【摘要】 尼日利亚中部纳萨拉瓦地区是典型的含锂铌钽稀有金属伟晶岩脉发育的地区.卡马花岗伟晶岩型稀有金属矿床位于尼日利亚锂铌钽锡多金属成矿带的中部,是新发现的以锂为主,伴生铌钽矿的大型矿床,为限定其成矿年龄,探讨其矿化过程的来源及演化,对含矿伟晶岩脉开展了岩石学、矿物学、锆石及锡石U-Pb年代学、锆石微量元素和Lu-Hf同位素等研究.锆石和锡石的U-Pb年代测定结果表明,锆石U-Pb定年为（577.3±2.5） Ma（n=18,MSWD=6.4）,锡石U-Pb定年为（582.6±8.6） Ma（n=25,MSWD=0.72）,推断马锂矿床伟晶岩形成于577～583 Ma,矿床成矿作用主要发生在新元古代晚期.微量地球化学研究表明,研究区伟晶岩在俯冲-碰撞作用中形成,其岩浆源区主要为变质沉积岩,起源自陆壳.岩浆演化过程可能经历了斜长石、磷灰石、锆石等矿物的分离结晶作用.岩浆的强烈分离结晶演化作用导致岩石具有高分异演化特征.伟晶岩的锆石、锡石和铌钽铁矿Hf同位素组成表明,锆石的ε_Hf（t）值在-20.6和-19.0之间,T_DM2值为2.7 Ga;锡石的ε_Hf（t）值在-17.7和-14.9之间,T_DM2值在2.4 Ga和2.6 Ga之间变化.铌钽铁矿的ε_Hf（t）值在-15.9和-7.4之间,T_DM2值在2.0 Ga和2.4 Ga之间变化,表明伟晶岩的母体熔体主要起源于新太古代-古元古代基底岩的重熔作用.尼日利亚稀有金属伟晶岩矿床成矿与冈瓦纳造山运动关系密切,与冈瓦纳形成造山运动的碰撞后伸展期相对应.更多还原

【Abstract】 The Nasarawa region in central Nigeria is a typical area with developed lithium-niobium-tantalum rare metal pegmatite veins.The Kama granitic pegmatite-type rare metal deposit,located in the central part of the Nigerian lithiumniobium-tantalum-tin polymetallic metallogenic belt,is a newly discovered large deposit mainly containing lithium with associated niobium and tantalum ores.To define its metallogenic age and explore the sources and evolution of its mineralization process,this paper conducts a study of petrology,mineralogy,zircon and cassiterite U-Pb geochronology,zircon trace elements,and Lu-Hf isotopes on the ore-bearing pegmatite veins The zircon U-Pb dating yields the ages of（577.3±2.5） Ma（m=18,MSWD=6.4）,and the cassiterite U-Pb dating yields the ages of（582.6±8.6） Ma（n=25,MSWD=0.72）,therefore the pegmatite of the Kama deposit is inferred to have formed between 577 and 583 Ma,with the main mineralization occurring in the late Neoproterozoic.Trace elementsgeochemical analyses indicate that the pegmatites in the study area were formed during subduction-collision processes,with their magma source primarily being metamorphic sedimentary rocks,originating from the continental crust.The magma evolution process may have involved fractional crystallization of minerals such as plagioclase,apatite,and zircon.The intense fractional crystallization evolution of the magma results in rocks with highly differentiated evolutionary characteristics.The Hf isotopic compositions of zircon,cassiterite and columbite-tantalite in pegmatite show that theε_Hf（t） value of zircon is between-20.6 and-19.0,and the T_DM2 value is 2.7 Ga;The ε_Hf（t） value of cassiterite is between-17.7and-14.9,and the T_DM2 value varies between 2.4 Ga and 2.6 Ga.The ε_Hf（t） value of Columbite-tantalite is between-15.9 and-7.4,and the T_DM2 values are between 2.0 Ga and 2.4 Ga,indicating that the parent melt of pegmatite mainly originated from the remelting of Neoarchean-Proterozoic basement rocks.The mineralization of rare metal pegmatite deposits in Nigeria is closely related to Gondwana orogeny,which corresponds to the post-collision extension period of Gondwana orogeny.更多还原