## 2 Geological Background
### Deposit Geology  
The Jiaojia gold deposit is located in the northwestern Jiaobei Terrane. The strata in the area include the Jiaodong Group and Quaternary strata (Figure 2). The Jiaodong Group primarily comprises tonalite-trondhjemite-granodiorite gneiss, with formation ages of 2.9 Ga [2]. The mining area is controlled by brittle faults, such as the Jiaojia fault, which is a first-level ore-controlled structure. The Jiaojia fault has a strike of 30\({}^{\circ}\) and a north-westward dip. The secondary ore-controlling structures are NE-oriented strikes that run approximately parallel to the first-level ore-controlled structure known as the Wangershan fault [11]. There are many magmatic rocks within the mining area, including Late Jurassic Granite (Linglong pluton), Early Cretaceous Granodiorite (Guojialing pluton), and Late Mesozoic dikes. The dikes include lamprophyre, diabase, diorite, and quartz-diorite. The gold ore bodies at Jiaojia are primarily emplaced in the Linglong Pluton, which is associated with lamprophyre and diorite-porphyriny dikes. There are five main ore bodies in the Jiaojia gold deposit (I, II, III, IV, and V) (Figure 2) [11]. The ore bodies are distributed in foliated altered cataclastic rocks near first-order faults and are stratified, lens-like, vein-like, and fusiform. They spread with an NE orientation of 10\({}^{\circ}\)-50\({}^{\circ}\), NW and SE trends, and a dip angle varying from 16\({}^{\circ}\) to 90\({}^{\circ}\). Wall-rock alterations are widely developed in Jiaojia. The alteration zones, distributed on both sides of the ore body, include the pyritized phyllite zone, k-feldspar alteration zone, sericitization zone, albitization silicification, carbonization, and chloritization. The main fault zone exhibits asymmetric alteration characteristics in the hanging wall and footwalls. Locally, vein-like occurrences of sericitized rock crosscut the K-feldspar alteration zone, with residual fragments of K-feldspar-altered granite within  
Figure 1: (**a**) Diagram of the North China Craton. (**b**) Geological map of the Jiaodong gold province [2]. the sericitization zone. The alteration of the footwall is uniformly intense and extensive, with alteration zone widths varying from several tens to hundreds of meters. Carbonatization, often superimposed on early mineralization alterations, occurs during the late mineralization stage (Figure 3). Figure 3: Characteristics of surrounding rock alteration in the Jiaojia gold deposit. (**a**) Pyrite–quartz stage (stage I) along with wall–rock k-feldspar alteration. (**b**) Quartz–pyrite stage (stage II) developing in sericitizated rock. (**c**) The polymetallic sulfide stage (stage III) along with silicification and sericitization. (**d**) Quartz–carbonate stage (stage IV). (**e,f**) The specimen of ore. Cal = calcite, Py = pyrite, Gn = galena, Qtz = quartz. Figure 2: (**a**) Simplified geological map of the Jiaojia gold deposit [32]. (**b**) Geological cross-sections along line 112 in the Jiaojia gold deposit [33]. The ore minerals are native gold, pyrite, chalcopyrite, galena, sphalerite, and hematite, with minor pyrrhotite and arsenopyrite. The gangue minerals were sericite, quartz, calcite, and K-feldspar, with minor chlorite and apatite (Figure 3). Mineralization occurred during four stages of precipitation: (1) The Pyrite-Quartz-Sercite Stage (Stage I) included quartz, sericite, and a small amount of pyrite (Figure 4a). (2) The Quartz-Pyrite Stage (Stage II) developed smoky-gray quartz and euhedral pyrite (Figure 4b). The native gold was filled within pyrite fractures. (3) The Quartz-Polymetallic Sulfide Stage (Stage III) developed polymetallic sulfides, including pyrite, chalcopyrite, galena, sphalerite, and magnetite (Figure 4c-d). Native gold occurs as fracture filling in pyrite and/or enclosed in the pyrite (Figure 4e). and (4) The Quartz-Carbonate Stage (Stage IV) developed the main minerals of quartz and carbonate, cutting the quartz in vein structures, with scattered occurrences of pyrite (Figure 4f).