Martite–goethite (M–G) ores are characterised by the pseudomorphic textural replacement of gangue phases (carbonate, silicate and quartz) in the primary banded iron formation (BIF) by fine-grained goethite. This differentiates them petrographically from rocks enriched in Fe as a result of lateritic weathering and leaching of gangue. A preliminary petrographic study of martite–goethite mineralisation from the Grand Central deposit at BHP’s South Flank in the central Hamersley Province reveals that pseudomorphic textures are abundantly preserved. The mineralisation occurs in the Marra Mamba Iron Formation. Magnetite is converted to martite, and the quartz–silicate–carbonate bands are pseudomorphed by goethite. Of the gangue phases, carbonate and silicate minerals are more susceptible to replacement than is quartz. The replacement of quartz by goethite does not always continue to completion, and relict quartz grains are typically preserved on the lower margin and down-dip extremity of the body of mineralised BIF. The mineralisation appears to take place in three stages. The first stage involves replacement of magnetite by hematite (martitisation) and of the carbonate–silicate–quartz gangue by very fine-grained goethite that pseudomorphs and thus preserves the original texture of the non Fe-oxide portion of the BIF protolith. This ‘Stage 1’ goethite generation appears to be ochreous. Micro-porosity development, most likely developing through dissolution of any remaining quartz that has escaped replacement by goethite, although possibly through the dissolution of goethite after quartz, forms the second stage. The third and final stage is characterised by infill of the micro-porosity to varying degrees by a second generation of coarser-grained goethite that typically rims pores, giving them a comb-textured, drusy appearance. This ‘Stage 3’ goethite generation appears to be brown goethite. This tripartite paragenesis has not been explicitly recognised in previous petrographic studies of M–G mineralisation. Subsequent lateritic weathering affects material in the vadose zone above the pre-mining water-table, introducing additional complexity to the mineralisation. Further dissolution takes place, resulting in meso-scale porosity that is clearly visible to the naked eye. Voids are rimmed by a colloform intergrowth of goethite and hydrohematite. This ‘Stage 4’ goethite is likely to be vitreous goethite. Previous studies have shown that the three different types of goethite (ochreous, brown and vitreous) have distinctly different chemical and physical characteristics, and behave differently during downstream processing of Fe ore, so it is important to understand their genesis and distribution in time and space. KEY POINTS The process of M-G mineralisation involves a tripartite paragenesis: Stage 1—replacement of magnetite by hematite (martitisation) and of the carbonate–silicate–quartz gangue by very fine-grained goethite that pseudomorphs the original texture, Stage 2—dissolution of remaining gangue phases (principally quartz), and Stage 3—infill of the micro-porosity to varying degrees by a second generation of coarser-grained goethite. Overprinting effects of weathering form Stage 4—further dissolution and reprecipitation of Fe as colloform goethite-(hydro)hematite layers lining vugs. Goethites formed during the three different stages are likely to have different chemical and physical properties and this has implications for geometallurgical and materials handling behaviour during processing.