Mineralogy Of The Huayangchuan Polymetallic Uranium Deposit In Shanxi Province And Genesis Of Ore-bearing Carbonatite

The Huayangchuan polymetallic U-Nb-REE-Pb deposit is a significant large-scale uranium polymetallic deposit in the Huaxian County,Huayin City,Shanxi Province.It is tectonically located at the south Qinling dome of the North China Block and boarded by the Taiyao Fault to the north and the Xiaohe and Qinggangping-Jinduicheng Fault to the south.Orebodies are hosted in the Archean Taihua Group gneisses and distributed along the NW-trending Huayangchuan Fault belt.Based on the study of the geological features,ore types,mineralogical characteristics,lithology of U-bearing carbonates of the Huayangchuan deposit,this study revealed mineralogical characteristics of U-bearing minerals and other ore minerals as well as gangue minerals.Some technological approaches,such as EPMA and SEM,are applied to understand uranium and niobium occurrence.Ore mineral in-situ trace element analysis,carbonate C-O isotope,and Sr isotope are used to track the source of ore-forming fluids and materials.Some conclusions and achievements have been obtained as follows:(1)The main uranium-bearing minerals in the Huayangchuan polymetallic U-Nb-REE-Pb deposit are betafite with a small amount of uraninite.Other ore minerals consist of galena,pyrite,magnetite,and chalcopyrite.Gangue minerals mainly consist of calcite,microcline,aegirine,biotite,zeolite,anhydrite,K-feldspar,epidote,sphene,monazite,celestite,apatite,zircon,etc.(2)The mineralization process of the Huayangchuan deposit can be divided into coarsegrained K-feldspar-quartz stage,carbonate stage,carbonatite-sulfide stage,and zeolite stage.Betafite mainly occurs in the carbonatite stage,followed by the coarse-grained potassium feldspar stage.Uraninite is identified as the principal ore mineral of the carbonatite stage.Sulfide minerals,including galena and pyrite,formed in the carbonate-sulfide stage.U-bearing minerals in carbonatite coexist with quartz,calcite,aegirine,apatite,allanite,and pyrite.In the coarse-grained K-feldspar stage,U-bearing minerals intergrow with quartz,K-feldspar,aegirine feldspar,calcium feldspar,and albite.(3)Uranium is dominantly hosted in betafite with minor in uraninite.Electron probe microanalysis(EPMA)analysis shows that: UO2 takes up 87.1% and 7.7% in batafite and uraninite,respectively.The rest of the uranium occurs as adsorption or isomorphism in allanite,sphene,apatite,and monazite.Niobium is mainly enriched in betafite.Nb2O5 composition of the betafite and uraninite is 99.7% and 0.1%,respectively.A small amount of Nb2O5 is hosted in monazite or as a dispersed element in other minerals.(4)The REE distribution patterns of calcite carbonatite can be classified into LREE-riched and HREE-riched types.Ore-forming fluids are derived from a mantle source.The carbonatite is calcite accumulation.When the carbonatite magma evolves to the late stage,HREE is further enriched and formed HREE-type ore.(5)C-O isotopic compositions of carbonatite in the Huayangchuan are homogeneous,with the ?¹³C range from-8‰ to-7‰,and the ?¹⁸O range from 7‰ to 8‰,and fall into the initial carbonatite field,indicating a mantle-derived source.The ⁸⁷Sr/⁸⁶Sr ratios of calcite are varied from0.704866 to 0.705534.The ?Nd(t)values range from-7.62 to-5.76 and close to the EM ?endmember of the enriched mantle,demonstrating that carbonatite directly originates from the low degree partial melting of the LREE-rich mantle.