江南造山带东段含钨岩体地球化学特征

Geochemical characteristic of tungsten-bearing pluton in the eastern Jiangnan orogen

江南造山带东段燕山晚期含钨的东源岩体与非含钨的旌德岩体、桃岭岩体,其地球化学特征具有埃达克质岩的亲缘性,是先前(新元古代)交代的岩石圈地幔发生部分熔融底侵到壳幔过渡带附近,导致加厚下地壳发生部分熔融的产物,可能与少量的幔源岩浆发生岩浆混合作用。含矿岩体与非含矿岩体存在不同的Sr-Nd同位素组成,表明含矿与非含矿岩体具有不同的源区。锆石LA-ICPMS定年显示含矿的东源岩体侵位时间<147 Ma,非含矿岩体侵位时间<140 Ma。含矿岩体的副矿物组合以独居石+辉钼矿+白钨矿+白钨矿+电气石为特征。岩体中富含成矿元素、富挥发分、富钾,黑云母中富F、低Fe和fO2,斜长石以钠长石为主,均可作为含矿花岗(斑)岩体的重要地球化学参数。

Geological and geochemical studies indicate that the tungsten-bearing （Dongyuan pluton） and barren granitoid （Jingde and Taoling plutons） in the eastern Jiangnan orogen have adakite-like geochemi-cal features. They may be directly generated from the partial melting of thickened lower continental crust, which was triggered by mafic magmas ascended from the metasomatized lithospheric mantle, with involve- ment of mantle components. The ore-bearing pluton has distinct Sr-Nd isotopic compositions from the barren plutons, suggesting they have different source regions. The accessory mineral assemblages in ore body is characterised by the combination of monazite, molybdenite, tungstite and tourmaline. The rock is rich in ore-forming elements, volatile, while the biotite is rich in Fluorine, low-Fe and fo2, sodium is the main element of anorthose. Those are the important geochemical parameters for the ore-bear9ng granite （porphyry） pluton.