HYDROGEOLOGY AND PALEOHYDROGEOLOGY OF THE KOONGARRA NATURAL ANALOGUE, NORTHERN TERRITORY, AUSTRALIA

Abstract

The Koongarra site is one of the most extensively studied natural analogues in the world. Data for the Koongarra site are re-examined to develop a hydrogeological and paleohydrogeological conceptual model of the natural analogue as a basis for simulating the development of the dispersion fan. Geological, geophysical, hydrologic, and paleoclimatic data are interpreted to determine present-day conditions on the boundaries of host schist and the hydrogeological structure of the host formation. The configuration of groundwater flow through host schist is inferred from the structure of the formation and boundary conditions. Groundwater level measurements and data describing the di stribution of aqueous uranium and other aqueous species and parameters are consistent with the proposed hydrogeological model. Information about the geochronology of the site and paleoclimate of the region are considered to show that sources of recharge to host schist, factors determining the hydrogeological structure of the host formation , and the configuration of groundwater flow through the site are essentially unchanged for the last two million years or more. The proposed flow field descended through the No. 1 orebody with the erosion (lowering) of the land surface and advance of the weathered profile to form the Koongarra dispersion fan. Data describing the three-dimensional distribution of uranium minerals comprising the dispersion fan are consistent with the proposed paleohydrogeological model. Paleoclimatic records and an estimate of the present rate of advance of the weathering front are used to approximate the age and rate of development of the fan, initiated two million years ago.