Characterisation of uranium-vanadium mineralisation at Bigrlyi, Ngalia Basin, Australia

The Ngalia basin uranium mineral system project is a research collaboration between CSIRO, surveys and industry. The aim of the project is to understand the physical and chemical processes that led to the formation of known uranium deposits within the basin, such as the Bigrlyi uranium-vanadium deposit. Uranium mineralisation in the Carboniferous Mt Eclipse sandstone is common throughout the basin, e.g. Dingos Rest, Walbiri and Camel Flat. The depositional environment is dominated by fluvial channels intercalated with floodplain siltstones, sandstones and shales. The channels are partly carbonate cemented which carbon and oxygen isotopes show is formed through groundwater processes. The mineralisation occurs in the base of stacked fluvial channel sub-arkosic sandstones. The source of the very immature sandstone is Proterozoic I-type granites within the Arunta block north of the deposit. Petrographic observation using BSEM and CL revealed several uranium and vanadium bearing minerals, such as roscoelite, coffinite, uraninite, montroseite, V-smectite/illite and APS minerals. The mineralisation occurred prior to compaction and cementation of groundwater calcite. Detrital roscoelite clasts containing APS minerals and uranium are interpreted to have originated from a hydrothermal system within the granitic source rock.