The Merensky Reef is one of the world’s iconic platinum group element (PGE) deposits, discovered by tracking PGEs that had weathered out from the platiniferous reef in the Bushveld Igneous Complex, South Africa. The bioleaching of Merensky Reef by Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans was studied to improve our understanding of PGEs migration and to identify any secondary minerals that might guide PGE exploration. The key materials comprising the Merensky Reef and targeted for bioleaching were chalcopyrite, pentlandite, pyrite and pyrrhotite, occurring within a matrix of clinopyroxene, orthropyroxene, chromite and norite, with the PGEs occurring as grains and distributed metals (Osbahr et al., 2013). Pyrrhotite and pyrite were shown to be important targets for bacterial weathering versus pentlandite and chalcopyrite, with dense bacterial colonization within 2 weeks, including iron phosphate and sulfur precipitation as secondary minerals. Pentlandite was oxidized in both abiotic and biotic systems, however, the colonisation of bacteria was only observed after 8 weeks bioleaching. Chalcopyrite was relatively inert to bioleaching in this silicate buffered system, which was consistent with the water chemistry. Orthopyroxene weathered easily under acid attack, and resulted in the release of silica and calcium. The chromite was found to be remarkably clean, and did not have any cells, i.e., any non-specific binding as observed with the silicates. No platinum or palladium was detected in the bioleaching solution, and no secondary, i.e., colloidal Pt or Pd was observed suggesting that weathering of PGE grains or distributed PGEs was not active. Most of the individual, micrometre-scale PGE grains identified at T=0 were found after leaching, demonstrating that while the matrix had deteriorated, most of the grains were still embedded in the ore specimen. Further mass wasting, including more active processes encountered during erosion are required before more active dispersion of grains, similar to PGEs migration in natural systems would occur.