大桥坞产铀火山-侵入杂岩的岩浆混合作用及其对赣杭构造带铀成矿潜力的指示意义

：浙江省大桥坞铀矿床赋矿围岩为一套火山-侵入杂岩，锆石U-Pb定年显示该套杂岩的成岩时代为138~125 Ma。Hf同 位素分析结果显示随着成岩时代变新，这些岩石中锆石ε Hf(t)值从约-13.0升高到约-3.0。锆石饱和温度同样表现出升高的趋 势，从~749℃升高到~846℃。以上特征表明大桥坞地区火山-侵入杂岩为壳幔岩浆混合成因，且幔源物质加入的比例随成岩 时代变新而增多。综合前人对赣杭构造带相山、芙蓉山和沐尘地区花岗质岩石的研究结果，发现这些岩石的全岩ε Nd (t)值和 锆石ε Hf(t)值在135~112 Ma期间分别从-9.0升高到-2.0和-10.0升高到2.0，表明其成因上可能同壳幔岩浆混合有关，且随着 成岩时代变新幔源岩浆的加入逐渐增多。Sr-Nd同位素模拟显示幔源岩浆加入的比例在135~112 Ma期间从0升高到~60%。 由于幔源岩浆较壳源岩浆贫U和Th，前者的加入会稀释壳源岩浆中U和Th的含量，降低其铀成矿潜力。幔源物质加入越 多，铀成矿潜力越低。赣杭构造带壳幔岩浆混合作用呈西弱东强的地质事实，可能是该带上铀矿床的分布呈西大东小格局 的重要原因之一。因此，赣杭构造带东段找矿需关注富铀基底（花岗岩或长英质变质岩基底） 与早白垩世火山岩盖层相结 合的地区。
The Daqiaowu uranium deposit is a volcanic-intrusive rock-hosted uranium deposit, where zircon ε Hf(t) values of the volcanic-intrusive complex (dated at 138~125 Ma) exhibit a remarkable rise from approximately -13.0 to -3.0 through time. Zircon saturation temperatures of these rocks also show an increase from ~749℃ to ~846℃. These characteristics suggest that volcanicintrusive rocks in the Daqiaowu were generated by mixing of magmas derived from mantle and crust, and that more inputs of mantle-derived materials were added to younger rocks. Together with a compilation of granitic intrusive rocks associated with magma mixing in Xiangshan, Furongshan and Muchen, we found that whole-rock εNd(t) and zircon εHf(t) values of these granitic rocks increased