桂北摩天岭岩体舒家湾地区沥青铀矿原位微区年代学及其地质意义OA

Shujiawan area is located in the northern part of the Motianling pluton,characterized by numerous uranium mineralization occurrences,anomaly points,diverse ore-bearing fractures,and bears significant metallogenic potential.To precisely determine the uranium mineralization age in the study area,this study conducted chemical composition analysis,U-Pb isotopic dating,and rare earth element(REE)characterization of pitchblende using in-situ microanalysis techniques(EPMA,LA-ICP-MS)based on optical microscopy and scanning electron microscopy backscatter observations.Results show that the mass fraction of pitchblende is of UO2(87.56%average),CaO(1.21%),PbO(0.58%),and P2O5(0.78%).The 206Pb/238U weighted average age was determined as(54.5±1.5)Ma(MSWD=2.2,n=16),while the Tera-Wasserburg concordia diagram yielded a lower intercept age of(55.0±1.5)Ma(MSWD=2.2,n=16).Both ages are consistent within error limit,indicating a mineralization age of approximately 55 Ma.REE characteristics of pitchblendes reveal relatively low total REE contents with insignificant LREE-HREE fractionation,but distinct negative Eu anomalies.The chondrite-normalized REE pattern displays a V-shaped curve with slight LREE enrichment and relatively flat HREE distribution.The ΣREE contents,ThO2 and Y concentrations,and Eu anomalies collectively indicate a low-temperature hydrothermal origin with corresponding fluid characteristics.The obtained mineralization age corresponds to the 45-55 Ma lithospheric extension period in South China and mate with the critical uranium mineralization period(87-47 Ma)during Late Yanshanian to Early Himalayan brittle-ductile extensional tectonic activities in Motianling structural dome.This demonstrates that uranium mineralization in Shujiawan area was formed under a Cretaceous-Paleogene lithospheric extension and thinning geodynamic background,representing a product of late-stage uranium mineralization events in South China.