## 3 Ore Deposit Geology  
The Hongtoushan deposit is a notable Archean VMS Cu-Zn deposit located in the Hunbei district. The local residents began surface mining in the early 1930s, and large-scale underground operations commenced in the 1960s after systematic drilling. The deposit holds a metal reserve of 0.5 Mt Cu with grades of 1.5-1.8%, 0.7 Mt Zn with grades of 2.0-2.5% and 20 t Au with grades of 0.5-0.8 g/t [11]. The mining operations have reached a depth of 1337 m [44]. The primary ore deposits in the region are confined within the \"rhythmic member\" of the upper section of the Hongtoushan formation, which comprises seven layers. These layers include: (1) a 12 m thick layer of biotite gneiss and quartz-feldspar gneiss with intercalations of plagioclase hornblende gneiss; (2) a 25 m thick layer of garnet quartz plagioclase gneiss intercalated with granulite; (3) a 20 m thick layer of plagioclase amphibie gneiss and biotite plagioclase gneiss intercalations; (4) a 20 m thick layer of plagioclase hornblende gneiss intercalated with thin biotite plagioclase gneiss; (5) a 20 m thick layer of biotite plagioclase gneiss with plagioclase hornblende gneiss; (6) a 10 m thick layer of plagioclase hornblende gneiss and biotite plagioclase gneiss; and (7) interbedded plagioclase hornblende gneiss (Figure 2A). The surrounding rocks comprise mainly amphibite gneiss, sillimanite-biotite gneiss, and biotite-plagioclase gneiss. The protoliths are believed to be basic-intermediate acid volcanic rocks and sedimentary rocks within volcanic formations [45]. The Archean Qingyuan greenstone belt has undergone multiple episodes of deformation, metamorphism, intrusion by granites, and mignatization, resulting in the Hongtoushan VMS deposit having a highly intricate structure. Above a depth of \(-\)467 m, the ore bodies exhibit a Y-shaped geometry, with two eastward-extending branches merging westward into a single ore zone (Figure 2B). According to previous research results [37], three periods of tectonic deformation have been identified in the Hongtoushan VMS deposit: (1) In the initial phase, the north-south tight fold was generated in response to the east-west extrusion force. (2) Following this, the north-south extrusion force led to the formation of the east-west plunging vertical fold in the subsequent stage. Under tectonic compression, the original ore body migrated from the limbs towards the hinge zone, resulting in the thickening and upgrading of the ore body and the formation of the \"ore pillar\". (3) Lastly, driven by east-west extrusion and north-south torsion, the third stage culminated in the development of the north-south open fold. Fold deformation not only transforms the morphology of the ore bodies but also playsa crucial role in controlling and hosting the mineralization, leading to the remobilization and enrichment of the ore-forming elements. The ores in the Hongtoushan deposit have been generally classified by previous researchers into two main types: massive ore and disseminated ore. These two ore types exhibit distinct differences in their mineralogical composition and textural characteristics [13]. The primary ore minerals include pyrite, pyrrhotite, sphalerite and chalcopyrite, accompanied by minor occurrences of magnetite, galena, molybdenum, argentite and electron. The gangue mineral assemblage comprises quartz, plagioclase, biotite, phlogopite, sercite, garnet, gahnite and sillimanite. The ore bodies have undergone extensive wall rock alteration, which is manifested by tremolitation, phlogopitization, sericitization, silicification, chloritization and carbonation. The pervasive high-grade metamorphism and deformation have significantly obliterated the primary sedimentary structures, posing challenges in deciphering the original depositional environment. To better understand the mineralogical  
Figure 2: (**A**) Stratigraphic column of Hongtoushan VMS deposit (after [PERSON], (2005) [37]); (**B**) Stereoscopic map of the ore body of the Hongtoushan VMS deposit (modified by [PERSON], 2010 [45]) Legends: 1.