Petrology of the Sokoman Iron Formation

The Proterozoic Sokoman Iron Formation in the Howells River area, at the western edge of the Labrador Trough, has undergone extensive diagenesis but probably only very low grade metamorphism. Comparison with oxygen isotope data for very similar assemblages in the Biwabik Iron Formation suggests that the iron-formation of this study has been subjected to temperatures of about 150øC or somewhat less. The iron-formation assemblages can be divided into four facies: sulfide, silicate, magnetite-carbonate, and hematite-carbonate. In ahnost all of the assemblages trong recrystallization has taken place of the original, sedimentary precursors. In some as-semblages, however, as in the underlying orthoquartzites and the green chert member of the iron-formation, very fine, fibrous and colloidal textures are still preserved in chal-cedony and chert. Representative assemblages in the various facies are as follows: Sulfide facies-chamosite-siderite-ankerite-pyrite-chert-carbon; ankerite-siderite- chamosite-"A1 greenalite"-chert-pyrite-carbon. Silicate facies-magnetite-greenatite-stitpnometane