晴隆锑矿床中萤石的稀土元素特征及其指示意义

本文系统地研究了黔西南晴隆锑矿床中萤石的稀土元素地球化学,表明不同颜色、不同矿物组合的萤石的稀土元素含量变化较大,但具有固定的REE分配模式,以明显的负Ce异常、富MREE、分配曲线相对平缓为特征;这种配分模式主要是受其晶体化学因素的控制,而与溶液中REE络合物的稳定性关系不大。萤石的稀土元素组成与其矿物共生组合关系不大,但与其颜色关系较密切。萤石的Ce、Eu异常主要是受氧逸度的控制,流体源区的氧逸度较高,矿物沉淀场所的氧逸度相对较低,从而导致该矿中萤石呈明显的负Ce异常,或正或负的Eu异常。晴隆锑矿床形成于开放体系条件下,水/岩反应很可能是导致萤石发生沉淀的主要机制。萤石中的Ca部分来自茅口组灰岩,部分来自大厂层玄武岩;而矿化剂F可能主要来自外部。

REE GEOCHEMISTRY OF FLUORITE FROM THE QINGLONG ANTIMONY DEPOSIT AND ITS GEOLOGICAL IMPLICATIONS

The REE geochemistry of fluorite from the Qinglong antimony deposit, located at southwestern Guizhou, was systematically studied. It was shown that the REE concentration of fluorite greatly varied with various colors and different mineral assemblages, and there existed a consistent REE distribution pattern among various colored fluorites, characterized by the obviously negative Ce anomaly, MREE enrichment and flat REE distribution curves. The REE distribution pattern of fluorite was predominately controlled by the crystallochemical factors rather than the stabilities of REE complexes in the hydrothermal solution. No obvious connection existed between the REE concentration of fluorite and its mineral assemblages; however, the REE concentration and its parameters of fluorite were closely associated with the intensity of the color. The Ce and Eu anomaly of fluorite were controlled by the oxygen fugacity, the relatively high oxygen fugacity at the fluid origin regime and the relatively low value at the ore deposition site resulted in the obviously negative Ce anomaly, positive or negative Eu anomaly for fluorite. The Qinglong deposit formed under an open system condition, the fluid rock interaction was likely to be responsible for the ore deposition. The calcium of fluorite was derived, partly from the Permian Maokou limestone and partly from the Emeishan basalt, and the mineralizer fluorine probably came from the exterior rather than from the Emeishan basalt as expected.