Metallogenesis of the Baidi Au-Sb deposit, southwest Guizhou Province, China: mineralogical and geochemical evidence from sulfur-bearing minerals

The Baidi Au-Sb deposit, which contains 8 t of Au and 10,979 Mt of Sb, is a typical and rare paragenetic deposit located in southwestern Guizhou Province, China. Previous studies have focused on individual ores, but have not combined them to identify their paragenetic mechanism or metallogenic regularity. Therefore, we used field investigations, microscopic observations, and in situ analyses to identify the spatial distribution, mineral paragenesis, compositional evolution, and metallogenic material sources of the ore bodies. We also determined the Au and Sb paragenetic characteristics and the metallogenesis of the deposit. The main Au-bearing minerals in the deposit were early (Apy1-2) and late (Apy3) stage arsenopyrites, as well as pre-mineralization (Py1), mineralization (Py2-5), and late mineralization (Py6-7) stage pyrites. The main Sb-bearing minerals were stibnite (Snt), skinnerite, bournonite, and valentinite. The minerals formed in the order of Py1, Py2-3 + Apy1, Py4-5 + Apy2, Snt, and Py6-7 + Apy3. The delta S-34 values of the arsenopyrites and pyrites ranged from - 5 to 5 parts per thousand, while those of stibnite were mostly less than - 5 parts per thousand in the later mineralization stages. Sulfur was provided by deep magmatic hydrothermal fluids, but sedimentary sulfur was added in the later stages. Moreover, the trace elemental contents fluctuated and eventually became similar to those of the sedimentary strata. By comprehensively considering the ores along with the geological characteristics of the deposit, we determined that deep magma provided the Au during ore formation. Later tectonic changes provided Sb from the sedimentary strata, which precipitated along fault expansion areas and produced Au and Sb paragenesis.