Metallogenic material source of the Qielong copper-gold mineralization occurrence in the western Bangong-Nujiang metallogenic belt: Constraints from in-situ sulfur isotopes of ore sulfides

The Qielong copper-gold mineralization occurrence is located in the Qulong area of the western Bangong-Nujiang metallogenic belt. The ore bodies mainly occur in and near the contact zone between the Late Cretaceous monzogranite and marble of the Xiala Formation. The ore bodies occur mainly as vein and lens in shape. The alteration of the host rock is characterized mainly by skarn. Research on the stable isotopes of this mineralization area is lacking, which to some extent hinders further research on the sources of ore-forming materials and the genesis of the Qielong Cu-Au mineralization. This article conducted in-situ S isotope analysis on ore sulfides such as the bornites, digenites, and chalcopyrites, and explored the source of ore-forming materials in the Qielong Cu-Au mineralization occurrence. The results show that the δ³⁴S_V-CDT values of bornites range from －0.29‰ to 2.15‰, with an average of 1.22‰; the δ³⁴S_V-CDT values of digenites range from －0.52‰ to －0.47‰, with an average of －0.50‰; the δ³⁴S_V-CDT values of chalcopyrites range from 0.22‰ to 1.67‰, with an average of 1.11‰, indicating the S isotope compositions have the characteristics of magmatic sulfur. Based on comparative studies on S isotopes between Qielong and the coeval Gaerqiong and Galale deposits, this article suggests that the conditions of surrounding rock lithology of the Qielong copper-gold mineralization occurrence are similar to those of the Gaerqiong and Galale deposits. However, there are certain differences in their ore-forming source regions. The ore-forming material of the Qielong Cu-Au mineralization area originates from deep magma, with little strata contributions to the ore-forming process; whereas, the ore-forming materials of the Gaerqiong and Galale deposits have mixed sources of deep magma and strata. In subsequent prospecting and exploration work in this area, attention should be focused on whether there is skarn-type mineralization in areas where intermediate-acidic intrusive rocks developed in the early Late Cretaceous (90 Ma～80 Ma) and at the contact parts between the intrusive rocks and carbonate rocks in the strata. Furthermore, the emplacement situation of the concealed rock mass in the Qielong copper-gold mineralization occurrence should also be investigated with emphasis, in the hope of discovering and exploring porphyry-type ore bodies.