## 7 Conclusions  
Based on the comprehensive discussion of sulfur isotopes, trace elements, and fluid inclusions, the following conclusions can be drawn:  
(1) Sulfur isotope analysis indicates that the sulfur in the Hongtoushan Cu-Zn VMS deposit is primarily derived from magmatic sources. Most sulfides have \(\delta^{34}\)S values distributed within a narrow range close to 0% (\(-\)0.7 to 4.2%), suggesting a magmatic origin, while slightly higher \(\delta^{34}\)S values may be attributed to hydrothermal fractionation processes.  
(2) Trace element studies reveal that the pyrite in Type-2 massive ores underwent a \"cleansing\" process during metamorphic recrystallization, resulting in a significant decrease in the trace element contents. The elements released during this process dissolved in thehydrothermal fluids, and may have played a crucial role in the re-enrichment of metal elements in Type-3 massive ones.  
(3) Fluid inclusion studies identified three types of fluid inclusions (Type-1 to Type-3) with distinct homogenization temperatures and salinity characteristics, representing different stages of ore-forming fluid evolution and corresponding to the formation of different types of massive ores. Type-1 fluids represent early high-temperature fluids, and Type-2 and Type-3 fluids were influenced by water-rock interactions and experienced further cooling and dilution.  
(4) Integrating the evidence from sulfur isotopes, trace elements and fluid inclusions, it is proposed that the Hongtoushan deposit underwent a complex, multi-stage metallogenic process: the early mineralization stage formed Type-1 and Type-2 ores; during peak metamorphic conditions, the Type-1 ores underwent recrystallization and coarsening, forming the Type-2 massive ores; in the late-stage mineralization, trace element-enriched fluids generated from the metamorphic recrystallization of the Type-2 ores migrated and cooled significantly, forming the Type-3 massive ores.  
(5) The Hongtoushan deposit is a product of multi-stage hydrothermal activity in a submarine volcanic setting, with the 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.  
Conceptualization and writing--original draft preparation, X.Y.; Writing--review and editing and supervision, E.W.; methodology and software, Y.M. and J.F.; validation, X.Y. All authors have read and agreed to the published version of the manuscript.  
This work was financially supported by the National Natural Science Foundation of China (Grant Numbers: 41372098) and the Fundamental Research Funds for the Central Universities (Grant Numbers: N2123030).  
Not applicable.  
The original contributions presented in the study are included in the article.  
We would like to thank Beijing GeoAnalysis Co., Ltd., Beijing, China; Geoanalytical Center of Nuclear Industry in Beijing; Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS) in Beijing; and Createch Testing Technology Co., Ltd., Beijing for their valuable services and assistance in the data testing conducted for this article. We also thank Hongtoushan Cu-Zn deposit for their kind help in field investigation and sampling.  
The authors declare no conflicts of interest.  
The following abbreviations are used in this manuscript:  
\begin{tabular}{l l} VMS & Volcanogenic Massive Sulfide \\ AVG & Average \\ Py & Pyrite \\ Cp & Chalcopyrite \\ Po & Pyrrhotite \\ Sp & sphalerite \\ Qtz & Quartz \\ REE & Rare earth element \\ wt.\% NaCl eqv. & Weight percent sodium chloride equivalent \\ \end{tabular}