Sulfur and lead isotope composition of hydrothermal vein type lead-zinc deposits in Zexue area, Tibet and its implications for the origin of ore-forming materials

The Dexin and Zhazhalong Pb-Zn deposits are the representative hydrothermal vein type lead-zinc deposits in the western part of the Gangdise Ag-Pb-Zn polymetallic metallogenic belt; nevertheless, the origin of ore-forming materials of the two deposits and their genetic relation with the Narusongduo Pb-Zn deposit remain unknown. A stable isotopic method for single mineral and whole rock was used to measure the S and Pb isotopic composition of the sulfide and ore-bearing granite porphyries from the two deposits and to trace their sources of ore-forming materials. It is shown that the δ³⁴S_VCDT values of sulfide and ore-bearing granite porphyry from Dexin and sulfide from Zhazhalong range from 3.5‰ to 7.4‰, from 4.4‰ to 6.2‰, and from 2.7‰ to 8.3‰, with an average being 6.1‰, 5.7% and 5.1%, respectively; the ratios of different lead isotopes in Dexin and Zhazhalong are stable, varying in similar ranges, and the μ values of lead isotope in the two deposits vary from 9.48 to 9.82 (9.64 on average) with similar △β, △γ variation ranges and average values, which suggests that the S and Pb isotopic compositions of the sulfide are consistent with those of the ore-bearing granite porphyries in the two deposits with normal lead characteristics, granitoid origin of sulfur isotope and upper crust origin of lead isotope predominately. With comprehensive analysis of geological background and previous researches, it is concluded that the Pb-Zn mineralization in Dexin, Zhazhalong and Narusongduo Pb-Zn deposits may be products of the same metallogenic system with consistent sulfur and lead isotopic characteristics, and the granite porphyries might have supplied ore-forming materials for the hydrothermal vein type lead-zinc deposits in Zexue area.