Sulfur, lead, strontium and neodymium isotope compositions of the Dongmozhazhua lead-zinc ore deposit in the Yushu area, southern Qinghai: Implications for the sources of ore-forming material in the deposit

The Dongmozhazhua Ph-Zn deposit in the Yushu area of Qinghai Province, located in the northeast margin of Qiang-tang terrane which is between Jinshajiang suture zone and Bangonghu-Nujiang suture zone, is the typical Ph-Zn deposit in the Cu-Ph-Zn polymetallic mineralization belt for the northern part of the Nujiang-Lancangjiang-Jinshajiang area. On the basis of geological field observations, the authors 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 -29 parts per thousand similar to 6 parts per thousand, and show peaks at -8 parts per thousand similar to -6 parts per thousand, reflecting the characteristic of light sulfur. delta S-34 values of barite are 18.3 parts per thousand similar to +22.8 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 18.387 similar to 18.703, 15.391 similar to 15.768 and 38.372 similar to 38.809, respectively. The Pb-206/Pb-204, Pb-207/Pb-204 and Pb-208/Pb-204 ratios for gangue minerals are between 18.423 similar to 18.612, 15.491 similar to 15.701 and 38.497 similar to 38.612, 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(Sr)(t), (Nd-143/Nd-104)(i) and epsilon(Nd)(t) ratios for gangue minerals vary in ranges of 0.70855 similar to 0.70928, 58.0 similar to 68.4, 0.512273 similar to 0.512353 and -6.2 similar to -4.7, respectively. The Sr-Nd isotope compositions of the gangue minerals indicate that their matter sources also came from the upper crust rocks.