxites have flat HREE (Er–Lu) shape relative to NASC, with variable weak depletion to weak enrichment patterns of LREE (La–Nd) and MREE (Sm–Ho) across the profiles. Strong positive Ce-anomalies (normalized to NASC) are also noticeable in the uppermost part of the profiles. Mass balance calculations suggest that an obvious fractionation exists among different REE and LREE are more mobile than HREE during the leaching process. In addition, the samples collected along a vertical profile show that a downward increase for the REE concentration and a remarkable enrichment of REE are found at the basement of the bauxite deposits. A similar downward increase trend is also observed in the values of La N /Yb N and Gd N /Yb N . The above characteristics show that the REE losses caused by leaching decreased gradually from the top to the bottom of the profile. The higher mobility of LREE in the profile might be due to differences in the stabilities of the original REE-bearing minerals during leaching process. The REE enrichment at the basement of bauxite deposits is attributed to the increase of pH around the parent rock as well as the presence of mineral ligands during bauxitization. The value of [Ce/Ce*] NASC decreased downwards, and increased again near the bottom of the profile. The positive Ce-anomaly in the uppermost part of the profile has been attributed to the redox change of Ce 3 + to Ce 4 + and the consequent precipitation of cerianite (CeO 2 ). A decrease in the oxidation state downwards causes the decrease of the value of [Ce/Ce*] NASC . The formation of parisite near the bottom of the profile leads up to the increase in the value of [Ce/Ce*] NASC again. The precipitation of parisite may occur via reactions between the fluoride complexes (CeF 2 + or CeCO 3 F 0 ) and Ca 2 + and HCO 3 − .