In the Xiaguxuan area of the eastern QF_Ⅴ ore belt in the Lujing uranium ore-field，siliceous vein type uranium mineralization occurs. The ore-bearing rock is medium-coarse-grained porphyritic biotite granite. The hydrothermal alteration near the ore mainly includes hematitization，silicification，chloritization and carbonatization. Zircon U-Pb chronology，petrography and petrogeochemical analysis show that the zircon U-Pb concordant age of the uranium-bearing fresh granite is 228.3 Ma and the weighted average age is 228.9 Ma，which was formed in the second stage of the Indosinian period (Late Triassic). The major elements are characterized by high potassium calc-alkaline series and weakly peraluminous granite，with high contents of silicon and titanium，low contents of magnesium and iron，slightly low aluminum，rich in alkalis and potassium and low in sodium. Among the trace elements，Ba，Sr and Ti are depleted, while Rb，Th，Pb and Nd are enriched. The rare earth distribution curve is of light rare earth enrichment type with right inclination，and there is obvious fractionation between light and heavy rare earth elements，with obvious negative Eu anomaly，which is consistent with the geochemical characteristics of S-type granite. It is considered through analysis that the ore-hosting granite in the Xiaguxuan area may be the product formed by the partial melting of the aluminous shallow metamorphic rock series in the upper crust due to decompression and temperature increase under the background of the transition from compression to extension in the Late Triassic. Compared with normal granite，the ore-bearing granite has a higher SiO₂ content, a multiple increase in the contents of CaO and P₂O₅，as well as the ratios of Fe₂O₃/FeO and HREE/LREE，and high contents of U and P，etc. All these indicate that the aggregation and precipitation of U in the study area are closely related to the chemical activities of P，LREE and HREE. These summarized chemical indexes are useful indicators for searching for siliceous vein type uranium mineralization in the inner zone of the granite body.