Geochemical characteristics of Hersinian middle-acidic intrusion and its uranium supply capability as basin provenance at the eastern margin of Junggar basin
To analyze uranium supply capability of Hersinian middle-acidic intrusive rocks at the eastern margin of Junggar basin,after comprehensive study,this paper selected 12 plutons from the middle-acidic plutons in this region to analyze major,trace and rare earth elements.The results show that granite,granodiorite and monzonite in this region contain 65.69%～77.66%SiO2,6.61%～9.39%(N2O+K2O),9.72%～16.60%Al2O3,0.11%～4.00%TFe,0.20%～3.70%CaO and 0.07%～1.43%MgO,rich in LILE(such as Rb,Th and K)and HFE(Zr,Hf)and poor in Ba,Sr and Nb-Ta,and the total REE is(100.47～309.12)×10-6 with LaN/YbN of 2.38～11.48,LREE/HREE of 3.09～9.77 and is depleted in Eu.The calculated Paleo-uranium content of most plutons is 4.02×10-6～14.66×10-6,higher than the average uranium content(3.5×10-6)in crustal granite,and the w(Th)/w(U)is over 4.2,indicating that there was uranium migration during weathering process and migrated uranium was in range of 0.08×10-6～8.11×10-6.It is believed that middle-acidic intrusion at the eastern margin of Junggar basin mainly formed in volcanic arc environments at post-collisional extension stage.The magma evolved continuously from calcalkalic to alkalic and appeared as high-K calcalkalic to alkalic pera-alluminium granites.The magma was mainly from crust and suffered from mixture of mantle materials.It is concluded that there are two kinds of granite with different uranium features in this region.One is Th and U fertile granite with high migration of paleo-uranium,which probably provided abundant uranium for the uranium mineralization in Karmst,Jabosar and Jiangjunmiao districts at the eastern margin of Junggar basin;the other kind is Th-rich but U-poor granite which is low in uranium migration and made little contribution to uranium mineralization.
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