Occurrence And Metallogenic Mechanism Of Nb And Ta In ShanAnBang Granite-type Nb-Ta Deposit,Suzhou

The Suzhou niobium-tantalum deposit is located in the west of Suzhou,which is a super large deposit in Jiangsu province.The Yanshanian magmatic activity was intense,forming multi-stage granite and volcanic rocks.The large-scale magmatic activities in this area be divided into two stages: the first stage is the magma intrusion in the early Yanshan period,forming the early Yanshan granite;subsequently for the large-scale volcanic activity,the formation of volcanic rocks;the second stage is the largest magma intrusion in the late Yanshan period,forming the late Yanshanian granite.The niobium-tantalum ore-forming granites are mainly fine-grained biotite granites in the late intrusive stage.Niobium-tantalum mineralization has developed in the biotite granite,topaz granite and albite granite.According to the petrographic characteristics,niobium tantalum ore is disseminated.In the late stage fine-grained biotite granite,niobate is an important Nb-Ta mineral.Most of it is encapsulated in mica,a few of it is intercrystalline distributed between feldspar,quartz and mica,and a few of it is associated with zircon.The biotite in the early and late stages is mainly iron leaf mica,and the biotite in the late stage has a higher content of Si,F,and Li,and a lower Mg content.The calculation results show that the formation T(?),emplacement D(km)and oxygen fugacity(f(O2))of mica in late stage granite are lower than those in early stage granite;the feldspar component of the two-stage granite is relatively single,very close to the end member component,namely K-feldspar or albite.A small amount of amphibole is found in the first stage granite,which is rich in Fe,Ca,Al and poor in Mg,K and Ti.The calculation also shows that it has the characteristics of high oxygen fugacity and low formation T and D.The data collection and collation of the 16 typical granite type Nb-Ta deposits(including Suzhou Shan Anb Bang Nb-Ta deposit)in East China south,combined with its deposit characteristics,metallogenic age,metallogenic rock mass and its petrogeochemistry,it is concluded that the deposit formed in 122?160Ma,which belongs to the Yanshanian period.Geochemical characteristics show that the concentration of P2O5 is different in different oreforming granites,with both high P and low P,A/CNK = 0.97?1.99(most of which are greater than1.1)and peraluminous characteristics;and it has peraluminous characteristics.The mean values of Nb/ TA and Zr/ HF were 3.39 and 10.72,respectively.Eu value with obvious negative anomaly.In general,REE shows a low trend.Ba,Ti and Sr were depleted,and Hf,Zr,Th,Ta,Nb and Ru were enriched.The ore-forming rock mass has lower total content of REE,lower content of Ba,Sr,Ti,Yb and higher content of Ta than the adjacent rock mass.Combined with the mineral and geochemistry characteristics,it is considered that the ore bearing rocks are all high fractionated granites.The metallogenic pluton is composed of the intergrowth or transitional muscovite-two mica-biotite granite assemblage.The mineralizing granite includes both S-type highly differentiated granite and topaz A-type granite,and topaz A-type granite Granite and S-type granite are symbiotic and formed by melting of the S-type granite.The ore-forming granites of Shananbang Nb-Ta deposit in Suzhou are highly differentiated S-type granites.Combined with regional research data,the deposits were formed in the subduction accretive orogenic process under the background,and the magma arc in the southeast coastal area subducted above the southeast margin of the Yangtze,resulting in the melting of buried sedimentary rocks.It is a collisional granite type Nb-Ta deposit.The content of F has a great influence on mineralization.The upper part of the orebody is rich in tantalum while the lower part is rich in niobium because of the interaction of magma and late hydrothermal fluid.