PGE and Re-Os isotope geochemistry and their constraints on mineralization of the Tulaergen Ni-Cu sulfide deposit in the East Tianshan

The East Tianshan located at the southern Central Asian Orogenic Belt is an important area of China's strategic resource of Ni. The Tulaergen deposit, one of the numerous Ni-Cu deposits in this area, is characterized by a high proportion of mineralization in the intrusion. The Late Carboniferous mafic intrusion ( gabbro, hornblende gabbro) and the Early Permian ultramafic intrusion ( lherzolite, hornblende peridotite). The lenticular and suspended ore bodies are located in middle and upper parts of the ultramafic intrusion, consisting of massive/semi-massive, net-textured, dense/sparsely disseminated and blotchy sulfide ores. The Sigma PGEs of different ore types show significant variations (10. 8 x 10(-9) similar to 208 x 10(-9)). Except for massive ores, other types ( S < 15% ) show positive correlations between S and PGE, between IPGE and PPGE, indicating that the PGE variations are mainly controlled by the R factor (100 similar to 5000). Such positive correlations are not observed on massive ore types, reflecting the influence of differentiation of monosulfide solid solution. The significant depletion of Pt and Pd in the parent magma and the decoupling of Cu and Pd indicate that the Tulaergen parent magma has experienced sulfide segregation in depth. The high-Mg basaltic magma and the possible low degree of partial melting of the water-bearing mantle source, indicate that sulfide retention in the source may also cause the PGE depletion. The Os-187/Os-188 ratios and gamma(OS) values are significantly higher than the orogenic peridotite mantle and the global typical Ni-Cu deposits, suggesting that the parent magma was strongly contaminated by crustal materials. This limited siliceous crustal contamination revealed by Os-Nd isotope mixing calculation cannot well explain the high Os-1(87)/Os-1(88) ratios, indicating that the Os isotopic signature of the Tulaergen deposit is mainly modified by crustal sulfides. Therefore, addition of crustal sulfur is one of the critical factors for the Tulaergen Ni-Cu sulfide mineralization.