摘要:
选择我国重要的离子吸附型稀土矿床产地——韩坊花岗岩体开展了锆石激光剥蚀-多接收器电感耦合等离子体质谱法(LA-MC-ICPMS)定年工作。研究结果表明,岩体中锆石的晶型较完整,环带明显,属于典型的岩浆锆石; 韩坊岩体存在两期岩浆活动,粗粒黑云二长花岗岩形成于加里东期,而细粒黑云二长花岗岩形成于燕山早期。加里东期的花岗岩是扬子陆块与华夏陆块拼接的结果,燕山期花岗岩是古太平洋板块向华南板块俯冲而导致岩石圈拆沉和减薄的结果。如果说南岭燕山期花岗岩控制了大规模钨锡成矿作用的发生,则加里东期花岗岩对南岭离子吸附型稀土矿床的形成具有重要贡献。加里东期的花岗岩含有褐帘石、锆石、萤石等易风化的富稀土副矿物,且因经受多起构造事件,断裂发育,加之多位于炎热多雨的地理位置,易于遭受强烈的风化作用。因此,易于形成离子吸附型稀土矿床。
Abstract:
Zircons collected from Hanfang intrusions in Ganxian, Jiangxi province, whose weathered crust produced many rare earth element (REE) deposits, have been dated by using Laser Ablation-Multicollector Inductively Coupled Plasma-Mass Spectrometry (LA-MC-ICPMS) and are presented here. The dating results from typical magmatic zircons with good shape and oscillatory zoning show that the coarse-grained biotite monzonitic granite intruded in the Caledonian era, during the convergence between Yangtse block and Cathaysia block, and the fine-grained biotite monzonitic granite intruded in the early Yanshan epoch as the results of lithospheric thinning and delamination during subduction of the old Pacific plate to the South China Plate. The granite intrusions formed in the Yanshan epoch have a close relationship with large scale mineralization of W, Sn in the Nanling district, while the intrusions formed in the Caledonian era have a significant contribution to the formation of ion adsorption type REE deposits. The intrusions in the Caledonian era host REE-rich accessory minerals, such as orthite, zircon and fluorite. The fractures of the intrusions were well developed as a result of a few tectonic events. The bad weathering was attributed to the hot and rainy climate in this region. Therefore, the intrusions in the Caledonian era tend to produce ion adsorption type REE deposits for the reasons previously mentioned.
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