Acta Petrologica et Mineralogica

The Hongnipo deposit is a large Cu deposit newly discovered in southwestern margin of Yangtze Block. In this study, fluid inclusion petrography, microthermometry, laser Raman and in-situ S isotope analysis of sulfide were carried out aiming to reveal the source of metallogenic materials, ore-forming fluid and mineral precipitation mechanism. The mineralization process includes volcano-sedimentary and hydrothermal stages. The fluid inclusions in the quartz from the quartz-calcite-polymetallic sulfide stage (I) include pure CO₂, aqueous-CO₂, aqueous-CO₂ with crystals, liquid-vapor aqueous with crystals and liquid-vapor. These inclusions are usually densely distributed, with a wide range of homogenization temperature (106~500℃) and salinity (8.8%~59.8%). The results of laser Raman spectrum analysis show the volatiles of ore-forming fluid are mainly H₂O, CO₂ and a little CH₄. Sulfides from the volcano-sedimentary stage have δ³⁴S values ranging from 9.18‰ to 9.34‰, suggesting the mixed derivation of sulfur from seawater sulfates and magmatic fluids. Sulfides from the hydrothermal stage have δ³⁴S values that range from 4.42‰ to 5.26‰, which implies a significant contribution of magmatic-sourced sulfur with minor stratal sulfur. Based on the geochronology, fluid inclusions and in-situ S isotopic composition of sulfides, it is considered that Paleoproterozoic volcano-sedimentary processes formed Fe and Cu containing source beds. In the Neoproterozoic, with the breakup of the Rodinia supercontinent, the magmatic hydrothermal fluid from the deep carrying a large number of ore-forming materials mixed with the metamorphic fluid of medium and low salinity and rich CO₂, which triggered the saturated precipitation of ore-forming materials and formed the industrial copper body of Hongnipo deposit.

southwestern margin of Yangtze Block; Hongnipo copper deposit; Laca ore concentration area; fluid inclusion; in-situ S isotope