## 6 Discussion
### Implications for Metallogenic Models  
The integrated evidence from sulfur isotopes, trace elements, and fluid inclusions suggests a complex, multi-stage metallogenic process for the Hongtoushan deposit:  
(1) Early mineralization stage: This stage mainly formed Type-1 and Type-2 ores. The seawater penetrated deep into the crust along fracture systems, mixing with magmatic hydrothermal fluids, and continuously circulated. This process leached the metallic elements from the basement rocks, forming Cu- and Zn-rich hydrothermal fluids. As the fluids ascended along the faults and fractures, they underwent cooling and decompression, leading to the precipitation of sulfides and the formation of the Type-1 massive sulfide ores. The high formation temperatures are evidenced by the high Co/Ni ratios in the pyrite and the characteristics of the Type-1 fluid inclusions.  
(2) Metamorphic recrystallization stage: During the peak metamorphic conditions, the Type-1 ores underwent recrystallization and coarsening, forming the Type-2 massive ores. This process is supported by the widespread triple-junction textures in the pyrite and pyrrhotite porphyroblasts. The recrystallization led to the release of trace elements from the pyrite into the hydrothermal fluids, as indicated by the depletion of the rare earth elements, Cu, and Zn in Type-2 ores. The characteristics of the Type-2 fluid inclusions, with lower homogenization temperatures but higher salinities, suggest that water-rock interaction played a significant role during this stage.  
(3) Late-stage mineralization: The trace-element-enriched fluids generated from the metamorphic recrystallization of the Type-2 ores migrated and cooled significantly. The decrease in temperature resulted in the precipitation of Cu, Zn, and other elements from the hydrothermal fluids, forming the Type-3 massive ores. The lower Co/Ni ratios in pyrite and the characteristics of the Type-3 fluid inclusions support a lower formation temperature for these ores. The negative \(\delta^{34}\)S values of the pyrite in the Type-3 ores indicate that the sulfur was likely derived from the desulfurization of pre-existing sulfides in the Type-1 and Type-2 ores.  
The Hongtoushan deposit is a product of multi-stage hydrothermal activity in a submarine volcanic setting, with mineralization influenced by both magmatic and seawater sources. The early stage involved high-temperature hydrothermal fluids leaching metals from the basement rocks and precipitating massive sulfides. Subsequent metamorphic recrystallization led to the release of trace elements, which were re-enriched in the late-stage ores. This complex interplay of magmatic, hydrothermal, and metamorphic processes highlights the dynamic nature of the VMS deposit formation.  
Further research on the regional tectonic setting, the timing of mineralization events, and the relationship between the Hongtoushan deposit and the other VMS deposits in the region will provide a more comprehensive understanding of the metallogenic system. Detailed geochemical and isotopic studies on the host rocks and the alteration zones may offer additional insights into the source of metals and the extent of the fluid-rock interaction. Investigating the potential role of biological activity in the precipitation of sulfides could also shed light on the complex processes involved in the formation of the Hongtoushan deposit.