Magmatic Evolution And Two-stage Mineralization Of The Dahutang World-class W-Cu Polymetallic Deposit In South China

Dahutang deposit is a large tungsten-copper polymetallic deposit found in northwestern Jiangxi Province,which is located in the middle part of Jiangnan Orogenic Belt.A large number of researchers have done considerable amount of work in Dahutang ore concentrated district on the geological characteristics,geochemical characteristics of ore deposits,geochronology and geochemistry of rocks and the age of mineralization.All of these works are valuable.However,due to the complexity of the Dahutang district,the deep origin,magmatic evolution process and mineralization in Dahutang are comparatively less discussed.In this paper,by means of petrology,whole-rock geochemistry,lead isotopes and mineralogy attempt to reveal the magmatic origin,magmatic evolution and fluid mineralization.The main results are as follows:?1?Whole-rock and feldspar lead isotope showed characteristics of radioactive.Correcting the whole-rock lead isotope and put together it with feldspar lead isotope in mode pattern diagram showing upper crust properties.Then compared samples with regional and adjacent region magmatic rocks and sedimentary rocks from this area which show that the Pb isotopes of the Yanshanian granite samples in Dahutang presenting the affinity to the Pb isotopes in the Proterozoic strata,indicating that the Proterozoic sediments should be the main source rocks of the Yanshanian granites.?2?Whole-rock geochemical data show typical characteristics of S-type granite with high Si and K and strongly peraluminous.Comparing the trace elements with Shuangqiaoshan group,obvious Nb depletion can be founded which indicated that the partial melting temperature was low.Porphyritic two-mica granite and biotite granite porphyry have higher initial melting temperature?mostly>725??and a relatively high CaO/Na₂O ratio?>0.3?suggest that they are formed at higher temperature by the partial melting of the meta-greywacke,while the middle-fine grain muscovite granite and the Li-mica granite may form by partial melting of meta-pelite at a lower temperature.?3?These four types of rocks in Pingmiao deposit can be divided into two stages according to chronology,the first stage is middle-fine grain muscovite granite and Li-mica granite and the second stage consists of porphritic two mica granite and biotite granite porphyry.By using whole-rock Zr-Hf to constrain the magmatic evolution process,the good linear relationship between Zr and Si O₂,TiO₂,Rb,Li,Fe₂O₃T+MgO,A/CNK indicates that granite samples experienced extensive crystalline fractionation.The correlation in muscovite between the K/Rb ratio and the Rb,Cs,MnO,Nb,Ta also indicates that the granite samples experienced a more thorough magmatic evolution.?4?Hydrothermal fluid events at the end of the magma evolution can be well documented by mica,based on the study of zoned Li-mica,it was found that the MnO,Li,Rb,Cs and Ta occurrence of lithium-rich mica cores were increased,while Sn and Nb were decoupled from Ta.?5?The early stage granites is related to the highly differentiated magmatic system,the metallogenic elements are enriched in the process of magmatic evolution and finally precipitate.And the early stage granites is more related to the mineralization of W.The late stage fluid mineralization is similar to the porphyry metallogenic system,fluid dissolves in the late magmatic evolution and the mineralization elements migrate with fluid and precipitated in the appropriate conditions in this process which is more related to Cu mineralization.It is under the superposition of two-stage diagenetic mineralization that the giant W-Cu polymetallic deposit is formed.