The Mohailaheng and Dongmozhazhua Pb-Zn deposits in the Yushu area of Qinghai Province, located in the northeast margin of Qiangtang terrane which is between Jinshajiang suture zone and Bangonghu-Nujiang suture zone, are the two typical Pb-Zn deposits in the Cu-Pb-Zn polymetallic mineralization belt for the northern part of the Nujiang-Lancangjiang-Jinshajiang area. The authors thought the sources of ore-froming material were derived from the sedimentary strata by the research of sulfur, lead, strontium and neodymium isotope compositions of the Dongmozhazhua lead-zinc ore deposit. On the basis of geological field observations, the authors also made the research on the Mohailaheng lead-zinc ore deposit and selected sulfide minerals and barite for S isotope compositions analyses, sulfide minerals, gangue minerals and regional strata for Pb isotope compositions analyses, and gangue minerals for Sr-Nd isotope compositions. delta S-34 values of sulfide minerals are -30. 0 parts per thousand similar to + 7. 4 parts per thousand, and show peaks at -18 parts per thousand similar to -2 parts per thousand, reflecting the characteristic of light sulfur. delta S-34 values of barite are 20. 2 parts per thousand similar to +24. 2 parts per thousand, implying the derivation of Tertiary continental facies basin. The ore deposit displays wide variations in sulfide delta S-34 values, indicating multiple sulfur sources. On account of the lack of magmatic activity, it is realistic to view the rocks in the basin as the source of sulfur. Sulfur in the rocks was transferred into hydrothermal fluids via fluid-rock interaction. Therefore, the variation in rock types across the basin is likely to influence the variation of sulfur isotopic compositions. Reduced sulfurs were mainly derived from the biogenic sulfate reduction or the thermochemical reduction of sulfur-bearing organic matter, implying that sulfur came from the sedimentary basin. The Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 ratios for sulfide minerals vary in ranges of 18. 298 similar to 18.694, 15. 298 similar to 15. 721 and 38. 169 similar to 38. 894, respectively. The Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 ratios for gangue minerals are between 18. 418 similar to 18. 672, 15. 418 similar to 15. 719 and 38. 403 similar to 38. 845, respectively. In the diagrams of Pb-207/Pb-204-Pb-206/Pb-204 and Pb-208/Pb-204-Pb-206/Pb-204, the Pb isotope compositions of the sulfide minerals and gangue minerals fall into the regional upper crust lead zone, similar to MVT deposit, implying that Pb might have come from the upper crust rocks. The (Sr-87/Sr-86)(i), epsilon(St) (t), (Nd-143/Nd-144)(i) and epsilon(Nd)(t) ratios for gangue minerals vary in ranges of 0. 70851 similar to 0. 70906, 57. 4 similar to 65. 2, 0. 512265 similar to 0. 512361 and -6. 5 similar to -4. 6, respectively. The Sr-Nd isotope compositions of the gangue minerals indicate that their matter sources also came from the upper crust rocks. On the whole, the characters of sulfur, lead, strontium and neodymium isotope compositions of the Mohailaheng lead-zinc ore deposit in the Yushu area are the same as those of the Dongmozhazhua lead-zinc ore deposit, implying that they both derived from the sedimentary strata. Together with the geological and geochemical features of the Mohailaheng and Dongmozhazhua Pb-Zn deposits, the authors dicussed their dynamical settings.
