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 ³⁴S values of pyrite and arsenopyrite coexisting with native gold lie in a range between −3.7 and +2.1‰ with a mean value of -0.8‰ and these values are markedly different from those of sedimentary pyrite (+7.0 to +23.3‰), 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.