Sun Da, Li Huaming, Xia Fei, Nie Fengjun, Huang Guangwen, Zhang Zhibo, Meng Fanmin, Pan Jiayong, Hu Yujie
School of Earth Sciences, East China University of Technology, Nanchang 330013, Jiangxi, China.
State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, Jiangxi, China.
ACS Omega. 2024 Jan 10;9(3):3324-3341. doi: 10.1021/acsomega.3c06163. eCollection 2024 Jan 23.
The Ordos Basin is an important sandstone-type uranium enrichment region in China, and the Lower Cretaceous Huanhe Formation has attracted significant attention as a newly discovered ore-bearing stratum. To elucidate the provenance, tectonic background, and sedimentary environment constraints on uranium enrichment in the Huanhe Formation sandstone-type uranium deposits, 10 representative sandstone samples from the study area were analyzed by using electron microscopy, X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and electron probe microanalysis. Independent uranium minerals in the Yihewusu area of Hangjin Banner were shown for the first time to be composed mainly of coffinite and titanium-uranium oxide, with trace amounts of pitchblende. The major element diagrams of the sandstone and ratios of Sr/Ba, V/Cr, and U/Th and enrichment factors of Mo and U revealed that the source rocks of the Huanhe Formation sandstone in the study area were intermediate-felsic igneous rocks. The tectonic setting is characterized as an active continental margin, with later deposition in brackish-to-marine water environments. The ore-bearing strata indicate a reducing environment, whereas the nonore-bearing strata indicate a weakly oxidizing environment. With reference to previous studies, the sedimentary material primarily originated from the medium-acidic intrusive rocks exposed in the northern portion of the basin, including the Daqing-Wula Mountains, the Yin Mountains, and middle-acidic intrusions along the eastern margin of the Alxa region in the western part of the basin. The uranium-rich granitic pluton of the source area contributed to the preenrichment of uranium in the target sandstone layer. Under oxidizing aqueous conditions, U migration was activated, whereas under reducing aqueous conditions, U was reduced to U, resulting in eventual sedimentation of coffinite as ore.
鄂尔多斯盆地是我国重要的砂岩型铀矿富集区，下白垩统环河组作为新发现的含矿地层备受关注。为阐明环河组砂岩型铀矿床铀富集的物源、构造背景及沉积环境制约因素，利用电子显微镜、X射线荧光光谱仪（XRF）、电感耦合等离子体质谱仪（ICP-MS）和电子探针微分析仪，对研究区10个代表性砂岩样品进行了分析。首次发现杭锦旗伊和乌素地区的独立铀矿物主要由铀石和钛铀氧化物组成，并有微量沥青铀矿。砂岩主元素图、Sr/Ba、V/Cr、U/Th比值及Mo和U的富集系数表明，研究区环河组砂岩的源岩为中酸性火成岩。构造背景为活动大陆边缘，后期沉积于半咸水至海水环境。含矿地层指示还原环境，而非含矿地层指示弱氧化环境。参照以往研究，沉积物质主要来源于盆地北部出露的中酸性侵入岩，包括大青山-乌拉山、阴山以及盆地西部阿拉善地区东缘的中酸性侵入体。源区富铀花岗岩体促使目标砂岩层铀预富集。在氧化水介质条件下，铀迁移被激活，而在还原水介质条件下，铀被还原为U，最终导致铀石沉淀成矿。
