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 Pb-Zn deposit 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, is the typical Pb-Zn deposit in the Cu-Pb-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. δ34S values of sulfide minerals are -29‰~6‰, and show peaks at -8‰~-6‰, reflecting the characteristic of light sulfur. δ34S values of barite are 18.3‰~+22.8‰, implying the derivation of Tertiary continental facies basin. The ore deposit displays wide variations in sulfide δ34S 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 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios for sulfide minerals vary in ranges of 18.387~18.703, 15.391~15.768 and 38.372~38.809, respectively. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios for gangue minerals are between 18.423~18.612, 15.491~15.701 and 38.497~38.612, respectively. In the diagrams of 207Pb/204Pb-206Pb/204Pb and 208Pb/204Pb-206Pb/204Pb, 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 (87Sr/86Sr)ⅰ, eSr(t), (143Nd/144Nd)ⅰ and eNd(t) ratios for gangue minerals vary in ranges of 0.70855~0.70928, 58.0~68.4, 0.512273~0.512353 and -6.2~-4.7, respectively. The Sr-Nd isotope compositions of the gangue minerals indicate that their matter sources also came from the upper crust rocks.