浙江天台盆地下陈萤石矿稀土元素地球化学特征及成因

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

为了探讨浙江天台盆地下陈萤石矿床的成矿机理、成矿物质来源与演化,对其地质背景、微量和稀土元素地球化学特征进行了研究。研究结果表明:天台盆地下陈萤石矿中围岩的稀土总量、轻稀土、中稀土和重稀土的含量远高于矿石。萤石、石英和围岩的稀土元素特征均为轻稀土相对富集,重稀土显示相对亏损,(La/Yb)_N通常多数大于8,配分曲线显示较陡的右倾斜。萤石的Eu均呈弱正异常,而石英则呈现弱的Eu负异常,萤石和石英的Ce基本不显异常。根据La/Ho-Y/Ho关系图,该成矿带上萤石的成矿物质是同源的,且萤石与石英为同期形成的产物。天台盆地下陈萤石矿的成矿物质Ca元素可能主要来自朝川组紫红色沉积岩,F的来源除了朝川组地层以外,陈蔡群变质岩系也应是F的主要来源之一。根据矿床地质特征及其Tb/Ca-Tb/La关系图可知,其为低温热液成因——断裂带充填交代型矿床。

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.