The Research On The Geochemical Characteristic And Genesis Of The Dawutang Tungsten Polymetallic Deposit In Jiangxi

The large tungsten polymetallic deposit of Dawutang was found last few years, which is in the central part of the Dahutang Orefield. The veinlet-disseminated scheelite is the most important type of ore, and there are also other types, such as type of quartz lode, greisen and cryptoexplosion breccia. On the basis of summarizing the geological background and metallogenic characteristics of Dawutang tungsten district, major and trace elements, fluid inclusions and stable isotope researches are systematically carried out, the genesis mechanisms of the deposit are analyzed, and the metallogenic model of the district is preliminarily established. Several major understandings are as follows:( 1) Dawutang Yanshanian granitic was with high silicon, alkaline, strong peraluminous, High differentiation, “S”-type characteristics; porphyritic granite characterized by rich of lil element Rb?U and loss of Ti?Ba?Sr?Nb; medium-coarse muscovite granite, medium-fine grained muscovite granite, granite porphyry characterized by rich of lil element Rb?U?Ta, strong loss of Ba?Ti, slight loss of Sr?Zr; ?REE range is very large, LREE relative enrichment, Significant Eu negative anomaly, REE distribution pattern shows type of right-dipping “gull”. The source of Yanshanian granitic region to argillite based, but the source of porphyritic granite region containing relatively more arenites.(2)From early to late, quartz veins of Dawutang ore district can be divided into three phases: Feldspar-wolframite-quartz veins(?-phase), scheelite-sulfide-quartz veins( ?- phase), carbonate-quartz vein( ?- phase). Temperature measurement of fluid inclusions shows that the homogenization temperatures of ore-forming fluids of ?~? phases were concentrated respectively in the range of 215~245??185~215??155~215?; the salinity of fluid inclusions have no significant difference in phases of?~?, and values range from 3.5~5.5 wt% NaCl, but values range from 2~4 wt% NaCl in phases of ?. And the density of metallogenic fluids tended to increase from ?to ? phase, and the focus range were of 0.86~0.88 g/cm3?0.88~0.92 g/cm3?0.90~0.94 g/cm3 successively. From deep into the ground in drilling, the homogenization temperature of inclusions has obvious decreasing trend, with pressure decreasing trend, while salinity has not changed regularly. In addition, ore-forming fluids in the process of evolution has gone through boiling, mixing with meteoric water of low temperature and low salinity, indicating that the physical and chemical conditions changes many times, which may be an important mechanism for the precipitation and concentration of tungsten to form ore.(3)Raman spectroscopy showed that the gas components of fluid inclusions are mainly of H2O?CH4?N2, also contain small amounts of CO2 gas, which indicates that tungsten polymetallic ore may precipitated from a less reducing environment.(4)Through the stable isotopes of Dawutang ore district studies have shown that H-O isotopic variation range is very small, with ?DV_SMOW values vary in the range of-71.3‰~-65.4‰ and ?18OH2O values vary in the range of 1.61‰~3.65‰, and falling on the left of magmatic water area in the ?D-?18OH2O diagram. This result indicates that mineralization fluid came from magmatic water and mixed with meteoric water in Dawutang ore district. C-O isotopic geochemistry show that the carbon of ore-forming fluids transferred from deep sources, lower crust or upper mantle, by methane. Pb isotopic compositions and related parameters show that Pb has many characteristics of the source, mainly from the lower crust, and mixing a small amount of up-crust contamination.(5)By the comprehensive study of geological characteristics, ore-controlling factors, ore-forming materials, age of diagenetic and metallogenic, metallogenic mechanism in Dawutang ore district, the metallogenic model is divided into two stages. The first phase of mineralization mainly associated with porphyritic granite, while the second phase of mineralization mainly associated with medium-coarse muscovite granite, medium-fine grained muscovite granite, granite porphyry, and the pattern of metallogenic model was established in Dawutang ore district.