## 2 Geological Setting and Ore Deposit Geology
### Ore Deposit Geology  
The Xiawolong gold deposit, 20 km or so northeast of the Jinqing gold deposit, is situated along the contact between the Sanfoshan granitic pluton and the Kunyushan granitoid in the southeast part of the Muping-Rushan gold metallogenic belt (Figure 2). It is dominated by Kunyushan monozogranite, where both the UHP metamorphic rocks and Paleoproterozoic Jingshan Group metamorphic rocks occur as discrete ellipsoidal xenoliths, as well as the Sanfoshan granitic pluton (Figure 3a-c). The Sanfoshan granitic pluton, a sheet-like NNW-trending intrusive body of medium- to fine-grained monzonite, intrudes the medium- to coarse-grained Kunyushan monozogranite (Figures 2 and 3a) and shows abrupt contact with the host rock (Figure 3d). The gold orebodies are hosted in the fine-grained granite, which mainly occurs as concealed dikes (Figure 3a-c). However, a few outcrops, showing abrupt contact with the medium- to coarse-grained Kunyushan monozogranite (Figure 3e), can be observed locally. Four fine-grained granite dikes, named I#, II#, III#, and IV#, are recognized based on a systematic drill hole in the Xiawolong gold mine (Figure 3a-c). They strike E-W, dip 20 to 50\({}^{\circ}\) to the S, and show varied thicknesses between 10 and 80 m (Figure 3a-c). No baked margins are observed at the contact between the Kunyushan monozogranite and fine-grained granite dike. The latter is generally fresh and non-deformed, where almost no alterations, faults, or fractures develop (Figure 3f). A total of 19 gold orebodies have been discovered in the Xiawolong gold mine to date. All of them are concealed with a lens shape, and most are located in the middle of the fine-grained granite dikes, with only a few in the lower or upper margins (Figure 3b,c). Lode II-1#, hosted in the II# fine-grained granite dike, is the main orebody and is approximately 366 m long, which accounts for 67% of the proven resource. It usually strikes 270 to 285\({}^{\circ}\) and dips 20 to 28\({}^{\circ}\) (average 25\({}^{\circ}\)) SW, showing the roughly S-shaped, vein-like lenses (Figure 3b,c). It has variable thickness ranging from 0.91 to 2.85 m (average 1.17 m), extending from the +44 m level down to below the \(-\)70 m level. The gold grade ranges between 1.5 and 52.6 g/t with an average of 11.47 g/t gold. All the gold orebodies in the Xiawolong gold mine are characterized by the disseminated and stockwork-style ores developed in the fresh fine-grained granite dikes (Figure 4a-c). The gangue minerals comprise K-feldspar, calcite, quartz, biotite, and plagioclase (Figure 4d-f), and the ore minerals mainly consist of include pyrite, magnetite, pyrrhotite, molybden, and chalcopyrite, with minor quantities native gold and electron (Figure 4g-l). Calcites mostly occur as subhedral fine-grained grains intergrown with quartz, K-feldspar, and plagioclase (Figure 4d). In general, the euhedral fine-grained pyrite is associated with the subhedral and anhedral quartz, biotite, and K-feldspar (Figure 4e-g), with the K-feldspar grain hosted in pyrite (Figure 4f). It is also common that the anhedral pyrite is intergrown with quartz (Figure 4h), which is associated with anhedral magnetite,pyrrhotine, chalcopyrite, and molybden (Figure 4i-k). Gold is the only economically viable element, and other elements such as S, Cu, and Mo are all sub-economic. The most important gold-bearing mineral is pyrite, followed by magnetite, pyrrhotite, chalcopyrite, and molybden. The gold is fine-grained (56%) and medium-grained (44%) gold, and mainly occurs on the margins of the individual grains (60%) (Figure 4l) or as inclusions in pyrite and other sulfides (35%), with only a few as filling microfractures in pyrite (5%). Figure 4: Photographs of (**a**,**b**) disseminated and (**c** fine-grained granite dikes.