Architectural control on uranium mineralization in meandering-river point bars: Insights from the upper cretaceous Sifangtai Formation, northern Songliao Basin, NE China

Sandstone-hosted uranium mineralization in meandering fluvial systems is commonly interpreted at the scale of facies belts and regional redox zones, but the role of internal point-bar architecture remains less well constrained. Here, we examine the Upper Cretaceous Sifangtai Formation on the Changyuan uplift, Songliao Basin, where uranium mineralization is hosted mainly by meandering-river sand bodies. The study integrates well logs from 38 wells, high-resolution 3D seismic data, and TOC, U concentration, backscattered electron (BSE) imaging, and thin-section observations from 24 lithological samples collected from four cored wells. The ore-hosting succession is dominated by point-bar deposits partitioned by third-order (L3) lateral-accretion surfaces and fourth-order (L4) channel-fill boundaries. These surfaces are commonly associated with fine-grained baffles and contain more carbonaceous debris and pyrite than adjacent sandstone intervals. U-bearing phases occur mainly around pyrite and within intergranular and intragranular pores, indicating a close spatial association between reductants and uranium precipitation. Uranium orebodies are concentrated along L3 lateral-accretion surfaces, forming wedge-shaped layers in well sections and crescent-shaped belts in plan view. We infer that oxidizing U-bearing groundwater migrated through sandy accretion packages and was locally slowed or redirected at reductant-rich L3 and L4 surfaces. This architecture-controlled model places uranium precipitation within mappable point-bar elements and provides practical criteria for refining exploration targets and assessing in situ leaching (ISL) well-pattern design in heterogeneous fluvial reservoirs.