## 5 Discussion
### Constraints on the Origin of Au Mineralization in the Xiawolong Deposit  
As mentioned above, all the gold orebodies in Xiawolong are hosted by the fine-grained granitic dikes, which have abrupt contact with Late Jurassic Kunyushan monzogranite with an emplacement age of 161-141 Ma. The zircon LA-ICP-MS U-Pb dates reported in this paper produce the first precise geochronology on the fine-grained granite and give the emplacement ages of 118 \(\pm\) 2 to 117 \(\pm\) 2 Ma, which are consistent with those of molybden Re-Os, within the margin of error, obtained for the gold-bearing ones in Xiawolong. In addition, the fine-grained granitic dikes have a similar lithology as those of the medium-grained monzogranite consisting of the marginal facies of the Sanfoshan batholith [15]. One monzogranite sample SD-11, located about 15 km south of the Xiawolong deposit (Figure 1) from the marginal facies was dated at 118 \(\pm\) 1 Ma by [PERSON] et al. [15] using the zircon SHRIMP U-Pb method, which is identical to those of LA-ICP-MS zircon U-Pb dated for the fine-grained granite in this study. Although no other zircon U-Pb dates for the central phase of the Sanfoshan batholith have been reported up to now, [PERSON] et al. [39] suggested that resulting from the abrupt change in the subduction direction of Paleo-Pacific plate under East China at ca. 120 Ma, the catastrophic lithospheric thinning accompanied with the late Early Cretaceous igneous magmatism occurred in Jiaodong, and thus the earliest emplacement timing for the Sanfoshan batholith is no earlier than 120 Ma. Therefore, it is reasonable that the fine-grained granite dike in Xiawolong is the crystallization product of granitic magma, related to the Sanfoshan batholith (Figure 8) in the late stage, considering that the fine-grained granite dikes are the branches of the Sanfoshan granitic pluton [19]. The previous research on the fluid inclusion and O isotopic composition suggests that the ore-forming fluid for the Xiawolong deposit is from magmatic water [20], which accords with the geologic characteristics at different scales. For example, the gold-bearing pyrite coexists with the magnetite and molybdenite in the gold ores, and the ores are characterized by the disseminated and stockwork-style. As well, no hydrothermal alteration occurs adjacent to the gold orebodies. Although the S and Pb isotope compositions indicate they mainly come from the Mesozoic Kunyushan granitoids [20], the large temporal gap between the gold mineralization and granite emplacement precludes the direct genetic relation between gold deposition and Kunyushan granite. Nevertheless, the O isotopic compositions indicate that the ore-forming fluid results from Sanfoshan granitic magma degassing during the magmatic-hydrothermal transition stage [20]. Furthermore, the occurrence of magnetite in the gold ores indicates the high oxygen fugacity (FO\({}_{2}\)) of both the magma and resultant hydrothermal fluids. During magma migration, the former would be able to scavenge and carry significant amounts of Au [91; 92], with the latter facilitating the transport of Au effectively during the magmatic-hydrothermal transition stage [91], which is similar to the Au transportation mechanism for the Zhongshangou gold deposit, hosted within the monzonite, in the Zhangjiakou orefield north of the NCC margin [93]. However, the change in FO\({}_{2}\) would result in significant Au precipitation during the fluid migration, as has been evidenced from the studies on the Panasqueira W-Sn deposit of Portugal [94; 95]; the W-Mo-Au deposit in San Judas Tadeo, southeastern Peru [96]; the Saint-Robert W-Bi-Ag deposit in Quebec [97] and the Lujing uranium field hosted within fine-grained granite in the Nanjing metallogenic belt, south China [98]. Overall, it is logical to infer that the Xiawolong gold deposit is genetically related to the Sanfoshan granitic magmatism, which occurred during the regional tectonic extensional process shifting from E-W to NW-SE induced by the Paleo-Pacific slab rollback initiated in ca.