## 3 Volcanic Rock Geology and Sample Characteristics  
Volcanic rocks and pyroclastic rocks are widely distributed in the Fuyun-Qinghe area and its vicinity. Volcanic rocks are found in thick layers in the field, primarily belonging to the Beitashan Formation as defined by previous researchers. Some parts of the rocks have undergone significant alteration, while the majority remain relatively fresh. Alteration is characterized by epidotization and chloritization (Figure 3a), a common phenomenon in the study region, particularly developed in mining areas such as the Qiaoxiahala and Laoshankou deposits. Volcanic rocks near the Ulungu River and the Qiaoxiahala mining area exhibit obvious orientations and developed cleavages. In the Qiaoxiahala mining area, strong cleavage and pronounced orientation are evident in the wall rocks where they contact the volcanic rocks. Although the overall deformation of the volcanic rocks is not pronounced, they exhibit a clear orientation. The overall degree of weathering is relatively weak, while epidotization alteration is pronounced. Closer to the ore body, the alteration becomes more severe, with heavier epidotization on rock fracture or joint surfaces. Away from the ore body or mineralization sites, epidotization is still present but much weaker. This suggests that the formation of the deposit was accompanied by fluids or hydrothermal solutions rich in epidotization. Additionally, some volcanic rocks contain relatively fresh diorite porphyry or diabase porphyry veins, which also exhibit epidotization. There is no distinct condensation or baking edge where the vein rocks contact the volcanic rocks, indicating that the vein rocks formed concurrently or slightly earlier than the orebody but later than the volcanic rocks. Local volcanic rocks include xenoliths, where epidotes are notably abundant, even forming individual rocks. Therefore, it is speculated that the volcanic rocks in this area originated from marine eruptions. Figure 3: Field characteristics of volcanic rocks in the Fuyun–Qinghe area. (**a**) Epidotized volcanic rocks in Qiaoxiahala, (**b**) hornblende phenocrysts are oriented, (**c**) breccia in volcanic rocks, (**d**) quartz veins in cleavage zones. On the north bank of the Ulungu River, near Kurt town, numerous directionally aligned hornblende grains appear in the phenocrysts of volcanic rocks. Some hornblende grains exhibit elongation (Figure 3b), with phenocryst particles becoming progressively larger towards the south. Breccia is present in certain volcanic rocks (Figure 3c), and quartz veins are visible in the cleavage zones (Figure 3d). The collected samples primarily consist of basaltic to andesitic volcanic rocks and pyroclastic rocks (Figure 4). Some sample characteristics are described as follows:  
Sample FY-80611, basalt (named from field and petrography, hereinafter the same), was collected from the hillside behind the eastern mining pit in the Qiaoxiahala mining area, Fuyun County (N46\({}^{\circ}\)48\({}^{\prime}\)60\({}^{\prime\prime}\), E89\({}^{\circ}\)38\({}^{\prime}\)39\({}^{\prime\prime}\)). The basalt is blue-gray in color and exhibits a porphyritic texture and a massive structure (Figure 4a). The phenocrysts are mainly hornblende (-8%, 0.5-1.5 mm), with long plate-like plagioclase (-10%, 0.3-1.5 mm), and a small amount of pyroxene (-5%, 0.5 mm). The hornblende grains are euhedral and long columnar in shape, and show chloritization, while the plagioclase grains are euhedral to subhedral and have undergone sericitization and kaolinization. The groundmass shows tholeiitic texture and is composed of plagioclase microcrystals, hornblende microcrystals, opaque minerals, microcryptcrystalline grains, and glassy materials (Figure 4b). Sample FY-80615, andesite, was collected from the same site as sample FY-80611. The andesite is dark gray in color, with calcite veins visible in the hand specimen. The sample exhibits a porphyritic texture and a massive structure (Figure 4c).