A metasedimentary origin for gold deposits in the Dian-Qian-Gui "Golden Triangle" of Southwest China

The Dian-Qian-Gui "Golden Triangle" area of Southwest China hosts a large number of Au deposits. However, the sources of the ore-forming fluids are still controversial, hampering the formulation of a sound genetic model and effective ore prospecting. Here we investigate the sources of ore-forming fluids by an integrated study of in-situ sulfur isotope analyses and available trace element (e.g., Co and Ni) data for the pyrite in the "Golden Triangle" area. We find that the ore stage pyrites are featured by low Co/Ni ratios (mostly < 2), which is distinct from pyrite formed in magmatic-hydrothermal systems but resemble typical sedimentary pyrite. In addition, the significant variation (from-7.5 to +20.0%o) in sulfur isotopes (& delta;34S) of the ore stage pyrite in these deposits also support a sedimentary origin of the ore-forming fluids. Considering the difference in sulfur isotopic compositions of ore-stage pyrite and the sedimentary host rocks, we suggest the metasedimentary basement rocks (>500 Ma) in the area may have supplied most of the sulfur and gold for the ore-forming fluids during the Triassic orogenesis in the Dian-Qian-Gui "Golden Triangle" area of Southwest China.