Using detrital zircon systematics to trace the sediment sources of Jurassic uranium-bearing sandstones in the western Ordos Basin, China: implications for uranium exploration in a sedimentary basin

The Jurassic Zhiluo Formation in the western Ordos Basin is known for hosting economically significant sandstone-type uranium deposits. However, the understanding of sediment sources for this formation, crucial for guiding uranium exploration, has been a subject of controversy. This study aims to address this issue by presenting a systematic dataset derived from detrital zircons found in the uranium-bearing sandstones of the Zhiluo Formation. The dataset includes U‒Pb dating, trace element analyses, and in-situ Hf isotope compositions. The detrital zircons analysed are predominantly of magmatic origin, as indicated by a Th/U ratio greater than 0.4. Their U‒Pb ages can be broadly categorized into a predominant population ranging from 170 to 500 Ma, with a peak ca. 300 Ma. Additionally, there are two minor age populations: 1600–2050 Ma (peaking at ca. 1850 Ma) and 2300–2650 Ma (peaking at ca. 2500 Ma). The εHf(t) values of these zircons exhibit a range from −27 to 7, concentrating mostly from −16 to 5. Importantly, none of them aligns above the deficit mantle evolutionary line in an εHf(t) vs. age covariant diagram. A comprehensive comparison of the analytical U‒Pb ages and Hf isotopic results with previously reported data from adjacent geological units surrounding the western Ordos Basin suggests that the primary provenance supply area for the sandstones is the Alxa Block, particularly the uranium-rich felsic rocks within it. Minor contributions are inferred from the Yinshan Block and the Qilian Orogenic Belt. The northwestern region of the study appears to be the primary prospect area for uranium exploration, and we have proposed effective measures to refine the exploration target area and enhance exploration efficiency. Overall, the study provided crucial insights into deducing provenance supply areas and transport paths, with implications for uranium exploration in sedimentary basins worldwide.

鄂尔多斯盆地西部的侏罗系直罗组（Jurassic Zhiluo Formation）以产出具有经济价值的砂岩型铀矿床而闻名。然而，该地层的沉积物源认知对铀矿勘探至关重要，长期以来却一直存在争议。本研究旨在解决这一问题，提供一套采自直罗组含铀砂岩中碎屑锆石（detrital zircons）的系统数据集。该数据集包含U-Pb定年（U-Pb dating）、微量元素分析（trace element analyses）以及原位Hf同位素组成（in-situ Hf isotope compositions）数据。所分析的碎屑锆石以岩浆成因为主，这一点可由其Th/U比值（Th/U ratio）大于0.4得到佐证。其U-Pb年龄可大致划分为三个年龄组：主体年龄组集中在170~500 Ma之间，峰值约为300 Ma；此外还存在两个次要年龄组，分别为1600~2050 Ma（峰值约1850 Ma）与2300~2650 Ma（峰值约2500 Ma）。这些锆石的εHf(t)值（εHf(t) values）分布范围为-27至7，主要集中在-16至5区间内。值得注意的是，在εHf(t)与年龄的协变图中，没有数据点落在亏损地幔演化线（deficit mantle evolutionary line）之上。通过将本次获得的U-Pb年龄与Hf同位素分析结果，与鄂尔多斯盆地西部周边相邻地质单元的已发表数据进行全面对比，研究认为该砂岩的主要物源供给区为阿拉善地块（Alxa Block），尤其是其中富含铀的长英质岩石（felsic rocks）；次要物源贡献则来自阴山地块（Yinshan Block）与祁连造山带（Qilian Orogenic Belt）。研究区西北部被认为是铀矿勘探的首选靶区，本研究还提出了优化勘探靶区、提升勘探效率的有效措施。总体而言，本研究为推断物源供给区与搬运路径提供了关键认识，对全球沉积盆地的铀矿勘探具有重要借鉴意义。