The Characteristics Of Fluid Inclusions In Dengbuxian Tungsten Deposit Hunan

The southeast of Hunan province is in the middle of Nanling polymetallic metallogenic belt. Deng Fuxian tungsten is one of the best important tungsten deposits. Although there have been one hundred years of mining history up till the present moment, geological research was confined to resources reserve, geochemical characteristics of rock mass and isotopic age. Ore-forming fluid had not available yet literature. As an important Tungsten-tin hydrothermal type deposit, the lack of research on metallogenic fluid and mineralization period time restricts the study of the deposit and regional metallogenic regularity in a way. In this paper, the mining area hydrothermal fluid is the main research targets, selected the ore vein and fluorite veins’ fluid inclusions as the research objects based on petrographic research, combined mining area formation, structure, orebody characteristics, occurrence point, comprehensive comparison and analysis the mining area of the ore-forming hydrothermal fluid evolution process and the precipitation mechanism of ore-forming materials and ore-forming fluid composition, etc. By Isotopic dating and Deng Fuxian mining granite rock geochemical characteristics analysis, new analysis results are expected as the late prospecting provides some valuable new knowledge.Orefield mainly developed quartz vein type wolframite. Intra-area has hundreds of ore quartz vein. By analyzing Deng Fuxian tungsten fluid inclusions in ore containing ore vein and the fluorite veins, the basic mineral assemblage is quartz-black tungsten-metal sulfide and quartz fluorite-metal sulfides, and inclusion types are including pure liquid phase (L) single phase H2O-NaCl inclusions (Ia), rich liquid two phase H2O (L+V)-NaCl inclusions (Ia), clastic particle inclusions (Ic) and rich gas phase (L+V) inclusions (Id).Except type la can’t be used for temperature measurement, the rest of the uniform temperature of the inclusions distributed from110-360℃(without pressure correction) with more kurtosis characteristics. We can identify three distinct temperatures:①The high temperature of240-290℃;②The medium temperature of170-240℃;③The low temperature of110-170℃. This shows that the mineral deposit ore-forming process is more complicated for the mineralization has multiple periods. According to the inclusion salinity data, ore-forming fluid salinity is below10w (NaCl)%and the salinity peak is5w (NaCl)%,20%f of the total, reflecting low salinity characteristics. To ascertain ore-forming fluid issue, the paper adopts the combination of fluid inclusions (FIA) method. Its distribution characteristics include the population distribution, orientation distribution, the healing of fracture distribution and beaded distribution, along the healed fracture distribution and beaded distribution. By petrographic observation and statistical measureing, the inclusions temperature results indicate primary inclusions, showing the third phase of ore-forming hydrothermal:140-160℃,180-210℃,240-270℃, accounting for the ore-forming stages in Deng Fuxian tungsten ore mining area went through at least three periods of hydrothermal activity.According to the uniform temperature of type I inclusions analysis of ore body and midpiece, both the statistical results of different ore bodies or midpiece are consistent with the overall distribution of inclusions in the mining area, and the test result can be divided into three main temperature ranges. With the change of sampling level from585m to260m, uniform temperature distribution decrease progressively from the high temperature range. From the bottom up, temperature gradually increased with reverse zoning characteristics. This may be related to multi-stage tectonic action which leads to edto tectonic fracture and make the volatile components escaped from the fluid. On the one hand, the boiling fluid gushed into the fracture and the upper part under the stress. On the other hand ore-forming fluid flowed to the vertical space. With the development of fractures in deep, the strong liquidity of the high temperature fluid migrated to further afield, along with the fracture to the deep development.Bain (1964) Haas (1976) formula was indtroduced to calculate the geological metallogenic pressure and count gas liquid two phase inclusion temperature measurement data. As this formula is aimed at different salinity NaCl-H2O system of boiling inclusion P-T relationship, therefore it can only speculate on what the mining area the minimum capture pressure. The fluid pressure of Deng Fuxian area is4.32-52.28MPa and average pressure is15.64Mpa. Appropriate pressure gradient formula was selected to estimate the metallogenic depth. hydrostatic pressure gradient formula P=pgh and litho static pressure gradient formula S=prgh were used to calculate the metallogenic depth, which is between0.32to1.94km, an average of1.1km. It is preliminary speculated that the deposit is a shallow hydrothermal deposit.The destructive smaller single inclusion laser Raman probe test was choosed in the inclusion composition analysis. The results show that both the inclusions in the quartz veins and inclusions in the fluorite veins was detected broad H2O envelope peak. Only a small number of N2envelope peak was detected in quartz vein Inclusions, combined with the beginning of melting temperature of the fluid inclusions, which is coincide with inclusion composition and temperature measuring results. This may indicate in the mineralization that H20gas overflow and temperature reduction are the main factors of Deng Fuxian tungsten mineralization.Deng Fuxian granitic pluton is a complex massif composed of biotite granite, mica granite and muscovite-granite. Mica granite has the closest relations with tungsten mineralization. In order to obtain more accurate diagenetic mineralization ages,13middle3w tungsten pulse zircon sample was picked. LA-ICP-MS U-Pb isotope was used to measure mica granite, and the average age was154.4+/-2.2Ma (MSWD=5.6, n=20), which is defined as the early yanshan emplacement. Based on the previous research results, Tin tin in tungsten polymetallic diagenetic mineralization concentration is between150and160Ma. Tungsten tin polymetallic mineralization was related to Deng Fuxian and tin field rock mass granitic magmatism, belonging to the same tectono-magmatic-the product of ore-forming fluid system.Deng Fuxian mica granite is charcterized with high silicon, alkali rich, poor magnesium, iron, and strong peraluminous. Granite relatively enrich of large ion lithophile Cs, Rb, K and high field strength elements Th, U, Pb, Ti, Ba and Sr loss, but low total rare earth (∑REE average90.59x10-6).Light rare earth elements are relatively rich (LREE/HREE averaged9.97), and europium showed negative abnormity (delta Eu average0.34), while the distribution patterns of rare earth elements intends to the right type. According to the regional geological and geochemical characteristics, the granite rock can be defined as type S granite which was formed in the post-tectonic stretch tectonic environment. Granite is closely related to tungsten mineralization, and contains independent accessory minerals, the tungsten tin. Therefore, the mineralization has an important instruction meaning.