Zircon and Cassiterite U-Pb Geochronology and Hf Isotopes of Kama Li-Nb-Ta Pegmatite Deposit and Its Geological Significance in Nasarawa,Central Nigeria
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 lithium-niobium-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(n=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 theεHf(t)value of zircon is between-20.6 and-19.0,and the TDM2 value is 2.7 Ga;The εHf(t)value of cassiterite is between-17.7 and 14.9,and the TDM2 value varies between 2.4 Ga and 2.6 Ga.The εHf(t)value of Columbite-tantalite is between-15.9 and-7.4,and the TDM2 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.
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