WANG Hong1,2, GU Jing1, HUANG Zhi-long1*, ZHAO Lang-ye1,2
(1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;
2. University of Chinese Academy of Sciences, Beijing 100049, China)
Abstract: The Xinmin bauxite deposit is an newly discovered large bauxite deposit in recent years in the Wuchuan－Zheng’an－Daozhen area, Northern Guizhou. It belongs to the paleo-weathering crust sedimentary deposit, with host rocks of the Lower Permian Liangshan Formation. Rare earth elements are extreamly enriched in the bottom part of the Liangshan Formation. In order to investigate the geochemical behavior of rare earth elements during the bauxite mineralization, in this study, we have analyzed compositions of major and trace elements in samples of bauxite-bearing rocks in the Liangshan Formation and adjacent formations from two borehole profiles and one outcrop profile. Our new data show that the bauxite-bearing rock series have Ti/Nb and Nb/Ta ratios similar to those of rocks in the underlying Hanjiadian Formation, suggesting that the Hanjiadian Formation could be the main source of the bauxite and REEs in the bauxite-bearing rocks. The variations of ΣREE contents, REE mobility coefficients (Kjw), and δCe values in samples of the weathering profiles indicate the abnormal enrichment of rare earth elements occurred in the stage of paleo-weathering crust before the deposition of bauxite-bearing rocks, though the thickness of paleo-weathering crust is relatively thin. In the stage of re-weathering of bauxite-bearing rocks, a certain amount of REEs was migrated but the REE migration has no significance to the REE mineralization. During the process of bauxite mineralization, the mobilities of REEs were gradually decreased from LREE to HREE. The Fe-rich chlorite of the bauxite-bearing rocks was deposited under weakly alkaline and weakly reduced conditions in the paleo-weathering crust. The underlying carbonate of the Huanglong Formation, meanwhile, promoted the enrichment of REEs in Fe-rich chlorite layers. The deposition and re-weathering of bauxite-bearing rocks occurred under acidic and oxidized conditions.
Keywords: The Wuchuan－Zheng’an－Daozhen area; bauxite deposit; REE geochemistry; element migration and enrichment
ACTA MINERALOGICA SINICA Vol. 41, No.4/5, 2021, page 439-453