A study of radionuclides, metals and stable lead isotope ratios in sediments and soils in the vicinity of natural U-mineralisation areas in the Northern Territory.

Australian guidelines recommend that tailings materials from uranium (U) mining and milling be contained without any detrimental impact on the environment for at least 1000 years. Natural analogue sites are being investigated to determine if they can provide data on the rates of natural erosion processes which occur over these timescales, for input into predictive geomorphic computer models. This paper presents radionuclide, metal and stable lead (Pb) isotope data from sediment cores and surface soils in the vicinity of two mineralised areas in the Alligator Rivers Region. Surface scrapes from the natural Anomaly #2, south of the Ranger mineral lease, exhibit radiogenic (206)Pb/(207)Pb and (208)Pb/(207)Pb ratios, and elevated U and metal concentrations typical for a near surface U anomaly. In contrast, samples taken from the Koongarra mineral lease (KML) show radionuclide activity and metal concentrations similar to natural areas elsewhere in the Alligator Rivers Region and Pb isotope ratios are closer to present day average crustal ratios (PDAC), as the orebodies at KML are covered by surficial sand. A sediment core collected from Anbangbang Billabong, downstream of KML, exhibits small variations in Pb isotope ratios that indicate that approximately 1% of the upper sediments in the sediment core may be derived from material originating from the U anomaly at Koongarra.

Radioactive and radiogenic isotopes in sediments from Cooper Creek, Western Arnhem Land.

Protection of the environment post-mining is a key objective of rehabilitation, especially where runoff and erosion from rehabilitated mine sites could potentially lead to contamination of the surrounding land and watercourses. As part of an overall assessment of the success of rehabilitation at the former Nabarlek uranium (U) mine, an appraisal of stable lead (Pb) isotopes, radionuclides and trace metals within sediments and soils was conducted to determine the off site impacts from a spatial and temporal perspective. The study found localised areas on and adjacent to the site where soils had elevated levels of trace metals and radionuclides. Lead isotope ratios are highly radiogenic in some samples, indicating the presence of U-rich material. There is some indication that erosion products with more radiogenic Pb isotope ratios have deposited in sediments downstream of the former ore body. However, there is no indication that the radiogenic erosion products found on the mine site at present have significantly contaminated sediments further downstream of Cooper Creek.