Major and trace elements data generated on 4 iron ore deposits (Daitari, Jajang, Joda East and Kalta) of Iron Ore Group of Orissa have been processed by using R-mode factor analysis. Total 10 elemental variables are expressed in terms of 3 common rotated factors to understand the mineralogical signatures and processes of metal formation and distribution in the ore. Three distinct processes have been identified: (1) formation of rich iron ores by weathering and erosion with simultaneous removal of silica and development of aluminium bearing minerals, (2) development of nickeliferous ferruginous laterites and (3) accumulation of residual Pb. Bivariate discriminant analysis has been applied to distinguish any pair of deposits of the 4 areas under investigation which are geochemically alike. A combination of 10 elements Fe₂O₃-SiO₂-Al₂O₃-Ni-Zn-Cu-Co-Cr-Mn-Pb can establish linear discriminant function for any pair without misclassification error.

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Phase relations have been determined for Mg₃Al₂Si₃O₁₂ (pyrope composition) in the system MgO-Al₂O₃-SiO₂ at temperatures from 1000°C to 1550°C under atmospheric pressure. As increasing temperature the phase assemblage changes as follows: enstatite+cordierite+spinel; forsterite+cordierite+spinel; forsterite+cordierite+spinel+melt; forsterite+spinel+melt; spinel+melt; melt. The pyrope composition is represented by two subsolidus assemblages, viz., enstatite+cordierite+spinel and forsterite+cordierite+spinel. At temperature between 1000°C and 1025°C, the subsolidus assemblage changes from enstatite+cordierite+spinel to forsterite+cordierite+spinel through the univariant reaction:

    5Mg₂Si₂O₆+2MgAl₂O₄↔5Mg₂SiO₄+Mg₂Al₄Si₅O₁₈    (1)
          En              Spl                 Fo             Crd

This indicates that enstatite and spinel is the low-temperature assemblage, and the forsterite-cordierite join is stable at high temperatures. Combining the present and previously published data, the entropy change of the reaction (1), ΔS₁^O, is evaluated as 7.59-7.66 cal/K, and we found the reaction boundary between enstatite, spinel, forsterite and cordierite has a slope of 2.0-2.5 bar/K in dP/dT. These results do not agree with the previous data obtained from the hydrothermal experiments.
    At temperatures from 1025°C to 1370°C, cordierite is a stable subsolidus phase in equilibrium with forsterite and spinel. At the solidus temperature of 1380°C cordierite is consumed to form the melt by the following reaction:

    forsterite+cordierite → spinel+melt

At 1400°C, cordierite disappears, and forsterite and spinel coexist with melt. At 1475°C euhedral spinels crystallize in the melt, and forsterite is not found. The liquidus temperature is to be 1500°C, and spinel disappears.

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Sandstones from the Lower Cretaceous Sasayama Group contain chromian spinel and chromian magnetite as accessory minerals. Microprobe analyses show that the chromian spinel has Cr/(Cr+Al) ratios between 0.21 and 0.59, Mg/(Mg+Fe²⁺) ratios between 0.39 and 0.72, Fe³⁺/(Fe³⁺Al+Cr) ratios less than 0.10, and TiO₂ contents less than 0.4 wt%. Comparison with spinels from literature suggests that they were derived from Alpine-type peridotite. The lithology of the Alpine-type peridotite was mostly clinopyroxene-bearing harzburgite and/or refractory lherzolite with subordinate cumulates. Chromitite did not contribute detritus to the Sasayama basin.
     The chemistry of the chromian spinel further suggests that the Alpine-type peridotite source was most probably formed under an oceanic back-arc basin rather than mid-oceanic ridge setting. Chemical compositions of chromian magnetite indicate that the Alpine-type peridotite provenance was subjected to metamorphism of up to the lower amphibolite facies. In comparison with ophiolitic rocks widely distributed north of the study area, no specific provenance is constrained although the ultramafic rocks distributed in the Chugoku Zone are the most likely candidates for provenance.

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