Origin of the Fule Pb–Zn deposit, Yunnan Province, SW China: insight from in situ S isotope analysis by NanoSIMS

AbstractThe Sichuan–Yunnan–Guizhou (SYG) Pb–Zn metallogenic province is one of the most productive areas of Pb–Zn resources in China. The Fule deposit occurs in Permian carbonate and contains Pb–Zn reserves exceeding 1 Mt. To investigate the sulphur source, in situ S isotopic analysis of sphalerite and pyrite was carried out using nanoscale secondary-ion mass spectrometry. The results show that the δ34S values of the sulphide minerals range from +16.1‰ to +23.0‰, higher than that of marine sulphates hosted in Permian carbonate rocks (+11‰), but similar to that of sulphates over a broader area (+12.9‰ to +25.9‰). The sulphates in the regional rocks could therefore represent an important source of S for the Fule deposit via thermochemical sulphate reduction. The S source of the Fule deposit is different from those of most other Pb–Zn deposits in the SYG Pb–Zn mineralization province, which were mainly derived from the ore-bearing strata. The δ34S values of the early to late generations and some single sulphide crystals from the cores to rims show a slight increasing trend, implying that partial Rayleigh fractionation took place in the Fule deposit. It is suggested that the Fule sulphide precipitation resulted from the mixing of a metalliferous fluid with a H2S-rich fluid derived from the regional strata. Combining the geology, mineralogy and S isotope results with previous Pb isotope studies, it is suggested that the Fule deposit should be attributed to a Mississippi Valley type deposit.