Muscovite 40Ar/39Ar and in situ sulfur isotope analyses of the slate-hosted Gutaishan Au Sb deposit, South China: Implications for possible Late Triassic magmatic-hydrothermal mineralization

The Gutaishan deposit is a slate-hosted Au-Sb deposit in the Xiangzhong metallogenic province, South China. The deposit has proven reserves of ca. 9 tonnes (t) of gold with an average grade of 13 g/t and 2,500 t of Sb with an average grade of 10%. In this study, muscovite 40Ar/39Ar and in situ sulfur isotope analyses of pyrite and arsenopyrite were performed to determine the mineralization age and the plausible source of S and Au. The 40Ar/39Ar dating result of muscovite limits the formation age of the Gutaishan deposit to ca. 223.6 +/- 5.3 Ma, coeval with the adjacent Baimashan granite (223-204 Ma). The in situ S-34 values of pyrite and arsenopyrite coexisting with native gold lie in a range between -3.7 and +2.1%o with a mean value of -0.8%o, and these values are markedly different from those of sedimentary pyrite (+ 7.0 to + 23.3%o), indicating a contribution from magmatic sulfur. A magma-derived genetic model may therefore be suitable for the Gutaishan deposit. Integrating the available ages of the Au-Sb and Sb-Au deposits and granites in the Xiangzhong metallogenic province, we propose that a widespread Late Triassic magmatic-hydrothermal Au-Sb mineralization event occurred.