Zircon U-Pb, molybdenite Re-Os and muscovite Ar-Ar geochronology of the Yashan W-Mo and Xiatongling W-Mo-Be deposits: Insights for the duration and cooling history of magmatism and mineralization in the Wugongshan district, Jiangxi, South China

Abstract

To test the impact of cooling history and prolonged hydrothermal activity on the grade and total endowment of the tungsten deposits, we obtained new and detailed geochronology from the Yashan W-Mo and the Xiatongling W-Mo-Be deposits in the Wugongshan mining district in Jiangxi Province, South China. Both deposits contain stockwork and greisen ores within contact zones between granitic plutons and wall-rock metasandstone and mudstone and within the granitic plutons. New SHRIMP U–Pb zircon analyses yielded weighted mean 206Pb/238U ages of 231.0 ± 5.0 Ma and 161.5 ± 1.8 Ma for the monzogranite and granite in the Yashan W-Mo deposit, and 154.7 ± 1.7 Ma for the granite in the Xiatongling W-Mo-Be deposit. Three molybdenite samples from stockwork ores in the Yashan deposit and four molybdenite samples from greisen and stockwork ores in the Xiatongling W-Mo-Be deposit yielded Re–Os isochron ages of 156.0 ± 2.8 Ma and 156.4 ± 8.7 Ma, respectively. Two muscovite samples from greisen W-Mo ores and W-bearing stockwork in the Yashan deposit gave 40Ar/39Ar plateau ages of 152.77 ± 0.78 Ma and 152.36 ± 0.78 Ma, and two muscovite samples from greisen W-Mo-Be ores and W-Mo-bearing muscovite-quartz stockwork ores in the Xiatongling deposit gave 40Ar/39Ar plateau ages of 146.85 ± 0.8 Ma and 146.31 ± 0.75 Ma, respectively. The age data indicate that the ore-forming granitic magmas were emplaced earlier at the Yashan deposit than the Xiatongling deposit, but Mo mineralization was concurrent at both deposits, and the last hydrothermal ore-forming alteration started earlier again in the Yashan deposit.The U-Pb, Re-Os and Ar-Ar geochronological data indicate that both deposits had similar durations of magmatic-hydrothermal process: 9.1 ± 1.9 m.y. for the Yashan deposit and 8.6 ± 1.8 m.y. for the Xiatongling deposit, but with different cooling path rate. The Yashan deposit experienced a slow cooling rate (36.4 °C/m.y.) followed by a moderately rapid cooling rate (48.6 °C/m.y.), whereas the Xiatongling deposit had an early rapid cooling rate (74.1 °C/m.y.) followed by a slow cooling rate (29.7 °C/m.y.). Unlike porphyry Cu systems, the longevity of magmatic-hydrothermal process is not likely to be a key controlling factor for the total endowment and grade of W deposits. However, our analyses show that rapid cooling rates might facilitate formation of high grade stockwork and greisen W deposits.