DU Sheng-jiang^1,2,3,4, WEN Han-jie^2*, LUO Chong-guang², GU Han-nian², YU Wen-xiu⁵, LI Yang², MENG Yong², YANG Ji-hua²

(1. State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, China;
2. Stake Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy Sciences, Guiyang 550081, China;
3. Chinese Academy of Geological Science, Beijing 100037, China;
4. Guizhou Geological Survey, Bureau of Geology and Mineral Exploration and Development of Guizhou Province, Guiyang 550081, China;
5. Kunming University of Science and Technology, Kunming 650000, China)

Abstract: A set of enriched Nb-Ga-REE polymetallic layer is widely developed in the eastern Yunnan－western Guizhou area, with its footwall of the Emeishan basalts. In this paper, microscopic mineralogy and geochemistry of the Emeishan basalts, especially the intensive analyses and systematic elemental scanning of sphene grains in the Emeishan basalts by using the electron probe microanalysis (EPMA), have been systematically studied to explore the contribution of footwall basalts to the Nb-Ga-REE polymetallic mineralization layer. The results show that most of basalts in the study area belong to the Ti-rich basalt type featured by the sphene enrichment. The Ti-rich basalt contains various morphological sphenes including euhedral, semi-euhedral, enveloped, grain shaped, cloudy, flaky, cross-shaped, crumby, and altered sphenes. Besides the enriched Nb，sphene contains a certain amount of Zr, Y and Ce. Combining with geochemical characteristics of the Emeishan basalts, sphene could be either as a product of primitive basic magma formed mainly in late stage of magmatism or generated from the hydration and oxidation of minerals, including ilmenite, grain sphene, and Ti-rich pyroxene, formed in the early and middle stages of magmatism. In addition, the surface weathering of sphane hosted in the Ti-rich basalt could be the main reason of Nb-mineralization in the research area as the weathered sphane could have provided ore-forming elements such as Nb, Zr, Y, and Ce for the overlying ore layer.

Keywords: Nb-rich sphene; Emeishan basalts; Ti-rich basalts; the eastern Yunnan - western Guizhou area; mineralogy

ACTA MINERALOGICA SINICA Vol. 39, No.3, 2019, page 253-263