Genetic Significances of Olivine from Magmatic Sulfide Ore-Bearing Intrusions in Central Zone of Emeishan Large Igneous Province
GUAN Jian-xiang
SONG Xie-yan
Leonid V.Danyushevsky
CHEN Lie-meng
NIE Xiao-yong
Abstract：Several mafic-ultramafic intrusions hosting economic Ni-Cu-(PGE) sulfide deposits and sub-economic sulfide mineralization occur in the central zone of the Emcishan large igneous province (LIP). These magmatic sulfide deposits can bc divided into the Ni-Cu type (e. g. Limahe and Qingshuihe), Ni-Cu-PGE type (e. g. Qingkuangshan and Huangcaoping) and PGE type (e. g. Jinbaoshan and Yanghewu), according to the variations in the content of platinum-group elements (PGE). Electron microprobe analyses of olivine show that almost all olivine crystals are chrysolite (Fo_(76.8)-Fo_(89.6)), with an exception of some grains from the Qingkuangshan intrusion which are forsterite (Fo_(90.1)-Fo_(93.1)). The compositions of olivine are distinct between intrusions containing different types of sulfides. For the Ni-Cu sulfide-bearing intrusions, the Fo and Ni contents of olivine range from 77 to 87 and from 976×10~(-6) to 2176×10~(-6), respectively. Olivine crystals in the Ni-Cu-PGE sulfide-bearing intrusions have Fo numbers varying from 80 to 86 and (1024-2543)×10~(-6) Ni. The PGE sulfide-bearing intrusions contain olivine crystals with Fo numbers ranging from 78 to 84 and Ni contents of 776×10~(-6) to 1755×10~(-6). The olivine from the Qingkuangshan intrusion, which contains economic Ni-Cu-PGE sulfides, is distinct from others by its high Fo numbers (up to 93. 1) and CaO content (0. 24%-1.14%) and extremely low Ni (266×10~(-6)). The Ni concentrations and Mg~# of parental magma have been estimated by using the compositions of most Fo-rich olivine crystals and the results show a high-MgO picritic-basaltic magma. Modeling of olivine fractional crystallization and sulfide segregation show that the parental magma for the Ni-Cu type mineralized intrusions has experienced the most extensive sulfide segregation (～0. 1%). For the Ni-Cu-PGE type intrusions, it is～0. 06%, and for the PGE type intrusions it is～0. 02%. Re-equilibration of the early formed olivine crystals with the trapped liquid can account for the variations of olivine compositions.
Keywords：central zone of Emeishan large igneous provincemagmatic sulfide depositolivinefractional crystallizationsulfide segregationtrapped silicate liquid effect.
Publication Date：2010-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：11( 224-234 )