The mobility of iron within the surficial zones of secondary metal deposits is well understood from a chemical processes perspective. However, here we examine the mobilisation of iron within the critical zone at the Salobo iron-oxide copper gold mine in Brazil from the perspective of iron-oxidising bacteria. The Salobo mine is an excellent study area due to a mineral assemblage exceptionally rich in iron (up to ~60 wt. %).A biogeochemical field study of weathered materials from the critical zone at Salobo was complemented by bench-top leaching experiments of fresh rocks, partly weathered rock and oxidised materials, using endemic, iron-oxidising acidophilic bacteria, e.g., Acidithiobacillus ferrooxidans. The bench-top study examined the interaction of iron-oxidising bacteria with ferrous iron-bearing minerals including sulphides, which are conventional substrates in supergene systems, as well as more refractory sources of energy, i.e., silicates and magnetite. The results are linked to detailed analyses of textures and secondary mineral assemblages within the critical zone at Salobo and shed light on the role of iron-oxidising bacteria in the mobilisation of iron as well as the mobility of other elements, such as copper, manganese and phosphorus as a by-product of microbial activity.