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Experimental Investigations of Chromite Spinels

Gene C. Ulmer
Gene C. Ulmer
Engineer in the Refractories Section of Reduction
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January 01, 1969


The techniques of oxygen-fugacity buffering have recently been applied to several ternary and quaternary systems for the purpose of studying the stability and extent of chromite spinel solid solutions. Examination of data at the subsolidus temperature of 1,300° C provides an insight into the phase relationships among the six spinel end-members: Magnesioferrite (MgFe2O4), Spinel (MgAl2O4), Picrochromite (MgCr2O4), Magnetite (Fe3O4), Hercynite (FeAl2O4), and Chromite (FeCr2O4). The phase equilibria data indicate that while complete solid solution among these spinels does exist at 1,300° C, the solid solutions may involve defect spinels that contain trivalent ions in excess of the 1:2 divalent to trivalent ratio. A summary of the spinel data shows that, at one atmosphere and 1,300° C, oxygen fugacities in the range of 10–5 to 10–7 atm are necessary to form the range of compositions observed for natural spinels.

Liquidus studies of the effects of oxygen fugacity on fractional crystallization are reviewed for the systems MgO-FeO-Fe2O3-SiO2 and MgO-CaO-SiO2-iron oxide and MgO-FeO-Fe2O3-CaAl2Si2O8-SiO2. These liquidus data are interpreted to show that both temperature and oxygen fugacity are important variables in the petrogenesis of chromite-silicate sequencs. It is hypothesized that variations in oxygen fugacity in the parent magma can control cyclic crystallization as well as compositional variations of the spinel and silicate layers of chromite deposits.

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Society of Exploration Geophysicists Geophysical Monograph Series

Magmatic Ore Deposits

H. D. B. Wilson
H. D. B. Wilson
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Society of Economic Geologists
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Publication date:
January 01, 1969




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