Geochemical Characteristics And Petrogenesis Analysis Of The Metallogenic Pluton Of The Huangshan Nb-Ta Deposit In Jiangxi Province

The Huangshan large niobium tantalum deposit in northeast Jiangxi is one of the most typical rare metal deposits in South China that is associated with granite.It has unique metallogenic conditions,huge resource potential and superior mining conditions,and has attracted much attention from the geological community.This paper selects medium-coarse-grained biotite diagenetic granite,granitic pegmatite,and albitization fine-grained biotite granite in the Huangshan niobium-tantalum ore-bearing pluton to carry out detailed petrographic studies of ore-bearing pluton and geochemical research and chronological research.Based on the existing research results of predecessors,genetic types of rocks closely related to mineralization and its mineralizing material,the structural background of formation and its mineralization and diagenesis process were discussed.The main elements of the whole rock show that the pluton has the characteristics of silicon-rich,high-alkali,calcium-poor,and low-magnesium,and the A/CNK values are all greater than 1,which belong to quasi-aluminum-peraluminous rocks.Trace elements show that pluton has high Rb/Sr and Rb/Ba values,obviously rich in high field strength elements Ta,Nb,Th,U,Zr,Hf and large ionophilic element Rb,loss high field strength elements Ti,P and large ionophilic elements Ba,Sr.The rare earth elements are shown to be high in total,the distribution map is right-tilt seagull type,obviously negative Eu anomaly.10000*Ga/Al ratio?5.25?5.88?5.43?is above 2.60,the Zr+Nb+Ce+Y element combination value is much higher than 350*10^-6,and the Rb/Sr?119.32?157.13?138.17?and Rb/Ba?60.79?95.14?68.86?ratios are much higher than the corresponding values of I and S-type rocks of?0.61?0.28and 1.81?0.46?,indicating that the pluton in the area belongs to A-type granite,formed in the tectonic extension background of the Pacific plate subduction and retreat.LA-ICP-MS monazite dating results show that the medium-coarse-grained biotite monzonite granite and granite pegmatite in the mining area are 129±1.4Ma and 119±1.2Ma,respectively,and the diagenesis time is Early Cretaceous.Consistent with the diagenesis time of the Lingshan pluton,it is further determined that the diagenesis time limit of Huangshan niobium-tantalite deposit is about 129Ma,and the time limit of metallogenesis is about 119Ma.Combining regional geotectonic,geochemical and geochronological studies of pluton,magmatic materials are derived from metaproterozoic metamorphic rocks,and a small amount of mantle components have been added.As the magma has undergone highly fractionated evolution,the separation of plagioclase and the crystallization and metasomatism of potash feldspar occurred.The strong fluid-melt interaction of late magma is an important prerequisite for its mineralization.The high degree of magma Differential evolution is the main controlling factor for the enrichment of Nb and Ta.The metallogenic process of Huangshan niobium tantalum ore can be briefly summarized as follows:under the extension of the tectonic setting,basement metamorphic rocks was affected by the mantle magma underflow,partially melted and formed A-type granitic magma,and carried volatiles such as F and Li and ore-forming elements such as Nb and Ta,which formed stable complexes in the form of Na₂[Nb F₇]?Na₂[Ta F₇]?K₂[Nb F₇]?K₂[Ta F₇]?Li₂[Nb F₇]?Li₂[Ta F₇],and migrated upward in the crust.Due to the decrease in temperature and pressure,the complex decomposes to form fluorinated compounds as well as hydrothermal fluids and gases.After undergoing crystallization differentiation evolution,hydrothermal fluids such as sodium feldsparization and potassium feldsparization occur in the late stage of magmatic activity.The ore-rich fluid crystallized and precipitated in the strong part of albitization,forming a niobium tantalum deposit.