## 2 Regional Geology  
The Hongtoushan Cu-Zn VMS deposit is located in the Qingyuan granite-greenstone belt, which is part of the North China Craton (NCC). The NCC consists of a metamorphic basement that ranges from the Archean to Paleoproterozoic ages, and is overlain by unmet-morphosed cover rocks that range from the Mesoproterozoic to Cenozoic. The metamorphic basement rocks have ages ranging from 3.8 to 3.2 Ga [28; 29; 30]. The Neoarchean metamorphic rocks are mainly composed of tonalite-trondhjemite-granodiorite (TTG) genisses with ages of 2.6-2.5 Ga, syntectonic granites at ~2.5 Ga, and various supracrustal rocks that underwent greenschist to granulite facies regional metamorphism and polyphase deformation around 2.5 Ga [31; 32; 33]. The NCC is divided into two major Archean to Paleoproterozoic blocks, the Eastern and Western Blocks, separated by the Paleoproterozoic Trans-North China orogenic belt [34]. The Qingyuan greenstone belt, comprising 60-70% Neoarchean plutons and 30-40% supracrustal rocks, is situated at the northern margin of the Eastern Block [35; 36] (Figure 1).  
Figure 1: (**A**) The distribution of the basement in the North China Craton. (**B**) The distribution of Archean–Paleoproterozoic exposed basement in the North China Craton. (**C**) The regional geological map of the Qingyuan Greenstone belt (modified after [PERSON] et al. 2005 [37]). Legends: 1, Sinian System. 2, Cambrian–Ordovician. 3, Liaohe Group. 4, Nantianmen Formation. 5, Shipengzi Formation. 6, Hongtoushan Formation. 7, Mixed granite. 8, Charnockite. 9, Flake and gneissic mixed granite. 10, Granite. 11, Granite migmatite. 12, Remote sensing interpretation area. 13, Large-scale linear structure. 14, Secondary linear structure. 15, Geological boundary. 16, Presumed lithofacies Boundary. 17, Copper (green points) iron (red points) gold (yellow points) ore deposits (points). 18, Position of Hongtoushan VMS deposit. red 19, The location of Beijing.  
The Qingyuan Group, which is older than 3.0 Ga, experienced upper amphibite facies metamorphism between 2.9 and 2.8 Ga [38; 39]. The medium- to coarse-grained Neoarchean Precambrian basement in Qingyuan mainly comprises TTG gneiss, and is divided into the Hunbei and Hunnan terranes by the Hunhe fault [39; 40]. The supracrustal rocks are further subdivided into the Shipengzi, Hongtoushan, and Nantianmen formations, which underwent amphibite to granulite facies metamorphism [38]. Over 100 occurrences of mineralization have been found within the Hunbei greenstone belt, with the Hongtoushan deposit being the largest VMS deposit in the area. Impermeable volcanic layers control the size and location of the Cu-Zn mineralization in the region. All VMS deposits in the area are confined to a 100 m thick stratigraphic interval within the upper part of the Hongtoushan Formation. This unit, termed the \"rhythmical member\" by local geologists, is primarily composed of alternating layers of biotite plagioclase gneiss and hornblende plagioclase gneiss [41].  
Regional tectonic evolution played a crucial role in controlling the formation of the Hongtoushan deposit. Previous studies have shown that the regional extensional tectonics during the late Paleoproterozoic to early Neoproterozoic led to basic magmatism, creating favorable volcanic environments and hydrothermal systems [35]. The regional metamorphism and granitic intrusions in the late Neoarchean may have promoted the activation and enrichment of ore-forming elements [42; 43].