| The Ziyunshan rock mass is located in the central eastern part of the junction between the Huaxia Plate and the Yangtze Plate,and is a typical tungsten rich uranium rich granite.For uranium rich granite,the developed zircons often have extremely high uranium content and are prone to metamorphism,which affects the accuracy of dating results.On the basis of previous work,detailed petrography,petrogeochemistry and uranium bearing mineral mineralogy studies have been carried out on Ziyunshan granite,and a variety of uranium bearing minerals have been used to carry out dating tests.Finally,in combination with the characteristics of laser Raman spectrum,various dating test methods have been compared and evaluated.The geochemical characteristics of rocks show that the Ziyunshan rock samples are characterized by rich silicon,high potassium,poor magnesium,poor titanium,and poor phosphorus.They are high potassium calc alkaline peraluminous S-type granites.At the same time,the granites are enriched with large ion lithophile elements K,Rb,Pb,and high field strength elements Th,U,and Nd,while Ba,Sr,Eu,P,and Ti are relatively deficient.The heavy rare earth elements in the entire rock are relatively depleted,while the light rare earth elements are relatively enriched.The uranium content of the entire rock is 7.02×10-6-17.45×10-6,with an average of 12.25×10-6,characterized by uranium enrichment.By using methods such as microscopy,scanning electron microscopy,and electron probe microanalysis,it was found that the uranium bearing minerals in the Ziyunshan granite include zircon,monazite,yttrium phosphate,thorite,uraninite,uraninite,and some uranium bearing niobate minerals.Among them,zircon,monazite,and yttrium phosphate minerals have a large number and particle size,and the uranium thorium content in the uraninite is extremely high with weak signs of transformation.Therefore,they were selected for dating testing.Laser Raman testing was conducted on dating minerals（zircon,monazite,and yttrium phosphate）,and the results showed that zircon in granite can be divided into crystalline zircon,metamorphic zircon,and highly metamorphic zircon,with the majority being highly metamorphic zircon;The monazite in the granite has not undergone significant crystallization;The majority of phosphate yttrium minerals in granite do not undergo metamorphosis.Using LA-ICP-MS,U-Pb isotope dating tests were conducted on zircon,monazite,and yttrium phosphate in the Ziyunshan granite.The results showed that the age of zircon was 142.8±1.0Ma,monazite was 150.5±0.8Ma,and yttrium phosphate was 135.2±1.0Ma.The electron probe U-Th-Pb chemical dating of uraninite was carried out,and the weighted average age measured was 151.4±1.7 Ma（MSWD=0.19,n=19）.The ages of monazite and uraninite are relatively similar,which is consistent with previous test results.The ages obtained from zircon and phosphorite are significantly lower than previous dating results.Combining the results of laser Raman spectroscopy and dating tests,it is found that zircon in uranium rich granite undergoes severe metamorphism,resulting in a smaller U-Pb age result.Therefore,it is not recommended to use zircon as a dating mineral for uranium rich granite;Monazite has strong radiation resistance and is not prone to crystallization,resulting in accurate U-Pb age results and is a suitable dating mineral;The phosphorus yttrium ore in high uranium granite does not undergo metamorphism,making it a more suitable U-Pb isotope... |
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