GEOMORPHIC ESTIMATES OF THE STABILITY OF A URANIUM MILL TAILINGS CONTAINMENT COVER - NABARLEK, NORTHERN-TERRITORY, AUSTRALIA

The geomorphic stability of the cover (cap) over the pit of Nabarlek U ranium Mine in Arnhem Land, Northern Australia, is important because r adon gas and other long-lived radio-nuclides arising from mill tailing s must be contained for long periods. The primary agents of denudation in the region's seasonally wet tropical environment of low relief are rainwash, overland flow, rilling and gullying. Other agents of erosio n are of less concern, although biogenic agents of erosion (e.g. termi tes and windthrow) may enhance fluvial activity. A combination of mode lling, using the Universal Soil Loss Equation, and analogue estimates of denudation and thresholds of rilling and gullying from areas with s imilar geology, topography and climate are used to estimate the stabil ity of the Nabarlek cover. Denudation rates are conservatively estimat ed at less than 100 mm ky-1. It is suggested that with some minor desi gn modifications the cover will retain its integrity for several thous and years.