Molybdenite Re-Os and muscovite ~(40)Ar/~(39)Ar dating of the Xihuashan tungsten deposit, central Nanling district, South China

摘要

The Xihuashan tungsten deposit in the central Nanling region, South China, is an important vein-type ore deposit hosted in Cambrian strata and Mesozoic granitic intrusions. Wolframite and molybdenite are the principal ore minerals. The gangue minerals are mainly quartz and muscovite. Wolframite and molybdenite are products of the first stage hydrothermal activity, whereas muscovite formed dominantly at the second stage. Molybdenite Re-Os and muscovite ~(40)Ar/~(39)Ar dating have been carried out to investigate the age of mineralizatioa Re-Os isotopic dating for molybdenite associated with wolframite yield a precise, well-constrained isochron age of 157.8 ±0.9 Ma (MSWD = 1.5). Ar-Ar isotopic analyses of muscovite yield a plateau age of 152.8 ±1.6 Ma, in agreement with an inverse isochron age of 152.8 ±1.6 Ma, which is ~5 mys younger than the Re-Os age. The molybdenite Re-Os age is interpreted as the age of tungsten mineralization. This age coincides well with the zircon U-Pb age of the host granitic intrusion reported previously. The ~5 mys difference between molybdenite Re-Os and muscovite ~(40)Ar/~(39)Ar ages probably represents the duration of hydrothermal activity. The results show that the Xihuashan tungsten deposit is one of many important tungsten-tin deposits formed during 150 to 160 Ma associated with large-scale lithospheric extension in South China.