Forty-seven specimens of the Wabush Iron Formation were collected from ten outcrop areas. Twenty-five specimens contain the assemblage (1), quartz+clinopyroxene+calcite with or without orthopyroxene, grunerite, magnetite, ankerite, and siderite. Five specimens contain assemblage (2), quartz+clinopyroxene+actinolite+calcite+magnetite+hematite, and two contain assemblage (3), quartz+orthopyroxene+actinolite+magnetite+hematite. In three specimens of assemblage (1), graphite occurs in the absence of magnetite; pyrrhotite and pyrite occur separately or together in specimens with assemblage (1).Thirty-nine clinopyroxenes, 38 orthopyroxenes, 18 grunerites, 7 actinolites, 16 calcites, 1 ankerite, and 1 siderite were analyzed for iron, manganese, and calcium by X-ray emission spectrography. Magnesium contents were estimated by assuming stoichiometric proportions.Minerals occurring with hematite show low Fe/(Fe+Mg) ratios, and those in the other assemblages show higher values with a wide range of variation. In orthopyroxene, Fe/(Fe+ Mg) ranges from 0·17 (with hematite) to 0·77.Regularity in the distributions of Fe, Mn, and Ca between pairs of coexisting minerals shows that equilibrium was attained in most of the rocks studied. This regularity is also accomplished in the distribution of Mn between calcite and coexisting silicates as well as between the silicates themselves. Small differences in the distributions of Ca and Fe depend on both outcrop area and mineral assemblage.Phase rule considerations suggest that the specimens with dolomite-ankerite or magnesitesiderite do not represent equilibrium assemblages. Variations in orthopyroxene compositions in assemblages with pyrite or pyrrhotite, or both, and magnetite indicate non-equilibration of sulfides with silicates. The presence of the oxygen buffer, magnetite+hematite, attests to the immobility of oxygen during metamorphism.Within each outcrop area, over which the temperature and pressure are assumed to have been uniform, variations in the compositions of the silicates in the sub-assemblages quartz+ orthopyroxene+grunerite and quartz+orthopyroxene+clinopyroxene+calcite indicate gradients of μH2O μCO2 and respectively. As characterized by the composition of orthopyroxene, both gradients are relatively low along strike, and high across strike. The direction of gradients across strike is almost without reversals, which is consistent with intergranular diffusion of H2O and CO2. Phase rule restrictions for a majority of assemblages are not in accord with the simultaneous imposition of μH2O and μCO2 gradients on the rocks, nor the formation of an H2O-CO2 fluid phase during metamorphism. © 1969 Oxford University Press.
