Crustal contribution for the formation of the Walali Au deposit and implications on the Early Cretaceous Au mineralization in the northern Great Xing’an Range

Abstract

The northern Great Xing’an Range (NGXR) gold (Au) metallogenic belt is characterized by the wide occurrence of the Early Cretaceous orogenic and arc-magma related epithermal Au deposits. Information of the newly discovered granite-hosted Walali Au deposits in this area could shed new light on the Early Cretaceous Au metallogenesis in NE China. The ore-hosting granite at Walali shows zircon U-Pb ages of 310.6 ± 2.2 Ma, which are significantly different from the ore-bearing pyrite Rb–Sr age (119.9 ± 1.7 Ma). The distinct ages indicate that the Au mineralization occurred at the Early Cretaceous and therefore preclude the genetic link between the Late Carboniferous magmatism and Au ore formation. The fluid inclusion studies show that the ore precitpitated from the hydrothermal fluids with a temperature range of 150–330 °C and a salinity range of 3.4–11.6 wt% equiv. H–O isotopic compositions indicate the involvement of both magmatic and meteoric water in the hydrothermal system. The pyrite and galena S (δ34SV–CDT values: 7.7–10.0‰) and Pb (206Pb/204Pb ratios of 18.177–18.217; 207Pb/ 204Pb ratios of 15.614–15.633) isotopic compositions suggest a crustal contribution for the ore-forming materials at Walali. By comparison, the Walali Au deposits are more comparable with the strata-hosted orogenic Au deposits in the north NGXR, but different from the epithermal- and porphyry-type Au deposits in this area. Combined with the Late Mesozoic tectonic evolution in NE China, we conclude that the Early Cretaceous extensional setting caused the large scale magmatism, which drove the remobilization of crustal materials and resulted in the formation of the granite- and strata-hosted Au deposits in the NGXR.