Baijianshan Zn-Cu polymetallic deposit, Xiaoshitouquan Ag-Cu ore field, Yizhou District, Hami Prefecture (Kumul Prefecture; Qumul Prefecture), Xinjiang, Chinai

Regional Level Types
Baijianshan Zn-Cu polymetallic deposit	Deposit
Xiaoshitouquan Ag-Cu ore field	Ore Field
Yizhou District	County
Hami Prefecture (Kumul Prefecture; Qumul Prefecture)	Prefecture-level City
Xinjiang	Autonomous Region
China	Country

The exposed strata within the mining area are dominated by the second subgroup of the Lower Carboniferous Yamansu Formation (C1y2), consisting of marine–continental transitional facies volcanic clastic rocks, limestones, and marbles. Influenced by the magmatic intrusion, these strata have undergone varying degrees of thermal contact metamorphism, forming hornfels zones and marble + skarn zones with thicknesses of 30–50 m. The marble + skarn zones are closely associated with the Zn-Cu polymetallic orebodies.
Three zinc polymetallic orebodies (Zn-I, Zn-II, and Zn-III) and one copper polymetallic orebody (Cu-I) have been delineated in the mining area. The proven and probable reserves of Pb, Zn, and Cu are 302 t, 12,211 t, and 88 t, respectively. All the orebodies occur at depth and are controlled by the contact zone between the granitic intrusion and surrounding carbonates. As the largest Zn orebody, the Zn-I orebody has a length of 300 m and an inclined dip length of up to 178 m. The dip direction of this orebody ranges from 95° to 165°, with a dip angle of 38° to 63°. The Zn grade ranges from 0.56% to 35.44% (average 2.93%). The Cu-I orebody is located below the Zn-I orebody, with a length of approximately 75 m and a width of 50 m. The Cu grade ranges from 0.22% to 1.03% (average 0.49%).
The textures of ores mainly comprise fine-vein, net-vein, disseminated, nodular, and spotted. the mineralization process of the Baijianshan deposit is divided into five stages. The prograde skarn stage (I) is characterized by the occurrence of garnet, wollastonite, and pyroxene. The garnet shows yellow-white in color, with medium-grained euhedral crystal structure. The pyroxene is encased by later calcite. The retrograde skarn stage (II) is characterized by the occurrence of yellowish-green epidote aggregates and crosscut by late-stage quartz-sulfide veins. The oxide stage (III) comprises abundant magnetite and ilmenite . Magnetite is commonly iron-gray in color, with a metallic luster. It is commonly intergrown with ilmenite and replaces the early-stage garnet. The early quartz-sulfide stage (IV) is characterized by the occurrence of quartz and metallic sulfides such as pyrite, chalcopyrite, sphalerite, and galena. Pyrite is typically pale yellow and exhibits euhedral to subhedral texture. Chalcopyrite is strongly associated with galena and sphalerite, forming a solid solution within sphalerite. The late quartz-carbonate stage (V) is characterized by the occurrence of calcite. Calcite is the dominant gangue mineral and the fills cavities left by skarn mineral assemblages.

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References