REE geochemistry and genesis of the Xiachen fluorite deposit in Tiantai basin, Zhejiang Province

Abstract: In order to investigate the metallogenic mechanism, ore source and evolution of the Xiachen fluorite deposit in Tiantai basin, the authors studied the geological background as well as trace and REE geochemical characteristics of this ore deposit. The results show that the ∑REE, LREE, MREE and HREE values of wall rocks are much higher than those of ores in the Xiachen fluorite deposit, and REE values of fluorite, quartz and wall rock are characterized by relative enrichment of LREE and depletion of HREE. In addition, (La/Yb）N ratios are mostly higher than 8, and REE patterns show a steeply right-oblique feature. Fluorite has weakly positive Eu anomaly and quartz shows weak negative Eu anomaly. Fluorite and quartz have no significant Ce anomaly. According to the La/Ho-Y/Ho diagram, the ore-forming materials of fluorite were derived from the same source, and fluorite and quartz were formed in the same period. The ore-forming material Ca might have been mainly derived from purple sedimentary rocks in Chaochuan Formation, whereas F was probably derived from both Chaochuan Formation sedimentary rocks and Chencai Group metamorphic rocks. According to the geological characteristics of the ore deposit and the Tb/Ca-Tb/La diagram, the authors hold that the ore deposit is an epithermal fault filling-metasomatic type deposit.