Genesis And Implications Of Peraluminous A-type Rhyolite In Haidewula Uranium Deposit,east Kunlun Orogen

The East Kunlun orogenic belt is located in the western section of the central orogenic belt,and the intense Paleozoic-Mesozoic tectonic-magmatic activities in the belt provide favorable conditions for uranium and polymetallic mineralization.However,the genesis and triggering mechanism of Paleozoic magmatic rocks in the East Kunlun orogenic belt have been controversial.Therefore,on the basis of systematically analyzing the research status and existing problems of A-type magmatic rocks,high-silica magmatic rocks and volcanogenic uranium deposits,this paper carried out research on petrography and rock geochemistry in the Haidewula area.Using zircon U-Pb chronology,Hf isotope studies and whole-rock major and trace elements to discuss the genesis of magmatic rocks in the area.The following conclusions were obtained:The magmatic activity in the Haidewula area is strongly,and the main rock types in this area include amygdaloidal basalt,diabase,trachyandensite-trachyte,rhyolite,tuff and volcanic breccia,with red sandstone and siltstone.The hydrothermal alteration of the deposit is strongly developed,mainly including pyritization,purple black fluoritization,hematization,flesh-red carbonation,silicification,white calcification,and illitization.The main ore mineral is pitchblende,which is symbiotic with quartz,fluorite,calcite,pyrite,hematite,chalcopyrite and lead-zinc ore.The rhyolite zircon in this area shows obvious oscillation rings and has a high Th/U ratio（0.46～0.95）,which is a typical magmatic zircon.Zircon LA-ICP-MS U-Pb isotopic dating results show that the Haidewula rhyolite was formed at 426.1±2.6 Ma,which is the product of Ludlow magmatic activity.The time coincides with the period when the East Kunlun orogenic belt entered the post collision extension environment.Zircon of the sampleε_Hf（t）is+0.60～+2.39,and the corresponding two-stage model age is between 1285～1370Ma.The rock geochemical data show that the Haidewula rhyolite is rich in Si O₂（73.17%～77.96%）,belonging to the high silicon rhyolite series;K₂O+Na₂O content is 7.21%～8.86%,K₂O/Na₂O ratio is between 0.92～2.69,belonging to high potassium calc alkaline to shoshonite series;A/CNK value is 1.04～1.14,belonging to peraluminous to strong peraluminous rock series.The∑LREES and∑HREES are obviously differentiated and relatively enriched∑LREES,with strong negative Eu anomaly（δEu=0.03～0.06）,the samples are enriched in Th and U,and lose Nb,Ta,Ti,Ba,Sr and Eu.The rhyolites in Haide Wula area are rich in high field strength elements（the average content of Zr+Nb+Ce+Y is 577.53 ppm）,and the zircon saturation temperature is 856°C～887°C,indicating that the rhyolites in Haidewula area are A-type rhyolites.The element geochemical characteristics show that the Haidewula rhyolite is the product of partial melting of felsic igneous rocks（calc alkaline granodiorite and tonalite）under middle crustal pressure.The pre-Ludlow granitic rocks in the East Kunlun orogenic belt mainly include Proterozoic granite and Ordovician-early Silurian granite.Using the coupling of zircon Hf isotopic composition,we propose that Haidewula A-type rhyolite may be the product of partial melting of Late Ordovician calc alkaline granodiorite in the East Kunlun orogenic belt under high temperature and middle crustal pressure.A series of middle Silurian-Devonian A-type magmatic rocks determined in the East Kunlun orogenic belt,It forms A-type magmatic rock belt.These A-type magmatic rocks belong to the product of post collisional magmatism,indicating that the East Kunlun orogenic belt has entered the post collisional extension environment since the Ludlow.The East Kunlun Orogen was involved in a series of collisional orogenic events in the northern margin of Gondwana during the Silurian-Devonian period.Combined with previous research results,we believe that the post collisional extension environment of the East Kunlun orogenic belt is caused by the thickening of the lithosphere after the plate convergence on the northeast edge of Gondwana continent.Based on the analysis of（sub）volcanic rock samples related to typical uranium deposits in the world and Haidewula rhyolite,it is considered that Haidewula rhyolite is similar to the volcanic rocks related to typical uranium deposits in the world.It is characterized by peraluminous A-type magmatic rocks rich in alkali,relatively rich in potassium,high Fe^#index,high field strength elements and rare earth elements and∑REE elements,and the Haidewula volcanic rocks have higher content of ore-forming elements（Th,U and∑REE elements）.Therefore,this paper holds that the Ludlow acid volcanic rocks rich in uranium in Haidewula can provide sufficient uranium source for uranium mineralization in the area.