Mineralogy And Deposit Characteristics On The Dajishan Tungsten Deposit In Jiangxi Province

The Dajishan tungsten deposit is the famous large-sized tungsten deposit which is located inthe Nanling metallogenic belt of Jiangxi Province. In order to find out mineralogical,petrological and chronological characteristics of this deposit, a geological investigation of themine was conducted along with collecting samples of tungsten. And several geological methodssuch as microscopic identification, geochemistry and isotopic test were used for this study.The Electron probe analysis, trace elements measurement and oxygen isotopic test wereused to analyze wolframite and quartz. The results of study are briefly summarized as follows.1)The main mineral component is wolframite, and there is a negative correlation in WO₃-MnO、WO3-FeO, and a positive correlation between MnO and FeO. The ratio of FeO/MnO in mostsamples is close to1.0. The obvious isomorphic phenomenon indicates that the Dajishantungsten deposit was formed by high temperature magma, reacting with surrounding rocks fully.Oxygen isotopic analysis shows that the process of rebalancing magmatic water along withmixing with little atmospheric precipitation is the main source of ore-forming hydrothermalalteration. There is a negative correlation between the contents of Nb, Ta in the wolframite andthe depth of deposit: As the deposit gets deeper, the contents of them decrease. It can beimproved by the truth that the magma mainly produces oxide under high temperature in the earlymetallogenic period. The Change of physical and chemical conditions occurs in the latermetallogenic period, which results in an increase of sulfide. This is an important evidence forreverse zones.2)The contents of trace elements in the quartz are very low. But Ti is rich in thequartz. It explains that quartz forms in high-temperature deposit, which is consistent withprevious conclusion.Analysis on the major elements, trace elements and rare earth elements of NO.69graniteshow that NO.69granite is rich in Si, Al, and K₂O+Na₂O, but is poor in Ca，Fe, Mg. NO.69granite belongs to S-type of granites. And it has the distinct characteristics of high levels offractionation and evolution in addition to rich ore-forming elements and the oxygen-poorformation environment.Precise Re-Os isotopic data of molybdenite from the Dajishan tungsten deposit producedthe result that an isochron age is161.0±1.3Ma. It determines metallgenic age of thequartz-tungsten type of deposit. The paper also gives a well-defined Rb-Sr isochron with ages of 150.9±2.4Ma. It represents the deposit was formed in Early Yanshanian period. According tothis, the deposit formed veins under the geological evolution before160Ma. The quartz veinswere crystallized and differentiated in150Ma. In this period, the full ore-forming materialscrystallizing and differentiating constantly resulted in the formation of the Dajishanquartz-tungsten deposit. All these factors influence to create the typical characteristics ofDajishan tungsten deposit.