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Mineralium Deposita

, Volume 39, Issue 2, pp 159–172 | Cite as

Compositional variations of olivine from the Jinchuan Ni–Cu sulfide deposit, western China: implications for ore genesis

  • Chusi LiEmail author
  • Zhanghua Xu
  • Sybrand A. de Waal
  • Edward M. Ripley
  • Wolfgang D. Maier
Article

Abstract

The Jinchuan Ni–Cu sulfide deposit is hosted by an elongated, olivine-rich ultramafic body that is divided by subvertical strike-slip faults into three segments (central, eastern, and western). The central segment is characterized by concentric enrichments of cumulus olivine crystals and interstitial sulfides (pyrrhotite–pentlandite–chalcopyrite intergrowth), whereas the eastern and western segments are characterized by an increase of sulfides toward the lower contacts. In all segments sulfides are concentrated at the expense of intercumulus silicates. Olivine re-crystallization is found to be associated with actinolite alteration in some samples. The compositional variations of primary olivine from the sulfide-poor samples can be explained by a small degree of olivine crystallization (<5%) from a basaltic magma followed by local re-equilibration of the olivine with up to 30% trapped silicate liquid. In the sulfide-bearing samples the compositions of primary olivine record the results of olivine-sulfide Fe–Ni exchange that occurred after the trapped silicate liquid crystallized. Our olivine data indicate that Ni in the original sulfide liquids increased inward in the central segment and laterally away from the lower contact in the eastern segment. Variations in the compositions of sulfide liquids are thought to result from fractional segregation of immiscible sulfide liquid from a basaltic magma in a staging chamber instead of in situ differentiation. High concentrations of olivine crystals (mostly >50 modal%) and sulfide (averaging ~5 wt%) in the rocks are consistent with the interpretation that the Jinchuan deposit was formed by olivine- and sulfide-laden magma successively ascending through a conduit to a higher, now-eroded, level. Sulfide enrichment toward the center in the central segment and toward the lower contact in the eastern and western segments may have, in part, resulted from flow differentiation and gravitational settling during magma ascent, respectively.

Keywords

Jinchuan Magma conduit Ni Olivine Sulfide 

Notes

Acknowledgements

We thank Tong Zongli and Jinchuan NF Metals Ltd. for their assistance in field work. Comments from Steve Barnes and Finn Barrett on an earlier draft of this paper and reviews by Mei-Fu Zhou, Grant Cawthorn, and Associate Editor Peter Lightfoot are greatly appreciated. Financial support for this work was provided through a grant (EAR 0104580) from the National Science Foundation of the United States to C. Li and E.M. Ripley, through a postdoctoral fellowship from University of Pretoria to Z.H. Xu, and through a fund from the Center for Research on Magmatic Ore Deposits of the University of Pretoria to S.A. de Waal.

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Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • Chusi Li
    • 1
    Email author
  • Zhanghua Xu
    • 2
  • Sybrand A. de Waal
    • 2
  • Edward M. Ripley
    • 1
  • Wolfgang D. Maier
    • 2
  1. 1.Department of Geological SciencesIndiana UniversityBloomingtonUSA
  2. 2.Centre for Research on Magmatic Ore Deposits, Department of Earth SciencesUniversity of PretoriaPretoria 0002South Africa

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