## 2 Geological Overview
### Geological Features of the Study Area  
The Paleozoic strata of the study area belong to the Xilamulun Stratigraphic Zone, with the northern part extending into the Zhongdong Ujumqin Stratigraphic Subzone of the Inner Mongolia-Xing'an Stratigraphic Zone. The lower Paleozoic is poorly developed, being eroded by plutons and covered by Mesozoic strata, with only sporadic exposures. The Carboniferous-Permanian strata are well developed and are the main ore-bearing strata, where the primary ore deposit type is magmatic hydrothermal. The Mesozoic strata belong to the Inner Mongolia-Songliao Stratigraphic Zone, specifically the Zhonglian Stratigraphic Subzone, where the Cretaceous is the most developed and widespread throughout the region. The Paleogene-Neogene strata are located in the Inner Mongolia Stratigraphic Zone, in the Xilingol Stratigraphic Subzone, mainly consisting of the Neogene Baogeda Ula Formation. The Quaternary is the most widely distributed, located in the Northeast Stratigraphic Region, Inner Mongolia Stratigraphic Zone, Erin-Genghe Stratigraphic Subzone (Figure 2).  
Figure 1: Geological sketch of the Southern Great Hinggan Mountains and distribution map of ore deposits: (**a**) tectonic setting; (**b**) regional geological map [10].  
The main tectonic features of the study area are folds and faults. The folds are primarily composite folds--oriented NE or NEE, formed during the Late Hercynian orogen. The faults mainly result from the NW-SE compressional folding of the strata during the Late Hercynian, creating reverse faults predominantly oriented NE-NEE. During the subsequent Yanshan period, the NE-oriented faults from the Late Hercynian were inherited and further developed [12; 13].  
Throughout the long geological history, regional tectonic movements have led to frequent and intense magmatic activity in the area. The intrusive rocks are characterized by multiple phases, types, and widespread distribution, extending from the northeast to the southwest across the study area. From the Late Paleozoic to the Mesozoic, intrusive rocks of mafic, intermediate, and felsic compositions have developed, generally exhibiting NE to nearly E-W orientations.  
Late Paleozoic intrusions are mainly distributed in the southwest and northeast of the study area, while Mesozoic intrusions are found in the central and eastern parts of the area. In terms of magmatic activity periods, the intrusive rocks in the study area experienced three tectonic-magmatic phases: the Hercynian, Indosinian, and Yanshan periods  
Figure 2: Regional geological map of the study area [10].  
(Figure 2). The Hercynian intrusive rocks mainly include Middle Devonian quartz diorite, Late Devonian granite diorite, and diorite; Early Carboniferous granite diorite, biotite granite, Late Carboniferous pyroxenite, diorite, hornblende diorite, diorite, granite diorite, and biotite granite; Early Permian hornblende diorite, biotite granite, and Middle Permian diorite, hornblende diorite, diorite, and quartz monzonite. The Indosinian intrusive rocks mainly include Middle Triassic medium-grained porphyritic biotite granite, Middle Triassic fine-grained porphyritic biotite granite, and Late Triassic fine-grained biotite granite. The Yanshan intrusive rocks mainly include Early Cretaceous fine-grained porphyritic granite and medium-grained porphyritic granite [10].