Mineralogy and elemental geochemistry of the Puxiong Nb-REE deposit in Jianshui City, southeast Yunnan Province, SW China

The Puxiong Nb-REE deposit is located in the Jianshui City, southeast Yunnan Province, SW China. It is a large-scale Nb-REE deposit in the weathering crust of Changlinggang granitic alkaline rock body. At present, the deposit has yielded 360 million tons of REE ores, 0.47 million tons of REE oxides, and 57000 tons of Nb metal, which are characterized by the enrichment of light rare earth elements (LREE). In this paper, the mineralogical and elemental geochemical characteristics of the deposit have been preliminarily identified through the analysis and testing of 20 kinds of niobium rare earth ore samples from No.60 drilling hole in the No.15 exploration line. The results of microscope, XRD and SEM studies show that there are orthoclase, plagioclase, nepheline, mica and magnetite in the remaining rock-forming minerals of the deposit, the secondary minerals are mainly kaolinite, gibbsite and montmorillonite, the main REE minerals and REE-containing minerals are monazite, bastnaesite, mianningite and thorianite. REE minerals and REE-containing minerals are mainly distributed in the fissures and cleavages of kaolinite, mica, and orthoclase, mainly in the shape of granular, needle-like and plate-like, and some of them are distributed independently. ICP-MS analysis results show that the REE contents also change greatly, ∑REE contents (766×10-6~8942×10-6) of No.Ⅰ ore body are higher than those of No.Ⅱ ore body (∑REE=1029×10-6~6043×10-6). The total contents of LREE (∑LREE=748×10-6~8841×10-6) were significantly higher than those of HREE (∑HREE=14×10-6~101×10-6), ∑LREE/∑HREE=42~114, (La/Yb)N=92~1001, and the internal differentiation of LREE ((La/Sm)N=21~52) was more obvious than that of HREE ((Gd/Yb)N=2~11). All the samples have negative Eu anomalies, with δEu values ranging from 0.44 to 0.72. Different ores types have different Ce anomaly characteristics. The samples of No. I ore body have obvious negative Ce anomalies (δCe=0.02~0.52, only δCe=1.34 for sample ZK15-60-02), and the samples of No.Ⅱ ore body have weak negative Ce anomalies (δCe=0.41~0.85, only δCe=1.97 for sample ZK15-60-18). The trace elements content also have a large range, but compared with the Clark values of the upper crust, Li, Zn, Ga, Zr, Nb, Cd, Sb, Cs, Tl, Pb, Th and U are relatively enriched, while Sc, V, Cr, Co, Ni, Cu and Sn are relatively depleted. The results show that the differentiation and enrichment of LREE and HREE were caused by the internal diagenesis and the external mineralization. The internal diagenesis provided the material source for the deposit, and the external mineralization resulted in the further enrichment of Nb-REE. © 2020, Science Press. All right reserved.