Yangchang Mo deposit, Bairin Right Banner (Balin Youqi), Chifeng City (Ulanhad League; Chifeng Prefecture), Inner Mongolia, Chinai

Regional Level Types
Yangchang Mo deposit	Deposit
Bairin Right Banner (Balin Youqi)	County
Chifeng City (Ulanhad League; Chifeng Prefecture)	Prefecture-level City
Inner Mongolia	Autonomous Region
China	Country

The main stratigraphic unit associated with this deposit is the Early Permian Dashizhai Formation, which strikes northeast and dips to the southeast at 30–55°. It comprises intermediate to basic volcanic rocks (including basaltic andesite, andesite, tuffaceous sandstone, and tuff with common alteration), with local lenticular or cystic Cu-Mo mineralization.
In the Yangchang deposit, late Paleozoic to Mesozoic intermediate–felsic intrusions are widespread. These include Middle Permian granite (266–263 Ma) and Early Cretaceous monzogranite and granite porphyry with U-Pb ages of 138–132 Ma. Among these, the Early Cretaceous intrusive activity, controlled by NE-trending faults, is closely associated with Cu-Mo mineralization. The monzogranite, in particular, is commonly regarded as a Cu-Mo-bearing granite. Notably, the monzogranite with a U-Pb zircon age of 138 ± 2 Ma is considered the host rock of the Yangchang vein-type Cu-Mo deposit. The Yangchang Cu-Mo ore veins are primarily hosted in Early Cretaceous monzogranite and are intruded by two isolated granite porphyry veins measuring approximately 300 m and 2,100 m in length, respectively. Based on our field observations, four orebodies have been identified (V1, V2, V3, and V4). The V1 veins intrude Permian strata and are exposed in six shallow trenches. These veins are 0.5–1.0 m wide, 265 m long, and dip 65–75° to the northeast. The V2, V3, and V4 veins are hosted in monzogranite, which shows no evidence of compression or deformation from regional tectonic activities. The V2 veins strike at 350°, dip 70–80° to the northeast°, and measure 450 m in length, 1.5 m in width, and 150 m in vertical extent, with an average Mo grade of 0.123 %. The V3 veins strike at 345°, dip 70–80° to the northeast, and measure 700 m in length, 1.0 m in width, and 120 m vertically, with an average Mo grade of 0.085 %. The V4 veins are exposed at the surface, strike at 300°, and dip 75–80° to the northeast. They are 126 m long and approximately 0.2–2 m wide. Individual V4 veins are typically subparallel, lenticular, or spindle-shaped bodies exhibiting pinch-and-swell structures.
Three paragenetic stages (I–III) were identified based on field observations, crosscutting relationships, and mineral assemblages. Stage I is defined as the pyrite–quartz stage. Stage II is characterized by molybdenite–chalcopyrite mineralization and is subdivided into generations IIa and IIb. Generation IIa consists of pyrite, quartz, and abundant Cu-Mo veins and is characterized by a higher Cu content than generation IIb. Stage III is marked by enrichment in sphalerite and galena.

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References