Discussion on the ore−forming fluids, materials sources and genesis of Erdaohe Pb−Zn−Ag deposit, Inner Mongolia

This paper is the result of mineral exploration engineering.

Objective The Erdaohe silver−lead−zinc deposit is located in the middle section of the Greater Khingan Range. It is a representative large−scale skarn−type deposit discovered in recent years. Studying the origin of this deposit will help guide the exploration of polymetallic deposits in the middle section of the Greater Khingan Range.

Methods On the basis of field geological survey, this paper made research on the fluid inclusion in the keatite selected at each stage of mineralization, and discussed the ore−forming fluid and material sources in combination with the S and Pb isotopes of ore and the C and O isotopes of calcite.

Results The research result showed the formation of the deposit throughout the process from the skarn stage to the quarte−sulfide stage and to the quartz carbonate stage. According to the temperature measurement result, the inclusion in keatite was mainly characterized by gas−liquid phase, with the homogenization temperature of 310–435℃ at the skarn stage, 195–310℃ at the quarte−sulfide stage and 148–195℃ at the quartz carbonate stage, and the salinity of 11.7%–0.71% NaCleqv at the skarn stage, 12.9%–0.35% NaCleqv at the quartz−sulfide stage and 4.18%–0.35% NaCleqv at the quartz−carbonate stage. The C and O isotopes of calcite indicated a water−rock reaction of the deposit, in which atmospheric precipitation was found. The δ³⁴S value of the S isotope of ore was 5.4‰–10.0‰ from a mixture of sulfurs in magma and strata; as per the characteristic parameter of lead isotope, the source of lead was associated with the orogeny−related magmatism, where the lead was mostly from the upper crust, and slightly from the deep source.

Conclusions Accordingly, the ore−forming fluid and material sources were considered the products of the large−scale magmatism caused by the extension after the closure of Mongolia−Okhotsk for orogeny.