The Mineralogical Characteristics Of The Rare-metal Granites In Jiuling District,jiangxi Province And The Implication For The Various Metallogenic Mechanism

The Neoproterozoic Jiuling batholith in northwestern Jiangxi Province,south China,with an exposed area of?2500 km2 and mainly biotite granodiorite(Ca.?820 Ma),is one of the largest batholiths in the Nanling Range.Reported that it hosts Mesozoic granites and deposits,including the world-class giant Dahutang W-Mo-Cu deposit in the northern part of the batholith.The Dahutang deposit is located at the junction of Wuning,Xiushui and Jing'an counties in northern Jiangxi,and is related to porphyritic granite and medium-fine granite.The Nb-Ta minratlizaion in granitic porphyry is also found in this study.The other is the Yifeng Li-Nb-Ta deposit in southern Jiuling batholith,which occurs in the granitic body of Li-Mus granite,lepidolite granite and felsite dikes.The mineralogical characteristics and mineralization of the Jiuling rare metal granites were studied.Aiming to understand the petrogenesis and mineralization of Dahutang and Yifeng rare-metal granites,the analyses have been conducted,such as whole-rock geochemistry,the texture and the chemical geochemistry of the rock-forming mineral(mica)and accessory minerals(columbite-group minerals,amblygonite,wolframite,rutile,cassiterite et al),and zircon and columbite LA-ICP-MS U-Pb isotope geochronology.It is proposed that(1)The zircon and columbite U-Pb isotopic age of the Nb-Ta-bearing granitic porphyry is 146±2 Ma and 144±5 Ma,respectively,closed to the age of the formation and W-mineralization of the W-bearing porphyritic granite.The Nb-Ta mineralization of the Yifeng Li-Mus granite took place at 144±5 Ma according to columbite U-Pb dating.The age of mineralization of rare metals in the south and north of jiuling is similar.(2)The mica in the Dahutang Nb-Ta-bearing granitic porphyry are Li-bearing muscovite,and including magmatic oxide minerals(columbite-group minerals,wolframoixiolite,wodginite,Nb-Ta bearing wolframite and Nb-bearing rutile).The indicator minerals in the W-bearing porphyritic granite are hydrothermal minerals such as wolframite,scheelite and secondary rutile.The whole-rock geochemistry and the chemistry of the micas and CGMs imply that the Dahutang Nb-Ta-bearing granitic porphyry is more evolved than W-bearing porphyritic granite.(3)the Yifeng plutons contain P-rich rare-metal-bearing Li-F granitic rocks that contain P-rich feldspars(?0.44 wt%P2O5),amblygonites,Cs-rich lepidolites(?3.9 wt%Cs2O),CGMs close to the Mn endmember,and Hf-rich zircons(20.6 wt%HfO2).It is similar to the Yichun pluton.The Yifeng felsite is more evolved than the lepidolie granites.(4)Yifeng felsite rare metal minerals include isolated grains of CGMs and cassiterite,but intense fluid activity in the later stages and quenching resulted in unique mineral aggregates of acicular cassiterite+granular CGMs+metamict zircon.In conclusion,the Dahutang granite with W-Nb-Ta mineralization in the north of Jiuling and the Yifeng granite body with Li-Nb-Ta-Sn mineralization in the south belong to the contemporaneous petrogenesis and mineralization,but they may come from different magma chamber and the mineralization mechanism is different.There is W original enrichment in the rare metal granite in Dahutang deposit,and Nb-Ta-beraing granite was formed after further evolution of magma,while the granite in Yifeng area in the south has a higher degree of evolution,characterized by rich Li and P,with Rb-Cs-Sn enrichment,but no W mineralization information.Based on the similarity of Li-rich granites in this area,it is inferred that there may be a Li-Nb-Ta mineralization belt in northwestern Jiangxi province.