滇东北矿集区茂租铅锌矿床萤石的稀土元素特征及其指示意义

REE Geochemistry of Fluorite from Maozu Pb-Zn Deposit and Its Geological Implications,Northeastern Yunnan,China

巧家茂租铅锌矿床是滇东北矿集区的代表矿床之一,除矿石矿物闪锌矿、方铅矿、黄铁矿外,萤石是其主要的脉石矿物。通过萤石的稀土元素地球化学特征研究,发现其中REE含量变化较大,特征参数也有差别,但其球粒陨石标准化曲线分配模式基本一致,不同矿化带萤石均具有明显的Ce负异常、中稀土富集、分配曲线相对平缓的特征。从铅锌矿体中心到外围矿化带,萤石稀土元素呈现∑REE逐渐减少、LREE富集变为HREE富集,δEu正异常变为δEu负异常,δCe逐渐变小的变化特征。表明该矿床萤石的形成是一个连续过程,不同矿化带的萤石是同一体系经历不同阶段的产物。通过萤石的形成机制分析,认为该矿床萤石是热液作用的产物,是由富含F的成矿流体沿构造活动带从下向上运移,与灯影组地层的白云岩发生水-岩的相互作用,使流体中的CaF_2产生过饱和而大规模沉淀析出形成的,且随着热液向两侧围岩迁移,不断与围岩发生水岩反应,分别形成了不同矿化带的萤石。本文研究对揭示矿床铅锌成矿机制具有重要意义。

The Maozu Pb-Zn deposit is a typical carbonate-hosted deposit in the Sichuan-Yunnan-Guizhou Pb-Zn metallogenic province. Sulfide ores are primarily composed of sphalerite, galena, pyrite and fluorite. Fluorite is the main vein mineral in the orefield. REE geochemistry of fluorite from the Maozu Pb-Zn deposit showed that REE content of fluorite varied greatly, their characteristic parameters were different, but the chondritc-normalized curve was quite consistent. Different fluorite from different mineralization showed obvious negative Ce anomalies. MREE was enrichment and the distribution curve was relatively gentle. From the center of the ore body to the mineralization periphery of the ore body, REE content reduced gradually, the LREE enrichment gradually became HREE enrichment. Eu gradually changed from positive anomaly to negative anomaly, negative Ce anomaly increased gradually. These features indicated that fluorite formed in a continuous process, different fluorites from different mineralization were produced by the same source at different metallogenic stages. The genetic type of fluorites in this deposit belonged to hydrothermal type. The ore-forming fluid rich in F flowed upward from below through the tectonic activity belt, and interacted with dolomite of upper Sinian Dengying Formation. The fluorite began to deposit from the fluid when CaF2 was supersaturated. With the ore-forming fluid evolved from ore body to the mineralization periphery and interacted with the host rocks constantly, which formed different fluorites of different mineralization. This study is meaningful to reveal the ore-forming mechanism of this deposit.