On the hydrology of the bauxite oases, Cape York Peninsula, Australia

- Little is known about the hydrology of bauxite deposits.
- A new super group of large permanent springs is revealed in northern Australia.
- Rich ecosystems supported by these springs are classified in a new sub-ecosystem.
- Chemistry reveals these new springs are not part of the Great Artesian Basin.
- Rather the springs are connected to one of the world's largest bauxite formation.

SummaryOne of the world's largest bauxite deposits is located in the Cape York Peninsula, North-East Australia. Little is known about the hydrology of these remote bauxite deposits. Here, we present results from a multidisciplinary study that used remote sensing, hydrochemistry, and hydrodynamics to analyse the occurrence of several large oases in connection with the bauxite plateaus. Across this vast region, otherwise dominated by savannah, these oases are sustained by permanent springs and support rich and diverse new sub-ecosystems (spring forests) of high cultural values to the local indigenous population. The spring water chemistry reveals a well-mixed system with minor inter-spring variation; TDS values of spring waters are low (27-72 mg L−1), major ion compositions are homogenous (Na-Si-DIC-Cl) and δ18O and δ2H values are reflective of rainwater origin with little evaporation prior to recharge. Dating of spring waters with anthropogenic trace gases (CFC-12 and SF6) indicates mean groundwater residence times ranging from <1 to 30 years. An artificial tracing experiment highlighted the existence of a flow pathway from the bauxite land surface to the sandy aquifer that feeds the springs through discontinuities in the ferricrete layer. In addition, the soil infiltrability tests showed the bauxite land surface has very high infiltrability (15 mm min−1), about four times greater than other adjacent land surfaces. Across the lower part of the Wenlock Basin, satellite data indicate a total number of 57 oases consistently located on the edge of the bauxite plateaus. This super-group of permanent hillslope springs and their ecosystems adds another important attribute to the list of natural and cultural values of the Cape York Peninsula.