Petrology and origin of iron-rich silicate–magnetite–quartz rocks from Flowerdale near Gairloch, Wester Ross

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Abstract
Synopsis: A body of banded iron formation occurs within amphibolite facies rocks of the supracrustal Lewisian Loch Maree Group in Flowerdale near Gairloch. The body exhibits a transition from oxide facies (banded quartz–magnetite rocks) to silicate facies (relatively massive garnet–grunerite rocks) which is probably related to variation of the original depositional environment. Intermediate lithologies consist of complex stratified mixtures of quartz, magnetite, grunerite, garnet (almandine), hornblende (ferro-pargasite), biotite (annite 85%), chlorite (ripidolite) and calcite. The rocks retain small-scale primary compositional heterogeneities and sedimentary structures. The silicate-bearing assemblages are derived from chamositic protoliths which were probably deposited in shallow water.