Trace element and multiple isotope (Pb-He-Ar) constraints on the origin of Ag-Pb-Zn mineralization at Erdaokan, NE China

Silver is widely associated with Pb-Zn mineralization worldwide, however, the genesis of high-grade silver ores in these systems remains highly debated. Here, we choose the newly-discovered Erdaokan Ag-Pb-Zn deposit (∼1800 t Ag with an average grade as high as 431 g/t) in northeastern (NE) China as a case study to decipher the above issue. The studied mineralization comprises four stages, among which three pyrite generations (Py1, Py2, Py3), two types of sphalerite (Sp1, Sp2) and galena (Gn1, Gn2) have been identified. In situ trace element analyses reveal that Py1 contains higher Mn, Pb, Zn, Co, and Ni than Py2 and Py3. The Py2 exhibits the highest Ag, As, Cu, Sb, and Tl contents, and Py3 shows wide variations in Ag, Cu, Pb, Zn, As, and Ni. Gallium, Cd, and In are generally low in all pyrite types, mostly below the detection limits. Trace element compositions reveal that the studied deposit formed under low temperature and low f O 2 conditions, with significant fluid-rock interactions during mineralization process. Extracted fluid inclusions in pyrite show elevated 3 He/ 4 He values (0.83–2.08 Ra) and 40 Ar/ 36 Ar ratios (320.6–410.2), indicating the presence of crust-mantle end-member reservoirs, along with meteoric water contributions to the ore-forming system. In situ Pb isotope contents of sulfides suggest that the metals are predominantly derived from magmatic sources. These new data collectively indicate that the formation of the Erdaokan high-grade Ag ores is caused by fluid-rock interactions. Combined with ore deposit geology, gangue assemblages and geochemical data, we interpret the Erdaokan deposit as an epithermal type silver deposit.