Earth Science Frontiers ›› 2009, Vol. 16 ›› Issue (5): 232-244.

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A possible new chromium mineralization: A discussion on the formation of chromespinel of Gangshang ultramafic rocks in Sulu UHP belt.

CHEN Shi-Zhong YANG Jing-Rui   

  1. 1Nanjing Institute of Geology and Mineral Resources, China Geological Survey, Nanjing 210016, China
    2Laboratory of Continental Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
  • Online:2009-09-10 Published:2009-09-10

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Abstract:

 Gangshang ultramafic rocks are mainly composed of garnet peridotites and dunite, which contain olivine, chromespinel, diopside, endiopside, and/or garnet, orthopyroxene, amphibole and phlogopite. Chromespinels in Gangshang ultramafic rocks are varied in composition, with Cr#［100Cr/(Cr+Al)］ ranging from 51 to 89, and its variation in composition is related to the four stages of the evolution of ultramafic rocks. Along with the evolution of ultramafic rocks, Cr# of chromespinels was increasing, Mg#［100Mg/(Mg+Fe2+)］ of chromespinels was decreasing and the oxygen fugacity was increasing.  In the course of amphibole facies and greenschist facies retrometamorphism, Cr, Mg and Al of chromespinels were reducing, but Fe was relatively increasing. The shearing deformation of the Gangshang ultramafic rocks in the late stage was also helpful to the enrichment of chromium and to the formation of chromespinel.

Key words: Key words: chromespinel; Sulu UHP belt; Gangshang ultramafic rock; chromium mineralization

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