LI Yu-hua1,2,3, ZHANG Zi-jun1,3, LONG Qing-bing1,3, LIU Feng-xiang1,3, LI Ming-xiao1,3, WANG Min2, ZHOU Jia-xi2,3,4*
(1. No. 209 Geological Team of Yunnan Nuclear Industry, Kunming 650032, China;
2. School of Resource Environment and Earth Sciences, Yunnan University, Kunming 650500, China;
3. Yunnan Exploration-Assessment and Study Center of Three Rare Mineral Resources, Kunming 650032, China;
4. MLR Key Laboratory of SanjiangMetallogeny and Resources Exploration & Utilization, Kunming 650500, China)
Abstract: The Puxiong Nb-REE deposit in Jianshui City, Yunnan Province, is a large-scale Nb-REE polymetallic deposit discovered in recent years. It occurs in the weathering crust of the Changlinggang alkaline intrusions composed of nepheline syenite and alkaline syenite, with the accumulated proven Nb resources of more than 57000 tons, and total REE resources of over 470,000 tons. At present, the researches on this deposit mainly focus on mineralogical characteristics and prospecting exploration technology. In terms of ore deposit geochemistry, previous researches are limited to the basic analysis of some ore-forming elements (such as Nb and REE) of the deposit. Based on in-depth field observations, we have carried out systematical sampling (24 pieces), and high-precision analysis of trace elements and REE contents for samples collected from cores of the No. 64 drill hole of the representative No. 12 exploration line. The results show that all samples are relatively rich in Li, Ga, Nb, Sb, Cs, Pb, Th and U in different degrees comparing to the average contents of trace elements of the upper crust, and are rich in rare earth element in different degrees compared with those of the chondrite, with the widely varied total REE contents. In general, the ∑REE contents of the fully weathered layer samples (1046×10-6－9154×10-6) are higher than those of the clay layer (630×10-6) and the semi-weathered layer samples (208×10-6－1369×10-6). These indicate that the diagenetic and weathering processes could lead to the enrichment of these elements in different degrees. In addition, there is obvious fractionation between the LREE and HREE as LREE/HREE ratios of all samples are relatively big, i.e. ∑LREE/∑HREE ratios of 20－58 and (La/Yb)N ratios of 25－143.The partial fractionation of LREE ((La/Sm)N=11－26) is more obvious than that of HREE ((Gd/Yb)N=1－6), indicating that there is differentiation and enrichment in different degrees among the REE. The REE patterns of all samples have obviously negative Eu anomalies (δEu=0.5－0.7), and both significantly positive and negative Ce anomalies (δCe=0.1－3.8), implying that the diagenetic and weathering processes did not cause the change of Eu anomaly, but did affect the Ce anomalies significantly. In summary, it is believed that various critical elements (rare, rare earth and dispersed elements) are enriched in different degrees by both the diagenetic and weathering processes in the Puxiong Nb-REE deposit.
Keywords: trace elements; Nb and REE; the Changlinggang alkaline intrusion; weathering crust; the Puxiong Nb-REE deposit
ACTA MINERALOGICA SINICA Vol. 39, No.4, 2019, page 474-483
