Genesis of the Mengxing Pb-Zn deposit in Baoshan block, SW China: Constraints from geology, fluid inclusion and isotopes

Abstract

The Mengxing Pb-Zn deposit is located in the central-southern Baoshan block, SW China, which contains over 1.02 Mt metals with the average Pb + Zn grade of 12.12 %. In this deposit, the orebodies are mainly stratabound and developed in the Silurian limestone of the Shangrenheqiao Formation. The mineral assemblage is mainly consisted of sulfides, quartz, calcite and barite. Based on petrographic observation, three mineralization stages have been recognized, including the pre-ore, syn-ore (including stage I and II) and post-ore stages. Fluid inclusion study shows that the ore-forming fluid in Mengxing deposit belongs to a NaCl-H2O-(CO2) system with medium–high temperature (187.3–320.1 °C) and medium–low salinity (2.1–17.9 wt% NaCl equiv.). H-O-S-Pb isotopic studies reveal that the ore-forming fluid dominantly originated from magmatic water, and reacted with organic matter preserved in sedimentary strata at stage I and mixed with metamorphic/meteoric water at stage II. The sulfur for mineralization was mainly contributed by magmatic sulfur. Marine sulfates preserved in Silurian sedimentary strata also contributed some ore-forming sulfur in stage II. The ore-forming metals in Mengxing deposit were jointly contributed by sedimentary strata and deeply concealed granitic magmatism. Based on these geological and geochemical characteristics, we suggest that the Mengxing Pb-Zn mineralization is Epithermal type and formed in multiple stages.