Two‐stage magmatism and mineralization of Tulaergen nickel‐copper deposit in eastern Tianshan, North‐west China: Evidence from bulk rock geochemistry and in situ mineral chemistry

• Published in: Geological journal (Chichester, England) England), 2021-07, Vol.56 (7), p.3808-3832
• Main Authors: Fang, Lin‐Ru, Tang, Dong‐Mei, Junge, Malte, Qin, Ke‐Zhang, Mao, Ya‐Jing, Evans, Noreen J., Wohlgemuth‐Ueberwasser, Cora C., Niu, Yan‐Jie
• Format: Article
• Language: English
• Subjects: Aggregation; Aluminum; Anomalies; Central Asian Orogenic Belt; Chalcopyrite; Chemical composition; Cobalt; Contamination; Copper; Crystallization; Earth mantle; Fractional crystallization; Geochemistry; Isotopes; Lava; Lead; Magma; magmatic sulphide deposit; mineral chemistry; Mineralization; Minerals; Nickel; Nickel ores; Olivine; Ores; Orogeny; Pentlandite; Platinum; Pyrrhotite; Rare earth elements; Rocks; Saturation; Segregation; Selenium; Silver; Sulfides; Sulfur; Sulphides; Sulphur; Tulaergen; two‐stage magmatism; Ultramafic materials; Ultramafic rocks
• ISSN: 0072-1050; 1099-1034
• DOI: 10.1002/gj.4129

The Tulaergen magmatic Ni–Cu deposit is related to mafic‐ultramafic rocks of the Central Asian Orogenic Belt. The ore‐host rocks are lherzolite and websterite and the major ore types are net‐textured and sparsely disseminated ores. The disseminated ores host high‐Fo (82–85) olivine and hornblende with low‐Al contents, high‐rare earth element (REE) abundances and negative Eu anomalies. The net‐textured mineralized lherzolite contains low‐Fo (74–82) olivine and high‐Al hornblende, the latter characterized by low REE concentrations and no Eu anomaly. The contrasting composition of olivine and hornblende suggests two stages of magmatism. In situ analysis of pentlandite, chalcopyrite and pyrrhotite shows that platinum‐group elements contents in sulphides are low. Contrasting Ni, Co, Se, Ag, Cd, and Pb contents in sulphides from net‐textured and in disseminated ores also supports two pulses of magmas, each with a distinct chemical composition. High‐Mg basaltic magma characterized the first stage, followed by a second‐stage less basic magma with a high H2O content. Whole‐rock Sr and Nd isotopic signatures suggest that about 4–6% crustal materials were added to the depleted mantle source. The fractional crystallization of olivine and crustal contamination play important roles in sulphur segregation at Tulaergen based on sulphur content at sulphide saturation modelling. Injection of magma enriched in H2O further enhanced sulphide aggregation and deposit forming. It is proposed that two pulses of magma injections occurred at the Tulaergen deposit, with the products of the first pulse settling at the base, and of the second one with dense mineralization laying at the top of the deposit. Tulaergen deposit has two stages of magmatism, which formed disseminated and net‐textured ores, respectively, suggested by the contrasting Fo values of olivine (a) and Al content of hornblende (b). Sulphur content at sulphide saturation modelling (c) reveals that fractional crystallization of olivine and crustal contamination play important roles in sulphur segregation at Tulaergen. In total, the mineralization of Tulaergen is closely related to the two pulses of magma, the olivine crystallization and the crustal assimilation.