Genesis of the Jianzhupo Sb–Pb–Zn–Ag deposit and formation of an ore shoot in the Wuxu ore field, Guangxi, South China

Abstract

The Jianzhupo Sb–Pb–Zn–Ag deposit in the southeastern Dachang Sn–polymetallic ore belt, Guangxi region, South China is the largest deposit in the Wuxu district and is hosted by Devonian limestone and mudstone. The deposit mainly comprises a stage I jamesonite–sphalerite ore shoot and stage II jamesonite–sphalerite–calcite–quartz (JSCQ) veins. We use homogenization temperatures, salinities, and the H–O isotopic compositions of fluid inclusions from the Jianzhupo deposit to constrain the genesis of the deposit and determine factors that controlled the formation of the ore shoot. Fluid inclusions from both stages of mineralization contain large volumes of CO2 and minor bitumen, C6H6, and CH4. Fluid inclusions from the ore shoot yield homogenization temperatures of 120 °C–290 °C (mainly 250 °C–270 °C) and salinities of 3.4–13.6 wt% NaCl equiv. Fluid inclusions from the stage II mineralization yield homogenization temperatures of 150 °C–350 °C (mainly 240 °C–310 °C) and salinities of 1.4–12.0 wt% NaCl equiv. Ore-forming fluids of the Jianzhupo deposit yield δ18OH2O and δDV-SMOW values of 4.9‰–9.9‰ and −78‰ to −111‰, respectively, and plot close to the composition of magmatic water on the δDV-SMOW vs. δ18OH2O diagram. CO2 in the ore-forming fluids was likely generated through deep skarnization beneath the Wuxu ore field rather than from metamorphism, thermal degradation, or the oxidization of organic matter. H–O isotopic compositions of ore-forming fluids that contain large volumes of CO2 (with minor bitumen and C6H6) indicate that they were derived from magmatic water that was mixed with basin brines. Ore-forming fluids of the stage I ore shoot yield lower δ18OH2O values (4.9‰–6.7‰) than those associated with the stage II mineralization (7.5‰–9.9‰). Moreover, ore-forming fluids of the ore shoot and the JSCQ veins yield strongly and weakly positive correlations between homogenization temperature and salinity, respectively. This difference suggests that rapid and large-scale mixing between magmatic water and basin brines was the key factor that controlled the formation of the ore shoot.