The Saima deposit is a newly discovered niobium deposit which is located in the eastern of Liaoning Province, NE China. Its mineralization age and geochemical characteristics are firstly reported in this study. The Nb orebodies are hosted by the grey–brown to grass-green aegirine nepheline syenite. Detailed petrographical studies show that the syenite consists of orthoclase (~50%), nepheline (~30%), biotite (~15%) and minor arfvedsonite (~3%) and aegirine (~2%), with weak hydrothermal alteration dominated by silicification. In situ LA-ICP-MS zircon U-Pb dating indicates that the aegirine nepheline syenite was emplaced in the Late Triassic (229.5 ± 2.2 Ma), which is spatially, temporally and genetically related to Nb mineralization. These aegirine nepheline syenites have SiO₂ contents in the range of 55.86–63.80 wt. %, low TiO₂ contents of 0.36–0.64 wt. %, P₂O₅ contents of 0.04–0.11 wt. % and Al₂O₃ contents of more than 15 wt. %. They are characterized by relatively high (K₂O + Na₂O) values of 9.72–15.51 wt. %, K₂O/Na₂O ratios of 2.42–3.64 wt. % and Rittmann indexes (σ = [ω(K₂O + Na₂O)]²/[ω(SiO₂ − 43)]) of 6.84–17.10, belonging to the high-K peralkaline, metaluminous type. These syenites are enriched in large ion lithophile elements (LILEs, e.g., Cs, Rb and Ba) and light rare earth elements (LREEs) and relatively depleted in high field strength elements (HFSEs, e.g., Nb, Zr and Ti) and heavy rare earth elements (HREEs), with transitional elements showing an obvious W-shaped distribution pattern. Based on these geochronological and geochemical features, we propose that the ore-forming intrusion associated with the Nb mineralization was formed under post-collision continental-rift setting, which is consistent with the tectonic regime of post-collision between the North China Craton and Paleo-Asian oceanic plate during the age in Ma for Indosinian (257–205 Ma). Intensive magmatic and metallogenic events resulted from partial melting of lithospheric mantle occurred during the post-collisional rifting, resulting in the development of large-scale Cu–Mo mineralization and rare earth deposits in the eastern part of Liaoning Province.

The Lower Cretaceous Jiufotang Formation in the Fuxin Basin contains a proven petroleum system. However, its southern part remains underexplored due to limited drilling and fragmentary sedimentary studies. To address this issue, we conducted detailed sedimentological logging of the two typical outcrop sections, Pijiagou and Tanjiagou. Field observations, petrographic data, and grain-size analysis were integrated to decipher hydrodynamic conditions, calibrate microfacies associations, and reconstruct the sedimentary evolution through facies stacking pattern analysis. The results show that the Jiufotang Formation predominantly consists of calcareous fine-grained clastic rocks, with poorly sorted sandstones indicative of low-energy conditions. Sediment transport mechanisms include both traction and turbidity currents, with suspension being predominant. The succession records a depositional transition from fan-delta to lacustrine environments. Two subfacies, fan-delta front and shore-shallow lacustrine, were identified and subdivided into seven microfacies: subaqueous distributary channels, interdistributary bays, subaqueous levees, mouth bars, muddy shoals, sandy shoals, and carbonate shoals. The sedimentary evolution reflects an initial lacustrine transgression followed by regression, interrupted by multiple lacustrine-level fluctuations. The alternating depositional pattern of lacustrine and deltaic facies has formed complete source-reservoir-seal assemblages in the Jiufotang Formation in the study area, making it a potential favorable target for hydrocarbon accumulation.