攀枝花大田地区角砾岩带铀矿化特征及其成因OA

Datian uranium deposit is located in Kangdian geoaxis.Previous studies mainly focused on the eastern end of the Zone I and Zone II and paid little attention to uranium mineralization within the breccia recently discovered at the western end of the Zone I.To investigate the geological characteristics of the breccia zone and the features and genesis of uranium mineralization,this study conducted a deep analysis with the methods of rock and mineral identification,chemical analysis and electron probe analysis based on the field geological survey,and achieved the following conclusions:The primary lithologies of the breccia zone include lamproite,granodiorite,pyroxenite,and a small amount of migmatite,with uranium mineralization concentrated in the pyroxenite breccia.The mineralized pyroxenite breccias bear gray-black granular texture and massive structure,with the breccia clasts cemented by grayish-white felsic veins.Under the microscope,the pyroxene grains display significant size variations,and there are notable differences in elemental composition,including silicon,aluminum,magnesium,and iron with a cumulatic textures.The total rare earth element(REE)content is higher in mineralized pyroxenite and lower in weakly mineralized samples,collectively showing a"seagull-shaped"pattern,indicating limited fractionation between light and heavy REEs,with significant REE enrichment accompanying uranium mineralization.Electron probe U-Th-Pb chemical dating results show that uraninite is of a peak age range of 840-860 Ma and a weighted average age of 853 Ma±20 Ma,indicating that uranium mineralization in the pyroxenite was formed during the Early to Middle Neoproterozoic,representing contemporaneous but different stages to that of Zone II(770-780 Ma).Electron probe detecting results demonstrate Th/U ratios in uraninite is 0.02-0.05,suggesting it was formed in magmatic or high-temperature hydrothermal environments.U content in the migmatites in Datian area range from 6.10×10-6 to 26.10×10-6 and can be regarded as an important uranium source in the region.The felsic magma and tectonic activity provided heat sources and migration channels for urinous fluids which extracted U from the mixed rocks and gradually precipitated and enriched while passing through the contact area between felsic veins and pyroxene rocks in the breccia belt.