Geodynamic Setting And Mineralization Of The Giant Veinlets-disseminated Tungsten Ore Field In Jiangxi Province, China

Dahutang in northwestern Jiangxi of south-central China is a representative tungsten deposit in Jiangnan massif Tungsten Belt. In this thesis, a comprehensive geological, mineralogical, geochemical and geochronological study is presented to discuss the metallogenic and geodynamic process.It is indicated that Dahutang tungsten deposit is closely related to the Yanshanian granitoids, and the wall rock is Neoproterozoic granodiorite and phyllite of Shuangqiaoshan group. Zircon U–Pb LA-ICP-MS analyses for the ore-related granitoids yield ages of 147.5±1.2~147.3±1.3Ma for porphyritic biotite granite, 146.0±1.4~144.67±0.96 Ma for fine-grained granite, and 143.1±1.2~142.0±1.6Ma for granite porphyry, showing identical ages that are consisitent with filed observations. The molybdenite Re-Os metallogenic age of the mining area ranges from 138.4Ma to 143.8Ma, suggesting a close spatial–temporal relationship with the paralleled YRB porphyry–skarn Cu–Au–Mo–Fe system. Three types of granite have A/CNK=1.09~1.26 and are enriched in Rb, Th, U and K, and depleted in Ba, Nb, and Ti, indicating them S-type intrusions crystallized from peraluminous melt and experienced high degree of fractionation. The molybdenite contains only 0.5~7.8ppm Re, which strongly contrast with that of the middle and lower reaches of the Yangtze River iron copper and gold belt(53~1169ppm). This result indicates the parent magma originate from remelting of upper crust. The three types of granite exhibit wide range of initial(87Sr/86Sr)(t=145) of 0.721 to 0.731 with two-stage model age(T2DM) of 1.3~1.6Ga. It is considered the three types of rocks may all derived from the Shuangqiaoshan group. Therefore, we proposed a metallogenic model with mutiple-pulses emplacement of highly fractionated granitic magmas.Three mineralization periods are recognized in Dahutang deposit. They are, from early to late, hornfels-pegmatite period, hydrothermal mineralization period and supergene period. Among these, hydrothermal mineralization period can be subdivided into three stages, including K-feldspar stage, tungsten mineralization stage and carbonate stage. Tungsten mineralization stage is the major scheelite deposition stage and characterized by the formation of veinlet-dissemination, cryptoexplosive breccia and quartz vein types ores. The fluid inclusion study indicates that the liquid-rich vapor liquid fluid inclusions are the mainly fluid inclusions type. The total homogenization temperature of fluid inclusions ranges from 144℃ to 364℃, and salinity from 0.18% to 7.73%. The results demonstrate that the ore forming fluid belongs to the NaCl-H2 O fluid system, and is characterized by medium to low temperature, low salinity magmatic fluid.A geodynamical model for the middle and lower reaches of the Yangtze River and its adjacent region tungsten and copper deposits is proposed. The model indicates that the Izanagi plate subducted from the south to the north east west at about 160 Ma. Such plate might be tear apart along the conjunction of North China Craton and Qinling Orogenic Belt and thus a series of high potassium calc-alkaline granitoids magma formed. The granitoids magma emplaced along the middle and lower reaches of the Yangtze River region, resulting in the formation of the copper polymetallic ore belt. Under the same geodynamic steeings, asthenosphere upwelled along the the EW trending slab fractured zone, leading to the partial melting of the upper crustal material and thus resulting in the formation of peraluminous granite magma and the related North Yangze Craton Tungsten ore belt(NYCT).