扬子西南缘拉拉IOCG矿床萤石稀土元素地球化学特征

REE geochemistry of fluorite from Lala IOCG deposit,SW margin of Yangtze block

以康滇地轴古元古代拉拉铁氧化物-铜-金(IOCG)矿床中不同期次萤石的稀土元素为研究对象,讨论其地球化学特征及指示意义。研究结果表明:拉拉IOCG矿床中有变质期和热液期2期萤石产出,变质期萤石分为早晚2个阶段,与铜钼矿化关系密切,形成温度较高,为同源不同阶段产物;热液期萤石与变质期不同源,为后期热事件产物。萤石整体表现出REE总量高的特征;从早期到晚期,萤石稀土总量呈逐渐减少趋势;变质期萤石是矿床中主要的REE载体之一。变质期成矿流体稀土含量较高,热液期成矿流体稀土含量较低。稀土配分模式呈LREE富集、HREE亏损的右倾型,轻重稀土分异明显,萤石的稀土配分模式受溶液体系中REE络合物稳定性的影响。变质期萤石继承了钠质火山岩的Ce、Eu异常特征,形成变质期萤石的高温变质流体具有负Ce异常且同时存在Eu2+和Eu3+;热液期萤石成矿流体具有温度低、氧逸度高的特征。Y的含量变化可能是引起本矿床萤石颜色变化的原因之一,其含量与颜色深浅呈负相关关系。

Rare earth element(REE) geochemistry and its geological implications of fluorite from the Lala IOCG deposit were studied.Following results were obtained:(1).Lala IOCG deposit has two stages of deposition of fluorite:a metamorphic stage(MS) and a hydrothermal stage(HS);The MS fluorite can be divided into an early stage and late stage.They are closely related to the copper and molybdenum mineralization precipitated in a high temperature metamorphic fluid.They are homologous products at different stages.The HS fluorite has a different source and is a product of later geological events.(2).The total content of REE(ΣREE) in fluorite at all stages is very high,especially in the MS fluorite.From the early stage to late stage,the ΣREE of fluorite decreases gradually.The MS fluorite is one of the main carriers of REE from Lala IOCG deposit.Metamorphic metallogenic fluid has a higher ΣREE than the hydrothermal metallogenic fluid.REE distribution patterns show that light REE(LREE) enrichment and heavy REE depletion,show a right dip type distribution pattern,characterized by strong differentiation between LREE and HREE.REE distribution patterns in the fluorite are dominated by the stability of the complexes in the hydrothermal solution.(3).MS fluorite inherited the Ce and Eu anomaly characteristic of the sodic volcanic rocks.The metallogenic fluid of MS fluorite is characterized by high temperature fluid,with a negative Ce anomaly,and containing both Eu2+ and Eu3+.The metallogenic fluid of HS fluorite is characterized by low temperature and high oxygen fugacity.(4).The content of Y may be one of the reasons for the pleochroism in fluorite from the Lala IOCG deposit,and correlates negatively to the depth of color.