It is proposed that the buried Tertiary Yarramba Palaeochannel feature hosting the sedimentary uranium mineralisation was incised into Cretaceous and Precambrian basement rocks. Within the channel, quartzose sands and abundant detrital organic matter were deposited. Subsequently, much diagenetic pyrite was formed during anaerobic microbial reworking of the organic material under alkaline conditions.Later deposition of fine-grained lacustrine sediments provided a seal for the uranium-bearing aquifer represented by the coarser channel fill, and the groundwater's pH was reduced as it was flushed with slightly acidic and mildly saline surficial waters. Uranium mineralisation was mobilised within the channel sands, and re-precipitated remnants of it are currently preserved on redox interfaces that resemble limbs of a "roll-front" ore-forming system.