## 5 Discussion  
### Timing of Au Mineralization  
The abovementioned petrographic observations detail that molybdene coexists with gold-bearing pyrite, galena and native gold (Figure 3), suggesting that the gold and molybden were precipitated from the ore-forming fluid simultaneously. Therefore, the molybden weighted average Re-Os model age of 118 \(\pm\) 1.7 Ma in this study should represent the timing of Au mineralization in the Xiawolong gold deposit. However, this molybden Re-Os mode age at Xiawolong is about 4 m.y. older than the 114.2 \(\pm\) 1.5 Ma monazite age for the Rushan gold deposit, about 20 km southwest of the Xiawolong gold mine (Figure 2a), dated by Ref. [67]. As mentioned above, focusing on the perspective of the whole eastern Jiaodong, i.e., the Muping-Rushan gold metallogenic belt, the other gold deposits, except for the Xiawolong gold deposit, i.e., the \"Linglong-type\" gold deposits, are controlled by a series of sub-parallel NE- to NNE-trending faults, named the Muping-Rushan Fault Zone (Figure 2a), and are composed of gold-bearing quartz veins with the alteration envelopment of silicification in the outer domain and sericitization in the inner [1, 68, 69, 70]. Of them, the Rushan gold deposit, endowed with the largest gold resource hosted by a single fault-controlled gold-bearing quartz vein in China, is the representative one of the \"Linglong-type\" deposits in eastern Jiaodong [71]. During the last few decades, much age data, including those by pyrite/K-feldspar Rb-Sr [72, 73], sercite \({}^{40}\)Ar/\({}^{39}\)Ar [74, 75, 76] and the hydrothermal zircon U-Pb [47], have been presented for the Rushan gold deposit. However, for the Jiaodong gold ores, due to the complex mineral growth history [77], the low Rb contents in the hydrothermal K-feldspar and pyrite [78, 79], as well as the issue of whether the zircon analyzed is crystallized at relatively low temperatures from ore-forming fluids or from the surrounding igneous rocks, is very difficult to identify [67]. A large spread of ages ranging between 121 Ma and 105 Ma was produced for those by pyrite/K-feldspar Rb-Sr [72, 73] and the hydrothermal zircon U-Pb [47]. Although the high-precision \({}^{40}\)Ar/\({}^{39}\)Ar dating for hydrothermal sercite has been deemed an effective dating technique for Jiaodong gold deposits recently [67, 77], the conflicting \({}^{40}\)Ar/\({}^{39}\)Ar ages for Rushan based on hydrothermal sercite, including those first reported to be ca. 109-108 Ma [75] and ca. 129 Ma [76], and more recently ca. 112-117 Ma [71] and ca. 120 Ma [77], indicate that, at least in part, it is very difficult to determine truly the syngold hydrothermal sercite without suffering later modification. Fortunately, with careful microscopic research with SEM and BSE imaging as well as electron probe microanalysis, trace amounts of syngold hydrothermal monazite, which was considered to be the robust chronometer [80, 81, 82, 83], was identified by [PERSON] et al. [67], who obtained the 114.2 \(\pm\) 1.5 Ma monazite age for Rushan using the LA-ICP-MS U-Pb in situ dating method and proposed that the ca. 114 Ma age is the most robust age for gold mineralization in eastern Jiaodong. In addition, molybden Re-Os dating is also a robust method, which can be applied to determine the mineralization age accurately and directly [84, 85, 86, 87]; thus, the molybden weighted average Re-Os model age of 118 \(\pm\) 1.7 Ma for Xiawolong in this study is highly precise and reliable. Furthermore, this giant gold event in Jiaodong, accompanied by rapid crustal exhundation, had a significantly shorter duration of over only a few million years [67, 77]. Therefore, the new molybden weighted average Re-Os model age obtained in this study suggests a gold event occurring ca. 4 m.y. before the other \"Linglong-type\" gold deposits in eastern Jiaodong. In addition, [PERSON] et al.