Mineralogically complex shale horizons interbedded with, and underlying, the Brockman Iron Formation at Mt Tom Price, Western Australia, are compared with equivalent sections at Wittenoom and Yampire Gorge. Despite the alteration by fairly intense post‐depositional folding, faulting and weathering, very limited evidence favouring a primary pyroclastic source is indicated. By acting as effective seepage horizons for percolating meteoric waters, the upturned shale bands, which are part of the truncated synclinal folds in the Brockman Formation, have actively promoted supergene enrichment of the iron ore during lateritization and have themselves undergone considerable mineralogical reconstitution. By means of semi‐quantitative mineralogical data from samples in a reconstructed weathering profile, it is postulated that the formation at Mount Tom Price was subjected to two periods of lateritization separated by a period of diagenesis. Of these cycles the first was probably the most intense and hence responsible for most of the supergene iron ore enrichment in the region. The deposits at Wittenoom and Yampire Gorge were also affected by a period of intense diagenesis. However, they formed in an essentially anaerobic environment with little tectonic disturbance, conditions which differed markedly from those at Mt Tom Price.