Using uranium as a proxy for understanding system scale fluid flow and channel belt connectivity

Uranium distribution in sandstone hosted deposits is strongly influenced by sandstone body connectivity, as uranium enriched groundwater preferentially flows through porous and permeable strata. Uranium distribution can... [ view full abstract ]

Uranium distribution in sandstone hosted deposits is strongly influenced by sandstone body connectivity, as uranium enriched groundwater preferentially flows through porous and permeable strata. Uranium distribution can therefore be used as a proxy to help understand fluid flow pathways at a regional scale.
The late Jurassic Salt Wash distributive fluvial system (DFS), located in SW USA, has previously been exploited for its uranium deposits. We plot uranium distribution alongside regional facies maps, and incorporate field observations from across the system to help understand where the uranium is concentrated on the Salt Wash DFS.
A strong relationship between sandstone percentage, channel belt percentage, architecture of the deposits and uranium distribution is observed. More than 90% of recorded uranium deposits are located where net sandstone represents 40-55% of the succession and where channel belts form 20-50% of the succession. Below the 40% sandstone and 20% channel belt cut-off levels, uranium deposits are rarely observed. This coincides with a change in gross scale architecture from medial DFS facies to distal type facies. In outcrop medial DFS facies are observed as having laterally extensive channel bodies, which amalgamate on occasion and are separated by laterally extensive floodplain packages. Downstream the channel belts decrease in size and presence, with little amalgamation observed and floodplain fines dominating the succession.
These relationships suggests that below that 40-55% sandstone and the 20-50% channel belt percentage contour lines effective connectivity of the channel belts is lost. This allows the enrichment and precipitation of uranium against permeability barriers, when all other conditions are met. The results from this rock record example allows a more quantified system scale model of channel belt connectivity in fluvial systems to be built.