## 4 Characteristics of Copper-Tin Mineralization  
The newly revealed copper-tin mineralization mainly appears in the Xinglongshan ore section. [PERSON] [10] found a large amount of tin mineralization in the NW-trending ore body and drill core at level 625 of the Xinglongshan ore section. The massive lead-zinc ore at level 625 contains copper (5.67%) and tin (2.35%), and the Cu and Sn grades in the Cu-rich ore in the drilling hole are 12.98% and 4.75%, respectively. There is a lack of Cu-Sn mineralization in the NE-trending ore body. [PERSON] [22] further divided the NW-trending silver polymetallic vein group into silver-copper polymetallic ore bodies developed on the hanging wall of the ductile shear zone and silver-lead-zinc polymetallic ore bodies on the football, with the silver-copper polymetallic ore bodies being the main tin-bearing ore  
Figure 2: Geological plan of Xinglongshan ore section in the Shuangjianzishan deposit **(a)**; typical profile **(b)** (modified after [21]).  
bodies. Tin mineralization is marked by the occurrence of large quantities of confieldite and cassiterite, accompanied by assemblages of medium- and high-temperature minerals such as chalcopyrrite, arsenopyrite, and wolframite. The selenite-rich confieldite is coeval with sphalerite and galena, and cassiterite is mainly produced in fine grains or fine columns, often parceled by sphalerite, galena, and chalcopyrite (Figure 3d), or may be produced in cassiterite-quartz veins. [PERSON] [11] pointed out that copper mineralization developed sporadically around \(-300\) m and developed on a large scale at a depth of \(-700\) m, and the spatial pattern of change in the vertical direction is as follows: \(-400\) m to the surface is dominated by fine-veined, low-dipping Py-Pb-Zn veins; between \(-400\) and \(-900\) m is characterized by thicker veins, high-dipping, or near-erect Pb-Zn veins; and there are lead-zinc-copper ore bodies below \(-900\) m. From west to east on the plane: At the same elevation, relatively high-temperature Cu-Sn assemblages are more developed in the western part of the mine than in the eastern part of the drill core. Copper ores are produced in massive (Figure 3a), disseminated (Figure 3b), brecciated (Figure 3c), and vein structures. The metallic minerals are mainly chalcopyrite, sphalerite, galena, pyrite, and arsenopyrite. Chalcopyrite in hand specimens is often coeval with quartz, chlorite, and calcite. Microscopic chalcopyrite is often metasomatized for by galena, sphalerite, etc. (Figure 3f), or chalcopyrite is distributed in sphalerite as an emulsion texture (Figure 3e), but it is not the focus of this study.  
Figure 3: Copper-tin mineralized hand specimen and microscopic characteristics of the Shuangjianzishan silver polymetallic deposit. (**a**) Massive structure; (**b**) dense disseminated structure; (**c**) brecciated structure; (**d**) chalcopyrite is replaced by sphalerite and cassiterite is parceled by chalcopyrite; (**e**) chalcopyrite is distributed in sphalerite as emulsion texture; (**f**) chalcopyrite and arsenopyrite are replaced by galena and sphalerite. Apy—arsenopyrite; Ccp—chalcopyrite; Sp—sphalerite; Gn—galena; Cst—casiterite; Q—quartz.