WU Sheng-wei1,2, XIAYong1*, TAN qin-ping1,2, XU Jian-bin1,2, XIE Zhuo-jun1,2, YANG Hai-ying1,2,HEShan1,2
(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:A large amount of REE resources is enriched in phosphorites within the Lower Cambrian Gezhongwu Formation in Zhijin County, Guizhou Province. However, the REE enrichment mechanism in phosphorites is not clear yet. In this paper, the research on the Zhijin phosphorites with different REE content ranges（＜262×10-6, 262×10-6－527×10-6,527×10-6－761×10-6,＞761×10-6）indicates that REE patterns of all phosphorites show features of the Ce negative anomaly, no obvious Eu anomaly, MREE and Y enrichment. The (La/Sm)N-δCe and δPr-δCe diagrams show that Ceanomalies of the Zhijin phosphorites represent the real Ce anomaly which means the phosphorites were formed in an oxidized environment. However, the oxidized environment of seawater was not the decisive factor controlling the MREE enrichment at that time. The (La/Sm)N-SmN and (Gd/Yb)N-YbN scatter diagrams show that the MREE enrichment was resulted from the differentiation in the process of REE enrichment. The (Dy/Sm)N-δEu scatter diagram and no obvious Eu anomaly indicate that no hot water could be involved in the formation process of the Zhijin phosphorites. It’s believed that “old phosphorites” of geological history are commonly characterized with the HREE depletion.
Keywords: phosphorites; REE geochemistry; REE enrichment; Zhijin
ACTA MINERALOGICA SINICA Vol. 39, No.4, 2019, page359-370
