二连盆地腾格尔坳陷都日木地区下白垩统赛汉组砂岩碎屑锆石U-Pb年代学、Hf同位素特征及其对铀源的制约

U-Pb chronology and Hf isotope characteristics of detrital zircons from sandstones of the Lower Cretaceous Saihan Formation within the Durimu area in the Tengger depression of the Erlian basin and their constraints to the uranium source

近年来在二连盆地中先后发现了哈达图、巴彦乌拉等大中型砂岩型铀矿床,这一地区因此成为国内铀矿勘查和开发的重要基地之一。腾格尔坳陷都日木地区的铀矿成矿背景相似,为限定含铀目的层下白垩统赛汉组铀源区位置及岩性,对其开展了岩相学、碎屑锆石U-Pb年代学和Hf同位素研究。结果显示,下白垩统赛汉组砂岩碎屑的锆石U-Pb年龄可分为2个主要区间:①129~152 Ma(峰值141 Ma),ε_(Hf)(t)值为-13.07~7.21,对应的t_(DM2)为731~2018 Ma;②243~281 Ma(峰值263 Ma),ε_(Hf)(t)值为-13.83~9.83,对应的t_(DM2)为668~2149 Ma。再结合古水流流向和源区地质背景的综合分析表明,都日木地区赛汉组物源主要来自温都尔庙-镶黄旗一带更靠近盆地一侧的二叠纪和早白垩世中酸性岩浆岩,而铀源主要来自该地区二叠纪花岗岩、火山岩和早白垩世火山岩,在砂岩型铀的矿化过程中盆地处于较为稳定的构造环境。

Many large and medium-sized sandstone-type uranium deposits,such as the Hadatu and Bayanwula deposits,have been discovered recently in the Erlian basin which has become one of the most important exploration and development bases for sandstone-type uranium deposits in China.Various sandstone-type uranium deposits in the Durimu area of the Tengger depression have similar ore-forming backgrounds.In order to contrain the location and lithology of uranium-bearing beds in the Lower Cretaceous Saihan Formation,we have undertaken the petrography of sandstone,and U-Pb chronologic and Hf isotopic study of detrital zircons from sandstones in the Saihan Formation in this paper.The results show that the U-Pb ages of detrital zirconre are mainly plotted in two age ranges of 129~152 Ma(peak value of 141 Ma)and 243~281 Ma(peak value of 263 Ma).Zircons with ages of 129~152 Ma haveε_(Hf)(t)values varying from-13.07 to 7.21 and their corresponding t_(DM2)ages varying from 731 Ma to 2018 Ma.,while zircons with ages ranging from 243 Ma to 281 Ma haveε_(Hf)(t)values varying from-13.83 to 9.83 and their corresponding t_(DM2)ages varying from 668 Ma to 2149 Ma.Based on the comprehensively comparative analysis of the ancient water flow direction and geological background of uranium source,it is believed that the provenance of the Saihan Formation in the Durimu area was mainly sourced from the Permian and early Cretaceous intermediate-acidic magmatic rocks distributed closely to the basin in the Wenduermiao-Xianghuangqi area,while the uranium was mainly sourced from the Permian granite and volcanic rocks,and early Cretaceous volcanic rocks in the Wenduermiao-Xianghuangqi area.The uranium mineralization of sandstone-type uranium deposits occurred in the basin with a relatively stable tectonic environment.