U-Pb Isotope Dating For Sandstone-type Uranium Deposits

Uranium is one of the most important critical elements around the world.Accelerating exploration and theoretical study on uranium deposit has been extremely imminent.Sandstone-type uranium ore deposit is the main research interest for the uranium exploration in northern China.Radioisotopic geochronology has been one of the most robust tools on deciphering the nature of uranium deposit.We in present contribution recorded the occurrence and characteristics of ore minerals of uranium deposit,and discussed the matrix effects of U-Pb dating on uranium-bearing minerals.We therefore proposed that three methods that can be applied onto geochronology of uranium deposits,namely Laser Ablation?LA?+Isotope Dilution-Thermal Ionization Mass Spectrometry?ID-TIMS?,Electron Probe Micro-analyzer?EPMA?+Laser Ablation Multi Collector Inductively Coupled Plasma Mass Spectrometry?MC-ICP-MS?and femtosecond LA-MC-ICPMS?fsLA-MC-ICPMS?.We in this study optimized procedures of ID-TIMS U-Pb dating on single-grain U-bearing minerals,and set up a new procedure combined LA with ID-TIMS.The zircon reference material PLESOVICE and uranium reference material GBW04420were analyzed,and we reported age of PLESOVICE at 337.5±0.6 Ma,and ²⁰⁶Pb/²³⁸U age of GBW04420 at 70.6±1.5 Ma.Such data are consistent with ages of the reference material.Such analytical technique is still immature as the effects of absorption efficiency and Pb background.We also set up analytical procedure that using EPMA combined with LA-MC-ICPMS for U-Pb dating on uranium-bearing minerals with cases studies of the Chentaigou granite-type uranium deposit in the Qinling orogeny and polycrase in Henan.This method provided data consistent to that collected by ID-TIMS,suggesting this method is able to stand the test.We conducted EPMA combined with LA-MC-ICPMS dating on two uranium ore samples collected from drill core at the Hongqinghe and Tarangaole at the Ordos basin.The Hongqinghe deposit has²⁰⁶Pb/²³⁸U age of 6¹7.8 Ma,and the Tarangaole yields ²⁰⁶Pb/²³⁸U age of 9³0Ma,in a variable range from 9 to 80 Ma.In addition,we set up analytical procedure by using fsLA-MC-ICPMS.The analytical data on apatite standard OTTER LAKE,monazite 44069,cassiterite standard AY-4,uranium standard GBW04420 suggest that the matrix effects can be or at least to some extent can be negligible when using fsLA-MC-ICPMS,and we can carry out U-Pb dating of non-matrix matching.The Sandstone-type Hongqinghe uranium ore deposit in the Ordos basin yields ²⁰⁶Pb/²³⁸U ages ranging from 0.50 to4.40 Ma,indicating that the loss of radioactive Pb is not uniform in one single grain or in the different parts of any aggregate.The thirty-three analyses are linear correlated,and has an upper point of intersection at 1800±50 Ma,suggest that they shared a same uranium source.