A reevaluation for the genesis of the Keyue Pb-Zn-Sb polymetallic deposit: Insights for Pb-Zn-Sb metallogenesis during the post-collisional Tethys Himalayan belt

The Keyue Pb-Zn-Sb polymetallic deposit is located within the Zhaxikang-Cuonadong ore concentration area in the eastern segment of the Tethyan Himalayan mineralization belt, with its orebodies controlled by north-eastern extensional fault structures. The genesis of this deposit remains a subject of debate. In this study, Ar-Ar isotope geochronology and in-situ sulfur isotope analyses were conducted on sericite and metallic sulfides within quartz-sulfide veins. Plateau ages of sericite, obtained within the temperature range of 650℃–1100℃, were determined to be (15.34 ±0.24) Ma, accompanied by corresponding isochron ages of (15.38±0.27) Ma. These results explicitly indicate that the mineralization of the Keyue Pb-Zn-Sb polymetallic deposit occurred approximately 15 Myr ago, during the post-collision stage of the Indian-Asian continental collision. The in-situ sulfur isotopic composition of metallic sulfides in the Keyue deposit exhibits remarkable stability with a narrow range, varying from 8.65‰ to 12.02‰ (with an average of 10.85‰). Owing to its close resemblance to the sulfur isotopic composition of the Cuonadong leucogranite and Ridang Formation strata within the ore concentration area, it is suggested that the sulfur was derived from both Miocene leucogranitic magmas and the strata. Comprehensive research demonstrates that the Keyue Pb-Zn-Sb polymetallic deposit is a hydrothermal vein-type deposit closely associated with Miocene magmatic activity. Additionally, the Zhaxikang-Cuonadong ore concentration area displays distinct deposit zoning characteristics. With the Cuonadong leucogranite as the core, beryllium-tungsten-tin deposits related to Miocene leucogranitic magmatism develop. Moving outward, hydrothermal vein-type Pb-Zn-Sb polymetallic deposits occur, and at the outermost periphery, gold or gold-antimony deposits are present. This spatial arrangement collectively forms a typical magmatic-hydrothermal W-Sn-Be → Pb-Zn-Sb → Au polymetallic mineralization system.