# Genesis of the Baiyangping Cu-Co and Pb-Zn Mineralizations in Lamping Basin, SW China
## 5 Discussion
### Sources of Metals and Ore-Forming Fluids  
The Baiyangping ore-bearing hydrothermal carbonates are characterized by \(\delta^{18}\)O\({}_{\text{SMOW}}\) values from +12.2%o to +22.0%o and the \(\delta^{13}\)C\({}_{\text{PDB}}\) variable from \(-5.5\)%o to +1.8%o. In the diagram of \(\delta^{18}\)O\({}_{\text{SMOW}}\) versus \(\delta^{13}\)C\({}_{\text{PDB}}\), most of the hydrothermal carbonates from Pb-Zn and Cu-Co mineralizations are plotted within or near the fields of continental or marine carbonates. This feature indicates that the carbon of both Pb-Zn and Cu-Co mineralizing fluids may originate from the regional continental carbonates, which are similar to the regional Triassic carbonates [35; 36; 37; 38; 39; 40]. Moreover, the \(\delta^{18}\)O\({}_{\text{SMOW}}\) of hydrothermal carbonates from the Pb-Zn and Cu-Co mineralizations show slight differences, with the latter showing lower \(\delta^{18}\)O\({}_{\text{SMOW}}\) values. During the relatively intense carbonate dissolution processes, namely water-rock interaction during the Cu-Co mineralizing phase, \(\delta^{13}\)C\({}_{\text{PDB}}\) remains unchanged while \(\delta^{18}\)O\({}_{\text{SMOW}}\) decreases. The \(\delta^{18}\)O\({}_{\text{SMOW}}\)-\(\delta^{13}\)C\({}_{\text{PDB}}\) ranges of marine carbonate and continental carbonate come from [PERSON], 1986 [41]. This may indicate that carbon sources may be driven by low-\(\delta^{18}\)O\({}_{\text{SMOW}}\) basinal brines or fluid input by meteoric water (Figure 8) [42; 43; 44; 45]. Carbonates generally have C-O isotope compositions between mantle-sourced carbon and continental carbonates (Figure 8). The homogenization temperatures of fluid inclusions in hydrothermal ankerite and calcite from Baiyangping are relatively low. The variation in the carbon and oxygen isotopic compositions of the veined carbonates are similar to those of the regional Triassic limestone country rocks [43; 44; 45; 46]. The \(\delta^{34}\)S values of sulfides from the Baiyangping deposit range from +5.2%o to +9.5%o. Samples of tetrahedrite from the Cu-Co ore have \(\delta^{34}\)S values between +5.2%o and +9.5%o, which resemble those of sphalerite from the Pb-Zn ore ranging from +7.5%o to +9%o. Such features may provide evidence for both consistent and stable sulfur sources, as well as sulfate reduction processes during Cu-Co and Pb-Zn mineralization, which is consistent with previous interpretations [44; 45]. Figure 7: Summary plot of homogenization temperatures, salinities, and pressure of fluid inclusions related to the two stages at the BaiyangpingCu–Co–Pb–Zn deposit. The sulfate reduction processes during sediment-hosted deposit mineralization are controlled by the geothermal gradients. Such processes may include thermal decomposition of sulfur-bearing matter at temperatures of \(\sim\)100-150 \({}^{\circ}\)C, thermochemical sulfate reduction in the presence of organic matter at 80-100 \({}^{\circ}\)C \(<\) T \(<\) 160-180 \({}^{\circ}\)C, and bacterially mediated sulfate reduction at a temperature of \(<\)80 \({}^{\circ}\)C [1, 41]. The fluid temperatures during ore-forming hydrothermal activity are between 140 \({}^{\circ}\)C and 200 \({}^{\circ}\)C, indicating that bacterially mediated sulfate reduction is unlikely to have taken place during Cu-Co and Pb-Zn mineralizations [45, 46, 47, 48, 49]. Thermochemical sulfate reduction may generate 0-15% sulfur isotope fractionations during the transition from marine sulfate to H\({}_{2}\)S within the temperature range of 80 \({}^{\circ}\)C \(<\) T \(<\) 180 \({}^{\circ}\)C [49]. Previous studies identified a large amount of organic matter and sulfates in the regional Triassic Sanhedong and Paleogene Yunlong formations [50, 51, 52, 53], which are available for interaction between sulfates and organic reactants. The \(\delta^{34}\)S sulfide values of \(+\)5.2 to \(+\)9.5% at the Baiyangping deposit also highlight the role of thermochemical sulfate reduction as a source of sulfur.