Genetic Relationship Between Granite And Pegmatite In The Kaluan' Lithium Deposit,Xinjiang:Evidence From Zircon Dating,Hf-O Isotopes And Whole-Rock Geochemistry

Rare metal minerals are crucial to the development of modern industry and technology.It is essential to do more studies about the genesis and mineralization of the pegmatite deposit which is the main source of rare metals.The Altai orogenic belt in northern Xinjiang is an important part of the Central Asian orogenic belt,where granite pegmatite and its related rare metal deposits are widely distributed.A potential large large-super Kaluan lithium deposit has been discovered in the Kaluan-Azubai pegmatite ore field which is located in the Halong-Qinghe rare metal metallogenic belt of the Central Altay structural unit.Due to the lack of systematic and reliable data on granite and pegmatite,the source and evolution process of the granite and pegmatite in the Kaluan deposit and its genetic relationship are still unclear.In order to reveal the formation age,potential material source and tectonic background of granite and pegmatite,even the relationship of both,we conducted some experiments with the samples of Kaluan mining area,such as main trace elements,Pb-Sr-Nd isotopes,zircon U-Pb dating,Hf-O isotopes and lithium isotopes.The results show that the periphery biotite granite samples contain high K₂O content?4.1⁵.3%?.The value of A/CNK is between 1.05 and 1.09,which is a peraluminous I-S type transition rock of high potassium calc-alkaline series.High K₂O content?0.4⁸.0%?presents in pegmatite as well.A/CNK value is between 1.08and 4.37.Pegmatites are peraluminous-strong peraluminous rocks of low-potassium tholeiite to high-potassium calc-alkaline series.The zircon U-Pb age of the peripheral biotite granite is about 407.9 Ma,the?_Hf?t?value is 1.3⁷.4;the pegmatite zircon U-Pb age is about 205 Ma,the?_Hf?t?value is-0.7⁸.1.The positive?_Hf?t?value of pegmatite indicates that the initial magma is derived from the partial melting of the mantle material,or the result of the interaction of the crust source material and the depleted mantle.The contents of principal and trace elements reveal that the periphery biotite granite is a clastic source area with poor clay,and the periphery pegmatite,spodumene-bearing pegmatites and spodumene-barren pegmatites source area transitions from the clastic source area of poor clay to the mudstone source area of rich clay.The above results and the similar Pb-Sr-Nd isotopic composition of granite and pegmatite indicate that pegmatite and granite could have a genetic relationship.There is no linear relationship between?⁷Li and Li content,which indicate that the?⁷Li value is independent of magma differentiation during the crystallization differentiation of granite magma.The characteristics of lithium isotope composition reflect the features of its source area.The absence of obvious correlation between?⁷Li and magma crystallization parameters Rb,Zr/Hf,Nb/Ta and SiO₂ content shows that there is no obvious lithium isotope fractionation during the process of granitic differentiation of granite magma.The?⁷Li value of the non-mineral pegmatite is higher,which represents the final melt part of the granite magma evolution.The?⁷Li value of the horn rock may be affected by the lithium isotope diffusion fractionation.The same?⁷Li value of pegmatite and biotite granite presents that the pegmatite is the product of partial melting of the periphery biotite granite.