Origin and evolution of the ore-forming fluids in the giant Dongping wolframite–quartz vein–type deposit in the Jiangnan Orogen, South China: fluid inclusions and H–O isotopic constraints

• Two pulsed exsolution of magmatic fluids takes place in the Dongping deposit. • The second-pulsed exsolved magmatic fluids produce wolframite mineralization. • The main mechanism of wolframite deposition is fluid cooling. Tungsten (W) is an indispensable strategic resource, and the wolframite–quartz vein–type deposit is an important W deposit type. The origin and delicate evolutionary process of the ore-forming fluid for wolframite–quartz vein–type deposits still lack precise constraints. The Dongping W deposit is the sole giant wolframite–quartz vein–type deposit in the Jiangnan Orogen, South China, with 214,000 tons of WO 3 . Based on the cross-cutting relationships and petrographic observations, four alteration and ore-forming stages were identified: (Ⅰ) pre-ore alteration, (Ⅱ) wolframite–quartz, (Ⅲ) quartz–sulfide, and (Ⅳ) fluorite–carbonate stages. Three types of fluid inclusions can be identified: liquid–rich two–phase (Type Ⅰ), vapor–rich two–phase (Type Ⅱ), and liquid inclusions (Type Ⅲ). Minor CH 4 can be detected in the inclusions from Qtz Ⅰ and Qtz Ⅱ , indicating that the initial fluid is probably relatively reduced. The fluid responsible for the pre-ore alteration and wolframite–quartz veins are medium–high temperature and medium–low salinity, and then evolve into ones with medium–low temperature and medium–low salinity during the post-ore two stages. The δD v-SMOW and δ 18 O v-SMOW values of Qtz Ⅰ and Qtz Ⅱ range from –80.4‰ to –62.0‰ and 10.22‰ to 13.44‰, respectively, suggesting a dominantly magma-derived fluid. The δD v-SMOW and δ 18 O v-SMOW values in the post-ore Qtz Ⅲ and Qtz Ⅳ vary from –76.3‰ to –69.4‰ and 7.63‰ to 13.92‰, respectively, and δ 18 O v-SMOW values are lower than those in the foregoing two stages, implying the addition of meteoric water. The fluid evolution displays a complex process: the initially exsolved reduced fluid from the Yanshanian hidden S-type granite produce pre-ore alteration; subsequently, cooling of second-pulsed exsolved magmatic fluid produces wolframite mineralization followed by quartz precipitation; with the evolution of the fluid and the involvement of meteoric water, the evolved fluid form both the quartz–sulfide and fluorite–carbonate assemblages. Our study shows that fluid cooling is decisive for the wolframite precipitation in the Dongping deposit. This contribution elucidates the multistage fluid evolution and the precise mineralization process of the Dongping deposit, providing new insights into the genesis of giant wolframite–quartz vein–type deposits.