Earth Science Frontiers ›› 2024, Vol. 31 ›› Issue (2): 249-269.DOI: 10.13745/j.esf.sf.2023.5.31

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Characteristics of mineral chemistry and geochemistry of the Late Triassic Hongqiling mafic-ultramafic intrusions: Implications for Ni-Cu mineralization

WANG Jian1,2(), YANG Yanchen1,2, LI Ai3, YUAN Haiqi1   

  1. 1. College of Earth Sciences, Jilin University, Changchun 130061, China
    2. Key Laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Natural Resources, Changchun 130026, China
    3. College of Computer Sciences and Technology, Qingdao University, Qingdao 266071, China
  • Received:2022-10-28 Revised:2023-04-24 Online:2024-03-25 Published:2024-04-18

Abstract:

The Hongqiling mafic-ultramafic rocks include three belts (I, II and III) and are composed of over 30 small intrusions. They are located in the southern margin of the eastern segment of the Central Asian Orogenic Belt (CAOB). Several intrusions in belt I develop Ni and Cu mineralization, with Nos.1 and 7 intrusions forming medium- and large-sized magmatic Ni-Cu sulfide deposits, respectively. The major host rocks for Ni-Cu ore bodies are harzburgite, lherzolite, orthopyroxenite, websterite, norite and gabbro. These mafic-ultramafic rocks are characterized by high Mg (w(MgO)~20.7%-31.1%), moderate Si (w(SiO2)~40.03%-53.01%) and low Ti (w(TiO2)~0.33%-0.79%) and alkalis (w(K2O+Na2O)~0.60%-2.29%) contents. The patterns of trace elements show weak enrichments of LREE (La, Ce, Pr, Nd) and LILE (Th) and depletions of HREE and HFSE (Nb, Ta, Ti). Whole-rock geochemical data and mineral (olivine, orthopyroxene, clinopyroxene, spinel, plagioclase, amphibole) chemistry indicate the Hongqiling mafic-ultramafic intrusions are different from OIB, Alaskan-type complex and komatiite, but similar to arc-type basalt and mafic-ultramafic rocks from the Huangshanxi and Huangshandong Ni-Cu sulfide deposits in the western CAOB. The parental magma for the Hongqiling mafic-ultramafic intrusions is a high-Mg and low Nb-Ta tholeiitic melt which has undergone crustal contamination and fractional crystallization during evolution. Ore-bearing parental magma for the Hongqiling deposit likely experienced “second” separation of sulfide, forming the PGE-depleted Ni-Cu sulfide deposit.

Key words: magmatic Ni-Cu sulfide deposit, high-Mg tholeiitic melt, separation of sulfide, depletion of PGE, post-collisional extensional setting, Hongqiling, Central Asian Orogenic Belt

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