Uranium mining in the Alligator Rivers Region
South Alligator Valley
The high mineral prospectivity of the Alligator Rivers Region, particularly for uranium, is evidenced by the 13 or so former uranium mines and numerous mineral deposits that are located in the upper South Alligator River Valley. Although there are no mines currently in operation in this area, in the past it has been a highly active area with numerous deposits, many of which were mined during the 1950s and 60s.
During the period between 1955 and 1965, exploration activities occurred in what can be described as a "uranium rush", with at least 16 deposits or occurrences (radiometric anomalies) of uranium being discovered in the South Alligator Valley. These deposits occurred in groups and singly; not all prospects were established as economically viable deposits but eventually 13 mines were operated between 1954 and 1964.
The area covered by this rush of activity stretched from Coronation Hill in the south to Teagues in the north. (SAV map) In addition, there was a separate discovery at Sleisbeck approximately 40 km south-east of Coronation Hill which was mined in 1957, with the ore being transported to Rum Jungle 85km south of Darwin for processing. The largest producers of uranium ore were El Sherana, Saddle Ridge and Coronation Hill and the mining methods employed included open cut operations as well as shaft mining techniques.
Environmental standards and practices during this period (1950s/60s) are not comparable with those currently in place and many of these older sites have been subject to some level of environmental rehabilitation in recent times. In 1986, a survey of abandoned mines in the South Alligator Valley was undertaken by the Commonwealth and in 1988, a follow up survey produced a series of proposals for the rehabilitation of the minesites. Due to funding constraints, complete rehabilitation was not possible. However, it was decided that as a priority, a program of physical and radiological hazard reduction would be carried out for the safety of National Park users. This involved identifying areas where radiation doses exceeded permitted levels for public exposure and arranging for the appropriate disposal of affected material. The work was completed in 1992 with target protection levels successfully achieved. Annual erosion inspections are ongoing and radiation surveys are carried out every three years.
There was also a program to recover gold which was present as a contaminant in the pitchblende, sometimes up to 20 ounces per ton (5.5 g/tonne). Approximately 312.5 kg (11,000 ounces) of gold were recovered from the South Alligator field as a by-product of the uranium mining.
A small uranium mill was built to service the mines located near Rockhole Mine Creek. Tailings from this mill were allowed to accumulate on the river bank and were often swept away by floods. The bulk of the tailings were transported from the site in 1986 to be re-processed to extract gold and the residues were placed in a new containment at Moline. During the hazard reduction studies and works some more tailings were discovered and these were relocated to suitable containments in the area. In 1999 a routine survey by OSS discovered that yet another deposit of tailings had been uncovered following road maintenance works. OSS advised Parks Australia North that remedial action was required and a series of intervention actions were put in place. Surveys were carried out to check that public safety was not compromised by the presence of the material. A program of remedial works was drawn up for the overall resolution of the problem. In 2000 all visible tailings and contaminated materials were cleaned up and placed in a temporary store for safe keeping. The affected area was then stabilised to ensure that there could be no erosion and dispersal of further material during the wet season.
In 2006, the Commonwealth Government provided $7.4 m to Parks Australian North to clean up all remaining sites within the South Alligator Valley to an acceptable standard. The program of works is expected to be complete by 2010.