The parental magma composition, crustal contamination process, and metallogenesis of the Shitoukengde Ni‐Cu sulfide deposit in the Eastern Kunlun Orogenic Belt, NW China. Issue 4 (9th June 2021)

• Record Type: Journal Article
• Authors: Li, Liang; Zhang, Dexin; Tan, Shucheng; Sun, Fengyue; Wang, Chao; Zhao, Tuofei; Li, Shijin; Yang, Yanqian
• Is Part Of: Resource geology. Volume 71:Issue 4(2021)
• Page Start: 339
• Page End: 362
• Publication Date: 2021-06-09
• Subjects: crustal contamination -- late Silurian -- NW China -- parental magma composition -- Shitoukengde Ni‐Cu deposit -- sulfide saturation; Mining geology -- Periodicals; Mining geology -- Pacific Area -- Periodicals; Mining geology -- Asia -- Periodicals; Geochemistry -- Periodicals; Environmental geology -- Periodicals; 553
• DOI: 10.1111/rge.12267
• Languages: English
• ISSNs: 1344-1698

Abstract

Abstract: Shitoukengde is an important magmatic Ni–Cu sulfide deposit in the Eastern Kunlun Orogenic Belt (EKOB). It comprises several mafic–ultramafic complexes and contains different kinds of mafic–ultramafic rocks. Lherzolite and olivine websterite are the most significant Ni–Cu‐hosted rocks. The No. I complex hosts six Ni–Cu ore bodies, and the depth of the intrusion has great exploration potential. Therefore, geochronology, geochemistry, and mineral chemistry of the Shitoukengde deposit were studied to constrain its mineralization time, parental magma composition, and crustal contamination process. Zircon U–Pb dating of olivine websterite shows the magmatic origin (Th/U = 0.40–1.05) and an age of 418.1 ± 8.7 Ma (MSWD = 0.01), which is coeval with the Xiarihamu, Akechukesai, and other Cu–Ni deposits in the EKOB. Geochemically, the mafic–ultramafic rocks are characterized by low SiO2, TiO2, and Na2 O + K2 O and high MgO (9.49–36.02%), with Mg # values of 80–87. They are relatively enriched in LREE and LILEs (e.g., K, Rb, and Th), with weakly positive Eu anomalies (δEu = 0.83–2.26), but depleted in HFSEs (e. g., Ta, Nb, Zr, and Ti). Based on the electron microprobe analyses, all of the olivines are chrysolite (Fo = 81–86), and the pyroxenes are dominated by clinoenstatite (En = 80–84) and augite (En = 49–55) in the mafic–ultramafic rocks. Therefore, the composition of parental magma is estimated to be picritic basaltic magma with SiO2 and MgO concentrations of 54.47 and 13.95%, respectively. The zircon ε Hf ( t ) values of olivine websterite vary from −0.8 to 4.6, with a TDM1 of 0.84–1.06 Ga, indicating that the parental magma was derived from relatively high degree partial melting (about 13.4%) of a depleted mantle source and experienced significant crustal contamination (about 12–16%). We propose that crustal assimilation, rather than fractional crystallization, played a key role in triggering the sulfide saturation of the Shitoukengde deposit, and the metallogenesis of "deep liquation–pulsing injection" is the key mechanism underlying its formation. The parental magma, before intruding, underwent liquation and partial crystallization at depth, partitioning into barren, ore‐bearing, and ore‐rich magma and ore pulp, and was then injected multiple times, resulting in the formation of the Shitoukengde Ni–Cu deposit. Abstract : The Shitoukengde magmatic Ni‐Cu sulfide deposit formed at late Silurian (418 ± 9 Ma), which was coeval with the Xiarihamu, Akechukesai and other Cu‐Ni deposits. The parental magma composition of the Shitoukengde intrusion is estimated to be picritic with the SiO2 and MgO contents of 54.47 and 13.95%, respectively, and was generated by a high proportion partial melting (about 13.5%) of depleted mantle. The primary magma of the Shitoukengde intrusion underwent about 12–16% crustal assimilation and contamination with the Jinshuikou Group gneiss, which resulted in sulfide saturation and sulfide immiscibility in the magma, creating ideal conditions for the sulfide deposition at Shitoukengde.