He and Ar isotopic compositions and genetic implications for the giant Shizhuyuan W–Sn–Bi–Mo deposit, Hunan Province, South China

Abstract

The Shizhuyuan ore deposit in southern Hunan Province is a world-class W–Sn–Bi–Mo occurrence hosted by Devonian limestone in the thermal aureole of the Qianlishan granite. Mineralization coincided with intrusion of the granite pluton during Mesozoic crustal extension in South China. We present new He and Ar isotope data for volatiles released from pyrite in the Shizhuyuan deposit. Concentrations of ⁴⁰Ar range from 0.21 to 2.38 × 10⁻⁶ cm³ STP ⁴⁰Ar/g, and ⁴He concentrations range from 0.8 to 65.1 × 10⁻⁶ cm³ STP ⁴He/g. ³He/⁴He ratios vary from 0.06 to 1.66 Ra (where Ra is the ³He/⁴He ratio of air = 1.39 × 10⁻⁶) and ⁴⁰Ar/³⁶Ar ratios range from 293 to 1072. The isotopic compositions of He and Ar indicate that the ore-forming fluids were mantle-derived, modified by air-saturated crustal fluids. Shallow-level boiling increased ³He concentrations, whereas crustal contamination decreased ³He/⁴He ratios in the magmatic fluids. The occurrence of mantle-derived components in the magmatic fluid indicates that the associated Qianlishan granite is not a typical S-type pluton that formed entirely by crustal melting. We propose that the mineralization was related to mantle upwelling and Mesozoic lithosphere extension of the South China Block.

Keywords:

• He and Ar isotopes
• Shizhuyuan W–Sn–Bi–Mo deposit
• Qianlishan granite
• crust–mantle interaction
• Hunan Province, China

Acknowledgements

We are grateful to Prof. Pete Burnard and Dr Mark Kendrick for their comments on the early version of the manuscript and to Prof. Chusi Li for his useful suggestions for improving the manuscript. We thank the geologists of the Shizhuyuan Mine for their field assistance. This research was supported jointly by the National Natural Science Foundation of China (40903023), the Major Programme of the National Natural Science Foundation of China (40634020), and the National Basic Research Development Programme of China (973 Programme) (2007CB411408; 2007CB411408).