## 6 Discussion  
### Source of Ore-Forming Fluids  
The \(\delta^{18}\)O values of hydrothermal quartzes have a narrow range of 6.8 to 9.3% (typically 8.4 to 8.7%) (Table 3), suggesting that these hydrothermal quartzes are formed during the same stage. Figure 9 shows that the value of \(\delta^{18}\)O\({}_{\text{water}}\) nearly lies within the field of primary magmatic water, indicating the origin of magmatic water [55]. The \(\delta\)Dwater values are \(-97.1\) to \(-77.4\)%, being slightly lower than those of the primary magmatic water and overlapping with the lower end of the Sanfoshan Granite magmatic waters (Figure 9), which likely results from the early degassing process in an open magma system [56; 57; 58; 59; 60]. In addition, none of the D-O isotopic data of ore-forming fluids in the Xiawolong gold deposit fall within the values for magmatic waters of the Mesozoic Kunyushan, or the metamorphic water of the Jingshan Group (Figure 9), indicating that it is impossible \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Ore Style** & **Sample** & **\(\delta^{34}\)SCDT (\%)** & **\({}^{208}\)Pb/\({}^{204}\)Pb** & **\({}^{207}\)Pb/\({}^{204}\)Pb** & **\({}^{206}\)Pb/\({}^{204}\)Pb** \\ \hline \multirow{6}{*}{Stockwork} & XML-g1 & 6.6 & 37.369 & 15.436 & 17.247 \\  & XML-g3 & 6.9 & 37.870 & 15.504 & 17.792 \\  & XML-g9 & 6.1 & 37.432 & 15.444 & 17.193 \\  & XML-g10 & 7.6 & 37.490 & 15.468 & 17.481 \\  & XML-g11 & 7.1 & 37.472 & 15.459 & 17.526 \\  & XML-g12 & 7 & 37.498 & 15.467 & 17.500 \\  & XML-g16 & 8.1 & 37.453 & 15.459 & 17.432 \\ \hline \multirow{6}{*}{Disseminated ones} & TZZK3-5 & \multirow{2}{*}{6.6} & 37.619 & 15.480 & 17.297 \\  & XTS-37-41 & & & & \\ \cline{1-1}  & TZZZK3-4 & & & & \\ \cline{1-1}  & XTS-32-36 & & & & \\ \cline{1-1}  & ZK317 & 4.5 & 37.745 & 15.520 & 17.586 \\ \cline{1-1}  & TS-21-25 & & & & \\ \cline{1-1}  & TS\(\oslneq\)2K2-43 & & & & \\ \cline{1-1}  & TS/ZK1-8 & & & & \\ \cline{1-1}  & XTS-42-45 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Sulfur isotopic compositions and lead isotopic ratios of pyrite in the Xiawolong gold deposit. Figure 9: Calculated \(\delta\)D and \(\delta^{18}\)O values of ore-forming fluids in the Xiawolong gold deposit. Data for the areas of magmatic water of the Kunyushn granite, magmatic water of the Sanfoshan granite, metamorphic water of the Jinshan Group, and the “Jiaoja-type” and “Linglong-type” gold deposits are from [20; 61] and references therein. Adapted with permission from Ref. [20]. 2017, Elsevier andRef. [61]. 2014, _Acta Petrol. Sin._that the ore-forming fluids were derived from these rocks. Furthermore, the \(\delta^{18}\)O and \(\delta\)D compositions possess a narrow region, without an obvious linear decreasing or increasing trend, as shown in Figure 9, which may indicated that during the ore-forming stage, no water-rock interaction and/or mixing with another source fluid occurred. This is consistent with the fact that no hydrothermal alteration, fault, or fracture developed in the Xiawolong gold deposit. Therefore, it is logical to conclude that the ore-forming fluid in the Xiawolong gold deposit is likely of a magmatic source. The type 1 aqueous inclusions have a eutectic temperature of 58.4 to \(-\)51.2 \({}^{\circ}\)C, indicating the existence of CaCl\({}_{2}\) in the fluid [62]. The identification of daughter minerals, such as sylvite and CO\({}_{2}\) in fluid inclusions, proves that KCl and CO\({}_{2}\) are important components. As a result, the ore-forming fluid of Xiawolong gold deposit should be ascribed to the NaCl-CaCl\({}_{2}\)-KCl-CO\({}_{2}\)-H\({}_{2}\)O system. Middle-high temperature mineral assemblages, such as molybdenite and magnetite, are usually associated with gold-bearing pyrite in disseminated and stockwork-style fine-grained granitic ones in the Xiawolong gold deposit. Furthermore, the type 3 daughter mineral-bearing inclusions are represented by high temperature (416 to 439 \({}^{\circ}\)C) and high salinity (32.87 to 28.59 wt.% NaCl equiv.