Search Results (3)

The Ordos Basin is a key district for sandstone-hosted uranium, yet host-rock controls and uranium sources remain debated. We integrate measured sections, whole-rock geochemistry, and detrital zircon U-Pb-Lu-Hf data from the Cretaceous Huanhe Formation (Yihewusu, northern Ordos) to resolve provenance, transport, and enrichment pathways. Uranium enrichment is concentrated in feldspathic-lithic sandstones deposited in proximal fluvial-lacustrine settings. Detrital zircon ages define three clusters—Phanerozoic (500–200 Ma), Paleoproterozoic (2000–1700 Ma), and Neoarchean (2600–2300 Ma)—with Proterozoic grains >60%, indicating derivation from Archean–Paleoproterozoic TTG gneisses, granulites, and khondalites of the Yinshan Block and the northern Central Orogenic Belt. Zircon εHf(t) values (−10.84 to +7.76) and crustal model ages (3.2–2.1 Ga) record substantial Meso- to Neoarchean crustal growth in the source terranes. Critically, Permian-Cretaceous intermediate-felsic igneous rocks along the northern margin of the Western North China Block—marked by elevated U, Th/U > 5 (indicative of U loss), pervasive feldspar micro-fractures, and proximity to basin-margin uranium belts—are identified as the principal uranium reservoirs. We propose a dual uranium supply: soluble uranium mobilized from leached igneous rocks during weathering and fluid-rock interaction, and U-enriched detritus delivered to the basin. Uranium concentrated in redox-sensitive, feldspathic-lithic sandstones of the Huanhe Formation, which effectively trapped advected uranium at proximal facies transitions. These findings establish a direct genetic link between basin-margin uranium sources and in-basin mineralization, providing a predictive framework for regional uranium exploration in North China. Full article

In order to evaluate the impact of groundwater drainage on groundwater flow, the Hetaoyu coal field was taken as a case study in the Longdong area, China, where the coal seam was covered with multilayer aquifers. A three-dimensional unsteady groundwater flow model and a one-dimensional fracture water flow model were calculated by joint equations for changing hydrogeological structures under coal mining. According to the results, mine construction had greatly affected groundwater reserves in the Quaternary phreatic aquifer, Cretaceous Huanhe confined aquifer, and Luohe confined aquifer. The groundwater drainage was mainly from the Cretaceous aquifer, in which the aquifer reserves of the Luohe Formation decreased by 30,861.8 m³/m, accounting for about 92% of the total changes in local groundwater reserves. A drop funnel with an area of about 2.3 km² would be formed under the groundwater discharge of 187.6 m³/h for the main inclined shaft excavation of the Hetaoyu coal mine. With the continuation of mining activities, the mine water flow will reach 806.83 m³/h and would result in descending funnel area of about 4.5 km², the groundwater level drawdown at least 16 m, which would exceed the limited value regulated by the government. Therefore, in order to ensure the safety of coal mining and protect groundwater resources, the Hetaoyu Coal Mine departments should take some water loss prevention and control projects to reduce the drawdown of groundwater. Full article

In adjustment to fulfill the requirements of the investigation regarding the lower Cretaceous sandstone uranium deposit in the Naogaodai area within the northwest of Ordos Basin, twenty-seven sandstone samples obtained from the Lower Cretaceous Huanhe Formation were analyzed for major, trace and rare earth elements (REE). The source of clastic and tectonic background was additionally analyzed. The results show that Huanhe sandstone is feldspar rich sandstone, and also the mineral composition is principally quartz, albite and plagioclase; the ratio of light to heavy rare earth elements (LREE/HREE) is 9.25–10.83, with an average value of 10.00; (La/Yb)_CN is 10.20–12.53, with an average value of 11.24, demonstrating that LREE is enriched and fractionated compared with HREE. REE distribution patterns are similar, which additionally reveals that Huanhe sandstone has a homogenous source; the Index of Compositional Variability (ICV) value is 1.17–1.73, with an average value of 1.35, both greater than 1, showing an immature property, which may be first-order cycle deposition. The average value of the Chemical Index of Alteration (CIA) is 50.29, suggesting that the source rock has encountered weak chemical weathering; sandstones are near-source first-cycle provenance, which is not significantly influenced by sedimentary sorting and recycling. The geochemical qualities further indicate that Huanhe sandstone was deposited in a passive margin and experienced moderate weathering. Full article