Volcanic-hosted Au-base-metal metasomatite. The basement rocks in the mine and in the area are metamorphic sequences of the Archean Wutai, Shizhui, Zhuangwang groups and the Archean Hengshan Complex. Mesozoic moderate-felsic igneous rocks intruded the area as small, varied shaped, hypabyssal intrusions accompanied by varied dykes and explosive pipes. Several veined zones, consisting of altered fault breccias and filled gold-bearing base metallic quartz veins, have been recognized in the area. The ore bodies are usually vein-, cake- and plate- shaped, and are strictly controlled by shear-fault zones. The ores are of idiomorphic-hypidiomorphic, xenomorphic-irregularly grained and fractured and crashed breccia textures and of massive, veined, banded and veinlet and stockwork structures. Alterations found in the deposit are mainly silicification, carbonatization and chloritization.

It is characterized by four breccia pipes and sixteen NW-trend auriferous quartz veins hosted in the Archean to Paleoproterozoic TTG basement. Additionally, amphibolite, metamorphic diabase, and carbonate wall rocks have been identified in the ore field. Yixingzhai features multiple generations of 135–140 Ma intermediate to felsic intrusive dikes, stocks, and plutons, including the Hewan granite porphyry, Nanmenshan quartz porphyry, and Sunzhuang quartz monzonite. Four breccia pipes in the Yixingzhai gold deposit are identified along these intrusions: Tietangdong, Hewan, Nanmenshan, and Jinjiling. Sixteen lode Au ore bodies are hosted in Paleo–Proterozoic TTG gneiss and/or granite porphyry, ranging in thickness from 0.05 to 4.30 m. These ore bodies extend for lengths of 150–2300 m and downdip for 500–1100 m.

The Yixingzhai gold deposit (Lat. 39°21′51″ N, Long. 113°35′46″ E) is the largest gold deposit in the CTD. It has sixteen lode Au ore bodies and four breccia pipes that also host gold mineralization. The Tietangdong breccia pipe is the most gold-rich breccia pipe (~20 t Au). Previous works have suggested a skarn crypto-explosive origin for Tietangdong based on samples collected from the shallow part of the breccia pipe. Moreover, the authors of analyzed zoning textures within garnet and epidote grains, inferring several magmatic–hydrothermal pulses and multiple crypto-explosion events in Tietangdong. Sixteen lode Au ore bodies are hosted in Paleo–Proterozoic TTG gneiss and/or granite porphyry, ranging in thickness from 0.05 to 4.30 m. These ore bodies extend for lengths of 150–2300 m and downdip for 500–1100 m.

The main mineralization is divided into four stages: the quartz sericite stage, the quartz-pyrite stage, the quartz polymetallic stage, and the calcite stage. The quartz-pyrite stage is the principal mineralization stage. The Tietangdong skarn breccia pipe is the most typical breccia gold ore body in the mining area. Its composition is complex, and its economic value is high. Not only is the gold-bearing ore body found, but also an iron ore body is found. In addition, the vein rocks in the mining area are extremely developed, mainly consisting of diabase dykes and lamprophyre dykes, which are mostly irregularly interspersed throughout the mining area. The Hewan porphyry gold ore body is roughly divided into the hematite zone, kaolinization zone, strong sericitization zone, sericitization zone, and weak sericitization zone, and mineralization is closely related to sericitization.

The Yixingzhai gold deposit is characterized by multiple ore genesis types, including porphyry, quartz vein, altered rock, breccia, and skarn types, with porphyry and quartz vein types being the most significant. The Yixingzhai Gold Mine is an underground operation that utilizes shaft and tunnel development, with shrinkage stoping and cut-and-fill as the primary methods; it yielded approximately 1.5 tonnes of gold in 2020. The gold-bearing quartz veins are arranged in a roughly north–south direction, with a higher density in the west and a lower density in the east. They are predominantly simple monovein-type structures, with minor compound veins and stockworks. The veins are typically 500–2000 m long, and are steeply dipping. The porphyry-type mineralization is best represented by the Hewan large altered porphyry gold orebody, which has an additional gold resource of over 57 tons. The gold mineralization intensity within the Hewan porphyry decreases outwards from the center. The altered porphyry is highly fractured and is filled with numerous fine veinlets of sulfides and quartz. These veinlets are associated with intense pyrite–sericite alteration on their margins.

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