Ergu-Xishan Ag-Pb-Zn deposit, Tieli City, Yichun, Heilongjiang, Chinai

Regional Level Types
Ergu-Xishan Ag-Pb-Zn deposit	Deposit
Tieli City	City
Yichun	Prefecture
Heilongjiang	Province
China	Country

Small-scale Zn-Pb-(Ag-Cu-W) skarn, located in the axial part of the Ergu-Xujiugou anticline in the Zhangguangcailing fold belt. The latter contains Early Permian siltstones and marbles, occurring as xenoliths in Hercynian medium-grained biotite plagiogranite, porphyritic biotite granites, and granodiorite. The deposit is controlled by EW-trending, N-dipping fractures, and intrusive contacts. The main wallrock alteration is skarn.
The Ergu Fe-Zn polymetallic deposit is located in the central Lesser Xing’an Range, NE China. This deposit hosts an estimated ore resource of 15.8 Mt Fe, 0.021 Mt Cu, 0.03 Mt Mo, 0.23 Mt Zn and 0.13 Mt Pb, with average grades of 34.66% Fe, 0.54% Cu, 0.05% Mo, 3.9% Zn and 3.4% Pb. Geochronology studies suggested that the Ergu skarn Fe-Zn polymetallic deposit was formed in the Early Jurassic (181.0 ± 4.2 Ma, 40Ar-39Ar dating of phlogopite), and the diagenetic age of the medium-grained granodiorite related to mineralization is 183.74 Ma (U-Pb dating of zircon), while the associated high-K calc-alkaline I-type granites that originated from partial melting of the lower crust. The formation of this deposit was related to the subduction of the Early Jurassic Paleo-Pacific plate beneath Eurasia.
A total of 21 valuable orebodies were discovered. These valuable orebodies have lenticular, veined or cystiform shapes. The lengths of them vary from 30 m to 887 m, while the widths of them vary from 0.92 m to 13.9 m. Based on the geological characteristics, it is believed that the locations of these orebodies are clearly controlled by the associated structures. Consequently, these orebodies show wavy distributions in the cross section. In particular, they can be found in the outer, middle and inner zones of the contact zone, which is located between the limestone rocks and granodiorite of the lower Cambrian Qianshan Formation. It was also observed that when the above-mentioned contact zone displays the shapes of curves or a shallower dip, there is an obvious increase in the thickness of the orebody. The sizes of the orebodies generated within the contact zone near the intruded granodiorite vary from 1 m to 28 m. These orebodies are mainly enriched in Fe and Cu. However, the sizes of the orebodies generated far from the intruded granodiorite vary from 15 m to 87 m. These orebodies are mainly enriched in Pb and Zn.
There are two periods involved in the ore-forming process. The first is a skarn forming period (i.e., period I), while the second is a quartz-sulfide period (i.e., period II). These two periods contain the following six mineralization stages [3]: a prograde skarn forming stage (i.e., stage I1), a retrograde skarn forming stage (i.e., stage I2), an oxide stage (i.e., stage I3), a quartz-Fe-Cu sulfide stage (i.e., stage II1), a quartz-Pb-Zn sulfide stage (i.e., stage II2) and a quartz-carbonate stage (i.e., stage II3). This means that there are three stages in each period. In stage I1, a large number of anhydrous silicate minerals, such as the garnet and diopside formed in the endoskarn, are distributed within the retrograde skarn. In stage I2, the hydrous alteration minerals, such as chlorite, hornblende, epidote, actinolite and a small amount of magnetite, are extensively formed. In stage I3, a large amount of magnetite, including lesser amounts of molybdenite, pyrrhotite and quartz, is predominantly generated. Particularly, the formations of orebodies at this stage primarily take place within the fractures between the exoskarn and endoskarn. In stage II1, which is the ore-forming stage of the Fe-Cu orebodies, the formations of orebodies are primarily in the form of veins or veinlets, which are disseminated and generated as the structural protrusions within the exoskarn. In stage II2, which is the ore-forming stage of Pb–Zn orebodies, the formations of orebodies are mostly in the form of net veins and veins occurring in the exoskarn. In this study, only the formation of galena at this stage is considered; although, the formations of other precious metals (e.g., Fe and Cu) in the other stage deserves consideration in future research. In stage II3, a large amount of calcite, fluorite, quartz and a small amount of pyrite and galena are primarily formed in the exoskarn.

Other Regions, Features and Areas containing this locality

References