GU Jing1, HUANG Zhi-long1*, JIN Zhong-guo2
(1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;
2. Guizhou Nonferrous Metal and Nuclear Industry Geological Exploration Bureau, Guiyang 550005, China)
Abstract: Based on a systematic analysis of major and rare earth elements in rocks and ores of the Xinmin-Yanxi bauxite deposit in the Wuchaun－Zheng’an－Daozhen area of the Northern Guizhou, we have discussed enrichment characteristics and mechanism of the REE in the bottom layer of ore-bearing rocks of the Xinmin－Yanxi bauxite deposit in this paper. It is believed that the pH value of medium and the degree of bauxite mineralization in profile of the deposit are the key factors affecting the enrichment of rare earth elements. Due to the reduction of activity of underground water and the influence of carbonate rock, the bauxite-bearing rocks have pH values varying from neutral to alkaline, which is beneficial to the REE enrichment in the bottom part of the ore-bearing rock series and the increase of REE contents in bauxite ores with the decrease of weathering degree of bauxite ores. The relatively high REE content of clay minerals in the bottom part of ore-bearing rock series is one of important factors for the enrichment of REE. The major REE hosting mineral of apatite can be easily preserved in the bottom part of the ore-bearing rock series. In addition, the presence of authigenic REE minerals in the bottom part of the bauxitic layer could also one of important factors for the enrichment of REE in the bottom part of the ore-bearing rock series. Goethite has played important role for adsorption of the REE especially the LREE. The relatively high Fe contents of the bottom part of bauxite layer of the Xinmu－Yanxi bauxite deposit and the weakly alkaline to alkaline pH values for the formation environment of the bottom part of the ore-bearing rock series are more favorable to the formation of goethite. The REE enrichment is associated with the redox environment. The obvious negative Ce anomalies of some samples in the bottom part of ore-bearing rock series of the Xinmu－Yanxi bauxite deposit indicate that an weakly oxidized sedimentation environment could be favorable to the REE enrichment. The weakly negative correlation between δCe and (La/Nd)N values of samples indicates that the enrichment of LREE may be related to the redox condition of the medium of sedimentation, with the relatively high enrichment of LREE in the bauxite-bearing rock series under the weakly oxidized condition.
Keywords: The Wuchuan－Zheng’an－Daozhen area; Xthe inmu－Yanxi bauxite deposit; rare earth element (REE); enrichment mechanism
ACTA MINERALOGICA SINICA Vol. 41, No.4/5, 2021, page 413-426