## 2 Geological Background  
The giant Jiaodong gold province is located at the eastern margin of the North China Craton, east of the Tan-Lu Fault Zone (Figure 1). It consists of the Jiaobei Terrane to the northwest and the Sulu Ultra-High-Pressure Metamorphic Belt to the southeast, bounded by the Wulian-Yantai lithospheric fault. As a consequence of the subduction of the Paleo-Pacific plate, the Jiaodong Peninsula suffered extensive and intense magmatic activities  
Figure 1: (**a**) Schematic map showing the position of the North China Craton. (**b**) Geological map of the Northwestern Jiaodong Peninsula (Modified from [57; 63]). and crustal deformation during the Mesozoic, accompanied by large-scale gold mineralization [52; 62]. The Jiaobei Terrane endows most of the gold reserves of the Jiaodong Peninsula, with basement rocks primarily comprising the Neoarchean Jiaodong Group and the Paleoproterozoic Jingshan and Fenzishan Group (Figure 1). Mesozoic magmatism in the region is widely distributed and is mainly grouped into (1) Late Jurassic granitoid associated with partial melting of the lower crust including Longlong, Kunyushan, Luanijahe, etc. ; (2) Early Cretaceous granitoid genesis from crust-mantle interactions, represented by Guojialing granitoid [64]; and (3) widely intruded mafic-felsic dykes. The vast gold mineralization is principally manifested as auriferous-quartz vein type and disseminated-/stockwork-type, with a peak age of \(\sim\)120 Ma [52]. The Xiadian gold deposit is located in the southern part of the Zhaoping regional detachment fault zone (Figure 1). There are different lithologies in the hanging wall and football of the Zhaoping fault (Figure 2), of which the former is dominated by the metamorphic rocks of the Jingshan Group and Jiaodong Group, and the other comprises Late Jurassic Linglong granite and a few metamorphic breccias. Figure 2: Geological map of the Xiadian gold deposit. The location of representative sections (Figure 3a,b) are also shown. At Xiadian, gold mineralization is spatially endowed predominantly in the football of the Zhaoping fault zone (Figure 3). The Zhaoping fault, marked by the dark fault gunge, is mainly NE- and NNE-striking, yet locally N-S striking, with variable dips between 35\({}^{\circ}\)-55\({}^{\circ}\) (average 45\({}^{\circ}\)). The fault underwent brittle-ductile deformation, with a several-meter-thick mlynolite and alteration zone developed proximal to the fault [26, 65]. During the mineralization period, the Zhaoping fault ordinary demonstrated a dextral strike-slip normal sense of movement, with NE-SW compression and NW-SE extension as the dominant tectonic regimes [54], reflecting vertical compressive and horizontal tensional stresses. The deformation of the Zhaoping fault controls the localization of hydrothermal alteration-mineralization showing that (1) the majority of gold orebodies are located in the footwall of the Zhaoping fault, (2) the hydrothermal alteration-mineralization zone is distributed along the fault (Figure 3a), and (3) the occurrence of orebodies is related to the fault geometry (Figure 3b). Gold orebodies in the Xiadian district mainly include Nos. 2, 7, Daobeizhuangzi (DBZZ), and Jiangjiayao (JJY). They are dominantly lenticular, pillar, vein-like, and discontinuous, with a NE-plunging ore shoot extending ~1400 m with an average gold grade of 3.4 g/t. Gold mineralization at Xiadian is closely associated with quartz-pyrite-sericite alteration and shows the disseminated and stockwork characteristics, with minor auriferous quartz veins in the steeply brittle fractures. Gold is mostly observed as \(\upmu\)m-scale electrum gains in the microcracks of sulfides, or as inclusion in sulfide minerals. Previous geochronological studies recorded a mineralization age of ~120 Ma at Xiadian, comparable to most gold deposits within the Jiaodong Peninsula. This period occurred with the rollback of the Paleo-Pacific Plate, leading to a transformation in the tectonic regime of the Jiaodong Peninsula from regional compression to extension [54, 64].