准噶尔盆地南缘头屯河地区砂岩型铀矿铀源区及其成矿构造背景分析--来自碎屑锆石U-Pb年龄及Hf同位素的证据

Provenance and ore-forming tectonic setting of sandstone-type uranium deposits in the southern margin of Junggar Basin--Insights from U-Pb ages and Hf isotopes of detrital zircons

准噶尔盆地是我国重要的多能源矿产产出盆地之一,而准噶尔盆地南缘头屯河地区也是我国砂岩型铀矿找矿的优选区段,为了厘定头屯河地区砂岩型铀矿赋矿层位沉积期的源区位置、母岩岩性及时代,本文在野外地质调查的基础上,对头屯河地区砂岩型铀矿赋矿层中的碎屑锆石进行了LA-ICP-MS U-Pb定年和Hf同位素分析,建立了碎屑锆石的U-Pb年龄及Hf模式年龄谱系。通过与周缘岩浆活动时代对比,并结合古流向数据进一步分析赋矿层位沉积期的源区位置及母岩岩性,讨论砂岩型铀矿的铀源条件。对采自侏罗系和下白垩统的4个砂岩样品进行碎屑锆石年龄分析表明:碎屑锆石U-Pb年龄存在140~180 Ma、240~320 Ma、340~420 Ma、440~480 Ma四个主峰值年龄段,年龄较平均的分布在210~480 Ma宽泛的区间内。研究表明头屯河地区早侏罗世物源来自北天山;中侏罗世物源来自中、南天山;中侏罗晚期开始转变为以北天山为主;早白垩世物源大部分来自中、北天山,少量来自博格达山地区。砂岩型铀矿化层铀源主要来自南侧天山地区的古生代中酸性火成岩,其成矿作用应该发生在盆地处于较稳定的构造环境中。

Junggar basin is one of the most important basins producing multi-energy mineral, and Toutunhe area in the southern Junggar basin is the prospect section of the sandstone-type uranium ore prospecting. In this paper, based on the field investigation, LA-ICP-MS U-Pb dating and Hf isotope analysis of detrital zircons from the ore-bearing target layer of the sandstone-type uranium deposit in the southern Junggar basin have been carried out and the zircon U-Pb age spectrum, Hf isotope and model age were established. By comparing with the age of magmatic activity and combining with the paleocurrent data, we further analysis the provenance of the strata and the uranium source in sandstone-type uranium deposits. Four sandstone samples from the Jurassic and the Lower Cretaceous were collected for detrital zircon U-Pb dating. The analysis result shows that the detrital zircon U-Pb ages were divided into four peak age groups: 140~180 Ma, 240 ~ 320 Ma, 340~420 Ma, 440~480 Ma, and the age is evenly distributed within the 210~480 Ma range;The provenance of the Lower Jurassic strata with sandstone-type uranium mineralization was derived from the north Tianshan area;The materials from central-south Tianshan area began to increase and dominate in Middle Jurassic strata. After that, the provenance began to change to the north Tianshan again since the late Middle Jurassic. The provenance of Early Cretaceous strata was mostly from the North Tianshan, and a small amount from the Bogda Mountains. The uranium source of sandstone-type uranium deposits in the southern margin of the Junggar basin should be related to the Paleozoic acidic magmatism in Tianshan area, and its mineralization should have occurred in a relatively stable environment.