拉拉IOCG矿床萤石的微量元素地球化学特征及其指示意义

Trace Elements Geochemistry of Fluorite and Its Implications in the Lala IOCG Deposit

康滇地区元古宙拉拉IOCG矿床中有与铜、钼矿化密切相关的萤石产出,其中,变质期有萤石(I)和萤石(II)2个世代萤石产出,前者与鳞片状辉钼矿共生,后者与条带状辉钼矿共生;热液期萤石(III)呈脉状穿插含变质期萤石的矿石;萤石的微量元素记录了成矿流体来源方面的重要信息。通过ICP-MS方法分析矿床中2期萤石样品的微量元素组成,运用微量元素含量、比值及蛛网图探讨微量元素特征、成矿流体来源及性质。结果表明:变质期萤石中各微量元素含量有一定的变化范围,热液期中各微量元素含量比较稳定,元素在萤石中的含量主要由元素在原始流体中的含量及元素本身性质所决定。结论认为:1变质期萤石(I)和萤石(II)为同源流体不同阶段演化产物,成矿流体来自于围岩,为具有高F-,Cu,Mo和Y含量的低p H值海水相流体,活动范围有限,没有发生大规模流动或迁移;2热液期萤石(III)与变质期萤石不同源,成矿流体由大气降水或地下水渗透淋滤围岩形成,为具有低F-含量的高p H值大陆淡水相流体,可能发生较远距离的渗入性流体流动或迁移。

The Lala Fe-Cu-REE deposit,reported as a typical IOCG deposit in the Kangdian region,is located at the western margin of Yangtze Block. Fluorite is one of the most important gangue minerals in the Lala IOCG deposit,which is intergrown with chalcopyrite and molybdnite,and recorded important information about the source and evolution of the ore-forming fluid. Trace elements geochemistry of fluorite and its implications for source of oreforming fluid are discussed through content,ratio and spider diagram of trace elements. Two stages of fluorite with three generations are identified in the Lala IOCG deposit. Fluorite（ I） and fluorite（ II） belongs to metamorphic metallization stage. Fluorite（ I） is intergrown with flaky molybdenite（ I）,and are isolated cube shaped. Fluorite（ II） is intergrown with banded molybdenite（ II） in the vein or massive-disseminated ores,light purple. Fluorite（ III） belongs to hydrothermal mineralization stage,intergrown with chalcopyrite and calcite veins,which cut the ores with fluorite（ I） and fluorite（ II）,with a cubic habit. It turned out that： the content of trace elements is variable in fluorite（ I） and fluorite（ II） while it is stable in fluorite（ III）,which is dominated by its content in the original fluid and the nature themselves. The results suggested that： 1Fluorite（ I） and fluorite（ II） are homogenous products at different generations,seawater phase ore-forming fluids derived from the host rock,characterized by high content of F,Cu,Mo,Y and low p H,and exhumation might migrated at small scale. 2Fluorite（ III） has a different source from fluorite（ I） and fluorite（ II）. Infiltration and leaching host rock by meteoric water or groundwater formed its freshwater phase ore-forming fluids,which is characterized by high p H and low content of F-,and exhumation might infiltration flew or migrated at a long distance.