伊犁盆地南缘砂岩型铀成矿年龄及其表征意义

Metallogenic age and its significance of sandstone-type uranium deposit at the southern margin of Yili basin

对伊犁盆地南缘砂岩型铀矿床中的沥青铀矿采用LA-ICP-MS方法分析U-Pb同位素年龄,同时,收集伊犁盆地南缘近年来的U-Pb同位素数据进行统计,综合数据表明:伊犁盆地南缘砂岩型铀矿具有连续性、多期性成矿的特点,沉积成岩期(199.6~145.5 Ma)、晚白垩世至古近纪(99.6~28.4 Ma)、中新世以来(23.3 Ma~)均存在铀成矿作用,且在中新世之后的铀成矿作用最为强烈。通过成矿期次划分与构造期次的对比发现,主要成矿年龄集中在新构造运动以来,说明天山揭顶作用是铀成矿的关键致矿构造事件。通过含矿层砂岩碎屑锆石U-Pb同位素年代学、含矿砂体和蚀源区原始铀含量及变化研究,验证了双铀源的成矿特点,并厘定脑盖吐组中酸性火山岩为主要外部铀源。

U-Pb isotope data of sandstone-type deposit at the southern margin of Yili basin was analyzed by LA-ICP-MS.Meanwhile,the U-Pb isotope data in recent years was collected here.The results showed that the mineralization of sandstone-type uranium deposit is characterized by continuity and multiple periods.There were continuous uranium mineralization in sedimentary diagenetic stage(199.6~145.5 Ma),late Cretaceous to Paleogene(99.6~28.4 Ma)and after Miocene(23.3 Ma~).Uranium mineralization is most intense after Miocene.Through the comparison of metallogenic times and tectonic events,it was found that the main metallogenic ages has been concentrated since the neotectonic period,indicating that Tianshan toppling plays the key role in uranium mineralization.Study of U-Pb isotope chronology of debris zircon,the original uranium content and its variation in the host sandstone and the source areas verified that dual uranium source was the metallogenic characteristics and the main external source is from inter mediate-acid volcanic rock of Naogaitu Formation.